A transformer consists in principle of a magnetic circuit, an iron core around which the conductors of at least two adjacent circuits in coils are wound, usually with different numbers of turns.
As a rule, copper wire is used for the windings. The winding on the line side is termed the primary side. The winding supplying the electrical load is termed the secondary side. An alternating voltage induces a varying magnetic field in the input winding and an induction voltage in the output winding. The size of this voltage depends on the winding ratio of the primary and secondary side of the transformer. If the number of turns on the primary side is greater than that on the secondary side, then the output voltage is less than the input voltage. This also applies conversely.
In order to insulate the live parts, the copper wires are varnished with synthetic resin or wrapped in fi lms or special papers. Supplementary protection against a sudden discharge is provided by specially designed transformer oils. These insulating oils based on mineral oils, esters or silicon must insulate, cool, be stable at low temperatures and resistant to oxidation and blend with winding and insulation materials.