a) Which components determine the excitation current of a transformer? How are they in transformer equivalent circuit modeled? b) Why is the polarity determination of a transformer made? Briefly explain how the experiment is done. c) If the direction of rotation of the motor changes when the feeding ends are changed in a DC motor, what can be said about its type? d) Why does the peak voltage increase as the serial DC generator is loaded? How long does this increase continue?

4- A double squirrel-cage induction motor has (a) Two series winding in stator (b) Two parallel windings in stator (c) Two parallel winding in rotor (d) Two rotors moving in opposite direction 5 The rotor slots are slightly skewed in squirrel cage induction motor to ---------- (a) Increase the strength of rotor bars (b) Reduce the magnetic hum and locking tendency of rotor (d) Provide ease of fabrication (c) Economize on the copper to be used 6- Stable operation of an induction motor is (a) Between zero slip and unity slip (b) Between zero slip and slip corresponding to maximum torque (e) Between 6.5 slip and 0.95 slip (d) Between slip corresponding to maximum torque and unity slip 7- Iron loss in the rotor of a 3-phase induction motor is negligible due to (a) Very low frequency of emf induced in the rotor (c) Very low flux density in rotor parts (b) Very low emf induced in the rotor (d) Constant magnitude of flux linking the rotor core

The frequency of emf in the stator of a 4 pole, 3 phase induction motor is 50 Hz and that in the motor is 1.5 Hz. Determine (i) the slip and (ii) speed of the motor.

a) The rotor of a 3 phase, 60HZ, 4 pole induction motor takes 120 KW at 3 Hz. Determine: 1- The rotor speed. 2- The rotor copper losses.

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

c) What is the physical meaning for each of the following induction motor parameters: R1 „R2 ,Rc ,X1 ,X2 ,Xm ? What is synchronous watt?

c) What is the physical meaning for each of the following induction motor parameters: R1 „R2 ,Rc ,X1 ,X2 ,Xm ?

Shunt generator will build up its voltage when: Olts field resistance higher than critical value. Olts field resistance is less than critical value.

In a three phase induction motor, voltage between the slip rings at standstill is 50 V. At full load the slip is 0.04. The voltage between slip rings at full load is?