Directional earth fault relay maloperation

[RRaghunath]

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.

 

[stevenal]

Polarity determines the direction.

 

[davidbeach]

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.