# The transformer which is smallest in size is and how to calculate that ? The options are 100 KVA, 50 Hz; 100 KVa, 100 Hz; 100 KVA, 25 Hz; 50KVA, 25 HZ ?

## The transformer which is smallest in size and how to calculate that ? The options are

- 100 KVA, 50 Hz
- 100 KVA, 100 Hz
- 100 KVA, 25 Hz
- 50KVA, 25 HZ

**Answer :** 100 KVA, 100 Hz

## Explanation

- The transformer equation
`E = 4.44(f)(B)(N)(a)`

Where, - E is the voltage in the winding either primary or secondary,
- f is the frequency,
- B is the flux density in the core,
- N are the number of turns on the winding, and
- a is the cross area of the core.
- At higher frequencies the number of winding turns N is reduced.
- This formula follows from the Faraday formula, E = N dθ/dt and θ = B(a).
- This formula is switching power supplies use a much higher frequency (thousands of hertz) than 60 hertz, they use smaller transformers that don't need as much wire as transformers operating at 60 hertz.