Question

When pull-out torque occurs in a synchronous motor, the poles of the rotor are _______.

• A. mid-way between N and S poles of stator
• B. coincident with stator pole
• C. $45^\circ$ (electrical) behind stator poles
• D. $45^\circ$ (electrical) ahead stator poles

Hint:

At pull-out, torque angle $\delta = 90^\circ$ → rotor is at maximum deviation from stator field.

Answer 1

The Correct Option is A

Step 1: Pull-out torque defined.
Maximum torque a synchronous motor can deliver before losing synchronism.
Step 2: Torque angle concept.
Torque $\propto \sin(\delta)$
At $\delta = 90^\circ$, max torque occurs → rotor is misaligned midway between N and S poles.
Step 3: Beyond pull-out torque.
If load torque increases further, motor can't maintain synchronism → rotor slips out.
Conclusion: $\boxed{\text{Midway between N and S poles}}$