Analysis on the Electric-stress Corrosion Characteristics of the Torsion Spring Contact in EHV bushing

When the temperature of the contact interface in the EHV bushing exceeds the maximum allowable operating temperature, the by-product such as SO₂F₂, SO₂ and H₂S will corrode the contact fingers and accelerate the fretting corrosion, which finally cause the overheating fault of power equipment. In this paper, taking the torsion spring contact finger used in an overheating faulted extra high voltage (EHV) bushing as example, the corrosion process was researched. Firstly, the electric and mechanical stress analysis based on the finite element method were conducted by software COMSOL. Then, combining the image with stress distribution contour and electron microscopy, the relationship of important areas and electric-stress distribution was obtained. The place where the principle stress of the finger is large is consistent with the place where the corrosion begins on the non-contact area. Surface cracking due to stress corrosion further accelerates corrosion of the internal material, which explains why there is also severe corrosion in the non-contact zone. In addition, the paper obtains the relationship between contact force, contact area and contact resistance to investigate the effect of bad contact on contact resistance and Joule loss at the plug structure. The above study would provide a basis for the overheat failure mechanism of the plug structure in the EHV converter transformer bushing.