US964742A - Dynamo-electric machine. - Google Patents

Description

B. A. BEHREND.

DYNAMO ELECTRIC MACHINE.

APPLIOATION FILED DBO. 23, 1904.

Patented July 19,1910.

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UNITED STATES PATENT OFFICE.

BERNARD ARTHUR BEHREND, 0F NORWOOD, OHIO, ASSIGNOR, BY DIRECT AND MESNE ASSIGNMENTS, TO THE BULLOCK ELECTRIC MANUFACTURING COMPANY, A COR- .PORATION 0F OHIO, AND ALLIS-CHAIJMERS COMPANY, A CORPORATION OF NEW JERSEY.

DYNAMO-ELECTRIC MACHINE.

To all whom it 'may concern:

Be it known that I, BERNARD A. BEHREND, citizen of the United States, residing a't Norwood, in the county of Hamilton and State of Ohio, have invented certain new and useful Improvements in Dynamo-Electric Machines, of which the following is a full, clear, and exact specification.

My invention relates to improvements in dynamo-electric machines with especial reference to machines of the double commutator type.

In operating double commutator generators, considerable diiiiculty has been experienced due to an unbalancing of the load on the machine; that is, due to an unsym- .metrical distribution of the current between the comlnutators of the generator armature. This is especially true of multipolar machines employing a large number of carbon brushes or collectors. In such machines there is a tendency for certain of the brushes on the machine, or all of the brushes on a, single commutator, to grab the load, as it called. This so called grabbing of the load takes place as follows As the result of some' local disturbance, such for instance as dirt or dust between the commutator and brushes, or a brush of peculiar composition, or due to a. relatively low resistance feeder connection, or for some other reason, the path for the current from the armature winding through certain of the brushes is at .first of slightly lower resistance than is the path through certain other brushes. This condition causes the first mentioned brushes to at rst take a little more current than is taken by the other brushes. As is well known, a carbon brush has less resistance when hot than when cool, and as the resistance of said brush drops very rapidly the current densi'ty and consequently the heat increases, itwillbe seen that the first mentioned brushes offer less and less resistance to the passage of current than do the other brushes. As a result said first-mentioned brushes heat up quite rapidly, and as they heat up, they take more and more of the current until, as sometimes happens, the brushes on a single eommutator are carrying the en'tire current of the machine, leaving the other commutator and brushes practically currentless, Under these conditions,

the commutator, brushes, and brush holders Specification of Letters Patent.

Application filed December 23, 1904.

Patented July 19, 1910.

serial No, 238,174.

on one side of the machine are greatly overloaded, since they are designed to carry onehalf of the current of the machine and not the whole current. This unbalanced condition is productive of considerable sparking and it often happens that the brushes, brush holders, and commutators are entirely destroyed as the resultof the sparking and eX- cessive heating. In large machines which are subject to heavy and sudden overloads, it sometimes happens that the commutator will flash over; that is, the current will jump from brush to brush along the surface of the commutator severely damaging the latter and often ruining it.

The objects of my invention are to overcome the dii'liculties above enumerated, to prevent burning of the brushes and brush holders, to prevent flashing on 'the commutator, and to simplify the connections to the brushes or collectors of such a machine.

In carrying out my invention I provide for each commutator of a multi-commutator dynamo-electric machine positive and negative collecting devices, the positive collect-- ing devices for one commutator having a resistance materially greater than the negative collecting devices for the same commutator, and the positive collecting devices for the second commutator having a resistance materially less than the negative collecting` devices for the second commutator, so that one commutator carries the bulk of the positive current and the second commutator carries the bulk of the negative current. The above result may be accomplished by employing positive and negative brushes of materially different resistances, or by employing between the positive and negative brushes of each commutator and the positive and negative mains respectively, leads or conductors of materially different resistances, Preferably, the positive collecting devices for one commutator have substantially the same resistance. as the negative collecting devices for the second commutator, and the negative collecting devices for the first commutator have a resistance substantially the same as the positive collecting devices for the second commutator but materially different from the resistance of the positive collecting devices for the iirst cominutator.

The invention further comprises other combinations of parts of the system, which will be hereinat'ter described and more specifically pointed out in the appended claims.

In the accompanying drawings, Figures 1 and 2 are side elevations of the armatures of bipolar double commutator machines with ditiierent brush connections; Figs. 3 and lare developments of the commutators ot nmltipolar double commutator machines with dillerent brush connections; and Figs. 5 and G are developments of the commutators of two multipolar double-commutator machines showing the brushes connected in a slightly ditlerent manner.

In Figs. 1 and 2 I have illustrated the development of a double commutator bi-polar generator from a condition ot' balanced, unstable equilibrium to a condition of artificially unbalanced stable equilibrium. In Fig. 1 the positive brushes are indicated by 21a and 2lb, resting on commutators 19 and respectively and connected together by lead 23, which in turn is connected to the positive main 2t. The negative brushes 22"L and 221 rest on connnutators 19 and 2O respectively and are connected together by lead which is connected to negative main 2G. This machine is supposed to be balanced, the brushes, including their leads being all ot the same resistance and current carrying capacity. rl`he commutators and brushes resting thereupon are each designed to carry one-halt the current otl the machine. Now, suppose for some reason or other, say for instance, dirt or dust between the brushes 2ln and 22ll and commutator 19, the circuit through this brush becomes of slightly higher resistance. either at starting or while running under load, than the remaining brushes, then there will be a tendency for more current to How through the brushes on commutator 20. It this unbalanced condition exists for a short time the commutator 2O and its contacting brushes grab7 the load of the machine in the following manner; as the current density in the carbon brushes 21h and 22" increases, the ohmic resistances ot' these brushes will drop very rapidly, the current density and consequent heating will increase, and the resistances will drop further until such a point is reached that the commutator 2O is carrying all, or practically all, the current of the generator. IVhile this is taking place it will be seen that as commutator 19 is being deprived of current, the brushes 21a and 22, having the current density therein reduced and thus becoming cooler offer more and more resistance to the passage of the current from commutator 19, thereby assisting the commutator 2O in grabbing the load. The brushes 21b and 22b and commutator 2O are now operating on a Very heavy current overload and practically double the current for which they were designed. The

result is obvious; the commutator 2O is pitted by sparking and ultimately destroyed, the brushes and brush holders burn out, and the operation olE the machine is anything butsatisfactory. To obviate these difficulties, and render the machine perfectly stable, I propose to unbalance the machine artilicially and divide the current between the commutator brushes in such a manner that it is impossible :t'or any one commutator to grab the entire load. This I accomplish as shown in Fig. 2 by making some ot the brushes, viz. brushes and leads 21n and 22" on each conunutator of relatively low resistance and large cin-rent-carrying capacity, and the remaining brushes of relatively high resistance and small currentcarrying capacity. The brushes 211 and 21 are connected to the positive main 2st and the brushes 22a and 22b are connected to the negative main 2G. rIhis forces the major part of the current ot' the machine to tlow t'rom the arlnature winding through the commutator 19 and brush 21'Ll to the positive main and return through the negative main 2G, brush 22b and commutator 20, to the armature winding. 'I`he remainder of the current flows through the comnnitator 20 and brush 211, returning through brush 22 and commutator 19.

In Figs. 3 and t I have shown the development of the commutators, and a diagrammatic representation ot' the brushes and connections thereto, of a multipolar generator ot' the double commutator type. Fig. 3 shows a balanced unstable condition with the brushes and leads 21, 21h, 22a and 22" ot equal resistance and connected to the distributing mains 2% and 26 in the manner shown. Fig. 4c shows a stable, artilicially unbalanced condition with the brushes and leads 21 aud 22bo low resistance and the brushes and leads 21b and 22a of high resistance, all connected to the same system ot' distribution.

Figs. 5 and (3 illustrate in development the commutators of machines similar to those illustrated in Figs. 3 and 4, but with the brushes connected in a slightly ditt'ereut manner, Fig. 5 showing a` balanced unstable operating condition and Fig. G showing' au artificially unbalanced, but stable condition. In Fig. 5 the brushes and leads are all ot equal resistance. The positive brushes 21"L and' i1b are connected to separate leads 24 and 24h on opposite sides of the machine instead of being connected across the machine to the same lead as in Figs. 3 and ft. The brushes 2211 and 22b are connected to separate leads 262L and 261 in a similar manner. These leads are connected to the distributing mains 24 and 26 as shown.

To unbalance this system artificially to produce a stable operating condition, I malte the brushes 222L and 2lb and the leads 26a and 24D of low resistance and the brushes 2la and 22" and leads 24a and 261 of high resistance, so that the first mentioned brushes and leads will carry the bulk of the current of the generator. The leads and connections of different resistances assist the brushes of diii'erent resistances in maintaining a stable operating condition.

It will be readily seen from the above statements that to artificially unbalance the current distribution between the positive and negative brushes of each commutator so as to maintain stable operation, it is necessary that the total resista-noos of the current conducting or collecting devices connecting each main to the two commutators be different, and that leads or connections of different resistances may assist brushes of differentresistances to maintain stable operation, or if the brushes are of the saine resistance leads of different resistances may be employed, and if the leads are of the same resistance brushes of different resistances may alone act to maintain stable operation. It will be understood that by the expression collecting devices I mean to include either brushes or the conductors which conneet the brushes to the mains.

Although I have illustrated my invention as applied to a double commutator machine, having commutators on opposite sides thereof, it will be readily understood that said invention is equally applicable to a machine having more than two commutators, and also to machines having more than one commutator at one end thereof. Therefore I aim in the appended claims to cover all modifications ot' the mechanism herein shown and described which do not involve a departure from its spirit and scope.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a muiti-commutator dynamo-electric machine, positive and negative collecting devices for each commutator, the positive collecting devices for one commutator having a resistance materially greater than the negative collecting devices for the same commutator, and the positive collecting devices t'or the second commutator having a resistance materially less than the negative collecting devices for the second commutator.

2. A double commutator dynamo-electric machine having means for artificially unbalancing the load on each commutator of the machine in a predetermined manner, said means comprising a brush or brushes of high resistance and a brush or brushes of low resistance on each commutator, the high resistance brush or brushes on one commutator and the low resistance brush or brushes on the other commutator being connected to one side of a system of distribution, and the remaining brushes being connected to the other side of said system of distribution in such a manner that one commutator carries the bulk of the positive current and the other commutator carries the bulk of the negative current.

3. In a double commutator dynamo-electric machine, high resistance brushes and low resistance brushes on each commutator, leads of high resistance connected to the high resistance brushes, leads of low resistance connected to the low resistance brushes, and connections between the high resistance leads from the brushes of one commutator and the low resistance leads from the brushes on the other commutator.

4. In a multi-commutator dynaino-electric machine, positive and negative collecting devices for each commutator, the positive collecting devices for one commutator having substantially the same resistance as the negative collecting devices for the second commutator, and the negative collecting devices for the iirst commutator having substantially the same resistance as the positive collecting devices for the second commutator, but having a materially dilierent resistance than the positive collecting devices for the iirst commutator.

5. In a dynamo-electric machine, an armature, two commutators connected to the winding of said armature, the positive brushes on one commutator having substantially the same resistance as the negative brushes on the other commutator, and the negative brushes on the first commutator having substantially the same resistance as the positive brushes on the second commutator but having a greater resistance than the positive brushes on the first commutator.

In testimony whereof I atliX my signature, in the presence of two witnesses.

BERNARD ARTHUR BEHREND.

Vitnesses LILLIAN J. BRrrToN, GRACE P. JONES.

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