WO2021230431A1 - Eco-friendly insulation composition for direct current power cable, and direct current power cable manufactured using same - Google Patents

Abstract

The present invention relates to an eco-friendly insulating composition for a direct current power cable, and a direct current power cable manufactured using same, the composition being effectively mixed with polypropylene and elastomer so as to exhibit high insulation and be useable under the condition of a maximum use temperature of 110℃ or higher.

Description

Eco-friendly insulation composition for DC power cables and DC power cables manufactured using the same

The present invention relates to an eco-friendly insulation composition for a DC power cable and a DC power cable manufactured using the same. More particularly, it relates to an eco-friendly insulating composition for a DC cable that can be stably used at high temperatures due to excellent electrical properties and heat resistance, and a DC power cable manufactured using the same.

The existing power grid is centered on the AC power transmission system that can flexibly transform the voltage level from the transmission stage to the end user stage and apply the optimal voltage for each use.

However, the AC power transmission system basically has a frequency component, and energy loss occurs under the influence of impedance including the resistance and capacitance of the transmission line.

In addition, since direct connection between two power systems having different frequencies is impossible, it acts as an obstacle to the efficient operation of power facilities.

High Voltage Direct Current Transmission System (HVDC), which has recently emerged for the purpose of long-distance transmission and linking with new and renewable energy, is a mutual conversion between the transmission distance limitation and linkage of systems with different frequencies, which are the disadvantages of the existing AC power transmission system described above. It can be solved through

Another advantage of such ultra-high voltage direct current transmission is that it provides power transmission capacity that is more than twice that of an AC power transmission system while using the same power line.

Recently, as a material constituting the insulating layer of a power cable, cross-linked polyethylene obtained by polymerizing polyethylene through a cross-linking reaction using organic peroxide is mainly used.

However, cross-linked polyethylene may cause environmental problems by generating cross-linking by-products such as methane gas, alpha methyl styrene, acetphenone, and carbon dioxide during the cross-linking process. There are problems that can cause it.

In addition, when used in a DC power cable, due to the problem of accumulating space charges by cross-linking by-products generated during the cross-linking process, a local or regional electric field distortion effect may occur, resulting in insulation breakdown.

On the other hand, in the case of cross-linked polyethylene for DC power cables that have been commercialized and used recently, although the problem of space charge accumulation has been solved, the maximum operating temperature for cable operation is limited to about 70°C due to the limitations of the thermal and mechanical properties of the material. .

In order to solve this problem, Korean Patent Application Laid-Open No. 10-2020-0004061 discloses a material using polypropylene as a base resin, which has excellent heat resistance and is environmentally friendly even without crosslinking, but insufficient cold resistance caused by high rigidity. , flexibility, flexibility, etc., there is a problem that the workability is reduced during the installation of the insulated cable and its use is limited.

Therefore, there is a demand for a new insulating composition capable of stably operating at a high temperature under a DC system.

The present invention provides an eco-friendly insulation composition for a DC power cable that can be used stably at high temperatures due to a low degree of increase in conductivity at high temperature and high dielectric breakdown strength under DC voltage conditions, and manufactured using the same in order to improve the conventional problems as described above. The purpose is to provide a cable.

In order to achieve the above object, the eco-friendly insulation composition for a DC power cable according to the present invention contains polypropylene and an elastomer to improve insulation properties and mechanical properties.

The polypropylene may be included in an amount of 30% by mass or more and 70% by mass or less, and the elastomer may be included in an amount of 30% by mass or more and 70% by mass or less.

The DC dielectric breakdown strength of the eco-friendly insulating composition may be 200 kV/mm or more and 250 kV/mm or less in the room temperature range of 15 ° C or more and 30 ° C or less, and the conductivity may be 10 ^-17 S/m or more and 10 ^-16 S/m or less.

The dielectric breakdown strength of the eco-friendly insulating composition may be 150 kV/mm or more and 200 kV/mm or less in the high temperature range that is the maximum use temperature of the conductor, and the conductivity may be 10 ^-14 S/m or more and 4 X 10 ^-13 S/m or less.

The polypropylene may include at least one of homopropylene, random propylene, block propylene, and reactive polyolefin produced in a polymerization facility.

The elastomer may include at least one of polystyrene-based, PVC-based, polyolefin-based, polyester-based, polyamide-based, and polyurethane-based materials.

The eco-friendly insulating composition of the present invention may further include an additive.

The additive may include at least one or more from the group consisting of an antioxidant, a nucleating agent, a slip agent, a lubricant, and an antifreeze agent.

In addition, the eco-friendly insulating cable for a DC power cable according to the present invention is manufactured including the eco-friendly insulating composition.

The eco-friendly insulating composition may be disposed between the first semiconducting layer and the second semiconducting layer in the insulating cable to form an insulating layer.

The eco-friendly insulated cable is characterized in that the maximum use temperature is 110 ℃ or more.

As described above, according to the eco-friendly insulation composition for a DC power cable according to the present invention and a cable manufactured using the same, since it does not include a crosslinking reaction, no crosslinking by-products are generated, so problems such as deterioration of insulation performance do not occur, and poly Efficient mixing of propylene and elastomer shows high insulation and can be used under the condition that the maximum operating temperature is 110℃ or higher.

1 is a cross-sectional view illustrating a DC power cable manufactured using an eco-friendly insulating composition according to an embodiment of the present invention.

2 is a graph of measuring the dielectric breakdown strength at which insulation is broken in the eco-friendly insulation composition for a DC power cable according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. This is not intended to limit the present invention to specific embodiments, and should be construed to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

In describing the present invention, terms such as first and second may be used to describe various components, but the components may not be limited by the terms. The above terms are only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component.

The term “and/or” may include a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but other components may exist in between. can be understood On the other hand, when an element is referred to as being “directly connected” or “directly connected” to another element, it may be understood that no other element is present in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression may include the plural expression unless the context clearly dictates otherwise.

In the present application, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, and one or more other features It may be understood that the presence or addition of numbers, steps, operations, components, parts or combinations thereof is not precluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, may have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary may be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, it is interpreted in an ideal or excessively formal meaning. it may not be

In addition, the following embodiments are provided to more completely explain to those with average knowledge in the art, and the shapes and sizes of elements in the drawings may be exaggerated for clearer description.

Referring to FIG. 1 , a DC insulated cable manufactured using an eco-friendly insulating composition according to an embodiment of the present invention is disposed between the first semiconducting layer 20 and the second semiconducting layer 40 to be insulated under high temperature conditions. An insulating layer 30 made of an eco-friendly insulating composition for a DC power cable is included to prevent the insulation of the cable from being destroyed.

In detail, the DC power cable includes a conductor 10 through which power is transmitted, a first semiconducting layer 20 surrounding the conductor 10, a sheath layer 50 protecting the cable, and a first formed in the sheath layer 50 . The second semiconducting layer 40, the first semiconducting layer 20, and the second semiconducting layer 40 are disposed between the insulating layer 30, which is an eco-friendly insulating composition of the present invention.

The insulating layer, which is the eco-friendly insulating composition, is characterized in that the maximum use temperature is 110 ℃ or higher. That is, since the insulation layer of crosslinked polyethylene that is generally used in the prior art has a maximum use temperature of about 70°C, the insulation composition of the present invention having a maximum useable temperature of 110°C or higher can be used at a higher temperature than the conventional one. Therefore, the allowable current value may increase according to the increase in the operating temperature.

The eco-friendly insulating composition is formed by including an elastomer in polypropylene to improve dielectric strength and mechanical properties. In addition, it may be formed by further comprising an additive.

More specifically, the eco-friendly insulating composition is formed by including 30% by mass or more and 70% by mass or less of polypropylene, and 30% by mass or more and 70% by mass or less of elastomer. Through this, it is possible to provide an insulating composition having high heat resistance and high strength characteristics of polypropylene and at the same time having sufficient flexibility by the elastomer.

When polypropylene is less than 30% by mass or elastomer is more than 70% by mass, it is mainly composed of elastomer, so it is difficult to obtain insulation properties required for insulated cables despite high elasticity.

In addition, if the polypropylene exceeds 70% by mass or the elastomer is less than 30% by mass, there is a problem in that the bending characteristic of the cable is increased and installation may be difficult.

The DC dielectric breakdown strength of the eco-friendly insulating composition may be 200 kV/mm or more and 250 kV/mm or less in the room temperature range of 15 ° C or more and 30 ° C or less, and the conductivity may be 10 ^-17 S/m or more and 10 ^-16 S/m or less.

The DC dielectric breakdown strength of the eco-friendly insulating composition may be 150 kV/mm or more and 200 kV/mm or less in the high temperature range that is the maximum conductor temperature, and the conductivity may be 10 ^-14 S/m or more and 4 X 10 ^-13 S/m or less.

Characteristics of the eco-friendly insulation composition for DC power cables show higher dielectric breakdown strength and lower conductivity than the comparative group, cross-linked polyethylene.

Polypropylene and elastomer are manufactured into an insulating material in the form of particles or pellets through extrusion and cutting processes after mixing.

When the insulation composition is manufactured using polypropylene as a basic raw material, the cross-linking process is not required, so the manufacturing process is simple, toxic substances such as methane gas and various by-products are not generated _{, greenhouse gases such as CO 2} are reduced, and even after disposal It can be recycled into various plastic products. When the crosslinking process is eliminated, the manufacturing speed and efficiency of the insulating composition are increased.

In addition, the insulation composition prepared by mixing polypropylene and elastomer can be used at a temperature of 110°C or higher, which is the maximum operating temperature (permissible temperature) of a power cable, or lower than the melting point of the composition due to the excellent heat resistance of polypropylene, so that the power transmission capacity can be increased. there are advantages to

The polypropylene may include homopropylene, random propylene, block propylene, and reactive polyolefin produced in a polymerization facility according to processing or manufacturing methods.

Polypropylene is at least one of random polypropylene randomly arranged according to the arrangement of propylene, homo polypropylene arranged in the same direction, block polypropylene in which a propylene monomer and heterogeneous monomers such as styrene are combined, and reactive polyolefin produced in a polymerization facility. contains more than one.

Impact strength and flexibility can be improved through random polypropylene with many irregularities, and high rigidity and heat resistance can be obtained through homo polypropylene with high crystallinity.

In addition, through block polypropylene polymerized by adding ethylene to propylene during the production process, impact resistance can be greatly improved without significantly lowering rigidity.

The elastomer may include at least one of polystyrene-based, PVC-based, polyolefin-based, polyester-based, polyamide-based, and polyurethane-based materials.

Preferably, the polystyrene-based elastomer closest to vulcanized rubber may be used because of high flexibility and less permanent deformation. Since the polystyrene-based elastomer is thermoplastic, it is easy to process or reuse, and excellent elasticity can be obtained.

In addition, when a PVC-based or polyolefin-based elastomer is used, it has the advantage of being inexpensive and easy to process.

In addition, the eco-friendly insulation composition for a DC power cable according to the present invention may include at least one or more from the group consisting of an antioxidant, a nucleating agent, a slip agent, a lubricant, and an antifreeze agent as an additive.

The additive may include more than 0 mass % and 1 mass % or less with respect to the total mass, and may be used for functional enhancement such as improvement of processability in addition to oxidation prevention.

When the additive exceeds 1% by mass, electric charges may be accumulated in molecules to cause dielectric breakdown despite improvement of thermal and mechanical properties of the insulating composition, thereby degrading electrical properties.

The antioxidant may be added to prevent oxidation by oxygen in the air and cause deterioration in quality during manufacture or use of the eco-friendly insulating composition. As the antioxidant, any antioxidant commonly used in the art may be used, but preferably one or more of phenolic and phosphorus antioxidants may be used.

The nucleating agent makes polypropylene crystals dense, prevents the accumulation of space charges in the eco-friendly insulation composition, improves the withstand voltage characteristics of power cables, and removes organic substances such as sorbitol, inositol, and glucose. Can be used.

Slip agents and lubricants improve the flowability of the eco-friendly insulating composition during extrusion, and may be added to improve the appearance of the extrusion.

A metal deactivator may be used to prevent decomposition by a small amount of ionic impurities contained in the insulator.

Hereinafter, the effects of the present invention will be described through experiments,

An eco-friendly insulating composition was prepared as an example in comparison with the commercial crosslinked polyethylene insulation composition for DC power cables that could be used in DC power cables according to the present invention, and the conductivity and DC breakdown field values according to temperature were measured and compared.

(Examples 1 and 2 / Comparative Example)

In the Examples and Comparative Examples, eco-friendly insulating compositions were prepared as reported in Table 1.

The eco-friendly insulating composition was manufactured by using a twin extruder having a diameter of 30 mm and an L/D of 40, and the processing temperature was set at 170 to 190°C of the cylinder, and the head and die parts were set at 200°C to proceed with the process.

The proportion of each polymer in the eco-friendly insulating composition is expressed in mass% with respect to the total weight of the composition.

	comparative example	Example 1	Example 2
crosslinked polyethylene	100
polypropylene		30	70
elastomer		70	30

As the crosslinked polyethylene used as a comparative example, commercially available crosslinked polyethylene for DC power cables was used (Borealis, LS 4258 DCE).

As the polypropylene used in Examples, block polypropylene prepared by copolymerizing propylene and ethylene to improve impact strength and reactive polyolefin prepared in a propylene polymerization facility were used, and MI (melt index) was 0.5 and 0.8, respectively.

As the elastomer, a reactive polyolefin-based elastomer prepared in a polymerization facility and a styrene-ethylene-butadiene copolymer having a polystyrene content of 12% by mass were used.

Antioxidants (phenol-based and phosphorus-based), which are additives, were added to the composition of Table 1 by adding 0.2% by mass relative to the total weight, followed by extrusion to prepare pellets, and then physical properties were measured.

The measured physical properties are shown in Table 2, Table 3 and Figure 2 below,

item		unit	comparative example	Example 1	Example 2
tensile strength		MPa	23.0	23.8	25.9
elongation		%	606	607	766
Residual rate after aging (Comparative Example: 135°C/168hr Example: 135°C/240hr)	tensile strength	%	-4.5	-4.5	-4.0
	elongation	%	-6.8	-12.0	-9.8
density		g/cm 3	0.92	0.89	0.88
MI		g/10 min	2.0	1.1	1.2
Cold hitting test (-40℃)		number of fractured specimens	0	0	0
flexural modulus		MPa	180	158	172

Referring to Table 2, Example 1 containing 30% by mass of polypropylene and 70% by mass of elastomer and Example 2 containing 70% by mass of polypropylene and 30% by mass of elastomer have elongation by the elastomer compared to Comparative Example. To provide an insulating composition with excellent tensile strength while improving.

In addition, since Examples 1 and 2 show very low values in Melt Index (MI) than Comparative Examples, it can be confirmed that excellent extrudability provides a composition suitable for manufacturing an insulated cable.

In addition, in the flexural modulus, Examples 1 and 2 showed a lower flexural modulus than the comparative example, so it can be confirmed that the processability was improved compared to the comparative example using crosslinked polyethylene.

Conductivity (S/m)	Measured temperature	comparative example	Example 1	Example 2
	Room temperature (15~30℃)	5x10 -16 to 3x10 -15	3x10 -17 to 7x10 -17	1x10 -17 to 2x10 -17
	Medium temperature (below 70℃)	8x10 -14 to 2x10 -13	1x10 -14 to 4x10 -14	8x10 -16 to 2x10 -15
	High temperature (70~110℃ or higher)	4x10 -13 to 6x10 -13	2x10 -13 to 4x10 -13	1x10 -14 to 2x10 -14

Referring to Table 3, Example 1 containing 30% by mass of polypropylene and 70% by mass of elastomer ^{shows a conductivity of 3x10 -17} S/m or more and 7x10 ^-17 S/m or less in the room temperature range (15-30° C.) ^{, shows conductivity of 1x10 -14} S/m or more 4x10 ^-14 S/m in the medium temperature range (less than 70℃ ^{), and 2x10 -13} S/m or more 4x10 ^-13 S/m in the high temperature range (70~110℃ or more) The following conductivity is shown.

Example 2 containing 70% by mass of polypropylene and 30% by mass of elastomer ^{exhibits a conductivity of 1x10 -17} S/m or more and 2x10 ^-17 S/m or less in the room temperature range, and 8x10 ^-16 S/m or more 2x10 in the intermediate temperature range ^It shows the conductivity of -15 S/m or more, and it shows the conductivity of 1x10 ^-14 S/m or more and 2x10 ^-14 S/m or less in the high temperature range.

On the other hand, the comparative example containing cross-linked polyethylene ^{exhibits a conductivity of 5x10 -16} S/m or more and 3x10 ^-15 S/m or less in the room temperature range, and 8x10 ^-14 S/m or more and 2x10 ^-13 S/m or more in the medium temperature range. ^{and shows the conductivity of 4x10 -13} S/m or more and 6x10 ^-13 S/m or less in the high temperature range.

Through this, it is confirmed that the eco-friendly insulating composition is more preferably contained in an amount of 40% by mass or more and 50% by mass or less of polypropylene, and 50% by mass or more and 60% by mass or less of elastomer.

Referring to FIG. 2, in order to measure the dielectric breakdown strength at which insulation is broken in the insulated cable manufactured by the eco-friendly insulating composition of Examples 1 and 2, a sample was prepared in a size of 50x50 mm, and the upper and lower identical electrodes were placed on both sides of the sample. The dielectric breakdown strength was measured by measuring the voltage at which the breakdown occurred by increasing the voltage step by step after interlocking and dividing by the thickness.

Comparative Example Measurement was also performed in the same manner.

In the room temperature range (15-30° C.), Example 1 shows a dielectric breakdown strength close to about 250 kV/mm, and Example 2 shows a dielectric breakdown strength exceeding 200 kV/mm, whereas Comparative Example is lower than 200 kV/mm It shows the dielectric breakdown strength.

From this, it can be confirmed that Example 1 is the most preferable eco-friendly insulating composition in the room temperature range.

Example 1 shows a dielectric breakdown strength of about 165 kV/mm in a high temperature range (70 to 110° C. or higher), and Example 2 shows an improved dielectric breakdown strength of about 180 kV/mm compared to Example 1, whereas Comparative Example is about It has a dielectric breakdown strength of 155 kV/mm.

From this, it can be confirmed that Example 2 is the most preferable eco-friendly insulating composition in the high temperature range.

As described above, since the optimum value is shown in different compositions depending on the temperature range, the practitioner can selectively select and utilize the composition.

Although the present invention has been described in detail through specific examples, it is intended to describe the present invention in detail, and the present invention is not limited thereto. It is clear that the transformation or improvement is possible by the person.

All simple modifications or changes of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

Claims (10)

1. An eco-friendly insulation composition for DC power cables containing polypropylene and elastomer to improve insulation and mechanical properties.
2. The method according to claim 1,

   The polypropylene is

   30% by mass or more and 70% by mass or less,

   The elastomer is

   An eco-friendly insulation composition for DC power cables containing 30% by mass or more and 70% by mass or less.
3. The method according to claim 1,

   Eco-friendly insulation for DC power cables, characterized in that at a temperature of 15℃ or more and 30℃ or less, the breaking strength of DC insulation is 200kV/mm or more and 250kV/mm or less, and the conductivity is 10 ^-17 S/m or more and 10 ^{-16 S/m or less.} composition.
4. The method according to claim 1,

   Eco-friendly insulation for DC power cables, characterized in that the dielectric breakdown strength is 150kV/mm or more and 200kV/mm or less, and the conductivity is 10 ^-14 S/m or more and 4 X 10 ^{-13 S/m or less in the high temperature range, which is the maximum operating temperature of the conductor} composition.
5. The method according to claim 1,

   The polypropylene is

   An eco-friendly insulation composition for DC power cables containing homopropylene, random propylene, block propylene, and reactive polyolefin manufactured in a polymerization facility.
6. The method according to claim 1,

   The elastomer is

   An eco-friendly insulation composition for a DC power cable, comprising at least one of polystyrene-based, PVC-based, polyolefin-based, polyester-based, polyamide-based, and polyurethane-based.
7. The method according to claim 1,

   further comprising an additive;

   The additive is

   An eco-friendly insulating composition for a DC power cable comprising at least one from the group consisting of antioxidants, nucleating agents, slip agents, lubricants and anti-freeze agents.
8. A DC power cable manufactured including the eco-friendly insulation composition according to any one of claims 1 to 7.
9. 9. The method of claim 8,

   The eco-friendly insulating composition,

   A DC power cable, characterized in that it is disposed between the first semiconducting layer and the second semiconducting layer to form an insulating layer.
10. 9. The method of claim 8,

    DC power cable, characterized in that the maximum operating temperature is 110℃ or higher.

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