AC Electrical Arcs with Graphite Electrodes

In order to improve the safety of potentially hazardous situations such as "hot" disconnections of equipment or deteriorated connections, a deeper knowledge of the characteristics of the arcs thus produced and their subsequent damage to contact materials, insulating and wiring, is needed. Numerous studies have been performed on DC arcs as they appear in automotive applications. There is however, a strong need to study arcs in the domain of alternating current, in order to understand their consequences to safety and reliability in domestic applications. The purpose of this study is to extend our knowledge of AC-arc characteristics and consequences (e.g. risk of fire ignition) in order to improve the reliability of security devices such as arc fault circuit interrupters (AFCI). Conditions when arcs could initiate and reinitiate are determined, for a voltage of 220V (50Hz), a current from 1A to 4A, electrodes made with copper or graphite and gaps from 10μm to 1000μm. The conclusion of this work is that arcs produced by graphite electrodes present some characteristics which differ significantly from metallic electrode arcs, especially regarding ignition and re-ignition capability. This behavior should be taken into count for safety considerations.