Properly selected electric meter will help the homeowner to save on utility bills. In order not to be mistaken with the choice, first of all you need to find out which device is suitable, depending on what you let in electrical networks - three-phase or single-phase, and what is the difference between such devices, how are they installed and what are their advantages and limitations?
If we consider a single-phase electricity metering device, then it is used in networks whose voltage corresponds to 220V. In turn, the three-phase analog is connected to the mains 380V. In this case, the first type of meters is familiar to every homeowner, as it is used in apartments, office buildings, garage boxes and other similar buildings.
Three-phase control devices have been used only at enterprises for quite a while, but more and more often they can be found in private houses as well. This was facilitated by the appearance of many household appliances requiring additional power. To this end, houses and apartments began to connect to the three-phase electric network the control of energy supplied through which should be carried out by special devices for metering of electricity consumed.
- 1 The principle of operation of three-phase meters
- 2 Types of connection diagrams
- 3 Three-phase meters with semi-direct connection
- 4 Direct connection of the three-phase device
- 5 Indirect way to connect meters
- 6 The right choice of three-phase meter
The principle of operation of three-phase meters
The three-phase electricity metering device differs from the single-phase analogue in the ability to function in sufficiently powerful networks. If standard 220V electric meters are installed in an electrical circuit whose power is not more than 10 kW, then, the devices of the three-phase type operate with power loads of 15 kW and much more. Such multifunctional devices work equally well in a standard household network, and control the energy consumption of three-phase electric motors. In this case, the standard control devices of this type consist of the following structural parts:
- conductive winding;
- voltage winding;
- the worm mechanism driving the dial;
- aluminum disc and magnet.
Standard induction energy metering devices used in 380V mains, such as “Mercury”, equipped with plastic casesthat protect all mechanisms from moisture or various contaminants. Inside the case there are 2 cores around one of which a current winding is wound, which is connected in parallel to the network. In turn, a voltage winding is wound around another element, the coils of which have an increased diameter compared to the current tax. In the middle between the coils in the formed space, there is a disk of aluminum, the rotation of which occurs through the fields created by the windings.
To ensure the demonstration of testimony in the meter is located worm gearthrough which a mechanical arrow is connected or an electronic scoreboard for data output. In turn, the magnet is designed to adjust the functioning of the control device. All winding leads are connected to the terminal contacts of the metering device and are output to the phase. In order to prevent interference with the work of the electricity meter by the consumer, the outputs are sealed by representatives of the electricity supplier company.
An important rule for the purchase of any type of electrical energy consumption monitoring device is Mandatory verification of the presence on the device of all necessary seals installed at the factory manufacturer. If such security elements are not detected, then the meter is unsuitable for use for its intended purpose and its installation has no practical significance.
Types of connection diagrams
First of all, the choice of a suitable connection scheme for a 380V electric meter depends on the type of control device. It should be noted that the three-phase meters are capable of operating in standard 220V electrical networks. At the same time, all household appliances for electricity consumption metering differ in the following connection diagrams:
- metering devices with direct inclusion;
- electric meters with semi-indirect type of connection;
- control devices with indirect type of inclusion.
The device of the direct-flow type of energy consumption metering is designed for current transmission not higher than 100 A. Because of this, there is a restriction on the use of such a device for power, which is not more than 60 kW. The terminal contacts of such electricity meters and the wiring holes are designed for the connection of wires of small cross section. In most cases, this wiring, the cross section of which varies from 16 to 25 mm square. Devices of direct inclusion have a standard wiring diagram, indicated on the back of the electric meter cover, which does not cause any special difficulties.
Three-phase meters with semi-direct connection
Electricity meters "Mercury" with the semi-indirect principle of connection are included in the AC 380V through a transformer. This makes it possible to carry out electricity metering with high network power. In the process of calculating the resources used, the transformation ratio is necessarily taken into account. To date, there are many schemes with semi-indirect inclusion, the most popular of which are the following options:
- transformer connection circuit according to the “star” principle;
- ten wire connection;
- wiring diagram using test terminal boxes;
- by combining current and voltage circuits.
Considering the shortcomings of the scheme with a semi-indirect connection, I would like to note the difficulty of conducting scheduled inspections regulatory authorities energy sales.
Direct connection of the three-phase device
The simplest method of connection, which resembles the standard installation of a single-phase meter, is the direct activation of an electrical energy consumption monitoring device. The main feature of such devices is the presence of a larger number of terminal contacts than in single-phase counterparts. In turn, the installation process itself of the three-phase device “Mercury” consists in a certain sequence of actions.
- Lead conductors are stripped of insulation and connected to a three-phase type protective circuit breaker.
- Immediately after the automatic connection, the phase conductors are connected in the amount of 3 pcs. to pair terminal contacts starting from the right side of the device. Accordingly, phase wiring is performed from odd-numbered clamps.
- The connection of the neutral conductor is carried out respectively to the two remaining pins 7 and 8.
- Immediately behind the electric meter are mounted tripolar circuit breakers.
- Standard household equipment can be connected to the “Mercury” meter. For this purpose, it is necessary to carry out a single-pole automatic tap-off from any phase conductor and, of course, from the zero terminal.
If planned installation of multiple consumers single-phase type, they should be evenly distributed, for which they are connected via automata with different phase conductors, taken immediately after the meter.
Indirect way to connect meters
If the parameters of the consumed loads of all devices exceed the rated values of the current passing through an electric meter, then additionally installs the current separation transformer. The installation of such a device is carried out in the rupture of the power current-carrying wire.
On the current transformer there are two main windings. The primary circuit is made of a powerful conductive bus that passes through the center of the device and connects to the gap of the power supply consumers of electrical energy. In turn, on the secondary winding there are many more turns of wires, but of smaller cross section. The connection of this winding is carried out directly to the metering device consumed electricity.
This method is much more difficult from the direct option and requires certain skills from the person. Therefore, if a person does not have confidence in the electrician’s own talents when a three-phase electric meter is connected through a transformer, then it is advisable to think about calling a specialist. In other situations, this the problem is completely solved.
- Three transformers are connected for each individual wire. They are mounted on the back of the entrance locker. The connection of the primary windings is carried out immediately after the input breaker in the gap of the phase power conductors. The installation of a three-phase meter is also carried out in a cabinet.
- A conductor with a diameter of 1.5 mm² is connected to the phase conductor before the transformer; the free end is connected to the second terminal of the meter.
- By analogy, the 2 remaining transformers are connected to the corresponding phase conductors on the electric meter "Mercury" at the terminal contacts 5 and 8.
- From the secondary winding of the transformer device, conductors with a cross section of 1.5 mm² are connected to the terminal contacts 1 and 3 on the meter. It is very important to observe the correct phasing of the windings. Otherwise, the readings of the electricity consumption monitor will be incorrect.
- By analogy, the remaining windings of transformers are connected to the corresponding contacts on the meter.
- The remaining 10th terminal contact is for connecting a neutral grounding bus.
However, considering indirect switching meters, we would like to note that they are more often used to account for current consumption. in powerful high-voltage networksand not for domestic purposes.
The right choice of three-phase meter
When choosing a three-phase electric meter, it is important to base on the reliability of the accuracy and durability of the device - the main criteria of a high-quality apparatus for metering electricity consumption. In this regard, the counters “Mercury”, which are produced both with switching on via a transformer, and directly, have proven themselves to be excellent.
The manufacturer presents a line of budget devices with an electromechanical control system. electricity as well as functional meters with an internal tariff that can keep track of different tariffs at the same time. Modern counters "Mercury" equipped with self-diagnosis and the ability to connect to a personal computer. All devices have electronic seals and have a long service life of up to 16 years. Also modern control devices "Mercury" have the following features:
- measurement of the active type of energy;
- reactive energy type accounting;
- the ability to control up to 4 different tariffs;
- presence of a function, logging of events;
- quality control of electrical energy;
- additional interfaces.
The importance of energy saving is clear to absolutely everyone, and the three-phase meters fully cope with the tasks assigned to them. The new devices have program setting functioncertain modes of operation. If during the daytime the tariffing is at one price, and at night at another cost, then the modern electricity control device records automatically.
Naturally, just choose a high-quality three-phase counter, far from enough. Each bona fide owner must understand the various schemes for connecting such devices. After all, everyone knows that an incorrectly connected electric meter to a three-phase AC network will show incorrect data and cannot talk about any savings.