# Transformer MCQs Part 7

Transformer MCQs Part 7

## Mutual flux in transformer remains constant at all loads since

Mutual flux in transformer remains constant at all loads since:

1. Leakage flux is small
2. It uses iron core
3. Applied voltage and frequency are constant
4. None of these

Correct answer: 3. Applied voltage and frequency are constant

## Certain transformer takes 0.4 A and absorbs 60 watts when the primary side is connected to a 230 V, 50 Hz, while secondary being open circuit. The iron loss current is

Certain transformer takes 0.4 A and absorbs 60 watts when the primary side is connected to a 230 V, 50 Hz, while secondary being open circuit. The iron loss current is:

1. 0.13 A
2. 0.26 A
3. 0.35 A
4. 0.5 A

Solution:

Formula for no load primary power is: Wo = Vp Io cos Φo

Iron loss current (Iw) = Io cos Φo = Wo/Vp = 60/230 = 0.26 A

## If a is defined as turns ratio of transformer and is equal to 5, then such a transformer will be

If a is defined as turns ratio of transformer and is equal to 5, then such a transformer will be:

1. Step up transformer
2. Step down transformer
3. Any of above
4. None of above

Correct answer: 2. Step down transformer

Explanation:

Turns ration (a) = Np/Ns = Vp/Vs

Suppose a = 5, and Vp = 2

Then Vs = 2/5 = 0.4

Since Vs < Vp, the transformer is a step down transformer

## If a transformer core possesses air gaps then

If a transformer core possesses air gaps then:

1. Its hysteresis losses are decreased
2. Magnetizing current increases
3. Eddy current increases
4. Reluctance of magnetic path is decreased

Correct answer: 2. Magnetizing current increases

## Certain transformer has an efficiency of 85% and works at 200 V, 5 kW. If secondary voltage is 240 V, considering the power factor to be unity, what is value of secondary current

Certain transformer has an efficiency of 85% and works at 200 V, 5 kW. If secondary voltage is 240 V, considering the power factor to be unity, what is value of secondary current:

1. 9.73 A
2. 17.70 A
3. 25.8 A
4. 33.83 A