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Single phase induction motor can be started by
Resistance start
Induction start
Capacitor start
All of above
All of above
A single-phase induction motor is naturally not self-starting because a single-phase AC winding produces a pulsating magnetic field rather than a rotating magnetic field. To make it self-starting, an auxiliary (starting) winding is used alongside the main winding to create a two-phase supply from a single-phase source, producing a revolving magnetic field. Common starting methods include resistance split-phase, capacitor-start, and induction/shaded-pole starting mechanisms.
A single-phase induction motor is naturally not self-starting because a single-phase AC winding produces a pulsating magnetic field rather than a rotating magnetic field. To make it self-starting, an auxiliary (starting) winding is used alongside the main winding to create a two-phase supply from a single-phase source, producing a revolving magnetic field. Common starting methods include resistance split-phase, capacitor-start, and induction/shaded-pole starting mechanisms.
TsтАЛтИЭImтАЛIaтАЛsin╬▒ тАФ Starting torque equation where ImтАЛ is main winding current, IaтАЛ is auxiliary winding current, and ╬▒ is phase angle between them.
TeтАЛ=TfтАЛтИТTbтАЛ тАФ Net electromagnetic torque according to double revolving field theory.
According to Double Revolving Field Theory, a pulsating magnetic field can be resolved into two equal and oppositely rotating fields, resulting in zero net starting torque. By introducing an auxiliary winding spaced 90┬░ electrically from the main winding and creating a phase difference between their currents, a rotating magnetic field is produced to generate starting torque.
A single-phase induction motor has zero starting torque because of pulsating stator flux.
Phase splitting methods (Resistance, Capacitor, or Shading ring) create a pseudo-two-phase rotating magnetic field.
Capacitor-start motors provide the highest starting torque among single-phase induction motors because the phase angle ╬▒ approaches 90┬░.
Versatile starting methods allow tailing torque requirements to specific load applications.
Capacitor-start gives very high starting torque with low starting current.
Resistance-start motors are simple, robust, and cost-effective.
Requires a centrifugal switch to disconnect the auxiliary winding once the speed reaches ~75% of synchronous speed.
Single-phase motors have lower power factor and efficiency compared to three-phase induction motors.
Capacitor-start motors: Compressors, pumps, and conveyors.
Resistance-start (split-phase) motors: Fans, blowers, and centrifugal pumps.
Shaded-pole / Induction-start motors: Small toys, hair dryers, and small desktop fans.
Option A (Resistance start) uses high resistance in the auxiliary winding to create a phase difference (~30┬░).
Option B (Induction/Shaded-pole start) uses inductive shading coils to delay flux in a portion of the pole pitch.
Option C (Capacitor start) uses a series capacitor to achieve nearly 90┬░ phase displacement.
Since all three methods are standard techniques to start single-phase induction motors, Option D is correct.
D is correct тАФ Resistance start, induction/shaded-pole start, and capacitor start are all valid and standard techniques used to make a single-phase induction motor self-starting.
In competitive exams, remember that Capacitor-Start gives the highest starting torque because sin╬▒тЙИ1 when ╬▒тЙИ90┬░.