Transformer function is based on the principle that electrical energy istransferred efficiently by magnetic induction from one circuit toanother. When one winding of a transformer is energized from an alternating current (AC) source, an alternating magnetic field is established in the transformer core. Alternating magnetic lines of force, called “flux,” circulate through the core. With a second winding around the same core, a voltage is induced by the alternating flux lines.
A circuit, connected to the terminals of the second winding, results in current flow. Each phase of a transformer is composed of two separate coil windings wound on a common core. The low-voltage winding is placed nearest the core; the high-voltage winding is then placed around both the lowvoltage winding and core. See figure 2 which shows internal construction of one phase. The core is typically made from very thin steel laminations, each coated with insulation.
Figure 2 – Transformer Construction
By insulating between individual laminations, losses are reduced. The steel core provides a ow resistance path for magnetic flux. Both high- and low-voltage windings are insulated from the core and from each other, and leads are brought out through insulating bushings. A three-phase transformer typically has a core with three legs and has both highvoltage and low-voltage windings around each leg. Special paper and wood are used for insulation and internal structural support.