Method of induction brazing transformer strands to base plate

Details Method of induction brazing transformer strands to base plate Method of induction brazing transformer strands to base plate

2000-12-04

2001-12-25

Leung, Philip H. (Department: 3742)

Electric heating

Inductive heating

Metal working

C219S605000, C219S603000, C228S224000, C228S262900

Reexamination Certificate

active

06333494

ABSTRACT:

This invention relates to the manufacture and/or repair of electrical components and specifically, to the joining by induction brazing of metal wires to metal bars, and specifically to the formation of lap joints between copper strands and a copper buss bar in transformer electrical connections.
BACKGROUND OF THE INVENTION
Current techniques for brazing the lap joints of copper wires or strands to a copper buss bars involve either electric brazing using brazing “tongs”or torches. Torch brazing is a labor intensive process, and can lead to damage to the insulation surrounding the copper strands due to the close proximity of the heat source to the buss bar. Thus, it would be desirable to provide a more efficient method to braze the lap joints of copper strands to copper buss bars without damaging the insulation surrounding the strands.
BRIEF SUMMARY OF THE INVENTION
This invention provides a more efficient means of induction brazing the lap joint between metal wires (e.g., copper strands) and a metal bar (e.g., a copper buss bar). Induction brazing involves the joining of two or more components without melting the component materials. In the process, a special filler alloy is melted between the components, i.e., the buss bar and copper strands, to form a complete sealing joint between the components. Specifically, the special alloy filler melts and wets both materials, with the filler held in the joint by capillary action. As the materials cool, the filler solidifies to form a joint. Induction brazing eliminates the need for heat shields and is thus beneficial in the close quarters of a transformer.
In accordance with an exemplary embodiment of the invention, the copper buss bar and the copper strands are thoroughly deburred and cleaned of any contaminants that may adversely effect the quality of the brazed joint. A special filler alloy, in shim or ribbon form, is placed in the joint area between the buss bar and the first of a group of copper strands. Filler alloy shims or ribbons are also placed in between each pair of copper strands. The wires are clamped in a specified location against the buss bar. An induction brazing coil is then located over the buss bar and centered over the stack of copper strands. The brazing coil design has been adapted to this particular process so that a separate coil is located on each side of the buss bar, but with a sufficiently small “profile” as not to engage adjacent buss bars. The joint is heated uniformly until the filler alloy begins to flow and sufficient time has passed for the alloy to flow throughout the joint. A fillet of the filler alloy will also form along the periphery of the joint. A braze alloy filler rod may be employed to supplement the filler alloy if not all areas have filler alloy evident. The finished braze should be smooth with no sharp edges.
According to one aspect, the invention relates to a method of brazing a metal strand to a metal bar comprising: a) positioning a thin filler shim on the surface of the bar; b) placing a metal strand on the filler strip; and c) heating the filler shim utilizing an induction brazing coil to a temperature sufficient to cause melting of the filler shim and to thereby form a brazed lap joint between the metal wire and the bar.
In another aspect, the present invention relates to a method of brazing a plurality of copper strands to a buss bar comprising: a) cleaning the buss bar and the copper strands; b) positioning a filler shim on the surface of the buss bar; c) placing a copper strand on the filler shim, the filler shim and the strand having substantially equal lengths; d) stacking additional copper strands on the buss bar, with a filler shim between each adjacent pair of strands; e) heating the filler shims utilizing an induction brazing coil to a temperature sufficient to cause melting of the filler shims and to thereby form a brazed lap joint between the copper strands and the buss bar.
Typically, the alloy filler shims are heated to about 1300°-1400° F., and each shim may have a thickness of about 0.005 inch.
The invention also relates to a buss bar and copper strand assembly formed by the above process.


REFERENCES:
patent: 2791667 (1957-05-01), Clark et al.
patent: 3431379 (1969-03-01), Yrene
patent: 3634705 (1972-01-01), Fidei
patent: 4307966 (1981-12-01), Spencer et al.
patent: 5504296 (1996-04-01), Sato et al.

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