CN115144693A - Cable fault positioning device and method based on electromagnetic method - Google Patents
Cable fault positioning device and method based on electromagnetic method Download PDFInfo
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- CN115144693A CN115144693A CN202210711031.2A CN202210711031A CN115144693A CN 115144693 A CN115144693 A CN 115144693A CN 202210711031 A CN202210711031 A CN 202210711031A CN 115144693 A CN115144693 A CN 115144693A
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- 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
- G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
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- G—PHYSICS
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- 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
- G01R31/088—Aspects of digital computing
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Abstract
The invention relates to a method for positioning a cable fault positioning device based on an electromagnetic method, which comprises the following steps: s1, detecting a metal pipeline through a magnetic field to obtain a cable path; step S2: acquiring electrification characteristic data of each cable joint, and judging which two joints the fault occurs between based on historical data of each cable joint; and S3, acquiring fault characteristic data to position the fault according to the two joints judged and obtained in the step S2. The invention observes the characteristic value of the joint by applying the voltage and current signals with reduced equal proportion to the cable in an off-line state so as to position the position of the fault cable joint, thereby further giving out the fault point in detail.
Description
Technical Field
The invention relates to the field of cable fault positioning, in particular to a cable fault positioning device and method based on an electromagnetic method.
Background
Cables are a carrier of power transmission, are widely used in power distribution networks in cities, and are often buried underground so as not to affect the city capacity, which presents a technical challenge for the treatment of cable failures. Common power cable faults mainly comprise mechanical damage faults, reduction of insulating property of an insulating layer of the power cable, overvoltage faults, insulation aging faults and the like, and according to statistics, the cable accidents account for more than 60% of all electrical accidents.
The diagnosis of the power cable fault mainly comprises the diagnosis of the fault, the distance measurement and the positioning of 3 parts. The fault diagnosis mainly comprises the steps of judging the fault type and identifying the severity, and the fault property of the cable can be judged by measuring the fault resistance of the cable by using a universal meter and a megohmmeter; fault location can be implemented by measuring the distance of a fault point at one end of a cable by using an instrument, wherein a traveling wave of a voltage wave and a current wave which are transmitted in a line at a certain speed is usually adopted, and the fault distance is measured by utilizing the back-and-forth transmission of the traveling wave in the line; the fault location is to accurately determine the specific position of the fault point within a certain range according to the ranging result, and the fault is often located by using a sound measuring method, a sound-magnetic synchronous receiving method, an audio signal induction method, a step voltage method and the like. The traveling wave method measures the propagation time of a traveling cable by using the reflection of a pulse signal at a fault point and determines the fault position by combining the wave speed of the signal, but the problems of signal attenuation, noise interference, frequency dispersion and the like exist, so that the identification of the signal is difficult.
The long-distance cable adopts the joint to connect a section of the outgoing cable, the joint is externally wrapped by metal of nearly two meters, if the positions of the metal of the joint can be accurately positioned in advance, the fault can be positioned in the section of the outgoing cable, and therefore the positioning precision is improved. Researches based on the aspect of cable connectors are developed at home and abroad, and a German student Y.Norouz i explains the accuracy of a frequency domain n ref estimation (FDR) method in the middle connector positioning compared with a traditional time domain n ref estimation (TDR) positioning method through simulation; the Japanese scholars Yosh imi ch i Ohki proves the superiority of the frequency domain reflection method in positioning the tiny defects of the cable. Domestic scholars use a Reflection Coefficient Spectrum (RCS) and a Broadband Impedance Spectrum (BIS) to realize the positioning of weak defects of the cable.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a cable fault location apparatus and method based on an electromagnetic method, which can locate the location of a faulty cable joint by observing the characteristic values of the joint by applying proportionally reduced voltage and current signals to the cable in an off-line state, so as to further specify the fault point.
In order to realize the purpose, the invention adopts the following technical scheme:
the utility model provides a cable fault positioner based on electromagnetic method, lives two cable head parcel through a tubular metal resonator in cable joint department to after contracting cable accessories parcel through the cold and hot, twine metal knitting, armor ground connection line again, still wrap up the cable explosion-proof box that is formed by glass steel material processing at the skin at last.
A method for positioning a cable fault positioning device based on an electromagnetic method comprises the following steps:
s1, detecting a metal pipeline through a magnetic field to obtain a cable path;
step S2: acquiring electrification characteristic data of each cable joint, and judging which two joints the fault occurs between based on historical data of each cable joint;
and S3, acquiring fault characteristic data to position the fault according to the two joints judged and obtained in the step S2.
Further, the step S1 specifically includes:
according to the Biot-Saval law, the magnetic field of any point P on the ground is measured by using a magnetic core coil as an antenna; marking the magnetic field intensity in the horizontal direction as Hx, marking the magnetic field intensity in the vertical direction as Hz, and processing the antenna measurement data in each direction and each position as follows
The magnetic field intensity generated by a single current-carrying infinite-length cable at a ground point P is as follows:
in the formula: mu.s 0 Is the magnetic permeability of the medium in vacuum; i current intensity in the cable; r is the distance from the cable to point P;
the horizontal magnetic field strength Hx and the vertical magnetic field strength Hz are each:
constructing signal intensity normalization distribution graphs of Hx, | Hz | at different positions, wherein the horizontal axis is the horizontal position of the ground, the projection point of the power cable on the ground is taken as the zero point of the horizontal axis, the left and right projection positions far away from the power cable are respectively in the negative direction and the positive direction, and the vertical axis is the normalization signal intensity;
obtaining whether the underground power cable is on the left or right of the current test point by comparing the positive and negative values of Hx and Hz, and adjusting the position of the test point according to the result until the peak amplitude is the maximum value in the front, back, left and right small areas, wherein the position of the test point at the moment is the position of the cable;
after a certain point of the power cable is positioned by using the magnetic core coil as an antenna, the next point of the power cable is positioned by spanning, and the path of the power cable and the position of a cable joint are obtained.
Further, in the magnetic field detection, the formula (1) is corrected, and the noise amount θ is added to generate the formula (4)
Establishing electrification characteristic big data of the cable joint by adopting a technology of online monitoring the state of the cable joint, wherein Hp measured each time is represented by a waveform amplitude F, and a current I is represented by a current input into the cable; the left and right quantities Hp and I in equation (4) are measured quantities, and the coefficients of I are unknown constants, only the noise quantity θ is randomly varied.
Further, the step S2 specifically includes:
step S21, after the position of each joint in the cable is determined, starting the collection work of the electrification characteristic data of each cable joint, wherein the electrification characteristic data comprises the current and voltage values of the cable, the waveform amplitude F and the width W of each joint and calculating a noise variable theta during each collection;
and S22, sequentially processing each joint on the cable line as follows:
firstly, searching out a record set in the same time period in a database according to the time of the fault monitoring moment, solving the sum of the noise variables theta at the moment, and dividing the sum by the number of the searched records to obtain the mean value theta of the noise variables theta at the moment; finding out theta with minimum error corresponding to mean value theta min Will contain θ min The recorded waveform amplitudes F and I are taken as the optimum reference quantity F min And I min ；
Next, I (I = I) was calculated from F measured at the linker min *(F min /(F-θ min )))。
And finally, judging which two joints the fault occurs between according to the change of the current I flowing through each joint.
Furthermore, for the fault on the cable body between the two joints, the step voltage is adopted for reverse calculation, namely the power value pi = F of each joint is calculated firstly ei /F y If the pressure drop from the ith connector to the fault point is measured to be Vi, the pressure drop from the (i + 1) th connector to the fault point is measured to be V i+1 When the strategy voltage is stepped from the i connector to the i +1 connector, the voltage value of each step shows a V-shaped trend from high to low and then from low to high, and obviously, the V-shaped valley bottom point is a fault point.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention is based on the on-line monitoring of the cable joint state, and can accurately provide the space and electrification characteristic data of the cable joint and the electromagnetic noise quantity of the environment where the joint is positioned by adopting a big data analysis technology;
2. the invention can obtain the electrification characteristic data of the non-fault point of the fault cable by inputting voltage and current signals with reduced equal proportion based on the electrification characteristic data of the cable joint;
3. the invention establishes the electrification characteristic of the cable joint and the electromagnetic noise big data of the environment by adopting the technology of online monitoring the state of the cable joint, analyzes the big data, can position the fault point of the cable, and overcomes the defect of inaccurate positioning precision of a fault positioning instrument caused by environmental interference.
Drawings
FIG. 1 is a graph of magnetic field distribution around a conductive wire in an embodiment of the present invention;
FIG. 2 is a graph illustrating normalized distribution of signal strength at different locations for Hx, | Hz | according to an embodiment of the present invention;
FIG. 3 illustrates an embodiment of the present invention in which Hx Hz confirms the left and right direction of the pipeline;
FIG. 4 illustrates an observation system and various types of strong interference sources in accordance with an embodiment of the present invention;
FIG. 5 is a schematic diagram of fault location from cable splice fault signature data in an embodiment of the present invention.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
Referring to fig. 1-5, the invention provides a cable fault positioning device based on an electromagnetic method, two cable heads are wrapped at a cable joint through a metal pipe, and are wrapped through a cold-hot shrinkage cable accessory, then a metal braided fabric and an armored grounding connecting wire are wound, and finally a cable explosion-proof box made of glass fiber reinforced plastic materials is wrapped on the outer layer.
In this embodiment, a method for positioning a cable fault positioning device based on an electromagnetic method is further provided, including the following steps:
s1, detecting a metal pipeline through a magnetic field to obtain a cable path;
the power cable has good conductivity, and when the power cable transmits power, the power cable generates a changing magnetic field around a metal pipeline, and the magnetic field at any point P on the ground can be measured by using a magnetic core coil as an antenna according to the Pieo-Saval law. The magnetic field intensity in the horizontal direction is marked as Hx, the magnetic field intensity in the vertical direction is marked as Hz, and the antenna measurement data in each direction and each position are processed as follows, so that the position and the depth of the underground power cable can be judged and predicted to a certain extent.
The magnetic field intensity generated by a single current-carrying infinite-length cable at a ground point P is as follows:
in the formula: μ 0 is the permeability of the medium in vacuum (μ 0=4 π × 10-7H/m); i current intensity in the cable; r is the distance from the cable to point P, as shown in fig. 1;
the horizontal magnetic field strength Hx and the vertical magnetic field strength Hz which can be obtained are respectively as follows:
fig. 2 is a normalized distribution diagram of signal intensities at different positions of Hx, | Hz | with the horizontal axis representing the ground horizontal position, the projection points of the power cable on the ground being the zero point of the horizontal axis, the projection positions left and right away from the power cable being the negative direction and the positive direction, respectively, and the vertical axis representing the normalized signal intensity.
It can be seen from equation (2), equation (3) and fig. 2 that Hx obtains the maximum value when x =0, that is, the ground strength of the horizontal magnetic field signal directly above the cable is the maximum, and the signal gradually decreases with the displacement of the position; i Hz | gets a minimum value of 0 when x =0, i.e. the vertical signal is minimal directly above the cable; meanwhile, the directions of Hz per se are different due to different observation positions, namely the vertical components of the magnetic fields on the left and the right of the cable are opposite in direction at the same moment. Since an alternating current signal is applied to the power cable, it is not significant to observe only the positive and negative of the vertical component of the magnetic field, but if the positive and negative of the vertical component of the magnetic field and the direction of the horizontal component at the same time are considered, the position of the current signal collecting antenna relative to the underground power cable can be confirmed, as shown in fig. 3. On the left side and the right side of the power cable, the left side or the right side of the underground power cable at the current test point can be known by comparing the positive value and the negative value of Hx and Hz, and the position of the test point is adjusted according to the result until the peak amplitude value is the maximum value in the front, back, left and right small areas, and the position of the test point at the moment is the position of the cable.
After a certain point of the power cable is positioned by using the magnetic core coil as an antenna, the next point of the power cable can be relocated in a span section, and the approximate path of the power cable can be found in turn.
Due to the manufacturing complexity of the cable joint, the cable joint is used as a special node on a power cable path, the measured waveform amplitude F and the measured waveform width W are greatly different from those of a cable body, and the positioning precision of the cable joint point can be improved by repeatedly measuring for many times.
In the process of magnetic field detection, the electromagnetic interference caused by field source noise, geological noise, communication cables, underground metal pipe networks, broadcasting stations, signal towers, various vehicles and the like can influence the observation data and seriously pollute the data obtained by the electromagnetic tester, so that the formula (1) can be corrected, the noise quantity theta is added, and the formula (4) is generated. Therefore, a denoising method is needed to improve the data quality, so as to lay a foundation for subsequently improving the fault positioning precision.
The noise amount θ is usually removed by signal filtering, such as Hilbert-Huang transform, wavelet analysis, statistical analysis, empirical mode decomposition, etc. in time domain processing.
In the present embodiment, it is preferable to establish the electrification characteristic big data of the cable joint by adopting the technology of online monitoring the cable joint state, wherein each measured Hp is characterized by the waveform amplitude F, and the current I is characterized by the current of the input cable. Thus, the left and right magnitudes Hp and I in equation (4) are measured magnitudes, and the coefficients of I are unknown constants, only the noise magnitude θ is randomly varied.
In this embodiment, the observation data is composed of an effective signal and interference noise, where the former is an electromagnetic signal after the power cable is powered on, and the interference noise mainly comes from power frequency interference, stray current, switches of electrical equipment, vehicle noise, etc., and generally has strong regularity, and the observation system and various strong interference sources are as shown in fig. 4: the power frequency interference is from a high-voltage transmission line near an observation point and mainly reflected in electric channels, power frequency components of two orthogonal electric channels have good correlation, and power frequency components can also appear in magnetic tracks occasionally. Although the interference is usually strong and influenced by weather, the interference is basically a constant and can be ignored after being processed by big data.
Stray current interference refers to noise interference caused by ground current introduced into the ground when an electric device is suddenly switched on or off or a load suddenly changes, generally appears in electric channel signals and magnetic track signals with various sampling rates, generally has sinusoidal damping oscillation on a time sequence, and has amplitude of several orders of magnitude of a normal useful signal.
The electronic equipment switch interference refers to strong interference caused by instant opening and closing of the electronic equipment switch, such noise usually appears in the electric field channel of the middle-low frequency band, the data time domain waveform correlation of the two orthogonal electric channels is good, the amplitude of the two orthogonal electric channels is generally large, and a normal magnetotelluric useful signal can be submerged, so that the impedance estimation has serious deviation.
The motor noise interference refers to the interference generated by motor speed regulation and valve control, is represented as an irregular triangular waveform in observed data, and generally appears in a magnetic channel.
The vehicle interference means that large-scale high-intensity electromagnetic interference can be generated when large-scale machinery works, the noise intensity is high, and the time domain waveform of observation data has obvious jump.
The analysis shows that the stray current, the electronic equipment switch, the motor noise and the vehicle interference are all related to human activities, and the human activities in the city have a certain rule in the long term, so that the change rule of the noise quantity theta can be obtained from the Hp value acquired at regular intervals.
Preferably, in this embodiment, after the cable joint location is determined, each time the instrument is placed in a fixed position, r is a fixed value, and in practice, the measurement can be performed every quarter of a second, resulting in Hp and I in equation (4), and from this the noise variance θ can be calculated, thus generating a record (time, hp, I, θ and waveform amplitude F).
Step S2: acquiring electrification characteristic data of each cable joint, and judging which two joints the fault occurs between based on historical data of each cable joint;
and S3, acquiring fault characteristic data to position the fault according to the two joints judged in the step S2.
In this embodiment, the collection of electrification characteristic data for each cable connector is initiated when the location of each connector in the cable is determined. These electrification characteristic data include the current and voltage values of the incoming cable, the waveform amplitude F and width W of each joint at each acquisition, and the noise variance θ calculated according to equation 4.
When the cable fails, the power supply is cut off to reduce loss, and at the moment, an additional testing power supply is needed to supply power to the off-line cable, so that the magnetic core coil can be used as an antenna to measure each joint of the power cable. The provided test power supply can adopt lower power, so that the measured electrical characteristic quantity of each joint is smaller than a normal value, and the electrical characteristic quantity of each joint in normal operation under the condition of test power needs to be recalculated in an equal proportion so as to prepare for positioning faults later.
And sequentially processing each joint on the cable line as follows: firstly, the record sets in the same time interval in a database are found out according to the time of the fault monitoring moment, the sum of the noise variables theta at the moment is solved, and the sum is divided by the number of the found records, so that the mean value theta of the noise variables theta at the moment is obtained. And finding out theta min with the minimum error corresponding to the mean value theta, and taking the waveform amplitudes F and I in the record containing the theta min as the optimal reference quantities Fmin and Imin.
Next, I was calculated from the measured F of the linker (I = Imin (Fmin/(F- θ min))).
And finally, judging between which two joints the fault occurs according to the change magnitude of the current I flowing through each joint.
Preferably, for the occurrence in twoThe fault on the cable body between the joints is reversely calculated by adopting step voltage, namely the power value pi = F of each joint is calculated ei /F y If the voltage drop from the ith connector to the fault point is measured to be Vi, the voltage drop from the (i + 1) th connector to the fault point is measured to be V i+1 When the strategy voltage is stepped from the i connector to the i +1 connector, the voltage value of each step shows a V-shaped trend from high to low and then from low to high, and obviously, the V-shaped valley bottom point is a fault point.
The above description is only a preferred embodiment of the present invention, and all the equivalent changes and modifications made according to the claims of the present invention should be covered by the present invention.
Claims (6)
1. The utility model provides a cable fault positioner based on electromagnetic method, its characterized in that lives two cable head parcel through a metal tube in cable joint department to after contracting cable accessories parcel through the cold and hot, twine metal knitting, armor ground connection line again, still wrap up at the skin at last by the explosion-proof box of cable that glass steel material processed and formed.
2. The method for positioning the cable fault positioning device based on the electromagnetic method according to claim 1, characterized by comprising the following steps:
s1, detecting a metal pipeline through a magnetic field to obtain a cable path;
step S2: acquiring electrification characteristic data of each cable joint, and judging which two joints the fault occurs between based on historical data of each cable joint;
and S3, acquiring fault characteristic data to position the fault according to the two joints judged in the step S2.
3. The method for positioning the cable fault positioning device based on the electromagnetic method according to claim 2, wherein the step S1 specifically comprises:
according to the Biot-Saval law, the magnetic field of any point P on the ground is measured by using a magnetic core coil as an antenna; marking the magnetic field intensity in the horizontal direction as Hx, marking the magnetic field intensity in the vertical direction as Hz, and processing the antenna measurement data in each direction and each position as follows
The magnetic field intensity generated by a single current-carrying infinite-length cable at a ground point P is as follows:
in the formula: mu.s 0 Is the magnetic permeability of the medium in vacuum; i current intensity in the cable; r is the distance from the cable to point P;
the horizontal magnetic field strength Hx and the vertical magnetic field strength Hz are each:
constructing signal intensity normalization distribution graphs of Hx, | Hz | at different positions, wherein the horizontal axis is the horizontal position of the ground, the projection point of the power cable on the ground is taken as the zero point of the horizontal axis, the left and right projection positions far away from the power cable are respectively in the negative direction and the positive direction, and the vertical axis is the normalization signal intensity;
obtaining the left side or the right side of the underground power cable at the current test point by comparing the positive value and the negative value of Hx and Hz, and adjusting the position of the test point according to the result until the amplitude of the wave peak is the maximum value in front, back, left and right small areas, wherein the position of the test point at the moment is the position of the cable;
after a certain point of the power cable is positioned by using the magnetic core coil as an antenna, the next point of the power cable is positioned by spanning, and the path of the power cable and the position of a cable joint are obtained.
4. The method as claimed in claim 3, wherein the formula (1) is corrected and the noise θ is added to generate the formula (4) during the magnetic field detection
Establishing electrification characteristic big data of the cable joint by adopting a technology of online monitoring the state of the cable joint, wherein Hp measured each time is represented by a waveform amplitude F, and a current I is represented by a current input into the cable; the left and right quantities Hp and I in equation (4) are measured quantities, and the coefficients of I are unknown constants, only the noise quantity θ is randomly varied.
5. The method for positioning the cable fault positioning device based on the electromagnetic method according to claim 2, wherein the step S2 specifically comprises:
step S21, after the position of each joint in the cable is determined, starting the collection work of the electrification characteristic data of each cable joint, wherein the electrification characteristic data comprises the current and voltage values of the cable, the waveform amplitude F and the width W of each joint and calculating a noise variable theta during each collection;
and S22, sequentially processing each joint on the cable line as follows:
firstly, finding out a record set in the same time period in a database according to the time of a fault monitoring moment, solving the sum of noise variables theta at the moment, and dividing the sum by the number of found records to obtain the mean value theta of the noise variables theta at the moment; and finding out theta with minimum error of corresponding mean value theta min Will contain theta min The recorded waveform amplitudes F and I are taken as the optimum reference quantity F min And I min ；
Next, I (I = I) was calculated from F measured at the joint min *(F min /(F-θ min )))。
And finally, judging between which two joints the fault occurs according to the change magnitude of the current I flowing through each joint.
6. The method as claimed in claim 2, wherein the step voltage is used to calculate the fault on the cable body between two joints in reverse direction by calculating the power value pi = F of each joint ei /F y If the voltage drop from the ith connector to the fault point is measured to be Vi, the voltage drop from the (i + 1) th connector to the fault point is measured to be V i+1 When the step-by-step strategy voltage is stepped from the i joint to the i +1 joint, the voltage value of each step shows a V-shaped trend from high to low and then from low to high, and obviously, a V-shaped valley bottom point is a fault point.
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| CN115389867A (en) * | 2022-10-26 | 2022-11-25 | 北京千尧新能源科技开发有限公司 | Submarine cable state monitoring method and system integrating multiple signals |
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| CN115389867A (en) * | 2022-10-26 | 2022-11-25 | 北京千尧新能源科技开发有限公司 | Submarine cable state monitoring method and system integrating multiple signals |
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