Power and/or distribution transformer equipped with on-load tap-changer

A power and/or distribution transformer comprising: a tank provided with a magnetic core, high- and low-voltage windings, adjustment windings. insulating partitions made of solid material which are interposed between the high- and low-voltage windings and a dielectric and cooling fluid; an on-load tap changer which comprises: at least one selector which is immersed in a lubricating fluid; at least one diverter switch which comprises arc contacts and a dielectric arc-quenching fluid; characterized in that the dielectric and cooling fluid of the transformer and/or the dielectric and arc-quenching fluid and/or the lubricating fluid of the selector are liquid perfluoropolyethers, and in that the tank and the diverter switch are each provided with a filter for reducing chemically reactive gas species generated by the decomposition of the fluids.