Uses and Advantages of Reactive Power

One application that uses a substantial amount Reactive Power is a magnetic lamp ballast.

A ballast is a current limiting device. While it is possible to use either a capacitor, inductor, or resistor in series with a lamp (i.e. fluorescent or other plasma type lamp)as a current limiting device only the inductor represents a "reasonable and easy to manufacturer" component for this purpose. Without a ballast, a plasma will become increasingly conductive, thereby increasing the current through it, until it melts its electrodes.

As far as simple ballast choices go, a resistor will work but the power dissipated in it is wasted as heat (i.e. Real Power). A capacitor will work but they are not as stable over the long term and do not lend themselves to starting the lamp as easily as an inductor. And finally an inductor is great for producing the high voltage spike needed to start a plasma discharge without other starting aids.

After the plasma type lamp starts, the circuit which consists of a lamp and ballast in series (or effectively in series) will limit the current as follows:

I=V/(Lamp Resistance + Inductor Reluctance)

This gives you a Real Power component which is converted to light and a little bit of heat and a Reactive Power component which can not (ideally) generate heat because the voltage and current are out of phase by 90º. In reality the wire used to make the inductor has some resistance so the ballast does actually dissipate some heat but it all depends on the type of wire and circuit current that determines the energy wasted as heat in the ballast.

Incidentally the Plasma Lamp Resistance before starting is several Meg.Ohms. After it starts it is on the order of 300 Ohms (± 250 Ohms depending on the lamp type). Lamp current can vary widely from one lamp type to the other. But a typical T12 four foot fluorescent wants to operate at about 0.460 Amps.

Typically a 40 watt fluorescent on a magnetic ballast would consume about 43+ watts because in the real world, there are no perfect inductors. To reduce that loss a larger diameter wire could be used but the cost and size becomes a problem of trying to be the low cost manufacturer.

Todays ballast are electronic. They waste less than 0.5 watts to do the same job as mentioned above. They do it by a very different method which is beyond the scope of this question. I hope that helps!

Thank you Joe. Your reply is really helpful.

Do you have any idea about the uses and advantages of reactive power in power generation and distribution systems?

As far as I know there are no advantages from the generation and distribution point. In fact, from the generator point of view, it is best to have no Reactive Power component. The size of the transmission conductors is determined by total current which is the vector sum of the real and reactive components. Therefore, the less reactive current you have, the smaller the conductors can be.

It so happens that some generation to the grid is set up primarily to supply reactive component power to the grid in order to relieve the main production generators from that task.

Note that reactive power is a real and present component of the forces that result in "real power" as shown by the power triangle where trigonometry is the language of electricity.

Your answer will include an understanding of the timing between real and reactive power, and their net result (kVa).

These clue will assist in heading you in the right direction as you search. I am assuming this to be a homework question, and therefore do not want to steal the learning experience from you.