AC Induction Motor

AC Induction Motors

Repair & Services

Repair and Refurbishment of AC Induction Motors

  • Perform these tests on the stator windings and record the results:
    Insulation resistance (IR) and polarization index (PI)
    Winding resistances (terminal-to-terminal resistances)
  • Rotate the rotor manually, and check for any defects in the bearings and shaft.
  • Run the motor at no load. Measure and record the currents, vibration, bearing temper- atures, and temperature rises.
  • Measure and record the rotor end play (axial and radial movement of the rotor in the bearings).
  • Dismantle the motor and remove the rotor.
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    Stator Work
  • Clean the windings, using low-pressure steam, if they are contaminated with dust, oil, or grease.
  • Dry the stator in an oven at a temperature of 105°C (220°F) for a period of 6 h.
  • Take IR and PI tests. Note: Following steam cleaning and drying of the windings, the results of IR and PI tests should improve.
  • Inspect the motor cable insulation for cracks, overheating, and brittleness.
  • Inspect the stator insulation for cracks, brittleness, and puffiness.
  • Inspect the slot wedges and bracing system in the stator for looseness.
  • Inspect the laminations in the stator core for looseness, damage due to rotor rubbing, localized overheating, and blockage of the vent ducts.
  • If there are no defects in the core or windings of the stator, perform these tests on the stator windings and record the results:
    Insulation resistance and polarization index tests
    Terminal-to-terminal resistances (winding resistances)
    DC high-potential test
    Surge (impulse) test
    • Rotor Work
  • If there is a dust, grease, or oil contamination on the rotor, clean it with low-pressure steam.
  • Inspect the rotor laminations for looseness, cracks, and damage due to rubbing with the stator and localized overheating.
  • Inspect the rotor shaft fans of the motor for cracks. If there are signs of cracks, perform dye penetrant and ultraviolet light inspection.
  • Inspect the bars and end rings of the rotor for cracks, looseness, and localized over- heating. If there are signs of cracks, perform the manual rotation test as well as dye penetrant and ultraviolet light inspection.
  • Inspect the rotor shaft for cracks.
  • Mount the rotor on a lathe and measure the eccentricity of the shaft. The total indicated reading should be less than 0.0038 cm (0.0015 in).
  • Bearings Inspect the bearings for cracks, wear, etc.
  • Oil and Water Heat Exchangers If heat exchangers are used, perform the following steps:
  • Perform chemical cleaning of the heat exchanger, using a weak acid solution
  • Inspect the heat exchanger for erosion and corrosion.
  • Perform a hydrostatic pressure test to confirm the integrity of the heat exchanger. The pressure of the water during the test should be 1.5 times the design pressure of the heat exchanger.
  • If there is evidence of corrosion or erosion, perform an eddy current inspection on the tubes of the heat exchanger. All tubes that experienced a reduction of more than 50 per- cent in the wall thickness should be plugged. If more than 10 percent of the tubes have experienced a reduction in wall thickness of more than 50 percent, consideration should be given to replace the heat exchanger.
  • Temperature Detectors Perform a visual and a functional check for all resistance temperature detectors (RTDs) and thermocouples used in the winding or bearings of the motor.
  • Motor Repair All defective components should be repaired or replaced.
  • Motor Rewind If the windings of the motor have serious damage, the motor should be rewound.