US 2348752 A
Description (OCR text may contain errors)
Patented May 16, 1944 2,348,752 ELEc'rmc CABLE Joshua Creer Quayle, Ashton, Chester, England, assignor to International Standard Electric Corporation. New York, N. Y.
i Application November 8, 1941, Serial No. 418,406
- In Great Britain September 17, 1940 7 Claims.`
This invention is concerned with cables, in which` a large part of the dielectric surrounding a conductor, particularly that in close proximity to the conductor, is formed of air, the conductor being spaced from its surroundings by solid material which occupies only a small proportion of the intervening space. In particular, it relates to that type of such cables in which the spacing is effected by a cord or string of insulating material wound over the conductor as an open helix. In some cases twoy helices may be arranged c oaxially and may occupy co-axial annular regions one outside the' other. two helices are of different pitch, or of diierent hand, or of both these diierences.
Such cables are most commonly used for communication purposes and -are employed where currents of relatively high frequency have to be transmitted, ,such cables being adopted because their construction is conducive either to low dielectric loss or to lowcapacity between the conductor and surrounding conductive bodies,
or for both of these reasons.
It is obviously desirable that in such cables the spacing helices should be of material which has low loss in the circumstances of its use. It is also desirable that the material should be readily capable of taking up a helical form and retaining this form, that is to say, it should be substantially self-supporting in the open helical disposition around the conductor when it has been formed into that shape. It has been .found that certain natural or artificial thermo-,plastic materials have the desired properties. On the other hand, a material which is thermo-plastic. while it can readily be placed in position and given the desired shape, has the tendency to yield under the pressure of the conductor, particularly if the cable is bent and/or if the temperature should rise above normal conditions. n such cases the conductor may be displaced from4 its intended position and thereby its electrical properties may be disturbed with corresponding ill eilects on the operation of the circuit of which it forms part.
The present invention provides an improved form of cable of the kind indicated, in which the helical spacer (or spacers) is formed of ne glass bres built up inthe form of cords or tapes and having embodied therein, and/or coated thereon, a suitable binding material. Suitable materials are plastics which have at normal atmospheric temperature a suiiicient rigidity to maintain their position in and on the `groups of bres and bind the bres together, and which have electric losses v vcount o f itsfilling or coating can readily be' In these latter cases the of a low order when operating under the conditions for which the cable is required, particularly at the range of frequency concerned. They are found in the classes known as thermo-plastic materials, thermo-setting materials, and cellulose esters and-ethers; e
By this combination of glass bres and binding material is produced a member which on account of its rigid skeleton of glass fibres will not be distorted when the cable is bent nor yield under the pressure of the conductor and on acformed, by the aid of heat, if necessary, into an open helix and will maintain this form subsel quently.
The glass skeleton of the' helical members may be in the form of roving, yarn or string, that is to say, fibres twisted together more or less, or it may consist of fibres laid side by sideA and bonded together solely by the binding material. 'I'his material must be applied in a liquid, or semi-liquid, state, which may be arrived at by the aid of a solvent, or by emulsifying, or by softening with the aid of plasticizers and/or heat. 'Examples of suitable materials are polystyrene, polythene that is thenormally solid products of the polymerisation of ethylene-Oppanol (registered trade-mark)that is polymerised isobutylenethermo-setting resins of the Novolak type, cellulose triacetate, and ethyl cellulose. It will be clear that if these are used with plasticisers, or
. any other added materials, .such materials should also have low loss characteristics. It will be understood that the binder will be applied to the spacing element before the latter is applied to the conductor.
A conductor with the helical spacing element,
Aor elements, of the kind indicated, may be built up in to a complete cable in known manner; for instance, it may be enclosed in an outer conductor forming a substantially complete tube with or Without the interposition of a tube of dielectric material. Alternatively, two or more conductors with their spacers can be combined together in a single cable.
Two forms of construction'of cable, in accordance with` the invention are shown as examples in the accompanying drawing wherein- Figure l is a longitudinal sectional view of one form;
Figure 2 is a similar view of the'second form of construction;
Figure 3 is an end sectional view of the cable shown in Figure 2; and
Figure 4 illustrates another modification.
In Figure 1 the cable comprises a central wire conductor l around which is wound an insulating spacing member 2. The latter has the form of an open helix of relatively long pitch and consists of a string made from tine glass fibres impregnated with an insulating binding material. Around the spacing member is disposed an insulating tubular member 3 example, a glass nbre braided tube or it may be a tube made of polythene. The assembly is surrounded by a conducting tubular member I made of wire braid.
The cable in Figures 2 wireconductors 5, i5
and 3 comprises two provided respectively with spacing members l and 8 each having the form of an open helix. The conductor 5 and spacing member 1 are enclosed in a tubular member 9 and the conductor t and spacing member in a tubular member 9 and I0 are made of glass nbre braid or of polythene, and are enclosed in a tubular member Il which is itself enclosed in a conducting tubun lar member l2 of wire braid. The tubularmember Il is of glass fibre braid or of polythene. The complete assembly space cable.
In Figure 1 the conductor I and in Figures f. and 3 the conductors E and 5 are surrounded largely by air as the dielectric material.
Fig. 4 illustrates a modification of the construction shown in Fig. l wherein two helices I4 and i5 are arranged coaxially around a central conductor l so as to occupy coaxial annular' regions, one outside the other.
What is claimed is:
l. An air space electric cable comprising in combination a pair oi conductors, a, spacing member surrounding each conductor in the form of a cord arranged in an open helix' and comprising a skeleton of glass ilbres bonded together with a thermo plastic dielectric binder, a tube of dielectric material surrounding each said forms a at twin air which may be for i it. The tubular members spacing member and a conducting screen embracing both-said tubes to form a flat twin air space cable. v
2. An air space electric cable as claimed in claim 1 wherein said tubes of dielectric material are composed ofbraided glass libres.
3.An air space electric cable as claimed in .claim 1 wherein said tubes of dielectric material are composed of polythene.
4. An air space electric cable as claimed in claim 1 wherein said tubes of dielectric material are enclosed in a tubular member of dielectric material positioned between said conducting screen and said tubes.
5. .An air space electric cable comprising a conduit, a conductor within the conduit and a spacing member between the conductor and the conduit, said spacing member being in the form of a cord of insulating material comprising glass bers pre-impregnated and bound together with a thermo plastic dielectric binder, wound in an open helix around the conductor and leaving substantial air space between the conductor and the conduit.
6. An air space electric cable comprising a conduit, a conductor within the conduit and al spacing cord wrapped in a loose helix around the conductor between the conduit and the conductor, said spacing cord being formed of ne glass bers impregnated with an insulating binding material, and being substantially unyielding under pressure.
'7. An air space electric cable comprising a conduit, a conductor concentrically within the conduit and a spacing cord wrapped in a loose helix around the conductor between the conductor `and the conduit, said cord containing a skeleton of iine glass fibers bound by a thermoplastic material and being substantially nondeformable and unyielding.
JOSHUA CREER QUAYLE.