The most desirable power factor varies with conditions. This may be an economic decision, but it is usually based on the need to reduce the reactive power load on a circuit. The amount of capacitance needed to effect a change in power factor can be determined from tables, by a graphic diagram, or by direct calculations. All of these methods are based on the relationship:
(Apparent Power)2 = (Real Power)2 + (Magnetizing Power)2
This can be diagrammed by a right-triangle with sides proportional to these three quantities. The power factor is the kilowatts divided by the kiloVoltAmperes (or kW/kVA).
Power Factor = (kilowatts)/(kiloVoltAmperes)
One of the most convenient ways to size the capacitor bank for power factor improvement is to use a table of capacitive kVA to kW, such as shown in POWER FACTOR CORRECTION Table in Appendix page 238. This technique assumes that only capacitors are being added; that the kilowatt load is not being changed. First, find the number of kilowatts, then the existing (initial) power factor. Next, choosing the desired power factor in the table indicates the value to multiply the kilowatts by to find the capacitive kVARs required (often designated kVAC to point up the capacitive nature).
Example: Use Of Tables For Sizing Capacitors
