APPARATUS IN A BALLAST OR TRANSFORMER FOR IMPROVING ITS COOLING

Abstract: The invention relates to an apparatus in a ballast or transformer for improving its cooling. The ballast or transformer comprises a core sheet pack (1, 2), a wind­ ing (6), whose ends extend beyond the core sheet pack, a shell (4) which surrounds the core sheet pack, and a bottom plate (3), to whose side edges (3a) the shell edges (4a) are fastened. Metal plates (5) leaning against the end of winding (6) are fastened to the gables of a housing made up by shell (4) and bottom plate (3). Between the end of winding (6) and said metal plate (5) is arranged a thin insulating layer.

Description: The present invention relates to means in combination with a ballast or transformer for improving its cooling, said ballast or transformer comprising a core sheet pack, a winding whose ends extend beyond the core sheet pack, a shell which surrounds the core sheet pack, a bottom plate to whose side edges the shell edges are fastened and metal end plates which are fastened to the gables of a housing made up by the shell and bottom plate and which abut the end of the winding with a thin insulating layer therebetween. A corresponding means is known from AU-B-488513. The disclosed housing for a choke has channels which run over the entire length of the housing parallel to the bottom plate. These channels are used for guaranteeing a good heat transfer from the sheet metal of the choke to the housing made preferably from aluminium or steel. When the ballast or transformer is screwed with the back of the bottom plate onto a flat, horizontal surface the channels formed within the housing have no further effect than the mentioned heat transfer by conductivity. An object of the invention is to provide an apparatus for improving or intensifying the cooling of the ballast or the transformator so that the physical size of a ballast or transformater relative to its VA-quantity or -capacity can be reduced so as to save in material costs and space requirements. This object is achieved according to the invention in that the means consist of bent or molded rib members in said end plates, the rib members being positioned in the free space between the winding end faces and the end of a core sheet pack at a distance from the end of the core sheet pack in a manner that, within the area of said rib members, cooling air can circulate on either side of the end plate, for which purpose the lower edge of end plate is positioned at a small clearance from bottom plate or the lower edge of the end plate is provided with holes or notches, and the upper edge of the end plate or the edge of shell connected therewith, is provided with holes or notches which open into the free spaces between the ribs and the end of core sheet pack. The rib members positioned according to the invention do not increase the maximum dimensions of a ballast or transformer. Thus, it has been realized that,if the size of a ballast or transformer is greater than approximately 100 VA (100 W), it is preferable to install metal plates abutting the winding ends and insulated from the winding only with a thin insulating material. The extra cost incurred by a metal plate is quite small compared to the saving in winding and magnetic material provided by a considerably increased cooling area. The end plates carrying said rib members are preferably made of aluminium. In a preferred embodiment of the invention, the rib members are designed in a manner that the edges of said metal plate are profiled to form grooves which increase its surface area. In the disposition of these grooves, it is possible to utilize the free spaces on either side of the winding end between the shell and the side face of a winding end portion. For more effective air circulation also along the inner surface of a metal plate, it is preferable to position the lower edge of said metal plate at a little distance clear of the bottom plate, or the lower edge of said metal plate is provided with holes or notches and the upper edge of said metal plate or the shell edge connected therewith is provided with apertures or notches. In this embodiment, it is preferable that, by a proper choice of the dimension "width/height" of a ballast, the rate of air flow can be increased on either side of the winding end (chimney effect). The air flowing inside a cooling plate serves to cool the winding simultaneously and directly. Above all, this arrangement prevents a characteristic drawback of the prior art solution, namely the formation of a hot, still air layer in the space between the winding end and the end insulation. By means of rib members according to the invention, the cooling effect is improved to such a degree that the size or a ballast or transformer can be reduced decisively, up to tens of percent compared to the present practice. The reduction of the size of a ballast also leads to additional savings because of the reduction of the dimensions of a lighting fixture. One embodiment of the invention will now be described by way of an example and in more detail with reference to the accompanying drawings, in which Fig. 1 shows a vertical longitudinal section of a ballast provided with means according to the invention; Fig. 2 shows a horizontal section of the same ballast; Fig. 3 shows a vertical cross-section of the same ballast; and Fig. 4 shows an alternative embodiment of a ballast according to the invention. The core sheet pack of a ballast, as shown in the drawing, consists of E-sheets 1 and I-sheets 2. A winding 6 is fitted between the E-arms and both ends of winding 6 extend beyond the ends of said core sheet pack as the winding must travel around the midmost E-arm. Regardless of what shape of sheets the core sheet pack has been made up, a typical feature in the structure is that the winding ends extend beyond the core sheet pack. A core sheet pack, together with its winding, has been laid on top of a bottom plate 3. The ends of bottom plate 3 are provided with holes 13 for using screws extending therethrough to fasten the ballast, for example to a lighting fixture. A shell 4, made of rather thin sheet metal, envelopes the core sheet pack and its winding. The edges of bottom plate 3 are provided with hock-shaped bends 3a to be grabbed by bends 4a at the edges of shell sheet 4. The ends of winding 6 must be provided with a protective insulation for preventing manual touch. In the invention, however, this protective insulation has been achieved in a rather exceptional manner in connection with metal cooling plates, explained in more detail hereinbelow. The gables of a housing consisting of a shell 4 and a bottom plate 3 are provided with fixed metal plates 5 abutting the ends of the winding 6 with just a thin insulating layer therebetween. This insulating layer can be a separate strip of insulant or it can be an insulating coating applied to the inner surface of the metal plates 5. The edges of the metal plates 5 are provided with profiled grooves 7 for increasing the cooling area of the metal plates 5. The grooves 7 do not increase the size of a ballast as they are positioned in the free spaces on either side of the winding end between the shell 4 and the side face of the end of the winding 6. At the same time, the outer edge of the groove 7 may serve as a fastening means for the attachment to the end edge of shell 4. This attachment can be achieved in various ways, e.g. by bending one edge around the other, by spot welding together the surfaces that are facing each other, or mechanically by shaping the edge surfaces which are facing each other. The direction of the rib members 7 is perpendicular to the E-arms and the bottom plate 3. Between the lower edge of the metal plate 5 and the bottom plate 3 is arranged at least one air circulation passage 9 and, correspondingly, between the upper edge of the metal plate 5 and the end edge of the shell 4 is arranged at least one air circulation passage 8. Thus, air flows around the winding ends with a chimney effect, which is more effective the greater the height dimension B of a ballast is relative to its width A. Passage 9 can be made by placing the lower edge of the metal plate 5 at a small gap away from the bottom plate 3 or by making holes or notches in the lower edge of the metal plate 5. In a corresponding manner, the upper edge of the metal plate 5, or the edge of the shell 4 connected therewith, is provided with holes or notches 8. Fig. 4 illustrates alternative cooling rib profiles 7', 7'', 7''' . The end plates are preferably made of aluminium or an aluminium alloy which has better heat conductivity than a shell 4 made of sheet steel. Ribs 7 are designed as grooves, whose outer edges are bent to extend in the direction of the shell 4 and fastened to the inner surface of the shell 4. The fastening is preferably carried out by pressing the end plate material into the holes of the shell 4 while, at the same time, urging the end plate against the end of winding 6. This secures a good heat conduction contact from the winding 6 to the shell 4 by way of the end plates 5.

Claims: Means in combination with a ballast or transformer for improving its cooling, said ballast or transformer comprising a core sheet pack (1, 2), a winding (6), whose ends extend beyond the core sheet pack, a shell (4), which surrounds the core sheet pack, a bottom plate (3), to whose side edges (3a) the shell edges (4a) are fastened, and metal end plates (5), which are fastened to the gables of a housing made up by shell (4) and bottom plate (3) and which abut the end of winding (6) with a thin insulating layer (10) therebetween, characterized in that the means consist of bent or moulded rib members (7) in said end plates, the rib members (7) being positioned in the free spaces between the winding end faces and the ends of a core sheet pack at a distance from the ends of the core sheet pack (1, 2) in a manner that, within the area of said rib members, cooling air can circulate on either side of the end plate, for which purpose the lower edge of each end plate (5) is positioned at a small clearance (9) from the bottom plate (3), or the lower edge of the end plate (5) is provided with holes or notches (9), and the upper edge of each end plate (5), or the edge of the shell (4) connected therewith, is provided with holes or notches (8) which open into the free space between the rib member (7) and the end of the core sheet pack (1, 2). Means as claimed in claim 1, wherein the rib members are in the form of grooves (7) profiled in the edges of the end plate (5) for increasing its surface area, said grooves being positioned in the free spaces on either side of the ends of the winding (6) between the shell (4) and the side faces of the end sections of the winding (6), and the outer edges of said grooves (7) being bent to extend in the direction of the shell (4) and fastened to the inner surface of said shell. Means as claimed in claim 1 or 2, wherein the end plate is made of aluminium or an aluminium alloy whose heat conductivity is better than that of the shell (4). Means as claimed in claim 1, 2 or 3, wherein the core sheet pack consists of E- and I-sheets and the direction of the rib members (7) is perpendicular to the E-arms and the bottom plate (3).

Inventors: PERTTI, LILJA
Applicants: OY HELVAR
Application year: 1987
Main classification: H01F27
IPC codes: H01F27