CN116087315A - Cable defect nondestructive detection system and method based on electromagnetic induction - Google Patents

Cable defect nondestructive detection system and method based on electromagnetic induction Download PDF

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CN116087315A
CN116087315A CN202310122475.7A CN202310122475A CN116087315A CN 116087315 A CN116087315 A CN 116087315A CN 202310122475 A CN202310122475 A CN 202310122475A CN 116087315 A CN116087315 A CN 116087315A
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cable
detection
wavelet
electromagnetic induction
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袁卫锋
王积硕
康健炜
黄楷焱
古斌
蒋雪丽
周志
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Southwest University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
    • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
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    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

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Abstract

The invention discloses a cable defect nondestructive testing system and method based on electromagnetic induction, wherein the method comprises the following steps: s1, closing a switch to enable a detection circuit to be a passage; s2, enabling the probe to move along the cable through the transmission device, and obtaining a detection signal through the oscilloscope in the moving process; and S3, processing the detection signals by using a Superlets signal processing method to obtain a time-frequency diagram of the detection signals when the probe is at different positions. The cable defect nondestructive detection system and method based on electromagnetic induction provided by the invention have the advantages that the detected object is not damaged, secondary damage is not caused, and the system and method are expected to be used for nondestructive detection of cables.

Description

Cable defect nondestructive detection system and method based on electromagnetic induction
Technical Field
The invention belongs to the technical field of industrial detection, and particularly relates to a cable defect nondestructive detection system based on electromagnetic induction.
Background
The urban underground cable construction is a trend of new times because of being replaced by underground cables which are less susceptible to severe weather and are increasingly occupied by overhead cables due to the demands of shortage of urban space resources and management of urban appearance. The cable damage position is accurately and rapidly detected, and the overhaul speed and the operation safety of the cable can be greatly improved. At present, nondestructive detection methods for cables are few, and a common detection method is X-ray nondestructive detection, but the method needs to be performed off-line, so that the operation is unchanged, and the detection cost is high, and therefore, the method is generally spot check detection. It is difficult to accommodate continuous on-line testing of underground cables, and thus, there is a need to study new nondestructive testing methods to accommodate complex underground cable environments.
Disclosure of Invention
Aiming at the defects in the prior art, the cable defect nondestructive testing system and method based on electromagnetic induction provided by the invention solve the problem that the conventional nondestructive testing method cannot adapt to complex underground cable environments.
In order to achieve the aim of the invention, the invention adopts the following technical scheme: a cable fault nondestructive testing system based on electromagnetic induction, the system comprising:
a function generator for generating an excitation voltage signal of a specific frequency;
a power amplifier for adjusting an operating voltage of the system;
the transmission device is used for fixing the positioning device and controlling the movement of the positioning device;
the positioning device is used for fixing two parallel probes;
the data processing device comprises an oscilloscope and a computer, wherein the oscilloscope is used for visualizing and storing detection signals, and the computer is used for processing and analyzing the detection signals.
Further: the probe is positioned outside the cable and equidistant from the axis of the cable, and an electromagnetic wave shielding cover is arranged around the probe;
the cable is located in a detection circuit, and the detection circuit is provided with a switch.
A method of an electromagnetic induction based cable defect nondestructive testing system, the method comprising the steps of:
s1, closing a switch to enable a detection circuit to be a passage;
s2, enabling the probe to move along the cable through the transmission device, and obtaining a detection signal through the oscilloscope in the moving process;
and S3, processing the detection signals by using a Superlets signal processing method to obtain a time-frequency diagram of the detection signals when the probe is at different positions.
Further: in the step S1, the voltage of the detection circuit is an alternating current.
Further: in the step S2, the method for obtaining the detection signal specifically includes:
s21, calculating the total magnetic flux of the measured point to obtain the magnetic induction intensity of the measured point;
s22, calculating the electric field intensity of the measured point according to the magnetic induction intensity of the measured point, and taking the electric field intensity as a detection signal.
Further: in S21, the total magnetic flux of the measured point is calculated
Figure BDA0004080507190000021
The expression of (2) is specifically:
Figure BDA0004080507190000022
wherein delta is defect depth, l is half of damage length, r 0 For the vertical distance between the measured point and the cable, s is the distance between the measured point and the damage center, mu 0 For vacuum permeability, s and
Figure BDA0004080507190000031
all are functions related to the detection time t, and the expression is specifically as follows:
s＝vt
Figure BDA0004080507190000032
wherein I is m For the current amplitude, ω is the angular frequency,
Figure BDA0004080507190000034
is the initial phase.
Further: in S22, the expression for calculating the electric field intensity E of the measured point is specifically the following expression:
Figure BDA0004080507190000033
further: the step S3 comprises the following substeps:
s31, establishing a wavelet set with a fixed center frequency;
s32, obtaining responses of all wavelets in the wavelet set to the detection signals, and obtaining a time-frequency diagram of the detection signals when the probe is at different positions.
The beneficial effects of the above-mentioned further scheme are: the advantage of using Superlets signal processing methods is that both high time and high frequency resolution can be achieved.
Further: in S31, a fixed center frequency f m Wavelet set of (2)
Figure BDA0004080507190000041
The expression of (2) is specifically:
Figure BDA0004080507190000042
where o is the order of SLs, c is the number of cycles of each wavelet in the wavelet set, and c=c 1 ,c 2 ,...,c o ，c o Is the total number of cycles of the wavelet,
Figure BDA0004080507190000043
for improved Morlet function, its expressionThe formula is specifically as follows:
Figure BDA0004080507190000044
wherein, c m The period number of the mother wavelet, B c The expression of the time expansion parameter is specifically as follows:
Figure BDA0004080507190000045
wherein k is sd Is a control parameter.
Further: in the S32, responses of each wavelet in the wavelet set to the detection signal
Figure BDA0004080507190000049
The expression of (2) is specifically:
Figure BDA0004080507190000046
in the method, in the process of the invention,
Figure BDA0004080507190000047
for the response of the wavelet i to the detection signal x, the expression is specifically as follows:
Figure BDA0004080507190000048
wherein, is the complex convolution product,
Figure BDA00040805071900000410
….
The invention has the beneficial effects that: the cable defect nondestructive detection system and method based on electromagnetic induction provided by the invention have the advantages that the detected object is not damaged, secondary damage is not caused, and the system and method are expected to be used for nondestructive detection of cables. The on-line detection can be realized, and the detection efficiency is high; the portable device can be detected on site.
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FIG. 1 is a schematic diagram of a nondestructive testing system for cable defects based on electromagnetic induction;
FIG. 2 is a schematic diagram II of a nondestructive testing system for cable defects based on electromagnetic induction;
FIG. 3 is a flowchart of a nondestructive testing method for cable defects based on electromagnetic induction;
FIG. 4 is a schematic diagram of the magnetic field in the damaged condition of a current carrying (infinitely long) straight wire;
FIG. 5 is a schematic diagram showing the effect of different cable depths on the electric field strength at the detection point;
FIG. 6 is a schematic diagram showing the effect of different cable lengths on the electric field strength at the detection point;
FIG. 7 is a graph of the result of the detection signal obtained by numerical value solving;
FIG. 8 is a graph showing the result of the detection signal after the result of FIG. 7 is subjected to the Superlets processing;
FIG. 9 is a schematic diagram of signals acquired by an oscilloscope;
fig. 10 is a graph showing the result of FFT processing of the signal in fig. 9;
FIG. 11 is a time-amplitude plot of test data;
fig. 12 is a graph of the detection results of the cable completion benefits and defects.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and all the inventions which make use of the inventive concept are protected by the spirit and scope of the present invention as defined and defined in the appended claims to those skilled in the art.
Example 1:
as shown in fig. 1, in one embodiment of the present invention, a cable defect nondestructive testing system based on electromagnetic induction, the system comprises:
a function generator for generating an excitation voltage signal of a specific frequency;
a power amplifier for adjusting an operating voltage of the system;
the transmission device is used for fixing the positioning device and controlling the movement of the positioning device;
the positioning device is used for fixing two parallel probes;
the data processing device comprises an oscilloscope and a computer, wherein the oscilloscope is used for visualizing and storing detection signals, and the computer is used for processing and analyzing the detection signals.
The probe is positioned outside the cable and equidistant from the axis of the cable, and an electromagnetic wave shielding cover is arranged around the probe;
the cable is located in a detection circuit, and the detection circuit is provided with a switch.
As shown in fig. 2, a method of a cable defect nondestructive testing system based on electromagnetic induction includes the following steps:
s1, closing a switch to enable a detection circuit to be a passage;
s2, enabling the probe to move along the cable through the transmission device, and obtaining a detection signal through the oscilloscope in the moving process;
s3, processing the detection signals by using a Superlets signal processing Method (Superlets Method) to obtain a time-frequency diagram of the detection signals when the probe is at different positions.
In the step S1, the voltage of the detection circuit is an alternating current.
In the step S2, the method for obtaining the detection signal specifically includes:
s21, calculating the total magnetic flux of the measured point to obtain the magnetic induction intensity of the measured point;
s22, calculating the electric field intensity of the measured point according to the magnetic induction intensity of the measured point, and taking the electric field intensity as a detection signal.
In the present embodiment, as shown in FIG. 3, the magnetic field is schematically shown in the defect state of the current-carrying straight wire (infinite length), wherein P is the measured point, Δ is the defect depth, l is half the damage length, r 0 S is the vertical distance between the measured point and the cableFor the distance between the measured point and the damage center, θ 1 Is the angle theta between the connecting line of the lower end point of the upper end intact section and the measured point and the axial direction of the cable 2 For the angle between the connecting line of the upper end point of the damaged section and the measured point and the axial direction of the cable, theta 3 For the angle between the connecting line of the lower end point of the damaged section and the measured point and the axial direction of the cable, theta 4 The angle between the upper end point of the lower end intact segment and the connecting line of the measured point and the axial direction of the cable is 180 degrees and 0 degrees respectively because the cable is regarded as infinite length.
From the law of pito-savory, the magnetic flux calculation formula of the current-carrying long straight wire is as follows:
Figure BDA0004080507190000071
the magnetic flux measured at the measured point P
Figure BDA0004080507190000072
Magnetic flux for upper end intact segment>
Figure BDA0004080507190000073
Magnetic flux of middle damaged section->
Figure BDA0004080507190000074
And magnetic flux of the lower end intact segment->
Figure BDA0004080507190000075
Is a sum of (a) and (b).
Figure BDA0004080507190000076
Figure BDA0004080507190000077
Figure BDA0004080507190000078
In S21, the total magnetic flux of the measured point is calculated
Figure BDA0004080507190000079
The expression of (2) is specifically:
Figure BDA00040805071900000710
wherein delta is defect depth, l is half of damage length, r 0 For the vertical distance between the measured point and the cable, s is the distance between the measured point and the damage center, mu 0 For vacuum permeability, s and
Figure BDA00040805071900000711
all are functions related to the detection time t, and the expression is specifically as follows:
s＝vt
Figure BDA0004080507190000081
wherein I is m For the current amplitude, ω is the angular frequency,
Figure BDA0004080507190000082
is the initial phase.
In S22, the expression for calculating the electric field intensity E of the measured point is specifically the following expression:
Figure BDA0004080507190000083
from the above equation, the electric field strength is related to the depth and length of the defect and the speed of the detection mobile device, and the theoretical analysis is performed on each parameter to obtain the rule of influence of each parameter on the detection result, as shown in fig. 4 to 5, and fig. 4 and 5 show the influence of the depth and length of the defect on the detection result, respectively. As can be seen from fig. 4, the electric field strength is smaller against the increase in depth while ensuring that other parameters are constant. As can be seen from fig. 5, the electric field strength is smaller as the damage length is larger. It follows that the electric field strength becomes smaller as the depth and length of the lesion increase.
In addition to the effect of defect depth and length on detection, the speed of movement of the detection device also has an effect on it. And analyzing the movement condition of the probe along the cable by using a numerical analysis method, and when the cable has a defect, setting the defect position at the middle position of the cable, and moving the probe from one section of the cable to the other end at a uniform speed. The detection results obtained by solving the expression of the electric field intensity E of the measured point are shown in fig. 6 to 7, and it can be seen that when the depth and length of the defect are fixed, the probe moves near the cable line at a certain speed, and when the movement time is 50s, the electric field intensity near the cable line has obvious change. Wherein the position corresponding to the lowest point time between two peaks corresponds to the center position of the defect. The defect position can be judged according to the method. In addition, in order to more precisely determine the precise location of the defect, the signal is processed using the Superlets method, resulting in the graph shown in fig. 7. The physical meaning of the curve is the same as that of fig. 6, except that more accurate defect positions and parameters such as length/depth thereof can be obtained by using the method. In terms of experimental verification, the processing of the data was performed using this method.
The step S3 comprises the following substeps:
s31, establishing a wavelet set with a fixed center frequency;
s32, obtaining responses of all wavelets in the wavelet set to the detection signals, and obtaining a time-frequency diagram of the detection signals when the probe is at different positions.
In this embodiment, the principle of the Superlets signal processing method is to build a wavelet set with a fixed center frequency and have a series of different periods, and the processing method is similar to wavelet transformation, and the method has the advantage of simultaneously giving consideration to high time and high frequency resolution.
In S31, a fixed center frequency f m Wavelet set of (2)
Figure BDA0004080507190000091
The expression of (2) is specifically:
Figure BDA0004080507190000092
where o is the order of SLs, c is the number of cycles of each wavelet in the wavelet set, and c=c 1 ,c 2 ,...,c o ，c o Is the total number of cycles of the wavelet,
Figure BDA0004080507190000093
for the improved Morlet function, the expression is specifically as follows:
Figure BDA0004080507190000094
wherein, c m The period number of the mother wavelet, B c The expression of the time expansion parameter is specifically as follows:
Figure BDA0004080507190000095
wherein k is sd For the control parameter, its value is typically set to 5, controlling the time variance of the wavelet.
In the S32, responses of each wavelet in the wavelet set to the detection signal
Figure BDA0004080507190000101
The expression of (2) is specifically:
Figure BDA0004080507190000102
in the method, in the process of the invention,
Figure BDA0004080507190000103
for the response of the wavelet i to the detection signal x, the expression is specifically as follows:
Figure BDA0004080507190000104
wherein, is the complex convolution product,
Figure BDA0004080507190000105
….
In the present embodiment, the response
Figure BDA0004080507190000106
The signal strength is not the actual strength of the signal, and only half of the actual strength of the signal can be recovered after being processed by the Superlets signal processing method; the Superlets signal processing method is similar to CWT, except that the wavelet set is used instead of the wavelet, so that the first-order SL transformation is CWT.
Example 2:
this example is directed to the specific experiment of example 1.
In the actual detection of cable defects, the moving speed of the probe has an influence on the electric field intensity, so that the experimental method can be divided into two methods, namely, the static state (the speed is 0) and the moving state (the speed is not 0) of the positioning device.
And analyzing the motion state of the positioning device, and replacing an actual cable by using a copper core as a lead. The copper core, the aluminum pipe, the insulating pipe, the shielding aluminum pipe and the insulating tape are sequentially arranged from inside to outside, wherein the defects in the copper core are artificial manufacturing defects.
Preparing an experimental instrument, wherein the experimental instrument comprises a function generator, a power amplifier, a detection device, an oscilloscope, a transmission device controller and other equipment, the detection device comprises a positioning device and the transmission device, and the transmission device controller is mainly used for mobile control of the positioning device.
After the preparation of the experimental instrument is completed, an online nondestructive testing experiment of the cable is preliminarily carried out, and in order to avoid the interference of external electromagnetic signals, the frequency of the excitation signal of the function generator is set to be 20Hz. The positioning device moves from one side of the cable to the other side at a constant speed, and signals obtained by detection of the positioning device are displayed and collected through an oscilloscope, and the signals are shown in fig. 8. The signal shown in fig. 8 is subjected to FFT processing, so that an amplitude-frequency curve of the signal can be obtained, and as shown in fig. 9, the working frequency of the cable line can be clearly seen to be 20Hz.
To further obtain the specific location of the cable fault, the data shown in fig. 8 was processed by using the Superlet signal processing method, and the result is shown in fig. 10. When the positioning device moves to the defect at a uniform speed, a peak is generated at the end part of the defect opening, and the position between the two peaks is the defect position of the cable. Under the same detection parameters, the error between the test result and the theoretical result is about 2.6 cm. It should be noted that the probe moves at a uniform speed along the axis direction of the cable, and the distance from the axis of the cable needs to be ensured to be equal.
The static state of the positioning device is analyzed, the probe spacing is set to be 15mm, the sampling frequency of the oscilloscope is 500Hz, the static state is respectively kept at the notch position and the perfect position of the cable line, the cable is detected, the data is processed and analyzed by using the Superlet method, and the result is shown in figure 11.
As can be seen from fig. 11, when the cable has a gap, the distance between the probe and the cable is relatively long, and the electric field intensity E at the detected point is lower than that at the intact point.
The beneficial effects of the invention are as follows: the cable defect nondestructive detection system and method based on electromagnetic induction provided by the invention have the advantages that the detected object is not damaged, secondary damage is not caused, and the system and method are expected to be used for nondestructive detection of cables. The on-line detection can be realized, and the detection efficiency is high; the portable device can be detected on site.
In the description of the present invention, it should be understood that the terms "center," "thickness," "upper," "lower," "horizontal," "top," "bottom," "inner," "outer," "radial," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be configured and operated in a particular orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be interpreted as indicating or implying a relative importance or number of technical features indicated. Thus, a feature defined as "first," "second," "third," or the like, may explicitly or implicitly include one or more such feature.

Claims (10)

1. A cable fault nondestructive testing system based on electromagnetic induction, the system comprising:
a function generator for generating an excitation voltage signal of a specific frequency;
a power amplifier for adjusting an operating voltage of the system;
the transmission device is used for fixing the positioning device and controlling the movement of the positioning device;
the positioning device is used for fixing two parallel probes;
the data processing device comprises an oscilloscope and a computer, wherein the oscilloscope is used for visualizing and storing detection signals, and the computer is used for processing and analyzing the detection signals.
2. The nondestructive inspection system for cable defects based on electromagnetic induction of claim 1 wherein the probe is located outside the cable equidistant from the axis of the cable and an electromagnetic shield is provided around the probe;
the cable is located in a detection circuit, and the detection circuit is provided with a switch.
3. A method based on the electromagnetic induction based cable defect nondestructive testing system of claims 1-2, characterized in that the method comprises the steps of:
s1, closing a switch to enable a detection circuit to be a passage;
s2, enabling the probe to move along the cable through the transmission device, and obtaining a detection signal through the oscilloscope in the moving process;
and S3, processing the detection signals by using a Superlets signal processing method to obtain a time-frequency diagram of the detection signals when the probe is at different positions.
4. The nondestructive testing method for cable defects based on electromagnetic induction according to claim 3, wherein in S1, the voltage of the testing circuit is ac.
5. The nondestructive testing method for cable defects based on electromagnetic induction according to claim 3, wherein in S2, the method for obtaining the test signal specifically comprises:
s21, calculating the total magnetic flux of the measured point to obtain the magnetic induction intensity of the measured point;
s22, calculating the electric field intensity of the measured point according to the magnetic induction intensity of the measured point, and taking the electric field intensity as a detection signal.
6. The method for non-destructive inspection of cable defects according to claim 5, wherein in S21, the total magnetic flux at the measured point is calculated
Figure FDA0004080507170000021
The expression of (2) is specifically:
Figure FDA0004080507170000022
wherein delta is defect depth, l is half of damage length, r 0 For the vertical distance between the measured point and the cable, s is the distance between the measured point and the damage center, mu 0 For vacuum permeability, s and
Figure FDA0004080507170000023
all are functions related to the detection time t, and the expression is specifically as follows:
s＝vt
Figure FDA0004080507170000024
wherein I is m For the current amplitude, ω is the angular frequency,
Figure FDA0004080507170000025
is the initial phase.
7. The nondestructive testing method for cable defects based on electromagnetic induction according to claim 6, wherein in S22, the expression for calculating the electric field intensity E of the tested point is specifically the following expression:
Figure FDA0004080507170000031
8. the electromagnetic induction based cable defect nondestructive testing method according to claim 7, wherein the step S3 comprises the following sub-steps:
s31, establishing a wavelet set with a fixed center frequency;
s32, obtaining responses of all wavelets in the wavelet set to the detection signals, and obtaining a time-frequency diagram of the detection signals when the probe is at different positions.
9. The nondestructive testing method for cable defects based on electromagnetic induction of claim 7, wherein in S31, there is a fixed center frequency f m Wavelet set of (2)
Figure FDA0004080507170000032
The expression of (2) is specifically:
Figure FDA0004080507170000033
where o is the order of SLs, c is the number of cycles of each wavelet in the wavelet set, and c=c 1 ,c 2 ,...,c o ，c o Is the total number of cycles of the wavelet,
Figure FDA0004080507170000034
for the improved Morlet function, the expression is specifically as follows:
Figure FDA0004080507170000035
wherein, c m The period number of the mother wavelet, B c The expression of the time expansion parameter is specifically as follows:
Figure FDA0004080507170000041
wherein k is sd Is a control parameter.
10. The method for non-destructive inspection of cable defects according to claim 9, wherein in S32, the response of each wavelet in the wavelet set to the inspection signal
Figure FDA0004080507170000042
The expression of (2) is specifically: />
Figure FDA0004080507170000043
In the method, in the process of the invention,
Figure FDA0004080507170000044
for the response of the wavelet i to the detection signal x, the expression is specifically as follows:
Figure FDA0004080507170000045
where is the complex convolution product.
CN202310122475.7A 2023-02-15 2023-02-15 Cable defect nondestructive detection system and method based on electromagnetic induction Pending CN116087315A (en)

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Cited By (1)

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Cited By (2)

* Cited by examiner, † Cited by third party
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CN117542585A (en) * 2024-01-08 2024-02-09 营口阿部配线有限公司 Wire harness shielding wire protective sleeve pushing and stretching device and application method thereof
CN117542585B (en) * 2024-01-08 2024-03-12 营口阿部配线有限公司 Wire harness shielding wire protective sleeve pushing and stretching device and application method thereof

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