| HVDC/UHVDC transmission technology is an effective measure to solve the present situation of China: energy base is far away from load center, so it expanded quickly in China. HVDC/UHVDC transmission has particular advantages of power grid interconnection and control and regulation and line corridor, but at the same time it brings all kinds of challenges on the grid’s operation, and the overvoltage is one of the focus issues. For high voltage and ultra-high voltage power grid, overvoltage will not only affect the insulation strength of power equipment, but also related to the safety and reliability of power system operation. The operating overvoltage of DC transmission system may occur on the AC side and DC side of converter station and the DC line, it is the main factor to determine the protection level of the converter arresters. The operating overvoltage of DC transmission system can be affected by the voltage rating, the converter structure, the transmission line structure and other factors, so it has important theoretical and practical engineering value to study the operating overvoltage characteristics of DC transmission system with different voltage levels and line structure.Firstly the electromagnetic transient simulation model of ±500k V single circuit HVDC transmission system, ±500k V double circuit on the same tower HVDC transmission system and ±800k V single circuit UHVDC transmission system based on the PSCAD/EMTDC power system simulation software are built. The characteristics of typical converter operating overvoltage of the three systems are simulated and analyzed and compared.Based on the method of phase-mode transformation, the fault traveling wave propagation characteristics of single circuit and double-circuit on the same tower DC transmission line are studied, and the refraction and reflection coefficients of modulus at the fault point are deduced. Furthermore the formation mechanism and the characteristics of the line overvoltage are compared, combined with the line structure characteristics of single circuit and double circuit on the same tower DC transmission line. The calculation results of different system DC transmission lines in the Bergeron model verify the theoretical analysis.On the basis of theoretical analysis, the line overvoltage characteristics of three DC transmission systems in the frequency dependent parameter model are simulated. The influence of the length of transmission line, the tower grounding resistance, the DC filter and the line arresters on the line overvoltage level are analyzed, the DC line voltage characteristics and variation law are obtained. |
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