About the nature of reactive energy

There are many legends around reactive energy, our man’s love for freebies and various theories of a global conspiracy actively contributed to the development of near-scientific folklore.

In RuNet, you can find many success stories about how a simple peasant from the hinterland has been exploiting free reactive energy for years ( which a household electricity meter does not register ) and lives on its own without knowing troubles. You can also find notes of people urging you to quit the useless pursuit of finding a freebie source in free jet energy. In order to finally dot the 'i' in this matter, I decided to write this post without further ado.


As you know, the energy consumed from an alternating current source consists of two components:

1. Active energy
2. Reactive energy

1. Active energy - that part of the energy consumed, which is completely and irrevocably converted by the receiver into other types of energy .

Example: Flowing through a resistor, the current does an active job, which is expressed in an increase in the thermal energy of the resistor. Regardless of the phase of the flowing current, the resistor converts its energy into heat. It does not matter to the resistor in which direction the current flows through it, only its magnitude is important: the more it is, the more heat will be released on the resistor (the amount of heat released is equal to the product of the square of the current and the resistance of the resistor ).

2. Reactive energy - that part of the energy consumed, which in the next quarter of the period will be completely given back to the source .

Example: Imagine that a capacitor is connected to an AC source. The initial charge on the capacitor plates is zero, the initial phase of the voltage source is also equal to zero. One full swing consists of four quarter periods:

1. The voltage of the source rises from 0 to the maximum instantaneous value (with the current value U of the source 230V, it is 230 * 1.4142 = 325V) In this case, the capacitor consumes the current required to fully charge it
2. The voltage of the source decreases rapidly (moves to zero), while the voltage on the charged capacitor is higher than on the source, which causes the current to flow in the opposite direction (because the current flows from a larger potential to a lower one) , that is, the capacitor discharges, giving back the stored energy back to the source!
3. For the next two quarter periods, the above history is repeated with the only difference that the charge and discharge currents of the capacitance flow in opposite directions.
   
   In the case of switching on an inductor instead of a capacitor, the essence of the process will not change.
   
   
   
   This is the main focus of reactive energy - at the time of 'high tide' we fill our tanks , at low tide, we merge their contents back . As you can see from this simple analogy, we just pour fluid (or current in electrical circuits) back and forth . If we are tempted to drain at least a little fluid 'to the left' (turn on the active resistor in series with the reactive capacitor) , then we will start to take 'a little morethan returning, and this 'somewhat more' is already an active energy by definition (after all, we are not returning this part back, right?) , which, as you know, has to be paid.
   
   Or another example: suppose we take a loan from a lender and immediately return to him the loan just taken. If we give back exactly as much as we took (pure reactivity), we will come to the initial state and no one will owe anything to anyone. If we spend part of the loan on any purchase and return what remains of the loan after the purchase (we add an active load to the circuit and part of the energy will leave the system)- we will still have to. This spent part is an active component of the loan we have taken.
   
   Now you may have one very reasonable question - if everything is so simple, and in order for energy to be considered reactive, you just need to completely return it to the source, why do enterprises have to pay for consumed (and fully returned) reactive energy?
   
   The thing is that in the case of a purely reactive load, the moment of maximum current consumption (reactive) falls at the time of the minimum voltage value, and vice versa, at the time of maximum voltage at the load terminals, the current flowing through it is zero.
   
   The flowing reactive current warms the supply conductors - but these are active losses caused by the flow of reactive current through conductors with limited conductivity, which is equivalent to an active resistor connected in series with the reactive load. Also, since at the maximum reactive current the voltage at the poles of the reactive element passes through zero, the active power supplied to it at this moment (the product of current and voltage) is zero. Conclusion - reactive current causes heating of the wires, without doing any useful work. It should be noted that these losses are also active and will be counted by the household meter of active energy.
   
   Large enterprises are capable of generating sufficiently large reactive currents that adversely affect the functioning of the power system. For this reason, both active and reactive components of the consumed energy are recorded for them. To reduce the generation of reactive currents (causing quite real active losses) , reactive power compensation plants are installed at enterprises.