US1623665A - Method and apparatus for producing alternating currents - Google Patents

Description

April- 51, 1927.

R. D. FAY ET'AIL IE'I'HQD AND APPARATUS FOR PRODUCING ALTERNATINGQCQRRENTS- Filed um 45 1922 4 sneets-shet 1 April 5, 1927. l ,523,5

R. D. FAY- ET-AL METHOD AND APPARATUS FOR raonucms, ALTERNATINfi'CURRENTi Filed Marh 15 1922 4' She e fIs -Sheet 2 "3 I I WgfQ/TURS 5 va -W n A ril 5.1927.

R. D. FAY ET AL METHOD AND APPARATUS FOR PRODUCING ALTERNATING CURRENTS FiledMarch 15. 1922 4 Sheets-Sheet 5 May/T055 ww Patented Apr. 5, 1927. v

UNITED STATES 1,623,665 PATENT OFFICE.

RICHARD D. FAY, 0F NAHANT, AND EZEKIEL WOLF, OF BOSTON, MASSACHUSETTS,

ASSIGNORS, BY MESNE ASSIGNMENTS, T

TON, MASSACHUSETTS.

O HAMMOND V. HAYES, TRUSTEE, OF BOS- METHOD AND APPARATUS FOR PRODUCING ALTERNATING CURRENTS.

Application filed March 15, 1922. Serial No. 544,034.

ments of which are connected alternately tothe two poles of the source of current. In such an arrangement the difference of potential between adjacent segments is, during a considerable portion of the time, equal to the full voltage of the current source and at times may be considerably greater. It has been usual to complete the circuit by means of brushes bearing upon the commutator which brushes are connected by wires with the condenser and the electro-magnetic device. It has been found by experience that such an arrangement has a very serious defect due to the fact that when the commutator is revolved, arcs are frequently formed between adjacent segments of the commutator.- When such arcing occurs the commutator is quickly destroyed if not sufliciently protected by fuses. Attempts have been made to overcome this defect by increasing the amount of insulation between the segments of the commutator. pedient has failed for therea on that after a little use portions of the brushes, which are Worn off by the revolving commutator, adhere to the surface of the insulating material between segments and produce a sufficiently conducting path to promote the formation of an are.

There is a second condition which also tends to produce flash overs and the consequent destruction of the commutator. This condition ari-cs when the circuit is made or broken by a key, switch or similar device included in the circuit but independent in its operation from that of the pole changer. In practically every installation a key .or switch of this kind must be used and is essential in an oscillator circuit when the oscillator is used for producing code signals. Inall. sy tems of this kind hereto fore used there has been no means provided to restrict the making or breaking of the circuit-through the action of this key to such Such an ex-- times as there is a minimum of current flowing across the polechanger. The result has been that the circuit has been liable to be broken at times of maximum current flow and consequently that flash overs are produced'at the pole changer with disastrous results. This ditliculty has been fatal to the successful operation of a device of this kind when fairly large currents at fairly high potentials are reversed at the pole changer.

There is a third and very practical limitation to an arrangement of this kind when the circuit and mechanisms are designed so that the condenser will be fully charged during the time of contact of the brushes on the live segments of the commutator or pole changer, with the object of having the make and break of the circuit occur at a time when the current across such contacts has ceased to flow. This limitation arises from the impossibility of obtaining under such conditions the alternating current required to actuate the electro-magnetic device from a source of direct current having usual commercial voltages.

The above can best be illustrated by a practical case of the application of such an arrangement under usual commercial condi tions. In most places 220 volts is the maximum voltage available from a direct current source. Let it be assumed that the electromagnetic device has a resistance of 9.5 ohms and an inductance of 1.25 milli-henries and that it. is desired to produce an alternating current, through the electro-magnetic device and a condenser in series with it, having a frequency of 500 per second. If the circuit is designed in such a way that the condenser is fully charged before the circuit is opened at the pole changer, a condenser having about 25 microfarads must be employed and with it a power of about 550 watts is derived. The capacity was limited to 25 microfarads in order to permit the condenser to be fully charged before the circuit was broken. If a condcnser having a capacity of microfarads were used, the other constants of the circuit remaining as before, the power obtained by the electromagnetic device. would be somewhat more than doubled or would be about 1260 watts. In this latter case, however, the current at the time of opening the circuit would be about 6.7 5 amperes. In other words, if the power required for the operation of the electro-magnetic device was more than 550 watts, if the voltage of. the source Was limited to 220 and it it was required that no current should be flowing at the time of making or breaking the circuit, then the system would be inoperative.

Our invention consists in the design of circuitmaking and circuit-breaking mechanisms wherewith there is no possibility of arcing even when a current of a reasonable strength is flowing. \Ve do not limit ourselves to the condition that the electrical circuit containing the condenser should have a time constant less than one half of'the period of the frequency desired but on the contrary so design the pole changer and key that they will care for current. of the strength requisite for the operation of the electro-magnetic device without the possibility of flash overs or destructive arcing.

In our invention we have abandoned the use of a commutator as a pole changer and have substituted a device wherein the necessary contacts are made and broken by the to and fro movements of two fairly large parallel conducting surfaces. The movements of these contact surfaces are so rapid and the opening between them is so great that there is on liability of an are following between the surfaces. Again we have-an ranged the devicein such a way that the contacts with the positive main of the supply circuit are all made in a compartment en tirely separate and insulated from a second compartment in which the contacts with the negative main of the current supply circuit are made. This arrangement insures complete immunity from the destructive arcing which has been inherent inthe commutating devices heretofore employed. The third feature which we have embodied in our invention is an electro-mechanical arrangement by the'use of which a key can be used to transmit telegraph or code signals with the certainty that the operation of the key will effect the making or breaking of the circuit onl when a minimum of current is passing an thereby eliminate the causes of the are which has been fatal in the operation of earlier devices of-this kind. Furthermore we employ a condenser of sufiicient capacity to obtain the required energy from the available direct current source and in doing this depend upon the non-arcing properties of our polei" changer to carry the current necessary to obtain'the required energy.

In the drawings accompanying the present specification Figure 1 shows diagrammatically the simplest form.

Fig. 2 shows diagrammatically the circuit arrangement inthe exact form which has been embodied in the pole changer which we have Yound most satisfactory.

circuit arrangement. in its the mechanism used in connection with the key or switch employed when thecurrent is interrupted for longer .or shorter intervals for producing code signals.

Fig.- 6 shows the circuit and arrangement of apparatus best suited to obtain an alternating current ot' nearly sinusoidal form.

n n I n Fig. 7 shows diagrammatically the circuit arrangement of the complete apparatus of Fig. 2 in its preferred form, there being added to a portion of this figure means whereby the circuit closers are held against the cam and also means for preventing the circuit closers from operating.

In Fig. 1, 2 is a continuous current dynamo, storage battery or similar sourceof direct current. 3 and 4 are conductors used to carry the current to the pole changer, 3 being connected with the positive pole and 4t with the negative pole of the source oi current. 5 and 6 are switch arms connected with the positively charged conductor 3 and 7 and 8 similar arms connected with the negative conductor 4. 9 and 10 are fixed contacts with which switch arms 5 and 8 can engage. Contacts 9 and 10 are connected with one side of condenser 12 by conductor 11. 13 and 14 are fixed contacts with which switch'arms 6 and 7 can engage. Contacts 13 and 14 are connected with one end of the secondary winding of electro-magnetic device 15, shown as a Fessenden oscillator (U. S. Patent No. 1,167,366) by conductor 16. The other end of the secondary winding is connected with conductor 17 and by it with the other side of condenser 12'. The switch arms 5, 6, 7 and 8 are actuated by cams, to be described later in detail, in such a way that when 5 and 9 are in contact 7 and 14 will also be in contact and 6 and 13 as well as 8 and 10 will be broken. As the cams revolve the contacts 5-9, and 714 will bebroken and later 613 and 8-10 made. The shape of the-cam or cams is's'uch as to give the desired relative periods of open or closed circuit at the usual contact points.

{To obtain a complete cycle of the alternat- Ill] ing current the sequence of making and [Ch of the four when lower frequencies are desired, we prefer to use for higher frequencies the arrangement shown diagrammatically in Fig. 2. This arrangement is in principle identical with that shown in Fig. 1 except that two more switch arms 18 and 19 are connected with the positive power main and two additional switch arms 20 and 21 are added to the negative mains. These swith arms engage contacts 22 and 23 and 24 and 25-respectively. The contacts 22 and 25 are connected with the wire 11 leading to one side of'the condenser and contacts 23 and 24 are connected with the electro-magnetic device and the other side of the condenser by wire 16 as before.

A practical means embodying our invention is shown in Figs. 3, 4 and 7, Fig. 3 showing at 32 one of the stationary plates carrying the mechanism, Fig. 4 showing in elevation the plate structure, and Fig. 7 illustrating the various circuits and the means for operating them, all in diagrammatic form. 28 is a motor having its casing mounted on a base 29 and driven from" any source, 281 bein its leads. Brackets 291 supported bythe ase 29 carry at their outer ends plates 32, 34. 33 is the motor shaft which passes through the plates .32, 34 and carries at each end a cam 26 which is thus rotated by the motor 28. The cams 26 are identical in shape and the parts operated by them and their electric connections are the same; As shown each cam vhas nine projections 27 each of which from the beginning to the limit of its rise subtends an'arc of 30 while the low space 271.between the highest limit of one projection and the beginning of the rise of the next projection subtends an arc of 10. In 'Fig. 3 is shown the plate 32 with the various parts attached. Around the cam 26 are arranged switch arms 5, 6, 18 and 19. The arms 7, 8, 20 and 21 are ai ranged aroundthe corresponding cam at the other end ofthe shaft 33. Describin the set shown in Fig. 3, each arm is pivote to the plate 32 and insulated therefrom and has a finger 51, 61, 181 and 191 which engages the edge of the cam, but is insulated therefrom. Each arm on plate 32 is electrically connected with the wire 3 and when its finger is riding over the low portion only of the cam, may make contact with 9, 13, etc., thus closing the circuit through wire 16. The switch arms on plate34 are arranged in all respects like those on plate 32, but are connected with wire 4, and the two cams are arranged on- :haft- 33 so that arms on the two plates operate synchronously (see Fig. 7). 'Thus'when one of the arms on plate 32 makes contact a corresponding arm on plate 34 also makes contact sii'nultaneously and the circuit is closed througlfthe wires 11 and 16 and through the device'15. This arrangement allows the contacts to be somewhatbroad rather than mere identical at the two ends of the shaft 33 and are set on that shaft so that two switch arms will be operated simultaneously, it will be seen that both positive and negative lines will be closed momentarily at the same instant.

This multiple arrangementofgswitch arms and projecting cam surface permits the cam as a whole to be revolved at a lower speed than would otherwise be required to obtain a given frequency of alternating current.

In Fig. 7 plate 32 is shown and on it are the parts shown in Fig. 3, these two views of 32 being substantially identical. The plate 34 shows arms 7, 8, 20 and 21 corresponding," respectively, to arms 5, 6, 18 and 19 on plate 32; Each arm has fingers 71, 81, 201 and 210 corresponding with the fingers 51, 61, 181 and 191-. The contacts-on 34 are numbered 14, 10, 24 and 25 corresponding with the contacts 9, 13, 22 and 23. It will be seen, for exam le, that when contact is closed by the arm at 14, thus connecting the line 4' with the line 16, contact 9 will be closed, thus connecting the arm 5 with the line 11 and the line 3.

In order to overcome the danger of arcin arising from breaking the circuit when sen 1 ing signals by the use of a key or switch due to the contact being made at a time of maximum current flow, the arrangement shown" enlarged in Fig. 5 as well as in Figs. 3, 4 and 7 ,is employed in connection with each switch arm. Each switch arm carries a spring latch member 361 adapted to engage with a latch member 36 mounted'on the end of a spring 40 attached to the plate 32 so that when the switch arm has been forced back by a pro jection- 27 of cam 26v the latches will normally engage and hold the switch arm from touching its associated contact until released. An'electromagnet 35 is located to control the portion of the spring 40 which acts as the armature of its electroanagnet 35. These electro-magnets preferably on both plates 32 and 34 are connected in circuit with a hat' tery 38 and key 39 in such a way that. when key 39 is depressed and the local circuit 'com pleted, all the electro-magncts will be encrgized and the latches on the arms released so that whenever an arm is in proper relabe in position to' catch and hold the switch arms as the switch arms are forced back by the cam. In this way it is impossible to have the main current supply circuit broken by the pole chan er except when the current is less than a de ite value.

It will be understood that'the plate 34 in fact carries parts identical with the abovenamed parts constructed and operating in the same way.

In Figs. 6 and 7 are shown diagrammatically a modified form of the circuit shown in Fig. 2. We have found that this latter arrangement of circuit and apparatus may be made to produce a current curve more nearly approaching the sinusoidal formobtainedfrom alternating current generators such as have been commonly used heretofore.

pedance coil of proper inductance Z and a proper resistance 1' are connected in series with the electromagnetic device, and a second condenser C, of smaller capacity than C, is connected in shunt about the electromagnetic device and auxiliary inductance. Z-.

by wires 401 and 41.

We have found that with the above arrangement of apparatus and by properly proportioning the-capacitiesof thecondensers to the resistances and inductances of the electro-magnetic elements connected in the circuit shown in Figi '6 and by the use] pass out through openings in plate 32 and nected in a manner which will be understood by one skilled in the art.

their respective -circuits are suitably con- What we claim as our invention is 1. In combination, a member adapted to be operated by alternating current and having a lead from each side-thereof, a direct current source having a lead from each side thereof, a pole changer comprising a motor,two cams rotated thereby, two groups of switch arms, one group being connected to the positive lead from said source and the other to the said contacts being connected to one sideof said member and the rest to the other side of said member, each cam being shaped to v allow one switch arm of each group at a time to engage its contact and said cams being arranged whereby both cams will operate one switch arm of both ously.

- 2. A- pole changer com rising a motor, a cam rotated thereby, an e ectric circuit comgroups simultane- In this second arrangement an auxilliary imprising switch members and contacts therefor,

said cam being adapted to control the engagement of said switch members with their contacts, latch members adapted normally to hold said switch members out of contact with said cam and said contacts, and means for releasing said switches from said latches comprising electro-magnets, a circuit, a

current source comprising two-grou s ofswitch arms, one-group connected wit one pole of a direct current source and the other group with the other "ole of the same source, and cards so arranged with relation to said switch arms that two switch arms, one from each group will at the same time be allowed to make and break the .circuit at the contacts associated therewith, and" that each switch arm of each group will in turn bear upon the contact with which it is associated.

4. In a pole changer for producin in a circuit alternatin current from a'direct'current source, switc ing means, means for openrent source, switching means comprising two sets of arms, each arm of oneset being connectible to a corresponding arm of the other set, means for causing connections between different pairs of arms to be operated consecutively, means -for retaining said'switching means when opened, and means for releasing said retaining -means whereby the circuit can be made and broken only at times of minimum current flow.

6. In a pole. changer for producing a circuit alternating current from a direct current sourceincluding a circuit, switching means, means for opening and closing said switching means, means for retaining said switchin means open comprising latches one mem r of each of, which is attached to one member of said switch, the other member thereofbeing'adapted to. engage said first member when said first member is in rei tracted position and hold it, and means for releasing saidaetaining means comprising an electro-magnet whereby the direct ourtimes of minimum current flow.

rent circuit can be made and broken'only at

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