| Along with the electricity load continuously growth in china, the requirements of the voltage level and transmission capacity in the whole network is constantly improved. At the same time, the area of heavy load and energy in china is serious uneven distribution. Heavy load area mainly distributed in the eastern region, and energy zone mainly distributed in the west. The long distance, high power and cross-regional electric transportation properties in china, make the transfer capability of the whole power network under great pressure.HVDC transmission system has many advantages:the cost of transmission line is low, without the system stability problems, limiting short-circuit current, regulating the speed is faster, operation performance is reliable, low frequency oscillations can be eliminated in DC interconnection, AC fault can’t be transfered in DC transmission system, chain effect in HVDC system contained, the possibility of blackouts in large area is lower, So dc transmission technology is very suitable for long distance, high power and cross-regional transmission. Compared with foreign, the research of dc transmission technology in our country is starting later, but it is developing very quickly and voltage grade of HVDC transmission has developed from±500kV to±800kV.Although China’s scholars and foreign scholars has carried out a lot of scientific research work to UHVDC transmission, and make some standards and guidelines. CIGE has proposed regulations to over-voltage protection requirements and insulation coordination for it. But the operation experience less for±800kVUHVDC transmission technology at home and abroad, electrical equipment manufacturing, long air insulation of saturated requirement and elevation higher factors on over voltage and insulation coordination demanding. So it is necessary for over voltage research.In this paper,±800kVUHVDC transmission system model is built in PSCAD/EMTDC simulation software, base on the research of converter model, converter transformermodel, transmission line modeland DC Control System etc. To bipolar ground return operation, the over voltage on dc transmission lines and the electrical components of ac and dc filter produce is analysed, it is caused by ac system fault and transmission system dc side fault. To metallic return operation, the over voltage on neutral bus and dc filter of the electrical components produce is analyzed, it is caused by converter transformer valve side fault, inverter side loss trigger pulse, smoothing reactor line side fault, rectifier sides fault between up and down the bridge. The simulation results show that the over voltage on transmission system dc lines is related to the position of fault occurring, the length and parameters of transmission line and earth-resistivity etc.The over voltage on neutral bus is caused by ac harmonic components which is induced by stray capacitance in the process of converter. From the maximum recovery to zero in over voltage, there is a long time concussion process in the neutral bus. The technical parameters and theoretical basis is provided for over voltage and insulation coordination on±800kV UHVDC transmission system. |
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