The Research And Realization Of Single Phase-to-Ground Fault Line Selection In Ineffective Grounded Systems Based On FTU

Middle voltage distribution power systems in our country are almost ineffective grounded systems (NUGS) , which include isolated neutral networks (NUS) and networks grounded with the neutral compensator coil(NES). The coefficient of single phase-to-ground fault is very high in NUGS, but the faulty current is so small that fault line selection problem has not been solved effectually until today.Based on many literatures of China and foreign countries, the principles and traits of current schemes are discussed and analyzed in this paper. Such fault line selection schemes as steady fundamental harmonic component for NUS and transient and steady harmonic component for NES are adopted in this article, which are based on deeply theory research and large numbers of dynamic model experiments. In this paper,SD-2210 feeder terminal unit(FTU) is used for collecting data unit to realize fault line selection in NUGS. SD-2210 FTU is composed of high-speed powerful data-processing ability TI's DSP TMS320F206 and high-speed high-accuracy 14-bit analog-to-digital chip MAX125. Such hardware advantages conquer the conventional SCM limitation in the speed of response and the accuracy of selection and meet the real time power system devices required. On software design, aiming at the limitations of past methods new applied line-selection criterion are optimized. Based on conventional peak value and phase compare, three perfect schemes are put forward for NUS, viz. 3C scheme,2C1V scheme and 1C1V scheme, which conquer "hour hand effect", augment phase action range and improve relay correctness. Integrated fault line selection scheme using the first half transient wave and the seventh harmonic is put forward for NES. The technique puzzle that how to catch the first half transient wave, how to locate the first half transient wave from collecting data are resolved. Peak value and phase compare conception is guided to the first half transient wave fault line selection scheme and applied criterion is given. The seventh harmonic line-selection scheme is proposed for the first time in this article, which break the conventional fifth harmonic line-selection method. The advantages of using seventh harmonic are analyzed after comparison and frequency track technique relating to seventh harmonic are also presented in this article. The combination of transient and steady effectively improve the veracity for NES. Dynamic model experiments better testify the correctness and practicability of line-selection schemes.