### Electrical Machines (Transformer)

1)         At what power factor, the voltage regulation of a transformer can be zero ?
B.         Lagging power factor
C.        Unity power factor
D.        Zero power factor

2)         In a three phase star - delta transformer, what is the angle difference between primary and secondary phase voltages.
A.        delta side lags by − 300
B.         star side lags by − 300
C.        star side leads by 300
D.        delta side leads by 300.

3)         What will be the the eddy current loss if the supply frequency of a transformer becomes double ?
A.        Eight times
B.         Remain same
C.        Doubled
D.        Four times

4)         The efficiency of a transformer is mainly dependent on
A.        core losses.
B.         copper losses.
C.        stray losses.
D.        dielectric losses.

5)         If supply frequency of a transformer decreases,
A.        Both eddy current and hysteresis losses will increase.
B.         eddy current loss will increase but hysteresis loss will decrease.
C.        Both eddy current and hysteresis losses will decrease.
D.        eddy current loss will decrease but hysteresis loss will increase.

6)         Transformers operating in parallel will share the load depending upon their
A.        Leakage reactance.
B.         Rating.
C.        Efficiency.
D.        Percentage impedance.

7)         No load primary current in a transformer
A.        lags behind applied voltage somewhat less than 900
B.         lags behind applied voltage by exactly 900
C.        leads the applied voltage by exactly 900
D.        leads the applied voltage somewhat less than 900

8)         Which of the following is minimized by laminating the core of a transformer?
A.        Hysteresis loss
B.         Eddy current loss
C.        Copper loss
D.        Stray loss

9)         Breather is provided in a transformer to
A.        absorb moisture from air entering in transformer as well as provide breathing to the transformer.
B.         provide cold air in transformer
C.        absorb moisture from air entering in transformer
D.        filter the transformer oil

10)       Iron loss in transformer mainly occurs in
A.        Iron made tank of transformer
B.         Steel core in transformer
C.        Winding of transformer
D.        Transformer insulating oil

11)       Which of the following losses in the transformer varies with load?
A.        Copper loss
B.         Eddy current loss
C.        Hysteresis loss
D.        Stray loss

12)       In a transformer the magnetic coupling between the primary and secondary winding can be increased by
A.        increasing the number of turns
B.         using soft material for winding
C.        using the magnetic core of low reluctance
D.        using transformer oil of better quality

1. a
2. d
3. d
4. a
5. c
6. b
7. a
8. b
9. a
10. b
11. a
12. c