Why industries are using Capacitor Banks

This phase difference can take two basics forms. 

• The current can “lag” the voltage when an inductive load (i.e., motors, magnetic HID ballasts) is used or
• The current can “lead” the voltage when a capacitive load(i.e., computers, electronic fluorescent ballasts) is used. 

When the current is out of phase with the voltage,the power utility has to supply more volt-amperes(VA) for a given wattage (W). Certain customers, such as industrial companies, may have to pay an additional charge if their power factor is too low which is why many industrial applications have banks of capacitors. These capacitors correct the poor power factor caused by the motors. This is also how manufacturers have been able to take a product that is inductive in nature, such as a magnetic HID ballast with a normal power factor, and include a “power factor correcting” capacitor to give the ballast a high 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). Consider this popular analogy to clarify the relationship between real and apparent power.

We all know a glass of draft beer generally has a "head" on it. Let's say your favorite pub institutes a new policy -you only pay for the beer, not the foam. While the foam is just aerated beer, it is not really usable in that form. If the glass of beer is half foam, you pay half the price. This is the same principle as electricity generation - the consumer only pays for the beer (real power), not the foam (the "VARS" mentioned above).

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