Working principle of induction type energy meter
Induction single-phase energy meter is also called mechanical single-phase energy meter, which is designed by using the principle of electromagnetic induction. When the meter is connected to the measured circuit, the measured circuit voltage U is added to the voltage coil and an alternating magnetic flux is formed in its core, and part of this flux ΦU passes through the aluminum disk from the return pole to the core of the voltage coil; similarly, after the measured circuit current I passes through the current coil, an alternating magnetic flux Φi is also formed in the U-shaped core of the current coil, and this flux passes from the bottom to the top of the U-shaped core and then passes through the aluminum disk. This flux passes from the bottom to the top of the U-shaped core through the aluminum disk, and then from the top to the bottom through the aluminum disk back to the other end of the U-shaped core. The circuit and magnetic circuit of the meter is shown in the figure below, in which the return plate 4 is made of a steel plate, the lower end of which extends into the lower part of the aluminum disk and corresponds to the core column separating the aluminum disk and the voltage component, in order to form a circuit for the working flux of the voltage coil.
（a）Iron core structure
(b)Circuit and magnetic circuit
Since the two fluxes passing through the aluminum disk are AC fluxes, and they pass through the aluminum disk at different locations, induced eddy currents are generated near the locations of the fluxes and eddy currents passing through the aluminum disk on the respective diagram, as shown in the figure, and the interaction of these two fluxes with these eddy currents generates a rotating torque on the aluminum disk that drives the rotation of the disk.
The rotating torque MP acting on the aluminum disk is proportional to the active power of the circuit under test. When the aluminum disk starts to rotate under the action of the rotating torque, the magnetic flux Φf cutting through the permanent magnet will produce an eddy current if. The interaction of this eddy current with the permanent magnet will produce a torque Mf acting on the aluminum disk in the opposite direction of its rotation, called the braking torque. Obviously, the faster the aluminum disk rotates, the faster it cuts through its magnetic lines of force, the greater the rate of flux change caused, the greater the eddy current generated, the greater the braking torque, when the aluminum disk is not moving, the braking torque does not exist. The braking torque is generated with the rotation of the aluminum disc and increases with the speed, always in the opposite direction of the rotation of the aluminum disc.
When the aluminum disc starts to rotate under the action of the rotating torque, the braking torque increases with the increase of the rotating speed until the braking torque is balanced with the rotating torque. At this point, the total torque acting on the aluminum disk is zero, and the speed of the aluminum disk no longer increases, but is stabilized at a certain speed.
Smart meter
Smart meter is a power meter composed of measurement unit, data processing unit and communication unit, which has the functions of electric energy measurement, data processing, real-time monitoring, automatic control and information interaction. The smart meter can supply electricity only after the user pays the fee to recharge the smart IC card and input it into the meter, and the meter will automatically pull the gate and cut off the electricity when the power is used up, thus effectively solving the problems of door-to-door meter reading and difficult electricity bill collection. It also implements microcomputer management of users’ electricity purchase information, which is convenient for inquiry, statistics, charging and printing bills.
Smart meters have the advantages of more accurate measurement, intelligent deduction, tariff inquiry, power memory, balance alarm and remote transmission of information than ordinary mechanical meters.
Classification of smart meters
At present, domestic smart meters are mainly divided into two types: one is electromechanical integrated type and the other is fully electronic type.
Electromechanical integrated type
Generally speaking, the design plan is to add a sensor device without destroying the original physical structure of the existing meter and without changing the national metering standard, and turn it into a smart meter with mechanical metering and electric pulse output at the same time.
The first type of combined mechanical and electrical meter is based on the original mechanical meter, adding electronic counting devices and corresponding control and communication circuits, or adding IC card reading and writing interfaces to achieve automatic metering and control; its basic structure is to punch holes or paint (paste) on the turntable of the original mechanical meter to absorb light materials, through photoelectric conversion, the rotation of the mechanical turntable is transformed into electrical pulse signals, and then the corresponding counting process. The corresponding counting process is carried out. This kind of meter, because its measurement principle is not changed, its measurement accuracy and characteristics are exactly the same as the mechanical meter, but the cost is relatively high.
The other type of combined electromechanical meter uses electronic metering circuit to obtain digital pulse signal and then drive the word code wheel by micro-motor to get the electrical energy count value, this structure is the most simple and feasible electronic meter solution, but unfortunately the requirements of the metering circuit are high, i.e., all meters are required to convert the electrical energy value into the corresponding number of digital pulses according to a fixed ratio, in order to drive the micro-motor to turn the word code at the correct speed. This is the ratio of the energy value to the number of digital pulses required to drive the micro-motor at the correct speed to turn the word wheel. This ratio is the so-called meter constant (imp/kWh), because the timing components used in the circuit to determine the pulse speed are mostly resistive components with large parameter dispersion, in order to ensure the measurement accuracy of the meter and the consistency of the product, it is necessary to strengthen the screening of components and the adjustment of semi-finished products in the production process, that is, to increase the corresponding human and material input and to delay the production cycle. Thus, the production cost and cost of the meter will be increased. In addition, this structure of the meter in the data collection and user payment method and the old mechanical meter is no different, should be eliminated products.
All-electronic smart meters
All-electronic smart meters use integrated circuit-based electronics from metering to data processing, thus eliminating mechanical components. All-electronic smart meters are smaller, more reliable, more accurate, and consume less power than mechatronic smart meters, and the production process is greatly improved. The all-electronic smart meters will gradually replace the meters with mechanical parts, which is the trend of future social development.
All-electronic electricity meter system composition:
1、Remote meter. Water meters, electricity meters, gas meters, heat meters and other meters with pulse output are remote meters, whose measurement method is the same as that of traditional meters, but the difference is that the pulse output function is added to the original base meter, and each pulse represents a certain measurement value. The collector collects pulses through the pulse output port of the remote meter.
2、Collector. The collector can collect pulse information from water meter, electricity meter, gas meter and heat meter at the same time, and convert these pulse information into physical quantity recognized by measurement, which is stored in the memory of each collector, and through the management microcomputer, it can query the energy consumption information of any household in the system and upload the user information under the command of the management microcomputer such as meter reading.
3、Converter. The main tasks of the converter are: to complete the data communication with the collector, to give the order to freeze the electricity data to the collector, to receive the electricity data from the collector in a regular cycle or to receive the data of a certain meter or a certain group of meters according to the system requirements. According to the system requirements, it completes the communication with the master station and transmits the information needed by the master station, such as customer electricity data, to the database of the master station. The downstream channel refers to the communication line between the converter and the collector, and there are mainly three types of meter reading systems, such as bus meter reading system, carrier wave meter reading system and infrared meter reading system. The communication channel uplink channel refers to the communication line between the converter and the master station, which can use telephone, wireless, private line and other communication media.
4、System management software function. System governance software is based on communication, with database as the core, providing data processing, query, statistics, reports, backup and other functions; using a combination of object-oriented and modular approach, flexible support for different customer requirements, such as special format reports, permission control, etc.; holding the customer’s original governance system, can interface with other governance software, providing data interfaces and communication interfaces, with network communication functions; can The system can set communication parameters for each cell; meter management, set the original parameters, address and status of the meter; rate management, set various rates and set the unit price of each energy source; user management, manage and control the consumption of each household and manage the settlement of users; real-time meter reading function, the system can copy the real-time data of each energy meter; automatic calculation of consumption, realize the uniform apportionment or proportional apportionment of public energy loss. Automatic calculation of consumption, to achieve the uniform distribution of public energy losses or proportional distribution to each household and according to the meter check data and unit price, automatically calculate the consumption payable by each output, so as to charge the user; printing function, print the list of consumption of each user; query function, you can query the energy consumption information of any household, all households in any unit and all households in the whole area at any time.
The working principle of a smart meter
The following diagram shows the block diagram of a smart meter:
The following diagram shows a hardware design:
The smart meter is mainly composed of electronic components. Its working principle is to use a dedicated electric energy meter integrated circuit to process the sampled voltage and current signals through real-time sampling of the user’s power supply voltage and current, and convert them into pulses proportional to electric energy. The output is finally processed and controlled by a single-chip microcomputer, and the pulse is displayed as power consumption and output. Usually, the number of pulses sent by the A/D converter when the smart meter measures one kilowatt-hour is called the pulse constant. For the smart meter, this is an important constant, because the A/D converter is The number of pulses sent will directly determine the measurement accuracy of the meter.
At present, most of the smart meters adopt the design principle of one A/D converter for each household, but some multi-user centralized smart meters produced by some manufacturers use a common A/D converter for multiple households. When queuing up, it will cause a drop in measurement accuracy.
Sampling method of smart meter
At present, there are two main ways for electronic energy meters to sample electricity consumption of users, one is to use transformers for sampling, and the other is for direct sampling.
Using transformer sampling is to use voltage transformer and current transformer to collect the user’s voltage signal and current signal respectively; while direct sampling is to use a resistor divider network with high thermal stability to obtain the voltage signal, and use manganin with a small temperature coefficient of resistance chip for direct current sampling.
The use of transformer sampling is not as good as direct sampling in terms of starting current, linear range, power consumption, and accuracy, especially when the current value is small. The advantages of transformer sampling are strong anti-interference, simple circuit and relatively low cost. For example, when the rated current is 20A, the starting current for direct sampling is 20mA, and the starting current for transformer sampling is 40mA. For another example, the error of a fully electronic watt-hour meter that uses a dedicated manganese-copper sheet for direct current sampling can be adjusted to +0.5%, while using a current transformer for sampling, if no compensation measures are taken, the error of the transformer itself may exceed 5%.
The meter reading scheme of the smart meter The meter is used as the measurement basis for electricity charges, which involves meter reading. From the current technology, there are mainly IC card type and remote meter reading type.
The cost of the IC card electric meter charging system is low, the reliability is high, and the service life is long. IC cards use silicon chips (EEPROM) to store information, and an IC card can be used for at least 10 years. The IC card electric meter charging system has high security, is not easy to imitate, charges are accurate, and is not easy to make mistakes. It has strong encryption. The use of the IC card meter charging system can improve the management level of residents’ electricity charges, and ensure that the electric part can receive electricity charges in time (users will not continue to buy electricity, they will be cut off). The system functions of the IC card meter include a pre-charge function, an alarm function, a power-off function, a display function and an encryption function.
The entire charging system of the IC card meter includes three parts: the host computer, the IC card meter and the IC card. The IC card electric meter charging system realizes the electronic charging of electricity consumption, and the technology is mature and reliable. Therefore, the IC card charging system has been widely promoted in our country. However, from the perspective of the system, since the user terminal is not directly connected with the system host, the user’s situation can only be known when the user pays the fee with the card, and the information feedback lags behind. It can be said that the user terminal is still out of touch with the entire network. From an economic point of view, it is not in line with the economic policy to charge the electric power first and then send the electricity. Look, the IC card charging system can only be used as a transitional product.
The remote automatic meter reading system realizes the automatic reading of electricity data, which can eliminate all the disadvantages of manual operation. The user’s electricity consumption data can directly enter the computer management system of the electricity consumption business, and the electricity consumption management personnel can monitor the electricity consumption situation at any time, and solve problems (such as faults, electricity theft, etc.) in time. The line loss directly affects the economic benefits of the power supply. In the past, neither manual reading nor IC card meters could accurately measure the line loss, and it was also difficult to find the cause of the line loss. However, the total meter reading can be obtained almost at the same time by using remote meter reading. And the total reading of the sub-meter, grasp the line loss situation at any time, and easily analyze the cause of the line loss for processing. With the development of the situation, residents open personal accounts in the bank, and the business computer management system is connected to the bank network to complete a full set of operations such as automatic data copying, processing, bank transfer and payment, etc., which can truly realize the automation of electricity management. At present, the remote transmission meter reading system in China mainly has two forms: 485 bus and carrier meter reading system. The carrier meter reading system uses a special chip to modulate and demodulate the electricity data, and communicates through the power line to realize centralized meter reading. The data transmission reliability of 485 bus is high, and the cost is low. The disadvantage is that wiring is required, the installation is more complicated, and the pull wire is easy to be damaged by human beings. The most commonly used solution is to use power line carrier communication from the user terminal to the data concentrator, and use a dedicated telephone line from the data concentrator to the upper computer. Of course, according to the different conditions of the community, there are also many schemes that use the 485 bus and the power carrier together.
Since the power consumption data of the all-electronic smart meter has been digitized, it can be easily combined with various data collection and transmission circuits to form an automatic metering and billing system. It is a replacement product for the current household watt-hour meter. It will save a lot of meter reading and calculation work for the power supply department, and can recover the electricity fee in time, that is, pay first before using electricity, which has huge economic and social benefits. There are two common meter reading schemes for such smart meters: bus system centralized meter reading and power carrier centralized meter reading. All are remote meter reading.
Bus-based centralized meter reading: the meter part adopts smart meters, and the signal lines of the smart meters of each household are connected to a bus. Centralized power supply.
Power carrier meter reading: a centralized meter reading system that directly uses the existing low-voltage transmission lines for data transmission, eliminating the need for laying lines, and has obvious advantages.
The system is a high-tech product integrating microelectronics technology, communication technology and computer technology. It has the characteristics of high reliability and simple installation. It is widely used in urban and rural electricity meter, gas meter reading, billing and monitoring. However, since the power line is used to transmit electric energy to the electrical equipment, not to transmit data, the power line has many restrictions on data transmission: (1) The distribution transformer has a blocking effect on the power carrier signal, so the power carrier signal can only be used in Transmission within a distribution transformer area; (2) Different signal coupling methods have different losses on the power carrier signal; (3) The power line has its own inherent pulse interference. In addition, the high reduction, high noise, and high deformation on the power line make the power line an unideal communication medium, but due to the development of modern communication technology, the power line carrier communication becomes possible, and the signal-to-noise ratio of the data signal determines the distance of the transmission distance . The key of power line carrier communication is to choose a powerful power line carrier dedicated Modem chip.
Working characteristics of smart meters Smart meters not only adopt the design of electronic integrated circuits, but also have remote communication functions, can be connected to computers and controlled by software. Therefore, compared with inductive meters, smart meters are superior in performance and operation. Functionally, it has great advantages.
- Power consumption: Since the smart meter adopts the design method of electronic components, the power consumption of each meter is generally only about 0.6w~0.7w. For multi-user centralized smart meters, the average power per household is smaller. Generally, the power consumption of each inductive meter is about 1.7w.
- Accuracy: As far as the error range of the meter is concerned, the error measured by the 2.0-level electronic energy meter within the range of 5% to 400% of the calibrated current is ±2%, and the accuracy level commonly used at present is 1. Level 0, the error is smaller. The error range of the inductive energy meter is +0·86%~-5·7%, and due to the insurmountable defect of mechanical wear and tear, the inductive energy meter moves slower and slower, and the final error becomes larger and larger. The State Grid once conducted spot checks on inductive ammeters, and found that more than 50% of inductive ammeters had errors exceeding the allowable range after five years of use.
- Overload and power frequency range: The overload multiple of the smart meter can generally reach 6~8 times, and it has a wide range. At present, the magnification of 8~10 is becoming the choice of more and more users, and some can even reach the wide range of 20 magnification. The working frequency is also wide, in the range of 40HZ~1000HZ. The overload multiple of the induction meter is generally only 4 times, and the working frequency range is only between 45~55HZ.
- Function: Since the smart meter adopts the electronic meter technology, it can be connected to the computer through the relevant communication protocol, and the control and management of the hardware can be realized through the programming software. Therefore, the smart meter not only has the characteristics of small size, but also has the functions of remote transmission control, multi-rate, identification of vicious loads, anti-stealing, prepaid electricity, etc., and can meet the needs of customers by modifying different parameters in the control software. Different requirements for control functions that are difficult or impossible to implement with traditional inductive meters.
