physics222project.pdf
It is possible for a device to take power on a 90 degree phase from the voltage. Both capacitors and inductors have this property.
If your load is only capacitive, or inductive, it will only dissipate power because of losses due to it's internal resistance. Appart from that, there can be large current flowing through that load, and take no power.
How this can be is because the voltave vs current is shifted 90 degree. You get the largest current drain where the voltage is zero. And current also get fed back to the source.
In a more day-to-day life (in real-life case), for ordinary applications, or small homes, this doesn't cause problems. However, if done on a larger scale, this can be a bit problematic. Taking current in this manner still put some load on the power company, and when you have a big company, with lots of motors, for examples, the electric co. have to take this into account, because the electric co still have to produce extra power. The electric company then also monitor the currect phase shift, and usually charge what thay call a 'phase penalty'. This is a bit like being charged for taking more than the allowed power, at a higher rate.
The power cables, running from the power facility to the end users, are very long (lots of miles of cables). The higher the frequency, the higher the cables act as an inductor. This is why the frequency is low (50 or 60 Hz), to minimize this problem. Even with low frequencies, with all the power lines, there is still a non-negligable inductances created over those lines. And the power co. have to take this into account. The inductive effect of an inductor can be eliminated by the capacitive effect of capacitors. Capacitors and inductors create an opposite effect. One take current 90 degree leading the voltage sine wave, the other 90 degree lagging the voltage wave. When combined, they cancel each others (they actually resonate togetter, but on the power source, they appear as an inert load). So, the power facilities have huge (and here I say *very huge*) capacitors at their line outputs. So, some people who also knew that thay had large capacitors, and they were thinking that those were to store electricity in case of brief power interruptions, this is a myth. Those caps are really for cancelling the inductive effect of the miles of power cables.
So, this is also why, on transformers, you usually don't see transformers rates like '10W' (10 Watt), but rather '10VA' which stand for 10 Volts-Amps. Although the power is the product of Volts x Amps (basic Ohm law), when applied to non-DC signals, as seen above, Power rating alone is not sufficient to rate the energy transfer capability of a transformer.