US2309874A - Electric discharge systems - Google Patents

Description

Feb. 2', 1943. R.' MisMERs y ELECTRIC DISCHARGE SYSTEMS' ,Filed April 6, 1949 104 lll Snventor Patented Feb. 2, 1943 ELECTRIC DISCHARGE SYSTEMS Richard M. Somers, West Orange, N. J., assignor to Thomas A. Edison, Incorporated, West Orange, N. J., a corporation of New Jersey Application April 6, 1940, Serial No. 328,238

8 Claims. ,(Cl. 176-124) 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. Throughout the speciiication the term gaseous has been employed to denote either a gas or a vapor or a combination of gases and/or vapors, while the termsfgas and vapor have each been used in a more specic sense.

This application is led as a continuation in part of my co-pending application, Serial No. 62,583, led February 6, 1936.

It is an object of my invention to provide generally improved means and methods for starting the main arc discharge. A

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

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

It is another object to provide improved means and methods for quick heating of the electrodes` preliminary to the establishment of the arc discharge.

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

Still another object is the provision, particularly in a system adapted for alternating current operation, of improved means and methods for equalizing the temperatures of a plurality of main electrodes, especially during the initial heating thereof.

Yet another object is the provision of improved means yand methods for synchronizing the arrival of a plurality of main electrodes at normal emissivity.

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

`In the description reference is had to the accompanying drawing, of which:

Figure-l is a view of a 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 2 is an enlarged sectional View of one ofV the electrode structures of the device of Figure l;

Figure 3 is an end view of the electrode structure shown in Figure 2; and

Figures 4 and 5 are Wholly schematic diagrams oi the system shown in Figure 1.

Reference being had to Figure l, there will be seen the discharge device la, which may for .example be a luminous U-shaped device comprising the elongated glass envelope 2 having the seals 2b and l02b at its respective extremities. The space 2' within the envelope 2 is evacuated of air and lled with a noble gas, such as neon, krypton or argon, or combination of gases. Ad ditionally to the gas lling there may be provided within the space 2' a source of metal vapor, such as the deposit 2 of mercury, 'adapted to vaporize to an extent depending on the heating of the device; the source 2" may be quantita'- tively in excess ofv the amount which can vaporize in the normal operation of 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 quantitatively limited to an amount which will always fully vaporize in normal operation to provide a predetermined vapor pressure.- I may mention by way of example that I have employed my invention to great advantage in connection with a device having a quantitatively limited source 2" of mercury vapor adapted to provide an operating vapor pressure of about 10 mm. Hg, and a noble gas lling of argon at a pressure of about 4 mm. Hg.

Passing through the seal 2b are the lead-in wires 4 and 4", and imbedded therein is the additional inwardly extending wire 4"; and passing through the seal |0212 are the lead-in wires |04' and |04", and imbedded therein is the additional inwardly extending wire 104'" On each of these two groups of wires is supported an lelectrode structure which is desirably of the furnace" type which I have disclosed and claimed in Patent No. 2,112,718. This structure involves relatively low masses, so that the time period required for its heating is inherently rela tively short. Since the two structures, which are identied in Figure 1 as 4a and |04a respectively, are entirely similar, a description of the structure 4a only will be given, it being understood that the structure lda, may comprise an identical arrangement of identical components Lto each of which has been assigned a number higher than to the corresponding component The structure 4a appears of the structure 4a). in detail in the enlarged cross-sectional Figur 'I'he main electrode proper, or 95, is shown by Way of non-limitative example as a nickel cup 96 which, while permissibly of solid material, is

desirably of ne'mesh. This cup is lled with a mixture 91 of alkaline cathode coating material (such as barium and strontium oxides or oarbonates) with ake nickel, permissibly in an organic carrier such as amyl acetate; the size of the flakes for example has been of the order of 116" by 11g" .00004". This mixture has been packed into the cup 96, and the filled cup baked at high temperature in a hydrogen atmosphere to remove the carrier, at least partially to degas the electrode, and to produce alkaline oxides from the carbonates if the latter have been employed. 'I'he exterior bottom of the cup 9S may be welded to the nickel or other supporting Wire b, 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 |a Supported about the electrode 95., co-axial therewith and spaced at least slightly 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 devie la than in the opposite direction. Surrounding the tube 6a is a nickel or other metallic shielding cylinder 1, of appreciably greater diameter than the tube 6a and preferably of slightly greater length; the cylinder 1 is maintained co-axial with the tube 6a by two mutually similar nickel or other metallic end-members 1a and 1b at the ends respectively toward and away from the center of the device ia. These end members may be outwardly flangedat their peripheries to fit within the end portions of the cylinder 1, and may be provided with the central holes 1o. and 1b', respectively, inwardly flanged to t within the end portions of the tube 6a. The hole 1a serves to pass the arc stream to and from the lmain electrode 95; 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 1b within its peripheral flange. The electrode-supporting wire 5b may pass through the disc 3| within an insulating bushing 3|'.

A heater winding 6, preferablyof relatively fine wire-closely spaced, is provided about the tube 6a., for example for nearly the full length of the tube. Desirably there is coated and dried over the heater winding a solution of alumina powder in amyl acetate, or the like, to form an insulating layer 6b in which the heater winding is imbedded; this reduces the danger o f shorting of turns 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 tube 33', outwardly of the chamber 35 formed between the tube 6a and the cylinder 1, the wire 33 being Welded to the lead-in wire fi' and thus electrically connected with the main electrode 95. The other winding extremity 34 is connected to the lead-in wire 4, which passesinto the chamber 36 and longitudinally thereof into adjacency with the extremity 34; the leadin wire 4, from seal 2b to substantially its extremity, may be covered by a refractory insulat- .ing tube 31. The additional inwardly extending wire 4" may be welded to the cylinder 1, for further mechanical support of the enclosure 1-1a-1b, which in its entirety is designated as 1.

The external circuit illustrated in Figure 1 in association with the device la comprises the connection of lead-in wires 4' and |04 to the line terminals 9 through ballasting means; these have been illustrated as the serially disposed choke coil |60, andthe incandescent lamp |6b, though it will be understood that no limitation as to form of ballast is intended, and that either choke coil or lamp might be omitted. The leadin Wires 4i" and |04" are connected together, optionally through an impedance such as resistor 40a. Thus the heater windings, together with 40a when employed, are mutually in series and together in parallel with the main discharge path between main electrodes and |95.

Adjacent the main electrodes 95 and |95 there are employed respective auxiliary electrodes. These are provided with emissive coatings; and they, as well as the main electrodes, are subjected to substantialheating. As the cathode fall of both auxiliary and main electrodes is reducing in response to their heating, a discharge between each auxiliary electrode and the respectively adjacent main electrode is initiated and rapidly increased, quickly forming a strong auxiliary arc discharge. In response to this auxiliary arc discharge the main discharge strikes through the device from one main electrode to the other.

The enclosures 1 and |01v have themselves been `employed to form the auxiliary electrodes. Each enclosure, being in very close thermal association with the heater winding for the adjacent main electrode-or, in other words, forming a portion of the electrode heating furnace-1s eiliciently heated in denite relationship to the heating of that electrode; this relationship will of course be somewhat different for different portions of the enclosure. In general, that portion of the enclosure principally active in performing the auxiliary electrode function will be that portion to which an emissive coating is applied, and I accordingly apply such a coating to that enclosure portion which heats in the most desirable relationship to the main electrode. While my invention is not limited thereto, I have found a preferred relationship to be one wherein the enclosure portion heats somewhat more slowly than the main electrode proper, and is separated from the latter by a reasonably short and direct auxiliary discharge path. I have found generally satisfactory as an enclosure portion to receive the emissive coating the outside surface 4| of the enclosure end-member 1a (and correspondingly the like surface of the end-member in the enclosure |01'); coating of this surface has been illustrated as 4|s in Figure 3.

As may be seen in the enlarged fractional cross-sectional Figure 2, each of the enclosures 1 and IUT-and thus each auxiliary electrodeis electrically connected to a point on the respective one of the heaters 6 and |06, as by welding to the enclosure of a tap 38 or |38 from the respective heater. Thus each auxiliary discharge path becomes a shunt connected internally of the device around at least a portion of the respective heater, this portion being designated as 6s or |06s.

In order for the auxiliary discharge to take place across either pf the auxiliary discharge paths, there must be available across that path a voltage slightly greater than the sum of the cathode fall (for small currents) and the ionization potential of the gaseous atmosphere in the path. As I ordinarily employ the system, the voltage available across each path is much less thanv the cathode fall with the electrodes coldf under these circumstances no discharge will take place when voltage is first applied across the system. But the cathode fall of each electrode is rapidly lowered as a result of the progressive heating thereof by the winding 6 or |06, and will presently have fallen to some value-predetermined by the applied voltage, ionization poten-` tial, etc.'at which there occurs establishment across each auxiliary discharge path of a discharge, of`which the currenty is at first negligible. The heating of the electrodes by the windings of course continues and the cathode falls for the cur/rent actually flowing progressively decrease tozero; then the dropv Iacross eachjkauxlliaryvdis- #chargepath may be vonly yslightly greater than' thegaseous ionization potential.

It will be appreciated that' since each auxiliary discharge path hasy thermally emissive, heated' ions; this critical valueis sufficient to have materially cleared away` electronic wall charges andv` otherwise to permit the strikingv of the main discharge between the mainelectrodes, and at such instant the main discharge will strike. I prefer so to adjust the parameters that critical ionizing value will be reached by the auxiliary discharge approximately as the main electrodes reach normal operating temperature and hence emissivity. Suchk adjustment may the voltage intially dropping across each aux-- iliary discharge path, which obviously is jointly affectedv by the resistance value of the resistor 40a relative to that of the heaters 6 and |06, and by the positioning of the taps 38 and |38 relative to the extremities of the respective heaters.

be performed by regulating I considered in connection-withv influence on auxiliary discharge ;1 there are, howeverconverse influences on the heater circuit and its electrodeheatirig functions. During theA time interval through which the auxiliary discharge is taking place, this discharge, in view of` the reducing cathode fall, is progressively lowering the volt'- age across thevshunted heater portions 6s and |06s, Vand hence the current therethrough;finally,` during thecontinuance of the main discharge,

the voltage acrossl each shunted heater portion ismaintain'ed.r at less than the gaseous ionization potential.. If theV resistance valuesinthe entire heater circuit arefso arranged that initially there -drops across eachshunted heater portion sand |06s a considerably higher voltage thanthis final one, the abovementioned progressive loweringof' heating effect of these portions Will be very appreciable. To securev a corresponding thermal, effect on the electrodes, however, the unshunted heater portions are preferably maintained small or eliminated (an appropriate value of external resistor 60a being employed). Figure 5 illustrates the schematic circuit of thesystem` in this instance. A reason for the minimization or elimination of the unshunted heater` portions in this instance is that, as the current in the shunted'heater portions is reducing, the current in the unshunted heater portions would tend It will be understood that, in view of theuse of resistor 48a., it is possible to place the taps 38 and |38 iff desired at or near the respective heater extremities\34 and |34, thu-s either com-r pletely or substantially eliminating any unshunted heater portions. stantial unshunted heater portions are employed, it is possible-to omit (i. e., by shortcircuiting) the resistor a. In the usual instance of employment of the circuit of Figure 1, I have preferred so to omit theresistor 40a, in order to avoid the inherent power loss therein; in this instance the schematic circuit of the system becomes essentially that shown in Figure 4. In typical such cases I have placed the taps 38 and |38 at points distant from the respective extremities 32 and |32 by about 1A; of the heater length, so that initially there-dropped across each shunted heater portion 6s and ||l6s a voltage of about. 1/lof the voltage across the device.A Assuming the latter to be 100 volts in View of the small drop caused in the ballasting means by heater current, thereV wouldappear across Veach shuntedv heater portion a Voltage of about 17 volts and across each unshunted heater portion a voltage of about 33 volts. When the auxiliary discharge develops and increases, these respective voltages would shift to the order lto 10 and 35--the system voltage having dropped in the order of l0 Volts due to increased drop in thev Conversely, when sub-4v The connection of the auxiliary electrodes 'I'- and |01 into the heater circuit has so far progressively to increase and counteract the former in effect on the,electrodes. The action discussed in4 this paragraph-taking place during. the progress of the auxiliary dischargeis of course not to be confusedwith that reduction which results from sudden great lowering of the voltage across the entire heating circuit upon striking of the main discharge. The action described in this paragraph is therefore most advantageous when, because of small ballast or other special factors, the degree of voltage reduction upon main discharge striking is not high.

Anotherinfluence on the` heater circuitof connection of 'the 'auxiliary 'electrodes' intotnat eir-v cuitis the establishment of a strong'tendency to equalization of temperature and emissivity of corresponding electrodes in the two ends of the symmetry of arrangement, in practise there fre- Y quently .tend to be some inequalities which the effect now under discussion greatly minimizes. Thus for example let it be assumed that as a result of discrepant electrode temperatures the auxiliary discharge is occurring with a given drop in `a rst of the paths, while in the second 'opposite path the discharge `either is occurring with a higher drop or has not yet started; it is then obvious that greater voltage and current appear across and pass through the second heater, speeding up the heating of the electrodes associated therewith. This equalizing tendency will be understood to continue throughout the duration of the auxiliary discharge in both paths; thus the arrival of the two main electrodes at normal high temperature is synchronized, and possibilities are precluded of one main electrode heating extra rapidly and causing the auxiliary discharge to reach critical ionizing value before the other main electrode is properly heated.

While the device and system which I have above disclosed are nicely adapted for operation beenfzs course omitted). It is further to be understood the existence of that emissivity of the appro-l priate one of those electrodes when the-system is connected without regard to polarity. vIt is also to be understood that certain of the advantages of particular features of my invention will be re tained, with either alternating or direct current, even though one of the auxiliary electrodes be omitted and the auxiliary discharge therefore employed in one end only of the device.

It will finally be understood that while I have disclosed my invention in terms of a particular embodiment thereof, I do not thereby intend any unnecessary limitation; rather the scope of my invention, including its several combinations, sub-combinations and elements, is intended to be expressed in the following claims.

I claim:

l. In combination in a gaseous vdischarge system: two main electrodes forming a main arc discharge path; two'thermally emissive auxiliary electrodes respectively Vadjacent said main electrodes; and two heaters for said auxiliary electrodes respectively,y said' heaters lbeing serially connected across^said discharge' path, and each of said auxiliaryelectrodes being connected to a point on the respective said heater.

2. In combination in a gaseous discharge system': two main electrodes forming a main arc discharge path; two auxiliary electrodes respectively adjacent said main electrodes; two heaters for said auxiliary electrodes respectively; and impedance means serially connected between said heaters, said heaters and impedance means being connected acrosssaid discharge path, and each of said auxiliary electrodes being connected to a point on the respective said heater.Y

3. In combination in a system for main arc dis'- charge between two separated'electrode structures: two heater windings respectively included in said structures and connected in series with each other, and means for energizing said serially connected windings to develop across each a voltage sufficient for ionization of said atmosphere, each of said windingshaving associated therewith, to be heated thereby and in conductive community with respective portions thereof between which appears a voltage sufficient for the establishment of a local arc discharge, mutually adjacent thermally emissive electrodes.

4. In combination in .a system for main arc discharge between two separated electrode structures: two heater windings respectively included in said structures, current-controlling means forming a series circuit with said windings, and

means for energizing said circuit to develop across each winding a Voltage suicient for ionization of said atmosphere, each of said windings having associated therewith, to be heated thereby and in conductive community with respective portions thereof between which appears a voltage sufcient for the establishment of a local arc discharge, mutually adjacent thermally emissive electrodes.

5, A pair of electrode systems for use in a gaseous atmosphere as respective terminals of a posarc discharge develops between said portions and thereafter regulates the voltage across and current in the winding therebetween.

6. A pair of electrode systems for use in a gaseous atmosphere as the respective terminals of a positive-column main arc discharge path energized by alternating current and having a heater circuit in shunt thereto, each of said electrode systems comprising, in combination, two portions each comprising material of high thermal emissivity, and a heater winding serially connected in said circuit to receive in the absence of discharge a voltage more than sufficient for ionization of said atmosphere, said portions in each of said sys-l tems being heated by the winding in that system and being conductively common with respective parts thereof between which initially appears a voltage more than suiicient for said ionization,

whereby in each of said systems a local bidirec-f tional arc discharge develops between said portions and thereafter regulatesthe voltage across and current in the winding therebetween.

7. A pair of electrode systems for use in a gaseous atmosphere as the respective terminals of apositive-column main arc discharge path having a heater circuit in shunt thereto, each of said electrode systems comprising, in combination, two portions each comprising material -of high' thermal emissivity, and a heater winding serially connected in said circuit to receive in the absence of discharge a voltage substantially more than sufllcient for ionization of said atmosphere, said portions in each of said systems being heated by the winding inthat system and being conductively common with at least substantially the respective extremities thereof, whereby in each of said systems a local arc discharge develops between said portions and thereafter regulates the voltage across and current in the winding.

8. A pair of electrode systems for use in a gaseous atmosphere as the respective terminals of a positive-column main arc discharge path energized by alternating current and having a heater circuit in shunt thereto, each of said electrode systems comprising, in combination, two portions each comprising material of high thermal emissivity, and a heater winding seriallyl connected in said circuit to receive in the absence of discharge a voltage substantially more than sufficient for ionization of said atmosphere, said portions in each of said systems being heated by the winding in that systemand being conductively common with at least substantially the respective extremities thereof, whereby in each of said systems a local bidirectional arc discharge develops between said portions and thereafter regulates the voltage across and current in the winding. l

RICHARD M. SOMERS.

Images