Research On Key Equipment's Transient Current And Grounding Current Of ±10 KV DC Power Distribution Grid

Flexible DC distribution system has been a heated research topic because of high power supply reliability,high power quality,renewable energy accessible and multiple operation modes.However,there are many problems needs to be solved since most of the research has just begun.Transient current of key equipment and system grounding current studies are both very important parts of system basic study,which results are essential for equipment design,protection scheme,grounding scheme and significant for the safety and economy of system.Based on a demonstration project of 863 program,±10 flexible DC distribution system,this paper mainly studies the transient current of key equipment and the influence on buried metal pipes of system grounding current.Firstly,based on the topological structure and main parameters of the system,it analyses the main electrical wiring forms,earth scheme and operation scheme.Then,considering control and protection schemes,simulation mode of transient current are made with PSCAD/EMTDC and steady state characteristics of the system are studied.Secondly,considering grounding scheme,simulation mode of influence on buried metal pipes of grounding current are made with CDEGS.Secondly,theoretical and simulation calculations are also established.Then,it theoretically calculates the transient current level of AC side equipment and analysis the mechanisms of DC side faults and the current-limiting methods,determining the scheme of current-limiting.Based on this,it calculates the transient current level of DC side equipment and presents the suggested engineering reference transient currents level referred the standard current level.Finally,thinking about the grounding scheme and operation modes of the system,it determines the system's grounding current level,analysis the factors that may influent ground potential of buried metal pipe lines caused by grounding currents.Based on the simulation model in CDEGS,it initializes the study on the influence on metal pipes caused by grounding currents and work out the minimum distance between earth electrode and buried metal pipes under different grounding current level,earth resistivity and different earth hieratical structure.The results of this paper may provide the design of DC power distribution system and the selection of key equipment with certain theoretical and engineering references.