A system and method for detecting and locating weak defects in a cable

Abstract

The present application relates to a kind of weak defect detection and positioning system and method of cable, comprising: signal generation module, with preset time interval generates incident signal;Signal mutual inductance module, for transmitting incident signal to signal acquisition module and injecting incident signal into the core of cable to be measured;Current generation module according to the temperature step of setting current is injected into the core of cable to be measured, and control signal acquisition module carries out signal acquisition;Signal acquisition module carries out acquisition processing to incident signal and obtains multiple groups of pre-processing signal;Data processing module carries out time-frequency processing and thermal floating variance processing to multiple groups of pre-processing signal obtains thermal floating variance curve, and carries out defect detection and positioning according to thermal floating variance curve.The present application carries out effective detection and positioning to weak defect of cable by time-frequency processing to signal and combining thermal stress processing, so as to solve the problem of poor accuracy and poor reliability of traditional detection method.

Description

Technical Field

[0001] This invention relates to cables, and more specifically, to a system and method for detecting and locating minor defects in cables. Background Technology

[0002] Instrumentation and control cables play a crucial role in transmitting signals, monitoring indicators, and providing real-time early warnings by connecting the control center and controlled equipment. They ensure the safe and orderly operation of all units and reactors within the station and containment, and are a vital link in maintaining the safety of personnel and equipment. In the environment where instrumentation and control cables are laid within the station, they are constantly exposed to high temperatures, high pressures, mechanical stress, chemical molecules, and nuclear radiation. This leads to wear and aging both externally and internally, especially for cables laid at cable tray corners, which are more susceptible to abrasion from sharp points and compression between cable groups, resulting in breakage of the outer sheath and shielding layer. While these minor fractures in the outer sheath and shielding layer do not affect the normal operation of the instrumentation and control cables, they will worsen over time during service, eventually affecting the transmission medium and disrupting the stability of the instrumentation and control system, thus endangering equipment and personnel safety.

[0003] For the above situation, there are many detection differences and location methods for strong hard defects in instrumentation and control cables. However, when these methods are applied to weak defects in instrumentation and control cables, there are large misjudgments and location errors, resulting in poor detection accuracy and reliability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a system and method for detecting and locating minor defects in cables.

[0005] The technical solution adopted by this invention to solve its technical problem is: constructing a detection and location system for weak defects in cables, comprising:

[0006] A signal generation module, which is used to generate an incident signal at a preset time interval;

[0007] A signal mutual inductance module is connected to the signal generation module. The signal mutual inductance module is used to transmit the incident signal to the signal acquisition module and inject the incident signal into the core of the cable under test, and output the reflected signal generated after transmission through the core of the cable under test to the signal acquisition module.

[0008] A current generating module is connected to both the cable under test and the signal acquisition module. The current generating module generates current and injects it into the core of the cable under test according to a set temperature step, and controls the signal acquisition module to acquire signals.

[0009] The signal acquisition module is used to acquire the incident signal and the reflected signal generated after transmission through the cable under test according to the control of the current generation module, and obtain multiple sets of reference signals and reflected signals; the signal acquisition module also processes each set of reference signals and reflected signals to obtain multiple sets of preprocessed signals;

[0010] The data processing module performs time-frequency processing and thermal floating variance processing on the multiple sets of preprocessed signals to obtain thermal floating variance curves, and performs defect detection and location based on the thermal floating variance curves.

[0011] In the cable weak defect detection and location system of the present invention, the signal mutual inductance module includes: an induction coil;

[0012] The induction coil includes: a first interface, a second interface, and a sensing part;

[0013] The first interface is connected to the signal generating module and is used to receive the incident signal output by the signal generating module;

[0014] The sensing part is connected to the first interface and the second interface respectively, and is used to inject the incident signal from the beginning of the cable under test into the core of the cable under test and transmit the reflected signal generated after passing through the core of the cable under test to the second interface.

[0015] The second interface is connected to the signal acquisition module and is used to transmit the incident signal received by the first interface and the reflected signal transmitted by the sensing unit to the signal acquisition module.

[0016] In the cable weak defect detection and location system described in this invention, the current generation module is also used to monitor the real-time temperature of the core of the cable under test, and when the real-time temperature of the core of the cable under test reaches the target temperature, control the signal acquisition module to perform a signal acquisition.

[0017] In the cable weak defect detection and location system of the present invention, the data processing module includes: a time-frequency distribution processing unit;

[0018] The time-frequency distribution processing unit is used to perform time-frequency distribution processing on each set of reference signals and reflected signals to obtain multiple sets of distributed signals.

[0019] In the cable weak defect detection and location system of the present invention, the data processing module further includes: a time-frequency cross-correlation processing unit;

[0020] The time-frequency cross-correlation processing unit is used to perform time-frequency cross-correlation processing on each group of distributed signals to obtain multiple time-frequency cross-correlation curves; the multiple time-frequency cross-correlation curves are a cluster of time-frequency domain cross-correlation curves.

[0021] In the cable weak defect detection and location system of the present invention, the data processing module further includes: a thermal floating variance processing unit;

[0022] The thermal floating variance processing unit is used to process the floating variance of the time-frequency domain cross-correlation curve cluster to obtain the thermal stress floating variance curve.

[0023] In the cable weak defect detection and location system of the present invention, the data processing module further includes: a defect location detection unit;

[0024] The defect detection unit is used to perform analysis and calculation based on the thermal stress fluctuation variance curve, and to determine and locate defects based on the analysis and calculation results.

[0025] The cable weak defect detection and location system of the present invention further includes: a calibration module;

[0026] The calibration module is used to calculate the time position of the end of the cable under test based on the actual length of the cable under test and the transmission speed of the incident signal, so as to complete the position calibration of the end of the cable under test.

[0027] This invention also provides a method for detecting and locating weak defects in cables, comprising the following steps:

[0028] The signal generation module outputs the incident signal to the signal mutual inductance module at preset time intervals;

[0029] The signal mutual inductance module transmits the incident signal to the signal acquisition module and injects the incident signal into the core of the cable under test through electromagnetic induction, and outputs the reflected signal generated after transmission through the core of the cable under test to the signal acquisition module.

[0030] The current generation module injects current into the core of the cable under test according to the set temperature step and monitors the real-time temperature of the core of the cable under test. When the real-time temperature of the core of the cable under test reaches the target temperature, the signal acquisition module controls the signal acquisition module to perform a signal acquisition.

[0031] The signal acquisition module acquires the incident and reflected signals transmitted by the signal inductance module according to the control of the current generation module, and obtains multiple sets of reference signals and reflected signals;

[0032] The signal acquisition module processes each set of reference signals and reflected signals to obtain multiple sets of preprocessed signals;

[0033] The data processing module performs time-frequency processing and thermal floating variance processing on the multiple sets of preprocessed signals to obtain thermal floating variance curves, and performs defect detection and location based on the thermal floating variance curves.

[0034] In the cable weak defect detection and location method described in this invention, the data processing module is specifically used to perform the following steps:

[0035] Each set of reference signals and reflected signals is processed using time-frequency distribution to obtain multiple sets of distributed signals.

[0036] For each group of distributed signals, time-frequency cross-correlation processing is performed to obtain multiple time-frequency cross-correlation curves; the multiple time-frequency cross-correlation curves form a cluster of time-frequency domain cross-correlation curves.

[0037] The time-frequency cross-correlation is processed for floating variance to obtain the thermal stress floating variance curve;

[0038] The thermal stress fluctuation variance curve is analyzed and calculated, and the defect is judged and located based on the analysis and calculation results.

[0039] The cable weak defect detection and location system and method of the present invention have the following beneficial effects: It includes: a signal generation module that generates an incident signal at a preset time interval; a signal inductance module for transmitting the incident signal to a signal acquisition module and injecting the incident signal into the core of the cable under test; a current generation module that injects current into the core of the cable under test according to a set temperature step and controls the signal acquisition module to acquire the signal; the signal acquisition module processes the incident signal to obtain multiple sets of preprocessed signals; and a data processing module performs time-frequency processing and thermal fluctuation variance processing on the multiple sets of preprocessed signals to obtain a thermal fluctuation variance curve, and performs defect detection and location based on the thermal fluctuation variance curve. The present invention achieves effective detection and location of cable weak defects by performing time-frequency processing on the signal and combining it with thermal stress processing, thus solving the problems of poor accuracy and reliability of traditional detection methods. Attached Figure Description

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0041] Figure 1 This is a schematic diagram of the cable weak defect detection and location system provided by the present invention;

[0042] Figure 2 This is a flowchart illustrating the method for detecting and locating weak defects in cables provided by the present invention.

[0043] Figure 3 This is a schematic diagram of the cross-correlation curve cluster of the circumferential 120° fracture defect of cable A provided by the present invention;

[0044] Figure 4 This is a schematic diagram of the thermal stress fluctuation variance curve of the circumferential 120° fracture defect of cable A provided by the present invention;

[0045] Figure 5 This is a schematic diagram of the cross-correlation curve cluster of the 240° circumferential fracture defect of the cable provided by the present invention;

[0046] Figure 6 This is a schematic diagram of the thermal stress fluctuation variance curve of the 240° circumferential fracture defect in cable B provided by the present invention;

[0047] Figure 7 This is a schematic diagram of the cross-correlation curve cluster of the 360° circumferential fracture defect of cable C provided by the present invention;

[0048] Figure 8 This is a schematic diagram of the thermal stress fluctuation variance curve of the 360° circumferential fracture defect of cable C provided by the present invention. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] To address the challenges of the harsh environment in nuclear power plants, where the outer sheath and shielding of instrumentation and control cables are prone to wear and cracking under mechanical stress, chemical stress, and nuclear radiation, these subtle defects that do not affect cable operation are difficult to detect accurately using traditional traveling wave detection methods (including time-frequency domain reflection methods, which rely on signal-based defect discrimination). This invention proposes a detection and location system for subtle cable defects in nuclear power plant instrumentation and control cables. This system utilizes time-frequency domain reflection (TFDR) and intervention with thermal stress for detection, enabling effective and accurate identification and location of subtle fracture defects.

[0051] Specifically, such as Figure 1 As shown, the cable weak defect detection and location system includes: a signal generation module 10, a signal mutual inductance module 20, a current generation and signal acquisition module 40, and a data processing module 50.

[0052] The signal generation module 10 generates an incident signal at preset time intervals. In this embodiment, the incident signal is a time-limited band-limited signal with a high-period envelope, and both the time width and frequency width of the time-limited band-limited signal are limited. Specifically, when the signal is transmitted in the cable, if the cable is defect-free, the signal can continue to pass through until it reaches the end of the cable. If there is a local defect in the cable, the signal will undergo reflection during this process, and the resulting reflected signal will travel in the opposite direction, returning to the measurement end at the beginning of the cable. The returned signal type is the same as the original input signal type, only the amplitude and frequency change, and the time-frequency characteristics remain consistent. It should be noted that regardless of whether there is a defect in the cable, the signal will undergo total reflection when it reaches the end of the cable, returning to the measurement end at the beginning of the cable. However, the reflected signal at the end of the cable can be determined through calibration and is therefore not used as a reference for defect detection.

[0053] The mathematical function expression for the incident signal is:

[0054]

[0055] (1) In the formula, s(t) is the incident signal; t represents the time position; π represents pi; j represents the imaginary unit; α and β are the quadratic coefficients of the real and imaginary parts of the function, which together determine the signal duration and the sweep bandwidth; t0 and ω0 represent the time center and frequency center of the signal, respectively.

[0056] In this embodiment, the signal generation module 10 is a single output, which outputs a time-limited band-limited signal of Gaussian window envelope at a preset time interval, which is 1000ns by default.

[0057] In this embodiment, the signal inductance module 20 is connected to the signal generation module 10. The signal inductance module 20 is used to transmit the incident signal to the signal acquisition module 40 and inject the incident signal into the core of the cable under test, and output the reflected signal generated after transmission through the core of the cable under test to the signal acquisition module 40. The signal inductance module 20 includes an induction coil. The induction coil includes a first interface 21, a second interface 23, and a sensing part 22. The first interface 21 is connected to the signal generation module 10 and is used to receive the incident signal output by the signal generation module 10. The sensing part 22 is connected to both the first interface 21 and the second interface 23, and is used to inject the incident signal from the beginning of the cable under test into the core of the cable under test and transmit the reflected signal generated after transmission through the core of the cable under test to the second interface 23. The second interface 23 is connected to the signal acquisition module 40 and is used to transmit the incident signal connected to the first interface 21 and the reflected signal transmitted by the sensing part 22 to the signal acquisition module 40.

[0058] Specifically, the signal inductance module 20 connects the signal generation module 10 and the signal acquisition module 40. It couples with the cable core through a non-contact method, wrapping around the measuring end of the cable under test. Here, "non-contact" does not mean the signal inductance module 20 does not contact the cable under test; rather, due to the shielding of the cable under test and the outer shell of the signal inductance module 20, there is no electrical connection between the cable core and the coil of the signal inductance module 20. The incident signal output from the signal generation module 10 is input to the signal inductance module 20 and has two transmission channels. One channel transmits directly to the signal acquisition module 40 through the first interface 21, the sensing unit 22, and the second interface 23. The other channel transmits the signal to the cable core through electromagnetic induction. After the signal is reflected within the cable core, the reflected signal is also transmitted to the signal inductance module 20 through electromagnetic induction, and then transmitted to the signal acquisition module 40 through the second interface 23 of the signal inductance module 20. Therefore, when the signal acquisition module 40 performs a signal acquisition, the acquired signal includes two parts: one part is the incident signal directly output by the signal generation module 10 (this part can be defined as the reference signal), and the other part is the reflected signal transmitted back through the cable under test. Since the reference signal is not transmitted through the core of the cable under test, while the reflected signal propagates in the cable under test, there is a certain time interval between the reference signal and the reflected signal, i.e., a time difference.

[0059] In this embodiment, the current generating module 30 is connected to both the cable under test and the signal acquisition module 40. The current generating module 30 generates current and injects it into the core of the cable under test according to a set temperature step, and controls the signal acquisition module 40 to acquire signals. Furthermore, the current generating module 30 also monitors the real-time temperature of the core of the cable under test, and controls the signal acquisition module 40 to perform a signal acquisition when the real-time temperature of the core reaches the target temperature.

[0060] Specifically, in this embodiment, the current generating module 30 is directly connected to all the cores of the cable under test. By supplying direct current to the cores of the cable under test, the temperature of the cores can be increased. Since direct current does not generate induced electromotive force, no electromagnetic induction occurs in the signal inductance module 20. Therefore, the current from the current generating module 30 only heats the cores of the cable under test and does not interfere with the transmission and reflection of high-frequency incident signals in the cores of the cable under test.

[0061] Furthermore, in this embodiment, the current generating module 30 is also connected to the signal acquisition module 40, which injects current into the core of the cable under test according to a set temperature step. When the core is heated to the target temperature of each step, the current generating module 30 controls the signal acquisition module 40 to perform a signal acquisition. Therefore, in one defect detection, the signal acquisition module 40 can acquire multiple sets of reference signals and reflected signals. The preset start temperature, preset end temperature, and preset temperature step can be set and input by the user through the human-machine interface module.

[0062] The signal acquisition module 40, under the control of the current generation module 30, acquires the incident signal and the reflected signal generated after transmission through the cable under test, obtaining multiple sets of reference signals and reflected signals. The signal acquisition module 40 also processes each set of reference signals and reflected signals to obtain multiple sets of preprocessed signals. Specifically, in this embodiment, the signal acquisition module 40, through an acquisition card, converts the acquired electromagnetic signals into delimited files that can be further processed at certain time intervals. The acquired signal segments are plotted with time on the horizontal axis and amplitude on the vertical axis. Based on the signal propagation speed in the cable core and the cable length, the time magnitude of the acquired signal segments is on the nanosecond level. Each set of preprocessed signals includes: a preprocessed reference signal and a preprocessed reflected signal.

[0063] In this embodiment, the probe grounding wires of the signal generation module 10 and the signal acquisition module 40, as well as the metal shielding layer of the cable under test, are all connected to the ground through grounding wires, forming a complete circuit with the core of the cable under test and each device.

[0064] The data processing module 50 performs time-frequency processing and thermal floating variance processing on multiple sets of preprocessed signals to obtain thermal floating variance curves, and performs defect detection and location based on the thermal floating variance curves.

[0065] In this embodiment, the data processing module 50 includes a time-frequency distribution processing unit 51; the time-frequency distribution processing unit 51 is used to perform time-frequency distribution processing on each set of reference signals and reflection signals to obtain multiple sets of distribution signals.

[0066] Specifically, the time-frequency distribution processing unit 51 separates the time and frequency domains of each set of reference and reflected signals onto the horizontal and vertical axes, respectively, resulting in two two-dimensional matrices. The pseudo-Wigner-Villi time-frequency distribution method can be used for the time-frequency surface processing of the reference and reflected signals. The mathematical expression of its distribution function is:

[0067]

[0068] In equation (2), D(t,ω) represents the smoothed pseudo-Wigner-Villi time-frequency distribution function of the signal, s(x) is the reference signal function or the reflected signal function, s*(x) is the conjugate function of the signal, t is the time position, τ represents the integration variable, and h(x) represents the window function. ds represents the incident signal as the integration variable, t-0.5τ and t+0.5τ in the function represent the left or right shift of the function by different time lengths, and ω represents the frequency.

[0069] In this embodiment, the data processing module 50 further includes: a time-frequency cross-correlation processing unit 52; the time-frequency cross-correlation processing unit 52 is used to perform time-frequency cross-correlation processing on each group of distributed signals to obtain multiple time-frequency cross-correlation curves; the multiple time-frequency cross-correlation curves are a cluster of time-frequency domain cross-correlation curves.

[0070] Specifically, in the time-frequency cross-correlation processing, each group of distributed signals undergoes a time-frequency characteristic correlation comparison. Using the horizontal axis as the time axis, the stronger the reflected signal in the preprocessed signal, the more similar its time-frequency characteristics are to the incident signal output by the signal generation module 10, resulting in a higher time-frequency cross-correlation and a higher time-frequency cross-correlation value at that time point. Since the time-frequency cross-correlation value can be calculated at each time point, a time-frequency cross-correlation curve can be obtained throughout the entire signal acquisition period. Because the incident signal has a Gaussian envelope, the cross-correlation peak of the reflected signal in the time-frequency cross-correlation curve is not an abrupt peak, but rather a Gaussian-like peak. Since a reference signal exists in the preprocessed signal, the cross-correlation between the reference signal and the incident signal is the highest, with a cross-correlation value of 1; this peak is defined as the autocorrelation peak.

[0071] In this embodiment, the calculation function expression for performing time-frequency cross-correlation analysis is as follows:

[0072]

[0073] (3) In the formula, C sr (τ) represents the time-frequency cross-correlation function between signals, and E(x) is the time-frequency domain energy of the signal. The subscripts s and r represent the incident signal and the reflected signal, respectively. D(t,ω) is the time-frequency distribution function, where the subscripts s and r represent the incident and reflected signals, respectively. s D represents the duration of the signal, where τ is the integral variable; s (t-τ,ω) represents the time-frequency distribution function when the incident signal moves τ units in time.

[0074] Specifically, because the current generation module 30 controls the signal acquisition module 40, the signal acquisition module 40 acquires multiple sets of reference signals and reflected signals, and then outputs multiple sets of preprocessed signals. For a single set of preprocessed signals, a time-frequency cross-correlation curve is obtained after time-frequency distribution processing and time-frequency cross-correlation processing. Therefore, for multiple sets of preprocessed signals, multiple time-frequency cross-correlation curves can be obtained, which can be defined as a cluster of time-frequency domain cross-correlation curves.

[0075] In this embodiment, the data processing module 50 further includes a thermal floating variance processing unit 53; the thermal floating variance processing unit 53 is used to perform floating variance processing on the time-frequency domain cross-correlation curve cluster to obtain the thermal stress floating variance curve.

[0076] Specifically, in this embodiment, the thermal floating variance processing unit 53 performs floating variance processing on the time-frequency cross-correlation curve cluster by calculating the variance value of the amplitude of the time-frequency cross-correlation curve cluster at each time point. The curve formed by the variance values ​​of the amplitude at each time point is the thermal stress floating curve. The horizontal axis of the thermal stress floating curve remains the time axis. Since the waveform of the peak of the time-frequency cross-correlation curve changes slightly with temperature, a peak will also exist in the thermal stress floating curve at the time point corresponding to the defect.

[0077] In this embodiment, the data processing module 50 further includes a defect detection unit 54; the defect detection unit 54 is used to perform analysis and calculation based on the thermal stress fluctuation variance curve, and to determine and locate defects based on the analysis and calculation results.

[0078] Specifically, in this embodiment, the defect location detection unit 54 performs analysis and calculation based on the thermal stress fluctuation variance curve as follows: The peak of the thermal stress fluctuation variance curve is used as the basis for defect location, and defect judgment and calibration are performed. That is, the peak of the thermal stress fluctuation variance curve is defined as the location peak; if a location peak exists, a defect is determined to exist. Further, the time position of the aforementioned autocorrelation peak is set to 0. Since there is a certain time delay between the location peak and the time position of the autocorrelation peak, this time difference and the transmission speed of the incident signal in the core of the cable under test can be used to calculate the distance from the defect to the measurement end of the cable under test. Its mathematical expression is as follows:

[0079]

[0080] (4) In the formula, L is the distance from the defect to the measuring end of the cable under test, v is the speed at which the incident signal is transmitted in the core of the cable under test, and Δt is the time difference between the time position of the positioning peak and the time position of the autocorrelation peak.

[0081] It should be noted that, according to transmission line theory, the waveform of the peak of the time-frequency cross-correlation curve will slightly change with temperature. This is mainly because: the resistivity of the conductor increases continuously with temperature, affecting the distributed resistance, characteristic impedance, and reflection coefficient of the transmission line; resistivity and reflection coefficient are non-linearly related, so the change in characteristic impedance due to temperature is not equal in the defective and normal segments; therefore, the reflection coefficient in the defective segment will change to a certain extent with temperature, thus altering the waveform of the positioning peak in the time-frequency cross-correlation curve. Furthermore, the change in characteristic impedance is equal in the normal segment, so the reflection coefficient in the normal segment remains 0, and there are no time-frequency cross-correlation peaks in the normal segment. Based on this principle, this invention heats the wire core using the current generation module 30 and utilizes the change in the positioning peak as the variance in amplitude to obtain a higher positioning peak value, thereby accurately identifying and locating defects.

[0082] Furthermore, in this embodiment, the cable weak defect detection and location system also includes a calibration module 60. The calibration module 60 is used to calculate the time position of the end of the cable under test based on the actual length of the cable under test and the transmission speed of the incident signal, so as to complete the position calibration of the end of the cable under test. Specifically, the user can input the actual length of the cable under test through the interactive panel, and the calibration module 60 calculates the time position of the end of the cable under test based on the signal transmission speed, thereby determining the time position of the end of the cable under test. At the same time, this time length also serves as the duration of the signal acquisition module 40, and also as the end time point of the cross-correlation curve and the thermal stress fluctuation curve. Moreover, the peak of this point and the positioning peak are not considered as defects existing in the cable under test.

[0083] refer to Figure 2 The present invention also provides a method for detecting and locating weak defects in cables.

[0084] Specifically, such as Figure 2 As shown, the method for detecting and locating minor defects in the cable includes the following steps:

[0085] Step S201: The signal generation module 10 outputs the incident signal to the signal mutual inductance module 20 at a preset time interval.

[0086] Step S202: The signal mutual inductance module 20 transmits the incident signal to the signal acquisition module 40 and injects the incident signal into the core of the cable under test through electromagnetic induction, and outputs the reflected signal generated after transmission through the core of the cable under test to the signal acquisition module 40.

[0087] Step S203: The current generation module 30 injects current into the core of the cable under test according to the set temperature step and monitors the real-time temperature of the core of the cable under test. When the real-time temperature of the core of the cable under test reaches the target temperature, the control signal acquisition module 40 performs a signal acquisition.

[0088] Step S204: The signal acquisition module 40 acquires the incident and reflected signals transmitted by the signal mutual inductance module 20 according to the control of the current generation module 30, and obtains multiple sets of reference signals and reflected signals.

[0089] In step S205, the signal acquisition module 40 processes each set of reference signals and reflected signals to obtain multiple sets of preprocessed signals.

[0090] In step S206, the data processing module 50 performs time-frequency processing and thermal floating variance processing on multiple sets of preprocessed signals to obtain thermal floating variance curves, and performs defect detection and location based on the thermal floating variance curves.

[0091] Specifically, in this embodiment, the data processing module 50 is used to perform the following steps: perform time-frequency distribution processing on each set of reference signals and reflected signals to obtain multiple sets of distributed signals; perform time-frequency cross-correlation processing on each set of distributed signals to obtain multiple time-frequency cross-correlation curves; the multiple time-frequency cross-correlation curves form a cluster of time-frequency domain cross-correlation curves; perform floating variance processing on the time-frequency domain cross-correlation to obtain a thermal stress floating variance curve; perform analysis and calculation based on the thermal stress floating variance curve, and perform defect judgment and defect location based on the analysis and calculation results.

[0092] Specifically, the method for detecting and locating weak cable defects can be implemented based on the cable weak defect detection and location system disclosed in this invention.

[0093] The following is a specific embodiment, which includes the following steps:

[0094] Step 1: The user inputs the actual length of the cable under test into the calibration module 60 via the interactive panel, and the step-by-step module performs verification and parameter correction. The verification and parameter correction mainly involve correcting and determining the length data of the cable under test and the time position of the end of the cable.

[0095] Step 2: Input the preset start temperature, preset end temperature, and preset temperature step size through the operation panel of the current generation module 30. Since the operating voltage and current of the instrument control cable are relatively low, according to thermal circuit theory, the applied temperature rise should be controlled within 90℃. The default preset temperature step size for the current generation module 30 is 5℃.

[0096] Step 3: The signal generation module 10 outputs a time-limited band-limited signal with a Gaussian envelope to the signal mutual inductance module 20, and simultaneously outputs it directly to the signal acquisition module 40 through the signal mutual inductance module 20.

[0097] Step 4: The time-limited band-limited signal of the Gaussian envelope is transmitted from the measurement end of the cable under test to the end of the cable via electromagnetic induction. During transmission, if the signal encounters a local defect point, it will be reflected until it reaches the end of the cable, where it will be totally reflected and transmitted in the opposite direction to the measurement end of the cable.

[0098] Step 4: The reflected signal segment is sensed by the signal mutual inductance module 20 through electromagnetic induction and output to the signal acquisition module 40.

[0099] Step 5: The current generating module 30 applies current to the core of the cable under test via a connection, causing the core temperature to rise continuously and monitoring the real-time temperature of the cable core. Using a preset initial temperature as a criterion, when the real-time temperature reaches the preset initial temperature, the current generating module 30 controls the signal acquisition module 40 to perform a data acquisition. The acquired signal is then output to the data processing module 50.

[0100] Step Six: When the real-time temperature monitored by the current generation module 30 reaches the next preset temperature step, the current generation module 30 controls the signal acquisition module 40 to perform a data acquisition. The acquired signal is output to the data processing module 50, and the next preset temperature step is used as the basis for controlling the action of the acquisition module.

[0101] Step 7: When the real-time temperature monitored by the current generation module 30 reaches the preset end temperature, the current generation module 30 controls the signal acquisition module 40 to perform a final acquisition. The acquired signal is output to the data processing module 50, carrying relevant end marker parameters to inform the data processing module 50 that this data is the last acquisition signal.

[0102] Step 8: The data processing module 50 begins processing the data. Based on the preset temperature range and step size, the data processing module 50 contains multiple different acquired signals. The data processing module 50 performs time-frequency distribution processing on each acquired signal.

[0103] Step 9: The data processing module 50 obtains a cluster of time-frequency cross-correlation curves by comparing the time-frequency distribution results of each acquired signal with the time-frequency distribution results of the original signal.

[0104] Step 10: The data processing module 50 performs floating variance processing on the time-frequency cross-correlation curve cluster to obtain the thermal stress floating variance curve.

[0105] Step 11: The data processing module 50 uses the peak of the thermal stress fluctuation variance curve as the basis for defect identification. By calculating the time difference between the above peak and the autocorrelation peak, the distance from the defect to the measurement end of the cable under test is further calculated. The above distance and the thermal stress fluctuation variance curve are presented to the user in an interactive panel.

[0106] Specifically, since the transmitted signal connects the cable core and the signal inductance module 20 via electromagnetic induction at the measuring section at the beginning of the cable under test, it is necessary to control surrounding interfering electromagnetic signals during the testing process of this invention. This could be done by cutting off power to surrounding instrument control systems or turning off the user's mobile phone.

[0107] More specifically, a preliminary experiment was conducted on three identical instrumentation cables, designated Cable A, Cable B, and Cable C. Three identical types of insulation / shield fracture defects of varying severity were artificially simulated at a length of 30m. For these three cables, to facilitate simple quantification of the degree of fracture, the circumferential direction was divided into three degrees based on the angle of the cut covering the entire circumference: 120°, 240°, and 360° (i.e., circumferential shear). Cable A simulated a defect degree of 120° circumferentially, Cable B simulated a defect degree of 240° circumferentially, and Cable C simulated a defect degree of 360° circumferentially. In the radial direction, all three defect degrees damaged the outer sheath, insulation layer, and shielding layer of the cable samples, leaving the cable core exposed.

[0108] Preliminary experiments were conducted on three identical multi-core instrumentation cables, designated as cables A, B, and C. Three different defects were artificially created on each cable. In cable A, the cable sheath was cut to the depth of the cable core without damaging it; the cut length, centered on the cable's center, was one-quarter of the cable's circumference. In cable B, the cable sheath was also cut to the same depth as in cable A, again without damaging the cable core; the cut length circled the cable. In cable C, a short circuit was created between the cable core and the shielding layer in the middle section, with two short-circuit defects created. The time-frequency cross-correlation curves obtained by data processing module 50 are shown below. Figure 3 (Cable A) Figure 5 (Cable B) and Figure 7 As shown in (cable C), the thermal stress fluctuation variance curve obtained by data processing module 50 is as follows: Figure 4 (Cable A) Figure 6 (Cable B) and Figure 8 (Cable C) is shown.

[0109] Among them, for the relatively minor defects within a circumferential 120° radius, the peak-to-peak value in the time-frequency cross-correlation curve cluster was only 0.08, while the peak-to-peak value in the defect location curve of the thermal stress fluctuation variance curve reached 0.19, an improvement of 137.5%. For the defect location results of the three cables, the location error rate was within 6%, which can meet the error requirements of actual nuclear power plant instrumentation and control cable operation and maintenance.

[0110] For multi-core instrumentation and control cables in operating nuclear power plants, the harsh operating environment makes the cable sheath and even the internal metal shielding susceptible to wear and breakage, affecting the reliability of the instrumentation and control system's safe operation. Common detection methods struggle to detect minor defects such as external wear and breakage in cables. Therefore, this invention incorporates thermal stress and utilizes time-frequency domain reflection to effectively detect these minor defects in instrumentation and control cables, meeting the defect detection requirements for routine maintenance of the plant's instrumentation and control system.

[0111] The application scenarios of the system for real-time defect monitoring of cables are not limited to nuclear power plant instrumentation and control cables. The system can also be used to detect defects in other cables with detachable end connectors that are easy to connect to signal inductance modules and current generation modules.

[0112] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0113] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0114] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0115] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They do not limit the scope of protection of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A system for detecting and locating minor defects in cables, characterized in that, include: A signal generation module, which is used to generate an incident signal at a preset time interval; The incident signal directly output by the signal generation module that is not transmitted through the wire core of the cable under test is defined as the reference signal; A signal mutual inductance module is connected to the signal generation module. The signal mutual inductance module is used to transmit the incident signal to the signal acquisition module and inject the incident signal into the core of the cable under test, and output the reflected signal generated after transmission through the core of the cable under test to the signal acquisition module. A current generating module is connected to both the cable under test and the signal acquisition module. The current generating module generates current and injects it into the core of the cable under test according to a set temperature step, causing the core temperature to rise continuously. It also controls the signal acquisition module to acquire signals. Furthermore, the current generating module monitors the real-time temperature of the cable core in real time. When the core heats to the target temperature of each step, the current generating module controls the signal acquisition module to perform a signal acquisition. The signal acquisition module is used to acquire the incident signal and the reflected signal generated after transmission through the cable under test according to the control of the current generation module, and obtain multiple sets of reference signals and reflected signals; the signal acquisition module also processes each set of reference signals and reflected signals to obtain multiple sets of preprocessed signals; The data processing module performs time-frequency processing and thermal floating variance processing on the multiple sets of preprocessed signals to obtain thermal floating variance curves, and performs defect detection and location based on the thermal floating variance curves. The data processing module includes: a time-frequency distribution processing unit, used to perform time-frequency distribution processing on each set of reference signals and reflected signals to obtain multiple sets of distributed signals; a time-frequency cross-correlation processing unit, used to perform time-frequency cross-correlation processing on each set of distributed signals to obtain multiple time-frequency cross-correlation curves; the multiple time-frequency cross-correlation curves are a cluster of time-frequency domain cross-correlation curves; a thermal floating variance processing unit, used to perform floating variance processing on the cluster of time-frequency domain cross-correlation curves, calculate the variance value of the amplitude of the cluster of time-frequency cross-correlation curves at each time, and obtain a thermal stress floating variance curve; and a defect detection unit, used to perform analysis and calculation based on the thermal stress floating variance curve, and use the peak of the thermal stress floating variance curve as the basis for defect judgment and defect location.

2. The cable micro-defect detection and location system according to claim 1, characterized in that, The signal mutual inductance module includes: an induction coil; The induction coil includes: a first interface, a second interface, and a sensing part; The first interface is connected to the signal generating module and is used to receive the incident signal output by the signal generating module; The sensing part is connected to the first interface and the second interface respectively, and is used to inject the incident signal from the beginning of the cable under test into the core of the cable under test and transmit the reflected signal generated after passing through the core of the cable under test to the second interface. The second interface is connected to the signal acquisition module and is used to transmit the incident signal received by the first interface and the reflected signal transmitted by the sensing unit to the signal acquisition module.

3. The cable micro-defect detection and location system according to claim 1 or 2, characterized in that, Also includes: Calibration module; The calibration module is used to calculate the time position of the end of the cable under test based on the actual length of the cable under test and the transmission speed of the incident signal, so as to complete the position calibration of the end of the cable under test.

4. A method for detecting and locating weak defects in cables, applied to the cable weak defect detection and location system described in claim 1, characterized in that, Includes the following steps: The signal generation module outputs the incident signal to the signal mutual inductance module at preset time intervals; The signal mutual inductance module transmits the incident signal to the signal acquisition module and injects the incident signal into the core of the cable under test through electromagnetic induction, and outputs the reflected signal generated after transmission through the core of the cable under test to the signal acquisition module. The current generation module injects current into the core of the cable under test according to the set temperature step and monitors the real-time temperature of the core of the cable under test. When the real-time temperature of the core of the cable under test reaches the target temperature, the signal acquisition module controls the signal acquisition module to perform a signal acquisition. The signal acquisition module acquires the incident and reflected signals transmitted by the signal inductance module according to the control of the current generation module, and obtains multiple sets of reference signals and reflected signals; The signal acquisition module processes each set of reference signals and reflected signals to obtain multiple sets of preprocessed signals; The data processing module performs time-frequency processing and thermal floating variance processing on the multiple sets of preprocessed signals to obtain thermal floating variance curves, and performs defect detection and location based on the thermal floating variance curves.

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