US2293296A - Arrangement for the sparkless interruption of currents - Google Patents

Description

Aug. 18, 19420 J. JONAS 2,293,296

ARRANGEMET FOR THE SPARKLESS INTERRUPTION OF CURRENTS Filed Jan. ,8; 1941 3 Sheets-Sheet l ARRANGEMENT FOR THE SPARKLSS INTERRUPTION OF CURRENTS Filed Jan. 85.1941 5 Sheets-Sheev'; 2

Patented Aug. 18, 1942 u ABRANGEMENT FOR THE SPARKLESS INTERRUPTION OF CURRENTS Julius Jonas, Zurich, Switzerland, assigner te Aktiengesellschaft Brown,

Baden, Switzerland Boveri & Cie.,

Application January 8, 1941, Serial No. 373,701

` In Switzerland July 28, 1939 17 Claims. (Cl. 175-364) It is often required that circuits in which very high currents are flowing should be interrupted by means of a mechanical switch. Various proposals have been made in order to prevent sparking or arcing occurring when the current is interrupted, but in practice these known means have not been found to be satisfactory. It has for instance been proposed that a reactor. already saturated at very low currents, should be arranged in series with the switch contact. By this means the current curve when passing through zero becomes flattened so that the switch has only to interrupt a small current. It is also known to connect condensers in parallel with the switch. These devices enable a certain. improvement to be achieved; they are, however, very expensive and cannot prevent sparking during commutation and the subsequent destruction of the switch contacts. while at the most they can only prolong the life of the contacts.

According to the invention a sparkless operation of a mechanically actuated switch is also achieved :for very high currents by connecting a rectifier in parallel with the switch and an auxiliary source of voltage in series with the rectier, the voltage from the auxiliary source being arranged to be positive with reference to the passage of current through the rectifier at least during the opening period of the switch and of such a magnitude that it at least equals the voltage at which the rectier becomes operative.

The objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawings, in which:

Fig. 1 is a diagrammatic representation of a single-phase arrangement according to the invention;

Figs. 2a to 2c are curve sheets showing the method of operation of the arrangement of Fig. l;

Fig. 3 is a diagrammatic representation oi the three-phase arrangement according to the invention; 4 Fig. 3a shows the voltage curve and Fig. 3b

the current curve for each phase;

Fig. 4 shows further details of a three-phase arrangement as regards the control of the auxiliary rectifier;

Figs. 5 and 6 show modified forms of the invention as applied to three-phase arrangements employing a single auxiliary rectiiier forA all phases.

which supplies the load V over the switch S. In parallel with the switch S is arranged a rectiiler G and in series with this latter the auxiliary voltage source En. As shown in the drawings this auxiliary rectiiler G preferably consists of a gas or vapor discharge vessel which is provided with a preignition device so that the rectifier has a definite operating or ignition voltage Ez and for instance an approximately equally high voltage drop when in operation. The magnitude and phase of the auxiliary voltage Ez when compared with the ignition voltage, the primary supply voltage E1 and the phase, at which the switch S for instance periodically interrupts the circuit, shows the difference between the various cases. In Figs. 2a, 2b and 2c it is assumed that the phase of the auxiliary voltage E2 lags 60 behind fler about corresponds to the voltage peak indicated above the ignition voltage line Ez. Soon after the switch is opened the current therein drops to zero, while immediately afterwards there is a current J2 owing through the rectifier in the same sense and which also sinks to zero` before the voltage E1 passes through zero value. The current Jz thus augments the interrupted current J1 of the load V, so that during the opening of the switch an approximately sinusoidal current flows through the alternating voltage source E1 and through the load V and thus effectively suppresses the high induced voltages and the resulting sparking and arcing in the mechanical switch S. If the voltage E2 is selected to equal the ignition voltage Ez as indicated in Fig. 2b, fundamentally the same effect is obtained but with the difference, however, that the current J2 lasts somewhat longer. If the voltage E2 is bigger than 'the voltage Ez (Fig. 2c) then there is no longer a sudden fall in J1 and a momentary rise in J2, but rather a continuous current transfer from the switch to the auxiliary rectiiier. Such an interrupted current transfer is particularly favorable in the case of threephase systems in order to be able to obtain good commutation between the phases.

The three-phase arrangement shown in Fis. 3

In Fig. 1 E1 is the alternating voltage source 55 deals with a system oi connections which is preferably used when a low voltage rectifier for very high currents is required. The delta connected primary winding P of a transformer T is supplied from the network N, the secondary winding Q of the transformer comprising two parts, each of which serves a diierent purpose. The three switch contacts U1, U11, Um are directly connected to the star-connected phase windings which are dimensioned for the main current and generate the voltages I, II, III. In series with the starconnected main winding is an auxiliary winding with the phase voltagesI', II', III' which supply the three anodes Ai, An, Ain of the rectier G. The entire secondary winding forms a zig-zag connection so that the auxiliary voltages with iridices lag by 60 behind the voltages without indices at the switch H. The common cathode K of the three discharge gaps in the auxiliary rectier G is connected with the rotating switch arm H to which also one terminal of the load V is connected. rI'he other terminal of the load V is connected to the neutral point O of the secondary winding Q of the transformer T. The switch H is driven by a synchronous motor not shown in the drawing and also preferably connected to the transformer T in such a manner that one period of rotation is exactly equal to the period of the alternating current in the network N. Electric lters for smoothing the direct current can also be arranged in series with the load V. In order to render the commutation, explained with reference to Fig. 1, as far as possible independent of the load, a regulating reactor can also be connected in series with the cathode of the rectier G, this reactor being controlled by a direct current transformer in series with the load V. With a large supply current the inductance of this reactor must be small in order to ensure that there is a large increase in the commutation current taken over by the rectier and'corresponding to the main current. On the other hand with a small supply current it is desirable, for the sake of economy, that the current flowing through the rectifier should be proportionately smaller. This can be readily achieved' by increasing the inductance of.the series reactor. An automatic regulation is, however, preferable. Such an auxiliary dev ice is indicated in the arrangement shown in Fig. l by means of dotted lines, F being the direct current-transformer and R the regulating reactor controlled by the former. This device can of course also be used with the arrangement illustrated in Fig. 3 and has only been omitted from the drawing for the sake of clearness. is also provided with a pre-igniter similar to that in Fig. 1. The curves for the voltages E of the three-phase arrangement are shown in Fig. 3a and the corresponding current curves J are indicated in Fig. 3b. In both figures the contact duration of the mechanical switch or commutatorv is indicated by the double lines drawn parallel to the time axis, and for instance H Uii indicates that the contact arm H remains connected to the contact segment Un during this period of time. The

curves I, II, III in Fig. 3a show the course of the voltage for each phase of the main winding, while the curves I', II', III represent the voltage for each phase of the auxiliary winding of the transformer T. The voltage on the anodes A1, An, Ani

The cathode K of the rectifier G in Fig. 3 i' in Fig. 3b by Ji, Jn, Jin, and the current taken by the various discharge gaps is indicated by J g. In connection with the current and voltage curves shown it is assumed that the load V is mainly ohmic.

For capacity or inductive loads and also for the purpose of the aforementioned automatic regulation of the commutation current taken by the auxiliary rectifier it is often an advantage when the anodes of the rectifier are controlled by known means so that the moment at which ignition occurs can be selected as desired. For this purpose a magneto ignition apparatus B, as shown in Fig. 4, can be coupled with the switch H for supplying the ignition impulses required for such a regulation. It is preferable if the anodes are controlled by means of a direct application of the spark to the anodes. The apparatus B should thus be connected to the anodes over spark gaps C. The ignition apparatus B can, however, also be used to impose voltage impulses on grids arranged in front of the anodes, whereby the moment when the rectifier is ignited is controlled in the desired manner, for instance in dependence on the load on the main current. The sparkless commutation of the current which can thus always be obtained, makes the arrangement according to the invention particularly suitable for rectifier plants in which with a high overall efficiency Very small direct voltages and high currents are to be produced. In the first place therefore this refers to installations in which the usual rectier entirely composed of discharge vessels would provide too poor an efficiency due to the inherent voltage drop of between 15 and 25 volts. Since the main current ows over mechanically operated contacts and the rectier only serves i or commutation purposes and is therefore only designed for a corresponding fraction of the output, the weight and space required by this new mechanical rectifier whenreferred to the total output will be comparatively favorable and is within the usual limits even at very low voltage.

The present invention also deals with further improvements in the mechanical rectiers with synchronously controlled contacts already referred to, and in which the current commutation is dealt with by means of an auxiliary rectifier having an additional voltage connected in series, mercury vapor rectifiers being preferably used for this purpose. The auxiliary rectifiers used hitherto for multi-phase operation are provided with an anode for each phase so that each individual anode has in turn to commutate the full current. The auxiliary rectifier is thus similar to a standard rectier designed for full current and full voltage and this increases the cost of the installation very considerably. It is therefore also an object of the invention to simplify and cheapen the auxiliary rectier and at the same time also to obtain more favorable operating conditions for the mechanical contact device or commutator thus enabling also its coristruction to be simplified.

In the constructional examples of the invention shown diagrammatically in Figs. 5 and 6 the auxiliary tube or rectier G has to relieve the contact device S during commutation, that is when current passes from one phase to the next. The rectifier G is therefore current conductive only during very short intervals of time. When the commutation process is properly carried out the individual phases do not overlap and it is thus possible to employ only one singleanode auxiliary rectier tube G if this latter is always switched over early enough to the commutating phase by means of an auxiliary contact device Sz. This auxiliary contact device or commutator must have the same number oi phases as the main contact device S and be controlled in synchronism with this latter, the contact periods being adjusted to suit the commutating conditions. 'I'he auxiliary commutator Sz closes and opens its contacts without current flowing when the commutation process is controlled accordingly and need only be dimensioned for a relatively small eifective current value owing to the short time during which current conduction takes place. The reduction in Vthe number of anodes from for instance six to one in a six-phase rectifier and therefore the corresponding reduction in size of the auxiliary rectifier G results in the following advantages: The maximum negative blocking voltage for the auxiliary rectiiier tube can be reduced if it is switched oil' as soon as commutation has iinished before the blocking voltage reaches its maximum value, and is only switched in again shortly before the beginning of the commutation when the blocking voltage has passed its maximum value. The single-anode tube has also the advantage when compared with a multiphase rectiier that during the non-conductive period there is no current conducting main anode in the tube which increases the back-arcing tendency of the rectifier. The auxiliary rectifier can therefore be considerably simplified because the usual elements such as the anode grids and shields can be omitted. An important simplitlcation is also achieved in connection with the simultaneous reduction in voltage drop. Discharge tubes with mercury vapor filling can be used in which the arc is reignited for each current conducting period. 'Ihe reduction in arc voltagev in the auxiliary rectiiier is not only of importance as regards eillciency but is also l important in connection with the magnitude of the auxiliary voltage and the stressing of the main contacts when the switch is opened.

The cost of such a mechanical rectiiier with an auxiliary discharge tube can .be further reduced if the commutating power is decreased because this latter directly determines the capacity of the auxiliary rectifier and the auxiliary commutating device. In arrangements having a plurality of phases this can be achieved by subaaforementioned measures it is possible reduce the auxiliary rectifier to one-tenth its former dividing the system into several multi-phase systems which are connected in parallel by means of absorption coils; for instance a six-phase system can be divided into two three-phase systems with a double-limbed absorption coil or into three two-phase systems with a triple-limbed absorption coil. These systems have, in addition to the advantage already known in connection with rectifier systems, also the valuable property that the power of the commutating device is also reduced in proportion to the number of systems operating in parallel, that is 1:2 or 1:3. This is due to the fact that the entire direct current in the absorption coil connections distributes itself simultaneously over several phases while only one phase and therefore only a fraction of the the main mechanical commutating device is also relieved by a reduction in the maximum and eective value of the current which it has to conduct. By a simultaneous application of thesize so that quite apart from the other advantages which result, the supplementary cost for the comparatively small auxiliary contact device is practically negligible.

In seriesy with the auxiliary rectiner or discharge tube is an auxiliary voltage source which initiates the ignition and current ilow in the auxiliary rectiner. This auxiliary voltage E: is a three-phase one for the arrangement shown in Fig. 5. It is, however, also possible to -use a single-phase voltage En which as indicated in Fig. 6 is arranged to be in series with the cathode of the single or multi-phase tube G. The frequency of this auxiliary voltage Ez must, however, be higher than that of the line frequency and depends upon the number of commutations occurring during each cycle. For a six-phase rectifier it will therefore be necessary to employ a voltage having a frequency o! 300 cycles. The

scribed. 'I'he plant is also considerably simplified when a single-phase auxiliary voltage with a` high frequency is employed. Further possibilities for simplifying the commutation process and adjusting it to suit varying operating and load conditions are provided by regulating the phase and amplitude of the voltage. The auxiliary rectiiier G can of course also be equipped with means for influencing the point of ignition. 'Ihese means can also be used in order to switch in the auxiliary commutator without sparking.

I claim:

l. Arrangement for the sparkless interruption of alternating current in 'a circuit containing a periodically actuatedmechanical switch, comprising a rectifier in parallel to the switch, and an auxiliary source of alternating voltage in series with the rectifier, said auxiliary source being adapted to supply a voltage displaced in phase from the voltage of the principal circuit so that the maximum amplitude of the half wave of the auxiliary voltage which is positive with respect fo the ilow of current in the rectifier substantially coincides with the opening of the switch and is at least approximately equal to the voltperiodically actuated switch in each phase, a rectifier in parallel to the switch, and an auxiliary source of alternating voltage in series with the rectiiier, said auxiliary source being adapted to supply a voltage displaced in phase from the voltage of the principal circuit so that the maximum amplitude of the half wave of the auxiliary voltage which is positive with respect to the now of current in the rectifier substantially coincides with the opening of the switch and is at least approximately equal to the voltage at which the rectier becomes operative.

5. Arrangement as claimed in claim 4 wherein the supply voltage and also the auxiliary voltage are obtained from a star-connected zig-zag secondary winding of a three-phase transformer,

=those phase parts of the secondary winding which lie directly at the neutral point providing the supply voltages and those phase parts oi the secondary winding which have a lag of 60 pro- `viding the auxiliary voltages.

6. Arrangement as claimed in claim 4 including a rectifier which is associated with the various phases consisting ofa number of discharge cells arranged in a common housing and having a common cathode.

7. Arrangement as claimed in claim 4 including a rectiiier which is associated with the various phases consisting of a number oi.' discharge cells arranged in a common housing and having a common cathode and provided with a special source of electrons.

8. Arrangement as claimed in claim 4 including a rectifier which is associated with the various phases consisting of a number of discharge cells arranged in a common housing and having a common cathode and provided with means for controlling the time cf ignition.

9. Arrangement for the sparkless interruption of multiphase alternating current comprising a synchronously operated multiphase switch, a rectiiier in parallel to the switch, and an auxiliary source of alternating voltage in series with the rectifier, said auxiliary source being adapted to supply a voltage displaced in phase from the voltage of the principal circuit so that the maximum amplitude of the half wave of ihe auxiliary voltage which is positive with respect to the iiow of current in the rectifier substantially coincides with the opening of the switch and is at least approximately equal to the voltage at which the rectiiier becomes operative, the. rectiiier which is associated with the various phases consisting of a number of discharge cells arranged in a common housing and having a common cathode, and a magneto ignition apparatus coupled with said switch to control the ignition of the rectifier.

10. Arrangement for the sparkless interruption of multiphase alternating current comprising a synchronously operated multiphase switch, a rectifier in parallel to the switch, and an auxiliary source of alternating voltage in series with the rectiiier, said auxiliary source being adapted to supply a voltage displaced in phase from the voltage of the principal circuit so that the maximum amplitude of the haii wave of the auxiliary ical rectier is switched over to the commutating phase as required.

12. Arrangement as claimed in claim 4 wherein the auxiliary rectiiier consists of a singlephase auxiliary discharge tube which by means of an auxiliary commutating device operated synchronously with the contacts of the mechanical rectiner is switched over tothe commutating phase as required, and the auxiliary commutating device rapidly disconnects the auxiliary rectifier during periods which fall outside the period required for commutation so that said auxiliary rectiiier does not require a maximum blocking voltage.

13. Arrangement as claimed in claim 4 wherein the auxiliary rectiner consists of a singlephase auxiliary discharge tube which by means of an auxiliary commutating device operated synchronously with the contacts of the mechanical vrectiner is switched over to the commutating V-phase'as required, and multi-phase connections with absorption coils are employed in order to reduce the size of the commutating device and the load which the contact device has to carry. 14. Arrangement as claimed in claim 4 wherein the auxiliary rectier consists of a singlephase auxiliary discharge tube which by means voltage which is positive with respect to the iiow of current in the rectier substantially coincides with the opening of the switch and is at least approximately equal to the voltage at which the rectier becomes operative, the rectier which is associated with the various phases consisting of a number of discharge cells arranged in -a common housing and having a common cathode, and a magneto ignition apparatus coupled with said switch to control the ignition of the rectier in dependence on the loading,

of the principal current circuit.

11. Arrangement as claimed in claim 4 wherein the auxiliary rectiiier consists of a singlephase auxiliary discharge tube which by means of an auxiliary commutating device operated synchronously with the contacts of the mechanof an auxiliary commutating device operated synchronously with the contacts oi' the mechanical rectiiier is switched over to the commutating phase as required, and the commutation voltage consists of an auxiliary voltage source of higher frequency, said voltage source being connected in series with the auxiliary rectifier.

15. Arrangement as claimed in claim 4, wherein the auxiliary rectifier consists of a singlephase auxiliary discharge tube which by means of an auxiliary commutating device operated synchronously with the contacts of the mechanical rectiiier is switched over to the commutating phase as required, and the commutation voltage consists of an auxiliary voltage source of higher frequency, said voltage source being connected in series with the auxiliary rectifier and the phase of the commutation voltage being variable in accordance with operating conditions.

16. Arrangement as claimed in claim 4 wherein the auxiliary rectier consists of a singlephase auxiliary discharge tube which by means of an auxiliary commutating device operated synchronously with the contacts of the mechanical rectier is switched over tc the commutating phase as required, and the commutation voltage consistsof an auxiliary voltage source of higher frequency, said voltage source being connected in series with the auxiliary rectiiier and the amplitude of the commutation voltage being variable in accordance with operating conditions. 17. Arrangement as claimed in-claim 4 wherein the auxiliary rectier consists of a singlephase auxiliary discharge tube which by means of an auxiliary commutating device operated synchronously with the contacts of the mechanical rectiiier is switched over to the commutating phase as required, and the main commutation device is so regulated that the auxiliary commutating devicecan be switched from phase to phase Without sparking.

JULIUS JONAS.

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