(a) Explain the required tests to construct the circle diagram of the induction motor. The stator leakage impedance of a star connected induction motor is (0.5+j1.4) § per phase, and the rotor leakage impedance referred to stator is (0.6+j1.5) 2 per phase. Neglect the magnitizing current, estimate the line current and torque if the machine runs with a slip of 5 percent when connected to a 400V three phase supply (i) normal operation, and (ii) with one line open.

Name three factors that determine the torque produced by an induction motor.

6- In a stepper motor, how is the speed of rotation determined? a) By the current supplied to the motor. b) By the magnitude of the voltage applied. c) By the load applied to the motor. d) By the frequency of the waveforms used. 7- A transformer core is laminated to a) reduce hysteresis loss b) reduce eddy current losses c) reduce copper losses d) reduce all above losses 8- An induction motor with 580 r.p.m. speed at 60 Hz will have a) 8 poles b) 6 poles c) 4 poles d) 2 poles 9- If any two phases for an induction motor are interchanged a) the motor will run in reverse direction b) the motor will run at reduced speed c) the motor will not run d) the motor will burn 10- No-Load speed of which of the following motor will be highest? a) Shunt motor b) Series motor c) Short-Shunt compound motor d) Long-Shunt compound motor

The resistance and reactance per phase of the rotor of a 3-phase induction motor are 0.6 ohm and 5 ohms respectively. The induction motor has a star-connected rotor and when the stator is connected to a supply of normal voltage, the induced e.m.f. between the slip rings at standstill is 80 V. Calculate the current in each phase and the power factor at starting when (i) the slip-rings are shorted, (ii) slip-rings are connected to a star-connected resistance of 4 ohm per phase.