CN113912778A - Insulating material for high-voltage cable, preparation method and preparation base material thereof - Google Patents

Insulating material for high-voltage cable, preparation method and preparation base material thereof Download PDF

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CN113912778A
CN113912778A CN202111228068.1A CN202111228068A CN113912778A CN 113912778 A CN113912778 A CN 113912778A CN 202111228068 A CN202111228068 A CN 202111228068A CN 113912778 A CN113912778 A CN 113912778A
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insulating material
photoinitiator
layer
photocrosslinking agent
voltage cable
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CN113912778B (en
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杨卓然
周平
王东海
姚天翼
刘霆
吕立翔
陈伟
王浩
高源�
漆家伟
许洪华
王春宁
王赫宇
韩涛
李忠磊
姚悦
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Nanjing Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
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Nanjing Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
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    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F255/00—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00
    • C08F255/02—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00 on to polymers of olefins having two or three carbon atoms
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/46—Polymerisation initiated by wave energy or particle radiation
    • C08F2/48—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/14—Peroxides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
    • C08K5/37—Thiols
    • C08K5/375—Thiols containing six-membered aromatic rings
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/56—Organo-metallic compounds, i.e. organic compounds containing a metal-to-carbon bond
    • C08K5/57—Organo-tin compounds

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Abstract

The invention relates to an insulating material for a high-voltage cable, a preparation method and a preparation base material of the insulating material, and belongs to the technical field of high-molecular compound compositions. The material comprises a crosslinked polyethylene layer produced by a non-photocrosslinking reaction; the photocrosslinking agent and the photoinitiator in independent molecular states are physically and uniformly distributed in the crosslinked polyethylene layer. The preparation method of the material comprises the steps of mixing low-density polyethylene, a non-photocrosslinking agent, an antioxidant and a stabilizer; adding a photocrosslinking agent and a photoinitiator additionally, and extruding to obtain a prepared base material after full blending; and extruding the obtained preparation base material by adopting a three-layer co-extrusion process by utilizing the existing high-voltage cable production line to obtain the insulating material for the high-voltage cable. When a high-voltage cable adopting the material is subjected to high-energy electron impact to cause the breakage of molecular chains or cross-linking points, the damaged cross-linking points and broken molecular chains can be repaired, so that the deterioration of the cross-linked polyethylene material is inhibited, and the service life of the cross-linked polyethylene material is prolonged.

Description

Insulating material for high-voltage cable, preparation method and preparation base material thereof
Technical Field
The invention relates to an insulating material for a high-voltage cable and a preparation method thereof, and also relates to a preparation base material of the insulating material for the high-voltage cable in preparation, belonging to the technical field of high-molecular compound compositions.
Background
The high-voltage cable transmission has the advantages of large transmission capacity, long distance, high efficiency, low loss and the like, is a reliable technical means for meeting the requirements of large-capacity and long-distance trans-regional transmission, and is also an optimal means for solving the problems of urban power grid capacity increase, new energy grid connection, offshore island power supply and the like. At present, the high-voltage alternating-current transmission cable generally adopts Cross-linked Polyethylene as an outer-layer insulating material, and the Cross-linked Polyethylene (abbreviated as XLPE) is taken as a main insulating material widely used by the high-voltage power cable, so that the cable has the advantages of light weight, good heat resistance, excellent electrical performance and the like. In the process of cable transmission operation, the insulation material can be subjected to electric heat aging or electric branch degradation due to the influence of external factors such as electricity, heat, machinery and the like and internal defect factors of the insulation material, so that cable breakdown accidents are caused.
The essence of analyzing the cable insulation operation condition to cause the crosslinked polyethylene insulation to generate the electric aging and the electric heating combined aging is that the cable insulation layer (crosslinked polyethylene layer) bears high electric field intensity to cause the crosslinked polyethylene material to be damaged or molecular chains to be broken to form defect points, high voltage electricity can form microscopic discharge at the defect points, high-energy electrons generated by the microscopic discharge impact the molecular chains or the crosslinked points of the crosslinked polyethylene to cause the molecular chains or the crosslinked points to be broken and damaged, a large number of molecular chain broken points form low-density regions to further cause the electrical dendritic degradation of the insulation material, further induce a larger local discharge phenomenon, and accelerate the degradation, the damage and the failure process of the insulation material. Therefore, the inhibition or repair of cross-linking point damage and molecular chain breakage is the fundamental means for prolonging the service life of the insulating material for the high-voltage cable.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: when a molecular chain or a crosslinked point is broken due to impact of high-energy electrons on a crosslinked polyethylene insulating layer of the conventional high-voltage cable, the broken crosslinked point and the broken molecular chain can be repaired, so that the material deterioration of a crosslinked polyethylene layer is inhibited, and the service life of the crosslinked polyethylene layer material is prolonged.
The invention provides a technical scheme for solving the technical problems, which comprises the following steps: an insulating material for high-voltage cables, comprising a crosslinked polyethylene layer produced by a non-photocrosslinking reaction; the photo-crosslinking agent and the photoinitiator in independent molecular states are physically and uniformly distributed in the crosslinked polyethylene layer.
The molecular state means that the photocrosslinking agent and the photoinitiator are distributed in the crosslinked polyethylene layer in a molecular state; independent means that the molecular structures of the photocrosslinking agent and the photoinitiator are independent and are not crosslinked with each other; the independent molecular state is that the cross-linking agent and the photoinitiator respectively have independent molecular structures; the physical uniform distribution means that the photocrosslinking agent and the photoinitiator do not have a chemical molecular connection structure with the substances such as polyethylene of the crosslinked polyethylene layer, and are physically mixed with the crosslinked polyethylene layer and uniformly distributed.
Further, the photocrosslinking agent is a trifunctional photocrosslinking agent, and the photoinitiator is a hydrogen abstraction polycyclic aromatic hydrocarbon photoinitiator.
Further, the trifunctional photocrosslinking agent is a functional group derivative of 1,3, 5-s-triazine, and the hydrogen abstraction polycyclic aromatic hydrocarbon photoinitiator is a derivative of benzophenone.
Further, the functional derivative of 1,3, 5-s-triazine is triallyl cyanurate or triallyl isocyanurate, and the derivative of benzophenone is 4-methylbenzophenone or 4,4' -dichlorobenzophenone.
Further, the photocrosslinking agent is dispersed in the crosslinked polyethylene layer at a concentration of 3.61 × 10-6~1.08×10-4mol/cm3The dispersion concentration of the photoinitiator in the crosslinked polyethylene layer is between 3.58 and 10-6~1.07×10-4mol/cm3In the meantime.
The reaction mechanism and the beneficial effects of the invention are as follows: the method is characterized in that photocrosslinking additives in independent molecular states (including photocrosslinking agents in independent molecular states and photoinitiators in independent molecular states) are additionally and uniformly distributed and mixed in a crosslinked polyethylene layer which is processed (generally extruded) to form the crosslinked polyethylene layer; therefore, when the high voltage cable is normally used, the photocrosslinking agent and the photoinitiator additionally added to the insulation layer (crosslinked polyethylene layer) are merely physically mixed in the crosslinked polyethylene layer; when the high-energy electrons generated by microscopic discharge locally of the high-voltage cable collide with molecular chains or crosslinking points of crosslinked polyethylene to generate fracture and damage, energy released at the local part can form light energy irradiation of an ultraviolet band, and the ultraviolet irradiation energy can excite photocrosslinking additives distributed at the crosslinking damage points or the molecular chain fracture points to perform secondary crosslinking reaction with the crosslinked polyethylene, wherein the specific reaction is as follows: the additional photoinitiator (mainly a derivative of benzophenone) is excited to firstly abstract hydrogen atoms on a polyethylene molecular chain, and then a functional group of the photocrosslinking agent (mainly a functional group derivative of 1,3, 5-s-triazine) is excited to connect two opened chain ends of the polyethylene molecular chain, namely, the functional group is embedded between the polyethylene molecular chains to form a local new polymeric structure; thereby forming repair to molecular chain or cross-linking point breaks.
The second technical scheme provided by the invention for solving the technical problems is as follows: in the first technical scheme, the base material for preparing the insulating material for the high-voltage cable is prepared by mixing low-density polyethylene, a non-photocrosslinking agent, an antioxidant and a stabilizer, adding a photocrosslinking agent and a photoinitiator additionally, and fully blending. Thus, the insulating material for high-voltage cables in the first technical scheme can be further produced by the base material.
The third technical scheme provided by the invention for solving the technical problems is as follows: in the first technical scheme, the preparation method of the insulating material for the high-voltage cable comprises the following steps:
step one, mixing low-density polyethylene, a non-photoinduced crosslinking agent, an antioxidant and a stabilizer by adopting an internal mixer or a double-screw extruder according to the existing crosslinked polyethylene insulation formula system for the high-voltage cable;
adding a photocrosslinking agent and a photoinitiator into an internal mixer or a double-screw extruder, and extruding to obtain a prepared base material after full blending;
loading the obtained preparation base material from a discharge hole by using a vertical tower type or catenary high-voltage cable production line, and extruding by adopting a three-layer co-extrusion process, wherein the extrusion temperature is 128-132 ℃, and the extrusion speed is 1.0-2.0 m/min; carrying out crosslinking reaction for 15 min at the ambient temperature of 220-300 ℃ in a nitrogen protection environment; obtaining the insulating material for the high-voltage cable.
Further, in the first step, the temperature range of the mixing process is 110-130 ℃, the non-photo-crosslinking agent is dicumyl peroxide (DCP), and the addition content of the DCP is 1.0-3.0 wt%.
Further, in the second step, the blending process time is more than 10 min; the photocrosslinking agent is triallyl cyanurate TAC or triallyl isocyanurate TAIC, the content of the TAC or the TAIC ranges from 0.1wt% to 3.0wt%, and the dispersion concentration of the TAC or the TAIC in the preparation base material is 3.61X 10-6~1.08×10-4mol/cm3To (c) to (d); the photoinitiator is 4-methylbenzophenone MBP or 4,4' -dichlorobenzophenone CBP, the content of the MBP or CBP ranges from 0.1wt% to 3.0wt%, and the dispersion concentration of the MBP or CBP in the prepared base stock is 3.58 x 10-6~1.07×10-4 mol/cm3In the meantime.
Further, the three layers of the three-layer co-extrusion process refer to an inner semiconductive layer, an insulation layer and an outer semiconductive layer.
Drawings
The insulating material for high voltage cable, the preparation method and the base material thereof according to the present invention will be further described with reference to the accompanying drawings.
FIG. 1 shows the molecular structural formula of the photo-crosslinking agent TAC and the photoinitiator MBP in example one.
FIG. 2 is the molecular structural formula of the photocrosslinker TAIC and the photoinitiator CBP in example II.
Fig. 3 is a graph comparing the initiation and growth experiments of the insulating material for high voltage cables of examples one and two and the conventional XLPE insulating tree according to the experimental part.
Fig. 4 is a graph comparing the deteriorated length and width of the insulation material for high voltage cables of examples one and two and the conventional XLPE insulation branch according to the experimental part.
Fig. 5 is a graph of the area of accumulated damage due to degradation of the insulation material for high voltage cables according to examples one and two and the conventional XLPE insulation in the experimental part.
Detailed Description
Example one
The insulating material for the high-voltage cable of the embodiment includes a Cross-linked polyethylene (XLPE) layer formed by a non-photocrosslinking reaction; the photocrosslinking agent and the photoinitiator in independent molecular states are physically and uniformly distributed in the crosslinked polyethylene layer. The molecular state means that the photocrosslinking agent and the photoinitiator are distributed in the crosslinked polyethylene layer in a molecular state; independent means that the molecular structures of the photocrosslinking agent and the photoinitiator are independent and are not crosslinked with each other; the independent molecular state is that the cross-linking agent and the photoinitiator respectively have independent molecular structures; the physical uniform distribution means that the photocrosslinking agent and the photoinitiator do not have a chemical molecular connection structure with the substances such as polyethylene of the crosslinked polyethylene layer, and are physically mixed with the crosslinked polyethylene layer and uniformly distributed.
Photocrosslinkers are trifunctional photocrosslinkers, specifically functional derivatives of 1,3, 5-s-triazine, more specifically triallyl cyanurate (TAC). The photoinitiator is hydrogen abstraction type polycyclic aromatic hydrocarbon photoinitiator, specifically is benzophenone derivative, more specifically 4-Methylbenzophenone (MBP). The molecular structural formulas of TAC and MBP are shown in figure 1.
The base material for preparing the insulating material for the high-voltage cable is prepared by mixing low-density polyethylene, dicumyl peroxide (DCP, which is a non-photo-crosslinking agent), an antioxidant (bis [3, 5-bis- (1, 1-dimethylethyl) -4-hydroxy- ] benzenepropanoic acid thiodiglycol ester) and a stabilizer (dibutyltin dilaurate), adding TAC and MBP additionally, and fully blending.
The preparation method of the insulating material for the high-voltage cable comprises the following steps:
step one, mixing low-density polyethylene, a non-photoinduced crosslinking agent, an antioxidant and a stabilizer by adopting a double-screw extruder according to the existing crosslinked polyethylene insulation formula system for the high-voltage cable.
Wherein the temperature of the mixing process is set to be 120 ℃; the content of the non-photocrosslinking agent DCP added is 2.0 wt%.
And step two, adding the photocrosslinking agent TAC and the photoinitiator MBP into a double-screw extruder, fully blending, and extruding to obtain the prepared base material.
Wherein the blending process time is 15 min (generally between 10min and 25 min), and the adding of the photo-crosslinking agent TAC and the photoinitiator MBP is used as a starting timing point.
Wherein the content of the photocrosslinking agent TAC is 1.6wt%, and the dispersion concentration of the TAC in the preparation base stock is 3.61 multiplied by 10- 5mol/cm3. It should be noted that: this dispersion concentration of TAC hardly changes before and after the whole production process, and therefore the dispersion concentration of TAC in the final product-produced insulation material for high-voltage cables (crosslinked polyethylene layer) is also the dispersion concentration.
Wherein the content of the photoinitiator MBP is 1.5 wt%; the dispersion concentration of MBP in the base stock is 4.59X 10-5mol/cm3. It should be noted that: this dispersion concentration of the MBP hardly changes before and after the whole production process, and therefore the dispersion concentration of the MBP in the final product of the insulation material for high voltage cables (crosslinked polyethylene layer) is also the dispersion concentration.
Loading the prepared base material obtained in the step two from a discharge hole by using a vertical tower type high-voltage cable production line, and extruding by adopting a three-layer co-extrusion process, wherein the extrusion temperature is set to be 130 ℃, and the extrusion speed is 1.5 m/min and is high; then, under the nitrogen protection environment, keeping the environment temperature at 260 ℃ for carrying out crosslinking reaction for 15 min; obtaining the insulating material for the high-voltage cable.
Example two
The insulating material for the high-voltage cable of the embodiment is a Cross-linked polyethylene (XLPE) layer generated by a non-photocrosslinking reaction; the photocrosslinking agent and the photoinitiator in independent molecular states are physically and uniformly distributed in the crosslinked polyethylene layer. Photocrosslinkers are trifunctional photocrosslinkers, specifically functional derivatives of 1,3, 5-s-triazine, more specifically triallyl isocyanurate (TAIC). The photoinitiator is hydrogen abstraction type polycyclic aromatic hydrocarbon photoinitiator, specifically is benzophenone derivative, more specifically 4,4'-Dichlorobenzophenone (4, 4' -Dichlorobenzophenone, CBP). The molecular structural formulas of TAIC and the photoinitiator CBP are shown in figure 2.
The base material for preparing the insulating material for the high-voltage cable is prepared by mixing low-density polyethylene, dicumyl peroxide (DCP, which is a non-photo-crosslinking agent), an antioxidant (4, 4-thiobis (6-tert-butyl-o-cresol)) and a stabilizer (di-sec-octyl phthalate), adding TAIC and CBP additionally, and fully blending.
The preparation method of the insulating material for the high-voltage cable comprises the following steps:
step one, mixing low-density polyethylene, a non-photoinduced crosslinking agent, an antioxidant and a stabilizer by adopting a double-screw extruder according to the existing crosslinked polyethylene insulation formula system for the high-voltage cable;
wherein the temperature of the mixing process is set to be 112 ℃; the content of the non-photocrosslinking agent DCP added is 1.1 wt%.
And step two, adding the photocrosslinking agent TAIC and the photoinitiator CBP into a double-screw extruder, fully blending, and extruding to obtain the prepared base material.
Wherein the blending process time is 11min, and the adding of the photocrosslinking agent TAIC and the photoinitiator CBP is used as a starting timing point.
Wherein the content of the photocrosslinking agent TAIC is 0.15wt%, and the dispersion concentration of the TAIC in the base stock preparation is 3.65X 10-6mol/cm3. It should be noted that: this dispersion concentration of TAIC hardly varies before and after the whole production process, and therefore the TAIC in the final product-produced insulation material for high voltage cables (crosslinked polyethylene layer) is also the dispersion concentration.
Wherein the content of the photoinitiator CBP is 0.13 wt%; the dispersed concentration of CBP in the base stock is 3.5X 10- 6mol/cm3. It should be noted that: this dispersed concentration of CBPThere is little variation before and after the entire production process, and therefore the CBP in the final product-produced insulation material for high voltage cables (crosslinked polyethylene layer) is also the dispersion concentration.
Loading the prepared base material from a discharge port by using a catenary high-voltage cable production line, and extruding by adopting a three-layer co-extrusion process, wherein the extrusion temperature is set to be 128.5 ℃, and the extrusion speed is 1.05 m/min; then carrying out crosslinking reaction for 15 min at the environmental temperature of 221 ℃ in the nitrogen protection environment; finally obtaining the insulating material for the high-voltage cable.
EXAMPLE III
The insulating material for the high-voltage cable of the embodiment is a Cross-linked polyethylene (XLPE) layer generated by a non-photocrosslinking reaction; the photocrosslinking agent and the photoinitiator in independent molecular states are physically and uniformly distributed in the crosslinked polyethylene layer. Photocrosslinkers are trifunctional photocrosslinkers, specifically functional derivatives of 1,3, 5-s-triazine, more specifically triallyl cyanurate (TAC). The photoinitiator is hydrogen abstraction type polycyclic aromatic hydrocarbon photoinitiator, specifically is benzophenone derivative, more specifically 4,4'-Dichlorobenzophenone (4, 4' -Dichlorobenzophenone, CBP). The molecular structural formulas of TAC and the photoinitiator CBP are shown in FIG. 1 and FIG. 2 respectively.
The base material for preparing the insulating material for the high-voltage cable is prepared by mixing low-density polyethylene, dicumyl peroxide (DCP, a non-photocrosslinking agent), an antioxidant (n-octadecyl beta- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate) and a stabilizer (di-sec-octyl phthalate), adding TAC and CBP additionally, and fully blending.
The preparation method of the insulating material for the high-voltage cable comprises the following steps:
step one, mixing low-density polyethylene, a non-photoinduced crosslinking agent, an antioxidant and a stabilizer by adopting a double-screw extruder according to the existing crosslinked polyethylene insulation formula system for the high-voltage cable;
wherein the temperature of the mixing process is set to be 129 ℃; the content of the non-photocrosslinking agent DCP added is 2.95 wt%.
And step two, adding the photocrosslinking agent TAC and the photoinitiator CBP into a double-screw extruder, and extruding after full blending to obtain the prepared base material.
Wherein the blending process time is 20min, and the adding of the photo-crosslinking agent TAC and the photoinitiator CBP is used as a starting timing point.
Wherein the content of the photocrosslinking agent TAC is 2.9 wt%; the dispersion concentration of TAC in the base stock is 1.075X 10-4mol/cm3. It should be noted that: this dispersion concentration of TAC hardly changes before and after the whole production process, and therefore the dispersion concentration of TAC in the final product-produced insulation material for high-voltage cables (crosslinked polyethylene layer) is also the dispersion concentration.
Wherein, the content of the photoinitiator CBP is 2.95 wt%; the dispersed concentration of CBP in the base stock is 1.06X 10- 4mol/cm3. It should be noted that: this dispersion concentration of CBP hardly varies before and after the whole production process, and therefore the dispersion concentration of CBP in the final product-produced high voltage cable insulation (crosslinked polyethylene layer) is also the dispersion concentration.
Loading the prepared base material from a material pouring port by using a catenary high-voltage cable production line, and extruding by adopting a three-layer co-extrusion process, wherein the extrusion temperature is set to be 131 ℃, and the extrusion speed is 2.0 m/min; then carrying out crosslinking reaction for 15 min at the ambient temperature of 298 ℃ under the nitrogen protection environment; finally obtaining the insulating material for the high-voltage cable.
Compared with the traditional XLPE insulation, the insulation material for the high-voltage cable produced by the embodiment has stronger tree degradation resistance, and the electrical tree growth experiments are respectively carried out on the insulation materials for the high-voltage cable obtained by the first embodiment and the second embodiment according to the IEC/TR 261072 standard, and the electrical tree growth experiments are compared with the electrical tree growth of the traditional XLPE insulation. The specific experimental process is as follows:
experiment step one
Respectively pressing the insulating materials for the high-voltage cables obtained in the first embodiment and the second embodiment and the traditional XLPE insulating materials into flaky samples with the length of 20.00 mm, the width of 10.00 mm and the thickness of 1.15 mm by a hot pressing method in a flat vulcanizing machine, and placing steel needles in the samples to be used as high-voltage needle electrodes;
experiment step two
Putting the three flaky samples with the needle electrodes obtained in the step into insulating oil, connecting the needle electrodes with an alternating-current high-voltage power supply, arranging a copper foil grounding electrode at the edge of the bottom of the sample, and arranging an optical microscope for observing the experimental result of the growth of the electric tree;
experiment step three
According to the IEC/TR 261072 standard, developing an insulation material branch-resistant growth evaluation experiment; set needle electrode AC voltageV rms =4.00 kV, duration of experiment 40 min.
The experimental data graph obtained by adopting the image processing method comprises the following steps:
FIG. 3 is a graph showing the comparison of the electrical tree morphology between the insulating material for high voltage cables of the first embodiment and the insulating material for high voltage cables of the second embodiment and the conventional XLPE insulating material when the electrical tree growth experiment is carried out for 10min, 20min, 30 min and 40 min, wherein the graph with the reference number (a) shows the electrical tree growth of the insulating material for high voltage cables of the first embodiment; the figure with the (b) label is the electric tree growth condition of the insulating material for the high-voltage cable of the second embodiment; the graph with the reference (c) shows the electrical tree growth of the conventional XLPE insulation.
Fig. 4 is a graph comparing the deteriorated length and width of the insulation material for high voltage cables of the first and second examples with those of the conventional XLPE insulation material.
Fig. 5 is a graph comparing the areas of electrical tree degradation damage of the insulation for high voltage cables of examples one and two with conventional XLPE insulation.
As can be seen from fig. 5, when the electrical tree growth experiment is performed for 40 min, the electrical tree degradation damage area of the insulation material for high-voltage cables in the first embodiment is reduced by 87.8% compared with that of the conventional XLPE insulation material, and the electrical tree degradation damage area of the insulation material for high-voltage cables in the second embodiment is reduced by 63.4% compared with that of the conventional XLPE insulation material.
In summary, compared with the conventional XLPE insulating material, the insulating materials for high voltage cables of the two embodiments have stronger tree resistance; the insulating material for the high-voltage cable of the second embodiment has more excellent tree resistance; moreover, the insulating material added with 1.0wt% of photocrosslinking agent TAIC and 1.0wt% of photoinitiator MBP has more excellent tree resistance.
The mechanism of the insulating material for high-voltage cables of the above two embodiments in the course of preparation and use after manufacture is explained and illustrated as follows:
the (I) photocrosslinking additive (TAC or TAIC) and the photoinitiation additive (MBP or CBP) are added in the material blending stage of polyethylene and the like, and are ensured to be uniformly distributed and stably exist in a material system.
And (II) in the production and manufacturing process of the insulating material for the high-voltage cable, only the non-photo-crosslinking agent DCP participates in the crosslinking reaction of the polyethylene in the crosslinking reaction stage, and the photo-crosslinking additive does not initiate the crosslinking reaction due to the fact that the photo-crosslinking additive is not excited by ultraviolet light energy. And, the photo-crosslinking type additive is only present in the crosslinked polyethylene layer where the crosslinking reaction is completed, and thus it does not contact the external ultraviolet radiation throughout the entire production process. After the production of the insulation material for high-voltage cables, the non-photocrosslinking agent DCP is completely consumed by reaction, and the photocrosslinking additives are still uniformly distributed and stably exist in the crosslinked polyethylene layer (high-voltage cable insulation layer).
And (III) in the operation process of the high-voltage cable, the cable insulation layer (the crosslinked polyethylene layer) bears high electric field intensity to cause the destruction of crosslinking points of the crosslinked polyethylene material or the breakage of molecular chains to form defect points. Partial Discharge (PD) phenomenon may occur at the defect point, the essence of the partial discharge is a positive and negative charge recombination process in a local area inside an insulating layer (crosslinked polyethylene layer), energy released in the process is reflected as ultraviolet band light energy irradiation, the ultraviolet irradiation energy excites photoinitiators distributed in the crosslinked polyethylene layer to enter a triplet excited state and generate free end groups, and therefore a carbon-carbon double bond characteristic functional group of the light crosslinking agent and polyethylene at a polymer crosslinking breaking point or a molecular chain breaking point perform re-crosslinking reaction, and the microscopic defect point inside the insulating material is repaired.
And (IV) re-crosslinking the internal crosslinking failure points or molecular chain fracture points of the insulating layer (crosslinked polyethylene layer) by the photo-crosslinking additive under the condition that ultraviolet radiation is released by partial discharge to realize the self-repairing behavior of the microscopic layer of the insulating layer, which is macroscopically represented by inhibiting the material degradation of the insulating layer (crosslinked polyethylene) and prolonging the service life of the material of the insulating layer (crosslinked polyethylene layer).
The insulating material for high-voltage cables of the above embodiments has the following outstanding advantages:
the photocrosslinking additive is physically uniformly dispersed and stably (in an independent molecular state) in the material of the cable insulation layer (crosslinked polyethylene layer);
(II) the photo-crosslinking additive does not participate in the crosslinking reaction generation process of the crosslinked polyethylene layer;
thirdly, the photo-crosslinking additive does not cause reaction when the high-voltage cable normally runs;
and (IV) carrying out re-crosslinking reaction on the crosslinking damage points and molecular chain fracture points of the insulating layer only under the excitation of ultraviolet wave band light energy released by the material degradation of the insulating layer (crosslinked polyethylene layer) in the operation process of the high-voltage cable, repairing the insulation degradation of the crosslinked polyethylene from a microscopic level, and prolonging the service life of the material of the insulating layer.
The invention is not limited to the above-described preferred embodiments, but is intended to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention.

Claims (10)

1. An insulating material for high-voltage cables, comprising a crosslinked polyethylene layer produced by a non-photocrosslinking reaction; the method is characterized in that: the photo-crosslinking agent and the photoinitiator in independent molecular states are physically and uniformly distributed in the crosslinked polyethylene layer.
2. The insulating material for high-voltage cables as claimed in claim 1, wherein: the photocrosslinking agent is a trifunctional photocrosslinking agent, and the photoinitiator is a hydrogen abstraction polycyclic aromatic hydrocarbon photoinitiator.
3. The insulating material for high-voltage cables as claimed in claim 2, wherein: the trifunctional photocrosslinking agent is a functional group derivative of 1,3, 5-s-triazine, and the hydrogen abstraction polycyclic aromatic hydrocarbon photoinitiator is a derivative of benzophenone.
4. The insulating material for high-voltage cables as claimed in claim 3, wherein: the functional derivative of 1,3, 5-s-triazine is triallyl cyanurate or triallyl isocyanurate, and the derivative of benzophenone is 4-methylbenzophenone or 4,4' -dichlorobenzophenone.
5. The insulating material for high-voltage cables as claimed in claim 1, wherein: the dispersion concentration of the photocrosslinking agent in the crosslinked polyethylene layer is 3.61 x 10-6～1.08×10-4mol/cm3The dispersion concentration of the photoinitiator in the crosslinked polyethylene layer is between 3.58 and 10-6～1.07×10-4mol/cm3In the meantime.
6. A base material for the preparation of an insulating material for high-voltage cables according to claim 1, characterized in that: the light-sensitive adhesive is prepared by mixing low-density polyethylene, a non-photocrosslinking agent, an antioxidant and a stabilizer, adding a photocrosslinking agent and a photoinitiator additionally, and fully blending.
7. A method for preparing an insulating material for high voltage cables according to claim 1, comprising the steps of:
step one, mixing low-density polyethylene, a non-photoinduced crosslinking agent, an antioxidant and a stabilizer by adopting an internal mixer or a double-screw extruder according to the existing crosslinked polyethylene insulation formula system for the high-voltage cable;
adding a photocrosslinking agent and a photoinitiator into an internal mixer or a double-screw extruder, and extruding to obtain a prepared base material after full blending;
loading the obtained preparation base material from a discharge hole by using a vertical tower type or catenary high-voltage cable production line, and extruding by adopting a three-layer co-extrusion process, wherein the extrusion temperature is 128-132 ℃, and the extrusion speed is 1.0-2.0 m/min; carrying out crosslinking reaction for 15 min at the ambient temperature of 220-300 ℃ in a nitrogen protection environment; obtaining the insulating material for the high-voltage cable.
8. The method for preparing an insulating material for high-voltage cables as claimed in claim 7, wherein: in the first step, the temperature range of the mixing process is 110-130 ℃, the non-photocrosslinking agent is dicumyl peroxide (DCP), and the addition content of the DCP is 1.0-3.0 wt%.
9. The method for preparing an insulating material for high-voltage cables as claimed in claim 7, wherein: in the second step, the blending process time is more than 10 min; the photocrosslinking agent is triallyl cyanurate TAC or triallyl isocyanurate TAIC, the content of the TAC or the TAIC ranges from 0.1 weight percent to 3.0 weight percent, and the dispersion concentration of the TAC or the TAIC in the preparation base stock is 3.61 x 10-6～1.08×10-4mol/cm3To (c) to (d); the photoinitiator is 4-methylbenzophenone MBP or 4,4' -dichlorobenzophenone CBP, the content of the MBP or CBP ranges from 0.1wt% to 3.0wt%, and the dispersion concentration of the MBP or CBP in the prepared base stock is 3.58 x 10-6～1.07×10-4 mol/cm3In the meantime.
10. The method for preparing an insulating material for high-voltage cables as claimed in claim 7, wherein: the three layers of the three-layer co-extrusion process refer to an inner semi-conducting layer, an insulating layer and an outer semi-conducting layer.
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