US1933859A - Electric current rectifier control - Google Patents

Description

Nov. 7, 1933.

E. KERN ELECTRIC CURRENT RECTIFIER CONTROL Filed April 28, 1932 1 1// 1 1, I //////1 11/;1/ 1 /1 I III/III! Patented Nov. 7, 1933 PATENT OFFICE ELECTRICCURRENT RECTIFIER CONTROL Erwin Kern, Ennetbaden, Switzerland, assignor to Aktiengesellschaft' Brown Boveri & Cie, Baden, Switzerland, a joint-stock company of Switzerland Application April 28, 1932, Serial No. 608,012, and

" in Germany May 2, 1932 3 Claims. (Cl. 175-354) This invention relates to improvements in electric current rectifiers of the metallic vapor arc type and more particularly to means associated with the anodes of such rectifiers by which the arc flowing therein may be controlled.

Electric current rectifiers may be used as circuit interrupters, in connection with condensers, for the disconnection of short circuits in high voltage direct current systems in which the use of quick acting switches is impractical due to problemsof construction of such. switches which have not yet been solved. The ignition vol ge for the anodes of a rectifier or the voltage which must be im-.

pressed upon one of several anodes when it is desired that such anode pick up the are within a rectifier, is generally controlled by grids arranged between the anodes and the cathode of a rectifier. To secure the best operation of such grids, it is necessary that the grids have. the maximumsurface area without being so constructed as to materially-decrease the free crosssection area of the are guides which partially enclose the anodes and Withinwhich the grids are arranged and supported. The above requirements for the construction of the grids are met by grids in which the greatest portion of the total surface area extends substantially coaxially with the are guides or in which a plurality of grids arranged over each other in each of the are guides have relatively small areas at right angles to the axis of the arc guide. 1

When a plurality of grids are arranged within each arc guide dependent from the anodes of a rectifier, contacting of the arc with the metallic portions of the structure may cause the formation of a cathode spot which is probably due to the action of the arcon and the potential difierence's of the several portions along the axis of the are guide. Formation of such cathode spots leads to unstable conditions in the arc and may cause the occurrence of over-voltages in the rectifier due to rapid changes in the arc drop. Such spots are formed particularly when the grids block a large portion of the area ofthe space enclosed by the are guides.

I All grid constructions cause an increase in the voltage required 'to cause the arc to be picked up' by an anode. When grid structures capable of interrupting the are are used, the resultant increase in ignition voltage is so great that picking up of the are by an anode becomes very difilcult which is occupied by the grids by which move- -ment of the are carrying electrons toward the anode may be accelerated. The use of a plurality of grids in an arc guide so increases the arc drop from the anodes to the cathode that the formation of cathode spots on the are guides is undesirably facilitated and the grids cannot perform their function for the reason that they are enclosed within the then conductive arc guide.

It isjt-herefore, an object of the present invention to provide a grid control system for electric current rectifiers in which a plurality of grids are arranged over each other within are guides partially enclosing the anodes.

Another object of the invention is to provide a grid control system for electric current rectifiers in which a plurality of grids, arranged over each other within the anode are guides and insulated from each other and from the guide, are supplied with different voltages from a common source.

Another object of the invention is to provide a grid control system for electric current rectifiers in whicha plurality of grids, arranged adjacent each anode within the path of the arc flowing therefrom, are supplied with voltage from a single source in such manner that a potential drop is present between the several grids and between the anode and the grid nearest thereto.

Another object of the invention is to provide a gridcontrol system" in which a plurality of grids are supplied with voltage from a single source in such manner as to produce a gradually increasing potential drop fromthe anode to the cathode when the rectifier is in operation and in the opposite direction when the rectifier is not in operation.

Another object of the invention is to provide a control grid structure for electric current rectifiersin which a plurality of grids are so arranged over each other within the are guides as to partially cover the inner surface of the guides.

Another object of the invention is to provide a control grid construction for electric current rectifiers in which a'plurality of grids extend partures embodying the present invention and showing the connections for applying potential from a common source to the several portions of such structure, and

Fig. 2 is an enlarged vertical sectional view of a multiple grid or inner arc guide structure embodying the invention and shown associated with one of the anodes of a rectifier as indicated diagrammatically in Fig. 1.

Referring more particularly to the drawing by characters of reference, the reference numeral 3 designates a container or tank having a pool of vaporizable material 4, such as mercury, in the bottom thereof to form a cathode. A plurality of anodes 6 are arranged to extend into the tank through insulators 7 and are partially enclosed by outer guides 8 and inner guide constructions to be described in detail hereinafter, for an arc which is to be picked up by the anodes from excitation anodes (not shown) and which arc flows from the anodes to the cathode during normal operation of the device as is usual in electric current rectiflers of the metallic vapor arcing type. The anodes are supplied with electric current from a transformer connected with a suitable source of alternating current (not shown), the secondary winding of the transformer only being indicated at 10. The neutral point of the transformer secondary winding 10 has connected therewith a conductor 11. The conductor 11 in combination with a conductor 12, connected with the cathode 4, forms a direct current output circuit for the supply of direct current consuming devices as indicated at 13.

An inner arc guide structure is arranged within and supported from the outer arc guide 8. The inner guide is composed of a shield or guide member 16 arranged about the anode head and resting on one set of a plurality of sets of insulators 17 secured in the outer arc guide and a plurality of tubular members 18, 19 and 20 spaced from the outer arc guide and supported by adjacent sets of insulators 1'7 respectively. The ends of the tubular members 18, 19 and 20 are formed with difierent diameters to permit adjacent ends of separate members to overlap each other in spaced parallel relation. Thus each tubular member is supported on one set of insulators 17 and is spaced from the outer arc guide 8 in such manner as to be coaxial therewith and to be retained in spaced relation from the other tubular members by a second vset of insulators 17 which supports another of the tubular members. The bottom of the outer arc guide 8 is partially closed by a member 22 which shields the sets of insulators from damaging contact with the arc during operationof the rectiher. A control electrode or grid 24 is mounted within the inner shield 16 in either conductive or insulated relation therewith as may be desired.

The construction of the inner arc guide is thus such that the entire inner guide structure is insulated from the anode and that the several portions thereof are insulated and retained in spaced relation from each other. Annular spaces are thus left free, except for the space occupied by the sets of insualtors 17, between the several inner guide portions and between the inner and outer arc guide structures. The parallel extending surfaces of the inner arc guide structure absorb the electrostatic field set up by the arc passing therethrough. The voltage drop which otherwise is present upon passage of the arc through such spaces is thus avoided. The are cannot therefore flow from the inner to the outer guide nor vice-versa and the formation of cathode spots on the are guides is avoided. To obtain the best results, the annular spaces between the two are guide structures should be kept as narrow as possible. The several portions forming the inner arc guide structure cannot be metallically connected and must be either insulated from the outer arc guide or connected therewith through ohmic resistance. If it is considered undesirable to extend a plurality of conductors through the arc guide, the tubular members 18, 19 and 20 need not have a potential impressed thereon and may then be made of insulating material. The inner arc guide construction then serves merely as a shield to prevent impingement of ionized vapor on the outer arc guide and thus prevents the formation of cathode spots.

When the tubular members 18, 19 and 20 are made of conductive material, and, together with the cathode 4 are connected with a source of potential as will be hereinafter described, a potential may be impressed on the control electrode or grid 24 and on the tubular members 18, 19 and 20 from different points of a resistance 26, the one end of which is connected with the positive bus bar 12 of the direct current output circuit. The other end of the resistance 26 may be con nected by means of a switch 27 with either the positive or the negative pole of a source of electric curernt 28. A resistance 29 is connected across the terminals of the voltage source 28 and is tapped at the mid point thereof to the positive bus bar 12.

When an anode 6 is to pick up the arc from an excitation anode (not shown), the switch 2'? is connected with the positive terminal of the source of current 28. The grid 24 and the tubular members 18, 19 and 20 then have a potential impressed thereon which is positive with respect to the cathode and the impressed potentials are different, the potential of each portion of the structure being that of the resistance 26 at the point of connection therewith of the several portions of the structure. The potential drop from one of the portions to the other may thus be controlled by changing the location of the conhection of the several portions with the resistance 26 and may be made large enough to secure proper ionization within the space occupied by the inner arc guide structure within the outer arc guide structure. Thus grid 24 is positive relative to tubular member 18, tubular member 18 is positive relative to tubular member 19, tubular member 19 is positive relative to tubular member 20, and tubular member 20 is positive relative to the potential of the cathode 4. Picking up of the are by the anode 6 is thus facilitated because the speed of the ions within the arc guide is accelerated.

When an arc is to be prevented from attaching on any of the anodes 6, the switch 27 is placed on the negative pole of the current source 28 which causes the tubular member 20 to become negatve relative to the potential of the cathode 4, the tubular member 19 becomes negative relative to the potential of the tubular member 20, the tubular member 18 becomes negative relative to the tubular member 19, the grid 24 becomes negative relative to the potential of the tubular member 18. The potential difference between the several tubular members and the grid structure thus causes a braking action on such electrons as are permitted to pass through the member 22.

The arrangement of the several portions of the inner arc guide over each other has the great advantage, over a single member constructed within the outer arc guide 8, that the occurrence of a cathode spot on the inner arc guide structural portions is avoided because the current supplied thereto must flow over resistance 26 which limits the current to a low value. The danger of the occurrence of a cathode spot on the arc guide 8 is minimized by the use of the shield 16 which partially surrounds the anode 6 and by the tubular members which overlap each other and the shield 16 thus causing an overlapping electrical action as well as an overlapping mechanical action on the vapor entering through the aperture in the member 22. Suflicient barriers are thus provided to prevent the flow of the electrons to the arc guide structure 8. The further advantage is also obtained from such construction that the insulators on which the shield 16 and the tubular members 18, 19 and 20 are supported from the outer arc guide 8 are protected from the action of the arc flowing from the anode 6 and may, therefore, be made much simpler and lighter than heretofore. Slight leakages of metallic vapor through apertures in the arc guide 8 such as at the point of attachment therewith of the inner arc guide structure supporting insulators and about the insulating bushing for the connection of the several portions of the inner arc guide structure with the resistance 26 will not permit an arc to flow therethrough due to the mechanical shielding action of the inner arc guide structure.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

rality of members arranged over each other within each outer arc guide and insulated therefrom, a source of potential supply, means for impressing a different potential upon each of the said membars from said source of supply to secure a gradually changing potential drop from the anodes to the cathode, and means for reversing the direction of the potential drop over said members.

2. In a. system for controlling the action of an are within an electric current rectifier of the vapor type having anodes, a vaporizable cathode and outer are guides partially enclosing the anodes; inner arc guide structures including a plurality of members arranged over each other within each arc guide and insulated therefrom, a source of potential supply connected with and common to all of said members, a resistance capable of connection at one end thereof with said source, the other' end of said resistance being connected with the cathode of the rectifier, each of said members being connected with said resistance at a different point thereof, and a switch for changing the connection of said resistance with said source from one pole to the other pole thereof.

3. In system for controlling the action of an arc wit an electric current rectifier of the vapor type having anodes, a vaporizable cathode and outer are guides partially enclosing the enodes; inner arc guide structures including a plurality of members arranged over each other within each outer arc guide, a single source of potential supply connected with said members, a resistance bridging said source, the mid-point of said resistance being connected with the cathode of the rectifier, a resistance capable of connection at one end thereof with said source, the other end of said resistance being connected with the cathode of the rectifier, each of said members being connected with said second mentioned resistance 'at a different point thereof, and a switch for changing the connection of said second mentioned resistance with said source from one pole to the other pole thereof.

ERWIN KERN.

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