近年来，高湿热地区500kV主网架输电线路发生多起双联串复合绝缘子断串事故，断点均为复合绝缘子高压端靠近均压环上方的区域，与复合绝缘子轴向电场最大值所在区域一致，因此分析断串与均压环配置不合理有关，这一问题将严重威胁电网运行可靠性。目前相关标准对复合绝缘子双联串均压环的规定仍不明确，对复合绝缘子端部场强限值的规定是否适用于高湿热地区存在疑问。因此，需要对高湿热地区复合绝缘子端部场强限值重新进行研究与界定，并为高湿热地区适用的复合绝缘子提出工程可行的均压环结构参数推荐值，为电网单位提供高湿热地区输电线路运维保障措施，对保证高湿热地区电网长期安全可靠运行具有重要意义。首先，论文进行了高湿热地区复合绝缘子端部场强限值的研究与界定。研究了单水珠的交流起晕特性，基于控制变量法通过仿真计算针对体积和接触角两个参数研究了水珠参数对端部场强畸变的影响。同时基于钢珠内部场强为零和不形变的特性，采用不同体积不同接触角的钢珠验证了体积和接触角对起晕的影响趋势。试验表明体积越大的水珠在电场力作用下接触角更小，更易产生电晕。针对自然湿润环境研究了凝露、淋雨和雨后三种条件下水珠的交流起晕特性，试验结果表明基础场强低于3kV/cm（有效值）可限制自然环境多水珠发生持续电晕。因此以3kV/cm为高湿热地区500kV复合绝缘子端部电场限值比较合适。其次，论文开展了500kV交流和±500kV直流典型输电线路不同串型复合绝缘子高压端均压环的仿真优化研究。搭建了与实际线路尺寸相同的1:1三维塔线绝缘子模型，计算了不同串型复合绝缘子表面及均压环表面电场分布。采用控制变量法研究了大小均压环配置下大均压环尺寸参数对复合绝缘子端部场强的影响规律，并依据此规律采用枚举法对不同串型复合绝缘子高压端均压环进行尺寸参数优化，使复合绝缘子端部表面电场低于高湿热地区复合绝缘子端部场强限值，均压环表面电场低于20kV/cm，满足复合绝缘子端部场强要求。最后，开展了优化均压环的性能试验研究。通过电晕试验、复合绝缘子雷电冲击试验、复合绝缘子高压端电场测量试验和挂网试运行4项试验，研究了优化均压环对复合绝缘子整体性能的影响及对端部电场的实际改善效果。

In recent years, double string composite insulators breakage accidents have occurred on 500kV main grid transmission lines in high humid and hot areas. The breakpoints are located in the area near the energized end of the composite insulator above the grading ring, consistent with the area where the maximum axial electric field of the composite insulator is located. Therefore, the analysis shows that the insulator breakage is related to the unreasonable configuration of the grading ring, which will seriously threaten the reliability of power grid operation. At present, the regulations on the grading ring of double string composite insulators in available standards are still unclear, and there are doubts about whether the regulations on E-field strength limit around the energized end of composite insulators are applicable to high humid and hot areas. Therefore, it is necessary to re-study and define E-field strength limit around the energized end of composite insulators in high humid and hot areas, and propose feasible recommended values for the grading ring structure parameters of composite insulators suitable for high humid and hot areas. This provides power grid units with measures to ensure the operation and maintenance of transmission lines in high humid and hot areas, and is of great significance for ensuring the long-term safe and reliable operation of power grids in high humid and hot areas.Firstly, the thesis conducted a study and definition of E-field strength limit around the energized end of composite insulators in high humid and hot areas. The AC onset corona discharge characteristics of single water droplet was studied. Based on the Control variates, the influence of the water droplet parameters on the distortion of the E-field around the triple point junction was studied through simulation for the two parameters of volume and contact angle. At the same time, based on the characteristics of zero internal E-field strength and no deformation of the steel ball, the influence trend of volume and contact angle on onset corona discharge was verified using steel balls with different volumes and contact angles. Experiments have shown that larger water droplets have a smaller contact angle under AC electric field forces and are more prone to excite corona discharge. The AC onset corona discharge characteristics of water droplets under three conditions of condensation, rain exposure, and after-rainning were studied for natural humid environments. The experimental results showed that the basic E-field strength below 3kV/cm (effective value) can limit the occurrence of continuous corona discharge in natural environments with multiple water droplets. Therefore, taking 3kV/cm as E-field strength limit around the energized end of 500kV composite insulators in high humid and hot areas is more suitable.Secondly, the thesis conducted simulation and optimization research on the energized grading rings of different string composite insulators for typical 500kV AC and ±500kV DC transmission lines. A 1:1 three-dimensional tower-line-insulator model with the same size as the actual line was built, and the E-field distribution on the surface of different string composite insulators and grading rings was calculated. The Control variates is used to study the influence of the structure parameters of the large grading ring on the E-field strength at the energized end of composite insulator under the configuration of one large and one small grading rings. According to this rule, the structure parameters of the grading ring at the energized end of different string composite insulators are optimized by enumeration method, so that the electric field at the end of composite insulator is lower than the energized end E-field strength limit of composite insulator in high humid and hot areas, and the electric field at the surface of the grading ring is lower than 20kV/cm. The optimized grading ring can meet the E-field strength requirements at the end of composite insulators.Finally, performance experiments were conducted to the optimized grading rings. Through four tests: corona test, composite insulator lightning impulse test, electric field measurement test of the energized end of composite insulator, and grid trial operation, the impact of the optimized grading rings on the overall performance of composite insulators and the actual improvement effect on the electric field around the energized end of composite insulator were studied.