Power Factor is the ratio of the true power of a load to the apparent power; a measure of the degree to which the voltage waveform and the current waveform are in phase with one another in an electrical circuit.
Leading Power Factor – A circuit in which the current waveform precedes (“leads”) the voltage waveform. CFLs can produce circuits with leading power factors.
Lagging Power Factor – A circuit in which the current waveform follows (“lags”) the voltage waveform. Motors or transformers can produce circuits with lagging power factors.
Non-Linear Loads – loads that change the shape of the current waveform from its original sine wave shape. This typically occurs because the load utilizes a switching action during its normal operation. Electric ballast and switch-mode power supplies (efficient power supplies used to power most modern electronic equipment) are non-linear loads.
Real (or Active) Power – the energy that is transmitted to a load to do work, expressed in Watts.
Reactive (or Non-Active) Power – the energy that is transmitted to a load but rather than doing work, it is stored in the load in an electrical or magnetic field. Reactive power is expressed in Vars.
Apparent Power – the vector sum of real and reactive power. Apparent power is expressed in VA and is relevant to utilities because they must deliver both real and reactive power (i.e. apparent power) to the loads that are on the distribution network.
Mixed Loads – An electrical circuit that has loads with a variety of load shapes (i.e. a “mix” of linear and/or non-linear loads of a variety of shapes). Most real-world electrical distribution systems consist of mixed load applications. Mixed loads tend to counteract some of the harmonics that would otherwise be present if the loads on the circuit were all of one type of load shape.
To understand power factor, visualize a horse pulling a railroad car down a railroad track. Because the railroad ties are uneven, the horse must pull the car from the side of the track. The horse is pulling the railroad car at an angle to the direction of the car’s travel. The power required to move the car down the track is the working (real) power. The effort of the horse is the total (apparent) power. Because of the angle of the horse’s pull, not all of the horse’s effort is used to move the car down the track. The car will not move sideways; therefore, the sideways pull of the horse is wasted effort or nonworking (reactive) power.
The phase angle of the horse’s pull is related to power factor, which is defined as the ratio of real (working) power to apparent (total) power. If the horse is led closer to the center of the track, the angle of side pull decreases and the real power approaches the value of the apparent power. Therefore, the ratio of real power to apparent power (the power factor) approaches 1. As the power factor approaches 1, the reactive (nonworking) power approaches 0.
Power Factor = Real Power / Apparent Power