Research And Design On The Technology Of Fault Diagnosis For Power System Based On Fuzzy Petri Net

Modern Power system net works have been expanding with UHV transmission and large generators, so inter-regional Power grid interconnection more closely. But as a result of the impact of man-made, climate and other factors, the generating of power system fault is inevitable, resulting in serious consequences, such as the interrupting of power supply of users, the declining in the quality of power supply and even damages of electrical equipments. When the transmission network faults occur, a lot of warning information which is generated by the automatic devices of each level will influx into the control center in a short time, which exceeds the processing capacity of the operating personnel. Therefore, it is necessary to study an effective diagnosis method of the power system, which can determine the fault components quickly and accurately.Petri nets have a perfect capacity of Parallel Proeessing and graphical representation, and it’s an ideal choice for dealing with diserete problems. FPN and WFPN is proposed based on the Petri net. WFPN has features of both Petri net and fuzzy logical theory and it can reflect the confidence degree of the uncertainty and incompleteness by the way of probability.In recent years, scholars have applied it to the fault diagnosis of power grid, however, the proposed methods have problems as following:it is difficult for the models to adapt to the changes of the network structures, meaning that the versatility and maintenance are weak; when the fault information is lost, diagnostic error will occur easily, which means that the fault tolerance is poor. Against to the above problems, the goal to improve the versatility and fault tolerance of the diagnostic model is set, based on the domestic and international relevant research results.This paper took the typical 220KV power net as the example and made some simulation analysis on sone uncertainty information. Weight Fuzzy Petri nets is applied to the power system fault diagnosis. The work content is mainly divided into the following aspects:(1) An extension study on the traditional probability Petri nets is carried out and the evaluation function of the transition and the weights of input and out put is fixed, which improves the performance of the probability Petri net diagnostic. According to the statistics of the relay protection and circuit breakers, with the method of probability the value of the initial marking probability is calculated in detail, which makes the initial marking to describe the uncertainty of the actions of the relay protection and the circuit breakers.(2) A new type of line model is proposed based on the fault information system, lead models of the line, the bus and the transformer components are established, which accurately simulates the logic relationship of protections. The model adapted to different system operating modes by the analysis of the structure of one topology is made by the fault net of suspicious components.(3) Against the problems of matrix dimension being too large, weak adaptability and combinatorial explosion of the Petri net models in complex power grid fault diagnosis, based on the above modeling method and combined with Petri nets simplification techniques, hierarchical subnet probability Petri net model of the fault diagnosis is constructed. Namely, the bottom subnet models of the main protection and backup protection as well as remote backup to the two ends of the lines and transformers are established firstly, and then the bottom subnets are integrated to establish the comprehensive diagnostic subnet; the bottom subnet models of each lead direction of the bus are established firstly, and then the bottom subnets are integrated to establish the comprehensive diagnostic subnet. Multiple examples show that the scale of the model effectively and the matrix dimension with strong adaptability are reduced by the method.(4) At last, to against the poor effect of the fitting curve of the Gauss function,Fuzzy Hyperbolic Model is introduced to this paper to replace it.,and it is applied into the fault diagnosis of electric power system based on Petri Net.Better effect is achieved.