Research On Improving System Security And Stability For Regional Power Network Splitting

In recent years, natural disasters such as snow, ice storms and mudslides haveoccurred in some places of China, highlighting the risk of splitting the regional powergrid and the main grid, so there is growing concern about ensuring stable and securefrequency of the regional power grid after its splitting. According to high-frequencyincidents caused by isolated grids recently, the paper sums up the high frequencycharacteristics, reviews the domestic and foreign research tendency on security andstability control measures after the splitting of regional power grids and then studiesabout the frequency stability control after splitting failure of regional power grids fromthree aspects. Now the paper summarizes its work as follows:(1)For splitting failures of power grids occurred in areas which are provided withpower by collection of small hydropower, this paper presents the configuration principlesfor high-frequency control measures of grids. Chain generator tripping andhigh-frequency generator tripping schemes are provided for the power grid of deliveryregion in a hydropower station of Yunnan. It is characterized by clear layer and easinessof implementation. During setting the high-frequency generator tripping for regionalpower grid, the following factors are considered: on the one hand, it should becoordinated with high-frequency generator tripping scheme of500kV main grid inYunnan; on the other hand, it should be able to deal with high frequency problems underdifferent situations such as delivery channel splitting fault outside the region andindependent splitting fault in different areas of the region. The effectiveness of theallocation scheme is verified through simulation of the splitting fault under typicaloperation mode.(2) This paper focused on the dynamic frequency characteristics and control strategyof hydropower unit located at regional sending end when separated from main network.The configuration of over-speed protection and overvoltage protection of hydroelectricunit were summarized. Taking the single generator infinite bus system as the testingexample, this paper studies hydroelectric generating frequency regulation characteristicsafter splitting and presents the improved frequency control method of hydropower unitfor separation fault. With the measurement of transfer power from regional network tomain network, the original control target is substituted by appropriate and new value andthe feed-forward signal showing attenuation characteristic is added to the valve commandposition, so as to control the increasing frequency and prevent the serious overshoot. Theeffectiveness of the improved method is confirmed by digital simulation.(3)This paper establishes a complete system model including the coordination control system (CCS) and boilers’ speed control system model of thermal power plant.On this basis, this paper studies thermal generators frequency regulation characteristicsafter splitting. Taken the typical power delivery system of large thermal power as anexample, this paper makes a study about impacts caused by important parameters of thespeed control system for thermal power units under the splitting failure of power grids atthe sending end on the frequency dynamic process of the power grids after its splitting.And taken a power grid at the receiving end in Henan as the research object, this paperstudies low-frequency characteristics of regional grids after its splitting and puts forwardproposals on improving the ability of unit’s frequency modulation.