Optical Sensing Techniques for Condition Monitoring of Transformer Insulation Material
Non contact optical sensing techniques—probing of surface flashover and probing of laser induced plasma, spectrally and temporally, were used to study the thermal ageing induced degradation of oil impregnated pressboard (OIP) insulation material of transformer. Optical probing of surface flashover discharge, gave parameter values comparable with, flashover discharge current measurements. Optical emission persistence time was increasing with ageing level of the insulation. Optical emission spectroscopy of impulse surface flashover gave atomic emissions from the copper sulphide contaminant, diffused in the OIP material due to ageing. Failed insulation samples showed larger Cu emission intensity. Optical emission intensity during AC, + DC and − DC flashover was used to indicate ageing and to identify initiation and arcing stages of surface flashover. Alternatively, laser induced breakdown spectroscopy (LIBS) indicated neutral Cu emission in the aged OIP material, indicating diffusion of Cu contaminants. Quantitative analysis was performed on OIP samples with surface deposited Cu and thermally aged specimen. A minimum detection limit of 4.5 µg/cm2 was achieved. LIBS plasma persistence time was identified as an alternative tool for understanding ageing level of OIP material of transformer.
KeywordsSurface flashover Oil impregnated pressboard Optical emission spectroscopy Laser induced breakdown spectroscopy
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