Dear all,
I'm newbie in this forum, hope this can solve my GT problem.

The problem is Gas turbine (said GT-1) Load hunting extremely, drop from Normal Load (8 MW) to 0.72MW in 1.8 second then back to 8.2MW, after 3 second load drop back to 0.6MW then back again to 8.3MW after that GT Load Normal for around 2 hour.

GT-1 operation in Droop Mode (Tie in with 3 other GT).

This Load Hunting effect to other GT (speed drop, caused by handle more load which release by GT-1). while Load Hunting, Exhaust temp. also indicate decrease (even only small amount, 365 decr. to 355 degC).

I analyze somethings happen in Fuel system (Bad fuel/Gas, Clogging in Nozzle or else), I still can't find what is the caused of our hunting problem.

Does any one has experience for this problem??

What point can make Load hunting so extreme in Very short time, because interlock trip for Generator breaker not yet touched (No Alarm Indication for This Problem.

Please help me.
Thanks for your help and support.

 

It will help on suggesting you some solution if you may provide some detail on the system overall installation.

As this stage I can suggest you check the load sharing line if there is any loose connection.

What is the behaviour if you put this turbine on load alone?

Check the fuel signal from control panel?

Hope it will help.

Regards,
Asif-KSA

 

Check your fuel control valve or its servo, one of them is most probably sticking. You can confirm this by observing the signal going to this valve. If the signal is going bang-bang, i.e. from one extreme to another, and at the same time the fuel valve is doing the same but delayed (i.e. signal goes to close, but valve is fully open, then all of a sudden valve closes, at which point signal goes to fully open), then something somewhere is sticking.

I would rule out fuel quality (unless you are pumping in a mixture of fuel and water) and nozzle clogging. These normally create different problems.

However I would check the quality of the lube oil, if this is used to operate the servo. If the lube oil is degrading, you can get gumming inside the servo spool, causing it to stick.

You could also have a worn servo valve, sticking at one place.

The fact that the GT settles after some time indicates that the sticking unit then settles at one position which is close to what the control system is requesting.

By the way does the hunting occur also before synchronisation (i.e. causing troublesome synchronisation) or at higher loads, or just at loads close to 8MW?

 

Pl.check if the hunting in frequency is periodic or is this just after synchronizing? If the hunting persists, then there is problem with the nozzles in the control valve or with the governor. The characteristics of the governor might have changed with long period of use. As this GT is running in parallel with 3 more GTs, hence any load fluctuation in one GT will inversely affect the load on the other GTs. Hope your problem can be sorted out.

If successful do contact.
Bye.

 

thanks alot for response,
i'm glad to provide detail data and trending, but i dont know how to attach to this forum, sorry i'm new w/ this forum.

your suggest (Load Sharing System) already include in our next GT shutdown progress. FYI, Our GT must be planned to our Managemant to Shutdown.

This GT also Already Stand Alone Tested for only 2hour and result stable. Because of our Managenment rules, Our GT must Tie In Load.

This Problem Happen Intermittent. this month only occurs one time, and load only hunting around 1MW (MW Setpoint = 7MW).

regard,
harry-pusri

 

Thanks for quick response.

I Already Check and Replace Both Servo Valve(SRV and GCV), but the problem still exist (intermittently). I check the existing servo valve, no sludge or clogging in micro filter. After that we do Manual Stroking Valve before Start, and result no Sticky Valve (good travel).

I think i could be better if i Provide Data Trending in this Thread, but i'm still don't know how to put it. Please guide me.

Our team also analyze, Bad Fuel Quality would not effect extreme Load Hunting (just little bit)and our Gas Fuel supply has a Gas Heater System before supply to All GT. Nozzle Clogging can be ruled out too, because GT has 18 nozzle.

we cannot do testing Stand Alone GT Running more than 1 day, it's depend on our management rules. but we already tested it for 2 hour, and result stable (4MW). This month this problem only occurs 1 time, and only 1 MW hunting. This is happen Intermittent.

regard,
harry-Pusri

 

It has been witnessed that abnormal rise/decay in frequency and voltage (mostly frequency) has an inverse effect on the generator loading.

I have witnessed machine coming to 4 MW from 30 MW and this has been only one of case and has not got repeated even in the entire year. The df/dt setting in the governor if exceeded, could result in load drop/rise and the severity is directly proportional to the changes in grid frequency.

But this can also be due to servo valve sticking for which parameters like FQR, FOROUT, FQL1 need to be monitored.