Wanted to share a recent experience that I had in troubleshooting ratchet mechanism of our 20 MW frame V Gas Turbine
Problems :
1. Jaw clutch failed to engage.
2. Forward stroke not achieved.
Observations :
1. Ratchet pump motor pressure was found to be 64 bar
2. No pressure in FS port of ratchet mechanism.
3. Low pressure in VM2 inlet.
Troubleshooting steps taken :
1. VR2 setting checked and was found to be at 70 bar.
2. FH1 filter cleaned and reinstalled
3. FH5 filter cleaned and reinstalled
4. 2.3 mm dia orifice cleaned and reinstalled
5. Operation of 20 CS was checked by forcing it from Control system and tested using the test point in the SOV. The test point went inside and got stuck when 125 DC was supplied and was released on cutting the supply off.
These steps didn't resolve the issue.
6. Further self sequencing valve was replaced. It was of no help.
7. 33 HR operation was checked and found OK.
8. 33 CSE was also checked and found OK.

Even after the above steps no improvement was found in the oil pressure to VM2 and FS. However, pressure was found to be around 64 bar after FH1 and the inlet tube to 20 CS got heated up with the ratchet pump motor in operation.

*20 CS was dismounted and it's operation was checked. The plunger inside the valve didn't move on applying 125 DC from the control system but the test point was energised and no ground fault was detected in the control system.
*20 CS was energised by providing external 125 VDC, the plunger now moved. Negative leg was found to be faulty and was replaced with a different negative leg.
*20 CS was remounted and ratchet pump motor was re-started.

**Jaw clutch got engaged and forward stroke achieved.

 

@Ankur1007,

What control system is being used for this Frame 5 GE-design heavy duty gas turbine? How "young" is this Frame 5 GE-design heavy duty gas turbine?

When did this problem start? After a maintenance outage where some electrical work was done in the Accessory Compartment or in one of the main JBs?

When you say the "...negative leg was found to be faulty..." precisely what do you mean by that?

Do you mean the negative lead between the nearest junction box and 20CS was not passing any current--either because the crimp terminals were bad or the wire had somehow disintegrated or the screws of the terminal blocks at either end of the wire were not properly tightened?

Or do you mean the negative lead from the turbine control system to the main JB (JB1 or JB2, I can't recall) was incapable of providing the proper current (loose crimps/terminals; disintegrating wire; etc.)?

How exactly did you "replace" negative leg?

Thanks for your clarifications!

 

@Ankur1007,

What control system is being used for this Frame 5 GE-design heavy duty gas turbine? How "young" is this Frame 5 GE-design heavy duty gas turbine?

When did this problem start? After a maintenance outage where some electrical work was done in the Accessory Compartment or in one of the main JBs?

When you say the "...negative leg was found to be faulty..." precisely what do you mean by that?

Do you mean the negative lead between the nearest junction box and 20CS was not passing any current--either because the crimp terminals were bad or the wire had somehow disintegrated or the screws of the terminal blocks at either end of the wire were not properly tightened?

Or do you mean the negative lead from the turbine control system to the main JB (JB1 or JB2, I can't recall) was incapable of providing the proper current (loose crimps/terminals; disintegrating wire; etc.)?

How exactly did you "replace" negative leg?

Thanks for your clarifications!

Thank you for the engagement!!
We are using Mark Vie Control System for our frame V Gas Turbine which is 30 years young.
The problem occured suddenly where no electrical work was involved.
By a faulty negative leg I meant that the negative leg was unable to throw the required current as there were insulation breakdown on the leg from the JB to 20 CS.
I replaced the negative leg by providing alternative negative path from the nearby negative loop of 20 DA1 as we are using 2.5 sq mm copper control cables and the current drawn by the both the devices is only 0.3 Amps. each.