US2146914A - Potential-regulating apparatus - Google Patents

Description

Feb. 14, 1939. P RAUHUT POTENTIAL REGULATING APPARATUS Filed April 1, 193"! 4 Sheets-Sheet l :Zhcre for Z Feb. 14, 1939. k P RAUHUT 2,146,914

POTENTIAL REGULATING APPARATUS Filed April 1, 1937 4 Sheets-Sheet 2 Feb. 14, 1939. P. RAUHUT 2,146,914

POTENTIAL REGULATING APPARATUS Filed April 1, 1957 4 Sheets-$heet 5 .Fig15a Fi s!) Ewe/550W @adfzu/Zad Feb. 14, 1939. RAUHUT 2,146,914

POTENTIAL REGULATING APPARATUS Filed April 1, 1937 4 Sheets-Sheet 4 i re/Z227 Z 7 644i Patented Feb. 14, 1939 UNITED STATES .PATENT OFFICE POTENTIAL-REGULATING APPARATUS Paul BauhutQBerIIn-Karlshorst, Germany, as-

This invention relates apparatus and consists signer to Julius Pintsch Kommanditgescllschaft,Bcrlln, Germany Y Application April 1, 1937, Serial No. 134,445

In Germany 13 Claims;

to potential-regulating of the various features defined in the claims hereof.

The inven tion has for object to provide im- 5 proved potential-regulating apparatus by means of which the heavy load such as that of potential of a load, particularly a an alternating current motor of a locomotive, can be varied, by as fine steps or as coarse steps as may be desired, not 0 on ly without ful arcing,

interruption of the current or powerbut with substantial uniformity throughout the entire range of regulation. In

such

iron core of the winding apparatus according to the invention the a regulating transformer consists of several component cores on which is distributed provided with tappings. Each part of the winding is linked with only a portion of the power flux passing through the entire iron core.

The component cores so that there results limbs. It is however component may be connected by yokes a single iron core of several advantageous to separate the cores from one another magnetically and to provide them with special magnetic return paths.

In order to prevent an ununiform distribution of flux over the entire component core system and consequently a nonlinear variation of the potential as the regulating contact passes from contact to contact and thus parts of the short-circuits the several winding successively, there is provided according to the invention an equalizing winding which is divided into coils connected in parallel and each individual coil of which embraces at least two component cores.

The equalizing winding has the effect that an asymmetric loading of the tapped winding of the regulating transformer not result in the entire iron by the load current does asymmetric flux distribution over core. This asymmetric flux distribution is in fact restricted to the part of the entire iron core ponent cores.

that comprises say only two comthe variation of the potential is practically uniform-i. 9;, the regulation potential curve of the transformer linear slope.

is a stepped curve with practically A regulating transformer according to the invention may therefore be used with special advantage as a fine-adjustment device for a large regul ating transformer, in particular one for an electriclocomotive motor. 7 In this case it is esential in particular that the regulating April 7, 1 936 (01. 1'z1 119) switch can remain stationary on the contact path in any position, even though short-circuiting of a part of the winding results. The invention also possesses important advantages as a potentialregulating apparatus for the purposes of arc welding.

i For the more detailed explanation of the invention reference will be made to the accompanying drawings.

In Figure 1 there is represented diagrammatically a network in which a regulating transformer constructed according to the invention may be employed.

Figure 2 shows diagrammatically an example of a regulating transformer according to the invention. V

Figure 3 shows a further example.

In Figures 4, 4a, and 4b there is represented partly diagrammatically an apparatus comprising a main regulating transformer and a fine-adjustment device according to the invention and the mode of operation of this arrangement is illustrated.

Figures 5 and 5a to 5a" show likewise apparatus comprising a main regulating transformer and a fine-adjustment transformer according to the invention in a somewhat modified constructional form.

In Figure 6, finally, there is represented a further constructional example in which both the main regulating transformer and the fine-adjustment transformer have straight contact paths and the coupling device between the regulating switch of the fine-adjustment transformer and the switch of the main regulating transformer is shown in detail.

The load (motor of the locomotive) V (Figure 1) is to be switched over for example from one to the other of two consecutive tappings. L1 and L2 of the transformer of the locomotive. The switching-over from one tapping to the other is effected by the switching in or out of turns of the fine-adjustment transformer D. k

In Figures 2 and 3 there are shown diagrammatically two examples of fine-adjustment transformers constructed according to the invention. The iron core of the fine-adjustment transformer consists of a series of component cores 1 of lami-= nated sheet-iron, which link with the regulating winding 2 which is under the potentials of the tappings L1 and L2. The winding 2 has tappings with contacts 3 which are passed over by the brush 4 leading to the load.

When, in the case of this arrangement two contacts 3 are short-circuited by the brush 4, the

short-circuit current flows round only for example the first of the component cores I. The power flux in this component core is reduced by the short-circuit current and the formation of a large short-circuit current is consequently avoided.

The equalizing winding, which serves for preventing an ununiform distribution of flux over.

the entire fine-adjustment transformer when the load current flows through only a portion of the fine adjustment transformer, consists of three coils 5, connected in parallel in the case of the constructional example diagrammatically represented in Figure 2. The power flux linked with each of these coils 5 is distributed over two separate component cores I. There are here consequently groups each consisting of two separate component cores. Now within each of these groups there may be formed an asymmetrical distribution of flux. It cannot, however, encroach upon the other component cores, because the potential cannot drop in' any of the coils 5; and it consequently produces practically no effect on the entire regulating potential curve. The total number of the several component cores I is not restricted; it may correspond to the difference between the potentials of the tappings Ll and L2 to be bridged over. In the case of the fine-adjustment transformer according to Figure 2 the regulating winding 2 surrounds each component core only once, as does the equalizing winding. In practice, however, in most cases several turns are advantageously arranged on one component core.

For the better understanding of the operation of the equalizing winding let it be assumed first of all that the equalizing winding is absent and that the regulation of the potential of the load circuit is being effected by the movement of the contact 4 towards the right and that the contact 4 is on the fourth contact 3 from the left. The load current flows from L1 to the load around three of the cores I and through the contact I and consequently produces in those cores I a comparatively high leakage flux, whereby they become saturated. This has the eifect that the inductance of the winding 2 becomes very small inasmuch as the winding 2 extends through the three left-hand cores I. The potential applied to the tappings L1 and L2 is applied consequently only to the part of the regulating winding 2 that extends through the three cores I on the righti. e., the exciting power flux produced by the potential at L1 and L2 is deflected from the three cores I on the left to the three cores I on the right in the figure. Although consequently three steps of the exciting winding have already been switched in the potential has practically not yet risen on account of the leakage flux produced by the load current. Only on further movement of the contact 4 and towards the right, when flux deflection by the load current gradually becomes no longer possible, does the voltage actually rise; it then, however, rises immediately and very quickly. Consequently, in the absence of the equalizing winding 5 on the movement of the contact 4 along the contacts 3 the potential would rise very slowly as the contact 4 passed over the first four contacts and would then rise at a much greater rate as the contact 4 passed from the fourth contact 3 to the last contact 3 of the series. The equalizing winding is intended to prevent such lack of unifomity. This winding divides the existing six cores I into three groups of two cores each and couples these three groups together magnetically-i. e., the magnetic flux is the same in each of the three groups. It is consequently no longer possible to deflect the exciting power flux for example from the first group of cores I (shown on the felt in Fig. 2) upon the 5 remaining core groups, for as soon as the exciting power flux became greater in those groups they would react upon the first group through the equalizing winding. The avoidance of the flux deflection by the load current brings it about 10 that the potential rises substantially uniformly as the contact 4 is moved from the left-hand end to the right-hand end of the series of contacts 3. The feature that each of the coils 5 of the equalizing winding embraces not only one core I but 15 two cores I, is based on the fact that on the shortcircuiting of two contacts 3 by the contact 4 it is desirable that some flux deflection should be possible for the purpose of reducing the shortcircuit current that would otherwise occur. This. 20 flux deflection is, however, prevented from extending over the entire core system; it is'restricted to deflection from one core I upon the other core I encircled by the same coil of the equalizing winding.

Figure 3 shows a further constructional example of the invention in which there are provided two component cores I of laminated sheet-iron that are magnetically separated from each other. Each component core I has in this case two mag- 30 netic return paths I and I". This construction of the iron core as an enveloping core has been found to be particularly advantageous. Each coil 5 of the equalizing winding encircles one component core I, on which there is placed further 5 in each case a portion of the regulating winding 2. The winding 2 is provided with tappings in such a manner thaton the short-circuiting. of two contacts 3 the short-circuit embraces only one of the return paths I and I". The equaliz- 40 ing coils 5 are again connected in parallel. In some cases it may be advantageous to connect the equalizing coils directly to the tappings L1 and L2.

In the example shown in Figure 3 the contacts 3 form an annular contact path, which is advantageous in many cases, especially when it is a question of a transformer that is to serve as a fine-adjustment device in combination with a main regulating transformer. In this case, the 59 brush is advantageously coupled with theregulating switch of the main transformer in such a manner that on the moving forward of the said switch the fine-adjustment transformer moves along the tappings of the main transformer byv one step after each complete regulation of the fine adjustment transformer, i. e., each time the brush has passed over all the contacts 3. The contacts of the fine-adjustment transformer are then advantageously arranged in such a manner that the brush can always be rotated in the same sense, the switching forward of the fine-adjustmerit transformer along the tappings of the main transformer taking place in a definite direction. According to one construction of the invention that is specially advantageous in many cases particularly when a large number of component cores (enveloping cores) is used, the component cores are assembled to form a ring in the interior of which is arranged the likewise annular contact path. The assembling of the component cores to form a closed ring has, as usually has the close packing together of the component cores, the advantage that heat can be well conducted from one component core to another. In this way an 75 injurious over-heating of a component core, possibly in consequence of a long continuing shortcircuiting of apart of the winding, is avoided with certainty.

In Figures 4, 4a, and 4b there is represented potential-regulating apparatus comprising a; main regulating transformer and a fine-adjustment transformer according to the invention. The main regulating transformer II has tappings l2, l3, l4, which are to be bridged by the fine-adjustment transformer. The fine-adjustment transformer consists of four separate component cores I with equalizing winding connected in parallel with one another anda regulating winding 2 which encircles all the component cores successively. The iron cores are preferably constructed in the same manner as that represented in Figure 3. The fine-adjustment transformer is connected through the contacts or terminals 6 and I to the tappings l2 and I3 of the main transformer. The potential applied at 30 to the load, for example the motor of a locomotive, is increased by turning the regulating switch 4 in the sense of the arrow. When the switch has reached the end position shown by dotted lines, the load is connected directly to the tapping l3 of the main transformer. The fine-adjustment transformer must now be switched on so as to place it between the tappings l3 and M. For this purpose the switch 4 is preferably coupled by means of a tapping selector with the movable contacts 6 and l in such a manner that the contacts 6 and l are moved forward on the further movement of the switch 4 from the position shown in broken lines. In order that there may be no interruption of current there is attached to the tapping selector a dead contact 9 which is connected directly with the conductor 30 and consequently to the switch 4 and which during this shifting ofthe contacts 6 and I connects the conductor 30 directly with the tapping l3 of the main transformer. In Figure 4a there is represented what occurs when the contact 6 is passing from the tapping l2 to the tapping l3 and the contact 1 is passing from the tapping l3 to the tapping The current is taken through the dead contact 9. When the regulating switch 4 is moved still further, the contacts 6 and I reach the tappings l3 and I4 respectively simultaneously shown in Figure 4b, and the dead contact 9 becomesvoid of potential. The potential regulation can now be started again in accordance with Figure 4. The arrangement has the advantage that in the case of potential regulation in a con stant sense (potential increase or potential reduction) the regulating switch 4 is likewise always moved in the same sense.

The movement of the contacts 6, l, and Symay be efiected reversely in the case of movement of the regulating switch 4 from the contact 7 towards the contact 6. It is, however, advantageous to couple the switches in such a manner that the movementof all the contacts 6, l, and 9 takes place continuously with the regulating switch 4.

In Figure 5 there is shown another constructional form of the subject-matter of the invention in which the load current flows not through the regulating winding of the'fine-adjustment transformer but through the fixed fiLgflllZll'lg winding. The arrangement'is shown first diagrammatically in Figure 5 for the sake of easier comprehension. The equalizing winding is divided into two groups of coils 25 and 25' to the middle of which is connected the conductor 30 leading to the load. The regulating winding co sists likewise of two parts 22 and 22', which can be more or less short-circuited by means of the regulating switch 24. The currents flow always in opposite directions in the winding parts 25 and 25' of the equalizing winding and theparts 22 and 22 of the regulating winding. It will be seen from, Figure 5 that the potential applied to the load V is switched over from the tapping 12 to the tapping l3 of the main transformer by the radual increase of the inductive resistance of the winding part 25 and the simultaneous reduction of the inductive resistance of the winding part 25.

In Figures 5a to 5d the several phases of the switohing-over'operation are represented in detail. The fine-adjustment transformed consists of two groups of separate cores 2| and 2i with two groups of equalizing coils 25 and 25' provided according to Figure 2 and connected oppositely to each other in relation to the fiow of current, and the groups of regulating windings 22 and 22. The equalizing coils are connected to the several tappings of the main transformer through the contacts or terminals 26 and 21 and are in a potentiometer connection. At 30 the potential is taken off for the load. The load can be gradually switched over from the tapping I2 to the tapping l3 by the more or less powerful short-circuiting of the several regulating-winding parts by means of the contact path 23 and the regulating switch 24. When the regulating switch 24 is-in the position shown in Figure 5a the entire regulating winding 22 is short-circuited and consequently the resistance of the windings 25 is reduced to practically nothing. The flow of current in the windings is represented by the arrows. One arrow corresponds in each case to the portion of current that pertains to one core.

On moving the regulating switch 24 on there is reached the position shown in Figure 5b in which one of the cores 2| is already switched out and there is switched in one of the cores 2|. The resistance of the windings 25 is consequently somewhat increased, whilst the resistance of the windings 25' has decreased. Three quarters of the current now flows through the core system 2| as is shown by the arrows, whilst a quarter of the current flows through the core system 2|.

In the case of Figure 5c the condition is reached in which all the cores 2| are switched in and all the cores 2| are switched out. The

load 30 has now reached the tapping I 3 and the v switching forward of the fine-adjustment transformer from the tappings l2and l3 of the main transformer to the tappings l3 and I4 respectively can now be effected. During this switching-over the regulating switch 24 moves over the large contacts 28, 23", and 23". The regulating switch 24 is preferably coupled directly with the contacts 26 and 21, maybe through Geneva gear,

In the position shown in Figure 5d, in which the contacts 26 and 21 have been moved so far that they both touch the tapping l3 of the main transformer, all the cores 2| and 2| are simultaneously switched-in. The current divides in this position equally between the groups of component cores 2| and 2|. 0n the further move ment of the regulating switch 24 and at the same time of the contacts 26 and 21 there is obtained arrangement a definite rotational sense of the regulation in a corresponding sense.

Figure 6 shows a; constructional example of the idea of the invention in which the contact 5 path of the fine-adiustment transformer is made as a straight path. The fine-adjustment transformer consists again of separate iron cores 48 with equalizing 45 which are provided thereon and each of which ,encircles two cores 10 and whichare' all connected parallelwith one another, and of. a regulating winding 42 which encircles the cores successively? The cores them-f go of the fine-adjustment transformer must be shifted by one tapping along the tappings 32 to 38 of the main transformer 3i; In order that this shifting maybe effected positively when the regulating switch 44 has reached thejend contacts 25 or 46 and ll of the fine-adjustment transformer, which are connected to the end con- V tacts Q3 and 43' rwpectively, are fastezred to a toothed rod, or tapping selector 88 which is coupled with the operating device of the regulating switch it by a toothed wheel Stand Geneva g'ear 52,53. The operating device itself consists of a'hand-wheel 54 located on the axle 55 and a crankIG-and is constructed in such a manner a that on the rotation of the hand-wheel Bl in a constant sense the regulating switch 44 is moved toand fro by means of the rod 49. "lhetappet arm-52 is arranged on the axle 55 in such a manno that a tappet comes into engagement with the 4 Geneva wheel 53 each time that the regulating' switch is on one of the' end contacts and "43'.

with this arrangement also for the regulation of the potential there need be operated only a single hand-wheel i the rotation of which in one sense 45 will produce the regulation of the potential in a constant direction. The operation, of the regulating switch may of course be effected by means ofa otor. Y

t I claim is:

' leadingto a contact path,- and an equalizing wlnding, said iron core consisting of a plurality of component cores, said equalizing winding consistingot a plurality of coils which are connected in parallel with one another and each of which embraces a plurality of said component cores, and said regulating winding being connected with said con path in such a manner that on the short- 60 circuiting of two adjacent contacts of said contact path the short-circuit will embrace only one of said component cores. V

2. A regulating transformer comprising an iron core, a regulating winding, a contact path, and an equalizingwinding, said iron core consisting of a plurality of enveloping cores each of which has a middle limb and at least tworeturn paths, said equalizing winding consisting of aeplurality of coils which are connected in parallel with one 70 another and each of which embraces said middle limb of one ofsaid enveloping cores, and said regulating winding being distributed over said middlelimbs of said enveloping cores and having toppings connected with said contact path in such 1 a manner that on the short-circuiting oftwo adregulating switch always producesa potential;

43' and 43" of the contactpath 43, the contacts 1. A regulating transformercomprising an iron-v a'pcaoie jacent contacts of said contact path the short-circult willembrace only one of said returnv paths I of one of said enveloping-cores.

3. Potential-regulating apparatus ,comprising v.a main transformerhaving a regulating winding the toppings of which lead to a contact, path, a fine-adjustment transformer for the division of the potential between two of said tappings of said main transformer, and means for moving said v fine-adjustment transformer along said contact path of said main transformer, said fine-adjust ment transformer comprising an iron core, a regulating winding, a second contact'path, and an equalizing winding, said iron core consisting of a plurality of component cores, said equalizing winding consisting at a plurality of coils which are connected in parallel with one another and each of which embraces a plurality of said component cores, and said regulatingwindlngof said fine-adjustment transformer being conngctedm with said second contact path in such a. manner that on the short-circuiting bf two adjacent contacts of said second contact path the short-circuit will embrace only ,one ofsaid component cores.

4. Potential-regulating apparatus comprising a 5 main transformer having a regulating winding a the 'tap'pings of which lead to a contact path, a 4 fine-adj tmerit transformer and means for move ing'said fine-adjustment transformer, along. said contact path of said main transformer, said-iineadjustment transformer comprising an iron core, a r'egulatingwinding, a second contact path, and

--anequalizing winding, said iron core consisting of a plurality of enveloping cores each having a1 middle limb and at least two return paths, said V equalizing winding consisting or a plurality of calls which are connected in parallel :with one another and each of which embraces said middle limb of one ofsaid enveloping cores, and said regulating winding being distributed over said y middle limbs of said enveloping cores and having toppings connected with saidsecondfcontact path in such a manner that on the short-,circulting of two adjacent contacts of said second contact path the short-circuit will embrace onlyone of said return paths of ,one of said enveloping cores. v

5. Potential-regulating apparatus comprising a. main transformer having a regulating ,windingthe' tappings of which lead to a first contact path, a

fine-adjustment: transformer, and av tapping so selector, said tapping selector having attached to it. the terminals; of said fine-adjustment trans former, said fine-adjustment transformer comprising an iron core, an equalizing winding, a regulatingwinding, a second contact path, and a x regulating switch, saidiron core consisting of, a-

plurality of component cores, said equalizing winding consisting of a plurality of coils each of which embraces a.- plurality of said component cores, said regulating winding of said flne-ad- 6n justment transformer being connected with said second contact path insucha manner that on the short-circuitng of two adjacent contacts of said second contact p th by said regulating switch the short-circuit wil embrace only one of said 5 -move said terminals of said fine-adjustment transformer forward on said first contact path by one tapping. Q) g. V

6. Potential-regulating apparatus according to claim 5,-comprising'a dead contact which is attached to said tapping selector and is connected to said regulating switch and which is adapted to be moved by said selector along said first contact path and to contact with one of the tappings of said main transformer while said terminals are core, an equalizing winding, a regulating winding,

and a second contact path, said iron core consisting of a plurality of component cores, said equalizing winding consisting of two groups of paral lelly connected coils each of which embraces at least two of said component cores, said two groups of parallelly connected coils being connected in series to said terminals, and being connected to,

oppose each other by a conductor having a tapping for taking off the load current, the tappings of said regulating winding of said fine-adjustment transformer being led to said second contact path through which in each case at least half of the total regulating winding is short-circuited, said tappings of said regulating winding of said fine-adjustment transformer being connected to said second contact path in such a manner that on the short-circuiting of two adjacent contacts of said second contact path the short-circuit will embrace only one of said component cores and that on the rotation of said regulating switch by the switching out and in of parts of said regulating winding of said-fine-adjustment transformer the inductive resistance of one of said groups of equalizing coils will increase and the resistance of the other of said groups will simultaneously decrease and vice versa.

8. Potential-regulating apparatus comprising a main transformer having a regulating winding the tappings of which lead to a first contact path, a fine-adjustment transformer, and a tapping selector for moving the, terminals of said fine-adjustinent transformer along said contact path of said main transformer, said fine-adjustment transformer comprising an iron core, an equalizing winding; a regulating winding, a second contact path, and a regulating switch, said iron core consisting of a plurality of component cores, said equalizing winding consisting of a plurality of coils which are connected in parallel with one another and each of which embraces a plurality of component cores, said regulating winding of said fine-adjustment transformer being connected with said second contact path in such a manner that on the short-circuiting of two adjacent contacts of said second contact path the shortcircuit will embrace only one of said component cores, said contact paths of said main transformer and said fine-adjustment transformer being made as straight paths, said regulating switch of said fine-adjustment transformer being cou pled with said tapping selector through gear in such a manner that said step selector willbe movedfcrward by one tapping after said regulating switch of said fine-adjustment transformer has reached one of the end contacts of said second contact path.

9. Potential-regulating apparatus according to claim 8, in which for operating said regulating switch and said selector there is provided gearing comprising a crank shaft, means for rotating said crank shaft, a crank fixed to said crank shaft, 2. rod connecting said crank with said regulating switch, and means adapted to cause the rotation of said crank shaft to operate said selector in the manner stated in claim 26.

10, Potential-regulating apparatus comprising a main transformer having a regulating winding the tappings of which lead to a contact path, a fine-adjustment transformer for the division of the potential between two of said tappings of said main transformer, and means for moving said fine-adjustment transformer along said contact path of said main transformer, said fine-adjustment transformer comprising an iron core, a regulating winding, a second contact path, and an equalizing-winding, said iron core consisting of a plurality of component cores, said equalizing winding consisting of a plurality of coils which are connected in parallel with one another and each of which embraces a plurality of said component cores, and said regulating winding of said fineadjustment transformer being connected with said second contact path in such a manner that on the short-circuiting of two adjacent contacts of said second contact path the short-circuit will embrace only one of said component cores.

11. Potential-regulating apparatus comprising a main transformer having a regulating winding the tappings of which lead to a contact path, a fine-adjustment transformer for the division of the potential between-two of said tappings of said main transformer, and means for moving said fine-adjustment transformer along said contact path of said main transformer, said fine-adjustment transformer comprising an iron core, a regulating winding, a second contact path, and an equalizing winding, said iron core consisting of a plurality of enveloping cores each having a middle limb and at least two return paths, said equalizing winding consisting of a plurality of coils which are connected in parallel with one another and each of which embraces said middle limb of one of said enveloping cores, and said regulating winding being distributed over said middle limbs of said enveloping cores and having tappings connected with said second contact path in such a manner that on the short-circuiting of two adjacent contacts of said second'contact path the short-circuit will embrace only one of said return paths of one of said enveloping cores.

12. Potential-regulating apparatus comprising a main transformer having a regulating winding the tappings of which lead to a contact path, a fine-adjustmenttransformer for the division of the potential between two of said tappings of said main transformer, and means for moving the fine-adjustment transformer along said contact path of said main transformer, said fine-adjustment transformer comprising an iron core, a regulating winding, a second contact path and an 'equalizing winding, said iron core consisting of a plurality of component cores, said equalizing winding consisting of a plurality of coils which are connected in parallel with one another and each of which embraces a plurality of said component 'cores, and said regulating winding of said fine-adjustment transformer being connected with said second'contact path in such a manner that on the short-circuiting of two adjacent contacts of said second contact path the short-circuit will embrace only one of said component cores.

13. Potential-regulating apparatus comprising a-main transiormer having a regulating winding the tappings 'of which lead to a contact path, a fine-adjustment transformer for the division of the potential betweentwo of said tappings of said 5 main transformer, and means for moving the finei w winding said iron core consisting of a plurality oi enveloping cores each having a middle limb and at least two retnm' paths, said equalizing means 7 'winding consisting of 7 paths of one of said enveloping cores.

are connected in parallelwith one another and a plurality oi coils which each of which embraces said middle limb of one Y of said enveloping cores, and said regulating wind= ing being distributed over said middle limbs of said enveloping cores and having tafipings connectedwith said second contact path in such a manner that on the short-circuiting of two adja= cent contacts of said second contact path the short-circuit will embrace only one of said return PAUL RAUHUT.

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