Zonal Protection

[Guardiano]

Hi forum members,
I understand that class X CT is always used for differential protection because you don't want the protection to work for external fault. I have seen some applications where 5P20 CT is used for differential protection. Does this compromise the installation?
Any comment is welcomed.
Thanks.
Guardiano

 

[sushilksk]

It depends, maximum through fault current for protected object needs to be calculated.

 

[davidbeach]

C800s seem to work everywhere.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[RRaghunath]

Guardiano, If the differential protection is based on High Impedance principle, Class-PX is recommended for CTs.
If the protection is biased or low impedance type, 5P20 is also acceptable.
Follow the instructions given in the protection relay technical literature.