Frequency setpoint on island mode

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Anonymous

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 the line 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.
 
Did you try clicking on SPEED/LOAD RAISE when you were running in "island" mode? (That's really a poor way to describe frequency control; it's usually done with Isochronous control or some form of modified droop speed control.) If so, what happened?

The SPEED/LOAD RAISE and -LOWER buttons should NOT be disabled during "island" mode. It's just that when you click on them when running in "island" mode (it's still a less-than-desirable term!) you can't increase load--only speed/frequency.

Did you try selecting 52L and automatically synchronizing the unit and letting the Mark VI adjust the frequency for positive slip and close the breaker?

Bumpless synch would be with the synchroscope spinning extremely slowly, imperceptibly slowly. When the generator breaker closes when the speed is 100.3% there is a positive power flow out to the grid.

It is possible to close with the synch scope spinning slowly in the anti-clockwise direction, also. It's just that when the breaker closed, there would be negative power flow since the grid would increase the generator (and turbine) speed by "motorizing" the generator and power would flow into the generator instead of out of the generator. This doesn't hurt a combustion turbine, and many older hydro turbines are actually synchronized with negative slip.
 
We tried to increase the speed but nothing happened. Also we don't have buttons for increase/decrease of speed while in isochronous mode. Neither do we have island mode ON/OFF buttons. The breaker synchronized on a negative slip and that was the reason that the power output of the generator was low. We received the alarm Q 1273 ALM FSR LIMITED DUE TO DWATT XDUCER FAILURE caused by the GT remaining at lower than 2MW for 5 sec after synch on the 52L. For me it is missing logic from the Mark VI controller. Also the speed setpoint at isochronous operation is 100% (TNRI) with foxed command TNRI_CMD 100%. If it was 100,3% it would be better.
 
There aren't any special buttons for Isoch mode; the SPEED of SPEED/LOAD means speed when in Isoch mode (or when the generator breaker is open). If you found TNRI, you should be able to see that TNRI can be increased or decreased with L70R4R_CPB and L70R4L_CPB.

As soon as the breaker closed, you should have been able to raise load with the SPEED/LOAD RAISE button. The Mark VI will close with negative slip as long as it's within the window; it doesn't have to wait for positive slip.

"Island" mode is generally not operator selectable; it's usually automatically enabled and disabled by a contact from the line breaker.

Without being able to see your .m6b file, it's really difficult to say if something's missing or not.
 
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