Voltage Stabilizing Transformer

Abstract

A voltage stabilizing transformer having a magnetic core formed of interleaved laminations defining a closed magnetic circuit and including a center winding leg and a pair of outer legs spaced therefrom. A first coil assembly, including at least a primary winding, is mounted on the center winding leg and a second coil assembly, including at least one secondary winding, is mounted on a center winding leg. Magnetic shunts are positioned between the first and second coil assemblies and extend substantially between the winding leg and the outer legs. A control winding is mounted on only a portion of the winding leg and is adapted to be short circuited for effectively removing that portion of the winding leg about which it is mounted from the magnetic circuit for the secondary winding.

Description

BACKGROUND OF THE INVENTION

This invention relates to transformers and more particularly to transformers for use in voltage stabilizers for maintaining a substantially constant output voltage over a wide range of variations in the input voltage and load.

Transformers utilized in voltage stabilizers are of the high leakage reactance type and are used in conjunction with a capacitor connected in parallel across a secondary winding or a part thereof. Such voltage stabilizers function as nonlinear ferroresonant circuits. The capacitor draws a leading current from the secondary winding so that the core of the high leakage reactance transformer operates in a saturated region, or, in effect, as a saturable reactor having a fixed volt-second capacity. So long as the volt-second capacity of the secondary winding remains fixed, the output voltage will not be affected by variations in input voltage. The output voltage is essentially a function of the frequency, of the saturation flux density, of the reactor turns and of the effective area of the core.

It is often desirable to have a single voltage stabilizing transformer structure which is capable of use with supply voltages of at least two frequencies. In the past the normal approach to providing a multi-frequency transformer construction was to provide an additional tap or taps on the input or primary winding so that a different tap could be used with voltages of different frequencies. This effectively changed the reactor turns from frequency to frequency so that the output voltages of the secondary windings would remain within the designed limits. However, if there was any substantial change between input frequencies, such as between 50 hertz and 60 hertz, the turns ratio between the input winding and the one or more output windings would be substantially altered by the alteration in the number of input windings turns. This required that the secondary or output winding also be tapped to maintain the desired turns ratio.

Such an arrangement makes the transformer construction substantially more complicated. This increases the cost of construction as well as the likelihood of a user connecting to an improper tap. These and other problems are particularly prevalent with such an approach when it is desired to have multiple outputs. For a multiple output transformer there are multiple output or secondary windings, each of which is designed to provide one of the desired outputs. A tapping approach to a multiple frequency transformer normally requires that each of the several output windings be provided with multiple taps, which multiplies the problems attendent to manufacture and use.

Accordingly a general object of the present invention is to provide an improved voltage stabilizing transformer.

Another object of the invention is to provide such a voltage stabilizing transformer adapted for use at multiple input frequencies.

It is yet another object of this invention to provide such an improved voltage stabilizing transformer which is simple in construction and easily used.

SUMMARY OF THE INVENTION

In accordance with one form of the invention there is provided an electrical inductive apparatus comprising a magnetic core formed with laminations of magnetic material and having a plurality of spaced apart legs and yokes connecting the legs to define a flux path. An input winding is mounted around one of the legs and at least one output winding is mounted around one of the legs so as to be inductively coupled with the input winding. A control winding is mounted around only a portion of the leg passing through the output winding and is adapted to be selectively short circuited for effectively removing that portion of the leg from the inductive path associated with the output windings.

The subject matter which I regard as my invention is set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof, may be better understood by reference to the following description taken in conjunction with the accompanying drawings wherein:

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a voltage stabilizing transformer incorporating one form of the invention;

FIG. 2 is an exploded perspective view, in schematic form, of the core and coil arrangement of the transformer of FIG. 1;

FIG. 3 is an exploded perspective view of laminations utilized in one portion of the core of FIG. 1;

FIG. 4 is an exploded perspective view of laminations used in another portion of the core of FIG. 1;

FIG. 5 is an exploded perspective view of laminations used in another portion of the core of FIG. 1;

FIG. 6 is a simplified partial cross-sectional view of the winding leg and control coil of the transformer of FIG. 1; and

FIG. 7 is a schematic electrical circuit diagram of a voltage stabilizer circuit utilizing the transformer of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more specifically to the drawings, and particularly to FIG. 1, there is shown a voltage stabilizing transformer 10 including a core and coil assembly 11 of the high leakage reactance type. The core and coil assembly 11 includes a magnetic core 12 formed of suitable magnetic material. The magnetic core 12 conveniently may be formed of a stack of relatively thin interleaved laminations of magnetic material to provide an interleaved core structure.

The magnetic core 12 includes a center winding receiving leg 13 and a pair of outer legs 14 and 15 which are spaced from the center leg to define windows 16 and 17 (FIG. 2) for receiving first and second coil assemblies 18 and 19. The coil assemblies are mounted about the center winding leg 13 and are received in the windows 16 and 17 so as to generally pass completely through the core. The first coil assembly 18 contains a primary winding P while second coil assembly 19 contains one or more secondary windings, a capacitor winding C and a control winding K. In the exemplification there are six secondary or output windings, which are more clearly seen in FIG. 7 as S.sub.1, S.sub.2, S.sub.3, S.sub.4, S.sub.5, and S.sub.6. While the secondary or output windings S.sub.1 - S.sub.6, the capacitor winding C and the control winding K may be spread along the length of the center winding leg 13, for the sake of compactness they generally are wound one over the other. The control winding is mounted around a portion of the center winding leg 13 then the capacitor winding and the output windings are wound over the control winding. The coil assemblies 18 and 19 are insulated from the magnetic core 12 by suitable insulation such as that shown at 20 and 21.

In order to provide suitable loose magnetic or inductive coupling between the first coil assembly 18 and the second coil assembly 19 magnetic shunts 22 and 23 are positioned in the windows 16 and 17 between the coil assemblies and substantially bridge the windows 16 and 17, i.e., at least a portion of each of the shunts 22 and 23 engages center winding leg 13 while a portion of shunt 22 engages outer leg 14 and a portion of shunt 23 engages outer leg 15. Leads 24 and 25 connect the ends of capacitor winding C to a suitable capacitor 26 so that the capacitor is connected across the winding C. The lamination stack forming core 12 conveniently may be held together by plurality of bolts 27 which pass through the four corners of the core and incorporate with nuts 28 to hold the individual laminations in juxtaposition. The nuts and bolts may also be utilized to secure a pair of mounting flanges 29 and 30 to the two opposite sides of the core to provide a suitable mounting means for the transformer. The capacitor 26 is mechanically attached to the transformer by a strap 31 which is secured to a upturn portion 32 of the flange 30 by suitable nut and bolts arrangement such as that shown at 33.

Referring now more specifically to FIG. 2 there is shown the overall configuration of various segments of the core 12. It will be understood that in FIG. 2 the segments of the core are shown in block form, without indicating individual lamination. First core section 12a has a center winding leg 13a and outer legs 14a and 15a spaced from the center leg 13a to form windows 16a and 17a. The ends of the legs are joined by transverse yokes 34a. The second or middle core section 12b includes only outer legs 14b and 15b joined by the yokes 34b and to define a central, generally rectangular aperture 35b which has the same area as windows 16a and 17a and central leg 13a combined. The third core section 12c including a center leg 13c outer legs 14c and 15c joined by yokes 34c. The center leg 13c of core section 12c is provided with a lower portion 13c' which is relatively wide and an upper portion 13c" which is relatively narrow. The first coil assembly 18 and the second coil assembly 19 (less the control winding K) are mounted within the windows 16 and 17 so as to extend completely through all three sections 12a, 12b, and 12c of the core. The control winding K is mounted about the reduced width portion 13c" only of the center winding leg 13c and a non-magnetic spacer 36 may be inserted between one side of winding K and the center winding leg to provide a tight fit there between.

Referring now to FIGS. 3-5 it will be seen that the first core section 12a is provided by an interleaved stack of E laminations 37 and I laminations 38 with the E and I laminations being alternately stacked as is well known in the art to provide an interleaved structure for section 12a of the core. In the illustrative embodiment the center core section 12b is provided by an interleaved, alternate stack of C laminations 39 and I laminations 38 so that, in the core section 12b, the center winding leg 13 is discontinuous. The core section 12c is formed from an alternating interleaved stack of E laminations 40 and 41 and I laminations 38. The E lamination 41, which extend upward from the bottom of the core (as seen in FIG. 1) have stepped center legs including a relatively wide portion 42 and narrow portion 43 while the E laminations 40 have a relatively narrow center leg 44. The wide center leg portions 42 of laminations 41 correspond in width to the center legs of E laminations 37 and the center legs 44 of laminations 40 correspond to the narrow portions 43 of the center legs of laminations 41. The difference in width between leg portion 42 of the one hand and leg portion 43 and leg 44 on the other hand corresponds to the thickness of control winding K and the thickness of second core section 12b also corresponds to the thickness of control winding K. With this arrangement, when the control winding K is assembled into the core it is received about the center leg portion 13c" and within the core is generally confined within the cross-sectional area of the larger center leg portion 13c'. The discontinuity of winding leg 13 provided by core section 12b provides an opening through the winding leg 13 to receive the inner side of control winding K. It will be obvious that other lamination configurations may be used in forming the core 12. For instance the lower C laminations 39 could be replaced by E laminations have a shorter center leg, which would correspond in height to the wide portion 42 of laminations 41. With such an arrangement the discontinuity and or opening in the center winding leg 13 would be completely filled by the control winding K.

When control winding K is opened circuited it is ineffective and the entire cross-sectional area of center winding leg 13 about which the capacitor winding C and secondary output windings S.sub.1 - S.sub.6 are wound is effectively in the magnetic circuit or flux path interconnecting the capacitor and secondary windings with the primary winding P. On the other hand, when control winding K is short circuited, it effectively removes the portion 13c" of winding leg 13 about which it is wound from the magnetic circuit associated with the secondary windings and capacitor winding. This effectively changes the magnetic circuit so that the voltage stabilizing transformer 10 may be used with a lower predetermined frequency when winding K is open circuited and a higher predetermined frequency when the winding K is short circuited. A pair of terminals 50 and 51 are connected to the ends of the winding K so that the winding is adapted to be selectively open and short circuited by the user. This enables the same transformer construction to be utilized with two different input frequencies merely by selectively open circuiting or short circuiting the control winding K.

As mentioned previously the output voltage is a function of both the frequency and the effective area of the core, particularly the winding leg 13. More specifically the output voltage is directly proportional to the frequency and inversely proportional to the cross-sectional area. The control winding K is mounted around a portion 13c" of the center winding leg 13 having a cross sectional area which, in relation to the total cross-sectional area of leg 13, is sufficient to offset the effect of the change in frequency. The cross-sectional area to be encompassed by the control winding K easily may be calculated as the effective cross-sectional area at the lower frequency divided by the effective cross-sectional area at the higher frequency will be substantially equal to the higher frequency divided by the lower frequency. This ratio will not be exact as the flux leakage of a transformer will affect the calculations. However, with well constructed transformers having low flux leakage the relationship is substantially correct.

Referring now to FIG. 7 there is shown an electric circuit in schematic circuit diagram form including a voltage stabilizing transformer arrangement designed to use the transformer of FIG. 1 to provide a number of different D.C. outputs from a 120 volt input signal which may be either 50 or 60 hertz. With this arrangement the core 12 had an overall height H of 5.88 inches a width W of 6.75 inches and a thickness T of 3.171 inches core sectoion 12a had a thickness of 2.188 inches core section 12b had a thickness of 0.31 inches and core section 12c had a thickness of 0.673 inches. As seen in FIG. 6, the portion 13c" of the center winding leg encompassed by the control winding K was 0.883 square inches and the remaining portion 13c'" of the center winding leg encompassed by the capacitor winding C and the output windings S.sub.1 - S.sub.6 was 3.965 square inches. Primary winding P was formed of 105 turns of 0.072 inch diameter wire. Capacitor winding C was formed of 431 turns of 0.0508 inch diameter wire and capacitor 26 at a value of 8 microfarads. Control winding K was 116 turns of 0.0641 inch diameter wire. Output coil S.sub.1 was 22 turns of 0.114 inch diameter wire with terminals 55 and 56. Output winding S.sub.2 was 18 turns of 0.0720 inch diameter wire between terminals 57 and 59, with an intermediate tap 58 positioned 5 turns from end tap 57. Output winding S.sub.3 also was 18 turns of 0.072 inch diameter wire between output terminals 60 and 62, with an intermediate terminal 61 five turns from output terminal 60. Output windings S.sub.4 was 13 turns of 0.0359 inch diameter wire between terminals 63 and 64. Output winding S.sub.5 was 13 turns of 0.0359 inch diameter wire between terminals 65 and 66. Output winding S.sub.6 was 21 turns of 0.0642 inch diameter wire between terminals 67 and 68.

Since it was desired that each of the outputs of the inverter provide D.C. power, each of the output windings S.sub.1 - S.sub.6 was provided with a rectifier bridge 69 having its input connected across the terminals of the associated output winding. A filter capacitor 70 was connected across the output of each of the bridge rectifiers so that the outputs would be a full wave rectified filtered D.C. signal. With a 120 volt input, at either 50 hertz or 60 hertz, a 28 volt output was obtained from winding S.sub.1 ; a 23 volt output was obtained from winding S.sub.2 across terminals 57 and 59 and a 16.5 volt output was obtained across terminals 58 and 59; a 23 volt output was obtained from winding S.sub.3 across terminals 60 and 62 while a 16.5 volt output was obtained across terminals 61 and 62; a 16.5 volt output was obtained from each of windings S.sub.4 and S.sub.5 ; and a 28.5 volt output was obtained from winding S.sub.6.

It will be understood that the second coil assembly 19 may include several separte output windings as indicated by the voltage stabilizer of FIG. 7 or may include only one output winding.

While, in accordance with the patent statutes, I have shown and described what at present is considered to be the preferred embodiments of the present invention, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention. It is therefore intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim is new and desire to secure by Letters Patent in the United States is:

Claims

1. An electrical inductive apparatus for maintaining a substantially constant output voltage for an input having plurality of input frequencies comprising:

a. a magnetic core formed of laminations of magnetic material and having a plurality of spaced apart legs and yokes connecting said legs to define a flux path;

b. an input winding for receiving electric energy at one of at least two input frequencies, said input winding being mounted around one of said legs;

c. at least one output winding mounted around one of said legs so as to be inductively coupled with said input winding;

d. a control winding adapted to be selectively short-circuited for a first input frequency and open circuited for a second input frequency, said control winding being mounted around only a portion of said one of said legs associated with said output winding for effectively removing said portion of said one of said legs from the inductive path associated with said at least one output winding when said control winding is short-circuited so that the output, voltage is substantially constant for an input having a plurality of input frequencies;

e. said one of said legs including a discontinuous section providing an opening therethrough parallel to said laminations to receive said control winding.

2. A voltage stabilizing transformer for maintaining substantially constant output voltage for an input having a plurality of input frequencies comprising:

a. a magnetic core formed of a plurality of interleaved laminations defining a closed magnetic circuit and including a center winding leg and a pair of outer legs spaced therefrom;

b. a first coil assembly including at least a primary winding for receiving electric energy at one of at least two input frequencies mounted on said center winding leg;

c. a second coil assembly including at least one secondary winding mounted on said center winding leg;

d. magnetic shunt means positioned between said first and second coil assemblies and extending substantially between said winding leg and said outer legs; and

e. a control winding adapted to be selectively short-circuited for a first input frequency and open circuited for a second input frequency, said control winding being mounted around only a portion of said winding leg for effectively removing said portion of said winding leg from the magnetic path associated with said at least one output winding when said control winding is short-circuited so that the output voltage is substantially constant for an input having a plurality of input frequencies;

f. said winding leg including a discontinous section providing an opening therethrough parallel to said laminations to receive said control winding.

3. A voltage stabilizing transformer adapted to have a substantially similar output voltage characteristic with an input at either of two predetermined frequencies, comprising;

a. a magnetic core defining a closed magnetic circuit and including a winding receiving leg;

b. magnetic shunt means dividing said winding receiving leg into first and second sections;

c. a first coil assembly including at least a primary winding for receiving electric energy at one of at least two input frequencies mounted about said first section of said winding receiving leg;

d. a second coil assembly including at least a secondary winding mounted about said second section of said winding receiving leg;

e. a control winding mounted about only a portion of said second section of said winding receiving leg, said control winding being adapted to be open circuited at the lower predetermined input frequency and to be short circuited at the higher predetermined input frequency for effectively removing said portion of said second winding receiving leg section from the magnetic circuit for said secondary winding;

f. the total cross-sectional area of said second section of said winding receiving leg divided by the effective cross-sectional area of said second section of said winding receiving leg when said control winding is short circuited is substantially equal to the higher of the predetermined input frequencies divided by the lower of the predetermined input frequencies.

4. An electrical inductive apparatus as set forth in claim 1 further including at least one magnetic shunt substantially bridging the space between adjacent spaced apart legs between said input winding and said at least one output winding.

5. An electrical inductive apparatus as set forth in claim 1 wherein said at least one output winding overlies said control winding.

6. A voltage stabilizing transformer as set forth in claim 2 wherein at least most of the lamination layers of said core include an E lamination with the center legs of said E lamination forming said winding leg of said core, an adjacent group of lamination layers being discontinuous to provide said opening in said winding leg to receive said control winding.

7. A voltage stabilizing transformer as set forth in claim 2 wherein said control winding is part of said second coil assembly.