The most common unit of measurement on the electricity meter is the kilowatt hour, which is equal to the amount of energy used by a load of one kilowatt over a period of one hour, or 3,600,000 joules. Some electricity companies use the SI megajoule instead. Panel-mounted solid-state electricity meter, connected to 2MVA three-phase electricity substation. ... Panel-mounted solid-state electricity meter, connected to 2MVA three-phase electricity substation. ... In electronics, solid state circuits are those that do not contain vacuum tubes. ... Usually hidden to the unaided eye, the 60Hz blinking of (non-incandescent) lighting powered by AC mains is revealed in this motion-blurred long exposure of city lights. ... A 115 kV to 41. ... For other uses, see Modem (disambiguation). ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... The kilowatt-hour (symbol: kW·h) is a unit for measuring energy. ... The kilowatt (symbol: kW) is a unit for measuring power, equal to one thousand watts. ... The hour (symbol: h) is a unit of time. ... The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... Look up si, Si, SI in Wiktionary, the free dictionary. ... A megajoule (abbreviation: MJ) is a unit of energy equal to 1000000 joules. ...
Demand is normally measured in watts, but averaged over a period, most often a quarter or half hour.
Reactive power is measured in "Volt-amperes reactive", (VARh) in kilovar-hours. A "lagging" or inductive load, such as a motor, will have negative reactive power. A "leading", or capacitive load, will have positive reactive power. Reactive power is an abstract quantity, typically used by power engineers to describe a certain type of energy flow in an electric distribution system. ... volt-amperes reactive (VAR): In alternating-current power transmission and distribution, the product of the rms voltage and current, the apparent power, multiplied by the sine of the phase angle between the voltage and the current. ... An electric current i flowing around a circuit produces a magnetic field and hence a magnetic flux Φ through the circuit. ... Various types of capacitors A capacitor is a device that stores energy in the electric field created between a pair of conductors on which equal but opposite electric charges have been placed. ...
Volt-amperes measures all power passed through a distribution network, including reactive and actual. This is equal to the product of root-mean-square volts and amperes.
Distortion of the electric current by loads is measured in several ways. Power factor is the ratio of resistive (or real power) to volt-amperes. A capacitive load has a leading power factor, and an inductive load has a lagging power factor. A purely resistive load (such as a fillament lamp, heater or kettle) exhibits a power factor of 1. Current harmonics are a measure of distortion of the wave form. For example, electronic loads such as computer power supplies draw their current at the voltage peak to fill their internal storage elements. This can lead to a significant voltage drop near the supply voltage peak which shows as a flattening of the voltage waveform. This flattening causes odd harmonics which are not permissible if they exceed specific limits, as they are not only wasteful, but may interfere with the operation of other equipment. Harmonic emissions are mandated by law in EU and other countries to fall within specified limits. The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power, and is a number between 0 and 1. ...
Other units of measurement
In addition to metering based on the amount of energy used, other types of metering are available.
Meters which measured the amount of charge (coulombs) used, known as ampere-hour meters, were used in the early days of electrification. These were dependent upon the supply voltage remaining constant for accurate measurement of energy usage, which was not a likely circumstance with most supplies. The coulomb (symbol: C) is the SI unit of electric charge. ... An ampere-hour (abbreviated as Ah or A-h) is a unit of electric charge. ...
Some meters measured only the length of time for which current flowed, with no measurement of the magnitude of voltage or current being made. These were only suited for constant load applications.
Neither type is likely to be used today.
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