US2666887A - Electric arc device - Google Patents

Description

1954 s. c. ROCKAFELLOW 2,666,887

ELECTRIC ARC DEVICE Filed Feb. 3, 1951 s Sheets-Sheet 1 AJQW Ihwentor (Ittomeg FIGT FlGZ

1954 s. c. ROCKAFELLOW 2,666,887

rsuacmxc ARC DEVICE I Filed Feb. 5, 1951 a Sheets-Sheet 2 FIG. 3

Ihwentor attorneg 1954 s. c. ROCKAFELLOW 8 7 ELECTRIC ARC DEVICE Filed Feb. 5, 1951 3 Sheets-Sheet I5 POT AT C-RID PoT AT 66 5' STUART C. ROCKAFELLOW INVENTOR.

ATTORNEY Patented Jan. 19, 1954 ELECTRIC ARC DEVICE Stuart 0. Rockafellow, Farmington, Mich., as-

signor to Robotron Corporation, Detroit, Mich., a corporation of Michigan Application February 3, 1951, Serial No. 209,282 g 3 Claims. (01. 323-24) This invention relates to electric are devices and has particular relation to an improved device for initiating a flow of current between a pair of conductors and has secondary reference, to means including said initiating means controlling the point on the wave form of an alternating current supply at which the arc discharge commences in order thereby to control the magnitude of the average current applied to a load.

In present forms of devices for initiating flow of current between a pair of conductors, such as in the common ignitron or as in the device shown in the United States Patent to Slepian, No. 2,069,283, it has been necessary to supply a relatively large quantity of current for starting purposes regardless of the requirements of the load being supplied by the starting device. Thus, where a relatively light load was involved, it has been necessary to add in parallel with said load suflicient load resistors to cause the drawing of enough current to meet the minimum requirements for starting purposes. 7 Thus, on these cases more current has been supplied to the system than was actually required by the load, with consequent wastage of current and the necessity of providing larger sizes of tubes than would actually be required by the current through the load.

Further, in present systems wherein the starting electrode is initially immersed in the mercury pool, it is believed that the starting function is effected in microscopicindentations in the coating on the starting electrode. The bottoms of such indentations are not wet by the mercury and this accordingly provides chambers of microscopic size in which arcing, and consequent ionization of the mercury, initially takes place. As the tube is used, the indentations become progressively larger and both more current and more voltage are required'to effect ionization through all of said indentations simultaneously. Eventually, this requirement exceeds the supply and the tube fails.

It is accordingly desirable to provide a starting tube which requires only an infinitesimal amount of current so that the current supplied to the system need not exceed the amount actually required by the load. Further, it is desirable to provide a starting tube in which an adjustment may easily be made as the starting electrode deteriorates from use to compensate for such deterioration and thereby prolong the effective life of the tube.

These requirements aremet by a combination including a tube in which the starting electrode is spaced away from the surface of the mercury pool, when said tube is in its normal position of operation, and wherein said tip of said starting electrode preferably is directly above the center of said mercury pool. The magnitude of said spacing is determined by the magnitude of potential which is conveniently available for application to the starting electrode together with the spacing required to effect ionization of the gas, commonly mercury vapor, with which the tube above the mercury pool is filled. Combined with this device are means controllably imposing onto the starting electrode a potential of high value and short duration.

The use of this type of starting device makes possible a number of advantageous circuits or greater simplicity and having parts of smaller sizes than is now possible with present starting devices. As one example of such advantageous circuit, there is herein disclosed a circuit by which there is obtained a high degree of accuracy of control over the magnitude of actual current flow through a load but in which the controlling means are extremely simple. In this circuit, there is provided means such that at a predeterminable point in the alternating current supply wave, there is caused an electric discharge between the starting electrode and the cathode pool, which discharge is of very short duration but which is effective to start ionization for permitting current flow between the main electrodes of the electric arc device. The potential used to start the initial discharge is many times greater than that used on present devices but it is extremely short in time and the average current consumed thereby is sufiiciently low that an eiiective and simple control thereof, as above mentioned, is rendered possible.

By this means the electric discharge devices involved for small loads, inasmuch as they carry only the current actually required by the load, can be made much smaller than in present conventional circuitswhere the electric discharge devices, as ignitrons, must carry a materially larger current in order to operate. Thus, where, for example, the load requirement is only 16 amperes, the electric discharge devices, and auxiliary equipment, may in the light of the foregoing, obviously be made much smaller than in present circuits where a load resistor may draw 40 amperes and a thyratron of proper size may have a filament requiring watts continuously in order to keep it hot and the thyratron will in addition require a relatively large filament trans former. Thus, the electric arc discharge device here contemplated may be made and sold in conjunction with a small peak transformer as a relatively convenient and small package unit which will be of much less size and materially less expensive than is now characteristic of equipment for performing corresponding functions by conventional circuits.

A further.requirement.of the i'circuitry of this type is simple but effective prevention of back firing, which sometimes occurs on negative cycles.

In the apparatus herein disclosed, there is pro-:=-- vided extremely simple means for this..pur.pose. which means are likewise made possible by the particular details thereofas describedihereinatter;

In the drawings:

Figure 1 represents a diagram of a preferred form of the invention.

Figure 2 represents a time comparison of the potential supplied from the alternating: current source and that applied to the starting electrodes.

Figure 3 in parts-A and/B thereof illustrate-the different average currents supplied to. theload-by adjustment .ofhthe; phaSewShift. ortion tofathe circuit.

Figure. 4 representsan alternate-.circuit showing. means. positively preventingarc-back in arc discharge. devices; i Figure 5 represents an alternate-circuit.show ingra different means .for applying. a pulse of- :high

value and shortdurationto thestartingelectrode. t

Figure 6 is a graph showing thepotential relationships. in the: various -.parts.- of theeircuitof Figured:

Figure 7 is a fragmentary diagram of a portionof thecircuitshowing-a still-furthermodificationwthereofa Figure B is a graph showing thapotentialrelationshipsainithel circuit of: Figure. 4.

GENERAU DESCRIPTION The, starting. device. whichmalres possible. the above described beneficial .resultsmay be generally described asonemwherein a starting electrode is spaced away fromv the surface of a mercury poollcathodea suitabladistance.sufiicient to efiect ionization, but. withinthe range. of l the. available potential, in combination with .means by which there: is applied acrosssuch starting electrode and .cathode-a momentary .potential oi a very high order. The .tip. of the starting electrode, .is

preferably, but. not necessarily, placed directly over. the center of the cathode pool.

In..one..particulai'. circuit made. possible by this improved .starting device, a pairlof such electricarc conductingdevices areconnected'inbacki DETAILED'DESCR'IPTION- Turning .first to .the .electric arc.,device, .iti'may besofany. conventional type, involving, a cathode 4 pool material, as mercury, vaporizable and ionizable at low voltage and capable, when ionized, of carrying heavy current, such as shown in some detail in the United States Patent No. 2,069,283, to Slepian, excepting that here the starting electrode is spaced a short distance from the surface of the cathode pool. This distance is normally about one-fourth inch wherera starting potential of about 5000 volts is to be used and=-=mercury vapor constitutes the atmosphere within the tube, but this spacing with a mercury vapor atmosphereinthe tube may vary from about one-eighth inch to about one-half inch. In any event, such spacing is suflicient .that the are passing between theistartinglelectrode and the cathode will ionize tliega'swithin the tube and it need not be materially greater.than such amount. Thus, this spacing will'be such, that depending upon the gas used as the atmosphere within said tube, the peak voltage will usually be between about 5000 voltsand about. 15,000 volts 9 However, .this:range is illustrative only and; not 'limitingl More specifically; iILIOIlB particular: instance here. utilized 'for illustrative. purposes, ,the a-ltennating supply sourcevis 115 volts, "and the peak voltage imposed by the"peak (transformer.across thestarting electrode of" the cathode poolisabout 10,000 volts. The current flow' throught-he starts ing electrodes is negligibla of the-orderrof aiew micro amperes. Theactualpowerrdra-wnato. the starting electrodes will in the ordinary case aver age about onewatt' for both of-the:back.-to-backl connected tubes herein" showm About '40 to 50 watts input is required to produce.thisawa-ttagesat the starting electrodes-due'to losses in peakitrans former 'and inthe- -phaseshiftcircuit;

It is thus seen that :whilethe-voltagafor start= ing the operation of .the' arc tdischarge 'dev-icewis relatively high thacurrent: flow isunegli'giblerand hencethe wattage isvery low.:.- This isxefiectiv'eito start the necessary ionization but :it still permits the useof therelatively simple control apparatus hereinafter described.-

Turning now totherest ofthe'devicawas lllustrated primarily irnliigure 1, thereare shown arc discharge devices I and Z, having .anodesiil and 8,.cathodes consisting of mercury "pools-'4 and 6 and starting electrodes 3 and 5, which latter are. each spaced a short distance from :surfaces of their respective cathodapoolsr and haveiitheir tips each :locatedin a line passing ithrough the centers 1 of the respective cathodepools-and peb pendicular' to the "surfaces thereof; This com struction is preferable inasmuch as it" brings the entire area ofathe cathode pools as' near as pos'- sible to being equidistant from 'the said. tipssin. the normal position of. operation of: said tubes; but it .is notsan' essential-element, These are-econ nested fromthe source through conductors 3 [land 3 I and. through a .loadxto each other in conven tional backto-back" arrangement. The starting electrodes-3 and-5 are each connectedthroughtthe co y windings 9 and H) of conventional peak transformers l3-and M tO-the"Cath0d6 pools 4 and 6 of thearc. devices I and 2.

The peak. transformers are constructed in a conventional manner and. each consists of at least two windings having a small core area with the. laminations thereof being, separated-by ,a small airgap. The. magnetic linesbreakthroughi the. air gapin anappreciableamcunt andaonly the highestipeaklofthe current wave, thus: cause. ing a transfer from the primary windinggtoithe secondary winding 1 tatake placein-an appreciable amount .at only. alimited. portion of. the sine wave representing the applied voltage. This is shown in Figure 2 wherein the solid line represents the output of the peak transformerand the broken line represents the voltage applied to the primary winding thereof. The peaks 2% and 2| illustrate the points at which the magnetic flux breaks through the air gap in the peak transformers.

A phase shift circuit is provided for supplying the primary windings II and I2 of said peak transformers. Said circuit here for illustration includes a capacitor IS, a variable resistor l6 and the secondary winding 32 of the transformer H. The center tap 33 is taken from said secondary winding 32 of the transformer H and acts as one terminal 34 of said phase shift circuit, and a point 35 between said capacitor and said variable resistor constitutes the other terminal of said phase shift circuit. Said. transformer il includes a primary winding 36 which is connected through the switch l8 to the A. C. source. It is understood that this switch may be of any effective type and may consist of an electronic circuit as well as being a switch of a mechanical or magnetic type.

The arc-back preventing circuit, being alternative, is illustrated separately in Figure 4. Though specifically illustrated with respect to are discharge device 2 and transformer M, it will, where used at all, be similarly applied also to are discharge device I and transformer l3. It consists of a rectifier 22 and a small semi-conductor 23 connected in series with each other and disposed between the cathode of the arc discharge device and a point on the secondary winding of each of the transformers l3 and M which point is intermediate the ends of said windings. This semi-conductor is of a conventional type, one being commercially distributed by the General Electric Company under the name of Thyrite.

It will be understood that the means supplying starting potential to the starting electrode must be of such capacity that it will effect a di electric break-down, i. e. ionization, of the-atmosphere in said are discharge device. After such break-down is initiated, sufficient ions are formed to continue conduction so long as potential exists between the principal electrodes. Thus, only an initial break-down is required to start conduction, which will then carry'through until the current is turned off. or until the particular half cycle of the supply current has been completed.

Thus far, in this description, the duration of the current flow between the starting electrode and the cathode pool has been referred to merely as for a very short'perio'd. More specifically, it is. at least as longas, but not materially longer than, the ionization time of the particular gas comprising the atmosphere in the chamber of the discharge device. Since a period of 100- micro-seconds will suffice for all presently used gases in cold cathode discharge devices, the peak output of the peak transformer will normally be suflicient for all gases which are likely to be used when it extends for a period of 100 microseconds.

OPERATION 6. charge device. With ionization thus started, flow of current is permitted to take place between the principal electrodes, complete the ionization of said atmosphere, and continue for so long as a potential exists therebetween.

With respect to the particular circuit disclosed as made possible by the starting device thus described, alternating potential is supplied from the source of the transformer thence through the phase shift circuit to the primary windings H and I2 of the peak transformers l3 and Id. The output of said peak transformers will be of extremely short duration as indicated by the peaks 20 and 2| in Figure 2. The potentials thus supplied to the starting electrodes 3 and 5 and will be of sufficient magnitude to initiate conduction, which, once started will continue for so long thereafter as potential remains between their re-' spective anodes and cathodes.

Thus, after the supplying of a starting potential to the starting electrodes, the electric are devices will continue to conduct for the balance of the cycle in the source which is being applied to its anode and cathode at the moment the starting potential appears at the starting electrode. Therefore, by utilizing the phase shift circuit to change the phase relationship of the output of the peak transformers with respect to the source potential, the electric arc discharge devices can be caused to conduct for whatever portion of the source cycle is desired. This is illustrated in Figure 3-A, wherein the peaks 20 and 2| are shown as being near the beginning of the source cycles, which cycles are indicated by the line 9, and Figure 3-3 illustrates the condition wherein the peaks 20 and 2| appear near the mid-point of the source cycles. In each of the parts A and B of Figure 3, the portion of the source cycles during which the electric are devices are conducting is shaded. Thus, it can be readily seen that by the shifting of the phase relationship between the output of the peak transformers and the source potential, the average current supplied to the load is readily and accurately controlled.

It will be further appreciated that the herein disclosed circuit for initiating a flow of current through the load circuit will commence operation upon the closing of the switch l8 and will cease operation upon the opening of said switch, and that no other switch, or other control, is actuated to start or terminate the controlled flow of such current.

The polarity of the rectifier 22 is such that on the negative cycles with respect to each electric arc device, the starting electrode and the cathode pool is short circuited and there is no possibility of ionization occurring during these half cycles, However, on the positive cycles, the rectifier, together with the semi-conductor, whose resistance is high when the potential drop across same is low, will insure against passage of current through this shorting path on the positive cycles, and thereby insure the effective imposition of the necessary potential between the starting electrode and the cathode pool to initiate ionization.

'It will also be observed that by proper phasing of the starting potential with respect to the principal potential, this device may function as a rectifier.

' M odifications'of Figures 5 and 6 Figures 5 and 6 illustrate one desired modification of the circuitshown in Figure l for produciing a high voltage pulse at the starting electrodes ties as that described above for the first 180 degree portion thereof.

Modification of Figure 7 Figure '7 shows a capacitor 38 appearing in series with the primary winding 36 of the transformer l3. This is for the purpose of introducing a 90 degree lead into the potential imposed onto the primary winding with respect to the potential imposed by the main lines 30 and 3| onto the electric discharge devices I and 2.

In this manner, it is possible to create the starting potential of the starting electrodes 3 and 5 at substantially any point in the cycle pertaining to each thereof rather than only at a point in the last half of said respective cycles. It is thus possible to secure a longer current flow through the load, where desired, by initiating same in the first half of each of said cycle than i possible Where said starting potential can occur only in the last half of each of said respective cycles.

This modification may be applied to either of the circuits shown foregoing.

I claim:

1. A device for initiating and terminating the flow of current through a load circuit, comprising: an alternating source of potential; a first transformer, the primary winding thereof being connected to said source, a switch selectively interrupting the energization of said primary L winding; a variable resistor and a capacitor and means connecting same in series with each other and means connecting said capacitor in series with one end of the secondary winding of said transformer and means connecting said variable resistor in series with the other end of said secondary winding; a first high voltage pulse pro ducing circuit; means connecting one energizing end of said pulse producing circuit to a point intermediate said capacitor and said variable resistor and means connecting the other energizing end of the pulse producing circuit to a point intermediate the ends of the secondary winding of said first transformer; a second pulse producing circuit and means connecting one of its energizing ends in parallel with, but in reversed polarity to, the corresponding ends of said first pulse producing circuit; a pair of electric arc discharge devices each having an anode and a liquid pool cathode spaced from said anode, and each having a starting electrode positioned intermediate said anode and said cathode means and spaced from each thereof; means connecting said electric arc discharge devices in back-to-back relationship with each other and means connecting said electric arc discharge devices, said source of alternating potential and said load in series relationship; said pulse producing circuits including a pair of thyratrons connected in opposite polarity and each having a capacitor and the primary winding of a transformer in series in the anode circuit thereof, a resistor in parallel with each of said last-named capacitors, the secondary of each of said last-named transformers being connected to the starting electrode and to the cathode pool of each, respectively, of said electric arc discharge devices; and one of said energizing ends of said pulse producing circuit comprising a point between the cathode of one of said thyratrons and the primary winding in the anode circuit of the other of said thyratrons and the other of said energizing ends comprising a point between the cathode of the other of said thyratrons and the primary winding of the anode circuit of said one of said thyratrons.

2. A device for initiating and terminating the flow of current through a load circuit, comprising in combination: a source of alternating potential; a first transformer, the primary winding thereof being connected to said source, a switch selectively interrupting the energization of said primary winding; a phas shift circuit connected to each end of the secondary winding of said transformer; a first high voltage pulse producing circuit; means connecting one input end of said pulse producing circuit to one output terminal of said phase shift circuit and means connecting the other input end of said pulse producing circuit to the other output terminal of said phase shift circuit; a second pulse producing circuit and means connecting the input ends of said second pulse producing circuit in parallel with the corresponding ends of said first pulse producing circuit but arranged in reverse polarity; a pair of electric discharge devices each having an anode and a liquid cathode and each having a starting electrode positioned intermediate said anode and said cathode; means connecting said electric discharge devices in back-to-back relationship with each other and means connecting said electric discharge devices, said source of alternating potential and said load in serie relationship; and said pulse producing circuits including a pair of thyratrons connected in opposite polarity and each having a capacitor and the primary winding of a transformer in series in the anode circuit thereof, a resistor in parallel with each of said last-named capacitors, the secondary of each of said last-named transformers being connected to the starting electrode and to the cathode pool of each, respectively, of said electric arc discharge devices, and one of the input ends of said pulse producing circuits comprising the cathode of one of said thyratrons and the primary winding in the anode circult of the other of said thyratrons and the other of saw. input ends comprising a point petween the cathode of the other of said thyratrons and the primary winding of the anode circuit of said one of said thyratrons.

3. A device for initiating and terminating the flow of current through a load circuit, comprising in combination: a source of alternating potential; a first transformer, the primary winding thereof being connected to said source; a phase shift circuit connected to each end of the secondary windmg 01' said transformer; a pair of electric arc discharge devices, each having an anode and a liquid cathode; and each having a starting electrode positioned intermediate said anode and said cathode; a first high voltage pulse producing circuit including a second transformer, a. thyratron, and a capacitor, and the primary winding of said second transformer being in series in the anode circuit of said thyratron, a first resistor in parallel with said last-named capacltor and the ends of the secondary winding of said second transformer being connected to the starting electrode and to the cathode pool of one of said electric arc devices, one input end of said pulse producing circuit comprising the oathode of said thyratron and the other input end comprising that end of the primary winding of said second transformer which is remote from said thyratron; means connecting one input end of said pulse producing circuit to one output terminal of said phase shift circuit and means connecting the other input end of said pulse producing circuit to the other output terminal of said phase shift circuit; a second pulse producing macaw 1' 1! circuit -inc1uding;a -,,third transformer, asecond thyratron anda second capacitor and-the primary winding of said third transformer being in series in the anode circuit of said second thyratron, a second resistor in parallel with said second capacitor, the ends of the secondary Winding of said, third transformer being connected to the starting electrode and to the cathode pool of the other of said electric arc discharge devices, one input end of said last named pulse producing circuit comprising the cathode of said second thyratron and the other input end comprising that endflof theprimary winding of said third transformer which is remote from said second thyratron, and means connecting one inputhend of thetsaid second pulse producing circuit in parallel with the corresponding input ends of said first ,pulse producing circuit with the thyratrons thereof in opposite polarity and means connect: ing saiduelectric arc, discharge ,devices in backto-back 'relationship- ,with each other, and means connecting said electric arc, discharge, derices, said source of alternating potential and said load in series relationship.

STUART C. ROCKAFELLOW. References Cited; in the .1116 Of thisdpate ntfl UNITED :STATES PATENTS

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