Arc discharge and contact reliability in switching and commutating contacts

Arc discharge at switching contacts has been investigated from the various aspects of arc types and their mechanisms since the research works at Bell System Laboratories during 1950s and many findings have been obtained. Recent reports have presented the transition from metallic phase arc to gaseous phase arc of steady arc discharge and the reconsideration on the minimum arc current. The relationship between arc discharge and contact reliability is a very important issue from practical viewpoint. There have been interesting papers, for example, describing that contact resistance is higher at gaseous arc condition than at metallic arc. This paper reviews recent findings and research trend for the relation between arc discharge and contact reliability. And as for sliding contacts, many small dc motors are used, especially in automotive appliances. In dc motors, a commutation arc is also an important problem for their reliability and lifetime. The influence of commutation arc on brush wear and commutator surface is described.