Explanation of Power Factor and kVA
Basic electricity states that: P (kW) = I (Amps) x V (Volts).
However this is only true in DC-circuits. In AC-circuits the correct formulae are: Apparent Power S (kVA) = I (Amps) x V (Volts)
Real Power P (kW) = I (Amps) x V (Volts) x PF (Power Factor is a number between 0 and 1; example .9, which may be expressed as a percentage 90%)
Real Power P (kW) = Apparent Power S (kVA) x PF The reason for this is that in AC circuits the current can lag behind, r lead the voltage. Inductance (Motors, Transformers, etc.) causes the current to lag, and Capacitance causes it to lead. In heavy industry where there are lots of motors, ballasts or transformers, the lag can be significant. In a typical home it usually runs between 90 and 100%.
With a low power factor, the system needs to work harder to create the same energy. Generally, Utilities charge only for Real Power. So if that is the case, why do we care and why does TED display it? A few reasons:
1. If you are using more current to accomplish the same work, then there is greater voltage drop and line losses. (Consumer does pay for the line losses on the load side of the meter.)
2. Some utilities will charge a penalty or a demand charge to make up for their added cost in providing more apparent power kVA. The charge usually works like this: If your system demand is under, for instance, 5 kVA there is no charge. (Demand is based on running 15-minute averages typically so motor starting does not affect it). If your demand over the month is, let's say, 15 kVA, then you have exceeded the threshold by 10 kVA and if they charge you a demand charge of $8.00 per KVA Demand Charge = 10kVA * $8.00 per kVA = $80.00 for the month.
There are only a few utilities in North America that currently make this kind of charge for residential customers, however it is becoming much more common as a way of capturing the added infrastructure costs. It is much more common in commercial facilities, and very common in industrial settings.
3. Poor power factor could be a sign of a poor electrical system.
4. Those with solar energy systems are usually quite interested in this information as they want all the current generated to be doing real work.
