US 2381768 A
Description (OCR text may contain errors)
Aug. 7 1945. v s. MINNEC'I 2,381,768
ELECTRIC CIRCUIT Filed Nov. 29, 1945 Figl. ,4
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Patented Aug. 7, 1945 ELECTRIC CIRCUIT Salvatore Minneci, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application November 29, 1943, Serial No. 512,130
This invention relates to electric circuits and more particularly to improvements in tap-changing circuits.
One well-known way of changing the effective turns of an inductive winding is to provide it with a plurality of taps and selectively change the tap connections by means of suitable switching means. This is done frequently in the case of transformers as it permits adjustment of the voltage ratio of the transformer and thus it can be' used to provide voltage regulation. The taps are usually equally spaced electrically in the winding; that is to say, the tap voltages usually form an arithmetical progression which is characterized by a common voltage difference between electrically adjacent taps. Usually, the ratio adjusting switch consists of a number of relatively fixed contacts which are equally spaced from each other and from a relatively movable contact which makes selective engagement with the relatively fixed contacts. In other words, the relatively fixed contacts are on a circle and they are equally spaced from each other on the circle, The taps are usually connected to the relatively fixed contacts in regular order so that the voltage stress between adjacent fixed contacts is equal to the common tap-tO-tap voltage diiference in all cases except in the case of the two adjacent fixed contacts which are connected respectively to the first and last taps. In that case the voltage stress is equal to the entire tap range voltagej Consequently, the switch and the spacing between its fixed contacts must be designed to with stand the entire tap range voltage between adjacent taps, although this voltage stress appears only between two of the contacts.
In accordance with this invention the maximum voltage stress between adjacent switch contacts is materially reduced by changing the connections between the taps and the switch contacts. This change is characterized by having successive taps connected to non-adjacent switch contacts which are separated by either one or two of the other switch contacts. In this arrangement it is necessary to move the movable contact past one or two of the fixed contacts before the tap change is completed, and consequently it is necessary to rotate the movable contact .two or three times in order to traverse the entire tap range, as contrasted with the conventional arrangement in which the movable contact need make only one revolution in order to traverse the entire tap range. 1
.An object .of the invention is to provide a new and improved electric circuit.
Another object of the invention is to provide a new andimproved tap-changing system.
A further object of the invention is to reduce the maximum voltage stress betweencontacts of tap-changing switches.
The invention will be better understood from the following description takenin connection with the accompanying drawing and its scope willbe pointed out in the appended claims.
In the drawing, Fig. 1 illustrates diagrammatically an embodiment of the'invention-applied to a variable ratio transformer whose ratio adjusting switch has an even number of tap contacts, and Fig. 2 illustrates diagrammatically an application of the invention-toa step voltage regulator having a ratio adjusting switch which is provided with an odd number of tap contacts.
Referring now to the drawing and more particularly to Fig. 1, there is shown therein a ratio adjusting switch provided with relatively fixed contacts 1-8, inclusive, which are equally spaced from each other along a circle. These areselectively engageable by a movable contact 9. The contacts |-8, inclusive, are connected respectively to eight taps brought out of an inductive winding ID. This winding, together with another winding H, is mounted on a magnetic core l2 so as to constitute a transformer. Either of the 'two windings may be considered the primary winding and for purposes of illustration it will be assumed that winding H is the primary winding and its excitation is controllable by a series disconnecting switch l3. The circuit of the secondary'win'ding I0 is completed through a'conductor 14 connected to the movable contact 9, the other sideof the circuit being completed through a conductor I5 connected to the lower terminal of the winding ID as viewed in the drawing. r
This ratio adjusting system is of the typewhich is not adapted to operate under load; that is to say, the ratio adjusting switch is of the nonarcing duty type and consequently the switch I 3 is opened so as to deenergize the transformer before each tap change is made. It will be noted that the outermost tap or top terminal of the winding ID, as viewed in the drawing, is connected to fixed contact I and that the next tap is connected to fixed contact 2 and that between contacts I and 2 are located contacts 4 andl. Similarly, the third tap is connected to contact 3 but taps 5 and 8 intervene between contacts 2 and 3. The connections are completed in this order, each successive tap being connected to a fixed contact which has-two of the fixed contacts intervening between it and the contact to which the preceding tap has been connected. Each tap change is made by moving the contact 9 to the next lower or higher numbered tap. For instance, if the voltage of the secondary winding circuit is to be reduced the contact 9 is moved counterclockwise from contact 2 to contact 3 in order to reduce the voltage one step and then the switch I3 is reclosed. If the voltage is to be reduced two steps the contact 9 is moved on from contact 3 to contact 4 after first opening the switch 13.
It will be noted that the voltage between contacts I and l is three times the tap-to-tap voltage because contact 4 is connected to the fourth tap and between it and the first tap there are three tap-to-tap intervals or tap-to-tap sections of the winding. Likewise, the voltage between contacts I and 'l is three times the tap-to-tap voltage. However, the tap-to-tap voltage between contacts 1 and 2 is five times the tap-totap voltage and it will be seen by following through the sequence in this manner that this is the maximum tap-to-tap voltage which exists between any pair of adjacent taps.
In Fig. 2 the invention is applied to a socalled step voltage regulator which comprises an autotransformer having a common winding I6 and a series winding l1 provided with eight taps which are equally spaced from each other and from the terminals of the winding. These terminals are connected to the fixed contacts of a so-called reversing switch 18 whose movable contact is connected to the ungrounded terminal of the common winding and to the load side of the circuit. The eight taps and the movable contact of the reversing switch l8 are connected to a ratio adjusting switch 19 having its fixed contacts equally spaced along a circle. These contacts are in general similar to the fixed contacts of the ratio adjusting switch of Fig. 1 and they are numbered l-9 inclusive. In this case the uppermost tap is connected to contact I as in Fig, 1 the second tap is connected to contacts 2 but only one fixed contact is skipped, namely, contact 6, so that only one contact intervenes between contacts I and 2. Similarly, the third tap is connected to contact 3 and only one contact is skipped, namely, contact I, and the connections are then completed in this way so that each succeeding tap is connected to every odd fixed contact. The fixed contacts are selectively engageable by movable ratio adjuster contacts 20 and 2!, in series with each of which are separate arcing contactors 22 and 23 which connect to the terminals of a mid-tapped reactor 24 whose midtap connects to the source side of the circuit.
The ratio adjuster contacts 2|] and 2| are operated in the conventional manner and they are interlocked with the contactors 22 and 23 so that before each ratio adjuster leaves one of the tap contacts its serially-connected arcing duty contactor opens so as to interrupt the current through it. With this arrangement it is necessary for the ratio adjusting contacts 20 and 2| to make two revolutions in order to traverse the entire tap range but it will b seen that the maximum voltage difference between the fixed contacts will be five times the tap-to-tap voltage difference, in contrast with the conventional arrangement in which the maximum voltage between fixed contacts would be eight times the tap-to-tap voltage difference.
In the case of an odd number of ratio adjuster contacts in which successive taps are connected to every odd contactor so as to require two revolutions of the ratio adjuster in order to traverse the tap range, the maximum voltage stress between any adjacent switch contacts is times the tap-to-tap Voltage difference where n is the number of contacts. In the case of an even number of contacts on the ratio adjuster switch, as in Fig. 1 where the movable contact skips, or more accurately passes over, two fixed contacts in going from tap-to-tap so that three revolutions of the movable contact are required in order to traverse the tap range, the expression for the maximum voltage between contacts in terms of the common tapto-tap voltage differenc is more complicated but it can be expressed as twice the nearest whole number to less 1. For example, in the case of the eight contacts shown in Fig. 1,
is 3 which is a whole number, twice 3 is 6, less 1 is 5 which, it will be seen, is the maximum voltage stress which exists in the case of Fig. 1. Similarly, if there are ten fixed contacts is 3 so that the nearest whole number is 4 and twice 4 is 8, less 1 is '7 which is the maximum voltage stress between any two adjacent fixed contacts in terms of the common tap-to-tap voltage difference when there are ten fixed contacts. From the above it will be seen that the greatest reduction is obtained in the case of an odd number of fixed contacts and that as n increases the limit for the maximum voltage stress between fixed contacts will be so that the limit will be one-half the tap range voltage, whereas in the case of an even number of fixed contacts th limit will be that is to say, the actual maximum voltage stress will always be greater than Although the load side of the circuit has been indicated as being connected to the ungrounded side of the common winding in Fig. 2 and the source side of the circuit has been indicated as being connected to the mid-tap of the reactor, this is f course not essential to the present invention and the direction of power flow can oi. course be reversed. However, the indicated connections are those which are usually found in actual practice.
While there has 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. In combination, an inductive winding, a series of taps brought out from said winding, the turns of said winding within the range of said taps being permanently connected together, said series of taps being characterized by a constant voltage difference between electrically adjacent ones thereof, tap-changing means having as many equally spaced contacts arranged in a circle as said winding has taps, means for connecting electrically adj acerit taps to non-adjacent contacts in a predetermined regular order so as to reduce the maximum voltage stress between adjacent contacts substantially below the total tap range voltage, each contact being connected to a different tap, and means for progressively making connection to said contacts which are connected to adjacent taps whereby said means goes more than once around said circle in progressively traversing said tap. range.
2. In combination, a winding having a plurality of electrically equally spaced taps, the turns of said winding within the range of said taps being permanently connected together, a tap-changing switch having a given number of equally spaced tap contacts arranged in a circle, and an additional contact for selectively engaging said circularly arranged contacts, all of said tap contacts being connected to respective taps of said winding in a predetermined order which is characterized by having each pair of adjacent taps connected to tap contacts which are separated by at least one intermediate tap contact whereby said additional contact goes more than once around said circle in progressively traversing said tap range and the maximum voltage stress between said adjacent spaced contacts is substantially below the total tap range voltage.
3. In combination, a winding having a plurality of electrically equally spaced taps, a tap-changing switch having an odd number of equally spaced tap contacts arranged in a circle, an additional contact for selectively engaging said circularly arranged contacts, all of said tap contacts being connected to respective taps of said winding in a predetermined order which is characterized by having each pair of electrically adjacent taps connected to tap contacts which are separated by one intermediate tap contact.
4. In combination, a winding having a plurality of electrically equally spaced taps, a tap-changing switch having an even number of equally spaced tap contacts arranged in a circle, and an additional contact for selectively engaging said circularly arranged contacts, all of said tap contacts being connected to respective taps of said winding in a predetermined order which is characterized by having each pair of electrically adjacent taps connected to tap contacts which are separated by two intermediate tap contacts. 5. In combination, a switch having an odd number of equally spaced contacts arranged in a circle, an inductive winding having a like number of electrically equally spaced taps, and means for connecting successive taps to alternate contacts when proceeding in the same direction around said circle so asto produce a maximum voltage stress between any two adjacent contacts of where n is the common voltage difference between any two electrically adjacent taps.
6. A tap-changing regulator comprising, in combination, a winding having a series of electrically equally spaced taps, a tap-changing switch having an odd number of equally spaced fixed contacts arranged in a circle, a movable contact for successively engaging said fixed contacts, and connections between saidtaps and fixed contacts such that said taps are progressively connected to every other contact until each contact is connected to a different tap whereby the maximum normal voltage stress between adlacent switch contacts is times the common tap-to-tap voltage difference where n is the number of circularly arranged switch contacts.