水分是影响电力变压器油纸绝缘性能的重要因素,如何通过油中水分含量简单、准确地判断变压器绝缘纸的老化状态成为当今研究的重点。本文首先分析了油纸绝缘系统的水分来源及其危害,然后基于频率因数a的Taylor展开式得出a与绝缘纸中水分...水分是影响电力变压器油纸绝缘性能的重要因素,如何通过油中水分含量简单、准确地判断变压器绝缘纸的老化状态成为当今研究的重点。本文首先分析了油纸绝缘系统的水分来源及其危害,然后基于频率因数a的Taylor展开式得出a与绝缘纸中水分含量间存在正比关系,进而得到了计及水分含量的修正Arrhenius定律。其次,结合化学反应动力学推得绝缘纸中水分含量与聚合度间的量化关系,并根据纤维素老化对Oommen油纸水分平衡的影响,获得了绝缘纸的聚合度（degree of polymerization,DP）与油中水分含量间数量关系的修正表达式;在此基础上推得了绝缘纸特征寿命的预测判据。最后,通过实验数据表明未考虑绝缘纸老化影响时,油纸水分与纸中水分间的表达式的计算误差为20%～50%,基于油中水分含量的DP表达式的计算误差为3.8%～38.4%;而修正表达式可分别将上述误差降低到12.5%以下及23.3%以下。当老化温度为140℃,油中水分的体积分数分别为10^（-6）和13×10^（-6）时,绝缘纸的特征寿命分别为65天和12天。展开更多
The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and verti...The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and vertical spacings) are calculated by the complex function and integration method to analyze their interacting mechanism and determine the strengthening and weakening zone of SIFs. The multi-crack initiation criterion is established based on the ratio of maximum tension-shear SIF to predict crack initiation angle, load, and mechanism. The results show that multi-crack always initiates in Mode Ⅰ and the vertical spacing is better not to be times of half crack-length for crack-arrest, which is in good agreement with test results of the red-sandstone cube specimens with three parallel cracks under uniaxial compression. This can prove the validity of the multi-crack initiation criterion.展开更多
文摘水分是影响电力变压器油纸绝缘性能的重要因素,如何通过油中水分含量简单、准确地判断变压器绝缘纸的老化状态成为当今研究的重点。本文首先分析了油纸绝缘系统的水分来源及其危害,然后基于频率因数a的Taylor展开式得出a与绝缘纸中水分含量间存在正比关系,进而得到了计及水分含量的修正Arrhenius定律。其次,结合化学反应动力学推得绝缘纸中水分含量与聚合度间的量化关系,并根据纤维素老化对Oommen油纸水分平衡的影响,获得了绝缘纸的聚合度（degree of polymerization,DP）与油中水分含量间数量关系的修正表达式;在此基础上推得了绝缘纸特征寿命的预测判据。最后,通过实验数据表明未考虑绝缘纸老化影响时,油纸水分与纸中水分间的表达式的计算误差为20%～50%,基于油中水分含量的DP表达式的计算误差为3.8%～38.4%;而修正表达式可分别将上述误差降低到12.5%以下及23.3%以下。当老化温度为140℃,油中水分的体积分数分别为10^（-6）和13×10^（-6）时,绝缘纸的特征寿命分别为65天和12天。
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51874351,51474251)Hunan Provincial Innovation Foundation For Postgraduate,China(CX2018B047)the Open Sharing Fund for the Large-scale Instruments and Equipments of Central South University,China(CSUZC201923).
文摘The maximum Mode Ⅰ and Mode Ⅱ stress intensity factors(SIFs), KI,kmax(θ) and KII,kmax(θ)(0°<θ<360°), of inclined parallel multi-crack varying with relative positions(including horizontal and vertical spacings) are calculated by the complex function and integration method to analyze their interacting mechanism and determine the strengthening and weakening zone of SIFs. The multi-crack initiation criterion is established based on the ratio of maximum tension-shear SIF to predict crack initiation angle, load, and mechanism. The results show that multi-crack always initiates in Mode Ⅰ and the vertical spacing is better not to be times of half crack-length for crack-arrest, which is in good agreement with test results of the red-sandstone cube specimens with three parallel cracks under uniaxial compression. This can prove the validity of the multi-crack initiation criterion.
