Research On Overvoltage And Insulation Coordination Scheme Of Medium Voltage Flexible DC Distribution Network

DC power distribution technology has become a hot spot in the domestic and international power distribution field due to its advantages of high power quality,high power transmission capacity,easy access to new energy,and small footprint of power supply corridors.With the advent of Modular Multilevel Converters(MMCs),flexible DC power distribution technology has been widely used and developed,and it has further promoted the development of multiterminal DC distribution networks.The multi-terminal flexible distribution network can realize multi-power supply and multi-point power receiving,and has various operation modes,which can better meet the construction of urban smart grid.However,the research on the flexible distribution system is still in its infancy,lacking practical operation experience,and there are many key technical problems that need to be solved urgently.One of them is the overvoltage and insulation of the system.Based on the electromagnetic transient simulation software PSCAD/EMTDC,the electromagnetic transient simulation model of ±10kV three-terminal flexible DC power distribution system with half-bridge and full-bridge sub-module topology and all cable transmission is built.The steady-state operating characteristics of the system verify the correctness of the system.According to the topology of the flexible distribution network,the typical fault conditions in the flexible distribution network are analyzed theoretically,and the overvoltage simulation analysis under typical fault conditions of the system is carried out.The topology of the converter station is studied.The effect of voltage.According to the overvoltage simulation results,three kinds of system arrester configuration schemes are proposed.The insulation level of the flexible distribution network under different arrester configuration schemes is compared and analyzed,and the system insulation coordination scheme is obtained.Finally,the lightning intrusion wave simulation model is built in PSCAD,and the influence of lightning intruding waves on the system equipment when the flexible straight distribution network is used for power transmission is studied and the lightning impulse insulation level is obtained.