Finally, we found the problem in the CT is located in the low side of the transformer.
Even do we tested the CT’s (CTR & saturation) and it was Ok, but we did not test the insulation of those CT (at that time we did not have a 500V megger).
CTs located on X1 and XO bushings are zero ohms to...
What we are going to do is change the CT's set for the differential, keep the diff blocked, monitor twice a week the relay looking for other event to see the behavior of the differential function.
Meanwhile, the transformer (20 MVA base) will be protected with overcurrent (the SEL-387 and the...
Marmite:
Is outside the protected zone. The CT's that I'm using for the differential protection, is the primary & secondary CT's located on the transformer bushing. Therefore, nothing else is in the protected zone, but the transformer.
Like I said before, our entire transformer are Dy1, and...
Stevenal, you are right. On Dy1 or Dy11 conections there is only a 30 degrees shift between high & low side. I was trying to say that when you feed a Dy1 transformer with CBA conections, the low side vector rotates 60 degrees, and now is leading the high side by 30 degrees. Thank for your...
ScottyUK:
First of all, thanks for your response.
The transformer vector group is Dy1, but we have C phase on H1, B phase on H2 and C phase on H3. Therefore, for the relay is a Dy11 because the low side is leading the high side by 60 degrees. All our system is like this.
This transformer is a...
Definitely, you need to review your relay coordination, since the delta was a filter to the high side world of zero sequence faults (L-G or LL-G) on the star side, but if now you are going to have star-star solidly grounded on both sides, you are going to have a path for this currents, and...
Hi..
I have a question for the relay engineers..
Recently we had a trip in one of our substations transformers where we are using a SEL-387 relay with an external single phase to ground fault.
One the event was downloaded; we sent it to SEL because it was not clear for us (operations put the...
