For power engineers at enterprises and large shopping centers, there is no doubt about the existence of reactive energy. Monthly bills and very real money that goes into payment reactive electricity, convince of the reality of its existence. But some electrical engineers seriously, with mathematical calculations, prove that this type of electricity is fiction, and that the division of electrical energy into active and reactive components is artificial.
Let's try and understand this issue, especially since the creators are speculating on ignorance of the differences between different types of electricity. Promising huge percentages, they knowingly or unknowingly replace one type of electrical energy with another.
Let's start with the concepts of active and reactive electricity. Without going into the jungle of electrical engineering formulas, we can determine active energy as that which does work: heats food on electric stoves, illuminates your room, cools the air using an air conditioner. And reactive electricity creates the necessary conditions for performing such work. There will be no reactive energy, and the motors will not be able to rotate, the refrigerator will not work. A voltage of 220 Volts will not be supplied to your premises, since not a single power transformer operates without consuming reactive electricity.
If current and voltage signals are simultaneously observed on an oscilloscope, then these two sinusoids always have a shift relative to each other by an amount called phase angle. This shift characterizes the contribution of reactive energy to the total energy consumed by the load. By measuring only the current in the load, it is impossible to isolate the reactive part of the energy.
Considering that reactive energy does not do work, it can be generated at the point of consumption. Capacitors are used for this. The fact is that coils and capacitors consume different types of reactive energy: inductive and capacitive, respectively. They shift the current versus voltage curve in opposite directions.
Due to these circumstances a capacitor can be considered a consumer of capacitive energy or a generator of inductive energy. For a motor that consumes inductive energy, a nearby capacitor can become its source. Such reversibility is possible only for reactive circuit elements that do not perform work. For active energy, such reversibility does not exist: its generation is associated with fuel consumption. After all, before you can do work, you need to expend energy.
In domestic conditions, power transmission organizations do not charge a fee for reactive energy, and a household meter only counts the active component of electrical energy. The situation is completely different in large enterprises: a large number of electric motors, welding machines and transformers, which require reactive energy to operate, create additional load on power lines. At the same time, the current and heat losses of the active energy increase.
In these cases, reactive energy consumption is taken into account by the meter and paid separately. The cost of reactive electricity is less than the cost of active electricity, but for large volumes of consumption, payments can be very significant. In addition, fines are imposed for the consumption of reactive energy in excess of the specified values. Therefore, it becomes economically profitable for such enterprises to generate such energy at the place of its consumption.
For this, either individual capacitors or automatic compensation units are used, which monitor consumption volumes and connect or disconnect capacitor banks. Modern compensation systems allow you to significantly reduce the consumption of reactive energy from the external network.
Returning to the question in the title of the article, we can answer it in the affirmative. Reactive energy exists. Without it, the operation of electrical installations in which a magnetic field is created is impossible. Without performing visible work, it is, nevertheless, a necessary condition for the performance of work performed by active electrical energy.
First, let's remember school.
What's happened electric power?
Electrical power is indicated when writing formulas with a Latin letter R and is measured in watts W or in Latin W, kilowatts (kW or kW), megawatts ( MW or MW) and so on.
Electrical power is equal to the product of voltage and current:
P (W) = U (V) * I (A)
There are the following types of electrical power, which, accordingly, are designated differently:
Active power:
Designation: P
Unit: Watts (W)
This is the power supplied when a load having active (ohmic) resistance is connected to a current source (generator). If the load has only active resistance and does not contain reactive resistance, then the active power will be equal to the total power.
P = U * I * cos φ
Examples: incandescent lamps, heating devices, etc.
Reactive power:
Designation: Q
Unit: VAR or VAr (volt-ampere reactive)
This is the power delivered when a network component or load that has inductive (electric motor) or capacitive (capacitor) elements is connected to a current source.
The calculation is made using the formula: Q = U * I * sin φ
Examples:
Consumers that give the load an inductive character: electric motors, welding transformers, etc.
Consumers that give the load a capacitive character: capacitors in compensating devices, capacitors that create reactive power in the excitation circuit of generators, etc.
Full power:
Designation: S
Unit: VA or VA (volt-ampere)
Total electrical power is equal to the product of phase-shifted voltage and current. Apparent power is directly related to active and reactive power. Its calculation is made using a formula expressing the Pythagorean law. Apparent electrical power is the maximum electrical current that can be produced by a generator or used.
The calculation is made using the formula: S = U * I or S = P + Q
The triangle shown in the figure shows the relationship between electrical powers or their corresponding voltages.
Now about calculating the generator power.
To accurately determine the scope and suitability of any electrical unit to perform the assigned tasks, it is necessary first of all to determine the total power of current consumers. Only in this way can it be determined which electrical unit can be used for these purposes. When choosing the required power of an electrical unit, you can use the empirical formulas given below.
1. Consumers that are only active loads (for example, electric heaters, incandescent lamps and similar devices with purely ohmic resistance).
The total power can be calculated by simply adding the powers of individual consumers that can be connected to the generator. In this case, the total electrical power, measured in VA or V.A.(Volt-amperes) is equal to active power, measured in W or W(Watt). The required power of the electrical unit is determined by increasing the total power of connected consumers by 10% (i.e., taking into account certain technical factors).
Example: Total consumer power * 110% = Power required from the generating unit.
If the total power of all consumers is 2000 W (in this case 2000 W = 2000 VA), then the required power of the electrical unit will be: 2000 VA * 110% = 2200 VA
2. Consumers with an inductive component of power (compressors, pumps and other electric motors). These loads consume a very large current when starting up and entering operating mode. In this case, it is first necessary to determine the exact power value of simultaneously connected consumers. Next, you should select the power of the electrical unit.
The total power of such an electrical unit must be no less than 3.5 times the total power of consumers. In exceptional cases, it should exceed the power of consumers by 4-5 times.
Example: Total consumer power * 3.5 = Power required from the generating unit.
If the total power of all consumers is 2000 VA, then the required power of the electrical unit will be: 2000 VA * 3.5 = 7000 VA
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 is measured 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, and with a capacitive load, it is advanced. Therefore, only part of the total 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.Power is an important factor for assessing the performance of electrical equipment in a power system network. Using its limit values can lead to network overloads, emergency situations and equipment failure. In order to protect yourself from these negative consequences, you need to understand what active reactive and apparent power are.
Power determination
The power that is actually consumed or used in an AC circuit is called active power, in kW or MW. Power that constantly changes direction and moves, both in direction in a circuit and reacts to itself, is called reactive, in kilovolts (kVAR) or MVAR.
Obviously, power is consumed only when there is resistance. A pure inductor and a pure capacitor do not consume it.
In a pure resistive circuit, the current is in phase with the applied voltage, whereas in a pure inductive and capacitive circuit, the current is shifted by 90 degrees: if an inductive load is connected to the network, it loses voltage by 90 degrees. When a capacitive load is connected, the current shifts 90 degrees in the opposite direction.
In the first case, active power is created, and in the second, reactive power.
Power triangle
Apparent power is the vector sum of active and reactive power. Full power elements:
- Active, P.
- Reactive, Q.
- Full, S.
Reactive power does not work, it is represented as the imaginary axis of a vector diagram. Active power works and is the real side of the triangle. From this principle of power decomposition it is clear how active power is measured. The unit for all types of power is the watt (W), but this designation is usually assigned to the active component. Apparent power is conventionally expressed in VA.
The unit for the Q component is expressed as var, which corresponds to reactive volt-amperes. It does not transfer any net energy to the load, yet it performs an important function in electrical networks. The mathematical relationship between them can be represented by vectors or expressed using complex numbers, S = P + j Q (where j is the imaginary unit).
Energy and power calculation
The average power P in watts (W) is equal to the energy consumed E in joules (J) divided by the period t in seconds (seconds): P(W) = E(J)/Δ t(s).
When the current and voltage are 180 degrees out of phase, PF is negative, the load supplies power to the source (an example would be a house with solar panels on the roof that feed power to the grid). Example:
- P is 700W and the phase angle is 45.6;
- PF is equal to cos (45, 6) = 0.700. Then S = 700 W / cos (45, 6) = 1000 VA.
The ratio of active to apparent power is called power factor (PF). For two systems carrying the same amount of resistive load, the system with the lower PF will have higher circulating currents due to the electrical power being returned back. These large currents create large losses and reduce overall transmission efficiency. A circuit with a lower PF will have a larger total load and higher losses for the same amount of resistive load. PF = 1, 0 when there is phase current. It is zero when the current leads or lags the voltage by 90 degrees.
For example, PF =0.68 means that only 68 percent of the total current supplied actually does work, the remaining 32 percent is reactive. Utility manufacturers do not charge consumers for its reactive losses. However, if there is an inefficiency at a customer's load source that causes the PF to fall below a certain level, the utility may charge customers to cover increased fuel use at power plants and deterioration in grid linear performance.
Characteristics of the full S
The total power formula depends on active and reactive power and is represented as an energy triangle (Pythagorean Theorem). S = (Q 2 + P 2) 1 / 2, where:
- S = total (measured in kilovolt-amperes, kVA);
- Q = reactive (kilovolt reactivity, kVAR);
- P = active (kilowatt, kW).
It is measured in volt-amperes (VA) and depends on the voltage multiplied by the total incoming current. This is the vector sum of the P and Q components, which tells you how to find the total power. Single-phase network: V(V) = I(A)x R (Ω).
P(W) = V(V)x I(A) = V 2(V)/ R (Ω) = I 2(A)x R (Ω).
Three-phase network:
Voltage V in volts (V) is equivalent to current I in amperes (A) multiplied by impedance Z in ohms (Ω):
V(V) = I(A)x Z (Ω) = (| I | x | Z |) ∠ (θ I + θ Z).
S(VA) = V(V)x I(A) = (| V | x | I |) ∠ (θ V - θ I).
Active P
This is the power that is used to operate, its active part, measured in W, is the power consumed by the electrical resistance of the system. P(W) = V(V)x I(A)xcos φ
Reactive Q
It is not used for networking. Q is measured in volt-amperes (VAR). An increase in these indicators leads to a decrease in power factor (PF). Q(VAR) = V(V)x I(A) x sin φ.
Network efficiency factor
PF is determined by the sizes P and S and is calculated using the Pythagorean theorem. The cosine of the angle between voltage and current (non-sinusoidal angle), the phase diagram of voltage or current from the energy triangle are considered. The PF coefficient is equal to the absolute value of the cosine of the complex energy phase angle ( φ ): PF = | cos φ | The efficiency of the power system depends on the PF factor and to improve the efficiency of use in the power system it is necessary to increase it.
Capacitive and inductive loads
Stored energy in the electric and magnetic fields under load conditions, such as from a motor or capacitor, causes an offset between voltage and current. As current flows through the capacitor, the buildup of charge causes an opposing voltage to appear across it. This voltage increases to a certain maximum dictated by the structure of the capacitor. In an alternating current network, the voltage across the capacitor is constantly changing. Capacitors are called sources of reactive losses and thus cause leading PF.
Induction machines are among the most common types of loads in the electrical power system. These machines use inductors or large coils of wire to store energy in the form of a magnetic field. When the voltage first passes through the coil, the inductor strongly resists this change in current and magnetic field, which creates a time delay with a maximum value. This results in the current being out of phase with the voltage.
Inductors absorb Q and hence cause delayed PF. Induction generators can supply or absorb Q and provide a measure of Q flow and voltage control to system operators. Because these devices have opposing effects on the phase angle between voltage and current, they can be used to cancel each other's effects. This usually takes the form of capacitor banks used to counteract the lagging PF caused by induction motors.
Suppression of reactive influence in electrical networks
Active reactive and apparent power determines PF as the main factor for assessing the efficiency of electricity use in the power system network. If PF is high, then it can be said that electricity is used more efficiently in the power system. As the PF is poor or decreases, the power efficiency of the power system decreases. Low PF or its decrease is due to various reasons. There are special correction methods to increase PF.
Using capacitors is the best and most effective way to improve network efficiency. A technique known as reactive compensation is used to reduce the apparent power flow to a load by reducing reactive losses. For example, to compensate for an inductive load, a shunt capacitor is installed close to the load itself. This allows the capacitor to consume all Q and not transmit them along transmission lines.
This practice saves energy because it reduces the amount of energy required to do the same amount of work. It also allows for more efficient transmission line designs using smaller conductors or fewer connector conductors and optimized transmission tower designs.
To maintain the voltage within the optimal range and prevent instability phenomena, various phase control devices are installed at optimal locations throughout the power system network, and various reactive control techniques are used.
The proposed system divides the traditional method into voltage and Q control:
- voltage control to regulate the voltage of the secondary bus of substations;
- Q regulation to regulate the primary bus voltage.
In this system, two types of devices are installed in substations for the interaction of voltage control and Q control.
Voltage and reactive power control
These are two aspects of the same impact that maintain reliability and facilitate commercial transactions in transmission networks. On an alternating current (AC) power system, the voltage is controlled by controlling the production and absorption of Q. There are three reasons why this type of control is necessary:
- Power system equipment is designed to operate over a range of voltages, typically within ±5% of rated voltage. At low voltage, equipment performs poorly, light bulbs provide less illumination, induction motors can overheat and be damaged, and some electronic devices will not work at all. High voltages can damage equipment and shorten its life.
- Q consumes transmission and generation resources. To maximize the actual power that can be transmitted over a congested transmission interface, Q flows must be minimized. Similarly, the production of Q can limit the actual output of the generator.
- The driving reactivity in the transmission network incurs real power losses. To make up for these losses, power and energy must be compensated.
The transmission system is a nonlinear consumer of Q depending on the system load. At very low load the system generates Q which must be absorbed, and at high load the system consumes large amounts of Q which must be replaced. System Q requirements also depend on the generation and transmission configuration. Consequently, system reactive requirements change over time as load levels and load and generation patterns change.
The system operation has three purposes for controlling Q and voltages:
- It must maintain sufficient voltage throughout the entire transmission and distribution system for both current and unexpected conditions.
- Ensure that congestion of actual energy flows is minimized.
- Strive to minimize actual power losses.
A bulk energy system consists of many pieces of equipment, any of which can be faulty. Thus, the system is designed to withstand the failure of individual equipment while continuing to operate in the best interests of consumers. This is why the electrical system requires real power reserves to respond to unforeseen circumstances and maintain Q reserves.
Units of measurement of electrical energy are designated and fixed in the International System of Units.
Using household electrical appliances at home forces users to count electricity and know the units in which it is measured.
Electricity unit of measurement
Voltage
The voltage (U) in the network is measured in volts (V).
In a single-phase network, which is usually used to supply electricity to private consumers, the voltage is 220V.
In a three-phase network the voltage is 380V. 1 kilovolt (kV) is equal to 1000V.
Voltage 220 and 380V is equivalent to voltage designation as 0.22 and 0.4 kV.
Current strength
The consumed load produced by household appliances, equipment and other consumers is called current strength (I) and is measured in amperes (A).
Resistance
Resistance (R) is an equally important indicator and demonstrates the amount of resistance of materials to the passage of electric current. In everyday life, measuring resistance indicates the integrity of electrical appliances, measured in (Ohm). To measure a large resistance value, for example, when measuring the integrity of an electric motor, use a megger; 1 ohm is equal to 0.000001 megaohm (mOhm).
1 kiloohm (kOhm) is equal to 1000 Ohm.
The resistance of the human body ranges from 2 to 10 kOhm.
The resistivity of the conductor is used to evaluate the resistance of materials for their subsequent use in the manufacture of electrical products; it depends on the cross-sectional area and length of the conductor.
Power
Power is the amount of electrical energy consumed by a particular household appliance for a certain unit of time, measured in watts (W) and kiloW (kW) - 1000 W; on an industrial scale, such units of measurement as megawatt - 1 million W and gigawatt ( gW) – 1 billion watts.
How is electricity measured on the meter?
To determine the amount of electricity consumed , Electric active energy meters are used to record it. There are also reactive energy meters in industry.
To determine how electricity consumption in an apartment is measured, 1 kW*hour is used. For reactive energy meters, integrated reactive power is measured as 1 kVar*hour. It should be noted that when recording the energy consumed, the meter must be written correctly, the power multiplied by the time.