Research Of Fault Line Selection Device On Small Current Grounding Power System

Because of a series of advantage, there are a lot national power distribution network with neutral-point grounding. But the fault current in single-phase grounding is so small that it is very hard to detect, single-phase grounding protect problem have no very effectual solution as yet. In fact with conventional relay protection we can not found out the fault line at all, the special fault line selection device must be used in the power distribution network. This kind of device for special purpose has been used in 80 decade in our country, but because of the complexity of fault line selection the correct activity rate of these device is so low very much that we have to select line with the method that cut-off supply one by one. According to fault line selection problem of small current grounding power system, paper analyses fault feature of single-phase grounding in detail and educe the expression of single-phase grounding fault current, besides paper gives a general overview of various neutral grounding modes. Some existing theories and schemes on the fault line selection have been summarized systematically. Then, it presents problems, which should be solved, and conclusions have been made. After summarizing other people's experience, the paper brings forward a new design of fault line selection that focus on transient arithmetic. This device makes it perfectly meet the special requirements on hardware that transient arithmetic requires. The device is approved to be of high practical value by experiments. Some issues associated with the algorithm such as wavelet function selection, analysis level, and boundary treatment and so forth have been discussed. During the research of how to improve the reliability and accuracy of device, paper puts forward some project technology. Modularized program is easy to debug, link and modified, so program is divided into many part and debugged separately. As a result the structure of software is distinct, simple, reasonable.Eventually, we make device realize many function such as real time detection, fault phase selection, fault line selection, fault recording, device satisfies the practical requirement. Besides, device is applicable for such power system as only furnished with CT on two phases, so the shortcoming of other methods presented in recent years is overcome.