Copper loss refers to the amount of heat or energy wasted when an electrical current travels through a coil or winding in an electrical device. A common example is the coils found inside a transformer winding which are made from copper or aluminum and allow an electric current to pass through them. Even if the winding is not made from copper, the process is still referred to as copper loss.
Transformers and other electrical devices pass electrical currents through them to move the current into a different circuit. During this transfer of energy, some of the energy is released in the form of heat. Copper loss is referred to as the loss of this energy because the heat given off is not used by the device and simply dissipates into the air around it.
The event of copper loss is unwanted but currently unpreventable. Heat lost like this results in a small amount of power loss in the device. In a perfect situation, all energy would be used in the electrical device and since no energy would be lost, the device could transfer more energy at a faster rate. While the energy loss is fairly small, the amount goes up in proportion to several factors about the electrical device.
Joule heating is a term that describes the heat lost during transfers like this. A man by the name of James Prescott Joule performed several experiments which led him to determine a formula for calculating the amount of heat that will be lost during a transfer. To calculate the amount lost, the person should square the amount of current — expressed in a measurement known as amperes — currently moving through the device and multiply that number by the amount of resistance — expressed in ohms — from the device itself. Once the person finds these numbers and works out the formula, he will know the copper loss for a specific device expressed in watts.
A person experiences copper loss on a daily basis when she uses a light bulb in her home. When the current moves through the light bulb, it meets a certain level of resistance. If she were to find out how strong the current is, square that number, and multiply it by how strong the resistance is she could find out the copper loss of her light bulb expressed in watts.