Effect of the Non-Linear Electric Conductivity of Mineral Insulating Oil on the Dielectric Strength at High DC Voltage Stress

This paper presents the non-linear and polarity-dependent electric conductivity of mineral insulating oil and its influence on the dielectric stress of oil-insulated arrangements. At various electrode arrangements major differences of several orders of magnitude in the specific electric conductivity can be measured. Furthermore, a polarity effect of the conductivity can be observed, which is mainly caused by different injection rates of homo charges. Due to their known effect on the electric field in oil-paper-insulated arrangements at high DC voltage stress, a polarity effect in the electric field distribution occurs at asymmetrical, homogeneous arrangements, which can be shown using a charge carrier-based approach. In addition, breakdown experiments at a similar homogenous, oil-paper-insulated arrangement confirm this polarity effect.