This column features helpful information, innovative equipment, systems and applications utilities around the nation can use to save energy and improve service.

Exploring power factor myths
by Johnny Douglass

Power factor is the most misunderstood and dreaded electrical phenomenon outside of ball lightning and zaps from door handles during cold dry weather, but in reality, it should not be that mysterious.

In AC circuits, simple resistance loads like incandescent light bulbs and baseboard heaters draw electrical current (the flow of electrons) exactly in sync with the voltage. Other loads, most notably induction motors, exhibit something like electrical inertia. They like to keep the current flowing in the same direction, which delays its rise and fall a few milliseconds relative to AC voltage. This delay is called phase lag.

Why does phase lag matter? Power is delivered to the load any instant during which current is moving in the direction voltage is trying to move it. AC voltage changes polarity 120 times per second. When there is a phase lag, current still coasts in the contrary direction for a few milliseconds after each change of AC voltage polarity. In those moments, the load is actually sending some of the energy back into the line.

That requires a higher capacity distribution system sized to handle all the energy traffic, not just that which flows in the desired direction. Power factor is the ratio of the net energy flowing to the load to the total energy traffic both to and from the same load. Reactive power is just the back and forth portion of the gross energy traffic.

There are quite a few myths about power factor. Some are sustained by unscrupulous or ill-informed sellers of power factor correction products. These myths need to be busted:

Myth 1A: Using capacitors to correct power factor of a motor helps the motor run better, cooler and more efficiently.

Fact: Correcting power factor only affects the electrical system ahead or upstream of where the capacitors are added. The motor does not even know the power factor has been corrected; the power factor at the motor terminals is unchanged.

Myth 1B: Efficiency and reliability are reduced for all devices powered from an electrical system with low power factor.

Fact: Connected devices only respond to voltage. They cannot detect or experience effects of reactive power flowing in the system from other loads.

Myth 2: Reactive power is a strange or weird form of power that represents energy somehow escaping from doing useful work.

Fact: There is no mysterious escaping energy associated with reactive power. There is just a small increase of additional distribution losses because the distribution system is carrying more current.

Myth 3: Correcting power factor brings large double-digit energy savings from the reduction of distribution losses in a facility's conductors and transformers.

Fact: The total distribution system losses on the customer's side of the meter from both reactive and real power are usually not more than 2 percent and very rarely as high as 4 percent. You cannot save more than you were losing in the first place.

(Note: Douglass is a registered professional engineer with the Energy Services Clearinghouse.)