How to Trouble shoot 3 Phase Induction Motor

Three phase induction motors are one of the most popular electric motors commonly found in processing plants or any manufacturing concern. They are used in situations where large power is required. The squirrel cage brand is the most popular and they perform various tasks wherever they are applied.

Because of the critical roles these motors play in any plant, a failure of the motor, inability to start, noisy operation and sundry other problems need to be remedied as soon as possible to avoid costly production downtime. The table below gives the commonly encountered problems in 3 phase squirrel cage induction motors, cause of problems and what remedy to apply to bring the motor back to production. This troubleshooting guide can also be applied to other types of three phase induction motors:

Motor ProblemCauseRemedy
Motor fails to startBlown fusesReplace fuse with proper type and rating
Overload TripsCheck and reset overload in starter
Improper power supplyCheck to see that power supplied agrees with nameplate specifications  and load factor
Improper line connectionsCheck connections with wiring diagram supplied with motor
Open circuit in winding or control switchThis is normally indicated by a humming sound when switch is closed. Check for loose wiring connections. Confirm that all control contacts are closing.
Mechanical failureCheck to see that motor and drive turns freely. Check bearings and lubrication
Short circuited statorIndicated by blown fuses.  Motor must be rewound
Poor stator coil connectionsRemove end belts. Locate poor connections with test lamp.
Rotor defectiveCheck for broken bars or end rings
Motor may be overloadedReduce motor load
Motor stallsOne phase may be openCheck supply lines for open phase
Wrong applicationChange type or size. Consult motor manufacturer
OverloadReduce load
Low voltageCheck that nameplate voltage is maintained. Check connection.
Open circuitFuses blown. Check overload relay, stator and push buttons
Motor runs and then dies downPower failureCheck for loose connections to line, to fuses and to control
Motor does not come up to speedMotor is applied for the wrong applicationConsult manufacturer for right application of motor
Voltage too low at motor terminals because of line dropUse higher voltage on transformer terminals or reduce load. Check connections. Check conductors for proper size.
Starting load too highCheck load motor is supposed to carry at start.
Broken rotor bars or loose rotorLook for cracks near the rings. A new rotor may be required as repairs are usually temporary not permanent
Open primary circuitLocate fault with testing device and repair.
Motor takes too long to accelerate and/or draws high current (Amps)Excessive loadReduce load
Low voltage during start upCheck for high resistance. Adequate wire size.
Defective squirrel cage rotorReplace with new rotor
Applied voltage too lowImprove voltage at terminals of transformer by tap changing.
Wrong rotationWrong sequence of phasesReverse connections at motor or at switchboard.
Motor overheats while running under loadOverloadReduce load
Frame or bracket vents may be clogged with dirt and prevent proper ventilation of motor.Open vent holes and check for a continuous stream of air from the motor.
Motor may have one phase openCheck to make sure that all leads are well connected.
Grounded coilLocate and repair
Unbalanced terminal voltageCheck for faulty leads, connections and transformers.
Motor vibratesMotor  misalignedRealign
Weak supportStrengthen base
Coupling out of balanceBalance coupling
Driven equipment unbalancedRe-balance driven equipment
Defective bearingsReplace bearing
Bearings not in lineLine bearings up properly
Balancing weights shiftedRe-balance motor
Poly-phase motor running single phaseCheck for open circuit
Excessive end playAdjust bearing
Unbalanced line current on poly-phase motors during normal operationUnequal terminal voltsCheck leads and connections
Single phase operationCheck for open contacts
Unbalanced voltageCorrect unbalanced power supply
Noisy OperationAirgap not uniformCheck and correct bracket fits or bearing.
Rotor unbalanceRebalance
Hot bearings generalBent or sprung shaftStraighten or replace shaft
Excessive belt pullDecrease belt tension
Pulley too far awayMove pulley closer to motor bearing
Pulley diameter too smallUse larger pulleys
MisalignmentCorrect by realignment of drive
Hot bearings ballInsufficient greaseMaintain proper quantity of grease in bearing
Deterioration of grease or lubricant contaminatedRemove old grease, wash bearings thoroughly in kerosene and replace with new grease.
Excessive lubricantReduce quantity of grease, bearing should not be more than 1/2 filled
Overloaded bearingCheck alignment, side and end thrust.
Broken ball or rough racesReplace bearing, first clean housing thoroughly

This troubleshooting guide is by no means exhaustive but can provide guidance for the resolution of commonly encountered problems as far as poly-phase induction motors are concerned

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