CN117491801A - Cross interconnection cable defect detection system, model and defect positioning method - Google Patents
Cross interconnection cable defect detection system, model and defect positioning method Download PDFInfo
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Abstract
The invention belongs to the technical field of defect detection of multiphase cross interconnection cable systems, and particularly relates to a cross interconnection cable defect detection system, a model and a defect positioning method. The method can synchronously and effectively identify the phase section and the type of the defect of the three-phase cross interconnection cable, and can accurately position the defect position and the cross interconnection position by utilizing the designed CB cable transmission line decoupling model and the three-phase synchronous orthogonal positioning function.
Description
Technical Field
The invention belongs to the technical field of defect detection of multiphase cross interconnection cable systems, and particularly relates to a cross interconnection cable defect detection system, a model and a defect positioning method.
Background
In order to realize the electric energy transmission and distribution requirements of long distance and large capacity, the single-core power cable with high insulation level is widely used in industry and power systems, along with the increase of the length of a transmission line, high-value induced voltage can be generated in a metal sheath, the main insulation of a body of the cable is extremely easy to damage, sheath circulation can be effectively reduced by adopting a three-phase cross interconnection structure, the internal induced voltage is reduced, however, signal mutual coupling in a three-phase cable sheath is caused by the inter-phase cross interconnection of the sheath, and the propagation path is quite complex, so that great challenges and difficulties are caused to the diagnosis and positioning problems of the three-phase cross interconnection transmission line system.
At present, the cable fault positioning method mainly comprises a partial discharge test and a reflection method; however, the above method is not applicable to diagnostic positioning of a three-phase cross-connect cable system;
firstly, partial discharge pulse signals have high-frequency attenuation characteristics when propagating along a cable, signal attenuation is extremely serious in a long-distance cable line, detection sensitivity is easily influenced by a field complex electromagnetic environment, in addition, partial discharge signals of a defect phase flow into cable jackets of other two phases, so that the detection and analysis of the signals are very difficult, the position and phase sequence of the discharge source are difficult to determine, a reflection method is mainly divided into a Time Domain Reflectometry (TDR) and a Frequency Domain Reflectometry (FDR), the TDR is difficult to identify local defects of a cable body due to the fact that injected pulse high-frequency components are less and influenced by chromatic dispersion, the FDR is essentially used for analyzing the transient transmission process of the signals, the similarity of reflected signals and reference signals is required to be compared, the influence of the reference waves by test frequencies is large and difficult to detect, the positioning accuracy in the long-distance transmission line is required to be improved, more importantly, the reflected signals are subjected to split-phase coupling transmission again after each time of crossing a switching point, the attenuation rate of the signals is accelerated, the fault reflected signals of a certain phase are also caused to be aliased to the other two phases, the fault points are difficult to distinguish due to the fact that the excitation voltage is extremely easy to form fault points.
In recent years, the Broadband Impedance Spectroscopy (BIS) technology has strong field anti-interference capability due to a simple test method, and is widely applied to diagnosis and positioning research of cables, and the main reasons why BIS cannot be applied to diagnosis of three-phase cross interconnection cables are as follows: first, the three-phase cross-connect cable creates geometric discontinuities in the BIS test loop due to the multiple transposition of the metal sheath in the cross-connect box. Secondly, when a certain phase has a defect, if the existing impedance analyzer is still used for testing, the detected impedance spectrum information is lost, and the phase sequence and the position of the defect section cannot be completely identified. The traditional single-core transmission model and the positioning method are not applicable any more, in addition, the output voltage of the traditional impedance analyzer is too low (1V), and the impedance spectrum test can only be carried out on a short-distance single-core cable under laboratory conditions, so that the traditional single-core transmission model and the positioning method cannot be applicable to a long-distance three-phase cross interconnection cable system.
In summary, the cable defect positioning technology in the prior art cannot effectively and accurately position the defect position and the cross interconnection position of the three-phase cross interconnection cable, so that a new detection system and a defect fault pattern recognition technology are urgently needed to realize a detection and pattern recognition method of defects and faults in a CB cable line.
Disclosure of Invention
The invention aims to provide a system, a model and a method for detecting defects of a cross interconnection cable, which can synchronously and effectively identify phase sections and types of defects of a three-phase cross interconnection cable, and can accurately position defect positions and cross interconnection positions by utilizing a designed CB cable transmission line decoupling model and a three-phase synchronous orthogonal positioning function.
The technical scheme adopted by the invention is as follows:
the utility model provides a cross interconnection cable defect detection system, includes test system, test system includes three-phase high frequency high voltage cooperation excitation unit, three-phase high frequency IV synchronous conversion unit, high frequency signal acquisition unit and host computer terminal output unit, the output of three-phase high frequency high voltage cooperation excitation unit is connected with the three-phase head end metal core of the CB cable that is surveyed respectively, the input of three-phase high frequency IV synchronous conversion unit is connected with the outer copper shielding layer of each looks head end of three-phase cross interconnection cable, the input of high frequency signal acquisition unit is connected with the output of three-phase high frequency IV synchronous conversion unit, the output of high frequency signal acquisition unit is connected with the host computer terminal.
Further, the three-phase high-frequency high-voltage co-excitation unit consists of a multi-channel programmable high-frequency signal generator, a photoelectric isolation driving unit and a three-phase high-frequency high-voltage amplifier.
Furthermore, the photoelectric isolation driving unit converts the high-frequency electric signal into a laser signal by driving the distributed feedback laser, realizes synchronous high-speed optical fiber isolation driving by using the integrated waveguide optical power distributor, and respectively converts the laser signal into n paths of laser in equal proportion.
Furthermore, the three-phase high-frequency high-voltage collaborative excitation unit adopts a cascaded differential buffer amplification topological structure to improve the output voltage.
Furthermore, the three-phase high-frequency IV synchronous conversion unit synchronously and accurately collects high-frequency insulation micro-current flowing through the copper shielding layer outside the head end of each phase of cable and converts the high-frequency insulation micro-current into response output voltage without phase shift.
Further, the high-frequency signal acquisition unit synchronously acquires three-phase difference frequency excitation and three-phase response output voltage discrete data in the frequency band of 100kHz-100MHz in real time, and then obtains the head-end impedance spectrum in the complete frequency band of each phase after the cross interconnection cable in the frequency band of 100kHz-100MHz is decoupled by utilizing an impedance spectrum frequency division decoupling algorithm.
A method for locating defects of a crossed interconnection cable comprises the following steps:
s1: acquiring head end test data of each phase of time domain crossing interconnection cable
Generating three-phase difference frequency high-voltage sine excitation signals through a detection system, namely, an A-phase sine fundamental frequency is f-delta f, a B-phase sine fundamental frequency is f, a C-phase sine fundamental frequency is f+delta f, wherein delta f is a step sweep frequency, synchronously injecting the three-phase difference frequency sine excitation signals into A, B, C three-phase head ends of the crossed interconnection cables, and synchronously collecting three-phase difference frequency sine excitation and three-phase response output voltage signals under the time domain of the head ends of the tested crossed interconnection cables; .
S2: determining the input impedance spectrum ZA, B, C (f) of the complete frequency band of the tested cross-linked interconnect cable
Processing three-phase difference frequency excitation voltage and response output voltage signals in a frequency band of 100kHz-100MHz under the time domain of a tested cable by utilizing a time-frequency domain conversion t-f and impedance spectrum frequency division decoupling technology, and obtaining decoupled three-phase cable head end impedance spectrums ZA (f), ZB (f) and ZC (f) through extraction and analysis of phase fundamental frequency components;
s3: establishing a cable defect and diagnosis judgment model
D(f 1 )＝Z d (f 1 )-Z h (f 1 )；
Wherein Z is d (f 1) Z is the peak at the first resonance frequency point in the input impedance spectrum h (f) Peak at the first resonance frequency point in the input impedance spectrum of the intact cable;
if D (f) 1 ) If the measured CB cable is 0, defect diagnosis and positioning are not needed, otherwise, the step S4 is carried out;
s4: diagnosing, locating and identifying cable defect type
When D (f) 1) When positive, it is C-defect; when D (f) 1) And when the number is negative, the number is C+ defect, and then the synchronous diagnosis and positioning of the three-phase cable are realized by using a three-phase synchronous frequency domain-space domain transformation diagnosis and positioning method.
Further, the three-phase synchronous frequency domain-space domain transformation diagnosis positioning method in S4 is to integrate the three-phase frequency division decoupling idea and the capacitance distribution parameter, construct a positioning kernel function based on the orthogonality of the impedance spectrum, and the kernel function K (f, x) has the expression as follows:
by utilizing the generalized orthogonality of the kernel function K (F, x) and the decoupling impedance spectrum, the abnormal mutation of the integral at the impedance discontinuity point can be realized, and the three-phase synchronous orthogonal positioning function F A,B,C (x)：
The three-phase diagnostic function is:
wherein F is d (x) F as a localization diagnostic function after the occurrence of the defect h (x) Is a reference diagnostic function for healthy cables.
Further, the step S3 is to compare the phase impedance spectrum of the actually measured cable after frequency division decoupling with the input impedance spectrum of the intact cable, and if the phase impedance spectrum is completely overlapped, the measured cable is the intact cable, and the defect is not required to be diagnosed and positioned; if the defects are different, the detected cable is required to be subjected to diagnosis positioning and pattern recognition;
intact cable input impedance spectrum Z h (f) The acquisition mode of (1) is any one of S301, S302 and S303;
s301, testing the cable before the new cable is put into operation to obtain an input impedance spectrum Z of the cable in a good state h (f)；
S302, testing the same type of cable to obtain the input impedance spectrum Z of the cable in a sound state h (f)；
S303, calculating R of the unit length of the cables according to the structural size of the cables or the parameter specification provided by manufacturers 0 、L 0 、C 0 、G 0 And then according to the characteristic impedance Z 0h And a propagation coefficient gamma h， Obtaining the input impedance spectrum Z of the cable in good condition h (f)。
A cross-over interconnect cable defect detection model:
let the excitation voltage of the head end of the phase A be V f-Δf (x) End load impedance Z L ；x 0 For cable head-end entry, x 1 And x 2 For cross-interconnect joint position, x 3 The single-phase cable is a cable terminal load side, and the length of the single-phase cable is L; in x 0 As the origin of coordinates, the voltage and current expression for the CB cable distance x from the head end is thus obtained as:
wherein V is + Injecting a sinusoidal voltage into the head end, f L And gamma is the load reflection coefficient and propagation coefficient, respectively, Z 0 The characteristic impedance of the CB cable is expressed as follows:
where α is the decay constant and β is the phase constant. The resulting input impedance spectrum of any phase of the finished CB cable can be expressed as:
the invention has the technical effects that:
(1) The defect detection system of the cross interconnection cable can synchronously and effectively identify the phase section and the type of the defect of the three-phase cross interconnection cable, and simultaneously can accurately position the defect position and the cross interconnection position by utilizing the designed CB cable transmission line decoupling model and the three-phase synchronous orthogonal positioning function.
(2) The invention constructs a multiphase high-frequency high-voltage cooperative test system through a differential cascade amplifier topological structure, breaks the limit of the product of the traditional gain bandwidth, realizes the output of high voltage class in a high-frequency range, and can reach 128V in the maximum excitation voltage within the test bandwidth of 100kHz-100MHz under the condition of n=8 of a cascade unit pp The output voltage level is improved along with the increase of the number of the cascade units, so that the anti-interference capability of the long-distance CB cable in field test can be further improved.
(3) The impedance spectrum frequency division decoupling technology and the three-phase synchronous diagnosis positioning function provided by the invention can effectively position the cross interconnection position and the body defect position, the positioning error rate is less than 0.127%, and an important solution is provided for defect diagnosis positioning of the multiphase CB cable.
Drawings
FIG. 1 is a diagram of a cross-over interconnect cable impedance spectrum frequency division decoupling defect localization method of the present invention;
FIG. 2 is a diagram of a high frequency high voltage cascade topology of the present invention;
FIG. 3 is a block diagram of a multiphase collaborative stimulus testing system of the present invention;
FIG. 4 is a plot of three-phase difference frequency excitation voltages versus response output of the present invention;
FIG. 5 is a graph of the amplitude spectrum and phase of the C+ defect (B phase thermal aging) of the present invention;
FIG. 6 is a graph of the amplitude spectrum and phase of the C-defect (C-phase copper shield) of the present invention;
fig. 7 is a three-phase CB cable diagnostic localization map of the present invention;
fig. 8 is a diagram of the diagnostic positioning results of the three-phase CB cable of the present invention.
Detailed Description
The present invention will be specifically described with reference to examples below in order to make the objects and advantages of the present invention more apparent. It should be understood that the following text is intended to describe only one or more specific embodiments of the invention and does not limit the scope of the invention strictly as claimed.
Example 1:
as shown in fig. 1-8, in this embodiment, a system for detecting defects of a cross interconnection cable is disclosed, and a detection object is exemplified, wherein the detection object is a three-phase cable transmission line constructed by three sections of YJLV8.7/15kV XLPE power cables each 150m long, and cross interconnection transposition is performed at positions x=50m and x=100deg.m.
(1) The a-phase cable is a sound cable, which is used as a reference control group.
(2) In B-phase cable x 4 Set c+ defect (heat aging defect) at =25 meters, pass heating tape pair Δl d Areas =10 cm were subjected to accelerated heat aging for 7 consecutive days.
(3) In C-phase cable x 5 Set C-defect (copper shield defect) at 125 m, copper shield breakage length Δl d ＝5cm。
The system is characterized by comprising a three-phase high-frequency high-voltage collaborative excitation unit, a three-phase high-frequency IV synchronous conversion unit, a high-frequency signal acquisition unit and an upper computer terminal output unit, wherein the output end of the three-phase high-frequency high-voltage collaborative excitation unit is respectively connected with a three-phase head end metal wire core of a tested CB cable, the input end of the three-phase high-frequency IV synchronous conversion unit is connected with each phase head end outer copper shielding layer of the three-phase crossed interconnection cable, the input end of the high-frequency signal acquisition unit is connected with the output end of the three-phase high-frequency IV synchronous conversion unit, and the output end of the high-frequency signal acquisition unit is connected with the upper computer terminal.
The three-phase high-frequency high-voltage co-excitation unit consists of a multi-channel programmable high-frequency signal generator, a photoelectric isolation driving unit and a three-phase high-frequency high-voltage amplifier, and adopts equal-proportion laser splitting to realize electric isolation of a control end and a high-voltage output end, so that the three-phase high-frequency co-excitation unit can output a 100kHz-100MHz three-phase isolated high-voltage sinusoidal signal, realize electric-optical-electric isolation conversion within a wide frequency band of 100kHz-100MHz, ensure that each stage of avalanche photodiodes in a cascading topological structure can receive laser signals in the same direction and energy, and ensure that the output amplitude and capacity of the system are not attenuated along with the increase of frequency.
The photoelectric isolation driving unit converts high-frequency electric signals into laser signals by driving the distributed feedback laser, realizes synchronous high-speed optical fiber isolation driving by using the integrated waveguide optical power distributor, and respectively uses the laser signals as n paths of lasers according to the equal proportion, thereby effectively establishing electrical isolation between the input end and the amplifier unit.
The three-phase high-frequency high-voltage collaborative excitation unit adopts a cascaded differential buffer amplifying topological structure to improve output voltage, namely adopts a high-speed operational amplifier and a high-speed buffer to carry out differential cascade output, and changes laser energy emitted by the DFB laser by adjusting the output voltage amplitude of the signal generator so as to further change the output voltage amplitude of the cascade amplifier. In the embodiment, the number of the cascade units is n=8, and the maximum excitation sinusoidal voltage of the system can reach 128V within the test bandwidth of 100kHz-100MHz pp ；
Because the energy and the direction of the n-path laser are consistent, the photocurrents generated by the avalanche type APD detectors in each stage are the same, and the rail-rail output voltage V is generated through a high-speed operational amplifier R-R After differential amplification by the buffer amplifier again, the output voltage of the single-stage unit can reach 2V at most R-R . Therefore, the output voltage of the n-level unit after differential cascade can reach 2n V at most R-R
The three-phase high-frequency IV synchronous conversion unit synchronously and accurately collects high-frequency insulation micro-current flowing through the copper shielding layer outside the head end of each phase of cable and converts the high-frequency insulation micro-current into response output voltage without phase shift. Providing accurate sampling data for subsequent impedance spectrum difference frequency decoupling.
The high-frequency signal acquisition unit synchronously acquires three-phase difference frequency excitation and three-phase response output voltage discrete data in the frequency range of 100kHz-100MHz in real time, and then utilizes an impedance spectrum frequency division decoupling algorithm to completely obtain the head-end impedance spectrum in the complete frequency range of each phase after the cross interconnection cable in the frequency range of 100kHz-100MHz is decoupled.
Example 2:
the embodiment discloses a method for detecting defects and faults and identifying modes of A, B, C three-phase crossed interconnection cables on the basis of embodiment 1, which comprises the following steps as shown in fig. 2:
s1: acquiring head end test data of each phase of time domain crossing interconnection cable
Generating three-phase difference frequency high-voltage sinusoidal excitation signals by using the cross interconnection cable defect detection system based on multiphase cooperative excitation, namely, an A-phase sinusoidal fundamental frequency is f-delta f, a B-phase sinusoidal fundamental frequency is f, a C-phase sinusoidal fundamental frequency is f+delta f, wherein delta f is a step sweep frequency, synchronously injecting the three-phase difference frequency sinusoidal excitation signals into A, B, C three-phase head ends of the cross interconnection cables respectively, and synchronously collecting three-phase difference frequency sinusoidal excitation and three-phase response output voltage signals under the time domain of the head ends of the tested cross interconnection cables; Δf in this case was chosen to be 500Hz.
S2: determining the input impedance spectrum ZA, B, C (f) of the complete frequency band of the tested cross-linked interconnect cable
The three-phase difference frequency excitation voltage and response output voltage signals in the frequency range of 100kHz-100MHz under the time domain of the tested cable are processed by utilizing the time-frequency domain conversion t-f and impedance spectrum frequency division decoupling technology, and the decoupled three-phase cable head end impedance spectrums ZA (f), ZB (f) and ZC (f) can be obtained through extraction and analysis of each pair of phase fundamental frequency components;
s3: establishing a cable defect and diagnosis judgment model
D(f 1 )＝Z d (f 1 )-Z h (f 1 )；
Wherein Z is d (f 1) Z is the peak at the first resonance frequency point in the input impedance spectrum h (f) Peak at the first resonance frequency point in the input impedance spectrum of the intact cable;
if D (f) 1 ) If the measured CB cable is 0, defect diagnosis and positioning are not needed, otherwise, the step S4 is carried out;
s4: diagnosing, locating and identifying cable defect type
The invention defines two main types of body insulation defects: c+ defects (heat aging, water tree aging, electrical tree aging), C-defects (copper shield corrosion, breakage), respectively;
when D (f) 1) When the number is a positive number, the number is equal to the positive number,is C-defect; when D (f) 1) And when the number is negative, the number is C+ defect, and then the synchronous diagnosis and positioning of the three-phase cable are realized by using a three-phase synchronous frequency domain-space domain transformation diagnosis and positioning method.
In step S4, the three-phase synchronous frequency domain-space domain transformation diagnosis positioning method integrates the three-phase frequency division decoupling idea and the capacitance distribution parameter, constructs a positioning kernel function based on the orthogonality of the impedance spectrum, and the kernel function K (f, x) has the following expression:
by using the generalized orthogonality of the kernel function K (f, x) and the decoupled impedance spectrum, abnormal abrupt changes in integration at impedance discontinuities can be realized. Three-phase synchronous orthogonal positioning function F A,B,C (x)：
Thus, the three-phase diagnostic function can be expressed as:
wherein F is d (x) F as a localization diagnostic function after the occurrence of the defect h (x) Is a reference diagnostic function for healthy cables.
Example 3:
the step S3 is further described based on the above embodiment, and the purpose of the step S3 is to determine whether the cable has an insulation defect and a fault, where the step S3 is to compare the frequency-divided and decoupled impedance spectrums of the actually measured cable with the input impedance spectrums of the intact cable, and if the frequency-divided and decoupled impedance spectrums are completely overlapped, the detected cable is the intact cable, and the defect is not required to be diagnosed and positioned; if the defects are different, the detected cable is required to be subjected to diagnosis positioning and pattern recognition;
intact cable input impedance spectrum Z h (f) Three acquisition modes are available:
testing the cable before the new cable is put into operation, thereby obtaining the input impedance spectrum Z of the cable in good condition h (f)；
(II) by testing the same type of cable, the input impedance spectrum Z of the cable in good condition is obtained h (f)；
(III) calculating R per unit length of the cables with reference to the cable structural dimensions or manufacturer-supplied parameter specifications 0 、L 0 、C 0 、G 0 And then according to the characteristic impedance Z 0h And a propagation coefficient gamma h Obtaining the input impedance spectrum Z of the cable in good condition h (f)。
Calculating the model parameters of the intact cable transmission line in the modes (II) and (III) comprises:
r1, L1, G1 and C1 respectively represent the distribution parameters of resistance, inductance, conductance and capacitance of the CB cable under unit length. R2, L2, G2 and C2 respectively represent the distribution parameters of resistance, inductance, conductance and capacitance of the MV cable in the cross interconnection system under unit length, and the transmission impedance of the MV cable is equivalent to impedance Zm as shown in the figure;
the cross-over interconnect cable defect detection model is as follows:
let the excitation voltage of the head end of the phase A be V f-Δf (x) End load impedance Z L ；x 0 For cable head-end entry, x 1 And x 2 For cross-interconnect joint position, x 3 The single-phase cable is a cable terminal load side, and the length of the single-phase cable is L; in x 0 As the origin of coordinates, the voltage and current expression for the CB cable distance x from the head end is thus obtained as:
wherein V is + Injecting a sinusoidal voltage into the head end, f L And gamma is the load reflection coefficient and propagation coefficient, respectively, Z 0 The characteristic impedance of the CB cable is expressed as follows:
where α is the decay constant and β is the phase constant. The resulting input impedance spectrum of any phase of the finished CB cable can be expressed as:
the foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention. Structures, devices and methods of operation not specifically described and illustrated herein, unless otherwise indicated and limited, are implemented according to conventional means in the art.
Claims (10)
1. The utility model provides a cross interconnection cable defect detection system, includes test system, its characterized in that, test system includes three-phase high frequency high voltage cooperation excitation unit, three-phase high frequency IV synchronous conversion unit, high frequency signal acquisition unit and host computer terminal output unit, the output of three-phase high frequency high voltage cooperation excitation unit is connected with the three-phase head end metal wire core of the CB cable that is surveyed respectively, the input of three-phase high frequency IV synchronous conversion unit is connected with each looks head end outer copper shielding layer of three-phase cross interconnection cable, the input of high frequency signal acquisition unit is connected with the output of three-phase high frequency IV synchronous conversion unit, the output of high frequency signal acquisition unit is connected with the host computer terminal.
2. The cross-connect cable fault detection system of claim 1 wherein: the three-phase high-frequency high-voltage co-excitation unit consists of a multi-channel programmable high-frequency signal generator, a photoelectric isolation driving unit and a three-phase high-frequency high-voltage amplifier.
3. The cross-connect cable fault detection system of claim 1 wherein: the photoelectric isolation driving unit converts high-frequency electric signals into laser signals by driving the distributed feedback laser, realizes synchronous high-speed optical fiber isolation driving by using the integrated waveguide optical power distributor, and respectively uses the laser signals with equal proportion as n paths of laser.
4. The cross-connect cable fault detection system of claim 1 wherein: the three-phase high-frequency high-voltage collaborative excitation unit adopts a cascaded differential buffer amplification topological structure to improve output voltage.
5. The cross-connect cable fault detection system of claim 1 wherein: the three-phase high-frequency IV synchronous conversion unit synchronously and accurately collects high-frequency insulation micro-current flowing through the copper shielding layer outside the head end of each phase of cable and converts the high-frequency insulation micro-current into response output voltage without phase shift.
6. The cross-connect cable fault detection system of claim 1 wherein: the high-frequency signal acquisition unit synchronously acquires three-phase difference frequency excitation and three-phase response output voltage discrete data in the frequency range of 100kHz-100MHz in real time, and then obtains the head-end impedance spectrum in the complete frequency range of each phase after the cross interconnection cable in the frequency range of 100kHz-100MHz is decoupled by using an impedance spectrum frequency division decoupling algorithm.
7. A method for locating defects of a cross-over interconnection cable, which is implemented by using the cross-over interconnection cable defect detection system as claimed in any one of claims 1 to 6, and is characterized in that: the method comprises the following steps:
s1: acquiring head end test data of each phase of time domain crossing interconnection cable
Generating three-phase difference frequency high-voltage sine excitation signals through a detection system, namely, an A-phase sine fundamental frequency is f-delta f, a B-phase sine fundamental frequency is f, a C-phase sine fundamental frequency is f+delta f, wherein delta f is a step sweep frequency, synchronously injecting the three-phase difference frequency sine excitation signals into A, B, C three-phase head ends of the crossed interconnection cables, and synchronously collecting three-phase difference frequency sine excitation and three-phase response output voltage signals under the time domain of the head ends of the tested crossed interconnection cables;
s2: determining the input impedance spectrum ZA, B, C (f) of the complete frequency band of the tested cross-linked interconnect cable
Processing three-phase difference frequency excitation voltage and response output voltage signals in a frequency band of 100kHz-100MHz under the time domain of a tested cable by utilizing a time-frequency domain conversion t-f and impedance spectrum frequency division decoupling technology, and obtaining decoupled three-phase cable head end impedance spectrums ZA (f), ZB (f) and ZC (f) through extraction and analysis of phase fundamental frequency components;
s3: establishing a cable defect and diagnosis judgment model
D(f 1 )＝Z d (f 1 )-Z h (f 1 )；
Wherein Z is d (f 1) Z is the peak at the first resonance frequency point in the input impedance spectrum h (f) Peak at the first resonance frequency point in the input impedance spectrum of the intact cable;
if D (f) 1 ) 0), the tested CB cable is not required to be defectiveDiagnosing and positioning, otherwise, entering step S4;
s4: diagnosing, locating and identifying cable defect type
When D (f) 1) When positive, it is C-defect; when D (f) 1) And when the number is negative, the number is C+ defect, and then the synchronous diagnosis and positioning of the three-phase cable are realized by using a three-phase synchronous frequency domain-space domain transformation diagnosis and positioning method.
8. The method for locating defects in a cross-connect cable of claim 1, wherein: the three-phase synchronous frequency domain-space domain transformation diagnosis positioning method in S4 is to integrate a three-phase frequency division decoupling idea and capacitance distribution parameters, construct a positioning kernel function based on the orthogonality of impedance spectrum, and the kernel function K (f, x) has the following expression:
by utilizing the generalized orthogonality of the kernel function K (F, x) and the decoupling impedance spectrum, the abnormal mutation of the integral at the impedance discontinuity point can be realized, and the three-phase synchronous orthogonal positioning function F A,B,C (x)：
The three-phase diagnostic function is:
wherein F is d (x) F as a localization diagnostic function after the occurrence of the defect h (x) Is a reference diagnostic function for healthy cables.
9. The method for locating defects in a cross-connect cable of claim 1, wherein: s3, comparing the frequency-divided and decoupled impedance spectrums of the actually measured cable with the input impedance spectrums of the intact cable, and if the frequency-divided and decoupled impedance spectrums are completely overlapped, indicating that the measured cable is the intact cable, and diagnosing and positioning defects are not needed; if the defects are different, the detected cable is required to be subjected to diagnosis positioning and pattern recognition;
intact cable input impedance spectrum Z h (f) The acquisition mode of (1) is any one of S301, S302 and S303;
s301, testing the cable before the new cable is put into operation to obtain an input impedance spectrum Z of the cable in a good state h (f)；
S302, testing the same type of cable to obtain the input impedance spectrum Z of the cable in a sound state h (f)；
S303, calculating R of the unit length of the cables according to the structural size of the cables or the parameter specification provided by manufacturers 0 、L 0 、C 0 、G 0 And then according to the characteristic impedance Z 0h And a propagation coefficient gamma h Obtaining the input impedance spectrum Z of the cable in good condition h (f)。
10. A cross interconnection cable defect detection model is characterized in that:
let the excitation voltage of the head end of the phase A be V f-Δf (x) End load impedance Z L ；x 0 For cable head-end entry, x 1 And x 2 For cross-interconnect joint position, x 3 The single-phase cable is a cable terminal load side, and the length of the single-phase cable is L; in x 0 As the origin of coordinates, the voltage and current expression for the CB cable distance x from the head end is thus obtained as:
wherein V is + Injecting a sinusoidal voltage into the head end, f L And gamma is the load reflection coefficient and propagation coefficient, respectively, Z 0 The characteristic impedance of the CB cable is expressed as follows:
where α is the decay constant and β is the phase constant. The resulting input impedance spectrum of any phase of the finished CB cable can be expressed as:
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