US2317844A - Luminescent tube system and apparatus - Google Patents

Description

April 27, .1943. c. P. BOUCHER ETAL 2,317,844

LUMINESCENT TUBE SYSTEM AND APPARATUS Filed July 14, 1941 iw/gr Patented Apr. 27, 1943 LUMINESCENT TUBE SYSTEM AND APPARATUS Charles Philippe Boucher, Paterson, and Frederick August Kuhl, Ridgewood, N. J., assignors to Boucher Inventions, Ltd., Washington, D. 0., a corporation of Delaware Application July 14, 1941, Serial No. 402,411

12 Claims.

Our invention relates to fluorescent tube lighting, and more particularly concerns a new electrical system for such illumination, as well as a new transformer forming part of, and for energizing such system.

One object of our invention, therefore, is to produce a new fluorescent tube lighting system, possessing the advantages of simplicity, small size, small number of parts, compactness and sturdiness, and which at the same time is characterized by its high system power factor, and the minimization of detrimental flicker or stroboscopic effect of the light emission therefrom.

Another object is to produce a high leakage reactance transformer for energizing such electrical system, comprising batteries or banks of two or more tubes, the tube-energizing circuits each requiring a different circuit input, which transformer serves to produce just the required current to energize those tube circuits properly and to maintain proper arc discharge across the respective tubes and to limit the current flow to the rated values.

Other objects and advantages in part will be obvious and in part pointed out hereinafter, in connection with the following description, considered in connection with the accompanying drawing.

Our invention accordingly resides in the several elements and features of construction, and the relation of each of the same to one or more of the others, all as described herein, the scope of the application of which is indicated in the claims at the end of this specification.

In the drawing Figures 1 and 2 comprises side and end elevations, respectively, of a transformer according to our invention, Figure 1 also illustrating the associated system connections according to one embodiment.

Figure 3 depicts in schematic manner, another embodiment of circuit connections, to be associated with the transformer core depicted in Figure 1.

Like reference characters denote like parts throughout the several views of the drawing.

As conducive to a more complete understanding of our invention, it may be noted at this time that the introduction of fluorescent tube lighting into the arts and sciences has been accompanied by the realization that there are certain serious drawbacks and disadvantages in the energizing systems for such tubes which have hitherto been in use. The importance of this comparatively new lighting technique, however, can be appreciated when a moments consideration is given to the widespread acceptance of this new type of lighting. Not only is the acceptance by the industries, but in the stores and in household lighting, as well. As soon as certain operational problems have been solved, we may safely predict the even more widespread acceptance of fluorescent lighting systems in all fields of illumination.

We confidently attribute the popularity of fluorescent tube lighting to the higher efiiciency and hence lower operational costs of such lighting as compared to the old incandescible lampstheir luminous efficiency is about 2% times as great, so that they cost less than half as much to operate for the same light output; they operate cooler, since not nearly so much current is dissipated in radiant energy; they produce a quieting, soothing light in a variety of color tones and combinations; they produce a more even distribution of light and are admirably adapted, when used in batteries, for flood lighting. Additionally, when used in batteries, such lamps are particularly well suited for color mixing and blending. Because of their comparatively long tube life, about 2%,times those of present day incandescible tubes, the higher first-cost of such systems is more than offset by the lower operational and maintenance costs.

Despite these many advantages attendant upon these new lighting systems, however, much room for improvement awaits the worker in the art. Hitherto, practically all development work has been directed to the use of fluorescent tubes having incandescible electrodes, incandesced to prepare the tube for striking the arc thereacross. Because of these incandescible electrodes the tubes are known as hot cathode tubes. The auxiliary equipment has all been designed for such tubes, with the purpose of both starting them and operating them on service voltages. Because auxiliaries were thought to be necessary in any event for providing starting voltage surge and for current limiting purposes, the use of transformers has been discouraged, to maintain both initial and operation costs at a minimum.

Furthermore, the presence of incandescible filaments introduces a factor of fragility in the system. When it is recalled that this filament, at each electrode, is essential in preparing the tube for starting, and when it is further recalled that after starting, the arc is maintained across these very same electrodes, then it will readily be appreciated that despite efforts made to hield these filaments, they are subjected to both ionic and electronic bombardment, and when the arc settles on the filament, to detrimental vaporization as well. Thus, despite the increased longevity of these tubes, their life span is definitely limited. Additionally, inasmuch as these filamentary electrodes are oxide coated, to increase their electron emission, blackening of the tube'walls occurs, due to deposit thereon of spent oxide material volatilized off the filaments.

Unstable operation at low temperatures limits the use of known tube lighting systems in outdoor use, or show window display use, to conditions where at least moderate temperatures prevail. Where the temperatures are low, or the tube is exposed to extreme cooling effects, such as winds or the like, the mercury tends to condense out, and the service voltage is found to be insufficient to maintain a steady arc in the rarefied atmospheres prevailing under such conditions. Somewhat similarly these known systems, operating at service voltages of from 120 up to 250 volts supply, are unable to operate at dimmer light outputs because with any appreciable decrease in impressed voltages, the peak voltage of the current supply will approximate or fall below the value at which an arc can be struck across the tubes. Experience shows that the arc extinguishes when the service voltage falls below rated values.

In our application for patent Serial No. 402,410, filed of even date herewith, and entitled Luminescent tube system and apparatus, we have set forth novel means for avoiding in large measure the difiiculties and disadvantages pointed out in the foregoing. To that end, we have described in that application a fluorescent tube lighting system in which the operational and maintenance costs are materially reduced below those hitherto current, which has a greater light output per unit of power input than was hitherto possible of achievement, in which the useful life of the tube is greatly increased, and which is capable of satisfactory dimming operation. However, no provision was made in the systems according to that application, for avoiding the detrimental flicker or stroboscopic effect. Our present invention is directed to the substantial decrease of that stroboscopic effect in systems according to our prior invention, and which employ our new high leakage reactance autotransformer for energizing the tube load, and also the production of a high leakage reactance autotransformer which will operate at high efficiencies while energizing such tube circuits, A further object of our invention is to produce a system of fluorescent tube lighting employing our new transformer, all as aforesaid, which system has high power factor, and which is capable of steady and satisfactory operation under cold weather'conditions.

While in incandescent lighting operation on alternating current supply, of say 60 cycles,

wherein the voltage rises and falls from zero to peak voltage and back again to zero some 120 times per second, the heat retentivity of the tungsten filament is such that the light emission persists during the momentary periods of no voltage, there is no such heat retentivity in the case of fluorescent gas discharge tubes; and even where the service mains are of as high as 60 ing each half-cycle of current flow gives rise to a perceptible and objectionable flicker, known in the'art as stroboscopic effect. Much attention has been directed by-the workers in the art to the satisfactory elimination of this source of annoyance.

Whilethe invention as set forth in our copending application presents an effective solution of many of the fluorescent tube lighting problems stated herein, nevertheless, while some effort is made according to that application to correct the system power factor by-the use of a large capacity condenser, without, however, disturbing the design of the transformer core to that end, we find that more effective use of the power factor regulating condenser can be obtained if it be disposed asymmetrically of the transformer load system, in one branch of its double current secondary. When so disposed, the condenser not only fulfills its function of 'power factor regulation, but at the same time, produces a phase unbalance in the double secondary circuits so that when one tube of a battery or bank of tubes is in its period of darkening when the arc is extinguished, the other tube will be energized and an arc struck thereacross.

The use of our high leakage reactance transformer as the power source interposes some interesting questions of design to ensure proper operation with high efficiency. The solution of these problems, forming the subject matter of this application, involves many features of novelty, and accordingly, a further object of our invention is to produce a system of fluorescent tube lighting characterized by the minimizing of detrimental flicker or stroboscopic effect, and having high system power factor, as well as to produce a new double circuit, high leakage reactance autotransformer capable of energizing such system at high efficiency while maintaining the current flow. thereacross within safe practical limits.

It will be recalled that, to prevent hysteresis loss, the iron core ballasts used in the conventional tube lighting systems have been constructed with cores which are formed of a number of iron laminations. In operation, however, these laminations give rise to a detrimental hum .or chattering which has been found to make the use of such systems objectionable in places where extreme quite ordinarily prevails, such for example, as in homes, libraries and the like,

. For the same reasons as controlled in connection with the iron core ballasts, the core of our new transformer likewise is comprised of a large number of iron laminations. In the absence of special precautions our new transformer, too. would therefore give rise to detrimental hum or chattering. An important object of our invention is thus seen to reside in the construction,

of a transformer which, when in operation, is substantially free from detrimental hum or chattering.

Referring now to the practice of our invention, attention is directed to Figure l, in which there is illustrated a double-circuit high'leakage reactance shell-type transformer, having parallel magnetic flux paths, and with its windings connected in autotransformer connection, which transformer is associated in novel circuit arrangement with fluorescent gas discharge tubes connected for cold cathode operation.

The transformer illustratively consists of a core frame, having a central leg l0, outer legs I I, I2, parallel and in spaced relation with, and arranged one on each side of central leg l0, and

end pieces l3, I3 and I4, l4 extending at right angles to said legs, and joining them at their respective ends. Mid core portions MI, M2 extend at right angles from outer legs II, I2, re-. spectively, towards central leg III. In practice we prefer to form the legs which comprise core portions MI, M2 about .002 inch longer than the ends comprising end pieces I3 and I4, for reasons which will appear hereinafter.

As will be apparent from Figure 2, the transformer core is comprised, in conventional manner and to prevent hysteresis loss, of a large number of lamina l5, shown in the illustrations as being of greatly exaggerated width, for clarity. As has already been suggested these lamina, under the influence of rapidly alternating electromagnetic stress, give rise to a detrimental chatteringa chattering which is also experienced in conventional installations employing iron-core inductive ballasts as current-limiting means, and retarding to a certain extent the acceptance of fluorescent lighting systems in household lighting and in other locales where the prevailing quiet is such that the hum of the inductance is noticeable.

To avoid this chattering we provide silencing clamps transversely about the core, and serving to clamp the lamina firmly together. Preferably We provide such clamps at the mid-portions of the core legs II and I2 and at both ends of these core legs. Each of the clamps consists of two substantially U-shaped members I6, I1. each terminating at their free ends in outwardly extending tabs or wings I8, I8. These tabs are bored for the reception of a clamping screw 20. As shown, these clamping screws are each associated with a pressure-distributing washer 2| and a takeup nut 22. When the pair of U-shaped clamps are disposed in opposed relation about the lamina I5, and the screws 20 are tightened down, the clamps engage firmly about the lamina, and ubstantially all chatter or hum in the transformer core is eliminated, and perfect magnetic butt joints are achieved. Moreover, when clamping pressure is properly exerted, the magnetic reluctance per unit of bearing area is the same at both the mid-core portions and end pieces. It is also advantageous at times to employ C-shaped silencing clamps (not shown) at shunts ShI, Sh2, Sh3 and SM.

Spaces for the reception of the transformer windings are formed in the core by the described association relative to each other of the outer and inner legs, the mid-core portions and the end pieces. These spaces, rectangular in shape, are disposed in pairs, one pair on each side of midcore portions, and the spaces of each pair being disposed on opposite sides of said central leg. The primary coils and secondary coils are disposed in pairs about said central leg, one pair of coils in each said pair of spaces.

A primary coil and a secondary coil constituting each pair, are disposed about and link each parallel flux path. Primary coils PI, P2 are disposed adjacent mid-core portions MI, M2, one of each side thereof. Secondary coils SI and S2 are disposed adjacent end pieces l4. I3 respectively. Primary coil PI and secondary coil SI are linked in magnetic circuit with each other,

while primary coil P2 is linked in magnetic circuit with secondary coil S2.

An important feature of our transformer is its high leakage characteristics. To impart these desired characteristics, in each said magnetic P2 is connected through leads 32,

circuit, between each primary and its associated secondary, intermediate magnetic shunts Shl, Sh2, Sh3, SM extend towards but short of central leg I0, thus providing corresponding air-gaps GI, G2, G3, G4 of magnetic reluctance calibrated in accordance with the load for which the transformer is adapted. Shunts Shl, S112 and air-gaps GI, G2 are associated with primary coil PI and secondary coil SI, while shunts Sh3, SM and air-gaps G3, G4 are associated with primary coil P2 and secondary coil S2. The function of these intermediate shunts will be developed at a later point herein.

The primary coils PI, P2 are connected across a source of electrical supply 23, which preferably is an ordinary alternating-current service line. While the primary coils may be parallel or seriesconnected across this service, in aiding or opposed relation, we prefer to connect them in parallel-opposed relationship, for reasons which will develop. Thus terminal 24 of primary coil PI is connected through lea'ls 25, 26 and 21 to left-hand side of source 23. Similarly, terminal 28 of primary coil PI is connected through leads 29, 30 to right-hand side of source.

In like manner, terminal 3| of primary coil 33. to the righthand side of source 23, while terminal 34 of the primary coil is connected through lead 21 to the left-hand side of the source.

For a given half-cycle of the alternating-current supply, current flows from the right-hand side of source 23, through leads 30, 29 to terminal 28, thence to the left (in Figure 1) through primary coil PI, terminal 24, and thence through leads 25, 26, 21 back to the left-hand side of the source. Simultaneously a parallel circuit may be traced from the right-hand side of source 23 through leads 33 and 32 to terminal 3|, thence to the right (in Figure 1) through primary coil P2, terminal 34, and thence through lead 21 back to the left-hand side of the source. During alternate half-cycles of the current supply the direction of current flow through the two par allel paths is of course "ust the reverse of those just traced. It will be observed that the primary coils are in bucking relation, so that the flux produced thereby tends to flow in opposite directions. This means that the principal body of flux courses the mid-core portions MI, M2, so that they must be designed to serve as conduits for the flux, without saturation effects.

By connecting the primary coils PI, P2 in parallel across the source 23, the full supply potential is impressed across their windings. Where series connection of the primary coils across the energy source prevails, however, each primary coil receives only its share of the total potential output of the supply source. For a given operating voltage, the number of turns in two parallel connected primary windings must be double the number in two series connected primaries of particular cross-section is employed and a constant flux density is desired, the number of turns in the primary coil sections must be altered when the particular manner in which the coil sections are connected is changed.

We prefer to connect each secondary-coil electrically in series across the network consistng of the two parallel opposed 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 fiows through the associated secondary coil. Thus current necessarily courses the network electrically connected therewith, and splits thereacross in accordance with the relative impedance of the branches of that network. 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 flows through that 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 flux is generated in this other magnetic path, so that increased voltage is induced in the associated secondary coil. This increased potential, impressed across the terminals of the tube in circuit with that secondary coil, ensures positive striking of are across that tube.

Thus a circuit may be traced from secondary coil SI, terminal 35, through conductor 30, to

junction 23'. The other leg of this circuit includes terminal 38 of the secondary coil, lead 31, tube TI, and lead 36, to junction 25. At junctions 29 and the secondary coil circuit is connected across the primary coil net-work. One

branch may be traced from junction 23', lead 29, terminal 28, to the left in Figure 1 across primary coil Pl, terminal 24, and lead 25 to junction 25. The other branch may be traced from junction 29, leads 30, 33, 32, terminal 3|, to the right in Figure 1 through primary coil P2,- terminal 34, leads 21 and 25, back to junction 25. During the next half-cycle, of course, the direction of current flow is just the reverse of that described. I

Since electrical disturbances are produced in tube TI due to electrical discharges across the gas and mercury vapor filling thereof, and since due to the autotransformer connections, primary coil P2 is in circuit therewith, any disturbance in tube Tl will be carried into the primary circuit. To elminate this detrimental source of annoying radio disturbance, condenser Cl is connected across the tube to trap the high-frequency oscillations which otherwise would reach the primary circuit. Since condenser Cl need have only a small capacity, say about .005 microfarad, and consequently has a high capacitative reactance, it consumes but little energy, and does not in any way interfere with tube starting. Condenser Cl has no effect on the normal operation of the transformer.

Similarly, secondary coil S2 is electrically connected across the same primary coil network. Circuit may be traced as follows: From terminal 39 of secondary coil S2, lead 40, across condenser tube T2, and lead 42 to junction 33. The other leg of this circuit includes terminal 44 of secondary coil S2, and leads 43 and 26 to junction 26'; The current flows through one parallel branch from junction 33 up through lead 32, terminal 3i to the right in Figure 1 through primary coil P2, terminal 34, lead 21 to junction 26'. The other branch can-be traced from terminal 33', leads 33, and 29, terminal 28, to the left in Figure 1 through primary coil Pl, terminal 24, and leads 25 and 26 back to junction 26'. In the next half-cycle, of course, the direction of current flow is the reverse of that described.

A large part of the foregoing, with the exception of the silencing clamps, has already been set forth in our said co-pending application, and

does not per se form part of this invention. The novelty herein resides in large measure in the production of a high leakage reactance transformer capable of satisfactory operation with a large capacity condenser disposed in one secondary circuit which results in power-factor correction with substantial minimizing of 'stroboscopic flicker, while maintaining high system and transformer efficiency.

Condenser 4i serves the dual function of cor recting system power factor, and due to its asymmetrical location in one branch of the secondary circuits, produces a phase unbalance so that the arc discharges across the two tubes are out of phase with each other. This minimizes flicker, or what is known as stroboscopic effect, in batteries of two or more lamps,

Condenser 41 is necessarily of considerable size to introduce such balancing impedance. Its capacity is comparatively large even though it is placed in the high voltage secondary side of the transformer. Because primary coil PI is connected in series with the condensive branch of the secondary, it has imposed on it not only the 60 cycle frequency of the service mains, but the superposed frequency of the condensive secondary circuit. Thus primary coil Pl must be wound of larger siz wire to handle the larger current resulting therefrom.

The high impedance of the condenser 4| tends to resist the coursing of flux through leg l0 and interlinking secondary coil S2. Shunts Sh3 and $11.4 accordingly must be designed to have reluctance such that when the arc across tube T2 is struck, they will at that time by-pass the greater part of the primary flux coursing that magnetic circuit, their design is such that a quantity of primary flux sufiicient to induce the required potential in secondary, coil S2 will still interlink that coil. This requirement necessitates designing shunts S723 and 812.4 of higher reluctance than shunts Shl and Sh2, for if they had an admittance as high as those two shunts, they would by-pass practically all the primary flux around coil S2, leaving the latter practically deenergized. Accordingly, shunts SM and SM are shorter than shunts Shl and Sh2, while air-gaps G3 and G4 are Wider than air-gaps GI and G2.

It is to be noted that since secondary coil section S2 has a leading current, the counterelectromotive force generated therein is not in phase with that of secondary coil SI. Moreover, the effective value of the primary flux in the condensive branch of the transformer remains higher than in the inductive branch. 'It follows from this that the primary coil P2 is not required to supply as much flux as does primary coil Pl. Advantage is taken of this fact to reduce the size of the transformer by reducing the size of the wire constituting primary coil P2.

It is advantageous at this time to consider the manner in which the flux courses the several magnetic circuits of thetransformer, and to consider how the leakage reactance of the transformer serves to limit the current flow through the fluorescent tube load.

Because of the leading current of the capacitative branch, flux is first generated in primary section P2. Choosing the path of least resistance, the flux may be considered as coursing to the right in Figure l, and splitting into two substantially equal streams (because of the substantially equal physical and magnetic characteristics of the two paths) passes in the direction of the arrows. One part passes up through core porthrough coil P2.

tion Ml, to the left along leg II, down through end piece I I, and the othe part passes down through M2 to the left along leg I2, up through end piece I3 and there reunites with the flux from the other path at central leg III. The reunited flux travels to the right across leg I back .to MI and M2 thereby linking P2 and S2. Potential is induced in secondary coil S2, which potential is impressed across the terminals of tube T2. Approximately 90 electrical degrees later, flux starts to flow from primary coil PI, and passing in the direction of the arrows, courses to the left along leg III. Bucking flux from the condensive branch of the transformer for the first 90 electrical degrees, the flux, choosing the path of least reluctance, branches and flows in substantially equal streams, one stream through core portion MI, to the right along leg II, down through end piece I4, and reuniting with the other stream of flux in leg I0, courses back to primary coil PI, traversing secondary coil SI. Meantime the other stream courses down through core por tion M2, to the right along leg I2, up through end piece I4, and joining the other stream at.leg III, courses back to primary PI.

One of the lamp circuits, usually the condensive branch of the secondary circuit containing lamp T2, may be expected to have an impedance sufflciently lower than the other to strike first, after the passage of but a few current cycles, assuming now a 440-volt supply.

Upon establishment of an arc across the tube, a high current flows through secondary S2. Consequently, this current flows through the primary network, electrically connected therewith. Since impedance builds up in primary coil P2 simultaneously with arcing of tube T2, because coils P2 and S2 are in the same magnetic path, it is the smaller part of this current which flows The larger quantity flows through coil PI, still of low impedance, and in-- duces a larger quantity of flux in the second magnetic path, which flux, interlinking coil SI, induces a higher voltage therein. Tube TI thus strikes more positively upon application of this high voltage across its terminals.

Of course, in alternate half-cycles of the energizing current, the direction in which the flux courses is the reverse of that just described. All

in all, the time consumed from the closing of the switch across the service mains until both tubes are energized is a matter of but a few current cycles, as contrasted to the some 4 to 6 seconds or more as has been the case with the systems currently in use.

As soon as both tubes are energized, steady current flow conditions maintain. The intermediate shunts Sh3Sh4, formerly paths of high reluctance, are now, due to the build-up of back magnetomotive force generated by secondary coils SI, S2, the paths of least reluctance. In fact, so great is the impedance in coil section S2 due to condenser II, that were not the air-gaps G3 and G4 so designed as to provide sufficient reluctance, they would by-pass practically all the flux around the secondary coil S2, and would render the latter practically inactive. An important feature of our present invention accordingly, is the design of these air-gaps so that they are made much larger than the airgaps GI, G2. These air-gaps Gil-G4 are calibrated so as to produce nearly unity power factor, in conjunction with condenser 4|.

The flow of larger currents through secondary coil S2 and tube T2 makes it necessary, as

pointed out hereinbefore, to provide primary coil PI of considerably larger gauge wire than that constituting primary coil P2.

More specifically, with steady flow conditions maintaining, flux flows to the right from primary coil P2, splits into two substantially equal and parallel streams and courses one stream up through core portion MI, thence to the left along leg II. A small amount of flux continues, coursing through secondary S2. To induce just the necessary voltage to maintain tube T2 energized, however, the greater quantity flows down through shunt Sh3, across air-gap G3 to leg III. The other stream flows down through core portion M2, thence to the left along leg I2, from whence the greater part flows up shunt Sh4 across airgap G4. The two streams of flux reuniting at leg I0, they flow back to the right along this leg, to primary coil P2. A half-cycle later the direction of flow of these flux streams is reversed.

About electrical degrees out of phase with the streams of'flux just traced, the flux coursing from primary coil PI passes to the left in Figure 1, and splitting at core portions MI, M2, passes one stream up and to the right along leg II, whence the greater part courses down across shunt ShI and air-gap GI, and the other stream down and to the right along leg I2, whence the greater part courses up across shunt 871.2 and airgap G2. All the flux reuniting at leg I0, including that part just sufficient to induce in secondary coil SI the voltage necessary to energize the tube TI, courses as a single stream to the left in Figure 1, back to primary coil PI. A half cycle later the direction of coursing of the flux is reversed.

The presence of the condenser 4| results in an increase in the voltage in the condensive circuit. Accordingly, to produce the same open circuit voltage in both secondaries, we find it advantageous to form coil S2 with a few less turns of wire than coil SI. In our watt unit, for example, this difference in potential is found to be 35 volts.

Another embodiment of our electrical system is illustrated in Figure 3. Since the core employed in connection with the embodiment now to be described is much like to that employed in the embodiment first-described, its description has been omitted from the illustration of Figure 3.

In this new embodiment, primary coils PI, P2 and secondary coils SI, S2 are provided, primary and secondary coils PI, SI and P2, S2, being paired in separate parallel magnetic circuits. Primary coils PI, P2 are connected together in series-opposed relationship across a source of alternating current supply 23, the winding of primary coil PI being wound in a direction reverse to that of the winding of coil P2. Secondary coils SI, S2 are associated in autotransformer connection across the primary coils PI, P2, and to avoid the necessity of a large number of turns in the secondary coils to produce rated secondary voltages since the primary coils are series connected, each secondary coil is in separate series circuit with both primary coils. Thus secondary coil SI, for example, is electrically series connected through conductor 45, first with primary coil P2 in the opposite magnetic circuit, thence by lead 46 to tube TI, and through lead 41 back to the secondary coil. Similarly, and in separate secondary circuit, an electrical seriescircuit may be traced from secondary coil S2 through lead 48, across condenser 49, first tothe primary coil Pl in the opposite magnetic circuit, thence through lead 45 to tube T2, through lead 50, back to the secondary coil. If desired, /a high resistance Rcan be provided about condenser 49; to bring about slow discharge of the condenser, after circuit operation and thus prevent electrical shock.

Just. as in the first embodiment, the conde'nsive branch of the secondary has a leading current. The increased current fiow from the 60 cycle induced supply plus the impressed harmonics from the condenser action requires the primary coil Pl to be wound of larger size wire.

Because of the impedance interposed by the condenser 49, the back magnetomotive force generated by coil S2 is so great that without proper" design of shunts S723, SM (Figure 1), practically all the flux would be shunted through the paths comprising these shunts and their associated air-gaps G3 and G4, around coil S2, leaving the latter de-energized. We purposely, therefore, increase the width of air-gaps G3, G4. and hence the reluctance of the shunts of which they form part, to an extent that even after energization of the load across secondary coil S2, and the consequent generation of back magnetomotive force from that coil, enough primary flux interlinks that coil to impress required operating potential across the secondary load.

The condenser 49 produces a condition of In this embodiment let us assume a half-cycle of charging current flow such that fiux is developed by primary coil Pl in the direction according to the arrows in Figure 1. Then the flux, passing to the left in coil Pl along leg l0, bucks the flux streaming in the opposite direction from primary coil P2. The streamirom,

coil Pi splits into two branches. One. bfaich courses up mid core portion MI and to the right along leg ll. Only a small part courses down the high-reluctance shunts Shl. The greater parts of it courses down first end piece H, to

the right hand end of leg l0. At the same time,

the other branch of flux from coil Pl courses down mid core portion M2 and to the right along leg l2. Only a very small part of the flux courses across the high reluctanceshunt $112. By far the greater part moves up second end piece It to the right hand end of central leg in. The two branches of the stream of primary flux reuniting at leg ill, the combined stream now courses to the left along leg [0, back to the primary coil Pl.- During its passage, it interlinks secondary coil SI and induces a high potential therein.

In the meantime, fiux from primary coil P2, which as indicated by the arrows, flows in a direction opposite from the flux in coil Pl, courses to the right in Figure 1 along central leg 10. Here the stream splits, and one branch courses up mid core portion MI' and to the left along leg ll. Only a small part of the flux courses across high reluctance shunt Sh3. The greater part courses down first end piece I3, to the lefthand end of central leg l0. Meanwhile, the other branch courses downcoreportion M2 and to the left along leg l2. Only a small part of this fiux courses across high reluctance shunt Sh3. The greater part courses up second end piece I3. The two branches reunite at leg ill. The combined stream then courses back to primary coil P2. During its passage it interlinks secondary coil P2 and generates a. high voltage therein.

During the next adjacent half-cycle, the direction of the magnetic fiux of course is reversed. It will be sufficient for purposes of illustration, to describe the reverse coursing of fiux at this time, for but a single one of the two parallel magnetic paths. Confining our attention, therefore, to the magnetic path about which are disposed coils PI and SLcoursing of the magnetic fiux will be observed to be in a direction opposite to that indicated by the arrows in Figure 1.' The flux from coil Pl courses to the right along leg ill, and only a small part of it branches across shunts Shl and $712, the greater part interlinking secondary splits into two branches. One branch courses up end piece l4" and tothe left along leg II. It is joined by the small quantity of fiux which courses shunt Shl. This branch courses down core portion Ml to central leg l0 and back to coil Pi: The other branch courses down second end piece It and to the left along leg l2. It is joined by that path of the flux which courses shuntSh2. This branch courses up core portion M2, to central leg i0 and back to col] PI.

The circuit for one of these tubes, usually for tube T2, will be found to have a lower impedance than the other tube circuit. After several reversals of the secondary current, therefore, the voltage impressed across the terminals of the tubes, excites the gas contents thereof to such a degree of excitation that the arc strikes across the tube. As soon as thathappens, alarge current begins to fiow in the related secondary coil S2. Since coil S2 is electrically in circuit with primary coil PI and P2, this same current fiows through these two coils. Furthermore, since the primary fiux depends on the ampere turns in the primary coils, this increased current flow induces increased primary fiux. This increase of flux in the second parallel magnetic paths, ineluding secondary coil Si, results in increase in the potential induced in that coil. The elevated potential impressed across tube Tl causes more positive striking of the arc thereacross.

The high impedance which the secondary coil S2 now has, causes by far the greater part of fiux from primary coil P2 to shunt along high reluctance shunts S113 and SM and their associated air-gaps G3, G4, in large measure by-passing secondary coil S2. The design of the shunts is such that only sufficient fiux now interlinks secondary coil S2 to induce therein voltage high enough to maintain arc discharge across tube T2.

Shortly after the arc strikes across tube T2,

tube Tl likewise becomes energized. These tubes 2,317,844 er-factor in the substantial absence of detrimen- 1. An eIectrical system for energizing a plu-- rality of fluorescent gas discharge tubes at high system power-factor and with stroboscopic effect reduced to a minimum, comprising a high leakage reactance transformer having a magnetic core and a primary winding and a plurality of secondary windings linking the same; a source of electrical energy across which said primary winding is connected; and a fluorescent gas discharge tube connected in circuit with each secondary winding and a power-factory regulating condenser in series circuit with one said secondary winding, the said transformer core including high leakage reactance shunts magnetically between primary and secondary windings for by-passing magnetic flux around the associated secondary winding when the load on the latter increases, the reluctance of said shunts. in each magnetic circuit being calibrated to provide more reluctance in that magnetic circuit which energizes the condenser.

. 2. A fluorescent tube lighting system for operation at high power-factor and with tube flicker minimized, comprising a high leakage reactance transformer having a core and a primary winding and a plurality of secondary windings linking said core; a fluorescent gas discharge tube connected in circuit with each secondary winding; and a power-factor regulating condenser in series circuit with one said secondary Winding, said transformer core including high leakage reactance shunts between the primary winding and the secondary windings, the reluctance of said shunts being calibrated to provide more reluctance in that magnetic circuit which energizes the condenser, the secondary winding in said last-mentioned magnetic circuit being comprised of such fewer number of turns of wire as compared to the other secondary winding that its open-circuit voltage will be the same as that of the other secondary winding.

3. A fluorescent tube lighting system for operation at high power-factor and with tube flicker minimized, comprising a high leakage reactance autotransformer having dou'ble magnetic circuits employing a common core leg, a primary coil and a'secondary coil linking each magnetic circuit with the primary coil disposed adjacent said common leg, the primary and secondary coils being associated in autotransformer connection; a fluorescent gas discharge tube in circuit with each secondary coil; and a power-factor regulating condenser in series circuit with one said secondary coil, said transformer magnetic circuits including high leakage reactance shunts in each magnetic circuit between magnetically paired primary and secondary coils, the reluctance of said shunts in each magnetic circuit being cali brated to provide more reluctance in that magnetic circuit which energizes the condenser, the primary coil in said last-mentioned magnetic circuit being wound of small size wire to provide the lessened quantity of primary flux required to energize the condenser branch of the transformer secondary, while the primary coil in the other magnetic circuit is wound of comparatively larger size wire, to provide the increased magnetic flux required to energize the inductive branch of the transformer secondary.

4. An electrical system for energizing batteries of fluorescent gas discharge tubes of high system power-factor with stroboscopic effect minimized, comprising a high leakage reactance autotransformer having double magnetic circuits, a primary coil and a secondary coil in each said magnetic circuit; a source of electrical energy across which said primary coils are energized in para]- lel-opposed connection, each' said secondary coil being electrically connected across the network consisting of the parallel-connected primary coil; a fluorescent gas discharge tube in circuit with each secondary coil; and a power-factor regulating condenser in series circuit with one said secondary coil, said autotransformer including high leakage reactance shunts in each magnetic circuit between magnetically paired primary and secondary coils, the reluctance of said shunts in each magnetic circuit being calibrated to provide more reluctance in that magnetic circuit which energizes the condenser, the opposed connection of the primary coils, and the electrical connection of the secondary coils across the network of primary coils, ensuring high flux in the other magnetic circuit upon increase of the load energized by one said magnetic circuit.

5. An electrical system for energizing batteries of fluorescent gas discharge tube of high system power-factor with stroboscopic effect minimized, comprising a high leakage reactance autotransformer having double magnetic circuits, a primary coil and a secondary coil in each said magnetic circuit, each said secondary coil being electrically series-connected first with the primary coil in the opposite magnetic circuit, and then with the primary coil in its own magnetic circut; a source of electrical energy across which said primary coils are energized in series-opposed connection; a fluorescent gas discharge tube in circuit with each secondary coil; and a powerfactor regulating condenser in series circuit with one said secondary coil, said autotransformer including high leakage reactance shunts in each magnetic circuit between magnetically paired primary and secondary coils, the reluctance of said shunts being calibrated to provide more reluctance in that magnetic circuit which energizes the condenser; the opposed connection of the secondary coils with the primary coils and the electrical connection of the secondary coils with the primary coils in the opposite magnetic circuit ensuring high flux in the other magnetic circuit upon increase of the load energized by one said magnetic circuit.

6. A luminescent tube lighting system comprising in combination, a high leakage reactance transformer having a magnetic core and a primary winding and a plurality of secondary windings mounted thereon, a corresponding plurality of luminescent tube loads individually connected to said secondary windings, and condenser means connected in series with one of said tube loads and its associated secondary winding to limit the current therein, said transformer having core shunt means associated with another of said secondary windings to provide a magnetic shunt path around the same of substantially lower reluctance than any magnetic leakage path around the first-mentioned secondary winding in order to limit the current in the tube load to which the second-mentioned secondary winding is connected.

7. A luminescent tube lighting system comprising in combination, an autotransiormer having a magnetic core and a primary winding and ,two secondary windings mounted thereon with the primary winding connected in autotransformer relation with at least one of said secondary windings, two luminescenttube loads individually connected to the two secondary windings, and a condenser connected in series with one tube and the secondary winding to which it is connected to limit the current in that tube, the said transformer having a core shunt to provide a magnetic path around the other secondary winding of lower reluctance than the leakage path around the first secondary winding in order to limit ,the current in the other tube.

8. A fluorescent tube lighting system, comprising a high leakage reactance transformer includ- .ing parallel magnetic paths having a leg in common, a primary coil and a secondary coil linking each or said paths, the primary coils being disposed adjacent and on' opposite sides of said common leg, each magnetic path including magnetic shunts wherein the magnetic reluctance of one is substantially less than that of the other; a fluorescent gas discharge tube connected in circuit with each of said secondary coils; and a condenser disposed in circuit with at least the one of said tubes connected to the secondary coil associated with the shunt of greater reluctance.

9. A luminescent tube lighting system comprising in combination, a shell-type transformer having a core with a central leg and two outside legs, a primary winding and two secondary windings mounted on said central leg with the primary being disposed between the secondary windings; a pair of luminescent tubes connected to said transformer, one being connected to one sec ondary winding and the other being connected to the other secondary winding; and a condenser connected in series with one tube and the secondary winding to which the same is connected, said transformer including a shunt core path from said central core leg to the outside core legs at a point between the other secondary winding and the primary winding of substantially lower reluctance than any shunt path between the first-mentioned secondary winding and 1 the primary winding 10. A luminescent tube lighting system comprising in combination, a transformer having a magnetic core with a primary winding and two secondary windings mounted thereon, two luminescent tube loads in parallel spaced relation individually connected to said secondary windings, two condensers individually connected in parallel with said two tubes, and a condenser connected in series with one secondary winding, said transformer having core shunt means to provide a shunt path between the other secondary winding and the primary or lower reluctance than any shunt path between the first-mentioned secondary winding and the primary winding.

11. In combination, a transformer having a core and a primary winding and two secondary coil sections mounted on said core, two luminescent tubes individually connected across the terminals of individual secondary coil sections, and

a condenser connected in series with one or said tubes and its associated secondary coil section, said condenser being of sufilcient capacity to substantially limit the current in said one tube and coil section, said transformer core having magnetic core shunt means around the other of said secondary coil sections for limiting the current in that coil section and its associated tube, said shunt means providing a shunt path of substantially lower reluctance than any shunt" path around the secondary coil section connected to said condenser.

12. In a luminescent tube lighting system, the combination of a transformer of the shell type having a primary and plurality of secondary coil sections mounted on a central core leg, a plurality of luminescent tube loads individually connected to individual secondary coil sections, condenser means included in the circuit of at least one of said tube loads and secondary coil sections and for reducing stroboscopic efiect of the tube loads, and magnetic core shunt means around at least one other of said secondary coil sections for limiting the current therein, said core shunt means being of substantially lower reluctance than any shunt path around the secondary coil section connected to said condenser means.

CHARLES PHILIPPE BOUCI-IER. FREDERICK AUGUST KUl-IL.

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