Exam Question

(a) Explain the principles of A.C. Motors starting, and speed control, including the effect on efficiency. (6)

(b) A 3-phase induction motor has a 4-pole, Y-connected stator winding. The motor runs on 50-Hz supply with 200V between lines. The motor resistance and standstill reactance per phase are 0.1Ω and 0.9Ω respectively.

Calculate: (10)

(a) The total torque at 4% slip

(b) The maximum torque

(c) The speed at maximum torque if the ratio of the rotor to stator turns is 0.67.

Neglect stator impedance.