Method and device for evaluating shielding defect of cable in electrified manner

Abstract

The invention provides a method and device for live evaluation of cable shielding defects, and belongs to the technical field of cable testing, and the method comprises the steps: installing a current transformer, determining the amplitude-phase data of a cable, and obtaining the number of grounding boxes and the number of grounding leads at a to-be-detected position of the cable shielding defects; determining a grounding box mode, and calculating a mode of a metal sheath connected with the grounding box; calculating circulation data of a cable metal sheath connected with the grounding box; and studying and judging the circulation running state of the cable metal sheath, studying and judging whether metal shielding and grounding lead abnormal grounding defects exist or not, and carrying out defect positioning on the cable metal sheath with the grounding defects. On the premise that equipment is not disassembled, detection efficiency and accuracy can be improved, potential hazards can be found in time, continuity and accuracy of live detection are guaranteed, the matching degree of data and actual working conditions is improved, safe and stable operation of a cable is guaranteed, and powerful support is provided for reliable power supply of a power system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cable testing, in particular to a method and device for testing and evaluating cable shielding defects under power. BACKGROUND

[0002] The existing cable shielding defect detection has long relied on traditional means, which has obvious limitations. Historically, detection often needs to be performed with power off, such as measuring insulation resistance by disconnecting the shielding layer ground or using a partial discharge detector to troubleshoot accessory faults, but power interruption occurs when power is off, and only during the equipment downtime window. In the current mainstream methods, time domain reflectometry is not sensitive to defects with weak impedance changes, infrared thermography can only detect heating faults, and ultra-low frequency dielectric loss testing focuses on overall insulation evaluation, which cannot accurately locate hidden defects such as metal shielding layer breakage and loose grounding leads under power. At the same time, there is a lack of effective quantitative analysis means for abnormal circulation in the cross-connection grounding system, which often leads to fault expansion due to missed detection, and there is an urgent need for a technical solution that can detect under power, comprehensively and accurately.

[0003] Therefore, the present application provides a method and device for testing and evaluating cable shielding defects under power. SUMMARY

[0004] The present application provides a method and device for testing and evaluating cable shielding defects under power, which determines the cable amplitude-phase data by installing a current transformer, obtains the number of grounding boxes and the number of grounding leads at the position to be detected for cable shielding defects, determines the grounding box mode, calculates the circulation data of the metal sheath connected to the grounding box and the metal sheath of the cable connected to the grounding box, judges the running state of the cable metal sheath circulation, judges whether there is an abnormal grounding defect of the metal shielding and grounding lead, and locates the defect of the cable metal sheath with the grounding defect. The detection efficiency and accuracy can be improved without disassembling the equipment, potential hazards can be found in time, the continuity and accuracy of the live detection can be ensured, the matching degree of data and actual working conditions can be improved, and the safe and stable operation of the cable can be ensured, which provides strong support for reliable power supply of the power system.

[0005] In one aspect, the present application provides a method for testing and evaluating cable shielding defects under power, comprising: Step 1: Install current transformers on both sides of the cable joint group connected to the cable grounding box at the position to be detected for cable shielding defects, determine the cable amplitude-phase data, and obtain the number of grounding boxes and the number of grounding leads at the position to be detected for cable shielding defects; Step 2: Determine the grounding box mode based on the cable amplitude-phase data and the number of grounding boxes at the position to be detected for cable shielding defects, and calculate the metal sheath mode connected to the grounding box based on the grounding box mode and the number of grounding boxes; Step 3: Based on the cable amplitude-phase data, the number of grounding boxes, the grounding box mode, and the grounding box connected metal sheath mode, the circulating current data of the cable metal sheath connected to the grounding box is calculated; Step 4: The running state of the cable metal sheath circulating current is analyzed, whether there is an abnormal grounding defect of the metal shield and grounding lead is analyzed, and the defect of the cable metal sheath with grounding defect is located.

[0006] According to the method for measuring and evaluating the cable shielding defect provided by the application, current transformers are installed on both sides of the cable joint group connected to the cable grounding box at the position to be detected of the cable shielding defect, and the cable amplitude-phase data is determined, including: Three current transformers of the detection 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 position to be detected of the cable shielding defect; Based on the same direction as the three current transformers installed on one side, the other three current transformers of the detection 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 position to be detected of the cable shielding defect; Based on the three current transformers installed on one side of the three-phase cable body of the cable joint group, the one-side current amplitude and one-side phase of one side of the three-phase cable body of the cable joint group are recorded, and based on the three current transformers installed on the other side of the three-phase cable body of the cable joint group, the other-side current amplitude and other-side phase of the other side of the three-phase cable body of the cable joint group are recorded; Based on the one-side current amplitude and one-side phase of one side of the three-phase cable body of the cable joint group, and the other-side current amplitude and other-side phase of the other side of the three-phase cable body of the cable joint group, the cable amplitude-phase data is determined.

[0007] According to the method for measuring and evaluating the cable shielding defect provided by the application, based on the cable amplitude-phase data and the number of grounding boxes at the position to be detected of the cable shielding defect, the grounding box mode is determined, including: Based on the number of grounding boxes at the position to be detected of the cable shielding defect, the one-side current amplitude and one-side phase of one side of the three-phase cable body of the cable joint group, and the other-side current amplitude and other-side phase of the other side of the three-phase cable body of the cable joint group, the grounding box mode is determined; ; ; ; ; ; ; ; ; ; ; ; ; ; wherein, represents a grounding box mode, respectively represent a first sub-grounding box mode, a second sub-grounding box mode, a third sub-grounding box mode, a fourth sub-grounding box mode, a fifth sub-grounding box mode, a sixth sub-grounding box mode, represents a grounding box number, Ix represents a maximum current amplitude caused by mutual inductor error and field interference, IA1, IB1, IC1 respectively represent A-phase, B-phase, C-phase cable test current vectors on one side of a cable joint group, IA2, IB2, IC2 respectively represent A-phase, B-phase, C-phase cable test current vectors on the other side of the cable joint group, IF1 represents an amplitude of a 3-phase current inductor current vector value on one side of the cable joint group, IF2 represents an amplitude of a 3-phase current inductor current vector value on the other side of the cable joint group, and IF represents a difference between the amplitude of the 3-phase current inductor current vector value of the cable body on one side of the cable joint group and the amplitude of the 3-phase current inductor current vector value of the cable body on the other side of the cable joint group, represents a maximum 3-phase current inductor current vector value amplitude of the cable joint group, represents a minimum 3-phase current inductor current vector value amplitude of the cable joint group, represents a first index of the current vectors on both sides of the cable joint group, represents a second index of the current vectors on both sides of the cable joint group.

[0008] According to the method for measuring and evaluating cable shielding defects provided by the application, the metal sheath mode connected to the grounding box is calculated based on the grounding box mode and the grounding box number, and the method comprises the following steps: If the grounding box number is 1 and the grounding box mode is a cross transposition grounding box of an insulation joint group, a third index and a fourth index of the current vectors on both sides of the cable joint group are calculated; ; ; wherein, respectively represent the third index and the fourth index of the current vectors on both sides of the cable joint group; The third index and the fourth index of the current vectors on both sides of the cable joint group are compared, if the third index is less than the fourth index, the metal sheath cross transposition connection mode is IA1-IB2, IB1-IC2, IC1-IA2, if the third index is greater than the fourth index, the metal sheath cross transposition connection mode is IA1-IC2, IB1-IA2, IC1-IB2; If the number of grounding boxes is 1, and the grounding box mode is a heterogeneous grounding box of the insulation joint group, and the judgment logic is , the single-ended grounding system and the cross transposition system on both sides of the joint are judged, if , the cable body metal sheath on the left side of the joint group is grounded through the lead wire and the heterogeneous grounding box; the cable body metal sheath on the right side of the joint is directly grounded through the lead wire and the heterogeneous grounding box, if , the cable body metal sheath on the left side of the joint is directly grounded through the lead wire and the heterogeneous grounding box; the cable body metal sheath on the left side of the joint group is grounded through the lead wire and the heterogeneous grounding box; the cable body metal sheath on the right side of the joint is grounded through the lead wire and the heterogeneous grounding box; If the number of grounding boxes is 1, and the grounding box mode is a heterogeneous grounding box of the insulation joint group, and the judgment logic is , it is judged that both sides of the joint are single-ended grounding systems, if , the cable body metal sheath on the left side of the joint group is grounded through the lead wire and the direct grounding box; the cable body metal sheath on the right side of the joint group is grounded through the lead wire and the protection grounding box, if , the cable body metal sheath on the right side of the joint group is grounded through the lead wire and the protection grounding box; If the number of grounding boxes is 1, and the grounding box mode is a direct grounding box of the straight-through joint group, the cable body metal sheaths on both sides of the joint cable of each phase of the cable are directly connected and grounded through the grounding lead wire and the direct grounding box, if , it is judged that both sides of the joint are cross transposition grounding systems, if , it is judged that both sides of the joint are single-ended grounding systems; If the number of grounding boxes is 2, the grounding box mode is an insulation joint group, and both sides are protection grounding boxes, the cable body metal sheaths on both sides of the joint cable of each phase of the cable are insulated; If the number of grounding boxes is 2, the grounding box mode is an insulation joint group, and both sides are direct grounding boxes, the cable body metal sheaths on both sides of the joint cable of each phase of the cable are insulated and grounded through the direct grounding box, if , both sides of the joint are cross transposition grounding systems, if , both sides of the joint are single-ended grounding systems; If the number of grounding boxes is 2, the grounding box mode is an insulation joint group, one side is a direct grounding box, and one side is a protection grounding box, and the judgment logic is , if If the judgment logic is 0, the left cable body metal sheath of the joint group is grounded through the lead and the direct grounding box, and the right cable body metal sheath of the joint group is grounded through the lead and the protection grounding box. If the judgment logic is 1, the left cable body metal sheath of the joint group is grounded through the lead and the protection grounding box, and the right cable body metal sheath of the joint group is grounded through the lead and the direct grounding box. If the number of grounding boxes is 2, the grounding box mode is that one side of the insulation joint group is the direct grounding box and the other side is the protection grounding box, and the judgment logic is 0, then: If the judgment logic is 0, the left cable body metal sheath of the joint group is grounded through the lead and the direct grounding box, and the right cable body metal sheath of the joint group is grounded through the lead and the protection grounding box. If the judgment logic is 1, the left cable body metal sheath of the joint group is grounded through the lead and the protection grounding box, and the right cable body metal sheath of the joint group is grounded through the lead and the direct grounding box. If the judgment logic is 1, the right cable body metal sheath of the joint group is grounded through the lead and the protection grounding box.

[0009] According to the method for measuring and evaluating cable shielding defects provided by the application, the loop current data of the metal sheath connected to the grounding box of the cable is calculated based on the cable amplitude-phase data, the number of grounding boxes, the grounding box mode and the metal sheath mode connected to the grounding box, and the method comprises the following steps: Based on the number of grounding boxes, the grounding box mode and the metal sheath mode connected to the grounding box, the cable core current amplitude of each grounding box number and each grounding box mode is calculated respectively, and the loop current data of the metal sheath connected to each grounding box number and each grounding box mode is calculated respectively.

[0010] According to the method for measuring and evaluating cable shielding defects provided by the application, the running state of the metal sheath loop current of the cable is analyzed, and whether there is an abnormal grounding defect of the metal shielding and grounding lead is analyzed, which comprises the following steps: The running state of the metal sheath loop current of the cable is analyzed, and whether there is an abnormal grounding defect of the metal shielding and grounding lead is analyzed based on the same branch metal shielding loop current data tested by the grounding box. If the metal sheath connected to the grounding box is single-ended grounding, then: If the metal sheath connected to the grounding box is single-ended grounding, then: If the metal sheath connected to the grounding box is single-ended grounding, then: If the metal sheath connected to the grounding box is single-ended grounding, then: If the metal sheath connected to the grounding box is single-ended grounding, then: If the metal sheath connected to the grounding box is single-ended grounding, then: If the metal sheath connected to the grounding box is single-ended grounding, then: If the metal sheath connected to the grounding box is single-ended grounding, then: |ILA1—ILA2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, judge as A phase branch metal sheath abnormal ground fault; |ILB1—ILB2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, judge as B phase branch metal sheath abnormal ground fault; |ILC1—ILC2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, judge as C phase branch metal sheath abnormal ground fault; Wherein, ILA1 is the ring current of the first end of the A phase metal shielding branch; ILA2 is the ring current of the end of the A phase metal shielding branch; ILB1 is the ring current of the first end of the B phase metal shielding branch; ILB2 is the ring current of the end of the B phase metal shielding branch; ILC1 is the ring current of the first end of the C phase metal shielding branch; ILC2 is the ring current of the end of the C phase metal shielding branch; F is the power frequency; U0 is the rated operating voltage of the cable; C0 is the unit length inductance capacitance of the cable; and L is the length of the metal sheath connected to the grounding box.

[0011] According to the method for evaluating the shielding defects of the cable under electricity provided by the application, the metal sheath of the cable with the grounding defect is pinpointed, and the method comprises the following steps: For the metal segment with the defect, the inductance current of the cable body is obtained by using the dichotomy or the step-by-step simultaneous test, and the inductance current is respectively ILi at the first end and IRi at the end; the current sizes 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 the test range until the defect is pinpointed accurately.

[0012] On the other hand, the application further provides a method and device for evaluating the shielding defects of the cable under electricity, which is used to execute any one of the methods for evaluating the shielding defects of the cable under electricity in embodiments 1 to 7.

[0013] Compared with the prior art, the application has the following beneficial effects: By installing the current transformer, the cable amplitude-phase data is determined, the number of grounding boxes and the number of grounding leads of the shielding defect of the cable to be detected are obtained, the grounding box mode is determined, the metal sheath mode connected to the grounding box and the ring current data of the metal sheath of the cable connected to the grounding box are calculated, the running state of the metal sheath ring current of the cable is analyzed, it is analyzed whether there is an abnormal grounding defect of the metal shielding and the grounding lead, and the metal sheath of the cable with the grounding defect is pinpointed. The detection efficiency and accuracy can be improved without disassembling the equipment, potential hazards can be found in time, the continuity and accuracy of the live detection can be ensured, the matching degree of the data and the actual working condition can be improved, and the safe and stable operation of the cable can be ensured, which provides strong support for reliable power supply of the power system. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a flowchart of a method for evaluating cable shielding defects with electric charge provided by an embodiment of the present application. DETAILED DESCRIPTION

[0015] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below with reference to the drawings in the present application. Obviously, the described embodiments are some embodiments of the present application, but not all embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0016] Embodiment 1 An embodiment of the present application provides a method for evaluating cable shielding defects with electric charge, as shown in the following figure, which comprises the following steps. Figure 1 Step 1: Install current transformers on both sides of a cable joint group connected to a cable grounding box at a position to be detected of a cable shielding defect, determine cable amplitude-phase data, and obtain the number of grounding boxes and the number of grounding leads at the position to be detected of the cable shielding defect. Step 2: Determine the grounding box mode based on the cable amplitude-phase data and the number of grounding boxes at the position to be detected of the cable shielding defect, and calculate the metal sheath mode connected to the grounding box based on the grounding box mode and the number of grounding boxes. Step 3: Calculate the circulating current data of the cable metal sheath connected to the grounding box based on the cable amplitude-phase data, the number of grounding boxes, the grounding box mode and the metal sheath mode connected to the grounding box. Step 4: Judge the running state of the cable metal sheath circulating current, judge whether there is an abnormal grounding defect of the metal shielding and grounding lead, and perform defect pinpointing on the cable metal sheath with the grounding defect.

[0017] In this embodiment, the grounding box is used for grounding treatment of the cable metal sheath (shielding layer) to avoid excessive sheath induced voltage.

[0018] ​In this embodiment, the metal sheath circulating current live test master control device can be realized by two ways: way one: one is including 2 channel data acquisition, through the relay switching switch to realize the input signal switching, specifically 6 channel input, 2 channel output switching switch module, 2 channel filter unit module, 2 channel amplification unit module, 2 channel analog-digital conversion unit module, 2 channel data acquisition unit module, vector operation and control unit module, machine display unit module and power module are composed. Further, adopting way one, the input end of the six channel input, two channel output switching switch module is connected with 6CT, the output end is connected with 2 channel filter unit module, the input signal of 6CT is realized, and the signal of 6CT is sequentially output to 2 channel filter unit module. The two channel filter unit is used for outputting the signal input by the node switching switch to the two channel amplification unit module after filtering. The two channel amplification unit module is used for receiving the signal output by the two channel filter unit and amplifying the signal and transmitting the signal to the two channel analog-digital conversion unit module. The two channel analog-digital conversion unit module is used for converting the signal output by the two channel signal amplification module from analog signal to digital signal and transmitting the digital signal to the two channel signal acquisition unit module. The two channel signal acquisition module is used for collecting, recording and storing the digital signal transmitted by the two channel analog-digital conversion unit module. The vector operation and control unit module is used for correcting the amplitude and phase angle of the collected and recorded current vector, calculating and controlling the signal acquisition and operation. The machine display unit module is used for displaying the results of the acquisition and operation. The power module is used for power supply of the metal sheath circulating current live test master control device.

[0019] Way two: one is including six channel data acquisition, through six channel filter unit module, six channel amplification unit module, six channel analog-digital conversion unit module, six channel data acquisition unit module, vector operation and control unit module, machine display unit module and power module are composed. Further, adopting way two, the six channel filter unit is used for outputting the signal input by the node switching switch to the six channel amplification unit module after filtering. The six channel amplification unit module is used for receiving the signal output by the six channel filter unit and amplifying the signal and transmitting the signal to the six channel analog-digital conversion unit module. The six channel analog-digital conversion unit module is used for converting the signal output by the six channel signal amplification module from analog signal to digital signal and transmitting the digital signal to the six channel signal acquisition unit module. The six channel signal acquisition module is used for collecting, recording and storing the digital signal transmitted by the six channel analog-digital conversion unit module. The vector operation and control unit module is used for calculating and controlling the signal acquisition and operation of the collected and recorded current vector. The machine display unit module is used for displaying the results of the acquisition and operation. The power module is used for power supply of the metal sheath circulating current live test master control device. The measurement CT is marked with direction, and the signal is independently acquired.

[0020] The beneficial effects of the above technical scheme are as follows: the current transformers are installed to determine the cable amplitude-phase data, the number of grounding boxes and the number of grounding leads of the cable shielding defect to be detected are obtained, the grounding box mode is determined, the circulating current data of the metal sheath connected by the grounding box and the metal sheath of the cable connected by the grounding box are calculated, the running state of the metal sheath circulating current of the cable is judged, whether the metal shielding and the abnormal grounding defect of the grounding lead exist are judged, and the defect of the cable metal sheath with the grounding defect is determined. 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 can be ensured, the matching degree of data and actual working conditions can be improved, the safe and stable operation of the cable can be ensured, and strong support can be provided for reliable power supply of the power system.

[0021] Embodiment 2 The embodiment of the present application provides a method for live evaluation of cable shielding defects, current transformers are installed on both sides of the cable joint group connected by the cable grounding box at the cable shielding defect to be detected, the cable amplitude-phase data is determined, including: Three current transformers of the detection equipment are installed on one side of the three-phase cable body of the cable joint group connected by the cable grounding box at the cable shielding defect to be detected; Based on the same direction as the three current transformers installed on one side, the other three current transformers of the detection equipment are installed on the other side of the three-phase cable body of the cable joint group connected by the cable grounding box at the cable shielding defect to be detected; Based on the three current transformers installed on one side of the three-phase cable body of the cable joint group, the one-side current amplitude and one-side phase of one side of the three-phase cable body of the cable joint group are recorded, and based on the three current transformers installed on the other side of the three-phase cable body of the cable joint group, the other-side current amplitude and other-side phase of the other side of the three-phase cable body of the cable joint group are recorded; Based on the one-side current amplitude and one-side phase of one side of the three-phase cable body of the cable joint group and the other-side current amplitude and other-side phase of the other side of the three-phase cable body of the cable joint group, the cable amplitude-phase data is determined.

[0022] In this embodiment, the installation position and number of current transformers are discussed. It is explicitly required to use 6 current transformers, divided into two groups, each with 3, corresponding to the three-phase cable (A, B, C). The first group of 3 current transformers is installed on "one side of the three-phase cable body of the cable joint group connected by the cable grounding box at the position to be detected for the cable shielding defect". Here, "cable joint group" is a high-risk area for shielding defects, as the joint needs to handle the connection or insulation isolation of the shielding layer, which is prone to problems such as poor contact and breakage; while "cable body" refers to the complete cable part including the core, insulation layer, and shielding layer (metal sheath). The choice of installing on both sides of the joint group is because the shielding layer defect 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 rule (such as similar amplitude and symmetrical phase), and when a defect exists, this rule will be broken.

[0023] In this embodiment, it is emphasized that the installation direction of the current transformers on both sides should be consistent. This is crucial because the measurement results of the current transformers are closely related to the installation direction (such as the positive and negative of the phase will be reversed due to different directions). If the directions on both sides are not consistent, the subsequent recorded phase data will lose comparability, which may lead to misjudgment of the current relationship. For example, if the "incoming end" of one side of the current transformer is towards the joint group, and the other side is towards the opposite direction, even if the actual current phase is the same, the recorded data will show opposite phases, thus masking the true defect signal. Therefore, "consistent direction" is a prerequisite for ensuring data effectiveness, which usually needs to be achieved through marking, unified installation specifications (such as taking the cable laying direction as the reference).

[0024] In this embodiment, based on the installed current transformers, the current information on both sides of the joint group is recorded, including "one side current amplitude and one side phase of one side of the three-phase cable body" and "another side current amplitude and another side phase of the other side of the three-phase cable body". Here, "amplitude" refers to the size of the current (in A), reflecting the strength of the current; "phase" describes the sequence of the current over time (expressed in degrees), embodying the symmetry relationship between the three-phase currents. When the shielding layer has a defect (such as shielding layer breakage, poor contact of grounding lead), it will destroy this symmetry, causing significant differences in the amplitudes of the currents on both sides and disorder in the phase relationship (such as phase difference deviating from 120°).

[0025] In this embodiment, by integrating the recorded current amplitude and phase data on both sides, "cable amplitude-phase data" is formed.

[0026] The beneficial effects of the above technical solution are: installing current transformers on both sides of the cable joint group connected by the cable grounding box at the position to be detected for the cable shielding defect, determining the cable amplitude-phase data, which can provide data support for determining the grounding box mode.

[0027] Embodiment 3: The embodiment of the present application provides a method for evaluating cable shielding defects with electrification, which is based on cable amplitude-phase data and the number of grounding boxes at a position to be detected of a cable shielding defect, determines a grounding box mode, and comprises the following steps: determining the grounding box mode based on the number of grounding boxes at the position to be detected of the cable shielding defect, one-side current amplitude and one-side phase of one-side three-phase cable bodies of a cable joint group, and other-side current amplitude and other-side phase of other-side three-phase cable bodies of the cable joint group; ; ; ; ; ; ; ; ; ; ; ; ; ; wherein, represents the grounding box mode, respectively represent a first sub-grounding box mode, a second sub-grounding box mode, a third sub-grounding box mode, a fourth sub-grounding box mode, a fifth sub-grounding box mode and a sixth sub-grounding box mode, represents the number of grounding boxes, Ix represents a maximum current amplitude caused by mutual inductor error and field disturbance, IA1, IB1 and IC1 respectively represent current vectors of A-phase, B-phase and C-phase cable tests on one side of the cable joint group, IA2, IB2 and IC2 respectively represent current vectors of A-phase, B-phase and C-phase cable tests on the other side of the cable joint group, IF1 represents an amplitude of a 3-phase current inductor current vector value on one side of the cable joint group, IF2 represents an amplitude of a 3-phase current inductor current vector value on the other side of the cable joint group, and IF represents a difference between the amplitude of the 3-phase current inductor current vector value of the cable body on one side of the cable joint group and the amplitude of the 3-phase current inductor current vector value of the cable body on the other side of the cable joint group, represents the maximum amplitude of the 3-phase current inductor current vector value of the cable joint group, represents the minimum amplitude of the 3-phase current inductor current vector value of the cable joint group, a first index representing the current vector on both sides of the cable joint group, a second index representing the current vector on both sides of the cable joint group.

[0028] In this embodiment, the cross transposition grounding box of the insulation joint group: the insulation joint group is characterized by the insulation isolation of the shielding layer (metal sheath) inside, which cannot be directly conducted, so different phase connections between different phases need to be realized through the cross transposition grounding box to offset the induced voltage.

[0029] In this embodiment, the heterogeneous grounding box of the insulation joint group: the structure of the heterogeneous grounding box is relatively special, and it may integrate multiple grounding functions (such as partial direct grounding and partial protective grounding), and is suitable for complex wiring scenes.

[0030] In this embodiment, the direct grounding box of the straight-through joint group: the shielding layer of the straight-through joint group is continuously conducted without insulation isolation, so the function of the direct grounding box is to directly connect the entire shielding layer to the ground.

[0031] In this embodiment, the insulation joint group and the protective grounding box on both sides: the insulation joint group divides the shielding layer into two sections, and the protective grounding boxes on both sides are grounded through protectors (such as zinc oxide arresters), which are in a high resistance state under normal circumstances, and the shielding layer at both ends is almost suspended.

[0032] In this embodiment, the insulation joint group and the direct grounding box on both sides: after the insulation joint group isolates the shielding layer, the two sides are connected to the ground through the direct grounding box, forming two independent grounding loops.

[0033] In this embodiment, the insulation joint group on one side is a direct grounding box and on the other side is a protective grounding box: this way combines the characteristics of direct grounding and protective grounding, and the number of grounding boxes is 2. The shielding layer current on the direct grounding side can flow freely, so the current amplitude of the corresponding phase on this side is larger and stable; the current amplitude on the protective grounding side is smaller and may fluctuate with the voltage. At the same time, the phase relationship of the currents on both sides is also asymmetric due to the different grounding methods - the phase on the direct grounding side is more closely related to the core current, and the phase on the protective grounding side is more affected by the characteristics of the protector.

[0034] The beneficial effects of the above technical solutions are: based on the cable amplitude-phase data and the number of grounding boxes at the position to be detected of the cable shielding defect, the grounding box mode is determined, which can realize accurate identification of various grounding box modes without power interruption or disassembly of equipment, and provide an accurate structural basis for subsequent defect diagnosis.

[0035] Embodiment 4: The embodiment of the present application provides a method for electrified evaluation of cable shielding defects, which is based on the grounding box mode and the number of grounding boxes, and calculates the metal sheath mode connected by the grounding box, comprising: If the number of grounding boxes is 1 and the grounding box mode is the cross transposition grounding box of the insulation joint group, the third index and the fourth index of the current vector on both sides of the cable joint group are calculated; ; ; wherein, the third index and the fourth index of the current vector on both sides of the cable joint group, respectively; The third index and the fourth index of the current vector on both sides of the cable joint group are compared, if the third index is less than the fourth index, the cross transposition connection mode of the metal sheath is IA1-IB2, IB1-IC2, IC1-IA2, if the third index is greater than the fourth index, the cross transposition connection mode of the metal sheath is IA1-IC2, IB1-IA2, IC1-IB2; If the number of grounding boxes is 1 and the grounding box mode is the heterogeneous grounding box of the insulation joint group, and the judgment logic is , then the single-ended grounding system and the cross transposition system on both sides of the joint are judged, if , then the cable body metal sheath on the left side of the joint group is protected and grounded through the lead and the heterogeneous grounding box; the cable body metal sheath on the right side of the joint is directly grounded through the lead and the heterogeneous grounding box, if , then the cable body metal sheath on the left side of the joint is directly grounded through the lead and the heterogeneous grounding box; the cable body metal sheath on the left side of the joint group is protected and grounded through the lead and the heterogeneous grounding box; the cable body metal sheath on the right side of the joint is protected and grounded through the lead and the heterogeneous grounding box; If the number of grounding boxes is 1 and the grounding box mode is the heterogeneous grounding box of the insulation joint group, and the judgment logic is , then it is judged that both sides of the joint are single-ended grounding systems, if , then the cable body metal sheath on the left side of the joint group is directly grounded through the lead and the direct grounding box; the cable body metal sheath on the right side of the joint group is grounded through the lead and the protection grounding box, if , then the cable body metal sheath on the right side of the joint group is grounded through the lead and the protection grounding box; If the number of grounding boxes is 1 and the grounding box mode is the direct grounding box of the direct joint group, the joint cable on both sides of each phase of the cable is directly connected, and is grounded through the grounding lead and the direct grounding box, if , then it is judged that both sides of the joint are cross transposition grounding systems, if , then it is judged that both sides of the joint are single-ended grounding systems; If the number of grounding boxes is 2 and the grounding box mode is the protection grounding box of the insulation joint group on both sides, the cable body metal sheath on both sides of the joint cable of each phase of the cable is insulated; If the number of grounding boxes is 2, the grounding box mode is the insulation joint group, and both sides are direct grounding boxes, the cable body metal sheath of each phase of the cable on both sides of the joint is insulated, and is grounded through the direct grounding box. If , then the two sides of the joint are the cross transposition grounding system. If , then the two sides of the joint are the single-end grounding system. If the number of grounding boxes is 2, the grounding box mode is the insulation joint group, one side is a direct grounding box, and one side is a protective grounding box, and the judgment logic is , if , then the cable body metal sheath on the left side of the joint group is grounded through the lead and the direct grounding box, and the cable body metal sheath on the right side of the joint group is grounded through the lead and the protective grounding box. If , then the cable body metal sheath on the right side of the joint group is grounded through the lead and the direct grounding box, and the cable body metal sheath on the left side of the joint group is grounded through the lead and the protective grounding box. If the number of grounding boxes is 2, the grounding box mode is the insulation joint group, one side is a direct grounding box, and one side is a protective grounding box, and the judgment logic is , if , then the cable body metal sheath on the left side of the joint group is grounded through the lead and the direct grounding box, and the cable body metal sheath on the right side of the joint group is grounded through the lead and the protective grounding box. If , then the cable body metal sheath on the right side of the joint group is grounded through the lead and the protective grounding box.

[0036] In this embodiment, the metal sheath cross transposition connection mode is IA1—IB2, IB1—IC2, IC1—IA2, which means that the A-phase cable metal sheath on the left side of the joint group is connected to the B-phase cable metal sheath on the right side of the joint group through the lead and the grounding box, the B-phase cable metal sheath on the left side of the joint group is connected to the C-phase cable metal sheath on the right side of the joint group through the lead and the grounding box, and the C-phase cable metal sheath on the left side of the joint group is connected to the A-phase cable metal sheath on the right side of the joint group through the lead and the grounding box.

[0037] In this embodiment, the metal sheath cross transposition connection mode is IA1—IC2, IB1—IA2, IC1—IB2, which means that the A-phase cable metal sheath on the left side of the joint group is connected to the C-phase cable metal sheath on the right side of the joint group through the lead and the grounding box, the B-phase cable metal sheath on the left side of the joint group is connected to the A-phase cable metal sheath on the right side of the joint group through the lead and the grounding box, and the C-phase cable metal sheath on the left side of the joint group is connected to the B-phase cable metal sheath on the right side of the joint group through the lead and the grounding box.

[0038] The beneficial effects of the above technical solutions are: based on the grounding box mode and the grounding box quantity, the metal sheath mode connected by the grounding box is calculated, the specific connection relationship of the sheath can be accurately determined without disassembling the equipment, the continuity of live detection is ensured, and the efficiency and accuracy of the connection mode judgment are improved.

[0039] Embodiment 5: The embodiment of the application provides a method for live evaluation of cable shielding defects, based on cable amplitude-phase data, grounding box quantity, grounding box mode and metal sheath mode connected by the grounding box, the circulating current data of the metal sheath of the cable connected by the grounding box is calculated, comprising: Based on the grounding box quantity, the grounding box mode and the metal sheath mode connected by the grounding box, the cable body cable core current amplitude of each grounding box quantity and each grounding box mode is calculated, and the circulating current data of the metal sheath connected by each grounding box quantity and each grounding box mode is calculated.

[0040] In this embodiment, if the grounding box quantity is 1 and the grounding box mode is the cross transposition grounding box of the insulation joint group, the cable body cable core current amplitude is calculated, and the phase cable metal shielding circulating current is calculated. When the metal sheath cross transposition connection mode is IA1-IB2, IB1-IC2, IC1-IA2, the calculation formula of the cable body cable core current amplitude and the phase cable metal shielding circulating current can be represented as: ; If ABC is in clockwise order, then: ; ; ; If ABC is in counterclockwise order, then: ; ; ; ; ; ; wherein, is the current amplitude of the three-phase cable body core, Ia is the vector of the A-phase cable body core current, Ib is the vector of the B-phase cable body core current, and Ic is the vector of the C-phase cable body core current, , , respectively represent the A-phase, B-phase and C-phase cable metal shielding circulating current on one side of the cable joint group, 、 They respectively represent the metal shield circulating currents of the A-phase, B-phase, and C-phase cables on the other side of the cable connector group.

[0041] When the metal sheath cross-transposition connection mode is IA1-IC2, IB1-IA2, IC1-IB2, the calculation method of the cable body cable core current amplitude and the metal shield circulating current of each phase cable is the same as when the metal sheath cross-transposition connection mode is IA1-IB2, IB1-IC2, IC1-IA2.

[0042] In this embodiment, the unit of current amplitude is A, and the unit of angle is radian.

[0043] In this embodiment, if the number of grounding boxes is 1 and the grounding box type is an insulated joint group heterogeneous grounding box, the current amplitude of the cable core of the cable body is calculated, and the metal shield circulating current of each phase cable is calculated: If the metal sheath of the cable on the left side of the connector is directly grounded through a lead wire and a heterogeneous grounding box, and the metal sheath of the cable on the right side of the connector is protectively grounded through a lead wire and a heterogeneous grounding box, then: Circulation current of the metal shielding sheath of the cable on the left side of the connector group: IAN1=|IA1 IA2| / ; IBN1=|IB1 IB2| / ; ICN1=|IC1 IC2| / ; Circulation current of the metal shielding sheath of the cable on the right side of the connector group: IAN2=IBN2=ICN2=0; If the metal sheath of the cable on the left side of the connector group is grounded through a lead wire and a heterogeneous grounding box, and the metal sheath of the cable on the right side of the connector is directly grounded through a lead wire and a heterogeneous grounding box, then: Circulation current of the metal shielding sheath of the cable on the left side of the connector group: IAN1=IBN1=ICN1=0; Circulation current of the metal shielding sheath of the cable on the right side of the connector group: IAN2=|IA1 IA2| / ; IBN2=|IB1 IB2| / ; ICN2=|IC1 IC2| / ; In this embodiment, if the number of grounding boxes is 1 and the grounding box mode is the direct grounding box of the straight-through joint group, the cable body cable core current amplitude is calculated, and the circulating current of the metal shielding of each phase cable is calculated: To test the circulating current of the metal shielding of the cable, the amplitude of the three-phase grounding lead current of the grounding phase of the test cable is required, that is, the amplitude of the circulating current of the metal shielding of the left A-phase cable of the joint group is IANL, the effective value is IAN1, and the unit is A; the amplitude of the circulating current of the metal shielding of the left B-phase cable of the joint group is IBNL, the effective value is IBN1, and the unit is A; the amplitude of the circulating current of the metal shielding of the left C-phase cable of the joint group is ICNL, the effective value is ICN1, and the unit is A; the amplitude of the circulating current of the metal shielding of the right A-phase cable of the joint group is IANR, the effective value is IAN2, and the unit is A; the amplitude of the circulating current of the metal shielding of the right B-phase cable of the joint group is IBNR, the effective value is IBN2, and the unit is A; the amplitude of the circulating current of the metal shielding of the right C-phase cable of the joint group is ICNR, the effective value is ICN2, and the unit is A. The three-phase lead current of the joint group metal shielding connected to the grounding box is I11, I12, and I13.

[0044] If |IA1+IB1+IC1|>Ix and |IA2+IB2+IC2|≤Ix, then IANL=I1, IBNL=I2, and ICNL=I3. If |IA1+IB1+IC1|≤Ix and |IA2+IB2+IC2|>Ix, then IANR=I1, IBNR=I2, and ICNR=I3. If |IA1+IB1+IC1|≤Ix and |IA2+IB2+IC2|≤Ix and MAX{|IA1—IA2|, |IB1—IB2|, |IC1—IC|}≤2×Ic, the grounding systems on both sides of the test joint are protective grounding, IANL, IANR, IBNL, IBNR, ICNL, and ICNR can be ignored, and the following is taken: IANL=IBNL=ICNL=IANR=IBNR=ICNR=0. If |IA1+IB1+IC1|>Ix and |IA2+IB2+IC2|>Ix Then, formula (1): IANL IANR=I1. Formula (2): IBNL IBNR=I2. Formula (3): ICNL ICNR=I3. Ignoring the influence of the interconnection grounding unbalance current, then Formula (4): IANL+IBNL+ICNL=0. Equation (5): IANR + IBNR + ICNR = 0; If the three-phase time sequence is reverse time sequence, then: Equation (6): (IANL IBNL) x 1 ∠ (2 x π / 3) (IBNL ICNL) = (IA1 IB1) x 1 ∠ (2 x π / 3) - (IB1 - IC1); Equation (7): (IBNL ICNL) x 1 ∠ (2 x π / 3) (ICNL IANL) = (IC1 IC1) x 1 ∠ (2 x π / 3) (IC1 IA1); Equation (8) (ICNL - IANL) x 1 ∠ (2 x π / 3) - (IANL - IBNL) = (IC1 - IA1) x 1 ∠ (2 x π / 3) - (IA1 - IB1); If the three-phase time sequence is forward time sequence, then: Equation (9): (IANL - IBNL) x 1 ∠ (-2 x π / 3) - (IBNL - ICNL) = (IA1 - IB1) x 1 ∠ (-2 x π / 3) - (IB1 - IC1); Equation (10): (IBNL - ICNL) x 1 ∠ (-2 x π / 3) - (ICNL - IANL) = (IC1 - IC1) x 1 ∠ (-2 x π / 3) - (IC1 - IA1); Equation (11): (ICNL - IANL) x 1 ∠ (-2 x π / 3) - (IANL - IBNL) = (IC1 - IA1) x 1 ∠ (-2 x π / 3) - (IA1 - IB1); Optionally, one of the equations (6), (7), (8), (9), (10), (11), one of the equations (4), (5), and (1), (2), (3) are combined to calculate IANL, IANR, IBNL, IBNR, ICNL, ICNR. Then: IAN1 = |IANL| / ; IAN2 = |IANR| / ; IBN1 = |IBNL| / ; IBN2 = |IBNR| / ; ICN1 = |ICNL| / ICN2 = |ICNR| ; Wherein, I1 is the current of the A-phase joint connecting the ground box lead, the current amplitude, unit A, angle unit radian; I2 is the current of the B-phase joint connecting the ground box lead, the current amplitude, unit A, angle unit radian; I3 is the current of the C-phase joint connecting the ground box lead, the current amplitude, unit A, angle unit radian; IA1, IB1 and IC1 are the current vectors of one side (such as the left side) of the cable joint group, IA2, IB2 and IC2 are the current vectors of the other side (such as the right side) of the cable joint group; IA1 is the current vector of the A-phase cable test of one side of the joint group, the current amplitude, unit A, angle unit radian; IA2 is the current vector of the A-phase cable test of the other side of the joint group, the current amplitude, unit A, angle unit radian; IB1 is the current vector of the B-phase cable test of one side of the joint group, the current amplitude, unit A, angle unit radian; IB2 is the current vector of the B-phase cable test of the other side of the joint group, the current amplitude, unit A, angle unit radian; IC1 is the current vector of the C-phase cable test of one side of the joint group, the current amplitude, unit A, angle unit radian; IC2 is the current vector of the C-phase cable test of the other side of the joint group, the current amplitude, unit A, angle unit radian; Ic is the maximum capacitive current amplitude of the longest section of the cable grounding system in the line, unit A.

[0045] In this embodiment, if the number of ground boxes is 2, and the ground box mode is the protection ground box of the insulation joint group, no test is required, and the metal shielding ring current of the cable on both sides of the joint group is judged as: IA1N = IB1N = IC1N = 0; IA2N = IB2N = IC2N = 0.

[0046] In this embodiment, if the number of ground boxes is 2, and the ground box mode is the direct ground box of the insulation joint group, the cable body cable core current amplitude is calculated, and the metal shielding ring current of each phase cable is calculated: The 6 current transformers of the detection equipment are installed on the direct ground lead of the cable ground box connected to the cable direct ground box, and the metal shielding ring current of the cable on both sides of the joint is directly tested and obtained.

[0047] The three-phase lead current of the ground box connected to the metal shielding of the left side of the joint group is I11, I12, I13.

[0048] The three-phase lead current of the ground box connected to the metal shielding of the right side of the joint group is I21, I22, I23.

[0049] IAN1 = |I11| ; IB1N = |I12| ; IC1N = |I13| ; IAN2=|I21| / IBN2=|I22| / ICN2=|I23| /

[0050] Wherein, I11 is the current of the A-phase joint connected to the ground box, the current amplitude unit is A, and the angle unit is radian; I12 is the current of the B-phase joint connected to the ground box, the current amplitude unit is A, and the angle unit is radian; I13 is the current of the C-phase joint connected to the ground box, the current amplitude unit is A, and the angle unit is radian; I21 is the current of the A-phase joint connected to the ground box, the current amplitude unit is A, and the angle unit is radian; I22 is the current of the B-phase joint connected to the ground box, the current amplitude unit is A, and the angle unit is radian; I23 is the current of the C-phase joint connected to the ground box, the current amplitude unit is A, and the angle unit is radian.

[0051] In the embodiment, if the number of ground boxes is 2, and one ground box is a direct ground box of the insulation joint group and the other ground box is a protective ground box of the insulation joint group, the operation method is the same as the method of the metal shielding of the ground box with one ground box and the heterogeneous ground box of the insulation joint group.

[0052] The above technical scheme has the beneficial effects that: based on the cable amplitude-phase data, the number of ground boxes, the ground box mode and the metal sheath mode connected to the ground box, the circulating current data of the cable metal sheath connected to the ground box is calculated, the precise derivation of the wire core current amplitude and the sheath circulating current data under different configurations can be realized, the continuity of detection is guaranteed, the matching degree of data and actual working conditions is improved, and the precision of live detection is enhanced.

[0053] Embodiment 6: The embodiment of the present application provides a method for live evaluation of cable shielding defects, judges the running state of the cable metal sheath circulating current, judges whether there is an abnormal grounding defect of the metal shielding and the grounding lead, and comprises the following steps: The running state of the cable metal sheath circulating current is judged based on the same branch metal shielding circulating current data tested by the ground box, and whether there is an abnormal grounding defect of the metal shielding and the grounding lead is judged. If the metal sheath connected to the ground box is single-ended grounding, then: |ILA1-ILA2|≥MAX{2×π×F×U0×C0×L× Ix}, and it is judged that there is an abnormal grounding defect of the A-phase branch metal sheath; |ILB1—ILB2|≥MAX{2×π×F×U0×C0×L× ,Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the B phase branch; |ILC1—ILC2|≥MAX{2×π×F×U0×C0×L× ,Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the C phase branch; If the metal sheath connected to the grounding box is cross-grounded, then: |ILA1—ILA2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the phase A branch; |ILB1—ILB2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the B phase branch; |ILC1—ILC2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the C phase branch; Among them, 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 inductive capacitance per unit length of the cable line; L is the length of the metal sheath of the cable connected to the grounding box.

[0054] In this embodiment, corresponding judgment conditions are set according to different grounding modes (single-end grounding or cross-transposed grounding), and the difference in circulating current at the beginning and end of the same branch is compared to determine whether the phase has a defect.

[0055] In this embodiment, the unit of ILA1, ILA2, ILB1, ILB2, ILC1, and ILC2 is A.

[0056] In this embodiment, the unit of the power frequency F is Hz, which is generally 50 Hz or 60 Hz.

[0057] In this embodiment, the rated operating voltage U0 of the cable is in V.

[0058] In this embodiment, the inductive capacitance C0 per unit length of the cable line is in μF.

[0059] In this embodiment, the length L of the metal sheath of the cable connected to the grounding box is in meters.

[0060] The above technical scheme has the beneficial effects that: the running state of the cable metal sheath circulating current is judged, and whether there is a metal shielding and ground lead abnormal grounding defect is judged, accurate defect identification can be realized, the detection accuracy of metal shielding and ground lead abnormal defects under different grounding modes is improved, and a scientific and quantitative criterion is provided for live evaluation.

[0061] Embodiment 7: The embodiment of the present application provides a method for evaluating cable shielding defects under voltage, and performs defect positioning on a cable metal sheath with a grounding defect, comprising: For the metal segment with a defect, the bisection method or the step-by-step simultaneous test is used to obtain the cable body induced current, which is ILi for the first end and IRi for the end, respectively. The current size is 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 the test range until the defect is accurately positioned.

[0062] In this embodiment, the bisection method test: determine the L / 2 segment where the defect is located; test the circulating current data of the beginning, middle and end of the L segment, wherein the current of the middle 1 / 2 segment is I(1 / 2), the current of the beginning is IL(0), and the current of the short end is IL(1). Comparison, if |I(1 / 2)-Iy|<Ix, the defect is not in the 1 / 2×L to y×L segment, if |I(1 / 2)-Iy|≥Ix, the defect is in the 1 / 2×L to y×L segment. Wherein y is the ratio of the beginning and short end of the test segment, dimensionless; Ix is the maximum current amplitude caused by the error of the mutual inductor and the field interference, unit A. For example, y=1, if |I(1 / 2)-I1|<Ix, the defect is not in the 1 / 2×L to 1×L segment, if |I(1 / 2)-I1|≥Ix, the defect is in the 1 / 2×L to 1×L segment. Repeat the above process to test the circulating current data of the beginning, middle and end of the L / 2, L / 4, … segment where the defect is located. By comparing I(1 / 4), I(1 / 8), I(1 / 16) … current data, until the smallest segment LW that can be identified by the naked eye to find the defect is found, and the defect positioning is realized.

[0063] In this embodiment, the test section is tested in sections: first, the test section L is divided into the minimum section Lw that can be visually identified to find defects, and the total number of sections is n=L / Lw; second, the first section, the second section,..., the kth section, the k+1th section,..., the n-1th section, and the nth section are tested to obtain the first-end current IkL and the last-end current IkR of the kth section; third, IkL and IkR are compared, if |IkL-IkR|<Ix, the defect is not in the kth section, and if |InL-InR|≥Ix, the defect is in the kth section. Ix is the maximum current amplitude caused by the mutual inductor error and the field interference, and the unit is A. InL is the current at the first end of the nth section, and the unit is A; InR is the current at the tail end of the nth section, and the unit is A.

[0064] The beneficial effects of the above technical solutions are: the defect of the cable metal sheath existing in the ground fault can be located, the limitations of traditional experience or large-area investigation can be broken through, the efficiency and accuracy of defect positioning are improved, the long-distance cable or complex wiring scene is suitable, efficient conversion from the existing defect to accurate positioning is realized, and clear targeting is provided for live maintenance.

[0065] Embodiment 8: The embodiment of the present application provides a device for live evaluation of cable shielding defects, which is used to execute the method for live evaluation of cable shielding defects in any one of claims 1 to 7.

[0066] The device embodiments described above are only schematic, wherein the units described as separate components can or can not be physically separate, and the components displayed as units can or can not be physical units, that is, they can be located in one place, or distributed on multiple network units. Part or all of the modules can be selected to achieve the purpose of the embodiment scheme according to actual needs. Those skilled in the art can understand and implement without creative labor.

[0067] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be realized by means of software and the necessary general hardware platform, and of course, it can also be realized by hardware. Based on such understanding, the above technical solutions can be embodied in the form of a software product, which can be stored in a computer readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes a plurality of instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute the method described in each embodiment or some parts of the embodiment.

[0068] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for evaluating cable shielding defects under power, characterized in that: include: Step 1: Install current transformers on both sides of the cable connector 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 grounding leads at the location where the cable shielding defect is to be detected; Step 2: Determine the grounding box type based on the cable amplitude-phase data and the number of grounding boxes at the location where the cable shielding defect is to be detected. Calculate the metal sheath type connected to the grounding box based on the grounding box type and the number of grounding boxes. Step 3: Calculate the circulating current data of the metal sheath of the cable connected to the grounding box based on the cable amplitude-phase data, the number of grounding boxes, the type of grounding boxes, and the type of metal sheath connected to the grounding box; Step 4: Determine the operating status of the cable metal sheath circulation, determine whether there are abnormal grounding defects in the metal shield and grounding lead, and locate the defects in the cable metal sheath with grounding defects.

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

3. The method for evaluating cable shielding defects under power-on conditions according to claim 2, wherein: Based on the cable amplitude-phase data and the number of grounding boxes at the location where the cable shielding defect is to be detected, determine the grounding box method, including: Determine the grounding box method based on the number of grounding boxes at the location where the cable shielding defect is to be detected, 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 mode, They represent the first sub-grounding box mode, the second sub-grounding box mode, the third sub-grounding box mode, the fourth sub-grounding box mode, the fifth sub-grounding box mode, and the sixth sub-grounding box mode respectively. Indicates the number of grounding boxes, Ix indicates the maximum current amplitude of the on-site test current caused by transformer error and on-site interference, IA1, IB1, and IC1 respectively indicate the current vectors of the A-phase, B-phase, and C-phase cables tested on one side of the cable joint group, IA2, IB2, and IC2 respectively indicate the current vectors of the A-phase, B-phase, and C-phase cables tested on the other side of the cable joint group, IF1 indicates the amplitude of the 3-phase current transformer current vector value on one side of the cable joint group, IF2 indicates the amplitude of the 3-phase current transformer current vector value on the other side of the cable joint group, and IF indicates the difference between the amplitude of the 3-phase current transformer current vector value of the cable body on one side of the cable joint group and the amplitude of the 3-phase current transformer current vector value of the cable body on the other side of the joint group. Indicates the amplitude of the maximum 3-phase current transformer current vector value of the cable connector group, Indicates the amplitude of the minimum 3-phase current transformer current vector value of the cable joint group, The first indicator of the current vector on both sides of the cable joint group, A second indicator representing the current vector on both sides of the cable joint group.

4. The method for evaluating cable shielding defects under power-on conditions according to claim 3, wherein: Based on the grounding box type and number of grounding boxes, calculate the metal sheath type connected to the grounding box, including: If the number of grounding boxes is 1 and the grounding box mode is a cross-transposed grounding box of the insulating joint group, calculate the third index and the fourth index of the current vector on both sides of the cable joint group; ； ； in, a third index and a fourth index of the current vector on both sides of the cable connector assembly; Compare the third and fourth indicators of the current vectors on both sides of the cable connector group. If the third indicator is less than the fourth indicator, the metal sheath cross-transposition connection mode is IA1-IB2, IB1-IC2, IC1-IA2. If the third indicator is greater than the fourth indicator, the metal sheath cross-transposition connection mode is IA1-IC2, IB1-IA2, IC1-IB2. If the number of grounding boxes is 1, and the grounding box mode is a heterogeneous grounding box of an insulating joint group, and the judgment logic is , then determine the single-ended grounding system and cross-transposition system on both sides of the joint. If , the metal sheath of the cable body on the left side of the connector group is protected by the ground through the lead wire and the heterogeneous grounding box; the metal sheath of the cable body on the right side of the connector is directly grounded through the lead wire and the heterogeneous grounding box. , the metal sheath of the cable body on the left side of the connector is directly grounded through the lead wire and the heterogeneous grounding box; the metal sheath of the cable body on the left side of the connector group is protectively grounded through the lead wire and the heterogeneous grounding box; the metal sheath of the cable body on the right side of the connector is protectively grounded through the lead wire and the heterogeneous grounding box; If the number of grounding boxes is 1, and the grounding box mode is a heterogeneous grounding box of an insulating joint group, and the judgment logic is , then it is determined that both sides of the connector are single-ended grounding systems. If |, the metal sheath of the cable body on the left side of the connector group is grounded directly to the grounding box through the 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. |, 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 mode is a direct grounding box with a straight-through connector group, the metal sheaths of the connector cables of each phase are directly connected on both sides and grounded through the grounding lead and the direct grounding box. , then it is determined that the two sides of the joint are cross-transposed grounding systems. If , it is determined that both sides of the joint are single-ended grounding systems; If the number of grounding boxes is 2, the grounding box type is an insulated joint group and both sides are protective grounding boxes, the metal sheath of the cable body on both sides of the joint cable of each phase is insulated; If the number of grounding boxes is 2, the grounding box mode is an insulated joint group and both sides are directly grounded boxes, then the cable body metal sheath on both sides of the joint cable of each phase is insulated and grounded through the direct grounding box. , then the two sides of the joint are cross-transposed grounding systems. If , then both sides of the joint are single-ended grounding systems; If the number of grounding boxes is 2, the grounding box mode is that one side of the insulation joint group is a direct grounding box and the other side is a protective grounding box, and the judgment logic is ,like , the metal sheath of the cable body on the left side of the connector group is grounded through the lead wire and the direct grounding box, and 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. , the metal sheath of the cable body on the left side of the connector group is grounded through the lead wire and the protective grounding box; the metal sheath of the cable body on the right side of the connector group is grounded through the lead wire and the direct grounding box; If the number of grounding boxes is 2, the grounding box mode is that one side of the insulation joint group is a direct grounding box and the other side is a protective grounding box, and the judgment logic is ,like |The metal sheath of the cable body on the left side of the connector group is grounded directly to the grounding box through the 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. |, 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 power-on conditions according to claim 4, wherein: Calculates the circulating current data of the metal sheath of the cable connected to the grounding box 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, including: Based on the number of grounding boxes, the type of grounding boxes, and the type of metal sheath connected to the grounding boxes, the current amplitude of the cable core of the cable body is calculated for each number of grounding boxes and each type of grounding boxes, and the circulating current data of the metal sheath connected to the grounding boxes is calculated for each number of grounding boxes and each type of grounding boxes.

6. The method for evaluating cable shielding defects under power-on conditions according to claim 5, characterized in that: Determine the operating status of the cable metal sheath circulation and whether there are any abnormal grounding defects in the metal shield or ground lead, including: To determine the operating status of the cable metal sheath circulation, the grounding box is used to test the metal shield circulation data of the same branch to determine whether there are abnormal grounding defects in the metal shield or 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× ,Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the phase A branch; |ILB1—ILB2|≥MAX{2×π×F×U0×C0×L× ,Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the B phase branch; |ILC1—ILC2|≥MAX{2×π×F×U0×C0×L× ,Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the C phase branch; If the metal sheath connected to the grounding box is cross-grounded, then: |ILA1—ILA2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the phase A branch; |ILB1—ILB2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the B phase branch; |ILC1—ILC2|≥MAX{2×π×F×U1×C0×L× ,2×Ix}, it is judged to be an abnormal grounding defect of the metal sheath of the C phase branch; Among them, 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 inductive 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 power-on conditions according to claim 6, wherein: And the defects of the cable metal sheath with grounding defects are located, including: For metal segments with defects, a binary method or simultaneous testing of each segment is used to obtain the induced current of the cable body, which are ILi at the head end and IRi at the end. The current sizes 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. Repeat the above process and narrow the test range until the defect is accurately located.

8. A device for evaluating cable shielding defects under power, characterized in that: A method for performing live cable shielding defect evaluation as claimed in any one of claims 1 to 7.

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