US3619766A - Vernier voltage regulator - Google Patents

Abstract

A split, tapped transformer winding and a current limiting reactor are connected between the two movable fingers of a conventional tap changer. Contacts of a second tap changer are coupled to the taps of the split transformer winding and to the center tap of the equalizing reactor, and engaged by two movable fingers for providing a vernier adjustment of output voltage.

Description

United States Patent Inventor James W. Simpson Plttslleld, Mass.

June 25, 1970 Nov. 9, 1971 General Electric Company Appl. No. Filed Patented Assignee VERNIER VOLTAGE REGULATOR 7 Claims, 2 Drawing Figs.

US. Cl 323/435 R, 336/150 Int. Cl. 1-l02pl3/ll6,

m 6051 1/14 Field of Search 323/435 R,

References Cited UNITED STATES PATENTS 1,905,249 4/1933 Snyder 323/435 R 3,365,655 1/1968 Simpson et al... 323/435 R 3,423,668 1/1969 Brennan 323/435 R 3,100,865 8/1963 Nielsen 323/435 R Primary Examiner-Gerald Goldberg Attorneys-Francis X. Doyle, Vale P. Myles, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. Forman ABSTRACT: A split, tapped transformer winding and a current limiting reactor are connected between the two movable fingers of a conventional tap changer. Contacts of a second tap changer are coupled to the taps of the split transformer winding and to the center tap of the equalizing reactor, and

' engaged by two movable fingers for providing a vernier adjustment of output voltage.

1 vaanma VOLTAGE REGULATOR BACKGROUND OF THE INVENTION The present invention relates to voltage regulators, and, more particularly, to step-type regulators wherein coarse and vernier tap windings are provided.

Voltage regulators are often utilized to maintain line voltages at some predetermined level, and also to provide a source of voltage which may be purposely varied over a given range. In order to prevent gross disturbances on the line and to provide, within very close limits, a voltage which is desired, it is necessary to be able to apply the voltage in very small, regulated increments. At the same time, should the demand for voltage change radically, it is necessary to rapidly change the applied voltage in order to meet the new requirements. To ful' fill such requirements requires voltage regulators which have means to vary supply voltages over large increments, usually by means ofstep-type regulators coupled to tapped transformer windings. To provide small incremental voltage changes, such regulators often have a vernier control which provides a further series of incremental steps superimposed upon the first-mentioned coarse steps.

The combination of vernier and coarse-step-type regulators is well known in the art, one example being U.S. Pat. No. 3,365,655 Simpson et al., issued Jan. 23, 1968 and assigned to the assignee of the present invention. In such mechanisms, at first transformer is provided with a winding having a plurality of tap sections, each section being connected to one of a plurality of separate, spaced contacts disposed in a circular configuration. A pair of rotatable fingers are provided to engage a single contact, or a pair of adjacent contacts, and a current equalizing reactor connected between the fingers, When both fingers are at a common contact, each finger passes substantially the same current, and the equal currents flow through the center tap of the equalizing reactor to a load. However, when the fingers bridge a pair of contacts which are at different voltages, the reactor prevents the short circuiting of the two fingers and thus the passage of destructively high circulating current therethrough, while presenting little impedance to the passage of load current.

According to the prior art, when a vernier adjustment is required a second transfonner may be connected across the aforementioned fingers in order to provide both the reactance necessary to reduce circulating currents to an acceptable level in lieu of an equalizing reactor, and to provide a plurality of tap sections which are coupled to the contacts of a vernier tap changer. The vernier tap changer is then adjusted to select the voltage desired, within the range made available by a first coarse tap changer. To prevent destructive circulating currents in the vernier transformer winding segments, a limiting reactor is connnected between the fingers of the vernier tap changer.

Unfortunately, however, such arrangements have certain disadvantages inherent in their design. Should the vernier transformer winding be a continuous one, the impedance of such winding would rarely be matched to that of the transformer segments, as is the case of a single purpose current limiting reactor. Further, no matter to which segment the vernier tap changer is connected, some load current would be drawn through both fingers of the coarse tap changer. In such a case, it would be impossible to move either finger of the coarse tap changer from one tap segment to another without breaking a substantial portion of the load current. One way to circumvent this problem is to remove the vernier winding from the conductive path, and insert a suitable limiting reactor while the coarse tap changer is being moved. However, with this scheme the load might be temporarily removed from the line, and in any case extra switching mechanisms are required. Further, the additional steps necessitate unwanted delay. On the other hand, should the limiting reactor be placed in shunt with the vernier winding, the continuous vernier winding would pass the circulating currents which limiting reactor is interided to restrict.

To obviate these difficulties, it has been suggested that a split type vernier winding be provided. By counter winding the two halves, and bridging the split-apart ends by the fingers of the vernier tap changer, a limiting reactor will be constituted which is disposed between the fingers of the coarse tap changer. The reactor consists of the series combination of a first portion of the split vernier winding, a first vernier finger, the vernier tap changer limiting reactor, a second vernier finger, and the second portion of the split vernier winding. Such an arrangement, however, compromises the design of one or both of the vernier tap winding and the vernier limiting reactor. In addition, it necessitates the moving of the vernier contacts to a particular position before a finger of the coarse tap changer may be moved to a new contact.

A still further device, embodied in the above-mentioned Simpson et. 211., patent, provides a limiting reactor permanently placed across the two fingers of the coarse tap changer. The center tap of the reactor is coupled to one of the stationary contacts of the vernier tap changer. A transformer winding having a plurality of output taps thereon is placed in parallel with the limiting reactor and the taps are connected to the remaining stationary contacts of the vernier tap changer. The fingers of the vernier tap changer must be moved to a position wherein they are both coupled to the center tap of the aforementioned current limiting reactor before the coarse tap changer may be moved. While this arrangement has advantages not previously found in the art, it still provides an inductive winding in parallel with the current limiting reactor, and necessitates the movement of the fingers of a vernier tap changer to a single, predetermined position before a coarse tap changer may be adjusted.

SUMMARY OF THE INVENTION The present invention contemplates the provision of a cur rent limiting reactor connected between the fingers of a coarse tap changer, the contacts of which are coupled to tap sections of a transformer. A first inductive winding is provided in bucking relationship to the transformer winding engaged by the coarse tap changer, and one end of said inductive winding is connected directly to a first finger of the coarse tap changer. A second, boosting inductive winding is provided, one end of which is connected directly to the second finer of the coarse tap changer. Both the bucking and boosting windings are divided into a plurality of tap segments, each of the segments being connected to a stationary contact of a vernier tap changer. The center tap of the current limiting reactor is connected to a further stationary contact of the vernier tap changer. When the fingers of the coarse tap changer are located on a common stationary contact, the voltage obtained thereby may be provided to the vernier tap changer by means of the aforementioned center tap on the limiting reactor. Higher voltages in small increments are provided by the boosting tap winding and lower voltages by the bucking tap winding. When, however, the fingers of the coarse tap changer are positioned so as tobridge a pair of adjacent contacts, the current limiting reactor conducts the resulting circulating current, unaffected by the bucking or boosting windings. The bucking vernier winding thus provides the vernier tap selector with voltages which incrementally decrease from that of the higher voltage finger, while the boosting winding provides voltages which incrementally increase from that of the lower voltage finger. in addition, the center tap of the limiting reactor provides the vernier tap changer with a voltage which is halfway between thosevoltages encountered by the fingers of the coarse tap changer.

While it will be seen that the arrangement so far described provides a vernier regulator without the disadvantage of incor porating a limiting reactor which is mismatched to the coarse tap winding characteristics, still further advantages inhere.

While it is desirable that the contacts of the vernier voltage regulator be positioned on the contact coupled to the center tap of the current limiting reactor when both fingers of the coarse tap changer are to traverse more than one contact, it is not necessary for the vemier tap changer to be so oriented for all adjustments of the coarse tap changer fingers. It will be seen, for instance, that if the fingers of the vernier tap changer are in engagement with contacts connected to that half of the vemier winding which is coupled to a first coarse tap changer finger, the only current which then flows through the second coarse tap changer finger is the circulating current from the coarse transformer winding itself. The second coarse tap changer finger, now conducting minimal current, may then be transferred to another contact without having to break any portion of the load current. The advantages from this arrangement are twofold. Firstly, arcing from the transferred finger is practically eliminated, thus greatly increasing the life of the finger and contacts. Secondly, it will be understood that in order to provide such a condition, the fingers of the vemier tap changer need only be in contact with that half of the vernier winding which is not coupled to the advancing finger. Since the contacts connected to the winding will comprise one half of all the contacts of vemier tap changer, less that one connected to the center tap of the current limiting reactor, in many cases the vemier tap changer will already be in a suitable position when such a coarse adjustment is necessary. Further, should the vemier fingers be coupled through a vemier winding to a coarse tap changer finger which is to be transferred to a new contact, it will only be necessary to move the vemier fingers to the nearest contact which is coupled to the other vemier winding. Relocation of the vemier fingers is thus not nearly as critical as in the prior art, facilitating a much more rapid response of the coarse tap changer mechanism.

It is thus an object of the present invention to provide a vemier voltage control whereby only a current limiting reactor is in series connection between the fingers of a coarse tap changer.

it is a further object of this invention to provide a step type voltage regulator in which a vernier tap changer need not be located on a particular contact before a coarse tap changer may be moved.

It is a further object of this invention to provide, in a vernier voltage regulator, a vemier tap winding employing substantially less material than prior devices.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention will be better understood from the following description of the preferred embodiment, taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic circuit diagram of a voltage regulator having a vemier control according to one embodiment of this invention;

FIG. 2 is a schematic circuit diagram of a modified form of the voltage regulator of FIG. 1 incorporating a reversing switch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The voltage regulator of this invention will be described with particular reference to the drawing, wherein like numerals are used to indicate like parts throughout the various figures. Considering first FIG. i, there is shown a transformer T, having a tap winding indicated at 10. The winding as shown is divided into six equal tap sections which are connected to circularly arranged stationary contact members 1211-12! of a coarse tap changer 12. As will be understood by those skilled in the art, winding 10 is used to provide voltage differentials whereby large changes in voltage output may be obtained by selecting appropriate taps. Of course, it will be understood that any convenient number of tap sections can be used, six being shown for purposes of illustration. Coarse tap changer 12 further lncludes a pair of radially extending contact fingers A and B. The fingers are electrically separate, and the distance between their extremities is somewhat less than the width of stationary contacts l2a-l2f, but greater than the distance between the contacts. Fingers A and B may thus both connect to a common contact, or alternatively may connect to adjacent contacts. Connected between the fingers is a first current limiting reactor 13 having a center tap, as is well known in the art. The limiting reactor comprises the only electrical path existing between fingers A and B, and prevents excessive current from circulating between adjacent tap segments when fin gers A and B lie on different contacts, while allowing current to pass through its center tap to a load with virtually no impedance thereto.

Coupled to either end of first limiting reactor 13 are a pair of windings l4 and 15 which together comprise what will be referred to as the split vemier winding of the regulating system. Windings l4 and 15 are each divided into a like number of tap segments, each segment being coupled to a stationary contact 16a-16f of a vemier tap changer generally indicated at 16. Again, it will be understood that any convenient number of vemier taps may be provided. The remaining contact 17 of the vemier tap changer is coupled directly to the center tap of current limiting reactor 13. As in the case of the coarse tap changer, a pair of radially extending fingers C and D are provided to engage the stationary contacts. Fingers C and D are electrically connected by means of a second center taped limiting reactor indicated at 19 which prevents excessive currents from circulating through the tap sections of windings 14 and 15. Output voltage is applied to a load (not shown) connected across output temtinals 21 and 22. Control means 20 operates to rotate the tap changers l2 and 16 in a manner that will hereinafter be described.

OPERATION The operation of the embodiment shown in FIG. I will now be described. To bring the output of the voltage regulator into the general range required, fingers A and b of coarse tap changer 12 are rotated to a position where they connect with a suitable contact or contacts of coarse winding 10. Fingers C and D of vemier tap changer 16 are then rotated until they encounter that contact or contacts which provide the desired output voltage at the center tap of second current limiting reactor 19. Should fingers A and B of coarse tap changer l2 lie upon a common contact, contact 17 would provide that identical voltage to the vemier tap changer, while contacts 16a, 16b, and 16c of bucking winding 14 would provide incrementally decreasing voltages, and contacts 16d, 16c, and 16] of boosting winding 15 would provide incrementally increasing voltages. Since windings l4 and 15 are split, when fingers C and D of vemier tap changer 16 are coupled to contacts 16d, 16e, 16f substantially all load current will flow through finger B. Similarly, should fingers C or D connect to contacts 16c, 16b, or Me, load current would be drawn through finger A.

If it is now desired to rotate fingers A and B of coarse tap changer 12 from a common contact, for instance 12], to bridge a pair of consecutive contacts 12c and 12f, it is apparent that finger B must leave the common contact, traverse a gap, and connect with a new contact. Should that finger have been carrying a substantial current, when it breaks contact with contact 12f arcing will occur with detrimental effects to both the finger and the contact from which the arc is drawn. lt is thus desirable that load current be drawn from finger A while the tap selector is actuated. This condition is effected in the following manner. Assuming that fingers A and B are initially located on contactor 12f, should fingers C or D of vernier tap changer i6 connect with contactors 16d, 16, or f load current will be drawn through finger B. When it is desired to move finger B to contact 12c, fingers C and D of vemier tap changer 16 are first rotated so that they connect with segments 16a, 16b, or 16 c. Full load current is now drawn through finger A of coarse tap changer 12, the current through finger B being only that circulating current which is passed by first limiting reactor 13. Tap changer 12 may now be rotated in a counterclockwise direction so as to cause finger B to disengage contact 12f and engage contactor 12c. Should the output voltage provided at the center tap of second limiting reactor 19 now require further, finger adjustment, this can be provided by locating fingers C and D on the appropriate contacts of vernier tap changer 16.

In some cases, however, it is necessary that gross changes, herein considered to be changes of more than one coarse tap segment, are to be made. Obviously load current cannot be removed from both fingers A and B of coarse tap changer 12 without opening the circuit, or providing a separate shunt contactor. Should the fingers of vernier tap changer 16 connect to either winding 14 or 15, full load current would then be drawn through one of the fingers A or B resulting in detrimental arcing when that finger moves from one contact to the next. To balance the current drawn through fingers A and B, fingers C and D are connected to contact 17 of the vernier tap changer. Full load current is now drawn entirely from the center tap of first limiting reactor 13, and the currents flowing through fingers A and B of tap changer 12 are constrained to be equal. Fingers A and B may now be rotated to the desired contact with minimal arcing.

As will be understood by those skilled in the art, rotating mechanism 20 may advantageously include a latching device for preventing the rotation of coarse tap changer 12 when the fingers of vernier tap changer 16 are in a disadvantageous position. For instance, when it is desired to move finger B of tap changer 12 from a common contact with finger A counterclockwise to a new contact, a simple latch may be provided which prevents such counterclockwise movement until fingers C and D of vernier tap changer 16 rest upon contacts 16a, 16b, and 160. Further, a second latch would prevent gross changes, i.e., a movement greater than the distance between consecutive contacts, of fingers A and B until fingers C and D of vernier tap changer 16 rest upon contact 17. It will be obvious to those skilled in the art that an almost limitless number of simple latching mechanisms may be adapted to prevent unwanted motion of tap changer 12 until the fingers of tap changer 16 are in a desired position, and the foregoing example is only one embodiment of such a device. Alternatively, a plurality of electrical switches may be provided to prevent the energization of means driving tap changer 12 unless tap changer 16 were in a desired position.

Regardless of the embodiment utilized for rotating mechanism 20, it will be seen that the orientation of fingers C and D of vernier tap changer 16 for small movements of coarse tap changer 12 is far less critical than in the devices taught by the prior art. Fingers C and D of vernier tap changer 16 should advantageously rest upon contacts connected to the split winding which is coupled to the finger of the coarse tap changer remaining upon its contact while the other finger jumps to a new contact. In such a case it is also feasible, however, to position fingers C and D on contact 17, so as to draw equal current from fingers A and B. It will thus be seen that it is possible to have fingers C and D lying on one of more than half of the available contacts of the vernier tap changer when providing single step adjustments in coarse tap changer 12. Due to the less critical positioning of the vernier tap changer fingers, it will oftentimes not be necessary to move tap changer 16 at all before initiating movement of coarse tap changer 12. If it is necessary to relocate fingers C and D of the vernier tap changer to contacts coupled to the opposite split winding, it will be seen that an arc of 90 or less is all that need be traversed by the fingers.

A further benefit flows from the split winding configuration used with the vernier tap changer. It will be seen from the embodiment disclosed in FIG. 1 that a total of seven taps are provided by the vernier tap changer through the provision of a total of only 4 tap sections, two such tap sections on each half 14 and 15 of the split winding. It will be understood by those skilled in the art that in general (n-l tap winding sections are necessary to provide mn taps. However, in the present case,

only (It-3) sections are necessary to provide the n taps desired. In the present case, for example, to provide the seven taps desired a total of six sections of winding would be required according to the prior art, while in fact only 4 are utilized with the split winding of the instant invention; a saving of 33 percent in material.

It will be recognized that it is possible to place windings l4 and 15 on a common core with coarse winding 10. While a saving would thus result in the increased utilization of core material, the incremental voltage available from windings I4 and 15 would be limited by the volts/turn ratio of transformer T By placing windings l4 and 15 on an independent core, however, this restriction is avoided and a greater flexibility in voltage steps is provided at the cost of additional core material.

Referring now to FIG. 2, a further embodiment of the present invention is shown which provides for an even more efficient utilization of material. A single vernier tap winding 23 is provided, which may advantageously correspond in size and type to windings 14 or 15 of FIG. I. The taps of windings 23 are coupled to stationary contacts 24a-24d of vernier tap changer 24. A first end of winding 23 is connected to finger A of coarse tap changer 12 through contacts 26 of a double pole, single throw switch generally indicated at 28. In this mode, winding 23 may be considered to be in boosting relationship the tap upon which finger A rests. When switch 28 is moved to its opposite position, contacts 27 are closed, and contacts 26 are simultaneously opened. The second end of winding 23 is now connected to finger B of coarse tap changer I2, in bucking or substractive relationship thereto. Before a finger is moved so as to disengage it from the contact upon which it then rests, switch 28 is actuated to couple winding 23 to the other finger, causing the first mentioned finger to be relieved of load current.

Similarly, before gross changes whereby fingers A and B both engage and disengage contacts may be made, fingers C and D of vernier tap changer 24 must be positioned so as to rest upon contact 25 corresponding to the center tap of current equalizer 13. As in the embodiment described above, a latching mechanism may be provided within rotating mechanism 20 to allow gross changes of coarse tap changer 12 only when vernier tap changer 24 is in this position.

In addition, a similar latching arrangement may be provided whereby switch 28 is allowed to change position only when fingers C and D of vernier tap changer 24 are in communication with contact 25. In this manner, load current is never interrupted and the proper switching sequency is ensured.

As described with regard to the embodiment of FIG. I, vernier tap winding 23 may be placed on a common core with coarse tap winding 10 or alternatively, may be placed upon a separate core. In either case, only half as much winding material is required than is the case with the vernier winding of FIG. 1.

From the above, it will be clear that by means of this invention there is provided a voltage regulator having vernier voltage control in which coarse voltage changes may be made without interrupting the circuit provided thereby. Further, coarse voltage changes may be made during which load current is removed from one finger of a tap changer before causing said finger to move to a ditferent contact. In addition, a

circuit has been taught which provides a separate tap vernier winding in conjunction with a coarse tap changer, without comprising the design of the current limiting reactor connected between fingers of the coarse tap changer.

While there has been shown and described presently preferred embodiments of this invention, it will of course be understood that various changes may be made in structural details without departing from the spirit and scope of the invention, particularly as set forth in the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A voltage regulator comprising: a. first induction means having a winding divided into a plurality of tap sections;

b. first tap changer means including a first plurality of spaced contacts, each of said first spaced contacts being connected to one of said plurality of tap sections, and further including a first pair of movable fingers for engaging said contacts, said fingers being movable in unison and spaced so that at least one of said fingers will always engage at least one contact;

c. first current limiting reactor means including a winding connected between said first pair of fingers and having a tap at the center of said winding;

d. second induction means comprising two individual windings, each of said windings being divided into a plurality of tap sections, each of said windings being connected to a different one of said movable fingers of said first tap changer means;

' e. second tap changer means including a second plurality of spaced contacts, one of said second spaced contacts being connected to said tap at the center of said first current limiting reactor winding, the rest of said contacts being connnected to said plurality of tap sections of said second induction means, and further including a second pair of movable fingers for engaging said contacts, said fingers being movable in unison and spaced so that at least one of said fingers will always engage at least-one of said second spaced contacts; and

second current limiting means including a winding connected between said second fingers and having a tap at the center of said winding.

2. A voltage regulator as recited in claim 1 wherein said first and said second induction means are disposed on a common magnetic core.

3. A voltage regulator as recited in claim 1, further including means for preventing said first fingers of said first tap changer means from traversing more than one of said first spaced contacts when said second fingers of said second tap changer means are not disposed upon said one of said second spaced contacts which is connected to said tap at the center of said first current limiting reactor winding.

4. A voltage regulator as recited in claim I, further including means for preventing either of said first fingers of said first tap changer means from disengaging one of said first spaced contacts when either of said second fingers of said second tap changer means is coupled to that winding of said second induction means which is connected to the disengaging finger.

S. A voltage regulator comprising:

a. first induction means having a winding divided into a plurality of tap sections;

b. first tap changer means including a first plurality of spaced contacts, each of said first spaced contacts being connected to one of said plurality of tap sections, and further including a first pair of movable fingers for engaging said contacts, said fingers being movable in unison and spaced so that at least one of said fingers will always engage at least one contact;

c, first current limiting reactor means including a winding connected between said first pair of fingers and having a tap at the center of said winding;

. second induction means including a second winding having a first and a second end and being divided into a plurality of tap sections;

. switch means for selectively connecting said first or said second end ofsaid second winding to predetermined ones of said first pair of movable fingers of said first tap changer means;

f. second tap changer means including a second plurality of spaced contacts, one of said second spaced contacts being connected to said tap at the center of said first current limiting reactor winding, the rest of said contacts being connected to said plurality of tap sections of said second induction means, and further including a second pair of movable fingers for engaging said contacts, said fingers being movable in unison and spaced so that at least one of said fingers will always engage at least one of said second spaced contacts; and t second current limiting means including a winding connected between said second fingers and having a tap at the center of said winding.

6. A voltage regulator as recited in claim 5 wherein said first and said second induction means are disposed on a common magnetic core.

7. A voltage regulator as recited in claim 5, further including means for preventing said first fingers of said first tap changer means form traversing more than one of said first spaced contacts when said second fingers of said second tap changer means are not disposed upon said one of said second spaced contacts which is connected to said tap at the center of said first current limiting reactor winding.

a i a: k a

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 9,7 Dated November 9, 1971 Inventor( James w. Simpson It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 74 After "which" insert the Col. 2, line M "finer" should be finger Col. t, line 27 "taped" should be tapped Col. 4, line 69 "1"" should be 16f Col. 5, line 75 "mn" should be n Col. 8, line 39 "form" should be from Signed and sealed this 20th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSGHALK Attesting Officer Commissioner of Patents

Claims (7)

1. A voltage regulator comprising: a. first induction means having a winding divided into a plurality of tap sections; b. first tap changer means including a first plurality of spaced contacts, each of said first spaced contacts being connected to one of said plurality of tap sections, and further including a first pair of movable fingers for engaging said contacts, said fingers being movable in unison and spaced so that at least one of said fingers will always engage at least one contact; c. first current limiting reactor means including a winding connected between said first pair of fingers and having a tap at the center of said winding; d. second induction means comprising two individual windings, each of said windings being divided into a plurality of tap sections, each of said windings being connected to a different one of said movable fingers of said first tap changer means; e. second tap changer means including a second plurality of spaced contacts, one of said second spaced contacts being connected to said tap at the center of said first current limiting reactor winding, the rest of said contacts being connnected to said plurality of tap sections of said second induction means, and further including a second pair of movable fingers for engaging said contacts, said fingers being movable in unison and spaced so that at least one of said fingers will always engage at least one of said second spaced contacts; and f. second current limiting means including a winding connected between said second fingers and having a tap at The center of said winding.

2. A voltage regulator as recited in claim 1 wherein said first and said second induction means are disposed on a common magnetic core.

3. A voltage regulator as recited in claim 1, further including means for preventing said first fingers of said first tap changer means from traversing more than one of said first spaced contacts when said second fingers of said second tap changer means are not disposed upon said one of said second spaced contacts which is connected to said tap at the center of said first current limiting reactor winding.

4. A voltage regulator as recited in claim 1, further including means for preventing either of said first fingers of said first tap changer means from disengaging one of said first spaced contacts when either of said second fingers of said second tap changer means is coupled to that winding of said second induction means which is connected to the disengaging finger.

5. A voltage regulator comprising: a. first induction means having a winding divided into a plurality of tap sections; b. first tap changer means including a first plurality of spaced contacts, each of said first spaced contacts being connected to one of said plurality of tap sections, and further including a first pair of movable fingers for engaging said contacts, said fingers being movable in unison and spaced so that at least one of said fingers will always engage at least one contact; c. first current limiting reactor means including a winding connected between said first pair of fingers and having a tap at the center of said winding; d. second induction means including a second winding having a first and a second end and being divided into a plurality of tap sections; e. switch means for selectively connecting said first or said second end of said second winding to predetermined ones of said first pair of movable fingers of said first tap changer means; f. second tap changer means including a second plurality of spaced contacts, one of said second spaced contacts being connected to said tap at the center of said first current limiting reactor winding, the rest of said contacts being connected to said plurality of tap sections of said second induction means, and further including a second pair of movable fingers for engaging said contacts, said fingers being movable in unison and spaced so that at least one of said fingers will always engage at least one of said second spaced contacts; and g. second current limiting means including a winding connected between said second fingers and having a tap at the center of said winding.

6. A voltage regulator as recited in claim 5 wherein said first and said second induction means are disposed on a common magnetic core.

7. A voltage regulator as recited in claim 5, further including means for preventing said first fingers of said first tap changer means form traversing more than one of said first spaced contacts when said second fingers of said second tap changer means are not disposed upon said one of said second spaced contacts which is connected to said tap at the center of said first current limiting reactor winding.

Images