It's called power physical quantity, which shows how much energy moves within the electrical circuit of a particular equipment. What is it, in what units is it expressed, how is power measured, what devices are there for this? More on this and more below.
Power is a scalar form of a physical quantity that is equal to the rate of change with the conversion, transmission or consumption of system energy. According to a narrower concept, this is an indicator that is equal to the ratio of time spent on work to the period itself spent on work. In mechanics it is designated by the symbol N. In electrical engineering the letter P is used. You can often also see the symbol W, from the word watt.
Power
There is a difference between useful, gross and nominal in a machine engine. The useful power is the engine power, excluding the costs that are spent on the operation of all other systems. Full is the indicated power without deductions, and nominal is indicated and guaranteed by the factory.
Additional Information! It is worth noting that there is also sound power and explosive sound. In the first case, it is a scalar quantity associated with sound waves and sound energy, which is also measured in watts, and the second is associated with the energy release of TNT decompositions.
Basic concept in the tutorial
What is it measured in?
Horsepower is considered an obsolete unit of measurement. Answering clearly the question of how mechanical power is measured, it is worth noting that according to modern international indicators, the unit of power is the watt. It is worth noting that the watt is a derived unit that is related to others. It is equal to Joule per second or kilogram times meter squared divided by second. Also, a watt is a volt multiplied by an ampere.
It is important to note that a watt is divided into mega, kilo and volt ampere.
Formulas for measurement
Power is a quantity that is directly related to other indicators. Thus, it is directly related to time, force, speed, force vector and speed, force and speed modulus, torque and rotation frequency. Often, in formulas when calculating the electrical power variety, the number Pi, the resistance indicator, and the instantaneous current with voltage in a specific area are also used electrical network, active, total and reactive force. A direct participant in the calculation is the amplitude with angular velocity and the initial current strength with voltage.
Electric
Electrical power is a quantity that shows the speed or transformation at which electrical energy moves. To study the instantaneous electrical power characteristic in a certain section of the circuit, it is necessary to know the value of the current and voltage of the instantaneous current and multiply these values.
To understand how much the active, total, reactive or instantaneous reactive power indicator is, you need to know the exact numbers of current amplitude, voltage amplitude, angle of current with voltage, as well as angular velocity and time, since all existing physical formulas are reduced to these parameters. The formulas also use the sine, cosine of the angle and the value 1/2.
Electric power concept
Hydraulic
The hydraulic power indicator in a hydraulic machine or hydraulic cylinder is the product of the machine pressure drop and the liquid flow rate. Typically, this is the basic formulation taken from the only existing formula for the calculation.
Note! More algebraic and engineering rules can be found in the applied science of the movement of liquids and gases, namely hydraulics.
Direct and alternating current
As for direct and alternating current power, they are most often classified as the electrical variety. There is no specific concept for the two varieties, but they can be calculated based on the available algebraic settings. Yes, power direct current is the product of current and constant voltage, or twice the current and electrical resistance, which, in turn, is calculated by dividing twice the voltage by the usual resistance.
As for alternating current, it is the product of the current strength with the voltage and the cosine of the phase shift. In this case, only the active and reactive varieties can be easily counted. You can find out the full power value through the vector dependence of these indicators and area.
To measure these indicators, you can use both the above instruments and a phase meter. This device is used to calculate the reactive variety according to the state standard.
Concept of variable current power
In general, power is a quantity whose main purpose is to show the strength of a particular device and, in many cases, the speed of activity interacting with it. It can be mechanical, electrical, hydraulic and for direct current and alternating current. Measured according to the international system in watts and kilowatts. The instruments for calculating it are a voltmeter and a wattmeter. The basic formulas for independent calculations are listed above.
Power- a physical quantity equal in the general case to the rate of change, transformation, transmission or consumption of system energy. In a narrower sense, power is equal to the ratio of the work performed in a certain period of time to this period of time.
Distinguish between average power over a period of time
and instantaneous power in this moment time:
The integral of instantaneous power over a period of time is equal to the total transferred energy during this time:
Units. The International System of Units (SI) unit of power is the watt, equal to one joule divided by a second. mechanical work power electrical
Another common, but now outdated, unit of power measurement is horsepower. In its recommendations, the International Organization of Legal Metrology (OIML) lists horsepower as a unit of measurement “which should be withdrawn from use as soon as possible where it is currently used and which should not be introduced if it is not in use.”
Relationships between power units (see Appendix 9).
Mechanical power. If a force acts on a moving body, then this force does work. Power in this case is equal to the scalar product of the force vector and the velocity vector with which the body moves:
Where F- force, v- speed, - angle between the vector of speed and force.
A special case of power during rotational motion:
M- torque, - angular velocity, - pi, n- rotation speed (revolutions per minute, rpm).
Electric power
Mechanical power. Power characterizes the speed at which work is done.
Power (N) is a physical quantity equal to the ratio of work A to the time period t during which this work was performed.
Power shows how much work is done per unit of time.
In the International System (SI), the unit of power is called the Watt (W) in honor of the English inventor James Watt (Watt), who built the first steam engine.
[N]= W = J/s
- 1 W = 1 J / 1s
- 1 Watt is equal to the power of a force that does 1 J of work in 1 second or when a load weighing 100 g is raised to a height of 1 m in 1 second.
James Watt himself (1736-1819) used another unit of power - horsepower (1 hp), which he introduced in order to compare the performance of a steam engine and a horse.
1hp = 735 W.
However, the power of one average horse is about 1/2 hp, although horses are different.
“Living engines” can briefly increase their power several times.
A horse can increase its power when running and jumping up to tenfold or more.
Making a jump to a height of 1 m, a horse weighing 500 kg develops a power equal to 5,000 W = 6.8 hp.
It is believed that the average power of a person during quiet walking is approximately 0.1 hp. i.e. 70-90W.
When running and jumping, a person can develop power many times greater.
It turns out that the most powerful source of mechanical energy is a firearm!
Using a cannon, you can throw a cannonball weighing 900 kg at a speed of 500 m/s, developing about 110,000,000 J of work in 0.01 seconds. This work is equivalent to lifting 75 tons of cargo to the top of the Cheops pyramid (height 150 m).
The power of the cannon shot will be 11,000,000,000 W = 15,000,000 hp.
The force of tension in a person's muscles is approximately equal to the force of gravity acting on him.
this formula is valid for uniform motion with constant speed and in the case of variable motion for average speed.
From these formulas it is clear that at constant engine power, the speed of movement is inversely proportional to the traction force and vice versa.
This is the basis for the operating principle of the gearbox (gearbox) of various vehicles.
Electric power. Electrical power is a physical quantity that characterizes the speed of transmission or conversion of electrical energy. When studying AC networks, in addition to instantaneous power corresponding to the general physical definition, the concepts of active power are also introduced, equal to the average value of instantaneous power over a period, reactive power, which corresponds to energy circulating without dissipation from the source to the consumer and back, and total power, calculated as the product of the effective values of current and voltage without taking into account the phase shift.
U is the work performed when moving one coulomb, and the current I is the number of coulombs passing in 1 second. Therefore, the product of current and voltage shows full time job performed in 1 second, that is, electrical power or electric current power.
Analyzing the above formula, we can draw a very simple conclusion: since the electrical power “P” equally depends on the current “I” and on the voltage “U”, then, therefore, the same electrical power can be obtained either with a high current and a low current voltage, or, conversely, at high voltage and low current (This is used when transmitting electricity over long distances from power plants to places of consumption, through transformer conversion at step-up and step-down power substations).
Active electrical power (this is power that is irrevocably converted into other types of energy - thermal, light, mechanical, etc.) has its own unit of measurement - W (Watt). It is equal to 1 volt times 1 ampere. In everyday life and in production, it is more convenient to measure power in kW (kilowatts, 1 kW = 1000 W). Power plants already use larger units - mW (megawatts, 1 mW = 1000 kW = 1,000,000 W).
Reactive electrical power is a quantity that characterizes this type of electrical load that is created in devices (electrical equipment) by energy fluctuations (inductive and capacitive in nature) of the electromagnetic field. For conventional alternating current, it is equal to the product of the operating current I and the voltage drop U by the sine of the phase angle between them:
Q = U*I*sin(angle).
Reactive power has its own unit of measurement called VAR (volt-ampere reactive). Denoted by the letter "Q".
Power density. Specific power is the ratio of engine power to its mass or other parameter.
Vehicle power density. In relation to cars, specific power is the maximum engine power divided by the entire mass of the car. The power of a piston engine divided by the displacement of the engine is called liter power. For example, the liter power of gasoline engines is 30...45 kW/l, and for diesel engines without turbocharging - 10...15 kW/l.
An increase in the specific power of the engine ultimately leads to a reduction in fuel consumption, since there is no need to transport a heavy engine. This is achieved through light alloys, improved design and boosting (increasing speed and compression ratio, using turbocharging, etc.). But this dependence is not always observed. In particular, heavier diesel engines can be more economical, as the efficiency of a modern turbocharged diesel reaches up to 50%
In the literature, using this term, the inverse value kg/hp is often given. or kg/kW.
Specific power of tanks. The power, reliability and other parameters of tank engines were constantly growing and improving. If in the early models they were content with essentially automobile engines, then with the increase in the mass of tanks in the 1920s-1940s. Adapted aircraft engines, and later specially designed tank diesel (multi-fuel) engines, became widespread. To ensure acceptable driving performance of a tank, its specific power (the ratio of engine power to the combat weight of the tank) must be at least 18-20 hp. With. /T. Specific power of some modern tanks (see Appendix 10).
Active power. Active power is the average value of instantaneous alternating current power over a period:
Active power is a quantity that characterizes the process of converting electricity into some other type of energy. In other words, electrical power, as it were, shows the rate of electricity consumption. This is the power for which we pay money, which is counted by the meter.
Active power can be determined using the following formula:
The power characteristics of the load can be accurately specified by one single parameter (active power in W) only for the case of direct current, since in a direct current circuit there is only one type of resistance - active resistance.
The power characteristics of the load for the case of alternating current cannot be accurately specified by one single parameter, since there are two different types resistance - active and reactive. Therefore, only two parameters: active power and reactive power accurately characterize the load.
The operating principles of active and reactive resistance are completely different. Active resistance - irreversibly converts electrical energy into other types of energy (thermal, light, etc.) - examples: incandescent lamp, electric heater.
Reactance - alternately stores energy and then releases it back into the network - examples: capacitor, inductor.
Active power (dissipated through active resistance) is measured in watts, and reactive power (circulating through reactance) is measured in vars; Also, to characterize the load power, two more parameters are used: apparent power and power factor. All these 4 parameters:
Active power: designation P, unit: Watt.
Reactive power: designation Q, unit of measurement: VAR (Volt Ampere reactive).
Apparent power: designation S, unit: VA (Volt Ampere).
Power factor: designation k or cosФ, unit of measurement: dimensionless quantity.
These parameters are related by the following relations:
S*S=P*P+Q*Q, cosФ=k=P/S.
CosФ is also called power factor.
Therefore, in electrical engineering, any two of these parameters are specified to characterize power, since the rest can be found from these two.
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 sources. AC power supply. Typically these two parameters are apparent power (VA) and active power (W).
Most office and household appliances are active (no or little reactance), so their power is indicated in Watts. In this case, when calculating the load, the UPS power value 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 are used in the calculation exit UPS data: kVA, kW, overload characteristics, etc.
Reactive power. Reactive power, methods and types (means) of reactive power compensation.
Reactive power is the part of the total power expended on electromagnetic processes in a load that has capacitive and inductive components. Doesn't perform useful work, causes additional heating of the conductors and requires the use of an energy source of increased power.
Reactive power refers to technical losses in electrical networks according to Order of the Ministry of Industry and Energy of the Russian Federation No. 267 dated October 4, 2005.
Under normal operating conditions, all consumers of electrical energy whose mode is accompanied by the constant occurrence of electromagnetic fields (electric motors, welding equipment, fluorescent lamps and much more) load the network with both active and reactive components of the total power consumption. This reactive component of power (hereinafter referred to as reactive power) is necessary for the operation of equipment containing significant inductances and at the same time can be considered as an unwanted additional load on the network.
With significant consumption of reactive power, the voltage in the network decreases. In energy systems that are deficient in active power, the voltage level is usually lower than the nominal one. Insufficient active power to complete the balance is transferred to such systems from neighboring power systems that have excess generated power. Typically, power systems are deficient in active power and deficient in reactive power. However, it is more efficient not to transfer the missing reactive power from neighboring power systems, but to generate it in compensating devices installed in a given power system. Unlike active power, reactive power can be generated not only by generators, but also by compensating devices - capacitors, synchronous compensators or static reactive power sources, which can be installed at substations of the electrical network.
Reactive power compensation, currently, is an important factor in solving the issue of energy saving and reducing loads on the power grid. According to estimates of domestic and leading foreign experts, the share of energy resources, and in particular electricity, occupies a significant amount in the cost of production. This is a strong enough argument to seriously approach the analysis and audit of an enterprise’s energy consumption, the development of a methodology and the search for means to compensate for reactive power.
Reactive power compensation. Reactive power compensation means. The inductive reactive load created by electrical consumers can be counteracted with a capacitive load by connecting a precisely sized capacitor. This reduces the reactive power consumed from the network and is called power factor correction or reactive power compensation.
Advantages of using capacitor units as a means of reactive power compensation:
- · low specific losses of active power (the own losses of modern low-voltage cosine capacitors do not exceed 0.5 W per 1000 VAr);
- · no rotating parts;
- · simple installation and operation (no foundation required);
- · relatively low capital investments;
- · the ability to select any required compensation power;
- · Possibility of installation and connection at any point in the electrical network;
- · no noise during operation;
- · low operating costs.
Depending on the connection of the capacitor unit, the following types of compensation are possible:
- 1. Individual or constant compensation, in which inductive reactive power is compensated directly at the point of its occurrence, which leads to unloading of the supply wires (for individual consumers operating in continuous mode with constant or relatively high power - asynchronous motors, transformers, welders, discharge lamps, etc.).
- 2. Group compensation, in which, similar to individual compensation for several simultaneously operating inductive consumers, a common constant capacitor is connected (for electric motors located close to each other, groups of discharge lamps). Here the supply line is also unloaded, but only before distribution to individual consumers.
- 3. Centralized compensation, in which a certain number of capacitors are connected to the main or group distribution cabinet. Such compensation is usually used in large electrical systems with variable loads. Such a capacitor installation is controlled by an electronic regulator - a controller that constantly analyzes the consumption of reactive power from the network. Such regulators turn on or off capacitors, with the help of which the instantaneous reactive power of the total load is compensated and, thus, the total power consumed from the network is reduced.
Power is physical indicator. It defines the work done over a period of time and helps measure energy change. Thanks to the unit of measurement of current power, the high-speed energy flow of energy in any spatial interval is easily determined.
Calculation and types
Due to the direct dependence of power on the voltage in the network and the current load, it follows that this value can appear both from the interaction of a large current with a low voltage, and as a result of the occurrence of a significant voltage with a low current. This principle is applicable for transformation in transformers and for transmitting electricity over vast distances.
There is a formula for calculating this indicator. It has the form P = A / t = I * U, where:
- P is an indicator of current power, measured in watts;
- A - current work on the chain section, calculated in joules;
- t is the time interval during which the current work was performed, determined in seconds;
- U is the electrical voltage of the circuit section, calculated in Volts;
- I - current strength, calculated in amperes.
Electrical power can have active and reactive indicators. In the first case, the transformation of power force into other energy occurs. It is measured in watts because it contributes to the conversion of volts and amperes.
The reactive power indicator contributes to the occurrence of self-inductive phenomenon. This conversion partially returns energy flows back to the network, causing current values shift and voltages with a negative impact on the power grid.
Definition of active and reactive indicator
The active power force is calculated by determining the total value of a single-phase circuit in a sinusoidal current for the desired time period. The calculation formula is presented as the expression P = U * I * cos φ, where:
- U and I act as rms current and voltage;
- cos φ is the interfacial shift angle between these two quantities.
Thanks to power activity, electricity is converted into other energy types: thermal and electromagnetic energy. Any electrical network with a current of sinusoidal or non-sinusoidal direction determines the activity of the circuit section by summing the powers of each individual circuit section. The electrical power of a three-phase circuit section is determined by the sum of each phase power.
A similar indicator of active power force is the magnitude of transmission power, which is calculated by the difference between its incidence and reflection.
The reactive indicator is measured in volt-amperes. It is a quantity used to determine the electrical loads created by electromagnetic fields within an alternating current circuit. The unit of measurement of electric current power is calculated by multiplying the rms value of the voltage in the network U by the alternating current I and the phase sine angle between these values. The calculation formula is as follows: Q = U * I * sin.
If the current load is less than the voltage, then the phase displacement is positive; if, on the contrary, it is negative.
Measurement value
The basic electrical unit is power. In order to determine how the power of an electric current is measured, it is necessary to study the main characteristics of this quantity. According to the laws of physics, it is measured in watts. In production conditions and in everyday life, the value is converted into kilowatts. Calculations of large power scales require conversion to megawatts. This approach is practiced at power plants to produce electrical energy. Work is calculated in joules. The value is determined by the following relationships:
The power consumption is indicated on the electrical appliance itself or in its passport. By determining this parameter, you can obtain the values of indicators such as voltage and electric current. The indicators used indicate how electrical power is measured; they can be in the form of wattmeters and varmeters. The reactive power of the power indicator is determined by a phase meter, voltmeter and ammeter. The state standard for how current power is measured is the frequency range from 40 to 2500 Hz.
Calculation examples
To calculate the kettle current with an electrical power of 2 kW, use the formula I = P / U = (2 * 1000) / 220 = 9 A. To power the device into the mains, the connector length of 6 A is not used. The above example is applicable only when the phase line is completely identical and current voltage. This formula is used to calculate the indicator of all household appliances.
If the circuit is inductive or has a large capacitance, then it is necessary to calculate the power unit of current using other approaches. For example, power in an AC motor is determined using the formula P = I * U * cos.
When connecting the device to a three-phase network, where the voltage will be 380 V, the power of each phase separately is summed up to determine the indicator.
As an example, we can consider a boiler with three phases with a power capacity of 3 kW, each of which consumes 1 kW. The phase current is calculated by the formula I = P / U * cos φ = (1 * 1000) / 220 = 4.5 A.
On any device the electrical power indicator is indicated. The transmission of large power volumes used in production is carried out through lines with high voltage. Energy is converted using substations into electric current and is supplied for use in the electrical network.
Thanks to simple calculations, the power value is determined. Knowing its value, you can make the correct selection of voltage for the full operation of household and industrial devices. This approach will help avoid burnout of electrical appliances and protect electrical networks from voltage surges.
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. This is very stressful. After all, everyone has long been accustomed to kilowatts. And the power of all devices is mainly indicated in kW.
Alexei. June 21, 2007
IN technical specifications of any UPS, the total power [kVA] and active power [kW] are indicated - they characterize the load capacity of the UPS. Example, see photos 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 appendix)
http://metz.by/download_files/catalog/transform/tsgl__tszgl__tszglf.pdf (TSGL transformers: see appendix) - Capacitor power 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 appendix) - For examples of other loads, see the appendices below.
The power characteristics of the load can be accurately specified by one single parameter (active power in W) only for the case of direct current, since in a direct current circuit there is only one type of resistance - active resistance.
The power characteristics of the load for the case of alternating current cannot be accurately specified by one single parameter, since in the alternating current circuit there are two different types of resistance - active and reactive. Therefore, only two parameters: active power and reactive power accurately characterize the load.
The operating principles of active and reactive resistance are completely different. Active resistance - irreversibly converts electrical energy into other types of energy (thermal, light, etc.) - examples: incandescent lamp, electric heater (paragraph 39, Physics grade 11 V.A. Kasyanov M.: Bustard, 2007).
Reactance - alternately accumulates energy and then releases it back into the network - examples: capacitor, inductor (paragraph 40,41, Physics 11th grade V.A. Kasyanov M.: Bustard, 2007).
Further in any textbook on electrical engineering you can read that active power (dissipated by active resistance) is measured in watts, and reactive power (circulating through reactance) is measured in vars; Also, to characterize the load power, two more parameters are used: apparent power and power factor. All these 4 parameters:
- Active power: designation P, unit of measurement: Watt
- Reactive power: designation Q, unit of measurement: VAR(Volt Ampere reactive)
- Apparent power: designation S, unit of measurement: VA(Volt Ampere)
- Power factor: symbol k or cosФ, unit of measurement: dimensionless quantity
These parameters are related by the relations: S*S=P*P+Q*Q, cosФ=k=P/S
Also cosФ called power factor ( Power Factor – PF)
Therefore, in electrical engineering, any two of these parameters are specified to characterize power, since the rest can be found from these two.
For example, electric motors, lamps (discharge) - in those. data indicated P[kW] and cosФ:
http://www.mez.by/dvigatel/air_table2.shtml (AIR engines: see appendix)
http://www.mscom.ru/katalog.php?num=38 (DRL lamps: see appendix)
(for examples of technical data for different loads, see the appendix below)
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 sources. AC power supply. Typically these two parameters are apparent power (VA) and active power (W). See, for example, the parameters of the diesel generator set and the UPS.
Most office and household appliances are active (no or little reactance), so their power is indicated in Watts. In this case, when calculating the load, the UPS power value 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 tool), 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 basis electrical engineering. - M.: Publishing center "Academy", 2004.
2. Nemtsov M.V. Electrical engineering and electronics. - M.: Publishing center "Academy", 2007.
3. Chastoedov L. A. Electrical engineering. - M.: Higher School, 1989.
Also see 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 Amperes)
http://metz.by/download_files/catalog/transform/tsgl__tszgl__tszglf.pdf (TSGL transformers)
| Single-phase autotransformers |
|
||
| TDGC2-0.5 kVa, 2A | AOSN-2-220-82 | ||
| TDGC2-1.0 kVa, 4A | Latr 1.25 | AOSN-4-220-82 | |
| TDGC2-2.0 kVa, 8A | Latr 2.5 | AOSN-8-220-82 | |
| TDGC2-3.0 kVa, 12A | |||
| TDGC2-4.0 kVa, 16A | |||
| TDGC2-5.0 kVa, 20A | AOSN-20-220 | ||
| TDGC2-7.0 kVa, 28A | |||
| TDGC2-10 kVa, 40A | AOMN-40-220 | ||
| TDGC2-15 kVa, 60A | |||
| TDGC2-20 kVa, 80A | |||
http://www.gstransformers.com/products/voltage-regulators.html (LATR / laboratory autotransformers TDGC2)
Example 2: the power of capacitors is indicated in VAR (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 for electric motors contains active power (kW) and cosF
For loads such as electric motors, lamps (discharge), computer blocks power supply, combined loads, etc. - the technical data indicates P [kW] and cosФ (active power and power factor) or S [kVA] and cosФ (apparent power and power factor).
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)
Appendix 1
If the load has a high power factor (0.8 ... 1.0), then its properties approach those of a resistive 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, many countries have adopted standards regulating the power factor of equipment.
Addendum 2
Single-load equipment (for example, a PC power supply unit) and multi-component combined equipment (for example, an industrial milling machine containing 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, nowadays most equipment has a power factor correction input unit. In this case, the input power factor is 0.9 ... 1.0, which corresponds to regulatory standards.
Appendix 3: Important Note Regarding UPS Power Factor and Voltage Stabilizers
The load capacity of the UPS and diesel generator set is normalized to a standard industrial load (power factor 0.8 with an inductive nature). For example, UPS 100 kVA / 80 kW. This means that the device can supply a resistive load with a maximum power of 80 kW, or a mixed (reactive-reactive) load with a maximum power of 100 kVA with an inductive power factor of 0.8.
With voltage stabilizers the situation is different. For the stabilizer, the load power factor is indifferent. For example, a 100 kVA voltage stabilizer. 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 power factor of a capacitive or inductive nature. Note that this is valid for a linear load (without higher harmonic currents). With large harmonic distortions of the load current (high SOI), the output power of the stabilizer is reduced.
Addendum 4
Illustrative examples of pure active and pure reactive loads:
- A 100 W incandescent lamp is connected to an alternating current network of 220 VAC - everywhere in the circuit there is conduction current (through the wire conductors and the tungsten filament of the lamp). Load (lamp) characteristics: power S=P~=100 VA=100 W, PF=1 => all electrical power is active, which means it is completely absorbed in the lamp and converted into heat and light power.
- A 7 µF non-polar capacitor is connected to an alternating current network of 220 VAC - there is a conduction current in the wire circuit, and 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.
Addendum 5
To indicate the predominant reactance (inductive or capacitive), the power factor is assigned the sign:
+ (plus)– if the total reactance is inductive (example: PF=+0.5). The current phase lags behind the voltage phase by an angle Ф.
- (minus)– if the total reactance is capacitive (example: PF=-0.5). The current phase advances the voltage phase by angle F.
Appendix 6
Additional questions
Question 1:
Why do all electrical engineering textbooks, when calculating AC circuits, use imaginary numbers/quantities (for example, reactive power, reactance, etc.) that do not exist in reality?
Answer:
Yes, all individual quantities in the surrounding world are real. Including temperature, reactance, etc. The use of imaginary (complex) numbers is only a mathematical technique that facilitates calculations. The result of the calculation is a necessarily real number. Example: reactive power of a load (capacitor) of 20 kVAr is a real energy flow, that is, real Watts circulating in the source-load circuit. But in order to distinguish these Watts from the Watts irretrievably absorbed by the load, they decided to call these “circulating Watts” reactive Volt Amperes.
Comment:
Previously, only single quantities were used in physics, and when calculating, 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 were studied (light, waves, alternating electric current, atom, space, etc.), such a large number of physical quantities appeared that it became impossible to calculate each one separately. This is not only a problem of manual calculation, but also a problem of compiling computer programs. To solve this problem, close single quantities began to be combined into more complex ones (including 2 or more single quantities), subject to transformation laws known in mathematics. This is how scalar (single) quantities (temperature, etc.), vector and complex dual quantities (impedance, etc.), triple vector quantities (magnetic field vector, etc.), and more complex quantities appeared - matrices and tensors (dielectric constant tensor, tensor Ricci and others). To simplify calculations in electrical engineering, the following imaginary (complex) dual quantities are used:
- Total resistance (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 a complex, that is, imaginary / non-existent plane. What does all this have to do with reality?
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Answer:
It is difficult to carry out calculations with real sinusoids, therefore, to simplify the calculations, use a vector (complex) representation as in Fig. higher. But this does not mean that the S P Q shown in the figure are not related to reality. Real values of S P Q can be presented in the usual form, based on measurements of sinusoidal signals with an oscilloscope. The values of S P Q Ф I U in the alternating current circuit “source-load” depend on the load. Below is an example of real sinusoidal signals S P Q and Ф for the case of a load consisting of active and reactive (inductive) resistances connected in series.
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Question 3:
Using a conventional current clamp and a multimeter, a load current of 10 A and a load voltage of 225 V were measured. We multiply and get the load power in W: 10 A · 225V = 2250 W.
Answer:
You have obtained (calculated) the total load power of 2250 VA. Therefore, your answer will only be valid if your load is purely resistive, then indeed Volt Ampere 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, for example APPA137:
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See further reading, 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.
Chastoedov 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
The most important task of equipment statistics is to measure the power of plant engines. Engine power is called its ability to perform certain work per unit of time (second). The basic unit of power is the kilowatt (kW). Since a plant's power equipment may include motors whose power is expressed in different units, the total power of all motors is expressed in kilowatts. To do this, use the following constant relationships:
Engine power can be characterized from different points of view.
Depending on the design of the engine, power is distinguished between theoretical, indicator and effective (real).
Theoretical power(#) is determined by calculations based on the assumption that there are no mechanical losses (from friction) and thermal losses (from radiation) in the engine. Theoretical power can be calculated for any engines.
Power indicator(#/s) - engine power taking into account thermal, but excluding mechanical losses. Measured M.nd on the part of the engine where radiation losses end.
The third type of design capacity is effective power (G This is the actual power, taking into account thermal and mechanical losses. Measured at the engine working shaft.
Depending on the intensity of engine operation, its power can change, therefore, there are such power with load: normal (economic), maximum long and maximum short time.
Power is normal(L/^g) is the power at which the engine most economically consumes fuel and energy per unit of force, that is, it has the highest efficiency (efficiency). When the load deviates up or down from normal efficiency. decreases.
Mainly for the purpose of obtaining maximum quantity energy during operation power devices for them, a maximum load mode is established, in which the engine can operate for an indefinitely long period without damage to its condition. The power characteristic of the maximum load of most power engines is called maximum duration (Mmt()-
Maximum short-term power (No.) is the maximum load of the engine, beyond which it can operate for a short time without an accident, usually no more than 30 minutes.
All three types of load power are potential, since they determine not the actual, but the possible load. To fully characterize the power of an engine, its power, by design and by load, should be taken into account simultaneously. As a rule, this will be the maximum continuous effective power.
To characterize engine power according to operational purpose They distinguish between connected power, installed, available, peak, reserve, average actual and average annual.
Connected capacity (Mprisd) is the power of all receivers connected to the power plant, including the power of the electric motors of someone else's current for subscribers and the electric motors of their own current.
Large power plants provide electricity to subscribers with different load schedules. For example, in the morning the energy demand for production and urban transport (trams, trolleybuses) sharply increases, but for lighting decreases; In the evening hours, the work of some enterprises stops, but the need for entertainment venues for electrical energy increases sharply. Due to the frequent connection of subscribers to the station, the connected power is usually 2-2.5 times greater than the station capacity. So, a station with a capacity of 30 thousand kW can serve subscribers whose current receiver power is 60 thousand kW or more.
Power installed(l/) is the total maximum continuous effective power of the installed engines (for a power plant - the power of electric generators).
Since some of the engines undergoing repair and awaiting repair cannot be used, it is of great importance available power (Мяві)- the total power of all devices, minus those that are under repair or awaiting repair.
For a certain period, for example per day, month or quarter, it is important to determine the maximum load, which is called peak power of the ShA.
The difference between available and peak power is called reserve power. It consists of two parts that have different economic significance: the power of reserve engines, intended to replace those that are running in the event of an accident, and the underload of engines operating during rush hour.
For many practical calculations it is determined average actual power L. It is calculated for an individual engine by dividing the energy generated during the period in kilowatt-hours by the actual operating time in hours, that is
To calculate the average actual power of several engines that work together, the energy they produce must be divided by the operating time of all engines, reduced by the time they work together. Thus, the formula for the average actual power of two engines operating together in one or another combination will have the form
Example 7.1
Calculate the average actual power of two engines, of which the first worked from 6 to 16 hours and produced 630 kW x hour of energy, and the second worked from 8 to 23 hours and produced 715 kW x hour of energy.
Total amount of energy produced: 630 + 715 = 1345 kW x h.
Total engine operating time: (16-6) + (23-8) = 25 hours.
Engine operation time: (16-8) = 8 hours.
In addition to the average actual power, calculate average annual power (M), which shows how many kilowatt-hours of energy are produced per hour on average per year.
To do this, the energy produced is divided by the number of lesson hours - 8760. is always less than and their ratio A^UL^ characterizes the degree of engine utilization over time over an annual period.
The enterprises have engines installed that perform various functions: primary engines produce mechanical energy, and secondary engines transform mechanical energy energy into electrical(electric generators) or electrical into mechanical and thermal (electric motors and electrical devices).
If, to determine the total power of an enterprise, the power of the primary and secondary engines is added, then a repeated count will be allowed; In addition, the total power calculation should only include the power that is used in the production process. Consequently, the power of the engines installed at the power station of the enterprise, the energy of which is supplied to the side, should not be taken into account when determining the energy capacity of a certain enterprise, since it will be taken into account at the enterprises that consume energy.
Rice. 7.1. V
From Fig. 7.1 shows that prime movers can directly drive working machines or transmit mechanical energy to electric generators to transform it into electrical energy; The electricity from your own electric generators can be used both to power electric motors and electric devices of your own and mixed current, and to meet the economic needs of the enterprise. Part of the electricity can be released to the side. At the same time, energy received from outside ensures the operation of electric motors and electrical devices of foreign and mixed current. The power of direct primary engines and the power of transport engines are taken into account independently. By summing the powers of the primary and secondary engines, we will allow double counting. Therefore, the calculation formula is applied energy capacity of the enterprise, which completely eliminates double counting:
The total power of prime movers No.) also takes into account the power of direct-acting motors and those used in factory vehicles.
Formula 7.3 not only eliminates the repeated calculation of power, but also distinguishes between the power of a mechanical and electric drive.
The power of the mechanical drive is equal to the difference between the power of all primary engines of the enterprise and the power of that part of them that serves electric generators (Mpd-M^^^^). This the difference is the power of the prime movers directly connected to the working machines (using a transmission or gear system).
The power of an electric drive is defined as the sum of the powers of electric motors and electrical devices, that is, secondary engines that directly serve the production process.
Sometimes, when calculating the energy power of an enterprise, the power of the primary engines servicing electric generators Gp.d.obs.el.gen)> unknown. To determine it, you need to multiply the power of electric generators by a factor of 1.04. The origin of this coefficient is as follows: the average efficiency of electric generators is taken to be 0.96, which means that the power of the prime movers that serve them can be obtained by dividing the power of the prime movers by 0.96 or multiplying by = 1.04. 0.96
For determining the amount of energy consumed by the enterprise, use a formula similar to that used to calculate the total power:
Example 7.2
Calculate the potential and average actual capacity of the enterprise, knowing that the enterprise worked for 200 hours and little his The following power equipment is at our disposal:
^^=400+50+350 0.736+100 0.736 - 250-1.04 + 220 + 600 = І34І.2l5zh.
To calculate If it is necessary to determine the energy consumed by the enterprise:
Yeschipr = 80000 + 42000 o 0.736+10000 - 0.736 - 48000 o 1.04 + 42000 + 90000 = 200352 kW.
