Address-dividing cascade extra-high voltage direct current contact line protection method, system and equipment

Abstract

The invention discloses an addressing cascade extra-high voltage direct current connection line protection method, system and device. High-end station direct current connection line low-voltage protection comprises a high-end station low-voltage protection criterion and a direction auxiliary criterion. The low-end station direct current connection line traveling wave protection comprises a low-end station traveling wave protection criterion and a direction auxiliary criterion, and the low-end station direct current connection line voltage break variable protection comprises a low-end station voltage break variable protection criterion and a direction auxiliary criterion. The low-end station direct-current contact line low-voltage protection comprises a low-end station low-voltage protection criterion and a direction auxiliary criterion; and when the protection criterion and the direction auxiliary criterion are both met, performing protection action. According to the technical scheme, the problem of selectivity of low-voltage protection of the direct-current connection lines of the high-end station and the low-end station, traveling wave protection of the direct-current connection lines of the low-end station and voltage break variable protection of the direct-current connection lines is solved, protection maloperation caused by external faults is avoided, and the reliability of the system is improved.

Description

Technical Field

[0001] This invention belongs to the field of DC power transmission technology, specifically relating to a method, system and equipment for protecting cascaded ultra-high voltage DC interconnection lines. Background Technology

[0002] In a cascaded DC transmission system, the converter stations housing the two cascaded converters are a high-end station and a low-end station, respectively. The high-end station is connected to the DC line on one side and to the low-end station on the other via a DC tie line. Therefore, the traveling wave protection and voltage surge protection of the DC tie line at the high-end station can distinguish whether a fault occurs within the DC tie line area based on changes in the tie line voltage and / or current, a feature commonly referred to as selectivity. However, for the low-end station, the characteristics of DC tie line faults, high-end station neutral bus area faults, and DC line faults are very similar. It is difficult to distinguish whether a fault occurs within the DC tie line area based solely on changes in the tie line voltage and / or current. Therefore, when a fault occurs in the neutral bus area of ​​the high-end station or a DC line fault, the traveling wave protection and / or voltage surge protection of the low-end station's DC tie line are at risk of maloperation.

[0003] For DC tie line undervoltage protection, both high-end and low-end stations currently only judge the fault based on the magnitude of the DC tie line voltage, which is completely unselective. The DC voltage drop caused by the fault in the neutral bus area of ​​the high-end station may also cause the DC tie line undervoltage protection of both high-end and low-end stations to malfunction. Summary of the Invention

[0004] The purpose of this invention is to provide a method, system, and equipment for the protection of cascaded UHVDC interconnection lines, which solves the problems of low voltage protection for DC interconnection lines at high and low end stations, as well as the selectivity of traveling wave protection and voltage surge protection for DC interconnection lines at low end stations. It avoids protection maloperation caused by faults outside the protection zone and improves the reliability of the system.

[0005] To achieve the above objectives, the solution of the present invention is:

[0006] A protection method for a cascaded ultra-high voltage direct current (UHVDC) interconnection line, wherein the two cascaded converters are located at a high-end station and a low-end station respectively, and the high-end station and the low-end station are connected via a DC interconnection line; including,

[0007] Based on the traveling wave protection criteria of the high-end station, the traveling wave protection action of the DC interconnection line of the high-end station is performed;

[0008] Based on the voltage surge protection criteria of the high-end substation, the voltage surge protection action of the DC interconnection line of the high-end substation is performed.

[0009] The low voltage protection action of the DC interconnection line of the high-end station is performed according to the low voltage protection criterion and the direction auxiliary criterion of the high-end station; wherein, the low voltage protection action is performed when both the low voltage protection criterion and the direction auxiliary criterion of the high-end station are met.

[0010] Based on the traveling wave protection criteria and direction auxiliary criteria of the low-end station, the traveling wave protection action of the DC tie line of the low-end station is performed; wherein, the traveling wave protection action is performed when both the traveling wave protection criteria and the direction auxiliary criteria of the low-end station are satisfied.

[0011] The voltage surge protection action of the DC tie line at the low-end station is performed according to the low-end station voltage surge protection criterion and the direction auxiliary criterion; wherein, the voltage surge protection action is performed when both the low-end station voltage surge protection criterion and the direction auxiliary criterion are satisfied.

[0012] The low-voltage protection action of the DC tie line at the low-end station is performed according to the low-voltage protection criterion and the direction auxiliary criterion; wherein, the low-voltage protection action is performed when both the low-voltage protection criterion and the direction auxiliary criterion are satisfied.

[0013] The direction auxiliary criterion adopts one of the differential flow criterion and the direction information criterion, or a logical combination of the two.

[0014] The differential current criterion includes,

[0015] The inter-station communication status between the high-end station and the low-end station is normal and the differential current between the high-end station connection line and the low-end station connection line is continuously greater than the threshold value within a preset time period, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the differential current criterion is met, the corresponding protection is opened, and when it is not met, the corresponding protection is opened or blocked.

[0016] Wherein, the differential current between the high-end station connecting line and the low-end station connecting line is the absolute value of the difference between the current of the high-end station connecting line and the current of the low-end station connecting line.

[0017] When the differential current criterion is applied to the high-end station, the high-end station interconnection line current is the current after the measured current of the high-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the low-end station interconnection line current is the low-end station current transmitted through inter-station communication.

[0018] When the differential current criterion is applied to the low-end station, the low-end station tie line current is the current after the measured current of the low-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the high-end station tie line current is the high-end station current transmitted through inter-station communication.

[0019] The direction information criteria include a first direction information criterion applied to the high-end station connection line area and a second direction information criterion applied between the high-end station and the low-end station; wherein...

[0020] The first directional information criterion includes a fault occurring in the high-end station interconnection line area. The conditions for determining that a fault has occurred in the high-end station interconnection line area are that the high-end station traveling wave protection directional information meets the set conditions, and / or the high-end station voltage surge protection directional information meets the set conditions.

[0021] The second directional information criterion includes the following: the inter-station communication status between the high-end station and the low-end station is normal and the low-end station receives the first directional information sent by the high-end station, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the communication status is normal and the low-end station receives the first directional information sent by the high-end station, the low-end station opens the corresponding protection; when the communication status is interrupted, the low-end station opens or closes the corresponding protection.

[0022] The traveling wave protection direction information of the high-end station meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end station during the traveling wave protection of the DC tie line, or triggering an action signal during the traveling wave protection of the DC tie line of the high-end station.

[0023] The high-end substation voltage mutation protection direction information meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end substation during the high-end substation tie line mutation protection process, or triggering an action signal during the high-end substation tie line mutation protection process.

[0024] This also includes,

[0025] Based on the differential protection criteria for high-end substations, the differential protection action for the DC interconnection lines of high-end substations is performed.

[0026] Based on the differential protection criteria for low-end stations, the differential protection action of the DC interconnection line at the low-end station is performed.

[0027] Normal inter-station communication between high-end and low-end stations means that the hardware channel and software between the high-end and low-end stations are operating normally, and the high-end and low-end stations can exchange data through inter-station communication; interrupted inter-station communication between high-end and low-end stations means that the hardware channel between the high-end and low-end stations is interrupted or the software is malfunctioning, and the high-end and low-end stations cannot exchange data through inter-station communication.

[0028] A cascaded ultra-high voltage direct current (UHVDC) interconnection line protection system, comprising two cascaded converters located at a high-end station and a low-end station respectively, the high-end station and the low-end station being connected via a DC interconnection line; including,

[0029] The traveling wave protection module for the DC interconnection line of the high-end station is configured to perform traveling wave protection action for the DC interconnection line of the high-end station according to the traveling wave protection criterion of the high-end station;

[0030] The high-end station DC interconnection line voltage surge protection module is configured to perform high-end station DC interconnection line voltage surge protection action according to the high-end station voltage surge protection criterion.

[0031] The low voltage protection module for the DC interconnection line of the high-end station is configured to perform low voltage protection action for the DC interconnection line of the high-end station based on the low voltage protection criterion and the direction auxiliary criterion of the high-end station; wherein, the low voltage protection action is performed when both the low voltage protection criterion and the direction auxiliary criterion of the high-end station are satisfied.

[0032] The traveling wave protection module for the DC tie line at the low-end station is configured to perform traveling wave protection action on the DC tie line at the low-end station based on the traveling wave protection criterion and the direction auxiliary criterion at the low-end station; wherein, the traveling wave protection action is performed when both the traveling wave protection criterion and the direction auxiliary criterion at the low-end station are satisfied.

[0033] The low-end station DC tie line voltage surge protection module is configured to perform low-end station DC tie line voltage surge protection action based on the low-end station voltage surge protection criterion and the direction auxiliary criterion; wherein, the voltage surge protection action is performed when both the low-end station voltage surge protection criterion and the direction auxiliary criterion are satisfied.

[0034] The low-voltage protection module for the DC interconnection line at the low-end station is configured to perform low-voltage protection action for the DC interconnection line at the low-end station based on the low-voltage protection criterion and the direction auxiliary criterion; wherein, the low-voltage protection action is performed when both the low-voltage protection criterion and the direction auxiliary criterion are satisfied.

[0035] The direction auxiliary criterion used for the actions of each module is one of the differential flow criterion and the direction information criterion, or a logical combination of the two.

[0036] The differential current criterion includes,

[0037] The inter-station communication status between the high-end station and the low-end station is normal and the differential current between the high-end station connection line and the low-end station connection line is continuously greater than the threshold value within a preset time period, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the differential current criterion is met, the corresponding protection is opened, and when it is not met, the corresponding protection is opened or blocked.

[0038] Wherein, the differential current between the high-end station connecting line and the low-end station connecting line is the absolute value of the difference between the current of the high-end station connecting line and the current of the low-end station connecting line.

[0039] When the differential current criterion is applied to the high-end station, the high-end station interconnection line current is the current after the measured current of the high-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the low-end station interconnection line current is the low-end station current transmitted through inter-station communication.

[0040] When the differential current criterion is applied to the low-end station, the low-end station tie line current is the current after the measured current of the low-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the high-end station tie line current is the high-end station current transmitted through inter-station communication.

[0041] The direction information criteria include a first direction information criterion applied to the high-end station connection line area and a second direction information criterion applied between the high-end station and the low-end station; wherein...

[0042] The first directional information criterion includes a fault occurring in the high-end station interconnection line area. The conditions for determining that a fault has occurred in the high-end station interconnection line area are that the high-end station traveling wave protection directional information meets the set conditions, and / or the high-end station voltage surge protection directional information meets the set conditions.

[0043] The second directional information criterion includes the following: the inter-station communication status between the high-end station and the low-end station is normal and the low-end station receives the first directional information sent by the high-end station, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the communication status is normal and the low-end station receives the first directional information sent by the high-end station, the low-end station opens the corresponding protection; when the communication status is interrupted, the low-end station opens or closes the corresponding protection.

[0044] The traveling wave protection direction information of the high-end station meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end station during the traveling wave protection of the DC tie line, or triggering an action signal during the traveling wave protection of the DC tie line of the high-end station.

[0045] The high-end substation voltage mutation protection direction information meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end substation during the high-end substation tie line mutation protection process, or triggering an action signal during the high-end substation tie line mutation protection process.

[0046] This also includes,

[0047] The differential protection module for the DC interconnection line of the high-end station is configured to perform differential protection action for the DC interconnection line of the high-end station according to the differential protection criteria of the high-end station.

[0048] The differential protection module for the DC tie line at the low-end station is configured to perform differential protection action for the DC tie line at the low-end station based on the differential protection criteria for the low-end station.

[0049] Normal inter-station communication between high-end and low-end stations means that the hardware channel and software between the high-end and low-end stations are operating normally, and the high-end and low-end stations can exchange data through inter-station communication; interrupted inter-station communication between high-end and low-end stations means that the hardware channel between the high-end and low-end stations is interrupted or the software is malfunctioning, and the high-end and low-end stations cannot exchange data through inter-station communication.

[0050] A cascaded ultra-high voltage direct current (UHVDC) tie-line protection device includes a memory, a processor, and a computer program stored in the memory and executable on the processor; when the processor executes the computer program, it implements the steps of the cascaded UHVDC tie-line protection method as described above.

[0051] A computer-readable storage medium storing a computer program; when executed by a processor, the computer program implements the steps of the address-cascaded UHVDC interconnection line protection method described above.

[0052] By adopting the above solution, compared with the prior art, the present invention has the following technical effects:

[0053] This invention utilizes the differential current between high-end and low-end stations to construct directional criteria, and / or uses the directional information of traveling wave protection and voltage surge protection at high-end stations to construct directional criteria. This can effectively solve the problems of low voltage protection for DC interconnection lines at high and low-end stations, as well as the selectivity of traveling wave protection and voltage surge protection for DC interconnection lines at low-end stations. It avoids protection maloperation caused by faults outside the protection zone and improves the reliability of the system. Attached Figure Description

[0054] Figure 1 This is the topology of a cascaded ultra-high voltage direct current transmission system in an embodiment of the present invention, in which the high- and low-end converters at the sending end are cascaded and the high- and low-end converters at the receiving end are co-located.

[0055] Figure 2 In this embodiment of the invention, both the high-end and low-end converters at the sending and receiving ends adopt a cascaded ultra-high voltage direct current transmission system topology.

[0056] Figure 3 This is a schematic diagram of the DC tie line protection logic with direction auxiliary criterion according to an embodiment of the present invention.

[0057] Figure 4(a) is a schematic diagram of the direction-aided judgment logic constructed using the differential current of high- and low-end tie lines implemented in a high-end substation according to an embodiment of the present invention. Figure 4(b) is a schematic diagram of the direction-aided judgment logic constructed using the differential current of high- and low-end tie lines implemented in a low-end substation according to an embodiment of the present invention. Figure 4(c) is a schematic diagram of the direction-aided judgment logic constructed using the traveling wave protection direction information determined by the tie line protection of the high-end substation according to an embodiment of the present invention. Figure 4(d) is a schematic diagram of the direction-aided judgment logic constructed using the voltage surge protection direction information determined by the tie line protection of the high-end substation according to an embodiment of the present invention. Figure 4(e) shows the differential current judgment implemented in the high-end substation and the differential current judgment implemented in the low-end substation according to an embodiment of the present invention. Figure 4(f) is a schematic diagram of the direction auxiliary criterion logic constructed after ANDing the differential current criterion implemented in the high-end station and the differential current criterion implemented in the low-end station according to an embodiment of the present invention. Figure 4(g) is a schematic diagram of the direction auxiliary criterion logic constructed after ANDing the differential current criterion implemented in the high-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station according to an embodiment of the present invention. Figure 4(h) is a schematic diagram of the direction auxiliary criterion logic constructed after ORing the differential current criterion implemented in the high-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station according to an embodiment of the present invention. Figure 4(i) is a schematic diagram of the direction auxiliary criterion logic constructed after ORing the differential current criterion implemented in the high-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station according to an embodiment of the present invention. Figure 4(j) is a schematic diagram of the direction auxiliary criterion logic constructed by ANDing the differential current criterion implemented in the high-end station and the voltage change protection direction information determined by the tie line protection of the high-end station. Figure 4(k) is a schematic diagram of the direction auxiliary criterion logic constructed by ANDing the differential current criterion implemented in the low-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station. Figure 4(l) is a schematic diagram of the direction auxiliary criterion logic constructed by ANDing the differential current criterion implemented in the low-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station. Figure 4(m) is a schematic diagram of the direction auxiliary criterion logic constructed after the direction information is ORed with the differential current criterion implemented in the low-end station and the voltage change protection direction information determined by the tie line protection of the high-end station in an embodiment of the present invention. Figure 4(n) is a schematic diagram of the direction auxiliary criterion logic constructed after the differential current criterion implemented in the low-end station and the voltage change protection direction information determined by the tie line protection of the high-end station in an embodiment of the present invention. Figure 4(o) is a schematic diagram of the direction auxiliary criterion logic constructed after the traveling wave protection direction information determined by the tie line protection of the high-end station and the voltage change protection direction information determined by the tie line protection of the high-end station.Figure 4(p) is a schematic diagram of the direction auxiliary criterion logic constructed by taking the traveling wave protection direction information and voltage surge protection direction information determined by the tie line protection of the high-end station according to an embodiment of the present invention after performing an OR logic. Figure 4(q) is a schematic diagram of the direction auxiliary criterion logic constructed by taking the differential current criterion implemented in the high-end station, the traveling wave protection direction information and voltage surge direction information determined by the tie line protection of the high-end station according to an embodiment of the present invention after performing an OR logic. Figure 4(r) is a schematic diagram of the direction auxiliary criterion logic constructed by taking the differential current criterion implemented in the high-end station, the traveling wave protection direction information and voltage surge direction information determined by the tie line protection of the high-end station according to an embodiment of the present invention after performing an OR logic. Detailed Implementation

[0058] This invention provides a protection method for a cascaded ultra-high voltage direct current (UHVDC) interconnection line, wherein two cascaded converters are located at a high-end station and a low-end station, respectively, and the high-end station and the low-end station are connected via a DC interconnection line; the method includes,

[0059] Based on the traveling wave protection criteria of the high-end station, the traveling wave protection action of the DC interconnection line of the high-end station is performed;

[0060] Based on the voltage surge protection criteria of the high-end substation, the voltage surge protection action of the DC interconnection line of the high-end substation is performed.

[0061] The low voltage protection action of the DC interconnection line of the high-end station is performed according to the low voltage protection criterion and the direction auxiliary criterion of the high-end station; wherein, the low voltage protection action is performed when both the low voltage protection criterion and the direction auxiliary criterion of the high-end station are met.

[0062] Based on the traveling wave protection criteria and direction auxiliary criteria of the low-end station, the traveling wave protection action of the DC tie line of the low-end station is performed; wherein, the traveling wave protection action is performed when both the traveling wave protection criteria and the direction auxiliary criteria of the low-end station are satisfied.

[0063] The voltage surge protection action of the DC tie line at the low-end station is performed according to the low-end station voltage surge protection criterion and the direction auxiliary criterion; wherein, the voltage surge protection action is performed when both the low-end station voltage surge protection criterion and the direction auxiliary criterion are satisfied.

[0064] The low-voltage protection action of the DC tie line at the low-end station is performed according to the low-voltage protection criterion and the direction auxiliary criterion; wherein, the low-voltage protection action is performed when both the low-voltage protection criterion and the direction auxiliary criterion are satisfied.

[0065] The direction auxiliary criterion adopts one of the differential flow criterion and the direction information criterion, or a logical combination of the two.

[0066] The differential current criterion is as follows: when the inter-station communication between the high-end station and the low-end station is normal, the difference between the high-end station's tie line current (IDM2) after inter-station communication delay compensation and the low-end station's tie line current (IDM1) is calculated, and the absolute value of this difference is taken to obtain the differential current. When the differential current is greater than the threshold value I_havecur and lasts for a duration of T0, it is determined that a fault has occurred in the tie line area, and the high-end station's DC tie line undervoltage protection, and / or the low-end station's DC tie line undervoltage protection, and / or the low-end station's DC tie line traveling wave protection, and / or the low-end station's DC tie line voltage surge protection are activated; when the inter-station communication between the high-end station and the low-end station is interrupted, the high-end station's DC tie line undervoltage protection, and / or the low-end station's DC tie line undervoltage protection, and / or the low-end station's DC tie line traveling wave protection, and / or the low-end station's DC tie line voltage surge protection are activated or deactivated.

[0067] When the differential current criterion is applied to the high-end station, the high-end station interconnection line current is the current after the measured current of the high-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the low-end station interconnection line current is the low-end station current transmitted through inter-station communication.

[0068] When the differential current criterion is applied to the low-end station, the low-end station tie line current is the current after the measured current of the low-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the high-end station tie line current is the high-end station current transmitted through inter-station communication.

[0069] The directional information criteria are as follows: when the traveling wave protection directional information determined by the high-end station's interconnection line protection meets the set conditions, and / or when the voltage surge protection directional information determined by the high-end station's interconnection line protection meets the set conditions, it is determined that a fault has occurred in the interconnection line area, and the high-end station's DC interconnection line undervoltage protection is activated; when the inter-station communication between the high-end station and the low-end station is normal, the above-mentioned directional information determined by the high-end station is sent to the low-end station through inter-station communication; when the low-end station receives the directional information and it meets the set conditions, it is determined that a fault has occurred in the interconnection line area, and the low-end station's DC interconnection line undervoltage protection, and / or low-end station's DC interconnection line traveling wave protection, and / or low-end station's DC interconnection line voltage surge protection is activated; when the inter-station communication between the high-end and low-end stations is interrupted, the low-end station's DC interconnection line undervoltage protection, and / or low-end station's DC interconnection line traveling wave protection, and / or low-end station's DC interconnection line voltage surge protection is activated or deactivated.

[0070] The traveling wave protection direction information of the high-end station meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end station during the traveling wave protection of the DC tie line, or triggering an action signal during the traveling wave protection of the DC tie line of the high-end station.

[0071] The high-end substation voltage mutation protection direction information meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end substation during the high-end substation tie line mutation protection process, or triggering an action signal during the high-end substation tie line mutation protection process.

[0072] Normal inter-station communication between high-end and low-end stations means that the hardware channel and software between the high-end and low-end stations are operating normally, and the high-end and low-end stations can exchange data through inter-station communication; interrupted inter-station communication between high-end and low-end stations means that the hardware channel between the high-end and low-end stations is interrupted or the software is malfunctioning, and the high-end and low-end stations cannot exchange data through inter-station communication.

[0073] The method for protecting cascaded UHVDC interconnection lines also includes,

[0074] Based on the differential protection criteria for high-end substations, the differential protection action for the DC interconnection lines of high-end substations is performed.

[0075] Based on the differential protection criteria for low-end stations, the differential protection action of the DC interconnection line at the low-end station is performed.

[0076] This invention also provides a cascaded UHVDC interconnection line protection system, wherein the two cascaded converters are located at a high-end station and a low-end station respectively, and the high-end station and the low-end station are connected via a DC interconnection line; the system includes,

[0077] The traveling wave protection module for the DC interconnection line of the high-end station is configured to perform traveling wave protection action for the DC interconnection line of the high-end station according to the traveling wave protection criterion of the high-end station;

[0078] The high-end station DC interconnection line voltage surge protection module is configured to perform high-end station DC interconnection line voltage surge protection action according to the high-end station voltage surge protection criterion.

[0079] The low voltage protection module for the DC interconnection line of the high-end station is configured to perform low voltage protection action for the DC interconnection line of the high-end station based on the low voltage protection criterion and the direction auxiliary criterion of the high-end station; wherein, the low voltage protection action is performed when both the low voltage protection criterion and the direction auxiliary criterion of the high-end station are satisfied.

[0080] The traveling wave protection module for the DC tie line at the low-end station is configured to perform traveling wave protection action on the DC tie line at the low-end station based on the traveling wave protection criterion and the direction auxiliary criterion at the low-end station; wherein, the traveling wave protection action is performed when both the traveling wave protection criterion and the direction auxiliary criterion at the low-end station are satisfied.

[0081] The low-end station DC tie line voltage surge protection module is configured to perform low-end station DC tie line voltage surge protection action based on the low-end station voltage surge protection criterion and the direction auxiliary criterion; wherein, the voltage surge protection action is performed when both the low-end station voltage surge protection criterion and the direction auxiliary criterion are satisfied.

[0082] The low-voltage protection module for the DC interconnection line at the low-end station is configured to perform low-voltage protection action for the DC interconnection line at the low-end station based on the low-voltage protection criterion and the direction auxiliary criterion; wherein, the low-voltage protection action is performed when both the low-voltage protection criterion and the direction auxiliary criterion are satisfied.

[0083] The direction auxiliary criterion used for the actions of each module is one of the differential flow criterion and the direction information criterion, or a logical combination of the two.

[0084] The differential current criterion includes,

[0085] The inter-station communication status between the high-end station and the low-end station is normal and the differential current of the high-end station connection line and the low-end station connection line is continuously greater than the threshold value within a preset time period, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the differential current criterion is met, the corresponding protection is opened, and the differential current criterion is in working state. Once the criterion is met, the corresponding protection is performed and the protection action is initiated; if the criterion is not met, the corresponding protection is opened or blocked.

[0086] Wherein, the differential current between the high-end station connecting line and the low-end station connecting line is the absolute value of the difference between the current of the high-end station connecting line and the current of the low-end station connecting line.

[0087] When the differential current criterion is applied to the high-end station, the high-end station interconnection line current is the current after the measured current of the high-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the low-end station interconnection line current is the low-end station current transmitted through inter-station communication.

[0088] When the differential current criterion is applied to the low-end station, the low-end station tie line current is the current after the measured current of the low-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the high-end station tie line current is the high-end station current transmitted through inter-station communication.

[0089] The direction information criteria include a first direction information criterion applied to the high-end station connection line area and a second direction information criterion applied between the high-end station and the low-end station; wherein...

[0090] The first directional information criterion includes a fault occurring in the high-end station interconnection line area. The conditions for determining that a fault has occurred in the high-end station interconnection line area are that the high-end station traveling wave protection directional information meets the set conditions, and / or the high-end station voltage surge protection directional information meets the set conditions.

[0091] The second directional information criterion includes the following: the inter-station communication status between the high-end station and the low-end station is normal and the low-end station receives the first directional information sent by the high-end station, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the communication status is normal and the low-end station receives the first directional information sent by the high-end station, the low-end station opens the corresponding protection; when the communication status is interrupted, the low-end station opens or closes the corresponding protection.

[0092] The traveling wave protection direction information of the high-end station meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end station during the traveling wave protection of the DC tie line, or triggering an action signal during the traveling wave protection of the DC tie line of the high-end station.

[0093] The high-end substation voltage mutation protection direction information meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end substation during the high-end substation tie line mutation protection process, or triggering an action signal during the high-end substation tie line mutation protection process.

[0094] This also includes,

[0095] The differential protection module for the DC interconnection line of the high-end station is configured to perform differential protection action for the DC interconnection line of the high-end station according to the differential protection criteria of the high-end station.

[0096] The differential protection module for the DC tie line at the low-end station is configured to perform differential protection action for the DC tie line at the low-end station based on the differential protection criteria for the low-end station.

[0097] Normal inter-station communication between high-end and low-end stations means that the hardware channel and software between the high-end and low-end stations are operating normally, and the high-end and low-end stations can exchange data through inter-station communication; interrupted inter-station communication between high-end and low-end stations means that the hardware channel between the high-end and low-end stations is interrupted or the software is malfunctioning, and the high-end and low-end stations cannot exchange data through inter-station communication.

[0098] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0099] The two cascaded converters are located at the high-end and low-end stations, respectively, and are connected via a DC tie line. The high-end station is equipped with DC tie line traveling wave protection, DC tie line voltage surge protection, DC tie line undervoltage protection with directional auxiliary criteria, and DC tie line differential protection. The low-end station is equipped with DC tie line traveling wave protection with directional auxiliary criteria, DC tie line voltage surge protection with directional auxiliary criteria, DC tie line undervoltage protection with directional auxiliary criteria, and DC tie line differential protection. Figure 1 This is a schematic diagram of the topology of a UHVDC transmission system with separate addresses for the high- and low-end converters at the sending end and a shared site for the high- and low-end converters at the receiving end. The converters at the sending end are cascaded with separate addresses, with the two converters located at the high-end station and the low-end station, respectively. The high-end station and the low-end station are each equipped with corresponding protection. Figure 2 This diagram illustrates a topology of a cascaded ultra-high voltage direct current (UHVDC) transmission system where both the high-end and low-end converters at the sending and receiving ends are cascaded at different addresses. At the sending end, the two converters are located at the high-end and low-end stations, respectively, and each station is equipped with appropriate protection systems. Similarly, at the receiving end, the two converters are also cascaded at different addresses, with each station located at the high-end and low-end stations, and each station is equipped with appropriate protection systems. This invention includes, but is not limited to, cascading topologies. Figure 1 , Figure 2 The illustrated cascaded power transmission system is shown.

[0100] Figure 3 This is a schematic diagram of the DC tie line protection logic with directional auxiliary criteria according to an embodiment of the present invention. The tie line protection action will only be executed when both the main criteria and the directional auxiliary criteria meet the conditions. The main criteria include the high-end station traveling wave protection criterion, the high-end station voltage change protection criterion, the high-end station undervoltage protection criterion, the low-end station traveling wave protection criterion, the low-end station voltage change protection criterion, and the low-end station undervoltage protection criterion.

[0101] Figure 4(a) is a schematic diagram of the direction auxiliary criterion logic implemented in the high-end station of the present invention using the differential current of the high-end and low-end interconnection lines. When the communication between the high-end and low-end stations is normal, the current of the interconnection line of the high-end station is compensated for the inter-station communication delay to obtain IDM2. The difference is made with the current of the low-end station interconnection line IDM1 sent through the inter-station communication, and the absolute value of the difference is taken to obtain the differential current. When the differential current is greater than the threshold value I_havecur and lasts for a duration of T0, it is determined that a fault has occurred in the interconnection line area, the auxiliary criterion is met, and the DC interconnection line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion is no longer effective because the current of the other station cannot be received. At this time, from the perspective of preventing the protection from maloperation when there is a fault outside the area, the protection using the above-mentioned direction auxiliary criterion can be turned off. If it is considered that the line protection maloperation is acceptable when the communication is interrupted and a fault occurs outside the area, and the line protection can still operate correctly when a fault actually occurs inside the area, the protection can also be opened. Therefore, the auxiliary criterion can be set to 1 or 0 according to the actual situation, thereby opening or blocking the DC interconnection line protection.

[0102] Preferably, the threshold value I_havecur is between 10 and 5000A; the delay T0 is between 1 and 5000ms.

[0103] Figure 4(b) is a schematic diagram of the direction auxiliary criterion logic implemented in the low-end station using the differential current of the high-end and low-end interconnection lines in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, the current of the interconnection line of the low-end station is compensated for the inter-station communication delay to obtain IDM1. The difference is made with the current of the high-end station interconnection line IDM2 sent through the inter-station communication, and the absolute value of the difference is taken to obtain the differential current. When the differential current is greater than the threshold value I_havecur and lasts for a duration of T0, it is determined that a fault has occurred in the interconnection line area, the auxiliary criterion is met, and the DC interconnection line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC interconnection line protection.

[0104] Preferably, the threshold value I_havecur is between 10 and 5000A; the delay T0 is between 1 and 5000ms.

[0105] Figure 4(c) is a schematic diagram of the direction auxiliary criterion logic constructed by the traveling wave protection direction information determined by the high-end station's tie line protection in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the traveling wave protection direction information determined by the tie line protection of this high-end station is positive, it is determined that a fault has occurred in the tie line area, the auxiliary criterion is satisfied, and the DC tie line protection is opened; when the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0106] Figure 4(d) is a schematic diagram of the direction auxiliary criterion logic constructed by the voltage change protection direction information judged by the high-end station's interconnection line protection in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the voltage change protection direction information judged by the interconnection line protection of this high-end station is positive, it is determined that a fault has occurred in the interconnection line area, the auxiliary criterion is satisfied, and the DC interconnection line protection is opened; when the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC interconnection line protection.

[0107] Figure 4(e) is a schematic diagram of the direction auxiliary criterion logic constructed by ANDing the differential current criterion implemented in the high-end station and the differential current criterion implemented in the low-end station according to an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, the high-end station of this pole determines whether there is a fault in the tie line area through the differential current criterion and sends the result to the low-end station of this pole through inter-station communication. Similarly, the low-end station of this pole determines whether there is a fault in the tie line area through the differential current criterion and sends the result to the high-end station of this pole through inter-station communication. When both the local station and the counterpart station of this pole (received through inter-station communication) determine that there is a fault in the tie line area, the auxiliary criterion is satisfied and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0108] Figure 4(f) is a schematic diagram of the direction auxiliary criterion logic constructed by ORing the differential current criterion implemented in the high-end station and the differential current criterion implemented in the low-end station according to an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, the high-end station of this pole determines whether there is a fault in the tie line area through the differential current criterion and sends the result to the low-end station of this pole through inter-station communication. Similarly, the low-end station of this pole determines whether there is a fault in the tie line area through the differential current criterion and sends the result to the high-end station of this pole through inter-station communication. When the local station or the local station opposite the local station (received through inter-station communication) determines that a fault has occurred in the tie line area, the auxiliary criterion is satisfied, and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0109] Figure 4(g) is a schematic diagram of the auxiliary criterion logic constructed by taking the differential current criterion implemented in the high-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station after ANDing logic in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the high-end station determines that there is a fault in the tie line area through the differential current criterion, and the traveling wave protection direction information determined by the tie line protection of the high-end station is in the positive direction, then the auxiliary criterion is satisfied, and the DC tie line protection is opened; when the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0110] Figure 4(h) is a schematic diagram of the auxiliary direction criterion logic constructed by taking the differential current criterion implemented in the high-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station after ORing logic in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the high-end station determines that there is a fault in the tie line area through the differential current criterion, or the traveling wave protection direction information determined by the tie line protection of the high-end station is positive, then the auxiliary criterion is satisfied and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0111] Figure 4(i) is a schematic diagram of the auxiliary criterion logic constructed by ANDing the differential current criterion implemented in the high-end station and the voltage change protection direction information judged by the tie line protection of the high-end station in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the high-end station judges that the fault is in the tie line area through the differential current criterion and the voltage change protection direction information judged by the tie line protection of the high-end station is positive, then the auxiliary criterion is satisfied and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0112] Figure 4(j) is a schematic diagram of the auxiliary criterion logic constructed by taking the differential current criterion implemented in the high-end station and the voltage change protection direction information judged by the tie line protection of the high-end station after OR logic in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the high-end station judges that there is a fault in the tie line area through the differential current criterion, or the voltage change protection direction information judged by the tie line protection of the high-end station is positive, then the auxiliary criterion is satisfied and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0113] Figure 4(k) is a schematic diagram of the auxiliary criterion logic constructed by ANDing the differential current criterion implemented in the low-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the low-end station determines that there is a fault in the tie line area through the differential current criterion and the traveling wave protection direction information determined by the tie line protection of the high-end station is positive, then the auxiliary criterion is satisfied and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0 to open or close the DC tie line protection.

[0114] Figure 4(l) is a schematic diagram of the direction auxiliary criterion logic constructed by taking the differential current criterion implemented in the low-end station and the traveling wave protection direction information determined by the tie line protection of the high-end station after OR logic in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the low-end station determines that there is a fault in the tie line area through the differential current criterion, or the traveling wave protection direction information determined by the tie line protection of the high-end station is positive, then the auxiliary criterion is satisfied and the DC tie line protection is opened; when the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0115] Figure 4(m) is a schematic diagram of the auxiliary criterion logic constructed by taking the differential current criterion implemented in the low-end station and the voltage change protection direction information judged by the tie line protection of the high-end station after AND logic in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the low-end station judges the fault to be in the tie line area through the differential current criterion and the traveling wave protection direction information judged by the tie line protection of the high-end station is positive, then the auxiliary criterion is satisfied and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0116] Figure 4(n) is a schematic diagram of the auxiliary criterion logic constructed by taking the differential current criterion implemented in the low-end station and the voltage change protection direction information judged by the tie line protection of the high-end station after ORing logic in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the low-end station judges the fault in the tie line area by the differential current criterion, or the voltage change protection direction information judged by the tie line protection of the high-end station is positive, then the auxiliary criterion is satisfied and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0117] Figure 4(o) is a schematic diagram of the direction auxiliary criterion logic constructed by ANDing the traveling wave protection direction information and voltage surge protection direction information determined by the tie line protection of the high-end station in an embodiment of the present invention. When the communication between the high-end and low-end stations is normal, if the traveling wave protection direction information and voltage surge protection direction information determined by the tie line protection of this high-end station are both positive, it is determined that a fault has occurred in the tie line area, the auxiliary criterion is satisfied, and the DC tie line protection is opened; when the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0118] Figure 4(p) is a schematic diagram of the direction auxiliary criterion logic constructed by taking the traveling wave protection direction information and voltage surge protection direction information determined by the tie line protection of the high-end station according to an embodiment of the present invention after ORing. When the communication between the high-end and low-end stations is normal, if the traveling wave protection direction information or voltage surge protection direction information determined by the tie line protection of the high-end station is positive, it is determined that a fault has occurred in the tie line area, the auxiliary criterion is satisfied, and the DC tie line protection is opened; when the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0119] Figure 4(q) is a schematic diagram of the direction auxiliary criterion logic constructed by taking the differential current criterion implemented in the high-end station, the traveling wave protection direction information and the voltage change direction information determined by the tie line protection of the high-end station, and the AND logic of the three. When the communication between the high-end and low-end stations is normal, if the high-end station determines that the fault is in the tie line area through the differential current criterion, and the traveling wave protection direction information and the voltage change direction information determined by the tie line protection of the high-end station are in the positive direction, then the auxiliary criterion is satisfied, and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0, thereby opening or blocking the DC tie line protection.

[0120] Figure 4(r) is a schematic diagram of the direction auxiliary criterion logic constructed by taking the differential current criterion implemented in the high-end station, the traveling wave protection direction information and the voltage change direction information determined by the tie line protection of the high-end station, and the OR logic of the three. When the communication between the high-end and low-end stations is normal, if the high-end station determines that there is a fault in the tie line area through the differential current criterion, or the traveling wave protection direction information determined by the tie line protection of the high-end station is positive, or the voltage change protection direction information determined by the tie line protection of the high-end station is positive, then the auxiliary criterion is satisfied and the DC tie line protection is opened. When the communication between the high-end and low-end stations is interrupted, the auxiliary criterion can be set to 1 or 0 to open or close the DC tie line protection.

[0121] This invention also provides another address-cascaded UHVDC tie line protection device, including a processor and a memory configured to store a computer program capable of running on the processor; wherein, when the processor is configured to run the computer program, it executes the method steps in the foregoing embodiments.

[0122] In practical applications, the aforementioned processor includes a Field-Programmable Gate Array (FPGA), and the processor can be a Central Processing Unit (CPU) or a Digital Signal Processor (DSP). It is understood that for different devices, the electronic devices used to implement the functions of the aforementioned processor can also be other types, and this embodiment of the invention does not impose specific limitations.

[0123] The aforementioned memory can be volatile memory, such as random-access memory (RAM); or non-volatile memory, such as read-only memory (ROM), flash memory, hard disk drive (HDD), or solid-state drive (SSD); or a combination of the above types of memory, and provides instructions and data to the processor.

[0124] In an exemplary embodiment, the present invention also provides a computer-readable storage medium for storing a computer program.

[0125] Optionally, the computer-readable storage medium can be applied to any of the methods in the embodiments of the present invention, and the computer program causes the computer to execute the corresponding processes implemented by the processor in the various methods of the embodiments of the present invention. For the sake of brevity, these will not be described in detail here.

[0126] In the several embodiments provided by this invention, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0127] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0128] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0129] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0130] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0131] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0132] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A protection method for a cascaded ultra-high voltage direct current (UHVDC) interconnection line, wherein two cascaded converters are located at a high-end station and a low-end station respectively, and the high-end station and the low-end station are connected via a DC interconnection line; characterized in that: include, Based on the traveling wave protection criteria of the high-end station, the traveling wave protection action of the DC interconnection line of the high-end station is performed; Based on the voltage surge protection criteria of the high-end substation, the voltage surge protection action of the DC interconnection line of the high-end substation is performed. The low voltage protection action of the DC interconnection line of the high-end station is performed according to the low voltage protection criterion and the direction auxiliary criterion of the high-end station; wherein, the low voltage protection action is performed when both the low voltage protection criterion and the direction auxiliary criterion of the high-end station are met. Based on the traveling wave protection criteria and direction auxiliary criteria of the low-end station, the traveling wave protection action of the DC tie line of the low-end station is performed; wherein, the traveling wave protection action is performed when both the traveling wave protection criteria and the direction auxiliary criteria of the low-end station are satisfied. The voltage surge protection action of the DC tie line at the low-end station is performed according to the low-end station voltage surge protection criterion and the direction auxiliary criterion; wherein, the voltage surge protection action is performed when both the low-end station voltage surge protection criterion and the direction auxiliary criterion are satisfied. The low-voltage protection action of the DC tie line at the low-end station is performed according to the low-voltage protection criterion and the direction auxiliary criterion; wherein, the low-voltage protection action is performed when both the low-voltage protection criterion and the direction auxiliary criterion are satisfied.

2. The method as described in claim 1, characterized in that: The direction-aided criterion adopts one of the differential flow criterion and the direction information criterion, or a logical combination of the two.

3. The method as described in claim 2, characterized in that: The differential current criteria include, The inter-station communication status between the high-end station and the low-end station is normal and the differential current between the high-end station connection line and the low-end station connection line is continuously greater than the threshold value within a preset time period, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the differential current criterion is met, the corresponding protection is opened, and when it is not met, the corresponding protection is opened or blocked.

4. The method as described in claim 3, characterized in that: The differential current between the high-end station connection line and the low-end station connection line is the absolute value of the difference between the current of the high-end station connection line and the current of the low-end station connection line. When the differential current criterion is applied to the high-end station, the high-end station interconnection line current is the current after the measured current of the high-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the low-end station interconnection line current is the low-end station current transmitted through inter-station communication. When the differential current criterion is applied to the low-end station, the low-end station tie line current is the current after the measured current of the low-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the high-end station tie line current is the high-end station current transmitted through inter-station communication.

5. The method as described in claim 2, characterized in that: The direction information criteria include a first direction information criterion applied to the high-end station connection line area and a second direction information criterion applied between the high-end station and the low-end station; wherein... The first directional information criterion includes a fault occurring in the high-end station interconnection line area. The conditions for determining that a fault has occurred in the high-end station interconnection line area are that the high-end station traveling wave protection directional information meets the set conditions, and / or the high-end station voltage surge protection directional information meets the set conditions. The second directional information criterion includes the following: the inter-station communication status between the high-end station and the low-end station is normal and the low-end station receives the first directional information sent by the high-end station, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the communication status is normal and the low-end station receives the first directional information sent by the high-end station, the low-end station opens the corresponding protection; when the communication status is interrupted, the low-end station opens or closes the corresponding protection.

6. The method as described in claim 5, characterized in that: The traveling wave protection direction information of the high-end station meets the set conditions, including triggering a fault positive direction signal in the high-end station's DC tie line traveling wave protection process based on the high-end station's voltage and / or current characteristics, or triggering an action signal during the high-end station's DC tie line traveling wave protection process.

7. The method as described in claim 5, characterized in that: The high-end substation voltage mutation protection direction information meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end substation during the high-end substation tie line mutation protection process, or triggering an action signal during the high-end substation tie line mutation protection process.

8. The method as described in claim 1, characterized in that: It also includes, Based on the differential protection criteria for high-end substations, the differential protection action for the DC interconnection lines of high-end substations is performed. Based on the differential protection criteria for low-end stations, the differential protection action of the DC interconnection line at the low-end station is performed.

9. The method as described in claim 3 or 5, characterized in that: Normal inter-station communication between high-end and low-end stations means that the hardware channel and software between the high-end and low-end stations are operating normally, and the high-end and low-end stations can exchange data through inter-station communication; interrupted inter-station communication between high-end and low-end stations means that the hardware channel between the high-end and low-end stations is interrupted or the software is malfunctioning, and the high-end and low-end stations cannot exchange data through inter-station communication.

10. A cascaded ultra-high voltage direct current (UHVDC) interconnection line protection system, wherein two cascaded converters are located at a high-end station and a low-end station respectively, and the high-end station and the low-end station are connected via a DC interconnection line; characterized in that: include, high-end The DC tie line traveling wave protection module of the high-end station is configured to perform traveling wave protection action on the DC tie line of the high-end station according to the traveling wave protection criterion of the high-end station; The high-end station DC interconnection line voltage surge protection module is configured to perform high-end station DC interconnection line voltage surge protection action according to the high-end station voltage surge protection criterion. The low voltage protection module for the DC interconnection line of the high-end station is configured to perform low voltage protection action for the DC interconnection line of the high-end station based on the low voltage protection criterion and the direction auxiliary criterion of the high-end station; wherein, the low voltage protection action is performed when both the low voltage protection criterion and the direction auxiliary criterion of the high-end station are satisfied. The traveling wave protection module for the DC tie line at the low-end station is configured to perform traveling wave protection action on the DC tie line at the low-end station based on the traveling wave protection criterion and the direction auxiliary criterion at the low-end station; wherein, the traveling wave protection action is performed when both the traveling wave protection criterion and the direction auxiliary criterion at the low-end station are satisfied. The low-end station DC tie line voltage surge protection module is configured to perform low-end station DC tie line voltage surge protection action based on the low-end station voltage surge protection criterion and the direction auxiliary criterion; wherein, the voltage surge protection action is performed when both the low-end station voltage surge protection criterion and the direction auxiliary criterion are satisfied. The low-voltage protection module for the DC interconnection line at the low-end station is configured to perform low-voltage protection action for the DC interconnection line at the low-end station based on the low-voltage protection criterion and the direction auxiliary criterion; wherein, the low-voltage protection action is performed when both the low-voltage protection criterion and the direction auxiliary criterion are satisfied.

11. The system as described in claim 10, characterized in that: The direction auxiliary criteria used for the actions of each module are one of the differential flow criteria and the direction information criteria, or a logical combination of the two.

12. The system as described in claim 11, characterized in that: The differential current criteria include, The inter-station communication status between the high-end station and the low-end station is normal and the differential current between the high-end station connection line and the low-end station connection line is continuously greater than the threshold value within a preset time period, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the differential current criterion is met, the corresponding protection is opened, and when it is not met, the corresponding protection is opened or blocked.

13. The system as described in claim 12, characterized in that: The differential current between the high-end station connection line and the low-end station connection line is the absolute value of the difference between the current of the high-end station connection line and the current of the low-end station connection line. When the differential current criterion is applied to the high-end station, the high-end station interconnection line current is the current after the measured current of the high-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the low-end station interconnection line current is the low-end station current transmitted through inter-station communication. When the differential current criterion is applied to the low-end station, the low-end station tie line current is the current after the measured current of the low-end station is compensated according to the inter-station communication delay between the high-end station and the low-end station, and the high-end station tie line current is the high-end station current transmitted through inter-station communication.

14. The system as described in claim 11, characterized in that: The direction information criteria include a first direction information criterion applied to the high-end station connection line area and a second direction information criterion applied between the high-end station and the low-end station; wherein... The first directional information criterion includes a fault occurring in the high-end station interconnection line area. The conditions for determining that a fault has occurred in the high-end station interconnection line area are that the high-end station traveling wave protection directional information meets the set conditions, and / or the high-end station voltage surge protection directional information meets the set conditions. The second directional information criterion includes the following: the inter-station communication status between the high-end station and the low-end station is normal and the low-end station receives the first directional information sent by the high-end station, or the inter-station communication status between the high-end station and the low-end station is interrupted; wherein, when the communication status is normal and the low-end station receives the first directional information sent by the high-end station, the low-end station opens the corresponding protection; when the communication status is interrupted, the low-end station opens or closes the corresponding protection.

15. The system as described in claim 14, characterized in that: The traveling wave protection direction information of the high-end station meets the set conditions, including triggering a fault positive direction signal in the high-end station's DC tie line traveling wave protection process based on the high-end station's voltage and / or current characteristics, or triggering an action signal during the high-end station's DC tie line traveling wave protection process.

16. The system as described in claim 14, characterized in that: The high-end substation voltage mutation protection direction information meets the set conditions, including triggering a fault positive direction signal in the fault zone based on the voltage and / or current characteristics of the high-end substation during the high-end substation tie line mutation protection process, or triggering an action signal during the high-end substation tie line mutation protection process.

17. The system as claimed in claim 10, characterized in that: It also includes, The differential protection module for the DC interconnection line of the high-end station is configured to perform differential protection action for the DC interconnection line of the high-end station according to the differential protection criteria of the high-end station. The differential protection module for the DC tie line at the low-end station is configured to perform differential protection action for the DC tie line at the low-end station based on the differential protection criteria for the low-end station.

18. The system as described in claim 12 or 14, characterized in that: Normal inter-station communication between high-end and low-end stations means that the hardware channel and software between the high-end and low-end stations are operating normally, and the high-end and low-end stations can exchange data through inter-station communication; interrupted inter-station communication between high-end and low-end stations means that the hardware channel between the high-end and low-end stations is interrupted or the software is malfunctioning, and the high-end and low-end stations cannot exchange data through inter-station communication.

19. A cascaded ultra-high voltage direct current (UHVDC) interconnection line protection device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor; characterized in that: When the processor executes the computer program, it implements the steps of the address-cascaded UHVDC interconnection line protection method as described in any one of claims 1 to 9.

20. A computer-readable storage medium storing a computer program; characterized in that: When the computer program is executed by the processor, it implements the steps of the address-cascaded UHVDC interconnection line protection method as described in any one of claims 1 to 9.

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