Research On Grounding Line Selection Technology Of Coal Mine Power Based On Improved Admittance Method

With the further betterment of the mechanization and automation of the coal mining industry in my country,the power supply load of the coal mine power grid has increased substantially,the power supply system is more complex,and electrical failures are more likely to occur.Statistics show that the type of fault may occur in the mine power grid is single-phase grounding fault Mainly,accounting for about 80%of the total electrical faults in the mine power grid.Due to the special environment during underground construction,when a single-phase grounding accident occurs somewhere,it is more harmful,which may damage electrical equipment,and even cause explosions,fires and other accidents.At present,there has been no worthy solving to the difficulty of single-phase grounding fault line selection in coal mines.For this reason,this article will discuss the problem of grounding line selection of coal mine power grids.This paper analyzes the formation principle and features of the steady-state and transient processes of the neutral point ungrounded system and the single-phase grounding fault of the arc suppression coil grounding system in the coal mine power grid,and theoretically discusses the related characteristics of the zero sequence voltage and zero sequence voltage.The simulation model of the underground coal mine power grid was built by Matlab,and the zero sequence power direction method,the fifth harmonic method and the first half wave method were simulated,and the advantages and disadvantages of each method and the scope of application were analyzed.At the same time,this paper analyzes the basic principles of the zero-sequence admittance method in detail and simulates and analyzes it.On this basis,the improved admittance method is proposed.The improved admittance is composed of the fundamental waveguide and the fifth and seventh harmonic admittance.And the improved admittance values of five cycles are accumulated and phasor summed,and finally a clear fault direction is obtained.The simulation results show that the improved admittance method effectively reduces the misoperation area on the zero-sequence admittance complex plane.This paper uses ONLLY-A430 relay protection instrument to simulate the fault signal,set the different phase difference between the zero sequence voltage and the zero sequence current to simulate possible fault conditions and conduct experimental verification.The experimental data shows that the improved admittance method can accurately select the fault line.Finally,the safety performance verification device of the power supply monitoring system is used to set the grounding at different locations of the mine three-level substation,and the signals are collected at different measurement points to verify the effectiveness of the improved admittance method.The experimental results show that the improved admittance method is suitable for single-phase ground fault line selection in underground multi-level power supply systems.