Abnormal Operating Condition and Causes of Induction Motors

• Blockage in Pump/Gear Systems: Obstruction in mechanical systems (e.g., pumps or gears) connected to the motor.
• Damaged Bearings or Lack of Lubrication: Worn-out bearings or insufficient lubrication leading to increased friction.
• Locked Rotor or Prolonged Starting Time: A rotor that fails to rotate (locked rotor) or extended starting duration due to mechanical resistance.
• Motor Stalling: Inability to start due to excessive load, requiring the motor to be disconnected from both the power supply and mechanical load before restarting to resolve the overload.

Abnormal Supply Conditions

• Low Supply Voltage: Reduced voltage below the rated value.
• Unbalanced Supply Voltage: Uneven voltage distribution across the three phases.
• High Supply Voltage: Excess voltage exceeding the rated value.
• Low Frequency: Operating frequency lower than the motor’s rated frequency.
• Supply Circuit Faults:
  • Loss of one or more phases (single-phasing).
  • Short circuits in supply cables.
  • Damaged contactor terminals or links.
  • Blown fuses.

Internal Motor Faults

• Phase-to-Phase Faults: Short circuits occurring between stator windings of different phases.
• Phase-to-Earth Faults: Insulation failure leading to a short circuit between a phase winding and the motor’s grounded frame.
• Open Circuit: Breaks in windings or electrical connections, interrupting current flow.
• Insulation Degradation: Deterioration of winding insulation (typically tested with a megger to check continuity and resistance).