Question

The torque equation for non salient pole machine is Te = -(P/2)(μoΠrl/g)(FsFr)sinλNm. What does the negative sign in the torque expression indicates?

(a) stator and rotor MMF tend to reduce angle λ

(b) stator and rotor MMF tend to increase angle λ

(c) stator tend to reduce the air gap g

(d) rotor tend to reduce the air gap g

The question was posed to me during an interview.

The query is from Production of Torque in Non-Salient Pole Machines in chapter Synchronous Machines of Electrical Machines

Answer 1

The correct option is (a) stator and rotor MMF tend to reduce angle λ

The best I can explain: The torque acts in such a direction as to align the two MMFs Fs and Fr and thereby reduce the angle λ between them.