Method and apparatus for detecting local defect of cable, and storage medium

Abstract

A method and apparatus for detecting a local defect of a cable, and a storage medium. The method comprises: acquiring a reflected signal of a testing signal at a head end of a cable to be subjected to detection; generating a first reflection coefficient of the head end of said cable, and on the basis of a real part of the first reflection coefficient, determining whether said cable has a defect, and if so, determining the location of the defect on the basis of the real part of the first reflection coefficient, and acquiring a frequency component and a first reflection intensity at the location of the defect, and a corresponding correction angle value; and determining the polarity of the defect, and generating a first-reflection intensity cosine function, calculating the difference between the first-reflection intensity cosine function and the real part of the first reflection coefficient to generate a second reflection coefficient, wherein the first reflection coefficient is a reflection coefficient when said cable has no defect, and determining the type of the defect on the basis of the ratio of a second reflection intensity regarding the second reflection coefficient to the first reflection intensity. Thus, cable defect locating and defect type identification and classification are realized, thereby improving the cable fault detection efficiency.

Description

A method, device and storage medium for detecting local defects in a cable Technical Field

[0001] The present invention relates to the technical field of cable fault detection, and in particular to a method, device and storage medium for detecting local defects in a cable. Background Art

[0002] Various defects may occur in the cable during the manufacturing and installation process. Cables buried underground for a long time will suffer from local damage and aging due to the long-term effects of factors such as temperature, humidity, chemical corrosion, mechanical and physical effects, such as local aging, corrosion, copper shield damage and moisture.

[0003] Among the existing cable fault detection methods, the frequency domain reflectometry (FDR) method using a swept frequency signal is based on the principle that when an incident signal is reflected at an impedance discontinuity point, the reflection coefficient spectrum at the head end will change. By analyzing the reflection coefficient spectrum at the head end, the position of the cable impedance discontinuity point can be calculated based on the propagation speed of the cable, and the position of the defect can be located. However, the current FDR method cannot accurately identify the defect length type. Due to the inaccurate identification and classification of defect types, the efficiency of cable fault detection is poor.

[0004] Summary of the Invention

[0005] The present invention provides a cable local defect detection method, device and storage medium to achieve cable defect positioning and defect type identification and classification, thereby improving the efficiency of cable fault detection.

[0006] The present invention provides a method for detecting local defects in a cable, comprising: obtaining a reflection signal of a test signal at the head end of a cable to be detected; injecting the test signal into the head end of the cable to be detected; generating the reflection signal by injecting the test signal into the head end of the cable to be detected, transmitting the test signal to the end of the cable to be detected for total reflection, and then transmitting the reflection signal to the head end of the cable to be detected; generating a first reflection coefficient of the head end of the cable to be detected based on the reflection signal; judging whether the cable to be detected has a defect based on the real part of the first reflection coefficient; and if so, determining the location of the defect based on the real part of the first reflection coefficient, and obtaining the frequency component and first reflection intensity of the location of the defect;

[0007] Based on the position of the defect, a corresponding correction angle value is generated, and the polarity of the defect is determined; based on the frequency component of the defect position, the first reflection intensity, and the polarity of the defect, a first reflection intensity cosine function is generated; the first reflection intensity cosine function is subtracted from the real part of the first head-end reflection coefficient to generate a second reflection coefficient; the first head-end reflection coefficient is the reflection coefficient when the cable to be detected has no defects; based on the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity, the defect type of the defect is determined.

[0008] Further, judging whether the cable to be inspected has a defect according to the real part of the first reflection coefficient specifically includes:

[0009] Generating a propagation coefficient of the cable to be detected based on the attenuation constant and phase constant of the cable to be detected; substituting the propagation coefficient into the first reflection coefficient; and expanding the first reflection coefficient according to the Euler formula to generate an expanded expression of the first reflection coefficient;

[0010] If the cable to be tested does not have any defects, the expanded expression of the first reflection coefficient is:

[0011] The expression of the real part of the first reflection coefficient is:

[0012] Where α is the attenuation constant, f is the test frequency of the test signal, v is the propagation speed of the test signal in the cable to be tested, Γ l is the first reflection coefficient, l is the total length of the cable to be tested;

[0013] Otherwise, the cable to be tested is defective.

[0014] Furthermore, the position of the defect is determined according to the real part of the first reflection coefficient, specifically:

[0015] Obtaining a frequency component of a first reflection signal at a position of a defect according to a real part of the first reflection coefficient, and determining the position of the defect;

[0016] The expression for the position of the defect is: Wherein, f1 is the frequency component of the first reflection signal at the defect position.

[0017] Furthermore, according to the position of the defect, a corresponding correction angle value is generated, and the polarity of the defect is determined, specifically:

[0018] According to the position of the defect, a corresponding correction angle value is generated;

[0019] The expression of the correction angle value is: n=2π(f n f min -F floor (f n f min ));

[0020] Among them, f n is the frequency component of the first reflection signal at the nth defect; f min F is the lower limit frequency of the test signal; floor Indicates rounding down;

[0021] According to the correction angle value, it is determined whether the correction angle of the defect is in the first quadrant or the fourth quadrant. If so, the polarity of the defect is determined to be positive; if not, the polarity of the defect is determined to be negative.

[0022] Furthermore, a first reflection intensity cosine function is generated according to the frequency component of the defect position, the first reflection intensity, and the polarity of the defect, specifically:

[0023] The expression of the first reflection intensity cosine function is:

[0024] in, is the cosine function value of the first reflection intensity of the i-th defect, represents the polarity of the i-th defect. If the polarity of the i-th defect is positive, then If the polarity of the i-th defect is negative, then is the first reflection intensity at the position of the i-th defect; is the frequency component of the position of the i-th defect; f is the test frequency.

[0025] Furthermore, the defect type of the defect is determined according to the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity, specifically:

[0026] Based on the second reflection coefficient, a second reflection intensity at the position of the i-th defect is obtained; and a determination is made as to whether the ratio of the absolute value of the second reflection intensity to the absolute value of the first reflection intensity is less than or equal to a preset threshold; if so, the i-th defect is a point fault type; if not, the i-th defect is a segment fault type.

[0027] Furthermore, after determining the defect type of the defect, the method further includes:

[0028] If the defect type of the defect is a point fault type, the expression of the real part of the first reflection coefficient is:

[0029] Where x is the distance from the defect location to the head end, ρx is the reflection coefficient at the defect, the nth term in the formula is the nth reflection signal at the defect position; n is a natural number;

[0030] If the defect type of the defect is a segment fault type, the expression of the real part of the first reflection coefficient is:

[0031] Among them, α Δx is the attenuation coefficient of the defect segment, v x is the propagation speed of the signal in the defect section, and the nth term in the formula is the nth reflection signal at the defect position.

[0032] As a preferred solution, the present invention obtains the signal attenuation intensity of the test signal during the transmission process of the cable to be detected based on the reflection coefficient of the acquired test signal in the cable to be detected. According to the frequency component of the first reflection signal at the position of the defect, the defect can be located. After the defect is located, the signal attenuation intensity is further used to analyze and determine the specific defect type. The present invention determines the length type of the defect by constructing a cosine function of the first reflection intensity and subtracting the first reflection coefficient intensity when the cable to be detected at the defect location is not defective; if the amplitude is significantly attenuated after subtracting the first reflection coefficient intensity when the cable to be detected at the defect location is not defective, it is determined to be a point fault; if the amplitude remains basically unchanged, it is determined to be a segment fault, thereby achieving the identification and classification of defect types and improving the efficiency of cable fault detection.

[0033] Accordingly, the present invention also provides a cable local defect detection device, comprising: a testing module, a defect judgment module and a type detection module;

[0034] The test module is used to obtain a reflection signal of a test signal at the head end of the cable to be tested; the test signal is injected at the head end of the cable to be tested; the reflection signal is generated by the test signal being injected at the head end of the cable to be tested, transmitted to the end of the cable to be tested for total reflection, and then transmitted to the head end of the cable to be tested;

[0035] The defect judgment module is configured to generate a first reflection coefficient of the head end of the cable to be detected based on the reflection signal; determine whether the cable to be detected has a defect based on the real part of the first reflection coefficient; and if so, determine the location of the defect based on the real part of the first reflection coefficient, and obtain the frequency component and first reflection intensity of the defect location;

[0036] The type detection module is used to generate a corresponding correction angle value based on the position of the defect and determine the polarity of the defect; generate a first reflection intensity cosine function based on the frequency component of the defect position, the first reflection intensity and the polarity of the defect; perform a difference processing on the first reflection intensity cosine function and the real part of the first head-end reflection coefficient to generate a second reflection coefficient; the first head-end reflection coefficient is the reflection coefficient when the cable to be detected has no defects; and determine the defect type of the defect based on the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity.

[0037] Furthermore, the defect judgment module includes: a defect judgment unit and a position judgment unit;

[0038] The defect judgment unit is configured to generate a propagation coefficient of the cable to be detected based on the attenuation constant and phase constant of the cable to be detected; substitute the propagation coefficient into the first reflection coefficient; and expand the first reflection coefficient according to the Euler formula to generate an expanded expression of the first reflection coefficient.

[0039] If the cable to be tested does not have any defects, the expanded expression of the first reflection coefficient is:

[0040] The expression of the real part of the first reflection coefficient is:

[0041] Where α is the attenuation constant, f is the test frequency of the test signal, v is the propagation speed of the test signal in the cable to be tested, Γ l is the first reflection coefficient, l is the total length of the cable to be tested;

[0042] Otherwise, the cable to be tested has defects;

[0043] The position determination unit is configured to obtain a frequency component of a first reflection signal at a position of the defect based on a real part of the first reflection coefficient, and determine the position of the defect;

[0044] The expression for the position of the defect is: Wherein, f1 is the frequency component of the first reflection signal at the defect position.

[0045] Furthermore, the type detection module includes: a polarity judgment unit, a first reflection intensity cosine function generation unit and a detection unit;

[0046] Wherein, the polarity judgment unit is used to generate a corresponding correction angle value according to the position of the defect;

[0047] The expression of the correction angle value is: n =2π(f n fmin -F floor (f n f min ));

[0048] Among them, f n is the frequency component of the first reflection signal at the nth defect; f min F is the lower limit frequency of the test signal; floor Indicates rounding down;

[0049] According to the correction angle value, determining whether the correction angle of the defect is in the first quadrant or the fourth quadrant, if so, determining that the polarity of the defect is positive; if not, determining that the polarity of the defect is negative;

[0050] The expression of the first reflection intensity cosine function generated by the first reflection intensity cosine function generation unit is:

[0051] in, is the cosine function value of the first reflection intensity of the i-th defect, represents the polarity of the i-th defect. If the polarity of the i-th defect is positive, then If the polarity of the i-th defect is negative, then is the first reflection intensity at the position of the i-th defect; is the frequency component of the position of the i-th defect; f is the test frequency;

[0052] The detection unit is used to obtain a second reflection intensity at the position of the i-th defect based on the second reflection coefficient; determine whether the ratio of the absolute value of the second reflection intensity to the absolute value of the first reflection intensity is less than or equal to a preset threshold; if so, the i-th defect is a point fault type; if not, the i-th defect is a segment fault type.

[0053] If the defect type of the defect is a point fault type, the expression of the real part of the first reflection coefficient is:

[0054] Where x is the distance from the defect location to the head end, ρ x is the reflection coefficient at the defect, the nth term in the formula is the nth reflection signal at the defect position; n is a natural number;

[0055] If the defect type of the defect is a segment fault type, the expression of the real part of the first reflection coefficient is:

[0056] Among them, α Δx is the attenuation coefficient of the defect segment, v xis the propagation speed of the signal in the defect section, and the nth term in the formula is the nth reflection signal at the defect position.

[0057] As a preferred solution, the test module of the device of the present invention obtains the signal attenuation intensity of the test signal during the transmission process of the cable to be detected based on the reflection coefficient of the acquired test signal in the cable to be detected. The defect judgment module can locate the defect based on the frequency component of the first reflection signal at the position of the defect. After the defect is located, the type detection module further uses the signal attenuation intensity to analyze and determine the specific defect type. The present invention determines the length type of the defect by constructing a cosine function of the first reflection intensity and subtracting the first reflection coefficient intensity when the cable to be detected at the defect site has no defects; if the amplitude is significantly attenuated after subtracting the first reflection coefficient intensity when the cable to be detected at the defect site has no defects, it is determined to be a point fault; if the amplitude remains basically unchanged, it is determined to be a segment fault, thereby achieving the discrimination and classification of defect types and improving the efficiency of cable fault detection.

[0058] Accordingly, the present invention also provides a computer-readable storage medium, which includes a stored computer program; wherein, when the computer program is running, it controls the device where the computer-readable storage medium is located to execute a cable local defect detection method as described in the content of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG1 is a schematic flow chart of an embodiment of a method for detecting local defects in a cable provided by the present invention;

[0060] FIG2 is a schematic diagram of incident signal reflection of an intact cable according to an embodiment of a cable local defect detection method provided by the present invention;

[0061] FIG3 is a schematic diagram of the reflection of an incident signal of a cable with a point defect according to an embodiment of a cable local defect detection method provided by the present invention;

[0062] FIG4 is a schematic diagram of incident signal reflection of a cable with a segment defect according to an embodiment of a cable local defect detection method provided by the present invention;

[0063] FIG5 is a comparison diagram of a new reflection coefficient spectrum and an old reflection coefficient spectrum of a cable according to an embodiment of a cable local defect detection method provided by the present invention;

[0064] 6 is a comparison diagram of a new reflection coefficient spectrum and an old reflection coefficient spectrum of a coaxial cable according to another embodiment of the cable local defect detection method provided by the present invention;

[0065] 7 is a comparison diagram of a new reflection coefficient spectrum and an old reflection coefficient spectrum of a power cable according to another embodiment of the cable local defect detection method provided by the present invention;

[0066] FIG8 is a schematic structural diagram of an embodiment of a cable local defect detection device provided by the present invention. DETAILED DESCRIPTION

[0067] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0068] Example 1

[0069] Referring to FIG. 1 , a method for detecting local defects in a cable according to an embodiment of the present invention includes steps S101 to S103:

[0070] Step S101: Acquiring a reflection signal of a test signal at the head end of a cable to be detected; the test signal is injected into the head end of the cable to be detected; the reflection signal is generated by the test signal being injected into the head end of the cable to be detected, transmitted to the end of the cable to be detected, undergoing total reflection, and then transmitted to the head end of the cable to be detected;

[0071] Step S102: generating a first reflection coefficient of the head end of the cable to be inspected based on the reflection signal; determining whether the cable to be inspected has a defect based on the real part of the first reflection coefficient; and if so, determining the location of the defect based on the real part of the first reflection coefficient, and obtaining a frequency component and a first reflection intensity at the location of the defect;

[0072] Further, judging whether the cable to be inspected has a defect according to the real part of the first reflection coefficient specifically includes:

[0073] Generating a propagation coefficient of the cable to be detected based on the attenuation constant and phase constant of the cable to be detected; substituting the propagation coefficient into the first reflection coefficient; and expanding the first reflection coefficient according to the Euler formula to generate an expanded expression of the first reflection coefficient;

[0074] If the cable to be tested does not have any defects, the expanded expression of the first reflection coefficient is:

[0075] The expression of the real part of the first reflection coefficient is:

[0076] Where α is the attenuation constant, f is the test frequency of the test signal, v is the propagation speed of the test signal in the cable to be tested, Γ l is the first reflection coefficient, l is the total length of the cable to be tested;

[0077] Otherwise, the cable to be tested is defective.

[0078] Furthermore, the position of the defect is determined according to the real part of the first reflection coefficient, specifically:

[0079] Obtaining a frequency component of a first reflection signal at a position of a defect according to a real part of the first reflection coefficient, and determining the position of the defect;

[0080] The expression for the position of the defect is: Wherein, f1 is the frequency component of the first reflection signal at the defect position.

[0081] In this embodiment, the incident signal is injected into the head end of the cable, the end is open, and the reflected signal is received at the head end. According to the refraction and reflection of the traveling wave, a good cable model is established. Please refer to Figure 2. When the cable is intact, if the total length of the cable is l and the impedance is Z0, the reflection coefficient P at the end is l =1, at this time the reflection coefficient Γ l for:

[0082] Γ l =e -2γl ; (1)

[0083] Where γ is the propagation coefficient of the cable, which can be calculated as follows:

[0084] γ=α+jβ; (2)

[0085] In the formula, α is the attenuation constant, which characterizes the signal amplitude attenuation characteristics per unit length of the cable; β is the phase constant, which characterizes the signal phase lag characteristics per unit length of the cable. Substituting formula (1) into formula (2) yields:

[0086] Where f is the test frequency and v is the propagation speed of electromagnetic waves in the cable. According to Euler's formula, (3) can be expanded as:

[0087] Then the real part of formula (4) is:

[0088] Among them, Real(Γ l ) is the head-end reflection coefficient Γ l The real part of is taken to obtain the reflection coefficient spectrum.

[0089] Please refer to Figure 3. When there is a point defect in the cable, a point defect model can be established, where l represents the total length of the cable, x is the distance from the ground fault to the head end, R is the transition resistance of the ground fault, and ρ xis the reflection coefficient at the grounding point, then the real part of the reflection coefficient at the head end is Real(Γ l ) can be expressed as (to simplify the analysis process, the influence of the head-end reflection is ignored):

[0090] In the formula, the first reflection signal of the ground fault is the first term, the second reflection signal of the ground fault is the second term, and the end reflection signal is the last term. The frequency component of the first reflection at the defect is f1 = 2x / v. The problem of locating cable defects can be converted into the problem of estimating the frequency f1 according to formula (7):

[0091] Please refer to Figure 4. When there is a segment defect in the cable, a segment defect model can be established, where l represents the total length of the cable, x is the distance from the ground fault to the head end, Δx is the distance from the joint section or the damp section, and ρ x is the reflection coefficient at the defect, then the real part of the head end reflection coefficient Real(Γ l ) can be expressed as (to simplify the analysis process, the influence of the head-end reflection is ignored):

[0092] Where, α Δx is the attenuation coefficient of the defective section, the first reflection signal of the defective section is the first term, the second reflection signal of the defective section is the second term, and the end reflection signal is the last term. Based on the frequency component f1 = 2x / v at the defect, the cable defect can be located according to formula (7).

[0093] Step S103: Generate a corresponding correction angle value according to the position of the defect, and determine the polarity of the defect; generate a first reflection intensity cosine function according to the frequency component of the defect position, the first reflection intensity and the polarity of the defect; perform a difference processing on the first reflection intensity cosine function and the real part of the first head-end reflection coefficient to generate a second reflection coefficient; the first head-end reflection coefficient is the reflection coefficient when the cable to be detected has no defects; determine the defect type of the defect according to the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity.

[0094] Furthermore, according to the position of the defect, a corresponding correction angle value is generated, and the polarity of the defect is determined, specifically:

[0095] According to the position of the defect, a corresponding correction angle value is generated;

[0096] The expression of the correction angle value is: n =2π(f n f min -F floor (f n f min )); (9)

[0097] Among them, f n is the frequency component of the first reflection signal at the nth defect; f min F is the lower limit frequency of the test signal; floor Indicates rounding down;

[0098] According to the correction angle value, it is determined whether the correction angle of the defect is in the first quadrant or the fourth quadrant. If so, the polarity of the defect is determined to be positive; if not, the polarity of the defect is determined to be negative.

[0099] In this embodiment, the amplitudes of reflection signals of different impedance mismatch types are equal, so the type of reflection signal can be determined by the amplitude. For ground faults (segment defects), the amplitude is the largest during the first reflection. Due to signal attenuation and the effects of refraction and reflection, the subsequent reflection coefficient amplitudes show an exponential decay trend. Therefore, the amplitude of the first reflection differs significantly from the amplitudes of subsequent multiple reflections, and the peak value in the positioning spectrum is primarily influenced by the first reflection. For damp segments and joint segments (point defects), multiple refraction and reflection occur within their internal segments. Therefore, the amplitude difference between the first reflection and the internal multiple reflections is not significant. The peak value in their positioning spectrum is the superposition of the first reflection peak and the multiple reflection peak.

[0100] Furthermore, a first reflection intensity cosine function is generated according to the frequency component of the defect position, the first reflection intensity, and the polarity of the defect, specifically:

[0101] The expression of the first reflection intensity cosine function is:

[0102] in, is the cosine function value of the first reflection intensity of the i-th defect, represents the polarity of the i-th defect. If the polarity of the i-th defect is positive, then If the polarity of the i-th defect is negative, then is the first reflection intensity at the position of the i-th defect; is the frequency component of the position of the i-th defect; f is the test frequency.

[0103] Furthermore, the defect type of the defect is determined according to the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity, specifically:

[0104] Based on the second reflection coefficient, a second reflection intensity at the position of the i-th defect is obtained; and a determination is made as to whether the ratio of the absolute value of the second reflection intensity to the absolute value of the first reflection intensity is less than or equal to a preset threshold; if so, the i-th defect is a point fault type; if not, the i-th defect is a segment fault type.

[0105] In this embodiment, the y obtained in formula (10) xi The new reflection coefficient spectrum (the real part of the second reflection coefficient) is obtained by performing a difference process with the real part of the original head-end reflection coefficient (the first reflection coefficient). The new reflection coefficient spectrum is converted into a positioning spectrum and the equivalent frequency component f is recorded. xi The new reflection intensity A' xi ; If |A' xi | / |A xi When |≤d, the defect is a ground fault; otherwise, it is moisture or an intermediate joint, and the value of d is selected as 0.5.

[0106] In this embodiment, a cosine function is constructed using each frequency component and its polarity, and a function of its first reflection intensity is established. The real part of the measured head-end reflection coefficient spectrum is then subjected to difference processing. If the amplitude after the difference is significantly different from the amplitude before the difference, the reflected signal is determined to be a ground fault. If the difference is small, the reflected signal is determined to be an intermediate joint or moisture.

[0107] Furthermore, after determining the defect type of the defect, the method further includes:

[0108] If the defect type of the defect is a point fault type, the expression of the real part of the first reflection coefficient is:

[0109] Where x is the distance from the defect location to the head end, ρ x is the reflection coefficient at the defect, the nth term in the formula is the nth reflection signal at the defect position; n is a natural number;

[0110] If the defect type of the defect is a segment fault type, the expression of the real part of the first reflection coefficient is:

[0111] Among them, α Δx is the attenuation coefficient of the defect segment, v x is the propagation speed of the signal in the defect section, and the nth term in the formula is the nth reflection signal at the defect position.

[0112] As a preferred implementation plan, modeling and simulation are performed for three defects: moisture on the main body, grounding fault, and intermediate joint. The total cable length is set to 200m, and the specific parameters are shown in the following table:

[0113] There is a moisture defect in the cable body 50m away from the head end, and the moisture length is set to 0.5m. Since moisture in the cable will cause the cable capacitance C to increase significantly, the capacitance change multiple is set to 1.2 times that of the original cable body; a ground fault is set at 100m away from the head end, and its transition resistance is 1.5Z0; an intermediate joint with a length of 0.8m and a capacitance change multiple of 0.848 is set at 150m away from the head end.

[0114] The real part of the first reflection coefficient of the cable, i.e., the original reflection coefficient spectrum (raw data), is processed using the cable local defect detection method described in the present invention to obtain the real part of the second reflection coefficient, i.e., the new reflection coefficient spectrum (data after difference calculation). Please refer to Figure 5, which compares the new reflection coefficient spectrum with the original reflection coefficient spectrum. As can be seen from Figure 5, for defects of a certain length such as moisture and joints, the reflection coefficient after difference calculation according to the method of the present invention is slightly larger than the original data. This is because the mutual influence of multiple defects in the reflection causes the reflection coefficient after difference calculation at the segmented defect to be larger than the original data. For ground faults, the reflection coefficient after difference calculation is much smaller than the original data. The cable local defect detection method of the present invention is then used to analyze the three defects, and the analysis results are shown in the following table:

[0115] According to the analysis results, combined with the previous polarity judgment analysis, the specific type of defect can be obtained. The type judgment results are shown in the following table:

[0116] From the type discrimination results, it can be found that the discrimination results of the three defects are consistent with the defects set in the simulation. Therefore, this method can identify defects when the three defects exist at the same time.

[0117] As another preferred embodiment, a test experiment was carried out on a coaxial cable with a total length of 27m. The coaxial cable consisted of three coaxial cables of different lengths (8m, 10m, and 9m), all of the same SYV50-5-1 type. The T-type connector at 8m was connected to a resistor with a resistance of 50Ω, and the T-type connector at 18m was unloaded.

[0118] The coaxial cable was subjected to an FDR test with a test frequency range of 150kHz to 80MHz and 3001 sampling points. Referring to Figure 6, the new reflection coefficient spectrum (after-difference data) of the coaxial cable is compared with the old reflection coefficient spectrum (original data). It can be seen that the reflection coefficient after difference calculation for the ground fault is significantly smaller than the original data. The original and after-difference reflection coefficients at the defect are 0.0091 and 0.0029, respectively. However, the reduction in the reflection coefficient after difference calculation for the joint is smaller. The original and after-difference reflection coefficients are 0.0032 and 0.0025, respectively. This is similar to the simulation results. The defect type discrimination results generated by the method of the present invention are shown in the following table:

[0119] From the defect type identification results, it can be found that the cable local defect detection method proposed in the present invention successfully identified the grounding fault and the middle joint of the 27m coaxial cable.

[0120] As another preferred embodiment, a defect is made on a YJLV22 8.7 / 15-1×95 10kV XLPE power cable with a total length of 20m. A moisture defect is set on the main body 10m away from the head end, where the length of the moisture section is 20cm. The defect section is first wrapped with a heat shrink tube, and then the two ends are sealed and then immersed in water. The test frequency band is 150kHz~80MHz, and the number of sampling points is 3001. Please refer to Figure 7 to compare the new reflection coefficient spectrum (data after difference calculation) of the power cable with the old reflection coefficient spectrum (original data). It can be seen that the reflection coefficient after difference calculation is reduced at the defect relative to the size of the original data. The size of the original reflection coefficient at the defect is 0.0295, and the size after difference calculation is 0.0229. The defect type discrimination results generated by the method of the present invention are shown in the following table:

[0121] From the defect type identification results, it can be found that the cable local defect detection method proposed in the present invention successfully identified the moisture defect of the 20m power cable body.

[0122] The above experimental test results demonstrate that the proposed method for local cable defect detection can determine the defect length. When the defect is a joint or moisture, the peak value is derived from the signal's multiple reflections within the segment, resulting in a difference between the peak value and the cosine function constructed by the present invention and the value still exceeding d. When the defect is a ground fault, the peak value is primarily influenced by the signal's first reflection, resulting in a difference between the peak value and the cosine function and the value less than d. Simulation and experimental verification demonstrate that the proposed method can specifically distinguish three typical defects: moisture in the cable body, ground faults, and intermediate joints.

[0123] The implementation of the present invention has the following effects:

[0124] The present invention obtains the signal attenuation intensity of the test signal during transmission of the cable to be detected based on the reflection coefficient of the acquired test signal in the cable to be detected. The defect can be located based on the frequency component of the first reflected signal at the position of the defect. After the defect is located, the signal attenuation intensity is further used to analyze and determine the specific defect type. The present invention determines the length type of the defect by constructing a cosine function of the first reflection intensity and subtracting the first reflection coefficient intensity when the cable to be detected at the defect location is free of defects. If the amplitude is significantly attenuated after subtracting the first reflection coefficient intensity when the cable to be detected at the defect location is free of defects, it is determined to be a point fault; if the amplitude remains basically unchanged, it is determined to be a segment fault. This achieves the identification and classification of defect types and improves the efficiency of cable fault detection.

[0125] Example 2

[0126] Please refer to FIG8 , which shows a cable local defect detection device provided by an embodiment of the present invention, including: a testing module 201 , a defect judgment module 202 , and a type detection module 203 ;

[0127] The test module 201 is configured to obtain a reflection signal of a test signal at the head end of the cable to be tested; the test signal is injected at the head end of the cable to be tested; the reflection signal is generated by the test signal being injected at the head end of the cable to be tested, transmitted to the end of the cable to be tested for total reflection, and then transmitted to the head end of the cable to be tested;

[0128] The defect judgment module 202 is configured to generate a first reflection coefficient of the head end of the cable to be detected based on the reflection signal; determine whether the cable to be detected has a defect based on the real part of the first reflection coefficient; and if so, determine the location of the defect based on the real part of the first reflection coefficient, and obtain the frequency component and first reflection intensity of the defect location;

[0129] The type detection module 203 is used to generate a corresponding correction angle value according to the position of the defect and determine the polarity of the defect; generate a first reflection intensity cosine function according to the frequency component of the defect position, the first reflection intensity and the polarity of the defect; perform a difference processing on the first reflection intensity cosine function and the real part of the first head-end reflection coefficient to generate a second reflection coefficient; the first head-end reflection coefficient is the reflection coefficient when the cable to be detected has no defects; and determine the defect type of the defect according to the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity.

[0130] The defect judgment module 202 includes: a defect judgment unit and a position judgment unit;

[0131] The defect judgment unit is configured to generate a propagation coefficient of the cable to be detected based on the attenuation constant and phase constant of the cable to be detected; substitute the propagation coefficient into the first reflection coefficient; and expand the first reflection coefficient according to the Euler formula to generate an expanded expression of the first reflection coefficient.

[0132] If the cable to be tested does not have any defects, the expanded expression of the first reflection coefficient is:

[0133] The expression of the real part of the first reflection coefficient is:

[0134] Where α is the attenuation constant, f is the test frequency of the test signal, v is the propagation speed of the test signal in the cable to be tested, Γ l is the first reflection coefficient, l is the total length of the cable to be tested;

[0135] Otherwise, the cable to be tested has defects;

[0136] The position determination unit is configured to obtain a frequency component of a first reflection signal at a position of the defect based on a real part of the first reflection coefficient, and determine the position of the defect;

[0137] The expression for the position of the defect is: Wherein, f1 is the frequency component of the first reflection signal at the defect position.

[0138] The type detection module 203 includes: a polarity judgment unit, a first reflection intensity cosine function generation unit and a detection unit;

[0139] Wherein, the polarity judgment unit is used to generate a corresponding correction angle value according to the position of the defect;

[0140] The expression of the correction angle value is: n =2π(f n f min -F floor (f n f min ));

[0141] Among them, f n is the frequency component of the first reflection signal at the nth defect; f min F is the lower limit frequency of the test signal; floor Indicates rounding down;

[0142] According to the correction angle value, determining whether the correction angle of the defect is in the first quadrant or the fourth quadrant, if so, determining that the polarity of the defect is positive; if not, determining that the polarity of the defect is negative;

[0143] The expression of the first reflection intensity cosine function generated by the first reflection intensity cosine function generation unit is:

[0144] in, is the cosine function value of the first reflection intensity of the i-th defect, represents the polarity of the i-th defect. If the polarity of the i-th defect is positive, then If the polarity of the i-th defect is negative, then is the first reflection intensity at the position of the i-th defect; is the frequency component of the position of the i-th defect; f is the test frequency;

[0145] The detection unit is used to obtain a second reflection intensity at the position of the i-th defect based on the second reflection coefficient; determine whether the ratio of the absolute value of the second reflection intensity to the absolute value of the first reflection intensity is less than or equal to a preset threshold; if so, the i-th defect is a point fault type; if not, the i-th defect is a segment fault type.

[0146] If the defect type of the defect is a point fault type, the expression of the real part of the first reflection coefficient is:

[0147] Where x is the distance from the defect location to the head end, ρ x is the reflection coefficient at the defect, the nth term in the formula is the nth reflection signal at the defect position; n is a natural number;

[0148] If the defect type of the defect is a segment fault type, the expression of the real part of the first reflection coefficient is:

[0149] Among them, α Δx is the attenuation coefficient of the defect segment, v x is the propagation speed of the signal in the defect section, and the nth term in the formula is the nth reflection signal at the defect position.

[0150] The above-mentioned cable local defect detection device can implement the cable local defect detection method of the above-mentioned method embodiment. The optional options in the above-mentioned method embodiment also apply to this embodiment and are not described in detail here. The remaining contents of the embodiment of this application can refer to the contents of the above-mentioned method embodiment and are not repeated in this embodiment.

[0151] The implementation of the present invention has the following effects:

[0152] The test module of the device of the present invention obtains the signal attenuation intensity of the test signal during the transmission process of the cable to be detected based on the reflection coefficient of the acquired test signal in the cable to be detected. The defect judgment module can locate the defect based on the frequency component of the first reflection signal at the position of the defect. After the defect is located, the type detection module further uses the signal attenuation intensity to analyze and determine the specific defect type. The present invention determines the length type of the defect by constructing a cosine function of the first reflection intensity and subtracting the first reflection coefficient intensity when the cable to be detected at the defect location has no defects; if the amplitude is significantly attenuated after subtracting the first reflection coefficient intensity when the cable to be detected at the defect location has no defects, it is determined to be a point fault; if the amplitude remains basically unchanged, it is determined to be a segment fault, thereby achieving the discrimination and classification of defect types and improving the efficiency of cable fault detection.

[0153] Example 3

[0154] Accordingly, the present invention also provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute the cable local defect detection method described in any one of the above embodiments.

[0155] Exemplarily, the computer program may be divided into one or more modules / units, which are stored in the memory and executed by the processor to implement the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing specific functions, and the instruction segments are used to describe the execution process of the computer program in the terminal device.

[0156] The terminal device may be a computing device such as a desktop computer, a notebook computer, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0157] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc. The processor is the control center of the terminal device, connecting various parts of the entire terminal device using various interfaces and lines.

[0158] The memory can be used to store the computer programs and / or modules, and the processor realizes various functions of the terminal device by running or executing the computer programs and / or modules stored in the memory, and calling the data stored in the memory. The memory can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, at least one application required for a function, etc.; the data storage area can store data created according to the use of the mobile terminal, etc. In addition, the memory can include a high-speed random access memory, and can also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage device.

[0159] Wherein, if the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the process in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and when the computer program is executed by the processor, it can implement the steps of the above-mentioned various method embodiments. Wherein, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc.

[0160] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A method for detecting local defects in a cable, characterized in that: include: A reflection signal of a test signal is obtained at the head end of a cable to be detected; the test signal is injected at the head end of the cable to be detected; the reflection signal is generated by the test signal being injected at the head end of the cable to be detected, transmitted to the end of the cable to be detected for total reflection, and then transmitted to the head end of the cable to be detected; a first reflection coefficient of the head end of the cable to be detected is generated according to the reflection signal; whether the cable to be detected has a defect is determined according to the real part of the first reflection coefficient; if so, the position of the defect is determined according to the real part of the first reflection coefficient, and the frequency component and the first reflection intensity of the position of the defect are obtained; According to the position of the defect, a corresponding correction angle value is generated, and the polarity of the defect is determined; A first reflection intensity cosine function is generated according to the frequency component of the defect position, the first reflection intensity and the polarity of the defect; the first reflection intensity cosine function is subtracted from the real part of the first head-end reflection coefficient to generate a second reflection coefficient; the first head-end reflection coefficient is the reflection coefficient when the cable to be detected has no defects; the defect type of the defect is determined according to the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity.

2. A cable local defect detection method according to claim 1, characterized in that: The step of judging whether the cable to be inspected has a defect according to the real part of the first reflection coefficient specifically includes: Generate a propagation coefficient of the cable to be detected according to the attenuation constant and phase constant of the cable to be detected; substitute the propagation coefficient into the first reflection coefficient; expand the first reflection coefficient according to the Euler formula to generate an expansion formula of the first reflection coefficient; If the cable to be detected has no defects, the expansion formula of the first reflection coefficient is: The expression of the real part of the first reflection coefficient is: Where α is the attenuation constant, f is the test frequency of the test signal, v is the propagation speed of the test signal in the cable to be tested, Γ l is the first reflection coefficient, l is the total length of the cable to be detected; Otherwise, the cable to be tested is defective.

3. A cable local defect detection method as claimed in claim 2, characterized in that: The determining the position of the defect according to the real part of the first reflection coefficient is specifically: According to the real part of the first reflection coefficient, a frequency component of a first reflection signal at the position of the defect is obtained to determine the position of the defect; The expression for the position of the defect is: Wherein, f1 is the frequency component of the first reflection signal at the defect location.

4. A cable local defect detection method according to claim 1, characterized in that: According to the position of the defect, a corresponding correction angle value is generated, and the polarity of the defect is determined, specifically: According to the position of the defect, a corresponding correction angle value is generated; The expression of the correction angle value is: n =2π(f n f min -F floor (f n f min )); Among them, f n is the frequency component of the first reflection signal at the nth defect; f min F is the lower limit frequency of the test signal; floor Indicates rounding down; According to the correction angle value, it is determined whether the correction angle of the defect is in the first quadrant or the fourth quadrant. If so, the polarity of the defect is determined to be positive; if not, the polarity of the defect is determined to be negative.

5. A cable local defect detection method as claimed in claim 4, characterized in that: The first reflection intensity cosine function is generated according to the frequency component of the defect position, the first reflection intensity and the polarity of the defect, specifically: The expression of the first reflection intensity cosine function is: in, is the cosine function value of the first reflection intensity of the i-th defect, represents the polarity of the ith defect. If the polarity of the ith defect is positive, then If the polarity of the i-th defect is negative, then is the first reflection intensity at the position of the i-th defect; is the frequency component of the position of the i-th defect; f is the test frequency.

6. A cable local defect detection method as claimed in claim 5, characterized in that: The determining of the defect type of the defect according to the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity is specifically: According to the second reflection coefficient, a second reflection intensity at the position of the i-th defect is obtained; and it is determined whether the ratio of the absolute value of the second reflection intensity to the absolute value of the first reflection intensity is less than or equal to a preset threshold value; If so, the i-th defect is a point fault type; if not, the i-th defect is a segment fault type.

7. A cable local defect detection method as claimed in claim 6, characterized in that: After determining the defect type of the defect, the method further includes: If the defect type of the defect is a point fault type, the expression of the real part of the first reflection coefficient is: Where x is the distance from the defect to the head end, ρ x is the reflection coefficient at the defect; If the defect type of the defect is a segment fault type, the expression of the real part of the first reflection coefficient is: Among them, α Δx is the attenuation coefficient of the defect segment, v x is the propagation speed of the signal in the defect section.

8. A cable local defect detection device, characterized in that: include: Testing module, defect judgment module and type detection module; The test module is used to obtain a reflection signal of a test signal at the head end of the cable to be detected; the test signal is injected at the head end of the cable to be detected; the reflection signal is generated by the test signal being injected at the head end of the cable to be detected, transmitted to the end of the cable to be detected for total reflection, and then transmitted to the head end of the cable to be detected; The defect judgment module is used to generate a first reflection coefficient of the head end of the cable to be detected according to the reflection signal; determine whether the cable to be detected has a defect according to the real part of the first reflection coefficient; if so, determine the position of the defect according to the real part of the first reflection coefficient, and obtain the frequency component and the first reflection intensity of the position of the defect; The type detection module is used to generate a corresponding correction angle value according to the position of the defect and determine the polarity of the defect; generate a first reflection intensity cosine function according to the frequency component of the position of the defect, the first reflection intensity and the polarity of the defect; perform difference processing on the first reflection intensity cosine function and the real part of the first head-end reflection coefficient to generate a second reflection coefficient; the first head-end reflection coefficient is the reflection coefficient when the cable to be detected has no defects; determine the defect type of the defect according to the ratio of the second reflection intensity of the second reflection coefficient to the first reflection intensity.

9. A cable local defect detection device as claimed in claim 8, characterized in that: The defect judgment module includes: a defect judgment unit and a position judgment unit; The defect judgment unit is used to generate a propagation coefficient of the cable to be detected according to the attenuation constant and the phase constant of the cable to be detected; substitute the propagation coefficient into the first reflection coefficient; and expand the first reflection coefficient according to the Euler formula to generate an expansion formula of the first reflection coefficient; If the cable to be detected has no defects, the expansion formula of the first reflection coefficient is: The expression of the real part of the first reflection coefficient is: Where α is the attenuation constant, f is the test frequency of the test signal, v is the propagation speed of the test signal in the cable to be tested, Γ l is the first reflection coefficient, l is the total length of the cable to be detected; Otherwise, the cable to be tested has defects; The position determination unit is used to obtain the frequency component of the first reflection signal of the position of the defect according to the real part of the first reflection coefficient, so as to determine the position of the defect; The expression for the position of the defect is: Wherein, f1 is the frequency component of the first reflection signal at the defect location.

10. A cable local defect detection device as claimed in claim 8, characterized in that: The type detection module includes: a polarity judgment unit, a first reflection intensity cosine function generation unit and a detection unit; Wherein, the polarity judgment unit is used to generate a corresponding correction angle value according to the position of the defect; The expression of the correction angle value is: n =2π(f n f min -F floor (f n f min )); Among them, f n is the frequency component of the first reflection signal at the nth defect; f min F is the lower limit frequency of the test signal; floor Indicates rounding down; According to the correction angle value, determine whether the correction angle of the defect is in the first quadrant or the fourth quadrant, if so, determine that the polarity of the defect is positive; if not, determine that the polarity of the defect is negative; The expression of the first reflection intensity cosine function generated by the first reflection intensity cosine function generation unit is: in, is the cosine function value of the first reflection intensity of the i-th defect, represents the polarity of the ith defect. If the polarity of the ith defect is positive, then If the polarity of the i-th defect is negative, then is the first reflection intensity at the position of the i-th defect; is the frequency component of the position of the i-th defect; f is the test frequency; The detection unit is used to obtain a second reflection intensity at the position of the i-th defect according to the second reflection coefficient; determine whether the ratio of the absolute value of the second reflection intensity to the absolute value of the first reflection intensity is less than or equal to a preset threshold; if so, the i-th defect is a point fault type; if not, the i-th defect is a segment fault type; If the defect type of the defect is a point fault type, the expression of the real part of the first reflection coefficient is: Where x is the distance from the defect to the head end, ρ x is the reflection coefficient at the defect; If the defect type of the defect is a segment fault type, the expression of the real part of the first reflection coefficient is: Among them, α Δx is the attenuation coefficient of the defect segment, v x is the propagation speed of the signal in the defect section.

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