Research And Implementation Of Sing-phase To Ground Fault Line Selection Algorithm In Mine Power Supply System

This project is a sub-project of Shanxi Youth Science and Technology Research Fund "Study on Stray Current Distribution and Prevention Methods of Mine Power Supply System"(Project Number: 201701D221240),which is proposed in view of the problems of low accuracy and poor reliability of fault line selection in single-phase to ground fault selective protection of mine power supply systems in China.With the extensive promotion and application of comprehensive mechanized coal mining technology,the probability of single-phase to ground faults significantly increased,because of the increase of mine load capacity and the improvement of power supply distance and power supply voltage level.Meanwhile,due to the frequent start and stop of mine large-capacity loads and extensive use of frequency conversion speed regulation devices,the misoperation,refusal to operate,and over-level tripping frequently occurred in single-phase to ground protection device.Therefore,researching the characteristics of singlephase to ground faults in mine power supply system,grasping their fault characteristics,and exploring single-phase to ground fault line selection algorithms with high sensitivity,reliability,and timeliness are very important to ensure the safe operation of mine power supply systems.This paper takes a mine power supply system of Jinmei Group as the research object,builds a typical mine power supply system simulation model with RTDS(Real Time Digital Simulator),and studies the transient and steady-state characteristics of single-phase to ground fault in the mine power supply system.With the in-depth comparison of CEEMD decomposition,MEEMD decomposition and wavelet packet transform,a single-phase ground fault line selection algorithm based on improved MEEMD has been proposed.In order to further verify the robustness and reliability of the line selection algorithm,a hardware test platform based on RTDS was built and simulated.The specific research contents are as follows:Through extensive investigation and basic theory study,on the basis of summarizing the main causes of single-phase to ground fault in mine power supply system and problems of the existing single-phase to ground fault line selection algorithm,a typical mine power supply system of Jinmei Group was built based on RTDS,and the effects of different fault factors on the transient steady-state characteristics of single-phase to ground fault are also been studied.Aiming at the problems of wrong selection and miss selection of the singlephase to ground fault line selection device in mine power supply system,three algorithms of CEEMD decomposition,MEEMD decomposition and wavelet packet transformation were studied,simulated and tested.The result shows: when single-phase to ground fault line selection is performed on ideal signals,the three line selection algorithms can show better line selection accuracy;when fault line selection is performed on non-ideal signals,MEEMD decomposition line selection accuracy is the highest,the second is wavelet packet transform,and CEEMD decomposition has the lowest accuracy of line selection.Aiming at the problem of insufficient noise component removal by MEEMD decomposition,an improved MEEMD decomposition algorithm and a singlephase to ground fault line selection algorithm based on improved MEEMD are proposed.According to reconstruction and Hilbert transform of the IMF component obtained by improved MEEMD decomposition,extract the instantaneous phase angle and energy ratio as double criteria for single-phase to ground fault line selection.The RTDS simulation test result shows: improved MEEMD decomposition has higher time-frequency decomposition characteristics than MEEMD decomposition;single-phase to ground fault line selection algorithm based on improved MEEMD decomposition has higher line selection accuracy.Based on mine power supply system model by RTDS real-time digital simulation system,a closed-loop test platform for the line selection algorithm based on RTDS,Bodian Power Amplifier and TMS320F28335 is built,and singlephase to ground fault line selection algorithm based on improved MEEMD decomposition is tested,the result shows: the algorithm can correctly choose fault line even when the single-phase to ground fault characteristic is not obvious.It has good line selection reliability and accuracy,and provides theoretical and technical guarantee to ensure the safe and reliable operation of mine power supply system.