US2476077A - Transformer system - Google Patents

Description

July 12, 1949. H WILLIS 2,476,077

TRANSFORMER SYS TEM Filed Nov. 8, 1945 Inventor: Clodius HWiHis,

His Attorney.

Patented July 12, 1949 TRANSFORMER SYSTEM Clodius H. Willis, Princeton, N. J., assignor to General Electric Company, a corporation of New York Application November 8, 1945, Serial No. 627,477

6 Claims.

This invention relates to load-ratio-control circuits and more particularly to improvements in circuits of this type which have a plurality of effectively parallel effectively variable turn winding sections.

By load-ratio-control is meant the control or variation of the ratio of a transformer while under load. The most common way of changing a transformers ratio is to vary the eiiective number of turns of one of its windings. One way of preventing interruption of the load during such operation is to divide the winding into two or more effectively parallel sections and alternately interrupt the current in the two sections during a ratio adjusting operation. In this way at least one section will carry the current while another section is open-circuited and is having its efiective number of turns changed. As a result of this operation the effectively-parallel winding sections are at any particular instant as apt to have unequal efiective turns and voltage as to have equal effective turns and voltage. Such unequal voltages cause a circulating current to flow in the winding sections and this is limited in magnitude by the impedance of the sections. Consequently, if the range of effective turn variation is a large percentage of the total number of turns of the winding sections the impedance which limits the circulating current will vary by a large percentage and thus there will be a correspondingly large variation in the circulating current.

In accordance with this invention there is provided a novel and simple arrangement which insures that the impedance which limits the circulating current is substantially constant re gardless of the range of effective turn variation. and consequently the magnitude of the circulating current is also constant throughout this wide range of ratio adjustment. This arrangement in its preferred form is characterized by the use of an auxiliary 1:1 ratio insulating transformer whose windings serve to interconnect corresponding ends of the Winding sections of the main transformer. This auxiliary transformer then forces an equal interchange of circulating cur rent between the winding sections.

An object of the invention is to provide a new and improved load-ratio-control circuit.

Another object of the invention is to provide an improved wide range load-ratio-control cir cuit. 1

A further object of the invention is to provide a variable ratio transformer having a Winding which is divided into a pair of effectively-parallel sections and in which the circulating current 55 between sections is constant throughout a substantially 100 per cent variation in effective turns of this winding.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 illustrates diagra1nmatically an embodiment of the invention applied to a variable ratio transformer of the sliding brush contact type, Fig. 2 is a modification in which ratio adjusting switch mechanism is used instead of a sliding brush, Fig. 3 is a further modification in which the main transformer is an autotransformer in which the range of regulation is all either bucking or boosting, and Fig; 4 is a modification of Fig. 3 in which the range of regulation includes both bucking and boosting actions.

Referring now to the drawing and more particularly to Fig. 1, there is shown therein a main transformer having a winding 1 connected to a circuit 2, and a winding 3 connected to a circuit 4. Either circuit may be the input circuit and consequently either winding may be the primary winding. Winding 3 consists of a pair of equal winding sections 5 and 6 whose effective turns are varied by means of a sliding brush contact 1 which engages directly their respective coil sides. The brush 1 is wide enough to bridge between the corresponding coil sides of the two sections so that as it moves across the coil sides (up and down. as viewed in the drawing) it is always in contact with at least one section; while in certain posi tions, one of which is illustrated in the drawing. it bridges between adjacent coil sides. However. it is not Wide enough to bridge between adjacent coil sides of the same section so that it cannot short circuit one turn of either coil section.

The winding sections 5 and 6 are interconnected at their ends by means of an auxiliary transformer 8 which is an insulating transformer and which has two equal. windings 9 and [0, winding 9 being connected between the lower terminals, as viewed in the drawing, and winding N3 being connected between the upper terminals of the sections 5 and 5. In this manner a closed loop is formed in which the sections 5 and 6 and the windings 9 and iii are all in series. In this closed loop the polarities of the sections 5 and 6 are opposed and the windings 9 and I U are so connected that their polarities are additive.

The circuit Al has one side or conductor connected directly to the brush i and the other side or conductor of the circuit is connected. to the loop consisting of the sections 5 and 6 of the winding 3 and the windings 9 and ill of the transformer 8. The particular place in the loop to which this conductor is connected is important and, as shown, it is connected near the lower end of the section 5.

The operation of Fig. 1 is as follows. Assume that winding 3 is the secondary winding of the main transformer. With the brush in the illustrated position a connection is made between coil sides of the sections 5 and 6 which do not have the same voltage. Thus, for example, starting from the lower ends of both sections and tracing the circuit up through the sections to the brush it will be seen that there is one more turn of section 5 than there is of section 6 included between their lower ends and the brush 1. Consequently, a circulating current will flow in the direction indicated by the full line arrowheads, the instan taneous direction of this current being assumed upwards in section 5, then through the brush 1 and downwards in section 6 and passing from right to left through the winding 9. At the same time the voltage between the upper terminals of the sections 5 and 5 and the brush l differs by one turn so that a circulating current flows in the direction of the dashed arrowheads, the direction being upwards in section 6 and downwards in section 5, the current path being completed through the brush l and the winding It of the auxiliary transformer, the direction being from left to right or opposite to that of the circulating current in winding 9.

The effect of the transformer 8 is to force an equal interchange of circulating current between the corresponding ends of the winding sections because only under these conditions will the transformer 8 he demagnetized and offer a minimuminrpedance to the flow of circulating current. If the circulating current in one winding of the transformer tends to exceed that of the other the consequent unbalance will produce a high reactance so that any substantial inequality in circulating current in the two paths which include the windings 9 and i respectively is prevented.

Therefore, in any bridging position of the brush 1 where it bridges coil sides having unequal voltages the circulating current will be the same. In efiect, the over-all impedance to the circulating current is substantially constant for all such positions of the brush 1 along the sections and 6 and this impedance will be approximately the impedance of one-half of one of the two equal sections 5 and 6.

The voltage of the circuit Ii will, of course, vary as the :position of the brush varies because this varies the effective number of turns of the winding 3 in the circuit 4.

When the brush bridges between coil sides which have equal voltage there is, of course, no circulating current and in these positions of the brush the effect of the transformer 8 is to cause the two sections 5 and 6 to divide the load current. Between each bridging position of the brush :there will be positions when it engages only one or the other section alone. When it engages only section 5 the load current will be carried by this winding alone and when it engages only section 5 the load current will be sup plied equally hy both sections, the current in section 6 being equal and in opposite directions on both sides of the point of brush contact.

It will thus be seen that when the brush 1 is moved dowmvardly, as viewed in Fig. 1, it will have four cyclical occurring operating positions or conditions, namely, (1) direct interconnection and simultaneous engagement of different, or unequal, voltage points on the winding sections 5 and 6, respectively, (illustrated in Fig. 1), (2) single engagement of a point on winding section 6 alone, (3) direct interconnection and sim ultaneous engagement of similar, or equal, voltage points on the winding sections 5 and 6, respectively, and (4) single engagement of a point on winding section 5 alone.

In Fig. 2 the sections 5 and 6 of the winding 3 have been shown mounted end to end instead of interwound as in Fig. 1, thus increasing their leakage reactanoe and thus further reducing the value of the circulating current. In addition, the brush 1 has been replaced by a ratio adjusting mechanism comprising ratio adjuster switches H and I2 which respectively make variable connections to the sections 5 and B. These ratio adjusters may be operated step by step alternately in any suitable manner and they pref era-bly engage contacts which are connected to taps which are brought out of the winding sections. The details of a well-known and suitable mechanism for operating such a pair of ratio adjusters is shown in Patent 1,588,204, granted June 8, 1926 on an application of Howard 0. Stephens and Arthur Palme and assigned to the assignee of the present application. The operation of Fig. 2 in principle is exactly the same as the operation of Fig. 1, the switches H and i2 alternately making bridging connections be tween points on the windings 5 and 6 which have equal and unequal voltages, these alternate bridging connections being separated by intermediate connections in which one switch alone makes contact with one section and the other switch is open. The two circulating current paths when the switches make bridging connections to unequal voltage points in the sections 5 and 6 are indicated by the solidand dashed arrows respectively and these show that the circulating currents flow through the windings 5 and ll of the auxiliary transformer 8 in opposite directions and as a result this transformer maintains equality of the total circulating current between the ratio adjusters throughout the entire range of operation from the upper to the lower ends of the Winding sections 5 and 6.

In Fig. 3 the main transformer is connected as an autotransformer in which the winding I acts as a shunt winding and the winding 3 acts as a series winding. In this figure the external circuit for the closed loop consisting of the winding sections 5 and 6 and the windings 9 and It is made to the electrical mid-point of the winding 9. This has no effect on the circulating current but it affects the distribution of the load current between the sections 5 and 6 as follows. The load current will be equal in both sections for all bridging positions of the ratio adjusters. For all positions when only one ratio adjuster makes contact the load current division will be in the ratio of 3 to 1 with engaged sections carrying the higher current.

The operation of Fig. 3 is essentially the same as that of the other figures except that as the ratio adjusters H and I2 move up and down so as to include more or less of the turns of the sections 5 and 6 in the circuit 4 the voltage of these sections either adds to or subtracts from the rest of the voltage of the circuit so that the action is either that of a variable boosting voltage or a variable bucking voltage.

acts as a buck and boost step voltage regulating autotransformer.

While there have been shown and described particular embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

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

1. A transformer having a winding with two equal voltage sections, means including ratio adjusting mechanism for connecting variable amounts of said sections effectively in parallel in an external circuit, said ratio adjusting mechanism under certain operating conditions serving directly to interconnect unequal voltage points on said sections whereby a circulating current is produced in said sections and mechanism, and an auxiliary transformer for making the value of said circulating current independent of the amounts of said sections which are connected in said external circuit, said auxiliary transformer having two insulated windings one of which is connected between a pair of corresponding voltage terminals of said sections and the other of which is connected between another pair of corresponding voltage terminals of said sections.

2. A transformer having a winding which is divided into two equal voltage sections, ratio adjusting mechanism for selectively making simultaneous connection to equal and unequal voltage points on said sections respectively, an external circuit for said winding having one conductor connected to said ratio adjusting mechanism and having another conductor connected to at least one of said sections, and an auxiliary transformer interconnecting said sections for insuring equal values of circulating current through said ratio adjuster mechanism when it makes connection with points on said sections having the same difference in voltageregardless of the location of said points on said sections, said auxiliary transformer having a pair of insulated windings one of which is connected between a pair of terminals on said sections having corresponding voltages and the other of which is connected between another pair of terminals on said sections having corresponding voltages which differ from the voltages of the first pair of terminals by the voltage of said winding.

3. A transformer having a winding which has two equal voltage sections, a second transformer having two identical windings, one of said identical windings being connected between one pair of equal voltage terminals of said sections, the other of said identical windings being connected between the remaining pair of terminals of said sections, ratio adjusting mechanism for selectively making connection to equal and unequal intermediate points on said sections respectively, and an external circuit connected to said ratio adjusting mechanism and to said sections.

4. A main transformer including two equal windings, an auxiliary transformer having two equal windings, means for serially connecting all four windings in a closed loop in which the windings of each transformer alternate with the windings of the other transformer and in which the polarities of the main transformer windings are subtractive and the polarities of the auxiliary transformer windings are additive, an external circuit connected to a predetermined point on said closed loop, and movable tap changing means having four operating positions for completing said external circuit, said positions being first a simultaneous direct interconnection of equal voltage points on both of said main transformer windings, second a single connection to one of said points, third a simultaneous direct interconnection of said last-mentioned point and a different voltage point on the other of said main transformer windings, and fourth a single connection to said different voltage point.

5. A transformer having a primary winding and a secondary winding, one of said windings having two equal sections, means for successively directly interconnecting intermediate points on said sections whose voltage difference varies alternately between zero and the same finite value, and an auxiliary one to one ratio insulating transformer interconnecting the ends of said sections so that circulating current passing from one section to the other must pass in equal amounts from both ends.

6, A transformer having a winding whose effective number of turns is to be varied for varying the transformer ratio, said winding having two sections of substantially the same number of turns, an auxiliary transformer having a pair of windings which are insulated from each other and which have substantially the same number of turns, one end of one of said sections being connected to the corresponding end of the other section by way of one only of the windings of said auxiliary transformer, the other two ends of said sections being interconnected by way of the other winding only of said auxiliary transformer, and movable circuit making and breaking means for selectively making electrical connection to individual points on either section to the exclusion of the other section and direct interconnections between points selectively at the same and different voltage which latter points are respectively on different ones of said sections.

CLODIUS I-I. WILLIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number

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