Method and apparatus for evaluating cable shield defects with induced charge

Abstract

The application provides a method and device for evaluating cable shielding defects with electric charge, and belongs to the technical field of cable testing, and comprises the following steps: installing a current transformer, determining cable amplitude-phase data, obtaining the number of grounding boxes and the number of grounding leads of a cable shielding defect to be detected; determining a grounding box mode, calculating a metal sheath mode connected with the grounding box; calculating circulation data of the metal sheath of the cable connected with the grounding box; judging the running state of the metal sheath circulation of the cable, judging whether there is an abnormal grounding defect of the metal shielding and the grounding lead, and performing defect pinpointing on the metal sheath of the cable with the grounding defect. The detection efficiency and accuracy can be improved without disassembling the equipment, potential hidden dangers can be found in time, the continuity and accuracy of live detection are ensured, the matching degree of data and actual working conditions is improved, the safe and stable operation of the cable is ensured, and strong support is provided for reliable power supply of the power system.

Description

Technical Field

[0001] This invention relates to the field of cable testing technology, specifically to a method and apparatus for evaluating cable shielding defects while the cable is energized. Background Technology

[0002] Current cable shielding defect detection relies heavily on traditional methods, which have significant limitations. Historically, detection often required power outages, such as measuring insulation resistance by disconnecting the shielding layer from ground or using partial discharge detectors to check for accessory faults. However, power outages disrupt power supply and can only be performed during equipment downtime. Among current mainstream methods, time-domain reflectometry is insensitive to defects with slight impedance changes, infrared thermal imagers can only detect heat-related faults, and ultra-low frequency dielectric loss testing focuses on overall insulation assessment; none of these can accurately locate hidden defects such as broken metal shielding layers or loose grounding leads under energized conditions. Furthermore, there is a lack of effective quantitative analysis methods for circulating current anomalies in cross-connected grounding systems, often leading to missed detections and subsequent fault expansion. Therefore, there is an urgent need for a technical solution capable of comprehensive and accurate detection under energized conditions.

[0003] Therefore, the present invention provides a method and apparatus for evaluating cable shielding defects while the cable is in operation. Summary of the Invention

[0004] This invention provides a method and apparatus for live-line testing of cable shielding defects. By installing a current transformer to determine the cable amplitude-phase data, the number of grounding boxes and grounding leads at the location of the cable shielding defect to be tested is obtained. The grounding box configuration is determined, and the configuration of the metal sheath connected to the grounding box and the circulating current data of the cable's metal sheath connected to the grounding box are calculated. The circulating current operating status of the cable's metal sheath is analyzed, and the existence of abnormal grounding defects in the metal shielding and grounding leads is determined. Defects in the metal sheath of cables with grounding defects are pinpointed. This method improves testing efficiency and accuracy without disassembling the equipment, promptly identifies potential hazards, ensures the continuity and accuracy of live-line testing, improves the matching degree between data and actual operating conditions, ensures the safe and stable operation of cables, and provides strong support for reliable power supply to the power system.

[0005] On one hand, the present invention provides a method for evaluating cable shielding defects while energized, comprising:

[0006] Step 1: Install current transformers on both sides of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be detected, determine the cable amplitude-phase data, and obtain the number of grounding boxes and the number of grounding leads at the location where the cable shielding defect is to be detected.

[0007] Step 2: Based on the cable amplitude-phase data and the number of grounding boxes at the locations where cable shielding defects need to be detected, determine the grounding box type; based on the grounding box type and the number of grounding boxes, calculate the metal sheath type connected to the grounding box.

[0008] Step 3: Based on the cable amplitude-phase data, the number of grounding boxes, the type of grounding box, and the type of metal sheath connected to the grounding box, calculate the circulating current data of the metal sheath of the cable connected to the grounding box;

[0009] Step 4: Analyze the circulating current operation status of the cable metal sheath, determine whether there are any defects in the metal shielding or abnormal grounding of the grounding lead, and pinpoint the defects in the cable metal sheath with grounding defects.

[0010] According to the present invention, a method for evaluating cable shielding defects while energized involves installing current transformers on both sides of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be detected, and determining the cable amplitude-phase data, including:

[0011] The three current transformers of the testing equipment are installed on one side of the three-phase cable body of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be tested.

[0012] The other three current transformers of the testing equipment are installed on the other side of the three-phase cable body of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be tested, based on the same direction as the three current transformers already installed on one side.

[0013] Based on three current transformers installed on one side of the three-phase cable body of the cable joint group, the current amplitude and phase of one side of the three-phase cable body of the cable joint group are recorded. At the same time, based on three current transformers installed on the other side of the three-phase cable body of the cable joint group, the current amplitude and phase of the other side of the three-phase cable body of the cable joint group are recorded.

[0014] Based on the current amplitude and phase of one side of the three-phase cable body on one side of the cable joint assembly, and the current amplitude and phase of the other side of the three-phase cable body on the other side of the cable joint assembly, the cable amplitude-phase data is determined.

[0015] According to the present invention, a method for evaluating cable shielding defects while energized, based on cable amplitude-phase data and the number of grounding boxes at the location of the cable shielding defect to be detected, determines the grounding box configuration, including:

[0016] The grounding box type is determined based on the number of grounding boxes at the location to be tested for cable shielding defects, the current amplitude and phase on one side of the three-phase cable body on one side of the cable joint group, and the current amplitude and phase on the other side of the three-phase cable body on the other side of the cable joint group.

[0017]

[0018] ; ;

[0019] ; ;

[0020] ;

[0021] ;

[0022] ; ; ;

[0023] ; ;

[0024] ;

[0025] ;

[0026] in, Indicates the grounding box method. These represent the first, second, third, fourth, fifth, and sixth sub-grounding box configurations, respectively. This indicates the number of grounding boxes. Ix represents the maximum current amplitude caused by transformer errors and field interference during on-site testing. IA1, IB1, and IC1 represent the current vectors of phases A, B, and C on one side of the cable joint group, respectively. IA2, IB2, and IC2 represent the current vectors of phases A, B, and C on the other side of the cable joint group, respectively. IF1 represents the amplitude of the current vector value of the three-phase current transformer on one side of the cable joint group. IF2 represents the amplitude of the current vector value of the three-phase current transformer on the other side of the cable joint group. IF represents the difference between the amplitudes of the three-phase current transformer current vector values ​​of the cable body on one side of the cable joint group and the amplitudes of the three-phase current transformer current vector values ​​of the cable body on the other side of the joint group. This represents the magnitude of the maximum three-phase current transformer current vector value in the cable joint assembly. This represents the amplitude of the smallest three-phase current transformer current vector value in the cable joint group. The first index representing the current vector on both sides of the cable joint assembly. The second index represents the current vector on both sides of the cable joint assembly.

[0027] According to the present invention, a method for evaluating cable shielding defects under live conditions, based on the grounding box type and the number of grounding boxes, calculates the metal sheath type connected to the grounding box, including:

[0028] If the number of grounding boxes is 1, and the grounding box type is a cross-transposed grounding box of an insulated joint group, then calculate the third and fourth indices of the current vectors on both sides of the cable joint group.

[0029] ;

[0030] ;

[0031] in, The third and fourth indices of the current vectors on both sides of the cable joint assembly, respectively;

[0032] Compare the third and fourth indices of the current vectors on both sides of the cable joint group. If the third index is less than the fourth index, the cross-transfer connection method of the metal sheath is IA1—IB2, IB1—IC2, IC1—IA2. If the third index is greater than the fourth index, the cross-transfer connection method of the metal sheath is IA1—IC2, IB1—IA2, IC1—IB2.

[0033] If the number of grounding boxes is 1, and the grounding box type is a heterogeneous grounding box with insulated joint group, and the judgment logic is... Then determine whether it is a single-end grounding system or a cross-transposition system on both sides of the connector. The metal sheath of the cable body on the left side of the connector assembly is grounded through a lead wire and a heterogeneous grounding box; the metal sheath of the cable body on the right side of the connector assembly is directly grounded through a lead wire and a heterogeneous grounding box. If the metal sheath of the cable body on the left side of the connector is directly grounded through a lead wire and a heterogeneous grounding box, the metal sheath of the cable body on the left side of the connector group is protected by a lead wire and a heterogeneous grounding box; the metal sheath of the cable body on the right side of the connector is protected by a lead wire and a heterogeneous grounding box.

[0034] If the number of grounding boxes is 1, and the grounding box type is a heterogeneous grounding box with insulated joint group, and the judgment logic is... If the connection is a single-ended grounding system on both sides, then it is determined that both sides of the connection are single-ended grounding systems. | Then, the metal sheath of the cable body on the left side of the connector group is grounded through a lead wire and directly to the grounding box; the metal sheath of the cable body on the right side of the connector group is grounded through a lead wire and a protective grounding box. | Then the metal sheath of the cable body on the right side of the connector group is grounded through the lead wire and the protective grounding box;

[0035] If the number of grounding boxes is 1, and the grounding box type is a direct grounding box with a straight-through connector group, then the connectors on both sides of each phase of the cable, the metal sheath of the cable body, are directly connected and grounded through the grounding lead and the direct grounding box. If the two sides of the connector are determined to be a cross-transposed grounding system, then... If so, it can be determined that the two sides of the connector are a single-ended grounding system;

[0036] If the number of grounding boxes is 2, the grounding box type is an insulated joint group and both sides are protective grounding boxes, then the metal sheath of the cable body on both sides of the cable joint of each phase is insulated.

[0037] If there are two grounding boxes, and the grounding box type is an insulated joint group with direct grounding boxes on both sides, then the metal sheath insulation of the cable body on both sides of the cable joints of each phase is all grounded through a direct grounding box. Then the two sides of the connector are a cross-transposed grounding system. Then the two sides of the connector are a single-ended grounding system;

[0038] If the number of grounding boxes is 2, and the grounding box configuration is such that one side of the insulating joint group is a direct grounding box and the other side is a protective grounding box, and the judgment logic is as follows: ,like If the metal sheath of the cable body on the left side of the joint assembly is grounded through a lead wire and directly to the grounding box, and the metal sheath of the cable body on the right side of the joint assembly is grounded through a lead wire and a protective grounding box, then... The metal sheath of the cable body on the left side of the connector group is grounded through a lead wire and a protective grounding box; the metal sheath of the cable body on the right side of the connector group is grounded through a lead wire and a direct grounding box.

[0039] If the number of grounding boxes is 2, and the grounding box configuration is such that one side of the insulating joint group is a direct grounding box and the other side is a protective grounding box, and the judgment logic is as follows: ,like The metal sheath of the cable body on the left side of the connector assembly is grounded directly to the grounding box via a lead wire; the metal sheath of the cable body on the right side of the connector assembly is grounded via a protective grounding box via a lead wire. The metal sheath of the cable body on the right side of the connector group is grounded through the lead wire and the protective grounding box.

[0040] According to the present invention, a method for evaluating cable shielding defects under live conditions calculates circulating current data of the metal sheath of the cable connected to the grounding box based on cable amplitude-phase data, the number of grounding boxes, the grounding box method, and the method of connecting the grounding box to the metal sheath. The method includes:

[0041] Based on the number of grounding boxes, the type of grounding boxes, and the type of metal sheath connected to the grounding boxes, calculate the current amplitude of the cable core for each type of grounding box and the number of grounding boxes, and calculate the circulating current data of the metal sheath connected to each type of grounding box.

[0042] According to the present invention, a method for evaluating cable shielding defects under live conditions is provided, which analyzes the circulating current operating status of the cable's metallic sheath and determines whether there are defects in the metallic shielding or abnormal grounding of the grounding lead, including:

[0043] To assess the circulating current status of the cable's metal sheath, the circulating current data of the metal shield of the same branch tested by the grounding box is used to determine whether there are any abnormal grounding defects in the metal shield or the grounding lead.

[0044] If the metal sheath connected to the grounding box is single-ended grounded, then:

[0045] |ILA1—ILA2|≥MAX{2×π×F×U0×C0×L× The defect is identified as an abnormal grounding fault in the metal sheath of phase A branch.

[0046] |ILB1—ILB2|≥MAX{2×π×F×U0×C0×L× Ix} was determined to be an abnormal grounding defect in the metal sheath of phase B branch;

[0047] |ILC1—ILC2|≥MAX{2×π×F×U0×C0×L× The defect was identified as an abnormal grounding fault in the metal sheath of the C-phase branch.

[0048] If the metal sheath connected to the grounding box is a cross-transposed grounding, then:

[0049] |ILA1—ILA2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of phase A branch;

[0050] |ILB1—ILB2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of phase B branch;

[0051] |ILC1—ILC2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of the C-phase branch;

[0052] Wherein, ILA1 is the circulating current at the beginning of the metal-shielded branch of phase A; ILA2 is the circulating current at the end of the metal-shielded branch of phase A; ILB1 is the circulating current at the beginning of the metal-shielded branch of phase B; ILB2 is the circulating current at the end of the metal-shielded branch of phase B; ILC1 is the circulating current at the beginning of the metal-shielded branch of phase C; ILC2 is the circulating current at the end of the metal-shielded branch of phase C; F is the power frequency; U0 is the rated operating voltage of the cable; C0 is the induced capacitance per unit length of the cable line; L is the length of the metal sheath of the cable connected to the grounding box.

[0053] According to the present invention, a method for evaluating cable shielding defects while energized, and for pinpointing the defects in the metal sheath of cables with grounding defects, includes:

[0054] For defective metal segments, the induced current of the cable body is obtained by using a binary method or by testing each segment simultaneously, namely ILi at the beginning and IRi at the end. The current magnitudes are compared. If the currents are equal, the defect is not in the test segment. If the currents are not equal, the defect is in the segment. The above process is repeated to narrow down the test range until the defect is accurately located.

[0055] On the other hand, the present invention also provides a method and apparatus for live testing of cable shielding defects, for performing any one of the live testing of cable shielding defects in Examples 1 to 7.

[0056] Compared with the prior art, the beneficial effects of this application are as follows:

[0057] By installing current transformers to determine cable amplitude-phase data, the number of grounding boxes and grounding leads at the locations to be inspected for cable shielding defects is obtained. The grounding box type is determined, and the type of metal sheath connected to the grounding box and the circulating current data of the cable's metal sheath connected to the grounding box are calculated. The circulating current operating status of the cable's metal sheath is analyzed, and the existence of abnormal grounding defects in the metal shielding and grounding leads is determined. Defects in the metal sheath of cables with grounding defects are pinpointed. This method can improve detection efficiency and accuracy without disassembling the equipment, promptly identify potential hazards, ensure the continuity and accuracy of live-line testing, improve the matching degree between data and actual operating conditions, ensure the safe and stable operation of cables, and provide strong support for reliable power supply to the power system. Attached Figure Description

[0058] Figure 1 This is a flowchart illustrating a method for evaluating cable shielding defects under live conditions, as provided in an embodiment of the present invention. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0060] Example 1:

[0061] This invention provides a method for evaluating cable shielding defects while the cable is energized, such as... Figure 1 As shown, it includes:

[0062] Step 1: Install current transformers on both sides of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be detected, determine the cable amplitude-phase data, and obtain the number of grounding boxes and the number of grounding leads at the location where the cable shielding defect is to be detected.

[0063] Step 2: Based on the cable amplitude-phase data and the number of grounding boxes at the locations where cable shielding defects need to be detected, determine the grounding box type; based on the grounding box type and the number of grounding boxes, calculate the metal sheath type connected to the grounding box.

[0064] Step 3: Based on the cable amplitude-phase data, the number of grounding boxes, the type of grounding box, and the type of metal sheath connected to the grounding box, calculate the circulating current data of the metal sheath of the cable connected to the grounding box;

[0065] Step 4: Analyze the circulating current operation status of the cable metal sheath, determine whether there are any defects in the metal shielding or abnormal grounding of the grounding lead, and pinpoint the defects in the cable metal sheath with grounding defects.

[0066] In this embodiment, the grounding box is used for grounding the cable's metal sheath (shielding layer) to prevent excessively high induced voltage in the sheath.

[0067] In this embodiment, the main control equipment for metal sheath circulating current live testing can be implemented in two ways: Method 1: This method includes a 2-channel data acquisition module, with signal switching achieved via a relay switching switch. Specifically, it consists of a 6-channel input / 2-channel output switching module, a 2-channel filtering unit module, a 2-channel amplification unit module, a 2-channel analog-to-digital converter module, a 2-channel data acquisition unit module, a vector operation and control unit module, a display unit module, and a power supply module. Further, in Method 1, the input terminal of the 6-channel input / 2-channel output switching module is connected to the 6CT, and the output terminal is connected to the 2-channel filtering unit module. This allows the 6CT input signal to be received and sequentially output to the 2-channel filtering unit module. The 2-channel filtering unit filters the signal input from the node switching switch and outputs it to the 2-channel amplification unit module. The 2-channel amplification unit module receives the signal output from the 2-channel filtering unit, amplifies it, and sends it to the 2-channel analog-to-digital converter module. The 2-channel analog-to-digital converter module converts the signal output from the 2-channel signal amplification module from analog to digital and transmits it to the 2-channel signal acquisition unit module. The two-channel signal acquisition module is used to acquire, record, and store the digital signals transmitted by the two-channel analog-to-digital converter module. The vector calculation and control unit module is used to perform amplitude and phase angle correction, conversion calculations, and control the signal acquisition and calculation of the acquired and recorded current vectors. The display unit module displays the results of the acquisition and calculations. The power supply module supplies power to the main control equipment for metal-sheathed circulating current live-line testing.

[0068] Method Two: One method includes a six-channel data acquisition module, consisting of a six-channel filtering unit module, a six-channel amplification unit module, a six-channel analog-to-digital converter module, a six-channel data acquisition unit module, a vector calculation and control unit module, a display unit module, and a power supply module. Further, in Method Two, the six-channel filtering unit filters the signal input from the node switching switch and outputs it to the six-channel amplification unit module. The six-channel amplification unit module receives the signal output from the six-channel filtering unit, amplifies it, and sends it to the six-channel analog-to-digital converter module. The six-channel analog-to-digital converter module converts the analog signal output from the six-channel signal amplification module into a digital signal and transmits it to the six-channel signal acquisition unit module. The six-channel signal acquisition module acquires, records, and stores the digital signal transmitted from the six-channel analog-to-digital converter module. The vector calculation and control unit module performs conversion calculations on the acquired and recorded current vectors and controls signal acquisition and calculation. The display unit module displays the results of the acquisition and calculation. The power supply module supplies power to the main control equipment for the metal sheath circulating current live-line test. The measuring CT is marked with directions and acquires signals independently.

[0069] The beneficial effects of the above technical solution are as follows: By installing current transformers to determine cable amplitude-phase data, the number of grounding boxes and grounding leads at the locations to be inspected for cable shielding defects can be obtained, the grounding box type can be determined, the type of metal sheath connected to the grounding box and the circulating current data of the cable metal sheath connected to the grounding box can be calculated, the circulating current operating status of the cable metal sheath can be analyzed, and the existence of abnormal grounding defects in the metal shield and grounding leads can be determined. Defects in the cable metal sheath with grounding defects can be pinpointed. This improves detection efficiency and accuracy without disassembling the equipment, promptly identifies potential hazards, ensures the continuity and accuracy of live-line testing, improves the matching degree between data and actual operating conditions, ensures the safe and stable operation of cables, and provides strong support for reliable power supply to the power system.

[0070] Example 2:

[0071] This invention provides a method for live-line testing of cable shielding defects. Current transformers are installed on both sides of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be tested. The method determines the cable amplitude-phase data, including:

[0072] The three current transformers of the testing equipment are installed on one side of the three-phase cable body of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be tested.

[0073] The other three current transformers of the testing equipment are installed on the other side of the three-phase cable body of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be tested, based on the same direction as the three current transformers already installed on one side.

[0074] Based on three current transformers installed on one side of the three-phase cable body of the cable joint group, the current amplitude and phase of one side of the three-phase cable body of the cable joint group are recorded. At the same time, based on three current transformers installed on the other side of the three-phase cable body of the cable joint group, the current amplitude and phase of the other side of the three-phase cable body of the cable joint group are recorded.

[0075] Based on the current amplitude and phase of one side of the three-phase cable body on one side of the cable joint assembly, and the current amplitude and phase of the other side of the three-phase cable body on the other side of the cable joint assembly, the cable amplitude-phase data is determined.

[0076] In this embodiment, regarding the installation location and number of current transformers, it is explicitly required that six current transformers be used, divided into two groups of three, corresponding to the three-phase cable (phase A, phase B, and phase C). The first group of three current transformers is installed on one side of the three-phase cable body of the cable joint group connected to the cable grounding box at the location where cable shielding defects are to be detected. Here, the "cable joint group" is a high-incidence area for shielding defects because the connection or insulation isolation of the shielding layer needs to be handled at the joint, which is prone to problems such as poor contact and breakage; while the "cable body" refers to the complete cable part including the conductor, insulation layer, and shielding layer (metal sheath). The reason for installing them on both sides of the joint group is that defects in the shielding layer will directly cause abnormal current distribution on both sides of the joint group—under normal circumstances, the current on both sides should follow a specific pattern (such as similar amplitude and symmetrical phase), but when defects exist, this pattern will be broken.

[0077] In this embodiment, it is emphasized that the installation directions of the current transformers on both sides must be consistent. This is crucial because the measurement results of the current transformers are closely related to the installation direction (e.g., the positive and negative phases will be reversed due to different directions). If the directions on both sides are inconsistent, the subsequently recorded phase data will lose comparability, potentially leading to misjudgments of the current relationship. For example, if the "inlet terminal" of one current transformer faces the connector group, while the other faces the opposite direction, then even if the actual current phases are the same, the recorded data will show opposite phases, thus masking the true defect signal. Therefore, "consistent direction" is a prerequisite for ensuring data validity, and it is usually achieved through marking and standardized installation specifications (e.g., all based on the cable laying direction).

[0078] In this embodiment, based on the installed current transformer, the current information on both sides of the connector group is recorded separately, specifically including "the current amplitude and phase on one side of the three-phase cable body" and "the current amplitude and phase on the other side of the three-phase cable body". Here, "amplitude" refers to the magnitude of the current (in A), reflecting the strength of the current; "phase" describes the order of current changes over time (expressed in angle), reflecting the symmetrical relationship between the three-phase currents. When there are defects in the shielding layer (such as a broken shielding layer or poor contact of the grounding lead), this symmetry will be disrupted, resulting in a significant difference in the amplitude of the current on both sides and a disordered phase relationship (such as a phase difference deviating from 120°).

[0079] In this embodiment, the recorded current amplitude and phase data from both sides are integrated to form "cable amplitude-phase data".

[0080] The beneficial effects of the above technical solution are as follows: Installing current transformers on both sides of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be detected, and determining the cable amplitude-phase data, can provide data support for determining the grounding box method.

[0081] Example 3:

[0082] This invention provides a method for live-line testing of cable shielding defects. Based on cable amplitude-phase data and the number of grounding boxes at the location of the cable shielding defect to be tested, the method determines the grounding box configuration, including:

[0083] The grounding box type is determined based on the number of grounding boxes at the location to be tested for cable shielding defects, the current amplitude and phase on one side of the three-phase cable body on one side of the cable joint group, and the current amplitude and phase on the other side of the three-phase cable body on the other side of the cable joint group.

[0084]

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[0090] ; ;

[0091] ;

[0092] ;

[0093] in, Indicates the grounding box method. These represent the first, second, third, fourth, fifth, and sixth sub-grounding box configurations, respectively. This indicates the number of grounding boxes. Ix represents the maximum current amplitude caused by transformer errors and field interference during on-site testing. IA1, IB1, and IC1 represent the current vectors of phases A, B, and C on one side of the cable joint group, respectively. IA2, IB2, and IC2 represent the current vectors of phases A, B, and C on the other side of the cable joint group, respectively. IF1 represents the amplitude of the current vector value of the three-phase current transformer on one side of the cable joint group. IF2 represents the amplitude of the current vector value of the three-phase current transformer on the other side of the cable joint group. IF represents the difference between the amplitudes of the three-phase current transformer current vector values ​​of the cable body on one side of the cable joint group and the amplitudes of the three-phase current transformer current vector values ​​of the cable body on the other side of the joint group. This represents the magnitude of the maximum three-phase current transformer current vector value in the cable joint assembly. This represents the amplitude of the smallest three-phase current transformer current vector value in the cable joint group. The first index representing the current vector on both sides of the cable joint assembly. The second index represents the current vector on both sides of the cable joint assembly.

[0094] In this embodiment, the cross-transposition grounding box of the insulating joint group: The insulating joint group is characterized by its internal shielding layer (metal sheath) being insulated and isolated, and cannot be directly connected. Therefore, it is necessary to use the cross-transposition grounding box to realize the connection between different phases in order to cancel the induced voltage.

[0095] In this embodiment, the heterogeneous grounding box of the insulating joint group has a relatively special structure and may integrate multiple grounding functions (such as partial direct grounding and partial protective grounding), which is suitable for complex wiring scenarios.

[0096] In this embodiment, the direct grounding box of the straight-through connector group: the shielding layer of the straight-through connector group is continuously conductive and has no insulation isolation. Therefore, the function of the direct grounding box is to directly connect the entire shielding layer to the ground.

[0097] In this embodiment, the insulating joint assembly has protective grounding boxes on both sides: the insulating joint assembly divides the shielding layer into two sections, and the protective grounding boxes on both sides are grounded through protectors (such as zinc oxide surge arresters). Under normal circumstances, the protectors are in a high-resistance state, and the two ends of the shielding layer are almost suspended.

[0098] In this embodiment, the insulating joint assembly has two direct grounding boxes on both sides: after the insulating joint assembly is isolated by the shielding layer, the two sides are connected to the ground through the direct grounding boxes respectively, forming two independent grounding loops.

[0099] In this embodiment, the insulating joint assembly has a direct grounding box on one side and a protective grounding box on the other: this method combines the characteristics of direct grounding and protective grounding, with a total of two grounding boxes. The shielding current on the direct grounding side can flow freely, resulting in a larger and more stable current amplitude for the corresponding phase on this side; the protective grounding side is restricted by the protector, resulting in a smaller current amplitude that may fluctuate with voltage. Furthermore, the phase relationship between the currents on both sides will exhibit asymmetry due to the different grounding methods—the phase on the direct grounding side is more closely related to the conductor current, while the phase on the protective grounding side is more significantly affected by the characteristics of the protector.

[0100] The beneficial effects of the above technical solution are as follows: Based on the cable amplitude-phase data and the number of grounding boxes at the locations of cable shielding defects to be detected, the grounding box type can be determined. This allows for accurate identification of multiple grounding box types without power outages or equipment disassembly, providing an accurate structural basis for subsequent defect diagnosis.

[0101] Example 4:

[0102] This invention provides a method for evaluating cable shielding defects while energized, which calculates the metal sheath type connected to the grounding box based on the grounding box type and number of grounding boxes, including:

[0103] If the number of grounding boxes is 1, and the grounding box type is a cross-transposed grounding box of an insulated joint group, then calculate the third and fourth indices of the current vectors on both sides of the cable joint group.

[0104] ;

[0105] ;

[0106] in, The third and fourth indices of the current vectors on both sides of the cable joint assembly, respectively;

[0107] Compare the third and fourth indices of the current vectors on both sides of the cable joint group. If the third index is less than the fourth index, the cross-transfer connection method of the metal sheath is IA1—IB2, IB1—IC2, IC1—IA2. If the third index is greater than the fourth index, the cross-transfer connection method of the metal sheath is IA1—IC2, IB1—IA2, IC1—IB2.

[0108] If the number of grounding boxes is 1, and the grounding box type is a heterogeneous grounding box with insulated joint group, and the judgment logic is... Then determine whether it is a single-end grounding system or a cross-transposition system on both sides of the connector. The metal sheath of the cable body on the left side of the connector assembly is grounded through a lead wire and a heterogeneous grounding box; the metal sheath of the cable body on the right side of the connector assembly is directly grounded through a lead wire and a heterogeneous grounding box. If the metal sheath of the cable body on the left side of the connector is directly grounded through a lead wire and a heterogeneous grounding box, the metal sheath of the cable body on the left side of the connector group is protected by a lead wire and a heterogeneous grounding box; the metal sheath of the cable body on the right side of the connector is protected by a lead wire and a heterogeneous grounding box.

[0109] If the number of grounding boxes is 1, and the grounding box type is a heterogeneous grounding box with insulated joint group, and the judgment logic is... If the connection is a single-ended grounding system on both sides, then it is determined that both sides of the connection are single-ended grounding systems. | Then, the metal sheath of the cable body on the left side of the connector group is grounded through a lead wire and directly to the grounding box; the metal sheath of the cable body on the right side of the connector group is grounded through a lead wire and a protective grounding box. | Then the metal sheath of the cable body on the right side of the connector group is grounded through the lead wire and the protective grounding box;

[0110] If the number of grounding boxes is 1, and the grounding box type is a direct grounding box with a straight-through connector group, then the connectors on both sides of each phase of the cable, the metal sheath of the cable body, are directly connected and grounded through the grounding lead and the direct grounding box. If the two sides of the connector are determined to be a cross-transposed grounding system, then... If so, it can be determined that the two sides of the connector are a single-ended grounding system;

[0111] If the number of grounding boxes is 2, the grounding box type is an insulated joint group and both sides are protective grounding boxes, then the metal sheath of the cable body on both sides of the cable joint of each phase is insulated.

[0112] If there are two grounding boxes, and the grounding box type is an insulated joint group with direct grounding boxes on both sides, then the metal sheath insulation of the cable body on both sides of the cable joints of each phase is all grounded through a direct grounding box. Then the two sides of the connector are a cross-transposed grounding system. Then the two sides of the connector are a single-ended grounding system;

[0113] If the number of grounding boxes is 2, and the grounding box configuration is such that one side of the insulating joint group is a direct grounding box and the other side is a protective grounding box, and the judgment logic is as follows: ,like If the metal sheath of the cable body on the left side of the joint assembly is grounded through a lead wire and directly to the grounding box, and the metal sheath of the cable body on the right side of the joint assembly is grounded through a lead wire and a protective grounding box, then... The metal sheath of the cable body on the left side of the connector group is grounded through a lead wire and a protective grounding box; the metal sheath of the cable body on the right side of the connector group is grounded through a lead wire and a direct grounding box.

[0114] If the number of grounding boxes is 2, and the grounding box configuration is such that one side of the insulating joint group is a direct grounding box and the other side is a protective grounding box, and the judgment logic is as follows: ,like The metal sheath of the cable body on the left side of the connector assembly is grounded directly to the grounding box via a lead wire; the metal sheath of the cable body on the right side of the connector assembly is grounded via a protective grounding box via a lead wire. The metal sheath of the cable body on the right side of the connector group is grounded through the lead wire and the protective grounding box.

[0115] In this embodiment, the cross-connection method of the metal sheath is IA1-IB2, IB1-IC2, IC1-IA2, which means that the metal sheath of the A-phase cable on the left side of the connector group is connected to the metal sheath of the B-phase cable on the right side of the connector group through the lead wire and grounding box; the metal sheath of the B-phase cable on the left side of the connector group is connected to the metal sheath of the C-phase cable on the right side of the connector group through the lead wire and grounding box; and the metal sheath of the C-phase cable on the left side of the connector group is connected to the metal sheath of the A-phase cable on the right side of the connector group through the lead wire and grounding box.

[0116] In this embodiment, the cross-connection method of the metal sheath is IA1—IC2, IB1—IA2, IC1—IB2, which means that the metal sheath of the A-phase cable on the left side of the connector group is connected to the metal sheath of the C-phase cable on the right side of the connector group through the lead wire and grounding box; the metal sheath of the B-phase cable on the left side of the connector group is connected to the metal sheath of the A-phase cable on the right side of the connector group through the lead wire and grounding box; and the metal sheath of the C-phase cable on the left side of the connector group is connected to the metal sheath of the B-phase cable on the right side of the connector group through the lead wire and grounding box.

[0117] The beneficial effects of the above technical solution are as follows: Based on the grounding box method and the number of grounding boxes, the method of connecting the metal sheaths of the grounding boxes can be calculated. The specific connection relationship of the sheaths can be accurately determined without disassembling the equipment, which ensures the continuity of live detection and improves the efficiency and accuracy of connection method identification.

[0118] Example 5:

[0119] This invention provides a method for live-line testing of cable shielding defects. Based on cable amplitude-phase data, the number of grounding boxes, the type of grounding boxes, and the type of metal sheath connected to the grounding boxes, the method calculates the circulating current data of the metal sheath of the cable connected to the grounding boxes, including:

[0120] Based on the number of grounding boxes, the type of grounding boxes, and the type of metal sheath connected to the grounding boxes, calculate the current amplitude of the cable core for each type of grounding box and the number of grounding boxes, and calculate the circulating current data of the metal sheath connected to each type of grounding box.

[0121] In this embodiment, if the number of grounding boxes is 1, and the grounding box type is a cross-transposed grounding box with an insulated joint group, then the current amplitude of the cable core in the cable body is calculated, and the circulating current of the metal shield of each phase of the cable is calculated:

[0122] When the cross-connection method of the metal sheath is IA1—IB2, IB1—IC2, or IC1—IA2, the calculation formulas for the current amplitude of the cable core and the circulating current of the metal shield of each phase can be expressed as follows:

[0123] ;

[0124] If ABC are in clockwise order, then:

[0125] ;

[0126] ;

[0127] ;

[0128] If ABC is in counter-clockwise order, then:

[0129] ;

[0130] ;

[0131] ;

[0132] ;

[0133] ;

[0134] ;

[0135] in, Let Ia be the vector current of the core conductor of the three-phase cable, Ib be the vector current of the core conductor of phase A, Ic be the vector current of the core conductor of phase B, and Ic be the vector current of the core conductor of phase C. , , These represent the circulating current of the cable's metallic shield on one side of the cable joint assembly, specifically for phases A, B, and C. , These represent the circulating current of the cable metal shield on the other side of the cable joint assembly for phases A, B, and C, respectively.

[0136] When the cross-transfer connection method of the metal sheath is IA1—IC2, IB1—IA2, IC1—IB2, the calculation method of the current amplitude of the cable core and the circulating current of the metal shield of each phase is the same as when the cross-transfer connection method of the metal sheath is IA1—IB2, IB1—IC2, IC1—IA2.

[0137] In this embodiment, the current amplitude is measured in amperes (A) and the angle is measured in radians.

[0138] In this embodiment, if the number of grounding boxes is 1, and the grounding box type is an insulated joint group heterogeneous grounding box, then the current amplitude of the cable core in the cable body is calculated, and the circulating current of the metal shield of each phase cable is calculated:

[0139] If, on the left side of the connector assembly, the cable body's metal sheath is directly grounded via a lead wire and a non-standard grounding box; and on the right side of the connector assembly, the cable body's metal sheath is protectively grounded via a lead wire and a non-standard grounding box, then:

[0140] Circulation of the metal shielding sheath of the cable on the left side of the connector assembly:

[0141] IAN1=|IA1 IA2| / ;

[0142] IBN1=|IB1 IB2| / ;

[0143] ICN1=|IC1 IC2| / ;

[0144] Circulating current in the metal shielding sheath of the cable on the right side of the connector assembly:

[0145] IAN2=IBN2=ICN2=0;

[0146] If the metal sheath of the cable body on the left side of the joint assembly is grounded via a lead wire and a non-standard grounding box; and the metal sheath of the cable body on the right side of the joint assembly is directly grounded via a lead wire and a non-standard grounding box, then:

[0147] Circulation of the metal shielding sheath of the cable on the left side of the connector assembly:

[0148] IAN1=IBN1=ICN1=0;

[0149] Circulating current in the metal shielding sheath of the cable on the right side of the connector assembly:

[0150] IAN2=|IA1 IA2| / ;

[0151] IBN2=|IB1 IB2| / ;

[0152] ICN2=|IC1 IC2| / ;

[0153] In this embodiment, if the number of grounding boxes is 1, and the grounding box type is a direct grounding box with a straight-through connector group, then the current amplitude of the cable core in the cable body is calculated, and the circulating current of the metal shield of each phase of the cable is calculated:

[0154] To test the circulating current of the cable's metallic shield, it is necessary to test the amplitude of the three-phase grounding lead current of the grounding phase of the cable. Let: the amplitude of the circulating current of the metallic shield of phase A cable on the left side of the joint group be IANL, with an effective value of IAN1, in A; the amplitude of the circulating current of the metallic shield of phase B cable on the left side of the joint group be IBNL, with an effective value of IBN1, in A; the amplitude of the circulating current of the metallic shield of phase C cable on the left side of the joint group be ICNL, with an effective value of ICN1, in A; the amplitude of the circulating current of the metallic shield of phase A cable on the right side of the joint group be IANR, with an effective value of IAN2, in A; the amplitude of the circulating current of the metallic shield of phase B cable on the right side of the joint group be IBNR, with an effective value of IBN2, in A; the amplitude of the circulating current of the metallic shield of phase C cable on the right side of the joint group be ICNR, with an effective value of ICN2, in A.

[0155] The three-phase lead currents of the ground box connected to the metal shield of the connector cable are I11, I12, and I13.

[0156] If |IA1+IB1+IC1|>Ix and |IA2+IB2+IC2|≤Ix, then IANL=I1, IBNL=I2, ICNL=I3;

[0157] If |IA1+IB1+IC1|≤Ix and |IA2+IB2+IC2|>Ix, then IANR=I1, IBNR=I2, ICNR=I3;

[0158] If |IA1+IB1+IC1|≤Ix, and |IA2+IB2+IC2|≤Ix, and MAX{|IA1—IA2|、|IB1—IB2|、|IC1—IC|}≤2×Ic, then the grounding systems on both sides of the test connector are protective grounds. The values ​​of IANL, IANR, IBNL, IBNR, ICNL, and ICNR can be ignored.

[0159] IANL=IBNL=ICNL=IANR=IBNR=ICNR=0;

[0160] If |IA1+IB1+IC1|>Ix, and |IA2+IB2+IC2|>Ix

[0161] Then: Formula (1): IANL IANR=I1;

[0162] Formula (2): IBNL IBNR=I2;

[0163] Formula (3): ICNL ICNR=I3;

[0164] If the influence of unbalanced current in interconnected grounding is ignored, then

[0165] Formula (4): IANL+IBNL+ICNL=0;

[0166] Formula (5): IANR+IBNR+ICNR=0;

[0167] If the three-phase timing is reversed, then:

[0168] Formula (6): (IANL IBNL)×1∠(2×π / 3) (IBNL ICNL)=(IA1 IB1)×1∠(2×π / 3)—(IB1—IC1);

[0169] Formula (7): (IBNL ICNL)×1∠(2×π / 3) (ICNL IANL)=(IC1 IC1)×1∠(2×π / 3) (IC1 IA1);

[0170] Formula (8) (ICNL—IANL)×1∠ (2×π / 3)—(IANL—IBNL)=(IC1—IA1)×1∠ (2×π / 3)—(IA1—IB1);

[0171] If the three-phase timing sequence is in clockwise order, then:

[0172] Formula (9): (IANL—IBNL)×1∠ (—2×π / 3)—(IBNL—ICNL)=(IA1—IB1)×1∠ (—2×π / 3)—(IB1—IC1);

[0173] Formula (10): (IBNL—ICNL)×1∠ (—2×π / 3)—(ICNL—IANL)=(IC1—IC1)×1∠ (—2×π / 3)—(IC1—IA1);

[0174] Formula (11): (ICNL—IANL)×1∠ (—2×π / 3)—(IANL—IBNL)=(IC1—IA1)×1∠ (—2×π / 3)—(IA1—IB1);

[0175] Choose one of the following formulas: (6), (7), (8), (9), (10), (11), and (4), (5). Combine these formulas with (1), (2), and (3) to calculate: IANL, IANR, IBNL, IBNR, ICNL, ICNR.

[0176] but:

[0177] IAN1=|IANL| / IAN2=|IANR| / ;IBN1=|IBNL| / ;

[0178] IBN2=|IBNR| / ;ICN1=|ICNL| / ;ICN2=|ICNR| / ;

[0179] Wherein, I1 is the current of the A-phase connector connected to the grounding box lead, current amplitude in A, and angle in radians; I2 is the current of the B-phase connector connected to the grounding box lead, current amplitude in A, and angle in radians; I3 is the current of the C-phase connector connected to the grounding box lead, current amplitude in A, and angle in radians; IA1, IB1, and IC1 are the current vectors on one side of the cable connector group (e.g., left side), IA2, IB2, and IC2 are the current vectors on the other side of the cable connector group (e.g., right side); IA1 is the current vector of the A-phase cable tested on one side of the connector group, current amplitude in A, and angle in radians; IA2 is the current vector of the other side of the connector group... The current vector and amplitude of the A-phase cable on one side of the joint group are measured in A, and the angle is measured in radians. IB1 is the current vector and amplitude of the B-phase cable on one side of the joint group, measured in A, and the angle is measured in radians. IB2 is the current vector and amplitude of the B-phase cable on the other side of the joint group, measured in A, and the angle is measured in radians. IC1 is the current vector and amplitude of the C-phase cable on one side of the joint group, measured in A, and the angle is measured in radians. IC2 is the current vector and amplitude of the C-phase cable on one side of the joint group, measured in A, and the angle is measured in radians. Ic is the maximum capacitive current amplitude of the longest section of the cable grounding system in the line, measured in A.

[0180] In this embodiment, if the number of grounding boxes is 2 and the grounding box type is the protective grounding box of the insulated joint group, then no test is required. The circulating current of the cable metal shield on both sides of the joint group is determined as follows: IAN1=IBN1=ICN1=0; IA2N=IBN2=ICN2=0.

[0181] In this embodiment, if the number of grounding boxes is 2, and both grounding boxes are direct grounding boxes with insulated joint groups, then the current amplitude of the cable core is calculated, and the circulating current of the metal shield of each phase of the cable is calculated:

[0182] The testing equipment has six current transformers installed on the grounding lead of the cable grounding box connected to the cable grounding box to directly test and obtain the circulating current of the cable metal shield on both sides of the joint.

[0183] The three-phase lead currents of the ground box connected to the metal shield of the cable on the left side of the connector group are I11, I12, and I13.

[0184] The three-phase lead currents of the ground box connected to the metal shield of the cable on the right side of the connector group are I21, I22, and I23.

[0185] Then: IAN1 = |I11| / ;IBN1=|I12| / ;ICN1=|I13| / ;

[0186] IAN2=|I21| / ;IBN2=|I22| / ;ICN2=|I23| /

[0187] Wherein, I11 represents the current of the A-phase connector connected to the grounding box at the cable metal shield on the left side of the connector group, with the current amplitude in A and the angle in radians; I12 represents the current of the B-phase connector connected to the grounding box at the cable metal shield on the left side of the connector group, with the current amplitude in A and the angle in radians; I13 represents the current of the C-phase connector connected to the grounding box at the cable metal shield on the left side of the connector group, with the current amplitude in A and the angle in radians; I21 represents the current of the A-phase connector connected to the grounding box at the cable metal shield on the right side of the connector group, with the current amplitude in A and the angle in radians; I22 represents the current of the B-phase connector connected to the grounding box at the cable metal shield on the right side of the connector group, with the current amplitude in A and the angle in radians; I23 represents the current of the C-phase connector connected to the grounding box at the cable metal shield on the right side of the connector group, with the current amplitude in A and the angle in radians.

[0188] In this embodiment, if the number of grounding boxes is 2, and the grounding box type is one direct grounding box with an insulating joint group and the other protective grounding box with an insulating joint group, then the calculation method is the same as the method for grounding box type metal shielding for 1 grounding box and is a heterogeneous grounding box with an insulating joint group.

[0189] The beneficial effects of the above technical solution are as follows: Based on the cable amplitude-phase data, the number of grounding boxes, the grounding box method, and the metal sheath method connected to the grounding box, the circulating current data of the metal sheath of the cable connected to the grounding box can be calculated. This enables accurate derivation of the conductor current amplitude and sheath circulating current data under different configurations, ensuring the continuity of detection, improving the matching degree between the data and the actual working conditions, and enhancing the accuracy of live-line detection.

[0190] Example 6:

[0191] This invention provides a method for evaluating cable shielding defects while energized, assessing the circulating current operating status of the cable's metallic sheath, and determining whether defects exist in the metallic shielding or abnormal grounding of the grounding lead, including:

[0192] To assess the circulating current status of the cable's metal sheath, the circulating current data of the metal shield of the same branch tested by the grounding box is used to determine whether there are any abnormal grounding defects in the metal shield or the grounding lead.

[0193] If the metal sheath connected to the grounding box is single-ended grounded, then:

[0194] |ILA1—ILA2|≥MAX{2×π×F×U0×C0×L× The defect is identified as an abnormal grounding fault in the metal sheath of phase A branch.

[0195] |ILB1—ILB2|≥MAX{2×π×F×U0×C0×L× Ix} was determined to be an abnormal grounding defect in the metal sheath of phase B branch;

[0196] |ILC1—ILC2|≥MAX{2×π×F×U0×C0×L× The defect was identified as an abnormal grounding fault in the metal sheath of the C-phase branch.

[0197] If the metal sheath connected to the grounding box is a cross-transposed grounding, then:

[0198] |ILA1—ILA2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of phase A branch;

[0199] |ILB1—ILB2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of phase B branch;

[0200] |ILC1—ILC2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of the C-phase branch;

[0201] Wherein, ILA1 is the circulating current at the beginning of the metal-shielded branch of phase A; ILA2 is the circulating current at the end of the metal-shielded branch of phase A; ILB1 is the circulating current at the beginning of the metal-shielded branch of phase B; ILB2 is the circulating current at the end of the metal-shielded branch of phase B; ILC1 is the circulating current at the beginning of the metal-shielded branch of phase C; ILC2 is the circulating current at the end of the metal-shielded branch of phase C; F is the power frequency; U0 is the rated operating voltage of the cable; C0 is the induced capacitance per unit length of the cable line; L is the length of the metal sheath of the cable connected to the grounding box.

[0202] In this embodiment, corresponding judgment conditions are set according to different grounding methods (single-end grounding or cross-transposed grounding), and the presence of defects in a phase is determined by comparing the circulating current differences at the beginning and end of the same branch.

[0203] In this embodiment, the units of ILA1, ILA2, ILB1, ILB2, ILC1, and ILC2 are all A.

[0204] In this embodiment, the unit of the power frequency F is Hz, which is generally 50Hz or 60Hz.

[0205] In this embodiment, the rated operating voltage U0 of the cable is in V.

[0206] In this embodiment, the inductive capacitance C0 per unit length of the cable line is in μF.

[0207] In this embodiment, the length L of the metal sheath of the cable connected to the grounding box is in meters.

[0208] The beneficial effects of the above technical solution are: to assess the circulating current operation status of the cable's metal sheath, to determine whether there are abnormal grounding defects in the metal shielding or grounding leads, to achieve accurate defect identification, to improve the detection accuracy of abnormal defects in the metal shielding and grounding leads under different grounding methods, and to provide scientific and quantitative criteria for live-line testing.

[0209] Example 7:

[0210] This invention provides a method for live-line testing of cable shielding defects, and for pinpointing the defects in the metal sheath of cables with grounding defects, including:

[0211] For defective metal segments, the induced current of the cable body is obtained by using a binary method or by testing each segment simultaneously, namely ILi at the beginning and IRi at the end. The current magnitudes are compared. If the currents are equal, the defect is not in the test segment. If the currents are not equal, the defect is in the segment. The above process is repeated to narrow down the test range until the defect is accurately located.

[0212] In this embodiment, the bisection method test is used: the L / 2 segment where the defect is located is determined; the circulating current data of the beginning, middle and end of the L segment are tested, where the current of the middle 1 / 2 segment is I(1 / 2), the current of the beginning segment is IL(0), and the current of the short tail is IL(1). If |I(1 / 2)-Iy|<Ix, then the defect is not in the segment from 1 / 2×L to y×L; if |I(1 / 2)-Iy|≥Ix, then the defect is in the segment from 1 / 2×L to y×L. Where y is the ratio of the beginning and the short tail of the test segment, which is dimensionless; Ix is the maximum current amplitude caused by the error of the transformer and the interference on site, in A. For example, if y=1, if |I(1 / 2)-I1|<Ix, then the defect is not in the segment from 1 / 2×L to 1×L; if |I(1 / 2)-I1|≥Ix, then the defect is in the segment from 1 / 2×L to 1×L. Repeat the above process to test the circulating current data at the beginning, middle and end of the L / 2, L / 4, ... section where the defect is located. By comparing the current data of I(1 / 4), I(1 / 8), I(1 / 16) ... until it is less than the smallest segment LW that can be identified by the naked eye, the defect can be located.

[0213] In this embodiment, the test is performed segment by segment: First, the test segment L is divided into the smallest segment LW that is visually identifiable for defects, resulting in a total of n segments = L / LW. Second, the current data of the first, second, ..., k, k+1, ..., n-1 segments, and the first and last segments are tested and obtained respectively. The first current IkL and the last current IkR of the k-th segment are obtained. Third, IkL and IkR are compared. If |IkL-IkR| < Ix, the defect is not in the k-th segment; if |InL-InR| ≥ Ix, the defect is in the k-th segment. Here, Ix is the maximum current amplitude caused by transformer error and field interference during the field test, in A. InL is the current at the beginning of the n-th segment, in A; InR is the current at the end of the n-th segment, in A.

[0214] The beneficial effects of the above technical solution are as follows: it can pinpoint the defects in the metal sheath of cables with grounding defects, which can overcome the limitations of traditional reliance on experience or large-scale inspection, improve the efficiency and accuracy of defect location, and is applicable to long-distance cables or complex wiring scenarios. It realizes the efficient transformation from the existence of defects to precise location, and provides a clear target for live maintenance.

[0215] Example 8:

[0216] This invention provides an apparatus for live testing of cable shielding defects, used to perform any one of the methods for live testing of cable shielding defects according to claims 1 to 7.

[0217] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0218] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0219] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating cable shielding defects while the cable is energized, characterized in that, include: Step 1: Install current transformers on both sides of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be detected, determine the cable amplitude-phase data, and obtain the number of grounding boxes and the number of grounding leads at the location where the cable shielding defect is to be detected. Step 2: Based on the cable amplitude-phase data and the number of grounding boxes at the locations where cable shielding defects need to be detected, determine the grounding box type; based on the grounding box type and the number of grounding boxes, calculate the metal sheath type connected to the grounding box. Step 3: Based on the cable amplitude-phase data, the number of grounding boxes, the type of grounding box, and the type of metal sheath connected to the grounding box, calculate the circulating current data of the metal sheath of the cable connected to the grounding box; Step 4: Analyze the circulating current operation status of the cable metal sheath, determine whether there are any defects in the metal shielding or abnormal grounding of the grounding lead, and pinpoint the defects in the cable metal sheath with grounding defects.

2. The method for evaluating cable shielding defects under live conditions according to claim 1, characterized in that, Current transformers are installed on both sides of the cable joint group connected to the cable grounding box at the location where cable shielding defects are to be detected, to determine the cable amplitude-phase data, including: The three current transformers of the testing equipment are installed on one side of the three-phase cable body of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be tested. The other three current transformers of the testing equipment are installed on the other side of the three-phase cable body of the cable joint group connected to the cable grounding box at the location where the cable shielding defect is to be tested, based on the same direction as the three current transformers already installed on one side. Based on three current transformers installed on one side of the three-phase cable body of the cable joint group, the current amplitude and phase of one side of the three-phase cable body of the cable joint group are recorded. At the same time, based on three current transformers installed on the other side of the three-phase cable body of the cable joint group, the current amplitude and phase of the other side of the three-phase cable body of the cable joint group are recorded. Based on the current amplitude and phase of one side of the three-phase cable body on one side of the cable joint assembly, and the current amplitude and phase of the other side of the three-phase cable body on the other side of the cable joint assembly, the cable amplitude-phase data is determined.

3. The method for evaluating cable shielding defects under live conditions according to claim 2, characterized in that, Based on the cable amplitude-phase data and the number of grounding boxes at the locations of cable shielding defects to be inspected, the grounding box type is determined, including: The grounding box type is determined based on the number of grounding boxes at the location to be tested for cable shielding defects, the current amplitude and phase on one side of the three-phase cable body on one side of the cable joint group, and the current amplitude and phase on the other side of the three-phase cable body on the other side of the cable joint group. ； ； ； ； ； ； ； ； ； ； ； ； ； in, Indicates the grounding box method. These represent the first, second, third, fourth, fifth, and sixth sub-grounding box configurations, respectively. This indicates the number of grounding boxes. Ix represents the maximum current amplitude caused by transformer errors and field interference during on-site testing. IA1, IB1, and IC1 represent the current vectors of phases A, B, and C on one side of the cable joint group, respectively. IA2, IB2, and IC2 represent the current vectors of phases A, B, and C on the other side of the cable joint group, respectively. IF1 represents the amplitude of the current vector value of the three-phase current transformer on one side of the cable joint group. IF2 represents the amplitude of the current vector value of the three-phase current transformer on the other side of the cable joint group. IF represents the difference between the amplitudes of the three-phase current transformer current vector values ​​of the cable body on one side of the cable joint group and the amplitudes of the three-phase current transformer current vector values ​​of the cable body on the other side of the joint group. This represents the magnitude of the maximum three-phase current transformer current vector value in the cable joint assembly. This represents the amplitude of the smallest three-phase current transformer current vector value in the cable joint group. The first index representing the current vector on both sides of the cable joint assembly. The second index represents the current vector on both sides of the cable joint assembly.

4. The method for evaluating cable shielding defects under live conditions according to claim 3, characterized in that, Based on the type and number of grounding boxes, calculate the type of metal sheath connected to the grounding box, including: If the number of grounding boxes is 1, and the grounding box type is a cross-transposed grounding box of an insulated joint group, then calculate the third and fourth indices of the current vectors on both sides of the cable joint group. ； ； in, The third and fourth indices of the current vectors on both sides of the cable joint assembly, respectively; Compare the third and fourth indices of the current vectors on both sides of the cable joint group. If the third index is less than the fourth index, the cross-transfer connection method of the metal sheath is IA1—IB2, IB1—IC2, IC1—IA2. If the third index is greater than the fourth index, the cross-transfer connection method of the metal sheath is IA1—IC2, IB1—IA2, IC1—IB2. If the number of grounding boxes is 1, and the grounding box type is a heterogeneous grounding box with insulated joint group, and the judgment logic is... Then determine whether it is a single-end grounding system or a cross-transposition system on both sides of the connector. The metal sheath of the cable body on the left side of the connector assembly is grounded through a lead wire and a heterogeneous grounding box; the metal sheath of the cable body on the right side of the connector assembly is directly grounded through a lead wire and a heterogeneous grounding box. If the metal sheath of the cable body on the left side of the connector is directly grounded through a lead wire and a heterogeneous grounding box, the metal sheath of the cable body on the left side of the connector group is protected by a lead wire and a heterogeneous grounding box; the metal sheath of the cable body on the right side of the connector is protected by a lead wire and a heterogeneous grounding box. If the number of grounding boxes is 1, and the grounding box type is a heterogeneous grounding box with insulated joint group, and the judgment logic is... If the connection is a single-ended grounding system on both sides, then it is determined that both sides of the connection are single-ended grounding systems. | Then, the metal sheath of the cable body on the left side of the connector group is grounded through a lead wire and directly to the grounding box; the metal sheath of the cable body on the right side of the connector group is grounded through a lead wire and a protective grounding box. | Then the metal sheath of the cable body on the right side of the connector group is grounded through the lead wire and the protective grounding box; If the number of grounding boxes is 1, and the grounding box type is a direct grounding box with a straight-through connector group, then the connectors on both sides of each phase of the cable, the metal sheath of the cable body, are directly connected and grounded through the grounding lead and the direct grounding box. If the two sides of the connector are determined to be a cross-transposed grounding system, then... If so, it can be determined that the two sides of the connector are a single-ended grounding system; If the number of grounding boxes is 2, the grounding box type is an insulated joint group and both sides are protective grounding boxes, then the metal sheath of the cable body on both sides of the cable joint of each phase is insulated. If there are two grounding boxes, and the grounding box type is an insulated joint group with direct grounding boxes on both sides, then the metal sheath insulation of the cable body on both sides of the cable joints of each phase is all grounded through a direct grounding box. Then the two sides of the connector are a cross-transposed grounding system. Then the two sides of the connector are a single-ended grounding system; If the number of grounding boxes is 2, and the grounding box configuration is such that one side of the insulating joint group is a direct grounding box and the other side is a protective grounding box, and the judgment logic is as follows: ,like If the metal sheath of the cable body on the left side of the joint assembly is grounded through a lead wire and directly to the grounding box, and the metal sheath of the cable body on the right side of the joint assembly is grounded through a lead wire and a protective grounding box, then... The metal sheath of the cable body on the left side of the connector group is grounded through a lead wire and a protective grounding box; the metal sheath of the cable body on the right side of the connector group is grounded through a lead wire and a direct grounding box. If the number of grounding boxes is 2, and the grounding box configuration is such that one side of the insulating joint group is a direct grounding box and the other side is a protective grounding box, and the judgment logic is as follows: ,like The metal sheath of the cable body on the left side of the connector assembly is grounded directly to the grounding box via a lead wire; the metal sheath of the cable body on the right side of the connector assembly is grounded via a protective grounding box via a lead wire. The metal sheath of the cable body on the right side of the connector group is grounded through the lead wire and the protective grounding box.

5. The method for evaluating cable shielding defects under live conditions according to claim 4, characterized in that, Based on cable amplitude-phase data, the number of grounding boxes, the type of grounding box, and the type of metal sheath connected to the grounding box, calculate the circulating current data of the metal sheath of the cable connected to the grounding box, including: Based on the number of grounding boxes, the type of grounding boxes, and the type of metal sheath connected to the grounding boxes, calculate the current amplitude of the cable core for each type of grounding box and the number of grounding boxes, and calculate the circulating current data of the metal sheath connected to each type of grounding box.

6. The method for evaluating cable shielding defects under live conditions according to claim 5, characterized in that, Assess the circulating current status of the cable's metal sheath and determine if there are any defects in the metal shielding or abnormal grounding of the grounding leads, including: To assess the circulating current status of the cable's metal sheath, the circulating current data of the metal shield of the same branch tested by the grounding box is used to determine whether there are any abnormal grounding defects in the metal shield or the grounding lead. If the metal sheath connected to the grounding box is single-ended grounded, then: |ILA1—ILA2|≥MAX{2×π×F×U0×C0×L× The defect is identified as an abnormal grounding fault in the metal sheath of phase A branch. |ILB1—ILB2|≥MAX{2×π×F×U0×C0×L× Ix} was determined to be an abnormal grounding defect in the metal sheath of phase B branch; |ILC1—ILC2|≥MAX{2×π×F×U0×C0×L× The defect was identified as an abnormal grounding fault in the metal sheath of the C-phase branch. If the metal sheath connected to the grounding box is a cross-transposed grounding, then: |ILA1—ILA2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of phase A branch; |ILB1—ILB2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of phase B branch; |ILC1—ILC2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, is judged to be an abnormal grounding defect in the metal sheath of the C-phase branch; Wherein, ILA1 is the circulating current at the beginning of the metal-shielded branch of phase A; ILA2 is the circulating current at the end of the metal-shielded branch of phase A; ILB1 is the circulating current at the beginning of the metal-shielded branch of phase B; ILB2 is the circulating current at the end of the metal-shielded branch of phase B; ILC1 is the circulating current at the beginning of the metal-shielded branch of phase C; ILC2 is the circulating current at the end of the metal-shielded branch of phase C; F is the power frequency; U0 is the rated operating voltage of the cable; C0 is the induced capacitance per unit length of the cable line; L is the length of the metal sheath of the cable connected to the grounding box.

7. The method for evaluating cable shielding defects under live conditions according to claim 6, characterized in that, And pinpoint the defects in the metal sheath of cables with grounding defects, including: For defective metal segments, the induced current of the cable body is obtained by using a binary method or by testing each segment simultaneously, namely ILi at the beginning and IRi at the end. The current magnitudes are compared. If the currents are equal, the defect is not in the test segment. If the currents are not equal, the defect is in the segment. The above process is repeated to narrow down the test range until the defect is accurately located.

8. A device for evaluating cable shielding defects while energized, characterized in that, The method for performing any one of claims 1 to 7 to evaluate cable shielding defects while energized.

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