A method for improving the DC electrical performance of low-density polyethylene insulation material

Abstract

This invention discloses a method for improving the DC electrical performance of low-density polyethylene (LDPE) insulation materials, belonging to the technical field of electrical insulation materials. The key technical points are: LDPE is blended with organic small-molecule fillers, using LDPE as the substrate to obtain a LDPE composite insulation material. This material exhibits good compatibility between the matrix and the filler, avoiding the agglomeration of inorganic fillers within the LDPE matrix. It also eliminates the complex chemical reactions and difficulty in controlling the grafting rate inherent in traditional grafting methods, while reducing byproducts from chemical reactions, thus offering greater application value in practical engineering.

Description

Technical Field

[0001] This invention relates to the field of electrical insulation materials technology, specifically to a method for improving the DC electrical performance of low-density polyethylene insulation materials. Background Technology

[0002] High-voltage direct current (HVDC) cables are key components of HVDC transmission systems, and the long-term stable operation of these systems depends on the electrical performance of the cable insulation materials. As the voltage level of HVDC transmission increases, the electrical stress on the insulation materials gradually increases. This easily leads to the accumulation of space charge, causing distortion of the electric field distribution within the insulation material, accelerating its deterioration, aging, and even breakdown. Therefore, improving the DC electrical performance of insulation materials is of great value for the development of HVDC transmission.

[0003] Polyethylene (PE) is widely used as insulation material for high-voltage direct current (HVDC) cables due to its excellent electrical properties and stable chemical properties. To meet the demands of higher transmission voltage levels and improve the DC electrical performance of PE insulation materials, common strategies include material purification and modification. Currently used PE insulation matrices are typically ultra-pure materials; further improvements to the purification process not only present technical challenges but are also not economically viable.

[0004] Material modification is divided into inorganic doping and organic doping. For inorganic doped composite insulating materials, the poor compatibility of inorganic fillers with the matrix and their tendency to agglomerate within the polyethylene matrix remain persistent problems, thus limiting their engineering applications. Organic molecules exhibit better compatibility and dispersibility with the matrix, showing potential value in engineering applications. Although grafting organic molecules into polyethylene can effectively improve the material's DC electrical properties, the complex grafting process and the need to eliminate byproducts increase the complexity of material processing. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for improving the DC electrical performance of low-density polyethylene insulation material, so as to solve the problems in the background technology.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for improving the DC electrical performance of low-density polyethylene insulation material includes adding small organic molecule fillers to low-density polyethylene for blending, using low-density polyethylene as a base, to obtain a low-density polyethylene composite insulation material.

[0008] As a further aspect of the present invention, the blending ratio is 0.05 to 1.0 parts of organic small molecule filler added to 100 parts of low-density polyethylene matrix.

[0009] As a further aspect of the present invention, the blending step is as follows:

[0010] Step 1: Turn on the torque rheometer and set the temperature and speed;

[0011] Step 2: Place the low-density polyethylene into a torque rheometer for blending, so that the low-density polyethylene is transformed into a molten state;

[0012] Step 3: Add small organic molecule fillers to the molten low-density polyethylene, and continue blending while keeping the temperature and rotation speed constant;

[0013] Step 4: After blending, remove the material and allow it to cool to obtain low-density polyethylene composite insulation material.

[0014] As a further aspect of the present invention, the temperature of the torque rheometer is set to 105–120°C, and the rotational speed is set to 50–70 rpm.

[0015] As a further embodiment of the present invention, the mixing time in step two is 5 to 10 minutes.

[0016] As a further embodiment of the present invention, the mixing time in step three is 5 to 30 minutes.

[0017] As a further embodiment of the present invention, the organic small molecule filler is one of 1,4-dimethoxybenzene, Span 60, bimethyl acetophenone, 4-methoxyacetophenone, octadecylamine polyoxyethylene ether, and bisphenol A polyoxyethylene ether.

[0018] In summary, the embodiments of the present invention have the following beneficial effects compared with the prior art:

[0019] 1. Doping organic small molecule fillers into low-density polyethylene matrix results in good compatibility between the matrix and the fillers, avoiding the agglomeration of inorganic fillers in the low-density polyethylene matrix.

[0020] 2. The low-density polyethylene matrix and organic small molecule filler are blended to prepare composite materials. The preparation process is simple, avoiding the complex chemical reactions and difficulty in controlling the grafting rate in traditional grafting. At the same time, it reduces the by-products of chemical reactions, making it more valuable for practical engineering applications.

[0021] 3. By adding organic molecules, the DC electrical properties of low-density polyethylene insulation materials can be improved, the accumulation of space charge within the low-density polyethylene insulation materials can be suppressed, the DC breakdown field strength can be increased, and the DC conductivity can be reduced.

[0022] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0023] Figure 1 This is a Weibull distribution diagram of the DC breakdown performance of the comparative example and the embodiment;

[0024] Figure 2 The conductivity of the control example and the embodiment under a DC electric field of 40 kV / mm;

[0025] Figure 3 This is the space charge curve of the control example;

[0026] Figure 4 This is the space charge curve of Example 1;

[0027] Figure 5 This is the space charge curve of Example 2;

[0028] Figure 6 This is the space charge curve of Example 3;

[0029] Figure 7 This is the space charge curve of Example 4;

[0030] Figure 8 The average space charge volume density is compared with that of the control example and the embodiment. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0033] In one embodiment, a method for improving the DC electrical performance of low-density polyethylene insulation material is described in [reference needed]. Figures 1 to 8 This includes blending low-density polyethylene with small organic molecule fillers, using low-density polyethylene as a base, to obtain a low-density polyethylene composite insulation material.

[0034] Furthermore, the blending ratio is 0.05 to 1.0 parts of organic small molecule filler added to 100 parts of low-density polyethylene matrix.

[0035] Furthermore, the blending step is as follows:

[0036] Step 1: Turn on the torque rheometer and set the temperature and speed;

[0037] Step 2: Place the low-density polyethylene into a torque rheometer for blending, so that the low-density polyethylene is transformed into a molten state;

[0038] Step 3: Add small organic molecule fillers to the molten low-density polyethylene, and continue blending while keeping the temperature and rotation speed constant;

[0039] Step 4: After blending, remove the material and allow it to cool to obtain low-density polyethylene composite insulation material.

[0040] Furthermore, the temperature of the torque rheometer is set to 105–120°C, and the rotational speed is set to 50–70 rpm.

[0041] Furthermore, the mixing time in step two is 5 to 10 minutes.

[0042] Furthermore, the mixing time in step three is 5 to 30 minutes.

[0043] Furthermore, the organic small molecule filler is one of 1,4-dimethoxybenzene, Span 60, bimethyl acetophenone, 4-methoxyacetophenone, octadecylamine polyoxyethylene ether, and bisphenol A polyoxyethylene ether.

[0044] Example 1: The temperature of the torque rheometer was set to 110℃ and the rotation speed to 60 rpm. Low-density polyethylene was placed in the torque rheometer and blended for 5 minutes to bring it to a molten state. Then, 0.05 wt% of 1,4-dimethoxybenzene was added to the molten low-density polyethylene, and the blending was continued for 10 minutes while maintaining the temperature and rotation speed. After blending was completed, the material was removed and allowed to cool to obtain a low-density polyethylene composite insulation material.

[0045] Example 2: Unlike Example 1, the added organic small molecule mass fraction was 0.1 wt%.

[0046] Example 3: Unlike Example 2, the added organic small molecule mass fraction was 0.3 wt%.

[0047] Example 4: Unlike Example 3, the added organic small molecule mass fraction was 1.0 wt%.

[0048] Comparative Example: Unlike Example 4, the added organic small molecule mass fraction was 0 wt%.

[0049] Five groups of samples, including the examples and control examples, were subjected to breakdown field strength tests, conductivity tests, and pulse electroacoustic (PEA) tests.

[0050] The breakdown field strength test was conducted using a ball-to-ball electrode testing system. Based on the obtained DC breakdown field strength, the failure probability and the Weibull distribution function of the applied DC electric field were plotted.

[0051] The conductivity was measured using a three-electrode system, and the DC conductivity of the sample was obtained after being pressurized for 20 minutes under an electric field strength of 40 kV / mm.

[0052] The space charge density of the sample was measured using the pulse electroacoustic (PEA) method at a temperature of 30℃ and an applied electric field strength of 40 kV / mm. The polarization time and short-circuit time were both 30 min. The average space charge volume density was calculated based on the sample thickness and the positions of the upper and lower electrodes using the following formula:

[0053]

[0054] In the formula, Q is the average space charge volume density, L is the sample thickness, x1 and x2 are the upper and lower electrode positions in the space charge test results, respectively, ρ(t,x) is the space charge distribution result inside the sample, x is the space position inside the sample, and t is time.

[0055] like Figure 1 As shown in Figure 2, compared with the control example, the DC breakdown field strength of each group of embodiments was significantly increased, and the DC conductivity was significantly reduced. Among them, Embodiment 2 had the highest breakdown field strength, which was 22% higher than the control example; and Embodiment 2 had the lowest DC conductivity, which was 76 times lower than the control example.

[0056] like Figure 3-7 As shown, the control example accumulated a large amount of opposite-polarity space charge near the cathode; the opposite-polarity space charge accumulated near the cathode in each of the embodiments was significantly reduced. Among them, Embodiment 2 had the least amount of opposite-polarity space charge accumulated near the cathode.

[0057] like Figure 8 As shown, the control example had the highest average volume charge density; the average volume charge density of each group of examples decreased significantly. Among them, Example 2 had the lowest average volume charge density, which was reduced by 37% compared to the control example; while Example 4, which had the highest filler content, had an increased average volume charge density compared to Example 2, but it was still lower than that of the control example.

[0058] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the DC electrical performance of low-density polyethylene insulation material, characterized in that, The invention includes blending low-density polyethylene with organic small molecule fillers, using low-density polyethylene as a base to obtain a low-density polyethylene composite insulation material, wherein the organic small molecule filler is 1,4-dimethoxybenzene. The blending ratio is 0.05 to 1.0 parts of organic small molecule filler added to 100 parts of low-density polyethylene matrix.

2. The method for improving the DC electrical performance of low-density polyethylene insulation material according to claim 1, characterized in that, The blending steps are as follows: Step 1: Turn on the torque rheometer and set the temperature and speed; Step 2: Place the low-density polyethylene into a torque rheometer for blending, so that the low-density polyethylene is transformed into a molten state; Step 3: Add small organic molecule fillers to the molten low-density polyethylene, and continue blending while keeping the temperature and rotation speed constant; Step 4: After blending, remove the material and allow it to cool to obtain low-density polyethylene composite insulation material.

3. The method for improving the DC electrical performance of low-density polyethylene insulation material according to claim 2, characterized in that, The temperature of the torque rheometer is set to 105~120 ℃, and the rotation speed is set to 50~70 rpm.

4. The method for improving the DC electrical performance of low-density polyethylene insulation material according to claim 2, characterized in that, The mixing time in step two is 5-10 minutes.

5. The method for improving the DC electrical performance of low-density polyethylene insulation material according to claim 2, characterized in that, The mixing time in step three is 5-30 minutes.

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