US2611885A - Fluorescent tube lighting system and apparatus - Google Patents

Description

J. H. BRIDGES Sept. 23, 1952 FLUORESCENT TUBE LIGHTING SYSTEM AND APPARATUS Filed Aug. 20. 1948 INVENTOR.

JOHN HEROLD Bmoszs H\5 ATTORNEY Patented Sept. 23, 1952 UNITED STATES PATENT OFFICE "FIJUORESCENT TUBE LIGHTING SYSTEM AND APPARATUS 361m Herold Bridges, Atlanta, Ga, 'as s'ignor ft'o National 'Inventions Corporation, .a corporation of New Jersey Application August 20,1948, Serial'No. 45,357 5 Claims. (01. 315-455) My invention relates generally to electrical lighting systems and'applicationsand more;particularly concerns a fluorescent tube lighting system and the several parts comprisin thesame. An object of my invention is to provide a fluorescent tub lighting system which is simple and inexpensive of production; which is highly efficient, economical and certain in operation, at the same time insuring 'instantstarting .of the tubes, and subsequent maintenance thereof, in certain manner under even the most adverse weather conditions; and which has a high system power-factor with low stroboscopic effect, and in which the tube currents are effectively controlled.

Another object is to provide axpower unit fora fluorescent tube lightingtsystem which is unitary and compact, involving a minimum ofspace requirements; which is comprised ofcor'nponent parts which are in themselvessimple and economical of production; and which is; sturdy and reliable in operation,"having'long useful life and involving a minimumiron'and coppercontent, at the same time giving rise :to highly efficient, reliable and economical system operation.

Yet another objectis to provide at-transformer and associated ironcorezchoke coil for use in a fluorescent tube lighting system *where .initial cost are to beat a minimum and where-space requirements are at a premium, but wherereliable and efficient operationisrequired.

Other advantages in part will be obvious and in part more fully pointed out hereinafter during the course of the following description.

Accordingly, my invention resides in :the several parts, elements and "features of construction, as well as in the combination of each of the same with one or more of the others, the-scope cfthe application of all of which will be more fully set forth in the claims at'the end of this speification. I

Throughout the several views of "the drawings, wherein I have disclosed that embodiment of my invention which I prefer atpresent, and in which like reference characters denote like parts:

Figure 1 is a schematic wiring diagram, disclosing the basic principles of 'my invention; while Figure 2 is a view, partly inperspective and partly schematic, disclosing the power unit/according to my invention a installed in a practical embodiment.

As conducive to a more thorough understanding of my invention, it maybe noted-at this-point that wide acceptance in the'arts, commerce and 2 industry, has been achieved by fluorescent tube lighting systems. The growth has been .so rapid that fluorescent tube lighting is closely approachin in incandescent lighting in popularity.

Equipment displaying better and better operating characteristics is produced, while both production and operating costs-areundergoing .constant reduction.

Savings in the amountrof copperand iron employed are constantly sought for. Reduction in the space requirements of the operating units is a constant objective. Efforts are continuously being made to reduce the cost of the power unit required and yet maintainsatisfactory operating characteristics.

An important object of my invention, therefore, is to provide a-compact, .inexpensiveand efficient-power unit-for operating apairof'fiumrescent tubes with unobjectionable stroboscopic effect, satisfactory power factor and instant startin under'the varying conditions of actual use. a l

In accordance with'the practice of my invention, I operate paired fluorescent tubes from a transformer common to both of them. LPIr'efe'rably, although not necessarily, lthis transformer has a shell-type core, and the primary and secondary windings are mounted on the centrallleg thereof, preferably but not necessarily side-byside, in autotransformer connection.

I Now, to insure good operating characteristics, with high systempower-factonl connectgthetwo fluorescent tubes in series with each other and with the transformer. iron core inductive reactance also is included in this series circuit, preferably being introduced between thesecondvary winding .ofthe transformer and the fiuorescent tube to which it is connected. lhisseries has ashore to prevent excessive current while the tubes are intheir 'conductiize' condition. I

also connecta condenser across one tubapreferably across the reactance andJthe tube to which it is immediately connected. This permits initial striking-of the .un'shunted tube followed by striking of the shuntedftube. ,Thevdltage'requirements of the transformer are only that of one tube.

In my novel construction, "the close-coupled tran'sfornier is compact'a nd inexpensive. Moreover, the inductance-likewise is compact'andinexpensive. 'Addi tionally, "I am enabled to achieve the further simplification of fOIh'lillg" the transwarm r secondarywinding and thec'hoke coil winding of the same size wire since a common current flows -th rough boith, Asubstantialegaving in manufacturing 'c'osts thus is achieved.

For a more precise understanding of my lighting system and apparatus, reference is had more particularly to the schematic embodiment illustrated in Figure 1 of the accompanying drawing wherein the transformer is indicated generally by the reference number I 0. It consists of a shell-type iron core indicated generally at H, having a central leg HA and outer legs IIB, I IC disposed parallel with and in spaced relation to the central leg II, one on each side thereof. The core is completed by end pieces IID and HE. A primary winding I2 and a secondary winding I3 are disposed on the central leg HA. Leads I4, I5 extend from the extremities of the primary I2 to a suitable source of alternating current power, indicated generally at I6.

For reasons which will be developed more particularly hereinafter, the primary and secondary windings I2 and I3 are disposed side-by-side on the central leg IIA. That is, they are not disposed in superimposed relation, one on top of the other. It will be noted that the transformer windings are close-coupled, the only flux leakage being to the air from the margins of the core. Preferably, although not necessarily, the primary and secondary windings are connected in autotransformer connection. Such connection is entirely permissible, under the regulations of the Fre Underwriters, for potential of 600 volts or less. Illustratively, the primary may be wound for 118 volts while the secondary is wound for 332 volts, giving an output potential for the autotransformer of 440 volts.

To achieve a high degree of economy, the winding I2 is constructed of wire of sufiicient diameter to carry the higher primary current, while the winding I3 is formed of wire size just sufficient to carry continuously the prevailing secondary current. For two 40 watt fluorescent tubes, this amounts to approximately 0.9 amperes. With the current-carrying capacities of the windings I2 and I3 being accurately determined, and as well, the number of turns of both primary and secondary windings being nicely selected for inducing the proper secondary voltage, the minimum copper requirement is accurately determined, and is maintained at a very low figure.

The central leg IIA of the transformer core is dimensioned to carry, just short of magnetic saturation, the maximum flux required for in ducing the required secondary voltage, while the outer members IIB, IIC, IID and HE are dimensioned as to accommodate, just short of magnetic saturation, about one-half of the maximum flux coursing the central leg I IA.

Minimum iron content is determined by maintaining the core length at the smallest possible value consistent with placing the primary and secondary windings I2 and I3 in side-by-side relation thereon, and by insuring that the spacing between outer legs HB and HG, on the one hand, from the central leg I IE on the other hand, is maintained at the smallest possible value consistent with suppression of mutual induction between the central and outer legs. That is, the pieces IID and HE are maintained at minimum length. In this manner, and by the observance of the several precautions hereinbefore recited, the greatest possible transformer efiiciency is achieved, both from an operational and practical, economical standpoint, and both the first costs and the costs of subsequent operation are brought to a theoretical minimum.

From a manufacturing standpoint, the cost is minimized since the elements of the transformer are of the greatest possible simplicity. To facilitate simplicity in manufacture, although the following does not necessarily constitute a material part of my invention, the outer legs I IB and I IC may be formed with integral end pieces I ID and HE giving a pair of generally C-shaped core pieces abutting the linear central leg HA (see Fig. 2), the several elements being tightly clamped together against chattering.

Paired fluorescent lamps I8, I9, in the present instance comprising conventional 40 watt lamps, although this is not an essential prerequisite, are connected in series with each other through leads 20 and 2|, joined together at junction 22. A current-limiting choke indicated generally at 23 is likewise connected in series with the tubes I8 and I9 by means of a lead 24 between one terminal of tube I8 and a corresponding terminal of choke coil winding 25. The ensemble consisting of the choke 23 and tubes I8 and I9 is connected to the transformer auto-connected windings I2 and I3, in part by means of lead 26 extending from tube I9 to lead I4, which it joins at junction 21, and in part by lead 28 extending from choke coil winding 25 to junction 29 with lead II as shown in Figure 1.

Novelty resides in the construction of the iron choke 23. The core thereof is of generally E- shaped configuration, having an end portion 30A and outer legs 30B and 300. These latter abut against one of the end piecesIID, HE of the transformer core II, in Figure 1 shown as comprising the end member HE. Thus the E-shaped choke core is disposed towards the transformer I0 and abuts snugly thereagainst. The central leg 30D of the choke core 23 extends towards, but terminates short of, the end member HE of the transformer core, so as to provide an included air-gap 30E which tends to suppress within certain calibrated limits the coursing f flux induced by the choke coil winding 25 within the core 30. As is evident fromconsideration of the Figure 2, the width of the transformer and choke cores are identical so that the two elements nest snugly against each other, in neat compass.

I have provided for effective starting and for effective and eificient and subsequent operation, however, through the provision of an ingenious expedient, simple in itself. That is, I insert a condenser 32 of appreciable capacity in shunted relation across the choke 23 and its associated series-connected tube I8, by means of leads 33 and 34 extending between junctions 29, 22. This condenser 32 is thus seen to be series-connected by means of lead 20 with tube I9, the unit comprising this condenser 32 and tube I9 being in turn series-connected to the transformer by means of leads I! and 25. Inspection will show that upon removal of the tube I9 from its socket the entire secondary system is de-energized, while upon removal of tube I8, it is still possible for the tube I9 to operate through the path including condenser 32, shunting out tube I8 and choke 23- The function of the choke 23 is of course to serve as a current-limiting device for the seriesconnected tubes I 8, I9, which possess negative resistance characteristics. That is, the characteristics of these tubes is that once the arc is struck, the internal resistance across the are decreases tremendously. By consequence, currents of large value tend to :course through the tubes. This would result in rapid destruction thereof unless current-limiting means are provided.

The effect of the introduction of the condenser 32 is that initially, with static conditions maintaining, the transformer potential in large measure is impressed across the condenser 32 and tube I9; Since at this instant the tubes are in their non conductive conditions and no current flows substantially the entire transformer voltageis impressed across the terminals of the tube I9. This tube: then ignites.

Immediately upon the striking of the arc in tube I9 the internal resistance of the tube falls on appreciably, so that the voltage necessary to maintain the arc already struck likewise lowers to a comparatively small value. Accordingly, substantially all of the secondary voltage with the exception of the small amount required to maintain the arc in tube I9, is impressed across the terminals of the tube I8. The ensemble of choke 23 and tube [8 now displays less resistance than does the condenser 32 because the impedance of condenser 32 assumes its normal value with the flow of current supplied tube IS. The are is there fore quickly established across tube I8, once tube 59 has been ignited.

The accompanying decrease in the internal resistance of tubes I3 and I9, would result in the flow of an excessive current, since the transformer It is of the close-coupled type, except for the choke 23. It will be noted that this choke is provided in the main secondary circuit, and is series-connected with the secondary winding I3. Therefore, it carries the same current as the secondary I3. For efiiciency, it is formed of the same wire size. Thus, an additional factor of simplicity is thereby introduced, namely, that the choke and secondary windings are wound with the same size wire. As a result thereof only two sizes of wire are required in my power unit.

The eifect of the choke is of course to induce a back magnetomotive force which develops a back electromotive force tending to buck the main secondary electromotive force, and through selfinduction, diminishing the current flow first through the tube I9 and then, after the tube I8 has struck, through tubes I8 and I9 together. To control in accurately predetermined manner the self-induction in the choke 23, I provide the air-gap 32E of calibrated dimensions in the leg MD.

The stack of laminations comprising central, short arm 30D of the choke 23 is cross-sectional- 1y dimensioned so as to carry the maximum flux which is required for proper choking action. The end-portion 30A and the outer legs- 38B and 36C have cross-sectional areas sufficient to carry approximately one-half of the flux which courses the central leg Bill). The number of turns of winding and the current flowing therethrough, which of course is the current flowing through the main secondary winding, determine the magnetomotive force generated in the leg D and hence is determinative, along with the air-gap 30E, of the choking effect of the choke 23, having given fixed cross-sectional areas of the legs 30A- SflD inclusive, as well as selected material fro-m which the choke laminations are formed.

It is preferred that the choke winding 25 be wound in the same direction or phase as the primary coil 12, so that as the primary flux courses to the right in Figure 1, along central transformer leg IIA, the secondary flux induced from the secondary winding I3, and which courses central choke leg 36D, will pass to the left in Figure 1, across included air-gap 30E, and thence will split in transformer end piece HE and pass upwardly anddownwardly to, and back across, outer legs 36B, 39C of the iron core choke 23. During the reverse half-cycle of current now, of course, the direction of coursing of both the primary flux and the choke flux will be in directions exactly opposite that just traced, as will be more fully pointed out hereinafter.

It is now in order, for precise understanding of the operation of my new system, to trace the several circuits involved. The primary circuit for a given half-cycle will be from the left side of the source of alternating current supply I6, as seen in the drawing, through lead I l, across junction 27, to the left side of the primary winding 62. The primary current then courses across pri- .mary winding I2 to the right and thence through lead I5 back to the right side of source It. For the succeeding half-cycle, the current flow of course will be in the opposite direction.

For the first-mentioned half-cycle of current flow in the primary winding, the resulting secondary potential is applied across lead -23, choke winding 25, and lead 24 to tube I8. Also, it is applied through lead 33 to condenser 32, lead 2! and tube is. Tube i9 is connected by way of lead 255, junction 2'] and lead M, to the lefthand end of the primary winding portion E2 of the auto-transformer.

The voltage difference between leads 2% and 28. however, is not sufficient to obtain the initial ignition of the tubes I8 and I9 together. Thus, open-circuit conditions maintain. Since at this point there is no current flow, full potential is applied by way of condenser 32 to the tube I9.

As soonas the tube I9 is rendered conductive, the voltage demand thereacross reduces appreciably, due to the negative resistance characteristic of the tube. Only a few volts is required to maintain the arc thereacross. Moreover, as soon as the arc is struck across tube I9, a current begins to flow. Now condenser 32 interposes a substantial quadrature reactance, so that the shunt path around tube I3 and choke 23 now displays high impedance to the passage current therethrough. Substantially full transformer potential is therefore impressed across tube I8 (since in absence of current flow in choke 23 there is no voltage drop there). The comparatively large voltage which is now impressed across tube I8 quickly strikes the arc thereacross, and current flows through lead 28, through lead 2|, junction 22, lead 20, choke 23, lead 24 to tube I8, thence through tube I9, across which the arc has already been struck, and back through lead 28, junction 2'! and lead I4 to the left-side of the primary winding I2 of the autotransformer I2-!3.

With both tubes in conductive condition, the current flow across these tubes would be excessive, up to the magnetic saturation values of the transformer core II,- unless some current-limiting means such as the choke 23 were interposed therebetween. Choke 25 admirably serves this current-limiting function, and is so calibrated as to have an impedance under load conditions somewhat less than that of the condenser 32, so as to insure that tube I8 is energized during operation; Moreover, winding 25 of choke 23 is wound in such direction as to be in phase with that of the primary winding I2. Air-gap 30E is interposed between the short, central leg 30D of the E-shaped choke core and adjacent end piece HE of the transformer core I I, so as to limit effectively the choking action of the member until current beginsto flow in tube I8.

. Now, with'the flow of current established, both tubes being ignited, and with the assumption that the secondary current flow is to the right in Figure 1, current flows through lead I! away from the secondary winding l3 to junction 29. There a small quantity of current flows across lead 33, condenser 32, lead 34, junction 22, lead 20, tube l9, and back through lead 26, junction 21, and lead [4 to the left-hide of the auto-transformer winding. The larger portion of the current, however, courses from junction 29, down lead 28, across choke winding 25, lead 24, tube l8 and lead 2| to junction 22. From thence the flow is just the same as that traced with respect to the current flowing across the condenser 32. The amount of current in lamp l9 therefore somewhat exceeds that in lamp [8. This is not objectionable, however, because I find that greater current is required in tube I9 because of the irregular wave-form introduced by the condenser, in order to give balanced illumination from the two tubes.

During the reverse half-cycle of secondary potential the tubes I9 and [8 respectively are rendered conductive as more fully discussed above. With both tubes in conductive condition, the secondary current courses up from the left side of the auto-transformer through lead l4, to junction 21, across lead 26 to tube I9 and lead 20 to junction 22. There some of the secondary current courses lead 34, condenser 32, lead 33, junction 29, and lead I! back to the right side of the auto-transformer winding. Most of the secondary current, however, courses from junction 22, down lead 2|, across tube I8, up lead 24, through choke winding 25 and lead 28, back to junction 29.

The course of the magnetic flux through choke 23, for the direction of the primary current flow first traced, is to the left across short leg 30D of the choke core, across included air-gap 30E, to the right end portion HE of the transformer core II, where it splits into two branch streams. While one such branch stream joins one portion of the main magnetic flux in core piece I IE and courses up end-piece l [B to the right side of end portion 30B and down the web portion 30A back to the central leg 30D,the other branch stream joins the other portion of the flux in the main core and courses down end piece I IE to the right across leg 30C up web 30A and to the left across central leg 30D. During the next half-cycle of secondary current flow the direction of coursing of the induced flux is just the reverse of that just traced.

Since the choke Winding 25 carries the same current as the secondary winding l3, they are wound of the same size wire. The physical dimensions of the choke core are so selected as to be at a minimum consistent with proper physical location of the choke winding 25. Thus the amount of iron employed is at a minimum.

It is my desire to provide a power unit comprising the transformer, choke and condenser of minimum compass, and to correlate the outer dimensions of these three component elements so that they nest snugly against each other in endto-end abutting relationship, as can be more closely observed from consideration of the dis closure of Figure 2. It will be seen that the transformer, the yoke of the choke and the condenser have substantially the same transverse cross-section. The three elements are disposed in minimum compass, and provide a snug, compact and unitary construction. In overall size, my power unit, including case and compound, is somewhat more compact than the currently used ballast."

Consequently, it readily may replace the ballast. and its necessary starter, in a lighting fixture.

In the practice according to my new system, the transformer 10 is most compact, and is rendered highly efiicient because of the direct coupling between the primary and secondary windings. In point of fact, I have found in practice that the coupling is so close that in order to limit the size and hence cost of the choke which will effectively limit the secondary current flow, it is desirable not to position the primary and secondary winding one on top of the other, but to dispose them side-by-side so as to permit a certain amount of leakage from the shell-type core. This provides an additional limiting factor or control, over and above that interposed by the choke and condenser.

Oscillographic study discloses that highly symmetrical and advantageous wave form is achieved. Without intending to be limited thereby, I attribute this to the fact that the choke core is in series-connection with both tubes. The iron content of the transformer choke is reduced to a minimum, as has already been pointed out hereinbefore. The number of different component parts is likewise reduced to a minimum, and these are of the simplest possible configuration. Only two sizes of copper wire are required, and the copper content itself is reduced to a minimum. Illustratively, the iron core transformer is approximately three by five inches in dimension, and the iron core choke is correspondingly small.

While it is true that the condenser 32 is somewhat larger than is ordinarily used, it is not prohibitively large. Illustratively, where the condenser ordinarily used for power-factor regulation in a fluorescent tube lighting system operating two 40 watt tubes might be in the neighborhood of 1.85 microfarads capacity, the condenser 32 as employed in my new assembly is of say 2.00 microfarads capacity. Good powerfactor thereby is had in addition to substantial freedom from stroboscopic effect.

Since it is apparent that once the broad aspects of my invention are disclosed, many embodiments thereof will readily suggest themselves to those skilled in the art, I intend the foregoing to be construed as merely illustrative, and not in a limiting sense.

I claim:

1. A fluorescent gaseous discharge tube lighting system comprising a source of alternating current electrical energy of predetermined frequency, an auto-transformer having a shell-type core with central leg upon which primary and secondary windings are disposed in side-by-side relation and connected together in series and with the primary winding thereof connected to said source, a pair of series-connected fluorescent gaseous discharge tubes, an iron core reactor disposed in abutting relation on one end of said transformer core with the winding on said reactor connected at one end to the transformer secondary winding and at the other end connected to one end of said series-connected fluorescent tubes, and a condenser shunted across said reactor and one only of said tubes, said other end of said fluorescent tubes being connected to the primary winding, and the reactor and transformer secondary winding being formed of the same size Wire. I

2. A fluorescent gaseous discharge the lighting system comprising a source of alternating current electrical energy of predetermined frequency, an auto-transformer having a shell-type core with central leg upon which primary and secondary windings are disposed in side-by-side relation and connected together in series and with the primary winding thereof connected to said source, a pair of series-connected fluorescent gaseous discharge tubes, an iron core reactor of shell-type construction disposed in abutting relation to said transformer core with central leg thereof providing an air-gap to said core and with the winding on said reactor connected at one end to one end of the transformer secondary winding and at the other end to said fluorescent tubes, and a condenser shunted across said reactor and associated tube, said other end of said fluorescent tubes being connected to said primary winding, the reactor winding and primary being wound in the same direction or phase.

3. A power unit for a fluorescent tube lighting system, comprising a transformer having primary and secondary windings mounted on an iron core and connected together in series, a choke coil having an iron core disposed at one end of said transformer core, a condenser disposed snugly against a free end of the unit comprised of the transformer and choke cores, and means connecting together one end of each of said transformer secondary, choke coil and condenser.

4. A power unit for a fluorescent tube lighting system, comprising a transformer having a shelltype core with auto-transformer-connected primary and secondary windings positioned on the central leg thereof, a choke coil having an E-shaped iron core disposed at one end of said transformer core with the outer legs of the E-core abutting against the transformer and the central leg extending towards but terminating short of said transformer core to povide an included airgap, and a condenser disposed snugly against a free end of the unit comprised of the transformer and choke cores, one end of each of said transformer, choke and condenser being electricallyconnected together, and with the other ends of said transformer, choke and condenser adapted to be connected to fluorescent tubes.

5. In a power unit, the combination of a transformer having a shell-type core and primary and secondary windings disposed side-by-side in auto-transformer connection on the central leg thereof, and a choke coil having an E-shaped core with the outer legs directed towards and abutting against one end of said transformer core and with its central leg extending towards but terminating short of said end to provide an air-gap, said choke coil being of the same wire size as said secondary winding and connected in series therewith and wound in the same electrical direction as said primary.

J OHN HEROLD BRIDGES.

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

UNITED STATES PATENTS Number Name Date 2,056,661 Foulke Oct. 6, 1936 2,301,671 Abadie Nov. 10, 1942 2,305,153 Fries Dec. 15, 1942 2,312,867 Boucher Mar. 2, 1943 2,418,160 Campbell Apr. 1, 1947 2436,399 Nathanson Feb. 24, 1948 2,496,981 Boucher et al. Feb. '7, 1950

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