Cable insulation fault recognition and positioning method based on operating current and sheath circulating current

Abstract

The application provides a cable insulation fault identification and positioning method based on operating current and sheath circulating current, which comprises collecting three-phase operating current and three-phase sheath circulating current of a cable line; extracting a first fault component and a second fault component; performing fault starting logic judgment; when the result is true, it is determined that the cable line has insulation fault; calculating phase-phase current of the first fault component; calculating phase-phase current amplitude of the first fault component within a half cycle after the fault, judging whether the line has single-phase grounding fault, if yes, performing fault phase identification; after the fault phase identification, judging whether the correlation coefficient conforms to the fault coefficient relationship, if yes, continuing the fault phase identification, if the results of twice fault phase identification are consistent, it is finally determined that the line has single-phase grounding fault. The application has the advantages of long cable operating life, high cable safety, high accuracy, ability to determine fault section, high reliability, small error, high work efficiency and the like.

Description

Technical Field

[0001] This invention relates to the field of online monitoring technology for cable lines, specifically to a method for identifying and locating insulation faults in 35kV single-core cables based on operating current and sheath circulating current, which is unaffected by the neutral grounding method. Background Technology

[0002] Currently, the proportion of cables used in urban power distribution networks, especially in large and medium-sized cities, is increasing. Among them, 35kV single-core power cables are widely used in urban power distribution networks and power supply systems of industrial and mining enterprises such as petroleum, chemical, steel, and coal industries due to their advantages such as large current carrying capacity, small bending radius, low risk of phase-to-phase short circuit faults, and ease of manufacturing, transportation, and installation.

[0003] Single-core cable lines are independent three-phase cables with a relatively long phase-to-phase distance, and phase-to-phase short circuits are rare. However, the cable or cable accessories are prone to insulation failures under construction, external damage, and other conditions, resulting in multiple grounding points of the metal sheath and a significant increase in sheath circulating current. This can lead to localized heating and affect the cable's service life, or even damage to the cable's main insulation, endangering the safety of equipment and personnel.

[0004] When a single-core cable is in operation, the alternating magnetic field generated by its operating current will induce a voltage on the metal sheath. The magnitude of the induced voltage is proportional to the length of the cable line and the current flowing through the conductor. When the cable is very long, the induced voltage on the sheath can accumulate to a level that endangers personal safety. When the cable insulation is defective or damaged, and the metal sheath forms two grounding points, a circulating current will be generated on the metal sheath. According to GB50217-2017 "Code for Design of Cables for Power Engineering", the metal sheath of AC single-core cables should be directly grounded at at least one end. The maximum value of the normal induced voltage at any point that is not directly grounded should meet the following requirements: 1) When no effective safety measures are taken to prevent personnel from arbitrarily touching the metal sheath, it should not exceed 50V; 2) Under other circumstances, it should not exceed 300V.

[0005] To control induced voltage within a reasonable level, the appropriate grounding method for the metallic sheath of AC single-core cables must be selected based on cable length, transmission capacity, and economic considerations during the cable laying design. There are three types of grounding methods for the cable metallic sheath: direct grounding, protective grounding, and interconnected grounding, corresponding to direct grounding boxes, protective grounding boxes, and interconnected grounding boxes, respectively. To control sheath circulating current and prevent induced voltage from exceeding limits, the type of grounding box and the spacing between grounding boxes are carefully selected during cable laying, and an online monitoring device for sheath current is installed inside the grounding box.

[0006] During normal operation of a single-core cable, the metal sheath has only one grounding point. The circulating current in the sheath mainly originates from the capacitive current, induced current, and impedance of the circuit, and its magnitude is determined by the cable's structural parameters. When the induced voltage in the metal sheath is well controlled, the induced current amplitude is very small, having minimal impact on the cable. However, when the cable insulation fails, a short circuit is formed between the insulation failure point and the metal sheath, creating a second grounding point. At this point, the circulating current in the sheath increases rapidly, several times over, posing a threat to cable safety.

[0007] For 35kV distribution network systems including cable lines, according to GB / T 50064-2014 "Code for Overvoltage Protection and Insulation Coordination Design of AC Electrical Installations", if the single-phase grounding capacitive current is greater than 10A, a neutral point grounding method via an arc suppression coil is required. Currently, domestic 35kV lines mainly use the neutral point grounding method via an arc suppression coil. Its main advantage is that when a single-phase grounding fault occurs in the system, the steady-state fault current is not large, the system can operate with the fault for a period of time, and the power supply reliability is high. When the cable insulation fails, a short circuit is formed between the cable core and the metal sheath, at which point a single-phase grounding fault occurs in the 35kV system (see the schematic diagram of a single-phase grounding fault in a neutral point grounding system via an arc suppression coil). Figure 1 Currently, single-phase grounding faults on 35kV lines mainly rely on low-current grounding fault location devices installed in substations to locate the faulty line and trip it. However, these devices select the fault by comparing the amplitude and phase of the zero-sequence current of each line, which is easily affected by arc suppression coil compensation. This results in low accuracy and the devices can only identify the entire faulty line, not the specific faulty section.

[0008] Currently, some intelligent grounding boxes are equipped with cable sheath circulating current monitoring devices to detect insulation failure faults. However, cable sheath circulating current is easily affected by factors such as load current, laying length and grounding environment at the location, switching overvoltage, and lightning overvoltage. If cable sheath circulating current is relied upon alone to determine insulation failure faults, the reliability is low and it is prone to false alarms.

[0009] Accurate location of cable line faults currently relies mainly on methods such as the bridge method and traveling wave method, most of which are offline detection methods. After a fault occurs, it is necessary to measure the entire cable line on-site, which involves a large amount of preparatory work and maintenance work, and a long maintenance time. Summary of the Invention

[0010] This invention provides a cable insulation fault identification and location method based on operating current and sheath circulating current, which solves the problems of short cable service life, low cable safety, low accuracy, inability to determine fault sections, too many influencing factors, low reliability, easy to malfunction, large workload, and long maintenance time in the prior art.

[0011] Firstly, a method for identifying and locating cable insulation faults based on operating current and sheath circulating current is provided, which includes the following steps: real-time synchronous acquisition of the three-phase operating current of the cable line at the installation point of the intelligent grounding box. and three-phase protective layer circulation The process involves: extracting the first fault component of the three-phase operating current of the cable line; extracting the second fault component of the three-phase sheath circulating current of the cable line; performing fault initiation logic based on the first and second fault components; determining that an insulation fault has occurred in the cable line when the fault initiation logic is true, marking the initiation time, labeling the sampled data before the initiation time as pre-fault data, and labeling the sampled data after the initiation time as post-fault data; selecting the second half-cycle of the fault with the most concentrated transient components as the data window, and calculating the phase-to-phase current of the first fault component; calculating the phase-to-phase current amplitude of the first fault component within the second half-cycle of the fault, and determining whether a single-phase ground fault has occurred in the line. If it is determined that a single-phase ground fault has most likely occurred in the line, then fault phase identification is performed; after fault phase identification, the correlation coefficient of the phase-to-phase current curve of the first fault component is calculated, and it is determined whether the correlation coefficient conforms to the fault coefficient relationship. If so, it is determined that a single-phase ground fault has most likely occurred in the line, and fault phase identification is performed. If the results of the two fault phase identifications are consistent, then it is finally confirmed that a single-phase ground fault has occurred in the line.

[0012] In one possible implementation, the method further includes: after determining that the line belongs to the faulty line, continuing to perform the next section location judgment, which includes taking the pre-fault data and post-fault data of the three-phase sheath circulating current of the cable line as the center of the marked start time T0, taking one cycle of each, calculating the fundamental amplitude, determining whether the intelligent grounding box is in the faulty section, and if so, alarming and reporting to the main station.

[0013] Based on the above solution, this invention can determine which smart grounding box is located in the cable section where insulation failure has occurred. Since a smart grounding box is installed approximately every 500m of cable line, this technical solution can narrow down the fault range from the entire line length to the area where a specific smart grounding box is located.

[0014] In one possible implementation, the method further includes: real-time acquisition of the three-phase operating current and three-phase sheath circulating current of the cable line at the installation point of the intelligent grounding box; specifically, this can be real-time synchronous acquisition of the three-phase operating current of the cable line at the installation point of the intelligent grounding box. and three-phase protective layer circulation Where p = a, b, c, and the sampled value at the k-th point is denoted as . The operating current sampling rate is not less than 20kHz, the number of sampling points per cycle is N, and k is the current sampling point number.

[0015] In one possible implementation, the method further includes: a process of extracting fault components, specifically, extracting the current fault components of the three-phase operating current of the cable line. , expressed as formula (1): (1) Extracting the fault component of the three-phase sheath circulating current in the cable line , expressed as formula (2): (2).

[0016] In one possible implementation, the method further includes: a fault initiation logic judgment process, specifically including a first logic judgment and a second logic judgment, expressed as formulas (3) and (4): (3); (4); An OR operation is performed on the first and second logical judgments. If the result of the fault initiation logical operation is true, an insulation fault is determined to have occurred in the cable line, and the initiation time T0 is marked. The sampled data before the initiation time T0 is marked as the pre-fault data, and the sampled data after the initiation time T0 is marked as the post-fault data. If the result of the fault initiation logical operation is false, the cable line is considered to be normal, and no action is taken.

[0017] In one possible implementation, the method further includes: calculating the phase-to-phase current of the first fault component, specifically expressed as formula (5): (5) in, .

[0018] In one possible implementation, the method further includes: calculating the phase-to-phase current amplitude of the first fault component within the second half-cycle of the fault. If the amplitude satisfies formula (6), then it is considered that a single-phase ground fault has most likely occurred on the line, and then the first fault phase identification is performed, where, And sorted from largest to smallest, formula (6) is expressed as: (6) in, These are the maximum values ​​of the three phase-to-phase current amplitudes. K3 represents the minimum amplitude of the three phase-to-phase currents, and K3 is an adjustable reliability coefficient.

[0019] In one possible implementation, the method further includes: a first fault phase identification process, specifically which may be... If the minimum value is found, then the faulty phase is phase C; if If the minimum value is found, then the faulty phase is phase A; if... If the value is the smallest, then the faulty phase is phase B.

[0020] In one possible implementation, the method further includes: continuing to calculate the phase-phase current curve correlation coefficient of the first fault component. Specifically, after the fault phase is identified, the phase-phase current curve correlation coefficient of the first fault component is calculated. The correlation coefficient ranges between [-1, 1] and is expressed as formula (7).

[0021]

[0022] (7) ,

[0023] Wherein, if the correlation coefficient satisfies formula (8): (8) If the first fault is detected, it is assumed that a single-phase ground fault has most likely occurred on the line. A second fault phase identification process is then performed. If the result of the second fault phase identification matches the result of the first, a single-phase ground fault is finally confirmed. K is the minimum three-phase correlation coefficient, and K4 is an adjustable constant coefficient.

[0024] In one possible implementation, the method further includes: a second fault phase identification process, specifically: if yes Then the faulty phase is phase B; if yes Then the faulty phase is phase C; if yes If so, the faulty phase is phase A.

[0025] Based on the above scheme, this invention comprehensively utilizes fault information such as operating current and sheath circulating current at the installation location of the intelligent grounding box for line selection and location. First, it uses the abrupt changes in the three-phase operating current and three-phase sheath circulating current to initially determine whether insulation failure has occurred in the 35kV system. Through multi-criteria OR logic operations, the fault detection sensitivity can be improved, avoiding failure to operate under high-resistance grounding conditions. After the start-up criteria are met, this technical solution further utilizes the unbalanced components and waveform correlation in the three-phase current to detect whether the insulation failure fault occurs on this line. Using the phase-to-phase current of the fault component as a criterion further improves the reliability of the detection. Finally, after determining that an insulation failure fault exists on this line, the abnormal increase in the sheath circulating current of the faulty phase cable is used to determine whether the intelligent grounding box is located in the fault section, thereby determining the fault section range.

[0026] In a second aspect, an electronic device is provided, comprising: a memory for storing a computer program; and a processor for executing the computer program to implement the steps of the above-described cable insulation fault identification and location method based on operating current and sheath circulating current.

[0027] Thirdly, a storage medium is provided, on which a computer program is stored, which, when executed by a processor, is used to implement the steps of the above-described cable insulation fault identification and location method based on operating current and sheath circulating current.

[0028] Based on the above solution, the present invention provides an electronic device and a storage medium, comprising: one or more memories and one or more processors. The memories are used to store program code and intermediate data generated during program execution, storage of model output results, and storage of the model and model parameters; the processors are used for the processor resources occupied by the code execution and multiple processor resources occupied when training the model.

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a single-phase grounding fault in a neutral point grounding system via an arc suppression coil.

[0031] Figure 2 This is a flowchart of an embodiment of a cable insulation fault identification and location method based on operating current and sheath circulating current according to the present invention.

[0032] Figure 3 This is a waveform diagram of the three-phase current of a 35kV cable main cable in an embodiment of a cable insulation fault identification and location method based on operating current and sheath circulating current according to the present invention.

[0033] Figure 4 This is an embodiment of the cable insulation fault identification and location method based on operating current and sheath circulating current of the present invention, showing the waveform diagram of the three-phase current fault components of the main cable.

[0034] Figure 5 This is a waveform diagram of the phase-to-phase current of a single cycle fault component after a three-phase current fault, as shown in an embodiment of a cable insulation fault identification and location method based on operating current and sheath circulating current according to the present invention. Detailed Implementation

[0035] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0036] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0037] See Figure 1 , , , These represent the equivalent three-phase power supply electromotive force; the phase-to-ground distributed capacitance of line I is... The phase-to-ground distributed capacitance of line II is The equivalent capacitance per phase to ground of the busbar and the power supply behind it is: L is the arc suppression coil. This is for arc suppression coil compensation current. For faulty line II, the current flowing through phases B and C is its own capacitance current to ground. and The current flowing back from phase A is the sum of the capacitance currents of phases B and C to ground in the entire system, which is the current at the fault point. Therefore, when a ground fault occurs, the fault current flowing through the fault phase from the busbar to the fault point on the fault line is significantly greater than that of the other two non-faulty phases.

[0038] See Figure 2 The present invention provides a method for identifying and locating cable insulation faults based on operating current and sheath circulating current, which may include the following steps: Step S1: Real-time synchronous acquisition of the three-phase operating current of the cable line at the installation point of the intelligent grounding box. and three-phase protective layer circulation ; Step S2: Extract the first fault component of the three-phase operating current of the cable line; Step S3: Extract the second fault component of the three-phase sheath circulating current of the cable line; Step S4: Perform fault initiation logic judgment based on the first fault component and the second fault component; Step S5: When the fault initiation logic operation result is true, it is determined that an insulation fault has occurred in the cable line. The initiation time is marked, and the sampled data before the initiation time is marked as pre-fault data, and the sampled data after the initiation time is marked as post-fault data. The second half-cycle of the fault with the most concentrated transient components is selected as the data window, and the phase-to-phase current of the first fault component is calculated. Step S6: Calculate the phase-to-phase current amplitude of the first fault component in the second half-cycle after the fault, and determine whether a single-phase ground fault has occurred on the line. If it is determined that a single-phase ground fault has most likely occurred on the line, then perform fault phase identification. Step S7: After identifying the fault phase, continue to calculate the correlation coefficient of the phase-phase current curve of the first fault component, and determine whether the correlation coefficient conforms to the fault coefficient relationship. If so, it is determined that the line is likely to have a single-phase ground fault, and continue to identify the fault phase. If the two fault phase identification results are consistent, it is finally confirmed that the line has a single-phase ground fault.

[0039] Step S8: After determining that the line belongs to the faulty line, the next step of section location judgment is carried out. This includes taking the pre-fault data and post-fault data of the three-phase sheath circulating current of the cable line as the center of the marked start time T0, taking one cycle of each, calculating the fundamental amplitude, and determining whether the intelligent grounding box is in the faulty section. If so, an alarm is reported to the main station.

[0040] Based on the above solution, this application embodiment can determine which smart grounding box section the cable section where insulation failure occurs is located. Since a smart grounding box is installed approximately every 500m of cable line, this technical solution can narrow down the fault range from the entire line length to the area where a specific smart grounding box is located.

[0041] Optionally, embodiments of this application may also perform the following operations: The process of real-time acquisition of the three-phase operating current and three-phase sheath circulating current of the cable line at the installation point of the intelligent grounding box specifically includes: Real-time synchronous acquisition of three-phase operating current of cable lines at the installation point of the intelligent grounding box and three-phase protective layer circulation Where p = a, b, c, and the sampled value at the k-th point is denoted as . The operating current sampling rate is not less than 20kHz, the number of sampling points per cycle is N, and k is the current sampling point number.

[0042] Optionally, embodiments of this application may also perform the following operations: The process of extracting fault components specifically includes: Extracting the current fault component of the three-phase operating current of the cable line , expressed as formula (1): (1) Extracting the fault component of the three-phase sheath circulating current in the cable line , expressed as formula (2): (2).

[0043] Optionally, embodiments of this application may also perform the following operations: The fault start logic judgment process specifically includes a first logic judgment and a second logic judgment, expressed as formulas (3) and (4): (3) (4) An OR operation is performed on the first and second logical judgments. If the result of the fault initiation logical operation is true, an insulation fault is determined to have occurred in the cable line, and the initiation time T0 is marked. The sampled data before the initiation time T0 is marked as the pre-fault data, and the sampled data after the initiation time T0 is marked as the post-fault data. If the result of the fault initiation logical operation is false, the cable line is considered to be normal, and no action is taken.

[0044] Optionally, embodiments of this application may also perform the following operations: The process of calculating the phase-to-phase current of the first fault component is specifically expressed as formula (5): (5) in, .

[0045] Optionally, this embodiment may also perform the following operations: Calculate the phase-to-phase current amplitude of the first fault component within the second half-cycle after the fault. If the amplitude satisfies formula (6), then it is considered that a single-phase ground fault has most likely occurred on the line, and then the first fault phase identification is performed, where, And sorted from largest to smallest, formula (6) is expressed as: (6) in, These are the maximum values ​​of the three phase-to-phase current amplitudes. K3 represents the minimum amplitude of the three phase-to-phase currents, and K3 is an adjustable reliability coefficient.

[0046] Optionally, this embodiment may also perform the following operations: The initial fault phase identification process specifically includes: like If the minimum value is found, then the faulty phase is phase C; if If the minimum value is found, then the faulty phase is phase A; if... If the value is the smallest, then the faulty phase is phase B.

[0047] Optionally, this embodiment may also perform the following operations: The process of continuing to calculate the correlation coefficient of the phase-phase current curve of the first fault component can be, specifically, after the fault phase is identified, continuing to calculate the correlation coefficient of the phase-phase current curve of the first fault component. The correlation coefficient ranges between [-1, 1], and is expressed as formula (7).

[0048]

[0049] (7)

[0050] Wherein, if the correlation coefficient satisfies formula (8): (8) If the first fault is detected, it is assumed that a single-phase ground fault has most likely occurred on the line. A second fault phase identification process is then performed. If the result of the second fault phase identification matches the result of the first, a single-phase ground fault is finally confirmed. K is the minimum three-phase correlation coefficient, and K4 is an adjustable constant coefficient.

[0051] Optionally, this embodiment may also perform the following operations: The second fault phase identification process specifically includes: like yes Then the faulty phase is phase B; if yes Then the faulty phase is phase C; if yes If so, the faulty phase is phase A.

[0052] Based on the above scheme, this application embodiment comprehensively utilizes fault information such as operating current and sheath circulating current at the installation location of the intelligent grounding box for line selection and location. First, the sudden changes in the three-phase operating current and three-phase sheath circulating current are used to initially determine whether insulation failure has occurred in the 35kV system. Through the "OR logic" operation of multiple criteria, the fault detection sensitivity can be improved, avoiding failure to operate under high-resistance grounding conditions. After the start-up criteria are met, this application embodiment further utilizes the unbalanced component and waveform correlation in the three-phase current to detect whether the insulation failure fault occurs in this line. Among them, using the phase-to-phase current of the fault component as a criterion can further improve the reliability of detection. Finally, after determining that there is an insulation failure fault in this line, the abnormal increase in the sheath circulating current of the faulty phase cable is used to determine whether the intelligent grounding box is located in the fault section, thereby determining the fault section range.

[0053] In practical applications, the cable insulation fault identification and location method based on operating current and sheath circulating current provided in this application specifically includes: 1. Real-time synchronous acquisition of three-phase operating current of cable lines at the installation point of the intelligent grounding box. and three-phase protective layer circulation Where p = a, b, c, and the sampled value at the k-th point is denoted as . The operating current sampling rate is not less than 20kHz, the number of sampling points per cycle is N, and k is the current sampling point number.

[0054] 2. Extract the current fault component of the three-phase operating current of the cable line. The formula is as follows:

[0055] 3. Extract the fault component of the three-phase sheath circulating current in the cable line. The formula is as follows:

[0056] 4. Regarding and The fault initiation logic is determined by performing an OR operation on criteria 1 and 2 below. If the result is true, the cable line is considered to have an insulation fault, and the initiation time T0 is marked. The sampled data before initiation time T0 is marked as pre-fault data, and the sampled data after initiation time T0 is marked as post-fault data. If the result is false, the cable line is considered normal, and no action is taken.

[0057] The formulas for Criterion 1 and Criterion 2 are as follows: Criterion 1:

[0058] Criterion 2:

[0059] Wherein, K1 and K2 are adjustable reliability coefficients, with a default value of 1.1 for K1 and K2.

[0060] 5. When the fault initiation logic operation result is true, select the second half-cycle of the fault with the most concentrated transient components as the data window, and calculate the phase-to-phase current of the fault component of the operating current, as shown in the following formula:

[0061] 6. Calculate the phase-to-phase current amplitude of the fault component within the second half-cycle after the fault. The values ​​are sorted from largest to smallest. If the following formula is satisfied, it is considered that a single-phase ground fault has most likely occurred on this line, and then the fault phase is identified.

[0062]

[0063] in, The maximum amplitude of the three phase-to-phase currents, K3 represents the minimum amplitude of the three phase-to-phase currents, and K3 is an adjustable reliability coefficient with a default value of 2. The fault phase identification method is as follows: If... If the minimum value is found, then the faulty phase is phase C; if If the minimum value is found, then the faulty phase is phase A; if If the value is the smallest, then the faulty phase is phase B.

[0064] 7. Under the premise that the conditions in the previous step are met, continue to calculate the correlation coefficient of the phase-phase current curve of the fault component. The correlation coefficient ranges from [-1, 1], as shown in the following formula:

[0065]

[0066]

[0067] 8. If the correlation coefficients satisfy the following relationship, it is considered that a single-phase ground fault has likely occurred on this line. Then, fault phase identification is performed. If the fault phase identification result is consistent with the fault identified in step 7, then it is finally confirmed that a single-phase ground fault has occurred on this line. Otherwise, this line is considered a healthy line.

[0068]

[0069] In the formula, K is the minimum three-phase correlation coefficient, and K4 is an adjustable constant coefficient, which defaults to -0.6.

[0070] The fault phase identification method is: if yes Then the faulty phase is phase B; if yes Then the faulty phase is phase C; if yes If so, the faulty phase is phase A.

[0071] 9. If, based on the above assessment, it can be determined that this line is a faulty line, proceed to the next step of section location determination. Otherwise, return directly.

[0072] 10. Taking the start-up time T0 as the center, take one cycle of the cable line sheath circulating current before and after the fault, calculate the fundamental amplitude, and mark them as follows: and If the following criteria are met, the intelligent grounding box is determined to be in a fault zone, and an alarm is sent to the main station.

[0073]

[0074] in, To obtain the maximum amplitude after a three-phase fault, To take the maximum amplitude before a three-phase fault. K3 is an adjustable reliability coefficient with a default value of 1.2.

[0075] Therefore, when a ground fault occurs, the voltage to ground of the faulty phase drops to zero, and the capacitance to ground of the faulty phase in each line discharges rapidly; the voltage to ground of the healthy phase rises to the line voltage, and the capacitance to ground of the healthy phase in each line charges rapidly. A transient component inevitably appears during the charging and discharging process, with an amplitude several to ten times that of the steady-state component, and is unaffected by the arc suppression coil. Simultaneously, the line voltage and load current of each outgoing line can be considered essentially unchanged before and after the ground fault. Therefore, the three-phase current mutation signal of a healthy line (including the part after the fault point of the faulty line) is the capacitance current of each phase to ground in that line, with similar amplitudes and consistent waveforms; while in the part of the faulty line before the fault point, only the fault components of the two healthy phases have similar amplitudes and consistent waveforms, while the faulty phase, because it contains the capacitance current of the entire system flowing from the ground point, has a significantly different amplitude and phase from the two healthy phases. Based on the transient components of the operating current fault, a single-phase ground fault identification criterion can be designed.

[0076] Meanwhile, cable line grounding is caused by a short circuit between the cable core and the cable metal sheath, resulting in multiple grounding points in the cable metal sheath and forming a circulating current. The circulating current only flows between the grounding point of the cable metal sheath and the insulation failure point in this section of the cable. Therefore, the circulating current of the cable metal sheath can be used to further identify the grounding fault and the fault section, narrowing the fault range from the entire line to the possible fault area, which can greatly reduce the workload of long-distance cable fault repair.

[0077] To illustrate the implementation process of the embodiments of this application in detail, the calculation process of the embodiments of this application is explained based on the waveform of the dynamic simulation test.

[0078] To facilitate understanding, the technical principles of the embodiments of this application will be introduced first: First: Cable insulation failure is a short-circuit fault with transition resistance between the main cable and the cable metal sheath. It can be decomposed into two relatively independent parts: 1) a single-phase grounding fault of the 35kV neutral point on the main cable through the arc suppression coil grounding system; 2) a two-point grounding fault in a section of the cable sheath under the induced voltage of the cable sheath.

[0079] Second: For a single-phase ground fault on the main cable, since the system line voltage remains unchanged before and after the ground fault, the load current can be considered unchanged before and after the fault. The change in the three-phase current of a healthy line is mainly due to the change in the corresponding phase-to-ground capacitance current, with approximately equal amplitudes and similar waveforms. However, the faulty phase of the faulty line will carry the ground current at the fault point, while the two healthy phases will only carry the capacitance current of their own line. Therefore, the amplitude and waveform of the faulty phase are significantly different from those of the other two healthy phases.

[0080] Third: Since the models, lengths, and laying paths of three-phase single-core cables are basically the same, the abrupt change and amplitude difference of the sheath circulating current are relatively small when the insulation is intact. However, when the insulation of a phase fails, a two-point grounding fault is formed, and the cable sheath circulating current will be superimposed with a portion of the fault point's ground current, causing a significant increase in the cable sheath circulating current, which can reach more than 50% of the operating current. The amplitude of the cable sheath circulating current of the faulted phase changes significantly before and after the grounding.

[0081] The embodiments of this application will now be described based on the following waveforms: Depend on Figure 3 visible, Figure 3 The waveform diagram shows the three-phase current of the main cable of a 35kV cable. The three-phase load current on the main cable remained basically unchanged before and after the fault, but a sudden change occurred in the fault phase (phase A).

[0082] Depend on Figure 4 visible, Figure 4 The extracted waveforms of the three-phase current fault components in the main cable show a significant difference between the fault component waveforms of the faulty phase and the fault components of the other two healthy phases. Furthermore, due to the abrupt change in the faulty phase's transient response, the fault detection logic can determine that the system is malfunctioning and proceed to the subsequent fault line identification stage.

[0083] like Figure 5 As shown, one cycle of data after the fault was collected, and correlation analysis was performed on the phase-to-phase current waveforms of the fault components. It can be seen that the current waveforms of phases BC are basically the same, while the current waveforms of phases AB and CA are significantly different. After calculation according to the technical solution process, the minimum correlation coefficient is less than -0.9, and the faulty phases are the same, which confirms that a single-phase ground fault has occurred in phase A of this line.

[0084] When a single-phase ground fault is located within the cable section containing a smart grounding box, the circulating current in the metal sheath of that section changes from a single-point grounding to a two-point grounding. Due to the presence of induced voltage, the circulating current in the metal sheath between the two grounding points of the faulty phase increases significantly. Analysis and calculation of over 1000 simulated and on-site waveforms showed that the circulating current in the metal sheath of the faulty section generally increased to more than 1.5 times its original value. The amplitudes of the three-phase circulating currents in sections with intact metal sheaths showed little correlation and no significant change before and after the fault.

[0085] In one embodiment, a computer device is provided, which may be a server. The computer device includes a processor, memory, and a network interface connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The database stores data. The network interface communicates with external terminals via a network connection. When the computer program is executed by the processor, it implements a cable insulation fault identification and location method based on operating current and sheath circulating current.

[0086] Those skilled in the art will understand that the computer device structure shown in this embodiment is only a partial structure related to the solution of this application and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than shown in this embodiment, or combine certain components, or have different component arrangements.

[0087] In one embodiment, a computer device is also provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above method embodiments.

[0088] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon that, when executed by a processor, implements the steps in the above method embodiments.

[0089] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0090] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0091] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for identifying and locating cable insulation faults based on operating current and sheath circulating current, characterized in that, Includes the following steps: Real-time synchronous acquisition of three-phase operating current of cable lines at the installation point of the intelligent grounding box and three-phase protective layer circulation Where p = a, b, c, and the sampled value at the k-th point is denoted as . The operating current sampling rate is not less than 20kHz, and the number of sampling points per cycle is N, where k is the current sampling point number; Extract the first fault component of the three-phase operating current of the cable line. Extract the second fault component of the three-phase sheath circulating current in the cable line; Fault initiation logic is determined based on the first fault component and the second fault component. When the fault initiation logic operation result is true, it is determined that an insulation fault has occurred in the cable line. The initiation time is marked, and the sampled data before the initiation time is marked as pre-fault data, and the sampled data after the initiation time is marked as post-fault data. The second half-cycle of the fault with the most concentrated transient components is selected as the data window, and the phase-to-phase current of the first fault component is calculated. Calculate the phase-to-phase current amplitude of the first fault component within the second half-cycle after the fault to determine whether a single-phase ground fault has occurred on the line. If it is determined that a single-phase ground fault has most likely occurred on the line, then perform fault phase identification. After fault phase identification, the correlation coefficient of the phase-phase current curve of the first fault component is calculated to determine whether the correlation coefficient conforms to the fault coefficient relationship. If so, it is determined that the line is likely to have a single-phase ground fault, and the fault phase identification is continued. If the two fault phase identification results are consistent, the line is finally confirmed to have a single-phase ground fault. The extraction of fault components specifically includes: Extracting the current fault component of the three-phase operating current of the cable line , expressed as formula (1): （1） Extracting the fault component of the three-phase sheath circulating current in the cable line , expressed as formula (2): （2） The fault initiation logic judgment includes a first logic judgment and a second logic judgment, expressed as formulas (3) and (4): （3）； （4）； An OR operation is performed on the first and second logical judgments. If the result of the fault initiation logical operation is true, an insulation fault is determined to have occurred in the cable line, and the initiation time T0 is marked. The sampled data before the initiation time T0 is marked as the pre-fault data, and the sampled data after the initiation time T0 is marked as the post-fault data. If the result of the fault initiation logical operation is false, the cable line is considered to be normal, and no action is taken. The phase-to-phase current for calculating the first fault component is expressed as formula (5): （5） in, Calculate the phase-to-phase current amplitude of the first fault component within the second half-cycle after the fault. If the amplitude satisfies formula (6), then it is considered that a single-phase ground fault has most likely occurred on the line, and then the first fault phase identification is performed, where, And sorted from largest to smallest, formula (6) is expressed as: （6） in, These are the maximum values ​​of the three phase-to-phase current amplitudes. K3 represents the minimum amplitude of the three phase-to-phase currents, and K3 is an adjustable reliability coefficient. The first fault phase identification includes: like If the minimum value is found, then the faulty phase is phase C; if If the minimum value is found, then the faulty phase is phase A; if... If the minimum value is found, then the faulty phase is phase B. The continued calculation of the phase-phase current curve correlation coefficient of the first fault component includes: After identifying the faulty phase, the correlation coefficient of the phase-phase current curve of the first fault component is calculated. The correlation coefficient ranges from [-1, 1] and is expressed as formula (7): （7） Wherein, if the correlation coefficient satisfies formula (8): （8） If the first fault is detected, it is assumed that a single-phase ground fault has most likely occurred on the line. A second fault phase identification process is then performed. If the result of the second fault phase identification matches the result of the first, a single-phase ground fault is finally confirmed. K is the minimum three-phase correlation coefficient, and K4 is an adjustable setpoint coefficient; The second fault phase identification includes: like yes Then the faulty phase is phase B; if yes Then the faulty phase is phase C; if yes If so, the faulty phase is phase A.

2. The method according to claim 1, characterized in that, After confirming that the line is a faulty line, the next step is to determine the section location, including: Centered on the marked start time T0, take one cycle of the three-phase sheath circulating current of the cable line before and after the fault, calculate the fundamental amplitude, and determine whether the intelligent grounding box is in the fault section. If so, an alarm is reported to the main station.

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