变压器耐高温型匝间绝缘材料的放电特性研究

Study on discharge characteristics of heat resistant inter-turn insulation materials in power transformers

变压器匝间绝缘长期处于不均匀电场下,既是绕组绝缘结构中最薄弱的环节之一,也是电力变压器绝缘设计的重点。为此以Nomex绝缘纸、改性DMD绝缘纸、PET薄膜以及聚酰亚胺薄膜等耐高温型绝缘材料为研究对象,在0～20kV正弦波电压下开展了固体匝间绝缘材料的放电特性实验,利用V-t特性曲线对比各种绝缘材料的击穿特性,通过沿面闪络实验探究放电间距对沿面闪络电压的影响规律,并采用双参数Weibull统计方法计算待测材料绝缘失效的Weibull分布密度表达式,为电力变压器匝间绝缘材料的合理选取提供依据。实验测试及理论分析的结果表明,在不均匀电场下,薄膜材料的击穿场强远高于绝缘纸,但同时其电老化速率也较高;沿面闪络电压随放电间距的变化规律与材料类型的关联性较大,纤维类绝缘纸闪络电压呈近似线性变化;四种绝缘材料的闪络电压远低于各自的绝缘击穿电压,且呈现出较大分散性,利用Weibull分布密度表达式可有效估算绝缘失效率,上述研究为电力变压器的耐高温型匝间绝缘材料的寿命预测提供了理论支持。

The inter-turn insulation often runs in an inhomogeneous electric field.This is the weakest link in the insulation structure of the winding,and it is also the focus of the insulation design of the power transformer.In order to obtain insulation properties of insulating materials,we conducted insulation characteristics tests with Nomex insulation paper,modified DMD composite insulation paper,PET film and polyimide film under 0~20kV excitation voltage.We plotted the V-t characteristic curve to compare the breakdown characteristics of various insulating materials and explored the influence rule of discharge distance on flashover voltage along the surface by creepage experiment.The two-parameter Weibull statistical method was used to calculate the Weibull distribution density of insulation failure of materials,which provided the basis for the reasonable selection of insulation materials for power transformers.The experiment results show that,the breakdown strength of the film material is much higher than that of the insulation paper,but the electrical aging rate of the film is higher than that of the insulating paper under the inhomogeneous electric field.The variation of the surface flashover voltage with the discharge distance is related to the type of material,and the change of fiber insulation paper is approximately linear.The flashover voltages of the four insulation materials are much lower than their respective breakdown voltages,and they all exhibit a large dispersion.The Weibull distribution density expression can be used to estimate the insulation failure rate and provides theoretical support for the prediction of insulation life of power transformers.