电老化对大型电机定子线棒主绝缘频域介电谱特性的影响

Effect of Electric Aging on Frequency Domain Dielectric Properties of Main Insulation of Generator Stator

为研究电老化对大型电机定子线棒主绝缘频域介电谱特性的影响,对不同电老化状态下的少胶真空压力浸渍(vacuum pressure impregnation,VPI)少胶绝缘和多胶模压(resin-rich molding,RRM)多胶绝缘进行频域介电响应测试,利用扫描电镜(scanning electron microscopy,SEM)和傅里叶红外光谱(Fourier transform infrared spectroscopy,FTIR)对电老化前后主绝缘试样的微观结构和化学成分变化进行分析,并采用Havriliak-Negami弛豫模型对复介电常数进行拟合分析,以探究介电谱随电老化时间增加的变化规律。试验结果表明:电老化后绝缘介质结构发生破坏,极性基团数量增加,界面极化和偶极子转向极化作用得到增强,从而使电老化后VPI和RRM主绝缘的介电性能,如复介电常数实部ε′和虚部ε″以及介损因数tanē在低频区大幅上升;VPI少胶和RRM多胶绝缘体系受电老化影响程度不同,VPI绝缘结构劣化更为严重,而RRM绝缘极性基团增量更多;对电老化前后复介常数分析结果表明,界面极化弛豫强度Δε2数值远远大于偶极子极化弛豫强度Δε1,其在绝缘介质整体松弛极化强度中占主导地位,可通过Δε2分析主绝缘的老化程度,研究成果可为评估电机定子线棒主绝缘老化状态、分析电老化机理提供参考。

In order to study the influence of electrical aging on the frequency domain spectroscopy(FDS)characteristics of the main insulation in large generator stator bars,the FDS tests of Vacuum Pressure Impregnation(VPI)less-resin insulation and Resin-Rich Molding(RRM)insulation,which were under different electrical aging states,were carried out,the microstructure and chemical composition of the main insulation specimen were analyzed by Scanning Electron Microscopy(SEM)and Fourier Transform Infrared Spectroscopy(FTIR)before and after electrical aging,and the complex permittivity was fitted and analyzed by the Havriliak-Negami relaxation model in order to research how the FDS changed with the electrical aging times.The results show that the insulation microstructure is destroyed and the quantity of polar groups increases after electrical aging,and the interface polarization and dipole turning-direction polarization are also enhanced,so that the dielectric properties of the VPI and RRM insulation rise significantly in the low frequency region after electrical aging,such as the real partε′and the imaginary partε″of the complex permittivity and the dielectric loss factor tanē.VPI and RRM insulation systems are affected to different extent by electrical aging,and the destruction of the VPI insulation structure is more serious,while the polar group of RRM insulation is more than that of VPI.The analysis results of complex permittivity before and after electrical aging reveal that the interfacial polarization relaxation intensityΔε2 is much larger than the dipole polarization relaxation intensityΔε1.TheΔε2 dominates the whole relaxation polarization strength in the insulation,and the electrical aging degree of the main insulation can be analyzed byΔε2.The research findings provide a theory reference for the aging state evaluation and the ageing mechanism analysis of the large generator stator bars main insulation.