US3461379A - Slide transformers and slide reactor devices - Google Patents

Description

Aug. 12, 1969 HIDEKI OKITA 3,461,379

SLIDE TRANSFORMERS AND SLIDE REACTOR DEVICES Filed Sept. 1. 1967 2 Sheets-Sheet 1 (a) (fi) b I l0 /Z /0 I2 /0 17/2 l0 li/Z INVENTOR. mow! 0mm k V m5 AWTOR WY Aug. 12, 1969 HIDEK! OKITA ,461,

smma Tnwyonmnns AND suns: REACTOR DEVICES I Filed Sept. 1, 1967 2 Sheets-Sheet 2 United States Patent O 3,461,379 SLlDE TRANSFORMERS AND SLIDE REACTOR DEVICES ll-Iideki Okita, Shimonoseki, Japan, assiguor to The Osaka Transformer 60., Ltd., Osaka, Japan, a company of the prefecture of Osaka, Japan Filed Sept. 1, 1967, Ser. No. 665,167 Claims priority, application Japan, Sept. 10, 1966, 41/ 59,463, ll/59,464; Sept. 14, 1966, 41/60,?)13

Int. Cl. H02p 13/06 US. Cl. 323-43.5 5 Claims ABSTRACT OF THE DISCLOSURE A slide transformer or a slide reactor device in which at least one leg of the iron core has two partially insulated windings wound thereon and a slidable contactor assembly having impedance elements in series connected thereto is in contact with the windings for selective contact with conductor portions in selected turns of said windings thereby to provide power to the load side.

BACKGROUND OF THE INVENTION In the conventional slide transformers or slide reactor devices, there was the possibility of overheat in the single slidable contactor which was .adapted to slidably move in contact with the windings wound on one leg of the iron core and therefore, the conventional slide transformers or slide reactor devices could not be operated with large current. Accordingly, in such conventional slide transformers partially insulated two windings were wound on one leg of the iron core in such a manner that the alternately arranged non-insulated or conductor portions of the windings might be positioned opposite to each other with the insulated portions interposed between the opposing conductor portions and the opposite ends of both the two windings were connected to balanced reactors whereby the neutral points of the reactor windings were employed as the input terminals while the single slidable contactor and the neutral point of either one of the two reactor windings were employed as the output terminals. However, in such conventional slide transformers, when current was supplied to the load side by the contact of the slidable contactor with only one of the two windings, current was allowed to fiow through only the one winding with which the slidable contactor was in contact and therefore, the two windings should be formed from some conductors which has a capacity capable of permitting a rated current to flow through. Accordingly, the windings required conductive material in amount more than necessarv to cause the rated current to flow and this is undesirable from the point of economy and in addition such conventional slide transformers were generally large in size and expensive in manufacture.

The conventional slide reactors had also the disadvantages similar to those inherent to the conventional singlephase slide transformers as referred to just above.

And in the conventional slide transformers having both the primary and secondary windings the latter of which comprised the two windings of the same construction and arrangement as those described in connection with the first-mentioned conventional slide transformers, at least one adjacent ends of the two windings of the secondary winding were connected to the opposite ends of a balanced reactor and the neutral point of the reactor winding and the single slidable contactor were employed as the output terminals. However, in this type of slide transformer, the same disadvantages inherent to the above-mentioned slide transformers and slide reactor device are also seen.

SUMMARY OF THE INVENTION A main object of the present invention is to provide a slide transformer or a slide reactor device in which as a slidable contactor assembly, which is in contact with two windings wound on one leg of the iron core of said transformer, is moved along the winding-wound iron core leg in contact with the windings, short-circuit current which may flow between particular turns of the windings with which said contactor assembly is in contact can be absorbed by balanced reactors connected to the windings and short-circuit current which may flow through the individual slidable contactors of the contactor assembly can be blocked by impedance elements connected to the individual contactors.

Another object of the present invention is to provide an improved and economical slide transformer or reactor device in which at least two of the three slidable contactors of said contactor assembly are adapted at all times and simultaneously to contact particular turns of said two windings whereby each of said windings may permit current at one half of load current to flow through the windings to the load side.

In one form of slide transformer by the present invention, as seen in the conventional equivalent slide transformer, two partially insulated windings having alternate conductor portions and insulator portions are wound on one leg of the iron core of said transformer in such a manner that adjacent conductor portions in adjacent turns of said two windings are disposed in opposing relation to each other and both the opposite ends of said two windings are respectively connected to the windings of their respectively associated balanced reactors with the neutral points of said reactor windings employed as the input terminals. Also in one form of slide reactor device or a modified form of slide transformer according to the present invention the latter of which comprises the primary winding of a prior art transformer in addition to the above-mentioned first two alternately insulated windings, as seen in the conventional equivalent devices, at least one adjacent ends of said first two windings are connected to a balanced reactor with the neutral point of the winding of said balanced reactor employed as one input or output terminal.

However, one of the abovearnentioned slide transformers and slide reactor device by the present invention are different from the conventional equivalent devices in that said slidable contactor assembly, which is adapted to move along the iron core leg on which said two windings are wound in slide contact with the windings, comprises three individual slidable contactors adapted to simultaneously slidably contact two or three adjacent conductor portions in particular turns of the windings and spaced from each other with an equal space and that the outer two contactors of said three slidable contactors are connected directly or through their respectively associated linear or non-linear impedance elements to the center contactor interposed between the outer contactors or connected through a similar impedance element associated with said center contactor to each other so as to form one input terminal (in case of the slide transformer) or one output terminal (in case of the slide reactor device).

Accordingly, in the above-mentioned slide transformer by the present invention, when said slidable contactor .assembly is moved along the iron core leg, on which said two windings are wound, in slide contact with said windings, in order to provide output'to the load side, at least two slide contactors of said contactor assembly are caused to simultaneously and slidably contact adjacent conductor portions in particular adjacent turns of the two windings thereby to provide power to the load side. Therefore, each of the two windings at all times permit current at substantially one half of that to be provided to the load side to flow through the same. And shortcircuit current, which may flow between the adjacent particular turns of the two windings with said two slide contactors are now in contact, can be effectively absorbed by the balanced reactors connected to both the ends of the two windings and short-circuit current, which may flow between the two contactors, can be also blocked by the impedance elements connected respectively to the contactors. Therefore, in the above-mentioned slide transformed or slide reactor device by the present invention, since each of the two windings is only requested to permit current of substantially one half of a rated current to flow through the same, the windings may be formed of smaller diameter wires as compared with the windings of the conventional slide transformers which must be formed of larger diameter wires for operating the devices at the same rated current.

The above-mentioned function of the novel slide contactor assembly comprising the three slide contactors can be also attained by a modified slidable contactor assembly comprising a wider slide contactor which can slidably contact one or two adjacent conductor portions in one or two adjacent turns of the two windings and a narrower slide contactor which can slidably contact only one conductor in one turn of either of the two windings.

The above and other objects and attendant advantages of the present invention will be more readily apparent to those skilled in the art from the following description when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagram of a slide transformer embodying the present invention;

FIG. 2 is a diagram showing the voltage-current characteristics of non-linear impedance elements to be in series connected to the slidable contacts of said slide transformer;

FIG. 3 is an enlarged fragmentary schematic view of said slide transformer especially showing the relationship between the slidable contactors and the conductor portions in the turns of two windings adapted to be contacted by contact said contactors;

FIGS. 4a-4d are enlarged fragmentary schematic views of said slide transformer especially showing relative positions of the slidable contactors to the conductor portions in the turns of two windings adapted be contacted by said contactors in various different operative conditions of the slide transformer;

FIG. 5 is a schematic circuit diagram of a modified form of slide transformer which includes the primary and secondary windings embodying the present invention;

FIG. 6 is a schematic circuit diagram of a slide reactor device embodying the present invention;

FIG. 7 is schematic circuit diagram of a still further modified form of slide transformer embodying the present invention in which a wider slidable contactor and a narrower slidable contactor are employed;

FIG. 8 is an enlarged fragmentary schematic view of said slide transformer of FIG. 7 illustrating the relationship between said wider and narrower slidable contactors and the conductor portions in the turns of said two windings to be contacted by the contactors; and

FIGS. 9a-9d are enlarged fragmentary schematic views of said slide transformer of FIG. 7 especially illustrating relative positions of said slidable contactors to the conductor portions in the turns of the said two windings in various different operative positions of the transformer.

PREFERRED EMBODIMENTS OF THE INVENTION Referring now to the accompanying drawings and especially to FIG. 1 through FIG. 4d thereof in which a preferred form of slide transformer embodying the present invention is illustrated. The slide transformer generally comprises a conventional transformer iron core 1 surrounded by an insulator (not shown and having a pair of opposite and parallel legs which are connected at the opposite ends to each other by yokes. One leg 1a of the pair of iron core legs has two partially insulated windings 2 and 3 wound there-on with insulator portions 4, 4' and 4" in the adjacent turns of the two windings positioned in opposing relation. The two windings 2 and 3 comprise conductors having the same rectangular cross-sectional shape having equally spaced alternate conductor portions and insulator portions throughout the length of the windings and each of which windings can permit current to flow through the same at one half value of a rated current. The two windings 2 and 3 are wound on the one iron core leg 1a in such a manner that adjacent conductor portions in adjacent turns of the two windings may be arranged in opposing relation to each other. One ends 2a and 3a of the two windings 2 and 3 are connected to the opposite ends of the winding 6 of a balanced reactor 5 and the other ends 2b and 3b of the windings are similarly connected to the opposite ends of the winding 8 of a similar balanced reactor 7 having substantially the same characteristics as those of the balanced reactor 5. The neutral points 6a and 8a of the reactor windings 6 and 8 are connected to the input terminals 16 and 16 of the respectively associated power sources (not shown) and the one input terminal 16' is in turn connected to the output terminal 17. The slide transformer further comprises a contactor assembly 9 which comprises three parallel slidable contactors 10, 11 and 12 in the illustrated embodiment and these slidable contactors are arranged in a predetermined equal spaced relation to one another with suitable insulators (not shown) interposed between adjacent ones. The three slidable contactors 10, 11 and 12 are at a'l times in slide contact with the windings 2 and 3 in such a manner that the contactors may simultaneously come to slidably and selectively contact two or three adjacent exposed or conductor portions in adjacent windings of the windings 2 and 3 as the slidable contactor assembly '9 is moved along the length of the iron core leg 1a on which the windings are wound. The two outer contactors 10 and 12 of the three slidable contactors are connected through impedance elements 13 and 15 such as resistors, reactors and the like, which are respectively in series connected with the associated contactors 10 and 12, to the output terminal 17. The center or intermediate contactor 11 is connected directly or through an impedance element 14 such as a resistor, reactor or the like, which, if provided, is in series connected to the contactor 11, to the abovementioned output terminal 17. As seen in FIG. 3, the distance between these slidable contactors 10, '11 and 12 are so selected that the distance S between the adjacent contactors 1t) and 11 and that between the adjacent contactors 11 and 12 may be smaller than the length D of each of the exposed or conductor portions 2, 2", in each winding of the associated winding and the distance S between the outer contactors 10 and 12 may be greater than the exposed or conductor portion length D, but smaller than the combined length of three exposed or conductor portions.

When the above-mentioned slide transformer is operated so as to slidably move the contactor assembly 9 along the leg 1a of the iron core 1 in contact with the windings 2 and 3 in order to obtain a desired output, the relationship between the individual contactors 10, 11 and 12 and the windings 2 and 3 will vary as shown in FIGS, 4a through 4d, for example.

In'the condition of the slide transformer shown, FIG. 4a, the two outer slidable contactors and 12 are in contact with the conductor portions 2 and 2" in two adjacent alternate turns of the winding 2, respectively while the intermediate slidable contactor 11 is in contact with the conductor portion 3 in one turn of the winding 3 which is interposed between the above-mentioned two alternate adjacent turns of the winding 2 thereby to provide power to the load side. In such a condition, shortcircuit current between the contactors 10 and 12 which are now in contact with the winding 2 is blocked by the impedance elements 13 and and a voltage develops at one half value of that of the voltage at one turn in the winding 2 between the adjacent turns of the two windings 2 and 3 with which the adjacent contactors 10' and 11 and the adjacent contactors 11 and 12 are respectively in contact, but such a voltage is absorbed by the balanced reactor 5 and 7 and current flowing between the contactors 10 and 11 and between the contactors 11 and 12 is blocked by the impedance elements 13 and 14 and the impedance elements 14 and 15. Therefore, substantially no short-circuit current flows between the contactors 10 and 11 and between the contactors 11 and 12.

Then, when the contactor assembly 9 is slightly moved to the positions as shown in FIG. 4b in which the contactors 11 and 12 are in contact with the conductor portions 3 and 2" in the adjacent turns of the windings 3 and 2 while the contactors 10 is positioned at the insulator portion 4- between the conductor portion 2' and conductor portion 3 thereb to provide power to the load side. In such a condition, voltage developing between the adjacent turns of the windings 3 and 2 with which the conductors 11 and 12 are now in contact is absorbed by the balanced reactors 5 and 7 and current flowing between the contactors 11 and 12 is blocked by the impedance elements 14 and 15 and therefore, no short-circuit current flows between the contactors 11 and 12 in the condition of the slide transformer as shown in FIG. 4b.

Then, when the contactor assembly 9 is further moved to the position as shown in FIG. 40 in which the contactors 1t and 11 are in contact with the same one conductor portion 3' in one turn of the winding 3 while the contactor 12 is in contact with the conductor portion 2" in one turn of the winding 2 thereby to provide power to the load side. In such a condition, since the contactors 10 and 11 are at the same potential, the condition of FIG. 40 is substantially the same as that of FIG. 4b and therefore, no short-circuit current flows between the contactors 11 and 12 because of the same reason as mentioned in connection with FIG. 4b.

Thereafter, when the contactor assembly 9 is further moved to the position as shown in FIG. 4d in which the intermediate contactor 11 is positioned at the insulator 4 between the conductor 3 in one turn of the winding 3 and the adjacent conductor 2 in one turn of the winding 2 which the two outer contactors 10 and 12 are respectively in contact with the conductor portions 3' and 2" in the adjacent turns of the windings 3 and 2 with the insulator portion 4 interposed therebetween thereby to provide power to the load side. In such a condition of the slide transformer, voltage developing between the adjacent turns of the windings 3 and 2 with which the contactors 1t and 12 are now in contact is absorbed by the balanced reactors 5 and 7 and current flowing between the contactors 10 and 12 is blocked by the impedance elements 13 and 15 and therefore, no short-circuit current flows between the contactors 10 and 12.

It should be noted that even when the contactor assembly is further moved along the iron core leg 1a in slide contact with the windings 2 and 3, the relationship between the contactor assembly 9 and the windings 2 and 3 will be any one of the four-types of relationship as illustrated in FIGS. 4a through 4:! and accordingly, all the conditions of the novel transformer, which the same may assume as the slidable contactor assembly 9 moves along the iron core leg 1a in slide contact with the windings 2 and 3, may be represented by those shown in FIGS. 4a through 4b.

FIG. 5 illustrates a modified form of slide transformer embodying the present invention and this modified embodiment is substantially similar to the embodiment of FIGS. 1 through 4d referred to hereinabove except for that the leg 1b opposite to the leg 1a on which the windends of the winding connected to the input terminals 16 ings 2 and 3 are wounded is also wound thereon the primary winding 18 of a transformer with the opposite and 16' of the power source (not shown) and the balance reactor 5 in an optional element, but not an absolutely necessary element as in the preceding embodiment. In other words, if the other balanced reactor 7 is designed so as to have a capacity twice as much as that of the same reactor 7 in the preceding embodiment and the terminals 2a and 3a of the two windings 2 and 3 are formed as open terminals, the balanced reactor 5 may be eliminated in the embodiment of FIG. 5.

FIG. 6 illustrates a further modified embodiment of the present invention which embodied in the form of a reactor device. The reactor device of FIG. 6 is substantially the same as the slide transformer of FIG. 5 in construction except for that the other leg 1b of the iron core 1 is not provided with the primary winding 18 of the transformer and the reactor device is supplied with input at the terminals 17 and 17'.

In any of the above-mentioned embodiments, each slidable contractor has a linear impedance element connected thereto such as a resistor or a reactor and a voltage drop develops at the impedance attributable to current which flows through the output terminals to the load side and accordingly, the voltage-current characteristics of the above-mentioned transformer and reactor devices can be termed as the so-called dropping characteristic in which the output voltage drops attributable to the load current. However, in the above-mentioned transformers and reactor devices, if the impedance elements are formed as non-linear impedance elements having the voltage V Current I characteristics as indicated by the curves in FIG. 2, for example, saturable reactors, semiconductor rectifying elements connected in reverse connection or voltage regulator diodes (Zener diodes), and the voltage drop of Vs due to the non-linear impedance elements is set smaller than voltage to be developed in each turn of the windings 2 and 3, but greater than one half of the turn voltage, the voltage drop at the non-linear impedance elements due to the load current can be maintained at a substantially constant value thereby to maintain the voltage-current characteristics of the slide transformers and slide reactor devices as the constant voltage characteristics.

FIG. 7 illustrates a further modified form of slide transformer of the present invention in which a slidable contactor assembly comprising a wider slidable contactor and a narrower slidable contactor is employed. In FIG. 7, the slidable contactor assembly 9 comprises a wider slidable contactor 20 and a narrower slidable contactor 21 which are spaced from each other with an insulator (not shown) interposed between the two contactors. The two contactors 20 and 21 are adapted to simultaneously and slidably move along the length of the leg 1a of the iron core 1 on which the windings 2 and 3 are wound for selective contact with turns of the windings. The narrower contactor 21 is connected through a linear impedance element 23 such as a resistor or reactor or a non-linear impedance element having the voltage-current characteristics as shown in FIG. 2 to the output terminal 17 while the wider contactor 20 is connected through a non-linear impedance element 22, the latter of which provides a voltage drop less than that by the above-mentioned impedance element 23 associated with the narrower contactor 21, to the same output terminal 17. It will be understood that when the impedance elements 22 and 23 as referred to just above are formed as linear impedances, the transformer of FIG. 7 will have the dropping characteristic, but when the impedance elements are formed as non-linear impedance elements, the transformer will have a substantially constant voltage characteristic.

In FIG. 8, the width of the contacting surfaces of the wider and narrower contactors 20 and 21 are given as d and d respectively and the distance between the wider and narrower contactors 20 and 21 is given as S. And the length of each conductor portion in the windings 2 and 3 is given as D and the length of each insulator portion in the windings 2 and 3 is given as D Then these factors are selected to satisfy the following inequalities:

In the slide transformer of FIG. 7 in order to provide a desired output, when the slidable contactor assembly 9' is moved along the iron core leg 1a on which the partially coated or insulated windings 2 and 3 are wound the relationship of the wider and narrower contacts 20 and 21 relative to the windings 2 and 3 may vary as shown in FIGS. 9a through 9d.

First, referring to FIG. 9a, in the condition shown in this figure the wider contactor 20 is in contact with one conductor portion 3' in one turn in the winding 3 and with insulator portions 4 and 4' adjacent to the opposite ends of the conductor portion 3 while the narrower contactor 21 is in contact with the conductor portion 2" in one turn in the winding 2 which is adjacent to the turn of the winding 3 with which the wider contactor 20 is now in engagement thereby to provide power to the load side. In this condition of the transformer, voltage may develop between the adjacent turns in the windings 2 and 3 with which the wider and narrower contactors 20 and 21 are now in contact, but this voltage is absorbed by the balanced reactors 5 and 7 and short-circuit current flowing between the two contactors 20 and 21 is blocked by the impedance elements 22 and 23, and accordingly, load current will flow through the contactors 20 and 21.

Next, when the slidable contactor assembly 9 is moved to the position as shown in FIG. 9b, in this position of the contactor assembly the wider contactor 20 is in contact with the conductor portions 3', with the insulator portion 4' and with the conductor portion 2" while the narrower contactor 21 is in contact with the conductor portion 2" with which the wider contactor 20' is also now in contact thereby they provide power to the load side. In this condition of the slide transformer, voltage developing between the adjacent turns of the windings 2 and 3 including the conductor portions 3' and 2" is absorbed by the balanced reactors 5 and 7 and short-circuit current between the two contactors 20 and 21 in this condition is blocked by the impedance elements 22 and 23. Also in this condition shown in FIG. 9b, load current flows through the wider contactor 20 to which the impedance element 22, which provides a smaller voltage drop, is connected. When the contactor assembly 9' is further moved to the position as shown in FIG. 90, in this condition of the slide transformer the wider contactor 20 is in contact with the conductor portion 3', with the insulator portion 4 and with the conductor portion 2" while the narrower contactor 21 is in contact with the insulator 4" between the conductor portions 2" and 3" thereby to provide power to the load side. As in the case of FIG. 9b, load current flows through the wider contactor 20 to which the impedance element 22, which provides a smaller voltage drop, is connected. When the contactor assembly 9' is further moved to the positions shown in FIG. 9d, the wider contactor 20 is in contact with the conductor portion 3, with the insulator portion 4' and with the conductor portion 2 while the narrower contactor 21 is in contact with the insulator portion 4" and with the conductor portion 3" thereby to provide power to the load side. In this condition of the slide transformer, voltage between the adjacent turns including the and conductor portion 3', and conductor portion 2" with which the wider contactor 20 is now in contact is absorbed by the balanced reactors 5 and 7 and short-circuit current between the two contactors 20 and 21 is blocked by the impedance elements 22 and 23. And in this case, load current does scarcely flows through the narrower contactor 21 and instead the current flows through the wider contactor 20 as in the case of FIGS. 9a, 9b and 90.

It should be noted that even the contactor assembly is further moved along the iron core leg 1a in slide contact with the windings 2 and 3, the relationship between the contactor assembly 2 and the windings 2 and 3 will be one of the four types of relationship as illustrated in FIGS. 9a through 9d and accordingly, all the conditions of the transformer of FIG. 7 which the same may assume as the slidable contactor assembly 9" moves along the iron core leg 1a in slide contact with the windings 2 and 3 may be represented by those shown in FIGS. 9a through 9d.

Although the present invention has been described in connection with single-phase transformers and singlephase reactor devices hereinabove, it is, of course, appreciated that the present invention may be also applicable to multi-phase transformers and multi-phase reactor devices without departing the spirit of the present invention and within the scope thereof. And the slidable contactor assembly in the transformer comprising the wider and narrower contactors as shown in FIG. 7 may be employed in place of the contactor assemblies of the slide transformer in FIGS. 5 and 6 without departing from the spirit of the present invention.

What is claimed is:

1. A slide transformer or slide reactor device comprising an iron core having legs; two partially insulated windings wound on one of said iron core legs and having alternately arranged conductor portions and insulator portions in the full length thereof, said windings being wound on said one iron core leg so that adjacent conductor portions in adjacent turns of said two windings may be arranged in opposing relation to each other; at least one balanced reactor having one winding the opposite ends of which are connected to adjacent one ends of said windings; and a slidable contactor assembly adapted to move along said winding-wound iron core leg in slide contact with said windings whereby the neutral point of said reactor winding and said slidable contactor assembly may form output terminals for said slide transformer or input terminals for said slide reactor device, characterized by that said slidable contactor assembly comprises three parallel slidable contactors arranged in spaced relation with an equal distance between adjacent ones and adapted to slidably contact two or three adjacent conductor portions in particular turns of said two windings as said slidable contactor assembly is moved along said windingwound iron core leg and the two outer contactors of said three slidable contactors are connected directly or through linear or nonlinear impedance elements connected to the two contactors to the center contactor or connected through a similar impedance element connected to said center contactor to each other.

2. A slide transformer as set forth in claim 1, in which two separate balanced reactors are connected to both the opposite and adjacent ends of said two windings and the neutral points of the windings of said two balanced reactors are employed as input terminals.

3. A slide transformer as set forth in claim 1, in which the primary winding is wound on one leg of said iron core for connection to input terminals and the secondary winding comprising said partially insulated two windings is wound on another leg of said iron core so that alternate adjacent conductor portions in adjacent turns of said two windings may be arranged in opposing relation to each other, one adjacent ends of said two windings being open and the other adjacent ends of said secondary Wire-forming windings being connected to the opposite ends of the winding of one of said two balanced reactors with the neutral point of said one reactor forming one output terminal.

4. A slide reactor device as set forth in claim 1, in which one adjacent ends of said two windings .are open and the winding of one of said balanced reactors is connected to the other adjacent ends of the two windings whereby the neutral point of said reactor winding may form one input terminal.

5. A slide transformer or a slide reactor device as set forth in claim 1, in which said slidable contactor assembly comprises a wider slidable contactor and a narrower slidable contactor which are spaced from each other with a distance smaller than the distance between two alternate adjacent conductor portions of each of said two windings, said narrower contactor being connected through a linear or nonlinear impedance element associated therewith directly to said wider contactor or through a separate linear on non-linear impedance element as- References Cited UNITED STATES PATENTS 920,925 5/1909 Darlington 3237-48 3,090,906 5/1963 Jablonsky 323-43.5 3,302,098 1/1967 Perrins 32343.5

JOHN F. COUCH, Primary Examiner G. GOLDBERG, Assistant Examiner U.S. Cl. X.R.

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