US3243651A - Ballast structure for fluorescent lamps - Google Patents

Description

March 29,- 1966 A. E. FEINBi-:RG r-:TAL 3,243,551

BALLAST STRUCTURE FLUORESCENT LAMPS 2 Sheets-Shea?l l Filed Oct'. l, 1962 March 29, 1966 A, E. FEINBERG ETAL 3,243,651 BALLAST STRUCTURE FOR FLUORESCENT LAMPS med oct. 1, 1962 2 sheets-sheet a j?? V572 for d Zerfwzefy ya u ey second lamp thereafter ignites.

UnitedStates Patent )F BALLAST STRUCTURE FOR rLUoREsCENT l LAMPS Albert E. Feinberg and Paul Berger, Chicago, Ill., assignors to Advance Transformer C0., Chicago, Ill., a corporationof Illinois Filed Oct. 1, 1962, Ser. No. 227,469 8 Claims. (Ci.315'-187) .This'invention relates generally to a ballast structure for gaseous discharge devices andmore particularly, is`

concerned with the construction of a ballast in which laminations which -form the core arelmade with a minimum of scrap.l The invention is also concerned with a novel ballast for gaseous discharge devices including a transformer which has a secondary winding intended tocarry 4a `leading current.

a radical extent thatunless in. some way, prevented from4 e. -doing so, the ydevice will destroykitself. vThe ballasting provides this deterrent.

. Itnis wellknown in this art that a high leakage reactance transformer Will perform all `of the'desired functions mentioned above. The high leakage reactance transformer i-s one in which at least a principalsecondary winding is loosely` coupled relative to' the primary winding so that although the benefits of transformation in accordance with turns'ratio are available on open circuit, as soon as 'current flows through the circuit, the high leakage reactance impedes the flow of current lowering the voltage across the load.

The ballast which will bevdescribed hereinafter and which comprises the inventionherein, is one which is intended for Vuse with fluorescent lighting lamps of the socalled` rapid-start variety. These lamps Ahave filaments in their envelope 'ends which yare continuously 'energized and consequently a ballast must also serve the function of providingcu'rrent continuously to these Iilaments. The

vlballast of the invention is constructed to provide such filament windings. e

Rapid-start-fluorescent lamps are normally operated in pairs, each' pair being served by a single ballast.v lThe circuit of the arrangement is such that on open circuitfull output voltage of the ballast is applied to one of the lamps because of a by-pass or shunt circuit across the second lamps Upon ignition of the first lamp, the current iiows through the shuntihg circuitoffhthe second lamp and produces a` voltage in a condenser in the shunt which raises the voltage across the lamp to such an extent that the i Current then flows in series through bo'thof the lamps and the ballast windings. In order to provide good power factor in the ballast as a whole, `a power factor correcting condenser is included in series with the lamps. Thiscauses a leading current to flowrin thel principal secondary Winding of the ballast.

As described inU.S. PatentNo. 2,461,957, core saturation and resultingA wave shape distortion will occur in the -current flowing through the lamps unless one places a bridged' gap inthe magnetic circuit in the vicinity of the secondary winding which carries the leadingcurrent.

Attention is also invited to U.S. Patent No. 2,892,249 i which describes amethod of manufacturing a transformer core. It is contemplatedthat the ballast of the invention herein will be manufactured in accordance with the teachingsof the said AU.S. Patent No. 2,892,249. g

`length of the inward 3,243,651 Patented Mar. 29, 1966 lCe .guration punched matingly from strips of steeland thereafter rearranged to form the necessary windows for the windings of the ballast. This will be brought out in more detail hereinafter and reference may 'be had to the said' patent for additional information.

The center projection of the F-shaped laminations, in accordance with the teachings of the said Patent 2,892,249,

*are punched intothe side edges of the elongate portion of the T-shaped laminations so that when rearranged to form the core, the center winding leg has notches and the side legs have Ainward protrusions. Proper adjustment of the protrusions provides the gaps for the shunt. By proper choice of dimension, the notches in the center winding leg will be located on the interior ofthe secondary winding and thereby provide a bridged gap in the center core giving the benefits of increased efficiency, Igood lighting characteristics, etc.

This invention relates specifically to an improvement on the last described structure.

e The position of thebridge gap in the T-shaped, lamination, that is in Athecenter winding leg, was determined in the previous structure by the provision of the shunt and the relative dimensions required in the windows produced to accommodate the primary and secondary windings.

Heretofore it was believed that the dimensions of the resulting transformer core were more or less limited because the distance between the resulting shunt and the bridged gap controlled to a great extent the characteristics ofthe ballast. Attempts made to decrease the size and weight of the core, or to cut down on the amount of copper wire were not successful. Problems arose in heating, Wave shape distortion and the ballast was more expensive. As an important example, the structure above referred to which was devised for two 40watt rapid-start fluorescent lamps was a ballast having a transformer core formed -of laminations 4% inches long and a little over 2 inches fwide stacked .Sinch high. The width of the center Winding leg was somewhat more than of an inch, the width of the side legs was a little more than 1/3 of aninch, the

-width of the bridgingy portions and hence the distance VVdecrease the length of the core by one-half inch, decrease lthe. number of turns of Wire, and hence cut down on the size, weight and cost of the ballast without loss of lighting efficiency. A complete comparison of dimensions will 'be set forth in describing the specfic example of the invention hereinafter. e

The primary object of the invention is to provide a construction for a ballast which will enable the achievement of advantages described immediately above.

In prior attempts to decrease the size of the ballast, as by merely shortening the same, and making slight adjustments for the accommodation of the windings, it was found that the dis-tance between the shunt and bridged gap was insuiicient to give good operating characteristics. Magnetizing current increased requiring a heavier size of primary winding wire to carry the added primary current. The lspace occupied by the primary winding was thus increased and necessitated a complete re-juggling of the f3 other dimensions which `could not practically be done without added expense. A completely satisfactory design could not be achieved in this manner.

Another attempt was made in which the shunt projec- Vtions were made longer than usual to decrease the size of the high lreluctance gaps in the shunt. It was thought that this would decrease the magnetizing current, but it was found that too much flux was by-passed by the shunt giving rise to a lower open circuit voltage with consequent bad starting characteristics. Attempts to increase open circuit voltage would require more turns of wire on the secondary winding, which in turn would change operating characteristics, -require changes in window dimension, etc. Furthermore, the metal removed from the bridged gap became excessive with this expedient.

Still another attempt involved punching vthe F-shaped and T-shaped laminations in a somewhat nested configuration but spaced lengthwise of one another, so `that the displacement of the shunt from the bridged gap when the -core was assembled Was not the same as the width of the bridging ends. This produced a greater spacing between the shunt and bridged gap, but unfortunately it was 'found that the resulting increase in scrap offset the savings achieved by the resulting shorter ballast.

In accordance with the invention, the projections o'f `the F-shaped laminations are formed with a narrow extension on their free ends, these .extensions approaching the opposite side edges of the central winding leg and being spaced therefrom by a high ,reluctance .air-gap of ordinary width. The notches thus removed from Ithe T- shaped lamination are of identical configuration so that .the 4bridged gap comprises a pair of `aligned notches which are fairly wide but each having a narrow portion at its bottom end defining the narrow bridge therebetween.

Through the use of this type of structure, it was found that the laminations may be kpunched fully nested without any scrap; that the close proximity of the shunt and bridged gap did not result in any increase o'fmagnetizing current; that the crest factor and vlighting efficiency were excellent. It was found that the amount ,of copper wire needed was decreased; that the resulting ballast was constructed at a reduced cost; and that the ballast was quieter than heretofore.

Accordingly, other lobjects Vof the invention .are to achieve the advantages mentioned by the structure describedabove.

The invention has been applied only to ballasts which are constructed by the .method of Patent 2,892,249 and which are intended for use in circuits whereinV the secondary winding carries a leading current, but it is believed thatother ballasts .for circuits of this same ltype may ywell use the invention with advantage, even-thoughthe laminations are not Stamped as nestedfgroups.

.Other objects of the invention and advantages will become apparent to those skilled in this art as a preferred embodiment is described in some vdetail hereinafter, in connection with the drawings thereof.

' In the said drawings:

FIG. 1 is a diagrammatic top plan view of a transformer constructed in accordance .with the invention and using the .novel core thereof, vthecoils of the apparatus being shown in section.

FIG. 2 is afragmentary top plan-view ofa strip o electrical steelshowing the vlayout ofthe parts of the core of FIG. 1 along the same in order to illustrate the manner in which the laminations are punched from ,the strip.

FIG. 3 isa View similar to that of FIG. 2 except in this case 'the strip of electrical steel is intended to pass through the punching machine in a direction at right angles to that of FIG. 2.

FIG. 4 is a circuit diagram of a ballast of the invention using the transformer of FIG. 1.

The invention herein is characterized by the provision of a ballast having a core that is formed by the method lthat isdescribed in said `Patent 2,892,249, butin which the projections on the F-shaped laminations, which will Y the bridged gap formed at such a locationy along the length Aof the .center `winding leg so .that lit will AOccur under a secondary Winding which carries a leading current. In addition to achieving the advantages of #high klighting eiciency, low current and Agood regulation, lsuch a construction provides flexibility of design and enables the manufacture of a highlylefficient ballasthaving an overall length much less than heretofore.

IThe circuit diagram of the rapid-,start lighting arrangement with which the invention is intended to 'be used uis shown in FIG. 4. This circuit `isfconventional in all respects although the shunt and 'bridged gap resulting "from the invention should be understood to lbe different from previous structures.

In said FIG. 4, there isa ,transformer 10-which ,is designated by straight lines indicating the conventional symbol for an iron core structure. The gap yin the core structure at 12 indicates the bridged jgap .of lthe 'invention which will be described hereinafter, .and the 'lines ,representing lthe shuntat 14 represent the `shunt constructed .in accordance with the invention. The ,core of. the `transformer will be designated 16.

There is a primary winding P which .is connected Yacross line terminals 1.8` and 20 by suitable .leads A.r nark,e,d black and white and indicating the preference .respectively for the ungrounded and grounded line terminals. There .-is a secondary winding S which is mounted on the corel ,16 separated from ,the primarywinding P `by the 4shunt 14 .but connected `therewith lat ythe terminal 22. .A pair -of nuarescent discharge lamps L1 vand L2, preferably of-,thesacalled rapid-start variety, are :connected in `series ,withone Yanother by -the jumper 24 and vthrough `the conductors 2,6

and 28 across boththe primary vand secondari/windings; The conductor 26 extends to the junction 3.0 .which is .the left-hand terminal of the primary winding -P., .and .the conductor 28 extends Ythrough the Ipower factorcondenser CPL to the right-hand-terminal ofthe secondary winding S, The circuit described is I,one `in which lthe Y,two lamps L1 and L2 are connected in series with one another and together in autotransformer.connection withthe prim-any and lsecondary windings. Each of the lamps ,L1y and L2 has a 'filament sealed in the respectiveenvelope-ends `thereof as shown at F, and the filaments .are served by -c-ontinuous flow of current through the medium v(1f-filament windings. F1, F2, and F3 mounted on the core lclosely coupled with the primary Iwinding P and connected as shown. There is a shunting path 32 around the lamp L2 which has a condenser CS infsaidpath.

Theoperation of this circuit is `well known but 4may briefly be .reviewed with'advantage. `Onyopen circuit, the total open circuit voltageacross the primary and -secondary windings in additive relationfappears -acrossfthe lamp 'L1 since the condenserfCs and Cp are not effective in circuit `under `open circ-uit conditions. Ihe lamp f1-.2

The resulting voltage is'suicient to `ignite -the ,lamp

,L1 and current immediately commences toflow'therein.

Since the 'lamp L2 ha-s notas yetbeen ignited, fit presents a very highimpedance to iow of currentsofthat all of the current of lamp L1 will prefer to pass through-the condenser CS. As soon as the by-pass path 32 has current owing in it,'a voltageis produced inthe condenser CS which appear-s across the lamp L2 anldis sufcientito ignite the lamp. Thereafter current prefers the lamp L2 to the by-pass path l32,l and the result-ing operating circuit consists of the two lamps L1 and'L2in series with thepower factor condenser CP across `the primary and secondary windings. The loose coupling between Vthe primary and secondary windings provides the leakage reactance to prevent excessive flow of current and keep the operating voltage to the desired level. The power factor condenser is needed so that the total power factor of the line 18 and 20 will be close to one hundred percent. Consequently, a leading current will flow in the secondary Winding. S.

FIG. 1 illustrates a transformer 10 constructed in .accordance with the invention. The transformer is formed of a 'laminated iron core 16 which has a center T-shaped part 40 and two side parts, each of which will be designated 42, of F-shaped conguration.

The type of transformer core with which this invention is concerned is that which is made of lam-inations punched from thin steel sheeting arranged in stacks and secured together.k The individual laminations are of course identical for any given part, and hence, no effort will be made hereinafter to distinguish between the use-of the reference numerals 40 and 42 to designate stacks or individual laminations of identicalcong-uration.

Ther T-shaped part 40 provides the center winding leg 44 of the core 16 and its cross-head provides the lefthand bridging part 46. The F-shaped parts 42 provide the'side legs 48 which Iare parallel with the center winding leg 44 and spaced therefrom to form windows at 50 and 5,2.. The F- shapedparts have their left-hand or straight ends `54 butted .against the cross-head or bridging part 46 at the joints 56 to close the magnetic circuit of the core 416 at the `left-hand end thereof. The right-hand or inwardly projecting end l58 of the F-shaped parts 42 extend inwardly of the core 16 toward and abut against the side edges of .the free end of the center winding leg 44 at 60to close the magnetic circuit thereat. The center inwardly extending projections 62 of the side legs 48 extend toward the center `wind-ing leg 44 and in cooperation with a high reluctance gap 64 formed `thereat provide the shunt 1 4. The .windings P, F1, F2, and F3 are'rnounted in the window 52 and the winding S is mounted in the-window 50. p Ituwilll be seen from the description above that the transformer 10 has its core 16 of the so-called shell variety with anlouyter rect-angular framing portion and a center winding leg. The parts are formed of stacks of laminations a-s previously explained, and suitable notches 66 at the corners enable the core 16 to be held together by clamps symbolically illustrated .at 68.

, As lpreviously mentioned, the laminati- ons 40 and 42 are formed by the scrapless method of Patent 2,892,249. A strip of suitable steel is run through a punch press at high speed, and the individual laminations are punched out in nestedV configuratiomy Apair of F-shaped laminations 42 are nested on opposite sides of a T-shaped lamination sothat the long inner edge of each of the F-shaped laminations is common with the long outer edge of the T-shaped lamination. Such groupings may be arranged edge to edge Ias shown in FIG. 2, then pas-sed through the machine in the direction indicated by the arrow of FIG. 2. The only scrap which results will be the crosshatched portions marked S which, it will be noted, include punch-outs for the notches 66. In addition, there may be a narrow holding strip on oppos-ite edges of the wide metal strip in accordance with normal high-speed punch press technique-s.

The orientation of the steel grain can be made parallel with the long dimension of the laminations by arranging the groupings of .a pair of F-sh-aped laminations 42 and their inter-nested T-shaped lamination-s 40 end to end along .a narrow strip as shown in FIG. 3 and passing this strip through the punching rriachiney in the direction as shown by the arrow to give rise to the scrap parts shown. A holding strip may also be required along t-he edges of the strip of FIG. 3.

It will be appreciated that in arriving at the assembly of the core 16 from a grouping such as shown in either FIG. 2 yor FIG. 3, the F-shaped parts are first moved 6 sideways away from the TJshaped part and then translated lengthwise thereof to the orientation shown. Consequently, for a complete absence yof scrap 4at the points designated A and B, in FIG. 2, for example, it is essential that the dimensions X, Y and Z in FIG.,1 be equal.

, When the core 16 is formed, there will be a notch 70 the brid-ged gap 12. Likewise, the characteristics of the ballast in opera-tion will be affected by the distance between the shunt 14 and t-he bridged gap 12.

As previously mentioned, through the medium of the invention, a ballast previously manufactured yand sold was considerably decreased in size with lattendant savings and improvement in operation. In laccordance with the invention, each of the inward projections 62 ofthe side legs 48 is provided with a narrow en-d extension 74, and resulting in a narrow recess 76 being formed at the bottom of each lof the notches 70. Through this construction, the optimum bridge 72 readily may be established and the width of the extensions 74 adjusted along with the gaps 64 for optimum crest factor, magnetizing current, and lighting eiiiciency.

As previously indicated, in the prior structure Where projections 62 were made very long in order to bring them close to the edge of the center winding leg, the resulting notches at 70 would be so deep as to leave insufficient iron at the bridging -center 72 to carry normal iiux. This would reduce the light output through peaking of the current wave. t When the extensions 74 with their resulting recesses 76 are used, there appeared to be no difficulty through distortion. It is believed that sufficient iiux passed through the recesses 76 to give a good current wave shape. v

With this structure, thereforepthe configuration of the shunt could be used to achieve lower magnetizing current and lower primary current. A fair gap and the extensions 74 kept reluctance high enough to give good open circuit characteristics. It was found that the structure was quieter than the previous structure, probably caused by by-passing more flux at peak voltage wave.

A practical example of a ballast for operating two rapid-start fluorescent lamps will be described below, but in order to show thespeciiicadvantages of the invention, a comparison will be-made with the previous structure. It will first be pointed out that the' same capacitors Cs and CPF were used',.these lbeing .05 m.f.d. and 3.83 m.f.d., respectively withl a l385 volts A.C. rating; the lamps were the same, requiring about 430 milliamperesof current, gniting at about 260 volts, and operatingat about volts. Live voltage wasV volts A.C. `at,60 cycles. Lamp current was .400 ampere with-a crest factor of 1.35. Primary current was the same for both ballasts.

Ballasts for two A40-watt rapid-start fluorescent lamps Item or characteristic Previous Present Structure Structure Overall length of core 16 inehes. 4. 25 3. 74 Overall width of coredo- 21 17 2. 14 Width oi center winding le do- 85 85 X, Y and Z do 385 .305 Width or' Projections 62 do. 188 200 Bridging distance 72 do 40 290 Gap 64 -do .085 040 Window Width do 310 320 Primary winding #26 gauge wir urns 790 745 Secondary winding #27% gauge w .do 1, 455 1, 340 Filament windings #26 gauge wire do 26-29 25-28 Primary current amperes 620 580 Crest factor 1. 35 1. 35

As indicated above, the structure of the invention has 7 beerifapplied` practically to ballasts for operating two 40 watt rapid start uorescentlamps, but there is no reason why the` advantagesl of.v the invention should not be achieved in rapid-start or the like circuits of different kinds using one or more such lamps. Furthermore, althoughmost of t-heben'etits are p rovided when the laminations are 'stamped by scrapless methods, it is believed that the use' of shunting projections with narrow extensions combined with a bridged gap under a secondary windingA carrying a leading current is new, especially where the lgap is formed by means of what might be termed notches of non-uniform width.

Accordingly, notwithstanding-the somewhat specific detail inthe description hereinabove, it should be appreciatedthat variations arepssible without departing from the spirit or scope of the invention as defined'in the appended claims.

What` is desired to secure United States is;

1. A ballast` structure for igniting and` operating at least one gaseous discharge device from an alternating current source and which comprises a transformer having a core madeup of laminations of nested configurations, butre-arranged to providea center T-shaped part formed of onel stackof laminations `and two outer F-shaped parts formed oftwo` additional stacks of laminations, but with the long legs ofthe parts spaced to provide winding windows, a pair ofA lateral projections one in the center of each F-shaped part lextending across the space toward the long leg of the T-shaped part but each projection having its free end terminatingshort of said longleg of the T- shapedpart to form gaps thereby and provide a shunt, said free ends being of substantially lesser width than the respective projections to form narrow extensions at said gaps respectively,` primary and secondary windings in transformer relation mounted on the long leg of the T- shaped part and disposed in windows on opposite sides respectively ofy said. shunt, a condenser, first lead means for connecting the primary winding across the source and second lead means for connectingI at least thesecondary winding. in` series with the condenser and the discharge device,4 anotch in each edge of the long leg of the T- shaped` part under ,the secondary winding and adjacent each projection, of a conguration and` of dimensions substantially theA same asthe configuration and dimensions ofsaid adjacent projection.

2. A structure as claimed in claim 1 in which the primary and; secondary windings are connected in autotransformer relationship.

3; A structure. as claimed in claim 1 in which every point on each projection is spaced from the equivalent pointr onVA its adjacent notch` by.: a distance measured along the length of-the long leg of the T-shaped` part which is substantially equal to the width of the cross-head of said T-shaped part.

4.. In a ballast construction for operating at least one gaseous discharge device from an alternating current source, in which there isa transformer having a shell type core mounting a primary' winding and a secondary windby Letters Patent of the ing, .there being a shunt between the windings and a bridged gap beneath the secondary winding, the corev being formed of a center T-shaped part and a pair ot in-i wardly facing outer F-shaped parts, the shunt being provided by the center projections of the F-,shaped parts extending toward the center T-shaped part but stopping short thereof to form gaps t-hereat, the bridged gap being provided by notches in the side edges of ythe center T-shaped vwidth at their inner ends.

6. The invention as claimed in claim 4 in whichI the notches and Iprojections including the extensions thereof are ofthe same dimensions and configurations.

7. A fluorescent lamp ballast for igniting and operating at least a pair of lamps from an alternating current source, said lamps being connected in series, said ballast including a transformer having a shell `type core formed of a T-shaped center leg and F-shaped side legs, a primary winding and a secondary winding mounted on the center leg and separated by a shunt, the center projections of the F-shaped parts extending toward the center leg to provide said shunt and' being slightly spaced therefrom to provide the gaps of the shunt, the windings beingconnected in auto-transformer relation to said lamps, a power factor correcting condenser in series with the secondary winding and effective during operation of the ballast to cause a leading current to flow in said secondary winding; a bridged' gap in the center leg beneath the secondary winding, said gap being provided by notches cutting into the center windingleg from opposite edgcsth'ereof, the notches each having an inner-most recess' the width of which is substantially less than the remainder of the notch, thereby reducing the amount ot iron in the'bridge but the widthof the recesses being such as to permit some passage of flux during operation to prevent undue saturation of the bridge. Y

8. A structure as claimed in claim 7 in which the center projections have a configuration and dimensions substantially the same as the notches to provide extension tips on the ends thereof adjacent the gaps, respectively.

References Cited by the Examiner UNITED STATES PATENTS 3,114,861 12/1963 Berger B15-109 GEORGE N. WESTBY, Primary Examiner, C, R, CAMPBELL, Assistant Examiner,

Claims (1)

1. 7. A FLUORESCENT LAMP BALLAST FOR IGNITING AND OPERATINGG AT LEAST A PAIR OF LAMPS FROM AN ALTERNATING CURRENT SOURCE SAID LAMPS BEING CONNECTED IN SERIES, SAID BALLAST INCLUDING A TRANSFORMER HAVING A SHELL TYPE CORE FORMED OF A T-SHAPED CENTER LEG AND F-SHAPED SIDE LEGS, A PRIMARY WINDING AND A SECONDARY WINDING MOUNTED ON THE CENTER LEG AND SEPARATED BY A SHUNT, THE CENTER PROJECTIONS OF THE F-SHAPED PARTS EXTENDING TOWARD THE CENTER LEG TO PROVIDE SAID SHUNT AND BEING SLIGHTLY SPACED THEREFROM TO PROVIDE THE GAPS OF THE SHUNT, THE WINDINGS BEING CONNECTED IN AUTO-TRANSFORMER RELATION TO SAID LAMPS, A POWER FACTOR CORRECTING CONDENSER IN SERIES WITH THE SECONDARY

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