Phase Differential on Ground Faults
Phase Differential on Ground Faults
(OP)
With the new relay technology nowadays (i.e. GE SR735, Areva 634), are these phase digital differential relays capable of protecting Delta-wye (400A resistor grounded) power transformers on ground faults on the secondary (within its differential zone)?






RE: Phase Differential on Ground Faults
RE: Phase Differential on Ground Faults
What David saied. REF is covered ground fault in such appliaction with resistive grounding.
Best Regards.
Slava
RE: Phase Differential on Ground Faults
We have a three winding transformer wherein, the two secondaries are connected to the SR745. That leaves us one more CT input for the primary. Our primary is connected to an upstream tee with two power circuit breakers (which are part of the ring bus system). Is it possible to connect the relay in two primary CTs (on the two circuit breakers) where the CTs will be connected in "summation" (or parallel).
Will this affect the settings of the two CTs?
RE: Phase Differential on Ground Faults
RE: Phase Differential on Ground Faults
RE: Phase Differential on Ground Faults
RE: Phase Differential on Ground Faults
CTs on a ring being paralleled is quite common. Both sets of CTs have their wye point toward the transformer. Current into the transformer is summed, current around the ring is positive in one CT and negative in the other CT and they cancel. Always better to have the right number of restraints. Four restraint relays are available from many manufacturers; I know of one five restraint transformer differential.
RE: Phase Differential on Ground Faults
I look into this matter seriously and look at the relay manual and come back with further queries as needed.
Do I need to to do CT saturation calculations for this?
RE: Phase Differential on Ground Faults
For transformer differential, there are relays on the market that can have up to 4 separate inputs.
Companies that we have used are SEL (387), Basler (BE1-CDS240) & Areva (P634). We haven't needed to parallel CTs for transformer differential.