On the conduction process of dielectric liquids based on mineral oil

Summary

Recently a technical brochure describing the electrical conductivity of oil was published by CIGRÉ that discusses different approaches to describe the physical phenomena when mineral oil is subjected to a DC-field. Moreover, the round robin tests presented in the brochure show that it is still not possible to obtain reproducible and comparable results when measuring the electrical conductivity of mineral oil in different laboratories. Consequently, it can be stated that the relevant electrical conduction process of mineral oil as well as the influencing parameters are still not properly understood. This contribution therefore reviews the relevant electrode and bulk processes that need to be considered if a liquid dielectric is subjected to an electric DC-field. Since technical liquid dielectrics like mineral oil consist of many different chemical species measurement results can hardly be related to the materials chemical composition. Therefore, paraffins that are the main component of paraffinic mineral oils are used as specimens in this contribution since they provide a defined chemical structure along with a very similar chemical structure compared to mineral oils. Moreover, a paraffin that is solid under room temperature was investigated since this behavior can be used to prepare high purity deionized samples. It is shown that the deionized sample provides an electrical conductivity that is by a factor of 2.6-2.7 lower compared to the pristine sample. Furthermore, it is shown that in case of paraffins the prehistory of a sample influences the result of an electrical step-response measurement. This contribution is a first step towards a physically based conduction model of liquid dielectrics that is indispensable for optimized and reliable insulting systems in future.

Additional informations

Authors

KOBAYASHI, MONTANA, MENTLIK

Keywords

Electrical Conductivity, HVDC, Transformer Oil