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2
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pwrengrds
Electrical
- Mar 11, 2002
- 232
This isn't a question but something I learned over the past month due to a loss of exciter failure.
The generator was being commissioned and the exciter feeder breaker was undersized and tripped, causing a loss of excitation. It did not trip on loss of excitation, but caused some serious voltage fluctuations. After a couple of minutes the fuel valve was manually tripped and the generator tripped on reverse power (via the G60 relay). The generator was protected by a G60 relay which did not trip on loss of excitation.
From my review of the event files it should have operated. The settings calculations were all correct. The relay was tested and did operate correctly per the off line testing (a well known software test).
GE Multilin reviewed the fault data and after a few emails back and forth found the loss of excitation was blocked during the fault by Under Voltage Supervision. The under voltage supervision was set at 70% and the voltage dropped to 90% during the fault. I understood, falsely, that the under voltage supervision would block on undervoltage, it turns out that it releases.
If under voltage supervision set to 70% it will only operate at less than 70%. If you have a stiff bus and under voltage supervision is on the loss of excitation will likely not operate.
Every one of the G60 relays I have seen have the under voltage supervision turn on and at 70% thinking it's blocking for loss of PT fuse. It's not and I recommend caution using the under voltage supervision on the loss of excitation for this relay. I let my customers know the issue and thought I would spread the word, it's not clear from the manual.
David
The generator was being commissioned and the exciter feeder breaker was undersized and tripped, causing a loss of excitation. It did not trip on loss of excitation, but caused some serious voltage fluctuations. After a couple of minutes the fuel valve was manually tripped and the generator tripped on reverse power (via the G60 relay). The generator was protected by a G60 relay which did not trip on loss of excitation.
From my review of the event files it should have operated. The settings calculations were all correct. The relay was tested and did operate correctly per the off line testing (a well known software test).
GE Multilin reviewed the fault data and after a few emails back and forth found the loss of excitation was blocked during the fault by Under Voltage Supervision. The under voltage supervision was set at 70% and the voltage dropped to 90% during the fault. I understood, falsely, that the under voltage supervision would block on undervoltage, it turns out that it releases.
If under voltage supervision set to 70% it will only operate at less than 70%. If you have a stiff bus and under voltage supervision is on the loss of excitation will likely not operate.
Every one of the G60 relays I have seen have the under voltage supervision turn on and at 70% thinking it's blocking for loss of PT fuse. It's not and I recommend caution using the under voltage supervision on the loss of excitation for this relay. I let my customers know the issue and thought I would spread the word, it's not clear from the manual.
David