Ratchet fails to brake Frame-5 Gas Turbine


Thread Starter


Ratchet motor on cooldown ON fails to brake the Gt rotor.

The machine is GE Frame-5. we have put the machine on cooldown after completion of major inspection.

The control system is Mark-V. It is observed that L33HR is not able to pick up.

There have been tens of threads on control.com about GE-design heavy duty gas turbine ratchet troubles <b><i>breaking</i></b> the shaft away from zero speed. Most of them all have the same questions, and the same advice. control.com has a very cleverly hidden 'Search' feature at the far right edge of the Menu bar at the top of every control.com page. While not intuitive (use the 'Search' Help feature), it is fast and good--as long as you don't give up when the first result on the first search isn't exactly what you're looking for. As with any search engine when looking for information, sometimes it takes several searches using different terms and words to find exactly what you're looking for.

Presuming the turbine at your site uses the hydraulic ratchet self-sequencer mechanism, VH-14 (which you didn't tell us--there are several versions of ratcheting mechanisms in use on GE-design Frame 5 heavy duty gas turbines around the world), 33HR-1, which should be driving L33HRF, changes state at the END of a forward stroke, and then again at the END of a retraction stroke. L33HRF should be a logic "1" when the ratchet reaches the END of a forward stroke, and remain a logic "1" during the retraction stroke, and then change to a logic "0" at the END of the retraction stroke, and remain a logic "0" during the forward stroke.

So, if L33HR (or L33HRF) is not changing from a logic "0" to a logic "1" after some time then it would seem that something is preventing the hydraulic ratchet from reaching the end of a forward stroke--presuming the wiring between 33HR-1 and the Mark V is intact.

Have you located 33HR-1 and toggled it while observing L33HRF (or L33HR if that's the signal name in the Mark V at your site) to see if it changes state when 33HR-1 is toggled? If 33HR-1 is located on VH-14, it's usually a small limit switch actuated by a plunger that protrudes out of the mechanism. Do not try to push the plunger back up in to the mechanism if it's fully extended; the mechanism can be damaged. If the plunger is not extended (i.e., the limit switch is not actuated) then it should be possible to use a small screwdriver to actuate/de-actuate the limit switch, and observe logic state changes on the Mark V operator interface. If there is no change of state, then it's likely a wiring problem. Was the ratchet mechanism removed/replaced/refurbished during the maintenance outage?

One of the most common problems with hydraulic ratchet mechanisms after a maintenance outage is that VH-2, the manual hand-valve that controls the flow of hydraulic oil to the jaw clutch, is not in the proper position. Have you verified the position of VH-2?

You didn't say if the jaw clutch is engaged or not.

You didn't say if the clutch tried to rotate the shaft or not.

Another common problem with failures to rotate the shaft after a major outage are related to mechanical problems with reassembly. Sometimes, if new bearings are installed, they are too tight, or they were not properly aligned during installation. Sometimes, the alignment was not done correctly. Sometimes a wrench is left in the axial compressor and it is preventing the shaft from turning (yes; this has happened on more than one site and more than several occasions).

Unfortunately, there are almost never any pressure gauges installed in the hydraulic ratchet piping by the packager, or even by the operator--until there is a problem, and then the operators want to know what the pressures should be. That varies with different ratchet mechanisms, so it's difficult to say--without prior operating data taken from gauges installed <i>before a problem arose</i>--what the pressures should be for a particular turbine.

If the tubing for the ratchet mechanism was disturbed during the maintenance outage, was it bled of air at any time after it was reassembled?

The ratchet mechanism is not that complicated. Have a look at the 'Starting Means' P&ID (GE calls them Piping Schematic drawings). The sequencing is not usually very complicated either, and it doesn't usually change during a maintenance outage unless someone was modifying sequencing improperly.

Have you checked the current being drawn by the ratchet pump motor? It should be close to the motor's nameplate rating.

If the ratchet was working properly before the outage, it should be working properly after the outage. Either something is preventing the shaft from being rotated (mechanical issue), or VH-2 is not in the proper position, or the limit switch wiring is not correct, or there is air in the ratchet system tubing, or some dirt has caused a problem with the self-sequencer mechanism (not likely, but sometimes when things are disassembled and reassembled this does happen).

You also didn't tell us if the torque converter was removed/refurbished/replaced during the outage. There have been several refurbished torque converters of late (not refurbished by the OEM or an OEM-approved vendor!) which did not work properly and had to be returned to the refurbisher for repair. If the ratchet mechanism at your site is the type where the ratchet mechanism is integral to the torque converter, it usually doesn't just stop working if it wasn't disturbed--unless it's not getting pressure/flow from the self-sequencer/pump.

When writing for help, please provide as much information about the circumstances regarding the problem as possible. Please tell us what you've done to try to resolve the problem--and what the results were. Please tell us as much about the conditions leading up to the problem as possible (such as if the torque converter was replaced/refurbished during the outage). And, please tell us as much about the type of equipment at your site--again, there have been several types of ratchet mechanisms used on Frame 5s over the decades they have been produced, and Mark Vs were commonly used to upgrade older control systems, so it's possible your ratchet mechanism is not like others. We're not there; we can't see it--so the more information you can provide the more concise our responses can be.

Please write back to let us know how you fare in resolving the problem--and provide answers to the questions above if you need more assistance in resolving your problem.
You can check all switch/pump by yourself through different checking procedures, except "Hydraulic Sequencer".

So based on previous experiences replacing of hydraulic sequencer may rectify your problem. but it all depends on time availability to rectify this problem.