Can someone please explain reactive power for me in a easy to understand way?
Did you try googling it?
I’m not sure if this is correct in the textbook sense, but I believe reactive power is power that is stored and retrieved (and not turned into low-grade heat).
Case in point: let’s say you apply a sine wave voltage source to an ideal inductor. You then want to measure the power “dissipated” by the inductor (P=VI), so you stick a voltmeter across the inductor and an ammeter in series with the inductor. You then multiply the voltage and the current to come up with the power.
So is this the correct way to do it? Not really. What you just measured was * apparent power*, and in the case of a perfect inductor, apparent power = reactive power. The real power dissipated by the inductor is zero.
So in essence you have three power measurements: reactive power, total apparent power, and real power. Real power is the average power dissipated by the load (i.e. turned into heat). Total apparent power is a power measurement as a result of simply multiplying the voltage and the current. Reactive power is the difference between total apparent power and real power.
Note also that these things can be mathematically described. As an example, the cosine of the phase difference between the voltage and current waveforms (which is related to the power factor) can be used to determine how much reactive power you have.
Mecanical analogs sometimes help.
Suppose you have a hand-crank powered coffee grinder, like in an old-time general store. The work you do actually grinding coffee is so called “real” power.
Now attach a 10# lead weight to the crank handle. Every time the handle moves upward you have to do some extra work to lift the weight, but you have to do less work to grind coffee when the handle is moving downward.
The weight stores energy in one part of the cycle, and releases it during another part. This is analogous to the concept of reactive power in an AC system.
Now suppose you have to turn the crank using a 10 foot pole instead of your hand. The pole now has to be strong enough to lift the weight as well as to grind the coffee. The ratio between the total force applied with the pole, and the part of the force needed just to grind the coffee is the “power factor”.
This is why utilities don’t like reactive power. Moving that energy back and forth between the load and the generating station causes extra power loss in thier transmission lines. AND just like the pole, thier generators must supply the total, not just the “real” part, so they lose some useful capacity.
So suppose you add a spring that pulls upward and balances the weight. Now the 10 foot pole only has to carry the force needed to grind the coffee. The spring is a “power factor corrector” and the electrical analog is a PFC power factor correcting capacitor bank.
Now I’m a EE so if you want the “real” explaination I can do that, but the above is the best I can do without lapsing in to complex math.
The BIG problem with the complex math explaination is that you use “imaginary” numbers to discribe REAL physical things. People see “imaginary” and make the leap that you are discribing something less than real.
Here’s an even simpler explanation:
A generator sends electrical power to a load. Some of the power is “absorbed” by the load. We call this “real” power. (In most cases, the load turns this power it into low-grade, irreversible heat. But not always. The load could also be converting the power to light, chemical energy, etc.) Some of the power is not absorbed by the load, and instead is reflected back to the generator. This power is called “reactive” power.
So how do you measure these things? If you were to stick a voltmeter across the load, an ammeter in series with the load, and you multiplied the two numbers (which we would call “apparent” power), would it be equal to the real power or the reactive power?
The answer: it depends on the load.
If the load were purely resistive, your apparent power reading would be equal to the real power.
If the load were purely reactive, your apparent power reading would not be equal to the real power. In fact, if the load were purely reactive, the real power would be zero, and all power would be “reactive” power. Therefore, your apparent power reading would be equal to the reactive power.
If the load had a resistive component and a reactive component (such as a motor, an inductor in series with a resistor, a capacitor in parallel with a resistor, etc.), your apparent power reading would not be equal to the real power. It would also not be equal to the apparent power. In order to calculate the reactive power, you would first have to determine what the real power is. There are various ways of doing this. One method is to measure the rms of the voltage waveform, rms of the current waveform, the cosine of the phase angle difference, and then multiply all three numbers. Another method is to simultaneously sample the current and voltage waveforms at high speed. Each “voltage current pair” is multiplied together to obtain instantaneous power. These values are averaged over one or more periods, which gives you your real average power. Once you have calculated this, reactive power can be easily calculated; it is simply the apparent power minus the real power.
BTW: There is no such thing as a purely resistive load or a purely reactive load; all loads have a resistive component and a reactive component.
I screwed up. The beginnning of the second-to-last paragraph should read:
If the load had a resistive component and a reactive component (such as a motor, an inductor in series with a resistor, a capacitor in parallel with a resistor, etc.), your apparent power reading would not be equal to the real power. It would also not be equal to the reactive power.
Inductors and capacitors are energy storage devices. Take a capacitor for example. You can charge it up by applying electricty to it, then turn around and connect it to something else and have it discharge (this is how an arc welder works).
When you have AC power, during part of the AC sine wave cycle these devices will be charging up and during other parts of the cycle they will be discharging. This energy isn’t really doing anything, it’s just getting stored and released and stored and released. This is what is called reactive power.
Inductors and capacitors kinda work opposite to each other. When an inductor is charging a capacitor is discharging, and vice versa. Power systems are at their most efficient when the capacitance and inductance cancels each other out, because basically while the capacitors are discharging that energy will go into charging the inductors, and when the inductors are discharging that energy will go into charging the capacitors. This means that the generator doesn’t have to supply the extra current to charge the inductors and capacitors. Motors tend to be inductive loads, and there are very few common things that are capacitive, so overall power systems have a tendency to be a bit on the inductive side. The power company will install banks of capacitors that they will switch on and off of the line to compensate for the inductance so that they balance out the reactive load.