A modified Maxwell model for modeling dielectric response of oil-paper insulation affected by radial and axial temperature gradients

Abstract

Aging sensitive information related to cellulosic insulation can be obtained from the monotonically decaying dielectric relaxation function φ(ί). Several circuits comprising of energy storing and dissipating elements are reported for modeling the dielectric relaxation function. Maxwell's ladder structure is one of the most popular approaches for modeling the dielectric response. For better modeling of dielectric response, a modified Maxwell's ladder structure is also reported that considers the effect of the aging due to the presence of a radial temperature gradient. In this paper it is proposed that for more accurate modeling of the dielectric response, the axial temperature gradient present in an operating transformer must also be taken into consideration. A further improved Maxwell two parameter model has been proposed that incorporates the effect of such axial temperature distribution. In the proposed technique each series branch of the two parameter model has been further divided into a number of parallel branches representing the effect of aging due to axial temperature gradient.