US2608675A - Magnetically influenced arc device - Google Patents

Description

5 w. D. BUCKINGHAM 2,608,675

MAGNETICALLY INFLUENCED ARC DEVICE Original Filed Aug. 10, 1949 2 SHEETSSHEET 1 FIG. as 34 23 ai -1 1d INVENTORL W. D. BUCKINGHAM AT TORNEY 1952 w. D. BUCKINGHAM MAGNETICALLY INFLUENCED ARC DEVICE Original Filed Aug. 10, 1949 2 SHEETS--SHEET 2 FIG. 3

INVENTOR.

W. D. BUCKINGHAM ATTORNEY Patented Aug. 26, 1952 MAGNETICALLY INFLUENCED ARC DEVICE William D. Buckingham, Southampton, N. Y., assignor to The Western Union Telegraph Company, New York, N. Y., a corporation of New York Original application August 10, 1949, Serial No. 109,456. Divided and this application August 4, 1950, Serial No. 177,612

4 Claims. 1

This invention relates generally to improved means for magnetically'controlling arc discharge devices, and more particularly to suitable means for causing the arc stream to maintain a predetermined path between electrodes in concentrated arc discharge lamps of the type described in Buckingham and Deibert Patent No. 2,453,118, and in my copending application Serial No. 83,151, filed March 24, 1949, which operates with a highly concentrated arc discharge in contradistinction to a low pressure diffused or glow discharge, the disclosure of which patent is incorporated herein by reference thereto.

This application is a division of application Serial No. 109,456, filed August 10, 1949, now Patent No. 2,541,028, issued February 13, 1951.

With suitable construction, such as illustrated herein, a concentrated arc device of the foregoing type is particularly adapted for use in high wattage lamps, such as those used in flood lamps, search lights and the like, operating in the open air and powered from a source of alternating current supply. The lamp utilizes two electrodes, which in an alternating current type may be identical in construction if desired, and which alternately operate as anodes and cathodes during each cycle of the alternating current supply which may be the 110 volt, 60 cycle current'commonly available. Each of the electrodes may comprise agenerally cylindrical metal tube or shell that is closed at one end and is filled with the electrode material. The thin active surface film of the electrode material at the open end of the tube comprises a molten metal, such as zirconium, or hafnium, when the lamp is in operation, and underlying. this active surface film is an oxide of the metal. This oxide has a melting point much higher than that of the base metal which has high electron emissive properties at the very high temperature at which the device operates, but which isnot a sufficiently good electron emitter at lower temperatures to cause the electrons to be emitted in sufficient quantity to support an .arc of high current density until the metal has reached incandescent temperatures, well above the melting point of the metal.

Either zirconium or hafnium metal is a better electron emitter at high temperatures than is its oxide, andit also has a lower melting temperature; thus, under the intense ionic bombardment ing oxide solidifies and supports the film of nioltenmetal onits surface. It is this thin film of 2 molten metal that is the chief source of the visible radiation from the lamp. It is so thinthat surface tension holds it to the oxide backing so that the lamps may be burned in any position.

It is desirable to dispose'the electrodes at an angle to each other in order to provide an unobstructed light output from the active surface films thereof. In this case the arc stream between the active surfaces of the electrodes should follow a curved path, but sometimes the arc stream would tend to concentrate on the edges of the electrodes closest to each other, and at other times would tend to rise due to convection currents and also when the arc stream became too long.

An object of the invention is the provision of suitable means for automatically controlling and maintaining a desired position of the arc stream between the electrodes.

Another object is to cause the arc streamto maintain a predetermined pathbetween the electrodes when disposed at an angle to each other thereby to prevent the arc stream from concentrating on the edges of the electrodes closest to each other and also to prevent the are from rising due to convection currents or other causes! Other objects and advantages of the invention will be apparent in the following detailed description of two illustrative embodiments thereof, taken in connection with the accompanying drawings in which:

Fig. 1 is a view, in elevation, of a high wattage open air lamp adapted to be powered from alternating current, in which the electrodes are mounted approximately at rightangles to each other, with suitable magnetic structure for automatically controlling the position of the arc stream, the figure also showing means for automatically maintaining the correctdistancebetween the electrodes;

Fig. 2 is a fragmentary view of the magnetic structure for controlling the position of the arc stream, taken along the line 2-2 of Fig.1;

Fig. 3shows a circuit arrangement for use with smaller sizes ofthe alternating current lamp with means for automatically controlling the position of the arc stream; i

means for automatically maintaining the correct distance between the electrodes; and

Fig. 6 shows a circuit arrangement for controlling the position of the arc stream in the manner illustrated in Fig. 4, together with a modified startingand running circuit for the lamp.

Referring to Fig. 1 of the drawings, there is shown a construction adapted for use with high wattage lamps, capable of operating in the open air and powered from a source of alternating current supply. The lamp utilizes two electrodes [2, which may be identical in construction if desired, and which alternately operate as anodes and cathodes during each cycle of the alternating current supply. The electrodes are disposed at an angle of approximately 90 to eachother, as shown in the figure, in order to'provide an unobstructed light output from the lamp. The light, which principally comes from the active surfaces 16, passes through a condenser lens 44 and thence through a light aperture. 45 and projecting lens 46. Means hereinafter described are provided for rotating the electrode to insure proper centering'of the light spots on the activated surfaces [6 of the electrodes, the arrangement enabling this to bedone without having the electrode-rotating mechanism in the field of projection of the light.

The interior construction of. each of the elec trodes is preferably in accordance with that dis= closed in the parent case of which this, is a division. The electrode material may comprise zirconium. or hafnium metal powder with which is mixed a material that protects all but the active end of the core from oxidation, whereby progressive oxidation of the zirconium or hafnium metal beneath the underlying oxide layer can be prevented. A suitable powdered metal, such as nickel, in the proportion of about one part of nickelto three .parts of zirconium metal powder, when zirconium is employed, has been found to produce a mixture which does not progressively oxidize. throughout its, entire volume as would be the; caseif. zirconium, alone wasused'. Such electrodesacquire only a thin cap of; zirconium oxide at, the; active end, and. the underlying conductive nickel and zirconium mixture remains to aid in starting the lamps. Preferably there is also added to. the zirconium-nickel mixture a small percentage of a metallic substance, such as magnetite, which is an oxide of iron, the magnetite increas ing: the electrical conductivity through the fused oxide cap when the electrode is cold, and thus aids in, starting. The exact proportions of the metals. and oxides in the whole mixture do not seem to be critical. However, if more than 40% of nickel is employed in the mixture, excessive smoking occurs and the electrode erodes away more quickly; if less than 5% of nickel is employed, the protective action of the nickel is not present. With respect to the conductive materiaLsuch. asmagnetite, from 2% to may be employed.

It will be understood that as the electrode slowly erodes during operation of the lamp, that .po'rtion of the zirconium which is exposed to the arc does oxidize thereby to maintain the underlying. oxide layer, but further oxidation of the holder I 8 which is carried bya rotatable metal "shaft-23; Surrounding each shaft, and in good '4 electrical contact therewith, is a metal collector block or collar 20 to which is secured, as by soldering or by screws, the external terminals [3 of the lamp. The collector block is secured to an insulating block 21 that. is mountedon a slidable block 41, one of the blocks resting on the top surface of a cabinet or supporting frame 50, and the other block 41 being mounted on a vertical side of the structure 50. Each of the blocks carries a motor 26, and the shaft of each motor is connected, by an electrically insulating coupling 34, to the shaft 23 thereby to rotate the associated electrode 12 about its longitudinal axis. The motors 26 may be either direct or alternating current type, and the electrodes are thereby rotated at suitable speeds about their longitudinal axes in opposite directions relative to each other. This speed may be quite low, for example, one revolution per minute, and should not be so high as to cause appreciable centrifugal forces to be exerted on the active surfaces of the electrodesor to cause rotation of the are spot. A symmetrical oxide. bead is thus formed and maintained on each elec trode and the position of the luminous spot on each electrode is stabilized. H

Fig. 1 also show means. for automaticallybringing the electrodes together for starting the arc and for maintaining themat. a correct dis-- tance. from each other duringv operation of the lamp, which feature, relates to divisible subject matter and hencev is not claimedherein. The. operation is based. on a differential 861310111138!- tween the arc voltage, i. e.-, the voltage drop. across. the arc, and the arc. current flowing atany-instant. A satisfactory, control is obtained by the. use of a small two phase alternating currentmo tor asthe balance detecting unit; Each'of the blocks 41 has a lug 18 which passes througha slot 49 inthe frame structure 50, the. lug 48 being I internally threaded and receiving athreaded shaft 5|, so that rotationof the twoshafts-lil in either direction moves the slidable: blocks '41- inn-a direction either to-increase. or decrease the spacing between the ends of the electrodes. The shafts 5! are geared to each OthGPthIOUg hTbEV" elled gears 52, and the vertical shaft'is driven by the two' -phase motor 41' which i controlled inza manner hereinafter described'in orderto. main.- tain the desired spacing between the electrodes. It will be seen from Fig. 1 that thearc stream between the active surfaces ll; of the. electrodes should follow a curved'path, but. sometimes: the arc stream would tend to concentrate. on. the edgesof the electrodes closest-toeach: othem-and at other times would tend to rise due. to: convey tion currents andalso vwhentli'earc. streamlbe= came too long. In order 'tozprevent this there-is provided an electromagnet comprising. a.- coil?! which is in. series. with the arc electrodes-of' the lamp, and an electromaenetf55 which is bridged across-theelectrodes, these magnets ibeing mounted on an insulating'support structure '56 which; is secured to the casing 50. The magnet 51-, which is the current coil, is wound arounda straight core 51 of magnet'izable material ,"and*the coil 55 is wound around a U-shaped core of mag 'neti'zable material having projeetirigfieg-pozt'ions 58, as seen Figs; '1 and 'The'eleetromagjne't 51-, which is in series with-'thee'lec-trodes, may comprise for example 200 ampere turns for" use with'a 750 watt lamp, andthe'secon'dele'ctro magnet 55 which is connected acrossthe "electtrodes may; have 'f'or'exampl'e ampere The current coil 54 is=poled so that-its; external magnetic field tends to for'ce the arc stream outwardly, whereas the voltage coil 55 is poled so that its external magnetic field tends to. force the arc stream inwardly and keep. the are from rising. The resultant field maintained by the two electromagnets operates to keep the arc stream centered on each of the active surfaces I6 of the electrodes and cause it to follow the curved path indicated by the broken lines in Fig. 1. Since the magnetic effect of one of the windings is proportional to the current flowing in the arc stream and the magnetic effect of the oppositely poled winding is proportional to the voltage drop across the arc, the resultant effect of their magnetic fields tends to maintain the voltage-current relationship and hence the length of the are constant. s

Fig. 3 shows a: starting and running circuit suitable for use with smaller sizes of the concentrated arc lamp in'which it ,isnot necessaryto rotate the electrodes or to provide means for automatically maintaining the proper distance between the electrodes. When the line switch 60 is closed, currentis applied over a circuit comprising conductors GI and 64 to a high leakage reactance transformer 62 of the constant current type. The transformer shown is an auto-transformer, and conductor 6| is connected to the midpoint thereof so that if 110 volts of alternating current is applied to the primary part of the transformer, 220 volts will be generated across the secondary of the transformer. Bridged across the transformer is a vacuum switch 55,, the

switch being of the type in which the circuit is made and broken between solid contacts ina vacuum in response to a magnetic field, such a switch having been found to b very effective to provide the surge required in starting concentrated arc lamps of the type disclosed herein. The transformer 62 has an iron core and an open air gap and hence sets up a magnetic field which, when line switch 60 is closed, attracts the magnetizable bar or armature 66 of the vacuum switch, opening the circuit formerly through the switch contacts, the latter circuit including the electrodes I2 of the arc lamp. Various kinds of such switches are well known; one particularly suitable for the purpose is disclosed in ,my copending application Serial No. 35,928, filed June 29, 1948, now Patent No. 2,564,877, issued August 21, 1951, the structure of which enables the switch to be mounted in an aperture in the core of transformer 62. Opening the circuit of switch 65 causes a surge of from 1000 to 2000' volts to appear across the electrodes I2 of the lamp, the surge being due to collapse of the field in the transformer 62, this circuit including; a

resistor 6'! and the winding of electromagnet; 54

which is a current coil such as referred to in the foregoing description of Figs. 1 and 2. 'When the gap between theelectrodes I2 breaks down due to the voltage surge, the current flowing through transformer .62 from the supply line 60 maintains the arcacross the electrodes and also keeps the contacts of switch 65 open so long as the lamp is operating.

Fig. 5 shows a starting and running circuit similar. to Fig. 3 and also discloses a suitable circuit arrangement for the operation of regulating means such as the two-phase motor device M in Fig. 1. Connected between one end of the transformer 62 and the electrode terminalsis a transformer through which the arc. current flows. The secondary winding of the transformer 10 has a variable tap connection II, the upper end of the secondary winding being: connected by means of a conductor I4 to one of thewinding's A of the two-phase motor, the other 1 end of winding A being connected by a conductor I5 to the right-hand end of the transformer 62. The winding B of the two-phase motor 4| is con nected across the supply conductors BI and 64, a condenser 13 being connected in circuit there with in order to give a phase displacement so that there will be a suitable phase difference between the currents in the two windings A and B of the motor to provide the necessary start ing torque for the motor.

The adjustable contact II on the secondary winding of transformer I0 enables the voltage VI developed across the winding to equal the voltage V2 across the lamp terminals at the proper spacingof the electrodes. Whenv voltage VI equals voltage V2, the two-phase motor 4] has no voltage on one phase represented by its winding A. When the supply current is applied to the lamp through transformer 62 and before the lamp has started, the voltage V2 is high and voltage VI is substantially zero, and the motor 4I rotates in a direction to close the gap'between the electrodes until they either touch each other or'are suificiently close to start the arc. The voltage V2 then drops rapidly, and the voltage VI rises rapidly from zero and usually will be greater than V2. Under these conditions the motor M will operate to separate the electrodes to the correct spacing as previously determined by the adjustment of the contact Ii.

If the arc spacing becomes too great, the voltage V2 increases, and the current through the.

arc decreases and hence voltage VI decreases, so that there is a difference between VI and V2 and this difference causes current to flow through winding A of the motor and causes'the motor to rotate in a direction to bring the electrodes towards each other. If the arc spacing becomes too small, the voltage V2 decreases, and the current through the lamp and also the voltage Vi increases, and the current fiow through winding A of the motor is opposite in phase to that in the previous case when the gap was too long, so that the motor will turn in a direction to in-' crease the separation between the electrodes. The arrangement thus automatically causes the lamp to be started and to maintain the electrodes at their proper spacing during operation-of the lamp; The arrangement has substantially linear characteristics which result in accurate control, and there are no overrunning or hunting difficulties involved. i v

Fig. 4 shows an arrangement in which the position of the arc streamis maintained in a manner such that rotation of the electrodes -I2 is unnecessary to maintain proper centering of the incandescent light spots on the active surfaces of the electrodes, and also shows how the desired spacing between the electrodes may manually be maintained. In this modification, the electrode holders I8 have shafts which are received within metal bushings 20 to which .the external circuit may be connected, and these bushings are mounted in insulating brackets 16. The brackets are carried by the slide blocks 41, and the positions of the slide blocks andhence the spacing between the electrodes I2 may be adjusted by means of lugs 48 which pass through slots 49 inthe supporting structure 50, the lugs 48 being internally threaded, and coactingwith the threaded shafts 5I. The, verticalshaftjl may be rotated in either direction by 'axc'rank emanate 11- .thereby .to. .either advance or -.:retract. the. electrodes,..-as desirable or necessary; V.

I. Thecurrent coil 54* .(seen: in Fig.6), andirthe voltage coil 55are both wound on a straightcore -1..Eig.;4,.of magnetizable material. 'The electro magnets arev supported by an insulatingv structure 18 which is secured to the frame or casing..5ll. Extending from one end of the structure .18 .isa rod'19 which has securedthereto a small permanent magnet having its poles-80 disposed atone side of the arc stream, for example, an inch to an inch and a half away fromthe stream. The two poles'ofv the magnet straddle the 'arc' stream, as seen in the figure-and theexternal field of the magnetlies in a direction-which is transverse to the; desiredv direction of the arc: stream. The electromagnet's 54. and. 55 maintain vertical stability of the arc stream and the permanent magnet maintains lateralpstability of the, arc stream; The resultant effect causes two closely spaced centers to be maintained in'the outer. end of; the flame in the arc stream and thereis much less tendency for the arc. stream as a whole'either to .rise or to fall, and the arc stream does not get .too hot in any one place so that disturbing convection currents are not so likely to develop. The arrangementv centers the arc. stream as a whole so that rotation-of the electrodes hasrbeen found unnecessary even in. the larger size lamps. The permanent magnet 80 may be relatively small in size; for a 750 watt lamp a magnetv which oneg'inch across its ipole pieces has been found sufiicient to stabilize the arc in conjunction with therelectromagnets 54 and 55. It will be understood. that the coils 54 and 55 are differentially wound-with respect'to each-other; and since they maybe wound on a common core, this substan tiaily' simplifies the construction.- ,In Fig. 4, the permanent magnet is shown behind the arc stream, with its legs 80 facing the observer, but the position of themagnetjmay be reversed, that is.- theU-shaped portion may face the observer in which case the legs 80 would be, spaced ap-. proximately an inch topan inch and a halfin front of the arc stream as viewed-inthe figure. Instead of a permanent: magnet 80 an electro magnet-may,- of course, be employed. 1' r The, are la-mpofthe instant invention may also be .used with 1a direct' current source :of power, in whichjcaseone of. the electrodes always operates as-an anode. 'Ihe anode may comprise a p1ate., :j 1.od or other known anode construction and, in fact, may beja: solid copperxrodwhich is of I such construction. asto; prevent overheating and vaporization at the point of'arcrcontactu ;Whi1e there are shown and described herein certain embodiments of v the invention, many 7 other and variediprmsaand uses will present themselves to :thoseversed .inthe art without departing from the invention,- and the invention is therefore not limited;eitherainstructure or in use except as, indicatedby the scope of itheappended claims;

predetermined stable position of 'the arc stream comprising electromagnetic structure having-' 'two oppositely-poled windings whose -'ex ternal magnetic fields influence 'the arc streams; said 'electi'oma'gneticstructureincluding a magneti em her having projecting leg portions with the ends thereof positicnedadiacent to: opposite sides. re, spectively of. said;arc stream; said,- windings .loeing operatively connected; tothe arc circuit so that the.- magnetic; .efiec't of fonepof: Lthe windings proportional to the-current; flowing in the-arc. stream.and the mag-netic effect oi the. other; winding islproportional to the voltage drop across the arc, the resultant "effect of said magnetic fields'includingsthe 'field established by saidprojecting leg portions tending to maintain thevoltage-current relationshipand hence: .the length of the .are constant during fop'eration otthe device; ji'i.. I l 2. An arc discharge device comprising. electrodes operating in a gaseous :medium at a pressure sufliciently high to cause the discharge bee tween-the electrodes to 'assume thel shapefo'f a concentrated-arc, and means for maintaining .a predetermined stable position crane are stream comprising electromagnetic structure having two oppositely poled windings whose external mag'-' netic fields'influencethe 'arc stream, said electromagneticstructure'including a magnetic member having projecting leg portions withtheends thereof positioned adjacent to opposite sides respectively ofsaid arc stream, one-of said windings being operatively connected in "series inthe arc circuit so-that it's magnetic efiect is propor-J tional to the current flowing in the' arc stream and the other winding being: connected across the arc'termlnals so th'atits magnetic effect'is proportional to the voltage drop-acrossthe arc, the"res'ultant efiec't' of said magnetic 'fildsincluding the field established by said projecting leg portions tending to maintain the voltage current relationship and hence the" length -of the arc constant during operation of the device? 3. a'rcdischarge device -comprising'elec trodes operating-in agaseous medium at a pres: sure sufiiciently high to cause the discharge be tween the 'elect'rodes to assume the shape of'a concentrated arc, andfl means for maintaining a predetermined stable position of the arc stream comprising electromagnetic structure having two oppositelypoled windings whose external magnetic fields influence the arc stream, said windings being operatively connected to the arc cir unit so that the magnetic'efiect of one ofthe windings is'proportional to the current flowing in thearc stream and the-mag'netic efiect of the other winding is proportional to the voltage drop across the are, another magnet positioned ad ja'cent to the arc-stream and having a constant external magnetic field extending in a direction transverseto that of "the arc stream, the resultant eifect of said magnetic-fields tending to maintain the voltagecurr'ent relationship and hence the length of the arc constants-during operaltiorii'of the device, I 1: "y: i 1'. An are discharge -device comprising elec trodes operating in a ga's'eous'medium 'at a 'pres sure suflljciently high to" cause the dischargebe tween the electrodes to assmne 'the'shape -ofa concentrated arc}: and means formaintaining a predetermined stable position of: the :arc' stream comprising electromagnetic structure having two oppositely poled'windings whose external r'nag' netic fieldsinfluence the arc stream ma directron-transverse to lihfifliOf the'arc-stream, said windingsbeing operatively'connected to the arc circuit :so :that the magneticreifect :of one i of the windings is proportional fto th'ewcnn'ent flowing in the: azrczstream :and the .tma'gnetic' efiect of the otherwindin'g is proportional to .theavoltage-drob across: the. :arc .aino'therl; magma-positioned '1 adi- 2,608,675 9 l0 jacent to the arc stream and having a constant REFERENCES CITED external magnetic field which influences the are The following references are of record in the stream in a direct1on transverse to that of the me of this patent; arc stream and in a direction substantially at a right angle to the direction of influence of said 5 UNITED STATES PATENTS two windings, the resultant effect of said mag- Number Name Date netic fields tending to maintain the voltage- 729,114 Baker May 26, 1903 current relationship and hence the length of the 743,237 Bremer Nov. 3, 1903 are constant during operation of the device. 2,037,387 Maxted Apr. 14, 1936 WILLIAM D. BUCKINGHAM. 10

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