Understanding Power Factor and why it’s important

Correction of power factor with capacitors

Power factor is the relationship (phase) of current and voltage in AC electrical distribution systems. Under ideal conditions current and voltage are “in phase” and the power factor is “100%.” If inductive loads (motors) are present, power factor less than 100% (typically 80 to 90%) can occur.

Low power factor, electrically speaking, causes heavier current to flow in power distribution lines in order to deliver a given number of kilowatts to an electrical load.

The effects?
The power distribution system in the building, or between buildings, can be overloaded by excess (useless) current.
Generating and power distribution systems owned by Edisto Electric have their capacity measured in KVA (kilo amps).
KVA = VOLTS X AMPS X 1.73 (three phase system) / 1,000.

With unity power factor (100%), it would take 2,000 KVA of generating and distribution network capacity to deliver 2,000 KW. If the power factor dropped to 85%, however, 2,353 KVA of capacity would be needed. Thus, we see that lower power factor has an averse effect on generating and distribution capacity.

Low power factor overloads generating, distribution, and networks with excess KVA.

If you own a large building, you should consider correcting poor power factor for either or both of these reasons:
• To reduce the possibility of additional power factor charges in the event that Edisto Electric starts billing for PF corrections and
• To restore the (KVA) capacity of overloaded feeders within the building or building complex.

There are several methods of correcting lower power factor. Commonly used are:capacitors.

Capacitor Banks
The most practical and economical power factor correction device is the capacitor. It improves the power factor because the effects of capacitance are exactly opposite from those of inductance.

The var of KVAR rating of a capacitor shows how much reactive power the capacitor will supply. Since this kind of reactive power cancels out the reactive power caused by inductance, each kilovar of capacitance decreases the net reactive power demand by the same amount. A 15 KVAR capacitor, for example, will cancel out 15 KVA of inductive reactive power.

Capacitors can be installed at any point in the electrical system and will improve the power factor between the point of application and the power source. However, the power factor between the load and the capacitor will remain unchanged. Capacitors are usually added at each piece of offending equipment, ahead of groups of motors (ahead of motor control centers or distribution panels) or at main services.


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