**Electric power** is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second.

- Definition
- Explanation
- Passive devices (loads)
- Active devices (power sources)
- Passive sign convention
- Resistive circuits
- Alternating current without harmonics
- Electromagnetic fields
- Production
- Generation
- Electric power industry
- Use
- See also
- References
- Bibliography
- External links

Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries. It is usually supplied to businesses and homes (as domestic mains electricity) by the electric power industry through an electric power grid.

Electric power can be delivered over long distances by transmission lines and used for applications such as motion, light or heat with high efficiency.^{ [1] }

Electric power, like mechanical power, is the rate of doing work, measured in watts, and represented by the letter *P*. The term *wattage* is used colloquially to mean "electric power in watts." The electric power in watts produced by an electric current *I* consisting of a charge of *Q* coulombs every *t* seconds passing through an electric potential (voltage) difference of *V* is

where

*Q*is electric charge in coulombs*t*is time in seconds*I*is electric current in amperes*V*is electric potential or voltage in volts

Electric power is transformed to other forms of energy when electric charges move through an electric potential difference (voltage), which occurs in electrical components in electric circuits. From the standpoint of electric power, components in an electric circuit can be divided into two categories:

When electric charges move through a potential difference from a higher to a lower voltage, that is when conventional current (positive charge) moves from the positive (+) terminal to the negative (−) terminal, work is done by the charges on the device. The potential energy of the charges due to the voltage between the terminals is converted to kinetic energy in the device. These devices are called * passive * components or *loads*; they 'consume' electric power from the circuit, converting it to other forms of energy such as mechanical work, heat, light, etc. Examples are electrical appliances, such as light bulbs, electric motors, and electric heaters. In alternating current (AC) circuits the direction of the voltage periodically reverses, but the current always flows from the higher potential to the lower potential side.

If the charges are moved by an 'exterior force' through the device in the direction from the lower electric potential to the higher, (so positive charge moves from the negative to the positive terminal), work will be done *on* the charges, and energy is being converted to electric potential energy from some other type of energy, such as mechanical energy or chemical energy. Devices in which this occurs are called * active * devices or *power sources*; such as electric generators and batteries. Some devices can be either a source or a load, depending on the voltage and current through them. For example, a rechargeable battery acts as a source when it provides power to a circuit, but as a load when it is connected to a battery charger and is being recharged.

Since electric power can flow either into or out of a component, a convention is needed for which direction represents positive power flow. Electric power flowing *out* of a circuit *into* a component is arbitrarily defined to have a positive sign, while power flowing *into* a circuit from a component is defined to have a negative sign. Thus passive components have positive power consumption, while power sources have negative power consumption. This is called the * passive sign convention *.

In the case of resistive (Ohmic, or linear) loads, Joule's law can be combined with Ohm's law (*V* = *I·R*) to produce alternative expressions for the amount of power that is dissipated:

where *R* is the electrical resistance.

In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of energy flow (power) that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power (also referred to as active power).^{ [2] } The amplitude of that portion of energy flow (power) that results in no net transfer of energy but instead oscillates between the source and load in each cycle due to stored energy, is known as the absolute value of reactive power.^{ [2] }^{ [3] }^{ [4] } The product of the RMS value of the voltage wave and the RMS value of the current wave is known as apparent power. The real power * P* in watts consumed by a device is given by

where

**V**_{p}is the peak voltage in volts**I**_{p}is the peak current in amperes**V**_{rms}is the root-mean-square voltage in volts**I**_{rms}is the root-mean-square current in amperesis the phase angle by which the voltage sine wave leads the current sine wave, or equivalently the phase angle by which the current sine wave lags the voltage sine wave**θ = θ**_{v}- θ_{i}

The relationship between real power, reactive power and apparent power can be expressed by representing the quantities as vectors. Real power is represented as a horizontal vector and reactive power is represented as a vertical vector. The apparent power vector is the hypotenuse of a right triangle formed by connecting the real and reactive power vectors. This representation is often called the *power triangle*. Using the Pythagorean Theorem, the relationship among real, reactive and apparent power is:

Real and reactive powers can also be calculated directly from the apparent power, when the current and voltage are both sinusoids with a known phase angle θ between them:

The ratio of real power to apparent power is called power factor and is a number always between −1 and 1. Where the currents and voltages have non-sinusoidal forms, power factor is generalized to include the effects of distortion.

Electrical energy flows wherever electric and magnetic fields exist together and fluctuate in the same place. The simplest example of this is in electrical circuits, as the preceding section showed. In the general case, however, the simple equation *P* = *IV* may be replaced by a more complex calculation. The closed surface integral of the cross-product of the electric field intensity and magnetic field intensity vectors gives the total instantaneous power (in watts) *out of* the volume: ^{ [5] }

The result is a scalar since it is the * surface integral * of the * Poynting vector *.

The electric power industry provides the production and delivery of power, in sufficient quantities to areas that need electricity, through a grid connection. The grid distributes electrical energy to customers. Electric power is generated by central power stations or by distributed generation. The electric power industry has gradually been trending towards deregulation – with emerging players offering consumers competition to the traditional public utility companies.^{ [9] }

Electric power, produced from central generating stations and distributed over an electrical transmission grid, is widely used in industrial, commercial and consumer applications. The per capita electric power consumption of a country correlates with its industrial development. ^{ [10] } Electric motors power manufacturing machinery and propel subways and railway trains. Electric lighting is the most important form of artificial light. Electrical energy is used directly in processes such as extraction of aluminum from its ores and in production of steel in electric arc furnaces. Reliable electric power is essential to telecommunications and broadcasting. Electric power is used to provide air conditioning in hot climates, and in some places electric power is an economically competitive source of energy for building space heating. Use of electric power for pumping water ranges from individual household wells to irrigation projects and energy storage projects.

**Electricity** is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others.

An **electrochemical cell** is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic or galvanic cells and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells. A common example of a galvanic cell is a standard 1.5 volt cell meant for consumer use. A *battery* consists of one or more cells, connected in parallel, series or series-and-parallel pattern.

**Voltage**, **electric potential difference**, **electromotive force (emf), electric pressure **or **electric tension** is the difference in electric potential between two points, which is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage is named *volt*. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule per 1 coulomb. The old SI definition for *volt* used power and current; starting in 1990, the quantum Hall and Josephson effect were used, and recently (2019) fundamental physical constants have been introduced for the definition of all SI units and derived units. Voltage or electric potential difference is denoted symbolically by ∆*V*, simplified *V*, or *U*, for instance in the context of Ohm's or Kirchhoff's circuit laws.

In electrical engineering, the **power factor** of an AC power system is defined as the ratio of the *real power* absorbed by the load to the *apparent power* flowing in the circuit, and is a dimensionless number in the closed interval of −1 to 1. A power factor of less than one indicates the voltage and current are not in phase, reducing the average product of the two. Real power is the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of RMS current and voltage. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power. A negative power factor occurs when the device generates power, which then flows back towards the source.

In electrical engineering, **electrical impedance** is the measure of the opposition that a circuit presents to a current when a voltage is applied.

**Direct current** (**DC**) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was **galvanic current**.

**Ohm's law** states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

In electromagnetism and electronics, **electromotive force** is the electrical action produced by a non-electrical source. Devices provide an emf by converting other forms of energy into electrical energy, such as batteries or generators. Sometimes an analogy to water pressure is used to describe electromotive force..

In electric and electronic systems, **reactance** is the opposition of a circuit element to the flow of current due to that element's inductance or capacitance. Greater reactance leads to smaller currents for the same voltage applied. Reactance is similar to electric resistance in this respect, but differs in that reactance does not lead to dissipation of electrical energy as heat. Instead, energy is stored in the reactance, and a quarter-cycle later returned to the circuit, whereas a resistance continuously loses energy.

The **output impedance** of an electrical network is the measure of the opposition to current flow (impedance), both static (resistance) and dynamic (reactance), into the load network being connected that is *internal* to the electrical source. The output impedance is a measure of the source's propensity to drop in voltage when the load draws current, the source network being the portion of the network that transmits and the load network being the portion of the network that consumes.

In power engineering, the **power-flow study**, or **load-flow study**, is a numerical analysis of the flow of electric power in an interconnected system. A power-flow study usually uses simplified notations such as a one-line diagram and per-unit system, and focuses on various aspects of AC power parameters, such as voltages, voltage angles, real power and reactive power. It analyzes the power systems in normal steady-state operation.

In physics and engineering, a **phasor**, is a complex number representing a sinusoidal function whose amplitude (*A*), angular frequency (*ω*), and initial phase (*θ*) are time-invariant. It is related to a more general concept called analytic representation, which decomposes a sinusoid into the product of a complex constant and a factor depending on time and frequency. The complex constant, which depends on amplitude and phase, is known as a **phasor**, or **complex amplitude**, and **sinor** or even **complexor**.

**Instantaneous power** in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductors and capacitors may result in periodic reversals of the direction of energy flow.

The **wattmeter** is an instrument for measuring the electric active power in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements.

A **capacitor** is a device that stores electrical energy in an electric field. It is a passive electronic component with two terminals.

A **battery** is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices such as flashlights, mobile phones, and electric cars. When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode. The terminal marked negative is the source of electrons that will flow through an external electric circuit to the positive terminal. When a battery is connected to an external electric load, a redox reaction converts high-energy reactants to lower-energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Historically the term "battery" specifically referred to a device composed of multiple cells, however the usage has evolved to include devices composed of a single cell.

A **permanent magnet synchronous generator** is a generator where the excitation field is provided by a permanent magnet instead of a coil. The term synchronous refers here to the fact that the rotor and magnetic field rotate with the same speed, because the magnetic field is generated through a shaft mounted permanent magnet mechanism and current is induced into the stationary armature.

**Leading and lagging current** are phenomena that occur as a result of alternating current. In a circuit with alternating current, the value of voltage and current vary sinusoidally. In this type of circuit, the terms *lead, lag,* and *in phase* are used to describe current with reference to voltage. Current is in phase with voltage when there is no phase shift between the sinusoids describing their time varying behavior. This generally occurs when the load drawing the current is resistive.

In electrical engineering, the **passive sign convention** (**PSC**) is a sign convention or arbitrary standard rule adopted universally by the electrical engineering community for defining the sign of electric power in an electric circuit. The convention defines electric power flowing out of the circuit *into* an electrical component as positive, and power flowing into the circuit *out* of a component as negative. So a passive component which consumes power, such as an appliance or light bulb, will have *positive* power dissipation, while an active component, a source of power such as an electric generator or battery, will have *negative* power dissipation. This is the standard definition of power in electric circuits; it is used for example in computer circuit simulation programs such as SPICE.

*Most of the terms listed in Wikipedia glossaries are already defined and explained within Wikipedia itself. However, glossaries like this one are useful for looking up, comparing and reviewing large numbers of terms together. You can help enhance this page by adding new terms or writing definitions for existing ones.*

- ↑ Smith, Clare (2001).
*Environmental Physics*. London: Routledge. ISBN 0-415-20191-8. - 1 2 Thomas, Roland E.; Rosa, Albert J.; Toussaint, Gregory J. (2016).
*The Analysis and Design of Linear Circuits*(8 ed.). Wiley. pp. 812–813. ISBN 978-1-119-23538-5. - ↑ Fraile Mora, Jesús (2012).
*Circuitos eléctricos*(in Spanish). Pearson. pp. 193–196. ISBN 978-8-48-322795-4. - ↑ "IEEE Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions". IEEE. 2010. p. 4. doi:10.1109/IEEESTD.2010.5439063. ISBN 978-0-7381-6058-0.
- ↑ Hayt, William H.; Buck, John A. (2012).
*Engineering Electromagnetics*(8 ed.). McGraw-Hill. p. 385. ISBN 978-0-07-338066-7. - ↑ "Electricity". International Energy Agency. 2020. Data Browser section, Electricity Generation by Source indicator. Retrieved 17 July 2021.
- ↑ "battery" (def. 4b),
*Merriam-Webster Online Dictionary*(2009). Retrieved 25 May 2009. - ↑ Power Shift: DFJ on the lookout for more power source investments Archived 2005-12-01 at the Wayback Machine .
*Draper Fisher Jurvetson*. Retrieved 20 November 2005. - ↑ The Opportunity of Energy Group-Buying
*EnPowered*, April 18, 2016, - ↑ Ignacio J. Pérez-Arriaga (ed),
*Regulation of the Power Sector*, Springer Science & Business Media, 2014 ISBN 1447150341, page 8

- Reports on August 2003 Blackout, North American Electric Reliability Council website
- Croft, Terrell; Summers, Wilford I. (1987).
*American Electricians' Handbook*(Eleventh ed.). New York: McGraw Hill. ISBN 0-07-013932-6. - Fink, Donald G.; Beaty, H. Wayne (1978).
*Standard Handbook for Electrical Engineers*(Eleventh ed.). New York: McGraw Hill. ISBN 0-07-020974-X.

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