Morphological Study on Corrosive Sulphur Development in Transformer Windings

This study presents morphological study on transformer windings with the presents of corrosive sulphur. The thermal ageing experiment was conducted at 150 ∘ C for 5 days. The mineral oil and Kraft paper's moisture content post drying were maintained less than 30 ppm and $0.5 %$, respectively. Several analyses were carried out such as Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDX) and $A C$ breakdown voltage to understand the influence and the formation mechanism of copper sulphide (Cu₂ ~S) deposits on copper strip, the deterioration mechanism of Cu₂ ~S on Kraft paper and oil. The presence of Cu₂ ~S changes the color appearance of oil to yellowish. The copper strip and Kraft paper have noticeable grey-black deposits on the surface upon unwrapping the paper from copper strip. The SEM results reveals that the Cu₂ ~S deposits alter the surface structure of copper strip with numerous granular sediments present on the copper surface. The fibre texture of Kraft paper on the mid (5ᵗʰ) layer becomes fuzzy and worst on the 1ˢᵗ layer. The actual dielectric breakdown strength of corrosive oil reduces close to half as compared to non-corrosive oil.