US1244569A - Means for interconverting alternating and direct currents. - Google Patents

Description

J. L. WOODBRIDGE Mms ron mmcowvzmme mumums AND DIRECT CURRENTS.

APPLICATION FILED JULY 16. I915- N 1,244,569, 7 Patented Oct. 30, 191.

2 SHEETS-SHEET I.

l i i l'm lll l IIIVEN TOR WI TIMES I TTOBIIEV.

J. L. WOODBRIDGE.

MEANS FOR INTERCONVERTING ALTERNATlNG-AND DIRECT CURRENTS.

APPLICATION HLED JULY 16. I915.

Patented Oct. 30, 1917.

2 SHEETS-SHEET 2.

INYENTDR v/dsgdfi lesfer 145M522" e W (as ITTDRHEY.

; nivrra JOSEPH LESTER WOODBRIDGE, 0F PHILADELPHIA, PENNSYLVANIA.

MEANS FOR INTEBCONVERTING ALTERNATING AND DIRECT CURRENTS.

Application filed July 16, 1915.

To all whom it may concern Be it known that I, JOSEPH Lns'rnn VVoonnnrnsn, a citizenof the United States, and a resident of the city of Philadelphia, in the State of Pennsylvania, have invented certain new and useful Improvements in Means for Interconverting Alternating and Direct Currents, of which the following is a specification.

My invention relates to apparatus for converting alternating current into direct current, or vice versa, and especially to such converting apparatus in which there is a magnetic structure, all parts of which are relatively fixed, upon which are wound suitable coils or windings connected to the AC and DC circuits; such apparatus, for example, as described in my Patent No. 880,705.

The object of my invention is to provide more eflicient and less expensive means for effecting the interconversion of alternating and direct currents, to improve the commu tation in apparatus designed for this purpose, and further to provide improved means for rotating such converting apparatus.

These and other objects of the invention -will be more clearly understood by reference to the following description in connection with the accompanying drawings, in which, I Figure l is a diagrammatic view of apparatus involving features of the invention, and arranged for converting 2 phase alternating currents into direct current or vice versa.

Fig. 2 illustrates details of one section of the winding shown in Fig. 1.

Fig. 3 is a diagrammatic view of apparatus similar to that shown in Fig. 1, except that it is designed for connection to a 6 phase circuit, and a special split pole converter is used for driving, and

Fig. 1 shows an alternative method of connecting the alternating current circuit to the windings of Fig. 3.

Referring to Fig. 1, 1 is a magnetic structure similar to the iron core of a dynamo armature, preferably made up of laminations of iron, and provided with 4 openings, 2, 3, 4E, and 5 near the periphery, through which openings pass the conductors of the windings 6, 7, 8 and 9. The winding is Specification of Letters Patent.

Patented Oct. 30, 1917.

Serial No. 40,190.

thus divided into four sections, all of the turns of each section passing through the corresponding opening in the iron core so that all of the turns in any one section embrace the same portion of the magnetic circuit. The object of this construction is to insure that any magnetic flux that passes through one turn of the winding shall pass through all the other turns in the same section, In order to secure this result more effectively and prevent leakage of flux between adjacent turns of the winding the conductors are preferably made of flat strip, as shown more in detail in Fig. 2, which shows the conductors of sections 6 of the winding to an enlarged scale and partly in section. This construction increases the reluctance of the leakage path for magnetic lines between adjacent conductors by increasing the length and reducing the cross sectional area of such paths.

The object of this construction will be explained later.

Referring to Fig. 1 a commutator 10 is shown connected in the usual manner to the windings 6, 7, 8 and 9. Upon this commutator rear four brushes, 11, 12, 13 and 14, of which one pair, 13, 14 is short-circuited by conductor 26, while the other pair, 11, 12, is connected'to the direct current circuit 15, 16. The magnetic structure 1 with its commutator and windings is mounted on a shaft 17, which may be driven by a suitable direct current motor M connected across the circuit 15, 16. A. suitable source of direct current, such as the battery B may be connected across the circuit 15, 16. On the shaft 17 are also mounted collector rings 18, 19, 20 and 21 connected to points in the winding intermediate between the sections 6, 7, S and 9. Suitable brushes bearing upon the collector rings are connected to the two phase alternating current circuit 22, 23, 24, 25. To the latter circuit a source of two phase alternating current A is connected, as well as translating devices L. A two phase synchronous motor M is also shown mechanically connected to the shaft 17 and electrically connected to the two phase circuit 22, 23, 2 1, 25. Suitable switches are shown for connecting or disconnecting the motors M and M to the corresponding cir- ;ringslS, :19, 20, 21, and alternating currents may,itherefore,s.be taken from these collector rings fforthe translating-devices L, or-the alternating currentv source A, .if operating .Assuming firstthat the source of alternating currentaA iszdisconnected and'the magnetic structure 1 with its windingsandcommutator is being rotated by meansof the motor M, a. small amount. of. direct current passing pfronrthe circuit 15, 16 through the windings 56,11,18, Qlby way .of the brushes 11 andf12 willproduce a primaryicomponent.of mag- .netic flux in thescwindings in the direction of the arrows K K :K and 'K. Inthe position showninthc drawing, currenttfrom 25:

two parts, one partpassing through sections 6 and 7, and the other through sections 9 and .-8 to brush '12. .As the rotation progresses-in thedirection of the arrow X,'the

conductor '15 entering brush '11 dividesinto current in someofthe coils of sections 7 5311(1 8 is reversed, thus reducing and finally -revers1ng=the magneticfluxin these two secations. Thischange of'magnetic fluxinduces an electro-motive-force in the coils affected ;thereby, and .this electroTmotive-force .de-

velops a difference of potential between .brushes 13 and 14. Since these two brushes :are short-circuited-by conductor 26, a small flow of current will take place between these brushes. This current passingthrough the .windin'gsb, 7,'8,'9 produces a secondary component of magnetic flux -represented by the arrows K K K and K The rota- :tionof the converter causes a similar varia- .tion and-reversal-of this secondarycompo- .nent of'magnetic flux in the. sections of the -.windings, resulting in an .electro-motiveforce between brushes '11 and *12,'which will be counterto-that of the circuit -15, 16. If .the apparatus is properly designed and operated ,at'a suitable speed this counterelectrosmotive-iforce will be nearly. equal .to

'athat'of-the circuit 15, 16,.but just enough :less to permitthe. smallfiow: of current into the brushes 11, 12, necessary to establishthe primaryanagnetio flux described above.

The counter-elcctro-motive-force developedacross the-brushes 11, 12, as described above, will also appear as an alternating current electro+motive-force at the collector at; a suitable voltage. and frequency may be magnetic :flux above described. efiect, therefore, .of any such alternating connected to the alternating current circuit 22, 23, 24, 25. Obviously the rotatlon of the converter .1 must be mainta ned in synchro- .nism with the source A, and .to insure this the synchronous motor M should be used for driving the converter whenever the source A is connected. Under these conditions the direct current motor M should preferably be disconnected. When alternating currents are taken from the collector rings '18, '19, 20, 21 in phase with the alternating.electro motive-force across these collector rings, these currents in the windings (3, 7, 8, 9 will, in generalbe opposed to the small direct current input at :the brushes '11, 12 necessary to maintain the primary The first current output .from the converter will be atendency to reduce the counter-electro-motivezforce developed 111 lts w1ndmgs,.and this reduction will permit an in-put of .direct site to :the alternating currents taken rom thecollector rings. Similarlyif the voltage .OfftllG source A is raised sufliciently, alternating currents will be supplied 1 to the concurrent atithe brushes '11, 12 equal and o povcrterincreasing the counter-clectro motiveforceiatthebrushes 11 and :12 until'this exceeds'the .voltage.-of:the battery B and energy willbe transferred from the. source A to the battery. The apparatus, therefore,

.acts as a true :inductive comerter rbetween he' alternating and the dlrect current circuits.

'lVhen thedirect current brushes are in the position shown in thediagram, direct currententeringthe'brush 11 may pass-directly to collector ring'lS by way of-tap 27 without passing around the magnetic cir- .cnit.of;the converter. lVhen,however, the

rotationhas.proceededuntil thebrush 11 is 111 contact with oneof the commutator bars connected .to an intermediate pointof sectionsGof the winding,.the current entering -brush 11 .will divide, apartofit passing to .the tap.27.and the balancegoing to tap 28.

This division of current will be such as to reduce 'thetotal-ampere turns in section 6 practically to. zero, except for the small exciting'currcntsnecessary to maintain the counter-electro anotive force as described above. Forexample,.if'brush llis in contact .with the next commutator bar to that shown so that. there will be one turn between rbrush illand tap 27, and5 turns between ibrush 11.and tap 2S, thenonesixth of the total current entering brush 11 with pass to tap 28, andifive-sixths.totap127, thus the one-sixth of :the current passing through fivezturns ofsection 6 willjust balanceithe 'fiye1sixths ofithe current passingin the opposite: direction'through. one turn. This division of current at any. point in the rotation will: be: brought about owing tothe fact that there are direct current brushes.

any small departure from it will produce brush. In other Words, there must be the same'num'ber of alternating current taps as struction very materially reduces the tendency to sparking at the brushes, and also avoids the tendency to magnetic saturation in sections of the magnetic circuit.

The short-circuit conductor 26 in addition to providing a path for the exciting current necessary to develop thecounter-electro-motive-force required across the brushes 11, 12 has also another important function. If the alternating current on the two phases of the circuit is unbalanced, for example, if all of the load is taken from the two conductors 22, 24,0r if the load on these two is greater than that taken from the conductors 23, 25, a part of this excess current will pass through conductor 26 in certain positions of the brushes'on the commutator. This result also occurs if the converter is used for transforming single phase alternating current into direct current.

In F 1g. 3 a modificatlon of the invention is shown in which the converter is adapted for connection to a 6 phase alternating current circuit. The magnetic core 51 is provided with six openings 52, 58, 54, 55, 56 and 57 on which 'are wound, respectively, the groups of coils 58 to 63. These coils are connected to the commutator 6a in the usual manner, but in order to avoid confusion most of the conductors connecting the coils to the commutator bars have been interrupted on the drawing. SiX brushes are shown bearing on the commutator numbered from 65 to 7 O, inclusive. Brushes 65 and 69 are short circuited as well as brushes 66 and 68. Brushes 6a and 67 are connected to the opposite terminals of a storagebattery B and brushes 70 and 68 are connected to the opposite terminals of a second storage battery B Under usual conditions of operation the positive terminal of the battery B will have a different potential from the corresponding terminal of the battery 13 There will, however, be certain points in the two batteries which will have the same potential and may be connected together as. by the switch S. This intermediate circuit between the two batteries will under some conditions of unbalanced AC load, and some positions of the brushes on the commutator carry a part of the unbalanced current. Under other conditions this circuit will carry no current This con-' and the switch S need not be closed. The converter 51 is mounted on a shaft 88 which carries 6 collector rings numbered from 71 to 76, inclusive, which are connected to corresponding taps between the adjacent sections of the converter winding, as shown. These collector rings by means of suitable brushes are connected to the six conductors of the (3 phase circuit, numbered from 78 to 83, inclusive. To this 6 phase circuit is connected a source of 6 phase alternating current A and translating devices L.

The shaft 88 is driven by a split pole converter Q, constructed in the usual manner with a bi-polar wound armature 90 provided with the usual commutator, and six collector rings. The latter are connected to the 6 phase circuit, while the commutator through suitable brushes is connected to the tcrmi nals of the battery B Double throw switches 91 and 92 permit the direct current terminals of the converter Q to be disconnected from the battery B and connected to the battery 13 if desired. The converter Q, is provided with main poles 93 and 94s and regulating poles 95 and 96. These latter have their usual function of varying the direct current electro-motive-force developed in the armature without changing the value of the alternating current electromotive-force in any marked degree when their excitation is varied.

The converter Q, is designed to act as a motor for driving the converter 51, either from the AC circuit or the DC circuit. It is, however, so designed as to prevent any considerable transfer of energy between these two circuits, such transfer being accomplished through the converter 51. This result is secured by a special winding on the regulating poles 95 and 96.

The main poles 93 and 9% are provided with an ordinary shunt field winding connected across the brushes of the machine so that the excitation of the main poles is substantially constant. The regulating poles 95 and 96 are provided with a series winding 97, 98 connected between one brush of the machine and the direct current circuit. This series winding is wound in the direction to increase the direct current voltage of the machine with any increase of direct current input to the DC brushes. If, therefore, there should occur any tendency to transfer energy between the AC and the DC circuits through the machine Q, a change in the direct current input or output of this machine will vary the counter-electro motive force developed in the machine in the direction to counteract such tendency.

Furthermore, the regulating poles 95 and 96 are located on thetrailing side of the main poles. This produces a shift of the alternating current electro-motive-force of the machine with any change in the excita- Cji tion of these regulating poles in the direction to further'counteract the transfer of energy between the AC and DC circuits. Thus if there is a small .increase of direct current input to the machine Q the strength of the regulating poles is increased, thus shifting the mean position of the total field flux in the direction of armature rotation. This shift will retard the phase of the alternating current electro-motive-force de veloped in the armature of the machine Q causing it to take additional energy from the AC circuit in accordance with the usual law of synchronous machines of this type. This input of energy from the AC circuit will oppose any further increase of input from the DC circuit. The shunt field excitation of the machine Q may be adjusted by means of the rheostat B, so that when running at synchronous speed the energy required to drive the apparatus will be taken substantially all from the DC circuit. Any slight variation in the energy required will be supplied from the AC circuit on account of the action of the regulating poles as above described. It the supply of alternating current energy from the source A is interrupted, the machine Q will still continue to drive the converter 51 and energy will be supplied to the translating devices L through this converter from the batteries B and B \Vhile Figs. 1 and 3 show the AC taps taken from points intermediate between the various sections of the converter winding, this arrangement is not necessary, and these taps may betaken from intermediatepoints in each winding section instead of from points between'adjacent sections, as shown in Fig. 4:. In suchcase it is preferable to take these taps from the middle point of each section, in order to secure a symmetrical wave shape of alternating electro-motive-force. One of the advantages of the construction shown in Figs. 1 and 3, and especially thatshown in Fig.3 lies in the fact that when current is being transmitted between the AC and the DC circuit, the average current value in the windings of the converter 51 is comparatively small. It will be noted that there are (ipoints in each revolution of the converter, at which the current passes directly from the AC to the DC circuit or vice versa without passing through the converter winding at all.

In other positionsthe current is divided in inverse ratio to the number of coils through which it is transmitted, so that the heaviest current is transmitted through the fewest number of coils. This reduces the total amount of heating in the winding and permits a smallmachine to carry comparatively large loads.

Itwill be notedthat in some positions of ,thebrushes, direct current flows inopposite directions to ,or from an intermediate point in each of the Winding sections, the ampere turns on each Side of this intermediate point beingequal and opposite. In order to reduce to a minimum the leakage of magnetic flux across the openings 2, 3, 4, 5 under these conditions, the leakage path should be as long and of as small cross section as possible. This result is accomplished by making the conductors of thin strips as shown in Fig. 2.

Having described my invention what I claim and desire to secure by Letters Patent is 1. In apparatus of the type described for interconverting alternating and direct currents, the combination of a plurality of closed magnetic circuits, a group of conducting coils embracing each of said circuits, said groups connected in series to form a continuous closed circuit Winding, a commutator connected to said Winding, brushes bearing upon and spaced apart around said commutator at contact points equal in number to the number of coil groups, short circuiting connections interconnecting some of said brushes, alternating current taps to said winding, one for each coil group, and means for producing relative rotation of commutator and brushes.

2. In apparatus of the type described for interconverting alternating and direct currents, the combination of winding sections, a closed magnetic circuit and an alternating current tap for each section, a commutator connected to the sections and direct current brushes equal in number to the taps and equally spaced around the commutator.

3. In apparatus of the type described for interconverting alternating and direct currents, the combination of winding sections, a closed magnetic circuit and an alternating current tap for each section, a commutator connected to the sections, direct current brushes equal in number to the taps and immovable in respect to each other, and means for short circuiting some of said brushes.

4. In apparatus for inter-converting alternating and direct currents, the combination ofa converter devoid of motor function and a motor devoid of converter function for driving the converter, said motor drivable from both the alternating and direct current source simultaneously.

5. In apparatus of the type described the combination of groups of coils, closed magnetic circuits one of which passes through all the coils of each of the respective groups, a commutator connected to the coils, and alternating current taps and direct current brushes equal in number to the number of groups and symmetrically spaced.

6. In apparatus of the type described the combination of six winding sections, a closed taps to a six phase alternating current cir 10 magnetic circuit and an alternating current cuit.

tap for each section, a commutator 0011- In testimony whereof I have duly exenected to the sections, six direct current cuted these presents this 18th day of July,

: brushes whereo1 two pair are short-cir- 1 915.

cuited, two sources of direct current each JOSEPH LESTER WOODBRIDGE. of which is connected between one of the WVitnesses:

pairs of short circuited brushes and one of J. L. MACBURNEY,

the single brushes, and connections from the WV. G. ROGERS.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. C.

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