US1488573A - Current-collecting device - Google Patents

Description

April 1 1924.

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j 1,488,573 c. F.. WAGNER CURRENT COLLECTING DEVICE Filed April 13. 1922 Bras/9 Drop 1/? Drop INVENTOR harass fies/bran Char/es Wayne/r Amp erea BY I I I l '7 I00 200- 300 40a WW i Patented Apr. 1, 1924.

UNITED STATES PATENT OFFICE. I

CHARLES F. WAGNER, 0F PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

CURRENT-COLLECTING DEVICE.

To all whom it may concern:

Be it known that 1, CHARLES F. acuna, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in lurrent -Collectin Devices, of which the fol lowing is a speci cation.

My invention relates to current-collecting devices and it has particular relation to means for equalizing or balancing the flow of current through the various brush members thereof.

Heretofore, it has been observed that the current collecting brushes of dynamo-electric machines, and particularly machines of the rotary converter type which employ a large number of brushes connected in par allel relation and which co-operate with a collector ring, are subject to unequal wear. Extensive experiments have, therefore, been conducted with a view to determining the cause of this inequality of brush wear.

As a result of theexperiments, it has been ascertained that one of the principal causes of the inequality of brush wear is the unequal fiow of current through the various brush members which, it is believed may possibly cause the decomposition of the brushe subjected to excess current flow. The inequality of current flow in the various brushes may be attributed to several causes, such as the formation of a substantially wedge-shape film of air between a brush member and the collector ring, a carbon deposit on the contact surface of certain brushes, unequal pressure exerted by the brush springs, uneven contact surfaces of the brushes, inequalities in the chemical constituents of the contact surfaces, particularly those of the brush members, the unstable volt-ampere characteristics of brushes in general, and the effect of non-uniform external conditions, such as the resistance and reactance of the paths of the current to the brushes, as in the brush holder stand to which the brush shunts are grounded.

One of the objects of my invention is to provide means for overcomingthe difference in impedance existing in the current paths, of a plurality of brushes connected in parallel relation, and to stabilize or balance the current flow therethrough.

Another object of my invention is to provide a device of the character described that may be quickly and easily connected in the brush circuits of a dynamoelectric machine without changing the structure thereof and that may be manufactured at relatively small expense.

In the accompanying drawings:

Figure 1 i a diagrammatic view of a collector ring having a plurality of brushes connected in parallel relation and co-operating therewith and which are provided with a transformer connected in series with each of the brush members for the purpose of balancing the current flow through the various brushes.

Fig. 2 is a view similar to Fig. 1, but illustrating a plurality of brushes assembled in group and co-operating with a collector ring, the individual brushes, of each group being connected in parallel relation and the various groups being similarly connected, and in which a resistor is connected in series with each of the brush members.

Fig. 3 is a diagram illustrating the difference between the volt-amperage characteristics of a brush operating respectively with and without a resistor element.

Referring to the drawings, and-particularly to Fig. 1 thereof, a plurality of brush members 1, provided with the usual pig-tail or shunt attachment 2, are diagrammatically illustrated as cooperating with a collector ring 3. A transformer, comprising a core member 4 having a plurality of legs 5 which correspond in number to the number of brushes 1 co-operating with the collector ring 3, is provided with a plurality of windings, 6 which embrace the respective legs 5 of the transformer and which are each connected in series with one ofthe brush members 1. The other terminals of the winding 6 are connected together and to a common lead 7.

The windings 6 are disposed upon their respective legs 5 in the same direction and, therefore, when the current flowing theretl'irough is of the same value there will be no flux traversing the core 4:. This is by reason of the fact that the tendency is for each of the windings to produce equal and opposed magnetomotive forces the resultant flux of which i zero.

If, however, more currenttraverses one winding than another, the flux set up in the core will thereby be greater than that established by the winding carrying the lesser current. The result is that the stronger magnetomotive force overcomes the opposing force and will tend to build up or boost the current in the Winding carrying the less amount of current and to also set up a counter-electron1otive force in the Winding carrying the greater current. A state of equilibrium of current flow in the windings is, therefore, quickly obtained. lVhen this condition is effected, the fluxes through the various magnetic circuits Will again become equal and will oppose each other.

In machines having a large number of brush members, it may be inconvenient to provide a transformer constructed with a leg for each individual brush member. In such cases, the brush members are grouped together in parallel relation and the various groups are, in turn, similarly connected as indicated in Fig. 2. lVhen such an arrangement is employed, it is necessary merely to provide a transformer having a leg for each group of brush members, which will equalize the current flov: only so far as the respective groups are concerned. In order, therefore, that the currents in the individual brushes of the groups may be maintained substantially equal, I provide a resistor S in series with each of the brush members. The effect of providing a resistor in series with each of the brush members is best explained with reference to Fig. 3 of the drawings, which diagramniatically illus trates the volt-ampere characteristics of a brush operating respectively vvith and without a resistor element. From an inspection of the figure referred to, it will be observed that the volt-ago drop across a metallized carbon brush throughout its current range, is substantially constant, as indicated at 9. This voltage drop across a single brush is insutlicient to function as a regulating voltage to maintain the currents through the several associated brushes substantially equal. A resistor S is, therefore, connected in series with each of the individual brushes and the respective brush and resistor elements are, in turn, connected in parallel re lation. A greater regulating voltage is, therefore, obtained by reason of the fact that if more current tends to How through one of the brushes and its resistor than through another similar element, the potential difference established across the first resistor, being proportional to the current of greater value, will be large enough, as illustrated by the curve 10, to function as a regulating voltage to ei'fect an increased flow of current through the br ";h and resistor being traversed by the. lesser current.

The regulating action of this potential difference, established across the brush and the resistor carrying the larger current, ellccted by reason of the fact that the larger potential difference is available to cause more current to traverse the other brush and resistor than would be caused by the relatively small potential ditt'ercnce a ross the brush alone.

From the foregoing it Will be apparent that by means of the constructions above set forth an accurate regulation of current flow through the brushes is obtained and the destructive action of evcess current traversing the brushes is materially diminished.

I claim as my invention:

1. A current-collecting device comprising a collector ring, a plurality of groups of brush members co-operating therewith, the brushes of each group being electrically connected in parallel relation and each group being sin'iilarly connected with each other, means associated with the individual brush members for equalizing the flow of current through the brush. members of each group, and means for equalizing the total current llOW in the respective groups.

2. A current-collecting device comprising a collector ring, a plurality of groups of brushes co-operating therewith, the brush members of each group being electrically connected in parallel relation, resistors respectively in series with the individual brush members of each group for equalizing the floiv of current through the respective brushes thereof, and reactance devices respectively in series with the groups of brushes for equalizing the flow of current through the respective groups.

8. A current-collecting device comprising a collector ring, a plurality of groups of brush members co-operating therewith, each of said groups of brush members being electrically connected in parallel relation and the individual brushes of each group being similarly connected, a resistor connected in series relation with the individual brushes of each group, and a transformer provided with a plurality of windings connected in parallel relation with respect to each other and in series relation with respect to said groups of brushes.

In testimony whereof, I have hereunto subscribed my name this th day of April CHARLES F. VAGNER.

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