1.
A single phase transformer rated for 220/240V, 50Hz operates at no load at 220 V , 40 Hz. This frequency operation at rated voltage results in which one of the following

A

Increase of both eddy current and hysteresis losses.

B

Reduction of both eddy current and hysteresis losses

C

Reduction of hysteresis loss and increase in eddy current loss.

D

Increase of hysteresis loss and no change in the eddy current loss.

Answer/ Hint

2.
A 50 Hz transformer having equal hysteresis and eddy current losses at rated excitation is operated at 45Hz at 90% of its rated voltage . Compared to rated operating point, the core loses under thi

A

Reduce by 10%

B

Reduce by 19%

C

Reduce by 14.5%

D

Remain unchanged

Answer/ Hint

3.
A single phase transformer when supplied form 220V , 50 Hz has eddy current loss of 50W. If the transformer is connected to a voltage of 330V, 50Hz the eddy current loss will be

A

168.75W

B

112.5W

C

75W

D

50W

Answer/ Hint

4.
1 kVA, 230V, 50Hz single phase transformer has an eddy current loss of 30 watts. The eddy current loss when the transformer is excited by a dc source of same voltage will be

A

30 watt

B

More than 30 W

C

Less than 30 watts

D

Zero will

Answer/ Hint

5.
At 50 Hz operation, a single phase transformer has hysteresis loss of 200 W and eddy current loss of 100 W. Its core loss at 60 Hz operation will be

A

432W

B

408W

C

384W

D

360W

Answer/ Hint

6.
Can a 50Hz transformer be used for 25Hz, if the input voltage is maintained constant at the rated value corresponding to 50H

A

Yes, since the voltage is constant current level will not change

B

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

C

No, owing to decreased resistance of transformer, input current will be doubled at the load

D

Yes, at constant voltage , insulation will not be overstressed.

Answer/ Hint

7.
On no load phasor diagram of transformer, the core loss component of the current remains in phase with

A

No load current

B

Primary supply voltage

C

Core flux

D

Primary induced voltage

Answer/ Hint

8.
In a transformer core, third and fifth harmonic components of fluxes are respectively 10% and 4% of the fundamental flux. The third and fith harmonic induced emfs in the winding in terms of the fun

A

30%, 20%

B

10%, 12%

C

50%, 20%

D

50%, 12%

Answer/ Hint

9.
If a sinusoidal voltage source is connected to a power transformer, its no load current would be

A

Sinusoidal and lagging the voltage by 90^{0}

B

Sinusoidal and lagging the voltage by less than 90^{0}

C

Rich in third harmonic and its fundamental would lag the voltage by 90^{0}

D

Rich in third harmonic and its fundamental would lag the voltage by less than 90^{0}

Answer/ Hint

10.
In a transformer , the exciting current will be in phase quadrature with the impressed voltage provided

A

Only the leakage impedance drop is ignored

B

Only the core loss is ignored

C

Both the leakage impedance drop and the core loss are ignored

D

Only the no load copper loss is ignored

Answer/ Hint

11.
The power factor of a power transformer on no load will bne about

A

Unity

B

0.75

C

0.5

D

0.35

Answer/ Hint

12.
The power factor of a transformer on no loadis poor due to

A

Magnetizing reactance of the transformer

B

Open circuited secondary

C

Low primary winding resistance

D

Low no load current

Answer/ Hint

13.
If in a transformer core a material having high reluctance path but having same hystersis loop is employed

A

_{Ie} will increase

B

I_{m} will increase

C

I_{m} will decrease

D

Both I_{m} and I_{e} will increase

Answer/ Hint

14.
Primary winding of a transformer comprises of two identical windings in parallel. If one winding is removed, magnetizing current will b

A

Halved

B

The same

C

Doubled

D

Increased four times

Answer/ Hint

15.
The core flux of a practical transformer with a resistance load

A

Is strictly constant with load changes

B

Increases linearly with load

C

Increases as the square root of the load

D

Decreases with increase of load

Answer/ Hint

16.
The inductive reactance of a transformer depends on

A

Electromotive force

B

Magneto motive force

C

Magnetic flux

D

Leakage flux

Answer/ Hint

17.
The flux in transformer core

A

Increases with load

B

Decreases with load

C

Remains constant irrespective of load

D

None of the above

Answer/ Hint

18.
The mutual flux in a loaded transformer can be varied by varying

A

Primary current

B

Load impedance

C

Secondary current

D

Reluctance of he magnetic path

Answer/ Hint

19.
The primary ampere turns are counter balanced by

A

Secondary ampere turns

B

Primary flux

C

Increase in mutual flux

D

Increase in secondary current

Answer/ Hint

20.
In a transformer_____ decreases with the increase in leakage flux

A

Primary induced emf

B

Secondary induced emf

C

Secondary terminal voltage

D

None of the above

Answer/ Hint