New experimental system for the study of the effect of temperature and liquid to solid transition on streamers in dielectric liquids: application to cyclohexane

An experimental setup for dielectric testing of insulating liquids in the temperature range from -60 °C to +250 °C has been built. The system uses point-plane geometry, a sensitive differential charge measurement technique, a computer controlled temperature regulator, a photomultiplier and a pulse generator with a fast rise time. This paper presents a detailed overview of the functionality of the system and results obtained in cyclohexane under positive and negative polarity below and above freezing point. Pre-inception current, inception probabilities, streamer charge and emitted light from streamers are reported. The results found in cyclohexane at room temperature compares well to results obtained in other similar setups. A temperature dependence on the injected streamer charge for liquid cyclohexane under positive polarity was observed. No polarity differences were observed for any of the measured quantities in frozen cyclohexane.

I. Introduction

Dielectric materials are used as electrical insulation in all power systems. It is therefore of vital importance to understand the limitations and possibilities of these materials. In order to do so, good experimental procedures for testing of dielectrics under high electrical fields are needed. Several different test-setups have been proposed, and have formed the basis of international standards for testing dielectric liquids [1]–[3]. These standard tests have many shortcomings [4], and non-standardized tests have been used extensively to study pre-breakdown phenomena in liquids [5]–[13] and similar setups have also been used to study pre- breakdown phenomena in solids (electrical trees/carrier mobilities/partial discharges) [14].