Ground Fault Analysis And Grounding Design Of DC Distribution System

The rise of DC distribution technology, based on voltage sourced convertor and dc grid technologies, brings new energy into urban distribution network. As the study of DC distribution network has just started, there is a lot of work to do in this field such as network architecture design, primary equipment development, and control and protection system research. In this thesis, the DC distribution network for urban power supply is viewed as the research object. The ground faults of that are analyzed and on this basis the grounding issues of DC distribution network are studied. First, the process of single phase-to-ground fault at the internal AC bus of the VSC, as well as the recovery process after fault, is analyzed. And value of the grounding resistance of DC capacitor midpoint is discussed, based on both the following points, to maintain the balance of DC positive and negative capacitor voltages under fault, and to achieve fast restoration of the DC voltage after fault. Then, the process of pole-to-ground fault on DC cables as well as the recovery process after fault is analyzed. And different grounding methods of the DC distribution network are discussed in comparison with each other. At last, a grounding scheme of DC distribution network is proposed from the perspective of system operation.