The Application Of Device For Fault Line Selection Based On The Model Parameter Identification Method In Neutral Indirect Grounding Power System

Neutral indirect grounding power system, possessing the advantage of high power supplyreliability, is applied widely in China. Because of complex distribution power system, faintfault current and unstable grounding arc, fault line selection in neutral indirect groundingnetwork has always been an unsolved problem in protection research.There is an obvious transient process when single-phase earth fault occurs, and transientcurrent is a few times bigger than steady current. This advantages fault line selection. So themethods using transient signals can take advantage of fault information by the transientsignals. However, they need select the feature frequency brand, which can distinguish faultline and sound line.This paper analyzs phase-frequency characteristic of zero sequence network in neutralindirect grounding power system after the single-phase-to-ground fault. By simulationanalysis, for a single line, the factors such as transmission line parameter, length, structure andbranch can affect on phase-frequency characteristic of zero sequence impedance. Furthermore, simulation analyzes the relations of phase-frequency characteristic between neutralunearthed network and neutral via arc-suppression coil network; between faulty line andsound line. The relations between fault feature and phase-frequency characteristic are alsoanalyzed. It is opened out that the principle of feature frequency band selection, and all thisprovides a research basis for the fault line selection using transient signals.Based on microcomputer protection hardware, device for fault line selection and currentprotection is developed successfully. Fault line selection method is parameter identificationalgorithm based on adaptively capturing special frequency band. The mathematical model forevery line are been established when its external fault occurs in the zero sequence network,the capacitance value of every line which have been established mathematical model are beencalculated,by judging the positive and negative of the capacitance to select the fault line andthe sound line.In the paper the integral design of the device is been given,the plug-in type structure isbeen designed,and convenient extension; the hardware and software for the device are beengiven,including the feature of hardware and the program for one and interrupt service, themain algorithms and implementation of device are been given,and so on.