Study Of Earth Fault Detection In Small Current Grounding Network Based On Evidence Theory

Earth fault detection in small current grounding network is the technology of detecting the fault line correctly when single-phase-to-earth fault occurs in small current grounding network. The Paper aims that single detection method has the disadvantages of being limited to apply and not very credible and puts forward the method of earth fault detection in small current grounding network based on evidence theory. The state and transient signals of network are distilled first, in virtue of the differences of fault line and right lines in state and transient signals, the state signal detection criterion,the high frequency power criterion and the transient current direction criterion are constructed. In order to indicate the degree to trust that the line we detected is the fault line, the three criterions are all numerical. The three criterions are simulated and the fault measures of each line in kinds of fault cases are found. On this basis, combining the practical situation of small current grounding network and the correlative conception of evidence theory, the discernment frame is defined, the belief assignment function is constructed and the three evidences used for the final fusion are obtained. On the foundation of the analysis of each evidence, proper fusion rule is used according to the characteristic of each evidence. The detection regulation is constituted and the detection result can be gained. Six typical fault cases are simulated and the result indicates that the method of earth fault detection in small current grounding network based on fusion rule improved evidence theory can detect the fault line correctly, the method can be wide used and its detection reliability is high.