US1957984A - High voltage terminal construction - Google Patents

Description

May 8, 1934- F. s. SMITH HIGH VOLTAGE TERMINAL CONSTRUCTION Filed Feb. 2, 1951 A TTORNE .V

Patented May 8, 1934 A UNITED STATES PATENT OFFICE 1,957,984 HIGH VOLTAGE TERMINAL CONSTRUCTION Franklin s. smith, Brooklyn, N. Y; Application February 2, 1931, Serial No. 513,031 25 Claims. (Cl. 173-318) This invention relates to high voltage terminal to the wall 10, as at 16, to form a secure meconstruction. chanical and sealed connection.

One of the objects of this invention is to provide The upper end of bushing 14 is interiorly and a terminal construction that will be well adapted exteriorly threaded as at 17 and 18, and supportfor outdoor service at high potentials, that will ed by the portion 18 thereof is a metallic ring GU be of inexpensive construction, simple, and of member 19 of substantial outside diameter and dependable action. Another object is to provide having formed in its upper Surface an annular rea construction of the abovementioned characcess 20 within which is received the lower end ter for use in connection with high voltage appa- 21a O an insulator 21, the latter being tubular ratus enclosed in a casing with a gaseous dielec and tapered substantially as shown in the drawtric under high pressure, in which the possibility lng. Insulator 21 is cemented into the recess 20 of leakage of gaseous dielectric under this high oi ring 19 by any suitable cement indicated at pressure is dependably precluded while at the 22, and if desired lelle surfaces 0f ring member same time reliable action of the high voltage ter- 19 and of insulator 21 that are to contact with mlnal under varying weather Conditions may be the cement may be suitably roughened or corru- T achieved. Other objects Will be in part obvious gated. or in part pointed out hereinafter, Insulator 21 is made of any suitable material 'I'he invention accordingly consists in the feathat is well adapted to resist the action of such tures of construction, combinations of elements, elements i0 Whieh it is eXDOsed When Operating and arrangements of parl-,s as will be exemplified out-ofdoors and conveniently it may be formed 75 in the structure to be hereinafter described and of suitable Ceramic materiel such as porselein, the scope of the application of which will be in- Preferably glaZed- All its uploer end insulator 21 dicated in the following claims, is closed by a disk-like plate 23 flanged as at 23?L 1n the accompanying drawing the single view So as to overlap laterally the upper portion 2lb 25 is a central vertical sectional view through one of insulator 21, meiellio disk member 23 being S0 0f the Various possible embodiments 0f my in.. cemented t0 the pOIOIl 2lb Of the lIlSll-i'rltOl, aS 1S vention, indicated at 24. Here also the surfaces with In the drawing there is indicated at 10 a porwhich the Cement is to Contact may be approtion of the wall of a casing, the latter being made pliaiely Toughened or Corrugated if desired.

preferably of pressed steel so as to withstand high Extending Centrally through the COD plaie 23 S5 pressures, within which is contained a high voltis a boli? 25, to the inner end of Which iS Conage apparatus which, by way of illustration, may nected a high tension conductor 26 and to the take the form of a condenser diagrammatically Outer end of Which eollneeiiorl may be mede, as indicated at l1 and one terminal of which is by Confilloior 27, to the high tension Circuit With grounded to the casing 10 as by the conductor l2, which the apparatus Within the casing 10 is to be JU The other terminal 13 is to be passed through the associatedcasing 10, which may be assumed to be positioned The tube-like insulator 21 is of suttlcient length Outdoors. The Condenser 1l may be 0f any Suitin an axial direction safely to withstand the difable construction for appropriate coaction With ference of potential eXisiirlg'beiWeen the Connectthe gaseous dielectric under pressure contained in lng bolt 25 and the lower Img member 19 Which J5 the casing 10; this dielectric, under a pressure 1S grounded to the Casing 10 and preferably the on the order of fifteen atmospheres, may take the upper and lower members 23 and 19 funtlm 95S form of any suitable chemically neutral gas, such Controlling mempersor the ux of th? dlelectrlc as nitrogen for example. The conductor 13 is eld Set up by thls dlerence .of potntlal Pref' 1 dthl1ou h the Casing in a manner so as to erably, also, the member 21 1s petticoated as at 1GO tu be e g 21c thus further to increase the potential at which depenfia'bly preclude loss of the hlh pressure d1' flash-over might occur particularly when the outdecirle and also to pemlt the malntenancfi de' side surface of member 21 is Wet, the petticoats pendably, of an electrical connection outside of 21e substantially preventing the entire external the Casing 10 nder Varying Weather Conditions surface of member 21 from becoming wet and also 105 met with in Praeiieegreatly lengthening the path of surface leakage Casing 10 is provided With e suitable Opening in a direction from member 23 to member 19.

through which is passed a metallic bushing 14 Member 21, preferably, as above noted, made whose ange 15 abuts against the inner face of of porcelain or the like, while Well adapted for .the wall of the casing, bushing 14 being welded dependable functioning under the varying 11o weather conditions of outdoor installations, is relieved from being subjected to the relatively very great pressure of the gaseous dielectric by means of a combined insulating and sealing construction indicated as a whole at 28; this construction includes a metal bushing 29 in tight or scaled threaded engagement with the interior threaded portion 17 of the bushing 14, member 29 being substantially sleeve-like, having an inside surface substantially cylindrical and extending vertically, and having an upper threaded portion 29. The gaseous dielectric within the casing 10 extends upwardly into the members 14 and In threaded engagement with portion 29a of the sleeve member 29 is a tubular housing 30 made preferably of a phenolic condensation product or bakelite but closed at its upper end by means of a metallic plug 31 in threaded engagement therewith; plug 3l has extending therethrough a tubular conductor 32, conductor 32 extending downwardly and coaxially with the interior cylindrical surface of sleeve member 29 and extending also upwardly and out of the plug 3l.

The upper outer portion of tubular conductor 32 is threaded as at 32a to receive a nut 33 for clamping the lower end of the connector 26 into electrical connection with the tubular conductor 32` The latter is closed or sealed at its upper end, as at 34, and conveniently the sealing means 34 has the end of conductor 13 embedded therein. This sealing means may comprise a plug made of any suitable metal.

The bakelite housing is preferably tapered somewhat, as shown in the drawing, and is of sucient thickness to withstand the pressure of the gaseous dielectric which extends into the space between tubular conductor 32 and the inside of housing 30 and which coacts with the latter in achieving dependable insulation of the high tension conductor 32 from the casing 10 and associated metallic parts.

The threaded connections between the bakelite housing 30 and the members 29 and 31 are also of a mechanical strength adequate to withstand this pressure of the gaseous dielectric and preferably are sealed by means of a permanently elastic and resilient cement. The housing 30 is of an axial length and also of a thickness adequate to withstand the dielectric stress to which it is subjected, but these dimensions are much less than they would be otherwise, due to the coaction with the solid dielectric housing 30 of the gaseous dielectric under pressure and of certain other parts of the apparatus.

More particularly, the construction thus indicated as a whole at 28 is such that in the field of highest voltage gradient, namely, the eld that exists between the sleeve-like bushing 29 (at ground potential) and the tubular conductor 32 (at the high potential) is in the layer of gaseous dielectric between these two parts; the gaseous dielectric under pressure on the order of fteen atmospheres or so has very great dielectric strength and can best withstand this high voltage gradient and do so, more particularly, without requiring an unwieldy mass or impracticable dimensions.

The bakelite housing 30, tapered both interiorly and exteriorly and less capable of withstanding high voltage gradients, is disposed, due to its shape, in the eld of lowest voltage gradient, generally in the field extending from the plug 31 to they grounded ring member 19. In elds of intermediate voltage gradient. there exists both gaseous dielectric under pressure and the solid dielectricl 0I member 30, these dielectrics being in series, the series relation causing the two dielectrics to assume dielectric stresses in inverse proportion to their permittivities; thus the solid dielectric 30, having a much greater permittivity than the gaseous dielectric under pressure is relieved from assuming too great a stress. Furthermore, the gaseous dielectric under pressure vastly increases the resistance to surface leakage along the inside surface of member 30 in a direction from plug 31 to sleeve 29.

The above-described construction 28 thus compactly and dependably supports and carries the high tension conductor 32 through the opening in the wall of the casing 10, utilizing as an important factor the gaseous dielectric under pressure, while at the same time it dependably seals the casing 10 against escape of the gaseous dielectric, the bakelite member 3G being impervious and having so high a tensile strength that undue bulk or volume thereof is avoided.

The upper plate member 23 is provided with a threaded opening 35 through which the space between the interior wall of member 21 and the parts contained therein is lled with an insulating medium of a character that may be poured into this space upon heating and that will harden or solidify upon cooling. A suitable material for this purpose is halowax which, upon being heated, may be readily poured in through the opening 35 which is thereupon closed by a threaded plug 36, the halowax, upon cooling, assuming a plastic form. This insulating medium is indicated at 37. Halowax is a chloronaphthalene substitution product. 'Ihe halowax, when cool, becomes substantially vrigid and may thus be classied as a solid dielectric material; moreover, the halowax enters all of the irregularities, recesses, and the like, of the peculiarly shaped space between the outer tube-like member and the inner tube-like member 28, thus becoming interlocked with each and thus interlocking these two members themselves.

The insulating medium 37 insures that no moisture can get to the structure 28 even if leakage through the member 23 or through any of the joints between members 23, 21 and 19 were to take place, and it also greatly minimizes the possibility of surface leakage along the interior wall of member 21 and along the exterior surface of member 30. Aside from such coactions as these, insulating medium 37 is also interposed in certain portions of the dielectric eld and coacts with the other dielectrics in achieving dependable insulation of the high tension conductor from the grounded casing 10.

The conductor 32, it will be noted, presents a cylindrical surface that is concentric with the inside surface of member 29; these surfaces are of such radii as to form a fast discharge gap across which break-down occurs without being preceded by corona; the action of the gap is thus instantaneous. The critical voltage of the gap is such that it breaks down at a voltage less than that which will injureany of the associated devices or apparatus. For example, I may give it a critical voltage such that it will break-down when, forany reason, the voltage, either transient or otherwise, impressed upon conductor 27 and hence upon member 23, is greater than that which will cause break-down of any of the insulating part or parts of the structure abovedescribed or which will cause injury to the apparatus within the casing 10.

Member 19 is threaded as at 19a and has an inside diameter at this portion somewhat greater than the greatest outside diameter of bakelite housing 30. Before assembling the housing 30 and/or sleeve member 29 with respect to the bushing 14, there is threaded upon the threaded portion 18 thereof a collar 38 which is externally threaded. After members 29 and 30 have been assembled with respect to bushing 14, ring member 19 is slipped down over the housing 3o and is threaded onto the collar 38, whence the assembly may proceed as will be clear from the foregoing.

It will thus be seen that there has been provided in this invention a high voltage outdoor terminal construction in which the various objects hereinbefore noted, together with many thoroughly practical advantages, are successfully achieved.

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 hereinbefcre set forth, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a metallic bushing externally threaded and forming an extension of said opening, a ring-like member in threaded engagement with said bushing, a sleeve-like insulator made of a material adapted to withstand weather supported by said ring-like member and having its upper end sealed and provided with means for connecting thereto a high volt-age circuit, a high voltage conductor in connection at its upper end with said connecting means and extending through said bushing into said casing, and means for insulatingly supporting said conductor and sealing said opening, said means including a sleeve-like member made of phenolic condensation product supported at its lower end by said bushing and sealed thereto and having said conductor passing through its upper end and in sealed connection therewith, said gaseous dielectric extending into the space between said conductor and said second-mentioned sleeve-like member, and an insulating compound lling the space between said two insulating sleeve-like members, the radii of said bushing and said conductor being proportioned so as to form a fast discharge gap adapted to break-down at a critical voltage less than that which would injure one of said insulating sleevelike members, and said ring-like member having an inside diameter greater than the maximum outside diameter of said second-mentioned sleeve-like insulating member.

2. In high voltage terminal construction, in combination, a casing having therein an electrical apparatusv and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a metallic bushing externally threaded and forming an extension of said opening, a ring-like member in threaded engagement with said bushing, a sleeve-like insulator made of a material adapted to withstand weather supported by said ringlike member and having its upper end sealed and provided with means for connecting thereto a high voltage circuit, a high voltage conductor in connection at its upper end with said connecting means and extending through said bushing into said casing, and means for insulatingly supporting said conductor and sealing said opening, said means including a sleeve-like member made of phenolic condensation product supported at its lower end by said bushing and sealed thereto and having said conductor passing through its upper end and in sealed connection therewith, said gaseous dielectric extending into the space between said conductor and said second-mentioned sleeve-like member.

3. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a metallic lbushing externally threaded and forming an extension of said opening', a ring-like member in threaded engagement with said bushing, a sleeve-like insulator made of a material adapted to withstand weather supported by said ringlike member and having its upper end sealed and provided with means for connecting thereto a high voltage circuit, a high voltage conductor in connection at its upper end with said connecting means and extending through said bushing into said casing, and means for insulatingly supporting said conductor and sealing said opening, said means including a sleeve-like member made of phenolic condensation product supported at its lower end by said bushing and sealed thereto and having said conductor passing through its upper end and in sealed connection therewith, said gaseous dielectric extending into the space between said conductor and said second-mentioned sleeve-like member, and an insulating compound filling the space between said two insulating sleeve-like members, the radii of said bushing and said conductor being proportioned so as to form a fast discharge gap adapted to break-down at a critical voltage less than that which would injure one of said insulating sleevelike members.

4. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a metallic bushing externally threaded and forming an extension of said opening, a ring-like member in threaded engagement with said bushing, a sleevelike insulator made of a material adapted` to withstand weather supported by said ring-like memf ber and having its upper end sealed and provided with means for connecting thereto a high voltage circuit, a high voltage conductor in connection at its upper end with said connecting means and extendingr through said bushing into said casing, and means for insulatingly supporting said conductor and sealing said opening, said means including insulating means in sealed connection with both said high voltage conductor and sald bushing and contained within said sleeve-like insulating member.

5. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a metallic bushing externally threaded and forming an extension of said opening, a ringllke member in threaded engagement with said bushing, a sleeve-like insulator made of a material adapted to withstand weather supported Lul by said ring-like member and having its upper end sealed and provided with means for connecting thereto a high voltage circuit, a high voltage conductor in connection at its upper end with said connecting means and extending through said bushing into said casing, and means for insulatingly supporting said conductor and sealing said opening, said means including an insulating member in sealed connection with both said high tension conductor and said bushing and made of a material poorly adapted to withstand weather and contained within said sleeve-like insulator.

6. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a metallic bushing externally threaded and forming an extension of said opening, a ring-like member in threaded engagement with said bushing, a sleevelike insulator made of a material adapted to withstand weather supported by said ring-like member and having its upper end sealed and provided with means for connecting thereto a high voltage circuit, a high voltage conduct-or in connection at its upper end with said connecting means and extending through said bushing into said casing, means for insulatingly supporting said conductor and sealing said opening, said means including an insulating member in sealed connection with both said high tension conductor and said bushing and made of a material poorly adapted to withstand weather and contained within said sleeve-like insulator, and a dielectric filling the space between said two insulating members.

7. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a metallic bushing externally threaded and forming an extension of said opening, a ring-like member in threaded engagement with said bushing, a sleevelike insulator made of a material adapted to withstand weather supported by said ring-like member and having its upper end sealed and provided with means for connecting thereto a high voltage circuit, a high voltage conductor in connection at its upper end with said connecting means and extending through said bushing into said casing, andmeans for insulatingly supporting said conductor and sealing said opening, said means including a sleeve-like member made of phenolic condensation product supported at its lower end by said bushing and sealed thereto and having said conductor passing through its upper end and in sealed connection therewith, said gaseous dielectric extending into the space between said conductor and said second-mentioned sleeve-like member, and an insulating medium impervious to moisture and lling the space between said two sleeve-like insulating members.

8. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric underv pressure and having an opening through which a high voltage conductor is to be passed, a high voltage tube-like insulating member made of a material adapted to withstand, weather, means forming a sealed connection between one end of said member and said'casing, means forming a. high voltage conductor extending from the other end of said member through said opening,

and means in sealed connection with said casing and with said conductor for preventing access of said gaseous dielectric under pressure to the interior of said insulating member, thereby preventing the lattergfrom being subjected to the high pressure of said gaseous dielectric, said last-mentioned means being made of a. solid dielectric material adapted to withstand high pressures.

9. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a high voltage tube-like insulating member made of a material adapted to withstand weather, means forming a sealed connection between one end of said member and said casing, means forming a high Voltage conductor extending from the other end of said member through said opening, and means in sealed connection with said casing and with said conductor for preventing access of said gaseous dielectric under pressure to the interior of said insulating member, thereby preventing the latter from being subjected to the high pressure of said gaseous dielectric, said lastmentioned means being tube-like in form and extending upwardly into said rst-mentionesd tube-like insulating member and being made of a solid dielectric material adapted to withstand high pressure.

10. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a high voltage tube-like insulating member made of a material adapted to withstand weather but incapable of withstanding the pressure of said gaseous dielectric, means forming a sealed connection between one end of said member and said casing, means forming a high voltage conductor extending from the other end of said member through said opening, and a tube-like member of phenolic condensation product extending upwardly into said first-mentioned tubelike member and having one end thereof in sealed connection with said casing and the other end thereof in sealed connection with said high voltage conductor, said second-mentioned tube-like member being of a radius and wall thickness to withstand the pressure of said gaseous dielectric, thereby to prevent said first-mentioned tube-like member from being subjected to said pressure.

11. In high Voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, a high voltage tube-like insulating member made of a material adapted to withstand weather but inl capable of withstanding the pressure of said gaseous dielectric, means forming a sealed connection between one end of said member and said casing, means forming a high voltage conductor extending from the other end of said member through said opening, a tube-like member of phenolic condensation product extending upwardly into said first-mentioned tube-like member and having one end thereof in sealed connection with said casing and the other end thereof in sealed connection with said high voltage conductor, said second-mentioned tube-like member being of a radius and wall thickness to withstand the pressure of said gaseous dielectric,

thereby to prevent said rst-mentioned tube-like ,remember from being subjected to said pressure,

'and a solid dielectric medium iilling the space between said two tube-like members.

12. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, and two concentric substantially tubular insulating members, one within the other, a high voltage conductor extending through said two members and into said opening, means forming a sealed connection between one end of the inside tubular member and said casing, means forming a sealed connection between the other end of said inside tubular member and said conductor, said inside tubular member being made of an insulating material adapted to withstand the pressure oi said gaseous dielectric and having a wall thickness and radius suicient to resist the said pressure, thereby to prevent said outside tubular member from being subjected to said pressure, and said outside tubular member being made of a solid dielectric material adapted to withstand weather, and means engaging that end of said outside tubular member that is nearest said casing for holding it in assembled relation to said inner tubular member.

13. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, and two concentric substantially tubular insulating members, one within the other, a high voltage conductor extending through said two members and into said opening, means forming a sealed connection between one end of the inside tubular member and said casing, means forming a sealed connection between the other end of said inside tubular member and said conductor, said inside tubular member being made of an insulating Vmaterial adapted to withstand the pressure of said gaseous dielectric and having a wall thickness and radius sufficient to resist the said pressure, thereby to prevent said outside tubular member from being subjected to said pressure, the space between said conductor and the interior of said inside tubular member being iilled with gaseous dielectric under pressure, and the space between said two tubular members being filled with a solid dielectric medium.

14. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, and two concentric substantially tubular insulating members, one within the other, a high voltage conductor extending through said two members and into said opening, means forming a sealed connection between one end of the inside tubular member and said casing, means forming a sealed connection between the other end of said inside tubular member and said conductor, said inside tubular member being made of an insulating material adapted to withstand the pressure of said gaseous dielectric and having a wall thickness and radius sufficient to resist the said pressure, thereby to prevent said outside tubular member from being subjected to said pressure, said inside tubular member having external dimensions adapted to resist flashover from said conductor -to said casing at substantially operating voltages and said external tubular member having external dimensions adapted to withstand iiash-over to said casing under weather conditions, and means forming sealed connections between the adjacent-ends or said two tubular members.

15. In high voltage terminal construction, in combination, a casing having therein an electrical apparatus and a gaseous dielectric under pressure and having an opening through which a high voltage conductor is to be passed, and two concentric substantially tubular insulating members, one within the other, a high voltage conductor extending through said two members and into said opening, means forming a sealed connection between one end ci the inside tubular member and said casing, means forming a sealed connection between the other end of said inside tubular member and said conductor, said inside tubular member being made of an insulating material adapted to withstand the pressure of said gaseous dielectric and having a wall thickness and radius sufficient to resist the said pressure, thereby to prevent said outside tubular member from being subjected to said pressure, said inside tubular member being made of phenolic condensation product and said outside tubular member being made of a ceramic material and having a greater length of external surf ace than said inside tubular member.

16. In high voltage terminal construction in combination, a wall member having an opening through which a high voltage conductor is to be passed, a high voltage conductor extending through said opening, and means for insulatingly supporting said high voltage conductor, said means including a plurality of tube-like insulators, one within the other, the innermost insulalator having an inside diameter larger than the outside diameter of said conductor, thereby to form a space therebetween an inside insulator being made of phenolic condensation product and the outermost insulator being made of a material adapted to withstand weather, and solid dielectric means in mechanical interlocking relation with both of said insulators.

17. In high voltage terminal construction, in combination, a wall member having an opening through which a high voltage conductor is to be passed, a high voltage conductor extending through said opening, and means for supporting and insulating said high voltage conductor from said wall, said means including a gaseous dielectric under pressure, solid dielectric means mechanically supporting said conductor and adapted to withstand the pressure of said gaseous dielectric, and an outer exposed insulating means enveloping and interlocked with said rst-mentioned insulating means and having exposed portions made of a material adapted to withstand weather.

18. In high voltage terminal construction, in combination, a wall member having an opening through which a high voltage conductor is to be passed, a high voltage conductor extending through said opening, and means for supporting and insulating said high voltage conductor from said wall, said means including a gaseous dielectric under pressure, solid dielectric means mechanically supporting said conductor and adapted to withstand the pressure of said gaseous dielectric, means made of a refractory material encompassing said insulating means and sealing the latter against exposure to weather, and means acting independently of said conductor for securing said refractory means in place.

19, In high voltage terminal construction, in combination, a wall member having an opening through which a high voltage conductor is to be passed, a high voltage conductor extending through said opening, means for insulatingly supporting said high voltage conductor, said means including a plurality of tube-like insulators, one within the other, the innermost insulator having its inside walls spaced from said conductor, a iluid dielectric filling the said space between said conductor and said innermost insulator, an inside insulator being made of phenolic condensation product and the outermost insulator being made of a material adapted to withstand weather, and an intermediate insulator being made of a plastic material that is solid at ordinary operating temperatures.

20. In high voltage terminal construction, in combination, metallic bushing means adapted to be related to an opening in a wall member, a conductor extending through said bushing means and spaced from the walls thereof, means of solid dielectric material forming a sealed connection between said conductor and an end of said bushing means and holding said conductor spaced from the walls of said bushing means, said solid dielectric means being substantially tubular and said bushing means having a threaded portion of greater diameter than the outside diameter of said tubular dielectric means, a sleeve-like solid dielectric member adapted to be slipped over said tubular means, and a threaded ring member at one end of said sleeve-like member in threaded engagement with said threaded portion .of said bushing means.

21. In high voltage terminal construction, in combination, metallic bushing means adapted to be releated to an opening in a wall member, a conductor extending through said bushing means and spaced from the walls thereof, means of solid dielectric material forming a sealed connection between said conductor and an end of said bushing means and holding said conductor spaced from the walls of said bushing means, said bushing means having a portion projecting laterally beyond said solid dielectric means, and insulating means shaped to encompass said solid dielectric means and having mounting means adapted to be passed over said solid dielectric means and into engagement with said projecting part of said bushing means.

22. In high voltage terminal construction, in combination, a bushing interiorly threaded and having a portion exteriorly threaded, a conductor passing through said bushing and spaced from the walls thereof, solid dielectric means supported from the interiorly threaded portion of said bushing and holding said conductor in said spaced relation, and solid dielectric means adapted to withstand weather encompassing said first-mem tioned solid dielectric means and supported by said exteriorly threaded portion of said bushing.

23. In high voltage terminal construction, in combination, a bushing having an interiorly threaded part and an exteriorly threaded part; a rigid conductor extending through said bushing but spaced from the walls thereof; means supporting and insulating said conductor from said bushing comprising a metallic bushing threaded to said interiorly threaded part of said rst bushing and having a tube-like housing of organic solid dielectric material secured thereto, said conductor being supported by and extending through said housing; and a solid dielectric housing made of a refractory material encompassing said iirstmentioned housing and supported by said exteriorly threaded part of said rst bushing.

24. In high voltage terminal construction, in combination, a bushing having an interiorly threaded part and an exteriorly threaded part; a rigid conductor extending through said bushing but spaced from the walls thereof; means supporting and insulating said conductor from said bushing comprising a metallic bushing threaded to said interiorly threaded part of said rst bushing and having a tube-like housing of organic solid dielectric material secured thereto, said conductor being supported by and extending through said housing; a solid dielectric housing adapted to encompass said first housing; and a metallic annulus in threaded engagement with said exteriorly threaded part of said first bushing and having said second housing secured thereto.

25. In high voltage terminal construction, in combination, a bushing having an interiorly threaded part and an exteriorly threaded part; a rigid conductor extending through said bushing but spaced from the walls thereof; means supporting and insulating said conductor from said bushing comprising a metallic bushing threaded to said interiorly threaded part of said iirst bushing and having a tube-like housing of organic solid dielectric materialsecured thereto, said conductor being supported by and extending through said housing; a solid dielectric housing adapted to encompass said rst housing; and a metallic annulus in threaded engagement with said exteriorly threaded part of said iirst bushing and having said second housing secured thereto, the diameter of said exteriorly threaded part being greater than the diameter of said first-mentioned housing whereby said annulus may be passed over the latter.

FRANKLIN S. SMITH.

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