KR102020069B1

KR102020069B1 - Compact power cable with increased capacitance

Info

Publication number: KR102020069B1
Application number: KR1020130047148A
Authority: KR
Inventors: 소철호; 권중지; 유익현; 박대진
Original assignee: 한국전력공사; 엘에스전선 주식회사
Priority date: 2013-04-29
Filing date: 2013-04-29
Publication date: 2019-11-04
Also published as: KR20140128585A

Abstract

The present invention relates to a compact power cable with increased capacity. Specifically, the present invention is more recyclable than the conventional power cable because it is recyclable, environmentally friendly, has excellent heat resistance, flexibility, mechanical and electrical properties, and has an optimum insulation thickness derived by a new method. The present invention relates to a power cable having improved capacity and improved construction convenience such as laying property due to light weight due to a reduction in insulation thickness.

Description

Compact power cable with increased capacitance

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

In recent years, as the operating temperature of high voltage cables has been improved from 90 ° C to 110 ° C, it is possible to maintain the original mechanical and electrical properties without deterioration at higher temperatures and to reduce the weight of the cable by minimizing the thickness of the insulating layer. There is a need for an insulating material capable of improving construction convenience such as installation properties.

Conventionally, crosslinked polyolefin-based polymers such as polyethylene, ethylene / propylene elastic copolymer (EPR), and ethylene / propylene / diene copolymer (EPDM) have been generally used as the base resin constituting the 90 ° C insulating material. For example, Korean Patent Laid-Open No. 2011-0020126 discloses a crosslinked polyethylene material for a power cable that satisfies increased transmission current capacity and maximum conductor allowable temperature characteristics.

However, the crosslinked polyethylene (XLPE) and the like, which have been used as the base resin constituting the insulating material, are crosslinked and thus are difficult to recycle, and methane gas, which is a representative greenhouse gas, is not only generated in the manufacturing process, but also polyvinyl chloride as a material of the sheath layer. When chloride (PVC) is used, it is difficult to separate it from cross-linked polyethylene (XLPE) constituting the insulating material, and thus has a disadvantage in that it is not environmentally friendly, such as generating toxic chlorinated material upon incineration.

On the other hand, non-crosslinked high density polyethylene (HDPE) or low density polyethylene (LDPE) is environmentally friendly, such as recyclable, but its use is low due to its low operating temperature and insufficient mechanical and electrical characteristics compared to crosslinked polyethylene (XLPE). In particular, in the case of a high-capacity cable, the thickness of the insulating layer is too thick, and there is a disadvantage in that construction workability such as laying property of the cable is significantly reduced.

On the other hand, since the melting point of the polymer itself is 160 ° C or higher, it is possible to consider using an environmentally friendly polypropylene as a base resin that can improve the operation temperature of the cable to 110 ° C without crosslinking. As a thermoplastic material having excellent mechanical properties, it means high crystalline isotactic polypropylene.

However, the polypropylene is a crystalline polymer, and the size of the polypropylene crystal produced varies depending on the cooling rate of the polypropylene resin applied to a conductor in a molten state during the extrusion process of the cable including the insulating layer made of a crystalline polymer. Specifically, if the cooling rate is increased, the productivity is increased and the size of the crystal to be produced is smaller, thereby improving the electrical characteristics of the insulating layer. However, the crystallinity is lowered, so that the heat resistance and mechanical strength are lowered. Degradation and the size of the resulting crystals are increased, the electrical properties of the insulating layer is lowered, but the crystallinity is increased, heat resistance, mechanical properties and the like are improved. That is, in the insulating layer containing the polypropylene resin as the base resin, it is very difficult to simultaneously satisfy the electrical characteristics, the productivity of the cable, the heat resistance, the mechanical characteristics, and the like. In addition, it is limited and difficult to quench the polypropylene resin in the extrusion process of the cable in order to improve the productivity of the cable and the electrical properties of the insulating layer produced.

In addition, the polypropylene resin is usually synthesized under a Ziegler-Natta catalyst having a low stereospecificity, typically a complex salt consisting of titanium trichloride and diethylaluminum chloride, and specific synthesis methods are described in Albizzati et al. in "Polypropylene Handbook", Chapter 2, page 11 on wards (Hanser Publisher, 1996). When the polypropylene resin is synthesized under the Ziegler-Natta catalyst, the molecular weight distribution of the synthesized resin is rather wide, so that the processability is excellent, but the residual amount of the catalyst in the polypropylene resin is rather high, such that electrical characteristics such as insulation performance are deteriorated.

In addition, the polypropylene has a problem in that workability is limited and its use is limited when laying a cable including an insulating layer manufactured therefrom due to insufficient flexibility due to its high rigidity.

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

Furthermore, when designing a power cable, insulated by considering minimum AC breakdown voltage, minimum impulse strength, transmission voltage, cable life, etc. according to Association of Edison Illuminating Companies (AEIC), Institute of Electrical and Electronics Engineers (IEEE), etc. Although the thickness of the layer has been appropriately selected, in this case, the thickness of the insulating layer is set to be thicker than necessary according to the type of insulating material, thereby reducing the workability of the cable such as the laying property of the cable, or setting the thickness excessively, thereby shortening the life of the cable. May be induced.

On the other hand, in the power cable, the inner semiconducting layer improves the interfacial roughness between the conductor and the insulating layer during cable manufacture, forms a gradient of insulation resistance, and the outer semiconducting layer serves as a shielding of the cable and the insulating layer It plays a very important role in terms of enhancing the electrical characteristics of the cable, such as making the electric field uniform.

In recent years, the melting point of the polymer itself is 160 ° C or more, a technique using an environmentally friendly polypropylene as a base resin that can improve the continuous use temperature of the inner semiconducting layer to 110 ° C class without crosslinking. However, the internal semiconducting layer cannot avoid contact with the metallic material constituting the conductor for the purpose of use, and unlike the polyethylene, the polypropylene contains a large amount of tertiary carbon in the polymer main chain. The problem of deterioration was found to be a very fatal drawback.

Therefore, the base resin forming the insulating layer and the semiconducting layer is environmentally friendly such that it can be recycled by including a non-crosslinked resin, and despite its non-crosslinked form, its heat resistance, flexibility, mechanical and electrical properties, etc. are excellent. How to calculate the optimal insulation layer thickness according to new insulation materials and insulation materials that can increase the capacity of the power cable without excessively increasing the thickness of the layer and can improve the construction workability, such as cable laying properties In addition, there is a demand for a semiconductive material capable of suppressing heat and heat and extending a cable life.

The present invention has excellent heat resistance, mechanical and electrical properties, and can be used as an insulating layer and a semiconducting layer without crosslinking, and thus can be recycled. An object of the present invention is to provide a power cable comprising a.

In addition, the present invention includes an insulating layer manufactured from an insulating material having excellent electrical characteristics, thereby increasing the capacity of the power cable and at the same time not excessively increasing the thickness of the insulating layer. It is an object to provide a power cable that can be improved.

In addition, an object of the present invention is to provide a power cable having an optimum insulating layer thickness according to the insulating material.

Furthermore, an object of the present invention is to provide a power cable including a semiconducting layer which can significantly suppress deterioration and extend the life of the cable.

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

A power cable comprising at least one conductor, an inner semiconducting layer surrounding each conductor, and an insulation layer surrounding each inner semiconducting layer, wherein the insulation layer comprises a base resin comprising a non-crosslinked polypropylene resin; Insulating oil 1 to 10 containing a naphthenic hydrocarbon of formula C _n H _2n where n is an integer of 20 to 60, wherein the cyclic hydrocarbon and the acyclic hydrocarbon are alternately arranged based on 100 parts by weight of the base resin. The inner semiconductive layer is prepared from an insulating composition including parts by weight, and the base semiconductive layer includes 30 to 70 parts by weight of conductive particles and 0.1 to 9 parts by weight of non-active additive based on a base resin including a non-crosslinked polypropylene resin and 100 parts by weight of the base resin. It provides a power cable, characterized in that prepared from a semiconducting composition comprising 5 parts by weight.

Wherein the base resin comprises a non-crosslinked propylene homopolymer and a noncrosslinked propylene copolymer polymerized under a metallocene catalyst, and a blending ratio of the noncrosslinked propylene homopolymer and the noncrosslinked propylene copolymer polymerized under the metallocene catalyst Provides a power cable, characterized in that 80:20 to 50:50.

In addition, the non-crosslinked propylene copolymer provides a power cable, characterized in that the copolymer of propylene monomer and ethylene monomer.

In addition, the content of the ethylene monomer is 15 mol% or less based on the total number of moles of the total monomer constituting the non-crosslinked propylene copolymer, provides a power cable.

Furthermore, the remaining amount of the catalyst of the non-crosslinked polypropylene resin polymerized under the metallocene catalyst provides a power cable.

On the other hand, the insulating composition, based on 100 parts by weight of the base resin, 1,3: 2,4-bis (3,4-dimethyldibenzylidene) sorbitol (1,3: 2,4-Bis (3,4- 0.1 to 0.5 weight of at least one nucleating agent selected from the group consisting of dimethyldibenzylidene) Sorbitol, bis (p-methyldibenzulidene) Sorbitol, and substituted Dibenzylidene Sorbitol Provided is a power cable, characterized in that it further comprises a portion.

In addition, there is provided a power cable, characterized in that the size of the polypropylene crystal in the insulating layer prepared from the insulating composition is 1 to 5 ㎛.

On the other hand, the naphthenic hydrocarbon is characterized in that the monocyclic naphthenic hydrocarbon, it provides a power cable.

And, it provides a power cable, characterized in that the ring of the cyclic hydrocarbon is pentagonal or hexagonal.

Furthermore, the insulating composition, the semiconductive composition, or both of these may further comprise 0.2 to 5 parts by weight of an amine-based, dialkyl ester-based, thioester-based or phenolic antioxidant based on 100 parts by weight of the base resin. It is characterized by providing a power cable.

On the other hand, the outer semiconducting layer surrounding the insulating layer, and a sheath layer surrounding the outer semiconductive layer further comprises, wherein the outer semiconducting layer and the sheath layer from a composition comprising the same base resin as the base resin of the insulating composition Provided is a power cable, characterized in that the manufacturing.

In addition, the metal inactive additive provides a power cable, characterized in that it has a molecular structure of the chelate ligand (chelate legand) form two or more coordination bonds with one metal atom.

Here, the metal inactive additive has at least two Lewis base sites serving as electron donors in the molecular structure, and the Lewis bases are amine groups, amide groups or carboxyl groups. To provide a power cable.

In addition, the metal inactive additives are N, N'-bis (salicylidene) -1,2-propanediamine, 1,2-bis (3,5-di-t-butyl-4-hydroxycinnamoyl) hydrazine Or N, N'-1,2-ethane diylbis- (N- (carboxymethyl) glycine).

Furthermore, it provides a power cable, characterized in that the solubility of the metal-inert additive in paraffin oil at 20 ° C. is 0.01 g / 100 ml or less.

On the other hand, in the power cable comprising at least one conductor, and an insulation layer surrounding each conductor, the insulation layer is a non-crosslinked polypropylene having a residual amount of polymerization catalyst 200 to 700 ppm, crystal size of 1 to 5 ㎛ Provided is an electric power cable made from an insulating composition comprising a resin.

In addition, a power cable comprising at least one conductor, and an insulation layer surrounding each conductor, wherein the thickness of the insulation layer is characterized in that the power cable is 3.65 times to 4.68 times Tmin defined in the following equation, to provide.

The power cable according to the present invention exhibits an excellent environmentally friendly effect such as being recycled by including polypropylene in an uncrosslinked form as the base resin of the insulating layer and the semiconducting layer constituting the same.

In addition, the power cable according to the present invention has an excellent effect of increasing the capacity of the cable by including a non-crosslinked polypropylene excellent in its heat resistance, mechanical and electrical properties as the base resin of the insulating layer constituting it.

In addition, the power cable according to the present invention does not excessively increase the thickness of the insulating layer in spite of increasing the capacity of the cable shows an excellent effect to improve the construction workability, such as cable laying properties.

Furthermore, the power cable according to the present invention has an excellent thickness of the insulating layer according to the insulating material exhibits an excellent effect of optimizing the construction workability, such as cable laying properties and the life of the cable at the same time.

On the other hand, the power cable according to the present invention exhibits an excellent effect of extending the life by including a semi-conducting layer that is significantly suppressed heat.

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 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 invention.

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 Located between (3) to suppress partial discharge at the interface with the conductor (1), to eliminate the air layer between the conductor (1) and the insulating layer (3), to mitigate local electric field concentration, etc. Inner semiconducting layer (2) to play a role, outer semiconducting layer (4) to play a role of shielding the cable and an electric field evenly to the insulator, metal shielding layer (5) to provide electrical shielding function, cable Sheath layer 6 for protection and the like. In addition, a predetermined semiconductive tape layer may be further provided between the outer semiconducting layer 4 and the metal shielding layer 5.

The inner or outer semiconducting layers 2,4 of the power cable may be manufactured in a conventional manner, and preferably the semiconducting layers 2 and 4 and the insulating layer 3 may cause shortening of the power cable life. In order to prevent peeling of the resin, it may be prepared from a composition comprising the same base resin constituting the insulating layer 3 capable of ensuring excellent adhesion with the insulating layer 3. In addition, the inner or outer semiconducting layers 2 and 4 may include conductive fillers such as carbon black for semiconducting properties. In addition, the sheath layer 6 of the power cable may also be manufactured from a composition comprising the same base resin constituting the insulating layer 3.

Standards of the conductor 1, the insulating layer 3, the semiconductive layers 2 and 4, the sheath layer 6, and the like may vary according to the use of the cable, the transmission voltage, and the like. The materials constituting the entire layers 2 and 4 and the sheath layer 6 may be the same or different.

The insulating composition and semiconductive composition for forming the insulating layer 3 and the semiconductive layers 2, 4 of the power cable according to the present invention include a non-crosslinked polypropylene resin as the base resin.

The polymer constituting the non-crosslinked polypropylene resin may be a propylene homopolymer and / or propylene and ethylene or an α-olefin having 4 to 12 carbon atoms, such as 1-butene, 1-pentene, 4-methyl-1-pentene, Comonomers selected from 1-hexene, 1-octene, 1-decene, 1-dodecene, and combinations thereof, preferably copolymers with ethylene. This is because copolymerization of propylene and ethylene shows hard 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 the comonomer may be 15 mol% or less, preferably 10 mol% or less, based on the total moles of monomers constituting the propylene copolymer. In particular, propylene / ethylene copolymers are preferred. In addition, the propylene copolymer may be a random copolymer or a block copolymer in which propylene and ethylene and / or α-olefins are polymerized without regularity. In addition, the polypropylene may include a mixture with polyolefin 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)). 90 ° C. conditions where the polypropylene homopolymer and / or copolymer is melted or the continuous use temperature of the cable at aging test conditions (135 or 150 ° C.) required by IEC international standards when the highest crystallization temperature is less than 110 ° C. If the maximum crystallization temperature exceeds 125 ℃ can be a problem that the crystallization rate during the cooling is faster and the tensile elongation at room temperature is lowered.

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 lowered, and if it is more than 450,000, workability may be lowered 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, the workability may be lowered due to the high viscosity, and if it is more than 8, the mechanical properties before and after heating may be lowered.

On the other hand, the propylene homopolymer or copolymer, for example, the melt index of 0.01 to 1000 dg / min (measured by ASTM D-1238), the melting point (Tm) of 140 to 175 ℃ (differential scanning calorimetry (DSC) Melt enthalpy of 30 to 85 J / g (measured by DSC), flexural modulus at room temperature of 30 to 1400 MPa, more preferably 60 to 1000 MPa (measured according to ASTM D790-00). May be used).

As the base resin of the insulating composition for forming the insulating layer 3 of the power cable according to the present invention, the non-crosslinked polypropylene is preferably synthesized under a metallocene catalyst. The metallocene is a generic term for bis (cyclopentadienyl) metal, which is a new organometallic compound in which a cyclopentadiene and a transition metal are bonded in a sandwich structure, and the general formula of the simplest structure is M (C ₅ H ₅ ) ₂ (where M Ti, V, Cr, Fe, Co, Ni, Ru, Zr, Hf and the like).

The metallocene may be prepared by reacting a cyclopentadiene metal compound with a halide of a transition metal such as titanium, zirconium, and hafnium. Methods of making such metallocenes are described in US Pat. Nos. 4,752,579, 5,017,714, and European Patents 320,762, 416,815, 537,686, 669,340, and H. H. Brintzinger et al .; Andrew. cam. Andrew, Chem., 107 (1995), 1255, H. H. Brinzinger et al .; J. Organomet. cam. (Organomet. Chem), 232 (1982), 233, and the like.

The metallocene catalyst has its basic characteristics can be systematically controlled by a specific substitution pattern of ligand spheres, so that the polymerization activity, stereoselective, regioselectivity, melting point in the polypropylene polymerization The Ziegler-Natta catalyst, which has been used as a conventional polypropylene polymerization catalyst, can synthesize only polypropylene having an isotactic structure in which methyl groups are arranged in the same direction. Can be.

In addition, the metallocene catalyst has a low catalyst residual amount of the synthesized polypropylene, thereby exhibiting an excellent effect of not causing or minimizing the electrical properties of the polypropylene. Specifically, in the case of the polypropylene synthesized by the metallocene catalyst, the remaining amount of the polymerization catalyst is only 200 to 700 ppm, so that electrical properties such as insulation performance of the synthesized polypropylene are not reduced or minimized, whereas the conventional Ziegler-Natta In the case of the polypropylene synthesized by the catalyst, the residual amount of the catalyst corresponds to 1,000 to 3,000 ppm, so that such a large amount of the catalyst may slightly lower electrical characteristics such as insulation performance of the synthesized polypropylene.

The method of polymerizing the polypropylene resin under the metallocene catalyst is not particularly limited. For example, the polymerization of the polypropylene resin can be carried out continuously or batchwise, in bulk, in suspension or in gas phase, at a temperature of -60 to 300 ° C., under a pressure of 0.5 to 2,000 bar. It may be prepared in one or a plurality of steps.

As described above, in the power cable according to the present invention, the non-crosslinked polypropylene resin, which is the base resin of the insulating layer 3, has a high melting point due to its own melting point even though it is in a non-crosslinked form, thereby providing continuous heat resistance. Not only can it provide an improved power cable, but it is also non-crosslinked, so it can be recycled.

On the other hand, conventional cross-linked resins are not environmentally friendly due to difficulty in recycling, and when cross-linking or scorch occurs early when forming the insulating layer 3, the long-term extrudability is lowered such that uniform production capacity cannot be exhibited. May cause.

In addition, since the non-crosslinked polypropylene resin is synthesized under a metallocene catalyst rather than a conventional Ziegler-Natta catalyst, the catalyst residual amount is low so that damage to electrical characteristics such as insulation performance of the insulating layer 3 manufactured therefrom may be avoided or minimized. That shows excellent effect.

The insulating composition constituting the insulating layer 3 of the power cable according to the present invention contains a nucleating agent in addition to the base resin. The nucleating agent may be a sorbitol-based nucleating agent. That is, the nucleating agent is a sorbitol-based nucleating agent, for example, 1,3: 2,4-bis (3,4-dimethyldibenzylidene) sorbitol (1,3: 2,4-Bis (3,4-dimethyldibenzylidene) Sorbitol ), Bis (p-methyldibenzulidene) Sorbitol, Substituted Dibenzylidene Sorbitol, and mixtures thereof.

The nucleating agent not only improves the productivity of the cable by promoting the curing of the non-crosslinked polypropylene resin, which is the base resin, but also reduces the size of crystals formed during curing of the non-crosslinked polypropylene resin, Preferably, by limiting to 1 to 5 ㎛, it is possible to improve the electrical properties of the insulating layer to be manufactured, and further increase the degree of crystallinity by forming a plurality of crystallization sites from which the crystals are produced to increase the heat resistance, mechanical properties, etc. of the insulating layer At the same time exerts an excellent effect of improving.

Since the nucleating agent has a high melting temperature, injection and extrusion processing should be performed at a high temperature of about 230 ° C., and it is preferable to use a combination of two or more sorbitol-based nucleating agents. When two or more different sorbitol-based nucleating agents are used in combination, the expression of the nucleating agent may be increased even at low temperatures.

The nucleating agent may be included in the insulation composition at 0.1 to 0.5 parts by weight based on 100 parts by weight of the base resin. When the content of the nucleating agent is less than 0.1 part by weight, the heat resistance, electrical and mechanical properties of the insulating composition and the insulating layer prepared therefrom may be increased due to large crystal size, for example, crystal size exceeding 5 μm and uneven crystal distribution. On the other hand, if the content of the nucleating agent exceeds 0.5 parts by weight, too small crystal size, for example, due to an increase in the surface interface area between the crystal and the amorphous portion of the composition due to the crystal size of less than 1 μm AC dielectric breakdown (ACBD) characteristics, impulse characteristics, etc. of the insulating composition and the insulating layer prepared therefrom may be degraded.

In this regard, Figure 3 is an insulating composition constituting the insulating layer 3 of the power cable according to the present invention, that is, an insulation composition added 0.2 parts by weight of the nucleating agent to the mixture of the non-crosslinked polypropylene resin and the non-crosslinked propylene / ethylene copolymer resin As a polarized optical microscope (POM) photograph of, as shown in FIG. 3, the size of the polypropylene crystal produced in the composition was found to be 1 to 5 ㎛.

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

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

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

In contrast to the monocyclic naphthenic oils, 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, as shown in the following formula (2) When cyclic hydrocarbons are attached to each other in the molecule, that is, an insulating oil having a multicyclic structure such as bicyclic or tricyclic, the insulating oil has low mixing properties with the base resin and thus is used as insulating oil. Since the performance is lowered, the mechanical and electrical properties of the insulating layer produced therefrom may be lowered.

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

In addition, the insulating oil is characterized in that the carbon number in the molecular formula of 20 to 60, when the carbon number is less than 20 due to the low molecular weight, the insulating oil may be vaporized and decomposed during extrusion of the insulating layer, when the carbon number is higher than 60 high molecular weight As a result, the insulating oil may be eluted during extrusion of the insulating layer.

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 1 to 10 parts by weight based on 100 parts by weight of the non-crosslinked propylene homopolymer or copolymer which is the base resin. When the amount of the insulating oil is less than 1 part by weight, the insulating layer manufactured by the insulating composition may not have sufficient flexibility, and thus may cause problems such as difficulty in laying the cable. If the portion is exceeded, the production of the cable may be difficult, such as a phenomenon in which the insulating oil is eluted during the extrusion of the insulating layer.

As described above, the insulating oil improves the flexibility of an insulating layer made from an insulating composition comprising a polypropylene resin having a very high rigidity and having a low flexibility. Eggplant has an excellent effect of maintaining excellent heat resistance and mechanical and electrical properties. Furthermore, the insulating oil is much cheaper in spite of the same or rather superior flexibility, heat resistance, mechanical and electrical properties as the conventional insulating oil having an aromatic hydrocarbon structure, thereby exhibiting an excellent effect of reducing the manufacturing cost of the cable.

The insulation composition constituting the insulation layer 3 of the power cable according to the invention may further comprise other additives such as antioxidants.

Moreover, the said antioxidant can use an amine type, a dialkyl ester type, a thioester type, a phenol type antioxidant, etc., For example, distearyl thio 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- Hydroxyphenyl) propanoate, thiodiethylene bis (3,5-di-tert butyl-4-hydroxyhydrocinnamate), 3,5-bis (1,1-dimethylethyl) -4-hydroxy Benzenepropionic acid octadecyl ester, propionic acid, 3,3'-thiobis-1,1'- dioctadecyl ester, and the like. Here, the content of the antioxidant may be 0.2 to 5 parts by weight based on 100 parts by weight of the base resin.

The semiconducting composition constituting the inner semiconducting layer 2 of the power cable according to the invention comprises conductive particles to control the electrical conductivity of the inner semiconducting layer 2. There is no particular limitation on the conductive particles, and for example, carbon black such as furnace black, acetylene black, or the like, or graphite, graphene or the like may be used.

The conductive particles such as carbon black are not particularly limited in shape, and may be, for example, spherical, plate-shaped, rod-shaped, or tubular. In addition, the surface area of the conductive particles may be 20 m 2 / g or more, for example, 40 to 1,200 m 2 / g, and preferably, the volume resistance of the expandable polymeric material may be less than 500 Ωm, more preferably less than 20 Ωm. have. In particular, the conductive particles content such as carbon black may be 30 to 70 parts by weight based on 100 parts by weight of the base resin. When the conductive particle content, such as carbon black, is less than 30 parts by weight, it may be difficult to implement the desired semiconducting properties, and when it is more than 70 parts by weight, extrusion may be disadvantageous.

The semiconducting composition for forming the inner semiconducting layer 2 of the power cable according to the present invention is a metal inert additive which is an additive for deactivating the metallic material flowing from the conductor 1 of the power cable to the inner semiconducting layer 2. Include. In the case of the metallic material, for example, transition metal ion atoms such as copper ions, due to the relatively large atomic radius, an additional coordinate bond may be formed in addition to the ionic bond by a given ion order. In order to deactivate the transition metal ion, an additive having a molecular structure in the form of a chelate legand forming two or more coordination bonds with one metal atom is preferable.

The metal inactive additive preferably has at least two Lewis-base sites serving as electron donors in the molecular structure, and the Lewis bases preferably have functional groups such as amines, amides, and carboxyls. Do.

In addition, it is preferable that the metal inactive additive has a solubility in insulating oil such as paraffin oil of 0.01 g / 100 ml (gram of solute dissolved in 100 ml of solvent at 20 ° C) or less. When using a paraffinic insulating oil in the insulating layer (3) in contact with the inner semiconducting layer (2) containing the metal inactive additive in the power cable, if the solubility of the metal inactive additive in the paraffinic insulating oil is large, Since the metal inactive additive may be eluted outwards or transferred to the insulating layer 3, it may be difficult to realize the original characteristics of the metal inactive additive.

In this regard, the metal inactive activator may be preferably a compound of Formulas 3 to 5. The compound of formula 3 is N, N'-bis (salicylidene) -1,2-propanediamine (N, N'-bis (salicylidene) -1,2-propanediamine), the compound of formula 4 is 1, 2-bis (3,5-di-t-butyl-4-hydroxycinnamoyl) hydrazine (1,2-bis (3,5-di-tert-butyl-4-hydroxycinnamoyl) hydrazine) of Formula 5 The compound is N, N'-1,2-ethane diylbis- (N- (carboxymethyl) glycine) (N, N'-1,2-ethane diylbis- (N- (carboxymethyl) glycine).

The metal inactive additive may be 0.1 to 5 parts by weight based on 100 parts by weight of the base resin. When the content of the metal inactive additive is less than 0.1 parts by weight, the desired effect, that is, the anti-deterioration effect of the internal semiconducting layer 2 due to deactivation of the metal material flowing from the conductor 1 cannot be achieved, and more than 5 parts by weight. In the case of bleaching may occur due to compatibility problems with the base resin after extrusion.

The semiconducting composition for forming the inner semiconducting layer 2 of the power cable according to the present invention may further include other additives such as antioxidants, lubricants, etc. in addition to the base resin, conductive particles, and metal inactive additives. The antioxidant may be an amine, dialkyl ester, thioester, phenol-based antioxidant, and the like, for example, [3- [3- (3,5-di-t-butyl-4-hydroxy Oxyphenyl) propanoyloxy] -2,2-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propanoyloxymethyl] propyl], 3- (3,5- Di-tert-butyl-4-hydroxyphenyl) propanoate, thiodiethylene bis (3,5-di-tert-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. In addition, the lubricant may be, for example, a polypropylene wax or polyethylene wax having a number average molecular weight (Mn) of 1,000 to 10,000.

The content of each of the other additives such as the antioxidant and the lubricant may be 0.2 to 3 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 invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the present invention to those skilled in the art.

1. Example of Insulation Composition

1) Production Example

The insulating composition was prepared according to the components shown in Table 1 and their contents, and extruded using a 30 mm single screw extruder (manufacturer: Royle, USA) attached with a T-die, followed by a hot press. Sheets having a thickness of 2 mm and a size of 30 cm × 30 cm were prepared respectively.

Ingredient Example Comparative example One 2 3 One 2 3 4 Base Resin 1 50 80 - 50 80 50 50 Base Resin 2 - - 50 - - - - Base resin 3 50 20 50 50 20 50 50 Nuclear agent 0.3 0.3 0.3 - 0.3 0.3 0.3 Insulation oil 1 5 5 5 5 - 0.5 13 Insulating oil 2 - - - - 5 - -

-Base resin 1: polypropylene resin polymerized under metallocene catalyst (manufacturer: PolyMirae; product name: RM5100; melting index (MI): 3)

Base resin 2: Polypropylene resin polymerized under Ziegler-Natta catalyst (Manufacturer: SK Synthetic Chemical; Product Name: H920Y; Melting index, MI: 3)

-Base resin 3: Propylene-ethylene copolymer (Manufacturer: SK synthesis chemical; Product name: R520Y)

-Nucleating agent: Sorbitol-based nucleating agent (Manufacturer: Milliken, Product name: NX8000)

-Insulating oil 1: Monocyclic naphthenic oil (C ₃₀ H ₆₀ ): Insulating oil No. 4 (Dongnam Petrochemical)

-Insulating oil 2: Multicyclic naphthenic oil (C ₃₀ H ₅₄ ): Insulating oil 35 (Dongnam Petrochemical)

2) Property evaluation

A) Evaluation of mechanical properties at room temperature

Tensile strength and elongation were measured at a tensile rate of 250 mm / min at room temperature for each of the sample sheets prepared in Examples and Comparative Examples according to the IEC-60811-1-1 standard. According to the specification, the tensile strength should be at least 1.27 kgf / mm 2 and the tensile elongation at least 200%.

B) Mechanical property evaluation after heating

Each sample sheet prepared in Examples and Comparative Examples was subjected to heat aging at 150 ° C. for 168 hours, and then mechanical properties were measured in the same manner as in the above 1) room temperature mechanical property measurement method. Here, the residual strength and tensile elongation must be 75% or more, respectively.

C) Flexural strength assessment

Flexural strength was measured for each sample sheet manufactured in Examples and Comparative Examples according to the IEC 60811-1-1 standard. The lower the value, the more workability such as flexibility and laying property of insulation layer and cable This is considered to be excellent.

D) Insulation breakdown strength evaluation

Insulation breakdown strength was measured for each of the sample sheets prepared in Examples and Comparative Examples according to ASTM D149 standard, and the higher the value, the better the electrical properties. The dielectric breakdown strength was statistically treated by testing fifteen sheets in each of Examples and Comparative Examples.

According to the method for evaluating the physical properties of the sheet described above, the heat resistance, the bendability, the mechanical and electrical properties of each sheet manufactured in Examples and Comparative Examples were evaluated, and the results are shown in Table 2 below.

Properties Example Comparative example One 2 3 One 2 3 4 Room temperature tensile strength (kgf / ㎡) 1.9 2.4 2.0 1.9 2.1 2.05
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tablet
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end
Room Temperature Tensile Elongation (%) 712 650 680 698 605 680 Tensile strength residual after heating (%) 85 88 90 81 100 90 Residual elongation after heating (%) 80 76 80 79 70 60 Flexural Strength (MPa) 32 33 34 35 33 42 Insulation Breaking Strength
(kV / mm) medium 125.25 126.63 118.93 105.28 105.98 105.74 Deviation 13.62 12.86 10.40 15.40 14.98 15.12

As shown in Table 2, the insulating sheet according to Comparative Example 1 was found to have a low dielectric breakdown strength (kV / mm). This is because the insulating composition of Comparative Example 1 does not contain a nucleating agent, unlike the insulating compositions of Examples 1 to 3, and the crystal sites are nonuniform and crystals are large when the crystals of the polypropylene resin are produced in the base resin.

In the insulating sheet according to Comparative Example 2, the insulating oil (C ₃₀ H ₆₀ ) contained therein has a multi-cyclic water tank, which is insufficient in mixing with the base resin, and thus does not exhibit the original function of the insulating oil. The mechanical properties were insufficient, such as 70% and less than 75%, and the dielectric breakdown strength was 105.98 kV / mm, which was found to be considerably lower than those of Examples 1 to 3.

Furthermore, since the insulating sheet according to Comparative Example 3 has a very small amount of insulating oil (C ₃₀ H ₆₀ ) contained in it, the flexural strength is the highest as 42 MPa, and the flexibility, flexibility, and laying property are the poorest, and the dielectric breakdown strength is also 105.74. kV / mm was found to be significantly lower compared to Examples 1-3.

In addition, since the insulating sheet according to Comparative Example 4 has an excessive amount of insulating oil (C ₃₀ H ₆₀ ) contained therein, the insulating oil was eluted during the extrusion process for preparing the sample sheet, and a slip phenomenon occurred in the extruder. Could not be prepared could not specify the physical properties.

On the other hand, Examples 1 to 3 according to the present invention improves the heat resistance, mechanical properties, and electrical properties simultaneously by increasing the crystallinity of the base resin by using a nucleating agent and limiting the crystal size produced, and excellent flexibility by the addition of a specific insulating oil. It was confirmed that it satisfies the flexibility, the degree of laying, and the like. However, Example 3 includes the polypropylene polymerized under the Ziegler-Natta catalyst as the base resin, and thus the residual amount of catalyst in the insulating composition is increased compared to the case where the polypropylene polymerized under the metallocene catalyst in Examples 1 and 2 is increased. It was confirmed that the electrical properties were somewhat degraded.

2. Preparation Example of Semiconductive Composition

1) Production Example

After preparing a semiconductive composition with the components and contents shown in Table 3 below, extrusion coating the semiconductive composition melted on a copper conductor of a certain standard, and then adding an insulating composition to which polypropylene resin was added paraffin oil as an insulating oil. The cable specimens of Example 3 and Comparative Examples 6 and 7 were produced by extrusion coating, respectively. Here, the unit of component content is parts by weight.

Ingredient Example 3 Comparative Example 6 Comparative Example 7 Base material resin 100 100 100 Conductive particles 55 55 55 Metal inactive additives1 0.3 - - Inert Metal Additives2 - - 0.3 Antioxidants 1 0.5 0.5 0.5 Antioxidants 2 0.3 0.3 0.3 Lubricant One One One

Base resin: uncrosslinked polypropylene copolymer (manufacturer: Basell; product name: CA-7441)

Conductive particles: Carbon black (acetylene black)

Metal inactive additive 1: 1,2-bis (3,5-di-t-butyl-4-hydroxycinnamoyl) hydrazine (manufacturer: BASF); product name: IR-MD1024; solubility in paraffin oil: 0.01 g / 100 ml (20 ° C))

Metal inactive additive 2: stearyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (manufacturer: BASF); product name: IR-1076; solubility in paraffin oils : 31 g / 100 ml (20 ° C))

Antioxidant 1: Ciba IR-1035

Antioxidant 2: Ciba PS-802

Lubricant: Polypropylene wax with a number average molecular weight of 7,000 (manufacturer: Mitsui Kical; Product Name: NP056)

The cable specimens of Example 3 and Comparative Examples 6 and 7 were measured for tensile strength and elongation at a tensile rate of 250 mm / min in accordance with IEC 60811-1-1, respectively, and were subjected to mechanical properties after heat aging at 150 ° C. for 168 hours. The change was measured and the results are shown in Table 4 below.

Properties Example 3 Comparative Example 6 Comparative Example 7 Tensile strength (kgf / ㎡) 1.45 1.44 1.44 Elongation (%) 550 550 550 Tensile strength residual after aging (%) 95 132 117 Elongation Remaining Rate after Aging (%) 90 45 60

As shown in Table 4, the cable specimen of Example 3 including the specific metal inactive additive according to the present invention in the inner semiconducting layer has a tensile strength residual ratio and elongation residual ratio of 95% and 90% after aging, respectively, according to the standard. Since 75% or more of phosphorus, the aging characteristics of the semiconducting layer was found to be remarkably improved, whereas the cable specimen of Comparative Example 6, which does not contain a metal inactive additive in the inner semiconducting layer, had a tensile strength due to deterioration of the inner semiconducting layer after aging. Increasingly, the mechanical properties were markedly deteriorated such that the elongation was not much lower than the standard 75%.

In addition, the cable specimen of Comparative Example 7 comprising an additive having a solubility in paraffin oil of 31 g / 100 ml (20 ° C.) as a metal inactive additive other than the specific metal inactive additive according to the present invention in the inner semiconducting layer, The metal inactive additive contained in the semiconducting layer is eluted and carried out in paraffin oil impregnated in the insulating layer in contact with the inner semiconducting layer, thereby failing to realize the characteristics of the original metal inactive additive, so that tensile strength is increased and elongation is a reference value. It was confirmed that the mechanical properties were reduced, such as less than 75%.

3. Calculation method of insulation layer thickness

The present invention relates to a power cable having an optimum insulating layer thickness depending on the insulating material. Since the insulating layer of the power cable may exhibit different electrical characteristics according to the type of insulating material constituting the power cable, it is necessary to set the optimum insulating layer thickness according to the type of the insulating material. That is, when the thickness of the insulating layer is thicker than necessary, workability such as laying property of the cable may be degraded, whereas when the thickness of the insulating layer is excessively thin, the life shortening due to the decrease of electrical characteristics of the cable may be reduced. This can be caused.

Conventionally, when designing a 22.9 kV class power cable including an insulation layer made of crosslinked polyethylene (XLPE) resin, the thickness of the insulation layer was set to 6.6 mm, and the background thereof is as follows.

In the 22.9 kV class crosslinked polyethylene cable, since the minimum dielectric breakdown voltage according to the AEIC standard is 24.4 kV / mm and the dielectric breakdown reference voltage according to the IEEE standard is 160 kV, the dielectric breakdown reference voltage is 160 kV and the minimum dielectric breakdown voltage is 24.4 kV. / mm divided by 160kV / 24.4kV / mm ≒ 6.6mm, the minimum impulse breakdown voltage according to the AEIC standard is 47.2kV / mm, and the impulse reference voltage according to the IEEE standard is 310kV, so the impulse reference voltage 310kV is the minimum Since the impulse breakdown voltage divided by 47.2kV / mm is 310kV / 47.2kV / mm ≒ 6.6mm, in the 22.9kV class crosslinked polyethylene cable, the thickness of the insulating layer is set to 6.6mm.

However, the conventional method of calculating the insulation layer is for a crosslinked polyethylene cable, and when the insulation material constituting the insulation layer is an insulation material having different electrical properties from the crosslinked polyethylene, when the thickness of the insulation layer manufactured therefrom If the conventional insulating layer calculation method is applied as it is, it may be difficult to calculate the optimum thickness.

Accordingly, the present invention provides a method for calculating an optimal insulating layer thickness according to the electrical properties of the insulating material constituting the insulating layer of the cable, and a power cable having an insulating layer having a thickness calculated therefrom, wherein the optimum insulating layer The thickness calculation method is specifically as follows.

The average dielectric breakdown voltage (kV / mm) is 88.51 kV / mm for the conventional crosslinked polyethylene insulation layer and 113.47 kV / mm for the non-crosslinked polypropylene insulation layer according to the invention.

For a 22.9 kV class crosslinked polyethylene power cable, 160 kV, the dielectric breakdown reference voltage proposed by the IEEE standard, is divided by 88.51 kV / mm, the average dielectric breakdown voltage of the conventional crosslinked polyethylene insulation layer, to 160 kV / 88.51 kV / mm ≒ 1.808 mm. About 3.65 times of this becomes 6.6 mm calculated by the conventional method of calculating the thickness of the insulating layer. In addition, the 160 kV, which is the dielectric breakdown reference voltage proposed by the IEEE standard, is divided by the average dielectric breakdown voltage of 113.47 kV / mm of the non-crosslinked polypropylene insulating layer according to the present invention, which is 160 kV / 113.47 kV / mm ≒ 1.410 mm, about 4.68 times becomes 6.6 mm calculated by the conventional insulating layer thickness estimation method.

Based on this, the optimum insulating layer thickness according to the insulating material can be calculated from about 3.65 times to about 4.68 times T _min shown in Equation 1 below, and the insulating layer satisfying the optimum insulating layer thickness is the purpose of the cable. At the same time, the weight of the cable can be improved, and construction workability, such as laying property, can be improved, and a proper life can be achieved.

Although the present specification has been described with reference to preferred embodiments of the invention, those skilled in the art may variously modify and change the invention without departing from the spirit and scope of the invention as set forth in the claims set forth below. It could be done. Therefore, it should be seen that all modifications included in the technical scope of the present invention are basically included in the scope of the claims of the present invention.

1: conductor 2: inner semiconducting layer
3: insulation layer 4: outer semiconducting layer
5: metal shielding layer 6: sheath layer

Claims

A power cable comprising at least one conductor, an inner semiconducting layer surrounding the at least one conductor, and an insulating layer surrounding the inner semiconducting layer,
The insulating layer is a chemical formula C _n H _2n in which a base resin including an uncrosslinked polypropylene resin and an cyclic hydrocarbon and an acyclic hydrocarbon are alternately arranged based on 100 parts by weight of the base resin, wherein n is A power cable prepared from an insulation composition comprising 1 to 10 parts by weight of insulating oil containing a monocyclic naphthenic hydrocarbon.

The method of claim 1,
The base resin includes a non-crosslinked propylene homopolymer and a noncrosslinked propylene copolymer polymerized under a metallocene catalyst, and a blending ratio of the noncrosslinked propylene homopolymer and the noncrosslinked propylene copolymer polymerized under a metallocene catalyst is 80 Power cable, characterized in that: from 20 to 50:50.

The method of claim 2,
Wherein said non-crosslinked propylene copolymer is a copolymer of propylene monomer and ethylene monomer.

The method of claim 3,
Wherein 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.

The method according to any one of claims 2 to 4,
The remaining amount of the catalyst of the non-crosslinked polypropylene resin polymerized under the metallocene catalyst, characterized in that 200 to 700 ppm, power cable.

The method according to any one of claims 1 to 4,
The insulating composition is based on 100 parts by weight of the base resin, 1,3: 2,4-bis (3,4-dimethyldibenzylidine) sorbitol (1,3: 2,4-Bis (3,4-dimethyldibenzylidene) 0.1 to 0.5 parts by weight of at least one nucleating agent selected from the group consisting of Sorbitol, bis (p-methyldibenzulidene) Sorbitol and substituted Dibenzylidene Sorbitol Characterized in that it comprises a power cable.

The method of claim 6,
A power cable, characterized in that the size of the polypropylene crystal in the insulation layer made from the insulation composition is 1-5 μm.

delete

The method according to any one of claims 1 to 4,
Power ring, characterized in that the ring of the cyclic hydrocarbon is pentagonal or hexagonal.

The method according to any one of claims 1 to 4,
The insulation composition further comprises 0.2 to 5 parts by weight of an amine-based, dialkyl ester-based, thioester-based or phenolic antioxidant based on 100 parts by weight of the base resin.

The method according to any one of claims 1 to 4,
An outer semiconducting layer surrounding the insulating layer, and a sheath layer surrounding the outer semiconducting layer, wherein the outer semiconducting layer and the sheath layer are made from a composition comprising the same base resin as the base resin of the insulating composition. Characterized in that the power cable.

The method according to any one of claims 1 to 4,
The inner semiconducting layer is prepared from a semiconducting composition comprising a base resin comprising an uncrosslinked polypropylene resin, and 30 to 70 parts by weight of conductive particles and 0.1 to 5 parts by weight of a metal inactive additive based on 100 parts by weight of the base resin. Become,
The metal inactive additive is characterized in that it has a molecular structure of the chelate ligand (chelate legand) form two or more coordination bonds with one metal atom, power cable.

The method of claim 12,
The metal inactive additive has at least two Lewis base sites serving as electron donors in the molecular structure, and the Lewis bases are amine groups, amide groups or carboxyl groups. Power cable.

The method of claim 13,
The metal inactive additive may be N, N'-bis (salicylidene) -1,2-propanediamine, 1,2-bis (3,5-di-t-butyl-4-hydroxycinnamoyl) hydrazine or N And N'-1,2-ethane diylbis- (N- (carboxymethyl) glycine).

The method of claim 12,
A power cable, characterized in that the solubility at 20 ° C. of paraffin oil of the metal inactive additive is 0.01 g / 100 ml or less.

A power cable comprising at least one conductor, an inner semiconducting layer surrounding the at least one conductor, and an insulating layer surrounding the inner semiconducting layer,
The insulating layer is prepared from an insulating composition comprising an uncrosslinked polypropylene resin and an insulating oil having a residual polymerization catalyst of 200 to 700 ppm and a crystal size of 1 to 5 μm,
The insulating oil includes a monocyclic naphthenic hydrocarbon of formula C _n H _2n where n is an integer of 20 to 60, wherein the cyclic hydrocarbon and the acyclic hydrocarbon are arranged alternately.
The inner semiconducting layer is prepared from a semiconducting composition comprising a base resin comprising an uncrosslinked polypropylene resin, and 30 to 70 parts by weight of conductive particles and 0.1 to 5 parts by weight of a metal inactive additive based on 100 parts by weight of the base resin. Become,
The metal inactive additive has a molecular structure in the form of a chelate ligand (chelate legand) forming two or more coordination bonds with one metal atom, and Lewis-base that serves as an electron donor in the molecular structure. and at least two sites, wherein said Lewis base comprises at least one member selected from the group consisting of amine groups, amide groups and carboxyl groups.

The method of claim 1,
The thickness of the insulating layer, characterized in that from 3.65 times to 4.68 times the Tmin defined in the following equation, power cable.