US2669621A - Contact device for synchronous switches - Google Patents

Description

Feb. 16, 1954 DUFFlNG I 2,669,621

CONTACT DEVICE FOR SYNCHRONOUS SWITCHES Filed May 8, 1951 2 Sheets-Sheet 1 F 40 44 .9 K #2 II I J: a :4

1954 P. DUFL-FING 2,669,621

comm DEVICE FOR SYNCHRONOUS SWITCHES Filed May a. 1951 2 Sheets-Sheet 2 Patented Feb. 16, 1954 CONTACT DEVICE FOR SWITCHE SYN CHRONOUS S Paul Dufling, Berlin-Siemensstadt, Germany, assignor to Siemens-Schuckertwerke, Aktien- Siemensstadt, Germany, a

gesellschaft, Berlinccrporaticn of Germany Application May 8, 1951, Serial No. 225,228

7 Claims.

My invention relates to contact devices for synchronous switches such as used, for instance, for controlling an electric circuit or performing a rectifying or other translating operation in the rythm of an alternating current.-

Such synchronous switches are supposed to open an alternating-current circuit at or near the current zero passages without occurrence of arcing. To meet this requirement, the switches must operate with extremely little delay so as to open their contacts immediately upon impulse reception. Switches of this kind have been equipped with a magnetizable contact bridge which is forced against a countercontact by the pulling force of a magnet in opposition to a kickout spring capable of tearing the bridge away from the magnet when the magnet force is weakened or vanishes due to an impulse. To secure the necessary high speed of interruption, the force of the kick-out spring must be rather large as it is called upon to produce a high acceleration of the bridge. The holding magnet in this device must provide the contact pressure in addition to the forces needed for overpowering the kick-out spring.

It is an object of my invention to devise a contact device for synchronous switches that can be given smaller dimensions than heretofore required, and that secures a high speed of circuit interruption without necessity for the largesize or large-mass kick-out springs of the kind heretofore used in such devices.

According to the invention, a synchronousswitch contact device is designed in such a manner that the movable and magnetizable contact bridge, when in the fully switched-in or make position, is elastically abutted by resilient countercontacts so that, in this bridge position, the magnetic force closing the contact device is substantially fully balanced by the elastic opposing forces imposed upon the bridge by the then deflected countercontacts. When the holding force of the bridge-controlling magnet drops below a given value, the elastic contacts operate as stop when in the fully switched-in position. In devices of the latter type, the resiliency of the countercontacts serves merely for securing a proper contact engagement but is not the exclusive means for accelerating the contact bridge, a separate kick-out spring being provided for the latter purpose.

It is therefore essential for the invention that the required high acceleration of the contact bridge be supplied substantially only by the spring forces of the countercontacts against which the contact bridge is resiliently abutted when in the fully switched-in position. While thus a separate kick-out spring is eliminated, a resilient structural part furnishing a slight spring force, of course, may be used for guiding the magnetizable contact bridge.

According to another feature of my invention, the two stationary or countercontacts to coact with the movable and magnetizable contact bridge are given respectively different spring characteristics, and the countercontact having the steeper spring characteristic is disposed to be engaged by the contact bridge at a later moment than the countercontact having the shallower characteristic. This permits adapting the spring forces over a wide range to the behavior of the magnetic holding force in dependonce upon the air gap distance so that even during rapid switching there is no danger that the resilient countercontacts will be overpowered to a point Where the magnetic countercontact bridge abuts against the holding magnet. According to still another feature of the invention, the contact bridge is equipped with two contact members disposed at the right and at the left of a magnet armature. These two contact members cooperate with four legs or parts of the stationary contact structures, and each two diagonally opposite contact parts are given the same spring characteristics.

According to a further feature of the invention, the contact bridge is equipped with elastic extensions to serve as a guide means. The contact faces or points of the bridge are preferably produced by embossing because then the countercontacts can be disposed within a single plane without obviating the possibility of accurately adjusting the device for a sequential engagement of the countercontacts by the moving bridge.

The foregoing and more specific objects, advantages and features of the invention will be apparent from the following description in conjunction with the drawing in which:

Fig. 1 is explanatory and shows schematically a side view of a contact device previously proposed for synchronous switches;

Fig. 2 shows, in perspective, an embodiment of a switching device according to the invention, Fig. 3 is a top view of the device, and Figs. 4 and 5 are, respectively, a bottom view and a side View of a contact bridge pertaining to the same device;

Figs. 6 and 7, respectively, show bottom views of two modified contact bridges of devices accord-- ing to the invention; and

Fig. 8 is a complete illustration of circuit interrupting apparatus comprising a switching device according to Figs. 2 to 5, shown in perspective, in conjunction with diagrammatically shown circuit connections.

In the illustration of a previously proposed device shown in Fig. 1, an electrically conductive contact bridge l of magnetizable material is disposed in the field of a stationary magnet 2 and operates with stationary contact structures 3 and d. The contact bridge 5 consists of a ferromagnetic armature which, for instance, may directly. serve for conducting the electric current between the stationary contacts, or which may carry a current-conducting member to electrically bridge the stationary contacts. Connected with the bridge 5 is a kick-out spring 5. Denoting the force of the holding magnet 2 by M, the force of the kick-out spring 5 by F, and the mechanical reaction forces of the countercontacts 3 and 4 by K1 and K2, these forces being represented in Fig. 1 by respective arrows, it will be recognized that when the bridge 5 is in the illustrated make position, the magnet force M must be equal to the sum of the spring force F and the reaction force K1 and K2. If the stationary countercontacts are rigid, the forces K1 and K2 are merely abutment forces which do not participate in causing acceleration of the bridge. As mentioned, it has also been proposed to give the countercontacts some resiliency, for instance, as illustrated for the countercontact 4. This resiliency, however, serves only for improving the contact engagement. Hence, when the contact bridge is in fully attractedposition, the bridge'is not counterbalanced by the resiliency of the stationary contact, the abutting force being provided by the stationary and rigid back 5 of the structure against which the resilient portion is forced when the contact bridge is fully in the make position.

In Fig. 2, showing in comparison a device according to the invention, the stationary magnet 2 and the countercontacts 3 and 5 correspond as to arrangement and switching function to the equally designated respective elements of the device according to Fig. 1. However, the stationary countercontacts 2i and 4 in the device of Fig. 2 are resilient and the pertaining movable and ferromagnetic contact bridge when in fully attracted position is resiliently abutted by the stationary contact structures so that then the magnetic force M of magnet 2 is balanced by the elastic reaction forces. Consequently, a kickout spring is not required for accelerating the bridge. When the bridge isbeing attracted toward the final make position, it touches the contact points of the stationary contact structures and thereafter deflects these structures to a distance of elastic deflection at which the reactive forces K1 and K2 are just equal to the magnet holding force. When in fully attracted position, the bridge is still sufliciently spaced from the magnet 2 to exclude the occurrence of a rigid abutment. When the force of magnet 2 is caused to vanish or to drop. below a given value, for

instance, by means of an impulse applied to a control coil (not illustrated) of the magnet, the reaction forces imposed upon the bridge by the deflected stationary contact structures produce the acceleration of the bridge required for the desired extremely rapid interruption of the electric circuit. In such a device, the accelerating force of the spring contacts can be made as large as the magnetic holding force.

To facilitate adapting the spring forces of the countercontacts to the pulling force of the magnet, the two countercontacts can be given respectively different spring characteristics and the countercontacts having the stiffer spring characteristic can be made to be engaged by the countercontact bridge at a later moment than the countercontact having the softer characteristic. This permits adapting the behavior of the spring force of the countercontacts to the characteristic of the attractive magnet force so that, even at a rapid switching-in movement of the contact bridge, the deflection of the elastic stationary contacts remains within the limits needed to prevent the contact bridge from abutting against the holding magnet. Hence, the bridge remains exclusively force-balanced by the elastic resiliency of the countercontacts.

It is especially favorable, as shown in Fig. 2 to compose the contact bridge of a magnet armature member H and of two current conductor members l3 and I l bordering the left and right sides of the armature member H. The members l3, l4 consist of highly conductive material and are firmly joined with the armature member II, for instance, by hard soldering or brazing. As apparent from Fig. 3, the four elastic contacts 3, 3", 4' and 4" engageable by the bridge contact members l3, l4 may form parts or legs of the stationary contactstructures 3 and 4. As explained, these four parts or legs of the stationary contact structures can be given different spring characteristics, preferably so that each two diagonally opposite contact parts 3' and l, or 3" and 4" have the same spring characteristic. The contact parts having the steeper or stiffer spring characteristic are engaged by the contact bridge during the make movement at a later moment than the contact parts having the shallower spring characteristic. The spring characteristic is preferably so chosen that in the end position of the contact bridge i. e. when this bridge has reached the fully switched-in make position, the contact pressures then exerted upon the bridge by the respective parts of the countercontacts are approximately equal to one another.

For facility of manufacture, it is preferable to have all parts of the countercontacts disposed in the same geometric plane because the pertaining contact faces can then be readily machined by grinding. In order to have the countercontact parts of the steeper spring characteristic engaged by the contact bridge at a later moment than the countercontact parts of the shallow spring characteristic, the contacts points or contact faces of the bridge are preferably manufactured by embossing. The small protuberances or bosses thus produced are denoted in Figs. 4 and 5 by I, 8, 9 and II! respectively. The top surface of each boss forms a contact face for engagement with the adjacent part of the stationary contact structures, the bosses I and 9 being higher than the bosses 8 and In.

For guiding the magnetizable contact bridge, the bridge structure may be given resilient ex tension as shown in Fig. 6. The resilient extensions l and I6 form an integral part with the armature portion I l of the bridge in order to avoid difficulties otherwise due to the necessity of providing a permanently secure connection. The resilient extensions serve merely for guiding the armature i. e; they do not appreciably con tribute to tearing the bridge away from its make position. The spring forces of extensions l5 and I6 are considerably smaller than the spring force of the counter-contacts. To secure the desired softness of the extensions, they may be given a wavy configuration such as exemplified in Fig.7.

It will be understood that the contact bridge, after the opening of the contacts, is generally held in the open or-bre'ak position by means of a second magnet located at the armature side opposite the magnet 2. Just as the above-mentioned magnet 2, the additional holding magnet is also equipped with impulse windings that permit reducing or substantially eliminating the magnet flux, as will be understood from the embodiment shown in Fig. 3 and described presently.

The synchronous switching apparatus of Fig. 8 serves to open an alternating-current circuit upon receipt of a control impulse determined by the actuation of a control contact. The apparatus is equipped with a switching device according toFigs. 2 to 5 and, as far as similar elements concerned, is denoted by the same respective reference numerals.

The movable armature H with the pertaining contact bridges l3 and M is suspended by steel wires 60. If desired, the wire suspension may be replaced by providing the armature with elastic extensions as described in the foregoing with reference to Figs. 6 and 7.

The lower holding magnet 2 has laminated iron core 22 whose pole shoes face the armature. The iron core 2i has a recess into which a permanent magnet 22 is inserted. The iron core is shaped to form a magnetic shunt 23 across the magnet 22. The shunt has a gap so that normally most or an appreciable portion of the unidirectional fiux from the permanent magnet 22 passes through the pole shoes. However, when winding 26 is sufficiently excited, the permanent flux is forced away from the pole shoes so that then the armature H is released and, under the force exerted by the 4, will swing upward away from the pole shoes of the holding magnet.

The upper hoiding magnet for maintaining the armature in its other, uppermost position is denoted as a whole by 39. Similar to the lower holding magnet 22, the magnet 39 has a laminated iron core 35 with an inserted permanent magnet 32, and its pole shoes face the upper surface of the armature The core of magnet 39 also has a magnetic shunt portion 33 and a control winding 34.

The alternating-current load circuit to be controlled by the synchronous switching apparatus is shown in heavy lines. When this circuit is closed through the stationary contacts 3, 4 and the contact bridges l3, M of the armature II, the current flowing through the circuit passes through the main winding 4| of a saturable reactor 45. The reactor has a secondary winding 42 and an auxiliary premagnetizing winding 43. The auxiliary winding 43 is connected through a resistor 44 to a suitable source 45 of constant direct voltage. The magnetizable core of the reactor 40 has a nearly rectangular magnetization characteristic. The excitation of the reacelastic contacts 3 and responsive coil means for tor by the alternating current in the main winding 4| has such a magnitude that the reactor core passes through the unsaturated portion of its magnetic characteristic only in the vicinity of the current zero passages but is saturated at all other instants of its operating period. Consequently, a current pulse is induced in the secondary winding 42 for each zero passage of the current in winding 4|. In order to have these current pulses occur at a moment shortly before the current zero passage, the reactor core is premagnetized by direct current with the aid of the auxiliary winding 43. The circuit of the control winding 34 pertaining to the holding magnet includes a suitable source 36 of direct voltage and an ohmic resistor 31.

The synchronous switching apparatus in the illustrated embodiment is controlled by a push button switch 50 to be actuated manually or by limit switches or the like automatic devices. Switch 50 has a set of .normally closed break contacts 5| and a set of normally open make contacts and is biased by a spring 53 to the illustrated position. The secondary reactor winding 42 is normally connected with control winding 24 of holding magnet 2 through the break contacts 5|. The make contacts 52 are connected in the above-mentioned circuit of the control winding 34 for magnet 30.

When the switch 50 is in the illustrated normal position, the armature 2| is kept attracted by the upper holding magnet 30. When switch 50 is actuated to close contacts 52, the control winding 34 of magnet so is energized from source so that the permanent flux of magnet 32 is shunted away from the pole shoes and from the armature H, the magnetic shunt path 33 then preventing the permanent magnet 32 from being demagnetized. Consequently, the actuation of switch 50 has the eiTect of eliminating the holding force of the magnet 39. The armature H ters into the field of the magnet 2 from which the armature is now attracted. This causes the contact bridges l3, I l to interconnect the stationary contacts 3 and 4 thus closing the load circuit. Thereafter, the load circuit will remain closed as long as switch 59 remains actuated to close the make contacts 52. When switch 50 is released, contacts 5| become closed and a current pulse from secondary winding 42 of reactor is passed through the winding 2' shortly before the next following zero passage of the load current. These current pulses produce in the core of magnet 2 a flux opposed to the permanent flux from magnet 22. Hence, as soon as such a pulse is received, flux of magnet 22 is temporarily shunted away from the armature This releases the armature which returns into the field of the holding magnet 30 to be kept in the circuit opening position until the switch is again actuated.

I claim:

1. A synchronous contact device for interrupting alternating current near the current zero moment, comprising a magnetizable contact bridge movable between make and break positions, counteroontacts engaged by said bridge in said-make position, a magnet having a field traversing said bridge when said bridge is in said make position for forcing said bridge against said counteroontacts, said magnet having P lseweakening said field to release said bridge, said counteroontacts being elastically deflective and having an elastic reaction force in balance with the force of said magnet when said bridge is in said make position so as to provide substantially all of the force needed for moving said bridge to said break position upon receipt of a current pulse by said coil means.

2. A synchronous contact device for interrupting an alternating current near its zero passage, comprising a main circuit having two stationary contact structures spaced and insulated from each other, a magnetizable contact bridge having a make position in which it bridges said two stationary contact structures to close said main circuit, said bridge being movable away from said. two structures to a break position, a magnet magnetically coupled with said bridge when said bridge is in said make position and having a magnetic force holding said bridge in said make position, said magnet being spaced from said bridge in both said positions and having pulse-responsive coil means, a control circuit connecting said coil means with said main circuit for causing said coil means to weaken said magnetic force to release said bridge from said make position, said stationary contact structures being elastically deflectable due to said magnetic force when being contacted by said bridge and having an elastic force in balance with said magnetic force when said bridge is in said make position, whereby said stationary contact structures provide substantially all of the kick-out force needed for moving said bridge to said break position when said bridge is released by said magnet.

3. In a contact device according to claim 2, each of said stationary contact structures having a movable portion engageable by said bridge, said movable portion of one of said stationary contact structures having less resiliency than said movable portion of said other structure and being engageable with said bridge at a later moment than said movable portion of said other structure during the make movement of said bridge.

4. In a contact device according to claim 3, said bridge having two current-conducting members spaced from and parallel to each other, and each of said stationary contact structures having two portions engageable with said twomembers, each two diagonally opposite portions having the same resiliency.

5. In a contact device according to claim 2, said contact bridge having elastically deformable extensions, said extensions having respective stationarily mounted ends for movably suspending said armature, and said extensions having. negligible elastic force as compared with said kick-out force.

6. In a contact device according to claim 2, said stationary contact structures having respective bendable portions, and said contact bridge being embossed to form protuberances and having respective contact faces on said protuberances in engagement with said respective bendable portions when in said make position.

7. In a contact device according to claim 2, said contact bridge comprising a magnet armature portion and two current-conductor members joined with said armature portion at two respective parallel edges thereof, each of said members being embossed to form two protuberanccs mutually spaced along said member and forming respective contact faces. said contact faces being located in difierent planes, and each of said stationary contact structures having two bendingly resilient portions engageable with two of said contact faces of said respective members, said portions being disposed in a common plane so as to be successively contacted by said members during the make movement of said bridge, and said portions first contacted by said bridge during said movement being less resilient than the next contacted portions.

PAUL DUFFING.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 666,764 Lindstrom et a1. Jan. 29, 1901 803,486 Hill Oct. 31, 1905 841,215 Andrews Jan. 15, 1907 1,953,929 Droysen Apr. 10, 1934.

2,203,297 Granberg June 4, 1940 2,381,309 Powell Aug. '7, 1945 2,499,394 Kesselring Mar. 7, 1950- 2,5'70,062 Kesselring Oct. 2, 1951 FOREIGN PATENTS Number Country Date 492,262 Germany Feb. 21, 19 30

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