Cable outer sheath deterioration state evaluation method and system based on deterioration evaluation coefficient

Abstract

The application provides a cable outer sheath deterioration state evaluation method and system based on a deterioration evaluation coefficient, and belongs to the technical field of cable outer sheath deterioration state evaluation technology.The application comprises the following steps: measuring the Shore hardness value, dielectric strength value and breaking elongation rate of a cable outer sheath to be evaluated; calculating the deterioration evaluation coefficient of the cable outer sheath by using a pre-established deterioration evaluation coefficient calculation formula, wherein the deterioration evaluation coefficient calculation formula comprises a mathematical relationship between the deterioration evaluation coefficient and the Shore hardness value, dielectric strength value and breaking elongation rate; and evaluating the deterioration state of the cable outer sheath based on the deterioration evaluation coefficient.The application can evaluate the deterioration degree of a 110kV cable outer sheath by measuring the Shore hardness value, dielectric strength value and breaking elongation rate of the cable outer sheath and calculating the deterioration evaluation coefficient, and the method is simple and efficient, and can better evaluate the deterioration degree of a 110kV cable outer sheath.

Description

Technical Field

[0001] This invention belongs to the technical field of cable outer sheath deterioration status assessment, specifically relating to a method and system for assessing cable outer sheath deterioration status based on a deterioration assessment coefficient. Background Technology

[0002] Since the beginning of the 21st century, my country's economy has developed rapidly, and people's electricity demand in production and daily life has been continuously increasing. During the development of power grid construction, power cables, with their advantages of high power supply reliability and effective improvement of line power factor, have gradually replaced overhead transmission lines. In particular, cross-linked polyethylene cables are widely used in urban power distribution networks. Underground cables are prone to failure, mainly due to external factors such as construction damage and rodent infestation, as well as non-external factors such as improper cable installation and the natural environment. The economic losses caused by cable failures are enormous, seriously affecting industrial production and people's lives.

[0003] The cable outer sheath is the outermost layer of the cable structure, serving to isolate it from the environment and protect the cable. The integrity of the outer sheath directly affects the working life and insulation performance of the cable insulation. If the cable outer sheath is damaged, it can lead to increased circulating current in the metallic sheath layer, reducing transmission capacity, or even endanger the main insulation, causing insulation breakdown. Therefore, effectively assessing the degradation condition of the cable outer sheath and taking timely repair or replacement measures is a crucial step in ensuring stable power supply. During underground laying and commissioning, cable outer sheaths inevitably degrade, making the assessment of the 110kV cable outer sheath condition extremely important. There is an urgent need for an effective method to assess the degradation condition of the outer sheaths of 110kV cables operating in distribution networks over long periods. Summary of the Invention

[0004] In view of this, the present invention aims to provide a method for assessing the deterioration status of the outer sheath of 110kV cables based on a deterioration assessment coefficient, which is used to assess the deterioration status of the outer sheath of 110kV cables operating in a distribution network for a long period of time.

[0005] To achieve the above-mentioned technical effects, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a method for assessing the degradation status of cable outer sheaths based on a degradation assessment coefficient, comprising the following steps:

[0007] Measure the Shore hardness, dielectric strength, and elongation at break of the outer sheath of the cable to be evaluated;

[0008] The degradation assessment coefficient of the cable outer sheath is calculated using a pre-established degradation assessment coefficient calculation formula. The degradation assessment coefficient calculation formula includes the mathematical relationship between the degradation assessment coefficient and the Shore hardness value, dielectric strength value and elongation at break.

[0009] The degradation status of the cable outer sheath is assessed based on the degradation assessment coefficient.

[0010] Furthermore, the Shore hardness values ​​are as follows:

[0011] Several sets of Shore hardness values ​​were obtained by measuring the two ends of several cable segments of the same length using a Shore hardness tester. The several cable segments of the same length were obtained by cutting the outer sheath of the cable to be evaluated.

[0012] Furthermore, the dielectric strength value is specifically as follows:

[0013] Several dielectric strength values ​​were obtained by performing dielectric strength tests on several square samples using a pressure device. The several square samples were obtained by cutting multiple square samples of the same size from each cable segment of the same length.

[0014] Furthermore, in the dielectric strength test experiment, the voltage boosting method was slow voltage boosting, with a boosting rate of 0.1kV / s until the sample was broken down, and the test results were obtained.

[0015] Furthermore, the elongation at break is specifically as follows:

[0016] Several elongation at break were obtained by performing mechanical tensile tests on several dumbbell-shaped samples. The dumbbell-shaped samples were obtained by cutting multiple dumbbell-shaped samples of the same size from each cable segment of the same length.

[0017] Furthermore, the specific formula for calculating the degradation assessment coefficient is as follows:

[0018]

[0019] In the formula, γ represents the degradation assessment coefficient, and D i1 D i2 ds represents the Shore hardness values ​​at both ends of the outer sheath of the i-th cable segment. i1 ds i2 ds i3 ds i4 These represent the dielectric strength values ​​of the four square samples on the outer sheath of the i-th cable segment, respectively. imax e imin Let be the maximum and minimum elongation at break of the dumbbell-shaped sample of the outer sheath of the i-th cable segment.

[0020] Furthermore, the degradation status of the cable outer sheath is assessed based on the degradation assessment coefficient, specifically as follows:

[0021] If γ≤1.97, the outer sheath of the tested cable is slightly deteriorated;

[0022] If 1.97 < γ ≤ 2.19, then the outer sheath of the tested cable is moderately deteriorated.

[0023] If γ > 2.19, the outer sheath of the cable under test is severely degraded.

[0024] Secondly, the present invention provides a cable outer sheath degradation status assessment system based on a degradation assessment coefficient, comprising:

[0025] The acquisition unit is used to acquire the Shore hardness, dielectric strength, and elongation at break of the outer sheath of the cable to be evaluated.

[0026] The calculation unit is used to calculate the degradation evaluation coefficient of the cable outer sheath using a pre-established degradation evaluation coefficient calculation formula. The degradation evaluation coefficient calculation formula contains the mathematical relationship between the degradation evaluation coefficient and the Shore hardness value, dielectric strength value and elongation at break.

[0027] An evaluation unit is used to assess the degradation status of the cable outer sheath based on a degradation evaluation coefficient.

[0028] Furthermore, the specific formula for calculating the degradation assessment coefficient is as follows:

[0029]

[0030] In the formula, γ represents the degradation assessment coefficient, and D i1 D i2 ds represents the Shore hardness values ​​at both ends of the outer sheath of the i-th cable segment. i1 ds i2 ds i3 ds i4 These represent the dielectric strength values ​​of the four square samples on the outer sheath of the i-th cable segment, respectively. imax e imin Let be the maximum and minimum elongation at break of the dumbbell-shaped sample of the outer sheath of the i-th cable segment.

[0031] Furthermore, the degradation status of the cable outer sheath is assessed based on the degradation assessment coefficient, specifically as follows:

[0032] If γ≤1.97, the outer sheath of the tested cable is slightly deteriorated;

[0033] If 1.97 < γ ≤ 2.19, then the outer sheath of the tested cable is moderately deteriorated.

[0034] If γ > 2.19, the outer sheath of the cable under test is severely degraded.

[0035] In summary, this invention provides a method and system for assessing the degradation status of cable outer sheaths based on a degradation assessment coefficient. The method includes measuring the Shore hardness, dielectric strength, and elongation at break of the cable outer sheath; calculating the degradation assessment coefficient of the cable outer sheath using a pre-established formula, which includes a mathematical relationship between the degradation assessment coefficient and the Shore hardness, dielectric strength, and elongation at break; and assessing the degradation status of the cable outer sheath based on the degradation assessment coefficient. This invention assesses the degree of degradation of 110kV cable outer sheaths by measuring the Shore hardness, dielectric strength, and elongation at break of the cable outer sheath and calculating the degradation assessment coefficient. This method is simple, efficient, and can provide a good assessment of the degradation degree of 110kV cable outer sheaths. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A flowchart of a method for assessing the deterioration status of cable outer sheath based on a deterioration assessment coefficient, provided for an embodiment of the present invention. Detailed Implementation

[0038] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] Please see Figure 1 This invention provides a method for assessing the degradation status of cable outer sheaths based on a degradation assessment coefficient, comprising the following steps:

[0040] S1: Measure the Shore hardness, dielectric strength, and elongation at break of the outer sheath of the cable to be evaluated.

[0041] Shore hardness, also known as Shore scale hardness, is a method for testing and expressing the hardness of materials. Depending on the type of indenter, it can be divided into three types: Shore Type A, Type C, and Type D. Their measurement principles are completely the same; the only difference is the size of the measuring probe. For cable outer sheaths, the Shore hardness value is chosen as a factor to assess its degradation state.

[0042] Dielectric strength is a measure of the electrical strength of a material when it acts as an insulator. It is defined as the maximum voltage a unit thickness of a sample can withstand when it breaks down, expressed in volts per unit thickness. The higher the dielectric strength of a material, the better its quality as an insulator. Dielectric strength is chosen as another factor in assessing the degradation state of the outer sheath of cables.

[0043] The elongation at break of a fiber is generally expressed as the relative elongation at break, that is, the ratio of the fiber's elongation at break to its initial length, expressed as a percentage. It is an indicator of the fiber's softness and elasticity. A higher elongation at break indicates better softness and elasticity, and the fiber should have the required elongation at break depending on its intended use. Therefore, elongation at break is chosen as another factor in evaluating the outer sheath of cables.

[0044] In one embodiment of the present invention, the Shore hardness value of the cable outer sheath is measured by cutting the 110kV cable to be evaluated with an electric saw to obtain four groups of 25cm long short cable segments labeled i (i = 1, 2, 3, 4), and peeling off the cable PE outer sheath. The Shore hardness value D at both ends of the cable PE outer sheath is then measured using a Shore hardness tester. i1 D i2 (i = 1, 2, 3, 4), unit HD.

[0045] The process for measuring the dielectric strength of the cable outer sheath involves cutting four square samples, each 0.2 mm thick and 1 cm on each side, from each section of the PE outer sheath. A pressure testing device is used to conduct the dielectric strength test, with a slow voltage increase rate of 0.1 kV / s until the sample is broken down. The test result is recorded as ds. i1 ds i2 ds i3 ds i4 (i = 1, 2, 3, 4), unit kV / mm

[0046] The process for measuring the elongation at break of the cable outer sheath involves using a machine tool to cut dumbbell-shaped samples, each 15cm long and 5mm thick, from the PE outer sheath of each cable segment. Four samples are made from each cable segment, resulting in a total of 16 samples. These samples are then subjected to mechanical tensile testing, and the elongation at break of the samples is obtained as e. i1 e i2 e i3 e i4 (i = 1, 2, 3, 4).

[0047] S2: Calculate the degradation assessment coefficient of the cable outer sheath using a pre-established degradation assessment coefficient calculation formula. The degradation assessment coefficient calculation formula includes the mathematical relationship between the degradation assessment coefficient and the Shore hardness value, dielectric strength value and elongation at break.

[0048] Most cross-linked polyethylene (XLPE) cables of 110kV and above are single-core structures. XLPE cables exhibit excellent performance in terms of heat resistance, electrical properties, and mechanical properties. However, after long-term operation, dendritic aging can easily occur within the insulation layer, leading to a decrease in insulation performance and a shortened lifespan. The main characteristics of cable insulation aging include decreased insulation resistance, increased operating temperature, and increased dielectric loss.

[0049] There are many reasons for cable insulation degradation, and any factor causing insulation degradation will reduce the cable's insulation resistance. In this embodiment, from the perspective of the cable's mechanical properties, three factors—Shore hardness, dielectric strength, and elongation at break—are selected to assess the degree of change in the cable's mechanical properties, thereby evaluating the cable's degradation state. For cables used for a long time, selecting mechanical parameters for degradation state assessment can more accurately reflect its true degradation state, and the parameters used for assessment are also relatively easy to obtain.

[0050] S3: Evaluate the degradation status of the cable outer sheath based on the degradation assessment coefficient.

[0051] This embodiment provides a method for assessing the degradation status of cable outer sheaths based on a degradation assessment coefficient. The method includes measuring the Shore hardness, dielectric strength, and elongation at break of the cable outer sheath; calculating the degradation assessment coefficient of the cable outer sheath using a pre-established formula, which includes a mathematical relationship between the degradation assessment coefficient and the Shore hardness, dielectric strength, and elongation at break; and assessing the degradation status of the cable outer sheath based on the degradation assessment coefficient. This invention assesses the degree of degradation of 110kV cable outer sheaths by measuring the Shore hardness, dielectric strength, and elongation at break of the cable outer sheath and calculating the degradation assessment coefficient. This method is simple, efficient, and can provide a good assessment of the degradation degree of 110kV cable outer sheaths.

[0052] In one embodiment of the present invention, the formula for calculating the degradation assessment coefficient can be constructed as follows:

[0053]

[0054] In the formula, γ represents the degradation assessment coefficient, and D i1 D i2 ds represents the Shore hardness values ​​at both ends of the outer sheath of the i-th cable segment. i1 ds i2 ds i3 ds i4 These represent the dielectric strength values ​​of the four square samples on the outer sheath of the i-th cable segment, respectively. imax e imin Let be the maximum and minimum elongation at break of the dumbbell-shaped sample of the outer sheath of the i-th cable segment.

[0055] The cracking state analysis of cable outer sheaths can be evaluated based on their mechanical and electrical properties. Shore hardness and elongation at break are used to reflect mechanical properties. Cables laid underground for extended periods are subjected to the combined effects of ambient temperature and humidity, causing the sheath material to decompose and volatilize, essentially due to the breaking of molecular bonds. In actual test results, Shore hardness and elongation at break decrease with increasing cable service time. During the deterioration process of the cable outer sheath, the breakage of polymer bonds also affects its dielectric properties. Tests have shown that the change in dielectric strength is more significant than other electrical parameters; therefore, dielectric strength is chosen as the degradation assessment value. Since the primary function of the cable outer sheath is to provide protection and mechanical support, not electrical insulation, its degradation can still be reflected in electrical parameters. Considering that mechanical and electrical parameters can characterize degradation from multiple perspectives more comprehensively than a single mechanical parameter, two mechanical parameters and one electrical parameter are selected as evaluation parameters to make the assessment more accurate.

[0056] The coefficients in the formula are determined based on the fitting of experimental measured data with the formula. The purpose is to emphasize or de-emphasize certain measurement parameters, making the evaluation process simpler and more convenient when analyzing multivariate models. The formula coefficients affect the classification of the evaluation levels, and since the coefficients are determined based on experimental test data, this evaluation method can effectively assess the degradation status of cable outer sheaths, making it convenient, efficient, and practically valuable.

[0057] Based on the constructed degradation assessment coefficient calculation formula, and after calculating the degradation assessment coefficient using the actual values ​​of each measured parameter, in one embodiment of the present invention, the degradation assessment is specifically as follows:

[0058] If γ≤1.97, the outer sheath of the tested cable is slightly deteriorated;

[0059] If 1.97 < γ ≤ 2.19, then the outer sheath of the tested cable is moderately deteriorated.

[0060] If γ > 2.19, the outer sheath of the cable under test is severely degraded.

[0061] The above is a detailed description of an embodiment of a cable outer sheath degradation status assessment method based on degradation assessment coefficient of the present invention. The following will provide a detailed description of an embodiment of a cable outer sheath degradation status assessment system based on degradation assessment coefficient of the present invention.

[0062] This embodiment provides a cable outer sheath degradation status assessment system based on a degradation assessment coefficient, including:

[0063] The acquisition unit is used to acquire the Shore hardness, dielectric strength, and elongation at break of the outer sheath of the cable to be evaluated.

[0064] The calculation unit is used to calculate the degradation evaluation coefficient of the cable outer sheath using a pre-established degradation evaluation coefficient calculation formula. The degradation evaluation coefficient calculation formula contains the mathematical relationship between the degradation evaluation coefficient and the Shore hardness value, dielectric strength value and elongation at break.

[0065] An evaluation unit is used to assess the degradation status of the cable outer sheath based on a degradation evaluation coefficient.

[0066] Furthermore, the specific formula for calculating the degradation assessment coefficient is as follows:

[0067]

[0068] In the formula, γ represents the degradation assessment coefficient, and D i1 D i2 ds represents the Shore hardness values ​​at both ends of the outer sheath of the i-th cable segment. i1 ds i2 ds i3 ds i4 These represent the dielectric strength values ​​of the four square samples on the outer sheath of the i-th cable segment, respectively. imax e imin Let be the maximum and minimum elongation at break of the dumbbell-shaped sample of the outer sheath of the i-th cable segment.

[0069] Furthermore, the degradation status of the cable outer sheath is assessed based on the degradation assessment coefficient, specifically as follows:

[0070] If γ≤1.97, the outer sheath of the tested cable is slightly deteriorated;

[0071] If 1.97 < γ ≤ 2.19, then the outer sheath of the tested cable is moderately deteriorated.

[0072] If γ > 2.19, the outer sheath of the cable under test is severely degraded.

[0073] It should be noted that the degradation status assessment system provided in this embodiment is used to implement the degradation status assessment method provided in the aforementioned embodiment. The specific settings of each unit are based on the complete implementation of the method, and will not be repeated here.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the deterioration state of an outer sheath of a cable based on a deterioration evaluation coefficient, characterized by, The method comprises the following steps: measuring the Shore hardness value, dielectric strength value and elongation at break of the cable outer sheath to be evaluated; calculating the degradation evaluation coefficient of the cable outer sheath by using a pre-established degradation evaluation coefficient calculation formula, wherein the degradation evaluation coefficient calculation formula comprises a mathematical relationship between the degradation evaluation coefficient and the Shore hardness value, dielectric strength value and elongation at break; evaluating the degradation state of the cable outer sheath based on the degradation evaluation coefficient; the degradation evaluation coefficient calculation formula is specifically as follows: ； In the formula, This represents the degradation assessment coefficient. , They represent the first The Shore hardness values ​​at both ends of the outer sheath of the cable segment. , , , They represent the first The dielectric strength values ​​of four square samples on the outer sheath of the cable segment. , For the first The maximum and minimum elongation at break in dumbbell-shaped samples of the outer sheath of the cable segment; the Shore hardness value is specifically as follows: measuring a plurality of sets of Shore hardness values at both ends of a plurality of cable segments of the same length by using a Shore hardness tester, wherein the plurality of cable segments of the same length are obtained by cutting the cable outer sheath to be evaluated; the dielectric strength value is specifically as follows: obtaining a plurality of dielectric strength values by performing a dielectric strength test experiment on a plurality of square samples by using a pressure device, wherein the plurality of square samples are obtained by cutting a plurality of square samples of the same size from each cable segment of the same length; the elongation at break is specifically as follows: obtaining a plurality of elongation at break values by performing a mechanical tensile test on a plurality of dumbbell-shaped samples, wherein the plurality of dumbbell-shaped samples are obtained by cutting a plurality of dumbbell-shaped samples of the same size from each cable segment of the same length.

2. The cable outer sheath deterioration state evaluation method based on a deterioration evaluation coefficient according to claim 1, characterized by, In the dielectric strength test experiment, the voltage boosting mode is slow voltage boosting, and the voltage boosting rate is 0.1 kV / s until the sample is broken down, and a test result is obtained.

3. The cable outer sheath deterioration state evaluation method based on a deterioration evaluation coefficient according to claim 1, characterized by, evaluating the degradation state of the cable outer sheath based on the degradation evaluation coefficient, specifically as follows: If , then the measured cable outer jacket is slightly deteriorated; If , the outer sheath of the cable under test is moderately deteriorated; If , then the outer jacket of the cable under test is severely degraded.

4. A cable outer sheath deterioration state evaluation system based on a deterioration evaluation coefficient, characterized by, comprises: a collection unit configured to collect the Shore hardness value, dielectric strength value and elongation at break of the cable outer sheath to be evaluated; a calculation unit configured to calculate the degradation evaluation coefficient of the cable outer sheath by using a pre-established degradation evaluation coefficient calculation formula, wherein the degradation evaluation coefficient calculation formula comprises a mathematical relationship between the degradation evaluation coefficient and the Shore hardness value, dielectric strength value and elongation at break; an evaluation unit configured to evaluate the degradation state of the cable outer sheath based on the degradation evaluation coefficient; the degradation evaluation coefficient calculation formula is specifically as follows: ； In the formula, This represents the degradation assessment coefficient. , They represent the first The Shore hardness values ​​at both ends of the outer sheath of the cable segment. , , , They represent the first The dielectric strength values ​​of four square samples on the outer sheath of the cable segment. , For the first The maximum and minimum elongation at break in dumbbell-shaped samples of the outer sheath of the cable segment; the Shore hardness value is specifically as follows: measuring a plurality of sets of Shore hardness values at both ends of a plurality of cable segments of the same length by using a Shore hardness tester, wherein the plurality of cable segments of the same length are obtained by cutting the cable outer sheath to be evaluated; the dielectric strength value is specifically as follows: obtaining a plurality of dielectric strength values by performing a dielectric strength test experiment on a plurality of square samples by using a pressure device, wherein the plurality of square samples are obtained by cutting a plurality of square samples of the same size from each cable segment of the same length; the elongation at break is specifically as follows: obtaining a plurality of elongation at break values by performing a mechanical tensile test on a plurality of dumbbell-shaped samples, wherein the plurality of dumbbell-shaped samples are obtained by cutting a plurality of dumbbell-shaped samples of the same size from each cable segment of the same length.

5. The cable outer sheath deterioration state evaluation system based on a deterioration evaluation coefficient according to claim 4, characterized by, evaluating the degradation state of the cable outer sheath based on the degradation evaluation coefficient, specifically as follows: If , then the measured cable outer jacket is slightly deteriorated; If , the outer sheath of the cable under test is moderately deteriorated; If , then the outer jacket of the cable under test is severely deteriorated.

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