Fixed underground three-phase cable positioning device and method

Abstract

The present invention discloses a fixed underground three-phase cable positioning device and method, which utilizes multiple three-axis magnetic sensors to rotate in the horizontal direction, stops when the horizontal magnetic field amplitude reaches a minimum, and completes the rough positioning of the cable; takes the average value of the three-axis magnetic field amplitude as the magnetic field measurement value of the measuring point, and calculates the position of the pipeline in the reference coordinate system based on the inverse proportion between the magnetic field measurement value of the measuring point and the square of the distance between the measuring point and the pipeline, and combines the measuring point coordinates to solve the position of the pipeline in the reference coordinate system, including the direction and buried depth information. It can realize the rapid detection of underground metal pipelines without moving the detection device as a whole, and improve the detection accuracy.

Description

Technical Field

[0001] The invention belongs to the field of underground three-phase cable detection, and in particular relates to a fixed underground three-phase cable positioning device and method. Background Art

[0002] With the rapid economic development, three-phase cables play an increasingly important role in urban power transmission systems. Cables built and operated in the early stage face problems of unknown location, unknown buried depth, and unknown direction due to various reasons. Cable damage caused by urban construction often occurs. Therefore, it is necessary to quickly detect and locate buried three-phase cables. Only after the cable location is determined can construction work be carried out safely and efficiently. Among them, high-precision positioning of underground three-phase cables by detecting ground magnetic field information in a trenchless manner has always been the focus and difficulty of detection.

[0003] In the related technology, adding audio signal excitation after the cable is powered off is a method widely used in China: for example, an audio current signal is added to the metal sheath layer of the cable, and the magnetic field signal generated by the audio current signal is received on the ground to solve the cable position. However, some cable pipelines cannot be powered off, and the use of this method is very limited. For another example, the transient electromagnetic method is used to perform non-excavation detection of cables. A pulse current signal is emitted through the transmitting coil, and a secondary eddy current magnetic field signal is generated in the cable by the principle of electromagnetic induction. The position of the buried cable is obtained by detecting the secondary field information. However, this method is complex to solve, and usually requires comprehensive solution of information from multiple survey lines, which takes a long time. Summary of the invention

[0004] The object of the present invention is to provide a fixed underground three-phase cable positioning device and method, which can quickly solve the position of the underground three-phase cable without obtaining multiple measurement line data, and detect when the cable is operating normally.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A fixed underground three-phase cable positioning device, comprising:

[0007] A support frame, wherein five rotatable horizontal planes are installed on the support frame, a single magnetic sensor box is arranged on the horizontal plane, and a rotating shaft of a stepper motor is connected below the horizontal plane;

[0008] A numerical calculation unit, used for acquiring the magnetic field information transmitted by the magnetic sensor box and performing iterative calculation to obtain the position information of the three-phase cable;

[0009] The magnetic sensor box comprises:

[0010] Three-axis magnetic sensor, including high-precision magnetic measurement chip and high-precision ADC module, used to collect and transmit three-axis magnetic field data;

[0011] A signal processing control unit is connected to the three-axis magnetic sensor and the stepper motor respectively, and is used to process the magnetic field signal measured by the three-axis magnetic sensor and control the rotation of the stepper motor;

[0012] The signal transmission unit is connected to the signal processing control unit and is used to send the magnetic field amplitude information to the numerical calculation unit for iterative calculation.

[0013] Furthermore, the signal processing control unit is specifically used for:

[0014] Obtain the x-axis AC magnetic field component of the local coordinate system measured by the three-axis magnetic sensor, and solve the AC magnetic field amplitude to obtain the magnetic field amplitude And the angle θ of the three-axis magnetic sensor rotation at this time i ; Wherein, the local coordinate system is centered on the current three-axis magnetic sensor;

[0015] And, control the stepper motor to rotate a fixed angle Δθ i , the rotation angle is updated to θ i +Δθ i , until the rotation angle reaches 180°;

[0016] And, find the minimum value of the magnetic field amplitude on the x-axis and get the angle corresponding to the minimum value of the magnetic field

[0017] And, communicate with other magnetic sensor boxes to transmit angle data and calculate the average angle of the five magnetic sensor boxes Control the stepper motor to rotate in the opposite direction to θ min At the three-axis AC magnetic field components measured by the three-axis magnetic sensor, the AC amplitudes are calculated and obtained. Calculate the average value to get mag i , and sent to the numerical calculation unit.

[0018] Furthermore, the numerical calculation unit is specifically used for:

[0019] Calculate and record the coordinates (x1, y1, z1) to (x5, y5, z5) of the magnetic measuring points corresponding to the five magnetic sensor boxes in the reference coordinate system; wherein the reference coordinate system is the longitude and latitude of the fixed underground three-phase cable locating device in GPS positioning;

[0020] And, communicate with the signal processing control unit, obtain the magnetic field amplitude data mag1~mag5 of the five magnetic measurement points calculated by the signal processing control unit, establish a numerical solution model; obtain the three-axis magnetic sensor angle data θ min , bring in the initial iteration point for iterative solution, and obtain the location information of the three-phase cable.

[0021] Furthermore, the numerical solution model is as follows:

[0022]

[0023] Among them, E, a, b, c, and d are coefficients to be solved.

[0024] Furthermore, the initial iteration point is:

[0025]

[0026] A fixed underground three-phase cable positioning method, based on the above-mentioned fixed underground three-phase cable positioning device, comprises the following steps:

[0027] S1: Obtain the longitude and latitude of the fixed underground three-phase cable positioning device as the reference coordinate system, obtain the coordinates of the five three-axis magnetic sensors in the reference coordinate system, which are (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), (x4, y4, z4), (x5, y5, z5), and establish a local coordinate system centered on the three-axis magnetic sensor;

[0028] S2: The three-axis magnetic sensor rotates 180° step by step with the set angle as the step angle, collects the magnetic field data in the X-axis direction of the local coordinate system, and obtains the change of the AC signal amplitude with the angle

[0029] S3: Seek The angle corresponding to the minimum amplitude is averaged to obtain θ min , the angle θ min The corresponding direction is the direction of the three-phase cable in the reference coordinate system;

[0030] S4: Rotate the five three-axis magnetic sensors to θ min , perform three-axis magnetic field value measurement, and calculate a total of 15 magnetic field amplitude data The average value is calculated to obtain the synthetic magnetic field amplitude of the magnetic measuring point;

[0031] S5: Assume that the straight line equation of the three-phase cable in the reference coordinate system is: Establish a numerical solution model;

[0032] S6: Set the initial iteration point of numerical calculation;

[0033] S7: Iteratively solve and obtain the buried depth d of the pipeline in the reference coordinate system, and the direction equation of the three-phase cable is ax+by+c=0.

[0034] Furthermore, in step S4, the average value is calculated to obtain the synthetic magnetic field amplitude of the magnetic measuring point:

[0035]

[0036] Among them, (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), (x4, y4, z4), and (x5, y5, z5) are the coordinates of the five three-axis magnetic sensors in the reference coordinate system.

[0037] Furthermore, in step S5, a numerical solution model is established as follows:

[0038]

[0039] Among them, E, a, b, c, d are the coefficients to be solved.

[0040] Furthermore, in step S6, the initial iteration point of the numerical calculation is set to:

[0041]

[0042] Furthermore, during the rotation of the three-axis magnetic sensor, the reference coordinate system remains stationary, and the local coordinate system rotates around its own Z axis.

[0043] The beneficial effects of the present invention are as follows:

[0044] The fixed underground three-phase cable positioning method provided by the present invention utilizes each three-axis magnetic sensor to rotate in the horizontal direction, stops when the horizontal magnetic field amplitude reaches a minimum, and completes the rough positioning of the cable; takes the average value of the three-axis magnetic field amplitude as the magnetic field measurement value of the measuring point, and calculates the position of the pipeline in the reference coordinate system, including the direction and buried depth information, based on the inverse proportion between the magnetic field measurement value of the measuring point and the square of the distance between the measuring point and the pipeline, combined with the measuring point coordinates. It can realize the rapid detection of underground metal pipelines without moving the detection device as a whole, and improve the detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0046] Figure 1 This is a flow chart of a fixed underground three-phase cable positioning method according to an embodiment of the present invention;

[0047] Figure 2 This is a schematic structural diagram of a fixed underground three-phase cable positioning device according to an embodiment of the present invention;

[0048] Figure 3 This is a system structure diagram of the fixed underground three-phase cable positioning device of the present invention;

[0049] Among them, 1 is the horizontal plane and 2 is the stepper motor. DETAILED DESCRIPTION

[0050] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0051] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit exemplary embodiments according to the present invention.

[0052] Example 1

[0053] like Figure 2 and Figure 3 As shown, Embodiment 1 of the present invention provides a fixed underground three-phase cable positioning device, comprising:

[0054] A support frame is placed on the ground, and five rotatable horizontal planes 1 are installed on the support frame. A single magnetic sensor box is arranged on the horizontal plane 1, and the rotating shaft of the stepper motor 2 is connected below the horizontal plane 1. Specifically, the support frame includes two horizontal circular panels, one above and one below, and a support column connecting the two circular panels. Four magnetic sensor boxes are evenly distributed on the bottom circular panel along the circumference of the circular panel, and one magnetic sensor box is located at the center of the upper circular panel.

[0055] The numerical calculation unit is used to collect and obtain the magnetic field information transmitted by the magnetic sensor box and perform iterative calculations to obtain the position information of the three-phase cable; the returned magnetic field information includes mag i ,θ min , where θ min Used to generate the initial iteration point, mag i The parameters are known as iteration expressions.

[0056] The magnetic sensor box includes:

[0057] The three-axis magnetic sensor includes a high-precision magnetic measurement chip and a high-precision ADC module. The high-precision magnetic measurement chip collects three-axis magnetic field data, and the high-precision ADC module transmits the three-axis magnetic field data.

[0058] The signal processing control unit is connected to the three-axis magnetic sensor and the stepper motor 2 respectively, and is used to process the magnetic field signal measured by the three-axis magnetic sensor and control the stepper motor 2 to rotate.

[0059] The signal transmission unit is connected to the signal processing control unit and is used to send the magnetic field amplitude information to the numerical calculation unit for iterative calculation.

[0060] As a specific embodiment of the present invention, the signal processing control unit is specifically used for:

[0061] Obtain the x-axis AC magnetic field component of the local coordinate system measured by the three-axis magnetic sensor, and solve the AC magnetic field amplitude to obtain the magnetic field amplitude B xi And the angle θ of the three-axis magnetic sensor rotation at this time i ; Wherein, the local coordinate system is centered on the current three-axis magnetic sensor;

[0062] And, send pulses to control the stepper motor 2 to rotate a fixed angle Δθ i , the rotation angle is updated to θ i +Δθ i , repeat the first step until the rotation angle reaches 180°;

[0063] And, find the minimum value of the magnetic field amplitude on the x-axis and get the angle corresponding to the minimum value of the magnetic field

[0064] And, communicate with other magnetic sensor boxes to transmit angle data and calculate the average angle of the five magnetic sensor boxes Control stepper motor 2 to rotate in the opposite direction to θ min At the three-axis AC magnetic field components measured by the three-axis magnetic sensor, the AC amplitudes are calculated and obtained. Calculate the average value to get mag i , and sent to the numerical calculation unit.

[0065] It should be noted that the xy plane of the reference coordinate system is a horizontal plane, the direction perpendicular to the horizontal plane is the z direction, the coordinate system satisfies the right-hand rule, four of the five three-axis magnetic sensors are located on the positive x-axis, negative x-axis, positive y-axis, and negative y-axis of the reference coordinate system, and the fifth is located on the positive z-axis, and the five sensors are equidistant from the origin. The three-axis direction of the local coordinate system centered on the three-axis magnetic sensor is the positive direction of the three-axis magnetic field measurement of the three-axis magnetic sensor chip. The initial direction of the local coordinate system is the same as the three-axis direction of the reference coordinate system. The three-axis direction of the local coordinate system rotates with the rotation of the positive direction of the magnetic field measured by the three-axis magnetic sensor chip. A stepper motor is used to control the horizontal rotation of the three-axis magnetic sensor and record the rotation angle. The three-axis magnetic sensor is used to measure the amplitude of the AC magnetic field in the x direction of the local coordinate system during the rotation and record it. Plot the curve of the magnetic field amplitude changing with the rotation angle, find the minimum point, record the rotation angle corresponding to the minimum point, and calculate the average value as the fixed measurement angle θ of the sensor. min During the rotation of the three-axis magnetic sensor, the device as a whole remains stationary, that is, the reference coordinate system remains stationary, and the local coordinate system rotates around its own Z axis.

[0066] As a specific embodiment of the present invention, the numerical calculation unit is specifically used for:

[0067] Through the frame geometry design parameters, the coordinates (x1, y1, z1) to (x5, y5, z5) of the magnetic measuring points corresponding to the five magnetic sensor boxes in the reference coordinate system are calculated and recorded; wherein the reference coordinate system is the longitude and latitude of the fixed underground three-phase cable locating device in GPS positioning;

[0068] And, communicating with the signal processing control unit through the wireless module, obtaining the magnetic field amplitude data mag1-mag5 of the five magnetic measuring points calculated by the signal processing control unit, and establishing a numerical solution model;

[0069]

[0070] Among them, E, a, b, c, and d are coefficients to be solved.

[0071] Communicate with the signal processing control unit through the wireless module to obtain the angle data θ of the three-axis magnetic sensor min , bring in the initial iteration point for iterative solution, and obtain the location information of the three-phase cable. The initial iteration point is:

[0072]

[0073] It should be noted that the initial iteration point is a set of parameters that satisfy the equation of measurement point 1, the initial straight line direction is the estimated approximate pipeline direction, that is, the magnetic data measurement direction, and the initial burial depth is considered to be 1m.

[0074] The plane where the three-phase cable is located is set as z = d, and the straight line where the pipeline is located is set as a straight line on the plane. The general formula is ax + by + c = 0. The magnetic measurement point (x i ,y i ,z i ) to the pipeline straight line is expressed as:

[0075]

[0076] Embodiment 1 of the present invention proposes a fixed underground three-phase cable positioning device, which utilizes the weak magnetic field generated by the current in the three-phase cable to detect the minimum value of the horizontal magnetic field amplitude, thereby obtaining the approximate direction of the three-phase cable; through the characteristic that the magnetic field amplitude generated by the underground three-phase cable is inversely proportional to the square of the distance from the detection point to the cable, the magnetic data measured by five magnetic measuring points are iteratively solved for the precise position, burial depth and direction of the cable, thereby realizing the rapid positioning of the underground three-phase cable without moving the device.

[0077] Example 2

[0078] like Figure 1As shown, a fixed underground three-phase cable positioning method, based on the fixed underground three-phase cable positioning device of Example 1, can quickly solve the underground three-phase cable position when the detection device is fixed without obtaining multiple measurement line data, and detect when the cable is operating normally, including the following steps:

[0079] S1: Define the reference coordinate system, obtain the longitude and latitude of the reference coordinate system of the fixed underground three-phase cable locating device through GPS calibration, obtain the longitude and latitude of the fixed underground three-phase cable locating device as the reference coordinate system, and obtain the coordinates of the five three-axis magnetic sensors in the reference coordinate system, which are (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), (x4, y4, z4), (x5, y5, z5), and establish a local coordinate system centered on the three-axis magnetic sensor.

[0080] It should be noted that the xy plane of the reference coordinate system is a horizontal plane, the direction perpendicular to the horizontal plane is the z direction, the coordinate system satisfies the right-hand rule, four of the five three-axis magnetic sensors are located on the positive x-axis, negative x-axis, positive y-axis, and negative y-axis of the reference coordinate system, and the fifth is located on the positive z-axis, and the five three-axis magnetic sensors are equidistant from the origin. The three-axis direction of the local coordinate system centered on the three-axis magnetic sensor is the positive direction of the three-axis magnetic field measurement of the three-axis magnetic sensor chip, the initial direction of the local coordinate system is the same as the three-axis direction of the reference coordinate system, and the three-axis direction of the local coordinate system rotates with the rotation of the positive direction of the magnetic field measured by the three-axis magnetic sensor chip.

[0081] S2: The three-axis magnetic sensor rotates 180° step by step with the set angle as the step angle, collects the magnetic field data in the X-axis direction of the local coordinate system, and obtains the change of the AC signal amplitude with the angle

[0082] In step S2, the set angle may be 1°, 2°, 0.5°, etc.

[0083] In this step S2, a stepper motor is used to control the three-axis magnetic sensor to rotate horizontally and record the rotation angle, and the three-axis magnetic sensor is used to measure and record the amplitude of the AC magnetic field in the x direction of the local coordinate system during the rotation.

[0084] It should be noted that during the rotation of the three-axis magnetic sensor, the support frame remains stationary, that is, the reference coordinate system remains stationary, and the local coordinate system rotates around its own Z axis.

[0085] S3: Seek The angle corresponding to the minimum amplitude is averaged to obtain θ min , the angle θ min The corresponding direction is the running direction of the three-phase cable in the reference coordinate system.

[0086] In step S3, the magnetic field amplitude is plotted against the rotation angle to find the minimum point, record the rotation angle corresponding to the minimum point and calculate the average value as the fixed measurement angle θ of the sensor. min .

[0087] S4: Rotate the five three-axis magnetic sensors to θ min , perform three-axis magnetic field value measurement, and calculate a total of 15 magnetic field amplitude data The average value is calculated to obtain the synthetic magnetic field amplitude of the magnetic measuring point;

[0088] In step S4, the average value is calculated to obtain the synthetic magnetic field amplitude of the magnetic measuring point:

[0089]

[0090] Among them, (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), (x4, y4, z4), and (x5, y5, z5) are the coordinates of the five three-axis magnetic sensors in the reference coordinate system.

[0091] S5: Assume that the straight line equation of the three-phase cable in the reference coordinate system is: Establish a numerical solution model;

[0092] In this step S5, a numerical solution model is established as follows:

[0093]

[0094] Among them, E, a, b, c, d are the coefficients to be solved.

[0095] S6: Set the initial iteration point of numerical calculation;

[0096] In step S6, the initial iteration point of the numerical calculation is set to:

[0097]

[0098] It should be noted that the initial iteration point is a set of parameters that satisfy the equation of measurement point 1, the initial straight line direction is the estimated approximate pipeline direction, that is, the magnetic data measurement direction, and the initial burial depth is considered to be 1m.

[0099] S7: Iteratively solve and obtain the buried depth d of the pipeline in the reference coordinate system, and the direction equation of the three-phase cable is ax+by+c=0.

[0100] Specifically, the plane where the three-phase cable is located is set as z = d, and the straight line where the three-phase cable is located is set as a straight line on the plane. The general formula is ax + by + c = 0. The magnetic measurement point (x i ,y i ,z i ) to the pipeline straight line is expressed as:

[0101]

[0102] For example, in an embodiment of the present invention, the coordinates of the magnetic measuring points are selected as: (-1,0,0), (1,0,0), (0,1,0), (0,-1,0), (0,0,1), the unit is m, the underground cable is buried 2m deep, the horizontal distance from the center point of the device is 2.4m, the cable inclination is 53.13°, and the pipeline direction equation measured according to this method is 4.05x+2.94y+12.00=0, the pipeline is buried 1.96m deep, the horizontal position relative error is 0.09%, the burial depth relative error is 2%, and the positioning effect is good.

[0103] The fixed underground three-phase cable positioning method of embodiment 2 of the present invention utilizes the weak magnetic field generated by the current in the three-phase cable to detect the minimum value of the horizontal magnetic field amplitude, thereby obtaining the approximate direction of the three-phase cable; through the characteristic that the magnetic field amplitude generated by the underground three-phase cable is inversely proportional to the square of the distance from the detection point to the cable, the magnetic data measured by five magnetic measuring points are iteratively solved for the precise buried depth and direction of the cable, thereby realizing the rapid positioning of the underground three-phase cable without moving the device.

[0104] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

Claims

1. A fixed underground three-phase cable positioning device, characterized in that: include: A support frame, wherein five rotatable horizontal planes are installed on the support frame, a magnetic sensor box is arranged on the horizontal plane, and a rotating shaft of a stepper motor is connected below the horizontal plane; A numerical calculation unit, used for acquiring the magnetic field information transmitted by the magnetic sensor box and performing iterative calculation to obtain the position information of the three-phase cable; The magnetic sensor box comprises: A three-axis magnetic sensor for collecting and transmitting three-axis magnetic field data; A signal processing control unit is connected to the three-axis magnetic sensor and the stepper motor respectively, and is used to process the magnetic field signal measured by the three-axis magnetic sensor and control the rotation of the stepper motor; A signal transmission unit, connected to the signal processing control unit, for sending magnetic field amplitude information to the numerical calculation unit; The signal processing control unit is specifically used for: Obtain the x-axis AC magnetic field component of the local coordinate system measured by the three-axis magnetic sensor, and solve the AC magnetic field amplitude to obtain the magnetic field amplitude B xi And the angle θ of the three-axis magnetic sensor rotation at this time i ; And, control the stepper motor to rotate a fixed angle Δθ i , the rotation angle is updated to θ i +Δθ i , until the rotation angle reaches 180°; And, find the minimum value of the magnetic field amplitude on the x-axis and get the angle corresponding to the minimum value of the magnetic field And, communicate with other magnetic sensor boxes to transmit angle data, calculate the average angle of the five magnetic sensor boxes; control the stepper motor to rotate in the opposite direction to θ min At the three-axis AC magnetic field components measured by the three-axis magnetic sensor, the AC amplitudes are calculated and obtained. Calculate the average value to get mag i , and sent to the numerical calculation unit.

2. The fixed underground three-phase cable positioning device according to claim 1, characterized in that: The numerical calculation unit is specifically used for: Calculate the coordinates (x1, y1, z1) to (x5, y5, z5) of the magnetic measurement points corresponding to the five magnetic sensor boxes in the reference coordinate system; And, obtain the magnetic field amplitude data mag1~mag5 of the five magnetic measurement points calculated by the signal processing control unit, establish a numerical solution model; obtain the three-axis magnetic sensor angle data θ min , substitute the initial iteration point for iterative solution and obtain the location information of the three-phase cable.

3. The fixed underground three-phase cable positioning device according to claim 2, characterized in that: The numerical solution model is as follows: Among them, E, a, b, c, and d are coefficients to be solved.

4. The fixed underground three-phase cable positioning device according to claim 2, characterized in that: The initial iteration point is:

5. A method for locating a fixed underground three-phase cable, based on the fixed underground three-phase cable locating device according to any one of claims 1 to 4, characterized in that: The steps include: S1: Obtain the longitude and latitude of the three-phase cable positioning device as the reference coordinate system, obtain the coordinates of the five three-axis magnetic sensors in the reference coordinate system, which are (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), (x4, y4, z4), (x5, y5, z5), and establish a local coordinate system centered on the three-axis magnetic sensor; S2: The three-axis magnetic sensor rotates 180° step by step with the set angle as the step angle, collects the magnetic field data in the X-axis direction of the local coordinate system, and obtains the change of the AC signal amplitude with the angle S3: Seek The angle corresponding to the minimum amplitude is averaged to obtain θ min , the angle θ min The corresponding direction is the direction of the three-phase cable in the reference coordinate system; S4: Rotate the five three-axis magnetic sensors to θ respectively min , perform three-axis magnetic field value measurement, and calculate a total of 15 magnetic field amplitude data The average value is calculated to obtain the synthetic magnetic field amplitude of the magnetic measuring point; S5: Assume that the straight line equation of the three-phase cable in the reference coordinate system is: Establish a numerical solution model; S6: Set the initial iteration point of numerical calculation; S7: Iteratively solve and obtain the buried depth d of the pipeline in the reference coordinate system, and the direction equation of the three-phase cable is ax+by+c=0.

6. The method for locating a fixed underground three-phase cable according to claim 5, characterized in that: In step S4, the average value is calculated to obtain the synthetic magnetic field amplitude of the magnetic measuring point: Among them, (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), (x4, y4, z4), and (x5, y5, z5) are the coordinates of the five three-axis magnetic sensors in the reference coordinate system.

7. The method for locating a fixed underground three-phase cable according to claim 5, characterized in that: In step S5, a numerical solution model is established as follows: Among them, E, a, b, c, d are the coefficients to be solved.

8. The method for locating a fixed underground three-phase cable according to claim 5, characterized in that: In step S6, the initial iteration point of numerical calculation is set to:

9. The method for locating a fixed underground three-phase cable according to claim 5, characterized in that: During the rotation of the three-axis magnetic sensor, the reference coordinate system remains stationary, and the local coordinate system rotates around its own Z axis.

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