Power factor correction (PFC) capacitors FAQ

Power factor (PF) is the ratio of working power (kW) to apparent power (kVA). Power factor is expressed as a dimensionless number between 0 and 1.0; it is a representation of how efficiently power is being drawn from the grid. A high ratio indicates a very efficient electrical system, while a low power factor denotes a poor utilization of electrical power, meaning a higher proportion of current is being drawn from the utility than is necessary.

When power factor is at unity, the voltage and current waves are aligned or in phase with one another. This is expressed as a PF of 1.0.

Power factor is driven by the number of inductive loads on a system. Many industrial and commercial  electrical system loads are inductive, meaning they require reactive power (kVAR) to sustain a magnetic field needed in order for the equipment to operate, in addition to the kW which they use to perform work.  The larger the portion of a facility’s load that is inductive, the higher its kVAR draw from the utility and the lower its power factory will be. The loading of this type of equipment also plays an important role in a facility’s power factor.

Inductive loads always require the same amount of kVAR regardless of kW output, which results in motors operating at less than full load having extremely poor power factor. This often occurs in cycle processes where motors are sized for the heaviest loads, such as those using circular saws, ball mills, conveyors, compressors, grinders and punch presses. Low power factor at high loads can also be an issue. A facility operating at a high load has a higher current draw, which causes voltage to dip. Motors operate best at higher voltage levels, as low voltage can cause them to be sluggish or overheat.

Utility companies assess power factor charges in a variety of ways. Sometimes tariffs are clearly identified on a utility bill, while in other instances they may be rolled into other costs. Three of the most common ways a utility will charge for power factor are through kW demand adjustments, kVA demand billing, and kVAR demand charges.

If the charge is not easily identifiable when reviewing your bill, you may obtain tariff details from the utility to better understand these extra charges. 

Consumers can slash costly penalties by adding power factor correction capacitors to their facility distribution systems, as these units effectively lower kVAR demand. By adding capacitors as a local reactive current source to the system, they reduce the current drawn from the utility and improve voltage, resulting in more efficient motor performance and longer motor life.