Three-phase induction motors are widely used in industrial applications. Their abnormal operating conditions and causes can be summarized as follows:
Abnormal Operating Conditions and Causes of Induction Motors
The following are the abnormal operating conditions and causes of induction motors:
Mechanical Overload
- 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).
