The present invention relates to an electrical insulation system having a low environmental impact comprising two fundamental elements: a) a gaseous medium formed by one or more highly fluorinated fluoroketones having between 4 and 12 carbons, at least another additional dielectric gas, other than the fluoroketones, with a vapor pressure greater than 500 mbar and less than 15000 mbar at 0° C., such as fluoronitrile (CF3)2CF—CN, for example, and one or more vector gases; and b) a molecular sieve capable of discriminating water molecules from molecules of other gases present in the gaseous medium of the system. The invention also relates to the use of the insulation system and to the medium- or high-voltage electrical switchgear comprising a complete enclosure in which there are arranged live electrical components and an electrical insulation system according to the invention.