392 / 2022-03-15 19:26:11

Analysis of aging properties of epoxy resin based on physicochemical defect calculation

Epoxy resin; Molecular simulation; Crosslinking network

Purpose/Aim

Epoxy resin material has been widely used in power system due to its excellent insulation performance. However, long-term operation under complex working conditions will lead to thermal stress on the surface of insulation material, gradually fracture and degradation, seriously affecting the insulation performance. Therefore, insulation diagnosis and aging evaluation of epoxy resin materials are of great significance to the safe and reliable operation of power system.

Experimental/Modeling methods

In this paper, 11 groups of epoxy resin samples were subjected to thermal aging for 11 days at 250°C, and the changes of electrical properties, molecular structure, and other physical and chemical properties of epoxy resin materials were tested. In order to further study the effect of thermal aging on the breakdown performance of epoxy resin insulation, the thermal cracking process of epoxy resin material was studied based on molecular dynamics simulation of the ReaxFF field, and the effect of thermal aging on the material trap was calculated by density functional theory (DFT).

Results/discussion

Molecular dynamics simulation using Material Studio software found that chemical bonds in epoxy resin materials were gradually broken during thermal aging, resulting in the formation of small molecular segments and the introduction of new functional groups, such as C=C. Guassian software is used to compare and calculate the trap energy levels of epoxy resin materials before and after thermal aging. It is found that the trap in epoxy resin materials after thermal aging is shallower and the charge transport is easier under the action of voltage, which is an important reason for the deterioration of insulation performance of epoxy resin materials.

Conclusions

In the process of thermal aging, crosslinks between molecular chains of epoxy resin are broken, which reduces the stability of molecular network structure and introduces shallow physical traps. At the same time, the epoxy group was opened and a new functional group C=C was formed at the fracture point of the carbon skeleton, which introduced the deepening trap. Through quantum chemical calculation, it is found that chemical defects change the energy band structure of epoxy resin material, and at the same time lead to the breakdown voltage drop of epoxy resin material, and the insulation performance decreases.