I currently work on a 2+1 combined cycle, with a GE D-11 steam turbine, and two 7FA CTs, utilizing a Mk VI control system.
During a recent start-up of the steam turbine, we experienced an "excessive speed error" alarm when trying to roll the turbine. All permissives were met, the steam turbine was just slightly above turning gear speed, and the RH steam pressure was approximately 150 psi, which is normal for a warm start up.
The alarm persisted, preventing us from rolling the turbine each time we initiated an auto-start, until we tried lowering the RH steam pressure to around 90 psi, at which point we were able to successfully roll the turbine.
My question is, how is the Mk VI determining the "excessive speed error"? From what limited information I've found, speed error seems to be the difference between the turbine's actual speed and reference speed. Given this information, I don't see the correlation between lowering the RH steam pressure and the speed error no longer being excessive?
Any help in this matter would be appreciated!
During a recent start-up of the steam turbine, we experienced an "excessive speed error" alarm when trying to roll the turbine. All permissives were met, the steam turbine was just slightly above turning gear speed, and the RH steam pressure was approximately 150 psi, which is normal for a warm start up.
The alarm persisted, preventing us from rolling the turbine each time we initiated an auto-start, until we tried lowering the RH steam pressure to around 90 psi, at which point we were able to successfully roll the turbine.
My question is, how is the Mk VI determining the "excessive speed error"? From what limited information I've found, speed error seems to be the difference between the turbine's actual speed and reference speed. Given this information, I don't see the correlation between lowering the RH steam pressure and the speed error no longer being excessive?
Any help in this matter would be appreciated!