Risk Assessment And Strategy Research Of Islanding In Guangzhou Power Grid

With the multi-regional interconnecting and the scale development of power system, the connections of systems at all levels are getting more and more compact. The reasons which are partial electric network faults, extreme weather or manual operation failures can cause large-area power failure accidents, even the collapse of the whole system. In order to guarantee the safety and reliability of power system and the efficiency of preventive measures to harsh faults, the study of local power system islanding which can be used as a recovery measure to the blackout possesses great practical significance.Guangzhou power grid which has a high proportion of local distributed generators is studied to analyze the power supporting capacity of the 110kV zones, set the UFLS and UVLS schemes rationally used to prevent the island disintegration caused by the power disequilibrium or voltage collapse aiming at the possible islanding risk of Guangzhou power grid. The main research contents are outlined as following:(1) The variation characteristics of frequency and voltage at the time of islands formation are studied separately from the side of the generator and load. The island frequency and voltage variation characteristics are mainly related with the active power disequilibrium. When the total capacity of generators is less than the load power in an island, the frequency and voltage will decrease, the island could not run steadily; when the total capacity of generators is larger than the load power, the frequency and voltage will increase at the formation transient, the island can realize a long time steady running after the generator output decrease to balance with the load power. According to the static frequency characteristic of power system, the active power regulating capacity after the island processes a steady running is deduced.(2) Analyze the islanding risk of Guangzhou power system and the typical island operation mode of 110kV zones which have local distributed generators using the PSD-BPA power flow and transient stability analysis program. It is indicated that the main modes of islands formation are 220kV power loss and faults of some 110kV transmission lines. Proper control measures should be taken to ensure the stability after the island forms.(3) Analyze the influence of load model on the island frequency and voltage stability. The induction motor load in power system may deteriorate the frequency and voltage stability. The main influencing factors are as follows:load type, the proportion of induction motor load, the inertia time constant, loading percentage, stator reactance, rotor resistance and reactance.(4) Research the control strategy of islanding stability. It is indicated that UFLS and UVLS are the basic measures to make the islands with large power shortage run steadily. Make the UFLS and UVLS scheme of islands in Guangzhou power grid by the combining of the UFLS setting based on trajectories analysis and the UVLS.