非线性有限元法在出线装置复合绝缘结构电场计算中的应用

极性反转是换流变压器出线结构复合绝缘的一种特殊工作状态,极性反转时由于空间电荷作用可导致绝缘介质内部及界面处电场畸变。另一方面,绝缘介质电性能参数是温度的函数,因此温度梯度导致的电性能参数改变同样会影响绝缘结构在极性反转过程中的瞬态电场分布。基于此,为了较准确地模拟复合绝缘结构在考虑温度分布条件下的极性反转瞬态电场,提出应用非线性有限元法对以上2种瞬态电场影响因素进行耦合分析。首先研究了油浸纸复合绝缘体系电性能参数与温度的关系;然后详细介绍了基于非线性有限元法的瞬态电场计算流程,并通过双层同轴复合绝缘结构模型验证了其有效性;最后对实际换流变压器出线装置的油纸-环氧浸渍典型复合绝缘结构建立了二维轴对称仿真计算模型,在考虑材料非线性的条件下对其极性反转瞬态电场变化过程进行了仿真分析。计算结果表明传统模拟方法与考虑材料非线性时的结果存在较大差异,且极性反转过程中复合绝缘结构易出现畸变严重的局部高场强区。

Application of nonlinear finite element method in electric field calculation of composite insulation structure of transformer outlet

The polarity reversal is a special state of composite insulation in converter transformer’s outlet system,which can lead to electric field distortion within insulating dielectric and at the interface of insulating dielectric due to space charge effect.On the other hand,the electrical property parameters of insulating dielectric are function of temperature,thus,the changes of electrical parameters caused by temperature gra-dient will affect transient electric field distribution of insulation structure in process of polarity reversal.On this basis,to accurately simulate the polarity reversal transient electric field of composite insulation structure with temperature gradient,it is proposed to apply the nonlinear finite element method in the coup-led analysis of the above two affecting factors of transient electric field.Firstly,the relationship between electrical parameters of composite insulation dielectric of oil-immersed paper and temperature is investigated.Then,the flowchart of transient electric field calculation based on the nonlinear finite element method is introduced in detail and verified by the double coaxial composite insulation structure model.Finally,a 2D simulation model of oil impregnated paper insulating dielectric of actual converter transformer’s outlet sys tem is established to simulate and analyze the transient electric field during polarity reversal considering the nonlinear characteristics of materials,which shows that the results of traditional simulation are quite diffe-rent from those considering material non-linearity,and a local high electric field strength area easily appears during polarity reversal process.