Investigating the Effect of Aging on Space Charge Dynamics in Oil-Impregnated Paper Insulation

The performance of the power apparatus is qualitatively influenced by the state of the insulation system which ages with the service life. The aged state of insulation governs the charge injection, charge formation, and charge transport within it and may further stress the insulation electrically. Therefore it is inevitable to examine the space charge dynamics to monitor the health of the insulation. The Kraft paper samples impregnated in different aged oils are used to investigate the relevance of the space charge behavior with aged states of oil. From the available direct measurement techniques, a widely adopted PEA (Pulsed Electro-Acoustic) technique is used to estimate the trapped charge density and electric field distribution across the test samples. A noticeable space charge density and subsequent electric field enhancement are observed within fresh (unaged) oil-impregnated sample if compared with the aged oil-impregnated paper samples. Recombination of injected charges owing to the conductivity of aged oil, filled in the fibrous cellulose voids is accounted for the same. However, the electrical breakdown of the most aged oil-impregnated paper sample at lower applied voltage is observed which is followed by the less aged oil-impregnated samples. The space charge behavior in oil-impregnated paper insulation and the insulation breakdown is the manifestation of aged states of oil.