中文摘要：

750kV输电线路分布电容大、波阻抗较小，线路的工频过电压及操作过电压比一般超高压线路更为严重，为了合理确定绝缘配合，有必要对其各种过电压进行研究。结合西北地区官亭一西宁750kV输变电工程，分析了电抗器中性点电抗与潜供电流、恢复电压的关系，通过计算确定了中性点电抗的取值，保证了单相重合闸的成功率。研究了各种运行方式下的工频过电压及合闸操作过电压，包括三相合闸、单相自动重合闸过电压，同时分析了金属氧化物避雷器（MOA）、断路器并联电阻等措施对过电压的抑制效果，并与实际测量结果进行了比较。在此基础上，改变线路输送容量、线路长度及保护配置方案，对750kV交流输电线路取消合闸电阻的条件进行了研究。通过电磁暂态程序（EMTP）的仿真计算表明，线路两端装设电抗器后，工频过电压符合我国关于超高压线路工频过电压的要求。同时采用线路两端装设MOA和断路器装设并联电阻的方法，可以有效降低操作过电压，而且对MOA和并联电阻热容量要求不高。当线路输送功率为700Mw，线路长度〈60km时可以取消断路器合闸电阻，仅靠线路两端的MOA就可将操作过电压限制到线路设计水平以下。若沿线路增加一组MOA，满足同样的过电压要求，线路允许长度可达380km。

英文摘要：

The overvoltages of 750 kV transmission line are more serious because of its long length, small surge impedance and large distributing capacitance, hence it is necessary to study the power frequency and switching overvoltages, which provides reasonable reference for insulation coordination. Combined with 750 kV power transmission project from Guanting to Xining which has been reasoned by State Power Grid Corp. of China, the relationship between the neutral reactance of three phase reactor and the secondary arc current was analyzed. The value of neutral reactance was selected, which ensured the success of single-phase auto-reclosing. The power frequency overvoltage and switching overvoltage, including three-phase closing with no load and single-phase auto-reclosing, were studied. The protective effects of shunt reactor, MOA and parallel resistor in CB （circuit breaker） on the overvoltages above were also discussed. Based on the studies above, with the altering of distributing capacitance and the length of the transmission line, the condition of removing the parallel resistor in CB is studied, which are compared with the practical results. From the theoretical analysis and simulated results of Electro Magnetic Transient Program （EMTP}, it is shown that the power frequency overvoltage is under the concerned regulations of our country owing to the reactors connected to the line. Combining MOA and parallel resistor in CB is a good measure to limit switching overvoltage without such high requirement on thermal capacity of MOA and resistor. When eliminating closing resistor, MOA can work normally, but the magnitudes of switching overvoltage is too high to be against engineering request. For the distributing capacitance of 700 MW, the parallel resistor in CB could be removed if the line length is below 60 km. The arresters installed at both ends of the line could limit the overvoltages within the design allowable value. To meet the same regulation, the maximal length of the transmission line would be up to 380 km b