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The angle between the main winding and auxiliary winding is around ____________ in Resistance split-phase motor.
10тБ╗┬▓тБ░ degrees
30-40 degrees
70-90 degrees
90 degrees
30-40 degrees
In a resistance split-phase single-phase induction motor, the main winding and auxiliary (starting) winding are physically displaced by 90┬░ in space. However, due to the different resistance-to-reactance ratios (R/X) of the two windings, the temporal phase angle (time phase difference) between the auxiliary winding current (IaтАЛ) and main winding current (ImтАЛ) is around 30┬░ to 40┬░.
In a resistance split-phase single-phase induction motor, the main winding and auxiliary (starting) winding are physically displaced by 90┬░ in space. However, due to the different resistance-to-reactance ratios (R/X) of the two windings, the temporal phase angle (time phase difference) between the auxiliary winding current (IaтАЛ) and main winding current (ImтАЛ) is around 30┬░ to 40┬░.
TsтАЛтИЭImтАЛIaтАЛsin╬▒ тАФ Starting torque of a split-phase motor
╬▒=╧ХmтАЛтИТ╧ХaтАЛ тАФ Phase angle difference between main and auxiliary winding currents
tan╧ХmтАЛ=\frac{X_m}{R_m},tan╧ХaтАЛ=\frac{X_a}{R_a}$$ тАФ Phase shift of individual windings
A single-phase induction motor is not self-starting because a single-phase AC supply produces a pulsating magnetic field rather than a rotating one. To create a starting torque, the auxiliary winding is designed with high resistance and low inductive reactance (RaтАЛ>XaтАЛ), while the main winding has low resistance and high inductive reactance (XmтАЛ>RmтАЛ). This difference causes the current in the auxiliary winding to lead the main winding current, creating a time phase difference (╬▒тЙИ30┬░тИТ40┬░) that produces a revolving magnetic field at start.
Spatial angle between main and auxiliary winding is fixed at 90┬░ electrical.
Time phase angle difference (╬▒) between main winding current ImтАЛ and auxiliary winding current IaтАЛ is only around 30┬░ to 40┬░.
The auxiliary winding consists of fine wire (high resistance) and few turns (low reactance), whereas the main winding uses thick wire (low resistance) and more turns (high reactance).
A centrifugal switch disconnects the auxiliary winding when the motor reaches approximately 75% to 80% of synchronous speed.
Low initial cost and simple construction
No external capacitor required for operation
Low starting torque (around 1.5 to 2 times full-load torque)
High starting current and low power factor at start
Small fans and blowers
Washing machines
Centrifugal pumps
Small machine tools (grinders, drill presses)
Option A (10тБ╗┬▓тБ░ degrees) is too small to provide sufficient starting torque for practical split-phase operation.
Option C (70-90 degrees) is achieved in capacitor-start or capacitor-run single-phase induction motors, not in pure resistance split-phase motors.
Option D (90 degrees) represents the space phase displacement between windings, not the time phase angle between the winding currents.
B is correct тАФ In a resistance split-phase motor, the phase angle difference (time phase) between the main winding current and auxiliary winding current is limited to around 30 to 40 degrees due to practical resistance-to-reactance ratios.
For exam questions, carefully distinguish between 'Space angle' (which is always 90┬░ electrical between main and auxiliary windings) and 'Time phase angle' (which is 30┬░тИТ40┬░ for resistance split-phase and nearly 90┬░ for capacitor-start motors).