US1279887A - Method of operating dynamo-electric machines. - Google Patents

Description

H. LIPPELT. METHOD or omume DYNAMO ELECTRIC MACHINES.

, APPLICATION FILED JAN-9.1915.

Patented Sept. 24, 1918.

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H. LIPPELT.

METHOD OF OPERATING DYNAMO ELECTRIC MACHINES. APPLICATION FILED JAN. 9. 1915 1 ,279,887. Patented Sept. 24, 1918.

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APPLICATION FILED IAN-9.19M.

' PatentedSept. 24,1918.

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APPLICATION FILED JAN- 9, ISIS.

Patented'Sept, 24, 1918 5 SHEETSSHEET 4.

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UNITED STATES PATENT OFFICE.

HANS LIPPELT, OF BROOKLYN, NEW YORK.

METHOD OEOPERATING DYNAMIC-ELECTRIC MACHINES.

Specification of Letters Patent. Patented Sept. 24, 1918.

Original application filed October 13, 1909, :Serial No. 522,422. Divided and. this application filed January 9,

1915. Serial No.1,365. i

To all whom it mag concern:

v,Be it known that I, HANS LIPPELT, a citizen of theUnited States, and a resident of Brooklyn, in the county of Kings and State of New York, have invented certain new and.

useful Improvements in Methods of Oper- I ating Dynamo-Electric V Machines, of which the following is a specification.

My invention relates to a method of operating dynamo electric machines; and consists inlimprovements in the operation of machines, for example, of the type'shown and described in my prior U. S. Patents Nos. 7 56,7 93 and 919,604. In these patents I have described a dynamo electric machine having an. armature of the open-coil type with commutator and brushes to maintain each armature winding in circuit while cutting the flux of-the field poles, a'nd'in which thefield is arranged to induce a substantially uniform voltage in the armatureconductors as they pass the fieldpoles, both under load and at no load. The present application is a division of an application Serial No. 522,422 filed by me the 13th day of October, 1909, patented Jan. 12, 1915, No. 1,124,630, and in which a method of operation of open coil machines with sparkless commutation is disclosedbut not specifically claimed.

The nature of my invention willbe best understood when described in connection with the accompanying drawings,in which Figure 1 shows diagrammatically an end view of the machine designed in accordance with my aforesaid invention, both armature and field being developed along a straight line. I

Fig. 2 vshows a diagrammatic plan view of'the armature, which as well as the windings and the commutator are developed on a plane surface. I

Figs. 3 to 6 areiexplanatory diagrams. Fig. 7 is a diagram of the induced voltages in thearmature conductors of a generator, and Fig. 8 is adiagramof the-induced voltages in the armature conductors of a motor. Fig. 9 is an ex planatory diagram of the electrical changes occurring during the starting of a motor. I

Fig. 1 0 is a plan view of the armature of a motor constructed according to the present invention and developed on plane surface.

Fig. 11 is a diagrammatic, fragmentary v1ew illustratlngthe method and means of connection between the armature circuit,-

of the armature, the winding, the commutator and the accessories of the improved machine developed on a plane surface.

Figs.i13 to'15show diagrammatically end Fig.12 shows a diagrammatic plan view,

views, developed along a straight line,,of

various mam and auxiliary fields that may be employed. in my im-provedmachine.

. Fig. 16 is .a longitudinal section of a machine constructed according to the present invention, and which may be run either as a dynamo or as a motor; and Fig. 17 is a similar view ofv a dynamotor.

Similar characters of reference designate corresponding parts throughout the several views.

To a better understanding of the present invention a brief description of the operation of the machines set forth in the aforesaid patents will begiven, reference being had to Figs. 1 to 3 of the drawings. designates an armature, considered stationary; and 20 a rotating field, the poles N and S of same being numbered 21 to 28. 21 to '26 are the main field poles and are unevenly spaced, the center lines according to an equal spacing being drawn to show the uneven pole-pitch. The poles 27 and 28 are auxiliary polesinserted into the spaces left in its action maybeconsidered as a single pole. The machine itself is to be considered .as a six pole machine.

noted from the direction of current set forth that this auxiliary magnetlzation increases the main magnetlzation of certain of these poles and diminishes that of others. As more fully set forth in the aforesaid pat ents,the purpose of this arrangement 1s to by the main poles, 27 being'bifurcated but r or a multiple of the same.

pltch the number of poles,

In case of an even multiple, the ends of such conductors as are projecting from opposite ends of the armature core should be connected; and the end connections should run along a non-inductive path. Special conditions,however, may require special end connections.

By means of the rotating field 20, alternate electro-motive forces are induced in the armature windings, and in such a manner that always in at least three armature windings the same or nearly the same electric motive forces exist. The armature circuits thus energized are periodically connected in parallel through brushes 35 and a commutator 36, Fig. 2, the current being delivered to the terminals 37 and 38 of the machine through suitable collector rings 39 and 40. The direction of the current in the armature circuits is indicated in the conventional manner, Fig. 1. The commutator 36 consists, for the six pole machine under consideration, of six segments 41, 42, 43, 44, 45 and 46 arranged in two rows of three segments each, the segments 41, 42 and 43 being negative and the remaining segments 44, 45 and 46 positive. The segments of same polarity are connected to each other and with correspond ing collector rings 39 and 40. The position of the brushes is arranged to correspond with the position of the windings, in such a manner, that onlywhen a winding is efiectively vitalized through the induction of a field pole the respective brushes slide on a commutator segment; The armature circuits deliver power only so long as they are connected with the commutator segments, and thereby vwith the line. In the case of a dynamo, current is delivered from the collector rings; and in the case of a motor, it is delivered thereto.

The electrical changes occurring within the armature circuits, in the case of a dynamo, may be studied and discussed in connection with the explanatory diagram shown in Fig. '3, the arrow designating the relative motion of the armature with respect to the field magnets. E E designates one-half'of a wave of electro-n1ot1ve force, P'the collstant terminal voltage, I the current strength with a maximum value 1,, and 1' the resistance (assumed constant) of an armature circuit between thepoints at which it is connected in parallel with the other armature circuits. Ir represents then the ohmic drop in the armature circuit, and the curve I for the current is made to coincide therewith by assuming the proper scale. Beginning at the left side of the diagra1n,the E. F.

existing in the armature circuit is zero, and at the position Q it has risen to the terminal voltage P. At about this time the brushes 35 make contact with the proper commutator segments of commutator 36 and thearmature circuit is placed in action. Be cause of the further increase in the E. M. F. to the value E a gradually increasing cur rent I is developed. In consequence of the self-induction of the armature circuit this current does not rise in a straight line but approaches an asymptote, which asymptote has the same inclination to the Zero line as the line E. After the E. M. F. has attained its maximum value E the current curve I reverses its direction of curvature and attains after some delay its maximum value 1,. At the points B, the E. M. F. and the current begin to decrease again, the E. M. F., however, more rapidly than'the current which is again delayed owing to selfinduction. At D, the E. M. F. has fallen to a value equal to the terminalvoltage P, the difference being therefore zero. The current, however, has still an '7 appreciable value which becomes zero only at F. If the armature circuit be now switched out no sparking will occur since the current therein is at this instant equal to zero. As is apparent from the current curve, the current in the vicinity of its zero value varies rapidly,and in consequence ofwhich a faulty brush adjustment even to a' comparatively small degree renders a spark unavoidable.

are known but are based on a transformer action." Such means, however, are unsatisfactory in that they operate properly only at a particular speed of the machine andlwhich speed cannot behigh because, in consequence of the inagncticinertia of the transformer, the said transformer is'not capable of responding to the numerousswitching operations of short duration of the commutator,

A premature disconnec- I My invention consists essentially in the operation of a dynamoelectric machine in such a manner that it will not possess-these disadvantages, and will operate without fail at all speeds of the machine. This may be effected by employing an electrical condenser which is arranged to be connected with an armature circuit shortly before the same iscut out or in. In going in, the circuit will thereby be precharged with current.

For this purpose condensers 49 and are provided and which are cut into the two branches 31 and 31, etc., of the armature circuits as. followsreference being had to Figs. 11 and 12. I also provide auxiliary coml'nutator segments 51, 52, .53, 54, and 56 which are comparatively narrow and are insulated from the correspondingmain commutatorsegments 41, 42, 43, 44, 45. and 46 by small strips of insulating material, the segments 51, 52, and 53 being at the right of the corresponding negative segments 41, 42, and 43, while the segments 54, 55 and 56 are at the left of the corresponding positive segments 44,45 and 46. F or high voltages it is advisable to arrange all positive segments on one ring and all negative segments on another ring, as shown, in order to secure good insulation. The segments 51, 52 and 53 which are ofthe same polarity (negative) are connected to one another, and liliewise the positivev segments 54, 55 and. 56. The segments thus connected are then con; nected through suitable resistances 57 and. 58

-' respectively toone side-of the, condensers-49' and 50- respectively; The other sides of the condensers are connected respectively to the terminals 37 and 38. s

In addition to the armature circuits 31,31', 3232, 33-33, and 3434!. which are connected through the, brushes 35 with the commutator 36, shunts 6161 62-62 63.63, and 6464- may be provided. These shunts arethen connected.respectivelyto the correspondingbranches of saidarmatllre. circuits and are arranged to beconnected. to the commutator 36. through suitable brushes 65, which as well as. thebrushes 35, are of sufficient width to span the insulatingspaces between main and auxiliary segments of the commutator. Resistances 6666, 6767, 68 -68,, and. 69469 are inserted in the'corresponding shunts. The

arrangementof the-brushes issuch that for. each end of eacharmature ClFCllll'. a set of four brushes is-provided,.there being two adjacent brushes of slightuangular difference in positionfor each pol'arity (see Fig. 11 andtheconnections for each set of; brushes beingcrosswise. Through the arrangement above set forth, the connection ofeach end of each armature circuit to the commutator is in one case direct, and in the other through a resistance The brushes are in ad;

* 1 Vance of the brushes 35. going thedirection from an auxiliary commutator segment to amain commutator segment. i

In the positionshown (Fig. 11) the current, for example, will flow from one end 31' of thelarmature winding 3131, through the shunt61 and its resistance 66 and the brush 65, to the commutator segment 44, and

then to the terminal 38. The branch 31 also connectsthrough brush 35 with the auxiliary segn'ient 54, and thence through the resistance 58 and condenser 50 to the terminal 38. The resistances 66 and 58 are thus connected in parallel.

Thereturn circuit is from the terminal 37 directly to the commutator segment 41 and through brush 35 to the other branch 31 of the armature circuit 3131. No. appreciable current will flow through the resistance 66 of theshunt61 as the conductor in parallel therewith has very little resistance.

If" the brushes are now assumed displaced somewhat toward the left which characterizes the circuit 3131 as an outgoing circuit all of theadvancebrushes will lose their electrical connection with the commutator segments, the connection for the adjacent brushes, however, being maintained. The circuit is then as follows-+terminal 37 directly to segment 41, and throughbrush to the return branch 31, through'the armature winding, and back through the resist ance 66 of shunt 61, through brush 65 to auxiliary segment 54, the resistance 58, condenser 50-.to the terminal 38. The armature circuit 3131'., the condenser 50, and the resistances 58 and 66 are thus connectedin series. I

Ifthe brushes be moved still farther in the same. direction, the armature circuit l is completely disconnectedfrom the con'imutator and thereby from the line. Had the brushes been shifted in. the opposite direction and had the connectionsmade at the. other ends of the. commutator segments been investigated, it would have been found that first resistance 57 and condenser 49 would have been. connected; in parallel with qresistance 66. Further displacement would have placed the armature circuit, shortly before the disconnection of the'same from the commutator 36, in series with the condenser49 and the resistances 57 and 66. The. arrangement affords, therefore, the same succession of connections for both directions of revolution; For such armature windings as are going into circuit,'the succession of connections is of course the reverse, that vis tosay the series connectionis first made of the resistances 57 or 58 and66 or 66 and the condensers 49 or 50, and then the parallel connection of resistance 57 and condenser 49 with resistance 66; or, resist ance 58 and condenser 50 with resistance 66 and finally. the direct connection of armature circuit. through. main segments. of. the

commutator to the terminals (omitting the said resistance). The increase of resistance, therefore, does not take place suddenly, but step by step (gradually).

The electrical changes Occurring in the armature circuits under the conditions above set forth are indicated for a dynamo in Fig. 4. For the sake of simplicity it is at present to be assumed that the resistances 57, 58 are zero and the entire branches 61, 61 are omitted; and their purpose will hereinafter be set forth. Referring to Figs. 4 and 11, let it be now assumed that the field and the commutator, (Fig. 11) rotate to the left, and that the armature and brushes are stationary. This condition characterizes circuit 313l as an ingoing circuit. As soon as the segment 54 has moved under a brush 35, the position of armature winding 3131 with reference to the field, corresponds to the position Q, Fig. l. One branch of the circuit 3l31 will be connected with segment 54 and in series with condenser 50, while the other is connected through the segment 47 directly to the terminal 37. The current will therefore rise rapidly because of the capacity of the condenser 50 and steep gradient of E. M. F. The ohmic drop curve Ir (representing also current I) is shown between the lines Q and S, the current striving asymptotically to a constant positive limit. As soon as the E. M. F. attains the value E and remains constant, the curve I changes striving very rapidly but asymptotically to a zero value. It is therefore necessary to disconnect the armature circuit 31-81 from the condenser 50 as soon as, or shortly before, the E. M. F. attains a zero gradientmaximum value E The armature circuit is then already energized and may immediately begin its work in full measure effecting thereby a greater output than under the conditions set forth in Fig. 3. At the position B, the current I begins to drop, as shown, between B and D.

in the same manner as the similar curve shown in Fig. 3. At the position D, Fig. 4 the condenser 49 is to be introduced, that is, for example, before the E. M. F. curve E had dropped to the value P. The form of the curve I will change because of the new gradient of E. M. F., striving rapidly and asymptotically to a constant negative limit. This is a decided advantage over the condition set forth in Fig. 3 wherein the current continually decreases (in an algebraic sense). For the sake of completeness the tension at the condenser is shown by the curve 6, Fig. t. The disconnection of the armature circuit should again be made, as in the case set forth in Fig. 3, just before the position F where the current becomes zero.

The above set forth negative limit of the.

current is proportional to the trigonometric tangent of the angle of inclination of the line E, viz: the gradient of E. M. F. If now E, during this period of switching out be maintained substantially constant (horizontal)-zero gradient, Fig. 5, the negative limit of the current thereby becomes zero. In other words, the current I is forced to a rapid striving toward zero as its limiting value. It is not necessary, however, that for this purpose the said horizontal portion of the curve E should coincide with the line P. Since the current comparatively long before reaching F attains a value which practically equals zero, there remains a large margin for the accomplishment of disconnection, that is to say, an exact setting of the brushes is not necessary. Attention is particularly directed to the fact that with the aforesaid arrangement, the potential 6 of the condenser approaches a constant final limit, while the current approaches zero. It is thereby immaterial whether the horizontal value of E (Fig. 5) is greater, equal to, or smaller than the value of P. Thus, the operation is independent of E-P. Since E, and with dynamos, P is dependent upon the speed of the machine, the commutation is also independent of the speed of said machine.

With other arrangements in which a transformer is utilized instead of the condenser, the potential due to self-induction would become zero, but the current would approach a constant value. This latter would only then become zero when the horizontal portion of E would coincide exactly with the terminal voltage P, (E-P:O) which is a dCilflicult condition to obtain with variable loa In employing a condenser as above de scribed, there is only one, easily fulfilled requirement. If, as above, 1 is the resistance in ohms in the armature circuit, L the effective coefiicient of self-induction (difference between its own self-induction and the mu tual induction of the other circuits) in henries, and C the capacity of the condenser infarads then 7 In order that the condenser be not required to have too high a capacity, the. resistance r of the armaturecircuit must be sufiiciently increased during the switching period. For this .purpose the above described resistances 57, 58-and"66,66, etc., are provided and are arranged, as explained, to be introduced step by'step into the armature circuit before and simultaneously with the introduction of the condenser. The arrangement is such, also, that the condenser during the step by step introduction of the resistance prevents the formation of a spark, and likewise during the step by step disconnection of the resistarice atthef beginning of the working} period of the armature circuit. This becomes evident byreferenceto igl' ll. If-brush 35 is being displaced from segment 44 to segment 54, part of the current of armature circuit 31 is compelled to flow through resistance 66. Thiscauses a potential difference between brushes 35 and equal tothe resistance of 66 multiplied by the current flowin therethrough.

instant a break takes place between brush 35 and segment 44, and no spark can occur. Brush 35 should then run off segment 54 before brush 65 runs onto segment 54, Fig. 11, or segment 56, Figi12, and the resistance 66 only willbe in series with armature winding 3l -31. At the next instant brush 65 will contact both segments 54 and 44, Fig. 11, or 56and 46, Fig. l2'(thus also discharging condenser from previous charge) and will thencontact 54 or 56' only. The amount of resistance for the three stages is then as follows: positionshown:66 in parallel with 58 and 50 (less ohms than'66) 35 off 54; (66 alone) 65 011 54 or'5666 and58 in series (more ohms than 66). Todetermine these values of resistance it is to be noted that, al though the actual resistance of the condenser is infinite, yet thesame acts as a short circuit when not charged. (resistance zero) hence, only the values of resistances 57 and 58 are to be considered. After the condenser is fully charged it sets up a counter be not fulfilled, the electric current will be subject to damped oscillatlons.

Fig. 6 shows theelectrical conditions for a 7 motor, and in which, as is well known, the E. M. F. of the armature circuit is less than the terminal voltage The current has naturally the opposite direction to that existing in a dynamo, asis shown in Fig. 6.

For the production of E. M. F. curves, which after a short slope again follow a definite horizontalcourse, fiat curves EE as shown in Figs. 3 and are presumed. Their production and maintenance under all loads has been previously set forth. Through ad-. ditional induction, these flat curves are al- I Said potentialldifierence wi 1 be thrown upon the condenser 50 at the ar a at the ends the desired manner; Fig.7. shows theoriginalflat curve E foii a; dynamo, the additional curvesof inductlion 2 and the resulting curve EE Since the ma chines in general are to be adaptd to both 70 directi nscf revolution, a curve of induction 2 is provided atthe left side, of the curve. For the relative niotionof the, nts;- tu'rewith respect tothe field as, indicated by the arrow, thisis the beginning of the 'worlrmg period; and the supplementary induction strengthens at this place the original'E. M. F. whileat the other endlit weak'ens the" same. With a chang'e'ot direction ofrevolution, the effect" is reversed automatically. 8 shows the electrical coiiditionfor an InfFig's. and 8, E and P are represented by the distance between positive and nega tive values. It is, however, su'fiicient torefer to the half-wave only, if the scale of ordinates be reduced one-half ,(twice the number of division lines for the saine length). ,N

In the case wherethe machine is runas a motor,at the beginning of the starting. period vthe inductive efiiect of the field is zero, the E. M. F. is ezero, and the terminal voltage is equal to the drop in voltage, ref erence being had to Fig. 9. In switching in a circuit between a main segment of one polarity and an auxiliarysegment of oppo; site polarity, the current will rapidly rise on account of the condenser, and ,thenagain diminish. Yet, even; at moderate s eedand with ufliciently high resistances (5 ,58 Ian'd 66, 66, etc., Figs. 11 and 12 the:p0siti0n S which designates the passing overto the main segment adjacentto the auxiliarygseg ment, will be reachedat such time thatthe current is impeded in its complete decrease 105 and instead issustained now from the driving source of current charging over the main segments A premature decrease of current, however, would not signifyany: I thing detrimental. After the connection 'to 110 the main segments, the ,armature circ uit will do constant work untilit has passed the poloo sition Bandhas reached the position I). i At this momentthe condenser is connected into series with the same and thereuponthe ourrent'in the armature circuit is forced to av tendency to rapidly attain the zero value, sovthat a sparkless disconnection may take place before the position F is reached. a

In order to provide suflicient resistance. in the armature circuit for the support of the commutation it is advisable to locate the starting resistance, not outside ofthe arma ture, but Within the armature winding as shown in Fig. 10. Adjustable starting re- 12 5 sistanceg fl, 72, 73 and 74 are introduced into the correspondingarmature windings. 8131, 324-32, 33 -33, 3434, as shown in Fig. 10 and are jointlyand gradually;

cut out of circuit in the same degree as the speed of the motor increases, until they are finally completely out out. Of course, thls arrangement is suitable, also, for the control of the speed.

It is known that a condenser requlres time to absorb electricity even though it be extremely short, and that this time is lengthened by the introduction of resistance into the circuit. Should the machine run slowly, or at a moderate speed, the condenser during the switching out period even w th the large resistance 1' of the armature 01rcuit will suificiently quickly render the current zero. At high speed, however, it is advisable to assist the condenser by means of additional induction. The available time for extinguishing the current decreases at such increased speed, but the induction increases correspondingly and thus Works in harmony. WVith the switching in of an armature circuit the additional induction operates in a similar manner to accelerate the current development. In a similar manner it may be shown that the additional induction, also with dynamos, supports the commutation.

Asa more satisfactory means for providing such supplementary induction and to obtain the desired E. M. F. curves, I have designed the means shown in Figs. 12 to 16, Fig. 16 representing upper part of a complete machine. The armature 19 is stationary; and the field 20 rotating, as in the device shown in Figs. 1 and 2. In addition to the said field and armature, a small auxiliary armature 80 and an auxiliary field 81 are provided. The armature 80, is constructed in the same manner and wound similarly in the armature 19 only its axial length is considerably less, and its windings 76-76, 7777, 78-78, 7979 are connected in series with the windings 3131', 32-32, 3333 and 34-34 respectively (Fig. 12). \Vhile the main armature 19 is absolutely stationary, the auxiliary armature 80 is circularly adjustable, Fig. 16, as by sliding in guides 82, and locked by suitable bolts 83. The setting is done once for all, the adjustment being such that the additional inductions to be provided are introduced at the desired time, for example as set forth in Figs. 7 and 8. The connections from armature to terminals are the same as have already been explained, but because of better design the separation of the adjacent brushes is increased angularly by double the normal pole-pitch, Fig. 12, or a multiple of the double pole-pitch. In other words the displacement has been made to the next segment of same polarity.

Within the main armature 19 rotates the,

magnetic field 20 Figs. 13, 14 and 15 as in the machine illustrated in Figs. 1 and 2. The pole distribution of the main field, however, need not be uneven as set forth in compensation for armature reactionis provided practically entirely by the main field, the supplementary inductions being furnished by the auxiliary field. The auxiliary field 81 is much smaller than the main field 20 and rotates within the auxiliary armature 80, and should be designed to take care of the armature reaction and supplementary inductions not furnished by the main field. The pole-pitch, the size of the poles, and the magnetic polarities are so chosen that the supplementary induction provides the desired changes, satisfying, for example curve 2, Figs. 7 and 8. Exciting windings 88 are provided for these poles, but the current therein need not necessarily be proportional to the armature current. However, in many cases it will be convenient to utilize the armature current for the excitation so that a reversal of the direction of revolution of the armature will cause the polarities ofthe field to be reversed.

Instead of making the auxiliary armature 80, Fig. 16, adjustable as above set forth, the magnetic field 81 may be arranged to be adjusted. This arrangement will be especially desirable when the armaiure rotates and the field is stationary.

In a machine thus constructed with auxiliary' armature and field, the capacity of the auxiliary armature and field need be hardly more than a few per cent. of the entire capacity of the said machine. In thus employing auxiliary armature and auxiliary field, a decided advantage is obtained in that the same may be controlled independently of the main field and of the main armature, thus affording for the purpose of regulation the entire ranges of magnetic strength of said field magnets. If the regulation were to take place in the main field magnets, only a fraction of the latters magnetic strength would be available and the adjustment of exciting current would therefore have tobe more delicate.

In the case of a dynamotor Fig. 17, in addition to the main armature provided with the dynamo winding 90 and a motor winding 91, two auxiliary armatures 93 and 94 and two corresponding fields 95 and 96 are required. The auxiliary system 93, 95 serves for the dynamo, and the system 94, 96 for the motor. Corresponding sets of accessories and connection to the terminals are of course necessary, the designation for the dynamo side being the same as used throughout the drawing, while those of the motor sides are primed.

maximum value E is substantially uniform (horizontal) it is possible in certain cases to carry out the disconnection of the armature circuits without first diminishing the maximum value. The auxiliary armature and its field will then become unnecessary andmay be dispensed with. It will also be apparent that the step by step increase or decrease of the E. M. F. as shown in Figs. 7 and 8 may be made to take place gradually, care being taken, only, that it remains constant during the cutting out of the armature circuit. The extinction of the current may be accomplished solely by the introduction of resistance, by means of supplementary induction, of both.

In conclusion, it may be said that, generally speaking, the commutation of current in armature windings is a special case of varying the strength of said current. If the circuit carrying this current is loaded with inductance, any variation of its strength is opposed (delayed) by self-induction. In order to bring about rapid or predetermined changes in the strength of current, a new method is to be applied as, for example, that herein set forth, and which must necessarily employ a physical agent through whose ac tion the effects of self-induction are counteracted. For instance, reactive voltages (secondary voltages) as brought about by capacitance, may be introduced into the circuit; and, if controlled by the E. M. F. prevailing therein, or more strictly speaking by the rate of change of said E. M. F., they will lend themselves readily for the purpose. The ohmic drop in the circuit may also very well be considered a reactive voltage and by its proper variation the flow of electric current can be altered in a predetermined manner. Furthermore, the path of current can be divided, or led in succession through the respective sources of reactive voltages (parallel and series connections of capacitance and resistances, Figs. 11 and 12). This makes it possible to apply the method repeatedly and with different degree of effect. Fig. 11 with brushes situated as shown, refers to parallel action of secondary voltages. Generally, the current in the winding is, in this case, not completely extinguished but materially weakened. For the next following position of brushes, the method is applied again but in a stronger degree, forcing the remaining current toward a zero value.

I claim 1. The method of efiecting a variation of electric current in a circuit, loaded with inductance, which consists in accumulating a tively. controlling, during the period of current variation,*tl1e rate of change of the driving E. M. F., and repeating with {a diflerent value of impedance.

2. The method of eiiecting sparkless commutatlon of the current inwmdings of d1- rectcurrent dynamo electric machines,

which consists in accumulating a quantity of electricity to set up a reactive E. M. F., and positively controlling, during the commutation of said windings, the rate of change of the driving E. M. F. in the respective windings. I

3. The method of effecting sparkless commutation of the current in windings of direct-current dynamo electric machines,

which consists in accumulating a quantity of electricity to set up a reactive E. M. F during the commutation, and simultaneously therewith maintaining a zero gradient of the driving E. M. F., thereby eflecting a fall of current.

4. The method of effecting sparkless commutation of the current in windings of directcurrent dynamo electric machines, which consists in accumulating a quantity of electricity to set up a reactive E. M. F positively controlling, during the commutation, the rate of change of the driving E. M. F. in the respective windings, and discharging the accumulated quantity of electricity.

' 5. The method of effecting sparkless commutation of the current in windings of directcurrent dynamo electric machines, which consists in accumulating a quantity of electricity to set up a reactive E. M. F., positively controlling, during the commutation, the rate of change of the driving E. M. F. in the respective windings, and maintaining a predetermined voltage across the ends of the armature circuit. i

6. The method of effecting sparkless commutation of the current in windings of directcurrent dynomo electric machines, which consists in accumulating a quantity of electricity to set up a reactive E. M. F., changing the impedance of the armature circuit, and maintaining a predetermined of electricity to set up* a reactive E. M. F.,

changing the impedance of the armature circuit, and maintaining a predetermined voltage across the ends of said circuit, and

repeating with a different value of impedance.

8. The method of operating a direct-current dynamo electric machine of the open coil type, which consists in periodically effecting a variation of the electric current Within the armature circuits, and in conformity with the alternations of E. M. F. New York, and State of New York, this 8th therein, by accumulating a quantity of elecday ofJanuary, A. D. 1915. tricit to set 11 3 a reactive E. M. 4 and ositively controlling, during the period of hur- HANS LIPPELT' 5 rent variation, the rate of change of the Witnesses:

driving E. M. FREDH F. SGHURTZ, Signed at New York, in the county of H LAURA E. SMITH.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of. Iatents,

Washington, D. 0.

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