输电线覆冰在升温、自然风或人为外力作用下会发生覆冰整档或一档内部分位置脱冰,引起输电线跳跃,导致导线相间或导地线间闪络、线路跳闸、断股断线以及输电塔失稳倒塌等事故,严重威胁电力系统安全.参照实际750 kV输电线路工程,建立连续档分裂导线有限元模型,分析档数、档距、高差、覆冰厚度、风速、脱冰率和绝缘子串长度等因素对导线均匀和不均匀脱冰跳跃高度的影响;讨论均匀和不均匀两种脱冰方式下导线脱冰跳跃高度之间的联系,定义不均匀脱冰时发生脱冰的导线长度为换算档距;对比现有导线冰跳高度计算公式的准确性,提出不均匀脱冰跳跃高度系数.结果表明:当脱冰荷载相同时,不均匀脱冰引起的脱冰跳跃高度更大;不均匀脱冰时冰跳高度与换算档距下完全脱冰的冰跳高度存在一定比例关系;建立了导线均匀脱冰和不均匀脱冰跳跃高度计算公式,所提均匀脱冰跳跃高度计算公式的最大相对误差为11.8％,不均匀脱冰跳跃高度计算公式相对误差大于10％的结果仅占结果总数的13.2％,计算精度较高,有助于线路设计时确定相地或相间安全间隙.

数字化设计已成为输电线路设计行业发展的必然趋势.当前输电线路数字化设计从软件平台开发到工程应用均未有实质性突破,仍停留在将传统设计方式得到的设计成果三维模型化、结构化的浅层阶段.本文分析输电线路数字化设计的现状及误区,探讨改进方向,认为输电线路数字化设计应当合理定位,以提高设计效率、提升设计质量为原则,需要改变重三维建模、轻数字化集成的理念,并通过和软件供应商和需求单位的密切合作,积极探索集成勘测设计新技术,建设多专业协同设计数字化平台.

借鉴以往复合横担杆塔的设计经验,从绝缘配置、电磁环境、空气间隙、电位分布计算和纵向不平衡张力等方面对特高压直流线路杆塔的复合横担布置方式进行研究,通过对杆塔钢材、基础指标、绝缘子串费用以及线路走廊费用进行综合经济比较,选择出合理的复合横担布置方案,为特高压直流线路复合横担塔设计提供借鉴和参考.

The polarity distance of the ± 1 100kV transmission line has great influence on the tower head size,tower weight,distance to the ground,corridor width and electromagnetic environment.In order to optimize the polarity distance and improve economical and social benefits,the relationship between the electromagnetic environment,air gap,insulator string length,distance to the ground,corridor width,tower weight and polarity distance are studied in this paper based on the Zhundong-Huadong± 1 100kV transmission line project.The minimal annual cost method is used to analyze the economic conditions,and the optimal polarity distance under the influence of multiple factors is given.It has been proved that the polarity distance of the ± 1100kV transmission line is controlled by the insulator string length and air gap,and on this basis,the follow-up study on the insulation configuration is recommended.

Composite cross-arm of 750kV cup type tower bears both electric and mechanical loads. Owing to its high operation voltage and very complex insulation structure, potential and electric field distributions of composite cross-arm are extremely uneven. It may affect long-term stable operation of transmission line. Using three dimension finite element method (FEM), this paper presented research on voltage equalizing characteristics of composite cross-arms in 750 kV cup type tower. Computation model was established. The potential and electric field distributions of middle phase and side phase under several design schemes were computed. The program for grading and shielding devices was designed and then optimized. The electric field computation results showed that the electric field strengths on key positions were within permitted range. Corona tests showed that no visible corona discharge was found from insulators or fittings when the applied voltage was 1.2 times of test voltage. The design of the grading and shielding devices can be applied in actual projects.

Selection of the conductor is important in the design of power transmission lines.This paper demonstrates possibilities of using quadri-split conductors in 750 kV transmission lines,including comprehensive analysis and comparison of its electrical properties,mechanical performance and economic performance.The study results show that in the areas of lower altitude and smaller corona loss,the quadri-split conductors with the adequate aluminum cross-section meet the electromagnetic environment limits,reduce the preliminary investment,and their long-term operation economy are equivalent to those of the six-split conductors,therefore help substantially to reduce the project cost.

The external insulation of extra-high voltage overhead transmission line is depended on the operating voltage,switching overvoltage and lightning overvoltage.Based on the national standards,national rules and IEC standards,the 750 kV project use the first batch of research results and conclusions ofThe key technology research on 750 kV double circuit transmission line project in Northwest Power Gridand the related conclusions ofThe key technology research on 750 kV transmission and power transfer project in Northwest Power Gridfor reference.According to the specific features of the project,the successful design experiences for the first 750 kV Guanting-East Lanzhou transmission and power transfer project and the mature design experiences for 750 kV voltage grade transmission line in foreign countries are applied.Combining with the design and operation experiences of 330 kV and 500 kV double circuit transmission line in China,the conclusions of insulation coordination and selection of insulators for 750 kV East Lan-zhou-Pingliang project are proposed.