GE 9fa Generator Control

S

Thread Starter

sriram surya

Our machine is GE 9fa with MkVie controller.

Generally when we are importing or exporting the Vars Generator Control is in Var Control. But when the Var setpoint is zero (not exporting or importing Vars from the grid), I observed the Generator Control changed to Voltage Control.

Does this Generator control changeover is automatic, if yes why its needed. Even though our Gas turbine have 3 controls (Var control, voltage control, Pf) all the time i observed generator control shifted to Var control when we are exporting or importing Vars to grid and if not its under voltage control.

To my knowledge from the posts in control.com i came to understand that Generator control in Pf mode leads to maximum efficiency (when PF=1 as setpoint)..Can anyone please clarify about this...

As well as we have GE D11 steam turbine where we have only pf/var control only but no voltage control available.And all the time both pf and var control are in enable condition. I was unable to understand one thing Pf setpoint is .8 and when we are exporting or importing vars that time Pf is almost near to 0.97 lagging or leading ...but never i have seen PF value reaching to .8 (i think its not desirable to reach even I know) but as both PF and Var control enabled at a time i was in a confusion.

Our Plant is configured into 3 blocks. Each block constitutes 2 Gas turbines with 2 HRSG's and one Common Steam turbine. Each Turbine has its own Generator with its own corresponding Generator Step up transformer. So..Total 9 Generators...(6 Gas turbine+ 3 Steam turbine).

Gas turbine having 52G as synchronizing breaker which lies b/w generator terminals and corresponding step up transformer..(52L all the time in close condition corresponding to Gas turbine), where as steam turbine having 52L (line breaker) as synchronizing breaker.

Generally Grid operators used to call us to increase or decrease Grid KV by 1 or 2 kv like that...So according to that we give var setpoint to each and every generator equally (sharing) almost....

To control the grid voltage we are adjusting the vars flow of all turbine generators producing power at that time...
 
sriram surya,

Without being able to examine the application code running in the Mark VIe of the turbines, it's very difficult to say what has been done or why.

I can say for the gas turbine, it's not generally typical that generator control automatically shift from VAr or PF control to voltage control when the VAr setpoint is at 0.0, but it IS typical that if the operator uses the VOLTAGE RAISE or -LOWER targets while VAr or PF control is active then that will cancel automatic VAr or PF control and the generator control will revert to voltage control.

So, if the operators are using the VOLTAGE RAISE and/or -LOWER targets to get the actual VArs to zero (unity PF; 1.0 PF) instead of setting a VAr setpoint of 0.0 then that's what's likely causing the cancellation of VAr control and the shift to voltage control.

Having said that, the GE engineering group in Belfort, France, now responsible for Frame 9s (E- and F-class) has been doing some atypical things of late, just because they can and because the deem, in their infinite wisdom, that it's okay to change long-standing GE-design heavy duty gas turbine operating practices and philosophies. So, again, without being able to see exactly what application code is running in the gas turbine Mark VIe's it's virtually impossible to say for sure what was done, or why.

Having said that, I frequently find when troubleshooting this kind of "problem" that during commissioning some manager or Customer's representative demanded that this kind of change be made (because that's the way they thought it should operate) and then that person either leaves the site or conveniently forgets they "requested" (demanded) the change be made once they learn it isn't operating they way it should and is causing problems now (even though they were advised back then what the consequences would be). So, this is another possible reason for what you are seeing, because it's not typical operation <i>based on the information provided.</i>

I am hearing more an more about GE steam turbine exciters not having voltage control.... Odd, but, then, most of the time at combined cycle plants the steam turbines are just "followers"--meaning that the control valves are usually left wide open and the steam turbine output "follows" the steam input (i.e., the gas turbine output dictates the steam turbine output) so it's conceivable the designers thought the steam turbine exciter controls should be similar (not require voltage control--which is "manual"--and just have automatic VAr or PF control).

It seems odd, though, because one would think that for troubleshooting or emergency purposes the steam turbine exciters should be capable of voltage control.... Again, I'm hearing of this more frequently, but haven't actually encountered it myself.

Power factor is a measure of the efficiency of the machine at converting electrical energy to watts--real power. When all of the generator's output is making watts--real power--then the power factor is 1.0, and the generator efficiency is 100% (meaning that the torque input is, for all intents and purposes, going into producing watts, which then get converted back into torque at the other end of the wires connected to the generator).

When the generator output is split between watts and VAr, and let's say the power factor is 0.95, then the generator is 95% efficient at converting the energy into watts--because some of the energy is going into VArs (which is imaginary power). That's the gist of what's happening--use your preferred Internet search engine to look up AC power factor and related terms and words and you will find much more detailed information.

Hope this helps!
 
Top