Lectricity Meter

8/2/2019 Lectricity Meter

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lectricity meter

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Typical North American domesticanalogelectricity meter.

Typical North American domestic digital electricity meter
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An electricity meter or energy meter is a device that measures the amount ofelectric energyconsumed by aresidence,business, or an electrically powered device.

Electricity meters are typically calibrated in billing units, the most common one being thekilowatt hour. Periodic readings of electric meters establishes billing cycles and energy used

during a cycle.

In settings when energy savings during certain periods are desired, meters may measure demand,the maximum use of power in some interval. "Time of day" metering allows electric rates to bechanged during a day, to record usage during during peak high-cost periods and off-peak, lower-cost, periods. Also, in some areas meters have relays fordemand responseshedding of loadsduring peak load periods.[1]

Contents

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1 Historyo 1.1 Direct current (DC)o 1.2 Alternating current (AC)

2 Unit of measuremento 2.1 Other units of measurement

3 Types of meterso 3.1 Electromechanical meterso 3.2 Electronic meters

3.2.1 Communication 3.2.2 Solid-state design

o 3.3 Multiple tariff (variable rate) meters 3.3.1 Domestic usage 3.3.2 United Kingdom 3.3.3 Commercial usage

4 Appliance energy meters 5 In-home energy use displays 6 Smart meters 7 Prepayment meters 8 Time of day metering 9 Power export metering 10 Ownership 11 Location 12 Customer drop and metering equation 13 Tampering and security

o 13.1 Privacy issues 14 See also 15 Notes 16 References
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ershiphttp://en.wikipedia.org/wiki/Electricity_meter#Power_export_meteringhttp://en.wikipedia.org/wiki/Electricity_meter#Time_of_day_meteringhttp://en.wikipedia.org/wiki/Electricity_meter#Prepayment_metershttp://en.wikipedia.org/wiki/Electricity_meter#Smart_metershttp://en.wikipedia.org/wiki/Electricity_meter#In-home_energy_use_displayshttp://en.wikipedia.org/wiki/Electricity_meter#Appliance_energy_metershttp://en.wikipedia.org/wiki/Electricity_meter#Commercial_usagehttp://en.wikipedia.org/wiki/Electricity_meter#United_Kingdomhttp://en.wikipedia.org/wiki/Electricity_meter#Domestic_usagehttp://en.wikipedia.org/wiki/Electricity_meter#Multiple_tariff_.28variable_rate.29_metershttp://en.wikipedia.org/wiki/Electricity_meter#Solid-state_designhttp://en.wikipedia.org/wiki/Electricity_meter#Communicationhttp://en.wikipedia.org/wiki/Electricity_meter#Electronic_metershttp://en.wikipedia.org/wiki/Electricity_meter#Electromechanical_metershttp://en.wikipedia.org/wiki/Electricity_meter#Types_of_metershttp://en.wikipedia.org/wiki/Electricity_meter#Other_units_of_measurementhttp://en.wikipedia.org/wiki/Electricity_meter#Unit_of_measurementhttp://en.wikipedia.org/wiki/Electricity_meter#Alternating_current_.28AC.29http://en.wikipedia.org/wiki/Electricity_meter#Direct_current_.28DC.29http://en.wikipedia.org/wiki/Electricity_meter#Historyhttp://en.wikipedia.org/wiki/Electricity_meterhttp://en.wikipedia.org/wiki/Electricity_meter#cite_note-0http://en.wikipedia.org/wiki/Demand_responsehttp://en.wikipedia.org/wiki/Kilowatt_hourhttp://en.wikipedia.org/wiki/Businesshttp://en.wikipedia.org/wiki/Househttp://en.wikipedia.org/wiki/Electric_energy


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17 External links

[edit] History

[edit] Direct current (DC)

As commercial use of electric energy spread in the 1880s, it became increasingly important thatan electric energy meter, similar to the then existinggas meters, was required to properly billcustomers for thecost of energy, instead of billing for a fixed number of lamps per month. Manyexperimental types of meter were developed.Edisonat first worked on aDCelectromechanicalmeter with a direct reading register, but instead developed anelectrochemicalmetering system,which used anelectrolytic cellto totalize current consumption. At periodic intervals the plateswere removed, weighed, and the customer billed. The electrochemical meter was labor-intensiveto read and not well received by customers. In 1885Ferrantioffered a mercury motor meter with

a register similar to gas meters; this had the advantage that the consumer could easily read themeter and verify consumption.[2]The first accurate, recording electricity consumption meter wasaDCmeter byDr Hermann Aron, who patented it in 1883.Hugo Hirstof the BritishGeneralElectric Companyintroduced it commercially into Great Britain from 1888.[3]Meters had beenused prior to this, but they measured the rate of energy consumption at that particular moment,i.e. theelectric power. Aron's meter recorded the total energy used over time, and showed it on aseries of clock dials.

[edit] Alternating current (AC)

The first specimen of theACkilowatt-hour meter produced on the basis of HungarianOtt

Blthy's patent and named after him was presented by theGanzWorks at the Frankfurt Fair inthe autumn of 1889, and the first induction kilowatt-hour meter was already marketed by thefactory at the end of the same year. These were the first alternating-current watt meters, knownby the name of Blthy-meters.[4]The AC kilowatt hour meters used at present operate on thesame principle as Blthy's original invention.[5][6][7][8]Also around 1889,Elihu Thomsonof theAmericanGeneral Electriccompany developed a recording watt meter (watt-hour meter) basedon an ironless commutator motor. This meter overcame the disadvantages of the electrochemicaltype and could operate on either alternating or direct current.[9]

In 1894Oliver Shallenbergerof theWestinghouse Electric Corporationapplied the inductionprinciple previously used[10]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 madeproportional to the power in the circuit.[11][12]The Blthy meter was similar to Shallenberger andThomson meter in that they are two-phase motor meter.[13]Although the induction meter wouldonly work on alternating current, it eliminated the delicate and troublesome commutator of theThomson design. Shallenberger fell ill and was unable to refine his initial large and heavydesign, although he did also develop a polyphase version.

[edit] Unit of measurement
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ricity_meter#cite_note-12http://en.wikipedia.org/wiki/Electricity_meter#cite_note-12http://en.wikipedia.org/w/index.php?title=Electricity_meter&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Electricity_meter&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Electricity_meter&action=edit&section=4http://en.wikipedia.org/wiki/Electricity_meter#cite_note-12http://en.wikipedia.org/wiki/Electricity_meter#cite_note-10http://en.wikipedia.org/wiki/Electricity_meter#cite_note-10http://en.wikipedia.org/wiki/Electricity_meter#cite_note-9http://en.wikipedia.org/wiki/Westinghouse_Electric_Corporationhttp://en.wikipedia.org/wiki/Oliver_Shallenbergerhttp://en.wikipedia.org/wiki/Electricity_meter#cite_note-8http://en.wikipedia.org/wiki/General_Electrichttp://en.wikipedia.org/wiki/Elihu_Thomsonhttp://en.wikipedia.org/wiki/Electricity_meter#cite_note-6http://en.wikipedia.org/wiki/Electricity_meter#cite_note-6http://en.wikipedia.org/wiki/Electricity_meter#cite_note-4http://en.wikipedia.org/wiki/Electricity_meter#cite_note-4http://en.wikipedia.org/wiki/Electricity_meter#cite_note-3http://en.wikipedia.org/wiki/Ganzhttp://en.wikipedia.org/wiki/Ott%C3%B3_Bl%C3%A1thyhttp://en.wikipedia.org/wiki/Ott%C3%B3_Bl%C3%A1thyhttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/w/index.php?title=Electricity_meter&action=edit&section=3http://en.wikipedia.org/wiki/Electric_powerhttp://en.wikipedia.org/wiki/Electricity_meter#cite_note-Whyte.2C_1930-2http://en.wikipedia.org/wiki/General_Electric_Company_plchttp://en.wikipedia.org/wiki/General_Electric_Company_plchttp://en.wikipedia.org/wiki/Baron_Hirsthttp://en.wikipedia.org/wiki/Hermann_Aronhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Electricity_meter#cite_note-1http://en.wikipedia.org/wiki/Sebastian_Ziani_de_Ferrantihttp://en.wikipedia.org/wiki/Electrolytic_cellhttp://en.wikipedia.org/wiki/Electrochemicalhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Thomas_Edisonhttp://en.wikipedia.org/wiki/Cost_of_energyhttp://en.wikipedia.org/wiki/Gas_meterhttp://en.wikipedia.org/w/index.php?title=Electricity_meter&action=edit&section=2http://en.wikipedia.org/w/index.php?title=Electricity_meter&action=edit&section=1http://en.wikipedia.org/wiki/Electricity_meter#External_links


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Panel-mountedsolid stateelectricity meter, connected to a 2MVAelectricitysubstation. Remotecurrent and voltage sensors can be read and programmed remotely bymodemand locally byinfra-red. The circle with two dots is the infra-red port. Tamper-evident seals can be seen.

The most common unit of measurement on the electricity meter is thekilowatt hour, which isequal to the amount of energy used by a load of onekilowattover a period of onehour, or3,600,000joules. Some electricity companies use theSImegajouleinstead.

Demand is normally measured in watts, but averaged over a period, most often a quarter or half

hour.

Reactive poweris measured in "thousands ofvolt-ampere reactive-hours", (kvarh). Byconvention, a "lagging" orinductiveload, such as a motor, will have positive reactive power. A"leading", orcapacitiveload, will have negative reactive power.[14]

Volt-amperes measures all power passed through a distribution network, including reactive andactual. 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 factoris the ratioof 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 ofthe wave form. For example, electronic loads such as computer power supplies draw their currentat the voltage peak to fill their internal storage elements. This can lead to a significant voltagedrop near the supply voltage peak which shows as a flattening of the voltage waveform. Thisflattening causes odd harmonics which are not permissible if they exceed specific limits, as theyare not only wasteful, but may interfere with the operation of other equipment. Harmonicemissions are mandated by law in EU and other countries to fall within specified limits.
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[edit] Other units of measurement

In addition to metering based on the amount of energy used, other types of metering areavailable.

Meters which measured the amount of charge (coulombs) used, known asampere-hour meters,were used in the early days of electrification. These were dependent upon the supply voltageremaining constant for accurate measurement of energy usage, which was not a likelycircumstance with most supplies.

Some meters measured only the length of time for which charge flowed, with no measurement ofthe magnitude of voltage or current being made. These were only suited for constant-loadapplications.

Neither type is likely to be used today.

[edit] Types of meters

Mechanism ofelectromechanicalinductionmeter.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 - note that the 1/10, 10 and 1000 dials rotateclockwisewhile the 1, 100 and10000 dials rotate counter-clockwise.

Electricity meters operate by continuously measuring the instantaneousvoltage(volts) andcurrent(amperes) and finding the productof these to give instantaneouselectrical power(watts)which is thenintegratedagainst time to giveenergyused (joules, kilowatt-hours etc.). Meters forsmaller services (such as small residential customers) can be connected directly in-line between
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source and customer. For larger loads, more than about 200 ampere of load,current transformersare used, so that the meter can be located other than in line with the service conductors. Themeters fall into two basic categories, electromechanical and electronic.

[edit] Electromechanical meters

The most common type of electricity meter is theelectromechanicalinductionwatt-hourmeter.[15][16]

The electromechanicalinductionmeter operates by counting the revolutions of analuminiumdisc which is made to rotate at a speed proportional to the power. The number of revolutions isthus proportional to the energy usage. The voltage coil consumes a small and relatively constantamount of power, typically around 2 watts which is not registered on the meter. The current coilsimilarly consumes a small amount of power in proportion to the square of the current flowingthrough it, typically up to a couple of watts at full load, which is registered on the meter.

The metallic disc is acted upon by twocoils. One coil is connected in such a way that it producesamagnetic fluxin proportion to thevoltageand the other produces a magnetic flux in proportionto thecurrent. The field of the voltage coil is delayed by 90 degrees using a lag coil.[17]Thisproduceseddy currentsin the disc and the effect is such that aforceis exerted on the disc inproportion to the product of the instantaneous current and voltage. Apermanent magnetexerts anopposing force proportional to thespeed of rotationof the disc. The equilibrium between thesetwo opposing forces results in the disc rotating at a speedproportionalto the power being used.The disc drives a register mechanism whichintegratesthe speed of the disc over time bycounting revolutions, much like theodometerin a car, in order to render a measurement of thetotal energy used over a period of time.

The type of meter described above is used on asingle-phaseACsupply. Differentphaseconfigurationsuse additional voltage and current coils.
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Three-phaseelectromechanical induction meter, metering 100 A 230/400 V supply. Horizontalaluminum rotor disc is visible in center of meter

The aluminum disc is supported by a spindle which has aworm gearwhich drives the register.The register is a series of dials which record the amount of energy used. The dials may be of thecyclometertype, an odometer-like display that is easy to read where for each dial a singledigitisshown through a window in the face of the meter, or of the pointer type where a pointer indicateseach digit. With the dial pointer type, adjacent pointers generally rotate in opposite directionsdue to the gearing mechanism.

The amount of energy represented by one revolution of the disc is denoted by the symbolwhich is given in units of watt-hours per revolution. The value 7.2 is commonly seen. Using thevalue of , one can determine their power consumption at any given time by timing the discwith a stopwatch. If the time in seconds taken by the disc to complete one revolution is , then

the power in watts is . For example, if , as above, and onerevolution took place in 14.4 seconds, the power is 1800 watts. This method can be used todetermine 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 companyor by the customer. Where the customer reads the meter, the reading may besupplied to the power company bytelephone,postor over theinternet. The electricity companywill normally require a visit by a company representative at least annually in order to verifycustomer-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 occurswhen the meter disc rotates continuously with potential applied and the load terminals opencircuited. A test for error due to creep is called a creep test.
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Two standards govern meter accuracy,ANSI C12.20for North America and IEC 62053.

[edit] Electronic meters

Electronic meters display the energy used on anLCDor LED display, and can also transmit

readings to remote places. In addition to measuring energy used, electronic meters can alsorecord other parameters of the load and supply such as maximum demand,power factorandreactive powerused etc. They can also support time-of-day billing, for example, recording theamount of energy used during on-peak and off-peak hours.

Solid stateelectricity meter used in a home in theNetherlands.

[edit] Communication

Remote meter reading is a practical example oftelemetry. It saves the cost of a human meterreader and the resulting mistakes, but it also allows more measurements, and remoteprovisioning. Many smart meters now include a switch to interrupt or restore service.

Historically, rotating meters could report their power information remotely, using a pair ofcontact closuresattached to a KYZline.

A KYZ interface is a kind ofquadrature encoder. In a KYZ interface, the Y and Z wires areswitch contacts, shorted to K for half of a rotor's circumference. To measure the rotor direction,

the Z signal is offset by 90 degrees from the Y. When the rotor rotates in the opposite direction,showing export of power, the sequence reverses. The time between pulses measures the demand.The number of pulses is total power usage.[18]

KYZ outputs were historically attached to "totalizer relays" feeding a "totalizer" so that manymeters could be read all at once in one place.
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KYZ outputs are also the classic way of attaching electric meters toprogrammable logiccontrollers,HVACsor other control systems. Some modern meters also supply a contact closurethat warns when the meter detects a demand near a higherelectricity tariff, to improvedemandside management.

Some meters have anopen collectoroutput that gives 32-100 ms pulses for a constant amount ofused electrical energy. Usually 1000-10000 pulses perkWh. Output is limited to max 27 V DCand 27 mA DC. The output usually follows the DIN 43864 standard.

Often, meters designed for semi-automated reading have aserial porton that communicates byinfraredLED through the faceplate of the meter. In some apartment buildings, a similar protocolis used, but in a wired bus using aserialcurrent loopto connect all the meters to a single plug.The plug is often near the mailboxes. In the European Union, the most common infrared andprotocol is "FLAG", a simplified subset of mode C ofIEC 61107. In the U.S. and Canada, thefavoured infrared protocol isANSI C12.18. Some industrial meters use a protocol forprogrammable logic controllers(Modbus).

The most modern protocol proposed for this purpose isDLM/COSEMwhich can operate overany medium, including serial ports. The data can be transmitted byZigbee,WiFi,telephone linesorover the power lines themselves. Some meters can be read over the internet.

Electronic meters now uselow-power radio,GSM,GPRS,Bluetooth,IrDA, as well asRS-485wired link. The meters can now store the entire usage profiles with time stamps and relay them ata click of a button. The demand readings stored with the profiles accurately indicate the loadrequirements of the customer. Thisload profiledata is processed at the utilities for billing andplanning purposes.

AMR(Automatic Meter Reading) andRMR (Remote Meter Reading) describe various systemsthat allow meters to be checked without the need to send a meter reader out. An electronic metercan transmit its readings by telephone line or radio to a central billing office. Automatic meterreading can be done withGSM(Global System for Mobile Communications) modems, one isattached to each meter and the other is placed at the central utility office.

[edit] Solid-state design
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Basic block diagram of an electronic energy meter

As in the block diagram, the meter has a power supply, a metering engine, a processing andcommunication engine (i.e. amicrocontroller), and other add-on modules such as RTC, LCDdisplay, communication ports/modules and so on.

The metering engine is given the voltage and current inputs and has a voltage reference, samplersand quantisers followed by an ADC section to yield the digitised equivalents of all the inputs.These inputs are then processed using a Digital Signal Processor to calculate the variousmetering parameters such as powers, energies etc.

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 wildlybecause most meters are outdoors. Characterizing and compensating for these is a major part ofmeter design.

The processing and communication section has the responsibility of calculating the variousderived quantities from the digital values generated by the metering engine. This also has theresponsibility of communication using various protocols and interface with other addon modulesconnected as slaves to it.

RTC and other add-on modules are attached as slaves to the processing and communicationsection for various input/output functions. On a modern meter most if not all of this will beimplemented inside the microprocessor, such as the Real Time Clock (RTC), LCD controller,temperature sensor, memory and analog to digital converters.

[edit] Multiple tariff (variable rate) meters

Electricity retailersmay wish to charge customers different tariffs at different times of the day tobetter reflect the costs of generation and transmission. Since it is typically not cost effective tostore significant amounts of electricity during a period of low demand for use during a period of
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high demand, costs will vary significantly depending on the time of day. Low cost generationcapacity (baseload) such as nuclear can take many hours to start, meaning a surplus in times oflow demand, whereas high cost but flexible generating capacity (such as gas turbines) must bekept available to respond at a moment's notice (spinning reserve) to peak demand, perhaps beingused for a few minutes per day, which is very expensive.

Some multiple tariff meters use different tariffs for different amounts of demand. These areusually industrial meters.

[edit] Domestic usage

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 electricalstorage heatersorhotwater storagesystems.

Multiple tariffs are made easier by time of use (TOU) meters which incorporate or are connectedto atime switchand which have multiple registers.

Switching between the tariffs may happen via a radio-activated switch rather than a time switchto prevent tampering with a sealed time switch to obtain cheaper electricity.

[edit] United Kingdom

Economy 7Meter and Teleswitcher

Radio-activated switchingis common in the UK, with a nightly data signal sent within thelongwave carrier ofBBC Radio 4, 198 kHz. The time of off-peak charging is usually seven hoursbetween 11.30pm and 6.30am GMT, and this is designed to powerstorage heatersandimmersion heaters. In the UK, such tariffs are brandedEconomy 7or White Meter. Thepopularity of such tariffs has declined in recent years, at least in the domestic market, due to the(perceived or real) deficiencies of storage heaters and the comparatively low cost ofnatural gas.An "Economy 10" meter is also available, giving five hours of heating overnight, with boosts inmid-morning and mid-afternoon.[19]
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Most meters usingEconomy 7switch the entire electricity supply to the cheaper rate during the 7hour night time period,[20]not just the storage heater circuit. The downside of this is that thedaytime rate will be significantly higher, and standing charges may be a little higher too. Forinstance, normal rate electricity may be 9p per kWh, whereasEconomy 7's daytime rate might be14 to 17 p per kWh, but only 5.43p per kWh at night. Timer switches installed onwashing

machines,tumble dryers,dishwashersandimmersion heatersmay be set so that they switch ononly when the rate is lower.

[edit] Commercial usage

Large commercial and industrial premises may use electronic meters which record power usagein blocks of half an hour or less. This is because mostelectricity gridshave demand surgesthroughout the day, and the power company may wish to give price incentives to large customersto reduce demand at these times. These demand surges often correspond to meal times or,famously, to advertisements in populartelevision programmes.

[edit] Appliance energy meters

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 basicprinciple. The meter is plugged into an outlet, and the appliance to be measured is plugged intothe meter. Such meters can help inenergy conservationby identifying major energy users, ordevices that consume excessivestandby power. A power meter can often be borrowed from thelocal power authorities[21]or a local public library.[22][23]

[edit] In-home energy use displays

Main article:Home energy monitor

A potentially powerful means toreduce household energy consumptionis to provide convenientreal-time feedback to users so they can change their energy using behavior. Recently, low-costenergy feedback displays have become available. A study using a consumer-readable meter in500 Ontario homes byHydro Oneshowed an average 6.5% drop in total electricity use whencompared with a similarly sized control group.Hydro One subsequently offered free powermonitors to 30,000 customers based on the success of the pilot.[24]Projects such asGooglePowerMeter, take information from a smart meter and make it more readily available to users tohelp encourage conservation.[25]

[edit] Smart meters

Main article:Smart meter

Smart meters go a step further than simple AMR (automatic meter reading). They offeradditional functionality including a real-time or near real-time reads,power outagenotification,
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and power quality monitoring. They allow price setting agencies to introduce different prices forconsumption based on the time of day and the season.

These price differences can be used to reduce peaks in demand (load shifting or peak lopping),reducing the need for additional power plants and in particular the higher polluting and costly to

operate natural gas powered peaker plants. The feedback they provide to consumers has alsobeen shown to cut overall energy consumption.[citation needed]

Another type of smart meter usesnonintrusive load monitoringto automatically determine thenumber and type of appliances in a residence, how much energy each uses and when. This meteris used by electric utilities to do surveys of energy use. It eliminates the need to put timers on allof the appliances in a house to determine how much energy each uses.

[edit] Prepayment meters

Prepayment meter andmagnetic stripetokens, from a rented accommodation in the UK. Thebutton labeled A displays information and statistics such as current tariff and remaining credit.The button labeled B activates a small amount of emergency credit should the customer run out

A prepayment key

The standard business model of electricity retailing involves the electricity company billing thecustomer for the amount of energy used in the previous month or quarter. In some countries, ifthe 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 theavailable credit is exhausted then the supply of electricity is cut off by arelay.

In the UK, mechanical prepayment meters used to be common in rented accommodation.Disadvantages of these included the need for regular visits to removecash, and risk of theft ofthe cash in the meter.

Modern solid-state electricity meters, in conjunction withsmart cards, have removed thesedisadvantages and such meters are commonly used for customers considered to be a poorcreditrisk. In the UK, one system is thePayPointnetwork, where rechargeable tokens (Quantum cards
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for natural gas, or plastic "keys" for electricity) can be loaded with whatever money the customerhas available.

Recently smartcards are introduced as much reliable tokens that allows two way data exchangebetween meter and the utility.

InSouth Africa,SudanandNorthern Irelandprepaid 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. Thereare various groups, such as the Standard Transfer Specification (STS) association, whichpromote common standards for prepayment metering systems across manufacturers. Prepaidmeters using the STS standard are used in many countries.[26][27][28]

[edit] 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 higherrates at peak load periods and low tariff rates at off-peak load periods. While this can be used toautomatically control usage on the part of the customer (resulting in automatic load control), it isoften simply the customers responsibility to control his own usage, or pay accordingly (voluntaryload control). This also allows theutilitiesto plan their transmission infrastructure appropriately.See alsoDemand-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 occurringduring the day (non-holiday days only), such as from 1 pm to 9 pm Monday through Fridayduring the summer and from 6:30 am to 12 noon and 5 pm to 9 pm during the winter. Morecomplex arrangements include the use of critical peaks which 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 timepricing. Prices range from we pay you to take it (negative) to $1000/MWh (100 cents/kWh).[29]

Some utilities allow residential customers to pay hourly rates, such as Illinois, which uses dayahead pricing.[30][31]

[edit] Power export metering

See also:Net metering

Many electricity customers are installing their own electricity generating equipment, whether forreasons of economy,redundancyorenvironmental reasons. When a customer is generating more
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electricity than required for his own use, the surplus may be exported back to thepower grid.Customers that generate back into the "grid" usually must have special equipment and safetydevices to protect the grid components (as well as the customer's own) in case of faults (electricalshort circuits) or maintenance of the grid (say voltage potential on a downed line going into anexporting customers facility).

This exported energy may be accounted for in the simplest case by the meter running backwardsduring periods ofnet export, thus reducing the customer's recorded energy usage by the amountexported. This in effect results in the customer being paid for his/her exports at the full retailprice of electricity. Unless equipped with a detent or equivalent, a standard meter will accuratelyrecord power flow in each direction by simply running backwards when power is exported. Suchmeters are no longer legal in the UK[dubiousdiscuss][citation needed] but instead a meter capable ofseparately measuring imported and exported energy is required. Where allowed by law, utilitiesmaintain a profitable margin between the price of energy delivered to the consumer and the ratecredited for consumer-generated energy that flows back to the grid. Lately, upload sourcestypically originate from renewable sources (e.g.,wind turbines,photovoltaiccells), orgasor

steamturbines, which are often found incogenerationsystems. Another potential upload sourcethat has been proposed is plug-in hybrid car batteries (vehicle-to-gridpower systems). Thisrequires a "smart grid," which includes meters that measure electricity via communicationnetworks that require remote control and give customers timing and pricing options. Vehicle-to-grid systems could be installed at workplaceparking lotsand garages and atpark and ridesandcould help drivers charge their batteries at home at night whenoff-peakpower prices arecheaper, and receive bill crediting for selling excess electricity back to the grid during high-demand hours.

[edit] Ownership

Following thederegulationof electricity supply markets in many countries (e.g., UK), thecompany responsible for an electricity meter may not be obvious. Depending on thearrangements in place, the meter may be the property of themeter Operator,electricitydistributor, theretaileror for some large users of electricity the meter may belong to thecustomer.

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 readgas,waterand electricity meters at the same time.

[edit] Location
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Current transformersused as part of metering equipment forthree-phase400 A electricitysupply. The fourth neutral wire does not require a current transformer because current cannotflow in this wire without also flowing in one of the three phase wires

A commercial power meter

ADuke Energytechnician removes the tamper-proof seal from a electricity meter at a residenceinDurham, North Carolina

The location of an electricity meter varies with each installation. Possible locations include on apowerpylonserving the property, in a street-side cabinet (meter box) or inside the premisesadjacent to theconsumer unit/distribution board. Electricity companies may prefer externallocations as the meter can be read without gaining access to the premises but external metersmay be more prone tovandalism.

Current transformerspermit the meter to be located remotely from the current-carryingconductors. This is common in large installations. For example asubstationserving a single largecustomer may have metering equipment installed in a cabinet, without bringing heavy cables intothe cabinet.

[edit] Customer drop and metering equationSince electrical standards vary in different regions, "customer drops" from the grid to thecustomer also vary depending on the standards and the type of installation. There are severalcommon types of connections between a grid and a customer. Each type has a different meteringequation.
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Lectricity Meter

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