基于HN介电弛豫模型评估环氧云母绝缘的老化状态

Evaluation on Ageing State of Epoxy Mica Insulation Based on HN Dielectric Relaxation Model

为将频域介电谱法(FDS)用于发电机主绝缘老化状态的无损诊断,在热电联合作用下对定子线棒环氧云母绝缘试样进行加速老化试验,测试不同老化程度试样的频域介电谱,采用HN模型对不同老化状态下的复介电常数实部和虚部进行曲线拟合,提取出能够定量表征绝缘老化程度的特征参数,并用扫描电子显微镜观测老化前后微观结构的变化,分析绝缘在热电联合作用下的老化机理。结果表明:复介电常数实部和虚部均随老化时间的增加而增大,尤其是在低频段(10^-3~10^1Hz),增大趋势更加明显;HN模型中的特征参数τ和β可以表征绝缘的老化状态,τ随老化时间的增加呈指数增大,β随老化时间的增加呈线性减小。

In order to apply the frequency domain dielectric spectroscopy(FDS) to diagnose the ageing state of main insulation for generator nondestructively, the epoxy mica insulation samples of stator bars were conducted accelerated ageing tests under the combined action of heat and electricity, and the frequency domain dielectric spectra of the samples with different ageing states were tested. The HN model was used to fit the real and imaginary parts of complex permittivity under different ageing states,and the characteristic parameters, which can quantitatively characterize the ageing state of insulation, were extracted. The microstructure changes of the samples before and after ageing were observed by scanning electron microscope, and the ageing mechanism of insulation under the combined action of heat and electricity was analyzed. The results show that both the real and imaginary parts of the complex permittivity increase with the increase of ageing time, especially in the low frequency band(10^-3~10^1 Hz), the increase trend is more obvious. The characteristic parameters τ and β in the HN model can be used to characterize the ageing state of insulation, with the increase of ageing time,τ increases exponentially, and βdecreases linearly.