Power factor
What is a Power Factor
This is quite a "deep" subject when you get into all the detail, this article will attempt to cover some of the basics. A power factor (PF) is a concept that only usually applies to electrical loads being powered from an AC supply. Usually the power dissipated by a load is proportional to its resistance and the voltage applied to it. However when you start dealing with AC supplies things can get more complicated due to the effect of "reactive" elements in the load. These are typically components that can actually store energy. As you might imaging. having something that stores energy during one part of the mains cycle and then gives it back again at another can make the types of calculations that are easy to apply to loads that are only resistive somewhat more difficult.
How is a power factor expressed?
A power factor is expressed as a number between 0 and 1. A power factor of 1 (aka a "unity power factor") basically says the power in a load can be treated like a normal resistive load, and ohms law applies. A PF of 0 is a perfect reactive load, or one that actually dissipates no real power at all, it just stores and returns energy each half mains cycle.
Does a low power factor mean I am using more electricity?
Sort of. In a domestic situation a poor power factor will not result in you being charged for more electricity, although the load with a lower power factor will draw more current. Poor power factors are bad for distribution efficiency though, and can result in the mains supply waveform getting misshapen and noisy - so power supply companies tend to penalise big industrial users if they don't control their power factors.
The effect of the non unity (i.e. < 1) power factor is to cause the peak alternating current drawn by a load to not line up with the peak alternating voltage (there are other causes of poor PFs but we can skip those for the moment). This misalignment shows up as a lead or a lag in the respective waveforms. It comes about when the load contains components with an ability to store energy (i.e. a capacitors and inductors). Capacitive loads cause the current to lead the voltage, and inductive ones cause a lag.
If you want an analogy, imagine riding a bike up hill. You stick a certain about of push into the pedals to keep it moving overcoming resistance, and more to add the energy you are acquiring by climbing the hill. A poor PF is like someone attaching a big spring to one pedal and the seat post, such that every time you push the right pedal down you also need to stretch the spring. As you can imagine this will take more "push" from you to keep riding. However that extra push is only required on the right pedal. When you push the left pedal you have the energy stored in the spring pulling up on the right pedal and hence working for you. So the result is the bike is harder to ride, but the total energy required to get up the hill is actually the same.
Can you change or compensate for a poor power factor?
You can do what it called power factor correction. Worthwhile in an industrial setting where customers are usually charged based on their VA loading rather than their real power loading in watts, but less so in a domestic one where the meter will give a reasonable indication of the actual power consumption regardless of PF.
I have some poor PF appliances like an old fridge, should I apply correction to them?
No. Trading up to a modern low energy consumption one may help, but there it not much you can do for an old one.