Direct Current Arc Investigations in Liquid Nitrogen Using Asymmetrical Electrodes

Abstract

Liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) is one of the most effective insulation medium for the realization of a new and environment friendly power switchgear system. This novel power switchgear will be a promising alternative to the gas insulated switchgear system. Preliminary study about arc phenomenon is very important for the future design of this novel approach. The fundamental research on high-density arcs was demonstrated using LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> for the very first time and some important first-hand investigations were previously observed. These investigations were based on electrodes that were geometrically symmetrical. The thorough study of arc behavior in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , also demands the asymmetrical analysis be done in the same manner. These new results would further enrich our understanding of arcs in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and would be helpful for the future design of liquid nitrogen insulated metal enclosed switchgear (LNIS). The objective of this research is to study the arcing behavior in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> using asymmetrical electrodes. The research investigates the arcing times, arc energies, LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> consumption rates, temperature difference after arc occurrence, and surface erosion of the electrodes due to arcing. Experiments were done at four different dc voltage levels (i.e., 200-500, with a 100 V step) and arcs were intentionally created on asymmetrical electrodes with different electrode arrangements and materials, respectively. The geometrical arrangements for the experiments are sphere-plane and rod-plane, whereas the electrode materials are aluminum alloy (Al6061), pure copper (Cu), and stainless used steel (SUS) type, respectively. Arcing times, residual voltages, arc voltages, and arc currents were measured using different apparatuses. The results are quite in agreement with the previous investigations done by the first author. LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has the shortest arcing time in comparison to air insulation and sphere-plane quenches arcs quicker than rod-plane type electrodes in most of the cases. It was also observed that LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> consumption due to arcing is quite lower even at heavy interrupting currents and overall difference in temperature due to arcing is approximately zero when the volume of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is more than 100 L.