Research Of Single-phase Intermittent Arc Grounding Fault In Low Resistance Grounding System

There are several neutral grounding methods of the power system. The main methods of distribution systems in China are neutral point non-grounding model,neutral point grounding by arc-suppression coil method and neutral point grounding by low resistance,etc. The method of neutral point grounding by low resistance is preferred in urban power grid with the reconstruction of urban power grid and the process of overhead line changing into cable as well as the wide usage of power cable. The paper analyzes the advantages and disadvantages of the neutral point grounding methods.Single-phase grounding faults accounts about 60 to 70 percent of all the faults in distribution power system,it is helpful to better understand the main faults in distribution power system and also is important in directing power system operation. In previous simulation,the single phase grounding fault is represented as metallic grounding or grounding by fixed resistance while it's mostly grounding by arc-suppression coil in actual systems. The paper summarizes the electrical arc model proposed previously and constructs the electrical arc model suitable for single grounding faults in distribution systems. The simulating platform of single phase faults in distribution system is constructed in PSCAD and proves the validity of the electrical arc model proposed.Urban Power Supply Company of SMEPC is the pioneer in the field of neutral point grounding by low resistance in China and has plentiful experience of operation for years. However,there exits some problems unsolved,one of the serious problem is the disadvantage arising from the single intermittent arc grounding of the low resistance grounding system. Due to the lack of knowledge,the usage of traditional over-current relay in the single-phase intermittent grounding faults brings about the unreliable protection action which burns out resistance and results in large losses. The paper studies the influence of the intermittent arc to the NRG system and proposes some reasonable and appropriate rectifications for relay protection according to actual situation.