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Ratcheting problem in Gas Turbine
Shaft can't rotate when the jaw clutch is engaged but the input shaft rotates when disengaged from the gear box
1 out of 1 members thought this post was helpful...

We are operating a Frame 5 gas turbine, recently upgraded to mark VI E control.

When ratcheting is initiated, the shaft will not rotate rather you will hear an abnormal noise from the sequencing valve area. But when we manually disengage the jaw clutch everything seems to work well until the clutch is engaged again.

The pressure from 88-HR is about 65bar(it has been working well at this pressure before now or so I thought) though from manual it's operating pressure is about 80 bar. We are not experiencing leakages anywhere.

Could it be a problem from the gear box or clutch teeth? Could it be a pressure drop somewhere(where is the likely place to check)

Pls I will really appreciate your inputs.


1 out of 1 members thought this post was helpful...

The hydraulic ratchet pump motor is usually a DC motor, and the speed of the DC motor is proportional to the pump discharge pressure. There is often some kind of slide/wire resistor or potentiometer in the ratchet pump motor starter which can be used to adjust the current applied to the motor's field windings to adjust the speed. Check the speed of the motor, as well as the commutator brushes, which are often neglected in maintenance outage planning.

Also, the pump could be worn or failing.

If the problem is happening when the unit is at ambient temperature, it's likely something amiss with the hydraulic ratchet system; either the pump, pump motor, the self-sequencer, the jaw clutch limit switch adjustment, plugged filters, etc.

If you're trying to ratchet after a shutdown or trip and the shaft is hot, and hasn't been turned within 20-30 minutes or reaching zero speed; stop trying to turn the shaft by forcing the ratchet off while leaving the Aux. L.O. Pump running and just wait at least 24 hours for the axial compressor shaft to cool and straighten and then try ratcheting the unit again. If the shaft turns, ratchet for s few hours (3/4) and then start the unit in FIRE mode, and let the unit sit at low speed for approximately 30 minuets with flame in the combustion cans. Then select AUTO and the unit should go to FSNL.

It's not likely the problem is related to the Mark VIe upgrade, but it is possible.

Good luck, and please write back to let us know what you find!

You clean sequence valve INLET fillter.

1 out of 1 members thought this post was helpful...

I reckon that the strange noise that you are hearing is VR5 relieving (Is it a loud squealing noise?). Try removing VR5 and checking Its setting. If it is too low you will be short of operating pressure, from memory, it is set at around 90 Bar.