US3215963A

US3215963A - Adjustable voltage autotransformer

Info

Publication number: US3215963A
Application number: US227277A
Authority: US
Inventors: Gustav O Fredrickson
Original assignee: Superior Electric Co
Current assignee: Superior Electric Co
Priority date: 1962-10-01
Filing date: 1962-10-01
Publication date: 1965-11-02
Anticipated expiration: 1982-11-02

Description

Nov. 2, 1965 G. o. FREDRICKSQN ADJUSTABLE VOLTAGE AUTOTRANSFORMER 2 sheets-sheet 1 INVENTOR.

Filed 00L 1, 1962 United States Patent O 3,215,963 ADJUSTABLE VQLTAGE AUTOTRANSFORMER Gustav O. Fredricksou, Southington, Coun., assignor to The Superior Electric Company, Bristol, Conn., a corporation of Connecticut Filed Oct. 1, 1962, Ser. No. 227,277 6 Claims. (Cl. 336-148) The present invention relates to an adjustable voltage autotransformer of the type having an exterior winding formed to provide a commutating surface on which a brush is slidably movable in electrical engagement therewith to provide for adjusting the output voltage by locating the brush at different positions on the commutating surface.

The heretofore known construction of an autotransformer of the above type has generally had a winding toroidally wound as a single layer about a closed iron core which may be annular. Substantially each turn of the winding has a similar portion bared and preferably flattened so that the bared portions form a fiat commutating surface on which a brush may ride to be in electrical engagement with the bared portions to thus conduct current from the winding to an output terminal connected to the brush. The two end portions of the winding are connected to a source of alternating current and an output voltage appearing between the brush and an end portion of the winding may be adjusted by moving the brush to a different location on the commutating surface. While such an autotransformer has been found satisfactory there has been a definite limitation on the maximum power handling capabilities which such an autotransformer may have and yet retain the desirable characteristics. Thus for example, it has been found if the power handling capability is increased, by increasing the size of the core and also the size and/ or number of turns on the winding, that there is a substantial variation in the voltage between each turn which normally should be susbtantially constant to maintain proper functioning of the brush under load conditions. Moreover, there is a serious increase of regulation as the output current capability increases in addition to a reduction of eiciency due to a heating of the frame and other metallic parts of the autotransformer that are located adjacent the core. Even without the increase in power handling capability, the above unwanted effects are produced if a higher frequency of alternating current is controlled by the autotransformer and hence the usage of the autotransformer is thus limited because as the frequency becomes greater the power handling capabilities of an autotransformer because of the above effects are accordingly susbtantially reduced.

Normally while variation in the turn-to-turn voltage between turns would not be a problem, it has been found that in an autotransformer of the above type it creates a serious effect on the brush by reason of the brush being designed for a constant turn-to-turn voltage throughout the commutating surface and that variations therein cause substantial heating by reason of the failure of the brush resistance to fal-l within the generally acceptable limitations defined in the Karplus et al. Patent No. 2,009,013.

It is accordingly an object of the present invention to provide an adjustable voltage autotransformer of the above type having an exterior single layer winding formed to provide a commutating surface that is in electrical engagement with a movable brush in which the above deficiencies are substantially minimized or obviated.

Another object of the present invention is to provide in such an autotransformer for the maintenance of the t'urn-to-turn voltage at a substantially constant value in the turns forming the commutating surface when under load.

A further object of the present invention is to obviate the above disadvantages enabling the construction of the fects.

3,215,963 Patented Nov. 2, 1965 above-noted type of autotransformers having larger power handling capabilities and also being able to be used with higher frequency alternating current than is heretofore satisfactorily possible.

In carrying out the present invention, a feature resides in the manner in which the load current in the winding is distributed over the core so that the effective or net ampere turns caused by load current in the winding are substantially minimized. While the brush receives load current that is the sum of the incremental load current traveling in the exterior winding from one end portion of the winding to the brush and the incremental load current travelling from the other end portion of the brush, these two incremental load currents have not been able satisfactorily to sufiiciently minimize or totally cancel each others ampere turns or flux producing ef- According to the present invention, however, this is substantially accomplished by subdividing at least one of the incremental load currents to the brush into partial load currents that travel in different parts of the core and hence spaces the ampere turns produced by one of the incremental load currents throughout a major portion, if not all of the core. By so subdividing the partial load currents, one of the parial load currents of one incremental load current may be employed to substantially minimize the eifect of the other incremental load current. Moreover, at particular positions of the brush and with both incremental load currents being subdivided into partial load currents, the effects of the load currents may be substantially completely cancelled.

In one embodiment of the present invention, another or second winding is wound on the core but is wound beneath the exterior winding on which the commutating surface is formed with the second winding being so inter-` connected with the exterior winding that it carries partial load currents and it carries them in portions of the winding that are distributed around the core so that a partial lload current in the second winding is adjacent to a partial load current in the exterior winding. But by the relative direction of winding of the exterior and second winding and the direction of travel to the brush of the partial loa-d currents, the two partial load currents are made to produce opposite or cancelling effects on each other and thus substantially minimize the net ampere turns in that portion of the core.

The problem of undesirable ampere turns caused by load currents has been known in isolation type, i.e., primary and secondary winding transformers, and results in what has at times been referred to as leakage reactance. However, in maintaining the leakage reactance with desirable limits the heretofore generally utilized solution requires the structural interleang of the primary and secondary windings. In adjustable voltage autotransformers such a solution is not possible not only in view of the fact that there is no secondary winding but also because of the requirement of having the turns of the exterior winding accessible so that they may be formed to provide the commutating surface.

Other vfeatures and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is an elevation of an adjustable voltage autotransformer in which the present invention is incorporated and with a portion thereof shown enlarged.

FIG. 2 is an electrical schematic diagram of one embodirnent of the present invention showing the parts and their interconnections and with the windings being shown as they are physically disposed.

FIG. 3 is a view similar to FIG. 2 but showing a further embodiment of the present invention.

Referring to the drawing, an adjustable voltage autotransformer is generally indicated by the reference numeral 10 and carries a brush holder 11 on which is mounted abrush 12. The brush holder 11 is mounted for rotatable movement in a manner well known in the art and thus rotational movement of the brush holder will cause the brush to traverse a substantially annular path. The particular embodiment of the adjustable voltage autotransformer in which the present invention is incorporated and herein described is annular 'and includes an annular core 13 formed from a spirally wound strip of magnetic material. Toroidally wound on the core is an exterior winding 14. The winding 14 is of a s-ingle layer as shown and each turn 15 thereof, as illustrated in the enlarged portion of FIG. 1, is formed to provide a bared portion, as indicated by the reference numeral 16. Each bared portion 16 is preferably made flat, as by grinding, with the bared port-ions 16 of each turn positioned to form an arcuate commutating surface 17 that is located in the path of movement of the brush. The brush is slidably movable in electrical engagement with the commu-tating surface 17 by engaging the bared portions of one or more turns so that at different positions thereof a different value of output voltage is provided. While the core is annular, the exterior winding encircles only about 330 thereof and stops (not shown) are provided to prevent the brush holder from being so moved as to cause the brush to become disengaged from the commutating surface.

In carrying out the present invention there is provided beneath the exterior winding 14 another or second winding 18 which in the embodiment hereinafter shown is wound in the same direction and substantially coextensive with the winding. In addition, the second winding is preferably also a single layer winding and made from the same sized wire as the another winding in order that there will be substantially the same number of turns in each, but as hereinafter will be apparent other construction of the second winding may be employed.

FIG. 2 is an electrical schematic diagram with the

windings

14 and 18 being pictorially represented as they are physically positioned yon the core relative to each other. A source of alternating current 19 is connected to one input terminal 20 and another input terminal 21 of the autotransformer. The brush, indicated by the reference numeral 12, and a load to which the autotransformer may supply an adjusted voltage, depending upon the position of the brush 12 on the winding 14, is indicated by the reference numeral 22 and is interconnected between the terminal 21 and the brush 12. One end position 14a of the exterior winding 14 is connected to the terminal 21 while the other end portion 14b is connected to the terminal 20. As the autotransformer described in this embodiment is one whose maximum adjusted output voltage is no larger than the input voltage, the terminals are connected to the ends of the winding though of course it is within the scope of the present invention to connect the

input terminals

20 and 21 to the winding 14 at other than its ends to thereby enable the output voltage to be .stepped higher than the input voltage, as is well known in the art.

The second winding 18 is wound, as heretofore mentioned, as a single layer coextensive with but beneath the exterior winding 14 and thus as shown if the winding 14 extends 330, the winding 18 also extends the same arcuate length. In this embodiment of the invention shown in FIG.Y 2, the midpoint 14a` of the winding 14 is connected by a lead 23 to the midpoint 18e of the winding 18 wh-ile one end 18a is connected to the terminal 20 and the other end 18h of this winding 18 is connected to the input terminal 21.

In the operation of the above described autotransform- `er it will be appreciated that the load current denoted by the arrow Il, to the load 22 has an incremental cornponent which ows in the portion of the winding between end 14a and the brush 12 in the direction of the arrow and which incremental load current is denoted by K2IL. In addition, flowing in the portion of the winding 14 between its midpoint 14a` and the brush 12 is another incremental component of load current K1IL and whose direction is indicated by the arrow adjacent thereto. Moreover, according to the present invention the incremental load current KlIL is subdivided into partial load currents which are caused to flow in different locations around the core. Thus there is owing in the winding 18 from the input lterminal 20 to its midpoint 18C a current denoted K5IL and having its direction indicated by the arrow adjacent thereto and also a current K4IL which flows from the input terminal 21 to its midpoint 18e. The lead 23 directs the vector sum of these currents to the midpoint 14C of the winding 14 where it joins with a current denoted K3IL indicated by the arrow adjacent thereto and which flows in the winding 14 from the end 14b to the midpoint 14e. The currents K3II, and K5IL both coming from the input terminal 20 are Iat the midpoint 14C and 18e joined vectorially with the current K4IL to become the current KlIL.

There, of Course, is flowing within the windings a magnetizing current but according to the present invention while serving to provide tiux within .the core it does not produce the above-noted objectionable effects and hence for the purposes of the present invention is not material. It is of course understood that the load current is substantially larger than the magnetizing current.

It will be appreciated that in the particular embodiment herein shown with the winding 18 being wound in the same direction as the winding 14 on the core and each having substantially the same number of turns that the value of K5IL current will be substantially equal in amperes to the value of K3IL current and thus each will produce the same number of ampere turns. Thus a substantial part of the ampere turns due to the load current are distributed substantially equally over the core instead of just in one portion thereof. Moreover, with respect to the portion of the winding 14 between the end 14a and the brush 12, it will be appreciated that the KSIL current ows oppositely to the K2IL current as does IQIL and K3IL current and thus then produce a reduction 1n the net ampere turns in the core between the coextensive portion of the windings where these currents flow because the ampere turns produced by each oppose each other and hence reduce the net ampere turns caused by the load current in said coextensive portions of the winding. It will be understood that the load current IL is the sum of the incremental KZIL and KlIII currents.

While the operation of the autotransformer has been described with the brush in just one position on the extenor winding 14, it will be appreciated that the operation is the same for the brush in any location on the wlnding between the end portion 14a and the midpoint 14e. For the brush located on the other portion of the wlncling 14 between the end portion 14b and the midpoint 14e, the operation will be identical only the incremental load current from the end 14a to the brush will be subdivided to have a portion of it flow through the part of the winding 18h to 18e1 while the incremental load current from the end 14b flows to the brush and is subdivided to have a portion flow in the part 18a to 18C of the winding 18.

While the above structure has been found to reduce the above-noted deficiencies, it has been found that a more equal distribution of the ampere turns caused by the load current may be made by the embodiment of the invention shown in FIG. 3. Here a more equal distribution with greater minimizing of the deficiencies is achieved and also there is an increase in the power handling capability in the adjustable voltage autotransformer. In this embodiment rather than have both the exterior winding and the underlying winding divided into just two portions, this embodiment of the invention divides the windings into six portions and in addition has, as heretofore mentioned, a step-up portion so that the output voltage of the transformer may be adjusted to a value higher than the input Voltage. It will of course be appreciated that according to the present invention division of the six is merely arbitrary and any number may be selected up to and including a division equal to the number of turns in the exterior winding if so desired depending upon the power handling requirements, frequency of the alternating current source and the criticalness of maintaining a constant turn-to-turn voltage. f

In the embodiment of the invention shown in FIG. 3 the commutating or exterior winding is indicated by the reference numeral 30 and has one end 30a connected to an input terminal 31. There are provided taps 301), 30C, 30d, 30e, 30]c and 30g with the tap 30g being connected to another input terminal 32 and an end 30h. Similarly a secondary winding 33 is wound coextensive with the winding 30 on the core but beneath it has an end 33a connected to the input terminal 31 and taps formed therein indicated by

reference characters

33b, 33C, 33d, 33e, 33f and 33g, the latter being connected to the other input terminal 32, and an end 33h. Preferably the taps on each winding subdivide the windings between their connections to the input terminals into portions having an equal number of turns. Thus, for example, if the windings 30 and33 both have 192 turns between the

ends

30a and 33a and the taps 30g and 33g respectively then the taps are spaced to include 32 turns. The overvoltage portion between each winding between the tap 30g and 33g and the

end

30h and 33h may also have this number of turns if so desired but need not necessarily.

With the above structure it will be appreciated that the same result as achieved with the embodiment of the invention in FIG. 2 is attained but there is a more even distribution of the ampere turns due to the load current about the winding. With a brush 34 located in the position shown in FIG. 3 between the

taps

30e and 30f, there are incremental load currents flowing thereto as indicated by the arrows reference characters KlIL and K2IL and the direction of the current is shown by the arrows adjacent their respective reference characters. Moreover the incremental load current KlIL is the sum of the partial load current K3IL flowing in the winding 30 from the tap 30g to the tap 30]c and the partial load current K5IL owing between the taps 33g and 33]c which through the connection to the tap 30jc effects the combination of these two currents to the incremental load current KlIL. The other increment of load current K2IL is also subdivided into a partial load current K4IL fiowing in the winding 30 from the end 30a to the tap 30e and a partial load current KGIL which flows to the tap 30e from the tap 33e and is derived from the end 33a. It will be appreciated that KSIL substantially equals Klll and K4IL substantially equals KGIL and in addition KIIL-i-KZIL equals IL in View of both

windings

30 and 33 in this embodiment having the same number of turns and being interconnected inthe manner shown.

For other positions of the brush, the incremental load currents will also be subdivided to the taps of the exterior winding nearest the brush. Whenever there is a partial load current flowing in a part of the second winding 33 of one incremental load current, it ows in a direction that produces load current ampere turns that are opposite and cancel the partial load current -fiowing in the exterior winding of the other incremental load current. The parts of the two windings in which the opposing currents flow are moreover at least adjacently disposed to each other on the core while, in fact, generally the part of the exterior winding is specifically overlying the part of the second winding.

It will accordingly be appreciated that there has been disclosed an adjustable voltage autotransformer which while retaining the advantages of such an autotransformer obviates many deficiencies which have severely limited its use. Thus the present invention enables a higher frequency of alternating current to be controlled and/or have a larger power handling capability. Moreover, by the use of such a construction of an adjustable voltage autotransformer, disclosed herein, the turn-to-turn voltage is substantially made constant throughout the commutating turns of the exterior winding and better regulation and an increase in efciency are obtained.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. An adjustable voltage autotransformer comprising a closed magnetizable core, an exterior winding wound on said core to have turns encircle the core and a pair of end portions, said exterior winding being a single layer winding and having a commutating surface formed on the turns, a brush mounted for movement on said commutating surface to be in electrical engagement therewith, a pair of input terminals connected to the end portions of the exterior winding, a pair of output terminals with one being electrically connected to the brush and the other to an end portion of the winding, a second winding wound on said core, and means interconnecting the second winding to the exterior Winding and the input terminals for subdividing an incremental load current that fiows to the brush from one input terminal into a partial load current which flows through one part of the second winding and another partial load current which flows through one part of the exterior Winding at substantially all positions of the brush, said part of the second winding being connected in parallel with said one part of the exterior winding.

2. The invention as defined in claim 1 in which the one part of the second winding and the part of the exterior winding are normally located on different places of the core.

3. The invention as defined in claim 1 in which the one part of the second winding and the one part of the rgerior winding are wound on the core in a direction with respect to the direction of current flow therein which causes the partial load current flowing in the one part of the second Winding to flow in a direction which produces load current ampere turn fiux that is the same direction as the load current ampere turn flux produced by the partial load current flowing in the one part of the first winding.

4.. The invention as defined in claim 1 in which another incremental load current flows to the brush from the other input terminal through another part of the exterior winding, and wherein the one part of the second winding and the another part of the exterior winding are adjacently disposed on the core and wound in a direction with respect to the current flowing therein that causes the partial load current flowing in the one part of the second winding to produce ampere turns which are opposite to the incremental load current flowing in the another part of the exterior winding.

5. The invention as defined in claim 1 in which the interconnecting means includes at least one tap on the exterior winding subdividing the exterior winding into the one and another part with each having substantially the same number of turns, a tap on the Isecond winding subdividing the winding into the one and another part with each having substantially the same number of turns and the interconnecting means includes a connection between the two taps.

6. The invention as defined in claim 1 in which the interconnecting means includes the exterior winding having a plurality of taps subdividing the exterior winding into a plurality of parts including the one part with each part having substantially the same number of turns, the

7 8 second winding having a plurality of taps subdividing the References Cited by the Examiner second Winding into a plurality of parts including the one UNITED STATES PATENTS part with each part having substantially the same num- 3 O87 132 4/63 Snowdon et al 336 148 ber of turns, there being the same number of taps on each winding and the interconnecting means further includes a 5 FOREIGN PATENTS plurality of connections with each connection being only 857,141 12/60 Great Brltam.

from a tap of the exterior Winding to atap of the second LARAMIE E. ASKIN, Primary Examiner.

winding. JOHN F. BURNS, Examiner.

Claims

1. AN ADJUSTABLE VOLTAGE AUTOTRANSFORMER COMPRISING A CLOSED MAGNETIZABLE CORE, AN EXTERIOR WINDING WOUND ON SAID CORE TO HAVE TURNS ENCIRCLE THE CORE AND A PAIR OF END PORTIONS, SAID EXTERIOR WINDING BEING A SINGLE LAYER WINDING AND HAVING A COMMUNATING SURFACE FORMED ON THE TURNS, A BRUSH MOUNTED FOR MOVEMENT ON SAID COMMUTATING SURFACE TO BE IN ELECTRICAL ENGAGEMENT THEREWITH, A PAIR OF INPUT TERMINALS CONNECTED TO THE END PORTIONS OF THE EXTERIOR WINDING, A PAIR OF OUTPUT TERMINALS WITH ONE BEING ELECTRICALLY CONNECTED TO THE BRUSH AND THE OTHER TO AN END PORTION OF THE WINDING, A SECOND WINDING WOUND ON SAID CORE, AND MEANS INTERCONNECTING THE SECOND WINDING TO THE EXTERIOR WINDING AND THE INPUT TERMINALS FOR SUBDIVIDING AN INCREMENTAL LOAD CURRENT THAT FLOWS TO THE BRUSH FROM ONE INPUT TERMINAL INTO A PARTIAL LOAD CURRENT WHICH FLOWS THROUGH ONE PART OF THE SECOND WINDING AND ANOTHER PARTIAL LOAD CURRENT WHICH FLOWS THROUGH ONE PART OF THE ECTERIOR WINDING AT SUBSTANTAILLY ALL POSITIONS OF THE BRUSH, SAID PART OF THE SECOND WINDING BEING CONNECTED IN PARALLEL WITH SAID ONE PART OF THE EXTERIOR WINDING.