Gapped core CTs

[HamburgerHelper]

I see that there are manufactures that make gapped core Cts. Does anyone actually use these to help mitigate CT saturation during transformer inrush or other DC offset issues?

 

[submonkey]

Hi HH,

At the utility where I work, we commonly specify gapped core CTs for:

- 132 kV line differential protection schemes (40 kA, X/R can be over 30).
- 11 kV transformer differential protection (8 kA, X/R can be over 50).

With some negotiation, most major suppliers will source (or build) gapped CTs.
We've usually specified PX class to AS60044.1 with additional requirement of Kr < 10%.

I've never found inrush to be much of a problem for CT performance, because the
CTs on the high side of our transformers experience less demanding conditions.

Three phase bolted faults with a high X/R are a problem.

Thanks,
Submonkey