We have gas turbine. GE Frame 5 controlled by Speedtronic MKII. We have observed within 2 seconds sudden load drop from 7 MW to 2 MW, then it goes back to 7MW. this happens frequently every 10 min.

fuel pressure is 5 bar, and during interruption it vary between 6 and 3 bar.

 

meshal,

We would need a <b>LOT</b> more information to be of much help. But, rest assured: Load is directly proportional to fuel flow. Flow instability will cause load instability.

Your mission, should you choose to accept it, is to try to determine what inputs to the MIN SEL GATE might be causing the Speedtronic to want to reduce fuel flow by closing the fuel control valve or opening the liquid fuel bypass valve.

You say this is happening every 10 minutes or so. Is the fuel supply pressure increasing when the load drops, or is it decreasing when the load drops? An increase in fuel supply pressure could mean the Speedtronic is reducing fuel flow causing the supply pressure to increase. A decrease in fuel supply pressure could mean the Speedtronic is trying to increase fuel flow but there is insufficient pressure and/or flow capability because of some restriction (?) or other supply problem.

This can be difficult--determining whether the problem is caused by the Speedtronic or by the fuel supply system. We don't know what kind of fuel flow feedback is provided to the Speedtronic; it could be there is some intermittent problem with the sensor (speed pick-up; LVDT; etc.) or some problem with the card the fuel flow sensor is connected to.

Troubleshooting is a logical process of elimination. We don't know what you've done to try to troubleshoot the problem (we really don't even know what fuel is being burned!), nor do we know what the results of the troubleshooting efforts were. Help us to help you by anticipating the questions we might ask and letting us know what you've done and what the results of your efforts were.

There is some Mk II experience here on this site, but those systems are old and not very easy to troubleshoot (at least for people much more used to software tools and trends and data-gathering techniques).

Best of luck with your problem!