Influence of Insulating Gas on Pressure Rise due to Internal Fault Arcing in Switchgear

In view of the issue on fault arcing in an enclosed switchgear, the influence of different insulating gases on pressure characteristic due to fault arc in an enclosed tank is investigated experimentally. The developments in pressure rise, arc voltage, injected arc electrical energy and radiation energy are compared and analyzed under the condition of air, SF₆, CO₂ and N₂. With the thermal transfer coefficient determined based on standard calculation method, the variation of thermal transfer coefficient is analyzed quantitatively for different insulating gases. The results show that the pressure rise is lowest if SF₆ is used as filling gas and highest for air at the same arc electrical energy. The maximum pressure rise almost increases linearly with injected arc electrical energy. Regarding arc voltage, it is highest for CO₂ whereas is lowest for SF₆ at the same current. As the filling pressure rises, the fraction of arc radiation to input Joule heating increases for SF₆ while it tends to fall in the case of CO₂, N₂ and air instead. As the filling pressure decreases, the thermal transfer coefficient for air, CO₂ and N₂ all reduces. Inversely, it tends to increase in SF₆.