On the nature of reactive energy

A lot of legends have developed around reactive energy, our man’s love for freebies and various theories of the global conspiracy actively promoted the development of near-scientific folklore.

In Runet, you can find a lot of success stories about how a simple little man from the heartland has been using free reactive energy for years ( which a household electricity meter does not register ) and lives for itself, not knowing any ills. You can also find notes of people calling to abandon the useless task of finding a source of freebies in the free reactive energy. In order to finally dot the 'i' in this question, I decided to write this post, without further ado.


As you know, the energy consumed from the AC source is made up of two components:

1. Active energy
2. Reactive power

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

Example: Flowing through a resistor, the current performs active work, which results 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. The resistor does not matter in which direction the current flows through it, only its magnitude is important: the more it is, the more heat is 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 source voltage is also zero. One full swing consists of four quarter-periods:

1. The voltage of the source rises from 0 to the maximum instantaneous value (at the current U value of the 230V source, it is 230 * 1.4142 = 325V) In this case, the capacitor consumes the current required for its full charge
2. The source voltage rapidly decreases (moves to zero), while the voltage on the charged capacitor is higher than the source, which causes the current to flow in the opposite direction (because the current flows from a higher potential to a lower one) , that is, the capacitor discharges, giving back the accumulated energy 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 will flow in opposite directions.
   
   In the case of inclusion instead of the capacitor inductance coil, the process will not change.
   
   
   
   This is the main focus of reactive energy - at the moment of 'tide' we fill our tanks , at the moment of low tide, we merge their contents back . As can be seen from this simple analogy, we simply pour liquid back and forth (or current in electrical circuits) . If we are tempted to drain even a little liquid 'to the left' (turn on the active resistor in series with the reactive capacitor) , then we’ll take 'a little more' than to return, and this 'a little more' is already active energy by definition (after all, we don’t return back, is not it?) , for which, as you know, you have to pay.
   
   Or another example: suppose that we borrow a certain amount of money from a lender and immediately return to him the loan just taken. If we give exactly as much as we took (pure reactivity), we will return to the initial state and no one will owe anything to anyone. In the case, if we spend part of the loan on what kind of purchase and return what remains of the loan after making the purchase (add active load to the circuit and part of the energy leaves the system) , we will still have to. This spent part is an active component of the loan taken by us.
   
   Now you may have one very reasonable question - if everything is so simple, and in order for energy to be considered reactive, it just needs to be completely returned back to the source, why do companies have to pay for the consumed (and fully returned) reactive energy?
   
   The fact is that in the case of a purely reactive load, the moment of the maximum consumed current (reactive) falls at the moment 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 heats the power supply conductors - but these are active losses caused by the flow of reactive current through conductors with limited conductivity, which is equivalent to a resistor connected in series with a reactive load. Also, since at the moment of 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 - the reactive current causes the wires to heat up, without doing any useful work. It should be noted that these losses are also active and will be counted as a household counter of active energy.
   
   Large enterprises are capable of generating sufficiently large reactive currents that adversely affect the operation of the power grid. For this reason, they are recorded as active and reactive component of the consumed energy. To reduce the generation of reactive currents (causing very real active losses) , the enterprises place installations of reactive power compensation.