Ground protection circuit for overvoltage monitoring and related method and device thereof

Abstract

The invention discloses a grounding protection circuit for overvoltage monitoring and a related method and device thereof, and belongs to the technical field of overvoltage monitoring. Through parallel connection of the voltage dividing capacitor and the protection circuit formed by series connection of the resonance damping device and the inductor, an additional safety barrier is provided for the bushing end screen, when the voltage dividing capacitor faces a breakdown risk, the grounding protection circuit can rapidly respond, and overvoltage is effectively suppressed by using the impedance characteristic of the inductor and the energy absorption capability of the resonance damping device, so that the bushing end screen is protected. The breakdown of the voltage-dividing capacitor is prevented, so that the bushing end screen is ensured not to be grounded; meanwhile, based on the frequency response characteristic of the inductor, the impedance of the inductor is remarkably improved within the high-frequency overvoltage range needing to be measured, a short-circuit effect is not formed on the voltage-dividing capacitor any more, the voltage-dividing capacitor can give full play to the voltage-dividing function of the voltage-dividing capacitor, overvoltage signals are accurately measured, the measurement accuracy is improved, and the measurement cost is reduced. And potential interference of standard power frequency voltage on a measurement result is avoided, and authenticity and reliability of monitoring data are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of overvoltage monitoring, and particularly relates to a grounding protection circuit for overvoltage monitoring, and related methods and devices. Background Art

[0002] In the power system, overvoltage phenomena are one of the important threats to the safe operation of the power grid. There are various types of overvoltages, including lightning overvoltages (atmospheric overvoltages) caused by external lightning activities and internal overvoltages caused by internal energy transfer or conversion processes, such as temporary overvoltages, switching overvoltages, and resonant overvoltages. These overvoltage phenomena often have the characteristics of high amplitude, large steepness, and short duration, posing a severe challenge to the stable operation of the power system.

[0003] Traditional fault recording devices have limitations in capturing and recording overvoltage waveforms. These devices usually rely on voltage transformers to obtain voltage signals. However, voltage transformers are mainly designed for accurate measurement of standard 50Hz power frequency voltage signals. For signals in other frequency bands, especially high-frequency overvoltage signals, their measurement accuracy is often unreliable. In particular, capacitive voltage transformers are widely used in domestic high-voltage substations, but their measurement accuracy is limited to the 50Hz frequency band and cannot meet the requirements of high-frequency overvoltage measurement.

[0004] To overcome this limitation, the prior art achieves accurate measurement of overvoltage by installing an overvoltage monitoring device at the end screen of the transformer bushing. This device forms a capacitive voltage division circuit by connecting a voltage dividing capacitor in series with the main capacitor of the bushing, thereby achieving accurate measurement of the primary voltage. Although this method meets the amplitude and frequency requirements of overvoltage measurement to a certain extent, it brings new safety hazards during long-term operation.

[0005] Specifically, the end screen of the bushing needs to be well grounded during normal operation to ensure uniform distribution of the electric field inside the bushing, reduce the local electric field intensity, and prevent insulation breakdown caused by electric field concentration. However, after introducing the series voltage dividing capacitor, the voltage of the end screen of the bushing is lifted and is no longer at ground potential, resulting in a change in the electric field distribution of the bushing. In addition, the series voltage dividing capacitor may be broken down due to aging or other quality problems during long-term operation. Once broken down, it will cause the end screen of the bushing to lose ground, and then lead to breakdown between the capacitor screens of the bushing until a ground short circuit occurs. This not only destroys the electrical connection between the end screen of the bushing and the ground, resulting in the end screen of the bushing being unable to be effectively grounded, but also may generate floating voltages, increasing the risk of equipment failure.

[0006] Therefore, how to prevent the safety hazards brought by the breakdown of the voltage dividing capacitor while realizing overvoltage monitoring and ensure that the end screen of the bushing can maintain a long-term reliable grounding state has become an urgent technical problem for those skilled in the art to solve. Summary of the Invention

[0007] The purpose of the present invention is to provide a grounding protection circuit for overvoltage monitoring, its related methods and devices, aiming to overcome the potential risk of the potential loss of the bushing end screen caused by the introduction of series voltage-dividing capacitors in the prior art, as well as the safety hazard that the voltage-dividing capacitor may break down during long-term operation.

[0008] The present invention solves the above technical problems through the following technical solutions: A grounding protection circuit for overvoltage monitoring includes an equivalent circuit for overvoltage monitoring of the bushing end screen and a protection circuit. The equivalent circuit for overvoltage monitoring of the bushing end screen is formed by grounding after series connecting a voltage-dividing capacitor C 1 in series with a bushing equivalent capacitor C 2 . The protection circuit is formed by series connecting a resonance damping device S and an inductor L, and the protection circuit is connected in parallel with the voltage-dividing capacitor C 2 .

[0009] A further improvement of the present invention is that it further includes an overvoltage protection unit, and the overvoltage protection unit is connected in parallel with the voltage-dividing capacitor C 2 .

[0010] A further improvement of the present invention is that the overvoltage protection unit adopts a discharge gap structure to suppress extreme overvoltage impacts and achieve component protection.

[0011] A further improvement of the present invention is that the resonance damping device is one of an active damper or a notch filter, and is used to suppress the resonance point of the inductor L and the voltage-dividing capacitor C 2 .

[0012] A further improvement of the present invention is that the inductance value range of the inductor L is 1 μH to 100 mH.

[0013] The present invention also provides a grounding protection method for overvoltage monitoring. The grounding protection circuit for overvoltage monitoring as described above is used for the bushing end screen to be monitored. Based on the fact that the inductive reactance is proportional to the voltage frequency and the capacitive reactance is inversely proportional to the voltage frequency, when the voltage frequency is 50 Hz, the inductive reactance of the inductor L is lower than the capacitive reactance of the voltage-dividing capacitor C 2 , and the parallel circuit of the inductor L and the voltage-dividing capacitor C 2 is inductive. Based on the voltage borne by the voltage-dividing capacitor C 2 , the potential of the bushing end screen is equivalently in an effectively grounded state; When the voltage frequency is the overvoltage high frequency, the inductive reactance of the inductor L is higher than the capacitive reactance of the voltage-dividing capacitor C 2 , and the parallel circuit of the inductor L and the voltage-dividing capacitor C 2 is capacitive. Based on the voltage borne by the voltage-dividing capacitor C 2 , voltage division measurement is carried out, and the bushing equivalent capacitor C is calculated.1 True high-voltage side overvoltage waveform

[0014] A further improvement of the present invention lies in: adopting the above-mentioned grounding protection circuit for overvoltage monitoring for the bushing end screen to be monitored, including the following steps: Step 1: When the power system operates at a voltage frequency of the standard industrial frequency of 50 Hz, the potential of the bushing end screen is equivalent to an effectively grounded state, and the bushing end screen is in a grounding protection state. The equivalent capacitance C of the bushing is measured through a known voltage transformer in the substation of the power system 1 True high-voltage side standard industrial frequency voltage waveform Step 2: Based on the parameters of the grounding protection circuit for overvoltage monitoring, the frequency response function is calculated, and the parameters include the inductance value of the inductor L, the capacitance value of the voltage-dividing capacitor C 2 and the capacitance value of the equivalent capacitance C1 of the bushing; Step 3: When the power system operates at overvoltage high frequency, based on the voltage borne by the voltage-dividing capacitor C 2 , the overvoltage measurement signal y ( t ) is obtained through voltage division measurement. The overvoltage measurement signal y ( t ) is subjected to Fourier transform to obtain the frequency-domain expression of the overvoltage measurement signal y ( t ); based on the relationship between the frequency-domain expression of the overvoltage measurement signal y ( t ) and the frequency response function , through inverse Fourier transform, the true high-voltage side overvoltage waveform of the equivalent capacitance C of the bushing is obtained; 1 True high-voltage side overvoltage waveform Step 4: Combine the true high-voltage side standard industrial frequency voltage waveform and the true high-voltage side overvoltage waveform of the equivalent capacitance C of the bushing to obtain a complete voltage measurement waveform of the bushing end screen. 1 True high-voltage side standard industrial frequency voltage waveform and true high-voltage side overvoltage waveform of the equivalent capacitance C of the bushing to obtain a complete voltage measurement waveform of the bushing end screen.

[0015] A further improvement of the present invention lies in: the frequency-domain expression of the overvoltage measurement signal is specifically:

[0016] Wherein, F is the Fourier transform function, is the frequency; The relationship between the frequency-domain expression of the overvoltage measurement signal y ( t ) and the frequency response function is specifically:

[0017] Wherein, is the equivalent capacitance C of the bushing 1 in the form of the frequency domain expression of the true overvoltage signal on the high-voltage side; Then, the equivalent capacitance C of the bushing 1 true overvoltage signal on the high-voltage side x ( t ) is specifically:

[0018] wherein, is the inverse Fourier transform function.

[0019] The present invention also provides an electronic device, including the grounding protection circuit for overvoltage monitoring as described above.

[0020] The present invention also provides a system, including the electronic device as described above, for realizing overvoltage detection.

[0021] Compared with the prior art, the positive and progressive effects of the present invention are as follows: The grounding protection circuit for overvoltage monitoring provided by the present invention not only realizes the accurate measurement of overvoltage signals, but also can provide an effective protection mechanism during normal operation. Specifically, by connecting a voltage-dividing capacitor in parallel with a protection circuit formed by a resonant damping device and an inductor in series, an additional safety barrier is provided for the bushing end screen. When the voltage-dividing capacitor is at risk of breakdown, the grounding protection circuit can respond quickly, utilize the impedance characteristics of the inductor and the energy absorption ability of the resonant damping device to effectively suppress overvoltage, prevent the breakdown of the voltage-dividing capacitor, and thus ensure that the bushing end screen does not lose ground; at the same time, based on the frequency response characteristics of the inductor, in the high-frequency overvoltage range to be measured, the impedance of the inductor is significantly increased, no longer forming a short-circuit effect on the voltage-dividing capacitor, enabling the voltage-dividing capacitor to fully exert its voltage-dividing function, accurately measure the overvoltage signal, not only improving the measurement accuracy, but also avoiding the potential interference of the standard power frequency voltage on the measurement result, ensuring the authenticity and reliability of the monitoring data.

[0022] Furthermore, by connecting an overvoltage protection unit in parallel with the voltage-dividing capacitor, more comprehensive protection is provided for the bushing end screen. When high-frequency overvoltage occurs in the power system, the overvoltage protection unit can respond quickly, limit the amplitude of the overvoltage, effectively prevent equipment damage or failure caused by overvoltage, and further improve the safety of the power system.

[0023] The method for monitoring the overvoltage of the bushing end screen provided by the present invention calculates the frequency response function, fully considering the influence of inductance, voltage-dividing capacitance and bushing equivalent capacitance parameters on the measurement result, which helps to accurately measure the voltage waveform of the bushing end screen at high overvoltage frequencies and improve the accuracy and reliability of the measurement; uses Fourier transform to convert the overvoltage measurement signal from the time domain to the frequency domain, and then performs inverse transformation based on the frequency response function to obtain the true overvoltage waveform on the high-voltage side of the bushing equivalent capacitance, which can maximize the restoration of the true overvoltage waveform and provide accurate data support for power system fault analysis and processing; by combining the voltage waveform under standard power frequency and the voltage waveform at high overvoltage frequencies, a complete voltage measurement waveform of the bushing end screen is obtained, which provides strong support for the comprehensive monitoring and analysis of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings in the specification are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0025] Figure 1 It is a schematic diagram of a grounding protection circuit for overvoltage monitoring according to the present invention; Figure 2 It is an equivalent circuit diagram of the operating state of the bushing; Figure 3 It is an equivalent circuit diagram of the operating state of the bushing with a voltage-dividing capacitance added in the prior art.

[0026] Among them, C1 is the bushing equivalent capacitance; C2 is the voltage-dividing capacitance; G is the ground; P is the overvoltage protection unit; S is the resonance damping device; L is the inductance. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents the selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] Glossary: Transformer bushing: It is mainly composed of a capacitive core, an oil conservator, a flange, and upper and lower porcelain bushings. It is an insulating bushing that leads the high- and low-voltage leads inside the transformer to the outside of the oil tank. It not only insulates the leads from the ground but also plays the role of fixing the leads. The transformer bushing is one of the current-carrying components of the transformer. During the operation of the transformer, it passes the load current for a long time, and when a short circuit occurs outside the transformer, it passes the short-circuit current.

[0030] Capacitive screen: The capacitive core of a capacitive transformer bushing is to tightly wrap an insulating layer of a certain thickness with cable paper 0.08 - 0.12 mm thick outside a hollow conductive copper tube, and then wrap a layer of aluminum foil 0.01 mm or 0.007 mm thick outside it as a capacitive screen, and then alternately continue to wrap cable paper and aluminum foil until the required number of layers and thickness are reached.

[0031] Bushing end screen: For the capacitive core of a capacitive transformer bushing, the innermost layer is the bushing zero screen, and the outermost layer is the bushing end screen. In order to prevent voltage drift during operation, resulting in excessive voltage inside and damaging the equipment, the bushing end screen must be grounded.

[0032] The following further elaborates on the present invention in detail in conjunction with the accompanying drawings and specific embodiments, which is an explanation rather than a limitation of the present invention.

[0033] See Figure 1 , a grounding protection circuit for overvoltage monitoring, including a bushing end screen overvoltage monitoring equivalent circuit and a protection circuit. The bushing end screen overvoltage monitoring equivalent circuit is formed by grounding after series-connecting a bushing equivalent capacitance C 1 and a voltage-dividing capacitance C 2 . The protection circuit is formed by series-connecting a resonance damping device S and an inductor L, and the protection circuit is connected in parallel with the voltage-dividing capacitance C 2 .

[0034] The grounding protection circuit for overvoltage monitoring provided by the present invention not only realizes the accurate measurement of overvoltage signals but also provides an effective protection mechanism during normal operation. Specifically, by connecting the voltage-dividing capacitance in parallel with the protection circuit formed by series-connecting the resonance damping device and the inductor, an additional safety barrier is provided for the bushing end screen. When the voltage-dividing capacitance is at risk of breakdown, the grounding protection circuit can respond quickly, utilize the impedance characteristics of the inductor and the energy absorption ability of the resonance damping device to effectively suppress the overvoltage, prevent the breakdown of the voltage-dividing capacitance, and thus ensure that the bushing end screen does not lose ground; at the same time, based on the frequency response characteristics of the inductor, within the high-frequency overvoltage range that needs to be measured, the impedance of the inductor is significantly increased, no longer forming a short-circuit effect on the voltage-dividing capacitance, enabling the voltage-dividing capacitance to fully play its voltage-dividing function, accurately measuring the overvoltage signal, not only improving the measurement accuracy but also avoiding the potential interference of the standard power frequency voltage on the measurement result, ensuring the authenticity and reliability of the monitoring data.

[0035] Specifically, it further includes an overvoltage protection unit, and the overvoltage protection unit is connected in parallel with a voltage-dividing capacitor C 2 .

[0036] By connecting the overvoltage protection unit in parallel with the voltage-dividing capacitor, more comprehensive protection is provided for the bushing end screen. When overvoltage high frequency occurs in the power system, the overvoltage protection unit can quickly respond, limit the amplitude of the overvoltage, effectively prevent equipment damage or faults caused by overvoltage, and further improve the safety of the power system.

[0037] Specifically, the overvoltage protection unit adopts a discharge gap structure to suppress extreme overvoltage shocks and achieve component protection.

[0038] Specifically, the resonance damping device is one of an active damper or a notch filter, and is used to suppress the resonance point of the inductor L and the voltage-dividing capacitor C 2 .

[0039] Specifically, the inductance value range of the inductor L is 1 μH to 100 mH.

[0040] Based on the same inventive concept, the present invention also provides a grounding protection method for overvoltage monitoring. The bushing end screen to be monitored adopts the grounding protection circuit for overvoltage monitoring as described above. Based on the fact that the inductive reactance is proportional to the voltage frequency and the capacitive reactance is inversely proportional to the voltage frequency, when the voltage frequency is 50 Hz, the inductive reactance of the inductor L is lower than the capacitive reactance of the voltage-dividing capacitor C 2 , and the parallel circuit of the inductor L and the voltage-dividing capacitor C 2 is inductive. Based on the voltage borne by the voltage-dividing capacitor C 2 , the potential of the bushing end screen is equivalent to an effectively grounded state; When the voltage frequency is overvoltage high frequency, the inductive reactance of the inductor L is higher than the capacitive reactance of the voltage-dividing capacitor C 2 , and the parallel circuit of the inductor L and the voltage-dividing capacitor C 2 is capacitive. Based on the voltage borne by the voltage-dividing capacitor C 2 , voltage division measurement is carried out, and the true overvoltage waveform of the high-voltage side of the equivalent capacitor C 1 of the bushing is calculated.

[0041] Based on the same inventive concept, the present invention also provides a method for overvoltage monitoring of a bushing end screen. The bushing end screen to be monitored adopts the grounding protection circuit for overvoltage monitoring as described above, including the following steps: Step 1: When the power system operates at a voltage frequency of the standard power frequency of 50 Hz, the potential of the bushing end screen is equivalent to an effectively grounded state, and the bushing end screen is in a grounding protection state. The true high-voltage side standard power frequency voltage waveform of the equivalent capacitor C 1 of the bushing is measured through a known voltage transformer in the substation of the power system; Step 2: Calculate the frequency response function based on the parameters of the grounding protection circuit for overvoltage monitoring. The parameters include the inductance value of the inductor L, the capacitance value of the voltage-dividing capacitor C 2 and the capacitance value of the bushing equivalent capacitor C1. Step 3: When the power system operates at high overvoltage frequencies, based on the voltage borne by the voltage-dividing capacitor C 2 , measure the overvoltage measurement signal through voltage division y ( t ). Perform Fourier transform on the overvoltage measurement signal y ( t ) to obtain the frequency-domain expression of the overvoltage measurement signal y ( t ); Based on the relationship between the frequency-domain expression of the overvoltage measurement signal y ( t ) and the frequency response function , perform inverse Fourier transform to obtain the true high-voltage side overvoltage waveform of the bushing equivalent capacitor C 1 . Step 4: Combine the true high-voltage side standard power frequency voltage waveform and the true high-voltage side overvoltage waveform of the bushing equivalent capacitor C 1 to obtain the complete voltage measurement waveform of the bushing end screen.

[0042] By calculating the frequency response function and fully considering the influence of the inductor, voltage-dividing capacitor, and bushing equivalent capacitor parameters on the measurement results, it helps to accurately measure the voltage waveform of the bushing end screen at high overvoltage frequencies, improving the accuracy and reliability of the measurement; Using Fourier transform to convert the overvoltage measurement signal from the time domain to the frequency domain, and then performing inverse transform based on the frequency response function to obtain the true high-voltage side overvoltage waveform of the bushing equivalent capacitor, which can maximize the restoration of the true waveform of the overvoltage and provide accurate data support for power system fault analysis and processing; By combining the voltage waveform under standard power frequency and the voltage waveform at high overvoltage frequencies, the complete voltage measurement waveform of the bushing end screen is obtained, providing strong support for the comprehensive monitoring and analysis of the power system.

[0043] Specifically, the frequency-domain expression of the overvoltage measurement signal is specifically:

[0044] where F is the Fourier transform function, is the frequency; The relationship between the frequency-domain expression of the overvoltage measurement signal y ( t ) and the frequency response function is specifically:

[0045] Among them, is the equivalent capacitance C of the bushing 1 in the frequency domain expression form of the true overvoltage signal on the high-voltage side; Then, the equivalent capacitance C of the bushing 1 of the true overvoltage signal on the high-voltage side x ( t ) is specifically:

[0046] Among them, is the inverse Fourier transform function.

[0047] Based on the same inventive concept, the present invention also provides an electronic device, including the grounding protection circuit for overvoltage monitoring as described above.

[0048] Based on the same inventive concept, the present invention also provides a system, including the electronic device as described above, for realizing overvoltage detection.

[0049] Embodiment 1 The measurement object is a busbar with a voltage level of 110 kV. It is selected to measure at the end screen of the 110 kV bushing of the main transformer. The equivalent capacitance C of this bushing 1 is 500 pF. Disconnect the grounding of the capacitor end screen, and connect a voltage-dividing capacitor C 2 = 500 nF in series between the main capacitance of the bushing and the ground. At this time, the voltage division ratio is 1000:1. Under normal operating conditions, the voltage at the voltage-dividing capacitor C 2 is about 110 kV / √3 / 1000 = 63.5 V.

[0050] During long-term operation, if the voltage-dividing capacitor C 2 breaks down due to external or quality reasons, the equivalent capacitance C of the bushing 1 will have a ground loss phenomenon, which will seriously affect the operation safety of the bushing and may cause the discharge breakdown of the capacitor screen of the bushing, and then cause fire and explosion.

[0051] To avoid this problem, a small inductor with an inductance value of 1 μH is connected in parallel to the voltage-dividing capacitor C2. At 50 Hz power frequency, the impedance value of this inductor is 0.314 mΩ. At this time, the voltage division ratio is about 5.8×107, and the voltage borne by the voltage-dividing capacitor C 2 is about 110 kV / √3 / 1000 = 1.1×10-3 V. It can be seen that at this time, it is approximately short-circuiting both ends of the voltage-dividing capacitor C 2 so that the voltage-dividing capacitor C 2It does not bear voltage during operation, reducing the possibility of breakdown of the voltage-dividing capacitor C2; when the overvoltage to be measured appears, taking lightning overvoltage as an example, its frequency range is about 1 MHz. At this frequency, the inductive reactance value of the inductor increases sharply. At this time, the voltage-division ratio is about 955:1. At this time, the voltage borne on the voltage-dividing capacitor C 2 is about dozens to hundreds of volts, within its reasonable measurable range. According to the capacitance value of the voltage-dividing capacitor C 2 and the inductance value of L, the frequency response characteristic function of the measurement circuit can be obtained. The background data acquisition host computer calculates inversely based on this function through the waveform obtained by measurement, so as to obtain the standard original overvoltage waveform. The power frequency part in the original waveform, that is, the 50 Hz part, can be directly obtained from the nearby voltage transformer and synthesized by the background to form the complete waveform.

[0052] The method proposed by the present invention improves the original measurement system. Since the purpose of the overvoltage monitoring system is to measure the operating or lightning overvoltage that may occur in the power system, these waveforms have a relatively high frequency, above 10 kHz, while the power frequency voltage waveform (50 Hz) during normal operation is not the measurement target of this system, and this waveform can be obtained from devices such as nearby voltage transformers. Therefore, the present invention connects a small inductor in parallel with the original voltage-dividing capacitor C 2 to achieve the purpose of accurate measurement and also play a protective role during normal operation: 1. When the frequency is low, the impedance value of the inductor is also low, approximately short-circuiting the voltage-dividing capacitor C 2 to avoid breakdown of the voltage-dividing capacitor C 2 during long-term operation. And even if breakdown occurs, due to the existence of this inductor, it can ensure that the bushing equivalent capacitor C 1 will not lose ground.

[0053] 2. When the high-frequency overvoltage to be measured appears, for the high-frequency components in the measured signal, the impedance value of the inductor becomes large and loses the short-circuit effect on the voltage-dividing capacitor C 2 , and at this time, the voltage-dividing capacitor C 2 can effectively measure.

[0054] Finally, it should be noted that: the above-listed embodiments exist only as one or more specific forms of the technical solution of the present invention. Their purpose is to clearly elaborate the concept, principle and application method of the present invention through specific examples, rather than intending to limit the protection scope of the present invention to these specific embodiments. In fact, the real value of the present invention lies in the proposed technical idea and innovation point, rather than its form of expression or implementation means.

[0055] For those of ordinary skill in the art, after thoroughly reading and understanding the technical solution of the present invention, they are fully capable of making various forms of changes, modifications, or equivalent replacements to the specific implementation of the invention based on their own professional knowledge and skills. These changes may include, but are not limited to: adjusting the value range of technical parameters, optimizing the algorithm process to improve efficiency, replacing some technical components to achieve better compatibility or reduce costs, etc. As long as the changed technical solution still substantially maintains the technical features required to be protected by the original invention, that is, still can achieve the core functions and effects of the present invention, then these changes should be regarded as falling within the protection scope of the claims pending approval of the present invention.

[0056] In addition, with the continuous progress and development of technology, new technical means and methods are emerging continuously, which also provides a broad space for the further improvement and perfection of the present invention. Therefore, the protection scope of the present invention should also include those reasonably foreseeable improvements and expansions based on the existing technology. As long as these improvements and expansions do not deviate from the basic principles and core concepts of the present invention, they should be regarded as equivalents of the present invention and are equally protected by the patent right.

Claims

1. A ground protection circuit for overvoltage monitoring, characterized in that: It includes an equivalent circuit for monitoring overvoltage at the end screen of the bushing and a protection circuit. The equivalent circuit for monitoring overvoltage at the end screen of the bushing is formed by connecting a bushing equivalent capacitor C1 in series with a voltage-dividing capacitor C2 and then grounding. The protection circuit is formed by connecting a resonance damping device S and an inductor L in series, and the protection circuit is connected in parallel with the voltage-dividing capacitor C2.

2. A ground protection circuit for overvoltage monitoring according to claim 1, characterized in that: It also includes an overvoltage protection unit, which is connected in parallel to the voltage dividing capacitor C2.

3. A ground protection circuit for overvoltage monitoring according to claim 2, characterized in that: The overvoltage protection unit adopts a discharge gap structure to suppress extreme overvoltage impact and achieve component protection.

4. A ground protection circuit for overvoltage monitoring according to claim 1, characterized in that: The resonance damping device is a kind of active damper or notch filter, which is used to suppress the resonance point of the inductor L and the voltage-dividing capacitor C2.

5. A ground protection circuit for overvoltage monitoring according to claim 1, characterized in that: The inductance value range of the inductor L is 1μH~100mH.

6. A grounding protection method for overvoltage monitoring, characterized in that: The bushing end screen to be monitored adopts the grounding protection circuit for overvoltage monitoring as described in any one of claims 1 to 5, based on the fact that the inductive reactance is proportional to the voltage frequency and the capacitive reactance is inversely proportional to the voltage frequency. When the voltage frequency is 50 Hz, the inductive reactance of the inductor L is lower than the capacitive reactance of the voltage-dividing capacitor C2, and the parallel circuit of the inductor L and the voltage-dividing capacitor C2 is inductive. Based on the voltage borne by the voltage-dividing capacitor C2, the potential of the bushing end screen is equivalent to an effective grounding state; When the voltage frequency is the overvoltage high frequency, the inductive reactance of the inductor L is higher than the capacitive reactance of the voltage-dividing capacitor C2, and the parallel circuit of the inductor L and the voltage-dividing capacitor C2 is capacitive. Based on the voltage borne by the voltage-dividing capacitor C2, the voltage-dividing measurement is performed to calculate the real high-voltage side overvoltage waveform of the bushing equivalent capacitor C1.

7. A method for monitoring overvoltage at the end screen of a bushing, characterized in that: The bushing end screen to be monitored adopts the grounding protection circuit for overvoltage monitoring as claimed in any one of claims 1 to 5, comprising the following steps: Step 1: When the power system operates at a voltage frequency of 50 Hz, the bushing end screen potential is equivalent to an effective grounding state, and the bushing end screen is in a grounding protection state. The real high-voltage side standard power frequency voltage waveform of the bushing equivalent capacitance C1 is measured by a known voltage transformer in the substation of the power system; Step 2: Calculate the frequency response function based on the parameters of the ground protection circuit for overvoltage monitoring , the parameters include the inductance value of the inductor L, the capacitance value of the voltage divider capacitor C2 and the capacitance value of the bushing equivalent capacitor C1; Step 3: When the power system operates at an overvoltage high frequency, the overvoltage measurement signal is obtained by voltage division measurement based on the voltage borne by the voltage divider capacitor C2. y ( t ), for overvoltage measurement signal y ( t ) to perform Fourier transform and obtain the overvoltage measurement signal y ( t ) frequency domain expression; based on the overvoltage measurement signal y ( t )'s frequency domain expression and frequency response function The relationship between the two is then transformed by inverse Fourier transform to obtain the real high-voltage side overvoltage waveform of the bushing equivalent capacitance C1; Step 4: Combine the real high-voltage side standard power frequency voltage waveform and the real high-voltage side overvoltage waveform of the bushing equivalent capacitor C1 to obtain a complete bushing end screen voltage measurement waveform.

8. The method for monitoring overvoltage of bushing end shield according to claim 7, characterized in that: The frequency domain expression of the overvoltage measurement signal is as follows: in, F is the Fourier transform function, is the frequency; Overvoltage measurement signal y ( t )'s frequency domain expression and frequency response function The specific relationship is: in, is the frequency domain expression of the real high-voltage side overvoltage signal of the bushing equivalent capacitance C1; Then, the real high-voltage side overvoltage signal of the bushing equivalent capacitance C1 is x ( t ) specifically: in, is the inverse Fourier transform function.

9. An electronic device, characterized in that: It comprises a ground protection circuit for overvoltage monitoring as described in any one of claims 1 to 5.

10. A system, characterized in that: An electronic device as claimed in claim 9 is included for implementing overvoltage detection.

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