I my plant we have take shut down of gas turbine 6B after that turbine came to zero speed and cool down started and had four cycles only after that we came alarm of ratchet trouble again after we checked 20cs find ok and we waited for wheel Space temp 100 deg upto then we kept running aop continuouly and again we manually jogged but 88HR pump developing pressure 90kg/cm2 we checked any leakages found no at that lube oil header temp ltth 54deg and again when wheelspace temp reaches 36 deg we manually and that time ratchet happens at that llth is 27deg and we observed that cycle is time is more in forward stroke aprrrox cycle time take 40 sec and slowly it got decrease.can u explain the reason.(while ratchet is not happening that time we have checked current of 88HR found 9amps but its flc is 6amps).we found 88HR function by disengage the clutch it found ok.

 

Khan007,

Anything in this post catch your eye?

https://control.com/forums/threads/gas-turbine-ratcheting-issue.49222/

Communication is key.

So is reading other posts on Control.com for information!

 

Khan007,

I have re-read your post several times, and I just can't get the idea of what you're trying to convey--or why you're interested in wheelspace temperatures.

I have seen many GE-design Frame 6B heavy duty gas turbines which have, shortly after reaching zero speed after a shutdown or trip, which could not be turned with the ratchet mechanism. USUALLY, this happens for one of two reasons. Either someone has gone and opened the turbine compartment doors, and/or they have also manually turned on the turbine compartment vent fan(s). Both of these actions will almost always result in accelerated cooling of the axial compressor casing causing the axial compressor rotor blades to catch on the compressor casing and the ratchet mechanism cannot then turn the rotor. When this happens (as described) the DC hydraulic ratchet motor runs continuously--which is not good for the motor, or the hydraulic ratchet system (tubing and fittings and filters and pistons). (Actually, there was a period back in the 1980s where the GE factory personnel actually programmed the turbine compartment vent fan to run during initial cooldown operation, and if the ambient conditions were cold enough this caused the rapid cooling of the axial compressor casing which resulted in a failure of the ratchet to be able to rotate the shaft. This was reported to the GE factory engineers, and this practice was stopped.)

When this problem occurs, the Process Alarm RATCHET TROUBLE will be annunciated and will continue to be annunciated until the ratchet sequence finally completes a full cycle--and, again, all the while the DC ratchet pump motor will be running which is not good. In this case, the best thing to do is to: 1) make sure the Aux. L.O. Pump runs continuously (to supply cooling oil flow to the bearings); 2), force the ratchet mechanism off (by forcing COOLDOWN OFF); 3), closing the turbine compartment doors and shutting off the turbine compartment vent fan(s); and, 4) waiting for the hottest wheelspace temperature to drop below approximately 200 deg F before attempting to re-start COOLDOWN (ratcheting operation). This can take as long as 24 hours depending on ambient conditions--but I can assure you, if you try to force ratcheting using hydraulic rams and/or levers you WILL damage something, something very expensive, and it will take a LONG time to take the machine apart and repair it and put it back together and there will be a lot of lost generation and revenue in the process.

I understand that English is probably not your primary language, but it is very difficult to understand the sequence of events occurring at your site from your (and samba.auce's) descriptions. This topic of what to do if a hot turbine/axial compressor is unable to stay on cooldown has been covered MANY times before on Control.com--suffice it to say that patience is king. Keep the Aux. L.O. Pump running (again to supply cooling oil flow to the bearings), and just be patient. 24 hours is a short time compared to the time it can cost to repair the damage done to a machine by trying to force the rotor to turn (which can be months and cost hundreds of thousands of US dollars never mind the lost generation and revenue).

Anyway, best of luck. If you can be more specific, we might be able to help you. But, using the P&ID drawings and working through all of the components (the ones that can be seen--if the torque converter is a Twin-Disc make you will probably not be able to see the ratchet pistons inside the housing to see if they are leaking or not) is the best way to get to the root cause of a problem such as this. Remember, also, that torque converters and ratchet mechanisms do require maintenance and refurbishment over time; if the equipment has never been examined or refurbished, it is probably a good idea to do so sooner rather than later. As do jaw clutches--which are often damaged by forcing flying re-starts (pictures and/or video of the jaw clutch can be attached to threads in Control.com so others can see the equipment--it can be VERY helpful and informative).