Transformer MCQ Online Mock Test

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1) A 100/10, 50VA transformer is converted to 100V/110V autotransformer, the rating of the autotransformer will be

A) 550VA
B) 500VA
C) 110VA
D) 100VA

Show Answer

A) 550VA

2) A transformer has maximum efficiency at full load, when iron losses are 800 watts, copper losses at half load will be

A) 1600 W
B) 800 W
C) 400 W
D) 200 W

Show Answer

D) 200 W

3) The purpose of the conservator in a transformer is

A) to cool the winding
B) to prevent moisture in the transformer
C) to prevent short circuit of primary and secondary winding
D) to take up contraction and expansion of oil

Show Answer

B) to prevent moisture in the transformer
Conservator is a tank placed at the top of the transformer. It controls the expansion and conatraction of the transfomer oil on heating and cooling process repectively

4) In case of a power transformer, the no load current in terms of rated current is

A) 10 to 20%
B) 2 to 6%
C) 15 to 30 %
D) 30 to 50 %

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B) 2 to 6%
to prevent moisture in the transformer
In transformer the no load current is just 2-6% of full laod/rated current, hence it can be neglected however it is quite considerable in the induction motor about (30-40)% of full load current hence cannot be ignored.

5) If copper loss of transformer at 7/8th full load is 4900 W, then its full load copper loss would

A) 5600 W
B) 6400 W
C) 400 W
D) 373 W

Show Answer

B) 6400 W

6) If a 500 KVA, 200 Hz transformer is operated at 50 Hz its KVA rating will be

A) 2000 KVA
B) 125 KVA
C) 400 W
D) 1000 KVA

Show Answer

B) 125 KVA

7) The power factor at which transformer operates

A) is unity
B) is 0.8 lag
C) is 0.8 lead
D) depend upon the power factor of the load

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D) depend upon the power factor of the load
The power factor at which at transformer operates depends upon the power factor of the load. If can be leading pf, lagging pf or unity pf load depending on the load connected on the secondary side of the transformer corresponding to capacitive, inductive or resistive load respectively.

8) The efficiency at a 100 KVA transformer is 0.98 at full as well half load. For this transformer at full load. the copper loss

A) is less than core loss
B) is equal to core loss
C) is more than core loss
D) all the above

Show Answer

C) is more than core loss

9) Which of following will improve the mutual coupling between primary and secondary

A) Transformer oil of high breakdown voltage
B) High reluctance magnetic core
C) Winding material of high resistivity
D) Low reluctance magnetic core

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D) Low reluctance magnetic core
flux=mmf/Reluctance If the reluctance of the path is low in a coupled circuit, then mutual flux will be more hence the mutual coupling will get improved .Lower the reluctance, lesser will be the opposition to flux through the transformer core. Hence the core is made of high permeability material.

10) High leakage transformers are of

A) Small voltage ampere rating
B) High voltage ampere rating
C) High voltage rating
D) Low voltage rating

Show Answer

A) Small voltage ampere rating
1. Leakage transformer are those where magnetic flux of secondary is loosely coupled to the flux of primery
2. They are used in extra low voltage applications where short circuit conditions are epxpected. Hence the VA rating is low
3. These types of transformers are used for some negative resistance application such as neon signs, are welding sets.

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