Simulation Test System For Small Current Grounding Fault Based On Digital Simulation Results

80% of grounding faults in distribution network are small current grounding faults.In order to improve the power supply reliability of small current grounding systems,relay protection devices with functions such as line selection,positioning,and demarcation based on various protection methods have been developed.When it comes out,its application effect may be mixed due to the protection method or hardware structure used.It needs to be tested a lot before its development and application in the distribution network.The current test system is expensive,and the digital simulation model used also has the disadvantages of a single model,a line structure that is not in line with reality,poor versatility,and a large gap between the simulated results and the actual results.The development of the relay protection tester(RXRelay Tester)technology overcomes the shortcomings of its bulky and low precision.The test system consisting of the relay protection tester and the computer can not only output waveforms having high similarity with digital simulation waveform,can also make full use of the digital simulation's advantages that simulation scale without limitation,portability and scalability.This paper uses computer and relay protection tester to form a test system,focusing on the digital simulation of the test system.The work is as follows:(1)the influencing factors of single-phase ground fault characteristics was introduced,which was analyzed in detail through equivalent circuits and mathematical expressions.(2)The main protection methods adopted by relay protection devices was introduced,and the requirements on the structure of simulation models was analyzed;(3)According to the structure of distribution network and the requirements of various protection methods on the structure of simulation models,urban distribution network and rural distribution network was established by ATP-EMTP,of which parameters and calculation methods were given in detail.(4)The influence of the simulation step size on the test system was analyzed,of which setup method was given according to the sampling theorem.(5)The arc simulation model was built according to the Hochrainer arc model,and the test circuit was established,with which the arc characteristics during stable combustion were analyzed;(6)The process of intermittent arc grounding was analyzed.And the simulation of intermittent arc grounding was optimized by improving the conditions of arc ignition and arc extinguishing and setting ground conductance;(7)The simulation waveform was analyzed,and the usability of the test system was verified by comparing with the actual fault waveform and the theoretical analysis;(8)Finally,the convenience of using the test system is increased by establishing human-computer interaction interface and database.The simulation test system for small current grounding fault based on digital simulation results can simulate most types of small current grounding fault.While reducing the test cost,it can realize the comprehensive test of the small current grounding protection device with the function of line selection,location or demarcation,which is of great significance to improve the reliability of power supply in distribution network.