US2782359A - Adjustable contact converter - Google Patents

Description

Feb. 19, 1957 F. KOPPELMANN ADJUSTABLE CONTACT CONVERTER s sheets-het 1 Flled March 25, 1953 Feb. 19, 1957 F. KOPPELMANN 2,782,359

ADJUSTABLE CONTACT CONVERTER Filed March 25, 1953 f 3 Sheets-Sheet 2 v l 7 f F/g.2

CDNTRUL DEVICE if v '-77 5a y Z'm/enof:

Feb. 19, 1957 F. KOPPELMANN 2,782,359

ADJUSTABLE CONTACT CONVERTER Filed March 25, 1953 Sheets-Sheet 3 Figs ,al 1

Inventor.'

FLORIS KoPPELmA/Y/ United States Patent 2,'7s2,ssa

ADJUSTABLE CoNrAcr convnnrnri Floris Koppelmann, Berlin-Siemensstadt, Germany, ns-

sgnor to Licentie Patent-Verwaltungs@ m. h. H., Hamburg, Germany Application March 25, 1953, Serial No. 344,6@

19 Claims. (Cl. S21-48) The present invention relates to mechanical rectitiers or contact converters, particularly (though not exclusively) to converters of this type designed for large power outputs.

lt is known to provide contact converters with means for varying the output thereof by shifting the periods of contact closure with respect to the phase of the alternating input voltages, whereby (in analogy with the output control through phase shaft in the case of electronic rectiflers) the amount of power delivered to a load can be adjusted at will or else maintained substantially constant in the face of varying operating conditions. A drawback of these known arrangements resides in the fact that displacement of the closure periods of the rectifier contacts will cause the contacts to close at instants when a substantial voltage is present across these contacts and/or to open while a large current passes therethrough, thereby resulting in arcing and in the eventual destruction of the contact surfaces.

It is, accordingly, an object of the present invention to provide means for so controlling a converter of the character set forth as to enable adjustment of its output without incurring the danger' of undesirable discharges at the contact surfaces. More specifically, it is an object of this invention to provide means for shifting the phase of the intermittent current with respect to that of the alternating voltage in combination with mechanism for invariably closing the contacts of the converter substantially upon the occurrence of a voltage node thereacross and for invariably opening said contacts at a time of substantially minimum current flow therethrough.

The above objects are realized, in accordance with the present invention, by the provision of saturable electromagnetic reactance means for periodically including a high impedance in series with the mechanically actuated contacts, phase shifting means for varying the rhythm of saturation of said reactance means with respect to thephase of the input voltage, and a timer mechanism coupled to said phase shifting means and maintaining the cut-in of the contacts in ixed phase relationship with the input voltage while displacing the cut-out of the contacts in step with the dephasing of the saturation of said reactance means so that this cut-out will occur at a time when the reactance in series with the contacts is large enough to reduce the flow of current therethrough substantially to zero. in the case of polyphase input voltages, more particularly, the cut-in of the contacts will be controlled to coincide with the junction of successive phase voltages, i. e. to occur at a time when the instantaneous value of the descending portion of one voltage phase equals the instantaneous value of the ascending portion of the next phase.

The invention will be better understood from the following detailed description, reference being had to the accompanying drawing in which:

Fig. l is a set of graphs serving to explain the principles underlying the present invention;

ICS

Fig. 2 shows, partly diagrammatically, a contact converter according to this invention;

Pig. 3 is a fragmentary view of a converter representing a modification of that shown in Fig. 2; and

Fig. 4 is a diagrammatic View of the control device used in the embodiments of Figs. 2 and 3.

Graph (a), Fig. l, shows the phase voltages u, v, w of a three-phase network 1, Fig. 2, connected to the input of a converter according to this invention. An input transformer 2 comprises three primary phase windings Su, 3v, 3W, delta-connected to the respective conductors of network 1, and three secondary phase windings 4u, 4v, 4W, Y-connected in series with respective main windings 11, 12, 13 of saturable-core reactors S, 6, 7 whose cores are shown at 8, 9, 1@ bearing biasing windings 14, 15, 16. The neutral point of the Y of the secondary transformer windings is connected via a smoothing choke 27, having an armature 23, to one terminal of a load 29; the other load terminal is connected to a control device 76 and thence returned, in parallel over pairs of contacts 118-19, 2li- 21, 22-23, to the main reactor windings 11, i2, 13.

The contacts of each of the aforesaid pairs are intermittently and periodically interconnected by bridge pieces 24, 25, 26, respectively7 mounted on rods 4Z, 43, 44. These rods are pivotally connected at 33, 34, 35 to intermediate points of arms 30, 31, 32, respectively, each of which has one extremity linked at 36, 37, 3S to a depending piston 39, all, 41 guided in a sleeve d5, d6, 47, respectively. A shaft 51, forming an extension of the rotor 53 of a motor 52 which may be energized from the mains 1 over connections not shown, bears three staggered cams d8, 49, 50 of roughly crescent-shaped cross section, these cams cooperating with the pistons 39, dll, 41, respectively. The housing 54 of the motor 52, held in suitable supports (not shown), is angularly displaceable within certain limits, as indicated by an arrow, for a purpose presently to be described.

The other extremity of each of the arms 3l), 31, 32, indicated at 72, 73, 74, is fulcrurned on a rod 71. A bell crank lever composed of two arms 58, 61, and pivoted at the junction 62 of said arms to a ixed bracket 60, bears the rod 71 at the free end 75 of its shorter arm 61 and carries a roller or cam follower 57 on the free end of its longer arm 5S. The roller 57 rides on the curved surface of a cam member 55 which is lixedly mounted on the housing 54 of motor 52 and is urged into contact with the roller by a spring 56.

A variorneter or phase shifter 66 has a shaft 65 which carries a crank arm 64, the latter being linked at 69 to a lever 63 which at 59 pivotally engages an intermediate portion of the long arm 53 of bell crank lever 58, 61. The position of shaft 65, and, thereby, that of arms 64, 63, 5S and 61, is controlled by way of suitable transmission means, indicated schematically at 77, from the device 76 which may be a current-sensitive governor of, for example, the oil pressure type. The input to the variometer 66 is constituted by three conductors 70 connected to respective phase conductors of the network 1; the output circuit of the variometer comprises three similar conductors 67 connected in a Y to biasing windings 14, 15, 16, respectively.

The operation of the system of Fig. 2 will be described with further reference to Fig. l, where graph (b) shows at iv and iw the currents due to the phase voltages v and w, respectively. Let us assume that the connector 25, associated with the phase v, makes (i. e. interconnects it contacts 20 and 21) at a time to when the instantaneous values of phase voltages u and v are equal, thus at an intersection of the corresponding curves shown in graph (a). Since contacts 18, 19 of the preceding phase are still closed at 24 when the connector 25 descends, contact 21 will be substantially at potential u whereas contact 2t) will be substantially at potential v, so that virtually no voltage difference will exist across the two contacts to be bridged by the member 25; thus the cut-in will take place without areing.

it will be noted that the circuit now closed by the connector 25 (and, analogously, each of the circuits adapted to be closed by connectors 24 and 26) comprises two distinct reactances, namely the smoothing inductance 27 common to the three phase circuits and the inductance of the respective reactor, such as 6, individual to this one circuit. Thus the buildup of the current iv through winding 12 will be determined by the reactor impedance and, hence, by the degree of saturation of core 9 by biasing winding 15, whereas the commo-n smoothing means of the load circuit, such as choke 27, will tend to maintain constant the total current drawn` by the load 29. lf the reactor 6 becomes saturated with the proper polarity soon after the time to, the current iv may rise relatively rapidly to its maximum which it reaches at a time t1, the current in (not illustrated) through contacts 1S, 19 decaying at the same time to substantially zero whereupon the connector 24 is allowed to lift. At a time t2, when the instantaneous phase voltages v and w are equal, connector 26 closes without arcing and causes a current iw to pass through contacts 22, 23, this current reaching its full magnitude at a time t3 at which the current iv drops to substantially zero. If, now the current in biasing winding 15 is so phased as to leave core 9 unsaturated or incompletely saturated in the direcu tion of the negative halfcycle of phase current iv, then the onset of this negative half-cycle may be effectively delayed until a time l5, whereby substantially no current will tlow through contacts 20, 21 bridged by the connector 2.5. This establishes a period trs-t of safe cut-out `for this connector, hence the latter may be arranged to break without arcing at some intermediate instant as indicated at t4. The closed period TK of connector 25, being of the same length as the closed period of connectors Z4 and 26 under like operating conditions, thus extends between instants to and t4 as shown in graph (c).

If, for some reason, the flow of direct current through load 29 should change, the governor 76 will immediately respond with a corrective displacement of the shaft 65 of variometer 66. Let us assume, by way of example, that the D.-C. output of the converter has increased and that, as a result thereof, the shaft 65 has been rotated in such a sense (assumed to be counterclockwise) as to delay the phase of the biasing currents through windings 14, 15, 16 with respect to that of the voltages induced in the phase windings 4u, 4v, dw. This reaction will retard the saturation of the core 9 in the direction of current iv, hence this current will reach its full strength only at a time ti'; the effect of this delay will be the same as if the cut-in had been retarded by an interval t to occur at a time to instead of to. A like apparent delay, from t2 to t2', will occur at the cut-in of phase 3 and the current iv will only drop to substantially zero at a time ts', the period of safe cut-out for the phase v thus being the interval t3t5. Since the time la has been assumed to be subsequent to t4., a substantial current is would still be passing through the contacts 20, 21 at the time of cut-out if the member 25 were to break in the same time position of the voltage cycle as before. To avoid arcing, therefore, it is desirable to delay the interruption of the connection between these contacts by an interval substantially equal to At, and this is accomplished as follows:

When the crank arm 64 is swung counterclockwise about its shaft 65, it swings the bell crank lever 58, 61 clockwise about its pivot 62 and, thereby, lowers the rod 71 serving as the common upper lfulcrum for the arms 30, 31, 32. This `adjustment increases the elevation to which the crescent- shaped cams 48, 49, 50 must raise the pistons 39, 40, 41 in order to lift the connectors 24, 25, 26 oit their contacts, thereby lengthening the closed period of each of these connectors to the desired value of Trr-l-dt. In view, however, of the gently and symmetrically sloping leading and trailing edges of the cams 48, 49, 50, as shown in Fig. 2, the time increment At will be distributed between the onset and the termination of said period, so that without further adjustment the time of cut-in would be advanced and the time of cut-out would be delayed by substantially A172 with respect to the old cut-in and cut-out times to and It, respectively, as shown in graph (e) of Fig. l. In order to arrive at the desired delay of the cut-out by At without substantial displacement of the moment of cut-in, as shown in graph (4), the descending roller 57 so acts upon the cam surface of member 55 as to rotate the housing 54 of motor 52 in counterclockwise direction, i. e. against the sense of continuous rotation of shaft 53, through a suicient angle to accomplish this result.

It may be mentioned that a replacement of the gently sloping trailing edges of cams 48, 49, 50 by steep, radially directed edges would obviate the need for a compensatory displacement of the motor housing 54, since a change in the elevation of fulcrum 71 would no longer aiect the time of cut-in and would only result in a displacement of the moment of cut-out in accordance with the slope of the leading edges of these cams; the arrangement actually shown, however, entails the advantage of smooth contact closure without any chattering.

Referring now to Fig. 4, the operation of the control device 76 will be explained. In Fig. 4, the conductor 2.3-29 is in series with the load circuit as shown in Fig. 2. A D. C. current responsive means 76 is shown wound about this conductor. Such a current responsive means can be a conventional one as described inthe U. S. Patent No. 2,153,378, Fig. lb. The operation of means 76 is to increase or decrease the magnitude of current ilowing through a circuit including magnetic core 76 and variable impedance 76". This increase or dccrease in the magnitude of the current flow is in response to the-magnitude of the current flow of the load circuit.

Beneath the magnetic core 76 is a slide valve 761V. yThis valve is operated by oil under pressure i'lowing through conduit 11i). Upwardly extending from the slide valve is a piston 111 downwardly restrained by a compression spring 112. Conduits 113 and 11d extend from slide valve '761V to a servo-transmitter 76V. `Transmitter 76V is in turn coupled to the shaft 65 of the Variometer 66. It is known that displacement of the servo-mechanism 76V will cause a similar displacement of the variometer shaft 65.`

It is apparent that the piston 111 of the slide valve can be moved upwardly against the action of the spring 112 by the magnetic eld set up by the core 76". An increase of the magnetic lield causes the piston to be moved upwardly so that oil iiows to servo-mechanism 76V in conduit 113 and iiows back in conduit 114. This will result in a clockwise rotation of the core of servomechanism 76V and a similar rotation of the shaft 65.

Conversely a downward movement of the piston 111 will cause oil to ilow to the servo-mechanism in conduit 114 and return in conduit 113 with a concomitant counterclockwise rotation of the servo-mechanism 76V. yIt is apparent that the strength of the magnetic eld set up by the magnetic core 76' depends directly on the magnitude of current owing in the load circuit 23-29.

Fig. 3 illustrates a modiiied converter accor-ding to the invention, only so much of the mechanism common to both embodiments having been illustrated as is necessary for an understanding of the distinction between the systems of Figs. 2 and 3.

In Fig. 3 the means for shifting the phase of the biasing currents for the reactors 5, 6, 7 take the form of a -circuit arrangement for varying the magnitude of a component of each of thesek currents. Thus in Fig. 3

the reactor cores 8, 9, are each shown provided with a rst biasing winding 92, 93, 94, respectively, connected directly to conductors 70 leading to respective bus bars 1, and with a second biasing winding 89, 90, 91, respectively, connected via leads 87 to the variable taps 84, 85, 86 of respective rheostats 9'7, 96, 95 which are in turn connected to respective ones of the conductors 70. The contact arms 81, 82, 83 of the rheostats 97, 96, 95 are carried on a shaft 80 which takes the place of a variometer shaft 65 of Fig. 2, being positionable under the control of governor 76 by means of linkage '77. The system of levers 63, 64, etc. is connected with the shaft Si?.

It will be noted that the biasing current delivered to each of the reactors 5, 6, 7 of Fig. 3 is composed of a xed and a variable vector of different phases, the xed vector being impressed upon the windings 92, 93, 94 via conductors 88, the variable vector being furnished to windings 89, 915, 91 via conductors 87 and rheostats 97, 96, 95 (which may be purely ohmic). Since the phase of the biasing current will markedly change with Variations of the magnitude of the current components passed by the rheostats, it will be apparent that the systcm of Fig. 3 will function in precisely the manner described for the preceding embodiment with reference to Fig. l.

yl't will be understood that the adjustment of a phasing device as represented by shaft 65 or 80 need not occur under t'he control of a constant-current regulator, such as governor '76, bu-t may be effected manually or in some other manner for the purpose of producing a variable output. Particularly in the latter case, and with highpower converters, it will be desirable to limit adjustments by the herein disclosed control means to a relatively narrow range of output voltages (or output currents), e. g. within about 10%, and to provide conventional voltage divider means or the like for coarse stepby-step regulation, whereby the loss factor and voltage harmonics will be kept small. It will further be appreciated that additional reactance means, preferably inductances with armatures of high-quality, low-loss material (e. g. of a lamination thickness less than 0.05 mm.), may be connected in series with the converter contacts for the purpose of minimizing the current therethrough in the event of slight accidental displacement of the moment of cut-in with respect to the precise point of intersection of the phase voltages. Such inductances may act as chokes capable of reducing the cut-in current for periods of the order of from lO-4 to 11)-5 seconds to small values, e. g. between 1 and 5 amperes, whereby arcing will be substantially avoided even where the synchronization between the contact control mechanism and the phasing of the input voltages is not perfect; this will enable the construction of adjustable mechanical converters according to the invention designed for relatively high voltages per rectifier unit.

The invention is, of course, not limited to the specic embodiments hereinabove described and illustrated; thus it may be mentioned that the biasing windings of the reactors S, 6, 7 need not be energized directly from the mains it but that they may be connected to any other convenient source of current whose output is harmonically related to the mains frequency. It will also be apparent that the principles herein disclosed may be utilized, with obvious modifications, in converters whose alternatingcurrent input comprises more or less than three phases. Furthermore, the motor shaft 51 or its equivalent may be arranged to open and to close each associated pair of contacts, such as i3, 19, more than once during each revolution. These and other modifications and adaptations will be readily apparent to persons skilled in the art and are deemed to be embraced within the spirit and scope of the invention as defined in the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1.V In a contact converter, in combination, a load cir'- cuit including a pair of contacts, a source of alternating voltage in series with said contacts, mechanism for periodically opening and closing said contacts in step with said voltage, said mechanism being synchronized with said source for invariably closing said contacts at a time when the voltage across said contacts is substantially zero, saturable electromagnetic reactance means connected in said circuit as a variable impedance in series 4with said contacts, biasing means for said reactance means periodically varying the degree of saturation thereof, thereby changing the value of said impedance, and adjusting means for so synchronizing said biasing means with said mechanism as to delay the rise of current in said circuit, following the closure of said contacts, for a selected length of time.

2. ln a contact converter, in combination, a load circuit including a pair of contacts, a source of alternating voltage in series with said contacts, mechanism for periodically opening and closing said contacts in step with said voltage, saturable electromagnetic reactance means connected in said circuit as a variable impedance in series with said contacts, biasing means for said reactance means periodically varying the degree of saturation thereof, thereby changing the value of said impedance, said biasing means including a source of current of a frequency harmonically related to the frequency of said voltage source, said mechanism being synchronized with said voltage source for invariably closing said contacts at a time when the voltage across said contacts is substantially zero, and adjusting means for so phasing said current source with respect to said voltage source as to maintain said impedance at a value sutiiciently large, and for a suicient length of time following closure of said contacts, so as to delay the rise of current in said circuit for a selected period following said closure.

3. In a contact converter, in combination, a load circuit including a pair of contacts, a source of alternating voltage in series with said contacts, mechanism for periodically opening and closing said contacts in step with said voltage, saturable electromagnetic reactance means connected in said circuit as a variable impedance in series with said contacts, biasing means for said reactance means periodically varying the degree of saturation thereof thereby changing the value of said impedance, said biasing means including a source of current of a frequency harmonically related to the frequency of said voltage source, said biasing means causing said impedance to assume relatively high values at least twice during each cycle of said alternating Voltage, adjusting means for so phasing said current source with respect to said voltage source as to maintain said impedance at said relatively high-value for a selected length of time following the appearance of a voltage node across said contacts, and control means so synchronizing said mechanism with said biasing means as to cause said contacts to close invariably at the instant of said voltage node and to open at a subsequent instant when said impedance is again so high as to reduce the flow of current through said contacts to substantially zero.

4. In a contact converter, in combination, a load circuit including a pair of contacts, a source of alternating voltage in series with said contacts, mechanism for periodically opening and closing said contacts, said mechanism having an operating cycle equal to a cycle of said alternating voltage, first regulator means for Varying the length of the closed-contact portion of said operating cycle, second regulator means for varying the phase of said operating cycle relative to said alternating voltage, saturable electromagnetic reactance means connected in said circuit as a variable impedance in series with said contacts, biasing means for said reactance means periodically varying the degree of saturation thereof, thereby changing `the value of said impedance, said bia-sing means including a source cf current of a frequency harmonically related to the frequency of said voltage source, said biasing means causing said impedance to assume relatively high values at least twice during each cycle of said alternating voltage, adjusting means for so phasing said current source with respect to said voltage source as to maintain said impedance at said relatively high value for a selected length of time following the appearance of a voltage node across said contacts, and control means so operating said first and second regulator means as to cause said closed-contact portion to start invariably at the instant of said voltage node and to end at a subsequent instant, varying with different phasing of said current source with respect to said voltage source, at which said impedance is again so high as to reduce the flow of current through said contacts to substantially zero.

5. In a contact converter, in combination, a load circuit including a pair of contacts; a source of alternating voltage in series with said contacts; mechanism for periodically Opening and closing `said contacts, said mechanism comprising a rotating shaft, a contact-operating member, cam means on said shaft co-operating with said member, and supporting means for said member adjustable to vary `the length of time during which said cam means is effective to open and to close said contacts during each operating cycle of said mechanism, said operating cycle being equal to a cycle of said alternating voltage; saturable electromagnetic reactance means connected in said circuit as a variable impedance in series with said contacts; biasing means for said reactance means periodically varying the degree of saturation thereof, thereby changing the value of said impedance, said biasing means including a source of current of a frequency harmonically related to the frequency of said voltage source, said biasing means causing said impedance to assume relatively high values at least twice during each cycle of said alternating voltage; adjusting means for so phasing said current source with respect to said voltage source as to maintain said impedance at said relatively high value for a selected length of time following the appearance of a voltage node across said contacts; and control means for so synchronizing said mechanism with said biasing means as to cause said contacts to close invariably at the instant of said voltage node and to re-open at a subsequent instant, varying with diiferent phasing of said current source with respect to said voltage source, at which said impedance is again so high as to reduce the ow of current through said contacts to substantially zero, said control means including means for adjusting said supporting means.

6. ln a Contact converter, in combination, a load circuit inciuding a pair of contacts; a source of alternating voltage in series with said contacts; mechanism for periodically opening and closing said contacts, said mechanism comprising a motor with a housing and a shaft rotating in said housing, a contact-operating member, cam-means on said shaft co-operating with said member, supporting means for said member, iirst regulator means for so displacing said supporting means with respect to said cam means as to vary the length of time during which said cam means is effective to open and to close said contacts during each operating cycle of said mechanism, s id operating cycle being equal to a cycle of said alternating voltage. and second regulator means for varying the phase of said operating cycle relative to said alternating voltage by rotating said housing; saturable electromagnetic reactance means connected in said circuit as a variable impedance in series with said contact-s; -biasing means tor said reactance means periodically varying the degree of saturation thereof, thereby changing the value ot said impedance, said biasing means including a source of current of a frequency harmonically related to the frequency of said voltage source, said `biasing means causing said impedance to assume relatively high values at least twice during each cycle of said alternating voltage;

adjusting means for so phasing said current source with respect to said voltage source as to maintain said impedance at said relatively high value for a selected length of time following the appearance of a voltage node across said contacts; and means including said iirst and second regulator means for so synchronizing said mechanism with said biasing means as to cause said contacts to close invariably at the instant of said voltage node and to reopen at a subsequent instant, varying with different phasing of said current source with respect to said voltage source, at which said impedance is again so high as to reduce the How ot current through said contacts to substantially zero.

7. in a contact converter, in combination, a load circuit: including a pair of: contacts, a source of alternating voltage in series with said contacts, mechanism for periodically opening and closing said contacts in step with said voltage, a saturable-core reactor including a main winding connected in said circuit as a variable impedance in series with said contacts, said reactor being provided with at least one biasing winding, an energizing circuit for said `biasing winding connecting the latter to said source and including phase-shifting means, said phase-shitting means Ibeing operable to maintain said impedance at a relatively high value for a selected length of time following the appearance of a voltage node across said contacts, and control means so synchronizing said mechanism with said phase-shifting means as to cause said contacts `to close invariably at the instant of said voltage node and to re-open at a subsequent instant, determined by the position ot said phase-shifting means, at which said impedance is again so high as to reduce the iiow of current through said contacts to substantially zero.

8. in a contact converter, in combination, a load circuit including a pair of contacts, a source of alternating voltage in series with said contacts, mechanism for periodically opening and closing said contacts in step with said voltage, 4a saturablc-core reactor including a main winding connected in said circuit as a variable impedance in series with said contacts, said reactor being provided with a lirst and a second biasing winding, a first energizing circuit connecting said lirst biasing winding to said source, a second energizing circuit connecting said second biasing winding to said source, said two energizing circuits carrying currents of different phase, amplitude-varying means in said second energizing circuit adapted effectively to vary the phase of the alternating electromagnetic field due to the combined effect of said currents, said amplitudevarying means being thus operable to maintain said impedance at a relatively high value for `a selected length ot time following the appearance of a voltage node across said contacts, and control means so synchronizing said mechanism with said amplitude-varying means `as to cause said contacts to close invariably at the instant of said voltage node and to re-open at a subsequent instant, determined by the position ot said amplitude-varying means, at which said impedance is again so high as to reduce the iiow of current through said contacts to substantially zero.

9. ln a contact converter, in combination, a load circuit including a pair of contacts, a source of alternating voltage in series with said contacts, an operating member for periodically opening and closing said contacts, a motor having a housing and a shaft rotating in said housing, cam means on said shaft controlling said operating member and determining an operating cycle therefor equal vto a cycle of said alternating voltage, supporting means for said member displaceablc with respect to said cam means so as to vary the length of time during which said cam means is eective to open and to close said contacts during said operating cycle, a saturable-core reactor including a main winding connected in said circuit as a variable impedance in series with said contacts, said reactor being provided with at least one biasing-winding, an energizing circuit for said :biasing winding connecting the lat-ter to said source and including phase-shifting means, said phase-shifting means being operable to maintain said impedance iat a relatively high value for a selected length of time following the appearance of a voltage node across said contacts, rst regulator means connecting said phaseshifting means to said supporting means for displacing the latter in dependence upon the position or" said phaseshifting means, and second regulator means connecting said housing to said phase-shifting means for rotating said housing simultaneously with the displacement of said supporting means, said first and second regulator means by their combined action causing said contacts to close invariably at the instant of said voltage node and to re-open at a subsequent instant, determined by the position of said phaseshifting means, at which sai-d impedance is again so high as to reduce the .flow ot' current through said contacts to substantially zero.

i0. A contact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source, a respective pair of contacts in each of said input circuits, a load circuit connected across all of said input circuits, mech anisms for periodically opening7 and closing 'all of said pairs of contacts with staggered closure periods, said mechanism being synchronized with said source for invariably closing each pair of contacts at a time when the voltage -thereacross is substantially zero, variable impedance means in each of said input circuits, control means periodically increasing and decreasing the impedance of each of said variable impedance means so as to delay the rise of current in each of said input circuits for a variable period following `the closure of the respective pair of conta-cts, and adjusting means coupled with said control means for varying the length of said period by modifying the rhythm of operation of said control means.

l1. A contact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternatingecurrent source, a respective pair of contacts in each of said input circuits, a load circuit connected across all of said input circuits, mechanism for periodically opening and closing all of said pairs of contacts with overlapping closure periods, said mechanism being synchronized with said source for in- Variably closing each pair of contacts at Va time when the voltage thereacross is substantially zero, saturable electromagnetic reactance means connected in each of said input circuits as a variable impedance in series with the respective pair of contacts, biasing means for each of said 4reactance means periodically varying the degree of saturation thereof, thereby changing the value of said impedance, and adjusting means lfor so synchronizing said biasing means with said mechanism as to delay the rise `of current in each of said input circuits, following the closure of the respective pair of contacts, for a selected length of time.

l2. A yContact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source, a respective pair of contacts in each of said input circuits, a load circuit connected across all of said input circuits, mechanism for periodically -opening and closing all of said pairs of contacts with overlapping closure periods, reactive means in said load circuit tending to maintain constant the total ilow of current therein, thereby causing the phase current in any of said input circuits to decay following the closure of said contacts in another of said input circuits and the rise of the phase current within the latter, saturable elece tromagnetic reactance means connected in each of said input circuits as a variable impedance in series with the respective pair of contacts, biasing means for each of said saturable reactance means periodically varying the degree of saturation thereof, thereby changing the value of said impedance, said mechanism being synchronized with said source for invariably closing the pair of contacts of a given input circuit -at the instant when ythe phase voltage of said input circuit intersects the phase voltage of the input circuit previously closed and for opening the contacts of said previously closed circuit at a time when the phase current in the latter circuit has substantially decayed, and adjusting means for so synchronizing said biasing means with said source as to maintain said impedance of each input circuit 'at a relatively high value for a selected period following closure of its respective pair of contacts.

13. A contact converted comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source, `a respective pair `of contacts in each of said input circuits, a load circuit connected across all of said input circuits, mechanism for periodically opening yand closing all of said pairs of contacts with overlapping closure periods, reactive means in said load circuit tending to maintain constant the total iiow of current therein, thereby causing the phase current in any of lsaid input circuits to `decay following the closure of said contacts in another ol said input circuits and the `rise of the phase current within the latter, saturable electromagnetic reactance means connected in each of said input circuits as a variable impedance in series with the respective pair of contacts, biasing means for each of said saturable reactance means periodically varying `the degree of saturation thereof, thereby changing the value of said impedance, said mechanism being synchronized with said source for invariably closing the pair of contacts of a given input circuit at the instant when lthe phase voltage of said input circuit intersects the phase voltage of the input circuit previously closed and for opening the contacts of said previously closed circuit at la time when the phase current in the latter lhas substantially decayed, and adjusting means for so synchronizing said biasing means with said source as to maintain said impedance of each input circuit lat a relatively high value for a selected period following closure of its respective pair of contacts and again at about the time of re-opening of said contacts, thereby helping to maintain the flow of current through said contacts at negligible values lat the time of their re-opening.

14. A contact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source, a respective pair of contacts in each of said input circuits, mechanism for periodically opening and closing all of said pairs of contacts with overlapping closure periods, said mechanism having an operating cycle equal to a cycle of said polyphase source, first regulator means for simultaneously varying the length of the closure periods for all of said pairs of contacts, second regulator means for varying the phase of said operating cycle relative to the output of said source, a load circuit connected across all of said input circuits, reactive means in said load circuit tending to maintain constant the total ilow of current therein, thereby causing the phase current in any of said input circuits to decay following the closure ot said contacts in another of said input circuits and the rise of the phase current within the latter, saturable electromagnetic reactance means connected in each of said input circuits as a variable impedance in series with the respective pair of contacts, biasing means for each of said saturable reactance means periodically varying the degree of saturation thereof, thereby changing the value of said impedance, control means so operating said first and second regulator means as invariably to close the pair of contacts of a given input circuit at the instant when the phase voltage of said input circuit intersects the phase voltage of the input circuit previously closed, said biasing means causing the impedance of each input circuit to reach a irst peak at about the time of closure of its contacts and to reach a second peak roughly half a cycle thereafter, and adjusting means coupled with said biasing means and with said control means for displacing said peaks with respect to said time of closure, thereby delaying the rise of current in each input circuit for a selectively variable period, and for timing the re-opening of each pair of contacts to occur substantially at a time when the impedance of the respective input circuit is at its said second peak.

l5. A contact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source; a respective pair of contacts in each of said input circuits; mechanism for periodically opening and closing all of said pairs ot' contacts with overlapping closure periods, said mechanism comprising a rotating shaft, a respective operating member for each of said pairs of contacts, respective cam means on said shaft for each of said operating members, and supporting means for all of said operating members adjustable to vary the length of time during which each of said cam means is effective to open and to close the associated pair of contacts during each operating cycle of said mechanism, said operating cycle being equal to a cycle of said polyphase source; a load circuit connected across all of said input circuits and including reactive means tending to maintain constant the total flow of current in said load circuit, thereby causing the phase current in any of said input circuits to decay following the closure of said contacts in another of said input circuits and the rise of the phase current within the latter; saturable electromagnetic reactance means connected in each of said input circuits as a variable impedance in series with respective pair of contacts; biasing means for each of said saturable reactance means periodically varying the degree of saturation thereof, thereby changing the value of said impedance; control means so operating said mechanism as invariably to close the pair of contacts of a given input circuit at the instant when the phase voltage of said input circuit intersects the phase voltage of the input circuit previously closed, said control means including means for adjusting said supporting means, said biasing means causing the impedance of each input circuit to reach a first peak at about the time of' closure of its contacts and to reach a second peak roughly half a cycle thereafter; and adjusting means coupled with said biasing means and with said control means for displacing said peaks with respect to said time of closure, thereby delaying the rise of current in each input circuit for a selectively variable period, and for timing the re-opening of each pair of contacts to occur substantially at atime when the impedance of the respective input circuit is at its said second peak.

16. A contact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source; a respective pair of contacts in each of said input circuits; mechanism for periodically opening and closing all of said pairs of contacts with overlapping closure periods, said mechanism comprising a motor with a housing and a shaft rotating in said housing, a respective operating member for each of said pairs of contacts, respective cam means on said shaft for each of said operating members, supporting means for all of said operating members, rst regulator means for so displacing said supporting means with respect to all of said cam means as to vary the length of time during which each of said cam means is effective to open and to close the associated pair of contacts during each operating cycle of said mechanism, said operating cycle being equal to a cycle of said polyphase source, and second regulator means for varying the phase of said operating cycle relative to the output of said source by rotating said housing; a load circuit connected across all of said input circuits and including reactive means tending to maintain constant the total flow of current in said load circuit, thereby causing the phase current in any of said input circuits to decay following the closure of said contacts in another `of said input circuits and the rise of the phase current Within the latter; saturable electromagnetic reactance means connected in each of said input circuits as ia variable impedance in series with the res ective pair of contacts; biasing means for each of said saturable reactance means periodically varying the degree of saturation thereof, thereby changing the value of said impedance; control means so operating said lirst and second regulator means as invariably to close the pair ot contacts of a given input circuit at the instant when thc phase voltage of said input circuit intersects the phase voltage of the input circuit previously closed, said biasing means causing the impedance of each input circuit to reach a rst peak at about the time of closure of its contacts and to reach a second peak roughly half a cyclc thereafter; and adjusting means coupled with said biasing means and with said control means for displacing said peaks with respect to said time of closure, thereby delaying the risc of current in each input circuit for a selectively variable period, and for timing the re-opening of each pair of contacts to occur substantially at a time when the impedance of the respective input circuit is at its said second peak.

17. A contact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source, a respective pair of contacts in each of said input circuits, mechanism for periodically opening and closing all of said pairs of contacts with overlapping closure periods, said mechanism having an operating cycle equal to a cycle of said source, a load circuit connected across all of said input circuits and including reactive means tending to maintain constant the total flow of current in said load circuit, thereby causing the phase current in any of said input circuits to decay following the closure of said contacts in another of said input circuits and the rise of the phase current Within the latter, a plurality of saturable-core reactors each including a main Winding connected in a respective one of said input circuits as a variable impedance in series with the respective pair of contacts thereof, each of said reactors being further provided with at least one biasing Winding, an energizing circuit for said biasing windings connecting the latter to said source and including phaseshifting means, control means so operating said mechanism as invariably to close the pair of contacts of a given input circuit at the instant when the phase voltage of said input circuit intersects the phase voltage of the input circuit previously closed, said energizing circuit causing the impedance of each input circuit to reach a first peak at about the time of closure of its contacts and to reach a second peak roughly half a cycle thereafter, and adjusting means coupled with said phase-shifting means and with said control means for displacing said peaks with respect to said time of closure, thereby delaying the rise of current in each input circuit for a selectively variable period, and for timing the reopening of each pair of contacts to occur substantially at a time when the impedance of the respective input circuit is at its said second peak.

18. A contact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source, a respective pair of contacts in each of said input circuits, mechanism for periodically opening and closing all of said pairs of contacts with overlapping closure periods, said mechanism having an operating cycle equal to a cycle of said source, a load circuit connected across all ot said input c:4 nits and including reactive means tending to mainta constant the total flow of current in said load circuit, thereby causing the phase current in any of said input circuits to decay following the closure of said contacts in another of said input circuits and the rise of the phase current within the latter, a plurality of saturable-core reactors each including a main Winding connected in a respective one of said input circuits as a variable impedance in series withl the respective pair of contacts thereof, each of said reactors being further provided with a rst and a second biasing winding, a first energizing circuit connecting said first biasing windings to said source, a second energizing circuit connecting said second biasing windings to said source, said two energizing circuits delivering currents of diferent phase to the biasing windings of each of said reactors, amplitudevarying means in said second energizing circuit adapted efectively to vary the phase of the alternating electromagnetic eld of each reactor due to the combined eifect of the currents in its biasing windings, control means so operating said mechanism as invariably to close the pair of contacts of a given input circuit at the instant when the phase voltage of said input circuit intersects the phase voltage of the input circuit previously closed, said energizing circuits causing the impedance of each input circuit to reach a rst peak at about the time of closure of its contacts and to reach a second peak roughly half a cycle thereafter, and adjusting means coupled with said amplitude-varying means and with said control means for displacing said peaks with respect to said time of closure, thereby delaying the rise of current in each input circuit for a selectively variable period, and for timing the reopening of each pair of contacts to occur substantially at a time when the impedance of the respective input circuit is at its said second peak.

19. A contact converter comprising a plurality of input circuits each energized by a respective phase voltage of a polyphase alternating-current source, a respective pair of contacts in each of said input circuits, a plurality of operating members each adapted periodically to open and to close a respective one of said pairs of contacts, a motor having a housing and a shaft rotating in said housing, respective cam means on said shaft for each of said operating members, said cam means being positioned on said shaft in staggered relation for effecting closure of said pairs of contacts during overlapping periods, supporting means for said operating members displaceable with respect to said cam means so as to vary the length of time during which each of said cam means is elective to close the associated contacts in the course of an operating cycle equal to a cycle of said source, a load circuit connected across all of said input circuits and including reactive means tending to maintain constant the total ow of current in said load circuit, thereby causing the phase current in any of said input circuits to decay following the closure of said contacts in another of said input circuits and the rise of the phase current within the latter, a plurality of saturable-core reactors each including a main winding connected in a respective one of said input circuits as a variable impedance in series with the respective pair of contacts thereof, each of said reactors being further provided with at least one biasing winding, an energizing circuit for said biasing windings connecting the latter to said source and including phase-shifting means, first regulator means connecting said phase-shifting means to said supporting means for displacing the latter in dependence upon the position of said phase-shifting means, second regulator means connecting said housing to said phase-shifting means for rotating said housing simultaneously with the displacement of said supporting means, said first and second regulator means by their combined action causing the pair of contacts of any of said input circuits to close invariably at a time when the phase voltage of such input circuit intersects the phase voltage of the input circuits previously closed, said energizing circuit causing the impedance of each input circuit to reach a rst peak at about the time of closure of its contacts and to reach a second peak roughly half a cycle thereafter, and adjusting means coupled with said phase-shifting means and with said first and second regulator means for displacing said peaks with respect to said time of closure, thereby delaying the rise of current in each input circuit for a selectively variable period, and for timing the re-opening of each pair of contacts to occur substantially at a time when the impedance of the respective input circuit is at its said second peak.

References Cited in the tile of this patent UNITED STATES PATENTS 2,181,152 Rolf Nov. 28, 1939 2,227,937 Koppelmann Ian. 7, 1941 2,557,739 Goldstein et al. June 19, 1951 FOREIGN PATENTS 881,582 France Apr. 29, 1943

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