| Operation statistical results of±500kV HVDC transmission system showed that switching overvoltage due to faults or operation is the main threat to devices at the DC side of converter station. With the coming construction of UHVDC transmission project in China, research of the characteristic of inner-overvoltage in UHVDC converter station is one of essential subjects especially for insulation coordination design and steady operation of system. Therefore, it has important scientific significance and engineering practical value to carry out the characteristic of overvoltage in UHVDC converter station. This thesis discussed the characteristic of switching overvoltage at the DC side of±800kV UHVDC converter station.Due to the cause of switching overvoltage at the DC side of±800kV UHVDC converter station, this thesis with Electro-Magnetic Transient Direct Current (EMTDC) is a compute tool, builds up the calculation model of switching overvoltage on converter station's direct current side based on the mathematical model of Zinc oxide lightning arrester and switching overvoltage in power system, in which analyzes under many typical operation and faults condition of the converter station, the switching overvoltage probably appeared at the direct current side of converter station. Abundant simulating experimentations calculation are carried out to analyze, under various typical operation and fault work condition, the maximum overvoltage on AC buses, DC lines, Neutral Buses and so on which is main equipments inside of converter station. Then load of arresters relate to place above was also discussed.Based on the simulation results of switching overvoltage at the DC side of±800kV UHVDC converter station, this thesis analyzes both the influence of converter station direct current side's switching overvoltage to converter valve, converter transformer etc. Because of current±500kV arrester configuration not to satisfy the demand of overvoltage protection for±800kV converter station, and the installation of smoothing reactor for±800kV converter station that separately built in the DC line and neutral bus can reduce both the installation price and the peak value of harmonic voltage to ground in converter station. Thinking of the new problem produced by UHVDC arresters'more discharge capacity, this thesis compare with the protection level and safety margin under the two different arrester application based on the calculation result of switching overvoltage at the DC side of±800kV UHVDC converter station and the parameter of arrester provided by SIEMENS company, which for the better choice of arrester application. The conclusion of this thesis has some instructional function to study and design insulation coordination of±800kV UHVDC transmission system. |
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