Surge attenuating cable
First Claim
1. A shielded power cable comprising inner and outer conductors separated by a cable insulation system, the cable insulation system comprising at least two coaxial layers defining a displacement current path between the conductors for high frequency currents, namely an inner semiconductive layer presenting a conductance G1 and a capacitance C1 per unit length of cable, and an outer insulating layer presenting a capacitance C per unit length of cable, wherein the conductivity, relative permittivity, and thickness of said inner semiconductive layer are such that the power loss per unit length of cable is maximized with respect to the conductance G1 at least over the frequency range 0.1 MHz-50 MHz.
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Accused Products
Abstract
In a shielded power cable of the type comprising inner and outer conductors separated by cable insulation defining a displacement current path between the conductors for high frequency currents, the cable insulation incorporates one or more coaxial layers of semiconductive material consisting of cable insulation material loaded with a conductive filler, such as carbon fibres or spheres. The semiconductive layer is designed to maximize high frequency losses thereby to facilitate attenuation of high voltage surges caused by lightning or by switching.
56 Citations
16 Claims
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1. A shielded power cable comprising inner and outer conductors separated by a cable insulation system, the cable insulation system comprising at least two coaxial layers defining a displacement current path between the conductors for high frequency currents, namely an inner semiconductive layer presenting a conductance G1 and a capacitance C1 per unit length of cable, and an outer insulating layer presenting a capacitance C per unit length of cable, wherein the conductivity, relative permittivity, and thickness of said inner semiconductive layer are such that the power loss per unit length of cable is maximized with respect to the conductance G1 at least over the frequency range 0.1 MHz-50 MHz.
- 2. A shielded power cable comprising inner and outer conductors separated by a cable insulation system, the cable insulation system comprising at least three coaxial layers defining a displacement current path between the conductors for high frequency currents, namely the inner semiconductive layer presenting a conductance G1 and a capacitance C1 per unit length of cable, an outer semiconductive layer presenting a conductance G2 and a capacitance C2 per unit length of cable, and an intermediate insulating layer presenting a capacitance C per unit length of cable, wherein the conductivities, relative permittivities, and the thicknesses of said semiconductive layers are such that the power loss per unit length of cable is maximized with respect to both said conductance G1 of the inner semiconductive layer and said conductance G2 of the outer semiconductive layer at least over the frequency range 0.1 MHz-50 MHz.
- 4. A shielded power cable comprising inner and outer conductors separated by a cable insulation system which provides a displacement current path between the conductors for high frequency currents, the cable insulation system incorporating at least one semiconductive layer arranged coaxially therewith having a conductivity which remains substantially constant and a relative permittivity which does not exceed about 12, over the frequency range 0.1 MHz-50 MHz.
- 6. A shielded power cable comprising inner and outer conductors separated by a cable insulation system, the cable insulation system comprising three coaxial layers defining a displacement current path between the conductors for high frequency currents, namely an inner semiconductive layer, an outer semiconductive layer, and an intermediate insulating layer, wherein the materials of said semiconductive layers is an extrudable polymeric material loaded with a low structure particulate conductive filler, and wherein the material of said layers has a conductivity which remains substantially constant, and a relative permittivity which does not exceed about 12, over the frequency range 0.1 MHz-50 MHz.
- 11. An electrical power transmission system comprising inner and outer coaxial conductors separated by an insulation system, the insulation system extending longitudinally with respect to the conductors and comprising at least two coaxial regions defining a displacement current path between the conductors for high frequency currents, namely an inner region consisting of a semiconductive layer presenting a conductance G1 and a capacitance C1 per unit length, and an outer non-conductive region presenting a capacitance C per unit length, characterized in this that the conductivity, relative permittivity and thickness of said semiconductive layer are such that the power loss per unit length of the transmission system is maximized with respect to the conductance G1 at least over the frequency range 0.1 MHz-50 MHz.
Specification