US2434503A - Tap changing system - Google Patents

Description

Jan. 13, 1948. o. P. MCCARTY 2,434,503 1 TAP CHANGING SYSTEM Filed April 2'7, 1945 lnvencbr: Orin F. Mo Cart y,

His Attor hey Patented Jan. 13, 1948 TAP CHANGING SYSTEM Orin P. McCarty, Pittsfield, Mass, assignor to General Electric Company, a corporation of New York Application April 27, 1945, Serial No. 590,696

11 Claims. 1

This invention relates to tap changing systems, and more particularly to improvements in wide range load ratio control circuits.

Changing circuit connections to taps on an electrical device when done under load in relation to taps on a transformer winding without interrupting the load current is called load ratio control, whether or not the voltage ratio of the transformer is actually changed. Originally, load ratio control circuits were used only to produce a change in transformer voltage ratio, but subsequently the same load ratio control systems and techniques were also used for changing the phase of the transformer voltage.

A well known load ratio control system employs a nomarcing duty ratio adjuster switch in combination with an arcing duty contactor. The ratio adjuster switch ordinarily has substantially the same number of contacts as there are taps and it performs the actual tap changing operation. The arcing duty contactor is connected in series with the ratio adjuster switch and it interrupts the current through the switch each time the switch moves from tap contact to tap contact. The ratio adjuster switch and the arcing duty contactor are dual circuit devices and they are so interconnected that the dual circuits are effectively in parallel so that the transformer load current is not interrupted by reason of the operation of the arcing duty contactor, this contactor merely operating alternately to open two effectively parallel circuits. The non-arcing duty ratio adjuster switch usually consists of a plurality of fixed contacts which are connected respectively to the winding taps and which fixed contacts are arranged in a circular path. These fixed contacts are engaged by a pair of contact fingers which move in an effectively circular path in going from tap contact to tap contact. The arcing contactor, on the other hand, may be a relatively simple device having only two sets of alternatel operable contacts, but as this contactor performs the arcing duty of the circuit, it is relatively much more expensive than the ratio adjuster switch because in large power transformers the amount of energy which must be interrupted is quite large,

It is highly desirable that the ratio adjuster switches be standard zed as to the number of tap contacts that they have and the spacings between these tap contacts, which spacings are determined by the voltage range of the multi-tap winding. Sometimes, however, it is necessary to provide a wider tap range and a greater number of taps or voltage steps that can adequately be obtained from a standard ratio adjuster switch and under these conditions the ordinary solution of the problem is to design a special ratio adjuster switch having an extra large number of tap contacts and having extra wide contact spacings so as to be able to operate over the increased tap voltage range. That solution of the problem, however, is relatively expensive because of the special design and construction problems involved.

In accordance with this invention, I utilize a plurality of standard ratio adjuster switches for obtaining an extra wide range of voltage control of a single transformer, and furthermore, I interconnect these ratio adjusters in such a way that only one arcing duty contactor is used. In this manner the increased cost is relatively small and is nowhere near double the cost of a single load ratio control mechanism because, as has already been pointed out, the arcing duty contactor is the most expensive part of the system, and there is no increase in the number of arcing duty contactors.

An object of the invention is to provide a new and improved tap changing system.

Another object of the invention is to provide a new and improved wide range load ratio control circuit.

A further object of the invention is to provide a simple and inexpensive system for effectively doubling the tap range of a load ratio controlled transformer.

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 is a diagrammatic illustration of an embodiment of the invention, Fig. 2 is a somewhat schematic representation of a modification of the invention, Fig. 3 is a diagrammatic view of a three-phase arrangement embodying a further modification of the invention, and Fig. 4 illustrates a suitable arrangement of core and coils on a three-phase transformer with which my invention may be used.

Referring now to the drawing and in particular to Fig. l, I show therein four windings I, 2, 3 and 4 which collectively maybe considered one of the principal windings of a transformer, that is to say, either the primary winding or the secondary winding. These windings are all shown in line so that they may be considered as being threaded by the same flux or they may be considered as being on the same leg of a transformer core. The windings 2 and 4 are the main windings and they are each provided with a plurality of taps which connect respectively to the tap contacts of separate ratio adjuster switches 5 and 6.

In order to double the effective tap range of each ratio adjuster switch, the ratio adjuster switch has associated with it a reversing switch 2' and the ratio adjuster switch 6 has associated with it a reversing switch 8. These reversing switches each have a pair of fixed contacts which are connected respectively to the terminals of their associated main windings, that is to say, the fixed contacts of the switch I are connected respectively to the terminals of the winding 2 and the fixed contacts of the reversing switch 8 are connected to the terminals of the main winding 4. The common or movable. contacts of the reversing switches are connected respectively to tap contacts, of their associated ratio adjuster switches, which are between the tap contacts which are connected respectively to the outermost taps of their associated main windings. These common contacts are also connected respectively to their associated auxiliary windings. Thus, the common contact of reversing switch I is connected to a terminal of the winding l and the common contact of the reversing switch 8 is connected to a terminal of the winding 3.

Each ratio adjuster switch has a pair of contact fingers, those for ratio adjuster switch 5 being contact fingers 9 and I8 and those forratio adjuster switch 6 being contact fingers H and [2. The contact fingers of each ratio adjuster switch are so arranged that one or the other of them is always in contact with one of the tap contacts.

The circuit through the illustrated windings is completed by interconnecting the contact fingers of the ratio adjuster switches. Thus, contact fingers 9 and H are interconnected through a set of arcing contacts 13 of an arcing duty switch I t and the contact fingers l and [2 are interconnected through another set of contacts 55 on the arcing duty contactor M.

In order to prevent excessive circulating cur rents from flowing in the ratio adjuster contact fingers and their interconnections, when the fingers of any ratio adjuster switch are in a bridging position where they make contact with adjacent tap contacts, a split reactor I6 is provided. This reactor has a pair of equal windings i1 and IE on a common core, these windings being connected respectively in series with arcing contacts l3 and I5. They are so wound that circulating current will produce accumulative energization of the core of the reactor l6, thus introducing a high reactanc in the path of any circulating current. However, load current which flows through the two halves of the reactor in the same direction has no appreciable efiect upon the magnetization of the core and thus will introduce but negligibl impedance in the load circuit, except during th momentary intervals when one contact finger is moving between tap contacts. During these momentary intervals all of the load current will flow through one or the other of the halves of the reactor l6.

The ratio adjuster switches and 6 and the arcing duty contactor I4 are preferably mechanically interconnected by any suitable mechanism so that they will operate automatically in the proper sequence. Various mechanisms for accomplishing this result are well known in the art so that such mechanism is only illustrated schematically in the drawing. It may consist of a Geneva gear driver l9 which is directly connected to a cam 20 for operating the arcing contactor l4 and which driver operates Geneva gears 2! and 22 which are to operate the ratio adjuster switches 5 and 6 respectively. In practice, the reversing switches l and 8 will also be driven by this same mechanism as is customary in conventional load ratio control circuits which have only one ratio adjuster switch per phase of the transformer.

Th windings I and 3 are not essential. They merely, serve to increase the voltage or number of efiective turns of the entire winding. The terminals of'the entire winding, considered as the windings l, 25,. 3 and 4, in series, are indicated at 23 and 24-;

Theoperation. of Fig. 1 is as follows: The system is shown at one end or extreme position of its range ofoperation, and a circuit through it may be considered as starting at the terminal 23, going through th winding I, through the reversing switch I, then through the winding 2 to its lowermost tap, that is to say, to the tap which is closest to its lower, terminal. The circuit then divides into two parallel branches, beginning at the ratio adjuster fingers 8. and I 0, and these parallel branches continue through the halves l1 and 18501 the reactor l 6, then through th arcing contacts l3 and i5 of the contactor l4, and then through the ratio adjuster fingers H and I2. The circuitthen. continues as a single circuit to the lowermost tap. of the winding 4, thence through all of this winding and through the reversing switch 8 and through the winding. 3 to the other terminal 24. It will be assumed that the polarities of the windings I, 2, 3 and 4 are additive in the circuit which has just. been traced between terminals 23 and 2!.

Assume, now, that it is desired to reduce the efiective number of turns between the terminals 23; and 24. and thus to reduce the voltage between these terminals. This is accomplished by rotating the Geneva gear driver I9 counter-clockwise as viewed in the drawing. The first thing that will happen will be that the arcing contacts l3 will open, thus causing all of the current to flow through the other parallel branch. Next, contact finger II will move clockwise out of engagement with the tap contact with which it is shown in engagement, and in a short time it will move into engagement with th next tap contact in the clockwise direction. Arcing contacts [3 will noW close and arcing contacts [5 will open, thus transferring the current to the other of the two parallel branch circuits, and immediately thereafter contact finger l2 will move between tap contacts into engagement with the next tap contact in the clockwise direction. The arcing contacts 15 will then reclose. It will now be obvious that the section of the winding 4 between its two lowermost taps has been removed from the circuit.

Continued counterclockwise rotation of the Geneva gear driver [9 will next cause the cam 20 to reopen the arcing contacts l3. This will immediately b followed by the disengagement of the contact finger 9 with its tap contact and its movement clockwise to the next tap contact. Arcing contacts l3 then reclose and arcing contacts l5 open and this is followed by the disengagement of the contact finger H) from its tap contact and its movement into engagement with the next tap contact in a clockwise direction, whereupon arcing contacts l5 reclose. It will now be observed that the section of the winding 2 between its two lowermost taps has been removed from the circuit. This completes two steps of operation of the system and one complete rotation of the Geneva gear driver I9. Continued rotation will repeat the cycle described above except that progressively more and more sections of the windings 4 and 2 are alternately removed from the circuit until the ratio adjuster switches 5 and 6 have been rotated clockwise until their contact fingers make engagement with the lowermost tap contact of each switch. This will correspond to having all of the windings 2 and 4 cut out of the circuit 50 that only th windings I and 3 are in series between the terminals 23 and 24.

Reversing switches and 8 are now moved to their other position. This does not interrupt the main circuit as the main circuit is not through these switches at this time. If, now, counterclockwise rotation of the Geneva gear driver I9 is continued, the successive movement of the contact fingers I I and I2 clockwise back into engagement with the top contact with whichv they are shown in engagement will insert the lower end section of the winding 4, that is to say, the section between its lowermost tap and its lower ter minal, into the main circuit in the reverse direction. Similarly, when contact fingers 9 and I move clockwise back into engagement with the tap contact with which they are shown in engagement, the corresponding end section of Winding 2 will be reversely inserted in the circuit. Continued clockwise rotation of gear I9 will then cause the sections of the windings 4 and 2 to be alternately inserted in the circuit with reverse polarity until finally substantially all of these windings are back in circuit with their polarities reversed, at which time the system will be at the other extreme end of its range of operation. Obviously, reversal of the direction of rotation of the driving gear I9 will reverse the operations described above.

In Fig. 2 the tap contacts of the ratio adjuster switch have been arranged in a straight line instead of in a circle and all but one of them have been inserted directly between the sections of the winding 2, and the tap contacts of the ratio adjuster switch 6 have been rearranged in the same way relative to the winding 4. The remaining tap contact of each ratio adjuster switch, which corresponds in each case to the lowermost tap contact shown in Fig. 1, is inserted in or makes connection to an intermediate tap in an additional winding, this winding being a winding 25 for the tap contact which is engaged by the contact fingers 9 and III and'a winding 26 for the tap contact which is engaged by the ratio adjuster contact fingers II and I2.

The voltage of the windings 25 and 26 bears a special relation to the voltage of the windings 2 and 4 respectively, and also the tap in the windings 25 and 26 is inserted in a particular place relative to the terminals of these windings. This relation is as follows: Assuming that the winding 2 has N taps, including its terminals, (and therefore has N tap contacts) which divide this winding into (N-l) equal sections, each of voltage V, then the voltage of winding 25 is (N +1) V and the tap in the winding 25 to which a tap contact is connected is so placed that the voltage between this tap contact and the lower end of the winding 25 is V and the voltage between this tap contact and the upper end of the winding 25 is NV. The same relationship exists betwee the windings 4 and 26.

The switches I and 8, while having the same general purpose as in Fig. 1 of effectively doubling the range of operation of the system by permitting substantially two revolutions of the ratio adjuster switches within the operating range, are no longer reversing switches. The fixed contacts of switch 'I are connected to the terminals of the winding 25, and the movable contact of the switch I is connected to one end of the winding 2. Similarly, the fixed contacts of the switch 8 are connected to the terminals of the winding 26, and its movable contact is connected to a terminal of the winding 4.

The operation of Fig. 2 is as follows: The system is shown in approximately the mid-position of its range, and the circuit from one terminal to the other may be traced from terminal 23 through winding I and the large section of winding 25 in series, and then the circuit divides into two parallel branches at the contact fingers 9 and I0 and continues through the reactor I6, the arcing contactor I4 to the ratio adjuster fingers II and I2, where the parallel branch circuits come together again, and the circuit continues through the high voltage section of the winding 26 and the winding 3 in series to the terminal 24. As in Fig. l, the windings I and 3 are not essential and they may be omitted if desired.

If, now, it is desired to increase the voltage between terminals 23 and 24, arcing contacts I3 may first be opened and then contact finger 9 may be moved to the next lowermost tap contact which, as shown, is at the upper end of the winding 2. Arcing contacts I3 are then reclosed and arcing contacts I5 are opened, contact finger I0 makes a follow-up movement downward to the upper end tap contact for the winding 2, whereupon the arcing contacts I5 are reclosed. It will now be observed that the low voltage section of the winding 25 has been cut out of the circuit. The next step will be to cause the successive upward movement of the contact fingers II and I2 to the tap contact on the lower end of the winding 4, the movement of each contact finger being preceded by the opening of its serially connected arcing contacts and being followed by the reclosure of these contacts before the other contact finger is moved. Continued alternate operation of the contact fingers and arcing contacts in the above directed manner will cause successive sections of the windings 2 and 4 alternately to be inserted in the circuit, thus increasing the voltage of the circuit in equal increments of voltage V for each step.

If, instead of raising the voltage of the circuit, it is desired to lower the voltage of the circuit, then switches I and 8 would be moved to their other positions. This would not affect the circuit and no current would be interrupted because the windings 2 and 4 are open circuited for the condition of the system shown in Fig. 2 so that movement of the switches I and 8 to their other posi-- tions merely connects the windings 2 and 4 to the opposite ends of the windings 25 and 26 respectively. If, now, the arcing contacts I5 are opened and the contact finger I2 moved to the uppermost or upper end tap contact of the winding 4 and this is followed by the reclosure of the arcing contact I5 and a corresponding cyclic operation of the arcing contacts I3 and the contact finger II, it will be seen that the voltage of the circuit has been decreased by the voltage between any successive pair of tap contacts. In other words, the net result has been the substitution of the winding 4 for the high voltage section' of estates hewindine. a d. sth w nd s. lhasv v l ss h n t e h gh ta ct onor. the. wind.- ing 2 t e vo tage ofthe. circuit hasheenr duc d by V volts...

It will. be understood thatv he. tap. onta ts. o hewindings 4 and, .6. w ll. in pract se. lm st a ways e a eedin a circl as s. ho nin Ri 3. and Will be described hereafter, so that reversing the direction of operation of the systern merel means that the last described motion of, the contact fingers H and I2 from. the tap contact, with which they are shown in engagement to the tap contactat the upper endof the winding 4, is the same,- as their going from, one tap contact to the next adjacent tap, contact in the reverse or opposite direction, Similar, move ment of the contactfingersil. and; Ill to, the low.

ermost tap contact of, thewindingj, the current through them in eachcase being, of course, first interrupted. and then. reestablished by theoperationot their respectiveserially connected arcing contacts, will again, reduce. the voltage of the circuit by V volts. Continued operation, step by step, will then progressively cut out: sections of the windings land 2, thusprogressively decreasing the voltage until these windings are all cut out of the circuit andonly the windings l and 3 are in series between the- terminals 23 and 24.

In Fig. 3 a. three-phase system is indicated in which corresponding-elements in thethree phases have the; same reference numerals, and distinctionbetweenphases is made by primes and double primes. Only thecomplete circuitfor onephase is shown, anditwillbe; understood that the cir.- cuits for the other two phases are exactly the same.- The. circuit for the; phase; illustrated is the same asshown in Fig- 2v except that the tapped windings withwhichthe respective ratio adjuster switches- 5. and 6 are associated; are not;in line and are therefore indicated as; being on difierent core, legs or as having out-of phase voltages. F rm e i 'd n s; I ,1; nd may be considered collectively as a winding 21- on one legof the three-le ged; core, shown in Fig. 4, and wind:- ings 3, landlfilnhy be considered collectively as a winding. 28; on another leg of the core. The interconnection of these collectively considered windings, which the circuitshown in Fig. 3 pro duces, may correspond to azig-zag connection in that, for example, theterminal 2 4 maybe a common neutral for the three-phase: system.

The, circuit of, Fig. 3 may; be operated insuch a manner asto.producea phasesh-ift inthe voltage between the terminals 23 and 24: by operating. theratio adjusters so asto vary the relative proportionsof the windingszandl in thecircuit. Actually, the only physical difference; between Eig, 2 and. the completely illustrated phase in Fig. 3.is.that thetap-contacts for the windings 2, 4, 25and 2.6. arebrought out frombetweenthe sections ofv the, winding. and are arranged circularly.

In, practice, the correspondingly: numbered switches and arcing contacts will all operate in unisonso that conditionswill be thesameat all phases (not: shown), on the same corewinding leg or, in other words,.sp thatntheyall havegvoltages which arein phasea Thatls to ,-say,,a11.ofi

. otsaid reactor and the other of said contactors in the windings. associated with each phase of the systemwillfthen have i i-phase voltages;

'While there have been shown and described particular embodiments of the invention, it will beobviousto those skilled in: the art that various change can be made without departing'from the invention, and it is therefore aimed in the appended claims to cover all such changes and modificationsasfall 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 regulating system comprising, incombination electric induction apparatus having at least two insulated windings, one of said windings hay.- insN taps which divide it intoN-l equal secions achoi v0.1tage the other windin having. three, taps with thevoltages between the intermediate tap and the other two equal to V and NV, respectively, ratio adjuster switch having IVA-,1, contacts connected respectively to said N tapaandsaid intermediate tap and having a common. contact for selectively. engaging said N+1 contacts, and a secondswitch for selectively connecting the, remaining two taps of said other winding'toanend tap of said one winding.

2 Thecombination recited'inclaiml in which said insulatedrwindings-are on a common core.

3.,A dual regulating system comprising, in combination, electric induction apparatus hay.- ingiatleast .fourinsulated windings divided into twogroups of two each, each group having one winding provided with N taps which divide it into-N-1i equal. sections, each of voltage V, the winding of each set having three taps with the voltages between the intermediate tap and the othertwo equal to-V and NV respectively, separate ratio adjuster switches each having N+1 contacts connected respectively to the'N taps and the intermediate tap of the windings of each groupand having a common contact'forselectively engaging its N+1 contacts, a secondpair. of switches-each for selectively connecting theremaining two tapsof said other winding of each group to an end tap ofjsaid one winding ofeach group, andmeans for interconnecting the common contacts of saidratio. adjuster switches so asto connect .said, groups .of winding in series.

4.. The combination recited .in claim ,3 in which each ratioadjuster has twocommcn contacts, separate interconnecting, means for connecting each common contact of,0ne.ratio adjuster switch toga correspondingcommoncontact of the other ratio. .adiuster switch, separate arcing contactors connected, respectively insaid. interconnecting means, and asplit reactor the two halves of which are connected respectively; to said interconnecting means.

5,- Electric induction apparatus comprising, a pairof .multi-tapped windings on.a common core,

. af rst paircf contacts iorselectively making connect-ion,withthe-taps-pf one of said windings; a second pair of; contacts-for selectively; making connection. with thetaps of the other of said windings a splitireactor; a pair of'arcingduty contactors, means including one half of said reactor and, one -.of said. contactors-inseries -for interconnecting onecontact ofeach of said pairs on contacts, and means including the other half series. for interconnecting;theremaining two of saidcontacts.

6.-.The;combination;.as.recited inclaim 5.:in

which said windings are on the samecore leg;

7. The combination as recited in claim 5 in for operating said pairs of contacts for voltage which said windings are on different core legs. phase angle control.

8. The combination defined in claim 5 in which said windings have in-phase voltages; ORIN P. MCCARTY.

9. The combination defined in claim 5 in which 5 said windings have out-of-phase voltages. REFERENCES CITED 10. The combination definedin claim 5 in which The following references are of record in the said windings are on the same core leg, and means m of t patent: for operating said pairs of contacts for voltage magnitude control 10 UNITED STATES PATENTS 11. The combination as in claim 5 in which said Number Name Date windings are on different core legs, and means 1,914,907 Buchhold et a1 June 20, 1933

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