Inductor devices – Winding with terminals – taps – or coil conductor end...
Patent
1997-03-20
1998-09-08
Gellner, Michael L.
Inductor devices
Winding with terminals, taps, or coil conductor end...
336200, 336223, H01F 2729, H01F 2728, H01F 500
Patent
active
058050450
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a laminated power supply conductor of a power transformer with an air-cooled foil winding wound from a strip-shaped conductive foil, whose foil end forms a plurality of flag-type end pieces due to slots running in the longitudinal direction of the foil, which end pieces are folded into a power supply conductor stack excentric in relation to the longitudinal direction of the foil.
BACKGROUND INFORMATION
A conventional power supply conductor is described in an article "Electrical Equipment".
In air-cooled power transformers with a high rate of utilization, with low-voltage windings made of strip-shaped conductive foils, the power supply conductors, connected to the conductive foil of the winding in a connection area, can often be overheated. In a conventional embodiment of such a power transformer, conductive buses are provided as power supply conductors, onto which the conductive foil of the low-voltage winding is welded laterally. A current diversion arises freely in the foil according to the induced voltages and resistance conditions. This results in an exponential drop in the power supply conductor current, in the direction of the current from the bus to the foil, and from the first connecting point (corner) of the foil with the bus to the opposite corner of the foil. This causes high current densities to appear in the first corner of the foil, which result in high local thermal stresses. The more distant half of the bus no longer carries useful current due to the exponential drop in the power supply conductor bus current; this means that it no longer contributes appreciably to current transport in the foil. Only eddy currents are induced in the more distant half of the conductor bus, resulting in additional losses. Especially high eddy currents are induced in the power supply buses at the winding edges due to the foil winding. Here the foil winding has considerably increased current densities due to the current displacement effect. The increased amperage in the foil winding induces eddy currents in the cross section plane of the power supply buses and thus additional losses. If, in the case of transformers with a high degree of utilization, the sum of losses in the power supply conductors' area becomes excessive, a solution to this problem is sought by modifying the conducting cross section or the electric conductance through the use of another material or by improving cooling. Combined measures are also used for this purpose.
The "Electrical Equipment" article describes that for power transformers with foil windings that the foil end is subdivided into a plurality of flag-like end pieces in a connection area using slots running in the longitudinal direction of the conductive foil, which are kinked or folded in a right angle so that the flag-like end pieces form a stack of the laminated power supply conductor. Other specific embodiments of such a laminated power supply conductor are not found in the above-cited literature. It must be assumed that considerable eddy current losses arise even in such a laminated power supply conductor.
Therefore, the object of the present invention is to improve the conventional power supply conductor so that eddy current losses in its laminated stack are further reduced.
SUMMARY OF THE INVENTION
This object is achieved according to the present invention by insulating the flag-like folded end pieces of the conductor stack at least in the area of the winding edge of the unslotted foil portion.
With this measure, eddy currents can be suppressed to a high degree in the cross section plane of the power supply conductor. Namely, it is recognized that the danger of eddy current formation is particularly high exactly in the edge area of the unslotted foil portion. The flag-like end pieces need to be insulated from one another and guided only a few centimeters outward from the line of the extended longitudinal side of the unslotted foil portion; an insulation of the flag-like end pieces is not needed further outward (outside the
REFERENCES:
patent: 1160357 (1915-11-01), Agnew
patent: 2378884 (1945-06-01), Seifert
patent: 2961747 (1960-11-01), Lyman
Engineers' Digest, Bd. 28, No. 12, (Dec. 1967), London, England, p. 99.
Electrical Equipment, "Al Alloys for foil-wound coils", (Jul./Aug. 1974), pp. 60-62 (Based on a paper presented at Coilwinding Int'l '74 Convention, London, England by H. Witzig and D.A. Bennett).
Journal de l'equipment electrique et electronique, No. 295 (Nov. 1969), p. 123.
Gellner Michael L.
Mai Anh
Siemens Aktiengesellschaft
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