Hygrothermal aging mechanism of epoxy composites used for medium-frequency transformers

IF 6.3 2区化学 Q1 POLYMER SCIENCE Polymer Degradation and Stability Pub Date : 2024-07-06 DOI:10.1016/j.polymdegradstab.2024.110913

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Abstract

The integration of medium-frequency transformer design and the harsh service environment raise higher demands for the medium-frequency insulation performance of epoxy composites. As epoxy composite's frequency response characteristics and sensitivity to moisture intrusion are still unknown, its application as the insulation materials of medium-frequency transformers under hygrothermal conditions is limited. This paper investigates the mechanism of moisture intrusion damage to the molecular structure of the epoxy resin matrix and its cross-linking points with the curing agent. The regularity of medium-frequency insulation performance degradation of epoxy composites after hygrothermal aging is studied. Results indicate that after 40 days of hygrothermal aging, moisture together with high temperature damaged the main chain of the epoxy resin and its cross-linking points with the curing agent, resulting in a 23 °C decrease in the glass transition temperature and an 82 % decrease in cross-linking density of the epoxy composite. Moisture ionization and the increase of carriers due to epoxy resin hydrolysis lead to an increase in the amount of space charge. The temperature rise caused by dipole steering polarization facilitates the formation of internal conductive pathways in the epoxy composite, resulting in a 73 % decrease in the medium-frequency breakdown strength and a four-order magnitude decrease in the medium-frequency volume resistivity of the epoxy composite. This study can guide the insulation design of high-reliability medium-frequency transformers.

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中频变压器用环氧树脂复合材料的湿热老化机理

中频变压器设计的一体化和恶劣的使用环境对环氧复合材料的中频绝缘性能提出了更高的要求。由于环氧复合材料的频率响应特性和对湿气入侵的敏感性尚不清楚，因此其作为中频变压器绝缘材料在湿热条件下的应用受到了限制。本文研究了湿气入侵对环氧树脂基体分子结构及其与固化剂交联点的破坏机理。研究了环氧树脂复合材料在湿热老化后中频绝缘性能退化的规律性。结果表明，经过 40 天的湿热老化后，水分和高温破坏了环氧树脂的主链及其与固化剂的交联点，导致环氧树脂复合材料的玻璃化温度降低了 23 °C，交联密度降低了 82%。水分电离和环氧树脂水解引起的载流子增加导致空间电荷量增加。偶极转向极化引起的温度升高促进了环氧树脂复合材料内部导电通路的形成，导致环氧树脂复合材料的中频击穿强度降低了 73%，中频体积电阻率降低了 4 个数量级。这项研究可为高可靠性中频变压器的绝缘设计提供指导。

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来源期刊

Polymer Degradation and Stability 化学-高分子科学

CiteScore

10.10

自引率

10.20%

发文量

325

审稿时长

23 days

期刊介绍： Polymer Degradation and Stability deals with the degradation reactions and their control which are a major preoccupation of practitioners of the many and diverse aspects of modern polymer technology. Deteriorative reactions occur during processing, when polymers are subjected to heat, oxygen and mechanical stress, and during the useful life of the materials when oxygen and sunlight are the most important degradative agencies. In more specialised applications, degradation may be induced by high energy radiation, ozone, atmospheric pollutants, mechanical stress, biological action, hydrolysis and many other influences. The mechanisms of these reactions and stabilisation processes must be understood if the technology and application of polymers are to continue to advance. The reporting of investigations of this kind is therefore a major function of this journal. However there are also new developments in polymer technology in which degradation processes find positive applications. For example, photodegradable plastics are now available, the recycling of polymeric products will become increasingly important, degradation and combustion studies are involved in the definition of the fire hazards which are associated with polymeric materials and the microelectronics industry is vitally dependent upon polymer degradation in the manufacture of its circuitry. Polymer properties may also be improved by processes like curing and grafting, the chemistry of which can be closely related to that which causes physical deterioration in other circumstances.