A dc power transmission line fault traveling wave reflection suppression system, device and method

Abstract

The application discloses a kind of direct current transmission system fault transient state suppression system, device and method direct current transmission line fault travelling wave reflection suppression system, device and method, belong to high voltage direct current transmission field.Aiming at the defect that the fault travelling wave reciprocating reflection causes large sending end negative pressure impact, fault current rises too fast, protection margin is insufficient, scheme universality is poor when existing direct current line short-circuit fault, the application is connected in parallel with resistance-capacitance compensation unit in the line side of sending end smoothing reactor, resistance-capacitance parameters are designed based on line characteristic impedance matching, actively control sending end boundary voltage reflection coefficient, weaken fault travelling wave multiple reflection superposition effect from source.This application can inhibit transient overvoltage, reduce the rising rate of fault current simultaneously, and there is no active loss in steady-state operation;Core mechanism adapts monopolar / bipolar / multi-terminal direct current system, compatible with all line types such as submarine cable, land cable, overhead direct current line, and modular device can adapt to new and stock direct current engineering modification, to provide a new technical solution for full-scene direct current transmission fault protection.

Description

Technical Field

[0001] This invention relates to the field of high-voltage direct current (HVDC) transmission fault protection technology, and in particular to a transient fault suppression system, device, and method for HVDC transmission systems, and a traveling wave reflection suppression system, device, and method for HVDC transmission line faults. Background Technology

[0002] With the large-scale implementation of long-distance transmission of new energy, offshore wind power grid connection, and cross-regional large-capacity power grid interconnection projects, high-voltage direct current (HVDC) transmission technology has been widely adopted due to its advantages such as large transmission capacity, low line loss, and flexible control. When a DC transmission line experiences a single-pole grounding, bipolar short circuit, or inter-pole metallic short circuit fault, the voltage at the fault point drops instantaneously to near zero potential, generating a fault electromagnetic traveling wave that propagates at high speed along the line. DC cables and overhead lines are distributed parameter transmission lines, and the fault traveling wave will repeatedly reflect and superimpose between the two impedance discontinuities at the sending and receiving ends of the line, inducing a violent high-frequency electromagnetic transient process, which brings two major hazards: First, a large negative pressure impact is generated at the sending end, and the insulation of the converter valve and smoothing reactor is subjected to severe overvoltage stress; second, the fault current rises at an extremely fast rate, reaching the withstand limit of the power equipment within hundreds of microseconds, and the relay protection and DC circuit breaker have insufficient operating time margin, which can easily cause permanent damage to core primary equipment such as converter valves and reactors.

[0003] Existing DC transmission fault transient suppression schemes are mainly divided into three categories, all of which have obvious limitations: Current limiting by series smoothing reactor: The smoothing reactor can reduce the steady-state amplitude of the fault current to a certain extent, but it presents extremely high inductive impedance for high-frequency fault traveling waves. The sending end is close to the open circuit boundary, and the voltage traveling waves are totally reflected in the same polarity, which will aggravate the voltage oscillation at the sending end and amplify the negative voltage impact. It cannot weaken the superposition effect of traveling wave reflection from the root. Busbar parallel surge arrester voltage limiting: Surge arresters are passive energy absorption devices that can only clamp the voltage peak. They cannot slow down the rise of fault current or eliminate the physical process of continuous reciprocating oscillation of traveling waves. They have poor fault protection effect on short-distance DC lines. Adding DC fast circuit breakers to clear faults: DC circuit breakers have inherent mechanical / electronic delays in operation. For short-distance DC lines, the fault current rises much faster than the protection response speed, and the equipment has already suffered severe overcurrent impacts before the fault is cleared.

[0004] The existing limited RC absorption circuit technologies only passively absorb transient energy after a fault, without considering the transmission line traveling wave propagation and boundary reflection mechanisms to carry out targeted parameter matching design. They cannot actively adjust the sending end boundary reflection coefficient, resulting in limited transient suppression effects. Furthermore, the existing solutions are only designed for the single scenario of offshore cables and cannot be universally adapted to terrestrial cables, overhead DC lines, and DC systems with different topologies, resulting in poor engineering versatility.

[0005] In summary, the industry currently lacks a fault transient suppression solution that can suppress transient oscillations at the source of traveling wave reflection, accommodate all types of DC systems, achieve steady-state losslessness, and be retrofittable. Summary of the Invention

[0006] The purpose of this invention is to provide a transient fault suppression system, device, and method for DC transmission systems, and a traveling wave reflection suppression system and method for DC transmission line faults, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a transient fault suppression system, device, and method for DC transmission systems. The DC transmission line fault traveling wave reflection suppression system, device, and method include a sending-end DC unit, a smoothing reactor, a DC transmission line, and a receiving-end unit. The smoothing reactor is connected in series between the sending-end DC unit and the DC transmission line, and a resistance-capacitance compensation unit is connected in parallel on the side of the smoothing reactor closest to the DC transmission line. The RC compensation unit is used to adjust the equivalent impedance characteristics of the sending end boundary, change the voltage reflection coefficient of the fault traveling wave caused by the short-circuit fault at the sending end boundary, and suppress the rapid rise of transient overvoltage and fault current caused by the repeated reflection and superposition of the fault traveling wave between the sending end and the fault point.

[0008] Preferably, the DC transmission system is any one of a unipolar DC system, a pseudo-bipolar DC system, or a true bipolar DC system; The DC transmission line can be any one of a DC cable, an overhead DC line, or a hybrid land-sea DC transmission line.

[0009] Preferably, the DC transmission system is a two-terminal DC transmission system or a multi-terminal DC transmission system, and the sending-end DC unit is a grid-commutated converter or a modular multilevel converter.

[0010] Preferably, the RC compensation unit includes a compensation resistor and a compensation capacitor connected in series. One end of the RC compensation unit is connected to the pole conductor, and the other end is connected to the neutral bus or grounding electrode of the system. When the DC transmission system is a bipolar structure, a set of the RC compensation unit is independently connected in parallel on the line side of the smoothing reactor of the positive line and the negative line, respectively. The ratio of the resistance value of the compensation resistor to the characteristic impedance of the DC transmission line is 0.5~1, so that the voltage reflection coefficient at the sending end boundary is ≤0. The resistance value of the compensation resistor is equal to the characteristic impedance of the DC transmission line, so that the voltage reflection coefficient at the sending end boundary is 0, achieving impedance matching and no reflection of the fault traveling wave. The value range of the compensation capacitor is 0.5μF~10μF, and the capacitance value of the compensation capacitor is selected according to the fault transient main frequency range of the DC transmission line.

[0011] Preferably, the RC compensation unit has no continuous active power loss during steady-state operation of the system and does not affect the normal power transmission of the DC transmission system; it provides damping and consumes traveling wave energy during fault transients, suppressing transient oscillation amplitude; the fault transient is an electromagnetic transient process caused by a single-pole grounding short-circuit fault, a double-pole short-circuit fault, or an inter-pole short-circuit fault in the DC line.

[0012] Preferably, the smoothing reactor is also connected in parallel with a surge arrester and a DC circuit breaker on the line side, and the RC compensation unit works with the surge arrester and the DC circuit breaker to achieve fault transient suppression and fault isolation.

[0013] Preferably, a fault transient suppression device for a DC transmission system includes a compensation resistor and a compensation capacitor connected in series, and the device is used to be connected in parallel to the line side of the sending-end smoothing reactor of the DC transmission system. The device adjusts the equivalent impedance characteristics at the sending end boundary to change the voltage reflection coefficient of the short-circuit fault traveling wave at the sending end boundary, thereby suppressing the rapid rise of transient overvoltage and fault current caused by the superposition of repeated reflections of the fault traveling wave.

[0014] Preferably, the resistance value of the compensation resistor is configured such that the ratio of its resistance to the characteristic impedance of the target DC transmission line is 0.5 to 1, so that the reflection coefficient of the boundary voltage at the sending end after connection is ≤0; the value range of the compensation capacitor is 0.5μF to 10μF, which is suitable for the fault transient main frequency range of the DC transmission line; the device is a modular independent device with a standard DC access terminal, which can be directly connected in parallel to the output of the smoothing reactor of the existing DC transmission system.

[0015] Preferably, a method for transient fault suppression in a DC transmission system involves connecting a resistance-capacitance compensation unit in parallel at the connection node between the smoothing reactor at the sending end of the DC transmission system and the DC transmission line. The resistance-capacitance compensation unit alters the voltage reflection coefficient at the sending end boundary, thereby weakening the superposition effect of multiple reflections of the fault traveling wave caused by the short-circuit fault, thus suppressing transient overvoltage at the sending end and slowing down the rate of increase of the fault current.

[0016] Preferably, a method for transient fault suppression in a DC transmission system includes a parameter configuration step: Calculate the characteristic impedance of the target DC transmission line, calculate the resistance value of the compensation resistor based on the preset target voltage reflection coefficient, select the capacitance value of the compensation capacitor in combination with the fault transient main frequency range, and complete the parameter matching of the RC compensation unit. The target voltage reflection coefficient is set to ≤0, and the ratio of the compensation resistor value to the line characteristic impedance is 0.5~1. For bipolar DC transmission systems, independent parallel RC compensation units are connected on the line side of the smoothing reactors at the positive and negative poles to suppress the reflection of fault traveling waves at the two poles respectively. The RC compensation unit has no continuous active power loss during steady-state operation of the system, and only plays a damping and suppression role during fault transients. The method is applicable to transient suppression under single-pole grounding faults, bipolar short-circuit faults, and inter-pole short-circuit faults, and is suitable for DC cables, overhead DC lines, and mixed land-sea lines. The resistor-capacitor compensation unit works in conjunction with the relay protection device of the DC system to extend the protection action time window by slowing down the rise rate of the fault current, thereby improving the reliability of the protection action.

[0017] The technical effects and advantages of this invention are as follows: This application features an innovative mechanism and addresses the root cause of the problem. It abandons the traditional, passive energy absorption and current limiting approach to address the issue. Based on the underlying physical mechanism of traveling wave propagation and reflection in transmission lines, it actively regulates the boundary reflection coefficient to eliminate the conditions for the formation of traveling wave reciprocating oscillations from the source. It simultaneously solves three core problems: negative pressure impact, high-frequency voltage oscillation, and sharp increase in fault current. The protection mechanism is more advanced and the suppression effect is more thorough.

[0018] 2. This application is universally applicable and highly adaptable, breaking the limitation of traditional technologies that are only compatible with pseudo-bipolar submarine cables. Its core principle is the universal law of distributed parameter transmission lines, which can be adapted to all DC topologies, all line types, all converter models, and all voltage levels of DC transmission projects, with no application barriers.

[0019] 3. This application has zero steady-state loss and does not affect normal power transmission. The RC series structure isolates the DC path under DC steady-state conditions. The device has no continuous active or reactive power loss, does not reduce power transmission efficiency, and does not change the steady-state operating characteristics of the system. Damping is only engaged during millisecond-level fault transient processes.

[0020] 4. This application project is highly feasible, adopts modular and standardized design, can be pre-installed in new projects, and can be directly added in parallel to existing projects without modifying the original primary equipment or control strategies. It has a small construction workload, low modification cost, and good adaptability.

[0021] 5. This application significantly improves the system safety margin, greatly reduces the fault current rise slope, and extends the operating time window of relay protection and DC circuit breaker by several times. It effectively reduces the risk of insulation breakdown and overcurrent burnout of converter valves and smoothing reactors, and significantly improves the fault tolerance and operational reliability of DC power grid.

[0022] 6. The parameters in this application are standardized and quantifiable, and a complete design system of "line characteristic impedance calculation - reflection coefficient target setting - RC parameter matching" has been established. Technical personnel can quickly match device parameters based on any line parameters. The solution is standardized, replicable, and easy to promote in large-scale projects. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the overall topology of the DC transmission system of the present invention; Figure 2 This is a comparison diagram of the simulated waveform of the sending-end voltage of the present invention; Figure 3 This is a comparison diagram of the simulated fault current waveforms of the present invention; Figure 4 This is a flowchart of the fault transient suppression method of the present invention.

[0024] In the attached diagram: 1. Sending-end DC power supply; 2. Smoothing reactor; 3. RC compensation unit; 301. Compensating resistor; 302. Compensating capacitor; 4. DC transmission line; 5. Receiving-end load unit. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides, for example Figures 1-4 The diagram illustrates a transient fault suppression system, device, and method for DC transmission systems, including a traveling wave reflection suppression system, device, and method for DC transmission line faults, and an implementation method for a DC transmission system with a modular suppression device. This implementation method corresponds to the generalized application scenarios of the system and device claims, and is applicable to DC transmission projects of various topologies and line types.

[0027] System topology adaptation rules: The core structure of this invention is a "parallel RC compensation unit on the line side of the smoothing reactor," which can be directly adapted to all mainstream DC transmission topologies. Monopolar DC system: Only one set of RC compensation unit is connected in parallel on the line side of the monopolar smoothing reactor, and the other end of the unit is connected to the system grounding electrode or neutral line; Pseudo-bipolar / true-bipolar DC system: The line side of the smoothing reactors of the positive and negative poles are each connected to an independent set of RC compensation units. The parameters of the two units are consistent, they work independently, and they do not interfere with each other. Multi-terminal DC grid: Each converter station's output smoothing reactor is independently equipped with an RC compensation unit on the line side, and each branch adjusts the reflection characteristics of the fault traveling wave on its own side. Converter configuration adaptation: The sending-end DC unit can be a grid-commutated converter (LCC) or a modular multilevel converter (MMC). The converter station structure does not affect the traveling wave propagation and boundary reflection control mechanism, and this solution is applicable to both.

[0028] 2. Line type adaptation rules: The working mechanism of this invention is based on the universal traveling wave law of distributed parameter transmission lines, which is independent of the line laying environment and can be adapted to all types of DC transmission lines. Submarine DC cables and terrestrial DC cables have large capacitance and small inductance, resulting in low characteristic impedance. Therefore, a matching resistor with a smaller resistance value should be selected. Overhead DC lines have high inductance and low capacitance, resulting in high characteristic impedance. Therefore, a compensation resistor with a larger resistance value should be selected for matching. For hybrid onshore and offshore DC lines: the comprehensive characteristic impedance can be calculated based on the equivalent distributed parameters of the entire line, and the corresponding compensation parameters can be matched to achieve the full-area suppression effect.

[0029] 3. Modular suppression device implementation method: The fault transient suppression device is an independent modular unit, internally composed of a compensation resistor and a compensation capacitor connected in series, with standard high-voltage DC input terminals at both ends. The device casing is high-voltage insulated and has an independent heat dissipation structure and insulation margin.

[0030] For newly built DC projects, the device can be pre-installed in the outlet switch cabinet of the smoothing reactor; for existing DC projects already in operation, it can be directly connected in parallel to the busbar at the outlet of the smoothing reactor without removing the original equipment or changing the main circuit topology of the system, resulting in a short modification cycle and low implementation cost.

[0031] II. Step-by-step detailed implementation process of DC transmission fault transient suppression method This method is a standardized implementation process that is quantifiable and reproducible, consisting of 7 core steps covering the entire process of parameter design, system access, operation control, and collaborative protection: Step 1: Acquisition of basic parameters and calculation of characteristic parameters for DC lines: This step is fundamental to parameter matching. Its core is obtaining the line distribution parameters and calculating the traveling wave characteristics. The specific steps are as follows: The basic parameters of the target DC transmission line, such as resistance R0, inductance L0, capacitance C0, conductance G0, and total line length l, are collected. Based on these parameters, the core traveling wave characteristics of the line are calculated. Formula for calculating characteristic impedance of a line:

[0032] Formulas for calculating the propagation speed and one-way propagation time of traveling waves:

[0033] Based on the line length and traveling wave propagation characteristics, the core frequency band of transient oscillation was initially determined, providing a basis for subsequent capacitor selection.

[0034] Step 2: Match the suppression target setting with the compensation resistor parameters: This step is the core design element of this invention. By setting the target reflection coefficient, the value of the compensation resistor is derived to achieve active control of traveling wave reflection. The specific operation is as follows: Clarify the formula for calculating the voltage reflection coefficient: The voltage reflection coefficient at the sending end boundary is determined by the boundary equivalent impedance. With line characteristic impedance The decision was made jointly, and the calculation formula is as follows:

[0035] Setting the suppression target: This invention uses As the core suppression target, it can completely avoid the superposition of same-polarity reflections of incident negative fault voltage traveling waves, and eliminate negative voltage impacts and voltage oscillations at the sending end; the optimal target is This achieves perfect impedance matching and zero reflection of traveling waves.

[0036] Derivation of the range of values ​​for the compensation resistor: Considering the high-frequency impedance characteristics of a RC series structure, when the value of the compensation resistor R is related to the characteristic impedance of the line... When the ratio is in the range of 0.5 to 1, the reflection coefficient of the sending end boundary voltage can be guaranteed. It meets the suppression requirements; when the value of the compensation resistor is equal to the characteristic impedance of the line, it achieves optimal zero-reflection matching.

[0037] Engineering adjustments: The specific resistance value can be selected within the above range according to the actual suppression requirements, cost constraints, and installation space of the project; for scenarios with high suppression requirements, a lower resistance value can be selected, and for cost-sensitive scenarios, a resistance value close to 1 times the characteristic impedance can be selected.

[0038] Step 3: Selection and Characteristic Verification of Compensation Capacitor Parameters. The compensation capacitor serves three functions: DC steady-state isolation, transient current path, and main frequency matching. Selection must consider both suppression effect and engineering feasibility. The specific steps are as follows: Verification of the core function of the capacitor: Under steady-state DC conditions, the capacitor exhibits open-circuit characteristics, blocking DC current and ensuring that the device has no continuous active power loss; under fault transient conditions, the capacitor exhibits low impedance to high-frequency components, providing a path for transient current and working with the resistor to dissipate traveling wave energy.

[0039] Capacitor matching principle: The capacitance value must match the fault transient frequency to ensure that the high-frequency transient components can pass smoothly through the resistor-capacitor circuit; at the same time, the capacitance value should not be too large to avoid excessive device size and cost.

[0040] General value range: Considering the transient frequency range of various DC lines and engineering cost constraints, the preferred range for compensation capacitor value is 0.5μF~10μF; for scenarios with low transient frequency such as submarine cables, a larger capacitance value can be selected, and for scenarios with high transient frequency such as overhead lines, a smaller capacitance value can be selected.

[0041] Withstand voltage check: The rated voltage of the capacitor must match the rated DC voltage of the system and the amplitude of transient overvoltage, and retain sufficient insulation margin to ensure that insulation breakdown does not occur under fault transients.

[0042] Step 4: After completing the parameter design for the system connection configuration of the RC compensation unit, complete the field connection of the device according to the following rules: Installation location: The smoothing reactor should be connected in parallel on the side of the DC transmission line (line side). It should not be installed on the side of the smoothing reactor that is close to the converter station, to ensure that the reactor and the compensation unit together form the regulated sending-end boundary. Wiring method: One end of the RC compensation unit is connected to the pole bus, and the other end is connected to the neutral bus or grounding electrode of the system; the positive and negative poles of the bipolar system are connected independently, and the two sets of units share the neutral / grounding circuit; Supporting requirements: The device connection circuit can be equipped with a disconnecting switch to facilitate device maintenance and disconnection without affecting the normal operation of the system; when modular devices are connected, it is necessary to ensure good contact of the wiring terminals and minimize the circuit inductance to avoid affecting the high-frequency impedance characteristics.

[0043] Step 5: After the steady-state operation characteristic verification device is connected, the steady-state operation characteristics need to be verified to ensure that it does not affect the normal power transmission of the system. Under steady-state DC conditions, the compensation capacitor blocks the DC path, and there is no continuous DC current in the RC circuit. Therefore, the device has no active power loss and will not reduce the system's power transmission efficiency. Under steady-state conditions, the device does not change the voltage and current distribution of the system, nor does it affect the control characteristics and power transmission capacity of the converter station; The device only functions during the millisecond-level transient process after a fault occurs. It is a passive protection device that operates in "steady-state standby and transient action," requiring no additional control system and exhibiting high reliability.

[0044] Step 6: Traveling Wave Control Process under Fault Transient When a short-circuit fault occurs in the DC line, the device achieves transient suppression through the following physical process: Initial stage of the fault: The voltage at the fault point drops sharply, generating a negative voltage traveling wave and a positive current traveling wave that propagate towards the sending end. The traveling waves propagate towards the sending end along the line at their inherent speed. During this stage, the sending end region remains in a steady state, and the device does not operate.

[0045] Initial boundary action stage: After the fault traveling wave arrives at the sending end boundary, the RC compensation unit changes the high impedance boundary characteristics of the original smoothing reactor, and the boundary equivalent impedance matches the line characteristic impedance; the incident voltage traveling wave no longer undergoes total reflection of the same polarity, and the reflection coefficient drops below 0, thus avoiding the negative superposition of the incident wave and the reflected wave from the source, and the amplitude of the negative voltage impact at the sending end is greatly reduced.

[0046] Oscillation attenuation stage: A small number of reflected waves propagate to the fault point and are reflected again, but since the sending end boundary no longer provides total reflection gain, the traveling wave is continuously consumed by the line resistance and compensation resistance during multiple propagations, and the oscillation amplitude decays rapidly, without forming a continuous high-frequency oscillation.

[0047] Current suppression effect: After the negative voltage surge at the sending end is weakened, the voltage difference across the smoothing reactor is significantly reduced, according to the inductor current variation law. The slope of the fault current rise decreases synchronously, and the time it takes for the current to rise to the equipment's tolerance threshold is significantly extended.

[0048] Step 7: Coordination with Relay Protection and Primary Equipment The RC compensation unit of this invention can work in conjunction with existing DC protection equipment to construct a multi-layered protection system: When used in conjunction with DC circuit breakers: By slowing down the rate of rise of fault current, the time it takes for the current to reach the circuit breaker's breaking threshold is extended, thus compensating for the inherent operating delay of the circuit breaker, reducing the peak breaking current of the circuit breaker, and improving breaking reliability.

[0049] When used in conjunction with relay protection devices: After the transient oscillation is reduced, the fault electrical quantity is more stable, which can reduce the risk of false tripping or failure to trip of the protection device; at the same time, the protection action time window is extended, and more reliable protection criteria can be used to improve the accuracy of protection.

[0050] When used in conjunction with surge arresters: surge arresters are responsible for clamping extreme overvoltage peak values, while RC compensation units are responsible for reducing oscillation amplitude from the source. The combination of the two can achieve all-round overvoltage protection of "amplitude + oscillation", further reducing equipment insulation stress.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A transient fault suppression system for a DC transmission system, comprising a DC transmission line fault traveling wave reflection suppression system, including a sending-end DC unit, a smoothing reactor, a DC transmission line, and a receiving-end unit, wherein the smoothing reactor is connected in series between the sending-end DC unit and the DC transmission line, characterized in that: The smoothing reactor is connected in parallel with a resistance-capacitance compensation unit on the side closest to the DC transmission line. The RC compensation unit is used to adjust the equivalent impedance characteristics of the sending end boundary, change the voltage reflection coefficient of the fault traveling wave caused by the short-circuit fault at the sending end boundary, and suppress the rapid rise of transient overvoltage and fault current caused by the repeated reflection and superposition of the fault traveling wave between the sending end and the fault point.

2. The DC transmission system fault transient suppression system and DC transmission line fault traveling wave reflection suppression system according to claim 1, characterized in that, The DC transmission system can be any one of a unipolar DC system, a pseudo-bipolar DC system, or a true bipolar DC system; The DC transmission line can be any one of a DC cable, an overhead DC line, or a hybrid land-sea DC transmission line.

3. The DC transmission system fault transient suppression system and DC transmission line fault traveling wave reflection suppression system according to claim 1, characterized in that, The DC transmission system is a two-terminal DC transmission system or a multi-terminal DC transmission system, and the sending-end DC unit is a grid-commutated converter or a modular multilevel converter.

4. The DC transmission system fault transient suppression system and DC transmission line fault traveling wave reflection suppression system according to claim 1, characterized in that, The RC compensation unit includes a compensation resistor and a compensation capacitor connected in series. One end of the RC compensation unit is connected to the pole conductor, and the other end is connected to the neutral bus or grounding electrode of the system. When the DC transmission system is a bipolar structure, a set of the RC compensation unit is independently connected in parallel on the line side of the smoothing reactor of the positive line and the negative line, respectively. The ratio of the resistance value of the compensation resistor to the characteristic impedance of the DC transmission line is 0.5~1, so that the voltage reflection coefficient at the sending end boundary is ≤0. The resistance value of the compensation resistor is equal to the characteristic impedance of the DC transmission line, so that the voltage reflection coefficient at the sending end boundary is 0, realizing impedance matching and no reflection of the fault traveling wave. The value range of the compensation capacitor is 0.5μF~10μF, and the capacitance value of the compensation capacitor is selected according to the fault transient main frequency range of the DC transmission line.

5. The DC transmission system fault transient suppression system according to claim 1, a DC transmission line fault traveling wave reflection suppression system, characterized in that, The RC compensation unit has no continuous active power loss during steady-state operation of the system and does not affect the normal power transmission of the DC transmission system; during fault transients, it provides damping and consumes traveling wave energy, suppressing transient oscillation amplitude. The fault transient is an electromagnetic transient process caused by a single-pole ground fault, a double-pole short-circuit fault, or an inter-pole short-circuit fault in a DC line.

6. The DC transmission system fault transient suppression system according to claim 1, a DC transmission line fault traveling wave reflection suppression system, characterized in that, The smoothing reactor is also connected in parallel with a surge arrester and a DC circuit breaker on the line side. The RC compensation unit works with the surge arrester and the DC circuit breaker to achieve fault transient suppression and fault isolation.

7. A fault transient suppression device applied to a DC transmission system, characterized in that, The device includes a compensation resistor and a compensation capacitor connected in series, and is used to be connected in parallel to the line side of the smoothing reactor at the sending end of the DC transmission system. The device adjusts the equivalent impedance characteristics at the sending end boundary to change the voltage reflection coefficient of the short-circuit fault traveling wave at the sending end boundary, thereby suppressing the rapid rise of transient overvoltage and fault current caused by the superposition of repeated reflections of the fault traveling wave.

8. The fault transient suppression device for a DC transmission system according to claim 7, characterized in that, The resistance value of the compensation resistor is configured such that the ratio of its resistance to the characteristic impedance of the target DC transmission line is 0.5 to 1, so that the reflection coefficient of the boundary voltage at the sending end after connection is ≤0; the value range of the compensation capacitor is 0.5μF to 10μF, which is suitable for the fault transient main frequency range of the DC transmission line; the device is a modular independent device with a standard DC access terminal, which can be directly connected in parallel to the output of the smoothing reactor of the existing DC transmission system.

9. A method for transient fault suppression in a DC transmission system, characterized in that, A resistor-capacitor (RC) compensation unit is connected in parallel at the connection node between the smoothing reactor at the sending end of the DC transmission system and the DC transmission line. The RRC compensation unit changes the voltage reflection coefficient at the sending end boundary, weakens the superposition effect of multiple reflections of the fault traveling wave caused by the short-circuit fault, thereby suppressing the transient overvoltage at the sending end and slowing down the rise rate of the fault current.

10. The method for transient fault suppression in a DC transmission system according to claim 9, characterized in that, Including parameter configuration steps: Calculate the characteristic impedance of the target DC transmission line, calculate the resistance value of the compensation resistor based on the preset target voltage reflection coefficient, select the capacitance value of the compensation capacitor in combination with the fault transient main frequency range, and complete the parameter matching of the RC compensation unit. The target voltage reflection coefficient is set to ≤0, and the ratio of the compensation resistor value to the line characteristic impedance is 0.5~1. For bipolar DC transmission systems, independent parallel RC compensation units are connected on the line side of the smoothing reactors at the positive and negative poles to suppress the reflection of fault traveling waves at the two poles respectively. The RC compensation unit has no continuous active power loss during steady-state operation of the system, and only plays a damping and suppression role during fault transients. The method is applicable to transient suppression under single-pole grounding faults, bipolar short-circuit faults, and inter-pole short-circuit faults, and is suitable for DC cables, overhead DC lines, and mixed land-sea lines. The resistor-capacitor compensation unit works in conjunction with the relay protection device of the DC system to extend the protection action time window by slowing down the rise rate of the fault current, thereby improving the reliability of the protection action.

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