Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Patent
1988-02-18
1989-08-22
Hoke, Veronica P.
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
174110SR, 524183, C08K 555, H01B 318
Patent
active
048598100
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to polymer compositions suitable for use in the field of wire and cable insulation and to a process for the production of such compositions. More particularly the invention relates to polymer compositions which exhibit an improved resistance to the initiation and growth of water trees when employed as medium and high voltage electrical insulation.
Polymer compositions suitable for use as insulating layers for electrical cables are well known. Generally, such compositions are based on polyolefins such as, for example, homopolymers and copolymers of ethylene. The polymer compositions may be used as insulation in an uncross-linked form, but preferably the compositions are cross-linked in order to provide improved high temperature properties.
When used as insulation for medium or high voltage power cable, polyolefins tend to undergo a phenomenon known as "treeing". The term "treeing" has been applied to this type of insulation breakdown because the failure path looks somewhat like the profile of a tree. Two types of "tree" have been identified and these are generally known as "electrical trees" and "water trees". It is generally believed that electrical trees are generated by corona discharges causing fusion and eventual breakdown of the polymer whereas water trees tend to occur in solid dielectric material which is simultaneously exposed to moisture and an electric field. Water treeing is therefore a significant factor in determining the useful life of buried medium and high voltage power cables. Water trees tend to be initiated at sites of high electrical stress such as rough interfaces, protruding conductive points, voids or embedded contaminants. Electrical trees and/or water trees can lead to electrical power leakage or even complete breakdown of the insulation.
A number of proposals for retarding the growth of water trees are suggested in the prior art. DT-A-2737430 describes an insulation composition having reduced tendency to form water trees comprising a polyolefin and an alkoxy silane. US-A-4299713 describes an unfilled polymeric composition for electrical insulation comprising a polymeric component and, as a water treeing and electrical treeing inhibitor for the composition, at least one defined organic compound which is a silicon, tin, titanium, phosphorus or boron compound for example, vinyl-tris-(2-methoxyethoxy) silane. The patent does not disclose specific examples of suitable boron compounds.
It is an object of the present invention to provide a polymeric composition suitable for use as electrical insulation having improved resistance to the initiation and/or growth of water trees.
Accordingly the present invention provides a composition suitable for use as electrical insulation comprising a polymeric component and a water tree retardant additive characterised in that the water tree retardant additive is selected from the group consisting of: formula; from 4 to 24 carbon atoms and R.sup.1 and R.sup.2 are individually hydrogen or an alkyl, aryl, aralkyl, alkaryl or cycloalkyl group having from 4 to 24 carbon atoms and hydrocarbyl alcohol.
The present invention further provides a process for preparing a polymeric composition suitable for use as electrical insulation comprising mixing together a polymeric component and a water tree retardant additive characterised in that the water tree retardant additive is selected from the group consisting of: formula; from 4 to 24 carbon atoms and R.sup.1 and R.sup.2 are individually hydrogen or an alkyl, aryl, aralkyl, alkaryl or cycloalkyl group having from 4 to 24 carbon atoms and hydrocarbyl alcohol.
The present invention also includes an electric wire or cable comprising an electrical conductor insulated by an insulation layer comprising a polymeric component and a water tree retardant additive characterised in that the water tree retardant additive is selected from the group consisting of: formula; from 4 to 24 carbon atoms and R.sup.1 and R.sup.2 are individually hydrogen or an alkyl, aryl, aralkyl, alkaryl or cycloalkyl g
REFERENCES:
patent: 2949439 (1960-08-01), Fuchsman et al.
patent: 3131164 (1964-04-01), Doyle et al.
patent: 3193521 (1965-07-01), Jasching
patent: 4211679 (1980-07-01), Mark et al.
patent: 4299713 (1981-11-01), Maringer et al.
Cloetens Rudolphe C.
Umpleby Jeffrey D.
BP Chemicals Limited
Hoke Veronica P.
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