The Research Of Fault Line Selection In Resonant Grounded System And The Design Of Hardware Platform

Currently, resonance grounding has already been widely used in the mid-voltage distribution network. However, its fault line selection has never been well solved. Besides, the performance of fault line selection device is limited by hardware level such as microprocessor operation speed, the sampling rate of signal, storage capacity, etc. Most existing algorithms are based on steady-state fault feature and the information of fault cannot be fully utilized. The phenomenon of selecting the unwanted line still exists. Therefore, the problem of fault line selection in resonant grounded system remains to be further studied. Around this question, this paper carries on the research from two aspects of hardware and algorithm.The paper analyzes analyses the transient process of single-phase grounding fault in resonant grounded system. The expression of transient zero-sequence fault current is deduced based on the equivalent circuit. According to the simulation of different fault, the paper summarizes the fault feature of zero sequence voltage and zero sequence current in time domain and frequency domain. On the basis of wavelet packet analysis, a new adaptive algorithm is proposed, which is based on the distribution characteristics of frequency band energy. The wavelet packet algorithm is used to calculate the frequency band energy by normalization method. The fault is divided into three situations according to the energy of Band Zero. The specific criteria are selected to select the fault line according to each situation. The effectiveness of the presented algorithm has been proved by the simulation example of MATLAB.Approximate entropy(ApEn) is introduced into fault line selection according to the distribution of fault components of fault phase when single-phase grounding fault occurs in resonant grounded system. Simulation of various ground faults under different conditions is performed. The results show that ApEn is suitable as a kind of criteria in fault line selection. Given the accuracy of ApEn and the unreliability of single criterion, the paper uses the sample entropy(SampEn) of high precision. Based on SampEn and empirical mode decomposition(EMD), then the concept of intrinsic mode entropy(IMEn) is proposed. The method is accurate and reliable, according to the simulation example.A fault line selection device is designed based on FPGA and dual-core processor of ARM+DSP. The processor is responsible for lots of functions such as the algorithm implementation, human-computer interfaces, network communication, data storage, etc. FPGA is responsible for A/D sampling of 36 channels, including zero-sequence voltage of 4 channels and zero-sequence current of 32 channels. Sampling rate is 25.6 kHz. Finally, anti-jamming measure is proposed from a hardware and software aspect. The fault line selection device designed has strong data collection and processing ability. Besides, the device has numerous communication interface and friendly human-computer interface. It is suitable for the implementation of complex algorism.