Frequency setpoint on island mode 2

[npower0073]

On site we have a GE generator with Mark VI control system. The logic has the island mode scheme, when there is a load rejection somewhere upstream to the grid the turbine increases speed with a specific acceleration and when this happens the turbne goes to island mode supplying the auxiliaries of the plant. During the island mode operation the gas turbine keeps constant speed and the generator runs at 49.94 Hz, slightly lower than the 50Hz of the grid. The auto synch function of th eline breaker (52L) did not work becasue the synch scope rotated counter-clockwise and there is no facility to increase the frequnecy by increasing the gas through SRV. Can you advise on this issue? GE was made aware but with no actual work on that item. When you synchronize to the 52G breaker the turbine runs at 100.3% of nominal speed so the generator is alwways higher than the grid in order to have bumpless synch.

 

[byrdj]

I'm not familiar with CT controls at all, But wouldn't you need to transfer out of island mode BEFORE trying to close back on a grid?

 

[npower0073]

Unfortunately we don't have the buttons ISLAND mode ON/OFF and SPEED INCREASE/DECREASE. There is missing logic on the Mark VI.

 

[byrdj]

If you can not get the support from GE, have you considered a consulting company (usually very experainced ex-GE employees)

 

[ScottyUK]

A couple of possible leads...

Trans-Canada Turbines
TC Power

I've no connection either of them but they both do a lot work on GE aeroderivatives. Maybe worth an email or phone call.


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Sometimes I only open my mouth to swap feet...

 

[byrdj]

another possibility

http://www.pondlucier.com

 

[byrdj]

Again, I'm not familiar with M-IV or CTs.
But a thought-
If the rated speed referance is a non adjustable referance. then couldn't the calibration of the speed pickups be trimmed to provide the desired frequency (50.00?) when in isoc. This is the technique I use on one of the early Mark ST controls

 

[ScottyUK]

If the speed reference is non-adjustable then what does the synchroniser use? Luck? A grid-paralleling unit with a fixed speed governor seems incredible.


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Sometimes I only open my mouth to swap feet...

 

[byrdj]

Again, I'm only familair with ST controls.

In "droop", increase (or decreased) LOAD referance will result in a speed change to allow you to synch

Off subject I was in one country where the speed pulse to auto synch was removed since the grid swings were so bad and Yes, it was luck.

 

[abeltio]

byrdj is absolutely right.

You need to transfer out of isochronous mode to droop before synchronizing 52L

If the unit is under warranty, just send a warranty claim. If the unit is not under warranty, call your service manager.

saludos.
a.

 

[npower0073]

Unfortunately we dont have the buttons to take the unit from island mode to droop mode and GE is still struggling on that one, with their arrorant approach, so typical for GE. The unit is under warranty.

 

[npower0073]

Scotty UK, the suncronizer can work only in MANUAL MODE when you try to synch on the line breaker (52L). It worked on MANUAL BUT:
When the breaker closed we received the alarm
Q 1273 ALM FSR LIMITED DUE TO DWATT XDUCER FAILURE.
The output of GT remained lower than 2 MW 5sec after synch.
Also after the synch GT stayed to almost 0 output but with steady FSR (19%) and exhaust mass flow. That probably means that the generator synchronized with wrong angle because in order to have power transfer between two networks the voltage angle difference should be higher than 0, with the generator vector to lead the grid vector. Tell me if this is a correct explanation.

 

[byrdj]

If you have the resources to get a consultant, why not try PAL. If you visited their website, they show modifications to add island mode to the early Marks.

Again, not GT familair, But if the unit is slow freq in island, that might be the speed pick up translator is mis calibrated with too high output. Now when you synch in droop, the miscalibrated higher speed referance is negating the minimun load referace and you stayed at zero load. Just my wild a$$ guess.

 

[abeltio]

If the unit is under warranty, you cannot touch it, it will void the warranty.

The problem you are facing is one of oversight during the engineering.

One temporary solution would be to force out the signal that picks up isochronous mode as well as the latch that keeps isoch selected... the unit will default to droop

In the meantime, where are you located? May be it is just a matter of who you know and not what you know...

This seems like a very straightforward problem.



saludos.
a.

 

[ScottyUK]

Does your manual synchroniser still feed in to the turbine controller? I guess it must. How manual is 'manual'? Our LM6000 uses a Woodward controller so my limited understanding of that controller is of no use to you, but the synchroniser is tied into the Woodward governor controller.

I'm not sure what 'FSR' is an abbreviation for, but a technique we use on bigger Westinghouse turbines is to apply a small step of a couple percent in throttle position immediately on breaker closure. This ensures that the unit immediately takes up load and avoids the problem where the MW transducer reading goes bad. Incidentally, it is worthwhile ranging your MW transducers to ensure the data remains of a 'good' quality even if they go slightly negative. It stops annoying problems when the machine has a slightly rough sync and oscillates a little as it finds its load angle.

I am aware of problems with turbine pressure transmitters upsetting the control scheme on our LM6000 by preventing the throttle demand increasing. Not my area of expertise, but I will ask around for a little more info if I remember.


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Sometimes I only open my mouth to swap feet...