Research On The Overvoltage And Insulation Coordination Of ±10kV DC Power Distribution System

The DC distribution network has advantages of high power quality, no need for reactive power compensation, can isolate trouble areas and easy for renewable energy and energy storage to access, and it is becoming the research hotspot at home and abroad. The domestic research on DC distribution network is still in its infancy, there are many unresolved issues. Overvoltage and insulation coordination is one of the key technologies that must be solved in the research of DC distribution, the results will directly determine the insulation level of equipments in the system, and has an important impact on security, technical and economic of the system. Focused on a ±10 kV distribution system based on Flexible DC, which is put the 863 project named " Research and Application of Key Technologies of Intelligent Power Distribution Network Based on Flexible DC" which is undertaken by Shenzhen Power Supply Bureau, the research on the influences of the access mode and grounding scheme on the overvoltage and over-current of the system, as well as the overvoltage and insulation coordination of DC distribution system were conducted in this paper, and the access mode, the grounding scheme, the insulation scheme of system, and the insulation level of critical equipment were put forward.Based on the main circuit parameters of the system, the modeling method of key equipments were researched, such as the converter, DC circuit breaker, DC transformers, AC-DC micro-grid, energy storage devices, DC lines and other key equipments, then the electromagnetic transient simulation model of the system was established in PSCAD, and the simulations were carried out on the system model to obtain its stable operation characteristics. To study the access mode of DC distribution system to AC network, the theoretical and simulation analysis were carried out. First, the four possible main circuit structure under two access methods was theoretically analyzed, then combining simulation, the mutual effects between the AC and DC side under typical faults were analyzed, and the recommended access is determined; By considering the requirements that the system can continuous operation for a period under monopole ground fault, the grounding scheme that the system grounds via an shunt resistors in the neutral point of the coupling transformer was proposed and validated. According to the protection scheme of the system, typical faults that may occur in each area of the system were analyzed, and the key positions need to focus on in the overvoltage studies were identified. And then, by considering the characteristics of DC distribution system itself, the arrester configuration scheme was proposed, and the volt-ampere characteristics of each arrester were determined. Based on system modeling, the study results of access mode, the typical fault analysis and configuration scheme of the arrester, simulation calculations of the overvoltage under typical faults were carried out on the system model. Finally, based on the over-voltage calculation results and the protection level of the arresters, the insulation level of key equipments in the system were presented.