Hello,

This is case for CSA or Bob Johnston or similar level.

Our unit is not running at all and we have hired dryers for long term singleshaft preservation.

While forcing all the signals to have steam valves open, we noticed if we stop turning gear when unit reaches zero speed valves close immediately. I think all comes from TREG bypassing the logic. all this happens from the output of the TREG card. We were thinking about bringing straight the positive to the trip solenoids bypassing the relays at the card, but there are some resistors in the card so I did not want to do it because of fear harming the solenoids.

Have you done something similar previously in a MkVI? What is your opinion?

Any other solution proposed?

Thank you in advance.
Regards.

 

To add some more info. Signals forced are:

- lfy5040t (IGVs trip solenoid) and l4_XTP on the GT controller.

- l20PTR1 and 2 (ST hydraulic module trip solenoids) in the ST controller and L4_XTP in the ST controller.

- AO's cv1_out, iv1_out, iv2_out, acv_out reference to 100%

Why when we reach 0 speed ST control and stop valves go closed? At TG speed or 0 speed no issue,it is only when we reach 0 speed.

Any idea?

Thank you.

 

Javier,

I, personally, have no experience with this method of preservation, or with a request for prolonged opening of steam valves.

I am surprised that when the unit reaches zero speed the ETRs on the TREG drop out; it must be some single shaft-specific configuration that is done in Toolbox is all that I can think of. In the Mark V there was a signal, L97HP0T_BYP if I recall correctly, that had to be a logic "1" to be able to pick up the ETRs when forcing L4_XTP to a logic "0" when the unit was at zero speed. I'm guessing something similar is also done in the Mark VI, but that's just a guess.

It would also seem odd to me if the unit has to be on turning gear (NOT at zero speed) to calibrate LVDTs (fuel valves; IGVs; steam valves).

If the IGVs are operated by a separate hydraulic system from the steam valves, one trick I use to keep the IGVs open when shutting off the hydraulics is to keep L20TV1X forced to a logic "1" after shutting off the Aux. Hyd. Pump. Then, it's necessary to go to the Hydraulic Accumulator and open the drain valve to bleed off hydraulic pressure (it will otherwise take several minutes or longer for the hydraulic pressure to dissipate). Once the hydraulic pressure is zero, the IGV solenoid can be de-energized. The trick is to remember to close the Hydraulic Accumulator drain valve!

The steam valves, on the other hand, would seem to be a real problem. It's likely there are very large springs on the steam valves to close them when hydraulic pressure is lost, so how are you going to keep the steam valves open when hydraulic pressure is lost if they are closed by springs?

If they are not closed by springs, then would it be possible to do something similar to what was described for the IGVs above? In other words, with the valves opened under hydraulic pressure, just remove the hydraulic pressure by whatever means is possible (shutting off the Hydraulic Pump, and either letting hydraulic pressure dissipate or using some method similar to opening the drain valve on the Hydraulic Accumulator).

That's about all I can think of without being able to review the configuration of the Speedtronic turbine controls at your site.

Hope this helps!

[NOTE: The 0 in L97HP0T_BYP is a zero, not a capital "O".]

 

Thanks CSA.

How can I attach documents to the post? I would like to add m6bs (both).

This only happens when unit reaches 0 speed, only at that exact moment, if unit is at 4 rpm no issue, if the unit is stopped no issue, that is why no issue while doing calibrations as unit is usually stopped already when calibrating.

I am thinking several things but would like yor opinion:

- There is a BYPASS signal used in the GT m6b but not used in the ST. Should I enable temporarily the bypass in the ST controller and force both to 1??

- Another solution I thought is disable temporarily 14HE_ZE and see if it works. My fear is that P core is tripping trip solenoids even if they are forced, they loose the positive leg and solenoids loose voltage.

- As you say steam valves are big, don´t have accumulators locally. There are three accumulators in the skid, not sure closing the drain would work.Why would you open the drain valves for? I guess you want to maintain the hydraulic pressure through the accumulators.

- The last solution is to bring the positive leg to the trip solenoids but there are some resistors in the middle.That is my last preferred option.

Where could I send you the m6bs?

Thank you.
Regards.

 

Javier,

It's not
Possible to include attachments to control.com posts because of unscrupulous people who would embed viruses and malware in the attachments. Many people post files to web hosting services such tinypic.com or speedyshare.com.

As for me, I don't have Toolbox any longer so I wouldn't be able to view the file, but somebody else may be able to.

Regarding opening the accumulator drain valve, that would be necessary on the GT IGVs if one wanted to stop the Aux. Hyd. pump and de-energize 20TV-1 and keep the IGVs from closing. When the Aux. Hyd. Pump is de-energized it will take some time for hydraulic pressure to bleed down. If one de-energizes 20TV-1 while hydraulic pressure is still present the IGVs will close--even if the position reference is 90 DGA. So, before de-energizing 20TV-1 after stopping the Aux. Hyd. Pump it's necessary to <b>either</b> wait for the hydraulic pressure to go to zero (which can take several minutes or more) <b>or</b> open the drain valve on the Hydraulic Accumulator to quickly relieve the hydraulic pressure.

No matter what one decides to do to keep the IGVs open without Hydraulic Pressure <b>it MUST BE REMEMBERED that as soon as hydraulic pressure is re-established the IGVs will close--very quickly--so all personnel must be aware of the danger involved. </b>It would be best if the Aux. Hyd. pump(s) were locked out as long as the IGVs are to be open using this method, and that someone was stationed at the IGVs the first time the Hyd. Pump is re-started to prevent anyone from being injured by a moving IGV actuator ring or moving IGVs.

Without being able to see the P&IDs for the ST it's not possible to say how it would be possible to keep steam valves open without hydraulic pressure (it's presumed that it's not desired to keep the hydraulic pump(s) running during the layup period).

Best of luck with your plans and layup.

Again, I no longer have a copy of Toolbox and even if I did it probably wouldn't be the same version in use at your site. So, there's no point in sending me the .m6b files.