After working on accessory shaft of one of our gas turbines, on start up, the clutching system disengages after about 5 seconds of engaging and the cranking motor trips. Meanwhile the cranking motor breaker was racked out when the maintenance job was going on. I want to know what could possibly be the cause of this trouble? The magnetic speed pick-up was removed during the maintenance work and subsequently replaced. Our control system is GE mark V.

 

benjie,

You didn't say what machine you are working on....

What Process Alarm is annunciated when the jaw clutch disengages?

Are you certain the jaw clutch disengages and then the cranking motor breaker opens?

For a jaw clutch to open, no torque must be transmitted. So, that's one problem. When torque is being transmitted, the design of the jaw clutch teeth will hold the clutch halves together during starting.

Next, during starting the hydraulic ratchet is working to provide the "bump" necessary to break the shaft away from zero speed. And, if the unit doesn't break away during the forward stroke, it must go through a retraction stroke then go through another forward stroke. I'm thinking that the jaw clutch is opening when going into the retraction stroke. For this to happen, the starting clutch solenoid (20CS-1) must not be providing the force necessary to force the jaw clutch halves to stay together in the absence of torque from the cranking motor.

So, it looks like there are multiple problems--no torque is actually being transmitted, and the starting clutch solenoid isn't supplying the force necessary to keep the jaw clutch halves together in the absence of torque from the cranking motor/torque converter.

And, all of that is based on the presumption that the jaw clutch is opening, and then the cranking motor breaker is tripping/opening.