BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a core for an electrical induction device having a plurality of magnetizable metal sheets, which form a stack of metal sheets resting on each other, wherein spacers which are arranged between two metal sheets form at least one cooling channel.

A core of this type is known from the prior art, and is employed in electrical induction devices including, for example, transformers or reactance coils. For the suppression of eddy currents, the core comprises a plurality of flat magnetizable metal sheets, the flat sides of which are arranged one against another to constitute a sheet metal stack. Spacers can be arranged between two metal sheets which, in combination with the two metal sheets between which they are arranged, together delimit cooling channels. These cooling channels permit the evacuation of heat losses generated in the core. Disadvantageously, however, the spacers occupy additional space, and reduce the fullness factor of the core. Moreover, the spacers cover a substantial proportion of the surface of the two metal sheets with which they are in contact. As a result of the low thermal conductivity of the material of the spacers, this proportion of the respective metal sheet is not available for thermal convection.

Specifically in the light of the employment of new insulating fluids for the insulation and cooling of the active part of an induction device, it is desirable that the core, as a constituent of the active part, can be configured to be as compact as possible wherein, simultaneously, effective cooling is permitted.

SUMMARY OF THE INVENTION

The object of the invention is therefore the provision of a core of the above-mentioned type, which can accommodate greater thermal loads and which simultaneously allows improved cooling.

This object is achieved by the invention, in that the spacers are at least partially comprised of metal. By the use of at least partially metallic spacers, greater thermal conductivity in the core is provided.

The spacers in the cooling channel of the core are arranged and configured such that contact surfaces for the transmission of heat to the metallic spacers are constituted between the core metal sheets which delimit a cooling channel and the spacers, and the outer surfaces of the spacers which are not in contact with the core metal sheets constitute convection surfaces for the evacuation of the heat to the cooling fluid which is present in the cooling channel. The transmission of heat from the core to the insulating fluid is facilitated accordingly, such that a higher cooling capacity is achieved. In other words, in the context of the invention, the useful surface area which is available for thermal conduction and convection is increased. This results in more efficient cooling. The core according to the invention, for an equal cooling capacity, can be provided with smaller cooling channels or with a reduced number of cooling channels, such that the core is configured to be more compact.

In many cases, the materials of the spacers selected according to the prior art are not capable of withstanding the permissible temperatures, especially when insulating fluids which are capable of accommodating a higher thermal loading, such as ester oils, are used. The metallic spacers in the context of the invention can be exposed to higher temperatures, with no resulting damage.

According to the invention, the core can thus withstand higher thermal loads. Moreover, according to the prior art the mechanically soft spacers, which in many cases are manufactured from materials that can accommodate only limited thermal loading, are omitted. Furthermore, metallic spacers are cost-effective, such that the production costs for the core according to the invention are reduced in comparison with the prior art.

The at least partially metallic spacers employed are preferably configured as flat bars. In the sheet metal stack, the spacers engage, at their planar flat sides, with the core metal sheets which enclose the cooling channels.

Advantageously, the spacers, on each side thereof which faces a metal sheet, are provided with an electrically insulating insulation layer. Conversely, the two sides of the spacer which do not face a metal sheet are provided with no insulation layer. In this manner, any constitution of bridges between the core metal sheets which is conducive to ring currents or eddy currents in the spacers can be prevented. As an insulation layer, for example, a phosphate coating or a layer of insulating lacquer of low layer thickness can be considered.

In a preferred embodiment of the invention, the spacers are solid bars arranged with a mutual spacing, wherein semi-finished steel or aluminum parts are preferably employed for the production of the spacers. The spacers are preferably configured with an overhang in relation to the adjoining core metal sheets, in order to further increase the useful surface area available for convection.

According to a further advantageous configuration of the invention, the spacers are not configured as continuous bars, but constitute spacer segments, which are arranged with a mutual spacing on a sheet metal plane.

These spacer segments are preferably arranged on the core metal sheet surface with a mutual offset, in order to generate turbulence in the flow of the insulating fluid.

Preferably, the spacers are at least partially configured as hollow sections. As the inner surfaces of the latter are also in contact with the flowing insulating fluid, the available surface area for convection is increased, and the effectiveness of cooling is further enhanced accordingly. Cost-effective hollow sections are commercially available.

According to a further variant, the spacers are comprised of a plurality of mutually spaced spacer segments, which are connected to one another by means of connecting webs, wherein the height of the connecting webs corresponds to no more than half the height of the cooling channel, in order to prevent any impairment of the flux of the cooling fluid. Advantageously, these connecting webs are configured such that they contribute to the turbulence of the flux of the cooling fluid.

In a further variant, the spacers are at least partially configured as round-section bars.

According to a preferred configuration of the invention, the spacers are at least partially formed of a magnetizable material, and are specifically formed of layered magnetizable metal sheets. Accordingly, magnetizable spacers, in common with the other metal sheets of the core, can accommodate the magnetic flux and, in this manner, contribute to the increase in the magnetic cross section of the core. According to this further development of the invention, it is particularly advantageous if the spacers are comprised of layered magnetizable metal sheets. The layered design of the magnetizable metal sheets serves for the suppression of eddy currents in the spacers.

In a further configuration of the invention, only the respective outer regions of the spacers which engage with the metal sheets of the core are formed of a magnetizable material, whereas the inner region is comprised of a substantially non-magnetic metallic material.

The magnetizable material of the spacers preferably assumes a preferred direction of magnetization.

In a preferred configuration of the invention, the metal sheets of the spacers are arranged in the same layer direction and with the same preferred direction of magnetization as the core metal sheets which enclose the cooling channel.

The layered metal sheets of the spacers are preferably bonded by an adhesive or lacquer to form bar-shaped stacks.

The preferred direction of magnetization is appropriately oriented. The preferred direction of magnetization is thus appropriately oriented obliquely, or at an angle to a joint which extends through the core, for example in a region of the core in which sheet metal edges meet, thereby constituting the above-mentioned joint. This region of the core is described hereinafter as the abutment region. The joints respectively constituted by two mutually abutting metal sheets can be mutually offset from one sheet metal layer to the next. The joint is magnetically bridged by the magnetic spacers, and the magnetic resistance of the joint is reduced accordingly.

The spacers preferably extend above the abutment region of the core metal sheets. The spacers and the mutually abutting sheet metal edges of the sheet metal stack, in a sectional side view of the core, thus form an angle. In the context of the invention, in consideration of the preferred direction of magnetization of the core metal sheets and the preferred direction of magnetization of the spacer, this angle can be configured such that a desired magnetic flux distribution is achieved.

In a preferred configuration, the spacers, comprised of magnetic material having a preferred direction of magnetization, in the region of the joint between a limb metal sheet and a yoke metal sheet, are oriented such that the angle between the preferred direction of magnetization of the magnetic material of the spacers and the joint lies between 70° and 110°. By this arrangement, an effective bridging of the joints can be achieved, together with an advantageous magnetic flux distribution in the region of the core surrounding the cooling channel.

In a further configuration of the invention, the spacers are fitted with at least one spring element. The spring element provides a certain degree of damping. This therefore facilitates the production of the core, and additionally improves the mechanical load distribution within the core. By means of this effect, damping is achieved, with a consequent reduction in core noise caused by magnetostriction.

Advantageously, the spacers are comprised of an expanded metal mesh or a wire mesh. Expanded metal meshes or wire meshes are cost-effective, and can easily be fitted between two core metal sheets during manufacture of the core. Advantageously, a non-conductive locking mechanism is incorporated in openings in the expanded metal mesh structure. The manufacture of the core according to the invention is even further simplified accordingly. The metal sheets, for example, can thus be fitted with retaining pins which project from their stack surface.

Advantageously, the expanded metal mesh is secured in an elastically bent position in the sheet metal stack. According to this configuration of the invention, the expanded metal mesh delivers an advantageous spring action, as already described above, thereby permitting mechanical damping, simplified manufacture, and superior mechanical integrity of the core.

In an appropriate further development of the invention in this regard, the spacers are configured in the form of wire mesh. Wire mesh is also commercially available at a low cost. The constituent wire of the wire mesh preferably has a circular or elliptical cross section, such that edges or points are avoided in the wire mesh which might damage the insulation of the core metal sheet.

Corrugated wire nettings can be employed in numerous different variants, thus permitting straightforward adaptation to the geometrical characteristics of the core.

A wire mesh or wire netting is comprised, for example, of two interwoven wires and/or additional reinforcing wires, where applicable. Both wires can be alternately corrugated. In a deviation from this arrangement, corrugated wires enclose a straight, non-corrugated wire. In a further variant, the spacers are configured in the form of a spiral-wound spring-wire mesh.

Advantageously, a netting of this type is constituted such that the corrugations of constituent wires of the wire netting, which constituent wires are substantially horizontally arranged in the subsequent installation position of the core, are configured such that the coverage of the vertical cooling channel corresponds to a maximum of one half of the width of the cooling channel. Advantageously, these connecting webs are configured such that they contribute to the turbulence of the flux of the cooling fluid.

According to a preferred configuration of the invention, the spacers incorporate a fixing section, by means of which the spacer projects out of the sheet metal stack. The fixing section can be employed for the purposes of fixing, but also for the lifting or transport of the core. The formation of a mechanically stable fixing section is only permitted by the selection of a metallic material for the spacers.

Further advantages are provided by the constitution of the fixing section as a hook, an eye or similar, in order to facilitate the lifting or attachment of the core.

Appropriately, the fixing section is fitted with a mounting bracket. The mounting bracket, for example, is likewise formed of a metallic material, and is permanently attached to the fixing section, for example by the molding thereof onto the latter. The mounting bracket serves for the mechanical connection to components of the induction device, including e.g. the top cover of a transformer.

In the variant of the invention in which the spacers are comprised of a magnetizable material, it is advantageous that the spacers incorporate an inner region of a non-magnetic metallic material. In a cross-sectional view of the spacer, a sandwich arrangement is thus provided, wherein the inner region is embedded between two magnetizable outer sections of the spacer. The two magnetizable outer sections are respectively arranged to face the sheet metal stack of the core.

In a further development in this regard, the magnetizable outer regions are likewise comprised of layered magnetizable metal sheets.

Appropriately, the spacers of the upper yoke, on the side thereof which, in the case of an application in a transformer, faces a winding which carries a high voltage, are extended beyond the lower edge of the yoke and, in the region of overlap with the yoke (5), constitute an arch over the winding, which partially covers the yoke (5). The function of this arch is the prevention of high electric field strengths.

