CT, class S10, class 3/2 1

[slavag]

Dear All.
We prepare now retrofit of very old system ( 195..).
Customer was sent us data of CT at the object.
CT with class 3/2 and S10, I try found what it is.
Could you please help me with this issue.

Actually, we will replace CT's , VT's and protective relays, but maybe one step od retrofit old relays will operate with new CT's, for this reason I would like know, what is 3/2 and S10.

Thanks in advance.
Slava

 

[ppedUK]

These may be CTs to an old British Standard, possibly BS81, or BS2046 (1953). If so, class S10 is 5% composite error at 10x Primary rating. This is nearly equivalent to 5P10. I say nearly, because I believe CTs to the older standard had accuracy limit factor based on a Primary p.f. of 0.7.

The 3/2 class is probably a metering Class CT.

 

[slavag]

ppedUK.
Thanks a lot.
I decide use 5P20 for protection and 0.5 for metering.
According to calculataion, it's good for old system too.

Best Regards.
Slava