A question came to me on Twitter from @GERenewables and Chris Nelder, an energy futurist, software architect and music nut who was trying to understand “reactive power” (VArs). See my response below, along with a video where I explain more. Chris, hope this helps you “kinda-sorta, but really” get it!
- Jim
What is reactive power?
Reactive power is sometimes called “imaginary power” because it appears in the imaginary portion of the complex math notation used by electrical engineers to analyze power circuits. However, it is a very real phenomenon without which our electrical circuits cannot function properly. Reactive power only occurs in ac (alternating current) circuits, not dc (direct current) circuits, and represents stored energy in such circuits. All circuits have some capacitive and inductive properties, even when we don’t purposely put capacitors or inductors (coils) into the circuit. When electrical currents flow in these circuits, these elements store energy in the form of electric fields (for capacitors) or magnetic fields (for inductors). If we don’t allow for the filling these “energy storage places”, the current and electrical power can’t get to where we want it to go: the user (customer). The practical consequence of not doing this well is that the voltage drops so low at the user such that he/she can’t use the power any more. So, in electrical engineering terms where reactive power is measured in VARs (volt-amps reactive), we have to have enough VARs in our circuits to keep the voltage at the required levels for the user (usually around 120 volts in our homes in the US).
It turns out that the capacitive and inductive energy storage behave oppositely in many ways. This means that we can keep our reactive power (VARs) at good levels by balancing the inductors and capacitors in our circuits, and this is just what electric utilities do. It is the “real power” (meaning the real part of the complex math notation for the power flow) that drives our machines and lights and for which the utility charges us on our electric bills. However, now you should see why the reactive power (“imaginary power”) is also very important.
