PSP Chapter 2

Evaluate the performance of the multi-ratio CT in Figure with a 100:5 CT ratio, for the following secondary output currents and burdens:

I’ = 5 A and ZB = 0.5 ohm

I=? CT error=?

• I = 105 A

  CT error = 4.8%

• I = 90 A

  CT error = 2%

• I = 80 A

  CT error = 1%

• I= 100A

  CT error= 6%

Evaluate the performance of the multi-ratio CT in Figure with a 100:5 CT ratio, for the following secondary output currents and burdens:

I’ = 8 A and ZB = 0.8 ohm.

• I = 10A

  CT=20%

• I = 8A

  CT= 5%

• I = 168A

  CT = 4.8%

• I = 170A

  CT = 50%

Evaluate the performance of the multi-ratio CT in Figure with a 100:5 CT ratio, for the following secondary output currents and burdens:

I’ = 15 A and ZB = 1.5 ohm

An overcurrent relay set to operate at 8 A is connected to the multiratio CT with a 100:5 CT ratio. Will the relay detect a 200 A primary fault current if the burden ZB is 2 ohm ? why?

An overcurrent relay set to operate at 8 A is connected to the multiratio CT with a 100:5 CT ratio. Will the relay detect a 200 A primary fault current if the burden ZB is 5 ohm? why?

•The input current to a CO-8 relay is 10 A. Determine the relay operating time for the following current tap settings (TS) and time dial settings (TDS):

•(a) TS=1.0,TDS=1/2;

•(b) TS=2.0, TDS=1.5;

•(c) TS=2.0, TDS=7;

•(d) TS=3.0, TDS=7;