Different Faults in Three Phase Induction Motor & their Remedies

In this post, we shall discuss different types of fault in three-phase induction motor & their remedies. The induction motor is a very robust, reliable, and maintenance-free motor. We can enhance the life span of the motor by doing-periodic maintenance.

Though a three-phase induction motor is most reliable if we operate the motor within its operating criteria. The motor is most vulnerable if we operate the motor under overload conditions.

The overloading causes the motor to take more current. The motor drawing current more than its rated current cause winding heat up and eventually insulation failure. The intermittent overloading makes the insulation deteriorate over a period of time. Increased atmospheric temperature also hinders the proper cooling of the motor & it eventually reduces the life of the insulation.

In a nutshell, whatever factors increase the temperature rise and reduce the cooling of motor is vulnerable for motor operation.

Induction Motors – Possible faults and Remedies

There are the following different faults in the three-phase induction motor & their remedies

Motor fails to start

Supply may be cut-offCheck the supply with a multimeter or test lamp
SFU may be in the off conditionCheck the SFU, and made it on.
Overload relay may be in the trip conditionReset the overload relay
Loose connections at the feeder endTight all the connections in the feeder
The phase sequence is wrongIf you are using electronic protection relay, the motor may fail to start if the phase sequence is not correct. Correct the phase sequence.
Control circuitcheck the control circuit and find the cause of the non-operation of the main contactor.
Stator or Rotor winding openCheck the stator winding with help of a 4 & 1/2 digit multimeter. If winding resistance is infinite, replace the motor with a new one.
Stator Earthcheck the stator winding with an insulation tester(Megger)
BearingsGrease the bearing
OverloadingReduce the load on the motor

Motor Noisy operation after start

Single phasingThe single phasing may occur because of (1) one of the three fuses blown(2)contactor pole open(3) motor winding open. Under single phasing, the motor draws more current and produces noise.
Rubbing of the rotor with statorThe stator and rotor have physical separation and the gap between the stator & rotor is called the air gap. The rubbing may cause due to unbalanced magnetic pull(UMP) or due to other mechanical reasons.
Rotor unbalanceRotor unbalances cause noisy operation. The rotor should be balanced.
Loose couplingFix the coupling properly
Dry bearingsRe-grease the bearings
MisalignmentMisalignment causes noisy operations. Check horizontal, vertical, and axial vibration & correct it.
The belt may be too tightIn the case of belt drive, ensure proper tightening of the belt.

Bearing overheated

Dry running of the bearingRe-grease bearing & ensure periodic re-greasing
Belt too tightThe belt coupled to the motor pulley is too tight. Adjust the tension of the belt.
Rotor shaft bentstraight the rotor shaft
Lubrication qualityThe poor quality of lubrication cause overheating of the bearing. Use recommended lubrication.
Foreign material in lubricationReplace the old lubricant with a new one.

Types of Fault in Induction MotorMotor overheated

Motor overloadingOverloading causes an increase in current & it causes motor heating. Finally, it affects the life of insulation.
Reduce the load.
Poor ventilationThe improper ventilation increases the winding temperature that causes more heating in the winding. Therefore, maintain the proper ventilation.
Supply voltage too high or lowIn this condition, the motor draws more current than its rated current. It causes overheating of the core and winding of the motor. Therefore, Ensure supply voltage within the rated supply voltage of the motor.
Loose connectionsLoose connections
Stator winding earthCheck stator with Megger

Motor Starts & Stops

Switchgear may be defectiveCheck switch-gears
Loose connectionsTight all the connections
Timer defectiveCheck the control circuit timer.
Motor interlocking devices faultyCheck Speed monitor, tachometer, etc.

Types of Fault in Induction MotorMotor runs below its rated speed

OverloadingThe overloading causes motor speed reduction. Reduce the load on the motor to increase the speed.
Low supply voltageThe torque of the motor depends on the voltage. The torque reduces with a decrease in the supply voltage. In this condition, the motor may not be in a position to cater to the load torque & the speed of the motor decrease.
Ensure supply voltage should be within motor operating voltage range.

Motor Runs at Slow Speed when External Resistance Cutoff in case of Slip-Ring Induction Motor

Rotor open circuitCheck the Rotor winding of the slip ring induction motor
Open BrushesCheck the brushes for their proper contact with the slip-ring.
The rough Slip ring surfaceCheck slip-ring for any surface roughness
Eccentric Slip-ringCheck slip-ring for its eccentricity.