Investigation of the influence of boiling point shifting on the breakdown voltage in liquid nitrogen

In this work it is investigated how the shifting of the boiling point of liquid nitrogen influences the discharge voltage in the liquid. The experiments were conducted with ambient pressures of 0.3 MPa at 78.5 K and 0.4 MPa at 81.5 K. Two different electrode settings were used, Rogowski-shaped electrodes for a homogeneous field and a sphere opposite a plane-electrode for an inhomogeneous field. The electrode setup was stressed with lightning impulses at different electrode gaps (2 and 4 mm). Additionally a resistive heater in the bottom electrode generated bubbles on demand in order to investigate the influence of thermally induced bubbles. The measurement results are analyzed by comparing the discharge voltages under consideration of the time to breakdown.