Device 87 Operation

Perhaps it is designed to do that?

http://cr4.globalspec.com/thread/99587/Device-87-operation

Duplicate thread.

ESO

The electrical difference(s) between phases is outside the existing relay protection parameters.

It is important that you identify which element is not in compliance.

Frequency? Phase angle? Voltage level?

I strongly suggest you have a protection system engineer analyze the circuit and relay settings before you attempt another breaker closure.

If you close the breaker and there is too much difference between the systems the breaker can fail causing severe damage and/or personal injury.

Thank you all.But my worry,why does the breaker closes any time after serviral attermt. device 87 operates on first and second,then closes

Too bad, i work on device 88 & 86=]

Cheer, Stu.

The most likely cause will be installation, commissioning, and testing by someone who does not know how to do all of the above. Your 87 relay operates because the CTs are sensing an imbalance in the current entering and leaving their zone of protection. Usually this indicates a faulty component, but in your case I suspect that no one checked the polarity of the CTs and their wiring from the devices to the relay. Get someone knowledgeable out there before you actually cause an expensive failure.

Transformer differential protection you are talking about, if my understanding is right.

The transformer differential protections are known to trip during transformer energisation if 2nd harmonic detection (with appropriate threshold and duration set) and protection block is not enabled.

There are other settings also that are important to make sure that the protection is stable during transformer energisation as well as during normal working that follows.

Review the settings critically with the recommendations given in the relay technical manual. That should help alleviate the problem.

By the way, repeated energisation of transformer when there is differential trip is not an acceptable operating practice in the industry. It could be serious with fatal consequences.