US2109998A - Electric discharge device and method of starting - Google Patents

Description

March 1, 1938. |NMAN 2,109,998

ELECTRIC DISCHARGE DEVICE AND METHOD OF STARTING Filed Jan 25, 1936 Fig.5.

x fl" 3a Inventor George E Inmam,

by mfffrney Patented Mar. 1, 1938 UNITED STATES ELECTRIC DISCHARGE DEVICE AND IVIETI'IOI) 0F STARTING George E. Inman, East Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Application January 25, 1936, Serial No. 60,849

4 Claims.

My invention relates to electric discharge device such. as are lamps, and especially to the st ting of such devices without any mechanical provisions for drawing an arc. The invention is particularly applicable to enclosed alternating current devices having solid electrodes heated by the arc, and to devices in which relatively heavy currents and correspondingly massive electrodes are employed, although it is not necessarily so limited. It is applicable to metal-vapor arc lamps, as well as to the gas-filled types of lamp here illustrated and described.

In the case of electric discharge devices containing quite appreciable gas pressures (as contrasted with those containing such very low pressures as must be expressed in a few mm.) starting the arc is a matter of some difficulty, unless provisions are made for preheating an electrode torender it electron-emissive, or unless a highly heated tungsten or other filament is provided to supply electrons in the electrode gap. Both of these expedients are either wasteful of energy or otherwise undesirable in many cases. The use of very high starting voltages between the electrodes to initiate the arc has been proposed but this has the disadvantage that a transformer capable of giving the necessary high starting voltage is very inefficient for the relatively moderate or low voltages suitable for regular operation, after the arc has been established. The use of a special starting electrode located in the main electrode gap, so close to one of the main electrodes as to start an auxiliary are on a moderate- 1y increased voltage, has also been proposed, but has not proved wholly satisfactory.

I aim to provide for starting the are easily, quickly, reliably, and with comparatively simple and inexpensive equipment. For this purpose, I may -1se a special starting electrode in a novel way or I may provide easy-starting auxiliary electrodes, so associated with more massive main electrodes that an initial auxiliary arc, itself easily started, heats the main electrodes and renders them electron-emissive, thus permitting easy establishment of the main arc,whereafter the auxiliary electrodes need not remain in action or consume current. Such auxiliary electrodes may be connected to the main electrodes or their current leads, or-may be connected to some other source of current affording a potential suitable for initiating an arc in an atmosphere ionized by electrons, and afterward maintaining the arc,

. such, for example, as about 30 volts on open circuit, before the arc starts, and about 10 volts on closed circuit after the arc starts. Or, again, my starting electrode arrangement may be combined with the auxiliary electrode arrangement.

Other features and advantages of the invention will appear from the following description of species thereof, and from the drawing.

In the drawing, Fig. -l is a diagram of an arc lamp embodying my invention in very simple form, with its current supply arrangements; Fig. 2 is a fragmentary side view of main and auxiliary electrodes for another form of my device, the enclosing bulb being omitted, and different current supply arrangements being shown; and Fig. 3 is a side view of yet another form of my arc lamp, with a diagram of its current supply arrangements.

Fig. 1 shows a lamp or the like comprising electrodes l0, l0 mounted on aligned support wires II, II, which also serve as current leads and are in turn attached to current supply conductors or leads l2, l2. These parts are all enclosed in a glass bulb or envelope 13. The lead v wires I2, l2 may be sealed through a stem-press (not shown) as usual in incandescent lamps, and as illustrated in Fig. 3 and referred to hereinafter. The bulb or envelope l3 preferably contains an atmosphere of easily ionized gas such as argon, at an (absolute) pressure when cold of about 600 mm. of mercury. The electrodes II], In here shown are spheres (of tungsten, for example) considerably more massive than the wires H, II. A relatively high gas pressure such as 600 mm. is desirable in the bulb l3 to minimize evaporation of the electrodes l0, Ill.

With the electrodes l0, I0 is associated a separate starting electrode l5 (also of tungsten, for example) mounted on the upper end of a current supply conductor or lead l6 which may also be sealed through the stem-press (not shown.) The starting electrode [5 is preferably very slight in cross-section or metal as compared with the main electrodes I0, 10. It is here shown as consisting of a helical coil of a number of turns of fine. (tungsten) wire of decidedly finer gauge, even, than the electrode wires II, II. Its distance from either electrode Ill, I0 is only about half the gap between the latter. Preferably, its active upper end is substantially in the gap between the electrodes III, ill but a little below the direct line between them.

When a relatively moderate difference of potential equal to (or reasonably exceeding) the operating voltage is maintained between the main electrodes III, II), the basis and phenomena of starting with the starting electrode I5 are essentially as follows:

The gap between starting electrode [5 and either electrode l0, l0 being only half that between the electrodes in, Ill themselves, it is obviously easier to initiate a discharge to this starting electrode, by a suitable difference of potential created between electrode l5 and one of the electrodes III, III, than to initiate a discharge directly between the latter. Furthermore, the conduction of heat away from the minute point of incidence of the slight initial discharge is very Cal much more rapid in the mass of the electrode Ill than in the slight cross-section of the electrode I5 so that an initial discharge which is powerless to heat electrode Ill appreciably will readily heat the small active end of electrode I5 to a temperature of electron emission, thus multiplying the initial discharge many-fold. By such augmented discharge, electrode I5 is heated still more, and the discharge is thus further augmented, until it begins to heat up the electrode Ill with which it is coacting. This will provide a supply of electrons in the longer gap sutficient to initiate the main discharge, between the elec' trodes Ill, II), which will then be self-sustaining and grow very quickly to its full value corresponding to the operating voltage maintained between electrodes Ill, Ill.

With main electrodes I 0, I arranged and operating as just set forth in connection with Fig. 1, the starting voltage required is high. A transformer capable of giving it cannot operate efficiently for the much lower voltage normally required for the main arc at Ill, Ill. I have found, however, that with the starting electrode I this difficulty can be overcome by special provisions to supply high starting voltage across the gap between electrodes Ill and I5 temporarily, during the starting period, while the much lower operating voltage for the main are between electrodes Ill, I0 is otherwise supplied. Thus if a transformer is used for the main arc, it can be designed entirely with a view to efiiciency when iving the low operating voltage, because it will never be required to give a high starting voltage; while if a special or separate transformer 2| is used to give a high voltage for the starting or auxiliary arc to electrode I5, its ineiilciency for the much lower operating voltage is unimportant, because it need not continue in operation after the main are at Ill, Ill has started.

One such arrangement is illustrated in Fig. 1, where a (step-down) auto-transformer 20 is shown with its primary 22 connected across the main current supply or primary circuit 23, 24, and with its secondary 25 connected in a circuit 26, 21, across the main gap between electrodes Ill, Ill. As usual for auto-transformers, the primary 22 and secondary 25 are interconnected at 28, and are there also both connected to the side 26 of the secondary circuit. The other (step-up) autotransformer 2| is shown with its primary 30 connected in a supply or primary circuit 3|, 32 across the primary and secondary leads 23 and 24, so that the circuit 3|, 32 includes the primary 22 and secondary 25 of transformer 20. The primary 30 and secondary 33 of transformer 2| are interconnected at 34, where they are also both connected to the lead 32, which is common to the primary and secondary circuits of transformer 2|. The secondary 33 is connected in a secondary circuit 32-2I and 35 across the starting gap between electrodes I0 and I 5. A switch 36 is shown in one lead (24) of the supply circuit 23, 24, and a switch 31 (preferably of a self-opening pushbutton type) in one lead (3|) of primary circuit 3|, 32.

The transformers 20 and 2| may be so designed that if the supply voltage across circuit 23, 24 is the ordinary lighting voltage of 115 volts, for example the open-circuit voltage across secondary circuit 26, 21 and main electrode gap Ill, Ill may be 30 volts, and the closed circuit voltage 10 volts. On this basis, the voltage across primary circuit 3| 32 will be'115 volts and that across secondary circuit 21-32, 35 and starting gap I0, I5 may be about 600 volts,under the open circuit conditions before either arc starts, that is. Such a potential difference of 600 volts is ample to start an arc in argon of some 600 mm. pressure, under the conditions here involved, between the electrodes I0, I5; and after this has happened, the open-circuit potential difference of 30 volts is ample to bring about an arc between the electrodes Ill, Ill. All that is required is first to close switch 36, then to close switch 31 and hold it closed until the auxiliary and main arcs are observedto have started, and then to release switch 31 and allow it to open.

Fig. 2 shows relatively massive (tungsten) main electrodes Illa, Illa, with their support wires II, II and current leads I2, I2, intended to be used in a bulb or envelope (not shown) similar to that of Figs. 1 or 3. Instead of a starting electrode like that of Fig. 1, there are auxiliary electrodes 40, 40 associated with the main electrodes Illa, Illa, and in heating proximity to them, but extending thence (laterally and convergently downward) away from them to a relatively remote starting gap formed by their portions that are closest together,which in the present instance are their very ends 4|, 4|. For convenience, the auxiliary electrodes 40, 40 are preferably connected to the current supply leads of the main electrodes Illa, Illa, to take current from the same source and be subject to the same difference of potential, al-

though this is not absolutely essential. The auxiliary gap at 4|, 4| may about correspond in magnitude to that between starting electrode I5 and its coacting main electrode Ill in Fig. 1. The auxiliary electrodes 40, 40 are made much slighter in cross-section of metal than the main electrodes Illa, Illa so as to be much more easily heated by an initial discharge between them; and as here shown, they consist of helices of a considerable number of turns of (tungsten) wire. From the auxiliary gap 4|, 4|, the electrode wires 40, 40 extend divergently upward to the support and lead wires I I, I I behind the heads or masses of the electrodes Illa, Illa, and then coil around the lead wires outward to the leads I2, I2, to which said wires 40, 40 are Welded (or otherwise electrically connected) at-42, 42. The wrapping of the electrode wires 40, 40 around the supports II, II relieves the relatively brittle welded portions at 42, 42 of mechanical stress and protects the wires 40, 40 from risk of breakage close to the welds.

When a sufllcient difference of potential is created between the main and auxiliary electrodes Illa, Illa and 40, 40, a discharge will start across the auxiliary gap between their ends 4|, 4|, heating the latter to electron-emissive temperature. The resultant arc will tend to work upward along the auxiliary electrodes 40, 40 toward the main electrodes Illa, Illa, because the rise of the arc cuts out more and more of the electrode-circuit resistance represented by the length of the coiled electrode wires 40, 40, and under the influence of the convection currents which the heat causes in the surrounding gaseous atmosphere in the bulb. As the arc creeps upward, it heats the electrode wires 40, 40 closer and closer to the main electrodes Illa, Illa, until it provides an ionized atmosphere between these electrodes, establishes itself between them, and finally heats these main electrodes to emissive temperature. As soon as this happens-or, indeed, as soon as the arc starts to creep up the auxiliary electrodes 40, 4ll,the voltage between the electrodes Illa, Illa may be very greatly reduced, to a final normal operating value of about 10 volts, for instance.

In lFig. 2, the lamp is shown with its leads l2, l2 and electrodes Illa, Illa connected directly across the supply circuit 23, 24, and with a choke 20a in one lead 23 to limit the voltage and current across the electrode gap after the arc has been initiated. A switch 36 is also shown in one lead 24, as in Fig. 1. With an atmosphere of very pure argon of about 5 mm. pressure in the lamp bulb (not shown), and an auxiliary electrode gap 4|, 4| of about 2 to inch, the arc across this gap 4|, 4| will start on a supply circuit voltage of about 220 to 250 volts, more or less. If a highly emissive coating (such as barium oxide) is used on the electrodes, the starting voltage is much less. In any case the current required at the higher voltages to obtain the arc across the main electrodes is much less than if the two auxiliary electrodes are not present.

In the lamp shown in Fig. 3, the starting electrode W of Fig. 1 is shown combined withthe main and auxiliary electrodes Ma, Ma and 46, M of Fig. 2. The operation in starting represents a combination of what has been described in connection with Figs. 1 and 2: i. e., an auxiliary or starting arc is first started between one of the coiled electrode wires and the much finercoiled wire of the starting electrode IS. The main arc is thus started between the ends 4|, 4| of the electrode coils 40, 4D themselves, as in Fig. 1, and then this are creeps up the auxilia y electrodes 40, 4|] and establishes itself between the main electrodes llla, Illa, as just described in conhection with Fig. 2. The stem press through which the current leads |2, I2, and I6 are sealed is here shown. In this lamp, a gas pressure of argon around 600 mm. in the bulb l3 will not interfere with starting of the are by a voltage of 600 volts between electrodes l5 and Ill. The current supply arrangements and connections are equivalent to those shown in Fig. 1. These and other parts and features similar to those shown in Figs. 1 and 2 are marked with the same reference characters, as a means of dispensing with repetitive description. However, in this case the line voltage of volts is applied across the primary 22 of transformer 20 so that with an open circuit voltage of 30 volts across the secondary 25, the voltage across the primary 30 of transformer 2| will be volts, instead of 115 volts as in Fig. 1 where the line voltage is applied across the whole transformer 2|]. It may be observed that in Fig. 3 a resistance 46 is shown in the primary lead 32, in series with the primary 30 of transformer 2|. By absorbing part of the high voltage across the primary circuit 3|, 32, the resistance 46 allows of using a smaller transformer 2|, with fewer primary'turns. Also, a unitary switch device 41 is diagrammatically indicated, which combines the switch 31 of Fig. 1 with du plicate switches 36, 36 that make and break both sides'23 and 24 of the supply circuit. The contacts 48, 48 of switches 36, 36 are resiliently yielding, to permit one of them to be forced over into contact with the stationary contact which is the only special part required for the switch 31. Commercial rotary switch devices suitable for the purpose are also available, in which the first snap-turn closes both switches 36, 36, the second also closes switch 31, the third opens switch 31 again, and the fourth opens both switches 36, 36.

comprising a pair of relatively massive coacting main electrodes or cathodes; a pair of much slighter auxiliary electrodes or cathodes associated with and in heating proximity to corresponding main electrodes and extending away from them to a relatively remote starting gap, where said auxiliary electrodes are closest together; and a separate starting electrode located at an intermediate point just below the starting gap between said auxiliary electrodes, and very much slighter in cross-section than the latter.

2. The combination of an enclosed electric arc discharge device comprising a pair of coacting electrodes or cathodes, and a separate starting electrode at an intermediate point substantially in the gap between said first-mentioned electrodes; means including a step-down transformer for deriving from a circuit of ordinary lighting voltage a lower voltage for operation of an arc between said first-mentioned electrodes; and means including a step-up transformer for temporarily deriving from such a circuit of ordinary lighting voltage a higher voltage for initiating or starting an are between one of said first-mentioned electrodes and said starting electrode.

3. The combination of an enclosed electric arc discharge device comprising a pair of relatively massive coacting main electrodes or cathodes; a pair of much slighter auxiliary electrodes or cathodes associated with and in heating proximity to corresponding main electrodes, and extending away from them to a relatively remote starting gap, where said auxiliary electrodes are closest together; a separate starting electrode at an intermediate point substantially in the starting gap between said auxiliary electrodes; means for maintaining a relatively moderate diiference of potential between said main electrodes, and between their associated auxiliary electrodes; and means for temporarily creating a much higher difference of potential between one of said auxiliary electrodes and said starting electrode, and for subsequently doing away with said higher dillerence of potential, while said moderate difference of potential continues.

4. The method of starting an enclosed electric arc discharge device comprising a pair of relatively massive coacting main electrodes or cathodes, a pair of much slighter auxiliary electrodes or cathodes associated with and in heating proximity to corresponding main electrodes and extending away from them to a relatively remote starting gap where said auxiliary electrodes are closest together, and a separate starting electrode at an intermediate point substantially in the starting gap between said auxiliary electrodes, said method consisting in maintaining a relatively moderate difference of potential between said main and auxiliary electrodes, temporarily creating a much higher difference of potential between said starting electrode and one of said auxiliary electrodes until an auxiliary arc thereby started between said starting electrode and auxiliary electrode heats the latter and thus enables an arc to start between the two auxiliary electrodes under the moderate diflerence of potential between them, and allowing the are thus started between the auxiliary electrodes to travel along the latter, as it heats them, toward the main electrodes until it also heats the latter and brings about an are between them under their moderate difi'erence of potential.

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