Research & Development Of Small Current Grounding Fault Diagnosis Of Electric Power Distribution Network And Its Application

A large amount of electric power distribution systems are taking on the basic task of power supplying to widespread consumers. With the development of society and economy, the demand for electric power supply and its ability has been increased rapidly in recent years. Consequently, it is necessary to analyze the abnormal state and find out the insulation hidden trouble of the electric power distribution networks. Besides, faults should be detected rapidly and effectively in order to guarantee the operation of the distribution systems safely and reliably. Most of 3-66kV electric power distribution systems adopt the small current neutral grounding system. The research of single phase-to-earth fault location is the focus in this field nowadays.The fault diagnosis system of small current grounding contain two sections:one is fault line selection which is to select the fault line from all the lines in the electric power distribution network; the other one is fault detection distance which is to measure the location of fault accurately in the fault line.Based on many fault line selecting methods, a new approach based on the D-S evidence theory for fault line selection is proposed in this thesis. There are three methods of selecting line. When a single phase to earth happened, three methods of selecting line to make a decision which line is fault are used. Every method can give a result through computing the fault data. But the results may not be consistent and it may not be decided which result is right. It is the efficiency problem of the methods to the fault in the system. This problem can be solved based on the method proposed in this thesis. Firstly, a pretreatment is made for the collected fault data to enhance the useful information and take out the redundancy information. And then the method of selecting line which is proposed in this thesis to decide which line is fault. Secondly, a weight is given to every result according to the characteristic of the method of selecting line and synthesizes all the results. Then every result has a confident interval. According to the confident interval and judgment rules based on the evident theory, the final decision can be made with high accuracy. This approach is powerfully complementary for the other ones. The hardware of small current grounding system is also proposed. Meanwhile, a support management system is designed as well.By plenty of spot tests, the results show that the methods putting forward in the thesis are efificient and reliable.