| According to operation experience of the traditional HVDC power transmission project, the operating over-voltage caused by fault or operating and the lightning over-voltage seriously threat the safety of the equipments in converter station. Along with the construction of VSC-HVDC based on MMC (modular multilevel converter), the overvoltage characteristics of the converter station will directly affect the design of insulation coordination and system stability. Therefore, studying on overvoltage characteristics of the converter station has a great value. In this paper, overvoltage characteristics of the±320kv VSC-HVDC converter station based on MMC is studied, and the overvoltage protection measures are put forward.The overvoltage simulation model of MMC-HVDC system has been built under the PSCAD/EMTDC simulation environment. The control and protection system of MMC-HVDC has been considered minutely which can take control of converter station under steady state and fault state. The frequency dependent model of key equipment in converter station has been built which can be applied to the analysis of lightning overvoltage. The fault characteristics of key equipments in MMC-HVDC converter station have been analyzed in theory under typical faults. Based on the overvoltage simulation model of MMC-HVDC system, the overvoltage characteristics caused by typical faults have been simulated in detail.Unlike traditional HVDC project, the MMC-HVDC converter station has no general standards to guide its design of insulation coordination. Based on overvoltage characteristics of key equipments at converter station, a arrester protection scheme by a common calculation method has been designed and the arrester parameters for±320kV Dalian MMC-HVDC project has been configured. The protection level of arrester is obtained through simulation analysis and the equipment insulation level at converter station is determined by the recommended insulation margin. These works have the reference value for the insulation coordination of±320kV MMC-HVDC converter station. |
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