Transformer MCQs Part 6

Contents

- 1 What is the full load secondary current of a 2000/200 V, 20 kVA transformer
- 2 Certain transformer takes 0.5 A and absorbs 50 watts when the primary side is connected to a 200 V, 50 Hz, while secondary being open circuit. What is value of magnetizing current
- 3 The flux in core of single phase transformer is
- 4 A low voltage electrical system employs a 240V to 40 step down transformer for safety. The equivalent resistance of electrical system is 10 ohms. Considering the transformer to be ideal and overall system as lossless, what is the current in secondary coil
- 5 Design Engineers design transformer so that primary and secondary have

## What is the full load secondary current of a 2000/200 V, 20 kVA transformer

What is the full load secondary current of a 2000/200 V, 20 kVA transformer:

- 100 A
- 200 A
- 300 A
- 400 A

Correct answer: 1. 100 A

Solution: kVA/Secondary Voltage = 20*1000/200 = 100 A

## Certain transformer takes 0.5 A and absorbs 50 watts when the primary side is connected to a 200 V, 50 Hz, while secondary being open circuit. What is value of magnetizing current

Certain transformer takes 0.5 A and absorbs 50 watts when the primary side is connected to a 200 V, 50 Hz, while secondary being open circuit. What is value of magnetizing current

- 0.250 A
- 0.433 A
- 0.750 A
- 1.202 A

Correct answer: 2. 0.433 A

Solution:

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

Iron loss current (Iw) = Io cos Φo = Wo/Vp = 50/200 = 0.25 A

Magnetizing current (Im) = √Io^2 – IW^2 = √0.5^2 – 0.25^2=0.433 A

## The flux in core of single phase transformer is

The flux in core of single phase transformer is:

- Purely rotating one
- Purely alternating one
- Partly alternating and partly rotating
- None of these

Correct answer: 2. Purely alternating one

## A low voltage electrical system employs a 240V to 40 step down transformer for safety. The equivalent resistance of electrical system is 10 ohms. Considering the transformer to be ideal and overall system as lossless, what is the current in secondary coil

A low voltage electrical system employs a 240V to 40 step down transformer for safety. The equivalent resistance of electrical system is 10 ohms. Considering the transformer to be ideal and overall system as lossless, what is the current in secondary coil:

- 2 A
- 4 A
- 5 A
- 10 A

Correct answer: 2. 4 A

Explanation: Secondary current (Is) = Vs/R = 40/10 = 4 A

## Design Engineers design transformer so that primary and secondary have

Design Engineers design transformer so that primary and secondary have:

- Large resistance
- Tight magnetic coupling
- High leakage reactance
- None of above

Correct answer: 2. Tigh magnetic coupling