中文摘要：

首先对特高压输电线路的不平衡度进行了理论分析,分析结果表明,特高压同塔双回输电线路在不换位的时候,存在电气不平衡度。然后结合工程实例,利用PSCAD/EMTDC仿真软件建立同塔双回输电线路模型,研究了同塔双回输电线路的相序排列以及线路长度对输电线路不平衡度的影响,仿真结果表明,不同相序排列下的输电线路不平衡度各异,在6种输电线路的相序排列中,同相序（ABC-ABC）排列时不平衡度最大,逆相序（ABCCBA）排列下的输电线路电气不平衡度最小;同塔双回输电线路的不平衡度与输电线路的长度有关,并且不平衡度随着线路长度的增加而增大。

英文摘要：

Firstly,the UHV transmission line unbalance is analyzed in this paper,analysis results show that：UHV double circuit transmission lines on the same tower in the transposition of the time,there is electric unbalance degree;then combined with the engineering example,the establishment of double circuit transmission lines on the same tower model by using PSCAD/EMTDC simulation software,the double circuit on the same tower transmission line phase sequence and line length of transmission line affect imbalance,the simulation results show that：unbalanced degree of the transmission lines of different phase sequence is different,phase sequence in 6kinds of transmission lines,the same sequence（ABC-ABC）in the unbalanced degree is the largestand transmission line electric imbalance is minimalin the reverse phase sequence（ABC-CBA）;double circuit transmission lines on the same tower unbalance and transmission lines,and the unbalanced degree increased with increasing the length of the line.