US2743337A

US2743337A - Circuit interrupter

Info

Publication number: US2743337A
Application number: US174012A
Authority: US
Inventors: Fritz E Florschutz; Wayne S Aspey
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1950-07-15
Filing date: 1950-07-15
Publication date: 1956-04-24
Anticipated expiration: 1973-04-24
Also published as: FR1039737A; GB687051A

Description

April 24, 1956 F. E. FLORSCHUTZ ET AL 2,743,337

CIRCUIT INTERRUPTER Filed July 15, 1950 2 Sheets-Sheet 1 & Ll-

N] o m 2 WITNESSES: INVENTORS Fritz E.Florschutz and Wayne 5. Aspey Z'df/r,

United States Patent Ofiiice 2,743,337 CIRCUIT INTERRUPTER Fritz E. Florschutz, Pittsburgh, and Wayne S. Aspey, Turtle Creek, Pa., assignors to Westinghouse Eiectric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 15, 1950, Serial No. 174,012 24 Claims. (Cl. 200-150) This invention relates to circuit interrupters, in general, and more particularly to tank configurations therefor.

In United States patent application filed July 15, 1950, Serial No. 174,107, by Benjamin P. Baker and Winthrop M. Leeds, entitled Circuit interrupter, now U. S. Patent 2,693,519, issued November 2, 1954, and assigned to the assignee of the instant application, there is disclosed and claimed a novel type of circuit interrupter employing a tank construction having a very small fluid or oil content. It is a general object of our invention to provide an improved tank construction over that described in the aforesaid application. We provide improved features, such as a minimum fluid or oil volume, a low fabrication cost, the mechanical strength of the tank being high and there being a good voltage gradient on the inside of the tank by eliminating sharp corners, which would tend to concentrate the voltage stress.

Another object is to provide an improved tank configuration which may be easily fabricated, and which will have a maximum strength.

Another object is to provide an improved minimum oil-content circuit interrupter tank with improved internal electrical stress conditions having a rounded bottom, when viewed in side elevation, and with horizontal oval in which the upper portion of the tank may be formed of smoothly curved oval sections. An oval-shaped top with fiat portions may be included to support the inwardly directed terminal bushings.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

Figure l is a side elevational view of a three-pole liquid-break circuit interrupter embodying our invention;

Fig. 2 is a substantially vertical sectional view through the middle pole unit of the three-pole interrupter shown in Fig. 1, taken substantially on the line 11-11 of Fig. 1, looking in the direction of the arrows, and the contact structure being shown in the fully closed circuit position;

Figs. 3 and 4 are views in section, taken respectively on the lines IIIIII and IVIV of Fig. 2, looking in the direction of the arrows;

Fig. 5 is an enlarged fragmentary sectional view of the leverage mechanism taken along the line V-V of Fig. 2, looking in the direction of the arrows; and

Figs. 6 and 7 show the parts used in forming the lower portion of the tank.

Referring to the drawings, and more particularly to Fig. 1 thereof, it will be observed that we have shown a three-pole liquid-break circuit interrupter generally designated by the reference numeral 1. The individual poles may be designated by the

reference characters

2, 3 and 4, and may be utilized to control the three phases of a transmission system.

Preferably, the three

poles

2, 3 and 4 are simultaneously actuated by an operating mechanism, generally designated by the reference numeral 7, and enclosed within a mechanism housing 8. interconnecting the mechanism housing 8 with each of the three poles 2,

2,743,337 Patented Apr. 24, 1956 2 3 and 4 is a piping system 9, interio-rly of which is horizontally movable a pull rod 5. Preferably also the three

poles

2, 3 and 4 are fixedly spaced apart by means of a pair of spacing rods, or tie-rods, 10, which are bolted to lugs 11 associated with each of the three tanks.

Interiorly of each tank 12 is a leverage mechanism, generally designated by the reference character 6, and more fully shown in Figs. 2 and 5 of the drawings. It will be noted that the pull rod 5 is bifurcated, as at 20, and is pivotally connected, as at 21, to the crank arm 22 integrally formed with an operating shaft 23. Rotatable with the shaft 23 is a plate 24, to which is welded a toggle link 25. A knee pin 26 pivotally interconnects the toggle link 25 with a cooperating toggle link 27. A spring seat 28 is fixed, as by Welding, to the toggle link 27. A compression spring 29 surrounds the toggle link 27, being interposed between the spring seat 28 and an apertured spring seat 3%. The spring seat 36 is stationarily pivotally mounted between a pair of

support plates

31, 32, the latter being fixed, as by welding, to a head 17 of the interrupter 3. The

support plates

31, 32 also serve to journal the operating shaft 23.

The upper end of the toggle link nested, as at 33, to a link 34, the is pivotally connected, as at 35, to end of which is stationarily pivoted ing between the two support plates 31, 32-.

The upper end of the lever 36 is pivotally connected, as at 38, to a triangularly-shaped actuating plate 39. A moving pivot 4h interconnects the insulating lift rod 41 with the actuating plate 39, suitable guide means, not shown, being utilized to assist in guiding the vertical reciprocal motion of the lift rod 41.

The actuating plate 39 is also pivotally connected, as at 42, to a lever 43, the upper end of which is stationarily pivotally mounted, as at 44, between the two

support plates

31, 32.

The operation 25 is pivotally coniower end of which a lever 36, the lower on a pin 37 extendof the leverage mechanism 6 will now be described. To effect an opening operation of the interrupter, from the closed circuit position thereof, as shown in Fig. 2, the pull rod 5 is moved toward the left, as viewed in Fig. l, by the mechanism 7, which forms no part of our invention. The leftward movement of the pull rod 5, as viewed in Fig. 1, effects clockwise rotative motion of the operating shaft 23 (Fig. 5), which breaks the toggle 45, comprising the two

toggle links

25, 27, being assisted by the spring force 29. The breaking of the toggle 45 forces link 34 diagonally downwardly to rotate the lever 36 in a clockwise direction about the stationary pivot 37 to effect counterclockwise rotation of the triangularly-shaped actuating plate 39, to thereby cause downward opening motion of the insulating lift rod 41. The lever 43 swings slightly upwardly in a counterclockwise direction about the stationary pivot 44 during this opening motion.

The downward opening motion of the lift rod 41 correspondingly effects downward opening motion of the conducting bridging member 46 to thereby effect opening of the contact structure within arc-extinguishing units 47 to effect breaking of the circuit therein. Continued downward movement of the lift rod 41 and the conducting bridge 46 effects two isolating gaps in the circuit, as well known by those skilled in the art.

For a description of the manner of the interrupting of the arcs within the units 47, reference may be had to U. S. Patent 2,462,733, issued February 22, 1949 to Gilbert J. Easley, entitled Circuit interrupter," and assigned to the assignee of the instant aplication. This patent, in Fig. 2 thereof, shows the general arrangement of the sequential contact construction which may be utilized in the arcextinguishing units 47, but which forms no part of our invention, and consequently is not described.

eye-ass? Our invention is particularly concerned with the construction of the

tank structures

12, 12' and 12". In other words, we provide a tank 12, of the left hand pole unit of Fig. l, of novel configuration containing a minimum oil volume, and being economical to fabricate. We describe only one, the others being of similar configuration. As shown in Figs. 2-4, each of the tanks 12 is preferably fabricated by cutting a circular dome-flanged member 48 (Fig, 6) in half across the diameter 49 thereof, and taking the two halves thereof, A and B (Fig. 7), and welding the two halves A and B along the seam 13 (Fig, 1). After this is done, the top portion of each tank is preferably formed by bending two members C and D, so that after welding the members C and D upon the seam line 14, the top portion of the tank 12 resembles a truncated, but fiattened or elliptical, cone. Corresponding members of the other two poles of Fig. 1 are indicated by the prime or double prime reference characters as indicated on the drawings.

Thus the upper portion of the tank 12 resembles a figure having oval cross-sections and tapered sides converging in an upward direction. This figure appears like an oval truncated cone.

At the top of the tank 12 are employed three

flat plate members

15, 16 and a, constituting the oval head 17 of the interrupter, the plate members 15, 15a being apertured to support a pair of high

voltage terminal bushings

18, 15 preferably of the condenser type.

From the foregoing description of four improved tank configuration, it will be apparent that if a section is taken through the lower portion 12a (Fig. 2) of the tank 12, within the welded members A and B, the result will be an elliptic or oval section. It will also be apparent that a section taken through the top truncated conical portion 12b (Fig. 2) of the tank 12 will likewise lead to a substantially elliptic or oval section.

The upper portion 12b of the tank 12 between the oval head 17 and the lower portion 12a may be said to have a surface of the shape generated by a line, such as the seam line 14. each point of which moves in a closed oval path. As shown in Fig. 2, this line may be a straight line.

It will be observed that by the configuration shown, there is adequate electrical clearance between the two arc-extinguishing units 47 supported at the interior ends of the two terminal bushings 18, 1? and the interior walls of the tank 12. Moreover, it will be apparent that there is a good voltage gradient on the inside of the tank 12 from live parts to ground due to the smooth shape of the tank, there being no sharp corners to concentrate the voltage stress. Also the particular configuration, illustrated in the drawings, lends itself readily to high mechanical strength, due to the convex shape of the individual members and to their combination in such a manner as to support one another. The construction also requires a minimum of oil, and has low cost in fabrication.

It will be observed that the length X of the terminal bushings l 19 is over two times greater than the radius R of the semi-circular lower portion 12a of the tank 12, taken in a vertical plane through the tank 12 and also through the

terminal bushings

18, 19. Moreover, it will be apparent that any section taken through the lower half 12a of the tank 12, say on the planes A, B or C, has an oval-shaped cross-section. Also, horizontal sections taken 7 through the upper portion, or extension 1217 of the tank 2, above the horizontal plane D, have an oval shape. The cross-sectional area taken on a horizontal plane through the upper portion 12b of the tank 12 may be less than the cross-sectional area taken through the tank 12 on the plane D through the 'midportion of the tank 12.

Preferably, the

terminal bushings

18, 19 are of the condenser type so that the grounded leverage mechanism 6 is adjacent to surfaces 59, 51 of the

terminal bushings

13, 19, respectively, which are grounded. Furthermore, itwill be observed that the top corners 52 of the tank 12 are only adjacent the grounded surfaces 50, 51 of the

terminal bushings

18, 19, and are at a considerable distance from the live parts of the arc-extinguishing units 47 or the conducting bridging member 46.

By having a smooth interior shape, with no sharp corners, the voltage gradient is more uniform, and a concentration of voltage stress is avoided. Furthermore, the volume of the fluid contained within the tank 12 is at a minimum. Thus, if the invention is applied to a liquidtype oil breaker, the initial and maintenance costs of the interrupter are considerably reduced because of the small quantity of oil utilized in the tank 12, having a minimum volume with adequate electrical clearances between live parts of the interrupter and the grounded tank walls.

It will be noted that the configuration of the tank 12 with respect to the interrupting units 47 is such that substantially all of the surface elements of the tank 12 are spaced a minimum distance S away from the units 47 and the cross-bar 46 to prevent flashover therebetween. In other words, considering the distance S in Fig. 2 as the minimum distance which will prevent flashover between the live parts of the units 47, and the interior surface of the grounded tank 12, it will be noted that the distance S is substantially preserved between the units 47 and the interior walls of the grounded tank 12. Fig. 4 may be referred to in this connection.

Consequently, the envelope of the tank 12 is such as to provide only enough clearance between the interior walls of the tank 12 and the units 47 to prevent breakdown for the voltage considered. The result of such a construction is that the volume enclosed by the tank 12 is a mimimum and yet the surface elements of the tank or envelope 12 are spaced only the minimum distance from the units 47 and the conducting bridging member 46 to prevent flashover therebetween.

Although we have shown and described a specific structure it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the appended claims.

We claim as our invention:

1. A tank for a high voltage circuit interrupter of the type having two terminal bushings extending therea into, the lower portion of which has smoothly curved elliptic sections, and the upper portion having a truncated generally conical configuration joining to the lower portion.

2. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, two terminal bushings extending into the tank adjacent the upper end thereof, said tank having its lower half generally semi-circular in crosssection taken in a vertical plane extending through the tank and through the two terminal bushings, horizontal sections taken through the lower half of the tank being of smoothly curved oval configuration, said tank having an extended portion at its upper end for receiving the two terminal bushings, and said upper extended portion comprising a truncated generally conical member.

3, A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, two terminal bushings extending into the tank adjacent the upper end thereof, said tank having its lower half generally semi-circular in crosssection taken in a vertical plane extending through the tank and through the two terminal bushings, horizontal sections taken through the lower half of the tank being of smoothly curved oval configuration, said tank having an extended portion at its upper end for receiving the two terminal bushings, said upper extended portion comprising a truncated generally conical member, the radius of the semi-circular lower half portion of said tank taken in a vertical plane extending through the tank and through the two terminal bushings being less than half the length of the terminal bushings.

4. A circuit interrupter including a tank, the lower portion of the tank including a pair of half members seared together, each half member beinga semi-circular dished member, the upper portion of the tank comprising the two sides of a truncated oval-shaped generally conical member secured together and to the lower portion of the tank, said oval-shaped generally conical member having smoothly curved end portions, and a pair of terminal bushings extending into the tank through the outer end of said upper portion of the tank.

5. A circuit interrupter of the liquid-break type including a tank having a pair of terminal bushings extending thereinto, an arc-extinguishing unit supported at the interior end of each terminal bushing, a conducting bridging member electrically interconnecting the two areextinguishing units in the closed-circuit position thereof, the lower portion of the tank having smoothly curved elliptic sections with the bridging member extending in the direction of the major axes thereof, and the upper portion of the tank having a truncated generally conical configuration joined to the lower portion of the tank.

6. A circuit interrupter of the liquid-break type inupper end thereof, an arc-extinguishing unit supported at the interior end of each terminal bushing, a conducting bridging member electrically interconnecting the two arcextinguishing units in the closed-circuit positiont thereof, said tank having its lower half generally semi-circular in bushings being less than half the length of the terminal bushings.

8. A circuit interrupter including a tank, the lower porsaid lower portion of the tank being generally semicircular in vertical cross-section and oval in horizontal cross-section, an oval head for the tank having one or more flat surfaces, a pair of terminal bushings supported on and extending through said one or more fiat surfaces of the oval head and extending in the tank to adjacent the mid-portion thereof, and the upper portion of the tank between the oval head and said lower portion having a surface of the shape generated by movement of a straight line each point of which moves in a closed oval path.

9. A circuit interrupter including a tank, the lower portion of the tank including a pair of semi-circular dished members, a seam joining said pair of semi-circular dished members at the lower portion of the tank along the circumferential edges of the dished members, and the upper portion of the tank having a truncated generally conical configuration joined to the lower portion.

10. A circuit interrupter including a tank, means supporting the tank adjacent the lower end thereof, the lower portion of the tank including a pair of semi-circular dished members, a seam joining said pair of semi-circular dished members at the lower portion of the tank along the circumferential edges of the dished members, the upper portion of the tank having a truncated tapered configuration joined to the lower portion, and a pair of terminal bushings extending within the upper portion of the tank.

11. A circuit interrupter of the liquid-break type including a tank, means supporting the tank adjacent the lower end thereof, the lower portion of the tank including a pair of semi-circular dished members, and a seam joining said pair of semi-circular dished members at the lower portion of the tank along the circumferential edges of the dished members, the upper portion of the tank having a truncated conical configuration joined to the lower portion, a pair of terminal bushings extending within the upper portion of the tank, an arc-extinguishing unit supported adjacent the interior end of each terminal bushing, a conducting bridging member electrically interconnecting the two arc-extinguishing units in the closedcircuit position thereof, and the bridging member being disposed substantially in the vertical plane which extends through the seam of the lower portion of the tank.

12. A circuit interrupter including a tank, the lower portion of the tank including a pair of semi-circular dished members, with a seam at the lower portion of the tank along the circumferential edges of the dished members, the upper portion of the tank comprising two portions secured together to form a tapered truncated oval-shaped member secured to the lower portion of the tank and having smoothly curved end portions, and a pair of terminal bushings extending into the tank through the outer end of said upper portion of the tank.

13. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, two terminal bushings extending into the tank adjacent the upper endthereof, said tank having its lower portion generally senii-circular in crosssection taken in a vertical plane extending through the tank and through the two terminal bushings, a horizontal section taken through the lower end of the tank being of smoothly curved oval configuration, the upper portion of the tank having a surface of the shape generated by movement of a line each point of which moves in a smoothly curved oval path.

14. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, two terminal bushings extending into the tank adjacent the upper end thereof, said tank having its lower portion generally semi-circular in crosssection taken in a vertical plane extending through tr e tank and through the two terminal bushings, a horizontal section taken through the lower end of the tank being of smoothly curved oval configuration, the upper portion of the tank including two side pieces extending upwardly to the top of the tank and secured together with vertical seams, a horizontal section taken through the upper end of the tank being of smoothly curved oval configuration, and the radius of the serni-circular lower portion of said tank taken in a vertical plane extending through toe tank and through the two terminal bushings being less than half the length of the terminal bushings.

15. A circuit interrupter of the liquid-break type ineluding a tank, means supporting the tank adjacent the lower end thereof, the lower portion of the tank including a pair of semi-circular dished members, a seam joining said pair ofserni-circular dished members at the lower portion of the tank along the circumferential edges of the dished members, the upper portion of the tank being of generally oval shape and joined to the lower portion, a pair of terminal bushings extending within the upper portion of the tank, an arc-extinguishing unit supported adjacent the interior end of each terminal bushing, a conducting bridging member electrically interconnecting the two areextinguishing units in the closed-circuit position thereof, and the bridging member being disposed substantially in the vertical plane which extends through the seam of the lower portion of the tank.

16. A circuit interrupter of the liquid-break type including a tank, means supporting the tank adjacent the lower end thereof, a pair of terminal bushings extending into the top of the tank, the lower portion of the tank being generally semi-circular in vertical cross-section taken through the pair of bushings and being oval in horizontal cross-section, the upper portion of the tank being of oval shape in horizontal cross-section, said tank comprising members joined by a seam lying in the vertical plane through the pair of bushings and extending from the top of the tank near where one bushing enters down one side of the upper portion, around the generally semicircular lower portion of the tank and up the other side of the upper portion to the top of the tank near where the other bushing enters, an arc-extinguishing unit supported adjacent the interior end of each terminal bushing, a conducting bridging member electrically interconnecting the two arc-extinguishing units in the closedcircuit position thereof, the bridging member being disposed substantially in the vertical plane which extends through the said seam and the pair of bushings, and the radius of said semi-circular lower portion of said tank being not greater than half the length of the terminal bushings.

17. A circuit interrupter including a tank, a pair of terminal bushings extending into the tank at the upper end thereof, a pair of arc-extinguishing units secured to the interior ends of the terminal bushings, a conducting cross-bar electrically interconnecting the arc-extinguishing units in the closed-circuit position of the interrupter, said tank comprising at its upper end two side pieces secured together by vertical seams along their sides and shaped so that horizontal sections taken therethrough will be of smoothly curved oval configuration, said tank having its lower portion formed by a pair of semi-circular dished members joined together by a seam, and the seams between the two upper side pieces and the seam joining the lower semi-circular dished members being in substantially the same vertical plane.

18. A circuit interrupter including a tank, a pair of terminal bushings extending into the tank at the upper end thereof, a pair of arc-extinguishing units secured to the interior ends of the terminal bushings, a conducting cross bar electrically interconnecting the arc-extinguishing units in the closed-circuit position of the interrupter, said tank comprising at its upper end a portion having a'surface generated by movement of a straight line each point of which moves about a smoothly curved closed oval path having its major axis extending in the same direction as the cross bar, said tank having its lower portion of generally semi-circular cross-section in the vertical plane through the cross bar and being of smoothly curved oval cross-section in horizontal planes, said tank having seams at the sides of the upper portion and around the semicircular lower portion in substantially one vertical plane extending through the cross bar and the major axes of the oval cross-sections of the tank.

19. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, an oval head for the tank having a pair of fiat surfaces disposed at an angle relative to each other, two terminal bushings converging toward each other in a downward direction and each supported perpendicularly to one of said fiat surfaces, said two terminal bushings extending into the tank'adjacent the upper end thereof, said tank having its lower portion generally semi-circular in cross section taken in a vertical plane extending through the tank and through the two terminal bushings, a horizontal section taken through the lower end of the tank being of smoothly curved oval configuration, the upper portion of the tank beginning just above said lower portion of generally semi-circular vertical cross-section having a surface of the shape generated by movementof a line each point of which moves in a smoothly curved oval path.

20. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, an oval head for the tank, two terminal bushings diverging from each other in an upward direction and supported by said oval head, said two terminal bushings extending into the tank adjacent the upper end thereof, an arc-extinguishing unit on the lower end of each terminal bushing, a conducting bridging member electrically interconnecting the two arc-extinguishing units in the closed position of the interrupter, said tank having its lower portion generally semi-circular in crosssection taken in a vertical plane extending through the tank and through the two terminal bushings, a horizontal section taken through the lower end of the tank being of smoothly curved oval configuration, said conducting bridging member extending generally in the same direction as the major axis of said oval, and the upper portion of the tank which extends from said lower portion of generally semi-circular vertical cross-section to said oval head having a surface of the shape generated by movement of a line each point ofwhich moves in a smoothly curved oval path.

21. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, two terminal bushings extending into the tank adjacent the upper end thereof, an arcextinguishing unit on the lower end of each terminal bushing, a conducting bridging member electrically interconnecting the two arc-extinguishing units in the closed position of the interrupter, said tank having its lower portion generally semi-circular in cross-section taken in a vertical plane extending through the tank and through the two terminal bushings, a horizontal section taken through the lower end of the tank being of smoothly curved oval configuration, the upper portion of the tank above said lower portion having a surface of the shape generated by movement of a straight line each point of which moves in a smoothly curved oval path, and said conducting bridging member extending generally in the same direction as the major axes of said ovals and being movable substantially in said vertical plane.

22. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, an oval head for the tank having a pair of flat surfaces disposed at an angle relative to each other, two terminal bushings diverging from each other in an upward direction and supported perpendicularly to said pair of flat surfaces, said two terminal bushings extending into the tank adjacent the upper end thereof, said tank having its lower portion generally semi-circular in cross-section taken in a vertical plane extending through the tank and through the two terminal bushings, a horizontal section taken through the lower end of the tank being of smoothly curved oval configuration, the upper portion of the tank joined to the outer edges of the flat surfaces of said oval head and extending down to said lower portion having a surface of the shape generated by movement of a straight line each point of which moves in a smoothly curved oval path.

23. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, an oval head for the tank having a pair of flat surfaces disposed at an angle relative to each other, two terminal bushings converging toward each other in a downward direction cularly to said pair of fiat surfaces, said two terminal bushings extending into the tank adjacent the upper end thereof, said tank having its lower portion generally semicircular in cross-section taken in a vertical plane extending through the tank and through the two terminal bushings, a horizontal section taken through the lower end of the tank being of smoothly curved oval configuration, the upper portion of the tank including two side plane extending through the tank and through the two terminal bushings being less than half the length of the terminal bushings.

24. A circuit interrupter including a fixed tank of constant volume, means supporting the fixed tank adjacent the lower end thereof, an oval head for the tank having surfaces disposed at an angle relative to each other, two terminal bushings diverging from each other in an upward direction and supported perpendicularly to said pair of flat surfaces, said two terminal bushings extending into the tank adjacent the upper end thereof, said tank having its lower portion generally semi-circular in cross-section taken in a vertical plane extending through the tank and through the two terminal bushings, a horizontal section taken through the lower end of the tank being of smoothly curved oval configuration, the upper portion of the tank including two side pieces extending up to the outer edges of the flat surfaces of said oval head and secured together with seams lying in said vertical plane, said seams extending up to said oval head, a horizontal section taken through the upper end of the tank being of smoothly curved oval of the semi-circular lower portion of said tank taken in a vertical plane extending through the tank and through the two terminal bushings being less than half the length of the terminal bushings.

References Cited in the file of this patent UNITED STATES PATENTS 262,232 Kowalevsky Aug. 8, 1882 763,663 Edmiston June 28, 1904 1,129,635 Burke et a1. Feb. 23, 1915 1,156,542 Merriam Oct. 12, 1915 1,257,328 Donnelley Feb. 26, 1918 1,769,562 Wood July 1, 1930 1,899,658 Ainsworth Feb. 28, 1933 2,086,134 Ludwick July 6, 1937 2,362,657 Meyer Nov. 14, 1944 2,545,481 Maier Mar. 20, 1951 FOREIGN PATENTS 110,284 Australia Apr. 11, 1940 626,198 Great Britain July 11, 1949