US2868868A - Lead-in bushings - Google Patents

Description

Jan. 13, 1959 F J. CQREY 2,868,868

LEAD-IN BUSHINGS Filed April 26, 1957 @WWW v TTOR/EY United States Patent Manufacturing Company, Waltham, Mass., a corporan tion of Delaware Application April 2 6, 1957, Serial No. 655,220

31 Claims. (Cl. 174-153) This invention relates to a lead-in bushing, and, more particularly, to a bushing for providing a high electrical insulation and a hermetic seal to a terminal or other conducting member at its point of entry into a case container -or similar housing. f

lIn many types of electrical apparatus, for example, transformers, it is desirable and even necessary to enclose some element, such as a coil, in a housing. Frequently, the housing must be hermetically sealed to prevent the loss of fluid filling, such as oil, from the container or to prevent the entrance into the interior of air or moisture from the atmosphere. The lead-in connections for such apparatus must be well insulated from the metallic walls through which they pass, while at the same time the opening must be sealed against leakage even at considerable difference in pressure between the interior and the exterior of the container.

This has been done by means of Ia resilient insulating bushing constructed in tw-o parts, one tting inside of the other with a central opening through both pieces in which the conductor is mounted. The pieces can be held together by means of an eyelet that is somewhat longer than the bushing and is forced into the assembled bushing against a shoulder formed on the central conductor which results in crimping the outer end of the eyelet against the walls of the opening in the bushing to hold the parts together. With such a bushing, when used with a potting compound, the potting compound may shrink away from the materials from which the bushing is formed, leaving a void space Ibetween the metallic eyelet and the metallic case. With suii'icient potential diierence, there may be a breakdown between the eyelet or central conductor and the metallic case. When this type of terminal is used with yoil-filled units, the oil of .the filling tends to `be absorbed by the resilient ,plastic of the bus-hing, causing it to swell and destroy the seal.

By the construction of the invention, a cup-shaped washer of insulating material is mounted between the inner end of the bushing and the eyelet head. Where it is desired to prevent electrical breakdown through any void left between the shrinking potting material and the bushing, the washer is mounted with the lip pointed inward to present a longer leakage path to theelectrical potential. In this embodiment the washe-r is'made of a material to which the potting compound will adhere, preventing the formation of a void in this region. Where it is desired to limit the Iabsorption of an oil filling by the resilient plastic or rubber bushing, the cup-shaped Washer is mounted with its lip pointed outward toward the metallic casing to enclose the plastic parts of the washer and prevent the swelling of these parts Vby the absorption of the iiller iiuid. ln this embodiment of the invention, the washer is made of oil-resistant material.

The foregoing and other advantages, objects and features of the invention will be better understood from the following description taken in conjunction with the accompanying drawing wherein: v I

2,868,868 Patented Jan. 1 3, 1959 rice `Fig. l is an exploded view of the bushing of the invention', f

fFig. 2 is a longitudinal sectional lview of an assembled embodiment of the invention; and

Fig. `3 is a longitudinal sectional view of another assembled embodiment of the inventio-n.

=In the drawing, reference numeral 10 designates an electrical conductor which extends through an axial opening in a two-part bushing made of resilientinsulating material such as rubber or tetrafluoroethylene (Teflon).consisting ot' a male part 11 dimensioned for mating fitk in an opening into a fem-ale part 12. An eyelet13 passes through an opening in a cup-shaped washer 1.4 made. of insulating material suchv as fiber sheet. and `the opening inthe bushing dimensioned for interference tit with it. The conductor 10 is inserted into the eyelet, the inside diameter of which is dimensioned for press t with it, and the eyelet is forced against a shoulder 15 formed on the conductor 10, causing the eyelet to be crimped in the region 16 near its outer end, as best seen in Figs. 2 and 3. The two parts 11 and 12 of the bushing are positioned on either side of the mounting case or partition 17. The resilient material of the lbushing is compressed within an opening 18 in the case 17, and swells out beyond it to form a tight tit. When the bushing is used with a component having a case tilled with potting cornpound 20 of a type that does not adhere to the material of the bushing, a slight void 21 will `be left about the male part 11 of the bushing through which there can be an arc-over between the case 17 and the conductor lo, or eyelet 13. By mounting the cup 1-4 made Iof insulating material with its lips 22 extending inward, as shown in Fig. 2, the leakage path for this breakdown is made longer all around the lip 22 of the washer 14, so that an arc-over is less likely t-o occur. When the bushing is used with a cas-e 17 lled with insulating oil, or other 4material that is llikely to be absorbed by the bushing, causing it to swell and possibly pull away from the eyelet or the case, breaking the seal, the cup 14 can be mounted with its lip 22 extending outward, as shown in Fig. 3. This construction compresses the bushing and prevents it from swelling away from the opening in the case to `leave a Ibreak in the seal. Thus this construction protects the seal.

The construction of this invention provides a compact, cheap lead-in `bushing for encased components that is protected from electrical breakdown and leakage of the hermetic seal.

This `invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims lbe given a Ibroad interpretation `commensurate with the scope of the invention within the art.

What is claimed is:

1. A lead-in bus-hing mounted in an opening in a conductive case comprising a member of two resi-lient in sulating parts one on either side of the case one fitting in an opening in the other, each having a passage extending longitudinally therethrough, an eyelet dimensioned for interference t with said passage, an electrical conductor dimensioned for force tit in said eye-let and formed with a shoulder near one end, and a cup-shaped washer of insulating material mounted at the inner end of said bushing, said eyelet being crimped against the shoulder formed on the conductor and outward against the outer resilient insulating member, to fasten said bushing, said conductor and said washer together in the 'opening in the conductive case. e

2. A lead-in bushing mounted in an opening in a conductive case comprising a member of two resilient insulating parts one on either side of the case one tting in an opening in the other, each having a passage extending longitudinally therethrough, an eyelet dimensioned for interference t with said passage, an electrical conductor dimensioned for force t in said eyelet and formed with a shoulder near one end, vand a cup-shaped Washer of insulating material mounted at the inner end of said bushing opening inward, said eyelet being crimped against the shoulder formed on the conductor and outward against the outer resilient insulating member to fasten said bushing, said conductor and said washer together in the opening in the conductive case,

3. A lead-in bushing mounted in anfopening in a conductive case comprising a member of two resilient insulating parts one on either side of the case one fitting in an opening in the other, each having a passage extending longitudinally therethrough, yan eyelet dimensoned for interference t with said passage, and an electrical conductor dimensioned for force t in said eyelet and formed with a shoulder near one end, and a cupshaped washer of insulating material mounted at the inner end of said bushing opening `outward, said eyelet being crimped against the shoulder formed on the conductor and outward against the outer resilient insulating member to fasten said bushing, said conductor and said washer together in the opening in the conductive case.

References Cited in the le of this patent UNITED STATES PATENTS 2,195,029 Hathorn Mar. 26, 1940 2,647,432 Huck Aug. 4, 1953 2,682,570 Elliott June 29, 1954 2,816,950 Kruss et al Dec. 17, 1957 FOREIGN PATENTS 953,892 France May 30, 1949 511,447 Canada Mar. 29, 19,55

Images