After the discovery of high temperature superconductor in 1986, the interest in the power applications of superconducting has increased dramatically. With a number of successful in-field installations around the world, this technology promises great improvements in compactness, capability and efficiency of power systems. The development of HTS apparatus requires thermally stable, mechanically compatible and electrically efficient dielectrics. In addition, cryogenic dielectric materials must have high breakdown strength to withstand operating voltage as well as survive fault conditions. Liquefied gas is essential for the concept of high temperature superconducting (HTS) applications as coolant and insulator. With the boiling temperature of 77K and constituting 78% of earthââ¬â¢s atmosphere, liquid nitrogen (LN2) is a common choice. The electrical breakdown of LN2 subjects to various defects (i.e. bubbles, high stress points, free particles...) initiating partial discharges from which streamers are formed. If allow to propagate through the liquid the result is a complete breakdown. Previous work has demonstrated that streamers caused erosion to composite barriers, for example GRP (glass fibre reinforced plastic). In the case of more homogenous material such as PTFE, the same event can result in more catastrophic damage such as puncture through the solid board. The aim of this study is to further investigate on the pre-breakdown behaviour liquid nitrogen to improve the understanding on streamers initiation and propagation through the liquid. In addition, the project will consider the performance of solid materials for use as dielectrics at cryogenic temperature (below -196 degrees celsius).