JP2002171656A - Insulated connections of power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow reducing a rise in temperature of a conductor caused by heat in a semiconductor layer at insulated connections of a power cable. SOLUTION: The power cable 13 comprises the external semiconductor layer 16 and a metal sheath 17 sequentially formed on a surface of a cable insulator 15. In the insulated connections, the metal sheath 17 is partially cut and removed, an openings is covered and sealed with an insulating pipe 19, and a space formed within the insulating pipe 19 is filled with a compound 21 having low thermal resistance and an insulating property. The rise in temperature caused by heat in the external semiconductor layer 16, is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power cable having a metal sheath, and more particularly to a structure of an insulated connecting portion used for blocking a sheath current.

2. Description of the Related Art In a single-core power cable, since an induced voltage is generated in a metal sheath, it is necessary to ground both ends of the sheath. However, a current flows through the sheath and the allowable current decreases. That is, when a current flows through the conductor, a circulating current flows through the metal sheath, and Joule heat is generated in the metal sheath, which causes a sheath circuit loss and an apparent power loss. Therefore, in order to prevent this sheath current, in a short distance cable, one end of the sheath is grounded, and the other end is insulated and floated, thereby limiting the sheath voltage. In the case of a long-distance cable, the sheath is divided using an insulated connecting portion. Conventionally used insulated connection structures include a cross-bonding method shown in FIG. 3 and a one-end grounding method shown in FIG. In FIG. 3, the electric cables 1a, 1b, 1c for transmitting the three-phase alternating current have insulated connecting portions 2a,
2b and 2c are provided. The sheath at one end of the insulated connecting portion 2a and the sheath at the other end of the insulated connecting portion 2b
a, the sheath at one end of the insulated connecting portion 2b and the sheath at the other end of the insulated connecting portion 2c are connected by the lead wire 3b,
Further, the sheath at one end of the insulated connecting portion 2c and the insulated connecting portion 2a
Is connected to the sheath at the other end by a lead wire 3c. In the system shown in FIG. 4, the electric cables 1a, 1b,
1c, the insulating connecting portions 2a, 2b, 2c and the insulating connecting portion 4
a, 4b and 4c are provided. And one side (all the same side) of the insulated connection parts 2a, 2b, 2c and the insulated connection parts 4a, 4b, 4c is grounded. The number of insulated connection portions in each of the above-described systems is limited to one for the cable connection length (one for each length of the cable entry section). In addition, since the outer diameter of the insulated connecting portion is large, installation space for the insulated connecting portion is widened, and experience is required for assembly. For these reasons, it has been difficult to install the insulated connection at the optimum position. If an attempt is made to insulate the metal sheath at the insulated connection, the outer diameter of the insulated connection at that portion must be increased, otherwise the electrical reliability of the power cable will be reduced due to electric field concentration at the insulated connection. descend. A technique has been proposed which solves such a problem and can easily insulate the metal sheath and reduce the sheath circuit loss without increasing the outer diameter of the insulated connection portion at an arbitrary section length of the cable. I have. FIG. 5 shows a configuration of an insulated connecting portion based on this technique. The cable body 5 includes a cable conductor 6 (an inner semiconductive layer on the conductor is omitted), a cable insulator 7 formed concentrically outside the cable conductor 6, and an outer semiconductive layer 8 covering the cable insulator 7. , And a metal sheath 9 provided by extrusion (corrugated) outside the external semiconductive layer 8. In the cable having such a structure, only a part of the metal sheath 9 is cut and removed over a predetermined range, leaving the outer semiconductive layer 8 at an appropriate length position. Electrodes 10 bent into a "J" cross-section are inserted into both sides of the inner surface of the end of the metal sheath 9 at the cut and removed portion. Thereafter, an insulating tube 11 is covered so as to cover the openings of the electrode 10 and the metal sheath 9, and both ends thereof are adhered to the surface of the metal sheath 9 by a sealant 12,
Sealing is performed. With such a configuration, the metal sheath 9
Is interrupted.

In the prior art having the configuration shown in FIG. 5, the outer semiconductive layer 8 serves as a shielding layer in a portion where the metal sheath 9 is cut and removed. For this reason, when applying AC of commercial frequency to an electric cable, the electrode 1
A voltage is generated by electromagnetic induction of the cable conductor 6 during zero, and a current flows through the external semiconductive layer 8 by this voltage.
Also, the charging current of the cable insulator 7 flows to the metal sheath 9 through the external semiconductive layer 8. These currents cause the external semiconductive layer 8 to generate heat.
Partially raise the temperature. As a result, the cable conductor 6 in the heat-generating portion deviates from the conductor allowable temperature, which may limit the allowable current. Therefore, an object of the present invention is to provide an insulated connection portion of a power cable that can reduce a rise in temperature of a conductor caused by heat generation of a semiconductive layer.

In order to achieve the above object, according to the present invention, an outer semiconductive layer and a metal sheath are sequentially formed on the outer periphery of a cable insulator, and the metal sheath is partially cut and removed. A structure in which a space formed between the insulating cylinder and the external semiconductive layer is filled with a low-thermal-resistance insulating compound in an insulated connecting portion of the power cable whose opening is covered with an insulating cylinder and sealed. I have to. As the compound, a mixture of a flame retardant as a main agent and a curing agent can be used.

According to the means described above, the interior of the insulating cylinder covering the connection portion is conventionally a cavity, but in the present invention, the cavity is filled with a compound having a low thermal resistance, so that the outer semiconductive layer is formed. Is dissipated through the compound, and the temperature rise of the external semiconductive layer can be suppressed. As a result, the influence on the allowable current of the cable conductor due to the temperature rise can be reduced. The compound uses a mixture of the main agent of the flame retardant and the hardening agent that is liquid before pouring, so that it can be easily injected from the outside into the connection part, and after curing, has properties that are excellent in heat conductivity and insulation. be able to.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a structure of an insulated connection portion in a power cable according to the present invention. As shown in FIG. 1, a power cable main body 13 includes a single-core cable conductor 14 as a center, a cable insulator 15 that is coated to insulate the cable conductor 14, and a conductive external material that covers the cable insulator 15. It has a configuration including each of the semiconductive layer 16 and a metal sheath 17 provided outside the outer semiconductive layer 16. The metal sheath 17 is formed by extruding a metal material such as copper, iron, and aluminum, and is corrugated in the longitudinal direction. Further, the metal sheath 17 may include a tape-shaped or linear metal body provided by tape winding or longitudinal attachment. In the cable having such a structure, only a part of the metal sheath 17 is cut and removed over a predetermined range, leaving the outer semiconductive layer 16 at an appropriate length. Electrodes 18 are inserted into the inner surfaces of the cut-away portions at the longitudinal ends of the metal sheath 17. The electrode 18 has a semicircular cross-section bent at one end. After the electrode 18 is provided, an insulating cylinder 19 is fitted so as to cover the opening of the electrode 18 and the metal sheath 17,
Both ends are adhered to the surface of the metal sheath 17 by the sealing material 20, and sealing is performed. At this time, the sealing material 20
A small through-hole (not shown) is formed in a part of the hole, and an insulating compound 21 is injected into the cavity inside the insulating cylinder 19 from the through-hole using a needle or the like. This injection
The insulating cylinder 19 extends over the entire exposed surface of the external semiconductive layer 16.
To cover the entire inner surface of the This compound 21
Is a material having a low heat resistance, for example, a mixture of [a hardening agent composed of an adduct of a liquefied diphenyl metalesisocyanate and a monohydroxy compound] and [a main agent composed of castor oil / polyether polyol and a powdered flame retardant]. I have. With such a configuration, electrical conduction in the metal sheath 17 is cut off. The compound 21 is interposed on the surface of the external semiconductive layer 16 at the connection portion, so that heat generated in the external semiconductive layer 16 (compound 21
Irrespective of the presence or absence of the same) is radiated to the atmosphere through the compound 21 and the insulating tube 19. As a result, the temperature rise of the external semiconductive layer 16 can be suppressed low, and the influence on the allowable current of the electric cable can be reduced. That is, the compound 21 functions as a heat transfer material and a coolant. Incidentally, in the case of the configuration of FIG. 5, the thermal resistance in the space inside the insulating cylinder 11 is about 24 ° C. cm / W, whereas the thermal resistance of the compound 21 in FIG. become. Thus, the heat dissipation is greatly improved. FIG. 2 is a comparison diagram of the possible length of the cross bond section showing the effect of the present invention. Here, 500KV
For the CSZV 2500mm2 cable, the possible length of the cross bond section was compared between the case where the compound was not filled (conventional configuration) and the case where the compound was filled with a compound having a low thermal resistance (specific thermal resistance of 150 ° C.cm/W) (the present invention). As is clear from FIG. 2, when the distance between the electrodes is equal, the possible length of the cross bond section can be increased by 1.8 to 2 times by filling the compound as compared with the case without filling. Conversely, when comparing without changing the possible length of the cross bond section, the distance between the electrodes 10 can be shortened by filling the compound. Therefore, since the length of the exposed portion of the external semiconductive layer 8 can be shortened, the amount of heat generation can be greatly reduced because the heat radiation effect of the compound 21 is also taken into consideration, and the effect on the allowable current of the cable is greatly reduced. Be improved.

As is apparent from the above description, according to the present invention, the insulated connecting portion of the power cable has a structure in which the metal sheath is partially cut and removed, and the opening is covered with an insulating tube and sealed. Since the insulating compound is filled in the space formed inside the insulating cylinder with low thermal resistance, the heat of the external semiconductive layer is radiated through the compound and the temperature rise of the external semiconductive layer is suppressed. Can be. As a result, the influence on the allowable current of the cable conductor due to the temperature rise can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a structure of an insulated connecting portion in a power cable according to the present invention.

FIG. 2 is a diagram showing a possible length of a cross bond section showing the effect of the present invention.

FIG. 3 is a schematic drawing showing a configuration example of a conventionally used cross-bond type insulated connecting portion.

FIG. 4 is a schematic diagram showing a configuration example of a conventionally used one-end grounding type insulated connecting portion.

FIG. 5 is a cross-sectional view showing a configuration of a conventional insulated connecting portion capable of reducing sheath circuit loss.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 Electric cable main body 14 Cable conductor 15 Cable insulator 16 External semiconductive layer 17 Metal sheath 18 Electrode 19 Insulation cylinder 20 Sealing material 21 Compound

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G355 AA03 BA04 BA12 CA19 CA26 5G375 AA02 BA26 BB53 BB60 CA03 CA18 CB10 DB11 DB35 DB44 EA13

Claims (2)

[Claims] 1. An insulation of a power cable in which an outer semiconductive layer and a metal sheath are sequentially formed on an outer periphery of a cable insulator, the metal sheath is partially cut and removed, and an opening portion thereof is covered with an insulating tube and sealed. An insulated connection portion for a power cable, wherein the connection portion has a structure in which an insulating compound having a low thermal resistance is filled in a space formed between the insulating cylinder and the external semiconductive layer. 2. The insulated connection part of a power cable according to claim 1, wherein the compound has a configuration in which a curing agent is mixed with a flame retardant as a main agent.