US1064669A - Alternating-current generator. - Google Patents

Description

A. SGHBRBIUS, J. JONAS & H. MBYER-DELIUS.

ALTEENATING CURRENT GENERATOR.

APPLICATION FILED 313.28, 1912.

1,064,669. Patented June 10,1913.

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1,064,669. Patented June 10, 1913.

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A. SGHERBIUS, J. JONAS & H MEYER-DELIUS. ALTERNATING ommmw GENERATOR.

- APPLICATION FILED FEB.28,1912' 1,064,669, Patented June 10,1913.

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A. SOHERBIUS, J. JONAS & H. MEYER-DELIUS.

ALTERNATING CURRENT GENERATOR.

APYLIOATION FILED IEB.28, 1912. 1,064,669, Patented June 10,1913.

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UNITED STATES PATEN T OFFICE.

ARTHUR SCHERBIUS. JULIUS J'ONAS, AND HEINRICH MEYER-DELIUS, OF BADEN, SVITZERLAND, ASSIGNORS T0 AKTIENGESELLSCHAFT BROWN, BOVERI & CIE, OF

BADEN, SWITZERLAND.

ALTERNATING-CURRENT GEFLERATOR.

To a l whom, it may concern Be it known that we, ARTHUR SoHEnnIiis, JULIUS JoisAs, and I'lEIN-RICH MEYER- Dnmes, all subjects of the German Emperor, and all residing at Baden, in Switzerland, have made new and useful Improvements in Alternating-Eurrent Generators, of which the following is a specification.

It is well known that direct current series motors cannot be made to work as generators for feeding constant voltage mains, because it is notpessible to make such machines generate a constant voltage with changing load.

This invention has now for its object to enable alternating current collector ma chines having a series characteristic to be worked as generators.

The invention is illustrated in the accom panying drawings.

Figure 2 shows an arrangement of di-.. rect current machine for explaining the action thereof. Figs. 1 and 3 are ,vector diagrams of different conditions of Fig. 1. Fig. 4 is a further rector diagram, dealing with the operation of the machine shown in Fig. 2, either as motor or generator. Fig. 5 is a well known arrangement of alternating current machine for explaining the self excitation to be avoided by the present invention. Fig. 6 is an arrangement of alternating current machine for eX- plaining one term of the present invention; and Fig. 7 shows a series of curves explanatory of an arrangement according to this invention. Fig. 8 shows a form of alternating'current machine for purposes of comparison and Figs. 9 and 10 show arrange ments according to the present invention. Fig. ll illustrates for comparison a type. of repulsion motor and Figs. 12 and 13'modifications in connection with the present in- Vcntion. Figs. 14 to 17 illustrate further modifications showing different arrangements of inductances and transformers. Fig. 18 illustrates the. connections in one. manner with a two-phase machine and Figs. 19 to 24 examples of three-phase arrangements.

e]. in Fig. 1. denotes the E. M. F. at the terminals of a direct current series machine. as shown in Fig. 2. When this series ma-" chine is stationary the terminal E. M. F. (a works against the ohmic resistance R R Specification of Letters Patent.

Patented June 10,1913.

Application filed February 28, 1912. Serial No. 680,539.

where R. represents the internal resistance of the direct current machine and R the external resistance. When it is desired that the machine shall deliver energy to the mains, then a currentv i must flow (Fig. 3) having an opposite direction to the terminal E. M. F. Z The ohmic drop LR (where R is the total resistance of the circuit) has then the direction of the terminal E. M. F. and the rotation E. M. F., e,i.k.n., if there is to be. equilibrium. must be opposite to the terminal E. M. F. and the resistance drop. K is a constant factor and n, the number of revolutions. per minute. machine worked as a generator will give an output 216 to the mains. The E. M. F. diagram shown in Fig. 3 is possible but it is unsta'ble as will be readily understood on consideration. For instance if the current 2' increases somewhat, then an and'z'Jan. will increase proportionately to the current. Since z'Jmz. is greater than 21R this. will cause a very violent and rapid higher excitation of themachine. The same phenomenon appears in a series motor when it is connected to alternating current mains. Assuming that an alternating current E. M. F. 6,. is impressed at the terminals of an alternating current series motor as shown in Fig. 2. then the diagram of this motor (Fig. 4) will be composed of the following lines: c is the terminal E. M. F; 2.1M!) is the reactance E. hi. F.: illthe total ohmic drop and is the rotation E. M. F. proportionate to the current and the number of revolutions. Since the angle D A C is always a right angle the diagram of the motor will alter if the number of revolutions is altered, by the point A shifting along a circle K. having a diameter 61. while the point B shifts along a second circle K- in which 6,. is achord.

So long as the rotation E. M. F. is in the direction of the ohmic drop z'.R. the motor will convert the electrical energv into mechanical energv. while it is compelled to deliver mechanical energv as soon as is oppositelv directed t i.R. The motor portion lies in Fig. 4 abo e o and the generator portion lies below c There is a limit state, which is shown in dotted lines in Fig. 4. The reactance drop z'Lo is counteracted or balanced by the terminal E. M. F. e while the rotational E. M. F. acts ex- In this case the rotational E. M. F. is greater than the ohmic drop, the same state of affairs will occur as shown in Fig. 3 for the direct current machine, that is to say the machine excites itself with great violence. The lower part of the diagram (Fig. 4) has only a limited practical value.

-motor is stabilized by any means.

It applies only when the The dotted limit diagram also shows that the motor can still make up for its loss in ohmic drop by mechanical. work, but that self excitation will occur at the moment that the first watt ofenergy is to be returned to the mains. It is obvious that to the resistances R there must be added not only the external and internal ohmic resistances, but

also the resistance corresponding to the iron and eddy current losses so that actually the beginning of the useful work constitutes also the instant at which the self excitation occurs.

For all other electrical machines which have a series characteristic, the circumstances are substantially exactly the same as in the case of a purely series machine. On

account of physical reasons electrical energy cannot be returned by such machines to an alternating current supply by working them as generators, unless" special stabilizing means are employed. These circumstances are not altered substantially in any way when as indicates in Fig. 5 (this figure being illustrated for the purpose of explanation only) the exciting winding of the series ma chine is connected through a transformer T to its working circuit. The short circuited coil C in Fig. 5" represents a coil arranged in the working axis of the motor for the purpose of compensating the armature field,-

thc compensating flux being produced in the short circuited coil by currents induced therein by the armature fiux. In this case at the commencement of the self excitation there is produced exactly as in a direct current machine. a gradually increasing direct ,current which is transferred just like an alternating current from the transformer to the exciting winding. For this purpose such an arrangement is not sutlicient by any means apart from the fact whether the transformer is saturated or not saturated,

because instead of the direct current self excitation by the peculiar coiiperation of the transformer T with the rotational E. M. F. generated by the field 0, there is produced a peculiarly jerky alternating current with a strong peak maximum, as will be readily understood by the following explanation: If we consider a self-excitation current called 2', by itself, and assume that the self excitation has just begun in one of the two directions, then we find the current 2' is in its state-a current of continuous of the iron circuit of the machine has been.

attained. This circuit i produces in the transformer T an increasing field up to a complete saturation of the iron of the transformer. This increasing field induces in the secondary winding of the transformer likewise a direct current which flows through the field winding of the motor as an exciting current, the effect of which is to increase the current i,. This continues .in the same Way so long as the field in the transformer can increase and therefore exciting current is still induced. When however, the state of saturation is reached then the exciting current diminishes again because the potential by which it was generated becomes equal to zero; at the same time the motor field, the rotational E. M. F. and'therefore also i also diminish. Since however 2', excites the field in the transformer, the transformer field also diminishes. To the diminishing transformer field there corresponds in the secondary an E. M. F. which acts in opposition to the still existing current of the motor and which therefore accelerates the disappearance of the motor field, and finally produces a field of opposite polarity. This series of operations now begins again in the other direction of the current and is repeated periodically with a frequency depending on the reactancc of the entire system of winding which is traversed by the current. When therefore the direct current self excitation is converted by the use of the transformer into the described peculiar jerky excitation, this phenomenon occurring generally with great violence gives rise to serious inconveniences, so'that the entire question of the regenerative braking depends practically upon whether the disturbing self excitation can be successfully suppressed. This suppression cannot however he done if in the arrangement shown in Fig. 5, the transformer T be merely saturated by the current. 7', which has also the frequency of the supply. The reason for this is that during the time of a period of the current supplied by the mains the state of saturation of the transformer is not constant, and in each period there is a considerable portion of time during which the transformer can be considered as being non-saturated. The self both currents 4,

excitation begins during this portion of time and is also interrupted periodically by the time portions of high transformer saturation. Since however, the time constant of the current traversed system is very long compared to the time of a period of the supply current, the self excitation will not be substantially disturbed in its course by therelatirely short interruptions, so that the current curve of i shows only small steps. It will be understood that the curve of the self excitation current is not a regular one, but in consequence of the periodical saturation conditions of the transformer is for instance stepped. he momentary values of and 1' are. added in the circuit. The total current 2', however, has an extremely complex form in contradistinction to the direct series connection of the exciting and working windings Where the total current can be considered as a simple parallel shifting of the alternating current wave in the direction of the y axis.

The foregoing explanations explain fully the phenomena of self excitation which occur in working normal alternating current machines as generators, and they show that it is not possible to return useful energy to the mains without special means serving for suppressing the self excitation.

The present. invention has now for its objectto provide an alternating current, generator wherein the occurrence of an injurious excitation is successfully preyented. As already described, with theuse of a saturated intermediate transformer, the rotational F. M. F. is diminished per ampere of the ex citing currentonly when the field is atits maximum value in either positive or negatixc sense and also in the neighborhood of the said value so that the influence of the self exciting current greatly diminished only during this time fraction of a period It therefore only a single saturating magnetic flux that is a magnetic flux of such a strength that the iron through which it passes is saturated, takes part in the reaction between the working field, the rotational E. M. F. and the exciting field as is the case for instance in a normal series machine, then a great part of the whole time must necessarily afford suitable conditions for the production of the self excitation, that.- is to say during this time the permeability is so great that self excitation can take place.

The principle of the application consists generally in the inserti n of two ormore time-shifted saturating magnetic fluxes for the purpose of returning current to the mains at the mains frequency whereby effective regenerative braking is possible.

it is only by the introduction of a second saturating magnetic flux which is shifted as regards time preferably 90 relatively to the hitherto considered saturating magnetic flux, that it-is possible to entirely suppress the disturbing self excitation, because during a period of the main current there is no portion of time in which a transmission of the current to the exciting winding can be effected.

In the form of the invention illustrated by way of example in Fig. 6 the armature A of the commutator machine is connected in series with one winding of the transformer T, the other winding of which is connected to the mains e by way of the'field winding F. The iron of the transformer T as well as the magnetic iron for the main flux 0 are assumed to be saturated, and the circumstances are supposed to be surh'that the field Q) as well as the transformer field are in. a

similar high saturated condition forthe. number of revolutions at which the motor is intended to restore its maximnniene to the mains. As regards ope-ration tion is effected 01 21 great range f tl ing period because the saturation of the working field (t0) occurs at a different time to the saturation of the transformer T. The rotational working I). M. F. which is produced by the field and which must appear at the same time at the transformer T is in phase with the field (Z), while the field which generates this E. M. F. by transformation in a transformer T is at right angles asregards time to the first field. This is illustrated in Fig. 7 in which curves P and Q show the relation between time and flux, the curve P having reference to the flux in the core of the coil F and Q to that in the transformer core. In the time portion a- (Fig. 6) let it be assumed that the saturation state in the field (D is so great that a transference of energy can be affected on an average without producing self excitation. then for the time portion (1 the transformer T is saturated to such an extent that it will not allow of any self excitation during this period. Consequently only a short time is left in which self excitation could take place. This time is however too short for the formation of an injurious self exciting current and can be reduced to zero by suitable choice of the circumstances. The described arrangement has compared with similarar; rangements the great advantage that only it allows of reducing to a minimum the time during which self excitation can occur.

Modifications according to the present invention will now be describedwith reference to certain figures and for the purpose'of comparison Fig. 8 illustrates diagrammatically a series commutator machine of known form in which the armature A is connected in series with the compensating ninding C and the field winding F arranged in axes at right angles.

In the form of the invention illustrated in turn I Fig. 9 the armature A of the comnmtator machine is connected In series with the com pensatmg winding C and one wmdmg of 1 the transformer T the other winding of 4 sponding to those illustrated in Figs. 9 and,

which is inserted in to the second windim b which connected to the mains indicated by way of the field coil F. The machine is so dimensioned that the field of the winding-F produces great saturation in its axis. By this means two saturating magnetic fluxes are obtained as desired.

In the modification illustrated in Fig. 10 an additional transformer T. is employed.

The con'ipcnsating coil circuit remains'as in Fig. 9 but the field coil F is directly connected to one winding of a second transformer T the other windings in both trans formers beiin connected in series and to the mains. This arrangement obviates the neces ity for dimensioning the winding-F to give high saturation in its axis.

Fig. 11 shows for the purpose of comparison known arrangement of repulsion motor in which the armatureflk is short circuited and windings C and F are provided, connected in series and disposed in axes at right angles. An arrangement according to the present invention based on this construction is shown in Fig. 12 in which the compensating wint'ling C is joined to one winding of the transformer T the other winding of the circuit of the field winding F.

According to the further modification shown in Fig. 13 the compensating winding circuitremains as in Fig. 12 but an addi tional transformer T is provided, one winding of which is CODl'lCCt'Gtl to the ends of the field coil F, the other winding being joined of the first transl'ormcr T figs. 12 and lil show arrangements correto except that the former dealswith repulsion machine.

In the modifications illustrated in Figs 14 and 14* the connections shown arev similar to those given in Fig. 10 except that choking coils D and I), (or D and D )-are provided in parallel with a winding of each of the transformers T and T respectively. This enables transforn'iers with unsaturated iron to be employed, but the cores of the choking coils are to be saturated by their respective windings. Switches S are also illustrated for cutting out the choking coils when the machine is to run as a motor.

In the form illustrated in Fig. 15 a very simple arrangement is provided by. connecting the compensating winding C in series with the armature A choking coil D is arranged in parallel with the compensating winding C and armature A, and a second choking coil 1),, is placed in parallel relation to the field winding F. This figure is a modification of Fig. 14:; in the latter the stator windings F and C are fed via the transformers T and T while here they are fed direct. The choking coils D and D in Fig. 15 are arranged in parallel to the windings exactly as shown in Fig. '14. Additional connections are made as shown from the terminals of the winding D to the mains and to one terminal of the winding D,, the other terminal ofthis winding leading to the other main terminal.

In the modification illustrated in Fig. 16 an arrangement modified for use in a reptilsion motor is shown. In this form the windings C and F are connected in series and choking coils D and D joined in parallel with-these windings respectively.

Fig. 17 shows a form similar to Fig. 15 except that the choking coil D is replaced by an auxiliary winding H capable of generating a flux suflicientto saturate the iron core, which winding can con"niently be placed on the stator (if the heating of the machine will permit this) in the same axis as the winding C. A switch S is also provided for the purpose referred to above. The iron path for the flux generated by the winding H must, of course, be highly saturated (just as in Fig. 15 the iron of the chol ing coil D must be highly saturated). In this case commutation is favorably affected because the transformer E. M. F. is compensated by rotation of the short circuited armature coil in the lagging field.

Fig. 18 shows a two-phase arrangement in which sat-uratedchoking coils D and D are connected in parallel with the compensatin winding C plus the armature A and a fiel coil F respectively also similar choking coils I), and D are likewise connected as rel gards the coils I", and F respectively.

I I 19 shows a threephase arrangement saturated choking coils D are connected with the star connection to the 'windings C C" and C' and other saturated choking coils D' D and D are arranged as shunts to the windings F, F and F.

In the form illustrated in Fig. 20 each element C, C and C of the compensating winding is divided into two parts, across which parts are arranged respectively the saturated choking coils I), and D',,; D,, and D,; D and D.. In this case it will be noted that the compensating and j field windings are united to form a single winding. The principle of operation is that; two magnetic fluxes are obtained saturating the iron of the choking coils and relatively phase-displaced by about a quarter of a. period independently of in which axis of the machine these magnetic fluxes lie. Thus if as assumed in Fig. 20 the compensating winding is distributed over a large part of the periphery and sub-divided two parts of the windings shifted in space are ob- Fig. in which tained and utilized for the purposes required. This also constitutes a shifting of time of the two E. M. Fs. induced in these windings so. that the fluxes in the choking coils will also be shifted in time with relation to one another.

In the modification illustrated in Fig. 2 1 it is assumed that the compensating winding case choking coils .D,, D,, and arranged so that they can connect varying points on the compensating windings C, C and C. Also other saturated choking coils D D and D' are provided connecting the terminals with variable points on the same compensating windings. By this means it is possible to maintain the comparative saturation of the choking coils at the requisite value for all conditions of working.

In the modification illustrated in Fig. 22 three fixed choking coils D are provided in connection with the compensating windings, for example outside the machine and adjustable saturated choking coils H, H" and H of variable value connecting the coils D to the respective compensating windings. This arrangement is used in the case of machines in whiehthe brushes have to be shifted because altering the posit-ion of the brushes affects the relative phases of D and the windings D Fig. 23 illustrates a further modification in which the winding H is arranged as a distributed winding and connections made therefrom to the various coils as desired.

In the form of the invention shown in Fig. 24 in addition to the brushes b,, 6",, 6, connecting with the compensating windings G, C and C respectively auxiliary brushes b,, 6, and 32", are provided 0011- nectin with the coils I) and D,; D" and D",; TY, and D respectively arranged in parallel with their corresponding compensating windings C, C and C. By regulating the position of the auxiliary brushes in any suitable manner depending on the load the phase of the flux in the iron of the choking coils D',, D, and D can be maintained substantially at right angles to that depending on the coils D. D. and I);

The self-excitation is avoided in the following manner, namely: that on saturation of the transformer, the current supplied to the primary thereof from the generator, is not proportional to the secondary current. The latter will increase comparatively less is not uniformly distributed. In this D are than the infiowing or supplied current as soon as the knee of the magnetization curve is passed. The same applies if, instead of a saturated transt'mi'ner a saturated choking coil is interposed, for in this case the outgoing current increases to a smaller extent var in sJeeds and loads the de recs of saturation due to the various fluxes can be regulated in any desired manner. Also as choking coils any convenient winding may be employed, for instance the windings of dynamo electric machines or transformers, thus saving expense and space.

Having now described our invention what we claim as new and desire to secure by Letters Patent is 1. Apparatus for generating alternating currents comprising the combination with a main field winding and an armature winding connected in normal series relation, of two saturated inductive means, one for affecting the current in the field winding and the other for afiecting the current in the armature winding.

2. In combination with a series type alternating current commutator generator having main field windings, and means for introducing working currents into the armature, of means for stabilizing said generator comprising two choke coils, one connected at normal load, associated respectively with the field windings and the means for introducing working currents into the armature.

3. In combination an alternating current series type comi'nntator generator having compensating field and armature windings,

and means for stabilizing said generaton.

comprising two choke coils, one connected in parallel with said field windings and the other connected in parallel with both the compensating and armature windings, said choke coil being saturated at normal load at which the machine is to generate.

In testimony whereof, we atfix our signatures in presence of two witnesses. ARTHUR SCHERBIUS. JULIUS JONAS. HEINRICH MEYER-DELIUS. Witnesses CARL GUBLER, HARRY A. MCBRIDE.

Correct It is hereby certified that ih Letters Patent No.'1,'064,669,, 'rmha June 1621916,

upon the application of Arthur Scherhiua, Julius J ones, and Heinrich Meyer-belius, I w of Baden, Switzerland, for an improvement in Alternating-Current Generators,

an error appears in lshe printed specification requiring correctiolh as follows: Page 5,

line 95, for the words two choke coils, one connected read meaM adapted to be ar/WM,- and that the said Letters Patentshould be read with this chrrehhihh therein that the same may conform to the record of the case in the Patent Oliice.

Signed and sealed this 23rd day of September, A. D., 1913.

' e R. T. FRAZIER,

[SEAL] Acting Commissioner of Patents.

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