I have 4 GE MS9001E synchronized with the national grid and during the normal operation there was a frequency drop to 48 Hz at this moment the unit gave 154 mw although the baseload is 125 mw

was this load real generated mechanical power or just a disturbance due to grid voltage and frequency turbulence knowing that the gas control valve still fixed ?

 

sherif elzoghby,

The answer to your question lies in your description of "grid frequency turbulence."

Yes; the frequency probably dipped as low as 48 Hz (which is 96% of rated speed and frequency), and it was also probably not very stable as it was doing so.

It was most likely oscillating quite a lot during the frequency disturbance, which means the Speedtronic, if it was being operated at Base Load on exhaust temperature control at the time the frequency disturbance occurred, was trying just as "wildly" to try to keep the exhaust temperature as high as possible while not tripping the turbine on exhaust overtemperature. The fuel control valve was not "fixed" (unless FSR was being gagged (Manual FSR Control), and at the same time the gas control valve was moving the Stop-Ratio Valve was also moving--because the gas control valve was not stable AND because the turbine speed was not stable (because the frequency was not stable).

So a LOT of things were happening at the same time.

Now, if your site is like so many others, and it operates on Pre-Selected Load Control, sometimes with a setpoint higher than rated load, the unit was still on exhaust temperature control when the speed was fluctuating due to the frequency fluctuations, so the above is still true: the Speedtronic is trying to maximize exhaust temperature (per the CPD-biased exhaust temperature control curve) which means it's trying to put as much fuel into the machine as it can to make the actual exhaust temperature equal to the exhaust temperature control reference.

If this is happening when the frequency is increasing, then very high load swings can occur--which is most likely what happened at your site. Yes; it's real load, because there's a lot of fuel being put into the machine and when speed increases even more fuel can be put into the machine.

You really have to have a very high speed recorder to see the speed and load changes when the frequency changes. And, if it's "turbulent" then the load changes will be turbulent also, even if the machine was not operating on exhaust temperature control prior to the frequency fluctuations.

Because of the frequency excursions the turbine speed is also changing--just as much! And so will the fuel. It can be pretty scary sometimes. And, it's not good for the load coupling if it happens frequently.