A method for accelerated thermal oxidative aging testing of thermoplastic cable insulation

Abstract

The application discloses a kind of accelerated thermal oxygen aging test methods of thermoplastic cable insulation material, belong to high polymer material detection technical field, comprising the following steps: (1) the melting temperature of thermoplastic cable insulation material is determined, and it is Tm, unit is K;(2) the aging activation energy of thermoplastic cable insulation material is determined, and it is Ea, unit is kJ / mol;(3) thermoplastic cable insulation material is carried out accelerated thermal oxygen aging test under temperature T1 and air flow environment;(4) determine accelerated thermal oxygen aging test time t1, unit is day;(5) according to formula, the thermal oxidation aging life t2 of thermoplastic cable insulation material is calculated when working temperature is T2;The application can effectively reduce aging test time, shorten test cycle, the application is characterized by the breaking elongation or carboxyl index of thermoplastic cable insulation material to represent test end point, can further shorten test cycle, improve the accuracy of detection result.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high polymer material detection, and particularly relates to an accelerated thermal oxygen aging test method for thermoplastic cable insulation materials. BACKGROUND

[0002] With the development of science and technology, cross-linked polyethylene (XLPE) has excellent electrical properties, mechanical properties and heat resistance due to its chemical cross-linked network structure, and the working temperature of low-density polyethylene is improved. Because of these advantages, XLPE has gradually become the preferred material for the main insulation of extruded power cables. However, XLPE is a thermosetting material, and the chemical cross-linking produces a network structure, which improves the mechanical and heat resistance properties, but the chemical network structure has good thermal stability and is difficult to decompose, which makes it difficult to recycle XLPE.

[0003] As one of the potential alternative materials, thermoplastic polyolefin material has become one of the focuses of experts and scholars in this field at home and abroad due to its advantages in manufacturing, processing technology, energy consumption, easy recycling and recycling after the end of cable life. The International Council on Large Electric Systems (CIGRE) has established a working group to evaluate the energy consumption cost of new thermoplastic polyolefin materials and traditional XLPE throughout the life cycle. Through actual investigation and simulation, the new thermoplastic insulation material and the traditional XLPE used in high-voltage cable insulation are compared and analyzed. The results show that from the economic cost, the new thermoplastic insulation material reduces the material cost by about 14%, and when considering the material of the entire cable system, the overall cost is reduced by about 17%; in terms of energy consumption, the new thermoplastic insulation material extruded cable process does not need to cross-link, degas and other energy-consuming links, and in terms of carbon emissions, GWP (global warming potential) is about 20% lower than that of XLPE, which undoubtedly shows the advantages of thermoplastic polyolefin cable insulation material in the future development of cables.

[0004] In actual application process, due to the long-term high-voltage operation condition of the insulation equipment, heat phenomenon exists in most cases, and the polyolefin insulation material will appear thermal oxidative aging in the long-term operation process. Therefore, in order to be closer to the actual application, it is necessary to further study the electrical insulation performance of the insulation material under the thermal oxidative aging condition. The existing research shows that when the polyolefin material appears thermal oxidative aging, the tertiary carbon atoms of the molecular chain will undergo beta scission, so that the macromolecular chain is cracked into small molecular chains, and a large number of molecular groups such as hydroxyl and carboxyl groups and free radicals are generated. In this process, the mechanical properties of the material as a whole will decrease, which is manifested as the decrease of the elastic modulus and the decrease of the elongation at break, and at the same time, due to the degradation of the molecular structure of the amorphous region of the material, the number of defects in the material increases, so that the electrical insulation performance of the material also decreases, which is manifested as the decrease of the macroscopic breakdown field strength of the material, the increase of the dielectric loss and the increase of the space charge accumulation. That is, the occurrence of thermal oxidative aging will lead to the decrease of the mechanical and insulation properties of the polyolefin insulation material, which no longer meets the requirements of the cable insulation performance.

[0005] In order to evaluate the thermal oxidative aging resistance of the material, the insulation material is usually subjected to accelerated thermal oxidative aging test, and the material is placed in an environment higher than the actual working temperature to accelerate the thermal oxidative aging reaction of the material. Based on previous research, every time the temperature is increased by 8℃, the service life of the insulation material is reduced by half. At present, the standard for the accelerated thermal oxidative aging test of thermoplastic materials is mainly GB / T 11026 and IEC62895. The test characteristics of this standard are as follows: 1. This test standard is aimed at a plurality of cable insulation materials, including thermosetting materials represented by XLPE and thermoplastic materials represented by HDPE, and the material is not targeted. 2. In the current test standard, the accelerated aging temperature of the thermoplastic material is lower than the melting point of the material itself, and the test period is long. 3. The end criterion of the material aging test in the current test standard is single, and the representation means is few. The accelerated thermal oxidative aging test of the thermoplastic insulation material according to the current standard cannot completely meet the performance test requirements of the thermoplastic cable.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] The purpose of the present application is to overcome the deficiencies in the prior art and provide an accelerated thermal oxidative aging test method for thermoplastic cable insulation materials. The accelerated thermal oxidative aging test method of the present application carries out accelerated thermal oxidative aging test in an environment higher than the melting temperature of the material, which can effectively reduce the aging test time and shorten the test period. The present application uses the elongation at break or the carboxyl index of the thermoplastic cable insulation material to represent the test end point, which can further shorten the test period and improve the accuracy of the test results.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] An accelerated thermal-oxidative aging test method of thermoplastic cable insulation material, comprising the following steps:

[0010] (1) determining the melting temperature of the thermoplastic cable insulation material, denoted as Tm, unit K;

[0011] (2) determining the aging activation energy of the thermoplastic cable insulation material, denoted as Ea, unit kJ / mol;

[0012] (3) performing accelerated thermal-oxidative aging test on the thermoplastic cable insulation material at temperature T1 and air flow environment;

[0013] (4) determining the accelerated thermal-oxidative aging test time t1, unit day;

[0014] (5) calculating the thermal-oxidative aging life t2 of the thermoplastic cable insulation material at working temperature T2 according to the formula;

[0015]

[0016] Wherein, 0≤T1-Tm≤30;

[0017] R is the universal gas constant, unit J / (mol·K); T2 unit K, t2 unit day.

[0018] The accelerated thermal-oxidative aging test method of the present application performs accelerated thermal-oxidative aging test in an environment higher than the melting temperature of the material, which can effectively reduce the aging test time and shorten the test cycle. The present application uses the elongation at break or carboxyl index of the thermoplastic cable insulation material to represent the test endpoint, which can further shorten the test cycle and improve the accuracy of the detection results.

[0019] Compared with the existing Arrhenius formula test aging cycle as shown below, there is no need to measure and calculate the material aging reaction rate k and constant A, and the aging life t2 of the material at working temperature T2 can be obtained directly by selecting the test temperature T1 and the aging cycle t1 at this temperature.

[0020]

[0021] In the formula: k is the material aging reaction rate at temperature T, R is the universal gas constant, and A is a constant related to the material properties.

[0022] As a preferred embodiment of the present application, the melting temperature of the thermoplastic cable insulation material is obtained by differential scanning calorimetry test.

[0023] As a preferred embodiment of the present application, the size of the thermoplastic cable insulation material is (5-20) cm x (5-20) cm x (0.5-2) cm.

[0024] As a preferred embodiment of the present invention, the following condition is satisfied: 5≤T1-Tm≤30.

[0025] As a preferred embodiment of the present invention, the accelerated thermo-oxidative aging test time t1 is determined as follows: when the elongation at break of the thermoplastic cable insulation material is less than 350% at a tensile rate of 100 mm / min, the time t1 at this time is recorded.

[0026] As a preferred embodiment of the present invention, the accelerated thermo-oxidative aging test time t1 is determined as follows: when the internal carboxyl index of the thermoplastic cable insulation material is higher than that of the surface, the time t1 at this time is recorded.

[0027] In a preferred embodiment of the present invention, the carboxyl index = A 1720 / A 2010 ;

[0028] Where A 1720 The infrared spectrum is 1850–1690 cm⁻¹ -1 The carbonyl absorption peak area within the range, A 2010 To exclude 1480-1450cm -1 The area of ​​the methylene absorption peak within the range.

[0029] It should be noted that when testing the internal carboxyl index of thermoplastic cable insulation materials, a small sample of 2-3cm × 1cm × 1mm is cut, and a 100μm thin film is cut from the 2-3cm × 1mm cross section using a cold cutter at -15℃ as the sample.

[0030] It should be noted that, when testing the elongation at break, dumbbell-shaped samples are cut from the thermoplastic cable insulation material samples to be tested.

[0031] In a preferred embodiment of the present invention, the accelerated thermo-oxidative aging test is carried out in a test apparatus, the test apparatus having a plate and a support for supporting the plate inside.

[0032] The sheet material is required to have a melting point above 200℃ and not exhibit significant bending or shrinkage at 200℃, such as polytetrafluoroethylene (PTFE). The entire support frame is made of brass.

[0033] This invention does not require the use of specific testing equipment; conventional testing equipment can be used to complete the aging test experiments of this invention.

[0034] In a preferred embodiment of the present invention, the test apparatus is electrically connected to a heating device.

[0035] In a preferred embodiment of the present invention, the operating temperature of the cable is 233.15K to 363.15K.

[0036] In a preferred embodiment of the present invention, the test apparatus is connected to a blower to place the thermoplastic cable insulation material in an airflow environment.

[0037] The beneficial effects of the present invention are as follows: The accelerated thermo-oxidative aging test method of the present invention conducts accelerated thermo-oxidative aging tests in an environment higher than the melting temperature of the material, which can effectively reduce the aging test time and shorten the test cycle. The present invention uses the elongation at break or carboxyl index of thermoplastic cable insulation material to characterize the test endpoint, which can further shorten the test cycle and improve the accuracy of the test results. Attached Figure Description

[0038] Figure 1 This is a diagram of the experimental apparatus of the present invention.

[0039] Figure 2 This is a diagram showing the internal carbonyl index of the thermoplastic cable insulation material in Example 1.

[0040] Figure 3 This is a diagram showing the internal carbonyl index of the thermoplastic cable insulation material in Example 1.

[0041] Figure 4 This is a graph showing the variation of the internal carbonyl index of the thermoplastic cable insulation material in Example 1.

[0042] Figure 5 This is a graph showing the change in elongation at break of the thermoplastic cable insulation material in Example 2. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0045] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0046] In this application, there are no particular restrictions on the specific dispersion and mixing methods.

[0047] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0048] The following embodiments are provided to facilitate understanding of the invention. These embodiments are not intended to limit the scope of the claims.

[0049] Example 1

[0050] An accelerated thermo-oxidative aging test method for thermoplastic cable insulation materials includes the following steps:

[0051] (1) The melting temperature of the thermoplastic cable insulation material was determined to be 401.15 K by differential scanning calorimetry, and denoted as Tm;

[0052] (2) The aging activation energy of the thermoplastic cable insulation material was determined to be 184.23 kJ / mol, denoted as Ea;

[0053] (3) Estimate the number of samples required during the aging test cycle, and use a tablet press to prepare 10×10×1mm samples of thermoplastic cable insulation material for later use;

[0054] Provide such as Figure 1 The test apparatus shown has a plate 1 and a bracket 2 for supporting the plate inside. The test apparatus has multiple mounting parts 3, of which the upper mounting part is used to electrically connect to the heating device, and the left and right mounting parts are used to connect to the blower.

[0055] Place the thermoplastic cable insulation material in, for example... Figure 1 The test apparatus shown has an external heating device connected to the plate surface via wires, and the thermoplastic cable insulation material is placed in an airflow environment by a blower to conduct accelerated thermo-oxidative aging tests at 413.15K.

[0056] (4) During the accelerated thermo-oxidative aging test, a fixed time period of 5 days is set, such as... Figures 2-4 As shown, samples were taken at set intervals and the degree of material aging was evaluated by infrared testing. No obvious carbonyl peak index was found in the 15-day aged sample, but when the 20-day aged sample was tested, an obvious carbonyl index peak appeared in the material. When the internal carboxyl index of the thermoplastic cable insulation material was higher than that on the surface, the aging test ended, and the aging life of the material at 413.15K was recorded. The median value of 17.5 days between 15 and 20 days was taken.

[0057] (5) Calculate the thermal oxidation aging life t2 of the thermoplastic cable insulation material at the working temperature T2 according to the formula;

[0058]

[0059] Substituting the thermodynamic temperature of single-point thermal aging (140℃, 413.15K), the thermodynamic temperature T2 of the cable's operating temperature (90℃, 363.15K), and the aging time t1 = 17.5d into the equation:

[0060]

[0061] The calculation yields 17.5 × 5.092 × 10 -24 = t2 × 3.161 × 10 -27 From this, we can obtain t2 = 28354d, and calculate that the lifespan t2 of the thermally heated plastic cable insulation material at 90℃ will exceed 28354 days, or about 77 years.

[0062] Example 2

[0063] An accelerated thermo-oxidative aging test method for thermoplastic cable insulation materials includes the following steps:

[0064] (1) The melting temperature of the thermoplastic cable insulation material was determined to be 401.15 K by differential scanning calorimetry, and denoted as Tm;

[0065] (2) The aging activation energy of the thermoplastic cable insulation material was determined to be 184.23 kJ / mol, denoted as Ea;

[0066] (3) Estimate the number of samples required during the aging test cycle, and use a tablet press to prepare 10×10×1mm samples of thermoplastic cable insulation material for later use;

[0067] Provide such as Figure 1 The test apparatus shown has a plate 1 and a bracket 2 for supporting the plate inside. The test apparatus has multiple mounting parts 3, of which the upper mounting part is used to electrically connect to the heating device, and the left and right mounting parts are used to connect to the blower.

[0068] Place the thermoplastic cable insulation material in, for example... Figure 1 The test apparatus shown has an external heating device connected to the plate surface via wires, and the thermoplastic cable insulation material is placed in an airflow environment by a blower to conduct accelerated thermo-oxidative aging tests at 413.15K.

[0069] (4) During the accelerated thermo-oxidative aging test, a fixed time period of 3 days is set, such as... Figure 5As shown, samples were taken at set intervals and the degree of material aging was evaluated by tensile testing. When the sample aged for 18 days was tested, the elongation at break of the material was less than 350%, the aging test ended, and the aging life of the material at 140℃ was recorded. The midpoint between 15 and 18 days, 16.5 days, was taken.

[0070] (5) Calculate the thermal oxidation aging life t2 of the thermoplastic cable insulation material at the working temperature T2 according to the formula;

[0071]

[0072] Substituting the thermodynamic temperature of single-point thermal aging (140℃, 413.15K), the thermodynamic temperature T2 of the cable operating temperature (90℃, 363.15K), and the aging time t1 = 16.5d into the equation, it can be calculated that the lifespan t2 of the thermoplastic cable insulation material at 90℃ will exceed 26733 days, or approximately 73 years.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for accelerating thermo-oxidative aging testing of thermoplastic cable insulation materials, characterized in that, Includes the following steps: (1) Determine the melting temperature of the thermoplastic cable insulation material, denoted as Tm, in K; (2) The aging activation energy of thermoplastic cable insulation material is determined and denoted as Ea, with the unit being kJ / mol; (3) The thermoplastic cable insulation material was subjected to accelerated thermo-oxidative aging test at temperature T1 and in an airflow environment; (4) Determine the accelerated thermo-oxidative aging test time t1, in days; (5) Calculate the thermal oxidation aging life t2 of the thermoplastic cable insulation material at the working temperature T2 according to the formula; Where, 5≤T1-Tm≤30; R is the universal gas constant, with units of J / (mol·K); T2 is in K, and t2 is in day; The accelerated thermo-oxidative aging test time t1 is determined as follows: when the internal carboxyl index of the thermoplastic cable insulation material is higher than that on the surface, the time t1 is recorded; the carboxyl index = A 1720 / A 2010 ; Where A 1720 The infrared spectrum ranges from 1850 to 1690 cm⁻¹ -1 The carbonyl absorption peak area within the range, A 2010 To exclude 1480~1450cm -1 The area of ​​the methylene absorption peak within the range.

2. The accelerated thermo-oxidative aging test method for thermoplastic cable insulation materials according to claim 1, characterized in that, The melting temperature of the thermoplastic cable insulation material was obtained by differential scanning calorimetry.

3. The accelerated thermo-oxidative aging test method for thermoplastic cable insulation materials according to claim 1, characterized in that, The dimensions of the thermoplastic cable insulation material are (5~20)cm×(5~20)cm×(0.5~2)cm.

4. The accelerated thermo-oxidative aging test method for thermoplastic cable insulation materials according to claim 1, characterized in that, The accelerated thermo-oxidative aging test is conducted in a test apparatus, which contains a plate and a support for the plate.

5. The accelerated thermo-oxidative aging test method for thermoplastic cable insulation materials according to claim 4, characterized in that, The test apparatus is electrically connected to a heating device.

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