Simulation Of Transient Voltage And Current In HVDC VSC Networks

HVDC electrical power transmission system is an effective method to solve the problem derived from the rapid growth of power demand, long distance between energy and load center and land resources shortage in China. The realization of power transmission over long distance and large capacity makes the Multi-Terminal HVDC (MTDC) network has become inevitable. To ensure the safety and stability of HVDC system under normal condition and to recover quickly after falt occurs are important to economic development and social life. At present, MTDC technology is not very mature, many problems are needed to solve. Therefore, researches on the transient process under fault conditions of Multi-Terminal HVDC are very necessary.Firstly, summarizes on the research status and development prospects of HVDC technology are revealed,and discusses of the operation modes, network topology and fault types of HVDC system are developed. Then, with PSCAD/EMTDC software, a multi-terminal HVDC system are built to complete the simulation analysis of monopolar grounding fault, the highest frequency of fault in HVDC transmission system. Through the simulation of fault current, the fault current sources in DC transmission system can be identified and judged, and current of four factors of fault are analyzed, which are the grounding resistance, the DC capacitor, the adjacent AC system and the adjacent feeder.Then, three kinds of different grounding modes, which are the solid grounding, the high impedance grounding and the high-ohmic grounding busbars, are studied. The influence of different grounding modes on the transient voltage and current is studied. Theoretical basis for the selection of DC circuit breaker in HVDC system are provided. In the end, a high voltage DC circuit breaker model is built to simulate the ability of taking over voltage and current. The rationality and reliability of the circuit breaker model design are verified.