Medium Voltage Sweep Frequency Test Method for Harmonic Transfer Characteristics of Capacitor Voltage Transformer

Abstract

The invention relates to a capacitive voltage transformer, and in particular to a medium-voltage sweep frequency test method for the harmonic transfer characteristics of the capacitive voltage transformer. The method comprises the following steps: separating a voltage divider unit of a CVT from an electromagnetic unit, applying a fundamental wave test voltage and a harmonic wave test voltage between a high-voltage side terminal of the electromagnetic unit and the ground; synchronously detecting a voltage and a current on the high-voltage side of the electromagnetic unit to the ground, and a voltage on the low-voltage side of the electromagnetic unit, and calculating a harmonic equivalent impedance of the electromagnetic unit according to the voltage and the current on the high-voltage side of the electromagnetic unit to the ground; calculating a harmonic impedance of a medium-voltage capacitor, and calculating a harmonic equivalent impedance of the medium-voltage unit in combination with the harmonic equivalent impedance of the electromagnetic unit; calculating a harmonic impedance of a high-voltage capacitor, and calculating a harmonic voltage on the high-voltage side of the CVT in combination with the harmonic equivalent impedance of the medium-voltage unit and the harmonic wave test voltage; and the technical solution provided by the invention can effectively overcome the defects of the prior art in that the output voltage requirement of a test power supply is relatively high, and the wiring operation is relatively difficult.

Description

Technical Field

[0001] The invention relates to a capacitive voltage transformer, and in particular to a medium voltage sweep frequency test method for harmonic transfer characteristics of a capacitive voltage transformer. Background Art

[0002] At present, the new power system vigorously develops new energy power generation and high-voltage direct current transmission. The application of a large number of power electronic equipment has led to higher harmonics in high-voltage and ultra-high-voltage power systems. The capacitor voltage transformer (CVT), which consists of a voltage divider unit and an electromagnetic unit, has many advantages such as good insulation reliability and high fundamental wave measurement accuracy. It is widely used in high-voltage and ultra-high voltage power systems. However, due to the nonlinear frequency response caused by the inherent structure of CVT, there are significant errors in the measurement of harmonics. Therefore, the study of the transfer characteristics of CVT for harmonics in power systems is becoming increasingly important.

[0003] The harmonic transfer characteristics of CVT are usually accurately obtained by frequency sweeping, which applies the rated fundamental voltage and a certain proportion of harmonic voltage on the high-voltage side of CVT, and then synchronously detects the corresponding harmonic voltage of the reference voltage divider unit on the low-voltage side of CVT, thereby obtaining the harmonic transfer characteristics of CVT. However, the above method has the following problems:

[0004] 1) The actual height of CVT above 220kV is greater than 5m, and the high-voltage terminal of CVT is located at the top, making wiring operation difficult;

[0005] 2) The higher the voltage level of the CVT, the higher the output voltage requirement for the test power supply. Currently, there are still technical bottlenecks in achieving frequency control of the test power supply above 100kV;

[0006] 3) The higher the test voltage, the higher the insulation requirements, so there are certain safety hazards. Summary of the invention

[0007] In view of the above-mentioned shortcomings of the prior art, the present invention provides a medium-voltage sweep frequency test method for the harmonic transfer characteristics of a capacitive voltage transformer, which can effectively overcome the defects of the prior art in that the output voltage requirement of the test power supply is high and the wiring operation is difficult.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] The medium voltage sweep frequency test method for the harmonic transfer characteristics of a capacitor voltage transformer comprises the following steps:

[0010] S1. Separate the voltage divider unit of the CVT from the electromagnetic unit, and apply fundamental wave test voltage and harmonic wave test voltage between the high voltage side terminal of the electromagnetic unit and the ground;

[0011] S2, synchronously detecting the voltage and current of the high-voltage side of the electromagnetic unit to the ground, and the voltage of the low-voltage side of the electromagnetic unit, and calculating the harmonic equivalent impedance of the electromagnetic unit according to the voltage and current of the high-voltage side of the electromagnetic unit to the ground;

[0012] S3, calculate the harmonic impedance of the medium voltage capacitor, and calculate the harmonic equivalent impedance of the medium voltage unit in combination with the harmonic equivalent impedance of the electromagnetic unit;

[0013] S4. Calculate the harmonic impedance of the high-voltage capacitor and calculate the harmonic voltage on the high-voltage side of the CVT by combining the harmonic equivalent impedance of the medium-voltage unit and the harmonic test voltage;

[0014] S5. Calculate the harmonic transfer characteristics of the CVT according to the harmonic voltage on the high-voltage side of the CVT and the harmonic voltage on the low-voltage side of the electromagnetic unit, and draw a harmonic transfer characteristic curve of the CVT.

[0015] Preferably, in S1, the voltage divider unit of the CVT is separated from the electromagnetic unit, and a fundamental wave test voltage and a harmonic wave test voltage are applied between the high voltage side terminal of the electromagnetic unit and the ground, including:

[0016] Lift the voltage divider unit, place it in another location and ensure it is stable, and keep the electromagnetic unit;

[0017] Use a wire covered with epoxy insulation tube to connect the output voltage of the test power supply to the high-voltage terminal of the electromagnetic unit, so as to apply the fundamental wave test voltage and the harmonic wave test voltage between the high-voltage terminal of the electromagnetic unit and the ground;

[0018] The high-voltage side terminal of the electromagnetic unit is a connection point between the electromagnetic unit and the voltage divider unit.

[0019] Preferably, the fundamental test voltage It is expressed by the following formula:

[0020] ;

[0021] in, U 11 is the fundamental wave test voltage Amplitude, fundamental test voltage The amplitude U 11 It is equal to the rated voltage of the high voltage side of the CVT medium voltage transformer, which is between 10 and 20 kV. It can be obtained by looking up the CVT nameplate parameters. is the fundamental test voltage The phase angle of

[0022] n Subharmonic test voltage It is expressed by the following formula:

[0023] ;

[0024] in, U 1n for n Subharmonic test voltage The amplitude of n Subharmonic test voltage The amplitude U 1n is the fundamental test voltage The amplitude U 11 0.2%~5%, for n Subharmonic test voltage The phase angle of

[0025] When applying the harmonic test voltage, different single-frequency harmonic test voltages are applied multiple times. The frequency range is 50~2500Hz, and the duration of each harmonic superposition is 20s.

[0026] Preferably, synchronously detecting the voltage and current of the high-voltage side of the electromagnetic unit to the ground, and the voltage of the low-voltage side of the electromagnetic unit in S2 includes:

[0027] The voltage on the high voltage side of the electromagnetic unit to the ground is detected by a broadband high voltage probe U 1 ( t ), detect the current from the high voltage side of the electromagnetic unit to the ground through a wide-band current transformer I 1 ( t ), detect the low-voltage side voltage of the electromagnetic unit through a broadband low-voltage probe U 2 ( t ), the data acquisition device synchronously measures and records the entire process;

[0028] in, U 1 ( t ), I 1 ( t ), U 2 ( t ) include fundamental wave components and harmonic wave components. The voltage measurement of the wide-band high-voltage probe shall not be less than 20kV, and the bandwidth shall not be less than 5kHz; the current measurement range of the wide-band current transformer is 0.01~5A, and the bandwidth shall not be less than 5kHz; the voltage measurement of the wide-band low-voltage probe shall not be less than 100V, and the bandwidth shall not be less than 5kHz;

[0029] The sampling frequency of the data acquisition device is not less than 25.6kHz. It has the ability to measure the amplitude and phase of the 2nd to 50th harmonics, as well as the full waveform recording function, and meets the Class A accuracy requirements.

[0030] Preferably, in S2, calculating the harmonic equivalent impedance of the electromagnetic unit according to the voltage and current of the high-voltage side of the electromagnetic unit to the ground includes:

[0031] Voltage between the high voltage side of the electromagnetic unit and the ground U 1 ( t ) is subjected to Fourier decomposition, and we get n Subharmonic test voltage :

[0032] ;

[0033] Current from the high voltage side of the electromagnetic unit to the ground I 1 ( t ) is subjected to Fourier decomposition, and we get n Subharmonic test current :

[0034] ;

[0035] in, I 1n for n Subharmonic test current The amplitude of for n Subharmonic test current The phase angle of

[0036] according to n Subharmonic test voltage , n Subharmonic test current Calculate the harmonic equivalent impedance of electromagnetic units :

[0037] ;

[0038] ;

[0039] ;

[0040] in, Z n1 is the electromagnetic unit harmonic equivalent impedance The amplitude of is the harmonic equivalent impedance of the electromagnetic unit The phase angle.

[0041] Preferably, calculating the harmonic impedance of the medium voltage capacitor in S3 and calculating the harmonic equivalent impedance of the medium voltage unit in combination with the harmonic equivalent impedance of the electromagnetic unit include:

[0042] The medium voltage capacitor harmonic impedance is calculated using the following formula: :

[0043] ;

[0044] in, f n for n Subharmonic frequencies, C 2 is the medium voltage capacitance value;

[0045] According to the medium voltage capacitor harmonic impedance and electromagnetic unit harmonic equivalent impedance Calculation of harmonic equivalent impedance of medium voltage units :

[0046] .

[0047] Preferably, calculating the harmonic impedance of the high-voltage capacitor in S4 and calculating the harmonic voltage on the high-voltage side of the CVT in combination with the harmonic equivalent impedance of the medium-voltage unit and the harmonic test voltage include:

[0048] The following formula is used to calculate the harmonic impedance of high voltage capacitors: :

[0049] ;

[0050] in, C 1 is the high voltage capacitance value;

[0051] According to the high voltage capacitor harmonic impedance , medium voltage unit harmonic equivalent impedance and n Subharmonic test voltage Calculate the high pressure side of the CVT n Subharmonic voltage :

[0052] .

[0053] Preferably, in S5, the harmonic transfer characteristics of the CVT are calculated according to the harmonic voltage on the high-voltage side of the CVT and the harmonic voltage on the low-voltage side of the electromagnetic unit, and a harmonic transfer characteristic curve of the CVT is drawn, including:

[0054] Voltage on the low voltage side of the electromagnetic unit U 2 ( t ) is decomposed by Fourier to obtain the low-voltage side of the electromagnetic unitn Subharmonic voltage :

[0055] ;

[0056] in, U 2n For the low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude of For the low-voltage side of the electromagnetic unit n Subharmonic voltage The phase angle of

[0057] Calculate the high pressure side of the CVT n Subharmonic voltage The low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude ratio between k :

[0058] ;

[0059] in, k 1 is the rated transformation ratio of the transformer in the electromagnetic unit, U n For the high-voltage side of the CVT n Subharmonic voltage The amplitude of U 2n For the low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude of

[0060] Calculate the high pressure side of the CVT n Subharmonic voltage The low-voltage side of the electromagnetic unit n Subharmonic voltage The phase difference between :

[0061] ;

[0062] in, For the high-voltage side of the CVT n Subharmonic voltage The phase angle, For the low-voltage side of the electromagnetic unit n Subharmonic voltage The phase angle of

[0063] The CVT harmonic transfer characteristic curve is drawn based on the calculated amplitude ratio and phase difference.

[0064] Preferably, the capacitive voltage transformer CVT comprises a voltage divider unit and an electromagnetic unit, wherein the voltage divider unit comprises a high-voltage capacitor connected in series C 1 , Medium Voltage Capacitors C 2 , the medium voltage capacitor C 2 The medium voltage unit is connected in parallel with the electromagnetic unit to form a medium voltage unit. C 1 Series connection.

[0065] Compared with the prior art, the medium-voltage sweep frequency test method for the harmonic transfer characteristics of a capacitive voltage transformer provided by the present invention, by inputting a test voltage of a fundamental wave superimposed on a harmonic on the high-voltage side of an electromagnetic unit, calculating the harmonic equivalent impedance of the electromagnetic unit according to the harmonic test voltage and harmonic test current on the high-voltage side of the electromagnetic unit obtained by synchronous detection, and then calculating the harmonic voltage on the high-voltage side of the CVT according to the medium-voltage capacitor and the high-voltage capacitor, comparing it with the harmonic voltage on the low-voltage side of the electromagnetic unit obtained by detection, and obtaining the harmonic transfer characteristics of the CVT by calculating the amplitude ratio and the phase difference. The method can analyze the harmonic transfer characteristics of the CVT through relatively low fundamental wave test voltage and harmonic wave test voltage, greatly reducing the requirement for the amplitude of the fundamental wave test voltage output by the test power supply (the medium voltage voltage is usually not more than 20 kV), thereby effectively solving the problems of high output voltage requirements for the test power supply, greater difficulty in wiring operation, and potential safety hazards. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0067] Figure 1 It is a schematic diagram of the process of the present invention;

[0068] Figure 2 A schematic diagram of an equivalent circuit structure of a capacitive voltage transformer CVT in the present invention;

[0069] Figure 3 It is another schematic diagram of the equivalent circuit structure of the capacitive voltage transformer CVT in the present invention;

[0070] Figure 4 It is a schematic diagram of the circuit structure of performing a medium voltage frequency sweep test on the harmonic transfer characteristics of a capacitive voltage transformer CVT in the present invention;

[0071] Figure 5is a CVT harmonic amplitude transfer characteristic curve drawn according to the calculated amplitude ratio in the present invention;

[0072] Figure 6 It is a CVT harmonic phase transfer characteristic curve drawn according to the calculated phase difference in the present invention. DETAILED DESCRIPTION

[0073] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0074] In the technical solution of this application, Figure 2 and Figure 3 As shown, the capacitive voltage transformer CVT includes a voltage divider unit and an electromagnetic unit, and the voltage divider unit includes a high-voltage capacitor connected in series. C 1 , Medium Voltage Capacitors C 2 , medium voltage capacitor C 2 Connected in parallel with the electromagnetic unit to form a medium voltage unit, the medium voltage unit and the high voltage capacitor C 1 Series connection.

[0075] Medium voltage sweep frequency test method for harmonic transfer characteristics of capacitor voltage transformers, such as Figure 1 As shown, S1, the voltage divider unit of the CVT is separated from the electromagnetic unit, and a fundamental wave test voltage and a harmonic wave test voltage are applied between the high voltage side terminal of the electromagnetic unit and the ground, specifically including:

[0076] Lift the voltage divider unit, place it in another location and ensure it is stable, and keep the electromagnetic unit;

[0077] Use a wire covered with epoxy insulation tube to connect the output voltage of the test power supply to the high-voltage terminal of the electromagnetic unit, so as to apply the fundamental wave test voltage and the harmonic wave test voltage between the high-voltage terminal of the electromagnetic unit and the ground;

[0078] The high-voltage side terminal of the electromagnetic unit is a connection point between the electromagnetic unit and the voltage divider unit.

[0079] Fundamental wave test voltage It is expressed by the following formula:

[0080] ;

[0081] in,U 11 is the fundamental test voltage Amplitude, fundamental test voltage The amplitude U 11 It is equal to the rated voltage of the high voltage side of the CVT medium voltage transformer, which is between 10 and 20 kV. It can be obtained by looking up the CVT nameplate parameters. is the fundamental test voltage The phase angle of

[0082] n Subharmonic test voltage It is expressed by the following formula:

[0083] ;

[0084] in, U 1n for n Subharmonic test voltage The amplitude of n Subharmonic test voltage The amplitude U 1n is the fundamental test voltage The amplitude U 11 0.2%~5%, for n Subharmonic test voltage The phase angle of

[0085] When applying the harmonic test voltage, different single-frequency harmonic test voltages are applied multiple times. The frequency range is 50~2500Hz, and the duration of each harmonic superposition is 20s.

[0086] In the technical solution of the present application, the voltage divider unit is always placed elsewhere and away from any wires and ground potential objects during the entire test phase. After the rated voltage of the CVT is applied to the high-voltage side terminal of the electromagnetic unit, the electromagnetic unit operates close to the rated working conditions. The harmonic transfer characteristics measured and calculated under this condition can accurately reflect the actual harmonic transfer characteristics of the CVT, so the measurement result error of this method is very small.

[0087] In addition, for conductors covered with epoxy insulation tubes, since the medium voltage usually does not exceed 20kV, it is necessary to ensure that the insulation voltage level of the conductor is not less than 20kV, and the conductor should be as short as possible and as perpendicular to the axis of the CVT body as possible.

[0088] S2. Synchronously detect the voltage and current of the high-voltage side of the electromagnetic unit to the ground, as well as the voltage of the low-voltage side of the electromagnetic unit, and calculate the harmonic equivalent impedance of the electromagnetic unit according to the voltage and current of the high-voltage side of the electromagnetic unit to the ground.

[0089] 1) Synchronously detect the voltage and current of the high-voltage side of the electromagnetic unit to the ground, as well as the voltage of the low-voltage side of the electromagnetic unit, such as Figure 4 As shown, including:

[0090] The voltage on the high voltage side of the electromagnetic unit to the ground is detected by a broadband high voltage probe U 1 ( t ), detect the current from the high voltage side of the electromagnetic unit to the ground through a wide-band current transformer I 1 ( t ), detect the low-voltage side voltage of the electromagnetic unit through a broadband low-voltage probe U 2 ( t ), the data acquisition device synchronously measures and records the entire process;

[0091] in, U 1 ( t ), I 1 ( t ), U 2 ( t ) include fundamental wave components and harmonic wave components. The voltage measurement of the wide-band high-voltage probe shall not be less than 20kV, and the bandwidth shall not be less than 5kHz; the current measurement range of the wide-band current transformer is 0.01~5A, and the bandwidth shall not be less than 5kHz; the voltage measurement of the wide-band low-voltage probe shall not be less than 100V, and the bandwidth shall not be less than 5kHz;

[0092] The sampling frequency of the data acquisition device is not less than 25.6kHz. It has the ability to measure the amplitude and phase of the 2nd to 50th harmonics, as well as the full waveform recording function, and meets the Class A accuracy requirements.

[0093] 2) Calculate the harmonic equivalent impedance of the electromagnetic unit based on the voltage and current on the high-voltage side of the electromagnetic unit to the ground, including:

[0094] Voltage between the high voltage side of the electromagnetic unit and the ground U 1 ( t ) is subjected to Fourier decomposition, and we get n Subharmonic test voltage :

[0095] ;

[0096] Current from the high voltage side of the electromagnetic unit to the ground I 1 ( t ) is subjected to Fourier decomposition, and we get n Subharmonic test current :

[0097] ;

[0098] in, I 1n for n Subharmonic test current The amplitude of for n Subharmonic test current The phase angle of

[0099] according to n Subharmonic test voltage , n Subharmonic test current Calculate the harmonic equivalent impedance of electromagnetic units :

[0100] ;

[0101] ;

[0102] ;

[0103] in, Z n1 is the harmonic equivalent impedance of the electromagnetic unit The amplitude of is the harmonic equivalent impedance of the electromagnetic unit The phase angle.

[0104] S3. Calculate the harmonic impedance of the medium voltage capacitor and calculate the harmonic equivalent impedance of the medium voltage unit in combination with the harmonic equivalent impedance of the electromagnetic unit, including:

[0105] The medium voltage capacitor harmonic impedance is calculated using the following formula: :

[0106] ;

[0107] in, f n for n Subharmonic frequencies, C 2 is the medium voltage capacitance value;

[0108] According to the medium voltage capacitor harmonic impedance and electromagnetic unit harmonic equivalent impedance Calculation of harmonic equivalent impedance of medium voltage units :

[0109] .

[0110] S4. Calculate the harmonic impedance of the high-voltage capacitor, and calculate the harmonic voltage on the high-voltage side of the CVT by combining the harmonic equivalent impedance of the medium-voltage unit and the harmonic test voltage. Specifically include:

[0111] The following formula is used to calculate the harmonic impedance of high voltage capacitors: :

[0112] ;

[0113] in, C 1 is the high voltage capacitance value;

[0114] According to the high voltage capacitor harmonic impedance , medium voltage unit harmonic equivalent impedance and n Subharmonic test voltage Calculate the high pressure side of the CVT n Subharmonic voltage :

[0115] .

[0116] S5. Calculate the harmonic transfer characteristics of the CVT according to the harmonic voltage on the high-voltage side of the CVT and the harmonic voltage on the low-voltage side of the electromagnetic unit, and draw a harmonic transfer characteristic curve of the CVT, including:

[0117] Voltage on the low voltage side of the electromagnetic unit U 2 ( t ) is decomposed by Fourier to obtain the low-voltage side of the electromagnetic unit n Subharmonic voltage :

[0118] ;

[0119] in, U 2n For the low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude of For the low-voltage side of the electromagnetic unit n Subharmonic voltage The phase angle of

[0120] Calculate the high pressure side of the CVT n Subharmonic voltage The low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude ratio between k (Here the amplitude ratio k It can also be expressed as the fundamental voltage amplitude ratio):

[0121] ;

[0122] in, k 1 is the rated transformation ratio of the transformer in the electromagnetic unit, U n For the high-voltage side of the CVT n Subharmonic voltage The amplitude of U 2n For the low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude of

[0123] Calculate the high pressure side of the CVT n Subharmonic voltage The low-voltage side of the electromagnetic unit n Subharmonic voltage The phase difference between :

[0124] ;

[0125] in, For the high-voltage side of the CVT n Subharmonic voltage The phase angle, For the low-voltage side of the electromagnetic unit n Subharmonic voltage The phase angle of

[0126] The CVT harmonic transfer characteristic curve is plotted based on the calculated amplitude ratio and phase difference (e.g. Figure 5 and Figure 6 as shown).

[0127] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will 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 medium voltage sweep frequency test method for the harmonic transfer characteristics of a capacitor voltage transformer, characterized in that: The following steps are involved: S1. Separate the voltage divider unit of the CVT from the electromagnetic unit, and apply fundamental wave test voltage and harmonic wave test voltage between the high voltage side terminal of the electromagnetic unit and the ground; S2, synchronously detecting the voltage and current of the high-voltage side of the electromagnetic unit to the ground, and the voltage of the low-voltage side of the electromagnetic unit, and calculating the harmonic equivalent impedance of the electromagnetic unit according to the voltage and current of the high-voltage side of the electromagnetic unit to the ground; S3, calculate the harmonic impedance of the medium voltage capacitor, and calculate the harmonic equivalent impedance of the medium voltage unit in combination with the harmonic equivalent impedance of the electromagnetic unit; S4. Calculate the harmonic impedance of the high-voltage capacitor and calculate the harmonic voltage on the high-voltage side of the CVT by combining the harmonic equivalent impedance of the medium-voltage unit and the harmonic test voltage; S5. Calculate the harmonic transfer characteristics of the CVT according to the harmonic voltage on the high-voltage side of the CVT and the harmonic voltage on the low-voltage side of the electromagnetic unit, and draw a harmonic transfer characteristic curve of the CVT; S2 synchronously detects the voltage and current of the high-voltage side of the electromagnetic unit to the ground, as well as the voltage of the low-voltage side of the electromagnetic unit, including: The voltage on the high voltage side of the electromagnetic unit to the ground is detected by a broadband high voltage probe U 1( t ), detect the current from the high voltage side of the electromagnetic unit to the ground through a wide-band current transformer I 1( t ), detect the low-voltage side voltage of the electromagnetic unit through a broadband low-voltage probe U 2( t ), the data acquisition device synchronously measures and records the entire process; in, U 1( t ), I 1( t ), U 2( t ) include fundamental wave components and harmonic wave components. The voltage measurement of the wide-band high-voltage probe shall not be less than 20kV, and the bandwidth shall not be less than 5kHz; the current measurement range of the wide-band current transformer is 0.01~5A, and the bandwidth shall not be less than 5kHz; the voltage measurement of the wide-band low-voltage probe shall not be less than 100V, and the bandwidth shall not be less than 5kHz; The sampling frequency of the data acquisition device is not less than 25.6kHz, and it has the ability to measure the amplitude and phase of the 2nd to 50th harmonics, as well as the full waveform recording function; In S2, the harmonic equivalent impedance of the electromagnetic unit is calculated based on the voltage and current of the high-voltage side of the electromagnetic unit to the ground, including: Voltage between the high voltage side of the electromagnetic unit and the ground U 1( t ) is subjected to Fourier decomposition, and we get n Subharmonic test voltage : ； Current from the high voltage side of the electromagnetic unit to the ground I 1( t ) is subjected to Fourier decomposition, and we get n Subharmonic test current : ； in, I 1n for n Subharmonic test current The amplitude of for n Subharmonic test current The phase angle of according to n Subharmonic test voltage , n Subharmonic test current Calculate the harmonic equivalent impedance of electromagnetic units : ； ； ； in, Z n1 is the harmonic equivalent impedance of the electromagnetic unit The amplitude of is the electromagnetic unit harmonic equivalent impedance The phase angle of S3 calculates the harmonic impedance of medium voltage capacitors and combines the harmonic equivalent impedance of electromagnetic units to calculate the harmonic equivalent impedance of medium voltage units, including: The medium voltage capacitor harmonic impedance is calculated using the following formula: : ； in, f n for n Subharmonic frequencies, C 2 is the medium voltage capacitance value; According to the medium voltage capacitor harmonic impedance and electromagnetic unit harmonic equivalent impedance Calculation of harmonic equivalent impedance of medium voltage units : ； S4 calculates the harmonic impedance of the high-voltage capacitor and calculates the harmonic voltage on the high-voltage side of the CVT by combining the harmonic equivalent impedance of the medium-voltage unit and the harmonic test voltage, including: The following formula is used to calculate the harmonic impedance of high voltage capacitors: : ； in, C 1 is the high voltage capacitance value; According to the high voltage capacitor harmonic impedance , medium voltage unit harmonic equivalent impedance and n Subharmonic test voltage Calculate the high pressure side of the CVT n Subharmonic voltage : ； In S5, the harmonic transfer characteristics of the CVT are calculated based on the harmonic voltage on the high-voltage side of the CVT and the harmonic voltage on the low-voltage side of the electromagnetic unit, and the harmonic transfer characteristic curve of the CVT is drawn, including: Voltage on the low voltage side of the electromagnetic unit U 2( t ) is decomposed by Fourier to obtain the low-voltage side of the electromagnetic unit n Subharmonic voltage : ； in, U 2n For the low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude of For the low-voltage side of the electromagnetic unit n Subharmonic voltage The phase angle of Calculate the high pressure side of the CVT n Subharmonic voltage The low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude ratio between k : ； in, k 1 is the rated transformation ratio of the transformer in the electromagnetic unit, U n For the high-voltage side of the CVT n Subharmonic voltage The amplitude of U 2n For the low-voltage side of the electromagnetic unit n Subharmonic voltage The amplitude of Calculate the high pressure side of the CVT n Subharmonic voltage The low-voltage side of the electromagnetic unit n Subharmonic voltage The phase difference between : ； in, For the high-voltage side of the CVT n Subharmonic voltage The phase angle, For the low-voltage side of the electromagnetic unit n Subharmonic voltage The phase angle of The CVT harmonic transfer characteristic curve is drawn based on the calculated amplitude ratio and phase difference.

2. The medium voltage sweep frequency test method for harmonic transfer characteristics of a capacitor voltage transformer according to claim 1, characterized in that: In S1, the voltage divider unit of the CVT is separated from the electromagnetic unit, and a fundamental wave test voltage and a harmonic wave test voltage are applied between the high voltage side terminal of the electromagnetic unit and the ground, including: Lift the voltage divider unit, place it in another location and ensure it is stable, and keep the electromagnetic unit; Use a wire covered with epoxy insulation tube to connect the output voltage of the test power supply to the high-voltage terminal of the electromagnetic unit, so as to apply the fundamental wave test voltage and the harmonic wave test voltage between the high-voltage terminal of the electromagnetic unit and the ground; The high-voltage side terminal of the electromagnetic unit is a connection point between the electromagnetic unit and the voltage divider unit.

3. The medium voltage sweep frequency test method for harmonic transfer characteristics of a capacitor voltage transformer according to claim 2, characterized in that: Fundamental wave test voltage It is expressed as follows: ； in, U 11 is the fundamental test voltage Amplitude, fundamental test voltage The amplitude U 11 It is equal to the rated voltage of the high voltage side of the CVT medium voltage transformer, which is between 10 and 20 kV. It can be obtained by looking up the CVT nameplate parameters. is the fundamental test voltage The phase angle of n Subharmonic test voltage It is expressed by the following formula: ； in, U 1n for n Subharmonic test voltage The amplitude of n Subharmonic test voltage The amplitude U 1n is the fundamental test voltage The amplitude U 11 0.2%~5%, for n Subharmonic test voltage The phase angle of When applying the harmonic test voltage, different single-frequency harmonic test voltages are applied multiple times. The frequency range is 50~2500Hz, and the duration of each harmonic superposition is 20s.

4. The medium voltage sweep frequency test method for the harmonic transfer characteristics of a capacitor voltage transformer according to any one of claims 1 to 3, characterized in that: The capacitive voltage transformer CVT comprises a voltage divider unit and an electromagnetic unit, wherein the voltage divider unit comprises a high-voltage capacitor connected in series C 1. Medium voltage capacitor C 2. The medium voltage capacitor C 2 is connected in parallel with the electromagnetic unit to form a medium voltage unit, and the medium voltage unit is connected to the high voltage capacitor C 1 in series.

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