Life-Time of Oil Filled Insulation Paper under Nonstandard Voltage Stresses

Abstract

In the recent years, technological development gave rise to numerous systems that utilize power semiconductor devices. As much as these devices improve the performance of electrical systems, they also pollute the network with voltage distortions. A mutual interaction between switching pulses, emitted by power electronics, and passive parameters of power system produce high-frequency harmonics and oscillating impulses. Although there are quite strict rules that define the maximum levels of such distortions, they are still theoretically able to increase the electrical stress of some parts of the power network. The distortions could, therefore, accelerate the aging process of insulation systems, which would, among others, pose a threat to the stability of electrical networks. Recently, a new aging model that respects nonsinusoidal voltage stresses has been developed. The model introduces a trio of specific parameters to describe the shape of applied voltage stress. This model has been applied to polymeric insulation, but the validity of this model for other insulation materials has not been verified yet. For this purpose, laboratory measurements with oil filled transformer paper insulation samples were carried out in our research. Voltage-time characteristics of transformer insulation paper were measured and evaluated by Weibull distribution. Parameters of Weibull distribution were determined and discussed. The increased effect of nonstandard voltage stress on a life-time of paper insulation was detected. The experimental results were discussed with the calculated results of the theoretical aging model. Specific parameters of the mentioned model were also calculated and compared with other available research publications.