US2141943A - Electric circuit - Google Patents

Description

Dec. 27, 1938. suns 2,141,943

ELECTRIC CIRCUIT Filed Nov. 13, 1937 1 if E 15 6 [7 E ([mprarsed) Inventor: Chauncey G.Suits b iw y i y His Attorney.

PATENT OFFICE ELECTRIC cmcorr Chauncey G. Suits, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application November 13, 1937, Serial No. 174,481

12 Claims.

My invention relates to alternating current circuits and more particularly to electric circuits which have nonlinear volt-ampere charactcristics and are operated under a condition of nonlinear resonance.

It has been known for some time that certain unusual resonance effects occur in circuits employing capacitances in combination with inductances having closed iron cores which are adapted to saturate magnetically within the operating range of the circuit. Various characteristics and applications of the series-type nonlinear resonant circuit are disclosed in Reissue 'Patent 20,317 granted March 30, 1937, upon my application and assigned to the assignee of the present application. The series-type of nonlinear resonant circuit is generally characterized when subjected to a gradually increasing voltage of constant frequency by a sudden change in effective current at a critical value of applied voltage which I designate as the "resonant" voltage of the circuit. Similarly, for a gradually decreasing voltage at constant frequency the effective current decreases critically at a certain voltage which I designate as the dissonant" voltage. When the same circuit elements of the above-described series-type circuit are connected in parallel relation, it has been found that in general the properties of the circuit are analogous to those of the series type circuit except that the functions of current and voltage are reversed. This type of circuit is disclosed in Patent 1,994,326 granted March 12, 1935, and assigned to the assignee of the present application.

When circuits of the above-mentioned types are used for example, in operating relays, electric valves, or magnetic amplifiers, it has been found desirable in certain applications to increase the current ratio or voltage ratio of the circuit for the dissonant and resonant conditions of the circuit.

It is an object of my invention to provide a new and improved nonlinear resonant circuit.

It is another object of my invention to provide a new and improved nonlinear resonant circuit which shall exhibit a higher ratio between the low value and the high value of an electrical condition of a nonlinear resonant circuit which changes abruptly at a critical value of a difierent electrical condition of the circuit than is obtainable with nonlinear resonant circuits as heretofore utilized.

It is a further object of my invention to provide a new and improved nonlinear resonant circuit control means which shall provide a higher ratio between the "on" and "off" condition of the control means than has been heretofore available with circuits of this type.

It is a still further object of my invention to provide a new and improved nonlinear resonant circuit and nonlinear resonant circuit control means in which the ratio between the high and low value of the abruptly changing electrical condition is obtained without the employment of moving parts or moving contacts.

In accordance with the illustrated embodiments of my invention, I effect an increase in the current or voltage ratio of the nonlinear resonant circuit by establishing a resonant condition, or tuning the circuit at the fundamental frequency of the circuit with respect to the reactance element of the circuit which causes the relatively high value of the abruptly-changing electrical condition when the circuit is in the dissonant condition so as to decrease the dissonant current or voltage prior to the nonlinear resonant condition. With this correlation of the circuit elements, the voltage or current components of reactance elements are additive after the circuit goes into nonlinear resonance by reason of distortion and the consequent presence of harmonies so that the high value of the abruptlychanging electrical condition is increased over that of the corresponding electrical condition of elementary nonlinear resonant circuits in the nonlinear resonant condition,

My invention will be better understood by reference to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Figs. 1 and 3 are diagrammatic illustrations of embodiments of my invention as applied in a series-type nonlinear resonant circuit; Fig. 2 is an explanatory diagram for the embodiments of my invention illustrated in Figs. 1 and 3; Fig. 4 is a diagrammatic illustration of an embodiment of my invention as applied in a parallel-type nonlinear resonant circuit, and Fig. 5 is an explanatory diagram for the embodiment of my invention illustrated in Fig. 4.

Referring to Fig. 1 of the drawing, [0 indicates a source of alternating current which is connected to energize a series-type nonlinear resonant circuit comprising a series connected resistance H, a saturable inductance I2, and a capacitance I3. The usual practice heretofore has been to connect the relay winding or device to be controlled in series with the inductance and capacitance, or preferably to connect the the capacitance.

Fig. 2 illustrates by the dotted line X the voltampere characteristic of the usual series-type nonlinear resonant circuit. In this figure, the impressed voltage of the source i0 is plotted as abscissae and current I flowing in the resistance ii is plotted as ordinates. The ordinates may also be considered to represent the voltage Ec of the capacitor i3 as a function of the voltage E applied to the circuit. The line A on the curve is shown, by way of example, as the voltage required, positively to pick up the armature of a relay and the line B as the voltage required positively to drop out the armature of the relay. In most cases, the ratio between this high value A and the lower value B is sufficiently great for satisfactory operation of relays. In practical cases A may be from two to ten times as large as B. There have been cases, however, where it has been desirable to provide a much larger ratio for energizing the device to be controlled.

In accordance with the embodiment of my invention illustrated in Fig. 1, I energize the device to be controlled, which is illustrated as a relay ll having a winding l5, a core l8 and contacts l1, across the capacitance i3 and a portion of inductance l2. The object of this particular connection is to subtract a portion of the inductance voltage drop from the voltage drop of the capacitance which is opposite in phase. In other words, I select sufficient turns of the inductance to obtain a resonant condition with the capacitance l3 at the fundamental frequency of the circuit to obtain minimum voltage across the relay during the dissonant condition of the circuit and before the inductance becomes saturated sufficiently to cause an appreciable wave form distortion in the circuit. The decrease in the value of E0 just before nonlinear resonance is illustrated by the full line curve Y. It;was not anticipated, but was found in developmental studies, that the voltage A was raised instead of lowered, thus increasing the ratio between the low value and the high value of the abruptly changing electrical condition which in this case is represented by the current of the circuit I or the voltage Ec across the condenser. It is my belief that the voltage A is raised instead of lowered for the reason that when the circuit goes into nonlinear resonance, the inductance i2 is highly saturated and causes marked wave form distortion of the current and voltage. As a result, prominent third harmonics of the fundamental wave are produced in both the capacitive and inductive elements, whereas for the connection shown in Fig. 1 the fundamental components of the capacitive and inductive voltages are of opposite phase, the third harmonics are of like phase, and when present they are additive. They are present only in the high current or resonant condition of the circuit and act to increase the voltage applied to the relay winding in that case. In the dissonant condition of the circuit the wave form distortion is negligible, as noted, and only the phases of the fundamental components need be considered, and these are subtractive for the connection of Fig. 1. In a practical case, the ratio of voltage applied to the relay may be more than doubled. A 30:1 change in condenser voltage Ec for a three per cent change in line voltage E has been measured.

In Fig. 3 I have shown an embodiment of my invention in a series-type nonlinear resonant circuit, comprising the source II, the inductance i2 and the capacitance l3, wherein the relay I4 is v-unflwvu. w w yucsa lcu Au wuca rciuuun Will]. the circuit rather than in accordance with a voltage varying as a function of the current as in Fig. 1. In this embodiment a modification of the simple series-type nonlinear resonant circuit to obtain the greater current ratio is obtained in a manner analogous to that of the embodiment shown in Fig. 1. In this case it is necessary to supply a component of current through the load device or device to be controlled which will be subtractive from the current normally present. Before the circuit goes into nonlinear resonance, the current in the line is lagging by nearly ninety degrees. In accordance with my invention, I connect a capacitance I I in parallel relation to the inductance i2 and capacitance II. This additional capacitance ll may have a small ampererating compared to the other elements of the circuit so that it draws a leading current which compensates for the lagging current of the inductance l2 at the fundamental frequency of the circuit and before the circuit goes into nonlinear resonance. Another way of analyzing the circuit is to consider that the capacitance II and inductance I! are in parallel resonance at the fundamental frequency of the circuit before saturation of the inductance l2 and that therefore minimum current flows in the series circuit through the winding of relay ll. However, upon saturation of the inductance l2 the current components are additive due to harmonics and the resultant impedance is decreased and the current in the circuit is increased over that of the simple form of the series-type nonlinear resonant circuit. The improvement in current ratio that may be had in this case is comparable to the improvement in voltage ratio that is obtained by the previous method shown in Fig. 1. A developmental embodiment of this arrangement has exhibited by actual measurement a 30:1 current ratio for a few per cent change in applied voltage.

I have also found by investigation with developmental circuits that the voltage ratio' of the parallel-type of nonlinear resonant circuit may be improved by a method analogous to that employed in improving the series-type of nonlinear resonant circuit. In Fig. 4 I have illustrated a practical form of the parallel-type nonlinear resonant network in a circuit comprising a source of alternating current II, and a resistance II which may be a load device. In its simplest form, the parallel-type nonlinear network comprises a saturable inductance and a capacitance connected in parallel relation and in series in the circuit in which current variations are to be used for control, regulation or indication. Since this simple form requires that the capacitance must be relatively large in microfarad rating, I have shown a more desirable form of the parallel-type circuit which comprises-a current transformer I! having its core structure dimensioned to saturate within the operating range of the current to be controlled and provided with taps I9 in its primary winding to adjust the inductance characteristics. The primary winding I! is connected in seriesrelation with the source ll. A resistance 20 and a capacitance 2| are connected across the secondary winding of the transformer l9. With this arrangement the transformer it functions as the saturable inductance element of the parallel circuit as well as a transforming means to improve the capacitance economy. Small changes in the current I of the circuit result in relatively large changes in the current in the transformer secondary or in the voltage E across the primaryorsecondaryooils. 'lhediilere ence voltage between the voltage just before the nonlinear resonant condition and the voltage lust after the nonlinear resonant condition isnot as large as in the analogous series-type of circuit for practical cases. In particular, a voltage ratio greater than 3:1 is not easily obtained.

InFlg.5IhaveshownbythedottedcurveXa typical volt-ampere characteristic of the usual type of parallel-type nonlinear resonant circuit in which the series current of the circuit is plotted as abscisae and the voltage E across the capacitance 2i as ordinates. The ratio of voltage just before and just after nonlinear resonant condition is of the order of 1:3.

In accordance with my invention as illustrated in Fig. 4, I connect a small inductance 22 in series relation with the primary winding of transformer It. The phase of the voltage E across transformer ill just before the nonlinear resonant current is lagging the current by substantially In other words, the current transformer reflects the capacitance in the series circuit as though the capacitance were connected directly in series in the circuit. When the small inductance 22 is inserted in series relation with the primary winding of transformer it, the phase of the voltage across the inductance 22 will be leading the current by substantially 90". In other words, the voltage component across the transformer I! and the voltage component across the inductanee 22 are in opposition and substractive. As a result, the resultant voltage component E: across both the transformer i9 and the inductance 22 is smaller than the voltage across the transformer I9 or the capacitance 2i before the circuit goes into nonlinear resonance. The relay I4 is, therefore, connected to be energized in accordance with the resultant voltage across the parallel nonlinear resonant network and the additional inductance 22. However, in an analogous way to the arrangement shown in Fig. 1 the voltage components across the transformer i9 and the additional inductance 22 are additive when the circuit goes into nonlinear resonance and therefore the voltage E: is higher than in the prior arrangement of this type when the circuit goes into nonlinear resonance due to wave distortion and consequent occurrence of harmonics in the circuit. The increase in voltage ratio obtainable is shown by the full line curve Y in Fig. 5. In a specific case it was observed that the voltage Ea before and after resonance was of the order of 1:13 in contrast to the voltage ratio across transformer is which, as previously stated, was of the order of 1:3.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention and I, therefore, aim 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 as new and desire to secure by Letters Patent of the United States is:

1. In combination, an alternating current electric circuit comprising a saturabie inductance and a capacitance connected in circuit relation for nonlinear resonance to provide an abruptly changing electrical condition of said circuit at a critical value of another electrical condition of said circuit, and means for efi'ecting a resonant condition between certain reactance elements of said circuit at the fundamental frequency of said circuit to obtain a substantially minimum value of said first mentioned electrical condition priorto the condition of nonlinear resonance in said circuit.

2. In combination, an alternating current electric circuit comprising a nonlinear resonant network including a saturabie inductance and a capacitance, andmeans for including a reactance element in circuit with a reactance element of opposite sign of said nonlinear network to provide a resonant condition of said reactance elements prior to the condition of nonlinear resonance of said circuit.

3. In combination, an alternating current electric circuit comprising a nonlinear resonant network including a saturable inductance and a capacitance, and means for including a reactance element in circuit with a reactance element of opposite sign of said nonlinear network, said reactance elements of opposite sign being correlated to provide a resultant electrical characteristic which is equal to the difference between corresponding electrical characteristics thereof at the fundamental frequency of said circuit and to the sum of corres onding electrical characteristics thereof when nonlinear resonance exists in said circuit.

4. In combination, an alternating current circuit, a saturable inductance and a capacitance connected in series relation in said circuit and arranged for nonlinear resonance at a critical value of voltage applied to said circuit, and a branch circuit connected across said capacitance and such portion of said inductance as is sulficient substantially to neutralize said capacitance at the fundamental frequency of said alternating current circuit below the critical resonant voltage of said alternating current circuit.

5. In combination, an alternating current circuit, a saturable inductance and a capacitance connected in series relation in said circuit and arranged for nonlinear resonance at a critical value of voltage applied to said circuit, and an electroresponsive device connected across said capacitance and sufficient turns of said inductance to provide a resultant voltage across said electroresponsive device lower than the voltage across said capacitance below said critical voltage and a resultant voltage across said electroresponslve device higher than the voltage across said capacitance above said critical voltage.

6. In combination, a source of alternating current, a nonlinear resonant circuit comprising a saturable inductance and a capacitor connected in series relation to be energized from said source, and a winding connected across said capacitance and a portion of said saturabie inductance.

7. In combination, an alternating current circuit, a saturable inductance and a capacitance connected in series relation in said circuit and arranged for nonlinear resonance at a critical value of voltage applied to said circuit, and means comprising a second capacitance connected in parallel relation with said saturabie inductance and said first capacitance and having a capacitive reactance sufllcient substantially to neutralize the inductive reactance of said saturabie inductance below said critical value of applied voltage.

8. In combination, a nonlinear resonantcircuit comprising a saturable inductance and a capacitor connected in series relation and having a critical value of applied voltage at which nonlinear resonance occurs, a second capacitor connected saturable inductance and capacitor and having a capacitive current substantially equal to the inductive current of said saturable reactor below said critical value of applied voltage, and a load circuit connected to be energized in accordance with the current to the said parallel-connected circuit elements.

9. In combination, a source of alternating current, a nonlinear resonant circuit comprising a saturable inductance and a capacitor connected in series relation to be energized from said source, a second capacitor connected in parallel relation with said series connected saturable inductance and capacitor and having a volt-ampere rating small relative to the other elements of said nonlinear resonant circuit, and an electroresponsive device connected in series relation with said source and said parallel-connected elements.

10. In combination, an electric circuit, a parallel-type nonlinear resonant circuit comprising a saturable inductance in parallel relation with a capacitance and connected in series with said electric circuit, and a second inductance connected in series relation relative to said parallel connected elements for providing a branch voltage across said parallel connected elements and said series connected inductance which is lower than the voltage across said parallel connected elements prior to nonlinear resonance in m- "AA-VI. u Illucl vunu uuc YUAN- age across said parallel connected elements when nonlinear resonance occurs in said circuit.

11. In combination, an electric circuit, a nonlinear resonant network comprising a saturable inductance and a capacitance connected in parallel relation and in series with said circuit such that a voltage of said network varies a large amount relative to the change in total current to said network, and a second inductance connected in series relation with said network and having an inductive reactance substantially equal to the capacitive reactance oi said capacitance below the condition 01' nonlinear resonance in said circuit.

12. In combination, an electric circuit, a saturable transformer having a primary winding connected in said circuit and being provided with a secondary winding, a capacitance connected across said secondary windingya second inductance connected in series relation with said primary winding and having an inductive reactance substantially equal to the effective capacitive reactance of said capacitance as reflected in said primary circuit prior to the condition of nonlinear resonance in said circuit, and an electric translating device connected to be energized in accordance with the resultant voltage across said transformer and said second inductance.

CHAUNCE'Y G. SUITS.

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