The losses of a transformer comprise two parts – no-load (or core) losses and load (or copper) losses. No-load losses are a constant and are independent of the power being drawn while load losses vary according to the power being draw.
It is important to note that there are International Electrotechnical Commission (IEC) standards set up as to what the maximum allowable load and no-load losses may be. The higher the transformer’s losses are, the cheaper it is to produce.
When it comes to the design and manufacture of the core of a transformer, the use of high-grade, grain-orientated core steel is preferable if losses are to be minimised. However, it must be said that there are different classes of this steel.
Load losses depend on the winding material’s properties, including the diameter and purity of material, which have a direct effect on the resistance of the winding material. The greater the resistance, the higher the losses, as resistance of a material is affected by the temperature at which it is measured.
The losses need to be calculated at a reference temperature and the two reference temperatures are 75°C and 120°C. The metallurgical properties of copper and aluminium become more resistant as the temperature increases. From this, losses quoted at lower temperatures will always be better than those quoted at higher temperatures.
When comparing two datasheets, always ensure both load losses are at the same reference temperature which will allow a fair comparison.