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In Resistance split single-phase induction motor · The phase displacement between the running and starting windings current is __________.
20°-30°
30°-40°
50°-70°
60°-80°
30°-40°
In a resistance split-phase induction motor, the auxiliary (starting) winding is designed to have high resistance and low reactance, while the main (running) winding has low resistance and high reactance · This disparity in the R/X ratio causes a phase displacement between the currents Im and Is, typically ranging from 30° to 40°.
In a resistance split-phase induction motor, the auxiliary (starting) winding is designed to have high resistance and low reactance, while the main (running) winding has low resistance and high reactance · This disparity in the R/X ratio causes a phase displacement between the currents Im and Is, typically ranging from 30° to 40°.
Z=R+jXL — Impedance of the windings
ϕ=tan−1(RXL) — Phase angle of current relative to voltage
The stator windings are connected in parallel to the single-phase supply · Because the starting winding is made of thinner wire with fewer turns, its impedance is more resistive, while the running winding is more inductive · This phase shift creates a rotating magnetic field necessary for self-starting, governed by the current vectors Is and Im.
Starting winding is placed in parallel with the running winding.
The phase difference is insufficient for high starting torque, limiting usage to low-power applications.
A centrifugal switch is used to disconnect the starting winding once the motor reaches 75-80% of synchronous speed.
Simple and rugged construction
Low cost for fractional horsepower ratings
Low starting torque
High starting current
Not suitable for high inertia loads
Washing machines
Small fans and blowers
Centrifugal pumps
The phase angle is limited because the windings share the same magnetic circuit, preventing a full 90° shift without external capacitors.
Option A (20°-30°) is too low; Option C and D represent values closer to Capacitor Start motors (which achieve nearly 90°).
B is correct — The resistance split-phase motor achieves a modest phase displacement of 30°-40° between winding currents due to intentional differences in winding resistance and reactance.
Always remember that in electrical machines, the 'split' refers to phase-splitting; if the question asks for 90° shift, it refers to Capacitor-Start or Permanent Split Capacitor (PSC) motors, not Resistance-Split.