Study On The Test And Simulation Of Small Current Grounding Line-selection Device

The Small Current Grounding System is widely applied in medium and low voltage power distribution network for its small fault current and high power supply reliability, once occurring single-phase earth fault, the system is able to run with the fault for 1~2 hours. SCGS has three different neutral grounding modes(including ungrounded, via arc suppression coil grounded and via high resistance grounded). When single-phase earth fault happens, the small fault current makes it difficult for faulty line selection, so the small fault current is not only an advantage, but also can be described as a “shortcoming”, an effective and reliable line-selection protection principle has not been found. As the distribution network develops, more and more line-selection protection devices have been put into operation, but the practical results are not so good.This article makes a brief analysis of the three different neutral grounding modes, then makes a detail analysis of the characteristics of steady state and transition condition of the system when single-phase ground fault happens. And in this theoretical foundation, introduces some main line-selection principle, and the limitations of each principle has been given. In the test section, this article tests the line selection accuracy of two devices based on RTDS(Real Time Digital Simulator) under different fault conditions, including different neutral grounding modes, different fault trigger time, and different fault types, and the test results are given. For the test link of wrong judgments, medium resistance method is proposed to improve the accuracy of the lineselection devices, and simulates the principle of medium resistance method with Matlab/Simulink, then retests the test link of wrong judgments, verifies the feasibility of improving the accuracy of the line-selection devices by using medium resistance method.