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What happens if the capacitor of a single-phase induction motor gets short-circuited / Open-circuited?
The motor will run in a reverse direction
The motor will run in the same direction at reduced speed
The motor will not start
None of these
The motor will not start
Quick Trick: A single-phase induction motor has no starting torque on its own. The capacitor creates the required 90-degree phase shift for the starting winding; without it (open or shorted), no rotating magnetic field is created, so the motor can...
A single-phase induction motor has no starting torque on its own. The capacitor creates the required 90-degree phase shift for the starting winding; without it (open or shorted), no rotating magnetic field is created, so the motor cannot start.
Understand the Role of the Capacitor
Single-phase supply produces a pulsating magnetic field rather than a rotating one. To produce a rotating magnetic field and starting torque, an auxiliary winding with a capacitor is used to split the single phase into two out-of-phase currents.
Analyze Open-Circuit Condition
If the capacitor opens, current through the auxiliary starting winding becomes zero. The motor receives power only from the main winding, yielding zero starting torque.
Analyze Short-Circuit Condition
If the capacitor shorts, the phase angle difference between the main and auxiliary windings drops to nearly zero. Without the necessary phase displacement, a rotating magnetic field cannot be established, resulting in zero starting torque.
A: The direction depends on which winding is reversed, not on a faulty capacitor. B: The motor cannot produce starting torque to begin running at all, so running at reduced speed is incorrect. D: Option C accurately describes the failure to start.
C is correct because a shorted or open capacitor fails to create the phase shift required for starting torque, preventing the motor from starting.
Questions on single-phase motors frequently test starting mechanisms; remember that auxiliary windings split phase for torque, and if phase difference becomes 0 degrees, starting torque drops to zero.