The Power System Fault Diagnosis Method Based On Hierarchical Fuzzy Petri Nets Considering Time Sequence

With the increasing of scale and interconnection for the power grid, when the power system fault occured, especially in complex fault conditions, a large number of fault informations will go into the dispatching center. This situation has brought great difficulty in post processing for scheduling staff. It is necessary to study a high quality fault diagnosis system that can justify the misoperation and rejection of protection automatically, quickly and accurately. Fuzzy Petri nets can describe the relationship among the fault and the actions of protection and circuit breaker. It has the good characteristics such as simple reasoning and intuitive graphical expression. So the Petri net has been used for fault diagnosis in recent years, and some researches results have achieved.First, the improved methods of fuzzy Petri net has been studied, a fuzzy Petri net model with eight-tuple has been defined. The input and output arc weights are revised, and three calculation functions of the transition are defined, such as the calculation function of input probability synthetic fc, the calculation function of transitions excitation fF, calculation function of output probability fa), especially the calculation function of output probability fa. These working improve the diagnostic performance of fuzzy Petri nets.To improve the adaptability and to reduce the dimension of matrix, a hierarchical structure of fuzzy Petri net model is established. For the line, the subnet models in each end of the lines are established respectively for main protection, backup protection and remote backup protection, and then the intergrated subnet based on above subnets is construted to obtain the diagnosis results. For the bus, the subnets for each outgoing direction are established, and then the intergrated subnet. This method reduces the size of the model and reduces the dimension of the matrix, and improves the adaptability of the model. Finally, the different types of examples illustrate the validity of the fuzzy Petri net.By thinking about the time sequence of the protection and breakers to improve the performace of fault diagnosis, the fault diagnosis fuzzy Petri net based on timing sequence is proposed. The initial probabilities in the places of protection and breakers are corrected through the timing constraint checking, which makes the process of reverse reasoning obeys to the protection pricnlples and the actions of protection and breaker. So the the accuracy of diagnosis is improve. With the forward temporal reasoning of the fuzzy Petri nets, the information of protection and breakers can be evaluated after the fault diagnostic process. Finally, some different types of examples are made. The testing results illustrate that this method can improve the diagnostic accuracy, the rejection and misoperation of protection and breaker and the missing information can be found.