A method for calibrating a multi-voltage-grade capacitance current tester based on a uniform variable ratio

Abstract

The application relates to the technical field of metrological calibration, and discloses a multi-voltage-grade capacitor current tester calibration method based on unified transformation ratio. The method comprises the following steps: screening unified transformation ratio parameters meeting range constraints and error constraints, obtaining a ratio difference parameter of a corresponding electromagnetic voltage transformer, obtaining a capacitance ratio difference correction factor, calculating conversion coefficients under each voltage grade, determining a primary side capacitance setting value according to a preset primary side calibration capacitance value and the conversion coefficients, obtaining a secondary side output capacitance value of a standard capacitance tank, and collecting a displayed capacitance value and a displayed capacitance current value. The conversion coefficients between the unified transformation ratio and the theoretical transformation ratios of each voltage grade are established, single transformation ratio is used to cover multi-voltage-grade calibration, error components introduced by the ratio difference of the electromagnetic voltage transformer in the capacitance calibration process are reduced, and different transformation ratio equipment needs to be frequently replaced.

Description

Technical Field

[0001] This application relates to the field of power equipment metering and calibration technology, and in particular to a calibration method for a multi-voltage level capacitor current tester based on a unified turns ratio. Background Technology

[0002] The capacitance current tester is required to accurately measure the primary capacitance of distribution networks with voltage levels ranging from 1 kV to 66 kV, covering a measurement range of 0.3 microfarads to 125 microfarads. Its core calibration principle is to connect a standard capacitor bank to the primary side of a voltage transformer and convert the primary capacitance to the secondary capacitance using the square relationship of the turns ratio. After measuring the secondary side, the tester calculates back the primary capacitance value based on the built-in turns ratio. The accuracy of the tester is evaluated by comparing the difference between the displayed value and the standard value.

[0003] The current calibration method in the industry generally adopts the "one ratio, one level" model. That is, for different voltage levels such as 6 kV, 10 kV, 20 kV, 35 kV, and 66 kV, electromagnetic voltage transformers with strain ratios of 60, 100, 200, 350, and 660 are selected respectively, along with standard capacitor boxes with matching ranges. When calibrating a 10 kV level tester, a voltage transformer with a strain ratio of 100 is used, and when calibrating a 35 kV level tester, it is replaced with a voltage transformer with a strain ratio of 350, and so on, to complete the calibration of each level.

[0004] The existing one-ratio, one-level calibration mode has three prominent drawbacks. First, the calibration efficiency is extremely low. Each time the voltage level is switched, the current electromagnetic voltage transformer needs to be disassembled and a new electromagnetic voltage transformer with a different ratio needs to be installed. It takes a long time for a single tester to complete the calibration of all five voltage levels. Second, the equipment cost is high. It is necessary to configure five different high-precision 0.1-level electromagnetic voltage transformers with different ratios at the same time, which is a heavy investment burden for the entire set of equipment. Third, the risk of error accumulation is prominent. Frequent replacement of electromagnetic voltage transformers and standard capacitor boxes can easily introduce additional error sources such as changes in contact resistance, signal interference, and unstable cable connections. The cumulative error caused by multiple equipment switching often makes the comprehensive error of the full-level calibration exceed the allowable error requirements specified in the standard, affecting the reliability and accuracy of the calibration results. Summary of the Invention

[0005] This application provides a calibration method for a multi-voltage level capacitance current tester based on a unified turns ratio. This method solves the problems of low efficiency, high equipment cost, and significant risk of error superposition caused by the need to frequently replace electromagnetic voltage transformers with different turns ratios in the calibration of multi-voltage level capacitance current testers based on a unified turns ratio in the prior art. It solves the problem of establishing a turns ratio error conversion coefficient and reduces the error component introduced by the ratio difference of electromagnetic voltage transformers during the capacitance calibration process.

[0006] This application provides a calibration method for a multi-voltage level capacitance current tester based on a uniform turns ratio, the calibration method comprising:

[0007] Step S1: Substitute each candidate transformer ratio in the standard transformer ratio set into the transformer ratio conversion formula, where the secondary side capacitance is equal to the product of the square of the candidate transformer ratio and the primary side capacitance. Based on different candidate transformer ratios, convert the primary side capacitance range into the corresponding secondary side capacitance range, and screen the unified transformer ratio parameters that meet the secondary side capacitance range constraints and error constraints.

[0008] Step S2: Obtain the ratio difference parameter of the electromagnetic voltage transformer corresponding to the unified ratio parameter, add 1 to the ratio difference parameter to obtain the capacitance ratio difference correction factor;

[0009] Step S3: Calculate the conversion coefficient for each voltage level based on the unified transformation ratio parameter, the capacitance ratio difference correction factor, and the theoretical transformation ratio corresponding to the voltage level set by the test instrument under test.

[0010] Step S4: Connect the electromagnetic voltage transformer corresponding to the unified transformation ratio parameter to the standard capacitor bank. Determine the primary side capacitor setting value according to the preset primary side calibration capacitor value and the conversion coefficient corresponding to each voltage level. Multiply the primary side capacitor setting value by the square of the unified transformation ratio parameter to obtain the secondary side output capacitor value of the standard capacitor bank. Collect the display capacitor value of the test instrument under test at each voltage level. Calculate the theoretical capacitor current value according to the theoretical phase voltage, angular frequency and preset primary side calibration capacitor value corresponding to each voltage level.

[0011] Step S5: Using the preset primary-side calibration capacitor value as the theoretical value of the primary-side capacitor, calculate the relative error of capacitance between the displayed capacitance value and the theoretical value of the primary-side capacitor; calculate the relative error of capacitance current between the displayed capacitor current value and the theoretical capacitor current value, and determine whether the relative error of capacitance and the relative error of capacitance current both meet the allowable error range.

[0012] The technical solution provided in this application filters out unified ratio parameters by substituting each candidate ratio in the standard ratio set into the ratio conversion formula. This overcomes the technical limitation of existing technologies that require separate configuration of corresponding strain ratio electromagnetic voltage transformers for each voltage level. The filtering process integrates two dimensions of judgment conditions: secondary side capacitance range constraint and error constraint. This ensures that the selected unified ratio parameters satisfy the requirement that the capacitance conversion values ​​for all five voltage levels fall within the range of the standard capacitor bank, while also ensuring that the back-calculation relative error, considering the influence of electromagnetic voltage transformer ratio difference, is controlled within the allowable range. This achieves the technical feasibility of using a single ratio to cover calibration of multiple voltage levels from 6 kV to 66 kV. It fundamentally eliminates additional error sources such as equipment switching time loss and contact resistance changes caused by frequent replacement of electromagnetic voltage transformers with different ratios. This reduces the calibration time for a single tester across all voltage levels from over 4 hours to less than 1.5 hours, while avoiding the equipment investment costs of configuring five different high-precision electromagnetic voltage transformers with different ratios. This significantly improves calibration efficiency and reduces equipment costs.

[0013] This invention establishes a quantitative correction relationship between different voltage levels under unified ratio calibration conditions by calculating the conversion coefficients for each voltage level based on unified ratio parameters, capacitance ratio difference correction factors, and the theoretical ratio corresponding to the voltage level set by the test instrument under test. The calculation of the conversion coefficients comprehensively considers the interaction of three key parameters: unified ratio parameters, theoretical ratio, and electromagnetic voltage transformer ratio difference. By dividing the square of the unified ratio parameter by the product of the square of the theoretical ratio and the capacitance ratio difference correction factor, the numerical difference between the back calculation using the theoretical ratio and the conversion using the unified ratio in the test instrument under test is accurately quantified. This realizes the conversion from the capacitance value under the unified ratio to the theoretical value of the primary side capacitance under different theoretical ratios, enabling accurate calculation of the theoretical value of the primary side capacitance and the theoretical capacitance current value for each voltage level under the unified ratio calibration framework. This provides a reliable theoretical reference value for the subsequent dual determination of capacitance relative error and capacitance current relative error, overcoming the problem of difficulty in calculating theoretical values ​​due to ratio mismatch in the prior art. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of an embodiment of the calibration method for a multi-voltage level capacitor current tester based on a uniform turns ratio in this application.

[0016] Figure 2 This is a schematic diagram comparing the converted values ​​of the secondary capacitor under different turns ratios in the embodiments of this application;

[0017] Figure 3 This is a schematic diagram of the connection relationship of the calibration system for a multi-voltage level capacitor current tester based on a unified transformation ratio in an embodiment of this application. Detailed Implementation

[0018] This application provides a calibration method for a multi-voltage level capacitance current tester based on a uniform turns ratio. The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, the terms "comprising" or "having" and any variations thereof are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0019] For ease of understanding, the specific process of the embodiments of this application is described below. Please refer to [link / reference]. Figure 1 One embodiment of the calibration method for a multi-voltage level capacitor current tester based on a uniform turns ratio in this application includes:

[0020] Step S1: Substitute each candidate transformer ratio in the standard transformer ratio set into the transformer ratio conversion formula, where the secondary side capacitance is equal to the product of the square of the candidate transformer ratio and the primary side capacitance. Based on different candidate transformer ratios, convert the primary side capacitance range into the corresponding secondary side capacitance range, and screen the unified transformer ratio parameters that meet the secondary side capacitance range constraints and error constraints.

[0021] The selection of unified transformation ratio parameters is based on the transformation ratio conversion relationship to realize range conversion verification. Each transformation ratio value in the candidate transformation ratio set is substituted into the relationship that the secondary side capacitance is equal to the product of the square of the candidate transformation ratio and the primary side capacitance. By calculating the secondary side converted capacitance value corresponding to the selected theoretical values ​​of the primary side capacitance under the candidate transformation ratio, it is determined whether all converted values ​​fall completely within the secondary side range constraint range of the standard capacitor box. At the same time, the influence of the ratio difference of the electromagnetic voltage transformer on the back calculation accuracy is considered to verify whether the back calculation relative error of each voltage level under the candidate transformation ratio meets the allowable range. The candidate transformation ratio that can cover all voltage levels and ensure that the error is controllable is selected as the unified transformation ratio parameter.

[0022] Step S2: Obtain the ratio difference parameter of the electromagnetic voltage transformer corresponding to the uniform ratio parameter, add 1 to the ratio difference parameter to obtain the capacitance ratio difference correction factor;

[0023] The capacitance ratio difference correction factor is obtained by adding the value 1 to the ratio difference parameter. This factor is used to correct the manufacturing deviation between the actual ratio and the nominal ratio of the electromagnetic voltage transformer. The ratio difference parameter reflects the degree of deviation of the actual ratio from the nominal value. The correction factor obtained by adding 1 to the ratio difference parameter represents the proportional relationship between the actual ratio and the nominal ratio. This correction factor is used in square form when calculating the conversion coefficient in the subsequent calculation because there is a square relationship between capacitance and ratio. Through this correction mechanism, the manufacturing error of the electromagnetic voltage transformer is quantified into a calculable correction parameter and incorporated into the conversion coefficient calculation.

[0024] Step S3: Calculate the conversion coefficient for each voltage level based on the unified turns ratio parameters, capacitance ratio difference correction factor, and the theoretical turns ratio corresponding to the voltage level set by the test instrument under test.

[0025] The conversion factor calculation uses the square of the uniform turns ratio parameter as the numerator and the product of the square of the theoretical turns ratio and the square of the capacitance ratio difference correction factor as the denominator for division. The numerator reflects the square relationship between the primary side capacitance and the secondary side capacitance under the actual uniform turns ratio parameter. The denominator comprehensively considers the theoretical turns ratio built into the test instrument under test and the square correction of the ratio difference of the electromagnetic voltage transformer. The conversion factor obtained by dividing the two quantifies the numerical conversion relationship between the uniform turns ratio calibration conditions and the theoretical turns ratio back calculation of the test instrument under test. The conversion factor values ​​are calculated by substituting the corresponding theoretical turns ratios for the five voltage levels and establishing a mapping relationship with the voltage level.

[0026] Step S4: Connect the electromagnetic voltage transformer corresponding to the unified transformation ratio parameter to the standard capacitor bank. Determine the primary side capacitor setting value according to the preset primary side calibration capacitor value and the conversion coefficient corresponding to each voltage level. Multiply the primary side capacitor setting value by the square of the unified transformation ratio parameter to obtain the secondary side output capacitor value of the standard capacitor bank. Collect the display capacitor value of the test instrument under test at each voltage level. Calculate the theoretical capacitor current value according to the theoretical phase voltage, angular frequency and preset primary side calibration capacitor value corresponding to each voltage level.

[0027] The primary side capacitor setting value is determined based on the preset primary side calibration capacitor value and the conversion coefficient corresponding to each voltage level. The primary side capacitor setting value is equal to the preset primary side calibration capacitor value divided by the conversion coefficient of the corresponding voltage level. The secondary side output capacitor value of the standard capacitor box is obtained by multiplying the primary side capacitor setting value by the square of the uniform transformation ratio parameter. The preset primary side calibration capacitor value is the same for different voltage levels, but the primary side capacitor setting value is different. After the test instrument measures the capacitor value on the secondary side, it calculates the primary side capacitor display value according to the theoretical transformation ratio corresponding to the built-in voltage level range. The theoretical capacitor current value is calculated by multiplying the angular frequency, the theoretical phase voltage, and the preset primary side calibration capacitor value. The angular frequency is calculated based on the power frequency, and the theoretical phase voltage is calculated by dividing the line voltage corresponding to the voltage level range set by the test instrument by the square root of three. This theoretical capacitor current value is used as the benchmark value for subsequent error judgment.

[0028] Step S5: Using the preset primary-side calibration capacitor value as the theoretical value of the primary-side capacitor, calculate the relative error of capacitance between the displayed capacitance value and the theoretical value of the primary-side capacitor; calculate the relative error of capacitance current between the displayed capacitor current value and the theoretical capacitor current value, and determine whether the relative error of capacitance and the relative error of capacitance current both meet the allowable error range.

[0029] The preset primary-side calibration capacitance value is the theoretical value of the primary-side capacitance. This theoretical value represents the expected primary-side capacitance value corresponding to each calibration point, which remains consistent across different voltage levels. The relative capacitance error is obtained by subtracting the actual capacitance value displayed by the test instrument from the theoretical value, dividing by the theoretical value, and multiplying by 100%. The relative capacitance current error is obtained by subtracting the capacitance current value displayed by the test instrument from the theoretical capacitance current value, dividing by the theoretical capacitance current value, and multiplying by 100%. When the absolute values ​​of both errors are within the allowable range, the test point is deemed qualified. Error data from all voltage levels and all calibration points are statistically analyzed for a comprehensive overall assessment.

[0030] In one specific embodiment, step S1 includes:

[0031] The defined standard turns ratio set includes five candidate turns ratios: 60, 100, 200, 350, and 660. The secondary capacitance range of the standard capacitor bank is 0.36 millifarads to 54.45 farads. Therefore, under a unified turns ratio, the primary capacitance range is 36 picofarads to 5.445 millifarads. The theoretical value range of the primary capacitance under different candidate turns ratios can all meet the requirements of 0.3 microfarads to 125 microfarads.

[0032] The theoretical values ​​of primary side capacitance were selected as 0.3 μF, 1 μF, 5 μF, 10 μF, 20 μF, 30 μF, 50 μF, 75 μF, 100 μF, and 125 μF. Each candidate transformer in the standard transformer ratio set was substituted into the transformer ratio conversion formula, where the secondary side capacitance is equal to the product of the square of the candidate transformer ratio and the primary side capacitance. The secondary side converted capacitance value of each candidate transformer at all calibration points was calculated.

[0033] Determine whether all secondary-side converted capacitance values ​​of each candidate transformer ratio fall within the range constraint of the secondary-side capacitance. Select candidate transformer ratios whose converted values ​​all meet the range constraint to form a set of candidate transformer ratios that meet the range constraint.

[0034] For each candidate transformer ratio in the candidate transformer ratio set that meets the range constraint, the back calculation relative error of each candidate transformer ratio at different voltage levels is calculated based on the ratio difference parameter of the electromagnetic voltage transformer, and the back calculation relative error is verified to meet the allowable error range.

[0035] Candidate turns ratios that simultaneously meet range and error constraints and cover all voltage levels with theoretical primary-side capacitance values ​​are selected as unified turns ratio parameters. Specifically, range constraint verification involves substituting each turns ratio in the candidate turns ratio set into the conversion relationship where the secondary-side capacitance equals the product of the square of the candidate turns ratio and the primary-side capacitance. For each of the ten selected theoretical primary-side capacitance values, the corresponding secondary-side converted capacitance value under the candidate turns ratio is calculated. It is then determined whether all ten converted values ​​under the candidate turns ratio fall completely within the secondary-side range of the standard capacitor bank. Only when a candidate turns ratio makes the secondary-side converted values ​​of all calibration points within the range does the candidate turns ratio meet the range constraint condition. Through this verification, candidate turns ratios that can complete all calibration point tests within the equipment range are selected, forming a candidate turns ratio set that meets the range constraint. Error constraint verification involves calculating the back-calculation relative error of each candidate transformer ratio in the set of candidate ratios that meet the range constraint, based on the ratio difference parameter of the electromagnetic voltage transformer, at five voltage levels. The back-calculation relative error reflects the degree of deviation between the back-calculation using the theoretical ratio and the actual conversion using the candidate transformer ratio. The absolute value of the back-calculation relative error is obtained by dividing the square of the candidate transformer ratio by the product of the square of the theoretical ratio ratio and the ratio difference correction factor, and then subtracting 1. It is then determined whether the back-calculation relative error calculated for the candidate transformer ratio at all five voltage levels meets the allowable error range. Only when the back-calculation relative error of a candidate transformer ratio is within the allowable range at all voltage levels does the candidate transformer ratio meet the error constraint condition. Finally, candidate transformer ratios that simultaneously meet the range constraint and error constraint and can cover all voltage levels are selected as the unified transformer ratio parameter.

[0036] Figure 2 This is a schematic diagram comparing the converted values ​​of the secondary capacitor under different turns ratios in the embodiments of this application; Figure 2 This paper presents a comparison of the secondary-side capacitance values ​​corresponding to five candidate turns ratios (60, 100, 200, 350, and 660) under four theoretical primary-side capacitance values ​​(0.3μF, 10μF, 50μF, and 125μF). The vertical axis uses a logarithmic scale to clearly display the capacitance value range spanning multiple orders of magnitude, and the bar charts with different fill patterns represent the conversion results under different turns ratio conditions. The data in the figure allows for a direct assessment of whether the secondary-side capacitance values ​​calculated from each candidate turns ratio fall within the range constraints of the standard capacitor bank (0.36mF to 54.45F), providing a quantitative basis for selecting a unified turns ratio parameter. It verifies that turns ratio 100 can meet the range constraints of all four calibration points, supporting its selection as a unified turns ratio parameter.

[0037] In one specific embodiment, the formula for calculating the capacitance ratio difference correction factor is as follows:

[0038] ;

[0039] in, is the capacitance ratio difference correction factor, and f is the relative deviation between the actual ratio and the nominal ratio of the electromagnetic voltage transformer.

[0040] In one specific embodiment, step S3 includes:

[0041] Obtain the voltage level setting of the test instrument under test, and determine the corresponding theoretical transformation ratio based on the voltage level setting. The theoretical transformation ratio is 60 for the 6 kV setting, 100 for the 10 kV setting, 200 for the 20 kV setting, 350 for the 35 kV setting, and 660 for the 66 kV setting.

[0042] The conversion factor for each voltage level is obtained by dividing the product of the square of the uniform turns ratio parameter (numerator) and the square of the theoretical turns ratio and the capacitance ratio difference correction factor (denominator). The formula is shown below:

[0043] ;

[0044] in, For conversion factors, To unify the transformer ratio parameters, For theoretical ratios;

[0045] For the five voltage levels of 6 kV, 10 kV, 20 kV, 35 kV and 66 kV, the corresponding theoretical turns ratio and unified turns ratio parameters are substituted to calculate the conversion coefficient, and the conversion coefficient values ​​corresponding to the five voltage levels are obtained respectively.

[0046] Establish a mapping relationship between the conversion coefficient values ​​corresponding to the five voltage levels and the corresponding voltage level ranges, and store it as a conversion coefficient mapping table.

[0047] Specifically, the conversion factor calculation is based on the principle of compensating for the numerical difference between the uniform turns ratio and the theoretical turns ratio. The test instrument under test has built-in theoretical turns ratios of 60, 100, 200, 350, and 660 at five voltage levels: 6 kV, 10 kV, 20 kV, 35 kV, and 66 kV, respectively. These theoretical turns ratios are the nominal turns ratio values ​​under the standard configuration of each voltage level. The test instrument under test automatically calls up the corresponding theoretical turns ratio to perform capacitance back-calculation according to the voltage level set by the user. The back-calculation process involves converting the measured secondary capacitance value... Dividing by the square of the theoretical turns ratio yields the primary side capacitance value. However, in actual calibration, the turns ratio of the electromagnetic voltage transformer used is fixed with a uniform turns ratio parameter. Electromagnetic voltage transformers convert the primary-side capacitance into secondary-side capacitance using a squared multiple relationship of a uniform transformation ratio parameter. The actual relationship is as follows: , This is the primary side capacitance value, due to the uniform turns ratio parameters. Compared with the theoretical ratio built into the test instrument The formula for back-calculation using the theoretical ratio of the test instrument is as follows, depending on the numerical value: Substituting the actual relationship into the back calculation formula yields... Directly using the theoretical transformation ratio for back calculation will produce systematic deviations. The conversion factor serves to establish the conversion relationship between the theoretical primary-side capacitance value and the preset primary-side calibration capacitance value under a unified transformation ratio condition. (Ratio difference parameter) This reflects the manufacturing or measurement error between the actual and nominal values ​​of an electromagnetic voltage transformer; the actual ratio... A ratio difference parameter of 0.5% indicates that the actual ratio is equal to the nominal uniform ratio parameter. Dividing by 1.005, since the actual ratio is less than the nominal value, the back-calculation formula after considering the effect of the ratio difference can be simplified to: The theoretical capacitance values ​​at different levels are , This represents the theoretical primary capacitance value, where the conversion factor is... , This represents the ratio difference of the electromagnetic voltage transformer actually used. The capacitance ratio difference correction factor is obtained by adding 1 to the ratio difference parameter and then squaring the result. The capacitance ratio difference correction factor is used to correct the deviation between the actual turns ratio and the square of the nominal turns ratio. Conversion coefficient. The calculation will unify the ratio parameters. The square of the value is used as the numerator to represent the ratio between the secondary capacitor and the primary capacitor after adjustment according to the unified turns ratio parameters, which is the theoretical turns ratio. The square of the difference between capacitance and the correction factor The product of the two is used as the denominator. The square of the theoretical transformation ratio in the denominator represents the square relationship of the transformation ratio used in the back calculation of the test instrument under test. The capacitance ratio difference correction factor represents the square correction of the actual transformation ratio deviation. The product of the two is used as the denominator to reflect the actual back calculation coefficient of the test instrument under test considering the influence of ratio difference. The conversion coefficient is obtained by dividing the numerator by the denominator. This indicates that under uniform ratio calibration conditions, the preset primary side calibration capacitor value is... It needs to be multiplied by the conversion factor. Only then can the theoretical primary capacitance value that the test instrument should display be obtained. .

[0048] Theoretical transformer ratio for 6 kV range Conversion factor This indicates that the theoretical capacitance value displayed by the test instrument at the 6 kV setting should be 2.7471 times the preset primary side calibration capacitance value. For the 35 kV setting, the theoretical transformation ratio... =350, conversion factor This indicates that the theoretical capacitance value displayed by the test instrument at the 35 kV setting should be 0.0808 times the preset primary side calibration capacitance value. The conversion factor values ​​for the five voltage levels correspond to different theoretical turns ratios. A one-to-one mapping relationship is established between the conversion coefficient value and the voltage level, which is stored as a conversion coefficient mapping table. The data structure of the mapping table is in the form of key-value pairs, where the key is the voltage level identifier and the value is the corresponding conversion coefficient value. In subsequent error calculation, the corresponding conversion coefficient value is retrieved from the mapping table according to the voltage level currently set by the test instrument under test, so as to realize the calculation of the theoretical value quickly and accurately.

[0049] In one specific embodiment, step S4 involves connecting the electromagnetic voltage transformer with the unified transformation ratio parameters to the standard capacitor bank, including:

[0050] Select an electromagnetic voltage transformer with a uniform transformation ratio, an accuracy class of 0.1, and a secondary rated voltage of 100 volts. Connect the standard capacitor box to the primary side of the electromagnetic voltage transformer and connect the capacitance measurement port of the test instrument to the secondary side of the electromagnetic voltage transformer.

[0051] The capacitance value of the standard capacitor bank is determined according to the preset primary side calibration capacitance value, and the primary side capacitance range is 36 picofarads to 5.445 millifarads.

[0052] A test cable is connected between the capacitance measurement port of the test instrument under test and the output of the standard capacitor bank to establish a calibration test loop. Specifically, the accuracy class of the electromagnetic voltage transformer is 0.1, meaning that its ratio error and phase error are controlled within the 0.1 accuracy range. This accuracy requirement ensures the accuracy of the ratio conversion process. The secondary rated voltage is 100 volts, which is the standard secondary voltage value of voltage transformers in the power system. The secondary output of electromagnetic voltage transformers of all voltage levels is uniformly 100 volts, so that the calibration operation under different voltage levels maintains a consistent voltage reference on the secondary side. The standard capacitor bank is connected to the primary side of the electromagnetic voltage transformer as the object under test. The capacitance measurement port of the test instrument under test is connected to the secondary side of the electromagnetic voltage transformer for measurement. After measuring the secondary capacitance value, the test instrument under test calculates the primary capacitance display value based on its built-in theoretical ratio. The capacitance value of the standard capacitor bank is determined according to the preset primary side calibration capacitance value. The primary side capacitance range is from 36 picofarads to 5.445 millifarads. This range covers the capacitance conversion values ​​required for all voltage levels under a uniform turns ratio. Inside the standard capacitor bank, multiple sets of high-stability film capacitors are connected in series and parallel through relay control to achieve different capacitance values. The capacitance value resolution is less than or equal to 0.01 microfarads, ensuring the precision of capacitance setting. The temperature coefficient is less than or equal to 50 ppm per degree Celsius, ensuring that the influence of ambient temperature changes on the capacitance value is controllable. The test instrument measures the capacitance through a test cable. The test cable uses shielded cable to reduce the influence of electromagnetic interference on the measurement results. The contact resistance is controlled at the milliohm level to avoid introducing additional errors. Figure 3 This is a schematic diagram showing the connection relationship of the calibration system for a multi-voltage level capacitor current tester based on a unified turns ratio, as described in an embodiment of this application. Figure 3 As shown, a standard capacitor bank and an electromagnetic voltage transformer are connected to the primary side of the electromagnetic voltage transformer, and the capacitance measurement port of the capacitor current tester under test is connected to the secondary side of the electromagnetic voltage transformer, forming a calibration test loop. A primary-side capacitance linkage control device is connected to the standard capacitor bank via a dashed line, automatically controlling the standard capacitor bank to output the corresponding capacitance value based on the preset primary-side calibration capacitance value and unified transformation ratio parameters. The ratio difference correction and unified transformation ratio conversion coefficient determination module calculates the capacitance ratio difference correction factor and conversion coefficient based on the ratio difference parameters of the electromagnetic voltage transformer, and is connected to the electromagnetic voltage transformer via a dashed line to correct the errors introduced by the electromagnetic voltage transformer during calibration. Solid arrows in the figure indicate signal flow and physical connection relationships, while dashed lines indicate control and correction relationships, clearly demonstrating the connection methods and interaction mechanisms of each component in the unified transformation ratio calibration method, reflecting the technical solution of using a single unified transformation ratio to cover multiple voltage levels from 6 kV to 66 kV for calibration.

[0053] In one specific embodiment, determining the primary-side capacitor setting value and the secondary-side output capacitor value of the standard capacitor bank includes:

[0054] A preset primary-side calibration capacitance value sequence is obtained, which includes no less than 10 calibration points, including 0.3 μF, 1 μF, 5 μF, 10 μF, 20 μF, 30 μF, 50 μF, 75 μF, 100 μF, and 125 μF; the preset primary-side calibration capacitance value serves as the theoretical primary-side capacitance value corresponding to each calibration point and remains consistent across different voltage levels;

[0055] For each voltage level set by the test instrument under test, the corresponding conversion coefficient is obtained from the conversion coefficient mapping table; the primary side capacitance setting value of the standard capacitor box is determined according to the preset primary side calibration capacitance value and the conversion coefficient of the corresponding voltage level. The primary side capacitance setting value is equal to the preset primary side calibration capacitance value divided by the conversion coefficient of the corresponding voltage level. Under different voltage levels, the preset primary side calibration capacitance value is the same, but the primary side capacitance setting value of the standard capacitor box is different because the conversion coefficients corresponding to each voltage level are different.

[0056] Multiply the primary-side capacitor setting value for each voltage level by the square of the uniform turns ratio parameter to obtain the secondary-side output capacitor value of the standard capacitor bank.

[0057] Calculate the theoretical capacitance current value based on the theoretical phase voltage, angular frequency and preset primary side calibration capacitance value corresponding to each voltage level; collect the displayed capacitance values ​​of the test instrument under test for no less than 10 calibration points at each voltage level.

[0058] Specifically, the preset primary-side calibration capacitance value sequence includes ten calibration points: 0.3 μF, 1 μF, 5 μF, 10 μF, 20 μF, 30 μF, 50 μF, 75 μF, 100 μF, and 125 μF. These cover the minimum, intermediate typical, and maximum values ​​of the primary-side capacitance measurement range from 0.3 μF to 125 μF as specified in the DL / T1694.11-2024 standard. The preset primary-side calibration capacitance value is the theoretical primary-side capacitance value corresponding to each calibration point, and it remains consistent across different voltage levels. For each voltage level set by the test instrument under test, the corresponding conversion coefficient is obtained from the conversion coefficient mapping table. The preset primary-side calibration capacitor value is divided by the conversion coefficient of the corresponding voltage level to obtain the primary-side capacitor setting value of the standard capacitor box. The preset primary-side calibration capacitor value is the same for different voltage levels, but the primary-side capacitor setting value is different. The primary-side capacitor setting value is multiplied by the square of the uniform transformation ratio parameter to obtain the secondary-side output capacitor value of the standard capacitor box. The capacitor bank inside the standard capacitor box is configured in series and parallel according to the secondary-side output capacitor value to output the corresponding capacitor value. If the uniform transformation ratio parameter is 100 and the conversion coefficient is 1, the secondary-side output capacitor values ​​corresponding to 0.3 μF, 10 μF, 50 μF, 100 μF, and 125 μF are 3 mF, 100 mF, 500 mF, 1 FAD, and 1.25 FAD, respectively. The conversion coefficient mapping table stores the mapping relationship between each voltage level and the corresponding conversion coefficient value. When processing calibration data for a certain voltage level, the corresponding conversion coefficient is retrieved from the mapping table according to the voltage level. The preset primary side calibration capacitor value is directly used as the theoretical value of the primary side capacitor. This theoretical value represents the expected primary side capacitor value corresponding to each calibration point. The theoretical capacitor current value is calculated according to the capacitor current formula by multiplying the angular frequency, the theoretical phase voltage, and the preset primary side calibration capacitor value. The angular frequency is calculated as 314.16 radians per second based on the power frequency of 50 Hz. The theoretical phase voltage is calculated by dividing the line voltage corresponding to the voltage level set by the test instrument under test by the square root of three. The corresponding theoretical capacitor current value is calculated for all fifty test points of five voltage levels and ten calibration points.

[0059] In one specific embodiment, the displayed capacitance values ​​of the test instrument under test are collected at various voltage levels, including:

[0060] The secondary output capacitance value of the standard capacitor box is the product of the primary capacitance setting value and the square of the uniform turns ratio parameter.

[0061] The test instrument under test measures the capacitance value output by the standard capacitor box through the test cable. The test instrument under test injects a test voltage signal and detects the amplitude and phase of the current flowing through the capacitor. Based on the relationship between the voltage amplitude, current amplitude and phase, the secondary capacitance value is calculated. Then, the primary capacitance value is back-calculated according to the theoretical transformation ratio corresponding to the voltage level set by the test instrument under test. The back-calculation formula is that the primary capacitance value is equal to the secondary capacitance value divided by the square of the theoretical transformation ratio. The back-calculated primary capacitance value is displayed on the display screen of the test instrument under test.

[0062] The data acquisition module reads the primary side capacitance value and capacitance current value on the display screen of the test instrument under test, and records them as the display capacitance value and display capacitance current value corresponding to the current voltage level and the current preset primary side calibration capacitance value.

[0063] Specifically, the secondary output capacitance of the standard capacitor bank is the product of the primary capacitance setting value and the square of the uniform transformation ratio parameter. The primary capacitance setting value is equal to the preset primary calibration capacitance value divided by the conversion coefficient of the corresponding voltage level. The primary capacitance setting value is different for different voltage levels, and the corresponding secondary output capacitance value is also different. The series and parallel configuration of the capacitor bank inside the standard capacitor bank adopts a relay matrix control method. The corresponding relay control code is generated according to the required output capacitance value to drive the relay to switch and complete the capacitor combination. The relay switching process ensures reliable contact and controllable switching time. After the output of the standard capacitor bank is stable, it feeds back a ready signal to the control system to indicate that the measurement can start. The test instrument under test measures the standard capacitor bank through its capacitance measurement port, injects a test voltage signal into the capacitor under test and detects the current amplitude and phase flowing through the capacitor. The secondary capacitance value is obtained by calculating the capacitive reactance based on the ratio of voltage amplitude to current amplitude and the phase relationship. After obtaining the secondary capacitance value, the test instrument under test calls its built-in theoretical transformation ratio for back calculation. The back calculation formula is that the primary capacitance value equals the secondary capacitance value divided by the square of the theoretical transformation ratio. The theoretical transformation ratio is determined according to the current voltage level setting of the test instrument under test: 6 kV corresponds to a theoretical transformation ratio of 60, 10 kV to 100, 20 kV to 200, 35 kV to 350, and 66 kV to 660. The test instrument under test displays the back-calculated primary capacitance value on the display screen. The data acquisition module reads the primary capacitance value and capacitor current value on the display screen of the test instrument under test, establishes a correspondence between the read values ​​and the current voltage level setting and the current preset primary calibration capacitance value, and records them as the displayed capacitance value and displayed capacitor current value.

[0064] In one specific embodiment, step S5 includes:

[0065] For each preset primary side calibration capacitor value under each voltage level, the preset primary side calibration capacitor value is used as the theoretical value of the primary side capacitor.

[0066] The difference between the displayed capacitance value and the corresponding theoretical value of the primary side capacitance is divided by the theoretical value of the primary side capacitance, and then multiplied by 100% to calculate the relative capacitance error.

[0067] The actual capacitor current value is calculated based on the angular frequency, the theoretical phase voltage corresponding to each voltage level, and the display capacitor value. The theoretical capacitor current value is calculated based on the angular frequency, the theoretical phase voltage, and the preset primary side calibration capacitor value. The difference between the actual capacitor current value and the theoretical capacitor current value is calculated. The difference is divided by the theoretical capacitor current value and multiplied by 100% to calculate the relative error of the capacitor current.

[0068] Determine whether the absolute value of the relative error of the capacitor and the absolute value of the relative error of the capacitor current are both less than or equal to a preset absolute value threshold. If both are less than or equal to the preset absolute value threshold, the single point is determined to be qualified. If the absolute value of any relative error is greater than the preset absolute value threshold, the single point is determined to be unqualified.

[0069] The relative capacitance error and relative capacitance current error corresponding to all preset primary side calibration capacitance values ​​under all voltage levels are statistically analyzed. When the absolute value of all relative errors is less than or equal to the preset absolute value threshold, the test instrument under test is deemed to have passed the full voltage level calibration. When the absolute value of any relative error is greater than the preset absolute value threshold, the test instrument under test is deemed to have failed the full voltage level calibration.

[0070] Specifically, the preset primary side calibration capacitance value is directly used as the theoretical value of the primary side capacitance. This theoretical value represents the expected primary side capacitance value corresponding to each calibration point, which remains consistent under different voltage levels. The calculation of the relative capacitance error involves subtracting the actual capacitance value displayed by the test instrument from the theoretical value of the primary side capacitance to obtain the absolute value of the error. Then, the absolute value of the error is divided by the theoretical value of the primary side capacitance to obtain the decimal form of the relative error, and finally, it is multiplied by 100% to convert it into a percentage form. The actual capacitor current value is calculated using the capacitor current formula by multiplying the angular frequency, theoretical phase voltage, and displayed capacitor value. The theoretical capacitor current value has already been calculated in the previous steps. The difference between the actual capacitor current value and the theoretical capacitor current value is divided by the theoretical capacitor current value and then multiplied by 100% to obtain the relative error of the capacitor current. The single-point judgment rule requires that the absolute values ​​of both the capacitor relative error and the capacitor current relative error are less than or equal to the preset absolute value threshold, and the single point is judged as qualified. If the absolute value of any relative error is greater than the preset absolute value threshold, the single point is judged as unqualified. The comprehensive judgment of the entire level statistically analyzes the absolute values ​​of the capacitor relative error and the capacitor current relative error of fifty test points under ten preset primary side calibration capacitor values ​​at five voltage levels. The logical AND operation is used to determine whether all relative errors of all test points meet the conditions. Only when the absolute values ​​of the capacitor relative error and the capacitor current relative error of all fifty test points are less than or equal to the preset absolute value threshold is it judged as qualified.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A calibration method for a multi-voltage level capacitance current tester based on a uniform turns ratio, characterized in that, The method includes: Step S1: Substitute each candidate transformer ratio in the standard transformer ratio set into the transformer ratio conversion formula, where the secondary side capacitance is equal to the product of the square of the candidate transformer ratio and the primary side capacitance. Based on different candidate transformer ratios, convert the primary side capacitance range into the corresponding secondary side capacitance range, and screen the unified transformer ratio parameters that meet the secondary side capacitance range constraints and error constraints. Step S2: Obtain the ratio difference parameter of the electromagnetic voltage transformer corresponding to the unified ratio parameter, add 1 to the ratio difference parameter to obtain the capacitance ratio difference correction factor; Step S3: Calculate the conversion coefficient for each voltage level based on the unified transformation ratio parameter, the capacitance ratio difference correction factor, and the theoretical transformation ratio corresponding to the voltage level set by the test instrument under test. Step S4: Connect the electromagnetic voltage transformer corresponding to the unified transformation ratio parameter to the standard capacitor bank. Determine the primary side capacitor setting value according to the preset primary side calibration capacitor value and the conversion coefficient corresponding to each voltage level. Multiply the primary side capacitor setting value by the square of the unified transformation ratio parameter to obtain the secondary side output capacitor value of the standard capacitor bank. Collect the display capacitor value of the test instrument under test at each voltage level. Calculate the theoretical capacitor current value according to the theoretical phase voltage, angular frequency and preset primary side calibration capacitor value corresponding to each voltage level. Step S5: Using the preset primary-side calibration capacitor value as the theoretical value of the primary-side capacitor, calculate the relative error of capacitance between the displayed capacitance value and the theoretical value of the primary-side capacitor; calculate the relative error of capacitance current between the displayed capacitor current value and the theoretical capacitor current value, and determine whether the relative error of capacitance and the relative error of capacitance current both meet the allowable error range.

2. The calibration method for a multi-voltage level capacitance current tester based on a unified turns ratio according to claim 1, characterized in that, Step S1 includes: The defined standard turns ratio set includes five candidate turns ratios: 60, 100, 200, 350, and 660. The secondary capacitance range of the standard capacitor bank is 0.36 millifarads to 54.45 farads. Therefore, under a unified turns ratio, the primary capacitance range is 36 picofarads to 5.445 millifarads. The theoretical value range of the primary capacitance under different candidate turns ratios can all meet the requirements of 0.3 microfarads to 125 microfarads. The theoretical values ​​of primary side capacitance are selected as 0.3 μF, 1 μF, 5 μF, 10 μF, 20 μF, 30 μF, 50 μF, 75 μF, 100 μF, and 125 μF. Each candidate transformer in the standard transformer ratio set is substituted into the transformer ratio conversion formula, where the secondary side capacitance is equal to the product of the square of the candidate transformer ratio and the primary side capacitance. The secondary side converted capacitance value corresponding to each candidate transformer at all calibration points is calculated. Determine whether all secondary-side converted capacitance values ​​of each candidate transformer ratio fall within the range constraint of the secondary-side capacitance. Select candidate transformer ratios whose converted values ​​all meet the range constraint to form a set of candidate transformer ratios that meet the range constraint. For each candidate transformer ratio in the candidate transformer ratio set that meets the range constraint, the back calculation relative error of each candidate transformer ratio at different voltage levels is calculated based on the ratio difference parameter of the electromagnetic voltage transformer, and the back calculation relative error is verified to meet the allowable error range. Candidate turns ratios that simultaneously meet range constraints and error constraints and can cover all voltage levels are selected as the unified turns ratio parameter.

3. The calibration method for a multi-voltage level capacitance current tester based on a unified turns ratio according to claim 1, characterized in that, The formula for calculating the capacitance ratio difference correction factor is as follows: ； in, is the capacitance ratio difference correction factor, and f is the relative deviation between the actual ratio and the nominal ratio of the electromagnetic voltage transformer.

4. The calibration method for a multi-voltage level capacitance current tester based on a unified turns ratio according to claim 1, characterized in that, Step S3 includes: Obtain the voltage level setting of the test instrument under test, and determine the corresponding theoretical transformation ratio according to the voltage level setting. The theoretical transformation ratio is 60 for the 6 kV setting, 100 for the 10 kV setting, 200 for the 20 kV setting, 350 for the 35 kV setting, and 660 for the 66 kV setting. The conversion coefficients for each voltage level are obtained by dividing the square of the unified turns ratio parameter (numerator) by the product of the square of the theoretical turns ratio and the square of the capacitance ratio difference correction factor (denominator), as shown in the following formula: ； in, For conversion factors, To unify the transformer ratio parameters, For theoretical ratios; For the five voltage levels of 6 kV, 10 kV, 20 kV, 35 kV and 66 kV, the corresponding theoretical turns ratio and the unified turns ratio parameter are substituted into the calculation of the conversion coefficient to obtain the conversion coefficient values ​​corresponding to the five voltage levels respectively. Establish a mapping relationship between the conversion coefficient values ​​corresponding to the five voltage levels and the corresponding voltage level ranges, and store them as a conversion coefficient mapping table.

5. The calibration method for a multi-voltage level capacitance current tester based on a unified turns ratio according to claim 4, characterized in that, Step S4, which connects the electromagnetic voltage transformer corresponding to the unified transformation ratio parameters to the standard capacitor bank, includes: Select an electromagnetic voltage transformer with the uniform transformation ratio parameter, an accuracy class of 0.1, and a secondary rated voltage of 100 volts. Connect the standard capacitor box to the primary side of the electromagnetic voltage transformer and connect the capacitance measurement port of the test instrument to the secondary side of the electromagnetic voltage transformer. The capacitance value of the standard capacitor bank is determined according to the preset primary side calibration capacitance value, and the primary side capacitance range is from 36 picofarads to 5.445 millifarads. Connect a test cable between the capacitance measurement port of the test instrument under test and the output terminal of the standard capacitor box to establish a calibration test loop.

6. The calibration method for a multi-voltage level capacitance current tester based on a unified turns ratio according to claim 5, characterized in that, The step S4, which determines the primary-side capacitor setting value and the secondary-side output capacitor value of the standard capacitor bank, includes: A preset primary-side calibration capacitance value sequence is obtained, which includes no less than 10 calibration points, including 0.3 μF, 1 μF, 5 μF, 10 μF, 20 μF, 30 μF, 50 μF, 75 μF, 100 μF, and 125 μF; the preset primary-side calibration capacitance value serves as the theoretical primary-side capacitance value corresponding to each calibration point and remains consistent across different voltage levels; For each voltage level set by the test instrument under test, the corresponding conversion coefficient is obtained from the conversion coefficient mapping table; the primary side capacitance setting value of the standard capacitor box is determined according to the preset primary side calibration capacitance value and the conversion coefficient of the corresponding voltage level. The primary side capacitance setting value is equal to the preset primary side calibration capacitance value divided by the conversion coefficient of the corresponding voltage level. Under different voltage levels, the preset primary side calibration capacitance value is the same, but the primary side capacitance setting value of the standard capacitor box is different because the conversion coefficients corresponding to each voltage level are different. Multiply the primary-side capacitor setting value for each voltage level by the square of the uniform turns ratio parameter to obtain the secondary-side output capacitor value of the standard capacitor bank. Calculate the theoretical capacitance current value based on the theoretical phase voltage, angular frequency and preset primary side calibration capacitance value corresponding to each voltage level; collect the displayed capacitance values ​​of the test instrument under test for no less than 10 calibration points at each voltage level.

7. The calibration method for a multi-voltage level capacitance current tester based on a unified turns ratio according to claim 6, characterized in that, Step S4 involves acquiring the displayed capacitance values ​​of the test instrument under test at various voltage levels, including: The secondary output capacitance value of the standard capacitor box is the product of the primary capacitance setting value and the square of the uniform turns ratio parameter. The test instrument under test measures the capacitance value output by the standard capacitor box through the test cable. The test instrument under test injects a test voltage signal and detects the amplitude and phase of the current flowing through the capacitor. Based on the relationship between the voltage amplitude, current amplitude and phase, the secondary capacitance value is calculated. Then, the primary capacitance value is back-calculated according to the theoretical transformation ratio corresponding to the voltage level set by the test instrument under test. The back-calculation formula is that the primary capacitance value is equal to the secondary capacitance value divided by the square of the theoretical transformation ratio. The back-calculated primary capacitance value is displayed on the display screen of the test instrument under test. The data acquisition module reads the primary side capacitance value and capacitance current value on the display screen of the test instrument under test, and records them as the display capacitance value and display capacitance current value corresponding to the current voltage level and the current preset primary side calibration capacitance value.

8. The calibration method for a multi-voltage level capacitance current tester based on a unified turns ratio according to claim 7, characterized in that, Step S5 includes: For each preset primary side calibration capacitor value under each voltage level, the preset primary side calibration capacitor value is used as the theoretical value of the primary side capacitor. The difference between the displayed capacitance value and the corresponding theoretical value of the primary side capacitance is divided by the theoretical value of the primary side capacitance, and then multiplied by 100% to calculate the relative capacitance error. The actual capacitor current value is calculated based on the angular frequency, the theoretical phase voltage corresponding to each voltage level, and the display capacitor value. The theoretical capacitor current value is calculated based on the angular frequency, the theoretical phase voltage, and the preset primary side calibration capacitor value. The difference between the actual capacitor current value and the theoretical capacitor current value is calculated. The difference is divided by the theoretical capacitor current value and multiplied by 100% to calculate the relative error of the capacitor current. Determine whether the absolute value of the relative error of the capacitor and the absolute value of the relative error of the capacitor current are both less than or equal to a preset absolute value threshold. If both are less than or equal to the preset absolute value threshold, the single point is determined to be qualified. If the absolute value of any relative error is greater than the preset absolute value threshold, the single point is determined to be unqualified. The relative capacitance error and relative capacitance current error corresponding to all preset primary side calibration capacitance values ​​under all voltage levels are statistically analyzed. When the absolute value of all relative errors is less than or equal to the preset absolute value threshold, the test instrument under test is deemed to have passed the full voltage level calibration. When the absolute value of any relative error is greater than the preset absolute value threshold, the test instrument under test is deemed to have failed the full voltage level calibration.

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