Influence of contact materials on the current transfer thanks to the current distribution measurement in a low-voltage breaking device by means of a magnetic diagnostics

To bring off the breaking of a short-circuit current in a low-voltage installation, the circuit breaker must carry out a certain number of functions. One of them is the fast and significant arc voltage rise which opposes the network voltage. The arc is partly controlled by the internal structure of the breaking apparatus. In particular, the arc must leave the materials which constitute the initial electric contact as soon as possible. According to their nature, a more or less important erosion of the contacts can be observed due to a more or less constricted arc. In addition, these materials influence the arc dynamics: with some materials the arc seems to be transferred more easily from the moving contact towards the fixed electrode and penetrate the quenching chamber made up of splitter plates also more easily. For the observation we have developed a measurement system of the electrical current density. This system is based on a magnetic diagnostics achieved thanks to sensors placed outside the device and some hypotheses concerning the way of the current. The strongest point of this method is that it is non intrusive. The experiments were carried out on a model circuit breaker that nevertheless presents all the characteristics of the industrial units (arc ignition, transfer phase and splitting in a quenching chamber).