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dc motor

  1. 1. 1 PMI Revision 01
  2. 2. Motor Enclosures Energy Efficient Motors Classification of Motors Construction Details of Motor Motor Fundamentals CONTENTS 2 PMI Revision 01
  3. 3. ELECTRIC MOTOR • An electric motor is an electromechanical device that converts electrical energy to mechanical energy. • The mechanical energy can be used to perform work such as rotating a pump impeller, fan, blower, driving a compressor, lifting materials etc. Input = Electrical Power Output = Mechanical Power 3 PMI Revision 01
  4. 4. 4 How the Electric motors work PMI Revision 01
  6. 6. How Does an Electric Motor Work? 6 PMI Revision 01
  7. 7. DC Motor example 7 Dc motor working PMI Revision 01
  8. 8. 8 How Does an Electric Motor Work? PMI Revision 01
  9. 9. 9 How Does an Electric Motor Work? PMI Revision 01
  10. 10. How Does an Electric Motor Work? 10 PMI Revision 01
  11. 11. Type of Electric Motors Electric Motors Alternating Current (AC) Motors Direct Current (DC) Motors Synchronous Induction Three-Phase Single-Phase Self Excited Separately Excited Series Shunt Compound 11 PMI Revision 01
  12. 12. Stator Rotor Terminal Box Enclosure Insulation Structure of Motors 12 PMI Revision 01
  13. 13. DC Motor  Although AC motors are the most common type of motor used in industry, direct current (DC) motors are also used.  One common use for a DC motor is as a backup motor for a critical process.  DC motors can run on the direct current supplied by a battery when there is a failure in the alternating current supplied to an AC motor.  For example, a DC motor can used with a backup pump that supplies oil to the bearings in a large piece of equipment. 13 PMI Revision 01
  14. 14. DC Motor Parts  DC motor stator consists of permanent magnets.  The rotating part, which is shown as a loop of wire, is called the armature.  The armature is connected to a source of DC power.  Two components called brushes are connected to a DC power source.  A conducting ring, known as a commutator, is mounted on the end of the armature. The commutator is not a solid ring. It consists of conducting segments that are separated from each other. 14 PMI Revision 01
  15. 15. DC Motor  During operation, the commutator makes sliding contact with the brushes.  Current flows from the power source to armature, through the brush and commutator.  The current flow through the armature creates a magnetic field with a north pole and a south pole.  The poles are perpendicular to the armature. When current is supplied to the armature, motor action is produced.  The interaction between the stator's magnetic field and the armature's magnetic field causes the armature to rotate. 15 PMI Revision 01
  16. 16. Commutaor 16 PMI Revision 01
  17. 17. DC Motor  However, as the armature turns, the commutator physically changes the direction in which the current flows through the armature. This change in direction changes the polarity of the magnetic field created by the armature.  The brushes and the commutator in a DC motor enable the armature to change its magnetic field. As a result, the armature turns continuously. 17 PMI Revision 01
  18. 18. Commutaor 18 PMI Revision 01
  19. 19. DC Motor  The major parts of the example DC motor include the frame used to house the stator and armature; the stator, which may also be referred to as the field; the armature; the commutator; and end bells.  The stator is made of coils of wire that are wrapped around iron cores. The coils are electrically connected to a DC power source.  The armature contains several loops of wire that are wound back and forth. All of the loops make an electrical connection to the motor's commutator segments. The electrical connections to the commutator segments are protected and held in place by a wrapping of varnish- coated fibers. 19 PMI Revision 01
  20. 20. DC Motor  Current flows from one commutator segment, through the armature, and back through another commutator segment.  The commutator makes sliding contact with a set of brushes. The brushes, which fit in holders, are held against the commutator by springs to maintain contact and to provide a path for current flow from the power source to the commutator.  Brushes are a frequent maintenance item for DC motors. Because they rub against the commutator, they wear down, so they must be replaced periodically. 20 PMI Revision 01
  21. 21. Conventional (brushed) DC motor 21 PMI Revision 01
  22. 22. Types of D.C. Motors Shunt-wound motor  Field winding is connected in parallel with the armature  The current through the shunt field winding is not the same as the armature current. Shunt field having relatively large number of turns of wire having high resistance. 22
  23. 23. Types of D.C. Motors Series-wound motor  Field winding is connected in series with the armature.  Series field winding carries the armature current  Series field winding has a relatively small number of turns of thick wire and with a low resistance. 23
  24. 24. Types of D.C. Motors Compound-wound motor  It two field windings; one connected in parallel with the armature and the other in series with it. The compound machines always designed so that the flux produced by shunt field winding is considerably larger than the flux produced by the series field winding. 24
  25. 25. DC Motor  Sparking or arcing near the brushes or on the commutator can mean that the brushes need to be replaced or that they are not making good contact with the commutator.  In addition, brushes can chip, which impairs their effectiveness.  The commutator should also be checked periodically. Any scoring or grooving on the face of the commutator may indicate a problem. 25 PMI Revision 01
  26. 26. AC MACHINES NEMA MG 1-2003 has the following definitions:  An induction machine is an asynchronous machine that has a magnetic circuit interlinked with two electric circuits, or sets of circuits, rotating with respect to each other. Power is transferred from one circuit to another by electromagnetic induction.  A synchronous machine is an alternating-current machine in which the average speed of normal operation is exactly proportional to the frequency of the system to which it is connected. 26 PMI Revision 01
  27. 27. SYNCHRONOUS MOTOR  A synchronous motor is a synchronous machine used for a motor. A synchronous motor cannot start without being driven. They need a separate starting means.  There are several types of synchronous motors.  Direct current excited synchronous motor (field poles are excited by direct current)  Permanent magnet synchronous motor (field excitation is provided by permanent magnets)  Reluctance synchronous motor (starts as an induction motor, is normally provided with a squirrel cage winding, but operates at synchronous speed). 27 PMI Revision 01
  28. 28.  Synchronous motors have fixed stator windings electrically connected to the AC supply.  Three-phase stator is similar to that of an induction motor.  A separate source of excitation connected to a field winding on the rotating shaft.  The rotating field has the same number of poles as the stator, and is supplied by an external source of DC.  Magnetic flux links the rotor and stator windings causing the motor to operate at synchronous speed. 28 Synchronous Motor PMI Revision 01
  29. 29. 29 Synchronous Motor PMI Revision 01
  30. 30. Synchronous Motor  Synchronous motors can be classified as brush excitation or brushless excitation.  Brush excitation consists of cast-brass brush holders mounted on insulated steel rods and supported from the bearing pedestal. The number of brushes for a particular size and rating depends on the field current. Sufficient brushes are supplied to limit the current density to a low value. The output of a separate DC exciter is applied to the slip rings of the rotor.  A brushless excitation system utilizes an integral exciter and rotating rectifier assembly that eliminates the need for brushes and slip rings. 30 PMI Revision 01
  31. 31. Synchronous Motor  An important drawback of a synchronous motor is that it is not self-starting and auxiliary means have to be used for starting it.  A synchronous motor starts as an induction motor, until the rotor speed is near synchronous speed where it is locked in step with the stator by application of a field excitation.  When the synchronous motor is operating at synchronous speed, it is possible to alter the power factor by varying the excitation supplied to the motor field. 31 PMI Revision 01
  32. 32.  A synchronous motor runs at synchronous speed or not at all. Its speed is constant (synchronous speed) at all loads. 32 Synchronous Motor Speed PMI Revision 01
  33. 33.  In d.c. motors and induction motors, an addition of load causes the motor speed to decrease. The decrease in speed reduces the counter e.m.f. enough so that additional current is drawn from the source to carry the increased load at a reduced speed.  This action cannot take place in a synchronous motor because it runs at a constant speed (i.e., synchronous speed) at all loads. 33 Synchronous Motor On Load PMI Revision 01
  34. 34. 34 Synchronous Motor On Load  What happens when we apply mechanical load to a synchronous motor?  The rotor poles fall slightly behind the stator poles while continuing to run at synchronous speed. The angular displacement between stator and rotor poles (called torque angle a) causes the phase of back e.m.f. Eb to change w.r.t. supply voltage V. This increases the net e.m.f. Er in the stator winding. Consequently, stator current Ia ( = Er/Zs) increases to carry the load. PMI Revision 01
  35. 35. 35 Torque Angle PMI Revision 01
  36. 36. Pull-Out Torque  There is a limit to the mechanical load that can be applied to a synchronous motor. As the load increases, the torque angle α also increases so that a stage is reached when the rotor is pulled out of synchronism and the motor comes to a standstill.  This load torque at which the motor pulls out of synchronism is called pull—out or breakdown torque.  Its value varies from 1.5 to 3.5 times the full load torque. 36 PMI Revision 01
  37. 37. Synchronous motor power factor 37  One of the most important features of a synchronous motor is that by changing the field excitation, it can be made to operate from lagging to leading power factor. PMI Revision 01
  38. 38. Synchronous motor power factor 38  Under excitation: When the rotor is underexcited, i.e. the induced e.m.f. E is less than V, the stator current has a lagging component to make up for the shortfall in excitation needed to yield the resultant Weld that must be present as determined by the terminal voltage, V.  Normal excitation: With more field current , however, the rotor excitation alone is sufficient and no lagging current is drawn by the stator. PMI Revision 01
  39. 39. Synchronous motor power factor 39  Over excitation: And in the overexcited case, there is so much rotor excitation that there is effectively some reactive power to spare and the leading power factor represents the export of lagging reactive power that could be used to provide excitation for induction motors elsewhere on the same system. PMI Revision 01
  40. 40. Synchronous motor power factor 40 PMI Revision 01
  41. 41. INDUCTION MOTOR 41 PMI Revision 01
  42. 42. 42 Introduction: Induction motor Three-phase induction motors are the most common and frequently encountered machines in industry  Simple design  Rugged  Inexpensive  High power to weight ratio  Easy to maintain  Direct connection to AC power source  Easy maintenance  Wide range of power ratings: fractional horsepower to MW  Run essentially as constant speed from zero to full load PMI Revision 01
  43. 43. Squirrel Cage 3 phase winding in stator Copper bars in rotor Wound Rotor 3 phase winding in stator 3 phase winding in rotor (Shorted internally) Wound Rotor 3 phase winding in stator with Slip Ring 3 phase winding in rotor (Terminated to slip rings) Types of Induction Motors 43 PMI Revision 01
  44. 44.  The induction motor derives its name from the fact that AC voltages are induced in the rotor circuit by the rotating magnetic field of the stator  An Induction motor operates on the principle of induction.  The rotor receives power from the stator due to Induction The rotor is not connected to an external source of voltage (Singly excited m/c).  The induction motor is the most commonly used type of AC motor as It is simple, rugged in construction and low in cost Induction Motor 44 PMI Revision 01
  45. 45. 45 Rotating Magnetic Field PMI Revision 01
  46. 46.  The Stator in an AC motor is a wire coil, called a stator winding, when this coil is energized by AC power, a rotating magnetic field is produced  This rotating field is produced by the contributions of space-displaced phase windings carrying appropriate time displaced currents by 120 electrical degrees  When a magnetic field comes close to a wire, it produces an electric voltage in that wire  This is called induction – (as Faraday's law)  In induction motors, the induced magnetic field of the stator winding induces a current in the rotor  This induced rotor current produces a second magnetic field necessary for the rotor to turn Induction Motor 46 PMI Revision 01
  47. 47.  The rotating magnetic field generated in the stator induces a magnetic field in the rotor.  The two fields interact and cause the rotor to turn  To obtain maximum interaction between the fields, the air gap between the rotor and stator should be very small  As you know from Lenz's law, any induced emf tries to oppose the changing field that induces it, here the changing field is the motion of the resultant stator field  A force is exerted on the rotor by the induced emf and the resultant magnetic field  This force tends to cancel the relative motion between the rotor and the stator field and the rotor, as a result, moves in the same direction as the rotating stator field Induction Motor 47 PMI Revision 01
  48. 48.  It is, however, impossible for the rotor of an induction motor to turn at the same speed as the rotating magnetic field  If the speeds were the same, there would be no relative motion between the stator and rotor fields; without relative motion there would be no induced voltage in the rotor  In order for relative motion to exist between the two, the rotor must rotate at a speed slower than that of the rotating magnetic field  The difference between the speed of the rotating stator field and the rotor speed is called slip  The smaller the slip, the closer the rotor speed approaches the stator field speed Induction Motor 48 PMI Revision 01
  49. 49.  The speed of the rotating magnetic field of the stator can be calculated with the formula below (we shall not go into details of how it is derived, but it is simple, and follows from the equations for poly-phase machines): Ns=120fs / P where P is the number of poles and fs is the frequency of the stator applied voltage  When the stator is supplied by a balanced three- phase source, it will produce a magnetic field that rotates at synchronous speed determined by the above relation Induction Motor 49 PMI Revision 01
  50. 50.  The rotor reacts to the magnetic field, but does not travel at the same speed  Also the rotor speed actually lags behind the speed of the magnetic field and rotor runs at the speed Nr which is close to the speed of the stator field, Ns at no load, but the rotor speed decreases as the load is increased  The term slip quantifies the slower speed of the rotor in comparison with the rotating speed of the stator magnetic field and is expressed mathematically as: S=(Ns-Nr)/Ns SLIP 50 PMI Revision 01
  51. 51.  The rotor is not locked into any position and therefore will continue to slip throughout the motion  The speed of the rotor depends upon the torque requirements of the load, higher the load, stronger the turning force needed to rotate the rotor  The turning force can increase only if the rotor-induced e.m.f. increases and this e.m.f. can increase only if the magnetic field cuts through the rotor at a faster rate  To increase the relative speed between the field and the rotor, the rotor must slow down  Therefore, for heavier loads the induction motor turns slower than for lighter loads and the amount of slip increases proportionally with increase in load SLIP 51 PMI Revision 01
  52. 52.  Actually only a slight change in speed is necessary to produce the current changes required to accommodate the changes in load (this is because the rotor windings have a low resistance)  As a result, induction motors are called constant-speed motors (similarly to DC shunt motor) SLIP 52 PMI Revision 01
  53. 53. Typical torque-speed characteristics of induction motor Torque Speed Characteristic 53 PMI Revision 01
  54. 54. 54 Locked rotor torque – the minimum torque that the motor develops at rest for all angular positions of the rotor at rated voltage and frequency. Locked rotor current – the steady state current from the line at rated voltage and frequency with the rotor locked. Breakdown torque – the maximum torque that the motor develops at rated voltage and frequency without an abrupt drop in speed. Pull up torque – the minimum torque developed during the period of acceleration from rest to the speed that breakdown torque occurs. Common terms PMI Revision 01
  55. 55.  On start-up the slip is s=1 and the starting torque (also known as a breakaway torque) is sufficiently large to accelerate the rotor (the rotor has previously been 'locked' - stationary)  As the rotor runs up to its full-load speed the torque increases in essentially inverse proportion to the slip  After the torque reached its maximum, it rapidly falls to zero, at the synchronous speed, Ns  Looking backwards: as rotor speed falls below Ns the torque increases almost linearly to a maximum dictated by the full load (plus rotor losses)  the speed only falls a little when the load is raised from 0 to its full value - this is a normal operating region Analysis of Operation 55 PMI Revision 01
  56. 56.  Other key features:  The maximum speed is a synchronous speed, Ns, independent of the applied voltage  Torque is proportional to the V2 at an arbitrary speed  When operating at 90-95% Ns heat losses are at minimum Analysis of Operation 56 PMI Revision 01
  57. 57. Components Of Induction Motor A 3-phase induction motor has two main parts: • A stator – consisting of a steel frame that supports a hollow, cylindrical core of stacked laminations. Slots on the internal circumference of the stator house the stator winding. • A rotor – also composed of punched laminations, with rotor slots for the rotor winding. 57 PMI Revision 01
  58. 58. Stator  consisting of a steel frame that supports a hollow, cylindrical core  core, constructed from stacked laminations, having a number of evenly spaced slots, providing the space for the stator winding Induction Motor - Construction 58 PMI Revision 01
  59. 59. 59 Stator Frame PMI Revision 01
  60. 60. Wound Stator Core 60 PMI Revision 01
  61. 61. COMPONENTS OF INDUCTION MOTOR There are two-types of rotor windings: • Squirrel-cage windings, which produce a squirrel-cage induction motor (most common) • Conventional 3-phase windings made of insulated wire, which produce a wound-rotor induction motor (special characteristics) 61 PMI Revision 01
  62. 62. Induction Motor: Squirrel cage rotor  Squirrel cage rotor consists of copper bars, slightly longer than the rotor, which are pushed into the slots.  The ends are welded to copper end rings, so that all the bars are short circuited.  In small motors, the bars and end-rings are diecast in aluminium to form an integral block. 62 PMI Revision 01
  63. 63. Squirrel Cage Rotor 63 PMI Revision 01
  64. 64. Induction Motor: Wound Rotor  A wound rotor has a 3-phase winding, similar to the stator winding.  The rotor winding terminals are connected to three slip rings which turn with the rotor. The slip rings/brushes allow external resistors to be connected in series with the winding.  The external resistors are mainly used during start-up – under normal running conditions the windings short circuited externally. 64 PMI Revision 01
  65. 65. Squirrel cage rotor Wound rotor Notice the slip rings Rotor 65 PMI Revision 01
  66. 66. Cutaway in a typical wound- rotor IM. Notice the brushes and the slip rings Brushes Slip rings Induction Motor 66 PMI Revision 01
  67. 67. 67 Induction motor speed  At what speed will the IM run?  Can the IM run at the synchronous speed, why?  If rotor runs at the synchronous speed, which is the same speed of the rotating magnetic field, then the rotor will appear stationary to the rotating magnetic field and the rotating magnetic field will not cut the rotor. So, no induced current will flow in the rotor and no rotor magnetic flux will be produced so no torque is generated and the rotor speed will fall below the synchronous speed  When the speed falls, the rotating magnetic field will cut the rotor windings and a torque is produced PMI Revision 01
  68. 68. Specifications Following basic parameters are embossed on motor name plate Voltage Bearing Frequency Insulation class Current Degree of protection Kilo Watt Duty Phase RPM Serial number Cooling Frame Mfg. details Efficiency Ambient Temperature 69 PMI Revision 01
  69. 69. 70 Temperature : Insulating materials are divided into seven classes in terms of withstanding maximum temperature Y up to 90°C Un impregnated Paper, Cotton, Silk …. A up to 105°C Paper, Cotton, Silk impregnated with oil E up to 120°C Phenol formaldehyde mouldings B up to 130°C Inorganic fibrous and flexible materials (mica glass etc) bonded with suitable organic resins such as shellac bitumen, alkyd, epoxy etc. F up to 155°C As Class B – but with resins such as alkyd, epoxy, silicone alkyd etc. H up to 180°C As Class B – but with silicone resins C above 180°C – mica, asbestos, ceramics, glass (alone or with inorganic binders or silicone resins), polyamides or polytetrafluoroethylene - PTFE Electrical Insulation PMI Revision 01
  70. 70. 71 PMI Revision 01
  71. 71.  f = P N / 120 (Where f is frequency in Hz, P is no. of pole and N is speed in rpm)  1 H.P. = 746 Watts = 0.75 KW (approx.)  P α D2 L n (Where P is output, D is diameter, L is length and n is speed)  slip s = (ns - nr) / ns (Where ns is synchronous speed in rpm and nr is rotor speed in rpm ) Motor Fundamentals 72 PMI Revision 01
  72. 72. The nameplate details of a motor are given as Power, P = 15 kW, Efficiency, η = 0.9 Using a power meter the actual three phase power drawn is found to be 8 kW Find out the loading of the motor Example 73 PMI Revision 01
  73. 73. The nameplate details of a motor are given as Power, P = 15 kW, Efficiency, η = 0.9 Using a power meter the actual three phase power drawn is found to be 8 kW Input power at full-rated power in kW, Pir = 15 / 0.9 = 16.7 kW Percentage loading = 8 / 16.7 = 48 % Example 74 PMI Revision 01
  74. 74.  Input Power Measurements  First measure input power Pi with a hand held or in-line power meter, Pi = Three-phase power in kW  Note the name plate rated kW and Efficiency  The figures of kW mentioned in the name plate is for output conditions  So corresponding input power at full-rated load ηfl = Efficiency at full-rated load Pir = Input power at full-rated power in kW  The percentage loading can now be calculated as follows Loading of Motor 75 PMI Revision 01
  75. 75. Performance Terms and Definitions 76 Efficiency : The efficiency of the motor is given by in loss in out P P 1 P P     Where Pout – Output power of the motor Pin – Input power of the motor PLoss – Losses occurring in motor Motor Loading : Motor Loading % = Actual operating load of the motor Rated capacity of the motor PMI Revision 01
  76. 76. Motor Efficiency 77 Electric motors are electromagnetic energy converters whose function is based on the force exerted between electrical currents and magnetic fields – which are usually electrically excited as well. A typical value for an 11 kW standard motor is around 90 per cent and, for 100 kW, up to 94 per cent. PMI Revision 01
  77. 77. Efficiency of Electric Motors Motors loose energy when serving a load • Fixed loss • Rotor loss • Stator loss • Friction and Windage • Stray load loss 78 PMI Revision 01
  78. 78. Motor Losses  Core Losses: A combination of eddy-current and hysteresis losses within the stator core. Accounts for 15 to 25 percent of the overall losses.  Friction and Windage Losses: Mechanical losses which occur due to air movement and bearings. Accounts for 5 to 15 percent of the overall losses.  Stator Losses: The I2R (resistance) losses within the stator windings. Accounts for 25 to 40 percent of the overall losses.  Rotor Losses: The I2R losses within the rotor windings. Accounts for 15 to 25 percent of the overall losses.  Stray Load Losses: All other losses not accounted for, such as leakage. Accounts for 10 to 20 percent of the overall losses. 79 PMI Revision 01
  79. 79. 80 Motor Losses PMI Revision 01
  80. 80. kVA kW Cos Factor Power    As the load on the motor reduced, the magnitude of active current reduces. However, there is not a corresponding reduction in the magnetizing current, with the result motor power factor reduces, or gets worse, with a reduction in applied load. Power Factor 81 PMI Revision 01
  81. 81. Energy Efficiency Opportunities 82  Use energy efficient motors  Reduce under-loading (and avoid over-sized motors)  Size to variable load  Improve power quality  Rewinding  Power factor correction by capacitors  Improve maintenance  Speed control of induction motor PMI Revision 01
  82. 82. 83  Reduce intrinsic motor losses  Efficiency 3-7% higher  Wide range of ratings  More expensive but rapid payback  Best to replace when existing motors fail Use Energy Efficient Motors PMI Revision 01
  83. 83. 84 Reduce Under-loading • Reasons for under-loading • Large safety factor when selecting motor • Under-utilization of equipment • Maintain outputs at desired level even at low input voltages • High starting torque is required • Consequences of under-loading • Increased motor losses • Reduced motor efficiency • Reduced power factor PMI Revision 01
  84. 84. 85 Sizing to Variable Load • Motor selection based on • Highest anticipated load: expensive and risk of under-loading • Slightly lower than highest load: occasional overloading for short periods • But avoid risk of overheating due to • Extreme load changes • Frequent / long periods of overloading • Inability of motor to cool down X  Motors have ‘service factor’ of 15% above rated load PMI Revision 01
  85. 85. 86 Improve Power Quality Motor performance affected by • Poor power quality: too much fluctuations in voltage and frequency • Voltage unbalance: unequal voltages to three phases of motor • Keep voltage unbalance within 1% • Balance single phase loads equally among three phases • Segregate single phase loads and feed them into separate line/transformer PMI Revision 01
  86. 86. 87 Rewinding • sometimes rewinding reduces motor efficiency considerably • Can reduce motor efficiency • Maintain efficiency after rewinding by • Using qualified/certified firm • Maintain original motor design • Replace 40HP, >15 year old motors instead of rewinding • Buy new motor if cost of rewinding is more than 50 cost of new motor. PMI Revision 01
  87. 87. 88 Improve Power Factor (PF) • Use capacitors for induction motors • Benefits of improved PF • Reduced kVA • Reduced losses • Improved voltage regulation • Increased efficiency of plant electrical system PMI Revision 01
  88. 88. Power Loss Area Efficiency Improvement 1. Fixed loss (iron) Use of thinner gauge, lower loss core steel reduces eddy current losses. Longer core adds more steel to the design, which reduces losses due to lower operating flux densities. 2. Stator I2R Use of more copper & larger conductors increases cross sectional area of stator windings. This lower resistance (R) of the windings & reduces losses due to current flow (I) 3 Rotor I2R Use of larger rotor conductor bars increases size of cross section, lowering conductor resistance (R) & losses due to current flow (I) 4 Friction & Windage Use of low loss fan design reduces losses due to air movement 5. Stray Load Loss Use of optimized design & strict quality control procedures minimizes stray load losses 89 Use Energy Efficient Motors PMI Revision 01
  89. 89. 90 PMI Revision 01
  90. 90. PMI Revision 01 91 Motor Efficiency Electric motors are electromagnetic energy converters whose function is based on the force exerted between electrical currents and magnetic fields – which are usually electrically excited as well. A typical value for an 11 kW standard motor is around 90 per cent and, for 100 kW, up to 94 per cent.
  91. 91. PMI Revision 01 92 Motor losses The % losses indicated are for 3000 rpm motors, and 1500 rpm motors in brackets. Core Loss : approx 18% (22%) of total loss at full load Stator and Rotor Resistance (I2R) Loss: approx 42% (56%) of total loss at full Load Friction and Windage Loss approx 30% (11%) of total loss at full load Stray Load Loss : approx 10%(11%) of total loss at full load
  92. 92. Range of losses in Induction motors 93 Range Energy Loss at Full Load (%) 1 - 10 HP 14.0 - 35 10 - 50 HP 9.0 - 15 50 - 200 HP 6.0 - 12 200 - 1500 HP 4.0 - 07 1500 - HP & ABOVE 2.3 - 04 PMI Revision 01
  93. 93.  Type of Enclosures (IP55, IP23 etc.)  Provides protection to person against contact with live wire and moving parts and to machine against ingress of solid foreign bodies and harmful ingress of water  Ingress protection code consists of the letter ‘IP’ followed by two numbers, first numeral designates the extent of protection to person and protection to machine against solid foreign bodies, while the second designates the extent of protection to machine against water  General suffix letter for protection IP XY Types of Enclosures 94 PMI Revision 01
  94. 94. Types of Enclosures 95 PMI Revision 01
  95. 95. Types of Enclosures 96 PMI Revision 01
  96. 96.  S1: Continuous operation at rated load  S2: Short time operation  S3: Intermittent periodic operation  S4: As for S3 but with starting  S5: As for S3 but with electric braking  S6: Continuous cyclic operation  S7: As for S6 but with electric braking  S8: As for S6 but with related load/speed characteristic Duty Cycles 97 PMI Revision 01
  97. 97.  Air cooled motors  70 deg. C by resistance method for both class B&F insulation.  Water cooled Motors  80 deg. C over inlet cooling water temperature mentioned elsewhere, by resistance method for both class B&F insulation 98 Temperature Rise PMI Revision 01
  98. 98. Cooling All motors shall be either Totally enclosed fan cooled (TEFC), Totally enclosed tube ventilated (TETV), or Closed air circuit air cooled (CACA) type. However, motors rated 3000kW or above can be Closed air circuit water cooled (CACW) Suitable single phase space heaters shall be provided on motors rated 30KW and above to maintain windings in dry condition when motor is standstill. Separate terminal box for space heaters & RTDs shall be provided 99 PMI Revision 01
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  104. 104. THANK YOU 105 PMI Revision 01