1. Theoretical background

Generally speaking, an electrical circuit undergoing a disturbance has a response composed of the forced response and the natural (free) response. The natural response is related to the circuit's natural frequencies, while the forced response is related to imposed sources.

In the case of the circuit shown in figure 1 , supplied by a sinusoidal voltage source, it can be shown that the current of circuit breaker S, switched on to supply a load RL, is given by equation :