Characterisation of partial discharge behaviour in liquid nitrogen

Interest in superconductors for use in the transmission and distribution of power has grown since the advent of high temperature superconductors (HTS). The benefits of reduced ohmic losses leading to greater operational efficiency appear attractive to power transmission and distribution companies. Potentially this technology will increase power transfer for the same or lower voltage and for the same or smaller physical dimensions. For the successful employment of this technology in the field, power utilities must be convinced of the operational reliability of designs. Many of these designs make use of liquid nitrogen as the system coolant and also as a dielectric fluid. It is therefore vital that liquid nitrogen be well characterised as a dielectric medium. This work describes an experiment to characterise partial discharge behaviour in a nonuniform field geometry. A technique is described which allows synchronised capture and measurement of apparent charge and images of density change streamer activity. A /spl phi/qn analysis of AC results has been completed and characterisation of partial discharge behaviour is presented and discussed.