A cable axial force measurement correction method suitable for high-drop serpentine laying environment

Abstract

The application discloses a cable axial force measurement correction method suitable for high-drop serpentine laying environment, which comprises the following steps: S1, integrating a pressure sensor in a fixing clamp of a cable to be measured, clamping the fixing clamp to the outer surface of the cable to be measured, and collecting the gripping force of the fixing clamp applied to the outer surface of the cable through the pressure sensor; S2, calculating the friction force suffered by the cable according to a pre-marked friction coefficient and the gripping force; S3, establishing a mechanical balance equation along the laying path direction of the cable according to the geometric characteristics of the cable laying path and the friction force, and calculating the axial force of the cable through the mechanical balance equation. The application does not need to lay strain sensors on the cable body or perform structural excavation, avoids the dependence on the strain transmission path, and effectively eliminates the interference of non-axial strain.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage cable product measurement technology. Specifically, it relates to a method for measuring and correcting the axial force of cables suitable for high-drop serpentine laying environments in 500kV pumped storage substations. Background Technology

[0002] In the construction of pumped-storage power stations, cables often need to be laid along steep mountainsides, vertical shafts, or inclined shafts with significant elevation differences to connect the power generation and transmission systems between the upper and lower reservoirs. During the serpentine laying and operation of pumped-storage cables, complex axial force distributions are generated due to multiple factors such as gravity, path inclination angle, support friction, and bending deformation. If the axial force is out of control, it can easily lead to damage to the cable sheath, conductor stretching, or even breakage, seriously threatening the safe and stable operation of the power station. Therefore, there is an urgent need for a method that can accurately and in real-time sense and correct the axial force of pumped-storage cables to support safe laying and intelligent operation and maintenance.

[0003] Currently, monitoring technologies for axial force in cables mainly fall into two categories: series-connected force measuring devices and surface-mounted strain sensors. The former requires interrupting the cable structure, making it unsuitable for existing or long-distance lines; while the latter offers the advantage of non-invasiveness, most solutions only use uniaxial strain gauges, failing to effectively distinguish non-axial strain interference caused by support friction, bending, or temperature changes. Especially in the unique environment of pumped-storage power stations with large elevation differences and varying inclination angles, existing methods lack reasonable modeling of the coupling effect between the self-weight component and the path geometry, leading to severely distorted measurement results and failing to meet the accuracy and reliability requirements of practical engineering. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and provide a cable axial force measurement and correction method suitable for high-drop serpentine laying environments. It can indirectly calculate the cable axial force by measuring the gripping force of the clamp, without the need to install sensors on the cable body or carry out structural excavation.

[0005] The objective of this invention is achieved through the following technical solution: a method for measuring and correcting the axial force of cables in high-drop serpentine laying environments, comprising the following steps:

[0006] S1. A pressure sensor is integrated into the fixing clamp of the cable under test, the fixing clamp is clamped on the outer surface of the cable under test, and the gripping force applied by the fixing clamp to the outer surface of the cable is collected by the pressure sensor.

[0007] S2. Calculate the frictional force on the cable based on the pre-calibrated friction coefficient and the gripping force;

[0008] S3. Based on the geometric characteristics of the cable laying path and the frictional force, establish a mechanical equilibrium equation along the cable laying path direction, and calculate the axial force of the cable using the mechanical equilibrium equation.

[0009] Preferably, in step S1, the pressure sensor is arranged with multiple measuring points evenly along the inner surface of the fixed clamp, and the number of measuring points is not less than 8; the average value of the pressure value of each measuring point is taken as the gripping force.

[0010] Preferably, in step S2, the frictional force is calculated according to the following formula:

[0011] F f =μF N ,

[0012] Among them, F f F represents the frictional force acting on the cable, μ is the coefficient of interfacial friction between the cable outer sheath and the fixing clamp, and F is the frictional force acting on the cable. N The gripping force is described.

[0013] Preferably, the interfacial friction coefficient is pre-calibrated based on the characteristics of the cable outer sheath material, surface roughness, and ambient temperature and humidity conditions.

[0014] Preferably, in step S3, the mechanical equilibrium equation is:

[0015] ,

[0016] Among them, F a F is the axial force of the cable, mg is the weight of the cable, θ is the inclination angle of the laying path, and F fi Let N be the frictional force at the i-th fixed fixture, and N be the total number of fixed fixtures. This is the resultant force of friction at each fixed clamp.

[0017] Preferably, in step S1, when the cable is laid in a horizontal serpentine pattern, the fixing clamp is installed at the inflection point of the serpentine waveform; when the cable is laid in a longitudinal serpentine pattern, the fixing clamp is installed at the crest of the serpentine waveform.

[0018] Preferably, the pressure sensor is a strain gauge.

[0019] Preferably, in step S1, the fixing clamp is a ring-shaped structure.

[0020] Preferably, after step S3, a verification step is also included: comparing and verifying the theoretical axial force under cable temperature changes with the calculation results of the mechanical equilibrium equation; the formula for calculating the theoretical axial force is:

[0021] ,

[0022] ,

[0023] -B,

[0024] Among them, F a1 F a2 EI represents the axial force of the serpentine arc of the cable insulation core when the temperature rises and falls, respectively; B represents the bending resistance of the cable core; n represents the serpentine arc width; α represents the serpentine arc axial slip; α represents the linear expansion coefficient of the cable insulation core; Δt represents the temperature rise; and L represents the half-serpentine length.

[0025] The present invention has the following advantages and effects compared with the prior art:

[0026] (1) This invention measures the gripping force applied to the outer surface of the cable by a fixing clamp, calculates the frictional force by combining the pre-calibrated friction coefficient, and then uses the mechanical equilibrium equation to inversely deduce the axial force, thus realizing an indirect measurement path of "gripping force - frictional force - axial force". This method does not require the installation of strain sensors on the cable body or structural excavation, avoids dependence on the strain transmission path, and effectively eliminates the interference of non-axial strain.

[0027] (2) Based on the geometric features of the cable laying path, such as the inclination angle, the width of the serpentine arc and the length of the half-serpentine, the present invention establishes a mechanical equilibrium equation and a theoretical calculation model, which fully considers the coupling effect of the self-weight component and the geometric features of the path under the conditions of large height difference and variable inclination angle, and solves the problem of serious distortion of measurement results in the existing method under the high drop laying environment.

[0028] (3) This invention verifies the experimental calculation results of the mechanical equilibrium equation by using the theoretical axial force calculation formula, and establishes a dual guarantee mechanism of mutual verification between experimental measurement and theoretical calculation, which ensures the accuracy and reliability of the axial force measurement results. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall process of a cable axial force measurement and correction method applicable to high-drop serpentine laying environments according to the present invention.

[0030] Figure 2 The diagram shows the fixed clamp structure and the arrangement of the pressure sensor in the embodiment, where (a) is a schematic diagram of the fixed clamp structure and (b) is a schematic diagram of the fixed clamp structure from another perspective.

[0031] Figure 3 The following are schematic diagrams of two serpentine laying fixture arrangements in the embodiments, where (a) is a horizontal serpentine laying and (b) is a longitudinal serpentine laying.

[0032] In the diagram, 1 represents the location of the pressure sensor, and 2 represents the angle of the ramp. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0034] Example 1

[0035] like Figure 1 The diagram shows a flowchart of a cable axial force measurement and correction method suitable for high-drop serpentine laying environments, including the following steps:

[0036] Step 1: Grip strength measurement

[0037] A pressure sensor is integrated into the fixing clamp of the cable under test. The fixing clamp is held on the outer surface of the cable under test, and the gripping force applied by the fixing clamp to the outer surface of the cable is collected by the pressure sensor.

[0038] (1) Fixture structure

[0039] The fixing clamp is a ring-shaped clamp structure. The clamp adopts an open ring structure design, such as... Figure 2 As shown, the cable clamp consists of two precision-machined semi-circular clamping bodies. These clamping bodies are rigidly connected by M12-grade high-precision force-measuring bolts. The inner surface is covered with a uniformly thick neoprene rubber lining layer to ensure a continuous and uniform force transmission interface with the cable's outer sheath. The cable clamp is made of AC7A high-strength, corrosion-resistant aluminum alloy, a fire-resistant, heat-resistant, and non-magnetic material with extremely strong resistance to salt spray corrosion. It has a tensile strength of 180 MPa, an elongation greater than 8%, and a hardness of 50 HB.

[0040] (2) Sensor arrangement

[0041] In this embodiment, the pressure sensor is a strain gauge, with multiple measuring points evenly arranged circumferentially along the inner surface of the fixing fixture, the number of measuring points being no less than 8. The pressure sensor has a range of 0–5000 N, and a nonlinearity error ≤0.1%FS (full scale). The sensor signal is filtered and then output as raw force data. The sampling frequency can be set according to the dynamic response requirements during the laying process. The data is transmitted to the acquisition terminal in real time via a shielded cable, ensuring that the gripping force measurement drift is ≤0.5%. The average pressure value of each measuring point is taken as the gripping force.

[0042] (3) Differentiated fixture layout

[0043] The clamp placement needs to be designed according to the laying type: the deformation characteristics of cables are different under different serpentine laying methods, and the axial force transmission path is different. Therefore, it is necessary to determine the optimal clamp placement position according to the geometric characteristics of the path so that the pressure sensor can effectively capture the interaction force between the cable and the clamp.

[0044] like Figure 3As shown in (a), when the cable is laid in a horizontal serpentine pattern, the fixing clamps are placed at the inflection points of the serpentine waveform (i.e., the transition points between the crests and troughs). The number of fixing clamps for a complete horizontal serpentine section is 2. In the horizontal serpentine laying, the cable bends in a serpentine shape in the horizontal plane. The inflection point is the transition position where the bending direction of the cable changes. At this point, the direction of the interaction force between the cable and the clamp is consistent with the direction of the axial force transmission. Placing the clamp at this point can effectively capture the axial force signal.

[0045] like Figure 3 As shown in (b), when the cable is laid in a longitudinal serpentine pattern, the fixing clamp is placed at the crest of the serpentine waveform (i.e., the highest point of the waveform), and the number of fixing clamps for a complete longitudinal serpentine section is 1. In the longitudinal serpentine laying, the cable bends in a serpentine shape along the slope direction, and the crest is the highest point of the cable in the direction of gravity. The axial force changes most significantly at this position, and placing the clamp at this position can capture the axial force change characteristics to the maximum extent.

[0046] Step 2: Friction Calculation

[0047] The present invention calculates the frictional force on the cable based on the pre-calibrated friction coefficient and the gripping force.

[0048] The interfacial friction coefficient between the cable outer sheath and the fixing clamp padding layer is pre-calibrated based on the cable outer sheath material characteristics, surface roughness, and ambient temperature and humidity conditions. In this embodiment, for the material characteristics of the 500kV, 1600mm² cable outer sheath, the pre-calibrated friction coefficient μ=0.2.

[0049] A calculation model is established using Coulomb's law of friction. This relationship is applicable to the calculation of sliding friction or maximum static friction at the contact surface of two solid materials under dry friction conditions. The formula for calculating friction force is:

[0050] F f =μF N ,

[0051] Among them, F f F represents the frictional force (N) acting on the cable, μ is the coefficient of interfacial friction between the cable and the clamp (μ=0.2 in this embodiment), and F N Total gripping force (N) applied to the clamping clamp.

[0052] Combining the gripping force data collected in real time by the pressure sensors arranged in the inner ring of the clamp in step one, the frictional force value of a single clamp position is calculated through data processing. The gripping force data is directly obtained from the real-time readings of the pressure sensors integrated into the fixed clamp, and the average value of the pressure values ​​at each measuring point is taken as the total gripping force.

[0053] Step 3: Axial Force Calculation

[0054] Based on the geometric characteristics of the cable laying path and the frictional force, a mechanical equilibrium equation is established along the cable laying path direction, and the axial force of the cable is calculated using the mechanical equilibrium equation.

[0055] In high-altitude, serpentine laying environments, cables are subjected to multiple forces, including gravity and clamp friction, forming a mechanical equilibrium along the laying path. By measuring the friction force and combining it with the path inclination parameter, a mechanical equilibrium equation along the laying path can be established, thereby inferring the axial force on the cable.

[0056] (1) Establishment of the mechanical equilibrium equation

[0057] Based on the inclination angle and serpentine layout characteristics of the cable laying path, and the frictional force data calculated in step two, a mechanical equilibrium equation is established along the laying path direction. The cable is subjected to three main forces along the laying path direction: the component of gravity along the path direction (mg·sinθ), the resultant force of friction at each fixing clamp, and... ), and the axial force to be determined (F) a ).

[0058] Considering the influence of cable gravity, the mechanical equilibrium equations along the laying path are as follows:

[0059] ,

[0060] Among them, F a F is the axial force of the cable (N), mg is the weight of the entire cable (N), θ is the angle between the cable laying path and the horizontal plane, and F fi Let N be the frictional force (N) at the i-th fixed fixture, where N is the total number of fixed fixtures. This is the resultant force of friction at each fixed clamp.

[0061] (2) Calculation of axial force

[0062] In this embodiment, the cable laying path inclination angle θ = 30°, i.e., sinθ is taken as 0.5. The cable unit length mass and laying length are known, and the total cable weight mg is calculated based on the actual laying parameters. The frictional force at each clamp position is calculated based on the real-time gripping force measurement and the pre-calibrated friction coefficient. Substituting the above parameters into the mechanical equilibrium equation, the axial force F of the cable during the high-drop laying process can be calculated. a By distinguishing between the heating and cooling processes, the measured values ​​of axial force under heating and cooling conditions can be obtained separately.

[0063] Step 4: Verification Steps

[0064] To further ensure the accuracy of the measurement results, the calculation results of the mechanical equilibrium equation were verified based on the theoretical axial force when the cable temperature changes.

[0065] During operation, cable temperature fluctuations occur due to load changes. These temperature variations cause thermal expansion and contraction of the cable insulation core, resulting in axial force. The theoretical calculation is based on the cable's temperature change characteristics, establishing a theoretical model through bending resistance, serpentine parameters, and thermal expansion effects. The theoretical formula for calculating the axial force of the cable under temperature changes is as follows:

[0066] ,

[0067] ,

[0068] -B,

[0069] Among them, F a1 F is the axial force (N) in the serpentine arc of the cable insulation core as the temperature rises. a2 EI is the axial force (N) of the serpentine arc of the cable insulation core when the temperature drops, B is the bending resistance of the cable insulation core (N·mm²), n is the serpentine arc width (mm), α is the linear expansion coefficient of the cable insulation core (1 / K), Δt is the temperature rise (K), and L is the half-serpentine length (mm).

[0070] In this embodiment, EI is 7.9 × 10⁻⁶. 9 N·mm 2 B is 270mm, L is 2500mm, and α is 2×10 -5 / K, Δt is taken as 65K. Substituting into the above formula, the slippage n = 23.08mm is calculated, and the theoretical axial force F a1 =-672.20N (when temperature rises), F a2 =407.41N (when the temperature drops).

[0071] The measured values ​​of axial force under the heating and cooling conditions in step three are compared with the theoretical value F. a1 and F a2 A comparative verification is performed. If the deviation between the two is within the preset engineering allowable range, it indicates that the experimental measurement results are reliable, and the measurement correction method is accurate and effective, and can be used for monitoring the axial force of cables in actual engineering. In this invention, theoretical calculations and experimental measurements are mutually verified to ensure the accuracy and reliability of the measurement correction method.

[0072] The above embodiments are preferred embodiments of the present invention and are not intended to limit the present invention. Any changes or other equivalent substitutions made without departing from the technical solution of the present invention are included within the protection scope of the present invention.

Claims

1. A method for measuring and correcting the axial force of cables in high-drop serpentine laying environments, characterized in that, Including the following steps: S1. A pressure sensor is integrated into the fixing clamp of the cable under test, the fixing clamp is clamped on the outer surface of the cable under test, and the gripping force applied by the fixing clamp to the outer surface of the cable is collected by the pressure sensor. S2. Calculate the frictional force on the cable based on the pre-calibrated friction coefficient and the gripping force; S3. Based on the geometric characteristics of the cable laying path and the frictional force, establish a mechanical equilibrium equation along the cable laying path direction, and calculate the axial force of the cable using the mechanical equilibrium equation.

2. The cable axial force measurement and correction method suitable for high-drop serpentine laying environments according to claim 1, characterized in that, In step S1, the pressure sensor is arranged with multiple measuring points evenly along the inner surface of the fixed clamp, and the number of measuring points is not less than 8; the average value of the pressure value of each measuring point is taken as the gripping force.

3. The cable axial force measurement and correction method applicable to high-drop serpentine laying environments according to claim 1, characterized in that, In step S2, the frictional force is calculated according to the following formula: F f =μF N , Among them, F f F represents the frictional force acting on the cable, μ is the coefficient of interfacial friction between the cable outer sheath and the fixing clamp, and F is the frictional force acting on the cable. N The gripping force is described.

4. The cable axial force measurement and correction method suitable for high-drop serpentine laying environments according to claim 3, characterized in that, The interfacial friction coefficient is pre-calibrated based on the characteristics of the cable outer sheath material, surface roughness, and ambient temperature and humidity conditions.

5. The method for measuring and correcting the axial force of cables in high-drop serpentine laying environments according to claim 1, characterized in that, In step S3, the mechanical equilibrium equation is: ， Among them, F a F is the axial force of the cable, mg is the weight of the cable, θ is the inclination angle of the laying path, and F fi Let N be the frictional force at the i-th fixed fixture, and N be the total number of fixed fixtures. This is the resultant force of friction at each fixed clamp.

6. The cable axial force measurement and correction method applicable to high-drop serpentine laying environments according to claim 1, characterized in that, In step S1, when the cable is laid in a horizontal serpentine pattern, the fixing clamp is installed at the inflection point of the serpentine waveform; when the cable is laid in a longitudinal serpentine pattern, the fixing clamp is installed at the crest of the serpentine waveform.

7. The method for measuring and correcting the axial force of cables in high-drop serpentine laying environments according to claim 1, characterized in that, The pressure sensor is a strain gauge.

8. The method for measuring and correcting the axial force of cables in high-drop serpentine laying environments according to claim 1, characterized in that, In step S1, the fixing clamp is a ring-shaped clamp structure.

9. The method for measuring and correcting the axial force of cables in high-drop serpentine laying environments according to claim 1, characterized in that, Following step S3, a verification step is also included: comparing the theoretical axial force under cable temperature changes with the calculated results of the mechanical equilibrium equation; the formula for calculating the theoretical axial force is: ， ， -B， Among them, F a1 F a2 EI represents the axial force of the serpentine arc of the cable insulation core when the temperature rises and falls, respectively; B represents the bending resistance of the cable core; n represents the serpentine arc width; α represents the serpentine arc axial slip; α represents the linear expansion coefficient of the cable insulation core; Δt represents the temperature rise; and L represents the half-serpentine length.

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