Electrical power is a quantity that characterizes the rate of transmission, consumption or generation of electrical energy per unit of time.

The higher the power value, the more work the electrical equipment can perform per unit of time. Power can be apparent, reactive and active.

S - total power is measured in kVA (kiloVolt Amperes)

A - active power is measured in kW (kilowatts)

P - reactive power is measured in kVar (kiloVar)

Definition

Volt-Ampere (VA as well as V A)- unit of measurement of total power, respectively, 1 kVA = 10³ VA, i.e. 1000 VA. The total current power is equal to the product of the current acting in the circuit (A) and the voltage acting at its terminals (V).

Watt (W as well as W)- unit of measurement of active power, respectively, 1 kW = 10³ W, i.e. 1000 W. 1 Watt is the power at which 1 Joule of work is done in one second. The part of the total power that is transferred to the load during a certain period of alternating current is called active power. It is calculated as the product of the effective values ​​of electric current and voltage and the cosine of the angle (cos φ) of the phase shift between them.

Cos φ is a value characterizing the quality of electrical equipment from the point of view of saving electrical energy. The larger the cosine phi, the more electricity from the source goes to the load (the amount of active power approaches the total value).

The power that was not transferred to the load, but was spent on heating and radiation, is called reactive power.

Comparison

When choosing a power plant or stabilizer, you must remember that kVA is the total power (consumed by the equipment), and kW is the active power (i.e., spent on performing useful work).

Apparent power (kVA) is the sum of active and reactive power. All consumer electrical appliances can be divided into two categories: active (incandescent lamp, heater, electric stove, etc.) and reactive (air conditioners, TVs, drills, fluorescent lamps, etc.).

Different consumers have different ratios of active and apparent power, depending on the category.

Conclusions website

1. To determine the total power of all consumers for active devices, it is enough to add up all active powers (kW). That is, if according to the passport the device (active) consumes, for example, 1 kW, then exactly 1 kW is enough to power it.
2. For reactive devices, the addition of the total powers of all electrical equipment is required, because For reactive consumers, part of the energy is converted into light or heat. In engineering calculations for such devices, the total power is calculated using the formula: S = A/cos φ.

Difference between kVA and kW | What is the difference between kVA and kW

| Convert kVA to kW

In consumer terms: kW is useful power, and kVA is total power. kVA-20%=kW or 1kVA=0.8kW. To convert kVA to kW,it is required to subtract 20% from kVA and you get kW with a small error, which can be ignored.

For example, a household voltage stabilizer indicates a power of 10 kVA, and you need to convert the readings into kW, you should use 10 kVA * 0.8 = 8 kW or 10 kVA - 20% = 8 kW. Thus, to convert kVA to kW, the formula is applicable:

How to convert kW to kVA

Now let's look at how to get the total power (S) indicated in kVA.For example, on a portable generator the power is indicated as 8 kW, and you need to convert the reading data into kVA, it should be 8 kW / 0.8 = 10 kVA.Thus, to convert kW to kVA, the formula is applicable:

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Content:

In everyday life, electrical appliances are widely used. Typically, the differences between models in terms of their power are the basis of our choice when purchasing them. For most of them, a larger difference in watts gives an advantage. For example, when choosing an incandescent bulb for a greenhouse, it is obvious that a 160-watt bulb will provide much less light and heat compared to a 630-watt bulb. It is also easy to imagine how much heat this or that electric heater will provide thanks to its kilowatts.

For us, the most familiar indicator of the performance of an electrical appliance is watt. And also a multiple of 1 thousand watt kW (kilowatt). However, in industry the scale of electrical energy is completely different. Therefore, it is almost always measured not only in megawatts (MW). For some electric machines, especially in power plants, the power can be tens or even hundreds of times greater. But electrical equipment is not always characterized by the unit of measurement kilowatt and its multiples. Any electrician will tell you that electrical equipment uses mainly kilowatts and kilovolt-amperes (kW and kVA).

Surely many of our readers know what the difference is between kW and kVA. However, those readers who cannot correctly answer the questions of what determines the ratio of kVA and kW will, after reading this article, become much better at understanding all this.

Features of converting values

So, what needs to be remembered first of all if the task is to convert kW to kVA, as well as convert kVA to kW. And we need to remember the school physics course. Everyone studied the SI (metric) and GHS (Gaussian) measurement systems, solved problems, expressed, for example, length in SI or another measurement system. After all, the English system of measures is still used in the USA, Great Britain and some other countries. But pay attention to what links the translation results between systems. The connection is that, despite the name of the units of measurement, they all correspond to the same thing: foot and meter - length, pound and kilogram - weight, barrel and liter - volume.

Now let's refresh our memory on what kVA power is. This is, of course, the result of multiplying the current value by the voltage value. But the point is what current and what voltage. Voltage mainly determines the current in an electrical circuit. If it is constant, there will be constant current in the circuit. But not always. It may not exist at all. For example, in an electrical circuit with a capacitor at constant voltage. Direct current determines the load and its properties. The same as with alternating current, but with it everything is much more complicated than with DC.

Why are there different powers?

Any electrical circuit has resistance, inductance and capacitance. When this circuit is exposed to a constant voltage, inductance and capacitance only appear for some time after switching on and off. During so-called transient processes. In steady state, only the resistance value affects the current strength. At alternating voltage, the same electrical circuit works completely differently. Of course, resistance in this case, as well as with direct current, determines the release of heat.

But besides this, an electromagnetic field appears due to inductance, and an electric field appears due to capacitance. Both heat and fields consume electrical energy. However, only the energy associated with resistance and creating heat is expended with obvious benefit. For this reason, the following components appeared.

• An active component that depends on resistance and manifests itself in the form of heat and mechanical work. This could be, for example, the benefit of heat, the release of which is directly proportional to the amount of kW of electric heater power.
• The reactive component, which manifests itself in the form of fields and does not bring direct benefit.

And since both of these powers are characteristic of the same electrical circuit, the concept of total power was introduced both for this electrical circuit with a heater and for any other.

Moreover, not only resistance, inductance and capacitance by their values ​​determine the power at alternating voltage and current. After all, power, by its definition, is tied to time. For this reason, it is important to know how voltage and current change over a set time. For clarity, they are depicted as vectors. This produces an angle between them, denoted as φ (angle “phi”, a letter of the Greek alphabet). What this angle is equal to depends on the inductance and capacitance.

Translating or calculating?

Therefore, if we are talking about electrical power of alternating current I with voltage U, there are three possible options:

• Active power, determined by resistance and for which the basic unit is the watt, W. And when we are talking about its large quantities, kW, MW, etc., etc. are used. Denoted as P, calculated by the formula

• Reactive power, defined by inductance and capacitance, for which the basic unit is var, var. They can also be kvar, mvar, etc., etc. for high powers. Denoted as Q and calculated using the formula

• Apparent power, defined by active and reactive power, and for which the basic unit is volt-ampere, VA. For larger values ​​of this power, kVA, MVA, etc., etc. are used. Denoted as S, calculated by the formula

As can be seen from the formulas, kVA power is kW power plus kvar power. Consequently, the task of how to convert kVA to kW or, conversely, kW to kVA always comes down to calculations using the formula in point 3 shown above. In this case, you must either have or obtain two values ​​out of three - P, Q, S. Otherwise, there will be no solution. But it is impossible to convert, for example, 10 kVA or 100 kVA into kW as easily as 10 $ or 100 $ into rubles. For exchange rate differences, there is an exchange rate. And this is the coefficient for multiplication or division. And the value of 10 kVA can consist of many values ​​of kvar and kW, which, according to the formula in paragraph 3, will be equal to the same value - 10 kVA.

• Only in the complete absence of reactive power is the conversion of kVA to kW correct and performed according to the formula

The article has already answered the first three questions stated at the beginning. There is one last question about cars. But the answer is obvious. The power of all electric machines will consist of active and reactive components. The operation of almost all electrical machines is based on the interaction of electromagnetic fields. Therefore, since these fields exist, it means that there is reactive power. But all these machines heat up when connected to the network, and especially when performing mechanical work or under load, like transformers. And this indicates active power.

But often, especially for household machines, only W or kW power is indicated. This is done either because the reactive component of this device is negligible, or because the home meter only counts kW anyway.

The basic unit of power measurement for electrical equipment is kW (kilowatt). But there is another unit of power that not everyone knows about - kvar.

kvar (kilovar)– unit of measurement of reactive power (volt-ampere reactive – var, kilovolt-ampere reactive – kvar). In accordance with the requirements of the International Standard for Units of Measurement Systems SI, the unit of measurement of reactive power is written “var” (and, accordingly, “kvar”). However, the designation "kvar" is widely used. This designation is due to the fact that the SI unit of measurement for total power is VA. In foreign literature, the generally accepted designation for the unit of measurement of reactive power is " kvar". The unit of measurement of reactive power is equated to non-system units, acceptable for use on a par with SI units.

Aristotle and the science of existence. Ancient and modern interpretations

The Search function can be used to search for a specific author or subject. . Aristotle gives four definitions of what is now called metaphysics: wisdom, first philosophy, theology and the science of existence. The main points that will be developed are as follows.

Current interpretations. A summary of the theory of reduplication. An annotated bibliography of contemporary research. Why doesn't Aristotle simply say that ontology is a theory of being? Is there a difference between a "theory of being" and a "theory of being of existence"? In short, the problem is to decide whether the two expressions "theory of being" and "theory of being" are equivalent.

AC power receivers consume both active and reactive power. The power ratio of an AC circuit can be represented as a power triangle.

On the power triangle, the letters P, Q and S indicate active, reactive and apparent power, respectively, φ is the phase shift between current (I) and voltage (U).

It should be noted that the reduplication functor is widely used by Aristotle in his theory of mathematics. Reduplication is a tool that Aristotle uses to avoid the pitfalls of Platonism. References are made to: Aristotle - Metaphysics. What were Aristotle's metaphysical statements, and what is Aristotle's metaphysics? The last question is simpler: the work, as we now have it, is divided into fourteen books of unequal length and complexity. Alpha's book is introductory: it formulates the concept of science about the first principles or causes of things and offers a partial history of the subject.

The value of reactive power Q (kVAr) is used to determine the apparent power of the installation S (kVA), which in practice is required, for example, when calculating the apparent power of a transformer supplying equipment. If we consider the power triangle in more detail, it is obvious that by compensating for reactive power, we will also reduce the consumption of total power.

The second book, known as Little Alpha, is a second introduction, mainly methodological in content. a long sequence of puzzles or aporias: possible answers are lightly sketched out, but the book is programmatic, not definitive. Next in The Delta comes Aristotle's philosophical vocabulary: some 40 philosophical terms are explained, and their various senses are soon expounded and illustrated. The books Zeta, Eta and Theta hang together, and together they form the core of Metaphysics.

It is extremely unprofitable for enterprises to consume reactive power from the supply network, since this requires increasing the cross-sections of supply cables and increasing the power of generators and transformers. There are ways to receive (generate) it directly from the consumer. The most common and effective way is to use capacitor units. Since the main function performed by capacitor units is reactive power compensation, the generally accepted unit of their power is kVAR, and not kW as for all other electrical equipment.

Their common theme is substance: its identification, its relation to matter and form, to actuality and potentiality, to change and generation. The argument is tortuous in the extreme, and it is far from clear what Aristotle's final views on the topic were, if he had any final views. The next book, Iota, deals with the concepts of unity and identity. From: Jonathan Barnes - The Cambridge Companion to Aristotle - Cambridge, Cambridge University Press Release Chapter 3 - Metaphysics - Jonathan Barnes - page 66.

Whether the fourteen books of the Metaphysics constitute a unity or a collection of disparate treatises is a matter of considerable debate. Aristotle clearly recognizes a special study corresponding to metaphysics, which he variously calls wisdom, first philosophy and theology.

Depending on the nature of the load, enterprises can use both non-regulated capacitor units and units with automatic regulation. In networks with sharply variable loads, thyristor-controlled installations are used, which allow capacitors to be connected and disconnected almost instantly.

But the Metaphysics books seem to present a different concept of what metaphysics is. His hypothesis is summarized by Takatura Ando in: Metaphysics. A Critical Review of Its Significance - The Hague, Martinus Nijhoff. page 4. S. made a list of philosophical works before Herpips and Diogenes presumably used it when he compiled his list. The origin of the name metaphysics, traced back to one century after Aristotle's death, might reasonably be assumed to reflect the sequence followed by Aristotle himself.

The working element of any capacitor installation is a phase (cosine) capacitor. The main characteristic of such capacitors is power (kVAr), and not capacitance (μF), as for other types of capacitors. However, the functioning of both cosine and conventional capacitors is based on the same physical principles. Therefore, the power of cosine capacitors, expressed in kVAr, can be converted into capacitance, and vice versa, using correspondence tables or conversion formulas. Power in kVAr is directly proportional to the capacitance of the capacitor (μF), frequency (Hz) and square of the voltage (V) of the supply network. The standard range of capacitor power ratings for the 0.4 kV class ranges from 1.5 to 50 kVAr, and for the 6-10 kV class from 50 to 600 kVAr.

More about power

Bibliographic references to works cited can be found in the Selected Bibliography. For much of this century, Aristotelian scholarship has been dominated by one question: how might Aristotle's intellectual development be used to shed light on his philosophical doctrines? Opinions varied widely as to how this growth might be charted; eventually, the reaction to the entire enterprise came into play. Over the past thirty years, this question has lost its importance as scholars have returned to studying the corpus without developing Aristotle as a primary concern.

An important indicator of energy efficiency is the economic equivalent of reactive power kE (kW/kVAr). It is defined as a reduction in active power losses to a reduction in reactive power consumption.

Values ​​of the economic equivalent of reactive power

There are also “larger” units of measurement of reactive power, for example megavar (Mvar). 1 Mvar is equal to 1000 kVAr. Megavars usually measure the power of special high-voltage reactive power compensation systems - static capacitor banks (SCB).

Recently, the question of Aristotle's philosophical development has been reopened. Together they may signal a new interest in development, and offer philosophers an opportunity to assess the challenges and prospects facing any such revival. For fifty years after it was first raised, to the small notice of Oxford professor Thomas Case, and then loudly by Werner Jaeger in a pioneering study two years later, scholars devoted themselves to the question of Aristotle's rise as a thinker.

The basic tenets of his thesis are familiar. Aristotle began his philosophical career as a follower of Plato, and only later, after a long transitional period, did philosophical maturity emerge as an opponent of Platonic forms and an explorer of empirical nature and living beings. Much of Jaeger's data for early Aristotle was derived from fragments of literary remains, many of which were considered false before his work. He then turned to works often regarded as collections of independent lectures or small fragments, and to the three ethical treatises that have come down to us under the name of Aristotle.

Length and distance Mass Measures of volume of bulk solids and foodstuffs Area Volume and units of measurement in culinary recipes Temperature Pressure, mechanical stress, Young's modulus Energy and work Power Force Time Linear velocity Plane angle Thermal efficiency and fuel efficiency Numbers Units for measuring the amount of information Exchange rates Dimensions women's clothing and footwear Sizes of men's clothing and footwear Angular velocity and rotation frequency Acceleration Angular acceleration Density Specific volume Moment of inertia Moment of force Torque Specific heat of combustion (by mass) Energy density and specific heat of combustion of fuel (by volume) Temperature difference Coefficient of thermal expansion Thermal resistance Specific thermal conductivity Specific heat capacity Energy exposure, thermal radiation power Heat flux density Heat transfer coefficient Volume flow rate Mass flow rate Molar flow rate Mass flow density Molar concentration Mass concentration in solution Dynamic (absolute) viscosity Kinematic viscosity Surface tension Vapor permeability Vapor permeability, vapor transfer rate Sound level Microphone sensitivity Sound pressure level (SPL) Brightness Luminous intensity Illumination Computer graphics resolution Frequency and wavelength Optical power in diopters and focal length Optical power in diopters and lens magnification (×) Electric charge Linear charge density Surface charge density Volumetric charge density Electrical current Linear current density Surface current density Electric field strength Electrostatic potential and voltage Electrical resistance Electrical resistivity Electrical conductivity Electrical conductivity Electrical capacitance Inductance American wire gauge Levels in dBm (dBm or dBm), dBV (dBV) , watts and other units Magnetomotive force Magnetic field strength Magnetic flux Magnetic induction Absorbed dose rate of ionizing radiation Radioactivity. Radioactive decay Radiation. Exposure dose Radiation. Absorbed Dose Decimal Prefixes Data Communication Typography and Image Processing Timber Volume Units Molar Mass Calculation Periodic table chemical elements D. I. Mendeleev

Using these works, he constructed a picture of Aristotle's development in which Aristotle moved toward increasing independence from Plato. He then looked for parallels with doctrines in other works that were not considered internally contradictory. For example, his claim that Aristotle came to empiricism late in his career, which led to him assigning biological work during the Lyceum period.

Others have sought to dismiss Jaeger's approach as simply a product of the positivist or historicist dogmas popular in turn-of-the-century Germany. Gradually Jaeger has fewer and fewer supporters of his version of the development thesis. Perhaps the decisive problems arose in the work of Dühring and Owen. At the time, argued that Aristotle opposed Plato and his transcendental view of reality from the very beginning. His growing interest in natural history developed, in turn, under the influence of his own talented student Aristotle and eventual successor Theophrastus.

1 kilowatt [kW] = 1 kilovolt-ampere [kVA]

Initial value

Converted value

watt exawatt petawatt terawatt gigawatt megawatt kilowatt hectowatt decawatt deciwatt centiwatt milliwatt microwatt nanowatt picowatt femtowatt attowatt horsepower horsepower metric horsepower boiler horsepower electric horsepower pump horsepower horsepower (German) Brit. thermal unit (int.) per British hour. thermal unit (int.) per minute brit. thermal unit (int.) per second brit. thermal unit (thermochemical) per hour Brit. thermal unit (thermochemical) per minute brit. thermal unit (thermochemical) per second MBTU (international) per hour Thousand BTU per hour MMBTU (international) per hour Million BTU per hour refrigeration ton kilocalorie (IT) per hour kilocalorie (IT) per minute kilocalorie (IT) per minute second kilocalorie (therm.) per hour kilocalorie (therm.) per minute kilocalorie (therm.) per second calorie (interm.) per hour calorie (interm.) per minute calorie (interm.) per second calorie (therm.) per hour calorie (therm) per minute calorie (therm) per second ft lbf per hour ft lbf/minute ft lbf/second lb-ft per hour lb-ft per minute lb-ft per second erg per second kilovolt-ampere volt-ampere newton meter per second joule per second exajoule per second petajoule per second terajoule per second gigajoule per second megajoule per second kilojoule per second hectojoule per second decajoule per second decijoule per second centijoule per second millijoule per second microjoule per second nanojoule per second picojoule per second femtojoule per second attojoule per second joule per hour joule per minute kilojoule per hour kilojoule per minute Planck power

Owen's analysis was even more influential. Owen argued that early in his career Aristotle issued an uncompromising rejection of Plato's metaphysics and the corresponding magisterial science of dialectic. Later, the key insight into how we relate to one thing by another—the now famous doctrine of "pluralism" of "focal meaning"—motivated him to make room for a universal science of being after all. In fact, Aristotle's Platonism was more complex than Jaeger made it out to be.

Turning to Aristotle's own works, we are immediately surprised: Aristotle began his last scientific works during Plato's lifetime. By a curious coincidence, in two different works he mentions two different events as being contemporary with the time of writing, one in 357 and the other in the Politics, he mentions how now Dion's expedition to Sicily, which took place in the Meteorologica, he mentions how Now the temple in Ephesus is burning, which occurred in order to preserve his hypothesis as a recent composer, Zeller resorts to the vagueness of the word “now”.

More about power

General information

In physics, power is the ratio of work to the time during which it is performed. Mechanical work is a quantitative characteristic of the action of force F on a body, as a result of which it moves a distance s. Power can also be defined as the rate at which energy is transmitted. In other words, power is an indicator of the machine's performance. By measuring power, you can understand how much work is done and at what speed.

But Aristotle describes individual events graphically and can hardly speak of events 357 and 356 as happening "now" in or around that time. These two works provide further evidence that they both began before this date. Indeed, the whole truth about this great work is that it was left unfinished at Aristotle's death. The logical conclusion is that Aristotle began writing it back in 357 and continued to write it in 346, in 336, and so on until he died.

Likewise, he began Meteorology as early as 356 and was still writing it in both books, which were begun several years before Plato's death; both were works of many years; both were intended to form parts of the Aristotelian system of philosophy. It follows that Aristotle, out of early courage, not only wrote dialogues and didactic works, surviving only in fragments, but also began some of the philosophical works that are still part of his surviving writings. He continued them and no doubt started others during the prime of his life.

Power units

Power is measured in joules per second, or watts. Along with watts, horsepower is also used. Before the invention of the steam engine, the power of engines was not measured, and, accordingly, there were no generally accepted units of power. When the steam engine began to be used in mines, engineer and inventor James Watt began improving it. To prove that his improvements made the steam engine more productive, he compared its power to the performance of horses, since horses had been used by people for many years, and many could easily imagine how much work a horse could do in a certain amount of time. In addition, not all mines used steam engines. On those where they were used, Watt compared the power of the old and new models of the steam engine with the power of one horse, that is, with one horsepower. Watt determined this value experimentally by observing the work of draft horses at a mill. According to his measurements, one horsepower is 746 watts. Now it is believed that this figure is exaggerated, and the horse cannot work in this mode for a long time, but they did not change the unit. Power can be used as a measure of productivity because as power increases, the amount of work done per unit of time increases. Many people realized that it was convenient to have a standardized unit of power, so horsepower became very popular. It began to be used in measuring the power of other devices, especially vehicles. Although watts have been around for almost as long as horsepower, horsepower is more commonly used in the automotive industry, and many consumers are more familiar with horsepower when it comes to power ratings for a car engine.

Thus, having slowly matured his individual writings, he was better able to unite them increasingly into a system in last years. But it may have been started long before and it received additions and changes. However, the early Aristotle started a book, as long as he held the manuscript he could always change it.

Finally, he died without finishing some of his works, such as the Politics, and especially that the work of his entire philosophical career and the basis of all his philosophy - metaphysics - which, as predicted in his early criticism of Plato's philosophy, the universal forms , gradually developed into his positive philosophy of individual substances, but in the end remained incomplete. In general, then, Aristotle wrote his last works very gradually over a period of about thirty-five years, much as Herodotus considered the additions, continued to write them more or less together, not so sequentially as simultaneously, and did not finish writing them at his death.

Power of household electrical appliances

Household electrical appliances usually have a wattage rating. Some fixtures limit the wattage of the bulbs they can use, such as no more than 60 watts. This is done because higher wattage lamps generate a lot of heat and the lamp socket may be damaged. And the lamp itself high temperature It will not last long in the lamp. This is mainly a problem with incandescent lamps. LED, fluorescent and other lamps typically operate at lower wattages for the same brightness and, if used in fixtures designed for incandescent bulbs, wattage is not an issue.

There is a curious characteristic associated with this gradual composition. This is evident enough in Metaphysics: it has two openings; then an almost consistent theory of being occurs, but is interrupted by the philosophical lexicon Δ; then comes the theory of unity; then a summary of the previous books and doctrines of physics; the next new beginning about being and that wants to complete the system, the theory of God in relation to the world; finally, a critique of mathematical metaphysics, in which the argument against Plato is repeated almost verbatim.

Metaphysics is undoubtedly a compilation made up of essays or discourses; and this illustrates another characteristic of Aristotle's gradual method of composition, which refers to passages "in the first discourses" - an expression not uncommon in Aristotle's writings. Sometimes we are talking about the beginning of the entire treatise, for example, Metaph. However, according to one alternative, the "said first discourses" may have originally been a separate discourse, since Book Γ begins quite fresh with the definition of the science of being, long ago called "Metaphysics", and Book Ζ begins with Aristotle's fundamental doctrine of being.

The greater the power of an electrical appliance, the higher the energy consumption and the cost of using the device. Therefore, manufacturers are constantly improving electrical appliances and lamps. The luminous flux of lamps, measured in lumens, depends on the power, but also on the type of lamp. The greater the luminous flux of a lamp, the brighter its light appears. For people, it is the high brightness that is important, and not the power consumed by the llama, so lately alternatives to incandescent lamps have become increasingly popular. Below are examples of types of lamps, their power and the luminous flux they create.

Do you find it difficult to translate units of measurement from one language to another? Colleagues are ready to help you. Post a question in TCTerms and within a few minutes you will receive an answer.

The Reference section provides explanations of the various terms used to describe technical characteristics equipment that may not be easy for an untrained person to understand.

Differences between "kVA" and "kW"

Often, in the price lists of various manufacturers, the electrical power of equipment is indicated not in the usual kilowatts (kW), but in “mysterious” kVA (kilovolt-amperes). How can a consumer understand how many “kVA” he needs?

There is a concept of active (measured in kW) and apparent power (measured in kVA).

The total power of alternating current is the product of the effective value of the current in the circuit and the effective value of the voltage at its ends. It makes sense to call total power “apparent,” since this power may not all participate in doing work. Total power is the power transmitted by the source, while part of it is converted into heat or does work (active power), the other part is transmitted electromagnetic fields chains - this component is taken into account by introducing the so-called. reactive power.

Total and active power are different physical quantities that have the dimension of power. In order to avoid the need to once again indicate on the labels of various electrical appliances or in technical documentation what power we are talking about, and at the same time not to confuse these physical quantities, volt-amperes are used as a unit of measurement for total power instead of watts.

If we consider the practical value of total power, then this is a value that describes the loads actually imposed by the consumer on the elements of the supply electrical network (wires, cables, distribution boards, transformers, power lines, generator sets...), since these loads depend on the current consumed, and not from the energy actually used by the consumer. This is why the power rating of transformers and distribution boards is measured in volt-amperes rather than watts.

The ratio of active power to apparent power of a circuit is called power factor.

Power factor (cos phi) is a dimensionless physical quantity that characterizes the consumer of alternating electric current from the point of view of the presence of a reactive component in the load. Power factor shows how much the alternating current flowing through a load is out of phase relative to the voltage applied to it.

Numerically, the power factor is equal to the cosine of this phase shift.

Power factor values:

Most manufacturers define the power consumption of their equipment in watts.

If the consumer does not have reactive power (heating devices such as a kettle, boiler, incandescent lamp, heating element), information about the power factor is irrelevant, since it is equal to unity. That is, in this case, the total power consumed by the device and required for its operation is equal to the active power in Watts.

P = I*U* С os (fi) →

P = I * U *1 →

P=I*U

Example: The data sheet for an electric kettle indicates the power consumption is 2 kW. This means that the total power required for the successful operation of the device will be 2 kVA.

If the consumer is a device that contains reactance (capacitance, inductance), the technical data always indicates the power in Watts and the power factor value for this device. This value is determined by the parameters of the device itself, and specifically by the ratio of its active and reactive resistances.

Example: The technical data sheet of a rotary hammer indicates power consumption - 5 kW and power factor (Cos(fi)) - 0.85. This means that the total power required for its operation will be

P total= Pact./Cos(fi)

P full = 5/0.85 = 5.89 kVA

When choosing a generator set, a reasonable question often arises: “How much power can it still produce?” This is due to the fact that the characteristics of generator sets indicate the apparent power in kVA. This article is the answer to this question.

Example: 100 kVA generator set. If consumers have only active resistance, then kVA = kW. If a reactive component is also present, then the load power factor must be taken into account.

That is why the specifications of generator sets indicate the apparent power in kVA. And how you will use it is up to you to decide.