Hi all.

It's about generator load fluctuation causing reverse power relay activation.

We are operating a combined cycle power plant. After synchro of our 1 gas turbine we load up it up to 100MW for steam synchronization. Suddenly in 60MW the load dropped immediately to zero and our gas turbine tripped with reverse power activation. What is the possible problem?

 

Hmmmm..... Let's think about this for a split-second.

What would make a unit suddenly lose load and trip on reverse power?

Could it be... Nah.

Maybe it's... Nah.

Perhaps... Nah.

Loss of fuel flow? YOU BET!

Load (power production) is directly proportional to fuel flow-rate. Increase the fuel flow-rate and the power output increases.

Decrease the fuel flow-rate and the power output decreases. Decrease it quickly enough and the power output decreases equally as quickly.

But, you didn't tell us what Process Alarms were annunciated during this event? If it's a Speedtronic turbine control panel it probably has Diagnostic Alarm capability, and if so, were there any Diagnostic Alarms?

What fuel was the unit running on? Gas fuel? Does the site use a gas compressor to raise gas pressure for operation? If so, did the gas compressor trip or go into recirculation mode causing the fuel flow-rate to decrease?

You really haven't given us much at all to help you. But, one thing you can be sure of: reduce the fuel flow-rate quickly enough for whatever reason and the load will go down equally quickly. If the fuel flow-rate is reduced sufficiently, the unit will lose flame, but it doesn't sound like that happened in this instance (though it might have come very close to flaming out, but we don't have enough data or information to know).

Some unit control systems have one or more "schemes" that either reduce load at some pre-programmed rate in response to some condition or even reduce load and open the generator breaker in response to some condition, leaving the unit running so that if the problem can be quickly resolved the breaker can be re-closed without having to go through a complete shutdown and re-start. Sometimes these types of events are caused by generator- or bus problems or even generator excitation system ("AVR") problems.

It's *extremley* unlikely that some kind of Process Alarm wasn't annunciated or generator/system protective relay flag wasn't set, unless the fuel flow-rate just suddenly dropped because of something like a failed gas compressor or something like that (again, we don't even know what fuel the unit was running on!).

In the future, you need to provide more information, like the fuel the unit was running on and any Process- or Diagnostic Alarms that were annunciated just prior to and immediately after the event. Some turbine control systems have the ability to look at some limited historical data for a few important, critical signals when a trip occurs (GE Speedtronic systems usually call this feature "Trip History" or "Trip Log", and it includes a list of alarms prior to and immediately after the trip event). Also, if there were no Process- or Diagnostic Alarms annunciated it's wise to look at the generator protective relays to see if any flags have been dropped or set; I've seen one or two relays which weren't configured to generate Process Alarms when operated. Also, since gas compressors aren't usually controlled by the turbine control system (except to start and stop them) it's wise to look at the gas compressor control system to see if it annunciated any alarms.

If it was a liquid fuel system, I've seen a slug of water and slugs of air cause similar problems.

But again, you haven't given us enough information to really help you. You will find that people who provide lots of information get the most concise, quickest and meaningful responses.

We also like to get feedback from our responses. Feedback helps others to know if the information provided was helpful, or completely off the mark. Lots of people use the very powerful 'Search' function here at control.com, which accepts multiple word searches as well or better than many Internet search engines used to, and feedback helps those people looking at older responses know if the information was helpful or not. Even if we don't provide the exact, correct answer or diagnosis or analysis if the information helps you to find the cause or resolve the problem it would be helpful to know what you determined or did to solve the problem in the end.

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So, let us know some details of the event, and then let us know what was determined to be the cause.