Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1993-10-15
1995-05-16
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524496, 252500, 252511, 525535, 525540, 528377, 528423, C08K 304, H01B 100
Patent
active
054161550
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a material for semiconductive screening and to use of the material in manufacturing cables and in electromagnetic shielding of electrical and electronic apparatus.
In a conventional configuration, a cable is constituted by a length of twisted-together metal strands, which length is covered by copper foil and surrounded by an insulating sheath, e.g. made of polyethylene. In another conventional configuration, given by way of example, the twisted-together metal strands are directly covered by an insulating sheath. Such cables are used on a very large scale in various fields, such as telecommunications, transporting power, etc. Such cables convey electromagnetic energy in DC form or at low, high, and very high frequency with or without repeaters. When in use, such cables are therefore subjected to electric fields and to space charges, characterized by depolarization currents with high time constants, which currents, for certain polarization voltages, give rise to anomalies in behavior.
In those configurations and in other conventional configurations where the insulating sheath is, for example, placed on the body of the cable, which cable body is either a central or an outer body, the maximum field is situated at the conductor-insulator interface. A typical value for the field lies in the range a few kV/mm to about ten kV/mm. Therefore, the interface is particularly stressed. In addition to the maximum field being localized, there are problems of conductor uniformity. If the conductor has irregularities, they generate concentrations of electric field, and this in turn reduces the capacity of the cable to withstand voltage gradients. It is therefore necessary to increase the thickness of the insulation so as to ensure that no breakdown will occur even if there are projections. Such a solution is expensive.
The problem of insulation size is particularly critical at splices, at branches and at the ends of high tension cables.
The problems encountered when using and making cables also occur in substantially the same way in electrical energy storage devices, and in particular in capacitors. Such problems also occur when using electrical or electronic equipment in which an insulator protects a region containing apparatus sensitive to an electric field source. For example, the source may be a current generator, electrical cables or pins, transmitter antennas, etc. For example, the sensitive apparatus may be measuring apparatus, an F.M. type receiver, or printed circuits of the type contained in a micro-computer. In all these types of apparatus, it is necessary to insert an insulator which is sometimes situated in direct contact both with the equipment and the source of the field.
In order to mitigate these problems, it has been proposed to interpose a semiconductive screen between the conductor and the insulator, or between the source and the insulator. Semiconductive screening used up until now is formed of carbon black dispersed in an extruded, calendered or molded matrix usually formed of EVA (ethylene vinyl acetate) or EBA (ethylene butyl acrylate). The main drawbacks with that type of semiconductive screening are that its conductivity remains constant as a function of field, and that it does not make it possible to reduce the volume of insulation sufficiently.
It has also been proposed, e.g. in Document WO 90/09027, to make semiconductive screening from an intrinsically conductive composite material constituted by a polymer matrix, e.g. made of polyolefin, polyvinyl chloride, or polystyrene, which matrix has a substituted polythiophene incorporated therein. The conductivity of such a material is a function of the quantity of doping agents it contains. But the very presence of the doping agents is a major drawback to the physical and chemical stability of the screening under high tension, and in the presence of a high electric field.
An object of the present invention is to implement a material for semiconductive screening, which material has a conductivity that increases as a fun
REFERENCES:
patent: 4971726 (1990-11-01), Maeno et al.
patent: 5294694 (1994-03-01), Epstein et al.
Aladenize Bernard
Franquinet Claude
Galaj Stanislas
Hannecart Etienne
Le Mehaute Alain
Alcatel Cable
Michl Paul R.
Solvay
Yoon Tae H.
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