Broadband impedance spectroscopy cable fault identification method and device, and storage medium

Abstract

The invention relates to a broadband impedance spectroscopy cable fault identification method and device and a storage medium, and the method comprises the steps: building a cable equivalent model according to any preset cable fault type; frequency sweep signals are input into the model, parameters of a cable core, a sheath and a steel armor under different frequency sweep signals are obtained, input impedance of the head end of the cable under different frequency sweep signals is calculated based on a cable modulus matrix and an input impedance formula, and a fault broadband impedance amplitude spectrum and a phase spectrum are drawn; repeating the steps to obtain a broadband impedance amplitude spectrum and a phase spectrum of the cable fault; the input impedance of an actual cable is collected in real time, a real-time broadband impedance amplitude spectrum and a real-time broadband impedance phase spectrum are drawn and compared with a cable fault broadband impedance amplitude spectrum and a cable fault phase spectrum, and the cable fault type and the distance between a fault point and the head end are recognized; and evaluating the health state of the cable and predicting the residual life of the cable by analyzing the characteristic parameters of the real-time impedance spectrum. Compared with the prior art, rapid cable fault identification and fault point determination are realized.

Description

Technical Field

[0001] This invention relates to the fields of high voltage and insulation, online monitoring and fault diagnosis of power equipment, and in particular to a broadband impedance spectrum cable fault identification method, device and storage medium. Background Technology

[0002] In the rapid development of urbanization, the laying of power cables plays an increasingly important role in urban power supply and is therefore widely used. However, with the continuous commissioning of cables, the probability of failure is also increasing. Affected by cable materials, laying process, and operating environment, high-resistance faults and short-circuit faults account for the majority of cable failures. Once a fault occurs, if corresponding measures are not taken in time, it will cause incalculable losses to the safe and reliable operation of the power system.

[0003] Currently, numerous studies have been conducted by scholars both domestically and internationally on cable fault detection methods, primarily focusing on traditional impedance methods and traveling wave methods. The principle of the impedance method lies in transforming the cable into a lumped parameter model. Based on this, the specific location of the cable fault is determined according to the proportional relationship between the cable's impedance and its length. This method measures the impedance value of the faulty cable by applying the Wheatstone bridge balance principle. However, when the resistance at the fault location is high, the current flowing through the bridge is small, and the impedance testing method is not applicable to cable models, leading to its gradual obsolescence. The traveling wave method mainly includes low-voltage testing (time-domain reflectometry) and high-voltage testing. The time-domain reflectometry uses a step pulse generator to produce low-voltage pulses to the cable under test, and detects cable faults by calculating the time difference between the pulse input signal and the reflected signal. However, due to signal attenuation during propagation and interference from the ambient magnetic field, the time-domain reflectometry method has a relatively large testing error. High-voltage testing detects and locates cable faults by using high-voltage pulses to break down the cable. Because it can transform high-resistance faults into low-resistance faults, it allows for the detection of high-resistance faults even in low-voltage environments. This method is simple to operate and fast, but it also carries certain risks and can worsen cable faults, exhibiting some destructiveness. While all the above methods play a role in locating cable faults, their ability to identify and determine the specific type of cable fault remains limited.

[0004] Chinese patent application CN116953569A discloses a fault type identification method for 10kV three-core cables based on input impedance spectrum. It innovatively identifies short-circuit and open-circuit faults in cables based on the input impedance spectrum and the changes in the number of resonance points of the amplitude spectrum and the initial phase angle of the phase spectrum. It focuses on solving the decoupling and accurate fault classification problems of multi-conductor cables, which are complexly coupled in three-core armored cables. However, it fails to solve the mutual impedance between the cable core and the insulation layer inside a single cable, and is not applicable to fault identification of single cables. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a broadband impedance spectrum cable fault identification method, device and storage medium, which realizes rapid cable fault identification and fault point determination.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for identifying broadband impedance spectrum cable faults, the method comprising:

[0008] Step S1: Establish an equivalent cable model based on any preset cable fault type;

[0009] Step S2: Input a sweep frequency signal into the cable equivalent model to obtain the parameters of the cable core, sheath, and steel armor under different sweep frequency signals. Calculate the input impedance at the cable head end under different sweep frequency signals based on the cable modulus matrix and input impedance formula, and plot the fault broadband impedance amplitude spectrum and phase spectrum. The cable modulus matrix includes the outer modulus describing the coupling between the steel armor and sheath, and the inner modulus describing the coupling between the cable core and sheath.

[0010] Step S3: Repeat steps S1-S2 above to obtain the broadband impedance amplitude spectrum and phase spectrum of the cable fault.

[0011] Step S4: Real-time acquisition of the actual cable's input impedance and plotting of the real-time broadband impedance amplitude spectrum and phase spectrum. Comparison with the cable fault broadband impedance amplitude spectrum and phase spectrum to identify the cable fault type and the distance of the fault point from the beginning.

[0012] Step S5: If the cable is fault-free, assess the current cable health status index and predict its remaining life based on the real-time broadband impedance amplitude spectrum and phase spectrum.

[0013] Furthermore, the preset cable fault types include, but are not limited to, short-circuit faults, high-resistance faults, and open-circuit faults. The cable equivalent model is also established based on the cable impedance, cable admittance, geometric parameters, and material parameters of the actual cable.

[0014] Furthermore, the process of obtaining the parameters of the cable core, sheath, and steel armor under different frequency sweep signals of the cable equivalent model includes:

[0015] The voltage and current to ground of the cable core, sheath and steel armor of the cable equivalent model under different frequency sweep signals are collected. Combined with cable impedance, cable admittance, cable impedance formula and cable admittance formula, the mutual impedance and mutual admittance of the cable core, sheath and steel armor of the cable equivalent model under different frequency sweep signals are calculated.

[0016] The formula for the cable impedance is:

[0017]

[0018] Where U is the cable-to-ground voltage, U C U is the voltage between the cable core and ground. S For the sheath to ground voltage, U A I is the voltage of the steel armor to ground. C For the cable core current, I S For the sheath current, I A For the steel-clad current, U C U S and U A These represent the voltages to ground of the cable core, sheath, and armor layer, respectively. C I S and I A Z represents the current flowing through the cable core, sheath, and armor layer, respectively. CS Z CA and Z AS These are the mutual impedances between the cable core and sheath, the cable core and steel armor, and the steel armor and sheath, respectively. CC Z SS and Z AA These are the self-impedances of the cable core, sheath, and steel armor, respectively.

[0019] The cable admittance formula is:

[0020]

[0021] Among them, Y CS Y CA and Y AS These represent the mutual admittance between the cable core and sheath, the mutual admittance between the cable core and the steel armor, and the mutual admittance between the steel armor and the sheath, respectively, with Y representing the cable admittance.

[0022] Furthermore, the cable modulus matrix includes a cable modulus impedance matrix and a cable modulus admittance matrix;

[0023] The cable modulus impedance matrix is:

[0024]

[0025] Among them, Z m1 Z m2 Z m3 Z m4 Z is the external modulus of impedance. m5 Z m6 U is the internal modulus of impedance. m I is the voltage modulus of the cable. m For the cable current modulus, [Z m [ ] represents the cable modulus impedance matrix.

[0026] [U] = [S][U] m],

[0027] [I] = [Q][I] m ],

[0028] Where [U] is the cable voltage matrix, [I] is the cable current matrix, [S] is the cable voltage transformation matrix, and [Q] is the current transformation matrix;

[0029] The cable modulus admittance matrix is:

[0030] [Y m ] = [Y m1 Y m2 Y m3 Y m4 Y m5 Y m6 ] = 2[Y AC Y AC Y SA Y SA Y CS Y CS ],

[0031] Among them, Y m1 Y m2 Y m3 Y m4 For admittance external modulus, Y m5 Y m6 For admittance internal modulus, [Y m [Y] is the cable modulus admittance matrix. CS Y CA and Y AS These are the mutual admittance between the cable core and sheath, the mutual admittance between the cable core and the steel armor, and the mutual admittance between the steel armor and the sheath, respectively.

[0032] Furthermore, when calculating the input impedance at the cable head end under different sweep frequency signals, the input impedance is solved using the fault parameters of the cable equivalent model, any admittance internal modulus, and any impedance internal modulus; the fault parameters include the fault resistance corresponding to the cable fault type and the distance of the cable fault point from the head end.

[0033] Furthermore, the input impedance formula is as follows:

[0034]

[0035] Where Z(0) is the input impedance at the beginning of the cable, V(x) is the voltage at a distance x from the beginning of the cable, and I(x) is the current at a distance x from the beginning of the cable. m0 τ is the characteristic impedance of the cable modulus. la Let γ be the reflection coefficient at the cable fault point, γ be the propagation coefficient of the cable, and l be the cable length.

[0036]

[0037] Where R is the resistance of the cable, G is the conductance of the cable, and Z is the resistance of the cable. m Y is the internal modulus impedance of the cable. m For the internal modulus admittance of the cable, l a Z(l) represents the distance from the fault point to the beginning of the line. a R is the impedance from the fault point to the beginning of the circuit. f The equivalent resistance at the cable fault point is the fault resistance.

[0038] Furthermore, the real-time broadband impedance amplitude spectrum and phase spectrum are compared with the cable fault broadband impedance amplitude spectrum and phase spectrum. If the real-time broadband impedance amplitude spectrum and phase spectrum coincide with the waveform of any fault broadband impedance amplitude spectrum and phase spectrum, the corresponding cable fault type and the distance from the cable fault point to the beginning end are obtained according to the fault parameters of the model set when the fault broadband impedance amplitude spectrum and phase spectrum are generated.

[0039] The process of assessing the current health status index of cables and predicting their remaining life includes:

[0040] Based on the real-time broadband impedance amplitude spectrum and phase spectrum, the impedance amplitude, phase angle or resonant frequency at the characteristic frequency is extracted as characteristic parameters.

[0041] The characteristic parameters are compared with the baseline characteristic parameters under the cable health condition, and the difference value is calculated.

[0042] Based on a pre-established mapping model between the difference value and the degree of cable aging, the current health status index of the cable is assessed and its remaining lifespan is predicted.

[0043] An electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the broadband impedance spectrum cable fault identification method as described above.

[0044] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the broadband impedance spectrum cable fault identification method as described above.

[0045] Compared with the prior art, the beneficial effects of the present invention include:

[0046] 1. This invention achieves rapid cable fault identification and fault point determination by comparing the fault broadband impedance amplitude and phase spectra obtained from cable simulation with the actual real-time broadband impedance amplitude and phase spectra. When calculating the input impedance at the cable head end, the calculation is based on the cable modulus matrix and the input impedance formula. The cable modulus matrix decouples the complex coupling relationships between the cable layers, making the final fault identification more accurate. The input impedance formula incorporates reflection coefficient analysis, establishing a mapping between the input impedance, the distance of the fault point from the head end, and the cable fault type. This allows the invention to ultimately reflect the cable fault type and fault point through the broadband impedance amplitude and phase spectra of the input impedance, avoiding the signal attenuation problem of traditional time-domain methods and improving the accuracy of fault type judgment.

[0047] 2. This invention focuses on clearly defined fault types that have occurred, quickly providing fault location and classification, thus overcoming the shortcomings of existing fault identification methods in diagnosing mature faults. This method of acquiring fault data through cable modeling is adaptable to different cable models and complex operating conditions, and has strong versatility. It has significant advantages in the comprehensiveness of fault type coverage, breakthrough identification of high-resistance faults, and engineering universality, thus making up for the deficiencies of waveform learning methods in diagnosing mature faults.

[0048] 3. This invention uses frequency sweep signal injection and frequency domain response analysis to perform fault detection and judgment without applying high voltage pulses or breaking down fault points, avoiding secondary damage to cables caused by traditional high voltage testing methods and improving detection safety. By pre-building a wideband impedance amplitude spectrum and phase spectrum library through the cable model, it also reduces the repetitive cost of on-site measurements.

[0049] 4. The fault identification method in this invention also supports integration with machine learning algorithms to achieve automated classification, which can further reduce operation and maintenance costs. In the future, it can be extended to the online monitoring system of smart grids to achieve real-time fault early warning. Attached Figure Description

[0050] Figure 1 This is a flowchart of the method of the present invention;

[0051] Figure 2 This is a diagram of the cable structure and equivalent model of the present invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0053] Example 1

[0054] This embodiment aims to disclose a method for fault identification in broadband impedance spectrum cables, the method as follows: Figure 1 As shown, the specific steps are as follows:

[0055] S1. Based on any preset cable fault type, establish a cable equivalent model. The fault parameters of the cable equivalent model include the fault resistance corresponding to the cable fault type and the distance from the cable fault point to the beginning of the cable.

[0056] S2, input the sweep frequency signal into the cable equivalent model to obtain the parameters of the cable core, sheath and steel armor under different sweep frequency signals, and calculate the input impedance of the cable head end under different sweep frequency signals based on the cable modulus matrix and input impedance formula, and plot the fault broadband impedance amplitude spectrum and phase spectrum. The cable modulus matrix includes the outer modulus describing the coupling between the steel armor and the sheath and the inner modulus describing the coupling between the cable core and the sheath. The input impedance formula establishes a mapping between the input impedance and the distance from the fault point to the head end and the cable fault type.

[0057] S3, repeat S1-S2 above to obtain the broadband impedance amplitude spectrum and phase spectrum of the cable fault;

[0058] S4: Real-time acquisition of the input impedance of the actual cable and plotting of the real-time broadband impedance amplitude spectrum and phase spectrum. Comparison with the broadband impedance amplitude spectrum and phase spectrum of the cable fault to identify the cable fault type and the distance of the fault point from the beginning.

[0059] S5. If the cable is fault-free, assess the current cable health status index and predict its remaining life based on the real-time broadband impedance amplitude spectrum and phase spectrum.

[0060] The real-time broadband impedance amplitude spectrum and phase spectrum are compared with the cable fault broadband impedance amplitude spectrum and phase spectrum. If the real-time broadband impedance amplitude spectrum and phase spectrum coincide with the waveform of any fault broadband impedance amplitude spectrum and phase spectrum, the corresponding cable fault type and the distance from the cable fault point to the beginning end are obtained according to the fault parameters of the model set when the fault broadband impedance amplitude spectrum and phase spectrum are generated.

[0061] In this embodiment, the equivalent cable model is a single-core coaxial cable with an armor layer. During the transient process of a line fault, the coupling effect between internal components of the cable needs to be considered. The XLPE cable, from the inside out, consists of the cable core, inner insulation, sheath, outer insulation, armor, and outer sheath. Its structure and equivalent model are as follows: Figure 2 As shown; where Z CS Z CA Z AS These are the mutual impedances between the cable core and sheath, between the cable core and steel armor, and between the steel armor and sheath, respectively; Y CS Y CA YAS These represent the mutual admittances between the cable core and sheath, the mutual admittance between the cable core and the steel armor, and the mutual admittance between the steel armor and the sheath, respectively. In the figure, Y... SA With Y AS The same meaning applies below.

[0062] The preset cable fault types include, but are not limited to, short circuit faults, high resistance faults, and open circuit faults.

[0063] First, an initial structure for the cable equivalent model is established based on the actual cable impedance, cable admittance, geometric parameters, and material parameters. Then, by selecting a preset cable fault type and inputting the fault resistance corresponding to the cable fault type and the distance from the cable fault point to the beginning of the cable into the initial structure, the complete cable equivalent model used in this embodiment can be established.

[0064] Step S2, the process of obtaining the parameters of the cable core, sheath, and steel armor under different frequency sweep signals in the cable equivalent model, includes:

[0065] The voltage and current to ground of the cable core, sheath, and armor are collected under different frequency sweep signals in the equivalent cable model. The mutual impedance and mutual admittance of the cable core, sheath, and armor under different frequency sweep signals are calculated by combining the cable impedance, cable admittance, cable impedance formula, and cable admittance formula.

[0066] The formula for cable impedance is:

[0067]

[0068] Where U is the cable-to-ground voltage, U C U is the voltage between the cable core and ground. S For the sheath to ground voltage, U A I is the voltage of the steel armor to ground. C For the cable core current, I S For the sheath current, I A For the steel-clad current, U C U S and U A These represent the voltages to ground of the cable core, sheath, and armor layer, respectively. C I S and I A Z represents the current flowing through the cable core, sheath, and armor layer, respectively. CS Z CA and Z AS These are the mutual impedances between the cable core and sheath, the cable core and steel armor, and the steel armor and sheath, respectively. CC Z SS and Z AA These are the self-impedances of the cable core, sheath, and steel armor, respectively.

[0069] The formula for cable admittance is:

[0070]

[0071] Among them, Y CS Y CA and Y AS These represent the mutual admittance between the cable core and sheath, the mutual admittance between the cable core and the steel armor, and the mutual admittance between the steel armor and the sheath, respectively, with Y representing the cable admittance.

[0072] The cable modulus matrix includes the cable modulus impedance matrix and the cable modulus admittance matrix;

[0073] The cable modulus impedance matrix is:

[0074]

[0075]

[0076] Among them, Z m1 Z m2 Z m3 Z m4 Z is the external modulus of impedance. m5 Z m6 U is the internal modulus of impedance. m I is the voltage modulus of the cable. m For the cable current modulus, [Z m [ ] represents the cable modulus impedance matrix.

[0077] [U] = [S][U] m ],

[0078] [I] = [Q][I] m ],

[0079] Where [U] is the cable voltage matrix, [I] is the cable current matrix, [S] is the cable voltage transformation matrix, and [Q] is the current transformation matrix;

[0080] The cable modulus admittance matrix is:

[0081] [Y m ] = [Y m1 Y m2 Y m3 Y m4 Y m5 Y m6 ] = 2[Y AC Y AC Y SA Y SA Y CS Y CS ],

[0082] Among them, Y m1 Y m2 Ym3 Y m4 For admittance external modulus, Y m5 Y m6 For admittance internal modulus, [Y m [Y] is the cable modulus admittance matrix. CS Y CA and Y AS These are the mutual admittance between the cable core and sheath, the mutual admittance between the cable core and the steel armor, and the mutual admittance between the steel armor and the sheath, respectively.

[0083] When calculating the input impedance at the cable end under different sweep frequency signals, the input impedance is solved using the fault parameters of the cable equivalent model, any admittance internal modulus, and any impedance internal modulus.

[0084] In this embodiment, the impedance internal modulus Z m5 and Z m6 The values ​​of Y are the same. m5 and Y m6 The values ​​are also the same, so one value can be randomly selected from each of the two sets of inner membrane values ​​as the cable's inner modulus impedance Z. m and cable internal modulus admittance Y m Solve for the input impedance.

[0085] Let the cable length be l, then the input impedance at a distance x from the cable end can be expressed as:

[0086]

[0087] Where γ is the propagation coefficient of the cable, l is the cable length, V(x) is the voltage at a distance x from the cable start point, I(x) is the current at a distance x from the cable start point, and τ l Z is the reflection coefficient at the end of the cable. m0 The characteristic impedance of the cable modulus,

[0088]

[0089] Where R is the resistance of the cable, G is the conductance of the cable, and Z is the resistance of the cable. m Y is the internal modulus impedance of the cable. m This is the admittance of the cable's internal modulus.

[0090] During the input impedance acquisition process, the cable end is generally open-circuited, at which point Z(L) is infinite, so it can be derived that τ l =1.

[0091] Further derivation leads to the following conclusion:

[0092]

[0093] Where Z0 is the input impedance at the beginning of the cable.

[0094] Let the distance from the fault point to the beginning be l. a Then the reflection coefficient of the corresponding fault point can be obtained, and its expression is:

[0095]

[0096] Among them, Z(l a R is the impedance from the fault point to the beginning of the circuit. f The equivalent resistance at the cable fault point is the fault resistance.

[0097] When calculating the reflection coefficient at the fault point, the fault resistance and input impedance are in parallel relative to the entire cable segment, so Z(l) is used here. a ) and R f Perform parallel (‖) calculations.

[0098] When an open-circuit fault occurs in the cable, R f It is infinite;

[0099] When a short circuit fault occurs in the cable, R f =0;

[0100] When a high-resistance fault occurs in the cable, R f >1000Ω.

[0101] In summary, the formula for input impedance can be obtained as follows:

[0102]

[0103] Where Z(0) is the input impedance at the beginning of the cable, V(x) is the voltage at a distance x from the beginning of the cable, and I(x) is the current at a distance x from the beginning of the cable. m0 τ is the characteristic impedance of the cable modulus. la Let γ be the reflection coefficient at the cable fault point, γ be the propagation coefficient of the cable, and l be the cable length.

[0104]

[0105] Where R is the resistance of the cable, G is the conductance of the cable, and Z is the resistance of the cable. m Y is the internal modulus impedance of the cable. m For the internal modulus admittance of the cable, l a Z(l) represents the distance from the fault point to the beginning of the line. a R is the impedance from the fault point to the beginning of the circuit. f The equivalent resistance at the cable fault point is the fault resistance.

[0106] Step S5, the process of assessing the current health status index of the cable and predicting its remaining life includes:

[0107] Based on real-time broadband impedance amplitude spectrum and phase spectrum, the impedance amplitude, phase angle or resonant frequency at the characteristic frequency is extracted as characteristic parameters.

[0108] The characteristic parameters are compared with the baseline characteristic parameters under the cable health condition, and the difference value is calculated.

[0109] Based on a pre-established mapping model between the difference value and the degree of cable aging, the current health status index of the cable is assessed and its remaining lifespan is predicted.

[0110] The baseline characteristic parameters of the cable in its health state are obtained from a pre-established baseline characteristic parameter library. The baseline characteristic parameter library will be updated as the cable is used. When the cable is initially put into use, the baseline characteristic parameter library is initially established based on the impedance spectrum parameters of the initial health state provided by the cable manufacturer. If the cable to be evaluated has been monitored for a long time, the broadband impedance spectrum characteristic parameters of its initial health state are taken as the baseline characteristic parameters of this cable, and the baseline characteristic parameter library is updated.

[0111] The difference is obtained by subtracting the characteristic parameter from the baseline characteristic parameter under the cable's healthy condition.

[0112] The mapping model between the difference value and the degree of cable aging is constructed based on a large amount of aging test data and physical mechanisms. The mapping model includes: an empirical fitting model, a machine learning model and a physical mechanism model.

[0113] The empirical fitting model is used for cable types with sufficient data accumulation. It obtains the correspondence between the difference value and the degree of cable aging through accelerated aging tests, and establishes a mathematical fitting model for the data.

[0114] Machine learning models are used for cables with complex aging mechanisms and multiple coupled factors, such as cables where insulation aging and sheath corrosion occur simultaneously. The process of building and training these models includes:

[0115] Establish basic machine learning models based on convolutional neural networks;

[0116] Construct a training dataset. The input features in the dataset are cable difference values, ambient temperature, operating load, laying years, and environmental and operating condition parameters. The output label is the actual health status index of the cable.

[0117] The basic machine learning model is trained based on the constructed training dataset, and the training dataset is updated regularly to retrain the model.

[0118] The physical mechanism model is used for cables where the physical process of aging needs to be clearly defined. The model is constructed based on the physical equations of insulation aging. The physical mechanism model includes: dielectric parameter conversion formula, HN relaxation formula, aging kinetics formula, and aging degree and health status index mapping formula.

[0119] Conversion formula for dielectric parameters ε′ and ε″:

[0120]

[0121] Where ε′ is the relative dielectric constant of the insulating material on the cable, ε″ is the dielectric loss factor of the insulating material on the cable, Z(ω) is the impedance amplitude of the cable, and C0 is the capacitance per unit length of the cable;

[0122]

[0123] Where ε0 is the permittivity of free space, with a value of 8.85×10 -12 F / m in this embodiment, r1 is the outer radius of the cable core, r2 is the inner radius of the sheath, tanδ is the aging-sensitive parameter, i.e., the tangent of the dielectric loss angle, which increases with the degree of aging, is the impedance phase angle that can be directly measured in the broadband impedance spectrum.

[0124] Based on the dielectric parameter conversion formula, the relative dielectric constant and dielectric loss factor of the insulating material on the cable can be obtained, reflecting the nature of the material. The change in the polarization relaxation characteristics of the insulating material caused by aging needs to be described by the H-N relaxation formula for the variation of ε′ and ε″ with frequency.

[0125] The expression of the H-N relaxation formula is:

[0126]

[0127] Where ε s is the static dielectric constant, i.e., the low-frequency limit value, ε ∞ is the optical-frequency dielectric constant, i.e., the high-frequency limit value, τ is the characteristic relaxation time, a and b are shape parameters, 0 < a ≤ 1, 0 < b ≤ 1, describing the width and symmetry of the relaxation peak. Aging will cause a and b to decrease and the peak to become wider.

[0128] Aging causes molecular chain breakage, increasing the number of dipoles inside the insulating material on the cable and hindering their movement, manifested as an increase in ε s , an extension of τ, a decrease in a and b, and ultimately a shift in the resonance point of the broadband impedance spectrum.

[0129] Therefore, a relationship (aging kinetics formula) is established between ε s or τ and the degree of aging, and the actual health state index of the cable can be calculated from the aging time.[[ID=4,4]]

[0130] The aging kinetics formula is:

[0131]

[0132] Where τ fail and ε s,failω1 and ω2 are the relaxation time and static dielectric constant of the cable at failure, obtained through accelerated aging tests, and are weights determined based on the sensitivity of the parameters to aging.

[0133]

[0134] Where τ0 is the relaxation time of the initial healthy state, E a The aging activation energy is determined by accelerated testing, R is the gas constant, which is 8.314 J / (mol·K) in this example, T is the actual operating temperature, and t0 is the reference time;

[0135]

[0136] Where, ε s0 Let k be the initial static dielectric constant. ε This is the proportionality coefficient obtained from the accelerated aging test. The formula for mapping aging degree to health status index is:

[0137] HSI(t) = 100·(1-A(t))

[0138] Wherein, HSI(t) is the health status index at time t.

[0139] In step S5, the prediction of the current remaining life of the cable is divided into linear prediction and nonlinear prediction. If the cable aging time is lower than the preset aging threshold, the linear formula is used to directly calculate the remaining life based on the health status index. Otherwise, a pre-trained time series model is used to predict the future change curve of the health status index, and the remaining life is calculated from the curve.

[0140] Example 2

[0141] This embodiment aims to demonstrate the feasibility of building an equivalent cable model and using broadband impedance amplitude spectrum and phase spectrum to identify faults, based on the above embodiment 1, taking high-resistance faults and open-circuit faults as examples.

[0142] Input impedance spectrum can characterize the impedance information of a cable at different locations. By changing the frequency of the input signal, the corresponding input impedance value can be obtained. The impedance spectrum of the test cable can be obtained under high-frequency input signals with a wide frequency range.

[0143] First, taking a high-resistance fault as an example, a 10kV coaxial cable model with an armored layer was simulated. The total cable length was set to 150m, and a 1000Ω high-resistance fault was applied at 100m of the cable. The line end was open-circuited, and the impedance spectrum test frequency was 0.1MHz-50MHz. The collected impedance admittance parameters were calculated, and the simulation results of the broadband impedance amplitude spectrum and phase spectrum were compared with those of a normal cable.

[0144] By comparing the broadband impedance spectrum images of cables under high-resistance faults and normal cables, it can be seen that, compared with normal cables, when a cable experiences a high-resistance fault, its impedance spectrum amplitude generally shows a decreasing trend, which is particularly obvious below 10MHz. The peak input impedance decreases from 515.24Ω to 162Ω, and the resonant point does not shift. The phase of its impedance spectrum decreases overall, with the maximum phase value decreasing from 87.98° to 83.93°, while the oscillation period remains unchanged.

[0145] Next, taking an open-circuit fault as an example, a 10kV coaxial cable model with an armored layer was simulated. The total cable length was set to 150m, and an open-circuit fault was applied at 100m of the cable. The line end was open-circuited, and the impedance spectrum test frequency was 0.1MHz-50MHz. The collected impedance admittance parameters were calculated, and the simulation results of the broadband impedance amplitude spectrum and phase spectrum were compared with those of a normal cable.

[0146] By comparing the broadband impedance spectrum images, it can be seen that when an open-circuit fault occurs in a cable, the amplitude of the fault broadband impedance spectrum increases compared to the normal broadband impedance spectrum amplitude image. The peak impedance increases from 515.24Ω to 546.24Ω, and the resonant point shifts to the right. The maximum phase value of the impedance spectrum increases from 87.98° to 88.34°, and the oscillation period increases.

[0147] In summary, the broadband impedance spectrum cable fault identification method proposed in this invention can obtain the changes in the impedance spectrum of faulty cables by comparing the broadband impedance spectra of cables with normal cables of different fault types, thereby realizing the identification and analysis of cable faults. The analysis results can provide a reference for detection under actual working conditions.

[0148] Example 3

[0149] Based on Embodiment 1, this embodiment provides an electronic device, including: one or more processors and a memory, wherein the memory stores one or more programs, the one or more programs including instructions for executing the aforementioned broadband impedance spectrum cable fault identification method.

[0150] At the hardware level, the electronic device includes a processor, internal bus, network interface, memory, and non-volatile memory, and may also include other hardware required for the business. The processor reads the corresponding computer program from the non-volatile memory into memory and then runs it to implement the aforementioned broadband impedance spectrum cable fault identification method. Of course, in addition to software implementation, this invention does not exclude other implementation methods, such as logic devices or a combination of hardware and software, etc. That is to say, the execution subject of the following processing flow is not limited to individual logic units, but can also be hardware or logic devices.

[0151] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0152] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0153] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for identifying broadband impedance spectrum cable faults, characterized in that, The method includes: Step S1: Establish an equivalent cable model based on any preset cable fault type; Step S2: Input a sweep frequency signal into the cable equivalent model to obtain the parameters of the cable core, sheath, and steel armor under different sweep frequency signals. Calculate the input impedance at the cable head end under different sweep frequency signals based on the cable modulus matrix and input impedance formula, and plot the fault broadband impedance amplitude spectrum and phase spectrum. The cable modulus matrix includes the outer modulus describing the coupling between the steel armor and sheath, and the inner modulus describing the coupling between the cable core and sheath. Step S3: Repeat steps S1-S2 above to obtain the broadband impedance amplitude spectrum and phase spectrum of the cable fault. Step S4: Real-time acquisition of the actual cable's input impedance and plotting of the real-time broadband impedance amplitude spectrum and phase spectrum. Comparison with the cable fault broadband impedance amplitude spectrum and phase spectrum to identify the cable fault type and the distance of the fault point from the beginning. Step S5: If the cable is fault-free, assess the current cable health status index and predict its remaining life based on the real-time broadband impedance amplitude spectrum and phase spectrum.

2. The broadband impedance spectrum cable fault identification method according to claim 1, characterized in that, The preset cable fault types include, but are not limited to, short-circuit faults, high-resistance faults, and open-circuit faults. The cable equivalent model is also established based on the actual cable's cable impedance, cable admittance, geometric parameters, and material parameters.

3. The broadband impedance spectrum cable fault identification method according to claim 1, characterized in that, The process of obtaining the parameters of the cable core, sheath, and steel armor under different frequency sweep signals of the cable equivalent model includes: The voltage and current to ground of the cable core, sheath and steel armor of the cable equivalent model under different frequency sweep signals are collected. Combined with cable impedance, cable admittance, cable impedance formula and cable admittance formula, the mutual impedance and mutual admittance of the cable core, sheath and steel armor of the cable equivalent model under different frequency sweep signals are calculated. The formula for the cable impedance is: Where U is the cable-to-ground voltage, U C U is the voltage between the cable core and ground. S For the sheath to ground voltage, U A I is the voltage of the steel armor to ground. C For the cable core current, I S For the sheath current, I A For the steel-clad current, U C U S and U A These represent the voltages to ground of the cable core, sheath, and armor layer, respectively. C I S and I A Z represents the current flowing through the cable core, sheath, and armor layer, respectively. CS Z CA and Z AS These are the mutual impedances between the cable core and sheath, the cable core and steel armor, and the steel armor and sheath, respectively. CC Z SS and Z AA These are the self-impedances of the cable core, sheath, and steel armor, respectively; The cable admittance formula is: Among them, Y CS Y CA and Y AS These represent the mutual admittance between the cable core and sheath, the mutual admittance between the cable core and the steel armor, and the mutual admittance between the steel armor and the sheath, respectively, with Y representing the cable admittance.

4. The broadband impedance spectrum cable fault identification method according to claim 1, characterized in that, The cable modulus matrix includes the cable modulus impedance matrix and the cable modulus admittance matrix; The cable modulus impedance matrix is: Among them, Z m1 Z m2 Z m3 Z m4 Z is the external modulus of impedance. m5 Z m6 U is the internal modulus of impedance. m I is the voltage modulus of the cable. m For the cable current modulus, [Z m [ ] represents the cable modulus impedance matrix. [U]=[S][U] m ], [I]=[Q][I m ], Where [U] is the cable voltage matrix, [I] is the cable current matrix, [S] is the cable voltage transformation matrix, and [Q] is the current transformation matrix; The cable modulus admittance matrix is: [AND m ]=[And m1 AND m2 AND m3 AND m4 AND m5 AND m6 ]=2[Y AC AND AC AND SA AND SA AND CS AND CS ], Among them, Y m1 Y m2 Y m3 Y m4 For admittance external modulus, Y m5 Y m6 For admittance internal modulus, [Y m [Y] is the cable modulus admittance matrix. CS Y CA and Y AS These are the mutual admittance between the cable core and sheath, the mutual admittance between the cable core and the steel armor, and the mutual admittance between the steel armor and the sheath, respectively.

5. The broadband impedance spectrum cable fault identification method according to claim 4, characterized in that, When calculating the input impedance at the cable head end under different sweep frequency signals, the input impedance is solved using the fault parameters of the cable equivalent model, any admittance internal modulus, and any impedance internal modulus. The fault parameters include the fault resistance corresponding to the cable fault type and the distance from the cable fault point to the beginning of the cable.

6. The broadband impedance spectrum cable fault identification method according to claim 1, characterized in that, The formula for the input impedance is: Where Z(0) is the input impedance at the beginning of the cable, V(x) is the voltage at a distance x from the beginning of the cable, and I(x) is the current at a distance x from the beginning of the cable. m0 τ is the characteristic impedance of the cable modulus. la Let γ be the reflection coefficient at the cable fault point, γ be the propagation coefficient of the cable, and l be the cable length. Where R is the resistance of the cable, G is the conductance of the cable, and Z is the resistance of the cable. m Y is the internal modulus impedance of the cable. m For the internal modulus admittance of the cable, l a Z(l) represents the distance from the fault point to the beginning of the line. a R is the impedance from the fault point to the beginning of the circuit. f The equivalent resistance at the cable fault point is the fault resistance.

7. The broadband impedance spectrum cable fault identification method according to claim 1, characterized in that, The real-time broadband impedance amplitude spectrum and phase spectrum are compared with the cable fault broadband impedance amplitude spectrum and phase spectrum. If the real-time broadband impedance amplitude spectrum and phase spectrum coincide with the waveform of any fault broadband impedance amplitude spectrum and phase spectrum, the corresponding cable fault type and the distance from the cable fault point to the beginning end are obtained according to the fault parameters of the model set when the fault broadband impedance amplitude spectrum and phase spectrum are generated.

8. The broadband impedance spectrum cable fault identification method according to claim 1, characterized in that, The process of assessing the current health status index of cables and predicting their remaining life includes: Based on the real-time broadband impedance amplitude spectrum and phase spectrum, the impedance amplitude, phase angle or resonant frequency at the characteristic frequency is extracted as characteristic parameters. The characteristic parameters are compared with the baseline characteristic parameters under the cable health condition, and the difference value is calculated. Based on a pre-established mapping model between the difference value and the degree of cable aging, the current health status index of the cable is assessed and its remaining lifespan is predicted.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the broadband impedance spectrum cable fault identification method as described in any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps of the broadband impedance spectrum cable fault identification method as described in any one of claims 1-8.

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