Question

Reluctance motor can produce torque at ________

(a) any speed less than synchronous speed

(b) synchronous speed only

(c) any speed greater than synchronous speed

(d) all of the mentioned

I have been asked this question in a job interview.

My question is based upon Reluctance Motor topic in section Basic Concepts in Rotating Machines of Electrical Machines

Answer 1

Correct choice is (b) synchronous speed only

Easiest explanation: Te(av) = -1/4 ∅max^2(Rlq – Rld)(1/2 sin⁡(-2δ)), w = synchronous speed

if wr≠w then Te(av)=0, and  if wr=w then Te(av)≠0, as the last term in the equation 1/2 sin⁡(-2δ) does not vary with time, and  hence average torque is not equal to zero.