US2523021A - Starting arrangement for electric discharge devices - Google Patents

Description

D. D. HINMAN Sept. 19, 1950 STARTING ARRANGEMENT FOR ELECTRIC DISCHARGE DEVICES Filed July 19, 1945 noon rR U

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H5 A T TERA/E Y Patented Sept. 19, 1950 STARTING ARRANGEMENT FOR. ELECTRIC DISCHARGE DEVICES Y 7 Donald D. Hinman, Cleveland Heights, Ohio, as- I w I signor to General Electric Company, acorporation of New York Application July'19, 1945, Serial No. 605,900

4 Claims, (01. 315-98 This invention relates to the starting control ofelectric discharge devices, and is very useful for fluorescent tubes of positive column discharge type, as well as for various other dischargedevices. The" invention is especially adaptable for starting discharge devices quickly,

without the delay usually entailed by preheating their cathodes.

As is wellknown, the voltage required to start a discharge through an ionizable atmosphere (gas or vapor, or both) is considerably higher than that required to maintain it after it has started. Even this operating voltage is often different from ordinarylighting supply .circuit voltages, so that a transformer is generally interposed between the supply circuit and :the operating circuits of an installation, to give the requiredvoltage. In any case, current-limiting chokes orballasts-are commonly interposed in the operating circuits. Such ballasts usually have inductance, and may also include capacitance. Very commonly, the'ballast is structurally built into the transformer. In the case of D; Cfidischarges, means otherthan transformers are employed to give the desired voltage, but resistive or reactive ballasts are used to control the discharge current. I A

'Mostfluorescent lamps of positive column low pressure discharge type are at present hotstarting? with flow of heating current through their cathodes to preheat them before discharge is initiated. For this purpose, a starting circuit with an automatic switch therein is connected across the operating circuit, in parallel with the discharge gap of the lamp and through heating means embodied in the cathodes. The automatic switch passes current through the oathode-heating means long enough to bring the cathode (s) ofalamp up to an adequate emissive temperature, and then suddenly opens the startingcircuit, giving rise to a high voltage kick 7 between the electrodes (due to the inductance in=theoperating circuit, and much higher than the operating voltage of that circuit) which generally sufiices to initiate the discharge.

7 The time required to preheat the cathodes to the operating temperature of adequate thermionic emission is appreciable, so that at best an undesirable brief interval elapses between the closing of the manual switch controlling an installation and the actual lighting up of the lamps; Moreover, the action of starters in common use is often irregular, so thatthe lapse of time a between J closing the control switch and lightingnp all the lamps may oftenamount to a quarter of aminute, moreor less. These-draw+ backs have heretofore been unavoidable in practice, because starting .of lamps coldf without cathode preheat, resulted in rapid disintegration of the cathodes and blackening of the lamps. j

Recently, cathodes have beenevolved which stand cold starting so much better thatv it is feasible to do away with hot starting and with starting switches, so that fluorescent lamps .will light instantly (or practically so) when the controlling switch :is .closed, just like incandescent lamps. For this purpose, a leakage-neactance transformer may be used between lightingsupe ply circuit and the dischargecircuits, togive high open-circuitvvoltage for initiating discharge, rot lowed by suitably lower voltage for ordinary operation. i 1

While this arrangement is generally successful, it has the disadvantage of requiringglarger and more expensive transformers than those now inusefor hot-starting installations, in order to assure starting .under unfavorable atmospheric conditions of very high humidity; For example, LO-watt fluorescent lamps of tubular, low-pressure, positive column'type may require as high as 1800 volts or more to insure starting under the :most adverse conditions, asagainst a voltage of some volts (more or less) insubsequent operation. The size and cost of the-auxiliaries for :such voltages would be well-nigh prohibitive.

In my copending application Serial N0.; 564,479, now Patent No.-2,451,830, issued October 19, 1948, 1 have disclosed novel arrangements which afford ample voltageoto assure starting off the discharge under the most adverse conditions, without necessity :for large orexpensive auxiliaries, and without the irregularity of starting lthat is almost characteristic of certain. muchused types of starting switches. This is ,accomplished 'by induced. high voltage generated and applied in ,a novel way, which is applicable ,to discharge lamps operating on D. ,C,.,,as well as to A. C. systems. For this purpdse,;a starting ,circuit that 'is connected across the operatin v Sir. cuit in parallel with the main-discharge device includes a branch. .or vloop circuit which has therein ;a capacitor: ;or ,=condenser. ,and an,auxiliaryelectric discharge device (e.:g.,, a thyratrqh,

:spark-gap, or other :auxiliary discharge. device) and this loop isginductivelycoupled ,to ,a circuit that is connected "to the main discharge .,;electrodes. In the particular species or -type ,of :starting arrangementiillustrated in my said application, the circuit ato which the loop in equestion is inductively coupled is the main operatduced in essentially the same way can be applied to start the main discharge in a different way,

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without necessity for radical changes in existing installations. For this purpose, the loop circuit wherein the high voltage is generated is inductively coupled to a portion of the starting circuit that is in series with the loop, instead of to the main operating circuit. Though high voltage impulses thus applied to the starting circuit may be less effective, becausethey may be partly dissipated in a portion of the operating circuit that includes the ballast andthe transformer (or its equivalent in the case of D. 0), yet I have nevertheless found it possible to generate voltage impulses powerful enough to efiect starting even under these less favorable conditions. At the same time, the great practical advantage is gained that the startingunit can be a two contact device requiring only to be connected into the starting circuit in. lieu of the starter previously used, without also being connected into the main operating circuit.

Other features and advantages of my invention will appear from the description of species or forms of embodiment, and from the drawings.

In the drawings, Fig. l is a circuit diagram showing starting and operating arrangements for discharge lamp(s) operating on A. C.; Fig. 2 is a fragmentary diagram illustrating a modification; and Fig. 3 is a tilted View of one form of spark-gap device that is suitable and convenient for use in the starting circuits illustrated in Figs.

1 and 2. i

Figs. 1 and 2 illustrate the application of the coiled or coiled-coil tungsten filament type, coatedor charged with activatingoxides such as a mixture including barium and strontium oxides. The envelope may contain a low-pressure atmosphere of ionizable starting gas, such as argon at a pressure of 2 to 6 mm. of 'mercury, or other inert rare gas(es) at a corresponding pressure, and also a vaporizable and ionizable working substance or metal such as mercury, which is indicated by a droplet 3 inside the envelope. An internal coating of fluorescent material orphosphor 4 on the envelope walls 'is also indicated.

The discharge device is shown connected across an operating or discharge circuit 5 including the inductive ballast 6. For'energizing it, the operating circuit 5 is shown connected across the secondary of an autotransforrner 1 whose primary is connected across a voltage source such as an ordinary cycle A. C'. lighting circuit 8 of some 110 to 120 volts, for example. The'usual '4 shown in the circuit 8. To illustrate usual conditions of operation, two similar discharge devices I, I are shown connected across the transformer secondary in parallel lead and lag circuits 5, 5. As usual, the lead circuit 5 includes a condenser I0, which besides other functions also serves as ballast to limit the discharge current. The transformer 'I is of course chosen to give or assure the desired voltage across each of the operating circuits 5, 5. Once the discharge has started, the voltage across each device I is regulated or reduced by its ballast 6 to a favorable value for the operation of the device I, which may be the closed circuit voltage on which the device would be operated in present hot-starting practice.

For the purposes of my invention, a starting circuit I I is shown connected across the operating circuit 5 of each of the discharge devices I, I. Each circuit II is provided with means for generating high voltage oscillations and applying them across the discharge gap between the electrodes 2, 2 of the corresponding device I, such means comprising a capacitor or condenser I2 and an auxiliary electric discharge device I3 in shunt with one another in said circuit auxiliary II, with an inductive coupling between one side of the shunt and the starting circuit II, and, as shown, an impedance I4 in series with the shuntconnected condenser and electric discharge device or spark-gap. The circuit I I here shown includes a loop circuit I5 in which the condenser I2 and spark-gap I3 are connected in parallel, so as to be in series with the rest of circuit I I including impedance I4; and the loop circuit I5 also includes the primary I6 of a high frequency transformer in inductive relation to the secondary I! in the starting circuit I I, in series with loop I5 and impedance l4. Specifically, the inductive primary I6 is shown connected to the circuit I'I between the spark-gap I3 and the connection of said circuit II to the operating circuit 5 through the cathode coil 2; and the secondary I1 is interposed in the circuit II between the connection of the loop side including primary I6 to said circuit II' and the connection of the latter to circuit 5. It makes no difference whether the impedance M is connected in said circuit II at one side of the parallel-connected condenser I2 and the spark-gap I3 or at the other side thereof. Nor is it very important which of the direct connections between condenser I2 and device l3 includes the primary I6, or which end of this primary is connected to the condenser, and which to the spark-gap.

The discharge device(s) or spark-gap(s) I3 should have a break-down voltage less than the open-circuit voltage across the secondary of transformer I, and, therefore, less than the breakdown voltage of any device I which the transformer cannot start unaided. The device I3 should preferably show a large difference between break-down and maintaining voltages; but the maintaining voltage should preferably be higher than the voltage on said device I3 during ordinary operation of the discharge device(s) I, 'so as to assure cessation of the dischargein' device I3 during the ordinary operation of said discharge device(s) I, as hereinafter explained.

One suitable device I3 is of moderately lowpressure gaseous discharge type, resembling a glow-lamp in general'construction, but showing opposite characteristics: i. e.,'an unstable glowdischarge which is sustained largely by field emismake-and-break wall'or other control switch 9'is sion and tends to hot-spot. Such a device I3 is seam iiiii raise "in e s comprising a" (seats at.

reousenvelope I8 containing a flare and stem ss type'of mount T9, with a pair of flat elec tro" es an, 28 (resembling halves of a circular thepress. These electrodes 20, 20 may have a thickness of about inch and a semi-circle diameterof about g'inch. They may consist,'for example, 'of anemissive nickel-tungsten composition activated with barium, which may be mainly in the form of barium oxide, BaO. They may be prepared from a batcnmixture or finelydivid'ed ingredients comprising by weight:

V Parts r325 inesh'grains) 80 mo 1'0 BaC;; '10

This mixture is pressed into the desired shapes of the device.

.A-mode of operation of the system shown in 1 is that when the switch 9 is closed to turn on thelamps Li, A. C. voltage is appliedin each operating circuit and in each starting circuit I I, charging the corresponding condenser I2 through the correspondingresistance I4, and also tending to breakdown the corresponding dischange device or spark-gap. I3. When the device It breaks down or becomes conducting, the condenser IZ discharges through it, producing in the oscillating loo'p circuit I5 and in the primary I6 a current surge orsurges, or a series of high frequency electrical oscillations. Such breakdown in'ay occur once or several times during each olicycle or other A. 0. wave in :the circuits 8, 5. Ifhe rapidly changing current in primary I6 induces in secondary I'I a high voltage which appears across the discharge gap in the discharge device or lamp I. When such a voltage impulse coincides with a corresponding impulse due to the A. C. supply in circuit '8, or occurs in such phase relation thereto that the algebraic sum of the voltages suiiices to break down or render conductive the discharge atmosphere in the device I-which happens in a fraction of a second after switch 9 is closed-discharge in the device I is successfully initiated. Moreover, the high frequency from I! after a glow discharge has started in the device I helps to change this over into a positive column or are discharge.

When the discharge starts, the resistance of the device I falls off to a minor fraction of its value before breakdown (which is of the order of megohms), and the voltage across the sparkgap I3 (as limited by the impedances 1, 6, I4, I2,

I6 when current is flowing through them) decreases so inuch that the device I3 drops out and ceases to carry current. During ordinary operation, therefore, current flow in the circuit I I is 1imited by the impedances I4, I2, I6 to a trifling value which may be no more than a couple of milliamperes, representing an energy loss that is inappreciable.

Because of the high frequency of the electrical oscillations produced as above described i the primary I6, the number ofturns that are needed in the secondary IT to produce the desired starting voltage-isfarless tnan it would be for ordinary commercial frequencies of 60, 50, ,or 25 cycles, sothat this secondary and the inductive device or transiormer embodying it may be of relativelysinallsize and weight. For oscillations of, suflicie'ntly high frequency, the transformer I6, II maybe of air-core type; however, an iron core makes for smaller dimensions, with less copper, and lower secondary resistance.

' For the convenience of persons wishing to practice invention, I will now give specific details of design for a system such as shown in Fig. 1; but theselare to be understood as illustrative, andnot as limiting or defining the invention. For starting and operating iii-watt fluorescent lamps of the present T-12, 48 inch tubular, positive column, low pressure type, the open-circuityoltage produced by the transformer 'I across the operating circuit(s)' F3 maybe some 200'jvolts. Accordingly, a unit comprising ballasts 6', 6, transformer l, and condenser is which is now in common use for lead-and-lag pairs of fluorescent lamps may likewisebe chiployed in thef'system here illustrated. 'Thebondensers I2 may be of 5 0t25 inicroifarad each, and the resistances i l of 250 ohms each. The transformer sl IS; Il may beof auto type, or may have separate primary and secondary windings. In general, their design is not atall critical. One satisfactory transformer of this latter character has separate primary and secondar windings, the primaryponsisting of 10 turns of #30 enamel'led copper, on andnext to a A; inch square core '1 inch "long consisting of 4-mil thick lamina of transformer iron, the secondary consisting of 200 turns of #30 enamelled copper wire wound over the primary.

For use with a 40-watt fluorescent lamp starting system embodying the'particulars above set forth, the gap between the electrodes'Zll, 2:) of discharge device I3 may be about 15 to 20 mils, and the gas filling ',in the envelope in may be argon at a pressure of about to 200 mm. Thus constructed, the device I3 shows a breakdown voltage of about volts R. M. S., and the voltage across it becomes negative during part of each cycle of the discharge voltage in the circuits 8, 5.

In Fig. 1, the starting circuits I I are shown as connected across the operating circuit 5 through the cathode coils 2, 2 of the lamp I, since this is the usual arrangement of starting circuits in existing installations where the cathodes are preheated for starting. However, the starting circuit II can just as well be connected across the operating circuit 5 directly, between points of said circuit 5 in advance of the cathodes 2 or even of the sockets or other means with which discharge circuits are usually equipped for making connection to the lamp electrodes 2, 2 through contact terminals on the lamps (not shown). This discharge circuit connection is illustrated in Fig. 2 where various parts and features are marked with the same reference characters as in Fig. 1, as a means of dispensing with repetitive description. For simplicity, only the parts directly associated with a single lamp I are included in Fig. 2, the corresponding ballast 6 and the parts I, 8, 9 being omitted.

In D. C. systems involving my invention, the means for providing the desired voltage across the discharge circuit will of course be different from the transformer I here illustrated; the lead and lag circuit features will be omitted; and the discharge-controlling ballast 6 may be purely resistive instead of inductive or capacitative, or it may be both resistive and inductive. However, the starting circuit II and the condenser 12, discharge device or spark-gap I3, transformer l6, l1, and current-limiting impedance 14 may be essentially the same as shown in Fig. 1.

What I claim as new and desire to secure by Letters Patent of the United States is:

In combination, an electric discharge device containing an ionizable atmosphere and coacting electrodes, an operating circuit connected to said electrodes, a starting circuit connected across said operating circuit and including a loop circuit and a current-limiting impedance in series with said loop, a capacitor and an auxiliary electric discharge device connected in said loop in parallel with one another with respect to said impedance, said auxiliary discharge device having a break-down voltage less than the starting voltage of the first-mentioned device and a maintaining voltage greater than the operating voltage of the first-mentioned device, and an inductive coupling between said loop and a portion of the starting circuit that is in series with the loop.

2. A starter for connection across the operating circuit of an electric discharge device containing an ionizable atmosphere, said starter being connected across said device and comprising an oscillating loop circuit and a current limiting impedance connected in series with the loop, a

capacitor and an auxiliary electric discharge device connected in said loop in parallel with one another with respect to said impedance, said auxiliary discharge device having a break-down voltage less than the starting voltage of the firstmentioned device and a maintaining voltage greater than the operating voltage of the firstmentioned device, and a transformer having its primary connected in said loop and its secondary connected in series with said loop.

3. A starter for connection across the operating circuit of an electric discharge device containing an ionizableatmosphere, said starter being connected across said discharge device and comprising an oscillating loop circuit and a current limiting impedance connected in series with the loop, a capacitor and an auxiliary electric discharge device connected in said loop in parallel with one another with respect to said impedance, said auxiliary discharge device having a break-down voltage less than the starting voltage of the first-mentioned device and a maintaining voltage greater than the operating voltage of the first-mentioned device, and a high-frequency transformer having its primary connected in said loop and its secondary connected in series with said loop.

4. In combination, an alternating current supply ,circuit, an electric discharge device containing an ionizable medium and cooperating electrodes, a starting circuit for said discharge device connected thereacross and comprising an oscillating loop circuit and a current-limiting impedance in series with the loop, a capacitor and an auxiliary electric discharge device connected in said loop in parallel with one another with respect tosaid impedance, said auxiliary electric discharge device having a break-down voltage lower than the supply voltage in said supply circuit and a maintaining voltage higher than the voltage on the first-mentioned discharge device during operation thereof, and a high-frequency transformer having its primary winding connected in said loop circuit and its secondary Winding connected in series with said loop circuit.

DONALD D. HINMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,555,547 Bethenod Sept. 29, 1925 1,976,645 Westendorp Oct. 9, 1934 2,326,597 Abernathy Aug. 10, 1943

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