This question was previously asked in

ISRO (VSSC) Technician (Electrician) Sept 2016 Official Paper

Option 3 : 8 A

__Transformer:__

- A transformer is a static device that transfers power from one circuit to another circuit without a change in the frequency.
- In the transformer, two windings are electrically isolated but magnetically coupled. Hence the transformer is a coupled circuit.
- The transformer is a singly excited device since it requires only one external voltage source to energize any number of windings placed on its core.
- The transformer can be treated as a phase-shifting device since it offers a displacement of approx 1800 between two circuits.
- As the amount of flux in the transformer core is constant irrespective of power transfer, it can be treated as a "Constant flux device".
- The transformer is a negative feedback circuit because it satisfies 'Lenz's law'.

The power is given by the formula:

P = I × V

__Calculation__:

Given,

Power = 1 kVA

Low voltage side current = I

Low voltage side voltage = 125 V

**P = I × V**

1 kVA = I × 125 V

**I = 8 A**