Calibration method of electric energy meter power frequency magnetic field interference test device

Abstract

The invention provides a calibration method for a power frequency magnetic field interference test device of an electric energy meter, relates to the technical field of calibration methods for power frequency magnetic field interference test devices of electric energy meters, standardizes the calibration rules of the power frequency magnetic field interference test device of the electric energy meter, and comprehensively confirms the metering performance of the device. Comprising the steps of calibrating an electric energy basic error, power stability, a current indication error, a current distortion degree, a magnetic field coil constant error, magnetic field uniformity and a phase difference; the invention aims to reduce the workload and comprehensively confirm the metering performance of the device by optimizing and improving the existing test items and test methods, is worthy of popularization and application, stipulates some technical parameters of the power frequency magnetic field interference test device for the electric energy meter, improves and perfects the traditional calibration method, and improves the test efficiency. And a technical guarantee is provided for the anti-electromagnetic interference capability detection of the alternating current measuring equipment.

Description

Technical Field

[0001] The invention relates to the technical field of calibration for a power frequency magnetic field interference test device, and in particular to a calibration method for a power frequency magnetic field interference test device for an electric energy meter. Background Art

[0002] If the installation and wiring of the electric energy meter at the work site are unreasonable, the electric energy meter is in the power frequency magnetic field space, such as the operation of the power system, the operation of the motor, etc. If the anti-interference ability of the electric energy meter is insufficient, the magnetic flux generated by the power frequency magnetic field will generate an induced electromotive force in the current sampling circuit of the electric energy meter, which may cause the meter to "run away" and cause erroneous measurement, or even damage the electric energy meter. The anti-interference performance of the electric energy meter is tested with the power frequency magnetic field interference test device of the electric energy meter. Through the power frequency magnetic field anti-interference test, the anti-interference ability problem of the meter can be discovered in time, and corresponding measures can be taken to improve and optimize the product.

[0003] The power frequency magnetic field interference test device for electric energy meters is widely used, for example, in legal metrology technical institutions, electric measuring instrument manufacturers, State Grid technical institutions, etc. For example, the fully automatic alternating magnetic field immunity test device mentioned in the patent application number 202110420850.7 for an external power frequency magnetic field test method for electric energy meters is also an improved power frequency magnetic field interference test device for electric energy meters. The power frequency magnetic field interference test device for electric energy meters is shown in the attached figure. Figure 1 As shown, it is generally composed of an electric energy meter calibration device, an excitation unit (including an industrial frequency current source and a magnetic field coil), a power supply differential module and a motion control unit.

[0004] The International Electrotechnical Commission (IEC) has issued the IEC 61000-4-8 standard, which specifies the test methods and requirements for the immunity of equipment to power frequency magnetic field interference, mainly including: the characteristics of power frequency magnetic field interference, test equipment and methods, and the level of power frequency magnetic field interference. Correspondingly, my country has successively issued national standards for various products based on international standards and international recommendations, such as the GB / T 17215 series of standards for electrical measuring equipment (AC). This standard only puts forward requirements for the test methods of products, but there are no relevant national technical regulations on how to calibrate the power frequency magnetic field interference test equipment of electric energy meters.

[0005] GB / T 17215 Electrical Measuring Equipment (AC) standard series proposes three tests: external power frequency magnetic field test, external power frequency magnetic field (no load condition) test, and external power frequency magnetic field interference test. For the excitation unit, the test items apply to the magnetic field strength of 0.5mT and 1.25mT. For the electric energy meter calibration device, the test items apply to I tr , 10I tr and I max Importantly, the test items mention the “most unfavorable direction and phase”.

[0006] An analysis of the reported calibration schemes revealed the following problems: (1) It is not advisable to calibrate all items of the electric energy meter calibration device according to the relevant calibration procedures, as the power frequency magnetic field test items only concern the partial metering performance of the electric energy meter calibration device; (2) Only the magnetic field strength in the center area of ​​the magnetic field coil is measured, and the error of the magnetic field strength should be calculated to give a conclusion, and a correction method for the magnitude of the magnetic field strength should be given when necessary; (3) The area where the electric energy meter is tested is not involved, and the uniformity of the magnetic field should be considered, and the impact of the magnetic field uniformity cannot be ignored; (4) The requirements of the test device for the "most unfavorable direction and phase" test conditions are ignored, and there is a lack of a method to measure the phase difference.

[0007] In view of the above, the present invention provides a calibration method for an electric energy meter power frequency magnetic field interference test device to solve the above problems. Summary of the invention

[0008] The present invention aims to reduce the workload and fully confirm the metering performance of the device by optimizing and improving the existing test items and test methods, and is worthy of promotion and application. The present invention stipulates some technical parameters of the power frequency magnetic field interference test device of the electric energy meter, improves and perfects the traditional calibration method, and provides technical guarantee for the electromagnetic interference immunity detection of the AC measuring equipment.

[0009] A calibration method for an electric energy meter power frequency magnetic field interference test device standardizes the calibration rules of the electric energy meter power frequency magnetic field interference test device, comprehensively confirms the metering performance of the device, and is characterized in that it includes calibration of basic error of electric energy, power stability, current indication error, current distortion, magnetic field coil constant error, magnetic field uniformity, and phase difference.

[0010] The beneficial effects of this technical solution are:

[0011] (1) This solution only needs to measure the basic error and power stability of the combined electric energy, eliminating unnecessary test items, and can verify the metering performance of the electric energy meter calibration device, and also greatly reduces the workload;

[0012] (2) This scheme provides a method for measuring the magnetic field coil constant error and magnetic field uniformity, and provides a method for correcting the magnetic field strength when it does not meet the requirements;

[0013] (3) This scheme measures the phase difference between the reference voltage of the input electric energy meter and the angle between the excitation current, which can verify the measurement capability of the power frequency magnetic field test device for the most unfavorable phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structure of a typical power frequency magnetic field interference test device for electric energy meters in the prior art;

[0015] Figure 2 This is a schematic diagram of current indication error measurement in the present invention;

[0016] Figure 3 This is a schematic diagram of current distortion measurement of the present invention;

[0017] Figure 4 This is a schematic diagram of the measurement points in the uniform area of ​​the magnetic field coil of the present invention. DETAILED DESCRIPTION

[0018] The present invention provides a calibration method for an electric energy meter power frequency magnetic field interference test device, which aims to standardize the calibration rules of the electric energy meter power frequency magnetic field interference test device, and comprehensively confirm the metering performance of the device, including the calibration of basic error of electric energy, power stability, current indication error, current distortion, magnetic field coil constant error, magnetic field uniformity, and phase difference. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail in conjunction with the accompanying drawings and specific implementation methods.

[0019] The power frequency magnetic field interference test device of the electric energy meter is generally composed of the electric energy meter verification device, the excitation unit (including the power frequency current source and the magnetic field coil), the power supply differential module and the motion control unit. According to the three test items in the GB / T17215 series of national standards, for the electric energy meter verification device, the focus is on I tr , 10I tr and I max The electric energy error, the test items determine the "most unfavorable direction and the most unfavorable phase" according to the maximum variation, so the stability of the electric energy meter verification device has a great influence on the variation.

[0020] 1. Basic error of electric energy

[0021] Connect the reference standard to the output end of the electric energy meter verification device. After preheating and stabilization, compare the electric energy E0 measured by the reference standard with the electric energy E indicated by the electric energy meter verification device. i Substitute into formula (1) to calculate the basic error r of the electric energy meter verification device i , respectively measure the power factor The basic error of the combined electric energy of single-phase, three-phase three-wire and three-phase four-wire wiring methods when they are 1.0 and 0.5L.

[0022]

[0023] 2. Power stability

[0024] Select the control limit (such as 220V, 5A or 100V, 1.5A), and then When the power is 1 or 0.5L, a power reference standard with high enough stability and resolution is selected. The power is read once every 1s to 1.5s. The measurement time is at least 2min. The output is not allowed to be adjusted in the meantime. The stability of the output load power of the electric energy meter verification device is calculated according to formula (2):

[0025]

[0026] Among them, p i is the power measured in a single shot, To measure the average power over a period of time, gross errors should be removed from the calculation.

[0027] 3. Current indication error

[0028] Using the standard meter method, the output end of the power frequency current source is connected in series with the magnetic field coil and the ammeter. Using the direct comparison measurement method, the ammeter is used to measure the current value output by the power frequency current source. The measured value is I s The current output value of the calibrated power frequency current source is I x , then the current indication error of the calibrated power frequency current source output is expressed by formula (3):

[0029] ΔI=I x -I s (3).

[0030] 4. Current distortion

[0031] The output end of the industrial frequency current source is connected in series with the magnetic field coil, the current-voltage conversion standard or the standard resistor, and the distortion is measured at both ends of the current-voltage conversion standard or the standard resistor using a distortion meter to obtain the distortion.

[0032] 5. Magnetic field coil constant

[0033] Connect the output end of the power frequency current source in series with the magnetic field coil and the ammeter, adjust the current output of the power frequency current source, so that the magnetic field coil generates 0.5mT and 1.25mT magnetic field strength respectively, place the AC magnetometer probe with an accuracy better than Class 2 at the center of the magnetic field coil axis, adjust the probe angle so that the probe plane is perpendicular to the magnetic field direction, and the AC magnetometer displays the maximum indication. Read the indication of the AC magnetometer B i And record the current output value I of the AC source i , calculate the error ε of the magnetic field coil constant according to formula (4):

[0034]

[0035] Where K is the nominal value of the magnetic field coil constant, in mT / A; B i is the magnetic field strength indication of the AC magnetometer, in mT; I i is the current value, the unit is A;

[0036] The magnetic field coil constant error is measured at 0.5mT and 1.25mT magnetic field strengths, and the maximum error value is taken as the magnetic field coil constant error. If the magnetic field strength does not meet the test requirements, the calculated value of the magnetic field coil or the current correction value corresponding to each magnetic field strength is input into the operating system of the test device for correction.

[0037] 6. Magnetic field uniformity

[0038] The test device is connected normally, and the industrial frequency current source outputs a certain current value to make the magnetic field coil generate an appropriate magnetic field strength (recommended 0.5mT or 1.0mT). The AC magnetometer probe is placed on 7 points of the magnetic field coil for measurement, including the center of the magnetic field coil (point O); the two intersections of the magnetic axis of the magnetic field coil and the edge of the uniform zone (points 1 and 2); and the four intersections of the two orthogonal lines that are orthogonal to the magnetic axis and pass through the center of the magnetic field and the edge of the uniform zone (points 3, 4, 5, and 6). Determine the position of each measurement point by measuring with a ruler. The spherical area formed by the 7 points should be larger than the area where the electric energy meter is located during the test. Calculate the relative difference between the magnetic field strength of the 6 points and the center of the magnetic field coil (point O). The maximum relative difference is the uniformity, see formula (5):

[0039]

[0040] Among them, δ i is the relative difference between the magnetic induction intensity measured at the i-th point and the center point of the magnetic field coil; B i is the measured value of the magnetic field strength at the i-th point of the magnetic field coil, mT; B0 is the measured value of the magnetic field strength at the center point of the magnetic field coil, mT.

[0041] 7. Phase difference

[0042] In a patent for an external power frequency magnetic field test method for an electric energy meter with application number 202110420850.7, it is mentioned that "when the angle between the excitation current of the coil and the reference voltage of the input electric energy meter is ±90°, the external power frequency magnetic field has the greatest impact on the electric energy meter, which is the most unfavorable phase". The angle between the excitation current and the reference voltage of the input electric energy meter is generally adjusted by the power supply and differential signal module. The angle is related to the most unfavorable phase, so the calibration of the angle phase difference is very important.

[0043] For the electric energy meter that collects load current through a manganese copper shunt, the most unfavorable phase has been derived as ±90° in the patent with application number 202110420850.7; for the electric energy meter that collects load current through a current transformer, the influence of the power frequency magnetic field on the magnetic conductive material of the current transformer changes the magnetic flux vector balance of the current transformer and produces a metering error. It is necessary to find the most unfavorable phase through testing, which will be used for subsequent external power frequency magnetic field experiments to test the anti-interference performance of the electric energy meter under the most unfavorable direction and the most unfavorable phase conditions.

[0044] Connect the voltage end of the phase meter in parallel to the voltage output end of the electric energy meter verification device, clamp the current clamp on the connection line between the power frequency current source and the magnetic field coil, set the phase angle to 0°, 30°, 60°, 90°, 120°, 150°, 180°, 210°, 270°, 300°, 330°, and other phase angles can also be set according to the experimental conditions. The difference between the measured value and the set value of the phase angle is the phase difference, see formula (6):

[0045]

[0046] in, is the phase difference, in degrees; is the phase angle setting value, in degrees; is the measured value of the phase angle, in degrees.

[0047] In summary, by measuring the above 7 technical parameters, the detection performance of the power frequency magnetic field interference test device of the electric energy meter can be comprehensively evaluated.

[0048] The above description is only for illustrating the present invention. It should be understood that the present invention is not limited to the above embodiments, and various variations that conform to the concept of the present invention are within the protection scope of the present invention.

Claims

1. A calibration method for an electric energy meter power frequency magnetic field interference test device, which aims to standardize the calibration rules of the electric energy meter power frequency magnetic field interference test device, comprehensively confirm the metering performance of the device, and is characterized in that: It includes calibration of basic electric energy error, power stability, current indication error, current distortion, magnetic field coil constant error, magnetic field uniformity and phase difference.

2. The calibration method of the power frequency magnetic field interference test device of an electric energy meter according to claim 1 is characterized in that: The method for calibrating the basic error of electric energy specifically includes connecting a reference standard to the output end of the electric energy meter calibration device, and after preheating and stabilization, comparing the electric energy E0 measured by the reference standard with the electric energy E indicated by the electric energy meter calibration device. i Substitute into formula (1) to calculate the basic error r of the electric energy of the electric energy meter verification device i , respectively measure the power factor The basic error of the combined electric energy of single-phase, three-phase three-wire and three-phase four-wire wiring modes when the L is 1.0 and 0.5:

3. The calibration method of the power frequency magnetic field interference test device of an electric energy meter according to claim 1 is characterized in that: The power stability calibration method specifically includes connecting the reference standard to the output end of the electric energy meter calibration device, and after preheating and stabilization, the control limit can be selected as 220V, 5A or 100V, 1.5A, and the power factor When the power is 1 or 0.5L, a power reference standard with high enough stability and resolution is selected. The power is read once every 1s to 1.5s. The measurement time is at least 2min. The output is not allowed to be adjusted in the meantime. The stability of the output load power of the electric energy meter verification device is calculated according to formula (2): Among them, p i is the power measured in a single shot, To measure the average power over a period of time, gross errors should be removed from the calculation.

4. The calibration method of the power frequency magnetic field interference test device of an electric energy meter according to claim 1 is characterized in that: The calibration method of the current indication error specifically includes: using a standard meter method, connecting the output end of the power frequency current source in series with the magnetic field coil and the ammeter, using a direct comparison measurement method, and using the ammeter to measure the current value output by the power frequency current source, and the measured value is I s The current output value of the calibrated power frequency current source is I x , then the current indication error of the calibrated power frequency current source output is expressed by formula (3): ΔI=I x -I s (3)。 5. The calibration method of the power frequency magnetic field interference test device of an electric energy meter according to claim 1 is characterized in that: The current distortion calibration method specifically includes connecting the output end of the power frequency current source in series with the magnetic field coil, the current-voltage conversion standard or the standard resistor, and measuring the current-voltage conversion standard or the standard resistor at both ends with a distortion meter to obtain the distortion.

6. The calibration method of the power frequency magnetic field interference test device of an electric energy meter according to claim 1 is characterized in that: Since the magnetic field strength is proportional to the current value and the coil constant, several representative magnetic field strengths can be selected to measure the magnetic field coil constant error. The calibration method of the magnetic field coil constant error specifically includes connecting the output end of the power frequency current source in series with the magnetic field coil and the ammeter, adjusting the current output of the power frequency current source so that the magnetic field coil generates 0.5mT and 1.25mT magnetic field strengths respectively, placing an AC magnetometer probe with an accuracy better than level 2 at the center of the magnetic field coil axis, adjusting the probe angle so that the probe plane is perpendicular to the magnetic field direction, and the AC magnetometer displays the maximum indication at this time, and reading the indication B of the AC magnetometer. i and record the current value I i , calculate the error ε of the magnetic field coil constant according to formula (4): Where K is the nominal value of the magnetic field coil constant, in mT / A; B i is the indication of magnetic field strength of AC magnetometer, in mT; I i is the current value, the unit is A; The magnetic field coil constant error is measured at 0.5mT and 1.25mT magnetic field strengths respectively, and the maximum error value is taken as the magnetic field coil constant error. If the magnetic field strength does not meet the test requirements, the calculated value of the magnetic field coil or the current correction value corresponding to each magnetic field strength is input into the operating system of the test device for correction.

7. The calibration method of the power frequency magnetic field interference test device of an electric energy meter according to claim 1 is characterized in that: The magnetic field uniformity calibration method specifically includes: the test device is normally connected, the power frequency current source outputs a certain current value so that the magnetic field coil generates an appropriate magnetic field strength (recommended 0.5mT or 1.0mT), and the AC magnetometer probe is placed on 7 points of the magnetic field coil for measurement: the center point of the magnetic field coil, the two intersection points of the magnetic axis of the magnetic field coil and the edge of the uniform area, and the four intersection points of two orthogonal lines orthogonal to the magnetic axis and passing through the center of the magnetic field and the edge of the uniform area. The position of each measuring point is determined by measuring with a ruler. The spherical area formed by the 7 points should be larger than the area where the electric energy meter is located during the test. The relative difference between the magnetic field strength of the center point of the magnetic field coil and the other 6 points is calculated. The maximum relative difference is the uniformity, see formula (5): Among them, δ i is the relative difference between the magnetic induction intensity measured at the i-th point and the center point of the magnetic field coil, B i is the measured value of the magnetic field strength at the i-th point of the magnetic field coil, in mT; B0 is the measured value of the magnetic field strength at the center point of the magnetic field coil, in mT.

8. The calibration method of the power frequency magnetic field interference test device of an electric energy meter according to claim 1 is characterized in that: Since the angle between the excitation current and the reference voltage of the input electric energy meter is generally adjusted by the power supply and differential signal module, the angle is related to the most unfavorable phase, so the calibration of the phase difference is very important. For the electric energy meter that collects the load current through the manganese copper shunt, the most unfavorable phase is ±90°. For the electric energy meter that collects the load current through the current transformer, the influence of the power frequency magnetic field on the magnetic conductive material of the current transformer changes the magnetic flux vector balance of the current transformer and produces a measurement error. It is necessary to find the most unfavorable phase through testing. The calibration method of the phase difference includes connecting the voltage end of the phase meter in parallel to the voltage output end of the electric energy meter calibration device, clamping the current on the connecting line connecting the power frequency current source to the magnetic field coil, setting the phase angle to 0°, 30°, 60°, 90°, 120°, 150°, 180°, 210°, 270°, 300°, 330°, and other angles can also be set according to the experimental situation. The difference between the measured value and the set value of the phase angle is the phase difference, see formula (6): in, is the phase difference, in degrees; is the phase angle setting value, in degrees; It is the measured value of the phase angle in degrees. The calibration result is used for the subsequent external power frequency magnetic field experiment to detect the anti-interference performance of the electric energy meter under the most unfavorable direction and the most unfavorable phase conditions.

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