US1396839A - High-voltage direct-current system - Google Patents

Description

- R. E. HELLMUND. HIGH VOLTAGE DIRECT CURRENT SYSTEM.

APPLICATION FILED SEPT. 10. 19H.

1,396,839. Patented Nov. 15, 1921.

3 SHEETS-SHEET I.

MTNEs'sEsG) i I? d/ IZYE/NfTC/J; d I 010/ a man 2 4 W m ATTORNEY R. E. HELLMUND.

HIGH VOLTAGE DIRECT CURRENT SYSTEM.

APPLICATION FILED SEPT- 10, 1911.

1,396,839. Emma Nov. 15, 1921.

3 SHEETS-SHEET 2.

WITNESSES: 7 I INVENTOR 71.4,; 4Q fiw/fn/ /mm M ATTORNEY R. E. HELLMUND.

HIGH VOLTAGE DIRECT CURRENT SYSTEM.

APPLICATION FILED SEPT-10. 1917.

9 39 Patented Nov. 15, 1921.

3 SHEETS-SHEET INVENTOR WITNESSES:

BY M U ATTORNEY RUDOLF E. HELLMUND, OF SVJ'ISSVALE, PENNSYLVANIA, ASSIGNOR TO \VESTING- HOUSE ELECTRIC SYLVAN IA.

& MANUFACTURING COMPANY, A CORPORATION OF PENN- HIGH-VOLTAGE DIRECT-CURRENT SYSTEM.

Specification of Letters Patent.

Patented Nov. 15, 1921.

Application filed September 10, 1917. Serial No. 190,503.

To all whom it may concern:

Be it known that I, RUDoLr E. HELLMUND, a citizen of the German Empire, and a resident of Swissvale, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in High-Voltage Direct-Current Systems, of which the following is a specification.

My invention relates to high-voltage, direct-current systems, and particularly to the inherent overload protection of powerstation or substation generators for supplying voltage to the operating circuits of a hi h-voltage railway system.

Tn the operation of high-voltage, directcurrent railway systems; for example, 3000- volt systems, considerable difiiculty has been encountered in preventing station generators from flashing over, in the event of short circuits upon the railway system. well known, the circuit breakers commercia-lly available, although operating to open a circuit in a very small fraction of time, nevertheless permit the short-circuit current to instantaneously rise to a dangerous value. Consequently, further protection, preferably of an inherent character, is desirable, if not necessary, for satisfactory operation of the station generators.

The object of my present invention, therefore, is to provide a relatively simple system of the above-indicated character, whereby the instantaneous rise of short-circuit current is sufficiently delayed by the inherent characteristics of the generator system to permit the circuit-breaker to open the generator circuit before dangerously high currents are attained. 1

My invention may best be understood by reference to the accompanying drawings, wherein Figure 1 is a diagrammatic view of the component elements, namely, station generating apparatus and railway rolling stock, of a high-voltage direct-current railway system embodying the invention; Fig. 2 is a diagrammatic view of a modified form of generator system constructed and arranged in'accordance with the invention; Fig. 3 is a sequence chart of well-known form, indicating the preferred order of operation of the switches that are shown in Fig. 2; Fig. 4 and Fig. 5, Fig. 6 and Fig. 7, Fig. 8 and Fig. 9, are views, respectively corre- As is sponding to Fig. 2 and Fig. 3, of further modifications of my invention.

eferring to Fig. l of the drawings, the system shown comprises supply-circuit conductors Trolley and Ground; a power-sta- C1011. or substation direct-current generator having an armature A and an exciting field winding F; a driving induction motor M for the direct-current generator; an auxiliary exciter 5 that is also driven by the motor M a transformer 6 that is associated with the various machine circuits in a manner to be set forth; a variable resistor 7 for adjusting the exciting circuits, and a railway vehicle 8 that operates in the customary manner, receiving energy from the trolley and returnmg it through the rails to ground.

It will be understood that, in lieu of the driving induction motor M, any suitable type of prime mover, such as a steam turbine or a gasolene-engine, may be employed, if desired.

The exciter 5 comprises a commutaton type armature 15, which is mounted upon the operating shaft 16 of the main motor generator set, and a series-related field windlng 17.

The transformer 6 comprises a winding 18 having a relatively large number of turns and a second winding 19 having a smaller number of turns, both of the windings being disposed, in any suitable manner, upon a common core member 20.

s is customary station practice, a suitable circuit-breaker is connected in series relation with the main generator armature A to interrupt the generator circuit under overload conditions. Since the particular type of circuit-breaker that is employed is immaterial to my present invention, I have not deemed it necessary to illustrate any circuit-breaker in detail, but have merely shown the trip-coil and contact members, which are labeled Circuit breaker.

Under normal operating conditions, the main generator current, indicated by the solid arrows, is established from the ground through transformer winding 19, main armature A and the circuit-breaker trip-coil and contact members to the trolley. The auxili ary exciting circuit, indicated by the dotted arrows, is established from the positive terminal of the eXciter armature 15 through increased voltage drop obtains across thewinding 19.

- ing predominates, and,

armature current in the opposite direction to the current through the other transformer relatively large number of turns, this'windunder normal operating conditions, the transformer core 20 is highly saturated, so that slight changes of generator current or slight voltage fluctuations produce a substantially negligible effect in the transformer 6. The few-turn transformer winding 19, furthermore, inherently operates to generated for the following reasons. Upon an incipient rise of such current, a correspondingly transformer winding 19, since both the main current and the exciting current-traverse the winding in the same direction. Consequently,'a decreased voltage is available for delivery to the main field winding F from the exciter armature 15, whereby'the mainarmature current is inherently caused to subside to its average value. 'The converse action takes place in the event of an incipient decrease of generated current, as will be understood. r

In addition, under short-circuit conditions uponthe railway system, or other conditions involving a. dangerously'heavy surge of generator current, the transformer 6 1nherently acts to delay the rise of short-circuit current until the station cicuit-breaker can open the generator circuit and thus eliminate the short-circuitconditions. i

The additional inherent transformer action just mentioned may be explained as follows: upon the incipient rise of shortcircuit current, the total transformer flux is materially diminished by reason of the traversal of the. main-generator current through the transformer winding 19 differentially to the current in the normally predominating many-turn winding 18, and a certain opposing vo tage is induced, under such abnormal conditions, across the manyturn transformer winding 18. In this way,"

by reason of the inherenttendency of the winding 19 to maintain its former energization, a material value of current is drawn from the auxiliary field winding 17 into the transformer winding 18, thus reducing the excitation of the main Since the winding 18 has a" maintain a substantially constant current lIl the'main armature A,

voltage; of the exciter and, therefore, the correspondingly decrease the voltage of the main armature A. By reason of the nherent actionjust rec1ted, therefore, the rise of short-circuit current is sufficiently retarded to permit thecircuit-brealrer to open the generator circuit before dangerously high currents are reached.

The normal starting operation of the illustrated motor-generator set requires but a brief description; The induction motor M may be started in any familiar manner to.

dr1ve the main armature Aand the exciter armature 15,'the voltage of which rapidly builds up by reason of theillustrated closedcircuit connections through the field-winding 17. The voltage of the main armature A may be varied by the station operator in any suitable manner; for example, by manipulating the illustrated resistor 7.

Referring'now to Fig. 2, the system shown comprises the supply-circuit conductors trolley and ground; the driving induction motor M and the main station generator with its related circuit breaker, as illustrated in 1; and, in addition, a motor-generator set 25 for exciting purposes; an auxiliary source of energy, such as a battery B; a plurality and R-2, for purposes field winding F to of variable resistors 3,111

to'be set forth; and;

a plurality of electrically controlled switches 1, 2, 3 and et.

The motor-generator set driving or motor coupled-b V 25 comprises a armature 27, WillCll' is means of a shaft 28, for example,

to a generator'or exciting armature 29. V A' series-related field winding: 30; a shuntfield winding 31, which may be varied through the agency of the resistor R2,; and a commutating and neutralizing. field winding 32 are provided for the auxiliary driving armature27, while the generator armature29 has an exciting field winding 33 that is energized in accordance with the load of the motor-generator set, and a commutatingfield windingBi, Under normal operating conditions, the energization of the auxiliary field winding 33 in Fig. 2;-Fig. h Fig. 6" and Fig. 8'is sufiiciently great tohighly saturate the corresponding magnetic circuit (not shown). Consequently, ordinary current or voltage fluctuations have practically no effect upon the flux corresponding to the field winding 33, which is thusioperative for current-limiting purposes only under abnormal overload conditions, as hereinafter fully set forth.

The main generator armature A is connected, through. the circuit-breaker, across the supply circuit, while the auxiliary generator armature 29.is connected, throughthe switch 3 and variableresistor R, across the main field winding F. 'As previously stated, the field winding 33 for the auxiliary generinherent regulation.

of the main armature ator armature'is connected in series relation with the auxiliary-motor circuits, connection being completed to the respective supplycircuit conductors Trolley and Ground, through switch 1 and variable resistor R1.

Assuming that the induction motor M is driving the main generator at normal speed, and that it is desired to supply voltage to the trolley circuit, the switches 2 and 4 are first closed, as indicated in step a of the sequence chart, Fig. 3, to connect the 'battery B through the variable resistor R across the main-field winding F, and to initially short-circuit the auxiliary field winding 30. By suitably adjusting the re sistor R, the voltage of the main armature A may be increased to the desired operating value.

Switch 1 may then be closed to start the motor-generator set, after the supply-circuit voltage has thus been established, and, by suitable regulation of the resistors R1 and R2 and by auxiliary field winding 30 in circuit, the voltage of the auxiliar generator armature 29 may be increased to a value equivalent to quent energization of the main generator from the motor-generator set alone.

Assuming short-circuit conditions in the railway system after the generator system is normally operating, the voltage of the main generator A instantaneously decreases materially, in accordance with familiar principles, whereby the simultaneous voltage of the auxiliary driving armature 27 is instantaneously held 'at a value greater than that of the supply-circuit voltage, which causes a rapid reduction of the current in that armature and in the series-related field winding 33 for the auxiliary generator armature, by reason of the materially different-from-normal relation of the supplycircuit voltage and the counter-electromotive force of the auxiliary driving armature. The action just recited is aidedby the damping eifect of the shunt field winding 31 for the auxiliary driving motor. Since the speed of the armature 27' is only slightly affected by changes of supply-circuit voltage, by reason of such shunt excitation,

under the short-circuit conditions in question and the consequent instantaneous drop of supplycircuit voltage, the damping effect of the shunt field winding 31 tends to maintain a relatively high counter-electromotive force in the armature 27 to effect the desired The voltage of the auxiliary generator armature 29 is thus quickly diminished to correspondingly reduce the excitation of the main-field winding F. In this way, the generator voltage A is further decreased to retard the rise of short-circuit current and permit the circuit-breaker to open the generator circuit before dangerous current conditions have been attained.

eference may now be had to Fig. 4, wherein the system shown comprises supplycircuit conductors and a main motor-generator set similar to those illustrated in Fig. 3, and, in addition, an auxiliary motor-generator set 40, a battery B1 for exciting one of the field windings thereof, variable resistors R and R1, and an inductive device 41.

The auxiliary motor-generator set is driven by, or mechanically coupled to, the main set in any suitable manner, a belt drive 42 being indicated for the sake of simplicity and clearness. Under operating conditions, however, the auxiliary set functions electrically in a manner similar to a mechanically independent set.

Electrically, the motongenerator set 40, in general, is similar to the previouslydescribed set 25, the chief difference residing in the connection of the battery B1 through the switch 1, across the field winding 33 for the auxiliary generating armature 29, which ield winding is normally energized in ac cordance with the load-current of the motorgenerator set 40. Furthermore, a shunt-field winding 44- for the auxiliary driving armature 27 is connected through switch 3, to one terminal of the commutating field winding 32 and through variable resistor R1, switch 2, and variable resistor R, to the lower terminal of the auxiliary motor armature. 7

By reason of connecting the battery B1 across the auxiliary field winding 33, a materially smaller-capacity battery may be utilized than is necessary in the system shown in Fig. 2, wherein the storage battery is employed to energize the main-field winding F.

The inductive device l-l may be of any well-known type and is employed for the customary purpose of limiting or choking down sudden variations of current in the circuits wherein it is connected. lVhen traversed by both the main-armature current and the exciting current, a double currentlimiting function is performed by the inductive device, which also acts, in a similar manner to the transformer winding 19 of Fig. 1, to inherently prevent current changes. 7

In the present case, the main-armature circuit, indicated by the solid arrows, is established from the ground through the inductive device 41, the main armature A and the circuit-breaker to the trolley.

The exciting or main-field winding circuit, indicated by the dotted arrows, is established from the positive terminal of the generator armature 29, through the inductive device 41, main-field winding F and commutating field winding 3 1, to the negative terminal of the generator armature 29. As indicated in the sequence chart, Fig. 5, switch 1 is initially closed after the two motor-generator sets are operating at normal-speed conditions, whereby the voltage .of the auxiliary generator arn'iature 29 is quickly built up to the desired value in accordance with the adjustment of the resistor R. V

The second step of the control involves the closure of switch 3 toinclude the field windingdl for the auxiliary driving armature 27 in circuit. v

As soon as the exciting system conditions have become stable, the switch 2 maybe closed and the switch 1 may be opened, as indicated in the sequence chart, to connect the motor armature 27 in circuit and to disconnect the battery B1 to effect the normal excitation of the main generator from the auxiliary motor-generator set alone.

The inherent operation of. the illustrated system to retard the rise of short-circuit current issubstantially identical with the op ration set forth in connection with Fig.

2, by reason of the connection of the field winding 33 for the auxiliary generator armature 29 in series relation with the aux iliary motor armature 27. Consequently, no further exposition-of deemed necessary. v V 7 The system of Fig. odiffers from that shown in Fig. .1; chiefly in th entire omission of storage batteries, and also in the connection of a shunt field winding 46 for the auxiliary driving variable resistor R2 across that armature and another variable resistor R1, and in the connection of the variable resistor B through.

switch 1 across the entire auxiliary generating machine, comprising armature 29 and field windings 34: and 83.

By reference to the sequence chart, Fig. 7, itwill be seen running, whereby the voltage of the auxiliary generator armature 29 rapidly builds up by reason ofthe local exciting circuit including switch 1, variable resistor Rand field windings 33- and 3a. 7 1

In the second step of the control, switch 3 is closed to energize thev main-field winding F. As soon as stable excitation conditions obtain in the system, switch '2 may be next closed and switch l'may be opened, as indicated in step 0 of the sequence chart, to permit the full auxiliary-motor current to traverse the field winding 33 for the gen-.

erator armature 29; further regulation, if necessary, being accomplished by suitable manipulation of the resistors R1 and R2.

. Inasmuch as the inherent action of the exciter system, toprevent a dangerous rise .of overload;ma n generator current,.is similar to that set such inherent action is '9, sw tch 4 1s closed, afterthe ma n motorarmature 27, through a that switch 1 is initially closed after the motor-generator sets are switch 1 may be'closed forth in connection with Fig. 2, no further description of such operation is considered necessary.

lnFig. 8, the shaft 16 of the main motorgenerator set carries, in addition to the driving induction-motor rotor generator armature A, an auxiliary machine 50, which is employed for starting purposes, to be set forth. 7 l v 'An auxiliary motor-generator set 51, comprising.- armatures 27 and 29 andfield windings 33: and 4A, is utilized for separately exciting the main-field winding F, variable resistors R1 and R2 being connected in series circuit relation with the auxiliary field windings 33 andll, respectively. i

.The auxiliary machine 50 comprises a commutator-type armature 55, which is driven by the induction motor M, andja field winding, 56, which is connected throughswitch 4 and variable resistor R- across the supply circuit. The induction device 41 and a fxed-resistjor 52 are connected in seriescircuit relation with the auxiliary farmature .55, which may likewise beconnectedto the'supply-circuit conductor Trolley by switch 4;, theprovision of such impedance devices effectively preventing dangerous current conditions in the auxiliary armature 55, at any time. H

As indicated in-the sequence chart, Fig.

field winding 1 maybe increased to any deto establish a supsired value by adjusting the resistors R1 HHCl RQ. 7 I i r l,

After stable excitation conditions obtain, to connect the main through the circuit breaker,to the a supply circuit, and, if desired, switch l may then be'opened to allow the auxiliary machine 50 to run, idle, or the machine 50 maybe utilized to supply a portion of the Zne'cessaryenergy tothe highe generator armature A,

volta e railway s stem.

. As hereinbefore mentioned, the auxiliary machine 50 isprotected against short-circuit conditions, through the agency of the impedance devices {l1 and 52, while dangerous increases of main generator current are again prevented through the previouslydescribed inherent action of the field winding 33 for the auxiliary generator armature .29, which field windingis connected in series relation with the auxiliary driving motor. V I do not wish to be restricted tot-he speand the maincific circuit connections or arrangement of parts herein set forth, as various further modifications thereof may be effected without departing from the spirit and scope of my invention. I desire, such limitations shall be dicated in therefore, that only imposed as are inthe appended claims.

I claim as my invention:

1. In a system of distribution, the combination with a direct-current generator, of an auxiliary exciting system therefor, an inductive means in said system for inherently counteracting overload generator currents of large amplitude to a greater extent than upon smaller load increments.

2. In a system of distribution, the combination with a direct-current generator, of an auxiliary exciting system therefor, and inductive means inherently active only under predetermined abnormal conditions for retarding the rise of enerator current.

3. In a system of istribution, the combination with a main direct-current generator, of an auxiliary generator for exciting the main generator, and means dependent upon the inherent action of the auxiliary generator circuits for retarding the rise of main-generator current under predetermined abnormal overload condition only.

4. In a system of distribution, the combination with a main direct-current generator, of an auxiliary generator for exciting the main generator, and a motor for driving said auxiliary generator, said auxiliary generator having a field winding energized in accordance with the load current of said motor to normally produce magnetic saturation conditions.

In a system of distribution, the combination with a mam direct-current generator, of an auxiliary generator for exciting the main generator, a motor for driving said auxiliary generator, said auxiliary generator having a field winding energized in current of said magnetic saturaior initially enerfield winding.

accordance with the load motor to normally produce tion conditions, and means gizing the main generator In a system of distribution, the combination with a main direct-current generator, of an auxiliary generator for exciting the main generator. a motor for driving said auxiliary generator, said auxiliary generator having a field winding energized in accordance with the load current of said motor to normally produce magnetic saturation conditions, and means for initially energizing said auxiliary generator field winding.

7. In a system of distribution, the combination with a main direct-current gen-erator, of an auxiliary generator for exciting the main generator, a motor for driving said auxiliary generator, said auxiliary generator having a field winding energized in accordance with the load current of said motor to normally produce magnetic-saturation conditions, and means for initially closing an auxiliary exciting circuit around said auxiliary generator.

8. In a system of distribution, the combination with a load circuit, of a main directcurrent generator, an auxiliary direct-current generator, and a driving motor for said auxiliary generator, the field winding of said main generator being energized by said auxiliary generator, the field winding of said auxiliary generator being energized from said load circuit in series circuit with said driving motor, and said series circuit be ing so designed that the magnetic flux of said auxiliary generator is only slightly affected by slight voltage fluctuations of said load circuit but is materially decreased by an abnormal voltage drop in said load circuit.

In testimony whereof, I have hereunto subscribed my name this 30th day of August, 1917.

RUDOLF E. I-IELLMUN D.

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