Q5. Explain the difference for the following paragraphs, answer five only A. Auto transformers and Transfer rectifier units B. Stator and rotor frequenency C. Ram Air Turbine(RAT)and Axillary Power Unit (APU) D. Conventional and Auto transformers E. Synchronous speed and rotor speed of an induction motor F. primary and a secondary cell.

Given a 25 hp, three-phase, 230-volt, squirrel cage induction motor. The ambient temperature of the place ofinstallation is 40°C. Use TW wires

A three – phase induction motor is taking 40 kW, the slip being 4%, stator losses amount to 800 watts, calculate the total power developed. (a). 39,200 kW              (b). 40,800 kW (c). 37,632 kW              (d). 36,732 kW

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) 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?

Provide Solution

13.a. A bridge circuit is used to measure the loss of larger transformers because the circuitA. promotes safety.B. eliminates calculations.C. increases measuring convenience.D. improves measurement accuracy.13.b. A synchronous machine is run as an unloaded motor. If a low voltage is supplied at the ratedfrequency, and if the full-load armature current flows, a test is being run to determine theA. windage loss.B. I²R loss.C. stray-load loss.D. core loss.

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

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