Method, device and system for compensating arc extinguishing capability failure of three-terminal direct current engineering metal loop switch

Abstract

The invention relates to a zero-current opening method, device and system for a metal loop switch in a three-terminal direct-current power transmission system, and belongs to the technical field of high-voltage direct-current power transmission. The invention provides a system-level compensation scheme for solving the problem of operation mode conversion failure or system shutdown caused by failure of self arc extinguishing capability of the MRS. A precise mathematical model of an MRS current and a rectification station high-voltage line current is established, a two-station current proportion enabling a target switch current to be zero is calculated, and the two-station current proportion is cooperatively controlled to be output to the proportion, so that a zero current state is formed at the target switch, and finally, safe opening without arc extinguishing is realized. The system parameters which do not meet the direct calculation condition can be adjusted by switching the dynamic resistor. According to the method, safe arc-free opening under the switch fault is realized, non-planned shutdown is avoided, the power supply reliability and the system availability are remarkably improved, and the method is easy to implement and popularize.

Description

Technical Field

[0001] This invention relates to the field of high voltage direct current transmission technology, and in particular to a compensation method, device and system for the failure of arc extinguishing capability of a three-terminal DC engineering metal return line switch. Background Technology

[0002] Multi-terminal DC transmission systems, especially the "two-to-one" type three-terminal DC system (two rectifier stations transmitting power to one inverter station), have become a key direction for power grid development due to their flexible operation and suitability for multiple power sources and multiple receiving points. In such systems, depending on operational needs, it is often necessary to switch between single-pole metallic return and single-pole large return modes without power interruption. The core of the traditional switching logic lies in establishing a ground return path by closing the Metal Return Transfer Breaker (MRTB), and then relying on the arc-extinguishing capability of the Metal Return Switch (MRS) to cut off the current in the corresponding metallic return branch, thereby transferring all current to the ground return.

[0003] However, this traditional approach has significant drawbacks: its success depends entirely on the physical arc-extinguishing performance of the metallic return switch (MRS). In actual operation, the switch's arc-extinguishing capability may decrease or completely fail due to factors such as the breakdown of parallel surge arresters or arc chamber faults. Once the switch's arc-extinguishing capability fails, the arc cannot be extinguished during tripping, leading to switch protection operation, switching failure, and even equipment damage. In this situation, the only solution is to shut down the entire DC monopole to isolate the faulty switch, resulting in unplanned power outages that severely impact the reliability and economy of the power grid. Furthermore, compared to two-terminal DC systems, the current network of a three-terminal system is more complex, with currents in each branch coupling with each other, making it difficult for maintenance personnel to intuitively judge and control, further increasing the difficulty of safely completing switching operations in the event of equipment failure.

[0004] Existing technologies lack a systematic method to safely and reliably complete the circuit switching operation without interrupting system operation in the event of a fault where the arc extinguishing function of critical switching equipment fails. Summary of the Invention

[0005] To address the problems existing in the prior art, the main objective of this invention is to provide a compensation method, device, and system for the failure of the arc-extinguishing capability of a three-terminal DC engineering metal loop switch. This system can achieve the following: when the arc-extinguishing capability of the metal loop switch itself fails or is insufficient, through active and precise system-level current coordinated control, the current in the branch where the target switch is located is reduced to zero before the target switch is opened, thereby achieving "zero-current opening" without arc extinguishing. Ultimately, this ensures that the system can safely complete the transition from a unipolar metal loop to a unipolar polar loop operation mode without interrupting power transmission.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a compensation method for the failure of the arc-extinguishing capability of a three-terminal DC power transmission system with a metallic return line, applicable to a DC transmission system comprising a first rectifier station, a second rectifier station, and an inverter station, wherein the DC transmission system is operating in parallel with a unipolar metallic return line and a unipolar polar return line. The method includes: A quantitative relationship model is established between the metal loop switch current of the first rectifier station and the second rectifier station and the high voltage DC line current of the two stations. Based on the quantitative relationship model and DC transmission system parameters, the target ratio of the high-voltage DC line current between the first rectifier station and the second rectifier station is determined when the target metal loop switch current is zero. Control the output current of the high-voltage DC lines of the first rectifier station and the second rectifier station to make them operate at the target ratio, so that the current of the target metal return line switch is zero. When the current of the target metal return line switch is zero, a tripping operation is performed on it.

[0007] Optionally, the DC transmission system parameters mentioned above include: the equivalent resistances a, b, and c of the grounding electrode lines of the first rectifier station, the second rectifier station, and the inverter station, as well as the metal loop resistances d and e between the first rectifier station and the second rectifier station, and between the second rectifier station and the inverter station. The quantitative relationship model is a linear function of the metal loop switch current with respect to the high-voltage DC line current.

[0008] Optionally, in the above compensation method, the linear function is: v=([b(a+c)+a(c+e)]xb·e·y) / M, w=(-(a·ec·d)x+[b(a+c+d+e)+c(a+d)]y) / M, Where M = b(a+c+d+e)+(a+d)(c+e); v is the metal loop switch current of the first rectifier station, w is the metal loop switch current of the second rectifier station, x is the high voltage DC line current of the first rectifier station, and y is the high voltage DC line current of the second rectifier station.

[0009] Optionally, when the target metal return switch is the switch of the first rectifier station, the target ratio is x:y=b•e:[b(a+c)+a(c+e)].

[0010] Optionally, in the above compensation method, when the target metal return switch is the switch of the second rectifier station and a•e>c•d is satisfied, the target ratio is x:y=[b(a+c+d+e)+c(a+d)]:(a•ec•d).

[0011] Optionally, when the target metal loop switch is the switch of the second rectifier station and the initial parameters satisfy a•e≤c•d, the above compensation method further includes a parameter adjustment step before determining the target ratio: Increase the equivalent resistance a of the grounding electrode line of the first rectifier station, and / or increase the metal loop resistance e between the second rectifier station and the inverter station, so that the adjusted parameters satisfy (a+Δa)•e>c•d or a•(e+Δe)>c•d, where Δa and Δe are the resistance adjustment amounts; Subsequently, the step of determining the target ratio is re-executed based on the adjusted parameters.

[0012] Optionally, the above compensation method may be implemented by using a dynamically adjustable resistor connected to the grounding electrode line of the first rectifier station or to the metal return line between the second rectifier station and the inverter station to perform the step of increasing resistance.

[0013] In a second aspect, the present invention provides an apparatus for implementing the above-described compensation method, applied to a DC transmission system, the apparatus comprising: The processing unit is configured to: establish the quantitative relationship model and calculate the target ratio based on the DC transmission system parameters; The control unit is configured to: generate and send current control commands to the first and second rectifier stations based on a target ratio calculated by the processing unit, so as to adjust their high-voltage DC line output current; and, After confirming that the target metal return line switch current is zero, a trip command is generated and sent to the switch.

[0014] Optionally, the above-mentioned device may further include a parameter adjustment unit; The parameter adjustment unit is configured to: when the target is the metal return line switch of the second rectifier station and the initial parameters do not meet the zero current tripping condition, before the control unit sends the current control command, start and control a dynamically adjustable resistor device to increase the equivalent resistance of the grounding electrode line or the metal return line resistance of the DC transmission system. The processing unit is further configured to recalculate the target ratio based on the DC transmission system parameters adjusted by the parameter adjustment unit.

[0015] In a third aspect, the present invention provides a three-terminal DC transmission system comprising the above-described apparatus.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) In this invention, the traditional approach of repairing or replacing faulty switches is abandoned. Instead, the loss of arc-extinguishing function of underlying equipment is compensated by establishing a model, calculating the ratio, and coordinating current control. When the arc-extinguishing capability of a station's MRS is detected or known to be faulty, the DC transmission system does not stop operating. Instead, the current distribution is reshaped at the system level by controlling the output current ratio of the two rectifier stations, actively creating a current zero point at the faulty switch. This allows a physically faulty arc-extinguishing switch to be logically used as an ideal current-free isolation point, avoiding unplanned outages of the entire DC system due to a single equipment failure, minimizing the impact of equipment failure, and significantly improving the power supply reliability and operational economy of the power grid. Overall, functional compensation is achieved, greatly improving system availability and power supply continuity.

[0018] (2) In this invention, after precisely controlling the target switch current to zero, a conventional tripping command is issued. Since the current between the switch contacts is actually zero or close to zero at the moment of tripping, the physical conditions for arc generation are fundamentally eliminated. This not only solves the core problem of arc-extinguishing capability failure, but also completely avoids a series of secondary equipment damage and safety risks that may be caused by arc breaking, such as contact erosion, insulation material carbonization, SF6 gas decomposition, overvoltage generation, and strong electromagnetic interference, making the safety of the operation process itself reach the highest level. Overall, the inherent safety of "arc-free tripping" is achieved, eliminating secondary operational risks.

[0019] (3) In this invention, a precise linear mathematical model based on the circuit topology is first established, and specific control formulas applicable to different stations are derived accordingly. The mathematical model provides a deterministic theoretical basis and quantitative target for control, ensuring the accuracy and repeatability of control. Overall, it provides a universal and adaptive solution based on a precise mathematical model.

[0020] (4) Furthermore, this invention innovatively introduces a dynamic resistance adjustment mechanism for specific DC transmission system parameter combinations (a·e ≤ c·d) that do not meet the direct control conditions. Working principle and effect: The dynamic resistance adjustment strategy greatly expands the applicability of this method, making it independent of specific, ideal system parameters. Regardless of the DC transmission system parameters, a feasible zero-current tripping path can be adaptively found through the "calculation-judgment-adjustment-re-control" process, demonstrating strong robustness and engineering practical value.

[0021] (5) In this invention, further, the technical means are as follows: the core actions of the entire scheme (current regulation, resistor switching, and switch opening) all rely on the existing control execution mechanisms (such as converter valve control and switch controller) and optional mature primary equipment (dynamic resistors) of the converter station. Working principle and effect: The innovation of this invention is mainly focused on the algorithm and logic upgrade of the control and protection system (secondary system), rather than the invention of entirely new high-voltage primary equipment. For existing projects, it can be mainly achieved through software upgrades or the addition of standard resistor devices. The transformation cost is relatively low, the implementation path is clear, and it is easy to promote and apply in the power grid, providing an effective tool for realizing intelligent operation and maintenance and improving the efficiency of existing assets. Overall, it has clear advantages in engineering feasibility and low transformation cost.

[0022] The invention will now be further described with reference to the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the current when a single-pole metal circuit and a single-pole polarity circuit are connected in parallel in a two-terminal DC engineering process in the prior art. Figure 2 This is the current waveform of the metal return switch failing to trip during the unipolar metal-to-unipolar polarity conversion operation in existing two-terminal DC engineering. Figure 3 This is a flowchart illustrating the compensation method for the failure of the arc-extinguishing capability of a three-terminal DC engineering metal return line switch according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the current when a three-terminal DC engineering unipolar metal circuit and a unipolar ground circuit are connected in parallel according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the current when a three-terminal DC engineering unipolar metal circuit and a unipolar ground circuit are connected in parallel after the dynamic resistor is installed in series, according to an embodiment of the present invention. Figure 6 This is a schematic diagram showing the control of the metal return line switch of Luquan Station to zero when the single-pole metal circuit and the single-pole large circuit of the Lugaozhao three-terminal DC engineering pole 1 are connected in parallel according to an embodiment of the present invention. Figure 7 This is a schematic diagram showing the control of the metal return line switch of Gaopo Station to zero when the single-pole metal circuit and the single-pole large circuit of the Lugaozhao three-terminal DC engineering pole 2 are connected in parallel according to an embodiment of the present invention. Figure 8 This is a schematic diagram showing that the metal return line switch of Gaopo Station cannot be controlled to zero when the single-pole metal circuit and the single-pole large circuit of the Lugaozhao three-terminal DC engineering pole 2 are connected in parallel according to an embodiment of the present invention. Figure 9 This is a schematic diagram illustrating the control of the metal return line switch of Gaopo Station to zero when the single-pole metal circuit of the grounding electrode line of Luquan Station of the Lugaozhao three-terminal DC project in an embodiment of the present invention is connected in parallel with the single-pole metal circuit of the second pole and the single-pole grounding circuit. Detailed Implementation

[0024] To better illustrate the objectives, technical solutions, and advantages of the present invention, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] In conventional two-terminal high-voltage direct current (HVDC) transmission projects, the conversion from a monopolar metallic return line to a monopolar polar return line requires coordinated sequential control between the two stations. For example... Figure 1 As shown, the rectifier station closes the metallic return transfer switch (MRTB) to establish a ground return current path. At this time, the low-voltage side current path forms a structure in which the metallic return and the ground return are connected in parallel.

[0026] Let Re1 be the sum of the grounding electrode line resistance and the grounding electrode-to-ground resistance of the rectifier station, Re2 be the sum of the corresponding resistances of the inverter station, RL12 be the metal loop resistance between the two stations, and Id be the DC pole current. Then the current flowing through the rectifier station metal loop switch (MRS) is: ; The current flowing through the metallic return transfer switch (MRTB) of the rectifier station is: .

[0027] For typical DC projects, regardless of the ratio of the metallic return resistance RL12 to the sum of the ground return resistances of the two stations (Re1+Re2), a portion of the current always flows through the metallic return switch (MRS). Therefore, to successfully complete the conversion from unipolar metallic to unipolar mode, the rectifier station's metallic return switch (MRS) must have sufficient arc-extinguishing (or breaking) capability to transfer all metallic return current to the ground return line. If the rectifier station's metallic return switch (MRS) loses its arc-extinguishing capability due to a fault (such as a parallel surge arrester breakdown), the conversion operation will fail. Typically, the DC system must be shut down unipolarly before this can be addressed, severely impacting power supply reliability.

[0028] In one example: At a certain moment, during the transition from unipolar metallic return mode to unipolar large metallic return mode at Xing'an DC pole 1, after the sequential control operation disconnects the metallic return switch 0030 at Xingren converter station, the metallic return switch protection (82MRS) activates and recloses the switch. Figure 2 It can be seen that the current in the metallic return line was not completely transferred after the tripping command was issued. Subsequent shutdown inspection revealed that the surge arrester connected in parallel with the switch had broken down and was unable to absorb the LC oscillation current, causing the switch to fail to trip.

[0029] To address the aforementioned problems, this invention proposes a compensation method for the failure of the arc-extinguishing capability of a metallic return line switch in a three-terminal DC transmission system. The following explanation uses a typical "two-to-one" three-terminal DC project (two rectifier stations and one inverter station) as an example.

[0030] refer to Figure 3 This invention relates to a compensation method for the failure of the arc-extinguishing capability of a three-terminal DC transmission line switch in a metallic loop, according to an embodiment of the present invention. The compensation method is applied to a "two-to-one" type three-terminal DC transmission system, which includes a first rectifier station, a second rectifier station, and an inverter station. When the DC transmission system is operating in parallel with a unipolar metallic loop and a unipolar polar loop, the method includes the following steps: S1. System Modeling and Analysis. Establish a quantitative relationship model between the metal loop switch current of the first and second rectifier stations and the high-voltage DC line current of both stations.

[0031] Under unipolar load operation, during the unipolar-to-unipolar metallic conversion process, after both the first and second rectifier stations close their metallic return line switches (MRS), the low-voltage side of the three stations enters a state where the ground return line and the metallic return line are connected in parallel. Figure 4 As shown. Figure 4 This is a schematic diagram of the DC current on the low-voltage side of a three-terminal DC power supply project. Following the direction of the current arrows in the diagram, assume the high-voltage side DC line currents of the first and second rectifier stations are x and y, respectively; the grounding electrode currents of the first and second rectifier stations are z and u, respectively; the metallic return line currents of the first and second rectifier stations are v and w, respectively; the sum of the grounding electrode line resistances and the grounding electrode-to-ground resistances of the three stations are a, b, and c, respectively; and the metallic return line resistances between the first and second rectifier stations and between the second rectifier station and the inverter station are d and e, respectively.

[0032] The linear equations for the ground and metallic loop currents of the first and second rectifier stations and the DC currents on the high-voltage side of the two rectifier stations are established as follows: (1); (2); (3); (4).

[0033] Define the following parameters: the equivalent resistance (including the grounding electrode resistance) of the grounding electrode lines of the first rectifier station, the second rectifier station, and the inverter station are a, b, and c, respectively. The metal loop resistance between the first rectifier station and the second rectifier station is d, and the metal loop resistance between the second rectifier station and the inverter station is e. The high-voltage DC line currents of the first rectifier station and the second rectifier station are x and y, respectively (independent variables, constrained by the unidirectional conductivity of the converter valve, x>0, y>0). The currents flowing through the metal loop switches (MRS) of the first rectifier station and the second rectifier station are v and w, respectively (dependent variables, whose values ​​can be positive or negative; negative values ​​indicate that the actual flow direction is opposite to the reference direction shown in the figure).

[0034] according to Figure 3 Based on the circuit topology and Kirchhoff's laws, a linear relationship can be established between v, w, and x, y. Solving this system of equations yields the analytical expression: (5); (6).

[0035] S2. Based on the quantitative relationship model and DC transmission system parameters, determine the target ratio of the high-voltage DC line current between the first rectifier station and the second rectifier station when the target metal loop switch current is zero.

[0036] 1. For the metal return line switch of the first rectifier station: Let v=0, the condition for making the MRS current of the first rectifier station zero can be derived from formula (5), that is, the current of the high voltage DC lines of the two stations needs to be controlled to meet the following ratio: ; As long as x and y are adjusted to meet this ratio, the circuit breaker can be tripped when the MRS current of the first rectifier station is zero, without the need for it to have arc-extinguishing capability.

[0037] II. For the metallic return line switch of the second rectifier station: Let w=0, and from formula (6), we can see that its feasibility depends on the system parameters: Case A: When the target metal return switch is the switch of the second rectifier station, and a•e>c•d, the target ratio is: ; In scenario B, when the target metal loop switch is the switch of the second rectifier station, and the initial parameters satisfy a•e≤c•d, the equivalent resistance a of the grounding electrode line of the first rectifier station is increased, and / or the metal loop resistance e between the second rectifier station and the inverter station is increased, so that the adjusted parameters satisfy (a+Δa)•e>c•d or a•(e+Δe)>c•d, where Δa and Δe are resistance adjustment amounts; subsequently, the step of determining the target ratio is re-executed based on the adjusted parameters. The step of increasing the resistance is performed by a dynamically adjustable resistor connected to the grounding electrode line of the first rectifier station or connected to the metal loop between the second rectifier station and the inverter station.

[0038] S3. Control the output current of the high-voltage DC lines of the first and second rectifier stations to operate at the target ratio, thereby making the current of the target metallic return switch zero. The two-station converter valve control system receives the instruction and coordinates to adjust the firing angle so that the actual operating current is stabilized near the DC line current range, and the ratio meets the target ratio set by the system control unit.

[0039] S4. When the current of the target metallic return switch is zero, a tripping operation is performed on it. Specifically, after the current regulation stabilizes, the current is monitored by the current transformer of the Luquan Substation MRS. When the monitored V value drops to near zero (e.g., <5A) and remains for a short delay, the DC protection system or sequential control logic sends a tripping command to the Luquan Substation Metallic Return Switch (MRS). The switch successfully mechanically trips under no-current conditions, completing a safe operation under the assumption that its arc-extinguishing capability is failed.

[0040] In summary, the present invention has the following beneficial effects:

[0041] (1) It can safely complete the conversion of the operation mode from unipolar metal return line to unipolar large return line without interrupting DC power transmission in the event that the arc extinguishing capability of the metal return line switch (MRS) fails, greatly improving the system availability and power supply reliability.

[0042] (2) Through precise mathematical model and system-level current coordinated control, “zero current tripping” is achieved, which essentially avoids the generation of tripping arc and related risks, and has high operational safety.

[0043] (3) The proposed method has universality and adaptability. For different system parameters, the control strategy can be directly obtained through calculation; for parameter combinations that do not meet the direct control conditions, the system parameters can be adjusted by adding dynamic resistors, and the application range is wide.

[0044] (4) The core of the solution lies in the control logic and algorithms, which require low modification to the existing primary equipment. It can be mainly achieved by software upgrade and installation of conventional resistor devices, facilitating popularization and application in the already commissioned projects.

[0045] In view of the above problems, the embodiment of the present invention also proposes a device for implementing the above compensation method, and a three-terminal DC transmission system including the device. The device can be integrated into the existing DC control and protection system and applied to a two-in-one type three-terminal DC transmission system such as "Lugaozhao". The following combines the scenario where when the system operates in a pole, the metal return line switch of the second rectifier station (Gaopo Station) needs to be tripped with zero current and the parameters need to be adjusted to illustrate the specific working process of the device.

[0046] The processing unit is configured to establish the quantitative relationship model and calculate the target ratio based on the parameters of the DC transmission system. It is usually implemented by a high-performance processor in the converter station control host or DC protection device. In this embodiment, when the system enters the single-pole metal / earth return line parallel state and it is identified that the arc extinction ability of the MRS in Gaopo Station fails, this unit is started. Its built-in algorithm module automatically obtains the current system parameters and performs calculations based on the pre-stored mathematical models (i.e., formulas (5) and (6)). It first determines that a·e < c·d, and direct calculation cannot obtain the current ratio that makes the current of the target switch (MRS in Gaopo Station) zero. Immediately, it sends a start instruction to the parameter adjustment unit.

[0047] The parameter adjustment unit is configured to: when the target is the metal return line switch of the second rectifier station and the initial parameters do not meet the zero-current tripping condition, before the control unit sends a current control instruction, start and control a dynamically adjustable resistor device to increase the equivalent resistance of the grounding electrode line or the metal return line resistance of the DC transmission system. This unit includes a dynamically adjustable resistor device installed on the grounding electrode line of Luquan Station (the first rectifier station) and its local controller. After receiving the instruction from the processing unit, this unit controls the vacuum contactor or thyristor valve group to put into the preset resistance section, increasing the equivalent resistance of the grounding electrode line of Luquan Station from 1.0425Ω to 4Ω. After the input is completed, this unit feeds back the "resistor has been input" signal and the new resistance value a' = 4Ω to the processing unit.

[0048] The processing unit is further configured to: recalculate the target ratio based on the parameters of the DC transmission system adjusted by the parameter adjustment unit. After receiving the new parameter a' fed back by the parameter adjustment unit, the processing unit performs the calculation again. At this time, it is judged that the condition a'·e > c·d is satisfied. Immediately, a new current target ratio K2' = 7.26 that can achieve zero-current tripping is calculated according to the model, and this ratio instruction is sent to the control unit.

[0049] The control unit is configured to generate and send current control commands to the first and second rectifier stations based on the target ratio calculated by the processing unit, in order to adjust their high-voltage DC line output current; this unit is typically a power / current regulation module in the station control system. It receives the target ratio K2'=7.26 from the processing unit. Combined with the current total power command, it calculates the respective current reference values ​​for Luquan and Gaopo stations (e.g., x_ref=2500A, y_ref≈344.4A). Subsequently, through the inter-station communication link, it sends precise current regulation commands to the converter valve control systems of Luquan and Gaopo stations, driving the converter valves to adjust their firing angles, thus stabilizing the actual output current of both stations near the target ratio.

[0050] The control unit is also configured to generate and send a tripping command to the target metallic return switch after confirming that the current is zero. The unit continuously monitors the current signal from the MRS at the high-slope station. When the monitored current value drops to the zero current threshold (e.g., <5A) and stabilizes, its built-in tripping logic module (or linked independent protection device) automatically generates a tripping command, drives the output relay, and sends a tripping pulse to the target metallic return switch (MRS) at the high-slope station, allowing the switch to open smoothly in a current-free state.

[0051] This embodiment demonstrates that the device, through closed-loop collaboration between the processing unit, parameter adjustment unit, and control unit, achieves a fully automated processing flow from "fault identification and parameter diagnosis" to "active adjustment of system parameters," then to "precise coordinated current control," and finally to "safe tripping." When the switch itself fails, the device successfully transforms it from a critical breaking element into a passive isolation point that can be controlled by the system, thus ensuring a smooth transition of operating mode without interrupting power transmission, demonstrating the practical engineering value of this invention.

[0052] Example A: Zero-current tripping of the metal return line switch at the first rectifier station (Luquan station). Step S1: Establish a quantitative relationship model.

[0053] Under the condition that the Lu Gao Zhao Ji 1 single-pole metal loop and the earth loop are operating in parallel, according to Figure 3 The circuit topology shown is used to obtain and set the system parameters as follows: Equivalent resistance of the grounding electrode line: Luquan station a = 1.0425Ω, Gaopo station b = 1.019Ω, Zhaoqing station c = 1.22Ω. Metal loop resistance: between Luquan and Gaopo stations d = 3.8408Ω, between Gaopo and Zhaoqing stations e = 8.7799Ω. High-voltage DC line current: Luquan station current is x, Gaopo station current is y. Metal loop switch current: Luquan station MRS current is v, Gaopo station MRS current is w. Based on Kirchhoff's laws, the following established mathematical model is established and adopted: ; Step S2: Determine the target current ratio.

[0054] To achieve zero-current tripping of the target MRS at Luquan Station, let v=0. Substituting the above model parameters, calculate the required ratio K1 of the two-station HVDC line currents to achieve v=0: .

[0055] Step S3: Control the current to the target ratio.

[0056] Assume the current DC line current at Luquan Station is x = 1200A. The system control unit calculates and issues a command based on the target ratio K1 to adjust the DC line current y at Gaopo Station to: ; The two-station converter valve control system receives the command and coordinates the adjustment of the firing angle to stabilize the actual operating current (x,y) around (1200A,1707.5A), so that the ratio meets K1.

[0057] Step S4: Zero Current Confirmation and Tripping Operation. After the current regulation stabilizes, the current v of the MRS at Luquan Station is monitored via the current transformer. When the monitored v value drops to near zero (e.g., <5A) and remains there for a short delay, the DC protection system or sequential control logic sends a tripping command to the Luquan Station Metallic Return Switch (MRS). The switch smoothly mechanically trips in a current-free state, completing the safe operation under the assumption that its arc-extinguishing capability has failed. This process is as follows: Figure 6 As shown.

[0058] Example B: Zero-current tripping of the metallic return line switch in the second rectifier station (Gaopo station) (direct control) Step S1: Establish a quantitative relationship model.

[0059] The same system parameters (a, b, c, d, e) as in Example A are used. A previously established mathematical model for the MRS current w at the Gaopo station is employed. ; Step S2: Determine the target current ratio. First, determine the condition: a•e≈9.15>c•d≈4.69, which satisfies the direct control condition. To achieve zero-current tripping of the target MRS at the high-slope station, let w=0. Substitute the parameters to calculate the required current ratio K2: ; That is, x:y≈4.728:1.

[0060] Step S3: Control the current to the target ratio. Assume the current of the current line at Luquan station is x = 2400A. The control unit calculates based on K2 and adjusts the current at Gaopo station to: ; The system controls the current of the two stations to remain stable at the target ratio.

[0061] Step S4: Zero Current Confirmation and Opening Operation. After monitoring the MRS current w at the high-slope station to drop to zero, the switch is opened, successfully completing the switching process. This process is as follows: Figure 7 As shown.

[0062] Example C: Zero-current tripping of the metallic return line switch in the second rectifier station (Gaopo station) (parameter adjustment required) This embodiment is for the Lugo Zhaoji 2 system, and its parameters are changed as follows: d=8.7799Ω, e=3.8408Ω (metal loop resistance is interchanged), a, b, and c remain unchanged.

[0063] Step S1 and Preliminary Judgment: The model is established as in Example B. Initial condition for judgment: a•e≈4.00≤c•d≈10.71. Under these parameters, directly executing step S2 will reveal that adjusting the current ratio x / y alone cannot make w=0, meaning there is no real solution for the target ratio K.

[0064] Step S2a (New Sub-step): System Parameter Adjustment. To enable zero-current tripping, the dynamic resistance device installed on the grounding electrode line at Luquan Station is put into operation, such as... Figure 9 As shown. This device adds a resistor Δa≈2.9575Ω, adjusting the total resistance of Luquan Station to ground to: .

[0065] Step S2 (Recalculation): Determine the target current ratio. Replace a with the adjusted new parameter a', and re-evaluate the condition: a'•e=4.0×3.8408=15.36>c•d=10.71, the condition is met. Recalculate the new target ratio K2' that makes w=0: .

[0066] Step S3: Control the current to the target ratio. Assume the current at Luquan station is x = 2500A at this time. The control unit adjusts the current at Gaopo station to: (The original text abruptly ends here, so the translation stops as well.) .

[0067] Step S4: Zero Current Confirmation and Circuit Breaker Operation. After monitoring and confirming that the MRS current w at the high-slope station is zero, the circuit breaker operation is performed to complete the switching.

[0068] The above three embodiments fully demonstrate the specific implementation process of the step-by-step method of the present invention in different application scenarios (different target switches, different system parameters). This method systematically solves the problem of safe tripping when the arc-extinguishing capability of a metallic return line switch fails, through rigorous mathematical modeling, precise proportional calculation, coordinated current control, and optional dynamic parameter adjustment.

[0069] The above embodiments mainly describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A compensation method for the failure of arc extinguishing capability of a three-terminal DC engineering metal loop switch, characterized in that, The method, applied to a DC transmission system comprising a first rectifier station, a second rectifier station, and an inverter station, wherein the DC transmission system is operating in parallel with a unipolar metallic return line and a unipolar polar return line, includes: A quantitative relationship model is established between the metal loop switch current of the first rectifier station and the second rectifier station and the high voltage DC line current of the two stations. Based on the quantitative relationship model and DC transmission system parameters, the target ratio of the high-voltage DC line current between the first rectifier station and the second rectifier station is determined when the target metal loop switch current is zero. Control the output current of the high-voltage DC lines of the first rectifier station and the second rectifier station to make them operate at the target ratio, so that the current of the target metal return line switch is zero; When the current of the target metal return line switch is zero, a tripping operation is performed on it.

2. The compensation method as described in claim 1, characterized in that, The parameters of the DC transmission system include: the equivalent resistances a, b, and c of the grounding electrode lines of the first rectifier station, the second rectifier station, and the inverter station; and the metal loop resistances d and e between the first rectifier station and the second rectifier station, and between the second rectifier station and the inverter station. The quantitative relationship model is a linear function of the metal loop switch current with respect to the high-voltage DC line current.

3. The compensation method as described in claim 2, characterized in that, The linear function is: v=([b(a+c)+a(c+e)]xb·e·y) / M, w=(-(a·ec·d)x+[b(a+c+d+e)+c(a+d)]y) / M, Where M = b(a+c+d+e)+(a+d)(c+e); v is the metal loop switch current of the first rectifier station, w is the metal loop switch current of the second rectifier station, x is the high voltage DC line current of the first rectifier station, and y is the high voltage DC line current of the second rectifier station.

4. The compensation method as described in claim 3, characterized in that, When the target metal return switch is the switch of the first rectifier station, the target ratio is x:y=b•e:[b(a+c)+a(c+e)].

5. The compensation method as described in claim 3, characterized in that, When the target metal return switch is the switch of the second rectifier station, and a•e>c•d, the target ratio is x:y=[b(a+c+d+e)+c(a+d)]:(a•ec•d).

6. The compensation method as described in claim 1, characterized in that, When the target metal return switch is the switch of the second rectifier station, and the initial parameters satisfy a•e≤c•d, the method further includes a parameter adjustment step before determining the target ratio: Increase the equivalent resistance a of the grounding electrode line of the first rectifier station, and / or increase the metal loop resistance e between the second rectifier station and the inverter station, so that the adjusted parameters satisfy (a+Δa)•e>c•d or a•(e+Δe)>c•d, where Δa and Δe are the resistance adjustment amounts; Subsequently, the step of determining the target ratio is re-executed based on the adjusted parameters.

7. The compensation method as described in claim 1, characterized in that, The step of increasing resistance is performed by a dynamically adjustable resistor connected to the grounding electrode line of the first rectifier station or to the metal return line between the second rectifier station and the inverter station.

8. An apparatus for implementing the compensation method according to any one of claims 1 to 7, characterized in that, The device, used in DC transmission systems, includes: The processing unit is configured to: establish the quantitative relationship model and calculate the target ratio based on the DC transmission system parameters; The control unit is configured to: generate and send current control commands to the first and second rectifier stations based on a target ratio calculated by the processing unit, so as to adjust their high-voltage DC line output current; and, After confirming that the target metal return line switch current is zero, a trip command is generated and sent to the switch.

9. The apparatus according to claim 8, characterized in that, The device also includes a parameter adjustment unit; The parameter adjustment unit is configured to: when the target is the metal return line switch of the second rectifier station and the initial parameters do not meet the zero current tripping condition, before the control unit sends the current control command, start and control a dynamically adjustable resistor device to increase the equivalent resistance of the grounding electrode line or the metal return line resistance of the DC transmission system. The processing unit is further configured to recalculate the target ratio based on the DC transmission system parameters adjusted by the parameter adjustment unit.

10. A three-terminal DC transmission system, characterized in that, It includes the apparatus as described in claim 8 or 9.

Images