The Research Of Single-Phase-to-Ground Fault Line Selection And Location In Neutral Un-effectual Grounded Systems

Non-Grounded or Petersen-Grounded systems are called neutral un-effectual grounded systems (NUGS), which are widely used in the middle and low voltage distribution networks in China. The fault rate of single-phase-to-ground of NUGS is high, but its fault line selection and location have not been well solved yet. It mostly because the fault current is small and the fault trait is not obvious. With the improvement of the distribution network automation, the fault line selection and location need to be solved urgently.Based on the summary of the line selection and location methods existed, this paper presents a new method of line selection and location by obtaining the step response of the lines. The analysis indicates that the spectrum characters are greatly different between the fault and the normal lines: the frequency-amplitude characteristic of the fault line is bigger than the normal, and the magnitude-frequency characteristic of the fault line is reverse to the normal. By the analysis of fault line selection simulation, this result presented can select the true line. This paper also analyzs the relation between the peak point of frequency-amplitude characteristic and its corresponding frequency and the fault distance, and takes this two as the locating diagnostic values. By ATP simulation, the sampling data can be got and a BP neural net is trained for establishing the relation between the locating diagnostic values and the fault distance. The simulation result indicates that this method can measure the fault distance accurately.This paper designed the scheme of the hardware and software of the line selection and location device for NUGS. This paper presented the hardware scheme based on modularized designing; and offered the principle for IC device selection, the plan for the system designing and its realization; analyzed the rationality of constructing the data-sampling system with DSP and CPLD and successfully designed a control system based on them. This article presented the scheme of the software designing with the software engineering method, analyzed the each function module and presented their designing method; analyzed the importance of the software anti-jamming and produced the methods for enhancing the software reliability; established the software debugging platform and finished the module software writing.The simulation result indicates that the line step response method presented in this paper for fault line selection and location is feasible, and has certain practical value; the hardware and software system designed have higher project significance.