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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Which of the abnormality possible in induction motor?
Single phasing
Short circuit
Stalling
All of above
All of above
Quick Summary: An induction motor is subject to several electrical and mechanical abnormalities that can lead to failure if not protected. These include single phasing (loss of one supply phase), short circuits (phase-to-phase or phase-to-ground faults), and stalling (mechanical locking of the rotor).
An induction motor is subject to several electrical and mechanical abnormalities that can lead to failure if not protected. These include single phasing (loss of one supply phase), short circuits (phase-to-phase or phase-to-ground faults), and stalling (mechanical locking of the rotor).
Ploss=3I2Rs — Stator copper loss leading to thermal damage during fault conditions
Tem∝R2°2+(sX2)2sE2°2R2 — Torque equation relevant to stalling (when s=1)
Single phasing causes a negative sequence torque that leads to motor overheating. A short circuit results in massive stator currents exceeding the thermal capacity of the insulation. Stalling causes the motor to draw the locked-rotor current (starting current) indefinitely, leading to rapid insulation failure due to excessive ohmic losses (I2R).
Single phasing is detected using negative sequence relays or under-current sensors.
Short circuit protection is primarily handled by HRC fuses or circuit breakers (instantaneous trip).
Stalling protection is provided by thermal overload relays with inverse time characteristics.
Induction motors are essentially constant-speed machines, and any mechanical load blocking causes immediate over-current.
Protective relays prevent permanent damage to the winding insulation.
Early detection of abnormalities reduces motor downtime.
Complex protection schemes increase the overall cost of the motor control system.
False tripping can lead to unnecessary production interruptions.
Industrial conveyor belts and pump systems
Centrifugal fans and compressor drives
During single phasing, the motor continues to run but with reduced capacity and high vibrations.
Stalling current is often 5 to 7 times the rated full-load current.
D is correct — All listed conditions represent critical electrical or mechanical abnormalities that require protective intervention in induction motor operation.
Always remember that in an induction motor, a stalled rotor condition is electromagnetically equivalent to a transformer with a short-circuited secondary, leading to massive primary current flow.