NO141479B - MAST FOR CARRYING LIGHTING FITTINGS - Google Patents

Description

Rectifier systems with semiconductor rectifier elements such as electric valves.

The invention concerns a rectifier system with semiconductor rectifier elements, preferably such based on a semiconductor of germanium or silicon or an inter-metallic compound or of a similar nature, where several parallel branches in each valve device of the rectifier system each contain a semiconductor rectifier element or several semiconductor rectifier elements in series. In the case of such rectifier systems, which for each valve device contain several semiconductor rectifier elements in different parallel branches, it is important for a good utilization of the possibilities for loading the semiconductor rectifier elements that the total current passing through the individual electric valve device, as far as possible is distributed in equal proportions to all parallel branches in the valve arrangement. However, when performing such rectifier systems, it has been shown that such a proportionally equal current over the parallel branches is not ten! to achieve without further ado. Aids have therefore already been proposed to achieve such an even proportional distribution of the total current passing over the electric valve device, on the parallel branches. Thus, it is known for this purpose to arrange an iron core on each of the wires in the parallel branches or on the holder device for the rectifier elements in the parallel branches, so that corresponding inductances then act in the parallel branches which force a proportionally equal division of the currents on the parallel branches. However, this requires a corresponding equipment of such iron cores or makes it necessary to choose a special construction for the individual rectifier elements so that they can be supplied with resp. carry corresponding iron cores.

The invention is now based on the realization that the aforementioned task of distributing the total current that passes through the electric valve device, with equal shares on the parallel branches, can also be solved without the need to add extra connecting elements in the device.

In this connection, it is assumed that a proportionally different distribution of the valve device's local valve current on its parallel branches can be largely attributed to the different commutation inductances that, during the commutation of the current between the phases that follow each other in the current flow , leads to different steepness of the current rise in the individual parallel branches. According to the invention, this difference between the commutation inductances is now counteracted in such a way that they have the same size as far as possible.

According to the invention, the basis for the implementation of this precaution is the consideration that the different commutation inductances have their cause in the previously given mutual geometric assignment of the parallel wire branches, an assignment which simultaneously for the individual parallel branch with regard to the parallel branches in the other phases determine an area-specific flux linkage for the parallel branch wire and thus the respective inductance that it realizes in the relevant commutation circuit.

In order to provide a somewhat more in-depth principled explanation of this, one must first go into it in fig. 1 showed a schematic diagram for an example three-phase star connection.

Here, 1-3 denote the connections to a three-phase network. This feeds three semiconductor valve devices 4-6, each of which has two parallel branches 7, 8, resp. 9, 10, resp. 11, 12, which contain each of the semiconductor rectifier elements 13-18. 19 denotes the positive busbar of the rectifier device with the connection 20. The installation's negative direct current busbar is not indicated separately. It would e.g. exit from the star point on the secondary side of the feed transformer, which is also not shown, and lead to the consumer.

It shall now be assumed that the current at a considered moment is commutated from the valve device 4 to the valve device 5. At the beginning of this commutation process, a current it flows from point 1 in one phase line over the valve device 4 and the busbar 19 to the plant's positive direct current pole 20. During the commutation process -the session builds up a current i2 that runs from point 2 on the second phase line over the valve device 5 and the busbar 19 to the direct current pole 20. To the same extent as this current i rises, the current i decreases, so that the current i2n which decreases provided by the rectifier device, remains practically constant. This commutation process can, according to an auxiliary concept, also be perceived so that in the commutation circuit, in addition to the currents ij and i2n which remain unchanged, a current i19 builds up which runs from point 2 on the second phase supply line over the valve device 5, the busbar 19 and the valve device 4 to point 1 on the first phase supply line. This current i19 builds up the current i2 in the valve device 5, while it counteracts current i in the valve device 4 to the same extent. The commutation process is finished as soon as the current i19 has reached the value of the current i, in the opposite direction, whereby the sum current above the valve device 4 has then become zero. The steepness of rise for the currents i9 and i10 over the parallel branches 9 and 10 respectively is determined to a decisive extent by the inductances that flow through the branch currents in the commutation circuit.

If one now with regard to the connection diagram in fig. 1 assumes that at the same time, to a certain extent, this should make visible a mutual geometrical assignment of the different wire branches, then it will be realized that a smaller inductance is assigned to the rate of rise for the current i9 than the rate of rise for the current i1(1, for the current flow from 2 over 15 to 9 and so over 19 and 4 to 1 is linked with a weaker magnetic flux than the current flow from 2 over 16 to 10 and so on over 19 and 4 to 1, the latter current flow enclosing a larger surface. During the course of the commutation time, the current will therefore i9 assume a higher value than the current iin.

Within the framework of the task position for the invention, it is now necessary to obtain a mutual approximation of the currents i9 and i10, which according to the invention's objective takes place without additional connecting elements, namely by mutual approximation of the inductances that determine the steepness of the current rise resp. - the speed in the parallel branches. According to the considerations indicated, this means obtaining an equally large determining inductance for the current flow over the individual of the respective parallel branches in the relevant commutation circuit. It also means, based on pure considerations, the following: When one of the parallel branches carries a smaller proportion of the valve device's valve current than another branch, a larger inductance than time must be provided in the path of this larger current in the commutation circuit, than current which runs over this branch, over the valve device to be replaced in the current flow, and over the alternating phases in the multi-phase system.

In practice, this is realized by e.g. already during the production of the plant, on the basis of the normal mutual geometric arrangement of the lines in the parallel branches within the same valve arrangement and with regard to the lines in the other valve arrangements resp. the return line for a one-way rectifier system, determines these lines' predictable proportional current take-over, but after this finding, the actual definitive laying of the supply lines to the rectifier elements in such a way that such inductances are now obtained in the respective commutation circuit with the phase to be replaced in the current flow, for the individual branches that a proportionally equal distribution of the total current that passes through the individual valve device, on the individual branches of this valve device is forced by the shape and nature of the course of the wires in the parallel of the valve device branches in the room.

What has just been stated as a solution within the scope of the invention for the case of the design of a plant, can be done in a similar way with an already manufactured plant, as a first step is to measure the individual current shares in the parallel branches of a valve device and then changes the existing wiring in a way that is favorable for the purpose of the invention, so that the effect which is sought according to the invention, and whose nature has already been described above, is achieved with the new wiring resp. -embarrassment.

The application of the precautionary rule according to the invention will now with reference to fig. 2 be visualized in more detail with regard to its practical application.

In this figure, a star-point rectifier system made up of uniform connection elements corresponding to the example in fig. is again partially shown. 1. For the coupling elements that already occur in the coupling in fig. 1, the same reference numbers are also retained in fig. 2.

As already appears from a superficial consideration of this fig. 2, the connections for the individual parallel branches of the valve device to the positive busbar 19, which is shown here to consist of three parts 19a-19c between its left end and the connection 20, are no longer all made in the same way with respect to the shape of the wires above which the various semiconductor rectifier elements are connected to this busbar. Thus, with the valve arrangement 4, it can be seen that the connecting line from the cathode in the semiconductor element 14 is no longer simply led directly in a straight line to the busbar 19. Instead, this connecting line, which is denoted by 21, is now routed so that it encloses an outer lower surface in addition below the busbar 19, so that this surface also becomes part-determining for the magnetic flux linkage with the supply from the valve 14. However, since the inductance is proportional to the quotient where

d J

<D is the magnetic flux linked with the conductor and J the current through the conductor, then the larger surface enclosed by the conductor branch 8 means that a larger inductance will now be decisive for the steepness of the rise resp. -the speed of the flow ig. Therefore, the strength of current i8 across branch 8 at the end of the commutation process approximates the simultaneous value of current i7 across branch 7.

Corresponding precautions are in accordance

to fig. 2 also met for the branches 15 and 17 in the valve devices 5 and 6 respectively. It is assumed here that the parallel branch 9 in the valve device 5 carried a larger proportion of current than the branch 10, and in a similar way it is assumed for the valve device 6 that the parallel branch 11 carried one

greater proportion of the total valve current 6 than the parallel branch 12, which in the case of a three-phase alternating current system appears from the time sequence 1—2—3—1 etc. of the voltage half-waves in phases 1, 2, 3 according to the theoretical explanation that was developed above in connection with the connection diagram in fig. 1 for the course of the commutation of the current from phase 1 to phase 2. The line from the cathode in the semiconductor rectifier element 15 in the parallel branch 9 of the valve device 5 to the line resp. the busbar 19 is denoted by 22 and is arranged so that it encloses a magnetic flux surface which is increased in relation to that which would be given by a simple straight-line wiring according to the diagram in fig. 1. For the portion of current that goes over the branch 9 and the rectifier element 15, the gradient is thus resp.

- the speed reduced and thus also the final value of the current at the end of the time for the commutation of the current from phase

1 to phase 2. In the valve arrangement 6, the inductance of the parallel branch 11 is likewise

increased by means of a new layout of the line 23 and a magnetic flux surface which is thus drawn in as well, whereby the steepness of the rise resp. - the speed and thus the final value of the current in across the semiconductor rectifier valve 17 is again reduced.

In fig. 3 and 4, which constitute two drawings corresponding to each other, an example of the geometric arrangement of the connection lines from the cathodes of the semiconductor rectifier elements to the common busbar 19, resp. the one direct current pole 20, the wires lying below the dashed line L—L in fig. 2, is reproduced in the form of rails. To indicate the connection between these figures and fig. 2 in a simple way, the same reference number with the addition of a marking line is used for the correspondingly occurring cables which are the same in terms of connection.

In fig. 3 and 4, the rails 7'—12' can be seen again, which correspond to the wires 7—12. The conductor part 19a of the busbar 19 is shown as a rail 19a' which is bent into a U-shape, and which is electrically conductively attached partly to the rail 7' and partly to the rail 10'. The part 19b of the busbar 19 is likewise shown as a U-shaped bent rail 19b' which is attached partly to the rail 10' and partly to the rail 12'. To the wire 21 in fig. 2 corresponds to fig. 4 again a U-shaped bent rail 21', but the U is turned upside down in relation to the wire rail 19a'. Hereby, the U-shaped bent rail 21' directly opposite the busbar part 19a' encloses a surface which determines the inductance of the line branch 8' in the relevant commutation circuit. The same applies to the U-shaped bent wire rail 22', which corresponds to the wire 22 in fig. 2, with regard to the parallel branch line 9'. The cable rail 23', corresponding to the cable 23 in fig. 2, has on fig. 3 a U-shape with a downward-facing yoke, which determines the inductance of the conductor rail 11' in the respective commutation circuit.

Within the framework of the invention, it is now not absolutely necessary that the individual U-shaped bent rail is bent beforehand in a particularly suitable manner from a single piece. Instead, you can also use a build-up system that has rectilinear cable rails in connection with suitable angle pieces, so that it becomes possible to produce a variety of suitable cable routings from a small number of basic shapes as building elements.

An example of such an embodiment is shown in the corresponding drawings in fig. 5 and 6. These two figures show connection lines which are shaped practically in the same way as in fig. 3 and 4, only with the difference that the individual rail, which according to these figures was bent into a U-shape, now according to fig. 5 and 6 are only composed of interconnected rectilinear and angular pieces as structural elements. Thus, the line 21' in fig. 3 and 4 now according to fig. 5 and 6 of straight rail pieces 21'A— 21'C and the angle pieces 21'D and 21'E. The U-shaped rail 22 in fig. 3 and 4 now consist according to fig. 5 and 6 of the straight rails 22'A—22'E and the angle pieces 22'F and 22'G. The U-shaped rail 23' according to fig. 3 and 4 consist according to fig. 5 and 6 now of the rectilinear rails 23'A—23'C and the angle pieces 23'D and 23'E. The busbar part 19a' in fig. 3 and 4 consist according to fig. 5 and 6 of the rectilinear parts 19a'A

—19a'E and the angles 19a'F and 19a'G. The busbar part 19b' now consists of the straight rails 19b'A—19b'C and the angle pieces 19b'D and 19b'E. The busbar part 19c' now consists of the rectilinear rails

pieces 19c'A and 19c'B as well as the angle piece 19c'C.

In fig. 7 finally illustrates how, in connection with a specific design of connection lines, it is also possible to use a specific cross-sectional shape of part of a connection line with the aim of achieving a specific induction value in accordance with the invention. For the sake of simplicity, this is visualized directly by a line that corresponds to the line 23' in fig. 3-6. While in fig. 3-6, rails were used which had a practically uniform cross-section, the hoop-shaped connection line 23' in the detailed sketch in fig. 7 now made up of two rail parts 23'F and 23'H as well as a cylindrical massive part 23'G which is joined to each of the two first-mentioned rail parts via a screw connection. As is well known, a round massive body has the largest self-inductance of all possible cross-sectional shapes for a conductor. If use is made of this feature in connection with the invention, the bulging of the wire's loop shape, which is otherwise required to provide a sufficiently large enclosed magnetic flux surface, can therefore be brought down to a correspondingly lower value. It can be important from the point of view of the need for space, but also with a view to saving material. Possibly, the new cross-sectional shape may also be of importance from the point of view of increased mechanical stability.

For the mutual mechanical and electrical connection of the rail parts, screw connections or clamp connections can be used. At the same time, the rails, rods or pipes can be arranged so that the pieces that help to form the overall wire can be adjusted steplessly or in small steps in relation to each other. Optionally, one can also make use of both precautions at the same time in certain individual areas of the device. To achieve a stepless setting of the wiring parts below

the use of a screw connection can

one e.g. supply one rail with

one or more slot-shaped recesses, so that the screws used for the mutual mechanical connection in the slot or slots in question can be displaced in the loosened state of the connection rail. In the event that pipes or rods are used, clamp connections can also be used, such as is made in the same way as cone clamps and, after tightening an overhead nut, provides a working clamping connection by tightening the cone. In connection with the invention, prefabricated

kert angular T-shaped or cross-shaped auxiliary elements at the connection points for the rails, rods or pipes.

Claims (5)

1. Rectifier system with one or more valve devices, where each valve device contains several parallel branches with at least one semiconductor rectifier element each, characterized by the fact that wires in the parallel branches running between the valves and common connection points for these branches or to a busbar that is common to the branches are laid in this way in the space below taking into account the inductances they form, that for the currents that pass over the different parallel branches of the individual valve devices, such new —■ increased or decreased — inductances act with the help of which a relative division of the individual valve device's overall current on its parallel branches, in the direction of a mutual approximation of the strength of these current shares. 2. Rectifier system as stated in claim 1, characterized by the fact that cables which in and of themselves from a purely constructive point of view are to be laid in a straight line, are laid in an angular, loop-shaped or winding-shaped manner in such a way that an increase is caused or reduction of the magnetic flux enclosed by them flat, corresponding to the desired induction value. 3. Rectifier system as stated in claim 1 or 2, characterized in that lines leading to or from the rectifier elements and connecting these in the parallel branches with a common branching point at the valve device or a busbar, are made up of pipes, rods or rails in such a way that tubular, rod or rail-shaped connecting lines can be set at or between these, preferably steplessly, preferably using mutual clamp connections, until the desired even proportional distribution of the current over a valve device on its parallel branches is enforced. 4. Rectifier system as specified in claim 3, characterized in that in the same and/or different parallel branches, pieces of wire with different cross-sectional shapes are used to achieve different specific inductance per unit of length. 5. Rectifier system as stated in one of the preceding claims, characterized in that connection lines are composed of rectilinear and angular construction elements.