How to choose single-phase electronic energy meter

Because the electronic energy meter has higher accuracy, lower power consumption, smaller starting current, wide load range, no mechanical wear and the like than the inductive electric energy meter, it is more and more widely used. However, there are many manufacturers of electronic energy meters on the market, the quality is uneven, and the choice is not good, not only can not play the advantages of electronic energy meters, but will bring undue losses and increase the workload of maintenance management. Electronic energy meters and our familiar inductive energy meters (commonly known as mechanical watches) have the same place, different places, and more different places, especially inside the watch, the inductive energy meter is powered Magnetic induction components, inside which are iron cores, iron rings and mechanical transmissions; while electronic energy meters mainly use electronic components, namely: resistors, capacitors and integrated circuits. Therefore, the choice should be based on this characteristic of the electronic energy meter. In other words, it is necessary to select the technical requirements of electronic equipment, and it is not possible to simply copy the electronic energy meter that was previously selected for the mechanical energy meter (of course, there are places to learn from). Now we are in the work to understand, the purchase of single-phase electronic energy meter, for the reference of the relevant staff.

1. Check the basic technical conditions that the manufacturer must have.

The electric energy meter is a national mandatory inspection measuring instrument. According to the measurement law, the selected electric energy meter must have a manufacturing measuring instrument license (CMC certificate) issued by the technical supervision bureau at or above the provincial level. This is a necessary condition for the manufacturer of the electric energy meter and the legal procedures that must be fulfilled. It can prove that the manufacturer has basic facilities, personnel and testing equipment, and can be produced and sold. However, in the current fierce market competition, power supply companies have more choices, so you can also compare other documents that prove the quality of products. Such as: the authoritative department's appraisal report, life test report, listed in the National Economic and Trade Commission "national urban and rural power grid construction and transformation of equipment products and manufacturers recommended catalogue", ISO9000 quality certification and so on. These are all important documents to prove the quality of the product.

Due to the fierce price competition among various manufacturers, it is not enough to rely solely on these documents based on experience. It can only prove that there is a basis for selection. The next step is to inspect the physical energy meter produced by the manufacturer according to the performance characteristics of the electronic energy meter and the national inspection regulations, according to the actual situation of the local power grid and climate.

2. Examine the physical quantity of the electric energy meter

The inspection of the physical energy meter sent by the manufacturer is mainly carried out from the following aspects. Namely: mechanical requirements, climatic conditions, electrical requirements, electromagnetic compatibility, accuracy requirements. These five aspects are clearly defined in the national standard "Class 1 and Class 2 Static AC Active Energy Meter" (GB/T17215-1998). Some test and inspection projects in the regulations generally have conditional inspections at municipal and county-level power supply companies, but there are quite a few projects that do not have conditional inspections. The following will give a brief description of the places to be noted and the solutions.

(1) Mechanical requirements:

Most of the mechanical requirements can be verified by visual inspection and simple test methods. Such as: four anti-shock (anti-electric shock; anti-high temperature; anti-flame spread; anti-solid foreign matter, dust and water into); lead seal is convenient and reliable (only after breaking the seal can touch the internal parts of the instrument); the terminal should have enough Insulation performance and mechanical strength; the structure and assembly of the case should ensure that the instrument does not interfere with the normal operation when non-permanent deformation occurs; the nameplate, wiring diagram, terminal mark meet the requirements and so on. These requirements are the most basic requirements for ensuring the safe operation of the energy meter, and can be observed and identified by experience. Selection must not be ignored. Special terminal plates should use flame retardant materials, such as injection phenolic resin; when using ABS engineering plastics, the casing should be checked for flame retardancy; the casing should not have obvious deformation and affect the sealing performance and the internal components have obvious relative displacement.

(2) Accuracy requirements:

Accuracy requirements include current and power factor changes, voltage changes, frequency changes, start-up tests, potential tests, and word-testing. These items are generally inspected by municipal and county-level power supply companies. The electronic energy meter is generally better in the load range specified by the regulations, but the load range of the actual accurate metering of different manufacturers is very different. Since the actual load current in the field is constantly changing, the load can be accurately measured. The wider the range, the better the load performance of the watch. In some areas of rural areas, grid voltage fluctuations are relatively large. Pay attention to the error of the energy meter when checking the voltage fluctuation limit. In particular, the light load error at low voltage and the power meter movement are powerful. The DC power supply voltage in the checklist cannot be lowered below the operating voltage of the meter and the chip, and the ripple of the DC power supply cannot be significantly increased.

Accuracy requirements include harmonics, external magnetic induction, and high frequency electromagnetic fields. Generally, municipal and county-level power supply enterprises do not have conditional inspections, and can be inspected by provincial power testing institutes.

(3) Electrical requirements:

The electrical power consumption test, including the voltage line and the current line, can be used to calculate the power consumption of the energy meter under the rated voltage and rated current after measuring the voltage, current and load impedance of the energy meter with the transformer calibrator. This method is both accurate and convenient; power supply influence, voltage drop and short-term interruption, self-heating effect can be simulated on the electric energy meter calibration table; short-time over-current will affect the inspection, and it is more difficult to strictly follow the rules. Under 2 times the maximum current, gradually extend the time to detect the temperature rise (current terminal and sampling resistance) and error of the energy meter. This can be done to understand the extent of damage to the meter after it has been overloaded.

In order to prevent the neutral point of the low-voltage power supply line from being disconnected, the voltage of a certain phase rises and burns the electric energy meter due to the imbalance of the load. The input voltage of the single-phase electric meter is raised to 420V, and after 4 hours, it is rated again. The electric energy meter under the voltage shall be qualified (the person shall be on duty during the test, pay attention to safety, and find an abnormal power-off check immediately).

(4) Climatic conditions and electromagnetic compatibility:

Both of these are important for electronic energy. In particular, the electromagnetic compatibility performance has a very serious impact on the electronic energy meter, and the table with poor electromagnetic compatibility performance often causes "dead" and "flying characters" in the field operation, and even internal electronic components are damaged. This is an important feature of electronic energy meters that differ from mechanical energy meters. There are five items in the electromagnetic compatibility test, namely: electrostatic discharge test, high frequency electromagnetic field test, electric fast transient pulse group test, surge test, radio interference suppression test. Among them, the surge and the pulse group are close to some transient conditions in the power grid. It is recommended that the prefecture-level and county-level power supply enterprises purchase corresponding equipment to conduct spot check on the electric energy meter.

In addition, it should be noted that due to the current mechanical meter of the electronic watch, the card problem has not been solved fundamentally. It is mainly to ensure the quality of the energy meter by selecting the meter with good manufacturing process and strict screening when entering the factory. Therefore, pay special attention to the quality of the meter. The stepping motor has shielding to prevent electromagnetic interference. The outer casing adopts aluminum alloy bracket, fine gear, no burr, material is not easy to be deformed, self-lubricating performance, strong magnetic performance of stepping motor, and precise machining, all of which can reduce the problem of card characters. Be careful to check and understand. Then it is necessary to carry out the word test. In order to more strictly assess the quality of the meter and ensure that the meter installed on the site can be correctly metered within the allowable range of voltage, it is recommended to use the lowest possible voltage (without considering the transient) voltage in the local grid.

3. Quality check of the energy meter in operation

The above checks still cannot fully guarantee that the electric energy meter is installed in the grid without any problems. Therefore, after installation and operation for a period of time, a spot check must be performed. The time interval of spot checks and the proportion of spot checks can be determined according to the quality of the energy meter in operation. The same batch of electric energy meter of the same manufacturer, the failure rate is small, the error variation is small, and the qualification rate is high, which can reduce the sampling ratio and the sampling time interval. Under normal circumstances, the first-time selection of factory products should not be less than 5%. The ratio of random checks within one year shall not be less than 10%. If the quality is stable and the error changes are small, the sampling ratio can be reduced, but at least 1% of the sampling should be taken every year to monitor the quality of the energy meter over time. Extend the selection of the electric energy meter to the whole use process, and further improve the purchase level by monitoring the situation in use.