we have gas turbine MS5001-MARK II-TP. when shutdown gas turbine, speed not reduce more than 80%. only by emergency stop can reduce speed. came this problem without any alarm.

we did annual maintenance for this turbine in last year Jan.
you can tell me any reason for this problem?

 

GE Speedtronic turbine control panels used several shutdown fuel control schemes, anything from just shutting off the fuel at around 95% speed to a controlled ramping down of fuel to lower speeds.

If this panel uses the latter, then something is wrong with either the fuel valves or the calibration of LVDTs on the fuel valve (gas fuel), or something like this that is causing more fuel to be flowing than was previously flowing.

If the fuel make-up has changed recently (higher heat content) this could also be causing the problem.

Please write back to let us know how you resolve this problem.

 

Also, what type of 5001 is this? Since you say it goes down to 80% speed, I am inclined to believe it may be a 5001R rather than a 5001P, and maybe a mechanical drive rather than a generator drive.
And, as CSA asked, when it worked correctly, did it remained fired until a lower speed (typically, 40 to 60%)?