Question

An induction motor will develop maximum torque when the phase difference between the stator flux and the rotor current is_______.

• A. $90^\circ$ Electrical
• B. $45^\circ$ Electrical
• C. $30^\circ$ Electrical
• D. $0^\circ$ Electrical

Hint:

Remember: \( \sin(90^\circ) = 1 \) → That’s why torque is max at this angle.

Answer 1

The Correct Option is A

Step 1: Torque in induction motor.
Torque is proportional to the sine of the angle between stator field and rotor field: \[ T \propto \sin(\delta) \] Step 2: Maximum torque condition.
For \( \sin(\delta) \) to be maximum, \( \delta = 90^\circ \). This occurs when the induced rotor EMF is in quadrature (90° out of phase) with stator flux.
Step 3: Practical interpretation.
At this phase angle, interaction between stator and rotor fields is strongest, delivering maximum torque.
Conclusion: Maximum torque is developed at a $90^\circ$ electrical phase difference.