We are operating 2 Frame 6B machine only gas firing DLN1 mark V control. Torque converter E7WAT by Voith. After stopping ratcheting not taking place. Hydraulic pressure checked and found as per fluid flow diagram at 56 bar. (As per Voith it has to be 93 bar). We follow GE fluid flow diagram and was fine last 5 years. Last MI 1.5 years. After the ratchet issue 2 week before whole Control module including 20 CS were replaced filters were replaced. Still ratchet does not take place properly. If it goes it is not stopping till 88HR trips. Or else it is not moving. Machine was later started and is smooth with vibration 2 mm/sec. Still ratchet problem unresolved.

Can you throw some light with this information? Ready to share more if required.

 

I don't have a set of P&IDs at hand but check the VR in the Ratchet System and check the filter in the ratchet system. Running all the time means the ratchet is not making a forward stroke and therefore not initiating 33HR so it keeps running trying to make a forward stroke.

 

Desr Mr Bob,

Thank you for the prompt response. Filters already checked and replaced. VR also and is set as per setting in fluid flow diagram. Control module replaced.

 

Excellent suggestion about checking the relief valve by Bob Johnston.

You need to used the Starting Means P&ID to check/eliminate each of the elements in the piping/tubing system.

Have you measured the current drawn by 88HR during ratcheting?

Have you observed the rotor when the unit is trying to ratchet? What is happening--does the rotor turn at all?

The hydraulic ratchet sequence has been described in other threads on control.com. But the basics are thus:

1) When ratchet starts 20CS is energized to engage the jaw clutch halves or to be sure it remains engaged during ratcheting.

2) Assuming the ratchet was last stopped during a forward stroke, the forward stroke completes, at which time a high pressure is sensed which actuates 33HR to tell the Speedtronic the forward stroke has completed. There is a small plunger that extends out from the hydraulic ratchet self-sequencer to actuate 33HR. Are you sure the limit switch is adjusted properly? Have you monitored the pluger/33HR to see if the plunger extends outward and 33HR is actuated?

3) The hydraulic ratchet self-sequencer then switches the flow from 88HR to the retraction cylinder; 33HR remains actuated until the retraction stroke is completed, at which time a high pressure is again encountered and the hydraulic ratchet self-sequencer deactuates 33HR and switches the flow from 88HR to the forward cylinders.

4) When the Speedtronic sees 33HR go to zero (L33HRF, to be specific) it starts a short timer. This allows the forward stroke to start, engaging the jaw clutch teeth, and when the time expires the ratchet is de-energized until the three-minute period expires at which time the sequence starts over.

If 33HR isn't changing state, it's because either the forward stroke is not completing (possibly because the VR (Valve-Relief)) is passing. It's hard to understand how this would eventually lead to a trip of 88HR (probably on overload--which should be a process alarm on the Speedtronic). Have you observed L33HRF on the Speedtronic to see if it changes state at all? Have you tried jumpering or lifting the wires at 33HR to cause L33HRF to change state? It may be a simple wiring problem, or a problem with the contact input circuit of the Speedtronic.

Another possible scenario is that the forward stroke has completed, causing the high pressure which would lead to an 88HR overload--but 33HR is not being actuated, or the contact change of state is not being sensed by the Speedtronic. This would indicate a problem with the hydraulic ratchet self-sequencer, which does the change of flow based on high pressure when the stroke (forward and retraction) reach the end of travel. It's not clear if you replaced the self-sequencer; did you? (I think some self-sequencers include 20CS so you hay have.)

Clogged filters eventually rupture (there is NEVER differential pressure gauges installed across the filters (HINT; HINT) and when they rupture they pass a LOT of dirt through the self-sequencer.

Another possibility is that the ratchet mechanism is broken. But, that doesn't really explain how 88HR is tripping.

Please write back to let us know the answers to the questions, and what you find as you troubleshoot and resolve the issue.

 

The control module VH 14 itself was replaced. FH! was replaced, FH5 was cleaned. P&I if required shall be send in email.

 

A.K,

These two specific questions were asked at the top of the previous reply:

> Have you measured the current drawn by 88HR during ratcheting?

> Have you observed the rotor when the unit is trying to ratchet? What is happening--does the rotor turn at all?

While many people (most, actually) want to blame every problem on the Speedtronic, or on some control element (VH-14, for example) a LOT of problems can be traced to mechanical issues. So, that's why you were asked: Have you observed the rotor when the unit is trying to ratchet? And, have you measured 88HR current?

If the rotor doesn't turn at all, then it's likely something amiss with the ratchet mechanism. I recently learned of a unit that was experiencing similar issues, and the root cause was ultimately determined to be broken teeth on the forward stroke rack, and worn teeth on the gear.

Simply replacing components without verifying they are all working or not before replacing them (such as the plunger driving 33HR, and the discrete input monitoring 33HR's status) isn't going to solve a problem that is outside the component you replaced. If you are certain that VH-14 is working correctly after replacement (and it seems the original was also working correctly before replacement--since the problem has not been resolved by replacing VH-14) then all you have done is eliminate one possible cause of the problem: VH-14.

I have two more questions to add to the list of information being asked of your site:

Have you checked the brushes on the DC Hydraulic Ratchet Pump motor? What condition are they in?

What speed is the DC hydraulic ratchet pump motor operating at?

People at your site need to use the P&ID from your site to systematically eliminate each component--this is called troubleshooting. When your first couple of attempts at solving a problem don't, then one needs to step back and start proving each component is working correctly--until the one that isn't working correctly is found and the problem can be resolved.

Sure, people have had ratchet problems before, but NOT every ratchet problem is the same. We have suggested what has worked for others in the past; it seems your site is different. The great thing about control.com is that when new solutions are encountered to similar problems if the original poster writes back to tell us how the troubleshooting is progressing and when the problem is resolved and how it was resolved a great many people benefit from the thread. There is more than a decade's worth of GE-design heavy duty gas turbine control-related threads here on control.com, and lots of people use the Search feature (cleverly hidden at the far right of the Menu bar at the top of every control.com page) to search past threads for information and solutions.

When we ask for information, it's because we believe the information being asked for is relevant to the problem being discussed. Providing the answers to questions asked helps us to help you. The more information you can provide the more help we can provide. We realize that English is not everyone's native language, but we have helped a LOT of people for whom English is a second, or third, or fourth language here on control.com. So, please try to take a few minutes, read the replies, provide the requested information, and you will likely be very pleased with the results.

Lastly, I don't know if newer units still have a manual valve, VM2-2, in the hydraulic ratchet system, but this valve can easily be kicked or put into the wrong position. It doesn't usually result in tripping the 88HR motor, but it has caused a lot of grief for many sites over the years. (It's not well labeled; and it's usually under the jaw clutch, somewhere between the torque converter and the Access. Gear Box. You will know if your site has this valve if it appears on the Starting Means P&ID for your site. If it's not on the P&ID, I wouldn't bother looking for the valve. But if it is on the P&ID, finding this two-position valve handle and making sure it's in the right position is definitely worth the effort.)

 

Thank you for the prompt reply and support.

Informations available now is: Current drawn by 88HR during ratcheting was not measured. Normal ratcheting cycle was taking 40 seconds but here 88HR was running about110 seconds without movement and motor gets tripped. Afterwards when ratcheting is taking place (not consistent) it is smooth, and later when machine was put on cranking and on stop command costing down observed 12 minutes which is normal for our machine. Now machine is in line and max vibration is 2.5 mm/ sec.

VM2 was checked during the troubled cycle and found working without any passing. VR5 was checked and is set as per P&I.

 

It seems the problem is resolved.?.?.? You said:

> Afterwards when ratcheting is taking place (not consistent) it is smooth,...

Coast-down time is not related to hydraulic ratchet problems--unless there is a rub somewhere in the turbine that is causing the unit to coast down faster than normal, and then when the unit is at zero speed it is making ratchet operations very difficult....

The hydraulic ratchet pump motor is usually a DC motor. DC motors have brushes; brushes need maintenance, and eventual replacement. Also, DC contactors ("starters") need maintenance, and contacts may need to be replaced.

It seems the problem is inconsistent, and the problem description is unclear. If a turbine is "hot" (tripped or shut down from high load) and doesn't go on ratchet within about 20-30 minutes, the axial compressor can bow under it's own weight causing one or more of the rotating compressor blades to contact the compressor casing and making it very difficult for the ratchet to operate. When this happens, it's dangerous to keep trying to ratchet the machine--a compressor blade (or several) can be broken, causing serious damage and cost to repair, not to mention loss of generation.

And, usually when this happens (a trip or shutdown from high load and an inability to get the unit on ratchet within about 20-30 minutes) people rush out to the unit and open compartment doors which can cause the compressor casing to cool even faster than the rotor and exacerbate the rub even more. Even opening the turbine compartment doors when the unit goes on ratchet normally can cause accelerated compressor casing cooling and a rub which can prevent ratcheting. Leaving or turning the turbine compartment vent fan on during cooldown can also cause the same problem.

If the unit doesn't go on ratchet within 20-30 minutes, or if a rub develops that prevents ratcheting, best to just wait 24 hours. The axial compressor rotor, when it cools, will return to nearly straight--not exactly, but close enough that CRANKing or FIREing for a few minutes at low speeds will help to straighten the rotor and prevent high vibrations during acceleration to rated speed.

Again, it's not clear when this inability to ratchet is occurring. It's not clear if it starts right after the unit reaches zero speed; or if it occurs sometime after reaching zero speed. The conditions are unclear. But, if it occurs when the rotor is warm--the <b>BEST</b> to do is just to wait. Trying to "force" the rotor to turn if the axial compressor rotor has bowed can be disastrous. Patience is key, and prudent. I have seen people take hydraulic jacks and try to make the rotor move, and cause millions of USD (US Dollars) in damage by breaking one or more compressor blades (rotating and stationary).

Hope this helps! If you want more help, you're going to need to tell us much more about the conditions when the inability to ratchet occur:

1) Does it happen immediately when the unit reaches zero speed?

2) Does it happen sometime after the unit reaches zero speed?

3) Was the rotor hot (had the unit been running at high/Base Load for some time before being shutdown or tripped)?

4) Are the turbine or turbine/accessory compartment vent fans running during ratcheting/cooldown?

5) Are the turbine compartment doors open during this inability to ratchet?

6) What's different when the unit does ratchet successfully than when it doesn't?

It certainly seems as if you've checked to most obvious things. Troubleshooting is a logical progression of elimination. Sometimes, as has been noted in a recent post to control.com on hydrogen-cooled generator leaks, it's necessary to go back to an area/component that was previously checked (possibly not well enough).

Write back with more information and conditions (the answers to the above questions).