GB2142789A - High voltage rectifier - Google Patents

Abstract

A high voltage rectifier comprises two thyristor stacks (7, 8) connected in parallel through cross-connections and poled in parallel opposition section by section. In order that the ignition energy for the individual thyristors (1 to 6), driven by means of optical conductors from earth potential, can be coupled out from the thyristor power circuit, transformers (9, 10, 11) are arranged at their primary sides in cross-connections between the thyristor stacks (7, 8). in each thyristor stack (7, 8), the thyristors are directed in terms of polarity one opposite the other section by section so that the load current flows in meander shape through the double stack and thereby by way of the cross- connections. <IMAGE>

Description

SPECIFICATION High voltage rectifier The present invention relates to a high voltage rectifier, especially a rectifier with two thyristor stacks connected in parallel section by section and poled in parallel opposition.

A circuit arrangement of that kind is known .from the journal "Wissenschaftliche Berichte AET-TELEFUNKEN" No. 50 (1977), Volume 1/2, pages 22 to 31.

High voltage rectifiers usually operate on the principle of indirect light drive, i.e. a command for the delivery of an ignition pulse to an associated thyristor is transmitted through an optical signal connection to a drive component group disposed at the respective thyristor potential. The drive component group receives the necessary auxiliary energy for ignition of the thyristor from the current flowing in a resistance-capacitance member of the thyristor circuit or from the thyristor blocking potential.

If the high voltage rectifier is used as thyristor switch, the previously mentioned possibility of coupling-out the auxiliary energy virtually exists only in the blocked state. In the current-conducting state, only very short and low blocking voltage peaks arise, which do not ensure an adequate auxiliary energy supply. Additional auxiliary energy must therefore be coupled out of the load current by way of transformers. In that case, however, difficulties arise, because high voltage rectifiers of that kind usually have water cooling which is provided by cooling cells arranged between the individual thyristors in the stacks.The transformers for the coupling-out of the auxiliary energy must then be either pushed over the cooling cells, which is unnecessarily expensive and constructionally difficult, or else arranged at the ends of the stacks, which obliges use of a multi-winding transformer, in any case having disadvantageous characteristics, with high insulation requirements.

There is thus a need for a circuit arrangement in which the effort for inclusion of the transformers is relatively small and which provides a simpie and easily surveyable constructional arrangement.

According to the present-invention there is provided a high voltage rectifier comprising a plurality of thyristors arranged in two stacks connected in parallel between two poles, each thyristor in each stack being poled oppositely to the or each adjacent thyristor in that stack and the thyristors in each stack being so connected by cross-connections to the thyristors of the respective other stack as to provide two, current paths each in a respective direction between the poles and each by way of the thyristors of the two stacks in alternation, and a respective transformer with a primary winding thereof in each cross-connection to couple out energy for ignition of the thyristors.

In consequence of the thyristor polarities being interchanged section by section within the thyristor stacks, the load current flows by way of the cross-connections so that the transformers, which are arranged in these crossconnections, can couple out sufficient auxiliary energy even in the opened state of the switch.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawing, the single figure of which is a circuit diagram of a high voltage rectifier embodying the invention.

Referring now to the drawing, there is shown a high voltage rectifier, which is applied to an alternating voltage between terminals 18 and 1 9 and which operates as an alternating current switch.

The rectifier is formed, as indicated in dashed lines, with two thyristor stacks 7 and 8. Each of the thyristor stacks 7 and 8 consists of thyristors, which are constructed as disc cells and are layered alternately with cooling cells (not shown) serving for liquid cooling of the thyristors to form columns and are pressed together. For clarity, only three thyristors per stack are shown, namely thyristors 1, 2 and 3 in the case of stack 7 and thyristors 4, 5 and 6 in the case of stack 8.

As a rule, however, the stacks are formed with more thyristors and a corresponding number of cooling cells.

The thyristor stacks 7 and 8 are connected in parallel by way of individual cross-connections so that sections represented by the thyristors 1, 2 and 3 in the case of the stack 7, and sections represented by thyristors 4, 5 and 6 in the case of the stack 8, arise. The thyristors of corresponding sections of the two stacks 7 and 8 are respectively connected in parallel opposition, thus the thyristor 1 of the stack 7 with the thyristor 4 of the stack 8, the thyristor 2 with the thyristor 5, and thyristor 3 with the thyristor 6.

The ignition of the thyristors 1 to 6 takes place on the principle of indirect light drive, i.e. an ignition command is transmitted by way of a light signal connection (not shown) from earth potential to the respective thyristor, whilst the required ignition energy is coupled out of the power circuit between the terminals 18 and 19 by way of transformers .

For this purpose, inductive transformers 9, 10 and 11 are arranged at their primary sides in the cross-connections between the thyristor stacks 7 and 8. In addition, the load current is constrained to flow through the double stack along a meandering path, thus by way of the cross-connections. This is achieved by arranging the polarities of the thyristors 1 to 3 and 4 to 6 to be opposite to one another section by section in each of the stacks 7 and 8. This means that, instead of arranging the thyristors all with the same forward direction in a stack, the anode of the thyristor 1 is connected with the anode of the thyristor 2 and the cathode of the thyristor 2 with the cathode of the thyristor 3 in the case of thyristor stack 7.

Correspondingly, the cathode of the thyristor 4 is connected to the cathode of the thyristor 5 and the anode of the'thyristor 5 to the anode of the thyristor 6 in the case of thyristor stack 8. On appropriate ignition of the thyristors of one polarity, the current flows during the one half period of the alternating voltage from terminal 19 to terminal 18 by way of the thyristors 3, the transformer 11, the thyristor 5, the transformer 10, the thyristor 1 and the transformer 9. During the other half period, a meandering opposite current flow takes place from terminal 1 8 to terminal 1 9 by way of the transformer 9, the thyristor 4, the transformer 10, the thyristor 2, the transformer 11 and the thyristor 6.

In order, in the case of the cross-connection with the transformer 9, to couple out energy during both half periods of the alternating voltage, this transformer is exceptionally equipped with two primary windings.

The transformers 9, 10 and 11 conduct, as explained, half sine waves of equal polarity and preferably have a clipped characteristic.

In that case they may be so dimensioned as to go into the saturation after a short time, since the auxiliary energy requirement for the ignition of the thyristors 1 to 6 is relatively small.

In order to keep the effectiveness of the damping equal for both thyristors of one section of the transformer arranged in the crossconnection, it is advantageous to connect resistance-capacitance members of the thyristor circuit "diagonally", thus to connect the members directly between the terminals of equal polarity of the thyristors connected in parallel opposition. Thus, a resistor 1 2 is connected in series with a capacitor 15 between the cathode of the thyristor I and the cathode of the thyristor 4. Correspondingly, a resistor 1 3 and a capacitor 16 are connected between the anode of the thyristor 2 and the anode of the thyristor 5, while a resistor 14 and a capacitor 1 7 are connected between the cathode of the thyristor 3 and the cathode of the thyristor 6.

Claims (5)

1. A high voltage rectifier comprising a plurality of thyristors arranged in two stacks connected in parallel between two poles, each thyristor in each stack being poled oppositely to the or each adjacent thyristor in that stack and the thyristors in each stack being so connected by cross-connections to the thyristors of the respective other stack as to provide two current paths each in a respective direction between the poles and each by way of the thyristors of the two stacks in alternation, and a respective transformer with a primary winding thereof in each cross-connection to couple out energy for ignition of the thyristors.

2. A rectifier as claimed in claim 1, wherein each transformer has a clipped characteristic.

3. A rectifier as claimed in either claim 1 or claim 2, wherein each of the transformers has a low saturation characteristic.

4. A rectifier as claimed in any one of the preceding claims, comprising respective resistance-capacitance means connected between one of the electrodes of each thyristor in one stack and the corresponding electrode of a parallelly connected oppositely poled thyristor in the other stack.

5. A high voltage rectifier substantially as hereinbefore described with reference to the accompanying drawing.