A Study on Mechanical Durability of Insulating Materials for Dry-type Transformers

The winding of dry-type transformers is primarily cast with epoxy resin insulation material. During a short-circuit fault, the winding is subjected to a huge short-circuit electromagnetic force, which can cause changes in the insulation performance. This paper investigates the maximum stress of transformers under short-circuit impact based on simulation experiments, and explores the mechanical tolerance performance of epoxy resin insulation materials using this as a basis. Tensile tests have been carried out to demonstrate that the extreme short-circuit electromagnetic stress does not reach the tensile strength limit of epoxy resin insulation materials. Through fatigue testing, it was confirmed that a single short-circuit fault of short duration would not cause epoxy resin to fracture and fail.Furthermore, considering that a short-duration short-circuit impact fault does not result in insulation failure, the dielectric properties of epoxy resin before and after short-circuit impact fatigue degradation have been tested. By comparing the dielectric parameters of epoxy resin specimens before and after degradation, the evolution of electrical insulation performance characteristics caused by changes in the mechanical properties of insulation materials under the stress of dry-type transformer winding has been analyzed. The results show that under short-circuit electromagnetic stress, the complex capacitance and dielectric loss factor of the dielectric material change with the same trend as before degradation, and the maximum dielectric loss factor rises to 103.7% of the value before degradation. The insulation dielectric performance decreases, and this law can provide a reference for the assessment of the life expectancy of dry-type transformers.