Loss of Excitation on 10 MW Turbo Power Generator: Generator Main Breaker opened due to issue on ex 1

[bkarim55]

Dear All
We have 3 Power GT PGT10 driving a JEUMONT Generator. Usually 2 generators are running in parallel mode and the 3rd one is on Standby. We lost the PMG (Permanent magnet generator) on one of those GENs and the root cause of the damage was due to the PMG Bearings failure.

A new genuine PMG has been installed but we still have the same trouble. The Gen Main Breaker opens due to excitation failure.
During the PMG replacement we also removed the exciter end cover and we cleaned all the armature/Stator area from dirt and dust than we checked diodes and found fine.
My questions are:
How to solve this problem? And what’s going wrong with this GEN and its exciter?? .
When the PMG has stuck and has burned, what’s its effect on the other components of the generator?

Thanks In advance
Karim

 

[catserveng]

I recently had a similar problem on a larger diesel engine driven generator, the unit tripped due to a loss of excitation fault and the PMG was damaged, we made repairs similar to what you described, the unit was put back on line and ran about 2 hours, then tripped on loss of field. Unit was checked, no obvious problem, restarted and put back on line, tripped again after a short time. Unit had a Basler DECS regulator, we found the AVR was failing after being on line for a short time, noted that each time we put it online it took less time to trip. Perhaps you have a similar issue? Not sure what type of voltage regulator you have, but if the PMG rotor comes in contact with the PMG stator, it may produce a spike or power issue that could damage the AVR, at least in my experience.

What provides the excitation fault indication for your system, a loss of field (ANSI 40 device), or a signal from the AVR?

Hope that helps, MikeL.

 

[bkarim55]

Dear Mikel;
Thanks a lot for sharing your experience.. And sorry to be so long to reply
Yes! It’s a similar problem to what you had… And the PMG rotor went in contact with its stator when failed.
After PMG replacement, the unit was put back online and run about 2 days and tripped on loss of excitation. At the 2nd time, the unit run only about 2 hours and tripped for same raison.
A double check has been done and the electrical team had replaced the 12 diodes of the rectifier. Now, the unit is running about a week and no trip happened. I hope the problem is solved.

Again thanks a lot...
Karim

 

[itsmoked]

bkarim55; Thank you for the update. Much appreciated!

Keith Cress
kcress -

http://www.flaminsystems.com