Laminated Core

A transformer comprises a primary and a secondary coil that are electromagnetically linked. This means that alternating current passed through the primary creates a varying magnetic field around it, which in turn induces an alternating current in the secondary. This implementation of Faraday’s law of induction is valuable because the ratio of input to output voltages – and currents – can be set by adjusting the ratio of primary turns to secondary turns. Transformers are according widely used as step-up or step-down devices in alternating-current circuits. They are also useful for safety isolation.

Within practical transformers, primary and secondary coils are wound around a common iron core to maximise energy transfer efficiency between them. However, electric currents flow in the core as well, as it is also a conducting medium experiencing a varying magnetic field. These currents, known as eddy currents, are an unwanted source of inefficiency and waste heat generation in the transformer.

Accordingly, transformer designers seek to minimise the iron core’s conductivity and therefore the eddy currents that can flow. One way of achieving this is to laminate the core, by building it from a set of metal plates that are glued together, rather than using a monolithic iron block. This has the desired effect of increasing electrical resistance within the core and therefore reducing the current flow, loss of efficiency and heat waste.

The same principle applies to other devices, such as armatures, that use iron cores to maximise magnetic field strength associated with an electrical winding.