US1969911A - High voltage terminal construction - Google Patents

Description

1934- F. 5. SMITH HIGH VOLTAGE TERMINAL CONSTRUCTION Filed Ja11. 26, 1951 I NVENTOR 27/4444? 'ITORNEY Patented Aug. 14, 1934 UNITED STATES PATENT OFFICE HIGH VOLTAGE TERMINAL CONSTRUCTION Franklin S. Smith, Brooklyn, N. Y.

Application January 26, 1931, Serial No. 511,308

16 Claims. (01. 173-318) This invention relates to terminal construction.

One of the objects of this invention is to provide a thoroughly practical terminal construction for dependably leading a plurality of relatively high voltage conductors between which exist relatively small potential differences through a wall member, such as the wall of a transformer or condenser casing, for example. Another object is to provide a construction of the above-mentioned character which will be inexpensive, simple, capable of rapid manufacture and assembly, and capable of thoroughly dependable action in practical use. Another object is to provide a single high voltage terminal construction capable of dependably handling a number of high voltage conductors in such a way as to avoid the necessity of employing a separate high voltage terminal insulator for each conductor. Another object is to provide a high voltage terminal construction well adapted to meet the peculiar conditions of practical use met with, for example, where it is necessary to insulate, for relatively high voltages, a number of conductors passing through a wall member, even though the potential'difference between the conductors themselves is relatively low. Another object is to provide a terminal construction of the above-mentioned character that will be well adapted to meet the varying conditions of hard practical use. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, and arrangements of parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of various possible embodiments of my invention,

Figure 1 is a central vertical sectional view of the terminal construction illustratively shown as applied to a transformer, certain parts of the latter being shown diagrammatically or broken away, and

Figure 2 is a diagram of a circuit illustrative of one of the various conditions met with in practical use and which the terminal construction of Figure 1 adequately meets,

Similar reference characters refer to similar parts throughout the several views in the drawing.

Referring now to the drawing and particularly to Figure 1, I have diagrammatically shown a transformer 10-11 which may, for purposes of achieving a better understanding of certain features of my invention, be considered as a socalled current transformer, the winding 10 of which is adapted to carry the entire, or a portion of the, current flowing, for example, in a high tension transmission line, the latter being indicated by the conductors 12, 13 and 14 and the secondary winding 11 of which is connected to a current-indicating instrument 15. In so far as certain features of my invention are concerned, the current transformer 10-11 may be of any suitable construction, but preferably the transformer is contained within a hermetically sealed tank or casing 16 containing a suitable gaseous dielectric under pressure, such as nitrogen under a (0 pressure on the order of fifteen atmospheres, within which the transformer 10-11 is immersed, the gaseous dielectric under pressure coacting with suitable solid dielectrics in achieving insulation between the windings l0 and 11. The casing 16 is preferably of steel and of suificient strength to withstand pressures on the order of that abovementioned and, though the casing 16 is broken away in Figure 1, it is to be understood that the low potential conductors 17-18, which lead from so the winding 10 to the instrument 15, are passed through suitable insulating terminals, or the like, associated with the wall of the casing 16.

Preferably the casing 16 is grounded and, assuming the illustrative circuit shown as a transs5 mission line to have effective across its line conductors a potential on the order, for example, of 150,000 volts, it is necessary that the windings 10 and 11 be insulated from each other safely to withstand this potential difference and for this purpose I prefer, as above pointed out, to use the gaseous dielectric under pressure in coaction with solid dielectric material. Thus the circuit of the instrument 15 may be insulated from the primary winding 10, the latter being wholly at a relatively 5 high potential, above assumed to be on the order of 150,000 volts, with respect to the ground, though the actual potential difference across the terminals of the winding 10, which, as above noted, is substantially in'series with one of the line conductors of the high transmission line, may be relatively small compared to the potential difference of 150,000 volts.

It is, however, likewise necessary effectively to insulate the conductors passing through the transformer casing 16 not only with respect to each other, and hence with respect to the potential difference existing between them, but also with respect to the relatively very high potential difference (above assumed to be 150,000 volts) existing between the conductors and the ground ed transformer casing 16, thus further to insure effective electrical isolation of the circuit of the current instrument 15, the conductors leading to which pass, as above noted, through the transformer casing.

As illustrative of another condition sometimes met with in practice and which my invention effectively meets, I have shown in Figure 2 an X-ray tube 19 across the filament cathode and the anode 21 of which is connected a suitable source of relatively high voltage, illustratively in the form of a transformer 22 connected through a suitable rectifier 23, for energizing the X-ray tube. The filament of the cathode 20, though forming part of a high voltage circuit, requires but a relatively small voltage for supplying it with heating current and this relatively low voltage may be supplied from a low voltage winding 10 of a transformer, the secondary winding 11 of which may be connected to any suitable source of alternating current, such as a 110-volt commercial supply circuit. The conductors l3 and 14 connecting the filament cathode 20 to the winding 10' of thetransformer are at a high potential with respect to the potential of the winding 10 or of the casing 16 housing the transformer, and the conductors 13 and 14 must be brought into the casing 16 in a manner not only to insulate the conductors from each other but also to insulate both conductors from the transformer casing and from the circuit of the winding 11.

To meet these peculiar practical conditions I provide the transformer casing 16 with a suitable opening into which is fitted a metallic bushing 24, preferably flanged as at 25, the flange abutting against the inner periphery of the opening in the casing wall 16 and the bushing being welded to the wall 16, as is indicated at 26. The bushing 24 may be considered as forming an extension of the opening through which the high voltage conductors leading to the low voltage winding of the transformer are to pass.

Secured in fluid-tight connection to the bushing 24 is a tube-like housing 27, preferably of integral construction, and preferably made of molded phenolic condensation product or Bakelite. The bushing 24 is preferably threaded exteriorly and the housing 27 threaded interiorly at its lower end, thus to secure a good mechanical interconnection well able to withstand the high pressure of the gaseous dielectric, and the coacting surfaces of the threaded portions having interposed therebetween a suitable cement, such as a compound of shellac and tar, for insuring fluidtightness. This housing 27 extends upwardly in a manner and to an extent more clearly set forth hereinafter.

At its upper end the housing 27 supports a metallic sleeve-like member 28, the latter being exteriorly threaded at its lower portion and being in threaded engagement with the interiorly threaded upper end portion of the housing 27, the connection between these two parts being substantially similar to that above described in connection with the bushing 24 and the lower portion of the housing 27.

The sleeve 28 extends upwardly and beyond the upper end of the solid dielectric member 27, being preferably of smaller outside diameter at this upwardly extending portion which also is exteriorly threaded for threaded engagement interiorly with a member 29 of solid dielectric material such as molded phenolic condensation product or Bakelite. The member 29 is shaped so that the external surface of an intermediate portion 28 of the sleeve is exposed to the atmosphere and between the two members 27 and 29, for a purpose more clearly set forth hereinafter and it substantially closes the upper otherwise open end of the sleeve 28.

The lower portion of sleeve 28 has secured thereto a rigid conductor, preferably in the form of a tube 30 which extends downwardly through the opening in the bushing 24, being held substantially concentrically with respect to the bushing 24 and also with respect to the solid dielectric housing 2'7. At its lower end the tubular conductor 30 is connected in any suitable manner, as by means of a wire 39, to one terminal of the current winding 10 of the transformer l0--l1.

The exposed intermediate portion 28 of the sleeve 28 is provided with suitable means for making an electrical connection thereto exteriorly, and this means may take the form of a split ring member 32 clamped about the portion 28 as by the clamping screw 33, a suitable post or stud 34 being carried by the member 32 and extending upwardly adjacent the solid dielectric portion 29 and being provided in turn with suitable means such as a binding screw for connecting thereto one of the high voltage conductors, as the conductor 13.

The upper portion of the solid dielectric mem ber 29 has extending therethrough a metal stud 35 having a threaded portion 36 in threaded engagement with the member 29, the threaded col nection being sealed by a suitable cement, as above-mentioned, to secure fluid-tightness. The stud 35 extends upwardly out of the housing member 29 and is provided with a suitable connecting device such as a binding screw in order that the other of the two high voltage conductors, such as the conductor 14, may be electrically connected thereto.

The shank portion of the stud 35 will be seen to be arranged concentrically with the interior end the conductor or bar 38 is connected, as by wire 59, to the other terminal of the current winding 10 of the transformer 10-11.

As will be made clearer hereinafter, the solid dielectric means, particularly the portion 27, is of substantial length and hence the concentrically arranged conductors 30 and 38 are likewise of substantial length; in order to safeguard against possible short-circuiting between these two conductors, in case the conductor 38 is of flexible construction, I surround the conductor 38 with any suitable solid dielectric material generally indicated at 40. This material 40 may take any suitable form; for example, it may comprise a tube or solid-dielectric material such as Bakelized paper.

The spaces between the housing members 27 and 29 and the concentrically arranged but spaced conductors 38-30 is filled with gaseous dielectric under pressure such as nitrogen under a pressure on the order of fifteen atmospheres, this dielectric coacting with the solid dielectric members in achieving effective insulation between certain parts of the construction.

The gaseous dielectric'under pressure has a dielectric strength of a very high order and,

though the potential difference between the bushing 24 and the conductors 38-30 is relatively very high, above assumed for illustrative purposes to be about 150,000 volts, I am enabled to achieve relatively small dimensions of these parts since this excellent dielectric exists preferably alone in the field of highest voltage gradient, namely, in the dielectric field between these conductors and the bushing 24. The gaseous dielectric under pressure also extends between the concentric interior walls of the sleeve 28 and the tubular conductor 30 and the exterior wall of the stud 35, and the space between these walls I may make relatively very small because a relatively thin layer of gaseous dielectric under pressure suflices safely to insulate these portions from one another, these portions having existing therebetween but a relatively small potential difference.

' I am also enabled to space the stud 35 relatively closely to the upper end of the sleeve 28, due to the unique action of the gaseous dielectric under pressure in increasing the surface resistance to the passage of leakage currents from one to the other along the interior surface of the solid dielectric member 29. And by way of illustration merely, I might note that this spacing, for a given voltage, may be as small as one-tenth, where I employ the gaseous dielectric under pressure as above-mentioned, as would be the case if this gaseous dielectric medium were absent.

On the other hand, the solid dielectric member 29, having its exterior surface exposed to the atmosphere, will be seen to be so shaped and so related to the stud 35 and the exposed portion or portions of the sleeve 28 that the possible surface leakage path along the outside surface of the member 29 is long enough to safely preclude surface leakage at the'existing potential difference between these two conductive members.

Moreover, the space between the stud 35 and the sleeve 28, being subjected to a field of highest voltage gradient (considering the potential difference between these two parts), is filled with the gaseous dielectric under pressure and this spacing may therefore be made relatively small in view of the high dielectric strength of the intervening dielectric medium. The solid dielectric member 29 is also proportioned so as to be in the field of relatively lowest voltage gradient between the conductive members 35 and 28, and at intermediate voltage gradients the solid dielectric material is in series with the gaseous dielectric under pressure.

The sleeve member 28, carrying as it does the high potential conductor 30 and also supporting the high voltage conductor 38 through the solid dielectric member 29 and the stud 35, is, with these other high potential parts, (such as stud 35 and solid dielectric member 29) insulated from the grounded bushing 24 or grounded wall member 16 by means of the solid dielectric material 27 which, aside from being of sufficient thickness to safely withstand the high pressure of the gaseous dielectric, is shaped, substantially as indicated in Figure 1, whereby it is positioned in the field of lowest voltage gradient existing between these high voltage parts and the grounded parts, and is made of sufiicient length so that this voltage gradient is one which it can per se safely withstand. At intermediate portions the gaseous dielectric under pressure is in series with this solid dielectric material 2''! in fields of intermediate voltage gradients, while the gaseous dielectric under pressure also acts to minimize the possibility of the surface leakage from the sleeve 28 along the interior surface of the solid dielectric member 27 to the bushing 24.

In electrical connection with one of the high voltage conductors, preferably the conductor 30, is a sheet metal so-called corona shield 41 shaped substantially as indicated in Figure 1. This shield 41 conveniently rests upon the upper end of the solid dielectric member 2'7 and is mechanically and electrically connected to the ring member 32 as by a suitable number of screws 42. The shield 41 will be seen to extend laterally of and about the exposed connecting binding posts 34 and 35 and coacts with a suitable shield 43 extending about the lower portion of the terminal construction and connected in any suitable manner, as by grounding upon the tank or casing 16, to the bushing 24.

The shields 41 and 43 coact with each other to prevent an olherwise greater concentration of flux along the outer surface of the solid dielectric member 2'7. In addition, the member 41, by shielding the exposed angular portion of the sleeve 28 and also members 32, 33 and 42, prevents the formation of corona thereon.

I preferably so proportion the inner radius of the bushing 24 and the outer radius of the conductor 30 that these two concentrically arranged members form a fast discharge gap, that is, a gap across which disruptive discharge takes place without being preceded by corona and these parts are proportioned so that break-down occurs at a voltage below that at which injury to the apparatus, such as the transformer 10l1, would take place, and by this means I am enabled adequately to safeguard the apparatus against transients, and the like.

The radii of the stud 35 and of the inner surface of the sleeve 28 are similarly proportioned to form a fast discharge gap so that any currents of abnormal characteristics or voltages, such as those mentioned above, as might be initiated in or occur in the high tension circuit, are discharged across this fast gap 3528 and thence across the fast gap 30--24, these two fast gap: being in series. Such abnormal potentials are thus quickly discharged to ground.

Thus it will be seen that there has been provided in this invention a high voltage terminal construction in which the various objects hereinabove pointed out, together with many thoroughly practical advantages, are successfully achieved. It will be seen that a number of relatively high voltage conductors may be dependably insulated, not only from each other but also from associated circuits or parts, and that I am enabled to achieve these and other advantages with a construction that is simple, inexpensive, durable, and of thoroughly dependable action. It will furthermore be seen that the construction is well adapted to mee; the varying conditions of hard practical use.

As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a high voltage term'nal, in combination, a wall member having an opening therein and having a conductive bushing secured thereto and forming substantially an extension of said opening, a plurality of spaced conductors maintained at potentials relatively high with respect to the potential of said bushing but the potential difference between which is relatively small, said conductors passing through said bushing and being concentrically arranged with respect to each other and with respect to said bushing, a tube-like housing of solid dielectric material secured in fluid-tight relation to said bushing and extending about said conductors with a space therebetween, a metallic sleeve-like member having one end thereof in fluid-tight relation with the other end of said housing and having the outermost of said conductors secured thereto, said sleeve member having an inside diameter greater than the outside diameter of an inner conductor, a solid dielectric member secured in fluid-tight relation to the other end of said sleeve member and substantially closing the latter, conductive means passing in fluid-tight relation through said solid dielectric member and supporting said inner conductor, said means being adapted to have an electrical connection made thereto at its outer end, means for making an electrical connection to a portion of said sleeve member intermediate of said housing and said solid dielectric member, and a gaseous dielectric under pressure filling the spaces between said concentric conductors and between the latter and said housing and said bushing and between said inner conductor and said sleeve member and said solid dielectric member, said housing and said gaseous dielectric being proportioned to withstand said relatively small potential difference between said two conductors.

2. In a high voltage terminal, in combination, a wall member having an opening therein and having a conductive bushing secured thereto and forming substantially an extension of said opening, a plurality of spaced conductors maintained at potentials relatively high with respect to the potential of said bushing but the potential difference between which is relatively small, said conductors passing through said bushing and being concentrically arranged with respect to each other and with respect to said bushing, a tube-like housing of solid dielectric material secured in fluid-tight relation to said bushing and extending about said conductors with a space therebetween, a metallic sleeve-like member having one end thereof in fluid-tight relation with the other end of said housing and having the outermost of said conductors secured thereto, said sleeve member having an inside diameter greater than the outside diameter of an inner conductor, a solid dielectric member secured in fluid-tight relation to the other end of said sleeve member and substantially closing the latter, conductive means passing in fluid-tight relation through said solid dielectric member and supporting said inner conductor, said means being adapted to have an electrical connection made thereto at its outer end, means for making an electrical connection to a portion of said sleeve member intermediate of said housing and said solid dielectric member, a corona shield adjacent the outer end of said housing and in electrical connection with one oi said conductors, and a gaseous dielectric under pressure filling the spaces between said concentric conductors and between the latter and said housing and said bushing and between said inner conductor and said sleeve member and said solid dielectric member, said housing and said gaseous dielectric being proportioned to withstand said relatively small potential difference between said two conductors.

3. In a high voltage terminal, in combination, a wall member having an opening therein and having a conductive bushing secured thereto and ing, a plurality of spaced conductors maintained at potentials relatively high with respect to the potential or said bushing but the potential diflerence between which is relatively small, sectionalized solid dielectric means connected in fluidtight relation to said bushing, means including a metallic sleeve member for connecting adjacent sections together in fluid-tight relation, one oi said conductors being secured to a connecting sleeve, means supporting another of said conductors from and passing the latter in fluid-tight relation through the outermost section of said solid dielectric means, said last-mentioned conductor passing through said connecting sleeve and being spaced therefrom, means for making an exterior electrical connection to the connecting sleeve having one of said conductors connected thereto, and a gaseous dielectric under pressure filling the spaces between said conductors and between the latter and said connecting sleeve and between said conductors and said solid dielectric means, the portion of said solid dielectric means extending from said bushing to the connecting sleeve having one of said conductors connected thereto being proportioned with respect to said gaseous dielectric to withstand said relatively high potentials with respect to said bushing and the portion of said solid dielectric means remote from said connecting sleeve being proportioned with respect to said gaseous dielectric to withstand said relatively small potential difference existing between said conducors.

4. In a high voltage terminal, in combination, a wall member having an opening therein and having a conductive bushing secured thereto and forming substantially an extension of said opening, a plurality of spaced conductors maintained at potentials relatively high with respect to the potential of said bushing but the potential difference between which is relatively small, said conductors being arranged concentrically with respect to each other and with respect to said bushing, at least one of said conductors being rigid, solid dielectric means connected at one end thereof in fluid-tight relation to said bushing and having connected in fluid-tight relation to its other end a plurality of conductive members separated by solid dielectric means, each conductive member having a conductor secured thereto, a gaseous dielectric under pressure filling the spaces within said housing, said housing being proportioned with respect to said gaseous dielectrio under pressure so as to insulate said conductors of relatively high potential from said bushing, and said solid dielectric means being proportioned to insulate said conductors from each other.

5. In a high voltage terminal, in combination, a wall member having an opening therein and a plurality of conductors passed therethrough, said conductors being maintained at potentials relatively high with respect to said wall member but having relatively low potential differences between themselves, means including solid dielectric material and conductive members for supporting said conductors in spaced relation, said solid dielectric material insulating said conductive members against said relatively small potential differences existing therebetween, a corona-controlling member of relatively large radius in electrical connection with one of said conductors and serving both of said conductors and means for supporting and insulating said supporting means with respect to said wall member comprising solid dielectric means connected at one end to said wall'member and at the other end to said supporting means.

6. In a high voltage terminal, in combination, a wall member having an opening therein and a plurality of conductors passed therethrough, said conductors being maintained at potentials relatively high with respect to said wall member but having relatively low potential differences between themselves; said conductors including a tube-like conductor and being arranged concentrically with respect to each other; means for holding said conductors in spaced concentric relatio and insulated from each other including a sleeve-like metallic member to which said tubelike conductor is secured and through which an inner conductor passes, and means including solid dielectric material for supporting in depending re-V latlon and insulating an inner conductor with respect to said sleeve-like metal member; and means including solid dielectric material and a gaseous dielectric under pressure proportioned with respect to each other to insulate said conductors from said wall member for said relatively high potentials of the former with respect to the latter for supporting said holding means with respect to said wall member and thereby supporting both of said conductors in free depending relation through said opening in said wall member, said gaseous dielectric coacting with said first-mentioned solid dielectric material to prevent surface leakage along the interior surface of the latter between said conductors at the normal potential difference between said conductors, and said first-mentioned solid dielectric material providing a possible surface leakage path along its exterior surface sufficiently great to pre= vent surface leakage between adjacent conductors at the normal potential difierence between the latter.

'7. In a high voltage terminal, in combination, a wall member having an opening therein and a plurality of conductors passed therethrough, said conductors being maintained at potentials relatively high with respect to said wall member but having relatively low potential differences between themselves; tube-like solid dielectric means secured at one end thereof in fluid-tight relation to said wall member and extending about but spaced from said conductors and having a gaseous dielectric under pressure therein; and a plurality of conductive means exposed through said solid dielectric means and adjacent the oth-' er end thereof, each of said conductive means having a conductor electrically connected thereto and freely depending therefrom into the opening in said wall member and being adapted to have an electrical connection made thereto from the exterior of said solid dielectric means, said plurality of conductive means being relatively closely spaced upon the interior of said solid dielectric means and said gaseous dielectric under pressure coacting therewith to prevent surface leakage between adjacent conductive means, and said solid dielectric means and said gaseous dielectric under pressure being proportioned with respect to each other to withstand insulating said plurality of conductive means from said wall member for the relatively high potential differences existing between said conductive means and said wall member, the surface leakage path between said conductive means being longer along the exterior surface of said solid dielectric means than along the interior surface of said solid dielectric means.

' 8. In a high voltage terminal, in combination, a wall member having an opening therein and a plurality of conductors passed therethrough, said conductors being maintained at potentials relatively high with respect to said wall member but having relatively low potential diiferences between themselves; tube-like means of solid dielectric material closing said opening and provided with a plurality of conductive means adjacent its end remote from said wall member for passing the circuits represented by said conductors through said solid dielectric means, a gaseous dielectric under pressure within said tubelike means, the solid dielectric material between said conductive members being proportioned with respect to said gaseous dielectric under pressure to insulate said conductive members for the potential differences existing therebetween and the solid dielectric material that extends between said plurality of conductive means and said wall member being proportioned with respect to said gaseous dielectric under pressure to insulate all of said conductive members for the relatively high potentials thereof with respect tosaid wall member, and electrode means associated with said wall member and having 'a radius so proportioned with respect to the radius of at least one of said conductors to form a fast discharge gap therebetween.

9. In a high voltage terminal, in combination, a wall member having an opening therein and a plurality of conductors passed therethrough, said conductors being maintained at potentials relatively high with respect to said wall member but having relatively low potential differences between themselves; tube-like means of solid dielectric material closing said opening and provided with a plurality of conductive means adjacent its end remote from said wall member for passing the circuits represented by said conductors through said solid dielectric means, a gaseous dielectric under pressure within said tube-like means, the solid dielectric material between said conductive members being proportioned with respect to said gaseous dielectric under pressure to insulate said conductive members for the potential differences existing therebetween and the solid dielectric material that extends between said plurality of conductive means and said wall member being proportioned with respect to said gaseous dielectric under pressure to insulate all of said conductive members for the relatively high potentials thereof with respect to said wall member, a ring-like electrode member near that end of said tube-like means adjacent said wall member, said conductors passing through said ring-like electrode and being arranged concentrically with respect to each other and with respect to said electrode, one of said conductors having a radius proportioned to the radius of said electrode to form therebetween a fast discharge gap.

10. In terminal construction, in combination, a wall member having an opening therein, a plurality of concentric conductors passing through and spaced from the walls of said opening, and means for supporting and insulating said conductors from each other and from said wall member, said means including solid dielectric tube-like means secured to said wall member, a metallic tube-like member carried by the remote end of said solid dielectric means and having the outermost of said concentric conductors secured thereto and having an inner one of said conductors passing therethrough but spaced from the inside walls thereof, and solid dielectric means closing the remote end of said metallic tube-like member and having said inner conductor secured thereto and holding the latter in spaced relation to the walls of said metallic tube-like means, said outer and inner conductors being rigid and being rigidly supported respectively by said metallic tube-like member and said solid dielectric means and being thereby held in depending relation and in spaced relation with respect to each other and with respect to said solid dielectric tube-like means and the opening therein.

11. In terminal construction, in combination, a wall member having an opening therein, a plurality of concentric conductors passing through and spaced from the walls of said opening, and means for supporting and insulating said conductors from each other and from said wall member, said means including solid dielectric tube-like means secured to said wall member, a metallic tube-like member carried by the remote end of said solid dielectric means and having the outermost of said concentric conductors secured thereto and having an inner one of said conductors passing therethrough but spaced from the inside walls thereof, solid dielectric means closing the remote end of said metallic tube-like member and having said inner conductor secured thereto and holding the latter in spaced relation to the walls of said metallic tube-like means, said outer and inner conductors being rigid and being rigidly supported respectively by said metallic tube-like member and said solid dielectric means and being thereby held in depending relation and in spaced relation with respect to each other and with respect to said solid dielectric tube-like means and the opening therein, and means including a gaseous dielectric under pressure in the space between said concentric conductors and in the space between said inner conductor and the inner walls of said metallic tube-like member, said metallic tube-like member being sealed to said solid dielectric tube-like means and said second-mentioned solid dielectric means being sealed to the remote end of said metallic tube-like member, thereby to retain said gaseous dielectric under pressure.

12. In terminal construction, in combination, a wall member having an opening therein, a plurality of concentric conductors passing through and spaced from the walls of said opening, and means for supporting and insulating said conductors from each other and from said wall member, said means including solid dielectric tube-like means secured to said wall member, a metallic tube-like member carried by the remote end of said solid dielectric means and having the outermost of said concentric conductors secured thereto and having an inner one of said conductors passing therethrough but spaced from the inside walls thereof, said tube-like member being exteriorly stepped and thereby having a lower portion of larger exterior diameter than the upper portion thereof, said lower portion being in connection with said solid dielectric tube-like means, and solid dielectric means in connection with said smaller diametered portion of said metallic tube-like member for closing the remote end of said metallic tube-like member and having said inner conductor secured thereto and holding the latter in spaced relation to the walls of said metallic tube-like means.

13. In terminal construction, in combination, a wall member having an opening therein, a plurality of concentric conductors passing through and spaced from the walls of said opening, and means for supporting and insulating said conductors from each other and from said wall member, said means including solid dielectric tube-like means secured to said wall member, a metallic tube-like member carried by the remote end of said solid dielectric means and having the outermost of said concentric conductors secured thereto and having an inner one of said conductors passing therethrough but spaced from the inside walls thereof, solid dielectric means closing the remote end or said metallic tube-like member and having said inner conductor secured thereto and holding the latter in spaced relation to the walls of said metallic tube-like means, and a solid dielectric and a gaseous dielectric under pressure arranged serially in the space between said concentric conductors.

14. In terminal construction, in combination, a bushing having an opening therethrough of circular cross-section, a plurality of concentric conductors passing through said opening, and means forming a cantilever support at the ends of said conductors remote from said bushing for mechanically holding said concentric conductors with their axis coincident with the center of said opening in said bushing, said means including a sold dielectric tubular housing having at its end remote from said bushing a plurality of metallic members separated from each other by solid dielectric means, said metallic members each having means for holding one of said conductors with its axis coincident with the center of said opening.

15. In terminal construction, in combination, a bushing having an opening therein of circular cross-section, a plurality of concentric conductors passing through said opening with the outermost thereof spaced from the walls of said opening and means forming a cantilever support at the ends of said conductors remote from said bushing for mechanically but insulatingly holding said concentric conductors with their axis substantially coincident with the center of said opening, said means including metallic members rigidly connected with but alternated with solid dielectric members, the lowermost of the latter being connected to said bushing, and means rigidly connecting each of said concentric conductors to one of said metallic members.

16. In terminal construction, in combination, a wall member having an opening therein, a plurality of conductors passing through and spaced from each other and from the walls of said opening, both of said conductors being of high potential but with a small difference of potential therebetween, means of solid dielectric material at their ends remote from said opening rigidly holding said conductors, said solid dielectric material beingproportioned towithstand said relatively low potential diflerence, a corona shield in electrical connection with one of said conductors and substantially enveloping said solid dielectric material, said shield functioning for both of said conductors, and solid dielectric tube-like means connected to said wall member at one end and supporting said insulated conductors at its other end and being proportioned to insulate said conductors from said wall member.

FRANKLIN S. SMITH.

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