换流变压器电荷赋值型直流电场外推计算方法

直流电场计算校核是换流变压器设计的重要环节。研究表明直流电压下油纸界面电荷积聚分布与传统阻容模型计算结果之间存在很大差异,基于理想模型的电场校核方法失效。该文提出一种基于油纸界面电荷特性、直接在换流变压器实际结构中进行电荷分段赋值的外推方法。首先,对于均匀场区域,用离子迁移模型计算出各个油纸界面的电荷密度,进行均一化赋值。其次,对于非均匀场区域,从均匀场区域向非均匀场区域推算,根据具体赋值部位的界面电荷分布曲线,划分区间并分段赋值。最后,将电荷场与外施电场叠加合成,获得全域内直流电场分布情况。在换流变压器阀侧出线结构模型中的实测验证表明,电荷分段映射叠加外推方法得到的电场计算值与电场实测值之间偏差较小。该方法解决了传统方法依赖材料宏观参数、无法准确计算和反映大尺寸油纸绝缘系统电场分布真实情况的问题。

DC Electric Field Calculation Method Based on Charge Assignment Extrapolation of Converter Transformer

Calculation and verification of DC electric field is an important part of converter transformer design. There is a great difference between the experimental results of the oil-pressboard interface charge accumulation and distribution under DC voltage and the calculation results based on the traditional resistivity-capacitance model. The electric field checking method based on ideal model is no longer in force. In this paper, an extrapolation method based on the oil-pressboard interface charge characteristics was proposed, which could be directly used in the complex structure of converter transformer. Firstly, for the uniform field region, the charge density of each oil paper interface was calculated by the ion drift-diffusion model, and the homogenization assignment was carried out. Secondly, for the non-uniform region of the electric field, the value to the non-uniform region should be assigned according to the region of the non-uniform field. According to the interface charge distribution curve of the specific assignment position, the interval was divided and the value was assigned in segments. Finally, the charge field and the applied electric field were superimposed to obtain the whole DC electric field distribution. The experimental verification in the valve-side outlet structure model of converter transformer used shows that the calculated electric field and the measured electric field is pretty close. The method solves the problem that traditional method relys on macroscopic parameters of materials and can not accurately calculate and reflect the real electric field distribution of oil-pressboard insulation system.