Space Charge Dynamics in Oil-Impregnated Kraft Paper and its Relation to the Aged States of Oil

The reliability of the power apparatus is essentially governed by the health of its insulation system which is often subjected to various superimposed stresses. These stresses may accelerate the aging process and influence the charge dynamics which may further stress the insulation electrically. Thus, it is inevitable to investigate the space charge dynamics within the aged states of insulation which may intuitively help to predict the insulation remnant life. Kraft paper samples with a thickness of 0.1 mm and 0.13 mm, impregnated in different naturally aged oils have been examined to describe the relevance of space charge dynamics with aged states of oil. The space charge density and electric field distribution profiles are recorded using a widely adopted PEA (Pulsed Electro-Acoustic) method. Space charge density and electric field enhancement are more pronounced with the thicker paper sample impregnated in the virgin oil because of the higher resistivity of virgin oil and more trap sites in the continuum space of thickness. A comparatively better conductivity of aged oil promotes charge transport and subsequently encourages charge recombination which leads to reduced charge density in the bulk. The electric field alteration is not entirely evident in thinner samples, however, moderate to high is evident in thicker samples.