Space charge self-elimination type high-voltage direct-current cable shielding material based on molecular dipole field regulation and control, and preparation method and application of space charge self-elimination type high-voltage direct-current cable shielding material

Abstract

The invention belongs to the technical field of cable materials, and relates to a space charge self-elimination type high-voltage direct-current cable shielding material based on molecular dipole field regulation and control and a preparation method and application of the space charge self-elimination type high-voltage direct-current cable shielding material. The shielding material comprises the following raw materials in percentage by weight: 60-65% of base resin, 5-10% of ferroelectric P (VDF-TrFE) nanoparticles, 5-10% of carbon nanotubes, 15-20% of conductive filler and 2-5% of a passivating agent, wherein the sum of the weight percentages of the raw materials is 100%; and the passivating agent is nano cerium dioxide, a magnesium oxide-silicon dioxide core-shell material or a zinc oxide-aluminum oxide core-shell material. The prepared shielding material is used for preparing a high-voltage direct-current cable, the ferroelectric polymer P (VDF-TrFE) in the material is a core carrier for molecular dipole field regulation and control, the conductive filler with high structural degree is in bridge connection with the carbon nanotubes to form a three-dimensional charge dredging path, space charges are eliminated, and the high-voltage resistance of the cable is improved.

Description

Technical Field

[0001] This invention belongs to the field of cable material technology, specifically relating to a space charge self-eliminating high-voltage DC cable shielding material based on molecular dipole field regulation, its preparation method, and its application. Background Technology

[0002] With the continuous development of industries such as communications and electrical engineering, high-voltage direct current (HVDC) transmission technology is being used more and more extensively. HVDC transmission is used for long-distance or ultra-long-distance power transmission, through... Overhead line and submarine cable It can transmit electrical energy over long distances, and it is also used to connect independent power systems in situations where traditional AC connections are not suitable, and it is more economical than traditional AC transmission.

[0003] Although the development prospects of high-voltage direct current (HVDC) transmission technology are promising, there are still some limiting factors, such as the limitations in the performance of its cable materials. Currently, high-voltage insulation material technology, especially in DC cables, particularly ±320kV and above high-voltage power cables, places extremely high demands on the electrical performance of the insulation materials and the surface finish of the shielding materials during cable operation. Slight negligence can easily lead to cable breakdown. Research has found that this is mainly caused by the following reasons: First, the injection of charge carriers under the DC electric field causes the accumulation of space charge inside the material, which, when excessively high, leads to cable insulation layer breakdown; second, the high interfacial charge migration barrier of traditional composite shielding materials results in low charge transfer efficiency, causing space charge accumulation; third, the existence of temperature gradients can cause charge redistribution effects, leading to uneven distribution of space charge in the cable insulation layer, creating potential hazards.

[0004] Based on this, the present invention adjusts and innovates the raw material composition of cable materials to eliminate space charge during cable operation, thereby indirectly improving the high voltage resistance of the cable. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems in the prior art. It proposes a space charge self-eliminating high voltage DC cable shielding material based on molecular dipole field regulation, its preparation method and application. The shielding material incorporates ferroelectric polymer ferroelectric P (VDF-TrFE) as the core carrier for molecular dipole field regulation, and at the same time, it synergistically cooperates with high-structure conductive filler to bridge carbon nanotubes to form a three-dimensional charge conduction path, thereby eliminating the influence of space charge and improving the high voltage resistance of the cable.

[0006] The technical solution of this invention is:

[0007] This invention provides a space charge self-eliminating high-voltage DC cable shielding material based on molecular dipole field modulation, the shielding material comprising the following raw materials by weight percentage:

[0008] The composition consists of 60-65% base resin, 5-10% ferroelectric P(VDF-TrFE) nanoparticles, 5-10% carbon nanotubes, 15-20% conductive filler, and 2-5% passivating agent, with the sum of the weight percentages of the above raw materials being 100%.

[0009] In this invention, the weight percentage of the base resin can be 60%, 61%, 62%, 63%, 64%, or 65%, or other values ​​within the range of 60-65%; the weight percentage of the ferroelectric P(VDF-TrFE) nanoparticles can be 5%, 6%, 7%, 8%, 9%, or 10%, or other values ​​within the range of 5-10%; the weight percentage of the carbon nanotubes can be 5%, 6%, 7%, 8%, 9%, or 10%, or other values ​​within the range of 5-10%; the weight percentage of the conductive filler can be 15%, 16%, 17%, 18%, 19%, or 20%, or other values ​​within the range of 15-20%; and the weight percentage of the passivating agent can be 2%, 3%, 4%, or 5%, or other values ​​within the range of 2-5%.

[0010] The shielding material also includes a crosslinking agent, which accounts for 1-2% of the total weight of the above raw materials;

[0011] The conductive filler is any one or more of furnace black, acetylene black, or graphene oxide.

[0012] The passivating agent is any one or more of nano-cerium dioxide (CeO2), magnesium oxide-silica core-shell material (MgO-SiO2), or zinc oxide-alumina core-shell material (ZnO-Al2O3).

[0013] Among the aforementioned raw materials, the ferroelectric polymer ferroelectric P (VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene copolymer) is the core carrier for molecular dipole field modulation. Its space charge elimination process follows the logic of "electric field response - dipole reversal - polarization antagonism - charge trapping - bond neutralization":

[0014] When the shielding material is placed in a high-voltage DC electric field environment of ±320 kV or above, the permanent dipoles in the P(VDF-TrFE) molecular chain (formed due to the difference in electronegativity between VDF and TrFE monomers) will be subjected to electric field forces, resulting in a directional flip of the dipoles under DC electric field excitation, changing from a disordered state to a directional arrangement (the direction of the dipole moment is opposite to the direction of the applied DC electric field). The directionally arranged dipoles will form a "reverse polarization electric field" inside the material, which is opposite to the direction of the applied DC electric field. This electric field is equivalent to "establishing an anti-field" against the applied electric field, directly weakening the injection force of charge carriers (electrons and ions), and reducing the generation of space charge from the source. The reverse polarization electric field not only weakens the injection of charge carriers, but its electric field gradient can also actively "capture" the charge carriers that have been injected into the material and are migrating (including free charges injected from the electrodes and ionic charges generated at the material interface), preventing the accumulation of charge carriers into the insulating layer. The trapped charge carriers (especially the ionic charges in the interface region) will form coordination bonds with the polar groups (such as -CF2-, -CH2-) on the surface of the P (VDF-TrFE) molecule, ultimately transforming the originally positive / negative charge carriers into "neutral molecular clusters"—completely eliminating the electrical properties of the charge and preventing it from forming charge traps or accumulation areas inside the material.

[0015] Furthermore, the base resin is any one or more of low-density polyethylene (LDPE), ethylene-vinyl acetate (EVA), or ethylene-butyl acrylate (EBA).

[0016] Furthermore, the crosslinking agent is dicumyl peroxide (DCP) or 2-tert-butylperoxide (BIBP).

[0017] The present invention also provides a method for preparing the aforementioned shielding material, comprising the following steps:

[0018] (1) Material blending and melting: The base resin is mixed with carbon nanotubes, conductive fillers, ferroelectric P (VDF-TrFE) nanoparticles and passivating agents in a weight percentage ratio, melted and plasticized in a twin-screw extruder, and then granulated; the screw length-to-diameter ratio is 20:1, the temperature range is 110-150℃, the twin-screw speed is 400-500 rpm, and the pelletizer speed is 800-1000 rpm;

[0019] (2) Crosslinking absorption molding: The granules obtained in step (1) are passed through a crosslinking agent in a shaking tank for post-absorption. The temperature is set to 50-60℃, and the temperature is slowly reduced after 1.5-3 h to obtain the finished product.

[0020] Furthermore, this includes the following steps:

[0021] Low-density polyethylene was mixed with carbon nanotubes, graphene oxide, ferroelectric P (VDF-TrFE) nanoparticles, and nano-cerium dioxide in a weight percentage ratio, and then melt-plasticized in a twin-screw extruder. The screw length-to-diameter ratio was set to 20:1, the temperature range was 110-150℃, the twin-screw speed was 400-500 rpm, and the pelletizer speed was 800-1000 rpm for granulation.

[0022] The obtained granules were subjected to post-absorption by introducing 2% DCP into a shaking tank. The temperature was set at 50-60℃ for 2 hours, and then the temperature was slowly lowered to obtain the finished shielding material.

[0023] This invention provides the application of the shielding material or the shielding material prepared by the method described above in the manufacture of cables.

[0024] Furthermore, the cable is a high-voltage DC cable.

[0025] The beneficial effects of this invention are:

[0026] The shielding material provided by this invention utilizes a ferroelectric polymer ferroelectric P (VDF-TrFE) as a core carrier for molecular dipole field modulation to prepare a space charge self-eliminating high-voltage DC cable shielding material. When exposed to a high-voltage DC electric field, this shielding material actively eliminates space charge through a series of processes, including dipole directional reversal under DC electric field excitation, the construction of a reverse polarization electric field, active capture of migrating charge carriers, and coordination bonding and neutralization conversion of interfacial ions. Simultaneously, the raw material also employs high-structure acetylene-based carbon black to bridge carbon nanotubes (CNTs), forming a three-dimensional conductive network. This allows space charge to be transported along the CNT axis, captured by pGO surface functional groups (-COOH / -OH), and transferred to the ferroelectric dipole annihilation region, ultimately eliminating the space charge. Detailed Implementation

[0027] The present invention will be further described below with reference to the embodiments thereof, and the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment provides a space charge self-eliminating high-voltage DC cable shielding material based on molecular dipole field modulation, the raw materials of which, by weight percentage, comprise:

[0030] Low-density polyethylene 60%, ferroelectric P (VDF-TrFE) nanoparticles 10%, carbon nanotubes 10%, acetylene black 18%, nano-cerium dioxide 2%;

[0031] It also includes 1% dicumyl peroxide by weight of the above raw materials;

[0032] The preparation method includes the following steps:

[0033] Weigh out 60% low-density polyethylene, 10% carbon nanotubes, 18% acetylene black, 10% ferroelectric P (VDF-TrFE) nanoparticles, and 2% nano-cerium dioxide by weight percentage and mix them. Melt and plasticize them in a twin-screw extruder with the screw length-to-diameter ratio set to 20:1, the temperature range to 110-150℃, the twin-screw speed to 400 rpm, and the pelletizer speed to 800 rpm for granulation.

[0034] The obtained granules were subjected to post-absorption by introducing 1% of the total weight of dicumyl peroxide into a shaking tank. The temperature was set at 50°C for 2 hours, and then the temperature was slowly lowered to obtain the finished shielding material.

[0035] Example 2

[0036] This embodiment provides a space charge self-eliminating high-voltage DC cable shielding material based on molecular dipole field modulation, the raw materials of which, by weight percentage, comprise:

[0037] Low-density polyethylene 65%, ferroelectric P (VDF-TrFE) nanoparticles 5%, carbon nanotubes 5%, acetylene black 20%, nano-cerium dioxide 5%;

[0038] It also includes 2-tert-butylperoxyisopropylbenzene, which accounts for 2% of the total weight of the above raw materials;

[0039] The preparation method includes the following steps:

[0040] 65% low-density polyethylene, weighed by weight, is mixed with 5% carbon nanotubes, 20% acetylene black, 5% ferroelectric P (VDF-TrFE) nanoparticles, and 5% nano-cerium dioxide. The mixture is then melt-plasticized in a twin-screw extruder with a screw length-to-diameter ratio of 20:1, a temperature range of 110-150℃, a twin-screw speed of 500 rpm, and a pelletizer speed of 1000 rpm for granulation.

[0041] The obtained granules were subjected to post-absorption by introducing 2% (by weight of 2-tert-butylperoxyisopropylbenzene) into a shaking tank. The temperature was set at 60°C for 2 hours, and then the temperature was slowly lowered to obtain the finished shielding material.

[0042] Example 3

[0043] This embodiment provides a space charge self-eliminating high-voltage DC cable shielding material based on molecular dipole field modulation, the raw materials of which, by weight percentage, comprise:

[0044] Ethylene-vinyl acetate 63%, ferroelectric P (VDF-TrFE) nanoparticles 8%, carbon nanotubes 8%, graphene oxide 18%, magnesium oxide-silica core-shell material 3%;

[0045] It also includes dicumyl peroxide, which accounts for 2% of the total weight of the above raw materials;

[0046] The preparation steps are the same as in Example 1.

[0047] Example 4

[0048] This embodiment provides a space charge self-eliminating high-voltage DC cable shielding material based on molecular dipole field modulation, the raw materials of which, by weight percentage, comprise:

[0049] Ethylene-butyl acrylate 62%, ferroelectric P (VDF-TrFE) nanoparticles 7%, carbon nanotubes 7%, furnace black 17%, zinc oxide-alumina core-shell material 4%;

[0050] It also includes 1% by weight of 2-tert-butylperoxyisopropylbenzene;

[0051] The preparation steps are the same as in Example 1.

[0052] Comparative Example 1

[0053] Traditional high-voltage semiconducting shielding material was used as a comparison, namely imported commercial cable shielding material, Borealis 0592 grade.

[0054] Experimental Example 1

[0055] Space charge distribution test (electroacoustic pulse method)

[0056] Experimental equipment: PEA system (manufacturer: FiveLab, model: PEANUT-C30); high voltage DC power supply (accuracy ±0.5%); temperature control platform (-40~150℃).

[0057] (1) Sample preparation:

[0058] The shielding materials prepared in Examples 1 and 2, and the shielding material of Borealis 0592 grade in Comparative Example 1, were hot-pressed together with the insulating layer (XLPE) at 175°C with a pressure of 15 MPa for 10 min using a flat vulcanizing machine to form a composite sheet.

[0059] Dimensions: Φ100×1.5 mm (0.75 mm for shielding / insulation)

[0060] The sample was immersed in silicone oil and compacted between the two electrodes of a DC power supply, then awaited testing.

[0061] (2) Depolarization Method (PDC) Test Procedure

[0062] Step 1, Vacuum Environment Pretreatment (10 -3 Pa, 70℃, 24 h);

[0063] Step 2: Initial state scan (0 kV, 70℃) as baseline;

[0064] Step 3: Apply an electric field strength of 150 kV / mm;

[0065] Step 4: Collect data at the following stages: a) Immediately upon pressurization (t=0); b) t=60 min; c) 5 min after depressurization;

[0066] Step 6: Read the data at the corresponding time.

[0067] The experimental results are shown in Table 1.

[0068] Table 1. Test results of space charge distribution of shielding materials in Examples 1 and 2 and Comparative Example 1

[0069] Pressurized for 0 min (C / m³) Pressurize for 60 min (°C / m³) Depressurize for 5 minutes (°C / m³) Example 1 2.12 2.88 1.74 Example 2 2.57 3.24 1.91 Comparative Example 1 4.81 9.25 7.20

[0070] Based on the above data, it can be determined that under the action of a DC electric field, the space charge density of the new semiconducting shielding material with added ferroelectric material is significantly lower than that of the traditional semiconducting shielding material of the same grade without added ferroelectric material. This indicates that under the action of a DC electric field, the electric dipoles inside the ferroelectric material will interact with the external electric field, which can effectively regulate and weaken the influence of external charge, reduce the accumulation of space charge in the insulation layer, and the space charge density decreases within a certain range as the amount of ferroelectric material added increases.

[0071] Experiment Example 2

[0072] DC breakdown field strength test of shielded-insulating composites (step voltage method)

[0073] Test standard: IEC 60243

[0074] (1) Sample preparation: The shielding material prepared in Examples 1 and 2 of this invention, and the shielding material of Borealis 0592 in Comparative Example 1, were hot-pressed together with the insulating layer (XLPE) at 175 degrees Celsius with a pressure of 15 MPa for 10 minutes using a flat vulcanizing machine to form a composite sheet.

[0075] Dimensions: Φ100×1.5 mm (0.75 mm for shielding / insulation)

[0076] The sample was immersed in silicone oil and compacted between the two electrodes of a DC power supply, then awaited testing.

[0077] (2) Test program:

[0078] Step 1: Vacuum impregnate the sample (silicone oil, 0.5 h) to eliminate interfacial bubbles.

[0079] Step 2: Apply initial voltage U0 = 10 kV

[0080] Step 3: Stepped voltage boost (step size ΔU = 2 kV, hold for 1 min per step)

[0081] Step 4: Increase the pressure until the sample breaks down.

[0082] Step 5: Record the breakdown voltage, and then calculate the electric field strength by testing the insulation thickness.

[0083] The test results are shown in Table 2.

[0084] Table 2. DC breakdown field strength test results of the shielding materials in Examples 1 and 2 and Comparative Example 1

[0085] Breakdown electric field strength at room temperature (kV / mm) Breakdown electric field strength at 90℃ (kV / mm) Example 1 367 288 Example 2 342 269 Comparative Example 1 297 203

[0086] Through experimental comparison of the examples and comparative examples, it can be found that the breakdown field strength of the semiconducting shielding material with added ferroelectrics is higher than that of ordinary semiconducting shielding materials at normal room temperature and cable operating temperature. The materials with added ferroelectrics prepared in Examples 1 and 2 of this invention have a more uniform electric field distribution and less space charge, which verifies the advantages of the shielding material prepared by this invention compared with traditional shielding materials from another perspective.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, alterations, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A space charge self-eliminating high-voltage DC cable shielding material based on molecular dipole field modulation, characterized in that, The shielding material comprises the following raw materials by weight percentage: The composition consists of 60-65% base resin, 5-10% ferroelectric P(VDF-TrFE) nanoparticles, 5-10% carbon nanotubes, 15-20% conductive filler, and 2-5% passivating agent, with the sum of the weight percentages of the above raw materials being 100%. The shielding material also includes a crosslinking agent, which accounts for 1-2% of the total weight of the above raw materials; The conductive filler is any one or more of furnace black, acetylene black, or graphene oxide. The passivating agent is any one or more of nano-cerium dioxide, magnesium oxide-silica core-shell material, or zinc oxide-alumina core-shell material.

2. The shielding material according to claim 1, characterized in that, The base resin is any one or more of low-density polyethylene, ethylene-vinyl acetate, or ethylene-butyl acrylate.

3. The shielding material according to claim 1, characterized in that, The crosslinking agent is dicumyl peroxide or 2-tert-butylperoxide.

4. The method for preparing the shielding material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Material blending and melting: The base resin is mixed with carbon nanotubes, conductive fillers, ferroelectric P (VDF-TrFE) nanoparticles and passivating agents in a weight percentage ratio, melted and plasticized in a twin-screw extruder, and then granulated; the screw length-to-diameter ratio is 20:1, the temperature range is 110-150℃, the twin-screw speed is 400-500 rpm, and the pelletizer speed is 800-1000 rpm; (2) Crosslinking absorption molding: The granules obtained in step (1) are passed through a crosslinking agent in a shaking tank for post-absorption. The temperature is set to 50-60℃, and the temperature is slowly lowered after 1.5-3 h to obtain the finished product.

5. The preparation method according to claim 4, characterized in that, Includes the following steps: Low-density polyethylene was mixed with carbon nanotubes, graphene oxide, ferroelectric P (VDF-TrFE) nanoparticles, and nano-cerium dioxide in a weight percentage ratio, and then melt-plasticized in a twin-screw extruder. The screw length-to-diameter ratio was set to 20:1, the temperature range was 110-150℃, the twin-screw speed was 400-500 rpm, and the pelletizer speed was 800-1000 rpm for granulation. The obtained granules were subjected to post-absorption by introducing 2% DCP into a shaking tank. The temperature was set at 50-60℃ for 2 hours, and then the temperature was slowly lowered to obtain the finished shielding material.

6. The use of the shielding material according to any one of claims 1-3 or the shielding material prepared by the preparation method according to any one of claims 4-5 in the preparation of cables.

7. The application according to claim 6, characterized in that, The cable is a high-voltage DC cable.