Question

The supply voltage to an induction motor is decreased by 10%. By what percentage, approximately, will the maximum torque decrease?

(a) 5%

(b) 10%

(c) 20%

(d) 40%

The question was asked by my school teacher while I was bunking the class.

Query is from Synchronous Machine Stability in division Synchronous Machine Stability of Electrical Machines

Answer 1

Right answer is (c) 20%

To elaborate: Torque is proportional to V^2.

             Torque will change by twice percentage of the change in voltage i.e. 20%.