According to the national standard GB/T15283-94 and the international standard IEC521-1988 electric energy meters are marked with two current values, such as 10⒇A. The 10A marked here is the basic current, and the symbol is the current value that determines the relevant characteristics of the instrument, which is also called the calibration current. The mark ⒇A in the bracket is the rated maximum current, and the symbol is the maximum current value that the instrument can meet the accuracy specified by the standard. The current passing through the electric energy meter can be as high as 2 to 8 times the basic current, which is less than twice the basic current value marked on the meter. In other words, if the electric energy meter installed by a user is only marked with a current value, such as 5A, this is only the basic current value, not the maximum current allowed to pass. For this kind of electric energy meter, it can generally be overloaded to 120% without problems, and it can meet the accurate measurement of the electric energy meter. On the other hand, due to the large resistance of the rotating mechanism of the induction electric energy meter, according to the standard, the starting current cannot be lower than 0.5% of the basic current (the accuracy of the electric energy meter). It can be seen that the electric energy meter is lightly loaded to the basic current. It may not start when it is less than 0.5%.
In China, the power supply line voltage of the family residence is 220V and the frequency is 50Hz. The rated voltage and applicable frequency of the selected electric energy meter should be consistent with the line voltage and frequency, and it should also be 220V, 50Hz.
When choosing an electric energy meter, the current value selection is the most important and the most complicated. One is the starting current, which is the minimum current that can make the turntable rotate continuously; the other is the multiple of the maximum rated current relative to the basic current. In addition, there are differences in performance between old and new watches. Old-style watt-hour meters still in use in old houses have a relatively large starting current, generally (5%-10%); the maximum rated current is small, generally ≤2, only one current value is marked on the dial surface, and it is generally called Rated current. Therefore, it is pointed out in the old electrician manual that the current of the load circuit should be greater than 10% of the rated current, less than 120% or less than 125%. According to the electric energy meter produced by the national standard GB/T15283-94 and the international standard IEC521-1988, the starting current of the electric energy meter used in the newly built residence is small, 0.5% for the grade meter; the maximum rated current is large, and the general maximum rated current is ( 2～4), some can reach (6～8). Two current values are marked on the dial surface of the new electric energy meter, such as 5 (20A). When choosing this electric energy meter, pay attention to the minimum load current not lower than the starting current, that is, 0.5%×≥5A=0.025A; On the other hand, the value of the ammeter used for a long time cannot be higher than the maximum rated current value of 20A. When choosing an electric energy meter, it should be considered that the number of electrical appliances entering the home is increasing, and there should be a margin, and it should be reasonable and moderate, because the larger the multiple, the higher the price.
The current value 10 before the brackets is called the calibration current, which is used to calculate the base current value of the load. The current 20 in the brackets is the rated maximum current, which is the maximum current that can make the energy meter work normally for a long time, and the error and temperature rise fully meet the specified requirements. value. According to the requirements of the regulations, the rated current of the direct-access electric energy meter should be determined according to the rated maximum current and the overload multiple. Among them, the rated maximum current should be determined according to the approved load capacity reported by the customer; the overload multiple is for normal operation If the actual load current of the electric energy meter in the watt-hour meter exceeds 30% of the maximum rated current, a double meter should be used; if the actual load current is less than 30%, a 4 times meter should be used.
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