US2546968A - Transformer - Google Patents

Description

April 3, 1951 J. H. BRIDGES 2,546,968

TRANSFORMER Filed Nov. 25, 1944 76a @y 20a- L20 s (lttorneg Patented Apr. 3, 1951 atteste 'raANsFonMEn John Herold Bridges, Paterson, N. E., assignor, by mesne assignments, to National Inventions Corporation, a corporation of New Jersey Application November 25, 1944;, Serial No. 565,129

(Cl. S23-*60) 5 Claims.

My invention is a continuation in part of my copending application Serial No. 448,471, tiled June 25, i942, and entitled Luminescent Tube System now Patent 2,878,635 of March 6, 1945. The invention is directed to a new and improved transformer unit displaying many advantageous features of great practical importance, as well as to a new luminescent tube power unit embodying the new transformer, and to a new tube lighting system incorporating the new power unit and itself giving many practical advantages in actual operation.

An important object oi my invention is to provide a transformer particular adapted for powering gaseous electric di: rarge tube lighting eqnipment, which transformer is simplified and stream-lined in external conguration, itself cccupying an overall minimum of volumetric capacity, and in which iron content is reduced to a minimum, all windings are securely anchored in a minimum o space, and with which high leakage reactance and excellent voltage regulation are obtained.

Another object is to produce an autotransformer embodying many of the aforementioned advantages, and in which mutual reaction between the various coils and windings is reduced to a minimum.

Another object is to provide a power unit for gaseous electric discharge tube lighting, of low cost, embodying a transformer unit of the type described, and displaying extreme ruggedness, durability and compaotnsss, wherein all available space is effectively and advantageously utilized, thereby minimizing space requirements, and which is simple and inexpensive, both in construction and in subsequent operation and maintenance.

Still another object is t0 provide a new tube lighting system, employing as an element thereof a power unit embodying the several advantageous features set forth hereinbefore, and which is cperable in entirely efficient. reliable and satisfactory manner under practically all extremes of weather conditions, and with substantally all types and shapes of reflectors, whether they be constructed entirely or in part of electrically conducting or non-conducting materials, and which is neat, simple, compact and possesses small and symmetrical space requirements.

Another object is to provide a iiuorescent tube lighting system of the general type described, displaying quick-starting characteristics, steady and reliable operation in cold weather in the substantial absence of detrimental `flicker, which has high system power factor and good, smooth wave form, which operates in the substantial absence of undesirable stroboscopic el'i'ect, and moreover, will iunction in entirely satisfactory manner, both in starting and in subsequent operation, with substantial decrease for any cause in service potential.

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

v'y invention accordingly resides in the several parts, elements, and features of construction, and in the several operational steps, as well as in the relation of each of the same to one or more of the others, all is more fully described hereinafter, the scope or" the application or all of Which is more fully set forth in the claims.

In the drawings,

Figure l is a View, largely schematic, partly in side elevation and partly in section, of one embodiment of the improved system according to my invention;

Figure 2 is an end View of the same embodiment; while Figure 3 constitutes a wiring diagram of another embodiment of my invention, and disclosing certain advantageous features inherent therein.

As conducive to a clearer understanding of certain features of my invention reference is made at this point to an autotransiormer-energized lighting system disclosed in the hereinbefore noted parent application for patent in which system several secondary coils of the transformer are employed for operating plurality of coldcathode gaseous electric discharge tubes at high voltages. Among the beneficial aspects oi this system are improved light emission and longer Vvube life g ed irom improved wave form more nearly approaching ideal sine wave form, all with material suppression of disturbing and undesirable harmonics.

I achieve the improved wave form by electrically isolating one of the secondaries from the other transformer windings, associating it solely in ordinary lor inductive transformer relationship both with the primary and with the other seconda-ry or secondaries. In this manner no electrical connections exist between the several secondaries, and the transient disturbances in one secondary circuit are effectively damped out before they reach the other secondaries. In the same measure resonating conditions are substantially avoided.

A condenser of large capacity, in circuit with the electrically-independent secondary, is relied 3 upon to interpose a proper impedance upon load conditions prevailing. This condenser serves the additional highly advantageous dual function of restoring the system power factor to substantial unity, and of eliminating undesirable system flicker in emitted radiation, by throwing the moment of illumination of one tube during each half cycle out of phase with the corresponding moment of emission of the other tube or tubes. This eliminates, or at least minimizes, undesirable stroboscopic effects.

Although markedly superior results are observed by the practice of my invention as set forth inthe co-pending application, certain difficulties are found to remain without correction, and require further investigation.

I have found in way of example that where a battery of two or more tubes, of generally similar characteristics, are powered on a single, balanced power unit, then when Masonite or other non-metallic reflectors are associated with the tubes, a practice which frequently is desirable for electrical reasons, as in outdoor installations, the power unit will not function reliably in the absence of certain precautions so as to maintain arcs across the tubes.

Moreover, power units of the general type described in the cci-pending application, while reduced in dimensions over many prior installations, nevertheless interpose space requirements 1 which on occasions are found to be excessively large. When it is considered that these power units frequently are installed on the tube reflectors, it is readily appreciated that available space must be utilized with maximum efficiency for it to sufice.

While material improvement in wave form has already been achieved according to the teaching of my parent application, further smoothing action is always desirable, and with my new construction is achieved with even greater success.

Accordingly, an extremely important object of my present invention is to minimize the disadvantages and difficulties encountered in the practice of the art as it existed heretofore, and to provide a new transformer unit, a power unit embodying the same, and a lighting system incorporating my newpower unit, which system will function with entire satisfaction, and with quick energizing and stable arc characteristics with substantially all types of tube housings or reflectors even under extreme weather conditions; in which space requirements are made symmetrical and are reduced tc the barest minimum; and which in operation displays both improved wave form and entirely satisfactory system performance.

.With these and many other thoroughly practical obectives in mind, reference is now had to the illustrative embodiments disclosed in the accompanying drawings to facilitate a more detailed description of certain features of my invention.

Referring now more particularly to the practice of my invention, I provide a transformer having a core generally indicated by reference numeral I!) (see Figure l) which core in the preferred embodiment comprises three separate elements rigidly clamped together in firm juxtaposition. In the embodiment illustrated the core comprises two similar core elementsVV II substantially E-like in configuration, disposed on their sides, facing each other and with a central bar I5 clamped firmly between their end legs. This greatly simplies the process of stamping the core laminaticns and reduces waste metal to a minimum.

The E-shaped members each include a shunt portion which terminates a calibrated distance short of the central bar. These core elements are clamped together by co-operating bolted core bands clasped about the end legs; while clamp-like U-shaped clips are sprung snugly along the extent 0f the shunt legs so as to minimize hysteresis losses and in large measure suppress undesired chatter of the core lamination.

lin a typical instance the core E-members II will have an over-all length of about 6 inches. They are comprised of a stack, about l inch thick, of laminations stamped from 26 gauge transformer grade, prime quality low loss iron, with silicon content ranging from about 1.10% to about 4.5%. A longitudinal core portion I2, of each E member, extending horizontally in Figure l, is provided with substantially perpendicularly disposed like end legs I3, Hi, and with an intermediate shunt leg I 9 strategically disposed in accordance with the teachings hereinafter set forth substantially in perpendicular relation, along its length. This intermediate leg is a calibrated distance shorter than the outer legs as measured from the core portion i2.

Bar l5, about 61/2 inches long, and about l inch square in section, extends longitudinally of the E-members il.

U-shaped clamps I5 are provided, with yoke portions Ia embracing core portions l2 of E- members II in the region of end legs I3, Ill, and with substantially perpendicular leg members lh, Ib engaging snugly along opposite sides of each end leg I3, Ill, all in a manner fully depicted in Figure l of the drawings. These bands preferably stamped from cold rolled steel, are provided with terminal flanges IBc at each end thereof, flaring outwardly substantially at right angles, as shown in Figure 2, and provided with suitable bolt holes. Thus, when assembled, the clamp members i6, I@ on opposed legs I3, I3 of like E- members Ii are disposed in opposed relation, with their flange portions IEC, Ic adjacent each other. Similar conditions maintain at the other end of the transformer core, with end legs Ill, I4. A suitable bolt Il extends through each pair of holes in adjacent nanges IIc, while a suitable nut I8 is threadedly received thereon. When nuts i8 are threaded down on bolts I1, the clamps I6 are drawn firmly about the transformer core elements. They thereby secure these elements firmly together, and as well, effectively suppress detrimental lamination chatter.

The spring clamps or clips 2B engaging about shunts I9, I9 r'ely entirely upon spring action to clamp the laminations of these shunts against chatter. The yoke portions 20a of these clamps engage transversely about core portion I2 of the E-members in the regions where the shunts are struck off. rThe legs Zub, 25h of these clamps are sprung slightly inwardly, to provide the required spring clamping action, and extend along the outer longitudinal extent of these shunts. Chatter of the shunts isthus effectively prevented.

It will be noted that the intermediate shunts is, IS aid in defining two asymmetrical sets of paired like spaces in the assembled core, the pair on the right in Figure l being larger than the pair on the left. The left-hand pair of core spaces is adapted to receive a transformer secondary coil which is electrically connected to the transformer primary, while the larger pair of core spaces receive. both a primary winding and a secondary coil which is preferably electrically independent of the primary.

, resid by means of lead 26, to one terminal 21 of a large capacity condenser 28. The condenser serves as an impedance for fluorescent tube 3|, with which it is connected by lead 30 extending from condenser terminal 29.- A lead 32 connects the other tube terminal to the other terminal of secondary 25. It will be appreciated that the coil 25 is electrically independent of primary winding 2|, but is closely coupled in magnetic circuit therewith as will be pointed out more fully hereinafter.

In the smaller pair of core spaces, at the left in Figure 1, secondary coil 33, wound about core bar I5, is connected at one terminal, by lead 34, to nuorescent tube 35. The secondary coil 33 is electrically connected in autotransformer rela tion with primary winding 2|: "To provide this connection, lead 36 extends from `the right end of tube 35. Figure 1,-.to junction 31 with lead 23 of.k the primary circuit. Similarly, lead 39 extends from junction 38 with lead 22 of the primary circuit, to the right side of secondary coil 33. An autotransformer secondary circuit is thus established for secondary coil 33 which may be traced as follows: From the left end of secondary 33, Figure 1, through lead 34, tube 35, lead 36. junction 31, lead 23, to the right side of primary winding 2|; through the primary winding thence along lead 22 to junction 38, over lead 39, and back to the right side of the secondary coil.

A primary circuit may be traced as follows: From the left side of primary winding 2|, lead 22, service supply 24, lead 23, and back to the right side of the primary winding.

Finally, a secondary circuit may be traced for secondary 25 as follows: From the left side of secondary 25, Figure 1, lead 32, tube 3|, lead 30, terminal 29, condenser 28, terminal 21, and lead 26, back to secondary 25.

Of course, during the next subsequent halfcycle of current flow, the direction in`which the current traverses the several circuits is just the reverse of that just traced.

In the preferred embodiment of my invention, both .tubes are of the hot-cathode type, with the incandescible cathode terminals thereof shorted by suitable jumpers or the like, to adapt the same for cold-cathode operation; and are preferably of like rating. Moreover, they are preferably powered off seconder-ies, of substantially like outputs,

with, however, a, slight variation therefrom in accordance with the teachings of this invention, 8s will be morefully pointed out hereinafter. It is entirely possible, where desired, to employ tubes of different characteristics, and to impose corresponding changes in the characteristics of the several secondaries.

In the embodiment-iliustrated. tube 3| is pria` vided with a suitable reflector 48, while tube 35 is similarly provided with a reflector 4|. One of the outstanding features of my present invention as has been pointed out hereinbefore, in the association of my tube lighting system with these reectors. It frequently arises,`in the use of fluorescent tube lighting equipment, that it Ais desirable to construct the associated reflectors of Masonite or other suitable and durable nonmetallic materials. Particularly is this true, where the installations are intended for outdoor service, where accumulated moisture, packed snow, rain or the like would tend towards shortcircuit where metal reectors are used.

In earlier tube systems employing so-called multiple output transformers-that is, transformers having more than one secondary'coil* as Well as in the system according to the parent application referred to hereinbefore, I have found that due to some phenomenon not yet complete#- ly or satisfactorily explained, these -tubes 'frequently are not energized properly, or once energized will not maintain the arc satisfactorily, where non-metallic reectors are employed. Where-secondary coils of balanced output were used, satisfactory performance simply could not be achieved.. y

After considerable 'experimentation 'I found that a difficulty resided in the power-unit itself. If ful1`pen circuit voltage is provided across the tube load of the 'electrically-connectfd secondary .coil as of coil 33 and still higher opencircuit potentialgisimpressed across-the 'tube of the electrically-independent secondary coil as of coil 25, I have found thatfthenthe--tubes will ignite properly, and continue --in-operation in entirely satisfactory mannenregardless of the type of reflector employed. To `facilitate a clearer understanding of the operation of "my -llghtmagnetic Acircuits-involved.` "f fse- V-.

Upon passage ofcurrent from the-service mains at 24 through thetransformerfprimary winding 2|, a primary -flux is developed, *whichtendsto course in one direction during one-half cycle of exciting current, and in the-reverse direction during the reverse half cycle.

Assume a direction of current flow-such that the generated iiux tends to flow to the right in Figure l along central bar I5. Also'assume that no voltage has been built up in either secondary coil, and that the tube loads across these secondaries have not been energized. The flux developed by the primary winding courses without substantial restraint along bar I5, linking the turns of secondary coil 25. At the end of bar I5 the iiux in part courses up along leg I 4, to the left along upper core portion I2 and thence down end leg I3, and in part courses down leg I4, to the left along coreportion I2 of lower' E-member Il. and up leg I3. At the left end of bar I 5 the iiux re-unites, and courses to the right along the bar back to primary winding 2 I, linking the turns of secondary coil 33. During these open circuit conditions, rthe primary flux,which of course selects quantitatively-the path of least resistance, tends toavoid the'high reluctance of magnetic .shunts I9, .I 9, 'with'their associated airgaps GI, G2, disposed between-the shunts I9, I9, and bar I5, so that .during .these no-load conditions,'only asmallquantity'ofilux courses these shunts and associated air-gaps; .Any flux which does course across .the shunts passes'doarn from upper core portion I2 in one the airgap GI, and thence b ack along bar I5'to the primary. In the other case, theiiux oourses'from lower core portion I2 -up-acro 'air-gapGZ, and thence back along bar I5 'tothe primary.

During the next subsequent half-cycle, the direction of current flow is 'just reversed. In this instance the 'ux courses to Athe left -along bar I5. A small quantity `up across airshunt I9 to lower core portion I2, to the right.

therealong, up leg I4, and back through bar to the primary. By far the greater 'part of the flux courses along bar I5. to the left end,.thence along legs I3 of the E-shaped members, to the right along ,core portions 2|', along legs I4 back to the right end of bar I5, and thence to the left along bar I5 back to the primary. e

With the coursing of ilux during successive current half-cycles, potentials are being induced in the secoudaries. The induced voltage' in secondary 33 is dependent upon the combined number of turns in coils'33 and 2|, because of the autotransformer connection. These induced potentials are impressed across'the terminals of the associated tube loads, and quickly bring the tubes into a condition of excitation. Shortly one of the tube circuits is fully energized. Usually, for reasons to be developed, this will be the circuit including tube 35. Later, upon passage of but a relatively few cycles of the charging current, the other tube circuit containing tube 3| is energized. Thereafter, during each halfcycle, the induced voltage will rst build up to an instantaneous value corresponding to energizing 'potential of the associated tube, whereupon the tube is energized; The energization will endure while the voltage builds up to peak value and until-the voltage falls below that necessary to maintain light` emission. The tube then extinguishes and no light is emitted while .the voltage falls through zero value; and builds up in the opposite direction. When the necessary potential isreached the tube once more is energized. This cycle-of space-discharge phenomenon is repeatedv duringeach full cycle of primary current liow. E.

-Let us translate the foregoing phenomena into terms of llux coursing throughthe magnetic cir cuits. First it is. assumed that primary flux courses to the right alongbar I5 in lifigurel, and that thel tube 35 has just been energized. Immediately with the`energlzationf`a back magnetomotive force isv developed in winding 33. Secondary iiux generated thereby tends -to buck the primary flux. The magnetic path tthrough4 legs I3, the left ends of' core portions I2, I2 and bar I5, formerly of low reluctance, now with tube 35 energized interposes high reluctance to the passage of primary llux. The shunts I9, I9, formerly of high reluctance compared to the main ilus path, are now of appreciably lower reluctance. The primary llux, always seeking the paths of highest admittance, 'accordingly now tends to course the shunt paths.

The calibration of the shunts and associated air-gaps preferably is such that during the times when the tube loads are energized,.just sufcient iiux courses the main flux path to satisfy the voltage and current requirements of tube 35.

Under these conditions of operation, the following flux circuits may be traced: From the primary winding 2|, ux courses to the right in Figure 1, to ends legs I4, I4. There the ux divides along two paths. In part the ilux courses up along leg |4, to the left along upper core portion l2, to shunt I 9 and then courses down this shunt, across air-gap GI, and to the right along bar I5, back to primary 2|. Only sufficient ilux continues across upper core portion 8 I2, and down leg I3, and thence to the right along bar I5. Similarly, flux also courses down leg I4, to the left along lower core portion I2,

and thence up shunt I9, across air-gap G2, to

bar I5, linking secondary 33, as is required, together with flux coursing the upper E-chamber II to maintain the voltage and current necessary to continue discharge across the tube load.

During the next subsequent half-cycle, the flux will be reversed. From primary 2 I, the flux courses to the left along bar I5 and so divides as to cross the shunt air-gaps and return to the subsequent half-cycle.

primary winding alongthe two shunts I9, core portions I2,Y end legs I4 and bari-I5. Only enough flux continues along bar I5 to the left.'

beyond the shunts to link secondary coil 33. This ilux returns to the primary Winding along end legs I3, core portions i2, end legs I4 and bar I5.

The back magnetomotve forces developed in .opposition to the primary flux exist only during the tube energized portions of each half-cycle of charging current. As soon as the tubes extinguish in each half-cycle, the back magnetomotive forces disappear, nc-ioad conditions resume, and full primary flux courses along the main magnetic circuit, completely linking the secondaries, until the tubes are again energized in the This action tends to develop quickly the induced potentials necessary to energize the tubes at an early point in each current half-cycle, thereby ensuring greatest' possible interval of light production during each half-cycle.

Discussion has been had of shunt phenomena only in connection with secondary 33, which, electrically-connected to primary winding 2| in conventional autotransiormer connection, is disposed on opposite side of shunt I9, I9 from the primary winding.

With a close magnetic coupling maintaining between primary winding 2| and secondary coil 25, Without interposed shunts the back magnetomotive force developed in coil 25 when tube 3| is energized tends to buck the primary ux, but does not eectively do so. The voltage and current induced in the secondary coil 25 in-a few cycles of charging current in fact would soon give rise to system failure, but to prevent this action I provide the large capacity condenser 28 series-connected between secondary coil 25 and tube 3|. With this condenser chosen of proper rating-as for example a condenser of the order o 1.8 microfarads at rated 550 volt input is entirely,satisactory-sulcient impedance to abnormal current flow is effectively introduced, and tube. operation of desired character is achieved.

Returning now, following the foregoing preliminary treatment of the magnetic circuits involved, to the discussion of proper operation of the tubes 3| and 35 o the double transformer even when Masonite or other non-conductive retlectors are employed, the main magnetic circuit, the primary winding and the secondary coils are so provided that with rated input of or 220 volts as the case may be oil service 24, full open circuit voltage across secondary 25 will be about 443 volts. When the tube 3| is energized, however, then due to impedance 28, the effective tubeoperating voltage will drop to about 10G-108 volts. When the tube extinguishes for any reason, however, while the primary 2| is still connected across service 24,-iull open circuit potential of about 448 volts again is established across terminalsof tube 3l, quickly conditioning it for energization.

In furtherance of the objective of proper tube operation with use of non-metallic reflectors, I design the number of turns of secondary 33 so that in the autotransformer connection described, a still higher secondary voltage on open circuit is achieved, of say about l1:60 volts. This slight increase in available open circuit voltage conditions associated tube 35 for energization a. few cycles ahead of tube 3l. The current-limiting effect of shunt I9, I9 on secondary 33 has already been described, and need not be repeated.

In addition to serving as a current-limiting impedance, condenser 28 fulfills at least two additional important functions. One of these is to throw lamp 3l out of phase with lamp 35. With negligible system resistance, the inductive load across secondary 33 would lag about 90 behind the charging` current, while condenser 28 would.'

cause the associated load to lead by about 90. Even in the actual system, however, where some ohmic 'resistance is necessarily present, the two secondaries are substantially out of phase with each other. As a result, one tube is ignited during the period of extinguishrnent across the other tube, this condition reversing during each halfcycle. Detrimental flicker, or what is known inI the art as stroboscopic eiect, is thereby minimized, since at practically all times during operation visible radiation is emitted.

Another advantage made available by condenser 28 is restoration of an'otherwise lagging system power factor to practically unity value. Quadrature or useless current requirements are eliminated, service supply is thereby improved, and advantage can be taken of the lower'rates usually available to near-unity power factor consumers.

Inasmuch as the secondary coils 33 and 25 are electrically independent of eachother, and additionally, since secondary 25 is not only electrically independent of primary 2|, but is wound separately therefrom on central core bar I5, mutual induction between the several coils is maintained at a minimum. For this reason transient phenomena. arising during starting and stopping, energization and extinguishment of the tubes, and for practically all 'other reasons, are substantially damped out as between the windings. Thus rescnating or near-resonating effects are effectively suppressed. Wave forms are irnproved., that on the condenser side being symmetrical, with no oscillating peaks, while that on the inductive side approaches the ideal sine wave form. Radio frequency condensers 42 and 43 respectively shunt tubes 3| and 35, and serve to damp out oscillations and ripples attendant upon energization and extinguishment of the tubes during each half cycle.

Excessively high voltages, transient in nature, and including detrimental harmonics, are substantially eliminated. Electrical and mechanical shock on the tube parts are materially reduced. Electrode life is prolonged. sputtering of electrode material substantially no longer occurs. Volatilization of electrode material and subsequent deposition on the tube walls, with consequent darkening of the tube, is diminished and tube hardening, due to occluded gases in volatilized electrode material deposited out on the tube walls, gives no substantial difficulty. The oxidecoating, provided on the cathode for electronemitting purposes, remains undisturbed for a prolonged period of time.

When desired, it is entirely possible, to reduce the over-all length of the power unit while increasing its lateral dimensions, by providing secondary coil 25 wound directly with the primary 2| as in superimposed relationship. This will permit decrease in length of the larger pair of core spaces or openings to about the same dimensions of the smaller pairof-opem'ngs housing secondary coil 33'. In turn, core portions l2, l2 and =bar I5 may be decreased in length. This presents an advantage in certain cases where variants in shape and over-all contour is required, to satisfy special problems. However,

some disturbance in wave form is observed, due

probably to transmission -of transient disturbances from one secondary to another through the more closely coupled primary.

Additionally, and where desired, both secondaries of my new transformer unit may be electrically connected in autotransfcrmer connb tion across the primary, the secondary circuits otherwise being electrically independent 0i each other. Such an arrangement is disclosed in Figure 3. 'Iherein a primary 4d is connected by leads 45, 46 across service d1. Secondary 48 is series-connected at one end by lead 49 to one terminal of associated fluorescent tube 5B. The other end of tube 50 is connected by lead 5l to junction 52 with lead 46, and thence to primary 44'. Lead 54 connects the other end of secondary d8 at junction 53 with lead 4.5. Shunts I9, IQ disposed vbetween primary 44 and .this secondary 4S, and. corresponding to similar shunts I9, l5 of Figure l,.a1e schematically disclosed.

Similarly, secondary 55 is connected at one end by lead 55.*to junctionA 5i with lead'. At its other end-lead 5.8. connects to secondary 55 to -large capacity condenser 5B, lead '60 extending thence to tubel. From the other end of tube 6l, lead E2 entends to junction 63 with lead d5.

Aprimary circuit may be traced from the left end of primaryv 44, lead 45, service It?, lead 4t to the other end of primary 44.

For secondary coil 48, autotransormer circuit may be traced from the left end of coil 48, lead fig, tube 58, lead 5I, junction 52, lead 45, primary 44, lead 45, junction 53, lead 5ft, back to secondary 4S.

For the other secondary coil 55. circuit may be traced from the left end of the secondary, lead 56, junction 57, lead 4E, primary 4d, lead d, junction B3, lead 62, tube-6l, lead (ill, condenser 59, and lead 58, back to the right side of the same secondary.

While this full autotransformcr connection affords certain economies in the number of turns required in secondary 55, 'the closer magnetic coupling involves some impairment of wave form, with attendant diminution of system life,

and of certain of the elements thereof.

Convenience has dictated the accepted practice of mounting the power unit on tube reflectors, so that the system is encompassed Within the smallest possible dimensions. rl'his practice imposes definite limitations on the over-all dimensions of the power pack. It is both desirable and necessary, therefore, to reduce the exterior dimensions of the power unit to the greatest degree possible, and to impart the utmost. compactness thereto.

A .preferred manner in which compactness can be achieved is by the proper associations of the condenser 28lWiththe transformer unit. In this connection it should be recalled that it is the transformer unit which in operation gives rise to heat, both in its windings and in the iron. On the other hand, it is necessary that the condenser operate in the substantial absence of heat to prevent damage thereto. rIhis means that intimate contact between the transformer and condenser must be avoided, and that the latter must be thermally shielded from the transformer. The problem, then, is to provide close spacing without the detrimental transmission of heat. This I achieve in simple yet ingenious manner.

Casing 84, which has a suitable cover or lid not shown, is designed to fit snugly about the power unit, with its exterior dimensions but little greater than those of the component power unit elements, themselves including the transformer condenser. The condenser is provided with over-extending sidewalls which terminate in a flange 23a. This flange 'advantageously passes completely about one end of the condenser, so that a working top of the latter constitutes o.

sort of recessed deck 25D, on which terminals 2l, V

23 are mounted. The condenser is positioned on its side in one end of casing 84, with its working head disposed towards the adjacent outer legs I4, I, of the transformer and terminating brit a short distance therefrom. A sheet or partition 55 of thermal and electrical insulation in the casing G4 is interposed between the transformer and condenser and effectively shields the latter against injury. The recess formed by flange 28a provides all necessary space and protection for connections between the condenser and the transformer, so that these two units are assembled in the smallest practical compass.

Further to reduce the exterior dimensions of the transformer unit, and additionally to effect economies by reduction in the quantity of iron required, I nd it extremely advantageous to anchor the windings of the transformer by means of wedges pounded home between the windings and the transformer core. Thus a plurality of such wedges EB, Ipreferably of non-- metallic substance such as wood or the like, are placed at strategic points between the windings and the core. Upon being pounded home, they anchor the windings tightly against all mechanical and electrical stresses, and hold the windings snugly in a minimum of space. Chattering is minimized.

To reduce transformer hum, the casing 64 preferably is filled with transformer compound, after the power unit has been assembled therein. Upon final assembly, the power unit is substantially the shape f a simple rectangular or oblong block, readily fitted to the top of a reflector or other suitable mounting.

As a further refinement, fibre or other nonrnetallic insulating shims B1 may conveniently be inserted between yoke ISa and the associated ends of the core members, to prevent any possiility of building up hysteritic ux flow.

A system of the type described displays markedly superior operation on all types of outdoor operation. It functions just as successfully, regardless of whether associated tube reectors are of electrically conductive or electrically insulating material. Quick energization of tubes in the system is observed, and the associated tube discharge endures steadily without appreciable flicker or stroboscop-ic effect. Satisfactory dimmer" operatic-n of the lighting tubes is entirely practicable, and in fact, the reserve of energy is such that satisfactory performance is achieved even when the service potentials fall or are reduced as much as 50% below rated values. Improved wave form results in the improved tube life, and in light production and emission with substantially unabated efficiency throughout the useful tube life. Through the action of the shunts on the one hand, and of the condenser 28 on the other, excellent voltage regulation is obtained.

For purposes of symmetry, and of simplicity in stamping the E-shaped elements I I, I I, and more importantly, for improved flux distribution, preferably these latter are formed of like dimensions and configurations. It is entirely feasible, however, to provide the core so that the dimensions of one such member I I vary from those of the other, or even to eliminate entirely one such element. It will be also understood that apart from the illustrative embodiments described herein other forms of magnetic core induction apparatus may be employed which is consistent with the operational demands of my new lighting system. I prefer, however, to use the symmetrical shelltype core described.

As many possible modifications and embodiments may be made of my invention, once the essential elements thereof are disclosed, and as many changes may be made in the embodiments herein disclosed, it is to be understood that all matter herein described is to be interpreted as illustrative and not by way of limitation.

I claim:

l. As a new manufacture, a power unit for tube lighting equipment, comprising, in combination, a transformer itself comprising a shell-type magnetic core; magnetic shunts disposed on the outer core legs intermediate their length and extending towards but short of the central core leg, and dividing the core into two pairs of core spaces, one being larger than the other; a primarying winding and a secondary winding disi posed side by side about said central leg in the pair of larger spaces; a secondary winding disposed about said central leg in the pair of smaller spaces, this winding being wound to give an open-circuit potential substantially greater than that of said first-mentioned secondary winding; and a large capacity condenser disposed closely adjacent said transformer and series-connected to the secondary winding of low open-circuit potential.

2. As a new manufacture, an electrical power unit, comprising a transformer and an associated large-capacity condenser, said transformer comprising an iron core, a primary winding and two secondary windings positioned thereon with the primary Winding lying between the wo second- -ary windings and with the number of turns of one secondary substantially exceeding the number of turns of the other secondary, and magnetic 'core shunt means positioned between said primary winding and said secondary winding of the greater number of turns, said condenser being disposed on its side closely adjacent to but insulated from said transformer at the end adjacent to and being connected to said secondary of the lesser number of turns.

3. A transformer, comprising a shell-type magnetic core including central and outer legs, magnetic shunts intermediate said outer legs extending towards but short of said central leg, a secondary about said central leg on one side of said shunts, and a primary and a secondary disposed side-by-side about said central leg on 13 the other side of said shunts, said secondaries being connected in auto-transformer relation with said primary, and said first-mentioned secondary having a substantially greater number of turns than said other secondary.

4. An iron-core transformer comprising, a shell-type core having a central leg and two outer core legs with interconnecting core ends, windings including a primary and two secondaries disposed in side-by-side relation on the central leg of said core, magnetic core shunts between said primary and one only of said secondary windings, and non-magnetic wedges between the several windings and the core legs and core ends for securely anchoring the primary and secondaries in small compass on said core, said one-only secondary winding having substantially higher open-circuit potential than said other secondary winding.

5. A power unit comprising a transformer, a condenser and a, casing snugly fitting about the transformer and condenser; said transformer comprising an iron core, a primary winding and two secondary windings positioned thereon with the primary winding lying between the two secondary windings and with the number of turns of the one secondary substantially exceeding the REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,212,198 Sola Aug. 20, 1940 2,317,844 Boucher Apr. 27, 1943 2,336,665 Boucher Dec. 14, 1943 2,354,879 Ranney Aug. l, 194:4 2,370,635 Bridges Mar. 6, 1945 2,382,638 Keiser et al. Aug. 14, 1945

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