Method for monitoring voltage by zinc oxide surge arrester and impedance conversion system thereof

Abstract

The application discloses a method for monitoring system voltage by using zinc oxide lightning arrester and an impedance conversion system thereof. The voltage signal on the low-voltage arm valve sheet of the zinc oxide voltage divider is acquired, and the impedance conversion circuit matched with the voltage parameter, the signal transmission medium and the measuring instrument is selected to adjust the signal, and then the voltage measuring instrument is inputted, so that the wideband voltage measurement from the power frequency 50Hz to MHz of the zinc oxide voltage divider is realized.

Description

Technical Field

[0001] This invention belongs to the field of surge arrester technology and voltage signal acquisition technology, specifically relating to a method for monitoring system voltage using a zinc oxide surge arrester and its impedance transformation system. Background Technology

[0002] Overvoltage is a major factor affecting the reliability and stability of power systems. Overvoltage monitoring is of great value for studying the causes of overvoltage and designing insulation coordination. How to obtain overvoltage signals is the key to overvoltage monitoring technology. Currently available voltage measurement devices, due to their inherent limitations, are insufficient to meet the practical needs of online overvoltage monitoring.

[0003] Zinc oxide surge arresters, as the main devices for protecting electrical equipment, are directly connected to the primary side of the power system. The principle of zinc oxide surge arresters for monitoring overvoltage is to select zinc oxide valve plates with the same nonlinear characteristics as the zinc oxide surge arrester and connect them in series below the surge arrester. The overvoltage signal is extracted from the voltage divider valve plates in a series voltage division manner.

[0004] Existing research on zinc oxide surge arresters as voltage dividers is too idealistic and fails to accurately grasp the core issue that zinc oxide varistors possess nonlinear volt-ampere characteristics that are dually correlated with voltage amplitude and frequency. That is, once the measured voltage changes, the nonlinear network impedance of the zinc oxide surge arrester will change immediately, and related parameters such as phase angle, bandwidth, voltage divider characteristics, and amplitude-frequency characteristics will also respond accordingly.

[0005] On the other hand, current research has neglected the important influencing factor of input impedance. According to the measurement requirements, the input impedance needs to be much greater than the impedance value of the voltage divider valve to ensure measurement accuracy. Otherwise, it will lead to ratio error, angle error and waveform distortion. Especially at low voltage and low frequency, the zinc oxide valve exhibits a high resistance state, while the input impedance of most commonly used voltage measuring instruments on the market is less than 1MΩ, which obviously cannot meet the requirements, and the measured signal will inevitably be distorted.

[0006] Besides adapting to signal sources and loads, impedance transformation systems can also modify signal characteristics, improve signal quality, and achieve specific functions. For example, the frequency range of common overvoltages in power systems is very wide, and the input impedance can improve the lower frequency limit of the measurement bandwidth. By adjusting the impedance transformation system, it is possible to meet the measurement of various voltage forms such as power frequency voltage, switching impulse, and lightning impulse. Unlike the impedance transformation system of linear voltage measuring devices, the circuit component parameters of the impedance transformation system of nonlinear voltage dividers need to be adjusted according to different measured voltages. This is determined by its unique nonlinear characteristics. However, the voltage acquisition devices on the market obviously do not have the function of wide-range adjustment and cannot meet the needs of wideband measurement. Therefore, it is necessary to design a reasonable impedance transformation network for nonlinear voltage dividers based on zinc oxide surge arresters, which can improve measurement accuracy and save costs. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a method for monitoring system voltage through a zinc oxide surge arrester and its impedance transformation system, which solves the technical problems of high difficulty, poor accuracy and high cost in online overvoltage monitoring.

[0008] The present invention adopts the following technical solution:

[0009] An impedance transformation system includes a zinc oxide voltage divider valve. The input terminal of the zinc oxide voltage divider valve is connected to the circuit under test via a zinc oxide surge arrester, and the output terminal of the zinc oxide voltage divider valve is grounded. The zinc oxide surge arrester and the zinc oxide voltage divider valve together form a zinc oxide voltage divider. The input terminal of an impedance transformation circuit is connected in parallel between the input and output terminals of the zinc oxide voltage divider valve, and the output terminal of the impedance transformation circuit is connected to a voltage measuring instrument.

[0010] The impedance transformation circuit includes an input impedance module, a signal transmission cable, and a signal compensation module connected in parallel.

[0011] Specifically, the nonlinear characteristics of zinc oxide voltage divider varistors are the same as those of zinc oxide surge arresters.

[0012] Specifically, the zinc oxide surge arrester is the high-voltage arm, and the zinc oxide voltage divider valve is the low-voltage arm.

[0013] Specifically, the bandwidth of the impedance transformation circuit is greater than the frequency of the signal measured by the zinc oxide voltage divider.

[0014] Furthermore, the bandwidth of the impedance transformation circuit is five times the maximum frequency of the measured signal from the zinc oxide voltage divider.

[0015] Specifically, the input impedance of the impedance transformation circuit is greater than or equal to the self-impedance of the zinc oxide voltage divider valve plate under the measurement signal.

[0016] Specifically, the output impedance of the impedance transformation circuit is less than or equal to the input impedance of the voltage measuring instrument.

[0017] Specifically, the distortion rate of the zinc oxide voltage divider is less than 5%, the voltage error is less than 3dB, and the phase difference is less than 1°.

[0018] Secondly, embodiments of the present invention provide a method for monitoring system voltage using a zinc oxide surge arrester, comprising the following steps:

[0019] The voltage signal of the low-voltage arm of the zinc oxide voltage divider is acquired. Based on the voltage frequency, a matching impedance transformation circuit is selected to perform amplitude and phase calibration. Then, the signal is input into a voltage measuring instrument to achieve wideband voltage measurement of the zinc oxide voltage divider from 50Hz to MHz.

[0020] When the measured voltage is 50Hz (power frequency), the input impedance of the impedance transformation circuit is greater than or equal to 100MΩ.

[0021] When the measured voltage is an operational overvoltage, the input impedance of the impedance transformation circuit is greater than or equal to 10MΩ;

[0022] When the measured voltage is a lightning overvoltage, the input impedance of the impedance transformation circuit is greater than or equal to 100kΩ.

[0023] Specifically, the length of the cable ranges from 2 to 1000 meters.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] An impedance transformation system is proposed, in which a zinc oxide surge arrester, as the main device for protecting electrical equipment, is directly connected to the primary side of the power system. When used for voltage measurement, it is low-cost, easy to install, and, when combined with an impedance transformation system, can effectively improve its measurement bandwidth, making it suitable for online monitoring of various types of overvoltages.

[0026] Furthermore, if the nonlinear characteristics are the same, then the nonlinearity is approximately equal to the linearity, meaning that the pressure distribution of each valve plate is the same, which can minimize the measurement nonlinearity error, ratio difference, and angle difference.

[0027] Furthermore, linear voltage dividers are limited by space constraints, making installation on the primary side of the power system impractical. By using zinc oxide surge arresters as the high-voltage arm and voltage divider valves as the low-voltage arm, as long as the nonlinearity of the two can be controlled to be as similar as possible, they can form a nonlinear voltage divider and have the effect of a linear voltage divider within a certain voltage and frequency range, effectively overcoming the limitation of space.

[0028] Furthermore, the bandwidth of the impedance transformation circuit must be greater than the bandwidth of the measurement signal to effectively ensure the accuracy of the measurement signal; otherwise, signal distortion is likely to occur.

[0029] Furthermore, since the input impedance is much greater than the impedance of the voltage divider valve itself, the voltage division of the input impedance can be much smaller than that of the voltage divider valve, which ensures that the voltage on the voltage divider valve is as close as possible to the ideal voltage, thereby improving measurement accuracy and measurement bandwidth.

[0030] Furthermore, the output impedance is much smaller than the input impedance of the voltage measuring instrument, so that the signal of the input voltage measuring instrument can be as close as possible to the real signal; otherwise, it will cause ratio difference, angle difference and waveform distortion.

[0031] Furthermore, it was developed based on existing national standards for voltage transformers, voltage dividers, etc., and incorporates simulation, theoretical analysis, and experimental verification, thus possessing both scientific rigor and practicality.

[0032] A wideband measurement method for zinc oxide voltage dividers fully considers the basic signal transmission path, including: a signal attenuation module (zinc oxide voltage divider), a signal transformation module (input impedance transformation), a signal transmission module (signal transmission cable), a signal compensation module, and finally an ADC module (voltage acquisition module), thus bringing the research results to fruition and giving them practical value.

[0033] Furthermore, for the three common overvoltages in power systems: power frequency, switching impulse, and lightning impulse, based on the theoretical research results in specific embodiments, specific parameters for monitoring these three overvoltages are given, and users can make reasonable selections according to the voltage parameters and actual conditions.

[0034] In summary, this invention has the advantages of wide measurement bandwidth, high measurement accuracy, low cost, and easy installation.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0036] Figure 1 This is a system structure diagram of the present invention;

[0037] Figure 2 This is the equivalent circuit diagram of the impedance transformation circuit of the present invention;

[0038] Figure 3 This is a measurement bandwidth diagram showing the frequency characteristics (sinusoidal voltage) of a nonlinear resistive voltage divider when different voltage peak values ​​and different input impedances meet different accuracy requirements.

[0039] Figure 4 This is an impedance transformation circuit diagram for measuring power frequency voltage using a zinc oxide surge arrester in Example 3;

[0040] Figure 5 This is the impedance transformation circuit diagram for measuring power frequency voltage using the second type of zinc oxide surge arrester in Example 3;

[0041] Figure 6 This is the impedance transformation circuit diagram for measuring the operating impulse voltage of the first type of zinc oxide surge arrester in Example 2;

[0042] Figure 7 This is the impedance transformation circuit diagram for measuring lightning impulse voltage using the first type of zinc oxide surge arrester in Example 1;

[0043] Figure 8 This is the impedance transformation circuit diagram for measuring power frequency voltage using the third type of zinc oxide surge arrester in Example 3;

[0044] Figure 9 This is the impedance transformation circuit diagram for measuring the operating impulse voltage of the second type of zinc oxide surge arrester in Example 2;

[0045] Figure 10 This is the impedance transformation circuit diagram for measuring lightning impulse voltage using the second type of zinc oxide surge arrester in Example 1;

[0046] Figure 11 This is the impedance transformation circuit diagram for measuring power frequency voltage using the fourth type of zinc oxide surge arrester in Example 3.

[0047] The components include: 1. Zinc oxide surge arrester; 2. Zinc oxide voltage divider valve; 3. Impedance transformation circuit; 4. Voltage measuring instrument. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0050] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0051] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0052] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0053] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0054] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0055] Please see Figure 1 This invention provides an impedance transformation system, including a zinc oxide surge arrester 1. One end of the zinc oxide surge arrester 1 is connected to the circuit under test, and the other end is connected to the input terminal of a zinc oxide voltage divider valve 2. The output terminal of the zinc oxide voltage divider valve 2 is grounded. The zinc oxide surge arrester 1 is the high-voltage arm, and the zinc oxide voltage divider valve 2 is the low-voltage arm, together forming a zinc oxide voltage divider. The nonlinear characteristics of the zinc oxide voltage divider valve 2 are the same as those of the zinc oxide surge arrester 1. The input terminal of an impedance transformation circuit 3 is connected in parallel between the input terminal and the output terminal of the zinc oxide voltage divider valve 2. The output terminal of the impedance transformation circuit 3 is connected to a voltage measuring instrument 4, where U1 is the high-voltage terminal voltage and U2 is the measuring terminal voltage. The impedance transformation circuit 3 includes an input impedance module, a signal transmission module, and a signal compensation module connected in parallel in sequence.

[0056] The bandwidth of impedance transformation circuit 3 is much greater than the frequency of the signal measured by the zinc oxide voltage divider, and much greater than 5 times the maximum frequency of the measured signal.

[0057] The input impedance of impedance transformation circuit 3 is greater than or equal to 100 times the self-impedance of zinc oxide voltage divider valve plate 2 under the measurement signal, and the output impedance of impedance transformation circuit 3 is less than or equal to one percent of the input impedance of voltage measuring instrument 4. Please refer to [link / reference]. Figure 2 The impedance transformation circuit 3 specifically consists of input impedance R1, input capacitor C1, and compensation capacitor C. comp The transmission line is connected to a matching resistor R2, one end of which is connected to the input impedance R1. An input capacitor C1 is connected in parallel across the input impedance R1, and a compensation capacitor C is connected in parallel across the other end of the transmission line. comp And matching resistor R2.

[0058] The impedance transformation system of this invention has the functions of amplitude calibration, phase calibration and response adjustment. In the frequency characteristic experiment based on sinusoidal voltage, the accuracy evaluation index includes nonlinear distortion rate, voltage error and phase error. The impedance transformation system can be verified as qualified when the nonlinear distortion rate is less than 5%, the voltage error is less than 3dB and the phase difference is less than 1°.

[0059] This invention discloses a method for monitoring system voltage using a zinc oxide surge arrester, comprising the following steps:

[0060] The voltage signal on the low-voltage arm valve of the zinc oxide voltage divider is acquired. After amplitude and phase calibration by selecting a matching impedance transformation circuit according to the voltage frequency, the signal is input into the voltage measuring instrument, thereby realizing wideband voltage measurement of the zinc oxide voltage divider from 50Hz to MHz.

[0061] Select a matching impedance transformation circuit based on the frequency of the measured signal;

[0062] When the measured voltage is 50Hz (power frequency), the input impedance of the impedance transformation circuit is greater than or equal to 100MΩ.

[0063] When the measured voltage is an operational overvoltage, the input impedance of the impedance transformation circuit is greater than or equal to 10MΩ;

[0064] When the measured voltage is a lightning overvoltage, the input impedance of the impedance transformation circuit is greater than or equal to 100kΩ.

[0065] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0066] In the specific embodiment, the zinc oxide surge arrester and voltage divider valve are selected from standard 10kV zinc oxide valves (U). 1mA =7kV, C=750pF), to ensure that the component parameters and nonlinear characteristics of each valve plate are the same to the maximum extent; Figure 1 Taking an oscilloscope as an example, the voltage measuring instrument in this example has an equivalent impedance of 1MΩ and an equivalent capacitance of 20pF. Figure 4 The transmission medium is twisted pair cable with a core cross-sectional area of ​​1.5 mm2, an insulation layer diameter of 3 mm, and a total length of 50 m. Figure 5 , Figure 6 and Figure 7 The transmission medium is a lossless coaxial cable with a total length of 2m and an equivalent impedance of 50Ω. Figures 8-10 The transmission medium is a lossy coaxial cable with line parameters R = 0.06Ω / km, L = 1.4×10-3H / km, G = 3.75×10-8S / km, C = 9×10-9F / km, and a total length of 50m.

[0067] Figure 3 It is the measurement bandwidth of a nonlinear resistive voltage divider based on zinc oxide surge arresters when meeting different accuracy requirements under different voltage peaks and different input impedances in frequency characteristic experiments; Figure 3 The results presented here are general conclusions drawn from the study of zinc oxide as a nonlinear resistive voltage divider, which have only theoretical value. Firstly, under laboratory conditions, various voltage measuring devices, such as linear voltage dividers, can already achieve high-precision measurements, eliminating the need for nonlinear voltage dividers. Secondly, the frequency bands of common overvoltages in power systems are known, and the voltage range of zinc oxide surge arresters is also determined due to insulation coordination principles. Therefore, if zinc oxide surge arresters are used to monitor overvoltages in power systems, impedance transformation circuits need to be specifically designed according to the type of overvoltage.

[0068] Figure 3The voltage in this text is a per-unit value. Based on the basic principles of substation insulation coordination (below 220kV, the insulation level is determined by lightning overvoltage; above 330kV, it is determined by switching overvoltage) and conventional insulation coordination methods, the actual operating voltage of zinc oxide surge arresters has an upper limit. The relevant parameters for typical surge arresters are given in "AC Gapless Metal Oxide Surge Arresters" (GB / T 11032). Statistical analysis shows that both lightning impulse residual voltage and switching impulse residual voltage are less than or equal to twice the DC 1mA reference voltage. In this paper, U... B =1p.u.=2U 1mA .

[0069] Figure 3 The voltage in the circuit is a sinusoidal voltage. According to the definition of frequency characteristics, when the frequency of the input sinusoidal signal changes continuously within the range of 0 to infinity, the change law of the amplitude ratio and phase difference of the steady-state sinusoidal output and sinusoidal input of the system with the change of the input frequency is the frequency characteristic of the system. This invention characterizes and analyzes the frequency characteristics of zinc oxide by applying sinusoidal signals with different peak values ​​and frequencies at the high-voltage end, connecting voltage acquisition devices with different input impedance values ​​in parallel at the measurement end, acquiring the time-domain waveforms at the high-voltage end and the measurement end, and calculating the amplitude-frequency characteristics, phase-frequency characteristics, and nonlinear distortion rate.

[0070] Linear voltage dividers are commonly characterized by ratio difference and angle difference. However, for nonlinear measuring devices, the frequency components of the output waveform are more complex, making ratio difference and angle difference insufficient for effective characterization. Therefore, a third dependent variable—voltage harmonic distortion rate—is introduced, expressed as the percentage of the root mean square value of each harmonic voltage to the effective value of the fundamental voltage. That is:

[0071]

[0072] Figure 3 The results show that the effective bandwidth of the nonlinear resistive voltage divider is affected by both voltage amplitude and input impedance; the higher the voltage, the higher the harmonic components of the time-domain waveform at the measurement end, the greater the input impedance, and the better the low-frequency characteristics of the voltage measurement device; specifically as follows:

[0073] 1) The effective bandwidth corresponding to the three indicators of amplitude frequency characteristics (ratio difference), phase frequency characteristics (angle difference), and nonlinear distortion rate is significantly different, that is, different conclusions will be drawn from different perspectives. This is because amplitude frequency characteristics and phase frequency characteristics are relatively one-sided. Both only focus on the performance at the peak value and ignore the distortion at low amplitude values. Therefore, when considering the three indicators in a comprehensive way, we should first focus on the impact of nonlinear distortion rate on bandwidth.

[0074] 2) Keeping the input impedance constant, observe the frequency characteristics under different voltages; the voltage starts from 0 and increases. When the voltage exceeds 0.5pu, i.e., after entering the nonlinear region, the amplitude-frequency and phase-frequency characteristics improve significantly (bandwidth widens). This is because at 0.5pu (U 1mA Below a certain voltage, the grain boundary layer of the zinc oxide valence plate is not broken down and is in a high-resistivity state. In this case, the voltage measuring device is equivalent to a capacitive voltage divider. If the input impedance is infinite, then... Where U1 is the high-voltage terminal voltage, U2 is the measurement terminal voltage, C1 is the total capacitance of the zinc oxide surge arrester, and C2 is the capacitance of the zinc oxide voltage divider measuring valve. Clearly, there is no ratio error or phase error in this case. However, in practice, the input impedance is finite, and its circuit model can be equivalent to a large resistor and a small capacitor in parallel. Let the resistance be R and the capacitance be C3. The voltage error (ratio error) and phase error (phase error) are as follows:

[0075]

[0076]

[0077]

[0078]

[0079] Where, ε U K is the ratio difference, K is the actual partial pressure ratio, K r Rated partial voltage ratio, φ U The difference is the angle.

[0080] The ratio difference and phase difference are related to the frequency, the resistance value of the input impedance, and the capacitance. The lower the frequency, the worse the amplitude frequency and phase frequency characteristics. Therefore, its low-frequency characteristics are poor. When the voltage exceeds 0.5 pu, the grain boundary layer is broken down, and the zinc oxide exhibits a low resistance state. The voltage division between the valve plates is mainly nonlinear. Since the impedance value of the zinc oxide valve plate in this voltage range is much smaller than the input impedance, the input impedance has a negligible effect on the ratio difference and phase difference.

[0081] The distortion rate changes in the opposite way with voltage. When the voltage is below 0.5 pu, the equivalent circuit of zinc oxide is linear with extremely low harmonic components. Once the voltage exceeds 0.5 pu, due to the presence of nonlinear resistance, the equivalent circuit naturally becomes nonlinear. When sinusoidal excitation is applied to the nonlinear circuit and the circuit has a periodic response, the waveform of the response is generally non-sinusoidal and contains high-order or sub-harmonic components, thus increasing the distortion rate.

[0082] 3) With a fixed voltage, compare the frequency characteristics under different input impedances; it can be seen that the input impedance mainly affects the low frequency range. As the input impedance increases (1MΩ→10MΩ→50MΩ→100MΩ), below 0.5pu voltage, the low frequency cutoff frequency of the amplitude frequency characteristic and phase frequency characteristic is continuously decreasing, which is manifested as a significant reduction in ratio difference, angle difference and distortion rate. That is, the low frequency characteristics of the zinc oxide surge arrester are significantly enhanced. This phenomenon can be explained by equations (2) to (3). Above 0.5pu voltage, the input impedance mainly affects the low frequency range under the distortion rate index. This is because in the nonlinear region, a slight decrease in resistance will cause an increase in nonlinearity, and the distortion rate will also increase. In the low frequency range, the capacitance of the zinc oxide varistor can be ignored. At this time, the smaller the input impedance, the smaller the equivalent impedance at the measurement end, and the higher the distortion rate. In the high frequency range, the capacitive reactance cannot be ignored, which will further reduce the impedance value of the zinc oxide varistor, which is equivalent to weakening the influence of the input impedance. Therefore, the distortion rate is almost the same.

[0083] Zinc oxide surge arresters actually operating in power systems do not possess [certain features]. Figure 3 The wide voltage range shown in the figure, specifically, taking a typical zinc oxide surge arrester with a nominal discharge current of 10kA or 5kA as an example, the peak value of the power frequency voltage is converted to a per-unit value of 0.4 to 0.5 pu, the upper limit of the peak value of the switching impulse residual voltage is 1.7 pu, and the upper limit of the peak value of the lightning impulse residual voltage is 1.9 pu.

[0084] On the other hand, the frequency bands of common overvoltages in power systems are also defined. Taking power frequency, switching impulse, and lightning impulse overvoltages as examples, the frequency band of power frequency overvoltage (excluding harmonics) is 50±0.5Hz, the upper frequency limit of standard switching impulse voltage (250 / 2500μs) is 1400Hz, and the frequency range of lightning impulse voltage is generally 20kHz~1MHz.

[0085] Example 1

[0086] Please see Figure 7 , Figure 10 If the zinc oxide surge arrester is to monitor only lightning impulse voltage, the input impedance should be selected within the range of ≥100kΩ. When the input impedance is 100kΩ, by adjusting the compensation capacitor Ccomp and the matching resistor R2 (Len=2m, Ccomp=25±5pF, R2=4±0.5kΩ; Len=50m, Ccomp=25±5pF, R2=200±5Ω), the zinc oxide surge arrester can have a measurement bandwidth of 10kHz~1MHz, which can only include the lightning impulse voltage frequency band. The measurement accuracy is that the deviation between the actual voltage division ratio and the rated voltage division ratio is not greater than 1%, and the oscillation amplitude near the peak value is not greater than 5% of the peak value.

[0087] Example 2

[0088] Please see Figure 6 , Figure 9 To monitor switching impulse voltage with a zinc oxide surge arrester, the input impedance should be selected within the range of ≥10MΩ. When the input impedance is 10MΩ, by adjusting the compensation capacitor Ccomp and the matching resistor R2 (Len=2m, Ccomp=30±5pF, R2=250±10kΩ; Len=50m, Ccomp=30±5pF, R2=250±10Ω), the zinc oxide surge arrester can have a measurement bandwidth of 200Hz~1MHz, covering both the switching overvoltage band and the lightning overvoltage band. It can simultaneously meet the needs of monitoring both types of overvoltage. The measurement accuracy is that the deviation between the actual voltage division ratio and the rated voltage division ratio is no more than 1%, and the oscillation amplitude near the peak value is no more than 5% of the peak value.

[0089] Example 3

[0090] Please see Figure 4 , Figure 5 , Figure 8 , Figure 11 To monitor power frequency overvoltage using a zinc oxide surge arrester, the input impedance should be ≥100MΩ. When the input impedance is 100MΩ and the transmission line is a coaxial cable, the compensation capacitor Ccomp and the matching resistor R2 can be adjusted (Len = 2m, Ccomp = 40±5pF, R2 = 5±0.1MΩ; Len = 50m, Ccomp = 40±5pF, R2 = 500±20Ω; Len = 500m, Ccomp = 40±5pF, R2 = 3m). The zinc oxide surge arrester (00±20Ω) can have a measurement bandwidth of 50Hz to 1MHz. Its performance in measuring power frequency overvoltage can achieve a nonlinear distortion rate of less than 3%, a voltage error of less than 1%, and a phase difference of less than 40′. At this time, the zinc oxide surge arrester can take into account the online monitoring of three types of overvoltages: power frequency, switching, and lightning. When the input impedance is 100MΩ and the transmission line is a twisted pair cable, the high-frequency part of the bandwidth will be reduced to 100kHz, which can only meet the monitoring requirements of power frequency and switching overvoltages.

[0091] In summary, the method for monitoring system voltage using a zinc oxide surge arrester and its impedance transformation system of the present invention have the following advantages:

[0092] 1. Ordinary voltage transformers have low sampling frequency and poor high-frequency transient response characteristics. The zinc oxide voltage divider in this invention has excellent frequency response and, when paired with a corresponding impedance transformation circuit, can achieve wideband voltage measurement from power frequency to MHz.

[0093] 2. Zinc oxide varistors possess excellent nonlinear current-voltage characteristics, high voltage gradient, and strong anti-interference capability in the field; moreover, the impedance transformation circuit has amplitude calibration, phase calibration, and response adjustment functions, which can effectively improve the fidelity of signal measurement.

[0094] 3. Due to space constraints, installing voltage dividers on the primary side of the power system is obviously impractical. This invention achieves voltage measurement without changing the original power equipment structure, and improves the performance of the zinc oxide surge arrester by increasing the number of series valves, making its protection level higher than the existing power standards.

[0095] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0096] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0097] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0098] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0099] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0100] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0101] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for monitoring system voltage using a zinc oxide surge arrester, characterized in that, The impedance transformation system includes a zinc oxide voltage divider valve. The input terminal of the zinc oxide voltage divider valve is connected to the circuit under test via a zinc oxide surge arrester, and the output terminal of the zinc oxide voltage divider valve is grounded. The zinc oxide surge arrester and the zinc oxide voltage divider valve together form a zinc oxide voltage divider. The input and output terminals of the zinc oxide voltage divider valve are connected in parallel to the input terminal of the impedance transformation circuit, and the output terminal of the impedance transformation circuit is connected to a voltage measuring instrument. The nonlinear characteristics of the zinc oxide voltage divider valve are the same as those of the zinc oxide surge arrester. The bandwidth of the impedance transformation circuit is greater than the frequency of the measurement signal of the zinc oxide voltage divider. The input impedance of the impedance transformation circuit is greater than or equal to the self-impedance of the zinc oxide voltage divider valve under the measurement signal. The output impedance of the impedance transformation circuit is less than or equal to the input impedance of the voltage measuring instrument. It includes an input impedance module, a signal transmission cable and a signal compensation module connected in parallel in sequence. Includes the following steps: The voltage signal of the low-voltage arm of the zinc oxide voltage divider is acquired. Based on the voltage frequency, a matching impedance transformation circuit is selected to perform amplitude and phase calibration. Then, the signal is input into a voltage measuring instrument to achieve wideband voltage measurement of the zinc oxide voltage divider from 50Hz to MHz. When the measured voltage is 50Hz (power frequency), the input impedance of the impedance transformation circuit is greater than or equal to 100MΩ. When the measured voltage is an operational overvoltage, the input impedance of the impedance transformation circuit is greater than or equal to 10MΩ; When the measured voltage is a lightning overvoltage, the input impedance of the impedance transformation circuit is greater than or equal to 100kΩ.

2. The method for monitoring system voltage using a zinc oxide surge arrester according to claim 1, characterized in that, The cable length ranges from 2 to 1000 meters.

3. The method for monitoring system voltage using a zinc oxide surge arrester according to claim 1, characterized in that, The zinc oxide surge arrester is the high-voltage arm, and the zinc oxide voltage divider is the low-voltage arm.

4. The method for monitoring system voltage using a zinc oxide surge arrester according to claim 1, characterized in that, The bandwidth of the impedance transformation circuit is 5 times the maximum frequency of the signal measured by the zinc oxide voltage divider.

5. The method for monitoring system voltage using a zinc oxide surge arrester according to claim 1, characterized in that, The distortion rate of the zinc oxide voltage divider is less than 5%, the voltage error is less than 3dB, and the phase difference is less than 1°.

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