A method for low cost acquisition of core magnetic properties to rate accuracy class of transformers

Abstract

The present application relates to the technical field of mutual inductor design, and particularly relates to a method for obtaining core magnetic performance at low cost to evaluate the accuracy level of a mutual inductor, which comprises using a mutual inductor calibrator to test a current mutual inductor; during the testing, by changing the data of primary current, the ratio of transformation difference and phase difference of the mutual inductor under different current points are obtained, and then the B-H curve and the delta-H curve of the core of the mutual inductor are derived by using the reverse deduction method based on the obtained ratio of transformation difference and phase difference data. The present application innovatively designs a method for obtaining core magnetic performance curve at low cost to evaluate the accuracy level of a mutual inductor without using a special core curve testing instrument, thereby providing a basis for the design of the mutual inductor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mutual inductor design, and particularly relates to a method for obtaining core magnetic performance at low cost to evaluate the accuracy level of a mutual inductor. BACKGROUND

[0002] The current transformer is composed of a closed core (ferrite) and a winding, and is an instrument for converting a large current on a primary side into a small current on a secondary side to realize current measurement according to the principle of electromagnetic induction.

[0003] The accuracy level of the current transformer is an important index reflecting the precision performance of the mutual inductor. In order to ensure that the mutual inductor has good precision level after being manufactured, the theoretical calculation and evaluation of the accuracy level of the mutual inductor need to be performed in the design stage of the mutual inductor. However, in order to theoretically calculate the accuracy level of the mutual inductor, the performance of the core, mainly the B-H and δ-H performance, must be known. However, the manufacturers of the core on the market usually only provide the B-H curve, and generally do not provide the δ-H curve, so that the theoretical calculation of the mutual inductor is very troublesome, and basically the sample must be tested, thereby greatly wasting labor and cost. There are very few core curve testing instruments on the market, which are expensive (the price is as high as hundreds of thousands of yuan), and the testing speed is slow, which is not conducive to popularization and use.

[0004] Therefore, for the manufacturers who specially design and manufacture mutual inductors, in the case where the expensive core curve testing instrument is lacking, it is hoped that a method for obtaining the core magnetic performance curve at low cost to evaluate the accuracy level of the mutual inductor can be found, so as to provide a basis for the design of the mutual inductor. SUMMARY

[0005] In order to solve the above problems, the present application provides a method for obtaining core magnetic performance at low cost to evaluate the accuracy level of a mutual inductor, which aims to find a method for obtaining the core magnetic performance curve at low cost to evaluate the accuracy level of the mutual inductor without a special core curve testing instrument, so as to provide a basis for the design of the mutual inductor. The specific technical scheme is as follows:

[0006] The method for obtaining core magnetic performance at low cost to evaluate the accuracy level of a mutual inductor comprises the following steps: using a mutual inductor calibrator to test the current transformer; changing the data of the primary current to obtain the ratio of the difference and the phase difference of the mutual inductor at different current points; and using the ratio of the difference and the phase difference data obtained by testing, and adopting a reverse deduction method to deduce the B-H curve and the δ-H curve of the core of the mutual inductor.

[0007] The reverse deduction method comprises the following steps:

[0008] (1) establishing a working vector diagram of the current transformer; the working vector diagram of the current transformer is provided with a primary current I1 vector The vector of the secondary current I2 The vector of excitation current I0 , The vector of magnetic flux density B The vector of the induced electromotive force E2 in the secondary winding Secondary voltage U2 vector The vector of the primary current I1 The vector of the secondary current I2 negative vector - A phase difference Δ is formed between them, and the vector of the magnetic flux density B is... The vector of the excitation current I0 The loss angle δ between them, and the vector of the secondary current I2. With the induced electromotive force vector of the secondary winding An impedance angle α is formed between them;

[0009] (2) Based on the working vector diagram of the current transformer, the formulas for calculating the specific slip F and phase difference Δ of the current transformer are established as follows:

[0010] Compared to the turnaround %

[0011] Phase difference Δ= ;

[0012] (3) Calculate the impedance angle of the current transformer:

[0013] Impedance angle ;

[0014] Among them, X b R is the load reactance of the transformer, X0 is the leakage reactance of the transformer, r0 is the internal resistance of the transformer, and R is the load reactance of the transformer. b The load resistance of the current transformer;

[0015] (4) Based on the specific slip F, phase difference Δ, and impedance angle α of the current transformer, the following formulas are derived for calculating the current transformer loss angle δ, magnetic flux density B, and magnetic field strength H:

[0016] Loss angle ;

[0017] magnetic flux density ;

[0018] magnetic field strength ;

[0019] Where Sc is the cross-sectional area of ​​the transformer core, f is the frequency of the transformer, N is the number of turns of the secondary winding of the transformer, and Lc is the magnetic circuit length of the transformer.

[0020] (5) using mutual inductor calibrator to test mutual inductor and process test data: selecting a current mutual inductor to be tested, using mutual inductor calibrator to test mutual inductor ratio conversion difference F and phase difference Δ; by designing different current points, different loads and other changes, mutual inductor different ratio conversion difference F data and phase difference Δ data under different current points, different loads and other changes are tested; then according to ratio conversion difference F data and phase difference Δ data obtained by testing, using current mutual inductor loss angle δ calculation formula, magnetic flux density B calculation formula, magnetic field intensity H calculation formula in step (4), magnetic flux density B, magnetic field intensity H and loss angle δ of mutual inductor under different current points, different loads and other changes are calculated, and a complete test result database is finally made;

[0021] Among them, the test result database contains secondary current I2, ratio conversion difference F, phase difference Δ, magnetic flux density B, magnetic field intensity H and loss angle δ data of mutual inductor under different current points, different loads and other changes;

[0022] (6) according to the database of magnetic flux density B, magnetic field intensity H and loss angle δ, the B-H curve and δ-H curve of mutual inductor core are drawn.

[0023] In order to improve the efficiency of mutual inductor test data processing, the further improvement scheme is: using EXCEL software, using EXCEL function in EXCEL software, inputting loss angle δ calculation formula, magnetic flux density B calculation formula and magnetic field intensity H calculation formula in step (4) into EXCEL form, and inputting mutual inductor test data in step (5) into EXCEL form, and EXCEL software automatically calculates and forms a test result database in the form.

[0024] Preferably, using test result database, EXCEL software automatically generates B-H curve and δ-H curve of mutual inductor core.

[0025] In the application, when mutual inductor is tested by using mutual inductor calibrator in step (5), the ratio conversion difference and phase difference of mutual inductor under different current points are obtained by changing primary current to gradually increase secondary current, until the inflection point saturation.

[0026] The method for obtaining core magnetic properties at low cost to evaluate the accuracy level of mutual inductor of the application further comprises step (7): calculation and evaluation of mutual inductor accuracy level: B-H curve and δ-H curve obtained in step (5) are used for calculation and evaluation of accuracy level of mutual inductor with different turns ratio and different loads of the same core.

[0027] The application has the following beneficial effects:

[0028] First, the method for obtaining the magnetic property of the core at low cost to evaluate the accuracy level of the mutual inductor uses a mutual inductor calibrator

[0029] The price is expensive (up to hundreds of thousands of yuan), and the test speed is slow, which is not conducive to popularization and use

[0030] However, as long as the manufacturers of mutual inductors are equipped with mutual inductor calibrators, which are instruments for testing the accuracy level of mutual inductors, the present application uses the mutual inductor calibrator to reversely deduce the core curve, and then uses the core curve as a database to calculate the accuracy level of mutual inductors with different turns ratios and different loads of the same core, which saves cost and is conducive to popularization.

[0031] With these two data, we have relatively reliable data support for quickly calculating the accuracy of mutual inductors with different turns ratios, and can quickly calculate the performance of mutual inductors using the formula. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a schematic diagram of the method for obtaining the magnetic property of the core at low cost to evaluate the accuracy level of the mutual inductor of the present application;

[0033] Figure 2 is a working vector diagram of the current transformer;

[0034] Figure 3 is a B-H curve diagram of the core of the mutual inductor;

[0035] Figure 4 is a δ-H curve diagram of the core of the mutual inductor. DETAILED DESCRIPTION

[0036] The specific embodiments of the present application will be further described below in combination with the drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0037] As Figures 1 to 4 shown is an embodiment of the method for obtaining the magnetic property of the core at low cost to evaluate the accuracy level of the mutual inductor of the present application, comprising the following steps:

[0038] Mutual inductor calculation formula:

[0039] The accuracy level of the mutual inductor includes the ratio difference (referred to as the ratio difference) and the phase difference (referred to as the angle difference),

[0040] The ratio difference is the rated percentage error between the primary current and the secondary current, and the unit is %; the angle difference is the phase difference between the primary current and the secondary current. The mutual inductor calibrator can directly test the ratio difference and the angle difference of the mutual inductor.

[0041] According to Figure 2(Working vector diagram of current transformer), the transformer ratio error formula can be calculated :

[0042] Formula 1

[0043] Since Δ is usually very small, it is calculated in minutes, so Δ ≈ sinΔ, that is, the phase difference Δ:

[0044] Formula 2

[0045] Because cos calculates the radian, the phase difference is in minutes, so the radian needs to be converted into minutes, 1 radian = 3438'.

[0046] Core data of transformer

[0047] According to the above formula, we can design a specific transformer, and test its ratio error and phase difference by the transformer calibration instrument to reverse B-H data and δ-H data. According to the design of different current points, different loads and other changes, we can test the B, H and δ of the transformer at different points, and finally make a complete database. The following is the formula derivation.

[0048] According to the ratio error formula and the phase difference formula, we can get the following formula:

[0049] Formula 3

[0050] Loss angle It is usually calculated in °, but the phase difference of the calibration instrument is usually calculated in minutes. In order to facilitate the conversion of the minutes of the transformer calibration instrument into °.

[0051] Get the sum of loss angle and impedance angle:

[0052] Formula 4

[0053] Tangent formula of impedance angle:

[0054] Formula 5

[0055] Can calculate the impedance angle

[0056] Formula 6

[0057] Can calculate the loss angle :

[0058] Formula 7

[0059] According to Faraday's law of electromagnetic induction, the magnetic induction intensity B at this time:

[0060] (T) - Equation 8

[0061] The more accurate magnetic field intensity H ( ) can be calculated as:

[0062] ( ) - Equation 9

[0063] According to this (Equation 8), (Equation 9), (Equation 7) three points of calculation are deduced, we will also find out which parameters are required to calculate the three values.

[0064] So our test is designed around these data.

[0065] Transformer core test example

[0066] Using our existing product SCT10 for testing, the winding parameters are φ0.1 enameled copper wire, 2960 turns, the core is made of PC40 ferrite material, the saturation B value is about 0.45.

[0067]

[0068] The tested internal resistance is 245.4Ω, the leakage resistance is not convenient to test, and the estimated value is 0.2Ω, (if the internal resistance is large enough, the influence of leakage resistance can be ignored.) In order to facilitate testing, the internal resistance is large enough, the core saturation B value is not high, so this test does not carry any load.

[0069] The core cross section is calculated as 0.784 ， The magnetic circuit length is 10.18cm, and the transformer frequency is generally 50HZ. Use our transformer verifier to test the SCT10 transformer's ratio difference and phase difference of different currents until saturation, the data is as follows in Table 1:

[0070]

[0071] Table 1: SCT10, ratio difference and angle difference of different currents until inflection point saturation.

[0072] According to B (Equation 8), H (Equation 9), ( Formula 7 ), we can calculate the data of different current points, in order to facilitate the calculation, we can use the function of EXCEL to calculate, the effect is as follows table 2.

[0073]

[0074] Table 2: according to the parameters of the test, the B value, H value and loss angle δ are calculated by using the function of EXCEL, according to the test and calculation results, we can draw B-H curve and -H curve, such as Figure 3 And Figure 4 .

[0075] The above only is the preferred embodiment of the present application, it should be pointed out that, for ordinary skilled in the art, without departing from the technical principles of the present application, can also make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A low-cost method for obtaining the magnetic properties of an iron core to evaluate the accuracy class of a current transformer, characterized in that, This includes using a current transformer calibrator to test the current transformer; during the test, by changing the primary current data, the specific slip and phase difference of the transformer under different current points are obtained; and then, using the specific slip and phase difference data obtained from the test, the BH curve and δ-H curve of the transformer core are derived by reverse derivation method. The reverse derivation method includes the following steps: (1) Establish the working vector diagram of the current transformer; the working vector diagram of the current transformer includes the vector of the primary current I1. The vector of the secondary current I2 The vector of excitation current I0 The vector of magnetic flux density B The vector of the induced electromotive force E2 in the secondary winding Secondary voltage U2 vector The vector of the primary current I1 The vector of the secondary current I2 negative vector - A phase difference Δ is formed between them, and the vector of the magnetic flux density B is... The vector of the excitation current I0 The loss angle δ between them, and the vector of the secondary current I2. With the induced electromotive force vector of the secondary winding An impedance angle α is formed between them; (2) Based on the working vector diagram of the current transformer, the formulas for calculating the specific slip F and phase difference Δ of the current transformer are established as follows: Compared to the turnaround % Phase difference Δ= ; (3) Calculate the impedance angle of the current transformer: Impedance angle ; Among them, X b R is the load reactance of the transformer, X0 is the leakage reactance of the transformer, r0 is the internal resistance of the transformer, and R is the load reactance of the transformer. b The load resistance of the current transformer; (4) Based on the specific slip F, phase difference Δ, and impedance angle α of the current transformer, the following formulas are derived for calculating the current transformer loss angle δ, magnetic flux density B, and magnetic field strength H: Loss angle ; magnetic flux density ; magnetic field strength ; Where Sc is the cross-sectional area of ​​the transformer core, f is the frequency of the transformer, N is the number of turns of the secondary winding of the transformer, and Lc is the magnetic circuit length of the transformer. (5) Use a current transformer calibrator to test the current transformer and process the test data: Select a current transformer to be tested, use a current transformer calibrator to test the specific slip F and phase difference Δ of the current transformer; by designing different current points, different loads and other changes, test the different specific slip F data and phase difference Δ data of the current transformer under different current points, different loads and other changes; then, based on the specific slip F data and phase difference Δ data obtained from the test, use the current transformer loss angle δ calculation formula, magnetic flux density B calculation formula, magnetic field strength H calculation formula in step (4) to calculate the magnetic flux density B, magnetic field strength H and loss angle δ of the current transformer under different current points, different loads and other changes, and finally make a complete test result database; The test result database contains data on the secondary current I2, specific slip F, phase difference Δ, magnetic flux density B, magnetic field strength H, and loss angle δ of the current transformer under different current points and different loads. (6) Based on the database of magnetic flux density B, magnetic field strength H and loss angle δ, draw the BH curve and δ-H curve of the transformer core. Step (7): Calculation and evaluation of the accuracy class of the instrument transformer: Use the BH curve and δ-H curve obtained in step (5) to calculate and evaluate the accuracy class of instrument transformers with the same iron core but different turns ratios and different loads.

2. The method for obtaining the magnetic properties of an iron core at low cost to evaluate the accuracy class of a current transformer according to claim 1, characterized in that, Using EXCEL software, the calculation formulas for loss angle δ, magnetic flux density B, and magnetic field strength H in step (4) are entered into the EXCEL form using EXCEL functions. The test data of the mutual inductor in step (5) is also entered into the EXCEL form. The EXCEL software automatically calculates and forms a form-based test result database.

3. The method for obtaining the magnetic properties of an iron core at low cost to evaluate the accuracy class of a current transformer according to claim 2, characterized in that, Using the test results database, the BH curve and δ-H curve of the transformer core are automatically generated by EXCEL software.

4. The method for obtaining the magnetic properties of an iron core at low cost to evaluate the accuracy class of a current transformer according to claim 1, characterized in that, In step (5), when testing the transformer using a transformer calibrator, the secondary current is gradually increased by changing the primary current to obtain the specific slip and phase difference of the transformer at different current points until the inflection point saturates.

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