GE Gas Turbine Trip on Generator Lockout Relay 86G-1

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Thread Starter

Reoji

Hi all,

I'm new with this gas turbine control system. yesterday our unit trip and the alarm generated was Generator Lockout Relay 86G-1, Generator breaker trip, and Generator Transformer feeder Fault trip and also found that at the unit ATG panel showing No.6 Generator Diff. trip.

We were able to reset the alarm and normalized everything, and currently the unit is running. We however have yet to understand why the tripping happened and means of preventing it.

any help or advice on it is very much appreciated.

Thank You
 
Reoji,

What was happening at the time the trip was initiated? Was the grid stable, or unstable? Was the generator load stable or unstable? Was the frequency stable or unstable? Was there some lightning strike or other weather-related event occurring at the time of the trip?

A lock-out relay is a device that's designed to prevent operation of a unit until such time as the cause of the trip is determined and understood, and then it has to be manually reset in order to allow a re-start.

An 86G lock-out relay is a device that's typically actuated by several other protective relays monitoring the operation of the generator, such as differential current protection, possibly generator neutral ground protection, etc. These different protections are in place to protect against faults that can cause very serious damage to the generator (in this case, since we're referring to the 86G lock-out relay which is related to the generator).

There should be an electrical schematic drawing that shows the various devices which will actuate the 86G lock-out relay when they detect a fault. Each device usually has its own "flag" to indicate the device which actuated the lock-out relay. (I'm referring to generator protective relays which are individual devices for each parameter (such as over current, differential current, etc.); newer protective relays are all-in-one electronic devices which can detect tens of fault conditions and will provide some indication on the front display of which fault was detected and actuated the lock-out relay. We don't know which type of generator protection scheme is used for the unit at your site.)

Resetting a lock-out relay without understanding the reason why it was actuated is not recommended (although it happens far too often). In decades past, a lock-out relay could not be reset without the signature of an authorized individual who had reviewed the fault which was detected and could provide assurance that the generator in good condition and was not in danger should it be re-started.

The various protective devices (or the all-in-one device) uses PT (Potential (Voltage) Transformer) and CT (Current Transformer) inputs to detect potential or actual faults and then actuate the lock-out relay. It's important to be certain that all of the PT and CT circuits are all properly working and connected and providing the necessary signals to the protective device(s).

So, in order to reset the 86G-1 lock-out relay it was likely necessary to reset one or more protective relays--hopefully you wrote down in the Operations Log which relay(s) had to be reset in order to be able to reset the 86G lock-out relay. Under ideal conditions, a knowledgeable person would review the relay(s) to ascertain what condition was detected and then do some investigation to determine if any damage had occurred as a result of the fault, or if something was amiss with the inputs to the relay which may have caused a false indication, etc. This would ensure the generator was not damaged, and that it could be re-started with a high degree of certainty that a true fault condition would actually be detected and the unit tripped to protect against catastrophic failure.
 
CSA,

Thanks for the reply, for your info the condition of the weather was fine and the was no report on interference from outside or GRID disturbance.

Prior to the trip the unit was generating was generating 16MW out of 31MW. System Freq was at 50.1 drop to 49.9 after tripping.
Trip log record the following:<pre>
Time  DWATT DVAR DV DF DPF
22:36:26 15.8 6.2 11.03 50.04 0.932
22:36:27 15.7 6.1 11.03 50.03 0.930
22:36:28 5.2 2.4 10.99 50.4 0.888
22:36:29 -12.5 -75 10.59 50.25 1.000
22.36:30 -12.5 -75 10.99 49.91 1.000

Alarm S P DROP Description
22:36:27:593 1 Q 0196 Generator Lockout Relay 86G-1 Trip
22:36:27:718 1 Q 0197 Generator Breaker Trip
22:36:27:718 1 Q 0399 Generator Transformer Feeder Fault Trip</pre>
The unit is connected to a step up transformer 11/33kV and to a 33kV bus bar(AB1). There is no outgoing feeder connected to the bus bar and there is bus section which connected it to another bus bar (AB2). Both breakers after trip during the incident causing black start engine to start and supply power for aux..

We manage to reset all alarm and the unit currently has been operating for almost 3 days without problem cross finger if the problem to re-occurred.
 
Reoji,

If you recorded all of the relays and devices you had to reset in order to be able to re-start the machine, can you list them here? Even if you didn't understand what the root cause of the trip was at the time--if something similar occurs again having this information can be helpful to troubleshooting and understanding the problem. This is fundamental to troubleshooting and understanding operation.

I suggest you locate and study the generator breaker close circuit. If the unit was packaged and provided by GE, there is usually a set of electrical schematics for the Generator Protection Panel (sometimes called the Generator Control Panel), and because that's usually where the generator protective devices are located, including the lock-out relay(s) you'll usually find the drawing for at least the lock-out relay and what devices actuate the lock-out relay.

The generator breaker can be located in several different places, and if GE provided the breaker and enclosure you will likely find the generator breaker trip (and close) circuits on two separate pages of this electrical schematic. You should see a pair of contacts from the 86G-1 in the generator breaker trip circuit to energize the breaker trip coil to open the breaker, and usually, there's also a set of contacts from 86G-1 in the generator breaker close circuit which will prevent closure of the generator breaker until the lock-out relay has been reset.

But, keeping track of all of the protective devices that were reset is critical to being able to establish--if the lock-out relay operates again--if it was the same device(s) that operated to actuate the lock-out relay, or if different device(s) operated to actuate the lock-out relay.

Again, there are usually several generator protective devices/functions that can trip the 86G-1 lock-out relay. While some may also annunciate an alarm in the turbine control panel some do not. And, every installation is different--so we can't tell you what devices/functions can actuate 86G-1 at your site. Only the electrical schematics for your site can tell you that (and we can't see those).

Even if we can't help you here via control.com, if the same or similar trip occurs in the future then having the information from this most recent trip will help whoever comes to help in the future. And we all hope it's not after a serious generator failure, in which case the information from this most recent event would still be helpful in determining the cause(s).
 
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