Internal thermal defect location detection method of vehicle-mounted cable terminal based on temperature differential

Abstract

The present invention discloses a method for locating and detecting internal thermal defects of a vehicle-mounted cable terminal based on temperature differential, which is characterized by comprising: S1, obtaining a two-dimensional surface temperature distribution and a one-dimensional curve temperature distribution of the vehicle-mounted cable terminal; S2, filtering the two-dimensional surface temperature distribution and the one-dimensional curve temperature distribution respectively to obtain a filtered surface and a filtered curve; S3: respectively obtaining the second-order, fourth-order, and sixth-order differential distributions of the temperature of the filtered surface and the filtered curve; S4, extracting the surface main peak position of the second-order, fourth-order, and sixth-order differential distributions of the filtered surface temperature, and extracting the curve main peak position and the main side peak spacing of the second-order, fourth-order, and sixth-order differential distributions of the filtered curve temperature; S5, determining the position and depth of the internal thermal defect of the vehicle-mounted cable terminal according to the surface main peak position, the curve main peak position, and the main side peak spacing.

Description

Technical Field

[0001] The invention relates to the technical field of road detection, and in particular to a method for locating and detecting thermal defects inside a vehicle-mounted cable terminal based on temperature differential. Background Art

[0002] High-speed railways play an important role in my country's national economic and social development. How to improve the service performance guarantee capability of high-speed trains is also a common concern of the world. As an important hub for energy transmission of high-speed trains, the service status of on-board cable terminals directly affects the safe operation of trains. On-board cable terminals adopt a multi-layer coating structure. Affected by factors such as construction technology, vehicle body vibration, and sudden changes in ambient temperature, insulation defects are prone to occur inside, expand, and generate heat, thus affecting the normal service of on-board cable terminals. Therefore, timely and accurate positioning and detection of internal defects of on-board cable terminals is the key to preventing cable terminal failures, which is of great significance to ensuring the safe and reliable operation of trains.

[0003] The partial discharge detection method is the main method for defect detection, but due to its poor anti-interference ability, it has extremely high requirements for the test environment. The operating environment of high-speed trains is complex, and there are serious electromagnetic interference and environmental noise at the test site, which makes the partial discharge detection method difficult to apply to the online detection of on-board cable terminals. The surface temperature rise difference can evaluate the overall status of the cable terminal, but due to the influence of strong airflow and ambient temperature changes, the surface temperature of the on-board cable terminal cannot accurately reflect the relationship between temperature and defect location, and cannot meet the needs of internal defect detection of on-board cable terminals. Summary of the invention

[0004] The purpose of the present invention is to provide a method for locating and detecting internal thermal defects of a vehicle-mounted cable terminal based on temperature differential, so as to solve the problem that the existing method for locating internal thermal defects of a vehicle-mounted cable terminal is affected by strong airflow, ambient temperature changes, etc., and the surface temperature of the vehicle-mounted cable terminal cannot accurately reflect the relationship between the temperature and the defect position, and cannot meet the demand for internal defect detection of the vehicle-mounted cable terminal.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] The present invention provides a method for locating and detecting thermal defects inside a vehicle-mounted cable terminal based on temperature differential, and the method for locating and detecting thermal defects inside a vehicle-mounted cable terminal based on temperature differential comprises:

[0007] S1, obtaining the two-dimensional surface temperature distribution and one-dimensional curve temperature distribution of the vehicle-mounted cable terminal;

[0008] S2, filtering the two-dimensional surface temperature distribution and the one-dimensional curve temperature distribution respectively to obtain a filtered surface and a filtered curve;

[0009] S3: respectively obtaining the second-order, fourth-order, and sixth-order differential distributions of the temperature of the filtered surface and the filtered curve;

[0010] S4, extracting the surface main peak position of the second-order, fourth-order, and sixth-order differential distribution of the filtered surface temperature, and extracting the curve main peak position and main side peak spacing of the second-order, fourth-order, and sixth-order differential distribution of the filtered curve temperature;

[0011] S5. Determine the position and depth of the internal thermal defect of the vehicle-mounted cable terminal according to the main peak position of the surface, the main peak position of the curve and the main side peak distance.

[0012] Optionally, the step S1 includes:

[0013] S11: Acquire a thermal image of the surface of the vehicle-mounted cable terminal;

[0014] S12: using thermal imaging processing software to select a temperature concentration area in the thermal imaging image to obtain a two-dimensional surface temperature distribution of the vehicle-mounted cable terminal;

[0015] S13: using thermal imaging image processing software to select a horizontal line passing through the highest temperature point in the thermal imaging image, to obtain a one-dimensional curve temperature distribution of the vehicle-mounted cable terminal.

[0016] Optionally, in step S2, the two-dimensional surface temperature distribution and the one-dimensional curve temperature distribution are filtered by using a smoothing filter to obtain a filtered surface and a filtered curve, so as to eliminate the influence of the background temperature and the shed structure of the vehicle-mounted cable terminal.

[0017] Optionally, in step S4, the position of the internal thermal defect of the vehicle cable terminal is determined by the surface main peak position and the curve main peak position; the depth of the internal thermal defect of the vehicle cable terminal is determined by the main side peak distance.

[0018] Optionally, the relationship between the depth of the internal thermal defect of the vehicle-mounted cable terminal and the main side peak spacing is expressed as:

[0019]

[0020] Among them, h represents the depth of the internal thermal defect of the vehicle cable terminal, and L2, L4 and L6 respectively represent the main side peak spacing of the second-order differential distribution of the filtered curve temperature, the main side peak spacing of the fourth-order differential distribution and the main side peak spacing of the sixth-order differential distribution.

[0021] The present invention has the following beneficial effects:

[0022] The present invention first obtains the two-dimensional surface temperature distribution and one-dimensional curve temperature distribution of the defective vehicle cable terminal, and then obtains its second-order, fourth-order, and sixth-order differential distributions, and calculates the position and depth of the internal defects through the main peak position in the multi-order differential distribution of the surface temperature and the main side peak spacing in the multi-order differential distribution of the curve temperature. Since the temperature gradient information is extracted during the differential process, the present invention can detect internal defects under extremely small surface temperature differences and is not affected by changes in ambient temperature. It is an accurate and efficient online positioning and detection method for internal thermal defects of vehicle cable terminals. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of the method for locating and detecting thermal defects inside a vehicle-mounted cable terminal based on temperature differential of the present invention;

[0024] Figure 2 It is a structural schematic diagram of a heat transfer model containing a single thermal defect in a vehicle-mounted cable terminal;

[0025] Figure 3 Schematic diagram of the second, fourth and sixth order differential distribution of the tangent temperature at y=0 under the action of a single thermal defect in the on-board cable terminal;

[0026] Figure 4 It is a schematic diagram of the structure of the heat transfer model containing multiple thermal defects in the vehicle-mounted cable terminal;

[0027] Figure 5 Schematic diagram of the surface temperature and its second-order, fourth-order, and sixth-order differential distribution under the action of multiple thermal defects in the on-board cable terminal. DETAILED DESCRIPTION

[0028] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0029] Example

[0030] The technical solution of the present invention to solve the above technical problems is as follows:

[0031] The present invention provides a method for locating and detecting thermal defects inside a vehicle-mounted cable terminal based on temperature differential, referring to Figure 1 As shown, the method for locating and detecting thermal defects inside a vehicle-mounted cable terminal based on temperature differential includes:

[0032] S1, obtaining the two-dimensional surface temperature distribution and one-dimensional curve temperature distribution of the vehicle-mounted cable terminal;

[0033] S2, filtering the two-dimensional surface temperature distribution and the one-dimensional curve temperature distribution respectively to obtain a filtered surface and a filtered curve;

[0034] S3: respectively obtaining the second-order, fourth-order, and sixth-order differential distributions of the temperature of the filtered surface and the filtered curve;

[0035] S4, extracting the surface main peak position of the second-order, fourth-order, and sixth-order differential distribution of the filtered surface temperature, and extracting the curve main peak position and main side peak spacing of the second-order, fourth-order, and sixth-order differential distribution of the filtered curve temperature;

[0036] S5. Determine the position and depth of the internal thermal defect of the vehicle-mounted cable terminal according to the main peak position of the surface, the main peak position of the curve and the main side peak distance.

[0037] Optionally, the step S1 includes:

[0038] S11: Acquire a thermal image of the surface of the vehicle-mounted cable terminal;

[0039] S12: using thermal imaging processing software to select a temperature concentration area in the thermal imaging image to obtain a two-dimensional surface temperature distribution of the vehicle-mounted cable terminal;

[0040] S13: using thermal imaging image processing software to select a horizontal line passing through the highest temperature point in the thermal imaging image, to obtain a one-dimensional curve temperature distribution of the vehicle-mounted cable terminal.

[0041] Optionally, in step S2, the two-dimensional surface temperature distribution and the one-dimensional curve temperature distribution are filtered by using a smoothing filter to obtain a filtered surface and a filtered curve, so as to eliminate the influence of the background temperature and the shed structure of the vehicle-mounted cable terminal.

[0042] Optionally, in step S4, the position of the internal thermal defect of the vehicle cable terminal is determined by the surface main peak position and the curve main peak position; the depth of the internal thermal defect of the vehicle cable terminal is determined by the main side peak distance.

[0043] Optionally, the relationship between the depth of the internal thermal defect of the vehicle-mounted cable terminal and the main side peak spacing is expressed as:

[0044]

[0045] Among them, h represents the depth of the internal thermal defect of the vehicle cable terminal, and L2, L4 and L6 respectively represent the main side peak spacing of the second-order differential distribution of the filtered curve temperature, the main side peak spacing of the fourth-order differential distribution and the main side peak spacing of the sixth-order differential distribution.

[0046] Specifically, in the embodiment of the present invention, the specific calculation method of the internal thermal defect position and depth is as follows:

[0047] refer to Figure 2As shown, taking the single-layer heat transfer model as an example, there is a thermal defect at the origin O, whose heat generation power is Q, and the distance to the upper surface of the model is h. The density, specific heat capacity, thermal conductivity, and temperature of the model are ρ, C respectively. p , λ, T. According to the heat conduction theory, the model satisfies the heat conduction equation under the action of internal thermal defects:

[0048]

[0049] When the heat transfer reaches a steady state, At this time, the above formula can be written as:

[0050]

[0051] When the defect size is much smaller than the model size, the defect at the origin can be regarded as a point heat source. It can be expressed as:

[0052]

[0053] in:

[0054] The origin is used as the center of the sphere. Spherical coordinate system, due to the symmetry of the spherical coordinate system, It can be written as:

[0055]

[0056] The temperature expression of point P on the model surface is:

[0057]

[0058] Furthermore, in the rectangular coordinate system, the surface temperature at a distance h from the thermal defect is expressed as:

[0059]

[0060] For the tangent line at y=0 on the surface, its temperature is:

[0061]

[0062] Construct the analytical function F(x) for the tangent temperature at y=0:

[0063]

[0064] Furthermore, the second, fourth, and sixth order derivatives of F(x) are:

[0065]

[0066] Assume that the heat generation power Q of the thermal defect is 2W, the heat transfer coefficient λ is 0.516, the depth of the thermal defect h is 0.15m, and the second-order, fourth-order, and sixth-order derivative function curves of the tangent temperature at y=0 are shown in Figure 3 Assume that L2, L4, and L6 are the main side peak spacings of the second-order, fourth-order, and sixth-order derivative functions, respectively, and are also the x-axis coordinates corresponding to the side peak peaks. Since the side peak peak is an extreme point on the curve, we have:

[0067] F (3) (L2)=0

[0068] Similarly, |x=L4 and x=L6 are the extreme points of the fourth-order and sixth-order derivative functions, respectively, and they also satisfy:

[0069] F (5) (L4) = 0

[0070] F (7) (L6) = 0

[0071] The third, fifth, and seventh order derivatives of F(x) are:

[0072]

[0073] Therefore, the relationship between the thermal defect depth h and the main side peak spacing can be obtained:

[0074]

[0075] Therefore, the internal thermal defect depth can be given by Calculated.

[0076] See also Figure 3 , the tangent temperature multi-order derivative function curves all have a main peak at x = 0, that is, the main peak position can reflect the position of the internal thermal defect. The two-dimensional position of the internal thermal defect can be obtained by taking the second-order, fourth-order, and sixth-order differential distributions of the surface temperature distribution. The main peak position of the curve can reflect the position of the defect in the one-dimensional coordinate. For example Figure 3 The main peak is located at y = 0, and the position of the thermal defect is also at the origin of the coordinate system, which is consistent. In order to better illustrate the positioning characteristics of the multi-order differential distribution of surface temperature, see Figure 4 There are multiple thermal defects inside the model, and its surface temperature and its second-order, fourth-order, and sixth-order differential distributions are as follows: Figure 5 As shown, it can be seen that the main peak position of the multi-order differential of the two-dimensional surface temperature field is the position of the thermal defect.

[0077] The present invention has the following beneficial effects:

[0078] The present invention first obtains the two-dimensional surface temperature distribution and one-dimensional curve temperature distribution of the defective vehicle cable terminal, and then obtains its second-order, fourth-order, and sixth-order differential distributions, and calculates the position and depth of the internal defects through the main peak position in the multi-order differential distribution of the surface temperature and the main side peak spacing in the multi-order differential distribution of the curve temperature. Since the temperature gradient information is extracted during the differential process, the present invention can detect internal defects under extremely small surface temperature differences and is not affected by changes in ambient temperature. It is an accurate and efficient online positioning and detection method for internal thermal defects of vehicle cable terminals.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for locating and detecting thermal defects inside a vehicle-mounted cable terminal based on temperature differential, characterized in that: The following steps are involved: S1, obtaining the two-dimensional surface temperature distribution and one-dimensional curve temperature distribution of the vehicle-mounted cable terminal, specifically including the following sub-steps: S11: Acquire a thermal image of the surface of the vehicle-mounted cable terminal; S12: using thermal imaging processing software to select a temperature concentration area in the thermal imaging image to obtain a two-dimensional surface temperature distribution of the vehicle-mounted cable terminal; S13: Using thermal imaging image processing software to select a horizontal line passing through the highest temperature point in the thermal imaging image, obtain a one-dimensional curve temperature distribution of the vehicle-mounted cable terminal S2, filtering the two-dimensional surface temperature distribution and the one-dimensional curve temperature distribution respectively to obtain a filtered surface and a filtered curve; S3: Obtain the second-order, fourth-order, and sixth-order differential distributions of the temperature of the filtered surface and the filtered curve, respectively, as follows: Construct the analysis function F(x): Wherein, T(x) represents the temperature when the vertical axis coordinate of the distance from the thermal defect is 0 in the rectangular coordinate system, Q represents the heat generation power of the thermal defect, π represents the pi, λ represents the heat transfer coefficient, x represents the horizontal axis coordinate of the distance from the thermal defect in the rectangular coordinate system, and h represents the depth of the thermal defect; let x=L2, x=L4, x=L6, and calculate the second-order, fourth-order, and sixth-order derivative functions of the analysis function F(x), that is, the second-order, fourth-order, and sixth-order differential distributions of the temperature of the filtered curve are obtained, wherein L2, L4, and L6 respectively represent the main side peak spacing of the second-order differential distribution of the temperature of the filtered curve, the main side peak spacing of the fourth-order differential distribution, and the main side peak spacing of the sixth-order differential distribution; S4, extracting the surface main peak position of the second-order, fourth-order, and sixth-order differential distribution of the filtered surface temperature, and extracting the curve main peak position and main side peak spacing of the second-order, fourth-order, and sixth-order differential distribution of the filtered curve temperature; S5, determining the position and depth of the internal thermal defect of the vehicle cable terminal according to the main peak position of the surface, the main peak position of the curve and the main side peak distance; The position of the internal thermal defect of the vehicle-mounted cable terminal is determined by the main peak position of the surface and the main peak position of the curve; The depth of the internal thermal defect of the vehicle-mounted cable terminal is determined by the main side peak spacing; The relationship between the depth of the internal thermal defect of the vehicle-mounted cable terminal and the main side peak spacing is expressed as follows:

2. The method for locating and detecting thermal defects inside a vehicle-mounted cable terminal based on temperature differential according to claim 1 is characterized in that: In the step S2, the two-dimensional surface temperature distribution and the one-dimensional curve temperature distribution are filtered by using a smoothing filter to obtain a filtered surface and a filtered curve, so as to eliminate the influence of the background temperature and the shed structure of the vehicle-mounted cable terminal.

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