Energy based evaluation of gas cooling related to arc faults in medium voltage switchgear

An arc fault inside metal enclosed switchgear causes a rise in gas temperature and pressure and may endanger the safety of personnel. Passive devices that effectively cool down the gas with limited extra cost are of special interest to investigate. An energy based evaluation of different gas cooling installations and materials related to internal arc faults in medium voltage switchgear has been carried out. Temperature measurement in inhomogeneous gas flows constitutes a central part of this study. A thermal efficiency of 79 % (ΔT of 540 K) is observed with an aluminium mesh as absorption material. The energy distribution in the system is visualized in a Sankey diagram showing that 2/3 of the energy is absorbed in the arc compartment. The remaining energy enters a buffer room, from which about 50 % escapes through an energy absorber. Depending on design, between 5 and 10 % of the total energy input from the electric arc escapes to the surroundings. By introducing boric acid in the absorber, cooling by ablation seemed to take place. Depending on buffer and absorber design, the observed pressure rises in the arc compartment indicate that some precautions may have to be taken to avoid excessive stress on the switchgear compartment (arc compartment). Based on the experimental setup presented in this paper, 5 of 6 tests with different designs passed the standard safety test.