Differential protection, different CTs

[Power0020]

Talking about high impedance differential protection, would a higher min. pickup current compensate the lower CT class? say 5P20 instead of CLX?

I understand that this will compromise the protection accuracy but still be of very satisfactory for in zone faults esp. with solidly grounded wye-wye.

any clue?

 

[burntcoil]

Pick-up is always minimum in terms of time and you will need to calculated a voltage accross relay resistor that results due to external faults, so your relay can ride through external faults. So whats the advantage of using a high impdennce differential if you are going to compromise on CTs. Go with C800. Or use partial differential scheme using overcurrent relays with 5P20 CTs