US3335379A - Adjustable voltage transformer - Google Patents

Description

Aug. 8, 1967 c. G. HOWARD 3,335,379

ADJUSTABLE VOLTAGE TRANSFORMER Filed July 20, 1965 United States Patent 3,335,379 ADJUSTABLE VOLTAGE TRANSFORMER Carl G. Howard, 261 Lakeside Place, Highland Park, Ill. 60035 Filed July 20, 1965, Ser. No. 473,376 1 Claim. (Cl. 336-100) This invention relates -to the art of railway lighting, particularly at crossings, and more speciiically to an improved transformer for such lighting.

Railway signal lights operate at relatively low voltages, generally in the order of ten to iifteen volts. Where practical, power is supplied by step-down transformers from power lines, generally with stand-by batteries to insure proper operation should the power line supply fail. The requiremen-ts for power in any given installation can vary quite substantially. For example, some intersections or crossings may have as little as one or two lights, while others :may have as many as sixteen lights. Most transformers have a certain amount of regulation variance, whereby the voltage output changes to a greater or lesser degree with load. T-he best prior art transformers for this purpose have utilized a iixed core and have had a plurality o-f taps on the secondary or output winding. A considerable degree of effort was necessary vin order for the installer to connect the load to the proper tap or taps to obtain the correct volt-age.

There is in existence another type of transformer having a core which is in part movable. This allows ready setting of the output voltage to quite a precise level. Unfortunately, prior art transformers of this type have had very poor output voltage regulation. For example, with an eight lamp circuit with the transformer set at ten volts, if one lamp were to burn out, the voltage might easily go up to :as much as fteen volts, thus greatly overvoltlaging and quickly burning out the remaining lamps.

In my copending prior U.S. patent -applic-ation Ser. No. 358,350, now Patent No. 3,260,975, I? have disclosed an improved railway signal lighting transformer which is =less expensive than prior art transformers for this purpose, which 'gives satisfactory regulation and has a simplified micrometer yadjustment and which specifically has a movable core portion and having a dual output winding providing micrometer adjustment and satisfactory regulation.

My aforesaid transformer works quite satisfactorily from an electrical standpoint, but in higher size ranges produces too much noise under heavy load. The core in said transformer is an E and I laminated core with the primary winding on the center leg of the E, and with the secondary winding split on the center leg and the two end legs. In large size transformers and under heavy load the I piece, lying across the ends of the legs, tends to vibrate up and down and also Ito rotate about an axis longitudinal of the center leg.

It is an object of the present invention to provide a transformer similar to my aforesaid transformer, but quite satisfactorily quiet in operation. 'p

It is another object of the present invention to provide such a transformer in which vibrational and rotational tendencies of the I piece are substantially eliminated.

More specifically, it is an object of the present invention to provide an E and I transformer of the type under consideration in which stray liux is substantially eliminated from the vicinity of the I piece.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying iigures wherein:

lFIG. 1 is a front view of -a transformer constructed in accordance with my present invention;

FIG. 2 is a side view thereof;

3,335,379 Patented Aug. 8, 1967 ICC FIG. 3 is a horizontal View partly in section taken substantially along the line 3-3 in FIG. l;

FIG. 4 is a fragmentary vertical sectional view taken substantially along the line 4-4 in FIG. 3; and

FIG. 5 is .an electrical wiring diagram of the transformer.

Referring now in greater particularity to the drawings, and first to FIGS. 1-3, there will be seen a transformer 10 constructed in accordance with the principles of the present invention. The transformer includes a core 12 of the usual E and I lamination type. The core comprises first and second uprightlegs 14 and 16 on which the secondary 18 and primary 20 windings .are mounted. A third -upright leg 22 is spaced to the right of the secondary coil or winding and all three legs upstand from and are integral with la base 24. A movable laminated I piece,

magnetic shunt, bar or slug 26 is mounted across-the upper ends of the upstanding legs 14, 16 and 22, and the mounting structure therefor will be set forth shortly hereinafter.

The core laminations are held together at the bottom by bolts 28 extending through apertures in the laminations, -and also through the upstanding flange 30' of a bracket 32. The bracket -has a horizontal web 34, and a rear upstanding flange 36. yBoth the rear ange 36 and the web 34 are provided with apertures for receipt of screws or bolts for mounting the transformer. End portions of the bracket web 34 and iiange 36 extend past the ends of the core 12 to provide .access for a screwdriver or the like for .securing the bracket 32 in place. As will be apparent, nuts 40 are threaded on the rear ends of the bolts 28.

A clamping plate 42 is provided at the top of the core and has a name plate 44 directly in front thereof. Bolts 46, preferably having washers under the heads thereof, as also is preferably the case with the bolts 28, extend through the plates 44 and 42, and also through apertures in the tops of the vertical legs 14, 16 and 22 of the transformer core. At the rear end, these bolts also pass through apertures in an angle bracket 48, and have nuts threaded on the ends thereof, preferably with washers therebeneath.

The angle bracket 48 includes vertical flange 52 through which the bolts 46 pass, and also a horizontal ange 54. Bolts 55 pass through apertures in the horizontal flange 54 and also through a horizontal ange 56 of a right angle bracket 58 which also has an upstanding vertical wall 60. Nuts 62 are threaded on the bolts 55 beneath the ange 56. As may be seen in FIG. 3 the ange 56 is in the form of a pair of ears with a central discontinuity therebetween, except for a rather narrow connecting shelf 64. Similarly, the horizontal flange 54 of the bracket 48 is provided with a central cut out 66. The cut out and the discontinuity provide clearance for wires, as will be apparent shortly hereinafter.

As readily may be seen in FIGS. l and 3, the bracket S8 extends in each direction beyond the core 12. The limit at one side is approximately coterminous with that of the secondary coil, as is the corresponding portion of the bracket 32. Key hole shaped slots 68 are provided in the vertical ange 60 for mounting the transformer against a vertical wall.

An insulating terminal block 70 is mounted at the upper end of the vertical flange 60 and carries a plurality of binding posts of the screw and nut type at 72 in horizontal alignment and extending from the front thereof, conveniently with a label plate 74 for indicating the connections. The insulating block and binding posts are standard, and hence tive binding posts are shown. The left and center binding posts are connected to the primary winding 20, while the two right-most binding posts are connected to the secondary winding 18.

As will be seen particularly in FIGS. 2 and 3 (and schematically in FIG. 5), the magnetic shunt or core 26 rests on top of two or three of the legs 14, 16 and 22 and ts closely between the plates 42 and 52. A bolt 76 extends through these plates and has a nut 7.8 on the front thereof for drawing the plates toward one another to clamp the shunt 26 in adjusted position. A leaf spring member 80 is held down by the bolt 76 against the magnetic shunt 26 whereby to hold it down against the tops of the upright legs, and also to provide a frictional resistance to movement.

The front wall 42 and name plate 44 are provided with a horizontally elongated slot 82. An L-shaped stud 84 extends from the magnetic shunt 26 through this slot and is provided with a threaded shank portion 86. This threaded shank portion is received in the nut member 88 having a knurled thumb wheel 90 and an axially extending internally threaded sleeve 92. The sleeve or cylinder 92 is provided with a reduced neck portion 94. The reduced neck is received in a slot or recess 96 in an ear or lug 98 formed on the edge of the wall 42 and extending at right angles therefrom. Thus, with the nut 78 loosened, turning of the thumb wheel 90 will shift the shunt to the left or to the right, according to the direction of rotation of the thumb wheel. When the proper output voltage has been obtained, then the nut 78 is tightened to clamp the plates 42 and 52 against the magnetic shunt, and thereby to hold it firmly in place.

Reference now should be had to the magnetic and electric circuit of FIG. 5. The primary coil previously indicated generally by the numeral 20 is provided with the leads 100, which go to the left and to the center binding posts, as previously indicated. This primary coil is wound on only the top half of the center upstanding leg 16. The secondary coil heretofore indicated by the number 18 is actually a split coil. Somewhat over half of the secondary coil is wound at 102 on the bottom half of the leg 16, and the remainder of the secondary coil is wound at 104 on the leg 14, that leads to the primary coil being identified at 106, and leading to the two right binding posts, as heretofore noted. The two portions of the secondary are connected in series additive relationship.

The portion of the secondary winding on the bottom half of the leg 16 is suicient to give the minimum desired output voltage. With the magnetic shunt or slug 26 all of the way to the right, it will overlie the legs 20- and 22, but will be spacedl slightly to the right of the top of the leg 14. In one actual specimen rated at eight amperes, 13.5 volts, the aforesaid spacing is about one-eighth of an inch, wtih the total distance across the core amounting to approximately four and three-eights inches.

As the magnetic shunt is advanced to the left, more voltage is obtained from the windingy 104 of the secondary, and this adds to the voltage obtained from the winding 102. Approximately an additional four volts (could be wound for any voltage) can be obtained by shifting the magnetic shunt all of the way to the left, thus placing substantially all of the magnetic flux through the legs 14 and 16, whereas substantially all of it was through the legs 16 and 22 with the magnetic shunt all of the way to the right. Obviously, at intermediate positions part of the magnetic ux will be through the leg 14, and part through the leg 22. The portion of the output voltage obtained from the winding 102is substantially invariable regardless of load, at least within rated limits. The voltage obtained from the winding portion 104 drops somewhat with increasing load, but the portion of the output voltage obtained from this winding 104 is never more than about half of that obtained from the Winding portion 102, and hence regulation in the winding portion 104 is minimized. In actual tests it has been found that for load changes of zero to five amperes the total change in voltage, is not more than about one volt, and this is not sufficient to ca use rapid burning out of lamps.

In my prior transformer Ias disclosed in my copending application Ser. No. 358,350, therev was a tendency for the I-lamination piece to try to rotate about an axis through the center leg of the core. The I-lamination piece also tended to bounce up and down on the core legs, all of which combined -to make too much noise, particularly when the lock was loosened to allow adjustment.

I have discovered that it is the secondary winding that causes the trouble. The primary winding substantially saturates the core when the transformer is under load, and the :added flux from the secondary is too much. This results in a good deal .of stray ux. With the prior design in my aforesaid copending patent application, the stray flux acted on the I-piece and produced the untoward results noted. In the present case, wherein all of the primary winding is at the top of the center leg, and the secondary winding is all at the bottom, stray flux from the secondary winding is mostly in the back of the E-piece, and this of course is fixed relative to its adjacent parts, and cannot vibrate as did the I-piece. This change in winding location, apparently simple in retrospect, has allowed the use of the same size laminations, the same current through the coils, the same number of turns, and the same excellent voltage regulation, while avoiding the noise and vibration.

By way .of specific example, I have tested a transformer constructed in accordance with the principles of this invention and rated at twelve volts, sixteen amperes secondary output. The following table indicates the results with three different settings of the shunt or I-piece, and it will be appreciated that the output voltage is very nearly constant in each instance with a change from zero to a full load of sixteen amperes. Other transformers at different ratings or Icapacities have been tested with similar results. The results in question are as follows:

Secondary Secondary, Load, amps. volts SETTING 1 SETTING 2 SETTING 8 Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of the present invention insofar as they-fall within the spirit and scope of the appended claim.

The invention is claimed as follows:

A voltage transformer comprising: a magnetic core having three substantially parallel legs, respectively, a first leg, a second middle leg, and a third leg, said core further having a fixed magnetic interconnection integrally formed with .and connecting each of said three legs together at a first end portion of said legs, the second end portion of said legs being separate from each other, there being a first dimension spanning said first and second legs and a second dimension spanning said first and third legs; a magnetic shunt movable across said second end portion of said legs, said shunt having a length greater than said first dimension and less than said second dimension, said shunt being adjustably movable from a rst position spanning said first and second legs to a second position spanning substantially all of said second legs and part of both said first and third legs to a tlnrd position spanning said second leg and substantially all of said third leg and back through said second position to said rst position to vary the reluctance of the magnetic path between said first and second legs; a primary Winding on said second middle leg, said primary winding being disposed entirely adjacent the second end portion of said second middle leg; a irst secondary winding on said second middle leg disposed between said primary winding and said ixed magnetic interconnection and of such size as to produce substantially the minimum rated voltage for said transformer; a second secondary winding on the rst leg in series additionwith the rst secondary winding on 15 said second middle leg, the secondary winding on said first leg providing substantially one half the voltage of the secondary Winding .on the second middle leg; screw thread means for moving said magnetic shunt on the 6 second end portion of said three legs; and lock means for locking said magnetic shunt in a predetermined position relative to said three legs.

References Cited UNITED STATES PATENTS 2,080,177 5/1937 Lucas et al 336-134 XR 3,154,756 12/1964 Bojarski 336-133 FOREIGN PATENTS 762,685 1/ 1934 France. 255,688 1926 Great Britain. 634,426 3/ 1950 Great Britain.

LEWIS H. MYERS, Primary Examiner. T. J. KOZMA, Assistant Examiner.

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