Air-Cooled Converter Assembly, Having Heat Sinks Shaped as Isosceles Triangles

This invention relates to air-cooled converter assemblies employing disc thyristors in general, and more particularly, to an improved arrangement which permits arranging the disc thyristors such that they are essentially parallel to the front surface of the arrangement.

Air-cooled converter assemblies using disc thyristors have previously been developed. For example, in British Pat. No. 992,442, a plurality of disc thyristors are clamped together between heat sinks arranged in tandem. The power connections are made using terminal lugs on the conducting heat sinks. Because of the nature of the design, the disc thyristors are parallel to each other with their contact surfaces and all contact surfaces are at right angles to the front surface of the converter assembly. Clearly, this does not lead to ease of connection and requires large amounts of space.

Also previously known are liquid-cooled converter assemblies employing disc thyristors in which are individually clamped and arranted with their contact surfaces parallel to the front surface of the arrangement. An example of such a device is that disclosed in German Offenlegungsschrift No. 1,924,011. This type of design, with the disc thyristor surfaces parallel to the front surface and which has not been heretofore common in air-cooled converter assemblies is possible since, with liquid-cooled disc cells, heat sinks required are not as large as those required for air-cooled operation. A typical design of an air-cooled converter assembly using the thyristors arrangement of German Offenlegungsschrift No. 1,924,011 is disclosed in detail in German Offenlegungsschrift No. 1,913,546. From the arrangement disclosed therein, it is evident that the juxtaposition of large heat sinks results in a bulky design. Furthermore, from this disclosure, it is obvious that only threaded-stud thyristors with ratings smaller than those typically found in disc thyristors can be conveniently used. Using disc thyristors in this type of design would require even larger heat sinks and thus, more space.

Thus, there is a need for an air-cooled converter assembly employing disc thyristors which includes heat sinks which are large enough to dissipate the heat produced by the thyristors and at the same time are arranged in a space saving design.

The present invention provides such an arrangement. In accordance with the present invention, a converter assembly having disc thyristors clamped between heat sinks, and which is air-cooled, has pairs of heat sinks arranged side-by-side in such a manner that the axes penetrating from the front surfaces of the heat sinks of a pair are essentially parallel to each other with a disc thyristor clamped between two heat sinks of a pair with its contact surfaces essentially parallel to the front surface of the pair of heat sinks and of the overall arrangement. Furthermore, the heat sinks are constructed so that as seen from the front surface, they have an outline which is essentially that of an isosceles triangle.

Preferably, in an arrangement of this type it is advantageous if two disc thyristors are jointly clamped with a respective two pairs of heat sinks to form an assembly which comprises essentially a retangular block having an essentially square base area. With such an arrangement, the heat sink in the rear can be made of a single piece and used for two disc thyristors. As seen from the front, it will then have an essentially square outline. In the preferred embodiment, the two disc thyristors of an assembly are clamped between their heat sinks using a spring element which is placed in an insulated manner across the front surfaces of the two heat sinks with an insulated screw brought to the center of the spring element from the front surface to a fastening device on the rear side of the assembly with the whole block-shaped assembly pressed together using the spring element and the screw connection.

With a design such as this with the parallel arrangement of the contact surfaces of the disc thyristors and the front surface of the apparatus, the equipment is easy to maintain permitting replacement of the thyristors of each pair without necessity of loosening the clamping of other thyristors while doing so. Each thyristor pair is individually accessible without affecting adjacent units. By dividing the rectangular, approximately square front surface for two adjacent pairs of heat sinks diagonally, a very compact design is obtained. In addition, a central arrangement of the disc thyristors with optimized heat removal is obtained. The thermal paths are approximately equal in all directions. By jointly clamping two adjacent disc thyristors, which in the case of a bridge circuit are usually used with a common current phase, it becomes possible to obtain substantially equal contact pressure for the two disc thyristors of a current phase, using the diagonally arranged leaf spring and screw connection. At the same time, using a common rear heat sink allows a single unit to provide individually clamped bridge elements belonging to a single current phase, thereby greatly simplifying the installation and making diverse applications of the assembly possible.

FIG. 1 is a plan view, partially in cross section illustrating two sets of two disc thyristors each, along with their heat sinks and associated fuses and connecting bus bars.

FIG. 2 is a front view of the arrangement of FIG. 1.

FIG. 3 is a second side view of a portion of the arrangement of FIG. 1, partially schematic in form, illustrating various interconnections.

FIG. 4 is a front view of a heat sink and thyristor arrangement of the present invention, showing the joint clamping of two disc thyristors.

FIG. 4a. is a partial sectional view of the clamping arrangement of FIG. 4.

FIG. 1 illustrates two of what would normally be three assemblies according to the present invention. Although only two assemblies are shown, assemblies such as that to be described will normally be found in groups of three, particularly when used in three-phase bridge circuits. In the illustrated embodiment, the front of the overall assembly is in the left and the back to the right. A piece of insulating material 4 serves as the base member for the arrangement. The base 4 is provided with a plurality of feedthroughs 41 for connecting to the power bus bars 7 or power cables. The power bus bars are either connected directly to bosses 21 of the heat sinks 2, or to current carrying bars 8 which are arranged in an insulated manner running from the front of the assembly to the rear. At the front, for covering the thyristor assemblies at that point, plates 5, made of insulating material are installed, which plates have cutouts 51 for bringing out the connection bosses 22 of the heat sinks 2, along with the current carrying bars in a manner such that they are insulated. The heat sinks 2 between which the disc thyristors 1 are clamped, are thus situated between two plates of insulating material. As illustrated, the current carrying bar 8 is led in an insulated manner from the front to the rear. In order to permit insulation of the individual assemblies from each other, plates 6 of insulating material are also installed. When used in a bridge circuit, the two disc thyristors clamped between a pair of heat sink 2 will preferably be assigned to one current phase. In that case, the heat sink 2 at the rear can be made of a single piece for two disc thyristors so that the overall assembly will have an essentially square shape as seen from the front. This shape is more clearly illustrated on FIGS. 2 and 4, to be described in detail below. Also illustrated on FIG. 1 are branch fuses 3. Branch fuses herein refer to fuses associated with the individual branches of the converter (in contrast to phase fuses which are fuses for each a-c circuit.) As shown, the branch fuses 3 are attached to the connection bosses of the heat sink 2. The fuses 3 are then connected by their connecting lugs 31 to lugs 81 of the current carrying bars 8 by means of a cable 32. By using the current carrying bar 8 running to the rear of the assembly, all power connections can be made from the rear and all control connections from the front.

FIG. 2 is a front view of the arrangement of FIG. 1. In this figure, the fuses have been omitted in the assembly to the right for sake of clarity. FIG. 2 illustrates clearly that the two pairs of heat sinks are arranged side-by-side in such a manner that the axes 24 of FIG. 1, which pass through the front surfaces 23 of the heat sinks of a pair, are parallel to each other. From this figure it is also clearly seen that the heat sinks as viewed from the front have an outline which is essentially that of an isosceles right triangle. The heat sinks, which are located below the plate of insulating material 5 (see FIG. 1) are shown in dotted lines. The connection bosses 22 of the heat sinks along with the current carrying bars 8 are brought through the cutouts 51 of the front insulating plate 5. The lugs 33 of the fuses 33 are connected to the connection bosses 22 of the heat sinks. With their second terminal 31, the fuses 3 are connected to the lugs 81 of the current carrying bars 8 through current carrying cables 32. The geometrical arrangement of the disc thyristors 1 is best illustrated by the assembly to the right where the disc thyristors are shown in broken lines. The indication on this figure of the cross section I-I shows the plane of the cross section of FIG. 1.

FIG. 3 is a side view of the arrangement of FIG. 1. Again, the geometrical position of the disc thyristors 1 is illustrated. The insulating plates 4 and 5 insulate the arrangement at each side. The individual polarity of the bus bars 7 is shown to illustrate the fact that all power connections can be made from the rear. This figure illustrates particularly well the attachment of the fuse 3 which has its one lug 33 connected to a connection boss 22 of the heat sink and its other lug 31 connected to a lug 81 of the current carrying bar 8 through a current carrying cable 32. As illustrated, underneath the heat sinks 2, a separate space 30 is provided in which associated circuitry subassemblies may be placed. In this regard, it is also possible to assign a circuit separately to each disc thyristor. The dot-dash frame of the box 20 is indicated to schematically illustrate the fact that a driver group can be attached directly to the thyristor assembly. The driver assembly will advantageously be constructed, as a common assembly for driving all thyristors, on a single circuit board.

FIG. 4 illustrates the mechanical device used for clamping the disc thyristors between two heat sinks as viewed from the front. FIG. 4a. is a side view of a screw 91 and associated spring element 92. In assembling a thyristor assembly, the rear plate of insulating material 4 along with the rear heat sink made of a single piece serves as the base element. To this space element are then mounted in succession, the heat sinks and the disc thyristors. The heat sinks in front are covered at their front surface 23 with plates 52 of insulating material to provide insulation for the spring element. At least one spring element 92 is placed over these cover plates with the spring element having a screw connection 9 provided in its center as viewed from the front. The front side of the thyristor assembly is tensioned against the rear side using the screw 91, the spring element 92 and the insulating plates 52. Because of the design of the spring element, which is supported at three points, a uniform contact pressure for both disc thyristors of an assembly is achieved. The pressure provided by the screw connection 9 is distributed uniformly over both halves of the assembly by means of the spring element 92. After clamping, the front surface of the assembly is insulated from the outside by a plate of insulating material 5, as illustrated on FIGS. 1 and 3.

As illustrated on FIG. 1, the fins of the heat sinks 2 are arranged so that they are at right angles to the front surface 23 and to the bottom side 25 of the arrangement, thereby forming air ducts through which cooling air may be passed, the ducts being formed by the heat sinks in combination with the front and rear insulating plates 5 and 4 respectively.

Thus, an improved air-cooled converter arrangement in which disc thyristors are clamped between pairs of heat sinks with the heat sinks having essentially the outline of an isosceles right triangle has been shown. Although a specific embodiment has been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from the spirit of the invention which is intended to be limited solely by the appended claims.