Assume that a multi ratio CT has taps of 1005 and 2005 If th

Assume that a multi ratio CT has taps of 100/5 and 200/5. If the rated load current in 110 Amps which tap you will use If the CT secondary resistance is 0.09 Ohms and is connected to a relays with 0.007 Ohms in series with a meter with a burden of 0.003 Ohms (assume that the CT is connected with a 40 meter of wire with resistance of 3.0 Ohms/km) and the maximum fault current is 2000 Amps determine if the CT will saturate? Use the given CT saturation curve

Solution

a)

For 110A rated current ,we will be using 100/5 tap

as rated current should be 10% greater than current.

b)

Total Secondary resistance R=0.09+0.007+0.003=0.1 Ohm

Maximum fault current is 2000Amps

secondary current =2000*(5/100)=100 Amps

We observe from the graph that for tap 100/5,

For secondary current of 100 amps CT is in saturation region.So CT will saturate.