A broadband impedance spectroscopy cable fault identification method and system and storage medium

Abstract

The present application relates to a kind of broadband impedance spectrum cable fault identification method, system and storage medium, comprising: according to any preset cable fault type, establish cable equivalent model;Frequency-sweep signal is input to model, obtain the parameter of cable core, sheath and steel armor under different frequency-sweep signals, and the input impedance of cable head under different frequency-sweep signals is calculated based on cable modulus matrix and input impedance formula, draw fault broadband impedance amplitude spectrum and phase spectrum;Repeat the above steps, obtain cable fault broadband impedance amplitude spectrum and phase spectrum;Real-time acquisition actual cable input impedance and draw real-time broadband impedance amplitude spectrum and phase spectrum, compare with cable fault broadband impedance amplitude spectrum and phase spectrum, identify cable fault type and fault point distance from head end.Compared with prior art, the present application realizes the quick cable fault identification and fault point determination.

Description

Technical Field

[0001] This invention belongs to the field of high voltage and insulation, online monitoring and fault diagnosis technology of power equipment, and more specifically, relates 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 methods for detecting cable faults, 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 defect location is high, the current flowing through the bridge is small, and the impedance testing method is not suitable for cable models, leading to its gradual obsolescence.

[0004] The traveling wave method mainly includes low-voltage testing (time-domain reflectometry) and high-voltage testing. 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 has a relatively large testing error. High-voltage testing uses a high-voltage pulse to break down the cable fault location for fault detection and localization. Because it can transform high-resistance faults into low-resistance faults, it can detect 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. All of these methods play a role in locating cable faults, but their ability to identify and determine the type of cable fault is not yet significant.

[0005] For example, but not limited to, prior art document 1 (CN116953569A) discloses a method for identifying fault types in 10kV three-core cables based on input impedance spectrum; prior art document 2 (CN115754611B) discloses a cable fault location method based on impedance spectrum digital reconstruction using pseudo-trapezoidal wave excitation; prior art document 3 (CN115389877B) discloses a method, device, terminal, and storage medium for locating cable insulation faults; and prior art document 4 (CN105699843A) discloses a cable operating status diagnosis method and system. The areas for improvement in these prior art include: focusing on solving the decoupling and accurate fault classification problems of multi-conductor cables, but failing to address the mutual impedance between the cable core and insulation layer within a single cable, making it unusable for fault identification in single cables; the process of obtaining the input impedance of the faulty cable is cumbersome, requiring the injection of a pseudo-trapezoidal wave signal into the test cable; and obtaining the geometric parameters of the cable under test and the dielectric function of the insulation material is relatively difficult, etc. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a broadband impedance spectrum cable fault identification method, system, and storage medium, which enables rapid cable fault identification and fault point determination.

[0007] The first aspect of the present invention provides a method for identifying broadband impedance spectrum cable faults, comprising the following steps:

[0008] Based on any preset cable fault type, an equivalent cable model is established. The fault parameters of the equivalent cable model include the fault resistance corresponding to the cable fault type. R f and the distance from the cable fault point to the beginning of the cable l a ;

[0009] The equivalent cable model is collected to obtain the voltage and current to ground of the cable core, sheath and steel armor under different frequency sweep signals. Combined with the fault parameters, the input impedance of the cable head end under different frequency sweep signals is calculated to obtain the cable fault broadband impedance amplitude spectrum and phase spectrum.

[0010] Change the fault type and repeat the above steps until the broadband impedance amplitude spectrum and phase spectrum of the cable fault for all fault types are obtained.

[0011] The input impedance of the actual cable is collected in real time, and the real-time broadband impedance amplitude spectrum and phase spectrum are plotted. The spectrum is compared with the broadband impedance amplitude spectrum and phase spectrum of the cable fault to identify the cable fault type and the distance of the cable fault point from the beginning.

[0012] Preferably, establishing a cable equivalent model based on any preset cable fault type includes:

[0013] An equivalent model framework for a single-core coaxial cable with an armored layer is established. The single-core coaxial cable with an armored layer consists of a cable core, inner insulation, sheath, outer insulation, steel armor, and outer sheath from the inside out.

[0014] Preset cable fault types, including one of the following: short circuit fault, high resistance fault, and open circuit fault;

[0015] Based on the aforementioned cable equivalent model framework, an initial structure for the electrical equivalent model is established according to the actual cable impedance, cable admittance, geometric parameters, and material parameters. Then, by selecting any preset cable fault type, the fault resistance corresponding to the cable fault type is input into the initial structure. R f and the distance from the cable fault point to the beginning of the cable l a The equivalent model of the cable is obtained.

[0016] Preferably, the calculation of the input impedance at the cable end under different sweep frequency signals includes:

[0017] The voltage and current to ground of the cable core, sheath and steel armor of the cable equivalent model are collected under different frequency sweep signals. 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 by combining the cable impedance model and the cable admittance model.

[0018] Based on the equivalent model of the cable, the voltage and current to ground of the cable core, sheath and steel armor under different frequency sweep signals are calculated to obtain the cable modulus matrix, including the cable modulus impedance matrix and the cable modulus admittance matrix.

[0019] Using the cable modulus matrix and fault parameters, an input impedance model at the cable head is established. Based on this, the input impedance at the cable head under different sweep frequency signals is calculated, and the broadband impedance amplitude spectrum and phase spectrum of the fault are plotted.

[0020] Preferably, the calculation of the cable modulus matrix based on the ground voltage and current of the cable core, sheath, and armor under different frequency sweep signals using the cable equivalent model includes:

[0021] Transform the cable voltage matrix and cable current matrix into cable voltage modulus matrix and cable current modulus matrix;

[0022] Calculate the cable modulus impedance matrix based on the cable voltage modulus matrix and the cable current modulus matrix;

[0023] Based on the cable admittance matrix, the cable modulus admittance matrix is ​​established.

[0024] Preferably, the cable modulus matrix and fault parameters are used to establish an input impedance model at the cable head, thereby calculating the input impedance at the cable head under different sweep frequency signals, including:

[0025] Based on the cable modulus impedance matrix and cable modulus admittance matrix, calculate the characteristic impedance of the cable modulus and the propagation coefficient of the cable.

[0026] Calculate the reflection coefficient at the cable end.

[0027] The characteristic impedance of the cable modulus, the propagation coefficient of the cable, and the reflection coefficient at the cable end are used to establish the distance from the cable head. x Input impedance model at the location;

[0028] Based on the distance from the cable head end x The input impedance model at the fault point is used to calculate the reflection coefficient at the fault point.

[0029] Based on the characteristic impedance of the obtained cable modulus, the propagation coefficient of the cable, the reflection coefficient of the fault point, and the cable length, an input impedance model at the cable head is established, thereby establishing a mapping between the input impedance and the distance of the fault point from the head and the type of cable fault.

[0030] Preferably, the input impedance model at the beginning of the cable is expressed by the following formula:

[0031]

[0032] In the formula:

[0033] Z (0) represents the input impedance at the beginning of the cable.

[0034] V ( x () is the distance from the beginning of the cable x Voltage at that point

[0035] I ( x () is the distance from the beginning of the cable x The current at that point,

[0036] Z m0 The characteristic impedance of the cable modulus,

[0037] τ la The reflection coefficient at the cable fault point.

[0038] γ The propagation coefficient of the cable,

[0039] l This refers to the cable length.

[0040] Preferably, the characteristic impedance of the cable modulus, the propagation coefficient of the cable, and the reflection coefficient at the fault point are expressed by the following formulas:

[0041]

[0042]

[0043]

[0044] In the formula:

[0045] Z m0 The characteristic impedance of the cable modulus,

[0046] R The resistance of the cable. L For the inductance of the cable, G For the electrical conductivity of the cable, C For the capacitance of the cable, ω Angular frequency,

[0047] Z m The modulus impedance of the cable. Y m For cable modulus admittance;

[0048] γ The propagation coefficient of the cable,

[0049] τ la The reflection coefficient at the cable fault point.

[0050] Z ( l a () represents the impedance from the fault point to the beginning of the circuit.

[0051] R f This is the fault resistor.

[0052] Preferably, the comparison with the broadband impedance amplitude spectrum and phase spectrum of the cable fault to identify the cable fault type and the distance from the cable fault point to the beginning includes:

[0053] 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.

[0054] A second aspect of the present invention provides a broadband impedance spectrum cable fault identification system, which operates a broadband impedance spectrum cable fault identification method according to the first aspect, comprising:

[0055] The modeling and simulation module is used to build an equivalent cable model based on any preset cable fault type.

[0056] A waveform generator is used to send a sweep frequency signal to the cable equivalent model;

[0057] The input impedance calculation module is used to collect the ground voltage and current of the cable core, sheath and steel armor of the cable equivalent model under different frequency sweep signals, and calculate the input impedance of the cable head under different frequency sweep signals in combination with the fault parameters to obtain the cable fault broadband impedance amplitude spectrum and phase spectrum.

[0058] The fault identification module is used to collect the input impedance of the actual cable in real time and draw the real-time broadband impedance amplitude spectrum and phase spectrum. It compares the spectrum with the broadband impedance amplitude spectrum and phase spectrum of the cable fault to identify the cable fault type and the distance of the cable fault point from the beginning.

[0059] A third aspect of the present invention provides 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 the first aspect.

[0060] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0061] 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.

[0062] 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.

[0063] 3. This invention enables fault detection and determination without applying high-voltage pulses or breaking down fault points by injecting swept-frequency signals and performing frequency domain response analysis. This avoids secondary damage to cables caused by traditional high-voltage testing methods, improves testing safety, and reduces the cost of repeated field measurements by pre-building a broadband impedance amplitude spectrum and phase spectrum library through a cable model.

[0064] 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

[0065] Figure 1 This is a flowchart of the method of the present invention;

[0066] Figure 2 This is a diagram showing the cable structure and equivalent model of the present invention;

[0067] Figure 3 This is a comparison chart of the amplitude of the broadband impedance spectrum of a high-impedance fault and the amplitude of the normal broadband impedance spectrum according to an embodiment of the present invention;

[0068] Figure 4 This is a comparison diagram of the phase of a high-impedance fault broadband impedance spectrum and the phase of a normal broadband impedance spectrum according to an embodiment of the present invention;

[0069] Figure 5 This is a comparison chart of the amplitude of the broadband impedance spectrum of an open-circuit fault and the amplitude of the normal broadband impedance spectrum according to an embodiment of the present invention;

[0070] Figure 6 This is a comparison diagram of the phase of the broadband impedance spectrum of an open-circuit fault and the phase of the normal broadband impedance spectrum according to an embodiment of the present invention. Detailed Implementation

[0071] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0072] like Figure 1 As shown, Embodiment 1 of the present invention provides a broadband impedance spectrum cable fault identification method, comprising the following steps:

[0073] Step 1: 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. R f and the distance from the cable fault point to the beginning of the cablel a ;

[0074] Preferably, but not limitingly, step 1 specifically includes:

[0075] Step 1.1: Establish the equivalent model framework for a single-core coaxial cable with an armor layer. During the transient process of a line fault, the coupling effects between internal components of the cable need to be considered. The single-core coaxial cable with an armor layer consists of, from the inside out, the cable core, inner insulation, sheath, outer insulation, armor, and outer sheath. Its structure and equivalent model are as follows: Figure 2 As shown.

[0076] in, Z CS , Z CA , Z AS These are the mutual impedances between the cable core and sheath, the mutual impedances between the cable core and the steel armor, and the mutual impedances between the steel armor and the sheath, respectively. Y CS , Y CA , Y AS 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. It is understandable that when representing mutual impedance and mutual admittance, the text in the diagram... C , S , A When subscripts are interchanged, the overall meaning of the parameter remains unchanged; for example, but not limited to, Y SA and Y AS The two terms have the same meaning and refer to the mutual admittance between the steel armor and the sheath.

[0077] Step 1.2: Preset cable fault types, including but not limited to short circuit fault, high resistance fault and open circuit fault.

[0078] Step 1.3: Based on the cable equivalent model framework in Step 1.1, establish the initial structure of the electrical equivalent model according to the actual cable impedance, cable admittance, geometric parameters, and material parameters. Then, by selecting any cable fault type preset in Step 1.2, input the fault resistance corresponding to the cable fault type into the initial structure. R f and the distance from the cable fault point to the beginning of the cable l a This allows us to obtain a complete cable equivalent model that can be used.

[0079] Step 2: 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 the input impedance formula. 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. The input impedance formula establishes a mapping between the input impedance and the distance from the fault point to the head end, as well as the cable fault type.

[0080] Preferably, but not limitingly, step 2 specifically includes:

[0081] Step 2.1: Collect the voltage and current to ground of the cable core, sheath and steel armor of the cable equivalent model under different frequency sweep signals, and calculate the mutual impedance and mutual admittance of the cable core, sheath and steel armor of the cable equivalent model under different frequency sweep signals by combining the cable impedance model and the cable admittance model.

[0082] Specifically, the cable impedance model is expressed by the following formula:

[0083]

[0084] In the formula:

[0085] U This is the cable-to-ground voltage matrix. U C This is the voltage between the cable core and ground. U S For the voltage of the sheath to ground, U A These are the voltages of the steel armor to ground, namely the voltages of the cable core, sheath, and armor layer to ground, respectively.

[0086] I C For cable core current, I S For sheath current, I A These are the steel armor currents, specifically the currents flowing through the cable core, sheath, and armor layer, respectively.

[0087] Z CS , Z CA and Z AS These are the mutual impedances between the cable core and sheath, between the cable core and the steel armor, and between the steel armor and the sheath, respectively. Z CC , Z SS and Z AA The self-impedances of the cable core, sheath, and steel armor are respectively. Z] is the cable impedance matrix.

[0088] The cable admittance model is expressed by the following formula:

[0089]

[0090] In the formula:

[0091] [ I [This is the cable current matrix.]

[0092] Y CS , Y CA and Y AS These are the mutual admittances between the cable core and sheath, the mutual admittances between the cable core and the steel armor, and the mutual admittances between the steel armor and the sheath, respectively. Y ] is the cable admittance matrix.

[0093] Step 2.2: Based on the equivalent cable model, calculate the voltage and current to ground of the cable core, sheath, and steel armor under different frequency sweep signals, and obtain the cable modulus matrix. Specifically, 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. More specifically, it includes the cable modulus impedance matrix and the cable modulus admittance matrix.

[0094] Further preferred, but not limiting, step 2.2 specifically includes:

[0095] Step 2.2.1: Transform the cable voltage matrix and cable current matrix into cable voltage modulus matrix and cable current modulus matrix, expressed by the following formula:

[0096] [ U ] = [ S ][ U m ]

[0097] [ I ] = [ Q ][ I m ]

[0098] In the formula:

[0099] [ U ] represents the cable voltage matrix, [ I [This is the cable current matrix.]

[0100] [ U m [ is the cable voltage modulus matrix, [ I m [This represents the cable current modulus matrix.]

[0101] [ S [ is the cable voltage transformation matrix, [ Q [ ] represents the current transformation matrix. Step 2.2.2: Based on the cable voltage modulus matrix and the cable current modulus matrix, calculate the cable modulus impedance matrix. Z m Expressed as follows:

[0102]

[0103] In the formula:

[0104] Z m1 , Z m2 , Z m3 , Z m4 For the external modulus of impedance, Z m5 , Z m6 For impedance internal modulus,

[0105] Um For cable voltage modulus, Im The current modulus of the cable.

[0106] [ Z m ] is the cable modulus impedance matrix.

[0107] Step 2.2.3: Based on the cable admittance matrix, establish the cable modulus admittance matrix, expressed by the following formula:

[0108] [ 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 ]

[0109] In the formula:

[0110] Y m1 , Y m2 , Y m3 , Y m4 For admittance external modulus,

[0111] Y m5 , Y m6 For admittance internal modulus,

[0112] [ Y m [ ] is the cable modulus admittance matrix.

[0113] Y 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.

[0114] 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.

[0115] In this embodiment, the impedance internal modulus Z m5 and Z m6 The values ​​are the same. Y 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 is used to solve for the input impedance.

[0116] Step 2.3: Based on the cable modulus matrix and fault parameters obtained in Step 2.2, establish an input impedance model at the cable head end. This establishes a mapping between the input impedance and the distance from the fault point to the head end, as well as the cable fault type. The input impedance at the cable head end under different frequency sweep signals is then calculated, and the broadband impedance amplitude and phase spectra are plotted. In other words, when calculating the input impedance at the cable head end under different frequency sweep signals, the fault parameters of the cable equivalent model, any admittance internal modulus, and any impedance internal modulus are used to solve for the input impedance. The fault parameters include the fault resistance corresponding to the cable fault type. R f and the distance from the cable fault point to the beginning of the cable la .

[0117] Further preferred, but not limiting, step 2.3 specifically includes:

[0118] Step 2.3.1: Based on the cable modulus impedance matrix and the cable modulus admittance matrix, calculate the characteristic impedance of the cable modulus and the propagation coefficient of the cable; wherein, the characteristic impedance of the cable modulus is expressed by the following formula:

[0119]

[0120] In the formula:

[0121] Z m0 The characteristic impedance of the cable modulus,

[0122] R The resistance of the cable. L For the inductance of the cable, G For the electrical conductivity of the cable, C For the capacitance of the cable, R , L , G , C For example, but not limited to, taking the resistance, inductance, capacitance, and capacitance per unit length of the cable. ω Angular frequency,

[0123] Z m The modulus impedance of the cable. Y m This is the cable modulus admittance.

[0124] The propagation coefficient of the cable is expressed by the following formula:

[0125]

[0126] In the formula:

[0127] γ The propagation coefficient of the cable, R The resistance of the cable. L For the inductance of the cable, G For the electrical conductivity of the cable, C For the capacitance of the cable, ω ω is the angular frequency.

[0128] Step 2.3.2: Calculate the reflection coefficient at the cable end. It's understandable that during input impedance acquisition, the cable end is generally open-circuited; therefore, the input impedance at the cable end will be... Z ( l Since the reflection coefficient is infinite, we can conclude that the reflection coefficient at the end of the cable is 1, expressed by the following formula:

[0129]

[0130] In the formula:

[0131] τ l The reflection coefficient at the end of the cable.

[0132] Z (0) Z ( l ) are the input impedances at the beginning and end of the cable, respectively.

[0133] Step 2.3.3: Establish distance from the cable start end x The input impedance model at the point, specifically, if the cable length is... l Then the distance from the beginning of the cable x The input impedance at the point is expressed by the following formula:

[0134]

[0135] In the formula:

[0136] l For cable length,

[0137] V ( x () is the distance from the beginning of the cable x Voltage at that point

[0138] I ( x () is the distance from the beginning of the cable x The current at that point,

[0139] τ l The reflection coefficient at the end of the cable.

[0140] Z m0 The characteristic impedance is the modulus of the cable.

[0141] Step 2.3.4: Based on the distance from the cable head end x The input impedance model at the fault point is used to calculate the reflection coefficient at the fault point; specifically, if the distance from the fault point to the beginning is... l a Then the reflection coefficient of the corresponding fault point can be obtained by the following formula:

[0142]

[0143] In the formula:

[0144] τ la The reflection coefficient at the cable fault point.

[0145] Z ( l a () represents the impedance from the fault point to the beginning of the circuit.

[0146] R f The equivalent resistance at the cable fault point is the fault resistance.

[0147] Z m0 The characteristic impedance is the modulus of the cable.

[0148] 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 here... Z ( l a )and R f Perform parallel (‖) calculations.

[0149] Understandably, when an open-circuit fault occurs in a cable, R f It is infinite; when a short circuit fault occurs in the cable, R f =0; When a high-resistance fault occurs in the cable R f >1000 Ω .

[0150] Step 2.3.5: Based on the characteristic impedance of the cable modulus and the propagation coefficient of the cable obtained in Step 2.3.1, the reflection coefficient of the fault point obtained in Step 2.3.4, and the cable length, establish the input impedance model at the cable start-up end. This establishes a mapping between the input impedance and the distance from the fault point to the start-up end and the cable fault type, expressed by the following formula:

[0151]

[0152] In the formula:

[0153] Z (0) represents the input impedance at the beginning of the cable.

[0154] V ( x () is the distance from the beginning of the cable x Voltage at that point I ( x () is the distance from the beginning of the cable x The current at that point,

[0155] Z m0 The characteristic impedance of the cable modulus,

[0156] τ la The reflection coefficient at the cable fault point. γ The propagation coefficient of the cable, l This refers to the cable length.

[0157] Step 3: Change the fault type and repeat steps 1 and 2 above until the broadband impedance amplitude spectrum and phase spectrum of the cable fault are obtained for all fault types.

[0158] Step 4: Real-time acquisition of the actual cable's input impedance and plotting of the real-time broadband impedance amplitude spectrum and phase spectrum. Compare 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.

[0159] 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.

[0160] Embodiment 2 of the present invention provides a broadband impedance spectrum cable fault identification system, which operates a broadband impedance spectrum cable fault identification method according to Embodiment 1, including:

[0161] The modeling and simulation module is used to build an equivalent cable model based on any preset cable fault type.

[0162] A waveform generator is used to send a sweep frequency signal to the cable equivalent model;

[0163] The input impedance calculation module is used to collect the ground voltage and current of the cable core, sheath and steel armor of the cable equivalent model under different frequency sweep signals, and calculate the input impedance of the cable head under different frequency sweep signals in combination with the fault parameters to obtain the cable fault broadband impedance amplitude spectrum and phase spectrum.

[0164] The fault identification module is used to collect the input impedance of the actual cable in real time and draw the real-time broadband impedance amplitude spectrum and phase spectrum. It compares the spectrum with the broadband impedance amplitude spectrum and phase spectrum of the cable fault to identify the cable fault type and the distance of the cable fault point from the beginning.

[0165] Embodiment 3 of the present invention provides 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 in Embodiment 1.

[0166] To more clearly illustrate the outstanding substantive features of this invention and the significant progress it brings to the prior art, an application example of implementing this invention is described below.

[0167] 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.

[0168] 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.

[0169] 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. The results are as follows. Figure 3 and Figure 4 As shown.

[0170] By comparing the broadband impedance spectrum images, 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.

[0171] 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. The results are as follows. Figure 5 and Figure 6 As shown.

[0172] By comparing the broadband impedance spectrum images, it can be seen that when an open-circuit fault occurs in a cable, compared to a normal cable, the amplitude of the fault broadband impedance spectrum increases, the peak impedance increases from 515.24Ω to 546.24Ω, and the resonant point shifts to the right; while the maximum phase value of the impedance spectrum increases from 87.98° to 88.34°, and the oscillation period increases.

[0173] 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.

[0174] In particular, compared with existing technologies, this invention, based on simulation software, generates the cable impedance admittance modulus by setting internal cable parameters, and finally calculates the cable input impedance using a formula. The process is simple and efficient. When identifying cable faults using the broadband impedance spectrum method, this invention can be used for simulation, and the results can be used for experimental reference, saving a lot of experiments in actual operation. This invention elaborates on the process of obtaining cable input impedance so that subsequent processing of impedance spectrum focuses on analyzing cable fault identification. This method is relatively fast and convenient for obtaining cable input impedance parameters under different fault types, providing a reference for broadband impedance spectrum results under actual working conditions.

[0175] It is worth noting that in the embodiments of the present invention, "steps + numbers" is only an expression for clearly describing the specific implementation of the broadband impedance spectrum cable fault identification method, and not an absolute restriction on the order of the steps. Under the guidance of the core concept of the present invention, changing the order of these steps to obtain the same or similar technical effects all fall within the scope of the present invention.

[0176] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A broadband impedance spectroscopy cable fault identification method, characterized by, The method comprises the following steps: According to any preset cable fault type, an equivalent cable model is established, and the fault parameters of the equivalent cable model include a fault resistance corresponding to the cable fault type R f and a distance from the cable fault point to the head end l a ; The step of establishing the cable equivalent model according to any preset cable fault type comprises: The step of establishing the cable equivalent model framework of the single-core armored coaxial cable comprises: The preset cable fault type comprises one of a short-circuit fault, a high-resistance fault and an open-circuit fault; Based on the cable equivalent model framework, the initial structure of the cable equivalent model is established according to the cable impedance, the cable admittance, the geometric parameters and the material parameters of the actual cable, and then any preset cable fault type is selected, and the fault resistance corresponding to the cable fault type is input into the initial structure R f and the distance from the cable fault point to the head end l a , to obtain the cable equivalent model; The step of collecting the voltage and current of the cable core, the sheath and the steel armor of the cable equivalent model under different sweep signals, combining the fault parameters and calculating the input impedance of the cable head under different sweep signals to obtain the cable fault broadband impedance amplitude spectrum and the phase spectrum comprises: The step of replacing the fault type and repeating the above steps until the cable fault broadband impedance amplitude spectrum and the phase spectrum of all fault types are obtained comprises: The step of collecting the input impedance of the actual cable in real time and drawing the real-time broadband impedance amplitude spectrum and the phase spectrum, comparing the real-time broadband impedance amplitude spectrum and the phase spectrum with the cable fault broadband impedance amplitude spectrum and the phase spectrum, identifying the cable fault type and the distance from the cable fault point to the head comprises:

2. The method according to claim 1, wherein: The step of calculating the input impedance of the cable head under different sweep signals comprises: The step of collecting the voltage and current of the cable core, the sheath and the steel armor of the cable equivalent model under different sweep signals, combining the cable impedance model and the cable admittance model and calculating the mutual impedance and the mutual admittance of the cable core, the sheath and the steel armor of the cable equivalent model under different sweep signals comprises: The step of calculating the cable modulus matrix based on the voltage and current of the cable core, the sheath and the steel armor of the cable equivalent model under different sweep signals comprises: The step of establishing the input impedance model at the cable head based on the cable modulus matrix and the fault parameters and calculating the input impedance of the cable head under different sweep signals to draw the fault broadband impedance amplitude spectrum and the phase spectrum comprises:

3. The method according to claim 2, wherein: The step of calculating the cable modulus matrix based on the voltage and current of the cable core, the sheath and the steel armor of the cable equivalent model under different sweep signals comprises: The step of transforming the cable voltage matrix and the cable current matrix into the cable voltage modulus matrix and the cable current modulus matrix comprises: The step of calculating the cable modulus impedance matrix based on the cable voltage modulus matrix and the cable current modulus matrix comprises: The step of establishing the cable modulus admittance matrix based on the cable admittance matrix comprises:

4. The method according to claim 2 or 3, wherein: The step of establishing the input impedance model at the cable head based on the cable modulus impedance matrix and the cable modulus admittance matrix and calculating the input impedance of the cable head under different sweep signals comprises: The step of calculating the characteristic impedance of the cable modulus and the propagation coefficient of the cable based on the cable modulus impedance matrix and the cable modulus admittance matrix comprises: The step of calculating the reflection coefficient of the cable end comprises: characteristic impedance of the cable modulus, propagation coefficient of the cable and reflection coefficient of the cable end, building a model of input impedance at a distance from the cable head x end. Based on a model of input impedance at a distance from a cable head x point of the fault. The step of establishing the input impedance model at the cable head based on the obtained characteristic impedance of the cable modulus and the propagation coefficient of the cable, the reflection coefficient of the fault point and the cable length and mapping the input impedance with the distance from the fault point to the head and the cable fault type comprises:

5. The broadband impedance spectroscopy cable fault identification method of claim 2 or 3, wherein: the input impedance model at the cable head end is represented by the following equation: Zin = Z0 tanh (jωτ) / (1 + (Z0 / Z0) tanh (jωτ)), wherein: Z0 = 60 / (ω0C0), ω0 = 2πf0, τ = L / (Z0C0), and C0 = 2πf0ε0, and wherein: f0 = 1 MHz, L = 100 km, C0 = 1 nF / km, and ε0 = 8.854 x 10-12 F / m.

6. The broadband impedance spectroscopy cable fault identification method of claim 5, wherein: the characteristic impedance of the cable modulus, the propagation coefficient of the cable, and the reflection coefficient of the fault point are represented by the following equations, respectively: Z0 = 60 / (ω0C0), γ = 1 / (Z0C0), and R = (Z0 / Z0) tanh (jωτ), wherein: ω0 = 2πf0, τ = L / (Z0C0), and C0 = 2πf0ε0, and wherein: f0 = 1 MHz, L = 100 km, C0 = 1 nF / km, and ε0 = 8.854 x 10-12 F / m.

7. The broadband impedance spectroscopy cable fault identification method of claim 2 or 3, wherein: the comparing the real-time broadband impedance amplitude spectrum and phase spectrum with the cable fault broadband impedance amplitude spectrum and phase spectrum to identify the cable fault type and the distance of the cable fault point from the head end comprises: comparing the real-time broadband impedance amplitude spectrum and phase spectrum with the cable fault broadband impedance amplitude spectrum and phase spectrum, and if the real-time broadband impedance amplitude spectrum and phase spectrum coincide with any of the cable fault broadband impedance amplitude spectrum and phase spectrum, then obtaining the cable fault type and the distance of the cable fault point from the head end according to the fault parameters of the model set when the cable fault broadband impedance amplitude spectrum and phase spectrum are generated. Z (0) is the input impedance of the cable head end, Z m0 is the characteristic impedance of the cable modulus comprises: a modeling simulation module configured to establish a cable equivalent model according to any preset cable fault type; a waveform generator configured to send a sweep signal to the cable equivalent model; an input impedance calculation module configured to collect voltages and currents of the cable core, the sheath, and the steel armor of the cable equivalent model under different sweep signals, and calculate input impedance of the cable head end under different sweep signals in combination with the fault parameters to obtain the cable fault broadband impedance amplitude spectrum and phase spectrum; and a fault identification module configured to collect input impedance of an actual cable in real time, draw a real-time broadband impedance amplitude spectrum and phase spectrum, and compare the real-time broadband impedance amplitude spectrum and phase spectrum with the cable fault broadband impedance amplitude spectrum and phase spectrum to identify the cable fault type and the distance of the cable fault point from the head end. la the reflection coefficient of the cable fault point, The computer program, when executed by a processor, implements the steps of the broadband impedance spectroscopy cable fault identification method of any one of claims 1-7. is the propagation coefficient of the cable, l L is the cable length. ​ ​ ​ Z m0 is the characteristic impedance of the cable modulus R the resistance of the cable, L the inductance of the cable, G the conductance of the cable, C the capacitance of the cable, ​ the angular frequency, Z m Z0= 2.5 kQ Y m Z0= 2.5 kQ ​ is the propagation coefficient of the cable, ​ la the reflection coefficient of the cable fault point, Z l a ) is the impedance from the fault point to the head end,​ R f Fault resistance. ​ ​ ​ 8. A broadband impedance spectroscopy cable fault identification system operative to perform a broadband impedance spectroscopy cable fault identification method according to any one of claims 1 to 7, characterized in that, ​ ​ ​ ​ ​ 9. A computer-readable storage medium having stored thereon a computer program, characterized in that ​

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