Electric discharge apparatus

Aug. 22, 1939.

2,170,446

M. A. EDWARDS

ELECTRIC DISCHARGE APPARATUS

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Maritin A. Ed wands , by £. &amp;

His Attoriney

Patented Aug. 22, 1939

2,170,446

Claims.

My invention relates to gaseous electric dis^{devlces 311(1} apparatus employed in opί^ί,¹¹⁸?¹¹® ^sa?^{e from} alternating current circuits particularly when the discharge devices are used Ind ^{Of glVlng Ught}> ^namely as lamps, ^and .^wh®^{p thelr} construction is such that they require the application of a higher voltage for starting than for their subsequent operation in in,™. °^^JeCt °^f ?^{y lnvention} is the provision of ^{10 apparatus for} such use which will proride the voltage necessary to cause a discharge in the device to start and after starting has occurred wil! reduce automatically to the value required for the continued operation of the device there¹⁶ Sid ^Ano^^{her oWect of} W invention is the unproved apparatus for such use whereby the amount of flicker incidental to the circuit frequency is reduced to a low if not im_n perceptible, value. A further objecl of my ta20 vention is the provision of such apparatus which will operate with high efficiency, will have a ^^characteristic which is not injurtous to the device, will provide a circuit which has a _ high degree of stability and one wherein the 25 current supplied to the device is not critical to reasonable variations in the line voltag” ^lpve?^{tion wiu} he better understood from

Sth the™ ^descrlptlon taken in connection -- n^hu^{th accom}Panying drawing and its scope ^{0 W1}Retorrin^^dfh^UV^{n the appended}-claims.

. ^Re?f^rJ.^ing to the drawing, Fig. 1 is a combined n/nnl ^{and diagra}mmatic side elevation of one embodiment of my invention; Fig 2 is a 35 iTw °^{f the apparatus}shown ^{35 3 shows} curves illustrating the

M?T?&lt;i^aa^Cri^{Oi device 311(1} the apparatus and tion ^{4 S} circuit diagram showing a modiflcaWhile my invention is applicable to apparatus 4° employing various forms of electric gas discharge devices it is of particular interest and his ^In especially developed for use where the devices lueh^e^°^{yed Ught}· ^{A prefer}rad form of ^Pch ‘tey^{101518 a lam}P ^of the positive column type ⁴⁵ ®^pippnsipg a tubular envelope haring electrodes at its ends and containing a gaseous atmosphere such as a few millimeters of a rare gas for example argon, and a small quantity of a vaporizable metal, such as mercury. Preferably the envelope 50 is coated internally with a suitable fluorescent material m order that the electric discharge which in itself may be scarcely risible, shall pro^de8ired high degree of illumination.

description to follow, therefore, I shall refer 55 to the discharge devices as lamps. It is well

UNITED STATES PATENT OFFICE

2,170,446

ELECTRIC DISCHARGE APPARATUS

Martin A. Edwards, Schenectady, N. γ

New Vⁿ_o^ i «^85*2

1’CW aUFK

Application March 22, 1938, Serial No. 197,526 (Cl. 176—124)

Se ^Sta^ ^{a discharge} in such a lamp by i highervon± °^f ? J^{oItage to lts} electrodes I ί qifired to mnlnTV £ ^empl°y^ed than that re Sn started ^{β ώ5οΙ13Γ}»θ ^after « has derice^t lamn &lt;^h°^{Wn the electric di}«*arge ⁵frj or lamp at I provided at one end with S _h“^0nlc.^{cathode 2 and at} other end with the two similar anodes 3 and 4 preferablv sired a⁶ wen ^lnsuIating Partition 5. If 10 ^{a wel1 known} form of separately heated helted^ecattt !^mp£°^{yed lnstead of} the directly neatea catnode as shown.

and^efmlt^starti?^g’ ^{the lamp 1138 a} high resistance thm^hat^rIfTI^e t ^V°^{ltage consider}ably higher 15 nn^ °1 the circuit from which it is supplied to start a discharge therein. A lamo for ch-rni?^le’^{that 1S adap}ted to operate on a 110 volt ^requlre the application of approxi^{lts anode and} cathode 20 th_eT7‘ ^{1 Start}- it has started however the arc drop may be approximately only 100 volts ma^Vn ^{than that} * ^uired to maintain tne discharge.

nhIL^e0t^{mP 18 supplied} from the source 7 of single 25 ^ealternatlllg current which for example may the iinn ^CyC1&lt;7 ^{110 V01t llg}hting circuit through lrL^Unltary structure represented at 8 and comprising a combined high reactance transformer and reactor. The core of the structure comprises 30 IXprt’^Sh-t?^{e&lt;i members} 9 and 10 reverse!? arranged with respect to each other and with corresponding legs spaced from each other to fom &lt;h^SI^etf^{iC Saps}‘ ^{In the drawin}g these gaps are rat,ZV°^{r Slmpllci}ty as air gaps but as the appa- 35 manufactured they comprise a suitable ^8116110 ,^matenal against which the two members are clamped. Between the legs of the member 10 are magnetic shunts slS at H thereby increasing the flux leakage to provide a An higher leakage reactance. ^{P de a 40}

On each of the outer legs of the core structure is a, primary winding consisting of the coir 12 a mam secondary winding consisting of the coil 13 Plus the coil 12 thereby constituting _an auto 45 transformer and a separate auxiliary secondary winding comprising the coil 14. The ends ofthl primary, thus composed of the two coils I? Le connected by the leads 15 and switch 16 with the opposite sides of the source 7. The opposite κη ®^{Pds main secondar}y. composed of^the thett^{01S 2}„^an,^{d the two colls ,3}> connect with the two anodes 3 qnd 4 and the mid-point thereof connects with the cathode 2. The latter connection includes the conductor 17 and the auxil- 55 iary secondary, made up of the two coils 14, the purpose of which is to supply heating current to the lamp cathodes. .

As shown by the drawing the magnetic shunts ₆ It are arranged adjacent the upper ends of the primary coils and extend between the outer legs of the core structure and the middle leg 15 thereof being spaced from those legs by magnetic gaps, which preferably comprise netic material. Tt will be seen that by ^arrangement the amount of leakage of the primary flux is greatly increased since the shunts provide a relatively low reluctance leakage path, with the result that the leakage reactance between the nrimary and the secondary is accordingly increased. The middle leg 18 also provides a return path for the uni-directional component of the flux in each of the two outer legs during the operation of the lamp, such a component being present by reason of the fact that since the lamp acts as a bi-phase rectifier the secondary current is unidirectional. By reason of the middle leg, moreover, I obtain an exceptionally high reactance hence a low,mutual reactance, between the two halves or coils of the secondary winding because of the magnetic shunt effect thereof .whereby they are virtually isolated from each other.

To assist one in the understanding of the several flux paths which the above described structure provides, I have represented the alternating flux at any instant by dash lines and the unidirectional flux by dot and dash lines. In order to cause the magnetization of the core by the primary to have a linear characteristic and also to limit the voltage produced in the secondary by the condition of partial resonance obtained at the time of starting, which condition will be described later, I provide a magnetic gap in each of the outer legs. I also provide a gap in the middle leg 40 18 so as to prevent saturation therein due to the uni-directional flux through this leg when the lamp is operating. , . .

In the operation of the lamp, an important advantage of the high leakage reactance between 4K the secondary coils together with the high reactance between the primary and the secondary is that it results in obtaining a long commutating angle between the currents supplied to the two anodes and consequently a long conducting time κη for each anode. Oscillograph records made with apparatus such as disclosed herein show that each anode carries current for approximately 230 degrees so that a large overlap of the anode currents occurs at the beginning and end of each 55 half cycle. With such a large overlap of anode currents the ripple in the total unidirectional or cathode current through the lamp is reduced to a low value and the amount of flicker in the light emitted by the lamp is very small, if not imperG0 ceptible. This is illustrated by the curves of Fig.

3. In that figure I have represented at 20 and 21 the wave form of the currents in the anodes 3 and 4 respectively plotted against electrical degrees. This illustrates the -large overlap of the anode currents resulting from the above described structure. At 22 I have shown the cathode current which, it will be observed, has but a small amount of ripple therein; this results in the lamp producing light which is substantially without flicker.

It is well known that a high reactance transformer produces a low power factor but that the power factor may be improved by the use of a capacitor across the primary or across another winding closely coupled therewith. A capacitor so used, however, is objectionable because of the

2®

2,170,446 current harmonics of large magnitude which it draws from the line when lamps of the arc discharge type are being operated by the apparatus and because the high current peaks due to such harmonics are found to be injurious to the elec- 5 trodes of the lamp if allowed to continue for any appreciable length of time. With apparatus such as that disclosed by this application -should a capacitor be connected directly across the secondary for the purpose of improving the power 10 factor it would be objectionable not only for the reasons mentioned above but for the additional reason that it would decrease the angle of commutation thereby off-setting to a certain extent the good effect of the high reactance of the sec-. 15 ondary. In the arrangement which I have devised I employ the capacitor 24 across the secondary for improving the power factor and I overcome the objections noted above by connecting in series therewith the reactor or choke coil 25 ₂₀the reactance of which is materially less than that of the capacitor. The inductive reactance supplied by the reactor is sufficient to dissipate or smooth out the objectional high current peaks originating in the capacitor while the combina- 25 tion of capacitor and reactor is sufficiently capacitatively reactive to effect the desired power factor correction.

The capacitor 24 and the reactor 25 thus bridged across the secondary performs the addi- 30 tional function of raising the voltage applied between the cathode and the anodes of the lamp. This is because the relative amounts of capacitative and inductive reactance in the closed circuit including those members and the leakage react- 35 ance between the primary and its secondary is such that a condition of partial resonance exists therein. A condition of actual or complete resonance is not desired, the natural resonance frequency of the circuit being somewhat higher than 4® the supplied frequency. For example, if the supplied frequency is 60 cycles per second the natural resonance frequency of the circuit may be 65 cycles. For stability reasons it is desirable that the operating frequency shall be on the low fre- 45 quency side of the resonance curve.

The reactor 25 may have any desired core provided it is not the same as the transformer core, in other words, is not in the path of the transformer, flux. It may, however, be of a form that co constitutes an incomplete magnetic circuit in itself but, for purposes of economy, may be arranged adjacent to a part of the transformer core which part thereby serves to complete its magnetic circuit. Such ia core construction is shown 55 by the E-shaped member 26 separated from the 1 transformer core by the magnetic gaps 27.

_; Inasmuch as the voltage applied between the cathode and either anode, namely the voltage of one-half of the secondary plus that obtained co

I by the above described bridge circuit, is not sufficient to cause a discharge to start in the lamp, I have provided means now to be described for applying a higher voltage between the cathode and one anode to cause the discharge to start. In connection therewith I employ a time delay means whereby the high starting voltage is not applied to the lamp electrodes until the cathode has had time to become heated to the desired degree. For obtaining the higher starting voltage I connect the capacitor 28 across one-half (the left half as shown in Figs. 1 and 2) of the secondary, this capacitor being of such a value that it forms therewith a circuit in partial resonance. The connection of the .capacitor jn65 eludes the electro-magnetie switch 29 which is biased to closed position by the spring 30 and which has a small armature 31 arranged opposite the gap 32 in the middle leg 18. The capacitor connection also includes the time delay apparatus to insure the heating of the cathode to the desired temperature before the starting voltage is applied. As an example of such apparatus I have shown a well known form comprising a thermal switch having the bi-metallic blade 34 and the resistance heater 35 adjacent thereto and in shunt therewith, the blade being constructed to short circuit the heater when heated thereby

When the switch 16 is first closed to energize the lamp and the controlling apparatus therefor, a discharge does not immediately start in the lamp since the voltage applied thereto is not sufficient. Heating of the cathode, however immediately starts. The switch 29 remains in closed position since before the discharge in the lamp starts there is substantially no flux in the middle leg of the transformer and the switch 34 being cool is open. Because of the resistance of the heater 35, the current flow through the capacitor 28 is not sufficient to produce a starting voltage between the cathode and the anode 4 to which the capacitor Is connected. However, by the time that the cathode has reached the’ required temperature the switch 34 will have been bent down by the heat received from its heater soas to short circuit the heater. That being done, the circuit including the capacitor 28 and that half of the secondary to which it is connected immediately comes into partial resonance and the resulting high voltage across the capacitor is applied between the cathode 2 and anode 4. With the starting of a discharge in the lamp between those electrodes, the other anode 3 also comes into action. The uni-directional flux now passing through the middle leg of the core attracts the armature 3! toward the gap 32 and opens the switch 29. It will be seen that the operation of this switch opens the circuit of the capacitor 28 which will be held open as long , as the lamp continues in operation. As the switch 34 cools it will open the short circuit around the heater 35 in readiness for a subsequent starting of the lamp.

In the modified form of my invention illustrated by the circuit diagram comprising Fig. 4, the apparatus is substantially the same as that shown by Figs. 1 and 2 except that the lamp is provided with the non-thermionic cathode 38' hence, no secondary coils are needed for cathode heating and the cathode connects directly with the mid-point of the secondary. Moreover, since the cathode is not initially heated, it is unnecessary to provide any means for delaying the application of the starting voltage. The operation of the apparatus represented by Fig. 4 otherwise is like that already described above in connection with Figs. 1 and 2.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various other modifications may be made without departing from the spirit and scope of my invention which modifications I am to cover by the appended claims.