Aux CT
Aux CT
(OP)
Can someone explain why a set of my transformer differential currents are passing through an auxilliary set of wye-delta CT's?
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RE: Aux CT
Depending on the relay, web sites such as ABB's discusses the calculations, settings and issues - look at their instruction leaflet 41-347.12C for the type HU and HU-1.
RE: Aux CT
thanks for the explanation. i think all 3 of your assumptions are correct about my setup. we are installing a new set of 5kV aux swgr (typical gen plant arrangement)and will certainly be using solid state relaying to cover the diffs.
thanks again!
RE: Aux CT
If you don't do it, the relay may trip unwanted for external faults, necause the delta side of the power transformer blocks zero sequence fault current, but not the star side, so you have to compensate at aux. CT's level.
For numerical relays, this is also done automatically in the algorithm, or it is settable.
RE: Aux CT