With the enhancement of the power grid's transmission capacity

power devices such as bushings are subjected to higher voltages and larger currents

posing more stringent operational challenges to electrical connection components. To investigate the early causes of failures in electrical connection components

this paper focuses on the electrical connection components of the valve-side bushings in converter transformers

conducting static current-carrying tests on contactor and constructing a three-dimensional refined model for electro-thermal coupling multi-physical field calculations to obtain the temperature field distribution of the contactor. Based on static current-carrying tests

an analysis of the early failure causes of contactors in transformer oil environments is conducted from following three aspects: surface morphology

microstructure

and chemical corrosion. The research results indicate that

when the oil temperature is 80 ℃ and a single contactor carries a full-load current of 60 A

the temperature in the contact area can reach 120.6 ℃. During the initial contact phase

the resistance of the contactor exhibits significant fluctuations. After five days of operation

the contact resistance is stabilized

oscillating around a mean value of 159.71 μΩ with an amplitude of less than 1.6%. Micro-welding phenomena can be observed on the contact surface between the contactor and the conductor. Through the characterization of the recrystallization behavior in the microstructure of the contact area

the phenomenon of contact overheating is demonstrated

explaining the occurrence of micro-welding. Significant corrosion marks can be observed on the surface of the contactor

with sulfides being the primary corrosion products. Copper materials are more prone to react with corrosive sulfides in oil

leading to the migration and attachment of corrosion products on the silver-plated surface. The findings of this study can provide a theoretical basis for research on the early failure causes of electrical connection components and the domestic design of strap-type contactors.