US2331369A - Transformer - Google Patents

Description

1943- c. P. BOUCHER 2,331,369

TRANSFORMER Filed June 13, 1940 2 Sheets-Sheet l s /77 ra /vs Y Oct. 12, 1943. c. P. BOUCHER TRANSFORMER Filed June 13, 1940 2 Sheets-Sheet 2 Patented .Oct. 12, 1943 t Charles Philippe Boucher,

or to Boucher Inventi D. 0., a corporation of Paterson, N. J assignons, Ltd., Washington,

Delaware Application June 13, 1940, Serial No. 340,391

11 Claims. (01. 171 119) This invention relates to electrical transformer apparatus and more particularly to transformer apparatus suitable for the operation of negative loads such as luminous gas discharge tubes.

One of the objects of my invention is to provide simple; compact and thoroughly reliable transformer apparatus which is well adapted to withstand the many varying conditions of load and whole or partial short-circuit encountered in actual practical use.

Another object-is the provision of power transformer apparatus which is highly efficient and particularly economical in construction, installation, and operation, enjoying low copper and iron losses, a high rate of heat dissipation and good operating power factor.

A further object of my invention is to provide a transformer of symmetrical construction which is balanced in operation and which provides individual protection for each coil section of the secondary winding in the event of short circuiting of that coil section or its load.

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

The invention accordingly consists in the combination of elements, features of construction and arrangement of parts, .and in the several steps and the relation of each of the same to one or more of the others as described herein, the scope of the application of which is indicator in the following claims.

In the accompanyingdrawings, Figure 1 is a diagrammatic representation of my transformer apparatus in single form, and

Figure 2 is a diagrammatic representation of a modified form of my transformer apparatus in double form.

As conducive tov 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 tubes of desired size and configuration high potential electrical energy is required. Ordinarily the desired high potential electrical energy issupplied by alternating current transformer apparatus connected to a standard single phase sixty cycle source at either one hundred and ten operation. In certain heretofore known and/or used transformer systems, the plurality of tubes necessary for operation of a single sign or display have been energized by way of a corresponding plurality of transformers in order that the energizing potential may not reach values in excess of those specified by the Fire Underwriters. The cost of equipment for such a system is excessively high and also the labor cost is high since a separate charge is made for the installation of each unit. In some heretofore known and/or used transformers these objections have been alleviated somewhat by providing a transformer hav- ,,ing two secondary winding coil sections connected in series with the midpoint of the winding grounded. In even the moderately large luminascent signs several of these transformers are required in order to energize the complete display.

One of the outstanding objects of my invention is the provision of transformer apparatus which further alleviates the'se difliculties, giving a single, compact, inexpensive unit requiring but a single connection to the source of supply and yet giving eflicient and thoroughly reliable operation of a plurality of luminescent tubes of a display or sign.

It may be further noted that in the actual operation of a luminescent tube system the tubes frequently become grounded between electrodes by moisture, insect bodies, or other conditions, or the coil sections may themselves become grounded. In the usual transformer employing economical fine-wire secondary coil sections, the short-circuiting of a coil permits the flow of an excessive current until the coil becomes Burned out. The only way to .avoid this result-is by increasing the size of the copper wire of the secondary coil sections until it is large enough to carry. the short-circuit current. Such an expedient materially increases the cost of the transformers.

In the construction oftr-ansformers it is customary to form the core parts of many laminations bound together to form a compact mass, this construction serving to materially reduce eddy current losses. together and the separate core parts are also united by means of rivets or bolts in transformers as they are now constructed. The presence of the rivets or bolts counteracts to some extent the advantages of a laminated core because they promote the formation of eddy currents,--with a consequent reduction in efliciency.

An important item of cost in the construction .of transformer cores is the expense involved in providing the dies'u'sed in stamping laminations The laminations are held manner more particularly described hereinafter.

The transformer III comprises a core, a primary winding, and a seconday winding mounted on the core. The core includes two parallel linear members II and I2 between which are interposed the substantially C-shaped members I3 and I4. The primary winding P is mounted on the linear member II in the space between the O-shaped members I3 and I4. Two coil section S1 and 52, forming the secondary winding, are mounted respectively on the long legs I31:

I and Ma of the C-shaped members I3 and I4.

The long leg I3a abuts the member I I at its left end and the member I2 intermediate its ends but near the left end thereof. Likewise the long leg I4a abuts the member II at its right end and the member I2 intermediate its ends but near the right.end. In order to prevent relative longitudinal motion of the parts without requiring additional holding means for this purpose,

notches one or two thousandths of an inch in depth have been punched in the member II at I5 and I6 to accommodate the legs I31: and Ila. Similarly, shallow notches I1 and I8 are formed in the member I2 to hold the legs I3a and. a

from shifting longitudinally. As a further means of preventing such motion the notches I5 and I6 in the member II terminate in spurs I9 and 20 which fit into notches cut in the members I3 and I4 respectively.

such'asto place the coils in series where the load is not grounded, but when the mid-point of the load is grounded, the coils may be connected in opposition, that is, so that their output terminals are at the same potential, positive or negative, at the same instant. Where the load'mid-pointis grounded, a separate circuit is formed for each cell and its half of the load. The transformer core is grounded as at 32.

As the current flowing through the primary winding P changes in magnitude and direction in response to the alternations of voltage impressed across its terminals by the source 21, a magneticfiux of correspondingly varying magnitude and direction is generated in thecore member II and traverses a complete circuit including the member I I, the long legs I 30. and Ila and the member I 2 and linking the secondary winding' coil sections S1 and S2. The path fol- The other legs I31) and Nb of the C-shaped members I3 and I4 are shorter than thelegs I31: and I 4a and extend closely toward. but do not abutthe leg I2 at its ends, forming therewith air gaps G1 and G2, respectively, of high magnetic reluctance. The central parts of the members I3 and I4 are designated by the characters Ho and I4 0.

When the parts are assembled in their proper relationship, with the various .coil sections in place, the core members are placed under heavy pressure, as by an arbor press, and core bands 2I and 22 of steel plate are put into the positions shown, the ends of each band being united as by welding or riveting. To make as tight a fit as possible, wedges 23 and 24 of hardinsulating material are inserted between thebands 2I and 22 and the member I I while the parts are under pressure. The transformer is preferably enclosed in a. casing similar to the one shown in Figure 2.

The primary winding coil section P is energized by way of the leads 25 and 26 from a source of alternating current electrical energy 21, such as the standard single phase sixty cycle commerical mains at llO or 220 volts.

One terminal of the coil S1 is grounded to the core at 28 and its other terminal is connected by a lead 29 to one terminal of the tube T, Similarly, one terminal of the coil S2 is grounded tothe core at 30 andits other terminal is connected by a lead 3I to the other terminal of the tube T. The grounding of the coils S1 and S2 is lowed by the fiux during one half cycle of the ap-' plied potential is indicated in the figure by arrows. Due to the constantly changing nature of the flux, a voltage is induced across the terminals of the secondary coil sections S1 and S2.

S2 will generate counter magnetomotive forces,

opposing the coursing of the main fiux and causing the major portion of thatfiux to seek a path of less reluctance. Such a path is found from member II through the central part I3c, the

short leg I31) and its included air gap G1, member I2, air gap G2, short; leg llb, and central part I Ic back to member II. By virtue of this shunting of the major portion of the flux around the coils S1 and S2 the current in those coils is limited to a safe value.- Enough flux continues to link the coils S1 and S: to maintain a steady fiow of current through the tube T until the electrical potential from source 21 applied across the primary coilP decreases almost to zero near the end of its half cycle. Upon further decrease in potential in following through the cycle, the tube T becomes extinguished. I

When the primary current has alternated to its other half cycle, the tube meanwhile having become extinguished, as the potential across the secondary winding builds up and the tube strikes again the paths of magnetic flux will be the same as those outlined above, except that the flux will course in the opposite direction. Thus, the flux will course through bar II, central portion I40, short leg Mb, airgap G2, bar I2, air gap G1, short leg I31), and central part I3c back to bar II.

In the event the tube T should become'shortcirculted, as by a film of moisture, matted insect bodies and the like about the terminals, the operif tube T is short-circulted, the current beginning to fiow in its secondary coils S1 and $2, from the beginning of the half cycle of applied potential will commence to develop strong counter mag netomotive forces which-will cause the main body long legs |3a and Ma of core members [3 and l4, thereby interlinking the primary winding and the coils S1 and S2, is insuflicient to induce such electromotive forces in coils S1 and S2, as to cause an excessive flow of current through them. The value of the current flowing under short-circuit conditions is substantially the same as that flowing during the conductive period of the luminescent tube. Neither is suflicient to cause substantial heating and consequent damage to'the winding. Y

Should one of the coil sections, say the coil S1, become grounded in operation, the tube T will not be operated because the potential of the other collSz will not be suflicient to ionize the gas in the tube. The current flowing in the grounded coil S1 will not be excessive due to the shunting of the main magnetic fluxaround the coil. As the current induced in the grounded coil S1 rises from a zero value in response to the rising of the potential applied across the terminals of the formed-by the abutting ends of the long legs 39a and 40a. The other ends of the long legs 31a, 38a, 39a and 40a abut the bars 35 and 36, intermediate their ends, in shallow notches 4|, 42, 43, and 44, respectively, formed in those bars. Secondary winding coil section S1, S2, S3 and S4 are mounted on the inner ends of the long legs 31a, 38a, 39a and 40a, respectively.

The core parts are held in their proper relationship by metal bands 45 an 46; which extend around the bars 35 and 36 and along' the lengths primary winding P, a counter magnetomotive force is generated by the coil S1, bucking the main flux and causing a major portion of it to course along a-path of high reluctance extending out wardly around the coil S1. This path is from the bar ll through the central portion I30, short arm [3b, air gap G1, bar l2, and long leg I4a back to bar ll, excluding the coil S1 but including and linking the coil S2; A similar condition of operation will obtain when it is the coil S: which becomes grounded. In that situation, a major portion of the flux .will pass through the .shunt path including the air gap G2 and short leg 'l4b but will continue to link the coil S1.

On the other hand, when the tube T is opencircuited, as by the breaking of the tube or a substantial increase in the pressure of its gas, there will be no need to divert flux around the secondary coils. There is no current flowing through the coils S1 and S2 and accordingly no counter magnetomotive forces are developed therein. Hence with coils S1 and S2 in opencircuit condition, the flux continues to course through the long legs [3a and [4a of the members I3 and I4, linking the coils S1 and S2. Likewise, when one of the coils, say the coil S1, is opencircuited, the whole. secondary circuit is thereby broken. No counter magnetomotive forces are then developed by the secondary coils and the magnetic flux will course through the core as it does in normal operation when the tube is not ionized. 1

Where desired the highly beneficial operating characteristics of my transformer apparatus are achieved by modifying the onstruction of the apparatus as by doubling the number of c-shaped members and secondary coil sections thereon-and providing two instead of one long linear member and having the (i-shaped members abutting each other impairs, their long legs being extended to i'orm bar portions on which primary coil sections are mounted.

Thu's referring to Figure 2 of the drawings, I have shown a transformer having a core comprisiiig two parallel linear members 35 and 36 back of the C-shapes and are paired in abutting,

relationship, forming bar portions on which p imary coil sections ar mounted. Thus on primary coil section P1 is mounted over the abutting ends of the long legs 31aand 38aand the other primary coil section P: is positioned on the bar of the long legs'3la and 36a in the case of the band 45 and along the long'legs 39a and 4lla in the case of the band 46. The part are placed in an arbor press in which they are subjected to a force between ten and forty tons and tight joints are assured by inserting wedges 41, 48, 49 and 50 under the metal bands.

The transformer is preferably enclosed in a casing 5|, cushioning pads 52 and 53 of felt or other suitable material being interposed between the core and the casing.

The primary winding coil sections P1 and P2 are connected together in series by a lead 54 at their inner terminals. Their outer terminals are connected by leads 55 and 55 to a source of alternating current electrical energy 51 which i similar tothe source 21 of Figure 1.

The secondary winding coil sections S1, S2, S3, and S4 are grounded to the core at 58, 59, 60, and BI, respectively. Their other terminals are connectedto the one terminals of luminescent tubes T1, T2, T3, and T4 by lead 62, 63, 64, and 65, respectively. The other terminals of the tubes are grounded at 66, 61, 63, and 69 respectively. The ground connections 58 and 60 for the coils S1 and S: are preferably those which will place their other terminals, and thus the leads 62 and 64, in

corresponding phase relationship. For this reason tials of corresponding phase relationship. Ac-

cordingly, only one bushing H is necessary for both leads 53 and 65, which may be parts of a multi-conductor cable'instead of separate cables. The core itself is grounded, as at 12.

The core member 31 has, in addition to the long leg 31a, 9. short leg 31b and a central portion 310. The short leg 31b forms with the end of the bar35 an air gap G1 of high magnetic reluctance. Similarly, the core members 38, 39, and

40 have short legs 38b, 39b, and 40b and central portions 380, 39c, and 400. The short legs 38b, 39b, and 40b form air gaps G2, G3 and G4 with the bars 35 and 36.

In the operation of the transformer illustrated in Figure 2, as the voltage impressed across the terminals-of the primary winding coil sections P1 and P2 by the source 51, rises from a zero value at the beginning of a half cycle, a current begins to. flow in the primary winding. This current generates a flux in the iron core which courses through the core along a path of low reluctance interlinking the primary and secondary windings. The path followed by the flux in one half cycle of theapplied potential is illustrated in the figure by arrows. As the flux changes in magnitude it inimpressed across the terminals of the tube T1 by way of the lead 6'2 and the ground connections, it ionizes thegas in tube T1 and thereby renders the tube conductive, a current begins to flow in this tube and the coil. The current will not reach an excessive value because it creates a back ma netomotive force causing a major portion of the main magnetic flux to be by-passed outwardly around the coil from the long leg 31a through the central part 31c, short leg 31b and air gap G1 to the bar 35. If'the other tubes have not yet become ignited, the flux then passes from the bar 35, through the long legs 39a and Me, the bar 36 and the long leg 380: back to the member 31. Enough flux still continues to link the coil S1 to maintain a steady flow of current in the tube T1 until the current in th primary winding P1--P2 decreases almost to zero near the end of the half cycle of applied voltage, at Whlch'tlme the tube becomes extinguished. It will be apparent that the flux shunted around the coil S1 will continue to link the coils S2, S3, and S4 and hence that their operation will not be afiected.

In like manner, the coils S2, S3 and S; will light the tubes T2, T3 and T4 respectively, when the voltages induced in those coils reach values suiliciently high to ionize the gas in the tubes. The current in any of the secondary circuits will not reach an excessive value because it will generate a back magneto-motive force in the coil section, causing the major portion of the main magnetic -flux to be by-passed around the coil section through its associated shunt member 38b, 391),

or 43b and the included air gap G2, G3 or G4.

The main flux will continue to link the inoperative coil sections at this time. Enough flux will link the operative coil section to maintain a steady-fiow of current'in its tube load untilthe current in the primary winding approaches a zero value near the end of a half cycle of applied -tion of the main flux will course along a path including the right hand end of long leg 31a,

central part 310, short leg 31b, air gap G1, bar

35, air gap Ga, shortleg 39b, central part 390, the right hand end of long leg 39a, long leg 401:, bar 36 and-long leg 38a back to the member 31.

' Also, a similar situation is met where the other two coils S2 and S4 are operating but the coils S1 and S; are not operating. In that case, the major portion of the'main magnetic flux will course along a path of high reluctance passing outwardly around and excluding the coils S2 and S4 but linking the'ico lls 'si and S3. Moreover, in any other condition of operation with some coils operative and some inoperative, a major portion of the fiux will be by-passed around the operative coils but will continuevto link the inoperative ones.

It will be understood that, while-"I have described the operationfof the transformer during one half cycle of the applied electromotive force,

the operation will-be the same during the other half cycle. .-.The paths followed by the flux will bucking the main flux.

. tubes T1, T2,-T3 and conditions, a major portion of the magnetic flux courses along the longest possible magnetic path which includes the central portions 3'lc,38c, 39c and 400 and the short legs 31b, 38b,.39b and b will be lighted 120 times a second. Due to persistence of vision the tubes will appear to emit a steady glow of light.

While, as a matter of convenience in describ-' ing the operation of my transformer apparatus, the various stages in the operation of the four luminescent tubes T1, T2, T3 and T4 and the possibilities attending this operation are treated separately, each without special regard to the operating of the-other, it will be understood that under actual operating conditions all the luminescent tubes are rendered conductive and luminous at about the sameinstant and at about the same instant become non-conductive and non-luminous. During those brief periods when the tubes are in their non-conductive states, the total magnetic flux courses along the linear core members 35 and 36 and the long leg portions 31:11 38a, 39a and 40a of the Q-shaped members 31, 38, 39, and 40 efiecting the closure of the magnetic circuit. During those periods when all the T4 are in their conductive of the c-shaped members 31, 38, 39, and 40 and the included air gaps G1, G2, G3 and G4, the remaining portion of the magnetic flux continuing along the short path of low reluctance and inter-.

linking the primary and secondary windings.

Where one tube becomes grounded in opera- S1 dueto the peculiar magnetic shunt construction provided. As in normal operation when the tube T1 is ionized and conductive, the current flowing through the coil S1 under short-circuit conditions will set up a magnetomotive force v This back magnetomotive force will cause the major portion of the main flux to pass outwardly around the coil S1 through the magnetic shunt path of high reluctance comprising the centralpart 310, the short leg 3'"; and the included air gap G1 into the bar 35 and through the members 39, 40, 36 and 38, back to member 31. 'By virtue of this action,

current which flows under normal operating conditions. It will be apparent that the same protection is afforded when it is the coil sections;

by-passed-around the secondary coil through a magnetic shunt path of high reluctance including the short leg of the C-shaped core member on which that coil is mounted and its associated be identical except that the flux will then be coursing in the opposite direction. Where a 60- cycle course of primary current is used, the tubes air gap.

-Where one of the tubes, say the tube'Ti, be-

comes open-circuited as by breaking of the tube or a substantial reduction in its vacuum, it will be apparent that no current will flow through the secondary winding coil section S1 of that tube. The operation of the other tubes will not be affected and the main magnetic flux will continue to course through the long leg 31a. of the o-shaped member 31, linking the coil S1, as well as the other coils S2, S3, and S4.

Similarly, when any of the other tubes or coil sections becomes open circuited in operation, no ,current will flow through that coil section although the main flux continues to interlink it with the primary winding. The other coil sections and tubes will continue to operate normally.

It will be understood that my transformer is capable of many modifications within the spirit of my invention. Thus, the secondary coil sections of the transformer shown in Figure 2 may be connected together in series in any combination desired so as to operate a tube requiring twice the voltage of the tubes illustrated. With such a connection, the maximum voltage to ground at no point will exceed the maximum voltage generated by any one coil section, al-

though the voltage across the tube terminals is double that across any one coil section. It is also feasible to connect pairs of coils in opposition to operate a load where that load is grounded approximately at its midpoint.

In the transformer of Figure 2 it may be desired to make the C-shaped members 31 and 38, on the one hand, and the members 39 and 40 on the other hand, of one integral piece. Such a construction would eliminate two butt joints in the core and would therefore reduce the reluctance of the main magnetic path. Where the core is so made, the primary coil sections P1 and, P2 are wound upon their core members. I

Another possible modification of the transformer is one in which the positions of the C-shaped members are reversed, that is, the members are turned around so that the main magnetic path is on the outside of the core and the shunt legs are inside. That construction has the advantage that fringing of the magnetic flux to the'transformercasing and consequent loss in efliciency are diminished.

It will be apparent that my transformer isexceedingly compact, there being a minimum of interior space which is not utilized. The space occupied by the windings is all inside the outer confines of the core. Because of the compact arrangement, a minimum of expensive insulat- Inasmuch as the output terminals of adjacent coil sections are designed to correspond in phase, only one bushing is required for the two high potential leadsfrom those coil sections. Moreover, since the other terminals of thecoil section are grounded, no bushings are required for them. As there is substantially no voltage difference between adjacent high potential leads, multi-conductor cables can be used for them in-- stead of individual cables. Finally, due to the groundingof the one sides of the coil sections, no high tension cable is required for that side of the circuit.. The elimination of high potential cables and bushings on the ground sides and the reduction in the number of them required on the other sides of the secondary circuits constitute reduced to a minimum. There is high coupling of the secondary coils at the start of each half cycle of primary current. The transformer is symmetrical in shape and it is balanced in operation.

Each individual secondary winding coil section of my transformer is protected from overheating in case of its becoming short-circuited to ground-by a magnetic shunt associated with that coil section. Accordingly, a minimum of copper is required in the secondary windings, as the wire does not have to be large enough to withstand an excessive flow of current. Where each coil operates an individual load, each coil is independent of the others, so that inoperativeness of one coil due to short or open-circuiting of the coil or its tube load aii'ects only the,

to bind the laminations together, eddy currents in the core are reduced to a minimum. Therefore, most of the magnetic flux in the cone serves a -useful purpose and virtually none 'of it is wasted. Moreover, heating of the core due to eddy currents is substantially eliminated.

Since the core shunt members are integral parts of main core members, changes in the reluctances of the shunt paths due to varying temperature conditions or to stresses set up in long usage are reduced toa minimum.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments hereinbefore set forth,

- it will be understood that all matter described herein, or'shown in the drawings, 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 core includin two spaced substantially parallel linear port ons and at least a spaced pair of substantiallv C-shaped portions, said C-shaped portions having one legs extending between the linear members and forming therewith a closed ma netic circuit of low reluctance and other legs forming therewith shunt circuits of high reluctance, secondary windings mounted on said one legs of said C-shaped portions with their one terminals grounded to the core and their other ter- .minals connected to load means,,and a primary winding mounted on said core and linked thereby with said secondary windings.

2. In electrical transformer apparatus of the character described, in combination, a primary winding, a plurality of secondary windings each of which comprises one coil section, a core interlinking said primary and secondary windings, said core including a plurality of individual C-shaped portions corresponding in number to said plurality of secondary winding coil sections symmetrially positioned with respect to the remainder of the core and the primary winding mounted thereon the one legs of said C-shaped portions abutting another portion of the core and forming a short main magnetic circuit of low reluctance said secondary coils being respectively mounted on said legs of said C-shaped portions and the other legs forming parts of shunt paths of high reluctance around each of said secondary winding coil sections, and binding means holding said individual C-shaped portions to the remaining C-shaned members.

portions of said core in said abutting relationship;

3. In electrical transformer apparatus of the character described, in combination, a transformer core comprising two straight parallel portions and two C-shaped portions with their one arms facing and abutting one of said straight portions and with their other arms facing but not abutting said one straight portion and with their backs abutting said other straight portion, forming thereby a closed magnetic circuit and two auxiliary circuits, a primary winding mounted on one of said straight core portions, and a secondary winding comprising two coil sections each of which is mounted on the abutting arms of said c-shaped portions.

4. In electrical transformer apparatus of the character described, in combination, a transformer core comprising two straight parallel portions, and two O-shaped portions abutting therewith at opposite ends thereof with their open sides facing a straight portion, said C-shaped portions each having a fore-shortened leg apshunt paths away from parts of the closed path. 5. In electrical transformer apparatus of the character described, in combination, a transformer core comprising two straight parallel portions, and two C-shaped portions each one of which is in abutting relationship with adjacent ends of said parallel portions with the open parts of said C-shapedportions facing one of said parallel portions, said c-shapedportions each having a fore-shortened leg approaching an abutting relationship with an end of 'one said parallel portion and forming therewith an air gap, whereby there is achieved a short main path for magnetic flux and also two fshunt paths around parts of the main path.

6. In electrical transformer apparatus of the character described, in combination, a transformer core comprising two straight parallel pieces having correspondingly inwardly facing recessed sections, two c-shaped pieces facing one of said straight pieces with their one leg portions set within the recessed sections of said piece and their other leg portions being fore-shortened and forming air gaps therewith and with their backs set within the recessed. sections of said other straight piece, and binding means maintaining said straight and C-shaped pieces in assembled relationship.

7. In electrical transformer apparatus of the character described, in combination, two linear core members spaced in parallel relationship, two substantially c-shaped core members each having a long leg portion so positioned as to abut the linear core members to effect a closed magnetic circuit of low reluctance and each having a short leg portionso positioned as to form a shunt path 8. In electrical transformer apparatus of the character described, in combination, two linear parallel core members, two substantially C- shaped core members spaced apart and cooperatively associated with said first-mentioned core members efiecting a closed magnetic circuit therewith by way of their one legs and establishing shunt core paths including air gaps by way of their other legs, a primary winding mounted on one of said linear core members, and two secondary windings mounted on said o-shaped core members, each of said secondary windings consisting of one coil section with its one terminal grounded to said core members and its other'terminal connected to an individual negative load.

9. In electrical transformer apparatus .of the character described, in combination, two linear core members spaced in parallel relationship; four substantially c-shaped core members each having a long leg portion so positioned as to abut at its one end one of said linear core members intermediate the ends thereof and to abut at its other end another of said C-shaped members to efiect a closed magnetic circuit, each of said O- shaped members also having a short leg portion so positioned as to form a shunt path and efiect a lengthening of the magnetic circuit; a primary winding comprising two coil sections mounted over the abutting ends of the long leg portions of said C-shaped members; and four secondary windings, each comprising one coil section mounted on a long leg portion of one of said 0- shaped members.

10. In electrical apparatus of the character described, a double transformer comprising,.in combination a magnetic core, a primary windin consisting of two coil sections positioned on opposite legs of said core, and, two secondary windings positioned on said opposite legs of the core each secondary winding consisting of two coilsections located on opposite sides of one of the primary coil sections and connected together in series, said core including offset portions individuala magnetic circuit, a primary winding mounted on one of said linear core members, and two secondary windings each comprising one coil section mounted on a long leg portion of one of said of said secondary winding coil sections to provide paths for magnetic flux which does not link said secondary winding coil sections with said primary winding during closed-circuit-operation of the secondary coil sections.

11. In electrical transformer apparatus of the character described, a-double transformer core comprising, in combination, two parallel straight core portions, two pairs of abutting interconnecting core portions, each of which pair corprises two core portions abutting each other and each of said abutting core portions having offset arm portions approaching a butt relation with said straight core portions and forming an air gap therewith, whereby there is achieved-a short closed main magnetic circuit of low reluctance and-a plurality of individual departures from this mainmagnetic circuit of high reluctance by way of the ofiset arm portions of said interconnecting core portions and adjacent parts of said straight portions and the air gaps. included herewith.

CHARLES PHILIPPE BOUCHER.

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