1. The problem of interrupting direct currents

1.1 DC current interruption

Let's consider the apparently simplest case of an inductive circuit (R, L) supplied with direct current (figure 1 a).

To interrupt the current flowing through this circuit, it is necessary and sufficient that the resistance r of the switch, initially assumed to be zero, increases and becomes infinite (figure 1 b) or, in other words, that its conductance decreases and then becomes zero. When this single condition is met, no current flows through the device, which has become insulating.

• At first sight, the variation of the...