Oil pressure problem of main valve of steam turbine

I still don't know exactly what the situation is. If the main valve oil pressure is not enough, that is to say, the security oil pressure is not enough, and the automatic main valve cannot be opened, or slightly opened. In this case, the steam turbine can run at full speed, because the main valve opening is not enough, resulting in insufficient steam intake, so the unit can not carry the load.

first of all, find out the reason of low oil pressure in the main valve, and the unit can run normally after eliminating the defects.