US1901612A - Mercury arc rectifier - Google Patents

Description

March 14, 1933. M. SCHENKEL MERCURY ARC RECTIFIER Filed April 25, 1929 xNvENToR Nar/'fz Sr//en/fel yA'TTor-zlmiv Patented Mar. 14, 1933 UNITED STATES lPMEN-'f OFFICE- MORITZ SCHENKEI, or BERLIN-CHARLOTTNNBURQ- GER-MANY, ASSIGNOR To 'WEs'r- INGHoUsE ELECTRIC en MANUFACTURING COMPANY, A CoRPonA'rIoN .or PENN- SYINANIA` l. p

l MERCURY ARC RECHNER applicati@ flied April 234,'19295`seria1 No.

My inventionrelatesvto means for minimizing backfire in large metal-tank, 'mer' cury-arc rectiiiers, andA it has particular relation to the arrangement Vof grids in the anode shields of such rectiiiers. f

Heretofore, it'has been-the universal practice to enclose the anodes vof a multi-anode, metal-tank rectifier in'individual protecting sleeves, of tubular shape, which were sometimes slightly restricted 'in' diameter near their lwer ends. Various theories as to the functionsperformed by these anode shields have been held by various yinvestigators. For oneA thing,the shields help to create an island-of more or less quiescent, low-pressure vapor around each anode,`as distinguished from the turbulent condition of the vapors in the rest of the tank, accompanied by many sudden gusts or blasts of vapor, Vof very short time-duration, which must bev prevented from reaching'the regions vof the anodes.

lAnother function of the Y anode shield, which may be mentioned, is the deionization'v of the highly conducting ionized vapor path, in the region of an anode, at the termination of the conducting period of the anode, so that when thearc goes out, the space sur# rounding the anode will become suihciently non-conducting soon -enough to prevent an arc restriking between that anode as a cathode and another anode inthe tank. The exclusionr of even momentary vapor-gusts from the region ofthe anode is for the same pur'- pose of maintaining 'the insulating quality of the space surrounding each anode during the time when it is negative with respect to the other anodes, the breakdown voltage which this space will withstand being very rapidly lowered with increase in the vapor density in said space. f Y It is my beliefjthat the 'slight restrictions which have been found to be necessary at the lower ends of these anode shields have been necessitatedin order to Amore perfectly exclude the sudden blasts of vapor, or waves of vapor pressure, which occur within the tank during the operation of the rectifier. vHeretofore, various grids have beenproposed and placed inside of the anode shields.

357,434, and in Germaiiyiarii a8, ieee:

Usually, one grid has i been used in each'v shield, and it has -beeneither insulated from the shield lor in electrical Contact thereto. Whenfthe grid has beeninielectrical Contact with the shield, it has .been necessary toplace the grid near 'the ,bottom of the shield at some distance below the anode, say about six to seven inches, in orderto preventthe f grid itself from developing a' temporaryi cathode spot which causes a backfire during the period when lits associatedi'anode sheuld be non-conducting.l It ismy belief thatthe grid, when so far away from the anode, actsV merelymechanically,` as a means'for preventing transient vapor-pressure blasts from reaching .the space under the anode. In other words, a grid placed so far below the anode operatesmerely yto create' a quiescent,

non-turbulent, low-pressure zoneV above the grid, so that momentary paths of relatively high vapor-density are not formed between the anode and any' other'anode of the recti-I fier, during the time when the ing on the first anode.- 'n

Lately, -many designers have preferredfto arc is not play-v mount their grid insulatedly inthe'respectiveA anode shields. This has .added some-A what to the cost'and complication of the grid-mounting, but it has enabled the designers to place the gridscloser tothe anode,

say from three-fourths of aninch to two inches below the anodes.' In this position, it is ymy belief that theV grids are too vclose to the anodes to have much effect as ame-` chanical baffling means for preventing vapor-pressure gusts from f reaching-the' anode. Iny otherwords, there isnot sufficient space abovey the grid toestablishr a zone of quiescentzvapcrs inthe immediate vicinity of the' anode.f However, with .this close spacing of the grids, with respect to the Sanodes, I believe that the grids exercise a strong deionizingeffect upon the vapor immediately surrounding the anode, so that the y vapor is quickly rendered non-conducting at the end of each arcing period.- It is my belief that this electrical lfunction of deionizing the vvapor at'the surface 'of the anode is almost entirely alOsentfin the grids which are conductively connected `to` the shields.

because such grids aretoo far away from vthe anode to materially affect thgionization of the vapor immediately surrounding the same during the brief time-intervals which are involvedin the operation of the rectifier. According to my present invention,-I combine the functions of both types of grids by utilizing an electrically operativedeionizinggrid placed close tothe anode, and a mechanically operative Vbaffling grid placed at Vsome' distance from the anode, near the bottom of the, anode shield, the spacings of the grids being v as previously indicated. The rst grid isperforce insulated from the shield inv order toprevent the grid itself 'from promoting backfire. The second grid need not be insulated and is preferably electrically connected to theshield for facilitating the mechanical mounting of the grid, although I do not wish Vtorbe limited to the electrical connection of even` thejbottom rid.' A g The :double arrangement of grids just de,-

' scribedisl particularly advantageous in rectifiers of very large current-capacities, be-

cause, in"l such cases, itis `particularly .diffi-y cult-to obtain` a grid which will be effective duringthe periods of non-conduction of the .anode and yet will permit-the necessary current flow during the arcing periods. If the vspacesprovided by the grid areftoo small,

the arc willrbe restricted to such anextent that .the larc current cannot be increased I Y beyond a certain pointwithout enormously increasing the arcv drop at this constriction,r

Vthev design-limit as toy the current capacity of each anode, heretofore encountered in the art, when only one type-of grid was utilized, is completely avoided.

v Furthermore, by my invention, am enabled to dispense with the slightly converging ,restriction at the bottom of the anode shieldand `may/.utilize either astraight cy- Hadrien Shield kom Shield having, an out wardly flaringvlower end.k Each grid. increases the voltage-drop in the arc to some extent, but the outwardly flaring lower end of the shield reduces vthe voltage-drop byl removing some of the "restriction fromgthe arc path. Hence, by utilizing an anode shield having an outwardly flaring lower end, and protecting that lower end by means'of a grid which servesI the function of mechanically preventing the vapor-pressure blasts from .reaching'the anode, and also vutilizing an electrically ope1ative,insulated grid disposed close to the anode for deionizing the Y killustrating aV modification, and

space therearound, I am enabled effectively to shield the anodes of rectiliers of very large capacity, without increasing the lvoltage drop in the arc beyond theJ values which have been heretofore obtained in smaller rectifiers.A .j 1 y -1 My invention is shown, by way of illustration, in the accompanying drawing,

whereinv4 i Y* Y v Y l Figure 1 is Va cross-Sectional 'view of a portionv `of a 'metal-tank, mercurysarc yrectifier utilizing my special grid arrangement in connectionwith an anode shield of a common type.heretoforeusedprior,to Ymy invention," i

Figure 2 is `across-sec'tional'viewofpone anode, together with Vits ,shieldrv and grids,

F igure 3 i'sga similarvview illustrating .ha

third formV offmy invention, which at presentmy preferred forni.'

jMy invention is applicableto any mercury-arc rectifier, but is particularly applicable to a rectifier which is enclosed within a Ahighlyevacuatedmetal tank, a portion of which is shownv at 4 inQFig'ure 14.v 4The tank is of the multi-anode type, Aas will be well understood, only two insulatedly sup.-y ported anodes kand 6 being visible inthe fragmentary 'cross-sectional viewy of KVFig- At the bottolnlof the tank an insulated kcathode-receptacle, containing f liquid.,.r1ner cury S. Itwill be understoodthat suitable v electrical connections are provided between two grids 11 and 12 disposed therein. The

upper grid 11 is-disposed` close under the anode, say from about threeffourths of ran inch to about two inches below the anode: as previously described, and is insulatedly supported by means of insulators 13.` Thebottom anode 12 is disposed near the vbottom end of the anode shield', say about six inches, or somewhat more below the :anode as 'previously described and may, forconvenience, be electrically connectedthereto. Y. f

In Figurelthe anode shield-10 is'slightly constricted at `its lower end, by vreason of a converging tapering portion 15.

In Figure 2, the anode shield- 10a isfof the saineV diameter throughout its* length. In Figure 3, the anode shield 10b isr somewhat larger at its lower end, by reason of the outwardly flared 'portion 17. f

Two grids are provided, as above described, in every instance.

The grids may be identical in size and shape, as indicated in Figure 1, or they may be separately designed with aS view'to their separate functions, as Ihave outlined above. Thus, in Figure 3, the bottom grid is shown with slightly inclined slats or louvres ,19 which are designed for the purpose of more eectively baffling the blasts of mercuryvapor that may impinge thereon.

I claim as my invention:

1. In a multi-anode mercury-arc rectifier, the combination, with each anode, of an insulatingly mounted conductive anode shield having an outwardly Haring lower end terminating in an open mouth, means for deionizing the space within the shieldvclosest to the anode, and a baffling grid extending across the mouth of the shield for impeding the entrance of vapor-pressure blasts.

2. In a multi-anode mercury-arc rectifier, the combination, with each anode, of an insulatinglyv mounted conductive anode shield having an outwardly flaring lower end terminating in an open mouth at least about six inches below the anode, whereby a quiescent space is produced, and a baiiiing grid extending across the mouth of the shield for impeding the entrance of vapor-pressure blasts, said baiiiing grid including means for providing a plurality of passageways therethrough at spaced intervals over the entire area of the grid.

3. A metal-tank mercury-arc rectifier characterized by having a plurality of anodes surrounded by individual metallic anode shields having two metallic grids apiece, the top grid being insulatedly supported and being from about three-fourths of an inch to about two inches below the anode, and the lower grid being in electrical Contact with the shield and about six inches or more below the anode.

In testimony whereof, I have hereunto subscribed my name this 9th day of April, 1929 at Berlin-Siemensstadt, Germany.

MORITZ SCHENKEL.

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