US2595024A - Contact arc suppression - Google Patents

Description

Ap 1952 P. M. G. TOULON CONTACT ARC SUPPRESSION 4 Sheets-Sheet 1 Filed Jan. 14, 1949 April 1952 P. M. G. TOULON CONTACT ARC SUPPRESSION 4 Sheets-Sheet 2 Filed Jan. 14, 1949 INVENTOR.

P!ERRE M. G. TOULON April 29, 1952 P. M. G. TOULON CONTACT ARC SUPPRESSION Filed Jan. 14, 1949 4 SheetS-Sheet 3 1 PIERRE M. G. TOULON April 29, 1952 P. M. G. TOULON 2,595,024

CONTACT ARC SUPPRESSION Filed Jan. 14, 1949 4 Sheets-Sheet 4 INVENTOR.

PIERRE M G. TOULON Patented Apr. 29, 1952 CONTACT ARC SUPPRESSION Pierre Marie Gabriel Touln, Paris, France, as signor to Products & Licensing Corporation, New York, N. Y., a corporation of Deiaware Application J anuary 14, 1949, Serial No. 79,926 In France J anuary 19, 1948 1.!) Claims. 1

The present invention relates to a new method and apparatus for breaking electrical circuits, which carry currents of a relatively high in tensity, without the resultant emissicn of sparks or arcs.

The invention relates more particuiariy to the separation of contacts through which flows a strong current, without initiation of an arc, such as usually coeurs between such contacts.

The invention is applicable more particularly to break switch systems for industrial currents at high voltage and current, as well as to all electrical machines which present the problem of commutation, and in which the invention would permit the suppression of sparks resulting therefrom.

According to the general concept of the invention, a rectifier is inserted in series with the break switch in the first case, or with the commutation brush in the second case; and previous to the break, or to the commutation, an auxiliary voltage is introduced into the circuit (voltage which will be designated in the text as countervoltage), and in the opposite direction to the one which causes the current, and of an amplitude which would only need to be at least equal to it, but which may be greater.

The combined actions of the counter-vcltage and of the rectifier have the effect of bringing about a progressive reduction of the current to zero, which operation permits the separation of the contacts without any sparks; because of the rectifier the counter-voltage, no matter what its amplitude, can never reverse the current in the circuit and thereby prevent the desired result, since no current in the reverse direction can be caused to fiow through the rectier. Of course, this rectifier must be inserted into the circuit in such a way as not to obstruct the flow of normal load current.

This concept of using counter-voltage of any.

value whatsoever, permits one to generate this counter-vcltage by means of a generator of relatively very simple design and which requires no precise regulation, a gencrator which on the other hand rentiers the operation very certain.

In case electromotive forces should appear in the circuit that one is seeking to open, resulting from variation in current in that circuit, one should give to the counter-voltage a minimum amplitude sufiicient to compensate these electromotive forces, in addition to those which exist normally in the circuit. This situation occurs notably if the circuit offers a certain self-induction, as in the case of commutation machines. The counter-voltage must be released in an excessively short time, and this brings about the passage 01' very strong instantaneous currents.

In crder to obtain abruptly the very great powcr one needs at the desired moment, the

invention provides a preferred means to introduce this counter-voltage, without requiring a mechanically controlled device. Specifically, I employ an are in air relay, based upon the use of two spark gaps, placed at a certain distance one from the other, with an electron control device situated in the vicinity. This relay requires only an infinitesimal amount of energy to control a large current.

According to a variant of the invention, the current is reduced in the circuit at the contacts which are to be separated, by making it pass progressively in a line shunted on this circuit:

in this case, the counter-vcltaga may be introduced either directly into the first circuit, or into the shunt, in reversing the polarity.

In the case in which one applies the invention to a circuit breaker switch, a variation of the invention consists of putting a rectifier in series with the switch, and of branching in parallel to this circuit a condenser in series with a coil into which has been introduced the countervoltage in question. The eiect of this latter is to switch the current progressivcly from the switch towards the condenser, which is progressivcly charged and the switch is opened when the current in the contacts has completely stopped. The effect of this is that the condenser continues to be charged, until it has balanced the voltage of the network. The condenser employed must be consequently capable of handling the total voltage of the network, and it must on the other hand have great enough capacity to be able to absorb suificient charge.

T0 recluce the size of this capacity, according to another variation of the invention, the operation of circuit opening may be executed in two steps, by twice following the procedure to which the invention relates. Tvvo interrupters arranged in series one with the other are utilized. Th opening of the first interrupter brings about a primary' reduction of the current, by inserting a resistance in series. Afterwards the second interrupter is opened, thereby completely opening the circuit, in the same way as has been described in the variation mentioned above.

The arrangement consists therefore in introducing in series with the principal interrupter, an auxiliary circuit opening devise with a shunt in parallel,- which will have an appropriate resistance. In conformity with the procedure already described, all of the current is diverted into this shunt and the auxiliary interrupter is then opened. A resistance is thereby inserted into the circuit, the efiect of which is to reduce the current to a-small fraction of its original value.

The principal interrupter then comas into use, and one succeeds in cutting the current without producing sparks by diverting momentarily the current into a condenser, in the manner already described above. But the current to be annulled being much weaker, the required size of condenser is notably reduced.

The invention is applicable also to cases in which the break is due to an accidental cause, for example, a short circuit. The invention provides in this case means, controlled by the abrupt increase in current, to introduce a circuit in shunt with a breaker switch, and to .SWitch the current into the latter, the resistance of the shunt preventing the current from acquiring dangerous proportions.

According to a variation of the invention, in a case where it would be applied to a rectifier or to the commutator of a D.C.-=A.C. rotary trans-' former, each brush ordinarily used is replaced by two rotary brushes which bear on the fixed segments, and which Will be coupled to the secondary of a transformer laid out in so many rows; and in series with each brush is connected a rectifier and a coil into which a voltage may be induced.

One applies alternately in the circuit of these brushes a counter-voltage for reclucing progressively the current of the brushes. This operation begins before the brush has left its segment; and the counter-voltage is introduced by means of a source of voltage controlled by the rotation of the brush.

According to a prefzerred variation of the invention, this Voltage is applied by means of a transformer whose secondary has its terminals connected to the brushes. The brushes are driven by a motor, synchronized With the frequency of the network. The shaft of this motor drives a small alternator which will furnish a frequency in synchronism with that of the network. This Irequenoy is used to feed the primary of the auxiliary transformer.

The alternator may be either two-phase, in which case there is required only two rows of brushes, or poly-phase, for example hexaphase, in which case the steps are arranged on six independent rows regularly shifted with respect to one another.

The drawirigs accompanying the text will help in understanding better the new method, to which the invention relates, together with the means employed for its execution.

Figure 1 illustrates an embodiment of the invention which employs a rectifier and an auxil iary voltage, to suppress current fiow at the moment et circuit opening.

Figure 2 represents, as a function of time, the currents and voltages in the diierent circuits of Fi ure 1.

Figure 3 illustrates a variant of the, system 01 Figure 1, in which two parallel circuits are employecl.

Figure 4 is a circuit diagram of a system for breaking current at high voltage, in accordance with the invention.

Figure 5 is a circuit diagram of a system for providing protection against short-circuits, in electrical systems, in accordance With the invention.

Figure 6 illustrates the application of the invention to a high tension commutator.

Figure 7 illustrates a perfected variant of the system of Figure 6, utilizing a polyphase commutation voltage.

Figure 8 illustrates on a greatly enl&rged scale, 2. portion of the r0Ws of brushes, showing et. ea ch 4 instant the relative position of the brushes in relation to the commutator segments.

In referring to the accompanying drawings, l provide examples, which are not limitative, of the invention in operation.

Figure 1 is a circuit diagram of a system which illustrates the principle of the new procedure to which the invention relates. W may be a source of either continuons current. or of. variable current, provided however that the frequency of this current be relatively small in relationship to the speed of the phenomena occurring in the system. This source fiows into a circuit presenting a resistance N and an inductance L. The problem that 1 propose to solve is that 01 interrupting the current by means of an interrupter C (whose points 01 contact have been represented by semicircles in the drawing) without any sparks being produced at the moment of the interruption.

In conformity With the invention, a rectifier R placed in series with the circuit, oriented in such et direction that it 1ets the current flow normally, and a device U (generally the secondary of a transformer) is introcluced in which one can momentarily cause to appear a tension X, thanks to an exterior device G (for example by throwing into the primary of the transformer U a variable current).

Let us call i the current which circulates in the circuit, and E the voltage betvveen one of the terminals of source W and a terminal of the interrupter C.

According to the invention, the current which circulates in the contactor C is annulled by generating, by means of the device G, a voltage U, which will be equal to or greater than E.

In Figure 2, the first curve, 2a, represents as a function of time, the voltage U.

The curve, 2b, represents, in function of time, the voltage at the terminale of the rectifier R; the third curve, 2c, represents, as a function ci time, the current 2; and the fourth curve, 2:1, represents as a function of time, the voltage be tWeen the electrodes of the contacter C.

Let us suppose that one wishes to interrupt the current 2' at the time T1, the generator G induces progressively in U a voltage, which, in conformity With the invention, exceecls the voltage E. In proportion as the voltage U increases, the current i is reduced progressively. If the voltage U is greater than W, the current 2' is annulled. At the time T2, beginning With this moment, the rectifier assumes a voltage of reverse polarity, as shown on curve 2b. Thanks to the pres ence of the rectifier R, the current romains zero from T2. At any time whatsoever, for example, at the moment T3, one may separate the two points of contacts C without any sparks being produced.

The voltage between the electrodes C, which is at first nul], increases progressively and attains finally, after a fairly long time, the value W (time T4). Meanwhile the voltage at the terminals of the rectifier, which was originally equal to Va at the moment of the cutting oi, cornes progressivcly back to zero.

The instant of the cutting off, 'I3, may be set anywhere in the interval XX, during which the voltage induced by G on U furnishes a voltage greater than W.

In all cases, sepamtion of the contacts C does not cause any spark resulting from the break, since, because of the rectifier B, the current flowing in the circuit h as not been able to reverse itself, and since the current is consequently zero.

The invention solves therefore the problem of breaking current fiow, without sparks, the only condition being that the induced voltage generated in U be sufficiently high.

Figure 3 illustrates a variant of Figure 1, in which two circuits in parallel are employed. This system is particularly interesting when the input voltage W is very high and when one is trying to break the circuit without using too high tensions U.

We find again in this figure, the supply voltage W, the resistance N, the inductance L, in which circulates the current X 2, but instead of only one circuit, I utilize two parallel branches, a first branch, U1, R, C, traversed by the current il, and a second branch U2, traversed by the current i2. We designate as above, by E the voltage across U1+R+C. According to this second variant, the generator G can induce either a voltage U1 et the opposite sign to E, in one of the parts branches of the circuit or a voltage U1, of the saine sign as E, in the other branch.

In conformity with the invention the voltage provided by generator G has the eifect of annulling the current 7:1, and of thereby permitting the separation of the contacts C without sparks or arcs resulting from the break.

Figure 4 illustrates in detail a system corresponding with the systems schematically illustrated in Figure 3, as applied to the interruption of a high voltage circuit.

Let us suppose that the source W feeds a circuit l including an inductance 3, and a resistance 2; and in conformity with the invention, a

rectifier 4, in series With contacts 5, both in parallel with a winding 6 and the resistance 1. Let, us call E1 the tension et the terminals of these two circuits in parallel With each other, and in series with the latter a rectifier [2 and contacts l3, with a circuit in parallel With the latter comprising a.transformer 14 and a condenser I5, and let E2 be the voltage across the latter parallel circuit.

To induce in the transformer 6 a transient voltage in Figure 4, I employ a source of continuous current Il, feeding, across a high resistance l0, a condenser 9. The discharge of thecondenser 9 can, in the primary coil of transformer 6, be obtained at the moment desired, thanks to the switch 8.

T induce in the coil l4 a transient voltage, I employ a source Il, feeding, across a high resistance Il, a condenser 16. The discharge of the condenser l6 in the primary winding of the transformer [4, may be initiated at the moment desired, by means of the device F2 contained in the block 8l. This device comprises two electrodes l8 and [9, between which an arc may arise, and an electrod 20 placed in the vicinity of these two electrodes, and the potential of which controls release of the arc. This potentia1 of the electrode 20 is modified by utilising a small auxiliary source 2l, a resistance, and a small auxiliary switch 22.

Let us examine first the operation of the first system of breaking contacts 5. In conformity with Figure 3, one succeeds in discharging in the parallel branch 61, all of the current 2', which, until then, could circulate in the two branches in parallel at the same time.

The opening of the contacts has. the effect of inserting in the principal circuit et resistance, which in turn has the eifect of reducing consid- 6 erably the current I. The operation of this system has already been described in connection with Figure 3.

Let us consider now the operation of the second system of opening contacts [3. On account of the capacity 15, which is progressively charged, there is induced in condenser 16 a voltage equal instantaneously to the voltage E2. Beginning with this moment, it is possible to open the contacts [3, because if the fiow of the current 72 is totally utilized to assure the charging of the condenser l5, and if no current circulates in the contacts l3, but, to the contrary of the preceding case, the current i can now arinul itself, because, after a certain time, the charging current of the condenser l5 terminates and the total voltage W appears at the terminals of the condenser.

The two step operatioh above described is of great interest, because the condenser must have a capacity large enough to take a charging current as great as the current which is to be interrupted. In the case where the current is great, one is led to employ very great capacities.

The voltage at the terminals of these condensers corresponds finally to the voltage W, it is necessary that the break clown voltage of th condenser be very high; it follows that the price of these condensers is very high.

In reducing at first, by means of the resistance 1, the current 2' to a fraction only of its original value, one reduces the necessary capacity to the same extent. Instead of a single pair et contacts 5 and a single resistance 1, one can very well, evidently, place several of them in series, and one Will reduce then successively the current, for example: to /3, to ,6, to /27, etc. of its value. The same rectifier 4 and the same coil 6, can successively be utilized to carry out these successive insertions by employing a suitable switch.

In a case where the system must b used as break switch, the closing of the switch 8 (or 3),

which assures the discharge of the condenser 9 (01' IS), must be very rapid and it is necessary that this switch, which permits a very strong instantaneous current to pass, be controlled by a minimum current. The relay spark gap shown in the block *8 is therefore of great interest, because it has no movable parts and it can operate in an extremely short time, and is not slowed by the mechanical inertia cf parts. Its operation is based upon the observation of the following physical phenomenon: if a ring 20 is installed in the vicinity of two electrodes, for example, two bars of tungsten, between which a r'ather strong diflerence in continuous potential, one observes that for a certain distance of the electrodes a spark shoots forth or on the contrarv does not shoot forth, according to the potential of the electrode 20 in relationship to one of them, for example, the electrode l9. If the voltage cf the ring is of the same sign as that of electrode I3, the spark has a tendency to prime itself much sooner and for a much less great distance of the electrode than if the tension is of the opposite sign. A variation in voltage of a few hundred volts applied to the electrode 20, is thus sufiicient (for a judicious distance of the prinicpal elec trodes I8 and l9), to enable flow of th current.

Figure 5 is a variation of Figure 4,'more ecpecially adapted to protection against short circuits. Crie finals again on this diagram the same principal elements (source W, load 2, contacts [3, rectifier l2; and a coii I in which is induced the voltage U, etc.)

The short circuit of the line is represented in the Iorm of switch 25, When this short circuit 15 produced, the generator W has a tendency to give out a much stronger current than th normal one. But, thanks to the self-induction 3 of the generator and of the line, this current increases progressively and relatively slowly.

In conformity with the invention one utilizes this increase to open the contacts l3, which inserts very rapidly into the circuit a resistance 24, having the eifect cf limiting the augmentation of the current to an admissible value. In conformity with the invention, one installs in series with this resistance 24, a coil I, in which a variation of current flow is provoked, which has the efiect of balancing completely the current which was fiowing until then. There is shown at 12, as previously, the rectifier which prevents the current from reversing itself in the contacts [3.

There is shown, at 28, in the form of a relay, the element Which controls the intensity, either for the absolute value appropriately high of the current, or for the eifect of its rapid increase. There is shown, at 2", the coil of the mechanism 26 which eects separation of the contacts [3.

Th relay 28 closes the switches 29 and 30. The switch 30 has the effect of closing the circuit of the first transformer I4, the current in which annuls momentaneously the current in the contacts I3. I utilize the discharge of a condenser H5, maintained at high voltage by a source Il, through a resistance Il. The switch 29 closes the circuit of an auxiliary battery 31 and applies current to the C011 2! which actuates the mechanism 26, for opening contacts 13. Because of the self-induction of the coil 28 (and of the inertia of the mechanism 25) the separation of the contacts l3 is produced noticeably at the moment when the variation of current flow (due to the discharge current of the condenser l6) attains its maximum, that is to say at the moment when th voltage in the secondary M passes through its maximum. The resistance 24 is chosen to have a value comparable to that of the resistance 2, in such a way that, in case of a short circuit, the current after having momentarily exceeded slightly the normal value corne progressively back to it aiter a fairly short time. Of course, one can join to this system of protection against short circuits and excessive voltage anormal system of breaking the current ,such as is described in Figure a, this latter having the purpose of limiting t a very short time interval the duration of the passage of the current in the resistance 24 (Which must as a matter of fact, collect a considerable quantity of calories per second) This last group is then released automatically, immediately iter the putting into service of the first.

Figure 6 shows the application of the system of Figure 3 to a system of rectification cf alternating triphase current into a continuous current.

The triphase feeding current is supposed to excite a coil winding 31, in the form of a ring gramme immovable in space. Rotary brushes driven by a little synchronous motor Will rub against this ring.

In order not to complicate the dravving unnecessarily, the wires of the primary power sources have not been shown, and the ring 8 nected respectively to the segments 34 and to the segments 35, arranged alternately on two coaxial rows.

On these rows run respectively the rotary brushes 32 and 33. In series with the brush 32 is a rectifier R1; and in series With the brush 33 is a rectifier R2. The other terminals of the rectifiers R1 and R2 are connected respectively to the terminals of a group of two secondary coils SI and S2. The junction of these two coils, ar ranged in series, are bound to the load W.

The brushes 32 and 33 are supposed to turn at the speed of synchronism, by a mechanism which is not shown and which comprises a synchronous motor driven by a shaft coupled to the brushes.

This mechanism drives also a group of symmetrical brushes, not shown. To simpliy the diagram, only one brush 40 has been shown at the bottom of the drawing, in order to make clear how the circuit is closed, but it must be admitted evidently that the disposition of the circuits in the lower part of the drawing, is exactly analogous to that described above.

The arrangement comprising a single group of brushes (such as d) running in synchronism, is well known in the art.

The use of a single positive and a single negative brush, such as 49, causes, as is known, a difiicult commutation problem.

The procedure of the invention, which makes freedom from arcs and sparks possible, solves this problem completely.

As a matter of tact, the two brushes 32 and 33 utilized in conjunction With the coils S1 and S2 (in which one induces an appropriate voltage) and associated with the rectifiers R1 and R2, assure, as a matter of fact, a perfect commutation, even for Very great voltages.

To create the appropriate voltage necessary to efiect sparkless commutation, one feeds the primary P by means of an alternator G, whose fre quency corresponds to half of the frequency of commutation, that is to say, to the product of the number of steps of the segments 34 (or of the segments 35) by the frequency of the feeding network of the ring gramme. The voltage generated in the secondary windings Si and S2, has the eifect of annulling alternately the current of the brushes 32 and 33.

I arrange the steps (or sections) in relationship to the brushes, in such a way the brush gives forth no current from the moment when it is going to leave the section and that this current is only produced after it rests in full on the following section.

While one of the brushes, such as 32 is discharged, the other, such as 33, receives all the current given forth by the circuit or vice versa.

There has been previously mentioned the selfinductance and the resistance of the circuit, as has been already represented by R and L. This self-inductance L can be considerable without any inconvenience, being given that the current is never interrupted, but is only carried integrally alternatively from one brush to the other. One profits by the moment when each brush is discharged, to connect it from one step to the following and this commutation is effectuated without any arc.

The turns in course of Commutation are designated on the drawing by .36. Being given that these turns present a certain self-inductance the commutation is not instantaneous, and it is necessary to provide for this a rather large period cf overlapping of the sectors in order to leave enough time for the current, which was fiowing by one of the brushes, to be entirely carried over on the other. This time is so much the greater as the current is itself higher, that is to say, the machine is charged more and one is obliged to foresee very large sectors, which fact renders the isolation between these sectors difficult.

In the examples mentioned with the figures, I have presented the case of 2. machine rectifying a current and giving a voltage of given polarity, but it is evident that in changing the direction of the rectifiers R}. and R2, the appliance may be used in the reverse way, that is to say, as a wave generator, on the condition that voltages of appropriate phases are induced on the coils S1 and S2.

Figure 7 illustrates a variant of the system of Figure 6, but instead of using an arrangement, in form of a ring, I use simple monophase transformers, appropriately connected. The system is applicable also to the case of a rectifier permitting the transformation of the energy of a triphase source il to a source of continuons currnt at high voltage 68. I multiply the number of phases of the triphase distribution by means of a number of static transformers. In Figure 7, use is made of 12 monophase transformers, the primaries of which are connected in a triangle, 4.2, and in a star, 43, and the secondary windings 44, 45, 4&6, 41, 48, 49, 511, 5l, 52, 53, 54, 55, of which were connected in series, in such a way as to constitute a polygon with 12 sides (resembling a ring gramme). Suppose that on each of the secondaries of each transformer are 5 equidistant contacts which are connected alternately to the sectors il, I2, I3, 14, I5, "5, alranged in fixed independent rows. On these rows suppose that two groups of brushes I1, 18, le, 853, 8l, 82, and H, I8, I9, 8D, 81, 32, are disposed at 180 one from the other. T0 simplify the drawing, one has not shown junction rings between the fixed and rotating parts. These brushes are fixed a common rotating frame 60 driven at the speed of synchronism, by means of a small synchronous motor 64, fed by the sector 4l.

in conformity With the invention, I install on the axis of the motor 64, a little alternator, 63, of commutation without sparks, in conformity With the new patened procedure. The receptacles are connected alternately to 6 independent rows il,l2,l3,l4, 15,16. The steps of these rows are shifteol one in relation to the other by of the distance which separates the axes of two successive sectors.

In conformity with the invention, I install on the axis of the motor 64, an alternator 63 furnishing a triphase voltage 84, the frequency of this alternator being equal to the product of the number of steps situated on each row by the number of rotations per second efiectuated by the frame 60. With the assistance of the power source 84, I feed the primaries 85 and 85 of the two polyphased transformers. The secondaries 86 and 86 are connected each in a 6 branched star, the neutral points of these stars connected to the terminals of the load. Each of the phases of each of the secondaries feeds a rotary brush, across arectifier, such as 81 and 81. The direction of this rectifier is established in such a fashion that the current can only circulate in it in the desired direction of the feeding of the load 10 circuit 68, when the system is used to feed this circuit with continuous current.

The rectifiers in liaison with the transformers 86, are sufiicient to assure sparkless commutation, as has already been described above. The alternator 63 carries with it an excitation shunt field winding 86, but preferably, it has also an excitation series field winding 61, so that the voltage induced in the transformers and 85' augments a great deal with the charge, and this assures excellent commutation no matter what the charging regime: as a matter of tact, the voltage of self-induction induced in the windings during commutation increases with the charge, and it is therefore advisable to create an auxiliary commutation voltage, to assure the commutation without sparks, proportionately greater as the charge is greater.

Figure 8 represents, on a large scale, and in their respective positions, the sectors of the different rows il, I2, 13, 74, 15, 16 on which the 6 brushes 11, I8, 19, 80, al, 82, contact.

In idle running or with a weak charge, the current begins to circulate in one brush (such as 11) as soon as the voltage of commutation furnished to the brush surpasses that of the preceding brush and the brush ceases to pass current /6 period after.

The current in the brush 11 only increases slowly and when the electromotive force of selfinduction is equal to that of the voltage of commutation, one may observe in the intensity a level run. It is only when the current attains in the following brushes, a notable current that the current is progressively reduced, and it only stops slowly. The commutation time is found to be considerably augmented, nevertheless, thanks to the new disposition, several brushes 2 or 3 for example, such as I1, I8, I9, can give current forth simultaneously. Because of this, for a machine of a given power the current in each brush is considerably reduced. Vice versa, for a given dimension of the brush, it is possible to design a much more powerful machine.

On the other hand, the isolation between the successive steps may be much greater. As a matter of fact, as can be seen on Figure 8, there is represented at 88, the position of the brush in relationship to the step 1]. There is shown on the other hand, at 89, the slope which permits the brush to mount progressively on the following step, and where, consequently, the contact may be bad. It is only when the brush occupies the position Il, that the current can begin to circulate without disadvantage in the brush. one may see, in Figure 8, in the most disadvantageous position that the remaining distance remains considerable.

In the examples mentioned (for example, in the case of Fig. 6-) one has only represented a machine destined to transform alternating current into a continuous voltage of known polarity; but it is evident, that one could obtain a polarity in the opposite direction by changing the shifting of the brushes on the synchronous motor at the same time as that of the rectifiers R1 and R2; it is also evident that the appliance may be used as an A.C. generator on condition that the direction of the rectifiers R1 and R2 and the phases of the voltages induced in the coils S1 and S2 are chosen appropriately. In a more general way still, one can advantageously replace the rectifiers, each one by 2 thyratrons arranged in inverse parallel, the grids of these thyratrons serving to block alternately, at will, the working of one or the other of the little rectifiers: one can thon with this appliance change, at will, the frequency, the amplitudes of the currents and tensions, etc.

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

1. An electrical circuit interrupting system comprising a source of voltage, a load circuit, a pair of normally closed circuit making and breaking contacts, a rectifier poled to pass current in response to said voltage, means connecting in series said source of voltage, said load circuit, said contacts and said rectifier, means for temporarily impressing in opposition to said voltage an auxiliary voltage at least as great as said fi1st mentioned voltage, and means for thereaiter opening said contacts, whereby said contacts are opened during a condition of zero current flow in said load circuit.

2. A system for interrupting fiow of electric current in a high voltage circuit, comprising, in combination: means for interrupting said circuit, means for generating a transient voltage having a polarity opposite to and in magnitude at least as great as said high voltage, means for impressing said transient voltage in said circuit, rectifier means connected in said circuit and poled to prevent reversal of Current fiow in response to said transient voltage, and means for actuating said means for interrupting during said transient voltage 3. A system in accordance with claim 2 Wherein said transient voltage is connected in series With said means for interrupcing.

e. A system in accordance with claim 2 wherein said transient voltage is connected in parallel with said means for interrupting.

5. A system for interrupting the fiow of electrie current in a circuit at high voltage, comprising, in ccmbination: means for interrupting said circuit, means for generating a transient voltage, said last means comprising a condenser and a primary winding of a transformer connected in series, a secondary winding coupled to said primary Winding, means connecting said secondary winding in said circuit, said transformer being adapted and arranged to induce into said secondary winding a transient voltage opposing said fiow of electric current in response to discharge of said condenser and of magnitude greater than said high voltage, rectifier means connected in said circuit and poled to prevent reversal of said electric current in response to said transient voltage, and means for actuating said means for interrupting during said transient voltage.

6. A system for interrupting fiow of electric current in a high voltage circuit, comprising, in combination: first means for interrupting said circuit, second means for interrupting said circuit, said first and second means connected in series in said circuit, et resistive circuit shunting said first means for interrupting, means for reducing transiently t zero voltage existing across said first means for interrupting, means for actuating said first means for interrupting to interrupting condition during said zero voltage, said electric current then fiowing to said second means for interruptin via said resistive circuit, means for reducing current fiow in said circuit to zero for an interval of time, and means operative during said interval of time for actuating 12 said second means for interrupting to interrupting condition.

7. A system for interrupting fiow of electric current in a high voltage circuit, ccmprising, rst means for interrupting circuit, a first reetifier in series with said first means and poled to conduct said current in response said hign voltage, a resistance, an inductancc, in ans connecting said resistance and inductance in series Wilh each other and in shunt with said first means for interrupting and said first rectifier, second means for interrupting circuit, a second rectifier in series with said second means for interrupting and poled to conduct said current in response to said high voltage, a condenser, a second inductance, means connecting said condenser and said second inductance in series with each other and in shunt to said second means for interrupting and said second rectifier, means for inducing in said first inductance a transient voltage adapted to reduce current fiow in said first means for interrupting to zero and for actuating said first means for interrupting t0 interrupting condition during said transient voltage, and means for thereafter inducing in said second inductance a further transient voltage adapted to reduce currnt fiow in said second means for interrupting to zero and for actuating said second means for interrupting to interrupting condition during said further transient voltage.

8. The combinaticn in accordance with claim 7 whercin each of said means for inducing comprises a condenser, a winding, means for charging said condenser to a predetermined potential, and means for rapidly discharging said condenser into said winding to provide a rapid rate of change of current in said winding.

9. A commutator system, comprising, a ring transformer, a plurality of pairs of ring segments, a pair of moving brushes each contacting successive corresponding ones of said pairs of ring segments, means connecting predetermined points of said ring transformer to predetermiued ones of said ring segments, means for inducing alternating current in said ring transformer at irequency f, means for actuating said brushes at a rotative velocity of f rotations per second, a rectifier connected in series With each of said brushcs, a transformer having a primary winding and a secondary winding, means connecting said secondary winding between said rectifiers, and means for energizing said primary winding With current at frequency f.

10. A system in accordance With claim 9 wherein is further provided a brush making continuons contact with said ring transformer. means for rotating said last mentioned brush at frequency f, a load circuit, and means for connecting said load circuit between said last mentioned brush and a center point of said secondary winding.

PIERRE MARIE GABRIEL TOULON REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,188,361 Koppelmann Jan. 30, 1940 2,195,818 Koppelmann et al. Apr. 2, 1940 2,293,296 Jonas Aug. 18, 1942 2,301,752 Schulze Nov. 10, 1942 2,358,926 Hansen Sept. 26, 1944

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