KR102097236B1 - Power cable - Google Patents

Abstract

The present invention relates to a power cable. Specifically, the present invention relates to a power cable including an insulating layer made from an insulating composition that is recyclable and is not only environmentally friendly, has excellent flexibility, heat resistance, and mechanical and electrical properties, and is inexpensive to manufacture.

Description

Power cable

The present invention relates to a power cable. Specifically, the present invention relates to a power cable including an insulating layer made from an insulating composition that is recyclable and is not only environmentally friendly, has excellent flexibility, heat resistance, and mechanical and electrical properties, and is inexpensive to manufacture.

A typical power cable includes a conductor and an insulating layer surrounding it, and in the case of a high voltage or ultra high voltage cable, an inner semiconducting layer between the conductor and the insulating layer, an outer semiconducting layer surrounding the insulating layer, a sheath layer surrounding the outer semiconducting layer, etc. It may further include.

Recently, as the operating temperature of a high-voltage cable has improved from 90 ° C to 110 ° C, there has been a need for an insulating material for manufacturing an insulating layer that can maintain its original mechanical and electrical properties without deterioration at a higher temperature. Conventionally, a crosslinked polyolefin polymer such as polyethylene, ethylene / propylene elastic copolymer (EPR), and ethylene / propylene / diene copolymer (EPDM) has been generally used as a base resin constituting a 90 ° C insulating material.

However, the crosslinked polyethylene (XLPE), etc., which has been used as a base resin constituting the insulating material, is not only difficult to recycle because it is a crosslinked form, but also uses the polyvinyl chloride (PVC) as a material for the sheath layer. It is difficult to separate from the cross-linked polyethylene (XLPE) constituting the, there is a disadvantage that is not environmentally friendly, such as toxic chlorinated substances are produced during incineration.

In addition, non-crosslinked high-density polyethylene (HDPE) or low-density polyethylene (LDPE) is environmentally friendly, such as recyclable, but its use is very limited due to its low operating temperature compared to cross-linked polyethylene (XLPE).

On the other hand, the melting point of the polymer itself is 160 ° C or higher, and a technique using an environmentally friendly polypropylene capable of improving the operating temperature of the cable to 110 ° C without crosslinking is known as a base resin. Here, polypropylene refers to a high crystalline isotactic polypropylene as a thermoplastic material having excellent mechanical properties.

However, the polypropylene, due to its high rigidity (rigidity) due to insufficient flexibility (flexibility), there is a problem that the workability is lowered and its use is limited when laying a cable including an insulating layer prepared therefrom.

In this regard, a technique of mixing a base resin, polypropylene and an insulating oil having an aromatic structure, etc. in order to improve the flexibility of an insulating layer made from the polypropylene is known, but since the insulating oil having an aromatic hydrocarbon structure is expensive, There is a problem that the production cost of the cable increases.

Accordingly, there is a need for a power cable including an insulating material for an electric power cable and an insulating layer made therefrom, which are environmentally friendly, recyclable, and have excellent flexibility, heat resistance, and mechanical and electrical properties. .

An object of the present invention is to provide a power cable comprising an insulating layer made from an environmentally friendly insulating material such as recyclable because it has excellent heat resistance and can be used as an insulating layer without crosslinking.

In addition, an object of the present invention is to provide an electric power cable including an insulating layer made from an insulating material that can improve flexibility while maintaining heat resistance, mechanical and electrical properties, and the like.

Furthermore, it is an object of the present invention to provide a power cable comprising an insulating layer made from an insulating material having a low manufacturing cost.

In order to solve the above problems, the present invention,

The power cable according to the present invention is a base resin of an insulating layer constituting the same, and has excellent heat resistance, and thus has excellent environmentally friendly effects such as recyclability by including non-crosslinked polypropylene that can be used for the purpose of the insulating layer without crosslinking. Shows.

In addition, in the power cable according to the present invention, although the insulating layer constituting it contains a specific insulating oil, the polypropylene is insufficient in flexibility due to high rigidity, and the flexibility is improved, at the same time heat resistance, mechanical and electrical It shows an excellent effect that properties and the like can be maintained.

Furthermore, since the power cable according to the present invention does not contain an insulating oil having an expensive aromatic hydrocarbon structure as the insulating oil, it has an excellent effect of low manufacturing cost compared to a power cable comprising an insulating layer made from a conventional insulating material including the same. Indicates.

1 is a cross-sectional view schematically showing a cross-sectional structure of a power cable according to the present invention.
2 is a longitudinal cross-sectional view schematically showing a cross-sectional structure of a power cable according to the present invention.

1 and 2 show an embodiment of a power cable according to the present invention.

As shown in Figures 1 and 2, the power cable according to the present invention is a conductor (1) made of a conductive material such as copper, aluminum, an insulating layer (3) made of an insulating polymer, the conductor (1) and the insulating layer (3) It is located between to suppress partial discharge at the interface with the conductor (1), eliminate the air layer between the conductor (1) and the insulating layer (3), relieve local electric field concentration, etc. It may include an inner semiconducting layer (2) performing a role, an outer semiconducting layer (4) performing a role of shielding the cable and a uniform electric field applied to the insulator, a sheath layer (5) for protecting the cable, etc. have.

The inner or outer semiconducting layers 2 and 4 of the power cable may be manufactured by a conventional method, and preferably, the semiconducting layers 2 and 4 and the insulating layer 3 that may cause shortening of the power cable life. In order to prevent the peeling of, it can be prepared from a composition comprising the same base resin constituting the insulating layer 3 that can ensure excellent adhesion with the insulating layer 3. Further, the inner or outer semiconducting layers 2 and 4 may include a conductive filler such as carbon black for semiconducting properties. In addition, the sheath layer 5 of the power cable may also be prepared from a composition comprising the same base resin constituting the insulating layer 3.

Specifications of the conductor (1), insulating layer (3), semiconducting layer (2,4), sheath layer (5), etc. may vary depending on the purpose of the cable, transmission voltage, etc., and the insulating layer (3), The materials constituting the front layers 2 and 4 and the sheath layer 5 may be the same or different.

The insulating composition forming the insulating layer 3 of the power cable according to the present invention includes a non-crosslinked polypropylene resin as a base resin.

The polymer constituting the non-crosslinked polypropylene resin is a propylene homopolymer and / or propylene and ethylene or an α-olefin having 4 to 12 carbon atoms, for example, 1-butene, 1-pentene, 4-methyl-1-pentene, And a comonomer selected from 1-hexene, 1-octene, 1-decene, 1-dodecene, and combinations thereof, and preferably copolymers with ethylene. This is because the copolymerization of propylene and ethylene shows rigid and flexible properties. Here, the mixing ratio of the propylene homopolymer and the propylene copolymer may be, for example, 80:20 to 50:50.

In the propylene copolymer, the content of comonomer may be 15 mol% or less, preferably 10 mol% or less, based on the total number of monomers constituting the propylene copolymer. In particular, propylene / ethylene copolymers are preferred. Further, the propylene copolymer may be a random copolymer or a block copolymer in which propylene and ethylene and / or α-olefin are polymerized without regularity. In addition, the polypropylene may include a mixture of polyolefins such as low density polyethylene and linear low density polyethylene.

The propylene homopolymer or copolymer preferably has a maximum crystallization temperature of 110 to 125 ° C (measured by differential scanning calorimetry (DSC)). When the maximum crystallization temperature is less than 110 ° C, the polypropylene homopolymer and / or copolymer is melted under the aging test conditions (135 or 150 ° C) required by IEC international standards, or 90 ° C, the continuous use temperature of the cable. When the maximum crystallization temperature exceeds 125 ° C, the crystallization rate during cooling may increase, resulting in a decrease in tensile elongation at room temperature.

In addition, the propylene homopolymer or copolymer preferably has a weight average molecular weight (Mw) of 200,000 to 450,000. When the weight average molecular weight (Mw) is less than 200,000, mechanical properties before and after heating may be deteriorated, and when it is more than 450,000, workability may be deteriorated due to high viscosity. Furthermore, the propylene homopolymer or copolymer preferably has a molecular weight distribution (Mw / Mn) of 2 to 8. When the molecular weight distribution (Mw / Mn) is less than 2, processability may be reduced due to high viscosity, and when it is greater than 8, mechanical properties before and after heating may be reduced.

Meanwhile, the propylene homopolymer or copolymer has, for example, a melt index of 0.01 to 1000 dg / min (measured by ASTM D-1238), and a melting point (Tm) of 140 to 175 ° C (differential scanning calorimeter (DSC) ), Enthalpy of melt is 30 to 85 J / g (measured by DSC), flexural modulus at room temperature is 30 to 1400 MPa, more preferably 60 to 1000 MPa (measured according to ASTM D790-00) May be).

As described above, in the present invention, the propylene homopolymer or copolymer has a high melting point, and exhibits improved deterioration inhibiting properties at higher temperatures of the insulating layer made from the propylene homopolymer or copolymer, thereby In addition to providing a power cable with an improved operating temperature, it has an environmentally friendly advantage such as recyclability because it is non-crosslinked.

On the other hand, unlike the non-crosslinked propylene homopolymer or copolymer according to the present invention, the polymer of the conventional crosslinked form is not eco-friendly because it is difficult to recycle, and when crosslinking or scorch occurs early in the production of the insulating layer It may cause long-term extrudability deterioration, such as inability to exhibit uniform production capacity.

The non-crosslinked propylene homopolymer or copolymer is a conventional method, i.e., homopolymerization of propylene in the presence of a Ziegler-Natta catalyst with low stereospecificity, or α-olefins other than propylene and ethylene or propylene. It can be prepared by copolymerization with. For details on the method for preparing the non-crosslinked propylene homopolymer or copolymer, see, eg, Albizzati et al. in "Polypropylene Handbook", Chapter 2, page 11 on wards (Hanser Publisher, 1996).

The insulating composition constituting the insulating layer 3 of the power cable according to the present invention may contain a specific insulating oil in addition to the base resin.

The insulating oil may include naphthenic hydrocarbons. Here, naphthene is a generic term for saturated hydrocarbons having a structure in which carbon atoms are cyclically bonded in a molecule, and is also called cycloparaffin because its properties are similar to paraffinic hydrocarbons. In particular, the insulating oil is a monocyclic (mono-cyclic) naphthenic hydrocarbon having a general molecular formula of C _n H _2n (where n is an integer from 20 to 60), that is, a cyclic hydrocarbon as shown in Formula 1 below It may include a naphthenic hydrocarbon having a structure in which the cyclic hydrocarbons are alternately arranged. Here, the cyclic hydrocarbon may be 3 to hexagonal, preferably pentagonal or hexagonal.

In Chemical Formula 1, a large circle is a carbon atom and a small circle is a hydrogen atom.

As compared to the monocyclic naphthenic oil, the general molecular formula is C _n H _2n-m (where n is an integer from 20 to 60, m is an integer from 4 to 8) and is shown in Formula 2 below. When cyclic hydrocarbons are attached to each other in the molecule, that is, an insulating oil having a multi-cyclic structure such as bicyclic or tricyclic has low mixing property with a base resin, and thus is used as an insulating oil. Since the performance is deteriorated, the mechanical and electrical properties of the insulating layer produced therefrom may be deteriorated.

In Chemical Formula 2, the large circle is a carbon atom and the small circle is a hydrogen atom.

In addition, the insulating oil is characterized in that the carbon number in the molecular formula is 20 to 60, when the carbon number is less than 20, due to the low molecular weight, the insulating oil can be vaporized and decomposed upon extrusion of the insulating layer, and when the carbon number is more than 60, the high molecular weight Due to this, a phenomenon in which the insulating oil is eluted during extrusion of the insulating layer may occur.

In the insulating composition constituting the insulating layer 3 of the power cable according to the present invention, the content of the insulating oil may be 2.5 to 10 parts by weight based on 100 parts by weight of a non-crosslinked propylene homopolymer or copolymer as a base resin. When the content of the insulating oil is less than 2.5 parts by weight, the insulating layer produced by the insulating composition may not have sufficient flexibility, which may cause problems such as difficulty in laying cables, and the content of the insulating oil is 10 weight. In case of exceeding the portion, a problem in which the cable is difficult to be manufactured and processed may occur, such as a phenomenon in which the insulating oil is eluted during extrusion of the insulating layer.

As described above, the insulating oil has a very high rigidity and improves flexibility of an insulating layer made from an insulating composition using a polypropylene resin having low flexibility as a base resin, while the polypropylene resin is essentially Eggplant has excellent heat resistance and excellent effect of maintaining mechanical and electrical properties. Furthermore, the insulating oil is the same as or better than the conventional insulating oil having an aromatic hydrocarbon structure, but in spite of inducing superior flexibility, heat resistance, and mechanical and electrical properties, the price is much cheaper, and thus exhibits an excellent effect of reducing the manufacturing cost of the cable.

The insulating composition constituting the insulating layer 3 of the power cable according to the present invention may further include other additives such as an antioxidant in addition to the base resin and the insulating oil. The antioxidant may be an amine-based, dialkyl-ester-based, thioester-based, phenol-based antioxidant, etc., for example, distearylthio-propionate, pentaerythryl-tetrakis [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate], [3- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propanoyloxy] -2 , 2-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propanoyloxymethyl] propyl], 3- (3,5-di-t-butyl-4-hydroxy Phenyl) propanoate, thiodiethylene bis (3,5-di-tertyl butyl-4-hydroxyhydrocinnamate), 3,5-bis (1,1-dimethylethyl) -4-hydroxybenzenepropionic acid Octadecyl ester, propionic acid, 3,3'-thiobis-1,1'-dioctadecyl ester, and the like. Here, the content of each of the other additives such as the antioxidant may be 0.2 to 5 parts by weight based on 100 parts by weight of the base resin.

[Example]

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed contents are thorough and complete, and that the spirit of the present invention is sufficiently conveyed to those skilled in the art.

Insulating compositions were prepared according to the components and their contents shown in Table 1 below, and each sample sheet having a thickness of 2 mm and a size of 30 cm × 30 cm was prepared using a hot press. Here, the unit related to the content of the constituents is parts by weight.

Ingredient
Example Comparative example One One 2 3 4 5 Base resin 100 100 100 100 100 100 Monocyclic naphthenic oil (C ₃₀ H ₆₀ ) 5 - - - One 13 Monocyclic naphthenic oil (C ₁₀ H ₂₀ ) - 5 - - - - Monocyclic naphthenic oil (C ₈₀ H ₁₆₀ ) - - 5 - - - Multicyclic naphthenic oil (C ₃₀ H ₅₄ ) - - - 5 - -

-Base resin: 50:50 mixture of polypropylene (manufacturer: Basel, product name: Q200) and ethylene-propylene copolymer resin (manufacturer: SK General Chemical, product name: R520Y)-monocyclic naphthenic oil (C ₃₀ H ₆₀ ) : Insulation Oil No. 4 (Dongnam Petrochemical)

-Monocyclic naphthenic oil (C ₁₀ H ₂₀ ): Insulation oil No. 1 (Dongnam Petrochemical)

-Monocyclic naphthenic oil (C ₈₀ H ₁₆₀ ): Insulation oil No. 6 (Dongnam Petrochemical)

-Multicyclic naphthenic oil (C ₃₀ H ₅₄ ): Insulation oil No. 35 (Dongnam Petrochemical)

<Physical property evaluation of sheet>

1) Evaluation of mechanical properties at room temperature

Tensile strength and elongation at a tensile rate of 250 mm / min at room temperature were measured for each sample sheet prepared in Example 1 and Comparative Examples 1 to 5 according to the IEC-60811-1-1 standard. According to the above standard, the tensile strength should be 1.27 kgf / ㎟ or more, and the tensile elongation should be 200% or more.

2) Evaluation of mechanical properties after heating

For each sample sheet prepared in Example 1 and Comparative Examples 1 to 5, mechanical aging was performed after heating and aging at 150 ° C for 168 hours. Here, the residual strength of the tensile strength and the tensile elongation should be 75% or more, respectively.

3) Evaluation of flexural strength

Flexural strength was measured for each sample sheet prepared in Example 1 and Comparative Examples 1 to 5 according to the IEC 60811-1-1 standard, and the lower the value, the more flexible and flexible the insulating layer and the cable. The workability of the back is considered to be excellent.

4) Insulation breakdown strength evaluation

The dielectric breakdown strength was measured for each sample sheet prepared in Example 1 and Comparative Examples 1 to 5 according to the ASTM D149 standard, and the higher the value, the better the electrical properties.

The flexibility, mechanical and electrical properties of each sample sheet prepared in Example 1 and Comparative Examples 1 to 5 were evaluated according to the method for evaluating the physical properties of the sheet described above, and the results are shown in Table 2 below.

Ingredient
Example Comparative example One One 2 3 4 5 Room temperature tensile strength (kgf / ㎟) 2.0 2.4

Measurement impossible


2.1 2.05

Measurement impossible


Elongation at room temperature (%) 698 660 605 680 Tensile strength residual ratio after heating (%) 81 88 100 90 Elongation after heating (%) 79 58 70 60 Flexural strength (MPa) 30 37 33 42 Dielectric breakdown strength (kV / mm) 65 57 55 55

As shown in Table 2, the insulating composition of Comparative Example 1 has a low molecular weight (140) of the insulating oil (C ₁₀ H ₂₀ ) contained therein, so that the insulating oil is vaporized and decomposed after heating, so that the sheet prepared by the insulating composition After heating, not only the mechanical properties such as insufficient elongation rate (58%) are insufficient, but also, the insulating oil is decomposed during the sample sheet manufacturing process, so that the flexural strength of the sheet is high (37 MPa), resulting in poor flexibility and breakdown of insulation. It was confirmed that the electrical properties were insufficient due to the low strength (57 kV / mm). In addition, the insulating composition of Comparative Example 2 had a large molecular weight (1120) of insulating oil (C ₈₀ H ₁₆₀ ) contained therein, and the insulation of Comparative Example 5 Since the composition contains an excessive amount of insulating oil (C ₃₀ H ₆₀ ) contained therein (13 parts by weight), insulating oil eluted during the extrusion process for preparing the sample sheet, resulting in slippage in the extruder, and as a result, the sample sheet Since it could not be produced, physical properties could not be measured.

In addition, the insulating composition of Comparative Example 3, the insulating oil (C ₃₀ H ₆₀ ) contained therein has a multi-cyclic structure, the mixing property with the base resin is insufficient, and the original function of the insulating oil is not exhibited. %) Was less than 75%, and mechanical properties were insufficient, and the dielectric breakdown strength (55 kV / mm) was low, indicating that electrical properties were also insufficient.

Furthermore, the insulating composition of Comparative Example 4 had the smallest amount (1 part by weight) of the insulating oil (C30H60) contained therein, so the flexural strength was the highest as 42 MPa, which was the most inflexible, and the dielectric breakdown strength was 55 kV / mm It was also found to be the lowest and the poorest electrical property.

On the other hand, the insulating composition of Example 1 was not only excellent in mechanical properties after room temperature and heating, but also by using an appropriate insulating oil, the lowest flexural strength (30 MPa), that is, the best flexibility, the highest dielectric breakdown strength (65 kV / mm) ), That is, it was confirmed to exhibit the best electrical properties.

Although this specification has been described with reference to preferred embodiments of the present invention, those skilled in the art variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims set forth below. You can do it. Therefore, if the modified implementation basically includes the components of the claims of the present invention, it should be considered that all are included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Conductor 2 Internal semiconducting layer
3: Insulation layer 4: External semiconducting layer
5: sheath layer

Claims (6)

Formula C _n H _2n in which cyclic hydrocarbons and non-cyclic hydrocarbons are alternately arranged, based on 100 parts by weight of the base resin and a base resin comprising a non-crosslinked propylene homopolymer, a non-crosslinked propylene copolymer, or both. An insulating composition comprising 2.5 to 10 parts by weight of an insulating oil comprising a monocyclic naphthenic hydrocarbon of (where n is an integer from 20 to 60). According to claim 1,
Insulating composition, characterized in that the ring of the cyclic hydrocarbon is pentagonal or hexagonal. The method according to claim 1 or 2,
The base resin comprises a non-crosslinked propylene homopolymer and a non-crosslinked propylene copolymer, and the blending ratio of the non-crosslinked propylene homopolymer and the non-crosslinked propylene copolymer is 80:20 to 50:50, the insulating composition . According to claim 3,
The non-crosslinked propylene copolymer is characterized in that the copolymer of a propylene monomer and an ethylene monomer, insulating composition. According to claim 4,
The content of the ethylene monomer is 15 mol% or less based on the number of moles of the total monomers constituting the non-crosslinked propylene copolymer, insulation composition. The method according to claim 1 or 2,
Based on 100 parts by weight of the base resin, characterized in that it further comprises 0.2 to 5 parts by weight of an amine-based, dialkyl ester-based, thioester-based or phenolic antioxidant, insulation composition.

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