高频变压器绝缘材料的环氧预浸处理对放电特性的影响

Effect of epoxy prepreg treatment on discharge characteristics of insulation materials in high frequency transformers

高频变压器长期运行于频率1~20kHz的非正弦电压下,绕组层间绝缘材料的合理选取对样机可靠性具有重要意义。为此以GHG纸、GHG环氧预浸纸、DMD纸以及DMD环氧预浸纸为研究对象,在0~20kV、1~20kHz双极性方波电压下开展层间绝缘材料放电特性实验,对比材料在环氧预浸处理前后高频绝缘特性,基于热击穿机理解释高频下预浸处理前、后的击穿场强变化规律,利用SEEA模型分析预浸处理技术对闪络电压的影响,最后提出环氧预浸技术在绕组层间绝缘中的应用建议。实验测试及理论分析结果表明,预浸处理后材料内部及表层的气隙被填充,在介电损耗尤为显著的高频条件下,发热点与周围环境有效散热面积下降,加速了材料热老化,导致击穿场强下降;对GHG纸预浸处理后,电子陷阱俘获作用减弱,导致闪络电压显著下降,而DMD纸在预浸处理前后表面状况变化较小,闪络电压基本不变;在利用环氧预浸技术提升材料机械、电气性能的同时,应充分考虑高频下预浸处理对材料散热性能、表面状况的影响,上述研究为高频变压器层间绝缘材料选取与绕组绝缘优化设计提供借鉴。

High-frequency transformers are usually operated under the non-sinusoidal voltage with a frequency of 1~ 20 kHz. The reasonable selection of the inter-layer insulation material is of great significance to the reliability of the prototype. In order to obtain discharge characteristics of inter-layer materials,GHG paper and DMD paper with their prepreg paper are tested under the bipolar square wave voltage. Comparing the insulation properties of materials before and after epoxy prepreg treatment,the variation of breakdown voltage with frequency is explained based on thermal breakdown mechanism,and the influence of prepreg treatment on flashover voltage is analyzed by SEEA model. Finally,the application of epoxy prepreg in the insulation of high-frequency transformers is proposed. Experiment results show that,air gaps inside the material is filled after the prepreg treatment. Under the high-frequency condition the dielectric area of heating point and surrounding environment is reduced,which accelerates the thermal aging of materials,and eventually leads to a decline in breakdown field strength. Prepreg treatment of GHG paper reduces the trapping effect of electron trap,resulting in a decrease in flashover voltage,while the surface condition of DMD paper changes little before and after prepreg treatment. While using epoxy prepreg technology to improve the properties of materials,the effects of prepreg treatment on heat dissipation performance and surface condition should be considered. The research provides a reference for the inter-layer design of windings.