Current transformer error verification method and system

Abstract

The invention relates to the technical field of current transformer error verification, and particularly discloses a current transformer error verification method and system, and the method comprises the steps: reading a current transformer verification report, and inputting the basic parameters and calculation coefficients of a current transformer; using an error curve method to calculate the leakage reactance of the secondary winding, the internal electromotive force, the allowable secondary load and the short-circuit current multiple; fitting the short-circuit current multiple list and the allowable secondary load list, drawing a graph, and drawing a 10% error curve; and judging whether the current 10% error of the current transformer meets the requirement or not, and outputting a calculation and drawing result to obtain a test report. According to the invention, required data in an original report can be automatically read, and data calculation and error study and judgment are completed. And various data and intermediate variables in the calculation process are visually displayed, so that checking and data processing are facilitated. The real-time performance is high, a test conclusion can be obtained immediately after the current transformer is tested, and the error condition of the current transformer can be judged conveniently.

Description

Technical Field

[0001] The present invention relates to the technical field of current transformer error calibration, and specifically refers to a current transformer error calibration method and system. Background Art

[0002] Significance of 10% error calibration: The relay protection device reflects the fault condition of the primary system. When a fault occurs in the primary system and the protection device operates, the primary current of the current transformer is usually much larger than the current during normal operation. Therefore, the error of the current transformer will also increase. To enable the protection device to correctly reflect the condition of the primary system and operate correctly, it is required that the ratio error of the current transformer is less than or equal to 10%.

[0003] When a short-circuit fault occurs in the line, the primary current surges, and the error of the current transformer will increase. Through 10% error calibration, it can be determined that under the short-circuit current, the error of the current transformer can still meet the requirements of the protection device, ensuring that the protection device can operate in a timely and accurate manner.

[0004] Through 10% error calibration, it can be determined whether the maximum secondary load impedance of this current transformer meets the requirements under the maximum primary current. If the error exceeds the allowable range, it may indicate that there is a quality problem with the current transformer, and further inspection or replacement is required.

[0005] In actual work, the volt-ampere characteristic method is often used to first measure the volt-ampere characteristic curve of the CT, and then the 10% error curve of the CT is drawn based on the volt-ampere characteristic curve of the CT. According to the 10% error curve of the current transformer, the maximum allowable impedance ZYmax of the secondary circuit is obtained and compared with the actual impedance ZL of the secondary circuit. If ZL < ZYmax, it is considered that the current transformer meets the 10% error requirement.

[0006] At the relay protection work site, after the secondary maintenance personnel complete the test using the current transformer tester, they do not immediately perform 10% error conversion and calculate the maximum allowable impedance ZYmax. Instead, they view the inflection point voltage data and judge whether the inflection point voltage data is large enough based on experience to determine the situation of the current transformer. This empirical judgment actually uses the inflection point voltage method, which lacks rigor. For the situation where the inflection point voltage is low, it is impossible to judge whether the current transformer is unqualified at the work site, and subsequent calculations and verifications are still required. Moreover, the subsequent calculations still use the manual calculation method, and there is no simple tool to complete the cumbersome calculation work, delaying the progress of the actual renovation and acceptance project.

[0007] Therefore, a current transformer error calibration method and system have become an urgent problem to be solved by people. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method and system for calibrating the error of a current transformer. Through a complete set of data analysis of the current transformer, after importing the test results generated by the tester into the system of the present invention, corresponding data analysis and calculations will be completed. Through a series of formulas, the maximum allowable impedance ZYmax and all relevant intermediate data can be directly calculated, and the tester can conveniently compare it with the actual secondary burden data. Secondary maintenance personnel can immediately analyze the test data on the job site to determine whether the current transformer is qualified.

[0009] To solve the above technical problem, the technical solution provided by the present invention is: a method for calibrating the error of a current transformer, comprising the following steps,

[0010] S1. Read the calibration report of the current transformer and input the basic parameters and calculation coefficients of the current transformer;

[0011] S2. Use the error curve method to calculate the leakage reactance of the secondary winding, the internal electromotive force, the allowable secondary load, and the short-circuit current multiple;

[0012] S3. Fit and plot the short-circuit current multiple list and the allowable secondary load list to draw a 10% error curve;

[0013] S4. Determine whether the 10% error of the current of the current transformer meets the requirements, and output the calculation and drawing results to obtain a test report.

[0014] Further, the calibration report of the current transformer is a doc-format word document.

[0015] Further, in step S2, the exciting current and the test voltage list are obtained by looking up the excitation characteristic curve, and the excitation rounding data with consistent current steps is obtained.

[0016] Further, in step S2, the leakage reactance of the secondary winding is obtained by multiplying the internal resistance of the secondary winding of the current transformer in the internal resistance information by the calculation coefficient.

[0017] Further, in step S2, the short-circuit current multiple list is obtained through the proportional relationship with the exciting current; the current short-circuit current multiple is calculated from the maximum short-circuit current and the primary rated current.

[0018] Further, in step S4, the basis for determining the qualification of the current transformer is that the polarity of the current transformer is correct and whether the 10% error meets the requirements; the polarity criterion is "same polarity -", the primary and secondary windings have the same polarity, and it is marked as subtractive polarity; the 10% error criterion is that the calculated maximum allowable secondary load is greater than the actually measured secondary burden.

[0019] The present invention also provides a current transformer error calibration system, which includes a basic parameter area, an operation interaction area, a data display area, and a parameter description area;

[0020] The basic parameter area is used to input the basic parameters of the current transformer, corresponding to the rated primary current of the CT, the rated secondary current of the CT, the balance coefficient, and the winding leakage reactance coefficient respectively;

[0021] The operation interaction area is used to select test reports, read reports, calculate parameters, and save reports;

[0022] The data display area includes several lists. The first list displays the CT parameters read, the second list displays the parameters required for 10% error calculation, and the third list displays each intermediate parameter during the calculation process;

[0023] The parameter description area is used to display the operation log and necessary parameter descriptions.

[0024] The advantages of the present invention compared with the prior art are as follows: The present invention can automatically read the data required in the original report, complete data calculation and error judgment. Intuitively display various data and intermediate variables during the calculation process, which is convenient for inspection and data processing. It has strong real-time performance and can obtain the test conclusion immediately after the current transformer test, which is convenient for judging the error situation of the current transformer. Description of the Drawings

[0025] Figure 1 is the operation schematic diagram of exporting the CT test report from the tester and converting it into a word document.

[0026] Figure 2 is the operation schematic diagram of exporting one by one when the number of CT test reports is small.

[0027] Figure 3 is the software interface diagram of a current transformer error calibration system of the present invention.

[0028] Figure 4 is the interface diagram of reading the CT test report.

[0029] Figure 5 is the interface diagram of calculating and displaying data.

[0030] Figure 6 is the interface diagram of generating word documents and excel documents in a fixed format.

[0031] Figure 7 is the calculation result display interface diagram.

[0032] Figure 8 is the excel generation result diagram.

[0033] Figure 9It is a schematic diagram of the console log. Detailed implementation mode

[0034] Various exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that: unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention.

[0035] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way a limitation on the present invention or its application or use.

[0036] Techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered as part of the specification.

[0037] In all the examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0038] The following further details a method and system for calibrating the error of a current transformer according to the present invention with reference to the accompanying drawings.

[0039] Combined with the attached Figures 1-9 , the present invention is introduced in detail.

[0040] A method for calibrating the error of a current transformer includes the following steps:

[0041] I. Data reading:

[0042] Read the calibration report of the current transformer and automatically read the word document in doc format. The basic parameters and calculation coefficients of the current transformer are filled in according to the actual situation.

[0043] II. Data calculation:

[0044] The principle of data processing mainly uses the error curve method to calculate data such as the leakage reactance of the secondary winding, the internal electromotive force, the allowable secondary load, and the short-circuit current multiple.

[0045] The exciting current and test voltage are obtained by looking up the excitation characteristic curve in the list, and the excitation rounded data with consistent current steps is obtained;

[0046] The leakage reactance of the secondary winding is obtained by multiplying the internal resistance of the secondary winding of the current transformer in the internal resistance information by the calculation coefficient:

[0047] Z = K1 * R2;

[0048] The list of internal electromotive forces is obtained by calculation using the formula:

[0049] E=U-I0*Z2;

[0050] The list of allowable secondary loads is calculated by the formula:

[0051] Z max =(E0 / 9I0)-Z2;

[0052] The short-circuit current multiple table is obtained by the proportional relationship with the excitation current:

[0053]

[0054] The current short-circuit current multiple is calculated from the maximum short-circuit current and the primary rated current:

[0055] m = K*(Imax / I1n);

[0056] The present invention can draw a 10% error curve, that is, show the relationship between the allowable secondary load and the short-circuit current multiple, by fitting the short-circuit current multiple list with the allowable secondary load list and drawing a graph.

[0057] 3. Generate report:

[0058] It intuitively displays data such as short-circuit current multiple, calculation coefficient, excitation current, secondary winding leakage reactance, allowable secondary load, actual secondary load, measured polarity, etc., and outputs the results to the test report.

[0059] A current transformer error calibration system consists of several parts, including a basic parameter area, an operation interaction area, a data display area, and a parameter description area. The basic parameter area is used to input the basic parameters of the current transformer, which correspond to the CT primary rated current, CT secondary rated current, balance coefficient, and winding leakage reactance coefficient. The operation interaction area can select test reports, read reports, calculate parameters, and save reports. The parameter description area is used to display operation logs and necessary parameter descriptions. The data display area consists of three lists, among which the first list displays the read CT parameters, the second list displays the parameters required for the 10% error calculation, and the third list displays the various intermediate parameters in the calculation process, which is convenient for calibration personnel to check data.

[0060] This system uses the QT designer that comes with pyside6 for graphical interface design. It has a friendly interface and is easy to operate, ensuring that users can quickly get started and perform effective test data processing.

[0061] The specific implementation process of a current transformer error calibration method and system of the present invention is as follows:

[0062] 1. Implementation methods:

[0063] (I) Use the file generation tool provided with the Bodian tester to generate a word document

[0064] 1. Combine with the attached Figure 1 , before the test, please export the CT test report that needs to be analyzed from the tester and convert the report into a word document. Note that the measured value of excitation should not be checked, and the rounded value of excitation must be checked. Otherwise, the calculation result will not be reliable.

[0065] 2. Combine with the attached Figure 2 , if the number of test reports is small, it is recommended to set the current fixed step size and then export them one by one.

[0066] (2) Usage method of the present invention

[0067] 1. Input basic parameters: primary rated current, secondary rated current, balance coefficient, winding leakage reactance coefficient. The rated current parameter must be consistent with the actual CT transformation ratio. The balance coefficient and winding leakage reactance coefficient are filled in according to the parameter description on the right;

[0068] 2. Combine with the attached Figure 4 , click "Select CT Test Report" to select the word document, the file path will appear on the right, and click Read.

[0069] 3. Input two parameters, the maximum short-circuit current and the actual secondary load, at the 10% error data below. The maximum short-circuit current can use the primary operating current of overcurrent section I (instantaneous trip). See the CT card EXCEL table, that is, the attached Figure 8 . The actual secondary load is the measured data of the secondary burden, which is about 0.2 or so.

[0070] 4. Combine with the attached Figure 5 , click the calculation button, and the software will automatically calculate and display the data, and draw and display the 10% error curve.

[0071] 5. Combine with the attached Figure 6 , after clicking the save button, the software will automatically read the previous test file and automatically add the data of this test, and generate word documents and excel documents in a fixed format.

[0072] II. Data verification:

[0073] The calculation process of the 10% error accounting data in Excel is as follows, and the calculation formula is shown in the data source item of the program interface:

[0074] 1. Calculate the current multiple from the maximum short-circuit current and the primary rated current;

[0075] 2. Calculate the exciting current from the proportional relationship between the current multiple m and the exciting current I0. I0 = m / 2 (when the secondary rated current is 5A) or m / 10 (when the secondary rated current is 1A);

[0076] 3. Search for the I0 data corresponding to the excitation characteristic curve and find the test voltage U0 at this excitation current;

[0077] 4. Calculate the internal electromotive force E0 from the test voltage and the excitation current;

[0078] 5. Calculate the maximum allowable secondary load at the current short - circuit current from the formula of the allowable value of the secondary load Z;

[0079] 6. Compare the allowable value of the secondary load with the measured data of the secondary burden, and the actual value should be less than the allowable value.

[0080] Combined with Appendix Figure 7 、 8 , compare the software calculation results, the results generated by the word document, and the results generated by excel. The actual running data of the program is placed in the "Program Verification Test" folder.

[0081] The results generated by the word document are shown in Table 1 - 3 below:

[0082] Table 1: Volt - Ampere Characteristic and Variation Verification Table

[0083]

[0084] Table 2: Insulation Resistance Test Using a 1000V Megger Unit: MΩ

[0085] Phase Between primary and secondary Secondary winding to ground Between secondary windings A 1000 1000 1000 B 1000 1000 1000 C 1000 1000 1000

[0086] Table 3: 10% Error Calculation

[0087]

[0088] Taking the internal electromotive force data 270.705 under 2S1 - 2S2 as an example, according to the internal electromotive force calculation formula, the program automatically searches for the voltage data U closest to the current short - circuit current 1.25 in the excitation rounded - off data 0＝ which is 271.699. The current secondary impedance is 0.8. After calculation, E = U 0 - I 0 *Z2 = 270.699, with a difference of 0.006 from the program calculation result 270.705, due to the precision of the program calculation data.

[0089] The console log is as shown in Appendix Figure 9 shown.

[0090] The excitation rounded - off data is shown in Table 4 below. The program selects 271.699 as the calculation parameter.

[0091] Table 4

[0092] Serial number Voltage (V) Current (A) Serial number Voltage (V) Current (A) Inflection point 213.8V 0.06663A 12 271.699 1.00000 1 2.11955 0.00500 13 274.364 2.00000 2 7.86609 0.01000 14 277.642 3.00000

[0093] The above describes the present invention and its embodiments. Such description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. In general, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural modes and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A current transformer error calibration method, characterized in that: The following steps are included: S1. Read the current transformer calibration report and enter the basic parameters and calculation coefficients of the current transformer; S2. Use the error curve method to calculate the secondary winding leakage reactance, internal electromotive force, allowable secondary load, and short-circuit current multiple; S3, fitting and drawing a graph of the short-circuit current multiple list and the allowable secondary load list, and drawing a 10% error curve; S4. Determine whether the 10% error of the current transformer current meets the requirement, and output the calculation and drawing results to obtain a test report.

2. A current transformer error calibration method according to claim 1, characterized in that: The current transformer verification report is a word document in doc format.

3. A current transformer error calibration method according to claim 1, characterized in that: In step S2, the excitation current and test voltage are obtained by looking up the excitation characteristic curve, and excitation rounding data with consistent current step length is obtained.

4. A current transformer error calibration method according to claim 1, characterized in that: In step S2, the secondary winding leakage reactance is obtained by multiplying the secondary winding internal resistance of the current transformer in the internal resistance information by a calculation coefficient.

5. A current transformer error calibration method according to claim 1, characterized in that: In step S2, the short-circuit current multiple list is obtained through a proportional relationship with the excitation current; the current short-circuit current multiple is calculated from the maximum short-circuit current and the primary rated current.

6. A current transformer error calibration method according to claim 1, characterized in that: In step S4, the basis for judging whether the current transformer is qualified is whether the polarity of the current transformer is correct and whether the 10% error meets the requirements; the polarity criterion is "same level -", the primary and secondary windings are of the same level, and are marked as minus polarity; the 10% error criterion is that the calculated maximum allowable secondary load is greater than the actually measured secondary load.

7. A current transformer error calibration system, characterized in that: Used to implement the current transformer error calibration method according to any one of claims 1 to 6, the system comprises a basic parameter area, an operation interaction area, a data display area, and a parameter description area; The basic parameter area is used to input the basic parameters of the current transformer, which correspond to the CT primary rated current, CT secondary rated current, balance coefficient and winding leakage reactance coefficient respectively; The operation interaction area is used to select test reports, read reports, calculate parameters, and save reports; The data display area includes several lists, the first list displays the read CT parameters, the second list displays the parameters required for 10% error calculation, and the third list displays various intermediate parameters in the calculation process; The parameter description area is used to display the operation log and necessary parameter descriptions.

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