Question

1. Calculate the VA output required from a current transformer of 5A rated secondary current when the burden consists of relays requiring 10VA at 5A plus a loop lead resistance of 0.8 ohms.

2. What output VA would be required from a current transformer of 1A rated secondary current for a burden of 10VA at 1A plus lead resistance as in part 1.

3. An earth fault relay has a burden of 1VA at setting and is set at 0.2A. What output voltage must a current transformer produce to ensure linear operation of the relay at 20 times setting? Assume that ct plus lead resistance is 1.5 ohms and that the relay coil impedance saturates to 1/2 its unsaturated value at 20 times setting.

Answer 1