Differential Relays

Are you using your differential relay to trip both your 132kV circuit breaker AND local (11kV) circuit breaker (by paralleling the both circuit breaker trips)?

If not (ie- the local and 132kV circuit breakers operate independently of each other), then it sounds like you have not got your protection coordination set correctly. Check the trip curves and operation speed of both your circuit breakers to ensure proper protection coordination.

For any fault out the zone of differential relay range,the diff relay should not trip.

Please give the sld,relay locations and trip circuit details to advise properly.

ADMIN: Deleted Content

From the Rules: Do not post personal contact information on the forum space. You can share this information via the forum's internal messaging system.

If you asking this then you are not qualified to be dealing with protection of these devices.....I recomend that you cantact a High Voltage company do assist you.

There is what we call discremination of faults, so definately there is a problem on your setting. dont take chances get the HT company to help you with the sittings.

Mr. Jahanzeb,

I did not get your cotact phone, any way here is what could be the problem:

1- If the relay was recently put in service the fault could be in A)The wiring from 132kV and 11 kV CT's and/or mis-matched Auxiliary CT's if used. B) Low set Operating Current on the Relay. C) Faulty relay.

2. If the relay was working correctly then the fault could be A) Loose connection/s in the CT wiring anywhere between the CT terminals in the field and terminal blocks at the relay panel and wiring therefrom to the relay terminals.

I could better explain and pinpoint the fault if I had more details which I expected to get on contacting you. Wishing you good hunting.

MIQ

As indicated by a 'Guest' above, Differential Relays should never operate when the fault is outside the Differential Relay Zone. This zone is between the HV terminals of current transformers on all (2 or 3) windings. Current flow in the Trasformer Primary winding is compared with the current flow in the Transformer Secondary/Tertiary windings. Primary and Secondary/Tertiary currents should match and cancell each other leaving a fraction only (10-15% of FL current) and the relay is set to operate at about 30% of FL current. Currents flowing in the Primary and Seconary/Tertiary of the transformer outside this zone should cancell each other leaving the differential relay unoperated. However, a fault within the zone is detected much faster and all feeding sources are tripped in order to limit damage to equipment in the Differential zone.

The above is an attempt to inform you as a layman. I hope you will find the cause and take remedial action soon.