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Directional earth fault relay maloperation

Directional earth fault relay maloperation

Directional earth fault relay maloperation

(OP)
Directional earthfault relay receives VT input from the VT in the switchgear incomer cable box and CT input from that in the transformer neutral-to-earth connection. The relay is set to look away from the transformer.

Now, can some one tell me - whether the VT location is the reference for the directionality or the CT location? I think it is the CT location.

RE: Directional earth fault relay maloperation

Polarity determines the direction.

RE: Directional earth fault relay maloperation

The phase angle difference between the zero-sequence voltage measured by the VTs and the zero-sequence current measured by the CT is what determines the direction.  So, it takes both, with proper polarity, to have directionality.

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