The general dependence of electric power on electric current and voltage has long been known: this is a product. We multiply the current by the voltage - we get the value of this quantity consumed by the circuit from the network.
But in reality, things may not be so simple. Because by simply multiplying the voltage by the current, we get the value of the apparent power. It would seem - this is what you need! After all, we are usually interested in the full value of any quantity.
However, such an attitude cannot be extended to electric power, since electricity and power, on the basis of which the readings of our apartment meter change, are not full, but active.
Active power- this is the power that is consumed at the moment when there is both voltage and an electric current synchronous with it in the network at the same moment. In fact, in DC circuits, with the exception of on-off transients, this is exactly what happens.
The voltage constantly “presses”, if the circuit is closed, a certain current constantly “presses”. As a result, the apparent and active power become equal, since the current and voltage act in concert.
Another thing is AC circuits. The voltage in them changes direction fifty times a second, and the current ... sometimes lags behind, and sometimes ahead of the voltage. For example, if there is “inductance” in the circuit, that is, a coil of wire with many turns, then the current on such a circuit element will “lag behind” the voltage.
The reason is the back-EMF of self-induction resisting the change in current in the coil. It turns out that the voltage has already been applied to the inductor, and the current cannot increase in any way due to interference from the back-EMF.
Among the students of many electrical universities, there is such an artistic comparison: “It takes time for the current to run through each turn, and the voltage is already at the ends of the coil.”
The counter-induction emf causes a voltage drop and a decrease in current in the circuit. That is, the coil is a source of inductive resistance. But it differs from active resistance in that no heat is generated on it and no power is consumed at all in the usual sense.
There is simply an "empty" transfusion of electricity from the source to the inductance. And the energy that is redirected back and forth like a table tennis ball does not leave the network anywhere. This is reactive energy and the consumer in the home does not have to pay for it to the power supply company.
Reactive energy, produced in the network per unit of time, can be considered reactive power. It is calculated in the same way as the active one - by the product of the reactive component of the current and the voltage.
The reactive component of the current is one that does not coincide with the voltage in its phase. The value of "mismatch" is characterized by the angle of the phase shift. In the case of pure inductance, the phase shift is a maximum of -90°. This means that when the voltage reaches its highest value, the current just starts to rise.
And if a capacitor (capacitance) is located in the circuit, then the voltage, on the contrary, will lag behind the current by 90 degrees due to the fact that for the occurrence of a voltage drop, the capacitor needs to charge its plates.
In the same way, a source and a capacitor in the same circuit will exchange reactive energy, which will not be spent on anything.
In a real circuit, there is no purely resistive or purely reactive load, so the apparent power always consists of an active and reactive component, and the phase angle is between zero and 90 °.
The reactive component of the current is equal to its product by the sine of the phase shift angle, and the active component is equal to the product by the cosine of this angle:
Q=I*sinφ; P=I*cosφ
The total power can be found using the Pythagorean theorem:
S=√(P^2+Q^2);
At the same time, reactive power, unlike active power, cannot be calculated in watts, because it is inefficient. Therefore, for reactive power, they came up with a special unit of measurement - reactive volt-amperes (VARs). And the total is measured in volt-amperes, without specifying the nature of the load.
"Handbook" - information on various electronic components: transistors, microchips, transformers, capacitors, LEDs etc. The information contains everything necessary for the selection of components and carrying out engineering calculations, parameters, as well as the pinout of cases, typical wiring diagrams and recommendations for the use of radio elements.
On the one hand, the work of the current can be easily calculated, knowing the current strength, voltage and load resistance. Painfully familiar formulas from the course of school physics look like this.
Rice. 1. Formulas
And there is not a word about the reactive component.
On the other hand, a number of physical processes actually impose their own characteristics on these calculations. It's about reactive energy. Problems with understanding reactive processes come along with electricity bills in large enterprises, because in household networks we pay only for active energy (the sizes of reactive energy consumption are so small that they are simply neglected).
Definitions
To understand the essence of physical processes, let's start with definitions.
Active electricity is the fully convertible energy supplied to the circuit from the power source. The transformation can take place into heat or into another type of energy, but the essence remains the same - the received energy does not return back to the source.
An example of the work of active energy: the current, passing through the resistance element, converts part of the energy into heat. This perfect work of the current is active.
Reactive electricity is the energy returned back to the current source. That is, the current previously received and taken into account by the meter, without doing work, is returned. Among other things, the current makes a jump (for a short time, the load increases greatly).
It's hard to understand the process without examples.
The most obvious is the work of a capacitor. By itself, the capacitor does not convert electricity into useful work, it accumulates and releases it. Of course, if part of the energy is still spent on heating the element, then it can be considered active. Reactive looks like this:
1. When the capacitance is supplied with alternating voltage, along with an increase in U, the charge of the capacitor also increases.
2. At the moment the voltage drop begins (the second quarter period on the sinusoid), the voltage on the capacitor is higher than that of the source. And so the capacitor begins to discharge, giving energy back to the power circuit (current flows in the opposite direction).
3. In the next two quarter-periods, the situation is completely repeated, only the tension changes to the opposite.
Due to the fact that the capacitor itself does not perform work, the received voltage reaches its maximum amplitude value (that is, √2 \u003d 1.414 times more than the current 220V, or 220 1.414 \u003d 311V).
When working with inductive elements (coils, transformers, electric motors, etc.), the situation is similar. The graph of indicators can be seen in the image below.
Rice. 2. Graphs of indicators
Due to the fact that modern household appliances consist of many different elements with and without a "reactive" power effect, the reactive current, flowing in the opposite direction, does a very real job of heating the active elements. Thus, the reactive power of the circuit is essentially expressed in collateral losses and power surges.
It is very difficult to separate one power indicator from another in calculations. And the system of high-quality and efficient accounting is expensive, which, in fact, led to the refusal to measure the volume of consumption of reactive currents in everyday life.
In large commercial facilities, on the contrary, the volume of reactive energy consumption is much larger (due to the abundance of power equipment supplied with powerful electric motors, transformers and other elements that generate reactive current), so separate accounting is introduced for them.
How is active and reactive electricity calculated?
Most manufacturers of electricity meters for enterprises implement a simple algorithm.
Q \u003d (S 2 - P 2) 1/2
Here, the active power P is subtracted from the total power S (in a simplified form).
Thus, it is not necessary for the manufacturer to organize completely separate accounting.
What is cosϕ (cosine phi)
For a numerical expression of the ratio of active and reactive power, a special coefficient is used - cosine phi.
It is calculated according to the formula.
cosϕ = P act / P total
Where apparent power is the sum of active and reactive power.
The same coefficient is indicated on the nameplates of power tools equipped with motors. In this case, cosϕ is used to estimate the peak power demand. For example, the rated power of the device is 600 W, and cosϕ = 0.7 (the average for the vast majority of power tools), then the peak power required to start the electric motor will be considered as Pnom / cosϕ, = 600 W / 0.7 = 857 VA ( reactive power is expressed in volt-amperes).
Application of reactive power compensators
In order to encourage consumers to operate the power grid without reactive load, electricity suppliers introduce an additional paid tariff for reactive power, but they charge only if the average monthly consumption exceeds a certain coefficient, for example, if the ratio of full and active power is more than 0.9, the reactive power bill is not exhibited.
In order to reduce costs, enterprises install special equipment - compensators. They can be of two types (in accordance with the principle of operation):
- capacitive;
- Inductive.
The power characteristics of the installation or network are the main ones for most known electrical appliances. Active power (transmitted, consumed) characterizes the part of the total power that is transmitted over a certain period of AC frequency.
Definition
Active and reactive power can only be for alternating current, since the characteristics of the network (current and voltage) for direct current are always equal. The unit of measurement of active power is Watt, while the unit of reactive power is reactive voltampere and kiloVAR (kVAR). It is worth noting that both full and active characteristics can be measured in kW and kVA, it depends on the parameters of a particular device and network. In industrial circuits, it is most often measured in kilowatts.
Electrical engineering uses the active component as a measure of the energy transfer of individual electrical appliances. Consider how much power some of them consume:
Based on the foregoing, active power is a positive characteristic of a particular electrical circuit, which is one of the main parameters for choosing electrical appliances and controlling electricity consumption.
Reactive component designation:
This is a nominal value that characterizes the loads in electrical devices using EMF fluctuations and losses during operation of the device. In other words, the transmitted energy goes to a certain reactive converter (this is a capacitor, a diode bridge, etc.) and appears only if the system includes this component.
Calculation
To find out the active power index, it is necessary to know the total power, the following formula is used to calculate it:
S = U \ I, where U is the mains voltage and I is the mains current.
The same calculation is performed when calculating the energy transfer level of a coil with a symmetrical connection. The schema looks like this:
The active power calculation takes into account the phase angle or factor (cos φ), then:
S \u003d U * I * cos φ.
A very important factor is that this electrical quantity can be both positive and negative. It depends on what characteristics cos φ has. If the sinusoidal current has a phase shift angle in the range from 0 to 90 degrees, then the active power is positive, if from 0 to -90, then it is negative. The rule is valid only for synchronous (sinusoidal) current (used to operate an asynchronous motor, machine equipment).
Also, one of the characteristic features of this characteristic is that in a three-phase circuit (for example, a transformer or generator), the active indicator is fully developed at the output.
Maximum and active is denoted by P, reactive power - Q.
Due to the fact that the reactive is determined by the movement and energy of the magnetic field, its formula (taking into account the phase shift angle) is as follows:
Q L = U L I = I 2 x L
For non-sinusoidal current, it is very difficult to select standard network parameters. Various measuring devices are used to determine the required characteristics in order to calculate active and reactive power. This is a voltmeter, ammeter and others. Based on the level of load, the desired formula is selected.
Due to the fact that the reactive and active characteristics are related to the apparent power, their ratio (balance) is as follows:
S = √P 2 + Q 2 , and all this equals U*I .
But if the current passes directly through the reactance. There is no loss in the network. This is determined by the inductive inductive component - C and resistance - L. These indicators are calculated by the formulas:
Inductance resistance: x L = ωL = 2πfL,
Capacitance resistance: xc = 1/(ωC) = 1/(2πfC).
A special coefficient is used to determine the ratio of active and reactive power. This is a very important parameter by which you can determine what part of the energy is misused or "lost" during the operation of the device.
If there is an active reactive component in the network, the power factor must be calculated. This value has no units of measurement; it characterizes a specific current consumer if the electrical system contains reactive elements. With the help of this indicator, it becomes clear in which direction and how the energy is shifted relative to the mains voltage. To do this, you need a voltage triangle diagram:
For example, in the presence of a capacitor, the coefficient formula has the following form:
cos φ = r/z = P/S
To obtain the most accurate results, it is recommended not to round the received data.
Compensation
Considering that at the resonance of the currents, the reactive power is 0:
Q=QL-QC=ULI-UCI
In order to improve the quality of a particular device, special devices are used to minimize the impact of losses on the network. In particular, this is the UPS. This device does not need electrical consumers with a built-in battery (for example, laptops or portable devices), but for most others an uninterruptible power supply is necessary.
When installing such a source, you can not only establish the negative consequences of losses, but also reduce the cost of paying for electricity. Experts have proven that on average, a UPS will help save from 20% to 50%. Why is this happening:
In some cases, specialists do not use full-fledged UPSs, but special compensating capacitors. They are suitable for home use and are available and sold at every electrical supply store. All of the above formulas can be used to calculate planned and realized savings.
From a client letter:
Tell me, for God's sake, why the power of the UPS is indicated in Volt-Amps, and not in the usual kilowatts for all. It's very stressful. After all, everyone has long been accustomed to kilowatts. Yes, and the power of all devices is mainly indicated in kW.
Alexei. June 21, 2007
The technical specifications of any UPS indicate the apparent power [kVA] and the active power [kW] - they characterize the load capacity of the UPS. Example, see pictures below:
 |
The power of not all devices is indicated in W, for example:
- The power of transformers is indicated in VA:
http://www.mstator.ru/products/sonstige/powertransf (TP transformers: see attachment)
http://metz.by/download_files/catalog/transform/tsgl__tszgl__tszglf.pdf (TSGL transformers: see attachment) - The power of capacitors is indicated in Vars:
http://www.elcod.spb.ru/catalog/k78-39.pdf (capacitors K78-39: see appendix)
http://www.kvar.su/produkciya/25-nizkogo-napraygeniya-vbi (UK capacitors: see attachment) - For examples of other loads, see the appendices below.
The power characteristics of the load can be precisely set with one single parameter (active power in W) only for the case of direct current, since there is only one type of resistance in the direct current circuit - active resistance.
The power characteristics of the load for the case of alternating current cannot be accurately specified with one single parameter, since there are two different types of resistance in the alternating current circuit - active and reactive. Therefore, only two parameters: active power and reactive power accurately characterize the load.
The principle of operation of active and reactive resistances is completely different. Active resistance - irreversibly converts electrical energy into other types of energy (thermal, light, etc.) - examples: incandescent lamp, electric heater (paragraph 39, Physics class 11 V.A. Kasyanov M .: Bustard, 2007).
Reactance - alternately accumulates energy and then gives it back to the network - examples: capacitor, inductor (paragraph 40.41, Physics class 11 V.A. Kasyanov M .: Bustard, 2007).
You can read further in any electrical engineering textbook that active power (dissipated in ohmic resistance) is measured in watts, and reactive power (circulated through reactance) is measured in vars; two more parameters are also used to characterize the load power: total power and power factor. All these 4 options:
- Active power: designation P, unit: Watt
- Reactive power: designation Q, unit: VAr(Volt Ampere Reactive)
- Gross power: designation S, unit: VA(Volt Amp)
- Power factor: designation k or cosФ, unit of measure: dimensionless quantity
These parameters are related by the relations: S*S=P*P+Q*Q, cosФ=k=P/S
Also cosФ is called the power factor ( power factor – PF)
Therefore, in electrical engineering, any two of these parameters are given for power characteristics, since the rest can be found from these two.
For example, electric motors, lamps (discharge) - in those. data are P[kW] and cosФ:
http://www.mez.by/dvigatel/air_table2.shtml (AIR engines: see attachment)
http://www.mscom.ru/katalog.php?num=38 (DRL lamps: see appendix)
(see appendix below for examples of technical data for different loads)
It's the same with power supplies. Their power (load capacity) is characterized by one parameter for DC power supplies - active power (W), and two parameters for source. AC power. Usually these two parameters are apparent power (VA) and active power (W). See for example genset and UPS parameters.
Most office and household appliances are active (there is no or little reactance), so their power is indicated in watts. In this case, when calculating the load, the value of the UPS power in Watts is used. If the load is computers with power supplies (PSUs) without input power factor correction (APFC), a laser printer, a refrigerator, an air conditioner, an electric motor (for example, a submersible pump or a motor as part of a machine), fluorescent ballast lamps, etc., all outputs are used in the calculation. . UPS data: kVA, kW, overload characteristics, etc.
See electrical engineering textbooks, for example:
1. Evdokimov F. E. Theoretical foundations of electrical engineering. - M.: Publishing center "Academy", 2004.
2. Nemtsov M. V. Electrical engineering and electronics. - M.: Publishing center "Academy", 2007.
3. Chastoyedov L. A. Electrical engineering. - M.: Higher school, 1989.
See also AC power, Power factor, Electrical resistance, Reactance http://en.wikipedia.org
(translation: http://electron287.narod.ru/pages/page1.html)
Application
Example 1: The power of transformers and autotransformers is indicated in VA (Volt Amps)
http://metz.by/download_files/catalog/transform/tsgl__tszgl__tszglf.pdf (TSGL transformers)
| Single-phase autotransformers |
|
||
| TDGC2-0.5kVa, 2A | AOSN-2-220-82 | ||
| TDGC2-1.0kVa, 4A | Latr 1.25 | AOSN-4-220-82 | |
| TDGC2-2.0kVa, 8A | Latr 2.5 | AOSN-8-220-82 | |
| TDGC2-3.0kVa, 12A | |||
| TDGC2-4.0kVa, 16A | |||
| TDGC2-5.0kVa, 20A | AOSN-20-220 | ||
| TDGC2-7.0kVa, 28A | |||
| TDGC2-10kVa, 40A | AOMN-40-220 | ||
| TDGC2-15kVa, 60A | |||
| TDGC2-20kVa, 80A | |||
http://www.gstransformers.com/products/voltage-regulators.html (LATR / laboratory autotransformers TDGC2)
Example 2: the power of capacitors is indicated in Vars (Volt Amperes reactive)
 |
http://www.elcod.spb.ru/catalog/k78-39.pdf (capacitors K78-39)
 |
http://www.kvar.su/produkciya/25-nizkogo-napraygeniya-vbi (UK capacitors)
Example 3: technical data of electric motors contains active power (kW) and cosФ
For loads such as electric motors, lamps (discharge), computer power supplies, combined loads, etc. - the technical data indicate P [kW] and cosФ (active power and power factor) or S [kVA] and cosФ (apparent power and power factor power).
http://www.weiku.com/products/10359463/Stainless_Steel_cutting_machine.html
(combined load - steel plasma cutting machine / Inverter Plasma cutter LGK160 (IGBT)
http://www.silverstonetek.com.tw/product.php?pid=365&area=en (PC power supply)
Addition 1
If the load has a high power factor (0.8 ... 1.0), then its properties approach the active load. Such a load is ideal both for the network line and for power sources, because. does not generate reactive currents and powers in the system.
Therefore, in many countries standards have been adopted that normalize the power factor of equipment.
Supplement 2
Single-load equipment (for example, a PC power supply) and multi-component combined equipment (for example, an industrial milling machine that includes several motors, a PC, lighting, etc.) have low power factors (less than 0.8) of internal units (for example, a PC power supply rectifier or an electric motor have power factor 0.6 .. 0.8). Therefore, at present, most equipment has an input power factor corrector. In this case, the input power factor is 0.9 ... 1.0, which is in line with the regulatory standards.
Addendum 3. Important note regarding the power factor of UPS and voltage stabilizers
The load capacity of UPS and DGU is normalized to a standard industrial load (power factor 0.8 with inductive character). For example, UPS 100 kVA / 80 kW. This means that the device can supply a maximum power active load of 80 kW, or a mixed (active-reactive) load of maximum power 100 kVA with an inductive power factor of 0.8.
In voltage stabilizers, the situation is different. For the stabilizer, the load power factor is indifferent. For example, a voltage regulator of 100 kVA. This means that the device can supply an active load with a maximum power of 100 kW, or any other (purely active, purely reactive, mixed) power of 100 kVA or 100 kVAr with any capacitive or inductive power factor. Note that this is true for a linear load (no higher current harmonics). With large harmonic distortion of the load current (high THD), the output power of the stabilizer is reduced.
Supplement 4
Illustrative examples of pure resistive and pure reactive loads:
- A 100 W incandescent lamp is connected to the AC mains 220 VAC - there is conduction current everywhere in the circuit (through the wire conductors and the tungsten hair of the lamp). Load characteristics (lamps): power S=P~=100 VA=100 W, PF=1 => all electric power is active, which means it is completely absorbed in the lamp and turns into heat and light power.
- A non-polar 7 uF capacitor is connected to the 220 VAC AC network - there is a conduction current in the wire circuit, a bias current flows inside the capacitor (through the dielectric). Characteristics of the load (capacitor): power S=Q~=100 VA=100 VAr, PF=0 => all electrical power is reactive, which means it constantly circulates from the source to the load and back, again to the load, etc.
Supplement 5
To indicate the prevailing reactance (inductive or capacitive), the sign is assigned to the power factor:
+ (plus)– if the total reactance is inductive (example: PF=+0.5). The current phase lags the voltage phase by an angle F.
- (minus)– if the total reactance is capacitive (example: PF=-0.5). The phase of the current leads the phase of the voltage by an angle F.
Supplement 6
Additional questions
Question 1:
Why do all electrical engineering textbooks use imaginary numbers / quantities (for example, reactive power, reactance, etc.) that do not exist in reality when calculating AC circuits?
Answer:
Yes, all individual quantities in the surrounding world are real. Including temperature, reactance, etc. The use of imaginary (complex) numbers is just a mathematical trick that makes calculations easier. The result of the calculation is necessarily a real number. Example: the reactive power of a load (capacitor) of 20 kvar is the real energy flow, that is, the real watts circulating in the source-load circuit. But in order to distinguish these Watts from the Watts irretrievably absorbed by the load, these "circulating Watts" decided to call Volt·Amps reactive.
Comment:
Previously, only single quantities were used in physics, and in the calculation, all mathematical quantities corresponded to the real quantities of the surrounding world. For example, distance equals speed times time (S=v*t). Then, with the development of physics, that is, as more complex objects (light, waves, alternating electric current, atom, space, etc.) were studied, such a large number of physical quantities appeared that it became impossible to calculate each separately. This is not only a problem of manual calculation, but also a problem of compiling computer programs. To solve this problem, close single values began to be combined into more complex ones (including 2 or more single values), obeying the laws of transformation known in mathematics. This is how scalar (single) quantities appeared (temperature, etc.), vector and complex dual (impedance, etc.), vector triple (magnetic field vector, etc.), and more complex quantities - matrices and tensors (dielectric permittivity tensor, tensor Ricci and others). To simplify calculations in electrical engineering, the following imaginary (complex) dual quantities are used:
- Impedance (impedance) Z=R+iX
- Apparent power S=P+iQ
- Dielectric constant e=e"+ie"
- Magnetic permeability m=m"+im"
- and etc.
Question 2:
The page http://en.wikipedia.org/wiki/Ac_power shows S P Q Ф on the complex, that is, imaginary / non-existent plane. What does all this have to do with reality?
 |
Answer:
It is difficult to carry out calculations with real sinusoids, therefore, to simplify the calculations, a vector (complex) representation is used, as in Fig. above. But this does not mean that the S P Q shown in the figure are not related to reality. The real values of S P Q can be represented in the usual way, based on measurements of sinusoidal signals with an oscilloscope. The values of S P Q Ф I U in the source-load AC circuit depend on the load. Below is an example of real sinusoidal signals S P Q and F for the case of a load consisting of series-connected active and reactive (inductive) resistances.
 |
Question 3:
With conventional current clamps and a multimeter, a load current of 10 A was measured, and the voltage at the load was 225 V. We multiply and get the load power in W: 10 A 225V \u003d 2250 W.
Answer:
You have received (calculated) the total load power of 2250 VA. Therefore, your answer will only be valid if your load is purely resistive, then indeed Volt Amp is equal to Watt. For all other types of loads (for example, an electric motor) - no. To measure all the characteristics of any arbitrary load, you must use a network analyzer, such as APPA137:
 |
See additional literature, for example:
Evdokimov F. E. Theoretical foundations of electrical engineering. - M.: Publishing center "Academy", 2004.
Nemtsov M.V. Electrical engineering and electronics. - M.: Publishing center "Academy", 2007.
Chastoyedov L.A. Electrical engineering. - M.: Higher school, 1989.
AC power, Power factor, Electrical resistance, Reactance
http://en.wikipedia.org (translation: http://electron287.narod.ru/pages/page1.html)
Theory and calculation of low power transformers Yu.N. Starodubtsev / RadioSoft Moscow 2005 / rev d25d5r4feb2013
At the same time, two indicators are distinguished that reflect the costs of full power when servicing the consumer. These indicators are called active and reactive energy. Gross power is the sum of these two figures. About what active and reactive electricity is and how to check the amount of accrued payments, we will try to tell in this article.
Full power
According to the established practice, consumers pay not for the useful capacity, which is directly used in the economy, but for the full one, which is released by the supplier enterprise. These indicators are distinguished by units of measurement - total power is measured in volt-amperes (VA), and useful power is measured in kilowatts. Active and reactive electricity is used by all mains-powered electrical appliances.
Active electricity
The active component of the total power performs useful work and is converted into those types of energy that the consumer needs. For some household and industrial electrical appliances, the active and apparent power in the calculations are the same. Among such devices are electric stoves, incandescent lamps, electric furnaces, heaters, irons, and so on.
If the active power of 1 kW is indicated in the passport, then the total power of such a device will be 1 kVA.
The concept of reactive electricity
This type of electricity is inherent in circuits that include reactive elements. Reactive electricity is the portion of the total power input that is not used for useful work.
In DC electrical circuits, the concept of reactive power is absent. In circuits, the reactive component occurs only when there is an inductive or capacitive load. In this case, there is a mismatch between the phase of the current and the phase of the voltage. This phase shift between voltage and current is denoted by the symbol "φ".
With an inductive load in the circuit, a phase lag is observed, with a capacitive load, it is ahead of it. Therefore, only a part of the full power comes to the consumer, and the main losses occur due to the useless heating of devices and devices during operation.
Power losses occur due to the presence of inductive coils and capacitors in electrical devices. Because of them, electricity accumulates in the circuit for some time. The stored energy is then fed back into the circuit. Devices that include a reactive component of electricity include portable power tools, electric motors and various household appliances. This value is calculated taking into account a special power factor, which is referred to as cos φ.
Calculation of reactive electricity
The power factor lies in the range from 0.5 to 0.9; the exact value of this parameter can be found in the passport of the electrical appliance. The apparent power must be defined as the quotient of active power divided by a factor.
For example, if the passport of an electric drill indicates a power of 600 W and a value of 0.6, then the total power consumed by the device will be 600/06, that is, 1000 VA. In the absence of passports for calculating the total power of the device, the coefficient can be taken equal to 0.7.
Since one of the main tasks of existing power supply systems is to deliver useful power to the end consumer, reactive power losses are considered a negative factor, and an increase in this indicator casts doubt on the efficiency of the electrical circuit as a whole. The balance of active and reactive power in a circuit can be visualized in the form of this funny picture:
The value of the coefficient when taking into account losses
The higher the value of the power factor, the less will be the loss of active electricity - which means that the final consumer of the consumed electrical energy will cost a little less. In order to increase the value of this coefficient, various methods of compensating for non-target losses of electricity are used in electrical engineering. Compensating devices are leading current generators that smooth out the phase angle between current and voltage. Capacitor banks are sometimes used for the same purpose. They are connected in parallel to the working circuit and are used as synchronous compensators.
Calculation of the cost of electricity for private customers
For individual use, active and reactive electricity is not separated in the bills - in terms of consumption, the share of reactive energy is small. Therefore, private customers with power consumption up to 63 A pay one bill, in which all consumed electricity is considered active. Additional losses in the circuit for reactive electricity are not separately allocated and not paid.
Reactive electricity metering for enterprises
Another thing - enterprises and organizations. A huge number of electrical equipment is installed in industrial premises and industrial workshops, and in the total incoming electricity there is a significant part of reactive energy, which is necessary for the operation of power supplies and electric motors. Active and reactive electricity supplied to enterprises and organizations needs a clear separation and a different way of paying for it. In this case, the standard contract serves as the basis for regulating relations between the electricity supplier and end consumers. According to the rules established in this document, organizations that consume electricity above 63 A need a special device that provides reactive energy readings for metering and payment.
The grid company installs a reactive electricity meter and charges according to its readings.
Reactive energy factor
As mentioned earlier, active and reactive electricity in the invoices for payment are allocated in separate lines. If the ratio of the volumes of reactive and consumed electricity does not exceed the established norm, then the payment for reactive energy is not charged. The ratio coefficient can be written in different ways, its average value is 0.15. If this threshold value is exceeded, the consumer enterprise is recommended to install compensatory devices.
Reactive energy in apartment buildings
A typical consumer of electricity is an apartment building with a main fuse that consumes electricity in excess of 63 A. If such a building has only residential premises, there is no charge for reactive electricity. Thus, residents of an apartment building see in charges only payment for the full electricity supplied to the house by the supplier. The same rule applies to housing cooperatives.
Special cases of reactive power accounting
There are cases when there are both commercial organizations and apartments in a multi-storey building. The supply of electricity to such houses is regulated by separate Acts. For example, the division can be the size of the usable area. If commercial organizations occupy less than half of the usable area in an apartment building, then payment for reactive energy is not charged. If the threshold percentage has been exceeded, then there are obligations to pay for reactive electricity.
In some cases, residential buildings are not exempt from paying for reactive energy. For example, if the building has elevator connection points for apartments, the charge for the use of reactive electricity occurs separately, only for this equipment. Apartment owners still pay only active electricity.
Understanding the essence of active and reactive energy makes it possible to correctly calculate the economic effect of installing various compensation devices that reduce losses from reactive load. According to statistics, such devices allow you to raise the value of cos φ from 0.6 to 0.97. Thus, automatic compensating devices help save up to a third of the electricity provided to the consumer. A significant reduction in heat losses increases the service life of devices and mechanisms at production sites and reduces the cost of finished products.
