Break arc study for the new electrical level of 42 V in automotive applications

In order to fulfil the increasing need for electric power in automobiles, to satisfy the new environmental requirements and to decrease the weight of cars, the electrical supply, must be changed from the current 14 V to 42 V. In the present work using 42 V, we have studied are parameters such as break arc duration and extinction gap(1) for different materials, contact opening speeds and circuit loads (correlated with the time constant of the circuit, L/R). We have established that these main are parameters are greatly enhanced compared to the 14 V arc studied in our previous work. In the case of an inductive or a resistive load, it has been found that there are two domains: a low current domain where the material has no significant effect, and a high current domain where some materials (primarily AgSnO2) induce high arc durations and large extinction gap. In addition, increasing the opening speed reduces arc duration in all cases. The increased opening speed can however, increase the extinction gap for inductive loads and decrease it for resistive circuits. We have found that reducing arc duration is always beneficial with regards to erosion but in some cases, however it may increase the extinction gap. At 42 V, the erosion and the material transfer, from the cathode to the anode, are similar to that obtained at low extinction gaps (<1 min) at 14 V. At large extinction gap, however, these transfer phenomena are considerably modified by a new mechanism that induces the erosion of the cathode and the anode. It has been found that the classification of material behavior versus erosion is completely different at this voltage. For example AgSnO2, which is claimed as a best compromise at 14 V for all loads, cannot be used at 42 V for two reasons. It exhibits high erosion and requires a larger contact gap to ensure a successful break.