Commissioning of NP turbine is going on in the site. whenever they start the sequence, the fuel gas valve closes immediately due to some some shutdown signal through a Dump solenoid . NP engineers is looking into this problem. has anyone faced the similar problem in Mark VI.

 

I've seen something similar happen many times before, when some signal provided from a control system belonging to the "Customer" doesn't change state when it should, or changes state when it shouldn't, or isn't the right sense (NC or NO) to begin with.

Please write back to let us know how simply this issue was resolved.

 

Hello Over There...

Your analysis on the problem is very generic. These kinds of problems are part of commissioning activities. Just like the MKV, the MKVI has excellent diagnostic and trip/alarm capturing capabilities. From the trip log, one can trace back the initiator of the trip. The dump solenoid (L20HD) is the final element which will shut down the GT in case trip initiated via the trip logic output L4T. The dump solenoid will depressurize the hydraulic system as a result the gas valve will close (SRV). Again, the MKVI system is robust and most likely the problem will be from the hardware side (assuming the trip is NOT initiated as part of required protective signal in case of unsafe condition). To understand the problem you may suggest the following to the NP FSE's.

Hardware;

1. Check the resistant of the dump valve solenoid (expected value is >100 Ohm).

2. Ensure that the supply voltage of the MKVI output is above 110Vdc. Verify also that the dump solenoid rated voltage is corresponding with the MKVI output voltage.

3. Ensure that the hydraulic supply pressure is > 75 barg.

4. Due to improper lube oil flushing, sometimes the valve of the solenoid is partially blocked which will restrict the hydraulic oil flow during transient conditions. You may consider to hammer (gently) on to the dump valve with a rubber hammer in order to crack open the line.

5. Last but not least, possible ground fault (maybe intermittent) may cause this problem. Ensure that there is no ground fault in the system. In addition verify the loop integrity of the dump valve (loose / defective wiring in the JB).

Quick fix for this problem is replacing the dump valve (if there is a spare one). If not the dump valve can be serviced. The location of this valve is for older units downstream right side in the Aux. compartment near the gas valves (bulky and heavy). Newer units use smaller Parker valves which is located between the SRV and GCV valve.
Software;

1. Once found the hardware is functional, one can consider to assign new solenoid output in the MKVI I/O board.

2. If this will not solve the problem, consider replacing the designated I/O board.

Good Luck...
A. Oztas