Current Transformer (CT) Protection

The resistive burden is the Resistance Component of the total impedance connected to the CT Secondary side. The deciding factor would be the Knee Point Voltage of the TPS Class CT.

Higher the Rb than the design rating, the saturation will be quicker and vice versa. The actual resistive burden connected to the CT Secondary will decide the actual saturation of the CT and hence the protective system performance.

Thank-you very much for your reply.

As you may know, as per IEC 60044-6, Eal=Kssc*Ktd*(Rct+Rb)*Isc, in which, as a purchaser,I specify the Eal,Rct,Isc and Kssc(=Issc/CT ratio) in my CT specification.

So, the CT supplier has the option to to supply the CT complying IEC with higher 'Rb' & lesser 'Ktd' or with the lesser 'Rb' & higher 'Ktd', as the remaining factors are fixed in the above equation.

In the above context, which CT I can prefer in terms of performance, or is there any guidlines in the IEC for the minimum value of Rb or Ktd.

Thanks.