Microelectronics are being used increasingly in the power indus- tries and in locations which may be geometrically close to sources of interference. The main sources of interference come from the operation of switchgear which are normally accompanied by closing or opening arcs [1], [2], [3], [5]. These arcs radiate interference at high frequencies which are dependent on the type of switchgear, the most onerous of which is expected to come from SF, insulated systems where high dv/dt and di/dt exist. In any case, the magnitude of these fields can be significantly higher than those specified in relevant immunity standards [6].