A cable fault location device and method based on electromagnetic method

Abstract

The application relates to a positioning method of a cable fault positioning device based on electromagnetic method, which comprises the following steps: step S1: detecting a metal pipeline through a magnetic field to obtain a cable path; step S2: obtaining electrical characteristic data of each cable joint, and judging which two joints the fault occurs between based on historical data of each cable joint; and step S3: obtaining fault characteristic data to position the fault according to the two joints obtained in step S2. In an offline state, the application can position the position of a fault cable joint by observing characteristic values of the joint through an equal proportionally reduced voltage and current signal, so that the fault point can be further given in detail.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cable fault location, in particular to a cable fault location device and method based on electromagnetic method. BACKGROUND

[0002] Cable is a carrier of power transmission, which is widely used in urban power distribution network and is buried underground without affecting the city appearance, which poses a technical challenge to the treatment of cable faults. Common power cable faults mainly include mechanical damage, reduced insulation performance of power cable insulation layer, overvoltage fault and insulation aging fault, etc. According to statistics, cable accidents account for more than 60% of all electrical accidents.

[0003] The diagnosis of power cable fault mainly includes fault diagnosis, fault distance measurement and fault location. Fault diagnosis is mainly to determine the fault type and identify the severity, which can be determined by measuring the fault resistance of the cable with a multimeter or megohmmeter; fault distance measurement can be measured by using an instrument at one end of the cable to determine the distance of the fault point, and the traveling wave of voltage and current wave propagating at a certain speed in the line is often used, and the return propagation in the line is used to measure the fault distance; fault location is to accurately determine the specific position of the fault point in a certain range, and methods such as acoustic method, acoustic-magnetic synchronous receiving method, audio signal induction method and step voltage method are often used to locate the fault. The traveling wave method uses the reflection of the pulse signal at the fault point to measure the propagation time in the cable, and determines the fault location combined with the signal wave speed, but there are problems such as signal attenuation, noise interference and frequency dispersion, which make it difficult to identify the signal.

[0004] Long-distance cables are connected by joints to connect the factory cables one by one, and the outside of the joint is wrapped with a metal of nearly two meters. If the position of the metal of the joint can be accurately located in advance, it is possible to locate the fault to a section of the factory cable, thereby improving the positioning accuracy. Domestic and foreign researches have been carried out based on cable joint. Y. Norouzi, a German scholar, illustrates through simulation that the accuracy of frequency domain reflection (FDR) method in intermediate joint positioning is higher than that of traditional time domain reflection (TDR) positioning method; Yoshimichi Ohki, a Japanese scholar, proves the superiority of frequency domain reflection method in positioning small defects of cable. Domestic scholars use reflection coefficient spectrum (RCS) and broadband impedance spectrum (BIS) to realize the positioning of weak defects of cable. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a cable fault positioning device and method based on electromagnetic method, which can locate the position of the faulty cable joint by observing the characteristic value of the joint under the condition of off-line state through applying voltage and current signals with equal proportion reduction to the cable, and further give the fault point in detail.

[0006] To achieve the above purpose, the present application adopts the following technical solutions:

[0007] A cable fault positioning device based on electromagnetic method, which wraps two cable heads with a metal pipe at the cable joint, and then wraps the pipe with a cold and hot shrinkable cable accessory, and then wraps the pipe with metal braid and armored ground connection wire, and finally wraps the pipe with a cable explosion-proof box made of glass steel material.

[0008] A positioning method of a cable fault positioning device based on electromagnetic method, comprising the following steps:

[0009] Step S1: detecting the metal pipe through the magnetic field to obtain the cable path;

[0010] Step S2: obtaining the electrification characteristic data of each cable joint, and judging which two joints the fault occurs between based on the historical data of each cable joint;

[0011] Step S3: obtaining the fault characteristic data to locate the fault according to the two joints obtained in step S2.

[0012] Further, the step S1 is specifically:

[0013] According to the Biot-Savart law, the magnetic field of any point P on the ground is measured using a magnetic core coil as an antenna; the horizontal magnetic field intensity is marked as Hx, and the vertical magnetic field intensity is marked as Hz. The antenna measurement data of each direction and each position are processed as follows:

[0014] The magnetic field intensity generated by a single current-carrying infinite cable at point P on the ground is:

[0015]

[0016] In the formula, μ0 is the magnetic permeability of vacuum; I is the current intensity in the cable; r is the distance from the cable to point P;

[0017] The horizontal magnetic field intensity Hx and the vertical magnetic field intensity Hz are respectively:

[0018]

[0019]

[0020] Construct the signal intensity normalized distribution diagram of Hx and |Hz| at different positions, the horizontal axis is the horizontal position on the ground, the projection point of the power cable on the ground is the zero point of the horizontal axis, the left and right directions away from the projection position of the power cable are the negative direction and the positive direction respectively, and the vertical axis is the normalized signal intensity;

[0021] By comparing the positive and negative values of Hx and Hz, it is obtained whether the underground power cable is on the left or right of the current test point, and the position of the test point is adjusted according to the result until the wave peak amplitude is the maximum value in the small area in front and back, left and right. At this time, the position of the test point is the position of the cable;

[0022] After using the magnetic core coil as an antenna to locate a certain point of the power cable, the next point of the power cable is repositioned across the section to obtain the path of the power cable and the position of the cable joint.

[0023] Further, in the process of magnetic field detection, formula (1) is modified, noise amount θ is added, and formula (4) is generated

[0024]

[0025] An online monitoring technology for the state of the cable joint is adopted to establish the electrification feature big data of the cable joint, wherein each measured Hp is represented by a waveform amplitude F, and the current I is represented by the current of the input cable. In formula (4), the left amount Hp and the right amount I are the measured amounts, and the coefficient of I is an unknown constant, and only the noise amount θ is randomly changed.

[0026] Further, the step S2 is specifically:

[0027] Step S21: After determining the positions of the joints in the cable, the collection of the electrification feature data of each cable joint is started, and the electrification feature data includes the current and voltage values of the input cable, the waveform amplitude F and the width W of each joint at each collection time, and the noise variable θ is calculated;

[0028] Step S22: Each joint on the cable line is processed in turn as follows:

[0029] First, the record set of the same period in the database is found according to the time of the fault monitoring moment, the total sum of the noise variable θ at this moment is calculated, and then the noise variable θ at this moment is obtained by dividing the number of record sets found, thereby obtaining the average value θ of the noise variable θ at this moment; and the θ with the smallest error corresponding to the average value θ is found min The waveform amplitude F and I in the record containing θ min are taken as the best reference amount F min and I min ;

[0030] Secondly, the I of the joint is calculated according to the F measured by the joint (I = Imin *(F min / (F-θ min )))。

[0031] Finally, according to the current I flowing through each joint, the fault is determined between which two joints.

[0032] Further, for the fault occurring on the cable body between two joints, the step voltage is used for reverse calculation: first, the power value pi=F ei / F y of each joint is calculated, if the voltage drop from the i-th joint to the fault point is Vi, and the voltage drop from the i+1-th joint to the fault point is V i+1 , when the step voltage is stepped from the i-th joint to the i+1-th joint, the voltage value of each step presents a V-shaped trend from high to low, and then from low to high, obviously, the V-shaped valley point is the fault point.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] 1. Based on the online monitoring of the cable joint state, the present application can accurately give the spatial and electrification characteristic data of the cable joint, and the electromagnetic noise amount of the environment where the joint is located, by using big data analysis technology;

[0035] 2. Based on the electrification characteristic data of the cable joint, by inputting the voltage and current signals which are proportionally reduced, the electrification characteristic data of the non-fault point of the fault cable can be obtained;

[0036] 3. By using the technology of online monitoring of the cable joint state, the present application establishes the electrification characteristics of the cable joint and the electromagnetic noise big data of the environment where the joint is located, and by analyzing the big data, the fault point of the cable can be located, which overcomes the defect that the positioning accuracy of the fault positioning instrument is not accurate due to environmental interference. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a magnetic field distribution diagram around the wire in an embodiment of the present application;

[0038] Figure 2 is a signal intensity normalized distribution diagram of Hx and |Hz| at different positions in an embodiment of the present application;

[0039] Figure 3 is a left and right direction of the pipeline confirmed by Hx*Hz in an embodiment of the present application;

[0040] Figure 4 is an observation system and various strong interference sources in an embodiment of the present application;

[0041] Figure 5is a schematic diagram for locating a fault by cable joint fault feature data in an embodiment of the present application. DETAILED DESCRIPTION

[0042] The present application is further described below in conjunction with the accompanying drawings and embodiments.

[0043] Please refer to Figures 1-5 The present application provides a cable fault locating device based on electromagnetic method, two cable heads are wrapped by a metal pipe at the cable joint, and then wrapped by a cold and hot shrinkable cable accessory, and then wrapped by metal braid and armored ground connection wire, and finally wrapped by a cable explosion-proof box made of glass steel material.

[0044] In the embodiment, a positioning method of the cable fault locating device based on electromagnetic method is also provided, including the following steps:

[0045] Step S1: detecting the metal pipe by the magnetic field to obtain the cable path;

[0046] The power cable has good conductivity, and when the power cable transmits power, it will generate a changing magnetic field around the metal pipeline. According to the Biot-Savart law, the magnetic field of any point P on the ground can be measured by using a magnetic core coil as an antenna. The horizontal magnetic field intensity is marked as Hx, and the vertical magnetic field intensity is marked as Hz. The antenna measurement data of each direction and each position are processed as follows, so that the position and depth of the underground power cable can be determined and predicted.

[0047] The magnetic field intensity generated by a single current-carrying infinite cable at point P on the ground is:

[0048]

[0049] In the formula, μ0 is the magnetic permeability of the medium in vacuum (μ0=4π×10-7H / m); I is the current intensity in the cable; r is the distance from the cable to point P, as shown in Figure 1 ;

[0050] The horizontal magnetic field intensity Hx and the vertical magnetic field intensity Hz are respectively:

[0051]

[0052]

[0053] Figure 2 is a normalized signal intensity distribution diagram of Hx and |Hz| at different positions, 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 negative direction and the positive direction are respectively away from the projection position of the power cable, and the vertical axis is the normalized signal intensity.

[0054] As can be seen from formula (2) formula (3) and Figure 2 Hz at x = 0, that is, the vertical signal is minimum at the top of the cable; meanwhile, Hz itself has a directional difference due to the different observation positions, that is, the vertical components of the magnetic field on the left and right of the cable are in opposite directions at the same time. Since an alternating signal is applied to the power cable, the positive and negative of the vertical component of the magnetic field is not significant, but if the positive and negative of the vertical component of the magnetic field is combined with the direction of the horizontal component at the same time, the current signal collection antenna position relative to the underground power cable can be confirmed, as shown in Figure 3 On the left and right of the power cable, therefore, by comparing the values of Hx and Hz, it can be known whether the underground power cable is on the left or right of the current test point, and the position of the test point is adjusted accordingly until the wave peak amplitude is the maximum in the small area in front and back, left and right, at which time the test point position is the position of the cable.

[0055] After using the magnetic core coil as an antenna to locate a certain point of the power cable, the next point of the power cable can be repositioned across the segment, and the approximate path of the power cable can be found in turn.

[0056] Due to the complexity of the cable joint, the wave amplitude F and width W measured at the special node on the path of the power cable will be very different from those of the cable body, and the positioning accuracy of the cable joint point can be improved by repeated measurements.

[0057] During the magnetic field detection process, electromagnetic interference caused by field source noise, geological noise, communication cables, underground metal pipe network, radio stations, signal towers, and various means of transportation will affect the observation data, seriously polluting the data obtained by the electromagnetic tester, so formula (1) can be modified by adding noise quantity θ to generate formula (4). Therefore, a denoising method is needed to improve the data quality, thereby laying a foundation for subsequent improvement of fault positioning accuracy.

[0058]

[0059] Signal filtering methods are commonly used to eliminate noise quantity θ, such as Hilbert-Huang transform, wavelet analysis, statistical analysis, empirical mode decomposition, etc. in time domain processing.

[0060] In the embodiment, preferably, the electrification characteristics of the cable joint are established by using the technology of online monitoring of the cable joint state, wherein each measured Hp is represented by the waveform amplitude F, and the current I is represented by the current of the input cable. Thus, the left and right quantities of equation (4) are the measured quantities, and the coefficient of I is an unknown constant, and only the noise quantity θ is randomly changed.

[0061] In the embodiment, the observation data is composed of two parts, i.e. the effective signal and the interference noise. The former is the electromagnetic signal after the power cable is electrified, and the interference noise mainly comes from the power frequency interference, stray current, switching of electrical equipment, vehicle noise, etc., and usually has strong regularity. The observation system and various strong interference sources such as Figure 4 : wherein the power frequency interference comes from the high-voltage transmission line near the observation point, mainly in the electric channel, and the power frequency components of the two orthogonal electric channels have good correlation, and the power frequency components may also appear in the magnetic channel occasionally. Although such interference usually has great intensity and is affected by the weather, it is basically a constant, and its influence on fault location can be ignored after big data processing.

[0062] The stray current interference refers to the noise interference caused by the grounding current introduced into the ground when the electrical equipment is suddenly turned on or off or the load suddenly changes, which usually appears in the electric channel signal and the magnetic channel signal of various sampling rates, and usually presents a sinusoidal damped oscillation in the time sequence, and the amplitude is several orders of magnitude of the normal useful signal.

[0063] The electronic equipment switching interference refers to the strong interference caused by the switching of the electronic equipment, which usually appears in the low-frequency electric field channel, and the correlation of the two orthogonal electric channel data time domain waveforms is good, and the amplitude is usually large, which can drown the normal ground electromagnetic useful signal and cause serious deviation of impedance estimation.

[0064] The motor noise interference refers to the interference caused by the motor speed regulation and valve control, which appears as an irregular triangular waveform in the observation data, and generally appears in the magnetic channel.

[0065] The vehicle interference refers to the large-scale high-intensity electromagnetic interference generated when large machinery is working, and the noise intensity is large, and the observation data time domain waveform has obvious jump.

[0066] As can be seen from the above analysis, the stray current, electronic equipment switching, motor noise and vehicle interference are all related to human activities, and the human activities in the city have certain regularity in the long term, so the change rule of the noise quantity θ can be obtained from the Hp values collected every certain time length.

[0067] Preferably, in the embodiment, after the cable joint positions are determined, the instrument is placed at a fixed position each time, then r is a fixed value, in the implementation, it can be measured every half an hour, to obtain Hp and I in formula (4), and the noise variable θ can be calculated therefrom, thereby generating a record (time, Hp, I, θ and waveform amplitude F).

[0068] Step S2: Obtain the electrification characteristic data of each cable joint, and determine between which two joints the fault occurs based on the historical data of each cable joint.

[0069] Step S3: Obtain the fault characteristic data according to the two joints determined in step S2, to locate the fault.

[0070] In the embodiment, after the positions of the joints in the cable are determined, the collection of the electrification characteristic data of each cable joint is started. The electrification characteristic data includes the current and voltage values of the input cable, the waveform amplitude F and width W of each joint at each time of collection, and the noise variable θ calculated according to formula 4.

[0071] When the cable fails, the power supply is cut off to reduce the loss, at this time, an additional test power supply is needed to supply power to the offline cable, to ensure that the magnetic core coil can be used as an antenna to measure each joint of the power cable. The test power supply provided can use a lower power, which makes the measured electrical characteristic quantity of each joint smaller than the normal value, and the electrical characteristic quantity of each joint under the condition of normal operation under the test power needs to be recalculated in proportion, to prepare for the subsequent fault positioning.

[0072] Each joint on the cable line is processed in turn as follows: first, the record set of the same period in the database is found according to the time of the fault monitoring moment, the total noise variable θ of the moment is calculated, and then divided by the number of record sets found, to obtain the average noise variable θ of the moment. Find the θmin with the smallest error corresponding to the average θ, and take the waveform amplitude F and I in the record containing θmin as the best reference quantity Fmin and Imin.

[0073] Secondly, the F measured by the joint is used to calculate I (I = Imin*(Fmin / (F-θmin))).

[0074] Finally, according to the change of the current I flowing through each joint, it is determined between which two joints the fault occurs.

[0075] Preferably, for the fault on the cable body between two joints, the step voltage is used to calculate reversely: first, the power value pi = F ei / F y, if the measured pressure drop from the i th joint to the fault point is Vi, the pressure drop from the i+1 th joint to the fault point is V i+1 When the voltage is stepped from the i th joint to the i+1 th joint, the voltage value of each step presents a V-shaped trend from high to low and then from low to high, and obviously the bottom point of the V-shaped valley is the fault point.

[0076] The above merely describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A location method for a cable fault location device based on electromagnetic methods, characterized in that, Includes the following steps: Step S1: Obtain the cable path by detecting the metal pipe with a magnetic field; Step S2: Obtain the electrical characteristic data of each cable joint, and based on the historical data of each cable joint, determine which two joints the fault occurred between; Step S3: Based on the two connectors determined in step S2, obtain fault feature data to locate the fault; Step S1 specifically involves: According to the Biot-Savart law, the magnetic field at any point P on the ground is measured using a magnetic core coil as an antenna; the horizontal magnetic field strength is marked as Hx, and the vertical magnetic field strength is marked as Hz. The magnetic field strength generated by a single, infinitely long current-carrying cable at point P on the ground is: In the formula: μ0 is the magnetic permeability of the medium in vacuum; I is the current intensity in the cable; r is the distance from the cable to point P; Construct a normalized distribution map of signal strength Hx and |Hz| at different locations. The horizontal axis represents the horizontal position on the ground, with the projection point of the power cable on the ground as the zero point of the horizontal axis. The left and right directions away from the projection position of the power cable are the negative and positive directions, respectively. The vertical axis represents the normalized signal strength. By comparing the positive and negative values ​​of Hx and Hz, we can determine whether the underground power cable is to the left or right of the current test point. Based on this result, we can adjust the position of the test point until the peak amplitude is the maximum value in the small areas in front, behind, left, and right. At this point, the test point position is the position of the cable. After using a magnetic core coil as an antenna to locate a point on a power cable, the system then moves across the cable to locate the next point, thus obtaining the cable path and the location of the cable joint. Step S2 specifically involves: Step S21: After determining the location of each joint in the cable, start collecting electrical characteristic data of each cable joint. The electrical characteristic data includes the current and voltage values ​​of the input cable, the waveform amplitude F and width W of each joint, and the noise variable θ at each collection. Step S22: Perform the following treatments on each joint in the cable line in sequence: First, retrieve the records from the database for the same time period based on the fault monitoring time. Calculate the sum of the noise variables θ at this time and divide it by the number of records retrieved to obtain the mean θ of the noise variables θ at this time. Then, find the θ with the smallest error corresponding to the mean θ. min , will include θ min The waveform amplitudes F and I in the recording are used as the best reference values ​​F min and I min ; Secondly, the current through the flow path I' is calculated from the measured F, where I' = I min *(F min / (F-θ min )); Finally, based on the magnitude of the change in the current I' flowing through each connector, it can be determined which two connectors the fault occurred between.

2. The positioning method of the cable fault location device based on electromagnetic method according to claim 1, characterized in that, During the magnetic field detection process, formula (1) is modified by adding a noise variable θ to generate formula (4): The technology of online monitoring of cable joint status is adopted to establish big data of electrical characteristics of cable joint. The measured Hp is characterized by waveform amplitude F, and the current I is characterized by the current of the input cable. In formula (4), the quantity Hp on the left and the quantity I on the right are the measured quantities, and the coefficient of I is an unknown constant. Only the noise variable θ is randomly changing.

3. A cable fault location device based on electromagnetic method, characterized in that, The cable fault location device is implemented using the location method described in any one of claims 1-2. At the cable joint, two cable heads are wrapped with a metal tube, and then wrapped with heat-shrinkable cable accessories. After that, metal braiding and armored grounding connection wire are wrapped around it, and finally, a cable explosion-proof box made of fiberglass is wrapped around the outer layer.

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