A multi-terminal cascaded DC transmission insulation coordination system and method

Abstract

This invention belongs to the field of DC power transmission technology and relates to a multi-terminal cascaded DC power transmission insulation coordination system and design method. It includes: several converter stations connected in series via tie lines; each converter valve in each converter station is equipped with a surge arrester at its bottom, middle, and top; the negative terminal of the DC pole of the lowest voltage converter station is grounded; the grounding line includes several grounding poles, with a set of grounding surge arresters at the outlet of each grounding pole, and a neutral line surge arrester on the side of the grounding surge arrester furthest from the grounding pole; each metallic return jumper of each converter station is equipped with a set of surge arresters; a series DC field surge arrester and a line surge arrester are configured at the positive output terminal of the DC pole of the highest voltage converter station; a converter station outlet surge arrester is installed at the input end of the tie line, and a converter station internal surge arrester is installed at the input end of the tie line. Based on traditional DC power transmission insulation coordination, it offers better flexibility, reliability, and scalability.

Description

Technical Field

[0001] This invention relates to a multi-terminal cascaded DC transmission insulation coordination system and method, belonging to the field of DC transmission technology. Background Technology

[0002] Currently, most ultra-high voltage direct current (UHVDC) projects in operation are point-to-point transmissions, but the demand for multi-point collection and transmission is gradually becoming more prominent. Multi-point collection and transmission DC systems represent a new trend in UHVDC development. By constructing two converter stations at the sending or receiving end, or at both ends, high and low-end power can be collected from two locations or distributed power can be transmitted, thus accommodating coordinated development across multiple regions.

[0003] For ultra-high voltage direct current (UHVDC) transmission systems, the insulation coordination scheme and overvoltage level of converter stations directly affect the cost of equipment within the stations and the reliability of system operation. Due to the multi-terminal construction, one or more connecting lines will be added between converter stations, thereby increasing DC harmonics in the circuit and posing difficulties for the insulation coordination design and overvoltage suppression of the UHVDC system.

[0004] Reasonable insulation coordination design needs to take into account the characteristics of the main wiring of the multi-terminal system, consider the parameter coordination relationship of each surge arrester in the circuit, and suppress the maximum transient overvoltage, current and energy levels under various faults on the AC and DC sides to an acceptable level, so as to achieve the optimal fit between the economic efficiency of converter station equipment and insulation coordination scheme. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a multi-terminal cascaded DC transmission insulation coordination system and method, which has better flexibility, reliability, and scalability.

[0006] To achieve the above objectives, the present invention proposes the following technical solution: a multi-terminal cascaded DC transmission insulation coordination system, comprising: a plurality of converter stations and a plurality of tie lines connecting the converter stations; the plurality of converter stations are connected in series and via the tie lines, and each converter valve of each converter station is equipped with a surge arrester at its bottom, middle, and top; the negative terminal of the DC pole of the lowest voltage converter station is provided with a grounding line; the grounding line includes a plurality of grounding poles, and a set of grounding surge arresters is provided at the outlet of each grounding pole, and a neutral line surge arrester is provided on the side of the grounding surge arrester away from the grounding pole; each metallic return jumper of each converter station is equipped with a set of surge arresters; and a series DC field surge arrester is provided at the positive output terminal of the DC pole of the highest voltage converter station. Line surge arresters; a converter station outlet surge arrester is installed at the input end of the tie line, and a converter station in-station surge arrester is installed at the output end of the tie line.

[0007] Furthermore, a surge arrester at the bottom of each converter valve in the converter station is connected to a reactor, and a surge arrester at the top of each converter valve is connected to a reactor; each reactor is equipped with a smoothing reactor surge arrester parallel to it.

[0008] Furthermore, a plurality of reactors are installed at the positive output terminal of the DC pole of the highest voltage converter station, and a smoothing reactor surge arrester is connected in parallel with the reactors; a plurality of reactors are installed at the negative output terminal of the DC pole of the lowest voltage converter station, and a smoothing reactor surge arrester is connected in parallel with the reactors.

[0009] Furthermore, a DC filter is installed between the positive and negative poles of each converter station.

[0010] This invention also discloses a multi-terminal cascaded DC transmission insulation coordination method for the multi-terminal cascaded DC transmission insulation coordination system described in any of the above claims, comprising the following steps: determining the maximum continuous operating voltage of the station outlet surge arresters and station-in-station surge arresters at both ends of the tie line; determining the maximum continuous operating voltage and coordination relationship of the surge arresters at the bottom, middle, and top of the lowest voltage converter station; determining the continuous operating voltage of the DC field surge arresters and line surge arresters of the highest voltage converter station; determining the reference voltage and coordination relationship of other surge arresters in the multi-terminal cascaded DC transmission insulation coordination system; generating a simulation model based on the maximum continuous operating voltage of the station outlet surge arresters and station-in-station surge arresters, the maximum continuous operating voltage of the lowest voltage converter station, the continuous operating voltage of the DC field surge arresters and line surge arresters, and the reference voltage and coordination relationship of other surge arresters; comparing the output results of the simulation model with the actual results and iterating until the preset results are met, generating the final simulation model; inputting the parameters to be determined into the final simulation model to obtain the multi-terminal cascaded DC transmission insulation coordination results.

[0011] Furthermore, the maximum continuous operating voltage of the station outlet surge arresters and station interior surge arresters at both ends of the tie line is the sum of the maximum DC operating voltage corresponding to the tie line and the harmonic voltages on the tie line; the surge arrester at the bottom of the lowest voltage converter station is the maximum voltage drop of the grounding electrode line; the surge arrester in the middle of the lowest voltage converter station is the sum of the maximum voltage drop of the grounding electrode line and the maximum continuous operating voltage of one bridge arm of the converter valve; the surge arrester at the top of the lowest voltage converter station is the sum of the maximum continuous operating voltage of the middle surge arrester and the maximum continuous operating voltage of one bridge arm of the converter valve.

[0012] Furthermore, the method for determining the maximum continuous operating voltage and coordination relationship of the surge arresters at the bottom, middle, and top of the converter station is as follows: Assume the highest voltage converter station N corresponds to tie line M; select the continuous operating voltage at the midpoint of tie line M as the Mth reference point; the voltage U at the Mth reference point... 0M For: U 0M =U DC M / N+U harmM The continuous operating voltage U of the surge arrester at the bottom of the converter valve of the connecting line M Bt For: U Bt =U 0M +U lineM / 2, where U DC U is the highest DC operating voltage of the DC system including control errors, N is the total number of cascaded converter stations, and U is the maximum DC operating voltage of the DC system including control errors. harmM U represents the harmonic voltages at the midpoint of the tie line M. lineM The maximum voltage drop on tie line M; the continuous operating voltage U of the surge arrester in the middle of the converter valve. Ct For: U Ct =U Bt +U v ; Continuous operating voltage U of the surge arrester at the bottom of the converter valve Dt For: U Dt =U Ct +U v Among them, U v This is the maximum continuous operating voltage of one arm of the converter valve.

[0013] Furthermore, the continuous operating voltage of the DC field surge arrester at the highest voltage converter station is the same as the continuous operating voltage of the line surge arrester, which is the highest DC operating voltage U of the DC system including control error. DC .

[0014] Furthermore, the grounding surge arrester, the metallic return jumper, the neutral line surge arrester, and the surge arrester at the bottom of the converter valve of the lowest voltage converter station are all included. The reference voltage ranges from 200kV to 350kV, and increases sequentially. The lightning protection level of the parallel surge arrester on the negative pole of the smoothing reactor at both ends of the tie line is taken as the maximum value of the lightning protection level of the two surge arresters: the station outlet surge arrester and the top surge arrester of the converter valve. The lightning protection level of the parallel surge arrester on the positive pole of the smoothing reactor at both ends of the tie line is taken as the maximum value of the lightning protection level of the two surge arresters: the bottom surge arrester of the converter valve and the station surge arrester. The lightning protection level of the parallel surge arrester of the smoothing reactor on the DC pole is taken as 1 to 1.1 times the lightning protection level of the line surge arrester.

[0015] Furthermore, the simulation model output is compared with the actual results and iterated until it meets the preset results. The method for generating the final simulation model is as follows: check whether the coordination current and energy of all surge arresters exceed the expected range. If they do not exceed the range, the surge arrester parameters are valid. If they exceed the range, increase the number of surge arrester columns, increase the reference voltage and protection level, rescan all unexpected fault conditions, and iterate continuously until the coordination current and energy of all surge arresters are within the preset range.

[0016] The present invention has the following advantages due to the adoption of the above technical solutions:

[0017] 1. Based on the traditional DC transmission insulation coordination, this invention has advantages such as better flexibility, reliability and scalability;

[0018] 2. The insulation coordination design scheme of the present invention has the characteristics of simple and clear steps in use. It can still effectively suppress the overvoltage of the entire DC system in the event of lightning intrusion into the DC line or lightning strike due to the failure of DC field shielding.

[0019] 3. The insulation coordination design method and system of the present invention provide a very valuable reference for the insulation coordination design of subsequent multi-terminal DC transmission systems, and can be widely applied to various multi-terminal DC transmission systems. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a multi-terminal cascaded DC transmission insulation coordination system in one embodiment of the present invention;

[0021] Figure 2 This is a flowchart of a multi-terminal cascaded DC transmission insulation coordination method according to an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the energy absorption process of the newly added line surge arrester when a line fault occurs in a multi-terminal converter station according to one embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of the energy absorption process of the line fault metal return arrester when a line fault occurs in a multi-terminal converter station according to an embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the specific embodiments are provided only for a better understanding of the present invention and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terminology used is for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0025] To address the problems in existing technologies where multi-terminal construction adds one or more connecting lines between converter stations, thus increasing DC harmonics in the circuit and posing difficulties for insulation coordination design and overvoltage suppression in UHVDC systems, this invention proposes a multi-terminal cascaded DC transmission insulation coordination system. Its reasonable insulation coordination design requires consideration of the characteristics of the main wiring of the multi-terminal system, the parameter coordination relationship of each surge arrester in the circuit, and the suppression of the maximum transient overvoltage, current, and energy levels under various faults on both the AC and DC sides to acceptable levels, achieving an optimal fit between the economic efficiency of converter station equipment and the insulation coordination scheme. The insulation coordination design scheme of this invention is characterized by its simple and clear steps. Even in the event of lightning strikes intruding into the DC line or lightning strikes due to DC field shielding failure, it can still effectively suppress overvoltages in the entire DC system. The insulation coordination design method and system of this invention provide a valuable reference for subsequent insulation coordination design of multi-terminal DC systems and can be widely applied to various multi-terminal DC transmission systems. The following detailed description of the invention, in conjunction with the accompanying drawings and embodiments, illustrates the solution in detail.

[0026] Example 1

[0027] This embodiment discloses a multi-terminal cascaded DC transmission insulation coordination system, such as Figure 1 As shown, in this embodiment, the multi-terminal cascaded DC transmission insulation coordination can be used for the sending-end converter station's high-end system to directly connect to the high-end station's 500kV AC grid, and the low-end system to connect to the low-end station's 500kV AC grid. The receiving-end converter station adopts conventional DC hierarchical connection to the 500kV AC grid. The rated power is bipolar 8000MW. It includes: N converter stations and M tie lines connecting the converter stations, ordered from low to high voltage. The sequence number of the converter station is t, t=1, 2, ..., N, and the sequence number of the tie line is a, a=1, 2, ..., M. The relationship between N and M is N=M+1.

[0028] Several converter stations are connected in series and via tie lines. In this embodiment, each converter station includes two converters. According to the topology of multi-terminal converter stations, each converter valve in the converter station is equipped with a surge arrester at its bottom, middle, and top. , , Where t is the converter station designation, t≤N. That is, two converters, the positive terminal of one converter is connected to the positive terminal of the converter station, the negative terminal of that converter is connected to the positive terminal of the other converter, and the negative terminal of the other converter is connected to the next…

[0029] The negative terminal of the DC pole of the lowest voltage converter station is equipped with a grounding line; the grounding line consists of several grounding poles, and a set of grounding surge arresters is installed at the outlet of each grounding pole. Where t is the converter station designation, t≤N; this surge arrester is not configured for converter stations without grounding electrodes; a neutral line surge arrester is installed on the side of the grounding surge arrester furthest from the grounding electrode. .

[0030] Metallic return surge arresters are configured according to the metallic return connection configuration of the multi-terminal converter station, and each metallic return jumper of each converter station is equipped with a set of surge arresters. , where a is the tie line number, a≤M; this surge arrester is not configured for converter stations without grounding electrodes.

[0031] A series DC field surge arrester is configured at the positive output terminal of the DC pole of the highest voltage converter station. Line surge arrester .

[0032] Two sets of surge arresters are installed at each end of each tie line; that is, a surge arrester at the converter station outlet is installed at the input end of the tie line, and a surge arrester at the converter station interior is installed at the output end of the tie line. They are named accordingly. , , ), where 'a' is the tie line number, a≤M; 'b'∈{1,2}, b=1 represents the high-voltage side surge arrester of the tie line, b=2 represents the low-voltage side surge arrester of the tie line; 'c'∈{1,2}, c=1 represents the station-side surge arrester, c=2 represents the converter station outlet surge arrester, and the naming follows the same logic. Specifically: the station-side surge arrester of the first tie line of the first converter station. The first surge arrester at the first interconnection line outlet of the first converter station The surge arrester in the first interconnection line of the second converter station Lightning protection at the first interconnection line outlet of the second converter station The surge arrester inside the second tie line of the second converter station. Lightning protection at the first interconnection line outlet of the second converter station Up to the surge arrester of the Mth interconnection line between the N-1th converter station and the Nth converter station. , , , .

[0033] Each converter valve in the converter station has a surge arrester at its bottom connected to a reactor, and a surge arrester at its top connected to a reactor. Except for the negative DC line of the lowest voltage converter station and the positive DC line of the highest voltage converter station, each reactor is equipped with a smoothing surge arrester parallel to it. That is, the smoothing reactor surge arrester on the first tie line of the first converter station. The first tie line smoothing reactor surge arrester of the second converter station The second tie line smoothing reactor surge arrester of the second converter station ..., until the smoothing reactor surge arrester of the Mth interconnection line between the N-1th converter station and the Nth converter station. .

[0034] Several reactors are installed at the positive output terminal of the DC pole of the highest voltage converter station, and smoothing reactor surge arresters are connected in parallel with the reactors. Several reactors are installed at the negative output terminal of the DC pole of the lowest voltage converter station, along with smoothing reactor surge arresters connected in parallel with the reactors. A DC filter is installed between the positive and negative terminals of each converter station.

[0035] The surge arrester configuration in the converter area of ​​the ±800kV converter station is basically the same as that in the high-voltage converter area of ​​a conventional ±800kV UHVDC project. However, due to the addition of a ±400kV multi-terminal cascaded connection line, the original valve-top surge arrester of the low-end converter cannot protect the low-voltage side of the high-end converter. Therefore, an additional surge arrester is added at the bottom of the valve of the high-end converter. Surge arresters. The configuration of surge arresters in the pole area, neutral area, and smoothing reactor is the same as that in conventional 800kV UHVDC projects. The difference is that with the addition of ±400kV multi-terminal cascaded connecting lines, both substations have added ±400kV pole and line areas, requiring additional surge arresters in these areas. , , , Line surge arresters. Each end is equipped with a set of multi-terminal cascaded tie-line surge arresters, and each set of arresters is configured to protect a corresponding line area. Furthermore, in the aforementioned high-reliability, separately located cascaded converter station insulation coordination design scheme, the key feature is the separate location construction at the sending end (high and low ends). Due to access to different AC systems, the surge arresters are symmetrically distributed on the ±800kV pole line, ±400kV pole line, and neutral bus, or only on the ±800kV pole line and neutral bus. DC filters are connected across the DC side of the high-end and low-end valve groups respectively. , , , The voltage contains certain harmonics, and the impact of ±400kV multi-terminal cascaded interconnections and reactance on the ±400kV DC voltage should be considered. The high- and low-end ±400kV switchyard equipment consists of ±400kV DC pole-line surge arresters. , , , Protection. The most severe overvoltage condition of ±400kV DC pole bus is caused by lightning strikes intruding into the DC line or by lightning strikes due to failure of DC field shielding. The lightning current in the latter case is limited to a very small amount due to the appropriate shielding system above the DC pole equipment, and is zero for the indoor DC field.

[0036] The maximum amplitude of a lightning strike entering through a DC line is determined by the highest withstand voltage of the DC line, and the lightning strike is controlled by a DC pole arrester. , DC filter is affected , The limitations of this design include separate high- and low-end locations at the sending end. Due to access to different AC systems, the transformers are symmetrically positioned on the ±800kV pole line, ±400kV pole line, and neutral bus. DC filters are connected across the DC side of the high-end and low-end valve groups, respectively. , All voltages contain certain harmonics.

[0037] Example 2

[0038] Based on the same inventive concept, this embodiment discloses a multi-terminal cascaded DC transmission insulation coordination method for any of the above-mentioned multi-terminal cascaded DC transmission insulation coordination systems, comprising the following steps:

[0039] S1 determines the maximum continuous operating voltage of the surge arresters at the station exit and inside the station at both ends of the tie line;

[0040] Surge arresters at the station exit and within the station at both ends of the tie line of a multi-terminal cascaded DC system , Maximum continuous operating voltage U Xa11ccov U Xa12ccov U Xa21ccov U Xa22ccov The maximum DC operating voltage U corresponding to the tie line Xa11DC The sum of the harmonic voltages on the superimposed interconnect line, U Xa11harm The harmonic voltage should take into account the stray parameters of the inter-station tie line, the parameters of the smoothing reactor, and the DC filter configuration scheme. The harmonic voltage is determined through DC system simulation calculation. In this embodiment, the maximum DC operating voltage of 408kV is superimposed with the sum of the harmonic voltages on the tie line of 30kV, and a margin is taken to obtain the maximum operating voltage of the tie line surge arrester as 450kV.

[0041] S2 determines the surge arresters at the bottom, middle, and top of the lowest voltage converter station. , , Maximum continuous operating voltage and matching relationship;

[0042] The surge arrester at the bottom of the lowest voltage converter station represents the maximum voltage drop of the grounding electrode line, i.e., U. Bt =U g U g This represents the maximum voltage drop across the grounding electrode line.

[0043] The surge arrester in the middle of the lowest voltage converter station is the sum of the maximum voltage drop of the grounding electrode line and the maximum continuous operating voltage of one arm of the converter valve, i.e., U. Ct =U g +U v ;

[0044] The voltage of the surge arrester at the top of the lowest voltage converter station is the sum of the maximum continuous operating voltage of the surge arrester in the middle section and the maximum continuous operating voltage of one arm of the converter valve, U. Dt =U Ct +U v .

[0045] Among them, U v This is the maximum continuous operating voltage of one arm of the converter valve.

[0046] Based on the topology of multi-terminal converter stations and inter-station tie lines, determine the bottom, middle, and top surge arresters of the converter valves at the high-voltage side converter station of the tie line. , , (When N≥2) The maximum continuous operating voltage and its coordination relationship; select the continuous operating voltage at the midpoint of the inter-station tie line 1 with the lowest voltage level in the DC circuit as the first reference point, and the voltage of the first reference point U 01 =U DC / N+U harm1 U DC U is the highest DC operating voltage of the DC system including control errors, N is the total number of cascaded converter stations, and U is the maximum DC operating voltage of the DC system including control errors. harm1 U represents the harmonic voltages at the midpoint of tie line 1. harm2 Simulation calculations determined that the surge arrester at the bottom of the converter valve of converter station 1 on the high-voltage side of inter-station interconnection line 1 was... The continuous operating voltage is: U Bt =U 01 +U line1 / 2, where U line1 The maximum voltage drop on tie line 1; surge arresters in the middle and top of the converter valve of converter station 2. , The continuous operating voltage is: U Ct =U Bt +U v U Dt =U Ct +U v If the number of inter-station tie lines is greater than or equal to 2 and the number of cascaded converter stations is greater than or equal to 3, then the maximum continuous operating voltage at each point is determined sequentially from low voltage to high voltage. The determination method is as follows: the continuous operating voltage at the midpoint of the inter-station tie line M is selected as the Mth reference point, and the voltage U of the Mth reference point is... 0M =U DC M / N+U harmMThe surge arrester at the bottom of the converter valve of converter station N on the high-voltage side of the inter-station connecting line M. The continuous operating voltage is: U Bt =U 0M +U lineM / 2, where U lineM The maximum voltage drop on tie line M; surge arresters in the middle and top of the converter valve of converter station N. , The continuous operating voltage is: U Ct =U Bt +U v U Dt =U Ct +U v .

[0047] In this embodiment, the surge arresters at the bottom, middle, and top of the converter valve of the lowest voltage converter station are determined. , , The maximum continuous operating voltages are 20kV, 274.99kV, and 450kV, respectively.

[0048] S3 determines the continuous operating voltage of the DC field surge arresters and line surge arresters of the highest voltage converter station.

[0049] DC field surge arresters of the highest voltage converter station Continuous operating voltage and line surge arresters The continuous operating voltage is the same, which is the highest DC operating voltage U of the DC system including control error. DC In this embodiment, the highest DC operating voltage U of the DC system DC The voltage is 800kV + 50kV = 850kV. The surge arresters at both ends of the tie line in a multi-terminal cascaded DC system. , Surge arresters at the bottom, middle and top of each converter valve , , DC field surge arrester of the highest voltage converter station N and line surge arresters The reference voltages are all taken as 0.82 to 0.85 times the maximum continuous operating voltage of each surge arrester, and the operating and lightning protection levels of each surge arrester are taken as 1.2 to 1.5 times its reference voltage. In this embodiment, , , , , The reference voltages, calculated to be 333kV, 373kV, 574kV, 574kV, 840kV, and 1106kV, respectively, and the lightning protection levels are 476kV / 2kA, 540kV / 2kA, 803kV / 2kA, 803kV / 2kA, 1108kV / 2kA, and 1500kV / 2kA, respectively. The switching protection levels are / ( Main lightning protection), 509kV / 0.5kA, 753kV / 0.2kA, 753kV / 0.2kA, 1025kV / 0.2kA, 1391kV / 0.2kA.

[0050] S4 determines the reference voltage and coordination relationship of other surge arresters in the multi-terminal cascaded DC transmission insulation coordination system;

[0051] grounding surge arrester Metallic return jumper arrester Neutral line surge arrester And the surge arrester at the bottom of the converter valve of the lowest voltage converter station The reference voltages need to be selected in coordination, and their values ​​range from 200kV to 350kV, increasing sequentially; the operating and lightning protection levels of each surge arrester are taken as 1.4 to 1.6 times their reference voltage. , The reference voltages of the surge arresters are 202kV, 219kV, 202kV, 219kV, and 219kV, respectively. The operating and lightning protection levels of each surge arrester are taken as 1.4 to 1.6 times its reference voltage.

[0052] The lightning protection level of the parallel surge arrester on the negative pole of the smoothing reactor at both ends of the tie line is taken as 1 to 1.1 times the maximum value of the lightning protection level of the surge arrester at the station outlet and the top surge arrester of the converter valve. The lightning protection level of the parallel surge arrester on the positive pole of the smoothing reactor at both ends of the tie line is taken as 1 to 1.1 times the maximum value of the lightning protection level of the surge arrester at the bottom of the converter valve and the surge arrester in the station. The lightning protection level of the parallel surge arrester of the smoothing reactor on the DC pole line is taken as 1 to 1.1 times the lightning protection level of the line surge arrester.

[0053] S5 generates a simulation model based on the maximum continuous operating voltage of the surge arresters at the station outlet and within the station, the maximum continuous operating voltage of the lowest voltage converter station, the continuous operating voltage of the DC field surge arresters and line surge arresters, and the reference voltages and coordination relationships of other surge arresters. The simulation model output results are compared with the actual results and iterated until they meet the preset results, generating the final simulation model. The parameters to be determined are input into the final simulation model to obtain the insulation coordination results of the multi-terminal cascaded DC transmission.

[0054] A multi-terminal cascaded DC transmission system model including all surge arresters is established. The number of surge arresters, reference voltage, and protection level parameters are set. Fault conditions at all AC / DC nodes are scanned to obtain the coordination current and energy of all surge arresters, generating a simulation model. The simulation model output is compared with the actual results, and iteratively performed until it meets the preset results. The method for generating the final simulation model is as follows: check whether the coordination current and energy of all surge arresters exceed the expected range. If they do not exceed the range, the surge arrester parameters are valid; if they do exceed the range, increase the number of surge arresters, increase the reference voltage and protection level, rescan all unexpected fault conditions, and iterate continuously until the coordination current and energy of all surge arresters are within the preset range.

[0055] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied 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.

[0056] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. 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... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0057] 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.

[0058] 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.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific embodiments of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention. The above content is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A multi-terminal cascaded DC transmission insulation coordination system, characterized in that, include: A number of converter stations and a number of connecting lines connecting the converter stations; Several converter stations are connected in series and via the tie line. Each converter valve in each converter station is equipped with a surge arrester at its bottom, middle, and top. The negative terminal of the DC pole of the lowest voltage converter station is grounded. The grounding line includes several grounding poles, and a set of grounding surge arresters is installed at the outlet of each grounding pole. A neutral line surge arrester is installed on the side of the grounding surge arrester away from the grounding pole. Each metallic return jumper of each converter station is equipped with a set of surge arresters. A series DC field surge arrester and a line surge arrester are installed at the positive output terminal of the DC pole of the highest voltage converter station. A converter station outlet surge arrester is installed at the input terminal of the tie line, and a converter station internal surge arrester is installed at the output terminal of the tie line.

2. The multi-terminal cascaded DC transmission insulation coordination system as described in claim 1, characterized in that, Each converter valve in the converter station has a surge arrester at its bottom connected to a reactor, and a surge arrester at its top connected to a reactor; each reactor is equipped with a smoothing reactor surge arrester parallel to it.

3. The multi-terminal cascaded DC transmission insulation coordination system as described in claim 2, characterized in that, The highest voltage converter station has several reactors installed at the positive output terminal of the DC pole line, and smoothing reactors and surge arresters connected in parallel with the reactors; the lowest voltage converter station has several reactors installed at the negative output terminal of the DC pole line, and smoothing reactors and surge arresters connected in parallel with the reactors.

4. The multi-terminal cascaded DC transmission insulation coordination system as described in claim 1, characterized in that, A DC filter is installed between the positive and negative poles of each converter station.

5. A method for insulation coordination in multi-terminal cascaded DC transmission, characterized in that, For a multi-terminal cascaded DC transmission insulation coordination system as described in any one of claims 1-4, the following steps are included: Determine the maximum continuous operating voltage of the surge arresters at the station exit and inside the station at both ends of the connecting line; Determine the maximum continuous operating voltage and coordination relationship of the surge arresters at the bottom, middle and top of the lowest voltage converter station; Determine the continuous operating voltage of the DC field surge arresters and line surge arresters of the highest voltage converter station; Determine the reference voltage and coordination relationship of other surge arresters in a multi-terminal cascaded DC transmission insulation coordination system; Based on the maximum continuous operating voltage of the station outlet surge arrester and the station inside surge arrester, the maximum continuous operating voltage of the lowest voltage converter station, the continuous operating voltage of the DC field surge arrester and the line surge arrester, and the reference voltage and coordination relationship of other surge arresters, a simulation model is generated. The output results of the simulation model are compared with the actual results and iterated until they meet the preset results, thus generating the final simulation model. Input the parameters to be determined into the final simulation model to obtain the insulation coordination results of the multi-terminal cascaded DC transmission.

6. The multi-terminal cascaded DC transmission insulation coordination method as described in claim 5, characterized in that, The maximum continuous operating voltage of the surge arresters at the station outlets and inside the station at both ends of the tie line is the sum of the maximum DC operating voltage corresponding to the tie line and the harmonic voltages on the tie line; the surge arrester at the bottom of the lowest voltage converter station is the maximum voltage drop of the grounding electrode line; the surge arrester in the middle of the lowest voltage converter station is the sum of the maximum voltage drop of the grounding electrode line and the maximum continuous operating voltage of one arm of the converter valve; the surge arrester at the top of the lowest voltage converter station is the sum of the maximum continuous operating voltage of the middle surge arrester and the maximum continuous operating voltage of one arm of the converter valve.

7. The multi-terminal cascaded DC transmission insulation coordination method as described in claim 5, characterized in that, The method for determining the maximum continuous operating voltage and coordination relationship of the surge arresters at the bottom, middle and top of the converter station is as follows: Assume the highest voltage converter station N corresponds to the tie line M; The continuous operating voltage at the midpoint of the tie line M is selected as the Mth reference point; The voltage U at the Mth reference point 0M For: U 0M =U DC *M / N+U harmM The continuous operating voltage U of the surge arrester at the bottom of the converter valve of the connecting line M Bt For: U Bt =U 0M +U lineM / 2, where U DC U is the highest DC operating voltage of the DC system including control errors, N is the total number of cascaded converter stations, and U is the maximum DC operating voltage of the DC system including control errors. harmM U represents the harmonic voltages at the midpoint of the tie line M. lineM The maximum voltage drop on the tie line M; the continuous operating voltage U of the surge arrester in the middle of the converter valve. Ct For: U Ct =U Bt +U v ; Continuous operating voltage U of the surge arrester at the bottom of the converter valve Dt For: U Dt =U Ct +U v Among them, U v This is the maximum continuous operating voltage of one arm of the converter valve.

8. The multi-terminal cascaded DC transmission insulation coordination method as described in claim 5, characterized in that, The continuous operating voltage of the DC field surge arrester at the highest voltage converter station is the same as the continuous operating voltage of the line surge arrester, which is the highest DC operating voltage U of the DC system including control error. DC .

9. The multi-terminal cascaded DC transmission insulation coordination method as described in claim 5, characterized in that, The grounding surge arrester, metallic return jumper, neutral line surge arrester, and converter valve bottom surge arrester of the lowest voltage converter station. The reference voltage ranges from 200kV to 350kV, and increases sequentially. The lightning protection level of the parallel surge arrester on the negative pole of the smoothing reactor at both ends of the tie line is taken as the maximum value of the lightning protection level of the surge arrester at the station outlet and the top surge arrester of the converter valve. The lightning protection level of the parallel surge arrester on the positive pole of the smoothing reactor at both ends of the tie line is taken as the maximum value of the lightning protection level of the surge arrester at the bottom of the converter valve and the surge arrester in the station. The lightning protection level of the parallel surge arrester of the smoothing reactor on the DC pole line is taken as 1 to 1.1 times the lightning protection level of the line surge arrester.

10. The multi-terminal cascaded DC transmission insulation coordination method as described in claim 5, characterized in that, The method for generating the final simulation model by comparing the output of the simulation model with the actual results and iterating until the results meet the preset requirements is as follows: check whether the coordination current and energy of all surge arresters exceed the expected range. If they do not exceed the expected range, the surge arrester parameters are valid. If they exceed the expected range, increase the number of surge arresters, increase the reference voltage and protection level, rescan all unexpected fault conditions, and iterate continuously until the coordination current and energy of all surge arresters are within the preset range.

Images