Influence of Bubbles in Pressurized Liquid Nitrogen on the Discharge Behavior in a Homogeneous Electric Field

The influence of gaseous nitrogen on the discharge behavior in liquid nitrogen is investigated in this work. The experiments were conducted in pressurized liquid nitrogen with an ambient pressure of 3 and 5 bar_abs. Rogowski-shaped electrodes were used to guarantee a homogeneous field. The bubbles were created on the lower electrode with a resistive heater. In order to identify the discharge behavior, the setup was stressed with lightning surge and ac voltage at electrode gaps up to 5 mm. The measurement results were compared with calculations of the discharge field strength in the bubble with Paschens law. For these calculations, a fictive pressure is introduced to take the higher density of the gas caused by the cryogenic temperature into account.