KR101668307B1 - Insulating structure superconducting DC cable joint box - Google Patents

Abstract

The present invention provides an insulation structure of a joint box for a superconducting DC cable in which liquid nitrogen is filled therein, the insulation structure comprising: a connection degree conductor disposed inside the joint box and connected to both ends of the superconducting DC cable; An epoxy insulating layer surrounding the outer circumferential surface of the connection conductor so that the central region has the greatest thickness and the thickness decreases in an inclined manner as the connection is further away from the central region in the longitudinal direction of the conductive member; And a polypropylene laminate paper (PPLP) layer which is laminated on the outer circumferential surface of the epoxy insulation layer so as to be inclined. Accordingly, the insulation structure of the joint box for the superconducting DC cable provides the effect of optimizing the surface insulation characteristics of the superconducting DC cable at the cryogenic temperature by applying the epoxy insulation layer and the laminated PPLP insulation layer together.

Description

Technical Field [0001] The present invention relates to an insulation structure of a superconducting DC cable joint box,

The present invention relates to an insulation structure of a joint box for a superconducting DC cable, and more particularly, to a superconducting DC cable which optimizes the insulation properties of a superconducting DC cable at a cryogenic temperature by applying an epoxy insulating layer and a laminated PPLP insulation layer together And more particularly to an insulation structure of a joint box.

Recently, in a wide area such as a high temperature superconducting cable, a superconducting transformer, a superconducting fault current limiter, a superconducting magnetic energy storage, a superconducting generator, The high-temperature superconducting technology used is attracting great attention from the viewpoint of energy technology development.

In particular, superconducting cables are evaluated as being the most applicable, and research and development is actively being carried out in various countries around the world. Until now, it was mainly aimed at R & D of high-temperature superconducting AC cable. However, in recent years, in the large-capacity power transportation for long distance in the land, or the large capacity power transportation using cable in the sea floor, Cable (High temperature superconducting DC cable) is under research and development.

Generally, when connecting cables to each other, conductors should be placed between a pair of cables and connected to each other by using a cryogenic joint box that encloses the cables. These joint boxes must be designed to be insulated, and the electrical and mechanical characteristics of the insulation material must be considered. This is a technique that must be established to increase cable life, reliability and compactness. However, in the case of a joint box of a high-temperature superconducting DC cable, it is necessary to include a liquid nitrogen at a very low temperature inside. Therefore, it is difficult to apply the insulation design technique of a common cable joint box.

The insulation design of the joint box of superconducting DC cable is mainly developed as a complex insulation system of liquid nitrogen and polymer. Therefore, in order to develop superconducting DC cable, it is important to establish insulation technology at cryogenic temperature in addition to insulation material technology in DC environment. However, the DC and impulse insulation characteristics data of superconducting cables in liquid nitrogen have not been satisfactorily reported, and the insulation design of a superconducting DC cable joint box is very inadequate.

Korean Patent Registration No. 10-0886341 Korean Patent Application Publication No. 10-2009-0110258

Accordingly, an object of the present invention is to provide an insulation structure of a joint box for a superconducting DC cable in which an epoxy insulation layer and a laminated PPLP insulation layer are applied together to optimize the surface insulation characteristics of a superconducting DC cable at a cryogenic temperature.

The above object is achieved by an insulation structure of a joint box for a superconducting DC cable in which liquid nitrogen is filled therein, the insulation structure comprising: a connection conductor disposed inside the joint box and connected to both ends of the superconducting DC cable; An epoxy insulating layer surrounding the outer circumferential surface of the connection conductor so that the central region has the greatest thickness and the thickness decreases in an inclined manner as the connection is further away from the central region in the longitudinal direction of the conductive member; And a polypropylene laminate paper (PPLP) layer formed on the outer circumferential surface of the epoxy insulation layer and being obliquely stacked.

Preferably, the epoxy insulation layer is sloped in a stepwise manner, and the polypropylene laminate layer is laminated stepwise along the step of the epoxy insulation layer, and the polypropylene laminate layer is laminated on the axis And is preferably laminated in an overlapping manner.

The polypropylene laminate layer is formed by pressing a kraft paper and a polypropylene and the polypropylene laminate paper layer is laminated on the epoxy insulation layer such that the fiber direction of the kraft paper and the longitudinal direction of the conductive paper are perpendicular to each other.

Wherein the epoxy insulation layer comprises 55 to 65 wt% silicon oxide (SiO ₂ ), the polypropylene laminate layer has a thickness of 100 to 150 탆, the polypropylene laminate layer is a space formed between the polypropylene laminate layers It is preferable to further include an invert gap (Butt-gap).

The connection conductor may be formed of a material selected from the group consisting of Copper, Tungsten, Stainless steel, Titanum, Aluminum, Iron, Nickel, Chromium, It is preferably selected from the group consisting of molybdenum, silver, gold, platinum, and mixtures thereof.

According to the structure of the present invention, the insulation structure of the joint box for a superconducting DC cable provides the effect of optimizing the insulation characteristics of the superconducting DC cable in the cryogenic temperature by applying the epoxy insulation layer and the laminated PPLP insulation layer together.

1 and 2 are sectional views of an insulation structure of a joint box for a superconducting DC cable according to an embodiment of the present invention,
3 is a view showing a surface discharge electrode system of an epoxy sample,
4 is a graph showing respective surface discharge characteristics of an insulating structure composed of an epoxy layer, a PPLP layer, and an epoxy + PPLP layer,
5 is a view showing a surface discharge electrode system of stacked PPLP,
6 is a graph showing dependency of the DC and impulse surface discharge voltage dependence on the creepage distance in the MD and CD directions,
7 is a photograph showing the surface of PPLP along the MD and CD directions,
8 is a graph showing the DC surface discharge voltage of the non-stacked and stacked PPLPs.

Hereinafter, an insulation structure of a joint box for a superconducting DC cable according to an embodiment of the present invention will be described in detail with reference to the drawings.

1, the insulation structure 100 is disposed inside a joint box 10 for a superconducting DC cable. Inside the joint box 10, liquid nitrogen for filling the joint box 10 into a cryogenic state is filled do. The resistance of the superconducting DC cable 30 disposed inside the joint box 10 by the liquid nitrogen becomes close to zero.

The insulating structure 100 disposed within the joint box 10 includes a connection conductive member 110, an epoxy insulating layer 130, and a polypropylene laminated paper 150 surrounding the epoxy insulating layer 130 , Hereinafter referred to as PPLP layer).

The connection conductive member 110 is formed in a long wire shape, and ends of the superconducting DC cable 30 are connected to both ends of the connection conductive member 110, respectively. When the superconducting DC cable 30 is connected, electricity flowing in one superconducting DC cable 30 can flow to the other superconducting DC cable 30 through the connection conductor 110. Here, the connection conductor 110 may be formed of a material such as copper, tungsten, stainless steel, titanium, aluminum, iron, nickel, chromium, It is preferable to use metals having good conductivity such as molybdenum, silver, gold, platinum and the like.

An epoxy insulating layer 130 for insulating the periphery of the connection conductive member 110 is formed on the outer circumferential surface of the connection conductive member 110. The epoxy insulation layer 130 is formed of epoxy resin containing 55 to 65 wt% of silicon oxide (SiO ₂ ). If the amount of the silicon oxide is less than 55 wt%, the epoxy insulating layer 130 is broken or the molding is not easy. When the amount of the silicon oxide exceeds 65 wt%, the epoxy insulating layer 130 can not withstand the cryogenic temperature formed by the liquid nitrogen.

The epoxy insulation layer 130 is formed such that the central region of the wire-like connection conductive material 110 has the greatest thickness in the longitudinal direction, and the epoxy insulation layer 130 has a greater thickness in the central region than in the longitudinal direction of the connection conductive material 110, (130) is formed to be inclinedly reduced. When the thickness of the epoxy insulating layer 130 is decreased, the PPLP layer 150 may be stacked on the inclined region. 2, the epoxy insulation layer 130 'is sloped in a stepwise manner, and the PPLP layer 150' extends along the step of the epoxy insulation layer 130 'and the PPLP layer 150' . ≪ / RTI > When formed in a stepwise manner in this manner, the surface insulation characteristic becomes better.

The PPLP layer 150 formed along the inclined region of the epoxy insulating layer 130 is stacked while being inclined while surrounding the outer circumferential surface of the epoxy insulating layer 150. The PPLP layer 150 is formed by squeezing kraft paper and polypropylene. The kraft paper has a fiber orientation.

The PPLP layer 150 is wrapped along the axis from the end region to the central region with respect to the longitudinal direction of the connection conductor and is connected to the PPLP layer 150 from the central region to the end region to laminate the PPLP layer 150 Wrap it. The lapping process is repeated so that the PPLP layer 150 is laminated as shown in the drawing. PPLP layer 150 In the lapping process, it is preferable that the PPLP layers 150 are overlapped and stacked on each other. There is an advantage that the surface insulation characteristic becomes larger when overlapped.

When the PPLP layer 150 is laminated on the epoxy insulating layer 130, it is preferable that the fiber direction of the kraft paper and the longitudinal direction of the connection conductive material 110 are perpendicular to each other. When the electricity generated from the superconducting DC cable 30 is transmitted to the PPLP layer 150 in a direction perpendicular to the fiber direction of the craft paper, Since the transfer is not easy, the surface insulation characteristics are excellent.

The PPLP layer 150 may further include a butt-gqp which is a space formed between the PPLP layers 150 to be stacked. The butt-gap refers to a fine space formed between the upper layer and the lower layer when the PPLP layer 150 is overlapped with the superconducting DC cable 30 and overlaps with the electricity transmitted to the PPLP layer 150 when the butt- May be partially discharged by the micro space. Therefore, the butt-gap affects the insulation properties in the insulation structure.

The PPLP layer 150 has a thickness of 100 to 150 mu m. If the PPLP layer 150 is less than 100 탆, the PPLP layer 150 may be broken. If the PPLP layer 150 is more than 150 탆, the number of the PPLP layer 150 may not be increased.

In order to confirm the surface insulation characteristics of the joint box 10 for the superconducting DC cable 30 with respect to the insulation structure 100, experiments were conducted through the following examples. In this example, the surface discharge electrode system of the epoxy sample was used.

≪ Example 1 >

1) Insulation structure composed of epoxy layer: As an insulation material for a superconducting DC cable, epoxy is used, wherein epoxy is 60 wt% of silicon oxide filler. 3 shows a surface discharge electrode system of the epoxy sample. As shown in the figure, the epoxy sample 200 was made of a cylindrical foam having a diameter of 58 mm. A cylindrical-cylindrical electrode 210 was attached to the epoxy sample 200 so as to surround the epoxy surface.

2) Insulation structure composed of PPLP layer: For PPLP test, PPLP was wound on a cylindrical epoxy sample and an aluminum electrode was attached thereon. Here, PPLP having a thickness of 119 占 퐉 is used.

3) Insulation structure composed of epoxy + PPLP layer: In the epoxy-PPLP composite test, an aluminum electrode was attached to the epoxy and the PPLP was wound thereon.

DC and impulse surface discharge voltages were applied to each sample of the insulation structure.

The sample 200 provided with the electrode 210 was dried in a drier and fixed to a sample holder. The sample holder was attached to the bottom of the high pressure bushing attached to the cryostat. After commercial liquid nitrogen was introduced, DC and impulse voltages were applied between the electrodes of the sample under a pressure of -0.4 MPa at atmospheric pressure. The dielectric breakdown and surface discharge voltage were tested 10 to 15 times under given conditions. For high voltage application, the DC voltage was increased at a rate of 2kV / sec using a power supply device with a maximum voltage of 100kV, and a standard impulse having a waveform of 1.2 × 50μs having a maximum voltage of 400kV and a capacity of 15KJ was used.

4 shows the surface discharge characteristics of an insulation structure composed of 1) an epoxy layer, 2) a PPLP layer and 3) an epoxy + PPLP layer under 0.4 MPa. Since the PPLP sheet saturates under 0.4 MPa of liquid nitrogen, this experiment was also carried out at 0.4 MPa under the same conditions. As shown in FIG. 4A, the surface discharge lengths of the DC test are 4, 6 and 8 mm, respectively, and 8, 12 and 16 mm for the impulse, respectively, as shown in FIG. In this experiment, the DC ground plane length was limited due to the limitation of the DC power supply maximum. As shown in the figure, the discharge voltage of DC and impulse surface was 3) Epoxy + PPLP layer, 1) Epoxy layer, and 2) PPLP layer. This is due to the slow progress of the surface discharge due to the increase of the contact surface at the interface between the epoxy layer and the PPLP layer. The results show that the composite structure of epoxy + PPLP layer has high insulation properties in the insulation design of cable joint box.

≪ Example 2 >

In the case of PPLP, the kraft paper included in the PPLP has two different orientations such as a macine direction (MD) and a fiber direction (Cross direction, CD). The following tests were conducted to confirm this. FIG. 5 shows a surface discharge electrode system of a stacked PPLP. The laminated PPLP 300 having no inclination was wound into a circular bobbin having a diameter of 75 mm in multiple layers and an electrode system 310 was installed thereon. The electrode system 310 is a needle of aluminum (tip angle: 30 ^° ) - a flat electrode.

6A and 6B show the dependence of the DC and impulsive surface discharge voltage on the creepage distance of the PPLP 300 along the MD and CD directions. As can be seen from the graph, in any case, the surface discharge voltage increases linearly with the creepage distance, and the impulse surface discharge voltage of the PPLP 300 in the CD direction is higher than that of the MD.

FIG. 7 shows a surface photograph of the PPLP 300 along the MD and CD directions obtained using a camera after a surface discharge under an impulse voltage. The damage of the surface was visually confirmed. As can be seen from FIG. 7A, in the case of the MD direction, traces of deterioration in the direction of the electrode were observed on the surface of the surface discharge trace, but it was confirmed that the PPLP 300 was damaged due to cracks or severe breakage of CD as shown in FIG. These results indicate that, in the case of MD, the discharge is promoted in the direction of the fibers of the craft paper included in the PPLP 300 to be deteriorated in the horizontal direction, while the fibers are broken at the right angle in the direction of the fibers, and the surface of the PPLP 300 is broken . This is because the impulse surface discharge voltage of the PPLP 300 in the CD direction is higher than that of the MD in the PPLP 300 because the discharge advances in a zigzag fashion at a right angle to the fiber direction,

≪ Example 3 >

The surface discharge voltage of PPLP laminated and PPLP not laminated was checked and compared. The surface roughness of the laminated PPLP was measured with a surface roughness meter (Mitutoyo, SJ-201), and the average surface roughness was 26.15 μm when laminated and 2.84 μm when laminated.

8 is a graph showing DC (+) surface discharge voltages of the non-stack PPLP and the stack PPLP, respectively. The DC (+) surface discharge voltage of laminated PPLP is 1.2 times higher than the surface discharge voltage of nonplanar PPLP. This is because the increase of the PPLP surface roughness leads to a longer creepage length, which improves the surface discharge voltage. Therefore, the surface insulation property of the PPLP laminated in the epoxy-PPLP composite system of the present invention is greatly improved.

The insulation structure of the joint box 10 for a superconducting DC cable according to the present invention includes the epoxy insulation layer 130 and the PPLP layer 150. Particularly since the PPLP layer 150 is laminated, It is expected that the insulation characteristics will be high. In addition, when the fiber direction is arranged perpendicular to the longitudinal direction of the connection conductor, the PPLP layer 150 is expected to have a high level of surface insulation because the discharge advances in a zigzag fashion perpendicular to the fiber direction.

10: Joint box
30: Superconducting DC cable
100: Insulation structure
110: Connection diagram
130, 130 ': Epoxy layer
150, 150 ': PPLP layer
200: epoxy sample
210: electrode
300: PPLP
310: Electrode system

Claims (8)

An insulation structure device for a joint box for a superconducting DC cable in which liquid nitrogen is filled in,
A connection degree conductor disposed inside the joint box and connected to both ends of the superconducting DC cable;
An epoxy insulating layer surrounding the outer circumferential surface of the connection conductor so that the central region has the greatest thickness and the thickness decreases in an inclined manner as the connection is further away from the central region in the longitudinal direction of the conductive member;
And a polypropylene laminate paper (PPLP) layer surrounding the outer circumferential surface of the epoxy insulating layer and being obliquely stacked,
Wherein the polypropylene laminate layer is laminated in an overlapping manner along an axis of the connection conductor,
Wherein the polypropylene laminate layer is formed by squeezing a kraft paper and a polypropylene,
Wherein the polypropylene laminate layer is laminated on the epoxy insulation layer so that the fiber direction of the kraft paper and the longitudinal direction of the connection conductor are perpendicular to each other. The method according to claim 1,
Wherein the epoxy insulation layer is formed to be inclined stepwise,
Wherein the polypropylene laminate layer is laminated stepwise along the step of the epoxy insulation layer. delete delete The method according to claim 1,
Wherein the epoxy insulation layer comprises 55 to 65 wt% silicon oxide (SiO ₂ ). The method according to claim 1,
Wherein the polypropylene laminate layer has a thickness of 100 to 150 mu m. The method according to claim 1,
Wherein the polypropylene laminate layer further comprises a butt-gap which is a space between the polypropylene laminate layers. ≪ RTI ID = 0.0 > 11. < / RTI > The method according to claim 1,
Wherein the connection degree conductor comprises:
Copper, Tungsten, Stainless steel, Titanum, Aluminum, Iron, Nickel, Chromium, Molybdenum, Silver ), Gold (Gold), platinum (Platinum), and mixtures thereof. [Claim 6] The insulation structure of a joint box for a superconducting DC cable according to claim 1,

Images