We constantly use electrical appliances at home or in factories and trade, they are responsible for much of our legwork. For an electrical appliance to do its job, it is necessary to introduce electrical energy into it, this appliance will transform this electrical energy into another type of desired energy. A light bulb, for example, transforms electrical energy into light energy, as does a motor that transforms electrical energy into mechanical energy.
However, not all electrical energy introduced in a device is effectively converted into work, always part of this energy will be converted into an unwanted form of energy, usually in the form of heat. This portion transformed into unwanted energy is energy loss.
In old incandescent lamps, for example, approximately 20% of the electrical energy used is only converted into light energy, the other 80% is converted into heat.
In this way it is possible to conclude that the final energy desired and released by an electrical appliance is equal to the energy that is introduced into the appliance less the energy lost. Therefore, the amount of energy released is always less than the energy introduced.
Performance is nothing more than the relationship between released energy and introduced energy. In the area of electricity, however, it is common for the performance to be calculated by electrical power. The Greek letter η is used to express income. See the income formula:
Because the output power is always less than the input power, the output will always have a value less than 1 and is usually expressed in percentage terms. The lamp mentioned above has a performance of only 20% as it is the amount of energy actually delivered at the output without losses.
In some processes, the transformation of energy can take place in several stages, such as in a nuclear generation plant. In this case, nuclear fission is used to vaporize water, this steam drives a turbine that ultimately moves a generator. This process has three stages of energy transformation.
- Water vaporization with η1 yield;
- Turbine movement with η2 efficiency;
- Generator movement with efficiency η3.
Therefore, the total income from this transformation is the sum of the income from each particular transformation.
The performance information as a percentage is generally described on the nameplate of electric motors, in household appliances, the performance will be linked to energy efficiency and through an INMETRO label, it is separated into consumption and performance categories.