"Our power plant is a facility that has been operational for nearly 20 years. The gas turbine is a GE-produced PG9171E model, and the control system in place is the Mark V system. I have recently taken over the maintenance of this plant as the previous maintenance personnel have left. We are planning to perform a shutdown and water wash after some time. During the unit shutdown, it will be necessary to manually fully open the IGV (Inlet Guide Vane) to facilitate mechanical work. Could you please advise on the procedure for fully opening the IGV during unit shutdown?

Based on my understanding, I believe that initially, the lubricating oil pump and hydraulic oil pump should be started. Are there any other tasks required at this point? In the previous maintenance records, it was mentioned that four signals need to be forced in the Mark V control logic, and then manual operation is needed on the servo valve LVDT auto-calibration screen. However, the specific details about which four signals need to be forced were not provided in the maintenance records. Does anyone know which four signals need to be forced?

After analyzing the control logic, I think there are several signals that might need to be forced:
1、 Trip master signal;
2、 20TV solenoid valve command;
3、20FG solenoid valve command;
4、IGV output command CSRGVOUT.
I am unsure if my analysis is correct and would greatly appreciate assistance from the community. Thank you.

 

Using the Mark* V it's NOT possible to force analog signals--inputs or outputs.

The steps below are for a typical GE-design Frame 7E/EA heavy duty gas turbine with a Mark* V turbine control system. Unfortunately, some of the signal names ARE NOT always the same on EVERY Mark* system....

With personnel clear of the bellmouth area:

1) Start the Aux. L.O. Pump by forcing L4QAZ to a logic "0".

2) Start the Aux. Hyd. Pump by forcing L4HQZ to a logic "0".

3) Force L20TV1X to a logic "1".

There is a logic signal that can be used to apply CSKGVMAX (the maximum operating angle) to the CSRGV algorithm to move the IGVs to the value of CSKGVMAX (which is usually 86 DGA or something like that). I believe the signal name is L83GVMAX (or something very similar to that).

4) Force L83GVMAX to a logic "1".

I STRONGLY recommend that if people are going to be in the inlet/bellmouth area that you:

a) Shut down the Aux. Hyd. Pump (by unforcing L4HQZ; it should automatically return to logic "1")
b) Shut down the Aux. L.O. Pump (by unforcing L4QAZ; it should automatically return to logic "1")
c) Go to the Hydraulic Accumulator and open the bleed valve (it's NOT usually marked as such; but one of the small handwheels should be CLOSED and that will be the bleed valve; the other valve should be OPEN and that will be the block (manual isolation) valve); this will drop the Hydraulic System pressure to 0 psig/barg which will take all hydraulic pressure off the IGV actuator and the IGVs should remain in the maximum operating angle (CSKGVMAX) position (This is a GREAT time to identify the block and bleed valves of the Hyd. Accumulator....!!!)
d) Unforce L20TV1X (it should automatically return to logic "0")

The IGVs should remain in the open position and work can begin. (Unlike most other hydraulically-operated devices on a GE-design heavy duty gas turbine there is no spring return to some safe condition on the IGV actuator; it requires hydraulic system pressure to open or close.) There is NO hydraulic pressure now and there is no danger of the IGVs moving--unless someone starts the Aux. L.O. Pump AND the Aux. Hyd. Pump AND forces L20TV1X to a logic "1" AND unforces L83GVMAX AND closes the Hyd. Accumulator bleed valve (OR closes the Hyd. Accumulator block valve). It's safe, in other words, as long as there's no Hydraulic System pressure.

LEAVE THE HYD. ACCUMULATOR BLEED VALVE IN THE OPEN POSITION AS LONG AS PEOPLE ARE WORKING OR WILL BE WORKING IN THE INLET/BELLMOUTH.

When finished and everyone is clear of the bellmouth:

aa) Close the Hyd. Accumulator bleed valve (the other valve, the block (manual isolation valve), should be open and needs to be open for the Hyd. Accumulator to work correctly)
bb) Unforce the logic signal L83GVMAX (it should automatically return to a logic "0")
cc) Start the Aux. L.O. Pump and the Aux. Hyd. Pump in that order (by forcing L4QAZ and L4HQZ to logic "0"--in that order)

The IGVs should return to the CLOSED position (around 32-34 DGA, normally).

That should be it.

SAFETY FIRST. Before anyone reading this tries forcing L83GVMAX to a logic "1" when the turbine is running--JUST DON'T DO IT! ESPECIALLY on a machine with DLN combustors. The results can be really, Really, REALLY bad. This procedure is ONLY for zero-speed operation (not even on Cooldown!).

Again, analog signals (inputs AND outputs) cannot be forced in the Mark* V turbine control system.

You should try this by observing the IGV pointer on the side of the axial compressor casing before sending personnel inside. And, it will allow you (or someone) to locate the Hyd. Accumulator and identify the block and bleed valves (and hopefully mark them for future reference--if they haven't already been so marked). And if it doesn't work as expected, write back with the exact steps you performed and the results of each step.

Now, if there's OTHER mechanical work going on, someone might want to start the Aux. L.O. or Aux. Hyd. Pump while people are working in the inlet/bellmouth. Just don't do it.

 

Using the Mark* V it's NOT possible to force analog signals--inputs or outputs.

The steps below are for a typical GE-design Frame 7E/EA heavy duty gas turbine with a Mark* V turbine control system. Unfortunately, some of the signal names ARE NOT always the same on EVERY Mark* system....

With personnel clear of the bellmouth area:

1) Start the Aux. L.O. Pump by forcing L4QAZ to a logic "0".

2) Start the Aux. Hyd. Pump by forcing L4HQZ to a logic "0".

3) Force L20TV1X to a logic "1".

There is a logic signal that can be used to apply CSKGVMAX (the maximum operating angle) to the CSRGV algorithm to move the IGVs to the value of CSKGVMAX (which is usually 86 DGA or something like that). I believe the signal name is L83GVMAX (or something very similar to that).

4) Force L83GVMAX to a logic "1".

I STRONGLY recommend that if people are going to be in the inlet/bellmouth area that you:

a) Shut down the Aux. Hyd. Pump (by unforcing L4HQZ; it should automatically return to logic "1")
b) Shut down the Aux. L.O. Pump (by unforcing L4QAZ; it should automatically return to logic "1")
c) Go to the Hydraulic Accumulator and open the bleed valve (it's NOT usually marked as such; but one of the small handwheels should be CLOSED and that will be the bleed valve; the other valve should be OPEN and that will be the block (manual isolation) valve); this will drop the Hydraulic System pressure to 0 psig/barg which will take all hydraulic pressure off the IGV actuator and the IGVs should remain in the maximum operating angle (CSKGVMAX) position (This is a GREAT time to identify the block and bleed valves of the Hyd. Accumulator....!!!)
d) Unforce L20TV1X (it should automatically return to logic "0")

The IGVs should remain in the open position and work can begin. (Unlike most other hydraulically-operated devices on a GE-design heavy duty gas turbine there is no spring return to some safe condition on the IGV actuator; it requires hydraulic system pressure to open or close.) There is NO hydraulic pressure now and there is no danger of the IGVs moving--unless someone starts the Aux. L.O. Pump AND the Aux. Hyd. Pump AND forces L20TV1X to a logic "1" AND unforces L83GVMAX AND closes the Hyd. Accumulator bleed valve (OR closes the Hyd. Accumulator block valve). It's safe, in other words, as long as there's no Hydraulic System pressure.

LEAVE THE HYD. ACCUMULATOR BLEED VALVE IN THE OPEN POSITION AS LONG AS PEOPLE ARE WORKING OR WILL BE WORKING IN THE INLET/BELLMOUTH.

When finished and everyone is clear of the bellmouth:

aa) Close the Hyd. Accumulator bleed valve (the other valve, the block (manual isolation valve), should be open and needs to be open for the Hyd. Accumulator to work correctly)
bb) Unforce the logic signal L83GVMAX (it should automatically return to a logic "0")
cc) Start the Aux. L.O. Pump and the Aux. Hyd. Pump in that order (by forcing L4QAZ and L4HQZ to logic "0"--in that order)

The IGVs should return to the CLOSED position (around 32-34 DGA, normally).

That should be it.

SAFETY FIRST. Before anyone reading this tries forcing L83GVMAX to a logic "1" when the turbine is running--JUST DON'T DO IT! ESPECIALLY on a machine with DLN combustors. The results can be really, Really, REALLY bad. This procedure is ONLY for zero-speed operation (not even on Cooldown!).

Again, analog signals (inputs AND outputs) cannot be forced in the Mark* V turbine control system.

You should try this by observing the IGV pointer on the side of the axial compressor casing before sending personnel inside. And, it will allow you (or someone) to locate the Hyd. Accumulator and identify the block and bleed valves (and hopefully mark them for future reference--if they haven't already been so marked). And if it doesn't work as expected, write back with the exact steps you performed and the results of each step.

Now, if there's OTHER mechanical work going on, someone might want to start the Aux. L.O. or Aux. Hyd. Pump while people are working in the inlet/bellmouth. Just don't do it.

Thank you very much for WTF's detailed response.

I carefully examined the wiring terminals related to the lubricating oil pump, hydraulic pump, and IGV solenoid valve on our site's control logic and wiring diagram. It is indeed as you mentioned – after the unit is shut down, forcing the above four signals should allow for the IGV to be fully open.

Just as Mr. WTF mentioned, some of the signal names are not always the same on every Mark* system. Slightly different in our case, I found that the final command output signal for our on-site lubricating oil pump is L4QAZ1, as shown in the diagram below:

Once again, thank you for WTF's detailed response.