Electricity: conductors and insulators – Conduits – cables or conductors – Conductive armor or sheath
Patent
1991-10-17
1993-07-27
Nimmo, Morris H.
Electricity: conductors and insulators
Conduits, cables or conductors
Conductive armor or sheath
174 75R, 174 75C, 174 84R, 174120SC, H01B 902, H02G 1508
Patent
active
052312496
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a resin composition suitably used for an insulation layer and semiconductor layers of rubber or plastic insulated power cables, power cables improved in high-temperature properties by using the resin composition, and a joint of the power cables.
BACKGROUND ART
A conventional rubber or plastic insulated power cable (hereinafter referred to simply as power cable) generally comprises a cable core which includes a conductor clad with an inner semiconductor layer and an insulation layer, or with an inner semiconductor layer, an insulation layer, and an outer semiconductor layer. These individual layers are formed by extruding a resin composition, which is based on an olefin resin blended with a crosslinking agent, onto the outer peripheral surface of the conductor by means of an extruder, then heating the resultant structure under pressure to decompose the crosslinking agent blended with the base resin, so that crosslinking is effected by means of the resultant radicals.
Conventionally, moreover, power cables of the 154-kV class or higher are connected by the so-called moulded joint method as follows.
First, the respective conductors of two power cables are exposed at their end portions, and those portions of inner semiconductor layers, insulation layers, and outer semiconductor layers near the exposed end portions of the conductors are cut substantially in the desired shape of a cone. Thereafter, the exposed conductors are connected to each other, and a semiconductive tape, which is made of an olefin resin composition compounded with the crosslinking agent, or a heat-shrinkable semiconductive tube made of the aforesaid resin composition is wound or put on the conductor joint and the vicinities thereof to form an inner semiconductor layer. Then, the inner semiconductor layer is wound with an insulation tape made of an olefin resin composition compounded with the crosslinking agent, or is coated with an insulating olefin resin compound blended with the crosslinking agent by extrusion into a mold, thereby forming an insulation layer. Further, this insulation layer is wound with the semiconductive tape or fitted with the heat-shrinkable semiconductive tube in the same manner as in the formation of the inner semiconductor layer, thereby forming an outer semiconductor layer. After these individual layers are formed in this manner, they are crosslinked by heating under pressure, whereby the power cables are connected together.
Conventionally, dicumyl peroxide is used as the crosslinking agent for the olefin resin, which constitutes the insulation layers and semiconductor layers of the power cables and a joint thereof.
In manufacturing the power cables, resins having higher melting points than conventional ones are tentatively used as materials for the insulation layer and semiconductor layers so that the high-temperature properties of the resultant power cables, and therefore, the reliability thereof, are improved. In particular, this improvement is in a great demand for high-voltage power cables. However, the preset temperature of the extruder should be heightened in the case where the insulation layer and semiconductor layers made of a resin with a high melting point are extruded. In this case, the following problem may arise under some conditions.
The resin composition is heated due to the shearing force of the screw of the extruder, so that its resin temperature becomes too high. Accordingly, the crosslinking agent such as dicumyl peroxide in the resin composition is partially decomposed, so that fine, amber-colored contaminants or the so-called "amber" comes about in an extruded piece. This "amber" triggers insulation breakdown, thus lowering the properties, and therefore, the reliability, of the power cables. If the "amber" is frequent, moreover, protrusions develop on the surface of the extruded piece, thereby spoiling the external appearance of the cables.
Moreover, during the manufacture of the power cable core or the manufacture of the tape for the taped
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Kimura Hitoshi
Matsumoto Tetsuo
Shimada Michihiro
Nimmo Morris H.
The Furukawa Electric Co. Ltd.
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