Electrical Protection

[xuxu]

Hi..

I have one directional Earth fault(51N)relay that trips in the opposite direction(reverse)..

what must i do to trip in the direction that is supposed to be triping?
must i chang the VT or CT polarity?
Or must i chang Both?

Regards..

xuxu

 

[RRaghunath]

Directional Earth fault relay current input - verify that the same is not from the neutral (star point) CT. This will make the relay non-directional. The current input should be from residual connection of phase CTs.

Any directional relay directionality can be reversed by reversing the current input wires.

 

[cranky108]

First you need to determine how it is determining the direction. You then need to either reverse the directional input, or the measured current.
Change one quantity but not both.
However, there are relays that are dual polorized, so there are two directional quantities.

Why do you want to change it? Be sure it wasen't put that way for a reason.

 

[DiscoP]

I might be pedantic here, but 51N is the number for a non-directional relay.

Could it actually be a non-directional element that is tripping.

67N is the directional number.

 

[slavag]

Hi.
What Raghun, Cranky and DiscoP said.
What is a your grounding system, what is a setting, what is a CT input connection ( residual connection of all 3xCT's or dedicated toroidal CT)?
Regards.
Slava