US2490542A - Mercury arc rectifier - Google Patents

Description

Dec. 6, 1949 J. c. READ MERCURY ARC RECTIFIER Filed Jan. 9, 1945 Inventor John Carleg Read,

by W

'His Attorney.

Patented Dec. 6, 1949 John Carley Read, :Inwoods, Rugby, England, as-

signor to General Electric Company, a corpo ration of New York Application January 9, 1945', s mi so. 571,978 In Great Iiritain January 14, 1944 2 was. (o1. ass-27.5)

This invention relates to mercury arc rectiflers lower, side oi the baiile or grid. These ions which and the like, and more particularly to a method i of reducing the tendency to backflres, especially at high voltages.

It is generally considered that a contributory cause of such backflres is the bombardment of the anode by positive ions which occurs during the time when the anode is negative. the higher voltages a considerable part "of this positive ion bombardment is produced by positive ions attracted into the anode from beyond the de-ionising baflle or grid. It is the object of the invention to reduce the effectiveness for initiating backfires of the bombardment produced by these positive ions.

According to one form of the invention 1 reduce the quantity of positive ions that are able In rectifiers for to be attracted to the anode from the iar side of the grid, by certain arrangements of multiple grids with suitable potentials applied tothem. In another form I cause this bombardment to be less continuously concentrated on the same part of the anode surface. In another form I cause this bombardment to fall on parts of the' 'anode" surface where the electrostatic field strength is low. In another form I divide theanode into a main part which does not receive the bombardment and an auxiliary part, connected to the main part through a suitable high impedance, so arranged that this'bombardment fallson the auxiliary part of the anode.

The invention will be better understood by ref erence to the accompanying drawings, in which Figures 1 to 6 represent various forms oi the invention. In the drawings corresponding parts 1 all cases.

Referring to Fig. 1, l represents an anode of a V high-voltage mercury arc rectifier or'thelike,"

to enable a control potential to be applied to it.-

During the time when the anoderis-negative a;

considerable part of the positive 191 bombardmentiwhich it is subjected to is producedby ions are designated by thesame reference numerals in 3 attracted to the anode from the further, i. ate;-

reach the anode from the further side of the grid are not distributed over the'surface of the anode, but their bombardment is concentrated on particular points 6 which are respectively about opposite the centres of the holes 8 in the grid, the ions falling on these spots along paths represented by the dotted lines' l. The intensity of bombardment at the points 8 greatly exceeds that .over' the remainder of theanode surface.

According to one form of the invention I may reduce the average intensity of bombardment on these spots by rotating the anode or grid on their own axes; and the various holes in the grid may be so located that the tracks of the centres of different holes which are thus traced out on the anode face do not coincide. Alternatively the spots 8 where the local bombardment takes place from each of the grid holes may be caused to rotate or oscillate by applying a tranverse magnetic field, for example as indicated by the coils shown dotted at M. In either case the bombardment is thus spread over arelatively large area of the anode face. I

Another form of the invention is shown in Fig. 2, in which two grids 4 and 9 respectively, are provided one above the other and fairly closely spaced apart. In using this arrangement the control potentials applied ito the two grids are maintained such that, at least during the time when the anode is negative with respect to the cathode, the nearer grid 4 is positive with respect to the farther grid 9. The. potential difierence between grids 4 and 9, the spacing between them, and the size of holes are so-chosen that the electrostatic field in the spacebetween 4 and '9' due entering one of the holes in 9 will first experience a repelling field due to the potential on 4 and thus the" anode is unable to attract to itself positive ions iron: the space below the lower grid 9. Conveniently this potential' hetwfeen 4 and 9 may be applied by applying to -both 4 and 9 identically similar A. C. voltages superimposed on different D, C. bias voltages, in the manner commonly understood. In this way, providing the dimensions and grid potential difference are suitable as described above; the concentrated bombardment of the anode bypositive ions irom the far side of the grids can be practically-eliminated.

Fig. 3 shows another; in which; again two grids?! and 9, are employed,

with different potentials on' them. In this case, J

orm oi the invention,

however, during the time when the anode is negative the upper grid 4 is'allowed to be negative with respect to the lower grid 9, either by having such a potential applied to it by external means, or by acquirin this potential by virtue 5 of its capacity to the negatively charged anode, the upper grid 4 in thisf'lfittGFCB-Sltbd-DEBBMIY. or completely insulated. In this formof the invention, however, the passages 8 through the upper grid 4 are made of tortuous form so that: a particle can only pass through 8 by following a...

4 H to depart far from that of I, but at the same time the presence of the high impedance in series with H prevents the establishment of a backthe on l4 as a result of the ion bombardment to which this is subjected.

Further, similar results can be obtained with simpleranodeconstruction than that in Fig. 5. Ingeneral any form 01" anode may be employed where the anode is similarly divided into a main m part which carries the normal power current and .anfllauxiliary part connected to the main part sharply curved path. The actual form'of the" tortuous passages through Lia mother. realest;

not relevant to this present: invention, :hut. for

through 4 is made too sharp for a. particle a-1-- ready possessing this: velocity to be-abIe to get. round thecorners without: striking some: part of, the grid. 4; Thus again few or none of the noeltive ions entering. from below the lower able'to bombard the-anode. I

It has already been explained inconneetiolrwith. Fig. 1- that the. ints 6- on theanodeface: where the intense bombardment occurs are verysmall and exactly located- According to-an'other form of the invention, shown in Fig.4. small 1 holes or grooves I3 are provided in the anode;- face exactly located. where-theserpoints of; intense bombardment occur. The velocityof theionby the time that it approaches the anode'face. is'so high that it travels almost in a straight line,. and consequently the bombardingparticles then strike; the anode down inside these holes or grooves... The bombarding particles therefore: impinge on: a point wherethe electrostaticfieldstrengthzis through a high impedance as described, providing; thatthe main: and auxiliary parts of the anode. which; should preferably be closely adjacnfitoone another, are so located relative to the holes in. the. adjacent de-ionislng baflle or ,gridi' thatisuclr bombarding positive ions enteringj through the latter will fall on the auxiliary Withi this" part: of: the anode. For practical purposes this means that all the electrostatic stress lines from the grid. holes tothe anode will fall on the auxiliarypartotithe anode;

-Manyconstructions that would comply with these requirements will be obvious to those skilled in-the art. An example of such a construction is shownin Fig. 6..

.In' Fig. 6 the anodeis thus divided into an annular main-part. l which carries the normal power current and is connected through its tubular support: stem 2 tov the connection l5 leading to the main transformer; and an auxiliary part H of die -like: form closely adjacent. to the main part l,.- and connected through its steml6 and the external high impedance 11 to- I. The main part of .the anode is supported and insulated from the vacuum chamber l8 of-the rectifier by a leadin.;insulator l9 of any of the known forms; and the auxiliary anode is inturn insulated from this by a -further lead-in insulator 2. The grid 4 which is mounted on its support insulator 5 par--- tially surrounds' themain and auxiliary parts of the anode, and during the time whenthe anode is. negative the electrostatic stress lines conse-.

quently take: the form. approximately sketched by the dotted lines 2|. The location of theauxmuch lower than on the: outer surface of the rs' pan of amde with respect to the anode; and furthen'the material sputtered out. of the anode by the bombardment tendslargely to be retained inside the holes orgrooves. The

positive ion bombardmentis in. this.- case: lessei- 5 fectlve in producing backfires. I

Alternatively, as shown iII'Fig;' 5; the anode: may actually be made hollow with theholes on grooves I3 passing right through ttrthe'interion. If the hollow space inside the; anode is left. empty the ions will then bombard ztheinterior surface of: the anode; where: the-field strength is; zero;

In a further form. of the inventiom-horvevem" anadditional electrodeor auxiliary anode; shown dotted at M- in. Fig. 5- may be provided inside the:

hollow anode, so placed that if it is: at or about the same potential. as the main ano'de "l: the ions passing in through the holes 13' along passagx as indicated by the dotted'lines i "will be. col-er. lected on this auxiliary anode.. 'The actual rent. flow corresponding to this flow/oi. bomBlmting ions is very small. I therefore connectthe: auxiliary anode H to the-main anode I through a very high impedance; which may be either internal 01' external tothe rectifier, thishigh im-- holes. 8 in. the grid. is such that thestress lines from theseholesto the anode-all fall on the auxiliary partof the: anode, and thus bombarding. positive ionsentering from outside the grid will.

0- impinge on the auxiliary part ofthe anode,

5550f values. as already describedin connection with Fig. 5.

Alternatively thehigh impedance can take'the form. of. a1 semi-conducting rod forming" part of the-length of the auxiliary anode stem l6, i. 6:. inside the rectifier: In this casev the additional lead-in-insulator 20 is not required. If the impedance is thus internal it should preferably be weli' screened-from the generalionisation' of the arc; as would in'fact 'bethe case with a construction on the lines: illustrated in Fig. 6.

Arrangements such as shown in Fig. S'may be used in conjunction with any of the arrangementsin Figs. 1 to 52 For example, the auxiliary part M of the anode may have holes or' grooves pedance taking the form of: a high. resistance or 7 provided inits bottom face at the points where current this current. is. ableto pass throughthehigh. impedance withoutcausing-the potential at the bombardingpositive ions strike it, as in Fig. i. 'I'lie'Jcharacter'istic featureof constructions according to theinvent'ion, in which the anode ls' divided into two parts thus that'theload as; exemplified in Fig. 6, is

current is carried on one part while the other part, which is incapable of sustaining a backfire, receives the positive ion bombardment, by utilising the fact that the bombarding positive ions entering through the grid holes travel in nearly straight lines, whereas the normal flow of load current can follow a relatively curved path and thus can flow from the grid holes to the main part of the anode.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In discharge apparatus of the type in which the discharge takes place between an anode and a cathode through an ionizable medium, the combination which comprises an anode having a discharge receiving surface, an electrode interposed between said surface and the cathode of the apparatus, said electrode having a plurality of openings positioned transversely of the discharge path for sub-dividing the forward discharge, and means producing an electromagnetic field in the region between said discharge receiving surface and said electrode for causing relative motion between the discharge receiving surface of the anode and the sub-divided forward discharge to spread the discharge over an extended portion of the discharge receiving surface.

2. In discharge apparatus of the type in which the discharge takes place between an anode and a cathode through an ionizable medium, the combination which comprises an anode having a discharge receiving surface, an electrode interposed between said surface and the cathode of the apparatus, said electrode having a plurality of openings positioned transversely of the discharge 6 path for sub-dividing the forward discharge, and means producing relative motion between the discharge receiving surface of the anode and the sub-divided forward discharge to spread the discharge over an extended portion of the discharge receiving surface.

JOHN CARLEY READ.

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

UNITED STATES PATENTS Number Name Date 841,386 De Forest Jan. 15, 1907 1,066,505 Kraus et a1. July 8, 1913 2,097,490 Kobel Nov. 2, 1937 2,116,393 Griffith May 3, 1938 2,148,300 Krines Feb. 21, 1939 2,320,685 Von Bertele June 1, 1943 FOREIGN PATENTS Number Country Date 339,022 Great Britain Dec. 4, 1980 341,578 Great Britain Jan. 22, 1931 395,383 Great Britain July 6, 1933 422,870 Great Britain Jan. 21, 1935 425,896 Great Britain Mar. 25, 1935 430,915 Great Britain June 27, 1935 432,434 Great Britain July 26, 1935- 448,545 Great Britain June 10, 1936 458,777 Great Britain Dec. 28, 1936 493,534 Great Britain Jan. 4, 1937

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