Differential Current Fault on generator multi differential relay protection 1

[successwale]

What might be causes of differential current on generator multi differential relay protection unit of MV panel. once the generator synchronized, carry a few a KW load it shutdown the engine on differential current on GPU.

 

[Hoxton]

1. Has it running without problems previous to this?
2. If brand new, never run before, was it commissioned by a competent engineer?

 

[successwale]

The engine has been running for past 4 years without problem.

 

[davidbeach]

What do the relay event reports show?

 

[ScottyUK]

Possibly an inter-turn fault on the stator.

 

[catserveng]

Well, could be a number of things,

So unit has been in service for four years. What kind of service? Prime, peaking, continuous or standby?

Does your protective relay have fault recording? If so has someone reviewed the fault event?

Are the neutral side CT's mounted in the generator connection box?

Has there been any recent work done on the generator?

What I usually see in the field with these types of complaints, in order of frequency, Note most machines I work on have the neutral side CTs in the generator connection box, and usually not well mounted.

Loose terminations/connections of the CT secondary circuits of the neutral CT's.

Damaged or broken neutral side CT's.

Wiring problems at the switchgear or relay. Usually loose connections, or wiring damage due to chaffing or vibraion.

Mistakes the result of recent service work, almost always when the original wring had been "field modified" to make the differential circuits work and no one went back and made sure the wire markers and prints were corrected.

Generator stator problems. Have you done a basic set of tests to the generator to make sure it's ok?

Hope that helps, MikeL.

 

[itsmoked]

Always love your in-depth coverage Mike.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[catserveng]

Keith,

This is actually one of my most common service calls, 90% of the time after a repair or service. If the unit has a good quality protective relay, then the event report makes life way easy. Pretty much points you right where to go. But a lot of the units I work on are older, and the protection isn't very helpful. Those units require a lot more effort sometimes.

I was on one this weekend, the unit had been down several days for an overhaul, on restart the lockout tripped and the differential relay flagged. The customer restarted the unit 5 times until a fireball came out of the generator. In this case there really was a generator problem, but it was an old generator, in a pretty severe environment, off several days in damp weather with no generator space heater on.

The list above has served me well, hope it helps the OP

Thanks!

 

[waross]

Hi Mike. I saw the aftermath of a couple of those fireballs after Hurricane Mitch.
A 350 KW and a 400 KW.
The air around these sets was filled with blowing swirling sea water mist.
The 350 KW unit was started in disregard of my clear instructions that it was not to be started.
That was the last day of its life!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ZapSib]

What happened when 87G operated ?
did you energized a power transformer or similar beast ?
Did the relay recorded a COMTRADE file ?