The present invention relates to a core for a transformer that comprises a plurality of bent metal sheets that are all bonded to form a structure that surrounds a core opening and forms the core, wherein in each case the sheet ends of each metal sheet do not touch one another within the core, so that within the core the metal sheets form at least one air gap with the core or at a periphery of the core at their respective sheet ends.
In transformer construction, the cores of the transformers are often built as what are known as wound cores that consist of many layers of thin metal sheets that are laid around each other with an offset with respect to one another, or pushed into one another, and form metal sheet windings with at least one cut.
One leg of the wound cores passes through the transformer windings. Multiple wound cores can be arranged next to one another or around one another. In some types of core, the “Unicore single” type for example, the wound cores are first disassembled manually into individual “books” as they are known, in order then to be placed manually, book by book, through the ready-prepared transformer windings. Such a manufacturing process is performed manually, and can therefore not be carried out economically.
In other types of wound cores, such as for example wound cores of the “Unicore duo” type, the entire core can be separated into two halves, usually U-shaped or V-shaped, wherein each half can be passed through the prefabricated transformer windings from opposite directions, in order then to be brought together into a complete core. Such a core can be fitted automatically through the transformer windings.
At the cuts of the metal sheets of the wound cores, more or less wide air gaps form which present a magnetic resistance that increases with the width, and thereby cause corresponding no-load losses. While wound cores of the “Unicore single” type only have one cut per metal sheet winding, a wound core of the “Unicore duo” type, or a stacked core, has two cuts in each metal sheet winding. The result of this is that higher no-load losses occur with these types. These reduce the efficiency of the transformer. The no-load losses are an important criterion for the selection of a transformer type, in particular in energy distribution networks.
The object achieved by the invention therefore consists in minimizing the no-load losses in the transformers through the lowest possible magnetic resistances.
A core for a transformer comprising a plurality of bent metal sheets is provided. The sheets are all bonded to form a structure that surrounds a core opening and form the core, wherein in each case the sheet ends of each metal sheet do not touch one another within the core, so that within the core the metal sheets form at least one air gap with the core or at a periphery of the core at their respective sheet ends. According to the invention, the core is impregnated or coated at least at the sheet ends of the metal sheets with a lacquer that contains magnetic particles, wherein the impregnation or coating fills at least the air gaps at the sheet ends of the metal sheets.
The impregnation thus fills at least the region of the air gaps between the ends of the metal sheets. As a result of this, the magnetic flux at the transition from one metal sheet, through the air gap filled with magnetic lacquer, to the next metal sheet end does not bulge as much as would be the case without a magnetically permeable filling, that is for example when filled with oil or air. When a core according to the invention is used the magnetic resistance of a transformer is thus reduced. Put in other words, the no-load losses with a core according to the invention are reduced in comparison with those of cores of the prior art.
Preferably the entire core is impregnated or coated with the lacquer containing the magnetic particles. The impregnation or the coating can thus be applied to the core as a whole, whereby the filling factor of the core, and thus the efficiency of the transformer, is improved. The magnetic particles introduced through the impregnation or the coating reduce the magnetic resistance of the core.
The magnetic particles are preferably superparamagnetic iron oxide nanoparticles. Such nanoparticles are so small that they form a suspension with the liquid lacquer, and can thus penetrate with the liquid lacquer even into narrow air gaps of a core.
In one preferred form of embodiment, the lacquer is a polyurethane lacquer. Such a lacquer is characterized by its hardness and its resistance to corrosion. The formation of a suspension with the superparamagnetic iron oxide nanoparticles is also possible with these lacquers.
The lacquer is preferably water-based. Possible environmental problems caused by harmful solvents are also avoided if a water-based lacquer is used.
The core is preferably composed essentially of U-shaped metal sheets that are arranged, pushed into one another, in such a way that the legs of a U-shaped metal sheet are at least partially in contact in each case with a leg of another U-shaped metal sheet, wherein the sections that bond the legs of these two metal sheets together are positioned lying opposite one another. Expressed in other words, the core is preferably a core of the “Unicore duo” type, or of the “Tranco” type. The impregnation or the coating of such core types with a lacquer containing magnetic particles is particularly preferred, since in this case the no-load losses arising due to the two air gaps of a metal sheet winding can largely be compensated for. The fabrication can furthermore be better automated with this type of core, in particular in that the core can automatically be pushed together. A large amount of manual work is thus avoided, and larger series can be manufactured economically. The manual insertion of “books”, as in the case of the “Unicore single” types, is also omitted here.
In one form of embodiment, also preferred, the metal sheets of the core are each bent around the core opening, wherein the metal sheets are each interrupted at one location by an air gap in such a way that the ends of the metal sheets are arranged aligned opposite to one another at this air gap. Expressed in other words, the core is also preferably implemented as a core of the “Unicore single” type. With a wound core of the “Unicore single” type, in which only one air gap is present in each metal sheet winding, an impregnation again increases the efficiency of the transformer. The technical advantages of this core type for fabrication are retained.
The core is preferably a wound core. Precisely in the case of design as a wound core, the impregnation or coating with the lacquer containing the magnetic particles helps to achieve a significant improvement in the efficiency of the transformer.
The core is preferably a stacked core. Again in the case of stacked cores, the lacquering described above leads to a reduction in the no-load losses. Expressed in other words, the impregnation or the coating is also applicable to stacked cores that have a common air gap extending over the metal sheets. This is filled with the lacquer that contains the magnetic particles, and the efficiency of the transformer thereby increased.
A transformer with a core according to the invention is further advantageously provided.
A method for the manufacture of a transformer is also provided, said transformer comprising a plurality of bent metal sheets that can all be bonded to form a structure that surrounds a core opening and form the core, wherein in each case the sheet ends of each metal sheet do not touch one another within the bonded core. As a result, within the bonded core the metal sheets form at least one air gap with the bonded core or at a periphery of the bonded core at their respective sheet ends. The method according to the invention comprises the following steps: passing the individual metal sheets through at least one transformer winding of the transformer; bonding the individual metal sheets to create the bonded core within the transformer; and impregnation or coating the sheet ends of the metal sheets with a lacquer that contains magnetic particles until the air gaps at the sheet ends of the metal sheets are filled with the lacquer.
The lacquer, furthermore, is preferably sprayed onto the ends of the metal sheets. In such an embodiment, the impregnation or coating of the core can be carried out particularly easily, quickly and economically.
The impregnation or coating of the core according to the invention, furthermore, preferably takes place by spraying the lacquer on to the metal sheets of the core. A cup gun is preferably used for this purpose.
In a dry transformer product, neither a housing nor a selective or complete coating with oil provides protection from corrosion. The impregnation or coating of the entire core of such a transformer with the lacquer containing the magnetic particles here in particular also leads to corrosion protection being provided, since the transformer, as well as its core, can here be exposed to the weather.
Various transformer cores are shown by way of example in the figures. The filling of the air gaps is illustrated schematically, here:
A stacked core 9 according to the invention is illustrated schematically in
Various combinations of core 3 are shown in
Although the invention has been illustrated and described in detail more closely through preferred exemplary embodiments, the invention is not restricted by the disclosed examples, and other variations can be derived from this by the expert without leaving the protective scope of the invention.
1 Metal sheet
2 Sheet end
3 Core
4 Core opening
5 Air gap
6 Lacquer
7 Unicore single
8 Unicore duo
9 Stacked core
10 Evans core
11 Outer wound core
12 Inner wound core
13 Transformer winding
Number | Date | Country | Kind |
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10 2018 203 087 | Mar 2018 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2019/055188 | 3/1/2019 | WO | 00 |