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Our 5MW BH make steam turbine has been facing hunting issue at the HP Lift Valve. RPM variation (300 to 350 RPM) started with variation in HP lift (19% to 26%).
HP Lift high Limiter was engaged at 24.5% which omitted the speed variation. However, when the Limiter was removed, Lift and RPM variations started again.
Process parameters and Control valves on the compressor side were also checked for any variations which may cause variations in speed and subsequent HP lift variations. This was also ruled out.
Initially, there was hunting in the control oil system and its PCV, but it got normalized when Control Oil accumulator was isolated. However, speed and HP lift variations remained the same. Hence, the initial hunting of PCV was not linked with the HP lift variations.
There are no leakages in the control oil or secondary oil circuit to the HP Lift Servo Cylinder either.
I have attached the trends for reference.
Would be really helpful if anyone can share their experience on a similar issue and how it was tackled.
HP Lift high Limiter was engaged at 24.5% which omitted the speed variation. However, when the Limiter was removed, Lift and RPM variations started again.
Process parameters and Control valves on the compressor side were also checked for any variations which may cause variations in speed and subsequent HP lift variations. This was also ruled out.
Initially, there was hunting in the control oil system and its PCV, but it got normalized when Control Oil accumulator was isolated. However, speed and HP lift variations remained the same. Hence, the initial hunting of PCV was not linked with the HP lift variations.
There are no leakages in the control oil or secondary oil circuit to the HP Lift Servo Cylinder either.
I have attached the trends for reference.
Would be really helpful if anyone can share their experience on a similar issue and how it was tackled.
