TRAINING AND BASICS ON MOTORS FOR BEGINNERS

POET CONSULTANTS PVT. LTD.
TRAINING
ON

TRAINING COURSE
ON
MOTORS

MOTORS
• GENERAL
• BASIC TECHNICAL REQUIREMENTS
• SAFETY ASPECTS
• APPROVED MAKES
• LV MOTORS
• HV MOTORS
• SELECTION CRITERION

MOTORS
• BRIEF SPECIFICATIONS
• PROTECTION & CONTROL REQUIREMENTS
• ENERGY EFFICIENT MOTORS & EVALUATION
CRITERION
• MAINTENANCE SCHEDULE
• APPLICABLE STANDARDS
• APPENDIX – 1
• APPENDIX - 2

GENERAL:
UNDER THIS HEADING, APPLICABLE STANDARDS AND
APPLICATION OF MOTORS ARE COVERED
APPLICABLE STANDARDS:
• USER COMPANY SAFETY STANDARDS
• IE ACTS AND RULES
• IS/ BS/ IEC/ IEEE STANDARDS
APPLICATION:
• TYPE OF INSTALLATION - INDOOR/ OUTDOOR
• AREA OF USAGE - FACTORY, WAREHOUSE,
OFFICE, OFF-SHORE, HAZARDOUS, etc.,
• TYPE OF MOTOR - GENERAL PURPOSE OR
SPECIAL PURPOSE
MOTORS

SAFETY ASPECTS:
DUE CONSIDERATION FOR THE SAFETY OF
PERSONNEL AND THE INSTALLATION IS
IMPORTANT. MAIN CATEGORIES ADDRESSED
UNDER SAFETY ASPECT ARE:
 RATINGS
 ENCLOSURE
 TERMINATION ARRANGEMENTS
 SAFETY ACCESSORIES
MOTORS

RATING ASPECT:
WHILE SELECTING THE RATINGS FOR ANY APPLICATION/
VERIFICATION OF RATING FOR ALREADY EXISTING
INSTALLATION THE FOLLOWING KEY CRITERION HAVE TO
BE LOOKED INTO:
 10% MARGIN OVER DRIVEN EQUIPMENT
 VOLTAGE AND FREQUENCY VARIATION SHALL BE +/-
10% AND +/-5% RESPECTIVELY WITH A COMBINED
VARIATION OF +/-10%
 DESIGN AMBIENT TEMP. SHALL BE PROPERLY
SPECIFIED. TEMP. RISE ABOVE DESIGN AMBIENT TO BE
AS PER PERMISSIBLE FINAL TEMP. OF THE SPECIFIED
CLASS OF INSULATION
MOTORS

MOTORS
 STARTING TORQUE SHOULD BE ADEQUATE EVEN
WITH 85% OF NOMINAL VOLTAGE FOR LT MOTORS
AND 80% FOR HT MOTORS.
 FOR NORMAL APPLICATIONS, THE STARTING TORQUE
SHALL BE MINIMUM TWICE THE FULL LOAD TORQUE.
 NORMALLY THE SELECTION OF ONE FRAME SIZE
HIGHER MOTOR THAN THAT RECOMMENDED BY THE
MOTOR SUPPLIER FOR GIVEN DRIVE DUTY WILL TAKE
CARE OF THE ABOVE REQUIREMENTS

ENCLOSURE:
THIS PLAYS AN IMPORTANT ROLE IN DECIDING THE
LIFE OF THE MOTOR. A WRONG ENCLOSURE LEADS TO
PRE-MATURE FAILURE OF INSULATION OR INCREASED
MAINTENANCE. THE FOLLOWING POINTS ARE TO BE
CONSIDERED:
• IP 54 FOR INDOOR AND IP 55 FOR OUTDOOR
APPLICATIONS (HOWEVER, FOR INDUSTRIES SUCH
AS PAPER, WHERE THE USAGE OF WATER IS VERY
HIGH, IP-55 MAY BE CONSIDERED EVEN FOR
INDOOR APPLICATION.
• FLAMEPROOF FOR HAZARDOUS AREA
MOTORS

MOTORS
ANY OTHER ENCLOSURE SHALL BE SELECTED WITH
CARE WITH FULL KNOWLEDGE OF SITE CONDITIONS.
SOME OF THEM ARE LISTED BELOW:
• DRIP-PROOF GUARDED FORCE VENTILATED
• DRIP-PROOF GUARDED SEPARATELY VENTILATED
• TOTALLY ENCLOSED AIR OVER-BLOWER COOLED
• TOTALLY ENCLOSED NON VENTILATED
• TOTALLY ENCLOSED FAN COOLED

MOTORS
• DUST PROOF TACONITE FEATURES ( BEARINGS
PROVIDED WITH PROTECTION AGAINST ABRASIVE
DUST)
• XT FEATURES (PROVIDES PROTECTION AGAINST
CORROSIVE, MOIST AND DUST LADEN ATMOSPHERE
AS ENCOUNTERED IN PAPER, CHEMICAL AND SIMILAR
INDUSTRIES)
• PAPER MILL DUTY FEATURES( FOR OPERATION OF
WET END OF PAPER MILLS)
• TOTALLY ENCLOSED PIPE VENTILATED ( COOLED BY
CUSTOMER SUPPLIED PIPED AIR)

MOTORS
TERMINATION ARRANGEMENT: GENERALLY IT IS
OBSERVED THAT DUE IMPORTANCE IS NOT GIVEN TO
TERMINATION ARRANGEMENT IN THE MOTORS. THIS
LEADS TO FAILURE OF MOTORS DUE TO INGRESS OF
MOISTURE, DUST, HEATING, RODENT ENTRY, etc. THE
FOLLOWING KEY POINTS SHALL BE TAKEN NOTE OF FOR
PROPER TERMINATION ARRANGEMENT IN A MOTOR:

• THE TERMINAL BOX SHALL WITHSTAND SPECIFIED
SHORT CIRCUIT CURRENT FOR 0.2 SEC.
• MINIMUM CLEARANCES FOR PHASE TO PHASE AND TO
EARTH BETWEEN CABLE LUGS AND BODY SHALL BE
MAINTAINED.
• FOR HV MOTORS PHASE SEGREGATION TO BE
CONSIDERED
• WHENEVER SEAL OFF BUSHINGS ARE USED, THEY
SHALL HAVE MINIMUM CREEPAGE DISTANCES AS PER
IS.
• TERMINALS HAVE TO BE MADE OF AT LEAST EPOXY
INSULATED, AND FOR HIGH VOLTAGES PORCELAIN
SHALL BE USED. PHENOLIC RESIN AND BAKELITE
SHALL NOT BE USED.
MOTORS

SIZE OF TERMINAL BLOCK SHALL BE LARGE ENOUGH TO
ACCOMMODATE ALUMINIUM CABLES PROPERLY
DEGREE OF PROTECTION OF TERMINAL BOX SHALL THE
SAME AS THAT OF THE MOTOR BODY.
SAFETY ACCESSORIES:
USE OF CERTAIN AVAILABLE ACCESSORIES ENHANCES
THE SAFETY AND RELIABILITY OF THE SYSTEM AND THE
EQUIPMENT. SOME OR ALL OF THE FOLLOWING
ACCESSORIES CAN BE CONSIDERED DEPENDING ON THE
TYPE OF THE MOTOR, INSTALLATION, etc.,
MOTORS

• SAFE LIFTING FACILITIES LIKE EYEBOLT, etc., FOR
MOTORS WEIGHING MORE THAN 25KGS.
• GREASING PLUG- RECOMMENDED FOR FRAME SIZE
200 AND ABOVE.
• EFFORTS SHALL BE MADE TO STANDARDISE THE
TYPE OF GREASE USED, PREFERABLY LITHIUM
BASED MP3. USE OF EXCESSIVE GREASE SHALL BE
AVOIDED
• BTD AND RTD FOR HV MOTORS.
MOTORS

MOTORS
• ANTI CONDENSATION HEATERS FOR MOTORS ABOVE
30KW. THESE SHALL BE INTERLOCKED WITH THE
MOTOR STARTER SUCH THAT THEY SHALL BE ON
ONLY WHEN THE MOTOR IS OFF
• SEPARATE EARTHING TERMINALS FOR BODY (MIN. 2
NOS.) AND EACH TERMINAL BOX.
• LOCAL BEARING TEMPERATURE INDICATORS FOR HV
MOTORS WITH ALARM AND TRIP CONTACTS

MOTORS
• HOW TO SELECT A MAKE OF MOTOR?
• WHAT ARE THE PARAMETERS WHICH NEED TO BE
LOOKED IN TO WHILE SELECTING A MAKE OF MOTOR:
WHILE SELECTING A PARTICULAR MAKE OF
EQUIPMENT, IT IS SUGGESTED THAT THE FOLLOWING
POINTS BE STUDIED BEFORE MAKING A FINAL
DECISION:
• EXISTING MAKES IN THE INSTALLATION

• PERFORMANCE OF THE EXISTING MAKES
• STANDARDISATION REQUIREMENTS FOR THE
INSTALLATION
• AVAILABILITY AND SERVICEABILITY AT THE PLACE OF
USAGE
• PREVIOUS EXPERIENCE WITH THE MAKE SELECTED
MOTORS

SOME OF REPUTED MOTOR MANUFACTURERS IN THE
COUNTRY AND THEIR RANGE OF MANUFACTURE:
MANUFACTURER LT AC HT AC DC
MOTOR MOTOR MOTOR
Crompton Greaves Yes No Yes
Kirloskar Electric co. ltd. Yes Yes Yes
Integrated Electric Co Ltd. No NO Yes
Siemens Yes No No
NGEF Yes Yes Yes
Bhel No Yes Yes
Bharath Bijlee Ltd. Yes No No
MOTORS

TYPE OF STARTING FOR MOTORS:
• FURTHER, TYPE OF STARTING FOR THE MOTORS HAS TO
BE DECIDED BASED ON THE ALLOWABLE VOLTAGE DIP ON
THE SYSTEM AND MAGNITUDE OF STARTING CURRENT.
• THE FOLLOWING POINTS NEED TO BE CONSIDERED WHILE
SELECTING TYPE OF STARTING/ MOTORS:
MOTORS ORDERED FOR DIRECT ON LINE (DOL) STARTING
ARE NOT SUITABLE FOR ASSISTED STARTING (LIKE STAR-
DELTA). HOWEVER MOTORS ORDERED FOR ASSISTED
START ARE SUITABLE FOR DOL. HENCE, THE TYPE OF
STARTING SHALL BE FIRMED UP BEFORE ORDERING.
MOTORS

• MOTORS SHALL BE CAPABLE OF STARTING AND
ACCELERATING THE LOAD EVEN AT 85% OF THE RATED
VOLTAGE WITHOUT EXCEEDING ACCEPTABLE WINDING
TEMPERATURE.
• THE STARTING CURRENT SHALL GENERALLY NOT
EXCEED 600% OF THE FULL LOAD CURRENT. HOWEVER
FOR LOW RATING MOTORS STARTING CURRENTS UPTO
800% CAN BE ACCEPTED SUBJECT TO STARTING
VOLTAGE DIPS BEING WITHIN LIMITS AS STATED
ABOVE, IF SUBSTANTIAL COST BENEFITS ARE
AVAILABLE.
• MOTORS SHALL BE DESIGNED TO WITHSTAND 120% OF
RATED SPEED FOR TWO MINUTES WITHOUT ANY
MECHANICAL DAMAGE, IN EITHER DIRECTION OF
ROTATION
MOTORS

• THE VOLTAGE DROP AT MOTOR TERMINALS DURING
STARTING SHALL NOT EXCEED 20% FOR HT MOTORS
AND 15% FOR LT MOTORS
• A STARTING VOLTAGE DROP CALCULATION SHALL BE
CARRIED OUT THE DECIDE THE TYPE OF STARTING. FOR
VERY LARGE MOTORS, SOFT STARTERS CAN BE
CONSIDERED.
• STAR DELTA STARTER UPTO 100 KW CAN BE WITHOUT
THE RESISTANCE TYPE. HOWEVER, MOTORS LARGER
THAN 100 KW SHALL BE PROVIDED WITH 4-
CONTRACTOR SCHEME WITH EXTERNAL RESISTOR AND
SHORTING CONTRACTOR TO AVOID BREAK IN THE
CURRENT DURING CHANGE FROM STAR TO DELTA.
MOTORS

• SELECTION OF SOFT STARTER DEPENDS ON THE
FOLLOWING-
• IF THE VOLTAGE DROP DURING STARTING IS HIGHER
THAN THAT DEFINED ABOVE WHILE STARTING ON IN-
HOUSE GENERATION LIKE DG SET OR TG SET
• IF THE NUMBER OF START-STOPS ARE MORE THAN 3
TIMES PER HOUR AS PER PROCESS REQUIREMENT
(HERE THE CONSTRAINT IS THE CIRCUIT BREAKER
WHOSE MECHANICAL LIFE IS ABOUT 5000 OPERATIONS;
THE COST OF SOFT STARTER HAS TO BE WEIGHED
AGAINST THE REPLACEMENT COST OF THE CIRCUIT
BREAKER OVER A FIXED LIFE TIME)
MOTORS

MOTORS
DC MOTORS:
• WHEN CONSTANT TORQUE AND SPEED CONTROL
APPLICATIONS ARE INVOLVED, DC MOTORS ARE
SELECTED. GENERAL GUIDELINES DETAILED FOR AC
MOTORS ARE ALSO APPLICABLE FOR DC MOTORS. IN
ADDITION TO THIS, THE FOLLOWING GUIDELINES ARE
ALSO APPLICABLE FOR THIS TYPE OF MOTORS:
• MOTORS SHALL BE CAPABLE OF GIVING RATED
OUTPUT WITHOUT REDUCTION IN THE EXPECTED LIFE
SPAN WHEN OPERATED CONTINUOUSLY AT A SUPPLY
VOLTAGE WITHIN 5% FROM THE RATED VALUE.

MOTORS
• CAPABLE OF STARTING AND ACCELERATING THE LOAD
WITH APPLICABLE METHODS OF STARTING, WITHOUT
EXCEEDING ACCEPTABLE WINDING TEMPERATURE,
WHEN THE SUPPLY VOLTAGE IS 85% OF THE RATED
VALUE.
• MOTORS SHALL BE DESIGNED TO WITH STAND 120%
OF RATED SPEED FOR TWO MINUTES WITHOUT ANY
MECHANICAL DAMAGE IN EITHER DIRECTION OF
ROTATION.
• PROPER DUTY CYCLE SELECTION HAS TO BE DONE.
• THE FIELD WINDINGS FOR THE MOTORS SHALL BE
CONTINUOUSLY RATED WITHOUT FORCED
VENTILATION

• LARGE SIZE MOTORS SHALL BE OF HORIZONTALLY
SPLIT CONSTRUCTION FOR EASY MAINTENANCE.
• THE FIELD WINDING SHALL NOT BE POWERED
WITHOUT FORCED VENTILATION, UNLESS IT IS A
SPECIAL APPLICATION.
• THE DUTY CLASS AS PER IEC STANDARD SHALL BE
FOLLOWED.
DC MOTOR SELECTION:
• GENERALLY, TYPES OF DRIVES ARE SELECTED BASED
ON THE SPEED TORQUE CHARACTERISTIC OF THE
LOAD, WHICH CAN BE CATEGORIZED AS FOLLOWS:
MOTORS

MOTORS
• CONSTANT TORQUE APPLICATION – eg. CONVEYOR,
MIXERS, EXTRUDERS, PELLATISERS, FEED MOTORS,
PROCESS-LINE SECTIONS, etc.,
• CONSTANT HORSE-POWER APPLICATION – eg., MACHINE
TOOL SPINDLES, PROCESS LINE CONVEYORS, etc.,
• VARIABLE TORQUE APPLICATION – eg., CENTRIFUGAL
FANS AND PUMPS, COMPRESSORS, etc.,
• RANDOM VARIATION OF TORQUE – eg., CRUSHERS,
GRINDING MILLS, etc.,
• DC MOTORS ARE WELL SUITED FOR THE FIRST TWO
APPLICATIONS CONSIDERING THE SIMPLICITY OF
CONTROLS. THIS IS IN CONTRAST TO AC MOTORS WHERE
THE SAME CAN BE ACHIEVED THROUGH EXPENSIVE
CONTROLS.

MOTORS
IN ADDITION TO THIS, SPEED CONTROL ALSO PLAYS AN
IMPORTANT ROLE IN THE SELECTION OF DC MOTOR FOR
A GIVEN APPLICATION. THERE ARE BASICALLY THREE
IMPORTANT SELECTION CRITERION, WHICH ARE
DETAILED AS BELOW:
• PERFORMANCE – WHILE SELECTING DC MOTORS
PERFORMANCE PARAMETERS ARE TO CONSIDERED:
• EFFICIENCY
• REDUCED SPEED OPERATION
• SPACE EFFICIENCY,

MOTORS
• CONSTANT HP
• SPEED RANGE,
• REGENERATION,
• DYNAMIC BRAKING.
• DC MOTOR SCORES OVER AC MOTORS IN MOST OF THE
ABOVE POINTS. IN ADDITION TO THIS THE FIRST COST
ALSO IS LOW WITH THESE FEATURES IN COMPARISON
WITH AC MOTORS.

MOTORS
LIMITATIONS
DUE TO NON-SINUSOIDAL SOURCE OF POWER SUPPLY,
SMOOTHENING OF RIPPLE REQUIRED FOR DC MOTORS.
WHEN SPEED VARIATION IS WIDE, DC MOTORS HAVE TO
BE COMPENSATED FOR ADVERSE COMMUTATION
CONDITIONS. PROLONGED OPERATION AT LOW SPEEDS
CALLS FOR FORCED COOLING, WHICH NEED TO BE
CONSIDERED FOR LOW SPEED APPLICATIONS,
PREFERABLY WITH AN EXTERNALLY POWERED
COOLING FAN MOTOR.

MOTORS
• HOWEVER, THE SELECTION OF TYPE OF DRIVE
REQUIRES A DETAILED APPLICATION STUDY
INCLUDING TECHNO-ECONOMIC FEASIBILITY.
• SOME TYPICAL APPLICATIONS OF DC MOTORS ARE
PROCESS INDUSTRIES:
• PAPER
• TEXTILES

MOTORS
Motor Speed 1500 RPM Efficiency η % Power Factor
Cos
DC Motors 1 to 10KW 70 to 84
11 to 100KW 84 to 92
101 to 1000KW 92 to 95 -
AC Slip Ring
Motors 11 to 100KW 0.79 to 0.87
101 to 500KW 93 to 95 0.87 to 0.91
AC Squirrel Cage
Motor < 1KW 53 to 74 0.67 to 0.78
1 to 11KW 74 to 88 0.81 to 0.85
12 to 132KW 88 to 95 0.86 to 0.88
133 to 400KW 95 to 97 0.88 to 0.89

MOTORS
CRITERION OF SELECTING THE TERMINAL
VOLTAGE FOR MOTORS:
FOR SQUIRREL CAGE INDUCTION MOTORS:
• MOTORS UP TO 175KW ARE RECOMMENDED TO BE
RATED AT 415 VOLTS.
• MOTORS RATED 175KW AND ABOVE ARE
RECOMMENDED TO BE RATED AT 3.3 KV OR 6.6 KV OR
11 KV DEPENDING ON THE OVERALL COST
ECONOMICS CONSIDERING TRANSFORMER COST, HT
SWITCHGEAR COST, CABLE COST AND MOTOR COST.

MOTORS
• WHEN THE POWER REQUIREMENTS FOR THE DRIVEN
EQUIPMENT ARE LARGE eg. > 400KW. NOTE: FOR
RATINGS IN THE RANGE OF 175 TO 400 KW COST
ECONOMICS NEEDS TO BE DONE CONSIDERING HV
AND MV MOTORS, WITH ASSISTED OR SOFT STARTERS
FOR MV.
• THE VOLTAGE DIP DUE TO STARTING TO BE LIMITED
TO SAFE LIMITS (SAY WITH IN 15%).

MOTORS
SALIENT FEATURES OF HV MOTORS:
• EMBEDDED TEMPERATURE DETECTORS – MINIMUM OF
SIX NUMBERS OF RESISTANCE TYPE TEMPERATURE
DETECTORS FOR THE STATOR WINDING AT LOCATIONS
WHERE HIGHEST TEMPERATURES MAY BE EXPECTED.
• BEARING THERMOMETERS – DIAL TYPE THERMOMETERS
HAVING TWO SEPARATE NO CONTACT, SHALL BE
PROVIDED FOR EACH BEARING.
• SPACE HEATERS – TO PREVENT MOISTURE
CONDENSATION ON THE INSULATION DURING SHUT
DOWN PERIODS, 240V, 50HZ OPERATED SPACE HEATERS
OF ADEQUATE CAPACITY TO KEEP THE INTERNAL
TEMPERATURE OF THE MOTOR ABOVE DUE POINT.

MOTORS
• DRAIN PLUGS – DRAIN PLUGS SHALL BE PROVIDED TO
DRAIN WATER RESULTING FROM CONDENSATION OR
OTHER CAUSES FROM ALL POCKETS IN THE MOTOR
CASING.
• FLOW SWITCHES – IN CASE OF CACW MOTORS, FLOW
SWITCHES TO BE PROVIDED FOR MONITORING COOLING
WATER FLOW.
• TERMINAL BOX – SEPARATE TERMINAL BOXES SHALL BE
PROVIDED FOR STATOR LEADS, SPACE HEATERS,
TEMPERATURE DETECTORS. METAL BARRIERS WITHIN
THE TERMINAL BOXES SHALL SEGREGATE HV PHASE
TERMINALS.
• THE INSULATION CLASS OF HV MOTORS SHALL BE
CLASS F LIMITED TO CLASS B TEMPERATURE RISE
LIMITS

MOTORS
PROTECTION REQUIREMENTS FOR MOTORS:
WHILE DECIDING ON THE TYPE OF PROTECTIONS FOR A
TYPICAL MOTOR APPLICATION THE FOLLOWING POINTS
CAN BE CONSIDERED AS GUIDELINES:
• DECIDE ON THE TYPE OF STARTING METHOD AND
CONTROL SCHEME FOR THE MOTOR BASED ON THE
APPLICATION.
• IF THE CONTROL GEAR IS REMOTELY LOCATED, ON LOAD
ISOLATOR AND OR LOCAL STOP PUSH BUTTON
STATIONS NEAR THE MOTOR TO BE CONSIDERED AS PER
IE RULES.
• IF THE MOTOR SERVICE IS ESSENTIAL, THEN, SELF-
STARTING FEATURE IS TO BE CONSIDERED FOR THE
CONTROL CIRCUIT.

MOTORS
• PROPER ANNUNCIATION/ ALARM SCHEMES SHALL BE
CONSIDERED FOR FAULT TRIPS, ABNORMALITIES, etc.,
WITH INDICATIONS AT BOTH LOCAL AND REMOTE ENDS
AS REQUIRED .
• BASIC METERING LIKE AMMETER MAY BE CONSIDERED.
• SPACE HEATERS FOR KEEPING THE WINDINGS WARM TO
AVOID CONDENSATION MAY BE CONSIDERED FOR
MOTORS RATED> 30KW.
• BASIC PROTECTIONS TO BE PROVIDED FOR MOTORS
SHALL INCLUDE SHORT CIRCUIT AND THERMAL
OVERLOAD PROTECTION.
• FOR MOTORS RATED > 100KW, LOCKED ROTOR
PROTECTION SHALL BE PROVIDED.
• SUFFICIENT NUMBER OF AUX. POTENTIAL FREE
CONTACTS TO BE CONSIDERED FOR INTERLOCKING
PURPOSES.

MOTORS
IN CASE OF HV MOTORS THE FOLLOWING POINTS NEED TO
BE CONSIDERED WHILE DESIGNING THE PROTECTIONS:
• AMMETER SHALL BE PROVIDED.
• SUFFICIENT NUMBER OF AUX. POTENTIAL FREE
CONTACTS TO BE CONSIDERED FOR INTERLOCKING
PURPOSES.
• SHORT CIRCUIT PROTECTION BY INSTANTANEOUS
OVERCURRENT RELAYS IN ALL THREE PHASES.
• OVERLOAD PROTECTION BY THERMAL OVERLOAD
PROTECTION RELAYS ON TWO PHASES. THE OVERLOAD
RELAY SETTING SHALL BE BASED ON THE HOT AND
COLD I2T CHARACTERISTICS OF THE MOTOR.
• LOCKED ROTOR PROTECTION BY TWO OVERCURRENT
INSTANTANEOUS RELAYS (IN R & B PHASES) AND ONE
COMMON TIMER.

MOTORS
• CENTRIFUGAL TYPE SPEED SWITCH OR OTHER
APPROVED TYPE OF SPEED SENSOR WITH AN
ADDITIONAL TIMER MAY BE USED FOR LOCKED
ROTOR PROTECTION WHERE THE STARTING TIME AT
LOWEST PERMISSIBLE VOLTAGE IS GREATER THAN
THE LOCKED ROTOR WITHSTAND TIME AT HIGHEST
PERMISSIBLE VOLTAGE (110%).
• FOR MOTORS > 1000KW RATING DIFFERENTIAL
PROTECTION BY A HIGH-SPEED TRIPLE POLE RELAY,
WHEN A MOTOR IS STAR WOUND.
• EARTH FAULT PROTECTION BY SINGLE POLE
CURRENT RELAY WHERE THE SYSTEM IS SOLIDLY OR
LOW RESISTANCE GROUNDED.

MOTORS
• EARTH FAULT PROTECTION BY A SENSITIVE EARTH
FAULT RELAY CONNECTED TO CORE BALANCE CT,
WHERE THE SYSTEM IS GROUNDED THROUGH A HIGH
RESISTANCE.
• UNDER VOLTAGE PROTECTION FOR PROLONGED UNDER
VOLTAGE (LESS THAN 80%) BY TWO NUMBERS BUS
UNDER VOLTAGE RELAYS AND A COMMON TIMER
• OVERLOAD ALARM BY A SINGLE POLE DEFINITE TIME
OVER CURRENT RELAY IN THE Y PHASE.
• COMPOSITE MOTOR PROTECTION RELAY SCHEME CAN
ALSO BE ADOPTED IF IT FULFILS ALL THE ABOVE
PROTECTION REQUIREMENTS
• TEMPERATURE MONITORING – RTD DEVICES IN THE
STATOR WINDINGS TO DETECT THE HOT SPOTS,
SHOULD BE CONNECTED TO TEMPERATURE INDICATOR
WITH ALARM CONTACTS.

MOTORS
• BEARING TEMP. MONITORING – THE INDICATORS
PROVIDED ON THE BEARINGS SHALL HAVE CONTACT
FOR ALARM PURPOSE.
• FOR CACW MOTORS THE FOLLOWING ADDITIONAL
PROTECTIONS SHALL BE CONSIDERED –
• MOTOR CLOSING CIRCUIT SHALL HAVE
PERMISSIVE INTERLOCK FOR NORMAL WATER
FLOW
• LOW WATER FLOW SHALL GIVE AN ALARM AND
AFTER A TIME DELAY SHALL TRIP THE MOTOR.
• AIR TEMPERATURE INDICATORS, WHEREVER
PROVIDED, SHALL BE CONNECTED FOR ALARM.

MOTORS
• LUBE OIL PRESSURE MONITOR TO BE CONSIDERED
WHERE FORCED OIL LUBRICATION IS PROVIDED.
MOTOR CLOSING CIRCUIT SHALL HAVE INTERLOCK
FOR NORMAL LUBE OIL PRESSURE.
• FACILITY OF AUTOMATICALLY SWITCHING ON THE
SPACE HEATER WHEN THE MOTOR IS STOPPED TO
PREVENT THE INGRESS OF MOISTURE.
• LOCKABLE TYPE STOP PUSH BUTTONS TO BE
PROVIDED NEAR THE MOTOR WHICH SHALL BE
INCLUDED IN THE CLOSING CIRCUIT.
TESTING OF MOTORS:
• TESTING IS DIVIDED IN TO ROUTINE AND TYPE TEST.

MOTORS
ROUTINE TESTS:
• MEASUREMENT OF WINDING RESISTANCE
• MEASUREMENT OF NO LOAD LOSS AND CURRENT
• REDUCED VOLTAGE RUNNING UP IN EITHER
DIRECTION OF ROTATION
• LOCKED ROTOR TEST FOR SQUIRREL CAGE
INDUCTION MOTOR
• OPEN CIRCUIT VOLTAGE MEASUREMENT FOR WOUND
ROTOR MOTORS
• INSULATION MEASUREMENT OF WINDINGS
• HIGH VOLTAGE TEST
• IR MEASUREMENT OF SPACE HEATERS, RTD, BTD
• CONTINUITY OF SPACE HEATERS, RTDS, BTDS

MOTORS
THE FOLLOWING ARE CLASSIFIED AS TYPE TESTS:
• LOAD TEST
• VARIABLE VOLTAGE TEST OR CALIBRATED MACHINE
TEST FOR SEPARATION OF LOSSES.
• TEMPERATURE RISE TEST
• MOMENTARY OVER LOAD TEST
SPECIAL TESTS:
• VIBRATION MEASUREMENT TEST
• DISSIPATION FACTOR
• POLARISATION INDEX
• CAPACITANCE AND LOSS ANGLE MEASUREMENT

MOTORS
MAINTENANCE OF MOTORS:
PHYSICAL CHECKS NEED TO BE DONE FOR-
• TIGHTNESS OF FOUNDATION/ FIXING BOLTS
• FREE ROTATION OF THE ROTOR IN DE-COUPLED
CONDITION
• SHAFT ALIGNMENT WITH THAT OF THE DRIVEN UNIT.
• ELECTRICAL PARAMETERS TO BE CONSIDERED ARE-
• THE TWO DISTINCT EARTH CONNECTING LEADS FROM
THE BODY OF THE MOTOR TO EARTH MAT ARE IN
GOOD CONDITION.
• CHECK THE IR VALUE OF STATOR WINDING WRIT
EARTH USING 1KV MEGGER (INDIVIDUAL PHASES
ALSO IF AVAILABLE). ALSO CHECK FOR THE
CONTINUITY OF THE WINDINGS.

MOTORS
• CHECK THE IR VALUE OF ROTOR WINDING WITH
BRUSHES LIFTED USING 500V MEGGER (FOR SLIPRING
MOTOR)
• CHECK THE SEC. CIRCUIT EXTERNAL TO ROTOR
WINDING FOR SLIPRING MOTOR.
• CHECK IR VALUE OF SPACE HEATER WITH RESPECT TO
STATOR WINDING AND EARTH USING A 500V MEGGER.
• CHECK FOR THE SEATING OF BRUSHES IN THE
SLIPRINGS.

MOTORS
• CHECK FOR THE SEATING OF BRUSHES IN THE
SLIPRINGS.
• CHECK IR VALUES OF CABLE CORES WITH RESPECT
TO EARTH/ ARMOUR/ CORE USING A 1KV MEGGER
AFTER DISCONNECTING THE TERMINATION AT BOTH
THE ENDS. ALSO CHECK FOR THE CONTINUITY OF
THE CABLES.
• CHECK FOR OVERLOAD RELAY SETTINGS (SET AT 90%
OF NAMEPLATE RATING).

MOTORS
TOTALLY ENCLOSED FAN COOLED
INDUCTION MOTOR

MOTORS
LARGE INDUCTION MOTOR

MOTORS
CLOSED AIR CIRCUIT AIR COOLED
INDUCTION MOTOR

MOTORS
HORIZANTAL FAN MOTOR
WITH TOP CABLE BOX

MOTORS
TOTALLY ENCLOSED FAN
COOLED MOTOR

MOTORS
SCREEN PROTECTED
SQUIRREL CAGE MOTOR

MOTORS
FLAMEPROOF SQUIRREL CAGE
MOTOR

MOTORS
VERTICALLY MOUNTED MOTORS

TRAINING AND BASICS ON MOTORS FOR BEGINNERS

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