About reactive energy

The “transformation of reactive energy to active energy using special devices” is often discussed on the pages of the Internet. Someone said “The idea to convert free or very cheap reactive energy into useful and very expensive active energy is very good. The special device can do such transformation.”

Let’s look at the technical possibilities of such idea. Someone needs to work for compressing the spring by hands to move the spring with some effort. Energy will be used to compress the spring .The energy will come from his hands into energy of compressing spring. The spring will be able to do the work after it was compressed – ideally the same quantity of energy that was for compressing it. Spring will not be able produce any additional energy; it will only give us the energy which has been accumulated before.

We will not consider the complicated mathematical formulas. They are written to simplify the calculations. But the physical processes are not always visible through these calculations.  Let’s look at the graph of voltage and reactive current into the capacitive load. The maximum voltage is 4B (red line), maximum current is 4A (blue line).


Fig.1 AC voltage (red line) curretnt (blue) and power (green line) for reactive energy. 

At any time point the energy is the result of multiplication of the current by the voltage. The green line in the figure is the result of the calculation of power. For the quarter of the period, power is positive – (capacitor is charging), another quarter of the period power is negative (capacitor is discharging). The capacitor gave out as much energy as it took before. Accumulation of energy happens in a quarter of a period, and then in a quarter of the period, it completely goes back into the network.

Process of receiving energy in one period of time and returning of the same amount of energy in a different time period is characteristic for reactive energy. And no scheme can be able force a capacitor to give a greater boost of energy, than it has received, and no tricks will make a spring to work as a perpetual motion machine.

About reactive energy
Text has been updated February 4, 2017 by the author: Vlad
Posted in Active and Reactive Energy