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87T Vs. 87REF

87T Vs. 87REF

87T Vs. 87REF

(OP)
what is the need for a REF on a wye-wye grounded 15 MVA trafo if a full differential (87T) is provided? I think that any winding to yoke fault on secondary or primary will be detected by the 87T and the OC/EF provides back up protection.

any clue?

RE: 87T Vs. 87REF

Maybe, maybe not, but when REF is available just by setting the enable setting from OFF to ON, why not?

RE: 87T Vs. 87REF

REF is better at detecting winding faults that are close to the neutral point.

RE: 87T Vs. 87REF

Use both of them. REF is good protection, always.

RE: 87T Vs. 87REF

As long as the neutral CTs are provided in the transformer, just connect it to the same relay as 87T and configure for REF. It will not do any harm.

Now regarding the advantage of having REF.
If any of the winding neutral is resistively earthed, probably the sensitivity of 87T may not be adequate to cover the faults which are close to the neutral point. The REF has an edge over 87T for such faults.

RE: 87T Vs. 87REF

(OP)
Thanks everyone it is clear now.

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