US1844974A

US1844974A - Electric condenser and method of making it

Info

Publication number: US1844974A
Application number: US497113A
Authority: US
Inventors: William H Priess
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1921-08-31
Filing date: 1921-08-31
Publication date: 1932-02-16
Anticipated expiration: 1949-02-16

Description

Feb. 16, 1932. w. H. PRIESS 1,844,974

ELECTRIC CONDENSER AND METHOD OF MAKING IT Original Filed Aug. 31, 1921 3 Sheets-Sheet 1 4 Feb. 16, 1932. w. H. PRIESS 1,844,974

ELECTRIC CONDENSER AND METHOD OF MAKING IT Original Filed Aug. 51, 1921 3 Sheets-Sheet 2 ZZZ Feb. 16, 1932. w. H. PRIESS 1,344,974

ELECTRIC CONDENSER AND METHOD OF MAKING IT Original Filed Aug. 31, 1921 5 Sheets-Sheet 5 Patented Feb. 16, 1932 UNITED STATES- PATENT OFFICE WILLIAM H. nurse, or NEW YORK, 1mm, Assmnoa, BY MESNE assmnmnurs, TO onu- ERAL mncrmc comm, a oonrona'rron or new YORK ELECTRIC CONbE-NSER AND METHOD OF MAKING IT Application filed August 31, 1921, Serial No. 497,113. Renewed .Tune 18, 1931.

This invention primarily relates to electrical condensers and method of making them. The invention, however, is of general application and can be embodied in condensers of the insulation are at a minimum.

Another object of the invention is to so construct the stack or condenser elements that, when assembled within its casing, clamped and embedded, it will have and I maintain the desired capacity.

Another object of the invention 'is to provide an improved lead and terminal.

The invention consists of the features described in detail hereinafter and illustrated in the accompanying drawings, in which Figure 1 is a sectional elevation of the Figs. 3 to 5 are sectional views of modified forms of insulators.

In high potential condensers now in use, especially in condensers used inradio transmitters, it is common practice to provide a metal casing which constitutes the low potenti al terminal of the condenser, the high poten tial terminal of the condenser extending through a suitable insulating cover on the casing.

In the embodiment of the invention herein illustrated, Figs, 1 and 2, I have provided such a casing 1, preferably of metal having a removable bottom or closure 2 which is Secured in place on the casingcproper by means of screws 3 or solder, a suitable gasket 4 being interposed between the lower edge of the casing and closure 2. The closure 2, if so desired, may be flexible to yield upon expansion of the filler W of insulating material 'exertedupon the stack, forcing is, the sheets composing the stack are arranged vertically at right angles to the bottom 2, and are maintained under pressure within the casing as follows. A plate 5 is placed against one of the vertical sides of the casing 1, this plate being machined andsmoothed and adapted to engage one end of the condenser stack S, thereby obviating the necessity for machining and smoothing off the interior of the casing 1, which is pref- -erably cast, and may comprise aluminum or any suitable alloy of it or any other suitable metallic material. The stack S is maintained under pressure by means of a pressure plate 16 arranged at the opposite endof the stack and engaged by ascrew 7 threaded.

through the opposite wall of the casing. By I adjusting screw 7 any desired pressure, of

the order of thousands of pounds, may be plate 5, the pressure plates 5 an 6 covering it against substantially the active area of the stack.

The pressure upon stack S is of an order to maintain the sheets of'foil and dielectric in intimate contact free from air and voids and I as nearly devoid as possible of insulating material such. as paraflin. The order of magnitude of the pressure exerted in an example of a commercial form of the condenser was bottomof the casin are flanges 8 constituting securing flanges w ereb the condenser. may be mounted in any suita 1e rack.

In the embodiment of the invention herein disclosed, the stack S comprises a number of sections 9 having their foil terminals connected in series alternately at opposite ends 10 by means of solder; Between the sections are located separators 11 preferably of mica.

The terminals of the outermost sections or the sections at opposite ends of the stack have soldered to them copper stri s or leads 12 which are bent around the en s of stack approximately 2,200 pounds over the ends of the stack. Intermediate the top and the S and clamped between the plates 5 and 6 respectivelyand the stack S, being electrically connected together through casing 1. In other words, the opposite ends of the stack S are at the same potential, being electrically connected to the casing which constitutes the low potential terminal of the condenser.

In the embodiment of the invention herein disclosed, a high potential lead 13 is secured to one of the foil connections 10 at the central upper portion 14 of the stack whereby the stack S is connected in series parallel; that is, the two parts of the stack, one at each side of the lead 13, are connected in parallel,

the individual parts comprising sections con-- nected in series. Lead 13 is universally flexible and is a stranded wire, preferably copper; that is, a wire which is made up of a number of strands of very fine wire. The inner end of the lead 13 is flared or fanned out as shown (Fig. 2) with the individual strands soldered at spaced points along the foil connection 14, whereby a very strong connection is secured between the lead 13 and the stack S. The fanned-out lead soldered to the foil terminal is disclosed in my co-pending application Serial No. 465,137, filed April 26, 1921, Patent No. 1,558,043, issued October 20, 1925, this present application constituting a continuation in part of said co-pending application as to this feature. In constructions heretofore used, it has been found that copper strips or similar connections when connected to the foil leads, which are very fragile, tend to become disconnected or torn therefrom and also tend to tear the foil terminals. By the present invention, this difficulty is obviated and strong permanent means is provided for connecting the high potential lead to the stack.

Inasmuch as the high potential lead 13 must be thoroughly insulated from the casing 1, which 'is the low potential terminal, and in order to mount lead 13 permanently upon the casing but insulated therefrom, I provide a rigid terminal such as a metal tube 15 through which the lead 13 is threaded, as illustrated, the terminal 15 being located on the casing at a point remote from closure 2. The metal tube 15 projects through asuitable opening 1a in the casing 1, and is thoroughly insulated from the casing by means of an insulating device 16. In the present embodiment, this insulating device comprises a disc or plate 17, of insulating material, which is of an area greater than the area of the opening 1a within the casing and extending over the boundaries of said opening. This disc is preferably of some material having high insulating qualities and low loss such as mica, and should be so designed as to withstand the difference in potential betweenthecasinglandthe fiexible lead 13 or the tube 15 throughwhich it passes. It is preferred that this plate 17 consist of mica, which is one of the best materials for this purpose,this plate 17 being clamped inwardly of its edge to the casing 1 by means of a metal ring 18 and screws 19 passing through the ring 18 into the casing 1, a suitable lead or rubber gasket 20 being interposed between the mica sheet andthe casinglto secure atight joint. The tubular member 1 5 extends through the disc 17. Mounted around tubular member 15 below the plate 17 is a lower insulating bushing 21 of reduced diameter compared to plate 17 and engaging the bottom of disc 17 and surrounding tube 15. This bushing is provided with one or more corrugations or grooves 22 arranged circumferentially therearound to increase the creepage distance and consists preferably of a laminated structure;

for instance a plurality of mica pieces or discs of diameter reduced compared with the disc 17 and compressed together in the manner hereinafter described. Mounted around the tubular member 15 below the bushing 21 is a second or bottom insulating bushing 23, likewise of reduced diameter compared to plate 17 and preferably of some hard insulating material which can be easily molded and machine-d such as phenolic condensation products and the like. The lower side of member 23 is provided with concentric grooves or corrugations 24, whereby the creepage distance between the lead 13 and tube 15'and the condenser casing 1 is increased, and with a central recess 25 between grooves 24 adapted to receive a round nut 26 which is threaded and sweated on the lower end of the member 15. The bottom bushing 23 is provided instead of mica because its flat surface, unlike mica, may be easil machined to form grooves 24 and recess 2 the bushing 23 insulating the lower end of tube 15 and nut 26. Upon the opposite side of the large mica plate 17 is an upper insulating bushing 27 of reduced diameter compared with disc 17 mounted thereon and surrounding and -insulating the upper portions of the member 15. Like the bushing 21, the bushing 27 is also of laminated insulating material preferably built up of superimposed pieces or discs of mica and of decreasing diameter upwardly as illustrated, forming an upwardly tapering bushing.

The device 16 is preferably constructed or assembled on member 15 by assembling thereon bottom bushing 23 and the mica discs, plates or washers in their proper order from bottom to top. In the embodiment herein illustrated, nut 26 is threaded on member 15 and bottom bushing 23 is placed in position, v

member 15 to hold the mica sheets and pieces in position against dislocation. The assembly of device 16 is then treated in a bath of hot molten insulating material, which will act more or less as an adhesive, for about fifteen minutes until bubbles cease, either with or without the application of vacuum. Suitable materials for this purpose are paraffin or sulfur. The assembly while hot and impregnated with molten insulating material is compressed or clamped tightly by nut 29 and allowed to cool, thus clamping the mica sheets together in a solid mass held together by nut 29 (which may be pinned to member 15) and by the fusible insulation which has now solidified. The upper bushing 27 is then cut, turned or ground to proper shape and polished, providing a smooth tapered surface 30. The bushings 21, 23 and 27 are thus retained and supported on p1ate17 and held under compression entirely by means of member 15 and nuts 26 and 29. The groove 22 in lower bushing 21 is provided by assembling intermediate mica washers of reduced diameter.

Above nut 29, in close contact with the nut and member 15, is a concave-convex metal member 31, having its concave side 32 facing the upper bushing 27 and having its edge 33.

in vertical alinement with and spaced from the clamping ring 18. The inclination of the surface 30 of the'bushing 27 and the curvature and spacin of the member 31 are so arranged with re erence to eachother and so proportioned that any difference of potential between the-opposite ends of the member 15 produces electrical stresses not through the upper insulator 27 but mainly through the air from member 31 to the casing 1, main-' taining the electrical field parallel with the bushing 27 instead of cutting the same. In other words, member 31 with casing 1 provides a static shield preventing losses in the insulator 16'and the destruction thereof. The member 31 also performs additional functions in that it provides a large-surfaced terminal for radiating heat generated in. the

stack and conducted through the lead 13 to member 31. The member 31 also serves as a protector or dust-guard for the insulating device 16, preventing deterioration thereof; that is, it is located above the insulating disc 17 and the bushing 27. The corona member 31 is secured in place by means of a nut 34 threaded upon the upper portion of the tubular member 15,'and above this are located washer 35 and nut 36 whereby any suitable lead may be attached to the high potential terminal in the usual manner.

I have also provided a novel spark-gap for association with the condenser-to preventthe formation of excessive differences of potential between the high and low potential portions thereof. For this purpose, the metal member 31 is struck down, forming a vertical part 37, on which is mounted a roundended spark-pin 38 having a longitudinal Patent No. 1,652,212, issued December 13,

1927. The process therein described covers the manufacture of a stack by preliminarily dipping the individual sheets ofmica in suitable insulating material, such as parafiin, and building what is called the material stack consisting of alternate sheets of foil and dielectric, and then treating the material stack thus formed in molten insulating material a such as parafiin and applying high compression and cooling, forming a solid block; After this, the material stack is split up into sections, such as the sections 9. The projecting foil terminals are connected as at 10, and,

the insulating separators 11 inserted. Of course, the sections may be assembled and connected by any desired method. For instance, each section maybe built up under wax, heated, compressed and cooled under pressure. Each section is then tested for capacity and voltage. The-sections are then connected in series and separators inserted between them. After the sections have been connected by solder and the sectional separators 11 positioned, the high potential flex. ible lead 13 is soldered in afanned-ont manner to the intermediate connection 10, and the two low potential leads 12 are soldered to the free ends of the end sections. The

stack is then placed on the base of a buihl ing stand provided with four vertical rods having vertical notches upon their innersides adaptedto receive the corners of the condensers stack; or, if so desired, a stand having six rods may be used, two rods engaging each' side of the stack and one at each end. 'A stand adaptable for this purpose is disclosed in a pending application of Pickard Serial No. 380,919, filed May 12, 1920, Patent No.

1,706,816, issued March 26, 1929. The stack when positioned in the stand is supported and braced by the'vertical rods against dislocation and side slip. The stack andstand are then placed in a hot moltenparaflin bath for approximatelytwenty minutes until the stack is warm, the bath being at approximately a temperature of 150- C., or in a bath of any suitable insulating material. The stack and stand are then removed from the bath, and the stack while still in the stand and while still hot is placed under a pressure slip while underthe great pressure- The of the order of magnitude of a ton per square inch over the active surface of the stack, and allowed to cool under pressure before being "placed in the final condenser structure of easing 1,'the vertical rods of the stand supporting and bracing the stack against side stack while under the pressure of the order of magnitude above-mentioned and after cooling is tested for capacity, and the capacity finally adjusted to its correct value, if this is necessary. Thus it will be seen that the final and correct capacity can be obtained before the stack is finally clamped in the casing 1 and embedded, thereby avoiding the removal of the filler after finally embedding for the purpose of obtaining desired capacity, if on test the capacity is found to be wrong. By cooling the stack under pressure outside of the casingl in the manner abovedescribed, the stack can also be tested for breakdown and phase angle before being placed in the casing 1 as well as measured for final length. Furthermore, by thus waxing and cooling the complete condenser stack,

including the separators 11, before being placed in casing 1, it can be handled as a block and side slip cannot occur during the filling operation afterthe stack S is placed Within the casing 1 and maintained under pressure by members 5 and 6. 7

In former processes and methods of bullding stacks and assembling them within the condenser casing, wax treating, compression and cooling operations on the completed stack, (including the separators 11 in place, as well as the final adjustment of capacity) usually were done with the s ack in a permanent clamp forming part of the condenser and in the condenser casing. In that process, however, it was dilficult to maintain good stacks where the length of the base exceeded by over twice the largest dimension of the stack or where sectional separators had been inserted. Such length of stack by reason of the greater number of sections and the greater number of sectional separators tended to cause the side slip above referred to, upon final compression, that is, where the stack was relatively high or had separators which ;had not previously been waxed, or both, upon "compression, the elements of the stack tended to be displaced relatively to each other. By

providing lateral support for the stack dur ing compression, this difliculty is obviated.

After the. stack S, including the separa-.

tors 11, has been waxed and compressed,

cooled and tested as above described, it'is in condition to be handled, being cold and covered with wax and is directly secured within the casing 1 by means of the clamping members 5 and 6 and adjusting screw 7. The terminal gasket 20 is then positioned and the flexiblelead 13 pulled up through the vertical hole through the member 15. The insulator 16, including the disc 17, is then clamped to the casing 1 by means of ring 18 and screws 19. The lead 13 is then pulled up taut through member 15 and its excess length cut 0E. The outer end of lead 13 is then soldered to the top of member 15, which is provided at its upper end with a recess or countersunk portion 41 (Fig. 1) which fills with solder, retaining lead-13 in place and electrically connecting it to member 15. The bell 31 and remaining nuts are then assembled and spark-pin 38 properly located. This method of connecting the flexible lead from the stack S to a rigid metallic terminal is novel, inasmuch as in the present instance the soldering of this lead to the terminal is at a point outside of the casing where it is accessible and where the soldered joint can be end 41. Furthermore, inasmuch as I have utilized in the present invention the stranded wire 13, the strands at their outer ends provide additional means for securing a very good electrical and mechanical connection with the terminal 15. After the parts have been assembled as illustrated in the drawings, with stack S held by members 5 and 6 under sufficient pressure to hold it in place, the whole condenser can be inverted, the bottom 2 being removed, and the same embedded in the manner described "in my Patent 1,652,212 above-mentioned to provide a compact, nonporous, holosteric embedment W for the stack and around lead 13 and terminal 15 withinthe condenser 1, which is free from air and voids. As described in such Patent 1,652,212, a head or extension issecured to the casing and thecasing and extension are preliminarily heated by filling the same with molten paraflin at a temperature around 140 0. While thus filled, the final pressure is applied to stack S by tightening up screw 7. The

molten parafiin is then-removed and vacuum applied and the head and extension filled with molten paraffin or other insulating filler which is allowed to solidify in the manner describedin said Patent 1,652,212. The diameter of the passage through member15 should be such as to allow lead 13 to be pulled through while the solder at 41 makes a tight joint. In some cases, the preliminary heating with parafiin may be omitted'and the stack S finally clamped under high pressure as soon as of by means of positioned. The condenser stack and terminal lead 13 are then emb dded and the head and surplus wax or insulating material removed as described in said Patent 1,652,212. After the embedment, the bottom 2, with its intervening gasket 1, is secured in place by means of the screws 3, the closure 2 being flexible, to allow the expansion of the wax, if rcqnired.

The soldering of the fanned-out stranded wire end to the foil terminal is a distinct advantage in cases of condensers'having sections of low capacity; that is, having a small number of foils in a tab, because the fewer foils you have the more easily the foils are torn. The connection of the lead 13 to the stud 15 at the upper end thereof is made after the stack and terminal are in place in the easing, and places the soldered joint outside the casing where it can be properly made and in spected. Before the top joint is soldered, however, the lead 13 should be pulled up tight with the hand.

The insulator 16 provided for the high potential terminal of the condenser, for the purpose of insulating such high potential terminal from the casing, provides a long creepagc path with short height. This increased creepage path is obtained by means of the ottom insulating bushing 23\turned with two concentric grooves 24 and machined at the center 25 to contain the lower end 26 of the high tension stud 15 whereby it is secured on the stud. Furthermore, additional creepage is obtained by providing circumferential grooves in either or both of the upper and lower micabushings 27 and 21 upon either or both sides of the mica disc 17. I have shown one such groove 22 in the mica bushing 21 below the disc 17. In'the present construction, the insulator 16 comprises a single mica disc 17 clamped to the casing 1, and built-up discs of mica of reduced diameter forming bushings 27 and 21 upon and supported by the disc 17, the bushings being clamped to the disc 17 at opposite sides therethe member 15 and co-operating nuts threaded thereon. The drawings show how, in order to permit a narrow casingopening, with electrical and mechanical safety, the casing and static shield (or corona shield as it has become known in the art),

are curved or inclined with relation to one another and to the stack, so that, allowing for the necessary distance between casingparts 1 and 18 from terminal lead 15, the casing is safely remote from the portions of the stack of the higher capacities, and even so, any

break-down which may occur will involve av discharge from corona shield to casing in shunt to the insulating material and the itself, (with orwithout the spark-gap elec-, trode according to the desired design). The narrow casing-opening is important because it is bridged by insulating material always stack 4 structurally weaker than metal. The invention in these respects is an improvement upon condensers of the type shown in patent to Dubilier 1,229,914 of 12 June 1917 where the cover which insulated the high potential lead from the metal casing was required in practice to be not only large in superficial area but very thick, in order to withstand the stress of a stack grown hot in service and tending to expand against the insulating cover which was one of the clamping members. In the present invention, not only is the insulating cover relieved of all functions of holding the stack under compression, but the casing-opening and therefore the insulating cover are so narrow as greatly to contribute to the practicability of the combination in cluding the insulating cover. In the form shown, as usually in practice, the insulating cover is so narrow that it will not permit passage thru it of the stack in making the assembly, both the stack and the molten wax being inserted thru the bottom casing-opening which is made large for the purpose of readily permitting insertion of the complete stack as a whole inside the casing.

In Figs. 3-, 4 and 5, I have illustrated slightly-modified forms of insulating devices 16 for use such as in condensers for insulating high potential terminals. In Fig. 3 is illustrated the large-diametered mica supporting sheet 17 clamped in the manner above described and having on opposite sides thereof the lower and upper bushings 21 and 27 as above described, of reduced diameter. In this form, however, the terminal member 15 by which the bushings 21 and 27 and disc 17 are clamped together has an integral head 15a at one end, and as here illustrated, at the outer end, and a nut 150at the opposite end which, upon being tightened, clamps the two bushings 21 and 27 and the insulating disc 17 together between the nut 150 and head 15a. The insulator illustrated in Fig. 3 is assembled substantially like that above described, but in the reverse manner; that is, from top to bottom the mica washers or pieces constituting the upper bushing 27 are first assembled upon head 15a and finally the mica washers or pieces constituting the bushing 21. The nut 150 is then positioned and tightened up, the whole being treated and impregnated as above described. In the con struction of Fig.3, instead of utilizing nuts threaded upon the member 15 for the purpose of securing an external lead, I have provided a vertically-arranged member 15?) to which the lead may be secured, this member 156 being at rig t angles to and integral with part 15a.

In the form of the invention illustrated in Fig. 3, the bakelite dilecto bushing 23illustrated in Figs. 1 and 2 is omitted, and in lieu thereof I have shown the bushing 27 corrugated at 27a whereby the creepage distance is increased without materially increasing the length of the insulator. The lead 13 is secured to the terminal 15 of Fig. 3 in the manner described in connection with Figs. 1 and 2.

Referring to Fig. 1, the construction shown therein differs from the construction of Figs. 1 and 2 in the omission of the bushing 23 composed of a phenolic condensation product or other suitable plastic, and in lieu thereof the upper bushing 27 is corrugated at 27 a. In other respects, the assembly is like that of Figs. 1 and 2, the nut 150 corresponding to the nut 26 of Figs. 1 and 2, directly engaging the lower bushing 21 instead of the bakelite dilecto bushing 23.

In Fig. 5, I have illustrated another form of the insulator 16 which comprises the main or large mica supporting sheet 17, which may be of any desirable configuration and secured as above described, and having on opposite sides thereof the lower and upper bushings 21 and 27 of reduced diameter and comprising laminated structures made up of sheets or pieces of mica above described. The construction of Fig. .5 differs from that of Figs. 1 and 2, however, in the provision of a high tension terminal 15 which may comprise a solid bolt upon which are threaded the mica discs, washers or pieces comprising the lower bushing 21, sheet 17 and the upper bushing 27. The inner end of the bolt or terminal 15 is provided with an integral head 15m having a transverse slot 15% therein, to which in the slot 150% the lead 18 is soldered. The parts are'assembled, as above described, upon the head 15m, and thereafter the nut 29 is tightened, holding the several discs or mica washers in position upon bolt 15, tightly between head 15m and nut 29, the

. parts being treated with wax as above described. It should be noticed that the construction of Fig. 5 difiers from the construction of Figs. 1 and 2 in the provision of a solid terminal 15 to which the lead 13 is attached at the inner end thereof instead of being threaded through the terminal 15 and soldered to the outside or outer end.

It is to be understood that the invention is not limited to the embodiments and fea tures specifically shown and described herein, but that such embodiments and features are subject to changes and modifications without any departure from the spirit of the invention.

I claim 1. In an electrical condenser, a metal casing having openings at opposite ends, a member of insulating material closing one of said openings, a terminal lead extending through I said insulating member, said insulating member surrounding a portion of said lead which projects outside the casing, a stack clamped within the casing and having electrical coni nections with the casing and stud respectively, a filler of insulating material filling the casing and engaging said insulating member, and placed within the casing through the opening remote from said terminal lead, and. a closure for said remote opening.

2. In an electrical condenser of the metal foil type comprising a metal casing enclosing condenser elements and having an opening for a terminal therefrom which is insulated from the casing, the improvement which comprises a tubular metal stud projecting through the casing; and a stranded conducting, lead having one end extending through said stud and electrically cormected to a part of the stud which is accessible from the out side of such casing, the other end of said lead having its strands separated from one another and conductively connected with a set of mutually connected foils at points located successively along the edge of the set of foils, to provide a strong connection relatively to the fragility of the foils.

3. In an electrical condenser of the metal foil type comprising a metal casing enclosing the condenser elements and having an opening for a terminal therefrom which is insu lated from the casing, and having an insulating embedment in the casing around the condenser elements and terminal, the improvement which: comprises a tubular terminal stud projecting through the casing; and a stranded conducting lead having one end extending through said stud and electrically connected to a part thereof which is accessible from the outside of such casing; the lead extending through said insulating embedment to'the condenser elements, said end of the lead havin its strands .separated from one another and conductively connected with a set of mutually connected foils at points located successively along-the edge of the set of foils, to provide a strong connection relatively to the fragility of the foils.

{1 In an electrical condenser comprising a. metal stack enclosing condenser elements and having an opening for a terminal therefrom, the improvement in supportingthe terminal independently of the condenser elements and insulating it from the casing, which comprises a centrally-perforated sheet of .mica mounted on the casing over its opening; an insulating material fluid when heated but solid at ordinary temperatures and compacted against the inner surface of said mica sheet; a metal annulus outside the casing arranged to secure the mica sheet thereto; a terminal stud' projecting through the central perforation in the mica sheet and extending on both sides thereof in and out of the casing and having electrically connected to its, inwardly projecting portion a flexible lead connected to the condenser elements within the casing, and a plurality of centrally-perforate'd mica sheets laterally surrounding said stud and lying adjacent thereto and v1 to said mica sheet, said stud projecting beyond said plurality of mica sheets.

5. In an electrical condenser comprising a metal casing enclosing the condenser elements and having an opening for a terminal therefrom which projects through said opening and is insulated from such metal casing, the improvement which comprises an insulating member supported by the casing and proecting eaterlorly thereof and surrounding such terminal, and a metal bellshapcd member mounted on said terminal and having its concavity facing and extending around said insulating member and towards the metal casing-and electrically spaced from the latter, said insulating member extending into the concavity of the metal bell having an exterior configuration generally corresponding with the configuration of the concavity of said bell and the exterior projecting portion of said bell and insulating member having relative configurations which aid in divertmg electrical stresses from the insulating member.

6. In an electrical condenser comprising a metal casing enclosing the condenser elements and having an opening for a terminal lead from such elements which extends through said opening and. is insulated from such casing, the improvement which comprises a metal bell-shaped member supported by such terminal lead outside such casing and arranged with its concavity toward the easing opening, said bell member being in good contact electrically and thermally with such terminal and having a diameter of the order of'that of the opening in such metal casing; said bell member being arranged to have atleast a portion of its rim closer to the casing than the distance between the rim of the easing opening and said terminal.

7 In an electrical condenser comprising a metal casing enclosing the condenser elements, electricallyconnected thereto to constitute a terminal thereof, and having an opening for another terminal thereof which extends through such open ng and is insulated from such casing, the improvement which comprises a metal shield mounted on] such terminal outside the casing and over the casing opening, the same being in good contact electrically and thermally with such terminal; and a spark-gap edectrode mounted on said metal shield and spaced from the metal of the casing to constitute a spark-gap between the metal shield and metal casing,

said electrode being located closer to the metal of the casing than is said second ter minal. a v

8; In an electrical condenser comprising a metal casing enclosing the condenser elements, electrically connected thereto to constitute a terminal thereof, and having an opening for another terminal thereof which extends through such opening and is insulated from such casing, the improvement which comprises a metal shield mounted on and electrically connected with said second terminal in position outside said casing and over the casing opening; and a metal member spaced from the metal of the casing and constituting an electrode to establish a spark-gap between said shield and easing, said electrode having a supporting connection with said shield for movement of the electrode to and from the casing independently of any such movements of said shield.

9. In a high potential capacitor of the type wherein the condenser itself is enclosed by a metal casing connected to the condenser as a terminal thereof and having an opening for the outward projection of another terminal of the enclosed condenser, the combination with such other terminal projecting a substantial distance outside of the casing beyond the metal of the casing around the casingopening; of an insulating member closing said opening and extending around the sides of the projecting terminal beyond the metal of the casing around the opening; and a metal member located between the metal of the casing around the opening and a portion of the projecting terminal extending beyond the insulatingmember, said metal member extending around the projecting terminal and insulating member and being inclined a substantial length of the insulating memberaround the projecting terminal away from the casing.

10. In a high potential capacitor of the type wherein the condenser itself is enclosed by and electrically connected to a metal casing having an opening and a terminal-lead from the enclosed condenser projecting out thru said'op'ening, the improvement which comprises, in combination with a member consisting of insulating material, perforated for roje'ction of the terminal lead, and located between the projecting terminal and the metal ,casing, of a substantially bellshaped member consisting of metal extending curvilinearly intermediate a portion of the terminal-lead lying beyond said insulating member, and the metal of the casing around said lead-opening, the rim of said bell extending closer than the projecting terminal lead to the metal of the casing and the bell terminal lead projecting from a high potential portion of the condenser out thru said opening to a substantial distancefrom the metal of the casing; the sides of the casing at their tops being inclined upwardly and inwardly to end at said casing opening-at a safe distance from the high potential portions of the enclosed condenser, said inclination providing a casing-opening of short diameter; an insulating member of correspondingly short diameter closing such casingopening and-projecting substantially beyond the casing and around a substantial length of the projecting portion of said terminal lead; and a corona shield extending from a position near'the metal rim of the short-diametered casing opening to a portion of the projecting terminal lead beyond the projecting portion to said insulating member, said shield in such arrangement having a diameter correspond ing with that of the casing-opening and insulating member and being inclined from the projecting terminal and toward the metal of the casing.

12. A high potential condenser in a metal casing formed with openings in opposite Walls, a terminal lead projecting out thru one of said openings from the condenser to a substantial distance from the'metal of the casing; the ends of the casingwalls near said terminal lead opening being inclined thereto to end at such opening at a safe distance from the high potential portions of the condenser and provide an opening too small for insertion of the condenser into the casing; an insulating member of small size corresponding to and closing saidsuch small casing-opening and a corona shield for said insulating member, said shield being ofsmall diameter corresponding with that of said smaller casingopening and insulating member and inclined toward the casing-wall of said opening from electrical connection with a portion of the projecting terminal lead which is remote from the metal of the casing said opposite ,casingopening being sufficiently large for insertion of the condenser in the casing.

13. In a high potential condenser, the combination with a series-sectional stack, of a metal casing therefor connected with a terminal thereof and formed with an opening, a terminal-lead projecting from a portion of the stack at high potential difference from the casing and out thru said opening to a suitable distance from the metal of the casing; an insulating member closing said opening and projecting outside the casing and extendmg around the projecting portion of the terminal-lead outside the casing; and a metal static shield extending around the sides of the projection portion of said insulating member electrically connected with a portion of said projecting terminal lead, and formlng an electrode of an air-gap between itself and the metal of the casing, said gap being shorter than the distance between the metal of the casing and the portion of the shield to which said terminal-lead is connected.

14. The improvement on the type of high potential condenser wherein the stack was clamped in a metal casing by a cover of insulating material and wherein the stack was connected to the casing as one terminal and the other such terminal .was a lead extending out centrally thru such insulating clamping cover, said improvement consisting in causing the stack to be clamped between the sides of the metal casing itself thereby reducing the necessary thickness of the insulatingcover necessary as a mechanical clamping element; and further, in combination, causing the sides of the metal casing to' be inclined toward the central projecting terminallead without unduly approaching an end or the portion of the stack'to which said lead is connected thereby reducing the width of the casing opening for said lead and reducing the superficial diameter of the insulating cover necessary when the casing sides are straight or inclined away from the central projecting terminal-lead.

15. The combination with a high potential condenser stack, of an enclosing casing of metal therefor connected with a terminal of said stack and having an opening opposite an intermediate portion of said stack, a second terminal of said stack projecting outside the casing thru said opening, an insulating member closing said opening and also projecting outwardly beyond said opening around the projecting portion of said terminal; and a bell-shaped member of metal located beyond said projecting portion of said insulating member, concave to the casing and extending conductively from a portion of said projecting terminal beyond the projecting portion of said insulating member to a position in space which is closer than said terminal to the metal of the casing; the bellshaped member being arranged for enclosing a correspondingly greater length of the insulating member around the projecting portion of the terminal, and constituting the more a mechanical protection for the material of the insulating member.

16. A high potential capacitor comprising a stack of capacitor elements, a metal casing enclosing and holding said stack under pressure and provided with an opening on one side through which said stack is inserted,

means for closing said opening, the opposite end of said casing being provided with a smaller opening smaller'than the stack dimensions, a terminal connection for said stack passing through the smaller opening, the opposite stack terminal being connected to the casing, an insulating member closing said smaller opening and extending around said terminal connection beyond said casing,

the walls of said casing between said smaller opening: v and tile :adjacent "portion of V the stack sloping inwardly-toward I said smaller opening andyterminal connection and away I from saidstack: at. a safe distance and being flattened around said smaller opening, and a fusible insulating material filling the casing surrounding the stack and contacting with said insulating closure for said smaller openmg. Y

1 17. A high, potential capacitorcomprising a metal casing, a stack of capacitor elements therein electrically connected at one end to said casing, the casing having anopening on one side of a size too small for insertion of said stack therethrough, and the walls of said casing engaging and compressing the stack-ends and being strong enough to withstand the pressure on said stack, a terminal conductor connected to said stack and passing out of the casing through said small opening, an insulating member closing said opening and projecting beyond said casing around said terminal conductor, means for opening the casing for insertion of said stack, a fusible insulating material surrounding said stack and filling said casing, at least two opposite walls of the casing being provided with integral extensions which are arched about the stack toward said small opening for supporting said terminal conductor, the

' spacing between said stack and at least a por tion of the arched extensions increasing with increase in the potential gradient between thestack elements and easing.

18. In an electrical condenser, a metallic casing-casting-formed with opposite openings, a condenser member therein located between said openings and the casing walls; an

insulating embedment-castin in the casing and around the encased con enser member; one of said openings being sufiiciently large forintroduction of the condenser member therethru into thecasing; a lead connected to the enclosed condenser 'member and extending'out from said casing thru the other opening;'and a cover of structural insulating material closin said other opening and extending arounf said lead insulating it from the casing, and secured to the casing, whereby the combinationof the casing, insulating cover-and said lead constitutes, when thecondenser member is in place inside the casing, a-mold for the filler-casting between the easing and the condenser v member which it; encloses: L 1

i219; an electrical condenser, 1 a metallic casing=casting formed-with opposite openings; a condenserstack encased thereby and arrangedwith its ends' facing-opposite closed walls-ofxthe casing and its opposite sides facing said opposite openings; means clamping said? stack ends :betweensaid closed casing 'wallsfiand tending to ,force' said :walls apart;-

one oi 'said o'pem being sufliciently large for introduction 0 said condenser member therethru into the casing; .alead connected to saidenclosed stack and extending thru the relative to the length of the enclosed stacks and to the distance between the walls of the casing, and a cover of structural insulating material closing said small opening, extending between the casing and said lead and surrounding the outwardly projecting portion of the lead for a substantial distance beyond the exterior of the casing; said casing having an arched formation between said small opening and the wider main casing portion and imparting substantial rigidity to the casing resisting the tendency of said clamping means to force apart the closed casing walls between which the stack is compressed.

20. In an electrical condenser, a metallic casing-casting formed with opposite openings; a condenser member encased thereby and located between said openings and the casing walls; an insulating embedment-casting in the casing and around the encased condenser member; one of said openings being sufficiently large for introduction of the condenser member therethru into the casing; a lead connected to the encased condenser member and extending thru the other and opposite opening to a substantial distance out? side of and beyond the metal of the casing; and a cover of structural insulating material closing said other opening, secured to the casing and extending around said lead insulating 1t from'the casin and extendlng a substantial distance beyon the metal of the being sufliciently large for intro uction, of the condenser member therethru into the. cas ing-;a lead connected to theeneas'ed condenser member and extending thru the other and opposite opening to .a substantial. distance denser member; one of said casin -openings outside of and 'be yondfthe metal of the casing, saidlead being centrally with respect to the interioroi thecas'ing and said lead-opening; and, a} cover of structural- "insulating material closing] said lead-opening se d. o th a in' idz s ir i g u said lead insulating it from thec'a'sing and a side facing the-larger casing-opening; an

therein, the casing bein ing and the lead whereby the lead-opening is relatively small; the metallic casing itself also having aform arched from its wider main portion to said smaller lead-opening and generally conforming with the potential gradient of the condenser member and centrally disposed lead.

22. In an electrical condenser, a metallic casing-casting formed with top and bottom openings; a-condenser member encased thereby and located between said casing-openings and casing-walls; an insulating embedmentcasting. in the casing and around the encased condenser member and between it and the casing walls; said bottom casing-opening being sufficiently large for introduction of the condenser member therethru into the casing; a lead connected to the encased condenser member and extending thru the top opening to a substantial distance outside, of and beyond the metal of the casing; and a cover of structural insulating material secured to the casing around said lead-opening closing the same and surrounding the lead and extending a substantial distance beyond the metal of the casing providing a long creepage path between the casing and the lead whereby the lead-opening is smaller than the enclosedcondenser-member; the combination of the casing, the insulating cover and the lead extending thru the cover constituting a closed mold for the insulating embedment- 'casting between the casing and the condensermember which it encloses.

23. In an electrical condenser, a box-like metallic casing, a condenser-member enclosed formed with an opening sufficiently large or the introduction of the condenser member therethru into the casing; an insulating embedment-casting inside the casing and aroundthe encased condenser-member; said casin being formed with a relatively small'lea -opening opposite said larger opening and smaller than the encased con enser member; a lead extending from the encased condenser member: and-out of the. casing thru said lead-opening; and an insulator surrounding said lead and closing said lead-opening;'said casing, insulator and lead constitutinga closed mold for the insulating embedment-castin 24. In an electrical con enser, a box-like I metallic casing formed with opposite large and small openings; a condenser-member enclosed therein, and arranged with its ends insulating embedment-casting in the casing- .and around the condenser member; a lead said lead and insulator closing the wall of the casing in which said smaller opening is formed; the larger casing-opening being sufficiently large for the introduction of the condenser-member therethru into the casing, and the assembly of the lead, lead-insulator and casing with large opening constituting a closed mold for said insulating embedmentcasing and around the condenser-member; a

lead from the encasedcondenser member and extending out of the casing thru the smaller top lead-opening, said lead and insulator closing the top of the casing; the larger bottomopening being sufliciently large for the in troduction of the condenser member therethru into the casing, and the assembly of the lead, top lead-insulator and easing with large bottom-opening constituting a closed mold for said insulating embedment-casting;

26. In a high potential electrical condenser, a metallic casing-casting formed with opposite large and small openings, a seriessectional high potential condenser stack encased thereby and arranged with its ends facing opposite closed casing wallsand its sides facing said 0 posite openings; means clamping said stac -ends between said closed casing-walls and tending to force said walls apart; one of said casing-openings being sufiiciently large for the introduction of the condenser-stack therethrn into the casing;

yond the metal thereof providing a longcreepage path between the latter and the projecting portion of the lead and providing for alead-opening smaller than the condenserstack; said lead being disposed centrally of the lead-opening of the casing, and the easing having an arched formation between the lead-opening. and the main casing-portion a nd im arting substantial rigidity to the casing reslstingthe tendency of said clamping means to force apart the closed casin -walls bet-w n which the stack is compresse said arche casing-portion generally conforming to the potential gradient of the condenser stack and centrally disposed lead; and the assembly of metallic casing, insulating cover and said lead constituting, when the con-.

denser stack is clamped in place inside the casing, a mold for said insulating embedment-casting. v

27. In a high potential condenser, a metallic casing-casting formed with opposite large and small openings, a condenser-member encased thereby, said larger casing-opening being sufficiently large for the introduction of the condenser member therethru into the casing; a lead extending from the condenser member thru the smaller casing-opening and extending a substantial distance outside the casing beyond the metal thereof; a

and closing the lead-opening, constituting a closed mold for said embedment-casting providing access for the latter to the interior sur faces of the insulating cover.

28. In an electrical condenser, a metallic casing-casting formed with opposite large and small openings, a condenser-member encased thereby said larger casing-opening being sufficiently large for the introduction of the condenser-member therethru into the casing; a lead extending from the condenser member thru the smaller casing opening and extending a substantial distance outside the casing beyond the metal thereof; a casingcover of structural insulating material secured to the casing, extendin around said lead and closing the lead-opening of the easing; an insulating embedment-casting inside the casing covering the surfaces of said insulating cover which face the interior of the casing thereby eliminating interior creepage surfaces along short distances between the metallic casing and the lead; the insulating cover extending a substantial distance outside and beyond the casing around the projecting lead constituting a long exterior creepage path between the metallic casing and the stituting a closed mold for said embedmentcasting providing access of the embedding material thru the larger casing-opening to the interior surfaces of the insulatin cover.

WILLIAM H.'PRI SS.

lead; and a metallic static shield electrically connected and secured to a portion of the lead lying beyond the insulating cover and surrounding the lead and desirably spaced from the metal of the casing; the assembly of the lead, casing and insulating cover secured thereto and closing the lead-opening, con-