Electric energy meter is used to measureelectric energyThe meters for measuring electricity, also called watt hour meters, fire meters and kilowatt hour meters, refer to the meters for measuring various quantities of electricity.
When using an electric energy meter, pay attention to the following:Small current(tens of amperes), the meter can be directly connected to the circuit for measurement.In the case of high voltage or large current, the electric energy meter can not be directly connected to the line, and needs to cooperateVoltage transformerorCurrent transformeruse.
With the rapid development of China's economy, the demand for electricity in all walks of life is increasing, and the phenomenon of unbalanced power consumption at different times is becoming increasingly serious.In order to alleviate the increasingly acute contradiction between power supply and demand in Chinaload curve Improve the imbalance of electricity consumption, fully implement the peak, flat and valley time of use electricity price system, "cut peak and fill valley", improve the national electricity efficiency, and rationally use power resources. Power departments in some provinces and cities in China have begun to gradually introduceMulti rate electricity meterTime sharing charging for users' electricity consumption.
In April 1995, the State Planning Commission, the State Economic and Trade Commission and the Ministry of Electric Power Industry jointly held the National Working Conference on Planned Electricity Use in Shanghai. It was decided to spend three to four years inpower gridInternal, planned and step by step comprehensive implementationPeak valley time of use electricity priceSystem.The overall goal is to transfer 10-15% of peak power from all networks, and to realize the transfer of 10 million to 20 million kilowatts of peak power nationwide. The scope of implementation is not only for industrial and commercial users, but also for non industrial and agricultural power.In areas where conditions permit, it has already been implementedOne meter for one householdThe residential power consumption area ofPeak valley powerPrice, so as to improve the utilization rate of electric energy and improve the power quality of residents.yesPower usersDifferent time periods and charging standards shall be adopted.Encourage electricity consumption during low periods.
In 1980, Henan first put forward the suggestion of measuring electric energy by peak and valley time segments to promote rational, balanced and scientific use of electricity by economic means, and then began to carry out pilot projects. Through practice, some valuable experiences were preliminarily explored.Subsequently, Shanxi Province has carried out joint pilot projects in a number of power users using simple equipment.
From 1982 to 1985, many provinces, cities and regions in China also successively implemented time-sharing metering of electric energy and the new charging system corresponding to it, and achieved great results.Some large power grid bureaus also regard it as an important part of technical improvement and one of the important measures to carry out scientific power utilization.So far, China has entered the ranks of countries that use various electricity prices as auxiliary management means and control power load.
The first generation of early main productionQuartz clockTime sharing electricity meter.This kind of watt hour meterwirewayConnect the quartz clock in different periods to drive the peak and valley respectivelyElectromagnetic counterThe peak, valley and total electric quantities are displayed respectively. The peak and valley electric quantities deducted from the total electric quantities are the ordinary electric quantities.Because of the poor reliability of the time-sharing meter.The timing segmentation accuracy is too low (the minimum segmentation is 5min), vulnerable to interference, and the time interval adjustment is also troublesome. The use function is single, which cannot meet some special requirements in time-sharing billing. At present, it has been basically eliminated.
Single phase electronic watt hour meter (sample drawing)
The second generation time-sharing electricity meter with electromechanical integration structure.This kind of watt hour meter adopts class 1.0Induction energy meterBased on the movement, it adopts infrared photoelectric converter, pulse output and central processing unit (CPU), single chip circuit, and uses the attached keyboard programming or infrared wireless keyboard to set various demands, clocks, time periods, weekends, which can protect the display and storage of the maximum demand of this month, the maximum demand of last month, and the maximum demand of this month's peak, average, and valley.With pulse output andRS-232Serial communication port is convenient for remote data transmission and monitoring.The performance of the instrument is relatively precise and reliable, the function can meet the current demand for time-sharing billing in China, the production process is relatively mature, the price is competitive, and it is the most widely used generation of products in China at present.However, the disadvantage is that each manufacturer has developed its own special MCU, which has the disadvantages of poor product compatibility and difficult maintenance.The common products in this series are DF68, DF93, DTF33, DF86, DSF20, DIF2, DF32, DTF864, MRZ, DSD66, etc.[1]
Classification of commonly used electric energy meters
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(1) Electric energy meters can be divided intoDC energy meterandcommunicationElectric energy meter.According to its phase line, AC watt hour meter can be divided intoSingle phase electric energy meter, three-phase three wire electricity meters and three-phase four wire electricity meters.
(2) According to its working principle, electric energy meters can be divided into electromechanical electric energy meters andElectronic energy meter(Also called static electricity meter, solid state electricity meter).Electromechanical watt hour meter is used for AC circuit as a common electric energy measuring instrument, among which induction watt hour meter is the most commonly used.Electronic energy meters can be divided intoFull electronic electric energy meterAnd electromechanical energy meters.
(3) According to its structure, electric energy meters can be divided into integral electric energy meters and split electric energy meters.
(5) Electric energy meters can be divided into ordinary mounted electric energy meters (0.2, 0.5, 1.0, 2.0, 3.0) and portable precision electric energy meters (0.01, 0.02, 0.05, 0.1, 0.2) according to their accuracy levels.[2]
Model of electric energy meter and meaning of nameplate symbols
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1. Model and its meaning
The model of electric energy meter is represented by the arrangement of letters and numbers, including category code+group code+design serial number+derived number.
(1) Category code.D - Electric energy meter.
(2) Group code.
1) Phase line: D - single phase;T - three-phase four wire active power;S - three-phase three wire active power;X - three-phase reactive power.
(3) Design serial number.Expressed in Arabic numerals.
(4) Derived number.T - both hot and humid, dry;TH - for hot and humid zone;TA - for dry tropical use;G - for plateau use;H - marine;F - for chemical anti-corrosion.
DZ refers to the maximum demand meter, such as DZL type.
DB refers to standard electricity meters, such as DB2 and DB3.
2. Nameplate
The nameplate shall include the following contents:
(1) Trademark.
(2) Metering license mark (CMC).
(3) Name or symbol of measurement unit, such as: active energy meter“Kilowatt·Hour "or" kWh ";Reactive energy meterIt is "kilovar · hour" or "kvarh".
In the window of the word wheel register, integer and decimal places are distinguished by different colors, with a decimal point in the middle;If there is no decimal point, each word wheel in the window has a multiple coefficient, such as × 100, × 10, × 1, etc.aboutLCDThe integer and decimal places of, with a decimal point in the middle.
(4) Name and model of electricity meter.
(5) Basic current and rated maximum current.The basic current (calibration current) is the current value to determine the relevant characteristics of the electric energy meter, and is the basic working current of the electric energy meterbexpress;The rated maximum current is the maximum current value that the instrument can meet the accuracy specified in its manufacturing standard.With Imaxexpress.For example, 1.5 (6) A means that the basic current value of the electricity meter is 1.5A, and the rated maximum current is 6A.If the rated maximum current is less than 150% of the basic current, only the basic current is indicated.For three-phase energy meters, the number of phases shall be multiplied in front, such as 3 × 5 (20) A.
(6) Reference voltage.The reference voltage is the voltage value to determine the relevant characteristics of the electric energy meter. It is the working voltage of the electric energy meternexpress.The reference voltage is expressed by the number of phases multiplied by the line voltage for three-phase three wire energy meters, such as 3 × 100V; for three-phase four wire energy meters, it is expressed by the number of phases multiplied by the phase voltage/line voltage, such as 3 × 220/380V;aboutSingle phase electric energy meterIt is expressed in phase voltage, such as 220V.
(7) Reference frequency.The reference frequency is the frequency value that determines the relevant characteristics of the electric energy meter, that is, the power frequency, in hertz (Hz).
(8) Energy meter constant.The constant of the electricity meter is the constant of the relationship between the electric energy recorded by the electricity meter and the corresponding revolutions or pulses,Active energy meterExpressed in the form of r (imp)/kwh or kwh/r (imp),Reactive energy meterIt is expressed in the form of r (imp)/kvarh or kvarh/r (imp).The two constants are reciprocal to each other.
(9) Accuracy class.It is represented by the level number recorded in the circle, such as surface, uniform, @. Xi. If there is no mark, the electricity meter is regarded as Level 2.
(10) Symbol of phase number and line number.
(11) The ability level of tolerance to environmental conditions is divided into 4 groups: P, S, A and B.
(12) Manufacturing standards.[2]
Working principle of electric energy meter
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When the electric energy meter is connected to the circuit to be tested, alternating current flows through the current coil and voltage coil, and these two alternating currents generate alternating magnetic flux in their iron cores respectively;The alternating magnetic flux passes through the aluminum disk and induces eddy currents in the aluminum disk;The eddy current is forced in the magnetic field, so that the aluminum disk can get torque (active torque) and rotate.The greater the power consumed by the load, the greater the current passing through the current coil, the greater the eddy current induced in the aluminum disk, and the greater the torque that makes the aluminum disk rotate.That is, the torque is proportional to the power consumed by the load.The greater the power, the greater the torque, and the faster the aluminum disk rotates.When the aluminum disk rotates, it is affected by the braking torque generated by the permanent magnet, and the braking torque is opposite to the active torque;The brake torque is proportional to the speed of the aluminum disc. The faster the aluminum disc rotates, the greater the brake torque.When the active torque and braking torque reach a temporary balance, the aluminum disk will rotate at a uniform speed.The electric energy consumed by the load is proportional to the revolutions of the aluminum disk.When the aluminum disk rotates, it drives the counter to indicate the consumed electric energy.This is the simple process of the electricity meter.[3]
Brief Introduction to Common Electric Energy Meters
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Mechanical energy meter
Although there are many types and models of mechanical watt hour meters (also called induction watt hour meters), their structures are basically similar, and they are all composed of measuring mechanism, compensation adjustment device and auxiliary parts (shell, frame, end button box, nameplate).The following are some commonly used mechanical energy meters.
(1) Long life electric energy meter.The service life of a mechanical watt hour meter in normal use mainly depends on the wear degree of its lower bearing.The duration from putting into use to the time when the basic error of the meter is out of tolerance due to the wear of the lower bearing is the life of the meter.The lower bearing of the watt hour meter has a great influence on the service life of the watt hour meter.
The bearing structure of modern watt hour meter mainly includes: steel ball jewel bearing, graphite bearing, magnetic bearing, etc.Jewel bearingIt can be divided into single gem bearing and double gem bearing.Double gem bearing has less friction and better wear resistance.The magnetic bearing suspends the rotating elements in space mainly by the repulsive force between the same polarity magnets.The magnetic bearing reduces the mechanical wear and prolongs the service life of the electric energy meter.At present, the long-life watt hour meters that are gradually popularized and applied mostly adopt magnetic structure on bearings.
Common mechanical electric energy meter adopts singleJewel bearingThe service life is generally 5 years.The bearing of the long-life electric energy meter adopts magnetic bearings orGraphite bearingOr new materials and technologies such as double gem bearings, which can extend its service life to about 10 years.
(2) Wide range electric energy meter.In recent years, due toLiving standard of residentsWith the improvement of, more and more household appliances are installed with large capacity, but the possibility of simultaneous use is small.If the old single range electric energy meter is selected, the rated current is too large, and the operating current may be lower thanRated current of electric energy meter10% to make the measurement inaccurate;On the contrary, if the rated current of the electric energy meter is selected to be smaller, once the household appliances are used at the same time, the electric energy meter may be burned due to overload.The wide range watt hour meter can overcome the above problems. As long as the total current of the household appliances used is within the rated current range of the watt hour meter, it can be measured safely and accurately.Therefore, the electric energy meters installed by residents in rural and urban power grid transformation are generally long-life, wide range electric energy meters.Wide range electric energy meter is also called high overload multiple electric energy meter, and its overload capacity can reach 2-4 times.That is, the rated current of the meter is not a fixed value, but an elastic range.If the nameplate of the single-phase meter is marked with: Grade 2.0, 220V, 10 (40) A, it means that the overload capacity of the meter is 4 times;When the rated current of the watt hour meter is within 10~40A, the accuracy can still meet the requirements of level 2.0.However, the overload capacity of the ordinary electric energy meter of level 2.0, 220V and 10A is only 1.5~2 times.[4]
Electronic energy meter
The mechanical energy meter with a single energy metering function is difficult to be competent for time-sharing metering, load control, parameter preset, measurement data acquisition, storage, real-time transmission and other functions at the same time, so a new type of electronic metering instrument came into being.
Multi function watt hour meter.No matter what electric energy meter, there are at least two functions to complete the measurement of electric energy, one is to generate power signal consistent with the actual power;The second is to accumulate the power signal to obtain the electric energy value.
Electronic energy meterIt is no exception.It first samples the voltage and current of the actual line, and generates power signals through the UI multiplier;Secondly, the U/f (voltage/frequency) converter is used to change the power signal into a pulse signal with a certain frequency, and the counter accumulates the pulse signals to generate power.The structure of multi-function electricity meter is shown in Figure 1.
Figure 1 Structure diagram of electronic multi-function electric energy meter
The metering chip W in Figure 1 is a highly integrated special three-phase metering chip, which completes the generation of power signal P (i.e. UI product);P-f frequency conversion.The functions of pulse accumulation, time-sharing metering, phase failure processing, LCD display, RS485 communication, etc. are controlled by the microprocessor CPU.
1) Metering and storage functions.It can measure single and two-way active and reactive electric energy in various periods;It can measure and display the current power, demand, power factor and other parameters.The data of the last meter reading cycle can be stored at least.
2) Monitoring function.It can monitor customers' power and maximum demand, and prevent them from stealing electricity by analyzing customers' power load curve.
3) Control function.Able to implement time period control and load control for customers.The former is used for multi rate time-sharing billing;The latter refers to receiving remote control commands through the communication interface or controlling the load through the programming inside the meter (considering the time period and load quota).With IC card interfaceElectronic energy meterIt can not only complete the prepayment function, but also have the control functions of alarm delay and power cut when the purchased electric energy is about to run out.
4) Management functions.The electronic watt hour meter is connected with the communication network or meter reading system of the power system through the communication interface to realize the remote data exchange with the outside world.The authorized client server in the power network can accurately set the time period, time period rate, time period power limit, residual power alarm limit, representative day, freezing day, demand mode, time and slip, etc. by using the address code of the electricity meter (generally 12 decimal digits);Call and view the customer's real-time power;Read the relevant electricity consumption, and transmit the electric energy measurement information to the corresponding departments as required for system dispatching, electric energy control, electric energy exchange, business billing, etc.[4]
Brief Introduction of New Type Electric Energy Meter
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Today, with the rapid development of science and technology, new types of electric energy meters have quickly entered thousands of households.The static watt hour meter and electric card with high technology content are introduced belowPrepaid electricity meter。
Static electricity meter
Static electric energy meter is based on the advanced mechanism of electronic electric energy measurement and inherits the traditionInduction watt hour meterIt adopts a fully shielded and sealed structure, has good anti electromagnetic interference performance, and is a new type of electricity meter that integrates electricity saving, reliability, lightness, high accuracy, high overload, and electricity theft prevention.
The static electric energy meter obtains the current sampling signal from the shunt, the voltage divider obtains the voltage sampling signal, the multiplier obtains the product signal of voltage and current, and then generates a counter pulse whose frequency is proportional to the product of voltage and current through frequency conversion, which is driven by frequency divisionStepping motorTo make the register measure.
Static electricity meters are divided intosingle-phaseElectronicthree-phaseElectronic type and three-phase four wire electronic type can be divided into single type and multi-function (active, reactive and composite type) according to the use.
The installation and use requirements of static electricity meters are roughly the same as those of general mechanical electricity meters, but the wiring should be thick to avoid heating and burning due to poor contact.
Prepaid electric energy meter with electric card
Figure 2 Outline Drawing of Electronic Energy Meter
Electric card prepayment electric energy meter is an electromechanical integration prepayment electric energy meter, also known as IC card meter or magnetic card meter, as shown in Figure 2.It not only hasElectronic energy meterIn addition, advanced microelectronics technology is used for data acquisition, processing and storage in electric energy measurement to realize the management function of paying before using electricity.
Electric cardPrepaid electricity meterThe voltage signal and current signal are sampled respectively through the resistance voltage dividing network and the shunt element, and sent to the power metering chip, where the differential amplificationA-D conversion and multiplier circuit perform multiplication operation, complete the instantaneous power measurement of the measured electric energy, and then output the frequency pulse signal proportional to the average power of the measured electric energy through filtering, digital and frequency converter. High frequency pulse output can be used for calibration, and low frequency pulse output can be used for data processing such as power display of the meter and communication reading by the CPU.
There are also single-phase and three-phase electricity card prepaid meters.[5]
Working characteristics of intelligent meters
The smart meter adopts the design of electronic integrated circuit, so compared with the induction meter, the smart meter has great advantages in both performance and operation functions.
1) Power consumption.As smart meters are designed with electronic components, the power consumption of each meter is only about 0.6~0.7W. For multi-user centralized smart meters, the average power of each household is smaller.Generally, the power consumption of each induction meter is about 1.7W.
2) Accuracy.In terms of the error range of the table, level 2.0Electronic energy meterThe measurement error is ± 2% within the range of 5%~400% of the calibration current, and the accuracy level of the current is 1.0, with smaller error.The error range of induction meter is 0.86%~5.7%, and due to mechanical wear, which is an insurmountable defectInduction watt hour meterThe slower you go, the greater the final error.The State Grid once conducted a spot check on induction meters, and found that more than 50% of induction meters had exceeded the allowable range after five years of use.
3) Overload, power frequency range.The overload times of smart meters can generally reach 6-8 times, with a wide range.At present, 8-10 power meters are becoming the choice of more and more users, and some can even reach a wide range of 20 power meters.The operating frequency is also wide, ranging from 40 to 1000 Hz.The overload times of induction meters are generally only 4 times, and the operating frequency range is only 45~55Hz.
4) Function.Because of the electronic technology, smart meters can be networked with computers through relevant communication protocols, and can control and manage hardware through programming software.Therefore, smart meters not only have the characteristics of small size, but also have the functions of remote control, multiple rate, identification of malignant load, anti stealing, prepaid electricity, etc., and can meet different requirements for control functions by modifying different parameters in the control software, which are difficult or impossible for traditional induction meters.[5]
