Our site has a 7EA WHRU with DLN running on Lean Fuel Gas. The generator outputs 13.8 kV. The unit has been running stable for over a year since commissioning, but we recently had a G60 Undervoltage Alarm about one second after closing of 52G. I request assistance on what area to look at to understand the possible causes. I would have thought that the controls would have just opened the breaker back up instead of shutting the unit down.

Any and all assistance would be appreciated.

 

10_ac,

What have you done to try to understand and resolve the issue? AND, more importantly, what were the results of your troubleshooting?

Have you re-started the unit to FSNL (Full Speed-No Load) and checked the generator terminal voltage of all three phases? If so, what were the individual phase voltages?

Have you looked at the G60 Manual for information on how the undervoltage condition is detected? I presume it's done with the PT (Potential Transformer) inputs to the device, so that would be one place to check. Have you checked the PT fuses, secondary disconnects, etc.?

Here is a link to many manuals for the various G60 variants; we don't know which one you have.

https://www.gegridsolutions.com/app/ViewFiles.aspx?prod=g60&type=3

As for why it "shut the unit down", the G60 is a generator protection relay and a generator terminal undervoltage condition could be an indication of more serious problems (failed phase connections; internal short(s); etc.).

Sometimes the severity of the action taken when a fault is detected is also a function of the type of excitation system (brushed or brushless); and we don't know what type of excitation system is in use on the turbine at the site.

But, it would be best to start by understanding how the G60 relay detects an undervoltage condition, then working to make sure the sensing/inputs to the relay are all working and good and intact.

Hope this helps Please write back to let us know how you fare in your troubleshooting!

 

Dear CSA:

Thank you for your reply. They did a restart and the three phase voltages checked out 13.8 kV. As well as the PT fuses are fine. We confirmed the installed G60 Generator Management Relay is for 3.4X (rev. F4). The Alarm specifics are G3.LG60_27_AL and the subsequent SOE - M3425A Alarm: Undervoltage [PDIO_33Contact05]. From the manual, the possibilities are phase (27P), neutral (27TN) and auxiliary (27X). Operators are hesitant to close breaker without first knowing root cause. We do not yet have full, 100% 27TN incorporated; more at 96%.

We will keep looking.

Thank you in advance for your responses.