Abstract: Due to the change of the power transmission network infrastructure, to be compliant with the N-1 principle in“Power System Security and Stability Guideline”, the Unit 3 in Zhoushan Power Plant has to reduce its MW generation from the original full load down to only 215 MW. In order to maximize the output power, a joint control mode integrated with the steam turbine, boiler and outgoing line together is adopted, which solves the dilemma of unit MW output limitation. In this paper, the study on the line overload determination via electrical signals and also the fast load-shedding control are introduced. The electrical overload signal is triggered by hardware configuration and logic optimization. Instructions are issued to trip the unit from the electrical dynamic monitoring control equipment when fast load-shedding scheme fails. The engineering application is put into practice, which shows great improvement of the utilization rate of the transmission line capacities.

Key words: transmission line, output power, load control, line overload, DEH valve, PCV valve, fast load-shedding