US2575093A - Transformer - Google Patents

Description

Nov. 13, 1951 J BR|DGE$ 2,575,093

TRANSFORMER Original Filed June 25, 1942 2 SHEETS-SHEET l INVENTOR Jan/v f/sxow 519/0655 Nov. 13, 1951 J. H. BRIDGES 2,575,093

TRANSFORMER Original Filed June 25, 1942 2 SHEETS-SHEET 2 E I E 5 2.9:! @F 280 /20 T/a lllllllllllulll I ml Illll IMF ll II I 'JHIIIIIIII HI Ill 1 VENTOR Jo/m Hero/0 Bridges HIS ATTORNEY Patented Nov. 13, 1951 TRAN SFORIVIER John Herold Bridges, Paterson, N. J., assignor, by mesne assignments, to National Inventions Corporation, a corporation of New Jersey Original application June 25, 1942, Serial No. 448,471. .Divided and this application August 12, 1943, Serial No. 498,345

4 Claims. (Cl. 171-119) My application is a division of my co-pending application Serial No. 448,471, filed June 25, 1942. entitled Luminescent Tube System, now Patent 2,370,635 of March 6, 1945, and the invention relates to fluorescent lighting equipment, and more particularly concerns a new transformer power unit and associated system, for powering fluorescent space discharge tubes.

I An object of my invention, therefore, is to produce a simple, compact, sturdy, reliable and inexpensive transformer, having high leakage reactance, characterized by the small iron content required, its low operation and maintenance costs, and its good voltage regulation.

Another object is to produce an autotransformer embodying all of the advantages set forth in the foregoing, and the windings of which are disposed in the smallest possible compass.

A still further object is to produce a new fluorescent tube lighting system embodying a transformer power unit having the advantages described, and possessing the qualities of quick striking, long tube life, steady tube operation in the substantial absence of detrimental flicker even during cold weather operation, the substantial elimination of undesired stroboscopic effect, and high system power factor.

Other objects and advantages will in part be obvious and in part pointed out hereinafter.

My invention, accordingly, resides in the several elements, features of construction, and op-' erational steps, and in 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 drawings, Figure 1 is a schematic elevation of a transformer and attendant system embodying the principles of my invention.

Figure 2 depicts the electrical circuits according to my invention; while Figures 3 and a are graphs illustrating wave forms on the condensive and inductive sides, respectively, of the system according to my invention; and

Figure 5 illustrates a modified embodiment of my invention.

To facilitate more thorough understanding of my new transformer and system, it may be noted that the illumination art has come more and more to accept fluorescent tube lighting as a customary and desirable expedient in a number of widely diversified fields involving both general and specialized illuminating problems. Many factors contribute to this rapid acceptance oi 2 fluorescent lighting. Among them may be cited, simply by way of illustration and by no means intended as exclusive, the high lighting efliciency of such tubes for unit power input, whereby maximum light output can be achieved at a minimum of cost; as well as the low temperatures at which such tubes operate, whereby in entirely practical manner, high intensity lighting of comparatively low brilliance can be achieved in enclosed spaces.

Because of the economies of such fluorescent lighting from a power standpoint, it makes entirely feasible, for the first time, the use of adequate lighting for advertising and other purposes, in those cases where for economic reasons. adequate illumination was hitherto impossible. The economy of such lighting is contributed to by the long life of the fluorescent tube, which at the present time, is rated at between 2 to 2%, times longer life than are the best grade of incandescent lamps now on the market.

The active light emission region of these tubes being long as compared to the light source in incandescent bulbs produces an intense but diffused light of low brilliance which lends itself admirably to flood light efi'ecm. It is entirely possible, because of the low operation costs and the low temperatures at which the tubes operate, to employ them in batteries of two, three, four, or more tubes. Thus arranged, they may be employed in extremely satisfactory flood lighting displays. Their use has become widespread in both indoor and outdoor fields where daylight conditions must be approximated, as for example, in factories, filling stations and the like.

It is possible to vary the characteristic color of particular tubes within wide limits to satisfy the particular lighting problem in question, simphr by employing different fluorescent salts or phosphors as liners for the tubes, the particular visible secondary radiation of such salts having previously been determined and calibrated by experiment. It is this feature. widely at variance with the substantially fixed quality of radiation available from the known filamentary lamp, which has constituted an important factor contributing to the present-day widespread use of fluorescent lighting in advertising, store and household lighting.

Despite, however, the rapid growth of fluorescent tube lighting practice, to its present day important position in the illumination field, many defects, serious from a practical standpoint, remain to be removed before fullest exploitation of such equipment can be undertaken.

To illustrate, for example, heretofore such fluorescent tubes have been designed for operation across ordinary 110 volt or 220 volt service lines. Difliculty is encountered, however, in that these low voltage tubes do not start with any degree of facility on the ordinary service potentials. Consequently, it frequently becomes necessary to equip them with an additional starting electrode, and in all instances a starting switch must be supplied for each such low potential tube. Such switches ordinarily take one of three conventional forms: the magnetic relay, the thermal, or the glow-discharge type. All of these switches are found to be comparatively slow in starting, requiring about six seconds on the average to strike the arc, while in the glow-discharge type of switch, difllculty is experienced in quickly restriking the arc, once it has extinguished for any reason, after being initially struck.

Additionally, where several tubes are operated in parallel, a starting compensator is found to be required, disposed in series circuit with that tube of leading current demand, to ensure that sufllcient voltage is applied initially to strike the arc across that tube. charge tubes have negative resistance characteristics, by which is meant that once the arc is struck, the resistance of the discharge path thereacross will decrease to such extremely small value that unless adequate current-limiting means are provided, the current across the arc will increase to a prohibitive value, either destroying the tube load or burning out or interrupting the electrical energy supply thereto. In low-voltage tube systems essential current-limiting means usually takes the form of an ohmic resistance on the less expensive installations, or of an iron-core choke coil in the more costly units.

All of these auxiliaries, as they are called, require complicated and expensive installation technique and demand many electrical connections. Their large number of auxiliaries for a battery or bank of tubes results in a bulky assembly, neat appearance of the complete assembly and simplicity in installation being dimcult, indeed, well-nigh impossible to achieve. Each such auxiliary separately constitutes a potential source of disturbance in the system and issubject to getting out of order or failure, giving rise to attendant maintenance or repair costs. Too, it-is evident that although the cost of each auxiliary may in itself be a comparatively small item, nevertheless when it is considered that it is customary to employ such tubes in banks or batteries of two or more, and that despite this, each tube still requires its own complement of auxiliaries, it is at once evident that the total cost cannot escape being high.

Furthermore, the comparatively small iron content of the iron .core ballasts and the absence of iron in the ohmic resistors, result in poor voltage regulation, so that the tube equipment is extremely sensitive to variation in line voltage.

The low terminal voltage at which these hot cathode tubes are operated gives rise to the series disadvantages in cold weather operation of either detrimental flicker, or in extreme cases, of extinguishment of the arc. For like reason, it is diflicuit or even impossible, where low-potential, hot-cathode tube equipment is employed, to strike the arc initially when extremely cold weather conditions prevail. This undesirable phenomenon is attributable to the fact that the striking potential of the tubes is close to the peak voltage obtainable from the ordinary service Finally, these are dis-- mains, whereby no reserve of impressed voltage is present to accommodate even slight increase over rated value of the striking potential of the arc.

Experience demonstrates that hot-cathode tubes employed in hot-cathode operation in lowvoltage systems are comparatively short-lived, this short life being contributed to by a number of causes. Among them may be listed by way of illustration, the inherent fragility of the incandescible filaments employed. It is wellrecognized to be characteristic of such filaments that in operation, the arc tends to settle locally at one point thereon, usually the high voltage end. Burning follows, shortly attended by failure of the electrode, whereupon the tube displays rectifier action, attended by continuous flicker and usually followed by early failure of the other electrode.

Additionally, reliance is placed in striking the arc across these low-voltage, hot-cathode tubes, on copious emission of electrons from the electrodes thereof. To this end, the electrodes are customarily coated with a suitable electron-emitting substance, usually a suitable oxide. During operation, however, this electron coating is gradually dissipated, so that for this, as well as for the other reasons set forth hereinbefore, the low-voltage, hot-cathode tubes do not display the long life which is desirable in this art.

Considerable research has been carried out by various workers skilled in the art, looking for one or more solutions for the various problems set forth in the foregoing. Among the more important developments, that of materially increasing the terminal voltages at which the fluorescent tubes are energized, at the same time employing them in cold-cathode operation, is outstanding. It has been proposed that those elevated voltages be transformed directly through the intermediary of a transformer from service mains of conventional voltage rating, such as or 220 volts.

For such transformer system operation, either a specially designed cold-cathode tube or an adapted hot-cathode tube is employed, Hotcathode tubes, which are readily available on the market, are conveniently adapted for coldcathode operation simply by short-circuiting the terminals of the electrodes thereof to ensure that all portions of a particular electrode are maintained at the same potential. It was found that by observing proper precautions in the operation of these hot-cathode tubes on cold-cathode operation, they display great ruggedness, and their effective lives are prolonged considerably over what had hitherto been experienced.

To economize on both space and materials required, and in general to reduce production cost to a minimum, recourse preferably has been had to autotransformer equipment. Up to the limiting voltage permitted by the Fire Underwriters, such transformer equipment is entirely satisfactory, although slightly higher in first cost than is the conventional hot-cathode tube lighting unit, including its necessary auxiliaries. The sturdiness of such equipment and the small amount of attention and supervision required thereby make its total cost, including maintenance, only a little, if any, greater than the comparable cost of the hot-cathode equipment. When such transformers are employed, either as single or double transformers, i. e., transformers having one or two separate secondaries, to

energize banks of two, three or more tubes, thenthe absence of the hitherto ail-essential auxiliaries is found to bring the unit cost to a value lower than that of the hot-cathode tubes.

It is not suiilcient, however, simply to interpose a transformer between the line and the fluorescent tube load, because such ordinary transformer, either with simple or autotransformer connection, does not provide sufllcient impedance to prevent enormous build-up of current and voltage across the secondary, once the arc across the tube is struck. On the other hand, if rccourse be had to auxiliaries to ballast the tubes. then one of the main purposes of employing transformer energization means, namely, keeping the over-all cost to a minimum, would be defeated. This difilculty has been alleviated by providing in the iron core of the transformer, between the primary and secondary windings. high leakage reactance shunts. These shunts normally have no effect when the secondary windings are de-energized, so that substantially all of the primary flux from the primary winding courses along the main magnetic path or paths, interlinking the secondary winding or windings. However, when the arc strikes across the load consisting of one or more tubes, changing the reluctance of the main flux path, these shunts then display a reluctance lower than that of the main magnetic path. This change in reluctance of the main magnetic path results from the back magneto-motive force set up by the energized secondary winding. The main stream of primary flux then courses across these high reiuctance magnetic shunts, with their included air-gaps, the calibration of the shunts being such that justsufilcient primary flux interlinks the secondary winding or windings to induce a voltage and current therein sufficient to maintain the are across the tube load.

Such new tube lighting equipment, consisting oi a transformer fluorescent tube lighting system and associated power unit, displays many extremely important and thoroughly practical advantages as contrasted with the lower voltage, hot-cathode tube lighting units theretofore employed. The are across the tube displays quick striking characteristics, and can readily be restruck, should it momentarily extinguish for any reason. The number of parts is reduced to a minimum. A far smaller number of external connections is required than had hitherto been the case. The power unit is simple and of small size. The sturdiness of the lighting unit, even with outdoor use and while subjected to severe weather conditions, is found to be outstanding.

The higher rated voltages make it entirely feasible, from a practical standpoint, to operate the tubes under dimmer conditions, i. e., at primary terminal voltages which are lower than the rated terminal voitages. The higher secondary voltages, substantially in excess of the striking potential of the tube, permit a reduction in the secondary voltage, while still maintaining the peaks of the second voltage wave form substantially in excess of the striking potentials of the tubes. When so operated, the period during which the arc remains energized across the tube during each current halt-cycle is decreased, so that the total quantity or" light per unit of time is diminished, thus giving rise to the dimmer action referred to.

Many further refinements and improvements upon the transformer-powered cold cathode fluorescent tube lighting systems of the type defore the full field of utilization'of this equipment can be exploited. For example, while the life of the tubes employed in transformer-powered units of the type described is satisfactory, measured on an absolute basis, the results nevertheless are somewhat disappointing in that this life is not quite as great as appears to be indicated, from theoretical considerations. The decrease in tube life, determined experimentally, from the anticipated ideal value constituted a most perplexing problem, no satisfactory solution for which was brought forward for a considerable time span. Finally, however, it was discovered that the double transformer, which had been used in so many lighting systems to achieve economies therein, was probably at fault. The combination of capacitative and inductive reactances, constituted by the tube load and secondary winding, frequently produces resonance effects in one or both secondaries which are then transmitted through the auto-connected primary winding to the other secondary winding, creating disturbances and surges therein. The eifect is cumulative and reciprocal, so that after the passage of a number of current cycles, extremely high resonating and transient voltages are built up, which particularly display themselves at the moments of striking and extinguishment of the arc during each current half-cycle. These high voltages have very disturbing effects on the tube, decreasing the life thereof appreciably, sputtering the electrode materials and destroying the electrodes themselves, depositing the sputtered electrode material on the walls of the tube so as to coat the fluorescent lining thereof serving as a trap in which toocclude the gas content of the tube, resulting in hardening of the tube, decreasing the electrode emissive qualities of the sputtered electrode, and perhaps eventually destroying either the tube or the associated equipment by puncturing the insulation thereof.

. An important object of my invention, therefore, is to eliminate in large measure the undesirable transient waves in transformer equipment referred to, and to produce a new transformer power unit and a new fluorescent tube lighting system which are characterized by their uniformly good wave form, the substantial absence of detrimental high-voltage transients, and by the long life of the tube units employed in such system.

Additionally, appreciable reduction in the iron content required of the transformer unit would result in appreciable savings in the cost of production, as well as in the size of the unit. This reasonably can be'expected to enhance appreciably the acceptance of this type of tube lighting equipment beyond even the already assured and established position and acceptance which such equipment occupies in the art. A further object of my invention, therefore, is to produce a transformer having high leakage reactance characteristics and which is adapted for powering fluorescent tube lighting systems, which transformer is characterized by its extremely small size for rated power output and which requires a minimum of ironcontent for rated efficiency and rated voltage regulation of the asso= ciated load, and which transformer is simple, compact, sturly and inexpensive, both to produce and to operate, and which at the same time is highly practical and complies fully with all of the requirements of the Fire Underwriters.

Referring now more particularly to the emscribed, however, remain to be accomplished, be- 4'6 bodiment of my invention depicted in Figure l,

therein the transformer core is indicated generally at I I. This core consists illustratively of a central, longitudinally extending leg II, flanked on opposite sides, preferably at equal distances therefrom, by two similar outer legs I2 and I3 extending parallel thereto. Corresponding ends similar outer legs or end pieces I4 and I5.

While as has been described, and for purposes of symmetry, and so that the flux courses through the branch magnetic paths to be described. will be substantially equal, I prefer to space the outer legs of similar magnetic proportions equally distant from the central leg II, it is not absolutely essential that this be done, and it is entirely possible that the spacing or magnetic properties of any or all of the outer legs, as well as the inner leg II, can be increased or dec eased within wide limits. In point of fact, an operable structure can be achieved with the removal of one of the outer legs in its entirety. However, I prefer to construct the core so as to produce the balanced, shell-type transformer illustrated, giving a trans' former which is reduced to the smallest possible compassconsistent with good magnetic and electrical characteristics and performance. Intermediate the lengths of the outer legs I2, I3, I provide high leakage reactance magnetic shunts Shi and Shz, respectively, extending towards but short of the central leg II', ,forming therebetween air-gaps G; and G2. Preferably, these shunts, as well as the other parts of the core structure, are constructed of laminated iron material.

The air-gaps G1, G2 are constructed to have a desired and predetermined high reluctance, calibrated in accordance with the admittance of that part of the main flux path illustrated at the left of the shunts in Figure 1, when that main flux path is operating under load conditions. More will be said-about this action at a later point in this description.

The shunts have the effect of dividing the openings provided between central and outer legs into two pairs of spaces, one pair on each side of said shunts. In one said space, to the right of the shunts in Figure 1, I provide a primary winding I6, about the central leg I I, which said winding is energized through leads I I and I 8. by a suitable source of altemating-current energy I9.

Since it is desirable to energize the system from the ordinary service mains, which usually are of approximately either 110 or 220 volt rating, and since I desire to operate by tubes at the maximum of 600 volts secondary terminal voltage permitted by the Fire Underwriters for autotransformer-connection, or even at higher voltages when the autotrasformer-connection and its resulting copper savings are dispensed with, and general transformer connection resorted to, I construct my transformer of the step-up type, with the eflective secondary windings having a substantially greater voltage per turn than does the primary winding.

I provide my transformer with two secondary windings, one in each -of the mentioned pair of spaces. The first secondary winding, indicated at 20, preferably is wound, as shown, directly on the primary winding I6, thus ffecting material economies in core material and in the total space requirement of the power unit. It is entirely feasible, if desired, however, to elongate legs II, I2 and I3, and to position the secondary winding 26 at the side of the primary winding, separate therefrom, but within the first pair of spaces as thus elongated as illustrated in Figure of the outer legs and central leg are closed by 34in which parts corresponding to those of Figes 1 and 2 are indicated by like numerals but with the subscript "0. added.

It is evident that the primary winding in the embodiments shown, is electrically separate and independent of the secondary winding 26, and has no direct electrical connection therewith. This secondary winding 20 is only inductively associated with the primary winding I6. 'Additionally, with the secondary winding 20 being mounted on central leg II and on the same side of shunts Shi, Shz as is the primary winding I6, the shunts exert no current-limiting effect when the arc strikes across the tube load of this secondary winding. A power-factor correcting condenser C ,advisedly is employed where it is desired to restore the system power-factor to approximately unity. Reliance also is placed upon this condenser for current-limiting action in the load circuit of secondary coil section 20, as is more fully described hereinafter.

In the secondary pair of-spaces, a second secondary winding 2| is provided, on the opposite side of shunts Shi, $712 from the primarywinding I6, and this secondary winding H is connected in autotransformer connection across the primary winding I6. Circuits may be traced from primary winding I6 to secondary winding 2i as follows: from the left-hand end of winding I6 in Figure 1, down through lead II to junction 22; thence through lead 23 to the right-hand end of secondary winding 2| in Figure 1, to the left across this secondary winding to the left-hand terminal thereof, then down through lead 24 to tube T2, lead 25, junction 26, and up through lead I 8. to the right-hand end of primary winding I6.

It may be pointed out at this time that secondary winding 20 directly energizes tube T1 and condenser C through leads 2! and 28. A circuit may be traced from the left-hand end of winding 26 in Figure 1, lead 28, tube T1, condenser C and lead 21 back to the right-hand end of secondary winding 20. The source I9 of alternating current electrical energy energizes winding I6 through a circuit of periodically reversing direction, traced as follows for a given current half-cycle: to the right in Figure 1 from source I9, up through lead I8, to the right-hand end of winding I6, across the winding and back through'lead I! to the lefthand end of the power source. During the next successive current half-cycle, of course, the direction of current flow is just the reverse of that traced.

It is interesting, as well as highly instructive, to consider at this point, the manner in which the primary flux courses the flux paths through the illustrative magnetic core which has been described. For this purpose, consideration is given to an instantaneous direction of flow of primary current through winding I6 such that the primary flux developed thereby courses to the right in Figure 1 along central leg II from winding I6. When the flux reaches end piece I4, it courses along two individual paths of low reluctance, one said path sequentially including end piece I4, core leg I2, and end piece I5 to leg II. Similarly, the second fiux path sequentially includes end piece I4, core leg I3, end piece I5 to leg II.

Since the flux seeks paths of least reluctance, the high reluctance magnetic by-passes Shl, G1 and Shz, G2, respectively are in large measure avoided, and only an extremely small part of the flux courses across these shunt paths. to the central leg II, and back to primary winding I6.

awaoas As has been stated, by far the greater part of the flux courses along the two individual paths of low reluctance; which paths reunite at the lefthand end of inner core leg H, and return along leg II to primary winding I6. It will be noted that at all times the full quantity of primary flux links the secondary winding 20, and develops a rated high voltage therein. Similarly, before the secondary tube load T: across winding 2| has been energized as a result of the arc strikin thereacross, either initially or during any current half-cycle, substantially the full primary flux links winding 2|, inducing a high voltage therein.

Because of the high secondary voltages employed, as has been stated hereinbefore. the terminal voltages oi the secondary windings, impressed directly across the electrodes of the associated tube loads, bring these tubes to a high degree of excitation so that after the passage of but a comparatively few cycles of current flow, the arcs in the several tubes ignite, and steady operating conditions maintain.

As soon as the tube load Tl becomes energized, a back magneto-motive force is developed in winding 20, tending to buck the primary flux from ll. Because no magnetic by-pass is provided bea tween windings 20 and I6; flux continues to course the main magnetic core.

when the are strikes across tube T2, the back magneto-motive force developed in winding II is found to afiord considerable reluctance to the coursing of the primary flux along the path encircled by winding 2|. Always seeking the path or paths of least reluctance, therefore, and since the magnetic by-passes Shr, G1, Shz, G1 are now oi lower reluctance than the main path interlinking winding 2|, the flux coursing the individual magnetic paths, travels down shunt leg Ski and across air-gap G1, and up shunt leg sh: and across air-gap Ga, respectively, directly back to primary winding i6, and in large measure bypasses winding 2|. At such times when the arc is struck across tube T2 and the tube remains energized, the shunts because of their design, permit only enough primary flux to interlink winding ii to provide sufiicient voltage and current to ensure energization of tube T2.

' During the next subsequent and alternate halfcycle of primary current flow, the direction of coursing of the primary flux is just the reverse oil that which has been traced. From winding it, the flux courses along leg II to the left in Figure l. Very small quantities of flux course, across air-gap G1, up shunt Shl, to the right along leg i2 and down end piece I4, leg ii, back to windin 96; and down across air-gap G2, shunt leg Sits, to the right along leg [3, up end piece it, leg ii, and back to winding l6. By far the greater part continues to the left along le ll, interlinking winding 2! and inducing a high voltage therein. At end piece I5, the main flux separates into two substantially equal branches. The flux courses, in part, up end piece iii, to the right in Figure 1 along leg l2, down end piece 14, to leg H; and, in part, courses down end piece 05, to the right in Figure 1 along leg l3, and up end piece it to leg II. There the flux reunites and courses along leg H back to winding IE, interlinking winding 20. When the are initially strikes across tube T1, and when it strikes anew in each current half-cycle, the back magnetomotive force developed thereby has relatively little cheat on the primary flux. for the reasons pointed out hereinbefore.

However, as soon as the arc strikes across tube 7 or paths of least reluctance, by far the larger part of the primary flux at this time courses across two shunt paths, eflectively by-passing in large measure the secondary winding 2|. Flux courses, in part, up across air-gap G1, Shi. to the right along leg l2, down end piece I, and back through leg H to winding l6; and courses, in part, down across air-gap G2, Shz; to the right along leg l3, up end piece I4, and back along leg II to winding It. Only a smallamount of the primary flux, sufllcient to maintain the voltage and current required for tube T2, continues coursing the length of leg I I, interlinking winding 2i and splitting at end piece l5 into two branches which course back to winding it through legs I2 and IS in the manner previously discussed.

Toward the end of each half-cycle primary charging flux, as the value of the flux decreases, the induced voltage drops to a point where the are across the associated tube load extinguishes, whereupon the back magneto-motive force at once disappears. The reluctance of the main flux paths drops to its former value, so that the flux no longer courses the high leakage reactance shunt paths, but resumes coursin the main flux paths until at such times as the arcs are re-lgnited.

Tubes T1 and T2 are of the usual fluorescent gas discharge type in that they are designed so that a large part or the input energy is converted to what is known as the reasonance line, 2537 3., in the ultra-violet portion of the tube spectrum. This radiation serves to excite the particular photoelectric coating or lining, known as a phosphor, provided on the interior walls of the tube, and which energized, gives rise to a desired characteristic radiation. As stated, the tubes may either be the available hot-cathode tubes now on the market, with short-circuited cathodes to ensure unipotential electrodes, or cold-cathode tubes designed especially for the particular use to which they are to be put.

Since secondary winding 20 from a magnetic standpoint is disposed on the same side of shunts Shi, G1, and Shz, G2 as is winding i8, and is in only inductive association with the primary wind-' ing, the transformer, certainly within the saturation limits of the iron core thereof, exercises no appreciable control action on the build-up of current flow across the tube load of negative resist-' ance characteristics. However, since the predominately inductive nature of the load across source l8 requires the use 01' a balancing capacitative reactance to restore somewhat the system power-factor, this capacitative reactance.-

iarads.

In operation, probably because the winding 20 is not in autotransformer connection with primary l6 but is only inductively associated theres l V with, disturbances arising in one of the secondary circuits are substantially damped from the other secondary circuit. Thus, in a lighting system according to our invention, all substantial teriiency towards cumulative resonating effects or transient disturbances between transformer secondary windings is substantially suppressed, giving improved light emission and prolonged .tube life.

- In Figure 3. for example, a graph is shown of one cycle of the current flow on the T1 or condensor side of the transformer system, while in Figure l is displayed one cycle on the T: or inductive side of the line; In the latter case, the wave form is nearly sine-wave in nature. In each case, the abcissae are current values, while the ordinates are units of time. Substantially all ripples at the striking and extinguishment of the are are avoided by directly shunting tubes T1 and T2,

- time achieving a thoroughly practical power unit and associated system in which the iron content is reduced to a minimum with no decrease in good voltage regulation. Theresulting unit is small, compact, requires a minimum of space and conveniently is mounted, for example, directly on the reflector of a tube assembly, and has a minimum number of external connections.

The new system which I produce has high system power factor, so that energy consumption, and hence costs, is reduced to a minimum, and

waste power, dissipated in heat, is negligible.

Transient harmonics of any appreciable 'or detrimental value are substantially eliminated, so that a smooth, almost ideal wave form results, with no detrimental'over -voltages, and so that both the new transformer and system comply fully with the requirements of the Fire Underwriters.

Attributable in large measure to the substantial absence of high voltage harmonics and the consequent presence only of rated voltages, the tube life is greatly prolonged, and the electrode material thereof is unharmed by sputteringor similar phenomena. Little if any electrode material is volatilized ofi and deposited as an opaque lining on the tube walls, so that light transmission remains substantially constant throughout the normallife of the tube. Similarly, there is no occlusion of the gas content of the tube by any such deposited coating, as a result of which there is a substantial absence of the detrimental phenomenon known as hardening. No appreciable .decrease in the electron-emitting qualities of the electrodes is experienced during the rated life of the tubes. These several last-mentioned advantageous features contribute to light emission of substantially uniform quality throughout the useful life of the tubes.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiment hereinbefore set forth, it is to be understood that all matter described herein is to be interpreted as illustrative, and not in a limiting sense.

I claim:

1. A transformer, comprising in combination, a

primary winding and two secondary winding coil sections only, with one secondary coil section nections for two loads, one including onesecondary winding coil section and the other including the other secondary coil section, at least one of said terminal connections also including said autoconnected primary winding.

2. A transformer, comprising in combination, a primary winding and two secondary winding coil sections only, with one secondary coil section tightly coupled with said primary and the other secondary coil section loosely coupled therewith; a main magnetic core linking said primary winding and two secondary winding coil sections; magnetic shunt core means positioned between the primary winding and said loosely coupled secondary coil sections; terminal connections for two loads, one including one secondary winding coil section and the other including the other secondary coil section; and electrical input connections to said primary winding.

3. A transformer comprising in combinatioma magnetic core; three windings only positioned on said core and comprising a primary winding and two secondary windings, with one of said secondary windings spaced from said primary winding and loosely coupled therewith and the other secondary winding positioned on top of the primary winding and closely coupled therewith; magnetic core shunt means positioned between the primary winding and said spaced secondary winding; terminal connections for two loads, one including one secondary winding and the other including the other secondary winding; and electrical input connections to said primary windmg.

4. A transformer comprising in combination, a shell-type core having a central leg and two outer legs; three windings only positioned along the central leg of said core and comprising a primary winding and two secondary windings, with one of said secondary windings positioned on one side of said primary winding, being spaced therefrom and loosely coupled therewith and the other secondary winding positioned on the other side of said primary winding and tightly coupled therewith; magnetic core shunt means positioned between the primary winding and said loosely coupled winding; and terminal connections for two loads, one including one secondary winding and the other including the other secondary winding.

JOHN HEROLD BRIDGES.

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

UNITED STATES PATENTS

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