Broadband impedance spectroscopy cable fault positioning method based on end function compensation

Abstract

The invention discloses a broadband impedance spectroscopy cable fault positioning method based on end function compensation, and the method comprises the steps: determining a voltage and current partial differential equation set of a healthy coaxial cable according to an infinitesimal equivalent model of the healthy coaxial cable, and calculating a general solution of the voltage and current partial differential equation set; calculating a reflection coefficient of a load end of the healthy coaxial cable according to the general solution, and calculating an impedance spectrum of the healthy coaxial cable about frequency according to the reflection coefficient and the general solution; measuring the impedance spectrum of the tested cable about the frequency, and comparing the impedance spectrum with the impedance spectrum of the healthy coaxial cable to determine whether the tested cable has a fault or not; constructing an orthogonal integral function according to the phase spectrum, introducing Gaussian filtering to eliminate local interference caused by a large fault, and extracting an extreme value and an extreme value of the function to form a compensation function; a fault diagnosis function based on the impedance phase spectrum is established, the local fault position and the local soft fault type of the detected cable are determined, accurate positioning of different fault positions is achieved, and meanwhile the detection and positioning precision is greatly improved compared with a traditional method.

Description

Technical Field

[0001] The invention relates to the technical field of fault diagnosis of electric power equipment in electrical engineering, and in particular to a broadband impedance spectrum cable fault locating method based on terminal function compensation. Background Art

[0002] The traditional faults that often occur in power cables are divided into: low-resistance faults, high-resistance faults, open-circuit faults and short-circuit faults. Among them, open-circuit faults and short-circuit faults are easier to explore through current engineering methods. The detection methods for low-resistance and high-resistance soft faults that have no serious impact on the operating status of the cable but have great hidden dangers include non-electrical parameter methods and electrical parameter methods. Non-electrical parameters mainly refer to the status diagnosis of the physical and chemical properties of the cable, which are often used to evaluate the overall life of the cable, such as the elongation at break method (EAB) of the cable material, compression modulus detection, infrared spectroscopy, oxidation induction time / temperature method, energy spectrum analysis (EDX), etc. The measurement of the power parameter method includes tests on the insulation resistance, dielectric constant, leakage current, withstand voltage, etc. of the cable. The above measurements only evaluate the status of the overall cable to a certain extent, but cannot detect local defects and latent defects of the cable.

[0003] At present, the broadband impedance spectrum method for cable defects has better sensitivity to local faults such as cable aging. For example, the input impedance spectrum of the cable head end is obtained, and the fault location function is obtained by integrating the input impedance spectrum of the head end using the integral transformation method; however, the measurement accuracy of this method depends on the measurement frequency or sweep bandwidth of the impedance spectrum. On the one hand, the higher the upper limit of the impedance spectrum measurement frequency, the better. However, too high a test frequency upper limit places high demands on the measurement equipment, and when the frequency is too high, the impedance mismatch at the connection of the measurement fixture will have an impact on the test system that cannot be ignored. In addition, serious faults in the existing multi-segment faults will cause the fault location point at the back end to be offset, and the positioning accuracy will be affected in the case of multiple fault segments. On the other hand, the positioning accuracy is limited by the sweep bandwidth. The larger the sweep bandwidth, the more accurate the positioning is, which often requires high-precision impedance analyzers and vector network analyzers, while low sweep bandwidth will introduce larger positioning fault ripples that may lead to misjudgment.

[0004] Therefore, the analysis of local faults such as cable aging based on the broadband impedance spectroscopy method needs further research to improve the accuracy of fault detection and location. Summary of the invention

[0005] The problem to be solved by the present invention is to provide a broadband impedance spectrum cable fault locating method based on terminal function compensation, which can accurately determine the local soft fault type of the tested cable and realize precise positioning of different fault positions, effectively improving the detection and positioning accuracy.

[0006] The present invention adopts the following technical solution: a broadband impedance spectrum cable fault location method based on terminal function compensation, comprising the following steps:

[0007] Step 1: Obtain the physical geometric parameters of the cable under test under the health standard, including: the radius r of the cable center conductor c , inner radius of cable shield r s , the total length L of the cable to be tested;

[0008] Step 2: According to the coaxial transmission line distributed parameter model, the distributed parameters of the cable are modeled to obtain the distributed parameters of the healthy cable, including four parts: distributed resistance R, distributed inductance L, distributed capacitance C and distributed conductance G; the admittance per unit length of each layer of the cable is calculated to obtain the total admittance containing N layers of insulating medium;

[0009] Step 3: According to the microelement equivalent model of the healthy cable, determine the voltage and current partial differential equations under the health standard of the cable to be tested, calculate the general solution, and obtain the phase spectrum of the input impedance spectrum of the head end of the healthy cable according to the transmission line theory;

[0010] Step 4: Use an impedance analyzer to measure the cable under test, obtain the input phase spectrum of the first end of the cable under test, and compare it with the phase spectrum of the input impedance spectrum of the first end of the healthy cable to determine whether there is a fault section in the cable under test;

[0011] Step 5: Establish an orthogonal integral function H1(x), select an orthogonal basis in the orthogonal integral function system to integrate the phase spectrum, and introduce a Gaussian smoothing function to eliminate ripples. On the basis of the orthogonal integral function, use the maximum peak value caused by the impedance mismatch caused by the line end break to form a compensation function for compensation, and obtain the final fault diagnosis function H(x), thereby obtaining the fault information of the cable to be tested.

[0012] Preferably, in step 2, the distributed resistance R, the distributed inductance L, the distributed capacitance C and the distributed conductance G are calculated according to the microelement distributed parameter model of the coaxial transmission line, and the method is as follows:

[0013] When current is freely conducted in a conductor, it will be affected by the skin effect. The conductor skin depth δ decreases with increasing frequency, satisfying the following relationship:

[0014]

[0015] In the formula, μ is the magnetic permeability of the metal. For copper and aluminum metal conductors, their magnetic permeability is the same as the vacuum magnetic permeability μ0. σ is the electrical conductivity. ω is the angular frequency, that is, the frequency f of the electromagnetic wave is converted into angular frequency, ω=2πf, and the unit is rad / s.

[0016] Due to the magnetic flux between the conductors, the leaving and returning currents also attract each other, known as the proximity effect, and the resistance per unit length of the cable, R(ω), can be approximated as:

[0017]

[0018] In the formula, r c and r s is the phase cable conductor radius and the inner radius of the cable shield; δ c and δ s are the skin effect coefficients of the core wire and the metal shielding layer respectively; σ c and σ s is the conductivity of the conductor and shield.

[0019] The self-inductance per unit length of coaxial cable is L in It can be approximated as:

[0020]

[0021] Where μ0 is the magnetic permeability of vacuum.

[0022] The external inductance is derived directly by considering the enclosed magnetic flux Φ between the center conductor and the shield in the surface s, caused by the current through the center conductor I (using Ampere's law for the transverse magnetic field):

[0023]

[0024] In the formula, B t is the transverse magnetic flux density.

[0025] In composite insulated cables, semiconducting layers are usually present between the insulation material and the two conductors (phase conductor and metallic screen), but since these layers have little effect on the magnetic field, their effect on the inductance is negligible.

[0026] The external inductance per unit length parameter can be described as:

[0027]

[0028] Therefore, the distributed inductance per unit length of the coaxial cable is:

[0029]

[0030] The distributed capacitance and distributed conductance correspond to the imaginary part and real part of the distributed admittance respectively:

[0031] C(ω)=imag(Y / ω) (2-7)

[0032] G(ω)=real(Y) (2-8)

[0033] Where Y is the distributed admittance, which is a function of frequency and is expressed as: Y(ω)=G(ω)+jωC(ω)

[0034] The admittance per unit length of each layer of the cable is calculated as follows:

[0035]

[0036] Where Y i is the dielectric admittance of the i-th layer, ε(ω) is the complex dielectric constant of the composite insulating material, r i With r i+1 are the inner and outer radii of the i-th layer of medium respectively, jω is the combination of the imaginary unit and the angular frequency in the complex function, and is the independent variable of the frequency domain angle analysis.

[0037] The total admittance of N layers of insulating medium is:

[0038]

[0039] The complex dielectric constant ε(ω) is fitted by the Cole-Cole formula:

[0040]

[0041] Where A, B and p are fitting parameters.

[0042] Preferably, in step 3, a transmission line equation is constructed, and a partial differential equation is established for the infinitesimal cable distribution parameters based on the cable distribution parameters obtained in step 2, and the voltage and current expressions to be solved are obtained by Kirchhoff's law:

[0043]

[0044] Taking the derivative of both sides of the equation, we get:

[0045]

[0046] In the formula, They represent the current and voltage at point x in the cable respectively, and dx represents the infinitesimal distance.

[0047] Before solving the voltage wave and current wave, it is necessary to clarify the concepts of propagation coefficient γ and characteristic impedance Z0. The two concepts are determined by the material properties of the transmission line itself, and the expressions are as follows:

[0048]

[0049] Characteristic impedance reflects the dielectric properties of the material. When the incident signal passes through the interface of heterogeneous materials during propagation, signal reflection will occur, resulting in different reflected signals and input impedance.

[0050] The propagation coefficient γ=α+jβ, where α is the attenuation coefficient, which is used to characterize the amplitude attenuation characteristics of the voltage wave and the current wave; β=2π / λ is the phase constant, which is used to characterize the phase change characteristics of the voltage wave and the current wave.

[0051] λ is the wavelength of the electromagnetic wave, which depends on its frequency and the properties of the transmission material:

[0052]

[0053] Where c is the speed of light 3×10 8 m / s, ε r and μ r are the relative permittivity and relative magnetic permeability.

[0054] Substituting equation (3-3) into (3-2), the solution of the second-order differential equation can be obtained as:

[0055]

[0056] In the formula, They represent the values ​​of voltage in the forward and reverse directions, respectively. By solving the transmission line equation and combining the boundary conditions, the voltage and current at any point on the transmission line can be determined.

[0057] In the theoretical analysis of transmission lines, the origin of the spatial coordinate system is often taken to be located at the load, and the positive direction points to the power supply end. If x is the distance from the load end, then formula (3-5) can be expressed at the load end (x = 0) as:

[0058]

[0059] If the load impedance is Z L ,because Substituting into (3-6) we get:

[0060]

[0061] In the formula, Γ L is the reflection coefficient at the load end, which is the ratio of the reflected voltage to the forward voltage. If the load is open circuit, the reflection coefficient is a real number 1.0. If the reflection coefficient is -1.0, Γ L Substituting into (3-5) we get:

[0062]

[0063] Based on the above formula, the input impedance at a distance x from the load end is:

[0064]

[0065] In the formula, Z xIt is the impedance of the cable line at a distance x from the load end. The value is the ratio of the voltage and current flowing through this point. It is a function of the cable distribution parameters and the load reflection coefficient, and has nothing to do with the external voltage and current. If x is equal to the total length of the cable l, it is the input impedance expression of the cable head end:

[0066]

[0067] The formula in (3-10) is the input impedance spectrum Z of the healthy cable at the head end. inH .

[0068] Preferably, in step 4, the Kelvin measurement bridge fixture is connected to the core wire and shielding layer of the cable to be tested, and the frequency impedance analyzer is swept to obtain the input impedance spectrum Z of the first end of the cable to be tested. inD , based on the input impedance spectrum Z of the healthy cable obtained in step 3 inH and the cable Z measured by the instrument inD To make a difference comparison, |Z inH -Z inD | is not zero, it means that there is a fault in the cable under test.

[0069] Preferably, the diagnostic function H(x) established in step 5 is a function of the distance variable x, and when a fault occurs at one point, different mutation peaks will appear.

[0070] First, the input impedance phase spectrum of the faulty cable head end, which is more sensitive to fault information, is obtained. phaseP Take (f) as an example:

[0071] Z phaseP (f,l)=rad_deg[angle(Z inD )] (3-11)

[0072] The measured impedance Z of the faulty cable inD Contains the real and imaginary parts, angle(Z inD )for:

[0073]

[0074] Where rad_deg() is the operation of converting radians to degrees, imag() is the operation of taking the imaginary part of a complex number, and real() is the operation of taking the real part of a complex number.

[0075] Furthermore, an orthogonal basis in the orthogonal function system is selected to integrate the phase spectrum, and a Gaussian smoothing function is introduced to eliminate ripples:

[0076]

[0077] In the formula, β is the phase constant, df is the differential element of the frequency independent variable;

[0078] Gaussian filter function G(x,σ):

[0079]

[0080] Define Δx as the compensation variable:

[0081]

[0082] In the formula, σ is the Gaussian smoothing factor, L is the length of the transmission line, and the extreme value and maximum value of the function are extracted. is the inverse positioning function, i.e. the distance l under the maximum value of the fault state, is the positioning function, that is, the distance l under the first extreme point.

[0083] Then the final fault diagnosis function is obtained:

[0084]

[0085] Furthermore, the final fault diagnosis function graph about x is plotted, and the fault point corresponding to the extreme point of the mutation peak is observed. The type of fault is further judged by the polarity of the mutation peak, where "minimum-maximum" is an aging fault, and the extreme point corresponds to the starting and ending position of the fault, and "maximum-minimum" is a local defect fault, and the extreme point corresponds to the starting and ending position of the fault.

[0086] The technical solution of the present invention also provides: an electronic device, comprising:

[0087] one or more processors;

[0088] a storage device having one or more programs stored thereon;

[0089] When the one or more programs are executed by the one or more processors, the one or more processors implement any of the above-mentioned broadband impedance spectrum cable fault location methods based on terminal function compensation.

[0090] The technical solution of the present invention also provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps in any of the above-mentioned broadband impedance spectrum cable fault location methods based on terminal function compensation are implemented.

[0091] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0092] 1. The broadband impedance spectrum cable fault location method of the present invention uses the impedance phase spectrum to construct a fault location function, and uses the terminal impedance mismatch to compensate for the location point in the location function. Compared with the existing method, it can more intuitively reflect the fault nature and fault degree of the fault point, and also compensate for a certain positioning error, making the positioning more accurate.

[0093] 2. Compared with other methods that rely on a wider sweep frequency range to reduce positioning errors, the broadband impedance spectrum cable fault positioning method of the present invention reduces ripples in fault diagnosis through integral compensation. The integration result is treated with a Gaussian smoothing function. The curve is still smooth at a narrow sweep frequency width, which will not cause misjudgment and greatly improves the accuracy of detection and positioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Figure 1 This is a flowchart of the broadband impedance spectrum cable fault location method of the present invention;

[0095] Figure 2 These are the cross-section and physical geometric parameters of the cable measured in the present invention.

[0096] Figure 3 It is a microelement distribution parameter model diagram of the coaxial cable transmission line of the present invention;

[0097] Figure 4 It is a schematic diagram of the difference comparison between the healthy cable and the unknown cable in the present invention;

[0098] Figure 5 Schematic diagram of the positioning effect of the traditional method in the embodiment;

[0099] Figure 6 It is a schematic diagram comparing the positioning effects of the method proposed by the present invention and the traditional method in the embodiment. DETAILED DESCRIPTION

[0100] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the application is further elaborated in detail below in conjunction with the accompanying drawings. The described embodiments are only a part of the embodiments involved in the present invention. All non-innovative embodiments of other researchers in the field on this embodiment belong to the protection scope of the present invention. At the same time, for the step numbering in the embodiment of the present invention, it is only set for the convenience of explanation, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0101] In one embodiment of the present invention, a broadband impedance spectrum cable fault location method based on terminal function compensation is provided. Figure 1 As shown, the specific steps are as follows:

[0102] Step 1: Use a micrometer to measure the cross-sectional geometric parameters of the target cable for simulation research.

[0103] In this embodiment, taking a certain XLPE cable as an example, its corresponding parameters are as follows: Figure 2 As shown, the radius of the cable center conductor r c The inner radius of the cable shield is 3.5 mm. s is 9.3mm, and the total length L of the cable to be tested is 100m.

[0104] Step 2: According to Figure 3 The microelement distributed parameter model shown in the figure includes four parts: distributed resistance R, distributed inductance L, distributed capacitance C and distributed conductance G. Its electrical connection diagram is shown in Figure 3 As shown, the respective calculation formulas are as follows:

[0105] The current is conducted freely in the conductor, so the current density near the surface of the conductor is greater than that in the center of the conductor. This phenomenon is called skin effect. This will cause the conductor inductance in the AC circuit to increase and the conductivity to decrease.

[0106] The conductor skin depth δ decreases as the frequency increases, satisfying the following relationship:

[0107]

[0108] Among them, μ is the magnetic permeability of the metal. For copper and aluminum metal conductors, their magnetic permeability is the same as the vacuum magnetic permeability μ0. σ is the electrical conductivity. ω is the angular frequency, that is, the frequency f of the electromagnetic wave is converted into angular frequency, ω=2πf, and the unit is rad / s.

[0109] Due to the magnetic flux between the conductors, the leaving and returning currents also attract each other, which is called the proximity effect. The current through the conductor is concentrated in the area determined by the skin depth. Therefore, due to the decrease in skin depth, the effective unit length resistance of the phase conductor and the metal screen will increase with the increase of frequency. The resistance R per unit length of the cable can be approximated as:

[0110]

[0111] In the formula, r c and r s is the phase cable conductor radius and the inner radius of the cable shield; δ c and δ s are the skin effect coefficients of the core wire and the metal shielding layer respectively; σ c and σ s is the conductivity of the conductor and shield.

[0112] The self-inductance per unit length of coaxial cable is L in It can be approximated as:

[0113]

[0114] Where μ0 is the magnetic permeability of vacuum.

[0115] Furthermore, the external inductance can be derived directly by considering the enclosed magnetic flux Φ between the center conductor and the shield in the surface s, which is caused by the current through the center conductor I (using Ampere's law for the transverse magnetic field):

[0116]

[0117] In the formula, B t is the transverse magnetic flux density.

[0118] In composite insulated cables, semiconducting layers are usually present between the insulating material and the two conductors (phase conductor and metal screen), but since these layers have little effect on the magnetic field, their effect on the inductance is negligible.

[0119] The external inductance per unit length parameter can be described as:

[0120]

[0121] Therefore, the distributed inductance per unit length of the coaxial cable is:

[0122]

[0123] Among them, the distributed capacitance and distributed conductance correspond to the imaginary part and real part of the distributed admittance respectively:

[0124] C(ω)=imag(Y / ω) (2-7)

[0125] G(ω)=real(Y) (2-8)

[0126] Wherein, Y is the distributed admittance, which is a function of frequency and is expressed as: Y(ω)=G(ω)+jωC(ω).

[0127] The admittance per unit length of each layer of the cable is calculated as follows:

[0128]

[0129] Where Y i is the dielectric admittance of the i-th layer, ε(ω) is the complex dielectric constant of the composite insulating material, r i With r i+1 are the inner and outer radii of the i-th layer of dielectric, respectively. The total admittance of N layers of insulating dielectric is:

[0130]

[0131] In the formula, the complex dielectric constant ε(ω) is fitted by the Cole-Cole formula:

[0132]

[0133] Where A, B and p are fitting parameters.

[0134] In this embodiment, the fitting parameters of the cable at different aging degrees are obtained by consulting relevant literature, and the specific parameters are shown in Table 1:

[0135] Table 1 Cable insulation aging fitting parameters

[0136]

[0137] Furthermore, in order to simulate local defect failure, the mathematical formula of cable distribution parameters under local damage is defined in this embodiment:

[0138] Combined with the resistance formula under good condition, a shielding layer damage coefficient K1 is added to the resistance of the corresponding shielding layer. When local damage occurs, its value is greater than 1. At this time, the expression of distributed resistance is:

[0139]

[0140] When K1=1, it is the same as expression (2-2) of a normal healthy cable.

[0141] However, the distributed inductance at the damaged part includes the self-inductance of the core wire and the shield layer as well as the mutual inductance of the two. The change of the self-inductance of the shield layer is similar to that of the resistance, and partial damage will cause its self-inductance to increase. After the shield layer is damaged, the magnetic field coupling between the core wire and the shield layer becomes weaker, resulting in a decrease in mutual inductance. The distributed inductance at the damaged part is determined by the following formula:

[0142]

[0143] Where K2 is the mutual inductance damage coefficient, and its value is less than 1, indicating that after the shielding layer is damaged, the magnetic field coupling between the core wire and the shielding layer is weakened, and the leakage magnetic flux increases.

[0144] When the insulating material at the damaged part is damaged, the shape of the insulating material will usually change, and the overall distributed admittance of the damaged part is determined by the following formula:

[0145]

[0146] Where K3 is the insulation layer damage coefficient, which can be expressed as:

[0147]

[0148] In the formula, is the average effective thickness of the insulation structure. It can be seen that the damage coefficient is a value less than 1. The damage coefficients K1, K2 and K3 are directly related to the degree of local damage to the cable. The more serious the damage, the larger the damage coefficient K1, and the smaller K2 and K3.

[0149] Step 3: Based on the cable distribution parameters obtained in step 2, Figure 3 The partial differential equations are established for the distributed parameters of the infinitesimal cables in the equation, and the voltage and current expressions are solved, which are obtained from Kirchhoff's law:

[0150]

[0151] Taking the derivative of both sides of the equation, we get:

[0152]

[0153] Before solving the voltage wave and current wave, it is necessary to clarify the concepts of propagation coefficient γ and characteristic impedance Z0. The two concepts are determined by the material properties of the transmission line itself, and the expressions are as follows:

[0154]

[0155] Characteristic impedance reflects the dielectric properties of the material. When the incident signal passes through the interface of heterogeneous materials during propagation, signal reflection will occur, resulting in different reflected signals and input impedance.

[0156] The propagation coefficient γ=α+jβ, where α is the attenuation coefficient, which characterizes the amplitude attenuation characteristics of the voltage wave and the current wave; β=2π / λ is the phase constant, which characterizes the phase change characteristics of the voltage wave and the current wave, where λ is the wavelength of the electromagnetic wave, which depends on its frequency and the properties of the transmission material.

[0157]

[0158] Where c is the speed of light 3×10 8 m / s, ε r and μ r are the relative permittivity and relative magnetic permeability.

[0159] Substituting equation (3-3) into (3-2), the solution of the second-order differential equation can be obtained as:

[0160]

[0161] By solving the transmission line equation and combining the boundary conditions, the voltage and current at any point of the transmission line can be determined. In the theoretical analysis of transmission lines, the origin of the spatial coordinate system is often located at the load, and the positive direction points to the power supply end. If x is the distance from the load end, then formula (3-5) can be expressed at the load end (x = 0) as:

[0162]

[0163] If the load impedance is Z L ,because Substituting into (3-6) we get:

[0164]

[0165] In the formula, Γ L is the reflection coefficient at the load end, which is the ratio of the reflected voltage to the forward voltage. If the load is open circuit, the reflection coefficient is a real number 1.0. If the reflection coefficient is -1.0, Γ L Substituting into (3-5) we get:

[0166]

[0167] Based on the above formula, the input impedance at a distance x from the load end is:

[0168]

[0169] In the formula, Z x It is the impedance of the cable line at a distance x from the load end. Its value is the ratio of the voltage to the current flowing through this point. It is a function of the cable distribution parameters and the load reflection coefficient, and has nothing to do with the external voltage and current.

[0170] If x is equal to the total length of the cable l, then the input impedance expression of the cable head end is:

[0171]

[0172] The derivation of the input impedance calculation (3-10) of the cable head end is based on differential analysis, that is, the line is equivalent to a distributed parameter, so that the voltage and current at any point on the line can be calculated. This analysis method is not limited to the medium and high frequency bands. At low frequencies, the propagation coefficient γ is very small, so that γl→0, at which time the cable input impedance is equal to the load impedance:

[0173]

[0174] When the frequency increases or the cable length becomes longer, the input impedance at the first end increases by an exponential factor e. -2γl Determined.

[0175] For cables, since their distributed parameters are frequency-dependent, the characteristic impedance Z0 and the propagation coefficient γ are both functions of frequency. Therefore, the impedance spectrum of the head end will also change with the change of the power supply frequency. The frequency variation curve of the head end impedance is called the broadband impedance spectrum of the cable. The broadband impedance spectrum can usually be divided into impedance amplitude spectrum and phase spectrum.

[0176] Step 4: Based on the input impedance spectrum Z of the healthy cable obtained in step 3 inH The fault cable Z measured by the instrument inD To make a difference comparison, such as Figure 4 As shown, there is a significant difference between the two, indicating that there is a fault.

[0177] Step 5: The diagnostic function H(x) established in this embodiment is a function of the distance variable x. When a fault occurs at one point, different mutation peaks will appear.

[0178] First, based on steps 2 and 3, the input impedance spectrum Z of a 100m long healthy cable head end is obtained. inH , it is assumed that there are fault sections on the 100m cable as shown in Table 2 below.

[0179] Table 2 Fault model settings

[0180]

[0181] The diagnostic function image constructed by the traditional method is obtained through simulation. Figure 5 As shown, it can be seen that the positioning image of the traditional method has large ripples at the fault location, and except for the first fault point which is relatively accurate, the other fault points have offsets and errors.

[0182] Then, the diagnostic function method constructed in this embodiment is as follows:

[0183] Obtain an impedance phase spectrum that is more sensitive to fault information. In this embodiment, the phase spectrum Z of the faulty cable is used as phaseP Take (f) as an example:

[0184] Z phaseP (f,l)=rad_deg[angle(Z inD )] (3-20)

[0185] Furthermore, an orthogonal basis in the orthogonal function system is selected to integrate the phase spectrum, and a Gaussian smoothing function is introduced to eliminate ripples:

[0186]

[0187] Where, Gaussian filter function G(x,σ):

[0188]

[0189] Define Δx as the compensation variable:

[0190]

[0191] Where angle is the phase angle of the impedance spectrum of the faulty cable, rad_deg represents the conversion of radians to degrees, and L is the length of the transmission line.

[0192] In this embodiment, σ is the Gaussian smoothing factor and is set to 0.3. is the inverse positioning function, i.e. the distance l under the maximum value of the fault state. Similarly is the positioning function, that is, the distance l under the first extreme point.

[0193] Then the final fault diagnosis function is obtained:

[0194]

[0195] Furthermore, in this embodiment, the cable fault diagnosis function image obtained based on the method of the present invention is as follows: Figure 6 As shown, it can be seen that compared with the traditional method, the positioning of the method of the present invention is more accurate, and the ripple effect caused by the fault is weakened, the possibility of misjudgment is reduced, and the type of fault can be judged by the polarity of the mutation peak. The "minimum-maximum" is an aging fault, and the extreme point corresponds to the starting and ending positions of the fault. The "maximum-minimum" is a local defect fault, and the extreme point corresponds to the starting and ending positions of the fault.

[0196] In an embodiment of the present invention, an electronic device is also provided, including: one or more processors; a storage device on which one or more programs are stored; when the one or more programs are executed by the one or more processors, the one or more processors implement the broadband impedance spectrum cable fault location method based on end function compensation described in any of the above embodiments.

[0197] In an embodiment of the present invention, a computer-readable storage medium is further provided, on which a computer program is stored. When the program is executed by a processor, the steps of any of the broadband impedance spectrum cable fault location methods based on terminal function compensation in the above embodiments are implemented.

[0198] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A broadband impedance spectrum cable fault location method based on terminal function compensation, characterized in that: The steps include: Step 1: Obtain the physical geometric parameters of the cable under test under the health standard, including: the radius of the cable center conductor, the inner radius of the cable shielding layer, and the total length of the cable under test; Step 2: Model the distributed parameters of the cable according to the coaxial transmission line distributed parameter model to obtain the distributed parameters of the healthy cable, including distributed resistance, distributed inductance, distributed capacitance and distributed conductance; calculate the admittance per unit length of each layer of the cable to obtain the total admittance containing N layers of insulating medium; Step 3: According to the microelement equivalent model of the healthy cable, determine the voltage and current partial differential equations under the health standard of the cable to be tested, calculate the general solution, and obtain the input impedance spectrum of the healthy cable head end according to the transmission line theory; Step 4: Use an impedance analyzer to measure the cable under test, obtain the input impedance spectrum of the first end of the cable under test, and compare it with the input impedance spectrum of the first end of a healthy cable to determine whether there is a fault section in the cable under test; Step 5, establish an orthogonal integral function, select the orthogonal basis in the orthogonal integral function system to integrate the phase spectrum, and introduce a Gaussian smoothing function to eliminate ripples. On the basis of the orthogonal integral function, use the maximum peak value caused by the impedance mismatch caused by the line end break to form a compensation function for compensation, and obtain the final fault diagnosis function, thereby obtaining the fault information of the cable to be tested.

2. The broadband impedance spectrum cable fault location method based on terminal function compensation according to claim 1 is characterized in that: In step 2, in the coaxial transmission line distributed parameter model, the distributed parameters of each section of the transmission line include: distributed resistance R, distributed inductance L, distributed conductance G and distributed capacitance C. The distributed parameters of the healthy cable are solved as follows: Step 2.1, calculate the resistance R(ω) per unit length of the cable, which is approximately: In the formula, r c and r s is the phase cable conductor radius and the inner radius of the cable shield; δ c and δ s are the skin effect coefficients of the core wire and the metal shielding layer respectively; σ c and σ s is the conductivity of the conductor and shield; Step 2.2: Calculate the self-inductance L per unit length of the coaxial cable in , which is approximately: Where μ0 is the vacuum magnetic permeability; Step 2.3, calculate the distributed inductance L(ω) per unit length of the coaxial cable, the formula is: Where, L e is the external inductance per unit length parameter.

3. The broadband impedance spectrum cable fault location method based on terminal function compensation according to claim 2 is characterized in that: In step 2, the admittance per unit length of each layer of the cable is calculated: Where Y i (ω) is the dielectric admittance of the i-th layer, ε(ω) is the complex dielectric constant of the composite insulating material, r i With r i+1 are the inner and outer radii of the i-th layer of medium respectively; jω is the combination of the imaginary unit and the angular frequency in the complex function and is the independent variable of the frequency domain angle analysis; The total admittance Y(ω) of a dielectric with N layers is: Where C(ω) and G(ω) are the imaginary and real parts of the distributed capacitance and distributed conductance corresponding to the distributed admittance.

4. The broadband impedance spectrum cable fault location method based on terminal function compensation according to claim 3 is characterized in that: In step 3, according to the microelement equivalent model of the healthy cable, the voltage and current partial differential equations under the target cable health standard are determined, and the general solution is calculated as follows: Step 3.1, based on Kirchhoff's law, construct the transmission line equation and obtain the voltage and current partial differential equations: Taking the derivative of both sides of the equation, we get: In the formula, They represent the current and voltage at point x of the cable, respectively, and dx represents the infinitesimal distance; Step 3.2, introduce the propagation coefficient γ and characteristic impedance Z0, and get the voltage and current expressions: In the formula, Represent the values ​​of voltage in forward and reverse propagation respectively; by solving the transmission line equation and combining the boundary conditions, the voltage and current at any point of the transmission line are determined; Step 3.3: Based on the transmission line theory, the origin of the spatial coordinate system is located at the load, with the positive direction pointing to the power supply end. If x is the distance from the load end, at the load end x = 0, the voltage Current It is expressed as follows: Step 3.4: Load impedance is Z L ,because Substituting into the formula in step 3.3, we get: In the formula, Γ L is the reflection coefficient at the load end, which is the ratio of the reflected voltage to the forward voltage; Step 3.5: Γ L Substituting into the formula in step 3.2, we get: Step 3.6: The input impedance at a distance x from the load end is the ratio of the voltage to the current flowing through point x: In the formula, Z x is the impedance of the cable line at a distance x from the load end, expressed as a function of the cable distribution parameters and the load reflection coefficient, and has nothing to do with the applied voltage and current; Step 3.7: When x is equal to the total length of the cable l, the input impedance Z at the beginning of the healthy cable is inH , which is expressed as follows:

5. The broadband impedance spectrum cable fault location method based on terminal function compensation according to claim 4 is characterized in that: In step 4, connect the Kelvin measurement bridge fixture to the core wire and shielding layer of the cable to be tested, sweep the impedance analyzer, and obtain the input impedance spectrum Z of the first end of the cable to be tested. inD (f,l), and subtract the impedance spectrum of the healthy cable head end obtained in step 3 to determine whether the impedance spectrum is consistent. If it is consistent, there is no fault in the cable under test. If it is inconsistent, there is a faulty section in the cable under test.

6. The broadband impedance spectrum cable fault location method based on terminal function compensation according to claim 5 is characterized in that: In step 5, obtain the fault cable impedance phase spectrum Z phaseP (f,l), the method is as follows: From phaseP (f,l)=rad_deg[angle(Z inD )] In the formula, Z inD is the impedance spectrum of the faulty cable measured, including the real part and the imaginary part; rad_deg means converting radians to angles, and angle is the phase angle of the impedance spectrum of the faulty cable; Among them, imag() is an operation to obtain the imaginary part of a complex number, and real() is an operation to obtain the real part of a complex number; Establish the orthogonal integral function H1(x): Where G(x,σ) is the Gaussian filter function, β is the phase constant, and df is the infinitesimal frequency variable. The Gaussian filter function is calculated as follows: Where σ is the Gaussian smoothing factor.

7. The broadband impedance spectrum cable fault location method based on terminal function compensation according to claim 6 is characterized in that: The maximum peak value caused by impedance mismatch due to line end disconnection is used to form a compensation function, and the extreme value and maximum value of the function are extracted to compensate the orthogonal integral function H1(x). Δx is defined as the compensation variable, and the calculation is as follows: Where L is the length of the transmission line, is the inverse positioning function, which represents the distance l under the maximum value of the fault state, To locate the inverse function, it represents the distance l below the first extreme point.

8. The broadband impedance spectrum cable fault location method based on terminal function compensation according to claim 7 is characterized in that: In step 5, the final fault diagnosis function H(x) is a function of the distance variable x, expressed as follows: Draw a diagnostic function graph about x to observe the fault point corresponding to the extreme point of the mutation peak, and judge the type of fault by the polarity of the mutation peak. "Minimum-maximum" is an aging fault, "maximum-minimum" is a local defect fault, and the extreme point corresponds to the starting and ending position of the fault.

9. An electronic device, characterized in that: include: one or more processors; a storage device having one or more programs stored thereon; When the one or more programs are executed by the one or more processors, the one or more processors implement the broadband impedance spectrum cable fault location method based on terminal function compensation as described in any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the program is executed by a processor, the steps in the broadband impedance spectrum cable fault location method based on terminal function compensation described in any one of claims 1 to 8 are implemented.

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