US2461029A - Luminescent tube system and apparatus - Google Patents

Description

F6118 1949- c, P. Bouc-HER ETAL 2,461,029v

LUMINESCENT TUBE-SYSTEM AND APPARATUS Original Filed July 14, 1941 2 Sheets-Sheet 1 Feb. 8, 1949. c. P. BOUCHER ETAL 2,461,029

LUMINESCENT TUBE SYSTEM AND APPARATUS Original Filed July 14, 1941 2 Sheets-Sheet 2 Patented Feb. 8, 1949 LUMINESCENT TUBE SYSTEM AND APPARATUS Charles Philippe Boucher, Fostoria, Ohio, and

Frederick August Kuhl, Ridgewood, N. J., assignors, by mesne assignments, to National Inventions Corporation, a corporation o! New Jersey original application July 14, 1941, semi No. 402,410. Divided and this application April 12, 1943, serai No. 482,892

6 Claims. (Cl. 171-119) Our application for United States Letters Patent is a division of our copending application Serial No. 402,410, led July 14, 1941, entitled Luminescent tube system and apparatus now U. S. Letters Patent 2,352,073 of June 20, 1944 and the invention relates to fluorescent tube lighting, and more particularly concerns a new autotransformer for use in uorescent tube illumination, as well as a new system for fluorescent tube lighting.

An object or our invention therefore, is to produce anew autotransformer capable of energizing twin loads, and serving upon energization of one said loads to provide additional potential across the other load for ensuring prompt energization of the latter.

Another object is to produce a new electrical system for fluorescent tube lighting, which is simple, durable, reliable, involves low cost of fixture manufacture, and low operating costs, and which is characterized by its quick and reliable starting characteristics even in cold weather, its good voltage regulation, the low power demand of the system, and the long life of the tubes, which lighting system has a long durationv of light emission during each half-cycle of current supply, and which is capable of operating satisfactorily when desired, at light emissions lower than lthe rated light emission o! the tube.

Still another object is to produce a fluorescent tube lighting unit employing simple, sturdy and dependable means for energizing the tubes, which system employs a transformer for supplying the required system potential, which transformer serves both to restrict the current through the system within safe limits and to supply suilicient potential to ensure proper starting and operationk oi the tubes. l

Other objects and advantages in part will be obvious, and in part will be pointed out hereinafter in connection with the following descrip-- tion.

Our invention accordingly resides in the several elements, features of construction, and operational steps, and inthe relation of each of the same to one or more of the others, all as de-v scribed herein, the scope ofthe application oi which is indicated in the claims at the end of this speciiication.

In the drawings:

Figures 1 and 3 are front and end elevations, respectively. of a preferred embodiment of our invention, the associated electrical circuits being illustrated schematically.

I sion of our invention, attention may here be di Figure 2 is a view similar to Figure 1 but illustrating another embodiment of our invention.

Figure 4 is a graph depicting certain important features of our invention, while Figure 5 illustures an application of our invention to a load consisting of but a single fluorescent tube.

As conducive to a more thorough comprehenrected to the present state of the art, and consideration given to the many advantages resulting from the introduction of fluorescent tube lighting, as well as the disadvantages attendant thereupon.

In recent years iluorescent tube lighting has come into. greater and greater use, and in many instances has in large measure replaced the more conventional incandescent lamps as sources of illumination. Many factors contribute to the wide-spread acceptance of these tube systems. For example, within wide iimits these sources may be produced in a variety of light emission ratings. They may be varied considerably as to predominant color of the light output, the practical importance oi which feature may be ap- Dreciated when it is considered that but one single predominant color is available directly from an incandescent light source. The light eiiiciency on the basis of wattage input is much greater than with incandescent lighting, so that in many instances a single tube of a 15 watt rating for example, will produce the desired light output. To illustrate the important advantages flowing from this feature, it may be noted that a typical gasoline lling station requires between 3000-4000 watt output for evening illumination, where ordinary incandescent lighting is resorted to. This makes the monthly lighting costs, depending somewhat upon the local rate tariis, range between zem-$65. Replacing the old-style'incandescent systems by the new fluorescent lamp system results in a power demand of only about 2000 watts for the same quantity of illumination of more pleasing color at a monthly tariil' of from $18 to $20. Briefly stated, the system is admirably suited for ilood light operation, at a watt input of only 50-60 per cent of that required for comparable results where incandescent lighting is employed. Additionally, uorescent tube lighting is found to be more penetrating, and because of its larger area of source, is less brilliant, and gives a more even distribution of light. Two or three tubes in parallel is foun to result in excellent ilood lighting. f

The tubes are guaranteed for 2500 hours, and

et hence have an ensured life span of about 2V,

times that of fllamentary lamps. Because the tubes run cooler, detrimental heating is avoided. Their higher eillciency, and the many practical advantag of such uorescent tube systems, have caused the arts and sciences, ordinarily so hesitant in adopting `new ideas, to endorseopenly the new system.

Nevertheless, in the practical operation of such system, several problems have arisen, so that considerable development work still confronts the art. To illustrate, it may be noted that for many reasons, the present-day practice is to employ iluorescent tubes having coated illamentary cathodes at each terminal, and to rely upon electrons emitted from such coating for supplying, in large measure, the electrons which ionize the gas filling of the tube, and thus to produce the arc-carrying medium. Usually such filling consists of a smalldrop of mercury together with a small amount of argon gas to serve to initiate and support discharge until the mercury vaporizes. However, as is true of the operation of all arc-discharge devices, some current-limiting means must be provided to prevent the flow of excessive current with consequent danger of burning out either the tube or the auxiliary apparatus, associated therewith. These auxiliary apparatus are usually known simply as auxiliaries.

Additionally, such systems require a starting switch for starting the flow of current through the i'llamentary cathodes in a metallic series circuit, and to break said circuit in the portion thereof between said filaments after the filaments have reached rated temperature, whereupon in the ordinary course of events, an arc is struck between the spaced laments. The so-called ballasts (part of the auxiliaries) comprise ordinary iron-core inductive reactors, which of course function best with a large iron content. The switches, which preferably are associated with l small capacitators for suppressing radio disturbance,.are conventionally of the thermal, magnetic relay, or glow discharge type.

While such systems are in large measure satisfactory, there are certain defects inherent therein. Among these may be cited the fact that a separate ballast must be employed for each tube. When it is considered that these tubes frequently are operated in banks or batteries of two or more tubes, it will be seen that the costs of such ballasts mount quickly. Additionally, a separate starting switch must be employed for each tube. Thus, while these switch and ballast auxiliaries may individually be of comparatively low cost, the total costs of al1 auxiliary equipment required in a complete lighting system may quickly mount up to an appreciable sum. Additionally, the use` of so many: auxiliaries increases the complexity of the fixtures for receiving the lamps and auxiliaries, increases the cost of producing them, and

. adds to the complexity of installing them. In

this ccnnection'it should be noted that if for anyreason the tube system cannot be operated on available service lines, so that transformer equipment is required, such transformer will be apart from and in addition to the conventional auxiliaries, and therefore represents an additional item of cost. The starting switches referred to have the defect in common that they succeed in starting the associated tube only after a time interval of from six to seven seconds or more, following connection across the service mains. This is true particularly of the inexpensive thermal type of switch. The magnetic relay switch is slightly faster in its operation, while the glow the tube during its cperation, the ommission of electrons from that lament will diminish during the continued energization of the lamp, so that rectier action may quite possibly be set up, resulting in overheating of the system with probably failure of one of the auxiliaries, usually the switch.

Accordingly, an important object of our invention is to avoid the afore-mentioned defects, and to produce a fluorescent tube lighting system characterized by its simplicity, its sturdiness, the small number of parts involved, the elimination of the use of the conventional auxiliaries, `and which system is noteworthy because of its quick starting characteristics by the steady operation of the tubes throughout their entire useful life, and by the fact that the power unit associated therewith can readily be mounted as a unit directly on the fixture forming part of the lamp unit.

It frequently is found necessary to employ the fluorescent tubes in batteries or banks of two or more tubes, to produce concentration of light, to achieve a source of suflicient brilliance. In such cases, the usual practice is to operate the tubes in parallel across the current supply, and to provide a starting compensator in series with one of the lamps for functioning while the lamp is starting. This is required to ensure that sufficient voltage maintains to produce adequate heating of the coiled filaments of the tube. A further andv additional piece of auxiliary equipment is thus seen to be required, representing an additional item of cost. Additionally, starting difliculties are encountered when these tubes approach the end of their life, due to the fact that ageing is evidenced by consumption of the greater part of the electron-omitting coating on the filaments.V

Thus, when this coating is nearly exhausted, then when the starting switch is opened and momentary high voltage surge occurs, there are not present sufficient free electrons to bombard the gas filling to establish the arc.

A further object of our invention, therefore, is to remove these afore-mentioned difficulties and disadvantages, and to produce a iluorescent tube illumination system capable of operation at voltages within safe practical limits, which presents no serious starting problems at any stage during the useful life of the tubes, and which system can be started without resort to starting compensators.

Not only are the systems at present in use slow in starting, but delay is encountered in restarting in those cases where a thermal switch is employed, because the heater for such thermal switch remains in circuit during the energization of the tube, and upon interruption of the tube circut, may have such residual heat that an appreciable time is required for the heater to cool suiiiciently to permit the bi-metallic switchV element again to close its circuit. Comparatively poor voltage regulation follows as an incident to the comparatively small iron content offthe ba!- last reactors. A large quantity of power is lost in the auxiliaries employed, a disadvantage which is emphasized when transformer apparatus is also required, since as already pointed out, these ordinary transformers do not serve as current limiters.

Thus a further object of our invention is to produce a fluorescent lighting unit which is free from the ldefects just set forth, and which unit requires a minimum expenditure of power other than across the tube, which has extremely rapid action both in initially striking and in restriking the arc, and which has good voltage regulation.

With the known low-voltage units experience has shown that it is necessary that the temperature of the surrounding atmosphere be maintained within certain definite limitations to ensure satisfactory arcing conditions. For example, these tubes cannot be operated where the surrounding temperature is much below 45 F. Additionally, under-voltage impressed across the tubes lowers the. electron emission to such an extent that -difficulty is encountered in starting, while if the arc is already established, it becomes unstable in its operation. For example, a reduca fluorescent tube system having long life, and

which gives rise to a comparatively stable arc even during operation under external low temperature conditions.

Lastly, these known tube systems, operating at or about service voltages, have only a comparatively short period of light emission during each half cycle of current supply, and cannot be operated satisfactorily at any appreciably lower luminosities than that for which the tube is rated. The arcs across the tubes strike at about the same point on the up slope of the wave form on the voltage half-cycle as that point on the down slope of the wave at which the tube extinguishes, and since these points are comparatively close to the peak of the half-cycle voltage wave form, then -it follows that, if attempt is made to decrease the voltage, thus lowering the amplitude of the wave form, the peak of the wave form will fallsc close to the striking point that the arc either cannot be struck, or if struck, cannot be maintained. An importantfeature of our invention, therefore, is to produce a fluorescent tube lighting system capable of efficient operation at both heated lighting emission and on dimmer operation.

Our new system may be considered as comprising primarily of a new autotransformer adapted for its particular purpose and its associated tube system. Turning now more particularly to the autotransformer shown in Figures i and 3, the

transformer core, rectangular in shape, comprises a central leg I0 extending lengthwise thereof, outer core legs Ii and i2 disposed in spaced parallel relation to said central leg and end pieces I3, I3 and i4, I4 serving to close the outer legs on the central. leg near their respective ends. Mid core portions MI and M2 close the outer legs II and I2 respectively in magnetic circuit on the central leg I0 at approximately the center of the core. These core portions MI and M2 separate the core into two groups of magnetic flux paths. In the rst of these groups a magnetic circuit may be traced from the mid point of leg I0, up through MI. through outer leg II, and piece Il and back to MI. `Also in this first group of magnetic circuits a like path may be traced from the mid point 'of leg I0 down through M2, through leg I2, up through end piece I4 and back to M2.

There are also two basic magnetic circuits estabdesigned especially for such use.

lished on the left of mid'core portions MI and M2, the first of these circuits being traced from a point at approximately the center of core portion I0, upwardly through mid core portion MI across outer leg II, downwardly through end piece I3 and back to MI. Similarly a like path may be traced from the mid point of leg I0 down through the mid core portion M2, across outer leg I2, upwardly through end piece I3 and back to M2. As will be described in greater detail hereinafter each magnetic circuit in group I or group 2 is associated with primary and secondary coils positioned on the transformer core. The manner in which the magnetic flux courses these windings will be developed during the progress of the description which follows hereinafter.-

Turning now to the second traced group of magnetic flux paths, primary coil P2 and extension coil E2 are mounted about central leg I0 in the first space adjacent core portions MI and M2, while secondary coil S2 is mounted in the second space enclosed by the second described group of magnetic flux paths.

Tubes TI and T2 are provided, respectively associated and in circuit with secondary coils Sl, S2. rIVhese tubes are of the uorescent gas discharge type. Since in accordance with the practice of our invention, we operate these tubes at higher voltages than has hitherto been the practice, with cold cathode operation, we can employ cold cathode tubes having solid electrodes, and An alternative expedient is to employ the conventional hot cathode tube, short-circuiting the illamentary terininals thereof to adapt it for cold cathode operation. This alternative expedient is preferable, inasmuch as such cold cathode tubes usually have to be made up on special order.

Extension coils El, E2 are 4associated in autotransformer connection across the primary coils PI, P2. The purpose of these extensions EI,E2 may be readily demonstrated. A condenser must be selected of suicient capacity to bring 'to approximate power-factor balance, the energizing current of the inductive load on the system. Because of its symmetrical location, this condenser has no effect on the system other than its control on the power-factor. While the use of such power-factor condenser is desirable, it may be omitted where system powerffactor may be disregarded. It is also feasible to omit the extensions entirely, and to place the condenser directly in the primary coil, although by so doing, it will be necessary to increase materially the capacity and size, and hence iirst cost of the condenser employed.

The outer legs il, i2 and core portions MI, M2 cooperate with the end pieces i3, i3 and i4, i4 respectively, to provide elongated openings or spaces about the central leg iii. Disposed in the spaces thus provided are the primary coils and secondary coils to be described hereinafter, one primary and one secondary coil being mounted in each space. The primary and secondary coils about each flux path are separated by intermediate magnetic shunts extending from the outer legs, through said space, towards but just short of the central leg I0. They thus provide between opposed surfaces of the ends of the shunts and the central legs, air-gaps of high reluctance, calibrated according to the particular loads for which the transformer is designed. Thus, in the group of magnetic flux paths first traced, intermediate shunts Shi, Sh2', extending respectively from outer legs II, I2, toward the central leg In,

provide between them calibrated air-gaps GI G2. Similarly, in the second traced group of magnetic circuits, intermediate shunts Sh3, Sh4, are provided extending, respectively, from outer legs II and I2 towards but just short of central leg Ill.

Conflning our attention rst to the first-traced group of parallel paths, we provide a primary coil PI in the first space therein, adjacent core portions MI, M2. Assuming now, as will be more fully pointed out hereinafter, that the system with which the transformer is associated is provided with a condenser I5 for improving the system power factor, we provide an extension coil EI associated with primary coil PI, and also mounted about central leg I0 in said `iirst space. As a possible alternative, the coil EI is wound on top of coil PI A secondary coil SI is mounted about central leg I0, in the other space in the parallel flux path undei discussion.

It is interesting at this time to trace the primary circuit through the source of energy I8, keeping in mind that the primary coils are connected in series-opposed relationship. Assuming that for a given half-cycle, the current flows to the right from the source I6, then it will be seen that the current iiows through conductor I1,

terminal I8, to the right through primary coil FI, terminal I9, lead 20, terminal 2 I primary coil P2, terminal 22, lead 23, lead 24, back to the lefthand side of source I6. Of course, during the next half-cycle the direction of iiow of current will be reversed.

As has been stated, extension coils EI, E2 serve to energize capacitator I5. These extension coils are connected in autotransformer connection across primary coils PI, P2, and are brought to their high terminal voltage by virtue of their inductive relationship with primary coils PI, P2. The condenser circuit for,a given half-cycle may be traced as follows: From right-hand side of condenser I5 in Figure 1, through conductor 25, left-hand terminal 26 of extension coil EI, through extension coil EI, right-hand terminal 21, lead 28,1eft-hand terminal 29, through extension coil E2, right-hand terminal 30, lead 3l conductor I1, terminal I8, thence through primary coil PI, terminal I9, lead 20, electrodel 2I, thence through primary coil P2, electrode 22, lead 23, lead 24, and lead 3|, back to the left-hand side of condenser I5. During the next subsequent voltage half-cycle, the direction of momentary current flow will be reversed. During each halfcycle, however, a charge is impressed on the condenser I5 with leading current, thus serving to balance the conductive load to be described hereinafter.

Each secondary coil SI, S2 is connected in a seperate electrical circuit in adding relation, first with the primary coil of the opposite magnetic path, and then with the primary coil with which it is in direct electro-magnetic circuit. Tubes forming the respective loads for these secondary coils are in direct series-circuit with their corresponding secondaryv coils- For example, for any given half-wave of charging current, a circuit may be `traced from secondary coil SI, right-hand terminal 32, lead 33, terminal 34, tube TI, terminal 35, lead 36, lead 23, terminal 22, through primary coil P2, terminal 2 I, lead 20, terminal I9, through primary coil PI, terminal I 8, lead 3|, and left-hand terminal 31, back to secondary coil SI. During the next halfcycle the direction of current flow through the traced circuit will be reversed.

A similar circuit may be traced for secondary coil 32. Starting with left-hand terminal 38, current passes through conductor 39, terminal 40, tube T2, terminal 4I, conductor 42, conductor I1, terminal I8, through primary coil PI, terminal I9, lead 20, terminal 2l, primary coil P2, terminal 22, lead 23, conductor 36 and back through righthand terminal 43 to secondary coil S2.

The tubes employed in our system may be of generally conventional design, having spaced and opposed electrodes for maintaining an arc discharge therebetween, and having a small amount of mercury and a lling of some starting gas such as argon or the like. However, as is conventional with such tubes, the general design is such that the greatest emission from the mercury isK operation of such arc discharge devices, someA current limiting means must be provided. Otherwise the current demand will grow out of all proportion, and either the arc discharge device itself or the equipment in circuit therewith will be destroyed due to overheating. Hitherto, some sort of current limiting ballast means, over and above the current supply source, was required to limit the current through said arc discharge within safe bounds. These ballasts, as they are known to the art, constitute a source of Waste energy, and tend towards a lowering of the system eiliciency. Our new system provided for current limitation in the arc load by means pf the transformer action itself, thus bringing about a ma-l terlal decrease in energy loss, and an attendant rise in system emciency. This important new action may be attributed to the high leakage reactance in our new transformer.

An understanding of this very important feature can best be had by tracing the electro-magnetic circuit in the transformer itself. We will assume that the momentary direction of current ow is such that the primary coils develop ux inthe parallel magnetic paths, coursing in the directions shown by the arrows. Thus directing attention for the moment to' primary coil PI, flux courses as a single stream towardthe left along central leg I0. When it reaches the mid portion of the transformer core it bucks the stream of ux in the opposite direction from primary coil P2. The flux from primary coil PI therefore splits into two stream's, and since the two halves of each parallel flux path are symmetrical and of the same physical and magnetic characteristics, these two streams are substantially equal. Now, since the ux seeks the path of least reluctance, and since no current as yet ilows through secondary coil SI, since the arc in tube TI has not yet struck, and consequently no back magnetomotive force has been generated in the associated secondary coil SI', the streams of ux shun the high reluctance magnetic shunts ShI, Sh2, and flowing thru end pieces I4, I4 fromV opposite directions, meet at central leg I0, there reuniting, the stream of flux courses central leg I0 to the left, interlinking secondary coil SI and building up an induced voltage therein. The

. pleting the magneticpath.

ning the shunt paths Sh, SM, of high reluctance,

and course through end piece I3, I3 from opposite directions. The two streams re-uniting at central leg I0, the flux courses through this leg to the right in Figure 1, back to primary coil P2, thus completing the magnetic circuit. The iiux coursing through secondary coil S2 induces a voltage therein which is impressed across the tube T2, in a manner pointed out hereinafter. During the next half-cycle of current flow, of

As soon as T2 and TI both strike, steady current ilow conditions maintain, and the bodies of iiux from primary coils PI and P2 choose the paths of least reluctance. Only enough flux courses the two secondary coils to induce the voltage required to maintain the arcs across tubes TI, T2. The main bodies oi' ilux are shunted around the shunt path containing the air-gaps GI-G4, which paths are now at least reluctance. Flux from primary coil PI for example, may be assumed to ilow to the left in central leg I0 during a given half-cycle of current ilow.' Splitting into two substantial streams when confronted bythe flux from primary coil P2 which courses in the opposite direction, one stream of flux from primary coil PI courses upwardly through core portion M I, to the right through leg II, down through shunt Shi,

course, the direction of coursing of ilux is re- I versed.

While tubes TI and T2 are supposedly of the same physical and electrical characteristics, small variance or deviations from the normal almost invariably occur. As a result of such variations, one tube is usually found to have slightly less vimpedance than the other, so that as the voltage thereacross from its corresponding secondary coil builds up toward its peak value,'the gas therein is brought to such a degree of excitation that an arc is struck across that tube, while .the other tube remains inactive. Let us assume for purposes of discussion that it is the tube T2 which, being oi lower impedance, is the one in which the arc strikes first. Immediately, a back magnetomotive force is induced by the flow of current in the associated secondary coil S2, this back mmf. opposing the main body oi ux from primary coil P2. Thus, the magnetic path through the ends oi legs I I and I2 and end pieces I3, which prior to energization of tube T2 was of low reluctance, now becomes a path of extremely high reluctance. The main body of ilux of course seeks the path of least reluctance, and accordingly, no longer flows through the path interlinking secondary coil S2. Inasmuch as the shunts Sh3, SM, and their associated air-gaps G3, G4, now have a reluctance which is less than that of the path through secondary coil S2, some part of the primary flux from primary coil P2 is shunted through these elements and courses back to the primary coll. Primary flux ows through the secondary coil path only in such amount as to induce in secondary coil S2 a voltage suicient to maintain the arc across tube T2.

Since current traverses secondary coil S2 upon and following the striking of tube T2, and since both primary coils PI and P2 are electrically in series with that secondary coil, the same current circulates through these two primary coils.

Accordingly, the current flowing through coil PI from S2, adds to the current in PI coming directly from source I6. When it is recalled that the magnetomotive force set up by a coil is a function of current and number of turns, it will be seen that as soon as tube T2 strikes, the quantity of flux linking primary coil PI-and secondary coil SI is increased by the additional current in PI coming from secondary coil S2. The-increased ilux linking secondary coil SI builds up the voltage therein so rapidly that the tube TI strikes substantially simultaneously'with tube T2.

across air-gap GI. The other stream of ilux from primary coil P2 flows downwardly through core portion M2, through the right along leg I2, up through shunt Sh2, across air-gap G2, to central leg I0. The two streams of flux there reuniting, a single flux stream courses back to primary coil PI.

Simultaneously, the flux from primary coil P2 splits into two parallel streams, one of which courses upwardly through core portion MI, to the left across leg I I, down through shunt SM, across air-gap G3 and back through central leg I0 to the right, to the primary coil P2. The other flux stream courses down through core portion M2, to the left across leg I2, up through shunt SM, across air-gap G4, and back to the right along leg I0 to the primary coil P2. In the next subsequent half-cycle of current flow the path which the flux traverses is reversed. During this halicycle the flux courses to the right along leg I0 from primary coil PI. Only so much ilux links secondary coil SI as is required to maintain the arc across the tube TI. The stream of flux which does traverse secondary coil Si splits at the end pieces Il, and approximately half thereof courses upwardly to the left along leg I I, while the other stream courses downwardly along leg I2. By far the larger stream of the flux splits on. just to the right of the primary coil, and one part courses upwardly across air-gap GI and shunt Shi to leg II, where it re-unites with the flux coursing through leg II from secondary coil SI. Flowing to the left across leg I I, this stream of iiux courses down through core portion MI to leg I0 and back to primary coil PI. Similarly, the other stream of this ux traverses air-gap G2 and ilows downwardly through shunts Sh2, and re-uniting at leg I2 with the flux coursing the leg from secondary coil SI, passes as a single stream to the left along leg i2 to core portion M2 and thence through leg III, back to the primary coil PI.

At the same time, ux passes to the left through leg I Il from primary coil P2. A small amount of the ux, sufficient to induce in secondary coil S2 a voltage high enough to maintain the arc across tube T2, links secondary coil S2, and splitting at end .pieces I3, I3, courses back, one stream to the right along leg II to core position MI and leg I0 to primary coil P2, and the other stream to the right along leg I2 to core position M2 and thence through leg IU to the primary coil P2. The major part of the iiux however, splits jus't short of the secondary coil S2, and courses in two streams, one stream across air-gap G3, up through shunt Sh3, to the right along leg I I, down through core position MI', and back through leg I0 to primary coil P2. The other stream courses down across airgap Gl, through shunt SM, to the right along leg 1l I2, up through core position M2, and back through leg In to`l primary coil P2.

It is of course to be understood that extension coils EI, E2 are in the nature of a second autotransformer and are in connection with primary coils sections PI, P2. Thus they build up a counter-magnetomotive force when a current flows in condenser I5, in a manner similar to that described with reference to secondary coils SI, S2 when they become energized. To a certain extent, therefore, these extension coils EI, E2 serve to oppose the flow of the principal bodies of ilux through central leg I 0. Their location so close to their respective primary coils PI, P2, however, in the absence of neighboring and advantageously disposed leakage paths, prevents their exerting any undue influence on the passage of ux.

It has been stated hereinbefore that a tube operated according to our new system has a greater luminous efficiency for rated power input than does the conventional hot cathode fluorescent tube when operated under its usual operating conditions. The validity of this assertion can readily be demonstrated having reference to Figure 4. Therein, the sine wave -ACB represents the curve of a half-cycle of supply voltage for energizing the ordinary hot cathode tube from a 220 volt service. Similarly, curve ACB, is a corresponding curve of the wave form of the 660 volt secondary for energizing a tube according to our present invention. With the h ot cathode tube prepared for striking by the warming effect of its incandescent electrodes, thus exciting the molecules of gas therein and vaporizing the mercury, and by the flow of electrons emitted from said electrodes, the arc is caused to strike at a point D along the wave ACB. This point D is earlier in the voltage half-cycle than is the point D at which the tube operating according to our invention strikes. According to our new invention it will be seen, however, that the tube operating on the wave form ACB extinguishes at the point E, which is a point considerably earlier in the voltage half-cycle than is the point E in the voltage half-cycle ACB for our new system. Thus, although in the conventional operation the arc strikes earlier than it does in our case, it extintinguishes much sooner, so that the total portion of the voltage half-cycle during which the arc remains struck is greater according to our new practice than is true of the prior art systems. Thus it will be seen that not only does the light emission endure longer during each half-cycle according to our new system. but that as well, the quantity of light for rated power input is materially greater. f i

Consideration of the curve according to Figure 4 will show that a further very important advantage residing in our invention flows from the use of the higher voltages. It may be stated at thispoint that Ithe use of higher voltages has hitherto been avoided by the workers in this art simply because those workers failed to appreciate the advantages which could be achieved upon the use of such high voltages. It is impossible with these known low voltage tube systems to produce a dimming action such as is desirable for night display in store windows or storerooms, or for decreased illumination in the household.

Such dimming action is quite possible, however, With our new construction, as can be demonstrated from Figure 4. Dimming is brought about simply by decreasing the supply voltage as by shifting to a new service, by connecting the secondary coils of the transformer along a smaller number of turns of the primary coils (decreasing the transformer ratio), or by inserting a voltage-consuming impedance in circuit with the tubes. Such a decreased voltage is shown at C" or the curve AC"B, illustrated in dotted lines. The signicant feature about this curve is that the point C" is substantially above the point D" at which the arc can be struck. Thus striking of the arc is ensured. Dimming action is brought about now due to the fact that in the wave form AF"D"E"GB, the total light emission F"D"E"G" is substantially reduced from the oase previously discussed, and additionally, the fraction F"G of each half-cycle during which the arc remains ignited is appreciably less than in the case previously discussed. Desired dimming action follows as a matter of course.

For example, with a mean effective secondary voltage of 660 volts from a 118 volt service, the peak voltage in each voltage half-cycle will be found to be about 900 volts. So long as this peak ranges from 660 volts or up, however, the

tubes in our system will strike and remain energized with stable arc discharge.

The system according to Figure 2 differs from that of Figure 1 primarily in that the condenser for power-factor regulation purposes is omitted, and with it the extension coils El, E2 of the primary winding, and that while in that embodiment the primary coils were connected series-opposed they are here connected, for illustration, in parallel-opposed relation. With these differences in mind, it will be seen that just as in Figure l, the transformer consists of acentral leg I0, outer legs II and I2 disposed in parallel-spaced relation on opposite sides of central leg I0, providing for the same functions as in the construction according to Figure 1, and end pieces I3, I3 and I4, I 4 together with mid core portions MI, M2. Similar to the construction shown in Figure 1, elongated spaces arev provided between central leg I0 and the outer legs II, I2, respectively, on each side of mid core portions MI, M2,

' which spaces receive the associated primary and secondary coils. In magnetic circuit with each other in that group of parallel magnetic paths extending to the left of core portions MI, M2 are primary coil P2 and secondary coil S2, while disposed in magnetic circuit in the group of parallel flux paths extending to the right of core portions MI, M2 are the primary coil PI and secondary coil SI. In each instance the coils are wound about central leg I0 in the elongated spaces -previously referred to, while the primary coils are each disposed more closely adjacent to core portions MI, M2 the secondary coils being disposed adjacent end,pieces I3, I3 and I3, I4 respectively. Still following the construction according to Figure 1, intermediate shunts of high reluctance are provided between the primary and secondary coils. Thus shunts Shi and ShLextend respectively from leg II and I2 towards but just short of central leg I0, between primary coil PI and secondary coil SI, providing air-gaps GI, G2, of calibrated high reluctance. Similarly, high reluctance intermediate shunts Sh3 and SM, disposed between primary coil P2 and secondary coil S2, extend from outer legs II and I2 respectively, towards but short of central leg I0, providing therebetween air-gaps G3, G4 of high reluctance calibrated according to the particular load to be energized by the transformer.

Parallel magnetic paths may be traced, one from leg I0, splitting and passing through core described.

annoso portion MI, to the right along leg Il. end piece I4 and back through leg I0; and through core portion M2, to the right along leg I2', and piece I4 and back, through leg I8. The other path may be traced from leg III, splitting and passing through core portion MI, to the left along leg I I, end piece I3, and back through leg I; and through core portion M2, to the left along leg I2, end piece I3, and back through leg I0;

As in the case of Figure 1, primary coils PI, P2 are connected in opposed-relation across a source I6 of alternating current`-. energy. Thus the streams of ilux generated by these primary coils and coursing through the said parallel magnetic paths tend to buck each other. Current accordingly flows from the right-hand side of source I6 through conductor I1, through lead 44, lead 45, terminal I8, through primary coil PI to the right in Figure 2, thence through terminal I9, conductor 20, lead 46 and lead 4l', back to the left-hand side of current source I6. A parallel path may be traced from the right side of current source I6, through leads Il, 44 and 48, to terminal 22, thence through primary coil P2 to the left in Figure 2, terminal 2|, and thence through conductors 28, 46, and 41 back to the left-hand side of the source of energy I6. lThe primary coils are seen to be connected in bucking relationship with each other.

In this embodiment, each secondary coil is connected across the net work'consisting of the parallel-connected primary coils. With the tubes in series circuit with their corresponding secondary coils, then with the electrical circuits as described, upon the arc across either tube striking, increased current flows through the associated secondary coil. This current necessarily courses the net work electrically connected therewith, and splits thereacross in accordance with the relative impedance of the branches of that net work. Since the impedance of the branch including the primary coil magnetically linked with the energized secondary coil increases materially in response to such energization, however, only a small part of this current iiows through the branch. By far the larger part flows through the other branch, including the primary coil linked with the other magnetic circuit. Consequently, an increased quantity of ilux is generated in this other magnetic path, so that increased voltage is instantly induced in the associated secondary coil. This increased potential, impressed across the terminals of the tube in circuit with that secondary coil, causes rapid striking of the arc across that tube.

A fluorescent gas discharge tube TI is associated in series with and comprises the load of secondary coil SI, while similarly, a fluorescent gas discharge tube T2 is in series with and constitutes the load of secondary coil S2. The electrical connections for secondary coil Sil may be traced as follows: From right hand terminal 32, lead 33, socket 84, Tube TI, thence through conductors 49 and 48 to junction 20'. The other leg of the secondary coil circuit is from terminal 31 and lead 50 to junction 44". One -branch circuit then can be traced from junction 20', lead 20, terminal 2l, to the vright in Figure 2 through coil P2, terminal 22, and leads 48 and 44 to junction 4'4. The other branch circuit can be traced from junction 20', lead 20, terminal I9, primary coil PI, terminal I3, and lead to terminal 44'. During the next circuit half-cycle, of course, the direction of current ilow is the reverse of that Similarly, a like circuit may be traced from secondary coil S2. One leg includes terminal 38, lead 39, socket 40, tube T2, socket 4I, leads 41 and 46 to junction 20. The other leg includes terminal 43 and lead 44 to junction 48. One branch of the parallel network across which the secondary circuit just traced is connected as follows: From junction 48', lead 48, terminal 22, to the left in Figure 1 through primary coil P2, downterminal 2| and lead 20 to junction 2U'. The other branch may be traced from junction 48', leads 44 and 45, terminal I8 through primary coil PI to the right, terminal I9, and lead 20 back to junction 20'. It is of course to be understood that the circuits just traced assume momentary current flow in given direction and that upon reversal of the current half-cycle, the direction of current flow will be precisely opposite to that indicated.

It will be noted that while in Figure 1 the primary coils are series-connected across the source of current supply, in the embodiment under discussion, the primary coils are connected in parallel, With parallel connection each primary coil carries the full potential of the service. For a certain number of turns in the secondary winding, parallel connected primary coils must contain twice as many turns as the-number of turns in series connected primaries so that the volt per turn will be equal in either hook-up.

Assuming now that the direction of the impressed current is the same as that maintaining in the construction according to Figure 1 during the discussion thereof, it will readily be appreciated that ilux passing to the left in Figure 1 from primary coil PI will buck the body of flux from primary coil P2, and splitting, will course upwardly and downwardly, about legs II, I2, and following .the paths of minimum reluctance, course through secondary coil SI. At the same time, ilux from primary coil P2 will course to the left through legs Il and I2 and link secondary coil S2. In the alternate half-cycle, of course, the directions of the passage of iiux are reversed, and the ilux from primary coil PI passes to the right thr ough secondary coil SI, thence through'end piece I4, to the left through legs Il, I2 to corev portions MI, M2, and thence back through leg I0 to primary coil PI. In like manner, ux from primary coil P2, passing to the left through leg ID, traverses secondary coil S2 and passes in two paths through end pieces I3, I3 and to the right through legs Il, I2, to core portions MI, M2, and thence to primary coil P2.

In operating our system, one or the other yof tubes Tl, T2 is ilrst brought to a condition where the arc can be established thereacross. Let us assume that it is tube TI which strikes first. Accordingly, when the arc strikes, a large current is induced in secondary coil SI. This current oi course flows through the primary coil P2 electrically connected with secondary coil SI. Because of the higher impedance which primary coil PI in the same magnetic circuit now has, however, it is only the smaller part of the current which courses the branch circuit including coil PI. The larger part of the current ilows through coil P2. Now, since the flux generated is a function of the number of turns and of the current ilowing through these turns, the quality of ilux generated by primary coil P2 promptly increases to a considerable extent. This increased quantity of iiux so materially increases vfor each tube, the construction does not represent quite as much advance as do the double circuit transformers according to the embodiments of Figures 1 and 3.

It will readily be appreciated from the foregoing that by the use of our new system the necessity for complicated, delicate and wasteful auxiliaries is completely avoided, and that one transformer is capable of operating two or more lamps. Thus a sturdier unit can be produced, characterized by its long life and low operating costs. The transformer itself serves as a currentlimiting means for the tubes.

Combined with the comparative simplicity of our new system are the advantages that the tubes will both start and restart quickly, and will operate satisfactorily even under cold weather conditions. To illustrate, whereas in conventional systems the arc will extinguish at ambient temperatures of about 50 F., tubes operated in accordance with our new invention will remain energized with temperatures as low as F.

Because of the large iron content of the transformer as contrasted with the iron-core ballast hitherto in use, the voltage regulation is better, and there i-s but little variation in the voltage drop across the tubes upon variation of the potential across the service mains. Thus the light output changes linearly or even to a lesser degree with the change of voltage, rather than as a power function of the impressed potentialy across the service mains. Thus the light output changes linearly or even to a lesser degree with change of potential, as has hitherto been the case.

Finally, our new system makes possible for the nrst time to employ fluorescent tubes satisfactorily with dimmer operation, wherein the tubes are operated at lower than rated light output, for producing pleasing soft light in the evenings or periods of quiet.

Inasmuch as Aautotransformer operation at secondary voltages of 600 volts or less, with pri- 18 tween `said primary and secondary coils o! each of said core sections.

3. A high leakage reactance autotransformer comprising, in combination, a main magnetic core; coils/ mounted on the core including a primary coil, an extension coil immediately adjacent thereto and a secondary coil spaced therefrom, with the primary coil individually connected in autotransformer relationship with said extension rand secondary coils respectively; and shunt core means separating said primary and secondary coils. y,

4. A high leakage reactance autotransformer comprising. in combination, a shell-type core including inner and outer core portions, a primary coil and an extension coil grouped on said inner core portion at one end thereof and connected together in autotransformer relationship, a secondary coil disposed about said inner core portion at the other end thereof and in separate autotransformer circuit connection with said primary coil, and core shunt means with included air-gaps of high reluctance extending across said inner and outer core portions intermediate said secondary coil and the primary andextension coil group.

5. A high leakage reactance autotransformer comprising, a core including two shell-type sections having individual inner longitudinal core portions substantially normal to a common intermediate core portion, two opposed primary coils interconnected and individually mounted on said inner longitudinal core portions adjacent said common core portion, two secondary coils individually mounted on the shell-type core sections and each connected in autotransformer relationship with the primary coils of both said core sections, and shunt core means between the primary grounded to earth ii' desired, is permitted by the iire underwriters, it will be understood that our new system satisiles all practical requirements.

We claim.

1. A high leakage reactance autotransformer comprising, in combination, a core including two main magnetic core sections each forming a closed magnetic circuit. two primary coils connected together and individually mounted on the main core sections. two secondary coils individually mounted on the main core sections and each connected in autotransformer relationship with the primary coils of both said core sections, and shunt coremeans with included air-gai positioned between the primary and secondary coils of each of said core sections.

mary and secondary coils of each of said core sections.

6. A high leakage reactance autotransformer comprising, a core including two shell-type sections having individual inner longitudinal core portions substantially normal to a common lnrmediate core portion: two primary and extension coil units individually mounted on said inner longitudinal core portions adjacent said common core portion. said primary coils being connected together and also in autotransformer connection with the extension coils; twov secondary coils individually mounted on the shell-type core sections; and shunt core means between the primary and secondary coils of each oi said core sections.

CHARLES PHILIPPE BOUCHER. FREDERICK AUGUST KUHL.. f

REFERENCES CITED The following references are of record in the me oikthis patent:

UNrrsn s'rs'rss Psm'rs Bouches' et al. Juno 20. 1244

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