US1470428A - Commutation of dynamo-electric machines - Google Patents

Description

2 Sheets-Sheet 1 INVENTOR. Q2

ATTORN YS.

J. w. DORSEY COMMUTATION OE DYNAMO ELECTRIC MACHINES Filed Feb. 14

Oct 9, 1923 Oct. 9, 1923. 1,470,428

J. w. DORSEY COMMUTATION OF DYNAMO ELECTRIC MACHINES 1 Filed Feb. 14 1920 2 Sheets-Sheet 3 C0- VOLTJ Ll/VE' INDUCED V0575 H 77MB I V EN TOR.

Patented Oct. 9, 1923.

UNITED STATES JOHN W. DOBSEY, 0F WINNI?EG, MANITOBA, CANADA.

COIMUTATION OF DYNAMO-ELECTRI C MACHINES.

Application filed February 14, 1920. Serial No. 358,783.

T 0 all whom it may concern Be it known that I, JOHN W. Donsnr, a citizen of the United States, residing at 'innipeg, in the Province of Manitoba, Dominion of Canada, have invented certain new and useful Improvements in Commutation of Dynamo-Electric Machines, of which the following is a specification.

My invention relates broadly to the suppression or prevention of sparking or arcing at the terminals of electric circuits, when such circuits carrying high voltage current are opened, and it relates more particularly to the suppression of arcing at the commutator of high voltage direct current dynamo electric machines.

The problem of eflicient commutation in high voltages has long received the earnest consideration of investigators in the electrical field, but, so far as applicant believes, has never been satisfactorily solved. One at tempted solution was to provide means for setting up a commutative electro-motive force in the armature coils adjacent the brush which would oppose the coil inductance electromotive force to such an extent as to prevent sparking. This commutative electromotive force was generated by commutative poles, or inter-poles properly placed; and also by shifting the brush towards the weakened pole of the machine. In either case the commutating electromotive force must balance the coil inductance volts. Sparking occurs unless an approximate balance is obtained between these voltages. Such arrangements have sometimes proved fairly satisfactory for moderately high voltages, for instance voltages up to 1500, but the regulation is not always satisfactory, and for very high voltages, such methods are entirely unsuitable.

The solution which I have devised for the problem comprises the provision of a vapor arc or vapor conductor arranged to shift in such a way during the changing relative positions of brush and armature segments that the trailing edge of the brush shall be without current in either direction at the time it breaks connection with the commutator segment. Assuming that a voltage is produced, by commutating poles or otherwise, in the armature coils counter to armature current, I provide a sectional brush and associate the sections thereof through suitable circuits with multiple postive electrodes of a vapor arc apparatus, the negative electrode of which -is connected to line. The sections of the brush structure are insulated from each other, and so positioned that each section comes successively into contact with the commutator segments. Instead of attempting to balance the selfinduction volts in the armature coil by the commutating volts, I provide an overwhelming commutative voltage and thereby force the current into the leading section or sections of the brush and reduce the current in the trailing section of the brush to zero. With this arrangement, current will flow through the leading section or sections of the brush to the are, but the trailing section or sections will be without current at the time such section or sections leave the commutator segments. Inasmuch as the current cannot flow from one positive multiple electrode to another, no current can flow from the leading sections to the trailing section of the brush. Condensers are combined in the arrangement, of circuits in the manner and for the purpose to be described hereinafter.

The above arrangement is applied to the brush on the side where the current leaves the machine; current enters the machine through the neutral of an auto-transformer connected in the usual manner through slip rings.

My invention as above briefly described, is capable of many applications, and renders possible the construction and efficient operation of high voltage, direct current motors, generators, rotary converters and machines for transforming direct current at high voltage into direct current at low voltage.

It applies also to open coil and to closed coil machines, to multipolar and bipolar machines, and is applicable to wave windings or to lap windings of closed coil machines.

I My invention consists,-therefore, in the novel method of commutation of dynamo electric machines, and. the novel arrangement of circuits and apparatus elements for accomplishing the desired results, all as hereinafter described, illustrated in the ac-.

companying drawings, and set forth in the appended claims.

In the drawings:

Figure 1 is a diagrammatic view showing certainelements of a dynamo electric machine with associated apparatus arranged and adapted to operate in accordance with the invention, the armature being of the closed coil type and the fields and portions of the circuits being omitted to avoid complicating the drawing;

Figure 2 is a diagrammatic view of the same. type of apparatus, including the fields and both sides of the circuit;

Figure 3 is a view similar to Figure 1, showing a modification of the invention;

Figure lis a diagrammatic view of an open circuit type of dynamo electric machine embodying the invention, two of the three armature coils being omitted; Y

Figure l is a diagram showingthe-induced voltage curve for the machine shown in Figure 4.

Referring first particularly to Figures 1 and 2, it will be observed that the armature shown is of the closed coil type, in which coils 10 are connected to commutator segments 11, 12, 13, 14, etc., the segments being separated by insulating portions 15.

Cooperating with the commutator is a brush shown as comprising several conducting sections 16, 17, 18, 1;) and 20, these brush sections being insulated from each other by mica or other suitable insulation 21. Although five sections are shown the number of sections may be varied in accordance with requirements, and may be greater or less than the number illustrated. The brush may be of any suitable size or thickness, and each section may be of any suitable thickness providing, however, that each section is less than the insulating space between the commutator segments, in order to avoid short circuiting of the segments by any given brush section.

Cooperating with the commutator and brush above described I provide an are device 22 which by way of illustration is shown as of the mercury vapor type. The are device is provided with multiple positive terminals 23, 24, 25, 26 and 27, the electrodes ofwhich are within the container and cooperate with the negative mercury electrode 28. Each of the-brush segments is connected in circuit with one of the positive arc terminals, as brush section 16 with are terminal 23 by conductor 29, brush section 17 with are terminal 24: by conductor 30, brush section 18 with arc terminal 25 by wire 81, brush section 19 with are terminal 26 by conductor 32, and brush section 20 with are terminal 27 by wire 33. Of course,

The conductor 35 connected to the negative electrode 28 of the arc device connects with the terminal through which current leaves the machine.

Cooperating with the circuits from the brush sections to the multiple positive terminals ot' the arcing device, I provide condensers a, Z), c, and (Z, each condenser being bridged across the circuits of adjacent brush sections. The purpose and operation of these condensers is, to prevent sparking between brush sections and the commutator segments, this being effected by compensation for the self-inductance of the main arcs.

The method of commutation employed, and the operation of the apparatus as thus far described, may now be understood. It being considered that the armature is rotating from right to left in the direction of arrow 0, and that the armature current is flowing in the directions as indicated by arrows 7*" and brush section 16 may be considered as the leading portion of the brush. The commutating volts supplied by the action of interpole 34 of course take direction to cause a reversal of current in the approaching armature coils, as shown by arrow 7. The commutating volts overbalance the inductance armature voltage to such an extent as to force the armature current to enter the leading brush section or sections 16, 17. The are in arcing device 22 being started in any suitable manner, current from armature coils will enter, in the position of the parts shown in Figure 1, through commutator segment 12, brush section 16, conductor 29, are terminal 23, and through the arc to negative electrode 28. Armature current will also flow, but to a less amount, through brush section 18, conductor 21 and are terminal 25, to negative electrode 28, so that the. positive electrodes of are terminals 23 and 25 will be arcing, brush sections 17 and 19 being on the insulation between segments of the commutator are without current. If the brush sections were of less width so as to make these relations with the coinmutator segments diiiercnt, a larger number .of the arc electrodes might be arcing at the same time.

As commutator segment 12 passes along in contact with brush section 16, it approaches and will engage the next brush section 17, when current will flow from segment 12 through brush section 17, conductor 30, and arc electrode multiple connection 24, So that the second electrode will also take the arc.

As commutator segment 12 passes further along, it will next leave brush section 16, thereby charging condenser a through brush section 17 and conductor 30, thereby preventing sparking at the time of the passing off of armature segment 12 from brush sec: tion 16. When this latter connection has been broken, the current will be flowing through conductor 30 to the are terminal 24, as stated, and the are at terminal 23 will be extinguished. In other words, the arc is shifted in the arcing device from the first mentioned terminal 23 to the second termi nal 24. When armature segment 11 makes contact with brush section 16, condenser a will be discharged and incondition to take its charge at the next breaking of the circuit at brush section 16.

In the same manner condenser bWlll prevent sparking at brush section 17 when the commutator segments passoff of'said section. and the same action is obtained with condensers c and (Z with respect to brush sections 18 and 19. It may be observed that as the greater part of the current enters at the leading edge of the brush, the leadin sections will carry most of the current an the following sections less and less current, and the organization and arrangement is such that with the training brush section 20, no current is. flowing from the armature coils through this section at the time the commutator segments break contact therewith. Inasmuch as the brush sections are insulated from each other and each is connected by its own circuit with one of the multiple positive electrodes of the are device, no short circuiting current from the leading brush portion can flow to the trailing brush portion or section either direct] through the brush structure itself or throng the are. 'It is obviousthat the flow from the leading sections to the trailing sections cannot pass through the are for the reason that the current can flow from the positive multi ple electrodes only in one direction, namely, to the negative terminal of the arc device.

The commutation will therefore be perfect,

and this irrespective of the high voltage of the machine.

Referring now to Figure 2, it will be observed that I have provided a different arrangement for allowing current to enter the armature from that shown in Figure 1 by means of which the current leaves the armature. I have also shown the field of the machine diagrammatically. at A and B.

Obviously the arrangement shown in Figure 1 cannot be employed at the terminal where current enters the machine for the reason that multiple negative electrodes would be impracticable. I therefore make use of the well known three-phase inductance, shown diagrammatically at C, current entering on-the conductor 36 and passing through the three coils wound upon three limbs of a single core. and then through conductors 37, 38 and 39, to the usual slip rings 40, 41 and 42', which are connected to the armature circuit at 120 degrees angular distance. As this arrangement is well un derstood in connection with three-phase vparatus not only is the commutation pracconverters, no further description is deemed necessary.

The operation of the machine is as described in connection with Figure 1, the current flowing to the armature coils through conductor 36, as stated, and from the armature coils as stated in connection with Figure 1. It will therefore be seen that in the operation of this method of aptically perfect, but'regulat-ion within wide limits is practicable by shifting the brush from neutral to an angular position of degrees.

In the foregoing description it will be noted that the machine may be either a generator of high tension direct current, or a motor operating on similar current, or it may be a rotary converter. All of such ap plications. and others which may be found suitable, I aim to include within the term dynamo electric machines to which my method of commutation is applicable.

Referring now to Figure 3, of the drawings, in which the invention is shown applied to a closed armature type of machine in which no interpole is employed for producing commutating voltage, I have indicated the use of batteries in place of the commutating pole for the purpose of causing the armature current to enter the leading portion of the brush. Here it will be observed that batteries 43, 44 and 45 are included respectively in circuit with brush sections 18, 19 and 20, so as to overbalance the armature induction voltage in a'manner similar to the action of the interpole. It is not. necessary that these batteries should be of equal strength, but desirable that the batteries of brush sections approaching the trailing sections should be of higher voltage than those toward the leading brush sections. The action is similar to that heretofore described with respect to Figure 1, that is, the action of the arc device in combination with the sectional brush and the condenser bridged across the circuits of adjacent brush sections. .It is therefore believed to be unnecessary to trace the circuits in the various cooperating positions of the 115 armature segments of the brush sections. This modification of the invention is particularly applicable to machines in which no interpoles are provided, and in which it is found undesirable to shift the brushes v applicable to open armature circuit machines, and this in combination with any of the methods heretofore described for producing the commutating volts. Such application of the invention to open armature circuit machines will next be considered.

Referring now to Figure 4, which illustrates an open coil electric motor as typifying such machines equipped with my invention, the armature coils are three in number although any number of coils could be employed.

A, B, indicate the motor field magnets, and 34 a powerful interpole. E represents the armature of which E, E and E are the three coils wound thereon. Each coil has a commutator segment a3 to which it is connected and brush sections 44 and 4% engage the commutator. Current enters the machine by conductor 36' and reaches the armature coils by brush 45 and slip ring 46, leaving said coils by the brush represented by sections A and A and by the wires 45' to are electrodes 47 and to return conductor 35. 48 is the condenser bridged between brush sections.

The brush sections 4.4 and 44 will at no time short circuit the coils under commutation because the width of each brush section is less than the thickness of insulation between segments 43. The action of the interpole reduces the current in the armature to zero, and tends to effect a reversal of the current in the armature. It is unable to cause reversal, however, due to the action of the arc in the armature circuit. The circuit is opened between the commutator segment and brush at the instant when no current is flowing, and sparking at the commutator is thereby prevented.

Figure at shows the induced volts and line volts plotted to time base. It will be observed that when the induced volts have risen to the line volts, the rise continues for a certain time and the induced volts then fall to the line volts. During this period of the induced volts above the line volts, as indicated by the dark shading, the current cannot reverse owing to the action of the arc. and the circuit is without current.

While I have described my invention as embodied in several types and varieties of dynamo electric machines, it will be understood that the invention is not thereby limited to such embodiments. It will also be understood that many changes in details of construction may be made without'departing from the invention, and all such changes I aim to include within the scope of the appended claims.

Throughout this specification I have used the terms armature and field in their generally accepted sense, but the armature and cummutator of the machines may be stationary and the field and brushes rotate.

Also in place of the mercury vapor arc device, any are or other device acting in the same manner may be employed.

I claim:

1. In a dynamo electric machine the combination of armature coils and a single commutator therefor, of a sectional brush and electric arc device having multiple positive terminals, one of said terminals being connected to each of said brush sections, and means for entirely preventing the flow of short circuit current in or between the brush sections for any position of brushes on said commutator.

2. In a dynamo electric machine, the combination of armature coils and a single commutator therefor, of a sectional brush, an interpole for causing armature current to enter leading section or sections of said brush, an electric arc device having multiple positive terminals, one for each of said brush sections, a circuit connection from each brush section to its respective arc terminal.

3. In a. dynamo electric machine, the combination with armature coils and a single commutator therefor, of a sectional brush, an electric arc device having multiple positive terminals, one for each biush section, a circuit connection from each brush terminal to its respective arc terminal and a condenser bridged across the said circuits of adjacent brush sections, said condenser operating to compensate for the inductance of are stream and assist in starting the respective arcs.

4. In a dynamo electric machine the combination with armature coils and a single commutator therefor, of a sectional brush the width of each section of which is less than the width of insulation between commutator segments, an electric arc device connected in each brush section and means to maintain the excitation of the arcs.

5. In a commutating dynamo electric machine comprising the combination of armature coils, commutator therefor, a sectional positive brush cooperating with said commutator, an electric arc device having two or more positive terminals, one for each of said brush sections, circuit connections from said brush sections to said terminals, and means for obtaining the negative terminal of the machine from slip ring connections.

In testimony whereof I afiix my signature.

JOHN W. DORSEY.

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