Progress toward operational designs of superconducting power apparatus has been aided by the advent of high temperature superconductors (IITS) and the availability of production quantities of I ITS tapes.  Prototype designs for HIS power apparatus, for example cables, terminations, current fault limiters. transformers and generators exist and many use liquid nitrogen as both coolant and dielectric. This study has sought to examine the effect of bubble dynamics caused by thermal and electrical induction on the performance of liquid nitrogen as an electrical insulation. To achieve this aim a unique liquid nitrogen cryostat has been designed and manufactured with optical ports and a high voltage bushing. The cryostat is fitted with an integrated cryo-cooler which allows the temperature to be controlled across the liquid range of nitrogen and experimentation with applied pressures to 2 MPa. This has allowed an experimental investigation of bubble dynamics in liquid nitrogen in the presence of electric fields which is distinct in its examination of bubbles as they are thermally nucleated. A comprehensive study of streamers and partial discharge behaviour within liquid nitrogen using point-plane electrode geometry for a range of applied 50 Hz voltages, temperatures and pressures has been completed. In order to do this a new technique to capture electrical partial discharge signals and images of density change streamers simultaneously has been developed and is described, φqn analysis has been employed to characterise the partial discharge and streamer activity in liquid nitrogen. Typical characteristics of density change streamers have been identified and theories of the physical mechanisms causing their formation are proposed.