Typical schemes for connecting a three-phase power meter

Preliminary stage

Connection of the electric meter( ES) is the final stage of electrical installation work. Before installing a three-phase ES, you must first have a wiring diagram. The device should be checked for seals on the cover screws. On these seals, the year and quarter of the last inspection and the seal of the witness must be indicated.

When connecting the wires to the terminals, it is better to make a stock of 70-80 mm. In the future, such a measure will make it possible to measure the power consumption / current and remounting, if the circuit was assembled incorrectly.

Each wire must be clamped in the terminal box with two screws( in the photo below it is clearly visible).The upper screw is tightened first. Before tightening the bottom, you need to make sure that the top wire is clamped by tugging it. If a multicore wire is used when connecting the meter, then its tips must be pre-pressurized.

Figure 1 - TC Mercury 231

Next, we will consider typical schemes for connecting a three-phase meter to an electrical grid.

Direct( direct) activation of

This is the simplest wiring diagram. When directly switched on, the vehicle is connected to the network without measuring transformers( figure 2).Most often this method of installation is used in household networks to account for electricity, where there are powerful installations with a rated current from 5 to 50 A, depending on the type of wiring( 4 to 100 mm2).The operating voltage here is usually 380 V. When connecting the wire to a three-phase meter, you must observe the color order: 1st phase A should be on the yellow wire, phase B - on the green, C - on the red. The neutral wire N should be blue, and the PE ground wire must be yellow-green. To protect against overloads at the entrance are installed machines.

network A short video instruction for connecting a three-phase meter is shown on this clip:

wiring. Switching to the single-phase

circuit. Before describing this connection of the meter to a 380-volt network, a brief description of the differences between the three-single-phase. In both views, one zero conductor N is used. The potential difference between each phase conductor and zero is 220 V, and the ratio of these phases to each other is 380 V. This difference is obtained due to the fact that the oscillations on each wire are shifted by 120 degrees(Figures 3 and 4).

Figure 3 - Voltage fluctuations

Single-phase voltage is used in private houses, in the country, as well as in garages. In such places, the power consumption rarely exceeds 10 kW.This also makes it possible to use cheaper wires with a section of 4 mm square meters on the site, since the current consumption is limited to 40 A.

If the power consumption in the network exceeds 15 kW, then the use of 3 phase wires is mandatory, even ifthere are no three-phase consumers, in particular, electric motors. In this case, the load is distributed over the phase conductors, which reduces the load if the same power is taken from one phase. Therefore, in office buildings and shops, as a rule, they use three-phase power.

The principle diagram of connecting a three-phase meter to a single-phase network( OC) is not so common, since single-phase meters are used in such cases. In most cases, the circuit is similar to the direct-wiring circuitry, but phases 2 and 3 are not connected( the connection occurs in one phase).In addition, after installation, problems with trusting organizations may arise.

You can also look at the possible problems of three-phase electricity meters when connecting to a two-wire network:

Connecting via current transformers

The maximum current of the electricity meter is usually limited to 100 A, so use them in high-powerelectrical installations impossible. In this case, the connection to the three-phase network goes not directly, but through transformers. This also allows you to extend the measuring range of current and voltage meters. However, the main task of input transformers is to reduce primary currents and voltages to safe values ​​for ES and protective relays.

Semi-indirect

When connecting the meter via a transformer, it is necessary to monitor the polarity of the beginning and end of the current transformer windings, both primary( L1, L2) and secondary( И1, И2).Similarly, you need to monitor the polarity when using a voltage transformer. The common point of the secondary windings of transformers must be grounded.

Assignment of current transformer contacts:

• L1 - input of phase( power) line.
• L2 - phase line output( load).
• И1 - input of the measuring winding.
• И2 - the output of the measuring winding.

Figure 5 - Ten-wire connection via TT

This type of power meter connection to a 380-volt network allows you to separate the current and voltage circuits, which increases electrical safety. The disadvantage of this electrical circuit of three-phase meter connection is a large number of wires necessary for connecting the ES.

Star

This type of connection of an electricity meter with ground to a 380 V network requires fewer wires. The star connection is achieved by combining the output I2 of all CT windings into one common point and by connecting to a neutral wire( Figure 6).

Figure 6 - Turning transformers into a "star"

The drawback of this method of connecting an electricity meter to a 380 Volt network is the lack of visibility of the wiring diagram, which can complicate the inclusion check for representatives of power supply companies.

Indirect

This connection scheme for a three-phase meter is used on high-voltage connections. This type of indirect connection is used in most cases only at large enterprises and is given only for acquaintance( Figure 7).

Figure 7 - Indirect inclusion of

In this case, not only high-voltage current transformers, but also voltage transformers are used. For a three-phase connection, it is necessary to ground the common point of the current and voltage transformers. To minimize the measurement error, if there is unbalance of phase voltages, it is necessary that the neutral conductor of the network be connected to the zero terminal of the counter.

The proposed wiring diagrams are typical. In case it is necessary, the connection diagram of the meter can always be viewed in the ES certificate. We hope that the information was interesting and useful for you!