AP ECET EEE 2020-4

1. When a two winding transformer is connected as an auto transformer,its efficiency

A. Raises to 100%
B. Increases
C. Remains the same
D. Decreases

Answer : B. Increases
Explanation:-

2. The main disadvantage of using short-pitch winding in alternators is that it

A. Reduce harmonics in the generated voltage
B. Reduces the total voltage around the armature coils
C. Produces asymmetry in the three phase windings
D. Increase cu of end connections

Answer : B. Reduces the total voltage around the armature coils
Explanation:-

3. The full load terminal voltage of an alternator is greater than no load terminal voltage when

A. load is highly induced
B. alternator is under excitation
C. load is highly capacitive
D. input mechanical power is increased

Answer : C. load is highly capacitive
Explanation:-

4. If two alternators are running in parallel and the excitation of one of the alternators is increased, then

A. power output will decrease
B. wattless component will change
C. both machines will start vibrating
D. Machine with excess excitaion will burn

Answer : B. wattless component will change
Explanation:-

5. If the field of a synchronous motor is under excited, the power factor will be

A. Lagging
B. Unity
C. leading
D. Greater than 1

Answer : A. Lagging
Explanation:-

6. A synchronous motor working at leading power factor can be used as

A. Voltage booster
B. Noise generator
C. Mechanical synchronizer
D. Phase advancer

Answer : D. Phase advancer
Explanation:-

7. The effect of increasing load on a synchronous motor running with normal excitation is to

A. Increase both its Ia and pf
B. Decrease Ia but increase pf
C. Increase Ia but decrease pf
D. Decrease both its Ia and pf

Answer : C. Increase Ia but decrease pf
Explanation:-

8. In squirrel cage induction motors, the rotor slots are given slight skew in order to

A. reduce windage losses
B. reduce eddy currents
C. reduce accumulation of dirt and dust
D. reduce magnetic hum

Answer : D. reduce magnetic hum
Explanation:-

9. A wound rotor induction motor runs with a slip of 0.03 when developing full load torque.Its rotor resistance is 0.25 ohms per phase.If an external resistance of 0.5ohm per phase is connected across the slip rings, what is the slip for full load torque?

A. 0.03
B. 0.06
C. 0.09
D. 0.1

Answer : C. 0.09
Explanation:-

10. Star-delta starting of motors is not possible in case of

A. single phase motors
B. variable speed motors
C. low horse power motors
D. high speed motors

Answer : A. single phase motors
Explanation:-