US2334756A - Electric conductor - Google Patents

Description

Nov. 23, 1943. P. E. H. EICHINGER ELECTRIC CONDUCTOR Filed March 6, 1959 zaazzzz er hitherto in these Patented Nov. 23, 1943 UNITED STATES PATENT 'oFF1c-E 2,334,756' Philippe EUIZZZOEFII: France;

vested in the Alien Property Custodian Application March 6, 1939, Serial No. 260,226

a In France March 7, 1938 1 Claim.- 7 (01. 174-,-1o2') The present invention relates to the manufacture of electric wires, cables or conductors composed of one or a plurality of single. 01 divided conducting or resistant cores which are insulated Irom a metal sheath 'by a powdered mineral insulating material.

It has already been proposed, for manufacturing wires, cables and conductors of this category, in particular when the finished product is obtained by elongationof. a suitably dimensioned rough shape, to use a mineral insulating material in the highly compact and totally dehydrated state.

The insulating material usually employed manufactures is ordinary magnesium oxide.

The applicant has proved that the. hitherto employed insulating materials, in particular or.-

dinary magnesium oxide in uncompacted form,

do not possess any natural dielectric strength and the breakdown voltage of the conductors they serve to form is of the same order of magnitude as it the insulating layer were replaced by air.

In fact, the breakdown voltage is, on an average, about 3,000 volts when the thickness of the insulating material is 1.5 mm. and 4,500 volts when the thickness reaches 3 mm., etc.

Now, these are precisely the breakdown voltages of conductors composed of a cylindrical core and of a likewise cylindrical outer sheath which are separated by air, the constant distance between the two armatures of the condenser thus formed being, according to cases, respectively 1.5 mm., 3 mm., etc.

It would therefore appear that, in these conductors, everything takes place as though the purpose of the insulating material employed was to define. and ensure the. geometrical position of the core in the transverse section of the sheath, without increasing the dielectric strength of the conductor. I 1

The drawing illustrates a cross section of a conductor made in accordance with the present invention.

The present invention provides a very conuncompacted insulating material used naturally possesses a property of dielectric strength that is only equal to that or air.

For this purpose, during its manufacturing process, the conductor will be subjected to a treatment of such a nature as to allow per-' manent pressures to subsist in the insulating material which substantially increase its dielectric strength.

Research work done by the applicant has shown him that the dielectric strength of a powdered mineral insulating material is, to a certain extent, proportional to the value of the pressures which -may occur between the particles of the insulating material. Now, for a conductor which is in the process of manufacture and at a certain phase of drawing, such pressures vary within wide limits, according to whether the metal of the sheath is in the coldhammered state or whether on the contrary it has just been annealed.

It will in fact be understood that, everything being equal, said pressures of the insulating material are greatest when the conductor has just undergone the final drawing operation'durin which it has reached its final dimensions, since economy is naturally an incentive to continueplaced in position and installed. I

siderable improvement in the processes for man- I uiacturing conductors of this category.

Said invention consists in imparting to the insulating material by an appropriate treatment, a property of dielectric strength which it does riot naturally possess and which will hereinafter be called extrinsic dielectric strength, so that the conductor will be characterized by a higher breakdown voltage than that of air, even if the By annealing the conductor, the insulating material will lose the state of pressure in which it was,- and its extrinsic dielectric strength will disappear with it.

Now, the applicant has proved that the state of pressure of the-insulating material varies to a very. slight extent between the instant when a conductor which has been annealed is' subjected for example to a very slight pass even without elongation of the rough shape, and the instant when, on the contrary, drawing. iscontinued up to the limit beyond which a break would be produced.

Thus, if the sheath of a previously drawn and annealed conductor is' very slightly" cold-ham- Jmered or shaped, i'or example by anappropriate additional pass, in such a manner as not to exceed for example Sjifof the total elongation" 2 01 the metal, it is found that the resilient pressure or the insulating material has returned to very substantially its maximumvalue, and'with it has realized its highest extrinsic dielectric strength, although the conductor can still undergo 95% oiits elongation and consequently, in

practice, still leaves the conductor itself with all 1 its mechanical flexibility;

It is an easy matter in practice to ascertain the extent of said additional pass. It may be said that it can ,be chosen in such a manner as to properties and in particular its "shape" the sheath until the instant-when. the

insulating material reaches the limiting pressure (defined in French Patent No. 795,277) that is to say until the instant when a more considerable pass, however small it may be, would cause the same sample of conductor which has beensubjected to an annealing treatment only.

In a practical example, a conductor of about 5.3. mm. outside diameter or sheath and having I an insulating layer of about 1.5 mm. thickness made of a mineral with no property of intrinsic dielectric rigidity, ordinary magnesium'oxideior example, is characterized by a breakdown voltage of about 3,000 volts, after the last annealing operation of the series or metallurgical treatments of the manufacture and ii the process Just described is not applied. If, on the contrary, a very slight shaping is eflected, for example by a drawing operation which reduces the outside diameter of the sheath to, 5.2, the breakdown voltage of the same conductor becomes higher than 4,000 volts.

Of cOurse the invention applies whatever be the number of cores of the conductor, the metal which they and the sheath are made of and the particular refractory powdered insulating material used. Said invention covers, by way oi new industrial products, conductors of the above mentioned category wherein the dielectric rigid property of extrinsic dielectric strength and in particularly the use, for the manufacture of the.

electric conductors in question and whatever he the process employed for carrying it out, of the method of operation of shaping the sheath, which method is characterized by the fact that the metals of the sheath and of the core have both retained almost their entire capacity of cold hammering and even of their property or elongation,

and by the further fact that the dielectric strength of the insulating "material of the conductor in the latter state considered is at least ity is at least 20% greater than the rigidityof the same conductor which has ing only.

Iclaim:

An electric conductor'comprising at least one condueting core, a metallic sheath and powdered min'eral insulating material interposed between said core and sheath, the said insulating material being under a pressure 01' such magnitude that its dielectric strength is at least 20% greater than the dielectric strength would be in the absence of pressure, said conductor being capable of elongation withoutrupture u to 95% of the elongation of which it would be capable in the absonce ofpressure, and possessing substantially the ca- 20% greater than the dielectric rigidity of the pacity for being bent which is characteristic of the conductor in annealed state;

emu EU ENE mm mcnmonaf undergone anneal-

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