US2086855A - Electric valve converting system - Google Patents

Description

J y 37- c. DEGOUMOIS 2,086,855 @LECTRIC VALVE CONVERTING SYSTEM 7 Filed July 5, 1955 2 sheets-sheet 1 ,July 13,1931,

c. DEGo'u Mols ELECTRIC VALVE CONVERTING SYSTEM Fil'e'dJuly 5, 1955" 2- Sheets-Sheet 2* Patented July 13, 1937 UNlTED STATES FATENT QFFIE to Aktiengeseiischaft Brawn Boveri & Ilia,

Baden, Switzerland, a joint-stock company of Switzerland Appiication .lu'iy 5, 1935, Serial No. 29,956 In Switzerland July 12, 1934 16 Glaims.

The present invention relates in general to electric valve converting systems, and more particularly to means for reducing the detrimental effects of local circulating currents in electric valve systems operable for transmitting energy in either direction of flow between two electric lines or circuits of different electrical characteristics.

Electric valves are frequently associated with suitable apparatus for constituting translating systems, connectible between electric current circuits, for converting energy to be translated therebetween, such circuits being either both alternating current circuits or both direct cur- 13 rent circuits or more frequently an alternating current and a direct current circuit. When the system must be adapted to transmit energy in either direction of flow, it is generally necessary to provide therein two circuits including separate valves or separate elements of a common valve, and such circuits frequently form a path for the flow of local circulating currents which increase the energy losses in the system. Such currents need not be completely suppressed, but should at least be controlled to reduce the detrimental effects thereof. Such result is most advantageously obtained by providing inductive means for the flow of useful current through the system, and in bridging such inductive means by one or more suitable capacitive circuits for sub stantially diverting the alternating components of the circulating current from the valves proper. The valves may then be so controlled that the unidirectional component of the circulating current is reduced to any desired extent.

It is therefore one of the objects of the present invention to provide an electric valve translating system for transmitting energy in either direction of flow between electric lines, in which the alternating components of the circulating ourand capacitive elements.

Another object of the present invention is to provide an electric valve translating system for transmitting energy in either direction of flow between electric lines, in which the unidirectional component of the circulating current may be reduced to any desired extent by controlling the operation of the valves.

50 Another object of the present invention is to provide an electric valve translating system for transmitting energy in either direction of flow between electric lines, in which the adjustment of the operation of the valves may be varied 55 either by the action of the control electrodes rent are reduced by the combination of inductive thereof, or by altering the connections of the valves in the system, or by both methods.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawings, in which:

Fig. l diagrammatically illustrates one embodiment of the present invention operable for transmitting energy in both directions of flow between an alternating current circuit and a direct current circuit;

Fig. 2 is a diagram of some of the voltages and currents present in the circuits of the embodiment illustrated in Fig. 1; and

Figs. 3, i and 5 diagrammatically illustrate modified forms of the tuned elements utilized in the embodiment illustrated in Fig. 1.

Referring more particularly to the drawings by characters of reference, reference numerals i, "la designate a pair of electric valves constituting part of a translating system utilized for 20 controlling the flow of current between electric circuits or lines 8 and 9 of diiierent electrical characteristics. The valves may be of any of the types known in the art and are each provided with one or more anodes ll, lid and with a cathode 52, Mic, but each valve structure may also be replaced by a plurality of valves each comprising one of the anodes and a separate cathode enclosed within a separate casing. Lines 8 and 9 may carry current of any desired form, the translating system being arranged in a suitable manner depending upon the nature of the current to be transmitted therethrough. In the embodiment herein illustrated, line 8 is assumed to be a polyphase alternating current line and line 9 a direct current line. Line 8 is accordingly connected with valves "i, la through transformers i3, iiia, each having a winding M, I ia, connected with line 8 and another winding i6, i'a having phase portions severally connected with anodes ii, lid and connected in star to form a neutral point. At least one of transformers 53, 53a is preferably of adjustable voltage ratio, such adjustment being effected by suitable means such as taps provided on winding Ma to thus operatively vary the connection of valve la with line 8.

Assuming that valve l is to transmit energy from line 8 to line 9 and that valve la is to transr mit energy from line 9 to line 8, cathode l2 and O the neutral point of winding 16a are then connected with the positive conductor of line 9, cathode ltd and the neutral point of winding l6 being connected with the negative conductor of such line. The operation of both valves, or at least of valve under control of control electrodes severally associated with the anodes oi the valve or valves, and which may be of the type causing the associated cathode to become emissive if a plurality of valves are substituted for each of valves 1 and Such control electrodes are herein represented as grids ll, Illa severally connected with the associated cathodes through the phase portions of star connected windings i8, 18:: of transformers ill, l9a having their primary windings 2i, Zia energized from line 8 through phase shifters 22, 22a. The how of current through the control electrode may be limited to the desired value thereof by means of resistor 23, 230, connected between the neutral points of windings l3, 98a cathodes l2, Cathodes i2, lfia are provided with suitable means for bringing and maintaining such cathodes in electron emitting condition, such means being well known and therefore not shown.

The system is so connected as to inherently form a local path for the flow of circulating current from the negative conductor of line 9 through winding 9 valve winding liict and valve la back to the negative conductor of line 9. Such path comprises suitable inductive means such as reactors E l, 24a so connected and di mensioned as to carry the flow of useful direct current between the associated valves 1, la and the positive conductor of line 5. A capacitive circuit co nected across such Lductive means cooperates therewith to render the useful current a d the circulating current more uniform. In e emboo nt illustrated -1g. 1, such circuit consists of capacitors 2G, severally connected across reactors 2 m through adjustable reactors 2's, 21a, and dimensioned as set forth hereinafter. Although all reactors are represented as having magnetic cores, some or all of such reactors may have cores provided with air gaps, or may even be of the air corc type.

The useful current flowing through the syst-em may be further smoothed by means such as further reactors E3 and capacitors 29 connected across line 9, and constituting resonant circuits tuned for the frequencies of some of the a1 nating components of such curre as is well known. Line 3 is assumed to be connected with suitable generators and vith current consuming devices (not shown) whereby such line may alternately constitute a supply line or an output line for the translating system. Line 9 is connected with suitable load devices, such as a motor 3! also operable as a generator to return energy to line 8 through valve la.

The operation of the system will be more clearly understood from a consideration of Fig. 2, in which sine wave 32, read with respect to its axis 33, represents the voltage present between one of anodes H and the neutral point of winding The voltages of the other anodes of valve l are represented by other sine waves displaced in time with respect to sine wave 32. Assuming the valve to be or" the discontinuously controllable type, phase shifter 22 may be adjusted to cause each control electrode E? to vary the conductivity of valve l by releasing the flow of current through the associated anode at variable times of the voltage cycle thereof, without affecting the conductivity of the anode path during the flow of current therethrough. An adjustment will be assumed such that the operating periods of successive anodes are defined by the intersections of the anode voltage curves, the voltages of the anodes successively in operation under substantially no load condition then being represented by curve 3d constituted of successive peaks of the anode voltage curves. Valve 1 then operates in the same manner as in the absence of control electrodes, and the analysis of operation of the system given hereinafter will also be applicable to a system employing a valve without control electrodes.

The voltage appearing between cathode l2 and the neutral point of Winding I6 is equal at every instant to the voltage between the anode then in operation and such neutral point, less the arc drop in valve 1, and may therefore be represented by curve 34 read with respect to an axis 38 distant from axis 33 by an amount representative of such are drop. Modifications in the operation of valve 1 resulting from readjustments of phase shifter 22 to vary the conductivity of the valve will readily be determined by those skilled in the art.

If transformers i3 and l3a are assumed to be wound to have the same ratio of transformation, the voltage between the anodes Ha and the neutral point of winding l6 may also be represented by curve 32 and the other similar curves considered above, as is well known. The conductivity of valve 1a must however be so controlled by control electrodes Ila that the operating periods of the anodes occur during negative half cycles of the anode voltages as above defined. The voltages of the operating anodes then follow a curve such as curve 31 consisting of successive portions of sine waves. The voltage present between cathode I 20. and the neutral point of winding [6a, which is equal to the anodeto-neutral voltage plus the arc drop in valve 1a, is then represented by curve 31 when read with respect to axis 36, the arc drops in valves 1 and la being usually substantially equal.

The voltage impressed n the local path is then the algebraic sum of the voltages present between cathode I2 and the neutral point of winding [6 and between cathode [2a and the neutral point of winding [6a, and is therefore represented by the algebraic sum of the ordinates of curves 34 and 31 each read with respect to axis 36. Such sum is represented by curve 38 drawn with respect to an axis 39. If the local path were substantially non-inductive, a pulsating current would flow therein of the same wave shape as the positive portions of curve 38. As a result of the presence in such path of reactors 24, 24a, such current will become an undulatory continuous current having a unidirectional component of magnitude equal to the average ordinate of curve 38, represented by line 4|, divided by the resistance of the local path, and having alternating components of joined amplitude less than the value of such unidirectional component. Such current is apt to reach considerable intensity and may then cause excessive losses in the system as the result of the flow thereof through the local path and more particularly through valves 1 and 1a included therein.

Such circulating current may be controlled by varying the conductivity of valve 1a or of both valves, but such adjustment may be utilized only within certain limits to avoid interfering with the safe commutation of the anode currents in valve la. The circulating current may be decreased in the first instance by increasing the phase voltages of winding Elia by changing taps of winding Ma. The voltage present between cathode Ma and the neutral point of winding |6a is then represented by a curve 42 read with respect to axis 36, and the voltage impressed on the local path is then represented by curve 43 obtained, by the same process as curve 38, from curve 62 instead as from curve 3i.

The operating condition of the system will be considered more in detail assuming that Valve "l supplies useful current to line 9 and motor 3!. The voltage between cathode l2 and the neutral point of winding l is then represented by curve 44 obtained from curve 36 by taking into account the effect of the overlap of successive anode currents. Valve Ea carries no useful current, and curve re ins substantially unaltered provided that the circulating current in the local path maintained at a comparatively low value. The voltage impressed on such path is then represented by curve 56 obtained by the same process as curves 38 and Curve db may be reolved into a plurality of compon nts, including a unidirectional component of magnitude re resented by line il and a principal alternating component represented by a sine wave 4 8 of axis having a frequency of predetermined value f, any other alternating components thereof being assumed to have no material effect upon the operation of the system. In the present embodiment, windings it and its being six phase windings, curve 48 is a sixth harmonic of curve 32.

It has been found that if only reactors 2%, 24a were utilized to reasonably limit the flow of current resulting from such alternating voltage component, such reactors would have to be of size as to increase the cost of the system to an excessive extent and also to cause the occurrence of excessive losses as a result of the flow of useful current therethrough. To overcome such disadvantages, the reactors are jointly tuned to resonance with the capacitive circuit comprising capacitors no, Zila, and reactors 2 E, Zl'a or the frequency, of value f, or" the voltage represented by curve 438. Such result is obtained by separately tuning reactor 2d with reactor 2'l and capacitor 26, and by also tuning reactor with reactor 22's and capacitor 255: to resonance for such frequency. If L is the value of the inductance of reactor E l, L1 the inductance of reactor 2'! and C the capacitance of capacitor 26, the resonant condition of such elements is expressed by equation w (L+L1)C=l, wherein m has the value 271").

Such resonant condition could also have been obtained by using reactor 26 and capacitor 26 only to the exclusion of reactor ill. From the above equation however it appears that the addition of reactor 21 which is usually compare. tively inexpensive, permits reducing the size of reactor and of capacitor 2% and thus decreasing the cost of the installation. In addition, re-- actor 221i and capacitor 2c are not conveniently made adjustable, and the imperfect tuning which will generally be obtained therewith may conveniently be perfected by adjustment of reactor 21 In general, the resistan e of reactor 2 is small compared to the resistance R of the capacitive circuit includin reactors 2i and capacitor it, the resistance R is also small compared with he reactance of reactor Under such conditions the impedance ofierecl by the reactors and the capacitor to the flow of current of frequency f is in the nature of a resistance substantially .equal to (wL) /R and is considerably greater than the reactance of value wL obtainable by means of reactor 2 alone. Such impedance substantially prevents the flow from valve 1 to line 9 of a material alternating current component of frequency f, which would otherwise be present. Reactor E la; and Na and capacitor 26a are similarly adjusted to resonance to substantially prevent the fiow of material alternating current component of frequency from line 9 to valve lo: the two groups of tuned elements are however primarily designed to cooperate to substantially prevent the flow of curent of frequency f through the local path, wherein such groups serially connected and therefore have cumulative eifects. Alternating current components of high frequencies, which tend to flow in lesser amounts through such path, are also affected by these two groups of elements, but to a lesser extent than the component of frequency f. In gen eral, however, such components of higher frequency are thus reduced to such values as to be negligible and may be further reduced by means of additional tuned circuits if desired.

Reactors fi l and 25a and valves l and in then carry a circulating current having a unidirectional component caused by the unidirectional voltage component ll of voltage it, such current having a value represented by line as with respect to an axis 5b in Fi ure 2. The voltage component -38 of frequency 1 which is impressed across reactors 24 and 25a causes the flow through such reactors only of an alternating current component of frequency f lagging substantially 99 behind the voltage and represented by curve of axis Such alternating component is diverted from the local path substantially to the exclusion of valves l and is by flowing through capacitors and reactors 27, 27a, where such current appears as a leading current represented by curve 53. The undulatory circulating current flowing through such path is then re duced to a substantially uniform current having a unidirectional component as and a residual iii-phase alternating component of frequency represented by curve 53 of axis 49. Such alternating component is smaller than the component st in the proportion of R to (0L. As the opera tion of the tuned elements would be disturbed by the valve action of valves l, la if the flow of circulating current tended to reverse through such valves, winding E la and phase shifters 22 and 22a are so adjusted that the flow of circulating current through the local path is continuous, or in other words, the unidirectional current component must be of greater amplitude than the alternating component 53. As component 3 may be reduced to any desired extent by making the resistance of the capacitive circuit small with respect to the reactance of reactors 24, the unidirectional current component may also be reduced to an extent such as to render the losses caused by the flow thereof negligible in amount.

It has been found in practice that if the cost, the impedance and the losses of a pair of reactors utilized alone for limiting the flow of alternating current in path 25 be taken as units for the purpose of comparison, then tuned elements dimensioned as above described may be designed to increase the impedance of the local path in the ratio of four and one-half to one, while costing only one-half of the price of reactors and causing only one-half of the reactor losses during the flow of useful current therethrough. The unidirectional component of the circulating current may then also be reduced substantially in the ratio of four and one-half to one by adjustment of winding Ma and of phase shifters 22 and 22a.

In the embodiment partially illustrated in Fig. 3, reactors 24 and 2451. are provided with a common core or, if such reactors are of the air core type, their windings are arranged in such proximity as to be in mutual inductive relation. The windings of reactors 21 and 21a are also shown as being in mutual inductive relation. Such modification of the reactors is more effective than the construction illustrated in Fig. l but may not always be utilized, as the joint reactors become larger than each of separate reactors, thus rendering their manufacture more difiicult and the cooling thereof less efficient.

As shown in Fig. 4 reactors 24 and 24a may also be bridged by a single capacitor 54 in series with a single reactor 56, the capacitive circuit thus constituted being tuned with the reactors 24 and 24a. taken jointly for the frequency f of the principal alternating component of the circulating current.

In the embodiment illustrated in Fig. 5, the tuned elements already shown in Fig. 1 are bridged by a likewise tuned combination of a reactor 5'! with a capacitor 58 cooperating therewith in carrying the circulating current.

The operation of these three modified embodiments is entirely similar to that of the embodiment illustrated in Fig. 1 and need not therefore be considered in detail.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that Various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. An electric valve translating system connectible between electric circuits of different characteristics to transmit energy in either direction of flow therebetween and forming a local path for the flow of a circulating current, inductive means in said path for the fiow of useful current and said circulating current through said system, and means cooperating with the said inductive means for rendering both the useful current and the circulating current more uniform.

2. An electric valve translating system connectible between electric circuits of different characteristics to transnnt energy in either direction of flow therebetween and forming a local path for the flow of a circulating current, inductive means in said path for the flow of useful current and said circulating current through said system, and a capacitive circuit connected across said inductive means and cooperating therewith for smoothing the fiow of the useful current and of the circulating current.

3. An electric valve translating system connectible between electric circuits of different characteristics to transmit energy in either direction of flow therebetween and forming a local path for the flow of a circulating current, inductive means in said path for the flow of useful current and said circulating current through the system, and a capacitive circuit connected in parallel with the said inductive means and tuned .therewith to resonance for the frequency of an alternating component of the circulating current.

4. An electric valve translating system adapted to transmit energy in either direction of flow between electric circuits of different characteristics and forming a local path for the flow of an undulatory circulating current, inductive means in said path for the flow of useful direct current and said circulating current through the system, and means cooperating with said inductive means for rendering the useful current and the circulating current more uniform.

5. An electric valve translating system adapted to transmit energy in either direction of flow between electric circuits of different characteristics and forming a local path for the flow of an undulatory circulating current, inductive means in said path for the flow of useful direct current and said circulating current through the system, and a capacitive circuit connected across said inductive means and cooperating therewith for smoothing the flow of the useful current and of the circulating current.

6. An electric valve translating system adapted to transmit energy in either direction of fiow between electric circuits of different characteristics and forming a local path for the fiow of an undulatory circulating current, inductive means in said path for the flow of useful direct current and said circulating current through the system, and a capacitive circuit connected in parallel with the said inductive means and tuned therewith to resonance for the frequency of an alternating component of the circulating current.

7. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from said direct current line to said alternating current line, the system forming a path serially including said valves for the fiow of an undulatory circulating current, inductive means in said path for the flow of useful direct current and said circulating current through the system, and a capacitive circuit connected in parallel with the said inductive means and tuned therewith to resonance for the frequency of an alternating component of the circulating current.

8. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from said direct current line to said alternating current line, the system forming a path serially including said valves for the flow of an undulatory circulating current, adjustable means for controlling the operation of said valves to cause impression of a voltage having a unidirectional and an alternating component on said path, inductive means in said path for the flow of useful direct current through the system and for the flow of a substantially uniform circulating direct current caused by the unidirectional voltage component, and a circuit for conducting the flow of alternating current caused in said inductive means by the alternating voltage component substantially to the exclusion of said valves.

9. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from said direct current line to said alternating current line, the system forming a path serially including said valves for the flow of an undulatory circulating current therethrough, adjustable means including means for varying the connection of one of said valves with said alternating current line tocause impression of a voltage having undirectional and alternating components on said path, inductive means in said path for the flow of useful direct current through the system and for the flow of a substantially uniform circulating direct current caused by the unidirectional voltage component, and a circuit for conducting the flow of alternating current caused in said inductive means by one of the alternating voltage components substantially to the exclusion of said valves.

10. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from said direct current line to said alternating current line, the system forming a path serially including said valves for the flow of an undulatory circulating current, adjustable means including means for varying the conductivity of one of said valves to cause impression of a voltage having a unidirectional and an alternating component on said path, inductive means in said path for the flow of useful direct current through the system and for the flow of a substantially uniform circulating direct current caused by the unidirectional voltage component, and a circuit for conducting the flow of alternating current caused in said inductive means by the alternating voltage component substantially to the exclusion of said valves.

11. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from said direct current line to said alternating current line, the system forming a path serially including said valves for the flow of an undulatory circulating current, adjustable means including means for varying the connection of one of said valves with said alternating current line to cause impression of a voltage having unidirectional and alternating components on said path, inductive means in said path for the flow of useful direct current through the system and for the flow of a substantially uniform circulating direct current caused by the unidirectional voltage component, a circuit for conducting the flow of alternating current caused in said inductive means by the alternating voltage component substantially to the exclusion of said valves, and a connection from said direct current line to a point intermediate the terminals of said inductive means for the flow of useful direct current through either of said valves.

12. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from said direct current line to said alternating current line, the system forming a path serially including said valves for the flow of an undulatory circulating current, adjustable means including means for varying the conductivity of one of said valves to cause impression of a voltage having a unidirectional and an alternating component on said path, inductive means in said path for the flow of useful direct current through the system and for the "flow of a substantially uniform circulating direct current caused by the unidirectional voltage component, a circuit for conducting the flow of alternating current caused in said inductive means by the alternating voltage component substantially to the exclusion of said valves, and a connection from said direct current line to a point intermediate the terminals of said inductive means for the flow of useful direct current through either of said valves.

13. In an electric translating system, an alter nating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from sai v current line to said alternating current system forming a path serially including said valves for the flow of an undulatory circulating current, adjustable means including means for varying the connection of either one of said valves with said alternating current line and including means for varying the. conductivity of either one of said valves to cause impression of a voltage having a unidirectional and an alternating component on said path, inductive means in said path for the flow of useful direct current through the system and for the flow of a substantially uniform circulating direct current caused by the unidi ectional voltage component, a circuit for conducting the how of alternating current caused in said inductive means by the alternating voltage component substantially to the exclusion of said valves, and a connection from said direct current line to a point intermediate the terminals of said inductive means for the flow of useful direct current through either of said valves.

14. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from said direct current line to said alternating current line, system forming a path serially including said valves for the flow of an undulatory circulating current, adjustable means for controlling the operation of said valves to cause impression of a voltage having a unidirectional and an alternating component on said path, inductive means in said path for the flow of a sub stantially uniform circulating direct current caused by the unidirectional voltage component, a circuit for conducting the flow of alternating current caused in said inductive means by the alternating voltage component substantially to the exclusion of said Valve, and adjustable inductive means in said circuit for tuning said circuit to resonance with the first said inductive means for the frequency of the alternating voltage component.

l5. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve for transmitting energy from said direct current line to said alternating current line, the system forming a path serially including said valves for the flow of an undulatory circulating current, adjustable means including means for varying the connection of either one of said valves with said alternating current line and including means. for varying the conductivity of either one of said valves to cause impression of a voltage having a unidirectional and an alternating component on said path, in-

ductive means in said path for the flow of useful direct current through the system and for the flow of a substantially uniform circulating irect current caused by the unidirectional volt age component, a circuit for conducting the flow of alternating current caused in said inductive means by the alternating voltage component substantially to the exclusion of said valves, a con nection from said direct current line to a point intermediate the terminals of said inductive means for the flow of useful direct current through either of said valves, and adjustable inductive means in said circuit for tuning said circuit to resonance with the first said inductive means for the frequency of the alternating vol age component.

16. In an electric translating system, an alternating current line, a direct current line, an electric valve for transmitting energy from said alternating current line to said direct current line, an electric valve. for transmitting energy from said direct current line to said alternating current line, the system forming a path serially including said valves for the flow of an undulatory circulating current, adjustable means for controlling the operation of said valves to cause impression of a voltage having a unidirectional and an alternating component on said path, inductive means in said path for the flow of useful direct current through the system and connected at an intermediate point thereof with said direct current line, capacitive circuits severally connected between the terminals of said inductive means and said intermediate point, another inductive means connected across the first said inductive means and cooperating therewith for carrying a substantially uniform circulating direct current caused by the unidirectional voltage component, and capacitive circuits severally connected in parallel with the portions of the first said inductive means and with the second said inductive means and severally tuned with the associated inductive means for the frequency of 20 the alternating voltage component.

CHARLES DEGOUMOIS.

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