US1928343A - Variable voltage transformer - Google Patents

Description

Sept. 26, 1933. w s WERNER 1,928,343

VARIABLE VOLTAGE TRANSFORMER Filed Jan. 19, 1933 INVENTOR. M45111? 5. Wm vs/e ziozzf ATTORNEY.

Patented Sept. 26, 1933 VARIABLE VOLTAGE TRANSFORMER Wilbur S. Werner, South Fort Mitchell, (lovington, Ky., assignor to Kelley-Koett Mfg. C0,, Inc., Covington, Ky., a corporation 01' Ohio Application January 19, 1933. Serial No. 652,525

7 Claims. (Cl. 171-119) This invention relates to a variable voltage transformer.

Among the objects of the invention are to produce an apparatus of this kind, the voltage of the output of which may be changed by extremely small degrees and with no abruptness at any stage. It is aimed to produce a transformer voltage regulator the output, voltage of which may be varied under load without the breaking of the circuit at any time. A third object is to produce an apparatus of high power factor, and such a construction has been achieved;

Referring to the accompanying drawing, Fig. 1 is a front elevation of my transformer. 5- Fig. 2 is a side elevation in section, this being taken on line 2-2 of Fig l. Fig. 3 is a sectional plan view, the section being U taken on line 3-3 of Fig. 1.

' Fig. 4 is a schematic wiring diagram illustratmg the principle involved. A

In the. drawing, 10 is a bundle of iron core lamlnations of the shell type. The middle leg, which is built up to circular section is indicated by 11. Holding the laminations together in all of the legs are two pairs of angle irons, the upper set of which are marked 12 while 13 indicates the lower set. These angled beams, of which there is a front member and a rear member in each set, are distinguished in Figs. 2 and 3 as 13a and 131), the latter being the rear member. 12a and 121) are also so differentiated on Fig. 2. Bolts 29 hold the angle iron pairs together.

Encircling the middle leg 11 there is a bakelite or fiber drum 14 which bears the secondary winding 16 which is made of flat bare wire and which may be wound to form a helix in a spiral groove previously cut in the drum. The leads of the primary winding are shown at 17 on Fig. 1 while the primary winding itself appears as 18 on Figs. 2 and 3, wound closely about the middle leg 11, yet separated by only a short distance from the secondary. .The edge of the drum 14 rests upon a plurality of lower rollers 19, the holders of which may be attached to the angle irons 13a and 13b. An upper set of rollers 20 also shown in Figs. 1 and 2, are carried on the upper angle irons 12 and guide the upper edge of the drum 14. Actually these rollers 20 rest upon the side oi. a spur ring gear 21 which encircles the drum 14 near the top thereof and is the means for transmitting power for the rotation of the drum when a change in voltage is to be made. This spur ring gear consists of a plurality of insulated segments so that it does not form a short circuited turn on the transformer.

on its contacting surface to accommodate the flat wire of the winding 16 which projects from the drum for a distance which is at least half of the wire thickness. The arm 26 is slidably carried by two upright bars which have smooth surfaces.

The uprights are in turn, carried between angle irons 12a and 13a. The brushes 15 are insulated from the cross arm 26, and carry a loose lead 27 which may be attached to the utilizing circuit.

Attached to the lower end of the drum 14 at the end of the secondary winding is a brush holder and pair of brushes, the assembly being in general designated by 28; Each brush in this assembly in electrical communication with the other.

Below the secondary, and arranged radially about the path of the drum are a plurality of conducting segments 30. The rollers 19 do not make contact'with these, but the brushes 28 do. Each segment is connected by means of an individual wire 31, to one lead 32 of the secondary output. This lead being of opposite polarity from lead 27. Each wire 31 is led out of the transformer through one of the outer legs of the core. Each wire 31 makes its exit from the core between the laminations thereof but at a different point,.that is, between diilerent laminations than its neighbors. Thesepoints are not selected at random, but are carefully chosen so that the series of points shall give definite and uniform differences in the amount of core and consequently 01' magnetic flux between them. In this way, means are provided for varying the indicated voltage by the insertion or elimination of flux interlinkage of the secondary circuit by uniform gradations. The wires 31 are connected to the segments so that the latter are at a uniform graduated series of potentials. I

Since there is, in operation, a difference of potential between the neighboring segments, and under some conditions of use these differences may be suiiicient to cause damage if brush 23 shoufld make contact with more than one segment, I have provided a means for making such short circuiting harmiees. The means adopted is choke coil 33, which is adapted to act to limit the current flow. In the choke 34, is a laminated or solid iron core which is preferably of toroidal shape. Wires 31 are wound a few timessay one or two, about one leg of this core before being attached to the output lead. In order to reduce the inductance of this coil as a whole, the individual coils are wound opposed. This is done by winding every other coil in the same direction. The choke coil may be replaced by resistances.

Referring to Fig. 4, this diagram is numbered as to its symbols to correspond with the numbering of the actual parts in the previous figures. From this diagram the principles involved will be at once clear to those skilled in the art.

The mechanical operation of my variable voltage transformer and the electrical effects thereof, are as follows: Current is supplied to leads 17. Primary winding '18 is energized directly and secondary winding 16 inductively. To vary the voltage taken from the secondary, electric motor 22 is energized, thus rotating drum 14. In the figures shown, rotating the drum clockwise results in a decrease in potential of the secondary winding and vice-versa. This is brought about by two actions, namely, the vertical movement of brushes 15 which follow the wire on the secondary by reason of the screw effect thereof; and the rotary movement of brush 28 over segments 30. The first of these acts to alter the number of turns of the secondary, while the second'results in a change of the flux interlinkages of the secondary in steps of less than a full turn. By reducing the size of segments 30 and by increasing their number, the size of the voltage steps obtainable can be made exceedingly small.

If the moving brush 28 stops so that it rests on two contacts, the resulting short circuit current is held to a small value by reason of the presence in the circuit of the choke coil 33; the opposing windings of this coil act so that supposing that v the value of the inductance, when brush rests on a single segment 30, is L, the value when it-rests upon two contacts, bringing about a short circuit, is 4 L, so the current is limited. If resistances are used, supposing the resistance of the circuit when brush 31 is contacting only one segment to be R, the resistance when shorting segments would be A R, but the resistance against a short circuit current would be 2 R.

By proper design of the inductance core so that the main load current saturates it, but the short circuit current does not, the pulsation of series reactance may be further reduced.

The choke coil or corresponding resistance may be omitted from the transformer if low voltages are handled.

It will be noted that both the brushes 15 and 28 move simultaneously. By such simultaneous movement twoelectrical adjustments are made at once, or more strictly speaking, one electrical and one magnetic adjustment. By reason of this simultaneous movement it is possible to extend greatly the range of duty of the regulating means altho not interfering greatly with its delicacy. In order to arrive at any selected voltage, the drum 14 is revolved while the operator watches the voltmeter. Rotation is stopped when the desired value is reached.

I claim:

1. In a transformer having a laminated core, means for smoothly varying the number of secondary turns in the circuit, means for varying the amount of flux interlinked with the secondary circuit, said latter means being operable simul-.

taneously with the first named means and including a plurality of secondary leads making exit from the transformer between the core laminations thereof at fixed points constituting a graduated series of fiux interlinkage steps.

2. In a transformer, a laminated core, a primary, a secondary, means for varying the number of turns in the latter circuit while permitting current to pass continuously thru said means and means coacting therewith for varying the number of laminations of the core magnetically linked with the secondary circuit while permitting current to pass continuously thru said means and said secondary circuit said means including a plurality of secondary leads making exit from the transformer between the core laminations thereof at fixed points constituting a graduated series of flux interlinkage steps.

3. In a transformer, a shell type core, a primary winding on the middle leg thereof, an insulating drum encircling said leg, a primary winding about the middle leg and a secondary about the said leg and said drum, means for rotating said drum, means actuated by said rotation for varying the number of secondary turns in the circuit and means also actuated by the rotation of the drum for varying the amount of flux interlinkage in the transformer circuits said means including a plu- .rality of secondary leads making exit from the transformer between the core laminations thereof at fixed points constituting a. graduated series flux interlinkage steps.

4. In a transformer, a shell type core, a primary winding on the middle leg of said core, an insulating drum encircling the middle leg and primary winding thereon, a secondary wound upon the said drum, a brush in moving contact with a point on the secondary, a brush at the lower end of the secondary, means for revolving the drum together with said latter brush and a series of contacts along the path of said latter brush, a conductor joining each contact with one arm of the secondary output circuit, each one of said conductors being joinedthereto thru a part of the core giving a different flux interlinkage to the current when it flows thru said conductor.

5. .A transformer according to claim 4 having,

the conductors which give the variable flux interlinkage, wound into a choke coil before joining an arm of the secondary output circuit.

6. In a transformer, a shell type laminated core, a primary wound about the middle leg of the core, a non-conducting drum encircling said leg and said primary, a secondary of rectangular section bare wire wound on said drum to form a helix, a brush in continuous contact therewith and vertically movable by the rotation of said drum, one lead of the output circuit attached to said brush, means for rotatably supporting the drum and for rotating the drum, a brush attached to the end of the secondary helix at the lower end of the drum, segmental contacts below said drum, said lower brush making contact therewith, a conductor attached to each segmental contact and being led out of the transformer thru a different portion of the laminations of the core to produce a series of graduated steps of varying flux interlinkage of the core with the secondary and each such conductor being finally joined to. the other lead of the output circuit.

'7. A transformer according to claim 6 in which the last mentioned flux interlinkage varying leads are wound into a choke coil before being joined to a lead of the output circuit.

WILBUR S. WERNER.

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