WO2019174462A1

WO2019174462A1 - Method for accurately measuring harmonic voltage of capacitor voltage transformer by means of interpolation

Info

Publication number: WO2019174462A1
Application number: PCT/CN2019/076393
Authority: WO
Inventors: 薛峰; 谢伟伦; 谢培成; 谢建容; 黄志威; 陈欣晖; 许家凤; 吴洁婷; 李世亨; 刘小沛
Original assignee: 广东电网有限责任公司东莞供电局
Priority date: 2018-03-15
Filing date: 2019-02-28
Publication date: 2019-09-19
Also published as: CN108535679B; CN108535679A

Abstract

A method for accurately measuring the harmonic voltage of a capacitor voltage transformer (CVT) by means of interpolation. In the method, by means of curve fitting, a mathematical interpolation calculation equation under the condition of different parameter combinations is obtained in an off-line state, then, for a specific CVT device, a nameplate parameter (an actual parameter) thereof is input to a harmonic correction device by means of man-machine dialogue, and a network transfer function for an arbitrary parameter at room temperature is obtained by means of the mathematical interpolation calculation equation, i.e., obtaining an amplitude-frequency curve and a phase-frequency curve of the CVT for a specific parameter at room temperature; then, according to the operation environment temperature of the CVT measured by a temperature sensor, correction curves of the amplitude-frequency curve and phase-frequency curve of the CVT which change with temperature is obtained by means of offline calculation of the equivalent circuit parameter offset caused by a temperature change. Thus, accurate correction measurement of the harmonic content of the CVT is achieved.

Description

Accurate Measurement Method of Harmonic Voltage of Capacitor Voltage Transformer Based on Interpolation Method

Technical field

The invention relates to the field of power system measurement methods, and more particularly to an accurate method for measuring harmonic voltage of a capacitive voltage transformer based on interpolation.

Background technique

Capacitor Voltage Transformers (CVT-Capacitor Voltage Transformer) have gained more and more applications in power systems with their unique advantages. However, due to the particularity of its working principle, the national standard GB/T 14549-1993 "Power Quality Utility Grid Harmonics" clearly stipulates that CVT can not be used for harmonic measurement, and with the increasing nonlinear load, for harmonic voltage The measurement has become a requirement for the power industry to ensure a safe operation. The development of the situation has led to the need for accurate measurement of harmonic voltage.

In the prior art, a harmonic measurement error correction device including a harmonic generation, a high voltage generation, an accurate value output, a measured CVT output, a data processing, and a result output is designed, and the specific After the experiment of the harmonic transfer characteristics of the CVT equipment, the harmonic measurement curve of the measured harmonics is used to correct the harmonic measurement. Although the device can accurately correct the harmonic measurement, there is a problem that it must be corrected separately for each CVT device, and the workload is large. The practical application is difficult, and the cost is high, the efficiency is low, and the speed is slow.

In the prior art, on the basis of the conventional capacitive voltage transformer, a method of measuring the harmonic voltage signal by adding a capacitive voltage divider as a measuring component of the harmonic measurement at the low voltage end is realized. An inherent flaw of this method is that the CVT must be modified. Theoretically, it is a subversive change of the CVT measurement principle. Some are similar to the working principle of the electronic transformer. The manufacturing and design cost will no longer have the characteristics of CVT. Moreover, since new components are added inside the CVT, its safety is difficult to evaluate and predict. It can be said that it is not suitable for the transformation of existing CVT applications, and there are defects such as complicated structure, high cost, and hidden dangers. .

In the prior art, two current sensors are added inside the CVT, and the current signals flowing through the CVT high voltage capacitor C1 and the low voltage capacitor C2 are respectively collected by the data acquisition card; and the collected current signals are further processed by a harmonic analysis program. After the harmonic analysis, the relationship between the current and the voltage is used to calculate the voltage harmonics of the CVT grid side.

In the prior art, the equivalent circuit component parameters of the preset model are fitted to obtain a ratiometric amplitude-frequency response curve and a phase-frequency response characteristic curve, and then different equivalent circuit component parameters of other models are adopted based on the fitting result. Adjust the curve by panning and other methods to achieve correction. The actual variation of the transfer characteristics (as shown in Figures 1 and 2) caused by the difference in the structural parameters of the CVT (ie, the high-voltage capacitor C ₁ , the medium-voltage capacitor C _{2 ,} and the voltage-divided ratio k parameter) The operability of the processing is considered less, and the influence on the stray capacitance is not considered adequately; and theoretical analysis and computer simulation studies show that the equivalent circuit component parameters of the CVT vary with temperature, although for the fundamental The transfer characteristics have little influence, but the harmonic signal has a great influence on the transmission of the harmonic signal. The harmonic measurement correction method that does not consider the temperature influence will cause a large additional error of the warming service in practical application. Figure 3 shows the consideration of the component. After the parameter changes with temperature, the sensing ratio of the harmonics of some times and the variation of the phase difference show that the temperature has a great influence on the accuracy of the CVT harmonic voltage measurement. The higher the harmonic frequency, the more serious the affected situation. Therefore, in the study of the accurate measurement method of CVT harmonic voltage, the influence of temperature on the measurement result must be considered.

Summary of the invention

The invention provides an accurate measurement method for harmonic voltage of a capacitive voltage transformer based on interpolation method with high precision.

In order to achieve the above technical effects, the technical solution of the present invention is as follows:

An accurate method for measuring harmonic voltage of a capacitive voltage transformer based on interpolation method, characterized in that it comprises the following steps:

S1: According to the equivalent circuit model of the capacitive voltage transformer, calculate an equivalent circuit structural parameter that satisfies the requirements of the fundamental wave measurement accuracy under the combination of different main capacitance parameter values;

S2: The equivalent circuit structure parameter obtained in S1, offline calculation of the network transfer function correction coefficient of each harmonic of the capacitive voltage transformer under normal temperature under different main capacitance values, ie: relative to the secondary side output The obtained basic amplitude frequency response curve and the correction coefficient of the phase frequency response curve;

S3: Considering the difference of the structural parameters of the capacitive voltage transformer due to the manufacturing parameters, the two-dimensional linear interpolation method is used to obtain the actual capacitive voltage transformer to be corrected at normal temperature under different structural parameter combinations and different temperatures. The correction coefficient of the transmission characteristic of each harmonic voltage is further obtained by the fast Fourier transform result of the secondary side output signal to obtain the correction value of the harmonic signal of the primary side at the normal temperature;

S4: Through the measurement of temperature, the one-dimensional linear interpolation method is used to achieve accurate correction measurement of voltage harmonics under different temperature conditions.

2 . The method for accurately measuring harmonic voltage of a capacitive voltage transformer based on interpolation according to claim 1 , wherein the method for calculating a structural parameter of a 110 kV capacitive voltage transformer is used, and the specific process of the step S1 is performed. Yes:

According to the standard GB/T 4703-2001 for the production of capacitive voltage transformers, the capacitor divider should meet the requirements of the coupling capacitor and capacitor divider standard JB/T 8169-1999: in the capacitor divider voltage divider capacitor unit When selected, the difference between the measured value and the nominal value of any series capacitor unit shall not exceed -5% to +10% of the nominal value, and the ratio of the measured capacitance values of any two capacitor units connected in series with the two units The difference between the rated capacitance ratios should not be greater than 5% of the latter ratio, determine the range of variation of the high voltage capacitor C1 and the medium voltage capacitor C2 of the capacitive voltage transformer; and within the range of variation, C1 and C2 are respectively used in the arithmetic progression. The form forms a sequence and is divided into different combinations of C1 and C2 in a combined manner;

Under the premise of ensuring the accuracy of the fundamental wave transfer, the combination of the above-mentioned known high-voltage capacitor C1 and medium-voltage capacitor C2 is based on the principle that the capacitive voltage transformer is in the state of resonance measurement under the fundamental wave condition, and the intermediate is calculated. The theoretical inductance value LS of the reactor, taking into account the manufacturing characteristics of the capacitive voltage transformer, set 1.005LS as the actual inductance value of the compensation reactor; the stray capacitance, damping circuit and load parameters are normal and rated The parameter settings are run; thus obtaining an equivalent circuit model of the capacitive voltage transformer under different specific parameters.

The method for accurately measuring the harmonic voltage of the capacitive voltage transformer based on the interpolation method according to claim 2, wherein the specific process of the step S2 is:

According to the combination of C1 and C2 according to claim 2, through the parameter configuration obtained in step S1, the simulation method is used to off-line calculation of different main capacitance value parameters of the capacitive voltage transformer under the condition of normal temperature nominal parameter, each harmonic The curve of the frequency response correction coefficient of each harmonic under different parameter combination conditions is obtained by the curve fitting method based on the correction coefficient of the fundamental ratio-frequency response curve and the phase shift-frequency response curve.

The method for accurately measuring harmonic voltage of a capacitive voltage transformer based on an interpolation method according to claim 3, wherein in step S3, the structural parameters of the capacitive voltage transformer are considered to be practical due to differences in parameters during manufacturing. The process of correcting the transfer characteristic of each harmonic voltage of the capacitive voltage transformer to be corrected at normal temperature is:

1) According to the nameplate parameter of the capacitive voltage transformer, the rated capacitance CN and the measured partial pressure ratio k are calculated by the formula:

And C ₂ = kC _N , calculate the high voltage capacitor C1 and the medium voltage capacitor C2 of the capacitive voltage transformer.

2) Under the condition of given parameters, the two-dimensional linear interpolation method is used to calculate the transformation ratio kh and the phase offset value of each harmonic voltage.

Value. Suppose the actual values of C1 and C2 fall by (C1(1), C2(1), kh1), (C1(2), C2(1), kh2), (C1(1), C2(2), kh3 ), (C1(2), C2(2), kh4) constitutes a computational space, where khi represents the ratio or phase shift of the hth harmonic at the four vertices of the range of values

Actual kh or phase shift of any hth harmonic

The calculation formula is:

among them:

3) The sampled value outputted by the secondary side of the capacitive voltage transformer is calculated by using the fast Fourier transform and its corrected interpolation algorithm to obtain the secondary side output after the primary side capacitive voltage transformer (CVT) is transformed. The amplitude U _sh and phase value of each harmonic

4) Calculate the actual corrected voltage value U _hc and phase value Φ of the primary side harmonic voltage at normal temperature according to the value of the secondary side harmonic voltage and the obtained harmonic transfer ratio and phase offset value. _Hc , whose calculation formula is:

The method for accurately measuring harmonic voltage of a capacitive voltage transformer based on an interpolation method according to claim 4, wherein the step of using the mathematical interpolation in the step S4 is to achieve accurate voltage harmonics under arbitrary temperature conditions. The specific process of measurement is:

1) The method of two-dimensional linear interpolation according to claim 4 can obtain the combination of the high-voltage capacitor C ₁ and the medium-voltage capacitor C _{2 of} any capacitive voltage transformer, and the actual correction voltage of each harmonic under normal temperature conditions. Value U _hc and phase value Φ _hc ;

2) Through the offline simulation of the influence of the parameters of the equivalent circuit on the transfer characteristics after the temperature changes, the harmonic curve of each harmonic parameter is measured by the temperature, and the measured capacitive voltage transformer is actually operated. The temperature obtains the transformation ratio of each harmonic voltage and the temperature correction coefficients λ _hb and λ _{hx of the} phase;

3) From the actual voltage value U _hc and the phase value Φ _hc under normal temperature conditions, using the temperature correction coefficients λ _hb and λ _hx values, calculate the actual voltage value U _ht of the primary side harmonic voltage at any operating temperature and The phase value Φ _ht is calculated as:

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

The method of the invention utilizes the curve fitting method to obtain the mathematical interpolation calculation equation under the condition of different parameters under the offline condition, and then inputs the nameplate parameter (actual parameter) to the harmonic for the specific CVT device by means of man-machine dialogue. The wave correcting device uses the mathematical interpolation calculation equation to obtain a network transfer function of an arbitrary parameter under normal temperature conditions, that is, obtains a CVT amplitude-frequency curve and a phase-frequency curve for a normal temperature under a specific parameter; and then, the CVT measured by the temperature sensor is used. Operating environment temperature, through the calculation of the equivalent circuit parameter offset caused by the temperature change obtained under off-line conditions, the corrected curve of the CVT amplitude-frequency curve and the phase-frequency curve with temperature is obtained, and the harmonic content of the CVT is realized. Accurately correct the measurement.

DRAWINGS

1 is a relative change curve of a method C ₁ and C ₂ in the range of 95% to 110% in the prior art;

2 is a relative curve of the phase of another method C ₁ and C ₂ in the range of 95% to 110% in the prior art;

3 is a trend diagram of a harmonic transfer characteristic curve in consideration of a component parameter as a function of temperature in a method in the prior art;

4 is a CVT equivalent circuit model of the present invention;

Figure 5 is a simplified circuit diagram of a CVT in the present invention;

6 is a basic amplitude-frequency response curve and a phase-frequency response curve of a CVT according to the present invention;

Figure 7 is a basic amplitude-frequency response curve of the CVT under different combinations of main capacitance parameters (C ₁ and C ₂ in the range of 95% to 110%) of the present invention, wherein 2, 3, 4, 5, 6 And 7 represent the second harmonic, the third harmonic, the fourth harmonic, the fifth harmonic, the sixth harmonic and the seventh harmonic respectively;

8 is a deviation curve of a phase-frequency response curve of each harmonic of a CVT under different main capacitance parameter combinations (C1 and C2 in 95% to 110%), wherein 2, 3, 4, 5, 6 represents the second harmonic, the third harmonic, the fourth harmonic, the fifth harmonic and the sixth harmonic;

9 is a schematic diagram of calculation of an interpolation correction method in the present invention;

Fig. 10 is a graph showing the amplitude change rate of each harmonic ratio as a function of temperature in the present invention.

detailed description

The drawings are for illustrative purposes only and are not to be construed as limiting the invention;

In order to better illustrate the embodiment, some components of the drawings may be omitted, enlarged or reduced, and do not represent the actual product size;

It will be apparent to those skilled in the art that certain known structures and their description may be omitted.

The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

Example 1

Since the structural parameters of the capacitive voltage transformer (CVT) and the influence of the ambient temperature on the parameters cause a large change in the harmonic transfer characteristics of the CVT, the present invention proposes a harmonic interpolation method based on the structural parameters of the CVT. A method for accurate measurement of wave voltage. The basic idea is: firstly calculate the equivalent circuit structure parameters that meet the requirements of fundamental wave measurement accuracy according to the nameplate parameters given by CVT; then obtain the network transfer function at room temperature, including its basic amplitude-frequency response, from this structural parameter. Curve and phase-frequency response curve; then consider the variation of CVT structure parameters due to manufacturing parameters and the influence of temperature, and obtain the transmission characteristics of each harmonic voltage in several typical structural parameter combinations and different temperatures, and then pass the temperature. The measurement uses mathematical interpolation to achieve accurate measurement of voltage harmonics, which provides a practical solution for the measurement of harmonic voltage in CVT.

Using the electrician principle, the working circuit of the CVT can be equivalent to the circuit model of Figure 4.

In the figure, U _p represents the measured voltage on the primary side of the primary side, U _s represents the secondary side output voltage measured on the secondary side of the CVT; C ₁ and C ₂ represent the high voltage and medium voltage capacitance; L _S is the compensation reactor inductance ; R _S is the equivalent resistance of the compensating reactor; C _C is the equivalent stray capacitance of the compensating reactor; R _m and L _m are the excitation resistance and magnetizing inductance of the medium voltage transformer T; R _T1 and L _T1 are the medium voltage transformers once. Side winding resistance and winding leakage inductance; R _T2 , L _T2 represent the winding resistance and winding leakage inductance of the secondary side of the medium voltage transformer; C _p1 represents the primary side winding to ground stray capacitance; C _p2 represents the secondary side winding to ground Stray capacitance; C _p12 represents the coupling capacitance between the primary side and the secondary side winding; L _Z and R _Z are the equivalent inductance and resistance of the damper; L _b and R _b are the load inductance and resistance converted to the primary side.

The circuit of Fig. 2 is equivalent by the Y-Δ conversion, and a simplified circuit is obtained as shown in Fig. 5.

In the figure: C = C ₁ + C ₂ ;

It is the voltage value after the voltage is divided by the capacitor.

Thus, the network transfer function of the CVT can be obtained as follows:

Theoretically, after knowing the parameters in equation (1), the ratio of the primary side voltage to the secondary output side voltage at different frequencies and the phase shift relationship can be obtained. However, in practical applications, because the calculation amount of this calculation process is too large, if the formula (1) is used for real-time calculation, the calculation amount will be large, and the programming software is large in scale, which is not suitable for the implementation of the microprocessor-based signal processing system. The delay of data output is very large, and it has little significance for the detection, evaluation, analysis and control of the system running state. Therefore, it is necessary to find a simple and fast algorithm to realize the analysis and calculation of the CVT transition characteristics.

The method proposed by the invention is to obtain the mathematical interpolation calculation equation under different parameter combination conditions under off-line conditions by off-line calculation of the transmission characteristics of some CVT structural parameter combinations, and then to the specific CVT device under the offline condition. The man-machine dialogue method is used to input the nameplate parameter (actual parameter) into the harmonic correction device, and the mathematical interpolation calculation equation is used to obtain the network transfer function of the arbitrary parameter under the normal temperature condition, that is, the CVT under the normal temperature for the specific parameter is obtained. The amplitude-frequency curve and the phase-frequency curve; then, using the CVT operating ambient temperature measured by the temperature sensor, the CVT amplitude-frequency curve obtained by calculating the equivalent circuit parameter offset caused by the temperature change under off-line conditions And the correction curve of the phase-frequency curve with temperature, to achieve accurate correction measurement of the harmonic content of CVT. The following is a specific implementation step and process described by taking the 110VV CVT structure parameters as an example:

1) According to the structure of the CVT, an equivalent circuit as shown in Fig. 4 is constructed. The basic component parameters are determined by the nominal high-voltage capacitor C ₁ , the medium-voltage capacitor C ₂ and the voltage-dividing ratio k parameter under the premise of ensuring the fundamental wave transfer accuracy, and then the CVT is in the fundamental wave condition. The principle of the resonance measurement state, the theoretical inductance value L _{S of the} intermediate reactor is calculated, and taking into account the manufacturing characteristics of the CVT, the 1.005L _{S is taken} as the actual inductance value parameter in Fig. 4, and the compensation reactor is set; the stray capacitance, The damping circuit and load parameters are set according to the normal and rated operating parameters;

2) According to the parameter configuration of step (1), the basic transformation ratio-frequency response curve and phase shift-frequency response curve of harmonic transfer of CVT under the condition of nominal parameters can be obtained by simulation method, as shown in Fig. 6;

3) According to the standard GB/T 4703-2001 for the production of capacitive voltage transformers, the capacitor divider should meet the requirements of the coupling capacitor and capacitor divider standard JB/T 8169-1999, namely: in the capacitor divider When the pressure capacitor unit is selected, the difference between the measured value and the nominal value (rated value) of any series capacitor unit shall not exceed -5% to +10% of the nominal value, and any two capacitor units connected in series (C _i , C _j ) The ratio of the measured capacitance value to the ratio of the rated capacitance (C _iN , C _jN ) of the two units should not be greater than 5% of the latter ratio, determining the possibility of the CVT main capacitors C ₁ and C ₂ Range of changes;

4) Select a combination of C ₁ and C ₂ of several groups (at least 10 groups or more, the more the number of groups is, the higher the interpolation calculation accuracy is), according to the method of step (2), obtain the CVT shown in FIG. 7 and FIG. The deviation curve from the basic amplitude-frequency response curve and the phase-frequency response curve under different combinations of main capacitance parameters;

5) According to the nameplate parameter of the CVT, the rated capacitance CN and the measured partial pressure ratio k are calculated by the formula:

And C ₂ = kC _N can calculate the high voltage capacitor C ₁ and medium voltage capacitor C ₂ of the CVT;

6) The sample value outputted by the secondary side of the CVT is calculated by the fast Fourier transform and its corrected interpolation algorithm to obtain the amplitude U _sh and the phase value of each harmonic of the secondary side output after the primary side CVT is transformed.

(Because the transfer function characteristic of harmonic transfer is different from the fundamental wave, the actual value of the primary side harmonic voltage cannot be obtained from this value, and the harmonic voltage of the primary side must be obtained by the following steps.

7) the actual parameters obtained based on the basic curve of FIG. 6, in conjunction with FIGS. 7 and 8, a method using linear interpolation to obtain any high voltage capacitors C ₁ and CVT Capacitance C ₂ parameter combination, at normal temperature Harmonic transfer ratio and phase deviation correction value.

The specific implementation process is:

(a) According to the input CVT nameplate parameter, the result calculated by the step (5), a calculation interval of FIG. 9 can be found in FIGS. 7 and 8 by the method of the interval search table. It can be seen from Fig. 9 that the amplitude ratio k _h and phase offset of each harmonic voltage are given under the given parameters.

The range of values.

(b) Assume that the actual values of C ₁ and C ₂ fall on (C ₁₍₁₎ , C ₂₍₁₎ , k _h1 ), (C ₁₍₂₎ , C ₂₍₁₎ , k _h2 ), ( The computational space formed by C ₁₍₁₎ , C ₂₍₂₎ , k _h3 ), (C ₁₍₂₎ , C ₂₍₂₎ , k _h4 ), where k _hi represents the hth harmonic in the range of values Ratio of four vertices (or phase offset)

). Then the ratio of any hth harmonic to k _h (or phase shift)

The formula for calculating is:

among them:

8) From the value of the secondary side harmonic voltage obtained in step (6), using the harmonic transfer ratio and phase offset value obtained in step (7), the harmonic voltage of the primary side can be calculated at normal temperature. The actual voltage value U _hc and the phase value Φ _hc are calculated as:

9) Since the equivalent parameters of the CVT will change under different temperature conditions, under the offline condition, the simulation calculation of the influence of the parameters of the equivalent circuit on the transfer characteristics after temperature change is obtained. The harmonic parameter shown in Fig. 10 is a curve with temperature, whereby the temperature correction coefficients λ _hb and λ _{hx of the} amplitude ratio and phase of different harmonic times can be obtained, thereby obtaining the actual harmonics at any temperature. Voltage value U _ht and phase value Φ _ht . The specific processing method and implementation process are as follows:

(a) It can be seen from the simulation curve that the effect of temperature on the transmission accuracy is approximately linear. Therefore, for each different harmonic parameter, the linear function can be used to obtain the slope. The slope (correction factor) λ _hb and λ _{hx of the} specific amplitude and phase as a function of temperature. For example, taking the calculation of the correction coefficient of the 5th harmonic as an example, at -30 °C, the transformation variable ratio produces a temperature additional error of 5.2 × 10 ^-3 , and the slope calculation formula can be calculated to obtain the transformation ratio correction coefficient. λ _hb is 1.04×10 ^-4 /°C; at -30 °C, a temperature additional error of about -0.435° is generated, and the temperature correction coefficient λ _hx obtained by the slope calculation formula can be calculated as -8.7×10 ^-3 /°C.

(b) Correct the temperature effect. The correction calculation formula is:

Where: T is the site temperature of the CVT operation, the unit is °C.

Correction calculations for harmonic voltage measurements of different voltage levels CVT can be achieved by steps (1) - step (9). It should be emphasized that the amplitude-frequency characteristic curve and the phase-frequency characteristic curve in the above introduction are all calculated based on the CVT parameters of the 110kV voltage level. The amplitude-frequency characteristic curve and the phase-frequency characteristic curve of different voltage levels may have certain differences. The amplitude-frequency characteristic curve and the phase-frequency characteristic curve must be drawn off-line respectively, and the correction calculation of the harmonic voltage measurement of different voltage levels CVT is realized by the steps (1)-step (9) of the method.

The same or similar reference numerals correspond to the same or similar parts;

The positional relationship is described in the drawings for illustrative purposes only and is not to be construed as limiting the invention;

It is apparent that the above-described embodiments of the present invention are merely illustrative of the present invention and are not intended to limit the embodiments of the present invention. Other variations or modifications of the various forms may be made by those skilled in the art in light of the above description. There is no need and no way to exhaust all of the implementations. Any modifications, equivalent substitutions and improvements made within the spirit and scope of the invention are intended to be included within the scope of the appended claims.

Claims

An accurate method for measuring harmonic voltage of a capacitive voltage transformer based on interpolation method, characterized in that it comprises the following steps:

S1: According to the equivalent circuit model of the capacitive voltage transformer, calculate an equivalent circuit structural parameter that satisfies the requirements of the fundamental wave measurement accuracy under the combination of different main capacitance parameter values;

S2: The equivalent circuit structure parameter obtained in S1, offline calculation of the network transfer function correction coefficient of each harmonic of the capacitive voltage transformer under normal temperature under different main capacitance values, ie: relative to the secondary side output The obtained basic amplitude frequency response curve and the correction coefficient of the phase frequency response curve;

S3: Considering the difference of the structural parameters of the capacitive voltage transformer due to the manufacturing parameters, the two-dimensional linear interpolation method is used to obtain the actual capacitive voltage transformer to be corrected at normal temperature under different structural parameter combinations and different temperatures. The correction coefficient of the transmission characteristic of each harmonic voltage is further obtained by the fast Fourier transform result of the secondary side output signal to obtain the correction value of the harmonic signal of the primary side at the normal temperature;

S4: Through the measurement of temperature, the one-dimensional linear interpolation method is used to achieve accurate correction measurement of voltage harmonics under different temperature conditions.
The method for accurately measuring the harmonic voltage of a capacitive voltage transformer based on the interpolation method according to claim 1, wherein the 110kV capacitive voltage transformer structural parameter is calculated by using the method, and the specific process of the step S1 is:

According to the standard GB/T 4703-2001 for the production of capacitive voltage transformers, the capacitor divider should meet the requirements of the coupling capacitor and capacitor divider standard JB/T 8169-1999: in the capacitor divider voltage divider capacitor unit When selected, the difference between the measured value and the nominal value of any series capacitor unit shall not exceed -5% to +10% of the nominal value, and the ratio of the measured capacitance values of any two capacitor units connected in series with the two units The difference between the rated capacitance ratios should not be greater than 5% of the latter ratio, determine the range of variation of the high voltage capacitor C1 and the medium voltage capacitor C2 of the capacitive voltage transformer; and within the range of variation, C1 and C2 are respectively used in the arithmetic progression. The form forms a sequence and is divided into different combinations of C1 and C2 in a combined manner;

Under the premise of ensuring the accuracy of the fundamental wave transfer, the combination of the above-mentioned known high-voltage capacitor C1 and medium-voltage capacitor C2 is based on the principle that the capacitive voltage transformer is in the state of resonance measurement under the fundamental wave condition, and the intermediate is calculated. The theoretical inductance value LS of the reactor, taking into account the manufacturing characteristics of the capacitive voltage transformer, set 1.005LS as the actual inductance value of the compensation reactor; the stray capacitance, damping circuit and load parameters are normal and rated The parameter settings are run; thus obtaining an equivalent circuit model of the capacitive voltage transformer under different specific parameters.
The method for accurately measuring the harmonic voltage of a capacitive voltage transformer based on the interpolation method according to claim 2, wherein the specific process of the step S2 is:

According to the combination of C1 and C2 according to claim 2, through the parameter configuration obtained in step S1, the simulation method is used to off-line calculation of different main capacitance value parameters of the capacitive voltage transformer under the condition of normal temperature nominal parameter, each harmonic The curve of the frequency response correction coefficient of each harmonic under different parameter combination conditions is obtained by the curve fitting method based on the correction coefficient of the fundamental ratio-frequency response curve and the phase shift-frequency response curve.
The method for accurately measuring the harmonic voltage of a capacitive voltage transformer based on the interpolation method according to claim 3, wherein in step S3, the structural parameters of the capacitive voltage transformer are considered to be actually corrected due to the difference in parameters during manufacturing. The process of the correction characteristic of the transfer characteristic of each harmonic voltage of the capacitive voltage transformer at normal temperature is:

1) According to the nameplate parameter of the capacitive voltage transformer, the rated capacitance CN and the measured partial pressure ratio k are calculated by the formula:
And C 2 = kC N , calculate the high voltage capacitor C1 and the medium voltage capacitor C2 of the capacitive voltage transformer.

2) Under the condition of given parameters, the two-dimensional linear interpolation method is used to calculate the transformation ratio kh and the phase offset value of each harmonic voltage.
Value. Suppose the actual values of C1 and C2 fall by (C1(1), C2(1), kh1), (C1(2), C2(1), kh2), (C1(1), C2(2), kh3 ), (C1(2), C2(2), kh4) constitutes a computational space, where khi represents the ratio or phase shift of the hth harmonic at the four vertices of the range of values
Actual kh or phase shift of any hth harmonic
The calculation formula is:

among them:

among them:

3) The sampled value outputted by the secondary side of the capacitive voltage transformer is calculated by using the fast Fourier transform and its corrected interpolation algorithm to obtain the secondary side output after the primary side capacitive voltage transformer (CVT) is transformed. The amplitude U sh and phase value of each harmonic

4) Calculate the actual corrected voltage value U hc and phase value Φ of the primary side harmonic voltage at normal temperature according to the value of the secondary side harmonic voltage and the obtained harmonic transfer ratio and phase offset value. Hc , whose calculation formula is:
The accurate method for measuring harmonic voltage of a capacitive voltage transformer based on interpolation method according to claim 4, wherein the step of using the mathematical interpolation in the step S4 is to achieve accurate measurement of voltage harmonics under arbitrary temperature conditions. The specific process is:

1) The method of two-dimensional linear interpolation according to claim 4 can obtain the combination of the high-voltage capacitor C 1 and the medium-voltage capacitor C 2 of any capacitive voltage transformer, and the actual correction voltage of each harmonic under normal temperature conditions. Value U hc and phase value Φ hc ;

2) Through the offline simulation of the influence of the parameters of the equivalent circuit on the transfer characteristics after the temperature changes, the harmonic curve of each harmonic parameter is measured by the temperature, and the measured capacitive voltage transformer is actually operated. The temperature obtains the transformation ratio of each harmonic voltage and the temperature correction coefficients λ hb and λ hx of the phase;

3) From the actual voltage value U hc and the phase value Φ hc under normal temperature conditions, using the temperature correction coefficients λ hb and λ hx values, calculate the actual voltage value U ht of the primary side harmonic voltage at any operating temperature and The phase value Φ ht is calculated as: