Internal arcs in electrical installations - Validity range of a pressure calculation method

Internal arcs cause a sudden pressure rise in electrical installations. This leads to an extreme pressure stress acting on switchgear compartments and switchgear rooms and could cause collapse of buildings. In order to predict the overpressure, pressure calculations become essential. Nowadays, pressure calculations are performed by two methods. The first method is the "CFD method" (Computational Fluid Dynamics calculation method), which employs the finite volume method yielding to spatially resolved results. The second one is the "ISC method" (Improved Standard Calculation method) providing spatially averaged results. However, the validity range of the ISC method needs to be investigated. The investigation of the validity range of the ISC method is done by varying some parameters like shape and size of the switchgear room, size and position of the pressure relief opening to the environment, etc. Then, the pressure developments from both methods are systematically compared. Based on these comparisons the ISC method tends to yield under estimated results due to the influence of pressure waves in the case of air-insulated switchgear. However, in the case of SF₆ insulated switchgear, the ISC method provides over estimated values of the maximum pressure compared to the CFD results.