US 3153212 A
Description (OCR text may contain errors)
Oct. 13, 1964 A. R. DAVIS VARIABLE TRANSFORMER AND WINDING 2 Sheets-Sheet 1 Filed June 6, 1961 III H I u IN V EN TOR. 49/154 Jar/s arra/wvy Oct. 13, 1964 A. R. DAVIS VARIABLE TRANSFORMER AND WINDING 2 Sheets-Sheet 2 Filed June 6, 1961 INVENTOR. flmsz flaw/5' BY at/4% 4; flffdfi/VE) United States Patent 3,153,212 VARIABLE TRANSFORMER AND WENDENG Ariel Davis, 3637 S. State, Salt Lake City, Utah Filed June (6, 1% Ser. No. 115,143 3 Claims. (6!. 336-449) This invention relates to autotransformers and particularly to autotranstormers providing a continuous range of voltages and currents. The invention is particularly directed to high wattage dimmers having a plurality of current taps for varying the intensity of illumination of lamps.
This is a continuation-in-part of the copending application Serial No. 23,457, filed April 20, 1960, which is a continuation of the now abandoned application Serial No. 597,623, filed July 13, 1956.
An object of this invention is to provide a variable current and voltage autotransformer having a rugged and sturdy structure and a high overload current capacity with the parts easily manufactured and assembled.
Other and further objects will be apparent from the following description taken in connection with the drawings in which FIG. 1 is a top view of the autotransformer without the clamping means and the contact members;
FIG. 2 is a full cross-sectional view taken along a section of a complete autotranstormer indicated by the lines 22 of P16. 3;
FIG. 3 is a fragmentary end sectional view taken along a section of a complete autotransformer indicated by the lines 33 of FIG. 2;
FIG. 4 is a perspective view the laminations of the winding spaced to illustrate the relationship of the winding laminations and insulating strips;
FIG. 5 is a side view of the laminations spaced to diagrammatically illustrate the relationship between the laminations and the insulating members;
FIG. 6 is a fragmentary side view of the windings compressed in position with insulating material between the connecting portions on the far side;
FIG. 7 is a sectional view of the brush assembly taken along lines 77 of FIG. 3;
FIG. 8 is a sectional view of the brush assembly taken along lines 88 of FIG. 3; and
FIG. 9 is a side view of an embodiment of the wind ing with the resin filler omitted to illustrate the double windings.
Referring to FIG. 1 of the drawings, an autotransformer in accordance with the invention is shown partially disassembled to illustrate the relationship of the core 10 and the laminated winding 11. The core 19 is formed from two oval shaped core pieces 12, 13 made of tape steel coiled in the general shape of an oval having parallel straight sides. Sides 12a, 13a are positioned side by side to form a center core piece passing through the winding 11 so that each core piece carries approximately hair" thefiux of the winding 11. The center core piece is electrically insulated from the winding 11 by four separate insulating pieces 14, 15, 1d and 17 (FIG. 2) extending the length of the side with pieces 14 and 16 extending to the connecting turns of the core pieces.
The winding 11 comprises U-shaped laminations 18, 19 preferably made from a highly conductive material such as sheet copper. The laminations 18, 19 are preferably identical in size and shape and when assembled form a turn of the winding. Each comprises two legs a and b and a connecting portion 0. alternately reversed so that the laminations 18 have the connecting portion 0 on one side of the winding and the laminations 19 have the connecting portion 0 on the other side or" the winding. The legs of the laminations are The laminations are 3,153,212 Patented Oct. 13 1964 contiguous with an insulating member between a pair of contiguous legs. The position of the insulating member is alternate so that a leg is insulated from an adjacent leg on one side and in good electrical contact with the adjacent leg on the other side.
Considering more specifically the stacking of the winding, reference is made to FIGS. 4 to 6. The laminations 18 and 19 are stacked so that the legs a are aligned to form a surface A and legs b are aligned to form a surface B. The legs 18:: and 19a are in electrical contact and legs Ilia-1 and ll la-el are in electrical contact. The legs and Isa-1 are separated by the insulating member 2%.
The legs 18!) and 1912 are separated by insulating member 2i and legs 1% and 1815-1 are in electrical contact.
Thus current entering leg 18b passes up through connecting leg to leg Ma. The current is carried by legs 18:: and 19a and passes through connecting leg to leg 1913. Since legs 15% and 1% are electrically separated and legs 1% and 1822-1 are in good electrical contact, the current is transferred to the laminations 18-1 and then to lamination lid-l and thus through the winding.
The connecting leg c of the lamination is twice as wide as either leg at or b in order to match the double thickness of the contacting legs. The laminations may be formed of several pieces and a plurality of insulating members may be inserted between the laminations.
The laminations lid, 19 are stacked around the insulating members l4, l5, l5 and 17. The insulating spacers Zil, 21 are alternately inserted between the legs on each side, as previously described herein. For compressing the laminations into good electrical contact and to hold the winding in a rigid assembled condition, nonmagnetic blocks and are provided on one side and nonmagnetic blocks 2'7 and on the other side. Rods 29 on each side of the core connect the blocks 25 and 26 and have nuts 3t? threaded thereon to compress the laminations and tightly hold the laminations together. Similarly, the blocks 27 and 28 are held by rods 31 and nuts 32. The rods 25" and 31 have insulating sleeves 33 and 34 to prevent shorts from occurring between the winding and the rods.
The current and voltage are supplied to the winding 11 by means or" the yokes 35 and 36 at opposite ends of the winding. Yoke 35 is shown in section in PEG. 2 and comprises a lJ-shaped strap member 37 with contact members 33 and 39 extending the breadth of the winding 11 and in contact with a leg 19:; of a lamination. The leg 1% is spaced by an insulating spacer member 21. The strip 37 has a terminal 40 for receiving a lead thereto. The current passes through the terminal 40, yoke 37 and contact member 38 to the winding. The contact members are spaced from the blocks 25, 26, 27 and. 28 by insulator pieces 41, 42 and the yoke is separated by the pieces 43, id recessed in a groove in the pressure blocks. A pair of supports 45 secured by the nuts is provided for spacing the pressure blocks and providing rigidity to the clamping means. A transverse insulator 46 extends across the ends of the core pieces 12 and 13 to insulate the yoke 35 from the steel core.
The laminations are preferably stamped from sheet copper and are silver coated to provide good electrical contact between the laminations. The laminations may be made of aluminum.
The surface A is ground and the edges of the laminations and insulating members polished to a very smooth surface. A current carrying means 5% with a carbon or graphite electric brush is supported by the mounting means (illustrated in FIGS. 7 and 8) to slide smoothly over the surface in electrical contact with the laminations.
The brush may be of a number of sizes or shapes. However, to reduce circulating currents in the brush the width of the brush is preferably greater than the width of two laminations and less than three. The brushes 51a and 51b bridge across an insulating member to connect two winding laminations and short a turn of the winding. The current circulating through the brushes is limited to the potential of a single winding which increases the heat dissipation of the brush. This increases the capacity to dissipate heat from other sources.
The separation of the laminations by the insulating members forms spaces between the laminations which are filled with an insulating plastic material such as an epoxy resin. The plastic is added after the winding is assembled and in compressed condition. The plastic assists in conducting the heat generated inside the wind- The fiat laminations have a high heat dissipation capacity and a high current capacity. The legs or leg portions have a substantially greater length than thickness and a high width to thickness ratio to provide a heat path for carrying heat developed at the brush contacting point on the edge of the leg inwardly and laterally through the leg and the adjacent members to rapidly remove the heat thereby preventing overheating at the point of contact. This permits a high wattage of current to be withdrawn from a single winding. A plurality of independently operated brushes may be mounted to engage the surface A. These brushes may be set in any desired position and draw different values of current. The opposite surface B may be similarly polished and have several sets of brushes independently engaging the surface. For example, with a lamination comprising #20 sheet copper and the legs of the lamination having a width of of an inch and a length of 5 inches, the transformer has a wattage rating of 40 nilowatts. Various combinations of contacts may be provided depending on the li hting requirements. Thus the winding has a great deal of versatility and adaptability. The brushes may be small and low in capacity and thereby provide a large number of variable voltages.
The heat developed by hot spots is rapidly conducted away by the high heat gradient provided by the connecting legs and the large surface and provided by the laminations. Thus, if a hot spot occurs in the winding at the brush, the heat is carried laterally by the legs a to the connecting legs which carry the heat to legs b. Also the thin insulating members do not form a substantial heat block and heat will flow through adjacent insulating members into adjacent legs a. This provides a large radiation area to dissipate the heat and maintain any local hot spots at a permissible temperature. This high heat dissipation provides the autotransformer with a high capacity for its size. This also permits the brushes to be close together, increasing the variable voltages that may be tapped from the winding. The laminations and insulating members, instead of being of the same thickness, may be varied to provide a nonlinear variation in voltage.
A plurality of contact assemblies Sii with brushes 51a, 51!) are slideably mounted on rails 52 supported at the ends of the autotransformer by insulating supports 53, 54. The rails 52 snugly fit in bottom recesses in the support 54 and in slots in the support 53. The rail has a step engaging the side of the support to secure the rail against longitudinal movement as the contacts are slid along the rails. The supports are secured to the blocks 25, 26 by bolts (not shown) passing through the supports 53, 54 and threaded in the blocks 25, 26.
The assembly 50 is sectionally illustrated in FIGS. 7 and 8 and has a U-shaped casing 56 with guides 57 at each end to form slots 58. The rail passes through the slots 58 and engages the current carrying members 59 which have long fiat contact surfaces 6% of approximately the same width as the rail. Leaf spring means 61 are positioned between the contact members and the casing to press the contact members against the rail. On the 4. bottom of the contact members are brushes 51a, 51b passing through holes in the bottom of the casing. Springs 62 are provided on the top surface of the contact member to en a e an insulatin iece 63 to ress the brushes U a b against the surface A of the winding.
An index plate as is mounted on top of the supports 53, 54 and has longitudinally extending slots above the rails 52. Grips 65 are fastened to the contact assemblies by means of the strips 6% and yokes 67 secured to the assemblies. Thus the contact assemblies may be moved smoothly across the laminated windings of the transformer.
Referring to FIG. 9 an embodiment of the invention is illustrated in which two windings are provided. The windings are formed in the same direction to carry parallel currents and produce the same incremental voltage across each turn. The windings are formed by U-shaped laminations identical to the U-shaped laminations of the single winding embodiment. in the drawing the epoxy resin filler has been omitted in order to better illustrate the relation of the laminations. The laminations with the reference numeral "/tl form one turn, and the laminations with the reference numeral 71 form the second turn. Each turn has two conductive strips for transferring current from one lamination to another so that between the insulating pieces four strips are provided, as illustrated.
The lamination file: is in electrical contact with lamination Fill; and lamination 7% in electrical contact with lamination itlc and lamination 70c is in electrical contact with lamination 79d, to form one winding. The lamination 71a is in electrical contact with lamination 71b and lamination 71b is in electrical contact with lamination 71c and lamination 71c is in electrical contact with lamination 71a. to form the other winding. The mica insulating strips 72, 73 are positioned between upper strip portions of the laminations and insulating strips 74-, 75, 76 are positioned between the lower strip portions of the laminations. Considering the lower strip portions, the strip portion Tile-ll contacts 'l'flb-ll to form one contacting pair and strip portion '7la-ll contacts 71b-1 to form the other pair. Strip portions 7012-1 and 7111-1 are in contact to electrically connect the strip portions. Similarly on the other side the strip portions 7011-2 electrically engage 700-2 and strip portions 71b-2 electrically engage 710-2. The strip portions 700-2 and 7lb-2 are in electrical contact. Thus two parallel paths are provided for the current.
The insulating members separate the two pairs of strip portions from the adjacent pairs of strip portions to produce the voltage between the turns. The voltages of the contacting strip portions are the same.
The long edge surfaces of the laminations may be polished for engagement by brushes, as illustrated in FIGS. 1 and 2. The double winding permits a higher current transfer through the winding and through the brushes.
Various types of cores may be utilized with the laminated winding and various types of clamping means may be utilized to press the laminations of the windings.
In addition to compactness and high wattage capacity for size, the winding is easily and accurately assembled and also the transformer is rugged and can withstand shock in transit.
Various other modifications and changes may be made in the winding of the transformer without departing from the scope of the invention as set forth in the appended claims.
1. A transformer for providing high currents over a range of voltages to a plurality of separate current loads comprising:
a continuous laminated ferromagnetic core for carrying an alternating magnetic flux and having a straight portion with opposite sides for supporting a current carrying winding,
insulating means around said straight portion,
an inductive winding mounted on said straight portion with said insulating means therebetween electrically isolating said winding from said straight portion,
a plurality of current tapping means engaging said winding in current transfer relationship,
a plurality of thin planar U-shaped single piece members having two parallel legs on opposite sides of said straight portion and a connecting portion therebetween,
insulating pieces for spacing legs of said U-shaped members,
said winding formed by said U-shaped members being arranged in stacked array with the legs on a respective side of said straight portion being in side by side relation and being connected in series to successively pass current therethrough by having legs of successive members electrically connected on one side of said straight portion and electrically isolated on the other side of said straight portion by said insulating pieces positioned therebetween and with said connecting portion of successive U-shaped members being on opposite sides of said straight portion to form inductive turns,
said legs and insulating pieces having exterior edge surfaces with the edge surfaces on at least one side of said straight portion being polished to form a commutatorlike surface engaged by said current tap ping means,
each of said legs and insulating pieces having a substantially greater length than width and a high width to thickness ratio to provide said leg edge surfaces with a long length for engagement by a plurality of current tapping means and with a large unobstructed heat path extending inwardly and lengthwise of said leg in relation to the thickness of the current transferring edge surface of said leg for the rapid transference of heat from the point of contact of a current tapping means on transference of high currents therewith.
2. A transformer as set forth in claim 1 wherein said U-shaped members have two immediately adjacent legs in electrical contact and the legs on the other side spaced by an insulating piece in engagement therewith to form a single winding.
3. A transformer as set forth in claim 1 wherein said U-shaped members form two electrically parallel windings comprising a first set of immediately adjacent legs in contact and a second set of immediately adjacent legs in contact, said sets being in electrical contact on one side of the core and on the other side of the core the legs of the U-shaped members of the first and second sets being on opposite sides of an insulating piece to form two parallel inductive turns of a respective parallel windmg.
References Cited in the file of this patent UNITED STATES PATENTS 540,323 Loomis et al June 4, 1895 2,361,384 Davis Oct. 31, 1944 2,756,358 Johnson July 24, 1956 2,907,968 Thurk Oct. 6, 1959 FOREIGN PATENTS 535,978 Germany Oct. 19, 1931