TRANSFORMERS

. The basic function of transformers is to change?

a) The level of voltage

2. The frequency of a voltage of the secondary is?

a) Equal to that of primary

3. The efficiency of the power transformer is around?

A) 95%

4. The core flux of the transformer mainly depends on?

a) Supply voltage and frequency

5. If the supply frequency of the transformer is increased, keeping the supply voltage constant, then?

a) Both the magnetizing component and core loss component of current will decrease.

6. Can a 50 Hz transformer be used for 25 Hz? If the input is maintained constant at the rated value corresponding to 50 Hz?

A) No, flux will be doubled which will drive the core to excessive saturation.

7. If a sinusoidal voltage source is connected to a power transformer, its no load current would be?

a) Lagging the applied voltage by less than 90 degrees.

8. What is the phase relation of magnetizing component and the core loss component of the current of a transformer to the applied voltage?

a) The former lags the supply voltage by 90 degrees while the latter is in phase with supply voltage.

9. Primary winding of the transformer comprises of the two identical windings in parallel. If one winding is removed, magnetising current will b?

a) Doubled

10. The inductive reactance if a transformer depends on?

A) Leakage flux

11. When a transformer is in operation on no load, the primary applied voltage is balanced by?

a) Primary induced elf

12. R1 is the resistance of the primary winding of the transformer. The turns ratio in terms of primary to the secondary id ‘k’.Then the equivalent resistance of the primary referred to secondary /

A) R1/k^2

13. In the transformer circuit mode, the core loss is represented as/

a) Shunt resistance

14. Voltage regulation of a transformer is given by?

a) (E2-V2)/E2

15. In a transformer zero voltage regulation is achieved at a load factor which is?

A) Leading

16. Full load voltage regulation of a power transformer is zero when power factor of the load is near?

a) Unity and leading

17. The regulation of the transformer is negative when its load is?

a) Capacitive

18. The constant losses of a transformer are?

a) Core losses (eddy current losses and hysteresis losses)

19. If the frequency of the input voltage of a transformer is increased keeping the magnitude of the voltage unchanged, then?

a) Hysteresis loss will decrease and eddy current loss is unchanged

20. in a transformer open circuit test is performed on ------- side and short circuit test is performed on   -------- side?

a) LV side and HV side

21. If Pc and Pac represents core and full-load holmic losses respectively, the maximum KVA delivered to load corresponding to a maximum efficiency to rated KVA multiplied by?

A)  square root of (Pc/Pac)

22. The function of the oil in the transformer is to provide?

A) Insulation and cooling

23. Stepped core construction is used to reduce?

A) Volume of copper material

24. In a 3-phase connection of a transformer which connection causes interference to the near by communication system?

A) star-star

25. scott-connection is used for?

a) 1.single phase to three phase conversion

    2. Three phase to single phase conversion

    3. Three phase to two phase conversion