A method and system for early warning of sheath current at a shared grounding point in multi-circuit cable lines

Abstract

This invention relates to a method and system for early warning of sheath current at a shared grounding point in multi-circuit cable lines. The method includes: obtaining the induced electromotive force (EMF) per unit length of the three-phase metallic sheath; calculating the induced current conduction component, induced current segment length component, and induced current grounding component based on the induced EMF per unit length of the three-phase metallic sheath; calculating the metallic sheath current based on the induced current conduction component, induced current segment length component, and induced current grounding component; calculating the ratio between the metallic sheath current and the line load current; determining whether the metallic sheath current of each cable circuit has increased abnormally; and analyzing the cause of the abnormal increase when it does. This invention considers the impact of the interconnection between the grounding systems of multiple cable circuits on the distribution of the metallic sheath current. It calculates the metallic sheath current when only the induced EMF parameters of the cable circuit's metallic sheath are known, and then determines whether the metallic sheath current has increased abnormally and analyzes the cause of the abnormal increase.

Description

Technical Field

[0001] This invention relates to the field of high-voltage cable line protection, specifically to a method and system for early warning of sheath current at a shared grounding point in multi-circuit cable lines. Background Technology

[0002] Thanks to their excellent electrical performance and the fact that they do not occupy ground space, high-voltage cables have become the main channel for urban power transmission. The grounding system is an important component of high-voltage cable lines. Excessive current within the metal sheath can not only cause local temperature rise and reduce line transmission efficiency, but may also lead to serious consequences such as cable joint explosions and tunnel fires. Therefore, the assessment and early warning of metal sheath current is very important.

[0003] In recent years, with the increase in high-voltage cable lines, underground space resources have become increasingly scarce. Due to considerations of construction cost and unified management, multiple high-voltage cable lines are often laid within a single cable tunnel. The cable joints of these lines are installed in the same area, and multiple grounding systems share the same grounding grid. In this laying method, all metal sheath circuits are interconnected, and the interconnection between different line grounding systems alters the current distribution characteristics of the metal sheath. Current calculations of metal sheath current only consider the metal sheath current generated by the three-phase cable of a single line, without considering the impact of a shared grounding point on the metal sheath current distribution. Therefore, they cannot be applied to the assessment of the sheath current of multi-circuit lines sharing a grounding point. Currently, there is a lack of effective methods for calculating the sheath current in scenarios where multiple interconnected lines share a grounding point, thus making it impossible to provide early warnings for situations with large sheath currents in this type of line. Summary of the Invention

[0004] This invention provides a method and system for early warning of sheath current at a shared grounding point in multi-circuit cable lines, in order to solve at least one of the above-mentioned technical problems.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for early warning of sheath current at a shared grounding point in multi-circuit cable lines, comprising:

[0006] S1, obtain the induced electromotive force per unit length of the three-phase metal sheath of each cable line when multiple cable lines are interconnected and share a common grounding point;

[0007] S2, based on the induced electromotive force per unit length of the three-phase metallic sheath of each cable line, calculate the induced current conduction component and induced current segment length component of each cable line, as well as the induced current grounding component of multiple cable lines.

[0008] S3. Calculate the metal sheath current of each cable line based on the induced current conduction component, induced current segment length component, and induced current grounding component of each cable line.

[0009] S4. Calculate the ratio between the metal sheath current and the line load current of each cable line. Based on the ratio between the metal sheath current and the line load current of each cable line, determine whether the metal sheath current of each cable line has increased abnormally, and analyze the cause of the abnormal increase when it does.

[0010] Based on the above-mentioned method for early warning of sheath current at a shared grounding point for multiple cable lines, the present invention also provides an early warning system for sheath current at a shared grounding point for multiple cable lines.

[0011] A common grounding point sheath current early warning system for multi-circuit cable lines includes:

[0012] The unit induced electromotive force acquisition module is used to acquire the induced electromotive force per unit length of the three-phase metal sheath of each cable line when multiple cable lines are interconnected and share a common grounding point.

[0013] The induced current component calculation module is used to calculate the induced current conduction component, induced current segment length component, and induced current grounding component of each cable line based on the induced electromotive force per unit length of the three-phase metal sheath of each cable line.

[0014] The metal sheath current calculation module is used to calculate the metal sheath current of each cable line based on the induced current conduction component and induced current segment length component of each cable line, as well as the induced current grounding component of multiple cable lines.

[0015] The anomaly detection and analysis module calculates the ratio between the metal sheath current and the line load current of each cable circuit. Based on the ratio, it determines whether the metal sheath current of each cable circuit has increased abnormally, and analyzes the cause of the abnormal increase when it does.

[0016] The beneficial effects of this invention are as follows: This invention provides a method and system for early warning of sheath current at a shared grounding point for multi-circuit cable lines. It considers the impact of the interconnection between the grounding systems of multiple cable lines on the distribution of the metallic sheath current. It can calculate the metallic sheath current when only the induced electromotive force parameters of the cable line's metallic sheath are known, and this metallic sheath current is determined by the induced electromotive force of all metallic sheaths. Then, it determines whether the metallic sheath current of the corresponding cable line has increased abnormally and analyzes the reasons for the abnormal increase, thus achieving early warning of the sheath current. Furthermore, this invention avoids the complex modeling and simulation process of metallic sheath current, significantly accelerating the efficiency of cable line design and sheath current calculation. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for early warning of sheath current at a shared grounding point in multi-circuit cable lines according to the present invention;

[0018] Figure 2 This is a schematic diagram of a single-circuit cable line cross-connection grounding.

[0019] Figure 3 Equivalent circuit diagram for the grounding metal sheath loop of multiple cable lines crossing and interconnecting;

[0020] Figure 4 This is a structural block diagram of a sheath current early warning system for a shared grounding point of a multi-circuit cable line according to the present invention. Detailed Implementation

[0021] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0022] like Figure 1 As shown, a method for early warning of sheath current at a shared grounding point in multi-circuit cable lines includes:

[0023] S1, obtain the induced electromotive force per unit length of the three-phase metal sheath of each cable line when multiple cable lines are interconnected and share a common grounding point;

[0024] S2, based on the induced electromotive force per unit length of the three-phase metallic sheath of each cable line, calculate the induced current conduction component and induced current segment length component of each cable line, as well as the induced current grounding component of multiple cable lines.

[0025] S3. Calculate the metal sheath current of each cable line based on the induced current conduction component, induced current segment length component, and induced current grounding component of each cable line.

[0026] S4. Calculate the ratio between the metal sheath current and the line load current of each cable line. Based on the ratio between the metal sheath current and the line load current of each cable line, determine whether the metal sheath current of each cable line has increased abnormally, and analyze the cause of the abnormal increase when it does.

[0027] The following is a detailed explanation of each step.

[0028] Specifically, S1 is:

[0029] Construct a circuit model for each of the multiple cable lines when they are interconnected and share a common grounding point;

[0030] Based on the line model of each cable line, the induced electromotive force per unit length of the three-phase metal sheath of each cable line is obtained through simulation or theoretical calculation.

[0031] Long-distance cable transmission lines generally use a cross-connected grounding method. During line design and planning, the grounding system is typically divided into multiple cross-connected grounding main sections based on the line length. Each main section's grounding system consists of 9 cable metal sheath segments, 12 intermediate joints, two end-to-end direct grounding boxes, and two intermediate cross-connection boxes. Each cable metal sheath segment has connecting wires at both ends within the joints to either the cross-connection box or the direct grounding box. The cross-connection box achieves cable metal sheath transposition, while the direct grounding box achieves cable metal sheath-to-ground connection. The three segments of the metal sheath in each phase of the cable are reconnected to form three metal sheath loops, such as... Figure 2 As shown (i.e., the circuit model constructed in S1 is as follows) Figure 2 (As shown). Specifically, Figure 2 In a multi-circuit cable line sharing a common grounding point, each circuit is divided into a first segment, a second segment, and a third segment. Specifically, the A-phase lines of each circuit are divided into segments A1, A2, and A3; the B-phase lines are divided into segments B1, B2, and B3; and the C-phase lines are divided into segments C1, C2, and C3. Each circuit is grounded at both ends through a direct grounding box, while the first and second segments, as well as the second and third segments, are grounded through a cross-connection box. When grounded through the cross-connection box, segments A1, B2, and C3 form the first metallic sheath loop; segments B1, C2, and A3 form the second metallic sheath loop; and segments C1, A2, and B3 form the third metallic sheath loop.

[0032] In some embodiments, after multiple cable lines share a common grounding point, the equivalent circuit of the grounding loop is as follows: Figure 3 As shown, R g1 and R g2 E represents the grounding resistance at both ends of a multi-circuit cable line. mA1 and Z mA1 Let A and B represent the induced electromotive force and impedance of segment A1 in the m-th cable line, respectively. Figure 3 The meanings of the other parameters shown are similar to those of E. mA1 and Z mA1 The explanation will not be repeated here. Combined with... Figure 3 The induced current conduction component, induced current segment length component, and induced current grounding component can be calculated.

[0033] In S2, the formula for calculating the induced current conduction component of each cable circuit is:

[0034]

[0035] Among them, I mcZ represents the induced current conduction component of the m-th cable line, where n represents the total number of cable lines. s0 E represents the impedance per unit length of the cable's metallic sheath. ms0 E represents the sum of the induced electromotive forces per unit length of the three-phase metallic sheath of the m-th cable line. s0n This represents the sum of the induced electromotive forces per unit length of the three-phase metallic sheaths of all cable lines, and:

[0036] E ms0 =E msA +E msB +E msC ;

[0037]

[0038] Concrete, E msA E msB and E msC These represent the induced electromotive force per unit length of the metal sheath of phases A, B, and C of the m-th cable line, respectively.

[0039] In S2, the formula for calculating the length component of the induced current segment of each cable circuit is as follows:

[0040]

[0041] Among them, I md1 I md2 and I md3 These represent the segment length components of the induced current in the first, second, and third metal sheath loops of the m-th cable line, respectively; t Indicates the total length of the cable line; d m1 d represents the difference in length between the first and second segments of the m-th cable line. m2 This represents the difference in length between the first and third segments of the m-th cable line.

[0042] In S2, the formula for calculating the induced current grounding component of a multi-circuit cable line is:

[0043]

[0044] Among them, I g R represents the induced current to ground component of a multi-circuit cable line. g1 and R g2 These represent the grounding resistance at both ends of a multi-circuit cable line.

[0045] The metallic sheath current of a cable line is the sum of the induced current conduction component, the segment length component, and the grounding component. In S3, the formula for calculating the metallic sheath current of each cable circuit is:

[0046]

[0047] Among them, I ms1 I ms2 and I ms3 These represent the metal sheath currents of the first, second, and third metal sheath circuits in the m-th cable line, respectively.

[0048] In S4, the formula for calculating the current ratio of each cable circuit is as follows:

[0049]

[0050] Where, k m1 k m2 and k m3 I represents the ratio of the metal sheath current to the line load current in the first, second, and third metal sheath circuits of the m-th cable line, respectively. L Indicates the line load current;

[0051] The criterion for determining whether the metallic sheath current of each cable circuit has increased abnormally is: if k m1 k m2 and k m3 If any value in the value exceeds a preset percentage threshold (in this embodiment, the preset percentage threshold is set to 20%), then the metal sheath current of the m-th cable line is determined to have increased abnormally.

[0052] In S4, the analysis of the cause of the abnormal increase is specifically as follows:

[0053] If k m1 Greater than the preset ratio threshold, and I md1 >I mc If the abnormal increase in the metal sheath current of the m-th cable line is determined to be due to the unreasonable division of the short section length of the cable line;

[0054] If k m1 Greater than the preset ratio threshold, and I md1 mc If the abnormal increase in the metal sheath current of the m-th cable line is determined to be due to the cable lines being arranged close together at a common grounding point.

[0055] Based on the above-mentioned method for early warning of sheath current at a shared grounding point for multiple cable lines, the present invention also provides an early warning system for sheath current at a shared grounding point for multiple cable lines.

[0056] A common grounding point sheath current early warning system for multi-circuit cable lines includes: ​

[0057] The unit induced electromotive force acquisition module is used to acquire the induced electromotive force per unit length of the three-phase metal sheath of each cable line when multiple cable lines are interconnected and share a common grounding point.

[0058] The induced current component calculation module is used to calculate the induced current conduction component, induced current segment length component, and induced current grounding component of each cable line based on the induced electromotive force per unit length of the three-phase metal sheath of each cable line.

[0059] The metal sheath current calculation module is used to calculate the metal sheath current of each cable line based on the induced current conduction component and induced current segment length component of each cable line, as well as the induced current grounding component of multiple cable lines.

[0060] The anomaly detection and analysis module calculates the ratio between the metal sheath current and the line load current of each cable circuit. Based on the ratio, it determines whether the metal sheath current of each cable circuit has increased abnormally, and analyzes the cause of the abnormal increase when it does.

[0061] The specific functions of each module in the multi-circuit cable line shared grounding point sheath current early warning system of the present invention are described in the steps of the multi-circuit cable line shared grounding point sheath current early warning method of the present invention, and will not be repeated here.

[0062] This invention provides a method and system for early warning of sheath current at a shared grounding point in multi-circuit cable lines. It considers the impact of interconnections between the grounding systems of multiple cable lines altering the distribution of the metallic sheath current. It can calculate the metallic sheath current even when only the induced electromotive force (EMF) parameters of the cable lines' metallic sheaths are known, and this metallic sheath current is determined by the induced EMF of all the metallic sheaths. Then, it determines whether the metallic sheath current of the corresponding cable line is abnormally increased and analyzes the reasons for the abnormal increase, thus achieving early warning of the sheath current. Furthermore, this invention avoids the complex modeling and simulation process of metallic sheath current, significantly accelerating the efficiency of cable line design and sheath current calculation.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for early warning of sheath current at a shared grounding point in multi-circuit cable lines, characterized in that, include: S1, obtain the induced electromotive force per unit length of the three-phase metal sheath of each cable line when multiple cable lines are interconnected and share a common grounding point; S2, based on the induced electromotive force per unit length of the three-phase metallic sheath of each cable line, calculate the induced current conduction component and induced current segment length component of each cable line, as well as the induced current grounding component of multiple cable lines. S3. Calculate the metal sheath current of each cable line based on the induced current conduction component, induced current segment length component, and induced current grounding component of each cable line. S4. Calculate the ratio between the metal sheath current and the line load current of each cable line. Based on the ratio between the metal sheath current and the line load current of each cable line, determine whether the metal sheath current of each cable line has increased abnormally, and analyze the cause of the abnormal increase when it increases abnormally. In the case of multiple cable lines sharing a common grounding point through cross-interconnection, each cable line is divided into a first segment, a second segment, and a third segment. Specifically, the A-phase lines of each cable line are divided into segments A1, A2, and A3; the B-phase lines of each cable line are divided into segments B1, B2, and B3; and the C-phase lines of each cable line are divided into segments C1, C2, and C3. Each cable line is grounded at both ends through a direct grounding box, and the first and second segments, as well as the second and third segments, are grounded through a cross-interconnection box. When grounded through the cross-interconnection box, segments A1, B2, and C3 are connected to form a first metallic sheath loop; segments B1, C2, and A3 are connected to form a second metallic sheath loop; and segments C1, A2, and B3 are connected to form a third metallic sheath loop. In S2, the formula for calculating the length component of the induced current segment of each cable circuit is as follows: ； in, , and These represent the segment length components of the induced current in the first, second, and third metal sheath circuits of the m-th cable line, respectively. This represents the impedance per unit length of the cable's metallic sheath; Indicates the total length of the cable line; , and These represent the induced electromotive force per unit length of the metal sheath of phases A, B, and C of the m-th cable line, respectively. Let represent the sum of the induced electromotive forces per unit length of the three-phase metallic sheath of the m-th cable line, and ; This represents the difference in length between the first and second segments of the m-th cable line. This represents the difference in length between the first and third segments of the m-th cable line.

2. The method for early warning of sheath current at a shared grounding point in multi-circuit cable lines according to claim 1, characterized in that, Specifically, S1 is: Construct a circuit model for each of the multiple cable lines when they are interconnected and share a common grounding point; Based on the line model of each cable line, the induced electromotive force per unit length of the three-phase metal sheath of each cable line is obtained through simulation or theoretical calculation.

3. The method for early warning of sheath current at a shared grounding point in multi-circuit cable lines according to claim 1, characterized in that, In S2, the formula for calculating the induced current conduction component of each cable circuit is: ； in, Indicates the first The induced current conduction component of the return cable line, Indicates the total number of cable loops. This represents the impedance per unit length of the cable's metallic sheath. This represents the sum of the induced electromotive forces per unit length of the three-phase metallic sheaths of the m-th cable line. This represents the sum of the induced electromotive forces per unit length of the three-phase metallic sheaths of all cable lines, and: ； ； Specifically, , and These represent the induced electromotive force per unit length of the metal sheath of phases A, B, and C of the m-th cable line, respectively.

4. The method for early warning of sheath current at a shared grounding point in multi-circuit cable lines according to claim 1, characterized in that, In S2, the formula for calculating the induced current grounding component of a multi-circuit cable line is: ； in, This represents the induced current grounding component of a multi-circuit cable line. Indicates the total number of cable loops. and These represent the grounding resistances at both ends of a multi-circuit cable line. This represents the impedance per unit length of the cable's metallic sheath. Indicates the total length of the cable line; This represents the sum of the induced electromotive forces per unit length of the three-phase metallic sheaths of all cable lines, and: ； Specifically, Let represent the sum of the induced electromotive forces per unit length of the three-phase metallic sheath of the m-th cable line, and ; , and These represent the induced electromotive force per unit length of the metal sheath of phases A, B, and C of the m-th cable line, respectively.

5. The method for early warning of sheath current at a shared grounding point in multi-circuit cable lines according to claim 1, characterized in that, In S3, the formula for calculating the metallic sheath current of each cable circuit is: ； in, , and Let represent the metal sheath currents of the first, second, and third metal sheath circuits in the m-th cable line, respectively. , and Let represent the segment length components of the induced current in the first, second, and third metal sheath circuits of the m-th cable line, respectively. Indicates the first The induced current conduction component of the return cable line, This indicates the induced current component that flows to ground in a multi-circuit cable line.

6. The method for early warning of sheath current at a shared grounding point in multi-circuit cable lines according to claim 1, characterized in that, In S4, the formula for calculating the current ratio of each cable circuit is as follows: ； in, , and These represent the ratios of the metal sheath current to the line load current in the first, second, and third metal sheath circuits of the m-th cable line, respectively. , and Let represent the metal sheath currents of the first, second, and third metal sheath circuits in the m-th cable line, respectively. Indicates the line load current; The criterion for determining whether the metallic sheath current of each cable circuit has increased abnormally is: if , and If any of the values ​​exceeds a preset proportional threshold, the metal sheath current of the m-th cable line is determined to have increased abnormally.

7. The method for early warning of sheath current at a shared grounding point in multi-circuit cable lines according to claim 6, characterized in that, In S4, the analysis of the cause of the abnormal increase is specifically as follows: like Greater than the preset ratio threshold, and I md1 >I mc If the abnormal increase in the metal sheath current of the m-th cable line is determined to be due to the unreasonable division of the short section length of the cable line; like Greater than the preset ratio threshold, and I md1 mc If the abnormal increase in the metal sheath current of the m-th cable line is determined to be due to the cable lines being arranged close together at a common grounding point.​ 8. A common grounding point sheath current early warning system for multi-circuit cable lines, characterized in that, include: The unit induced electromotive force acquisition module is used to acquire the induced electromotive force per unit length of the three-phase metal sheath of each cable line when multiple cable lines are interconnected and share a common grounding point. The induced current component calculation module is used to calculate the induced current conduction component, induced current segment length component, and induced current grounding component of each cable line based on the induced electromotive force per unit length of the three-phase metal sheath of each cable line. The metal sheath current calculation module is used to calculate the metal sheath current of each cable line based on the induced current conduction component and induced current segment length component of each cable line, as well as the induced current grounding component of multiple cable lines. The anomaly detection and analysis module calculates the ratio between the metal sheath current and the line load current of each cable circuit. Based on the ratio between the metal sheath current and the line load current of each cable circuit, it determines whether the metal sheath current of each cable circuit has increased abnormally, and analyzes the cause of the abnormal increase when it does. In the case of multiple cable lines sharing a common grounding point through cross-interconnection, each cable line is divided into a first segment, a second segment, and a third segment. Specifically, the A-phase lines of each cable line are divided into segments A1, A2, and A3; the B-phase lines of each cable line are divided into segments B1, B2, and B3; and the C-phase lines of each cable line are divided into segments C1, C2, and C3. Each cable line is grounded at both ends through a direct grounding box, and the first and second segments, as well as the second and third segments, are grounded through a cross-interconnection box. When grounded through the cross-interconnection box, segments A1, B2, and C3 are connected to form a first metallic sheath loop; segments B1, C2, and A3 are connected to form a second metallic sheath loop; and segments C1, A2, and B3 are connected to form a third metallic sheath loop. In the induced current component calculation module, the formula for calculating the induced current segment length component of each cable circuit is as follows: ； in, , and These represent the segment length components of the induced current in the first, second, and third metal sheath circuits of the m-th cable line, respectively. This represents the impedance per unit length of the cable's metallic sheath; Indicates the total length of the cable line; , and These represent the induced electromotive force per unit length of the metal sheath of phases A, B, and C of the m-th cable line, respectively. Let represent the sum of the induced electromotive forces per unit length of the three-phase metallic sheath of the m-th cable line, and ; This represents the difference in length between the first and second segments of the m-th cable line. This represents the difference in length between the first and third segments of the m-th cable line.

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