A method and device for protecting a metal return line of an extra-high voltage converter station

Abstract

The present application belongs to the technical field of DC transmission metal return line protection, and particularly relates to a UHV converter station metal return line protection method and device. When the high-end converter metal return line is in operation, the high-end converter station grounding electrode is used as the metal return line grounding point, and the metal return line fault is detected according to the metal return line grounding protection, metal return line longitudinal differential protection and metal return line transverse differential protection in the high-end converter station pole protection. When the double converter or low-end converter metal return line is in operation, the low-end converter station grounding electrode is used as the metal return line grounding point, and the metal return line fault is detected according to the metal return line grounding protection, metal return line longitudinal differential protection and metal return line transverse differential protection in the low-end converter station pole protection. The present application configures the metal return line protection function in the double converter stations, adapts to the metal return line operation condition of the double converter address construction UHV DC transmission project, and completes the detection and protection of the metal return line area fault.

Description

Technical Field

[0001] This invention belongs to the field of DC transmission metallic return line protection technology, specifically relating to a method and device for protecting metallic return lines in ultra-high voltage converter stations. Background Technology

[0002] In conventional UHV projects, the metallic circuit is fixed, and the metallic circuit protection strategy is relatively simple. The longitudinal differential protection of the metallic circuit is effective in the rectifier station when the metallic circuit is in operation. The grounding protection and transverse differential protection of the metallic circuit can only detect faults in the grounding station (usually the inverter station) when the metallic circuit is in operation, and therefore are effective in the inverter station.

[0003] When there are two power supply points at the sending end or two power receiving points at the receiving end of an ultra-high voltage direct current (UHVDC) transmission project, and they are far apart, a scheme can be adopted in which the high-end and low-end converter stations are built at separate sites and each converter station is equipped with a grounding electrode. The following are three operating conditions for the metallic return line:

[0004] 1) When the high-end converter is in operation with the metallic return line, the system is connected to the metallic return line through the neutral bus of the high-end converter station. The grounding electrode of the high-end converter station is usually selected as the grounding point when the metallic return line is in operation.

[0005] 2) When the high-end converter is running on the metallic return line, if the grounding electrode of the high-end converter station experiences a fault such as tower collapse or wire breakage, the grounding electrode of the low-end converter station shall be selected as the grounding point for the metallic return line during operation.

[0006] 3) When the dual converter or low-end converter is in operation with a metallic return line, the low-end converter station connects the metallic return line through three sections: the neutral busbar of the low-end converter station, the grounding electrode, and the grounding electrode of the high-end converter station. The grounding electrode of the low-end converter station must be in a connected state, serving as the grounding point of the metallic return line.

[0007] For UHV converter stations where high-end and low-end converter stations are built at separate sites and each converter station is equipped with a grounding electrode, the metallic return line operating circuit is complex and variable, and the conventional metallic return line protection configuration strategy for UHV projects is no longer applicable. Summary of the Invention

[0008] The purpose of this invention is to provide a method and device for protecting the metallic return line of an ultra-high voltage converter station, in order to solve the problem that the metallic return line protection configuration strategy of conventional ultra-high voltage projects is not applicable to the metallic return line protection configuration strategy of ultra-high voltage converter stations where high-end and low-end converter stations are built separately and the two converter stations are configured with grounding electrodes separately.

[0009] To solve the above-mentioned technical problems, the present invention provides a method for protecting the metallic return line of an ultra-high voltage converter station, including at least one of the following solutions:

[0010] Option 1: When the high-end converter's metallic return line is running, the high-end converter station's grounding electrode is used as the grounding point of the metallic return line. The metallic return line is checked for faults based on the metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection in the high-end converter station's electrode protection.

[0011] Option 2: When the dual converter or low-end converter is operating with a metallic return line, the grounding electrode of the low-end converter station is used as the grounding point of the metallic return line. The metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection in the low-end converter station electrode protection are used to detect whether there is a fault in the metallic return line.

[0012] Its beneficial effects are as follows: This invention configures metallic loop longitudinal differential protection, metallic loop transverse differential protection, and metallic loop grounding protection functions at high-end and low-end converter stations respectively. Depending on the operating conditions (including metallic loop operation only for the high-end converter, metallic loop operation only for the low-end converter, and dual-converter metallic loop operation), the metallic loop protection function of the high-end or low-end converter station is selected for activation. Furthermore, the measurement points of the criterion are automatically switched according to the different grounding electrode circuits, thus completing the detection of faults in the metallic loop area. The metallic loop protection strategy proposed in this invention, by configuring metallic loop protection functions at both converter stations, adapts to the fault operation conditions of UHVDC transmission projects with dual converters located at separate sites, completing the detection and protection against faults in the metallic loop area.

[0013] Furthermore, when the high-end converter's metallic return line is in operation, if the high-end converter station's grounding electrode fails, the low-end converter station's grounding electrode will be selected as the metallic return line's grounding point. The metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection in the high-end converter station's electrode protection will automatically switch measurement points according to the operating conditions and detect whether a fault has occurred in the metallic return line.

[0014] Its beneficial effects are as follows: When the high-end converter's metallic return line is running, considering the possibility of a fault in the grounding electrode of the high-end converter station, the grounding electrode of the low-end converter station is used as the grounding point of the metallic return line. The criteria for the grounding protection, longitudinal differential protection, and transverse differential protection of the metallic return line can be automatically switched to different measurement points to adapt to different operating conditions.

[0015] Furthermore, the criterion for grounding protection of metallic return lines in Scheme 1 is as follows:

[0016] |IDEL11+IDEL21+IDGND1|>Max(k1*|IDNE1|, Δ1)

[0017] The criterion for the metal loop longitudinal differential protection in Scheme 1 is:

[0018] IDME DEL -IDME S3 |>k2*IDME DEL

[0019] The criterion for the metal loop differential protection in Scheme 1 is:

[0020] |IDNE1-IDME|>Max(k3*|IDNE1|, Δ3)

[0021] In the formula, IDEL11 and DEL21 are the currents of the two lines of the grounding electrode of the high-end converter station, respectively; IDGND1 is the current of the grounding switch inside the high-end converter station; IDME is the current of the metallic return line of the high-end converter station; IDME DEL For delayed output of high-end converter station metallic return current; IDME S3 The current of the metallic return line at the converter station opposite the metallic return line is collected through inter-station communication; IDNE1 is the current of the neutral bus switch of the high-end converter station; k1, k2 and k3 are the proportional coefficients of each protection action; Δ1 and Δ3 are the starting settings of each protection action.

[0022] Its beneficial effects are: the above criteria are simple but highly reliable, and can adapt to changes in the operating conditions of UHV projects with dual converters located separately.

[0023] Furthermore, the criterion for grounding protection of the metallic return line in Scheme 2 is as follows:

[0024] |IDEE12+IDEE22-IDEE11-IDEE21+IDGND2|>Max(k1*|IDNE2|, Δ1)

[0025] The criterion for the metal loop longitudinal differential protection in Scheme 2 is:

[0026] |IDEE11 DEL +IDEE21 DEL -IDME S3 |>k2*IDEE11 DEL +IDEE21 DEL

[0027] The criterion for the metal loop differential protection in Scheme 2 is:

[0028] |IDNE2-IDEE11-IDEE21|>Max(k3*|IDNE2|, Δ3)

[0029] In the formula, IDEL12 and IDEL22 represent the currents of the two lines of the grounding electrode in the low-end converter station, respectively; IDEE11 and IDEE21 represent the currents of the two lines of the grounding electrode in the high-end converter station, respectively; IDEE11 DEL and IDEE21 DELThese are the two line address currents of the high-end converter station grounding electrode, respectively, with delayed output; IDGND2 is the grounding switch current in the low-end converter station; IDNE2 is the neutral line switch current in the low-end converter station; k1, k2, and k3 are the proportional coefficients of each protection action; Δ1 and Δ3 are the starting settings of each protection action.

[0030] Its beneficial effects are: the above criteria are simple but highly reliable, and can adapt to changes in the operating conditions of UHV projects with dual converters located separately.

[0031] Furthermore, the corresponding criterion for metallic return grounding protection is:

[0032] |IDEL12+IDEL22+IDGND1|>Max(k1*|IDNC1|, Δ1)

[0033] The criteria for protection against longitudinal differential in metallic loops are:

[0034] IDME DEL -IDME S3 |>k2*IDME DEL

[0035] The criteria for metal loop transverse differential protection are:

[0036] |IDNC1-IDME|>Max(k3*|IDNC1|, Δ3)

[0037] In the formula, IDEL12 and IDEL22 represent the grounding electrode currents of line 1 and line 2 in the low-end converter station, respectively; IDGND1 represents the grounding switch current within the high-end converter station; IDNC1 represents the intermediate current of the neutral bus in the high-end converter station; IDME... DEL For delayed output of high-end converter station metallic return current; IDME S3 Δ1 represents the metallic return current of the converter station at the opposite end of the metallic return line; Δ1 represents the metallic return current of the high-end converter station; k1, k2, and k3 are the proportional coefficients of each protection action, and Δ1 and Δ3 are the starting settings of each protection action.

[0038] Its beneficial effects are: the above criteria are simple but highly reliable, and can adapt to changes in the operating conditions of UHV projects with dual converters located separately.

[0039] Furthermore, k2*IDME also needs to be analyzed. DEL Amplification is applied, and the amplitude is limited to [0.04pu, 0.1pu].

[0040] Furthermore, k2*IDEE11 also needs to be optimized. DEL +IDEE21 DEL Amplification is applied, and the amplitude is limited to [0.04pu, 0.1pu].

[0041] Furthermore, grounding electrode faults include tower collapse faults and wire breakage faults.

[0042] To address the aforementioned technical problems, this invention also provides a metal loop protection device for ultra-high voltage converter stations, comprising a memory and a processor. The processor is used to execute program instructions to implement the ultra-high voltage converter station metal loop protection method described above, and can achieve the same beneficial effects as the method. Attached Figure Description

[0043] Figure 1 This is the operation circuit diagram of the high-end metal return line (high-end grounding electrode grounding) in the dual-converter site-separated construction of UHV converter stations according to the present invention;

[0044] Figure 2 This is the operation circuit diagram of the high-end metal loop (low-end grounding electrode grounding) in the dual-converter site-separated construction of UHV converter stations according to the present invention;

[0045] Figure 3 This is a diagram of the operating circuit of the dual converter metal loop in the construction of a dual converter-sited ultra-high voltage converter station according to the present invention (the metal loop diagram of the low-end metal loop is the same);

[0046] Figure 4 This is a schematic diagram of the simulated measurement points (taking pole 1 as an example) of the dual-converter site-separated construction of ultra-high voltage converter stations according to the present invention. Detailed Implementation

[0047] This invention addresses the structure of separate high-end and low-end converter stations with separate grounding electrodes for each station. It configures metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection functions for each converter station. Depending on the operating conditions (including metallic return line operation of the high-end converter, metallic return line operation of the low-end converter, and dual-converter metallic return line operation), the invention selects and activates the metallic return line protection function for either the high-end or low-end converter station. Furthermore, it automatically switches the measurement points for the judgment criteria based on the operating conditions, thus completing the detection of faults in the metallic return line area.

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, not all embodiments. Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of this invention.

[0049] Method Implementation Examples:

[0050] The ultra-high voltage converter station metallic circuit protection method of the present invention employs different protection strategies for different situations, as follows. The analog measurement points for different criteria in this protection strategy are as follows: Figure 4 As shown.

[0051] 1) When the high-end converter is operating with a metallic return line, the metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection in the high-end converter station pole protection system detect metallic return line faults. Both the high-end converter station grounding electrode and the low-end converter station grounding electrode can be used as the metallic return line grounding point, and the protection system adapts to the two operating conditions by switching the measuring points.

[0052] like Figure 1 As shown, under the operating conditions of the high-end converter's metallic return line, the grounding electrode of the high-end converter station is usually used as the grounding point of the metallic return line. The criteria for metallic return line protection are as follows:

[0053] Grounding protection: |IDEL11+IDEL21+IDGND1|>Max(k1*|IDNE1|,Δ1)

[0054] Longitudinal differential protection: |IDME DEL -IDME S3 |>k2*IDME DEL

[0055] Transverse differential protection: |IDNE1-IDME|>Max(k3*|IDNE1|,Δ3)

[0056] In the formula, IDEL11 and DEL21 are the currents of grounding electrode line 1 and line 2 of the high-end converter station, respectively; IDGND1 is the current of the grounding switch within the high-end converter station; IDME is the current of the metallic return line of the high-end converter station; IDME DEL This is the delayed output of the high-end converter station's metallic return current, with the delay time being the inter-station communication transmission time with the converter station at the opposite end of the metallic return line; IDME S3 The metallic return current of the converter station at the opposite end of the metallic return line is acquired through inter-station communication; IDNE1 is the neutral bus switch current of the high-end converter station; k1, k2, and k3 are the proportional coefficients of each protection action; Δ1 and Δ3 are the starting settings of each protection action. k2*IDME-DEL is usually subjected to amplitude limiting, with the limiting range being [0.04pu, 0.1pu].

[0057] When setting the proportional gain and starting setpoint, on the one hand, it is necessary to consider avoiding the maximum unbalanced current generated by the two grounding circuits during normal operation to prevent maloperation of the protection; on the other hand, the setpoint cannot be too large, causing the protection to fail to operate during a fault. k1 and k2 are usually taken as 0.1, k3 as 0.2; Δ1 and Δ3 are taken as 0.02pu and 0.07pu respectively. Additionally, the setting for the metallic return differential protection is k2*IDME. DEL Typically, a limiting process is applied, with the limiting range being [0.04 pu, 0.1 pu].

[0058] like Figure 2 As shown, under the operating conditions of the high-end converter's metallic return line, if a fault such as tower collapse or wire breakage occurs at the grounding electrode of the high-end converter station, the grounding electrode of the low-end converter station can be selected as the grounding point for the metallic return line. The metallic return line protection criterion automatically switches the measuring point, and the criterion is as follows:

[0059] Grounding protection: |IDEL12+IDEL22+IDGND1|>Max(k1*|IDNC1|,Δ1)

[0060] Longitudinal differential protection: |IDME DEL -IDME S3 |>k2*IDME DEL

[0061] Transverse differential protection: |IDNC1-IDME|>Max(k3*|IDNC1|,Δ3)

[0062] In the formula, IDEL12 and IDEL22 are the grounding electrode currents of line 1 and line 2 of the low-end converter station, respectively; IDNC1 is the intermediate current of the neutral bus of the high-end converter station; k1, k2 and k3 are the proportional coefficients of each protection action, and Δ1 and Δ3 are the starting settings of each protection action, and the setting is the same as above.

[0063] 2) When the operating condition is that of dual converters or low-end converters with metallic return lines, the grounding electrode of the low-end converter station is used as the grounding point of the metallic return line. The metallic return line grounding protection, metallic return line longitudinal differential protection and metallic return line transverse differential protection in the low-end converter station electrode protection are used to detect metallic return line faults.

[0064] like Figure 3 As shown, when the dual converter or low-end converter is operating with a metallic return line, the grounding electrode of the low-end converter station is used as the grounding point of the metallic return line. The criteria for metallic return line protection are as follows:

[0065] Grounding protection: |IDEE12+IDEE22-IDEE11-IDEE21+IDGND2|>Max(k1*|IDNE2|,Δ1)

[0066] Longitudinal differential protection: |IDEE11 DEL +IDEE21DEL -IDME S3 |>k2*IDEE11 DEL +IDEE21 DEL

[0067] Transverse difference protection: |IDNE2-IDEE11-IDEE21|>Max(k3*|IDNE2|,Δ3)

[0068] In the formula, IDEE12 and DEE22 are the currents at the grounding electrode lines 1 and 2 of the low-end converter station, respectively; IDEE11 and IDEE21 are the currents at the grounding electrode lines 1 and 2 of the high-end converter station, respectively; IDEE11 DEL and IDEE21 DEL These are the currents at the grounding electrode addresses of the high-end converter station (line 1 and line 2) with delayed output, respectively. The delay time is the inter-station communication transmission time with the converter station at the opposite end of the metallic circuit. IDGND2 is the grounding switch current within the low-end converter station. IDNE2 is the neutral line switch current of the low-end converter station. k1, k2, and k3 are the proportional coefficients for each protection action, and Δ1 and Δ3 are the activation settings for each protection action, with the settings being the same as above. Additionally, the setting for the metallic circuit longitudinal differential protection is k2*IDEE11. DEL +IDEE21 DEL Typically, a limiting process is applied, with the limiting range being [0.04 pu, 0.1 pu].

[0069] In summary, this invention provides a metallic loop protection strategy suitable for UHV converter stations constructed with dual converters at separate sites. The entire method has a simple formula, high reliability, and easy-to-set settings. It can adapt to changes in the operating conditions of UHV projects constructed with dual converters at separate sites, thereby accurately identifying faults in the metallic loop area and ensuring safe and reliable protection actions.

[0070] Device Example:

[0071] An embodiment of a metallic return protection device for an ultra-high voltage converter station according to the present invention includes a memory, a processor, and an internal bus. The processor and the memory communicate and interact with each other via the internal bus. The memory includes at least one software function module stored in the memory. The processor executes various functional applications and data processing by running the software programs and modules stored in the memory, thereby implementing the ultra-high voltage converter station metallic return protection method described in the method embodiment of the present invention.

[0072] The processor can be a microprocessor (MCU), a programmable logic device (FPGA), or other processing devices. The memory can be any type of memory that stores information using electrical energy, such as RAM and ROM; it can also be any type of memory that stores information using magnetic energy, such as hard disks, floppy disks, magnetic tapes, magnetic core memory, bubble memory, and USB flash drives; it can also be any type of memory that stores information using optical methods, such as CDs and DVDs; and of course, it can also be other types of memory, such as quantum memory and graphene memory.

[0073] Specific implementation methods have been given above, but the present invention is not limited to the described implementation methods. The basic idea of ​​the present invention lies in the above basic scheme. For those skilled in the art, designing various modified models, formulas, and parameters based on the teachings of the present invention does not require creative effort. Changes, modifications, substitutions, and variations made to the implementation methods without departing from the principles and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for protecting the metallic return line of an ultra-high voltage converter station, characterized in that, When the high-end converter's metallic return line is in operation, the high-end converter station's grounding electrode is used as the grounding point of the metallic return line. The metallic return line is checked for faults based on the metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection in the high-end converter station's electrode protection. When the metal loop of a dual converter or a low-end converter is in operation, the grounding electrode of the low-end converter station is used as the grounding point of the metal loop. The metal loop grounding protection, metal loop longitudinal differential protection and metal loop transverse differential protection in the low-end converter station electrode protection are used to detect whether the metal loop has a fault. When the high-end converter's metallic return line is in operation, if the high-end converter station's grounding electrode fails, the low-end converter station's grounding electrode will be selected as the metallic return line's grounding point. The metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection in the high-end converter station's electrode protection will automatically switch measurement points according to the operating conditions and detect whether a fault has occurred in the metallic return line.

2. The method for protecting the metallic return line of an ultra-high voltage converter station according to claim 1, characterized in that, When the high-end converter's metallic return line is in operation and the high-end converter station's grounding electrode is used as the metallic return line's grounding point, the criterion for metallic return line grounding protection is as follows: The criteria for protection against longitudinal differential in metallic loops are: The criteria for metal loop transverse differential protection are: In the formula, and These are the currents of the two lines at the grounding electrode of the high-end converter station; This refers to the grounding switch current within the high-end converter station. For the metallic return current of high-end converter stations; For the high-end converter station metal return current with delayed output; The metallic return current of the converter station at the opposite end of the metallic return line is collected through inter-station communication. This refers to the neutral bus switch current in the high-end converter station. , and The proportional coefficients for each protective action; and Set the activation values ​​for each protection action.

3. The method for protecting the metallic return line of an ultra-high voltage converter station according to claim 1, characterized in that, When a dual-converter or low-end converter is operating with a metallic return line, the criterion for metallic return line grounding protection is as follows: The criteria for protection against longitudinal differential in metallic loops are: The criteria for metal loop transverse differential protection are: In the formula, and These are the currents of the two lines at the grounding electrode of the low-end converter station, respectively. and These are the pole address currents of the two lines of the grounding electrode of the high-end converter station; and These are the two line address currents of the high-end converter station grounding electrode, respectively, for delayed output; This refers to the grounding switch current within the low-end converter station. This refers to the neutral line switch current in low-end converter stations. , and The proportional coefficients for each protective action; and Set the activation values ​​for each protection action.

4. The method for protecting the metallic return line of an ultra-high voltage converter station according to claim 1, characterized in that, When the high-end converter's metallic return line is in operation and the grounding electrode of the low-end converter station is used as the grounding point for the metallic return line, the criterion for metallic return line grounding protection is as follows: The criteria for protection against longitudinal differential in metallic loops are: The criteria for metal loop transverse differential protection are: In the formula, and These are the currents of grounding electrode line 1 and line 2 of the low-end converter station, respectively. This refers to the grounding switch current within the high-end converter station. This refers to the intermediate current of the neutral busbar in the high-end converter station. For the high-end converter station metal return current with delayed output; This refers to the metallic return current at the converter station opposite the metallic return line. For the metallic return current of high-end converter stations; , and For each protective action, the proportional coefficient is... and Set the activation values ​​for each protection action.

5. The method for protecting the metallic return line of an ultra-high voltage converter station according to claim 2 or 4, characterized in that, It is still necessary to Amplification is applied, and the amplitude is limited to [0.04pu, 0.1pu].

6. The method for protecting the metallic return line of an ultra-high voltage converter station according to claim 3, characterized in that, It is still necessary to Amplification is applied, and the amplitude is limited to [0.04pu, 0.1pu].

7. The method for protecting the metallic return line of an ultra-high voltage converter station according to claim 1, characterized in that, Grounding electrode faults include tower collapse faults and wire breakage faults.

8. A metallic return protection device for an ultra-high voltage converter station, characterized in that, It includes a memory and a processor, the processor being used to execute program instructions to implement the ultra-high voltage converter station metallic return line protection method as described below: When the high-end converter's metallic return line is in operation, the grounding electrode of the high-end converter station is used as the grounding point of the metallic return line. The metallic return line is checked for faults based on the metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection in the high-end converter station's electrode protection. When the metal loop of a dual converter or a low-end converter is in operation, the grounding electrode of the low-end converter station is used as the grounding point of the metal loop. The metal loop grounding protection, metal loop longitudinal differential protection and metal loop transverse differential protection in the low-end converter station electrode protection are used to detect whether the metal loop has a fault. When the high-end converter's metallic return line is in operation, if the high-end converter station's grounding electrode fails, the low-end converter station's grounding electrode will be selected as the metallic return line's grounding point. The metallic return line grounding protection, metallic return line longitudinal differential protection, and metallic return line transverse differential protection in the high-end converter station's electrode protection will automatically switch measurement points according to the operating conditions and detect whether a fault has occurred in the metallic return line.

9. The UHV converter station metallic return line protection device according to claim 8, characterized in that, When the high-end converter's metallic return line is in operation and the high-end converter station's grounding electrode is used as the metallic return line's grounding point, the criterion for metallic return line grounding protection is as follows: The criteria for protection against longitudinal differential in metallic loops are: The criteria for metal loop transverse differential protection are: In the formula, and These are the currents of the two lines at the grounding electrode of the high-end converter station; This refers to the grounding switch current within the high-end converter station. For the metallic return current of high-end converter stations; For the high-end converter station metal return current with delayed output; The metallic return current of the converter station at the opposite end of the metallic return line is collected through inter-station communication. This refers to the neutral bus switch current in the high-end converter station. , and The proportional coefficients for each protective action; and Set the activation values ​​for each protection action.

10. The UHV converter station metallic return line protection device according to claim 8, characterized in that, When a dual-converter or low-end converter is operating with a metallic return line, the criterion for metallic return line grounding protection is as follows: The criteria for protection against longitudinal differential in metallic loops are: The criteria for metal loop transverse differential protection are: In the formula, and These are the currents of the two lines at the grounding electrode of the low-end converter station, respectively. and These are the pole address currents of the two lines of the grounding electrode of the high-end converter station; and These are the two line address currents of the high-end converter station grounding electrode, respectively, for delayed output; This refers to the grounding switch current within the low-end converter station. This refers to the neutral line switch current in low-end converter stations. , and The proportional coefficients for each protective action; and Set the activation values ​​for each protection action.

11. The UHV converter station metallic return line protection device according to claim 8, characterized in that, When the high-end converter's metallic return line is in operation and the grounding electrode of the low-end converter station is used as the grounding point for the metallic return line, the criterion for metallic return line grounding protection is as follows: The criteria for protection against longitudinal differential in metallic loops are: The criteria for metal loop transverse differential protection are: In the formula, and These are the currents of grounding electrode line 1 and line 2 of the low-end converter station, respectively. This refers to the grounding switch current within the high-end converter station. This refers to the intermediate current of the neutral busbar in the high-end converter station. For the high-end converter station metal return current with delayed output; This refers to the metallic return current at the converter station opposite the metallic return line. For the metallic return current of high-end converter stations; , and For each protective action, the proportional coefficient is... and Set the activation values ​​for each protection action.

12. The UHV converter station metallic return line protection device according to claim 9 or 11, characterized in that, It is still necessary to Amplification is applied, and the amplitude is limited to [0.04pu, 0.1pu].

13. The UHV converter station metallic return line protection device according to claim 10, characterized in that, It is still necessary to Amplification is applied, and the amplitude is limited to [0.04pu, 0.1pu].

14. The UHV converter station metallic return line protection device according to claim 8, characterized in that, Grounding electrode faults include tower collapse faults and wire breakage faults.

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