Abstract: In order to improve the reliability of the control system for 1 000-MW ultra-supercritical steam turbines which are jointly designed and manufactured by Shanghai Turbine Company Ltd and Siemens, the faults of the digital electro-hydraulic (DEH) system occurred in routine operations are analyzed and summarized. The solenoid valve tripping control logic, fast valving protection logic, main steam pressure control switching logic, long load shedding logic, instantaneous load shedding logic, turbine speed control logic and switching logic after bypass opening are optimized without changing the original design ideas and protection principles. Therefore, the potential troubles, such as the EH oil low pressure tripping caused by the trip solenoid valve disconnection and the(long) load shedding caused by grid load fluctuation, are eliminated. Moreover, these optimized logics are also adopted by the 1 000-MW units installed later and used as the reference for the units of the same type.

Key words: 1 000 MW, steam turbine, DEH, quick closing logic, control logic, speed control logic, reliability, ultra supercritical unit