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Operating experience from different industries has shown a considerable number of reportable events with non-chemical explosions and rapid fires resulting from high energy arcing faults (HEAF) in high voltage equipment such as circuit breakers and switchgears. High energy arcing faults can occur in an electrical system or component through an arc path to ground or lower voltage, if sufficiently high voltage is present at a conductor with the capacity to release a high amount of energy in an extremely short time. High energy arcing faults may lead to the sudden release of electrical energy through the air. The significant energy released in the arcing fault of a high voltage component rapidly vaporizes the metal conductors involved and can destroy the equipment involved. The intense radiant heat produced by the arc can cause significant damage or even destructions of equipment and can injure people. However, this problem has been underestimated in the past (Owen, 2011a and 2011b). Arcing events are not limited to the nuclear industry. Examples for such events could be found, among others, in chemical plants, waste incineration plants, and in conventional as well as in nuclear power plants underlining that high-energetic arcing faults are one of the main root causes of fires in rooms with electrical equipment (HDI-Gerling, 2009). An evaluation of several loss incidents in different types of industrial plants has shown that causes for the generation of arcing faults are mainly due to (HDI-Gerling, 2009):  contact faults at the screw-type or clamp connections of contactors, switches and other components due to, e.g., material fatigue, metal flow at pressure points, faulty or soiled clamp connections,  Creeping current due to humidity, dust, oil, coalification (creeping distances, arcing spots),  Mechanical damage due to shocks, vibration stress and rodent attack,  Insulation faults due to ageing (brittleness), introduction of foreign matter and external influences. Investigations of HEAF events have also indicated failures of fire barriers and their elements as well as of fire protection features due to pressure build-up in electric cabinets, transformers and/or compartments, which could lead to physical explosions and fire. These events often occur during routine maintenance.

Investigation of High Energy Arcing Fault Events in Nuclear Power Plants