US2933551A - Terminal-bushing with means for controlling magnetic heating - Google Patents

Description

April 19, 1960 H. KRAMER -BUSHING WITH MEANS FOR TERMINAL CONTROLLING MAGNETIC HEATING 2 Sheets-Sheet 1 Filed Oct. 28. 1954 200 400 600 800 I000 I200 I400 I600 I80 Current Amperes Fig.5.

Fig .3. Magnetic Material outing of Conducting Material 5 Fig.4.

INVENTOR Hermon, Kramer WITNESSES W ATTORNEY ZKRW April 19, 1960 H. KRAMER TERMINAL-BUS 2,933,551 HING WITH MEANS FOR CONTROLLING MAGNETIC HEATING 2 Sheets-Sheet 2 Filed Oct. 28. 1954 Fig.9.

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United States Patent'O TERMINAL-BUSHING WITH MEANS FOR CONTROLLING MAGNETIC HEATING Herman Kramer, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a con poration of Pennsylvania Application October 28,1954, Serial No. 465,220

2 Claims. (Cl. 174-152) .This invention relates to terminal bushings in general, and, more particularly to terminal bushings carrying current of such magnitude as to make magnetic or eddy current heating a problem.

A general object of my invention is to provide an improved terminal-bushing construction in which magnetic heating is effectively controlled, or considerably minimized.

Another object of my invention is to provide an improved terininal-bushing construction suitable for carrying current of considerable magnitude in which suitable provision is made for controlling magnetic heating.

My invention is particularly adapted to terminal bushing structures in which considerable current is carried by the current-carrying stud. Although I show only certain applications in the following specification, it is to be clearly understood that bushings adaptable for use in other equipment such as large generators may incorporate features of my invention.

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

- Figure 1 is a side elevational view of a terminal bushing mounted through a tank structure, the latter being shown fragmentarily in vertical section;

Fig. 2 is an enlarged vertical sectional view through the flange assembly for the bushing of Fig. 1;

Fig. 3 is a vertical sectional view through the flange mounting ring of the flange assembly taken along the line III-III of Fig. 4;

Fig. 4 is a plan view of the flange mounting ring of Fig. 3;

Fig. 5 is a graph showing a comparison between temperature rise and current-carrying capacity for various flange structures, to indicate the marked improvement obtained by a utilization of my invention;

2,933,551 Patented Apr. 19, 1960 ICC 5 for structural support members, but since steel is magnetic, the result is that magnetic heating becomes a problem. Consequently, when the current passing through the electrical device is large, or the spacing between the current-carrying terminal stud and the structural support is small, it is necessary to make the disc, tube, or other structural support member of non-magnetic material, unless the magnetic flux within such a member is reduced in some other manner.

. On condenser bushings of the high-voltage type, or in bushings of lower voltage rating, which are not of the condenser type, many such structural parts are required and used. For example, on a particular type of 1200 ampere terminal bushing, the flange rim and the spring cap base are made of steel with a non-magnetic weld across the flux path. Development work on 1600 and 2000 ampere terminal bushings has shown that heating in these parts becomes a limitation.

Non-magnetic welds used, as described above, are relatively inexpensive and permit the use of steel flanges through 1200 amperes. The effectiveness varies with the width of the weld and the amount of diffusion of parent metal into the weld. However, even the best weld as used, permits less than 50% increase in current. I propose to accomplish the necessary reduction in magnetic 3 flux density by providing a conducting path that will act a metallic casing as a shorted transformer winding. For example, in a bushing of the type illustrated in Fig. 1, generally designated by the reference numeral 1, and mounted to a tank structure 2, a flange assembly 4, shown more particularly in Figs.-2-'4, includes a ring-shaped steel mounting flange 6, shown more particularly in Figs. 3 and 4. This is secured by soldering to the grounded brass supporting tube 7, which encircles the condenser wrappings of the bushing 1. Secured to the upper side of the flange ring 6 is 8 having an upper flange ring 9, against which the upper porcelain casing 10 of the bushing 1 rests.

A lower porcelain casing 11 abuts against a lower flange ring 12 secured to the lower end of the tube 7,

and an interiorly disposed terminal conductor stud 13 Fig. 6 is a vertical sectional view through the upper 5 cap assembly of the terminal bushing of Fig. 1, showing how my invention may be applicable to the spring base of the compression spring assembly enclosed within the terminal cap of the bushing;

Fig. 7 is a plan view of the spring base utilized in the compression spring assembly enclosed within the terminal cap illustrated in Fig. 6;

Fig. 8 is a vertical sectional view taken substantially alongthe line VIII-VIII of the spring base shown in Fig. 7;

Fig. 9 is a side elevational view of a disconnecting switch structure illustrating a further application of my invention;

Fig. 10 is an enlarged plan view of one of the mounting flanges used in the disconnecting switch structure of 60 Fig. 9;

Fig. 11 is a sectional view taken substantially along the line XI-XI of the flange support of Fig. 10; and

Figs. 12 and 13 are somewhat diagrammatic views indicating the principles pertinent to my invention;

aIn many applications it is necessary to use a metal. tube,

passes interiorly through the bushing 1, and serves as a tension member to maintain the two porcelain casings 10, 11 in compression against the intermediately disposed flange assembly 4.

As observed in Fig. 1, the tank structure 2 has an upstanding flanged collar 15, to the side of which is secured, as by welding, a mounting ring 16. Mounting bolts 17 and nuts 18 fixedly secure the mounting flange 6 of the flange assembly 4 of the terminal bushing 1 to the upper side of the flanged collar 15 in the manner illustrated in Fig. l, the mounting bolts 17 being positioned within slots 19 of the mounting flange 6, as illustrated in Fig. 4.

It is desirable to use for the mounting flange 6 a material which is of the requisite structural strength,

and steel is preferred for this purpose. However, as well known, steel is magnetic, and hence, when surrounding a current-carrying lead, may be subject to magnetic heating.

Fig. 12 diagrammatically represents the conditions present within the current-carrying stud 13 and the mounting flange 6 according to usual practice. The instantaneous current flow is represented through the stud 13 by the arrows 20. This gives rise to the establishment'of magnetic flux within the annularly shaped mounting flange 6 in the direction into the paper indicated by the crosses in Fig. 12. Circulating eddy currents are set up, which tend to oppose this establishment of magnetic flux, such direction to opposethe. establishment of thernagnetic field. When the current through the terminal stud 13 is alternating, as is the usual case, the continued establishment, decay, and reversal of magnetic flux within the magnetic mounting flange 6 gives rise to considerable heating caused by the circulating eddy currents 21.

I have run a heating test on a mounting flange of the type designated by the reference numeral 6 in Figs. 3, 4 and 12 for various current values through the currentcarrying stud, and curve A in Fig. 5 indicatesthe marked temperature rise in the flange 6 as a function of increasing amperage passing therethrough. This heating effect is, of course, caused by the circulating eddy currents 21 of Fig. 12, which tends to oppose the magnetic field set up in the mounting flange 6 by the passage of current through the terminal stud 13. It is to overcome this problem that my invention is directed.

Curve B in Fig. 5 shows the improvement resulting from making a V out completely through one side of the mounting flange 6 and running three passes of nonmagnetic weld into such a V slot. It will be noted that by an interposition of such a nonmagnetic weld the flux intensity is reduced, and consequently the heating effected within the mounting flange 6, as caused by circulating eddy currents, is somewhat reduced.

Curve C in Fig. 5 indicates a somewhat improved condition obtained by cutting a right-angle slot across one side of the mounting flange 6, placing therein anonmagnetic slug, such as copper, and making nine-passes of nonmagnetic weld about the slug to fill up the slot in the mounting flange 6. As shown by curve C this reduces the intensity of the magnetic flux within the mounting flange 6, and consequently reduces the heating effect caused by the circulating eddy currents.

I have discovered that by providing an adherent coat ing 22 of good conducting material upon the surface of the mounting flange 6 and integral therewith, as indicated in Fig. 3, that the heating effect is drastically reduced, asindicated by the curve D of Fig.5. The conducting path may be provided by plating the mounting flange 6 with copper, or other low resistance material, and with the plating thickness of approximately 0.050 inch the heating curve D of Fig. 5 was obtained. As shown in Fig. 5, the plated flange had a temperature rise of 13 C. at 2000 amperes compared to 110 C. for a plain flange and 60 C. to 88 C. for flanges with non-magnetic welds, all for the same current. It is, therefore, a purpose of my invention to provide steel or magnetic flanges with a heavy adherent copper or conducting coating, plated or sprayed on, or otherwise integrally placed, so that such magnetic flanges may be used on bushings and on other applications where desired. As illustrated in Fig. 3, the

conducting coating 22 completely encompasses a segassess- 1 3 H 4 the eflect oi, circulating eddy currentshas. the. conducting. adherent coating 22 provided on its surface.

As shown, a gasket 31 is provided betweenthe porcelain casing and the under surface of the spring base 30.. Figs. 7 and 8 more particularly show the configuration ofthe coated spring base 30. The external casing 32 of the cap assembly 24 may he formed of steel because it is positioned at a'relatively great distance away from the interiorly disposed current-carrying conductor stud 13, and hence, is not afiected to the extent that the spring base 39 is by the passage of current through the conductor stud 13. By providing the adherent integral conducting coating 22 about the spring base 30 magnetic heating is eliminated or considerably reduced.

13 illustrates somewhat diagrammatically the conditions arising in the conductor stud 13 and in the spring base 36) as a result of utilizing the adherent integral conducting coating 22. Assumcrthat the same magnitude of current 23 is. passing through the. conductor stud 13. in Fig. 13 as was present. under the conditions assumed in Fig. 12. Whereas the magnetic flux, set up in the mounting flange 6 of Fig. 12 caused circulating eddy currents 21 with their attendant heating eifect, in Fig. 13, by the use of the short-circuited loop 22 resulting from the plat ing, or coating, of the surface of spring base 30, the. establishment of an appreciable amount of magnetic flux ing prevents any build-up of magnetic flux within the spring base 39. The heating eifect is therefore considerably reduced as illustrated by the curve D of Fig. 5' contrasted with the other curves A, B and C there illustrated.

known by those skilled in the art, the compression-spring w plate 26 abuts against a shoulder 27 disposed on the conductor stud 13, and has a plurality of guide bolts.28 passing therethrough, which are threaded into a lower spring plate 29, as shown, in Fig. 6. The spring base 30 i is preferably formed of steel and,as shown, to minimize Fig. 9 illustrates still a further application of my in: vention involving a disconnecting switch structure 35. The terminal pad 36, to which a line connection is made, is integrally formed with a jaw contact 37, the latter being supported by a ceramic post 38 upon a channel support or base 32. A. disconnecting switch blade 40 is pivotally mounted at 41 to one end of a conductor stud 42,- which passes interiorly through a porcelain cylinder 43 and terminates at the terminal pad 44. The porcelain or ceramic cylinder 43 issupported by a mounting flange 45, more. particularly shown in Figs. 10 and 11, and preferably made of cast iron. To prevent the effect of magnetic heating, the mounting flange 45. is sprayed, or plated, with an adherent conducting coating 22 to form a short-circuited conducting loop about the sides of the flange 45. The coating 22 prevents or suppresses the build-up of magnetic flux within the interior of the mounting flange 45 in the manner illustrated in Fig. 13 of the drawings.

From the foregoing description of several embodiments of my invention, it will be apparent that it may be used in connection with any magnetic structural member utilized in conjunction with a current-carrying lead. The invention may be utilized in connection not only with bushings of the type shown in Figs. 1 and 9, but also with other types of bushings for carrying current, such as bushings associated with. generators, transformers or any type of rotating equipment. Wherever a current-carrying stud passes through a support member adjacent thereto composed of magnetic material, by an ap" plication of an adherent integral conducting coating, either plated or sprayed upon the surface of the structural member, the establishment of the magnetic flux therein is suppressed. Many applications utilizing the principles of my invention will readily suggest themselves to those skilled in the art.

Although I have shown and described specific structures it is tobe clearly understood that the same were merely for the purpose of illustration, and that changes and modification may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

I claim as my invention:

1. A terminal bushing including an axially disposed current-carrying terminal stud for carrying relatively high-amperage alternating currents during operation of the terminal bushing, the terminal bushing having at least one hollow insulating casing surrounding said axially disposed terminal stud and a mounting-flange assembly for supporting the bushing, the mounting flange assembly including a grounded metallic support tube and an annular metallic mounting flange composed of magnetic material and fixed adjacent one end of said metallic support tube, and a thin, adherent, conducting coating covering substantially the entire surface area on all sides of said metallic mounting flange including the inner side thereof, and said thin adherent conducting coating forming a short-circuited loop to suppress the build-up of magnetic flux within the metallic mounting flange during operation of the terminal bushing.

2. A terminal bushing including an axially disposed current-carrying terminal stud for carrying relatively high-amperage alternating currents during operation of the terminal bushing, the terminal bushing having a pair of hollow insulating casings surrounding said axially disposed terminal stud and an intermediately disposed mountingtlange assembly, the mounting-flange assembly including a metallic grounded support tube and a ring shaped steel mounting flange secured adjacent one end of the metallic support tube, a thin, adherent conducting coating covering substantially the entire surface area on all sides of said steel mounting flange including the inner side thereof, and said thin adherent conducting coating forming a short-circuited loop to suppress the build-up of magnetic flux within the steel mounting flange during operation of the terminal bushing.

References Cited in the file of this patent UNITED STATES PATENTS 1,699,342 Austin Jan. 15, 1929 1,726,097 Austin Aug. 27, 1929 2,020,090 Weed Nov. 5, 1935 2,388,848 Howe Nov. 13, 1945 2,559,738 Schweitzer July 10, 1951 FOREIGN PATENTS 312,614- Italy Nov. 21, 1933 312,626 Italy Nov. 21, 1933 OTHER REFERENCES Publication: Influence of Flux on Circuit-Breaker Top Design," by F. B. Johnson, The Electric Journal, vol. 26, No. 6, June 1928, pages 312 and 31,3.

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