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Restricted earth fault protection

Restricted earth fault protection

(OP)
Gents (and ladies),

What factors would you take into account when deciding to deploy REF protection to a transformer?

RE: Restricted earth fault protection

Assuming that you're already committed to using a relay rather than fuses, the only questions would be whether or not the transformer has a neutral (isn't a delta-delta transformer) and whether or not all of the necessary CTs exist. Beyond that deploying REF is simply turning it on and including it in the trip equation.

RE: Restricted earth fault protection

See section 16.7 of "Network Protection and Automation Guide" by Areva for an explanation on the uses of restricted earth fault protection. It depends on your system, grounding method, transformer size, how sensitive you want your differential elements, etc.

RE: Restricted earth fault protection

REF does provide more sensitive protection for some kinds of faults. However, there is a nominal cost of understanding how to properly set and test the REF element. Just because an element is available from the relay, it doesn't mean you have to use it.

RE: Restricted earth fault protection

(OP)
Hi,

I should have made myself clearer.

What factors would lead you to add or omit restricted earth fault protection in a particular situation ?

RE: Restricted earth fault protection

REF is more important with impedance grounded transformers because winding faults close to the neutral are harder to detect. The normal transformer differential protection will adequately protect solidly grounded transformers, but normally I would use REF if a neutral CT is available and the relay has the REF element built in.

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