Electricity is required in accounting. This task is assigned to electricity meters. Measured electrical energy in kilowatt-hours - this means that an electrical device that has a power consumption of 1000W is required to work one hour to spend 1 kW / h
Today's glut of various electronic (and not only) products, a variety of different models and types of electronic meters will be able to enter into the stupor of the ordinary consumer.
The counters in the domestic market are different - electronic (digital), simple mechanical, combined, simply “screwed” and interplanetary are very accurate.
The functionality of today's counters It is also impressive - in addition to a simple measurement of the power of electricity, meters can count tariffs for energy and environmental characteristics, monitor energy quality, and allow for the possibility of remote access.
In this article, consisting of several parts, we will try to answer a number of questions that appear when choosing, connecting and working principle of an electric meter.
Since we do not plan to consider this topic very deeply, some questions may not be touched. Therefore, it will not be superfluous to read in ПУЭ7, Chapter 1.5 - “Accounting for Electric Energy”.
To review the topic, we first need to somehow divide all electricity meters into groups according to their different characteristics. In other words, you need to deal with the classification of electric meters.
- 1 Key Features
- 2 Differences in type of electricity network
- 3 Design feature of electricity meters
- 4 Electronic meter - modern metering device
- 5 Electric meter accuracy class
- 6 About calibration of electricity meters
Separate by different indicators.
By way of work (constructive implementation):
- Three phase.
- Single phase.
Wherein Three-phase electric meters are divided:
- By the type of communication interface (for electric meters).
- By type of measured power - active and reactive power meters.
- By the type of connection to the network - transformer or live connection.
- According to the accuracy class.
- By the size of tariffs - single and multi-tariff.
Differences in type of electricity network
The main difference between electricity meters consists in the third paragraph, and more precisely, for which electrical network they are intended - for a single- or three-phase network.
Single-phase electric meters are used in single-phase two-wire networks with voltage 0,40 / 0,23 kW. Their main use is to account for the consumption of electric energy in apartments or individual houses.
Electric meters for a voltage of 220 (or 127) W, rated current - 5-60 amperes are produced. They are placed at the entrance or installed in interfloor (apartment) panels.
Three-phase electric meters are used for three-phase three- or four-wire networks.
And if with single-phase everything is simple and clear, then three-phase devices require a detailed description, as they are used in electronic installations that operate on three-phase current.
Three-phase electric meters of direct connection are connected to the network directly, without auxiliary devices - current transformers.
Rated current produced by direct connection electricity meters - 5-100 Ampere.
Accounting for electricity consumed is determined by subtracting the original reading of the electric meter (Mon.) from the final reading (Pk.):
E = Pk— Mon.
But there are cases when the electrical installation consumes a very large current and the electric meter of direct connection cannot pass this current through itself. Therefore, in these cases, the connection of electric meters using measuring current transformers (CT) is used.
The main purpose of the TT. - reduce the current to such indicators at which the device will work normally.
The calculation of electricity consumed here is also determined by subtracting the initial readings from the final and addition - by multiplying the resulting data difference by the transformation ratio (Kt.) current transformer:
E = (Pk. - Mon.) X Kt
To find out the transformation ratio of the TT., You can according to the information on the nameplate directly transformer
For example, the inscription 200/10 on the TT indicates that the initial winding of this transformer is designed for a current of 200 A, and the secondary winding for 10 A.
From this ratio, we have a transformation ratio, which is equal to 20. In other words - TT reduces primary electric current by 20 times.
Design feature of electricity meters
According to the design, or in other words, according to the type of measuring system, electricity meters are divided into induction and electrical. That is, the device of an electric meter can be both quite simple and quite complex - in the case of an electric meter.
Induction Counter - the method of its operation is based on the action of the magnetic field of the coils, through the wiring of which current flows, to the rotating part - the disk.
The rotation of the disk we see in the plastic window of the electric meter. Moreover, the number of revolutions of the disk is proportional to the energy expended. These electricity meters have a low price, as well as a fairly high reliability and quality.
Among the shortcomings can be identified:
- Low functionality.
- Low accuracy class (large error).
- Poor (almost no) protection against theft of electricity.
Electronic meter - modern metering device
Despite the large (as opposed to mechanical electricity meters) price, these meters have excellent technical characteristics and good service options.
- Durable, no rotating parts.
- The increased class of accuracy of electric meters.
- Ability to install a lot of tariff accounting system.
- Increased inspection interval.
- There is an internal memory for saving information on the energy consumed.
- The possibility of an automated accounting system consumed electricity (AMR).
The meter works by switching active power to a sequence of pulses, counted by the installed microcontroller. Moreover, the number of pulses is proportional to the expended (measured) energy.
Electric meter accuracy class
It's erabout the accuracy of the measurements. To be more exact, the largest possible relative error, which is indicated as a percentage.
Today, outdated electricity meters are being replaced with more modern devices everywhere. For a start, this is due precisely to the poor accuracy class of old electric meters, and with increased electrical loads. Therefore, all electric meters with an accuracy class of 2.5 must be replaced with electric meters with an accuracy class of 2 (or 1). All such measures are specified by the Decree of the Russian Federation No. 442.
About calibration of electricity meters
Electricity meters, like most measuring devices, need constant calibration. Or rather, they are subject to indispensable calibration, since they belong to the field of state regulation of creating uniform measurements.
The main task of this procedure is validation is frozenin and the possibility of subsequent operation of the device for its intended purpose. The verification is done in a state accredited organization at a specific time.
There is such an indicator of the electric meter as the interval between checks - this is the time interval, after completion, which needs the next calibration of the meter. Theoretically, the higher the interval, the better the quality of the device.
The initial (primary) calibration is done at the manufacturing plant and is written in the passport of the meter device - from this time the interval begins.
- Electrically counter - 9-15 years.
- Mechanical single-phase electric meter - 16 years.
- Electricity meters with accuracy class 0.5 - 5 years.
- Three-phase meter - 5-9 years, modern electric meters can have an interval of 15 years.