A series-parallel two-step measurement circuit and method for voltage transformer voltage coefficient

Abstract

The present invention provides a voltage transformer voltage coefficient series-parallel two-step measurement circuit and method in the field of voltage transformer voltage coefficient measurement. The circuit includes a voltage transformer to be measured T0, a semi-insulated voltage transformer T1, a fully-insulated voltage transformer T2, and a 23 , Power frequency high voltage generator T D , two-stage inductive voltage divider IVD; fully insulated voltage transformer T 23 After being connected in series or in parallel with the primary of the semi-insulated voltage transformer T1, it is connected to the power frequency high voltage generator T D Connection; Fully insulated voltage transformer T 23 The secondary of the semi-insulated voltage transformer T1 is connected in series, and the secondary output is cascaded with a two-stage inductive voltage divider IVD; the primary of the voltage transformer T0 under test is connected to the power frequency high voltage generator T D The advantages of the present invention are: it simplifies the process of measuring the voltage coefficient of the voltage transformer, and compared with the traditional "three-step method" of series addition, while reducing the workload of the experimental process, more importantly, it correspondingly reduces the change of the measurement inherent error caused by the change of the secondary series and parallel states, thereby significantly reducing the contribution to the measurement uncertainty.

Description

Technical Field

[0001] The invention relates to the field of voltage coefficient measurement of a voltage transformer, and in particular to a series-parallel two-step measurement circuit and method for a voltage transformer proportional error voltage coefficient. Background Art

[0002] In order to ensure fair trade of electric energy, the measuring transformers at the power supply and consumption points need to be regularly calibrated. Therefore, the accuracy of the standard voltage transformer is of great significance to fair trade of electric energy, accurate measurement of power equipment and line losses. For example, the typical value of the power factor of a large-capacity air-core reactor is 0.001 to 0.004. If the error traceability of the loss measurement is to be less than 1%, the accuracy of the voltage ratio standard needs to be higher than 0.001%. In 2014, the China National Institute of Metrology developed a set of 10kV to 0.0002 to 0.001, voltage coefficient (2-5)×10 -6 The double-stage standard voltage transformer (including semi-insulated and fully insulated) was developed, and the voltage coefficient of the transformer was evaluated by the voltage transformer series addition method and the high-voltage standard capacitor method (IEEE TIM, 2015, 64(6): 1381; Chinese invention patent number: ZL 2014 1 0483352.7).

[0003] The voltage coefficient measurement method of voltage transformer is the focus of high voltage ratio traceability research. In 1954, German scholars Forger and Zinn first proposed the principle of "series-parallel addition of transformer voltage", that is, a method of connecting two voltage transformers with known ratios in series to obtain a new ratio. In 1958, Zinn used this method to establish a 120kV electromagnetic power frequency voltage ratio standard at PTB in Germany after 12 additions starting from 100V, with an uncertainty of 1.2×10 -5 .

[0004] In 1991, the National High Voltage Metering Station improved on the basis of "series-parallel addition of transformers" and completed the "Research on series addition circuit based on fully insulated voltage transformers" (China invention patent number: CN 90100301.8), and established my country's 110kV power frequency voltage ratio standard device, with a ratio uncertainty of 1×10 -5 (Journal of Metrology, 1992, 13(3): 221).

[0005] In the research on series addition circuit based on fully insulated voltage transformer, the shield leakage caused by the change of shield potential during three measurements has a relatively large impact on the error characteristics, and the impact will increase further with the increase of voltage level. In 2009, the National High Voltage Metering Station proposed the "semi-insulated addition method" (China invention patent number 201110185680.9) based on the development of 1000kV series voltage transformer. The semi-insulated addition method is used to The power frequency ratio standard was measured with an accuracy of 0.002 and a measurement uncertainty reduced to 5×10 -6 (Electricity Supply and Use, 2013, 30(2): 71).

[0006] In 2013, the Electric Power Research Institute of Guangdong Power Grid Company proposed the "Circuit and Method for Measuring Voltage Coefficient of Voltage Transformer", which is summarized as "Single-stage Transformer Superposition Principle Measurement Method" (China Invention Patent No. 201310154185.7), which describes the use of two shielded grounded voltage transformers with the same rated voltage ratio and an isolation transformer to form a passive linear circuit. The superposition of linear circuit excitation and response is used to offset the shielding errors of the voltage transformers that constitute the passive linear circuit during the superposition process, thus overcoming the influence of the voltage transformer shielding error on the series addition circuit. However, the shielding structure and potential of voltage transformers designed by different manufacturers are different. For example, the shielding potential of some fully insulated voltage transformers is located at 1 / 2 of the high voltage rated potential. When using the superposition principle, the continuous points of the shielding potential are limited and may not be easy to implement.

[0007] like Figure 3 , Figure 4 , Figure 5 As shown, when measuring the voltage coefficient of the measured transformer (T1) based on the series addition of semi-insulated single-stage voltage transformers, it mainly includes the following three comparative measurements, namely: (1) Comparison measurement of the semi-insulated transformer T2 with the measured transformer T1 to obtain ε1; (2) Comparison measurement of the fully insulated transformer T3 with the measured transformer T1 to obtain ε2; ​​(3) Comparison measurement of the fully insulated transformer and the semi-insulated transformer in series with the measured transformer T1 to obtain ε3. Assume that the errors of the transformers T1, T2, and T3 under voltage U are α(U), β(U), and γ(U) respectively; e T2 、e T3 is the error introduced by the different states when the mutual inductors T2 and T3 are in series and T2 and T3 are used alone when the mutual inductors are added in series in step (3); ε3 is the error introduced by the different states when the mutual inductors T2 and T3 are used in series and T2 and T3 are used alone when the mutual inductors T2 and T3 are used in series and T2 and T3 are used alone. T2 、e T3 When the additional error is introduced, the error measured by comparing with the measured transformer T1 is: Then we have:

[0008] ε1=α(U)-β(U) (1)

[0009] ε2=α(U)-γ(U) (2)

[0010]

[0011] From equations (1), (2) and (3), we can get:

[0012]

[0013] In the existing transformer series addition method, steps (1) and (2) are performed by comparing T2 or T3 with T1 to obtain ε1 and ε2 respectively during the experiment, without considering the error e introduced by the mutual influence between T2 and T3. T2 、e T3 , but step (3) inevitably introduces e T2 、e T3 , so according to the formula When calculating the voltage coefficient of T1, e T2 、e T3 Experiments show that the error increment e introduced by the imperfect shielding of the transformer and the change of working state is T2 、e T3 , and the large nonlinearity of the single-stage transformer, in the voltage coefficient measurement of 110kV and above high voltage transformers, it is necessary to obtain 10 -6 It is more difficult to measure the uncertainty of magnitude.

[0014] The Chinese invention patent with application date of December 22, 2017 and application number CN201711406596.5 discloses a measurement circuit based on the superposition principle of a two-stage voltage transformer and its working method. The patent measures ε3' by connecting the primary and secondary windings of a fully insulated two-stage voltage transformer and a semi-insulated two-stage voltage transformer in series and comparing them with the measured transformer T1. Although the error e is still introduced, T2 、e T3 However, by adjusting steps (1) and (2) in the prior art to steps A and B with calibration, according to the formula When calculating the voltage coefficient of T1, the e introduced due to imperfect shielding T2 、e T3 The problem of imperfect shielding of two voltage transformers in series in the voltage transformer series addition self-calibration has been eliminated, overcoming the influence of the voltage coefficient measurement result on the voltage coefficient measurement result; due to the high precision requirements in the field of voltage coefficient measurement, even if the accuracy is only improved by a little bit, it has extraordinary significance to the industry. T2 、e T3Although it is offset in the process of calculating the voltage coefficient, three experimental steps are still required to calculate the voltage coefficient. Each additional experimental step will increase the workload and introduce the inherent error of the measurement system, thereby gradually accumulating and increasing the measurement uncertainty of the voltage coefficient. Summary of the invention

[0015] The technical problem to be solved by the present invention is to provide a two-step series-parallel measurement circuit and method for a voltage transformer voltage coefficient, so as to further reduce the measurement uncertainty of the voltage transformer voltage coefficient.

[0016] On the one hand, the present invention provides a voltage transformer voltage coefficient series-parallel two-step measurement circuit, comprising a voltage transformer to be measured T0, a half-insulated voltage transformer T1, a fully-insulated voltage transformer T 23 , a power frequency high voltage generator T that can provide half voltage output D and a two-stage inductive voltage divider IVD; the voltage transformer T0, the semi-insulated voltage transformer T1 and the fully-insulated voltage transformer T 23 The rated transformation ratio is K;

[0017] The fully insulated voltage transformer T 23 After being connected in series or in parallel with the semi-insulated voltage transformer T1, it is connected to the power frequency high voltage generator T D Connection: The fully insulated voltage transformer T 23 The secondary of the semi-insulated voltage transformer T1 is connected in series, and the secondary output is cascaded with the two-stage inductive voltage divider IVD; the primary high end of the voltage transformer T0 under test is connected to the power frequency high voltage generator T D Connection; the primary low ends of the measured voltage transformer T0 and the semi-insulated voltage transformer T1 are both grounded.

[0018] Furthermore, the voltage transformer T0, the semi-insulated voltage transformer T1 and the fully-insulated voltage transformer T 23 They are double-stage voltage transformers or single-stage voltage transformers respectively.

[0019] Furthermore, the two-stage inductive voltage divider IVD is a precision two-stage inductive voltage divider having two ratios of 0.5 and 1.

[0020] On the other hand, the present invention provides a two-step series-parallel measurement method for voltage transformer voltage coefficient, which requires the use of the above-mentioned measurement circuit and includes the following steps:

[0021] Assume that the voltage transformer to be tested is T0, the semi-insulated voltage transformer is T1, and the fully-insulated voltage transformer is T 23 In the power frequency high voltage generator T DThe output voltages under applied voltage U are u0(U), u1(U) and u 23 (U), the proportional errors are α(U), β(U) and γ(U), then: α(U) = f0(U) + j·δ0(U), where f0(U) and δ0(U) represent the ratio error and the angle error, respectively; Respectively represent the fully insulated voltage transformer T 23 Additional error introduced when connected in series with the secondary of semi-insulated voltage transformer T1;

[0022] Step A:

[0023] The fully insulated voltage transformer T 23 Connected in parallel with the primary of semi-insulated voltage transformer T1 and the power frequency high voltage generator T D Connection, power frequency high voltage generator T D Output voltage U; Fully insulated voltage transformer T 23 Connected in series with the secondary of the semi-insulated voltage transformer T1, the secondary output is cascaded with a two-stage inductive voltage divider IVD; the ratio K of the two-stage inductive voltage divider IVD is set IVD =0.5; Use the high-end differential measurement mode of the transformer tester to measure the voltage difference between the output of the two-stage inductive voltage divider IVD and the proportional output of the voltage transformer T0 under test, with the excitation output of the voltage transformer T0 under test as the reference.

[0024]

[0025]

[0026]

[0027]

[0028] Step B:

[0029] The fully insulated voltage transformer T 23 It is connected in series with the primary of the semi-insulated voltage transformer T1 and the power frequency high voltage generator T D Connection: Power frequency high voltage generator T D For fully insulated voltage transformer T 23 And the voltage of the primary high-end output 2U of the voltage transformer T0 under test, for the fully insulated voltage transformer T 23 The voltage of the primary low end and the primary high end output U of the semi-insulated voltage transformer T1; the fully insulated voltage transformer T 23 Connected in series with the secondary of the semi-insulated voltage transformer T1, the secondary output is cascaded with a two-stage inductive voltage divider IVD; the ratio K of the two-stage inductive voltage divider IVD is set IVD=1; Use the high-end differential measurement method with the transformer tester to measure the voltage difference between the output of the two-stage inductive voltage divider IVD and the proportional output of the voltage transformer T0 under test, taking the excitation output of the voltage transformer T0 under test as a reference.

[0030]

[0031]

[0032]

[0033]

[0034] Therefore, the error change of the measured voltage transformer T0 from voltage U to 2U is:

[0035]

[0036] The above formula shows that The voltage variation of T0 can be offset in the calculation of the above two-step series-parallel method, which is the basis for the present invention to achieve high-accuracy measurement.

[0037] That is, the changes in the ratio difference and angle difference of the voltage transformer T0 from voltage U to 2U are:

[0038]

[0039] By analogy, the voltage transformer T0 under test is obtained from the voltage 2 N-1 U to 2 N Error change of U Where N is a positive integer;

[0040] The voltage coefficient curve is:

[0041]

[0042] The advantages of the present invention are:

[0043] By introducing the two-stage inductive voltage divider IVD, the fully insulated voltage transformer T 23 After the secondary output of the semi-insulated voltage transformer T1 is connected in series with the two-stage inductive voltage divider IVD, it is compared with the voltage transformer T0 to be measured. Only two steps (step A and step B) are required to obtain the secondary voltage of the voltage transformer T0 to be measured. N-1 U to 2 N The proportional error change of U (voltage coefficient), although it introduces additional error and But in the calculation process, they are offset, and the ratio K of the two-stage inductive voltage divider IVD isIVD The proportional errors between 0.5 and 1 are controlled to be small enough to be negligible. Compared with the traditional three-step method to calculate the voltage coefficient, the workload of the experimental process is reduced. Since the secondary windings of the full and semi-insulated transformers remain in series, the inherent measurement error changes during the measurement experiment are reduced, so that they can be offset in the result calculation, thereby further reducing the uncertainty of the voltage transformer voltage coefficient measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0045] Figure 1 The invention discloses a measuring principle circuit of a double-stage voltage transformer in a two-step series-parallel measuring method of a voltage transformer voltage coefficient.

[0046] Figure 2 The invention discloses a measuring principle circuit of a single-stage voltage transformer in a two-step series-parallel measuring method of a voltage transformer voltage coefficient.

[0047] Figure 3 It is a traditional circuit based on the voltage series addition principle of semi-insulated single-stage transformer.

[0048] Figure 4 It is a traditional circuit based on the principle of direct comparison between T1 and T2 in series addition of semi-insulated single-stage transformers.

[0049] Figure 5 It is a traditional circuit based on the principle of direct comparison between T1 and T3 in series addition of semi-insulated single-stage transformers. DETAILED DESCRIPTION

[0050] The technical solution in the embodiment of the present application has the following general idea: by introducing the two-stage inductive voltage divider IVD, two steps are performed, namely, respectively setting the fully insulated voltage transformer T 23 The primary of the semi-insulated voltage transformer T1 and the power frequency high voltage generator T D The connection mode of the two-stage inductive voltage divider IVD is set to a ratio value (0.5 or 1), and the power frequency high voltage generator T is set to D The output voltage of the two-stage inductive voltage divider IVD is measured, and then the voltage difference between the output of the two-stage inductive voltage divider IVD and the proportional output of the voltage transformer T0 under test is obtained. N-1 U to 2 N The error change of U reduces one experimental step compared to the traditional series addition method, thereby further reducing the uncertainty of voltage transformer voltage coefficient measurement.

[0051] Please refer to Figures 1 to 5As shown, a preferred embodiment of a voltage transformer voltage coefficient series-parallel two-step measurement circuit of the present invention comprises a voltage transformer to be measured T0, a half-insulated voltage transformer T1, a fully-insulated voltage transformer T 23 , a power frequency high voltage generator T that can provide half voltage output D and a two-stage inductive voltage divider IVD; the voltage transformer T0, the semi-insulated voltage transformer T1 and the fully-insulated voltage transformer T 23 The rated transformation ratio is K;

[0052] The fully insulated voltage transformer T 23 After being connected in series or in parallel with the semi-insulated voltage transformer T1, it is connected to the power frequency high voltage generator T D Connection: The fully insulated voltage transformer T 23 The secondary of the semi-insulated voltage transformer T1 is connected in series, and the secondary output is cascaded with the two-stage inductive voltage divider IVD; the primary high end of the voltage transformer T0 under test is connected to the power frequency high voltage generator T D Connection; the primary low ends of the measured voltage transformer T0 and the semi-insulated voltage transformer T1 are both grounded.

[0053] The voltage transformer T0, the semi-insulated voltage transformer T1 and the fully-insulated voltage transformer T 23 They are double-stage voltage transformers or single-stage voltage transformers respectively. That is, the voltage transformer T0, the semi-insulated voltage transformer T1 and the fully-insulated voltage transformer T 23 The single-stage and double-stage voltage transformers can be arbitrarily combined. For example, all of them can be double-stage voltage transformers, all of them can be single-stage voltage transformers, T0 can be double-stage voltage transformers, T1 and T 23 is a single-stage voltage transformer or T0 is a single-stage voltage transformer, T1 and T 23 This is a combination of a double-stage voltage transformer.

[0054] The fully insulated voltage transformer T 23 After being connected in series with the secondary of the semi-insulated voltage transformer T1, the secondary output cascade of the two-stage inductive voltage divider IVD is specifically:

[0055] When the fully insulated voltage transformer T 23 When the semi-insulated voltage transformer T1 is a two-stage voltage transformer, the secondary proportional output after series connection is connected to the proportional input of the two-stage inductive voltage divider IVD, and the secondary excitation output is connected to the excitation input of the two-stage inductive voltage divider IVD; when the fully insulated voltage transformer T1 is a two-stage voltage transformer, the secondary proportional output after series connection is connected to the proportional input of the two-stage inductive voltage divider IVD, and the secondary excitation output is connected to the excitation input of the two-stage inductive voltage divider IVD; 23 When the semi-insulated voltage transformer T1 is a single-stage voltage transformer, the secondary output after series connection is simultaneously connected to the proportional and excitation inputs of the two-stage inductive voltage divider IVD.

[0056] The two-stage inductive voltage divider IVD is a precise two-stage inductive voltage divider.

[0057] A preferred embodiment of a two-step series-parallel measurement method for a voltage transformer voltage coefficient of the present invention comprises the following steps:

[0058] Assume that the voltage transformer to be tested is T0, the semi-insulated voltage transformer is T1, and the fully-insulated voltage transformer is T 23 In the power frequency high voltage generator T D The output voltages under applied voltage U are u0(U), u1(U) and u 23 (U), the proportional errors are α(U), β(U) and γ(U), then: α(U) = f0(U) + j·δ0(U), where f0(U) and δ0(U) represent the ratio error and the angle error, respectively; Respectively represent the fully insulated voltage transformer T 23 Additional error introduced when connected in series with the secondary of semi-insulated voltage transformer T1;

[0059] Step A:

[0060] The fully insulated voltage transformer T 23 Connected in parallel with the primary of semi-insulated voltage transformer T1 and the power frequency high voltage generator T D Connection, power frequency high voltage generator T D Output voltage U; Fully insulated voltage transformer T 23 Connected in series with the secondary of the semi-insulated voltage transformer T1, the secondary output is cascaded with a two-stage inductive voltage divider IVD; the ratio K of the two-stage inductive voltage divider IVD is set IVD =0.5; Use the high-end differential measurement mode of the transformer tester to measure the voltage difference between the output of the two-stage inductive voltage divider IVD and the proportional output of the voltage transformer T0 under test, with the excitation output of the voltage transformer T0 under test as the reference.

[0061]

[0062]

[0063]

[0064] Among them U ref Indicates the reference voltage;

[0065] Step B:

[0066] The fully insulated voltage transformer T 23 It is connected in series with the primary of the semi-insulated voltage transformer T1 and the power frequency high voltage generator T D Connection: Power frequency high voltage generator T DFor fully insulated voltage transformer T 23 And the voltage of the primary high-end output 2U of the voltage transformer T0 under test, for the fully insulated voltage transformer T 23 The voltage of the primary low end and the primary high end output U of the semi-insulated voltage transformer T1; the fully insulated voltage transformer T 23 Connected in series with the secondary of the semi-insulated voltage transformer T1, the secondary output is cascaded with a two-stage inductive voltage divider IVD; the ratio K of the two-stage inductive voltage divider IVD is set IVD =1; Use the high-end differential measurement method with the transformer tester to measure the voltage difference between the output of the two-stage inductive voltage divider IVD and the proportional output of the voltage transformer T0 under test, taking the excitation output of the voltage transformer T0 under test as a reference.

[0067]

[0068]

[0069]

[0070]

[0071] Therefore, the error change of the measured voltage transformer T0 from voltage U to 2U is:

[0072]

[0073] The above formula shows that β(U) and γ(U) and The voltage variation of T0 can be offset in the calculation of the above two-step series-parallel method, which is the basis for the present invention to achieve high-accuracy measurement.

[0074] That is, the changes in the ratio difference and angle difference of the voltage transformer T0 from voltage U to 2U are:

[0075]

[0076] By analogy, the voltage transformer T0 under test is obtained from the voltage 2 N-1 U to 2 N Error change of U Where N is a positive integer;

[0077] The voltage coefficient curve is:

[0078]

[0079] In summary, the advantages of the present invention are:

[0080] By introducing the two-stage inductive voltage divider IVD, the fully insulated voltage transformer T 23After the secondary output of the semi-insulated voltage transformer T1 is connected in series with the two-stage inductive voltage divider IVD, it is compared with the voltage transformer T0 to be measured. Only two steps (step A and step B) are required to obtain the secondary voltage of the voltage transformer T0 to be measured. N-1 U to 2 N The proportional error change of U (voltage coefficient), although it introduces additional error and But in the calculation process, they are offset, and the ratio K of the two-stage inductive voltage divider IVD is IVD The proportional error between 0.5 and 1 can be controlled to be small enough and negligible. Compared with the traditional three-step method to calculate the voltage coefficient, while reducing the workload of the experimental process, the secondary windings of the full and semi-insulated voltage transformer are always kept in series, which reduces the change of inherent measurement errors in the measurement experiment and allows them to be offset in the result calculation, thereby further reducing the uncertainty of the voltage transformer voltage coefficient measurement.

[0081] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A two-step series-parallel measurement circuit for voltage transformer voltage coefficient, characterized in that: It includes a voltage transformer T0 to be tested, a half-insulated voltage transformer T1, and a fully-insulated voltage transformer T 23 , a power frequency high voltage generator T that can provide half voltage output D and a two-stage inductive voltage divider IVD; the voltage transformer T0, the semi-insulated voltage transformer T1 and the fully-insulated voltage transformer T 23 The rated transformation ratio is K; The fully insulated voltage transformer T 23 After being connected in series or in parallel with the semi-insulated voltage transformer T1, it is connected to the power frequency high voltage generator T D Connection: The fully insulated voltage transformer T 23 The secondary of the semi-insulated voltage transformer T1 is connected in series, and the secondary output is cascaded with the two-stage inductive voltage divider IVD; the primary high end of the voltage transformer T0 under test is connected to the power frequency high voltage generator T D Connection; the primary low ends of the measured voltage transformer T0 and the semi-insulated voltage transformer T1 are both grounded.

2. A voltage transformer voltage coefficient series-parallel two-step measurement circuit as claimed in claim 1, characterized in that: The voltage transformer T0, the semi-insulated voltage transformer T1 and the fully-insulated voltage transformer T 23 They are double-stage voltage transformers or single-stage voltage transformers respectively.

3. A voltage transformer voltage coefficient series-parallel two-step measurement circuit as claimed in claim 1, characterized in that: The two-stage inductive voltage divider IVD is a precision two-stage inductive voltage divider having two ratios of 0.5 and 1.

4. A two-step series-parallel measurement method for voltage transformer voltage coefficient, characterized in that: The method requires the use of a measurement circuit as claimed in any one of claims 1 to 3, comprising the following steps: Assume that the voltage transformer to be tested is T0, the semi-insulated voltage transformer is T1, and the fully-insulated voltage transformer is T 23 In the power frequency high voltage generator T D The output voltages under applied voltage U are u0(U), u1(U) and u 23 (U), the proportional errors are α(U), β(U) and γ(U), then: α(U) = f0(U) + j·δ0(U), where f0(U) and δ0(U) represent the ratio error and the angle error, respectively; Respectively represent the fully insulated voltage transformer T 23 Additional error introduced when connected in series with the secondary of semi-insulated voltage transformer T1; Step A: The fully insulated voltage transformer T 23 In parallel with the primary of the semi-insulated voltage transformer T1, and with the power frequency high voltage generator T D Connection, power frequency high voltage generator T D Output voltage U; Fully insulated voltage transformer T 23 Connected in series with the secondary of the semi-insulated voltage transformer T1, the secondary output is cascaded with a two-stage inductive voltage divider IVD; set the ratio K of the two-stage inductive voltage divider IVD IVD =0.5; Use the high-end differential measurement mode of the transformer tester to measure the voltage difference between the output of the two-stage inductive voltage divider IVD and the proportional output of the voltage transformer T0 under test, with the excitation output of the voltage transformer T0 under test as the reference. Step B: The fully insulated voltage transformer T 23 It is connected in series with the primary of the semi-insulated voltage transformer T1 and the power frequency high voltage generator T D Connection: Power frequency high voltage generator T D For fully insulated voltage transformer T 23 And the voltage of the high-end output 2U of the primary series of the voltage transformer T0 under test, for the fully insulated voltage transformer T 23 The voltage of the primary low end and the primary high end output U of the semi-insulated voltage transformer T1; the fully insulated voltage transformer T 23 Connected in series with the secondary of the semi-insulated voltage transformer T1, the secondary output is cascaded with a two-stage inductive voltage divider IVD; the ratio K of the two-stage inductive voltage divider IVD is set IVD =1; Use the high-end differential measurement method with the transformer tester to measure the voltage difference between the output of the two-stage inductive voltage divider IVD and the proportional output of the voltage transformer T0 under test, taking the excitation output of the voltage transformer T0 under test as a reference. Therefore, the error change of the measured voltage transformer T0 from voltage U to 2U is: The above formula shows that β(U) and γ(U) and and The voltage variation of T0 can be offset in the calculation of the two-step series-parallel method, which is the basis for achieving high-accuracy measurement. That is, the changes in the ratio difference and angle difference of the voltage transformer T0 from voltage U to 2U are: By analogy, the voltage transformer T0 under test is obtained from the voltage 2 N-1 U to 2 N Error change of U Where N is a positive integer; The voltage coefficient curve is:

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