Impact of the Gas Environment on the Electric Arc

The influence of the oxygen concentration on the break arc is observed in a range of 0 to 50 % oxygen in an oxygen-nitrogen mixture under a resistive DC load of 55.5 V and 10 Omega. The arc characteristics are observed by means of oscilloscope traces and high speed camera images showing a clear correlation of the arc motion and the speed of the motion with the oxygen concentration. In contrast, the electrical characteristics change only little over all gases containing oxygen and show a large difference for pure nitrogen. The motion of the arc on AgSnO2 and AgNi 0.15 is influenced in different ways by the higher oxygen concentration. The average distance between cathode spots (arc step) from frame to frame (observed at 483'000 images/s) is lowest for pure nitrogen for both materials. For AgSnO2, the arc step increases with increasing oxygen concentration at low oxygen levels and reaches a maximum step size at 15 to 20 % oxygen. For AgNi 0.15 larger arc steps are observed at 5 % oxygen, decreasing with increasing oxygen concentration over the whole range. These experiments show the importance of oxygen on the arc behavior and, therefore, on the relay behavior.