US1480708A - Balanced phase-converting system - Google Patents

Description

Jan. 15 1-924. 1,480,708 C. LE G. FORTESCUE BALANCED PHASE CONVERTING SYSTEM Original Filed Dec. 13. 1917 4 Sheets-Sheet 1 INVENTOR I 4' WITNESSES. a mq kg/z fzxz/e I #5 7 ATTORNEY Jan. 15 1924. 1,480,708

C.ILE G. FORTESCUE BALANCED PHASE CONVERTING SYSTEM Original Filed Dec. 13. 1917 4 Sheets-Sheet 2 INVEINTOR (Aw/ls 1% frsalz WITNESSES:

' ATT-ORNEY Jan. 15, 192 4. 1,480,708

c. LE G. FQRTESCUE BALANCED PHASE CONVERTING SYSTEM Original Filed Dec. 13. 1917 4 Sheets-$heet 5 WITNESSES: INVENTOR I 4 i Jar/514 (212256212 y v BY Jan. 15, 1924.

C. LE G. 'FORTESCUE BALANCED PHASE CONVERTING SYS'IEII Original Filed Dec. 13. 1917 4 Sheets-Sheet 4 INVENTOR [bar/es lefil'scue Patented Jan. 15, 1924.

UNITED STATES PATENT OFFICE.

CHARLES LE G. FORTESCUE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WEST- INGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENN- SYLVANIA.

BALANCED PHASE-CONVERTING SYSTEM.

Application filed December 13, 1917, Serial No. 206,932.

ToaZZ whom it may concern:

Be it known that I, Crrannns Ln G. Foncrnsoon, a subject of the King of Great Britain, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in. Balanced Phase-Convert ing Systems, of which the following is a specification.

My invention relates to systems of phase conversion, as, for example, between singlephase and polyphase circuits or vice versa, and it has for its object to provide a system of the character designated wherein the polyphase circuits are automatically maintained in substantial balance, irrespective of voltage drops in the converter and associated apparatus.

Other objects of my invention are to provide means whereby a converter of the type above indicated may be maintained in operation under no-load conditions and to provide means for the interchange of magnetizing energy between the phase-converter and the polyphase system.

In the accompanying drawing, Fig. 1 is a diagrammatic view of a phase-converter, together with its associated apparatus embodying a preferred form of my invent-ion; Figs. 2 and 3 are vector diagrams illustrating the operation of the system shown in Fig. 1; Figs. 4, 5, 6, 7 and 9 are views similar to Fig. l and illustrating modified forms of my invention; and Figs. 8 and 10 are vector diagran'is explanatory of the systems of F T and 9, respectively.

It a well known fact that if a polyphase system be energized from a single-phase system through a phase-converter of the dy- 1'ik1II106lO(:t1'l0 type, the effect of the reactive and ohmic drops within the converter is to produce unbalancing of the polyphase electromotive forces. Similarly, when a singlephase circuit is energized from a polyphase circuit through a phase-converter of the dynamo-electric type, the energy for said single-phase circuit is not derived equally from the different phases of the polyphase supply because of the reactive and ohmic drops within the converter and, consequently, the polyphase supply circuit is unbalanced.

An unbalanced set of polyphase vectors may be considered as produced by the superposition of a fixed vector of oscillating mag- Renewed December 30, 1921. Serial No. 526,035.

nitude upon a set of balanced polyphase yectors and said fixed vector may be readily resolved into two oppositely rotating vectors of equal length and of half the max- 1I1111II1 magnitude of said fixed vector, the effect of each of said rotating vectors being produced by a polyphase system.

Thus, an unbalanced polyphase system may be resolved into a balanced major portion having a given phase sequence and into a minor portion con'iprising two oppositely rotating polyphase components or components having opposite phase-sequence. That component of the single-phase unbalancing electromotive force which is rotating in the same direction as said major polyphase component coalesces therewith, leaving the polyphase unbalanced, system resolved into a major balanced polyphase component having one phase-sequence and a. minor polyphase component having the opposite phasesequence, said latter component being produced in phase-converting systems by the ohmic and reactive drop. electromotive forces.

For more rigid proof of this subjectmatter, attention is directed to the appendix of an article by R. E. Gilman and the applicant appearing in the Proceedings of the American Institute of Electrical Engineers for October, 1916, and entitled Single phase power service from central stations.

In the past, attempts have been made to balance the output of phase-converters by eliminating said reversely rotating minor component, as by an auxiliary booster machine. In accordance with the present invention, I attack this problem from a radically dilferent viewpoint and, in effect, reverse the phase sequence of said major polyphase component, thus causing it to rotate in the same direction as the minor polyphase component produced by the ohmic and reactive drops. This effect is produced by coi'nbining with the major polyphase component auxiliary electromotive forces of such magnitude and phase as to produce a resultant system of polyphase electromotive forces of substantially the same magnitude as said component electromotive forces but having the opposite phascsequence in the distributing system. Said resultant polyphase system and the minor 'polyphase component being of like frequency, phase-number and phase sequence, coalesce to produce balanced polyphase resultant electromotive forces having slight phase displacement from the major component, as reversed, but otherwise being substantially unaffected by the minor component.

I am thus enabled to-supply substantially balanced polyphase electromotive forces from a single-phase source or to substantially equally distribute a single-phase load over the different phases of a polyphase system, irrespective of the magnitude of the load and, as my system embodies no relays or auxiliary machines, it is simpler and more effective in its operation than systems proposed in the past and en'ibodying shifting transformer taps and auxiliary booster machines for their operation.

Referring to the accompanying drawing for a more detailed understanding of my invention, ll show a phase-converter at 10 in Fig. 1, said converter embodying stator windings 03, 0-4: and 0 5 and a rotor 11 provided with a short-circuited winding 12 and with a direct-current exciting winch ing 13 for synchronous operation. In order to adjust the power-factor, the directcurrent excitation of the winding 13, derived from a source 14:, may be adjusted by a rheostat 15.

The converter 10 is shown as applied to locomotive service and is thus associated with a transformer 16 and with a propul sion motor 17. The transformer 16 embodies a primary winding 18, a main secondary winding 19 and an auxiliary secondary winding 20. Energy for the operation of the locomotive is derived from a trolley 21, the primary winding 18 being connected between said trolley and ground, indicated at The propulsion motor 17 is shown as our bodying a star-coni'iected stator member 23 and a rotor member 24; provided with a delta-connected winding 25. The speed regulation of the motor 17 may be efli'ected by interconnecting the terminals of the delta winding 25 to an adjustable rheostat 26, said rheostat being reached through suitable slip rings (not shown). The motor 17' is coupled to a vehicle wheel 27, supplying energy thereto during motoring and receiving energy therefrom during recuperative opera tion.

The three-phase windings 0-3, 0-4 and 0-5 of the converter 10 are mutually distinct and the phase-winding 0-3 may be connected between the left-hand terminal 1 of the main secondary winding 19 and a terminal of the motor stator winding 23 by a switch 28. In like manner, the converter phase winding 04 may be connected between the right-hand terminal of the main secondary winding 19 and a terminal of the motor stator winding 23 through a switch 29. The phase winding 05 of the converter 10 may be connected between sub stantially the mid point of the converter winding 19 and the remaining terminal of the motor stator winding 23 through a switch 30. The switches 28 and 29, when moved to their left-hand positions, discon nect the phase windings 03 and O-t from the motor stator winding and interconnect said windings through the auxiliary secondary winding 20 for a purpose to be hereinafter more fully pointed out. lVhile, for clearness and simplicity of illustration, I have shown the switches 28, 29 and 30 of the simple ltnife blade type interconnected for simultaneous operation, as by a rod 31, it will be understood by those skilled in the art that, in actual construction, power-operated switches would probably be employed in place thereof, said power operated switches being controlled by a suitable master controller and either mechanically or electrically interlocked so that connection to the motor stator winding must be broken before connection to the auxiliary secondary winding 20 is completed and vice versa.

Having thus described the arrangement of a system embodying my invention, the operation thereof, during motoring, may be explained as follows.

Upon starting the converter 10 into operation by any suitable means, such, for example, as a starting motor, the converter continues to run as a single-phase motor, deriving single-phase energy from the transformer 16 and supplying polyphase en w ergy to the motor 1'4". The phase-relation of the electromotive forces produced in the respective phase windings of the converter 10 may be indicated by the vectors 0-3,

0-5' and 0't in Fig. 2, said electromo tive forces being substantially balanced and having clockwise phase sequence, constituting the major component of the converter output. The drops within the converter phase windings may be indicated by the polyphase vectors 03, 0 1 and 0-- 5", having the opposite phase sequence from the main vectors because of the fact that, in the motoring phase or phases of the converter, the current is flowing against the generated electromotive force, whereas, in the generator phase or phases, the current is flowing with the generated electromotive force. The back electromotive forces of the respective motor windings are indicated by vectors 0-118, 0114t and O-115.

The effect of connecting the inner ends of the phase windings 0--3 and 0-4 to the outer ends of the winding 19, rather than connecting said inner ends to a neutral point in the converter, is to supply to the motor a system of polyphase resultant electromotive forces similar to the major component of the converter electromotive forces of F 2 but having the opposite phase sequence with respect to the distributing system. In effect, this result is secured by interchanging the location of the vectors ()'3' and .4, as will be noted by reference to Fig. 3. In this figure, the vector 05, denoting the generated electromotive force of. the phase winding 0-5, is shown'located as in Fig. 9. The inner terminal of the phase winding O is connected to substantially the mid point of the winding 19 and thus the electromotive force of the winding 19'may be plotted as a vector 12'. The phase converter is designed for operation at such voltage that the vector 12 is greater than the vector 05 in the ratio of 2J3 to 1. The fact that the inner end of the phase winding 0-3 is connected to the left-hand terminal of the winding 19 demands the construction of the vector 1 3, representing the generated electromotive force of said winding, from the left-hand end of the vector 12, thus locating the point 3' in Fig. 3, denoting the phase of the electromotive force of the point 3 in Fig. 1, at the location of the point 4 in the diagram of Fig. 2. In like manner, the vector 24' in Fig. 3, denoting the electromotive force of the phase winding 0 -4 in Fig. 1, must be constructed from the right-hand terminus of the vector 1.-2', thus locating the point 4. in Fig. 3 at the locus of the point 3 in Fig. 2.

Thus it will be noted that, by virtue of the inclusion of the transformer winding 19 in the circuit in the manner indicated, the phase-locations of the vectors 0-3 and 04', denoting the phases of the electromotive forces at the terminals 3 and 4 of the converten have in effect been interchanged, thus reversing the phase sequence of the major component of the output electromotive forces of the phase converter as applied to the load. The phase sequence of the drops 0-3, 0'4 and 0'5" has been unchanged by the connection and thus, in the system of Fig. 3, the major and minor components of the output electromotive forces of the phase-converter have the same phase sequence and may be combined into the resultant balanced electromotive forces O'3"', 05 and 0'4"', substantiallv equal and opposite to the respective motor back electromotive forces 0113, 0115 and 0-114.

The balanced polyphase electromotive forces thus produced may be applied to the propulsion motor to produce rotation thereof in the desired direction by suitable switching means and serve to operate the motor at maximum efiiciency, as is well understood.

During recuperation, the operation of my system is substantially the same as above doscribed. The effect of the ohmic and reactive drops in the converter 10 would tend to derive unbalanced polyphase electromotive forces from the machine 17 but said electromotive forces are reversed in phase sequence and forced to assume the same sequence as the drops by the system of connections shown and thus the resultant polyphase voltages supplied to the converter 10 by the machine 17 are substantially balanced and an effective recuperative effect may be produced.

7 If it be desired to disconnect the motor 17, the switches 28, 29 and 30 may be simultaneously opened and, immediately thereafter, the winding 20 may be connected between the terminals 3 and 4 of the phaseconverter, through the operation of the rod 31, thus providing a closed circuit through the windings 19 and 20 and the phase windings O3 and 0-4. This circuit serves to maintain the converter in operation, the electromotive force of the winding 20 opposing the winding 19 and thus holding the operating current down to areasonable value, performing the function of a current-limiting resistor without involving an appreciable ohmicloss.

While the system described to this point is effective in producing balanced output electromotive forces, the degree of over or under excitation of the phasaconverter rotor will exert a slight unbalancing effect and this undesired effect may be largely eliminated by permitting the circulation of wattless currents between the motor 17 and the converter 10 without causing said wattless currents to traverse the winding 19. In view of the phase reversal occasioned by the winding 19, however, the wattless currents for a phase of the motor 17 should be derived, not from the phase of the converter to which said motor phase winding is directly connected but from one of the other windings.

Referring to Fig. 4, the principal parts of the converter system are as previously shown. An auxiliary transformer comprises a primary winding 41 connected across the terminals of the. winding 0-3 and a secondary winding 42 connected be tween a neutral point 43 and the right-hand supply main at 44. In like manner, an auxiliary transformer 45 comprises a primary winding 46 in parallel relation to the winding 04 and a secondary winding 47 connected between the neutral point 43 and the left-hand supply main at 48. Likewise, an auxiliary transformer 49 may be employed comprising a primary winding 50 connected in parallel relation to the phase-winding O-5 and a secondary winding 51 connected between the neutral point 43 and the central supply main. By thus inductively coupling the phase-converter and the propulsion motor in proper phase sequence. a path for wattless circulating currents between the two machines is afforded, the effect of said circulating currents being to correct the power-factor in a degree determined by the over-excitation of the phaseconverter.

The system of Fig. 5 is in general, similar to that of Fig. at but the trans'lnrmer 49. together with the connection to the central main is eliminated. The neutral point may be connected to the system eithe r at the point 0, adjacent the winding 19 or at the neutral point 61 of the motor stator winding 23 by the manipulation ofa switch as is dictated by the specific operating conditions. The first connection is employed for power factor correction when the motor is disconnected and the atter is preferable when the motor is in operation. especially under heavy load.

In the system of Fig. (3, a wattless-current operating effect similar to that just described may be produced by suitable inodi tication and manipulation of the converter windings without the use-0t auxiliary transformers. The converter 10 is provided with phase windings 0i:3, (ll and (l-5, as he tore. and, inside the po nts of attachment of the leads to the winding "19. an auxiliary delta-connected converter winding may be provided. Said auxiliary winding provided with adjustable tap points at '71, T2 and 73. and a lead from the winding 0 5; may be connected to any oi the taps at 72. substantially in phase with the winding 0- 1. in lilte manner. a had "rem the winding i may be connected o any one of the taps '71, substantially in phase with the winding O 3. A lead from the winding 05 may be connected to any one of the taps at 73. By suit-able manipulation of the taps ll, 72 and 73 the phase and i'nagnitude oi? the circulating currei'its interchanged between the two machines may be modified and thus suitable power-factor rorrection may be obtained without voltage unbalance. l ly the crossing of the leads from the windings 0-3 and ()s.- to the winding To. the desired con'ipensation for the phase reversal occasioned by the specific connection ot" the winding it) is obtained.

The systems described to this point have embodied three-phase operation but the pr nciples oi my invention are equally appliable to systems embodying any desired phase number, either star or delta connected. Thus, in Fig. 'l' l illustn a four phase system embodying aquarter-phase converter 75 connected to a quartenphase motor 76. The converter 75 embodies primary windings 77 and 78, a secondary winding 7!) and a. tertia-y winding 80. The motor 76 en'ibodies primary windings 81 to 84, inclusive. Energy is supplied to the system through a. transformer 16, the secondary winding 19 01 said transformer being inserted between the inner terminals ot the converter windings (7 and 78..

Vectorially, the operation of the system thus described is similar to that of the systems of the earlier figures. Referring to l 8, the generated electromotive forces of the converter windings 7T, 78 and "50 may be indicated by vectors 77, 78 and 80, respec'tively assuming the converter '75 to be interconnected. The fact, however, that the windings 77 and 78 are connected together only through the supply winding 19 pro duces a reversal of the phases of the vectors 7'? and 78, as follows. The electromotive force of the winding lDinay be plotted as the vector 19" and thus the vector 78'' moved bodily to the position and the vector '77 is moved bodily to the position 77. As a result the electroinotire tone applied to the motor winding 82 is substantially that indicated by the vector 78', and the electroinotive iorce supplied to "the motor winding 8% is substantially that in dicated by the vector 77. The vector 80 being unaffected, the phase sequence of the generated electromotive forces of the converter 75 is reversed by the winding 19 due to the virtual interchange of the vectors and it", and thus the desired coincidence in phase sequence between the generated and drop @lGCtl'O-i1'l()tiV6 forces of the converter is secured.

Referring to Figs. 9 and it). a sin-phase system is illustrated. it converter 83 embodies 1 t try winding haviii"; two portions 86 and ST. 'ii aid converter lurthcr embodies a. primary winding having a. phase portion 88 spaced sul stantially 1.20 trom winding and enibodyii'ig distinct the ti ary portions 69 and 90 and an additional primary winding ill likewise spaced 120 from the tort y winding and en'ibodying distinct portions 92 and The outer tcrminals ot the ditterent converter windings 8S, 8?. 89, $70. 92 and 9 1 are connected respectively to tl -t(lll'll'il2illof the phase windings 96, T, l. l 10:], W23, respectively. ot a sitaph: e loud device such. for example. a motor or. 'lhe remainin 'i rcc tern'iinals oi" the conrerter winding; 1 SH) and 9:3 are in'terconnccted and jointl at chcd to the lower terminal of the tr ormcr supply winding 19 and, similarly. inc freiterminals oi? the windings 93 and 89 are intercomiected and jointly attached to the up r terminal of the winding 19. The mid point oi 'he converter tertiary winding is connected to substantially the mid point of the winding 15).

The resultant vector relations are shown in Fig. 1.0 and are substantially a duplication of those shown in Fig. 3. The coin erated tertiary electromotivo :lorces may be indicated by vectors 86 and 87'. respectively, in quadrature to a vector 19, iniilicating the rlcctroniotive force of the supply winding 19. Neglecting the displacing effect of said winding 1.9, the electromotive "forces of the supply. windings 89, 90, 92 and 93 may be indicated. respectively, by vectors 89. 90, 92 and 93. These last named vectors. however, must be plotted from the ends of the vector 19, because of the specific connection eniploycd, and thus said vectors are in reality located as indicated at 89". 90", 92 and 93, respectively. Thus, in effect, the positions of the vectors 89 and 93 and of the vectors 92 and 90 are inter-changer and the direction of phase rotation of the output electroinotivr-i forces of the converter is reversed without correspondingly affecting the drop electromotive forces, as is desired for balancing purposes.

It will be noted that the transformer secondary winding 19, having terminal connections and a mid-tap connection, is merely one specific case representing an extreme condition of an unbalanced three-phase system, since said winding provides three circuits or phases having dissymmetrical electromotive forces, which, when vectorially added, are capable of forming a closed poly gon of forces. It will be noted, also, that an unbalanced polyphase system of electromotive forces may be resolved into two balanced systems, one having the forward sequence of phases and the other the backward phase-sequence.

When the apparatus is viewed in this light it becomes evident that the series machine 10 is rotating in synchronism with one of said balanced component systems which we may call the backward phase-sequence system, thereby developing what may be termed a synchronous impedance against the backwardly rotating component electromotive forces. The forwardly rotating system of balanced electromotive forces produces, in the backwardly rotating rotor of the series machine, double-frequency electromotive forces. and the resultant double-frequency currents circulating in the low-impedance damper windings 12 serve to neutralize the impedance of the primary windng to currents of the forward phasesequence. In this manner, the phase-balancing function of the series machine is accomplishcd.

\Vhile I have shown my invention in a plurality of forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various minor changes and modifications without departing from the spirit thereof and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or indicated in the appended claims.

I claim as my invention:

1. The combination with a source of alternating electromotive forces providing two sets of polyphase electromotive forces of like phase-number but of opposite phasesequence, of means for, in effect, reversing the phase sequence of one of said sets with respect to the other, means providing an electric circuit, and means for supplying said reversed polyphase electromotive forces, together with the unchanged polyphase electromotive forces, to said circuit.

2. The combination. with a source of alternating electromotive forces providing two sets of substantially balanced polyphase electromotive forces of like phase-number but of opposite phase-sequence, of means for, in effect, reversing the phase-sequence of one of said sets with respect to the other, means providing an electric circuit, and means for supplying said reversed polyphase electromotive forces, together with the unchanged polyphase electromotive forces, to said circuit, whereby a substantially balanced resultant electromotive force is supplied thereto.

3. The combination with a polyphase dynamo-electric machine wherein the electromotive force drops in the different phase windings have the opposite phase sequence from the electromotive forces of said windings, of means for, in effect, reversing the phase sequence of one of said sets of electromotive forces relative to the other.

4. The combination with a polyphase dynamo-electric machine wherein the electromotive force drops in the different phasewindings embody the opposite phase-sequence from the electromotive forces of the respective windings, of means for, in effect. reversing the direction of phase sequence of said last-named winding electromotive forces without affecting the phase-sequence of said drops.

5. The combination with a polyphase dynamo-electric machine wherein certain of the phase-windings function as motor windlugs and certain other phase-windings funetion as generator windings, whereby the electromotive force drops in said windings have the opposite phasesequence from the electromotive forces of said windings, of means for, in effect, reversing the phase-- sequence of said last-named winding electromotive forces.

6. The combination with a phase-converter of the dynamo-electric type, of means for, in effect. reversing the phase-sequence of the generated electromotive forces thereof without reversing the phase-sequence of the electromotive force drops in the windings thereof.

7. In a system of distribution, the combination with a single-phase winding, of a polyphase winding, a polyphase phase-converter, connections from certain terminals of said polyphase winding through phase windings of said converter to the terminals of said single-phase winding, and other connections from the remaining polyphasc terminals through the remaining phase-corp verter windings to intermediate points in said single-phase winding, said connectiors being so arranged that the electroinotivc force of said single-phase winding produces the result of, reversing the phase-sequence of: the output electromotive forces of said phase-converter without reversing the phase-sequence of the drops therein.

8. In a system of distribution, the combination with a single-phase winding, of a three-phase winding, a three-phase, phase converter having distinct phase-windinga connections from two terminals of said three-phase windings through two windings of said phase-converter to the terminals of said single-phase winding, respectively, and a connection from the remaining terminal of said three-phase winding through the remaining converter winding to an intermediate point in said singlephase winding, the direction of connection and the electromotive torce of said sin le-phase winding being such that said electromotive force produces the elfect of reversing the phase sequence of the electromotive forces 01'? said converter without reversing the phase-scquence of the electroinotive force drops in the converter winding.

9. The combination with a phase-converter having non-intercomiected windings, of a load circuit adapted to close an operating circuit through said converter, and means for providing an auxiliary operating circuit to maintain. said converter in operation when said load circuit is open.

10. The combination with a transformer having a primary winding connected to a source of alternating current and having main and auxiliary secondary windings, ot a phase-converter having independent windings connected to said main secondary winding, a load circuit connected to close an operating circuit through said converter, and means whereby, it said loadcircuit is disconnected, said auxiliary secondary winding is connected to close an operating circuit through said converter, whereby said converter is maintained in operation.

11. In a system of distribution, the combination with a single-phase winding, of a polyphase winding, a polyphase, phase converter, connections tlroin cc main tei minals of said polyphase winding through phase-windings of said converter to the terminals of said single-phase winding, other connections from the remaining poly phase terminals through the remaining phase-converter windings to intermediate points in said singlephase winding, said connections being so arranged that the elec tromotive force of said singlephase windproduces the effect of reversing the phase-sequence oi the output electromotire forces of said phase-converter without rcversing the phase-sequence of the drops IAEOJOS therein, and additional means for inter" changing energy directly between said pol v phase winding and the windings of sai phase-converter.

12. in a system of oistrilniticn, the combination with singlephase winding, of a polyphase winding, a polyphase phase-coir verter, connections from certain terminals of said polyphase winding through phasewindings of said converter to the ten niinals of said single-phase winding, other connections from the remaining polvphase terminals to intermediate points in said single-phase winding, said connections being so arranged that the electromotive force of said single-phase winding produces the cli ect of reversing the phase-sequence ot the output electromotive forces of said phaseconverter without reversing the phase-sequence of the drops therein, means for inter changing energy directly with certain of the windings of said converter, respectively, and means for connecting said means to said polyphase winding in the phase sequence of said converter windings, whereby wattless currents may flow between said converter and said polyphase winding for powerfactor control.

13. In a system of distribution, the combination with a single-phase winding. of a three-phase winding, a three-phase, phaseconverter having distinct phase windings. connections from two terminals of said three-phase winding through two windings of said phase-winding, respectively, to the terminals of said single-phase *inding, a connection from the remaining terminal ot said three-phase winding through the re maining converter winding; to an intermediate point in said single-phase winding, the direction of connection and the electromotive force of said single-phase winding being such that said electromotive force produces the effect of rcversin the phase-sequence ot the electr nnotive tin-cos ot said converter without reversing the phase-sequence of the electron'iotive force drops in the converter winding, and means for interchanging energy between each converter phasewinding connected to a single-phase tern'iinal and the phase of said three-phase winding connected to the other single-phase terminal, whereby wattiess-energy interchange may take place between said converter and said polyphasc winding,

l t. The method of balancing an unbal unced polyphase system comprising a major balanced polyphase component having phasesequence in a given direction and a minor balanced polyphase component having the opposite phase-sequence, which coinprises, in edecnreversi g the phase-sequence of said major component without reversing the phasesequence ot said minor component, whereby said. two components are caused. to

have the same phase-sequence and coalesce to produce a single substantially balanced polyphase resultant.

15. The method of balancing the output electromotive forces of a phase-converter wherein the winding electron'iotive forces have one phase-sequence and the drop elec tromotive forces have the other phase sequence which comprises, in effect, reversing the phase-sequence of said winding electromotive forces without affecting the phasesequence of said drop electromotive forces.

16. An electrical system including, in combination, a three-phase translating device, two single-phase translating devices, said singlephase devices developing electromotive forces of the same frequency, a threephase dynamo-electric machine having a damper winding, and connections for connecting said three-phase machine in series circuit relation between said three-phase translating device and said single phase translating devices, said connections being made in such manner that said single-phase electromotive forces are in the proper directions for combining with the: three-phase electromotive forces of said machine to produce a resultant three-phase electromotive force having the opposite phase-sequence.

17. An electrical system including, in com bination, a three-phase translating device, a single-phase transformer including two winding elements, a three-phase dynamoelectric machine having a damper winding, and connections for connecting said threephase machine in series-circuit relation between said three-phase translating device and said single-phase winding elements, said connections being made in such manner that the single-phase electromotive forces are in the proper directions for combining with the three-phase electromotive forces of said machine to produce a resultant threephase electromotive force having the opposite phase-sequence.

18. An electrical system including, in combination, a three-phase translating device, a single-phase transformer winding provided with three taps dividing the same into two winding elements, a dynan'io-electric machine having non-interconnected threephase primary windings and a damper winding, and connections for connecting the three primary windings severally in seriescircuit relation between the respective transformer taps and the three-phase translating device.

19. The combination with a line having two sets of polyphase electron'iotive forces 1 like phase-number but of opposite phasesequence, of a. polyphase translating device having substantially balanced currents, a dynamo-electric machine having polyphase primary windings and damper wlndings, and means for associating said primary windings in series relation to said line and. said translating devlce, said prnnary and 1 damper windings having a relative rotation at substantially synchronous speed in such direction that the electromotive forces gen erated in said primary windings are opposite in phase sequence to the electron'iotive forces of said translating device.

20. The combination with a line having two sets of polyphase electromotive forces of like phase-number but of opposite phasesequence, of a polyphase translating device having substantially balanced currents, a dynamo-electric machine having polyphase primary windings and damper windings, means for associating said primary windings in series relation to said line and said translating device, said primary and damper windings having a relative rotation at substantially synchronous speed in such direction that the electromotive forces generated in said primary windings are opposite in phase sequence to the electromotive forces of said translating device, and means for supplying said machine with a variable direct-current excitation.

21. The combination with a line having two sets of polyphase electromotive forces of like phase-number but of opposite phasesequence, of a polyphase translating device having substantially balanced currents, a dynamo-electric machine having polyphase primary windings and damper windings, means for associating said primary windings in series relation to said line and said translating device, said primary and damper windings having a relative rotation at substantially synchronous speed in such direction that the electromotive forces generated in said primary windings are opposite in phase sequence to the electromotive forces of said translating device, and means for disconnecting said translating device and operating said machine with a shunt connection across said line.

22. The combination with a line having two sets of polyphase electromotive forces of like phase-number but of opposite phasesequence, of a polyphase translating device having substantially balanced currents, a dynamo-electric machine having polyphase primary windings and damper windings, means for associating said primary windings in series relation to said line and said translating device, said primary and damper windings having a relative rotation at substantially synchronous speed in such direction that the electromotive forces generated in said primary windings are opposite in phase sequence to the electromotive forces of said translating device, and switching means for disconnecting said translating device and providing a closed circuit for at least two of the phases of said polyphase primary winding.

IOU

123. The combination with a 'line liaVing two sets of polyphase 'electromotive forces o'fllike phase-number but of-opposite-phasesequence, of a polyphasetranslating device having substantially balanced currents, a dynarnoelectric machine having polypliase primary windings and damper windings,

means for associating said ipriinary windings in series relation-to said lineandsaid translating device, saidpriinary and damper windings having a relative rotation :at'subl1 ,esogzos stantially synchronous speed in such direc- 'phase sequence to the electroinoti've forces of said translating device, and means for maintaining the rotation of said machine when said-translating device is disconnected.

In testimony whereof, 1havehereuntosubscribed my name this 28th day of Nov., 1917.

CHAR-LES LE G. FORTESC-UE.

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