Aging of Environmentally Friendly Insulation Gases by Free-Burning Arcs: Technical Air

This article investigates the effect of aging due to free-burning arcs on the dielectric performance and the chemical composition of technical air (79% N2 and 21% O2) at 1.3-bar absolute pressure. The aging is performed by exposing the gas to a series of arcs dissipating an accumulated energy of more than 300 kJ, a level corresponding to relevant arcing energies for medium-voltage (MV) load break switches. To evaluate the long-term dielectric performance, lightning impulse (LI) and power frequency AC breakdown tests are conducted in a 10-mm rod–plane gap before and after aging. Gas decomposition is also investigated with gas chromatography coupled with mass spectrometry (GC–MS). Results indicate that the LI breakdown voltage of air may enhance temporarily after arcing. This is probably due to the formation of short-lived air byproducts (e.g., NO, NO2, NO3, and O3) which may reduce initial electron generation. However, changes in AC breakdown voltage might not be that significant as the presence of primary electrons is presumably guaranteed in the latter case.