CH629896A5 - Telephone cable provided with a fault-locating wire having an insulated central conductor - Google Patents

Description

The present invention relates to the field of cables and it aims more particularly at improving the efficiency of the locating wire inserted in long distance telephone cables.

Long distance telephone cables are generally made up of conductors insulated with thermoplastic materials, such as polyethylene, and have a wire, called a localization wire, to signal any accidental penetration of water inside the cable. This locating wire consists of a central conductor, usually made of copper, covered with an insulating layer of cellulose paper. Then, on the assembly formed by the conductors and the locating wire is disposed a belt made up of several tapes made of cellulosic paper. The cable thus obtained is then placed under external mechanical protection, for example under a metallic sheath.

However, before this sheathing, it is necessary to eliminate most of the water contained in the various papers of the core of the cable and in particular in the insulation of the locating wire. The elimination of most of the water present in this localization wire improves its isolation and thus makes it more sensitive to any accidental penetration of water which would lead to destruction of the insulation. This elimination is carried out by drying which is all the more difficult as it is necessary to dry the locating wire to the core, that is to say through a thickness of paper greater than one millimeter. Furthermore, the drying temperature is limited to 60 ° C to avoid deformation of the plastic insulation under the effect of excessive heat.

Under such conditions, steaming for a period of 36 h to 48 h under vacuum is necessary to obtain good insulation of the locating wire.

The object of the present invention is to provide insulation of the locating wire making it possible to avoid steaming and drying, without detracting from its proper role. This implies that the insulation must easily pass through the water, and be implemented without special precautions, therefore having, in particular, an acceptable mechanical resistance.

To achieve this object in accordance with the invention and in the context of the arrangements mentioned in claim 1, the central conductor of the locating wire is surrounded by a first layer of insulation formed by at least one strip of material made of polyester with continuous filaments arranged at random and not welded at all their crossing points.

The insulation layer can easily be crossed by water and has the characteristics of dielectric insulation and rigidity ensuring the level of quality demanded by users. It can, moreover, be implemented without special precautions due to its good mechanical strength.

As an example of polyester fiber ribbons according to the invention, mention may be made of “REEMAY” ribbons (trademark registered by Du Pont de Nemours) and, in particular, “REEMAY” ribbons in 2016 style which have a thickness close to 0, 19 mm, a weight per m2 close to 45 g and a breaking strength in the machine direction of the order of 3.2 kg on a strip of width 15 mm.

By way of non-limiting example, the embodiment of a cable provided with insulation according to the invention will be described below.

The localization wire of this cable is isolated by means of three REEMAY 2016 tapes superimposed, alternating with three 56 g / m2 cellulosic papers. This alternating superimposition improves the dielectric strength and the insulation of the "REEMAY" tape which is already 2000 volts when it is used alone and leads to an insulation higher than 20,000 MO / km without baking and a dielectric strength and a detection time. in contact with water less than 2 minutes.

Around the assembly formed by the conductors and the locating wire is arranged a belt formed by a cellulose paper 0.10 mm HT then three REEMAY 2016 ribbons then finally two creped cellulosic papers 72-100 g / m2. The characteristics obtained by such a belt are good thermal insulation and a dielectric strength greater than 2000 volts.

A summary table highlights the characteristics presented by the locating wire in the cable finished during the control according to the conventional version (cellulose paper) and the version according to the invention (REEMAY tape) without prior drying of the cable.

Location thread Classic version Version according to the invention

Isolation before baking 7 26 400

Mii / km

Isolation after 12 h steaming 3500 26400

MQ / km

Isolation after 48 h steaming 6000 48 000

MQ / km

Such insulation makes it possible to improve the efficiency of the wire for locating long distance telephone cables. It also simplifies the manufacture of these same cables by the total or partial elimination of their baking. The risks of deformation of the insulating layers of thermoplastic materials, such as polyethylene, under the effect of the drying temperature are thus avoided.

s

10

15

20

25

30

35

40

45

50

55

60

65

It is also possible, without changing the effectiveness of the insulation according to the present invention, to vary the composition of the insulation of the locating wire and of the belt by modifying the number and the reciprocal arrangement of the papers.

3 629896

or cellulosic and synthetic ribbons.

Such an improvement is essentially obtained by the total or partial replacement of the cellulosic papers by plastic ribbons of the polyester type with continuous filaments.

B

Claims (6)

629,896 2 1. Telephone cable provided with a central conducting wire constituting a locating wire and aiming to signal any accidental penetration of water inside this cable, said central conductor being covered by a first layer of insulation and said cable being surrounded by a second layer of insulation, called a belt, intended to provide good dielectric strength and good thermal insulation, characterized in that the first layer is formed of at least one polyester ribbon with continuous filaments, said filaments being randomly arranged and not welded at all of their crossing points. 2. Telephone cable according to claim 1, wherein said first layer and / or said second layer is partially formed of cellulosic paper. 3. Telephone cable according to claim 1 or claim 2, wherein the first layer surrounding the conductor of said locating wire is formed of three superimposed polyester tapes alternating with three cellulosic papers. 4. Telephone cable according to one of claims 1 to 3, wherein the belt consists of a superposition of a high-voltage insulating cellulosic paper, three polyester ribbons and two crested cellulosic papers. 5. Telephone cable according to one of claims 1 to 4, wherein the polyester ribbon has a thickness of approximately 0.19 mm, a weight per m2 of approximately 45 g and a breaking strength of l 3.2 kg on 15 mm wide strip. 6. Telephone cable according to one of claims 1 to 5, wherein said central conductor is copper.