16-01-2013, 04:28 PM
Power Factor
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What is power factor?
This is a very involved subject that will be dealt with in terms of field application and typical questions from end-users.
Power factor is characteristic of alternating current (AC) circuits. Always a value between (0.0) and (1.0), the higher
the number the greater/better the power factor.
Circuits containing only heating elements (filament lamps, strip heaters, cooking stoves, etc.) have a power factor of
1.0. Other circuits containing inductive or capacitive elements (ballasts, motors, personal computer, etc.) usually
have a power factor below 1.0. Normal power factor ballasts (NPF) typically have a value of (0.4) - (0.6). Ballasts
with a power factor greater than (0.9) are considered high power factor ballasts (HPF).
The significance of power factor lies in the fact that utility companies supply customers with volt-amperes, but bill
them for watts. The relationship is (watts = volts x amperes x power factor). It is clear that power factors below 1.0
require a utility to generate more than the minimum volt-amperes necessary to supply the power (watts). This
increases generation and transmission costs. Good power factor is considered to be greater than 0.85 or 85%.
Utilities may impose penalties on customers who do not have good power factors on their overall buildings.
Watts, or real power, is what a customer pays for. VARS is the extra “power” transmitted to compensate for a power
factor less than 1.0. The combination of the two is called "apparent" power (VA or volt-amperes).