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LV EF Protection for a power transformer

LV EF Protection for a power transformer

LV EF Protection for a power transformer

(OP)
Hi

I have 2 x 40/60MVA, 132/11kV, YNd1 transformers which are used to feed a mine site. Neutral earthing transformers (NET's)(one per trfr) are used to limit the 11kV earthfault current to 10A. I have thus ruled out LV REF and diff as unit protection system to provide fast and selective LV EF protection. Diff is still applied.

Is there a unit protection system that can cater for LV EF's within the trfr zone? Is it necessary? Only protection I can think of is a CT in the NET neutral set to about 1A with a time delay to allow clearance of downstream faults. I am aware that this is not unit protection.

Thanks.

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