Electric energy meters are commonly known as "electricity meters", or simply "electric meters", and are used to measure the active energy value of electricity. According to the number of measurable AC power phases, there are two types of single-phase and three-phase. Today, let's talk about single-phase energy meters.
Selection of low-voltage single-phase electric energy meters
Mantra:
The use of electrical energy must be counted, and electrical energy meters are not required.
The displayed value is kWh, and the people commonly call it degree.
To calculate the total electricity consumption, multiply the total kilowatts by five.
Choose the current value of the meter, three times the kilowatt can be satisfied.
There are two marked currents, one each inside and outside the brackets.
There are multiples from the outside to the inside, from double to quadruple.
The calibration value is outside the brackets, and the overcurrent number is inside the brackets.
Normally use the calibration value, and use the overcurrent with a degree.
Description:
(1) Introduction to the energy meter
The single-phase electric energy meter is the most widely used electricity consumption measuring instrument, which is used to measure the active energy value of electricity. In our country, there are probably more than hundreds of millions in use. This meter is commonly known as "electricity meter", or simply "electric meter".
There are two major types of electric energy meters: the traditional electromagnetic turntable type and the new electronic digital display type. In addition, there are various types such as card insertion and prepayment type.
The unit of electricity consumption displayed by the energy meter is kilowatt hour, which is abbreviated as "kW · h" with the symbol, commonly known as "degree", that is, 1 kilowatt hour is 1 degree. 1 kilowatt-hour is the power consumed by the electrical equipment with a power of 1 kilowatt (kW) for 1 hour (h).
When the power consuming element of the electrical equipment is pure resistance, the electric energy A (kW • h) consumed in a period of time t (h) is equal to the voltage U (V) and the current I (A) flowing across it And the product of the power-on time t (h), ie
A = Uit (W • h) = Uit / 1000 (kW • h)
(2) Basis for selecting electric energy meter
There are two reasons for choosing an energy meter: one is the rated voltage, and the other is the rated current (usually called the calibration current). China's single-phase power supply voltage is generally 220V, so the rated voltage of the energy meter should also be 220V. The selection of rated current should be based on the total current value of the powered equipment. The rated current calibrated by the energy meter should not be less than the total current value, but in order to ensure the accuracy of the instrument, it should not be greater than 4 times the total current value of electricity . When the electrical equipment is all resistive loads, the total electrical current value can be obtained by dividing the total power (active power) of the electrical appliances used by the rated voltage. When the rated voltage UN is 220V and the unit of power PN is kW, the total current value of electricity consumption IN (A) should be
IZ = 1000PZ / UZ = 1000PN / 220≈4.4545PN≈5PN
For simple calculations, IZ≈5PN can be used.
In modern life, most of the single-phase electrical equipment is no longer a purely resistive load. At this time, the total current is equal to the total power divided by the rated voltage and then divided by the total power factor of the electrical load cosφ (0.8 ~ 0.9), so The current is larger than the result calculated by the above formula, generally 10% ~ 20% larger. Therefore, it should be reasonable to calculate the total current value of electricity according to 5 times of the total power. This is the origin of "calculating the total current of electricity consumption, multiplying the total number of kilowatts by five."
However, considering the reality that all electrical appliances will not be used at the same time, and the "overload" capability of the energy meter 4 (or 2) times the calibrated current value, in order to save investment in the purchase of an energy meter, the calculation of the value of the rated current of the energy meter should not be based on The calculated total current value. Practice has proved that three times the total power of kilowatts can meet the requirements. This is the origin of "choosing the current value of the meter, three times the kilowatt can be satisfied" in the mantra.
The last few sentences of the mantra are about the current problem marked by the energy meter. There are two current values marked on the dial of the instrument, one of which is placed in parentheses, for example 5 (20) A. Both values are in a multiple relationship, generally 2 times or 4 times. The value outside the brackets is small, called the calibration value, or the rated value, which is the main basis for selecting the current of the supporting circuit, and the current value to ensure the accuracy and normal operation of the instrument; the larger value in the brackets is called the allowable overcurrent Value, the instrument can work within its range, but its accuracy will not be guaranteed, and it is not suitable for long-term use.
Direct wiring method of low-voltage single-phase electric energy meter
Mantra:
Single-phase electric meter with four ports, one, two, three, four left to right.
One and two are connected to three, four and zero.
The small contiguous piece next to the No. 1 terminal should not be removed as it is.