An ideal transformer have no energy losses i.e zero losses, and 100% efficient. but in real (In practical) transformers, energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those of distribution transformer usually perform better than 98%.
Experimental transformers using superconducting ( Super conductor is one that in which zero losses occur) windings achieve efficiencies of 99.85% i.e zero transformer losses, but it would be available in coming years.
Losses in Transformer
The different losses in the transformer are as follows,
Current flowing through the windings causes resistive heating of the conductors. At higher frequencies, skin effect and proximity effect create additional winding resistance and losses.
Total copper losses. = I12. R1+ I22R2 = I12. R 01+ I22R 02
Core or Iron Losses (Transformer Losses).
There are two types of core or iron losses in a Transformer.
1) Hysteresis losses (Transformer Losses)
Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the transformer losses are proportional to the frequency, and is a function of the peak flux density to which it is subjected.
We can find Hysteresis losses by this formula.
Wh = ηB1.6maxf.v watt
2) Eddy current Losess (Transformer Losses)
Ferromagnetic materials are also good conductors, and a core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness. Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other, rather than a solid block; all transformers operating at low frequencies using laminated or similar cores.
We can find Eddy currents losses by this formula.
We = PB2max.f2t2 Watt
Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers, and can cause losses due to frictional heating.
Mechanical losses (Transformer Losses)
In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise, and consuming a small amount of power.
Stray losses (leakage Flux) (Transformer Losses)
Leakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformer’s support structure will give rise to eddy currents and be converted to heat. There are also radiative losses due to the oscillating magnetic field, but these are usually small.
Reference : Wikipedia , Edited and compiled by: Engr. Wasim Khan.