A method for suppressing noise of electronic voltage transformer based on electrostatic charge escape

Abstract

The present invention proposes a novel electronic voltage transformer noise suppression method based on electrostatic charge escape. A bypass resistor with a relatively large resistance is connected in series on the escape channel of the sensor system, which can effectively suppress the random noise introduced by stray capacitance and ground impedance, so that the escape current waveform integrity of the novel electronic voltage transformer is higher than 99%, thereby improving the transformer's power frequency characteristics and harmonic transfer characteristics, and improving the measurement accuracy and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of high voltage measurement and electronic voltage transformer, and in particular relates to a method for suppressing noise of an electronic voltage transformer based on electrostatic charge escape. Background Art

[0002] As a key equipment of smart grid, the popularization and application of electronic voltage transformer is of great significance to the construction of smart grid. According to different measurement principles, the existing electronic voltage transformer can be divided into non-traditional transformers based on voltage division principle, optical sensing principle and other principles. The electronic voltage transformer based on voltage division principle has defects such as voltage division ratio drift and susceptibility to stray capacitance; the electronic voltage transformer based on optical sensing principle has serious temperature drift problems and insufficient measurement stability; the measurement accuracy of non-traditional electronic voltage transformer is low and most of them are in the laboratory research stage. In actual engineering applications, electronic voltage transformers have exposed defects such as poor measurement reliability and stability, and the failure rate in trial operation is much higher than that of electromagnetic voltage transformers. For this reason, the State Grid and other relevant companies have strengthened the operation management of existing electronic voltage transformers and required smart substations to suspend the use of electronic voltage transformers. Summary of the invention

[0003] In view of the defects and shortcomings of the prior art, the present invention first designs an electronic voltage transformer based on electrostatic charge escape, and its sensing system adopts a coaxial electrode voltage-dividing structure, including a high-voltage electrode, a ground electrode, an escape electrode, an escape channel and a DC polarized power supply, and the electrodes are all made of aluminum metal. When there is no external electric field acting on the escape electrode, the electric fields stimulated by the positive and negative charges inside the aluminum metal conductor cancel each other out, and no electrical properties are shown macroscopically. Affected by the polarization of the DC power supply, the positive and negative charges move to the surface of the conductor, generating static charges, causing the escape electrode to show electrical properties macroscopically. Its working principle is: after the escape electrode is polarized by the DC power supply, it carries static charges. Under the action of the external voltage to be measured, the static charges move in a directional manner along the escape channel to form an escape current. The escape current is linearly related to the voltage to be measured, so voltage measurement can be achieved by detecting the escape current. The electronic voltage transformer can linearly transmit and transform a primary voltage signal, has harmonic measurement capability and has good transient characteristics.

[0004] However, due to the influence of stray capacitance, ground impedance, etc., the random noise signal introduced by them is easily mixed with the emission current, which is difficult to separate and eliminate, affecting the accuracy and stability of the measurement. To this end, the present invention designs a method for suppressing the noise of an electronic voltage transformer based on electrostatic charge escape, and proposes to connect a bypass resistor with a larger resistance in series on the escape channel of the sensor system, which can effectively suppress random noise, so that the integrity of the escape current waveform of the electronic voltage transformer is higher than 99%, improves the power frequency characteristics and harmonic transfer characteristics of the transformer, and improves the accuracy and stability of the measurement.

[0005] The present invention specifically adopts the following technical solutions:

[0006] A method for suppressing noise of an electronic voltage transformer based on electrostatic charge escape, wherein the sensing system adopts a coaxial electrode voltage-dividing structure and comprises a high-voltage electrode (2), a ground electrode (3), an escape electrode (4), a DC polarized power supply (5) and an escape channel (6);

[0007] The voltage to be measured from the high-voltage transmission line (1) is applied between the high-voltage electrode (2) and the ground electrode (3). After the escape electrode (4) is polarized by a DC polarization power supply (5), the positive and negative charges move to the surface of the conductor, causing the escape electrode to show electrical properties macroscopically. Under the action of the AC voltage to be measured, the static charges (i.e., the positive and negative charges) move in a direction along the escape channel (6) and form an escape current. The escape current is linearly correlated with the voltage to be measured, and the voltage is measured by detecting the escape current through a signal processing unit.

[0008] A bypass resistor (9) is connected in series to the escape path (6) to suppress the influence of noise.

[0009] Furthermore, it can be observed on the host computer (10) that the integrity of the displayed escape current waveform is higher than 99%.

[0010] Preferably, in the electronic voltage transformer, the escape channel (6) is a conductor. Further, the high voltage electrode (2), the ground electrode (3) and the escape electrode (4) are all made of aluminum.

[0011] Preferably, in the power frequency measurement of the electronic voltage transformer, the escape current and the voltage to be measured show a sinusoidal function change, and the two satisfy the following relationship:

[0012]

[0013] Where i(t) is the escape current, K is the transmission coefficient, ω is the fundamental frequency, U m is the amplitude of the voltage to be measured; the amplitude ratio of the voltage to be measured to the escape current is ωK, and the phase difference is 90°.

[0014] In harmonic measurement, the escape current and the voltage to be measured satisfy the following relationship:

[0015]

[0016] Among them U jm represents the amplitude of the jth harmonic; represents the phase of the jth harmonic; K m Indicates the proportionality coefficient of the j-th harmonic.

[0017] It can be seen that the amplitude and phase of each harmonic voltage can be transmitted to the escape current, and the measurement bandwidth can meet the requirements of harmonic measurement.

[0018] Furthermore, based on the noise suppression improvement scheme proposed in the present invention, the escape current I0 taking into account the noise interference is:

[0019]

[0020] Where I1 is the current introduced by noise, C m Z is the capacitance formed by the static charge distribution of the escape electrode to the ground. b =R b +jX b is the noise impedance introduced by the escape channel and the DC polarized power supply, U c2 is the potential of the escape electrode, I is the frequency domain form of the escape current i(t), and ω is the angular frequency;

[0021] When the bypass resistor R connected in series with the escape channel is set large enough to make I1≈0, the influence of random noise on the electronic voltage transformer is eliminated.

[0022] Compared with the prior art, the present invention and its preferred solution aim at the problem that noise signals are easily mixed with escape current, which is difficult to separate and eliminate, affecting the stability and reliability of transformer measurement. The solution of connecting a bypass resistor with a larger resistance in series with the escape electrode of the electronic voltage transformer can effectively eliminate the influence of noise and improve the accuracy of transformer measurement. This method is simple and effective, significantly improves the anti-noise performance of the electronic voltage transformer, and ensures that the waveform integrity of the escape current is higher than 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0024] Figure 1 Schematic diagram of the measurement principle of the electronic voltage transformer according to an embodiment of the present invention;

[0025] Figure 2 1 is a schematic diagram of a coaxial electrode sensing structure of an electronic voltage transformer according to an embodiment of the present invention;

[0026] Figure 3 It is a schematic diagram of a multi-physical field coupling simulation model of an electronic voltage transformer according to an embodiment of the present invention;

[0027] Figure 4 1 is a schematic diagram of a coaxial electrode equivalent circuit of an electronic voltage transformer taking random noise into account according to an embodiment of the present invention;

[0028] Figure 5 It is a schematic diagram of the escape current waveform measured at power frequency by the electronic voltage transformer before and after the bypass resistor is connected in series according to an embodiment of the present invention;

[0029] Figure 6 Schematic diagram of the escape current waveform of harmonic measurement of the electronic voltage transformer before and after the bypass resistor is connected in series according to an embodiment of the present invention;

[0030] Figure 7 It is a schematic diagram of a verification platform of an electronic voltage transformer prototype according to an embodiment of the present invention.

[0031] Among them, 1 is a high-voltage transmission line, 2 is a high-voltage electrode, 3 is a ground electrode, 4 is an escape electrode, 5 is a DC polarized power supply, 6 is an escape channel, 7 is an escape current, 8 is random noise, 9 is a bypass resistor, 10 is a host computer, 12 is a voltage regulator, 13 is a standard voltage transformer, 14 is a booster, 15 is an electronic voltage transformer prototype, 16 is a calibrator, 17 is a signal generator, and 18 is a high-voltage amplifier. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions of the present invention through embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than comprehensive 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:

[0033] This embodiment provides a method for suppressing noise of an electronic voltage transformer based on electrostatic charge escape. Figure 1 As shown. The voltage to be measured from the high-voltage transmission line 1 is applied between the high-voltage electrode 2 and the ground electrode 3. The escape electrode 4 is polarized by the DC polarization power supply 5 and carries an electrostatic charge. Under the action of the AC voltage to be measured, the electrostatic charge moves in a direction along the escape channel (conductor) 6 and forms an escape current 7. Voltage measurement can be achieved by detecting the escape current. However, it is interfered by the random noise 8 introduced by stray capacitance, ground impedance, etc., which affects the measurement accuracy and stability of the electronic voltage transformer. This embodiment can effectively suppress the influence of noise by connecting a bypass resistor 9 in series with the escape channel, and the integrity of the escape current waveform displayed on the host computer 10 is higher than 99%.

[0034] Based on Gauss's theorem and the principle of dielectric polarization, the measurement mechanism of the electronic voltage transformer can be described in detail:

[0035] The structure of the coaxial electrode sensing system is as follows: Figure 2 As shown, C1 is the capacitance formed by the high voltage electrode and the escape electrode, C2 is the capacitance formed by the escape electrode and the ground electrode; r1 is the radius of the high voltage electrode; r2 is the inner radius of the escape electrode; r3 is the inner radius of the ground electrode; L1 is the longitudinal length of the overlapping part of the high voltage electrode and the escape electrode; L2 is the longitudinal length of the escape electrode and the ground electrode; L3 is the longitudinal length of the ground electrode; δ1 is the thickness of the escape electrode; δ2 is the thickness of the ground electrode; R is the bypass resistor; U D It is a DC polarized power supply.

[0036] Ignoring the electric field edge effect, according to Gauss's theorem, C1 is expressed as:

[0037]

[0038] Where ε0 represents the dielectric constant of vacuum; ε r Represents the relative dielectric constant of the insulating medium; L represents the longitudinal length of the overlapping part of the high-voltage electrode and the escape electrode.

[0039] Similarly, we can get C2:

[0040]

[0041] Wherein L' is the longitudinal length of the overlapping portion of the escape electrode and the ground electrode.

[0042] From this, the charge Q1(t) of the high voltage electrode can be calculated as:

[0043]

[0044] Where u(t) is the AC voltage to be measured.

[0045] According to the dielectric polarization theory, the charge surface density σ0 of the escape electrode and the charge surface density σ1 of the high-voltage electrode satisfy:

[0046]

[0047] Then the charge Q0(t) of the measured AC voltage acting on the escape electrode can be expressed as:

[0048]

[0049] The escape current of the escape electrode is obtained as follows:

[0050]

[0051] It can be seen that under the action of the AC voltage to be measured, the escape current changes in a sinusoidal function, in which the amplitude ratio of voltage to current is ω, and the phase difference between the two is 90. Voltage measurement can be achieved by detecting the escape current.

[0052] If u(t) contains high-order harmonic signals, it can be expressed as:

[0053]

[0054] According to formula (6), the harmonic transfer characteristics of the electronic voltage transformer are obtained:

[0055]

[0056] It can be seen that each harmonic information can be effectively transmitted to the secondary side, and the measurement bandwidth meets the requirements of harmonic measurement. By integrating the escape current, the voltage signals of each harmonic can be restored.

[0057] The above is the ideal working state of the electronic voltage transformer. When there is random noise interference, the noise signal is mixed with the escape current, affecting the accuracy and stability of the electronic voltage transformer measurement. The sources of random noise mainly include: the static charge distribution of the escape electrode changes with the change of the measured voltage, so the electrode forms a time-varying capacitance to the ground, and the impedance of the escape channel and the DC power supply to the ground and the capacitance coupling, the introduced random noise seriously affects the measurement results of the electronic voltage transformer.

[0058] The equivalent circuit of the coaxial electrode taking random noise into account is as follows: Figure 3 As shown, the capacitance formed by the static charge distribution of the escape electrode to the ground is C m , the noise impedance introduced by the wire and the DC polarized power supply is Z b =R b +jX b , C m With Z b The coupling changes the voltage divider ratio and introduces noise interference. In addition, the noise is affected by temperature, humidity and surrounding electromagnetic interference, showing obvious randomness, making it difficult to separate and eliminate the noise. Assume that the potential of the escape electrode is U c2 , then the noise interference can be expressed by current I1:

[0059]

[0060] Taking noise interference into account, the escape current I0 is:

[0061]

[0062] Where I is the frequency domain form of i(t). According to formula (10), if the bypass resistor R in series with the escape channel is large enough, I1≈0, thereby eliminating the influence of random noise on the electronic voltage transformer.

[0063] The performance of the solution of this embodiment is further illustrated by a specific example below.

[0064] The noise suppression effect of the bypass resistor is verified by using the COMSOL multi-physics coupled field simulation method. Taking the 110kV voltage level as an example, the current-circuit-electrostatic field coupling model of the electronic voltage transformer sensor system is as follows: Figure 4 As shown. In the current field, an AC voltage to be measured is applied to the high voltage electrode-ground electrode; in the circuit field, an escape channel is set at the escape electrode, including a polarization voltage (24V), a bypass resistor R and an ammeter. The electrode dimensions are as follows: r1 = 2cm, r2 = 4.5cm, r3 = 7.5cm, L1 = 50cm, L2 = 50cm, L3 = 50cm, δ1 = 0.5cm, δ2 = 0.5cm.

[0065] When the bypass resistor R is set to 0, the escape current waveform is seriously distorted due to the influence of random noise. Figure 5 , the current signal of the period t = 0-0.08s was recorded repeatedly, and the escape current recorded three times was inconsistent. As a comparison, R = 100k signal was set, and it can be seen that the noise of the escape current was almost eliminated. This conclusion is consistent with the theoretical analysis. By defining the waveform integrity T of the escape current to describe the interference degree of noise, as shown in formula (12), the higher T indicates the stronger the anti-noise performance. Figure 5 In the figure, T=95.424% without bypass resistor (I), T=86.148% without bypass resistor (II), T=81.863% without bypass resistor (III), and T=99.38% after series bypass resistor. It can be seen that the T of the escape current before and after the series bypass resistor is increased from 81.863% to 99.38%, and the effect is obvious.

[0066] The waveform integrity T is defined as:

[0067]

[0068] Where n = 1000 represents the amount of data collected in one cycle; X i Indicates theoretical value; Y i Indicates the simulation value.

[0069] The anti-noise effect of the bypass resistor is also effective for harmonic measurement of electronic voltage transformers, such as Figure 6As shown in the figure, T = 91.973% without bypass resistor (I), T = 85.932% without bypass resistor (II), T = 91.757% without bypass resistor (III), and T = 99.66% after series bypass resistor. After series bypass resistor, T of escape current is increased from 85.932% to 99.66%.

[0070] Referring to the dimensions of the above simulation model, this embodiment fabricated a coaxial electrode sensing structure and built an experimental platform, such as Figure 7 As shown, it includes components such as a voltage regulator 12, a standard voltage transformer 13, a booster 14, an electronic voltage transformer prototype 15 of this embodiment, a tester 16, a signal generator 17, and a high-voltage amplifier 18.

[0071] In the power frequency steady-state experiment, the output voltage of the booster was adjusted to 80%, 100% and 120% of the rated voltage, and the basic accuracy of the electronic voltage transformer was recorded by the calibrator, as shown in Table 1. Affected by random noise, the maximum ratio difference of the electronic voltage transformer was greater than 1.896% and the maximum angle difference was greater than 38.56' when there was no bypass resistor. Under the action of the bypass resistor R = 100k, the maximum ratio difference of the electronic voltage transformer was reduced to 0.391% and the maximum angle difference was reduced to 18.38', with significant results.

[0072] Table 1 Basic accuracy experimental data

[0073]

[0074] In the harmonic characteristic experiment, the signal generator generates 150Hz, 250Hz, 350Hz and other harmonics respectively, which are amplified 250 times by the high-voltage amplifier and added to the high-voltage-ground electrode of the electronic voltage transformer. The harmonic signals of each order are restored according to the output signal and compared with the standard signal to calculate the ratio difference and angle difference, as shown in Table 2. It can be seen that after the bypass resistor R=100k is connected in series, the ratio difference and angle difference of each harmonic are significantly improved, which verifies the improvement of the bypass resistor on the harmonic measurement capability of the electronic voltage transformer.

[0075] Table 2 Harmonic transfer experimental data

[0076]

[0077]

[0078] Obviously, the described embodiments are only some embodiments of the present invention, not all 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.

[0079] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of electronic voltage transformer noise suppression methods based on electrostatic charge escape under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A method for suppressing noise of an electronic voltage transformer based on electrostatic charge escape, characterized in that: The sensing system of the electronic voltage transformer based on electrostatic charge escape adopts a coaxial electrode voltage-dividing structure, comprising a high-voltage electrode (2), a ground electrode (3), an escape electrode (4), a DC polarized power supply (5) and an escape channel (6); The voltage to be measured from the high-voltage transmission line (1) is applied between the high-voltage electrode (2) and the ground electrode (3). After the escape electrode (4) is polarized by a DC polarization power supply (5), the positive and negative charges move to the surface of the conductor, causing the escape electrode to show electrical properties macroscopically. Under the action of the AC voltage to be measured, the static charge moves in a direction along the escape channel (6) and forms an escape current. The escape current is linearly related to the voltage to be measured, and the voltage is measured by detecting the escape current through a signal processing unit. By connecting a bypass resistor (9) in series with the escape channel (6), the influence of noise can be suppressed; Taking noise interference into account, the escape current I0 is: Where I1 is the current introduced by noise, C m Z is the capacitance formed by the static charge distribution of the escape electrode to the ground. b =R b +jX b is the noise impedance introduced by the escape channel and the DC polarized power supply, U c2 is the potential of the escape electrode, I is the frequency domain form of the escape current i(t), and w is the angular frequency; When the bypass resistor R connected in series with the escape channel is set large enough to make I1≈0, the influence of random noise on the electronic voltage transformer is eliminated.

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