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In a capacitor, split single-phase induction motor · The phase displacement between the running and starting windings current is __________.
20°-30°
30°-40°
50°-70°
60°-80°
60°-80°
In a capacitor-start single-phase induction motor, the phase displacement between the starting winding current (Is) and the running winding current (Im) is typically between 60° and 80°. This displacement is necessary to create a rotating magnetic field, which provides the starting torque required for the motor.
In a capacitor-start single-phase induction motor, the phase displacement between the starting winding current (Is) and the running winding current (Im) is typically between 60° and 80°. This displacement is necessary to create a rotating magnetic field, which provides the starting torque required for the motor.
θ=ϕm−ϕs — where θ is the phase displacement angle between main and auxiliary currents
The running winding is highly inductive, causing its current to lag the supply voltage significantly · By connecting a capacitor in series with the starting winding, the current in the starting branch is made more leading or less lagging, resulting in a large phase difference between the two currents · This phase difference produces the elliptically rotating magnetic field that exerts torque on the rotor.
Single-phase motors are not self-starting due to the pulsating nature of the magnetic field.
A phase-splitting device like a capacitor is required to achieve a phase difference.
The torque developed is proportional to sin(θ), where θ is the angle between winding currents.
Provides high starting torque
Improved power factor during starting
Capacitors are bulky and expensive
Requires centrifugal switch for disconnection in capacitor-start types
Compressors and Refrigerators
Pumps and industrial fans
Resistive phase-splitting (split-phase motor) provides much lower displacement, usually 20°-30°.
Higher displacement angles closer to 90° provide maximum torque, which is why capacitor-start motors are preferred for high-load applications.
D is correct — The capacitor forces a large phase angle (60°-80°) between winding currents, which is essential for producing the starting torque.
Always remember that in AC machines, torque production is maximized when the phase angle between the two magnetic flux components is exactly 90°.