Experimental diagnostic and numerical simulation of an internal arc fault in a medium voltag cell
Résumé
Internal arc faults are extremely rare phenomena characterized by a powerful non-controlled electric arc due to a dysfunction. Internal arc faults on medium voltage (MV) cells are a focal area where experimental tests are carried out to set the switchgear in conformity with IEC standards [1]. In order to limit the internal arc effects, a new protection filter constituted of a porous medium [2] was recently used providing better performance as compared with traditional filter technologies. The arcing fault process can be chronologically summarized as follows: • An internal arc fault involves a pressure rise in the initially sealed metal enclosure of a medium voltage cell due to an increase in the temperature and the vaporized mass (plastic and metal vapours). • To avoid explosion of the metal enclosure containing the insulating gas, a safety valve located at the bottom of the internal metal enclosure bursts when the pressure reaches a critical value. • After the valve has burst, the gas releases and a shock wave is generated: the hot gas flow is ejected towards the buffer area, then it penetrates into the porous filter. • The porous medium's aim is to absorb the shock wave generated at the valve opening and to cool the hot gas flow by heat exchange with the grains composing the protective filter. The final role of the filter is to obtain a gaseous outflow which is not harmful to the equipment and the people located in the MV cell vicinity. In order to simulate the process and to enhance the protection technology, several experimental investigations, and numerical simulation on the arcing fault in a MV cell have been carried out, and are presented in this paper.