Transient Kerr-effect Measurements of DC Electric Fields in a Mineral Oil Gap Combined with Synchronous Polarization Current Measurements

Abstract:
This contribution presents the synchronous measurement of DC electric fields and polarization currents in a mineral oil gap. Therefore, the existing electro-optic Kerr-effect measurement system is extended by a guard ring electrode arrangement to perform simultaneous measurements of electric fields and conduction processes. The developed test setup gives the opportunity to measure the local electric field stress at a certain location in the oil gap and the polarization current, which indicates the time-dependent dielectric behavior of the overall mineral oil gap. Furthermore, the synchronous field and polarization current measurement ensures the reproducibility of consecutive electric field measurements at different locations in the oil gap. The information about the local electric field stress and the related current are required for a deeper understanding of the physical processes in liquid dielectrics under transient and DC stress. Therefore, in this contribution, transient and DC field measurements are presented that show the time-dependent behavior of the intrinsic space charges in mineral oil for two different amounts of water content. Furthermore, the influence of water on the dielectric behavior is discussed by comparing mineral oil with and a model oil (n-dodecane) at comparable water content. Considering that the model oil contains significantly less impurities, it is possible to conclude, whether the observed conductivity is caused by the water itself or by the influence of the water on the dissociation processes of the oil-intrinsic components. In addition, measurement results with different electrode distances are presented. The different electrode distances give the opportunity to separate the physical processes in the bulk from the electro-chemical processes at the electrodes, which helps to improve knowledge about the influence of space charges on the dielectric behavior of mineral oil.