Abstract :
It is shown that the motion of an arc being described as a temperature cloud can be divided into two parts, one being the relative velocity of the arc phenomenon with respect to the mass flow and the other the mass motion itself. The first relative motion is determined by the equation for the change of internal energy with time, the second mass flow has to be calculated by means of the magnetohydrodynamic and continuity equations. Three groups of examples are given in each of which one of the three velocities disappears. In the first group, no mass flow exists and the motion of the arc is caused by various types of inhomogeneous heating. In the second group, the arc itself does not move due to the opposing effects of mass motion and relative arc motion. In the last group, the arc follows the mass flow without relative motion. As long as the boundary conditions do not change from the standpoint of the arc the motion continues steadily. If, however, the boundary conditions form any type of obstacles, the motion of the arc ends up in a new equilibrium position, a displacement occurring.
