Mechanical energy meter
Although there are many types and models of mechanical energy meters (also called induction energy meters), their structures are basically similar, and they are all composed of measuring mechanisms, compensation adjustment devices and auxiliary components (housing, frame, terminal box, nameplate). The following are several commonly used mechanical energy meters.
(1) Long-life electric energy meter. The life of a mechanical electric energy meter in normal use mainly depends on the degree of wear of its lower bearing. The time from the time the meter is put into use to the time when the basic error of the electric energy meter exceeds the tolerance due to wear of the lower bearing is the life of the electric energy meter. The lower bearing of the electric energy meter has a great influence on the service life of the electric energy meter.
The bearing structures of modern electric energy meters mainly include: steel jewel bearings, graphite bearings and magnetic bearings. Jewel bearings can be divided into single jewel bearings and double jewel bearings. Double jewel bearings have less friction and better wear resistance. Magnetic bearings mainly rely on the repulsive force between magnets of the same polarity to suspend the rotating elements in space. Magnetic bearings reduce mechanical wear and extend the service life of electric energy meters. Most of the long-life electric energy meters that are gradually being promoted and applied use magnetic structures on the bearings.
Ordinary mechanical energy meters use single jewel bearings, and their service life is generally 5 years. The bearings of long-life energy meters use new materials and technologies such as magnetic bearings, graphite bearings, or double jewel bearings, so their service life can be extended to about 10 years.
(2) Wide-range electric energy meter. In recent years, as the living standards of residents have improved, the number of household appliances installed has increased. The capacity is large, but the possibility of using them at the same time is small. If the old single-range electric energy meter is selected, the rated current is too large. When the actual load is very small, the operating current may be lower than 10% of the rated current of the electric energy meter, resulting in inaccurate measurement; on the contrary, if the rated current of the electric energy meter is too small, once the household appliances are used at the same time, the electric energy meter may burn out due to overload. The wide-range electric energy 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 electric energy meter, it can be measured safely and accurately. Therefore, the electric energy meters installed by residents in the transformation of rural and urban power grids are generally long-life, wide-range electric energy meters. Wide-range electric energy meters are also called high overload multiple electric energy meters, and their overload capacity can reach 2 to 4 times. That is, the rated current of this kind of electric energy meter is not a fixed value, but a flexible range. If the nameplate of a single-phase meter reads: Class 2.0, 220V, 10 (40)A, it means that the meter has an overload capacity of 4 times; when the rated current of the meter is within 10 to 40A, the accuracy can still meet the Class 2.0 requirements. However, the overload capacity of an ordinary Class 2.0, 220V, 10A meter is generally only 1.5 to 2 times. [4]
Electronic energy meter
Mechanical energy meters with a single energy metering function are difficult to perform multiple functions simultaneously, including time-sharing metering, load control, parameter preset, measurement data collection, storage and real-time transmission, etc. Therefore, new fully electronic metering instruments came into being.
Multifunctional electric energy meter. Regardless of the electric energy meter, it must have at least two functions to complete the measurement of electric energy. One is to generate a power signal that matches the actual power; the other is to accumulate the power signal to obtain the electric energy value.
Electronic energy meters are no exception. First, they sample the voltage and current of the actual line and generate a power signal through a UI multiplier. Second, they use a U/f (voltage/frequency) converter to convert the power signal into a pulse signal with a certain frequency, and a counter accumulates the pulse signal to obtain the energy. The structure of a multifunctional energy meter is shown in the figure.
The metering chip W in the figure is a highly integrated dedicated three-phase metering chip, which completes the generation of power signal P (i.e. UI product) and frequency conversion of P-f.
Electronic multifunctional energy meter structure diagram
Electronic multifunctional energy meter structure diagram
The functions of metering, time-sharing metering, phase loss processing, LCD display, RS485 communication, etc. are controlled by the microprocessor CPU.
Multifunctional energy meters generally have the following functions:
1) Metering and storage functions. It can measure single- and two-way active and reactive energy in various time periods; it can measure and display current power, demand, power factor and other parameters. It can store at least the data of the last meter reading cycle.
2) Monitoring function: It can monitor the customer's power and maximum demand, and prevent electricity theft by analyzing the customer's power load curve.
3) Control function. It can implement time period control and load control for customers. The former is used for multi-rate time-of-use billing; the latter refers to receiving remote control instructions through the communication interface or controlling the load through the internal programming of the meter (taking into account the time period and load quota). Electronic energy meters with IC card interfaces can not only complete the prepayment function, but also have the alarm delay and power outage control functions when the purchased electricity is about to run out.
4) Management function. The electronic energy meter is connected to the communication network or meter reading system of the power system through the communication interface to realize remote data exchange with the outside world. The authorized client server in the power network uses the address code of the energy meter (generally a 12-digit decimal number) to accurately complete the setting of the time period, time period rate, time period power limit, remaining power alarm limit, representative day, freezing day, demand mode, time and slip, etc.; call and view the real-time power of the customer; read its relevant power consumption, and transmit the energy metering information to the corresponding department as needed for system scheduling, power control, power exchange and business billing.