Cable contact resistance calculation method based on finite element software simulation of magnetic induction intensity

Abstract

The application relates to a cable contact resistance calculation method based on finite element software simulation of magnetic induction intensity, selects a C point on the outer surface of a crimping copper pipe corresponding to the contact surface of a first cable core and a second cable core as a magnetic induction intensity measuring point, measures the total resistance Rs of the AB section cable, constructs an equivalent circuit of the AB section cable, establishes a two-dimensional finite element model, and finally calculates the contact resistance R j1 , R j2 , R j3 The method can measure and calculate the contact resistance of each contact surface of the cable intermediate joint, and is convenient for finding and analyzing the problems existing in the cable intermediate joint.

Description

Technical Field

[0001] This invention belongs to the field of power cables, specifically relating to a method for calculating cable contact resistance based on finite element software simulation of magnetic induction intensity. Background Technology

[0002] The service life of a cable primarily depends on the aging degree of its insulation material, and the temperature of the insulation material is a crucial factor affecting its aging rate. Among these, the cable joint is the area most prone to heat generation in the entire cable line, mainly affected by its contact resistance. Therefore, accurately measuring the contact resistance of cable joints is of great significance for effectively assessing cable service life. However, current methods for calculating or measuring the contact resistance of cable joints can only measure the overall contact resistance of the joint, not the contact resistance of each individual contact surface. Chinese patent CN104635056B, entitled "A Method for Calculating the Contact Resistance of the Crimping Connector at a Three-Core Cable Joint," discloses a method for calculating the contact resistance of the crimping connector at a three-core cable joint. The method includes: 1) taking two equal-length sections of a 10kV three-core cable, one section containing the cable joint and the other the cable body; 2) drilling holes in the same core wire within both sections of the cable using an electric drill, with the holes located at both ends of each section; 3) applying a large current to the 10kV three-core cable using a current booster, and then measuring the voltage at both ends of the core wires in the two cable sections using an ohmmeter, recording the current and voltage data; 4) calculating the contact resistance between the crimping connector and the core wire at the cable joint based on the measured voltage at both ends of the core wires and the current flowing through the cable. Clearly, the contact resistance obtained by this method is the overall contact resistance of the joint. Chinese patent CN107203688A, entitled "A Method for Calculating Contact Resistance at the Crimped Connector of a Cable Intermediate Joint," discloses a method for calculating the contact resistance at the crimped connector of a cable intermediate joint. The method includes: S1, calculating the outer diameter D1 of the cable core based on the standard stranding process; S2, calculating the outer diameter D2 of the conductor's circumcircle after the cable core is crimped; S3, assuming the deformation of each conductor layer is the same after crimping, calculating the difference dc between the inscribed and circumscribed radii; S4, calculating the effective contact length le of the outer layer of the cross-section of the crimped conductor; S5, assuming full contact between the conductor and the sleeve, calculating the actual contact area As of the crimped connection of the intermediate joint conductor; and S6, calculating the contact resistance Rj between the cable core and the crimped connector. However, this method can only measure the overall contact resistance of the cable intermediate joint and cannot measure the contact resistance of each contact surface. Summary of the Invention

[0003] The technical problem of this invention is that existing methods for measuring and calculating cable intermediate joints can only measure the overall contact resistance of the cable intermediate joint, and cannot obtain the contact resistance of each contact surface of the cable intermediate joint.

[0004] The purpose of this invention is to solve the above-mentioned problems and provide a method for calculating cable contact resistance based on the simulation of magnetic induction intensity using finite element software. This method can measure the contact resistance of each contact surface of the cable intermediate joint, thereby discovering and analyzing problems existing in the cable intermediate joint and improving the safety of cable operation.

[0005] The technical solution of this invention is a cable contact resistance calculation method based on finite element software simulation of magnetic induction intensity. This method is used to measure and calculate the contact resistance of an AB section cable with an intermediate joint. Point C on the outer surface of the crimped copper tube corresponding to the contact surfaces of the first and second cable cores is selected as the magnetic induction intensity measurement point. The method includes the following steps:

[0006] Step 1: Select a 1-meter-long cable core of the same specification as the cable in section AB without any intermediate joints, and measure the resistance R0 of the cable core per unit length.

[0007] Step 2: Measure the total resistance R of cable segment AB. s ;

[0008] Step 3: Measure the geometric parameters of the AB section cable, including the diameter d of the cable core, the length L1 of the first cable core, the length L2 of the second cable core, the diameter D of the crimped copper tube, the length L3 of the overlapping part of the crimped copper tube and the first cable core, and the length L4 of the overlapping part of the crimped copper tube and the second cable core.

[0009] Step 4: Based on the rated current effective value I of cable section AB. m A DC current is passed through the AB section of the cable, and the magnetic induction intensity at point C on the outer surface of the crimped copper tube is measured using a gaussmeter. m ;

[0010] Step 5: Construct the equivalent circuit of the AB section cable and establish the mathematical relationship between the contact resistance of each contact surface of the intermediate joint and the total resistance Rs of the AB section cable.

[0011] Step 6: Establish a two-dimensional finite element model of cable segment AB using finite element software. Set the current magnitude in cable segment AB to be the same as the DC current magnitude in Step 4, and calculate the magnetic induction intensity B at the magnetic induction intensity measurement point. j And by changing the current Ix of the cable core and the current I of the crimped copper tube. m -I x This makes B j =B m ;

[0012] Step 7: Calculate the contact resistance of each contact surface of the cable joint;

[0013] Step 6 specifically includes the following sub-steps:

[0014] Step 6.1: Based on the axisymmetry of the AB section cable, establish a two-dimensional finite element model of the AB section cable, including the first cable core, the second cable core, the crimped copper tube, and the air region;

[0015] Step 6.2: Set the material properties of the first cable core, the second cable core, and the crimped copper tube respectively. Set the relative permeability of the first cable core, the second cable core, the crimped copper tube, and the air region to 1. Set the conductivity of the first cable core and the second cable core to the conductivity of the cable conductor. Set the conductivity of the crimped copper tube to the conductivity of copper. Set the conductivity of the air region to 0.

[0016] Step 6.3: Set the boundary conditions for the two-dimensional finite element model;

[0017] Step 6.4: Set the current source of the two-dimensional finite element model to I. m That is, the current flowing through ends A and B of the AB section cable is I. m I m The magnitude is the same as the DC current in step 4, and the current in the area where the first cable core overlaps with the crimped copper tube is set to I. x The current in the area where the second cable core overlaps with the crimped copper tube is set to I. x The current for crimping the copper tube is set to I. m -I x ;

[0018] Step 6.5: Let I x =0, start the finite element software to calculate the magnetic field strength distribution of the two-dimensional finite element model, and record the magnetic field strength B at point C of the two-dimensional finite element model. j0 ;

[0019] Step 6.6: Let I x =I m Start the finite element software to calculate the magnetic field strength distribution of the two-dimensional finite element model, and record the magnetic field strength B at point C of the two-dimensional finite element model. jm ;

[0020] Step 6.7: Change I x Size, such that B j =B m .

[0021] In step 5, the contact resistance of the intermediate joint contact surface includes R. j1 R j2 R j3 , where R j1 R is the contact resistance of the mating contact surface between the first cable core and the second cable core. j2 R is the contact resistance of the crimped contact surface between the first cable core and the crimped copper tube. j3This is the contact resistance of the crimped contact surface between the second cable core and the crimped copper tube.

[0022] Preferably, step 6.3 includes the following sub-steps:

[0023] Step 6.3.1: Set axisymmetric boundary conditions at the cable axis of the two-dimensional finite element model;

[0024] Step 6.3.2: Set boundary conditions with zero magnetic induction at the boundary of the two-dimensional finite element model with zero magnetic induction.

[0025] Furthermore, the total resistance R of cable segment AB s =R1+R j1 *(R j2 +R j3 ) / (R j1 +R j2 +R j3 )+R2,R j2 / R j3 =L3 / L4, the conductor resistance of the first cable core R1 = R0 * L1, the conductor resistance of the second cable core R2 = R0 * L2.

[0026] In step 6.7, B j =B m When, current I x =I m *(B m -B j0 ) / (B jm -B j0 ).

[0027] In step 7,

[0028] Contact resistance

[0029] Contact resistance

[0030] Contact resistance

[0031] Compared to existing technologies, the advantages of this invention are that it can measure and calculate the contact resistance of each contact surface of a cable joint, facilitating the identification and analysis of problems existing in the cable joint. Furthermore, the method for calculating contact resistance using magnetic induction intensity measurement points facilitates understanding the distribution of magnetic induction intensity in the cable joint area. Attached Figure Description

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Figure 1This is a schematic diagram of the AB section cable with an intermediate joint.

[0034] Figure 2 This is the equivalent circuit diagram for a cable segment AB with a mid-joint.

[0035] Figure 3 This is a flowchart of the cable contact resistance calculation method based on finite element software simulation of magnetic induction intensity according to the present invention.

[0036] Figure 4 This is a two-dimensional finite element model of cable segment AB.

[0037] The markings in the diagram are as follows: 1. First cable core; 2. Second cable core; 3. Crimped copper tube; 4. Butt joint contact surface between the first cable core and the second cable core; 5. Crimped contact surface between the first cable core and the crimped copper tube; 6. Crimped contact surface between the second cable core and the crimped copper tube; 7. First detection coil; 8. Second detection coil; 9. Air region in the two-dimensional finite element model. Detailed Implementation

[0038] Figure 1 The image shows a cable segment AB with an intermediate joint, where the first cable core 1 and the second cable core 2 have the same specifications.

[0039] like Figure 3 As shown, a method for calculating cable contact resistance based on finite element method (FEM) simulation of magnetic induction intensity is used to measure and calculate the contact resistance of an AB segment cable with an intermediate joint. Point C on the outer surface of the crimped copper tube 3, corresponding to the mating contact surface 4 of the first and second cable cores, is selected as the magnetic induction intensity measurement point. The method includes the following steps:

[0040] Step 1: Select a 1-meter-long cable core of the same specification as the cable in section AB without any intermediate joints, and measure the resistance R0 of the cable core per unit length.

[0041] Step 2: Measure the total resistance R of cable segment AB. s ;

[0042] Step 3: Measure the geometric parameters of the AB section cable, including the diameter d of the cable core, the length L1 of the first cable core 1, the length L2 of the second cable core 2, the diameter D of the crimped copper tube 3, the length L3 of the overlapping part of the crimped copper tube 3 and the first cable core 1, and the length L4 of the overlapping part of the crimped copper tube 3 and the second cable core 2.

[0043] Step 4: Based on the rated current effective value I of cable section AB. m A current of I is inserted into cable segment AB. m The DC current was measured using a gaussmeter to determine the magnetic induction intensity B at point C on the outer surface of the crimped copper tube. m ;

[0044] Step 5: Construct the equivalent circuit of cable segment AB, such as... Figure 2 As shown, construct the intermediate joint contact resistance R. j1 R j2 R j3 The total resistance R of cable section AB s The mathematical relationship, where R j1 R is the contact resistance of the mating contact surface 4 between the first cable core and the second cable core. j2 R is the contact resistance of the crimping contact surface 5 between the first cable core and the crimped copper tube. j3 The contact resistance of the crimping contact surface 6 between the second cable core and the crimped copper tube; the total resistance R of the AB section cable. s =R1+R j1 *(R j2 +R j3 ) / (R j1 +R j2 +R j3 )+R2,R j2 / R j3 =L3 / L4, the conductor resistance of the first cable core 1 is R1 = R0 * L1, and the conductor resistance of the second cable core 2 is R2 = R0 * L2;

[0045] Step 6: Use finite element software to establish a two-dimensional finite element model of cable segment AB, and calculate the magnetic induction intensity B at the magnetic induction intensity measurement point. j And by changing the current Ix of the cable core and the current I of the crimped copper tube 3 m -I x This makes B j =B m ;

[0046] Step 7: Calculate the contact resistance R j1 R j2 R j3 .

[0047] Step 6, which involves establishing a two-dimensional finite element model of cable segment AB using finite element software, includes the following steps:

[0048] Step 6.1: Based on the axisymmetry of cable segment AB, establish a two-dimensional finite element model of cable segment AB, as follows: Figure 4 As shown, it includes a first cable core 1, a second cable core 2, a crimped copper tube 3, and an air area 9;

[0049] Step 6.2: Set the material properties of the first cable core 1, the second cable core 2, and the crimped copper tube 3 respectively. Set the relative permeability of the first cable core 1, the second cable core 2, the crimped copper tube 3, and the air region 9 to 1. Set the conductivity of the first cable core 1 and the second cable core 2 to the conductivity of the cable conductor. Set the conductivity of the crimped copper tube 3 to the conductivity of copper. Set the conductivity of the air region 9 to 0.

[0050] Step 6.3: Set the boundary conditions for the two-dimensional finite element model;

[0051] Step 6.3.1: Set axisymmetric boundary conditions at the cable axis of the two-dimensional finite element model;

[0052] Step 6.3.2: Set boundary conditions with zero magnetic induction at the boundary of the two-dimensional finite element model where the magnetic induction intensity is zero;

[0053] Step 6.4: Set the current source of the two-dimensional finite element model to I. m That is, the current flowing through ends A and B of the AB section cable is I. m The current in the area where the first cable core 1 overlaps with the crimped copper tube 3 is set to I. x The current in the area where the second cable core 2 overlaps with the crimped copper tube 3 is set to I. x The current for crimping copper tube 3 is set to I. m -I x ;

[0054] Step 6.5: Let I x =0, start the finite element software to calculate the magnetic field strength distribution of the two-dimensional finite element model, and record the magnetic field strength B at point C of the two-dimensional finite element model. j0 ;

[0055] Step 6.6: Let I x =I m Start the finite element software to calculate the magnetic field strength distribution of the two-dimensional finite element model, and record the magnetic field strength B at point C of the two-dimensional finite element model. jm ;

[0056] Step 6.7: Change I x Size, such that B j =B m .

[0057] B j =B m When, current I x =I m *(B m -B j0 ) / (B jm -B j0 );

[0058] In step 7,

[0059] Contact resistance

[0060] Contact resistance

[0061] Contact resistance

Claims

1. A method for calculating cable contact resistance based on finite element method software simulation of magnetic induction intensity, used to measure and calculate the contact resistance of AB segment cables with intermediate joints, wherein point C on the outer surface of the crimped copper tube corresponding to the contact surfaces of the first and second cable cores is selected as the magnetic induction intensity measurement point, characterized in that... Includes the following steps: Step 1: Select a cable core of the same specification as the cable in section AB without any intermediate joints, and measure the resistance R0 of the cable core per unit length. Step 2: Measure the total resistance R of cable segment AB. s ; Step 3: Measure the geometric parameters of the AB section cable, including the diameter d of the cable core, the length L1 of the first cable core, the length L2 of the second cable core, the diameter D of the crimped copper tube, the length L3 of the overlapping part of the crimped copper tube and the first cable core, and the length L4 of the overlapping part of the crimped copper tube and the second cable core. Step 4: Based on the rated current effective value I of cable section AB. m A DC current is passed through the AB section of the cable, and the magnetic induction intensity at point C on the outer surface of the crimped copper tube is measured using a gaussmeter. m ; Step 5: Construct the equivalent circuit of the AB section cable and establish the mathematical relationship between the contact resistance of each contact surface of the intermediate joint and the total resistance Rs of the AB section cable. Step 6: Establish a two-dimensional finite element model of cable segment AB using finite element software. Set the current magnitude in cable segment AB to be the same as the DC current magnitude in Step 4, and calculate the magnetic induction intensity B at the magnetic induction intensity measurement point. j And by changing the current Ix of the cable core and the current I of the crimped copper tube. m -I x This makes B j =B m ; Step 7: Calculate the contact resistance of each contact surface of the cable joint; Step 6 specifically includes: Step 6.1: Based on the axisymmetry of the AB section cable, establish a two-dimensional finite element model of the AB section cable, including the first cable core, the second cable core, the crimped copper tube, and the air region; Step 6.2: Set the material properties of the first cable core, the second cable core, and the crimped copper tube respectively. Set the relative permeability of the first cable core, the second cable core, the crimped copper tube, and the air region to 1. Set the conductivity of the first cable core and the second cable core to the conductivity of the cable conductor. Set the conductivity of the crimped copper tube to the conductivity of copper. Set the conductivity of the air region to 0. Step 6.3: Set the boundary conditions for the two-dimensional finite element model; Step 6.4: Set the current source of the two-dimensional finite element model to I. m That is, the current flowing through ends A and B of the AB section cable is I. m I m The magnitude is the same as the DC current in step 4, and the current in the area where the first cable core overlaps with the crimped copper tube is set to I. x The current in the area where the second cable core overlaps with the crimped copper tube is set to I. x The current for crimping the copper tube is set to I. m -I x ; Step 6.5: Let I x =0, start the finite element software to calculate the magnetic field strength distribution of the two-dimensional finite element model, and record the magnetic field strength B at point C of the two-dimensional finite element model. j0 ; Step 6.6: Let I x =I m Start the finite element software to calculate the magnetic field strength distribution of the two-dimensional finite element model, and record the magnetic field strength B at point C of the two-dimensional finite element model. jm ; Step 6.7: Change I x Size, such that B j =B m ; B j =B m When, current I x =I m (B) m -B j0 ) / (B jm -B j0 ); In step 5, the contact resistance of the intermediate joint contact surface includes R. j1 R j2 R j3 , where R j1 R is the contact resistance of the mating contact surface between the first cable core and the second cable core. j2 R is the contact resistance of the crimped contact surface between the first cable core and the crimped copper tube. j3 The contact resistance is the contact resistance between the crimped contact surface of the second cable core and the crimped copper tube. The total resistance R of cable section AB s =R1+R j1 (R j2 +R j3 ) / (R j1 +R j2 +R j3 )+R2,R j2 / R j3 =L3 / L4, the conductor resistance of the first cable core is R1=R0 L1, the conductor resistance of the second cable core is R2 = R0 L2; In step 7, the contact resistance R is calculated. j1 R j2 R j3 , in , Contact resistance , Contact resistance , Contact resistance .

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