A method for drawing and using a direct current bias risk map

Abstract

The application provides a method for drawing and using a direct current bias magnet risk map, which comprises the following steps: firstly, establishing a risk grade division representation; then, positioning the geographic positions of each direct current pole and substation; dividing the risk area through a direct current pole circle drawing method and a triangular area division method; then, processing the risk area such as a risk overlapping area and an uncovered area; and finally, completing the drawing of the direct current bias magnet risk map. The serious or severe or general risk area is selected from the direct current bias magnet risk map, and a treatment scheme is selected according to the grounding condition of the substation, the distance from the grounding pole and the current size obtained through modeling calculation. The method of the application establishes a predicted risk map of the direct current bias magnet risk, proposes a direct current bias magnet treatment scheme under different conditions of a power system, can provide a theoretical reference and technical guidance for the power grid operation and maintenance department to carry out treatment work for the direct current bias magnet problem, and helps to maintain the safe and reliable operation of the power substation.

Description

Technical Field

[0001] This invention relates to the field of power system technology, specifically to a novel method for drawing and using a DC bias risk diagram. Background Technology

[0002] High-voltage direct current (HVDC) transmission has advantages such as large transmission capacity, long transmission distance, low line construction cost for the same transmission capacity, and low line loss. In recent years, it has seen significant development in China. For example, HVDC transmission projects such as the "West-to-East Power Transmission" have effectively alleviated energy and load conditions. However, HVDC transmission inevitably involves monopolar grounding line operation. In this mode, a large amount of DC current flows into the ground through the DC grounding electrode, causing the risk of DC bias magnetization.

[0003] DC bias refers to the generation of a DC component in the current of a transformer, causing half-cycle magnetic saturation of the transformer core and a series of electromagnetic effects resulting from this saturation. DC bias intensifies transformer mechanical vibration, generates numerous high-order harmonics, increases reactive power consumption, raises the requirements for relay protection, and affects the stable operation of the power system. Therefore, research on the assessment and mitigation of DC bias has significant theoretical and practical implications.

[0004] The research directions of domestic power research institutions on DC bias magnetization are mainly focused on two aspects: (1) the change of ground potential during the operation of converter station monopolar, and the distribution of DC current in the regional power grid; (2) the harm of DC bias magnetization to transformers and other coil equipment and corresponding control measures. Summary of the Invention

[0005] The purpose of this invention is to provide a novel method for drawing and using a DC bias risk map, which intuitively reflects the regional DC bias risk and provides a convenient and reliable solution for DC bias mitigation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for drawing a DC bias risk diagram includes the following steps:

[0008] Step 1: Establish a risk level classification representation;

[0009] Step 2: Locate the geographical location of each DC pole and substation, and determine the risk level of each substation based on the risk level classification.

[0010] Step 3: Based on the risk level classification, the risk level regions are divided using the DC pole circle method and the triangular region division method. Specifically, the area within a circle with a radius of 20km centered on the DC pole is designated as the highest risk level region. Adjacent substations are connected by lines, and these lines are divided equally according to the difference in risk levels between adjacent substations. The division points, substations, and grounding electrode O are connected to form triangular regions. Risk areas are then classified based on the risk levels of substations adjacent to these triangular regions. If a region has multiple risk levels, the higher risk level is used to cover the lower risk level as the final risk level for that region. For areas outside the enclosed region formed by the DC pole circle method and the triangular region division method, the sides of the triangles are extended to the region boundary. The risk level of the region is then reduced by one level, using the nearest risk area as a reference. Finally, regions with the same risk level are merged to obtain the DC bias risk map.

[0011] Furthermore, the risk level classification in step one is based on the magnitude of the high-voltage winding current and the common winding current. Specifically, a DC current less than 1A is defined as no risk, 1-5A as mild risk, 5-10A as moderate risk, 10-20A as severe risk, and greater than 20A as serious risk.

[0012] Furthermore, the DC pole circle drawing method described in step three is as follows: the area within a circle with the DC pole as the center and a radius of 20km is divided into serious risk areas.

[0013] Furthermore, in step three, the connecting line is divided equally according to the difference in risk levels between adjacent substations. The dividing points, the substations, and the grounding electrode O are connected to form a triangular region. Risk areas are then delineated based on the risk levels of the substations adjacent to the triangular region. Specifically:

[0014] If adjacent substations have the same risk level, the connection line will be divided into two equal parts, i.e., not divided equally; the substations will be connected to the grounding electrode O to form a triangular area, and the risk level of the triangular area will be the same as that of the substations.

[0015] If the risk level of an adjacent substation is the same as that of an adjacent substation, the line will be divided into two equal parts. The dividing point, the substation and the grounding electrode O will be connected to form two triangular areas. The risk level of the two triangular areas is the same as that of the substations they contain.

[0016] If the risk levels of adjacent substations are cross-risk levels, the connection line will be divided into multiple equal parts. The value of each division is the difference in risk levels between the corresponding adjacent substations. The division points, substations, and grounding electrode O will be connected to form multiple triangular regions. The risk level of the triangular region containing the adjacent substations at both ends is the same as the risk level of the substations it contains. The risk level of the middle triangular region will rise and fall sequentially according to the risk level of the triangular regions at both ends.

[0017] DL / T 437-2012, "Technical Guidelines for High Voltage DC Grounding Electrodes," stipulates that the permissible DC bias current for each phase winding of a transformer is: 0.3% of the rated current for a single-phase transformer, 0.5% for a three-phase five-limb transformer, and 0.7% for a three-phase three-limb transformer. Based on the guidelines, the maximum permissible DC bias current at the neutral point of transformers of different voltage levels is approximately 10A. To facilitate on-site implementation and considering the tolerance for errors in calculation and measurement, this invention divides the DC current into several thresholds: 1A, 5A, 10A, and 20A, and defines them as different risk levels and corresponding mitigation strategies.

[0018] Current DC bias assessments of substations require modeling the entire power grid topology and wide-area soil conditions each time, consuming significant computational resources and time. Furthermore, the acquired data only provides a discontinuous distribution of points, failing to represent a continuous geographical area. To address regional DC bias risk assessment and mitigation of new substations, this invention proposes a strategy for regional DC bias risk assessment and mitigation based on the DC pole circle method and the triangular region division method.

[0019] Theoretically, the DC bias current of a substation is equal to the potential difference between two connected substations divided by the DC resistance. The distance between the substation and the grounding electrode, the distance between substations, and the corresponding soil distribution are the most important factors affecting the potential difference. Because the deep soil characteristics are less abrupt within a range of tens of kilometers, the magnitude and risk level of the DC bias current of existing substations have largely reflected the soil model. Therefore, the magnitude of DC bias risk in adjacent areas is mainly affected by distance. This invention uses existing test / calculation data as the benchmark for substation risk assessment, and, guided by distance, establishes the risk level of the area enclosed by the grounding electrode and substations, generating a DC bias risk distribution map for the entire region. The DC bias risk map accurately and intuitively reflects the regional DC bias risk, providing effective support for substation location selection, DC bias risk assessment, and mitigation.

[0020] Specifically, the present invention also provides a method for mitigating DC bias risk maps obtained using the above-described drawing method, comprising:

[0021] (1) Based on the DC bias risk map, select the risk areas that need to be addressed according to the risk level;

[0022] (2) For risk areas that need to be addressed, determine whether the substations and their connected substations in the area are grounded. If they are not grounded, no treatment is needed. If they are all grounded, determine whether the distance between the substation and the grounding electrode is less than 10km. If it is less than 10km, capacitor treatment is carried out. If it is greater than 10km, the power grid in the area near the substation is modeled and calculated. DC bias analysis and treatment are carried out on the substation. Treatment schemes are selected for different winding currents.

[0023] Furthermore, in step (2), the risk areas that need to be addressed include areas with risk levels of general risk, severe risk, and serious risk.

[0024] Furthermore, the models used in step (2) include a calculation model of the power grid topology and a soil model of the relationship between soil resistivity and substation site depth.

[0025] Furthermore, in step (2), a treatment scheme is selected for different winding currents, specifically: if the current is less than 10A, no treatment is performed; if the current is between 10 and 50A, resistance treatment is performed; if the current is greater than 50A, capacitance treatment is performed.

[0026] The beneficial effects of this invention are: the method of this invention establishes a predicted risk map of DC bias risk, proposes DC bias mitigation schemes under different power system conditions, and can provide theoretical reference and technical guidance for power grid operation and maintenance departments to carry out mitigation work on DC bias problems, helping to maintain the safe and reliable operation of power substations. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process of this invention;

[0028] Figure 2 This is a table representing the regional risk level classification;

[0029] Figure 3 This is a risk area classification map under the same risk level;

[0030] Figure 4 This is a risk area delineation map under adjacent risk levels;

[0031] Figure 5 It is a risk area division map across risk levels;

[0032] Figure 6 This is a map showing the risk zones outside the enclosed area;

[0033] Figure 7 It is a map showing the coverage of risk areas;

[0034] Figure 8 Example diagram of regional risk level classification. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0037] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be used interchangeably where appropriate so that the embodiments of the invention described herein can be implemented in any order other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0038] As attached Figure 1 As shown, a novel method for drawing and using a DC bias risk map includes the following steps: establishing a risk level classification table; locating the geographical locations of each DC pole and substation; then using the DC pole circle method and the triangular region division method to divide the risk areas; and finally processing the risk areas.

[0039] Next, areas with severe, high, or general risks are selected; finally, a mitigation plan is chosen based on the substation's grounding conditions, distance from the grounding electrode, and the current magnitude calculated through modeling.

[0040] The DC pole circle method is applicable to the area centered on the DC pole with a radius of 20km. The triangular area division method is applicable to the area outside the circle centered on the DC pole with a radius of 20km. Specific situations include risk area division under the same risk level, risk area division under adjacent risk levels, and risk area division across risk levels.

[0041] Appendix Figure 2This is a regional risk level classification method, determined by the high-voltage winding current and common winding current before remediation. DC bias risk is divided into five levels: substations with current less than 1A are defined as no risk; substations with current ranging from 1 to 5A are defined as slightly risky; substations with current ranging from 5 to 10A are defined as moderately risky; substations with current ranging from 10 to 20A are defined as heavily risky; and substations with current greater than 20A are defined as severely risky.

[0042] Appendix Figure 3 This is a risk area division map under the same risk level. If substation A is at a severe risk, and substations B and C are also at severe risk (i.e., all three substations are at the same risk level), then area ABOCA is a severe risk area.

[0043] Appendix Figure 4 This is a risk area division diagram for adjacent risk levels. If substation A is classified as severe risk, and B and C as general risk (i.e., two of the three substations are at the same risk level, and the rest are at adjacent risk levels), the AC and AB segments are divided into two equal parts. The half adjacent to substation A is connected to the grounding electrode O. This area is the severe risk area; the other two parts are the general risk areas.

[0044] Appendix Figure 5 This is a risk area delineation map under different risk levels. If substation A is classified as severe risk, substation B as moderate risk, and substation C as high risk (meaning the three substations have different risk levels, and two of them have risk levels that cross risk levels), as shown in the attached diagram. Figure 6 In the case of substations A and B, divide line segment AC into two equal parts. Connect the half adjacent to substation A to grounding electrode O. This area is a severe risk area. Connect the half adjacent to substation C to grounding electrode O. This area is a moderate risk area. Divide line segment AB into three equal parts. Connect the third adjacent to substation A to grounding electrode O. This area is a severe risk area. Connect the third adjacent to substation B to grounding electrode O. This area is a moderate risk area. The middle third is a moderate risk area.

[0045] Appendix Figure 6 For the risk zone delineation map outside the enclosed area, the sides of the triangles dividing the triangular area are extended to the area boundary. The risk level of the area is reduced by one level based on the level of the nearest risk zone.

[0046] Appendix Figure 7 For a comprehensive risk area delineation map, if low-risk and high-risk areas overlap during the mapping process, the high-risk area will cover the low-risk area, and the risk level of that overlapping area will be consistent with the risk level of the high-risk area. (See attached map.) Figure 7 As shown, area A is a high-risk area and area B is a general-risk area. Since the risk level of area A is higher than that of area B, the area where the two overlap is designated as a high-risk area.

[0047] Appendix Figure 8 The example map shows the classification of regional risk levels. When drawing a regional risk map, the regional boundary should be used as the boundary.

[0048] Based on the obtained magnetic field risk map, it is possible to quickly and easily determine which areas require remediation, specifically including:

[0049] (1) Based on the DC bias risk map, select the risk areas that need to be addressed according to the risk level; generally, the risk areas that need to be addressed include areas with risk levels of general risk, severe risk and serious risk.

[0050] (2) For risk areas requiring remediation, determine whether the substations and their connected substations within the area are grounded. If not, no remediation is needed. If all are grounded, determine whether the distance between the substation and the grounding electrode is less than 10km. If less than 10km, capacitor remediation is performed. If greater than 10km, the power grid is modeled and calculated. The modeling calculation includes a calculation model of the power grid topology and a soil model showing the relationship between soil resistivity and substation site depth. Then, DC bias magnetization analysis is performed on the substations, and remediation is carried out. For different winding currents, remediation schemes are selected.

[0051] If the current is less than 10A, no treatment is required; if the current is between 10 and 50A, resistance treatment is required; if the current is greater than 50A, capacitance treatment is required.

[0052] 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. Furthermore, the present invention 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.

[0053] This invention refers to each block of a flowchart and / or block diagram of a method, apparatus (system), and computer program product according to embodiments of the invention, as well as combinations of blocks in the flowchart and / or block diagram. 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 process. Figure 1 A process and / or box Figure 1 A device that provides the functions specified in one or more boxes.

[0054] These computer program instructions may also be stored on a computer or other programmable data processing device that can direct a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable device 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.

[0055] 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 its scope of protection. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading the present invention, they can still make various changes, modifications or equivalent substitutions to the specific implementation of the invention, all of which are within the scope of protection of the pending claims.

Claims

1. A method for drawing a DC bias risk diagram, characterized in that, Includes the following steps: Step 1: Establish a risk level classification representation; Step 2: Locate the geographical location of each DC pole and substation, and determine the risk level of each substation based on the risk level classification. Step 3: Based on the risk level classification, the risk level regions are divided using the DC pole circle method and the triangular region division method; specifically: The area within a circle with a radius of 20km centered on the DC electrode is designated as the highest risk level area. Adjacent substations are connected in pairs, and the connecting lines are divided equally according to the difference in risk level between adjacent substations. The dividing points, substations, and grounding electrode O are connected to form triangular areas. Risk areas are then defined based on the risk levels of substations adjacent to the triangular area. If the same area has multiple risk levels, the higher risk level is used to cover the lower risk level as the final risk level of the area. For the area outside the enclosed area formed by the DC pole circle method and the triangular region division method, the side length of the triangles in the triangular region division is extended to the region boundary. The risk level of the nearest risk area is used as a reference, and the risk level of the region is reduced by one level. Finally, the regions with the same risk level are merged to draw a DC bias risk map.

2. The method according to claim 1, characterized in that, The risk level classification in step one is based on the magnitude of the high-voltage winding current and the common winding current. Specifically, DC current less than 1A is defined as no risk, 1-5A as mild risk, 5-10A as moderate risk, 10-20A as severe risk, and greater than 20A as serious risk.

3. The method according to claim 2, characterized in that, The DC pole circle method described in step three is as follows: the area within a circle with a radius of 20km centered on the DC pole is divided into severely risky areas.

4. The method according to claim 1, characterized in that, Step three involves dividing the connecting line into equal parts based on the risk level differences between adjacent substations. The dividing points, the substations, and the grounding electrode O are then connected to form a triangular region. Risk zones are then defined based on the risk levels of the substations adjacent to this triangular region. Specifically: If adjacent substations have the same risk level, the connection line will be divided into two equal parts, i.e., not divided equally; the substations will be connected to the grounding electrode O to form a triangular area, and the risk level of the triangular area will be the same as that of the substations. If the risk level of an adjacent substation is the same as that of an adjacent substation, the line will be divided into two equal parts. The dividing point, the substation and the grounding electrode O will be connected to form two triangular areas. The risk level of the two triangular areas is the same as that of the substations they contain. If the risk levels of adjacent substations are cross-risk levels, the connection line will be divided into multiple equal parts. The value of each division is the difference in risk levels between the corresponding adjacent substations. The division points, substations, and grounding electrode O will be connected to form multiple triangular regions. The risk level of the triangular region containing the adjacent substations at both ends is the same as the risk level of the substations it contains. The risk level of the middle triangular region will rise and fall sequentially according to the risk level of the triangular regions at both ends.

5. A method of using a DC bias risk diagram obtained by the drawing method according to any one of claims 1-4, characterized in that, include: (1) Based on the DC bias risk map, select the risk areas that need to be addressed according to the risk level; (2) For risk areas that need to be addressed, determine whether the substations and their connected substations in the area are grounded. If they are not grounded, no treatment is needed. If they are all grounded, determine whether the distance between the substation and the grounding electrode is less than 10km. If it is less than 10km, capacitor treatment is carried out. If it is greater than 10km, the power grid is modeled and calculated. DC bias analysis and treatment are carried out on the substations. Treatment schemes are selected for different winding currents.

6. The method according to claim 5, characterized in that, The risk areas that need to be addressed in step (2) include areas with risk levels of general risk, severe risk, and serious risk.

7. The method according to claim 5, characterized in that, The models used in step (2) include a calculation model of the power grid topology and a soil model of the relationship between soil resistivity and substation site depth.

8. The method according to claim 5, characterized in that, In step (2), a treatment scheme is selected for different winding currents. Specifically, if the current is less than 10A, no treatment is performed; if the current is between 10 and 50A, resistance treatment is performed; if the current is greater than 50A, capacitance treatment is performed.

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