JPS64768B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrically insulated cables. BACKGROUND OF THE INVENTION Electric wire cables having insulators mainly composed of olefin polymers such as polyethylene and crosslinked polyethylene are currently in wide use, and their voltage classes have been increasing significantly over the years. By the way, the biggest technical problem that these wires and cables currently have is that if they continue to be energized, they will gradually deteriorate and their breakdown voltage will drop. Generally, the guaranteed lifespan of electric wires and cables is extremely long at 30 years, so current design standards require thicker insulators to account for this reduction. Incidentally, the recent phenomenon of urbanization is creating a demand for increasing power transmission capacity without increasing the size of conduits for electric wires and cables. For this reason, in electric wires and cables using such olefin polymers as the main insulator, there is a demand to increase the transmission voltage without increasing the number of insulating layers. There are various ways to solve this problem, but one is that if the deterioration phenomenon in the future does not occur, there is no need to consider the deterioration over the next 30 years, and the above requirements can be met. I can do it. We focused on this point and conducted intensive research on the aging phenomenon of these electric wires and cables.As a result, we found that this deterioration phenomenon is caused by microvoids in the insulator or conductive layer.
It was found that this is due to the tree generation generated from the insulating layer interface. That is, by suppressing the tree caused by such microscopic defects in the insulator, the previous deterioration phenomenon can be prevented, and the initial insulation thickness can be reduced at once. The present invention provides an electrically insulated cable that suppresses the occurrence of such trees. That is, by extrusion coating an ethylene-4-methylpentene-1 copolymer and, if necessary, coating it with an electrically insulating resin composition containing a crosslinking agent, the tree can be suppressed and the conventional electric wires and cables can be We were able to obtain a lifespan several to several tens of times longer and succeeded in reducing the initial insulation thickness all at once. Here, the copolymerization ratio (number of molecules) of 4-methylpentene-1 is preferably 1 to 10%. If it is less than 1%, the effect will be reduced, and if it is more than 10%, the extrusion processing characteristics will deteriorate.Of course, in the electrically insulated cable of the present invention,
If necessary, an anti-aging agent or the like may be added. Examples and comparative examples are shown below. A 60 mm ² twisted conductor was first coated with an internal conductive layer by extrusion, and then coated with a copolymer having the polymerization ratio shown in Table 1 by extrusion to obtain an electric wire. Further, as shown in Table 1, those that required electron beam crosslinking were crosslinked by electron beam irradiation in a conventional manner after extrusion coating. For those requiring chemical crosslinking, a crosslinking agent was blended, extrusion coating was performed, and then crosslinking was performed by heating. The wire thus obtained was immersed in water at 70°C, an AC voltage of 20 KV was applied, and after a certain period of time, it was taken out and the state of tree growth was examined. Furthermore, Table 1 shows the results of a comparison with the time to failure set as 1 for polyethylene. 【table】

Claims (1)

[Claims] 1 4-methylpentene-1 in molecular number ratio 1 to 10
An electrically insulated cable having an insulating layer mainly composed of an ethylene-4-methylpentene-1 copolymer or a crosslinked ethylene-4-methylpentene-1 copolymer containing %.