交流和直流输电线路的经济比较

Economical Comparison of AC and DC Transmission Lines

为比较交直流输电线路的经济性能,首先指出,在采用可控并联电抗器的条件下,交流输电线路的长度和传输功率不受限制。交、直流输电经济比较的准则为线路长度、传输功率、导线功耗和导线电流密度均相同,因此交流相电压应与双极直流的极地电压相等,从而两者的导线重量和价格相同,线路杆塔总的机械负荷和价格亦大体相同,但直流线路的两侧要求设置十分昂贵的换流站和无功能源,故而直流输电的总费用远比交流高;对远距离输电线路常需与中间系统相连的问题,交流线路只用投入联络变压器,而直流线路则需设置代价高昂的换流站。过去人们常将直流极地电压等同于交流相间电压而作对比,得出≥1000km距离时的直流线路要比交流线路更为经济的不适当结论。由于以上主要原因,欧洲国家(包括俄罗斯)不采用架空直流输电线路。

This paper indicates that there is no limit in the length and transmitted power for AC lines when shunt controllable reactors are used. For economical comparisons between AC and DC transmission lines following criteria are to be considered： the same line length, the same transmitted power, the same power loss in conductors, while the full capacity is transmitted, the same current density in conductors. Under these conditions the phase voltage of AC lines is to be equal to the pole-voltage of DC lines, resulting in the same weight and cost of the two types of line conductors and the same total mechanical loading of towers for both lines. However DC lines require converter stations and additional reactive power sources, implying that the total cost of a DC line is significantly higher than that of an AC line. Moreover AC lines can be easily connected to intermediate systems through transformers, but such connections for DC lines require costly converter stations. Our results do not support the existing belief that DC lines have advantages comparing AC lines when the line length is over 1000 km. These results allow to understand why over-head DC lines have been not deployed in Europe including Russia with the vast territory.