Transformer MCQs Part 12

Transformer MCQs Part 12

An ideal transformer is the one that has

An ideal transformer is the one that has:

1. Same number of primary and secondary turns
2. Same voltage per turns on primary and secondary side
3. Both of above
4. No losses and leakage resistance

Correct answer: 4. No losses and leakage resistance

Explanation:

An ideal transformer possesses following features:

1. It has no leakage flux
2. It has no core losses
3. It has no winding resistance

However, the real-life transformer has some losses, possess some windage resistance and has some leakage reactance as well.

The no-load ratio of a 50 Hz single phase transformer is 7000/450 V. The value of flux in core is 0.05 Wb. What is the number of primary turns?

The no-load ratio of a 50 Hz single phase transformer is 7000/450 V. The value of flux in core is 0.05 Wb. What is the number of primary turns?

1. 400
2. 525
3. 550
4. 600

Correct answer: 600

Solution

From formula: Ep = 4.44 * f *   Np * Φm

7000 = 4.44 * 50 * Np *0.05

Np = 630

A two winding transformer operates at maximum efficiency when

A two winding transformer operates at maximum efficiency when:

1. Cu losses equal iron losses
2. Hysteresis losses equal eddy current losses
3. Primary reactance equals secondary resistance
4. None of these

Correct answer: 1. Cu losses equal iron losses

During short-circuit test of transformer, which winding of transformer is short-circuited:

During short-circuit test of transformer, which winding of transformer is short-circuited:

1. Low voltage winding
2. High voltage winding
3. Any of above
4. None of above

Correct answer: 1. Low voltage winding

Explanation: During short-circuit test the low-voltage winding of transformer is short circuited and measurements are carried out on high-voltage winding.

The transformer is an efficient device since

The transformer is an efficient device since

1. It is a static device
2. It uses inductive coupling
3. It uses capacitive coupling
4. It uses electric coupling

Correct answer: 1. It is a static device

Explanation: Because of its static nature, a transformer has no static and windage losses.