We are attempting to restart our steam turbine after a loss of trip oil. We are having issues with the MSV2 valve "popping" open once the operators select reset. The controller is a Mark V TMR. Once operators select reset on the controller, the turbine starts to roll off. The highest we let it roll off to was a little over 360 RPMs before we opted to trip the unit. It was noticed because in our procedure it states that the V2 extraction control valve should open to 86%, but due to the pressure from the MSV2 leak by, the logic told the V2 to stay shut.
We recently came out of an outage where the valves were rebuilt. The start after the outage was successful and we did not experience the MSV2 valve opening when the controller was reset. This was the first trip since the work was done.
MSV2 is the valve that has the startup pilot.
Valve command when stroked/Position Feedback
-25/.43
-5/.43
-1/.8
0/1.45
This is the same thing that we saw when attempting to start up; only the valve command goes from -25 to 0.
We have changed the servo on the MSV2 three times, all with the same result.
We have re-calibrated our LVDTs and they are all reading accurately. I adjusted them to when fully close and hydraulic pressure off, the feedback position is 0.00. That position is true as long as the controller is sending a -25 command signal. However, when given 0 command, the feedback would show between 1.8 to 2.
I have attempted to change the null bias. I adjusted it all the way from 40 to 3 but did not notice any change that would be considered significant. On the MSV2 it is set at 22.49. I do not have a super clear understanding of when to change that valve and to what extent.
Our understanding of the servos was that they were failsafe. In the event of a loss of all three servos, the control valve would go shut. That was not our experience. We pulled the cannon plug connector to the servo and enabled our hydraulic oil trip circuit. The valve went fully open.
We tested to see what we would experience if we completed a servo polarity check with the servo reversed and with only one servo connected to the controller, the valve went fully open.
We could also not get the valve to shut when driving the valve with only one servo either. It would open fairly easily, but when given a close command it would stop around 9%.
We were also under the impression that if one of the servo polarities was reversed that the other two servos proper wired would overcome the one reversed servo. That was not our case. The valve would open and travel fairly well, but when give a 0 command, it would hang up around 9% open.
I am out of ideas. Any direction on what may be the cause or advice on troubleshooting is appreciated.
We recently came out of an outage where the valves were rebuilt. The start after the outage was successful and we did not experience the MSV2 valve opening when the controller was reset. This was the first trip since the work was done.
MSV2 is the valve that has the startup pilot.
Valve command when stroked/Position Feedback
-25/.43
-5/.43
-1/.8
0/1.45
This is the same thing that we saw when attempting to start up; only the valve command goes from -25 to 0.
We have changed the servo on the MSV2 three times, all with the same result.
We have re-calibrated our LVDTs and they are all reading accurately. I adjusted them to when fully close and hydraulic pressure off, the feedback position is 0.00. That position is true as long as the controller is sending a -25 command signal. However, when given 0 command, the feedback would show between 1.8 to 2.
I have attempted to change the null bias. I adjusted it all the way from 40 to 3 but did not notice any change that would be considered significant. On the MSV2 it is set at 22.49. I do not have a super clear understanding of when to change that valve and to what extent.
Our understanding of the servos was that they were failsafe. In the event of a loss of all three servos, the control valve would go shut. That was not our experience. We pulled the cannon plug connector to the servo and enabled our hydraulic oil trip circuit. The valve went fully open.
We tested to see what we would experience if we completed a servo polarity check with the servo reversed and with only one servo connected to the controller, the valve went fully open.
We could also not get the valve to shut when driving the valve with only one servo either. It would open fairly easily, but when given a close command it would stop around 9%.
We were also under the impression that if one of the servo polarities was reversed that the other two servos proper wired would overcome the one reversed servo. That was not our case. The valve would open and travel fairly well, but when give a 0 command, it would hang up around 9% open.
I am out of ideas. Any direction on what may be the cause or advice on troubleshooting is appreciated.