US1163268A

US1163268A - Means and method for varying the voltage of alternating currents.

Info

Publication number: US1163268A
Authority: US
Inventors: Elmer H Schwarz
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1911-04-06
Filing date: 1911-04-06
Publication date: 1915-12-07
Anticipated expiration: 1932-12-07

Description

E. H. SCHWARZ. MEANS AND METHOD FOR VARYING THE VOLTAGE 0F ALTERNATING CURBENTS.

APPLICATION FILED APR. 5. I911.

Patented Dec. 7, 1915.

3 SHEETS-SHEET 1 Witnesses: Inventor 4 0 Elmer- H.5chwarz,

I M @W His Attorng E. H. SCHWARZ.

MEANS AND METHOD FOR VAHYING THE VOLTAGE 0F A'LTERNATING CURRENT APPLICATION FILED APR. s. 1911.

1,163,268. Patented Dec. 7, 1915.

3 SHEETS-SHEET 2- Fig.6. r

Inventor: Elmer H.5chwarz,

His fitter-neg,

E. H. SCHWARZ. MEANS AND METHOD FOR VARYING THE VOLTAGE 0F ALTERNATING CURRENTS.

APPLICATION FILED APR. s. 19H.

Patented Dec. 7, 1915.

3 SHEETSSHEET 3 Fi .H.

Witnesses:

zw w r m mm 0 n & e A VH xb .mr H 6 UNITED STATES PATENT OFFICE.

ELMER H. SCHWARZ, OF NEXV YORK, N. Y., ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MEANS AND METHOD FOR VARYING THE VOLTAGE OF ALTERNATING- CURRENTS.

Specification of Letters Patent.

Patented Dec. '7, 1915.

Application filed April 6, 1911. Serial No. 619,211.

7tuZ-l whom it mag/concern iieit known that I, Emma H. Scrrwanz, a citizen of the United States, residing at New York, county of New York, State of New York, have invented certain new and useful Improvements in Means and Methods for Varying the Voltage of Alternating Currents, of which the following is a specification.

My invention relates to a means and method for varying the voltage of alternating currents for various purposes.

It is often desirable, as for starting alternating current motors and rotary converters, to use, for a short time only perhaps, a lower voltage than is desirable in normal running conditions. Numerous schemes have been proposed which involve the changing of connections, but most of these schemes have objectional features. The scheme which I have shown and later specifically described in this specification gives the same phase to the starting currents as to the running currents, and at the same time preserves the balance in the three-phase circuit by the use of all the transformers in the starting as well as the running position.

' But my invention is not limited to obtaining low voltages for but a short period of time as will be apparent from the description following.

Figures 1, :3 and 3 are vector diagrams, each representing in the customary manner the secondary coils of three transformers connected in delta in various ways; Fig. 4 diagrammatically shows the switching arrangement; Figs. 5, 6 and 7 are diagrams representing various connections of the secondaries and their relation to the resistances later described; Fig. 8 shows diagrammatically the connections whereby a use may be made of the current which at times flows through the resistances; Figs. 9 and 10 show diagrammatically modifications of the connections in Fig. 8; Fig. 11 illustrates transforme and controller connections embodying my invention, and Fig. 12 is a diagram representing the connections of a plurality of sets of secondaries to obtain at the same time currents similar in phase but of different electromotive forces.

In Figs. 1, 2 and 8, the sides ab, ml and of represent by their length and direction, re spectively, the values and phase positions of the electromotive forces impressed upon the respective secondary coils of the transformers, which are connected in delta. For simplicity we will assume that the sides of these triangles represent the actual secondary coils of the transformers and their interconnections. The primary coils of the transformers are not shown and may be connected as desired. The arrows which are shown drawn parallel to the sides of the triangles point in the directions of corresponding ends of the coils, respectively, or we might say point in the directions in which the electromotive forces across the secondaries are measured at all times, respectively.

If a triangle be inscribed in the triangle ABC of Fig. 1 so as to connect the middle or

half voltage points

1, 2, 3 of the triangle ABC, the electromotive force across any side of the inner triangle when measured in given direction will be exactly in phase respectively with the electromotive force of the side of the larger triangle with which it is parallel, when measured in a similar direction. This is shown by the direction of the arrows for the inner triangle, and the value of the electromotive forces across the sides of the inner triangle will be respectively proportional to the lengths of the sides of this triangle. i

If, now, the leads are firstv connected to the

half voltage taps

2, 3,1 and then connected to the full voltage points C, A and B, respectively, it will be seen that the electromotive forces impressed on the leads at half voltage are 60 electrical degrees in advance in phase over those at full voltage. In order to obviate this change in phase, I have in Fig. 2 rearranged and connected the secondaries ab, 0d and ef in a new triangle in such a way that a

triangle

1, 2, 3 can be inscribed, the sides of which are respectively parallel to the sides of the larger triangle ABC of Fig. 1, when the triangles are traversed in the same direction, starting with point A of the larger triangle of Fig. l and with point 1 of the inscribed triangle of Fig. 2. In other words, the side 12 of the smaller triangle of Fig. 2 is parallel and in the same direction as the side cf of the larger triangle of Fig. 1, the side 23 of Fig. 2 is parallel and in the same direction as the side ab of Fig. 1 and the side 31 of Fig. 2 is arallel and in the same direction as the si e 0d of Fig. 1. Therefore if a motor is connected for starting to the

middle points

1, 2, 3 of the secondaries of the three transformers, when these secondaries are connected in accordance with Fig. 2, and then the same motor leads are connected respectively to the points ABC, when the secondaries are connected as shown in Fig. l, the electromotive forces impressed upon the motor windings in the two cases will be exactly in phase with each other respectively. It'will be seen in Fig. 2 that although the secondaries have been connected differently from Fig. 1, nevertheless their positions in Fig. 2 are parallel respectively to those of Fig. 1 and the arrows likewise point in the same direction. The arroWs of the inscribed triangle of Fig. 2 indicate, as in the case of Fig. 1, that the electromotive force of each side" of the inner triangle is'measured in the same direction as the side of the outer triangle with which it is parallel.

In Fig. 3, the triangle of Fig. 2 is merely turned around so as to be in the same position as the triangle of Fig. 1. It will be more readily seen by Fig. 3 that the change from Fig. 1 to Fig. 2 consisted in reversing each side of triangle ABC of'Fig. 1 and then reconnecting the sides together in delta.

The ideas above set-forth may be utilized in various ways to obtain currents of the same phase but of diii'erent electromotive force. Thus a single bank of transformers with a. single group of secondaries, provided with a suitable switching arrangement to make the proper connections, may-be used;

with such an arrangement either the higher electromotive force or the lower can be used at a time, but not both at the same time. Both, however, may be obtained by the use of a plurality of sets of secondaries reversely connected, or by the use of a plurality of sets of transformers with their secondaries reversely connected. I have immediately following described a means for changing the connections when but one set of secondaries is used.

Fig. 4 shows the switching arrangement for use with a single group of secondaries for connecting the motor or other leads k, Z, m to the

points

1, 2, 3 of Fig. 2 for starting, and then connecting the same leads respectively to the points ABC of Fig. 1 for running and at the same time connecting the secondaries together in the proper way for each position, respectively. The switching device shown in Fig. 4 consists of two threepole double-throw switches or it may consist of one six-pole double-throw switch.

The points of they switch are lettered in a manner corresponding to the difierent points marked on Figs. 1 and 2. If two three-pole switches are used it is not necessary that they be thrown in exactly at the same time in either-direction. It is obvious that when the change is made from Fig. 2 to Fig. 1, it necessitates openingthe delta. This is likely to be undesirable where the primaries are connected in Y and where the voltage is comparatively high, as, in the case of an open delta under such conditions, a magnetic disturbance will occur in the transformers which is due to what is generally known as the third harmonic which results in a high voltage wave induced in the primary coils of the transformer when these primaries are connected to the circuit in Y at the end of a long distance transmission line, if the secondaries should be open. I have, therefore, worked out a scheme to prevent the opening of the delta when the above-described changes, in the secondary connections are made. This is shown in Figs. 5 and 6 of the attached drawing. In Fig. 5 the secondary coils are connected in the manner of Fig. 1. In addition to the ordinary direct connection between the ends of the secondaries at the points of the triangle, an additional connection is made from the end of one coil to the beginning of the" next by a resistance 1'. \Vhen the connections between the secondaries are broken at the points ABC, the delta is not opened, as the circuit is kept closed by the resistances made is shown in Fig. 7, where wesee we have simply placed one of the resistances 7' across each of the secondaries. Instead of resistances 1' We might use reactive coils, but in either case the resistances or reactances should be low enough to-prevent third harmonies from attaining any considerable value. The resistances or reactive coils are permanently connected with the endsof the sides of the secondaries as shown in Fig.- 5, and when the switching mechanism of Fig. I 4 is used there will be produced at starting theconnections shown in Fig. 7 and at running the connections shown in Fig. In

coils will be simply short circuited. The arrangement shown in Fig. 7 suggests a novel substitute for the resistances or reactive coils connected across the sides of the tri-' angle. This novel use is shown in Fig. 8

where the shunt circuits are led through the cally throw the switch to the running position' after which the small motor would. stop as its coils would be short circuited as in the manner of the resistances shown in Fig. 5.

r. This is shown in Fig. 6. Now what happens when the connections of Fig. 2 are the latter case the resistances or reactive Fig. 9 is a modification of Fig. 8 as to the means for securing current for the small switch motor. Instead of the shunt circuits around the sides of the triangle leading directly to the windings of the switch motor they are connected, as in Fig. 9, across compensators or auto-starters and from these the motor receives its energy, at either a reduced or increased voltage, a method well known to those experienced in electricity. This would allow of a certain independence between the reactance of the compensator winding and the voltage of the switch motor. Resistances could be substituted for the compensator coils of Fig. 9, and fractional voltages for the starting motor winding could be taken off of these resistances with somewhat the same advantages as with the compensator coils.

Fig. 10 is still another modification of Fig. 8. Here instead of auto-transformers, as in Fig. 9, regular transformers are used, the primaries of which are placed in shunt circuit around the sides of the triangle. The secondaries are then connected in delta and the leads w y 2' are led to the motor by the regular three-phase three-wire method. Instead of three single transformers, as shown in Fig. 10, a single three-phase transformer might be used. The advantage of the method of Fig.-l0 lies in the fact that only three wires need to be used between the transformers and the small switch motor and that the windings of the switch motor can be permanently connected in either Y or delta.

In Fig. 11 of the attached drawings, I have shown the development of a controller and a diagram of connections corresponding to those more generally shown in Figs. 5 and 8. The stationary fingers are indicated by letters and numbers d, e, b, a, f, 0 1 is, 2 Z, 3 and m, from top to bottom in the order named. The letters and numbers correspond to the same letters and numbers on the different Figs. 1 to 10, inclusive. The fingers cooperate with the movable contact segments T to the left which are mounted on' the controller drum. Transformer windings are shown to the right of the drawing of Fig. 11, and are lettered similarly to those of Figs. 1 to 10, inclusive. A switch or controller motor M is shown above the movable contact segments T with windings for the three phases and squirrel-cage armature rotatable inside of them. The connections between the transformer secondaries and the switch motor M correspond to those of Fig.

8. These are not preferable connections but they are shown for simplicitys sake. Those of Figs. 9 and 10 are more desirable. It will be seen from Fig. 11 that the switch motor is out out of circuit, or its windings short circuited in the running position of the rotary or motor. It will be noted that the transformer secondaries are connected together similarly in the running and off positions. Of course, the movable segments for the off position might be arranged so that the secondaries are changed in connection from the running to the off position and connected the same as for the starting position. lVith the latter arrangement the switch motor, if connected as in Figs. 9 and 10, might be started in the off position so that it would not be necessary to turn the controller by hand from the off to the starting positions and the controller could be operated entirely by the motor from the ofl? to the running positions. This would require a widening of the movable segments corresponding to the starting position, and a switch in the switch motor circuit.

As before suggested, my invention covers also a plurality of secondaries for supplying at the same time in phase currents of higher and lower electromotive forces.

Fig. 12 represents diagrammatically the connections of two sets of secondaries to ob tain such currents. As in the preceding figures no primary is shown. These secondaries may have a common primary, or each secondary may have its own primary, in which latter case the primaries will be similarly connected to the line. I have shown here two sets of secondaries ab, 0d, ef and a'b', c'al and 6' the secondaries of the first set are connected in delta similar to the connections of the secondaries as previously described for normal running condition, and the secondaries of the second set are connected as the secondaries previously described for supplying the lower electromotive forces. It will also be observed that from each of the sets of secondaries the taps are taken from the same points as previously described, that is the taps from the first set are taken from the corners, and the taps from the second set are taken from the mid points. Thus it will be seen there are supplied at all times currents in phase and of the two electromotive forces. These currents may be utilized as will be apparent in various ways as desired.

Although I have shown and described the low voltage as one-half the full voltage, it will be understood, of course, that this relation of the values is not absolutely neces sary; that it may be desirable at times to use this method of connecting to produce other voltage relations.

What I claim as new and desire to secure by Letters Patent of the United States, is,

to interconnected windings, then at approximately the same time both disconnecting the leads from the windings and reversing the windings, and connecting the leads to other points of the windings.

3. The method of varying the voltage of a polyphase system, which consists in first connecting the leads to approximately half voltage points of delta-connected windings, then reversing the windings, and connecting the leads to the ends of said windings.

i. The method of deriving two polyphase currents of the same phase but diiferent electromotive forces from a single set of three phase delta connected transformer windings,

which consists in taking the lower voltage 4 connections from mid .points of the windings, and taking the higher voltage connections from the ends of said windings, their connections being reversed relative to their first mentioned connection.

5. The combination of a plurality of windings connected in delta, interior taps from said windings, a plurality of conductors, and means for connecting the conductors to the interior taps, and for reversing the windings and connecting the conductors to the ends of said windings.

6. The combination of a plurality of windings connected in delta, taps from mid points of said windings, a plurality of conductors, and means for connecting the conductors to the taps from mid points, and for reversing the windings and connecting the conductors to the ends of said windings.

7 The method of deriving two polyphase currents of the same phase but different electromotive forces from a plurality of three phase windings connectedin delta, which consists in taking the lower voltage connections from mid points of the windings and the higher voltage connections from the ends of the windings, the windings in the two cases being reversed with respect to each other.

8. The combination with a plurality of conductors, of a pluralitv of single phase sources of supply capable of supplying three phase energy, and means for connectingsaid conductors to mid voltage points of a plurality of said sources of supply connected in a delta relation and to higher voltage points of a plurality of said sources connected in a delta relation, the respectivemembers of the two deltas being relatively reversed.

9. The combination of a plurality of windings connected in delta, interior taps from said windings, a plurality of conductors, means for connecting the conductors to the interior-taps, and for reversing the windings and connecting the conductors to the ends of said windings, and means for preventing the complete disconnection of the windings from themselves.

10. The combination of a plurality of windings connected in delta, interior taps from said windings, a plurality of conductors, means for connecting the conductors to the interior taps, and for reversing the windings and connecting the conductors to the ends of said windings, and impedances connecting the ends of the windings.

11. The combination of a plurality of windings connected in delta, interior taps from said windings, a plurality of conductors, means for connecting the conductors to the interior taps, and for reversing the windings and connecting the conductors to the ends of said windings, a motor, and connections to the ends of the windings for supplying the motor.

12. The combination of a plurality of windings connected in delta, interior taps from said windings, a plurality of conductors, means for connectingthe conductors to the interior taps, and for reversing the windings and connecting the conductors to the ends of said windings, an induction motor, and connections for supplying the motor, each set of connections being to two windings.

In witness whereof, I have hereunto set my hand this third day of April, 1911.

ELMER H. SCHWARZ.

Witnesses:

HALL l HOXIE, T. A. DEMPSEY.

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