Experimental investigation of thermal transfer coefficient by a simplified energy balance of fault arc in a closed air vessel

The thermal transfer coefficient that represents the portion of energy heating the surrounding gas of fault arc is a key parameter in evaluating the pressure effects due to fault arcing in a closed electrical installation. This paper presents experimental research on the thermal transfer coefficient in a closed air vessel for Cu, Fe and Al electrode materials over a current range from 1-20 kA with an electrode gap from 10-50 mm and gas pressure from 0.05-0.4 MPa. With a simplified energy balance including Joule heating, arc radiation, the energies related to electrode melting, vaporization and oxidation constructed, and the influences of different factors on thermal transfer coefficient are studied and evaluated. This quantitative estimation of the energy components confirmed that the pressure rise is closely related to the change in heat transport process of fault arc, particularly in consideration of the evaluation of Joule heating and radiation. Factors such as the electrode material, arc current, filling pressure and gap length between electrodes have a considerable effect on the thermal transfer coefficient and thus, the pressure rise due to the differences in the energy balance of fault arc.