Orateur
Description
Electrical contacts are important components in a switching device. During the make operation, a mechanical bounce happen just after the first electrodes contact. In the beginning of this short separation, the contact force decreases and the number of contact zones and their surfaces reduce. Due to this, the current lines become tight, increasing the constriction resistance. The metal heats by the Joule effect until melting, which creates a molten bridge in between the contacts. Its explosion leads to an arc ignition, by the ionization of the gap inter-electrodes. The molten surfaces stick after the final closure.
The contacts are made of silver and anti-welding materials like tin-oxide although they increase the electrical resistance of the contacts.
To understand the mechanism of the contact welding and to define the best materials to decrease it, several materials based on silver tin oxide with two different shapes were tested. The tests were performed under 42 VDC and 90 A for an arc duration corresponded to 1,5 ms. This study showed that increasing the amount of tin oxide and changing the nature of doping influenced the welding tendency and decreased the welding force. A similar study will take place under aeronautical conditions. To initiate this study, the mechanical bounce produced in a power contactor of aeronautical application was characterized by using displacement sensors and the fast imaging.
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