Numerical Investigations on the Pressure Wave Absorption and the Gas Cooling Interacting in a Porous Filter, During an Internal arc Fault in a Medium-Voltage Cell

A mathematical model and a numerical method have been developed to simulate the mechanical and the thermal physical phenomena in a energy absorber like a porous filter, during an internal arc fault in a medium-voltage apparatus. A 1D gas flow model in porous medium with variable porosity is described. The main point is the introduction of a new numerical scheme to take accurately into account discontinuous variations of the porosity and correctly simulate the creation of the transmitted and reflected waves. Numerical simulations are compared to experimental measurements performed on apparatus specially adapted for tests to provide a better understanding of the physical phenomena involved, for instance, the gas cooling and the shock wave absorption by the porous medium of the filter.

I. Introduction

MEDIUM-voltage cells may be designed with adapted safety and protection systems in order to sustain a possible internal arc fault. During such an event, a considerable amount of energy is dissipated in the apparatus, which we intend to control for security and environmental conservation reasons by an energy absorber like a porous filter. An internal arc fault in a switchgear is an uncontrolled electric arc consecutive with a dysfunction, involving a huge energy dissipation. The internal arc results in strong overpressures in the tank apparatus with hot gas emissions and incandescent particle projections. Despite the fact that an internal arc fault is an extremely rare phenomenon in medium-voltage cells since the robust design makes it highly improbable, it should be considered for security reasons. Withstand of the internal arc fault is an optional requirement for medium-voltage cells defined in the standards as IEC 62271-200 or IEEE C37.20.7 specifications, but we would enhance the people security and material safety located in their vicinity.