KR102386728B1 - Joint for ultra high voltage cable and ultra high voltage cable joint system comprising the same - Google Patents

Abstract

The present invention relates to an intermediate junction box for an ultra-high voltage DC power cable and an ultra-high voltage DC power cable connection system including the same. Specifically, the present invention provides an intermediate junction box for an ultra-high voltage DC power cable, which can effectively prevent insulation breakdown of the intermediate junction box of the cable due to local electric field concentration by mitigating the electric field in the part where the electric field is structurally concentrated, and the intermediate junction box comprising the same It relates to an ultra-high voltage DC power cable connection system.

Description

Intermediate junction box for ultra-high voltage DC power cable and ultra-high voltage DC power cable connection system including the same

The present invention relates to an intermediate junction box for an ultra-high voltage DC power cable and an ultra-high voltage DC power cable connection system including the same. Specifically, the present invention provides an intermediate junction box for an ultra-high voltage DC power cable, which can effectively prevent insulation breakdown of the intermediate junction box of the cable due to local electric field concentration by mitigating the electric field in the part where the electric field is structurally concentrated, and the intermediate junction box comprising the same It relates to an ultra-high voltage DC power cable connection system.

An ultra-high voltage power cable is a device that transmits power using an internal conductor, and can be divided into an ultra-high voltage direct current (DC) power cable and an alternating current (AC) power cable.

The DC power transmission method using the ultra-high voltage DC power cable has an advantage in long-distance transmission due to low power loss. make up

1 schematically shows a cross-sectional structure of an intermediate connection system for a conventional ultra-high voltage DC power cable.

As shown in FIG. 1, the conventional intermediate connection system uses an intermediate junction box 300' to connect a conductor (not shown), an inner semiconducting layer (not shown), an insulating layer 214 and an outer semiconducting layer 216. and is configured by connecting a pair of power cables provided with the conductor, inner semiconducting layer, insulating layer and outer semiconducting layer sequentially exposed ends to face each other.

Specifically, the conductor connecting portion 310 ′ for electrically and mechanically connecting a pair of conductors exposed at the end of the power cable to the end of the power cable or the insulating layer or the outer semiconducting layer exposed at the end of the power cable is wrapped around the outside at room temperature. A joint sleeve 320 ′ made of a contractible elastic material may be provided, wherein the joint sleeve 320 ′ includes a first electrode 321 ′ electrically connected to a conductor, and a second pair provided to face each other. A junction box insulating layer 323 ′ provided to surround the electrode 322 ′, the first electrode 321 ′, and the second electrode 322 ′, provided outside the junction box insulating layer 323 ′ It may include a junction box shielding layer 324 ′ and the like.

However, the intermediate junction box for the ultra-high voltage DC power cable and the intermediate connection system for the ultra-high voltage DC power cable using the same have a resistive electric field distribution characteristic in which the electric field distribution therein depends on the volume resistivity. Specifically, in the conventional intermediate junction box for ultra-high voltage DC power cable or ultra-high voltage DC power cable, the interface between the power cable and the joint sleeve 320 ′ in which structures made of materials having different volume resistivity meet each other, the second The electrode 322 ′, the portion A, which is divided by a broken line in FIG. 1 as a portion where the insulating layer 214 of the power cable and the junction box insulating layer 323 ′ meet, or the first electrode 321 ′, the insulation of the power cable As the portion where the layer 214 and the junction box insulation layer 323 ′ meet, the portion where different materials contact each other, such as the part B separated by a broken line in FIG. There are problems such as void generation and intrusion of foreign substances, so it acts as a weak insulation part.

In order to solve the above problems, Prior Art 1 (KR10-2013-0105523 A) includes an electric field mitigating layer formed of a material containing polyaniline as a conductive filler to relieve the electric field applied to the interface between the cable and the junction box. do.

In addition, prior art 2 (WO2008/054308 A1) to prior art 3 (EP1975949 B1) include ZnO, which is a varistor particle that can selectively act as conductive particles by changing the resistance value of the insulating resin according to voltage, or The electric field is controlled by further including SiO ₂ serving as a bridge between the ZnO particles.

However, in the prior art 1 to the prior art 3, the volume resistivity of the electric field mitigating layer and the electric field mitigating layer and the junction box insulating layer in consideration of the heating phenomenon in the junction box and the electric field acting on the weak insulation part when DC voltage is applied or the relationship between the volume resistivity of the cable insulation layer and the like is not disclosed.

Therefore, in the intermediate connection box for ultra-high voltage DC power cable, it is possible to effectively prevent the insulation breakdown of the junction box due to the local concentration of the electric field by mitigating the electric field in the part where the electric field is structurally concentrated, and the heat generation phenomenon in the connection part can be alleviated. , an intermediate junction box for ultra-high voltage DC power cables and an ultra-high voltage DC power cable connection system including the same are urgently required.

The present invention provides an intermediate junction box for cables and a cable connection system including the same, which can effectively prevent insulation breakdown of the junction box due to local electric field concentration by mitigating the electric field in the part where the electric field is structurally concentrated as an intermediate junction box for cables. intended to provide

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

An intermediate connection box for connecting a pair of ultra-high voltage DC power cables comprising a conductor, an inner semiconducting layer surrounding the conductor, an insulating layer surrounding the inner semiconducting layer, and an outer semiconducting layer surrounding the insulating layer, the intermediate connection box comprising: A joint sleeve made of an elastic material that can be contracted at room temperature, formed as a hollow sleeve having a through hole in the longitudinal direction therein, and including a junction box insulating part to prevent current from leaking to the outside of the intermediate junction box, The junction box insulating portion includes a first insulating layer and a second insulating layer surrounded by the first insulating layer, wherein at least a portion of the innermost surface of the joint sleeve is made of the second insulating layer, and the second insulating layer has a volume resistivity lower than that of the first insulating layer, the first insulating layer and the second insulating layer have a volume resistivity of 1×10 ¹² to 1×10 ¹⁸ Ωcm, and the volume resistivity of the second insulating layer is It provides an intermediate junction box for ultra-high voltage DC power cables, characterized in that it is 10 times or more lower than the volume resistivity of the first insulating layer.

Here, the second insulating layer provides an intermediate junction box for ultra-high voltage DC power cables, characterized in that it is formed of a second insulating composition comprising a base resin and an additive for adjusting resistivity.

In addition, the base resin is liquid silicone rubber (LSR), fluororubber (FR), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), chloroprene rubber (CR) and ethylene propylene diene monomer (EPDM) rubber. It provides an intermediate junction box for ultra-high voltage DC power cables, characterized in that it contains at least one rubber selected from the group consisting of.

And, the additive for controlling the resistivity provides an intermediate junction box for an ultra-high voltage DC power cable, characterized in that it is a glycol-based organic conductive filler.

Here, the glycol-based organic conductive filler provides an intermediate junction box for ultra-high voltage DC power cables, characterized in that it contains polyglycol ether.

In addition, based on the total weight of the insulating composition, it provides an intermediate junction box for ultra-high voltage DC power cables, characterized in that the content of the organic conductive filler is 0.1 to 5% by weight.

And, the additive for controlling the resistivity provides an intermediate junction box for an ultra-high voltage DC power cable, characterized in that it further comprises an inorganic conductive filler.

On the other hand, the joint sleeve is formed such that the left and right ends of the first electrode are rounded in the longitudinal direction of the intermediate junction box and are spaced apart from each other by a predetermined distance to the left and right in the longitudinal direction of the intermediate junction box from the first electrode to face each other. and a pair of second electrodes that form gradually increasing in the direction, and the second insulating layer at least partially surrounds at least one surface selected from the group consisting of an interface between the first electrode and the junction box insulating part and an interface between the second electrode and the junction box insulating part. It provides an intermediate junction box for ultra-high voltage DC power cables, which is characterized.

Here, a junction box shielding layer provided outside the joint sleeve to shield an electric field leaking to the outside of the intermediate junction box, a housing made of a metal casing surrounding the joint sleeve, and disposed in a space between the housing and the joint sleeve It provides an intermediate junction box for ultra-high voltage DC power cables, characterized in that it further comprises a waterproofing material, or a combination thereof.

On the other hand, an ultra-high voltage DC power cable connection system comprising a pair of ultra-high voltage DC power cables and an intermediate junction box connecting the pair of power cables to each other, wherein the ultra-high voltage DC power cable includes a conductor, an inner semiconducting layer surrounding the conductor, and a cable core including a cable insulating layer surrounding the inner semiconducting layer and an outer semiconducting layer surrounding the insulating layer, wherein each end of the conductor, the inner semiconducting layer, the cable insulating layer and the outer semiconducting layer are sequentially exposed to each other It is provided to face and electrically connects a pair of conductors exposed at the ends of the power cable, and includes a conductor connection unit for fixing to each other, wherein the intermediate junction box is made of an elastic material that can be contracted at room temperature, and has a length inside A joint sleeve formed of a hollow sleeve having a through hole in the direction and including a junction box insulating part for preventing current from leaking to the outside of the intermediate junction box, wherein the junction box insulating part includes a first insulating layer and the first insulating layer a second insulating layer surrounded by a layer, wherein at least a portion of an innermost surface of the joint sleeve is made of the second insulating layer, the second insulating layer having a volume resistivity lower than that of the first insulating layer; The first insulating layer and the cable insulating layer have a volume resistivity of 1×10 ¹⁴ to 1×10 ¹⁸ Ωcm, and the volume resistivity of the second insulating layer is 10 times or more lower than the volume resistivity of the first insulating layer It provides an ultra-high voltage DC power cable connection system, characterized in that.

Here, the second insulating layer is composed of a second insulating composition, and the second insulating composition has a maximum volume resistivity (R _max ) defined by Equation 1 below at 70° C. or less, ultra-high voltage direct current power A cable connection system is provided.

[Equation 1]

R _max =f _min (aX,bY)

In Equation 1 above,

f _min (aX,bY) means the minimum value among aX and bY,

X is the volume resistivity at 70° C. of the cable insulation layer,

Y is the volume resistivity at 70° C. of the first insulating layer,

b is 2a or more,

b is 0.05 to 0.15,

a is 0.025 to 0.075;

And, the second insulating composition provides an ultra-high voltage DC power cable connection system, characterized in that it contains a base resin and an additive for adjusting resistivity.

Further, the base resin is liquid silicone rubber (LSR), fluororubber (FR), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), chloroprene rubber (CR) and ethylene propylene diene monomer (EPDM) rubber. It provides an ultra-high voltage DC power cable connection system, characterized in that it contains at least one rubber selected from the group consisting of.

In addition, the additive for controlling the resistivity provides an ultra-high voltage DC power cable connection system, characterized in that it is a glycol-based organic conductive filler.

Here, the glycol-based organic conductive filler provides an ultra-high voltage DC power cable connection system, characterized in that it contains polyglycol ether.

And, based on the total weight of the second insulating composition, it provides an ultra-high voltage DC power cable connection system, characterized in that the content of the organic conductive filler is 0.1 to 5% by weight.

In addition, the second insulating composition provides an ultra-high voltage DC power cable connection system, characterized in that it further comprises an inorganic conductive filler.

In addition, the joint sleeve is formed such that the left and right ends of the first electrode are rounded in the longitudinal direction of the intermediate junction box and are spaced apart from each other by a predetermined distance to the left and right in the longitudinal direction of the intermediate junction box from the first electrode to face each other. and a pair of second electrodes that form gradually increasing in the direction, and the second insulating layer at least partially surrounds at least one surface selected from the group consisting of an interface between the first electrode and the junction box insulating part and an interface between the second electrode and the junction box insulating part. It provides an ultra-high voltage DC power cable connection system, which is characterized.

Here, a junction box shielding layer provided outside the joint sleeve to shield an electric field leaking to the outside of the intermediate junction box, a housing made of a metal casing surrounding the joint sleeve, and disposed in a space between the housing and the joint sleeve It provides an intermediate junction box for ultra-high voltage DC power cables, characterized in that it further comprises a waterproofing material, or a combination thereof.

In addition, the second insulating layer may include a triple point where the first electrode, the junction box insulating part, and the cable insulating layer meet; a triple point where the second electrode, the junction box insulating part, and the cable insulating layer meet; Or it provides an intermediate junction box for ultra-high voltage DC power cables, characterized in that it is formed to surround all of them.

Meanwhile, the volume resistivity of the second insulating layer may be 10 times or more lower than the volume resistivity of the first insulating layer and the volume resistivity of the cable insulating layer, respectively, and the volume resistivity of the first insulating layer is the cable insulating layer may be 10 times or more higher than the volume resistivity of , and the volume resistivity of the cable insulating layer and the second insulating layer provides an intermediate junction box for an ultra-high voltage DC power cable, characterized in that it satisfies the following Equation (2).

[Equation 2]

(Volume resistivity of cable insulation layer / Volume resistivity of second insulation layer) ≥ 20

The intermediate junction box for ultra-high voltage DC power cable according to the present invention is made of a new material and has an electric field mitigating layer with precisely controlled resistance, thereby effectively mitigating the electric field in the region where the electric field can be structurally concentrated, thereby destroying the insulation of the junction box. It has an excellent effect to prevent

1 schematically shows a cross-sectional structure of an intermediate connection system for a conventional cable.
2 schematically shows a longitudinal cross-sectional view of a DC power cable of the ultra-high voltage DC power cable connection system according to the present invention.
3 schematically shows a cross-sectional structure of an ultra-high voltage DC power cable connection system according to the present invention.
4 is a graph showing electric field analysis and Joule loss at a triple point.
5 is a graph showing an equipotential line distribution between a first electrode and a second electrode in the embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 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 so that the disclosed subject matter may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art. Like reference numerals refer to like elements throughout.

2 schematically shows a longitudinal cross-sectional view of an ultra-high voltage DC power cable in the ultra-high voltage DC power cable connection system according to an embodiment of the present invention.

Referring to FIG. 1 , the power cable 200 includes a conductor 210 , an inner semiconducting layer 212 , an insulating layer 214 , and an outer semiconducting layer 216 in the cable length direction along the conductor 210 . It has a cable core that transmits only electric power and prevents current from leaking in the radial direction of the cable.

The conductor 210 serves as a path through which current flows to transmit power, and has excellent conductivity to minimize power loss, and a material having strength and flexibility suitable for cable manufacturing and use, for example, copper or aluminum, etc. can be composed of The conductor 210 may be a circular compressed conductor obtained by twisting a plurality of circular element wires to form a circular compression conductor, and a circular central element wire 210A and a flat element wire 210B twisted to surround the circular central element wire 210A. It may be a flat conductor having a flat element wire layer 210C formed therein and having an overall circular cross-section, and the flat conductor has a relatively high space factor compared to a circular compressed conductor, so that the outer diameter of the cable can be reduced.

However, since the conductor 210 is formed by twisting a plurality of strands, the surface thereof is not smooth, so that the electric field may be non-uniform, and corona discharge is likely to occur partially. In addition, when a void is formed between the surface of the conductor 210 and the insulating layer 214 to be described later, insulating performance may be deteriorated. In order to solve the above problems, an inner semiconducting layer 212 is formed outside the conductor 210 .

The inner semiconducting layer 212 has semiconductivity by adding conductive particles such as carbon black, carbon nanotubes, carbon nanoplates, and graphite to an insulating material, and is formed between the conductor 210 and an insulating layer 214 to be described later. It functions to stabilize the insulation performance by preventing a sudden electric field change from occurring. In addition, the electric field is made uniform by suppressing the non-uniform charge distribution on the conductor surface, and the formation of voids between the conductor 210 and the insulating layer 214 is prevented, thereby suppressing corona discharge, insulation breakdown, and the like.

An insulating layer 214 is provided on the outside of the inner semiconducting layer 212 to electrically insulate it from the outside so that the current flowing along the conductor 210 does not leak to the outside. In general, the insulating layer 320 has a high breakdown voltage, and insulating performance must be stably maintained for a long period of time. Furthermore, it must have low dielectric loss and resistance to heat such as heat resistance. Accordingly, the insulating layer 214 may be formed of a polyolefin resin such as polyethylene or polypropylene, and further preferably a polyethylene resin. Here, the polyethylene resin may be made of a crosslinking resin.

An outer semiconducting layer 216 is provided outside the insulating layer 214 . The outer semiconducting layer 216 is formed of a material having semiconductivity by adding conductive particles, for example, carbon black, carbon nanotubes, carbon nanoplates, graphite, etc., to an insulating material like the inner semiconducting layer, and the insulating layer Insulation performance is stabilized by suppressing non-uniform charge distribution between the 214 and the metal sheath 218 to be described later. In addition, the outer semiconducting layer 216 smoothes the surface of the insulating layer 214 in the cable to relieve electric field concentration to prevent corona discharge, and also functions to physically protect the insulating layer 214 . .

The core part may additionally include a moisture absorption part (not shown) for preventing moisture from penetrating into the cable. The moisture absorbing part may be formed between the stranded wires and/or on the outside of the conductor 210, and has a high rate of absorbing moisture penetrating into the cable and has excellent ability to maintain an absorption state (super absorbent polymer). ; SAP) in the form of powder, tape, coating layer, or film to prevent moisture from penetrating in the longitudinal direction of the cable. In addition, the moisture absorbing part may have semi-conductivity in order to prevent an abrupt electric field change.

A protective sheath is provided on the outside of the core, and the power cable to be installed in an environment exposed to a lot of moisture, such as the seabed, additionally includes an external part (not shown). The protective sheath part and the external part protect the cable core part from various environmental factors, such as moisture penetration, mechanical trauma, corrosion, which may affect the power transmission performance of the cable.

The protective sheath includes a metal sheath 218 and an inner sheath 220 to protect the cable from fault current, external force, or other external environmental factors.

The metal sheath layer 218 is grounded at the end of the power cable to serve as a passage through which an accident current flows when an accident such as a ground fault or short circuit occurs, protects the cable from external impact, and prevents an electric field from being discharged to the outside of the cable. there is. In addition, in the case of a cable to be laid in an environment such as the seabed, the metal sheath is formed to seal the core portion, so that foreign substances such as moisture are intruded and insulation performance is prevented from being deteriorated. For example, by extruding molten metal to the outside of the core part to have a seamless and continuous outer surface, excellent water-repellent performance can be achieved. Lead or aluminum is used as the metal. In particular, in the case of a submarine cable, it is preferable to use lead with excellent corrosion resistance to seawater, and lead alloy with metal elements added to complement mechanical properties. ) is more preferably used.

In addition, the metal sheath 218 may be coated with an anti-corrosion compound, for example, blown asphalt, etc. on the surface of the metal sheath 218 to further improve corrosion resistance, water resistance, etc. of the cable and to improve adhesion with the inner sheath 220 . can In addition, a copper wire straight-through tape (not shown) or a moisture absorption layer (not shown) may be additionally provided between the metal sheath 218 and the core part. The copper wire straight-through tape is composed of a copper wire and a non-woven tape, etc., and functions to facilitate electrical contact between the outer semiconducting layer and the metal sheath layer, and the moisture absorption layer (not shown) absorbs moisture penetrating into the cable. It is composed of powder, tape, coating layer or film containing super absorbent polymer (SAP) with high speed and excellent ability to maintain absorption, and prevents moisture from penetrating in the longitudinal direction of the cable. do In addition, in order to prevent an abrupt electric field change in the water absorption layer, a copper wire may be included in the water absorption layer.

An inner sheath 220 made of a resin such as polyvinyl chloride (PVC), polyethylene, etc. is formed on the outside of the metal sheath 218 to improve corrosion resistance, water resistance, etc. of the cable, mechanical trauma and heat, ultraviolet rays It can perform the function of protecting the cable from other external environmental factors such as In particular, in the case of a power cable to be installed on the seabed, it is preferable to use a polyethylene resin having excellent water resistance, and it is preferable to use a polyvinyl chloride resin in an environment where flame retardancy is required.

The protective sheath is formed of a metal reinforcing layer (not shown) composed of a galvanized steel cape, etc., and is formed on the upper and/or lower portion of the metal reinforcing layer and is made of a semi-conductive non-woven tape, etc. to cushion the external force applied to the power cable. A layer (not shown) and an external sheath (not shown) composed of a resin such as polyvinyl chloride or polyethylene are further provided to further improve corrosion resistance and water resistance of the power cable, and to prevent mechanical trauma and other external factors such as heat and ultraviolet rays The cable can be additionally protected from environmental factors.

In addition, the power cable laid on the seabed is easily injured by the anchor of the ship, and may be damaged by the bending force caused by ocean currents or waves, frictional force with the sea floor, etc. In order to prevent this, an external part ( not shown) may be formed.

The exterior part may include an armor layer (not shown) and a serving layer (not shown). The armor layer is made of steel, galvanized steel, copper, brass, bronze, and the like and may be composed of at least one layer or more by transversely winding a wire having a cross-sectional shape such as a circular shape or a flat shape. The armor layer 34 not only serves to strengthen the mechanical properties and performance of the cable, but also additionally protects the cable from external forces. The serving layer composed of polypropylene yarn, etc. is formed in one or more layers above and/or below the armor layer to protect the cable, and the serving layer formed at the outermost layer is composed of two or more materials with different colors. Visibility of cables laid on the seabed can be secured.

3 schematically shows a cross-sectional structure of an intermediate junction box for an ultra-high voltage DC power cable and an ultra-high voltage DC power cable connection system including the same according to an embodiment of the present invention.

3, the ultra-high voltage power cable connection system according to the present invention surrounds the ends of a pair of power cables, the conductors 210 and the insulating layer 214 of the pair of power cables, and the conductors ( It includes a conductor connection part 310 that electrically connects the 210), and a joint sleeve 320 that surrounds the outside of the conductor connection part 310 and the ends of the pair of power cables and is made of an elastic material that can be contracted at room temperature. It may include an intermediate junction box. In addition, the outer side of the joint sleeve 320 is electrically connected to the outer semiconducting layer 216 to the metal sheath 218 of the pair of power cables, so as to serve as an outer semiconducting layer of the power cable. A layer 324 , a housing (not shown) formed of a metal casing surrounding the joint sleeve 320 , and a waterproofing material (not shown) disposed in a space between the housing and the joint sleeve 320 are added. can be included as

As shown in FIG. 2, the pair of power cables includes a conductor 210, an inner semiconducting layer 212 surrounding the conductor 210, a cable insulating layer 214 surrounding the inner semiconducting layer 212, and the and a cable core including an outer semiconducting layer 216 surrounding the insulating layer 214 , wherein the conductor 210 , the inner semiconducting layer 212 , the cable insulating layer 214 and the outer semiconducting layer 216 at each end ) are sequentially exposed and provided to face each other.

The conductor connection part 310 includes a conductor fixing part for electrically connecting and fixing a pair of conductors 210 exposed at each end of the pair of power cables to each other, and the conductor fixing part and the pair of power cables. and a connecting sleeve surrounding the end of the insulating layer 214 exposed at the end. The conductor fixing part may be formed by inserting a sleeve into the pair of conductors and pressing the outer circumferential surface of the sleeve, fixing the pair of conductors inserted into the sleeve with a bolt penetrating the sleeve, or welding the conductor ends to each other, The conductor 210 or the conductor fixing part may be configured to be electrically connected to the connection sleeve through a braided wire or the like.

The joint sleeve 320 is made of an elastic material that can be contracted at room temperature, is formed as a hollow sleeve having a through hole in the longitudinal direction, and is a pair of cables electrically connected to each other by the conductor connection part 310, specifically Each of the insulating layers 214, the outer semiconducting layer 216, and the conductor connecting portion 310 exposed at the ends of the pair of cables are closely adhered to each other by an elastic restoring force. In addition, the intermediate junction box includes a junction box insulation to prevent current from leaking to the outside, and at least a portion of the innermost surface of the joint sleeve 320 may be formed of the junction box insulation portion. Specifically, the junction box insulating part may be in close contact with the conductor connection part by an elastic restoring force.

In addition, the joint sleeve 320 is provided in a pair to face each other in the first electrode 321 electrically connected to the conductor connection part 310 of the pair of power cables to the intermediate junction box 300, and the A second electrode 322 electrically connected to the outer semiconducting layer 216 to the metal sheath 218 of the pair of power cables may be provided, and the first electrode 321 and the second electrode 322 may be provided. may be surrounded by the junction box insulation.

The first electrode 321 and the second electrode 322 serve to spread the electric field evenly between them without being locally concentrated.

Specifically, the first electrode 321 has a shape in which left and right ends are rounded in the longitudinal direction of the power cable to the intermediate junction box, is made of a semi-conductive material, and is provided on the outside of the conductor connection part 310 . It is electrically connected to the conductor connection part 310 and the conductor 210, and serves as a so-called high-voltage electrode.

The second electrode 322 is made of a semi-conductive material, preferably the same material as that of the first electrode 321, and from the first electrode 321 to the left side of the power cable to the intermediate junction box in the longitudinal direction and A pair is provided so as to face each other by being spaced a predetermined distance to the right, and is electrically connected to the outer semiconducting layer 216 of the power cable, thereby serving as a so-called shielding electrode (Deflector). In addition, in the pair of second electrodes 322, the vertical distance from the innermost surface of the joint sleeve 320 or the cable insulating layer 214 increases in the direction toward the first electrode 321, The increase rate of the vertical distance is also provided in a shape that gradually increases in the direction toward the first electrode 321 , so that the surface facing the first electrode 321 is configured as a curved surface.

Accordingly, the first electrode 321 and the second electrode 322 have rounded or curved ends, and are formed between the first electrode 321 and the second electrode 322 according to the shape of each electrode. Equipotential lines are distributed at , and the electric field distribution can be controlled.

The junction box insulating portion is provided to surround the first electrode 321 and the second electrode 322 to prevent the current flowing in the ultra-high voltage cable connection system from leaking to the outside, thereby ensuring insulation performance.

On the other hand, in the case of an AC power cable connection system, the electric field in the cable insulation layer and the junction box insulation part of the connection system depends on the dielectric constant of the cable insulation layer and the junction box insulation part, and the dielectric constant does not change significantly with temperature. It is easy to predict the electric field distribution and design the junction box. On the other hand, in the case of a DC power cable connection system, the electric field distribution in the cable insulation layer and the insulation part of the junction box has a resistive electric field distribution characteristic that depends on the volume resistivity of the cable insulation layer and the insulation part of the junction box, so the volume resistivity is high. A high electric field acts on the junction box, and since this volume resistivity has temperature dependence, it is extremely difficult to design a junction box considering the electric field distribution.

In particular, in the portion where the first electrode 321 to the second electrode 322 is in contact with the junction box insulation part and/or the cable insulation layer, different materials having different volume resistivity come into contact with each other, so that the direct current is applied to the power cable. When an electric current flows and a temperature change occurs, not only the volume resistivity changes, but also the change rate is different depending on the material, so it is difficult to predict the electric field distribution and a problem of local concentration of the electric field may occur. In addition, when the connection system is manufactured, there is a possibility that a void may be generated or a foreign substance may enter the portion where the first electrode 321 to the second electrode 322 is in contact with the junction box insulation part and/or the cable insulation layer. When a high electric field is applied to a portion where a foreign material is generated, there is a risk of dielectric breakdown.

In order to solve this problem, the junction box insulating part of the present invention is surrounded by a first insulating layer 323 and the first insulating layer 323 and forms at least a part of the innermost surface of the joint sleeve 320 . An insulating layer 325 is provided.

The first insulating layer 323 is a liquid silicone rubber (LSR), fluororubber (FR), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR) having excellent insulating performance in order to guarantee the insulating performance of the intermediate junction box. ), chloroprene rubber (CR), ethylene propylene diene monomer (EPDM) rubber, or a first insulating composition comprising a combination thereof, preferably, the composition is excellent in long-term reliability such as tear strength and permanent change rate, , it may include a liquid silicone rubber having the advantage of improving productivity through a fast production process. In addition, the silicone rubber can be molded into various design products, so that moldability is improved, secondary vulcanization is unnecessary, and molding by double injection is possible.

The second insulating layer 325 is formed between the first insulating layer 323 and the cable insulating layer 214 in various forms such as a tube, a coating, a film, etc., in particular, the innermost surface of the joint sleeve, the first electrode At least partially surrounding at least one surface selected from the group consisting of an interface between 321 and the junction box insulating part and an interface between the second electrode 322 and the junction box insulating part, and preferably, the first Wrapping the triple point where the first electrode 321 or the second electrode 322, the junction box insulation part and the cable insulation layer 214 meet, there is a fear that the electric field is concentrated according to the change in volume resistivity according to temperature, It performs the function of suppressing the insulation breakdown of the intermediate junction box by alleviating the electric field in the part where the insulation performance is unstable because there is a risk of the occurrence of voids or intrusion of foreign substances.

The second insulating layer 325 is formed of a second insulating composition having a volume resistivity lower than that of the cable insulating layer 214, so that the electric field applied to the part with a risk of insulation breakdown is converted into a part with relatively stable insulating performance. can be dispersed.

The second insulating composition may include a base resin and an additive for controlling resistivity. The base resin may have a volume resistivity of 10 ¹⁵ Ωcm or less, an insulating strength of 10 kV/mm or more, preferably a breaking strength of 10 N/mm or more, and an elongation of 200% or more. The base resin is, for example, liquid silicone rubber (LSR), fluororubber (FR), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), chloroprene rubber (CR), ethylene propylene diene monomer (EPDM) rubber Or it may be made by including a combination thereof, it is preferable to include a liquid silicone rubber having the advantage of excellent long-term reliability such as tear strength and permanent change rate, and the productivity is improved through a fast production process, more preferably For close contact with the first insulating layer 323, it may be made of the same type of resin.

The additive for controlling resistivity may include an organic conductive filler alone or a combination of an organic conductive filler and an inorganic conductive filler. The organic conductive filler is a glycol-based filler such as ethylene glycol and propylene glycol, preferably polyglycolether, in consideration of compatibility with the base resin and electrical and mechanical properties of the second insulating layer 325 . ; PGE), and the organic conductive filler may further improve electrical properties and mechanical properties of the second insulating layer 325 by forming a chemical cross-linkage with the base resin. In addition, compared to the inorganic conductive filler, it can be easily dispersed in the base resin, thereby facilitating volume resistivity control.

The second insulating composition and the second insulating layer 325 formed therefrom are precisely formed according to the volume resistivity of each of the insulating layer 214 and the first insulating layer 323 of the cable in contact with the second insulating layer 325 . By maintaining a tightly controlled volume resistivity, it is possible to effectively disperse the electric field in the region where the electric field can be concentrated inside the intermediate junction box 300 .

Specifically, the second insulating composition may have a volume resistivity of less than or equal to the maximum volume resistance (R _max ) defined by Equation 1 below at 70°C. Accordingly, the second insulating layer 325 formed from the second insulating composition is a cable insulating layer, a first insulating layer, and a second insulating layer according to a temperature change due to the current state of the cable when the cable to be connected is a DC power cable. It is possible to maximize the electric field relaxation effect in the region where the electric field can be structurally concentrated by retaining the optimal volume resistivity according to the electric field distribution change in the back.

[Equation 1]

R _max =f _min (aX,bY)

In Equation 1 above,

f _min (aX,bY) means the minimum value among aX and bY,

X is the volume resistivity at 70°C of the cable insulation layer,

Y is the volume resistivity at 70° C. of the first insulating layer,

b is 2a or more,

b is 0.05 to 0.15,

a is 0.025 to 0.075;

When the second insulating composition has a volume resistivity exceeding the maximum volume resistivity (R _max ) defined by Equation 1 at 70° C., electric field dispersion by the second insulating layer 325 formed from the second insulating composition Insufficient effect may cause junction box insulation breakdown by electric field concentration.

The content of the additive for controlling resistivity, for example, based on the total weight of the second insulating composition, to maintain the maximum volume resistivity (R _max ) defined by Equation 1 at 70° C. This may be 0.1 to 5% by weight, preferably 0.5 to 3% by weight.

In addition, the first insulating layer 323, the second insulating layer 325 to the cable insulating layer 214 have a volume resistivity of 1×10 ¹² to 1×10 ¹⁸ Ωcm, and the second insulating layer 325 ) may be 10 times or more lower than the volume resistivity of the first insulating layer 323 and the volume resistivity of the cable insulating layer 214, respectively, and the volume resistivity of the first insulating layer 323 is the The volume resistivity of the cable insulation layer 214 may not be higher than 10 times. In particular, the volume resistivity of the cable insulating layer 214 may be 10 ¹⁴ to 10 ¹⁸ Ωcm, and the volume resistivity of the first insulating layer 323 may be 10 ¹⁴ to 10 ¹⁸ Ωcm. The volume resistivity ratio of the cable insulating layer 214 and the second insulating layer 325 preferably satisfies Equation 2 below, and the lower limit of the volume resistivity of the second insulating layer 325 is 10 ¹² Ωcm can

[Equation 2]

(Volume resistivity of cable insulation layer/Volume resistivity of second insulation layer)≥20

When the volume resistivity of the second insulating layer 325 is not less than 10 times lower than the volume resistivity of the first insulating layer 323 and the volume resistivity of the cable insulating layer 214, respectively, the electric field of the second insulating layer The dispersion effect may be significantly reduced, and when the volume resistivity of the first insulating layer 323 is 10 times or more higher than the volume resistivity of the cable insulating layer 214, an excessively large electric field is shared in the first insulating layer If the volume resistivity of the cable insulation layer 214 and the first insulation layer 323 is out of the above range, insulation characteristics required for ultra-high voltage DC power transmission may not be satisfied.

In addition, when the volume resistivity ratio of the cable insulating layer 214 and the second insulating layer 325 (volume resistivity of the cable insulating layer/volume resistivity of the second insulating layer) is less than 20, Similarly, the electric field at a triple point where the second electrode 322 , the second insulating layer 324 and the cable insulating layer 214 are in contact with each other rapidly rises, and the volume inherent of the second insulating layer 325 is When the resistance is less than the lower limit, excessively much heat is generated in the second insulating layer 325 due to Joule loss as shown in FIG. 4( b ).

As described above, the intermediate junction box for ultra-high voltage DC power cables according to an embodiment of the present invention having a junction box insulation including the first insulating layer 323 and the second insulating layer 325 and the ultra-high voltage DC including the same according to an embodiment of the present invention In the power cable connection system, it is preferable that the interface between the first insulating layer 323 and the second insulating layer 325 does not contact the first electrode 321 and the second electrode 322 .

Specifically, the first electrode 321 and the second electrode 322 are surrounded by the second insulating layer 325 without being in contact with the first insulating layer 323, and the joint sleeve 320 is A first triple point at which the first electrode 321 , the second insulating layer 325 and the cable insulating layer 214 are in contact with each other, the second electrode 322 , the second insulating layer 325 and the cable The insulating layer 214 may have a second triple point in contact with each other, and the junction box shielding layer 324 , the first insulating layer 323 and the second insulating layer 325 may have a third triple point in contact with each other.

In this case, the electric field acting on the first triple point and the second triple point according to the resistive electric field distribution characteristic during direct current transmission is generated by the difference in the volume resistivity of the second insulating layer 325 and the first insulating layer 323 . It is shifted to one insulating layer 323, and when the intermediate connection system is placed under a direct current electric field, an interval of equipotential lines generated in the second insulating layer 325 is evenly distributed in the second insulating layer 325 Since it is widened and relatively constant by the inorganic conductive filler, it is possible to suppress the local concentration of the electric field in the second insulating layer 325 , in particular, the concentration of the electric field at the first triple point and the second triple point.

In addition, on the interface between the first triple point and the second insulating layer 325 surrounding the first electrode 321 and the first insulating layer 323, the first insulating layer 323 is formed by the following equation It may have a thickness satisfying Equation 3.

[Equation 3]

Here, U _O is the rated voltage of the intermediate junction box having the joint sleeve 320, 1.85U _O is the lightning impulse test voltage (BIL; Basic impuls insulation level), D _PMJ is the first triple point and the The thickness of the first insulating layer 323 formed on the interface between the second insulating layer 325 surrounding the first electrode 321 and the first insulating layer 323, BDV _PMJ is the first insulating layer is the breakdown voltage of (323).

That is, the first insulating layer 323 is formed so that the value obtained by dividing the lightning impulse test voltage of the intermediate junction box by the thickness of the first insulating layer 323 is smaller than the breakdown voltage value of the first insulating layer 323 . can be In other words, the thickness of the first insulating layer 323 is greater than the value obtained by dividing the lightning impulse test voltage (1.85U _O ) of the intermediate junction box by the breakdown voltage value (BDV _PMJ ) of the first insulating layer 323 . can be formed

Since the first insulating layer 323 has a higher volume resistivity than the second insulating layer 325 , in particular, a higher electric field is shared on the first electrode 321 than the second insulating layer 325 . As described above, the thickness of the first insulating layer 323 having a high electric field share is the lightning impulse test voltage (1.85U _O ) of the intermediate junction box, and the breakdown voltage value (BDV _PMJ ) of the first insulating layer 323 ), the density of electric lines of force in the first insulating layer 323 may be increased, and thus dielectric breakdown may occur in the first insulating layer 323 .

Therefore, in one embodiment of the present invention, the thickness of the first insulating layer 323 is the lightning impulse test voltage (1.85U _O ) of the intermediate junction box, the breakdown voltage value of the first insulating layer 323 (BDV _PMJ ) By making it larger than the value divided by , it is possible to prevent dielectric breakdown in the first insulating layer 323 from occurring. As an example, the first insulating layer 323 may be formed on the first electrode 321 to have a thickness of at least three times the thickness of the second insulating layer 325 .

In addition, the third triple point is formed to be spaced apart from the end of the second electrode 322 facing the first electrode 321 by a predetermined distance in the opposite direction to the first electrode 321, and the junction box shielding layer At 324 , the first insulating layer 323 and the second insulating layer 325 are formed in a region in contact with each other. Accordingly, in the third triple point, an electric field is not applied because an equipotential line is not distributed due to the geometric shape of the second electrode 322 , and thus the insulating performance of the intermediate junction box can be improved.

In the intermediate junction box for cables according to the present invention, the joint sleeve 320 includes, for example, inserting a mold into a molding mold and injecting a semi-conductive material into the mold to connect the first electrode 321 and the second electrode 322 to each other. After molding, the composition for controlling electrical conductivity and the insulating composition are injected into the molding mold and then cured to form a second insulating layer and a first insulating layer. In addition, the second insulating layer may be formed to surround at least a portion of an interface or a point where the first electrode 321 to the second electrode 322 is in contact with the junction box insulating part and/or the cable insulating layer and is in contact with each other. It may be prepared by applying an insulating composition and curing it.

[Example]

1. Preparation example

Except for the intermediate junction box of the embodiment having the junction box insulating part having the volume resistivity as shown in Table 1 below and having the second insulating layer 325 shown in FIG. 3 and not having the second insulating layer And the intermediate junction box of the comparative example provided with the junction box insulation part having the same structure was manufactured, respectively.

Volume resistivity (Ωm) Example 1 Example 2 Comparative Example 1 Comparative Example 2 Volume resistivity of cable insulation layer (70℃) 8.70E+14 4.64E+14 8.70E+14 4.64E+14 Volume resistivity of the first insulating layer (70°C) 1.69E+15 2.10E+15 1.69E+15 2.10E+15 Volume resistivity of the second insulating layer (70°C) 9.14E+12 1.21E+13 - -

2. Equipotential line distribution and electric field value evaluation

The distribution of equipotential lines in the space between the first electrode and the second electrode measured at 70° C. with a voltage of 592 kV applied to the intermediate junction box of each of Examples and Comparative Examples is as shown in FIG. 5, and the electric field values for each region is as shown in Table 2 below.

Electric field value [kV/mm] interface 1 triple point interface 2 Example 1 1.1 2.5 8.5 Example 2 0.1 0.2 9.4 Comparative Example 1 26.6 61.1 17.1 Comparative Example 2 23.4 53.6 16.5

- Interface 1: Cable Insulation Layer - First Insulation Layer Interface

- Triple point: cable insulation layer - 1st insulation layer - 2nd electrode

- Interface 2: first insulating layer - first electrode

As shown in FIG. 5 , in the intermediate junction box of the embodiment according to the present invention having the second insulating layer, the electric field is not locally concentrated because the gap between the equipotential lines between the first electrode and the second electrode is not narrow. 2 In the intermediate junction box of the comparative example that does not have an insulating layer, there was a region where the electric field was concentrated locally due to the narrow interval between equipotential lines. It was confirmed that the electric field in the region where the electric field could be concentrated was sufficiently relaxed, while the intermediate junction box of the comparative example was structurally concentrated in the region where the electric field could be concentrated.

Although the present specification has been described with reference to preferred embodiments of the present invention, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims described below. will be able to carry out Therefore, if the modified implementation basically includes the elements of the claims of the present invention, all should be considered to be included in the technical scope of the present invention.

200: power cable 300: intermediate connection system for power cable

Claims (21)

An intermediate connection box for connecting a pair of ultra-high voltage DC power cables comprising a conductor, an inner semiconducting layer surrounding the conductor, an insulating layer surrounding the inner semiconducting layer, and an outer semiconducting layer surrounding the insulating layer,
The intermediate junction box is made of an elastic material that can be contracted at room temperature, and is formed of a hollow sleeve having a through hole in the longitudinal direction therein, and a joint sleeve including a junction box insulating part to prevent current from leaking to the outside of the intermediate junction box. to provide
The junction box insulating portion includes a first insulating layer and a second insulating layer surrounded by the first insulating layer,
At least a portion of the innermost surface of the joint sleeve is made of the second insulating layer,
The second insulating layer has a volume resistivity lower than that of the first insulating layer,
The first insulating layer and the second insulating layer have a volume resistivity of 1×10 ¹² to 1×10 ¹⁸ Ωcm, and the volume resistivity of the second insulating layer is 10 times or more lower than that of the first insulating layer, ,
The second insulating layer is formed of a second insulating composition comprising a base resin and an additive for controlling resistivity, and the additive for controlling resistivity is a glycol-based organic conductive filler. delete According to claim 1,
The base resin is a group consisting of liquid silicone rubber (LSR), fluororubber (FR), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), chloroprene rubber (CR), and ethylene propylene diene monomer (EPDM) rubber Intermediate junction box for ultra-high voltage DC power cables, characterized in that it contains at least one rubber selected from delete According to claim 1,
The glycol-based organic conductive filler is an intermediate junction box for ultra-high voltage DC power cables, characterized in that it contains polyglycol ether. According to claim 1,
Based on the total weight of the insulating composition, the content of the organic conductive filler is 0.1 to 5% by weight, characterized in that, ultra-high voltage DC power cable intermediate junction box. According to claim 1,
The intermediate junction box for ultra-high voltage DC power cables, characterized in that the additive for controlling the resistivity further comprises an inorganic conductive filler. According to claim 1,
As long as the joint sleeve is spaced apart from each other by a predetermined distance to the left and right in the longitudinal direction of the intermediate junction box from the first electrode and the first electrode of a shape in which left and right ends are rounded in the longitudinal direction of the intermediate junction box, the joint sleeve is formed to face each other a pair of second electrodes;
The first electrode and the second electrode are surrounded by the junction box insulation,
In the second electrode, the vertical distance from the innermost surface of the joint sleeve gradually increases in the direction of the first electrode,
The second insulating layer at least partially surrounds at least one surface selected from the group consisting of an interface between the first electrode and the junction box insulating part and an interface between the second electrode and the junction box insulating part. Intermediate connection box for delete An ultra-high voltage DC power cable connection system comprising a pair of ultra-high voltage DC power cables and an intermediate junction box for connecting the pair of power cables to each other,
The ultra-high voltage DC power cable includes a cable core including a conductor, an inner semiconducting layer surrounding the conductor, a cable insulating layer surrounding the inner semiconducting layer, and an outer semiconducting layer surrounding the insulating layer, the conductor, the inner semiconducting layer, Each end of the cable insulation layer and the external semiconducting layer exposed sequentially is provided to face each other,
and a conductor connecting portion for electrically connecting a pair of conductors exposed at the ends of the power cable and fixing them to each other,
The intermediate junction box is
It is made of an elastic material that can be contracted at room temperature, is formed as a hollow sleeve having a through hole in the longitudinal direction therein, and includes a joint sleeve including a junction box insulating part that prevents current from leaking to the outside of the intermediate junction box,
The junction box insulating portion includes a first insulating layer and a second insulating layer surrounded by the first insulating layer,
At least a portion of the innermost surface of the joint sleeve is made of the second insulating layer,
The second insulating layer has a volume resistivity lower than that of the first insulating layer,
The first insulating layer and the cable insulating layer have a volume resistivity of 1×10 ¹⁴ to 1×10 ¹⁸ Ωcm, and the volume resistivity of the second insulating layer is 10 times or more lower than that of the first insulating layer,
The second insulating layer is composed of a second insulating composition, and the second insulating composition has a volume resistivity of less than or equal to the maximum volume resistivity (R _max ) defined by Equation 1 below at 70° C. system.
[Equation 1]
R _max =f _min (aX,bY)
In Equation 1 above,
f _min (aX,bY) means the minimum value among aX and bY,
X is the volume resistivity at 70° C. of the cable insulation layer,
Y is the volume resistivity at 70° C. of the first insulating layer,
b is 2a or more,
b is 0.05 to 0.15,
a is 0.025 to 0.075; delete 11. The method of claim 10,
The second insulating composition comprises a base resin and an additive for adjusting resistivity, an ultra-high voltage DC power cable connection system. 13. The method of claim 12,
The base resin is a group consisting of liquid silicone rubber (LSR), fluororubber (FR), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), chloroprene rubber (CR), and ethylene propylene diene monomer (EPDM) rubber Ultra-high voltage DC power cable connection system, characterized in that it contains at least one rubber selected from 13. The method of claim 12,
The resistivity control additive is a glycol-based organic conductive filler, characterized in that the ultra-high voltage DC power cable connection system. 15. The method of claim 14,
The glycol-based organic conductive filler comprises a polyglycol ether, an ultra-high voltage DC power cable connection system. 16. The method of claim 15,
Based on the total weight of the second insulating composition, the content of the organic conductive filler is 0.1 to 5% by weight, characterized in that the ultra-high voltage DC power cable connection system. 15. The method of claim 14,
The second insulating composition, characterized in that it further comprises an inorganic conductive filler, ultra-high voltage DC power cable connection system. 11. The method of claim 10,
As long as the joint sleeve is spaced apart from each other by a predetermined distance to the left and right in the longitudinal direction of the intermediate junction box from the first electrode and the first electrode of a shape in which left and right ends are rounded in the longitudinal direction of the intermediate junction box, the joint sleeve is formed to face each other a pair of second electrodes;
The first electrode and the second electrode are surrounded by the junction box insulation,
In the second electrode, the vertical distance from the innermost surface of the joint sleeve gradually increases in the direction of the first electrode,
The second insulating layer at least partially surrounds at least one surface selected from the group consisting of an interface between the first electrode and the junction box insulating part and an interface between the second electrode and the junction box insulating part. connection system. delete 19. The method of claim 18,
The second insulating layer may include a triple point where the first electrode, the junction box insulating part, and the cable insulating layer meet; a triple point where the second electrode, the junction box insulating part, and the cable insulating layer meet; Or, characterized in that it is formed to surround all of them, ultra-high voltage DC power cable connection system. 11. The method of claim 10,
The volume resistivity of the second insulating layer may be 10 times or more lower than the volume resistivity of the first insulating layer and the volume resistivity of the cable insulating layer, respectively, and the volume resistivity of the first insulating layer is the volume resistivity of the cable insulating layer It may be more than 10 times higher than the resistivity, and the volume resistivity of the cable insulating layer and the second insulating layer is characterized in that it satisfies Equation 2 below, the ultra-high voltage DC power cable connection system.
[Equation 2]
(Volume resistivity of cable insulation layer / Volume resistivity of second insulation layer) ≥ 20

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