What is active and reactive electricity on the meter. Concepts of active, apparent and reactive power

Unlike DC networks, where power has an expression and does not change over time, this is not the case in AC networks.

Power in an alternating current circuit is also variable. At any section of the circuit at any time t, it is defined as the product of the instantaneous values of voltage and current.

Let's consider what active power represents

In a circuit with purely active resistance it is equal to:

If we accept and then it will come out:

Based on the expressions above, active energy consists of two parts - constant and variable, which changes with double frequency. Its average value

Graph Р(ωt)

The difference between reactive power and active power

In a circuit where there is reactance (take inductive resistance as an example), the value of instantaneous power is equal to:

Accordingly as a result we get:

This expression shows that reactive energy contains only a variable part, which changes with double frequency, and its average value is zero

Graph q(ωt)

If the current and voltage have a sinusoidal shape and the network contains elements of the R-L or R-C type, then in such networks, in addition to energy conversion in the active element R, the energy of the electric and magnetic fields in the reactive elements L and C also changes.

In this case, the total power of the network will be equal to the sum:

What is apparent power using the example of a simple R-L circuit

Graphs of changes in instantaneous values u,i:

φ - phase shift between current and voltage

The equation for S will take the following form

Let's substitute and replace the amplitude values with actual values:

The value S is considered as the sum of two quantities, where

And - instantaneous active and reactive powers in sections R-L.

Graphs p,q,s:

As we can see from the graph, the presence of an inductive component entailed the appearance of a negative part in the total power (shaded part of the graph), which reduces its average value. This occurs due to a phase shift; at some point in time, the current and voltage are in antiphase, so a negative value of S appears.

Final expressions for effective values:

The active component of the network is expressed in watts (W), and the reactive component in reactive volt-amperes (var).

The total power of the network S is determined by the nominal data of the generator. For the generator it is determined by the expression:

For normal operation of the generator, the current in the windings and the voltage at the terminals should not exceed the rated values I n, U n. For the generator, the values of P and S are the same, but in practice it was agreed to express S in volt-amperes (VA).

Also, the network energy can be expressed through each component separately:

Where S, P, Q are the active, reactive and impedance of the network, respectively. They form a power triangle:

Power triangle with predominantly inductive load

If we recall the Pythagorean theorem, then from a right triangle we can obtain the following expression:

The reactive component in the triangle is positive (Q L) when the current lags behind the voltage, and negative (Q C) when it leads:

Power triangle with dominant capacitive load

For the reactive component of the network, the algebraic expression is valid:

From which it follows that inductive and capacitive energy are interchangeable. That is, if you want to reduce the influence of the inductive part of the circuit, you need to add capacitance, and vice versa. Below is an example of this diagram:

Reactive component compensation circuit

The phasor diagram shows the effect of the capacitor on cosφ. As you can see, when the capacitor is turned on, cosφ 2 > cosφ 1 and I l
Vector diagram

The relationship between total and reactive energy is expressed:

сosφ is the power factor. it shows what proportion of the total energy is active energy. The closer it is to 1, the more useful energy is consumed from the network.

Conclusions about the three components of an alternating current circuit

Unlike direct current circuits, alternating voltage circuits have three types of power - active, reactive, apparent. Active energy, as in direct current circuits, performs useful work. Reactive - does not do anything useful, but only reduces the efficiency of the network, heats the wires, and loads the generator. Total is the sum of active and reactive, it is equal to the power of the network. The inductive component of reactive energy can be compensated by the capacitive one. In practice, in industry this is implemented in the form.

WHAT IS TOTAL, ACTIVE AND REACTIVE POWER? FROM COMPLEX TO SIMPLE.

In everyday life, almost everyone comes across the concept of “electrical power”, “power consumption” or “how much electricity does this thing consume”. In this collection, we will explain the concept of electrical power of alternating current for technically savvy specialists and show in the picture the electrical power in the form of “how much electricity does this thing consume” for people with a humanitarian mindset :-). We reveal the most practical and applicable concept of electrical power and deliberately avoid describing differential expressions of electrical power.

WHAT IS AC POWER?

In AC circuits, the formula for DC power can only be used to calculate instantaneous power, which varies greatly over time and is useless for practical calculations. Direct calculation of average power requires integration over time. To calculate power in circuits where voltage and current vary periodically, average power can be calculated by integrating the instantaneous power over the period. In practice, the greatest importance is the calculation of power in circuits of alternating sinusoidal voltage and current.

In order to connect the concepts of total, active, reactive power and power factor, it is convenient to turn to the theory of complex numbers. We can assume that the power in an alternating current circuit is expressed by a complex number such that the active power is its real part, the reactive power is the imaginary part, the apparent power is the modulus, and the angle φ (phase shift) is the argument. For such a model, all the relations written below turn out to be valid.

Active power (Real Power)

The unit of measurement is watt (Russian designation: W, kilowatt - kW; international: watt -W, kilowatt - kW).

The average value of instantaneous power over a period T is called active power, and

expressed by the formula:

In single-phase sinusoidal current circuits, where υ and Ι are the rms values of voltage and current, and φ is the phase shift angle between them.

For non-sinusoidal current circuits, the electric power is equal to the sum of the corresponding average powers of the individual harmonics. Active power characterizes the rate of irreversible conversion of electrical energy into other types of energy (thermal and electromagnetic). Active power can also be expressed in terms of current, voltage and the active component of the circuit resistance r or its conductivity g according to the formula. In any electrical circuit of both sinusoidal and non-sinusoidal current, the active power of the entire circuit is equal to the sum of the active powers of the individual parts of the circuit; for three-phase circuits, the electrical power is defined as the sum of the powers of the individual phases. With the total power S, the active one is related by the relation.

In the theory of long lines (analysis of electromagnetic processes in a transmission line, the length of which is comparable to the length of the electromagnetic wave), a complete analogue of active power is transmitted power, which is defined as the difference between the incident power and the reflected power.

Reactive Power

The unit of measurement is reactive volt-ampere (Russian designation: var, kVAR; international: var).

Reactive power is a quantity characterizing the loads created in electrical devices by fluctuations in the energy of the electromagnetic field in a sinusoidal alternating current circuit, equal to the product of the rms values of voltage U and current I, multiplied by the sine of the phase angle φ between them:

(if the current lags behind the voltage, the phase shift is considered positive, if it leads, it is considered negative). Reactive power is related to total power S and active power P by the ratio: .

The physical meaning of reactive power is energy pumped from the source to the reactive elements of the receiver (inductors, capacitors, motor windings), and then returned by these elements back to the source during one oscillation period, referred to this period.

reactive power can be either a positive value (if the load is active-inductive in nature) or negative (if the load is active-capacitive in nature). This circumstance emphasizes the fact that reactive power does not participate in the operation of electric current. When a device has positive reactive power, it is customary to say that it consumes it, and when it produces negative power, it produces it, but this is purely a convention due to the fact that most power-consuming devices (for example, asynchronous motors), as well as purely active loads, are connected through a transformer, are active-inductive.

The use of modern electrical measuring transducers on microprocessor technology allows for a more accurate assessment of the amount of energy returned from an inductive and capacitive load to an alternating voltage source.

Power can be either a positive value (if the load is active-inductive in nature) or negative (if the load is active-capacitive in nature). This circumstance emphasizes the fact that reactive power does not participate in the operation of electric current. When a device has positive reactive power, it is customary to say that it consumes it, and when it produces negative power, it produces it, but this is purely a convention due to the fact that most power-consuming devices (for example, asynchronous motors), as well as purely active loads, are connected through a transformer, are active-inductive.

Synchronous generators installed in power plants can both produce and consume reactive power depending on the magnitude of the excitation current flowing in the generator rotor winding. Due to this feature of synchronous electrical machines, the specified network voltage level is regulated. To eliminate overloads and increase the power factor of electrical installations, reactive power compensation is carried out.

The use of modern electrical measuring transducers based on microprocessor technology allows for a more accurate assessment of the amount of energy returned from an inductive and capacitive load to an alternating voltage source

Apparent Power

The unit of total electrical power is volt-ampere (Russian designation: VA, VA, kVA-kilo-volt-ampere; international: V A, kVA).

Total power is a value equal to the product of the effective values of the periodic electric current I in the circuit and the voltage U at its terminals: ; The ratio of total power with active and reactive powers is expressed as follows: where P is active power, Q is reactive power (with an inductive load Q›0, and with a capacitive load Q‹0).

The vector relationship between total, active and reactive power is expressed by the formula:

Total power has practical significance as a value that describes the loads actually imposed by the consumer on the elements of the supply network (wires, cables, distribution boards, transformers, power lines), since these loads depend on the current consumed, and not on the energy actually used by the consumer. This is why the total power of transformers and distribution boards is measured in volt-amperes and not in watts.

All of the above formulaic and textual descriptions of total, reactive and active powers are visually and intuitively clear in the following figure:-)

Specialists of the NTS-group company (TM Elektrokaprizam-NET) have extensive experience in selecting specialized equipment for building systems for providing vital facilities with uninterrupted power supply. We are able to take into account as efficiently as possible many electrical and operational parameters, which allow us to choose an economically feasible option for building an uninterruptible power supply system using fuel power plants, and other related equipment.

© The material was prepared by specialists of the NTS-group company (TM Electrokaprizam-NET) using information from open sources, incl. from the free encyclopedia Wikipedia https://ru.wikipedia.org

The calculation of the electrical energy used by a household or industrial electrical appliance is usually made taking into account the total power of the electric current passing through the electrical circuit being measured.

In this case, two indicators are identified that reflect the cost of full power when servicing the consumer. These indicators are called active and reactive energy. Total power is the sum of these two indicators.

Full power.
According to established practice, consumers do not pay for the useful power, which is directly used in the household, but for the full power, which is supplied by the supplier. These indicators are distinguished by units of measurement - total power is measured in volt-amperes (VA), and useful power - in kilowatts. Active and reactive electricity is used by all electrical appliances powered from the network.

Active electricity.
The active component of 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 coincide in the calculations. Among such devices are electric stoves, incandescent lamps, electric ovens, heaters, irons and ironing presses, etc. If the passport indicates an active power of 1 kW, 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 contain reactive elements. Reactive electricity is that part of the total incoming power that is not spent on useful work. In DC circuits there is no concept of reactive power. In AC circuits, a reactive component occurs only when an inductive or capacitive load is present. 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 indicated by the symbol “φ”. With an inductive load in the circuit, a phase lag is observed, while with a capacitive load, it is advanced. Therefore, only part of the full power reaches the consumer, and the main losses occur due to useless heating of devices and instruments 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. After this, the stored energy is fed back into the circuit. Devices whose power consumption includes 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 designated as cos φ.

Calculation of reactive electricity.
The power factor ranges from 0.5 to 0.9; The exact value of this parameter can be found in the electrical device data sheet. The apparent power must be determined as the active power divided by the 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 equal to 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 user, reactive power losses are considered a negative factor, and an increase in this indicator calls into question the efficiency of the electrical circuit as a whole.

The value of the coefficient when taking losses into account.
The higher the power factor value, the lower the losses of active electricity will be - which means that the consumed electrical energy will cost the end consumer a little less. In order to increase the value of this coefficient, various techniques are used in electrical engineering to compensate for non-target losses of electricity. 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 operating circuit and are used as synchronous compensators.

Calculation of the cost of electricity for private clients.
For individual use, active and reactive electricity are not separated in bills - on the scale 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 are not paid for. Accounting for reactive electricity for enterprises Another thing is enterprises and organizations. A huge number of electrical equipment are installed in production facilities and industrial workshops, and the total supplied electricity contains a significant portion of reactive energy, which is necessary for the operation of power supplies and electric motors. Active and reactive electricity supplied to enterprises and organizations requires a clear separation and a different method of payment for it. In this case, the basis for regulating relations between the electricity supply company and end consumers is a standard contract. 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 accounting and payment. The network company installs a reactive electricity meter and charges according to its readings.

Reactive energy factor.
As mentioned earlier, active and reactive electricity are highlighted in separate lines in payment invoices. If the ratio of the volumes of reactive and consumed electricity does not exceed the established norm, then no charge for reactive energy is 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 compensating devices.

Reactive energy in apartment buildings.
A typical consumer of electricity is an apartment building with a main fuse, consuming electricity in excess of 63 A. If such a building contains exclusively residential premises, there is no charge for reactive electricity. Thus, residents of an apartment building see in the charges payment only for the total electricity supplied to the house by the supplier. The same rule applies to housing cooperatives.

Special cases of reactive power metering.
There are cases when a multi-storey building contains both commercial organizations and apartments. 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 in an apartment building commercial organizations occupy less than half of the usable space, then reactive energy payments are not charged. If the threshold percentage has been exceeded, then obligations to pay for reactive electricity arise. In some cases, residential buildings are not exempt from paying for reactive energy. For example, if a building has elevator connection points for apartments, charges for the use of reactive electricity occur separately, only for this equipment. Apartment owners still pay only for active electricity.

Reactive power

Electrical power- a physical quantity characterizing the speed of transmission or conversion of electrical energy.

If the circuit element is a resistor with electrical resistance R, That

AC power

Active power

Average for the period T the value of instantaneous power is called active power: . In single-phase sinusoidal current circuits, where U And I- effective values of voltage and current, φ - phase shift angle between them. For non-sinusoidal current circuits, the electric power is equal to the sum of the corresponding average powers of the individual harmonics. Active power characterizes the rate of irreversible conversion of electrical energy into other types of energy (thermal and electromagnetic). Active power can also be expressed in terms of current, voltage and active component of circuit resistance r or its conductivity g according to the formula. In any electrical circuit of both sinusoidal and non-sinusoidal current, the active power of the entire circuit is equal to the sum of the active powers of the individual parts of the circuit; for three-phase circuits, the electrical power is defined as the sum of the powers of the individual phases. With full power S active is related by the relation . The unit of active power is watt ( W, W). For a microwave electromagnetic signal in transmission lines, the analogue of active power is the power absorbed by the load.

Reactive power

Reactive power is a quantity characterizing the loads created in electrical devices by fluctuations in the energy of the electromagnetic field in an alternating current circuit, equal to the product of effective voltage values U and current I, multiplied by the sine of the phase angle φ between them: Q = UI sin φ. Unit of reactive power - volt-ampere reactive ( var, var). Reactive power is related to apparent power S and active power R ratio: . Reactive power in electrical networks causes additional active losses (to cover which energy is consumed at power plants) and voltage losses (worsening the conditions for voltage regulation). In some electrical installations, reactive power can be significantly greater than active power. This leads to the appearance of large reactive currents and causes overload of current sources. To eliminate overloads and increase the power factor of electrical installations, reactive power compensation is carried out. For a microwave electromagnetic signal in transmission lines, the analogue of reactive power is the power reflected from the load.

It should be noted that the value of sinφ for values of φ from 0 to plus 90 ° is a positive value. The value of sinφ for values of φ from 0 to minus 90 ° is a negative value. According to the formula Q = UI sinφ reactive power can be a negative value. But a negative load power value characterizes the load as an energy generator. Active, inductive, and capacitive reactance cannot be sources of constant energy. Modulus of magnitude Q = UI sinφ approximately describes the real processes of energy conversion in the magnetic fields of inductances and in the electric fields of capacitors. The use of modern electrical measuring transducers on microprocessor technology allows for a more accurate assessment of the amount of energy returned from an inductive and capacitive load to an alternating voltage source. Reactive power transducers using the formula Q = UI sinφ, are simpler and much cheaper than measuring transducers based on microprocessor technology.

Full power

Apparent power - a value equal to the product of the effective values of the periodic electric current in the circuit I and voltage U on its clamps: S = U×I; is related to active and reactive powers by the ratio: , Where R- active power, Q- reactive power (with inductive load Q > 0, and with capacitive Q< 0 ). The unit of total electrical power is volt-ampere ( V.A., VA).

The vector relationship between total, active and reactive power is expressed by the formula:

Measurements

To measure electrical power, wattmeters and varmeters are used; you can also use the indirect method, using a voltmeter and ammeter.
Phase meters are used to measure reactive power factor

Literature

Bessonov L. A. - Theoretical foundations of electrical engineering: Electric circuits- M.: Higher. school,

Definition

Only alternating current can have active and reactive power, since the network characteristics (current and voltage) of direct current are always equal. The unit of measurement for active power is Watt, while reactive power is measured by reactive voltampere and kiloVAR (kVAR). It is worth noting that both full and active characteristics can be measured in kW and kVA, this depends on the parameters of the specific device and network. In industrial circuits it is most often measured in kilowatts.

Electrical engineering uses the active component to measure the energy transfer of individual electrical devices. Let's look at how much power some of them consume:

Based on everything said above, active power is a positive characteristic of a specific electrical circuit, which is one of the main parameters for selecting 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 specific reactive converter (this is a capacitor, diode bridge, etc.) and is manifested only if the system includes this component.

Calculation

To find out the active power indicator, you need to know the total power; the following formula is used to calculate it:

S = U\I, where U is the network voltage, and I is the network current.

The same calculation is performed when calculating the energy transfer level of the coil with a symmetrical connection. The diagram looks like this:

The calculation of active power takes into account the phase angle or coefficient (cos φ), then:

S = U * I * cos φ.

A very important factor is that this electrical quantity can be either positive or negative. It depends on what characteristics cos φ has. If the phase angle of a sinusoidal current is 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 or machine tool 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 completely generated at the output.

Maximum and active power is denoted by P, reactive power by Q.

Due to the fact that reactive is determined by the movement and energy of the magnetic field, its formula (taking into account the phase shift angle) has the following form:

Q L = U L I = I 2 x L

For non-sinusoidal current it is very difficult to select standard network parameters. To determine the required characteristics for the purpose of calculating active and reactive power, various measuring devices are used. This is a voltmeter, ammeter and others. Based on the load level, the desired formula is selected.

Due to the fact that the reactive and active characteristics are related to the total power, their relationship (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 are no losses in the network. This is determined by the inductive inductive component - C and resistance - L. These indicators are calculated using the formulas:

Inductance resistance: x L = ωL = 2πfL,

Capacitance resistance: xc = 1/(ωC) = 1/(2πfC).

To determine the ratio of active and reactive power, a special coefficient is used. This is a very important parameter by which you can determine what part of the energy is used for other purposes or is “lost” during operation of the device.

If there is an active reactive component in the network, the power factor must be calculated. This quantity has no units of measurement; it characterizes a specific current consumer if the electrical system contains reactive elements. Using this indicator, it becomes clear in which direction and how the energy shifts relative to the network voltage. To do this you will need a voltage triangle diagram:

For example, if there is a capacitor, the coefficient formula is as follows:

cos φ = r/z = P/S

To obtain the most accurate results, it is recommended not to round the data obtained.

Compensation

Considering that when the currents resonate, the reactive power is 0:

Q = QL – QC = ULI – UCI

In order to improve the quality of operation of a particular device, special devices are used to minimize the impact of losses on the network. In particular, this is a UPS. This device does not require 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 determine 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:

The wires heat up less, this not only has a positive effect on their operation, but also increases safety;

Signaling and radio devices have reduced interference;

Harmonics in the electrical network are reduced by an order of magnitude.

In some cases, specialists do not use full-fledged UPSs, but special compensating capacitors. They are suitable for household use, available and sold in every electrical store. To calculate the planned and received savings, you can use all of the above formulas.