Metal loop protection method and device

Abstract

The invention discloses a metal loop protection method and device, and relates to the field of flexible direct current power transmission systems.The method comprises the steps that when current collection of a metal loop connected with a local station is normal, current collection of a metal loop connected with an opposite station is normal, and the state of a direct current change-over switch is normal, whether a metal loop fault occurs or not is judged; when the operation mode is single-stage end-to-end operation and a metal loop fault occurs, a direct current circuit breaker of the station is controlled to be switched off; and when the operation mode is non-single-stage end-to-end operation and the metal return line has a fault, controlling the station to be closed or controlling the direct-current change-over switch on the metal return line to be switched off. And when the acquisition state of each metal return wire is determined to be normal, whether a metal return wire fault occurs or not is judged, so that maloperation of the direct-current power transmission system caused by wrong data is avoided. After the metal return wire breaks down, a subsequent protection strategy is determined according to whether the operation mode is a single-stage end-to-end mode, and the protection method is suitable for various operation modes.

Description

Technical Field

[0001] The present invention relates to the field of flexible direct current power transmission systems, and in particular to a metal return line protection method and device. Background Art

[0002] Flexible direct current transmission has flexible power control and can form a direct current grid through high-voltage direct current circuit breakers. When the flexible direct current grid adopts a bipolar structure, the redundancy of the entire flexible direct current grid is higher and the operation mode is more complicated. In order to ensure the safe and stable operation of the flexible direct current grid and minimize the transmission power loss when the system fails, high-voltage direct current circuit breakers can be fully utilized. Direct current circuit breakers can quickly cut off direct current and isolate faults, but different operation modes correspond to different connection relationships, so formulating different metal return line protection methods according to the connection relationship is an urgent problem to be solved. Summary of the invention

[0003] The purpose of the present invention is to provide a metal loop protection method and device to avoid malfunction of a DC power transmission system due to erroneous data. After a metal loop fails, a subsequent protection strategy is determined based on whether the operation mode is a single-stage end-to-end form, and the protection method is applicable to multiple operation modes.

[0004] In order to solve the above technical problems, the present invention provides a metal loop protection method, which is applied to a metal loop protection device. The metal loop protection device is used to protect a DC power transmission system. Each substation in the DC power transmission system is provided with a DC circuit breaker on the side of the positive DC line and the negative DC line close to itself, and a DC conversion switch is provided on the side of each metal loop close to itself. For any substation, the substation itself is regarded as the local station, and the substation connected to the substation is regarded as the opposite station. The local station outputs current to the opposite station through the positive DC line or the negative DC line, and returns current from the opposite station to the local station through the metal loop.

[0005] The metal return line protection method comprises:

[0006] Acquire the current of the metal loop connected to the local station, the current of the metal loop connected to the opposite station, and the state of the DC conversion switch on the metal loop connected to the local station, wherein the state includes on and off;

[0007] When the current collection of the metal loop connected to the local station is normal, the current collection of the metal loop connected to the opposite station is normal, and the state of the DC conversion switch is normal, determining whether a metal loop fault occurs;

[0008] When the operation mode is single-stage end-to-end operation and a metal return line fault occurs, the DC circuit breaker of the station is controlled to be disconnected. The single-stage end-to-end operation means that the station transmits electric energy only with one other station through the positive DC line and the metal return line or the negative DC line and the metal return line;

[0009] When the operation mode is non-single-stage end-to-end operation and a metal return line fault occurs, the station is controlled to be closed or the DC conversion switch on the metal return line is controlled to be disconnected.

[0010] On the other hand, the DC power transmission system further includes a mutual inductor, which is arranged on the metal loop line, and the metal loop line protection device further includes three measurement modules, which are all connected to the mutual inductor;

[0011] Obtaining the current of the metal return line connected to the station, including:

[0012] The current at the same measuring point on the metal loop collected by the three measuring modules is obtained, which are I M1 ,I M2 and I M3 ;

[0013] The current collection of the metal return line connected to the station is normal, including:

[0014] The current I at the same measuring point on the metal loop collected by the three measuring modules M1 ,I M2 and I M3 The absolute value of the difference between the maximum and minimum values ​​is greater than I M1 ,I M2 and I M3 When the current collection of the metal return line connected to the station is normal, it is determined that the current collection of the metal return line connected to the station is normal.

[0015] On the other hand, the metal loop protection device further comprises a collection module, and the collection module is connected to the DC conversion switch on the metal loop;

[0016] Obtaining the state of a DC conversion switch on a metal return line connected to the station, including:

[0017] Acquiring the feedback signal of the DC conversion switch collected by the collection module;

[0018] The state of the DC conversion switch corresponding to the feedback signal is determined according to the feedback signal.

[0019] On the other hand, after obtaining the current of the metal loop connected to the local station, the current of the metal loop connected to the opposite station, and the state of the DC conversion switch on the metal loop connected to the local station, the method further includes:

[0020] When there is a current anomaly in the metal loop connected to the local station, a current anomaly in the metal loop connected to the opposite station, an abnormal state of the DC conversion switch, or a communication interruption between the local station and the opposite station, a fault signal is generated.

[0021] On the other hand, the metallic return line protection device further comprises an inter-station communication module, the inter-station communication module is connected to the substation in a one-to-one correspondence, and the inter-station communication module of the station is communicatively connected with the inter-station communication module of the opposite station;

[0022] Also includes:

[0023] Send a heartbeat signal to the inter-station communication module of the opposite station through the inter-station communication module of the local station;

[0024] If the inter-station communication module of the opposite station cannot receive the heartbeat signal sent by the inter-station communication module of the local station, or the heartbeat signal does not change according to a preset period, it is determined that the communication between the local station and the opposite station is interrupted;

[0025] Obtaining the current of the metal return line connected to the pair of stations, comprising:

[0026] The current of the metal return line connected to the opposite station and forwarded by the opposite station through the inter-station communication module of the opposite station and the communication module of the own station is obtained.

[0027] On the other hand, when the operation mode is single-stage end-to-end operation, controlling the DC circuit breaker of the station to disconnect includes:

[0028] When the operation mode is single-stage end-to-end operation, the DC circuit breaker of the station and the DC short circuit breaker of the opposite station are controlled to be disconnected;

[0029] After the preset time, the DC circuit breaker of this station and the DC short circuit breaker of the opposite station are controlled to close;

[0030] Determine whether the current collection of the metal loop connected to the local station is normal, the current collection of the metal loop connected to the opposite station is normal, and the state of the DC conversion switch is normal;

[0031] If not, the DC circuit breaker of this station and the DC short circuit breaker of the opposite station will be disconnected, and this station will be closed.

[0032] On the other hand, when the operation mode is non-single-stage end-to-end operation, controlling the station to shut down or controlling the DC conversion switch on the metal return line to disconnect includes:

[0033] Determine whether the DC conversion switch near the station can connect the metal return line through the metal return line that has not failed to connect to the grounding resistance of the metal return line;

[0034] If it is possible to connect to the grounding resistance of the metal return line through a metal return line that has not failed, disconnect the DC conversion switch close to this station;

[0035] If it is not possible to connect to the grounding resistance of the metal return line through a metal return line that has not failed, the station will be controlled to be closed.

[0036] On the other hand, judging whether a metal return line fault occurs includes:

[0037] Determine the number of operations of the current action protection condition, wherein the action protection condition includes a first action protection condition, a second action protection condition, and a third action protection condition;

[0038] Among them, the expression of the first action protection condition is | I M1 +I OM1 |>Max(| I M1 -I OM1 |×k, Iset), the expression of the second action protection condition is | I M2 +I OM2 |>Max(| I M2 -I OM2 |×k, Iset), the expression of the third action protection condition is | I M3 +I OM3 |>Max(| I M3 -I OM3 |×k,Iset),I M1 ,I M2 and I M3 The current of the metal loop connected to the station, k is the proportionality coefficient, and Iset is the protection start setting;

[0039] When the number of operations is three, the first action protection condition, the second action protection condition and the third action protection condition are operated simultaneously, and when at least two action protection conditions are met, it is determined that a metal return line fault occurs;

[0040] When the number of operations is two, any two of the first action protection condition, the second action protection condition and the third action protection condition are operated, and when at least one action protection condition is satisfied, it is determined that a metal return line fault occurs;

[0041] When the operation number is one, one of the first action protection condition, the second action protection condition and the third action protection condition is operated, and when one action protection condition is met, it is determined that a metal return line fault occurs.

[0042] In order to solve the above technical problems, the present invention also provides a metal return line protection device, comprising:

[0043] Memory for storing computer programs;

[0044] The processor is used to implement the steps of the above-mentioned metallic return line protection method when executing the computer program.

[0045] On the other hand, it also includes:

[0046] A measuring module, used for obtaining the current of the metal return line connected to the station;

[0047] A collection module, the collection module is connected to the DC conversion switch on the metal return line, and is used to obtain the state of the DC conversion switch on the metal return line connected to the local station;

[0048] An inter-station communication module, wherein the inter-station communication module is connected to the substation in a one-to-one correspondence, and the inter-station communication module of the station is connected to the inter-station communication module of the opposite station for realizing communication between the station and the opposite station;

[0049] The processor includes a central processing module and a data processing module. The central processing module is connected to the measurement module, the acquisition module and the inter-station communication module respectively, and is used to communicate with the measurement module, the acquisition module and the inter-station communication module. The data processing module is used to control the metallic return line protection device to protect the DC transmission system based on the data obtained through communication.

[0050] A power supply module, wherein the power supply module includes a first power supply module and a second power supply module, wherein the first power supply module is connected to a first power supply, and the second power supply module is connected to a second power supply module, and the first power supply module and the second power supply module are used to power the memory, the processor, the measurement module, the acquisition module and the inter-station communication module after coupling.

[0051] The present invention discloses a metal loop protection method and device, which relates to the field of flexible direct current transmission system, including judging whether a metal loop fault occurs when the current collection of the metal loop connected to the station is normal, the current collection of the metal loop connected to the other station is normal, and the state of the direct current conversion switch is normal; when the operation mode is single-stage end-to-end operation and a metal loop fault occurs, controlling the direct current circuit breaker of the station to be disconnected; when the operation mode is non-single-stage end-to-end operation and a metal loop fault occurs, controlling the station to be closed or controlling the direct current conversion switch on the metal loop to be disconnected. When it is determined that the state of each metal loop collection is normal, it is judged whether a metal loop fault occurs to avoid malfunction of the direct current transmission system due to erroneous data. After the metal loop fails, the subsequent protection strategy is determined according to whether the operation mode is single-stage end-to-end, and the protection method is suitable for multiple operation modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the prior art and the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0053] Figure 1 A flow chart of a metal return line protection method provided by the present invention;

[0054] Figure 2 A schematic structural diagram of a direct current transmission system provided by the present invention;

[0055] Figure 3 A schematic diagram of a structure in which a fault occurs at a negative terminal end provided by the present invention;

[0056] Figure 4 A schematic diagram of the structure of a DC conversion switch provided by the present invention connected to a grounding resistor via a non-fault metal return line;

[0057] Figure 5 A schematic diagram of the structure of a DC conversion switch provided by the present invention that cannot reach the grounding resistor without passing through a faulty metal return line;

[0058] Figure 6 A schematic structural diagram of a metal return line protection device provided by the present invention;

[0059] Figure 7 A schematic structural diagram of another metal return line protection device provided by the present invention. DETAILED DESCRIPTION

[0060] The core of the present invention is to provide a metal loop protection method and device to avoid malfunction of the DC transmission system due to erroneous data. After a metal loop fails, the subsequent protection strategy is determined according to whether the operation mode is a single-stage end-to-end form, and the protection method is suitable for multiple operation modes.

[0061] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] Figure 1A flow chart of a metal loop protection method provided by the present invention, the metal loop protection method is applied to a metal loop protection device, the metal loop protection device is used to protect a DC power transmission system, each substation in the DC power transmission system is provided with a DC circuit breaker on the side of the positive DC line and the negative DC line close to itself, and a DC conversion switch is provided on the side of each metal loop close to itself, for any substation, itself is regarded as the local station, and the substation connected to itself is regarded as the opposite station, the local station outputs current to the opposite station through the positive DC line or the negative DC line, and returns current from the opposite station to the local station through the metal loop;

[0063] Metal return line protection method, including:

[0064] S11: obtaining the current of the metal loop connected to the local station, the current of the metal loop connected to the opposite station, and the state of the DC conversion switch on the metal loop connected to the local station, including the state of on and off;

[0065] S12: When the current collection of the metal loop connected to the local station is normal, the current collection of the metal loop connected to the opposite station is normal, and the state of the DC conversion switch is normal, it is determined whether a metal loop fault occurs;

[0066] When judging a metal return line fault, it is necessary to confirm whether a fault actually occurs based on the current. If the current acquisition is normal, it means that the acquired current value is correct. Based on this current value, it can be determined whether a metal return line fault actually occurs.

[0067] If the current collection is abnormal, it will not be accurate enough to determine whether the metal return line has a fault based on the collected current.

[0068] S13: When the operation mode is single-stage end-to-end operation and a metal return line fault occurs, the DC circuit breaker of the station is controlled to be disconnected. The single-stage end-to-end operation means that the station transmits electric energy only with one other station through the positive DC line and the metal return line or the negative DC line and the metal return line;

[0069] When operating in single-stage end-to-end mode, there may not be other metal return line connections that have not failed, and thus other metal return line connections cannot be used. Therefore, the DC circuit breaker of this station can only be controlled to disconnect.

[0070] S14: When the operation mode is non-single-stage end-to-end operation and a metal return line fault occurs, control the station to shut down or disconnect the DC conversion switch on the metal return line.

[0071] When the operation is not single-stage end-to-end, the metal loop connection relationship is more diverse. It may not be necessary to control the station to shut down, and the DC conversion switch can be controlled to disconnect. Of course, there are also situations where the station can be shut down.

[0072] Figure 2 A schematic structural diagram of a direct current transmission system provided by the present invention;

[0073] Figure 2 Among them, S1 is the first substation, S2 is the second substation, S3 is the third substation, S4 is the fourth substation, P1 is the positive pole, P2 is the negative pole. M12, M23, M34 and M41 are all metal return lines.

[0074] Current transmission can be achieved between substations. For example, if the positive pole (S2.P1) of the second substation wants to transmit electric energy to the positive pole of the first substation (S1.P1), it will reach the first substation from the high-voltage circuit breaker, DC line, and high-voltage circuit breaker on the side of the second substation, and then return to the second substation from the metal return line M12. The transmission between negative poles is the same as above, and this application will not be repeated here.

[0075] The present invention discloses a metal loop protection method, which relates to the field of flexible direct current transmission system, including judging whether a metal loop fault occurs when the current collection of the metal loop connected to the station is normal, the current collection of the metal loop connected to the other station is normal, and the state of the direct current conversion switch is normal; when the operation mode is single-stage end-to-end operation and a metal loop fault occurs, controlling the direct current circuit breaker of the station to be disconnected; when the operation mode is non-single-stage end-to-end operation and a metal loop fault occurs, controlling the station to be closed or controlling the direct current conversion switch on the metal loop to be disconnected. When it is determined that the state of each metal loop collection is normal, it is judged whether a metal loop fault occurs to avoid malfunction of the direct current transmission system due to erroneous data. After the metal loop fails, the subsequent protection strategy is determined according to whether the operation mode is single-stage end-to-end, and the protection method is suitable for multiple operation modes.

[0076] Based on the above embodiments:

[0077] In some embodiments, the DC power transmission system further includes a mutual inductor, which is arranged on the metal loop line, and the metal loop line protection device further includes three measurement modules, which are all connected to the mutual inductor;

[0078] Get the current of the metal return line connected to this station, including:

[0079] The current at the same measuring point on the metal loop collected by the three measurement modules is obtained, which are I M1 ,I M2 and I M3 ;

[0080] The current collection of the metal return line connected to this station is normal, including:

[0081] The current I at the same measuring point on the metal loop collected by three measurement modulesM1 ,I M2 and I M3 The absolute value of the difference between the maximum and minimum values ​​is greater than I M1 ,I M2 and I M3 When the current collection of the metal return line connected to this station is normal, it is determined that the current collection of the metal return line connected to this station is normal.

[0082] The three analog quantity acquisition modules collect the metal loop current at the same measuring point, and the sampling values ​​are I M1 ,I M2 ,I M3 , the collected current is sent to the central processing module, the central processing module determines whether the collected current is normal, if it is normal, it is sent to the data processing module, if it is abnormal, it exits the corresponding protection, and sends the current abnormality signal to the inter-station communication module. The specific judgment logic is: I M1 ,I M2 ,I M3 The absolute value of the difference between the maximum and minimum values ​​is greater than 0.2 times the average value.

[0083] In some embodiments, the metal return line protection device further includes a collection module, and the collection module is connected to the DC conversion switch on the metal return line;

[0084] Get the status of the DC switch on the metal return line connected to this station, including:

[0085] Acquire the feedback signal of the DC conversion switch collected by the collection module;

[0086] The state of the DC conversion switch corresponding to the feedback signal is determined according to the feedback signal.

[0087] The DC metal loop protection device includes three analog quantity acquisition modules to collect the metal loop current; and three switch quantity acquisition modules to collect the opening and closing status of the isolating switch and DC conversion switch in the metal loop. The DC metal loop protection device includes six inter-station communication modules to communicate with the DC metal loop protection of the opposite station, collect the metal loop current of the opposite station, whether the metal loop current measurement of the opposite station is normal, and the connection status of the metal loop, and send the above information of this station to the inter-station communication module of the corresponding protection device of the opposite station.

[0088] In some embodiments, after obtaining the current of the metal loop connected to the local station, the current of the metal loop connected to the opposite station, and the state of the DC conversion switch on the metal loop connected to the local station, the method further includes:

[0089] When there is an abnormal current in the metal loop connected to the local station, an abnormal current in the metal loop connected to the opposite station, an abnormal state of the DC conversion switch, or communication between the local station and the opposite station is interrupted, a fault signal is generated.

[0090] When it is confirmed that the communication is interrupted or the current value is abnormal, it is inaccurate to control the on and off of the DC transmission system according to the abnormal value, which is easy to cause malfunction, so a fault signal is generated for the user to handle.

[0091] In some embodiments, the metallic loop protection device further includes an inter-station communication module, the inter-station communication module is connected to the substation in a one-to-one correspondence, and the inter-station communication module of the station is communicatively connected with the inter-station communication module of the opposite station;

[0092] Also includes:

[0093] Send a heartbeat signal to the inter-station communication module of the opposite station through the inter-station communication module of the local station;

[0094] If the inter-station communication module of the opposite station cannot receive the heartbeat signal sent by the inter-station communication module of the local station, or the heartbeat signal does not change according to the preset period, it is determined that the communication between the local station and the opposite station is interrupted;

[0095] Obtain the current of the metal return line connected to the station, including:

[0096] The current of the metal return line connected to the opposite station is obtained, which is forwarded by the inter-station communication module of the opposite station and the communication module of the local station.

[0097] Metal return line current I OM1 ,I OM2 ,I OM3 The signal of whether the current measurement is normal and the signal of the metal loop connection status are sent to the inter-station communication module of the DC metal loop protection device of the station through the inter-station communication module in the DC metal loop protection device of the station, and the inter-station communication module of the station sends the above signals to the central processing module. If the inter-station communication module of the station does not receive the data of the station or the inter-station communication fails or the current measurement of the station is abnormal, the station will exit the corresponding protection.

[0098] The inter-station communication module in the protection device of this station sends a "heartbeat" signal to the inter-station communication module in the protection device of the other station. The heartbeat signal periodically changes from 1, 2, 3... to 100. If the inter-station communication module of the other station does not receive the "heartbeat" signal, or the signal does not change periodically, the inter-station communication module of the other station sends a "communication failure" signal to the inter-station communication module of this station.

[0099] Figure 3 A schematic diagram of a structure in which a fault occurs at a negative terminal end provided by the present invention;

[0100] In some embodiments, when the operation mode is single-stage end-to-end operation, controlling the DC circuit breaker of the station to disconnect includes:

[0101] When the operation mode is single-stage end-to-end operation, the DC circuit breaker of the control station and the DC short circuit breaker of the opposite station are disconnected;

[0102] After the preset time, the DC circuit breaker of this station and the DC short circuit breaker of the opposite station are controlled to close;

[0103] Determine whether the current collection of the metal loop connected to the local station is normal, the current collection of the metal loop connected to the opposite station is normal, and the state of the DC conversion switch is normal;

[0104] If not, the DC circuit breaker of this station and the DC short circuit breaker of the opposite station will be disconnected, and this station will be closed.

[0105] When the system is running in single-end peer mode, Figure 3 As shown in the figure, when a fault occurs in the metal return line, the DC metal return line protection is activated, and the high-voltage DC circuit breakers of the local station and the opposite station (each end corresponds to a converter station, the local station is the converter station at the local end, and the opposite station is the converter station at the opposite end) are tripped. After the fault is freed for a certain time (after the fault is sent, the fault recovery takes a certain amount of time, and it must be delayed until the fault disappears before closing, otherwise the fault still exists after closing and the circuit breaker must be tripped again), the DC circuit breaker is reclosed. If the fault still exists, the high-voltage DC circuit breaker is tripped again and the converter valve is locked.

[0106] Figure 4 A schematic diagram of the structure of a DC conversion switch provided by the present invention connected to a grounding resistor via a non-fault metal return line;

[0107] Figure 5 A schematic diagram of the structure of a DC conversion switch provided by the present invention that cannot reach the grounding resistor without passing through a faulty metal return line;

[0108] In some embodiments, when the operation mode is non-single-stage end-to-end operation, controlling the station to shut down or controlling the DC conversion switch on the metal return line to disconnect includes:

[0109] Determine whether the DC conversion switch near the station can connect the metal return line through the metal return line that has not failed to connect to the grounding resistance of the metal return line;

[0110] If it is possible to connect to the grounding resistance of the metal return line through a metal return line that has not failed, disconnect the DC conversion switch close to this station;

[0111] If it is not possible to connect to the grounding resistance of the metal return line through a metal return line that has not failed, the station will be controlled to be closed.

[0112] The operation mode of the DC power grid, the present application is a four-terminal, bipolar DC power grid, and the operation mode has two dimensions: unipolar / bipolar, four-terminal / bipolar (end-to-end), then the corresponding combinations are called unipolar end-to-end operation, bipolar end-to-end operation, bipolar four-terminal operation, unipolar four-terminal operation. When the system operation mode is not unipolar end-to-end operation, the metal loop fails, and the DC metal loop protection is activated, and the DC conversion switches on both sides of the metal loop are tripped. When executing the tripping DC conversion switch, it is necessary to determine the connection status of the metal loop. When the DC conversion switch is connected to the grounding resistor without passing through the faulty metal loop, the jump conversion switch instruction is executed, such as Figure 4 When the DC conversion switch cannot be connected to the grounding resistor without the faulty metal return line, the jump switch command is not executed and the converter valve is locked, such as Figure 5 shown.

[0113] In some embodiments, determining whether a metal return line fault occurs includes:

[0114] Determine the number of operations of the current action protection condition, where the action protection condition includes a first action protection condition, a second action protection condition, and a third action protection condition;

[0115] Among them, the expression of the first action protection condition is | I M1 +I OM1 |>Max(| I M1 -I OM1 |×k, Iset), the expression of the second action protection condition is | I M2 +I OM2 |>Max(| I M2 -I OM2 |×k, Iset), the expression of the third action protection condition is | I M3 +I OM3 |>Max(| I M3 -I OM3 |×k,Iset),I M1 ,I M2 and I M3 The current of the metal loop connected to this station, k is the proportional coefficient, and Iset is the protection start setting;

[0116] When the number of operations is three, the first action protection condition, the second action protection condition and the third action protection condition are operated simultaneously, and when at least two action protection conditions are met, it is determined that a metal return line fault occurs;

[0117] When the number of operations is two, any two of the first action protection condition, the second action protection condition and the third action protection condition are operated, and when at least one action protection condition is met, it is determined that a metal return line fault occurs;

[0118] When the number of operations is one, one of the first action protection condition, the second action protection condition and the third action protection condition is operated, and when one action protection condition is satisfied, it is determined that a metal return line fault occurs.

[0119] 1. The specific calculation logic is:

[0120] Protection 1 action condition: | I M1 +I OM1 |>Max(| I M1 -I OM1 |×k,Iset);

[0121] Protection 2 action condition: | I M2 +I OM2 |>Max(| I M2 -I OM2 |×k,Iset);

[0122] Protection 3 action conditions: | I M3 +I OM3 |>Max(| I M3 -I OM3 |×k,Iset);

[0123] Where k represents the proportional coefficient, and Iset is the protection start setting.

[0124] The data processing module sends the calculated protection action to the central processing module, which first performs a three-out-of-two logic process, that is, when three sets of protection are in operation, if two or more protections are in operation, the protection outlet is protected (protection tripping); when two sets of protection are in operation, if any one set of protection is in operation, the protection outlet is protected; if only one set of protection is in operation, the protection action is protected, and the protection outlet is protected. Combined with the operation mode of the DC power grid metal loop, the protection action result is given.

[0125] Figure 6 The present invention provides a schematic structural diagram of a metal loop protection device, the metal loop protection device comprising:

[0126] A memory 61, used for storing computer programs;

[0127] The processor 62 is used to implement the steps of the above-mentioned metallic return line protection method when executing the computer program.

[0128] Figure 7 A schematic structural diagram of another metal return line protection device provided by the present invention;

[0129] In some embodiments, it also includes:

[0130] A measuring module 63, used to obtain the current of the metal return line connected to the station;

[0131] A collection module 64, which is connected to a DC conversion switch on a metal return line and is used to obtain a state of the DC conversion switch on the metal return line connected to the station;

[0132] Inter-station communication module 65, the inter-station communication module 65 is connected to the substation in a one-to-one correspondence, and the inter-station communication module 65 of the local station is connected to the inter-station communication module 65 of the opposite station for realizing communication between the local station and the opposite station;

[0133] The processor includes a central processing module 621 and a data processing module 622. The central processing module 621 is connected to the measurement module 63, the acquisition module 64 and the inter-station communication module 65 respectively, and is used to communicate with the measurement module 63, the acquisition module 64 and the inter-station communication module 65. The data processing module 622 is used to control the metallic return line protection device to protect the DC transmission system based on the data obtained by the communication;

[0134] The power supply module includes a first power supply module 661 and a second power supply module 662. The first power supply module 661 is connected to a first power supply, and the second power supply module 662 is connected to a second power supply module. The first power supply module 661 and the second power supply module 662 are used to couple to supply power to the memory 61, the processor 62, the measurement module 63, the acquisition module 64 and the inter-station communication module 65.

[0135] For an introduction to the metal loop protection device provided in the present application, please refer to the above embodiments, which will not be described in detail here.

[0136] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0137] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0138] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A metal return line protection method, characterized in that: Applied to a metal loop protection device, the metal loop protection device is used to protect a DC power transmission system, each substation in the DC power transmission system is provided with a DC circuit breaker on the side of the positive DC line and the negative DC line close to itself, and a DC conversion switch is provided on the side of each metal loop close to itself. For any substation, itself is regarded as the local station, and the substation connected to itself is regarded as the opposite station. The local station outputs current to the opposite station through the positive DC line or the negative DC line, and returns current from the opposite station to the local station through the metal loop; The metal return line protection method comprises: Acquire the current of the metal loop connected to the local station, the current of the metal loop connected to the opposite station, and the state of the DC conversion switch on the metal loop connected to the local station, wherein the state includes on and off; When the current collection of the metal loop connected to the local station is normal, the current collection of the metal loop connected to the opposite station is normal, and the state of the DC conversion switch is normal, determining whether a metal loop fault occurs; When the operation mode is single-stage end-to-end operation and a metal return line fault occurs, the DC circuit breaker of the station is controlled to be disconnected. The single-stage end-to-end operation means that the station transmits electric energy only with one other station through the positive DC line and the metal return line or the negative DC line and the metal return line; When the operation mode is non-single-stage end-to-end operation and a metal return line fault occurs, the station is controlled to be closed or the DC conversion switch on the metal return line is controlled to be disconnected.

2. The metal loop protection method according to claim 1, characterized in that: The DC power transmission system further includes a mutual inductor, which is arranged on the metal loop line. The metal loop line protection device further includes three measurement modules, which are all connected to the mutual inductor. Obtaining the current of the metal return line connected to the station, including: The current at the same measuring point on the metal loop collected by the three measuring modules is obtained, which are I M1 ,I M2 and I M3 ; The current collection of the metal return line connected to the station is normal, including: The current I at the same measuring point on the metal loop collected by the three measuring modules M1 ,I M2 and I M3 The absolute value of the difference between the maximum and minimum values ​​is greater than I M1 ,I M2 and I M3 When the current collection of the metal return line connected to the station is normal, it is determined that the current collection of the metal return line connected to the station is normal.

3. The metal loop protection method according to claim 1, characterized in that: The metal loop protection device further comprises a collection module, and the collection module is connected to the DC conversion switch on the metal loop; Obtaining the state of a DC conversion switch on a metal return line connected to the station, including: Acquiring the feedback signal of the DC conversion switch collected by the collection module; The state of the DC conversion switch corresponding to the feedback signal is determined according to the feedback signal.

4. The metal loop protection method according to claim 1, characterized in that: After obtaining the current of the metal loop connected to the local station, the current of the metal loop connected to the opposite station, and the state of the DC conversion switch on the metal loop connected to the local station, the method further includes: When there is a current anomaly in the metal loop connected to the local station, a current anomaly in the metal loop connected to the opposite station, an abnormal state of the DC conversion switch, or a communication interruption between the local station and the opposite station, a fault signal is generated.

5. The metal loop protection method according to claim 4, characterized in that: The metallic return line protection device further comprises an inter-station communication module, the inter-station communication module is connected to the substation in a one-to-one correspondence, and the inter-station communication module of the station is communicatively connected with the inter-station communication module of the opposite station; Also includes: Send a heartbeat signal to the inter-station communication module of the opposite station through the inter-station communication module of the local station; If the inter-station communication module of the opposite station cannot receive the heartbeat signal sent by the inter-station communication module of the local station, or the heartbeat signal does not change according to a preset period, it is determined that the communication between the local station and the opposite station is interrupted; Obtaining the current of the metal return line connected to the pair of stations, comprising: The current of the metal return line connected to the opposite station and forwarded by the opposite station through the inter-station communication module of the opposite station and the communication module of the own station is obtained.

6. The metal loop protection method according to claim 1, characterized in that: When the operation mode is single-stage end-to-end operation, controlling the DC circuit breaker of the station to disconnect includes: When the operation mode is single-stage end-to-end operation, the DC circuit breaker of the station and the DC short circuit breaker of the opposite station are controlled to be disconnected; After the preset time, the DC circuit breaker of this station and the DC short circuit breaker of the opposite station are controlled to close; Determine whether the current collection of the metal loop connected to the local station is normal, the current collection of the metal loop connected to the opposite station is normal, and the state of the DC conversion switch is normal; If not, the DC circuit breaker of this station and the DC short circuit breaker of the opposite station will be disconnected, and this station will be closed.

7. The metal loop protection method according to claim 1, characterized in that: When the operation mode is non-single-stage end-to-end operation, controlling the station to shut down or controlling the DC conversion switch on the metal return line to disconnect includes: Determine whether the DC conversion switch near the station can connect the metal return line through the metal return line that has not failed to connect to the grounding resistance of the metal return line; If it is possible to connect to the grounding resistance of the metal return line through a metal return line that has not failed, disconnect the DC conversion switch close to this station; If it is not possible to connect to the grounding resistance of the metal return line through a metal return line that has not failed, the station will be controlled to be closed.

8. The metal loop protection method according to any one of claims 1 to 7, characterized in that: Determine whether a metal return line fault occurs, including: Determine the number of operations of the current action protection condition, wherein the action protection condition includes a first action protection condition, a second action protection condition, and a third action protection condition; Among them, the expression of the first action protection condition is |I M1 +I OM1 |>Max(|I M1 -I OM1 |×k, Iset), the expression of the second action protection condition is |I M2 +I OM2 |>Max(|I M2 -I OM2 |×k, Iset), the expression of the third action protection condition is |I M3 +I OM3 |>Max(|I M3 -I OM3 |×k,Iset),I M1 ,I M2 and I M3 The current of the metal loop connected to the station, k is the proportional coefficient, Iset is the protection start setting, I M1 ,I M2 and I M3 I is the current at the same measuring point on the metal loop of this station collected by the measurement module, OM1 ,I OM2 and I OM3 The current at the same measuring point on the metal loop of the opposite station collected by the measuring module; When the number of operations is three, the first action protection condition, the second action protection condition and the third action protection condition are operated simultaneously, and when at least two action protection conditions are met, it is determined that a metal return line fault occurs; When the number of operations is two, any two of the first action protection condition, the second action protection condition and the third action protection condition are operated, and when at least one action protection condition is satisfied, it is determined that a metal return line fault occurs; When the operation number is one, one of the first action protection condition, the second action protection condition and the third action protection condition is operated, and when one action protection condition is met, it is determined that a metal return line fault occurs.

9. A metal loop protection device, characterized in that: include: Memory for storing computer programs; A processor is used to implement the steps of the metallic return line protection method as claimed in any one of claims 1 to 8 when executing the computer program.

10. The metal loop protection device according to claim 9, characterized in that: Also includes: A measuring module, used to obtain the current of the metal return line connected to the station; A collection module, the collection module is connected to the DC conversion switch on the metal return line, and is used to obtain the state of the DC conversion switch on the metal return line connected to the local station; An inter-station communication module, wherein the inter-station communication module is connected to the substation in a one-to-one correspondence, and the inter-station communication module of the local station is connected to the inter-station communication module of the opposite station for realizing communication between the local station and the opposite station; The processor includes a central processing module and a data processing module. The central processing module is connected to the measurement module, the acquisition module and the inter-station communication module respectively, and is used to communicate with the measurement module, the acquisition module and the inter-station communication module. The data processing module is used to control the metallic return line protection device to protect the DC transmission system based on the data obtained through communication. A power supply module, wherein the power supply module includes a first power supply module and a second power supply module, wherein the first power supply module is connected to a first power supply, and the second power supply module is connected to a second power supply module, and the first power supply module and the second power supply module are used to power the memory, the processor, the measurement module, the acquisition module and the inter-station communication module after coupling.

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