On large buildings and facilities, special electricity control mechanisms are installed, which are designed for volumetric currents (over 100A). Therefore, there is a need to install step-down transformers. To correctly take readings from all devices, a calculated electricity metering factor is needed.
What is the transformation ratio
The transformation ratio of the electricity meter is a technical parameter that determines the accuracy of the readings of energy metering devices.
Electricity meters of large facilities (industrial, commercial, etc.) are not directly connected to the general house network, because classical devices do not provide the required voltage level. To reduce the likelihood of breakdown, it is necessary to reduce the given input power through the installed transformers.
The calculated electricity metering factor is an indicator that reflects the ratio of current strength and meter data. With a large amount of electricity consumed, the devices do not reflect the actual amount, therefore an additional calculation is applied. The figure of the coefficient is several points higher than one. When multiplied, the value of the actually consumed electricity is obtained.
Another point is the level of the transformer in terms of error. Energy meters correspond to 0.5 or 0.2. The higher the value, the less accurate the data is shown by the devices.
Formula for determining CT
The calculation of the readings of an electric meter with current transformers and the corresponding coefficients is carried out according to a certain formula. The result reflects the required scaling - up or down data. In other words - the transformer changes the voltage level and shows fluctuations in numbers.
To understand how to correctly read the readings of an electricity meter with current transformers, it is worth understanding the formula used. In most cases, the transformation ratio is encrypted with the English letters k and n (other characters are less common). If the designation on the transformer is k ˂ 1, then the device works for increasing, if k ˃ 1 - for decreasing.
The general formula is as follows:
where: U1 - input voltage level, U2 - output level, N1 - primary winding (number of turns), N2 - secondary winding (number of turns).
This formula is used when winding losses can be neglected. Otherwise, resort to the following calculations:
where: R1 and R2 - data on the resistance of the primary and secondary windings, respectively, I1 and I2 - the level of the power of the electricity on the corresponding turns.
For large objects, formulas can be more complicated than those indicated, so that the calculations take into account all the nuances and details of electricity consumption.
The transformation ratio (metering) of the electric meter is the value by which the meter readings are multiplied in order to obtain more correct data. For example, for home networks - 20 units. If you use the coefficient and numbers from the meter screen, you can get the amount of actually consumed energy.
Varieties of electricity metering devices
Electricity metering devices are multifunctional mechanisms that can reflect the current position of data, store and transmit important information. Today, three different versions of calculating mechanisms are used.
Mechanical or induction metering devices
The classic type of device that is most common. The design consists of two conventional coils. One of them limits the AC voltage data, preventing distortion and getting an electric current. The second converts the AC voltage flow.
The main advantages are ease of use, durability of the devices. The service life of meters of this type is high and the cost is low. Minus - the dimensions of the mechanism.
Mechanical devices have a large error, which is very noticeable when used in low voltage networks.
Electronic metering devices
The devices have a higher level of accuracy in calculations, but their price is also higher. An additional plus is the ability to operate in several modes (for example, morning and night, two- and three-tariff devices).
Electronic meters convert incoming analog readings into a special digital coding, which in turn is converted by a small microcontroller. The received data can be seen on the display. They are trying to install such devices more and more often, replacing outdated mechanical models.
Other advantages are compact size, remote control capability.
Hybrid metering devices
They are a middle option between an electronic and mechanical counter. On the one hand, the devices are equipped with a digital display for convenience. On the other hand, they use the classical induction method for obtaining and processing data.
Hybrid devices are rarely installed, preferring analog or electronic mechanisms.
Helpful hints
Electricity meters allow you to see the amount of energy consumed in order to adequately estimate the consumption and calculate the final payment. Devices differ in accuracy class, power, degree of permissible error. To obtain accurate data, readings are taken, using a coefficient and a calculator, the actual consumption is calculated.
For residential buildings in urban areas and villages, small devices are used - single-phase meters (for example, Mercury 230 ART-03 CN, manufactured in Moscow) or multi-tariff devices suitable for a 220 Volt or 120 Ampere network.
It is important that every new device has a government approved seal. Without this, the readings of the electric meter will not be considered reliable and will not be accepted by the regulatory authorities. You can choose a suitable meter and calculate the actual indicators yourself or through inspectors.
