UNDERSTANDING POWER FACTOR
In most modern electrical distribution systems, the predominant loads are resistive and inductive. Resistive loads include incandescent lighting and resistance heating. Inductive loads include motors, induction furnaces, transformers and ballast-type lighting. Inductive loads, such as motors, require two types of power: (1) active power to perform the work and (2) reactive power to create and maintain electro-magnetic fields. For a given device, active power varies with changes in load, while reactive power remains constant. The vector sum of active power and reactive power results in total power. Total power is the power that must be generated by the utility provider for the user.
- Active power, also referred to as real power, working power, or load power is commonly measured in kW (1000 Watts)
- Reactive power, also referred to as imaginary power, inductive power, or magnetizing power is measured in kVAr (1000 volt-amperes reactive)
- Total Power, also referred to as apparent power is measured in kVA (1000 volt-amperes).
Power factor then is the ratio of active power to total power. The vector diagram shown in Figure 1 illustrates this relationship.
Note that a low power factor requires a larger amount of total power for a given amount of active power, whereas a high power factor requires a lesser amount of total power for the same amount of active power. Utilities provide total power to the user, and by means of continuous metering determine actual values of the components of power shown in Figure 1. These values are provided on the monthly billing statements. If a facility operates at a low power factor, the utility provider may add a penalty. In like manner, a high power factor may result in a rebate or credit.