US2916669A - Starting circuit for gaseous discharge lamps - Google Patents

Description

STARTING CIRCUIT FOR GASEOUS DISCHARGE LAMPS Filed June 6; 1958 Dec. 8, 1959 'r. c. RETZER ETAL 2 Sheets-Sheet 1 5 MR 2 ME U ZA N 1 E L R V O Ill N E T u I .M T T C A U/ ER d R n I, III OT 0 A D m m m m E H F 5 [M R Y aw B v I l I I FIG. 2.

Dec. 8, 1959 'r. c. RETZER ETAL 2,916,669

STARTING CIRCUIT FOR GASEOUS DISCHARGE LAMPS Filed June 6, 1958 2 Sheets-Sheet 2 FIG. 4; FIG. 5.

"1 11 FILED Oil V03? 19%??? TLC M m [A k Jillill) CURRENT CURRENT I IN V EN TORS THEODORE C. RETZER ROBERT R. ME LA.

ATTORNEY.

United States Patent 2,916,669 STARTING CIRCUIT FOR GASEOUS DISCHARGE LAMPS Theodore C. Retzer, Cedar Grove, and Robert C. Meola, Parsippany-Troy Hills, N.J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 6, 1958, Serial No. 740,274

10 Claims. (Cl. 315183) This invention relates to gaseous discharge devices and, more. particularly, to a circuit for starting a high intensity gaseous discharge lamp of the so-called short-arc type.

As is well known, high intensity short-arc lamps require a higher potential and current during starting than when the lamp has been ignited and the arc discharge stabilized or rendered self-maintaining. This is particularly true if one attempts to restart a lamp while it is still hot or if the fill pressure of the cold lamp is around one atmosphere or more as in the case of the mercuryxenon and xenon type short-arc lamps now being marketed. The reason for this requirement is that the voltage applied to the lamp during the starting cycle must be at least equivalent to the sparking potential of the gas at the particular pressure involved before a gaseous discharge can be initiated between the electrodes. this condition has been reached sufficient starting current must then flow through the lamp to rapidly heat the electrodes, which are relatively massive, to electronemitting temperature in order that the arc voltage of the discharge may be reduced to a value such that said discharge will be maintained by the voltage applied to the lamp from the supply line on which the lampis normally operated.

Heretofore, lamps of this character were started by applying a series of extremely high voltage pulses (approximately 30 kv. to 50 kv.) to the lamp during the starting cycle from a suitable oscillatory circuit, as disclosed in U.S. Patent Nos. 2,708,251 and 2,727,188 to C. M. Rively and U.S. Patent No. 2,825,005 to L. F. Bird. While the single oscillatory loop type of high voltage pulse starting system described in the above-mentioned patents have proven quite satisfactory for starting mercury short-arc lamps when they are cold, that is, at room temperature, investigation has shown that in order to reliably hot start such lamps, especially those containing xenon, a larger number of high voltage pulses per half cycle of the applied line voltage are required. Since the number of pulses which can be generated by a spark-gap oscil- "ice 5 manner in which the aforesaid objects, and others which After latory circuit decreases as the gap spacing and magnitude of the pulses increase, the adjustment of the spark-gap under hot starting conditions becomes very critical and even-when properly set may not provide the necessary number of pulses of the desired magnitude if the other components in the starting circuit are not held within close manufacturing tolerances. In addition, it has been found that with repeated use the spark-gap terminals become oxidized thus changing the gap spacing and necessitating frequent cleaning and resetting of the electrodes to assure optimum hot starting conditions.

It is accordingly-the general object of the present invention to provide an improved starting circuit for gaseous discharge lamps which contain an ionizable medium and require a higher starting voltage than operating voltage.

Another and more specific object of this invention is the provision of a high voltage pulse type circuit for starting a high pressure short-arc lamp which will reliably start after described, and will accordingly have full line volt- Will become apparentto those skilledin the art to which the invention pertains as the description proceeds, reference should be had to the accompanying drawings where-; in: Y I f Fig. 1 is a-schematic illustration of-a starting circuit embodying this invention; 7

Fig. 2 is a side elevational view of a high-wattage shortarc lamp of double-ended construction which characterizes the type of lamp for which the circuit'of this invention is especially adapted; j

Fig. 3 is a graphic representation of-the normal operating voltage and current waveforms for a short-arc lamp of the type shown in Fig. 2; and

Figs. 4 and 5 are graphic representations of typical voltage and line current waveforms illustrating the starting:

characteristics of a single oscillatory loop type"starting circuit used heretofore-and the multiple loop type circuit of this invention, respectively, both of which have been tuned to, provide the same number'of pulses in'theextremelyhigh voltage range.

Although the principles of this inventionare broadly applicable to. various types of gaseous discharge devices which require a higher starting potential and current than are required to normally operate the device m ce the arc has been initiated and stabilized, especially those devices which can only be ignited .by the application of a series ofhigh voltage pulses of predetermined magnitudeand frequency during the starting cycle, the invention is particularly adapted for use with high pressure short-arc lamps and hence has been so illustrated and will be so-described.

With specific reference tothe form of the inventionih lustrated in Fig.1 of the drawings, alamp-10 of the wellknown short-arc type containing an ionizable medium,

such as argon or xenon and a measured amount of" safe limits during starting and after the' lamp has been lighted and is being normally operated directly from the voltage, source16. The secondary 36 of a pulse transformer 34 is connected in series between the ballast 18 and the lamp,-10' thereby providing in conjunction with the voltage source 16 a series circuit for operating said lamp after it has been lighted. The pulse transformer 34 has two primary windings 35 and 37 which areelec trically separate from each other and in conjunction with electric discharge devices 30 and 3'2 (here shown as spark gaps) and the secondary windings 23 and 27 of two ironcore step-up transformers. 20 and 24, respectively, con-' stitute two separate and independently adjustable oscillatory loop circuits C and D. 'One end of the step- up transformer primaries 21 and 25 are connected by means" of a lead 17 to the conductor 13 on either the line side of the ballast 1-8 as at point A as shown in Fig. l, or

betweensaid ballast and the secondary 36 of the pulse transformer 34. Connection to point A is preferred since the step-up transformers 20 and 24 will then be connected directly across the voltage source 16, as will be hereinage vapplied thereto at all times even when lamp current begins'to flow and there is a voltage drop across the ballast 18.

While the step-up voltage converting means has been here illustrated as comprising two separate transformers 20 and 24, it will be obvious that a single transformer having two electrically isolated secondaries and a com- QQI primary and core may also be utilized but since this WQllld, require a specially designed transformer to insure proper balancing of the voltage on the primary and would accordingly increase the cost of the starting cireuit, it isnot preferred. a

The other ends of the step-up transformer primaries 2 1 and 25, are connected to one side of a switch 26, preferably a push=button switch, which is normally open and is in turn connected to the conductor 14 thereby provrding means for connecting said primaries across the voltage source 16. The conversion or turns ratio of the step up, transformers 20 and 24 are selected to transfo r rn the line voltage to a predetermined value, such as 7500 volts for example, so that a sufi'iciently high voltage is applied to the electric discharge devices 30 and 32 and tothe capacitors 29 and 31 connected across the step- up transformer secondaries 23 and 27, respectively, to enable the aforesaid oscillating circuits C and D to generate a series ofvoltage pulses when the switch 26 is closed and said step-up transformers are energized. Thus, meansare provided'for separately generating two series of voltage pulsesof predetermined magnitude'and frequency and .then applying such pulses by means of the pplse transformer 34to the lamp along with the potential developed across saidlamp by the voltage source16. In order to prevent the high voltage pulses from feeding back into the supply line by- pass capacitors 38 and 40 .are connected to the conductors 13 and 140m thelamp side of the ballast 18 between said ballast and the secondary 36, and on the line side of saidballast (as for example at point A as shown in Fig. 1) respectively, so as to shunt the voltage source 16. If the.,s tep; up transformer primaries 21 and 25 are connected to the lamp energizing circuit at a point between the ballast 18 and secondary 36 then the second by-pass capacitor 40 can, of course, be eliminated.

nwhileonly two. oscillatory loop circuits C and D have been shqwn itwillbeobvious that any desired number can be employed by merely increasing the number of step-up transformer secondaries and, in like manner, the nu rnber of primaries on the pulse transformer. Similarly, while the capacitors 29 and 31 as here shown are connected in parallel with the step-up transformer secondaries ZS and 27,.and the spark- gaps 30 and 32 in series withsaid secondaries and the pulse transformer primaries 35 and 37, the electrical disposition of said cap 'itors and spark-gaps may be interchanged without materially changing the mode of operation of the oscillatory loop circuits as is well known in the art. Moreover sin ce the starting circuit in order to function merey requires a source of alternating current to energize the stepup transformers 20 and 24 'it is in this sense independent fromthe series operating circuit which energizesithe lamp after the latter has been ignited and is operating normally. Thus, the starting circuit of this invention may also be employed to start lamps which are normally operated from a DC power source by either incorporating in the, starting circuit means to ternporarily convert the DC. voltage to an AC. voltage, such as a vibrator forexample, or by providing a separate AC. voltage source for energizing the step-up transformers 20 and 24 during the starting cycle.

The starting circuit of this invention is particularly adapted for use in conjunction with a high pressure shortare lamp' of the double-ended construction type such as the lamp lfl illustrated in Fig. 2. As is well known, lamps ofthis character comprise briefly an envelope 42 of quartz. or the like having two oppositely-disposed sterns oranns 44, through which are sealed'suitable leadin assemblies each'having an electrode 12 and an outer terminal 46 attached, to their inner and. Qui ends respectively. Afiixed to the arms 44 are mounting collars 48 for securely and accurately orienting the lamp 10 in its position of use.

As shown by the typical voltage and current waveforms illustrated in Figs. 3a and 317, respectively, of a normally operating short-arc lamp such as that shown in Fig. 2, lamp current can only flow during each half cycle of the applied line voltage when thelatter reaches and exceeds a value equal to the re-ignition voltage 50 of the discharge. When this point on the leading por tion of the half cycle is reached current starts to flow through the lamp and continues to flow until the line voltage reaches the extinguishing point 52 during the latter part of the half cycle at which time the line voltage falls below the arc voltage and the current through the lamp stops. As shown, this'is' repeated every half cycle of the applied line voltage during normal operation so that the lamp current is somewhat pulsating in character, as illustrated in Fig. 3b, rather than perfectly sinusoidal as is the applied voltage, which voltage is indicated by the dotted line in Fig. 3a. Thus, line current can only flow through the lamp 10 or 10 during that portion of each half cycle when the applied line voltage is equal to or greater than the re-ignition and extinction voltages for the particular lamp and fill pressures involved.

It has been found that high-pressure mercury-xenon or xenon short-arc lamps of double-ended construction can be cold started within 3 seconds with from 5 to 10 pulses of approximately 12,000 volts per half cycle of applied line voltage, while lamps of the same construc tion but employing mercury alone as the ioniz'able thedium can be started with from 5 to 10 pulses of approxi mately 1,000 volts per half cycle. However, under the most adverse or hot starting condition, that is, when the lamp stops operating due to a power interruption and the lamp electrodes have cooled to a temperature well below their electron-emitting temperature whereas the lamp proper is still hot and near operating temperature and pressure, reliable starting can best be achieved with from 10 to 20 pulses of 50,000 volts (50 kv.) per half cycle.

With the single loop type high-voltage pulse starting system generally used heretofore only one series of pulses of a particular magnitude and frequency of occurrence can be obtained. While a suflicient number of pulses may readily be obtained with this type of circuit to cold start any of the aforementioned type lamps, it has proven very difficultand frequently impossible due to the criticality of the spark-gap spacing and mismatching of the circuit components to obtain the aforesaid 10 to 20 pulses of 50 kv. magnitude required to reliably hot start xenon orxenon-mercury type short-arc lamps. In most instances, the gap-spacing required to produce a voltage pulse of this magnitude with standardtype pulse starters now in use is so great that only about 3 or 4 such pulses 54 per half cycle of the applied line voltage can be obtained under practical operating conidtions (see Fig. 4a Thus, with this number of pulses only. two orpossibly three would occur during that portion .(see Fig. 3) of each half cycle of applied line voltage when line current could 'flow, as will be observed in Fig. 4a. The applied line voltage isindicated by the dotted line in .thedrawing and, as will be obvious, has been greatly exaggerated I for the purpose of illustration. In reality, the high voltage pulses 54 are many times greater in magnitude'than the applied line voltage and are superimposed thereon rather than blended therewith as here shown. However, since only a very small number of such pulses occur at the right'time of each half cycle, only a very small amount of line current will flow through the lamp during the first half cycle of applied voltage, the, amount of current gradually increasing with succeeding half Cycles as shown in Fig. 4b; The build up of the line current during the starting cycle with this 'numberof high voltage pulses is accordingly very slow, as indicated by the'slope of the broken line in Fig.'4b. While the lamp' would probably eventually start under these conditions, it is well known that if the high starting voltage -is applied to the lamp for too long a period excessive electrode material will be sputtered ofi and deposited on the bulb walls resulting in early blackening and prematurely shortening the useful life of the lamp. Itis,

accordingly, necessary that the lamp start within a predetermined period of time after the starting circuit has been energized, three seconds being the generally accepted figure to insure optimum lamp life.

In contrast, it will be observed in Fig. a that by properly selecting the various components and adjusting the spark gaps of the. oscillatory loop circuits C and D a corresponding number (four as in the case above-described) of 50 kv. pulses (pulses D in Fig. 5a) as was practically attainable heretofore may be provided and combined with a much greater number of pulses of small magnitude (pulses C in Fig. 511), as for examplefourteen pulses of approximately 20 kv. Thus, the gas between the electrodes 12 is'periodically broken down by the relatively small number of high voltage pulses D as before :but in this instance is maintained in an ionized state by the large number of relatively low-voltage pulses C thus permitting line current to flow for a much greater portion of each half cycle of the applied line voltage than heretofore. The line current, accordingly, builds up to its full value within the first two or three half cycles of applied'line voltage after the switch 26 is closed, which in time is represented by the left-hand edges of the graphs shown in Figs. 4 and 5, thereby rapidly heating the electrodes to electron-emitting temperature and providing almost instantaneous Starting.

It has been found that at least two voltage pulsesper half cycle of applied line voltage of approximately SOI kv. magnitude will reliably start the various types and sizes of short-arc lamps now being marketed under either hot or cold starting conditions, with the optimum being from about three to eight pulses within a range of approximately 30 to 50 kv., when such pulses are simultaneously applied to the lamp in accordance with the invention along with at least ten pulses of at least kv. magnitude, with the optimum number of such lower voltage pulses being from about twelve to twenty pulses within a range of approximately 10 to 30 kv. In contrast, experience has shown that in order to achieve the same degree of reliability during starting with the single loop type circuits generally used heretofore at least 10 to 20 pulses of approximately 50 kv. would be re-' quired. It will, of course, be obvious that various combinations as regards the number and magnitude of high and lower voltage pulses can be used depending on the particular lamp type involved and the starting conditions most likely to be encountered.

As will be apparent from the foregoing, the objects of the invention have been achieved by providing a starting circuit which is adapted to ignite lamps containing an. ionizable medium reliably and within a predetermined time limit, even under the most adverse starting conditions. In addition, by utilizing a plurality of oscillatory loop circuits an exceptionally versatile starting system is provided which not only obviates the criticality of adjustment and maintenance heretofore encountered with circuits having only one loop but which can supply a wide range of voltage pulses both as regards their magnitude' and frequency thereby permitting the same basic circuit to be used with the various types and sizes of I high-wattage double-ended lamps now being marketed.

variouschanges and modifications may be made without departing from thespirit and scope of the invention.

medium comprising, a first oscillating circuit comprising a transformer secondary and an electrc discharge device operable to generate a series of voltage pulses of predetermined frequency and magnitude, a'second oscillatin'g circuit comprising another transformer secondary and another electric discharge device operable'to generate a second series of voltage pulses of-predetermined frequency and magnitude, means for energizing said transformer secondaries, and means for simultaneously applying the outputs of said first and second oscillating circuits to said lamp.

2. A starting circuit for a lamp containing an ionizable medium comprising, a'tran'sformer having a primary and two secondaries, a first and second oscillating circuit each comprising one of said secondaries and an electric discharge device electrically disposed to generate a series of voltage pulses of predetermined frequency and magnitude when said transformer is energized, means for connecting said primary'to an alternating current power source, and means for simultaneously applying the outputs of said first and second oscillating circuits to said lamp.

3. A starting circuit for a lamp containing an ionizable medium comprising, first and second transformers each having a primary and secondary, each said secondary having a capacitor and an electric discharge device connected thereto electrically disposed to provide in conjunction with 'said'secondary a first and second oscillating circuit which are independently adjustable and operable, means for connecting each said primary to an alternating current power source, and means for simultaneously applying the outputs of said first and second oscillating medium comprising, first and second step-up transformers each having a primary and secondary, a pulsetransformer having two primaries and a secondary, each of the secondaries 'of said first and second step-up transformers having a capacitor in parallel and a spark-gap and one of the primaries of said pulse transformer in series therewith thereby to provide two oscillatory loop circuits which are independently adjustable and operable, and means including a switch for connecting the primaries of said first and second step-up transformers to an alternating current power source, the secondary of said pulse transformer being connected in series with said lamp and constituting a part of the circuit for normally operating said lamp after it has been lighted thereby providing means for simultaneously applying the outputs of'said oscillatory loop circuits to said lamp when said switch has been actuated and said first and second step-up transformers energized.

5. A starting and operating circuit for a lamp containing an ionizable medium comprising, conductor means for connecting said lamp to an alternating current power source, current limiting means connected in series with said lamp through said conductor means, first and second step-up transformers each having a primary and secondary, a pulse transformer having two primaries and a secondary, the secondary of said pulse transformer being connected in series with said lamp and said current limiting means through said conductor means and in conjunction therewith constituting a series circuit adapted to operate said lamp after it has been lighted, each of the secondaries of said first and second step-up transformers having a capacitor in parallel and a spark-gap and one of the primaries of said pulse transformer in series therewith thereby to provide two oscillatory loop circuits which are independently adjustable and operable, and switch means in series with the primaries of said first and second step-up transformers for connecting said primaries across the line side of said conductor means.

6. A starting and operating circuit for a high intensity lamp containing an ionizable medium comprising, conductor means for connecting said lamp to an alternating current power source, an inductive ballast connected in series with said lamp through said conductor" means, first and second iron-core step-up transformers each having a primary and secondary, a pulse transformer having two primaries and a secondary, the secondary of said pulse transformer being connected in series between said lamp and said inductive ballast and in conjunction with said conductor means constituting a series circuit for operating said lamp after it has been lighted, each of the secondaries of said first and second step-up transformers having a capacitor in parallel and a spark-gap and one of the primaries of said pulse transformer in series therewith thereby to provide two oscillatory loop circuits which are independently adjustable and operable, and means including a switch for connecting the primaries of said first and second step-up transformers across said conductor means at a point on the series operating circuit-closer to the input terminals thereof than the inductive ballast.

7. In an energizing circuit for a lamp which contains an ionizable medium, a starting circuit comprising a transformer having at least two secondaries which are electrically separate from each other, a plurality of oscillating circuits equal in number to the number of secondaries and each comprising one of said secondaries and an electric discharge device operable to generate a series of high voltage pulses, and means for energizing said transformer and simultaneously applying the outputs of said oscillating circuits to said lamp.

8. In an energizing circuit for a lamp which contains an ionizable medium, a starting circuit comprising a stepup transformer having two secondaries which are ele'ctrically separate from each other, means including a switch for connecting said step-up transformer to an alternating current power source, a pulse transformer having two primaries and a secondary which are electrically separate from each other, the secondary of said pulse transformer being connected in series with said lamp and constituting a part of the energizing circuit for operating said lamp after it has been lighted, two oscillatory loop circuits each comprising one of the secondaries of said step-up transformer and one of the primaries of said pulse transformer and an electric discharge device connected in series, each of the secondaries of said step-up transformer having a capacitor connected in parallel therewith, and means for simultaneously applying the outputs of said oscillatory loop circuits to said lamp, said electric discharge devices having breakdown characteristics such that the number and magnitude of the voltage pulses generated by one of said oscillatory loop circuitsdiifer 8 by a substantial and predetermined amount from those generated by the other loop circuit.

9. In an AC. energizing circuit for a lamp which contains an ionizable medium, a starting circuit comprising a step-up transformer having two secondaries, means for energizing said step-up transformer, a pulse transformer having two primaries and a secondary, two oscillating circuits each comprising one of the step-up transformer secondaries and one of said pulse transformer primaries and a spark-gap operable to generate a series of voltage pulsm when said step-up transformer is energized, and means including the secondary of said pulse transformer for simultaneously applying the outputs of said oscillating circuits to said lamp, the adjustment of said spark-gaps being such that one of said oscillating circuits generates at least two voltage pulses of approximately 50 kv. and the other of said oscillating circuits generates at least ten voltage pulses of at least 10 kv. during each half cycle of the voltage applied to said lamp from the energizing circuit during the starting cycle.

10. In an AC. energizing circuit for a lamp which contains an ionizable medium, a starting circuit comprising a step-up transformer having two secondaries which are electrically separate from each other, means for temporarily connecting said step-up transformer to said energizing circuit, a pulse transformer having two primaries and a secondary which are electrically separate from each other, two oscillatory loop circuits each comprising one of the secondaries of said step-up transformer and one of the primaries of said pulse transformer connected in series and a spark-gap and capacitor electrically disposed to generate in conjunction with said pulse transformer primary and step-up transformer secondary a series of voltage pulses of predetermined frequency and magnitude, and means including the secondary of said pulse transformer for simultaneously applying the outputs of said oscillatory loop circuits to said lamp, the adjustment of said spark-gaps being such that one of said oscillatory loop circuits generates from about three to eight voltage pulses within a range of approximately 30 to 50 kv. and the other of said oscillatory loop circuits generates from about twelve to twenty voltage pulses within'a range of approximately 10 to 30 kv. during each half cycle of the voltage applied to the lamp by said energizing circuit during the starting cycle.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,353 Willoughby Apr. 17, 1951 2,708,251 Rively May 10, 1955 2,723,366 Breeding Nov. 8, 1955 2,727,188 Rively Dec. 13, 1955 2,728,871 Morin Dec. 27, 1955 2,825,005 Bird Feb. 25, 1958

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