【作者】 王艳；

【导师】 李剑；

【作者基本信息】 重庆大学 ， 电气工程， 2014， 博士

【摘要】 换流变压器是高压直流输电系统的关键设备。与普通电力变压器相比，换流变压器的运行工况更为严厉，导致换流变压器故障率高于普通电力变压器。作者针对换流变压器油纸绝缘可靠性评估的需要，对油纸绝缘脉动直流电压耐受特性、电老化过程中油纸绝缘空间电荷特性以及油纸绝缘失效模型三个方面的问题进行了深入研究，论文主要内容有：①对油纸绝缘的脉动直流电压耐受特性及脉动系数与温度对油纸绝缘短时耐受电压和失效时间的影响规律进行了试验研究。采用均匀升压法，在五个温度下测量了油纸绝缘在脉动直流、交流和直流电压下的短时耐受电压，结合油纸绝缘相对介电常数和体积电阻率随温度的变化规律，对脉动直流电压下油纸绝缘短时耐受电压随温度变化的规律进行了分析；采用恒压法，测量了油纸绝缘在三种电压下的失效时间，分析了油纸绝缘失效时间随电压和温度的变化规律。测量结果表明，与交流和直流电压相比，脉动直流电压下的油纸绝缘电老化特性具有显著差异。②研究了油纸绝缘在脉动直流电压下电老化过程中的空间电荷变化特性。采用电声脉冲法测量了电老化油纸试品内部空间电荷密度，分析了电老化油纸试品的空间电荷注入、累积、积聚和消散过程，研究了电老化时间和温度对油纸试品空间电荷汇聚和消散特性的影响。试验与分析结果表明，电老化时间的增加和温度升高，均会导致油纸试品内部电荷密度增加，温度升高使得空间场强畸变更为严重。③研究了脉动直流电压下电老化油纸绝缘的空间电荷特征量及其变化规律，探究了油纸绝缘电老化特性。通过试品内部空间电荷密度，计算并对比分析了油纸绝缘空间电荷特征量随老化时间和温度变化的规律，提出了油纸绝缘空间电荷特征量与电老化特性相结合的分析方法，探究了老化时间和温度对油纸绝缘电老化特性的影响机制。研究结果表明，电老化时间的延长加速油纸绝缘老化。温度的升高增强了电场对油纸绝缘电老化特性的影响。④通过分析油纸绝缘失效时间和失效场强威布尔分布的变化规律，提出了油纸绝缘多风险失效模型的构建方法，建立了双变量威布尔失效模型，分析了脉动直流电压下油纸绝缘电老化失效率的准确性，提出了油纸绝缘失效率分布的综合检验指标反映失效模型估计正确性和精度的评估方法，验证了双变量威布尔失效模型的正确性和建模方法的有效性。结果表明，双变量威布尔失效模型更有效反映失效场强与油纸绝缘失效率之间的关系，提高了失效模型计算结果的准确性。上述研究工作是在换流变压器阀侧绕组绝缘的电老化特性方面的积极探索，揭示了在脉动直流电压下老化时间和温度对油纸绝缘电老化的影响机制。同时丰富了油纸绝缘电老化评估的研究成果，并为换流变压器油纸绝缘失效诊断以及可靠性评估提供了理论支撑和试验依据。更多还原

【Abstract】 Converter transformer is the key equipment and directly affects the reliability inHVDC transmission system. Operating conditions of converter transformers are moresevere than the power transformer which causing the coil insulation failure probabilityof converter transformer is higher than the power transformer. With the problems ofreliability evaluation methods of oil-paper insulation of converter transformer, thecharacteristics of withstand voltage, space charge and the failure model of oil-paperinsulation at the pulsating DC voltage are presented in the thesis. The main contents areshown as follows:①The withstand voltage characteristics of oil-paper insulation at pulsating DCvoltage were researched. The influence of the temperature and ripple factor on thewithstand voltage and failure time of oil-paper insulation at pulsating DC voltage wereresearched. The withstand voltage under pulsating DC, AC, and DC voltages wereobtained using short-term pressure method. The variation rules of relative dielectricconstant and volume resistivity of the oil-paper insulation were analyzed which changedwith temperatures. The failure time of oil-paper insulation were obtained using constantmethod; The variation rules of failure time of oil-paper insulation were analyzed whichchanged with voltage and temperatures. The results showed that, compared with the ACand DC voltage, the electrical aging properties of oil-paper insulation at pulsating DCvoltage have significant difference.②The space charge characteristics of oil-paper insulation were researched atpulsating DC voltage during electrical aging process. The space charge injection,accumulation and dissipation processes were analyzed using space charge density ofspecimens which tested by electro-acoustic pulse method; and the effect of electricalaging time and temperature on the space charge accumulation and dissipationcharacteristics of oil-paper insulation were researched. The results showed that thespace charge density of specimens increased with the electrical aging time extended andincrease of aging temperature. With temperature increasing, the field distortion distortedwas more serious.③The variation rules of space charge characteristics of electrical aging oil-paperinsulation at pulsating DC voltage were researched for electrical aging characteristics ofinsulation. The variation rules of failure time and temperatures which changed with space charge behavior were analyzed by space charge density of specimens. Theanalysis method of combined space charge characteristics and electrical aging ofoil-paper insulation was proposed. The influence of temperature and aging time on theelectrical aging of oil-paper insulation was researched. And the influence mechanism ofaging time and temperature on space charge characteristics of electrical aging insulationwas analyzed. The results showed that the extended aging time accelerate oil-paperinsulation aging; the temperature further strengthens its aging effect on oil-paper theinsulation.④The variation rules of weibull distribution of the failure time and electricstrength were analyzed. The multi-risk failure model and modeling method of oil-paperinsulation at pulsating DC voltages was proposed. And the dual-variable Weibull failuremodel was established. It shows the accuracy of failure probability of electrical aginginsulation at pulsating DC voltages. It solved the problem that the traditional weibullfailure model can’t reflect the relationship between failure time, electric strength andfailure probability of insulation. The evaluation method was proposed which the failureprobability distribution of comprehensive test index was used to estimate the accuracyof failure model.and it verified the validity of dual-variable weibull failure model andthe effectiveness of modeling method. The results show the dual-variable weibull failuremodel could effectively show the relationship between electric strength and failureprobability, and improve the accuracy of the calculation results.The above work is active exploration for electrical aging properties of valve-sidewindings insulation in converter transformer.It reveals the influence mechanism ofaging time and temperature on the electrical aging of oil-paper insulation at pulsating dcvoltage. The results offer the theory and experiment basis for the failure diagnosis andassessment of oil-paper insulation in converter transformer.更多还原