Method for improving direct-current electrical performance of low-density polyethylene insulating material

Abstract

The invention discloses a method for improving the direct-current electrical performance of a low-density polyethylene insulating material, and belongs to the technical field of electrical insulating materials, and the method is technically characterized by comprising the following steps: adding an organic small molecule filler into low-density polyethylene for blending, and taking the low-density polyethylene as a substrate to obtain a low-density polyethylene composite insulating material; according to the present invention, the matrix and the filler have good compatibility, the agglomeration phenomenon of the inorganic filler in the low density polyethylene matrix is avoided, the problems of complex chemical reaction and difficult grafting rate control in the traditional grafting are avoided, the by-products caused by the chemical reaction are reduced, and the application value in the practical engineering is provided.

Description

Technical Field

[0001] The invention relates to the technical field of electrical insulation materials, and in particular to a method for improving the direct current electrical performance of a low-density polyethylene insulation material. Background Art

[0002] High-voltage DC cables are key components of high-voltage DC transmission systems. The long-term stable operation of high-voltage DC transmission systems depends on the electrical properties of high-voltage DC cable insulation materials. With the increase of DC high-voltage transmission voltage levels, the electrical stress on insulation materials gradually increases, which easily accumulates space charges, causing distortion of the electric field distribution inside the insulation material, accelerating the degradation and aging of the insulation material, and even insulation breakdown. Therefore, improving the DC electrical properties of insulation materials is of great value to the development of high-voltage DC transmission.

[0003] Polyethylene is widely used as an insulating material for high-voltage DC cables due to its excellent electrical properties and stable chemical properties. To meet the needs of higher transmission voltage levels and improve the DC electrical properties of polyethylene insulation materials, common strategies include material purification and modification. The polyethylene insulation matrix currently used is usually an ultra-pure material. Further improving the purification process of the material is not only technically challenging but also not economical.

[0004] Material modification can be divided into two types: inorganic doping and organic doping. For inorganic doped composite insulating materials, the poor compatibility of inorganic fillers with the matrix and the easy agglomeration in the polyethylene matrix are always difficult to solve, thus limiting their application in engineering. Organic molecules have good compatibility and dispersibility with the matrix and have potential engineering application value. Although grafting organic molecules into polyethylene can effectively improve the DC electrical properties of the material, the complex grafting process and the elimination of by-products produced by the grafting process increase the complexity of the material processing process. Summary of the invention

[0005] In view of the deficiencies in the prior art, an object of an embodiment of the present invention is to provide a method for improving the DC electrical performance of a low-density polyethylene insulating material, so as to solve the problems in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for improving the DC electrical performance of a low-density polyethylene insulating material comprises adding an organic small molecule filler into the low-density polyethylene for blending, using the low-density polyethylene as a base, and obtaining a low-density polyethylene composite insulating material.

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

[0009] As a further embodiment 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: Put low-density polyethylene into the torque rheometer for blending, so that the low-density polyethylene is transformed into a molten state;

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

[0013] Step 4: After the blending is completed, take it out and cool it down to obtain a low-density polyethylene composite insulation material.

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

[0015] As a further solution of the present invention, the blending time in step 2 is 5 to 10 minutes.

[0016] As a further solution of the present invention, the blending 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, dimethyl acetophenone, 4-methoxyacetophenone, octadecylamine polyoxyethylene ether and bisphenol A polyoxyethylene ether.

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

[0019] 1. The low-density polyethylene matrix is ​​doped with organic small molecule fillers, which has 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 the organic small molecule filler are blended to prepare the composite material. The preparation process is simple, avoiding the complex chemical reactions in traditional grafting and the problem of difficult to control the grafting rate. At the same time, it reduces the by-products caused by the chemical reaction, which is more valuable in actual engineering.

[0021] 3. Improve the DC electrical properties of low-density polyethylene insulation materials by adding organic molecules, inhibit the accumulation of space charge in low-density polyethylene insulation materials, increase the DC breakdown field strength, and reduce the DC conductivity.

[0022] In order to more clearly illustrate the structural features and effects of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

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

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

[0030] Figure 8 is the average space charge density of the control example and the embodiment. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

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

[0034] For further information, see Figures 1 to 8 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] For further information, see Figures 1 to 8 , the blending steps are as follows:

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

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

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

[0039] Step 4: After the blending is completed, take it out and cool it down to obtain a low-density polyethylene composite insulation material.

[0040] For further information, see Figures 1 to 8 The temperature of the torque rheometer is set to 105-120°C, and the speed is set to 50-70 rpm.

[0041] For further information, see Figures 1 to 8 The blending time in step 2 is 5 to 10 minutes.

[0042] For further information, see Figures 1 to 8 The blending time in step three is 5 to 30 minutes.

[0043] For further information, see Figures 1 to 8 The organic small molecule filler is one of 1,4-dimethoxybenzene, Span 60, dimethyl acetophenone, 4-methoxyacetophenone, octadecylamine polyoxyethylene ether and bisphenol A polyoxyethylene ether.

[0044] Example 1: The temperature of the torque rheometer is set to 110°C and the speed is set to 60 rpm. Low-density polyethylene is placed in the torque rheometer and blended for 5 minutes to transform the low-density polyethylene into a molten state. Then, 0.05wt% of 1,4-dimethoxybenzene is added to the molten low-density polyethylene, and the temperature and speed are kept constant and the blending is continued for 10 minutes. After the blending is completed, the low-density polyethylene composite insulation material is taken out and cooled to obtain.

[0045] Example 2: The difference from Example 1 is that the mass fraction of the added organic small molecules is 0.1 wt%.

[0046] Example 3: The difference from Example 2 is that the mass fraction of the added organic small molecules is 0.3 wt%.

[0047] Example 4: The difference from Example 3 is that the mass fraction of the added organic small molecules is 1.0 wt%.

[0048] Control Example: Different from Example 4, the mass fraction of the added organic small molecules is 0 wt %.

[0049] A total of five groups of samples of the embodiments and control examples were subjected to breakdown field strength test, conductivity test and electroacoustic pulse method (PEA) test.

[0050] The breakdown field strength test uses a ball-ball electrode test system. Based on the DC breakdown field strength obtained, the failure probability and the Weibull distribution function of the DC applied electric field are plotted.

[0051] The conductivity test used a three-electrode system to obtain the DC conductivity of the sample after being pressurized at an electric field strength of 40 kV / mm for 20 minutes.

[0052] The space charge density of the sample was measured by electroacoustic pulse method (PEA) at a temperature of 30°C and an applied electric field strength of 40 kV / mm. The polarization time and short circuit time were both 30 minutes. The average space charge density was calculated based on the sample thickness and the position of the upper and lower electrodes. The calculation formula is as follows:

[0053]

[0054] Where Q is the average space charge density, L is the sample thickness, x1 and x2 are the upper and lower electrode positions in the space charge test results, ρ(t,x) is the space charge distribution result inside the sample, x is the spatial 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 is significantly increased, and the DC conductivity is significantly reduced. Among them, the breakdown field strength of Example 2 is the highest, which is increased by 22% compared with the control example; and the DC conductivity of Example 2 is the lowest, which is reduced by 76 times compared with the control example.

[0056] like Figure 3-7 As shown, the control example accumulates a large amount of heteropolar space charges near the cathode; the heteropolar space charges accumulated near the cathode in each group of examples are significantly reduced, among which Example 2 accumulates the least heteropolar space charges near the cathode.

[0057] like Figure 8 As shown, the average volume charge density of the control example is the highest; the average volume charge density of each group of examples has decreased significantly. Among them, the average volume charge density of Example 2 is the lowest, which is 37% lower than that of the control example; and the average volume charge density of Example 4, which has the highest filler content, has increased compared with Example 2, but is 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 in 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 method comprises adding organic small molecule fillers into low-density polyethylene for blending, using the low-density polyethylene as a base, and obtaining a low-density polyethylene composite insulating material.

2. The method for improving the DC electrical performance of low-density polyethylene insulation material according to claim 1, characterized in that: The blending ratio is 0.05-1.0 part of the organic small molecule filler added to 100 parts of the low-density polyethylene matrix.

3. 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: Put low-density polyethylene into the torque rheometer for blending, so that the low-density polyethylene is transformed into a molten state; Step 3: Add organic small molecule fillers to the molten low-density polyethylene and continue blending while keeping the temperature and speed unchanged; Step 4: After the blending is completed, take it out and cool it down to obtain a low-density polyethylene composite insulation material.

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

5. The method for improving the DC electrical performance of low-density polyethylene insulation material according to claim 3, characterized in that: The blending time in step 2 is 5 to 10 minutes.

6. The method for improving the DC electrical performance of low-density polyethylene insulation material according to claim 3, characterized in that: The blending time in step three is 5 to 30 minutes.

7. The method for improving the DC electrical performance of low-density polyethylene insulation material according to claim 3, characterized in that: The organic small molecule filler is one of 1,4-dimethoxybenzene, Span 60, dimethyl acetophenone, 4-methoxyacetophenone, octadecylamine polyoxyethylene ether and bisphenol A polyoxyethylene ether.

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