Breaker trip after Sync following ACB retrofit 3

[repsurfer]

I am on an offshore oil production platform. We have a 440V Diesel gen set running in island mode, supplying an emergency sw board. We attempted to auto sync our normal 440v power board fed from GT alternators through an intertie breaker

Normally the intertie ACB breaker closes at sync and the Emergency generator incomer ACB breaker opens normally after 2 secs. However, the intertie ACB closed and after a short delay (~2 sec) the Emergency generator ACB tripped on G Protection with fault current Ig = 675A. The intertie breaker stayed close, so we did not lose power to the em board

This is since we replaced the incomer ACB with a new modern breaker supposed to be like for like and all protection settings the same

There is no genuine earth fault as gen was running fine for a couple of days on own

The emergency incomer breaker is an ABB 3P emax 2 with neutral sensor replacing an obsolete emax breaker with neutral sensors

we are all baffled why the trip occurred, we don't believe there was a sync issue

any thoughts?

 

[thermionic1]

The with neutral sensor may be installed or wired incorrectly. Check the polarity of the with neutral sensor and verify it matches the manual for the breaker. Check the secondary wiring from the with neutral sensor to the trip unit and verify it's polarity is correct. It would probably be easier to fix the secondary wiring if the with neutral sensor was installed backwards. Ask whoever rebuilt / repaired the breaker to explain how they verified the with neutral sensor installation and wiring.

 

[RRaghunath]

Since it happened just after synchronised closing of inter tie breaker, we need to suspect the trip has something to do with the new ACB and its incoming and outgoing busbar sequence.
Is the phase sequence verified with new ACB?
How are the new ACB opening & closing times compare with those of old ACB?
If the above are ruled out, then we may have to suspect the generator protection and test it.
What is the relay type & model? Guess the relay takes all three phase current inputs for summing up vectorially to get Ig or does it use neutral CT current signal?

 

[edison123]

If those currents are from incoming DG after sync, they are pretty much balanced and hence such high neutral current indicates either reversed CT's or reversed CT secondaries.

Muthu

http://www.edison.co.in

 

[repsurfer]

Thanks for the replies. These are new ABB SACE Emax 2 LV air circuit breakers replacing 20-year-old originals. 3P 3200A on the Gen Incomer with Neutral sensor. The Inter Tie breakers are still the original 4P with no Senors to worry about. We have also replaced the transformer incomers on the main board 3P 4000A with neutral sensor. The Intertie breakers will be getting replaced next year

The transformer incomers were fitted first last week, and the one supplying the RHS Bus tripped on ground fault during sync. This left the Em Gen running in island mode. Now that the Em gen incomer has been replaced this is tripping first as the settings are lower.

I agree that the fault must be with the new breakers, but our main board runs with the two new incomers with no issue, only tripped when syncing with the DG. That would mean two breakers each having reversed CTs. The breakers were also fitted by ABB engineers. So maybe it will be a case of revised protection settings

I will feedback these comments, it will be interesting to see what our onshore support team comes up with, if anything soon. In the meantime, I will not be carrying out any loaded test runs with the DG