直流正极性下绞线电晕起始特性及影响因素分析

DC Positive Corona Inception Performances of Stranded Conductors and Its Affecting Factors

电晕是输电线路设计和运行中需考虑的重要问题之一。在多功能人工气候室内通过改变气压和湿度对3种不同直径钢芯铝绞线及光滑铜管进行正直流电晕试验,同时结合气体放电理论建立导线电晕起始放电模型以系统分析导线电晕起始特性影响因素。将试验数据和计算结果进行对比,两者吻合较好。电晕起始电压随相对空气密度下降、绝对湿度升高而减小,其主要原因是空气密度降低导致电离层厚度增大、湿度升高引起光子吸收系数增大及高场强区域内碰撞电离能力增强。此外,电晕起始电压随绞线半径增大和最外层股数增加而升高并呈现饱和趋势。文中还根据计算结果对绞线粗糙度系数与绞入率(绞线最外层铝线直径与绞线外径之比)的关系进行了探讨,从理论上得到表征绞线粗糙度系数的数学表达式。

Corona is one of key problems in the design and operation of transmission lines. Positive direct current （DC） corona tests of three various aluminium conductors steel reinforced （ACSRs） and smooth copper tubes were carried out in multi-functional artificial climate chamber by varying the air pressure and humidity, a computation model for evaluating the corona inception voltage on conductors was also established according to the gas discharge theory. The calculated onset voltage values agree satisfactorily with those measured experimentally. Corona onset voltage diminishes with the increase of absolute humidity and the decrease of relative air density. The main reasons are the thickness of ionization zone enlarges with the decline of air density and collision ionization intensity strengthens with the ascend of humidity as well as the photons absorption coefficient. Computation results also indicate that corona onset voltage increase with the increase of the overall conductor radius and tends to be saturated as well as the numbers of external aluminium strands. Besides, the relation between surface roughness coefficient of stranded conductor m and stranding ratio（the diameter of a aluminium strand divided by the external diameter of the stranded conductor）is discussed, a formula characterizing m is suggested theoretically in this paper.