A method for contactless voltage measurement self-adapting to changes in the earth capacitance

Abstract

The application discloses a kind of self-adapting adaptation to contactless voltage measurement method of earth capacitance variation, belong to power system voltage measurement technical field, solve the problem that the earth capacitance of voltage measurement device induction polar plate is difficult to adjust, the application includes: step 1: establish the electric field coupling model of single-phase line and single-path induction polar plate, obtain the equivalent circuit model of voltage measurement;Step 2: quantize the error caused by the change of earth capacitance in single-path voltage measurement model, establish double-path measurement model, utilize full rank equation set to eliminate the influence brought by the change of earth capacitance;Step 3: according to the mathematical model of double-path measurement, the parameter sensitivity of model is quantized, and the coupling mechanism parameters are optimized;Step 4: experiment setting fixed parameter r, b, design voltage calculation unit voltage signal acquisition and calculation measurement platform.The application is used to utilize the response equation of double-path coupling mechanism, eliminate the changing earth capacitance, so that the measurement device can adaptively match the changing measurement working condition.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of voltage measurement of power system, and particularly relates to a non-contact voltage measurement method for self-adaptive adaptation to changes of ground capacitance. BACKGROUND

[0002] With large-scale development of regional Internet engineering and large-scale grid connection of various distributed power sources in China, China has formed a super-large complex power grid, and there is an urgent need for a large number of electrical quantity monitoring devices to ensure the normal work of the power grid. A new type of voltage measurement device based on capacitive coupling is expected to be widely deployed in the power system due to its characteristics of miniaturization, low power consumption and easy installation, and to light up the voltage measurement blind area. However, the ground capacitance of the sensing plate used by the measurement device is related to the measurement environment, and this parameter is difficult to be set by the sensor manufacturer. During installation, the variable ratio is often calibrated by a pt, which limits the application range of the device. SUMMARY

[0003] The purpose of the application is:

[0004] To solve the problem of ground capacitance of the sensing plate of the voltage measurement device in the prior art, a non-contact voltage measurement method for self-adaptive adaptation to changes of ground capacitance is provided, and the response equation of the double-coupling mechanism is used to eliminate the changes of the ground capacitance, so that the measurement device can adaptively match the changing measurement conditions.

[0005] The technical scheme adopted by the application is as follows:

[0006] A non-contact voltage measurement method for self-adaptive adaptation to changes of ground capacitance comprises the following steps:

[0007] Step 1: an electric field coupling model of a single-phase line and a single-sensing plate is established, and an equivalent circuit model of voltage measurement is obtained by analyzing the electric field coupling mechanism;

[0008] Step 2: the error caused by the change of the ground capacitance in the single-voltage measurement model is quantified, and on this basis, a double-voltage measurement model is established, a group of voltage response equations are obtained by analyzing the equivalent circuit, and the influence of the change of the ground capacitance is eliminated by using a group of full-rank equations formed by the two paths;

[0009] Step 3: according to the mathematical model of the double-voltage measurement, the parameter sensitivity of the model is quantified by analyzing the condition number of the equation group for voltage solution, and the coupling mechanism parameters are optimized according to the analysis result;

[0010] Step 4: the fixed parameters r and b of the double-voltage measurement system are experimentally set, and a platform including a waveform sampling module, a 2.4G communication module, a voltage calculation unit, a voltage signal acquisition and calculation measurement module is designed.

[0011] Further, the step 1 specifically comprises the following steps:

[0012] Step 1.1: Establishing the electric field coupling model of single-phase line and single-path induction plate;

[0013] When the conductor is applied with a sinusoidal alternating voltage, the electric field lines are emitted from the energized conductor and terminated at the adjacent conductors, and the displacement current flows between the conductors, the size of which is proportional to the field source voltage. By measuring the displacement current and its transformation ratio, the line voltage value is obtained;

[0014] When the edge effect is ignored, the electric field of the system formed by the wire-copper foil-ground is as follows: D1 represents the electric displacement vector of the space domain formed by the line and the inner copper foil, D2 represents the electric displacement vector of the space domain formed by the inner copper foil and the outer copper foil, and D3 represents the electric displacement vector of the space domain formed by the outer copper foil and the ground;

[0015] The voltage measurement method based on the single induction displacement current method is adopted, and two cylindrical metal copper foils with different radii are placed close to the charged conductor. Since the potential of the charged conductor is different from the induced potential of the copper foil, a current, i.e., the displacement current, flows between the copper foil and the charged conductor. The displacement current is converted into a conduction current by the induction plate and the I-V converter, so as to measure the displacement current signal. The specific conversion method is as follows:

[0016] Suppose that the Gaussian surfaces s1 and s2 are the evacuated cylinders, wherein s1 completely wraps the inner copper foil, and s2 completely wraps the inner and outer copper foils. On the Gaussian surface s1, the Maxwell complete current law is used to obtain:

[0017]

[0018] wherein J is the current density in the conductor contained in the Gaussian surface s1, and by the integral property, the following is obtained:

[0019]

[0020] s1 inner represents the inner side of the Gaussian surface s1, and s1 outer represents the outer side of the Gaussian surface s1, and the directions of both are outward along the radius;

[0021] Since the open-loop gain of the high-precision operational amplifier, when the operational amplifier is operated in a closed loop, the inner and outer copper foil potentials are equal, so D2=0, and the following is obtained:

[0022]

[0023] Similarly, on the Gaussian surface s2, the complete current theorem is used to obtain:

[0024]

[0025] s2inner represents the inner side of the Gaussian surface s2, s2 outer represents the outer side of the Gaussian surface s2, and the directions of both are outward along the radial direction, because s2 inner is the same as s1 inner , then we have:

[0026]

[0027] Step 1.2: Analyze the electric field coupling mechanism to obtain the equivalent circuit model of the voltage measurement;

[0028] The above measurement model is equivalent to shorting the inner and outer copper foils and measuring the conduction current flowing between the copper foils; the equivalent capacitance C LI represents the displacement current path between the wire and the inner copper foil, and the capacitance C x represents the displacement current path between the outer copper foil and the ground, then analyzing the equivalent circuit of the measurement model can obtain:

[0029]

[0030] Therefore, the response voltage u1 of the measurement model is linearly related to the line voltage U, and the transformation ratio is k.

[0031] Further, the step 2 includes the following steps:

[0032] Step 2.1: Quantify the error caused by the change of the ground capacitance in the single-channel voltage measurement model;

[0033] When the measurement working condition changes, C LI is stable in value, but C x changes significantly, so the transformation ratio k is different under different working conditions;

[0034] Step 2.2: Establish a double-channel measurement model, obtain a set of voltage response equations by analyzing the equivalent circuit, and use the full-rank equation set formed by the two channels to eliminate the influence of the change of the ground capacitance;

[0035] The double-channel displacement current method is used to realize voltage measurement:

[0036] The coupling mechanism of the double-induction displacement current method is divided into two independent parts, and the two parts have the same coverage area, but the insulating medium filled between the inner copper foil and the power line is different, the left side is filled with a non-gas medium, and the right side is filled with air;

[0037] Due to the edge effect, there is a stray capacitance between the inner copper foil and the ground, which is the same as C x , and a capacitance C x1 related to the environment is introduced into the measurement model, and by laying the inner copper foil shorter than the outer copper foil, the value of the stray capacitance is reduced, so that the stray capacitance Cx1 The influence on the measurement model;

[0038] The equivalent circuit of the double-path displacement current method is established: LI1 , C LO1 respectively represent the equivalent capacitances formed by the wire and the inner and outer copper foils of the left coupling mechanism; C LI2 , C LO2 respectively represent the equivalent capacitances formed by the wire and the inner and outer copper foils of the right coupling mechanism; since the dielectric constant of the non-gas medium is greater than 1, we have:

[0039] C LI1 +C LO 1>C LI2 +C LO2 (24)

[0040] Analyzing the equivalent circuit of the double-path displacement current method, we have:

[0041]

[0042]

[0043] Under different working conditions, since the values of C x differ, the variable ratios k1 and k2 of the left and right measurement mechanisms are different under different working conditions; when the wire radius and sensor parameters are determined, C LI1 , C LO1 , C LI2 , C LO2 have stable values under different working conditions and are considered as constants; according to formulas (7)-(8), the parameters C x related to the working conditions are eliminated from the variable ratio coefficients, and k1 and k2 satisfy the linear relationship shown in formula (10):

[0044] k1=rk2+b (27)

[0045] wherein

[0046] From the above analysis, it is concluded that r and b are both constants, which are determined by experiments;

[0047] Since the measurement voltages of the left and right measurement mechanisms are the same at the same time, according to formulas (7)-(8), the variable ratio coefficients k1 and k2 of the left and right measurement mechanisms and the measurement values u1 and u2 satisfy the following formula:

[0048] k1·u1=k2·u2 (28)

[0049] By combining formulas (9)-(10), it is concluded that for any working condition, the variable ratio coefficients k1 and k2 are determined by the following formula:

[0050]

[0051] Finally, the line voltage estimation is realized by U=k1·u1; thus, only relying on real-time measured values u1, u2 and experimentally determined r, b parameter values, the adaptive adjustment of the transformation ratio coefficient is realized, thereby realizing the adaptive adaptation of the non-contact voltage measurement to the change of the ground capacitance.

[0052] Further, the step 3 comprises the following steps:

[0053] Step 3.1: According to the mathematical model of the dual-path measurement, the parameter sensitivity of the model is quantified by analyzing the condition number of the equation system solved by the voltage:

[0054] The error amplification mechanism of the transformation ratio coefficient is obtained by analyzing the condition number of the coefficient matrix in equation (12):

[0055] Let Using the infinite norm of the matrix A, the condition number thereof is obtained as follows:

[0056]

[0057] When κ ∞ (A) is larger, the parameter sensitivity in equation (12) is larger, and it is analyzed that r<1, so κ ∞ (A) is related to , and increasing the value thereof reduces the parameter sensitivity;

[0058] By simultaneously solving equations (7)-(8), the following is obtained:

[0059]

[0060] Since

[0061]

[0062] By simultaneously solving equations (14) and (15), the following is obtained:

[0063]

[0064] Step 3.2: The coupling mechanism parameters are optimized according to the condition quantification result;

[0065] It is known from the analysis of equation (16) that, in order to increase The following two methods (1) or (2) are adopted:

[0066] Method (1): C LI2 is reduced, and C LO2 is increased; x , so that is increased;

[0067] Method (2): CLI1 +C LO1 With C LI2 +C LO2 The numerical difference;

[0068] Further, the step 4 includes the following steps:

[0069] Step 4.1: Experimentally setting the fixed parameters r, b of the two-way measurement system:

[0070] Since the variable ratio coefficients of the left and right coupling mechanisms satisfy formula (10) at different heights, when setting, the variable ratio of the coupling mechanism at heights h1, h2 is measured to obtain:

[0071]

[0072] Where k1 h1 , k2 h1 , k1 h2 , k2 h2 are the measured values of the variable ratio of the left and right coupling mechanisms at different heights; the parameters r, b are set by formula (17), and the on-site voltage measurement is completed with the experimentally set values;

[0073] Step 4.2: Design a platform with a waveform sampling module, a 2.4G communication module, and a voltage calculation unit voltage signal acquisition and calculation measurement module:

[0074] The displacement current waveform is collected by the front-end conditioning circuit and STM32; the 2.4G communication of NRF401 is used in the sending end to realize waveform transmission; in the receiving end, STM32 sends the waveform to the host computer, and the host computer calculates the line voltage.

[0075] As described above, due to the adoption of the above technical solutions, the beneficial effects of the present application are:

[0076] 1. The present application uses the response equation of the two-way coupling mechanism to eliminate the varying ground capacitance, so that the measurement device can adaptively match the changing measurement conditions.

[0077] 2. The present application analyzes the condition number influence factors of the matrix by solving the variable ratio coefficient, obtains the key factors affecting the parameter sensitivity, and provides a solution to optimize the parameter sensitivity, further improving the measurement accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0078] Figure 1 The method flowchart of the present application;

[0079] Figure 2 The single-path displacement current method voltage measurement schematic diagram;

[0080] Figure 3Schematic diagram of displacement current-conduction current conversion mechanism;

[0081] Figure 4 Equivalent schematic diagram of single-channel displacement current method;

[0082] Figure 5 Coupling mechanism diagram of double-channel displacement current method;

[0083] Figure 6 Equivalent schematic diagram of double-channel displacement current method;

[0084] Figure 7 Trend graph of r;

[0085] Trend graph of r; Figure 8 Trend graph of relative dielectric constant εr of left coupling mechanism;

[0086] Block diagram of voltage measurement system. Figure 9 DETAILED DESCRIPTION In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0087] A non-contact voltage measurement method adaptively adapted to the change of earth capacitance, comprising the following steps:

[0088] Step 1: Establish an electric field coupling model of a single-phase line and a single-channel induction electrode plate, and obtain an equivalent circuit model of voltage measurement by analyzing the electric field coupling mechanism thereof;

[0089] Step 2: Quantify the error caused by the change of earth capacitance in the single-channel voltage measurement model, and on this basis, establish a double-channel measurement model, obtain a set of voltage response equations by analyzing the equivalent circuit thereof, and eliminate the influence of the change of earth capacitance by using a set of full-rank equations formed by two channels;

[0090] Step 3: According to the mathematical model of double-channel measurement, the parameter sensitivity of the model is quantified by analyzing the condition number of the equation set for voltage solution, and the coupling mechanism parameters are optimized according to the analysis result to reduce the influence caused by the measurement deviation of the measurement model parameters;

[0091] Step 4: Experimentally set the fixed parameters r and b of the double-channel measurement system, and design a voltage signal acquisition and calculation measurement platform with a waveform sampling module, a 2.4G communication module and a voltage calculation unit.

[0092] Step 1 comprises the following steps:

[0093]

[0094] ​Step 1.1: Establishing the electric field coupling model of single-phase line and single-path induction plate;

[0095] When the conductor is applied with sinusoidal alternating voltage, the electric field lines will be emitted from the energized conductor and terminated at the adjacent conductors, and the displacement current will flow between the conductors, the size of which is proportional to the field source voltage. By measuring the displacement current and its transformation ratio, the line voltage value can be obtained.

[0096] When the edge effect is ignored, the electric field distribution of the system formed by the wire-copper foil-ground is as shown in Figure 1 . In the figure, D1 represents the electric displacement vector of the spatial domain formed by the line and the inner copper foil, D2 represents the electric displacement vector of the spatial domain formed by the inner copper foil and the outer copper foil, and D3 represents the electric displacement vector of the spatial domain formed by the outer copper foil and the ground.

[0097] The voltage measurement method based on the single induction displacement current method is as shown in Figure 2 : Two cylindrical metal copper foils with different radii are placed close to the charged conductor. Since the potential of the charged conductor is different from the induced potential of the copper foil, a current, i.e. displacement current, will flow between the copper foil and the charged conductor. This displacement current is difficult to measure directly. The present application converts the displacement current into conduction current through the induction plate and I-V converter, so that the displacement current signal can be measured. The conversion mechanism is as follows:

[0098] As shown in Figure 3 : The Gaussian surfaces s1 and s2 are an evacuated cylinder, wherein s1 completely wraps the inner copper foil, and s2 completely wraps the inner and outer copper foils. On the Gaussian surface s1, the Maxwell complete current law can be used to obtain:

[0099]

[0100] where J is the current density in the conductor contained in the Gaussian surface s1. By the integral property, we can obtain:

[0101]

[0102] s1 inner represents the inner side of the Gaussian surface s1, and s1 outer represents the outer side of the Gaussian surface s1, and the directions of both are outward along the radius.

[0103] Since the open-loop gain of the high-precision operational amplifier is very high, when the operational amplifier is operated in closed loop, the inner and outer copper foil potentials are equal, so D2=0, and we can obtain:

[0104]

[0105] Similarly, on the Gaussian surface s2, the complete current theorem can be used to obtain:

[0106]

[0107] s2 inner Let s2 represent the inner side of the Gaussian surface s2. outer This represents the outer side of the Gaussian surface s2, with all directions pointing radially outward. Since s2 inner With s1 inner If they are the same, then:

[0108]

[0109] Step 1.2: Analyze the electric field coupling mechanism to obtain the equivalent circuit model for voltage measurement;

[0110] The above measurement model is equivalent to short-circuiting the inner and outer copper foils and measuring the conduction current flowing between the copper foils. If the equivalent capacitance C is used... LI This represents the displacement current path between the conductor and the inner copper foil, with capacitance C. x To represent the displacement current path between the outer copper foil and the ground, the equivalent circuit of the measurement model is as follows: Figure 4 As shown:

[0111] right Figure 4 Analysis shows that:

[0112]

[0113] Therefore, the response voltage u1 of the measurement model is linearly related to the line voltage U, and its transformation ratio is k.

[0114] Step 2 includes the following steps:

[0115] Step 2.1: Quantify the error caused by changes in capacitance to ground in the single-channel voltage measurement model;

[0116] When the measurement conditions change, C LI The values ​​are stable, but C x The changes are significant, therefore the turns ratio k will differ under different operating conditions. Simultaneously, due to the capacitance C of the outer copper foil to ground... x It is not easy to measure, and the device requires a PT to set the "ratio coefficient" during installation, which is inconvenient for installation and debugging and limits the application range of the measuring device.

[0117] Step 2.2: Establish a dual-path measurement model, obtain a set of voltage response equations by analyzing its equivalent circuit, and use a full-rank set of equations formed by the two paths to eliminate the influence of changes in ground capacitance;

[0118] To overcome the shortcomings of the single-channel displacement current method, this invention employs the dual-channel displacement current method to achieve voltage measurement.

[0119] The coupling mechanism of the dual-induction displacement current method is as follows: Figure 5As shown: the coupling mechanism is divided into two parts independently left and right. The two parts of copper foil cover the same area, but the inner layer of copper foil and the insulating medium filled between the power line are different, the left side fills the non-gas medium, and the right side fills the medium.

[0120] Due to the edge effect, there is a stray capacitance between the inner copper foil and the ground, and C x The characteristics are consistent, and the stray capacitance value will introduce another environment-related capacitance C x1 The invention can effectively reduce the stray capacitance value by laying the inner copper foil shorter than the outer copper foil, so as to not consider the stray capacitance C x1 The influence on the measurement model. The equivalent circuit of the double-path displacement current method is shown in Figure 6 .

[0121] Among them, C LI1 , C LO1 respectively represent the equivalent capacitance formed by the wire and the inner and outer copper foil of the left coupling mechanism, C LI2 , C LO2 respectively represent the equivalent capacitance formed by the wire and the inner and outer copper foil of the right coupling mechanism. Since the dielectric constant of the non-gas medium is greater than 1 (air), we have:

[0122] C LI1 +C LO 1>C LI2 +C LO2 (41)

[0123] Analysis shows that: Figure 6

[0124]

[0125]

[0126] Under different working conditions, due to the difference in the value of C x , the variable ratio k1 and k2 of the left and right measuring mechanisms are different under different working conditions. When the wire radius and sensor parameters are determined, C LI1 , C LO1 , C LI2 , C LO2 The values are stable under different working conditions and can be considered as constants. According to formulas (7)-(8), eliminate the parameters related to working conditions C x in the variable ratio coefficient, we can get k1 and k2 satisfy the linear relationship shown in formula (10).

[0127] k1=rk2+b (44)

[0128] Among them ​

[0129] From the above analysis, r and b are both constants, and their values can be set through experiments. The setting method will be shown in step 4.

[0130] At the same time, since the measurement voltages of the left and right measurement mechanisms are the same at the same time, according to equations (7)-(8), the variable ratio coefficients k1 and k2 of the left and right measurement mechanisms satisfy the following equation.

[0131] k1·u1=k2·u2 (45)

[0132] By combining equations (9)-(10), it can be seen that for any working condition, the variable ratio coefficients k1 and k2 can be determined by the following equation.

[0133]

[0134] Finally, the line voltage estimation is realized by U=k1·u1. The field measurement process does not rely on pt to set the variable ratio coefficient, but only relies on the real-time measurement values u1 and u2 and the experimentally determined r and b parameter values to realize adaptive adjustment of the variable ratio coefficient, thereby realizing adaptive adaptation to the change of the ground capacitance of the non-contact voltage measurement.

[0135] Step 3 includes the following steps:

[0136] Step 3.1: According to the mathematical model of the dual-path measurement, the condition number of the equation system solved by the voltage is analyzed to quantify the parameter sensitivity of the model:

[0137] Due to external environmental interference, limited precision of hardware circuits and other factors, the set values of the parameters r and b and the measurement values of u1 and u2 will deviate from their true values, and the error will be further amplified by equation (12), and the variable ratio coefficient to be solved will deviate greatly from its true value, causing the measurement error to be too large. The present application analyzes the condition number of the coefficient matrix in equation (12) to obtain the error amplification mechanism.

[0138] Let Using the infinite norm of matrix A, its condition number is:

[0139]

[0140] When κ ∞ (A) is larger, the parameter sensitivity in equation (12) is larger, and it is analyzed that r<1, so κ ∞ (A) is mainly related to , and appropriately increasing its value can effectively reduce the parameter sensitivity.

[0141] By combining equations (7)-(8), we get:

[0142]

[0143] Since

[0144]

[0145] By combining (14) and (15), we have

[0146]

[0147] Step 3.2: Optimizing the parameters of the coupling mechanism according to the quantitative results of the conditions;

[0148] By analyzing equation (16), in order to make as large as possible, the following two measures can be taken to make the two product factors of the right side of equation (16) as large as possible:

[0149] (1) Reducing C LI2 +C LO2 and the order of magnitude difference between C C and C x , so that is as large as possible.

[0150] (2) Increasing the numerical difference between C LI1 +C LO1 and C LI2 +C LO2 .

[0151] For the first measure, the parameter sensitivity can be reduced by adjusting the radius r of the coupling mechanism. When the device is erected at a height h = 6 m and the line diameter r = 4.8 mm, The change trend of the radius r is shown in Figure 7 . By observation, when the radius r of the polar plate is greater than 50 mm, the rate of decrease slows down, so in order to balance the size of the device and the parameter sensitivity, the radius r of the polar plate is preferably 50 mm.

[0152] For the second measure, a medium with a larger dielectric constant can be filled in the left coupling mechanism to increase the difference in capacitance between the left and right coupling mechanisms. Figure 8 For the change trend line of the dielectric constant of the left filling medium, when the relative dielectric constant εr of the left filling medium is greater than 22, the change is slow, so in order to balance the material selection and the parameter sensitivity, the medium with a dielectric constant of 22 is selected as the filling medium for the left coupling mechanism.

[0153] Step 4 includes the following steps:

[0154] Step 4.1: Experimentally setting the fixed parameters r and b of the two-path measurement system:

[0155] The parameters r and b contain the equivalent capacitance of the left-right coupling mechanism, and since the two layers of plates form a stable capacitance network with the line to be measured, when the capacitance between any two nodes is measured by using a digital bridge, the result measured is not the mutual capacitance between the two nodes but the equivalent capacitance between the two nodes, so the method of measuring the capacitance will make the setting process of the parameters r and b too complicated.

[0156] Since the variable ratio coefficient will be different at different heights, but the variable ratio coefficient of the left-right coupling mechanism at different heights all satisfies formula (10). During setting, the variable ratio of the coupling mechanism at the heights h1 and h2 is measured, and the following formula (17) is obtained:

[0157]

[0158] Wherein k1 h1 , k2 h1 , k1 h2 , k2 h2 are the measured values of the variable ratio of the left-right coupling mechanism at different heights. The setting of the parameters r and b can be realized by formula (17), and after that, the on-site voltage measurement will be completed by using the experimental setting values.

[0159] Step 4.2: design a voltage signal acquisition and calculation measurement platform with a waveform sampling module, a 2.4G communication module and a voltage calculation unit:

[0160] The voltage measurement system framework developed by the present application is shown in Figure 9 The waveform acquisition of displacement current is realized by the front-end conditioning circuit and STM32; the waveform transmission is realized by using the 2.4G communication of NRF401 in the sending end; in the receiving end, the STM32 sends the waveform to the upper computer, and the upper computer realizes the line voltage calculation by using the method of the present application.

[0161] The above only describes the preferred embodiments of the present application and should not be used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method of contactless voltage measurement self-adapting to changes in earth capacitance, characterized by, It comprises the following steps: Step 1: establishing a single-phase line and a single-path induction electrode plate electric field coupling model, and obtaining an equivalent circuit model of voltage measurement by analyzing the electric field coupling mechanism; Step 2: quantifying the error caused by the change of ground capacitance in the single-path voltage measurement model, and on this basis, establishing a double-path measurement model, obtaining a set of voltage response equations by analyzing the equivalent circuit, and eliminating the influence of the change of ground capacitance by using a set of full-rank equation groups formed by the two paths; Step 3: according to the mathematical model of the double-path measurement, quantifying the parameter sensitivity of the model by analyzing the condition number of the equation group of voltage solution, and optimizing the coupling mechanism parameters according to the analysis results; Step 4: experimentally setting the fixed parameters r and b of the double-path measurement system, wherein r and b are measurement system constants, and designing a platform comprising a waveform sampling module, a 2.4G communication module, a voltage calculation unit, a voltage signal acquisition and calculation measurement module.

2. The method of claim 1, wherein, The step 1 specifically comprises the following steps: Step 1.1: establishing a single-phase line and a single-path induction electrode plate electric field coupling model; When a conductor is applied with a sinusoidal alternating voltage, electric field lines are emitted from the energized conductor and terminated at the adjacent conductors, and displacement current flows between the conductors, the size of which is proportional to the field source voltage, and the line voltage value is obtained by measuring the displacement current and its transformation ratio; When the edge effect is ignored, the electric field of the system formed by the wire, the copper foil and the ground, D1 represents the electric displacement vector of the space domain formed by the line and the inner copper foil, D2 represents the electric displacement vector of the space domain formed by the inner copper foil and the outer copper foil, and D3 represents the electric displacement vector of the space domain formed by the outer copper foil and the ground; A voltage measurement method based on single induction displacement current method is adopted, two cylindrical metal copper foils with different radii are placed close to the charged conductor, and since the potential of the charged conductor is different from the induced potential of the copper foil, a current, i.e. displacement current, flows between the copper foil and the charged conductor, the displacement current is converted into conduction current by the induction electrode plate and the I-V converter, and the displacement current signal is measured, and the specific conversion method is as follows: Suppose that the Gaussian surfaces s1 and s2 are hollow cylinders, wherein s1 completely wraps the inner copper foil, and s2 completely wraps the inner and outer copper foils, and by using the Maxwell complete current theorem on the Gaussian surface s1, the following equation can be obtained: Wherein J is the current density in the conductor contained in the Gaussian surface s1, and by the integral property, the following equation can be obtained: s1 inner represents the inner side of the Gaussian surface s1, s1 outer represents the outer side of the Gaussian surface s1, both in the direction of the radius outwards; Since the open-loop gain of the high-precision operational amplifier, when the operational amplifier is closed-loop operated, the inner and outer copper foil potentials are equal, D2=0, and the following equation can be obtained: Similarly, by using the complete current theorem on the Gaussian surface s2, the following equation can be obtained: s2 inner represents the inner side of the Gaussian surface s2, s2 outer represents the outer side of the Gaussian surface s2, both in the direction radially outwards, since s2 inner is identical to s1 inner then it follows that: Step 1.2: analyzing the electric field coupling mechanism to obtain an equivalent circuit model of voltage measurement; The above measurement model is equivalent to measuring the conduction current flowing between the inner and outer copper foils after short-circuiting the two copper foils. The equivalent capacitance C LI represents the displacement current path between the wire and the inner copper foil, and the capacitance C x represents the displacement current path between the outer copper foil and the ground. Analysis of the equivalent circuit of the measurement model can obtain: Therefore, the response voltage u1 of the measurement model is in a linear relationship with the line voltage U, and the transformation ratio is k.

3. The non-contact voltage measurement method adaptively to changes in ground capacitance according to claim 2, characterized in that, The step 2 comprises the following steps: Step 2.1: quantifying the error caused by the change of ground capacitance in the single-path voltage measurement model; When the working condition changes, C LI The value is stable, but C x The change is obvious, so the variable ratio k is different under different working conditions; Step 2.2: establishing a double-path measurement model, obtaining a set of voltage response equations by analyzing the equivalent circuit, and eliminating the influence of the change of ground capacitance by using a set of full-rank equation groups formed by the two paths; A double-path displacement current method is adopted to realize voltage measurement: The coupling mechanism of the double-induction displacement current method is divided into two independent parts, and the two parts have the same copper foil coverage area, but the inner layer copper foil is filled with different insulating media between the power line, the left side is filled with non-gas medium, and the right side is filled with air; Due to the edge effect, there is a stray capacitance between the inner copper foil and the ground, and C x is consistent with the characteristics of the measurement model, introducing another stray capacitance C x1 related to the environment into the measurement model. x1 By laying the inner copper foil shorter than the outer copper foil, the value of the stray capacitance C x1 is reduced, so that the influence of the stray capacitance C on the measurement model is ignored; Establishes the equivalent circuit of double path displacement current method: C LI1 , C LO1 Respectively represent the equivalent capacitance formed by the wire and the left side coupling mechanism inside and outside copper foil, LI2 , C LO2 Respectively represent the equivalent capacitance formed by the wire and the right side coupling mechanism inside and outside copper foil; Because the dielectric constant of non-gas medium is greater than 1, so: C LI1 +C LO1 >C LI2 +C LO2 (7) The equivalent circuit of the double-path displacement current method is analyzed as follows: In different working conditions, the values of C x are different, so the variable ratios k1 and k2 of the left and right measuring mechanisms are different in different working conditions; when the wire radius and sensor parameters are determined, the values of C LI1 , C LO1 , C LI2 , and C LO2 are stable in different working conditions and are regarded as constants; according to formulas (7) and (8), the parameters C x related to working conditions are eliminated from the variable ratio coefficients, and the linear relationship of k1 and k2 shown in formula (10) is obtained: k1=rk2+b (10) wherein From the above analysis, r and b are constants, which are determined by experiments. Since the measurement voltages of the left and right measurement mechanisms are the same at the same time, according to equations (7)-(8), the transformation ratio coefficients k1 and k2 of the left and right measurement mechanisms and the measurement values u1 and u2 satisfy the following equation: k1·u1=k2·u2 (11) By combining equations (9)-(10), for any working condition, the transformation ratio coefficients k1 and k2 are determined by the following equation: Finally, the line voltage estimation is realized by U=k1·u1; thus, only relying on the real-time measurement values u1 and u2 and the parameter values of r and b determined by experiments, the adaptive adjustment of the transformation ratio coefficients is realized, thereby realizing the adaptive adaptation to the change of the grounding capacitance for non-contact voltage measurement.

4. The method of claim 3, wherein, The step 3 includes the following steps: Step 3.1: According to the mathematical model of the double-path measurement, the parameter sensitivity of the model is quantified by analyzing the condition number of the equation set for voltage solution: The error amplification mechanism of the transformation ratio coefficient is obtained by analyzing the condition number of the coefficient matrix in equation (12): Let Using the infinite norm of matrix A, its condition number is obtained as: When κ ∞ When (A) is larger, the sensitivity of the parameter in equation (12) is greater. After analysis, r < 1, therefore κ ∞ (A) Numerical values ​​and Increasing its value reduces parameter sensitivity. By combining equations (7)-(8), we have: Since By combining equations (14) and (15), we have Step 3.2: According to the condition quantification result, the coupling mechanism parameters are optimized. By analyzing the equation (16), it is known that, in order to increase The following two methods (1) or (2) are taken: Method (1): decrease C LI2 + C LO2 with C x of the order of magnitude, so that increase; Method (2): Increase C LI1 + C LO1 the numerical difference of C LI2 + C LO2 .

5. A method of self-adapting to changes in the earth capacitance for non-contact voltage measurement according to claim 4, characterized in that, The step 4 includes the following steps: Step 4.1: The fixed parameters r and b of the double-path measurement system are set by experiments: Since the transformation ratio coefficients of the left and right coupling mechanisms satisfy equation (10) at different heights; during setting, the transformation ratios of the coupling mechanisms at heights h1 and h2 are measured as follows: where k1 h1 , k2 h1 , k1 h2 , k2 h2 are the measured values of the transmission ratio of the left and right coupling mechanisms at different heights; the parameters r, b are set by equation (17), and the on-site voltage measurement is completed with the experimental set values. Step 4.2: A platform with a waveform sampling module, a 2.4G communication module, and a voltage calculation unit voltage signal acquisition and calculation measurement module is designed: The waveform acquisition of the displacement current is realized through the front-end conditioning circuit and the STM32; the waveform transmission is realized through the 2.4G communication of NRF401 in the sending end; in the receiving end, the STM32 sends the waveform to the host computer, and the host computer calculates the line voltage.

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