North American domestic analog electricity meter.
Electricity meter with transparent plastic case (Israel)
North American domestic electronic electricity meter
An electricity meter, electric meter, electrical meter, energy meter, or kilowatt-hour meter is a device that measures the amount of
electric energy
Electrical energy is energy related to forces on electrically charged particles and the movement of electrically charged particles (often electrons in wires, but not always). This energy is supplied by the combination of electric current and electr ...
consumed by a
residence
A residence is a place (normally a building) used as a home or dwelling, where people reside.
Residence may more specifically refer to:
* Domicile (law), a legal term for residence
* Habitual residence, a civil law term dealing with the status ...
, a
business
Business is the practice of making one's living or making money by producing or Trade, buying and selling Product (business), products (such as goods and Service (economics), services). It is also "any activity or enterprise entered into for pr ...
, or an electrically powered device.
Electric meter or energy meter measures the total power consumed over a time interval.
Electric utilities
An electric utility is a company in the electric power industry (often a public utility) that engages in electricity generation and distribution of electricity for sale generally in a regulated market. The electrical utility industry is a major pr ...
use electric meters installed at customers' premises for
billing and monitoring purposes. They are typically calibrated in billing units, the most common one being the
kilowatt hour
A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...
(''kWh''). They are usually read once each billing period.
When energy savings during certain periods are desired, some meters may measure demand, the maximum use of power in some interval. "Time of day" metering allows electric rates to be changed during a day, to record usage during peak high-cost periods and off-peak, lower-cost, periods. Also, in some areas meters have relays for
demand response
Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. Until the 21st century decrease in the cost of pumped storage and batteries electric energy could not be ...
load shedding during peak load periods.
History
Direct current
An Aron type DC electricity meter showing that the calibration was in charge consumed rather than energy
As commercial use of electric energy spread in the 1880s, it became increasingly important that an electric energy meter, similar to the then existing
gas meter
A gas meter is a specialized flow meter, used to measure the volume of fuel gases such as natural gas and liquefied petroleum gas. Gas meters are used at residential, commercial, and industrial buildings that consume fuel gas supplied by a gas ...
s, was required to properly bill customers, instead of billing for a fixed number of lamps per month.
DC meters measured
charge
Charge or charged may refer to:
Arts, entertainment, and media Films
* ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary
Music
* ''Charge'' (David Ford album)
* ''Charge'' (Machel Montano album)
* ''Charge!!'', an album by The Aqua ...
in ampere hours. Since the voltage of the supply should remain substantially constant, the reading of the meter was proportional to actual energy consumed. For example, if a meter recorded that 100 ampere hours had been consumed on a 200-volt supply, then 20 kilowatt-hours of energy had been supplied.
Many experimental types of meter were developed.
Thomas Edison
Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventio ...
at first worked on a
direct current
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 ...
(DC) electromechanical meter with a direct reading register, but instead developed an
electrochemical
Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...
metering system, which used an
electrolytic cell
An electrolytic cell is an electrochemical cell that utilizes an external source of electrical energy to force a chemical reaction that would not otherwise occur. The external energy source is a voltage applied between the cell′s two electrod ...
to totalise current consumption. At periodic intervals the plates were removed and weighed, and the customer billed. The electrochemical meter was labor-intensive to read and not well received by customers.
left, A 'Reason' meter
An early type of electrochemical meter used in the United Kingdom was the 'Reason' meter. This consisted of a vertically mounted glass structure with a mercury reservoir at the top of the meter. As current was drawn from the supply, electrochemical action transferred the mercury to the bottom of the column. Like all other DC meters, it recorded ampere hours. Once the mercury pool was exhausted, the meter became an open circuit. It was therefore necessary for the consumer to pay for a further supply of electricity, whereupon, the supplier's agent would unlock the meter from its mounting and invert it restoring the mercury to the reservoir and the supply. In practice the consumer would get the supply company's agent in before the supply ran out and pay only for the charge consumed as read from the scale. The agent would then reset the meter to zero by inverting it.
In 1885
Ferranti
Ferranti or Ferranti International plc was a UK electrical engineering and equipment firm that operated for over a century from 1885 until it went bankrupt in 1993. The company was once a constituent of the FTSE 100 Index.
The firm was known ...
offered a mercury motor meter with a register similar to gas meters; this had the advantage that the consumer could easily read the meter and verify consumption. The first accurate, recording electricity consumption meter was a
DC meter by
Dr Hermann Aron, who patented it in 1883.
Hugo Hirst
Hugo Hirst, 1st Baron Hirst (26 November 1863 – 22 January 1943), known as Sir Hugo Hirst, Bt, between 1925 and 1934, was a German-born British industrialist.
Born near Munich, Hugo Hirsch became a naturalized British subject in 1883 and change ...
of the British
General Electric Company
The General Electric Company (GEC) was a major British industrial conglomerate involved in consumer and defence electronics, communications, and engineering. The company was founded in 1886, was Britain's largest private employer with over 250 ...
introduced it commercially into Great Britain from 1888.
Aron's meter recorded the total charge used over time, and showed it on a series of clock dials.
Alternating current
The first specimen of the
AC kilowatt-hour meter produced on the basis of Hungarian
Ottó Bláthy
Ottó Titusz Bláthy (11 August 1860 – 26 September 1939) was a Hungarian electrical engineer. In his career, he became the co-inventor of the modern electric transformer, the tension regulator, the AC watt-hour meter. motor capacitor fo ...
's patent and named after him was presented by the
Ganz
The Ganz Works or Ganz ( or , ''Ganz companies'', formerly ''Ganz and Partner Iron Mill and Machine Factory'') was a group of companies operating between 1845 and 1949 in Budapest, Hungary. It was named after Ábrahám Ganz, the founder and the ...
Works at the Frankfurt Fair in the autumn of 1889, and the first induction kilowatt-hour meter was already marketed by the factory at the end of the same year. These were the first alternating-current watt-hour meters, known by the name of Bláthy-meters. The AC kilowatt hour meters used at present operate on the same principle as Bláthy's original invention.
[ Student paper read on January 24, 1896 at the Students' Meeting.][The Electrical engineer, Volume 5. (February, 1890)] Also around 1889,
Elihu Thomson
Elihu Thomson (March 29, 1853 – March 13, 1937) was an English-born American engineer and inventor who was instrumental in the founding of major electrical companies in the United States, the United Kingdom and France.
Early life
He was born ...
of the American
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
company developed a recording watt meter (watt-hour meter) based on an ironless commutator motor. This meter overcame the disadvantages of the electrochemical type and could operate on either alternating or direct current.
In 1894
Oliver Shallenberger
Oliver Blackburn Shallenberger (May 7, 1860 – January 23, 1898) was an American electrical engineer and inventor. He is associated with electrical inventions related to alternating current. He is most noted for inventing the first successful al ...
of the
Westinghouse Electric Corporation
The Westinghouse Electric Corporation was an American manufacturing company founded in 1886 by George Westinghouse. It was originally named "Westinghouse Electric & Manufacturing Company" and was renamed "Westinghouse Electric Corporation" in ...
applied the induction principle previously used only in AC ampere hour meters to produce a watt-hour meter of the modern electromechanical form, using an induction disk whose rotational speed was made proportional to the power in the circuit. The Bláthy meter was similar to Shallenberger and Thomson meter in that they are two-phase motor meter.
[ Although the induction meter would only work on alternating current, it eliminated the delicate and troublesome commutator of the Thomson design. Shallenberger fell ill and was unable to refine his initial large and heavy design, although he did also develop a polyphase version.
]
Units
Panel-mounted solid state electricity meter, connected to a 2 MVA electricity substation. Remote current and voltage sensors can be read and programmed remotely by and locally by infrared">modem and locally by infrared. The circle with two dots is the infrared port. Tamper-evident seals can be seen">infrared.html" ;"title="modem and locally by infrared">modem and locally by infrared. The circle with two dots is the infrared port. Tamper-evident seals can be seen
The most common unit of measurement on the electricity meter is the kilowatt hour
A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...
[''kWh''], 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.
Demand is normally measured in watts, but averaged over a period, most often a quarter- or half-hour.
Reactive power
Reactive may refer to:
*Generally, capable of having a reaction (disambiguation)
*An adjective abbreviation denoting a bowling ball coverstock made of reactive resin
*Reactivity (chemistry)
*Reactive mind
*Reactive programming
See also
*Reactanc ...
is measured in "thousands of volt-ampere reactive
A volt-ampere ( SI symbol: V⋅A or V A, simplified as VA) is the unit for the apparent power in an electrical circuit. The apparent power equals the product of root mean square voltage (in volts) and root mean square current (in amperes ...
-hours", (kvarh). By convention, a "lagging" or inductive load, such as a motor, will have positive reactive power. A "leading", or capacitive
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of a c ...
load, will have negative reactive power.
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
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. Real power is the average of the instantaneous product of v ...
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 filament 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.
In addition to metering based on the amount of energy used, other types of metering are available. Meters which measured the amount of charge (coulomb
The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI).
In the present version of the SI it is equal to the electric charge delivered by a 1 ampere constant current in 1 second and to elementary char ...
s) 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 most common application was in relation to special-purpose meters to monitor charge / discharge status of large batteries. Some meters measured only the length of time for which charge flowed, with no measurement of the magnitude of voltage or current being made. These are only suited for constant-load applications and are rarely used today.
Operation
Mechanism of electromagnetic induction">induction
Induction, Inducible or Inductive may refer to:
Biology and medicine
* Labor induction (birth/pregnancy)
* Induction chemotherapy, in medicine
* Induced stem cells, stem cells derived from somatic, reproductive, pluripotent or other cell t ...
meter. 1: Voltage coil: many turns of fine wire encased in plastic, connected in parallel with load. 2: Current coil: three turns of thick wire, connected in series with load. 3: Stator: concentrates and confines magnetic field. 4: Aluminum rotor disc. 5: rotor brake magnets. 6: spindle with worm gear. 7: display dials: the 1/10, 10 and 1000 dials rotate clockwise while the 1, 100 and 10000 dials rotate counterclockwise
Electricity meters operate by continuously measuring the instantaneous voltage (volts) and current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
(amperes) to give energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
used (in joules
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. ...
, kilowatt-hours etc.). Meters for smaller services (such as small residential customers) can be connected directly in-line between source and customer. For larger loads, more than about 200 ampere of load, current transformer
A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.
Current transformers, along with volt ...
s are used, so that the meter can be located somewhere other than in line with the service conductors. The meters fall into two basic categories, electromechanical and electronic.
Electromechanical
The most common type of electricity meter is the electromechanical
In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems ...
watt-hour meter.
On a single-phase
In electrical engineering, single-phase electric power (abbreviated 1φ) is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when load ...
AC supply, the electromechanical induction meter operates through electromagnetic induction
Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field.
Michael Faraday is generally credited with the discovery of induction in 1831, and James Clerk ...
by counting the revolutions of a non-magnetic, but electrically conductive, metal disc which is made to rotate at a speed proportional to the power passing through the meter. The number of revolutions is thus proportional to the energy usage. The voltage coil consumes a small and relatively constant amount of power, typically around 2 watts which is not registered on the meter. The current coil similarly consumes a small amount of power in proportion to the square of the current flowing through it, typically up to a couple of watts at full load, which is registered on the meter.
The disc is acted upon by two sets of induction coil
An induction coil or "spark coil" (archaically known as an inductorium or Ruhmkorff coil after Heinrich Rühmkorff) is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current (DC) supply. p.98 To ...
s, which form, in effect, a two phase linear induction motor
A linear induction motor (LIM) is an alternating current (AC), asynchronous linear motor that works by the same general principles as other induction motors but is typically designed to directly produce motion in a straight line. Characteristic ...
. One coil is connected in such a way that it produces a magnetic flux
In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the weber ( ...
in proportion to the voltage and the other produces a magnetic flux in proportion to the current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
. The field of the voltage coil is delayed by 90 degrees, due to the coil's inductive nature, and calibrated using a lag coil. This produces eddy current
Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a mag ...
s in the disc and the effect is such that a force
In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...
is exerted on the disc in proportion to the product of the instantaneous current and instantaneous voltage. A permanent magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...
acts as an eddy current brake
An eddy current brake, also known as an induction brake, electric brake or electric retarder, is a device used to slow or stop a moving object by generating eddy currents and thus dissipating its kinetic energy as heat. Unlike friction brakes, wh ...
, exerting an opposing force proportional to the speed of rotation
Rotational frequency (also known as rotational speed or rate of rotation) of an object rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second (cps), etc.
The symbol for ...
of the disc. The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power or rate of energy usage. The disc drives a register mechanism which counts revolutions, much like the odometer
An odometer or odograph is an instrument used for measuring the distance traveled by a vehicle, such as a bicycle or car. The device may be electronic, mechanical, or a combination of the two (electromechanical). The noun derives from ancient Gr ...
in a car, in order to render a measurement of the total energy used.
Different phase configurations use additional voltage and current coils.
Three-phase electromechanical induction meter, metering 100 A 240/415 V supply. Horizontal aluminium rotor disc is visible in centre of meter
The disc is supported by a spindle which has a worm gear
A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm wheel (which is similar in appearance to a spur gear). The two elements are also called the worm screw and worm gear. The terminolo ...
which drives the register. The register is a series of dials which record the amount of energy used. The dials may be of the ''cyclometer'' type, an odometer-like display that is easy to read where for each dial a single digit is shown through a window in the face of the meter, or of the pointer type where a pointer indicates each digit. With the dial pointer type, adjacent pointers generally rotate in opposite directions due to the gearing mechanism.
The amount of energy represented by one revolution of the disc is denoted by the symbol Kh which is given in units of watt-hours per revolution. The value 7.2 is commonly seen. Using the value of Kh one can determine their power consumption at any given time by timing the disc with a stopwatch.
.
Where:
:: = time in seconds taken by the disc to complete one revolution,
:: = power in watts.
For example, if = 7.2 as above, and one revolution took place in 14.4 seconds, the power is 1800 watts. This method can be used to determine the power consumption of household devices by switching them on one by one.
Most domestic electricity meters must be read manually, whether by a representative of the power company
An electric utility is a company in the electric power industry (often a public utility) that engages in electricity generation and distribution of electricity for sale generally in a regulated market. The electrical utility industry is a major pr ...
or by the customer. Where the customer reads the meter, the reading may be supplied to the power company by telephone
A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
, post
Post or POST commonly refers to:
*Mail, the postal system, especially in Commonwealth of Nations countries
**An Post, the Irish national postal service
**Canada Post, Canadian postal service
**Deutsche Post, German postal service
**Iraqi Post, Ira ...
or over the internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
. The electricity company will normally require a visit by a company representative at least annually in order to verify customer-supplied readings and to make a basic safety check of the meter.
In an induction type meter, creep is a phenomenon that can adversely affect accuracy, that occurs when the meter disc rotates continuously with potential applied and the load terminals open circuited. A test for error due to creep is called a creep test.
Two standards govern meter accuracy, ANSI C12.20 {{No footnotes, date=October 2009
ANSI C12.20 is an ANSI
The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processe ...
for North America and IEC 62053.
Electronic
Solid state Danish-made electricity meter used in a home in the ">Netherlands
Electronic meters display the energy used on an LCD
A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but in ...
or LED display, and some can also transmit readings to remote places. In addition to measuring energy used, electronic meters can also record other parameters of the load and supply such as instantaneous and maximum rate of usage demands, voltages, power factor and reactive power
Reactive may refer to:
*Generally, capable of having a reaction (disambiguation)
*An adjective abbreviation denoting a bowling ball coverstock made of reactive resin
*Reactivity (chemistry)
*Reactive mind
*Reactive programming
See also
*Reactanc ...
used etc. They can also support time-of-day billing, for example, recording the amount of energy used during on-peak and off-peak hours.
The meter has a power supply, a metering engine, a processing and communication engine (i.e. a microcontroller
A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable i ...
), and other add-on modules such as a real time clock (RTC), a liquid crystal display, infra red communication ports/modules and so on.
The metering engine is given the voltage and current inputs and has a voltage reference, samplers and quantisers followed by an analog to digital conversion section to yield the digitised equivalents of all the inputs. These inputs are then processed using a digital signal processor
A digital signal processor (DSP) is a specialized microprocessor chip, with its architecture optimized for the operational needs of digital signal processing. DSPs are fabricated on MOS integrated circuit chips. They are widely used in audio si ...
to calculate the various metering parameters.
The largest source of long-term errors in the meter is drift in the preamp, followed by the precision of the voltage reference. Both of these vary with temperature as well, and vary wildly when meters are outdoors. Characterising and compensating for these is a major part of meter design.
The processing and communication section has the responsibility of calculating the various derived quantities from the digital values generated by the metering engine. This also has the responsibility of communication using various protocols and interface with other addon modules connected as slaves to it.
RTC and other add-on modules are attached as slaves to the processing and communication section for various input/output functions. On a modern meter most if not all of this will be implemented inside the microprocessor, such as the RTC, LCD controller, temperature sensor, memory and analog to digital converters.
Communication methods
Remote meter reading is a practical example of telemetry
Telemetry is the in situ data collection, collection of measurements or other data at remote points and their automatic data transmission, transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Gr ...
. It saves the cost of a human meter reader and the resulting mistakes, but it also allows more measurements, and remote provisioning. Many smart meters now include a switch to interrupt or restore service.
Historically, rotating meters could report their metered information remotely, using a pair of electrical contacts
An electrical contact is an electrical circuit component found in electrical switches, relays, connectors and circuit breakers. Each contact is a piece of electrically conductive material, typically metal. When a pair of contacts touch, they ca ...
attached to a ''KYZ'' line.
A KYZ interface is a Form C contact supplied from the meter. In a KYZ interface, the Y and Z wires are switch contacts, shorted to K for a measured amount of energy. When one contact closes the other opens to provide count accuracy security. Each contact change of state is considered one pulse. The frequency of pulses indicates the power demand. The number of pulses indicates energy metered.
The KYZ relay
A relay
Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts
An automotive-style miniature relay with the dust cover taken off
A relay is an electrically operated switch ...
generates pulses. The term KYZ refers to the contact designations: K for common, Y for Normally Open, and Z for Normally Closed. When incorporated into an electrical meter, the relay changes state with each full or half rotation of the meter disc. Each state change is called a "pulse." When connected to external equipment, rate of use (kW) as well as total usage (kWh) can be determined from the rate and number of pulses.
KYZ outputs were historically attached to "totaliser relays" feeding a "totaliser" so that many meters could be read all at once in one place.
KYZ outputs are also the classic way of attaching electricity meters to programmable logic controller
A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity tha ...
s, HVAC
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
s or other control systems. Some modern meters also supply a contact closure that warns when the meter detects a demand near a higher electricity tariff
Electricity pricing (also referred to as electricity tariffs or the price of electricity) can vary widely by country or by locality within a country. Electricity prices are dependent on many factors, such as the price of power generation, gover ...
, to improve demand side management
Energy demand management, also known as demand-side management (DSM) or demand-side response (DSR), is the modification of consumer demand for energy through various methods such as financial incentives and behavioral change through education.
Us ...
.
Some meters have an open collector
An open collector is a common type of output found on many integrated circuits (IC), which behaves like a switch that is either connected to ground or disconnected. Instead of outputting a signal of a specific voltage or current, the output sig ...
or IR LED output that give 32-100 ms pulses for each metered amount of electrical energy, usually 1000-10000 pulses per kWh
A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...
. Output is limited to max 27 V DC and 27 mA DC. These S0-outputs usually follow the DIN 43864 standard.
Many meters designed for semi-automated reading have a serial port
In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. ...
that communicates by infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
LED through the faceplate of the meter. In some multi-unit buildings, a similar protocol is used, but in a wired bus using a serial current loop
In electrical signalling an analog current loop is used where a device must be monitored or controlled remotely over a pair of conductors. Only one current level can be present at any time.
A major application of current loops is the industry de ...
to connect all the meters to a single plug. The plug is often near a more easily accessible point.
In the European Union, the most common infrared and protocol is "FLAG", a simplified subset of mode C of IEC 61107. In the United States and Canada, the favoured infrared protocol is ANSI C12.18
A smart meter is an electronic device that records information such as consumption of electric energy, voltage levels, current, and power factor. Smart meters communicate the information to the consumer for greater clarity of consumption beha ...
. Some industrial meters use a protocol for programmable logic controller
A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity tha ...
s (Modbus
Modbus is a data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Modbus has become a ''de facto'' standard communication protocol and is now a commonl ...
or DNP3
Distributed Network Protocol 3 (DNP3) is a set of communications protocols used between components in process automation systems. Its main use is in utilities such as electric and water companies. Usage in other industries is not common. It was d ...
).
One protocol proposed for this purpose is DLMS/COSEM which can operate over any medium, including serial ports. The data can be transmitted by Zigbee
Zigbee is an IEEE 802.15.4-based specification for a suite of high-level communication protocols used to create personal area networks with small, low-power digital radios, such as for home automation, medical device data collection, and othe ...
, Wi-Fi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wave ...
, telephone line
A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or ot ...
s or over the power lines themselves. Some meters can be read over the internet. Other more modern protocols are also becoming widely used, like OSGP (Open Smart Grid Protocol).
Electronic meters now use low-power radio, GSM
The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such as ...
, GPRS
General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Insti ...
, Bluetooth
Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is limi ...
, IrDA
The Infrared Data Association (IrDA) is an industry-driven interest group that was founded in 1994 by around 50 companies. IrDA provides specifications for a complete set of protocols for wireless infrared communications, and the name "IrDA" also ...
, as well as RS-485
RS-485, also known as TIA-485(-A) or EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The st ...
wired link. The meters can store the entire usage profiles with timestamps and relay them at the click of a button. The demand readings stored with the profiles accurately indicate the load requirements of the customer. This load profile
In electrical engineering, a load profile is a graph of the variation in the electrical load versus time. A load profile will vary according to customer type (typical examples include residential, commercial and industrial), temperature and holi ...
data is processed at the utilities for billing and planning purposes.
''AMR'' ( Automatic Meter Reading) and ''RMR'' (Remote Meter Reading) describe various systems that allow meters to be checked remotely, without the need to send a meter reader. An electronic meter can transmit its readings by telephone line or radio to a central billing office.
Monitoring and billing methods
Commercial uses
Large commercial and industrial premises may use electronic meters which record power usage in blocks of half an hour or less. This is because most electricity grid
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
s have demand surges throughout the day, and the power company may wish to give price incentives to large customers to reduce demand at these times. These demand surges often correspond to meal times or, famously, to advertisements interrupting popular television programme
A television show – or simply TV show – is any content produced for viewing on a television set which can be broadcast via over-the-air, satellite, or cable, excluding breaking news, advertisements, or trailers that are typically placed betw ...
s.
Home energy monitoring
A potentially powerful means to reduce household energy consumption is to provide convenient real-time feedback to users so they can change their energy using behaviour. Recently, low-cost energy feedback displays have become available, that may be able to measure energy (Watt-hours), momentary power (wattage), and may additionally be able to measure the MAINS voltage, current, uptime, apparent power Apparent may refer to:
*Apparent magnitude, a measure of brightness of a celestial body as seen by an observer on Earth
* Apparent places, the actual coordinates of stars as seen from Earth
*Heir apparent, a person who is first in line of successi ...
, capturing peak wattage and peak current, and have a manually set clock. The display may indicate the power consumption over the week graphically.
A study using a consumer-readable meter in 500 Ontario homes by ''Hydro One
Hydro One Limited is an electricity transmission and distribution utility serving the Canadian province of Ontario. Hydro One traces its history to the early 20th century and the establishment of the Hydro-Electric Power Commission of Ontario ( ...
'' showed an average 6.5% drop in total electricity use when compared with a similarly sized control group. ''Hydro One'' subsequently offered free power monitors to 30,000 customers based on the success of the pilot. Projects such as Google PowerMeter
Google PowerMeter was a software project of Google's philanthropic arm, Google.org, to help consumers track their home electricity usage. The development of the software was part of an effort by Google to invest in renewable energy, electricity g ...
, take information from a smart meter and make it more readily available to users to help encourage conservation.
Plug-in electricity meters (or plug load meters) measure energy used by individual appliances. There are a variety of models available on the market today but they all work on the same basic principle. The meter is plugged into an outlet, and the appliance to be measured is plugged into the meter. Such meters can help in energy conservation
Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively (using less energy for continuous service) or changing one's behavior to use less service (f ...
by identifying major energy users, or devices that consume excessive standby power
Standby power, also called vampire power, vampire draw, phantom load, ghost load or leaking electricity ("phantom load" and " leaking electricity" are defined technical terms with other meanings, adopted for this different purpose), refers to ...
. Web resources can also be used, if an estimate of the power consumption is enough for the research purposes. A power meter can often be borrowed from the local power authorities or a local public library.
Multiple tariff
Electricity retailers may wish to charge customers different tariffs at different times of the day to better reflect the costs of generation and transmission. Since it is typically not cost effective to store significant amounts of electricity during a period of low demand for use during a period of high demand, costs will vary significantly depending on the time of day. Low cost generation capacity (baseload) such as nuclear can take many hours to start, meaning a surplus in times of low demand, whereas high cost but flexible generating capacity (such as gas turbines) must be kept available to respond at a moment's notice (spinning reserve) to peak demand, perhaps being used for a few minutes per day, which is very expensive.
Some multiple tariff meters use different tariffs for different amounts of demand. These are usually industrial meters.
Domestic variable-rate meters generally permit two to three tariffs ("peak", "off-peak" and "shoulder") and in such installations a simple electromechanical time switch may be used. Historically, these have often been used in conjunction with electrical storage heater
A storage heater or heat bank (Australia) is an electrical heater which thermal energy storage, stores thermal energy during the evening, or at night when electricity is available at lower cost, and releases the heat during the day as required. ...
s or hot water storage
A hot water storage tank (also called a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder) is a water tank used for storing hot water for space heating or domestic use.
Water is a con ...
systems.
Multiple tariffs are made easier by time of use (TOU) meters which incorporate or are connected to a time switch
A time switch (also called a timer switch, or simply timer) is a timer that operates an electric switch controlled by the timing mechanism.
Intermatic introduced its first time switch in 1945, which was used for "electric signs, store window light ...
and which have multiple registers.
Switching between the tariffs may happen via ripple control, or via a radio-activated switch. In principle, a sealed time switch can also be used, but is considered more vulnerable to tampering to obtain cheaper electricity.
Meter and Teleswitcher">Economy 7 Meter and Teleswitcher
Radio-activated switching is common in the UK, with a nightly data signal sent within the longwave carrier of BBC Radio 4
BBC Radio 4 is a British national radio station owned and operated by the BBC that replaced the BBC Home Service in 1967. It broadcasts a wide variety of spoken-word programmes, including news, drama, comedy, science and history from the BBC' ...
, 198 kHz. The time of off-peak charging is usually seven hours between midnight and 7:00am GMT/BST, and this is designed to power storage heater
A storage heater or heat bank (Australia) is an electrical heater which thermal energy storage, stores thermal energy during the evening, or at night when electricity is available at lower cost, and releases the heat during the day as required. ...
s and immersion heater
Electric heating is a process in which electrical energy is converted directly to heat energy at around 100% efficiency, using rather cheap devices. Common applications include space heating, cooking, water heating and industrial processes. A ...
s. In the UK, such tariffs are typically branded ''Economy 7
Economy 7 is the name of a differential tariff provided by United Kingdom electricity suppliers that uses base load generation to provide cheap off-peak electricity during the night.
Houses using the Economy 7 tariff require a special electricity ...
'', ''White Meter'' or ''Dual-Rate''. The popularity of such tariffs has declined in recent years, at least in the domestic market, because of the (perceived or real) deficiencies of storage heaters and the comparatively much lower cost of natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
per kWh (typically a factor of 3-5 times lower). Nevertheless, a sizeable number of properties do not have the option of gas, with many in rural areas being outside the gas supply network, and others being expensive upfront to upgrade to a radiator system.
An Economy 10
Economy 10 is the name of a tariff provided by United Kingdom electricity suppliers created in 2004. Similar to the Economy 7 this is designed to be used with high thermal mass heating such as storage heaters, underfloor heating, and is also used w ...
meter is also available, which gives 10 hours of cheap off-peak electricity spread out over three timeslots throughout a 24-hour period. This allows multiple top-up boosts to storage heaters, or a good spread of times to run a wet electric heating system on a cheaper electricity rate.
Most meters using ''Economy 7
Economy 7 is the name of a differential tariff provided by United Kingdom electricity suppliers that uses base load generation to provide cheap off-peak electricity during the night.
Houses using the Economy 7 tariff require a special electricity ...
'' switch the entire electricity supply to the cheaper rate during the 7 hour night time period, not just the storage heater circuit. The downside of this is that the daytime rate per kWh is significantly higher, and that standing charges are sometimes higher. For example, as of July 2017, normal ("single rate") electricity costs 17.14p per kWh in the London region on the standard default tariff for EDF Energy (the post-privatisation incumbent electricity supplier in London), with a standing charge of 18.90p per day. The equivalent Economy 7
Economy 7 is the name of a differential tariff provided by United Kingdom electricity suppliers that uses base load generation to provide cheap off-peak electricity during the night.
Houses using the Economy 7 tariff require a special electricity ...
costs are 21.34p per kWh during the peak usage period with 7.83p per kWh during the off-peak usage period, and a standing charge of 18.90p per day. Timer switches installed on washing machine
A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...
s, tumble dryer
A clothes dryer, also known as tumble dryer or simply dryer, is a powered household appliance that is used to remove moisture from a load of clothing, bedding and other textiles, usually shortly after they are washed in a washing machine.
Many dry ...
s, dishwasher
A dishwasher is a machine that is used to clean dishware, cookware, and cutlery automatically. Unlike manual dishwashing, which relies heavily on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, ...
s and immersion heater
Electric heating is a process in which electrical energy is converted directly to heat energy at around 100% efficiency, using rather cheap devices. Common applications include space heating, cooking, water heating and industrial processes. A ...
s may be set so that they only switch on during the off-peak usage period.
Smart meters
Smart meters go a step further than simple AMR ( automatic meter reading). They offer additional functionality including a real-time or near real-time reads, power outage
A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user.
There are many causes of power failures in an electricit ...
notification, and power quality monitoring. They allow price setting agencies to introduce different prices for consumption based on the time of day and the season.
Another type of smart meter uses nonintrusive load monitoring Nonintrusive load monitoring (NILM), or nonintrusive appliance load monitoring (NIALM), is a process for analyzing changes in the voltage and current going into a house and deducing what appliances are used in the house as well as their individual e ...
to automatically determine the number and type of appliances in a residence, how much energy each uses and when. This meter is used by electric utilities to do surveys of energy use. It eliminates the need to put timers on all of the appliances in a house to determine how much energy each uses.
Prepayment meters
Prepayment meter and magnetic stripe tokens, from a rented accommodation in the UK. The button labelled A displays information and statistics such as current tariff and remaining credit. The button labelled B activates a small amount of emergency credit should the customer run out
file:Smart card prepaid electric meter.jpg, A digital smart card type prepaid meter
file:London electricity keymeter key.jpg, A prepayment key
The standard business model of electricity retailing involves the electricity company billing the customer for the amount of energy used in the previous month or quarter. In some countries, if the retailer believes that the customer may not pay the bill, a prepayment meter may be installed. This requires the customer to make advance payment before electricity can be used. If the available credit is exhausted then the supply of electricity is cut off by a relay
A relay
Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts
An automotive-style miniature relay with the dust cover taken off
A relay is an electrically operated switch ...
.
In the UK, mechanical prepayment meters used to be common in rented accommodation. Disadvantages of these included the need for regular visits to remove cash
In economics, cash is money in the physical form of currency, such as banknotes and coins.
In bookkeeping and financial accounting, cash is current assets comprising currency or currency equivalents that can be accessed immediately or near-imm ...
, and risk of theft of the cash in the meter.
Modern solid-state electricity meters, in conjunction with smart card
A smart card, chip card, or integrated circuit card (ICC or IC card) is a physical electronic authentication device, used to control access to a resource. It is typically a plastic credit card-sized card with an embedded integrated circuit (IC) c ...
s, have removed these disadvantages and such meters are commonly used for customers considered to be a poor credit risk
A credit risk is risk of default on a debt that may arise from a borrower failing to make required payments. In the first resort, the risk is that of the lender and includes lost principal and interest, disruption to cash flows, and increased ...
. In the UK, customers can use organisations such as the Post Office Ltd
gd, Oifis a' Phuist kw, Sodhva an Post ga, An Post Ríoga
, logo = Post Office Logo.svg
, type = State-owned private company limited by shares
, genre =
, predecessor = General Post Office
, foundation = 1987
, founder =
, location_cit ...
or PayPoint
PayPoint plc is a British business offering a system for paying bills in United Kingdom, Ireland and Romania. It is listed on the London Stock Exchange.
History
The PayPoint network was set up in 1996 with the aim of enabling customers to load g ...
network, where rechargeable tokens (Quantum cards for natural gas, or plastic "keys" for electricity) can be loaded with whatever money the customer has available.
In South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
, Sudan
Sudan ( or ; ar, السودان, as-Sūdān, officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country in Northeast Africa. It shares borders with the Central African Republic t ...
and Northern Ireland
Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...
prepaid meters are recharged by entering a unique, encoded twenty digit number using a keypad. This makes the tokens, essentially a slip of paper, very cheap to produce.
Around the world, experiments are going on, especially in developing countries, to test pre-payment systems. In some cases, prepayment meters have not been accepted by customers. There are various groups, such as the Standard Transfer Specification (STS
STS, or sts, may refer to:
Medicine
* Secondary traumatic stress, a condition which leads to a diminished ability to empathize
* Sequence-tagged site, a gene-reference in genomics
* Soft-tissue sarcoma
* Staurosporine, an antibiotic
* STS (gen ...
) association, which promote common standards for prepayment metering systems across manufacturers. Prepaid meters using the STS standard are used in many countries.
Time of day metering
Time of Day metering (TOD), also known as Time of Usage (TOU) or Seasonal Time of Day (SToD), metering involves dividing the day, month and year into tariff slots and with higher rates at peak load periods and low tariff rates at off-peak load periods. While this can be used to automatically control usage on the part of the customer (resulting in automatic load control), it is often simply the customer's responsibility to control his own usage or pay accordingly (voluntary load control). This also allows the utilities
A public utility company (usually just utility) is an organization that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Public utilities are subject to forms of public control and r ...
to plan their transmission infrastructure appropriately. See also Demand-side Management (DSM).
TOD metering normally splits rates into an arrangement of multiple segments including on-peak, off-peak, mid-peak or shoulder, and critical peak. A typical arrangement is a peak occurring during the day (non-holiday days only), such as from 1 pm to 9 pm Monday through Friday during the summer and from 6:30 am to 12 noon and 5 pm to 9 pm during the winter. More complex arrangements include the use of critical peaks that occur during high demand periods. The times of peak demand/cost will vary in different markets around the world.
Large commercial users can purchase power by the hour using either forecast pricing or real-time pricing.
Some utilities allow residential customers to pay hourly rates, such as in Illinois, which uses day ahead pricing.
Power export metering
Many electricity customers are installing their own electricity generating equipment, whether for reasons of economy, redundancy or environmental reasons. When a customer is generating more electricity than required for his own use, the surplus may be exported back to the power grid
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
. Customers that generate back into the "grid" usually must have special equipment and safety devices to protect the grid components (as well as the customer's own) in case of faults (electrical short circuits) or maintenance of the grid (say voltage on a downed line coming from an exporting customers facility).
This exported energy may be accounted for in the simplest case by the meter running backwards during periods of net export
The balance of trade, commercial balance, or net exports (sometimes symbolized as NX), is the difference between the monetary value of a nation's exports and imports over a certain time period. Sometimes a distinction is made between a balance ...
, thus reducing the customer's recorded energy usage by the amount exported. This in effect results in the customer being paid for his/her exports at the full retail price of electricity. Unless equipped with a ratchet or equivalent, a standard meter will accurately record power flow in each direction by simply running backwards when power is exported. Where allowed by law, utilities maintain a profitable margin between the price of energy delivered to the consumer and the rate credited for consumer-generated energy that flows back to the grid.
Lately, upload sources typically originate from renewable sources (e.g., wind turbine
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...
s, photovoltaic
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially us ...
cells), or gas
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
or steam turbine
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...
s, which are often found in cogeneration
Cogeneration or combined heat and power (CHP) is the use of a heat engine or power station to generate electricity and useful heat at the same time.
Cogeneration is a more efficient use of fuel or heat, because otherwise- wasted heat from elect ...
systems. Another potential upload source that has been proposed is plug-in hybrid car batteries (vehicle-to-grid
Vehicle-to-grid (V2G), also known as Vehicle-to-home (V2H) or Vehicle-to-load (V2L) describes a system in which plug-in electric vehicles (PEV) sell demand response services to the grid. Demand services are either delivering electricity or by red ...
power systems). This requires a "smart grid
A smart grid is an electrical grid which includes a variety of operation and energy measures including:
*Advanced metering infrastructure (of which smart meters are a generic name for any utility side device even if it is more capable e.g. a f ...
," which includes meters that measure electricity via communication networks that require remote control and give customers timing and pricing options. Vehicle-to-grid systems could be installed at workplace parking lots and garages and at park and rides and could help drivers charge their batteries at home at night when Energy demand management, off-peak power prices are cheaper, and receive bill crediting for selling excess electricity back to the grid during high-demand hours.
Location
file:CurrentTransformers.jpg, Current transformers used as part of metering equipment for three-phase 400 A electricity supply. The fourth neutral wire does not require a current transformer because current cannot flow in the neutral without also flowing in metered phase wires. (Blondel's theorem)
file:Dunkin donuts electric power meter in framingham ma shot by brian katt with a canon digital rebel in June of 2006.JPG, A commercial power meter
file:Electricity meters in India.JPG, Electricity meters placed outside the homes of residents in a common place, which is accessible only for the department staff and concerned residents
file:2008-08-12 Technician disconnecting electricity for nonpayment.jpg, A Duke Energy technician removes the tamper-proof seal from an electricity meter at a residence in Durham, North Carolina
The location of an electricity meter varies with each installation. Possible locations include on a utility pole serving the property, in a street-side cabinet (meter box) or inside the premises adjacent to the consumer unit / distribution board. Electricity companies may prefer external locations as the meter can be read without gaining access to the premises but external meters may be more prone to vandalism.
Current transformers permit the meter to be located remotely from the current-carrying conductors. This is common in large installations. For example, a Electrical substation, substation serving a single large customer may have metering equipment installed in a cabinet, without bringing heavy cables into the cabinet.
Customer drop and metering equation
Since electrical standards vary in different regions, "customer drops" from the grid to the customer also vary depending on the standards and the type of installation. There are several common types of connections between a grid and a customer. Each type has a different ''metering equation.'' Blondel's theorem states that for any system with N current-carrying conductors, that N-1 measuring elements are sufficient to measure electrical energy. This indicates that different metering is needed, for example, for a three-phase three-wire system than for a three-phase four-wire (with neutral) system.
In Europe, Asia, Africa and most other locations, Single-phase electric power, single phase is common for residential and small commercial customers. Single phase distribution is less-expensive, because one set of transformers in a substation normally serve a large area with relatively high voltages (usually 230 V) and no local transformers. These have a simple metering equation: Watts = volts x Ampere, amps, with volts measured from the neutral to the phase wire. In the United States, Canada, and parts of Central and South America similar customers are normally served by split phase, three-wire single phase. Three-wire single-phase requires local transformers, as few as one per ten residences, but provides lower, safer voltages at the socket (usually 120 V), and provides two voltages to customers: neutral to phase (usually 120 V), and phase to phase (usually 240 V). Additionally, three-wire customers normally have neutral wired to the zero side of the generator's windings, which gives earthing that can be easily measured to be safe. These meters have a metering equation of Watts = 0.5 x volts x (amps of phase A − amps of phase B), with volts measured between the phase wires.
Industrial power is normally supplied as three phase power. There are two forms: three wire, or four wire with a system neutral. In "three wire" or "three wire delta," , there is no neutral but an earth ground is the safety ground. The three phases have voltage only relative to each other. This distribution method has one fewer wire, is less expensive, and is common in Asia, Africa, and many parts of Europe. In regions that mix residences and light industry, it is common for this to be the only distribution method. A meter for this type normally measures two of the windings relative to the third winding, and adds the watts. One disadvantage of this system is that if the safety earth fails, it is difficult to discover this by direct measurement, because no phase has a voltage relative to earth.
In the four-wire three-phase system, sometimes called "four-wire wye", the safety ground is connected to a neutral wire that is physically connected to the zero-voltage side of the three windings of the generator or transformer. Since all power phases are relative to the neutral in this system, if the neutral is disconnected, it can be directly measured. In the United States, the National Electrical Code requires neutrals to be of this type. In this system, power meters measure and sum all three phases relative to the neutral.
In North America, it is common for electricity meters to plug into a standardised socket outdoors, on the side of a building. This allows the meter to be replaced without disturbing the wires to the socket, or the occupant of the building. Some sockets may have a bypass while the meter is removed for service. The amount of electricity used without being recorded during this small time is considered insignificant when compared to the inconvenience which might be caused to the customer by cutting off the electricity supply. Most electronic meters in North America use a serial protocol, ANSI C12.18
A smart meter is an electronic device that records information such as consumption of electric energy, voltage levels, current, and power factor. Smart meters communicate the information to the consumer for greater clarity of consumption beha ...
.
In many other countries the supply and load terminals are in the meter housing itself. Cables are connected directly to the meter. In some areas the meter is outside, often on a utility pole. In others, it is inside the building in a niche. If inside, it may share a data connection with other meters. If it exists, the shared connection is often a small plug near the post box. The connection is often EIA-485 or infrared with a serial protocol such as IEC 62056.
In 2014, networking to meters is rapidly changing. The most common schemes seem to combine an existing national standard for data (e.g. ANSI C12.19 or IEC 62056) operating via the internet protocol with a small circuit board for powerline communication, or a digital radio for a mobile phone network, or an ISM band.
Accuracy
Electricity meters are required to register the energy consumed within an acceptable degree of accuracy. Any significant error in the registered energy can represent a loss to the electricity supplier, or the consumer being over billed. The accuracy is generally laid down in statute for the location in which the meter is installed. Statutory provisions may also specify a procedure to be followed should the accuracy be disputed.
For the United Kingdom, any installed electricity meter is required to accurately record the consumed energy, but it is permitted to under-read by 3.5%, or over-read by 2.5%. Disputed meters are initially verified with a check meter operating alongside the disputed meter. The final resort is for the disputed meter to be fully tested both in the installed location and at a specialist calibration laboratory. Approximately 93% of disputed meters are found to be operating satisfactorily. A refund of electricity paid for, but not consumed (but not vice versa) will only be made if the laboratory is able to estimate how long the meter has been misregistering. This contrasts with gas meters where if a meter is found to be under reading, it is assumed that it has under read for as long as the consumer has had a gas supply through it. Any refund due is limited to the previous six years.
Tampering and security
Meters can be manipulated to make them under-register, effectively allowing power use without paying for it. This theft or fraud can be dangerous as well as dishonest.
Power companies often install remote-reporting meters specifically to enable remote detection of tampering, and specifically to discover energy theft. The change to smart power meters is useful to stop energy theft.
When tampering is detected, the normal tactic, legal in most areas of the United States, is to switch the subscriber to a "tampering" tariff charged at the meter's maximum designed current. At US$0.095/kWh, a standard residential 50 A meter causes a legally collectible charge of about US$5,000.00 per month. Meter readers are trained to spot signs of tampering, and with crude mechanical meters, the maximum rate may be charged each billing period until the tamper is removed, or the service is disconnected.
A common method of tampering on mechanical disk meters is to attach magnets to the outside of the meter. Strong magnets saturate the magnetic fields in the meter so that the motor portion of a mechanical meter does not operate. Lower power magnets can add to the drag resistance of the internal disk resistance magnets. Magnets can also saturate current transformers or power-supply transformers in electronic meters, though countermeasures are common.
Some combinations of capacitive and inductive load can interact with the coils and mass of a rotor and cause reduced or reverse motion.
All of these effects can be detected by the electric company, and many modern meters can detect or compensate for them.
The owner of the meter normally secures the meter against tampering. Revenue meters' mechanisms and connections are sealed. Meters may also measure VAR-hours (the reflected load), neutral and DC currents (elevated by most electrical tampering), ambient magnetic fields, etc. Even simple mechanical meters can have mechanical flags that are dropped by magnetic tampering or large DC currents.
Newer computerised meters usually have counter-measures against tampering. AMR (Automated Meter Reading) meters often have sensors that can report opening of the meter cover, magnetic anomalies, extra clock setting, glued buttons, inverted installation, reversed or switched phases etc.
Some tampers bypass the meter, wholly or in part. Safe tampers of this type normally increase the neutral current at the meter. Most split-phase residential meters in the United States are unable to detect neutral currents. However, modern tamper-resistant meters can detect and bill it at standard rates.
Disconnecting a meter's neutral connector is unsafe because shorts can then pass through people or equipment rather than a metallic ground to the generator or earth.
A phantom loop connection via an earth ground is often much higher resistance than the metallic neutral connector. Even if an earth ground is safe, metering at the substation can alert the operator to tampering. Substations, inter-ties, and transformers normally have a high-accuracy meter for the area served. Power companies normally investigate discrepancies between the total billed and the total generated, in order to find and fix power distribution problems. These investigations are an effective method to discover tampering.
Power thefts in the United States are often connected with indoor marijuana grow operations. Narcotics detectives associate abnormally high power usage with the lighting such operations require. Indoor marijuana growers aware of this are particularly motivated to steal electricity simply to conceal their usage of it.
Regulation and legislation
Following the deregulation of electricity supply markets in many countries, the company responsible for an electricity meter may not be obvious. Depending on the arrangements in place, the meter may be the property of the meter Operator, electricity distribution, electricity distributor, the electricity retail, retailer or for some large users of electricity the meter may belong to the customer.
The company responsible for reading the meter may not always be the company which owns it. Meter reading is now sometimes subcontracted and in some areas the same person may read gas meter, gas, water meter, water and electricity meters at the same time.
The introduction of Automatic meter reading, advanced meters in residential areas has produced additional privacy issues that may affect ordinary customers. These meters are often capable of recording energy usage every 15, 30 or 60 minutes. Some meters have one or two IR LEDs on the front: one used for testing and which acts as the equivalent of the timing mark on the older mechanical meters and the other as part of a two-way IR communications port for reading / programming the meter. These IR LEDs are visible with some night vision viewers and certain video cameras that are capable of sensing IR transmissions. These can be used for surveillance, revealing information about peoples' possessions and behaviour. For instance, it can show when the customer is away for extended periods. Nonintrusive load monitoring gives even more detail about what appliances people have and their living and use patterns.
A more detailed and recent analysis of this issue was performed by the Illinois Security Lab.
See also
* Energy management software
* Energy monitoring and targeting
* Meter operator
* Utility submeter
* Zellweger off-peak
* Multimeter
Notes
References
*"Handbook for Electricity Metering" by The Edison Electric Institute
External links
*
{{Authority control
Electricity meters,
Electrical instruments