US2335910A - Transformer apparatus - Google Patents

Description

Dec. 7, l.1943. Q 1:` BQUCHER 2,335,910

TRANSFORMER APPARATUS A vFiled Aug. 21, y1940 1] 7 f77/gi e JMW? Mc Il@ j] )9 JM j@ Patented Dec. 7, 1943 2,335,910 TnANsFon'MEa APPARATUS Charles Philippe Boucher, Paterson, N. J., assignorto Boucher Inventions, Ltd., Washington, D. C., a corporation of Delaware Application August 21, 1940, Serial No. 353,571

,11 Claims. (Cl. lil-119) This invention relates to electrical transformer apparatus, and more particularly to electrical transformer apparatus for supplying one or more negative loads, as, for example, in the operation of a luminescent tube system.

One ofthe objects of my invention is to 'provide simple, practical and thoroughly reliable transformer apparatus which is exceedingly compact, inexpensive and highly efficient in operation.

Another object is to provide a transformer apparatus which is adapted to withstand the varying conditions encountered in actual use, including short-circuiting and grounding of the whole or parts of the apparatus, without damage to the apparatus and the consequent necessity for shutdown and replacement or repairs.

A further object is the provision of a transformer apparatus in which there is a minimum of iiux leakage to the casing, resulting in emcient operation and substantially no objectionable vi-- bration of the casing.

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

'I'he invention accordingly consists in the combination of elements, features of construction,

. and arrangement of parts, and in the several operational 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 appended claims.

In the accompanying drawing:

' Figure 1 is a diagrammatic representation o a transformer embodying the various features of my invention, the transformer being enclosed in a casing 'and energizing two luminescent tubes.

Figure 2 represents a similar transformer in which the primary coil sections are in different positions from those shown in Figure 1 and in which the load is a single luminescent tube.

Like reference characters denote like parts in the two views of the drawing.

As conducive to a clearer understanding of certain features of my invention, it may be noted at this point that in the operation of a luminescent sign or display employing one or more luminescent gas filled tubes of desired size and configuration, high potential electrical energy is required. The Fire Underwriters do not approve a circuit in which the maximum voltage to ground substantially exceeds seven thousand five hundred volts. Where it is desired to use a tube requiring a higher operating potential, for example flfteen thousand volts, the energy has in some instances been supplied by two separate transformers for each tube, the transformers being connected in series and each having an output voltage of about seven thousand ve hundred volts. Such an installation is expensive ,i both because of the amount of equipment involved and because a separate labor charge is made for eachunit installed. Moreover, a large space is required to accommodate such equipment.

In the manufacture of heretofore-known transformers having core parts of various sizes and configurations, a' corresponding number of dies of different sizes have been required for the manufacture of the various core members. These dies are very expensive and ladd considerably to the cost of manufacture of the transformers, particularly because a separate set of dies is required for each transformer of different capacity.

In certain heretofore known and used transformers, an excess of Weight. and space has been made necessary by core designs in which the iron has not been distributed with maximum eiliciency, that is, with the proper cross-sectional area in each portion of the core to accommodate the flux coursing through that portion, and with no greater area than that. Thus, in some transformers, the core has been shaped so that in some portions the core area is so small that the ux density has been too great and in other portions the flux density is less than that which the iron will accommodate. Such designs require the whole core to be enlarged to make large enough the portionsA wherethe flux density is greatest, thereby increasing the weight of the core and the space it occupies. The only alternative in those designs is to have a core which is ineillcient because certain portions are too small to accommodate the flux which should normally course through them and which therefore seeks other paths.

Where a core type of transformer is used the coils are mounted so that parts of them extend beyond the confines of the core. This structure has the disadvantage that a substantial portion of the magnetic flux flows into the casing instead of confining itself to the core, with a consequent loss in emciency. Moreover, there is much waste space in the casing so that a large amount of insulating compound is required to fill the casing. This insulating compound is expensive and adds to the cost of the transformer.

The shell type of transformer, on the other hand, has some or all of its coil sections mounted entirely within the coniines of the core so that there is less waste space than in the core type.

n the ordinary shell type of transformer, however, there is danger that one of the coils will become short-circuited or grounded and will be destroyed by the excess current which results. Such short-circuitingv may be caused by moist atmospheric conditions or by shock and vibration to which the transformer may be subjected. The excess current which iiows under short-circuit conditions causes heating of the coils and their insulation to such a degree that the insulation becomes charred and burned, rendering them' useless so that the transformer must be shut down for replacement or repair.v While some heretofore known and used transformers have provided magnetic shunts to limit the current in a whole circuit, these designs do not provide individual protection for each coil section. Accordingly, the coil sections must be designed to carry a heavy current and therefore must be larger, heavier and more expensive.

Another object of my invention, therefore, is to provide a transformer apparatus which is inexpensive in construction, employing windings of minimum necessary current-carrying capacity andA of minimum cost, and yet which is of such construction as to reliably withstand the many Ivarying conditions encountered in actual practical use by virtue of the individual protection pro- .vided for each secondary winding coil section.

Referring now more particularly to the practice of my invention, attention is invited to Figure 1 of the drawing in which I have shown av transformer, generally indicated by the numeral I0, enclosed in a casing II,.a source of single phase alternating-current electrical energy I2, and two luminescent tubes TI and T2 energized by -the transformer. The transformer I comprises a core, a primary winding and a secondary winding. 'I'he core is preferably made of laminated magnetic steel and co-mprises two outer longitudinal bars I3 and I4 and an inner longitudinal member I5. The member I3 has lateral extensions I 3a and I3b at its ends and an extension I3c at its center which extend into abutting relationship with opposite end and center portions of the member I5. Likewise the member I4 has lateral extensions I4a., Mb and IIIe which abut the ends and center of member I5. Member I3 also has lateral arms I3d and I3e which extend closely toward but do not abut the bar I5 aty points intermediate its ends, forming therewith air-gaps GI and G2 of high magnetic reluctance. Similarly, member I4 has lateral arms Md and I4e which form air-gaps G3 and G4 with portions of the bar I 5 intermediate its ends. The arms l3nt, I3e, I4d and I 4e are all preferably of the same cross-sectional area and therefore of the saine reluctance. Also, the air-gaps GI, G2, G3 and G4 are preferably of the same width and reluctance. The member I5 and the extensions I3c and Mc of the member I3 and III preferably have the same cross-sectional area,

which is double that of the main portions ofthe members I 3 and I4 and of their extensions I3a, Ib, irla'and Ilib. The cross-sectional areas are so proportioned because the number of lines of force normally coursing through the member I5 and extensions I3c and Iflc is twice as great as the number of lines normally coursing through the main portions of members I3 and. It and through their extensions i3d, I3b, Ilia and Ilib. The cross-sectional area of the shunt arms i3d, I3e, Id and Ille may be less than that of the extensions ISa, i322, Ilia and Ilb in order that the reluctances of the shunt magnetic paths may be considerably higher than the reluctances of the main magnetic paths. l

One primary winding coil section PI is mounted on the extension I3c and vanother coil P2 is mounted on the extension I4c. These coil sections are connected in series by the lead I6 or in parallel. 'Where the coils are of ne wire and high resistance they arefconnected in parallel. Where they are of heavy wire and low resistance they are connected in series. The connections Vare made in such a manner that both coils generate magnetic ux iiowing from the bar I5 into the members I3 and I 4, or in the reverse direction, at the same instant. The primary winding is energized through the leads I1 and I8 from the source I2, which may be the standard singlephase, 60-cycle commercial mains or any other suitable source of alternating current energy.

One secondary 'winding coil section SI is mounted on the member I5 near its left end in the space between the members I3 and I4 and between the extensions I 3a land I4a and the shunt arms i3d and I4d, respectively. Similarly, another secondary coil section S2 is mounted on the member I5 near its right end in the space between the members I3 and I4 and between the extensions I3b and I 4b and the shunt arms '13e and Ille, respectively.

After the primary and secondary winding' coil sections have been mounted in their proper positions on the core, steel core bands IS, 20 and 2| are put into the positions indicated for holding the'core parts in close contact. The core members I3, I4 and I5 are then forced together under heavy pressure, as by an arbor press, and wedges 22 are inserted under the bands to hold them taut, the wedges 22 being insulated from the core members by pads'23.

The coil SI is grounded to the core by a metal strip 24 connected to one terminal of the coil and held in contact with the core under the band I9. The other terminal of the coil SI is connected by a lead 25 to' one terminal of the tube TI, whose other terminal is grounded at 26 to complete the circuit. The core itself is grounded as at 27. Similarly, the coil S2 Ais grounded to the core by a metal strip 28 held under the band 2l andis connected from its other terminal to one terminal of the tube T2 by a lead 29. The tube T2 is also grounded at 26. Because of the ground connections two complete circuits are formed. One circuit includes the coil SI and tube TI. The other circuit includes coil S2 and tube T2. The coils SI and S2 can therefore be connected in their circuits either in a series or an opposition arrangement. In other words, it is feasibley to have the ungrounded terminals of the coils SI and S2, to which the leads 25 and 29, respectively, are connected, either at opposite potentials or at the same potential, at any given instant. The arrangement in which the two terminals are always at approximately the same potential is preferable where' the tubes TI and T2 are mounted in parallel relationship with their sides close together. Adjacent portions of the respective tubes with such a connection will always bel at substantially the same potential and therefore there will be no tube-puncturing dielectric discharge.

, opposes assumo magnetic iiux to iiow through the core as indicated by the arrows for one half cycle of the applied electromotive force. The path for the iiuX interlinking the secondary winding coil SI and the primary winding is in two parts. from the extension I3c through the One part is left half of `the member I5, extension I3a and the left half of the member I3, then back to the extension I3c. This part includes and interlinks the primary coil section Pt with the secondary coil SI. 'I'he other part is from the extension Mc through the left half of. member I5, extension I 4a, and the left half of member I4 back into extension llc, including and interlinking the primary coil P2 with the coil SI. Similarly, the iiux linking the coil S2 is in two parts. One part passes from I3c into the right half of member I5, `then through extension I3b and the right half of member I3 back into extension I3c. This part interlinks the coil S2 with the primary coilPI; I'he other part courses from extension I4c into the right half of member I5, then through extension I4b and the right half of member I4 back into extension |40, interlinking the coil S2 with the primary coil P2. It will be understood that during the other half cycle the iiux will course in a direction opposite tothat outlined above and shown by the arrows.

'I'he magnetic flux links the secondary winding coil sections SI and S2 and as it changes in magnitude induces an electromotive force in those coils. When the potential across the terminals of one coil, say the coil SI, and also across the terminals of the luminescent tube TI through the lead 25 and the ground connections, reaches a value sufficiently high to ionize and render conductive the gas in the tube TI, a current flows in the circuit comprising that tube and its coil section. This current renders the tube TI luminous. When the gas in the tube strikes or becomes ionized the resistance of the tube becomes very low. The current flowing through the circuit would therefore reach a high value were it seek a'path of less reluctance.

mounted closely together. As a result, no dielectric discharge will take place between the tubes.

When both tubes have become operative, the coil S2 as well as the coil SI generates a countermagnetomotive force which opposes the coursing of the main ux. That iiux which links the coil SI vuntil it becomes ionized will thereafter Thus the major portion of the iiux courses in two parts through the air-gaps and shunt arms. One part is from the extension I3c into the member I5, then across air-gap GI into shunt arm i3d and through the member I3 back to extension I 3c. The other part of the shunt path is from member Mc into member I5 and across air-gap G2 into shunt arm Hd, then through member I 4 back into extension Ilc. It will, of course, be understood that the major portion of the main flux will traverse the same path as that outlined above but in the opposite direction when the electromotive force applied across the terminals of the primary winding is in the other half cycle. By virtue of the magnetic shunt construction, the current in the coil SI is limited to a safe value, so that there is no danger of the coils becoming overheated and its insulation becoming charred. Enough current continues to flow through the coil SI and its load, tube TI, to maintain the tube in a luminous condition until the electromotive force applied across.

the primary winding decreases almost to zero in following through the cycle of alternation. The tube TI then becomes extinguished and remains so until the electromotive force across the primary winding reaches a value in the opposite direction such that a voltage is again induced in the coil SI which is suicient to ionize the gas in the tube TI and again render it conductive and luminous.

Similarly, when the voltage induced in the coil S2 is high enough to render ionized and conductive the gas in the tube T2, current iiows through `the circuit including the coil S2 and tube T2.

^ That current will not exceed a safe value because not for the peculiar magnetic shunt construcof less reluctance through one of those paths Thus if the tube TI has T2, would ordinarily pass through the left-hand end 'of the member I5 is through the right-hand end of that member, augmenting the ux 'normally coursing therethrough and linking the coil S2. Since the flux linking the coil S2 is greater in amount at this time, the potential induced in coil S2 will be increased and therefore the tube T2 will in normal operation become lighted very soon after the tube TI. A similar condition of operation is met when it is the tube T2 which strikes ilrst. In that case, however, the main portion -of the ux normally linking the coil S2 will be diverted to link the coil SI until tube TI strikes. Where the tubes become ionized and conductive at substantially the same instant, as is the case in this condition of operation, there is little potential difference between adjacent portions of the respective tubes when they are struck before the tube the path of least reluctance for the ilux which the countermagnetomotive force developed by the coil S2 will cause the major portion of the iiux to pass either through the left-hand end of the bar l5 when the tube TI has not yet become operative or, when it has, through the shunt paths which include the air-gap G2 and shunt arm I3e, on the one hand, and air-gap G4 and shunt arm I 4e, on the other hand. Enough flux continues to link the coil S2 to maintain a iiow of current through the tube T2 until the potential applied across the terminals of the primary winding approaches a zero value in .following through the cycle of alternation. Where a 60-cycle source of electromotive force is used, the tubes become luminous times per second. Due to persistence of vision, they appear to emit a steady glow.

Should the tube TI become grounded in operation, as by the formation of a, conductive film of moisture, dirt and the like between its electrodes or between the high potentiaI electrode and the ground, the iiow of current in the circuit will not substantially exceed that which hows during normal operation of the tube. This is due to the peculiar magnetic shunt construction which provides protectionfrom the flow of excessive current to each individual -coil in the same manner as the coil is protected during normal operation. The same protection will be aiorded where it is the coil SI itself, instead of the tube Tl, which becomes grounded. As current begins to flow in through air gap GI -through air-gap G3 and shunt arm the coil Si, a countermagnetomotive force is developed by that coil which causes the major portion of the main flux to seek a path of less reluctance. That path will be through the right-hand end of bar I linking the coil S2 when that coil has no current flowing through it. When current is flowing through coil S2, as, for example, when tube T2 is operating, the ilux follows two shunt paths. One shunt path is from extension I3c through member I5, air-gap GI, shunt arm |3d and member I3 back to extension I3c. The other shunt path is from extension |4c through member I5, air-gap G3, shunt arm Md and member I4 back to extension |40. Due to diversion of the major portion of the magnetic ux from thecoil SI the current flowing through that coil under short circuit conditions will be limited to a safe value so that the coil will not become overheated with consequent charring of its insulation. Similarly, where the coil S2 or its tube T2 becomes groundedE the current flowing through coil S2 will be limited to a safe value by virtue of the diversion of the major portion of the magnetic ilux from the coil S2 through the part of the core linking the coil SI or through two magnetic shunt paths. The shunt paths in this instance are those through the air-gap G2 and shunt arm I3e and through air-gap G4 and shunt arm I-4e. 'Where such individual protection is not provided forthe secondary coils, as in the ordinary transformer, those coils must be made of large diameter wire to withstand the heavyshort circuit current. Due to the magnetic shunt construction in my transformer the coils can be made of ne wire, which has the advantages of being cheaper and lighter in weight.

Where one coil, say the coil SI, becomes opencircuited, as by breaking of the tube TI or of one of the leads, no current will flow in that coil. Hence no countermagnetomotive force will be generated by coil SI and the core path linking it will be ofvery. low reluctance. Therefore, the iiux linking coil S2 will be diminished in amount since it will follow the path of least reluctance through the left-hand end of bar I5. The voltage generated in ,coil S2 will not be sufficient to ionize the gas in 4tube T2 and no current will flow in the coil S2. It will thus be apparent that both coils are fully protected. Similarly, when the coil S2 is open-.circuitell neither it nor the coil SI will be damaged.

It will be understood that, where desired, the tubes TI 'and T2 may be of different resistances.

For example, the tube TI may be of higher resistance than tube T2. Inthat-event the shunt vpaths and shunt arm |3d and |4d must be have comparatively high reluctances. At the same time, the shunt paths through air-gap G2 and shunt arm |3e and through air-gap G4 and shunt arm I4e should designed so as to be of somewhat lower reluctances.

Considering now another embodiment of mv invntion, attention is invited to Figure 2, in which are turned toward the inner member H5 against which they are forced under pressure and held in rmly abutting relationship by core bands IIB, |20, and |2| which are slipped over the parts. Wedges |22, insulated from the core by pads |23, are placed under the core bands to hold them tight. The member I I3 has shunt arms |I3d and ||3e which form air-gaps G5 and G6 with the member II5. Member H4 also has shunt arms IIlld and Iille which form air-gaps G'I and G8 with the member I I5. Since the amount of flux normally coursing through member ||5 and extensions |I3c and I|4c is twice as great as that normally coursing through the main portions of members II3 and ||4 and the extensions iI3a, II4a, I |3b and I |41), the former parts have crosssectional areas twice as great as the areas of the latter parts. The shunt arms |I3d, and ||4e preferably have smaller` cross-sectional areas than any other parts.

The primary winding comprises two coil sections P3 and P4 which are mounted on the member I I5 on opposite sides of the extensions I|3c and II 4c in the spaces between those extensions and the shunt arms I|3d and II-4d for the coil P3 and the shunt arms I |3e and Iie for the coil P4. The coils P3 and P4 are connected in series by the lead IIB or they may be connected in parallel. They are energized through the leads iII and IIB fromthe source H2 of alternating .current electrical energy. It is not necessary in this transformer that the primary coils be connected in any particular manner. The transformer will operate satisfactorily whether the coils P3 and P4 generate flux which courses in the same direction through the member ||5 at any given instant or which courses in opposite directions.

`and |I3b, |I4b. The coil S3 is grounded to the core at |24 and its other terminal is connected by lead |25 to one terminal of the tube T. Coil S4 is likewise grounded to the core at |28 and its I have shown a transformer I I0 energizing a single tube T and comprising a core, a primary winding and. a secondary winding. The transformer may be enclosed in a casing similar to theone shown in Figure 1. The core comprises three 'members II3. H4 and H5, which are preferably made of laminated magnetic steel. The members II3 and ||4 have lateral extensions |I3a, I| 3b,

I|4a and |I4b at their ends and extensions I|3c and ||4c at their centers, all 'of which extensions other terminal is connected to the other terminal of .tube T by a lead |29. The grounding connections must be such as to place the coils S3 and S4 in series. That is, when the potential of the lead |25 is at a maximum value. in a posi-l tive direction, the lead |29 must be at a maximum negative potential. The voltage across the tube T then is the sum of the voltages oi? the two coils and yet the maximum voltage to ground at no point exceeds the voltage across any one coil section. The core may be grounded as at |21.

In the operation of this transformer, as the lelectromotive force impressed by the source II2 across the terminals of the primary winding rises from a zero value a current flows through the primary winding andgenerates a magnetomotive force which causes flux to ow in the core. The flux generated bv each primary coil follows two parallel paths. With the connections shown, the flux generated by coil P3 during one half cycle of the applied electromotive force courses to the rightin the left-hand end of member II5, then lntwo paths through extensions II3c and II4c into the left-hand ends of members I I3 and II 4, returning to member I5 through extensions I I 3a and ||4a. Similarly the ux generated by coil P4 during the same half cycle courses to the left in the right-hand end Aof member H5, then in two paths through extensions II3c and I|4c, the

right-hand ends of members H3 and H4 and through extensions H3b and H4b back into member H5. These paths'are indicated in the gure by arrows. The flux links the secondary winding coils ,S3 and S4 and induces in them an electromotive force. When the electromotive force across the outer terminals of the secondary coils and across the terminals of the tube T reaches a value high enough to render the gas in the tube ionized and conductive, a current flows through the tube and through the secondary winding coil sections. As in the transformer of Figure 1, this current does not reach an unsafe value because of the magnetic shunt construction provided. The current flowing through the secondary `coils creates a back magnetomotive force which opposes the coursing of the main flux and causes it to seek a path of less reluctance through the magnetic shunt paths provided, thereby reducing the amount of flux which interlinks the primary and secondary windings and thus reducing the voltage and current in the secondary circuit. Thus the major portion of the flux normally linking the coil S3 is diverted laround that coil, following two paths from member H5 into extensions H3C and H4c, members H3 and H4, shunt arms H3d and H4d, across air-gaps G5 and G1 and back to member H5.,

the magnetic liux, the current in the secondary winding is limited to a safe value. Moreover, should either one of the coils become grounded in use, the iiux is diverted around that coil through the shunt paths indicated above for normal operation and damage to the coil is prevented. The full main flux continues to link the other coil but since the voltage across that coil is insufdcient to ionize the gas in the tube, no current ows in that coil. It will be understood that for the other half cycle of electromotive force applied across the terminals of the primary winding the flux will follow the paths outlined above but will be coursing in the opposite direction.

It will be seen that I have provided a transformer which is economical in construction and installation and which is highly eflicient and safe in operation. In both the embodiments I have shown there are only two dilerent shapes of core members. The outer core members have exactly the same configuration. Therefore, only two dies are needed for the manufacture of the core parts. This results'in a saving in manufacturing cost. Moreover, the cores are. efficiently deslgnedso that the flux is distributed symmetrically and with more or less uniform density. Accordingly, there is no waste iron in the core and it is of minimum weight. Moreover, the heat developed in the Atransformer is distributed evenly and dis- Sipated eilciently.

My transformer is compact in construction. All the coll sections are contained wholly within the core so that a minimum of liux is lost by Iringing to the casing. Moreover, the shunt .paths are all within the outer confines of the core. The casing in which the transformer is enclosed therefore does not affcet the reluctances of these shunt paths and is made to t my transformer closely. Thus there is no waste space in the casing. A minimum of insulating compound is required to ll the interstices in the transformer and the space between it and the casing. The 5 casing itself, being of minimum size, is cheap and light in weight and occupies a minimum of space in installation.

The embodiment of my invention shown in Figure 1 does the work of two transformers and therefore effects further savings in first cost and in operation. Less space is required for installation of this transformer than is required for the installation of two transformers to do the same work. Negative loads of either equal or unequal resistances may be energized from that transformer. Due ta the fact that one side of the circuit is througrfethe ground, expensive high potential cables and bushings need be used only on the other side. Where the connections are such that the high potential sides are always at the same potential, a single multi-conductor cable can be used to accommodate both high potential leads and thus effect a further economy. As many possible embodiments may be made of my invention and as many changes may be ma'le in the embodiments hereinbefore set forth, it will be understood that all matter described herein, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense. I claim: 1. In electrical transformer apparatus of the character described, in combination, a central linear core member, two parallel core members ldisposed on opposite sides of said central member, each of said parallel members having one central and two end extensions abutting said central member and also having two shunt arms intermediate said central and end extensions forming air-gaps with said central member;' a primary winding comprising two coil sections mounted on said central extensions of said parallel members and connected in bucking relationship; and a secondary winding comprising two coil sections each mounted on said central member near one of its ends.

2. In electrical transformer apparatus df the character described, in combination, a central linear core member, two parallel core members disposed on opposite sides of said central mem- Cal ber, each of said parallel members having one central and two end extensions abutting said central member and also having two shunt arms intermediate 'said central and end extensions forming air-gaps with said central member; a primary winding comprising two coil sections mounted on said central extensions and connected in bucking relationship; and two secondary windings mounted on said central member near its opposite ends.

3. In electrical transformer apparatus of the character described, in combination, a central linear core member,A two parallel core members disposed on opposite sides of said central member, said parallel members having a central and two end extensions abutting said central member and also having-two shunt arms intermediate said central and end extensions, forming airgaps with said central member; a primary winding comprising two coil sections mounted on the central part of the core and connected in bucking relationship; and a secondary winding comprising two coil sections mounted on said central member near its respective ends but inside the end extensions of said parallel members.

vLi. In electrical transformer apparatus ofv the character' described, in combination, a central l linear core member, two parallel core 4members Ydisposed on opposite sidesof said central member, said parallel members having long transverse arms at their centers and ends extending l n into abutting relationship with said central member and also having short transverse arms intermediate said-long arms separated from said central member by air-gaps'and forming shunt paths; a primary winding comprising two coil sections mounted on said long central arms and connected in bucking relationship; and a secondary winding comprising two coil sections mounted on said central member between said long end arms and said short arms of said parallel members.

5. In electrical transformer apparatus of the n character described, in combination, a central tween said long end arms and said short arms of said parallel members.

6. In electrical transformer apparatus of the character described, in combination, a central linear core member, two parallel core members disposed on opposite sides of said central member, each of said parallel members having one central and two end extensions abutting said central member and also having two shunt arms intermediate said central and end extensions forming air-gaps with said central member; a primary winding comprising two coil sections mounted on said central extensions of said parallel members and connected in parallel-bucking relationship; and a secondary winding comprising two coil sections each mounted on said central member near one of its ends.

7. In electrical transformer apparatus of the characterv described, in combination, a central linear core member, `two parallel core members disposed on opposite sides of said central member,- each of said parallel members having one central and two end extensions abutting said central member and also having two shunt arms intermediate said central and end extensions forming air-gaps with said central member; a primary winding comprising two coil sections mounted on said central extensions of said parallel members and connected in series-bucking relationship; and a secondary winding comprising two coil sections each mounted on said central member near one of its ends.

8. In electrical transformer apparatus of the character described, in combination, a central linear core member, two parallel core members disposedon opposite sides of said central member, said parallel members having long transverse arms at their centers and ends extending into abutting relationship with said central member and also having short transverse arms intermediate said long arms separated from said central member by air-gaps and forming shunt paths; a primary winding comprising two coil sections mounted on said long central arms and connected in parallel-bucking relationship; and a secondary winding comprising two coil sections mounted on said central member between said long end arms and said short arms of said parallel members. ,Y

9. In electrical transformer apparatus of the character described, in combination, a central linear core member, two parallel core members disposed on opposite sides'of said central member, said parallel members having long transverse arms at their centers and ends extending into abutting relationship with said central member and also having short transverse arms intermediate said long arms separated from said central member by' air-gaps and forming shunt paths; a primary winding comprising two coil sections mounted on said long central arms and connected in series-bucking relationship; and a secondary winding comprising two coil sections mounted on said central member between said long end arms and said short arms of said parallel members.

10. In electrical transformer apparatus of the I character described, in combination, a central linear core member, two parallel core members disposed on opposite sides of said central member, said parallel members having a central and two end extensions abutting said central member and also vhaving two shunt arms intermediate said central and end extensions, forming airgaps with said central member, a primary winding comprising two coil sections mounted on the core near the center of said central member and connected in bucking relationship; and a secondary winding comprising two coil sections mounted on opposite ends of said central member but inside the' end extensions of said parallel members.

11. In electrical transformer apparatus of the character described, in combination, a central linear core member, two parallel core members disposed on opposite sides of said central member, said parallel members having a central and two end extensions abutting said central member and also two shunt arms intermediate said central and' end extensions, forming air-gaps with said central member, a primary winding comprising two coil sections mounted on the core between said shunt arms and connected in bucking relationship; vand a secondary winding comprising two coil sections mounted on opposite ends of said centralmember but inside the end extensions of said parallel members.

CHARLES PHILIPPE BOUCHER.

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