US1905249A - Tap-changing-underload equipment - Google Patents

Description

Api-il 25, 1933. F, SNYDER 1,905,249

TAP CHANGING UNDERLOAD EQUIPMENT Filed Dec.` 12, 195o SEQUENCE OF OPER/1770 mw/2s 567os9 /l 1a /a 7? le 'ATTORNEY Patented Apr. 25, 1933 UNITED STATES 'PATENT OFFICE FRANKLIN L. SNYDER, OF SHARON, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

TAP-CHANGING-UNDERLOAD EQUIPMENT Application led December 12, 1930. Serial No. 501,871..

- My invention relates to tap-changing equipment for transformers and more particularly to the tap-changing under-load equipment for transformers wherein a relatively large number of tap positions are desired.

With many forms of tap-changingequipment used inthe past, the number of regulating voltage steps are limited because it is 4diiicult or impractical toprovide alarge number of tap connections to the main transformer winding. l

An object of my invention is to provide a tap-changing equipment having a large number of tap-changing positions that are obtainable with a comparatively few tapchanging switches.

The invention, with additional objects and advantages thereof, will be better understood from the following description, when read in conjunction with the accompanying drawing, in which:

Figure 1 is a diagrammatic view of circuits and apparatus illustrating one preferred embodiment of my invention, and

Fig. 2 is a portion of a sequence chart showing the sequence of operation of the several switches .illustrated in Fig. 1. l

Referring to the drawing, a transformer, which is illustrated as an auto-transformer 41,

is provided for supplying power to a load, such as the furnace transformer 5. The autotransformer is provided with a primary r winding 2 that is connected to power- circuit conductors 3 and 4, Vand supplies energy to the primary winding 29 of the transformer 5 by means of conductors 6 and 7. The conductor 7 is connected to the winding 2 through a preventive auto-transformer 8 and through an intermediate tap-changing transformer 17 and an intermediate auto-transformer 22. Switches 9, 10, 11, 12, 13 and 14 of tap-changer 15 are connected to tap points on the winding` 16 of the intermediate transformer 17. Reversing switches 1.8 and 19 are provided between one end of the winding 16 and opposite ends of the auto-transformer 22 f and are effective to connect the winding 1G across the one or the other of the windings l2O or 21 which comprise the intermediate auto-transformer 22. From the intermediate auto-transformer 22, the circuit to the transformer 1 is completed through two of the operating switches 23, 24, 25, 26 and 27 of tap-changer 28. i

The reversing switches 18 and 19 are effective to conne'ct the portion 20 or the portion 21 of the transformer 22 to the winding 16. A voltage will, therefore, be applied to the winding 16 that is one half the voltage between adjacent tap-changing switches 23 to 27, inclusive. The several switches are operated in accordance with the sequence of operation shown in the chart in Fig. 2.

The numerals reading from left to right across thetop of the chart of Fig. 2 indicate controller positions having definite voltageratio values. The numbers reading from top to bottom at the left of the chart refer to the correspondingly numbered switches shown in Fig. 1. The circles in the chart of Fig. 2 indicate that theswitchesdesignated by the numbers at the left of the chart are closed on the controller positions indicated at the vtop of the chart. l

In the controlled position 1 of Fig. 2, it will be noted that switches 9 and 14 of tap-changer 15, reversing switch 18, and switches 23 and 24 of the tap changer 28 are closed. Switch 14, in its closed position, causes the windings of the preventive auto-transformer 8 to neutralize each other, and, in effect, connects the conductor -7 directly to one end of the winding 16 through the switch 9. With the reversing switch 18 closed, a voltage, corresponding to that of the winding 20 of the intermediate auto-transformer 22, is impressed upon the winding 16. The voltage o f lthe primary windings 2O and 21 of the autotransformer 22 is the same as that impressed between the taps operated by switches 23 and 24 of the tap changer 28.

In position 2 of the controller, switch 14- 8 is connected to different pairs of adjacent taps of the intermediate transformer 17 to vary the voltage applied to the furnace transformer. The opening of switch 14 and the closing of switch 10 changes the voltage one step and connects the preventive auto-transformer 8 between the switches 9 and 10, thus, in effect, connecting the conductor 7 to a point on the winding 16 that is midway between the two taps connected to switches 9 and 10. The switches 23 and 24 remain closed in controller position 2. In controller position 3, switch 10 of tap-changer 15 remains closed, switch 9 is opened and switch 14 is closed. This changes the taps another step, and a voltage on the mid-tap of the preventive auto-transformer 8'is obtained that corresponds to that of tap 10. The switches 23 and 24 remain closed, as in controller position 2.

It will be noted that, during the first nine controller positions, the reversing switch 18 has remained closed, and the reversing switch 19 has remained open. On the controller position 9, the conductor 7 is connected, through closed switches 14 and 13, to the middle point of the winding 22. In the transition from the controller position 9 to the controller position 10, an intermediate step 9 appears, wherein the switch 18 is opened and the switch 19 is closed. This intermediate step does not produce a voltage change, since the connection of the conductor 7 to the winding 22 is not altered thereby. During the operation of the controller from position 9 to 17, inclusive, the tap-changer 15 reverses the sequence of steps from position 1 to 9, inclusive. At the controller position 17, the conductor is connected to the winding 2 through closed switches 14, 9, 19 and 24. Switch 23 is then opened and switch 25 closed, and the tap-changer 15 repeats a similar operation, as described above.

When the switches in the tap-changer 15 have been operated through their sequence of steps, the connection of the winding 16 to the winding 2 is changed either by operation of one of the reversing switches 18 and 19 or by one of the switches of the tap-changer 28, depending upon which step of the complete series is to be made.

The reversing switches 18 and 19 serve to connect one end of the winding 16 to one of the tap switches 23 to 27, inclusive, the other end of the winding 16, being, in effect, connected to a point in the winding 2 that is mid-way between the two switches of the groups 23 to 27 inclusive, that is closed. In a similar manner, the complete sequence of operation of the switches may be followed by further reference to the chart shown in Fig. 2. All switches may be either automatically or manually operated, as desired.

From the above discussion, it may be seen that I have devised means for varying the voltage ratio of a transformer that is easily constructed and operated. My described tapchanging system provides a large number of voltage steps with the use of a relatively small number of tap-changing switches.

Although I have shown and described a certain specific embodiment of my invention, I am fu ly aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and bythe spirit of the appended claims.

I claim as my invention:

1. In a tap-changing system for transformers, a primary power circuit comprising a pair of conductors, a transformer winding energized from said power circuit and provided with a plurality of tap connections, an intermediate transformer energized from said first-named winding, and a tap-changing transformer energized from said intermediate transformer, tap-changing switches for varying the connection of said intermediate transformer to said first-named winding, reversing means for changing the connection of tap-changing transformer to said lintermediate transformer, and a plurality of tapchanging switches for varying the connection of said tap-changing transformer to a power-circuit conductor.

2. In a tap-changing system for transformers, a transformer wmding connected to a power circuit and provided with a plurality of tap-changing switches, a pair of intermediate transformers connected to said tapchanging' switches, means for changin the polarity of one said intermediate trans ormers with respect to the other, the last-named intermediate transformer being provided with a plurality of tap connections, and means for varying the tap connections of said last-named intermediate transformer.

3. In a transformer-voltage-ratio-control system, a power circuit and a transformer winding energized thereby, two intermediate transformers connected in cascade, means for changing the polarity of one of said intermediate v transformers with respect to the other, a plurality of tap-chan ing switches connected to said first-name transformer winding for connecting one of said intermediate transformers between selected points thereon, and voltage-ratio control means at tached to the other of said intermediate transformers, said voltage-ratio control means comprising a plurality of tap-changing switches and a controlled preventive autotransformer, said reventive auto-transformer being connecte to said power circuit.

In testimony whereof, I have hereunto subscribed my name this 4th day of December FRANKLIN L. SNYDER.

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