US1859875A - Mercury vapor rectifier - Google Patents

Description

May 24, 1932. E, KERN MERCURY VAPOR RECTIFIER Filed May 12. 1927 w bo w j M i il/ l f /f,// f/ l////// Patented May 24, 1932 UNITED STATES PATENT @FFQ i EEWIN KERN, or WETT-INGEN, SWITZERLAND, AssIGNoE 'To AKTIENGESELLSCHAFT BROWN BovEnr a CIE, or BADEN, SWITZERLAND, A JOINT-STOCK COMPANY or SWITZERLAND MERCURY vAPoE RECT'IEIER i Application led May 12, 1927, Serial` No. 190,714, and inGermany '1,Eay'1'7r,l19.?.6.`v

This invention relates 4to mercury vapor rectiers, and has to do with construction of the electrodes, particularly the anodes or posi-v tive electrodes from which the current is disl5 charged in the rectifier. l

The general object of the present invention is the provision of an anode construction which will be eiective in eliminating or reducing the possibility of back ignition or reversals of current flow through the rectifier,

as well asshort circuits between anodes.

Another object is the provision of a construction which may be arranged and assembled in the apparatus with facility, which does not involve complications in related portions of the rectiiier construction, and which will be reliable in operation. Y

Other and further objects will be pointed out hereinafter or will appear to one skilled in the art upon an understanding of' the invention or its employment in practice; n

In the drawings forming a partof this speciication, I illustrate anumber of arrangements in which the invention `may be embodied, but it is to be understood that'these are presented for illustrative purpose only and that the invention is not limited to the particular .constructions or arrangements shown, and'hence that the present disclosure of particular constructions is not to be accorded any interpretation 'having the effect of limiting the claims short of the true and most comprehensive scope of the invention in the art.

In the drawings,

Fig. 7 is another diagram of similar ele- Fig. 1 is a diagrammatic illustrationof an anode construction, the same being in the mental nature, illustrating a modified con struction. u i

Mercury vapor reetiers, particularly those torV thel handling of polyphase currents of high power, are sometimes subject to short circuits between anodes -oi'.different phases,

which cause disturbanceso'r interruptions in the operation of the apparatus. 'These short circuits are sometimes caused by the forma-v tion of a cathode spot on one `of the anodes, the result of which is that current is able to traverse the anode in both directions, thus producing a conditionrvhich may establish a short circuit `withvanother anode. In normaloperation of such a rectifier, when current Hows in the normal direction, from anode to cathode, kthe whole of the anode surface takes part, to a greater or lesser extent,`- inthe passing ofthe current from the anode l'into the eXhau'sted space within ,1 the rectifier, whereas, whena condition of back ignition arises, the passing Vof the current'in the re-j verse direction takes place at onlya localized i point or area on the anode. At this point, the anode surface ceases to maintain the valvey action and receives the reverse current. fBy

virtue ofthe present' invention, the occur-v rence of such localized changes' in the current-transmitting nature of the anode Yis prevented orrendered less likely, and the capability ofthe'anode vfor passingcurrent inthe reverse direction is reduced to such a point that the proper valveaction of the anode is consistently maintained. Thus', the condi'- tions which contribute tovshortcircuits between the anodes are'obviated. This result is vattainedby the provisionof a construction Y s whereby the path which may be taken byf,

la reverse current in the anode is such as t0 offer aV resistance effective to prevent, or so limit suchcurrent to such extent that the anode cannot assume such acharacter or condition as to establish a short circuit with another anode. f n j A rllhe nature of the invention may be ascertained from the examples shown in the draw-` ings. In that represented in Fig. l, the refer` ence character 10 designates the end of theA anode which is within the rectifier cylinder,

said anode being supported in `an insulator lso I 11. rlhe actual surface of the anode exposed within the rectifier is subdivided into segregated areas by provision of elements 12, which may be in the nature of rods composed of material having dielectric or low electrical conductive characteristics, and qualified to resist the heat of the mercury vapor. These elements may be rods of quartz held together in a bundle by a surrounding tube 14 of insulating material, which covers the lateral surfaces of the electrode head 10 and holds the rods in lateral contact with one another and with their inner ends in contact with'the vsurface of the electrode head. By this arrangement, a large number of small channels 15 is provided, opening at their outer ends into the rectifier chamber and debouching at theirrinner ends on the surface of the anode. As a consequence of this arrangement, the only portions of the anode surfaces which can function to pass current into or from the rectifier chamber are those segregated areas which are exposed between the channels. W' hen the rectifier is operating in the normal way and discharging current into the rectifier chamber, all of these segregated areas function in parallel, and the flo-w of current through the passages 15 is likewise in parallel. Should a cathode spot occur on' one vof these segregated areas or elements of the anode surface, however, the only path available for the reverse current would be the particular passage which debouches on the'particular segregated area or element of surface so affected. Thus, iff the cross sections and the length of these passages are suitably chosen,

' it is possible, through the resistance offered to an arc by the passages, to limit the current striking back to such value as to prevent the establishment of a reversely flowing arc. A somewhat. similar arrangement is illustrated `in Fig. 3, whereby the exposed surface of the anode head 10 is subdivided into segregated areas by means of a foraminous shield 16 seated against the head of the anode and having the passages 16a affording communication between the rectifier chamber and limited surface areas of the anode. This foraminous shield is held in position bya sleeve 17, of heat resisting insulating material, which covers the lateral surface of the anode head.

The nature of the effect obtained is illustrated in elemental fashion in Fig. 6. Here the conductor A is the element representing the electrode head and the points a represent the segregated elements of surface thereonY which have communication with the rectifier chamber individually bytway of ohmic resistances 7", r1, r2, r3, and r4 the terminals of the conductive paths being indicated at t, t1, t2, 153 and t4. llhenthe rectifier is operating in the normal way. that is, when the current flows from anode to cathode, these conducting paths all work in parallel. 1f, however,the terminal t1 assumes a character such as would make it the objective of a backfire arc, the reverse-direction current is opposed by the relatively high resistance 111, which limits its value to a degree such that no injury, or interruption of the operation of the rectifier, results. The elements 16 represent the high resistances of the passageways interposed across the arc between the conductive paths to the respective segregated elements of the anode surface. By this means a reverse current arc reaching one of the points t, t1, 252, etc. is confined to the particular path of which that point is the terminus. As illustrated in Fig. 7, the anode is subdivided into a plurality kof segregated Velements A1, A?, A3 and Af each communicating with the common lead L by, way of respective resistances 7, r1, r2 and r3', and each of the elements A1, A2, A3 and A* is provided with a device such as illustrated in Figsfl or 3. As thus analyzed in the diagrams of Figs. 6 and 7 therefore, it is apparent that if all of theV anode circuits are resolved into a large number of conductive paths, each containing ak suflic-iently klarge ohmic resistance, the for ward 'current which flows underv normal working conditions is opposed by a resistance equal to that of one of the parallel paths divided byv the number of parallel paths per phase. The 'reverse current, however, which flows in the event of a back-fire, can pass along only one of the parallel paths atany given instant, and it therefore, is opposed by the Vwhole resistance of the circuit.' Or, to

state it another way, the effective resistance opposed to the back-ignition current and the normal working current, respectively, are in the proportion of the number of parallel conducting paths per phase.

The foraminous mask or shield, as exemf plied in Figs. 1, 2, and 3, contributesa further protective effect in that lit guards theV surfaceof the anode head from eddies of mercury vapor and from drops of liquid mercury which are liable to be thrownl off occa-y sionally from the cathode. Moreover, by use of a suitable material for the shield, the

anode surface may be protected from the` ultra-violet rays of the mercury arc.

With th-e arrangements above described,

the resistances in the respective arc-conducting paths of the anode should be so chosen that the back-ignition arc is broken after not more than one phase period. If theresistance in eachr arc path is dimensioned on this principle, the question as to whether the ohmic voltage drop in the parallel conductivev paths will be sufficiently low to enable the rectifier to operate with the required eiiiciency, depends on the way Iinl which the anode is subdivided. In order to keep the losses, due to these resistances, as low' as possible, the anode must be subdivided into a comparatively large number of conductive paths. The stationary back-ignition are @0.1i-

CIL

sists of dir-ect current and alternating current components. The controlling factor, therefore, for the breaking up of the backignition arc, is the ratio of resistance vto reactance in the circuit taken by the are. In order to insure that the back-ignition are shall be extinguished, therefore, the proportion of I). C. to A. C. component in the current must be kept below a certain value. To accomplish this, the ratio of resistance to inductance in the bach-ignition circuit must not fall belouT a certain value. Since the general arrangement of the rectifier and its transformer determines the value of the inductance, the 'same provides the basis for determination of the magnitude of the resistance necessary to limit the back-ignition current to a value at which the are Will be extinguished at the end ofa period. EX- perience has shown that it must be distributed among a relatively large number of parallel paths in order that its effect upon the normal current shall not lead to'excessive losses. In other Words, it must be so subdivided that the total losses, which with a given resistance per subdivision are reduced as the nuinberof parallel paths is increased, do not reach an inadinissable value. The minimum value for this resistance per subdivision is given by a short-circuit reactance per phase of the transformer at normal `frequeney measured from the secondary side. By an alternative arrangement, the effect may be attained by subdividing the anode itself into a plurality of parallel sections and incorporating' the resistance in the sections themselves. For such a construction, it follows from the considerations above pointed out, thata material of relatively high specic resistance must be used and the anode must be constituted of a large number of parallel subdivisions, each having a resistance not less than the critical value referred to above.

Illustrations of structures in which the resistance may thus be incorporated in the anode are shown in Figs. 4 and 5. In Fig. 4 the anode l0 has its arcing terminal 'subdivided into a large number of rod-like sections 10a with intervening slots 10b segregating the respective sections from one another throughout their length. lThe length of these sections, and the material of which they are composed, are so chosen that the resistance of each section is sufficient to limit the current of a back-ignition are, striking that section at its terminus, tovsueh an eX- tent that the are cannot maintain itself. rIhe sections are suitably sheathed With'insulating material Il in such fashion that only their ends are exposed Within the rectifier chamber. By this arrangement, the current from a back-ignition are is confined to the section on .vhichthe arc impinges, and the are is extinguished, -due to the resistance of that section, at the end of the phase period.

their length. Because of the limitations im-4 Y posed on the cross'sectional size of the ano-de by consideration of the rectifier design, these sectionsmust be comparatively short. Hence, in order to obtain the requisite resistanc'ein each section, the material of the ringsv must be one of fairly high specific resistance,such as graphite. With thisjconstruction, as With that illustrated in Fig. 4, a back ignition arc impinging one of the sections is confined theretoand extinguished at the end ofthe phase period through the ,eect of the resistance offered by the section. y Y n It will be observed thatin'each' ofthe arrangements above described, Vthe arc feeding current of each anode is discharged through a plurality of parallel paths, eachy of `which offers to a reverse-.direction arc a resistance such that it cannot maintain itself. By such arrangement and effects, short" circuits between anodes are 'prevented Without material losse-s in the'conversioneciency of the rectifier. i Y

I/Vhat I claim is:

l. In a vapor rectifier, an anode having its arcing surface constituting a `plurality of separated areas energized in parallel-and arranged in series with respective resistances.

2. In a vapor rectifier, an anode having its areing surface'constituting'a plurality of separated areas energized in vparallelfand arranged respectively in series with resistances sufficient to prevent the "maintenance of a re- Y verse direction are to any of said areas;

3. Ina vapor rectifier, an anode having its arcing surface arranged to subdivide the are among a plurality of paths through respective resistances; Y f 'i l 4. `In a vapor rectifier, an anode having its arcing surface constituting a plurality of areas separated by resistances Which are greater than the resistances in the are current.

5. In a vapor rectifier, an anode having its arcing surface constituting a plurality of areas energized in parallel and separated from'one another by resistances which are greater than the resistanees in the path of the arc current. Y l

6. In a vapor rectifier, an anode affording a 'plurality of separated areingV surface portions arranged respectively in` series vvith respective resistances which are in parallel in the path of the are current.

7; In a vapor rectifier, an anode aording a path of the y plurality of separated arcing surface portions energized n parallel through resistances which respectively are so proportioned With respect to the inductance of cuit as to preclude maintenance of a reverse direction arc on any of said surface portions.

8. In a vapor rectifier, an anode affording a plurality of separated arcing surface portions energized in parallel through respective resistances.

9. In a vapor rectifier, an anode having its arcing surface subdivided into a plurality of areas separated by resistances which are greater than that offered to the flow of the normal arc.

10. A polyphase rectifier of the vapor type With the arc surfaces of its respective phase anodes subdivided into separated areas which are arranged respectively in series With scparateresistances, said sepa-rated areas being energized in parallel, and said resistances being individually ofa value such as to prevent the maintenance of a reverse-direction arc on any of said areas.

11. In an electric current rectifier of the arc type, an anode having a restricted arcing surface subdivided into a plurality of arcing areas sepa-rated by passageways of higher resistance than the arcing areas.

12. In an electric current rectifier of the arc type, an vanode having a restricted arcing surface subdivided into a plurality of arcing areas operating in parallel and separated by passageways of higher resistance than the arcing areas.

13. In an electric current rectifier of the arc type, an anode having a restricted arcing surface, the said arcing surface comprising the ends of anode portions operating in parallel and separated by passagevvays of higher resistance than the arcing areas.

14. A mercury arc rectifier comprising an evacuated vessel, a cathode, an anode extending into said vessel and provided With a plurality of active and inactive surfaces, and an insulation shield mounted Within said vessel to cover said inactive surfaces of said anode.

In testimony whereof I have hereunto vsubscribed my namc this 22 day of April, A. D.

1927, at Zurich, Switzerland. y

' ERWIN KERN.

the rectifier cir-

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