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Examoogle • User • info@examoogle.com • EE-2024-8821
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The angle between the main winding and auxiliary winding is around ____________ in Capacitor split-phase motor.
A) 10-20 degrees
B) 30-40 degrees
C) 70-90 degrees
D) 20 degrees
70-90 degrees
In a capacitor split-phase induction motor, the angle between the main winding current and auxiliary winding current is around 70 to 90 degrees. The addition of a series capacitor in the auxiliary winding creates a large phase displacement (approaching 90°) between the currents flowing in the two windings. This phase shift produces a rotating magnetic field, which develops the necessary starting torque.
In a capacitor split-phase induction motor, the angle between the main winding current and auxiliary winding current is around 70 to 90 degrees. The addition of a series capacitor in the auxiliary winding creates a large phase displacement (approaching 90°) between the currents flowing in the two windings. This phase shift produces a rotating magnetic field, which develops the necessary starting torque.
α=θa+θm≈90° — Phase angle difference between auxiliary (Ia) and main (Im) winding currents
Ts∝ImIasinα — Starting torque proportional to the sine of the phase angle α
A single-phase supply creates an alternating magnetic field that cannot produce a starting torque on its own. By connecting an auxiliary winding in series with a capacitor parallel to the main winding, the current in the auxiliary winding leads the supply voltage while the main winding current lags it. This results in two spatial and temporal phase-displaced currents (Im and Ia), creating a forward-rotating magnetic field according to double-revolving field theory.
The capacitor causes the auxiliary winding current Ia to lead the supply voltage V.
The main winding is highly inductive, causing its current Im to lag the supply voltage V.
Because sin90°=1, a phase difference near 90° maximizes the starting torque per unit current.
Higher starting torque compared to resistance split-phase motors
Higher power factor during starting phase
Lower starting current for the same developed torque
Higher initial cost due to the requirement of a capacitor
Requires a centrifugal switch to disconnect the auxiliary winding after reaching ~75% speed (in capacitor-start motors)
Compressors and Refrigerators
Pumps and Conveyors
Air conditioners and heavy-duty blowers
| Feature | Resistance Split-Phase | Capacitor Split-Phase |
|---|---|---|
Phase Shift Angle (α) | 30° to 40° | 70° to 90° |
Starting Torque | Moderate (1.5 to 2 times rated) | High (3 to 4.5 times rated) |
Auxiliary Circuit Component | High Resistance Winding | undefined |
Option A (10-20 degrees) is too low for effective starting torque in split-phase motors.
Option B (30-40 degrees) corresponds to a standard resistance split-phase induction motor.
Option D (20 degrees) is insufficient to create a near-circular rotating magnetic field.
C is correct — A capacitor-start/split-phase motor uses a capacitor in the auxiliary winding to create a phase displacement of nearly 90 degrees (typically 70-90 degrees) relative to the main winding current.
Remember: Ts∝sinα. Resistance split-phase gives α≈30°−40°, whereas capacitor split-phase increases α up to 90°, producing maximum starting torque.