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This document provides information on electric motor specifications, including nameplate markings, insulation classes, frame sizes, and other technical details. It describes the key information that should be included on motor nameplates according to NEMA and IEC standards, such as voltage, current, speed, power rating, and insulation class. It also explains the NEMA system for standardized motor frame sizes and provides tables matching frame sizes to horsepower ratings.

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2010 Edition Electric Motors & Drives Technical Manual Through the initiative of: International Copper Association – South East Asia Institute of Integrated Electrical Engineers of the Philippines, Inc.
iii P R E F A C E This publication deals primarily with small and medium-sized induction motors which are the most common type of alternating current motor. They are internationally standardized and are efficiently manufactured in long production runs. The combination of new materials and more sophisticated methods for calculation, design and production have made the modern three-phase induction motor a robust and reliable prime mover. This publication was made possible through the initiative and support of the International Copper Association – South East Asia and administered, executed, and implemented by the Institute of Integrated Electrical Engineers of the Philippines All information and data contained in this publication is believed to be reliable, but all recommendations or suggestions are made without guarantee. Furthermore, suggestions for use of material supplied shall not be construed as a recommendation or inducement to violate any law or infringe any patent.
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v Table of Contents Section Title Page Motor Specifications 1.1 Nameplate 1 1.2 Insulation Class 3 1.3 Enclosure Type 11 1.4 Temperature Class 19 1.5 Mounting 30 1.6 Manufacturer’s Identification Number 51 1.7 Terminal Markings 55 1.8 Motor Design 67 1.9 Types of Duty 76 General Characteristics 2.1 System Nominal Voltage 103 2.2 Voltage 104 2.3 Power Factor 112 2.4 Efficiency 113 2.5 Speed 118 2.6 Vibration Characteristics and Balancing 119 2.7 Bearings 141 2.8 Torque 170 Asynchronous Motor Starting Systems 3.1 Starting Methods 175 3.2 Single-phase Motor Starting 187 Motor Protection and Coordination 4.1 Motors Protection 193 4.2 Protection Against Short Circuits 194 4.3 Protection Against Overload 203 4.4 Multifunction Relays 212 4.5 Motor Circuit Breakers 215 Motor Starter Co-ordination 5.1 Concepts 219 5.2 Solutions 220 5.3 Motor Overload Protection 229 5.4 Terminology 241
vi Motor Efficiency 6.1 Repair-Replace Decision Model 246 6.2 Premium Efficiency Motors 262 Installation, Testing, and Maintenance 7.1 Installation and Maintenance 273 7.2 Description of Routine Tests 309 7.3 Recommended Winding Tests 321 7.4 Other Tests 322 7.5 Motor Starting Capabilities and Considerations 323 7.6 Maintenance and Reliability 328 7.7 Maintenance Programs 332 7.8 Machinery Condition Monitoring 334 7.9 Maintenance Planning 338
1 Motor Specifications 1.1 Nameplate Motor standards are established on a country by country basis. Fortunately though, the standards can be grouped into two major categories: NEMA and IEC (and its derivatives). In North America, the National Electric Manufacturers Association (NEMA) sets motor standards, including what should go on the nameplate (NEMA Standard MG 1-10.40 "Nameplate Marking for Medium Single-Phase and Polyphase Induction Motors"). In most of the rest of the world, the International Electrotechnical Commission (IEC) sets the standards. Or at least many countries base their standards very closely on the IEC standards (for example, Germany's VDE 0530 standard and Great Britain's BS 2613 Standard closely parallel the IEC 34-1 standard). The NEMA and IEC standards are quite similar, although they sometimes use different terminology. Thus, if one understands the IEC nameplate, it is fairly easy to understand a NEMA nameplate, and vice- versa as shown in Fig 1.1A and B. Fig 1.1A – Typical IEC Motor Nameplate
2 Fig. 1.1B – Typical NEMA Motor Nameplate The nameplate of a motor provides important information necessary for proper application. For example, Fig. 1.1C – AC Induction Motor nameplate shows a 30 horsepower (H.P.) three-phase (3 PH) AC Induction motor. Fig. 1.1C – AC Induction Motor Nameplate
3 The following paragraphs explain some of the other nameplate information for this motor. Voltage Source (VOLTS) and Full-load Current (AMPS) AC motors are designed to operate at standard voltages. This motor is designed to be powered by a three-phase 460 V supply. Its rated full-load current is 35.0 amps. Base Speed (R.P.M.) and Frequency (HERTZ) Base speed is the speed, given in RPM, at which the motor develops rated horsepower at rated voltage and frequency. Base speed is an indication of how fast the output shaft will turn the connected equipment when fully loaded. This motor has a base speed of 1765 RPM at a rated frequency of 60 Hz. Service Factor Service factor is a number that is multiplied by the rated horsepower of the motor to determine the horsepower at which the motor can be operated. Therefore, a motor designed to operate at or below its nameplate horsepower rating has a service factor of 1.0. A 1.15 service factor motor can be operated 15% higher than its nameplate horsepower. 1.2 Insulation Class NEMA NEMA defines motor insulation classes to describe the ability of motor insulation to handle heat. The four insulation classes are A, B, F, and H. All four classes identify the allowable temperature rise from an ambient temperature of 40° C (104° F). Classes B and F are the most commonly used. Ambient temperature is the temperature of the surrounding air. This is also the temperature of the motor windings before starting the motor,
4 assuming the motor has been stopped long enough. Temperature rises in the motor windings as soon as the motor is started. The combination of ambient temperature and allowed temperature rise equals the maximum rated winding temperature. If the motor is operated at a higher winding temperature, service life will be reduced. A 10° C increase in the operating temperature above the allowed maximum can cut the motor’s insulation life expectancy in half. Fig.1.2A shows the allowable temperature rise for motors operated at a 1.0 service factor at altitudes no higher than 3300 ft. Each insulation class has a margin allowed to compensate for the motor’s hot spot, a point at the center of the motor’s windings where the temperature is higher. For motors with a service factor of 1.15, add 10° C to the allowed temperature rise for each motor insulation class. Fig 1.2A – Allowable Temperature Rise Permitted output at high ambient temperature or high altitude above sea level. Motors in their standard versions are intended to operate in an ambient temperature of 40 °C maximum and at not more than 1000 meters above sea level. If the motors are to be used at higher ambient temperatures or higher altitudes the rated output must normally be reduced by the percentage shown in the Table 1.2A.
5 Table 1.2A – Reduction of Rated Output at Higher Ambient Temperature of Altitudes Ambient Temperature, O C 40 45 50 55 60 70 Permitted output, % of rated output 100 96.5 93 90 86.5 79 Altitude above sea level 1000 1500 2000 2500 3000 3500 4000 Permitted output, % of rated output 100 97 94.5 92 89 86.5 83.5 Insulation classes According to EC 85, insulation is divided into insulation classes. Each class has a designation corresponding to the temperature that is the upper limit of the range of application of the insulating material under normal operating conditions and with satisfactory life. If this upper limit exceeded by 8 to 10 K (see below), the Life of the Insulation will be approximately halved. The correct insulation for the winding of a motor is therefore determined by both the temperature rise in the motor and the temperature of the ambient air. If a motor is subjected to an ambient temperature higher than 40 °C, it must normally be derated or an insulating material of a higher class must be used. According to international standards, temperature is measured in degrees Celsius (°C), whilst temperature difference is stated in the unit Kelvin (K). 1 Celsius degree is equivalent to 1 K. Fig 1.2.B - Temperature Limits According to IEC 85
6 For class F, for instance, the temperature rise must not exceed 105 K, provided that the ambient temperature does not exceed +40°C. This applies if the resistance measuring method is used. This involves first measuring the resistance of the winding at ambient temperature, then running a temperature-rise test of the motor to determine the temperature in the winding at rated power, then measuring the resistance of the winding at the end of the test. The temperature rise is calculated using this formula: Where: t2 = temperature of winding at end of temperature-rise test t1 = temperature of winding before temperature-rise test ta = temperature of cooling medium at end of temperature-rise test R2 = resistance of winding at end of temperature-rise test R1 = resistance of winding at temperature t1 Constant = 235 for copper winding: 225 for aluminum winding What this method determines is the mean temperature rise. This is why an extra thermal margin of 10 K, for example, is reserved between the mean temperature of the winding and the temperature at its hottest point. The graph in Fig.1.2.C illustrates the effect of exceeding the highest permitted winding temperature on the winding life.
7 Fig.1.2.C - Effect of Winding Temperature on Life of Insulation Frame Size Motor frame dimensions have been standardized with a uniform frame size numbering system. This system was developed by NEMA and specific frame sizes have been assigned to standard motor ratings based on enclosure, horsepower and speed. The current standardized frames for integral horsepower induction motors ranges from 143T to 445T. These standards cover most motors in the range of one through two hundred horsepower. Typical example of where you can locate the frame is shown in Fig 1.2.D – Frame No. Fig 1.2.D – Frame No
8 The numbers used to designate frame sizes have specific meanings based on the physical size of the motor. Some digits are related to the motor shaft height and the remaining digit or digits relate to the length of the motor. The rerate, or frame size reduction programs were brought about by advancements in motor technology relating mainly to higher temperature ratings of insulating materials, improved magnetic steels and improved bearings. At the present time, NEMA frame assignments do no exist for motors larger than 445T and each manufacturer may have different frame designations for these motors. One additional suffix that may be used on standard motors in frames 286T and larger is an “S” inserted after the “T”. This “S” stands for short shaft. In addition to having a short shaft, the motor will have a small diameter shaft (“U” dimension) and the bearing in the drive shaft end of the motor will be somewhat smaller than the equivalent long shaft motor. Short shaft motors are intended for use only on direct coupled centrifugal pumps and other direct coupled loads where there will not be a side pull (overhung load) exerted on the shaft by “V” belts. Table 1.2B – NEMA Frame Assignment – Three-Phase Motors OPEN MOTORS – GENERAL PURPOSE NEMA PROGRAM HP ORIG. 3600 RPM 1952 RERATE 1964 RERATE ORIG. 1800 RPM 1952 RERATE 1964 RERATE ORIG. 1200 RPM 1952 RERATE 1964 RERATE ORIG. 900 RPM 1952 RERATE 1964 RERATE 1 1.5 2 — 203 204 — 182 184 — 143T 145T 203 204 224 182 184 184 143T 145T 145T 204 224 225 184 184 213 145T 182T 184T 225 254 254 213 213 215 182T 184T 213T 3 5 7.5 224 225 254 184 213 215 145T 182T 184T 225 254 284 213 215 254U 182T 184T 213T 254 284 324 215 254U 256U 213T 215T 254T 284 324 326 254U 256U 284U 215T 254T 256T 10 15 20 284 324 326 254U 256U 284U 213T 215T 254T 324 326 364 256U 284U 286U 215T 254T 256T 326 364 365 284U 324U 326U 256T 284T 286T 364 365 404 286U 326U 364U 284T 286T 324T 25 30 40 364S 364S 365S 286U 324S 326S 256T 284TS 286TS 364 365 404 324U 326U 364U 284T 286T 324T 404 405 444 364U 365U 404U 324T 326T 364T 405 444 445 365U 404U 405U 326T 364T 365T 50 60 75 404S 405S 444S 364US 365US 404US 324TS 326TS 364TS 405S 444S 445S 365US 404US 405US 326T 364TS* 365TS* 445 504U 505 405U 444U 445U 365T 404T 405T 504U 505 — 444U 445U — 404T 405T 444T 100 125 150 445S 504S 505S 405US 444US 445US 365TS 404TS 405TS 504S 505S — 444US 445US — 404TS* 405TS* 444TS* — — — — — — 444T 445T — — — — — — — 445T — — 200 250 — — — — 444TS 445TS — — — — 445TS* — — — — — — — — — — — — — * When motors are to be used with v-belt or chain drives, the correct frame size shown but with suffix letter S omitted.
9 Table 1.2C – Suffixes to NEMA Frames TEFC MOTORS – GENERAL PURPOSE NEMA PROGRAM HP ORIG. 3600 RPM 1952 RERATE 1964 RERATE ORIG. 1800 RPM 1952 RERATE 1964 RERATE ORIG. 1200 RPM 1952 RERATE 1964 RERATE ORIG. 900 RPM 1952 RERATE 1964 RERATE 1 1.5 2 — 203 204 — 182 184 — 143T 145T 203 204 224 182 184 184 143T 145T 145T 204 224 225 184 184 213 145T 182T 184T 225 254 254 213 213 215 182T 184T 213T 3 5 7.5 224 225 254 184 213 215 182T 184T 213T 225 254 284 213 215 254U 182T 184T 213T 254 284 324 215 254U 256U 213T 215T 254T 284 324 326 254U 256U 284U 215T 254T 256T 10 15 20 284 324 326 254U 256U 284U 215T 254T 256T 324 326 364 256U 284U 286U 215T 254T 256T 326 364 365 284U 324U 326U 256T 284T 286T 364 365 404 286U 326U 364U 284T 286T 324T 25 30 40 365S 404S 405S 324U 326S 364US 284TS 286TS 324TS 365 404 405 324U 326U 364U 284T 286T 324T 404 405 444 364U 365U 404U 324T 326T 364T 405 444 445 365U 404U 405U 326T 364T 365T 50 60 75 444S 445S 504S 365US 405US 444US 326TS 364TS 365TS 444S 445S 504S 365US 405US 444US 326T 364TS* 365TS* 445 504U 505 405U 444U 445U 365T 404T 405T 504U 505 — 444U 445U — 404T 405T 444T 100 125 150 505S — — 445US — — 405TS 444TS 445TS 505S — — 445US — — 405TS* 444TS* 445TS* — — — — — — 444T 445T — — — — — — — 445T — — * When motors are to be used with v-belt or chain drives, the correct frame size shown but with suffix letter S omitted. The following explanations of the various fame suffixes used on NEMA frame motors have been compiled for the benefit of EASA members. The suffixes for NEMA frame motors are the letters that immediately follow the frame numbers. Notice that more than one suffix may be used on any given motor. Note: “D” dimension (shall height) of a motor or generator in these frame sizes equals 1 /4 the value of the first two digits in the frame number. Example: 284 frame: 28/4 = 7, D = 7" A — Industrial direct-current machine. B — Carbonator pump motors, (See NEMA MG 1-2006, 18.270 – 18.281) C — Type C face mounting on drive end. CM — Face mounting dimensions are different from those for the frame designation having the suffix letter “C” (The letters “CH” are considered as one suffix and should not be separated.) D — Type D flange mounting on drive end. E — Shaft extension dimensions for elevator motors in frames larger than 326T frames. FC — Face mounting on opposite drive end. FD — Flange mounting on opposite drive end.
10 G — Gasoline pump motors. (See NEMA MG 1-2006, 18.91.) H — Indicates a small machine having an “F” dimension larger than that of the same frame without the suffix letter “H”. (See NEMA MG 1-2006, 4.4.1 and 4.5.1.) HP or HPH — Type P flange-mounted, vertical sotid-shaft motors having dimensions in accordance with NEMA MG 1- 2006, 18.252. (The letters “HP” and “HPH” are considered as one suffix and should not be separated) J — Jet pump motors. (See NEMA MG 1-2006, 18.132.) JM — Face-mounted, close-coupled pump motor having antifriction bearings and dimensions in accordance with Table 1 of MG 1-2006, 18.250. (The letters “JM” are considered as one suffix and should not be separated.) JP — Type C face-mounted, close-coupled pump motor having antifriction bearings and dimensions in accordance with Table 2 of MG 1 -2006, 18.250. (The letters “MP” are considered as one suffix and should not be separated.) K — Sump pump motors. (See NEMA MG 1-2006, 18.78.) LP or LPH — Type P flange-mounted, vertical solid-shaft motors having dimensions in accordance with MG 1-2008, 18- 251. (The letters “LP” and “LPH” are considered as one suffix and should not be separated.) M — Oil burner motors. (See NEMA MG 1-2006, 18.106.) N — Oil burner motors. (See NEMA MG 1-2006, 18.108.) P or PH— Type P flange-mounted, vertical hollow-shaft motors having dimensions in accordance with NEMA MG 1- 2006, 18.238. R — Drive end tapered shaft extension having dimensions in accordance with NEMA MG 1-2008, 4.4.2. S — Standard short shaft for direct connection. T — Included as part of a frame designation for which standard dimensions have been established. U — Previously used as part of a frame designation for which standard dimensions had been established. V — Vertical mounting only. VP — Type P flange-mounted, vertical solid-shaft motors having dimensions in accordance with NEMA MG 1- 2008, 18.237. (The letters “VP” are considered as one suffix and should not be separated.)
11 X — Wound-rotor crane motors with double shaft extension. (See NEMA MG 1-2006, 18229 and 18.230.) Y — Special mounting dimensions, (Dimensional diagram must be obtained from manufacturer.) Z — All mounting dimensions are standard except the shaft extension(s). Also used to designate machines with double shaft extension. Note: Manufacturers may use any letter preceding the frame number, but such a letter will have no reference to standard mounting dimensions. Suffix letters shall be added to the frame number in the following sequences: Suffix Letter Sequence A, H ……………………………………………………… 1 G, J, M, N, T, U, HP, HPH, JM, JP, LP, LPH, & VP .......... 2 R, S ..................................................................................... 3 C, D, P, PH ………………………………………………. 4 FC, FD …………………………………………………… 5 V …………………………………………………………. 6 E, X, Y, Z ............................................................................ 7 Example: “T” frame motor with a “C” face mounted vertically with a nonstandard shaft extension; (Sequences 2.4.8 and 7) 184TCVZ. Note: This material is reproduced by permission of the National Electrical Manufacturers Association from NEMA Standards, MG 1-2006, 4.2.2. It was originally published as EASA Tech Note No. 7 (September 1985) and reviewed and updated as necessary in November 2007. 1.3 Enclosure Type The enclosure of the motor must protect the windings, bearings, and other mechanical parts from moisture, chemicals, mechanical damage and abrasion from grit. NEMA standards MG1-1.25 through 1.27 define more than 20 types of enclosures under the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed
12 windings. The most commonly used motor enclosures are open dripproof, totally enclosed fan cooled and explosionproof. Fig. 1.3A – Shows location of Enclosure Tag The Standards for IP Codes apply to the classification of degrees of protection provided by enclosure for all rotating machines. The designation used for the degree of protection consists of the letter IP (International Protection) followed by two characteristic numerals.
13 When the degree of protection is specified by only one numeral, the omitted numeral is replaced by the letter X. For example, IPX5 or IP2X. The first Characteristic Numeral indicates the degree of protection provided by the enclosure with respect to persons and also to the parts of the machine inside the enclosure. The Second Characteristic Numeral indicates the degree of protection provided by the enclosure with respect to harmful effect due to ingress of water. The two characteristic numerals signify conformity with the conditions indicated in Table 1.3.A. – Degrees of Protection Indicated by the Two Characteristic Numerals. Table 1.3.A - Degrees of Protection indicated by the Two Characteristic Numerals FIRST CHARACTERISTIC NUMERAL DEGREE OF PROTECTION SECOND CHARACTERISTIC NUMERAL DEGREE OF PROTECTION 0 Non-protected machine 0 Non-protected machine 1 Machine protected against solid objects greater than 2 inches (50 mm) 1 Machine protected against dripping water 2 Machine protected against solid objects greater than 0. 5 inches (12 mm) 2 Machine protected against dripping water when tilted up to 15o 3 Machine protected against solid objects greater than 0.1 inches (2.5 mm) 3 Machine protected against spraying water 4 Machine protected against solid objects greater than 0.04 inches (1 mm) 4 Machine protected against splashing water 5 Dust-protected machine 5 Machine protected against water jets 6* Dust-tight machine 6 Machine protected against heavy seas 7 Machine protected against the effects of immersion Machine protected against continuous submersion * Not include in IEC 60034-5, 1991 Standards Reference: NEMA Standards MG-1 2006, 5.8, Tables 5-1, and 5-2. IEC International Standard IEC 60034-5, 1991.
14 Classification According to Environmental Protection* IP CODE CLASSIFICATION IP CODE CLASSIFICATION IP 00 Open Machine IP 22 Dripproof guarded machine IP 10 Semi-guarded machine IP 44 Totally enclosed pipe-ventilated machine IP 12 Dripproof machine IP 54 Totally enclosed non-ventilated machine IP 13 Splash-proof machine IP 55 Water-proof machine * Reference: NEMA Standards MG-1 2006, 1.25, 1.26, and 1.27.
15 Open Dripproof. The open dripproof motor (ODP) has a free exchange of air with the ambient. Drops of liquid or solid particles do not interfere with the operation at any angle from 0 to 15degrees downward from the vertical. The openings are intake and exhaust ports to accommodate interchange of air. The open dripproof motor is designed for indoor use where the air is fairly clean and where there is little danger of splashing liquid. Refer to Fig. 1.3A – Open Dripproof (ODP) Fig. 1.3A – Open Dripproof (ODP) Totally Enclosed Fan Cooled (TEFC). This type of enclosure prevents the free exchange of air between the inside and outside of the frame, but does not make the frame completely airtight. A fan is attached to the shaft and pushes air over the frame during its operation to help in the cooling process. The ribbed frame is designed to increase the surface area for cooling purposes. There is also a totally enclosed non-ventilated (TENV) design which does not use a fan,
16 but is used in situations where air is being blown over the motor shell for cooling, such as in a propeller fan application. Refer to Fig. 1.3B – Totally Enclosed Fan Cooled (TEFC) Motor. Fig. 1.3B – Totally Enclosed Fan Cooled (TEFC) Motor Explosionproof The explosionproof motor is a totally enclosed machine and is designed to withstand an explosion of specified gas or vapor inside the motor casing and prevent the ignition outside the motor by sparks, flashing or explosion. These motors are designed for specific hazardous purposes, such as atmospheres containing gases or hazardous dusts. For safe operation, the maximum motor operating temperature must be below the ignition temperature of surrounding gases or vapors. Explosionproof motors are designed, manufactured and tested under the rigid requirements of the Underwriters Laboratories. Hazardous location motor applications are classified by the type of hazardous environment present, the characteristics of the specific material creating the hazard, the probability of exposure to the environment, and the maximum temperature level that is considered safe
17 for the substance creating the hazard. The format used to define this information is a class, group, division and temperature code structure. Class I (Gas or Vapor) Group: A - Acetylene B - Hydrogen and Manufactured Gases C - Ethyl-Ether, Ethylene and Cyclopropane D - Gasoline, Hexane, Naphtha, Benzine, Butane, Propane, Alcohol Lacquer Solvent Vapors and Natural Gas Division II: Hazard of fire or explosion is present only as a result of an accident. Motors may be dripproof or TEFC. Class II (Dusts) Group: E - Metal Dust (Special Seals) F - Carbon Black, Coal or Coke Dust G - Flour, Starch or Grain Dust Division I: Hazard is always present due to normal conditions. (Dust suspended in the atmosphere.) Motors must be explosionproof construction with Underwriter’s label. Division II: Motors may be TEFC or externally ventilated: (A) Where dust deposits on electrical equipment prevent safe heat dissipation. (B) Where deposit or dust might be ignited by arcs or burning material. Class III (Fibers) Fibers those are easily ignitable but not apt to be suspended in the air to produce mixtures. Examples include rayon, nylon, cotton, saw dust, and wood chips. Division II: Location in which easily ignitable fibers are stored or handled TEFC enclosure can be used if there is a minimal amount of fibers or flying in the air.
18 Converting from NEMA enclosure classifications to IEC enclosure classifications NEMA enclosure classifications are developed by NEMA and used in the U.S./American market. Ingress Protection - IP - ratings are developed by the European Committee for Electro Technical Standardization (CENELEC) (described IEC/EN 60529), and specifies the environmental protection and enclosure provided. The table below can be used to convert from NEMA Enclosure Types to IEC Enclosure Types:
19 Continuation of … Note: NEMA standards meet or exceed IEC standards. The conversion does not work in the opposite direction. 1.4 Temperature class Combustible gas or vapor and explosion-protected electrical equipment is divided into temperature classes T1 to T6 with regard to the ignition temperature of the gas or vapor and the maximum surface temperature of the equipment. Refer to Table1.4A - Temperature Class. Ignition temperature, thermal flashpoint, is the lowest temperature of a surface at which a substance ignites on contact with the surface.
20 Table1.4A - Temperature Class Hazardous area and zones Hazardous areas are rooms, spaces or areas in which an explosive gas mixture may occur under conditions such that electrical equipment, among other things, may have to meet certain requirements. Hazardous areas are categorized as zones as follows: Zone 0 - An area in which an explosive gas atmosphere is present continuously or is present for long periods. Zone 1 - An area in which an explosive gas atmosphere is likely to occur in normal operation. Zone 2 - An area in which an explosive gas atmosphere is not likely to occur in normal operation and if it does occur it will exist for a short period only. It is important that the mechanical design of installations should be such that hazardous areas should be few and of small extent. It should also be an aim to make hazardous areas chiefly Zone 2 areas.
21 Motors for Potentially Explosive Atmosphere The principle of design of explosion-safe motors. There are two main principles for explosion protection for electric motors. One is to design the motor so that no dangerous heat or spark occurs. This includes the increased safety version, EEx e. The other method is based on isolating any dangerous heat or spark inside the motor so as to prevent the ignition of any explosive mixture of gases outside the motor. This includes the version with flameproof enclosure, EEx d, and the version with pressurized enclosure, EEx p. These are the three internationally standardized versions that are suitable for motors to be installed in Zone 1. The "non-sparking" version, Exn, according to IEC 79-15 (1987) is intended for use in Zone 2. IEC 79-15 has not yet been transferred to a national standard, but this is expected to happen after it has been converted into a European standard in CENELEC. British Standard BS 5000, Part 16 has a similar version. Increased safety design, EEx e The motor must not have any parts that, in normal service, produce arcs or sparks, or reach a dangerous temperature. Special steps must be taken in the design to prevent the risk of ignition by arcs or sparks or by excessively high temperature as a consequence of poor contact, overloading or the like. The temperature limitation applies to internal and external surfaces. The degree of protection of the terminal box must not be lower than IP 54 and any enclosure that contains only insulated parts must have at least IP 44. However, in the case of motors installed in clean areas and supervised by trained personnel, IP 23 is permitted for motors complying with explosion group I, i.e. for use in coal mines, and IP 20 for explosion group II, i.e. other areas. The requirements to be met by the terminal box are unchanged, however. The limitation of the field of application must be stated on the motor.
22 The air gap between rotor and stator is subject to certain minimum dimensions. There are also minimum dimensions for creepage distance and the air gap between winding leads and earth. All connections between live parts must be secured so that they cannot work loose. Cable bushings and the cable branch in the terminal box are also subject to certain temperature limits. The motors must have both an internal and an external earthing screw. Flameproof enclosure, EEx d The housing of the motor must be so designed that ignition and combustion of any explosive mixture inside the housing cannot be propagated to a similar mixture outside the housing and that the housing can withstand without damage the explosion pressure thus caused. The motor need not be hermetically sealed; gas may therefore penetrate the motor. The permitted temperature inside the motor is limited only by the insulation class of the motor. The rated output depends on how hot the outer surface of the motor is permitted to be with regard to the relevant temperature class. Slip-ring motors, commutator motors and brake motors can all be made in flameproof versions. No external parts may cause sparks. The motors must have both an internal and an external earthing screw. Pressurized enclosure, EEx p In this version the motor must be under a given minimum positive pressure relative to the surroundings, so that the ambient atmosphere cannot penetrate the motor in service. The pressurization can take the form of positive pressure with compensation for leakage or positive pressure with continuous flushing.
23 Monitoring of the winding temperature is recommended in cases where the pressurization system is also responsible for cooling the motor. Before the motor is started, it and its associated ducting for supply and exhaust air must be flushed through with fresh air or a protective gas for long enough to ensure that any explosive gas mixture has been reliably removed. The amount of fresh air or protective gas flushed through must in any case be equivalent to at least five times the total free volume. A positive pressure of at least 0.5 mbar relative to the ambient pressure must be maintained in service. If the positive pressure is lost when the motor is in service, the motor must be automatically disconnected. The temperature of the outer surface of the motor must not exceed the stated figures for the temperature class in question. The motors must have both an internal and an external earthing screw. Fig. 1.4A – Pressurized Enclosure EEx p
24 Special requirements to be met by motors in increased safety version. EEx e. Non-sparking design, Exn This version to IEC 79-15 is a simpler version than EEx e. in general terms, a normal squirrel-cage motor may be approved, but, as for EEx e, there are certain minimum requirements for distances between moving and stationary parts, air gaps and creepage distances between winding leads and earth. The motor must be designed so that sparking cannot occur - "non- sparking" design. The outside temperature of the motor is determined in normal duty. The temperature rise on starting is not included if duty is continuous. The degree of protection must be IP 54 for the terminal box and IP 44 for those parts of the housing that contain only insulated parts. The motors must have an internal earthing screw and, if requested, an external earthing screw as well. There is no mandatory requirement for a certificate from a testing station. There are national rules for the installation of version Exn motors in zone 2. Version Ex N to British Standard BS 5000 Part 16 differs in certain respects from Exn to IEC 79-15. Following several years of international engagement by CENELEC, Comite European de Normalization Electrotechnique, common standards now apply regarding the design and testing of electrical equipment that is to be used in explosive atmospheres. These standards are based on the previously issued IEC Publication 79.
25 Only intrinsically-safe circuits of category EEx ia may be used in Zone 0. Motors are thus excluded. Motors of category EEx d, EEx e and EEx p may be used in Zone 1. In Zone 2, equipment permitted in zones 0 and 1 may of course be used. Under certain conditions the equipment, motors for instance, need not be of explosion-protected design. An example is shown in Fig. 1.4B. These conditions are as follows; they must all be met:  The degree of protection of the motors must not be below IP 54.  In service they must not produce a temperature of more than 200 °C. This requirement applies to both internal and external parts. In duties S1 (continuous) and S6 (continuous with intermittent load), the temperature may briefly exceed 200 °C in conjunction with starting.  The motors must not produce sparks or arcs in service.  They must be placed in a hazard area that has been assigned temperature class T1 to T3.
26 Fig. 1.4B - Example of classification and the extent of the hazardous areas in a ventilated tank Temperature limits, IA/IN and time tE for version EEx e The increased safety design, EEx e, Is the most common type of explosion-protected motor. They are subject to certain limits on temperature and on the relationship between the starting ratio lA/lN (which is the same as lst/l) and the time tE. Temperature limits To prevent the ignition of an explosive atmosphere, no part of the motor may, during starting, during operation at rated output or at a given overload, for example at the end of the time tE, have a higher temperature than that stated in the Table 1.4B - Temperature class and temperature limit in 0 C. The temperature depends on the temperature class of the motor.
27 Table 1.4B. – Temperature Class and Temperature Limit in 0 C The temperature limits also apply to uninsulated conductors such as rotor bars. However, during starting, it is permissible for the temperature of the rotor to reach 300°C maximum. To maintain the thermal stability of the insulation of the windings, the temperature limits in the Table 1.4C must be observed. Table 1.4C - The Temperature Limits Limit temperature and maximum temperature rise for insulated winding to temperature Class B and F, measured by the resistance method. IA/lN and time tE If a squirrel-cage motor is to remain secure, the motor protection must be correctly chosen. Current standards lay down that the rating plate of a motor and the type testing report must state the ratio IA/lN. IA is the starting current of the motor and IN its full-load current. The time tE is, also stated. This is the time taken for the stator or rotor winding to heat up from normal operating temperature at the highest permitted ambient temperature to the highest permitted limit
28 temperature, with the rotor locked and the stator winding loaded with the starting current IA. In other words, the highest permitted surface temperature for the temperature class or the insulation class of the winding, the lower of the two being the limit. Fig. 1.4C Surface temperature for the temperature class or the insulation class Where: 0 = temperature 0 °C. A = maximum ambient temperature, normally 40 °C. B = temperature at rated output. C = maximum permitted temperature at rated output for the insulation class. D = limit temperature at rated output for the insulation class or the temperature class. E = temperature rise at rated output. F = temperature rise in locked-rotor test. G = heating time during F. Relationship between IA/lN. and tE The time tE and the ratio IA/lN must be determined and stated so that suitable current dependent protection can be chosen to protect the motor from overheating. The value of tE must be such that, when the rotor is locked, the motor is disconnected by a current-dependent protection device before the time tE has expired. Generally this is possible if the time tE for the motor is longer than the value indicated by the curve for
29 the corresponding IA/lN. Values below the curve are only permitted if specially adapted current-dependent overload protection that has been proved effective in tests is used. This protection must be identified on the rating plate of the motor. Fig. 1.4D - Minimum values of tE as a function of IA/IN Fig. 1.4D Minimum values of tE as a function of IA/IN where normal overload relays are used. Temperature conditions in the stator and rotor of a squirrel-cage motor with rated output 1.3 kW at maximum permitted ambient temperature 40 °C. The time tE is limited by the temperature rise of the stator winding.
30 In no case must the time tE be shorter than 5 seconds, nor must the ratio IA/IN be greater than 10. If some form of protection other than current- dependent protection is used (temperature sensors built into the motor for example), IA/IN and tE are not stated. The rating plate of the motor states how it is protected against overheating. Temperature conditions in the stator and rotor of a squirrel-cage motor with rated output 10 kW at maximum permitted ambient temperature 40 °C. The time tE is limited by the temperature rise of the rotor winding. 1.5 Mounting NEMA Dimensions NEMA has standardized motor dimensions for a range of frame sizes. Standardized dimensions include bolt-hole size, mounting base dimensions, shaft height, shaft diameter, and shaft length. Use of standardized dimensions allows existing motors to be replaced without reworking the mounting arrangement. In addition, new installations are easier to design because the dimensions are known. NEMA divides standard frame sizes into two categories, fractional horsepower and integral horsepower. The most common frame sizes for
31 fractional horsepower motors are 42, 48, and 56. Integral horsepower motors are designated by frame sizes 143 and above. A T in the motor frame size designation for an integral horsepower motor indicates that the motor is built to current NEMA frame standards. Motors that have a U in their motor frame size designation are built to NEMA standards that were in place between 1952 and 1964. The frame size designation is a code to help identify key frame dimensions. The first two digits are used to determine the shaft height. The shaft height is the distance from the center of the shaft to the mounting surface. To calculate the shaft height, divide the first two digits of the frame size by 4. For example, In Fig. 1.5A - a 143T frame size motor has a shaft height of 3½ inches (14 ÷ 4). Fig. 1.5A – Importance of Frame Size The third digit in the integral T frame size number is the NEMA code for the distance between the center lines of the motor feet mounting bolt holes. The distance is determined by matching this digit with a table in NEMA publication MG-1. For example in Fig. 1.5B, the distance between the center lines of the mounting bolt holes in the feet of a 143T frame is 4.00 inches.
32 FRAME SIZE SERIES Third/Fourth Digit In Frame Number D 1 2 3 4 5 140 4.00 4.50 4.50 160 4.00 3.50 4.00 4.50 5.00 5.00 180 4.50 4.00 4.50 5.00 5.50 5.50 200 5.00 4.50 5.00 5.50 6.50 6.50 210 5.25 4.50 5.00 5.50 6.25 6.25 220 5.50 5.00 5.50 6.25 6.75 6.75 250 6.25 5.50 6.25 7.00 8.25 8.25 280 7.00 6.25 7.00 8.00 9.50 9.50 320 8.00 7.00 8.00 9.00 10.50 10.50 Fig. 1.5B – Importance of Frame Size IEC Dimensions IEC also has standardized dimensions, but these dimensions differ from NEMA standards. An example of the IEC dimensions are shown in the following drawing.
33 IEC Mounting Dimensions Foot-Mounted AC & DC Machines
34 IEC Flange-Mounted AC & DC Machines Dimensions for Flanges
35 IEC Shaft Extension, Key and Keyseat Dimensions for Continuous Duty AC Motors.
36 Dimensions for AC Machines – Millimeters NEMA Frame
37
38
39
40 Mounting Positions The typical floor mounting positions are illustrated in the following drawing, and are referred to as F-1 and F-2 mountings. The conduit box can be located on either side of the frame to match the mounting arrangement and position. The standard location of the conduit box is on the left-hand side of the motor when viewed from the shaft end. This is
41 referred to as the F-1 mounting. The conduit opening can be placed on any of the four sides of the box by rotating the box in 90° steps. With modification, a foot-mounted motor can be mounted on a wall and ceiling. Typical wall and ceiling mounts are shown in the following illustration. Wall mounting positions have the prefix W and ceiling mounted positions have the prefix C.
42 Mounting Faces It is sometimes necessary to connect the motor directly to the equipment it drives. In the following example a motor is connected directly to a gear box. C-face The face, or the end, of a C-face motor has threaded bolt holes. Bolts to mount the motor pass through mating holes in the equipment and into the face of the motor.
43
44
45 D-flange The bolts go through the holes in the flange of a D-flange motor and into threaded mating holes of the equipment.
46
47
48 JM Face Mounted NEMA FRAME DIMENSIONS* TYPE JM FACE-MOUNTING, CLOSED-COUPLED, AC PUMP MOTORS * DIMENSIONS IN MILLIMETERS FRAME DESIGNATIONS U AH* AJ AK BB BD MAX BF NUMBER TAP SIZE BOLT PENETRATION ALLOWANCE 143JM and 145JM 22.21 108 149.25 114.30 3.5 168 4 3/8-16 14 182JM and 184JM 22.21 108 149.25 114.30 3.5 168 4 3/8-16 14 213JM and 215JM 22.21 108 184.15 215.90 7 228 4 1/2-13 19 254JM and 256JM 31.73 134 184.15 215.90 7 254 4 1/2-13 19 284JM and 286JM 31.73 134 279.40 317.5 7 355 4 5/8-11 24 324JM and 326JM 31.73 134 279.40 317.5 7 355 4 5/8-11 24 FRAME DESIGNATIONS EL EM EN EP MIN EQ* ER MIN KEYSEAT ET* TAP SIZE TAP DRILL DEPTH MAX BOLT PENETRATION ALLOWANCE R ES MIN S 143JM and 145JM 29.35 25.40 3/8-16 28 19 30 16.0 108 19.5 42 4.80 73.0 182JM and 184JM 31.75 25.40 3/8-16 28 19 32 16.0 108 19.5 42 4.80 73.0 213JM and 215JM 31.75 25.40 3/8-16 28 19 45 16.0 108 19.5 42 4.80 73.0 254JM and 256JM 44.45 34.92 1/2-13 38 25 45 16.0 134 28.2 65 6.40 76.5 284JM and 286JM 44.45 34.92 1/2-13 38 25 54 16.0 134 28.2 65 6.40 76.5 324JM and 326JM 44.45 34.92 1/2-13 38 25 54 16.0 134 28.2 65 6.40 76.5 Reference: NEMA Standards MG 1-2006, 16.250. Dimensions, except for tap sizes, are shown in millimeters (rounded off). Tap sizes are in inches.
49 JP Face Mounted NEMA FRAME DIMENSIONS* TYPE JM FACE-MOUNTING, CLOSED-COUPLED, AC PUMP MOTORS * DIMENSIONS IN MILLIMETERS FRAME DESIGNATIONS U AH* AJ AK BB BD MAX BF NUMBER TAP SIZE BOLT PENETRATION ALLOWANCE 143JP and 145JP 22.21 186 149.25 114.30 3.5 168 4 3/8-16 14 182JP and 184JP 22.21 186 149.25 114.30 3.5 168 4 3/8-16 14 213JP and 215JP 31.73 207 184.15 215.90 7 228 4 1/2-13 19 254JP and 256JP 31.73 207 184.15 215.90 7 254 4 1/2-13 19 284JP and 286JP 31.73 207 279.40 317.5 7 355 4 5/8-11 24 324JP and 326JP 31.73 207 279.40 317.5 7 355 4 5/8-11 24 364JP and 366JP 41.26 207 279.40 317.5 7 355 4 5/8-11 24 FRAME DESIGNATIONS EL EM EN EP MIN EQ* ER MIN KEYSEAT ET* TAP SIZE TAP DRILL DEPTH MAX BOLT PENETRATION ALLOWANCE R ES MIN S 143JM and 145JM 29.35 25.40 3/8-16 28 19 30 40.0 186 19.5 42 4.80 151.0 182JM and 184JM 31.75 25.40 3/8-16 28 19 32 40.0 186 19.5 42 4.80 151.0 213JM and 215JM 44.45 34.92 3/8-16 38 25 45 60.5 207 28.2 65 6.40 149.5 254JM and 256JM 44.45 34.92 1/2-13 38 25 45 60.5 207 28.2 65 6.40 149.5 284JM and 286JM 44.45 34.92 1/2-13 38 25 54 60.5 207 28.2 65 6.40 149.5 324JM and 326JM 44.45 34.92 1/2-13 38 25 54 60.5 207 28.2 65 6.40 149.5 324JM and 326JM 53.95 44.45 1/2-13 38 25 54 60.5 207 35.9 65 9.55 149.5
50 Mounting arrangements IEC Publication 34—7 lays down two ways of stating how a motor is mounted. Code I covers only motors with bearing end shields and one shaft extension. Code II is a general code. The table below includes the designations for the most commonly occurring mounting arrangements according to the two codes.
51 IM..2. = IM.. 0. + IM..1. IM..4. = IM..0. + IM ..1. IM..3. IM..8. = The motor must be able to work in all mounting positions as per IM..0. to IM..7. IM..9. = The position of the shat cannot be specified with the third digit 0 – 8: instead it must be specified in each individual case. The electric motors execution and assembly type can be seen here 1.6 Manufacturer’s Identification Number This model and/or catalog number is used to establish motor identity and age for replacement parts and warranty.
52 Bearing Part Numbers. The bearing part numbers on U.S. Motors’ machines are made conveniently available on the nameplate so that, when required, procurement of replacement bearings can be carried out prior to motor disassembly. Ball and roller bearings (anti-friction bearings) are manufactured to very rigid tolerance specifications and must be treated as precision parts to insure that they don not fail prematurely. American Bearing Manufacturers Association (ABMA) Standard 20 specifies boundary dimensions, tolerance classes, and internal clearance for ball and roller bearings. Boundary Dimensions The ID (d), OD (D) and width (B) of bearings are standardized metric dimensions with the last two digits in the bearing nomenclature representing the bore size. Beginning with a 20 mm bore, the last two digits equal the bore in mm divided by 5. The smallest internal diameter interval is, therefore, 5 mm. This permits the two-digit value to span a bore range from 20 (04) to 480 mm (96). This system is used on all types of rolling element bearings.
53 Tolerance Classes The tolerance classes specified in the ABMA Standards have been established by the Annular Bearing Engineers Committee (ABEC). These tolerance classes have been accepted by the American National Standards Institute (ANSI) and conform essentially with standards of the International Organization for Standardization (ISO). ABEC Parameters ABEC Standards, which define tolerances for several major bearing dimensions and characteristics, are divided into mounting dimensions and bearing geometry. The geometric tolerances apply to both inner and outer rings and include:  Bore roundness  Bore runout with side  Bore taper  Race runout with side  Width variation  Radial runout ABEC standards do not address many other factors that affect bearing performance and life, including:  Materials  Ball complement – number, size and precision  Raceway curvature, roundness and finish  Cage design  Lubricant ABEC Precision Classes General – purpose ball bearing are manufactured to tolerances in accordance with precision classes ABEC1, ABEC3, BEC5, ABEC7 and ABEC9. The ascending numbers indicate stricter tolerances and additional requirement as found in ABMA Standard 20.
54 Bearing Manufacturer Numbering Systems The metric system of measurement has been widely adopted by all bearing manufacturers, which ensures ready interchangeability of most bearings types and sizes. Bearings can be identified by using ABMA numbers or by using each manufacturer’s discreet numbering system. In either case, it is imperative that repair firms record the name as well as all of the numbers on each bearing that is to be replaced. They should also check the nomenclature designations in catalogs from the makers of the bearings because there are some variations among manufacturers.
55 Example: 50BC03JPP3 – 50 mm bore diameter whose bearing last two digit is 50/5 = 10, standard Deep Groove Ball Bearing (BC), medium series (03), standard steel cage (J), double shield (PP), and loose internal fitup – ABMA 3 or C3. The equivalent SKF bearing no. is 6310 ZZ/C3.
56 Example: 50RU03K30 – 50 mm bore diameter whose last two digit is 50/5 = 10. RU – cylindrical roller bearing with prefix of NU, medium series (03), brass of bronze cage (K), internal clearance greater than normal – C3 with standard tolerance. This is equivalent to NU 310 ECJ/C3 for SKF brand. EC - Optimized internal design incorporating more and/or larger rollers and with modified roller/end flange contact, J - Pressed steel cage, roller centred, unhardened and C3 - Radial internal clearance greater than Normal.
57 Bearing Designation based on ISO 1.7 Terminal Markings IEC Publication 34-8 lays down that the stator winding, parts of it and the terminals of A.C motors must be designated with the letters U, V and
58 W. External neutral terminals are designated N. The letters used for the rotor winding are K, L, M and Q. 1. End points and intermediate points of a winding are indicated by a digit after the letter, e.g. U1, U2 etc. 2. Parts of the same winding are designated by a digit before the letter, e.g. 1U1, 2U1 etc. If there is no possibility of confusion, the digit before the letter, or both, may be omitted. Terminal Markings and Connections Single-Phase Motors – Capacitor-start, NEMA Nomenclature
59 The switch in the auxiliary winding circuit has been omitted from this diagram. The connections to the switch must be made so that both auxiliary windings become de-energized when the switch is open ROTATION: CC – Counter- clockwise CW - Clockwise The direction of shaft rotation can be determined by facing the end of the motor opposite the drive. (NEMA Standards MG 1-2006, 2.41. Note: May not apply for some definite-purpose motors.)
60 Three-Phase Motors – Part-Winding Start
61
62 Three-Phase Motors – Reduced-Current Starting
63 Three – Phase Motors Single Speed
64
65 Three-Phase Motors – Two Speed, Single Winding
66 Dahlander Motors Two – speed motor with a re-connectible winding (Dahlander Connection) Two-speed motor with two separate windings Note the two-speed motors with re-connectible windings (Dahlander connection) have a higher rated output than the corresponding size with separate windings.
67 1.8 Motor Design NEMA Design Letter Changes in motor windings and rotor design will alter the performance characteristics of induction motors. Motors are designed with certain speed torque characteristics to match the speed torque requirements of the various loads. To obtain some uniformity in application, NEMA has designated specific designs of general purpose motors having specified locked rotor torque, breakdown torque, slip, starting current, or other values. The following graph shows the relationship between speed and torque that the motor produces from the moment of start until the motor reaches full load torque at rated speed.
68 Locked rotor torque, or starting torque, is developed when the rotor is held at rest with the rated voltage and frequency applied. This condition occurs each time a motor is started. When rated voltage and frequency are applied to the stator, there is a brief amount of time before the rotor turns. At this instant, a NEMA B motor develops approximately 150% of its full load torque. The magnetic attraction of the rotating magnetic field will cause the rotor to accelerate. As the motor picks up speed, torque decreases slightly until it reaches pull up torque. As the speed increases the torque increases until it reaches it’s maximum at about 200%. This is called breakdown, pullout or stall torque. Torque decreases rapidly as speed increases beyond breakdown torque until it reaches full-load torque at a speed slightly less than 100% of synchronous speed. Full load torque is the torque developed when the motor is operating with rated voltage, frequency and load. The speed at which full-load torque is produced is the slip speed or rated speed of the motor. Minimum acceptable values for different motor designs have been established and are identified by the letters A, B, C and D. The general shapes of the four typical torque-speed characteristics are shown here.
69 NEMA Design A, B, C, D NEMA has established four different designs - A, B, C and D - for electrical induction motors. Different motors of the same nominal horsepower can have varying starting current, torque curves, speeds, and other variables. Selection of a particular motor for an intended task must take all engineering parameters into account. The four NEMA (National Electrical Manufacturers Association) designs have unique speed-torque-slip relationships making them suitable to different type of applications: NEMA design A Has maximum 5% slip, high to medium starting current, normal locked rotor torque, normal breakdown torque, and suited for a broad variety of applications - as fans and pumps.
70 NEMA design B Has maximum 5% slip, low starting current, high locked rotor torque, normal breakdown torque, suited for a broad variety of applications, normal starting torque - common in HVAC application with fans, blowers and pumps. NEMA design C Has maximum 5% slip, low starting current, high locked rotor torque, normal breakdown torque, and suited for equipment with high inertia starts - as positive displacement pumps. NEMA design D Has maximum 5% slip, low starting current, very high locked rotor torque, and suited for equipment with very high inertia starts - as cranes, hoists etc. IEC Design Motors covered by this IEC standard are classified by the following designs: Design N Normal torque three-phase cage induction motors intended for direct-on- line starting, having 2, 4, 6, or 8 poles and rated from 0.4 kW to 630 kW at frequencies of 50 Hz or 60 Hz. Design NY Motors similar to design N, but intended for star-delta starting. For these motors in star-connection, minimum values for Tl and TU of 25% of the values of design N as shown in Table 1.8A may be expected.
71 Table 1.8A – Minimum Values of Torque for Design N Starting Performance Design H High torque three-phase cage induction motors with 4, 6 or 8 poles, intended for Direct-online starting, and rated from 0.4 kW to 160 kW at a frequency of 60 Hz. Torques of IEC Design H are nearly identical to NEMA Design C. Design HY Motors similar to design H but intended for star-delta starting. For these motors in star-connection, minimum values for T1 and TU of 25% of the values of Design H as shown in Table 1.8B may be expected.
72 Table 1.8B – Minimum Values of Torques for Design H Notes: 1. The values of Tl are 1.5 times the corresponding values for design N starting performance, but arc not less than 2.0. 2. The values of Tu are 1.5 times the corresponding values for design N starting performance, but are not less than 1.4. 3. The values of Tb are equal to the corresponding values for design N starting performance, but are not less than 1.9 and the values of Tu. Design N starting torque The starting torque is represented by the locked rotor torque Tl, pull-up torque Tu and breakdown torque Tb, each expressed as a per unit value of the rated torque TN, and shall be in accordance with the appropriate values given in Table 1.8A. These values are minimum values at rated voltage, with no tolerance. Higher values are allowed. The starting torque at any speed between zero and that at which breakdown torque occurs shall be not less than 1.3 times the torque obtained from a curve varying as the square of the speed and being equal to rated torque at rated speed. Note. — The factor 1.3 has been chosen with regard to an undervoltage of 10% in relation to the rated voltage at the motor terminals during the acceleration period.
73 Design N locked rotor apparent power The locked rotor apparent power S1, is the apparent power input expressed as a per unit value of the rated output PN. This value shall be not greater than the appropriate value given in Table 1.8C. The values given in Table 1.8C are independent of the number of poles and are maximum values at rated voltage, with no tolerance. Table 1.8C. Design N starting requirements Motors of design N shall satisfy the following starting requirements: 1. They shall allow two starts in succession (coasting to rest between starts) from cold conditions or one start from hot after running at rated conditions. The retarding torque due to the driven load is in each case proportional to the square of the speed and equal to the rated torque at rated speed with the external inertia given in Table 1.8D. 2. In each case a further start is permissible only if the motor temperature before starting does not exceed the steady temperature at rated load. Note. — It should be recognized that the number of starts should be minimized since these affect the life of the motor. The values given are in terms of mr2 (m = mass; r = mean radius of gyration). Note. — Moment of inertia is defined in ISO Publication 31/111 1978, No. 3- 9.1.
74 Table 1.8D For intermediate output values, external inertia shall be calculated according to the following formula, from which the values in the table have been calculated: I = 0.04 P0.9 p2.5 kg m2 where: P is the power in kW and p is the number of pairs of poles. Design NY starting requirements The starting requirements are as for design N. In addition, however, a reduced retarding torque is necessary as the starting torque in 'star' may be insufficient to accelerate some loads to an acceptable speed.
75 Design H starting torque The starting torque is represented by the locked rotor torque Tl, pull-up torque TU and breakdown torque Tb, each expressed as a per unit value of the rated torque TN, and shall be in accordance with the appropriate values given in Table 1.8B - Minimum values of torques for Design H starting performance. These values given are per unit TN. These values are minimum values at rated voltage, with no tolerance. Higher values are allowed. Design H locked rotor apparent power The locked rotor apparent power S, is the apparent power input expressed as a per unit value of the rated output PN. This value shall be not greater than the appropriate value given in Table 1.8C. The values in Table 1.8C are independent of the number of poles and are maximum values at rated voltage, with no positive tolerance. Design H starting requirements Motors of design H shall satisfy the following starting requirements: 1. They shall allow two starts in succession (coasting to rest between starts) from cold conditions, or one start from hot after running at rated conditions. The retarding torque due to the driven load is assumed to be constant and equal to rated torque, independent of speed, with an external inertia of 50% of the values given in Table1.8D. 2. In each case a further start is permissible only if the motor temperature before starting does not exceed the steady temperature at rated load. Design HY starting requirements The starting requirements are as for design H. In addition, however, a reduced retarding torque is necessary as the starting torque in 'star' may be insufficient to accelerate some loads to an acceptable speed.
76 1.9 Types of duty Definitions Various types of duty have been defined in terms of how the load, and thus the output of the motor, varies with time. The rated output for each type of duty is determined in a load test which the motor must undergo without the temperature limits laid down in IEC Publication 34-1 being exceeded. Actual operating conditions are often of a more irregular nature than those corresponding to any of the standardized types of duty. It is therefore essential, both when choosing a motor and when rating and testing it, to decide on the type of duty that corresponds best to the thermal stresses that are expected to occur in practice. IEC (the International Electrotechnical Commission) uses nine duty cycle designations to describe electrical motor operating conditions:
77 S1 Continuous duty Operation at constant load long enough for thermal equilibrium to be reached. S2 Short-time duty Operation at constant load for a given time that is shorter than the time needed to reach thermal equilibrium, followed by a rest and de-energized period long enough to allow the motor to reach a temperature that does not deviate from the temperature of the cooling medium by more than 2 K.
78 S3 Intermittent duty A sequence of identical duty cycles, where each cycle is in two parts, one at constant load and the other at rest and de-energized, in this type of duty the starting current has no significant effect on the temperature rise. The duty cycle is too short for thermal equilibrium to be reached. S4 Intermittent duty with starting A sequence of identical duty cycles, where each cycle consists of a start that is long enough to have a significant effect on the temperature of the motor, a period at constant load and a period at rest and de-energized, in this type of duty the starting current has no significant effect on the temperature
79 S5 Intermittent duty with electrical braking A sequence of identical duty cycles, where each cycle consists of a start, a period at constant load followed by rapid electrical braking and a rest and de-energized period. The duty cycles are too short for thermal equilibrium conditions to be reached. S6 Continuous-operation periodic duty A sequence of identical duty cycles, where each cycle is in two parts, one at constant load and the other at no-load. No rest and de-energized period. The duty cycles are too short for thermal equilibrium conditions to be reached.
80 S7 Continuous-operation periodic duty with electrical braking A sequence of identical duty cycles, where each cycle consists of a start and a period at constant load, followed by electrical braking. No rest and de-energized period. The duty cycles are too short for thermal equilibrium conditions to be reached. S8 Continuous-operation periodic with related load/speed changes A sequence of Identical duty cycles, each cycle consisting of a period of operation at constant load corresponding to a predetermined speed, followed by one or more periods of operation at other constant loads corresponding to different speeds. There is no rest and de-energized period.
81 Duty with non-periodic load speed variations A duty in which generally load and speed are varying non-periodically within the permissible operating range. This duty includes frequently applied overloads that may greatly exceed the full loads. For this duty type suitable full load values should be taken as the basis of the overload concept. Direction of rotation If the mains supply is connected to the stator terminals marked U, V and W of a three-phase motor, and the phase sequence of the mains is L1, L2, L3, the motor will rotate clockwise as viewed from the drive end. For the opposite direction of rotation, interchange two of the three wires connected to the starter switch or the motor. Fig. 1.9 - Normal direction of rotation is clockwise as viewed from the D-end.
82 Braking Mechanical braking Mechanical braking with magnetic lifting is the technique most widely used for the braking of electric motors. At standstill brakes of this type provide a holding torque, and are therefore used where loss of braking in the event of power failure could be dangerous. However, in certain cases it may be necessary to lift the brake without starting the motor. This can be done by supplying the brake coil from a separate power source, or with a manual release device. The mechanical brakes used for electric motors are shoe, multiple-plate or disc brakes. ABB Motors brakes are disc brakes with asbestos-free brake pads or linings. Fig. 2.0 – Mechanical Braking During braking, the braking torque is constant with mechanical braking. At standstill the brake has a holding torque. On some brakes the braking torque can be reduced for softer deceleration. When the motor is started again, the holding torque ceases automatically.
83 Electrical Braking Countercurrent braking With countercurrent braking, an ordinary standard motor is switched at full speed for the opposite direction of rotation. This can be done with a reversing switch. After braking to a standstill, the motor starts in the opposite direction of rotation, unless the current is switched off at the right moment. A low speed detector is therefore used to cut off the supply to the motor when the speed approaches zero. Countercurrent braking gives a very high braking torque. The current during braking is about the same as during starting, so that there is a considerable temperature rise in the motor. Consequently the permitted frequency of braking with the countercurrent technique is only about one-quarter of the number of permitted brakings for a brake motor. Since the permitted frequency of braking can easily be exceeded with countercurrent braking, temperature sensors should always be used to protect the motor windings from overheating. For squirrel-cage motors the braking time can be calculated approximately with the formula: Where: tb = braking time, s K1 = constant depending on number of poles. See table below. Jm = moment of inertia of motor, kgm2 Jb = moment of inertia of load, referred to speed of motor, kgm2 Mmax = maximum torque of motor, Nm Mstart = starting torque of motor, Nm
84 For slip-ring motors the starting and braking times are both determined by the dimensioning of the rheostatic starter. With countercurrent braking there is no braking action in the event of power failure. The technique is therefore unsuitable for use in plant where loss of braking could cause danger. Direct-current braking When braking with this technique, the A.C. supply to the motor is disconnected and the stator is excited with direct current instead; this causes the motor to produce a braking torque. An ordinary standard motor and suitable equipment for D.C. excitation may be used. The A.C. voltage follows a decay curve, and the D.C. voltage must not be connected until the A.C. voltage has fallen to a value at which it will not harm the D.C. equipment. Direct-current braking gives a far longer braking time than countercurrent braking, however high the excitation current is, but thermal losses are lower, so more frequent braking is permissible. Derating Factors Several factors can affect the performance of an AC motor. These must be considered when applying a motor. Voltage Variation As previously discussed, AC motors have a rated voltage and frequency. Some motors have connections for more that one rated voltage. The following table shows the most common voltage ratings for NEMA motors.
85 A small variation in supply voltage can have a dramatic affect on motor performance. In the following chart, for example, when voltage is 10% below the rated voltage of the motor, the motor has 20% less starting torque. This reduced voltage may prevent the motor from getting its load started or keeping it running at rated speed. A 10% increase in supply voltage, on the other hand, increases the starting torque by 20%. This increased torque may cause damage during startup. A conveyor, for example, may lurch forward at startup. A voltage variation also causes similar changes in the motor’s starting and full-load currents and temperature rise.
86 Frequency A variation in the frequency at which the motor operates causes changes primarily in speed and torque characteristics. A 5% increase in frequency, for example, causes a 5% increase in full-load speed and a 10% decrease in torque. Altitude Standard motors are designed to operate below 3300 feet. Air is thinner, and heat is not dissipated as quickly above 3300 feet. Most motors must be derated for altitudes above 3300 feet. The following chart shows typical horsepower derating factors, but the derating factor should be checked for each motor. A 50 HP motor operated at 6000 feet, for example, would be derated to 47 HP, providing the 40°C ambient rating is still required. Example: 50 HP x 0.94 = 47 HP Ambient Temperature The ambient temperature may also have to be considered. The ambient temperature requirement may be reduced from 40°C to 30°C at 6600 feet on many motors. However, a motor with a higher insulation class may not require derating in these conditions.
87 Earthing of machines Machines shall be provided with means for connecting a protective conductor or an earth conductor, such means being identified by the appropriate symbol or legend. This requirement does not apply to machines with supplementary insulation, to machines with rated voltages up to and including 50 VAC or 120 VDC (see IEC 60364-4-41, clause 411 and IEC 60449), or to machines for assembling in apparatus with supplementary insulation. In the case of machines having rated voltages greater than 50 VAC or 120 VDC, but not exceeding 1 000 VAC, or 1 500 VDC, the terminal for the earth conductor shall be situated in the vicinity of the terminals for the line conductors, being placed in the terminal box, if one is provided. Machines having rated outputs in excess of 100 kW (or kVA) shall have in addition an earth terminal fitted on the frame. Machines for rated voltages greater than 1 000 VAC or 1 500 VDC shall have an earth terminal on the frame, for example an iron strap, and in addition, a means inside the terminal box for connecting a conducting cable sheath, if any. For other cross-sectional areas of live conductors, the earth or protective conductor shall have a cross-sectional area at least equivalent to: 1. That of the live conductor for cross-sectional areas less than 25 mm2 ; 2. 25 mm2 for cross-sectional areas between 25 mm2 and 50 mm2 ; 3. 50 % of that of the live conductor for cross-sectional areas exceeding 50 mm2 The earth terminal shall be identified in accordance with IEC 60445.
88 Speed Control General The relationship between rotational speed, supply frequency, number of poles and slip for induction motors is usually written: In principle the speed can be controlled by changing the number of poles, the slip or the frequency. All three possibilities are used. Changing the number of poles There are three ways to change the number of poles in an induction motor. The stator can be given: 1. Two or more separate windings 2. A pole changing winding 3. Combinations of the above Two-speed motors with separate windings Having separate windings makes it possible to combine different numbers of poles with considerable freedom, but the method does not utilize the motor well, since only half the stator winding is in use at each speed, in principle the possible rated power at each speed will thus only be half that of a single-speed motor of the same size. In addition, the stator and rotor cores are normally dimensioned for a given number of poles. This may also impose certain limitations on ways in which different numbers of poles can be combined in a given core design.
89 Two-speed motors with pole changing winding There are several ways of achieving a pole changing winding in order to utilize a motor better than with two separate windings, but some limits are set by the need for the switchgear to be kept simple. The most widely used systems are the Lindstrom-Dahlander connection, often simply called the Dahlander connection, and PAM, Pole Amplitude Modulation. The Dahlander connection gives a pole number ratio of 1:2. The winding of each phase is in two parts connected in series. These are two common applications that use Dahlander pole-changing:  "Constant torque", where the rated torque of the motor is approximately the same at both speeds. The ratio between the rated outputs is about 3:2. This is achieved by connecting the windings in double star for the higher speed and in delta for the lower speed. This is usually represented in catalogues by the symbols YY/Δ.  "Fan torque", where the torque varies as the square of the speed. "Falling torque" and "square-law torque" are other terms used for this. The ratio between the rated outputs at the two speeds is about 1:5. This is achieved by connecting the windings in double star for the higher speed and in star for the lower speed. This is usually represented in catalogues by the symbols YY/Y. PAM PAM (pole amplitude modulation) makes it possible to design a two- speed motor with a stator winding for pole number ratios other than 2:1. Pole number changing is achieved by changing the direction of the current in part of the winding, thus varying the excitation in the same way as with the Dahlander arrangement. Among the advantages of PAM is that a given motor size can be better utilized and a higher rated power can be extracted from it. Just as with the Dahlander connection, constant- torque or fan-torque versions are possible.
90 Multi-speed motors A pole changing winding can also be combined with another winding. This winding can be for a single speed or it too can be a pole-changing winding. In this way, three or even four-speed motors can be made. Even so, such motors are uncommon. Examples of stator windings and connection arrangements with different types of multi-speed motor There may be other variants. 1) Dahlander or PAM connected 2) For 8/6/4 poles, for example. One of the windings is Dahlander- or PAM- connected. 3) The winding can also be delta-connected. Slip-ring motor with control rheostat A simple way of controlling the speed of a slip-ring motor is to connect an external rheostat (variable resistor) to the rotor winding. If the load torque, and with it the rotor current, is kept constant, an increase in the rotor resistance will lead to increased slip. However, the motor speed will be highly load dependent. This type of speed control, often called slip control, is therefore only used where there are small load variations, for example with pumps, or where the speed can be continuously monitored and the rheostat setting adjusted to suit the torque, with cranes for example.
91 Thus the power supplied to the motor is always constant, regardless of the speed, whilst the output of the motor decreases in proportion to the speed. This means that the difference between the power output with the rheostat fully in circuit and fully out of circuit is consumed in the rheostat itself. Assuming for simplicity that the load torque is constant and the speed is reduced by 25%, for example, the power output will be 75% and the remaining 25% is dissipated in the rheostat. This type of speed control is therefore highly inefficient. 2.3 Converter control Primary voltage control For small changes the slip (s) can be approximately defined as: Reduction of the primary voltage by means of thyristor-type voltage regulators is a speed control technique that is suitable for certain applications. The motor to be controlled should have an adapted torque characteristic, which is achieved by means of increased rotor resistance. A slip-ring motor with external rheostat is therefore suitable. This control method is often used for cranes and similar applications, where the high losses in the rotor circuit are acceptable because the total running time is limited. Rotor power feedback If the speed of a large induction motor is to be reduced for a long time, the methods described above would be uneconomical because of rotor losses. Modern thyristor frequency converters provide quick, stepless control and, because they feed any losses back to the supply, high efficiency.
92 The basic principle of this form of speed control is that the rotor power is taken out via the slip-rings and rectified in a conventional uncontrolled rectifier. The voltage is then converted into alternating voltage in a controlled inverter and fed back to the supply via a transformer. The amount of power fed back to the supply can be varied by varying the firing angle in the inverter. Fig. 2.3A Typical torque/speed diagram for pump and fan duty with speed control using a slip recovery system. This method of operation is comparable to dual supply of slip-ring induction motors. If the rotor is supplied with an external voltage, synchronous speeds will be obtained, which are dependent on the frequency of the external voltage. With converter control the character of the torque/speed curve is different from that of the normal slip-ring motor, and the speed will be less dependent on the load. For accurate speed regulation, the motor is usually fitted with a tacho- generator or pulse generator connected to the controller.
93 Converter control gives deviations from the normal sinusoidal shape of the current in the rotor circuit. These results in additional thermal losses, and these must be compensated for by choosing a slightly larger motor. Reduced cooling due to constant load torque at reduced speed may also need to be compensated for by choosing a slightly larger motor or using forced cooling. There is no need to do this where the load torque follows a square law. Current harmonics in the rotor circuit give small torque pulsations at a frequency of six times the secondary frequency, i.e. the slip frequency. The shaft system must therefore be checked to ensure that it does not suffer harmful resonance stresses. Voltage and frequency control The most attractive way of controlling motor speed is to control the voltage and frequency simultaneously. Fig. 2.3B shows how the torque/speed curve varies when the frequency is reduced and the primary voltage is changed in proportion to the frequency. The maximum torque remains the same, and the motor can be loaded at constant torque within the control range. Fig. 2.3B - Examples of torque curves at different frequencies and with voltage proportional to frequency.
94 If the rated voltage of the motor corresponds to the supply voltage, the motor cannot be controlled to a speed higher than the rated speed if the load torque is to be maintained, since the inverter cannot provide a voltage higher than the supply voltage. Another limit to higher speeds has to do with rotor design. Particularly in large motors for high speeds, control to higher speeds is determined by the critical speed of the motor and the highest permitted runaway speed. One possible result of a wide speed range is that cooling of the motor might be insufficient at low speed and high torque, making it necessary to provide extra cooling. Alternatively, an over dimensioned motor must be chosen. Standard motors are generally used with frequency control, in any case for the lower power ranges. Standard motors are dimensioned for a fairly high starting torque. The shape of the rotor bars is often such that large amounts of heat are produced at the top of the bars during starting, when the rotor frequency is high. Because of the high harmonic losses, this type of rotor bar design is a disadvantage in frequency converter operation, in view of the high harmonic content of the supply voltage. After all, there is no need for a high starting torque when starting with a frequency converter and it may be preferable to use a different rotor bar shape. Fig. 2.3C - Schematic diagram of a frequency converter
95 CTU On-load switch and contactor LCU Rectifier CBU Intermediate filter INU Inverter CP1 Control unit Fig. 2.3D - Complete frequency converter Commutator Motor A motor that has come to be widely used for uninterrupted speed control is the commutator motor, also known as the Schrage motor, after its inventor, in principle it is an induction motor with built-in control gear. Unlike ordinary induction motors the commutator motor has its primary winding in the rotor; the winding is fed from the supply via slip rings. The rotor slots that contain the primary winding also contain a commutator winding, essentially in the form of a D.C. winding. The secondary winding is in the stator. The normal control range is 1 to 10, but it can be extended to 1 to 100 in special cases. So that full torque can be drawn from the motor over the entire control range, these motors are often fitted with a built-on separately driven fan.
96 Common fields of application include printing presses, packaging machines and ski-lifts. Speed control is achieved by supplying the secondary winding in the stator with a control voltage at the slip frequency from the commutator winding, via brushes running on the commutator. By moving the brushes the control voltage to the secondary winding can be varied continuously and stepless, so varying the speed. The speed is stable; the effect of load variations is insignificant. Fig. 2.3D - Three-phase commutator motor. Fig. 2.3E - Examples of brush positions on a commutator motor. Ust = control voltage sUs = secondary voltage s = slip at no load
97 Fig. 2.3F - Torque curves for three different brush positions As the figure shows, the characteristics of the torque curves are such that the change in speed for varying load is insignificant over the normal speed range. 2.4 Motor Efficiency Efficiency is reflected in the nameplate as shown in Fig. 2.4.A. Motor efficiency is the percentage of the energy supplied to the motor that is converted into mechanical energy at the motor’s shaft when the motor is continuously operating at full load with the rated voltage applied. Because motor efficiencies can vary among motors of the same design, the NEMA nominal efficiency percentage on the nameplate is representative of the average efficiency for a large number of motors of the same type. Both NEMA and the Energy Policy Act of 1992 (EPAct) specify the same process for testing motor efficiency. EPAct also specifies the efficiency requirements for a large class of AC motors manufactured after 1997. In 2001, NEMA established the NEMA Premium designation for three-phase AC motors that meet even higher efficiency standards than required by EPAct. Siemens High Efficient motors meet or exceed EPAct efficiency standards and our NEMA Premium Efficient motors with our new copper rotor technology exceed NEMA Premium efficiency standards.
98 Fig. 2.4.A – Efficiency
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103 General Characteristics 2.1 System Nominal Voltages There continues to be some confusion between the system or services voltage and utilization or equipment voltage. Table below provides these relationships for the normal range “A” and for range “B” when the voltage moves outside of the normal voltage range. NOMINAL SYSTEM VOLTAGE VOLTAGE RANGE “A” VOLTAGE RANGE “B” Minimum Maximum Minimum Maximum Three -wire Four-wire Utilization Voltage Service Voltage Utilization and Service Voltage Utilization Voltage Service Voltage Utilization and Service Voltage Single-Phase Systems 120/240 — 110 110/120 114 114/228 126 126/252 106 106/212 110 110/220 127 127/254 Three-Phase Systems 208Y/120 191Y/110 197Y/114 218Y/126 184Y/106 191y/110 220Y/127 240/120 220/120 228/114 252/126 (Note d) 212/106 (Note d) 220/110 220/127 240 480Y/277 220 440Y/254 228 456Y/263 252 504Y/291 212 424/245 220 440Y/254 254 508Y/293 480 440 456 504 424 440 508 600 550 570 630 530 550 635 2400 4160Y/2400 2160 3740Y/2160 2340 4050Y/2340 2520 4370Y/2520 2080 3600Y/2080 2280 3950Y/2280 2540 4400Y/2540 4160 3740 4050 4370 3600 3950 4400 4800 4320 4680 5040 4160 4560 5080 6900 6210 6730 7240 5940 6560 7260 8320Y/4800 8110Y/4680 8730Y/5040 7900Y/4560 8800Y/5080 12000Y/6930 11700Y/6760 12600Y/7270 11400/6580 12700Y/7330 Standard Nominal System Voltages and Voltage Ranges (ANSI C84.1-1995). Application of Voltage Ranges According to ANSI C84.1.2.4.1, applications of voltage ranges are as follows. C84.1.2.4.1 Range “A” – Service Voltage. Electric supply systems shall be so designed and operated that most service voltages will be within the limits specified for Range “A”. The occurrence of service voltages outside of these limits should be infrequent. C84.1.2.4.2 Range “A” – Utilization Voltage. User systems shall be so designed and operated that with service voltages within Range “A” limits, most utilization voltages will be within the limits specified for this range. Utilization equipment shall be designed and rated to give fully satisfactory performance throughout this range.
104 C84.1.2.4.3 Range “B” – Service and Utilization Voltages. Range “B” includes voltages above and below Range “A” limits that necessarily result from practical design and operating conditions on supply or user systems, or both. Although such conditions are a part of practical operations, they shall be limited in extend, frequency, and duration. When they occur, corrective measures shall be undertaken within a reasonable time to improve voltages to meet Range “A” requirements. Insofar as practicable, utilization equipment shall be designed to give acceptable performance in the extremes of this range of utilization voltages, although not necessarily as good performance as in Range “A”. It must be recognized that because of conditions beyond the control of the supplier or user, or both, there will be infrequent and limited periods when sustained voltages outside of Range “B” limits will occur. Utilization equipment may not operate satisfactorily under these conditions, and protective devices may operate to protect the equipment. When voltage occurs outside the limits of Range “B”, prompt corrective action is recommended. The urgency for such as location and nature of load or circuits involved and magnitude and nature of the deviation beyond Range “B” limits. 2.2 Voltage Single-speed three-phase motors (i.e. motors without pole changing) can usually be reconnected for two voltages. The usual way is to connect the three stator phase windings in star (Y) or delta (Δ). Another way is to connect the windings in series or parallel, Y or YY for instance. So if the rating plate of a three-phase motor shows voltages for both Y- and Δ connection, this means that the motor can be used for both 440 V and 220 V, for example. At 220 V the winding is connected in Δ by placing the connecting links as shown in the left-hand part of Fig 2.1A. If the supply voltage is 440 V, Y- Δ connection is used, and the strips are connected as shown in the right-hand diagram.
105 Fig. 2.1A - Arrangement of windings and terminal blocks for - Y- Connection Voltage Deviation If the supply voltage at constant output power deviates from the rated voltage of the motor, the starting and maximum torques of the motor vary approximately as the square of the voltage. The change in torque will also result in a change in the speed. The efficiency and the power factor are also affected.
106 Voltage deviations also affect the temperature rise in the winding of the motor. If the voltage is low, the temperature rises in both small and large motors; if the voltage is high the temperature may drop slightly in large motors, but rises sharply in motors with small output powers. It is therefore essential to dimension the windings generously enough to ensure that there is no significant voltage drop in them on starting or in service. Another effect is shown below, for every 100 C increase in winding temperature, the expected thermal life of the winding is reduced by half. There may also be notable decrease in bearing lubricant life as the operating temperature of the motor increases.
107 Unbalance Voltage Far too many assumptions are made when dealing with the symmetry of a voltage supply. In order to accurately assess the quality of the voltage supply, it is necessary to verify it at a number of places within the service and over a reasonable period of time and seasons. NEMA MG 1, 14.36 offers the following explanation of the effects of unbalance voltage, along with a load derating curve. Effects of Unbalance Voltages on the Performance of Polyphase Induction Motors. When the line voltages applied to a polyphase induction motor are not equal, unbalanced currents in the stator windings will result. A small
108 percentage voltage unbalance will result in a much larger percentage current unbalance. Consequently, the temperature rise of the motor operating at a particular load and percentage voltage unbalance will be greater than for the motor operating under the same conditions with balanced voltages. Voltages should be evenly balance as closely as can be read on a voltmeter. Should voltages be unbalance, the rated horsepower of the motor should be multiplied by the factor shown in Fig 2.2A to reduce the possibility of damage to the motor. Operation of the motor above a 5 percent voltage unbalance condition is not recommended. When the derating curve as shown in the left figure, it is applied for operation on unbalanced voltages, the selection and setting of the overload device should take into account the combination of the derating factor applied to the motor and increase in current resulting from the unbalance voltages. This is a complex problem involving the variation in
109 motor current as a function of load and voltage unbalance in addition to the characteristics for the overload device relative to Imaximum or Iaverage. In the absence of specific information, it is recommended that overload devices be selected or adjusted, or both, at the minimum value that does not result in tripping for the derating factor and voltage unbalance that apply. When unbalance voltages are anticipated, it is recommended that the overload devices be selected so as to be responsive to Imaximum in preference to overload devices responsive to Iaverage. Effect on Performance – General. The effect of unbalance voltages on polyphase induction motors is equivalent to the introduction of a “negative sequence voltage” having a rotation opposite to that occurring with balanced voltages. This negative sequence voltage produces in the air gap a flux rotating against the rotation of the rotor, tending to product high currents. A small negative- sequence voltage may product in the windings currents considerably in excess of those present under balanced voltage conditions. Unbalance Defined. The voltage unbalance in percent may be defined as follows: Example: With voltages of 460, 467, and 450, the average is 459, the maximum deviation from average is 9, and the percent unbalance equals: Torques. The locked-rotor torque and breakdown torque are decreased when the voltage is unbalanced. If the voltage unbalance should be extremely severe, the torques might not be adequate for the application.
110 Full-Load Speed. The full-load speed is reduced slightly when the motor operates with unbalanced voltages. Currents. The locked-rotor current will be unbalanced to the same degree that the voltages are unbalanced, but the locked-rotor kVA will increase only slightly. The currents at normal operating speed with unbalanced voltages will be greatly unbalanced in the order of approximately 6 to 10 times the voltage unbalance. Performance Comparison between Standard Efficient Motor vs. Premium Efficient Motor. Emerson Motor Technology Center in St., Louis, Missouri had conducted a study to compare standard efficient motor to premium efficient motor under unbalanced voltage conditions. MOTORS DESIGN DATA DESCRIPTION PREM. EFF. STD. EFF. Model No. 7965 E398 Type TCE CT HP Rating 5 5 Voltage/Freq. 230/60 230/60 No. of Poles 4 4 Syn. Speed 1800 1800 Connections Wye Wye Full Load Performance Amps RPM Slip P.U. Losses (Watts) Efficiency % Power Factor % 12.56 1750 0.0280 445 89.3 83.4 13.47 1738 0.0344 611 85.9 80.9 Flux Density: Kl/in2 Stator Core Stator Teeth Air Gap Rotor Core Rotor Teeth 107 114 0.0325” 43 116 110 120 0.0359” 51 116
111 The increase in winding temperature causes additional I2 R losses. The rotor losses also increase because of the impact the “Negative Sequence Component” has on the rotor. Therefore as shown in figure below, there is a significant drop in motor efficiency. Vibration and Noise Note that in both cases there is a significant impact on motor performance as it relates to acceptable vibration levels and sound power levels.
112 2.3 Power factor A motor consumes not only active power, which it converts into mechanical work, but also reactive power, which is needed for magnetization but does not perform any work. The active and reactive power, represented in the diagram on the right by P and Q together give the apparent power S. The ratio between the active power, measured in kW, and the apparent power, measured in kVA, is known as the power factor. The angle between P and S is usually designated cos φ. The power factor is equal to cos φ. The power factor is usually between 0.7 and 0.9. It is lower for small motors and higher for large ones. If there are many motors in an installation it will consume a lot of reactive power and will therefore have a lower power factor. Power supply utilities sometimes require the power factor of an installation to be raised. This is done by connecting capacitors to the supply; these generate reactive power and thus raise the power factor. Phase compensation With phase compensation the capacitors are usually connected in parallel with the motor or group of motors. However, in some cases an Induction
113 motor can run as a generator, and this can lead to self-excitation. To avoid complications, therefore, it is normal practice not to compensate for more than the no-load current of the motor. The capacitors must not be connected in parallel with single phases of the winding; such an arrangement may make the motor difficult or impossible to start with star-delta (Y-Δ) starting. If a two-speed motor with separate windings has phase compensation on both windings, the capacitors should not remain in circuit on the unused winding. Under certain circumstances such capacitors can cause increased heating of the winding and possibly vibration as well. 2.4 Efficiency Electric motors are simply devices that convert electrical energy into mechanical energy. Like all electromechanical equipment, motors consume some "extra" energy in order to make the conversion. Efficiency is a measure of how much total energy a motor uses in relation to the rated power delivered to the shaft. A motor's nameplate rating is based on output horsepower, which is fixed for continuous operation at full load. The amount of input power needed to produce rated horsepower will vary from motor to motor, with more- efficient motors requiring less input wattage than less-efficient models to produce the same output. Electrical energy input is measured in watts, while output is given in horsepower. (This convention applies in the USA; output power for motors manufactured in other countries may be stated in watts or kilowatts.) One horsepower is equivalent to 746 watts. There are several ways to express motor efficiency, but the basic concept and the numerical results are the same. For example: or its equivalent; Efficiency, % = 746 x Horsepower (output) Watts (input) x 100
114 The ratio describes efficiency in terms of what can be observed from outside the motor, but it doesn't say anything about what is going on inside the motor, and it is what's happening inside that makes one motor more or less efficient than another. For example, we can rewrite the equation as: or its equivalent; "Losses" stands for all the energy "fees" the motor charges in order to make its electrical-to-mechanical energy conversion. Their magnitude varies from motor to motor and can even vary among motors of the same make, type and size. In general, however, standard-efficiency motors (pre-EPAct) have higher losses than motors that meet EPAct standards, while NEMA Premium motors, or better, have lower losses still. Types of Losses Energy losses in electric motors fall into four categories:  Power losses (Stator and Rotor Losses)  Magnetic core losses  Friction and windage losses, and  Stray load losses. Efficiency, % = Watts (output) Watts (input) x 100 Efficiency, % = Watts (output) Watts (output) + Watts (losses) x 100 Efficiency, % = Watts (input) – Watts (losses) Watts (input) x 100
115 Fig 2.4A. A typical NEMA Design B motor showing components that can be modified to increase the motor's efficiency: (a) Stator windings; (b) Rotor length; (c) conductor bars and end rings; (d) air gap; (e) laminations; (f) bearings; (g) fan. Power losses and stray load losses appear only when the motor is operating under load. They are therefore more important — in terms of energy efficiency — than magnetic core losses and friction and windage losses, which are present, even under no-load conditions (when the motor is running, of course). Power losses, also called I²R losses, are the most important of the four categories and can account for more than one-half of a motor's total losses. Power losses appear as heat generated by resistance to current flowing in the stator windings and rotor conductor bars and end rings. Stator losses make up about 66% of power losses, and it is here that motor manufacturers have achieved significant gains in efficiency. Since increasing the mass of stator windings lowers their electrical resistance (and therefore reduces I²R losses), highly efficient motors typically contain about 20% more copper than standard efficiency models of equivalent size and rating. Rotor losses are reduced by decreasing the degree of slip. This is accomplished by increasing the mass of the rotor conductors (conductor bars and end-plates) and/or increasing their conductivity (see below), and to a lesser extent by increasing the total flux across the air gap between rotor and stator.
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So Tay Bao Duong Dong Co Dien

  • 2. 2010 Edition Electric Motors & Drives Technical Manual Through the initiative of: International Copper Association – South East Asia Institute of Integrated Electrical Engineers of the Philippines, Inc.
  • 3.
  • 4. iii P R E F A C E This publication deals primarily with small and medium-sized induction motors which are the most common type of alternating current motor. They are internationally standardized and are efficiently manufactured in long production runs. The combination of new materials and more sophisticated methods for calculation, design and production have made the modern three-phase induction motor a robust and reliable prime mover. This publication was made possible through the initiative and support of the International Copper Association – South East Asia and administered, executed, and implemented by the Institute of Integrated Electrical Engineers of the Philippines All information and data contained in this publication is believed to be reliable, but all recommendations or suggestions are made without guarantee. Furthermore, suggestions for use of material supplied shall not be construed as a recommendation or inducement to violate any law or infringe any patent.
  • 5. iv
  • 6. v Table of Contents Section Title Page Motor Specifications 1.1 Nameplate 1 1.2 Insulation Class 3 1.3 Enclosure Type 11 1.4 Temperature Class 19 1.5 Mounting 30 1.6 Manufacturer’s Identification Number 51 1.7 Terminal Markings 55 1.8 Motor Design 67 1.9 Types of Duty 76 General Characteristics 2.1 System Nominal Voltage 103 2.2 Voltage 104 2.3 Power Factor 112 2.4 Efficiency 113 2.5 Speed 118 2.6 Vibration Characteristics and Balancing 119 2.7 Bearings 141 2.8 Torque 170 Asynchronous Motor Starting Systems 3.1 Starting Methods 175 3.2 Single-phase Motor Starting 187 Motor Protection and Coordination 4.1 Motors Protection 193 4.2 Protection Against Short Circuits 194 4.3 Protection Against Overload 203 4.4 Multifunction Relays 212 4.5 Motor Circuit Breakers 215 Motor Starter Co-ordination 5.1 Concepts 219 5.2 Solutions 220 5.3 Motor Overload Protection 229 5.4 Terminology 241
  • 7. vi Motor Efficiency 6.1 Repair-Replace Decision Model 246 6.2 Premium Efficiency Motors 262 Installation, Testing, and Maintenance 7.1 Installation and Maintenance 273 7.2 Description of Routine Tests 309 7.3 Recommended Winding Tests 321 7.4 Other Tests 322 7.5 Motor Starting Capabilities and Considerations 323 7.6 Maintenance and Reliability 328 7.7 Maintenance Programs 332 7.8 Machinery Condition Monitoring 334 7.9 Maintenance Planning 338
  • 8. 1 Motor Specifications 1.1 Nameplate Motor standards are established on a country by country basis. Fortunately though, the standards can be grouped into two major categories: NEMA and IEC (and its derivatives). In North America, the National Electric Manufacturers Association (NEMA) sets motor standards, including what should go on the nameplate (NEMA Standard MG 1-10.40 "Nameplate Marking for Medium Single-Phase and Polyphase Induction Motors"). In most of the rest of the world, the International Electrotechnical Commission (IEC) sets the standards. Or at least many countries base their standards very closely on the IEC standards (for example, Germany's VDE 0530 standard and Great Britain's BS 2613 Standard closely parallel the IEC 34-1 standard). The NEMA and IEC standards are quite similar, although they sometimes use different terminology. Thus, if one understands the IEC nameplate, it is fairly easy to understand a NEMA nameplate, and vice- versa as shown in Fig 1.1A and B. Fig 1.1A – Typical IEC Motor Nameplate
  • 9. 2 Fig. 1.1B – Typical NEMA Motor Nameplate The nameplate of a motor provides important information necessary for proper application. For example, Fig. 1.1C – AC Induction Motor nameplate shows a 30 horsepower (H.P.) three-phase (3 PH) AC Induction motor. Fig. 1.1C – AC Induction Motor Nameplate
  • 10. 3 The following paragraphs explain some of the other nameplate information for this motor. Voltage Source (VOLTS) and Full-load Current (AMPS) AC motors are designed to operate at standard voltages. This motor is designed to be powered by a three-phase 460 V supply. Its rated full-load current is 35.0 amps. Base Speed (R.P.M.) and Frequency (HERTZ) Base speed is the speed, given in RPM, at which the motor develops rated horsepower at rated voltage and frequency. Base speed is an indication of how fast the output shaft will turn the connected equipment when fully loaded. This motor has a base speed of 1765 RPM at a rated frequency of 60 Hz. Service Factor Service factor is a number that is multiplied by the rated horsepower of the motor to determine the horsepower at which the motor can be operated. Therefore, a motor designed to operate at or below its nameplate horsepower rating has a service factor of 1.0. A 1.15 service factor motor can be operated 15% higher than its nameplate horsepower. 1.2 Insulation Class NEMA NEMA defines motor insulation classes to describe the ability of motor insulation to handle heat. The four insulation classes are A, B, F, and H. All four classes identify the allowable temperature rise from an ambient temperature of 40° C (104° F). Classes B and F are the most commonly used. Ambient temperature is the temperature of the surrounding air. This is also the temperature of the motor windings before starting the motor,
  • 11. 4 assuming the motor has been stopped long enough. Temperature rises in the motor windings as soon as the motor is started. The combination of ambient temperature and allowed temperature rise equals the maximum rated winding temperature. If the motor is operated at a higher winding temperature, service life will be reduced. A 10° C increase in the operating temperature above the allowed maximum can cut the motor’s insulation life expectancy in half. Fig.1.2A shows the allowable temperature rise for motors operated at a 1.0 service factor at altitudes no higher than 3300 ft. Each insulation class has a margin allowed to compensate for the motor’s hot spot, a point at the center of the motor’s windings where the temperature is higher. For motors with a service factor of 1.15, add 10° C to the allowed temperature rise for each motor insulation class. Fig 1.2A – Allowable Temperature Rise Permitted output at high ambient temperature or high altitude above sea level. Motors in their standard versions are intended to operate in an ambient temperature of 40 °C maximum and at not more than 1000 meters above sea level. If the motors are to be used at higher ambient temperatures or higher altitudes the rated output must normally be reduced by the percentage shown in the Table 1.2A.
  • 12. 5 Table 1.2A – Reduction of Rated Output at Higher Ambient Temperature of Altitudes Ambient Temperature, O C 40 45 50 55 60 70 Permitted output, % of rated output 100 96.5 93 90 86.5 79 Altitude above sea level 1000 1500 2000 2500 3000 3500 4000 Permitted output, % of rated output 100 97 94.5 92 89 86.5 83.5 Insulation classes According to EC 85, insulation is divided into insulation classes. Each class has a designation corresponding to the temperature that is the upper limit of the range of application of the insulating material under normal operating conditions and with satisfactory life. If this upper limit exceeded by 8 to 10 K (see below), the Life of the Insulation will be approximately halved. The correct insulation for the winding of a motor is therefore determined by both the temperature rise in the motor and the temperature of the ambient air. If a motor is subjected to an ambient temperature higher than 40 °C, it must normally be derated or an insulating material of a higher class must be used. According to international standards, temperature is measured in degrees Celsius (°C), whilst temperature difference is stated in the unit Kelvin (K). 1 Celsius degree is equivalent to 1 K. Fig 1.2.B - Temperature Limits According to IEC 85
  • 13. 6 For class F, for instance, the temperature rise must not exceed 105 K, provided that the ambient temperature does not exceed +40°C. This applies if the resistance measuring method is used. This involves first measuring the resistance of the winding at ambient temperature, then running a temperature-rise test of the motor to determine the temperature in the winding at rated power, then measuring the resistance of the winding at the end of the test. The temperature rise is calculated using this formula: Where: t2 = temperature of winding at end of temperature-rise test t1 = temperature of winding before temperature-rise test ta = temperature of cooling medium at end of temperature-rise test R2 = resistance of winding at end of temperature-rise test R1 = resistance of winding at temperature t1 Constant = 235 for copper winding: 225 for aluminum winding What this method determines is the mean temperature rise. This is why an extra thermal margin of 10 K, for example, is reserved between the mean temperature of the winding and the temperature at its hottest point. The graph in Fig.1.2.C illustrates the effect of exceeding the highest permitted winding temperature on the winding life.
  • 14. 7 Fig.1.2.C - Effect of Winding Temperature on Life of Insulation Frame Size Motor frame dimensions have been standardized with a uniform frame size numbering system. This system was developed by NEMA and specific frame sizes have been assigned to standard motor ratings based on enclosure, horsepower and speed. The current standardized frames for integral horsepower induction motors ranges from 143T to 445T. These standards cover most motors in the range of one through two hundred horsepower. Typical example of where you can locate the frame is shown in Fig 1.2.D – Frame No. Fig 1.2.D – Frame No
  • 15. 8 The numbers used to designate frame sizes have specific meanings based on the physical size of the motor. Some digits are related to the motor shaft height and the remaining digit or digits relate to the length of the motor. The rerate, or frame size reduction programs were brought about by advancements in motor technology relating mainly to higher temperature ratings of insulating materials, improved magnetic steels and improved bearings. At the present time, NEMA frame assignments do no exist for motors larger than 445T and each manufacturer may have different frame designations for these motors. One additional suffix that may be used on standard motors in frames 286T and larger is an “S” inserted after the “T”. This “S” stands for short shaft. In addition to having a short shaft, the motor will have a small diameter shaft (“U” dimension) and the bearing in the drive shaft end of the motor will be somewhat smaller than the equivalent long shaft motor. Short shaft motors are intended for use only on direct coupled centrifugal pumps and other direct coupled loads where there will not be a side pull (overhung load) exerted on the shaft by “V” belts. Table 1.2B – NEMA Frame Assignment – Three-Phase Motors OPEN MOTORS – GENERAL PURPOSE NEMA PROGRAM HP ORIG. 3600 RPM 1952 RERATE 1964 RERATE ORIG. 1800 RPM 1952 RERATE 1964 RERATE ORIG. 1200 RPM 1952 RERATE 1964 RERATE ORIG. 900 RPM 1952 RERATE 1964 RERATE 1 1.5 2 — 203 204 — 182 184 — 143T 145T 203 204 224 182 184 184 143T 145T 145T 204 224 225 184 184 213 145T 182T 184T 225 254 254 213 213 215 182T 184T 213T 3 5 7.5 224 225 254 184 213 215 145T 182T 184T 225 254 284 213 215 254U 182T 184T 213T 254 284 324 215 254U 256U 213T 215T 254T 284 324 326 254U 256U 284U 215T 254T 256T 10 15 20 284 324 326 254U 256U 284U 213T 215T 254T 324 326 364 256U 284U 286U 215T 254T 256T 326 364 365 284U 324U 326U 256T 284T 286T 364 365 404 286U 326U 364U 284T 286T 324T 25 30 40 364S 364S 365S 286U 324S 326S 256T 284TS 286TS 364 365 404 324U 326U 364U 284T 286T 324T 404 405 444 364U 365U 404U 324T 326T 364T 405 444 445 365U 404U 405U 326T 364T 365T 50 60 75 404S 405S 444S 364US 365US 404US 324TS 326TS 364TS 405S 444S 445S 365US 404US 405US 326T 364TS* 365TS* 445 504U 505 405U 444U 445U 365T 404T 405T 504U 505 — 444U 445U — 404T 405T 444T 100 125 150 445S 504S 505S 405US 444US 445US 365TS 404TS 405TS 504S 505S — 444US 445US — 404TS* 405TS* 444TS* — — — — — — 444T 445T — — — — — — — 445T — — 200 250 — — — — 444TS 445TS — — — — 445TS* — — — — — — — — — — — — — * When motors are to be used with v-belt or chain drives, the correct frame size shown but with suffix letter S omitted.
  • 16. 9 Table 1.2C – Suffixes to NEMA Frames TEFC MOTORS – GENERAL PURPOSE NEMA PROGRAM HP ORIG. 3600 RPM 1952 RERATE 1964 RERATE ORIG. 1800 RPM 1952 RERATE 1964 RERATE ORIG. 1200 RPM 1952 RERATE 1964 RERATE ORIG. 900 RPM 1952 RERATE 1964 RERATE 1 1.5 2 — 203 204 — 182 184 — 143T 145T 203 204 224 182 184 184 143T 145T 145T 204 224 225 184 184 213 145T 182T 184T 225 254 254 213 213 215 182T 184T 213T 3 5 7.5 224 225 254 184 213 215 182T 184T 213T 225 254 284 213 215 254U 182T 184T 213T 254 284 324 215 254U 256U 213T 215T 254T 284 324 326 254U 256U 284U 215T 254T 256T 10 15 20 284 324 326 254U 256U 284U 215T 254T 256T 324 326 364 256U 284U 286U 215T 254T 256T 326 364 365 284U 324U 326U 256T 284T 286T 364 365 404 286U 326U 364U 284T 286T 324T 25 30 40 365S 404S 405S 324U 326S 364US 284TS 286TS 324TS 365 404 405 324U 326U 364U 284T 286T 324T 404 405 444 364U 365U 404U 324T 326T 364T 405 444 445 365U 404U 405U 326T 364T 365T 50 60 75 444S 445S 504S 365US 405US 444US 326TS 364TS 365TS 444S 445S 504S 365US 405US 444US 326T 364TS* 365TS* 445 504U 505 405U 444U 445U 365T 404T 405T 504U 505 — 444U 445U — 404T 405T 444T 100 125 150 505S — — 445US — — 405TS 444TS 445TS 505S — — 445US — — 405TS* 444TS* 445TS* — — — — — — 444T 445T — — — — — — — 445T — — * When motors are to be used with v-belt or chain drives, the correct frame size shown but with suffix letter S omitted. The following explanations of the various fame suffixes used on NEMA frame motors have been compiled for the benefit of EASA members. The suffixes for NEMA frame motors are the letters that immediately follow the frame numbers. Notice that more than one suffix may be used on any given motor. Note: “D” dimension (shall height) of a motor or generator in these frame sizes equals 1 /4 the value of the first two digits in the frame number. Example: 284 frame: 28/4 = 7, D = 7" A — Industrial direct-current machine. B — Carbonator pump motors, (See NEMA MG 1-2006, 18.270 – 18.281) C — Type C face mounting on drive end. CM — Face mounting dimensions are different from those for the frame designation having the suffix letter “C” (The letters “CH” are considered as one suffix and should not be separated.) D — Type D flange mounting on drive end. E — Shaft extension dimensions for elevator motors in frames larger than 326T frames. FC — Face mounting on opposite drive end. FD — Flange mounting on opposite drive end.
  • 17. 10 G — Gasoline pump motors. (See NEMA MG 1-2006, 18.91.) H — Indicates a small machine having an “F” dimension larger than that of the same frame without the suffix letter “H”. (See NEMA MG 1-2006, 4.4.1 and 4.5.1.) HP or HPH — Type P flange-mounted, vertical sotid-shaft motors having dimensions in accordance with NEMA MG 1- 2006, 18.252. (The letters “HP” and “HPH” are considered as one suffix and should not be separated) J — Jet pump motors. (See NEMA MG 1-2006, 18.132.) JM — Face-mounted, close-coupled pump motor having antifriction bearings and dimensions in accordance with Table 1 of MG 1-2006, 18.250. (The letters “JM” are considered as one suffix and should not be separated.) JP — Type C face-mounted, close-coupled pump motor having antifriction bearings and dimensions in accordance with Table 2 of MG 1 -2006, 18.250. (The letters “MP” are considered as one suffix and should not be separated.) K — Sump pump motors. (See NEMA MG 1-2006, 18.78.) LP or LPH — Type P flange-mounted, vertical solid-shaft motors having dimensions in accordance with MG 1-2008, 18- 251. (The letters “LP” and “LPH” are considered as one suffix and should not be separated.) M — Oil burner motors. (See NEMA MG 1-2006, 18.106.) N — Oil burner motors. (See NEMA MG 1-2006, 18.108.) P or PH— Type P flange-mounted, vertical hollow-shaft motors having dimensions in accordance with NEMA MG 1- 2006, 18.238. R — Drive end tapered shaft extension having dimensions in accordance with NEMA MG 1-2008, 4.4.2. S — Standard short shaft for direct connection. T — Included as part of a frame designation for which standard dimensions have been established. U — Previously used as part of a frame designation for which standard dimensions had been established. V — Vertical mounting only. VP — Type P flange-mounted, vertical solid-shaft motors having dimensions in accordance with NEMA MG 1- 2008, 18.237. (The letters “VP” are considered as one suffix and should not be separated.)
  • 18. 11 X — Wound-rotor crane motors with double shaft extension. (See NEMA MG 1-2006, 18229 and 18.230.) Y — Special mounting dimensions, (Dimensional diagram must be obtained from manufacturer.) Z — All mounting dimensions are standard except the shaft extension(s). Also used to designate machines with double shaft extension. Note: Manufacturers may use any letter preceding the frame number, but such a letter will have no reference to standard mounting dimensions. Suffix letters shall be added to the frame number in the following sequences: Suffix Letter Sequence A, H ……………………………………………………… 1 G, J, M, N, T, U, HP, HPH, JM, JP, LP, LPH, & VP .......... 2 R, S ..................................................................................... 3 C, D, P, PH ………………………………………………. 4 FC, FD …………………………………………………… 5 V …………………………………………………………. 6 E, X, Y, Z ............................................................................ 7 Example: “T” frame motor with a “C” face mounted vertically with a nonstandard shaft extension; (Sequences 2.4.8 and 7) 184TCVZ. Note: This material is reproduced by permission of the National Electrical Manufacturers Association from NEMA Standards, MG 1-2006, 4.2.2. It was originally published as EASA Tech Note No. 7 (September 1985) and reviewed and updated as necessary in November 2007. 1.3 Enclosure Type The enclosure of the motor must protect the windings, bearings, and other mechanical parts from moisture, chemicals, mechanical damage and abrasion from grit. NEMA standards MG1-1.25 through 1.27 define more than 20 types of enclosures under the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed
  • 19. 12 windings. The most commonly used motor enclosures are open dripproof, totally enclosed fan cooled and explosionproof. Fig. 1.3A – Shows location of Enclosure Tag The Standards for IP Codes apply to the classification of degrees of protection provided by enclosure for all rotating machines. The designation used for the degree of protection consists of the letter IP (International Protection) followed by two characteristic numerals.
  • 20. 13 When the degree of protection is specified by only one numeral, the omitted numeral is replaced by the letter X. For example, IPX5 or IP2X. The first Characteristic Numeral indicates the degree of protection provided by the enclosure with respect to persons and also to the parts of the machine inside the enclosure. The Second Characteristic Numeral indicates the degree of protection provided by the enclosure with respect to harmful effect due to ingress of water. The two characteristic numerals signify conformity with the conditions indicated in Table 1.3.A. – Degrees of Protection Indicated by the Two Characteristic Numerals. Table 1.3.A - Degrees of Protection indicated by the Two Characteristic Numerals FIRST CHARACTERISTIC NUMERAL DEGREE OF PROTECTION SECOND CHARACTERISTIC NUMERAL DEGREE OF PROTECTION 0 Non-protected machine 0 Non-protected machine 1 Machine protected against solid objects greater than 2 inches (50 mm) 1 Machine protected against dripping water 2 Machine protected against solid objects greater than 0. 5 inches (12 mm) 2 Machine protected against dripping water when tilted up to 15o 3 Machine protected against solid objects greater than 0.1 inches (2.5 mm) 3 Machine protected against spraying water 4 Machine protected against solid objects greater than 0.04 inches (1 mm) 4 Machine protected against splashing water 5 Dust-protected machine 5 Machine protected against water jets 6* Dust-tight machine 6 Machine protected against heavy seas 7 Machine protected against the effects of immersion Machine protected against continuous submersion * Not include in IEC 60034-5, 1991 Standards Reference: NEMA Standards MG-1 2006, 5.8, Tables 5-1, and 5-2. IEC International Standard IEC 60034-5, 1991.
  • 21. 14 Classification According to Environmental Protection* IP CODE CLASSIFICATION IP CODE CLASSIFICATION IP 00 Open Machine IP 22 Dripproof guarded machine IP 10 Semi-guarded machine IP 44 Totally enclosed pipe-ventilated machine IP 12 Dripproof machine IP 54 Totally enclosed non-ventilated machine IP 13 Splash-proof machine IP 55 Water-proof machine * Reference: NEMA Standards MG-1 2006, 1.25, 1.26, and 1.27.
  • 22. 15 Open Dripproof. The open dripproof motor (ODP) has a free exchange of air with the ambient. Drops of liquid or solid particles do not interfere with the operation at any angle from 0 to 15degrees downward from the vertical. The openings are intake and exhaust ports to accommodate interchange of air. The open dripproof motor is designed for indoor use where the air is fairly clean and where there is little danger of splashing liquid. Refer to Fig. 1.3A – Open Dripproof (ODP) Fig. 1.3A – Open Dripproof (ODP) Totally Enclosed Fan Cooled (TEFC). This type of enclosure prevents the free exchange of air between the inside and outside of the frame, but does not make the frame completely airtight. A fan is attached to the shaft and pushes air over the frame during its operation to help in the cooling process. The ribbed frame is designed to increase the surface area for cooling purposes. There is also a totally enclosed non-ventilated (TENV) design which does not use a fan,
  • 23. 16 but is used in situations where air is being blown over the motor shell for cooling, such as in a propeller fan application. Refer to Fig. 1.3B – Totally Enclosed Fan Cooled (TEFC) Motor. Fig. 1.3B – Totally Enclosed Fan Cooled (TEFC) Motor Explosionproof The explosionproof motor is a totally enclosed machine and is designed to withstand an explosion of specified gas or vapor inside the motor casing and prevent the ignition outside the motor by sparks, flashing or explosion. These motors are designed for specific hazardous purposes, such as atmospheres containing gases or hazardous dusts. For safe operation, the maximum motor operating temperature must be below the ignition temperature of surrounding gases or vapors. Explosionproof motors are designed, manufactured and tested under the rigid requirements of the Underwriters Laboratories. Hazardous location motor applications are classified by the type of hazardous environment present, the characteristics of the specific material creating the hazard, the probability of exposure to the environment, and the maximum temperature level that is considered safe
  • 24. 17 for the substance creating the hazard. The format used to define this information is a class, group, division and temperature code structure. Class I (Gas or Vapor) Group: A - Acetylene B - Hydrogen and Manufactured Gases C - Ethyl-Ether, Ethylene and Cyclopropane D - Gasoline, Hexane, Naphtha, Benzine, Butane, Propane, Alcohol Lacquer Solvent Vapors and Natural Gas Division II: Hazard of fire or explosion is present only as a result of an accident. Motors may be dripproof or TEFC. Class II (Dusts) Group: E - Metal Dust (Special Seals) F - Carbon Black, Coal or Coke Dust G - Flour, Starch or Grain Dust Division I: Hazard is always present due to normal conditions. (Dust suspended in the atmosphere.) Motors must be explosionproof construction with Underwriter’s label. Division II: Motors may be TEFC or externally ventilated: (A) Where dust deposits on electrical equipment prevent safe heat dissipation. (B) Where deposit or dust might be ignited by arcs or burning material. Class III (Fibers) Fibers those are easily ignitable but not apt to be suspended in the air to produce mixtures. Examples include rayon, nylon, cotton, saw dust, and wood chips. Division II: Location in which easily ignitable fibers are stored or handled TEFC enclosure can be used if there is a minimal amount of fibers or flying in the air.
  • 25. 18 Converting from NEMA enclosure classifications to IEC enclosure classifications NEMA enclosure classifications are developed by NEMA and used in the U.S./American market. Ingress Protection - IP - ratings are developed by the European Committee for Electro Technical Standardization (CENELEC) (described IEC/EN 60529), and specifies the environmental protection and enclosure provided. The table below can be used to convert from NEMA Enclosure Types to IEC Enclosure Types:
  • 26. 19 Continuation of … Note: NEMA standards meet or exceed IEC standards. The conversion does not work in the opposite direction. 1.4 Temperature class Combustible gas or vapor and explosion-protected electrical equipment is divided into temperature classes T1 to T6 with regard to the ignition temperature of the gas or vapor and the maximum surface temperature of the equipment. Refer to Table1.4A - Temperature Class. Ignition temperature, thermal flashpoint, is the lowest temperature of a surface at which a substance ignites on contact with the surface.
  • 27. 20 Table1.4A - Temperature Class Hazardous area and zones Hazardous areas are rooms, spaces or areas in which an explosive gas mixture may occur under conditions such that electrical equipment, among other things, may have to meet certain requirements. Hazardous areas are categorized as zones as follows: Zone 0 - An area in which an explosive gas atmosphere is present continuously or is present for long periods. Zone 1 - An area in which an explosive gas atmosphere is likely to occur in normal operation. Zone 2 - An area in which an explosive gas atmosphere is not likely to occur in normal operation and if it does occur it will exist for a short period only. It is important that the mechanical design of installations should be such that hazardous areas should be few and of small extent. It should also be an aim to make hazardous areas chiefly Zone 2 areas.
  • 28. 21 Motors for Potentially Explosive Atmosphere The principle of design of explosion-safe motors. There are two main principles for explosion protection for electric motors. One is to design the motor so that no dangerous heat or spark occurs. This includes the increased safety version, EEx e. The other method is based on isolating any dangerous heat or spark inside the motor so as to prevent the ignition of any explosive mixture of gases outside the motor. This includes the version with flameproof enclosure, EEx d, and the version with pressurized enclosure, EEx p. These are the three internationally standardized versions that are suitable for motors to be installed in Zone 1. The "non-sparking" version, Exn, according to IEC 79-15 (1987) is intended for use in Zone 2. IEC 79-15 has not yet been transferred to a national standard, but this is expected to happen after it has been converted into a European standard in CENELEC. British Standard BS 5000, Part 16 has a similar version. Increased safety design, EEx e The motor must not have any parts that, in normal service, produce arcs or sparks, or reach a dangerous temperature. Special steps must be taken in the design to prevent the risk of ignition by arcs or sparks or by excessively high temperature as a consequence of poor contact, overloading or the like. The temperature limitation applies to internal and external surfaces. The degree of protection of the terminal box must not be lower than IP 54 and any enclosure that contains only insulated parts must have at least IP 44. However, in the case of motors installed in clean areas and supervised by trained personnel, IP 23 is permitted for motors complying with explosion group I, i.e. for use in coal mines, and IP 20 for explosion group II, i.e. other areas. The requirements to be met by the terminal box are unchanged, however. The limitation of the field of application must be stated on the motor.
  • 29. 22 The air gap between rotor and stator is subject to certain minimum dimensions. There are also minimum dimensions for creepage distance and the air gap between winding leads and earth. All connections between live parts must be secured so that they cannot work loose. Cable bushings and the cable branch in the terminal box are also subject to certain temperature limits. The motors must have both an internal and an external earthing screw. Flameproof enclosure, EEx d The housing of the motor must be so designed that ignition and combustion of any explosive mixture inside the housing cannot be propagated to a similar mixture outside the housing and that the housing can withstand without damage the explosion pressure thus caused. The motor need not be hermetically sealed; gas may therefore penetrate the motor. The permitted temperature inside the motor is limited only by the insulation class of the motor. The rated output depends on how hot the outer surface of the motor is permitted to be with regard to the relevant temperature class. Slip-ring motors, commutator motors and brake motors can all be made in flameproof versions. No external parts may cause sparks. The motors must have both an internal and an external earthing screw. Pressurized enclosure, EEx p In this version the motor must be under a given minimum positive pressure relative to the surroundings, so that the ambient atmosphere cannot penetrate the motor in service. The pressurization can take the form of positive pressure with compensation for leakage or positive pressure with continuous flushing.
  • 30. 23 Monitoring of the winding temperature is recommended in cases where the pressurization system is also responsible for cooling the motor. Before the motor is started, it and its associated ducting for supply and exhaust air must be flushed through with fresh air or a protective gas for long enough to ensure that any explosive gas mixture has been reliably removed. The amount of fresh air or protective gas flushed through must in any case be equivalent to at least five times the total free volume. A positive pressure of at least 0.5 mbar relative to the ambient pressure must be maintained in service. If the positive pressure is lost when the motor is in service, the motor must be automatically disconnected. The temperature of the outer surface of the motor must not exceed the stated figures for the temperature class in question. The motors must have both an internal and an external earthing screw. Fig. 1.4A – Pressurized Enclosure EEx p
  • 31. 24 Special requirements to be met by motors in increased safety version. EEx e. Non-sparking design, Exn This version to IEC 79-15 is a simpler version than EEx e. in general terms, a normal squirrel-cage motor may be approved, but, as for EEx e, there are certain minimum requirements for distances between moving and stationary parts, air gaps and creepage distances between winding leads and earth. The motor must be designed so that sparking cannot occur - "non- sparking" design. The outside temperature of the motor is determined in normal duty. The temperature rise on starting is not included if duty is continuous. The degree of protection must be IP 54 for the terminal box and IP 44 for those parts of the housing that contain only insulated parts. The motors must have an internal earthing screw and, if requested, an external earthing screw as well. There is no mandatory requirement for a certificate from a testing station. There are national rules for the installation of version Exn motors in zone 2. Version Ex N to British Standard BS 5000 Part 16 differs in certain respects from Exn to IEC 79-15. Following several years of international engagement by CENELEC, Comite European de Normalization Electrotechnique, common standards now apply regarding the design and testing of electrical equipment that is to be used in explosive atmospheres. These standards are based on the previously issued IEC Publication 79.
  • 32. 25 Only intrinsically-safe circuits of category EEx ia may be used in Zone 0. Motors are thus excluded. Motors of category EEx d, EEx e and EEx p may be used in Zone 1. In Zone 2, equipment permitted in zones 0 and 1 may of course be used. Under certain conditions the equipment, motors for instance, need not be of explosion-protected design. An example is shown in Fig. 1.4B. These conditions are as follows; they must all be met:  The degree of protection of the motors must not be below IP 54.  In service they must not produce a temperature of more than 200 °C. This requirement applies to both internal and external parts. In duties S1 (continuous) and S6 (continuous with intermittent load), the temperature may briefly exceed 200 °C in conjunction with starting.  The motors must not produce sparks or arcs in service.  They must be placed in a hazard area that has been assigned temperature class T1 to T3.
  • 33. 26 Fig. 1.4B - Example of classification and the extent of the hazardous areas in a ventilated tank Temperature limits, IA/IN and time tE for version EEx e The increased safety design, EEx e, Is the most common type of explosion-protected motor. They are subject to certain limits on temperature and on the relationship between the starting ratio lA/lN (which is the same as lst/l) and the time tE. Temperature limits To prevent the ignition of an explosive atmosphere, no part of the motor may, during starting, during operation at rated output or at a given overload, for example at the end of the time tE, have a higher temperature than that stated in the Table 1.4B - Temperature class and temperature limit in 0 C. The temperature depends on the temperature class of the motor.
  • 34. 27 Table 1.4B. – Temperature Class and Temperature Limit in 0 C The temperature limits also apply to uninsulated conductors such as rotor bars. However, during starting, it is permissible for the temperature of the rotor to reach 300°C maximum. To maintain the thermal stability of the insulation of the windings, the temperature limits in the Table 1.4C must be observed. Table 1.4C - The Temperature Limits Limit temperature and maximum temperature rise for insulated winding to temperature Class B and F, measured by the resistance method. IA/lN and time tE If a squirrel-cage motor is to remain secure, the motor protection must be correctly chosen. Current standards lay down that the rating plate of a motor and the type testing report must state the ratio IA/lN. IA is the starting current of the motor and IN its full-load current. The time tE is, also stated. This is the time taken for the stator or rotor winding to heat up from normal operating temperature at the highest permitted ambient temperature to the highest permitted limit
  • 35. 28 temperature, with the rotor locked and the stator winding loaded with the starting current IA. In other words, the highest permitted surface temperature for the temperature class or the insulation class of the winding, the lower of the two being the limit. Fig. 1.4C Surface temperature for the temperature class or the insulation class Where: 0 = temperature 0 °C. A = maximum ambient temperature, normally 40 °C. B = temperature at rated output. C = maximum permitted temperature at rated output for the insulation class. D = limit temperature at rated output for the insulation class or the temperature class. E = temperature rise at rated output. F = temperature rise in locked-rotor test. G = heating time during F. Relationship between IA/lN. and tE The time tE and the ratio IA/lN must be determined and stated so that suitable current dependent protection can be chosen to protect the motor from overheating. The value of tE must be such that, when the rotor is locked, the motor is disconnected by a current-dependent protection device before the time tE has expired. Generally this is possible if the time tE for the motor is longer than the value indicated by the curve for
  • 36. 29 the corresponding IA/lN. Values below the curve are only permitted if specially adapted current-dependent overload protection that has been proved effective in tests is used. This protection must be identified on the rating plate of the motor. Fig. 1.4D - Minimum values of tE as a function of IA/IN Fig. 1.4D Minimum values of tE as a function of IA/IN where normal overload relays are used. Temperature conditions in the stator and rotor of a squirrel-cage motor with rated output 1.3 kW at maximum permitted ambient temperature 40 °C. The time tE is limited by the temperature rise of the stator winding.
  • 37. 30 In no case must the time tE be shorter than 5 seconds, nor must the ratio IA/IN be greater than 10. If some form of protection other than current- dependent protection is used (temperature sensors built into the motor for example), IA/IN and tE are not stated. The rating plate of the motor states how it is protected against overheating. Temperature conditions in the stator and rotor of a squirrel-cage motor with rated output 10 kW at maximum permitted ambient temperature 40 °C. The time tE is limited by the temperature rise of the rotor winding. 1.5 Mounting NEMA Dimensions NEMA has standardized motor dimensions for a range of frame sizes. Standardized dimensions include bolt-hole size, mounting base dimensions, shaft height, shaft diameter, and shaft length. Use of standardized dimensions allows existing motors to be replaced without reworking the mounting arrangement. In addition, new installations are easier to design because the dimensions are known. NEMA divides standard frame sizes into two categories, fractional horsepower and integral horsepower. The most common frame sizes for
  • 38. 31 fractional horsepower motors are 42, 48, and 56. Integral horsepower motors are designated by frame sizes 143 and above. A T in the motor frame size designation for an integral horsepower motor indicates that the motor is built to current NEMA frame standards. Motors that have a U in their motor frame size designation are built to NEMA standards that were in place between 1952 and 1964. The frame size designation is a code to help identify key frame dimensions. The first two digits are used to determine the shaft height. The shaft height is the distance from the center of the shaft to the mounting surface. To calculate the shaft height, divide the first two digits of the frame size by 4. For example, In Fig. 1.5A - a 143T frame size motor has a shaft height of 3½ inches (14 ÷ 4). Fig. 1.5A – Importance of Frame Size The third digit in the integral T frame size number is the NEMA code for the distance between the center lines of the motor feet mounting bolt holes. The distance is determined by matching this digit with a table in NEMA publication MG-1. For example in Fig. 1.5B, the distance between the center lines of the mounting bolt holes in the feet of a 143T frame is 4.00 inches.
  • 39. 32 FRAME SIZE SERIES Third/Fourth Digit In Frame Number D 1 2 3 4 5 140 4.00 4.50 4.50 160 4.00 3.50 4.00 4.50 5.00 5.00 180 4.50 4.00 4.50 5.00 5.50 5.50 200 5.00 4.50 5.00 5.50 6.50 6.50 210 5.25 4.50 5.00 5.50 6.25 6.25 220 5.50 5.00 5.50 6.25 6.75 6.75 250 6.25 5.50 6.25 7.00 8.25 8.25 280 7.00 6.25 7.00 8.00 9.50 9.50 320 8.00 7.00 8.00 9.00 10.50 10.50 Fig. 1.5B – Importance of Frame Size IEC Dimensions IEC also has standardized dimensions, but these dimensions differ from NEMA standards. An example of the IEC dimensions are shown in the following drawing.
  • 40. 33 IEC Mounting Dimensions Foot-Mounted AC & DC Machines
  • 41. 34 IEC Flange-Mounted AC & DC Machines Dimensions for Flanges
  • 42. 35 IEC Shaft Extension, Key and Keyseat Dimensions for Continuous Duty AC Motors.
  • 43. 36 Dimensions for AC Machines – Millimeters NEMA Frame
  • 44. 37
  • 45. 38
  • 46. 39
  • 47. 40 Mounting Positions The typical floor mounting positions are illustrated in the following drawing, and are referred to as F-1 and F-2 mountings. The conduit box can be located on either side of the frame to match the mounting arrangement and position. The standard location of the conduit box is on the left-hand side of the motor when viewed from the shaft end. This is
  • 48. 41 referred to as the F-1 mounting. The conduit opening can be placed on any of the four sides of the box by rotating the box in 90° steps. With modification, a foot-mounted motor can be mounted on a wall and ceiling. Typical wall and ceiling mounts are shown in the following illustration. Wall mounting positions have the prefix W and ceiling mounted positions have the prefix C.
  • 49. 42 Mounting Faces It is sometimes necessary to connect the motor directly to the equipment it drives. In the following example a motor is connected directly to a gear box. C-face The face, or the end, of a C-face motor has threaded bolt holes. Bolts to mount the motor pass through mating holes in the equipment and into the face of the motor.
  • 50. 43
  • 51. 44
  • 52. 45 D-flange The bolts go through the holes in the flange of a D-flange motor and into threaded mating holes of the equipment.
  • 53. 46
  • 54. 47
  • 55. 48 JM Face Mounted NEMA FRAME DIMENSIONS* TYPE JM FACE-MOUNTING, CLOSED-COUPLED, AC PUMP MOTORS * DIMENSIONS IN MILLIMETERS FRAME DESIGNATIONS U AH* AJ AK BB BD MAX BF NUMBER TAP SIZE BOLT PENETRATION ALLOWANCE 143JM and 145JM 22.21 108 149.25 114.30 3.5 168 4 3/8-16 14 182JM and 184JM 22.21 108 149.25 114.30 3.5 168 4 3/8-16 14 213JM and 215JM 22.21 108 184.15 215.90 7 228 4 1/2-13 19 254JM and 256JM 31.73 134 184.15 215.90 7 254 4 1/2-13 19 284JM and 286JM 31.73 134 279.40 317.5 7 355 4 5/8-11 24 324JM and 326JM 31.73 134 279.40 317.5 7 355 4 5/8-11 24 FRAME DESIGNATIONS EL EM EN EP MIN EQ* ER MIN KEYSEAT ET* TAP SIZE TAP DRILL DEPTH MAX BOLT PENETRATION ALLOWANCE R ES MIN S 143JM and 145JM 29.35 25.40 3/8-16 28 19 30 16.0 108 19.5 42 4.80 73.0 182JM and 184JM 31.75 25.40 3/8-16 28 19 32 16.0 108 19.5 42 4.80 73.0 213JM and 215JM 31.75 25.40 3/8-16 28 19 45 16.0 108 19.5 42 4.80 73.0 254JM and 256JM 44.45 34.92 1/2-13 38 25 45 16.0 134 28.2 65 6.40 76.5 284JM and 286JM 44.45 34.92 1/2-13 38 25 54 16.0 134 28.2 65 6.40 76.5 324JM and 326JM 44.45 34.92 1/2-13 38 25 54 16.0 134 28.2 65 6.40 76.5 Reference: NEMA Standards MG 1-2006, 16.250. Dimensions, except for tap sizes, are shown in millimeters (rounded off). Tap sizes are in inches.
  • 56. 49 JP Face Mounted NEMA FRAME DIMENSIONS* TYPE JM FACE-MOUNTING, CLOSED-COUPLED, AC PUMP MOTORS * DIMENSIONS IN MILLIMETERS FRAME DESIGNATIONS U AH* AJ AK BB BD MAX BF NUMBER TAP SIZE BOLT PENETRATION ALLOWANCE 143JP and 145JP 22.21 186 149.25 114.30 3.5 168 4 3/8-16 14 182JP and 184JP 22.21 186 149.25 114.30 3.5 168 4 3/8-16 14 213JP and 215JP 31.73 207 184.15 215.90 7 228 4 1/2-13 19 254JP and 256JP 31.73 207 184.15 215.90 7 254 4 1/2-13 19 284JP and 286JP 31.73 207 279.40 317.5 7 355 4 5/8-11 24 324JP and 326JP 31.73 207 279.40 317.5 7 355 4 5/8-11 24 364JP and 366JP 41.26 207 279.40 317.5 7 355 4 5/8-11 24 FRAME DESIGNATIONS EL EM EN EP MIN EQ* ER MIN KEYSEAT ET* TAP SIZE TAP DRILL DEPTH MAX BOLT PENETRATION ALLOWANCE R ES MIN S 143JM and 145JM 29.35 25.40 3/8-16 28 19 30 40.0 186 19.5 42 4.80 151.0 182JM and 184JM 31.75 25.40 3/8-16 28 19 32 40.0 186 19.5 42 4.80 151.0 213JM and 215JM 44.45 34.92 3/8-16 38 25 45 60.5 207 28.2 65 6.40 149.5 254JM and 256JM 44.45 34.92 1/2-13 38 25 45 60.5 207 28.2 65 6.40 149.5 284JM and 286JM 44.45 34.92 1/2-13 38 25 54 60.5 207 28.2 65 6.40 149.5 324JM and 326JM 44.45 34.92 1/2-13 38 25 54 60.5 207 28.2 65 6.40 149.5 324JM and 326JM 53.95 44.45 1/2-13 38 25 54 60.5 207 35.9 65 9.55 149.5
  • 57. 50 Mounting arrangements IEC Publication 34—7 lays down two ways of stating how a motor is mounted. Code I covers only motors with bearing end shields and one shaft extension. Code II is a general code. The table below includes the designations for the most commonly occurring mounting arrangements according to the two codes.
  • 58. 51 IM..2. = IM.. 0. + IM..1. IM..4. = IM..0. + IM ..1. IM..3. IM..8. = The motor must be able to work in all mounting positions as per IM..0. to IM..7. IM..9. = The position of the shat cannot be specified with the third digit 0 – 8: instead it must be specified in each individual case. The electric motors execution and assembly type can be seen here 1.6 Manufacturer’s Identification Number This model and/or catalog number is used to establish motor identity and age for replacement parts and warranty.
  • 59. 52 Bearing Part Numbers. The bearing part numbers on U.S. Motors’ machines are made conveniently available on the nameplate so that, when required, procurement of replacement bearings can be carried out prior to motor disassembly. Ball and roller bearings (anti-friction bearings) are manufactured to very rigid tolerance specifications and must be treated as precision parts to insure that they don not fail prematurely. American Bearing Manufacturers Association (ABMA) Standard 20 specifies boundary dimensions, tolerance classes, and internal clearance for ball and roller bearings. Boundary Dimensions The ID (d), OD (D) and width (B) of bearings are standardized metric dimensions with the last two digits in the bearing nomenclature representing the bore size. Beginning with a 20 mm bore, the last two digits equal the bore in mm divided by 5. The smallest internal diameter interval is, therefore, 5 mm. This permits the two-digit value to span a bore range from 20 (04) to 480 mm (96). This system is used on all types of rolling element bearings.
  • 60. 53 Tolerance Classes The tolerance classes specified in the ABMA Standards have been established by the Annular Bearing Engineers Committee (ABEC). These tolerance classes have been accepted by the American National Standards Institute (ANSI) and conform essentially with standards of the International Organization for Standardization (ISO). ABEC Parameters ABEC Standards, which define tolerances for several major bearing dimensions and characteristics, are divided into mounting dimensions and bearing geometry. The geometric tolerances apply to both inner and outer rings and include:  Bore roundness  Bore runout with side  Bore taper  Race runout with side  Width variation  Radial runout ABEC standards do not address many other factors that affect bearing performance and life, including:  Materials  Ball complement – number, size and precision  Raceway curvature, roundness and finish  Cage design  Lubricant ABEC Precision Classes General – purpose ball bearing are manufactured to tolerances in accordance with precision classes ABEC1, ABEC3, BEC5, ABEC7 and ABEC9. The ascending numbers indicate stricter tolerances and additional requirement as found in ABMA Standard 20.
  • 61. 54 Bearing Manufacturer Numbering Systems The metric system of measurement has been widely adopted by all bearing manufacturers, which ensures ready interchangeability of most bearings types and sizes. Bearings can be identified by using ABMA numbers or by using each manufacturer’s discreet numbering system. In either case, it is imperative that repair firms record the name as well as all of the numbers on each bearing that is to be replaced. They should also check the nomenclature designations in catalogs from the makers of the bearings because there are some variations among manufacturers.
  • 62. 55 Example: 50BC03JPP3 – 50 mm bore diameter whose bearing last two digit is 50/5 = 10, standard Deep Groove Ball Bearing (BC), medium series (03), standard steel cage (J), double shield (PP), and loose internal fitup – ABMA 3 or C3. The equivalent SKF bearing no. is 6310 ZZ/C3.
  • 63. 56 Example: 50RU03K30 – 50 mm bore diameter whose last two digit is 50/5 = 10. RU – cylindrical roller bearing with prefix of NU, medium series (03), brass of bronze cage (K), internal clearance greater than normal – C3 with standard tolerance. This is equivalent to NU 310 ECJ/C3 for SKF brand. EC - Optimized internal design incorporating more and/or larger rollers and with modified roller/end flange contact, J - Pressed steel cage, roller centred, unhardened and C3 - Radial internal clearance greater than Normal.
  • 64. 57 Bearing Designation based on ISO 1.7 Terminal Markings IEC Publication 34-8 lays down that the stator winding, parts of it and the terminals of A.C motors must be designated with the letters U, V and
  • 65. 58 W. External neutral terminals are designated N. The letters used for the rotor winding are K, L, M and Q. 1. End points and intermediate points of a winding are indicated by a digit after the letter, e.g. U1, U2 etc. 2. Parts of the same winding are designated by a digit before the letter, e.g. 1U1, 2U1 etc. If there is no possibility of confusion, the digit before the letter, or both, may be omitted. Terminal Markings and Connections Single-Phase Motors – Capacitor-start, NEMA Nomenclature
  • 66. 59 The switch in the auxiliary winding circuit has been omitted from this diagram. The connections to the switch must be made so that both auxiliary windings become de-energized when the switch is open ROTATION: CC – Counter- clockwise CW - Clockwise The direction of shaft rotation can be determined by facing the end of the motor opposite the drive. (NEMA Standards MG 1-2006, 2.41. Note: May not apply for some definite-purpose motors.)
  • 67. 60 Three-Phase Motors – Part-Winding Start
  • 68. 61
  • 69. 62 Three-Phase Motors – Reduced-Current Starting
  • 70. 63 Three – Phase Motors Single Speed
  • 71. 64
  • 72. 65 Three-Phase Motors – Two Speed, Single Winding
  • 73. 66 Dahlander Motors Two – speed motor with a re-connectible winding (Dahlander Connection) Two-speed motor with two separate windings Note the two-speed motors with re-connectible windings (Dahlander connection) have a higher rated output than the corresponding size with separate windings.
  • 74. 67 1.8 Motor Design NEMA Design Letter Changes in motor windings and rotor design will alter the performance characteristics of induction motors. Motors are designed with certain speed torque characteristics to match the speed torque requirements of the various loads. To obtain some uniformity in application, NEMA has designated specific designs of general purpose motors having specified locked rotor torque, breakdown torque, slip, starting current, or other values. The following graph shows the relationship between speed and torque that the motor produces from the moment of start until the motor reaches full load torque at rated speed.
  • 75. 68 Locked rotor torque, or starting torque, is developed when the rotor is held at rest with the rated voltage and frequency applied. This condition occurs each time a motor is started. When rated voltage and frequency are applied to the stator, there is a brief amount of time before the rotor turns. At this instant, a NEMA B motor develops approximately 150% of its full load torque. The magnetic attraction of the rotating magnetic field will cause the rotor to accelerate. As the motor picks up speed, torque decreases slightly until it reaches pull up torque. As the speed increases the torque increases until it reaches it’s maximum at about 200%. This is called breakdown, pullout or stall torque. Torque decreases rapidly as speed increases beyond breakdown torque until it reaches full-load torque at a speed slightly less than 100% of synchronous speed. Full load torque is the torque developed when the motor is operating with rated voltage, frequency and load. The speed at which full-load torque is produced is the slip speed or rated speed of the motor. Minimum acceptable values for different motor designs have been established and are identified by the letters A, B, C and D. The general shapes of the four typical torque-speed characteristics are shown here.
  • 76. 69 NEMA Design A, B, C, D NEMA has established four different designs - A, B, C and D - for electrical induction motors. Different motors of the same nominal horsepower can have varying starting current, torque curves, speeds, and other variables. Selection of a particular motor for an intended task must take all engineering parameters into account. The four NEMA (National Electrical Manufacturers Association) designs have unique speed-torque-slip relationships making them suitable to different type of applications: NEMA design A Has maximum 5% slip, high to medium starting current, normal locked rotor torque, normal breakdown torque, and suited for a broad variety of applications - as fans and pumps.
  • 77. 70 NEMA design B Has maximum 5% slip, low starting current, high locked rotor torque, normal breakdown torque, suited for a broad variety of applications, normal starting torque - common in HVAC application with fans, blowers and pumps. NEMA design C Has maximum 5% slip, low starting current, high locked rotor torque, normal breakdown torque, and suited for equipment with high inertia starts - as positive displacement pumps. NEMA design D Has maximum 5% slip, low starting current, very high locked rotor torque, and suited for equipment with very high inertia starts - as cranes, hoists etc. IEC Design Motors covered by this IEC standard are classified by the following designs: Design N Normal torque three-phase cage induction motors intended for direct-on- line starting, having 2, 4, 6, or 8 poles and rated from 0.4 kW to 630 kW at frequencies of 50 Hz or 60 Hz. Design NY Motors similar to design N, but intended for star-delta starting. For these motors in star-connection, minimum values for Tl and TU of 25% of the values of design N as shown in Table 1.8A may be expected.
  • 78. 71 Table 1.8A – Minimum Values of Torque for Design N Starting Performance Design H High torque three-phase cage induction motors with 4, 6 or 8 poles, intended for Direct-online starting, and rated from 0.4 kW to 160 kW at a frequency of 60 Hz. Torques of IEC Design H are nearly identical to NEMA Design C. Design HY Motors similar to design H but intended for star-delta starting. For these motors in star-connection, minimum values for T1 and TU of 25% of the values of Design H as shown in Table 1.8B may be expected.
  • 79. 72 Table 1.8B – Minimum Values of Torques for Design H Notes: 1. The values of Tl are 1.5 times the corresponding values for design N starting performance, but arc not less than 2.0. 2. The values of Tu are 1.5 times the corresponding values for design N starting performance, but are not less than 1.4. 3. The values of Tb are equal to the corresponding values for design N starting performance, but are not less than 1.9 and the values of Tu. Design N starting torque The starting torque is represented by the locked rotor torque Tl, pull-up torque Tu and breakdown torque Tb, each expressed as a per unit value of the rated torque TN, and shall be in accordance with the appropriate values given in Table 1.8A. These values are minimum values at rated voltage, with no tolerance. Higher values are allowed. The starting torque at any speed between zero and that at which breakdown torque occurs shall be not less than 1.3 times the torque obtained from a curve varying as the square of the speed and being equal to rated torque at rated speed. Note. — The factor 1.3 has been chosen with regard to an undervoltage of 10% in relation to the rated voltage at the motor terminals during the acceleration period.
  • 80. 73 Design N locked rotor apparent power The locked rotor apparent power S1, is the apparent power input expressed as a per unit value of the rated output PN. This value shall be not greater than the appropriate value given in Table 1.8C. The values given in Table 1.8C are independent of the number of poles and are maximum values at rated voltage, with no tolerance. Table 1.8C. Design N starting requirements Motors of design N shall satisfy the following starting requirements: 1. They shall allow two starts in succession (coasting to rest between starts) from cold conditions or one start from hot after running at rated conditions. The retarding torque due to the driven load is in each case proportional to the square of the speed and equal to the rated torque at rated speed with the external inertia given in Table 1.8D. 2. In each case a further start is permissible only if the motor temperature before starting does not exceed the steady temperature at rated load. Note. — It should be recognized that the number of starts should be minimized since these affect the life of the motor. The values given are in terms of mr2 (m = mass; r = mean radius of gyration). Note. — Moment of inertia is defined in ISO Publication 31/111 1978, No. 3- 9.1.
  • 81. 74 Table 1.8D For intermediate output values, external inertia shall be calculated according to the following formula, from which the values in the table have been calculated: I = 0.04 P0.9 p2.5 kg m2 where: P is the power in kW and p is the number of pairs of poles. Design NY starting requirements The starting requirements are as for design N. In addition, however, a reduced retarding torque is necessary as the starting torque in 'star' may be insufficient to accelerate some loads to an acceptable speed.
  • 82. 75 Design H starting torque The starting torque is represented by the locked rotor torque Tl, pull-up torque TU and breakdown torque Tb, each expressed as a per unit value of the rated torque TN, and shall be in accordance with the appropriate values given in Table 1.8B - Minimum values of torques for Design H starting performance. These values given are per unit TN. These values are minimum values at rated voltage, with no tolerance. Higher values are allowed. Design H locked rotor apparent power The locked rotor apparent power S, is the apparent power input expressed as a per unit value of the rated output PN. This value shall be not greater than the appropriate value given in Table 1.8C. The values in Table 1.8C are independent of the number of poles and are maximum values at rated voltage, with no positive tolerance. Design H starting requirements Motors of design H shall satisfy the following starting requirements: 1. They shall allow two starts in succession (coasting to rest between starts) from cold conditions, or one start from hot after running at rated conditions. The retarding torque due to the driven load is assumed to be constant and equal to rated torque, independent of speed, with an external inertia of 50% of the values given in Table1.8D. 2. In each case a further start is permissible only if the motor temperature before starting does not exceed the steady temperature at rated load. Design HY starting requirements The starting requirements are as for design H. In addition, however, a reduced retarding torque is necessary as the starting torque in 'star' may be insufficient to accelerate some loads to an acceptable speed.
  • 83. 76 1.9 Types of duty Definitions Various types of duty have been defined in terms of how the load, and thus the output of the motor, varies with time. The rated output for each type of duty is determined in a load test which the motor must undergo without the temperature limits laid down in IEC Publication 34-1 being exceeded. Actual operating conditions are often of a more irregular nature than those corresponding to any of the standardized types of duty. It is therefore essential, both when choosing a motor and when rating and testing it, to decide on the type of duty that corresponds best to the thermal stresses that are expected to occur in practice. IEC (the International Electrotechnical Commission) uses nine duty cycle designations to describe electrical motor operating conditions:
  • 84. 77 S1 Continuous duty Operation at constant load long enough for thermal equilibrium to be reached. S2 Short-time duty Operation at constant load for a given time that is shorter than the time needed to reach thermal equilibrium, followed by a rest and de-energized period long enough to allow the motor to reach a temperature that does not deviate from the temperature of the cooling medium by more than 2 K.
  • 85. 78 S3 Intermittent duty A sequence of identical duty cycles, where each cycle is in two parts, one at constant load and the other at rest and de-energized, in this type of duty the starting current has no significant effect on the temperature rise. The duty cycle is too short for thermal equilibrium to be reached. S4 Intermittent duty with starting A sequence of identical duty cycles, where each cycle consists of a start that is long enough to have a significant effect on the temperature of the motor, a period at constant load and a period at rest and de-energized, in this type of duty the starting current has no significant effect on the temperature
  • 86. 79 S5 Intermittent duty with electrical braking A sequence of identical duty cycles, where each cycle consists of a start, a period at constant load followed by rapid electrical braking and a rest and de-energized period. The duty cycles are too short for thermal equilibrium conditions to be reached. S6 Continuous-operation periodic duty A sequence of identical duty cycles, where each cycle is in two parts, one at constant load and the other at no-load. No rest and de-energized period. The duty cycles are too short for thermal equilibrium conditions to be reached.
  • 87. 80 S7 Continuous-operation periodic duty with electrical braking A sequence of identical duty cycles, where each cycle consists of a start and a period at constant load, followed by electrical braking. No rest and de-energized period. The duty cycles are too short for thermal equilibrium conditions to be reached. S8 Continuous-operation periodic with related load/speed changes A sequence of Identical duty cycles, each cycle consisting of a period of operation at constant load corresponding to a predetermined speed, followed by one or more periods of operation at other constant loads corresponding to different speeds. There is no rest and de-energized period.
  • 88. 81 Duty with non-periodic load speed variations A duty in which generally load and speed are varying non-periodically within the permissible operating range. This duty includes frequently applied overloads that may greatly exceed the full loads. For this duty type suitable full load values should be taken as the basis of the overload concept. Direction of rotation If the mains supply is connected to the stator terminals marked U, V and W of a three-phase motor, and the phase sequence of the mains is L1, L2, L3, the motor will rotate clockwise as viewed from the drive end. For the opposite direction of rotation, interchange two of the three wires connected to the starter switch or the motor. Fig. 1.9 - Normal direction of rotation is clockwise as viewed from the D-end.
  • 89. 82 Braking Mechanical braking Mechanical braking with magnetic lifting is the technique most widely used for the braking of electric motors. At standstill brakes of this type provide a holding torque, and are therefore used where loss of braking in the event of power failure could be dangerous. However, in certain cases it may be necessary to lift the brake without starting the motor. This can be done by supplying the brake coil from a separate power source, or with a manual release device. The mechanical brakes used for electric motors are shoe, multiple-plate or disc brakes. ABB Motors brakes are disc brakes with asbestos-free brake pads or linings. Fig. 2.0 – Mechanical Braking During braking, the braking torque is constant with mechanical braking. At standstill the brake has a holding torque. On some brakes the braking torque can be reduced for softer deceleration. When the motor is started again, the holding torque ceases automatically.
  • 90. 83 Electrical Braking Countercurrent braking With countercurrent braking, an ordinary standard motor is switched at full speed for the opposite direction of rotation. This can be done with a reversing switch. After braking to a standstill, the motor starts in the opposite direction of rotation, unless the current is switched off at the right moment. A low speed detector is therefore used to cut off the supply to the motor when the speed approaches zero. Countercurrent braking gives a very high braking torque. The current during braking is about the same as during starting, so that there is a considerable temperature rise in the motor. Consequently the permitted frequency of braking with the countercurrent technique is only about one-quarter of the number of permitted brakings for a brake motor. Since the permitted frequency of braking can easily be exceeded with countercurrent braking, temperature sensors should always be used to protect the motor windings from overheating. For squirrel-cage motors the braking time can be calculated approximately with the formula: Where: tb = braking time, s K1 = constant depending on number of poles. See table below. Jm = moment of inertia of motor, kgm2 Jb = moment of inertia of load, referred to speed of motor, kgm2 Mmax = maximum torque of motor, Nm Mstart = starting torque of motor, Nm
  • 91. 84 For slip-ring motors the starting and braking times are both determined by the dimensioning of the rheostatic starter. With countercurrent braking there is no braking action in the event of power failure. The technique is therefore unsuitable for use in plant where loss of braking could cause danger. Direct-current braking When braking with this technique, the A.C. supply to the motor is disconnected and the stator is excited with direct current instead; this causes the motor to produce a braking torque. An ordinary standard motor and suitable equipment for D.C. excitation may be used. The A.C. voltage follows a decay curve, and the D.C. voltage must not be connected until the A.C. voltage has fallen to a value at which it will not harm the D.C. equipment. Direct-current braking gives a far longer braking time than countercurrent braking, however high the excitation current is, but thermal losses are lower, so more frequent braking is permissible. Derating Factors Several factors can affect the performance of an AC motor. These must be considered when applying a motor. Voltage Variation As previously discussed, AC motors have a rated voltage and frequency. Some motors have connections for more that one rated voltage. The following table shows the most common voltage ratings for NEMA motors.
  • 92. 85 A small variation in supply voltage can have a dramatic affect on motor performance. In the following chart, for example, when voltage is 10% below the rated voltage of the motor, the motor has 20% less starting torque. This reduced voltage may prevent the motor from getting its load started or keeping it running at rated speed. A 10% increase in supply voltage, on the other hand, increases the starting torque by 20%. This increased torque may cause damage during startup. A conveyor, for example, may lurch forward at startup. A voltage variation also causes similar changes in the motor’s starting and full-load currents and temperature rise.
  • 93. 86 Frequency A variation in the frequency at which the motor operates causes changes primarily in speed and torque characteristics. A 5% increase in frequency, for example, causes a 5% increase in full-load speed and a 10% decrease in torque. Altitude Standard motors are designed to operate below 3300 feet. Air is thinner, and heat is not dissipated as quickly above 3300 feet. Most motors must be derated for altitudes above 3300 feet. The following chart shows typical horsepower derating factors, but the derating factor should be checked for each motor. A 50 HP motor operated at 6000 feet, for example, would be derated to 47 HP, providing the 40°C ambient rating is still required. Example: 50 HP x 0.94 = 47 HP Ambient Temperature The ambient temperature may also have to be considered. The ambient temperature requirement may be reduced from 40°C to 30°C at 6600 feet on many motors. However, a motor with a higher insulation class may not require derating in these conditions.
  • 94. 87 Earthing of machines Machines shall be provided with means for connecting a protective conductor or an earth conductor, such means being identified by the appropriate symbol or legend. This requirement does not apply to machines with supplementary insulation, to machines with rated voltages up to and including 50 VAC or 120 VDC (see IEC 60364-4-41, clause 411 and IEC 60449), or to machines for assembling in apparatus with supplementary insulation. In the case of machines having rated voltages greater than 50 VAC or 120 VDC, but not exceeding 1 000 VAC, or 1 500 VDC, the terminal for the earth conductor shall be situated in the vicinity of the terminals for the line conductors, being placed in the terminal box, if one is provided. Machines having rated outputs in excess of 100 kW (or kVA) shall have in addition an earth terminal fitted on the frame. Machines for rated voltages greater than 1 000 VAC or 1 500 VDC shall have an earth terminal on the frame, for example an iron strap, and in addition, a means inside the terminal box for connecting a conducting cable sheath, if any. For other cross-sectional areas of live conductors, the earth or protective conductor shall have a cross-sectional area at least equivalent to: 1. That of the live conductor for cross-sectional areas less than 25 mm2 ; 2. 25 mm2 for cross-sectional areas between 25 mm2 and 50 mm2 ; 3. 50 % of that of the live conductor for cross-sectional areas exceeding 50 mm2 The earth terminal shall be identified in accordance with IEC 60445.
  • 95. 88 Speed Control General The relationship between rotational speed, supply frequency, number of poles and slip for induction motors is usually written: In principle the speed can be controlled by changing the number of poles, the slip or the frequency. All three possibilities are used. Changing the number of poles There are three ways to change the number of poles in an induction motor. The stator can be given: 1. Two or more separate windings 2. A pole changing winding 3. Combinations of the above Two-speed motors with separate windings Having separate windings makes it possible to combine different numbers of poles with considerable freedom, but the method does not utilize the motor well, since only half the stator winding is in use at each speed, in principle the possible rated power at each speed will thus only be half that of a single-speed motor of the same size. In addition, the stator and rotor cores are normally dimensioned for a given number of poles. This may also impose certain limitations on ways in which different numbers of poles can be combined in a given core design.
  • 96. 89 Two-speed motors with pole changing winding There are several ways of achieving a pole changing winding in order to utilize a motor better than with two separate windings, but some limits are set by the need for the switchgear to be kept simple. The most widely used systems are the Lindstrom-Dahlander connection, often simply called the Dahlander connection, and PAM, Pole Amplitude Modulation. The Dahlander connection gives a pole number ratio of 1:2. The winding of each phase is in two parts connected in series. These are two common applications that use Dahlander pole-changing:  "Constant torque", where the rated torque of the motor is approximately the same at both speeds. The ratio between the rated outputs is about 3:2. This is achieved by connecting the windings in double star for the higher speed and in delta for the lower speed. This is usually represented in catalogues by the symbols YY/Δ.  "Fan torque", where the torque varies as the square of the speed. "Falling torque" and "square-law torque" are other terms used for this. The ratio between the rated outputs at the two speeds is about 1:5. This is achieved by connecting the windings in double star for the higher speed and in star for the lower speed. This is usually represented in catalogues by the symbols YY/Y. PAM PAM (pole amplitude modulation) makes it possible to design a two- speed motor with a stator winding for pole number ratios other than 2:1. Pole number changing is achieved by changing the direction of the current in part of the winding, thus varying the excitation in the same way as with the Dahlander arrangement. Among the advantages of PAM is that a given motor size can be better utilized and a higher rated power can be extracted from it. Just as with the Dahlander connection, constant- torque or fan-torque versions are possible.
  • 97. 90 Multi-speed motors A pole changing winding can also be combined with another winding. This winding can be for a single speed or it too can be a pole-changing winding. In this way, three or even four-speed motors can be made. Even so, such motors are uncommon. Examples of stator windings and connection arrangements with different types of multi-speed motor There may be other variants. 1) Dahlander or PAM connected 2) For 8/6/4 poles, for example. One of the windings is Dahlander- or PAM- connected. 3) The winding can also be delta-connected. Slip-ring motor with control rheostat A simple way of controlling the speed of a slip-ring motor is to connect an external rheostat (variable resistor) to the rotor winding. If the load torque, and with it the rotor current, is kept constant, an increase in the rotor resistance will lead to increased slip. However, the motor speed will be highly load dependent. This type of speed control, often called slip control, is therefore only used where there are small load variations, for example with pumps, or where the speed can be continuously monitored and the rheostat setting adjusted to suit the torque, with cranes for example.
  • 98. 91 Thus the power supplied to the motor is always constant, regardless of the speed, whilst the output of the motor decreases in proportion to the speed. This means that the difference between the power output with the rheostat fully in circuit and fully out of circuit is consumed in the rheostat itself. Assuming for simplicity that the load torque is constant and the speed is reduced by 25%, for example, the power output will be 75% and the remaining 25% is dissipated in the rheostat. This type of speed control is therefore highly inefficient. 2.3 Converter control Primary voltage control For small changes the slip (s) can be approximately defined as: Reduction of the primary voltage by means of thyristor-type voltage regulators is a speed control technique that is suitable for certain applications. The motor to be controlled should have an adapted torque characteristic, which is achieved by means of increased rotor resistance. A slip-ring motor with external rheostat is therefore suitable. This control method is often used for cranes and similar applications, where the high losses in the rotor circuit are acceptable because the total running time is limited. Rotor power feedback If the speed of a large induction motor is to be reduced for a long time, the methods described above would be uneconomical because of rotor losses. Modern thyristor frequency converters provide quick, stepless control and, because they feed any losses back to the supply, high efficiency.
  • 99. 92 The basic principle of this form of speed control is that the rotor power is taken out via the slip-rings and rectified in a conventional uncontrolled rectifier. The voltage is then converted into alternating voltage in a controlled inverter and fed back to the supply via a transformer. The amount of power fed back to the supply can be varied by varying the firing angle in the inverter. Fig. 2.3A Typical torque/speed diagram for pump and fan duty with speed control using a slip recovery system. This method of operation is comparable to dual supply of slip-ring induction motors. If the rotor is supplied with an external voltage, synchronous speeds will be obtained, which are dependent on the frequency of the external voltage. With converter control the character of the torque/speed curve is different from that of the normal slip-ring motor, and the speed will be less dependent on the load. For accurate speed regulation, the motor is usually fitted with a tacho- generator or pulse generator connected to the controller.
  • 100. 93 Converter control gives deviations from the normal sinusoidal shape of the current in the rotor circuit. These results in additional thermal losses, and these must be compensated for by choosing a slightly larger motor. Reduced cooling due to constant load torque at reduced speed may also need to be compensated for by choosing a slightly larger motor or using forced cooling. There is no need to do this where the load torque follows a square law. Current harmonics in the rotor circuit give small torque pulsations at a frequency of six times the secondary frequency, i.e. the slip frequency. The shaft system must therefore be checked to ensure that it does not suffer harmful resonance stresses. Voltage and frequency control The most attractive way of controlling motor speed is to control the voltage and frequency simultaneously. Fig. 2.3B shows how the torque/speed curve varies when the frequency is reduced and the primary voltage is changed in proportion to the frequency. The maximum torque remains the same, and the motor can be loaded at constant torque within the control range. Fig. 2.3B - Examples of torque curves at different frequencies and with voltage proportional to frequency.
  • 101. 94 If the rated voltage of the motor corresponds to the supply voltage, the motor cannot be controlled to a speed higher than the rated speed if the load torque is to be maintained, since the inverter cannot provide a voltage higher than the supply voltage. Another limit to higher speeds has to do with rotor design. Particularly in large motors for high speeds, control to higher speeds is determined by the critical speed of the motor and the highest permitted runaway speed. One possible result of a wide speed range is that cooling of the motor might be insufficient at low speed and high torque, making it necessary to provide extra cooling. Alternatively, an over dimensioned motor must be chosen. Standard motors are generally used with frequency control, in any case for the lower power ranges. Standard motors are dimensioned for a fairly high starting torque. The shape of the rotor bars is often such that large amounts of heat are produced at the top of the bars during starting, when the rotor frequency is high. Because of the high harmonic losses, this type of rotor bar design is a disadvantage in frequency converter operation, in view of the high harmonic content of the supply voltage. After all, there is no need for a high starting torque when starting with a frequency converter and it may be preferable to use a different rotor bar shape. Fig. 2.3C - Schematic diagram of a frequency converter
  • 102. 95 CTU On-load switch and contactor LCU Rectifier CBU Intermediate filter INU Inverter CP1 Control unit Fig. 2.3D - Complete frequency converter Commutator Motor A motor that has come to be widely used for uninterrupted speed control is the commutator motor, also known as the Schrage motor, after its inventor, in principle it is an induction motor with built-in control gear. Unlike ordinary induction motors the commutator motor has its primary winding in the rotor; the winding is fed from the supply via slip rings. The rotor slots that contain the primary winding also contain a commutator winding, essentially in the form of a D.C. winding. The secondary winding is in the stator. The normal control range is 1 to 10, but it can be extended to 1 to 100 in special cases. So that full torque can be drawn from the motor over the entire control range, these motors are often fitted with a built-on separately driven fan.
  • 103. 96 Common fields of application include printing presses, packaging machines and ski-lifts. Speed control is achieved by supplying the secondary winding in the stator with a control voltage at the slip frequency from the commutator winding, via brushes running on the commutator. By moving the brushes the control voltage to the secondary winding can be varied continuously and stepless, so varying the speed. The speed is stable; the effect of load variations is insignificant. Fig. 2.3D - Three-phase commutator motor. Fig. 2.3E - Examples of brush positions on a commutator motor. Ust = control voltage sUs = secondary voltage s = slip at no load
  • 104. 97 Fig. 2.3F - Torque curves for three different brush positions As the figure shows, the characteristics of the torque curves are such that the change in speed for varying load is insignificant over the normal speed range. 2.4 Motor Efficiency Efficiency is reflected in the nameplate as shown in Fig. 2.4.A. Motor efficiency is the percentage of the energy supplied to the motor that is converted into mechanical energy at the motor’s shaft when the motor is continuously operating at full load with the rated voltage applied. Because motor efficiencies can vary among motors of the same design, the NEMA nominal efficiency percentage on the nameplate is representative of the average efficiency for a large number of motors of the same type. Both NEMA and the Energy Policy Act of 1992 (EPAct) specify the same process for testing motor efficiency. EPAct also specifies the efficiency requirements for a large class of AC motors manufactured after 1997. In 2001, NEMA established the NEMA Premium designation for three-phase AC motors that meet even higher efficiency standards than required by EPAct. Siemens High Efficient motors meet or exceed EPAct efficiency standards and our NEMA Premium Efficient motors with our new copper rotor technology exceed NEMA Premium efficiency standards.
  • 105. 98 Fig. 2.4.A – Efficiency
  • 106. 99
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  • 110. 103 General Characteristics 2.1 System Nominal Voltages There continues to be some confusion between the system or services voltage and utilization or equipment voltage. Table below provides these relationships for the normal range “A” and for range “B” when the voltage moves outside of the normal voltage range. NOMINAL SYSTEM VOLTAGE VOLTAGE RANGE “A” VOLTAGE RANGE “B” Minimum Maximum Minimum Maximum Three -wire Four-wire Utilization Voltage Service Voltage Utilization and Service Voltage Utilization Voltage Service Voltage Utilization and Service Voltage Single-Phase Systems 120/240 — 110 110/120 114 114/228 126 126/252 106 106/212 110 110/220 127 127/254 Three-Phase Systems 208Y/120 191Y/110 197Y/114 218Y/126 184Y/106 191y/110 220Y/127 240/120 220/120 228/114 252/126 (Note d) 212/106 (Note d) 220/110 220/127 240 480Y/277 220 440Y/254 228 456Y/263 252 504Y/291 212 424/245 220 440Y/254 254 508Y/293 480 440 456 504 424 440 508 600 550 570 630 530 550 635 2400 4160Y/2400 2160 3740Y/2160 2340 4050Y/2340 2520 4370Y/2520 2080 3600Y/2080 2280 3950Y/2280 2540 4400Y/2540 4160 3740 4050 4370 3600 3950 4400 4800 4320 4680 5040 4160 4560 5080 6900 6210 6730 7240 5940 6560 7260 8320Y/4800 8110Y/4680 8730Y/5040 7900Y/4560 8800Y/5080 12000Y/6930 11700Y/6760 12600Y/7270 11400/6580 12700Y/7330 Standard Nominal System Voltages and Voltage Ranges (ANSI C84.1-1995). Application of Voltage Ranges According to ANSI C84.1.2.4.1, applications of voltage ranges are as follows. C84.1.2.4.1 Range “A” – Service Voltage. Electric supply systems shall be so designed and operated that most service voltages will be within the limits specified for Range “A”. The occurrence of service voltages outside of these limits should be infrequent. C84.1.2.4.2 Range “A” – Utilization Voltage. User systems shall be so designed and operated that with service voltages within Range “A” limits, most utilization voltages will be within the limits specified for this range. Utilization equipment shall be designed and rated to give fully satisfactory performance throughout this range.
  • 111. 104 C84.1.2.4.3 Range “B” – Service and Utilization Voltages. Range “B” includes voltages above and below Range “A” limits that necessarily result from practical design and operating conditions on supply or user systems, or both. Although such conditions are a part of practical operations, they shall be limited in extend, frequency, and duration. When they occur, corrective measures shall be undertaken within a reasonable time to improve voltages to meet Range “A” requirements. Insofar as practicable, utilization equipment shall be designed to give acceptable performance in the extremes of this range of utilization voltages, although not necessarily as good performance as in Range “A”. It must be recognized that because of conditions beyond the control of the supplier or user, or both, there will be infrequent and limited periods when sustained voltages outside of Range “B” limits will occur. Utilization equipment may not operate satisfactorily under these conditions, and protective devices may operate to protect the equipment. When voltage occurs outside the limits of Range “B”, prompt corrective action is recommended. The urgency for such as location and nature of load or circuits involved and magnitude and nature of the deviation beyond Range “B” limits. 2.2 Voltage Single-speed three-phase motors (i.e. motors without pole changing) can usually be reconnected for two voltages. The usual way is to connect the three stator phase windings in star (Y) or delta (Δ). Another way is to connect the windings in series or parallel, Y or YY for instance. So if the rating plate of a three-phase motor shows voltages for both Y- and Δ connection, this means that the motor can be used for both 440 V and 220 V, for example. At 220 V the winding is connected in Δ by placing the connecting links as shown in the left-hand part of Fig 2.1A. If the supply voltage is 440 V, Y- Δ connection is used, and the strips are connected as shown in the right-hand diagram.
  • 112. 105 Fig. 2.1A - Arrangement of windings and terminal blocks for - Y- Connection Voltage Deviation If the supply voltage at constant output power deviates from the rated voltage of the motor, the starting and maximum torques of the motor vary approximately as the square of the voltage. The change in torque will also result in a change in the speed. The efficiency and the power factor are also affected.
  • 113. 106 Voltage deviations also affect the temperature rise in the winding of the motor. If the voltage is low, the temperature rises in both small and large motors; if the voltage is high the temperature may drop slightly in large motors, but rises sharply in motors with small output powers. It is therefore essential to dimension the windings generously enough to ensure that there is no significant voltage drop in them on starting or in service. Another effect is shown below, for every 100 C increase in winding temperature, the expected thermal life of the winding is reduced by half. There may also be notable decrease in bearing lubricant life as the operating temperature of the motor increases.
  • 114. 107 Unbalance Voltage Far too many assumptions are made when dealing with the symmetry of a voltage supply. In order to accurately assess the quality of the voltage supply, it is necessary to verify it at a number of places within the service and over a reasonable period of time and seasons. NEMA MG 1, 14.36 offers the following explanation of the effects of unbalance voltage, along with a load derating curve. Effects of Unbalance Voltages on the Performance of Polyphase Induction Motors. When the line voltages applied to a polyphase induction motor are not equal, unbalanced currents in the stator windings will result. A small
  • 115. 108 percentage voltage unbalance will result in a much larger percentage current unbalance. Consequently, the temperature rise of the motor operating at a particular load and percentage voltage unbalance will be greater than for the motor operating under the same conditions with balanced voltages. Voltages should be evenly balance as closely as can be read on a voltmeter. Should voltages be unbalance, the rated horsepower of the motor should be multiplied by the factor shown in Fig 2.2A to reduce the possibility of damage to the motor. Operation of the motor above a 5 percent voltage unbalance condition is not recommended. When the derating curve as shown in the left figure, it is applied for operation on unbalanced voltages, the selection and setting of the overload device should take into account the combination of the derating factor applied to the motor and increase in current resulting from the unbalance voltages. This is a complex problem involving the variation in
  • 116. 109 motor current as a function of load and voltage unbalance in addition to the characteristics for the overload device relative to Imaximum or Iaverage. In the absence of specific information, it is recommended that overload devices be selected or adjusted, or both, at the minimum value that does not result in tripping for the derating factor and voltage unbalance that apply. When unbalance voltages are anticipated, it is recommended that the overload devices be selected so as to be responsive to Imaximum in preference to overload devices responsive to Iaverage. Effect on Performance – General. The effect of unbalance voltages on polyphase induction motors is equivalent to the introduction of a “negative sequence voltage” having a rotation opposite to that occurring with balanced voltages. This negative sequence voltage produces in the air gap a flux rotating against the rotation of the rotor, tending to product high currents. A small negative- sequence voltage may product in the windings currents considerably in excess of those present under balanced voltage conditions. Unbalance Defined. The voltage unbalance in percent may be defined as follows: Example: With voltages of 460, 467, and 450, the average is 459, the maximum deviation from average is 9, and the percent unbalance equals: Torques. The locked-rotor torque and breakdown torque are decreased when the voltage is unbalanced. If the voltage unbalance should be extremely severe, the torques might not be adequate for the application.
  • 117. 110 Full-Load Speed. The full-load speed is reduced slightly when the motor operates with unbalanced voltages. Currents. The locked-rotor current will be unbalanced to the same degree that the voltages are unbalanced, but the locked-rotor kVA will increase only slightly. The currents at normal operating speed with unbalanced voltages will be greatly unbalanced in the order of approximately 6 to 10 times the voltage unbalance. Performance Comparison between Standard Efficient Motor vs. Premium Efficient Motor. Emerson Motor Technology Center in St., Louis, Missouri had conducted a study to compare standard efficient motor to premium efficient motor under unbalanced voltage conditions. MOTORS DESIGN DATA DESCRIPTION PREM. EFF. STD. EFF. Model No. 7965 E398 Type TCE CT HP Rating 5 5 Voltage/Freq. 230/60 230/60 No. of Poles 4 4 Syn. Speed 1800 1800 Connections Wye Wye Full Load Performance Amps RPM Slip P.U. Losses (Watts) Efficiency % Power Factor % 12.56 1750 0.0280 445 89.3 83.4 13.47 1738 0.0344 611 85.9 80.9 Flux Density: Kl/in2 Stator Core Stator Teeth Air Gap Rotor Core Rotor Teeth 107 114 0.0325” 43 116 110 120 0.0359” 51 116
  • 118. 111 The increase in winding temperature causes additional I2 R losses. The rotor losses also increase because of the impact the “Negative Sequence Component” has on the rotor. Therefore as shown in figure below, there is a significant drop in motor efficiency. Vibration and Noise Note that in both cases there is a significant impact on motor performance as it relates to acceptable vibration levels and sound power levels.
  • 119. 112 2.3 Power factor A motor consumes not only active power, which it converts into mechanical work, but also reactive power, which is needed for magnetization but does not perform any work. The active and reactive power, represented in the diagram on the right by P and Q together give the apparent power S. The ratio between the active power, measured in kW, and the apparent power, measured in kVA, is known as the power factor. The angle between P and S is usually designated cos φ. The power factor is equal to cos φ. The power factor is usually between 0.7 and 0.9. It is lower for small motors and higher for large ones. If there are many motors in an installation it will consume a lot of reactive power and will therefore have a lower power factor. Power supply utilities sometimes require the power factor of an installation to be raised. This is done by connecting capacitors to the supply; these generate reactive power and thus raise the power factor. Phase compensation With phase compensation the capacitors are usually connected in parallel with the motor or group of motors. However, in some cases an Induction
  • 120. 113 motor can run as a generator, and this can lead to self-excitation. To avoid complications, therefore, it is normal practice not to compensate for more than the no-load current of the motor. The capacitors must not be connected in parallel with single phases of the winding; such an arrangement may make the motor difficult or impossible to start with star-delta (Y-Δ) starting. If a two-speed motor with separate windings has phase compensation on both windings, the capacitors should not remain in circuit on the unused winding. Under certain circumstances such capacitors can cause increased heating of the winding and possibly vibration as well. 2.4 Efficiency Electric motors are simply devices that convert electrical energy into mechanical energy. Like all electromechanical equipment, motors consume some "extra" energy in order to make the conversion. Efficiency is a measure of how much total energy a motor uses in relation to the rated power delivered to the shaft. A motor's nameplate rating is based on output horsepower, which is fixed for continuous operation at full load. The amount of input power needed to produce rated horsepower will vary from motor to motor, with more- efficient motors requiring less input wattage than less-efficient models to produce the same output. Electrical energy input is measured in watts, while output is given in horsepower. (This convention applies in the USA; output power for motors manufactured in other countries may be stated in watts or kilowatts.) One horsepower is equivalent to 746 watts. There are several ways to express motor efficiency, but the basic concept and the numerical results are the same. For example: or its equivalent; Efficiency, % = 746 x Horsepower (output) Watts (input) x 100
  • 121. 114 The ratio describes efficiency in terms of what can be observed from outside the motor, but it doesn't say anything about what is going on inside the motor, and it is what's happening inside that makes one motor more or less efficient than another. For example, we can rewrite the equation as: or its equivalent; "Losses" stands for all the energy "fees" the motor charges in order to make its electrical-to-mechanical energy conversion. Their magnitude varies from motor to motor and can even vary among motors of the same make, type and size. In general, however, standard-efficiency motors (pre-EPAct) have higher losses than motors that meet EPAct standards, while NEMA Premium motors, or better, have lower losses still. Types of Losses Energy losses in electric motors fall into four categories:  Power losses (Stator and Rotor Losses)  Magnetic core losses  Friction and windage losses, and  Stray load losses. Efficiency, % = Watts (output) Watts (input) x 100 Efficiency, % = Watts (output) Watts (output) + Watts (losses) x 100 Efficiency, % = Watts (input) – Watts (losses) Watts (input) x 100
  • 122. 115 Fig 2.4A. A typical NEMA Design B motor showing components that can be modified to increase the motor's efficiency: (a) Stator windings; (b) Rotor length; (c) conductor bars and end rings; (d) air gap; (e) laminations; (f) bearings; (g) fan. Power losses and stray load losses appear only when the motor is operating under load. They are therefore more important — in terms of energy efficiency — than magnetic core losses and friction and windage losses, which are present, even under no-load conditions (when the motor is running, of course). Power losses, also called I²R losses, are the most important of the four categories and can account for more than one-half of a motor's total losses. Power losses appear as heat generated by resistance to current flowing in the stator windings and rotor conductor bars and end rings. Stator losses make up about 66% of power losses, and it is here that motor manufacturers have achieved significant gains in efficiency. Since increasing the mass of stator windings lowers their electrical resistance (and therefore reduces I²R losses), highly efficient motors typically contain about 20% more copper than standard efficiency models of equivalent size and rating. Rotor losses are reduced by decreasing the degree of slip. This is accomplished by increasing the mass of the rotor conductors (conductor bars and end-plates) and/or increasing their conductivity (see below), and to a lesser extent by increasing the total flux across the air gap between rotor and stator.