An electricity meter is a specialized instrument for measuring and recording the cumulative value of electrical energy. It is currently the most widely used and numerous electrical energy metering instrument. Also known as an energy meter, kilowatt-hour meter, or cumulative power meter, and commonly called a "fire meter," it is used to measure the electrical energy generated by a generator or consumed by a load within a specific time period. The difference between an electricity meter and a wattmeter is that an electricity meter is specifically used to measure the electrical energy generated by a generator or consumed by a load within a certain time period.
Electricity meters used to measure direct current (DC) energy are electric energy meters. Due to their complex structure and manufacturing process, they are expensive and unsuitable for measuring alternating current (AC) energy. Electricity meters used to measure alternating current (AC) energy are induction energy meters. They have a simpler structure and manufacturing process, are inexpensive, and have a larger torque. Induction energy meters can be classified according to their application into single-phase energy meters, three-phase active energy meters, and three-phase reactive energy meters. Single-phase energy meters are mainly used to calculate the electricity consumption of general users, while three-phase energy meters are used to calculate the electricity consumption of power plants, factories, mines, and enterprises.
With the development of science and technology, in addition to induction energy meters, new types of energy meters such as electronic energy meters and static energy meters have emerged in recent years.
I. Electricity Meter Models and Specifications
1. Model
Electricity meter model numbers are represented using a combination of letters and numbers. They typically consist of a category code, group code, application code, and design serial number (digits).
Category code: The first digit D indicates an electricity meter.
Group code: The second digit D indicates single phase; S indicates three-phase three-wire; T indicates three-phase four-wire; X indicates reactive power; B indicates standard.
Application codes: Z indicates maximum demand; F indicates time-of-use billing; S indicates electronic; Y indicates prepaid; D indicates multi-functional; M indicates pulse.
Design serial number: Represented by Arabic numerals, this is the serial number specified in the manufacturer's production design. The number following the hyphen indicates the maximum permissible overload multiple of the meter's rated current. For example, the DT864-4 type energy meter means a three-phase four-wire active energy meter with design serial number 864, and a rated maximum current of 4 times the rated current; the DTSD341 type energy meter means a three-phase four-wire electronic multi-function energy meter with design serial number 341.
Energy meters; DDY11 type indicates a single-phase prepaid energy meter with design serial number 11, etc.
In addition to the above-mentioned model designations, some electricity meters are also marked with derivative codes, such as T for both humid and dry conditions; TH for humid tropical conditions; TA for dry tropical conditions; G for high-altitude conditions; and F for chemical corrosion protection.
2. Specifications
Rated voltage (also known as reference voltage): This indicates the voltage at which the electricity meter is connected to the circuit. Common voltages include 220V; 3×380V; 3×380/220V; 3×100V; and 3×100/10,000V.
Rated current: This indicates the rated current and the rated maximum allowable current of the electricity meter connected to the circuit. The rated current is only used as a basis for calculating the load of the electricity meter, while the maximum rated current is the load current that the electricity meter is allowed to operate for a long time. For example, electricity meters marked as 1.5 (6) A and 10 (40) A have rated currents of 1.5 A and 10 (40) A, and maximum allowable load currents of 6 A and 40 A, respectively.
Rated frequency (also known as reference frequency): This represents the frequency value that determines the relevant characteristics of an electricity meter, measured in Hertz (Hz). The rated frequency of domestically produced electricity meters is 50Hz.
II. Main Technical Characteristics of Electricity Meters
(l) Accuracy Class and Load Range. Chinese national standards stipulate that the accuracy classes for active energy meters are 0.5, 1.0, and 2.0; and the accuracy classes for reactive energy meters are 2.0 and 3.0. Under rated voltage, rated current, rated frequency, and cos±1 conditions, after 5000 hours of operation for a 1.0 class three-phase energy meter and 3000 hours of operation for other energy meters, their basic error should still meet the requirements of the original accuracy class.
The rated current of an electricity meter serves only as a basis for calculating the meter's load, while the maximum current is the current allowed for long-term operation. One of the important indicators of an electricity meter's performance is the breadth of its applicable load current range. Wide-load electricity meters can operate at currents exceeding the rated current by two, three, four, or even six or seven times. Within this permissible range, its basic error should still not exceed the originally specified value. This performance is expressed as the "rated maximum current."
(2) Sensitivity. When the electricity meter is under rated voltage, rated frequency and power factor cos+=1, the load current is adjusted and increased uniformly from zero. Only when it reaches a certain size will the disc start to rotate continuously. The percentage of the minimum current that makes the electricity meter start to rotate continuously to the rated current is the sensitivity of the electricity meter. According to regulations, this current should not exceed 0.5% of the rated current.
(3) Creep (also known as no-load automatic). Creep refers to the phenomenon that the meter disc still rotates slightly when the load current is zero. According to regulations, when the current in the current circuit of the meter is zero, and the voltage applied to the voltage circuit is 800% to 110% of the rated value, the meter disc should not rotate a full revolution (for cam-type counters, this condition only applies to one cam rotation); otherwise, it is called "creep".
"Creeping" in an electricity meter is an abnormal phenomenon caused by improper assembly and adjustment of the meter's components.
(4) Power consumption. When there is no current in the current coil of the energy meter, the power consumed in the voltage line of a single-phase energy meter and in each voltage line of a three-phase energy meter should not exceed the specification under the rated voltage and rated frequency.
