# Transformers core total load in VA on the CT secondary

1. Mar 13, 2010

### Sanna Khan

1. The problem statement, all variables and given/known data
A current transformer has a primary winding of two turns and a secondary winding of 100 turns.
The secondary winding is connected to a ammeter with a resistance of 0.25 ohms.
the resistance of the secondary of the current transformer is 0.75 ohms.
The value of current in the primary winding is 250A.

Im finding it difficult to calculate the following

the total load in VA on the CT secondary?

2. Relevant equations
The secondary EMF = (5 Amps) x (0.75 Ohms + .25 Ohms) = 1 Volts. However 5 Amps x 0.75 Ohms = 3.75 Volts is dropped across the internal resistance of the transformer`s secondary winding leaving only 1.25 Volts across the external terminals of the the secondary. That is why the total load VA is only 6.25 VA.

3. The attempt at a solution

The Voltage across the the external terminals of the CT transformer is the same as the Voltage across the Amp meter. Therefore the external VA load on the CT secondary equals 1.25V x 5A = 6.25VA is this correct?