Understanding Power Factor

July 31, 2014

Understanding Power Factor

What is power factor and how does it affect your facility?

What is Power Factor?

Power Factor is a measure of the efficient use of power, the ratio of the Working Power to Apparent (or Total) Power. To determine power factor (PF), divide working power (kW) by apparent power (kVA).

Power Factor Equation

Power factor is a way to find out how effectively you are using your electrical power. A high power factor indicates effective utilization of electrical power, whereas low power factor signifies inefficient use of electrical power.

When you have low power factor, you are not fully employing the electrical power you are paying for. Poor power factor is costly for the utility and the end user – power system capacity is used, kW losses are increased and voltage at the load is low. Utilities often penalize customers for low power factor as an incentive to compensate for this inefficiency.

Example of calculating power factor:

Power Factor Example

Why you should be concerned about low power factor? Apparent power, kVA, decreases as power factor increases.

Real Power Used Power Factor Example
Figure 1. Power Factor Example

Example: At 80% power factor, it requires 125 kVA to produce 100 kW. At 97% power factor, it requires only 103 kVA to produce 100 kW. Another way to look at it is that at 80% power factor, it takes 21% more current to do the same work. See Figure 1.

What is VAR?

Active power, also called real power, is measured in Watts or kW and performs Useful Work. Electrical equipment like motors and transformers require reactive power, create a magnetic field and allow work to be performed.

VARs Example
The foam on the top of the beer is represents VARs, which is the wasted capacity of the actual beer, the useful work or watts produced.

This reactive power is called Volt-Amperes-Reactive or VAR. Reactive power is measured in VARs or kVARs. Working power and reactive power make up apparent power.

For example, take a mug of beer. The capacity of the mug represents apparent power (kVA), the summation of the reactive power and working power. When you have a lot of foam (kVAR) in your mug, the lower your working power (kW), which equates to lower power factor; not very efficient if you want to get your money’s worth!

Correcting Power Factor

Correcting poor power factor can significantly reduce the load on transformers and conductors, allowing for facility expansion.

Horse Pulling Boat on Canal Example
Consider a horse pulling a boat on a canal. The boat turns it’s rudder to stop from running into the bank. The turned rudder creates drag so less of the horse’s power is going toward moving the boat forward.

Buckles-Smith provides power factor correction solutions to help in maximizing the real power use in your facility. Please contact Buckles-Smith or your Account Manager for further details.

Get the printable version here: Understanding Power Factor.

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