in electrical technology is a device for increasing or reducing an alternating voltage without significant energy losses. A 1-phase transformer has the primary and secondary coils arranged at either end of a closed, O-shaped core. The alternating current flowing in the primary coil generates, by means of induction, a voltage in the secondary coil, which is proportional to the number of windings. In order to achieve the strongest possible common magnetic field of the two windings, these also sit on one arm of the O-shaped core.
In rotary current transformers, the primary and secondary windings of each phase are arranged on the three vertical arms of pillars. The primary coils consist of relatively thin wires or flat profiles. For the secondary coils, at high currents, conductor strips are used with widths of up to 1 m.