Classification and technical characteristics of induction measuring devices

There are single-phase and three-phase meters. Single-phase meters are used to measure electricity by consumers who are supplied with single-phase current (mainly domestic). Three-phase meters are used to measure three-phase electricity.

Three-phase meters can be classified as follows.

By type of measured energy — up to meters of active and reactive energy.

Depending on the power supply scheme for which they are intended - for three-wire meters operating in a network without a neutral wire and four-wire meters operating in a network with a neutral wire.

Counters can be divided into 3 groups according to the method of inclusion.

— Meters of direct connection (direct connection), are included in the network without measuring transformers. Such meters are produced for networks 0.4 / 0.23 kV for currents up to 100 A.

— Semi-indirect meters, with their current windings are switched on by current transformers. The voltage coils are connected directly to the mains.Area of ​​application — networks up to 1 kV.

— Inclined counters to include, are included in the network through current transformers and voltage transformers. Scope — networks above 1 kV.

Indirect connection measuring devices are produced in two types. Transformer Meters — are designed to be switched on by meter transformers with certain predetermined transformation ratios… These counters have a decimal conversion factor (10p). Universal Transformer Meters — designed to be switched on by meter transformers of any transformation ratio. For universal meters, the conversion factor is determined by the transformation factors of the installed measuring transformers.

Electricity meter designations

Depending on the purpose of the counter, a conventional designation is assigned. In the designations of counters, letters and numbers mean: C — counter; O — single-phase; L — active energy; P — reactive energy; U — universal; 3 or 4 for three or four wire networks.

Example of designation: CA4U — Three-phase transformer universal four-wire active energy meter.

If the letter M is placed on the plate of the meter, it means that the meter is designed to work at negative temperatures (-15 ° — + 25 ° C).

Electricity meters for special purposes

Active and reactive energy meters equipped with additional devices are classified as special purpose meters. Let's list some of them.

Two-speed and multi-speed meters - are used to measure electricity, the tariff for which varies depending on the time of day.

Prepaid meters - are used to measure electricity for household consumers living in remote and hard-to-reach settlements.

Counters with a maximum load indicator — are used for settlements with consumers under a two-tariff tariff (for consumed electricity and maximum load).

Telemetry meters - used to measure electricity and transmit readings remotely.

Special purpose counters include sample counters designed to verify general purpose meters.

Technical characteristics of electricity meters

The technical characteristics of the measuring device are determined by the following basic parameters.

Rated voltage and rated current of meters - for three-phase meters they are indicated as the product of the number of phases by the rated values ​​​​of current and voltage, for four-wire meters line and phase voltages are indicated. For example — 3/5 A; 3X380 / 220V.

For transformer meters, instead of the nominal current and voltage, the nominal transformation ratios of the measuring transformers for which the meter is designed are indicated, for example: 3X150 / 5 A. 3X6000 / 100 V.

On counters called overload meters, the value of the maximum current is indicated immediately after the nominal one, for example 5 - 20 A.

The rated voltage of direct and semi-indirect connection measuring devices must correspond to the rated voltage of the network, and of indirect connection measuring devices to the secondary rated voltage of the voltage transformers. Likewise, the rated current of the indirect or semi-indirect meter must match the secondary rated current of the current transformer (5 or 1 A).

Counters allow long-term overcurrent without disturbing the correctness of accounting: transformer and universal transformer — 120%; direct connection meters — 200% or more (depending on type)

The accuracy class of a meter is its maximum permissible relative error, expressed as a percentage. Active energy meters must be manufactured accuracy classes 0.5; 1.0; 2.0; 2.5; reactive energy meters — accuracy classes 1.5; 2.0; 3.0. Universal transformer and transformer meters for measuring active and reactive energy must be of accuracy class 2.0 and more accurate.

The accuracy class is set for the operating conditions called normal. These include: direct phase sequence; uniformity and symmetry of phase loads; sinusoidal current and voltage (linear distortion factor no more than 5%); nominal frequency (50 Hz ± 0.5%); nominal voltage (± 1%); rated load; cos phi = l (for active energy meters) and sin phi = 1 (for reactive energy meters); ambient air temperature 20 ° + 3 ° C (for internal measuring devices); absence of external magnetic fields (induction no more than 0.5 mT); vertical position of the counter.

The gear ratio of an induction meter is the number of revolutions of its disk corresponding to a unit of measured energy.

For example, 1 kWh equals 450 revolutions of the disc. The gear ratio is indicated on the nameplate of the meter.

Induction meter constant Is the amount of energy it measures per 1 revolution of the disk.

Induction meter sensitivity — is determined by the smallest value of current (as a percentage of nominal) at nominal voltage and cos phi = l (sin phi = 1) that causes the disk to rotate without stopping. In this case, the simultaneous movement of no more than two rollers of the counting mechanism is allowed.

The sensitivity threshold should not exceed: 0.4% — for measuring devices with accuracy class 0.5; 0.5% — for measuring devices with accuracy classes 1.0; 1.5; 2 and 1.0% — for measuring devices with accuracy class 2.5 and 3.0

Capacity of the counting mechanism - is determined by the number of hours of operation of the meter at nominal voltage and current, after which the glucometer gives initial readings.

Own energy consumption (active and full) of coils per meter — limited by the standard. So, for a transformer and universal transformer meters, the power consumption in each current circuit at rated current should not exceed 2.5 VA for all accuracy classes except 0.5. Power consumption of one coil of measuring voltage up to 250 V: for accuracy classes 0.5; 1; 1.5 — active 3 W, full 12 V -A, for accuracy classes 2.0; 2.5; 3.0 — 2 W and 8 V -A, respectively.

Some induction meters have the inscription «With plug» or «Locked reverse» on the plates.The plug prevents the disc from rotating in the opposite direction indicated by the arrow. Imported counters may have a graphic stop symbol.