CN115144693B - Cable fault positioning device and method based on electromagnetic method - Google Patents
Cable fault positioning device and method based on electromagnetic methodInfo
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- CN115144693B CN115144693B CN202210711031.2A CN202210711031A CN115144693B CN 115144693 B CN115144693 B CN 115144693B CN 202210711031 A CN202210711031 A CN 202210711031A CN 115144693 B CN115144693 B CN 115144693B
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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
- 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
- G01R31/088—Aspects of digital computing
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- Theoretical Computer Science (AREA)
- Locating Faults (AREA)
Abstract
本发明涉及一种基于电磁法的电缆故障定位装置的定位方法，包括以下步骤：步骤S1:通过磁场探测金属管道，获取电缆路径；步骤S2：获取各电缆接头的电气化特征数据，并基于各电缆接头历史数据，判断故障是发生在哪两个接头之间；步骤S3:根据步骤S2判断得到的两个接头，获取故障特征数据来定位故障。本发明在离线状态下通过对电缆外加等比例缩小的电压和电流信号，来观察接头的特征值，以此来定位故障电缆接头的位置，从而可再进一步详细给出故障点。
This invention relates to a fault location method for a cable fault location device based on electromagnetic methods, comprising the following steps: Step S1: Obtaining the cable path by detecting the metal conduit using a magnetic field; Step S2: Obtaining the electrical characteristic data of each cable joint, and determining, based on historical data of each cable joint, which two joints the fault occurred between; Step S3: Based on the two joints determined in Step S2, obtaining fault characteristic data to locate the fault. This invention, in an offline state, applies proportionally reduced voltage and current signals to the cable to observe the characteristic values of the joints, thereby locating the faulty cable joint and providing further detailed fault location information.
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 for power transmission, are used in a large number in urban distribution networks, and are buried underground without affecting urban capacity, which presents a technical challenge for handling after a cable failure. Common power cable faults mainly comprise mechanical damage faults, insulation performance reduction of an insulating layer of the power cable, overvoltage faults, insulation aging faults and the like, and according to statistics, cable accidents account for more than 60% of all electric accidents.
The diagnosis of the power cable fault mainly includes diagnosis of the fault, ranging, and locating 3 parts. The fault diagnosis is mainly to judge the fault type and the severity, the fault resistance of the cable can be measured by a universal meter and a megameter to judge the fault property of the cable, the fault distance measurement can be used for measuring the distance of a fault point by an instrument at one end of the cable, the fault distance measurement is usually carried out by adopting traveling waves of voltage and current waves which propagate in a circuit at a certain speed and utilizing the traveling waves of the voltage and current waves in the circuit to measure the fault distance, and the fault positioning is used for accurately measuring the specific position of the fault point in a certain range according to the distance measurement result and is usually carried out by adopting a sound measurement method, an acousto-magnetic synchronous receiving method, an audio signal induction method, a step voltage method and the like. The traveling wave method utilizes the reflection of pulse signals at fault points to measure the travel time of the signals in the cable and combines the wave speed of the signals to determine the fault position, but the problems of signal attenuation, noise interference, frequency dispersion and the like exist, so that the identification of the signals is difficult.
The long-distance cable adopts the joint to connect one section of the outgoing cable, and the joint is wrapped by metal of nearly two meters, so that if the positions of the joint metals can be accurately positioned in advance, faults can be positioned in one section of the outgoing cable, and the positioning accuracy is improved. Research based on the cable connector is developed at home and abroad, the German scholars Y.Norouz i demonstrate the accuracy of the frequency domain reflection (frequency domai n ref l ectometry, FDR) method in the middle connector positioning compared with the traditional time domain reflection (t ime domai n ref l ectometry, TDR) positioning method through simulation, and Japanese scholars Yosh imi ch i Ohki prove the superiority of the frequency domain reflection method in positioning the small defects of the cable. The domestic scholars use the reflectance spectrum (ref l ect ion coeffic ient spectrum, RCS) and the broadband impedance spectrum (broadband impedance spectrum, BIS) to realize the positioning of the 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 locating device and method based on an electromagnetic method, in which a voltage and current signal with equal scale reduced is applied to a cable in an off-line state to observe a characteristic value of a joint, so as to locate a position of a faulty cable joint, and further to give a fault point in detail.
In order to achieve the above purpose, the invention adopts the following technical scheme:
A cable fault positioning device based on electromagnetic method is characterized in that two cable heads are wrapped at a cable joint through a metal pipe, after being wrapped by a cold-heat-shrinkable cable accessory, a metal braid and an armored grounding connecting wire are wound, and finally an outer layer is further wrapped with a cable explosion-proof box formed by processing glass fiber reinforced plastic materials.
A positioning method of a cable fault positioning device based on an electromagnetic method comprises the following steps:
step S1, detecting a metal pipeline through a magnetic field to obtain a cable path;
S2, acquiring electrification characteristic data of each cable connector, and judging which two connectors the fault occurs between based on historical data of each cable connector;
And step S3, acquiring fault characteristic data to locate faults according to the two joints obtained in the step S2.
Further, the step S1 specifically includes:
Measuring the magnetic field at any point P on the ground by using a magnetic core coil as an antenna according to the Biao-Saval law, 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 of each direction and each position as follows
The magnetic field intensity generated by a single current-carrying infinite length cable at the P point of the ground is as follows:
wherein mu 0 is the magnetic permeability of medium in vacuum, the current intensity in the cable I, r is the distance from the cable to the point P;
The horizontal magnetic field strength Hx and the vertical magnetic field strength Hz are each:
constructing signal intensity normalization distribution diagrams of Hx and/Hz at different positions, wherein the horizontal axis is the ground horizontal position, the projection point of the power cable on the ground is the horizontal axis zero point, the projection positions far left and right from the power cable are respectively the negative direction and the positive direction, and the vertical axis is the normalized signal intensity;
obtaining whether the underground power cable is on the left side or the right side of the current test point through positive and negative comparison of the values of Hx and Hz, and adjusting the positions of the test points according to the results until the peak amplitude is the maximum value in the front-back small area, the left-right small area and the right-left small area, wherein the positions of the test points at the moment are the positions of the cable;
after a point of the power cable is positioned using the magnetic core coil as an antenna, the next point of the power cable is then repositioned across the segment, and the path and cable joint position of the power cable are obtained.
Further, in the process of detecting the magnetic field, the formula (1) is modified, and the noise amount θ is added to generate the formula (4)
The method comprises the steps of establishing large data of electrification characteristics of a cable joint by adopting a technology of on-line monitoring of the state of the cable joint, wherein each time measured Hp is characterized by waveform amplitude F, current I is characterized by current of an input cable, the left-hand quantity Hp and the right-hand quantity I of an equation in the formula (4) are measured quantities, the coefficient of I is an unknown constant, and only noise quantity theta is randomly changed.
Further, the step S2 specifically includes:
S21, after the positions of all joints in the cable are determined, starting the collection work of the electrification characteristic data of all the cable joints, wherein the electrification characteristic data comprises current and voltage values of the input cable, waveform amplitude values F and width W of all the joints and calculating noise variables theta when the electrification characteristic data are collected each time;
step S22, each joint on the cable line is sequentially processed as follows:
Firstly, searching a record set of the same time period in a database according to the time of fault monitoring time, obtaining the sum of noise variables theta at the time, dividing the sum by the number of the searched records to obtain the average value theta of the noise variables theta at the time, and finding out the theta min with the minimum error corresponding to the average value theta, wherein waveform amplitude values F and I in records containing theta min are used as optimal reference values F min and I min;
Second, the F measured from the linker calculates its I (i=i min*(Fmin/(F-θmin)).
Finally, judging the fault between the two connectors according to the change of the current I flowing through each connector.
Further, for faults occurring on the cable body between two connectors, step voltage is adopted to calculate reversely, namely, the power value pi=f ei/Fy of each connector is calculated first, 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 i connector steps over the strategy voltage to the (i+1) th 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 the fault point.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention is based on-line monitoring of the state of the cable joint, and can accurately give out 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. based on the electrification characteristic data of the cable connector, the invention can obtain the electrification characteristic data of the fault cable non-fault point by inputting voltage and current signals with equal proportion reduction;
3. The invention establishes the electrified characteristic of the cable joint and the electromagnetic noise big data of the environment where the cable joint is positioned by adopting the technology of on-line monitoring the state of the cable joint, analyzes the big data, can locate the fault point of the cable, and overcomes the defect of inaccurate positioning precision caused by environmental interference of a fault positioning instrument.
Drawings
FIG. 1 is a diagram illustrating a magnetic field distribution around a conductive line according to an embodiment of the present invention;
FIG. 2 is a graph showing normalized distribution of signal strength at different locations for Hx, |Hz|, in accordance with one embodiment of the present invention;
FIG. 3 is a side-to-side view of an Hx Hz acknowledge line in accordance with an embodiment of the present invention;
FIG. 4 is a diagram of an observation system and various types of strong interferers in an embodiment of the present invention;
FIG. 5 is a schematic diagram of locating faults from cable joint fault signature data in an embodiment of the present invention.
Detailed Description
The invention will be further described with reference to the accompanying drawings and examples.
Referring to fig. 1-5, the invention provides a cable fault positioning device based on an electromagnetic method, wherein two cable heads are wrapped at a cable joint through a metal pipe, and after being wrapped by a cold-heat-shrinkable cable accessory, a metal braid and an armored grounding connecting wire are wound, and finally, an outer layer is further wrapped with a cable explosion-proof box processed by glass fiber reinforced plastic materials.
In this embodiment, there is also provided a positioning method of a cable fault positioning device based on an electromagnetic method, including the following steps:
step S1, detecting a metal pipeline through a magnetic field to obtain a cable path;
the power cable has good electrical conductivity and when the power cable is transmitting electricity, it will generate a varying magnetic field around the metal pipeline, which magnetic field is measured according to the biot-savart law, at any point P on the ground, usually using a magnetic core coil as an antenna. The position and depth of the underground power cable can be judged and predicted to a certain extent by marking the magnetic field intensity in the horizontal direction as Hx and marking the magnetic field intensity in the vertical direction as Hz and processing the antenna measurement data of each direction and each position as follows.
The magnetic field intensity generated by a single current-carrying infinite length cable at the P point of the ground is as follows:
Wherein mu 0 is the permeability of the medium in vacuum (mu 0=4pi×10-7H/m), the current intensity in the I cable, r is the distance from the cable to the P point, as shown in figure 1;
the obtainable horizontal magnetic field strength Hx and vertical magnetic field strength Hz are each:
fig. 2 is a normalized distribution diagram of signal intensity of Hx, |hz| at different positions, the horizontal axis is the ground horizontal position, the projection point of the power cable on the ground is the horizontal axis zero point, the projection positions far from the power cable left and right are respectively the negative direction and the positive direction, and the vertical axis is the normalized signal intensity.
From equation (2) equation (3) and fig. 2, it can be seen that Hx obtains the maximum value when x=0, that is, the ground intensity of the horizontal magnetic field signal is maximum right above the cable, the signal gradually decreases with the position deviation, that is, the minimum value 0 when i Hz is x=0, that is, the vertical signal is minimum right above the cable, and that the direction difference exists between Hz itself due to the difference of the observation positions, that is, the vertical components of the magnetic field on the left and right of the cable are opposite at the same moment. Since the ac signal is applied to the power cable, only the positive and negative significance of the vertical component of the magnetic field is not great, but if the positive and negative of the vertical component of the magnetic field are considered in combination with the direction of the horizontal component at the same time, the position of the current signal acquisition antenna with respect to the underground power cable can be confirmed, as shown in fig. 3. The position of the test point is adjusted by comparing the values of Hx and Hz to the left and right of the power cable, so that the position of the test point is the position of the cable.
After locating a point of the power cable using the magnetic core coil as an antenna, the next point of the power cable can be relocated across the segment, which in turn can find the approximate path of the power cable.
Because of the complexity of the cable joint manufacture, 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 the cable body, and the positioning precision of the cable joint point can be improved by repeatedly measuring the waveform amplitude F and the waveform width W.
In the process of magnetic field detection, 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 observed data, and data obtained by an electromagnetic tester are seriously polluted, so that the formula (1) can be modified, noise quantity theta is added, and the formula (4) is generated. Therefore, a denoising method is required to improve the data quality, so that a foundation is laid for improving the fault location precision subsequently.
Signal filtering methods are often employed to eliminate the noise amount θ, such as Hilbert-Huang transform, wavelet analysis, statistical analysis, empirical mode decomposition, etc., in time domain processing.
In this embodiment, the electrical characteristic data of the cable joint is preferably established by using a technique of on-line monitoring of the state of the cable joint, wherein each measured Hp is characterized by a waveform amplitude F and the current I is characterized by the current of the input cable. Thus, the left and right amounts Hp and I of equation (4) are measured amounts, and the coefficient of I is an unknown constant, and only the noise amount θ is randomly varied.
In this embodiment, the observation data is composed of two parts, namely an effective signal and interference noise, wherein the former is an electromagnetic signal after the power cable is electrified, the interference noise mainly comes from power frequency interference, scattered current, a switch of an electric device, vehicle noise and the like, the regularity is strong, the observation system and various strong interference sources are as shown in fig. 4, the power frequency interference comes from a high-voltage transmission line near an observation point and is mainly reflected in an electric channel, the power frequency components of two orthogonal electric channels have good correlation, and the power frequency components occasionally appear in the magnetic track. Such disturbances, while typically strong and weather-affected, are substantially constant and have negligible impact on fault location after the big data processing.
The free-flowing current interference refers to noise interference caused by the fact that when the electric equipment suddenly turns on, turns off or suddenly changes in load, the ground current is led into the ground, the noise interference is usually generated in channel signals and track signals with various sampling rates, and the noise interference is usually in sine damping oscillation on a time sequence, and the amplitude of the noise interference is several orders of magnitude of normal useful signals.
The electronic equipment switch interference refers to strong interference caused by instantaneous opening and closing of the electronic equipment switch, noise of the type usually appears in an electric field channel of a medium-low frequency band, the correlation of two orthogonal electric channel data time domain waveforms is good, the amplitude of the waveform is usually large, normal magnetotelluric useful signals can be submerged, and serious deviation of impedance estimation is caused.
Motor noise disturbances are disturbances generated by motor speed regulation and valve control, which appear as irregular triangular waveforms in the observed data, typically occurring in the magnetic tunnel.
The vehicle interference refers to large-scale high-intensity electromagnetic interference generated when large-scale machinery works, the noise intensity is large, and the time domain waveform of the observed data has obvious jump.
From the above analysis, it can be seen that the free-flowing current, the electronic device switch, the motor noise and the vehicle interference are all related to the activities of the people, and the activities of the people in the city are regular in the long term, so that the change rule of the noise quantity theta can be obtained from the Hp values acquired at regular intervals.
Preferably, in this embodiment, after the cable joint position is determined, r is a fixed value each time the instrument is placed in a fixed position, and can be measured once every other hour in the implementation to obtain Hp and I in equation (4), and the noise variable θ can be calculated therefrom, so as to generate a record (time, hp, I, θ and waveform amplitude F).
S2, acquiring electrification characteristic data of each cable connector, and judging which two connectors the fault occurs between based on historical data of each cable connector;
And step S3, acquiring fault characteristic data to locate faults according to the two joints obtained in the step S2.
In this embodiment, after the location of each splice in the cable is determined, a collection of electrical characteristic data for each cable splice is initiated. These electrification characteristic data include the current and voltage values of the input cable, waveform amplitude F and width W of each joint at each acquisition, and noise variable θ is calculated according to equation 4.
When the cable fails, the power supply is cut off to reduce loss, and an additional test power supply is needed to supply power to the off-line cable so as to ensure that the magnetic core coil can be used as an antenna to measure all joints 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 the test power is required to be recalculated according to an equal proportion so as to prepare for positioning faults later.
And sequentially carrying out the following processing on each joint on the cable line, namely firstly searching out a record set of the same time period in the database according to the time of the fault monitoring moment, solving the sum of noise variables theta at the moment, and dividing the sum by the number of the searched records to obtain the average value theta of the noise variables theta at the moment. And finding out the θmin with the minimum corresponding average value θ error, and taking waveform amplitudes F and I in the record containing the θmin as optimal reference quantities Fmin and Imin.
Next, from the measured F of this linker, its I is calculated (i=imin (Fmin/(F- θmin))).
Finally, judging the fault between the two connectors according to the change of the current I flowing through each connector.
Preferably, for faults occurring on the cable body between two connectors, step voltage is adopted to calculate reversely, namely, the power value pi=F ei/Fy of each connector is calculated first, 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 i connector steps over the strategy voltage to the (i+1) th 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 the fault point.
The foregoing description is only of the preferred embodiments of the invention, and all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (3)
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| CN115389867B (en) * | 2022-10-26 | 2023-02-10 | 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 |
| CN116087315B (en) * | 2023-02-15 | 2026-01-02 | 西南科技大学 | A Non-destructive Testing System and Method for Cable Defects Based on Electromagnetic Induction |
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| CN208127453U (en) * | 2018-03-09 | 2018-11-20 | 东阳市光明电力建设有限公司 | A kind of cable connection structure convenient for detection |
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