Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Patent
1995-11-29
1998-06-30
Kincaid, Kristine L.
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
29854, H01B 732
Patent
active
057737614
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for producing an electric cable, wherein a short-circuiting layer is provided between an insulated conductor/insulated conductors and a protective covering surrounding the conductor/conductors, the short-circuiting layer comprising short-circuiting wires extending substantially parallel with the conductor/s, and a contact member positioned substantially transversely with respect to the short-circuiting wires and connecting the wires electrically. The invention also relates to an electric cable.
BACKGROUND AND PRIOR ART
Power cables are provided at the production stage with a special short-circuiting layer between the insulated cable conductors and the protective outer covering. The layer consists of mutually spaced short-circuiting wires, also called neutral wires, that extend longitudinally of the cable. The layer of short-circuiting wires surrounds all of the conductors. Short-circuiting wires running in parallel with each other are connected electrically together by a contact member extending helically upon the short-circuiting wires. The contact member is often formed as a metal ribbon. The purpose of the short-circuiting layer is to protect the conductors against external strains and to cause a short-circuit between the wires and the conductors if an external object, such as a spade, excavator bucket, crowbar, or other similar object penetrates through the protective covering of the cable up to the conductor for one reason or another.
An example of the prior art cable structures utilizing short-circuiting wires and a contact member formed of metal ribbon is disclosed in U.S. Pat. No. 4,360,704.
Another example of a prior art structure is described in Finnish Patent Application 911 600.
The short-circuiting layer of the cable is usually made by stranding the short-circuiting wires and the contact member connecting them by a cage-type stranding machine around the insulated conductors of the cable, after which the protective covering is formed upon the short-circuiting wires. This type of production is, however, slow and complicated. One factor contributing to the slowness of the production process is the use of ribbon as the contact member, as ribbon material is relatively difficult to handle. Another problem with ribbon material is that it is available only in limited continuous lengths, e.g. 1,500 m, which is the maximum continuous length of usable ribbon available. Still another problem is that when the contact member is made of ribbon material, the cable has a great bending stiffness and is thus relatively difficult to handle. The poor handling properties of ribbon also causes problems upon connecting the cable as the ribbon has to be exposed over a length such that the connecting point can be reached. The handling properties of ribbon material are also not the best possible in view of the connecting work itself. Moreover, ribbon material is expensive, so that its use increases the production costs.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method for producing an electric cable by means of which the drawbacks of the prior art can be avoided. This is achieved by a method according to the invention, which is characterized in that the contact member is formed of a bundle of several wires. The electric cable according to the invention is characterized in that the contact member is formed of a bundle of several wires.
A major advantage of the invention is that the cable production process will be speeded up substantially as compared with the prior art technique as a bundle of wires is simple to handle as compared with ribbon material. Another advantage is that, in practice, the length of the contact member has no upper limit, as wire material is available in continuous lengths of tens of kilometres. Still another advantage of the invention is that the completed cable is considerably less stiff than a corresponding cable made by the conventional technique. Due to the increased flexibility the cable according to the
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Hagelberg Torsten
Hartikainen Jukka
Kaakko Eero
Korhonen Pertti
Luoma Pekka
Kincaid Kristine L.
Machtinger Marc D.
Nokia Kaapeli Oy
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