Study On Under-Frequency/Voltage Load Shedding And Their Cooperation

The traditional technique of Under Frequency Load Shedding(UFLS) is based on the based on the single-machine model, which only the static effect of the load on the frequency is considered and the dynamic of system is ignored. As power system interconnection between utilities has increased,traditional technique of UFLS has no longer adapted to the modern power system. Under Voltage Load Shedding(UVLS), used as a measure of load control for the voltage stability,\ or as a reserve under the worst fault conditions. for in a part load control, have been more and more used by power companies. UFLS( Under Frequency Load Shedding) and the UVLS(Under Voltage Load Shedding) are the last line of defense as a safe and stable control in order to maintain power system security stability and economic operations, and it will become the important measures to ensure the power quality.A method which is based on the the simulation trajectories in the multi-machine is used to analyse the dynamics of the system frequency. This method not only takes advantage of numerical integral method,which is not limited by the model,but also uses the concept of uniform frequency of the single-machine model to compensates the shortage of numerical integral method effectively. The influences of different network structures,operation modes on the frequency dynamics have been analyzed. A new Under Frequency Load Shedding (UFLS) scheme is proposed which can not only meet the frequency security requirements of the entire network but also the one of the regional network.The analysis method of the voltage security in the receiving power network is summarized. The reason of the voltage untable have been analysized by the power flow menthod, modal method and simulation method. The system method of the UVLS is proposed in this paper, based on which a UVLS scheme is proposed for the Guangdong Power Grid.What's more, the cooperation of the UFLS and the UVLS is studied in order to make the power system more reliable.