JP7583369B2 - Power cable termination structure and tubular part - Google Patents

Description

This disclosure relates to a power cable termination structure, a tube unit, and a tube part.

Patent Document 1 discloses a structure in which an electric field mitigation adapter and a stress cone are arranged in this order on an insulating layer provided on a power cable as the terminal end of the power cable to which high-voltage direct current is applied. Hereinafter, the above structure disclosed in Patent Document 1 will be referred to as the first conventional structure.

The electric field mitigation adapter is a cylinder made of a linear or nonlinear resistive electric field mitigation material (FGM, Functionally Graded Material). The electric field mitigation adapter is electrically connected to the power cable so as to take a potential of 0% from 100% potential. In detail, one of the two ends of the electric field mitigation adapter is electrically connected to a portion having the same potential as the conductor provided in the power cable. The other of the two ends contacts the external semiconductive layer provided in the power cable. The end electrically connected to the conductor is the end with a potential of 100%, i.e., the end on the high potential side. The end in contact with the external semiconductive layer is the end with a potential of 0%, i.e., the end on the low potential side that is the ground potential. When direct current is applied to the electric field mitigation adapter, the resistivity of the electric field mitigation adapter changes linearly or nonlinearly depending on the magnitude of the electric field.

Special Publication No. 2017-529815

In the first conventional structure described above, the electric field stress imposed on the triple contact portion when a high voltage direct current is applied is reduced compared to the second conventional structure that does not have an electric field mitigation adapter. However, the first conventional structure described above has inferior impulse characteristics.

The triple contact portion is a portion where three different materials come into contact, and occurs at the high potential end of the stress cone. In the second conventional structure described above, the triple contact portion is a portion where the insulating layer provided on the power cable, the electrically insulating rubber portion provided on the stress cone, and the insulating oil filled on the outside of the stress cone come into contact. In the first conventional structure described above, the triple contact portion is a portion where the rubber portion, the electric field mitigation adapter, and the insulating oil come into contact.

One of the objectives of the present disclosure is to provide a power cable termination structure that can reduce electric field stress when direct current is applied and has excellent impulse characteristics. Another objective of the present disclosure is to provide a tube unit and a tube part that can be used in the power cable termination structure.

A termination structure of a power cable according to one embodiment of the present disclosure comprises a terminal portion of a power cable having, from the inside, a conductor, an insulating layer, an outer semiconducting layer, and a shielding layer, a stress cone arranged on the outside of the insulating layer, a resistor portion arranged on the outside of the insulating layer, and an insulating fluid arranged on the outside of the stress cone and outside the resistor portion.
The terminal portion of the power cable has a first exposed portion which is the outer semiconductive layer exposed from the shielding layer, and an exposed portion which is the insulating layer exposed from the outer semiconductive layer.
The stress cone has an insulating tubular portion that contacts a portion of the exposed portion of the insulating layer, and a semiconductive portion provided at an end of the insulating tubular portion so as to contact the first exposed portion.
The resistor portion is a cylindrical body made of a functionally gradient material whose resistivity changes depending on the magnitude of an electric field. The resistor portion has a first inner circumferential surface in contact with the entire outer circumferential surface of the insulating tubular portion, a second inner circumferential surface in contact with a portion of the exposed portion of the insulating layer that is not covered by the insulating tubular portion, and a first end portion in contact with the semiconducting portion without contacting the first exposed portion.
The insulating fluid comes into contact with the outer circumferential surface of the resistor portion without coming into contact with the exposed portion of the insulating layer and the insulating cylindrical portion.

A cylindrical unit according to one embodiment of the present disclosure is a cylindrical unit used in a termination structure of a power cable comprising a terminal portion of the power cable and an insulating fluid, and comprises a stress cone and a resistor portion arranged outside the stress cone.
The stress cone has an insulating cylindrical portion and a semiconductive portion provided at an end of the insulating cylindrical portion.
The resistor portion is a cylindrical body made of a functionally gradient material whose resistivity changes depending on the magnitude of an electric field. The resistor portion has a first inner circumferential surface in contact with the entire outer circumferential surface of the insulating tubular portion, a second inner circumferential surface that is not in contact with the outer circumferential surface of the insulating tubular portion, a first end portion in contact with the semiconducting portion, and an outer circumferential surface disposed so as to be in contact with the insulating fluid.

A tubular part according to one aspect of the present disclosure is a tubular part used in a termination structure of a power cable, the tubular part including a terminal portion of the power cable, a stress cone, and an insulating fluid. The tubular part is a molded body made of a functionally gradient material whose resistivity changes depending on the magnitude of the electric field. The tubular part has a first inner peripheral surface arranged to contact the entire outer peripheral surface of the insulating tubular part provided in the stress cone, a second inner peripheral surface arranged to contact the insulating layer provided in the terminal portion of the power cable without contacting the insulating tubular part, a first end portion arranged to contact the semiconductive part provided in the stress cone without contacting the external semiconductive layer provided in the power cable, and an outer peripheral surface arranged to contact the insulating fluid.

The power cable termination structure disclosed herein can reduce electric field stress when DC is applied and also has excellent impulse characteristics. The cylindrical unit and cylindrical component disclosed herein can construct a power cable termination structure that can reduce electric field stress when DC is applied and also has excellent impulse characteristics.

FIG. 1 is a partial cross-sectional view showing a typical termination structure of a power cable according to a first embodiment.

[Description of the embodiments of the present disclosure]
One of the reasons why the first conventional structure described above has inferior impulse characteristics is believed to be as follows. When an impulse is applied to the end of the power cable, an electric field is concentrated in the portion of the outer semiconductive layer of the power cable that is exposed from the shielding layer and around the portion. Since the low-potential side end of the electric field mitigation adapter described above is in contact with the exposed portion of the outer semiconductive layer, an electric field is concentrated at the low-potential side end. The concentration of the electric field may cause insulation breakdown at the low-potential side end. Therefore, the present disclosure proposes a structure in which the arrangement of the low-potential side end is different from that of the first conventional structure. First, the contents of the embodiments of the present disclosure are listed and described.

(1) A termination structure of a power cable according to one embodiment of the present disclosure comprises a terminal portion of a power cable having, from the inside, a conductor, an insulating layer, an outer semiconducting layer, and a shielding layer, a stress cone arranged on the outside of the insulating layer, a resistance portion arranged on the outside of the insulating layer, and an insulating fluid arranged on the outside of the stress cone and outside the resistance portion.
The terminal portion of the power cable has a first exposed portion which is the outer semiconductive layer exposed from the shielding layer, and an exposed portion which is the insulating layer exposed from the outer semiconductive layer.
The stress cone has an insulating tubular portion that contacts a portion of the exposed portion of the insulating layer, and a semiconductive portion provided at an end of the insulating tubular portion so as to contact the first exposed portion.
The resistor portion is a cylindrical body made of a functionally gradient material whose resistivity changes depending on the magnitude of an electric field. The resistor portion has a first inner circumferential surface in contact with the entire outer circumferential surface of the insulating tubular portion, a second inner circumferential surface in contact with a portion of the exposed portion of the insulating layer that is not covered by the insulating tubular portion, and a first end portion in contact with the semiconducting portion without contacting the first exposed portion.
The insulating fluid contacts the outer circumferential surface of the resistor portion without contacting the exposed portion of the insulating layer or the insulating cylindrical portion.

The resistance portion prevents the exposed portion of the insulating layer from coming into contact with the insulating fluid. The resistance portion comes into contact with the insulating fluid. Therefore, in the power cable termination structure disclosed herein, the triple contact portion is the portion where the exposed portion of the insulating layer, the insulating tube portion of the stress cone, and the resistance portion come into contact. Such a power cable termination structure disclosed herein can reduce the electric field stress imposed on the triple contact portion by the resistance portion.

The first end of the resistor portion is electrically connected to the first exposed portion of the outer semiconductive layer by contacting the semiconductive portion of the stress cone. Because the outer semiconductive layer is grounded, this connection causes the first end of the resistor portion to assume ground potential. In other words, the first end of the resistor portion is the end on the low potential side. However, the first end of the resistor portion does not directly contact the first exposed portion where the electric field concentrates when an impulse is applied. Such a termination structure of the power cable disclosed herein has superior impulse characteristics compared to the first conventional structure described above.

(2) As an example of a termination structure of a power cable of the present disclosure, the terminal portion of the power cable has a second exposed portion which is the outer semiconductive layer exposed from the shielding layer, the exposed portion of the insulating layer is disposed between the first exposed portion and the second exposed portion, the second exposed portion is electrically connected to an end of the conductor exposed from the insulating layer, and the resistor portion has a second end electrically connected to the second exposed portion.

The above configuration allows the length of the resistor section to be shorter than when the second end is directly connected to the conductor of the power cable.

(3) In one example of the termination structure of the power cable disclosed herein, the resistor portion is a molded body.

The above configuration allows the termination structure of the power cable to be constructed by fitting a resistor part into the exposed part of the insulating layer and the outer periphery of the stress cone.

(4) As an example of the termination structure of the power cable described above in (3), the insulating tube portion and the resistor portion are integrated.

The above configuration allows the stress cone and resistor portion to be fitted around the outer periphery of the exposed portion of the insulating layer at once.

(5) As an example of the termination structure of the power cable disclosed herein, the resistor portion is formed by winding a tape material made of the functionally gradient material in a cylindrical shape around the outer periphery of the insulating cylindrical portion.

The above configuration allows the resistor portion to be formed regardless of the size of the exposed portion of the insulating layer and the size of the stress cone.

(6) In one example of the termination structure of the power cable disclosed herein, the constituent material of the insulating layer includes an inorganic filler.

The above configuration can reduce the degradation of characteristics when DC is applied.

(7) In one example of the termination structure of the power cable disclosed herein, the constituent material of the insulating layer does not contain an inorganic filler.

The above form reduces manufacturing costs because no inorganic filler is required.

(8) A cylindrical unit according to one embodiment of the present disclosure is a cylindrical unit used in a termination structure of a power cable comprising a terminal portion of the power cable and an insulating fluid, and comprises a stress cone and a resistance portion arranged outside the stress cone.
The stress cone has an insulating cylindrical portion and a semiconductive portion provided at an end of the insulating cylindrical portion.
The resistor portion is a cylindrical body made of a functionally gradient material whose resistivity changes depending on the magnitude of an electric field. The resistor portion has a first inner circumferential surface in contact with the entire outer circumferential surface of the insulating tubular portion, a second inner circumferential surface that is not in contact with the outer circumferential surface of the insulating tubular portion, a first end portion in contact with the semiconducting portion, and an outer circumferential surface disposed so as to be in contact with the insulating fluid.

The tube unit of the present disclosure is arranged to cover the portion of the insulating layer of the power cable that is exposed from the outer semiconductive layer. In a termination structure of a power cable that includes the tube unit of the present disclosure, the triple contact portion is the portion where the exposed portion of the insulating layer contacts the insulating tube portion and the resistor portion of the stress cone. Such a tube unit of the present disclosure can be used to construct a termination structure of a power cable that can reduce the electric field stress applied to the triple contact portion.

In the termination structure of a power cable including the tube unit of the present disclosure, the semiconductive portion of the stress cone is arranged so as to contact the portion of the outer semiconductive layer of the power cable that is exposed from the shielding layer. The first end of the resistor portion is electrically connected to the exposed portion of the outer semiconductive layer by contacting the semiconductive portion. Since the outer semiconductive layer is grounded, this connection causes the first end of the resistor portion to assume the ground potential. In other words, the first end of the resistor portion is the end on the low potential side. However, the first end of the resistor portion does not directly contact the exposed portion of the outer semiconductive layer where the electric field is concentrated when an impulse is applied. Such a tube unit of the present disclosure can construct a termination structure of a power cable that has superior impulse characteristics compared to the first conventional structure described above.

(9) A tubular part according to one aspect of the present disclosure is a tubular part used in a termination structure of a power cable, the tubular part including a terminal portion of the power cable, a stress cone, and an insulating fluid. The tubular part is a molded body made of a functionally gradient material whose resistivity changes depending on the magnitude of the electric field. The tubular part has a first inner surface arranged to contact the entire outer surface of the insulating tubular part provided in the stress cone, a second inner surface arranged to contact an insulating layer provided in the terminal portion of the power cable without contacting the insulating tubular part, a first end portion arranged to contact a semiconductive part provided in the stress cone without contacting an external semiconductive layer provided in the power cable, and an outer surface arranged to contact the insulating fluid.

The tubular part of the present disclosure is arranged to cover the portion of the insulating layer of the power cable that is exposed from the outer semiconductive layer and the insulating tubular part of the stress cone. In a termination structure of a power cable that includes the tubular part of the present disclosure, the triple contact portion is the portion where the exposed portion of the insulating layer, the insulating tubular part of the stress cone, and the tubular part of the present disclosure come into contact. Such a tubular part of the present disclosure can be used to construct a termination structure of a power cable that can reduce the electric field stress applied to the triple contact portion.

In a termination structure of a power cable including the tubular part of the present disclosure, the semiconductive portion of the stress cone is arranged to contact a portion of the outer semiconductive layer of the power cable that is exposed from the shielding layer. The first end of the tubular part is electrically connected to the exposed portion of the outer semiconductive layer by contacting the semiconductive portion. Since the outer semiconductive layer is grounded, this connection causes the first end of the tubular part of the present disclosure to have a ground potential. In other words, the first end of the tubular part of the present disclosure is the end on the low potential side. However, the first end of the tubular part of the present disclosure does not directly contact the exposed portion of the outer semiconductive layer where an electric field is concentrated when an impulse is applied. Such a tubular part of the present disclosure can construct a termination structure of a power cable that has superior impulse characteristics compared to the first conventional structure described above.

[Details of the embodiment of the present disclosure]
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same objects. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[Embodiment 1]
(overview)
The termination structure of a power cable according to the first embodiment will be described with reference to FIG.
FIG. 1 is a cross section of the termination structure of the power cable of the first embodiment cut by a plane parallel to the longitudinal direction of the power cable. However, the power cable is shown not in cross section but in appearance. Also, FIG. 1 shows only the part where the stress cone is arranged and the surrounding part in the termination structure of the power cable of the first embodiment. Note that FIG. 1 shows only the right half of the termination structure, and the left half of the termination structure is omitted. The structure of the left half is the same as the structure of the right half. The upper side of FIG. 1 corresponds to the tip side of the power cable. The lower side of FIG. 1 corresponds to the rear end side of the power cable. The tip side of the power cable is the side where the end of the conductor exposed from the insulating layer described later is arranged. Also, for convenience of explanation, the size and size ratio of each component in FIG. 1 may differ from the actual size. Note that the longitudinal direction of the power cable corresponds to the up-down direction in FIG. 1.

The power cable termination structure 1 of the first embodiment is provided at the terminal portion 2 of the power cable to connect the power cable to an external connection object (not shown). The external connection object is, for example, a power device, an overhead transmission line, etc.

The power cable termination structure 1 of the first embodiment is an aerial termination connection part in which insulating oil 5 is filled around the terminal portion 2 of the power cable. The basic configuration of the power cable termination structure 1 of the first embodiment can be referred to a known aerial termination connection part of a power cable. The basic configuration will be described below. The power cable termination structure 1 of the first embodiment includes a terminal portion 2 of the power cable, a stress cone 3, a resistance portion 4, and insulating oil 5. The power cable terminal portion 2 includes a first exposed portion 221 which is the outer semiconductive layer 22 exposed from the shielding layer 23, and an exposed portion 210 which is the insulating layer 21 exposed from the outer semiconductive layer 22. The stress cone 3 is disposed on the outside of the exposed portion 210 of the insulating layer 21. The resistance portion 4 is also disposed on the outside of the exposed portion 210 of the insulating layer 21. The resistance portion 4 is a cylindrical body, and is made of a functionally gradient material (FGM) whose resistivity changes depending on the magnitude of the electric field. The first end 41 of the resistor portion 4 contacts the semiconducting portion 36 provided on the stress cone 3. Insulating oil 5 is disposed on the outside of the stress cone 3 and the outside of the resistor portion 4.

In the first conventional structure described above, the electric field mitigation adapter is disposed inside the stress cone. Also, the low potential side end of the electric field mitigation adapter is in contact with the exposed portion of the external semiconductive layer of the power cable. In contrast, one of the features of the power cable termination structure 1 of embodiment 1 is that the resistance portion 4 is disposed outside the stress cone 3, not inside the stress cone 3. Another feature is that the first end 41, which is the low potential side end of the resistance portion 4, is not in contact with the first exposed portion 221 of the external semiconductive layer 22.

Below, we will first explain the components. Next, we will explain the specific structure of the power cable termination structure 1.

(Components)
<Power cable>
The power cable has, in this order from the inside, a conductor 20, an insulating layer 21, an outer semiconductive layer 22, and a shielding layer 23. Furthermore, the power cable has an inner semiconductive layer (not shown) inside the insulating layer 21, and a sheath (not shown) outside the shielding layer 23. A typical example of such a power cable is a cross-linked polyethylene insulated vinyl sheath cable (CV cable).

The constituent material of the insulating layer 21 is an electrical insulating material. A specific example of the electrical insulating material is a resin composition such as the above-mentioned cross-linked polyethylene. The above-mentioned constituent material may be a resin composition containing one or more types of fillers. The constituent material of the insulating layer 21 in this example is cross-linked polyethylene containing an inorganic filler. Examples of inorganic fillers include silicon oxide and magnesium oxide. The inorganic filler has the effect of reducing the deterioration of the DC characteristics of the insulating layer 21 caused by the generation of space charges in the insulating layer 21 when a direct current is applied. The above-mentioned DC characteristics are volume resistivity, DC breakdown field strength, space charge characteristics, etc. If the inorganic filler is a fine particle having a particle size of the nano-order, it is easy to disperse uniformly in the base resin. As a result, the deterioration of the above-mentioned DC characteristics is easily reduced.

The constituent materials of the conductor 20, the inner and outer semiconductive layers 22, the shielding layer 23, and the sheath can be any known material.

The power cable termination structure 1 of the first embodiment is used for high-voltage power transmission, such as a power cable transmission voltage of 250 kV or more, 400 kV or more, or even 500 kV or more. The conductor cross-sectional area, the thickness of the insulating layer 21, etc. are set according to the transmission voltage.

Stress Cone
The stress cone 3 has an insulating cylindrical portion 30 and a semiconductive portion 36. The stress cone 3 of this example is a molded body in which the insulating cylindrical portion 30 and the semiconductive portion 36 are integrated together.

The insulating tube portion 30 typically has a spindle-shaped outer shape. More specifically, the portion of the insulating tube portion 30 on the first end 31 side and the portion on the second end 32 side are tapered. The thickness of the middle portion of the insulating tube portion 30 is thicker than the minimum thickness of the portions on both end portions 31, 32 sides. The insulating tube portion 30 has the above-mentioned two end portions 31, 32, a cylindrical hole, an inner peripheral surface 301, and an outer peripheral surface 300. The hole penetrates from the first end portion 31 to the second end portion 32. The inner peripheral surface 301 forms the hole.

The insulating tube portion 30 is made of, for example, electrically insulating rubber. A specific example of the rubber is ethylene propylene diene rubber (EPDM). If the material is rubber, the elasticity of the rubber causes the inner surface 301 of the insulating tube portion 30 to adhere closely to the exposed portion 210 of the insulating layer 21. The insulating tube portion 30 and the semiconducting portion 36, which will be described later, can be made of known materials. The stress cone 3 can be manufactured using known molding methods, etc.

A semiconductive portion 36 is provided on the first end 31 side of the insulating tube portion 30. More specifically, the semiconductive portion 36 is provided on the inner peripheral side of the first end portion 31 side. A portion of the semiconductive portion 36 is covered by the insulating tube portion 30. The remaining portion of the semiconductive portion 36 is exposed from the insulating tube portion 30. The portion of the portion of the semiconductive portion 36 exposed from the insulating tube portion 30 constitutes the inner peripheral surface of the stress cone 3 together with the inner peripheral surface 301 of the insulating tube portion 30.

The constituent material of the semiconductive portion 36 is a semiconductive material. A specific example of the semiconductive material is the following rubber composition. This rubber composition contains an electrically insulating rubber such as the above-mentioned EPDM and a conductive material such as carbon. By including rubber in the above-mentioned constituent material, the elasticity of the rubber allows a part of the above-mentioned exposed portion of the semiconductive portion 36 to adhere closely to the first exposed portion 221 of the outer semiconductive layer 22.

<Resistance section>
The resistance portion 4 is a cylindrical body as described above. In this embodiment, the resistance portion 4 is a molded body. In addition, the resistance portion 4 is integrated with the stress cone 3 as described later.

The resistance portion 4 has a first end 41, a second end 42, a cylindrical hole, an inner peripheral surface, and an outer peripheral surface 400. The hole penetrates from the first end 41 to the second end 42. The inner peripheral surface forms the hole. The inner peripheral surface also has a first inner peripheral surface 401 arranged on the first end 41 side and a second inner peripheral surface 402 arranged on the second end 42 side. The outer peripheral surface 400 is arranged on the opposite side to the inner peripheral surface.

The thickness of the resistor portion 4 can be selected as appropriate. In this example, the resistor portion 4 has a uniform thickness over the entire length of the resistor portion 4, but the resistor portion 4 may have locally thick or locally thin portions. The thickness here is the distance between the inner circumferential surface and the outer circumferential surface 400 of the resistor portion 4. The length of the resistor portion 4 is adjusted according to the length of the exposed portion 210 of the insulating layer 21. The length of the resistor portion 4 is longer than the length of the insulating tube portion 30. The length here is the size along the longitudinal direction of the power cable.

A specific example of the functionally gradient material that is a constituent material of the resistor portion 4 is the following rubber composition. This rubber composition contains an electrically insulating rubber such as the above-mentioned EPDM, a conductive material such as carbon, and one or more types of electrically insulating ceramics. Specific examples of the ceramics are silicon carbide, zinc oxide, zirconium oxide, etc. The functionally gradient material can be made of a known material. A known molding method or the like can be used to manufacture the resistor portion 4 made of the molded body of this example. Note that the cylindrical body that constitutes the resistor portion 4 includes, in addition to the molded body of this example, a tape material wound into a cylindrical shape as shown in Modification 1 described below.

The resistor portion 4 is electrically connected to the terminal portion 2 of the power cable so that the second end portion 42 is at 100% potential and the first end portion 41 is at 0% potential when a voltage is applied. With this connection, when an electric field is applied to the resistor portion 4 when a voltage is applied, the resistivity of the resistor portion 4 changes linearly or nonlinearly. In particular, it is preferable to adjust the composition of the functionally gradient material so that the resistivity of the resistor portion 4 decreases significantly when a relatively large electric field is applied. The power cable termination structure 1 having such a resistor portion 4 can effectively reduce the electric field applied to the triple contact portion 9 when a high-voltage direct current is applied.

<Cylinder unit>
The power cable termination structure 1 of the first embodiment includes a tubular unit 6. The tubular unit 6 includes a stress cone 3 and a resistance portion 4. The tubular unit 6 is an integrated body in which an insulating tubular portion 30 and a resistance portion 4 are integrated together.

The resistor portion 4 is arranged so as to cover the insulating tube portion 30. That is, the insulating tube portion 30 is arranged inside the resistor portion 4. Also, the stress cone 3 and the resistor portion 4 are integrated so that the first end portion 31 of the insulating tube portion 30, the semiconductive portion 36, and the first end portion 41 of the resistor portion 4 are in contact with each other. Therefore, the first end portion of the tube unit 6 includes the first end portion 31 of the insulating tube portion 30, the semiconductive portion 36, and the first end portion 41 of the resistor portion 4. Also, as described above, the length of the insulating tube portion 30 is shorter than the length of the resistor portion 4. Therefore, the second end portion 32 of the insulating tube portion 30 and the second end portion 42 of the resistor portion 4 are offset in the longitudinal direction of the tube unit 6. The second end portion of the tube unit 6 corresponds to the second end portion 42 of the resistor portion 4.

As described above, the length of the insulating tube portion 30 is shorter than the length of the resistance portion 4, so that the insulating tube portion 30 is covered by the resistance portion 4 over the entire length of the insulating tube portion 30. The first inner peripheral surface 401 of the resistance portion 4 contacts the entire outer peripheral surface 300 of the insulating tube portion 30. The second inner peripheral surface 402 of the resistance portion 4 does not contact the outer peripheral surface 300 of the insulating tube portion 30. Since the insulating tube portion 30 is shifted toward the first end portion 41 of the resistance portion 4, the inner peripheral surface of the tube unit 6 is mainly composed of the insulating tube portion 30 and the resistance portion 4. The inner peripheral surface of the tube unit 6 on the first end portion 31, 41 side is mainly the inner peripheral surface 301 of the insulating tube portion 30. The inner peripheral surface of the tube unit 6 on the second end portion 42 side is the second inner peripheral surface 402 of the resistance portion 4. In addition, the entire outer surface 300 of the insulating tube portion 30 is covered by the resistance portion 4, so that the outer surface of the tube unit 6 is mainly the outer surface 400 of the resistance portion 4.

The cylindrical unit 6 is manufactured, for example, as follows: After the stress cone 3 is molded, the constituent material of the resistance part 4 is molded onto the outer peripheral surface 300 of the stress cone 3 by injection molding or the like.

<Insulating oil>
The insulating oil 5 is an example of an insulating fluid. A specific example of the insulating oil 5 is silicone oil. The insulating oil 5 may have a known composition.

The insulating oil 5 is filled inside the porcelain tube 8. The porcelain tube 8 is used as a container for housing the terminal portion 2 of the power cable. The porcelain tube 8 is made of an electrically insulating material such as resin. Note that FIG. 1 shows the porcelain tube 8 virtually with a two-dot chain line. Also, FIG. 1 illustrates a case where the porcelain tube 8 has a two-layer structure, but a single-layer structure is also acceptable.

(Specific structure)
<Power cable terminal>
The terminal portion 2 of the power cable is step-stripped. Therefore, the ends of the above-mentioned members constituting the power cable are exposed. Specifically, the terminal portion 2 of the power cable includes the above-mentioned exposed portion 210 of the insulating layer 21, the first exposed portion 221 of the outer semiconductive layer 22, and the end of the conductor 20 exposed from the insulating layer 21. Furthermore, the terminal portion 2 of the power cable includes a portion exposed from the sheath in the shielding layer 23, etc. The terminal portion 2 of the power cable in this example includes a second exposed portion 222 which is the outer semiconductive layer 22 exposed from the shielding layer 23. The first exposed portion 221 and the second exposed portion 222 are arranged at an interval in the longitudinal direction of the power cable. The first exposed portion 221 is arranged on the rear end side of the power cable. The second exposed portion 222 is arranged on the tip side of the power cable. Therefore, the exposed portion 210 of the insulating layer 21 is arranged between the first exposed portion 221 and the second exposed portion 222.

The second exposed portion 222 is used as a conductive portion for electrically connecting the resistor portion 4 and the end of the conductor 20. Therefore, the second exposed portion 222 is electrically connected to the end of the conductor 20. Note that the end of the conductor 20 is not shown in the figure.

The exposed portion 210 of the insulating layer 21 is covered by the stress cone 3 and the resistor portion 4. In this example, the exposed portion 210 of the insulating layer 21 is covered by the tube unit 6. In more detail, the portion of the exposed portion 210 of the insulating layer 21 that is on the tip side of the power cable is covered by the resistor portion 4. The portion of the exposed portion 210 of the insulating layer 21 that is on the rear end side of the power cable is covered by the insulating tube portion 30.

The first exposed portion 221 of the outer semiconductive layer 22 is used as a conductive portion for connecting the semiconductive portion 36 of the stress cone 3 and the first end 41 of the resistor portion 4 to ground potential.

<Cylinder unit>
The inner circumferential surface 301 of the insulating tubular portion 30 is disposed so as to contact a rear end portion that is a part of the exposed portion 210 of the insulating layer 21. A part of the portion of the semiconductive portion 36 exposed from the insulating tubular portion 30 is disposed so as to contact a first exposed portion 221 of the outer semiconductive layer 22. Since the outer semiconductive layer 22 is grounded, the semiconductive portion 36 takes on a ground potential due to contact with the first exposed portion 221.

The first inner peripheral surface 401 of the resistor portion 4 contacts the outer peripheral surface 300 of the insulating tube portion 30 as described above. The second inner peripheral surface 402 of the resistor portion 4 is arranged so as to contact the tip side portion of the exposed portion 210 of the insulating layer 21 that is not covered by the insulating tube portion 30. With this arrangement, a triple contact portion where the exposed portion 210 of the insulating layer 21, the insulating tube portion 30 of the stress cone 3, and the insulating oil 5 contact each other is not generated at the second end portion 32 of the insulating tube portion 30. In addition, a triple contact portion composed of the insulating tube portion 30, the resistor portion 4, and the insulating oil 5 is not generated at the second end portion 32 of the insulating tube portion 30.

The first end 41 of the resistor portion 4 is disposed at the rear end side of the power cable. More specifically, the first end 41 is disposed so as to contact the semiconductive portion 36 without contacting the first exposed portion 221 of the outer semiconductive layer 22. As described above, by contacting the semiconductive portion 36, which is at ground potential, the first end 41 of the resistor portion 4 is also at ground potential. Therefore, the first end 41 of the resistor portion 4 is the end of the resistor portion 4 on the low potential side.

The second end 42 of the resistor portion 4 is disposed at the tip side of the power cable. More specifically, the second end 42 is electrically connected to the second exposed portion 222 of the outer semiconductive layer 22. In this example, the second end 42 and the second exposed portion 222 are connected by a joint 49. The joint 49 is made of a conductive material. The second end 42 of the resistor portion 4 is electrically connected to the end of the conductor 20 by the second exposed portion 222 and the joint 49. This connection allows the second end 42 of the resistor portion 4 to take on a 100% potential, and is therefore the high-potential end of the resistor portion 4.

The tube unit 6 covers the exposed portion 210 of the insulating layer 21. As described above, in the tube unit 6, the resistor portion 4 covers the insulating tube portion 30. Therefore, the outer surface 400 of the resistor portion 4, which is the outer surface of the tube unit 6, is arranged so as to be in contact with the insulating oil 5. The exposed portion 210 of the insulating layer 21 and the insulating tube portion 30 of the stress cone 3 do not come into contact with the insulating oil 5.

(Method of manufacturing a termination structure of a power cable)
The power cable termination structure 1 of the first embodiment is constructed, for example, as follows.
(1) The ends of the power cables are subjected to terminal processing such as stripping.
(2) The tube unit 6 is fitted into the terminal portion 2 of the step-stripped power cable from the end side of the conductor 20. If the tube unit 6 is in a state in which the diameter is expanded in advance, the terminal portion 2 of the power cable can be easily inserted into the hole of the tube unit 6. The fitting operation is performed until the semiconductive portion 36 of the tube unit 6 contacts the first exposed portion 221 of the outer semiconductive layer 22.
(3) After the tube unit 6 is placed on the exposed portion 210 of the insulating layer 21 , the second end portion 42 and the second exposed portion 222 are connected.
For other processing, known procedures can be referred to.

(Action and Effect)
The triple contact portion 9 generated at the second end portion 32 on the high potential side of the insulating tube portion 30 of the stress cone 3 is composed of the exposed portion 210 of the insulating layer 21, the insulating tube portion 30, and the resistance portion 4. The power cable termination structure 1 of the first embodiment does not have a triple contact portion composed of the exposed portion 210 of the insulating layer 21, the insulating tube portion 30, and the insulating oil 5. In the power cable termination structure 1 of the first embodiment, the insulating oil 5 contacts the resistance portion 4 but does not contact the insulating layer 21 and the insulating tube portion 30. When a high-voltage direct current is applied to the power cable termination structure 1 of the first embodiment, the electric field stress applied to the triple contact portion 9 by the resistance portion 4 is reduced.

The first end 41 on the low potential side of the resistor portion 4 is not in direct contact with the first exposed portion 221 of the outer semiconductive layer 22, but is in contact with the semiconductive portion 36 of the stress cone 3. When an impulse is applied to the power cable termination structure 1 of this embodiment 1, the concentration of the electric field at the first end 41 on the low potential side is reduced compared to the first conventional structure described above. Therefore, the first end 41 is less likely to undergo dielectric breakdown. Therefore, the power cable termination structure 1 of embodiment 1 also has superior impulse characteristics compared to the first conventional structure described above.

The power cable termination structure 1 of this embodiment also provides the following effects.
(A) In this example, the second end 42 of the resistor portion 4 is connected to the second exposed portion 222 of the outer semiconductive layer 22. This structure allows the length of the resistor portion 4 to be shorter than a structure in which the second end 42 is directly connected to the end of the conductor 20. Depending on factors such as the operating voltage of the power cable, the length of the resistor portion 4 can be, for example, 1 m or less. A resistor portion 4 with a short length is easy to mold. Such a resistor portion 4 has excellent manufacturability.

(B) In this example, the stress cone 3 and the resistor portion 4 are integrated into a molded body, i.e., a cylindrical unit 6. Therefore, the stress cone 3 and the resistor portion 4 can be fitted into the exposed portion 210 of the insulating layer 21 at once. This structure of this example can reduce the construction time of the termination structure compared to when the stress cone 3 and the resistor portion 4 are each independent molded bodies. In addition, the construction work is simple.

(C) In this example, the insulating layer 21 contains an inorganic filler. This structure of this example can reduce the degradation of DC characteristics such as volume resistivity, DC breakdown field strength, and space charge characteristics when DC is applied.

[Test Example]
We investigated how the distribution of electric field stress changes depending on the presence or absence of FGM material and the arrangement of FGM material in the termination structure of a power cable. The FGM material is a cylindrical body made of a functionally gradient material whose resistivity changes depending on the magnitude of the electric field.

(Sample Description)
The termination structures of Samples No. 1 and No. 101 include the FGM material described above.
The termination structure of Sample No. 1 corresponds to the termination structure 1 of the power cable of the above-mentioned embodiment 1. That is, the termination structure of Sample No. 1 includes an FGM member on the outside of the stress cone. The end of the FGM member on the low potential side is not in contact with the outer semiconductive layer of the power cable, but is in contact with the semiconductive part of the stress cone.
The termination structure of sample No. 101 corresponds to the first conventional structure described above. That is, the termination structure of sample No. 101 includes an FGM member inside a stress cone. The low-potential end of the FGM member contacts the external semiconductive layer of the power cable and also contacts the semiconductive part of the stress cone. That is, the low-potential end of the FGM member is sandwiched between the external semiconductive layer of the power cable and the semiconductive part of the stress cone.
The termination structure of sample No. 102 does not include an FGM member and corresponds to the second conventional structure described above. Therefore, in the termination structure of sample No. 102, the triple contact portion is composed of the insulating layer of the power cable, the insulating tube portion of the stress cone, and the insulating oil.

(Measurement method)
In this test, the distribution of electric field stress was obtained by performing an electric field analysis. For the electric field analysis, a known electric field analysis software using the finite element method (FEM) was used. For the termination structures of samples No. 1 and No. 101 with FGM members, the analysis was performed assuming a power cable with a working voltage of 525 kV. For the termination structure of sample No. 102 without FGM members, the analysis was performed assuming a power cable with a working voltage of 400 kV or less.

(Analysis results)
<When DC is applied>
For the termination structure of each sample, the absolute value (kV/mm) of the electric field stress applied to the triple contact portion when a direct current is applied was determined. The electric field stress applied to the triple contact portion of the termination structure of sample No. 102 was used as a reference to compare the relative values. If the electric field stress of sample No. 102 is set to 1, the electric field stress applied to the triple contact portion of the termination structures of samples No. 1 and No. 101 is 0.65 or less. The electric field stress of sample No. 1 was 0.46, which was even lower than the electric field stress of sample No. 101. This shows that the inclusion of an FGM member reduces the electric field stress applied to the triple contact portion when a direct current is applied.

<When AC impulse is applied>
For the termination structure of each sample, the electric field stress share (%/mm) applied to the end on the low potential side of the FGM member when an AC impulse is applied was obtained. The electric field stress share of the termination structure of sample No. 101 is used as a reference to compare the electric field stress share in relative values. If the electric field stress share of sample No. 101 is 1, the electric field stress share of sample No. 1 is 0.15. From this, it can be seen that the electric field stress applied to the end on the low potential side when an AC impulse is applied is significantly reduced by arranging the FGM member outside the stress cone and by not contacting the low potential end of the FGM member with the external semiconductive layer of the power cable.

From the above, it has been quantitatively demonstrated that the power cable termination structure 1 of embodiment 1 can reduce electric field stress when DC is applied and also has excellent impulse characteristics.

[Modification]
At least one of the following modifications can be made to the power cable termination structure 1 of the first embodiment.
(Variation 1)
The resistor portion 4 is not a molded body. For example, the resistor portion 4 is formed by winding a tape material made of the above-mentioned functionally gradient material in a cylindrical shape around the outer periphery of the insulating cylindrical portion 30 of the stress cone 3. The tape material is not shown in the figure.

In variant 1, there is no need to mold the resistor portion 4 to have a size that matches the size of the exposed portion 210 of the insulating layer 21 and the size of the stress cone 3. It is easy to change the area in which the tape material is wound, the width and thickness of the tape material, the number of times the tape material is wound, etc. Therefore, the resistor portion 4 can be formed regardless of the size of the exposed portion 210 and the size of the stress cone 3. Variation 1 like this can be applied to power cables of any size, so there is a high degree of freedom in design.

(Variation 2)
The resistance portion 4 and the stress cone 3 are each an independent molded body. For example, the resistance portion 4 is a cylindrical part 40 as described below. The cylindrical part 40 has a first end portion 41, a second end portion 42, a first inner peripheral surface 401, a second inner peripheral surface 402, and an outer peripheral surface 400. The cylindrical part 40 also has a cylindrical hole that penetrates from the first end portion 41 to the second end portion 42. The first inner peripheral surface 401 and the second inner peripheral surface 402 form this hole.

The first end 41 is arranged to contact the semiconductive portion 36 of the stress cone 3 without contacting the external semiconductive layer 22 of the power cable. The second end 42 is electrically connected to the end of the conductor 20 of the power cable. The first inner surface 401 is arranged to contact the entire outer surface 300 of the insulating tube portion 30 of the stress cone 3. The second inner surface 402 is arranged not to contact the insulating tube portion 30. The second inner surface 402 is also arranged to contact the exposed portion 210 of the insulating layer 21 of the power cable that is not covered by the insulating tube portion 30. The outer surface 400 is arranged to contact the insulating oil 5.

An example of such a tubular part 40 is a cylindrical molded body having uniform inner and outer diameters in the longitudinal direction of the tubular part 40, which can be shrunk and deformed by heating. If the inner diameter of the tubular part 40 before thermal shrinkage is larger than the maximum outer diameter of the insulating tubular part 30, the insulating tubular part 30 arranged on the exposed part 210 of the insulating layer 21 can easily be inserted into the hole of the tubular part 40. After arranging the tubular part 40 on the outside of the insulating tubular part 30 and the exposed part 210 of the insulating layer 21, the tubular part 40 is heated. By thermally shrinking the tubular part 40, it can be closely attached to the insulating tubular part 30 and the exposed part 210 of the insulating layer 21. As another example, the tubular part 40 may be formed into a tubular shape by combining two split parts. As another example, the tubular part 40 may be formed by arranging a plurality of strip-shaped materials in a tubular shape on the outer periphery of the insulating tubular part 30. For example, multiple strips are arranged in a cylindrical shape by being wound around the outer periphery of the insulating tube portion 30 or by being attached vertically to surround the outer periphery of the insulating tube portion 30. Adjacent strips may overlap in part so that no gaps are created between them. Another strip may be stacked to cover the seams between adjacent strips. Adjacent strips or stacked strips may be joined together with an adhesive. The strips can cover insulating tube portions 30 of various sizes and shapes.

When the tubular part of the second modification is provided in the power cable termination structure 1, it has the same effect as the resistance portion 4 described in the first embodiment. That is, by using the tubular part of the second modification, it is possible to construct a power cable termination structure 1 that can reduce the electric field stress applied to the triple contact portion 9. Furthermore, by using the tubular part of the second modification, it is possible to construct a power cable termination structure 1 that has superior impulse characteristics compared to the first conventional structure described above. Note that, when the tubular part 40 is provided in the power cable termination structure 1, the outer shape of the tubular part 40 follows the outer shape formed by the exposed portion 210 of the insulating layer 21 and the stress cone 3.

(Variation 3)
The material constituting the insulating layer 21 does not contain an inorganic filler. In the third modification, the manufacturing cost can be reduced because an inorganic filler is not required.

(Variation 4)
The insulating fluid is an insulating gas, which is lighter than insulating oil, and therefore the fourth modification can reduce the weight of the termination structure of the power cable.

1 Power cable termination structure 2 Power cable terminal portion 3 Stress cone 4 Resistance portion 5 Insulating oil 6 Cylindrical unit 8 Ceramic tube 9 Triple contact portion 20 Conductor, 21 Insulating layer, 22 Outer semiconductive layer, 23 Shielding layer 30 Insulating cylindrical portion, 31 First end portion, 32 Second end portion, 36 Semiconductive portion 40 Cylindrical part, 41 First end portion, 42 Second end portion, 49 Joint portion 210 Exposed portion, 221 First exposed portion, 222 Second exposed portion 300 Outer peripheral surface, 301 Inner peripheral surface,
400 outer peripheral surface, 401 first inner peripheral surface, 402 second inner peripheral surface

Claims (8)

An end portion of a power cable having a conductor, an insulating layer, an outer semiconducting layer, and a shielding layer in this order from the inside;
a stress cone disposed outside the insulating layer;
a resistor portion disposed outside the insulating layer;
an insulating fluid disposed outside the stress cone and outside the resistor;
The terminal portion of the power cable is
a first exposed portion of the outer semiconductive layer exposed from the shielding layer;
an exposed portion of the insulating layer that is exposed from the outer semiconducting layer;
The stress cone is
an insulating tube portion in contact with a part of the exposed portion of the insulating layer;
a semiconductive portion provided at an end of the insulating cylindrical portion so as to be in contact with the first exposed portion,
The resistor portion is
a first inner circumferential surface in contact with the entire outer circumferential surface of the insulating cylindrical portion;
a second inner circumferential surface in contact with a portion of the exposed portion of the insulating layer that is not covered by the insulating cylindrical portion;
a first end portion that is in contact with the semiconductive portion without being in contact with the first exposed portion;
A cylindrical body made of a functionally gradient material whose resistivity changes depending on the magnitude of the electric field,
the insulating fluid is in contact with an outer circumferential surface of the resistor portion without being in contact with the exposed portion of the insulating layer and the insulating cylindrical portion;
Power cable termination structure. the terminal portion of the power cable has a second exposed portion which is the outer semiconductive layer exposed from the shielding layer,
the exposed portion of the insulating layer is disposed between the first exposed portion and the second exposed portion,
the second exposed portion is electrically connected to an end of the conductor exposed from the insulating layer;
The power cable termination structure according to claim 1 , wherein the resistor portion has a second end electrically connected to the second exposed portion. The power cable termination structure according to claim 1 or 2, wherein the resistor portion is a molded body. The power cable termination structure according to claim 3, wherein the insulating tube portion and the resistor portion are integral. The power cable termination structure according to claim 1 or 2, wherein the resistor portion is formed by winding a tape material made of the functionally gradient material in a cylindrical shape around the outer periphery of the insulating cylindrical portion. The power cable termination structure according to any one of claims 1 to 5, wherein the insulating layer is made of a material that contains an inorganic filler. The power cable termination structure according to any one of claims 1 to 5, wherein the insulating layer is made of a material that does not contain an inorganic filler. A cylindrical part used in a termination structure of a power cable, the cylindrical part including a terminal portion of the power cable, a stress cone, and an insulating fluid,
A first inner circumferential surface is arranged to contact the entire outer circumferential surface of the insulating cylindrical portion of the stress cone;
a second inner circumferential surface that is arranged to contact an insulating layer provided at an end portion of the power cable without contacting the insulating tube portion;
A first end portion is arranged to contact a semiconductive portion of the stress cone without contacting an outer semiconductive layer of the power cable;
an outer circumferential surface disposed so as to be in contact with the insulating fluid;
A molded body made of a functionally gradient material whose resistivity changes depending on the magnitude of the electric field.
Cylinder parts.

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