An autotransformer is used to reduce the voltage of a 100-kilovolt amp, 480-volt secondary of an isolated type transformer, to supply a 100-kilovolt amp load with 277 volts. What size autotransformer is needed? (Use the co-ratio to determine the size.)

42KVA

Explanation:

Given data

High Voltage (HV) = 480V

Low Voltage (LV) = 277V

Fo find

Size of transformer=?

Solution

To find the size of transformer here we use the co-ratio. The Co-ratio is given as:

Co-Ratio = (HV - LV) / HV

where

HV is High Voltage

LV is Low Voltage

Now put the values we get

Co - Ratio = (480-277) / 480=.42

So the size of transformer is 42KVA