VC3 hunting of GE MS9001E Gas Turbine During Startup

The reason of the issue was remained unknown for 8 years and we were troubling with the hunting of VC3 during start-up. Interesting thing is this that this issue was not continuous but observed in almost every third start-up. Up-to 2900 RPMs the machine starts-up very smoothly but after this speed or during the synchronisation; VC3 starts hunting and the machine gets tripped. Sometimes the hunting starts before 1500 RPMs.

To rectify the problem; we charged N2 pressure in the fuel oil accumulator's bladder (Problem did not solve), replaced the inlet filter of VC3 servo-valve (Problem did not solve), replaced the main hydraulic oil filter (Problem did not solve), again performed the fuel oil priming (Problem did not solve), increased the pressure of fuel oil through PCV-355 up-to 0.3 bar above the normal operating pressure (Problem did not solve); this thing worked 1 time before, replaced the VC3 servo-valves (Problem did not solve). Previously, several times when we replaced the VC3 valve using same actuator; the turbine started but this was not meant to be solution because this time even we replace the VC3 the problem did not solve.

The hunting problem completely solved when we increased the spring tension of VC3. I recommend to increase the tension of VC3 actuator spring up-to 3mm from its spring free position, if the start-up and working of VC3 is smooth then it is better or other increase the tension up-to 5mm.

My taking this measure the hunting problem have not appeared yet.

All the Best