Multi-stage discharge gap device, insulation coordination setting method and overvoltage protection system

Abstract

The application provides a multi-stage discharge gap device, an insulation coordination setting method and an overvoltage protection system, relates to the technical field of overvoltage protection of a power system, and comprises a first electrode and a second electrode which are coaxially arranged oppositely, a suspended intermediate electrode assembly which is arranged between the first electrode and the second electrode and separates the gap into multiple sub-gaps, the suspended intermediate electrode assembly is configured to adjust a position in a transverse direction to change the spacing ratio of the multiple sub-gaps, and to adjust an equivalent thickness to change the length of a clear air insulation channel. The application realizes decoupling control of power frequency and lightning impulse discharge characteristics through double adjustment dimensions, solves the problem of serious coupling of discharge characteristics of a traditional gap, and improves the insulation coordination precision and protection reliability under complex working conditions.

Description

Technical Field

[0001] This application relates to the field of power system overvoltage protection technology, specifically to a multi-stage discharge gap device, an insulation coordination setting method, and an overvoltage protection system. Background Technology

[0002] In power systems, transformer neutral points are often partially grounded to limit single-phase short-circuit current and meet operational requirements. When the system experiences lightning strikes, single-phase grounding faults, or non-full-phase operation, overvoltages are prone to occur at the neutral point. Protection is typically achieved using a parallel structure of metal oxide surge arresters and protective gaps. Ideally, the surge arrester responds to transient overvoltages, while the protective gap breaks down under sustained power frequency overvoltages to protect the arrester from thermal collapse. However, the discharge characteristics of traditional single-stage rod-to-rod gaps are only related to the gap distance, leading to a high coupling between power frequency breakdown voltage and lightning impulse breakdown voltage. Especially in scenarios with high-proportion distributed photovoltaic and other renewable energy sources, islanded operation and reverse feedforward complicate the neutral point overvoltage waveform. Traditional gaps struggle to simultaneously prevent maloperation under lightning impulses and ensure reliable breakdown under power frequency overvoltages, exhibiting significant shortcomings in protection performance that urgently require improvement. Summary of the Invention

[0003] To address the problem that existing technologies suffer from severe coupling between the power frequency and lightning impulse discharge characteristics of the protection gap, making it difficult to adapt to complex overvoltage conditions, this application proposes a multi-stage discharge gap device, an insulation coordination setting method, and an overvoltage protection system to achieve decoupled control and precise setting of discharge characteristics.

[0004] To achieve the above objectives, this application adopts the following technical solution: A multi-stage discharge gap device includes a first electrode and a second electrode, coaxially arranged opposite each other; a suspended intermediate electrode assembly is disposed between the first electrode and the second electrode, dividing the gap between the first electrode and the second electrode into multi-stage sub-gap; wherein the suspended intermediate electrode assembly is configured to adjust its position laterally to change the spacing ratio of the multi-stage sub-gap, and to adjust its equivalent thickness to change the length of the clean air insulation channel.

[0005] The above scheme introduces a suspended intermediate electrode assembly with dual adjustment dimensions between the two poles, uses position adjustment to change the electric field distribution and sub-gap ratio, and uses equivalent thickness adjustment to change the net air insulation path, thereby achieving decoupled control of power frequency discharge characteristics and lightning impulse discharge characteristics in terms of physical structure.

[0006] Preferably, the suspended intermediate electrode assembly includes at least two parallel conductive plates; the suspended intermediate electrode assembly adjusts the equivalent thickness by changing the inner spacing between the conductive plates.

[0007] Preferably, the conductive plates are connected by conductive supports; the edges of the conductive plates are provided with chamfered structures to eliminate the tip discharge effect.

[0008] Preferably, the assembly also includes an electrode adjustment mechanism; the first electrode, the second electrode, and the suspended intermediate electrode assembly are all connected to the electrode adjustment mechanism to achieve lateral displacement adjustment.

[0009] Preferably, both the first electrode and the second electrode are telescopic adjustment structures; the discharge ends of the first electrode and the second electrode opposite to each other are hemispherical.

[0010] Furthermore, this application also provides an insulation coordination adjustment method for a multi-stage discharge gap, applied to a multi-stage discharge gap device. The multi-stage discharge gap device includes a first electrode and a second electrode arranged coaxially opposite each other, and a suspended intermediate electrode assembly disposed between the two. The method includes: acquiring the measured lightning impulse discharge voltage and the measured power frequency discharge voltage of the multi-stage discharge gap device; in response to a mismatch between the measured lightning impulse discharge voltage and a target lightning impulse discharge voltage, adjusting the lateral position of the suspended intermediate electrode assembly to change the measured lightning impulse discharge voltage; in response to the measured power frequency discharge voltage deviating from the target power frequency discharge voltage due to adjusting the lateral position of the suspended intermediate electrode assembly, synchronously adjusting the equivalent thickness of the suspended intermediate electrode assembly to compensate for the deviation of the measured power frequency discharge voltage.

[0011] The above scheme establishes a decoupled tuning logic based on a multi-dimensional adjustment structure. By prioritizing the adjustment of lightning impulse characteristics through lateral position and using equivalent thickness to synchronously compensate for the associated offset of power frequency characteristics, strong coupling interference between parameters is eliminated, significantly improving tuning efficiency and accuracy.

[0012] Preferably, adjusting the lateral position of the suspended intermediate electrode assembly and simultaneously adjusting the equivalent thickness of the suspended intermediate electrode assembly includes: when the suspended intermediate electrode assembly is laterally shifted towards the second electrode to increase the measured lightning impulse discharge voltage, the equivalent thickness is simultaneously reduced to compensate for the consequent decrease in the measured power frequency discharge voltage; when the suspended intermediate electrode assembly is laterally shifted towards the first electrode to decrease the measured lightning impulse discharge voltage, the equivalent thickness is simultaneously increased to compensate for the consequent increase in the measured power frequency discharge voltage.

[0013] Preferably, the suspended intermediate electrode assembly includes at least two parallel conductive plates, and the equivalent thickness is adjusted by changing the inner spacing between the conductive plates; the lateral offset is finely adjusted in a stepwise manner with a preset step size to match the measured lightning impulse discharge voltage with the target lightning impulse discharge voltage; the conditions for successful matching include: the deviation between the measured power frequency discharge voltage and the target power frequency discharge voltage does not exceed a first preset threshold, and the deviation between the measured lightning impulse discharge voltage and the target lightning impulse discharge voltage does not exceed a second preset threshold.

[0014] In addition, this application also provides an overvoltage protection system, including a surge arrester branch and a multi-stage discharge gap branch, wherein the surge arrester branch and the multi-stage discharge gap branch are connected in parallel; the multi-stage discharge gap branch includes the multi-stage discharge gap device as described in the above scheme.

[0015] Preferably, the surge arrester branch includes a metal oxide surge arrester; the ratio of the measured 50% discharge voltage of the multi-stage discharge gap branch to the residual voltage of the metal oxide surge arrester under the nominal discharge current is not less than a first preset ratio; the ratio of the measured power frequency breakdown voltage of the multi-stage discharge gap branch to the rated voltage of the metal oxide surge arrester is not greater than a second preset ratio.

[0016] Beneficial effects: The multi-stage discharge gap device provided in this application breaks through the limitation of traditional single-stage gap discharge characteristics relying solely on inter-electrode distance by setting a suspended intermediate electrode assembly between the coaxially opposite first and second electrodes and configuring this assembly to have both lateral position adjustment and equivalent thickness adjustment capabilities. The lateral position adjustment can change the spacing ratio and electric field distortion of the multi-stage sub-gap, mainly affecting the lightning impulse discharge voltage; while the equivalent thickness adjustment can change the effective length of the clean air insulation channel, mainly affecting the power frequency breakdown voltage. This structural design decouples the two discharge characteristics in terms of adjustment, solving the technical problem in the prior art where power frequency and lightning impulse breakdown voltages are highly coupled and cannot simultaneously meet the insulation coordination requirements under complex operating conditions.

[0017] The insulation coordination setting method provided in this application establishes a linkage setting logic based on the aforementioned decoupling structure, which adjusts the position for lightning impulse discharge voltage and compensates for power frequency discharge voltage with thickness. During the setting process, when adjusting the lateral position to correct the lightning impulse discharge voltage, if the power frequency discharge voltage deviates from the target value, the equivalent thickness is simultaneously adjusted for reverse compensation. This method effectively eliminates parameter coupling interference between mechanical adjustment dimensions, avoids the inefficiency of repeated iterations and neglecting certain aspects in traditional debugging, and can quickly and accurately enable the device to achieve the predetermined insulation coordination target. It is particularly suitable for scenarios with complex overvoltage characteristics, such as distributed photovoltaic grid connection.

[0018] The overvoltage protection system provided in this application constructs a clearly defined overvoltage protection system by connecting the aforementioned multi-stage discharge gap device in parallel with the surge arrester branch. The multi-stage discharge gap device, with its excellent discharge characteristics after decoupling, can reliably refuse to operate under lightning impulses to ensure priority current discharge from the surge arrester. Simultaneously, it prioritizes breakdown under continuous power frequency overvoltages to protect the surge arrester from thermal collapse, significantly improving the system's operational reliability and equipment safety in environments with a high proportion of renewable energy grid connection. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the multi-stage discharge gap device according to an embodiment of this application; Figure 2 This is a flowchart of the insulation coordination setting method according to an embodiment of this application.

[0020] Among them, 1-metal base, 2-surge arrester branch, 3-metal conductor, 4-first electrode, 5-adjustment knob No. 1, 6-insulating support column, 7-floating intermediate electrode assembly, 8-adjustment knob No. 2, 9-grounding column, 10-second electrode. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application 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 this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0023] Example 1 like Figure 1 As shown, this embodiment provides a multi-stage discharge gap device, which constitutes the core discharge unit of an overvoltage protection system. The multi-stage discharge gap device includes a first electrode 4, a second electrode 10, and a suspended intermediate electrode assembly 7.

[0024] Specifically, the first electrode 4 and the second electrode 10 are coaxially opposite each other. This coaxial arrangement ensures the axial symmetry of the electric field distribution between the electrodes, providing a geometric basis for stable control of the discharge characteristics. In practical applications, the first electrode 4 is usually used as the high-voltage side connection terminal, and the second electrode 10 is used as the grounding side or low-voltage side connection terminal. The axial distance between them constitutes the total gap distance of the device. It should be understood that although... Figure 1 The image shows a horizontal coaxial arrangement, but in other embodiments, depending on the installation space or insulation requirements, a vertical arrangement or other angled coaxial arrangement can also be used, as long as the discharge path between the two electrodes extends along the axis.

[0025] A suspended intermediate electrode assembly 7 is disposed between the first electrode 4 and the second electrode 10, dividing the gap between the first electrode 4 and the second electrode 10 into multi-level sub-gap. The term "suspended" here specifically refers to the assembly being electrically insulated and supported, meaning it is not directly connected to the first electrode 4, the second electrode 10, or ground potential. Instead, it is fixed to a specific spatial position by an insulating support column 6, allowing its potential to be determined by the electric field coupling induction between the two electrodes. This electrically suspended state makes the intermediate electrode an independent equipotential body, thereby physically dividing the originally single air gap into at least two series-connected sub-gap, altering the original electric field distribution.

[0026] In this embodiment, the suspended intermediate electrode assembly 7 is configured with dual adjustment dimensions to achieve decoupled control of discharge characteristics. One adjustment dimension is to change the spacing ratio of the multi-stage sub-gap by adjusting the lateral position. Specifically, lateral adjustment refers to the displacement of the suspended intermediate electrode assembly 7 along the line connecting the first electrode 4 and the second electrode 10. When the suspended intermediate electrode assembly 7 moves closer to one side electrode, the distance between the sub-gap on that side decreases, and the distance between the sub-gap on the other side increases, thereby changing the voltage division ratio and electric field distortion of each stage of the sub-gap. Since the lightning impulse discharge voltage is extremely sensitive to the electric field non-uniformity and the sub-gap ratio, this lateral position adjustment is mainly used to adjust the lightning impulse discharge characteristics of the device. For example, by adjusting the suspended intermediate electrode assembly 7 to be biased towards the grounding side or the high-voltage side, the breakdown threshold under negative polarity lightning impulse can be significantly changed, rather than relying solely on the linear change of the total distance as in a traditional single-stage gap.

[0027] Another adjustment dimension is adjusting the equivalent thickness to change the length of the net air insulation path. It should be noted that the equivalent thickness in this application is an electrical functional parameter, not simply a mechanical geometric dimension. It refers to the effective length occupied axially by the suspended intermediate electrode assembly 7, resulting in a reduction in the air insulation path. When the equivalent thickness increases, the length of the net air gap between the first electrode 4 and the second electrode 10, which allows for electron avalanche development, shortens accordingly; conversely, when the equivalent thickness decreases, the length of the net air insulation path increases. Since the power frequency breakdown voltage mainly depends on the absolute insulation distance of the air gap and is relatively less affected by electric field distortion, the adjustment of this equivalent thickness is mainly used to compensate for or set the power frequency discharge voltage of the device. Through this structural design, this embodiment allows the two discharge characteristics to be adjusted independently to a certain extent, solving the problem of setting difficulties caused by the strong coupling of traditional gap parameters. It should be understood that the specific mechanical form for achieving equivalent thickness adjustment is not limited to a single structure; any structure that can change the axial electrical occupancy length through its own deformation, combined displacement, or internal spacing adjustment falls within the protection scope of this application.

[0028] Example 2 Based on Embodiment 1, this embodiment further details the specific structure and multi-dimensional adjustment mechanism of the suspended intermediate electrode assembly 7. As a preferred embodiment, the suspended intermediate electrode assembly 7 includes at least two parallel conductive plates. Specifically, as... Figure 1 As shown, the conductive plates are arranged perpendicular to the axes of the first electrode 4 and the second electrode 10, and all conductive plates maintain electrical continuity. This parallel plate structure constitutes an equipotential body with a certain axial thickness, the physical thickness of which corresponds to the equivalent thickness mentioned in Embodiment 1. In actual manufacturing and assembly, although the figure shows the form of two conductive plates, those skilled in the art should understand that, depending on the insulation matching requirements, three or more conductive plates can also be stacked. As long as the function of adjusting the overall equivalent thickness by changing the distance between the plates can be achieved, it falls within the protection scope of this application.

[0029] The suspended intermediate electrode assembly 7 adjusts its equivalent thickness by changing the inner spacing between the conductive plates. Specifically, the conductive plates are not rigidly fixed but assembled using adjustable connectors, allowing the axial distance between adjacent conductive plates to be adjusted continuously or in stages. When the inner spacing between the conductive plates increases, the suspended intermediate electrode assembly 7 occupies more physical space in the axial direction, resulting in a corresponding shortening of the net air insulation channel length between the first electrode 4 and the second electrode 10, thereby reducing the power frequency breakdown voltage. Conversely, decreasing the inner spacing increases the net air insulation channel length, increasing the power frequency breakdown voltage. This equivalent thickness adjustment mechanism based on mechanical spacing adjustment provides a reliable hardware foundation for fine-tuning the power frequency discharge characteristics, and the adjustment process is intuitive and visible, facilitating operation and verification by on-site maintenance personnel.

[0030] To ensure structural stability and electrical performance consistency, the conductive plates are connected by conductive supports. These supports not only provide mechanical support and positioning but also ensure that the conductive plates are at the same potential, preventing internal partial discharges caused by poor contact or inconsistent potential. Simultaneously, the edges of the conductive plates are chamfered to eliminate the effect of sharp discharges. Specifically, this chamfer can be a rounded chamfer or a beveled chamfer, with its radius of curvature optimized. From the perspective of electric field control, the edges of parallel conductive plates are high-incidence areas of electric field concentration. If sharp edges exist, they are highly susceptible to initiating leader discharges under lightning strikes or power frequency voltage, resulting in actual breakdown voltages lower than theoretical values ​​and increased dispersion. By setting chamfered structures, the edge electric field distribution can be effectively smoothed, suppressing premature initiation of electron avalanches, thereby significantly reducing the dispersion coefficient of the discharge voltage and improving the accuracy and reliability of the protection device's operation.

[0031] The multi-stage discharge gap device in this embodiment also includes an electrode adjustment mechanism. The first electrode 4, the second electrode 10, and the suspended intermediate electrode assembly 7 are all connected to the electrode adjustment mechanism to achieve lateral displacement adjustment. Figure 1 As shown, the electrode adjustment mechanism specifically includes a first adjustment knob 5 and a second adjustment knob 8. The first adjustment knob 5 is connected to both the first electrode 4 and the second electrode 10, driving them to independently extend and retract along the axial direction. The second adjustment knob 8 is connected to the suspended intermediate electrode assembly 7, driving it to move laterally between the first electrode 4 and the second electrode 10. This three-terminal independent adjustment design completely decouples the adjustment of the sub-gap spacing ratio and the equivalent thickness mechanically. Operators can fine-tune the position or thickness of the intermediate electrode individually without changing the total gap distance, perfectly meeting the requirements for parameter decoupling adjustment in insulation fit tuning methods.

[0032] Furthermore, both the first electrode 4 and the second electrode 10 are telescopic adjustment structures. This telescopic structure allows for dynamic adjustment of the total gap distance based on on-site insulation coordination test results without disassembling the device, greatly improving the equipment's on-site adaptability. In addition, the opposing discharge ends of the first electrode 4 and the second electrode 10 are hemispherical. Compared to traditional rod-shaped electrodes, the hemispherical ends can form a slightly non-uniform electric field, improving the electric field distribution characteristics of the gap. In the multi-stage gap structure, the hemispherical ends cooperate with the plate edge of the suspended intermediate electrode assembly 7 to construct a more stable composite electric field model, ensuring both the withstand strength under lightning strikes and reliable breakdown under power frequency overvoltages. This effectively solves the technical problem of the traditional rod-to-rod gap having a single discharge characteristic and difficulty in simultaneously meeting multiple protection requirements.

[0033] Example 3 like Figure 2 As shown, this embodiment provides an insulation coordination setting method for a multi-stage discharge gap. This method is applied to the multi-stage discharge gap device in the aforementioned embodiment and aims to achieve precise setting of discharge characteristics through decoupling control logic. The multi-stage discharge gap device includes a first electrode 4 and a second electrode 10 arranged coaxially opposite each other, and a suspended intermediate electrode assembly 7 disposed between the two.

[0034] Specifically, the insulation coordination setting method first includes S1: acquiring the measured lightning impulse discharge voltage and measured power frequency discharge voltage of the multi-stage discharge gap device. This step constitutes the physical data basis of the setting method. It is important to emphasize that the measured values ​​here refer to the actual breakdown data obtained after conducting actual withstand voltage tests on the device, rather than values ​​obtained solely from theoretical calculations or simulations. Since the discharge characteristics of the multi-stage discharge gap are affected by various nonlinear factors such as electrode surface condition, ambient humidity, and assembly tolerances, only feedback adjustment based on measured data can ensure the engineering reliability of the setting results. During the acquisition process, power frequency withstand voltage tests and lightning impulse withstand voltage tests are usually performed separately, and the actual breakdown voltage value of the gap under the current mechanical structure parameters is recorded as the input reference for subsequent adjustment logic.

[0035] Based on this, the method further includes S2: in response to a mismatch between the measured lightning impulse discharge voltage and the target lightning impulse discharge voltage, adjusting the lateral position of the suspended intermediate electrode assembly 7 to change the measured lightning impulse discharge voltage. Specifically, this is the main tuning step in the decoupling tuning logic of this application. Since the lightning impulse discharge voltage is extremely sensitive to the non-uniformity of the electric field distribution and the spacing ratio of the inter-electrode gaps, and the lateral position of the suspended intermediate electrode assembly 7 directly determines the length ratio of the high-voltage side inter-electrode gap to the ground side inter-electrode gap, it significantly alters the degree of distortion of the inter-electrode electric field. Therefore, when the measured lightning impulse discharge voltage deviates from the target value, it is preferentially corrected by laterally moving the suspended intermediate electrode assembly 7. For example, if the measured value is too low, the suspended intermediate electrode assembly 7 can be shifted in a specific direction to enhance the electric field distortion or adjust the voltage division, thereby improving the lightning impulse withstand level; conversely, the same applies. This adjustment method utilizes the dominant influence of position parameters on lightning impulse characteristics, enabling rapid convergence of the lightning impulse discharge voltage to the target range.

[0036] Furthermore, the method also includes S3: in response to the deviation of the measured power frequency discharge voltage from the target power frequency discharge voltage caused by adjusting the lateral position of the suspended intermediate electrode assembly 7, the equivalent thickness of the suspended intermediate electrode assembly 7 is simultaneously adjusted to compensate for the deviation of the measured power frequency discharge voltage. This is the key compensation step for achieving parameter decoupling in this application. From a physical mechanism perspective, although the lateral position adjustment is mainly aimed at lightning impulse characteristics, it inevitably changes the length of the net air insulation channel or the local electric field strength between the two electrodes, thereby causing the power frequency discharge voltage to drift. If the lateral position is then adjusted in the opposite direction to correct the power frequency voltage, it will destroy the already adjusted lightning impulse index, falling into a vicious cycle of repeated iterations. Therefore, this embodiment introduces the equivalent thickness as an independent compensation dimension. When the lateral position adjustment causes the power frequency voltage to deviate, by simultaneously changing the equivalent thickness of the suspended intermediate electrode assembly 7, the effective length occupied by the metal body in the axial direction can be directly increased or decreased, thereby correcting the total length of the net air insulation channel in the opposite direction. Since the power frequency breakdown voltage mainly depends on the absolute insulation distance of the air gap, it responds significantly to changes in the equivalent thickness, but is relatively less sensitive to electric field distortion. Therefore, this compensation operation can pull the power frequency discharge voltage back to the target range without significantly interfering with the lightning impulse discharge voltage.

[0037] It should be understood that the above logic is not simply a numerical calculation rule, but a linkage adjustment strategy based on the specific physical structure of the multi-stage discharge gap device. It transforms the abstract insulation coordination target into a specific mechanical action sequence, establishing a closed-loop control paradigm for position adjustment for lightning strikes and thickness compensation for power frequency. This decoupled control logic is not only applicable to standardized manual operations, but also provides a clear control algorithm basis for the development of automated tuning systems, effectively solving the technical problems of strong parameter coupling and low tuning efficiency in traditional multi-stage gap tuning.

[0038] Example 4 Based on Example 3, this example further details the specific correspondence between adjusting the lateral position of the suspended intermediate electrode assembly 7 and simultaneously adjusting its equivalent thickness in the insulation coordination tuning method. Specifically, this correspondence constitutes the core execution logic of the decoupling tuning strategy of this application, and its physical basis lies in the differential influence mechanism of lateral position and equivalent thickness on the two discharge characteristics. When the suspended intermediate electrode assembly 7 is laterally shifted towards the second electrode 10 to increase the measured lightning impulse discharge voltage, the equivalent thickness is simultaneously reduced to compensate for the associated decrease in the measured power frequency discharge voltage. From a microscopic mechanism perspective, when the suspended intermediate electrode assembly 7 moves closer to the second electrode 10, which serves as the grounding side, the distance between the grounding side sub-gap is shortened, resulting in a significant increase in the electric field non-uniformity in this region. Under the action of a negative polarity lightning impulse voltage, this electric field distortion can effectively suppress the conversion of electron avalanches into streamers, thereby significantly improving the lightning impulse tolerance level of the gap. However, this position adjustment often comes with side effects: the displacement of the metal electrode towards the grounding side may lead to a redistribution of the local field strength in the effective insulation path between electrodes, or an unexpected drop in the power frequency breakdown voltage due to structural asymmetry. In this case, if the power frequency voltage is corrected solely by adjusting the lateral position, the already achieved lightning impulse voltage will inevitably be compromised. Therefore, this embodiment adopts a strategy of simultaneously reducing the equivalent thickness for compensation. For the suspended intermediate electrode assembly 7 composed of parallel conductive plates, reducing the equivalent thickness means reducing the inner spacing between the conductive plates. This mechanical action directly reduces the physical length occupied by the metal body in the axial direction, thereby increasing the total length of the net air insulation channel between the first electrode 4 and the second electrode 10 by an equal amount. Since the power frequency breakdown voltage mainly depends on the absolute insulation distance of the air gap, the extension of the net air channel can linearly improve the power frequency withstand capability, which precisely offsets the power frequency voltage drop caused by the position shift, while having little effect on the already increased lightning impulse voltage.

[0039] Conversely, when the suspended intermediate electrode assembly 7 is laterally shifted towards the first electrode 4 to reduce the measured lightning impulse discharge voltage, the equivalent thickness is simultaneously increased to compensate for the associated increase in the measured power frequency discharge voltage. Similarly, shifting towards the high-voltage side reduces the degree of electric field distortion on the grounding side, causing the lightning impulse discharge voltage to fall back to the target range; however, this operation may lead to an increase in the power frequency breakdown voltage due to improved overall electric field uniformity or increased effective insulation strength of the high-voltage side sub-gap. At this time, by increasing the spacing within the conductive plates to increase the equivalent thickness and shorten the length of the clean air insulation channel, the power frequency voltage can be accurately corrected downward to the target value without interfering with the tuning results of the lightning impulse characteristics. This clear directional correspondence transforms the complex multivariate coupling problem into an ordered superposition of two single-variable adjustments, enabling on-site commissioning personnel or automated control systems to quickly converge to the target parameters according to defined rules, completely eliminating the iterative dilemma of adjusting the lightning power frequency transformer and the power frequency lightning transformer in traditional multi-stage gap commissioning.

[0040] Furthermore, to ensure the operability and accuracy of the tuning process, this embodiment also standardizes and defines the fine-tuning step size and matching judgment criteria. The suspended intermediate electrode assembly 7 includes at least two parallel conductive plates. The equivalent thickness is adjusted by changing the inner distance between the conductive plates. The lateral offset is finely adjusted in a stepped manner with a preset step size to match the measured lightning impulse discharge voltage with the target lightning impulse discharge voltage. Specifically, stepped fine-tuning refers to avoiding the reading difficulties and repeatability errors caused by continuous stepless adjustment, and instead using a fixed mechanical displacement increment for operation. For example, in practical engineering applications, the preset step size for the lateral position can be set to 5 mm, and the adjustment step size for the equivalent thickness can be set to 2 mm or 5 mm. It should be understood that these values ​​are only illustrative examples and are not intended to limit this application. In devices with different voltage levels or different structural dimensions, the preset step size can be adaptively adjusted according to the thread lead, scale resolution, and sensitivity of the discharge characteristic curve of the adjustment mechanism. The advantage of using step-by-step fine-tuning is that it discretizes continuous physical adjustment into standardized operation units, which makes it easier to record the tuning trajectory, reproduce the debugging results, and provide a clear instruction reference for the step control of automated tuning equipment.

[0041] Based on this, the criteria for successful matching include: the deviation between the measured power frequency discharge voltage and the target power frequency discharge voltage does not exceed a first preset threshold, and the deviation between the measured lightning impulse discharge voltage and the target lightning impulse discharge voltage does not exceed a second preset threshold. Here, deviation refers to the degree of deviation of the measured value from the target value. As a preferred embodiment, the first preset threshold can be set within ±125% of the target power frequency discharge voltage, i.e., the measured value is not lower than 80% and not higher than 125% of the target value, or, based on the relative deviation limit defined by the specific insulation coordination safety margin, the second preset threshold can be set within ±15% of the target lightning impulse discharge voltage. It should be emphasized that the specific values ​​of these thresholds should be comprehensively determined based on the insulation coordination standards of the power system, the protection characteristics of the surge arrester, and the equipment safety margin; this application does not impose a unique limitation on this. When the measured data simultaneously falls within the above two threshold ranges, the insulation coordination setting is deemed complete. This dual threshold determination mechanism ensures that the protection device has sufficient tolerance margin to prevent maloperation under lightning strikes, while also ensuring reliable breakdown characteristics under power frequency overvoltages to fulfill its backup protection function. This achieves an optimal balance between safety and economy at the system level. Compared to traditional trial-and-error debugging methods relying on experience, the standardized step size and quantified determination conditions provided in this embodiment significantly improve the efficiency and consistency of the setting process, making it particularly suitable for complex scenarios with high requirements for protection coordination accuracy, such as distributed photovoltaic grid connection.

[0042] Example 5 like Figure 1 As shown, this embodiment provides an overvoltage protection system that integrates the multi-stage discharge gap device from the aforementioned embodiments into a complete protection architecture to achieve comprehensive protection of the neutral point of power equipment. This overvoltage protection system includes a surge arrester branch 2 and a multi-stage discharge gap branch, which are connected in parallel. Specifically, this parallel architecture is not a simple electrical connection, but a collaborative arrangement based on functional division. Physically, the surge arrester branch 2 and the multi-stage discharge gap branch are jointly installed on a metal base 1. Their high-voltage ends are electrically interconnected through a metal conductor 3 and connected to the neutral point of the protected equipment. The grounding ends are connected to the grounding grid via grounding posts 9 or directly. It should be understood that although... Figure 1 The diagram illustrates a horizontally parallel arrangement. However, in practical engineering applications, depending on the substation's spatial layout or insulation distance requirements, vertical stacking, triangular arrangement, or other compact installation methods can also be adopted, as long as the two branches are electrically connected in parallel and meet the safety clearance requirements. The multi-stage discharge gap branch includes the multi-stage discharge gap device described in any of the preceding embodiments. Its core lies in utilizing the dual adjustment dimensions of the suspended intermediate electrode assembly 7 to achieve decoupled control of discharge characteristics, thereby providing a hardware foundation for precise system-level coordination.

[0043] In this system, surge arrester branch 2 and multi-stage discharge gap branch perform distinct but complementary protection functions. Surge arrester branch 2 typically uses metal oxide surge arresters, which have excellent nonlinear volt-ampere characteristics. It is primarily responsible for rapidly responding to transient overvoltages such as lightning impulses, discharging lightning current within microseconds and clamping the neutral point potential at a safe level to prevent transformer insulation damage. The multi-stage discharge gap branch serves as a backup protection channel for power frequency overvoltages. When the system experiences continuous power frequency overvoltages due to single-phase grounding, incomplete phase operation, or distributed photovoltaic islanded power supply, if the voltage amplitude exceeds the long-term withstand capability of the surge arrester but has not yet reached the transformer insulation failure threshold, the multi-stage discharge gap should reliably break down and conduct, bypassing the power frequency overvoltage energy to ground, preventing the surge arrester from thermally collapsing due to prolonged exposure to high-amplitude power frequency voltages. This division of labor requires strict matching of the operating thresholds of the two protection units; there must be no protection dead zone or competing maloperation.

[0044] To ensure the reliable execution of the above-mentioned division of labor logic under complex operating conditions, this embodiment quantifies and limits the insulation coordination parameters of the system. Surge arrester branch 2 includes a metal oxide surge arrester; the ratio of the measured 50% discharge voltage of the multi-stage discharge gap branch to the residual voltage of the metal oxide surge arrester under the nominal discharge current is not less than a first preset ratio; the ratio of the measured power frequency breakdown voltage of the multi-stage discharge gap branch to the rated voltage of the metal oxide surge arrester is not greater than a second preset ratio. Specifically, the first preset ratio is set to not less than 1.15. This safety margin setting fully considers the statistical dispersion of the multi-stage gap discharge voltage and the possible positive deviation of the surge arrester residual voltage. If this ratio is too small, under the action of a lightning surge wave, the gap may break down prematurely before the arrester can fully operate, causing the gap to bear the lightning current surge that should be borne by the arrester, accelerating electrode ablation and even causing an explosion. Maintaining a matching factor of ≥1.15 ensures that under standard lightning impulse waveforms, the arrester always takes priority over the gap in discharging current, with the gap serving only as a redundant backup in extreme abnormal situations. The second preset ratio is set to no more than 0.95, a limit designed to ensure the thermal stability of the arrester. The rated voltage of a metal oxide surge arrester is the maximum effective value of the power frequency voltage that it can withstand for a short period of time without thermal runaway. If the power frequency breakdown voltage of the gap is higher than this value, when a continuous power frequency overvoltage occurs in the system, the surge arrester may enter a high energy consumption absorption state before the gap. The heat accumulated over a long period of time can easily lead to aging and failure of the valve plate or even explosion. Limiting the power frequency breakdown voltage of the gap to within 95% of the rated voltage of the surge arrester can ensure that the gap has broken down and established a low-resistance path before the power frequency overvoltage reaches the critical point that threatens the safety of the surge arrester, thereby effectively protecting the surge arrester from thermal damage.

[0045] Through the aforementioned quantified coordination parameters, this embodiment constructs an overvoltage protection system with clearly defined action selectivity. These parameters are not only the target boundaries of the system design but also the convergence criteria of the aforementioned insulation coordination setting method. During actual commissioning, operators use these two ratios as a guide, adjusting the lateral position and equivalent thickness of the suspended intermediate electrode assembly 7 to gradually bring the measured discharge characteristics closer to and within the safe range. Compared to traditional protection schemes that rely on experience-based estimation or fixed gap distances, the parameterized coordination strategy provided in this embodiment significantly improves the system's adaptability and reliability in complex scenarios such as distributed photovoltaic access and islanded operation, fundamentally solving the technical problem of both maloperation and failure to operate of the protection gap, and achieving precision and standardization of transformer neutral point overvoltage protection.

[0046] Example 6 This embodiment provides a specific implementation method for applying the aforementioned multi-stage discharge gap device and insulation coordination setting method to a transformer neutral point protection scenario adapted to distributed photovoltaic (PV) integration. In power systems with a high proportion of distributed PV integration, when the main power supply trips and forms an islanded operation, the PV inverter may continuously feed power back to the faulty line, causing the neutral point of the ungrounded transformer to generate overvoltages with large amplitude fluctuations and complex waveforms. This operating condition places extremely high demands on the insulation coordination accuracy of the protection device, requiring both prevention of maloperation under lightning strikes and ensuring reliable breakdown under power frequency overvoltages to protect the surge arrester. The complete setting process in this scenario is described in detail below with reference to the decoupling setting logic provided in the aforementioned embodiment.

[0047] First, benchmark data of the measured discharge characteristics of the multi-stage discharge gap device are obtained. Specifically, the multi-stage discharge gap branch installed on the metal base 1 is connected to the high-voltage test circuit. In the power frequency withstand voltage test, a uniform voltage increase method is used until the gap breaks down, and this is repeated at least 10 times, with the arithmetic mean taken as the measured power frequency breakdown voltage. In the lightning impulse withstand voltage test, a negative polarity standard lightning impulse voltage waveform is applied, and the voltage value corresponding to a 50% breakdown probability is statistically analyzed using the rise-fall method as the measured 50% lightning impulse discharge voltage. The key to this step is to obtain the actual electrical performance of the device under the current mechanical condition, rather than relying on theoretical calculations, because actual assembly tolerances, electrode surface conditions, and environmental factors will all have nonlinear effects on the discharge characteristics.

[0048] Subsequently, a preliminary verification of the insulation coordination relationship is performed. Based on the system-level coordination principle determined in Example 5 above, it is verified whether the ratio of the measured 50% discharge voltage of the lightning impulse to the residual voltage value under the nominal discharge current of the metal oxide surge arrester is not less than 1.15, and whether the ratio of the measured power frequency breakdown voltage to the rated voltage of the surge arrester is not greater than 0.95. If the initial state does not meet the above conditions, a fine-tuning strategy is initiated. Thanks to the fact that the suspended intermediate electrode assembly 7 has dual independent adjustment dimensions of lateral position and equivalent thickness, this embodiment can effectively solve the problem of repeated iterations caused by strong parameter coupling in traditional gap debugging.

[0049] The following example of a typical fine-tuning operation demonstrates the actual execution process of the decoupled setting logic. Assume that during a certain setting, the measured 50% lightning impulse discharge voltage is lower than the target value, while the measured power frequency breakdown voltage, although within the acceptable range, is close to the upper limit. According to the compensation direction correspondence described in Example 4 above, the operator first adjusts the second adjustment knob 8, laterally shifting the suspended intermediate electrode assembly 7 5mm towards the second electrode 10. From a physical mechanism perspective, this lateral displacement shortens the grounding side gap distance, enhancing the electric field non-uniformity in this area, thereby significantly improving the negative polarity lightning impulse withstand level. Upon retesting, the lightning impulse discharge voltage successfully rises to the target range.

[0050] However, the aforementioned lateral offset operation inevitably alters the inter-electrode electric field distribution and the clear air insulation path, resulting in a consequent decrease in the measured power frequency breakdown voltage during retesting, deviating from the target power frequency discharge voltage. While correcting the power frequency voltage by adjusting the lateral position at this point would damage the already achieved lightning impulse discharge index, this embodiment employs a compensation strategy of synchronously adjusting the equivalent thickness: keeping the lateral position of the suspended intermediate electrode assembly 7 unchanged, and adjusting the conductive support to reduce the inner distance between the two parallel conductive plates by 2mm. This operation reduces the equivalent thickness of the suspended intermediate electrode assembly 7, directly increasing the length of the clear air insulation channel between the first electrode 4 and the second electrode 10. Since the power frequency breakdown voltage primarily depends on the absolute insulation distance of the air gap, the extension of the clear air channel causes the power frequency breakdown voltage to linearly recover to the target range, while having minimal impact on the already increased lightning impulse discharge voltage. Through coordinated adjustment, only one composite operation is needed to simultaneously bring both key indicators to the acceptable range.

[0051] After completing the above fine-tuning, a successful matching is determined. The determination criteria include: the deviation between the measured power frequency discharge voltage and the target power frequency discharge voltage does not exceed 125%, and the deviation between the measured 50% lightning impulse discharge voltage and the target 50% lightning impulse discharge voltage does not exceed 15%. Furthermore, it must be confirmed that the lightning impulse matching coefficient is not less than 1.15, the power frequency matching ratio is not greater than 0.95, and the discharge voltage dispersion coefficient meets preset requirements (e.g., power frequency dispersion coefficient ≤ 3%, lightning impulse dispersion coefficient ≤ 5%). When all conditions are met, the tuning is considered complete. Compared to traditional single-stage gaps or fixed-structure multi-stage gaps, which typically require dozens of trials to achieve the target, the decoupling tuning method provided in this application usually completes the tuning in no more than 5 iterations in practical applications, significantly improving on-site operational efficiency.

[0052] Finally, the parameters were solidified and recorded. After confirming successful matching, the No. 1 adjustment knob 5, the No. 2 adjustment knob 8, and all positioning locking plates were locked to ensure that the structural parameters of the device would not drift under long-term operational vibration. Simultaneously, four sets of key values ​​were fully recorded: the extension distance of the first electrode 4, the extension distance of the second electrode 10, the lateral position of the suspended intermediate electrode assembly 7, and the spacing within the conductive plates, forming a dedicated gap setting parameter file for this substation. This file not only provides a precise basis for subsequent equipment maintenance, disassembly, and reassembly, but also accumulates standardized data support for the protection configuration of similar distributed photovoltaic grid-connected stations.

[0053] It should be understood that the above-described setting process is merely illustrative and not the only limitation on the application scenarios of this application. In systems with different voltage levels, different photovoltaic penetration rates, or different transformer neutral grounding methods, the specific target voltage value, adjustment step size, and coordination coefficient threshold can be adaptively adjusted according to actual insulation coordination requirements. As long as the decoupled setting logic based on the dual adjustment dimensions of the suspended intermediate electrode component 7 is adopted, it falls within the protection scope of this application. The application verification of this embodiment fully demonstrates the effectiveness and engineering practicality of the aforementioned multi-stage discharge gap device and setting method in solving the complex overvoltage protection problem of new energy grid connection.

[0054] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A multi-stage discharge gap device, characterized in that, include: The first and second electrodes are arranged coaxially opposite each other. A suspended intermediate electrode assembly is disposed between the first electrode and the second electrode, dividing the gap between the first electrode and the second electrode into multi-level sub-gap; The suspended intermediate electrode assembly is configured to adjust its position laterally to change the spacing ratio of the multi-level sub-gap, and to adjust its equivalent thickness to change the length of the clean air insulation channel.

2. The multi-stage discharge gap device according to claim 1, characterized in that, The suspended intermediate electrode assembly includes at least two parallel conductive plates. The suspended intermediate electrode assembly adjusts the equivalent thickness by changing the inner spacing between the conductive plates.

3. The multi-stage discharge gap device according to claim 2, characterized in that, The conductive plates are connected by conductive support members; The conductive plate has a chamfered edge to eliminate the tip discharge effect.

4. The multi-stage discharge gap device according to claim 1, characterized in that, It also includes an electrode adjustment mechanism; The first electrode, the second electrode, and the suspended intermediate electrode assembly are all connected to the electrode adjustment mechanism to achieve lateral displacement adjustment through the electrode adjustment mechanism.

5. The multi-stage discharge gap device according to claim 4, characterized in that, Both the first electrode and the second electrode are telescopic adjustment structures; The discharge ends of the first electrode and the second electrode are hemispherical.

6. A method for adjusting the insulation coordination of a multi-stage discharge gap, applied to a multi-stage discharge gap device, the multi-stage discharge gap device comprising a first electrode and a second electrode arranged coaxially opposite each other, and a suspended intermediate electrode assembly disposed between the two, characterized in that... include: Obtain the measured lightning impulse discharge voltage and the measured power frequency discharge voltage of the multi-stage discharge gap device; In response to the mismatch between the measured lightning impulse discharge voltage and the target lightning impulse discharge voltage, the lateral position of the suspended intermediate electrode assembly is adjusted to change the measured lightning impulse discharge voltage. In response to the deviation of the measured power frequency discharge voltage from the target power frequency discharge voltage caused by adjusting the lateral position of the suspended intermediate electrode assembly, the equivalent thickness of the suspended intermediate electrode assembly is simultaneously adjusted to compensate for the deviation of the measured power frequency discharge voltage.

7. The insulation coordination setting method for multi-stage discharge gaps according to claim 6, characterized in that, The adjustment of the lateral position of the suspended intermediate electrode assembly and the synchronous adjustment of the equivalent thickness of the suspended intermediate electrode assembly include: When the suspended intermediate electrode assembly is laterally offset toward the second electrode to increase the measured lightning impulse discharge voltage, the equivalent thickness is simultaneously reduced to compensate for the consequent decrease in the measured power frequency discharge voltage. When the suspended intermediate electrode assembly is laterally offset toward the first electrode to reduce the measured lightning impulse discharge voltage, the equivalent thickness is simultaneously increased to compensate for the associated increase in the measured power frequency discharge voltage.

8. The insulation coordination setting method for multi-stage discharge gaps according to claim 7, characterized in that, The suspended intermediate electrode assembly includes at least two parallel conductive plates, and the adjustment of the equivalent thickness is achieved by changing the inner spacing between the conductive plates. The lateral offset is finely adjusted in steps with a preset step size to match the measured lightning impulse discharge voltage with the target lightning impulse discharge voltage. The conditions for successful matching include: the deviation between the measured power frequency discharge voltage and the target power frequency discharge voltage does not exceed a first preset threshold, and the deviation between the measured lightning impulse discharge voltage and the target lightning impulse discharge voltage does not exceed a second preset threshold.

9. An overvoltage protection system, characterized in that, It includes a surge arrester branch and a multi-stage discharge gap branch, wherein the surge arrester branch and the multi-stage discharge gap branch are connected in parallel; The multi-stage discharge gap branch includes the multi-stage discharge gap device as described in any one of claims 1 to 5.

10. The overvoltage protection system according to claim 9, characterized in that, The surge arrester branch includes a metal oxide surge arrester; The ratio of the measured 50% discharge voltage of the multi-stage discharge gap branch to the residual voltage of the metal oxide arrester under the nominal discharge current is not less than a first preset ratio; the ratio of the measured power frequency breakdown voltage of the multi-stage discharge gap branch to the rated voltage of the metal oxide arrester is not greater than a second preset ratio.

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