机-热协同作用下绝缘纸机械性能的劣化机理

The Degradation Mechanism of Insulation Paper Mechanical Properties with Mechanical-Thermal Synergy

换流变压器铁心振动剧烈,影响其绝缘纸机械性能的劣化。基于设计的高温振动老化箱,进行了温度为130℃,频率为10 Hz,振幅分别为0 mm、1.99 mm和2.64 mm的加速机-热老化试验,并对试品的抗拉强度和聚合度进行了测试,采用X射线衍射(XRD)分析法和扫描电镜(SEM)谱图比较了老化前后绝缘纸的微观结构变化。结合测试数据,分析机械振动的振幅与绝缘纸抗拉强度损失率和聚合度损失率之间的关系。研究表明,机-热协同作用下纤维素降解既包含自由基链式化学反应,又包含纤维的拉伸与内力衰减的物理反应,这使得反应速度明显高于热老化速率。XRD和SEM分析表明,机-热协同老化没有改变纤维素的微晶类型,但使得纤维的相对结晶度和晶粒尺寸变小;同时,机械振动加速了纤维的细化、分叉和断裂以及孔洞的出现、增加与发展,各因素共同加速了机-热协同老化作用下绝缘纸机械性能的劣化。本研究可为分析机-热-电综合作用下绝缘纸的劣化机理及探索相应的抑制措施提供参考。

The iron core of converter transformer vibrates severely with the effect of DC bias,which affects the mechanical properties degradation of its insulation paper.Based on the purposely designed mechanical-thermal ageing oven,a series of accelerated ageing experiments were carried out at temperature 130℃,frequency 10 Hz and the amplitude 0 mm,1.99 mm and 2.64 mm respectively.The tensile strength(TS)and degree of polymerization(DP)of the specimen were measured,and the microscopic structures of the specimen before and after ageing were compared with the X-ray diffraction(XRD)analysis method and scanning electron microscopy(SEM)photos.Connected with test data,the relations between the vibration amplitude and the percentage TS loss and percent DP loss are researched.It indicates that there exists both chemical reaction of free radical chain and physical reactions including fibre drawing and internal force attenuation in the cellulose degradation process,which makes the reaction rate is much quickly than that of pure thermal ageing experiments.With XRD and SEM analysis,it can be found that the mechanicalthermal synergy does not change the microcrystal type of the cellulose,while the relative crystallinity and grain size of the cellulose fiber become smaller.Meanwhile,mechanical vibration accelerates degradation in two ways,the refinement,bifurcation and breakage of fiber and appearance,increase and development of holes,which promotes the deterioration of the insulation paper mechanical properties.The study provides a reference for the research of deterioration mechanism of converter transformer insulation paper under the complex effect of mechanicalthermal-electrical and for the exploration of the accordingly suppression methods.