Research On Fault Identification Algorithm And Action Strategy Of Regional Protection

Traditional backup protection relay based on local information has complex setting principle and long action time, can not meet the safety demand of power grid. With the development of wide-area measurement and digital substation technology, regional protection using wide-area information can solve the problems above. This paper aims at the difficult points of regional protection, focuses the algorithms of fault line recognition with different principles while the demand of synchronization is met or not and the action strategy for remote backup protection, the works are below:A kind of fault line recognition algorithm principle based on virtual transition impence is proposed, to distinguish the fault line when meeting the demand of synchronization condition. Firstly, the sequence voltage and current phasors on both ends of the line and the impence of the line are used to calculated virtual sequence voltage phasor at the fault point. Sencondly, the ration of virtual sequence voltage phasor and the sum of the sequence current phasors on both ends of the line is defined as virtual sequence transition impence. Finally, the fault identification criterion is made up through the value discrepancy of virtual sequence transition impence between internal and external fault. The method has no need to compensate the current of the capacitor, the simulation results of pratical power system show that the method has high sensitivity for all kinds of faults, and is not affected by the fault location, fault resistance, weak feed line failure and the influence of transformational fault.A transmission line pilot differential protection principle based on fault component virtual impedance is proposed, to distinguish the fault line when the system can not meet the demand of synchronization condition. The impact of distribution parameter is taken into acount. Firstly, the method utilizes the fault component of voltage and current at both two ends of the line to deduce the fault component of voltage and current at the middle of the line. Secondly, the ratio of the fault component of voltage to the fault component of current is defined as virtual impedance. Finally, by means of comparing the sum of the virtual impedance with the minimum of the virtual impedance, a ratio restraint criterion is constructed. The fault can be identified by analyzing the different characteristics of internal and external fault. The result of power grid simulation demonstrates that this method is able to identify the fault exactly with high sensitivity and reliability. Furthermore, it is immune to the fault location, transition resistance, load current, distributed capacitance and information synchronization. Even though transferring fault takes place, the method has high selectivity. Focusing on researching the regional protection action process, the criterion dealing with information of normal condition and missing of DC electrical source. Then, a tripping strategy of regional protection based on weighted direction is proposed. Firstly, the node-branch incidence matrix based on weighted direction is formed by network topology and positive sequence current information of the breakers, Secondly, based on the results of the fault judgment and circuit breaker failure, the related circuit breakers are recognized and tripped by constructed vector of component-circuit breaker related degree. The simulation result demonstrates that the method can not only recognize the related circuit breakers for local protection and circuit breaker protection by means of caculations, but also can recognize the related circuit breakers to provide back-up protection for adjacent substation and transmission line. On the other hand, The method does not need synchronization condition and has high reliability when the information of a circuit breaker is missing.