Although transformers are very efficient devices, small energy losses do occur in them due to four main causes:
- Resistance of windings – the low resistance copper wire used for the windings still has resistance and thereby contribute to heat loss
- Flux leakage – the flux produced by the primary coil may not be all linked to the secondary coil if the design of the core is bad.
- Eddy currents – the changing magnetic field not only induces currents in the secondary coil but also currents in the iron core itself. These currents flow in little circles in the iron core and are called eddy currents. The eddy currents cause heat loss. The heat loss, however, can be reduced by having the core laminated.(thin sheets of soft iron insulated from one another). (See image below)
- Hysteresis – The msgnetization of the core is repeatedly reversed by the alternating magnetic field. The repeating core magnetization process expends energy and this energy appears as heat. The heat generated can be kept to a minimum by using a magnetic material which has a low hysteresis loss. Hence, soft iron is often chosen for the core material because the magnetic domains within it changes rapidly with low energy loss.
Lamination of iron core:
As stated above, eddy currents generate resistive losses in the form of heat (Joule heating). This effect reduces the efficiency of iron-core transformers. (or any other devices which uses changing magnetic fields) Lamination (using thin sheets of magnetic material) is a way to counter the effect. In the image above, eddy current can circulate on wide arcs within a non-laminated iron core. This will generate a lot of resistive losses and is not ideal. Contrast it with the image below it where the iron core is laminated. The electrons (charge carriers) cannot cross the insulating gap between the thin sheets of magnetic material and so are unable to circulate on wide arcs. Hence, combating the resistive losses in transformers. However, the inclusion of lamination in the transformer design will increase the manufacturing costs and time.