Uhvdc Transmission System Reliability And Its Influence On Ac Power Grid

UHVDC transmission system is capable of delivering high power for a long distance with less energy loss in a flexible way. Developing UHVDC complies with the nation's resource strategy and is positively supported by the government. As more UHVDC projects are being built, UHVDC is playing a more important role in grid reliability. Research on UHVDC transmission system reliability and its influence on AC power grid are of great significance.UHVDC transmission system has two 12-pulse valves on each pole. This feature makes UHVDC system more sophisticated and also more flexible for operation. This paper proposes a new reliability evaluation method based on state space method. The proposed method takes topology and flexible operation schemes of a UHVDC system into consideration. Concepts of convertor sub-system and pole sub-system are introduced to avoid the'curse of dimensionality'and sophisticated state transitions in reliability modeling. A sensitivity analysis is conducted to determine weakness in the UHVDC system and to study contribution of equipment reliability parameters on that of the whole system.In order to evaluate the influence of UHVDC system reliability on AC power grid, available transmission capability and static voltage stability of an electric system are studied by using optimal power flow method, continuous power flow method and reliability theory.To prove validity of research in this paper, reliability of a typical UHVDC system is evaluated using the method proposed in this paper. Influence of UHVDC system on AC power grid is studied in three cases: two UHVDC-connected IEEE RTS-96 reliability test systems and an ultra-high voltage AC/DC interconnected power grid in eastern China.