# Transformer MCQs Part 9

Transformer MCQs Part 9

## A core type transformer provides

A core type transformer provides:

1. Shorter magnetic path
2. Longer magnetic path
3. Lesser average length per turn
4. None of these

Correct answer: 1. Shorter magnetic path

## Open-circuit test on transformer is carried out in order to determine

Open-circuit test on transformer is carried out in order to determine:

1. Iron losses
2. Copper losses
3. Friction losses
4. Total losses

## A low voltage electrical system employs a 100V 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 primary coil

A low voltage electrical system employs a 100V 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 primary coil:

1. 1.6 A
2. 4 A
3. 5 A
4. 10 A

Explanation:

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

Primary current (Ip) = (Vs * Is)/Vp = 1.6 A

## The maximum flux produced in core of transformer is

The maximum flux produced in core of transformer is:

1. Inversely proportional to primary voltage
2. Inversely proportional to supply frequency
3. Directly proportional to supply frequency
4. None of these

Correct answer: 2. Inversely proportional to supply frequency

Explanation:

## Transformer voltage equation is mathematically written in the form

Transformer voltage equation is mathematically written in the form:

V1 = 4.44 * N1 * Φmax * f

A 110/2300 V transformer takes no-load current of 5 Amps at a lagging power factor of 0.3. The core loss expressed in watts is:

1. 120 W
2. 150 W
3. 165 W
4. 200 W

Solution: Core loss, Wo = Vp Io cos Φo = 110 * 5 * 0.3 = 165 W

Or Alternatively:

Φmax = V1/(4.44 * N1 * f)

Where

V1 = Applied primary voltage

N1 = Number of primary turns

From equation one can understand that maximum flux produced in core is inversely proportional to supply frequency.