US2532108A - Static current converter with means for putting it out of function - Google Patents

Description

Patented Nov. 28, 1950 CONVERTER WITH MEANS FOR PUTTING IT OUT OF STATIC CURRENT FUNCTION Uno Lamm, Ludvika, Sweden, assignor to Alimanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application May 17, 1947, Serial No. 743,810 In Sweden May 25, 1946 9 Claims. 1

It is known, in connection with the putting of a static current converter out of function, to open a valve path in parallel to said converter in the shape of a bypass valve, which forms a direct connection between the direct current terminals of the converter through which a current may pass, which is maintained for instance by the inductance in the direct current circuit or by other direct current sources. The purpose of the said bypass valve has then mainly been looked upon as an unloading of the main valves of the converter. A close examination has shown, however, that such an unloading is not always necessary but that it is still desirable to create a bypass valve path in the sense that it does not contain any substantial voltage originating from the alternating current side. According to the present invention the bypass valve path is therefore created by the use of one or more of the main valves of the converter in such a connection that no substantial voltage originating from the alternating current side forms part of the current path. The opening of such a bypass path may especially be advisable as a preparatory step to put the converter entirely out of function by other means.

In order that the arcs arising in such a bypass path shall not influence the arc paths of the other main valves of the converter, it may be advisable to construct the valves forming part of the bypass path with separate cathodes, i. e. to make them of what is generally referred to as a monanodic type, which however, also comprises valve vessels having several anodes of the same polarity in parallel, such as are used for instance for high currents.

The invention is preferably applicable to twoway connected converters, because in these there are always valve paths between the direct current terminals, which do not contain any transformer winding complicating the connection. In this case two series-connected valves coupled to the same alternating current terminal form together the bypass path. Two valves connected in this way are as is known never simultaneously conducting in normal operation.

back-arcing one and that opposing thereto are blocked, they will gradually be extinguished as they obtain negative voltage, and in connection therewith the back-current in the back-arcing valve will cease and be replaced by a current of normal direction, provided that there is an electromotive force in this direction.

In practice it is generally most simple in such cases, when the selection of the valves forming part of the bypass valve path depends on a just occurring disturbancefor instance a back-arcingto block all the valves but to send at the same time an impulse releasing the blocking to the valves, which shall serve for the bypass path. For the selection, for instance the means to be described below can be employed.

If, on the other hand, the valves serving as bypass valves are selected beforehand, which may for instance be the case if the operation is intended to be made without a preceding disturbance, only the other valves are blocked, for instance by ceasing the sending of releasing impulses to them. In some cases, all such releasing impulses are suspended and special releas- 7 ing impulses are sent to the valves intended to serve as bypass valves.

In inverters one of the most common disturbance is, as is known, a failure of commutation, i. e. either a failing ignition of the valve in turn to be ignited or a failing extinction of the previously burning valve. If such a failure de-- pends on conditions outside the inverter, for instance on disturbances in the alternating current network fed thereby, it is, as a rule, arbitrary which pair of valves is selected to form the bypass path, although it is often most convenient to use the unduly burning valve and the valve opposite thereto for this purpose. The only step necessary may then be to cause the unduly burning valve to send a releasing impulse to the opposite one, while all the other valves are blocked. If, on the contrary, the missing commutation depends on such a defect in a valve or its control apparatus that the valve cannot be blocked, it is necessary to cause this valve to continue to burn,

i. e. to form part of the bypass path. Also in this case the step just described may be employed.

On the accompanying drawing, Figs. 1 and 2 show diagrammatically two forms of the invention, one of these being applied to a back-arcing rectifier and the other on an inverter with a failure of commutation.

In both figures, two-way converters operating in 3 pulsations pro cycle are shown, the

Nova 28, 195% 25 2 U. LAMM STATIC CURRENT CONVERTER WITH MEANS FOR PUTTING IT OUT OF FUNCTION Filed May 17, 1947 Q. and disconnecting switches 39, 40 in a manner analogous to that already described for the rectifier of Fig. 1.

I claim as my invention:

1. In a static current converter having a plurality of valves which are normally alternately blocked during one part of the cycle of operation and released during another part, means responsive to an abnormal disturbing condition likely to result in failure of operation of the converter to release at least one of said valves during the normal blocking part of its cycle to form a by-pass valve path for said converter containing substantially no voltage derived from the alternating current side of the converter.

2. A device as claimed in claim 1, in which said valves have separate cathodes.

3. In a static current converter having a plurality of valves connected in pairs in series to the same alternating current terminals which are normally alternately blocked during one part of the cycle of operation and released during another part, means responsive to an abnormal disturbing condition likely to result in failure of operation of the converter to release at least two of said valves connected in series during the normal blocking part of the cycle of one of said valves to form a bypass valve path for direct current.

4. A device as claimed in claim 3 in which one of said valves is a back-arcing valve.

5. A device as claimed in claim 3 in which one of said valves is one in which the commutation has failed.

6. In a device as claimed in claim 1, said means also blocking the remaining valves of the converter during parts of their cycles in which they are normally released,

7. In a static current converter having a plurality of valves, means for normally transmitting periodic releasing impulses to said valves so that said valves are normally blocked during one part of the cycle of operation and released during another part, means responsive to an abnormal disturbing condition likely to result in failure of operation of the converter to render said first means inoperative and to send a special releasing impulse to some of said valves to form a bypass valve path.

8. In a static current converter having a, plurality of ionic valves which are normally blocked during one part of the cycle of operation and released during another part, means responsive to an abnormal disturbing condition likely to result in failure of operation of the converter to transmit blocking impulses to all said valves and to send a special releasing impulse to some of said valves to form a bypass valve path.

9. In a device as claimed in claim 8, said means including biassed current transformers in series with some of said valves.

UNO LAMM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,064,021 Ludwig Dec. 15, 1936 2,119,865 Lamm June 7, 1938 FOREIGN PATENTS Number Country Date 88,730 Sweden Mar. 9, 1937 90,345 Sweden Sept. 28, 1937

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