Maintenance Procedure and Rewinding of Three-Phase Induction Motor

Maintenance Procedure and Rewinding of Three-Phase Induction Motor

Three-phase induction motors are widely used in industries, pumps, compressors, conveyors, and machine tools. Proper maintenance increases efficiency, reliability, and service life of the motor.

1. Maintenance Procedure of Three-Phase Induction Motor

Maintenance is generally divided into routine maintenance and preventive maintenance.

(A) Routine Maintenance

1. Cleaning

  • Remove dust, oil, and dirt from the motor body.

  • Clean cooling ducts and ventilation openings to avoid overheating.

2. Checking Electrical Connections

  • Tighten all terminal connections.

  • Loose connections may cause sparking and voltage drop.

3. Bearing Inspection

  • Check bearings for noise, vibration, or overheating.

  • Apply proper lubrication regularly.

4. Temperature Check

  • Ensure the motor operates within permissible temperature limits.

5. Insulation Check

  • Measure insulation resistance using megger.

  • Low insulation resistance indicates moisture or insulation damage.

(B) Preventive Maintenance

1. Rotor Inspection

  • Check rotor for damage or rubbing with stator.

  • Ensure proper air gap.

2. Shaft Alignment

  • Check alignment between motor and load.

  • Misalignment causes vibration and bearing wear.

3. Check Cooling System

  • Ensure cooling fan and air passages are clean.

4. Vibration Monitoring

  • Excessive vibration may indicate:

    • Bearing fault

    • Rotor imbalance

    • Loose mounting

2. Rewinding of Three-Phase Induction Motor

Rewinding is required when stator winding burns due to overload, short circuit, or insulation failure.

Steps in Rewinding

1. Fault Identification

  • Check whether the winding is open circuit, short circuit, or burnt.

2. Removal of Old Winding

  • Remove burnt coils from stator slots.

  • Record winding details before removing.

3. Recording Winding Data

Important data to note:

  • Number of slots

  • Number of poles

  • Coil pitch

  • Number of turns per coil

  • Wire gauge

  • Winding connection (Star/Delta)

4. Cleaning of Slots

  • Clean stator slots properly.

  • Insert new slot insulation paper.

5. Preparation of New Coils

  • Wind coils using correct copper wire size.

  • Maintain required number of turns.

6. Inserting Coils

  • Insert new coils carefully into stator slots.

  • Arrange according to winding diagram.

7. Insulation and Binding

  • Apply slot wedges and insulation varnish.

  • Bind coils properly.

8. Impregnation and Drying

  • Apply insulating varnish to the winding.

  • Dry the stator in oven or heating chamber.

9. Testing

After rewinding, perform tests:

  • Insulation resistance test

  • Continuity test

  • No-load test

  • Trial run

3. Advantages of Proper Maintenance

  • Increases motor life

  • Reduces breakdowns

  • Improves efficiency

  • Ensures safe operation

  • Reduces repair cost

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