Analysis of Damage on Oil-impregnated Insulation Paper Using Phase Distribution of Partial Discharge

Two-dimensional phase distribution of partial discharge(PD),statistical features of two-dimensional phase distribution,and surface damaging conditions on oil-impregnated insulation paper were studied during the damage process caused by PD within the cavity of the paper.According to two-dimensional phase distribution of PD,the damage process can be divided into five stages,and the variation law of statistical features was analyzed during the damaging process.At each of the stages,surface damaging conditions of insulation were analyzed by optical microscopy and scanning electron microscopy.Results reveal that,during the five damaging stages,asymmetry(Asy)and cross-correlation factor(Cc)of two-dimensional phase distribution gradually stabilize near the constant 1,and skewness(Sk)of two-dimensional phase distribution for discharge amount presents as negative value before incoming breakdown of insulation paper.Meanwhile,droplets and crystalline solids are generated in sequence.Droplets make Asyand Ccgradually stabilized,and cause periodical"cluster-like"featured.Crystalline solids generated on the insulation surface distort the electric field,which is an important cause for"pitting"and"electrical treeing"on insulation surface.Reference information for the assessment of surface conditions of oil-impregnated insulation paper is provided.