In an ideal circuit, all the power applied to the input terminals would reach the critical load with no energy wasted or dissipated in the wiring or components along the power path. In real circuits, however, these components always have some resistance, however small. This occurs with both AC and DC supplies, causing electrical losses which are dissipated as heat. These losses can be calculated as below:
Ohm’s Law: V = IR where V = voltage (Volts) across a component, R is the component’s resistance (in Ohms) and I is the current in Amps through it.
Power Law: W = VI where V and I are as above, and W = power dissipated in Watts.
From combining these, we can see that the loss W = (IR)I or I2R. This is known as copper loss.
Copper losses can be significant in AC circuits involving wound components like transformers. Such losses occur in their windings, so they are sometimes called winding losses. However, further losses will arise from induced currents flowing through resistance in the components’ iron core; these are called core losses.
Transformer or motor copper losses can be reduced by increasing the conductor’s cross-sectional area, improving the winding technique, and using materials with higher electrical conductivities.
With high-frequencies, the proximity effect and skin effect cause the current to be unevenly distributed across the conductor, increasing its effective resistance. This can be counteracted by using Litz wire, which forces current to be distributed evenly over its cross-section.