A high-voltage cable multi-dimensional monitoring method and system based on sheath current

Abstract

The application discloses a kind of high-voltage cable multidimensional monitoring method and system based on sheath current.The high-voltage cable multidimensional monitoring method of the application, comprising: establishing the cable grounding system multi-point monitoring system based on synchronous measurement system, and the composite current of three-phase cable body and sheath current are monitored;Utilize phasor operation to decompose composite current into load current and sheath current, and decompose sheath current into magnetic field induced current and main insulation leakage current;According to load current, magnetic field induced current and main insulation leakage current, calculate multidimensional characteristic variable;According to multidimensional characteristic variable, establish intelligent diagnosis model based on bidirectional long short-term memory network, through simulation calculation, the value and change rule of multidimensional characteristic variable when cable line appears various cable grounding system faults and main insulation defects are input into database, and form defect diagnosis criterion.The application can effectively diagnose cable grounding system defects, and greatly improve the reliability of high-voltage cable operation.

Description

Technical Field

[0001] This invention belongs to the field of online monitoring technology for high-voltage cables, specifically a multi-dimensional monitoring method and system for high-voltage cables based on sheath current. Background Technology

[0002] Compared to overhead lines, cable lines have advantages such as better environmental tolerance and higher reliability. Cross-linked polyethylene (XLPE) single-core high-voltage cables are increasingly prevalent in urban power grids, playing a more crucial role in ensuring safe and reliable power supply. The health status of these high-volume cable lines has a significant impact on the safe and stable operation of urban power grids. Furthermore, with the continuous increase in electricity demand and the year-on-year improvement in power supply reliability requirements, improving the accuracy of power cable operation status monitoring has become an urgent problem to solve. Strong magnetic and electric field coupling exists between the conductor and the metal sheath of a single-core cable. The load current carried by the three-phase cable core generates an alternating magnetic field around the core, which links with the metal sheath to induce a voltage. According to power safety regulations, the metal sheath of single-core high-voltage cables must be grounded. The main grounding methods are single-end grounding, cross-interconnection grounding, and double-end grounding. Cable lines with long transmission distances generally use cross-interconnection grounding, which can effectively reduce the induced voltage and circulating current on the metal sheath. Defects in the grounding system often cause changes in the metallic sheath current. Therefore, the metallic sheath current is one of the important state quantities used for cable line condition evaluation and fault diagnosis.

[0003] Du Boxue et al., Calculation and Application of Grounding Current of 220kV Cross-linked Polyethylene Power Cable, High Voltage Engineering, 2013, 39(5): 1034-1039, studied the analytical calculation formula of induced voltage in three-circuit cables without considering the mutual inductance between sheaths, which can be extended to multi-circuit cables with arbitrary arrangement. IEEE Std 575-2014 gives the form of grounding system of metal sheath of single-core AC cable, and simplified calculation formula of induced voltage of metal sheath of single-circuit and double-circuit cables. Tu Jingyun, Research on Fault Diagnosis and Location Technology of High Voltage Cable Based on Sheath Circulation Current Method, Huazhong University of Science and Technology, 2019, used the analytical method to calculate the induced voltage of sheath, considering the induced electromotive force generated on the sheath by the sheath current and the ground current. Yuan Yanling, Zhou Hao, Dong Jie, et al., Online monitoring and fault diagnosis technology of sheath current of high voltage power cable, High Voltage Engineering, 2015, 41(4): 1194-1203. They calculated the current based on the equivalent circuit model for three types of faults: water ingress in cross-connection box, open circuit fault caused by loose connection at the joint, and cable joint breakdown. They formulated fault diagnosis and location standards based on the ratio of fault current to normal current.

[0004] In summary, for a given operating cable line, the theoretical value of the sheath current under normal and fault conditions can be calculated using its cable structure and laying parameters, serving as a criterion for judgment in an online monitoring system based on sheath current. However, due to various unknown factors in the field, the results calculated using the ideal model differ significantly from the actual results, leading to misjudgments and omissions in field applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a multi-dimensional monitoring method and system for high-voltage cables based on sheath current. Based on a synchronous measurement system, the method performs online monitoring of multiple points on the cable line, processes the measurement data in real time and enters it into a database, analyzes the changing trend and law of the same characteristic parameter in the database over time, provides operational status diagnosis, and evaluates the defect type and severity by referring to the judgment results of multiple monitoring points, and completes the location of typical defects.

[0006] Therefore, the present invention adopts the following technical solution.

[0007] In a first aspect, the present invention provides a multi-dimensional monitoring method for high-voltage cables based on sheath current, comprising: Step 1: Establish a multi-point monitoring system for the cable grounding system based on a synchronous measurement system to monitor the composite current and sheath current of the three-phase cable body; Step 2: Use phasor operations to decompose the composite current into load current and sheath current, and decompose the sheath current into magnetic field induced current and main insulation leakage current. Step 3: Calculate multidimensional characteristic variables based on load current, magnetic field induced current and main insulation leakage current, which are used to diagnose the operating status of the cable grounding system and the performance of the main insulation. Step 4: Establish an intelligent diagnostic model based on a bidirectional long short-term memory network according to the multidimensional feature variables. Through simulation calculation, determine the values ​​and changes of the multidimensional feature variables when various cable grounding system faults and main insulation defects occur in the cable line. Record the data into the database to form diagnostic criteria.

[0008] Furthermore, in step 3, the multidimensional feature variables include the first to the fourth feature variables; the value of the third feature variable is used to determine whether there is a defect in the grounding system, and the fault type and fault location are located by combining the values ​​and variation patterns of the first and second feature variables; the fourth feature variable is used to diagnose the main insulation performance of the cable grounding system. The first characteristic variable is the ratio of the magnetic field induced current to the load current, used to eliminate sheath current fluctuations caused by load current changes; the second characteristic variable is the ratio of the maximum to minimum magnetic field induced current among the three monitoring points at the direct grounding box or cross-connection box, used to determine whether there is a three-phase imbalance fault in the cable grounding system; the third characteristic variable is the ratio of the first characteristic variable at the monitoring point at the beginning of the cross-connection loop to the first characteristic variable at the monitoring point at the end, used to identify faults where the sheath current amplitude does not change significantly; the fourth characteristic variable is the ratio of the main insulation leakage current of a certain section of cable at the current moment to the main insulation leakage current of the same section of cable at the previous measurement moment.

[0009] Furthermore, in step 1, the steps for establishing the multi-point monitoring system of the cable grounding system are as follows: three sheath current sensors are installed at both the direct grounding box and the cross-interconnection box to monitor the sheath current; three composite current sensors installed on the outside of the three-phase cable body are added at the direct grounding box located at the beginning of the cable to monitor the composite current; a measurement host is installed at each box to collect and transmit the current signals of each sensor.

[0010] Furthermore, the sheath current sensor is installed on the grounding wire in the direct grounding box and the transposition wire in the cross-interconnection box.

[0011] Furthermore, the synchronous measurement system includes multiple measurement hosts, each of which includes a timing module, a data acquisition module, and a communication module. The timing module synchronizes the time of each measurement host, the data acquisition module acquires the current signals of each sensor at high frequency, and the communication module aggregates the current signals to the cloud platform, thereby realizing multi-dimensional online monitoring of the operating status and main insulation performance of the cable grounding system.

[0012] Furthermore, in step 2, each current signal acquired by each measurement host is digitally low-pass filtered to extract the fundamental component, which is then used to determine the sheath current. Calculate its composite current using the reference phasor. Time difference across zero t 1 and convert it to sheath current phase angle ;

[0013] Calculate the sheath current using the following formula With load current The load current phase angle between :

[0014] At the phase angle of the load current Based on this, the load current amplitude is calculated using the vector triangle cosine theorem.

[0015] Furthermore, in step 2, the relationship between the load current and the sheath current is as follows:

[0016] in, for X Phase load current, X =A, B, C; It is a magnetic field-induced current. The main insulation leakage current is represented by dots on the physical quantity, indicating that it is in phasor form. This is the coupling ratio coefficient.

[0017] Furthermore, in step 2, take m Group monitoring data, each group of data includes data at a specific moment. X Phase load current and the first i The sheath current at each sensor monitoring point is used to obtain the coupling ratio coefficient through multi-data fitting. and main insulation leakage current The objective function for fitting the first-order linear equation is as follows:

[0018] In the formula, for j In the group data X Phase load current, For the first j Sheath current in the set of data, For the first i The coupling ratio coefficient at each sensor monitoring point For the first i Leakage current at each sensor monitoring point and All are complex numbers; the total leakage current of the cable section is obtained by subtracting the phasors of the main insulation leakage current at the first and last monitoring points of each cable section.

[0019] Furthermore, the first characteristic variable The calculation formula is as follows: ,in, This is the phase difference between the magnetic field-induced current and the load current. It is a magnetic field-induced current. This is the load current; Third characteristic variable The calculation formula is as follows:

[0020] in, , These are the first characteristic variables at the first monitoring point of the cross-connection loop and the first characteristic variables at the last monitoring point, respectively. The ratio of the amplitude of the first characteristic variable at the first and last monitoring points. The phase difference of the first characteristic variable at the first and last monitoring points; Fourth characteristic variable The calculation formula is as follows:

[0021] in, This represents the leakage current of the main insulation of a certain section of the cable line at the current moment. This represents the leakage current of the main insulation of this section of the cable at the previous measurement time. The phase difference between the leakage currents of the main insulation at two different moments is given.

[0022] Secondly, the present invention provides a high-voltage cable multi-dimensional monitoring system based on sheath current, for implementing the above-mentioned high-voltage cable multi-dimensional monitoring method, which includes a phasor calculation module, a current decomposition module and a data processing and analysis module. The phasor calculation module uses the load current of a certain phase as a reference phasor to calculate the amplitude and phase information of the remaining current and voltage signals. The current decomposition module decomposes the composite current into load current and sheath current through phasor operations; and decomposes the sheath current into magnetic field induced current and main insulation leakage current through an embedded algorithm. The data processing and analysis module performs calculations on the magnetic field induced current and the main insulation leakage current to obtain multi-dimensional feature parameters. It then compares these parameters with the defect diagnosis criteria embedded in the intelligent diagnostic model to provide cable operation diagnosis results. Simultaneously, it records the diagnosis results into the database, analyzes the changing trends of the multi-dimensional feature parameters, and predicts potential defects.

[0023] The beneficial effects of this invention are: 1. Relying on the multi-point monitoring system of cable grounding system based on synchronous measurement system, the phase amplitude of each current in the cable line can be obtained, and the phase relationship between each current can also be obtained. A phasor system based on load current can be established, and further decomposition of composite current and sheath current can be realized.

[0024] 2. Traditional monitoring criteria rely on sheath current amplitude for condition diagnosis, neglecting the influence of leakage current and failing to eliminate sheath current variations caused by load current fluctuations, leading to frequent missed or false diagnoses. This invention utilizes sheath current decomposition to obtain magnetic field induced current and leakage current, separating the leakage current and calculating the first characteristic variable based on the magnetic field induced current. This effectively eliminates the influence of load current. Furthermore, the second and third characteristic variables are used in conjunction with the diagnosis to accurately determine the fault type and location of the grounding system.

[0025] 3. Based on the leakage current obtained from each monitoring point, the total leakage current of each line segment can be calculated. Based on the leakage current amplitude, the aging of the line insulation can be effectively monitored. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a flowchart of a multi-dimensional monitoring method for high-voltage cables based on sheath current according to the present invention; Figure 2 This is a schematic diagram of the multi-point monitoring system for the cable grounding system of the present invention; Figure 3 This is a schematic diagram for fault diagnosis of the horizontally laid line according to the present invention; Figure 4 This is a structural block diagram of a high-voltage cable multi-dimensional monitoring system based on sheath current according to the present invention. Detailed Implementation

[0028] Specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0029] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings, and the drawings do not constitute a limitation on the embodiments of the present invention.

[0030] Example 1 This embodiment describes a multi-dimensional monitoring method for high-voltage cables based on sheath current, such as... Figure 1 As shown, the steps are as follows: Step 1: Establish a multi-point monitoring system for the cable grounding system based on a synchronous measurement system to monitor the composite current and sheath current of the three-phase cable body; Step 2: Use phasor operations to decompose the composite current into load current and sheath current, and decompose the sheath current into magnetic field induced current and main insulation leakage current. Step 3: Calculate multidimensional characteristic variables based on load current, magnetic field induced current and main insulation leakage current, which are used to diagnose the operating status of the cable grounding system and the performance of the main insulation. Step 4: Establish an intelligent diagnostic model based on a bidirectional long short-term memory network according to the multidimensional feature variables. Through simulation calculation, determine the values ​​and changes of the multidimensional feature variables when various cable grounding system faults and main insulation defects occur in the cable line. Record the data into the database to form diagnostic criteria.

[0031] Specifically, in step 1, the establishment of the multi-point monitoring system for the cable grounding system involves the following steps: Three sheath current sensors are installed at both the direct grounding box and the cross-connection box to monitor the sheath current; three composite current sensors, installed externally on the three-phase cable body, are added at the direct grounding box located at the cable's beginning to monitor the composite current; a measurement host is installed at each box to collect and transmit the current signals from each sensor. The composite current sensor has a measurement range of AC 0-2000A, the sheath current sensor has a measurement range of AC 0-500A, the measurement resolution is 0.1mA, and the measurement accuracy is ±1%.

[0032] The sheath current sensor is installed on the grounding wire in the direct grounding box and on the transposition wire in the cross-interconnection box.

[0033] The synchronous measurement system comprises multiple measurement hosts, each corresponding to a housing (either a direct grounding housing or a cross-connection housing). Each measurement host includes a timing module, a data acquisition module, and a communication module. The timing module synchronizes the time of each measurement host, employing BeiDou satellite navigation for high-precision timing, ensuring that the time synchronization error of each measurement host is controlled within 100 nanoseconds and the timestamp error within 1 microsecond in complex electromagnetic environments. The data acquisition module acquires current signals from each sensor at high frequency, with a sampling current frequency measurement error of less than 0.02%, providing a hardware foundation for subsequent current decomposition. The communication module aggregates all current signals to a cloud platform, enabling multi-dimensional online monitoring of the cable grounding system's operating status and main insulation performance.

[0034] Specifically, in step 3, the multidimensional feature variables include the first feature variable to the fourth feature variable; the value of the third feature variable RSE is used to determine whether there is a defect in the grounding system, and the fault type and fault location are located by combining the values ​​and changes of the first feature variable RML and the second feature variable RUB; the fourth feature variable is used to diagnose the main insulation performance of the cable grounding system.

[0035] The first characteristic variable is the ratio of the magnetic field induced current to the load current, used to eliminate sheath current fluctuations caused by load current changes; the second characteristic variable is the ratio of the maximum to minimum magnetic field induced current among the three monitoring points at the direct grounding box or cross-connection box, used to determine whether there is a three-phase imbalance fault in the cable grounding system; the third characteristic variable is the ratio of the first characteristic variable at the monitoring point at the beginning of the cross-connection loop to the first characteristic variable at the monitoring point at the end, used to identify faults where the sheath current amplitude does not change significantly; the fourth characteristic variable is the ratio of the main insulation leakage current of a certain section of cable at the current moment to the main insulation leakage current of the same section of cable at the previous measurement moment.

[0036] Specifically, in step 2, each current signal acquired by each measurement host is digitally low-pass filtered to extract the fundamental component, which is then used to determine the sheath current. Calculate its composite current using the reference phasor. Time difference across zero t 1 and convert it to sheath current phase angle ;

[0037] Calculate the sheath current using the following formula With load current The load current phase angle between :

[0038] The load current is consistent throughout the cable line. If the load current is replaced with a reference phasor, the magnitude and phase relationship between the sheath current and the load current at each monitoring point in the entire cable line can be obtained.

[0039] It is known that the sheath current at any point consists of magnetic field induced current and leakage current, and the magnetic field induced current is proportional to the load current. At the load current phase angle... Based on this, the load current amplitude is calculated using the vector triangle cosine theorem.

[0040] Taking phase A load current as an example, the relationship between load current and sheath current is as follows:

[0041] in, for A Phase load current, It is a magnetic field-induced current. The main insulation leakage current is represented by dots on the physical quantity, indicating that it is in phasor form. This is the coupling ratio coefficient.

[0042] The most commonly used numerical analysis method is the least squares method, taking...m Group monitoring data ( m (10-50 values ​​can be selected), each data set includes a specific moment. A Phase load current and the first i Sheath current at each sensor monitoring point ( i =1,2,3,…,12), the coupling ratio coefficient is obtained through multi-data fitting. and main insulation leakage current The objective function for fitting the first-order linear equation is as follows:

[0043] In the formula, for j In the group data A Phase load current, For the first j Sheath current in the set of data, For the first i The coupling ratio coefficient at each sensor monitoring point For the first i Leakage current at each sensor monitoring point and All are complex numbers. The total leakage current of a cable segment is obtained by subtracting the phasors of the main insulation leakage current at the monitoring points at the beginning and end of each segment.

[0044] The calculation of the above four characteristic variables will be explained in detail below.

[0045] First characteristic variable The ratio of the phasor of the magnetic field induced current to the phasor of the load current at the monitoring point is calculated using the following formula: ,in, This is the phase difference between the magnetic field-induced current and the load current. It is a magnetic field-induced current. This is the load current.

[0046] This characteristic variable can eliminate sheath current fluctuations caused by load current changes and effectively reflect changes in the operating status of the sheath circuit. When the operating status of the cable grounding system does not change, this characteristic variable remains unchanged and can only reflect defects that cause significant changes in the amplitude of the sheath current.

[0047] Second characteristic variable This is the ratio of the maximum to the minimum amplitude of the magnetic field induced current at three monitoring points in a directly grounded box or cross-interconnected box. It aims to reflect the imbalance of the sheath current in the three cross-interconnected loops, and this indicator can effectively determine whether a three-phase unbalanced fault exists in the grounding system. The calculation formula is as follows:

[0048] in, This represents the maximum value of the magnetic field-induced current at the three monitoring points inside the enclosure. It is the minimum value of the magnetic field induced current amplitude among the three monitoring points inside the box.

[0049] Third characteristic variable The first characteristic variable at the monitoring point at the first and last direct grounding box of any cross-connection loop. The ratio of this value to the value of the sheath current can be used to identify faults such as water immersion in cross-connection boxes and multi-point grounding, where the amplitude of the sheath current does not change significantly. The calculation formula is as follows:

[0050] in, , These are the first characteristic variables at the first monitoring point of the cross-connection loop and the first characteristic variables at the last monitoring point, respectively. The ratio of the amplitude of the first characteristic variable at the first and last monitoring points. The phase difference of the first characteristic variable at the first and last monitoring points.

[0051] Fourth characteristic variable This reflects the change in leakage current over time in a certain section of the line. When its amplitude is greater than 1 and the phase angle is less than 0, it indicates that the insulation of that section of the line has aged. The calculation formula is as follows:

[0052] in, This represents the leakage current of the main insulation of a certain section of the cable line at the current moment. This represents the leakage current of the main insulation of this section of the cable at the previous measurement time. The phase difference between the leakage currents of the main insulation at two different moments is given.

[0053] Taking a simulation model as an example, this invention implements a multi-dimensional monitoring method for high-voltage cables. The simulation uses PSCAD to establish a cross-interconnection model of a three-phase cable, as shown below. Figure 2 As shown, the main cross-connection section is 1500m long, and each smaller cross-connection section is 500m long. The cable used is 64 / 110YJLW02-630mm². 2 The structural parameters were simulated; the power supply adopted three 110kV single-phase AC voltage source models, with the three phase angles differing by 120°.

[0054] Establish a multi-point monitoring system for cable grounding systems based on synchronization systems, such as Figure 2 As shown in Table 1, the sheath current measured at each monitoring point and its corresponding characteristic variables are as follows.

[0055] Table 1. Protective layer current and its corresponding characteristic variables

[0056] Taking the current decomposition at each monitoring point of the first direct grounding box as an example, the load was adjusted and the load current and sheath current were measured to obtain 10 sets of data. The load current and the sheath current at each monitoring point of the first direct grounding box were obtained by decomposing the composite current using phasor operation, as shown in Table 2 below.

[0057] Table 2 Current Data

[0058] Number of sampling points m =10, substitute each set of data into the objective function:

[0059] The magnetic field induced current and the main insulation leakage current in the sheath current can be obtained.

[0060]

[0061] Based on the leakage current and magnetic field induced current obtained from step 2, the characteristic variables of each monitoring point at the first direct grounding box can be calculated. .

[0062]

[0063]

[0064]

[0065] Feature variables at other monitoring points The characteristic variables at each monitoring point can all be obtained using this method. After calculating the leakage current, the characteristic variables of the line can be calculated. , And the total leakage current of each section of the line.

[0066] By inputting the characteristic variables of each monitoring point during normal operation into the Bi-LSTM algorithm database, and similarly inputting the characteristic variables of the line when various faults occur in the grounding system into the training model, diagnostic criteria for various grounding system defects and main insulation defects can be formed.

[0067] The online monitoring criteria are listed below: Table 3 Online monitoring criteria during normal operation

[0068] Table 4. Online monitoring criteria for interlayer short circuits.

[0069] Table 5 Online monitoring criteria for multiple grounding of the sheath.

[0070] Table 6 Online monitoring criteria for the occurrence of open circuit in the sheath grounding wire

[0071] Table 7 Online monitoring criteria for cross-connect box immersion.

[0072] Table 8 Online monitoring criteria for cross-connect box transposition errors

[0073] Taking the diagnosis of horizontally laid lines as an example, the values ​​and variation patterns of characteristic variables are as follows: Figure 3 As shown, firstly based on the third characteristic variable The value of is used to determine whether there is a defect in the grounding system. If a defect exists, each characteristic variable is verified. If the value is 0, then the diagnosis is an open grounding fault; if each characteristic variable is 0, then the diagnosis is an open grounding fault. If it is not 0, then check whether its maximum value is greater than 1.7, based on the third characteristic variable. Second characteristic variable The value of the judgment can distinguish between short circuit faults between sheaths, cross-connection box transposition errors, multiple grounding of sheaths, and water immersion faults in cross-connection boxes.

[0074] Example 2 This embodiment provides a multi-dimensional monitoring system for high-voltage cables based on sheath current, used to implement the multi-dimensional monitoring method for high-voltage cables based on sheath current described in Embodiment 1, such as... Figure 3 As shown, it consists of a phasor calculation module, a current decomposition module, and a data processing and analysis module.

[0075] The phasor calculation module uses the load current of a certain phase as a reference phasor to calculate the amplitude and phase information of the remaining current and voltage signals. The current decomposition module decomposes the composite current into load current and sheath current through phasor operations; and decomposes the sheath current into magnetic field induced current and main insulation leakage current through an embedded algorithm. The data processing and analysis module performs calculations on the magnetic field induced current and the main insulation leakage current to obtain multi-dimensional feature parameters. It then compares these parameters with the embedded defect diagnosis criteria to provide cable operation diagnosis results. Simultaneously, it records the diagnosis results into the database, analyzes the changing trends of the multi-dimensional feature parameters, and makes predictions about potential defects.

[0076] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to the above embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A multi-dimensional monitoring method for high-voltage cables based on sheath current, characterized in that, include: Step 1: Establish a multi-point monitoring mode for the cable grounding system based on a synchronous measurement system to monitor the composite current and sheath current of the three-phase cable body. Step 2: Use phasor operations to decompose the composite current into load current and sheath current, and decompose the sheath current into magnetic field induced current and main insulation leakage current. Step 3: Calculate multidimensional characteristic variables based on load current, magnetic field induced current and main insulation leakage current, which are used to diagnose the operating status of the cable grounding system and the performance of the main insulation. Step 4: Establish an intelligent diagnostic model based on a bidirectional long short-term memory network according to the multidimensional feature variables. Through simulation calculation, determine the values ​​and changes of the multidimensional feature variables when various cable grounding system faults and main insulation defects occur in the cable line. Record the data into the database to form defect diagnosis criteria. In step 2, the current signals acquired by each measurement host in the synchronous measurement system are digitally low-pass filtered to extract the fundamental component, which is then used to determine the sheath current. Calculate its composite current using the reference phasor. Time difference across zero t 1 and convert it to sheath current phase angle ; Calculate the sheath current using the following formula With load current The load current phase angle between : At the phase angle of the load current Based on this, the load current amplitude is calculated using the vector triangle cosine theorem.

2. The multi-dimensional monitoring method for high-voltage cables according to claim 1, characterized in that, In step 3, the multidimensional feature variables include the first to the fourth feature variables; the value of the third feature variable is used to determine whether there is a defect in the grounding system, and the fault type and fault location are located by combining the values ​​and changing patterns of the first and second feature variables. The fourth characteristic variable is used to diagnose the main insulation performance of the cable grounding system; The first characteristic variable is the ratio of magnetic field induced current to load current, which is used to eliminate the fluctuation of sheath current caused by changes in load current. The second characteristic variable is the ratio of the maximum to the minimum value of the magnetic field induced current at the three monitoring points at the direct grounding box or cross-interconnection box, which is used to determine whether there is a three-phase imbalance fault in the cable grounding system; the third characteristic variable is the ratio of the first characteristic variable at the monitoring point at the beginning of the cross-interconnection loop to the first characteristic variable at the monitoring point at the end, which is used to identify faults where the sheath current amplitude does not change much. The fourth characteristic variable is the ratio of the leakage current of the main insulation of a certain section of cable at the current moment to the leakage current of the main insulation of the same section of cable at the previous measurement moment.

3. The multi-dimensional monitoring method for high-voltage cables according to claim 1, characterized in that, In step 1, the steps for establishing the multi-point monitoring system of the cable grounding system are as follows: three sheath current sensors are installed at both the direct grounding box and the cross-interconnection box to monitor the sheath current; three composite current sensors installed on the outside of the three-phase cable body are added at the direct grounding box located at the beginning of the cable to monitor the composite current; a measurement host is installed at each box to collect and transmit the current signals of each sensor.

4. The multi-dimensional monitoring method for high-voltage cables according to claim 3, characterized in that, The sheath current sensor is installed on the grounding wire in the direct grounding box and on the transposition wire in the cross-interconnection box.

5. The multi-dimensional monitoring method for high-voltage cables according to claim 3, characterized in that, The synchronous measurement system includes multiple measurement hosts, each of which includes a timing module, a data acquisition module, and a communication module. The timing module synchronizes the time of each measurement host, the data acquisition module acquires the current signals of each sensor at high frequency, and the communication module aggregates the current signals to the cloud platform, thereby realizing multi-dimensional online monitoring of the operating status and main insulation performance of the cable grounding system.

6. The multi-dimensional monitoring method for high-voltage cables according to claim 1, characterized in that, In step 2, the relationship between the load current and the sheath current is as follows: in, for X Phase load current, X =A, B, C; It is a magnetic field-induced current. The main insulation leakage current is represented by dots on the physical quantity, indicating that it is in phasor form. This is the coupling ratio coefficient.

7. The multi-dimensional monitoring method for high-voltage cables according to claim 6, characterized in that, In step 2, take m Group monitoring data, each group of monitoring data includes data at a specific time. X Phase load current and the first i The sheath current at each sensor monitoring point is used to obtain the coupling ratio coefficient through multi-data fitting. and main insulation leakage current The objective function for fitting the first-order linear equation is as follows: In the formula, For the first j In the group data X Phase load current, For the first j Sheath current in the set of data, For the first i The coupling ratio coefficient at each sensor monitoring point For the first i Leakage current in the main insulation at each sensor monitoring point and All are complex numbers. The total leakage current of the cable section is obtained by subtracting the phasors of the main insulation leakage current at the first and last monitoring points of each cable section.

8. The multi-dimensional monitoring method for high-voltage cables according to claim 6, characterized in that, First characteristic variable The calculation formula is as follows: ,in, This is the phase difference between the magnetic field-induced current and the load current. It is a magnetic field-induced current. This is the load current; Third characteristic variable The calculation formula is as follows: in, , These are the first characteristic variables at the first monitoring point of the cross-connection loop and the first characteristic variables at the last monitoring point, respectively. The ratio of the amplitude of the first characteristic variable at the first and last monitoring points. The phase difference of the first characteristic variable at the first and last monitoring points; Fourth characteristic variable The calculation formula is as follows: in, This represents the leakage current of the main insulation of a certain section of the cable line at the current moment. This represents the leakage current of the main insulation of this section of the cable at the previous measurement time. The phase difference between the leakage currents of the main insulation at two different moments is given.

9. A multi-dimensional monitoring system for high-voltage cables based on sheath current, used to implement the multi-dimensional monitoring method for high-voltage cables according to any one of claims 1-8, characterized in that, It includes a phasor calculation module, a current decomposition module, and a data processing and analysis module; The phasor calculation module uses the load current of a certain phase as a reference phasor to calculate the amplitude and phase information of the remaining current and voltage signals. The current decomposition module decomposes the composite current into load current and sheath current through phasor operations; and decomposes the sheath current into magnetic field induced current and main insulation leakage current through an embedded algorithm. The data processing and analysis module performs calculations on the magnetic field induced current and the main insulation leakage current to obtain multi-dimensional feature parameters. It then compares these parameters with the defect diagnosis criteria embedded in the intelligent diagnostic model to provide cable operation diagnosis results. Simultaneously, it records the diagnosis results into the database, analyzes the changing trends of the multi-dimensional feature parameters, and predicts potential defects.

Images