US2207276A - Electric discharge system - Google Patents

Description

y 9 1940- i R. M. SOMERS 2,207,276 I ELECTRIC DISCHARGE SYSTEM I Original Filed March 30, 1937 YINVENTOR Pw/aard M Somers BY TTORNEY Patented July 9, 1949 2,207,276 a i ELECTRIC DISCHARGE SYSTEM 7 Richard M. Somers, West Orange, N. J., assignor to Thomas A. E

dison, Incorporated, West Orange, N. .L, a corporation 01' New Jersey Application March 30, 1937, Serial No. 133,774

Renewed January 18, 1939 '12 Claims.

This invention relates to electric discharge systems, and more particularly to systems wherein a main arc discharge is maintained between appropriate electrodes in a gaseous atmosphere-by way of non-limitative example, for positive column light. Throughout the specification the term gaseous has been employed as an adjective to denote either a gas, or a vapor, or acom- I erally improved means and methods for starting the main arc discharge. I g

It is another object to provide improved and highly simple means and methods for automatically starting-the main discharge.

It is another object to provide starting means and methods adapted to eflect the establishment of the main arc discharge quickly after the supply of current to the system, but with the electrodes in a propercondition of emissivity.

It is another object to provide improved starting means and methods efllciently operative, with supply voltages of 110 volts and less, to start the main discharge in devices having material positive columns.

It is another object to improve the tolerance of the starting action to varying line voltages, device temperatures, and other variable factors.

It is another object to improve the action and effect of auxiliary-starting discharges.

It. is a particular but non-limitative object to efiect this improvement in systems operated from alternating current. i

Other objects are the provision of a generally improved discharge device and system, and ofimproved electrode structures and electrodes therefor.

Other and allied objects will more fully appear from the following description and the appended claims.

In the descriptionreierence is had to the accompanying drawing, of which: 4 I

1 Figure 1 is a view of a discharge system incorporating my invention, being a partly elevational and partly vertical sectional view of a typical discharge device together with a schematic diagram of further or circuit portions of the system;

Figure 1a. is an enlarged sectional view of one of 1 the electrode structures of Figure 1;

. 2,112,718 has since issued).

Figure 2 is a view similar to Figure 1 but illustrating amodification of the system of that figure in respect of the circuit portions;

Figure 3 is an end view of the electrode structure shown in Figure 10, being taken alongthe 5 line3-3 of that figure; and

Figures 4 and 4a comprise sectional and en views, respectively, of the main electrode of the structure illustrated in Figure 1a. Th'e description of this invention proper is best 10 presented after a general description of a discharge device in and with which it maybe incorporated; I have shown such a device as l in Figures 1 and 2 (which may be taken as differing only in the external circuits employed therein), 15 with the detail of the electrode structure 4 of each developed in Figure 10..

Reference being had for example to Figure 1, there will be seen the discharge 'device I, which may for example be a luminous, U-shaped device 20 comprising the elongated glass envelope 2 having the seals 2b and RD at its respective extremities. The space 2 within the envelope 2 is evacuated of air and filled with a noble gas, such as neon, krypton-or argon, or combination of gases. 25 Additionally to the gas filling there may be provided within the space 2' a sourceof metal vapor,

/ such as the deposit 2" of mercury, adapted to vaporize to an extent depending upon the heating of the device; the source 2" may be quantitatively in excess of the amount which can vaporize in the normal operation or the device, in which case the" operating vapor pressure will be determined among other things by the cooling facilities of the device, or the source 2" may be quan- 35 titatively limited to an amount, which will always {ally vaporize in normal operation to provide a predetermined vapor pressure. I may mention by way of example that I have employed myinventiqn to great advantage in connection with a de- .40 vice, having a source 2" of mercury vapor, adapted to provide an operating vapor pressure of several mm. Hg., and a noble gas filling of argon at a pressure of 2 to 4 mm. Hg.

Passing through the seal 2b are the lead-in 45 wires 4', 4" and 4', and through the seal I021; the lead-in wires I04, I04" and IM. On each of these two groups of lead-in wires is supported an electrode structure which is desirably of the furnace" type which I have disclosed and 50 claimed in my co-pending application Serial No. 30,798, filed July 11, 1935 (on which Patent No.

This structure involves relatively low masses, so that the time period required for its-heating is inherently short.

as 4 and I04 respectively, are entirely similar, a description of the structure 4 only will be given, it being understood that the structure I04 may comprise an identical arrangement of identical components (to each of which has been assigned a number higher than to the corresponding component of the structure 4). The structure 4 appears in detail in the enlarged cross-sectional Figure 1a.

In the structure 4 the main electrode proper, or 5, is shown in the form of a small member of shell formation, or cup, for example of nickel; the exterior bottom of the cup may be welded to the nickel or other supporting wire 5b, which in turn is welded to the lead-in wire 4, so as to maintain the open top of the cup facing the center of the device I. On the bottom interior of the cup may, if desired, be welded the grating or mesh 5a (see Figures 4a and 4); the interior bottom of the cup, including the mesh So if employed, is coated with a suitable oxide or other coating according to well-known cathode coating practice. Supported about the electrode 5, co-axial therewith and at least slightly spaced therefrom, is an alumina or other ceramic tube 6a, of length preferably exceeding by several times the axial length of the electrode; preferably this will overhang the latter to a greater extent in the direction of the center of the device I than in the opposite direction. Surrounding the tube 6a is a nickel or other metallic shielding cylinder I, of appreciably greater diameter than the tube 611 and preferably of slightly greater length; the cylinder I is maintained co-axial with the tube So by two mutually similar nickel or other metallic endmembers Ia.- and lb at the ends respectively toward and away from the center of the device I. These end-members may be outwardly flanged at their peripheries to fit within the end portions of the cylinder I, and may be provided with the central holes Ia and 1b respectively, inwardly flanged to fit within the end portions of the tube 61:. The hole Ia. serves to pass the arc stream to and from the main electrode 5; the hole 1b, however, is desirably at least substantially closed, wherefore I may provide the disc 3| secured against the outer face of the end-member lb within its peripheral flange. The electrode-supporting wire 5b may pass through the disc 3| within an insulating bushing 3|.

A heater winding 6, preferably of relatively fine wire closely spaced, is provided about the tube id, for example for nearly the full length of the tube. Desirably there is coated and dried over the heater winding a solution of aluminapowder in ainyl acetate,'or the like, to form an insulating layer 6b in which the heater winding is-embedded; this reduces the danger of shorting of turns of the heater and otherwise renders the heater more sturdy. The extremities of the winding 6 are designated as 32 and 34; the extremity 32 nearer the seal 2b is connected to a refractory wire 33 which passes, through a refractory insulating tubing 33, outwardly of the chamber 36 formed between the tube 6a and the cylinder 1, the wire 33 being welded to the lead- Since the two structures, which are identified wire 4" may be welded to the cylinder 1, thus forming a connection tothe entire enclosure 'I-Iw-lb, which in its entirety is designated as I.

That portion of the external circuits of Figures 1 and 2 which is identical in each case may be simply described as the connection of the lead-in wires 4' and I04 (and thus of the main electrodes 5 and I05) to the line terminals 9 through ballasting means; and the connection to ether of the lead-in wires 4" and I04", placing the heater windings 6 and I06 mutually in series and together in parallel with the main discharge path between main electrodes 5 and I05. The ballasting means have been illustrated as the serially disposed choke coil Ito and incandescent lamp I6b, though it will be understood that no limitation as to form of ballast is intended, and that either choke coil or lamp may for example be omitted.

In my co-pending application, Serial No. 62,583, above mentioned I disclosed discharge devices of this type; and showed that if there were provided near the main electrodes respective emissive auxiliary electrodes, forming with the main electrodes two auxiliary discharge paths, and if these auxiliary electrodes were subject to heating (preferably by the heater windings 6 and I06) and connected so that auxiliary arc discharges would take place simultaneously in the two paths, a very eificient arrangement for starting the main dischargewould be provided. I showed that the auxiliary electrode for each main electrode might be simply provided by the enclosure about the latter (e. g., I, I0I')more specifically for example by the outside surface of the endmember Ia (and I, of end-member I0'Ia), this having been accordingly in each instance emissively coated. I showed a variety of circuit arrangements for causing the desired simultaneous auxiliary arc discharges, two of which are shown herein in Figures 1 and 2, respectively.

Thus in Figure l the lead-in wires 4" and I04' are connected together through a resistor 40, this causing the formation of a circuit between the main electrodes comprising serially both the auxiliary discharge paths and the resistor 40. In Figure2 the lead-in wire 4" is connected to the lead-in wire I04 through the resistor 50, and the lead-in wlre- I04' to the lead-in wire 4' through the resistor 5|; this causes the formation between the main electrodes of two parallel circults, each comprising a respective one of the auxiliary discharge paths and a respective one of the resistors 50 and 5|.

It will readily be appreciated that in either case upon connection of the line terminals 9 to the line (for example of volts) an auxiliary discharge will form across each auxiliary discharge path (although, particularly in the case of Figure 1, this auxiliary discharge formation will not be instantaneous, as a short finite heating time for the electrodes will be required to reduce their normally high cold cathode falls sufliciently to permit the available voltage to initiate the auxiliary discharges). The two auxiliary discharges will be concurrent in each half- -cycle in either case: the electrodes acting cathodically will in one half-cycle be a first main electrode and the thereto opposite auxiliary electrode, will in the succeeding half-cycle be the second main electrode and the thereto opposite auxiliary electrode, and so on in alternation.

All the electrodes lower their normal cathode falls progressively in view of their progressive heating by the heater windings (this rise being preferably, and in the disclosed structure inherently, more rapid in the case of the main electrodes), and the auxiliary discharges correspondingly increase in rate (i. e., current value). At some instant in the progress of the auxiliary discharges they will have reached a critical ionizing value, which involves jointly their total production of ions and (since the produced ions are subject to some steady losses) the rate of their ion production; this critical value is suflicient to have materially cleared away electronic wall charges and otherwise to permit striking of the main discharge, and at such instant the main discharge will strike. Desirably the parameters are so adjusted that by this time the main electrodes will have reached a temperature sumcient to accommodate the main discharge without appreciably abnormal cathode fall for a fully heated electrode; under these circumstances they will appreciably before this time have ceased to be of much influence on the auxiliary discharges, the average (or over-a-cycle) rate of which it will be understood need be at most only a minor fraction of the main discharge rate. Accordingly the value of resistor 40, or of resistors 50 and and the heating and other characteristics of the auxiliary electrodes themselves, are the parameters whose variation will most significantly control the auxiliary discharges.

In my co-pending application last above mentioned I pointed out that if the value of the resistor or resistors were made too high, critical ionizing value might never be reached by the auxiliary discharges. I also pointed out that if the resistor value were too low, the critical'ionizing value would be reached and the main discharge would strike before the main electrodes were capable of accommodating the high main discharge without excessive and damaging cathode fall. It is of course normally possible to make an apt choice of resistor value between these opposed unfavorable conditions; but I have now found that if there also be suitably controlled the heating and other characteristics of the auxiliary electrodes themselves, there may be produced a starting action which is still more favorable, more tolerant to resistor value, and more consistent in its operation in the face of varying line voltages, device temperatures, and other variable factors.

Broadly, when carrying out my invention as hereinafter more particularly described, I again by heating lower the normal cathode falls of the auxiliary electrodes, so that an auxiliary discharge to each of these electrodes as a cathode may be early initiated and later maintained over a large portion of each of its cathodic half-cycles, with modest voltages across the auxiliary discharge paths; typically the heating is at least of sumcient degree to reduce'the normal cathode fall to half that obtaining with the auxiliary electrodes cold, and is permissibly of much greater degree. But I now operate each auxiliary electrode, over a considerable portion of each of its cathodic half-cycles during the latter portion of the starting period, as a saturated cathode-i, e., with a cathode fall which is abnormal, or greater than the normal for the temperature which the electrode at the particular time possesses-thereby investing a substantial percentage of the electrons which each emits with greater than normal ionizing ability. Of course upon main discharge striking the ensuing large reduction in voltage between the main electrodes, due to increased ballast drop, substantially eliminates the auxiliary discharge and with it the saturation and abnormality of cathode fall. It may also be noted that, in view of the just-mentioned reduction in voltage between main electrodes upon inception of the main discharge, the heating current passed (from the terminals 9 through the ballasting means lGa-lib) throughthe electrode-heating circuit (6-I 08) will have attained its full value prior to that inception; from which value the voltage reduction will serve to reduce it.

In slightly different terms, I, by heating, substantially lower the voltage required to produce a discharge across each auxiliary path during the cathodic half-cycles of its auxiliary electrode; but by the control of the auxiliary electrode characteristics Ilimit the reduction of the peak voltage which will actually appear across each of these paths during those half-cycles throughout the starting period so that the minimum such peak voltage will substantially exceed the ionization potential of the gas atmosphere, and will preferably betwo or more times that value,

I carry out my invention by suitably interrelating the discharge density on each auxiliary electrode and the temperature rise of the electrode, to produce the saturation or cathode fall effects abovementioned. Auxiliary electrode discharge density is of course affected by the value of the resistor 40 or of resistors 50 and 5!; but since a variation of resistor value has a firstorder eflect on average auxiliary discharge rate as well as on cathode fall effects, the main adjustment in producing desired discharge density conditions may more conveniently be of the area of the auxiliary electrode-i. e., of its emissive, or coated, active portion. This area, then, is restricted sufliciently in view of the electrode temperature rise as to produce the specified effects.

A preferred embodiment of my invention is the coating, with an oxide or other emissive compound, of a narrow circle 6| only on the outer surface 4| of end-member la in electrode structure 4 (and of course of a corresponding circle on the corresponding surface in electrode structure I04), as I have indicated in Figure 3, an end view of that structure;' this coating alsoappears in exaggerated thickness in Figure 1a. In Figure 1a there is also indicated a narrow band 62 of similar coating on the interior surface 42 of the onterlfiange of end-member la, which may be employed additionally or alternatively to 6|; it will be understood, however, that in any event the total 'coated area will be suitably restricted. to result in the saturation conditions-above mentioned. Purely by way of example of coated area, which will be understood however to be Subjbut to wide variation according to the establishment of other parameters, I may mention that I have satisfactorily employed a coated area -of about ,4 of a square centimeter: this in a device such as disclosed in Figure 1 hereof and of my co-pending application last above mentioned, employed on 110- volt line, wherein the ultimate auxiliary electrode temperature was roughly of the order of 600 degrees centigrade, and wherewith a resistor 40 of about 800 to 1,000 ohms was used.

It will be observed that each of the effective auxiliary electrodes which have been illustrated (coatings 6| and 62), as well as each of the surfaces 4! and 42, is symmetrically disposed about the axis of the electrode structure and about the main discharge path. In view of the uniform discharge distribution over an electrode insured by saturation, the saturated and symmetrically disposed auxiliary electrode has the advantage-not possessed by the unsaturated, symmetrical electrode or by a saturated, unsymmetrical electrodeof uniform distribution of the auxiliary discharge about the main discharge path. This resultsin the directing of the maximum field of the auxiliary discharge straight down the main discharge path toward the center of the device, and I believe it to be another factor leading to the improved results which I have observed in the preferred embodiments ofmy invention.

An advantage of providing the effective auxiliary electrode on the surface 4|, which faces away from the adjacent main electrode and toward the center. of the discharge device, is that the extent of the field of the auxiliary discharge in the direction of the center of the device is made a maximum. This advantage, though not peculiar to the case of restricted area of coating and of abnormal cathode fall, is nevertheless in such case of particular magnitude, in view of the higher velocity of the electrons leaving the auxiliary electrode and of their correspondingly greater ionizing power.

The practice of my invention is not to be confused with-the employment of one or more simple auxiliary electrodes not appreciably heated, or not specially arranged (as by choice of a coating or body material) for emissivity, or neither. Such an electrode during its cathodic action maintains a normal cathode fall which is not merely of useful magnitude, but is rather of such high magnitude as to require the use of quite excessive voltages; and normally the significant action of such an electrode is only anodic, or in alternate halfcycles. On the other hand an auxiliary electrode according to my invention, whether there be employed both auxiliary discharge paths or only one (as by omission of one of the resistors from Figure 2), results in an auxiliary discharge in every existing auxiliary discharge path in all halfcyclesthe discharge in each path during the half-cycles of cathodic action of the auxiliary electrode of that path being in cases the more effective. Accordingly I obtain-a generally raised effectiveness of auxiliary discharge.

Furthermore in the case of use of the simple auxiliary electrode, the main electrode temperature variationsto which the auxiliary discharge action should be nicely adjusted for main discharge striking at the proper time-become the only variable which in use significantly determines that auxiliary discharge action, and proper control is lost or made extremely difiicult. On the other hand, as brought out above, I am able according to my invention to predicate the striking of the main discharge principally on the auxiliary electrode action, over which effective control is available.

These advantages are generic to such arrangements as those of Figure l, of Figure 2 as illustn =ed, and of Figure 2 with one of the auxiliary discharge paths omitted. Additionally in the case of two-path arrangements such as I have shown in both figures, I obtain the advantage of simultaneous auxiliary discharges in both ends of the device and in mutually similar directions along the main discharge path, one (to a main electrode) being of at least conventional effectiveness and being reinforced by the other (to one of my auxiliary electrodes) of especial effectiveness. And still further in the case of the serial-path arrangement of Figure 1, I obtain all the advantages detailed above without the especially exorbitant voltage demands made, for less perfect action, by this arrangement when simple auxiliary electrodes are employed.

It will also be understood that, while the invention has particular utility in connection with alternating current operation of a discharge system, it is not intended to be unnecessarily limited thereto; it has various features of utility in connection with direct current operation-such, for example, as the simultaneous maintenance of effectiveness of auxiliary discharges in both ends of a device, irrespective of the polarity of connection of the device to the line.

It will finally be understood that while I have described my invention as applied to a particular device and to a few arrangements thereof in a discharge system, this has been done in an illustrative rather than in a limiting sense, and I intend no unnecessary limitations by virtue of the details of such device and arrangements. Rather in the appended claims I undertake to express the scope of my invention broadly, limited only by the state of the art.

I claim:

1. In a gaseous discharge system including a main electrode and means for causing a main arc discharge thereto: a thermally emissive auxiliary electrode near said main electrode; means for producing between said electrodes an auxiliary discharge, to a critical value of which said first mentioned means is responsive; and means for substantially heating said auxiliary electrode, said heating means and the discharge density on said auxiliary electrode being so interrelated that said auxiliary electrode after initial heating operates with abnormal cathode fall.

2. In a gaseous discharge system including a main electrode and means for causing a main arc discharge thereto: a thermally emissive auxiliary electrode near said main electrode; means for producing between said electrodes an auxiliary discharge, to a critical value of which said first mentioned means is responsive; and means for heating said auxiliary electrode at least sufliciently to reduce the normal cathode fall thereof to half its cold value, said heating means and the discharge density on said auxiliary electrode being so interrelated that said auxiliary electrode after initial heating operates with abnormal cathode fall.

In a gaseous discharge system including a main electrode and means for causing a'main arc discharge thereto: a thermally emissive auxiliary electrode near said main electrode; means for producing between said electrodes an auxiliary discharge, to a critical value of which said first mentioned means is responsive; and means for substantially heating said auxiliary electrode, the area of said emissive auxiliary electrode being sufilciently restricted so that after initial heating it operates with abnormal cathode fall.

4. In a gaseous discharge system including a main electrode and means for causing a main arc discharge thereto: means for starting said discharge comprising a thermally emissive auxiliary electrode near said main electrode, means for impressing between said electrodes a voltage insufficient to establish a substantial discharge to said auxiliary electrode as a cathode when cold, and means for heating said auxiliary electrode sufficiently for the establishment of such a diselectrode near said main electrode, means for impressing between said electrodes a voltage insufiicient to establish a substantial discharge to said auxiliary electrode as a cathode when cold, and means for heating said auxiliary electrode sufliciently for the establishment of such a discharge, the area of said emissive auxiliary electrode being sufficiently restricted so that after.

initial heating it operates with abnormal cathode fall.

6. In a gaseous discharge system including two main electrodes and means for causing a main arc discharge therebetween: means for starting said discharge comprising two thermally emissive and serially connected auxiliary electrodes respectively near said main electrodes and forming therewith serial auxiliary discharge paths, means for impressing between said main electrodes a voltage insuflicient to establish substantial discharges in said paths, and means for heating said auxiliary electrodes sufiiciently for the establishment of such discharges, said heating means and the discharge density on said auxiliary electrodes being so interrelated that after initial heating the auxiliary electrode acting cathodically is saturated.-

7. In a gaseous discharge system including two main electrodes and means for causing a main arc discharge therebetween: means for starting said discharge comprising two thermally emissive and serially connected auxiliary electrodes respectively near said main electrodes and forming,

therewith serial auxiliary discharge paths, means for impressing between said main electrodes a voltage insufiicient to establish substantial discharges in said paths, and means for heating said auxiliary electrodes sufilciently for the establishment of such discharges, the area of said' emissive auxiliary electrodes being sufliciently restricted so that after initial heating the auxiliary electrode acting cathodically is saturated.

8. The method of starting a. main are discharge in a gas between main electrodes, which comprises impressing between one of said electrodes and a thereto adjacent auxiliary electrode an alternating voltage insufhcient for the establishment of a substantial discharge to the auxiliary electrode as a cathode when cold, and heating the auxiliary electrode to establish such a discharge while maintaining the peak voltage drop in such discharge substantially in excess of the ionization potential of said gas.

9. The method of starting a main are discharge in a gas between main electrodes, which comprises impressing between said electrodes and respective adJacent auxiliary electrodes alternating voltages insuiilcient for the establishment of substantial discharges to the auxiliary electrodes as cathodes when cold, and heating the auxiliary electrodes to establish such discharges while maintaining the peak voltage drops in such discharges substantially in excess of the ionization potential of said gas.

10. The method oi starting a main arc discharge in a gas between main electrodes, which comprises impressing between said electrodes and respective adjacent auxiliary electrodes altemating voltages phased for the establishment of simultaneous discharges in similar directions along the main discharge path but insufiicient for the establishment of substantial discharges to the auxiliary electrodes as cathodes when cold, and heating the auxiliary electrodes to establish such discharges while maintaining the peak voltage drops in such discharges substantially in excess of the ionization potential of said gas.

11. In a gaseous discharge system, a main electrode and means for causing thereto a main arc discharge, an emissive auxiliary electrode spaced away from said main electrode and symmetrically disposed relative to the path of said main discharge, means for heating said auxiliary electrode, and means for establishing between said electrode an auxiliary discharge which saturates said auxiliary electrode as a cathode.

12. In a gaseous discharge system, a main electrode and means for causing thereto a main are discharge; an emissive auxiliary electrode of annular form spaced away from said main electrode along the line of, and symmetrically disposed relative to, the path of said main discharge; means for heating said auxiliary electrode; and means for establishing between said electrodes an auxiliary discharge which saturates said auxiliary electrode as a cathode.

' RICHARD M. SOMERS.

CERTIFICATE OF CORRECTION. Patent No. 2,337,276. July 9, 19 40.

RICHARD H. SOMERS.

It is hereby'certi'fied that error appears in the printed specificationof the above .numbered patent requiring correction as follows: Page 5, sec- 0nd column, line 11.0, claim ll, for the word "electrode" read --electrodes-; and that the said Letters Patent should be read with this correction therein that the gems may conform to the 'record of the case in the Patent Office.

Signed and sealed this 17th day of September, A. D. 19!;0.

Henry Van Ar sdale (Seal) Acting Commissioner of Patents.

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