Method and system for positioning poor connection defect of power transmission cable sheath grounding system

Abstract

The invention discloses a method and a system for positioning poor connection defects of a power transmission cable sheath grounding system. The method comprises the following steps of opening a total grounding piece and a grounding box connecting piece of a first terminal; opening the total grounding of the second terminal; obtaining a first loop resistance, a second loop resistance and a third loop resistance, and calculating to obtain an electric loop resistance; judging whether the single loop has defects or not based on the resistance value of the single loop; checking the connection condition in the second terminal grounding box; obtaining a fourth loop resistance and a fifth loop resistance; based on the fourth loop resistance value and the fifth loop resistance value, determining a defective single loop resistance abnormal section; judging the abnormal section; acquiring the resistance of an eighth loop and the resistance of a ninth loop, and determining an abnormal position based on the resistance values of the eighth loop and the ninth loop; and checking the abnormal position. According to the method, accurate judgment of the abnormal position is realized through a process and standardization monitoring method, and missed judgment and misjudgment of defects are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of cable defect detection, and specifically to a method and system for locating the defect of poor connection of the grounding system of a power transmission cable sheath. Background Technique

[0002] In recent years, due to advantages such as small floor area and high operation stability, high-voltage power transmission cables have become an important framework in urban power transmission networks. The intermediate joint is a weak link in cable operation, and grounding system components such as joint sealing lead and grounding box are the keys to ensuring the normal operation of the intermediate joint. Grounding system defects such as poor sealing lead, ineffective crimping of grounding wires, and moisture ingress into the grounding box have caused more than 60% of the intermediate joint failure incidents, which are the main hidden dangers threatening the safe operation of the power transmission cable network. Timely discovering and eliminating the defects of the high-voltage cable grounding system through online or offline methods, and avoiding power outages due to line faults, are of great significance for ensuring the safe and reliable operation of high-voltage cables and improving the pertinence and economy of maintenance work.

[0003] Partial discharge detection, temperature detection, and grounding loop current detection are important technical means for the operation and maintenance of power transmission cables. Through partial discharge detection, insulation aging defects of cables and accessories can be discovered. However, there are problems of large electromagnetic interference and poor application effect in dense cable channels; the operation unit mostly uses infrared temperature measurement to monitor the cable temperature, which has advantages such as non-contact, real-time, and non-destructive. Through infrared temperature measurement, defects such as poor sealing lead of cable accessories and oil leakage at cable terminals can be effectively discovered. However, defects such as poor connection of cable accessories may cause an open circuit in the grounding electrical circuit of the sheath without heating phenomenon, and infrared temperature measurement may miss defects; the live detection of grounding loop current uses an ammeter to detect the current on the grounding wires of cable joints and terminals. The grounding loop current can reflect the defects of the metal sheath grounding system and the main insulation defects, but it is impossible to accurately locate the defect position. In the offline detection method, only the contact resistance of the metal connecting piece in the grounding box is detected, and it is impossible to detect the metal connection parts of the grounding system of cables and accessories, with great limitations. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies existing in the prior art, and provides a method and system for locating the defect of poor connection of the grounding system of a power transmission cable sheath. The position of poor connection of the grounding system of the sheath is subdivided into the grounding box, cable joint, terminal sealing lead position, and inside the cable accessory. Through the design of a process-based and standardized detection method, accurate judgment of abnormal positions is achieved, and missed judgment and misjudgment of defects are avoided.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] In the first aspect, the present application proposes a method for locating the defect of poor connection of the grounding system of a power transmission cable sheath, including the following steps:

[0007] Step 1: Open the main grounding and grounding box connection piece of the first terminal, where the first terminal is the terminal at the head of the cross-bonding unit;

[0008] Step 2: Open the main grounding of the second terminal, where the second terminal is the terminal at the end of the cross-bonding unit;

[0009] Step 3: Obtain the first loop resistance, the second loop resistance, and the third loop resistance at the first terminal, and calculate the single-loop resistance; the first loop resistance is the sum of the resistances of the A1-B2-C3 loop and the B1-C2-A3 loop, the second loop resistance is the sum of the resistances of the B1-C2-A3 loop and the C1-A2-B3 loop, and the third loop resistance is the sum of the resistances of the A1-B2-C3 loop and the C1-A2-B3 loop; the single-loop resistance includes the A1-B2-C3 loop resistance, the B1-C2-A3 loop resistance, and the C1-A2-B3 phase loop resistance;

[0010] Step 4: Judge whether there is a defect in the single loop based on the magnitude of the single-loop resistance value. If there is a defect, proceed to the next detection, and define the single loop with a defect as the defective single loop. If there is no defect, end the detection;

[0011] Step 5: Check the connection inside the grounding box of the second terminal. If the connection state is good, proceed to the next detection; if there is a poor connection, restore the grounding box connection or replace the grounding box, re-obtain the first loop resistance, the second loop resistance, and the third loop resistance, calculate the single-loop resistance and perform defect judgment. If there is a defect, proceed to the next detection. If there is no defect, end the detection;

[0012] Step 6: Open the connection piece inside the first joint grounding box, and obtain the fourth loop resistance and the fifth loop resistance. The fourth loop resistance is the loop resistance measured towards the first terminal at the first joint after the defective single loop and any adjacent non-defective single loop are phase-shorted at the first terminal. The fifth loop resistance is the loop resistance measured towards the second terminal at the first joint after the defective single loop and any adjacent non-defective single loop are phase-shorted at the second terminal; the fourth loop resistance and the fifth loop resistance are measured based on the same defective single loop;

[0013] Step 7: Determine the abnormal section of the defective single-loop resistance based on the magnitudes of the fourth loop resistance value and the fifth loop resistance value; the abnormal section includes the first joint grounding box, the first section, and the middle and rear sections; the first section is the section from the first terminal to the first joint grounding box, and the middle and rear sections are the sections from the first joint grounding box to the second terminal;

[0014] Step 8: judge the abnormal section and perform the next step of detection; if the first joint grounding box is abnormal, process the first joint grounding box; if the first section is abnormal, perform the next step of detection; if the middle and rear sections are abnormal, open the connecting piece in the second joint grounding box, obtain the sixth loop resistance and the seventh loop resistance, and based on the sixth loop resistance value and the seventh loop resistance value, confirm that the abnormal section is located at the second joint grounding box, the middle section or the end section, if it is located at the second joint grounding box, process the grounding box, if the abnormal section is the middle section or the end section, perform the next step of detection; the sixth loop resistance is the loop resistance measured at the second joint toward the first terminal after the defective single loop and any adjacent non-defective single loop are short-circuited at the first joint, and the seventh loop resistance is the loop resistance measured at the second joint toward the second terminal after the defective single loop and any adjacent non-defective single loop are short-circuited at the second terminal; the middle section is the section from the first joint grounding box to the second joint grounding box, and the end is the section from the second joint grounding box to the second terminal.

[0015] Step 9: If the abnormal section is the beginning or the end, peel off the outer sheath of the cable outside the lead sealing position of the joint in the abnormal section to expose the metal sheath; if the abnormal section is the middle section, peel off the outer sheath of the cable outside the lead sealing position near the second joint to expose the metal sheath; obtain the eighth loop resistance and the ninth loop resistance, and determine the abnormal position based on the size of the eighth loop and the ninth loop resistance, the eighth loop resistance is the resistance between the metal sheath and the same-phase grounding wire in the adjacent grounding box, and the ninth loop is the resistance between the metal sheath and any non-same-phase grounding wire in the adjacent grounding box.

[0016] Step 10: Check the abnormal location.

[0017] Furthermore, the step 3 is specifically as follows:

[0018] Obtain the first loop resistance, the second loop resistance and the third loop resistance, where the first loop resistance is recorded as L, the second loop resistance is recorded as M, and the third loop resistance is recorded as N, and establish calculation formulas for the first loop resistance L, the second loop resistance M and the third loop resistance N:

[0019] Z A1-B2-C3 +Z B1-C2-A3 =L

[0020] Z B1-C2-A3 +Z C1-A2-B3 =M

[0021] Z C1-A2-B3 +Z A1-B2-C3 =N

[0022] Combining the above three equations, we can obtain:

[0023] ZA1-B2-C3 =(N + L - M) / 2

[0024] Z B1-C2-A3 =(L + M - N) / 2

[0025] Z C1-A2-B3 =(M + N - L) / 2

[0026] Wherein, Z A1-B2-C3 represents the resistance of the A - B - C loop, Z B1-C2-A3 represents the resistance of the B - C - A loop, Z C1-A2-B3 represents the resistance of the C - A - B loop.

[0027] Further, step 4 is specifically as follows:

[0028] Based on the magnitude of the single - loop resistance value, defect judgment is performed. If the magnitudes of the three - phase loop resistance values are all less than or equal to the first resistance threshold, it is determined that there is no defect in the cross - bonding unit, and the detection ends; if the magnitude of the single - phase loop resistance value of any one item is greater than the first resistance threshold, it is determined that there is a defect in this phase, and the next step of detection is carried out; the first resistance threshold is configured as the total resistance value of the three - section lines of a single loop of the cross - bonding unit.

[0029] Further, step 7 is specifically as follows:

[0030] If the fourth loop resistance value is less than or equal to the second resistance threshold and the fifth loop resistance value is less than or equal to twice the second resistance threshold, the abnormal section is located at the first joint grounding box; if the fourth loop resistance value is greater than the second resistance threshold, the abnormal section is located at the first section; if the fifth loop resistance value is greater than twice the second resistance threshold, the abnormal section is located at the middle - rear section; the second resistance threshold is configured as the total resistance value of the two - section lines of a single loop of the cross - bonding unit.

[0031] Further, in step 8, based on the sixth loop resistance value and the seventh loop resistance value, the position of the abnormal section is confirmed, specifically as follows:

[0032] If both the sixth loop resistance value and the seventh loop resistance value are less than or equal to the second resistance threshold, the abnormal section is located at the second joint grounding box; if the sixth loop resistance value is greater than the second resistance threshold, the abnormal section is located at the middle section; if the seventh loop resistance value is greater than the second resistance threshold, the abnormal section is located at the last section.

[0033] Further, in step 9, based on the eighth loop resistance and the ninth loop resistance value, the abnormal position is determined, specifically as follows:

[0034] When the abnormal section is located in the first section, if the resistance value of the ninth loop is greater than the second resistance threshold, the lead sealing of the first terminal of the abnormal section is poor; otherwise, the lead sealing of the first joint facing the first terminal side is poor or the internal connection of the first joint is poor;

[0035] When the abnormal section is located in the middle section, if the resistance value of the ninth loop is greater than the second resistance threshold, the lead sealing of the first joint facing the second terminal side is poor or the internal connection of the first joint is poor; otherwise, the lead sealing of the second joint facing the first terminal side is poor or the internal connection of the second joint is poor;

[0036] When the abnormal section is located in the last section, if the resistance value of the ninth loop is greater than the second resistance threshold, the lead sealing of the second terminal of the abnormal section is poor; otherwise, the lead sealing of the second joint facing the second terminal side is poor or the internal connection of the second joint is poor.

[0037] In a second aspect, the present application also proposes a positioning system for defects in the connection of a power transmission cable sheath grounding system, which is applied to a method for positioning defects in the connection of a power transmission cable sheath grounding system as described above, and includes a loop resistance acquisition module, a calculation module, and a judgment module; wherein,

[0038] The loop resistance acquisition module is configured to acquire the first to ninth loop resistances;

[0039] The calculation module is configured to calculate the A-B-C loop resistance, the B-C-A loop resistance, and the C-A-B loop resistance based on the first loop resistance, the second loop resistance, and the third loop resistance;

[0040] The judgment module is configured to judge whether there is a defect in the single loop based on the A-B-C loop resistance, the B-C-A loop resistance, and the C-A-B loop resistance; judge whether the defect is located in the first joint grounding box, the first section, or the middle and rear sections based on the fourth loop resistance and the fifth loop resistance; judge whether the defect is located in the second joint grounding box, the middle section, or the last section based on the sixth loop resistance and the seventh loop resistance; judge whether the defect is located at the first terminal, the first joint, the second joint, or the second terminal based on the eighth loop resistance and the ninth loop resistance.

[0041] Further, the loop resistance acquisition module includes a first acquisition module, a second acquisition module, a third acquisition module, and a fourth acquisition module. The first acquisition module is configured to acquire the first loop resistance, the second loop resistance, and the third loop resistance; the second acquisition module is configured to acquire the fourth loop resistance and the fifth loop resistance; the third acquisition module is configured to acquire the sixth loop resistance and the seventh loop resistance; the fourth acquisition module is configured to acquire the eighth loop resistance and the ninth loop resistance.

[0042] In summary, compared with the prior art, the present invention has the following beneficial effects: The present invention subdivides the positions of the defects in the sheath grounding system connection into grounding boxes, cable joints, terminal lead sealing positions, and the interiors of cable accessories. Through the design of a process-based and standardized detection method and reasonable threshold setting, accurate judgment of abnormal positions is achieved, avoiding missed and misjudged defects. The present invention can be carried out during the regular power outage and pre-test of the line. By regularly checking, defects in the sheath grounding system connection of the cable line are discovered, and an integrated maintenance plan is implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not constitute a limitation on the embodiments of the present invention. In the drawings:

[0044] Figure 1 is a flowchart of an embodiment of the present invention;

[0045] Figure 2 is a schematic diagram of the sheath grounding in the A-B-C cross-bonding method of an embodiment of the present invention;

[0046] Figure 3 is a schematic diagram of the DC resistance test at the first joint when the loop resistance in the A1-B2-C3 circuit of an embodiment of the present invention is abnormal;

[0047] Figure 4 is a schematic diagram of the DC resistance test at the second joint when the B2-C3 section of an embodiment of the present invention is abnormal;

[0048] Figure 5 is a schematic diagram of the test at the lead seal of the first joint when the A1 section of an embodiment of the present invention is abnormal;

[0049] Figure 6 is a schematic diagram of the sheath grounding of two sets of cross-bonding units in an embodiment of the present invention;

[0050] Figure 7 is a schematic diagram of the sheath connection in single-end grounding and double-end grounding in an embodiment of the present invention;

[0051] Figure 8 is a schematic diagram of the DC resistance test at the first terminal when the loop resistance in single-end grounding and double-end grounding of an embodiment of the present invention is abnormal. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the embodiments and the drawings. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and do not limit the present invention.

[0053] Embodiment 1:

[0054] As Figure 1As shown in the figure, a method for locating the defect of poor connection in the grounding system of a transmission cable sheath includes the following steps:

[0055] Step 1: Open the main grounding and the grounding box connection piece of the first terminal, where the first terminal is the terminal at the head of the cross-bonding unit;

[0056] Step 2: Open the main grounding of the second terminal, where the second terminal is the terminal at the end of the cross-bonding unit;

[0057] Step 3: Obtain the first loop resistance, the second loop resistance, and the third loop resistance at the first terminal, and calculate the single-loop resistance; the first loop resistance is the sum of the resistances of the A1-B2-C3 loop and the B1-C2-A3 loop, the second loop resistance is the sum of the resistances of the B1-C2-A3 loop and the C1-A2-B3 loop, and the third loop resistance is the sum of the resistances of the A1-B2-C3 loop and the C1-A2-B3 loop; the single-loop resistance includes the A1-B2-C3 loop resistance, the B1-C2-A3 loop resistance, and the C1-A2-B3 phase loop resistance;

[0058] Step 4: Judge whether there is a defect in the single loop based on the magnitude of the single-loop resistance value. If there is a defect, proceed to the next step of detection, and define the single loop with a defect as the defective single loop. If there is no defect, end the detection;

[0059] Step 5: Check the connection situation inside the grounding box of the second terminal. If the connection state is good, proceed to the next step of detection; if there is a poor connection, restore the connection of the grounding box or replace the grounding box, re-obtain the first loop resistance, the second loop resistance, and the third loop resistance, calculate the single-loop resistance and perform defect judgment. If there is a defect, proceed to the next step of detection. If there is no defect, end the detection;

[0060] Step 6: Open the connection piece inside the first joint grounding box, and obtain the fourth loop resistance and the fifth loop resistance. The fourth loop resistance is the loop resistance measured towards the first terminal at the first joint after the defective single loop is short-circuited phase by phase with any non-defective single loop adjacent to it at the first terminal. The fifth loop resistance is the loop resistance measured towards the second terminal at the first joint after the defective single loop is short-circuited phase by phase with any non-defective single loop adjacent to it at the second terminal; the fourth loop resistance and the fifth loop resistance are measured based on the same defective single loop;

[0061] Step 7: Determine the abnormal section of the defective single-loop resistance based on the magnitudes of the fourth loop resistance value and the fifth loop resistance value; the abnormal section includes the first joint grounding box, the first section, and the middle and rear sections; the first section is the section from the first terminal to the first joint grounding box, and the middle and rear sections are the sections from the first joint grounding box to the second terminal;

[0062] Step 8: judge the abnormal section and perform the next step of detection; if the first joint grounding box is abnormal, process the first joint grounding box; if the first section is abnormal, perform the next step of detection; if the middle and rear sections are abnormal, open the connecting piece in the second joint grounding box, obtain the sixth loop resistance and the seventh loop resistance, and based on the sixth loop resistance value and the seventh loop resistance value, confirm that the abnormal section is located at the second joint grounding box, the middle section or the end section, if it is located at the second joint grounding box, process the grounding box, if the abnormal section is the middle section or the end section, perform the next step of detection; the sixth loop resistance is the loop resistance measured at the second joint toward the first terminal after the defective single loop and any adjacent non-defective single loop are short-circuited at the first joint, and the seventh loop resistance is the loop resistance measured at the second joint toward the second terminal after the defective single loop and any adjacent non-defective single loop are short-circuited at the second terminal; the middle section is the section from the first joint grounding box to the second joint grounding box, and the end is the section from the second joint grounding box to the second terminal.

[0063] Step 9: If the abnormal section is the head end or the end, peel off the outer sheath of the cable outside the lead sealing position of the joint in the abnormal section to expose the metal sheath; if the abnormal section is the middle section, peel off the outer sheath of the cable outside the lead sealing position near the second joint to expose the metal sheath; obtain the eighth loop resistance and the ninth loop resistance, and determine the abnormal position based on the magnitude of the eighth loop and the ninth loop resistance, the eighth loop resistance is the resistance between the metal sheath and the same-phase grounding wire in the adjacent grounding box, and the ninth loop is the resistance between the metal sheath and any non-same-phase grounding wire in the adjacent grounding box;

[0064] Step 10: Check the abnormal location.

[0065] Furthermore, the step 3 is specifically as follows:

[0066] Obtain the first loop resistance, the second loop resistance and the third loop resistance, where the first loop resistance is recorded as L, the second loop resistance is recorded as M, and the third loop resistance is recorded as N, and establish calculation formulas for the first loop resistance L, the second loop resistance M and the third loop resistance N:

[0067] Z A1-B2-C3 +Z B1-C2-A3 =L

[0068] Z B1-C2-A3 +Z C1-A2-B3 =M

[0069] Z C1-A2-B3 +Z A1-B2-C3 =N

[0070] Combining the above three equations, we can obtain:

[0071] Z A1-B2-C3 =(N + L - M) / 2

[0072] Z B1-C2-A3 =(L + M - N) / 2

[0073] Z C1-A2-B3 =(M + N - L) / 2

[0074] In the formula, Z A1-B2-C3 represents the resistance of the A1 - B2 - C3 loop, Z B1-C2-A3 represents the resistance of the B1 - C2 - A3 loop, Z C1-A2-B3 represents the resistance of the C1 - A2 - B3 loop.

[0075] Furthermore, the specific step 4 is as follows:

[0076] Based on the magnitude of the single - loop resistance value, defect judgment is performed. If the magnitudes of the three - phase loop resistance values are all less than or equal to the first resistance threshold, it is determined that there is no defect in the cross - bonding unit, and the detection ends; if the magnitude of the single - phase loop resistance value of any one item is greater than the first resistance threshold, it is determined that there is a defect in that phase, and the next step of detection is carried out; the first resistance threshold is configured as the total resistance value of the three - section lines of a single loop of the cross - bonding unit.

[0077] Furthermore, the specific step 7 is as follows:

[0078] If the fourth - loop resistance value is less than or equal to the second resistance threshold and the fifth - loop resistance value is less than or equal to twice the second resistance threshold, the abnormal section is located at the first joint grounding box; if the fourth - loop resistance value is greater than the second resistance threshold, the abnormal section is located at the first section; if the fifth - loop resistance value is greater than twice the second resistance threshold, the abnormal section is located at the middle - rear section; the second resistance threshold is configured as the total resistance value of the two - section lines of a single loop of the cross - bonding unit.

[0079] Furthermore, in step 8, based on the sixth - loop resistance value and the seventh - loop resistance value, the position of the abnormal section is confirmed, specifically:

[0080] If both the sixth - loop resistance value and the seventh - loop resistance value are less than or equal to the second resistance threshold, the abnormal section is located at the second joint grounding box; if the sixth - loop resistance value is greater than the second resistance threshold, the abnormal section is located at the middle section; if the seventh - loop resistance value is greater than the second resistance threshold, the abnormal section is located at the last section.

[0081] Furthermore, in step 9, based on the eighth - loop resistance and the ninth - loop resistance value, the abnormal position is determined, specifically:

[0082] When the abnormal section is located at the first section, if the resistance value of the ninth circuit is greater than the second resistance threshold, the lead seal of the first terminal of the abnormal section is defective; otherwise, the lead seal of the first joint facing the first terminal side of the abnormal section is defective or the internal connection of the first joint is defective;

[0083] When the abnormal section is located in the middle section, if the resistance value of the ninth circuit is greater than the second resistance threshold, the lead seal of the first joint facing the second terminal side of the abnormal section is defective or the internal connection of the first joint is defective; otherwise, the lead seal of the second joint facing the first terminal side of the abnormal section is defective or the internal connection of the second joint is defective;

[0084] When the abnormal section is located at the last section, if the resistance value of the ninth circuit is greater than the second resistance threshold, the lead seal of the second terminal of the abnormal section is defective; otherwise, the lead seal of the second joint facing the second terminal side of the abnormal section is defective or the internal connection of the second joint is defective.

[0085] More specifically, taking the A-B-C cross-bonding method as an example, as Figure 2 shown in the schematic diagram of the sheath grounding of the A-B-C cross-bonding method, open the main grounding and the grounding box connecting piece of the first terminal, open the main grounding of the second terminal, obtain the resistance of the first circuit, the second circuit and the third circuit at the first terminal, that is, the AB phase circuit resistance, the BC phase circuit resistance and the CA phase circuit resistance, which are respectively denoted as L, M, N, and calculate the A-B-C circuit resistance Z A1-B2-C3 , the B-C-A circuit resistance Z B1-C2-A3 , the C-A-B circuit resistance Z C1-A2-B3 . If Z A1-B2-C3 ≤R 1 , Z B1-C2-A3 ≤R 1 , Z C1-A2-B3 ≤R 1 , where R 1 represents the first resistance threshold, then it is determined that there is no defect in the cross-bonding unit. If any value in Z A1-B2-C3 , Z B1-C2-A3 , Z C1-A2-B3 is greater than the first resistance threshold R 1 , then open the grounding box of the second terminal, check the connection inside the grounding box of the second terminal. If the connection is good, proceed to the next test; if the connection is bad, restore the grounding box connection according to the actual situation or replace the grounding box and then re-execute the above steps. If the test result is normal, end the test. If there is still an abnormality, proceed to the next test.

[0086] Taking the abnormal resistance of the A1-B2-C3 circuit as an example, that is, Z A1-B2-C3 >R 1 , as Figure 3As shown, open the connecting piece inside the first joint grounding box, short-circuit section A1 and section B1 at the first terminal, short-circuit section B3 and section C3 at the second terminal, and obtain the fourth loop resistance and the fifth loop resistance from the first joint to both left and right sides, denoted as Z a1-b1 and Z a2-b2 . If both Z a1-b1 and Z a2-b2 are normal, that is, Z a1-b1 ≤R 2 , and Z a2-b2 ≤2R 2 , where R 2 represents the second resistance threshold, then determine that the abnormal position is the first joint grounding box; if Z a1-b1 is abnormal, that is, Z a1-b1 >R 2 , and Z a2-b2 ≤2R 2 , then determine that the abnormal position is at the first section of the A1 - B2 - C3 loop, that is, section A1. If Z a2-b2 is abnormal, that is, Z a1-b1 ≤R 2 , and Z a2-b2 >2R 2 , then determine that the abnormal position is in the middle and later sections of the A1 - B2 - C3 loop, that is, section B2 - C3.

[0087] When it is confirmed that the abnormal position is in section B2 - C3, to further determine whether the abnormal position is in the middle section B2 or the last section C3, as Figure 4 shown, at the second joint grounding box, open the connecting piece inside the second joint grounding box, short-circuit section B2 and section C2 at the first joint, short-circuit section B3 and section C3 at the second terminal, and obtain the sixth loop resistance and the seventh loop resistance, denoted as Z b3-c3 and Z b4-c4 . If both Z b3-c3 and Z b4-c4 are normal, that is, Z b3-c3 ≤R 2 , and Z b4-c4 ≤R 2 , then determine that the abnormal position is at the second joint grounding box. If Z b3-a3 is abnormal, that is, Z b3-c3 >R 2 , and Z b4-c4 ≤R 2 , then determine that the abnormal position is in section B2. If Z b4-c4 is abnormal, that is, Z b3-c3 ≤R 2 , and Z b4-c4 >R 2 , then determine that the abnormal position is in section C3.

[0088] When it is determined that the abnormal position is in section A1, the outer sheath of the cable is peeled off outside the lead-sealing position of the joint in the abnormal section to expose the metal sheath, and phase A is short-circuited with the non-abnormal phase at the first terminal; when it is determined that the abnormal position is in section B2, the outer sheath of the cable is peeled off outside the lead-sealing position of the second joint to expose the metal sheath, and phase B is short-circuited with the non-abnormal phase at the first joint; when it is determined that the abnormal position is in section C3, the outer sheath of the cable is peeled off outside the lead-sealing position of the joint in the abnormal section to expose the metal sheath, and phase C is short-circuited with the non-abnormal phase at the second terminal; the eighth loop resistance and the ninth loop resistance are obtained, and the abnormal position is determined based on the magnitudes of the eighth loop and ninth loop resistance values. The eighth loop resistance is the resistance between the metal sheath and the ground wire of the same phase in the adjacent grounding box, and the ninth loop is the resistance between the metal sheath and the ground wire of a different phase in the adjacent grounding box.

[0089] Taking the abnormal resistance in section A1 as an example, as Figure 5 shown, phase A1 and phase B1 are short-circuited at the first terminal, the eighth loop resistance and the ninth loop resistance are obtained, and the ninth loop resistance is denoted as Z b1-x , and the eighth loop resistance is denoted as Z a1-x . If Z b1-x is abnormal, it is confirmed that the abnormal position is the poor lead-sealing of phase A at the first terminal; if Z a1-x is abnormal, it is confirmed that the abnormal position is the poor lead-sealing on the side of phase A of the first joint facing the first terminal or the poor internal connection of the first joint. Open the lead-sealing place for inspection. If there is no abnormality, it is confirmed that the abnormal position is inside the first joint, and the inside of the first joint is inspected.

[0090] It should be noted that in the embodiments of the present application, the names of the reference numerals in each drawing are as follows: 1, the first terminal; 2, the first joint; 3, the second joint; 4, the second terminal; 5, the third joint; 6, the fourth joint; 7, the fifth joint.

[0091] It should be noted that the resistance value of the 220 kV cable sheath resistance is 0.0267 - 0.0386 Ω / km, and the resistance value of the 110 kV cable sheath resistance is 0.0377 - 0.065 Ω / km. In actual applications, the length of a section of cross-bonding unit line is in the range of 1 km to 2 km. Considering the contact resistance and measurement error, for the 220 kV line, the first resistance threshold is set to 0.1 Ω, and the second resistance threshold is set to 0.067 Ω; for the 110 kV line, the first resistance threshold is set to 0.15 Ω, and the second resistance threshold is set to 0.1 Ω.

[0092] On this basis, the embodiment of the present application further proposes a positioning system for the defect of poor connection of the transmission cable sheath grounding system, which is applied to the positioning method for the defect of poor connection of the transmission cable sheath grounding system as described above, and includes a loop resistance acquisition module, a calculation module and a judgment module; among them,

[0093] The loop resistance acquisition module is configured to acquire the first to ninth loop resistances;

[0094] The calculation module is configured to calculate the A-B-C loop resistance, the B-C-A loop resistance and the C-A-B loop resistance based on the first loop resistance, the second loop resistance and the third loop resistance;

[0095] The judgment module is configured to judge whether there is a defect in the single loop based on the A-B-C loop resistance, the B-C-A loop resistance and the C-A-B loop resistance; judge whether the defect is located in the first joint grounding box, the first section or the middle and rear sections based on the fourth loop resistance and the fifth loop resistance; judge whether the defect is located in the second joint grounding box, the middle section or the end section based on the sixth loop resistance and the seventh loop resistance; judge whether the defect is located at the first terminal, the first joint, the second joint or the second terminal based on the eighth loop resistance and the ninth loop resistance.

[0096] Further, the loop resistance acquisition module includes a first acquisition module, a second acquisition module, a third acquisition module and a fourth acquisition module. The first acquisition module is configured to acquire the first loop resistance, the second loop resistance and the third loop resistance; the second acquisition module is configured to acquire the fourth loop resistance and the fifth loop resistance; the third acquisition module is configured to acquire the sixth loop resistance and the seventh loop resistance; the fourth acquisition module is configured to acquire the eighth loop resistance and the ninth loop resistance.

[0097] Embodiment 2:

[0098] This embodiment further limits the above embodiment to realize the positioning of the defect of poor connection of the sheath grounding system of multiple sets of cross-bonding units.

[0099] Specifically, taking two sets of cross-bonding units as an example, the sheath connection diagram is as Figure 6 shown, including two terminals, the first terminal and the second terminal, and five sets of joints, the first joint, the second joint, the third joint, the fourth joint and the fifth joint. Among them, the third joint is the common grounding end. The first terminal, the first joint, the second joint and the third joint form the first cross-bonding unit, and the third joint, the fourth joint, the fifth joint and the second terminal form the second cross-bonding unit.

[0100] Before detection, perform loop current analysis. If there is no obvious abnormality in the loop current of the first unit, open the connecting strip of the second joint grounding box to make the second cross-bonding unit an independent unit, and use the method described in Embodiment 1 to locate the defect for this unit; if there is no obvious abnormality in the second cross-bonding unit, open the connecting strip of the fourth joint grounding box to make the first cross-bonding unit an independent unit, and use the method described in Embodiment 1 to locate the defect for this unit.

[0101] Embodiment 3:

[0102] In addition to being able to locate the position of the cross-bonding sheath grounding defect, the defect location method described in this application can also locate the defects of the sheath connection methods of single-end grounding and double-end grounding. For example, Figure 7 The schematic diagrams of the sheath connections of single-end grounding and double-end grounding are shown as follows. The specific defect location method includes the following steps:

[0103] Step 1: Open the main grounding and the connecting strip of the grounding box of the first terminal;

[0104] Step 2: Open the main grounding of the second terminal;

[0105] Step 3: Obtain the first loop resistance, the second loop resistance, and the third loop resistance at the first terminal, and record them as L, M, and N respectively, and calculate the single-phase loop resistances Z A 、Z B and Z C of phase A, phase B, and phase C:

[0106] Z A +Z B =L

[0107] Z B +Z C =M

[0108] Z C +Z A =N

[0109] Solve the equations simultaneously to obtain:

[0110] Z A =(N + L - M) / 2

[0111] Z B =(L + M - N) / 2

[0112] Z C =(M + N - L) / 2

[0113] Step 4: If the loop resistance Z A of phase A, the loop resistance Z B of phase B, and the loop resistance Z Care all less than or equal to the third resistance threshold, it is determined that there is no defect and the detection ends; if the loop resistance Z of phase A A , the loop resistance Z of phase B B , and the loop resistance Z of phase C C any one of the values is greater than the third resistance threshold, it is determined that there is a defect in that phase; the third resistance threshold is configured as the total resistance value of a section of cable;

[0114] Step 5: Check the connection in the second terminal grounding box. If the connection state is good, proceed to the next detection; if there is a poor connection, restore the connection of the grounding box or replace the grounding box, re-obtain the first loop resistance, the second loop resistance, and the third loop resistance, calculate the single-loop resistance and perform defect judgment. If there is a defect, proceed to the next detection; if there is no defect, end the detection;

[0115] Step 6: As Figure 8 shown, peel off the outer cable sheath at the lead sealing position of the first terminal of the abnormal phase to expose the metal sheath. Obtain the tenth loop resistance and the eleventh loop resistance at the metal sheath towards the first terminal and the second terminal respectively, and record them as Z bc and Z ac . If Z bc is abnormal, it is determined that the lead sealing at the first terminal is poor; if Z ac is abnormal, it is determined that the lead sealing at the second terminal is poor.

[0116] The specific embodiments described above further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of 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 locating poor connection defects in a transmission cable sheath grounding system, characterized in that: The following steps are involved: Step 1: Open the main grounding and grounding box connection piece of the first terminal, where the first terminal is the terminal at the head end of the cross-connection unit; Step 2: Open the main ground of the second terminal, which is the terminal at the end of the cross-connection unit; Step 3: Obtain a first loop resistance, a second loop resistance and a third loop resistance at the first terminal, and calculate a single loop resistance; the first loop resistance is the sum of the A1-B2-C3 loop resistance and the B1-C2-A3 loop resistance, the second loop resistance is the sum of the B1-C2-A3 loop resistance and the C1-A2-B3 loop resistance, and the third loop resistance is the sum of the A1-B2-C3 loop resistance and the C1-A2-B3 loop resistance; the single loop resistance includes the A1-B2-C3 loop resistance, the B1-C2-A3 loop resistance and the C1-A2-B3 loop resistance; Step 4: judging whether the single circuit has defects based on the resistance value of the single circuit; if there is a defect, proceeding to the next step of detection, and defining the single circuit with defects as a defective single circuit; if there is no defect, ending the detection; Step 5: Check the connection status in the grounding box of the second terminal. If the connection status is good, proceed to the next step of detection. If there is a poor connection, restore the grounding box connection or replace the grounding box, re-obtain the first loop resistance, the second loop resistance and the third loop resistance, calculate the single loop resistance and make a defect judgment. If there is a defect, proceed to the next step of detection. If there is no defect, end the detection. Step 6: Open the connecting piece in the first joint grounding box to obtain the fourth loop resistance and the fifth loop resistance, wherein the fourth loop resistance is the loop resistance measured at the first joint toward the first terminal after the defective single loop and any adjacent non-defective single loop are short-circuited at the first terminal, and the fifth loop resistance is the loop resistance measured at the first joint toward the second terminal after the defective single loop and any adjacent non-defective single loop are short-circuited at the second terminal; the fourth loop resistance and the fifth loop resistance are measured based on the same defective single loop; Step 7: Based on the magnitude of the fourth loop resistance value and the fifth loop resistance value, determine the defective single loop resistance abnormal section; the abnormal section includes the first joint grounding box, the first section and the middle and rear sections; the first section is the section from the first terminal to the first joint grounding box, and the middle and rear sections are the section from the first joint grounding box to the second terminal; Step 8: judge the abnormal section and perform the next step of detection; if the first joint grounding box is abnormal, process the first joint grounding box; if the first section is abnormal, perform the next step of detection; if the middle and rear sections are abnormal, open the connecting piece in the second joint grounding box, obtain the sixth loop resistance and the seventh loop resistance, and based on the sixth loop resistance value and the seventh loop resistance value, confirm that the abnormal section is located at the second joint grounding box, the middle section or the end section, if it is located at the second joint grounding box, process the grounding box, if the abnormal section is the middle section or the end section, perform the next step of detection; the sixth loop resistance is the loop resistance measured at the second joint toward the first terminal after the defective single loop and any adjacent non-defective single loop are short-circuited at the first joint, and the seventh loop resistance is the loop resistance measured at the second joint toward the second terminal after the defective single loop and any adjacent non-defective single loop are short-circuited at the second terminal; the middle section is the section from the first joint grounding box to the second joint grounding box, and the end is the section from the second joint grounding box to the second terminal. Step 9: If the abnormal section is the head end or the end, peel off the outer sheath of the cable outside the lead sealing position of the joint in the abnormal section to expose the metal sheath; if the abnormal section is the middle section, peel off the outer sheath of the cable outside the lead sealing position near the second joint to expose the metal sheath; obtain the eighth loop resistance and the ninth loop resistance, and determine the abnormal position based on the magnitude of the eighth loop and the ninth loop resistance, the eighth loop resistance is the resistance between the metal sheath and the same-phase grounding wire in the adjacent grounding box, and the ninth loop is the resistance between the metal sheath and any non-same-phase grounding wire in the adjacent grounding box; Step 10: Check the abnormal location.

2. A method for locating poor connection defects in a power transmission cable sheath grounding system according to claim 1, characterized in that: The step 3 is specifically as follows: Obtain the first loop resistance, the second loop resistance and the third loop resistance, where the first loop resistance is recorded as L, the second loop resistance is recorded as M, and the third loop resistance is recorded as N, and establish calculation formulas for the first loop resistance L, the second loop resistance M and the third loop resistance N: WITH A1-B2-C3 +Z B1-C2-A3 =L From B1-C2-A3 +Z C1-A2-B3 =M WITH C1-A2-B3 +Z A1-B2-C3 =N Combining the above three equations, we can obtain: Z A1-B2-C3 =(N+L-M) / 2 Z B1-C2-A3 =(L+M-N) / 2 Z C1-A2-B3 =(M+N-L) / 2 In the formula, Z A1-B2-C3 Represents the resistance of the ABC loop, Z B1-C2-A3 Indicates the BCA loop resistance, Z C1-A2-B3 Indicates the CAB loop resistance.

3. A method for locating poor connection defects in a power transmission cable sheath grounding system according to claim 1, characterized in that: The step 4 is specifically as follows: Defect judgment is performed based on the size of the single-loop resistance value. If the sizes of the three-phase loop resistance values ​​are all less than or equal to the first resistance threshold, it is judged that the cross-interconnection unit has no defects and the detection is terminated; if the size of the single-phase loop resistance value of any item is greater than the first resistance threshold, it is judged that the phase has defects and the next step of detection is performed; the first resistance threshold is configured as the total resistance value of the three-segment line of the single loop of the cross-interconnection unit.

4. A method for locating poor connection defects in a power transmission cable sheath grounding system according to claim 1, characterized in that: The step 7 is specifically as follows: If the fourth loop resistance value is less than or equal to the second resistance threshold and the fifth loop resistance value is less than or equal to twice the second resistance threshold, the abnormal section is located at the first joint grounding box; if the fourth loop resistance value is greater than the second resistance threshold, the abnormal section is located in the first section; if the fifth loop resistance value is greater than twice the second resistance threshold, the abnormal section is located in the middle and rear sections; the second resistance threshold is configured as the total resistance value of the two-section line of a single loop of the cross-interconnection unit.

5. A method for locating poor connection defects in a power transmission cable sheath grounding system according to claim 1, characterized in that: In step 8, the abnormal section position is confirmed based on the sixth loop resistance value and the seventh loop resistance value, specifically: If the sixth loop resistance value and the seventh loop resistance value are both less than or equal to the second resistance threshold, the abnormal section is located at the second joint grounding box; if the sixth loop resistance value is greater than the second resistance threshold, the abnormal section is located in the middle section; if the seventh loop resistance value is greater than the second resistance threshold, the abnormal section is located in the end section.

6. A method for locating poor connection defects in a power transmission cable sheath grounding system according to claim 1, characterized in that: In step 9, the abnormal position is determined based on the eighth loop resistance and the ninth loop resistance, specifically: When the abnormal section is located at the first section, if the ninth loop resistance value is greater than the second resistance threshold, the first terminal of the abnormal section is poorly sealed; otherwise, the first joint of the abnormal section is poorly sealed toward the first terminal or the first joint is poorly connected internally; When the abnormal section is located in the middle section, if the ninth loop resistance value is greater than the second resistance threshold, the first joint of the abnormal section is poorly sealed toward the second terminal side or the first joint is poorly connected internally; otherwise, the second joint of the abnormal section is poorly sealed toward the first terminal side or the second joint is poorly connected internally; When the abnormal section is located at the end, if the ninth loop resistance value is greater than the second resistance threshold, the second terminal of the abnormal section is poorly sealed; otherwise, the second joint of the abnormal section is poorly sealed toward the second terminal side or the second joint has a poor internal connection.

7. A transmission cable sheath grounding system poor connection defect location system, applied to a transmission cable sheath grounding system poor connection defect location method as claimed in any one of claims 1 to 6, characterized in that: It includes a loop resistance acquisition module, a calculation module and a judgment module; wherein, The loop resistance acquisition module is configured to acquire first to ninth loop resistances; The calculation module is configured to calculate the ABC loop resistance, the BCA loop resistance and the CAB loop resistance based on the first loop resistance, the second loop resistance and the third loop resistance; The judgment module is configured to judge whether the single loop has a defect based on the ABC loop resistance, the BCA loop resistance and the CAB loop resistance; judge whether the defect is located in the first joint grounding box, the first section or the middle and rear section based on the fourth loop resistance and the fifth loop resistance; judge whether the defect is located in the second joint grounding box, the middle section or the last section based on the sixth loop resistance and the seventh loop resistance; judge whether the defect is located at the first terminal, the first joint, the second joint or the second terminal based on the eighth loop resistance and the ninth loop resistance.

8. A transmission cable sheath grounding system poor connection defect location system according to claim 7, characterized in that: The loop resistance acquisition module includes a first acquisition module, a second acquisition module, a third acquisition module and a fourth acquisition module, the first acquisition module is configured to acquire the first loop resistance, the second loop resistance and the third loop resistance; the second acquisition module is configured to acquire the fourth loop resistance and the fifth loop resistance; the third acquisition module is configured to acquire the sixth loop resistance and the seventh loop resistance; the fourth acquisition module is configured to acquire the eighth loop resistance and the ninth loop resistance.

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