What should be called the current marked on the energy meter?

Hello teacher: According to the national standard GB T15283-94 and the international standard IEC521-1988, the electric energy meter is marked with two current values, such as 10 (20) A. The marked 10A here is the basic current (basic current), and the symbol IB is the current value that determines the relevant characteristics of the instrument, and this current value is also called the calibration current.

The brackets marked (20)a are the rated maximum current, and the symbol is imax, which is the maximum current value for the meter to meet the accuracy specified in the standard. The current through the electric energy meter can be as high as two, three, four times of its basic current, and some are as high as eight times, and only the basic current value can not be reached twice. That is to say, if a user installs an energy meter with only one current value, such as 5A, this is only the basic current value, not the maximum current allowed.

For this kind of energy meter, generally speaking, an overload of 120% will not cause problems, and it can meet the accurate measurement of the energy meter. ......

In physics teaching, there is often a misunderstanding about the current selection of the electric energy meter, such as: "The electric energy meter is marked with a voltage value and a current value, the marked voltage is the rated voltage, and the marked current is the maximum current allowed to pass." An energy meter marked '220V5A' can be used in a home circuit with a maximum power of 220V 5A = 1100W, if the total wattage of household appliances used at the same time exceeds this value, the calculation of the energy meter will be inaccurate or even burn out.

This statement is not in line with reality, and some common practice questions and exam questions written on the basis of this are also inappropriate.

Excerpted from the junior high school physics special analysis series "Safe Electricity and Home Circuits" (People's Education Publishing House, 2003 edition) can be used for reference.

A is the normal current and 2A is the maximum current that can be used for a short time.

Equivalent to a wire. An ammeter is the equivalent of a wire in a circuit, and a voltmeter is equivalent to an open circuit in a circuit.

Under normal circumstances, we think that there is no voltage on the wire, in fact, there is voltage on the wire, but because it is very small, so it is regarded as no voltage, in the first series circuit voltage law experiment, we get the law is that in the series circuit, the sum of the voltages at both ends of the electrical appliances is equal to the total voltage. It can be seen that the resistance of the wire is indeed not considered.

Precautions for the use of ordinary ammeters.

1. The ammeter should be connected in series in the circuit.

2. The appropriate range should be selected according to the size of the measured current. For the ammeter with two ranges, it has three terminals, and when using, it is necessary to see the range mark of the terminal clearly, and connect the common terminal and one range terminal in series in the circuit under test.

3. When measuring DC current, the "+" polarity of the terminal of the DC ammeter should not be wrong, otherwise the instrument may be damaged. Magnetoelectric ammeters are generally only used to measure DC current.

Usually in use, the calibration current refers to the normal working current, that is, under the condition of this current, its accuracy is the highest, that is, you usually only use a few amperes of current, and the electric energy meter used is tens of amperes, which imitates the residual time when the electric energy meter records less than the actual electric energy.

In addition, the magnetoelectric energy meter (the old-fashioned energy meter with an aluminum disk) has a starting current, and the starting current is generally 5% of the calibrated current, and below this current, the electric energy meter does not rotate, and the electric energy cannot be recorded. The rated maximum current is twice the rated current, and if this current is exceeded for a long time, the meter will burn out.

The calibration current of the electric energy meter is 10A, the rated maximum current is 20A, and the calibration current is used to calculate the base current value of the load, and it is multiplied to calculate the starting current of the electric energy meter. That is to say, the smaller the calibration current, the smaller the starting current of the energy meter, and the more sensitive and accurate the energy meter is.

1.The calibration current refers to the current when the electrical equipment works continuously for a long time and the stable temperature reaches the maximum allowable temperature, which becomes the calibration current of the equipment.

2.Rated current refers to the current when the electrical equipment operates at the rated voltage and according to the rated power.

3.It can also be defined as the current at which electrical equipment can work continuously for a long time under rated environmental conditions (ambient temperature, sunlight, altitude, installation conditions, etc.).

4.The current of the appliance should not exceed its rated current when it is working normally.

5.The meaning of the calibrated current is completely different from the meaning of the rated current, for example, there is always a word indicating the current on the energy meter, such as 10 (20)A, 10 means that the calibrated current of the meter is 10A, and the maximum rated current is 20A.

6.The current 20 in parentheses is called the rated maximum current, which is the maximum current value that can make the electric energy meter work normally for a long time, and the error and temperature rise fully meet the specified requirements.

1. The calibration current refers to the continuous work of the electrical equipment for a long time, and the current when the stable temperature reaches the maximum allowable temperature becomes the calibration current of the equipment.

2. The rated current refers to the rated voltage of the electrical equipment.

, in accordance with the rated power.

Current at runtime. It can also be defined as the current at which the electrical equipment can work continuously for a long time under rated environmental conditions (ambient temperature, sunshine, altitude, installation conditions, etc.). The current of the appliance should not exceed its rated current when it is working normally.

3. The meaning of calibration current is completely different from the meaning of rated current, such as electric energy meter.

There is always a word indicating the current such as 10 (20) A, 10 means that the rated current of the meter is 10A, and the maximum rated current is 20A. The current 20 in parentheses is called the rated maximum current, which is the maximum current value that can make the electric energy meter work normally for a long time, and the error and temperature rise fully meet the specified requirements.

10 (20)A means that the rated current of this energy meter is 10 amps, and the rated maximum current is 20 amps. When this energy meter needs to work for a long time, the current cannot exceed 10 amps, and if it works for a short time, the current cannot exceed 20 amps.

The rated current refers to the current when working normally, that is, the above 10A, 20A is the maximum current, because the current work is unstable and will fluctuate up and down, there are fluctuations in 10 20A, 10A is the ideal state, the loss of equipment is small, 20A is the maximum current, the loss of equipment is large, and it is generally not allowed to work at the maximum current.

<> parameter circled in red in the figure: 5(20)a. Looking at the unit, we know that it writes about current, so what is the relationship between these two currents?

What happens when the current is exceeded? Let's talk about what the two currents refer to according to the parentheses (5) and parentheses (20).

Current in parentheses.

The current in parentheses – 20A in the example – refers to the maximum current rating of the energy meter. The electric energy meter is different from other equipment, its rated current is greatly affected by environmental factors, so when leaving the factory, a certain margin is generally left - the actual maximum rated current is 120% of the marked current. Therefore, if the number in parentheses is 20, then its maximum current rating is 24A – if it is not in a particularly harsh environment, it will generally not affect the maximum rated current by 20%.

Therefore, the maximum rated current of the meter marked 20A is generally about 22A when actually used.

Current outside parentheses.

The 5 in parentheses here is called the basic current, also known as the calibration current. It is determined by the starting current of the energy meter – the minimum current that allows the meter to rotate continuously and be metered continuously. Generally, the starting current of a smart meter is the calibration current.

That is, a meter with a calibrated current of 5A, when used, as long as the current in the circuit is reached, it will be charged. There will be a ratio between the rated current and the maximum rated current, such as 5 (20)a, which is a 4-fold relationship. This ratio is called the "load width".

Generally, there are 2 times, 4 times, 6 times, 8 times or even more than ten times - the larger the load width, the stronger the technical level required, and the ** of the meter is naturally higher.

Therefore, the numbers outside the parentheses have little to do with the actual use of the user - more than this value or below this value will not have an impact on the metering of the meter. There are two main factors that are affected by the calibration current: the meter** (which is related to the load width) and the starting current (which is calculated from the calibration current).

The rated current of the electric energy meter is the rated current and the maximum working current when the electric energy meter is working.