Hello,
We've been facing a problem with our 15 MW steam turbine recently. It has Woodward 505e governor controller installed and configured in 4% droop mode, although normally it is running alone. At other times (during startup), it is synchronized to other DGs.
The problem we faced recently was that when our turbine went up to about 11 MW (with all other DGs shut down), it kept normal for about 10-20 minutes. Then all of a sudden, without an increase in the load, its speed suddenly dropped from 3000 to 2950 rpm. Operators tried to increase Woodward speed setpoint manually, but it did not respond. Operators then switched off some 1.5 MW load manually and the turbine speed normalized to 3000 rpm. All this happened within 30-40 seconds. During this time there was no change in load, no change in steam pressure or flow (extraction was off at the time), no physical change in HP or LP valve.
The two questions which are looking to be answered are:
1. Why would the turbine suddenly slow down?
2. Even if somehow the turbine slowed down, why did 505e not respond by increasing its output to maintain the rpm?
Then yesterday we noticed that when we were running at 7 MW (without extraction), the HP output was 38% while the speed PID output had gone up to 83%. Then we opened up the extraction, and as soon as we did that, speed PID output came down to 37%.
My questions are:
1. What is the difference between speed PID output and HP output? I know there's a ratio/limiter block in between them, but how does it work? The ratio block has some equations written in the manual such as HP = K1S + K2P + K3. How do I calculate/find out the values for K1, K2, K3 etc?
2. I am afraid that if we had not opened up extraction and kept on increasing electric load, speed PID output would have been saturated. A similar incident happened a few days when were running at 11.2 MW with 42% HP output without extraction. All of a sudden the turbine rpm dropped. I am almost convinced that speed PID output would have reached 100%, though I do not have trends available for that.
3. I know the ratio block has something to do with the steam map/envelope fed into 505e, but am not sure how it works. Could somebody please explain that?
Any suggestions would be most welcome!
We've been facing a problem with our 15 MW steam turbine recently. It has Woodward 505e governor controller installed and configured in 4% droop mode, although normally it is running alone. At other times (during startup), it is synchronized to other DGs.
The problem we faced recently was that when our turbine went up to about 11 MW (with all other DGs shut down), it kept normal for about 10-20 minutes. Then all of a sudden, without an increase in the load, its speed suddenly dropped from 3000 to 2950 rpm. Operators tried to increase Woodward speed setpoint manually, but it did not respond. Operators then switched off some 1.5 MW load manually and the turbine speed normalized to 3000 rpm. All this happened within 30-40 seconds. During this time there was no change in load, no change in steam pressure or flow (extraction was off at the time), no physical change in HP or LP valve.
The two questions which are looking to be answered are:
1. Why would the turbine suddenly slow down?
2. Even if somehow the turbine slowed down, why did 505e not respond by increasing its output to maintain the rpm?
Then yesterday we noticed that when we were running at 7 MW (without extraction), the HP output was 38% while the speed PID output had gone up to 83%. Then we opened up the extraction, and as soon as we did that, speed PID output came down to 37%.
My questions are:
1. What is the difference between speed PID output and HP output? I know there's a ratio/limiter block in between them, but how does it work? The ratio block has some equations written in the manual such as HP = K1S + K2P + K3. How do I calculate/find out the values for K1, K2, K3 etc?
2. I am afraid that if we had not opened up extraction and kept on increasing electric load, speed PID output would have been saturated. A similar incident happened a few days when were running at 11.2 MW with 42% HP output without extraction. All of a sudden the turbine rpm dropped. I am almost convinced that speed PID output would have reached 100%, though I do not have trends available for that.
3. I know the ratio block has something to do with the steam map/envelope fed into 505e, but am not sure how it works. Could somebody please explain that?
Any suggestions would be most welcome!