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earth fault protection in delta networks

earth fault protection in delta networks

earth fault protection in delta networks

(OP)
G'Day,
We have a power system with a grounded neutral. The distribution to various loads are in delta and there is no neutral. when there is a ground fault on this distribution system the REF protection relay of the generating station trips. Although we have Over current earth fault system on the distribution feeders the fault passes through and both the relays trips.
is there any necessity to provide the earthing transformer to the system and provide REF protection in the distribution network.
Please advise

RE: earth fault protection in delta networks

It sounds like a case of mis-coordination of relay settings and/or application. Have someone with relay experience take a look at the system protection.

The system is already grounded, you do not need earthing protection. Although your system description is not very clear to me.

Rafiq Bulsara
http://www.srengineersct.com

RE: earth fault protection in delta networks

If REF trips for an out of zone fault there is something wrong in how it is set or in the CT wiring.

RE: earth fault protection in delta networks

The REF should only operate on internal fault in the protected equipment. If not there is a mistake (as said) in the CT connections. It can be also a neutral overcurrent that is operating. Often both functions are integrated in the same relay, such as the SPACOM series from Stromberg (ABB).

Is this a transformer or generator protection that you have?
More detail is needed. ratings, voltage levels, how many units, island system or not...  

rasevskii

RE: earth fault protection in delta networks

On delta systems, earth fault protection can be installed with residual current sensing - sum of all phase current and if this sum exceeds set value, it will trip the particular circuit.

REF should trip for internal fault only and not external fault.  Check for polarity of CT and / or relay circuits / wiring.  Is there nay time delay on REF what model it is?  Does it have any instantaneous element that is tripping?

NC

 

RE: earth fault protection in delta networks

Correction: In my post of July 31, I meant to say ...you do not need earthing "transformer"(not protection)....

Rafiq Bulsara
http://www.srengineersct.com

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