connection terminals secondary winding top terminals include the wires ending in contacts 11 and 12 with either contact engaging a conductor to connect the connection terminal with output terminal 8 via contact 10 the winding is carried out in such a manner that the ratio the of primary current i1 to the secondary current i2 defines two transformation or current ratios in the example illustrated at the terminal s2 the ratio is 100 5 while on the terminal s3 the ratio is 200 5 depending on the application the operator should connect its user module 7 between the terminals s1 and s2 if the primary current is of the order of 100 amperes maximum or to the terminals s1 and s3 if the primary current i1 is of the order of 200 amps according to the first characterizing feature of the present invention the transformer 1 comprises means 6 in the form of a transformer configuration device 13 and to adapt the configuration of transformer 1 to the selected operational range which effects at least the commutation of the secondary winding or windings 5 according to the selected range in the case of the single phase transformer shown in fig1 the definition.