Power Factor Correction
Is there a way to correct this inefficient use of current? The answer is yes, by using power factor correction capacitors. These capacitors are wired in parallel with the load. They may be installed at the service entrance of the building or be dedicated to a specific device with a low power factor.
PF correction capacitors are sized by the amount of KVAR they are able to correct. To determine proper sizing, the PF for the building or the device must be measured under normal operating conditions. A target PF such as 95 percent is selected. Using the Pythagorean theorem we can calculate the proper amount of correction as shown here:
If your home energy metering system can measure PF, take advantage of this information. Check the PF on the larger motors in your home such as HVAC compressors and fans or a pool pump if you have one. If it is below 80 percent you may want to consider power factor correction capacitors for these motors.
Limit correction to only your larger motors as power factor correction capacitors can introduce additional harmonic currents into your electrical system. Harmonics can interfere with power line carrier communications which may affect your home energy monitor system. Click here for more information about how PF and harmonics interrelate.
Running motors with a higher PF has its benefits. Using more efficient power can lower operating temperatures which extends bearing and motor life. It also reduces the load on your transformer and decreases the amount of reactive currents circulating in your household wiring although you probably won't see any direct savings on your electric bill.
This is because most residential utility rates only charge for kilowatt-hours (KWh), not kilovolt-amp hours (KVAh) nor do they apply a specific penalty for low power factor. Check the fine print on your power bill to be sure. This may change in the future as residential customers add more inductive loads with electronic power supplies and home automation equipment.
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