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Q9.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 0.1 Ω and 0.9 Ω respectively. Calculate (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. (10)