gas turbine IGV sticking problem

A

Thread Starter

AW

one of our gas turbine MS-5001P tripped on hydraulic oil low pressure but the IGV'S didn't come to their close position.hydraulic oil pressure that operates the IGV'S and the fuel servo valves drops to zero then on actuation of 14HS trip relay solenoid valve 20TV should be energized to close the IGV'S. in what are the possible cause of IGV'S sticking. on sudden drop of pressure did IGV'S solenoid valve 20TV get time to drain the oil behind the piston that operate the IGV'S
 
Please have a look at the Piping Schematics (P&IDs) for the Trip Oil System and the IGVs. Energizing 20TV should work to allow high-pressure hydraulic oil to flow through the servo-valve to the IGV actuator.

When there is no Trip Oil pressure because 20TV is de-energized then high-pressure hydraulic oil should be ported to the IGVs to close them.

There is no spring or mechanism to automatically close the IGVs when there is no hydraulic pressure (like there is on the fuel control valve(s)). Hydraulic pressure is required to open or close the IGVs. And, when the compressor is spinning and air is being drawn in through the IGVs, air flow usually is trying to open the IGVs.

You stated that hydraulic system pressure was low and that was the cause of the trip. Does the turbine have only an Accessory Gear-driven Main Hydraulic Pump? Or does it also have an AC motor-drive Aux. Hydraulic Pump? Does it have a Hydraulic Accumulator?
 
C

charlee_tango

Sir,

Please go through the TIL - 1132 for IGV spring washers, though it may not be applicable for Fr 5 machine. I don’t know but we found our self effected with this TIL in Fr 9E machine.
 
do you have a hydraulic accumulator? Is it pre-charged with nitrogen to approx half nominal hydraulic pressure?
 
Our gas turbine model is MS-5001P and we have only on accessory gear driven hydraulic pump and no hydraulic accumulator on downstream of pump. pump discharge goes the the hydraulic manifold (in which relief valve VR-21 and check valve) is provided and from filters to the fuel servo's and to IGV'S. when we shutdown the turbine for any plan maintenance IGV'S stuck and we have to close them by placing hydraulic jack at control ring it means 20TV is de-energized and oil was drained completely from back of actuator piston that operate IGV'S. in case of normal stopping of turbine what are the reasons of IGV'S sticking
 
>do you have a hydraulic accumulator? Is
>it pre-charged with nitrogen to approx
>half nominal hydraulic pressure?

we have only on accessory gear driven hydraulic pump and no hydraulic accumulator on downstream of pump. when we shutdown the turbine for any plan maintenance IGV'S stuck and we have to close them by placing hydraulic jack at control ring it means 20TV is deenergized and oil was drained completely from back of piston that operate IGV'S
 
I have neglected to ask: When did this problem start?

Again, I don't recall every seeing an IGV system drawing where when 20TV was de-energized that hydraulic pressure wasn't routed to cause the IGVs to move to the closed position. I haven't seen every system designed, but many of them. Can you post the IGV Piping Schematic (P&ID) to a site where we can view it?

And, I'm also very confused. Because the original post was about problems after tripping (which, to me, is different from a normal shutdown) and you are now saying that after every shutdown (or is it trip--an emergency shutdown) that you have to use a jack to close the IGVs, which is just not normal. Not at all.

As the unit is coasting down there should be Hydraulic Pressure down to at least cranking speed, and the IGV reference should be at minimum (closed) below approximately 75% speed, so the IGVs should be closing.

There's definitely something unusual here. But, the possibilities are vast. I would be very interested to know what Diagnostic Alarms associated with the IGV servo output are present during normal operation.

I would like to know if the servo current polarity has been verified.

We don't know if this is a TMR or SIMPLEX application.

We don't know at what angle the IGVs are sticking at. It might be that the actuator is mechanically binding. Have the IGVs been "stroked" by cranking the unit (to develop Hydraulic Pressure)? If so, do they move smoothly, and as anticipated?
 
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