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May 10, 1938.~ J. KALSEY 2,116,899 SYNCHRONOUS CONVERTER Filed Feb. 12, 1956 ' 5 Sheets-Sheet l INVENTOR. MM as)“ A TTORNEYZ . May '10, 1938. _j_ KALSEY 2,116,899 SYNCHRONOUS CONVERTER Filed Feb. 12, 1936 5 Sheets-Sheet 2 INVENTOR. A TTORNEY. May 10, 1938. J. KALSEY ' 2,116,899 SYNCHRONOUS CONVERTER Filed Feb. 12, 1936 5 Sheets-Sheet 4 INVENTOR. WWW. ATTORNEK May 10, 1938. J_ KALSEY '2,116,899 SYNCHRONOUS CONVERTER Filed Feb. 12, 1936 5 Sheets-Sheet 5 11%- ~20 /30 I IQIXIL/EN TO-R. BY 761444,. 5.0%. ATTORNEY. 2,116,899 Patented May 10, 1938 UNITED STATES PATENT OFFICE 2,116,899 .SYNCHRONOUS CONVERTER John Kalsey, North Palo Alto, Calif. .Application February 12, 1936, Serial No. 63,573 15 Claims. (Cl. 175—364) This invention relates to a rotary synchronous converter for the conversion or recti?cation of alternating current into direct current. The object of the present invention is generally to improve and simplify the construction and op eration of converters of the character described; to provide a rotary converter having a main and an auxiliary commutator with cooperating brushes to deliver alternating current thereto; to 10 provide means for relieving the brushes on the main commutator of current load while passing from one segment to another, or more speci?cally stated, to provide means for by-passing the cur rent to the brushes of the auxiliary commutator 15 While the brushes on the main commutator are passing from one segment to another; to pro vide means, including a ?xed and a variable re sistance, for preventing short circuiting be tween the brushes of the main commutator and p0 the brushes on the auxiliary commutator; to pro vide automatic means for maintaining the con verter in synchronous operation with the gen erator supplying the A. C. to be converted; to provide automatic means for selecting a prede termined current‘ polarity and for maintaining the D. C. output of the commutator at the se lected polarity; to provide means for automati cally breaking the A. C. current supply to the converter if it fails to operate in synchronism 30 with the A. C. supply; to provide a converter of high e?iciency; and, further, to provide a con— verter in which the D. C. output may be regulated and varied on the A. C. side of the circuit. The converter is shown by way of illustration 35 in the accompanying drawings, in which— Fig. 1 is a diagrammatic view showing the con verter whereby A. C. current is converted into D. C., said diagram also showing the synchro nous motor whereby the converter is driven, and, 40 furthermore, showing automatic control appa ratus for maintaining the driving motor in syn chronism with the generator supplying the A. C. current and also for selecting the proper polarity, _ said diagram, furthermore, disclosing means for 4” automatically breaking the supply of current to the converter if the driving motor gets out of phase and, furthermore, showing means for varying the current ?ow to the converter; / rent flow in an alternating current supply cir cuit during one complete cycle of operation; Fig. 6 is a diagram showing the pulsating D. C. current produced by the converter during one cycle of operation; 5 Figs. 7 to 11, inclusive, are diagrams showing the different positions assumed by the commuta tor B during one cycle of A. C. input; Figs. 12 to 15, inclusive, are diagrammatic views showing one of the collector rings D, the 10 main commutator ring B, and the auxiliary com mutator ring C, said view showing the relative positions assumed by the brushes H and H’ when passing from one segment of the respective com mutators to the other; 15 Figs. 12“, 13a, 14a and 15a are diagrammatic views showing how the resistance gradually in creases and decreases through the brushes H and H’ while passing from one segment to the other; 20 Fig. 16 is a longitudinal section through the converter as actually built; Fig. 17 is a cross section of the converter taken on line XVII-—XVII of Fig. 16; Fig. 18 is a cross section taken on line 2 XVIII—XVIII of Fig. 16 ; Fig. 19 is a perspective view showing the rela tive position of the commutators A, B and C and the collector rings D and E; and Fig. 20 is a diagrammatic view showing the 30 automatic control apparatus for maintaining the driving motor in synchronism with the generator supplying an A. C. current, also for selecting the proper polarity. Referring to the drawings in detail, and par- 35 ticularly Fig. 1, A, B and C indicate a series of commutator rings and D and E a pair of collec tor rings. All of the rings are secured on the shaft F mounted in suitable bearings and this is, in turn, driven by a synchronous motor, gen- 40 erally indicated at G, which derives its alternat ing current from the same source as the alter nating current to be converted. An alternating current synchronous motor is a motor whose speed is governed by the number 45 of cycles in the alternating current energizing the same. Thus, in the case of a synchronous motor with a certain number of poles, ‘and connected to the output of an alternating current generator Fig. 2 is a cross section of the main commu-t having the same number of poles, the speed of tator B; both machines will be the same and at any given Fig. 3 is a cross section of the auxiliary com instant the relative position of both armatures mutator C; will be identical. In the case where the num Fig. 4 is a cross section of the commutator A; ber of poles on both machines are not the same, 55 55 Fig. 5 is a diagrammatic view showing the cur 2 2,116,899 the resultant motor speed will be an exact ratio to the speed of the generator. Taking a two pole A. C. generator, one com plete revolution of the same will produce one complete A. C. cycle. During one-half of this cycle the ?ow of electricity will be in a positive di rection and during the other half the flow will be in a negative direction. These one-half cycles are known as alternations and are diagrammati cally illustrated in Fig. 5. Should a two pole A. C. generator revolve at a speed of sixty revolutions per second, it would produce a sixty cycle current. By increasing the poles and reducing the speed proportionately, 15 the current would still be sixty cycles. In other words a sixty cycle alternating current is a cur rent which reverses sixty times per second. Tak ing a two pole synchronous motor operating on sixty cycles A. (7., its speed will be 3600 R. P. M. If this motor has four poles the speed will be 1800 R. P. M. The motor’s armature motion is produced by what is known as a revolving mag netic ?eld and in this process the armature “locks in step” with the current cycle, From the foregoing it should be apparent that a predetermined point on the shaft of the syn chronous motor will at all times coincide with a predetermined point on the A. C. curve; in other words, if a point on the shaft is in a certain posi tion and the alternating current at that moment is in a negative direction and the value of the same bears a certain relation to the A. C. curve, when the shaft has made one complete revolu tion all the current conditions for that particu 35 lar period will be repeated. For the purpose of description let it be assumed that the commutator B, in Fig. 1, has four seg ments insulated from each other and the shaft F, and that the motor G driving the shaft is a four pole 1800 R. P. M. sixty cycle synchronous motor and, further, that segments 1 and 3 of the commutator B are connected to the collector ring D while the segments 2 and 4 are connected with the ring E. In addition thereto, let it be assumed that the shaft F is rotated in an anti-clockwise direction and that a sixty cycle alternating cur rent is impressed on the segments by means of brushes H and J, which are positioned at a 90° angle with relation to each other. Under these conditions with the commutator revolving, the various forces diagramed in Fig. 5 will be impressed upon the several segments of the commutator as follows. Assuming that the motor is running at its proper speed and when at 55 the zero point, or at a’ of Figs. 5 and '7, the brushes H and J will not be in contact with any of the segments, at which time there is no cur rent ?ow in this circuit but when the segments 5 and 2 are moved, just making contact with 60 the brushes H and J, there will be a positive flow of current starting in the circuit, and further rotation of the segments, as shown in Fig. 8, the positive ?ow of current in the circuit will be at its maximum value. The positive current flow 65 now starts to decrease until it reaches point 19’, shown in Figs. 5 and 9, (or 1/120 second of time) where there will be no flow of current and the brushes are out of contact with the segments, further rotation of the segments bringing the segments 4 and I in contact with the brushes H and J, respectively, and the current flow will be started in a reverse or negative direction through the circuit and increase in value until it reaches 75 its maximum negative value, then starts to de crease until the zero point is reached when one cycle is completed (or 1/60 second of time). Under this arrangement the segments l and 3 always receive a positive flow of current and 2 and 4 always receive a negative ?ow of current; these segments being connected to their respec~ tive rings D and E will rectify the A. C. input or convert it to a direct current and the cur rent will be a pulsating one as diagrammatically illustrated in Fig. 6. Condensers or ?lters of 10 suitable type, not shown, will, however, be placed in the D. C. line to smooth out the current flow. It should be evident that the commutator itself does not consume any energy and will convert one hundred percent of the current input. It should also be evident that the amount of energy and the pressure behind the same can be altered without changing the general arrangement as a variable transformer may be placed on the A. C. side of the circuit to vary the amount of energy and pressure. The synchronous motor G driv ing the commutator need only be large enough to provide the desired rotation and inasmuch as there is no electrical connection between the two it can be operated on the conventional 110 volt~ age. It should be evident that the variations impressed or converted will not change the load on the motor. The only requisite is that both currents have identical periods and cycles. Inas much as the supply is derived from one generat 30 ing system this is a practically assured condi~ tion. The consumption of energy by the synchronous motor driving the converter is constant, hence the cost of conversion depends upon the amount of energy converted. The motor driving the con-w verter in operation in my laboratory at the pres ent time consumes about 200 watts per hour and my average use of D. C. approximates 10,000 watts. In this particular instance the efficiency of 40 the converter is 98%. Regulation of D. C. voltage after delivery to a consumer is a complicated matter and in most cases is accompanied by the loss of considerable energy. Compared to this the regulation of A. C. supply is a simple matter consuming very little energy in the process. With the use of my converter the desired D. C. values are regulated at the A. C. side by means of the variable transformer shown, or the like. The converter so far described would seem‘ perfect. This, however, is far from being the case and I shall try to describe some of the faulty conditions. Referring to the diagram shown in Fig. 5, if the alternating current were in perfect phase with the generator and the resultant curve ‘F' were regular, then at the points‘ a’, b’, c’, where the flow reverses, there would be no voltage and hence no current. Thus if the brushes H or J had only the thickness of the imaginary zero line it could pass from one segment to the other at the time when the circuit is dead. However, a practical brush must have thickness and thus at some period the brush must contact both seg ments at the same time and though the energy at that instant would be very small there would be a momentary short circuit. Now, if the thick ness of the insulation be increased a width slight ly wider than the width of the brush this defect would be overcome but another condition would 70 appear; that is, as the trailing edge of the seg ment pulls away from the brush there would be a momentary break in the circuit. The tendency for an interrupted current is to continue contact after a break and this condition is carried on 75 3 2,116,899" “ through space, the result is a: disagreeable spark ing which‘ quickly pits‘ bothv the copper and brush which, in turn, intensi?es this’ phenomena until ?nally the device becomes useless. In‘ practice it is never possible to obtain an alternating current free from imperfections and position‘, Fig. 113, the: brush‘ H has partially left the segment I1 and is entirely bearing on the high resistance tip 6. Under this condition the H brush- can only deliver a fraction of the total we seldom have currents where all‘ conditions are in phase. Thus, the zero line of the alternating current curve, see Fig. 5‘, or rather the relation‘ of 10 the same with respect to-the curve is never‘ con stant and hence there maybe considerable cur rent in the circuit at the time? the brushes cross the joint. The result is sparking, pitting and scoring which, in turn, causesfaulty contact and load, meanwhile, the auxiliary brush H’ is bear CH ing directly on the load transfer segment ‘I and the main load2 or current is delivered from brush H through the special resistance, to be described, to H’ then to segment I» through wire 8 to seg ment I5 and: ?nally through wire‘ l4‘ tov the col 10 lector ring D. In this'p'osition the main load is delivered by the auxiliary segment. As motion‘ progresses brush H has diminishing contact with‘ the resistance tip 6 of segment I irregular commutation. Thus, in the case of a narrow joint we have short circuits, in wider joints we have sparking and ?ashing. To overcome this defect I have developed a system whereby the load carried by the segments 20' is- gradually reduced as the‘ joint comes under the brush and entirely ceases at the moment the trailing edge of the segment leaves the brush. At the same time the load is transferred to an auxiliary brush which continues to deliver thev 25 load to the circuit until‘ the main brush has traveled across the insulated joint. This system is of prime importance for it allows a continuous delivery of energy and hence eliminates all spark ing. The manner in which this is accomplished is, best illustrated? in Figs. 12 to 15, which are diagrams showing the relationship between the segments, brushes and current values at or near the A. C. zero line, said diagram indicating four different conditions while the brushes are cross until ?nally the segment becomes non-conductive until it reaches the‘ position shown in Fig. 14 where'the‘ flow through the segment has entirely ceasedi Meanwhile the load is being delivered. through’ the brush H’ but at this moment this brush begins to contact the resistance tip 9 of segment ‘I and as motion continues and resist ance offered by the segment becomes greater a small fraction of time after this condition and in the fourth position, see Fig. 15, brush H has con tacted segment 2 and brush H’ has ceased to 25 deliver current‘. Meanwhile the current has re versed so that the brush H is delivering current ing the joint between‘ segments. In these'diagrams D'represents one of' the col lector rings which delivers the converted or direct current‘to the'direct current side of the converter, B the main‘commutator, and IIandZ the segments thereoniwhich receive the alternating current to be converted, said current being introduced by the brush‘ H. In this case the insulation between the segments has been widened, the'width being slightly in excess of' that of the brush. In addi tion, the trailing edge of‘ each segment is con structed of material 6', such as nichrome, or the like, having a high‘ resistance to the passing of the'current. C indicates an auxiliary commuta tor containing conducting segments 1' positioned ' directly over the zero‘line; or‘ their position occu pies the corresponding space of the insulation between the segments I andZ. The segments 1 shown in‘ the diagram are insulated from the rest of the commutator but are'in electrical con nection with segment I through wire 8. The seg ments‘! also have a trailing edge 9 of high’ re sistance material.‘ The brush H’, which will be referred tov as the auxiliary brush; is only one half the width of the brush H.- In these diagrams 60 the auxiliary segment ‘I- and segment I' are directly connected by the wire 8. The brush H’ is con nected to brush H by means of a special resistance hereinafter to be described. Assuming‘ the‘converter‘v is in rotation and in the direction'of arrow is, and‘ again referring to Figs. 12 to 15', the diagrams show'four different positions of 'the commutatorv segments under the brushes and‘each-position' indicates on the load transfer diagram depicted at‘ the right just how the load is distributed; In the ?rst position, Fig.‘ 12, all‘ofth'e load or current is delivered by the brush‘H to segment I'andl‘ thence to the collector‘ ring'D by means of the‘wir'e' M‘. The auxiliary brush: at this? moment is inactive. In the second to segment 2 which is connected‘ to the negative side of the system. In the fourth position before brush H’ has left the auxiliary segment the brush H has contacted segment 2 and also the current ?ow has been reversed. The condition of dual contact maintains only for a small fraction of time, the facts are that for that period, current 35 is being delivered'by one leg‘ to both sides of the circuit. Though the actual short-circuit is through resistance, the value of the current may be such as tonullify the advantages of the re sistance‘tip of the auxiliary segment ‘I. To overcome this condition I have designed an automatically controlled variable resistance. Its function is to render brush-H’ conductive in pro portion to‘ the total value of the‘entire load im pressed upon the system. By calculation and 45 tests, the‘ energy transferred to the brush H’ should: be one-half? of one percent of the total energy going through the converter. Inasmuch as the total‘ energy varies according to the de mand, an arrangement whereby the energy pass 50 ing through brush H’ shouldv at all’ times be in the proper proportion is necessary. ' Fig. 1 depicts the two brushes H and H’ with a ?xed resistance l5 between'them. This resist ance is permanently adjusted to‘ta-ke care of a 55 minimum requirement. In addition there is a variable resistance 16 in shunt with this arrange ment. This resistance consists of'a unit plunger I‘I'mounted within'the coil l8 of a solenoid. The coil in‘the solenoid is fed'with D. C. current from 60 the wires 19 and 20 and the amount of current passing through the same'governs the position of acontact arm 2|. The contact arm travels over the resistance coil [6» and hence controls the amount of current‘ capable of passing. In many D. C. uses itis' of the utmost impor tance that the ?ow'of current is always in a pre determined‘direction therein; in other words, that the polarity is never reversedl Inasmuch as the synchronous motor may “lock in step” with either the top ‘or the bottom half'of the‘A. C. wave when started‘, or‘ after interruption of- service, a con trolling devicev to force the commutator to deliver D. C. with the desired polarity is essential. This control is'shownin Figs. Land-520'. In these ?g 75 4 2,116,899 ures, G indicated the synchronous motor whereby the converter as a whole is driven. Rotating with the converter is the commutator A. A section of this commutator is shown in Fig. 4. In this case it will be noted that there are two segments 23 and 2G oppositely disposed with relation to each other but electrically connected. Between them are disposed two insulating segments 25 and 26. Two brushes 2? and 28 make contact and the cur rent supply is taken directly from the A. C. feed line indicated by the numerals 3i! and 3!; the current value being controlled by the transformer M. The action is such that when a commutator is in the position shown, it will allow current to 15 pass through. When the commutator makes one quarter of a revolution no current can pass. In asmuch as the commutator A is synchronous with 20 the motor G, the resultant current flow through the commutator is a direct half-wave pulsating current. The numeral 33 indicates an evacuated tube containing a metallic dome electrode M. In addition thereto, there is a ring-shaped electrode 35, the lower portion of which is shielded with a non-conducting material as shown at 36. A 25 third electrode Si is also employed. It consists of a small concave disc, the concave side of which is covered with a photoelectric sensitive material. The tube contains a very small amount of inert gas, such as neon. The phenomenon here is that 30 all surfaces within the evacuated tube will attract this gas and following certain physical laws will spread evenly over the surfaces. The amount of gas introduced is slightly more than what is nec~ 35 essary to effect this covering, making the space between the electrodes slightly conductive for small electric charges. The conduction of the electrical charge in this tube is brought about by the movement of electrons. These electrons can only move from a negative surface to a posi 40 tive surface. The amount of energy actuating the two electrodes 34 and 35 is just enough to allow electronic movement between them. As the electrons impinge upon either of the electrodes the gas deposited will emit a glow on the surface of the dome. Should the ?ow be from the ring to the dome 34 the top interior surface will glow. Should the ?ow be from the dome to the ring, the ring surface will glow. In the ?rst case the glow would be transmitted to the disc 37. In the second case any downward glow from the ring would be stopped by the ring shield 36 and the upward glow toward the dome would be insuf?~ cient to cause any re?ection from the dome, thus whether the disc 31 would be energized or not would depend upon the direction of current flow passed by the commutator. The disc 31 is in cir cuit with a relay magnet 38 which, if energized, will cause the two contacts 39 and 4|] to separate (50 and hence will break the current to the synchro nous motor G. Assume when the motor G is started that the commutator will pass the current in such a direc tion as to cause the dome interior 34 to glow. If that is the case it will energize the photo electric disc 31 and cause the current to flow through the transformer N and the relay 38 and break the motor contacts 39 and 40 and thereby slow the motor down. When the motor has slowed down one-quarter of a revolution the rela~ tive position of the commutator has been changed and will now pass the current in the opposite direction. This will keep the dome’s interior dark and the motor will remain locked in the desired 75. position. One important feature of the control system just described is that it operates entirely on the same circuit as the motor G making it independent of the energy passing through the converter. If for any reason the synchronous motor should CR not function in synchronization with the current to be converted and while the D. C. current is in use, the result would be an introduction of A. C. current into the D. C. system and the rela tionship between the A. C. converter and the 10 D. C. would be upset; also the current ratio for the auxiliary brushes would be destroyed which might result in damage or total destruction of the converter. To prevent this a circuit breaking relay has been developed. This is shown in Fig. 1 and presents a system of passing a current to any standard circuit breaker only when the motor is out of synchronization with the alternating cur rent. This system, furthermore, allows the same current actuating motor G to operate the relay 20 and also the breaker, thus making the entire con trol independent of the energy across the con verter. The circuit connected to the breaker magnet 45 is open at the contact points (22, the current entering the magnet 43 passes through the commutator A and also through a condenser 44. The principle here is that a direct current will not pass through a condenser whereas an alternating current will. Now as long as the commutator passes direct 30 current the contact points 42 will remain open but as soon as the motor G is out of step the commutator A will pass alternating current, thereby energizing the relay 43 and permitting the current to pass through the contacts 42 and the breaker magnet 45, causing the same to open the circuit breaker 46. The break in the circuit feeding the converter is, of course, only momentary as the tube 33 per forms two functions ?rst that of selecting the ‘i proper polarity and, secondly, that of maintain ing the motor G in synchronism with the A. C. generator supplying the system. That is, if the commutator A is off phase alternating current will not only pass through the condenser 44 but also through the tube 33, causing a momentary break between the contacts 39 and 40, thereby breaking the circuit through the motor G and slowing it down sufficiently to not only maintain it in phase but also in proper polarity. The converter shown in Fig. 1 is intended for a large output of energy and in some instances an energy of very high voltage. It is for this reason that the transformer M and the third commutator are used as a direct current of com~ paratively low voltage; for instance, 1.10 volts are required for the operation of the control appa ratus such as the synchronous motor G, the con trol tube 33, the circuit breaker 46, etc. If the converter is used for a low voltage output of ?xed 60 value the current for the control apparatus may be taken directly from the D. C. line or stepped down through a transformer, and in that case, the commutator A may be eliminated. In the use of direct current it is important in 65 many instances that the polarity is in the correct direction; for instance, in the use of X—ray appa ratus, electroplating apparatus, high frequency actuated dust or gas precipitators, in battery charging, etc. Wherever alternating current is converted into direct current by synchronous con version, manual operation to insure the correct polarity is usually necessary. By using the appa ratus shown in Fig. 20 correct polarity is auto~ 75 2,116,899 matically insured, and while this and other fea tures of the present invention are more or less speci?cally described, I wish it understood that various changes may be resorted to within the scope of the appended claims. Similarly, that the materials and ?nish of the several parts em ployed may be such as the manufacturer may decide, or varying conditions or uses may demand. Having thus described my invention, what I 10 claim and desire to secure by Letters Patent is:— 1. In a. converter of the character described, a main and an auxiliary commutator, and a pair of collector rings connected therewith, each of said commutators having a plurality of conductor 15 segments spaced circumferentially with insulat ing material and the conductor segments on the auxiliary commutator being aligned with the in sulating space between the segments on the main commutator, a pair of brushes for impressing al ternating current on the segments of the main commutator, a pair of brushes engaging the seg ments on the auxiliary commutator, a common feed wire connecting the ?rst-named and second named brushes whereby alternating current is passed through the second-named brushes while the insulating spaces between the segments on the main commutator are passing under the ?rst named brushes, and a ?xed resistance in the con nection between the ?rst and second-named 30 brushes. 2. In a converter of the character described, a main and an auxiliary commutator, and a pair 5 5. In a converter of the character described having a main and an auxiliary commutator and -a pair of collector rings connected therewith, a synchronous motor for driving the converter, and means actuated by the direct current output of the converter for varying the alternating cur 'rent input to the auxiliary commutator. 6. In a converter of the character described having‘ a main and an auxiliary commutator and a pair of collector rings connected therewith, a synchronous motor for driving the converter, ~10 said motor being supplied with alternating cur rent from the same source as the A. C. to be con verted, a third commutator on the converter also supplied with alternating current from the same source, means actuated by current output of the 15 third commutator for breaking the A. C‘. sup plied to the converter if the synchronous, driving motor gets out of synchronism and other means for automatically selecting and maintaining the D. C. output of the converter at a ?xed polarity. 20 7. In a converter of the character described having a main and an auxiliary commutator and a pair of collector rings connected therewith, a synchronous motor for driving the converter, said motor being supplied with alternating cur rent from the same source as the A. C. to be converted, a third commutator on the converter also supplied with alternating current from the same source, means actuated by the current out- 0 put of the third commutator for automatically cc selecting and maintaining the D. C. output of the converter at a ?xed polarity, and means for of collector rings connected therewith, each of ‘varying the A. C. input to the converter to vary said commutators having a. plurality of conduc~ the D. C. output. tor segments spaced circumferentially with in 8. In a converter of the character described, sulating material and the conductor segments a main and an auxiliary commutator and a pair on the auxiliary commutator being aligned with of collector rings connected therewith, each of the insulating space between the segments on said-cornmutators having a plurality of conduc the main commutator, a pair of brushes for im tor segments spaced circumferentially with in 4 0 pressing alternating current on the segments of sulating material and the conductor segments the main commutator, a pair of brushes engag~ on the auxiliary commutator being aligned with ing the segments on the auxiliary commutator, the insulating space between the segments on a connection between the ?rst-named and sec the main commutator, brushes for impressing al ond-named brushes whereby alternating current ternating current on the segments of the main is passed through the second-named brushes‘ and auxiliary commutators, said brushes being while the insulating spaces between the segments connected, and a material having a high resist~ on the main commutator are passing under the a'nce to the ?ow of a current forming the trail ?rst-named brushes, and a ?xed and a variable ing end of each segment. resistance in the connection between the ?rst 9. In a converter of the character described, a and second-named brushes. ain and an auxiliary commutator and a pair 3. In a converter of the character described collector rings connected therewith, each of having a main and an auxiliary commutator and 5 id commutators having a plurality of conductor a pair of collector rings connected therewith, a segments spaced circumferentially with insulat synchronous motor for driving the converter, ing material and the conductor segments on the 55 said motor being supplied with alternating cur auxiliary commutator being aligned with the in rent from the same source as the A. C. to be con sulating space between the segments on the main verted, a third commutator on the converter also > 50 55 commutator, brushes for impressing alternating supplied with alternating current from the same current on the segments of the main and auxil source, and means actuated by the current out iary commutators, said brushes being connected, 60 a material having a high resistance to the ?ow 60 put of the third commutator for breaking the A. C. supplied to the converter if the synchro nous driving motor gets out of synchronism. 4. In a converter of the character described having a main and an auxiliary commutator and 65 a pair of collector rings connected therewith, a synchronous motor for driving the converter, said motor being supplied with alternating cur rent from the same source as the A. C. to be con verted, a third commutator on the converter also supplied with alternating current from the same source, and means actuated by direct current out 75 40 put of the third commutator for automatically selecting and maintaining the direct current out put of the converter at a ?xed polarity. of a current forming the trailing end of each segment, and a ?xed and a variable resistance in the connection between the brushes. 10. In a converter of the character described having a main and an auxiliary commutator and 65 a pair of collector rings connected therewith, a synchronous motor for driving the converter, said motor being supplied with alternating cur rent from the same source as the alternating 70 current to be converted, a third commutator on the converter also supplied with alternating cur rent from the same source, means actuated by the current output of the third commutator for breaking the alternating current supplied to the 75 6 2,116,899 converter if the synchronous driving motor gets out of synchronism, and means for varying the direct current output of the converter by vary ingjthe alternating current input. 11. In a converter of the character described halving a main and an auxiliary commutator and a pair of collector rings connected therewith, a synchronous motor for driving the converter, said motor being supplied with alternating current 10 from the same source as the alternating current to be converted, a third commutator on the con verter also supplied with alternating current from the same source, means actuated by the current 15 output of the third commutator for automatical ly selecting and maintaining the direct current output of the converter at a ?xed polarity, and means for varying the direct current output of the converter by varying the alternating current input. 20 . 12. In a converter of the character described a main and an auxiliary commutator and a pair of collector rings connected therewith, each of said commutators having a plurality of conductor segments spaced circumferentially with insulat: 7 ing material and the conductor segments on the auxiliary commutator being aligned with the in; sulating spaces between the segments on the main commutator, brushes for impressing alter nating current on the segments of the main and auxiliary commutators, said brushes being con nected, a material haying a high resistance to the flow of a current forming the trailing end of each segment, and a ?xed resistance in the connection between the brushes. " ~ 13. In a converter of the character described a main and an auxiliary commutator and a. pair of collector rings connected therewith, each of said commutators having a plurality of conduc tor segments spaced circumferentially with in 40 sulating material and the ".conductor segments on the auxiliary commutator being aligned with connected, a material having a high resistance to the flow of a current forming the trailing end of each segment, and a variable resistance in the connection between the brushes. 14. In a rotary converter for converting alter nating current to direct current, a synchronous motor for driving the converter in synchronism with the alternating current to be converted, means for automatically breaking the current to the alternating converter if the converter gets out of synchronism, said means including a switch in the alternating current supply circuit of the converter, a commutator driven by the motor and supplying alternating current to the control circuit to open the switch when the con verter is out of synchronism, said commutator supplying direct current when the converter is in synchronism, and a condenser interposed be tween the commutator and the control circuit to render the control circuit inoperative when direct current is supplied thereto. 15. In a rotary converter for converting alter nating current into direct current, a synchro~ nous motor for driving the converter in synchro nism with the alternating current, means for automatically selecting the polarity of the con vcrter’s curr'nt output and for automatically maintaining the cirect current output at the po larity selected, said means comprising a commutator driven by the synchronous motor, said commutator supplying current to a control cir cuit, a switch adapted to be opened or closed by . the control circuit, said switch controlling the alternating current supply to the synchronous motor, and a photoelectric relay in the control circuit, said relay preventing current of a selected polarity from passing through the control cir cuit but passing current of an opposite polarity, said current of opposite polarity actuating the the main commutator, brushes for impressing al control circuit to open the switch to momentarily 40 break the alternating current circuit through the synchronous motor and thereby change the polar ity of the output of the converter to the selected ternating current on the segments of the main polarity. the insulating spaces between the segments on and auxiliary commutators, said brushes being ' JOHN KALSEY.