Multi-loop cable line common grounding point sheath current early warning method and system

Abstract

The invention relates to a multi-loop cable line common grounding point sheath current early warning method and system. The method comprises the steps of obtaining unit length induced electromotive force of a three-phase metal sheath; calculating an induced current conduction component, an induced current section length component and an induced current ground component according to the induced electromotive force per unit length of the three-phase metal sheath; according to the induction current conduction component, the induction current segment length component and the induction current ground-in component, calculating a metal sheath current; and calculating the ratio of the metal sheath current to the line load current, judging whether the metal sheath current of each cable line is abnormally increased or not, and analyzing the reason of the abnormal increase when the metal sheath current is abnormally increased. According to the method, the influence of metal sheath current distribution change caused by mutual communication among multiple cable line grounding systems is considered, the metal sheath current is calculated under the condition that only the induced electromotive force parameters of the cable line metal sheath are known, then whether the metal sheath current is abnormally increased or not is judged, and the reason of abnormal increase is analyzed.

Description

Technical Field

[0001] The present invention relates to the field of high-voltage cable line protection, and particularly to a method and system for warning the sheath current of a multi-circuit cable line sharing a grounding point. Background Art

[0002] Benefiting from excellent electrical performance and the characteristic of not occupying ground space, high-voltage cables have become the main channel for urban power transmission. The grounding system is an important part of the high-voltage cable line. Excessive current in the metal sheath will not only cause a local temperature rise, reduce the line transmission efficiency, but also may cause serious consequences such as cable joint explosion and tunnel fire. Therefore, the evaluation and warning of the metal sheath current are very important.

[0003] In recent years, with the increase in high-voltage cable lines, the underground space resources have become increasingly tense. For the consideration of construction cost and unified management, multiple high-voltage cable lines are often laid in a 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 changes the distribution characteristics of the metal sheath current. The existing calculation of the metal sheath current only considers the metal sheath current generated by the three-phase cables of one circuit, without considering the influence of the shared grounding point on the metal sheath current distribution. Therefore, it cannot be applied to the evaluation of the sheath current of multi-circuit co-grounding lines. At present, there is still a lack of effective means for calculating the sheath current in the scenario of multi-circuit cross-connected lines sharing a grounding point, so it is impossible to warn of the large sheath current of this type of line. Summary of the Invention

[0004] The present invention provides a method and system for warning the sheath current of a multi-circuit cable line sharing a grounding point to solve at least one of the above technical problems.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: A method for warning the sheath current of a multi-circuit cable line sharing a grounding point includes:

[0006] S1, obtaining the three-phase metal sheath unit length induced electromotive force of each cable line in the case of multi-circuit cable lines cross-connected and sharing a grounding point;

[0007] S2, calculating the induced current conduction component, the induced current segment length component of each cable line and the induced current into the ground component of the multi-circuit cable lines according to the three-phase metal sheath unit length induced electromotive force of each cable line;

[0008] S3, calculating the metal sheath current of each cable line according to the induced current conduction component, the induced current segment length component of each cable line and the induced current into the ground component of the multi-circuit cable lines;

[0009] S4. Calculate the ratio between the metal sheath current and the line load current of each return cable line, and determine whether the metal sheath current of each return cable line increases abnormally according to the ratio between the metal sheath current and the line load current of each return cable line. When the increase is abnormal, analyze the reason for the abnormal increase.

[0010] Based on the above method for warning the sheath current at the common grounding point of multiple return cable lines, the present invention also provides a warning system for the sheath current at the common grounding point of multiple return cable lines.

[0011] A warning system for the sheath current at the common grounding point of multiple return cable lines includes:

[0012] A unit induced electromotive force acquisition module, which is used to acquire the unit length induced electromotive force of the three-phase metal sheath of each return cable line in the case of cross-connected common grounding points of multiple return cable lines;

[0013] An induced current component calculation module, which is used to calculate the conduction component of the induced current, the segment length component of the induced current of each return cable line, and the in-ground component of the induced current of multiple return cable lines according to the unit length induced electromotive force of the three-phase metal sheath of each return cable line;

[0014] A metal sheath current calculation module, which is used to calculate the metal sheath current of each return cable line according to the conduction component of the induced current, the segment length component of the induced current of each return cable line, and the in-ground component of the induced current of multiple return cable lines;

[0015] An abnormality judgment and analysis module, which calculates the ratio between the metal sheath current and the line load current of each return cable line, determines whether the metal sheath current of each return cable line increases abnormally according to the ratio between the metal sheath current and the line load current of each return cable line, and analyzes the reason for the abnormal increase when the increase is abnormal.

[0016] The beneficial effects of the present invention are as follows: The method and system for warning the sheath current at the common grounding point of multiple return cable lines according to the present invention consider the influence of the mutual connection between the grounding systems of multiple return cable lines on changing the metal sheath current distribution, and can calculate the metal sheath current when only knowing the parameters of the induced electromotive force of the cable line metal sheath, and the metal sheath current is determined by all the induced electromotive forces of the metal sheath; then determine whether the metal sheath current of the corresponding cable line increases abnormally and analyze the reason for the abnormal increase to realize the warning of the sheath current. In addition, the present invention can avoid the complex modeling and simulation process of the metal sheath current, and can significantly improve the design efficiency of the cable line and the calculation efficiency of the sheath current. Description of the Drawings

[0017] Figure 1 It is a flowchart of a method for warning the sheath current at the common grounding point of multiple return cable lines according to the present invention;

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

[0019] Figure 3 It is an equivalent circuit diagram of the metal sheath loop of the cross-connected common ground of multiple cable lines;

[0020] Figure 4 This is a structural block diagram of a sheath current early warning system for a common grounding point of multiple cable lines according to the present invention. DETAILED DESCRIPTION

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

[0022] like Figure 1 As shown, a method for early warning of sheath current at a common grounding point of a multi-circuit cable line 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 cross-connected and share a common grounding point;

[0024] S2, based on the induced electromotive force per unit length of the three-phase metal 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 into the ground component of multiple cable lines;

[0025] S3, calculating 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 and the induced current into the ground component of multiple cable lines;

[0026] S4, calculating the ratio between the metal sheath current of each cable line and the line load current, judging whether the metal sheath current of each cable line increases abnormally based on the ratio between the metal sheath current of each cable line and the line load current, and analyzing the cause of the abnormal increase if abnormal increase occurs.

[0027] The following describes each step in detail.

[0028] The S1 is specifically:

[0029] Construct line models for each cable line when multiple cable lines are cross-connected 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. When designing and planning the line, the grounding system is generally divided into multiple cross-connected grounding main sections based on the length of the line. The grounding system of each main section consists of 9 cable metal sheath sections, 12 intermediate joints, 2 direct grounding boxes at the head and tail, and 2 cross-connected boxes in the middle. The two ends of each cable metal sheath section are connected to the cross-connected box or direct grounding box through connecting wires in the joints. The cable metal sheath is transposed in the cross-connected box, and the cable metal sheath is connected to the ground in the direct grounding box. The three small sections of the metal sheath of each phase cable are reconnected to form three metal sheath loops, such as Figure 2 As shown (ie: the circuit model constructed in S1 is as shown Figure 2 Specifically, Figure 2 In the case of cross-interconnection of multiple cable lines with a common grounding point, each cable line is divided into a first section, a second section and a third section. Specifically, the A-phase line of each cable line is divided into sections A1, A2 and A3, the B-phase line of each cable line is divided into sections B1, B2 and B3, and the C-phase line of each cable line is divided into sections C1, C2 and C3; each cable line is grounded at both ends through a direct grounding box, and the first section and the second section, as well as the second section and the third section are grounded through a cross-interconnection box; when grounded through the cross-interconnection box, sections A1, B2 and C3 are connected to form a first metal sheath loop, sections B1, C2 and A3 are connected to form a second metal sheath loop, and sections C1, A2 and B3 are connected to form a third metal sheath loop.

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

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

[0034]

[0035] Among them, I mcThe conduction component of the induced current of the m-th cable line is denoted as, n represents the total number of cable lines, and Z s0 represents the impedance per unit length of the cable metal sheath, and E ms0 represents the sum of the induced electromotive forces per unit length of the three-phase metal sheaths of the m-th cable line, and E s0n represents the sum of the induced electromotive forces per unit length of the three-phase metal sheaths of all cable lines, and:

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

[0037]

[0038] Specifically, E msA , E msB and E msC respectively represent the induced electromotive forces per unit length of the A-phase, B-phase, and C-phase metal sheaths of the m-th cable line.

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

[0040]

[0041] where, I md1 , I md2 and I md3 respectively represent the segment length components of the induced current of the first metal sheath loop, the second metal sheath loop, and the third metal sheath loop in the m-th cable line; l t represents the total length of the cable line; d m1 represents the difference in the line lengths between the first small segment and the second small segment in the m-th cable line, and d m2 represents the difference in the line lengths between the first small segment and the third small segment in the m-th cable line.

[0042] In the step S2, the formula for calculating the component of the induced current entering the ground of multiple cable lines is:

[0043]

[0044] where, I g represents the component of the induced current entering the ground of multiple cable lines, and R g1 and R g2 respectively represent the grounding resistances at both ends of the multiple cable lines.

[0045] The metal sheath current of the cable line is the sum of the conduction component, segment length component, and component entering the ground of the induced current. In the step S3, the formula for calculating the metal sheath current of each cable line is:

[0046]

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

[0048] In the said S4, the calculation formula for the current ratio of each cable line is:

[0049]

[0050] Among them, k m1 、k m2 and k m3 respectively represent the ratios between the sheath currents of the first metal sheath circuit, the second metal sheath circuit, and the third metal sheath circuit and the line load current in the m-th cable line, and I L represents the line load current;

[0051] The criterion for judging whether the sheath current of each cable line increases abnormally is: if any of k m1 、k m2 and k m3 is greater than the preset ratio threshold (the preset ratio threshold is set to 20% in this embodiment), then it is determined that the sheath current of the m-th cable line increases abnormally.

[0052] In the said S4, when analyzing the reason for the abnormal increase during the abnormal increase, it is specifically:

[0053] If k m1 is greater than the preset ratio threshold, and I md1 >I mc , then it is determined that the reason for the abnormal increase in the sheath current of the m-th cable line is that the division of the small section length of the cable line is unreasonable;

[0054] If k m1 is greater than the preset ratio threshold, and I md1 <I mc , then it is determined that the reason for the abnormal increase in the sheath current of the m-th cable line is that the cable lines are arranged closely to the common grounding point.

[0055] Based on the above method for warning the sheath current of a multi-circuit cable line sharing a common grounding point, the present invention also provides a warning system for the sheath current of a multi-circuit cable line sharing a common grounding point.

[0056] A warning system for the sheath current of a multi-circuit cable line sharing a common grounding point, comprising:

[0057] A unit induced electromotive force acquisition module, which is used to acquire the unit length induced electromotive force of the three-phase metal sheaths of each cable line in the case of a multi-circuit cable line with a cross-connected common grounding point;

[0058] An induced current component calculation module, which is used to calculate the induced current conduction component, the induced current section length component of each cable line and the induced current into the ground component of the multi-circuit cable line according to the unit length induced electromotive force of the three-phase metal sheaths of each cable line;

[0059] A metal sheath current calculation module, which is used to calculate the metal sheath current of each cable line according to the induced current conduction component, the induced current section length component of each cable line and the induced current into the ground component of the multi-circuit cable line;

[0060] An abnormality judgment and analysis module calculates the ratio between the metal sheath current and the line load current of each cable line, judges whether the metal sheath current of each cable line increases abnormally according to the ratio between the metal sheath current and the line load current of each cable line, and analyzes the reason for the abnormal increase when the abnormal increase occurs.

[0061] For the specific functions of each module in the sheath current early warning system for a multi-circuit cable line with a common grounding point of the present invention, refer to each step of the sheath current early warning method for a multi-circuit cable line with a common grounding point of the present invention, which will not be elaborated here.

[0062] The sheath current early warning method and system for a multi-circuit cable line with a common grounding point of the present invention takes into account the influence of the mutual connection between the grounding systems of multi-circuit cable lines on changing the metal sheath current distribution, can calculate the metal sheath current when only knowing the metal sheath induced electromotive force parameters of the cable line, and the metal sheath current is determined by all the metal sheath induced electromotive forces; then it determines whether the metal sheath current of the corresponding cable line increases abnormally and analyzes the reason for the abnormal increase to realize the early warning of the sheath current. In addition, the present invention can avoid the complex modeling and simulation process of the metal sheath current, and can significantly improve the design efficiency of the cable line and the calculation efficiency of the sheath current.

[0063] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for warning the sheath current of a common grounding point of a multi-circuit cable line, characterized in that, Including: S1. Obtain the induced electromotive force per unit length of the three-phase metal sheaths of each cable line under the condition of cross-connected common grounding points of multiple cable lines; S2. Calculate the conduction component of the induced current, the segment length component of the induced current of each cable line, and the in-ground component of the induced current of multiple cable lines according to the induced electromotive force per unit length of the three-phase metal sheaths of each cable line; S3. Calculate the metal sheath current of each cable line according to the conduction component of the induced current, the segment length component of the induced current of each cable line, and the in-ground component of the induced current of multiple cable lines; S4. Calculate the ratio between the metal sheath current and the line load current of each cable line, and judge whether the metal sheath current of each cable line increases abnormally according to the ratio between the metal sheath current and the line load current of each cable line, and analyze the reason for the abnormal increase when it increases abnormally.

2. The method for warning of sheath current at a common grounding point of a multi-circuit cable line according to claim 1, characterized in that, The specific content of S1 is as follows: Construct the line model of each cable line under the condition of cross-connected common grounding points of multiple cable lines; Based on the line models of each cable line, obtain the induced electromotive force per unit length of the three-phase metal sheaths of each cable line through simulation or theoretical calculation methods.

3. The multi-circuit cable line shared grounding point sheath current early warning method according to claim 1, wherein, Under the condition of cross-connected common grounding points of multiple cable lines, each cable line is divided into a first small section, a second small section, and a third small section. Specifically, the A-phase line of each cable line is divided into section A1, section A2, and section A3, the B-phase line of each cable line is divided into section B1, section B2, and section B3, and the C-phase line of each cable line is divided into section C1, section C2, and section C3; each cable line is grounded through a direct grounding box at both ends, and the first small section and the second small section, as well as the second small section and the third small section, are grounded through a cross-connection box; when grounding through the cross-connection box, section A1, section B2, and section C3 are connected to form a first metal sheath loop, section B1, section C2, and section A3 are connected to form a second metal sheath loop, and section C1, section A2, and section B3 are connected to form a third metal sheath loop.

4. The sheath current warning method for the common grounding point of multi - circuit cable lines according to claim 1, characterized in that, In S2, the formula for calculating the conduction component of the induced current of each cable line is: Among them, I mc represents the conduction component of the induced current of the m-th cable line, n represents the total number of cable lines, Z s0 represents the impedance per unit length of the cable metal sheath, E ms0 represents the sum of the induced electromotive forces per unit length of the three-phase metal sheaths of the m-th cable line, E s0n represents the sum of the induced electromotive forces per unit length of the three-phase metal sheaths of all cable lines, and: E ms0 = E msA + E msB + E msC ; Specifically, E msA , E msB and E msC respectively represent the induced electromotive force per unit length of the metal sheaths of the A-phase, B-phase, and C-phase of the m-th cable line.

5. The method for warning of sheath current at the common grounding point of a multi-circuit cable line according to claim 3, characterized in that In S2, the formula for calculating the segment length component of the induced current of each cable line is: Among them, I md1 , I md2 and I md3 respectively represent the induced current segment length components of the first metal sheath circuit, the second metal sheath circuit, and the third metal sheath circuit in the m-th cable line; Z s0 represents the impedance per unit length of the cable metal sheath; l t represents the total length of the cable line; E msA , E msB and E msC respectively represent the induced electromotive force per unit length of the metal sheath of phase A, phase B, and phase C in the m-th cable line; E ms0 represents the sum of the induced electromotive forces per unit length of the metal sheaths of the three phases in the m-th cable line, and E ms0 = E msA + E msB + E msC ; d m1 represents the line length difference between the first small section and the second small section in the m-th cable line, and d m2 represents the line length difference between the first small section and the third small section in the m-th cable line.

6. The sheath current early warning method for the common grounding point of multi-circuit cable lines according to claim 1, characterized in that, In S2, the formula for calculating the in-ground component of the induced current of multiple cable lines is: Among them, I g represents the in-ground component of the induced current of the multi-circuit cable line, n represents the total number of circuits of the cable line, R g1 and R g2 respectively represent the grounding resistances at both ends of the multi-circuit cable line, Z s0 represents the impedance per unit length of the cable metal sheath, l t represents the total length of the cable line; E s0n represents the sum of the induced electromotive forces per unit length of the three-phase metal sheaths of all cable lines, and: Specifically, E ms0 represents the sum of the induced electromotive forces per unit length of the three-phase metal sheaths of the m-th cable line, and E ms0 = E msA + E msB + E msC ; E msA , E msB and E msC respectively represent the induced electromotive forces per unit length of the metal sheaths of phase A, phase B, and phase C of the m-th cable line.

7. The sheath current warning method for a multi - circuit cable line sharing a grounding point according to claim 3, wherein In S3, the formula for calculating the metal sheath current of each cable line is: Among them, I ms1 , I ms2 and I ms3 respectively represent the sheath currents of the first metal sheath loop, the second metal sheath loop, and the third metal sheath loop in the m-th cable line. I md1 , I md2 and I md3 respectively represent the component of the induction current segment length of the first metal sheath loop, the second metal sheath loop, and the third metal sheath loop in the m-th cable line. I mc represents the conduction component of the induction current of the m-th cable line. I g represents the component of the induction current entering the ground of the multi-circuit cable line.

8. The sheath current warning method for the common grounding point of multi - circuit cable lines according to claim 3, characterized in that, In S4, the calculation formula for the current ratio of each cable line is: where k m1 , k m2 and k m3 respectively represent the ratios between the sheath currents of the first metal sheath circuit, the second metal sheath circuit, and the third metal sheath circuit and the line load current in the m-th cable line, I ms1 , I ms2 and I ms3 respectively represent the sheath currents of the first metal sheath circuit, the second metal sheath circuit, and the third metal sheath circuit in the m-th cable line, and I L represents the line load current; The criterion for judging whether the current of the metal sheath of each return cable line increases abnormally is: if any of k m1 , k m2 and k m3 is greater than the preset proportional threshold, it is determined that the current of the metal sheath of the m-th return cable line increases abnormally.

9. The sheath current warning method for the common grounding point of a multi-circuit cable line according to claim 8, characterized in that, In S4, the specific content of analyzing the reason for the abnormal increase when it increases abnormally is: If k m1 is greater than the preset ratio threshold, and I md1 > I mc , it is determined that the reason for the abnormal increase in the metal sheath current of the m-th cable line is that the small section length division of the cable line is unreasonable; If k m1 is greater than the preset proportional threshold value, and I md1 < I mc , it is determined that the reason for the abnormal increase in the metal sheath current of the m-th cable line is that the cable lines are arranged closely to the common grounding point.

10. A sheath current warning system for a multi-circuit cable line sharing a grounding point, characterized in that, Including: A unit induced electromotive force acquisition module, which is used to obtain the induced electromotive force per unit length of the three-phase metal sheaths of each cable line under the condition of cross-connected common grounding points of multiple cable lines; An induced current component calculation module, which is used to calculate the conduction component of the induced current, the segment length component of the induced current of each cable line, and the in-ground component of the induced current of multiple cable lines according to the induced electromotive force per unit length of the three-phase metal sheaths of each cable line; A metal sheath current calculation module, which is used to calculate the metal sheath current of each cable line according to the conduction component of the induced current, the segment length component of the induced current of each cable line, and the component of the induced current entering the ground of multiple cable lines; An abnormality judgment and analysis module calculates the ratio between the metal sheath current and the line load current of each cable line, judges whether the metal sheath current of each cable line abnormally increases according to the ratio between the metal sheath current and the line load current of each cable line, and analyzes the reason for the abnormal increase when the abnormal increase occurs.

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