US2041663A

US2041663A - Means for converting alternating current into direct current and vice versa

Info

Publication number: US2041663A
Application number: US586622A
Authority: US
Inventors: Marx Erwin
Original assignee: Individual
Current assignee: Individual
Priority date: 1931-01-22
Filing date: 1932-01-14
Publication date: 1936-05-19
Anticipated expiration: 1953-05-19

Description

E. MARX May 19, 1936. MEANS FOR CONVERTING ALTERNATING CURRENT INTo DIRECT CURRENT AND viCE VERSA Filed Jan. 14, 1952 7 Sheets-Sheet l f 4 4 x/l & I

w a z i AI v W lnll r/n L 2 k May 19,1936. 5 X MEANS FOR CONVERTING ALTEBNATING CURRENT INTO DIRECT CURRENT AND- VICE VERSA Q Filed Jan. 14, 1932 7 t s t 2' Atty May 19, 1936. E. MARX 2,041,663 MEANS FOR CONVERTING ALTERNATING CURRENT INTO DIRECT CURRENT AND VICE VERSA File d Jan. 14, 1932 7 Sheets-Sheet 4 May .19, 1936. E. MARX 2,041,663

MEANS FOR CONVERTING ALTERNATING CURRENT INTO DIRECT CURRENT AND VICE VERSA Filed Jan. 14. 1952 v Sheets-Sheet s voltage V time a mli l q y ay May 19, 1936.

E. MARX 2,041,663 MEANS FOR CONVERTING ALTERNATING CURRENT INTO DIRECT CURRENT AND VICE VERSA Filed Jan. 14, 1952 'r Sheets-Sheet s [77 yew/0 r:

& y [1/13.

May 1 1936. E ARX 2,041,663

MEANS FOR CONVERTING ALTERNATING CURRENT INTO DIRECT CURRENT AND VICE VERSA Filed Jan. 14, 1932 7 Sheets-unset 'T Patented May 19, 1.936

PATENT, OFF-ICE MEANS EOR CONVERTING ALTEBNATING CURRENT INTO DIRECT CURRENT AND VICE VERSA Erwin Marx, Brunswick, Germany Application January 14, 1932, Serial No. 586,622

. In Germany January 22, 1931 34 Claims. (oi. 175-363) My invention relates to means for converting alternating current into direct current and vice versa and more especially to spark gaps adapted for use in equipments of this kind.

It has already been proposed to convert voltages by means of spark gaps. Such-conversion, however, could not be carried out in practice with large current intensities because a regular and secureiextinguishing of the arc could not be obtained since the contacts of the spark gaps were heated by the arc to inadmissibly high temperatures. The same difliculty occurs in spark gaps used in connection with switches or the like. In order to extinguish the are it has been suggested to quench the are by means of dompressed air; however in the known devices, a large quantity of compressed air is required for quenching the arc and even then the arc will not be extinguished with certainty so that an efiicient conversion of voltages and currents cannot be obtained in this manner.

It is an object of my invention to overcome these difficulties.

To this effect I provide a pressure chamber containing spark gap electrodes, means for feeding compressed air to this chamher and a. nozzle-shaped orifice in at least one electrode so that the base point of the arc is driven towards the orifice by the compressed air.

It is a further object of my invention to provide spark gap electrodes with nozzle-shaped orifices and to shape the electrode in suchmanner that the arc is lengthened by the wandering of the base points along the electrode only when the base points have entered the nozzle-like orifices of the electrode. 1

It is another object of my invention to pro- -vide means for rendering efiective the arcquenching means, for instance compressed air, at predetermined moments depending upon the variation of the alternating current to be interrupted.

It is a still further object of my invention to provide means for converting alternating current into direct current and vice versa. comprising spark gaps of the kind referred to and in connection with such converting means to provide means for )nitiating a flash-over in the spark gaps at predetermined times, a

In the drawings aflixed to this specification and forming part thereof some embodiments of my invention are illustrated diagrammatically by way of example.

In the drawings Fig. 1 is a longitudinal section'of a spark gap according to my invention,

Fig. 2 is a longitudinal section of another embodiment of a spark gap showing diagrammatically the piping for the compressed air.

Fig. 3 is a cross section along the line III-HI of the spark gap shown in Fig. 2,

Figs. 4 and 5 are longitudinal sections of two further embodiments of spark gaps according to this invention,

Fig.6 is a diagrammatic view, partly in section,

of another embodiment provided with blow-out coils,

Fig. l, i is a casing of insulating material and 2 and 3 are fixed spark gap electrodes. The electrode 2 is cylindrical and projects with its forward end 4 into the orifice 5 of a transverse insulating wall 6 subdividing the interior of the casing i into chambers l and 8. The electrode 3 is a disc-shaped electrode provided with a nozzle-shaped orifice 9 and a connecting terminal l0.

The operation of this device is as follows: When a flash-over has produced an are between electrodes 2 and 3 and this are shall be extinguished, compressed air is introduced into chamber I by means of a suitable device (not shown). The

, compressed air will flow through .the nozzle 5 into chamber 8. Since the air current is very strong inthe. opening 5, the base point of the arc will be driven towards the fiat portion 4 of electrode 2. 0n the opposite side the. air will 'escape through the nozzle 9 and the air flowing from the chamber 8 to the inlet I l of the nozzle will drive the base point or the arc towards the nozzle inlet. When the base point has reached the nozzle inlet it will be driven with high velocity from the inlet l l towards the flaring portion I2. Be it assumed that the current forming the arc is an alternating current, then the arc will be extinguished when the current passes through zero and the are will not be initiated again since the electrodes have been cooled by the air current and no free Referring now to Fig. 2 illustrating a spark gap operating substantially in the same manner as the spark gap shown in Fig. 1, I3 is a casing of insulating material provided with twometal end walls 14 in which the spark gap electrodes l5 are fitted by means of a slot and key connection I6 so as to permit a longitudinal adjustment of the electrodes. I! are terminal connections. Both electrodes are provided with nozzle-like orifices I! through which the compressed air escapes. is are entering tubes for the compressed air provided in the wall of the casing I 3. The electrodes 15 are shaped in such manner that the flash-over will occur between them at a lower voltage than along the inner wall of the casing l3. The flashover voltage can be adjusted by suitable adjustment of the electrodes l5 within the plates 14. If desired, a periodical displacement of the electrodes can be carried out by means of a suitable drive (not shown).

In order to obtain a uniform heating of the electrodes, they should be shaped in a suitable manner and an air movement should be obtained which causes the compressed air to uniformly contact with all points of the electrode surface. In order to accomplish this, the electrodes l5 have the shape of circles with relatively long radii with curved end surfaces and the compressed air is introduced into the casing 13 by means of tangentially arranged inlets l9 (as shown in Fig. 3) so that a spiral movement of the air occurs as in dicated in Fig. 3 by arrows 20.

In some cases, for instance if the spark gap is used in connection with circuit breakers for large currents, it is not necessary to introduce compressed air into the chamber since the are by its own heat expands the air contained in the chamber to the extent that it escapes through the nozzle orifices of the electrodes in the same manner as compressed air.

If desired the pressure of the compressed air can be controlled in dependency upon the load in order to provide the minimum air pressure required for extinguishing the are, because otherwise the efliciency of the device would be diminished. Preferably in the event of high overcurrents or short-circuited currents the air pressure is momentarily increased which can be accomplished by means of an auxiliary vessel containing compressed air of high pressure and connected with the chamber by means of a pipe containing a valve actuated by means of an overcurrent relay or the like. Preferably this relay should interrupt the auxiliary ignition of the are described herewith.

2| and 22 .are throttles arranged within the nozzles l8 and inlets l3, respectively, in order to control the pressure within the casing 13. The throttle valves may be controlled by suitable devices (not shown) in such manner that during the ignition of the are low pressure exists within the casing and that the air pressure is gradually increased during the burning of the are so that the highest pressure is obtained when the arc is quenched. The air pressure will then rise to its highest value when the maximum voltage stress occurs in the known rectifying direction. In some cases, for instance if an expensive gas is used, it is advisable to recool the gas after it has been used and to feed it again to the pressure chamber. In order to accomplish this, in Fig. 2 the outer openings of the nozzles l3 are closed by means of end walls 23 provided with outlets 24 connected by pipes 23 to a recooling and pumping device 28 from which the recooled gas is delivered to the inlets Is by means of pipes 21. The recooled gas exerts a cooling action on the electrodes. which can be increased if the compressed gas is vigorously expanded in the chamber cooled below condensation temperature. If desired saturated steam might be used which is expanded in the pressure chamber in which case the well known arc-extinguishing effect of expanding saturated steam can be utilized. The chemical reaction properties of the electric arc might also be utilized.

In order to further cool the electrodes feed pipes 28 and discharge pipes 29 for recooling fluid are provided. Cooling water or the like is fed by means of pipes 28 to the interstices 30 formed by the outer wall of the electrodes l5 and the walls of the nozzles I8 so that the electrode surfaces being in contact with the base points of the are are eihciently cooled. Preferably these portions of the electrodes are formed by a metal having a high heat conductivity and high temperature resisting properties.

In order to reduce the ignition voltage and to increase the arcing back voltage, the electrodes are preferably designed with greatly differing shapes as shown for instance in Fig. l and in Fig. 4 to be described hereinafter. In these devices the electrode which is positive during the ignition, is sharply curved while the other elec trode is relatively fiat. In the device shown in Fig. 2 the polarity effect has been renounced too. It should be understood, however, that the different shaping of the electrodes may be used in the device shown in Fig. 2 also.

In order to increase the efficiency of the spark gap particularly in order to adapt it to large outputs, the spark gap should be designed in such manner that the are burning between the electrodes is relatively short and that it is lengthened immediately before extinguishing the are which is preferably done a short time before the arc current passes through zero.

A device for accomplishing this is shown in Fig. 4 in which 3| is an insulating casing formed on the inner surface of its mid portion with ribs 32. Each electrode consists of two parts, one

surrounding the other. The outer parts 33 and 34 of the electrodes are fitted to the outer ends of the casing 3| by means of a screw thread 35 and 36 so that they are displaceable in longitudinal direction. The members 33 and 34 are hollow cylinders with tapered

front portions

31 and 33. concentrically within the members 33 and 34 are provided, the

electrodes

39 and 40, each being provided with a nozzle-shaped orifice 4| and 42, respectively, and fitted in the end Walls of the members 33 and 34 by means of screw threads 43 and 43', respectively, so that they are longitudinally displaceable with respect to the members 33 and 34 and to the casing 3|. Compressed air is fed through inlets 44 and enters the spaces 45 and 46-between the

electrodes

39, 40 and the members 33, 34, respectively. The compressed gas flows with relatively high velocity through the narrow slots 41 and 48 between the tapered portions 31 and 38 of the members 33 and 34 and the

electrodes

33 and 40 and enters the space 43 between the electrodes in which the air velocity is relatively small. The base points of the are are thus driven relatively slowly into the nozzles 4| and 42 of the electrodes. The air pressure and the velocity, the latter by means of throttles 50 provided within the inlets 44 and the outlets 5| for the gas, are controlled in such manner that the base points of the arc reach the nozzles 4| 42 a short time before the current passes through zero. If necessary the distance between the electrodes and the cross-section of the gaps 41 and 48 can be adjusted by displacing the members 33, 34 of the

electrodes

39 and 40. The optimum adjustment can be ascertained by means of a wattmeter indicating the power dissipation of the arc. The adjustment of the single parts is correct if 'the wattmeter shows a minimum power.

If necessary the adjustment can be effected in a different manner for the single electrodes. The adjustments can be carried out if desired during service.

Referring now to Fig. 5, 60 is the casing containing the electrodes GI and 62 provided with nozzle-like openings 63 and 64. 65 is a sleevelike movable electrode which can be advanced by means of an actuating-rod 66 so that it is pushed over the electrode 6|. Therefore during service no are forms and in order to interrupt the current the movable electrode 65 is withdrawn preferably before the current passes through zero. An arc will then be established between the electrodes 6| and 62 and will be quenched in the manner described in connection with Fig. 1. The compressed air is fed into the casing 60 by means of inlets 56.

In order to avoid non-uniform consumption of the electrode metal during operation it is necessary to cause the base points of the arc to travel along the electrodes. This can be obtained also by means of magnetic fields. I am aware that it is well known to provide magnetic fields in connection with arcing devices, the magnets being arranged in an axis perpendicular to. the axis of the electrode in order to lengthen the arc and to blow it out. In the present case, however, such an arrangement would not be advisable since with very high voltages the distance of the magnet winding from the electrode must be made very. large in order to avoid flash-overs. In order to avoid this drawback I arrange themagnet coil within the electrode and impart to it the same potential as to the associated electrode. Thus the magnet winding can be located very closely to the arc and magnet fields can be produced which are sufiiciently powerful to obtain a high supplies, for instance accumulators feeding the energizing current for the coil 12 by means of connections 14 and I5. 16 are angular casings enclosing the magnet windings and filled with an insulating cooling fluid. The casings are rotated together with the electrodes and. magnet windings by means of a shaft 11 rotated in a suitable manner, for instance by means of a gearing 18. Near the ends of shaft 11 gear wheels 19 are provided which mesh with toothed rings secured to the outer walls of the casings 16. In order to maintain connection of the terminals of the windings 12 with the connections 14 and I5

metallic slip rings

81 and 82 areprovided withinthe walls of the insulating casings 16, each slip ring being in contact with a pair of contact brushes for instance 83, connected to connection I5 and winding 12, respectively. The main current isfed to the electrodes 10 in a similar manner by means of a pair of

contactbrushes

85, 86, and a slip ring 81 provided near the inner wall of the angularcasing. 'As will be seen from the foregoing, by energizing the windings l2 and rotating the casings '16 together with the magnets and the electrodes the base points ,of the arc will travel in circular paths along the surfaces of the electrodes. In order. to drive the base points towards the inlets of the nozzle H U-shaped iron rods 88am provided embracing the windings in the manner shown in Figs. 6. and 8. As seen from Fig. 8 these rods are inclined to the circumference of the windings so as to-produce magnetic flux lines indicated in dotted lines in Fig. 8. Flux-lines of this are driven towards the inlet of nozzle 1|.

It should be understood that in order to energize the windings any desired current supply,

.for instance a generator or transformer, might be used. If desired, the windings could be energized with a port of the main current. An arrangement of this kind is shown in Fig. 7, the means for rotating the electrodes being omitted for the sake of simplicity.- The main current is fed to the electrodes 10 through

connections

90 and 9|. 92 is a resistance connected in the connection 90, this resistance being preferably of the kind the value of which is dependent upon the voltage, for instance decreasing with increasing voltage. The windings 12 are connected in parallel with resistance 92 and to eachother by means of

connections

93, 94, 95 and'96. In this embodiment "the electrodes 10 are formed as hollow electrodes provided with inlets 98 and 99 for feeding and discharging the cooling liquid.

The operation of the'device shown in Figs. 6-8 is substantially the same as the operation of the device shown in Fig. 1, except that by means of the magnet windings and the rotation of the electrodes a travelling of the base points of the arc is obtained as explained above.

It should be noted that the windings 12 might be replaced by a not-conductive, not magnetic ring provided with a winding. The magnetic field thereby produced could drive the base points of the arc to the nozzle inlet in a straight line. If the electrodes are moved or rotated simultaneously a suflicient arc velocity is obtained.

The invented spark gaps can be excellently employed where periodic ignition of an arc, prolonged burning of an arc, its dependable quenching within a certain time, as well as the requisite safety against re-ignition are necessary, viz. in particular for converting multi-phase alternating current into direct current and vice versa. This converting process can be effected by connecting one or several spark-gaps, complying with the invention, to each phase of the multiphase system.

At suitable moments, an arc must be produced at these spark-gaps and again quenched at a later moment. To secure an approximately constant direct current, it is firstly necessary that the production of the arc in one phase takes place when the arc in the previous phase still persists. This transition of the current of one phase to the next is in itself difiicultjto realize with the spark-gap rectifying process. However, according to the invention, this transition is appreciably facilitated in that the initiation which sends an ignition current over the sparkgap to be bridged) or mechanically (e. g. by moving the electrodes towards each other entirely or partly bridging the space between the electrodes, etc.) Themoment when ignition of each phase has to be eiiected anew in each period must, however, be accurately determined. The choice of the most suitable moment as well as the practical accomplishment of accurate ignition will be explained by means of an example in which electrical auxiliary ignition is selected.

Referring now to Fig. 9 illustrating a device for converting three-phase current into direct current, I00, IM and I02 are the secondaries of a three-phase transformer the primaries of which are not shown in the figure for sake of simplicity. The secondaries are connected star-fashion and the star point I03 is connected to ground. I04, I05 and I06 are condensers shunting the secondaries I00, IOI and I02 respectively for a purpose to be explained hereinafter. The secondaries I00, IOI, I02 are connected to choke coils I01, I00, I09, respectively. The latter are connected to rectifying spark gaps IIO, III, II2,

respectively. The spark gaps are connected to the direct current line II3 leading to the direct current load indicated at I I4 and being connected to ground. The spark gaps IIO, III and H2, are preferably designed in the manner described in connection with Figs. 1-8 The arcs are initiated by means of an auxiliary ignition device described hereinafter. In some cases, for instance, if positive and negative direct voltage is produced and an appreciable capacity exists between the direct current line and ground, it is advisable to connect the star point I03 not to ground but directly to the direct current load H4. The ripple of the'direct voltage, particularly if the number of phases is odd, is then very small. Before describing the auxiliary ignition device reference is had to Fig. 10 showing a diagram in which the abscissa is the time and the ordinate the voltage. The sine curves I00, IOI, and I02 indicate the voltages of the secondary windings I00, IM and I02. At the time ti the voltage of secondary I is at its peak value and at this time secondary I00 delivers current through choke coil I01 and spark gap IIO into the direct current line II3. If the load H4 is an ohmic resistance, the current is substantially proportional to the voltage of the secondary winding I00. At the time t: the voltage of secondary I00 has dropped below the voltage of secondary IOI having increased during the time intervals t1 and t2. At this moment, as will be explained hereinafter, the arc is initiated in the spark gap III so that a positive current is fed from secondary IOI to the direct current line II3. Since at this time the voltage of IilI exceeds the voltage of I00. the direction of the current in the spark gap IIO will be reversed and the arc extinguished as explained above in connection with Figs. 1-8. As will be seen from Fig. 10, the time at which the arc in the park gap III is initiated, somewhat lags behind the time at which the voltages of the secondaries I00 and II are equal. This slight difference of time has an optimum value depending upon the character of 2,041,003 which has' to be quenched must compulsively the direct current load. It is therefore advisable to design the auxiliary ignition device for the spark gaps in such manner that this difference of time can be adjusted preferably even during service.

Referring new again to Fig. 9 the arcs in the spark gaps I I0, III and H2 are initiated in the following manner: The terminal of the secondary I00 is connected to an intermediate point II of the choke coil I 09 by means of a resistance IIS and a capacity II1 connected in series. H8 is a rotating spark gap connecting the intermediate points of resistance H6 and capacity I I1 to a point I IQ of choke coil I09 intermediate point H5 and the terminal of the choke coil connectedto the spark gap I I2. Secondary winding I02 is connected to inductance I08 in a similar manner by means of resistance I20. capacity I 2I and rotating spark gap I22. Secondary IN is connected to choke coil I01 in an analogous manner by means of resistance I23, capacity I24 and rotating spark gap I25. Each rotating spark gap consists of two fixed electrodes, for instance I26 and I21 in spark gap I25 and a rotating arm carrying a pair of electrically connected movable electrodes. The rotating arms of the spark gap IIII, I22 and I25 are shifted towards each other about 60 and they are adjusted in such manner that each rotating spark gap initiates a flash-over at the moment when the corresponding main spark gap should be ignited. For instance the rotating spark gap I22 should initiate a flash-over at the moment t2. At this time condenser' I2I is loaded to a voltage equal to 1%; peak value of the alternating voltage provided that resistances II6, I20, I23 are not too large. When rotating spark gap I22 initiates a flash-over, an oscillation is produced which causes a flash-over between the contacts of the main spark gap III. The oscillations are drawn off from the secondary IN by means of the by-pass condenser I05. Some time after the arc of spark gap III has been initiated, the rotating spark gap II8 will initiate the arc in spark gap I I2 and the arc of spark gap III will be extinguished. The arc of spark gap IIO will now be initiated by the rotating spark gap I25 and the arc of spark gap I I2 will be extinguished and so on. If it is desired to adjust the difference of time between the ignition of an arc and the moment at which the phase of the arc has the same voltage as the preceding phase, the arms of the rotating spark gaps should be somewhat shifted.

If desired the rotating spark gaps II 8, I22 and I25 can be united into a single rotating spark of which is inserted into the circuit comprising I capacity I24 and rotary spark gap I25, the other being inserted into the main line between secondary I00 and spark gap IIO. Instead of this the ignition of the spark gap might be obtained by means of voltage shocks, a sinusoidal voltage or the like.

The ignition time can be adjusted in a corresponding manner it conversion is effected by be made to coincide as regards time.

and with which the path of the arc is periodically opened by shields, etc., or with which ignition and are quenching is eifected by other mechanical ways. In this instance, three processes must Namely, the moment indicated in Fig. 10 as is must, in view of the above reasons, coincide with ignition of the arc in one phase and on the other hand with the artificial quenching ofthe arc in the previous phase. If we-consider a mechanical rectifier, then in such case .the electrodes must be shaped and set in such a manner, that at the moment t2 the electrodes of the phase IilI come inclosest proximity, and the electrodes of the phase I60 go away from each other.

Similar conditions obtain-in the case of converting direct current into alternating current.

In this instance too, the ignition time in one phase can be so selected that the arc in the previous phase is quenched by initiating the new are. The process is again described in detail by Fig. 9. The same connection can be utilized for converting direct current into alternating current if the ignition time is altered. It is assumed that the direct current line is to feed an existing alternating current network or that the three-phase transformer is fed with alternating current by a small auxiliary generator so that the period of the alternating current voltage is thus provided. The process of ignition and quenching is then as follows: at the moment is, Fig. 10, the spark gap III operates, i. e. direct current fiows by way of the are from II3 via III to the phase IIII of the transformer. In order to do this, the voltage of H3 must be higher than that of IUI. The are at III persists up to the moment it when the arc is initiated at the spark-gap I I2. As may be seen from Fig. 10, the potential of I02 is lower than that of IM at this moment; accordingly a positive current must -fl0w from. IUI Via III, H3 and H2 to I02, i. e.

the direction ofcurrent in I II must reverse. The are in III .can'be extinguished in this moment. This occurs periodically in the other phases. It is evident from this, that in comparison to working from three-phase to direct-current, the ignition time must be advanced. Therefore in the case of converting direct current into threephase current, ignition must occur approximate ly, before the moment in which the voltages of two phases become equal. The ignition time will have to be selected at different periods, depending upon the kind of direct current network to be fed; in the case of multi-phase service and great capacity in the direct current network, quenching of the arc in one phaseis often best effected when the corresponding phase possesses the crest value of its voltage, because in such circumstances the current flowing through the spark gap is at its lowest value. The ignition time of the new am can therefore be correspondingly advanced. Moreover, when converting positive and negative direct current voltage itis often advisable not to connect the neutral point of the'transformer to earth.

By the pertinent selection of the connections of multi-phase transformers and by employing sible without very sudden alterations in current;

and that the voltage across the spark gap at which the arc is quenched cannot reappear too rapidly. Moreover it must be ensured by means of the connections and-auxiliary devices, that voltage and current are constant on the direct current side, and sinusoidal on the alternating current side. v

In order to eliminate the difficulties involved 5 with the former methods of ignition when converting high voltages due to the great distance between electrodes, and in order to ensure reliable ignition particularly in multi-phase operation when the difference of'the working voltage 10 between the electrodes is still small, the ignition current and the time during which this ignition current flows in the invented spark gap arc, in accordance with the further invention, made as large as possible, whilst the requisite ignition l5 plant is combined in a pertinent manner.

Fig. 11 shows such arrangement, by means of which the. ignition energyattains an appreciable value, in that the capacity and charging voltage of the condensers are increased, whilst the condensers serving to produce the ignition voltage are combined in the individual phases in order to save extra costs.

I30, I31, I32 are the secondaries of the threephase transformer connected in star-fashion 25 with the star point I33 connected to ground. I31, I38, I39 are choke coils connected in series with the secondaries I30, I3I, I32, I34, I35 and I36 are capacities shunting the secondary windings and'choke coils, respectively. I40, I4I, I42 are 30 the main spark gaps of the three phases connected to the direct current line I43 by means of the secondaries I44, I45 and I46 of a Tesla transformer, respectively. The primaries I48, I49 and I50 of the Tesla transformer are con- 35 nected with one of their terminals to a condenser I5I and with their other terminals to fixed electrodes I52, I53, I54 of a rotating. spark gap, the other fixed electrodes I55, I56, I51 of which are connected to the other terminal of condenser ISI or to ground. The fixed electrodes of the rotating spark gap forms three pairs of opposite movable electrodes are carried by a rotating. arm I synchronously driven by means of a suitable drive (not shown). The rotating spark gap consecutively connects the primaries I48, I 49 and I58 of the Tesla-transformer in shunt to condenser I5I, the latter being loaded from an auxiliarytransformer I6I through a rectifier I62, a large condenser I63 and a. resistance I64. The condenser I63 which isconnected between the intermediate point of rectifier I62 and resistance I64 and the connection connecting the secondary of transformer I6I and capacity I5l is arelatively 55 large condenser, the voltage of which does not appreciably change during service. Resistance I64 is dimensioned in such manner that capacity I5I is loaded quickly'enough each time after it single condenser I 5I is provided for all phasw and that this condenser is fully charged whenever the ignition takes place independently of the time at which ignition is initiated. If desired, instead of an auxiliary transformer I6 I the 65 main transformer might charge condenser I63. Instead of this the condenser I63 might be charged from the direct line I43, in which case rectifier I62 1might be dispensed with.

In order to produce ignition voltage Tesla transformer two methods can be followed, viz. to tune the Tesla circuit to resonance or to apply the so-called shock or impulse excitation. With the former the voltage in the secondary circuit gradually rises to its peak value. With with 8.

shock excitation the arrangement must be made in such manner that the voltage in the secondary circuit has already attained its maximum value approximately at the same time as the primary coil has obtained its first voltage. To attain this a particularly close coupling of the two coils is necessary. At high voltages such close coupling can be attained by placing both coils in oil, by distributing the primary coil practically over the entire length of the secondary coil, by using multilayer secondary coils or by using a section of the secondary coil as primary coil (auto-transformer connection) The operation of this device is as follows:

When a flash-over is initiated by the rotating spark gap, for instance, when the pair of movable contacts is in opposition to the fixed contacts I 52 and I55, as indicated in Fig. 11, a primary circuit of the Tesla transformer is closed through winding I48. Thus a secondary voltage is induced in the winding I44, causing a flash-over in the spark gap I40. Condenser I34 and choke coil I31 are designed insuch manner that primar I48 and secondary I44 are in resonance. The resonance current flows from ground to star point I33, condenser I34, spark gap I40, secondary I44, direct voltage line I 43 and through capacity I65, exist ing between line I43 and ground, to ground. These resonance currents have a relatively large intensity and long duration. choke coils I31, I38 and I39 might be omitted.

Capacity I65 is as a rule formed by the natural capacity between line I43 and ground. If necessary, a bodily condenser can be inserted as indicated in Fig. 11.

The resonance between the primary and secondary windings is not very sharp on account of the inductive windings.

A similar effect is obtained by making condenser I5l very large, since then the primary circuit supplies energy into the secondary circuit due to the short circuit occasioned by flash-over in the spark gap I40. I I

When the contact arm I rotating in the direction oi the arrow indicated in Fig. 11, initiates a flash-over between the fixed contacts I53 and I56, a flash-over is initiated in spark gap I4I in a similar manner, and shortly afterwards also in spark gap I42.

In Fig. 12 a modification of my invention is shown in which the ignition voltage is produced by multi-unit impulse generator excitation. For the sake of simplicity merely a single phase is shown in Fig. 12. I10 and I 'II are primary and secondary windings forming one phase of the main multi-phase transformer. Secondary I1I is shunted by a condenser I12. Spark gap I13 connects secondary I1I to direct voltage line I14. I15 is a choke coil inserted between direct voltage line I14 and point I16, in which the shock or impulse exciting device to be described hereinafter is connected to spark gap I13.

The shock exciting device comprises the following elements between ground and point I18, connected in series to each other: A spark gap I11, a condenser I18, a second spark gap I19, a second condenser I80, a third spark gap I8I, a third condenser I82, a fourth spark gap I83, afourth condenser I84, a fifth spark gap I85, a fifth condenser I88, an inductance I81, which might be replaced by a long conductor, and a rotating spark gap I88 comprising two fixed contacts I89 and I90 and a pair of electrically connected rotating contacts I9I. It should be noted that the number of fixed spark gaps and condensers I11 to In certain cases- I88 is not limited to five, but might be any suit able number. I92, I93, I94 and I95 are resistances connected in series, each resistance shunting a pair of condensers and spark gaps as shown in Fig. 12. For instance resistance I92 shunts condenser I18 and spark gap I19 and so on. I90, I91, I98 and I99 are a similar row of resistances connected in series; each resistance shunting. a pair of spark gaps and condensers in the manner indicated in Fig. 12. For instance resistance I98 shunts spark gap I19 and condenser I80. 200 is an auxiliary transformer, the secondary of which is connected to two branches, each branch connecting a rectifier 20I, 202 and a resistance 203,204, respectively. Rectifiers 20I and 202 are inserted in the associated branches with opposite polarity, as shown in the drawings. 205 and 208 are condensers connected in series and connecting the intermediate point between rectifier 202.and resistance v204 with the intermediate point between rectifier 20I and resistance 203. The intermediate point of

condensers

205 and 206 is connected to ground. The branch containing rectifier 202 and resistance 204 is connected to the lower terminal of resistance I95, the branch containing rectifier 20I and resistance 203 is connected to the lower terminal of resistance I92, as indicated in Fig. 12.

Resistances

203, 204 and I92 to I99 are to be designed in such manner that I80, I82, I84 and I86.

The operation of this device is as follows:-

Rotating contact I9I of the rotating spark gap initiates a flash-over between the fixed contacts I89 and I90 at predetermined moments, since arm 189 is synchronously driven in the direction of the arrow by means of a suitable drive (not shown). Hereby flash-overs are initiated in'the fixed contact spark gaps I11, I19, I8I, I83 and I85, so that condensers I18, I80, I82, I84 and I86 charged by transformer 200 through the rectifiers MI, 202

and'the resistances

203, 204 and I92 to I99 are connected in seriesyso that point I18 is charged to a very high voltage, the charging current flowing through inductance I81. Hereby an oscillation is caused, by which the voltage of I18 is increased above the amount provided by the multi-unit condenser. Simultaneously a high frequency oscillation is produced, by which the flash-over voltage of the spark gap I13 is diminished and the duration of the current is prolonged. The igniting current fiows from I18 through a spark gap I13 and condenser I 12 back to ground, since direct current line I84 is separated from point I16 by the choke I15. The polarity of the voltage shocks must be chosen so that the shock voltage is in phase with the voltage difference existing between the contacts 60 The effective capacity of the multi-connection 65 should be made larger than would be actually necessary in order to obtain a high voltage. On the other hand the voltage can be made higher than would be necessary in order to initiate a flash-over in'spark gap I13. Further the dura- 70 tion of the ignition current can be prolonged by suitably designing choke coil I81.

With single-phase plants rotating spark gap I88 is preferably arranged in the place of spark gap I11, because then it only needs being insu- 7 lated against ground for a low voltage. In multiphase plants the rotating spark gap is preferably arranged in the place indicated in Fig. 12, .since then the rotating gaps of the phases canbe united to a single rotating spark gap comprising a single pair of rotating contacts and the number of pairs of fixed contacts corresponding to the number of phases, ina similar "manner as the spark gaps shown in Fig. '11. In this case l. A spark gap comprising a discharge chamber, two electrodes in said chamber and an inlet for feeding compressed gas into said chamber,

said inlet being arranged in proximity of one of said electrodes, said inlet having the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof and. the other electrode being provided with an outlet for the compressed gas havingthe form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof.

2. A spark gap comprising a discharge chamber, two electrodes in said chamber and an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with an out.- let for the compressed gas having .the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle .to an intermediate point thereof.

3. A spark gap comprising a discharge chamber, two electrodes in said chamber and an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with an outlet' for the compressed gas having the form of a nozzle the cross-section of which gradually decreasesfrom the ends of the nozzle to an intermediate point thereof, said nozzles having relatively short convergent portions, relatively long divergent portions and curved intakeedges so that the arc between the electrodes is initiated at points influenced by the flow of pressure gas and so that the basic points of the are from the formation until quenching of the arc must travel long paths along said electrodes.

4. A spark gap comprising a discharge chamber, two electrodes in saidchamber. an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall; of said chamber, each electrode being provided with an outlet for the compressed gas having the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof and means for producing a gas flow uniformly playing around said electrodes.

5. A spark gap comprising 'a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with a nozzleshaped escaping opening for the compressed gas and means for producing a helical gas flow uniformly playing around said electrodes.

6. A spark gap comprising a discharge chamber,-- two electrodes arranged in said chamber, means for feeding compressed gas into said chamber, each electrode being provided with an outlet for the compressed gas having the form of a 5 nozzle the cross-section of which gradually decreases from the ends of the nozzleto an inter-. mediate point thereof and means forcontrolling the gas-pressure in said chamber.

7. A spark gap c'omprising'a discharge chamber, two electrodes arranged in saidchamber, means forfeeding compressed gas into. said chamber,

each electrode beingprovided with an outletfor l the compressed gas having the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof and means for controlling the gas velocity in said chamber. I

" 8 Aspark gap comprising a discharge chamber, two electrodes arranged in said chamber; means for feeding. compressed gas into said chamber, each electrode being provided with a nozzleshaped escaping opening for the compressedgas,

means for igniting an arc between said elec-.

trades and means for stopping said igniting means and for rapidly increasing the gas pressure in said chamberon the occurrence of a high overcurrent. I f

9. A spark gap comprising a discharge chamber, two electrodes arranged in said chamber, means 30 for. feeding compressed gas into said chamber,

each electrode being provided with an outlet for the compressed gas having the form of a nozzle thecross-section of which gradually decreases from the ends of the nozzle to an in-- 35 te'rmediate point thereof and means for'periodically changing the stream-of the gas in said chamber. v 10. A spark gap comprising a discharge chamber, electrodes arranged in said chamber and 40 means for feeding compressed gas into said.

chamber, each electrode being provided with an outlet for the compressed "gashaving the' form of a nozzle the cross-section of which gradually. decreases from the ends of the nozzle'to an intermediate point thereof, said electrodes being. shaped differently from'e'ach other seas to produce a polarity difference for the flash-over voltages between said electrodes.

11. A spark gap comprising adischarge chamber, two electrodes arranged in said chamber, means for feeding compressed gas into said chamber, each electrode being'provided with a nozzle-shaped escaping opening for the [compressed gas and means for recooling and returning the gas into said chamber.

12. A spark gap comprising a discharge chamber, two electrodes arranged in said chamber, means for feeding compressed gas into said. chamber, each electrode, being provided with-an outlet for the compressed gas having'the form-of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof and means for initiating the extinction of the are just before the current passes through zero with the minimum possible. length of the arc. v

1 -3. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber,

said inlet being arranged in the wallet said magnetic field for moving the basic points of the arc.

14. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with an outlet for the compressed gas having the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof and means for imparting a movement to said electrodes during the burning of the are between said electrodes.

15. A spark gap comprising a discharge chamber, two electrodes arranged in said chamber and means for feeding, under expansion, saturated steam into said chamber, each electrode being provided with an outlet for the steam having the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof.

16. A spark gap comprising a discharge chamber, two electrodes arranged in said chamber, means for feeding compressed gas into said chamber, each electrode being provided with an outlet for the compressed gas having the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof and means for controlling the gas pressure and velocity in said chamber in such manner that the arc is extinguished just before the current passes through zero.

ber, two electrodes arranged in said chamber, a.

nozzle in the wall of said chamber for feeding compressed gas into said chamber, each electrode being provided with an outlet for the compressed gas having the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof and means for controlling the cross-section of the gas pipe before said feeding nozzle.

19. A spark gap comprising a discharge chamber, two electrodes arranged in said chamber, a nozzle in the wall of each chamber for feeding compressed gas into said chamber, each electrode being provided with a nozzle-shaped escaping opening for the compressed gas and means for controlling the cross section of the gas pipe before said feeding nozzle and behind. said escaping opening. I

20. A' spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into'said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with an outlet for the compressed gas having the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof and means for controlling the gas pressures behind said outlets and means for controlling the cross-sections of said outlets in said electrodes, said controlling means for each electrode being independent from each other.

21. A spark gap comprising a discharge charnber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with an outlet for the compressed gas having the form of a nozzle the cross-section of which gradually de creases from the ends of the nozzle to an intermediate point thereof, means for controlling the gas pressures behind s'aid outlets and means for controlling the crosssections of the said outlets in said electrodes, said controlling means for each electrode being independent from each other and means for actuating by hand said controlling means during running.

22. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with an outlet for the compressed gas ha ing the form of a nozzle the cross-section of which gradually decreases from the ends of the nozzle to an intermediate point thereof, means for controlling the gas pressures behind said outlets and means for controlling the cross-sections of the said outlets in said electrodes, said controlling means for each electrode being independent from each other and means for automatically actuating said controlling means during running.

23. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being, provided with a nozzleshaped escaping opening for the compressed gas and a movable electrode being adapted to electrically connect said first-mentioned electrodes during running and to be displaced shortly after initiating the arc.

24. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding/compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with a nozzle-shaped escaping opening for the com pressed gas and coils arranged within said electrodes for producing an electromagnetic field for moving the basic points of the arc.

25. A spark gap comprising a discharge chamber, two electrodes in. said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with a nozzleshaped escaping opening for the compressed gas and collsarranged in the proximity of said electrodes for producing an electromagnetic field driving the basic points of the arc in spiral paths to the openings in said electrodes.

26. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with a nozzle- I shaped escaping opening for the compressed gas ing the basic points of the are and a current supply for energizing said coils.

28. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with a nozzle-shaped escaping opening for the compressed gas, coils arranged in the proximity of said electrodes for producing an electromagnetic field for moving the basic points of the arc and a cooling fluid container embracing said electrodes.

29. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with a nozzleshaped escaping opening for the compressed gas, coils arranged in the proximity of saidelectrodes for producing an electromagnetic field for moving the basic points of the arc and means for rotating said coils.

30. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feedingcompressed gas into said chamber, said inlet being arranged in the wall of said chamber,

each electrode being provided with a nozzleshaped escaping opening for the compressed gas, coils arranged in the proximity of said electrodes for producing an electromagnetic field for moving the basic points of the arc and means for rotating said electrodes.

31. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, each electrode being provided with a nozzleshaped escaping openingror the compressed gas,

32. A spark gap comprising a discharge chamber, two electrodes in said chamber, an inlet for feeding compressed gas into said chamber, said inlet being arranged in the wall of said chamber, eachelectrode being provided with a nozzleshaped escaping opening for the compressed gas, coils arranged in the proximity of said electrodes for producing an electromagnetic field for moving the basic points of the arc and means for imparting substantially equal potential to adjacently arranged electrodes and coils.

33. An equipment for converting high voltage direct currents into alternating currents comprising a spark gap in each phase of the alternating current and a device for periodically igniting the arc in each spark gap shortly before the arc current of the preceding phase passes through zero, said igniting means comprising a Tesla transformer, secondary windings forming part of said Telsa transformer and connected with said spark gap, respectively, primary windings forming part of said Tesla transformer and means for producing a shock excitation in said primary windings.

34. An equipment for converting high voltage direct currents into alternating currents comprising a spark gap in each phase of the alternating current and a device for periodically igniting the arc in each spark gap shortly before the arc current of the preceding phase passes through zero, said igniting means comprising a Tesla transformer, secondary windings forming part of said Tesla transformer and connected with said spark gap, respectively, primary windings forming part of said Tesla transformer and means for producing a shock excitation in said primary windings, the windings of said Tesla Qiransformer being tunednso as toabe resonant after the occurrence of a flash-over in said spark gaps.

ERWIN MARX.