US2680790A - Load changeover switch for tapped transformers using a combination of contact movements - Google Patents

Description

June 8, 1954 B. JANSEN 2,680,790

LOAD CHANGEOVER SWITCH FOR TAPPED TRANSFORMERS USING A COMBINATION OF CONTACT MOVEMENTS Filed March 7, 1951 4 Sheets-Sheet l INSULH TING WATER/AL June 8, B JANSEN 2,680,790

LOAD CHANGEOVER SWITCH FOR TAPPED TRANSFORMERS USING A COMBINATION OF CONTACT MOVEMENTS Filed March '7, 195

4 Sheets-Sheet 2 L m U M 4 W M w M June 8, 1954 JANSEN 2,680,790

LOAD CHANGEOVER SWITCH FOR TAPPED TRANSFORMERS USING A COMBINATION OF CONTACT MOVEMENTS Filed March 7, 1951 4 Sheets-Sheet 3 June 8, 1954 JANSEN 2,680,790

LOAD CHANGEOVER SWITCH FOR TAPPED TRANSFORMERS USING A COMBINATION OF CONTACT MOVEMENTS Filed March 7, 1951 4 Sheets-Sheet 4 BY Q1AM ow a Ml/ Patented June 8, 1954 UNITED STATES PATENT OFFICE LOAD CHANGEOVER SWITCH FOR TAPPED TRANSFORMERS USING A CQMBINATION OF CONTACT MOVEMENTS 2 Claims.

A load changeover switch of customary design accomplishes its task of changing over the Work ing current from the hitherto connected transformer tap to the next one by means of several main and auxiliary contacts and changeover resistances switched in between these contacts which are closed and opened consecutively in the required switching sequence and with the required switching velocity. Three patterns much used in practice are shown in the illustrations belonging to the patents DRP 474,613, 648,600 and 707,188. It is apparent, that the sequence of the contact closing and opening operations which in the case of using ohmic changeover resistances are supposed to be achieved within the shortest possible overall time, and the interrupt ing velocity of all contacts which for safe arc extinguishing is supposed to be as great as possible, is essentially influenced by three items, i. e.

firstly by the spatial arrangement of the stationary and movable main and auxiliary contacts, secondly by the cinematics of the movable contact and finally by the velocity trend of the primary driving organ. It is up to the designer to take these factors into account when designing such switches. The steadily increasing rated power of tapped transformers resulted in such dimensions of the load changeover switches as to require for reasons of mechanic strength great masses to be moved and consequently an expensive construction. Additional enlargement of the dimensions was required by two further phenomena which were hitherto considered inevitable, i. e. the factory inaccuracies of the load changeover switch contacts and the influence of burnt down contacts upon the process of the individual switching operations.

The present invention for which patent is applied increases the velocity of closing and opening by an unsteady secondary movement which is superimposed on the steady primary contact movement in the deciding moments and i using for this purpose technical means which at the same time paralyse the influence which factory inaccuracies of the load changeover switch contacts or their steadily increasing burning down might have upon the total duration of the changeover switching operation, thereby reducing the total changeover switching period to the lowest possible limit. Related to the same switching velocity, which is obviously prescribed by the extinguishing requirements of the switching arcs, the invention entails smaller dimensions, reduces in this way the masses of the moved load changeover switch parts and lowers the stresses which 2 arise in the material during the quick changeover switching operation.

The object of the invention realizes the increase of the closing and opening velocity of the :1. movable contacts by their movements being determined by two elements, i. e. the driving organ of the movable load changeover switch part and the main or auxiliary contact switched on at the moment. The driving organ transmits to all closing or opening contacts a steady primary movement which is accelerated or retarded in its individual phases, by using customary cinematic means which have partly been applied already hitherto in the design of load changeover switches. The contact which is closed presently, impresses on the contacts which are in the state of being closed or opened with the above-mentioned steady primary movement and which are connected with it over a common guide, an additional unsteady secondary movement which added to the steady primary movement, yields the desired and actually obtained combined movement of the switching contacts. The capability of the stationary switched-on contact to transfer an additional movement to other moved contacts, is based on the fact, that this contact is connected pliably over a common guide, moved directly or indirectly by the driving organ, with the other contacts engaged in the closing or opening movement, thus having an accelerating or retarding effect on them, dependent on the direction of movement of the guide. The impressed unsteady secondary movement is therefore a so called relative movement, and by designing the cinematics of the contact guide and its links to the switching contacts in accordance with the present invention it is possible to give the closing and opening contacts the greatest additional movement in the desired direction just in the deciding instant of opening or closing them.

At the same time, the elfects of factory inaccuracies on the load changeover switch contacts and of their increasing loss of substance by burning down are compensated by the causal dependence of the secondary movement on the fact of the actually completed closing of that contact which initiates the secondary movement. There is no more need of providing additional safety runs of the contacts for the timely overlapping of contact closing; for the secondary movement of the opening contact begins with a sudden start just in that instant when the controlling contact is actually closed, and the secondary movement of the closing contact finishes in the same sudden unsteady way in the moment of its actual closing and is used from that instant on for the benefit of the acceleration of the next opening contact. In this way, when moving the load changeover switch from the initial position to the final position, a continual alternation of increase of closing velocity up to the moment of actual closing and from then on of increase of opening velocity is attained for each switching contact, progressing from the first to the last contact coupled through the guide.

The application of the invention brings about a reduction of dimensions which is especially re markable in cases where the stationary main and auxiliary contacts of the load changeover switches are arranged on contact carriers which have the shape of circles or circle arcs. I'he application of the invention is also especially appropriate for load changeover switches, in which several changeover resistances are to be connected at the same time by corresponding contact pairs, in order to obtain a distribution of the current to several branch resistances, and in order to have to interrupt by consecutive openingand closing of'such parallel branch'circuits only small arc currents on the switching contacts what is much for the benefit of the lifetime of the contacts.

Figs. 1A, 1B and 10 show respectively a single embodiment of the present invention in three different positions which it assumes during the course of a complete cycle of operation.

Fig. 2 shows movement diagrams illustrating the eiiects of the secondary movements on the closing and opening velocities.

Fig. 3 shows velocity curves illustrating the same efiects as in Fig. 2.

Fig. 4 shows another embodiment of this invention for use with a slot guide on less than a full circle, and

Fig. 5 shows a difierent embodiment of this invention, employing a rocker type guide.

' Figs. 1A, 1B and 1C demonstrate on the example of a load changeover switch, the four stationary switching contacts of which Ha, ha, hb,

'Hb are distributed on a circular contact carrier Ta, how the problem can be solved by means of intermediate member shown as a starshaped guide L, which is connected to the movable contacts K1, K2, K3 over links pushing rods L1, L2,.L3 and how the changeover process from the initial position 1 to the final position 13 is going on in load changeover switches with ohmic potential dividers in severals phases (Jansen switch).

The two transformer tappings A and B which are to be changed are connected to the stationary main contacts Ha and H1). From there, the path of the current is going through the changeover resistances Wu and Wb to the two auxiliary contacts ha and hi) respectively. The current is led off from the center of the movable contact sys tem K1, K2, K3. These contacts are mounted on a circular contact carrier Ti which by means of an outer tooth system 1 to 12, is unrolling in an inner tooth system i to 16 which is mounted on the contact carrier Ta of the stationary contacts, so that the contact K1 moves during one complete changeover operation from the one main contact l-Ia (position 1) on a circular track to the right to the other main contact HZ); cf. Fig. 2. The unrolling of Ti in Ta is done in a customaryway by using a driving arm A which revolves around the axis M of Ta under the influence of the driving force and turns the axis m of Ti in a circular track.

'W'hen viewing the'positions shown inFigs. 1A, 1B and 10, it is evident, that always that contact is coming to bear which is situated in the direction of the arrow of the driving organ A. Since this arrow is coming progressively into the direction of each of the stationary contacts in consequence of the unrolling action of Ti in the stationary contact circle Ta, it is clear, that thereby the contact sequence planned by the designer is attained. From Fig. 1B it will be gathered however, that upon moving on from one closing position to the other always an intermediate position is happening, in which the arrow is passing just between two stationary contacts (e. g. Ha and ha, Fig. 13), two movable contacts (e. g. K1 and K2) touching two stationary contacts (e. g. Ha and ha) and connecting them with the leading-off point At. In order to expedite the said simultaneous closing of two neighbouring contacts which is necessary for changing over without interruption, the three movable load switching contacts K1 to K3 can glide in radial direction in slots of their contact carrier Ti. Their movement is however not free, but positively controlled, for they are connected by pushing rods L1 to L3 to the arms of starshaped guide L revolving around the axis in of the movable contact system. This star L enforces a simultaneous movement of all three load switching contacts K1 to K3 by the same radial way in relation to the axis m. In addition, a spring F acting upon the star L is taking care that there is always a tendency to push the three load switching contacts as far out of their contact carrier as possible. This tendency finds its limitation not by a stop within the contact carrier Ti, but merely by one of the contacts K1 to K3 firmly resting on one of the corresponding c0untercontacts I-ia or ha or 711) or Hb. In the intermediate positions (e. g. in the above treated Fig. 113) two contacts (e. g. K1 and K2) are transiently closed. Since from the geometrical point of View this intermediate position of the driving organ A in relation to Ha and ha is given only on one single point of its circular track, the duration of simultaneous contact making of Ha and ha with Al can last only a short moment (oscillograph recordings give A000 /1000 of a second.

A close examination of the movements going on in the intermediate positions shows that the time of contact overlapping i. e. the period, during which both contact pairs (e. g. Had-K1 and hurl-K2 in Fig. 1B) are closed simultaneously, always lasts a very short moment, irrespective of any factory inaccuracies and irrespective of the burning loss of substance of the individual switchthe unsteady secondary movement transmitted by the common guide L. The secondary movement is produced as follows:

If each of the three movable contacts Ki tolfis were spring-cushioned for itselfindependentof the others as usual with customary load changeover switches, it would rest before opening so long on the countercontact (e. g. K1. on Ha. in Fig. 1A tO-Fig. lBluntil taken along by. a latch or ther catch. Its opening velocity would then equal only the local velocity of the contact carrier Ti on point K1, and it would withdraw from its countercontact Ha only as quick as allowed by the movement of the contact carrier Ti. By introducing the common contact guide L, however, K1 is withdrawn from Ha, when moving on from position 3, not only with the local velocity of the contact carrier Ti on the point K1, but receives furthermore from its follow contact K2 which when moving on from position 3 is pressed back in its contact carrier Ti on account of its resting on ha, an additional (secondary) withdrawing impulse through the starshaped guide L. On account of the common contact control by this guide, K1 is retiring with double the velocity from Ha as would prevail in the case of the formerly used individually spring-cushioned contacts. This fact of doubled velocity upon opening the contacts by means of the unsteady secondary movement grants an essential diminution in size of the load changeover switch and in the masses of its moved parts.

Fig. 2 shows in thickly drawn lines the movement curves of the footings of the three contacts K1 to K3 from the initial positions 1 to the final position 13. The thinly plotted curves represent the steady primary movements of the three points near 1, 5, 9, which correspond to the footings of the three contacts on the contact carrier Ti. A

comparison of the mutual distances of the interare referring to the opening of the contact pair Ha-K1 during the movement, shown in Fig. 2 of the unrolling contact carrier Ti from position 1 to position 13. This movement originating from the movement, steady after a short starting period, of the driving organ A, the contact ways gained from positions 1 to 13 of Fig. 2 are in direct relation to the intervals ti-to Z13 of Fig. 3. Thus the way-time-diagram s =f(t) plotted in Fig. 3 in interrupted lines, is gained by compassing out of Fig. 2 the distances s of the two opening contacts Ha and K1 in the individual positions 1 to 13. The dotted velocity-timediagram of the steady primary movement is obtained by diirerentiation. A sine-shaped curve is resulting thereby, to which the unsteady secondary movement is superimposed in such manner that the vertically hatched negative way-areas and the horizontally hatched positive way-areas originate which compensate each other to zero three times during the total movement. The resulting actual contact velocity is thus represented by the solidly drawn unsteady curve g =fc which corresponds to the equally solidly drawn movement curve of Fig. 2. Only the passing from to in the contact positions 3, '7, 11' is ensuing in an unsteady way, whereas the passing from to in the fully closed positions 5 and 9 6 (closing of contacts ha and hb) is going on in a steady way.

The effect which is aimed at by the invention, 1. e. the increase of the closing velocity before the intermediate positions 3 and 7 and of the opening velocity behind these positions, is fully attained. The rate of velocity increase is proved by the solidly drawn curve of Fig. 3 to be a full doubling (n compared with 211. in Fig. 3) in the moment t=3 which is decidingly important for the main contact pair Ha-K1.

Figs. 4 and 5 give examples for a different design of the contact guide which transmits the unsteady secondary movement, for the case of arranging the stationary contacts on the third part of a full circle for use in a three-phase load changeover switch connected in the neutral point, whereas these contacts were arranged in a full circle in Fig. 1. In Fig. 4, the guide L consists of a mere axle with which the movable contacts K1 to K4 are pliably connected by means of guiding pushing rods L1 to L4. This guide L is mounted radially gliding in the driving organ A, revolving around the center M, of the movable load changeover switch part. Hence upon L is impressed in the first place the steady primary movement in tangential direction of and by the revolving driving organ A, but moreover the unsteady secondary movement is impressed in radial direction, upon turning of A, by the presently closed contact (in the position shown in Fig. 4 it is K1) by means of the corresponding pushing rod L1. The guide L transmits the movement which results from the tangential and radial components to the contacts K2 to K4 by means of the pushing rods L2 to L4, thus achieving the same way and velocity effect as described with the aid of Figs. 2 and 3 for the load changeover switch Fig, 1. It is, therefore, superfluous to show in a drawing the respective changeover positions of the load changeover switch of Fig. 4. There is still a third function of the guide L: the transmission of the contact pressing force exerted by the spring F upon the contacts K1 to K4, this force also being transferred by the pushing rods L1 to L4. The radial arrangement of the spring F on the driving organ A which turns from contact cu contact grants the possibility of using for all 4 contacts not more than one single spring which need not neutralize the steady primary contact movement, but only the much smaller unsteady secondary movements. Thus the lifetime of the spring F is long on account of short working ways.

For the radial alignment of the guide L also other methods can be made use of besides the slot guiding of Fig. 4. Fig. 5a shows for instance a rocker guiding, the spring F acting upon one arm of the rockers S a. This design is especially appropriate for big surface contacts with great axial length (vertically of the drawing plane), because the rocker Sa. which is supported above and below, is guiding the contacts K1, K3, K5 in parallel to the stationary countercontacts by means of parallel pushing rods L1, la, La, two for each contact, thus securing uniform burning down of the contacts.

The rocker guiding of the guide L is also well fit for the application of two separate contact groups according to Fig. 5. In this case, two independent contact systems are arranged with their guides La and Lb gearing in such a way, that each of the guides can make its unsteady secondary movement independent from the other on the same radial center line of the driving organ A, if theyare arranged above each other seen vertically to the drawing plane.

With. regard to the switching properties, the fact results therefrom, that always two neighbouring contacts (at first K1 and K2) arev closed at the same time, and that with the illustrated alternating contact arrangements the closings and openings are taking place alternately in the one (1, 3, 5) or other (2, 4, 6) group. Thereby the loading by the current is distributed to two parallel contacts, the closing and opening current in the individual contact is smaller, and it is up to the designer to obtain from step to step a transition, which is equalized with regard to current and tension, by an expedient gradation'of the ohmic values of the subdivided changeover resistances (cf. patent application J 70,675) These advantages are attained without enlarging the space required by'the load changeover switch of Fig. 5 as compared with the non-subdivided switch of Fig. 4. Thus, by subdividing into groups as in the present invention the capacity of the load changeover switch is further augmented.

The design as per Figs. 4 and 5 is especially suitable for threephase load changeover switches situated in the neutral point, whereas according to Fig. 1 a single-phase load changeover switch of advantageous dimensions is obtained. The latter type can also be enlarged by adding further contacts. in circular arrangement to serve as multiple step load tap selector (tap selector switching under load), whereby a very favourable saving of space results.

I claim:

1. A switch of the class described, comprising: a plurality of stationary contact members having contact surfaces, said contact members being disposed in spaced relationship about a first circular arc with their contact surfaces directed toward the center of said first arc; a movable contact carrier comprising a plurality of movable contact members having. contact surfaces, said movable contact members being disposed in spaced relationship about a second circular arc of radius smaller than the radius of said first are for consecutive engagement between said lastnamed contact surfaces and said contact surfaces of saidstationary contact members; a revoluble operating shaft concentric with said first are;

eccentric-contact actuating means carried by said shaft and movable therewith interconnecting said shaft and said carrier; and resilientmeans acting on said contact actuating means and urging engaging movable and stationary contact members into engagement with each other, said last means including-a common link so connected as to superimpose. on the normal continuous main motion a discontinuous additional motion.

2. A switch of the class described, comprising: a plurality of. stationary contactv members having contactv surfaces,,said contact members being ispcsed in spaced relationship about a first circular arc with. their contact surfaces directed toward the center of said first arc; a movablecontact carrier comprising a plurality of movable contact members having contact surfaces, said movable contact members being disposed in spaced relationship about a second circular arc of radius smaller than the radius of saidv first are for consecutive engagement between said last-named contact surfaces and said contact surfaces of said stationary contact members; arevoluble operating shaft concentric with said first arc; an arm carried by said shaft; an intermediatev member revolubly connected to said arm; a link connecting each movable contact to said intermediate member, each movable-contact being radially movable with respect to said second arc; and resilient means acting on said intermediate. member and urging said movable contacts radially outwardly by means of said connecting links, said switch further comprising arcuate interengaging means for maintaining said movable contact carrier positioned for said consecutive engagement between said contact surfaces.

References. Cited in the file of this patent UNI-TED STATES PATENTS Number Name- Date 1,626,970 Rooth May 3, 1927 1,931,869 Jansen Oct. 24, 1933 FOREIGN PATENTS Number Country Date 705,659 Germany May 6, 1941 886,836 France July 19,1943

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