US2942073A - Tap changing switch for electrical apparatus - Google Patents

Description

June 21, 1960 Filed March so, 1959 4J.R.BARR

TAP CHANGING SWITCH FOR ELECTRICAL APPARATUS 2 Sheets-Sheet 1 June 21, 1960 J. R. BARR TAP CHANGING SWITCH FOR ELECTRICAL APPARATUS Filed March 30, 1959 2 Sheets-Sheet 2 United States Patent TAP CHANGING SWITCH FoR ELECTRICALy APPARATUS t Filed Mar. 30, 19.59, Sel'. No. 803,025

13 Claims. (Cl. 20D-J4) This invention relates to a tap changing switch for electrical apparatus, and more in particular to an improved no-load tap changer especially adapted for use in changing the taps on a transformer. ous, of course, that While the following disclosure is directed primarily to the application of the tap changer to a transformer, I do not intend to limit my invention solely to such application.

Transformers, particularly the type that are employed in systems for the transmission and distribution of electrical power, are frequently operated under conditions requiring periodic variation in the voltage ratio of the transformer, and for this purpose the transformers are provided with taps. The taps are .connected to suitable switching means so that the number of active turns .in the transformer may be varied as desired. The present invention relates to a tap switch suitable for such application. A tap switch may `either be designed to vary the ratio of the transformer under load conditions, or it may be a no-load switch that is not intended to interrupt any current. The present invention is intended primarily to It is therefore, an object of this invention to provide an improved tap changing switch for electrical apparatus.

It isalso an object to provide an economical rio-load tap changing switch for electrical apparatus requiring less space than the previously disclosed rotary-type.

It is a further object of this invention to provide a noload tap changing switch especially adapted for transformers and the like, in which the clearance between all adjacent contacts is not dictated by the maximum voltage that may appear between any two contacts.

A still further object of this invention is to provide a no-load tap changing switch for transformers and the like characterized by the fact that it is more economical than previously employed rotary-type switches, does not require as much space as previously employed rotary-types and in which the contact bars are more conveniently arranged for connecting to the taps of the transformer windings.

It will be obvi- Briefly stated, in accordance with my invention, I provide a tap changer for electrical apparatus comprising a pair of parallel spaced apart rows of xed contacts. These contacts have arcuate contacting surfaces, preferably being cylindrical, and are staggered so that the fixed-contacts of one row are not in line with the 'fixed contacts of the other row. Means are provided for selectively bridging between the contacts of the rows comprising an operating means l movable between the rows of fixed contacts and parallel thereto. Contact holding means are pivotally mounted on the operating means, and bridging contact means held in the holding means are provided with a pair of arcuate contacting surfaces resiliently urged toward the rows of Y contacts. v

provide an improved switch of the latter type, i.e., a l

no-load tap switch.

Previous no-load tap changing switches of one type have generally been comprised of a plurality of parallel extending cylindrical contact bars uniformly spaced about a common axis and connected to the various taps of the transformer. A movable contact was arranged for rotation about the common axis, and was arranged to selectively bridge adjacent contact bars to provide the desired tap connections. While this arrangement is functionally satisfactory, the mountingl arrangements of the components required a relatively expensive structure in order to provide the necessary insulation and mechanical strength, and the circular arrangement of the components required an appreciable mounting space.

As an example of a previous application employing a rotary-type tap changer, a transformer was provided having a secondary winding comprised of two sections with three taps on the end of each section adjacent the other section. In this arrangement, the tap changing switch has six contact bars arranged in a circle, with adjacent contact bars being connected to the tap of opposite sections so that the number of total active turns in the winding would be increased or decreased progressively by rotation of the movable contact. When a rotary-type switch is employed in this type of system, the entire voltage of the tap portions of both sections appears between two of the adjacent rotary contacts, and thus in order to maintain symmetry, the insulation between each pair of adjacent contacts must be sucient to withstand the voltage of the entire tapped portions of the winding. In addition, the leads connecting the taps of the winding to the contact bars must be well' insulated since adjacent taps are connected to opposite sections of the winding. Consequently, the rotary-type of switch has not been found adaptable readily to minimization of space required for the changing of taps.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention, it is believed that the invention will be better understood Afrom the following description taken in connection with the accompanying drawing.

In the drawing:

Fig. l is a perspective view of a tap changing switch according to one embodiment of my invention, and illustrating the switch in one position.

Fig. 2 is -an enlarged cross-sectional view of the bridglrg clontact arrangement of the tap changing switch of A 1g.

Fig. 3 is a perspective view of the bridging contact arrangement of Fig. 2.

Fig. 4 is -a top View of a contact and -a portion of the bridging contact assembly of the switch of Fig. 1, and illustrating the electrical contact between these members,

Fig. 5 4is -a side View illustrating a portion of the switch of Fig. 1 in an intermediate position,

Fig. 6 is a perspective view of a portion of the switch rof Fig. l illustrating the bridging contact in an intermediate posit-ion, and

Fig. 7 is a circuit diagram illustrating a typical application of the tap changing switch of Fig. 1 as vconnected to the windings of a three-phase transformer.

Refering now to the drawing, and more in particular to Fig. 1, therein is illustrated a tap changing switch comprising a plurality of fixed contacts mounted on a rigid insulating panel 10. The contacts are disposed in two parallel rows, for example, with contacts 11, 12 and 13 comprising one row of contacts, and contacts 14, 15 and 16 comprising the other row of contacts. The six contacts 11, 12, 13, 14, 15 and 16 are preferably cylindrical and extend in parallel relationship with each other, preferably perpend-icularly to the panel 10. The six.contacts 11 through 16 are also staggered so that a perpendicular line joining a contact of one row would .cross the other row at a point equidistant between two contact-s of the other row. For example, a perpendicular line extending from the contact 14, to the row of con` g.. tacts including contacts 11, 12 and 13, would cross the latter row at a point equidistant betlween the contacts 11 and 12.

While the illustration of Fig. 1 shows a tap changing switch employing only three lfixed contacts in each row, it will beobvious that any number of such contacts 'may be Aemployed without departing rfrom the spirit or scope of my invention. Y

A movable contact for bridging the xed contacts of the two rows yis provided comprised of `a contact holding member 20, one movable contact 21 adapted to contact the fixed contacts of the row including fixed contacts 1 1, 12, and 13, and another movable contact 22 adapted vto contact the Vfixed contacts of the row including contacts 14, 15 and 16. Als may be more clearly seen in Fig. ,2, the contact holding member 20 may be a. tubular metallic member in which'an outerrtufbular contact holder M23 is slidably mounted. An inner tubular contact holder 2 4 is ly that'they do not interfere with the movable contact assembly when the movable assembly is bridging contacts between the two rows. As will be `disclosed in more detail in the following paragraphs the ends of the insulating bars 38 must'also be suiciently close that they will be able to nudge ithe movable contacts from engagement vwith the fixed contacts before axial force on "the bar's 38 'is transmitted --tg'o the movable contact assembly by way of Vthe slots 36. Thus, assuming that a vertical .upward force were `applied -to the insulating the bars 3S in the arrangement of Fig. l, ythe upper end 50 of Afdlerlower Yinsulating bar would contact the l movable contact 22 to nudge it slightly from engagement with the fixed yContact '16 'before the flower end of the slot 36 engages the pins 35. Any suitable operating mechanism may be provided for moving the insulating bars .3.8 axially..

slidably mounted in the outer contact Kholder 23. The

outercontactfholder 23 extends beyond the contact holding member at one end thereof, where it is rigidly fastened ,to the movable contactV 22. Similarly, the inner contact holder 24 "extends beyond the other end `o f the contact holding member 20, where it is rigidly fastened to the other contact 21. A helical spring 25 is provided within the -inner contact holder 24, the spring 25 biasing both of the movable contacts 21 and 22, along with their tubular holders 24 and 23 respectively, outwardly of the contact Hholding member 20. Means such as a screw 26 threadedto the wall of the Contact holding member 20, is provided to limit the inwardly and outwardly movement of the 'movable contacts, such as by engaging slots l 27 land 28 in the walls of the tubular contact holders 2,3

and 24 respectively. In order to assure electrical contact between movable contacts, a vflexible conductor, such as braid vconductor 29 may be provided extending between the contacts 21 rand 22 within the helical spring 25.

I n tthe arrangement of Fig. lu the moving Vcontact assembly bridges the liixed contacts 13 and '16, with the movable contact 2l contacting fixed contact ,13, and movable contact 22 contacting fixcd Contact 16. If `it is now desired to move the ,movable contact assembly so that it The contacts 21 and 22, which may be more clearly seen in Fig. 3, are provided with arcuate portions 30 joined on either 'side by `inclined portions 31. The linclined portions 31 may lalso be tapered, as shown in Fig. 3. As4 illustrated in Fig. 4, the Iarcuate surface` 30 has a radiiisofcurvature slightly less than` that ofthe fixed contacts such as the Contact 13, so that the movable contact 2,1v contacts the fixed contact V13 only at the lines of junction 32 between the arcuate surfaces 30 4and the inc-lined surfaces 31. This arrangement assures two spaced apart line or point contacts between the moving 'and 4fixed contacts, and is therefore preferred to the arrangement in which the contacts have Ithe same shape, sinc'ethe latter type electrical contact may be established at only one point.

Referring now to Fig. 5, the Contact holding member 20 is provided with a pair of pins 35 extending normal to the laxis of the member 20 and on opposite sides of the member 2,0. The'pins 35 extend through slots 36 in parallel extending plates 37 (see also Fig. l). The ends of the plates 37 are4 bolted or otherwise rigidly afxed to insulating bars 38 extending in opposite directions from the movable contact assembly. The bars 38 e'xtend parallel to the rows of `fixed contacts, and substan- Vtially intermediate the rows o f contacts. AxiallyV extending slots 39 are provided in the bars 38, and the bars 38 are supported for axial movement between the fixed rows o-f contacts by bolts 40 extending through the slots 39 tothe panel 1l). Spacers 41 may be provided `surrounding the bolts 40 "between the panel V10 and insulating bars 3 8 to space the bars 38 yfrom the panel. `In order to provide sutiicient clearance between4 the plates 37 for 4ther-moving contact assembly, spacers 42 may also be provided r'between the plates 37 and the bars 38 surrounding the bolts `holding the plates 37 to ythe insulating bars. v

Referring :again to Fig. l, the movmg contact assemblfyv is therein illustrated bridging the fixed contacts 13` and 16. The ends of the insulating bars l5S/toward bridges the'x'ed contacts 13 and 15 an upward force is applied to either of the'insulating bars 38. Reference to an upward direction, is of course purely descriptive to facilitate the description of the operation of the mechanis'm as disclosed in Fig. l, since the tap changing mechanism of my invention may be disposed at any angular position. The initial upward movement of the insulating bar 38 will not result in any movement of the movable contact assembly, until the upper end 5t) on the lower insulating bar engages the movable contact 22. At the time that the end 50 engages the contact 22, the upward movement of the bar 3S has not resulted in engagement between the bottom of the slot 36 and the pin 35, so that the lower .plate 50 nudges the contact 22 upwardly. This results in the compression of the spring 25 within the movable Contact assembly, to permit the upward movement of the Contact 22. After the contact 22has moved sufficiently upwardly, the lower inclined surface 31 of the YContact ,'22 engages the fixed contact 16 and vthecontact 22 is, free to move out of engagement with the fixed contact 16, upon further upward movement of the insulatingbars 38. After the contacting surface of movable contact 22 has moved out of engagement with the fixed contact ,16, fhe lower end of thc-slot 3o engages the pin 3'5, sothat further upward movement of the insula.ing bars 33 results in the .pivoting of the movable Contact assembly about hte axis of the fixed contact 13. This pivoral movement continues, with further upward movement ofthe bars 38, untilthe upperinclined surface 31 of the contact 2,2 engages the next adjacent contact 1S, as illustrated in Fig. 6. The Contact between the upward in'- clined surface of the movable contact 22 and the tixcd contact 15 results in the depression of the spring 25, which permits ythe contact 22 KVto snap into full contacting engagement with the fixed contact 15. This snap action permitsminor errors in alignment between individual tap selectors when severai selectors are operated from a common control, and also permits minor` errors Vin indexing of the operating mechanism for the selectors.

l The Vabov disclosed arrangement including 'the -slots 36 and plates 50 have been provided in order to assure the release of 'the correct movable contact upon the application of force to the insulating bars. T has, `for example, if asimple pivot were provided `for the pins 35, it WOuld. -be.poS,S.ibie thatupward force-ou the bars 38 would result` in the releaseof the movable contact 21 rather-than the movable-contact 22. Such a condition could occur as a result .of unequal friction within the movabler contact, assembly 'or between the'fixed'and 'movable. contacts. In thear'rang'ement of Fig. 1,'however, the desired? movable contact-is nudged out of.` contact relationship with the fixed contact before theapplicationofforce,

group 64is connected to the fixed contact 11.

by way of the pins 35, to the other movable contact. Further, in the arrangementof Fig. 1, if the movable contact 21 should accidentally move upwardly before the contact 22 is moved, itwould strike the upper plate 50, which would prevent its release. v

Referring now to Fig. 7, which illustrates a typical application ofthe tap changer of Fig. 1, a three-phase transformer is provided vhaving parallelinsulating cylinders 60,61 and 62. Each of the insulating cylinders is provided with a winding having an upper portion 63 of a plurality of turns separated from a lower portion 64 of a plurality of turns. The insulating cylinders 60, 61 and 62 may surround the winding legs of a magnetic core (not shown) according to conventional practice, and other windings (not shown) may also be employed inductively coupled to the winding groups 63 and 64. A tap changing device of the type illustrated in Fig. 1 is mounted on each winding cylinder between the upper and lower groups of windings 63 and 64, with the panels lying in a vertical plane and the axes of the insulating bars 38 being horizontal. All of the panels 10 lie in the same plane, and the insulating bars 38 .of adjacent switches may be joined as illustrated in Fig. 7. The insulating panels 10 may be spaced from their respective winding cylinders to permit connection of tap leads to the undersides of the panels, and any suitable support structure may be provided for rigidlyholding thetap switches in place. A rack 66 may be provided on the extremities of one of the insulating bars 38, and a pinion gear V67 engages the rack to translate rotary motion of a suitable tap operating means 68 by way of a gear box 69 if desired, to axial movement of all of the insulating bars 38'and hence the movable contact assemblies.

The lower end 70 of each upper winding group 63 is and similarly the upper end 71 of each lower winding A tap 72 of each upper winding group is connected to the fixed contact 1,6 and a corresponding tap 73 on each lower winding group is connected to the fixed contact 13. An intermediate tap 74 on each upper winding group is connected to the intermediate fixed contact on the upper row of contacts, and 'similarly an intermediate tap 75 on each lower winding group is connected to the intermediate fixed contact 12. With this arrangement, when the movi,

able contact bridges the contacts X11 and 14, the maximum number of turns will appear between the upper terminal l80 of each winding group63 and the lower terminal 8-1 of each winding group 64. When contact is made between the fixed contacts 12 and 14, the total number of .turns between the winding terminals 80 and 81 is reduced by the number of turns appearing between the end 71 of the winding group 64 and the intermediate tap 75 of the winding group 64. When the movable contact assembly bridges the contacts 15 and 12, the total number of turns .between terminal 0 and 81 isrfurther reduced by the number of turns between the lower end 70 of the upper winding group and the intermediate tap 74 ofthe upper winding group. When the movable contact assembly bridges the yfixed contacts 13 and 15, the number of active turns between the terminals 80 and 81 'is still further reduced by the number of turns between the taps 75 and 73 of the lower winding group, and when contacts 13 and 16 are bridged, the minimum number of turns appears between the terminals 80 and 81.

In the arrangement of Fig. 7, it is to be noted that they dition, Fig. 7 illustrates that the tap changing switch of my invention may be conveniently placed adjacent the ends of the winding groups of a transformer without thc necessity for heavily insulating the tapped leads, since adjacent contacts in each row of fixed contacts are all connected to the same winding group. Thus with this arrangement the tap leads may be very short and still be physically separated so that they require little or no insulation. The tap leads may be sufficiently short that they are self supporting.

When the tap changing switch of my invention is employed as illustrated in Fig; 7, tap changes may be made simultaneously on each of the switches of a three-phase transformer by the use of a simple hand crank connected to the bar of one of the switches. The assembly also requires a minimum space since the dimension of the switches radially of the windings is minimized and no complex connecting system is required between the adjacent tap changing switches.

It will be understood, of course, that, while the form of my invention herein shown and described constitutes the preferred embodiment of my invention, it is not intended herein to illustrate all of the possible equivalent forms or ramifications thereof. It will also be understood that the words employed are words of description rather than of limitation, and that various changes may be made without departing from the spin't or scope of the invention herein disclosed, and `it is aimed inthe appended claims to cover all such changes as fall within the true spirit and scope ofi the invention.

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

l. A tap changer for electrical apparatus comprising a pair of parallel spaced apart rows of staggered fixed concontacts, and means for selectively bridging between the contacts of said rows comprising operating means movable between said rows in parallel relation thereto, contact holding means pivotally mounted on said operating means, and bridging contacting means held in said holding means and having contact surfaces resiliently urged toward said rows.

2. A tap changer for electrical apparatus comprising first and second parallel spaced apart rows of staggered parallel extending fixed cylindrical contacts adapted to be connected to said apparatus, and movable contact means for selectively connecting one contact of said first row to one contact of said second row, said movable contact means comprising operating means movable parallel to said contact rows and between said rows, contact holding means pivotally mounted on said operating means, and first and second bridging contacts held by said holding means and resiliently' urged towards said first and second rows respectively.

3. A tap changer for electrical apparatus comprising first and second parallel spaced apart rows of staggered parallel extending fixed cylindrical contacts adapted to be connected to said apparatus, and movable contact means for selectively connecting one contact of said first row to one contact of said second row, said movable contact means comprising operating means disposed between said rows of contacts and adapted for linear movemen-t parallel to said rows, contact holding means pivotally mounted on said operating means on an axis parallel to the axes of said fixed contacts and equal distance from said rows, and first and second bridging contacts held by said holding means and resiliently urged towards said first and second rows respectively.

4. A tap changer for electrical apparatus comprising first and second parallel spaced apart rows of staggered parallel extending fixed cylindrical contacts adapted to be connected to said apparatus, and movable contact means for selectively connecting one contact of said first row to one contact of said second row, said movable contact means comprising operating means disposed between said rows and adapted for linear movement parallel to said rows vin a plane vnormal to the axesof said fixed contacts, Contact holding 'means pivotally mounted about an axis parallel, to `the axes of fsaid fixed contaetsjand equal distance from said irows, and -rst jands'econ'd bridging c"ontacts having' accurate contacting surfaces, said bridging contacts being held by said holding means and being resiliently 'urged toward contacting relationship with the contactsfof said iirst and -second rows respectively.,

'5. The tap changer of claim `4 in which the radius of curvature of the accurate contacting surfaces of said bridging contacts 'i'ssrnaller' 'than ythe radius of curvature of said xed cylindrical contacts.

6. A 'tap changer for electrical apparatus comprising iirst and second parallel spaced apart rows of staggered parallel extending iixe'd cylindrical contacts adapted to be connected lto, said apparatus, and movable contact means Ytor vselectively connecting one Contact of said first row to one contactof said lsecond row, said movable contact means comprising operating-means disposed between said rows and adapted for linear movement parallel `to said rows `in a plane normal to the axes of said fixed contacts, contact 'holding means pivoted about an axis parallel to the axesof fsaid' fixed contacts and equal distance from vsaid rows, first and second bridging contacts held by said holding means and resiliently urged toward said nrst and second rows-respectively, said holding means being pivoted 'in slots in saidy operating means, and means for'urging saidbridging contacts from contacting relationship with said xed contacts upon movement of said operating meansl before movement is transmitted to said holding vmeans by way of said slots. i

7.` A tap changer for electrical apparatus comprising first and second'parallel spaced apart rows of staggered parallel extending iixed cylindrical contacts adapted to be connected to said apparatus, and movable contact means for selectively connecting one contact :of said first row to one lcontact of said second ro-w,l said movable contact means comprising operating means disposed between said rows and adapted for linear movement parallel to Asaid rows contact holding means pivoted in slots in said operating means about an axis parallel to the axes of said tixed contacts, Vsaid slots extending parallel to said rows, first and second bridging contacts held by said holding means and resiliently urged toward said first and second rows respectively, and means for urging said bridging contacts from contacting relationship with said iixed contacts upon movement of said operating means before movement is transmittedto said holding means by way of said slots.

S. A tap changer for electrical apparatus comprising first and second parallel spaced apart rows of staggered parallel extending fixed cylindrical contacts adapted to be connected to said apparatus, and movable contact means for selectively connecting one contact of said iirst row to one Contact of said Vsecond row, said movable contact means comprising insulating shaft means disposed betweensaid rows and adapted `for linear movement parallel to said rows, parallel spaced apartslotted members 'aiiixed to said shaft means for movement therewith, slots in said parallel members, contact holding means pivotally lmounted in said slots about an axis parallel to the axes of -said iixed'c'ontacts, first-and second bridging contacts held by said holding means and resiliently urged toward said lfirst and. second rows respectively, and means on said 'insulating shaft adapted to selectively engage said bridging "contacts to urge them from contacting relationship with "fixed lcontacts upon movement of said insulating shaft before movement is transmitted tosaid holding means by lway of said slots.

9. A tap changer for electrical apparatus comprising -flrst and second parallel spaced apart rowsfolf :staggered 'parallel extending Aited cylindrical contacts :adapted 'to be vconnected to said apparatus,` and miovablc'icofnta't means for selectively connecting lon'e'cont'act of said `first -roW to rone contact of'said second row, Ysaid movable fcontact means fcom'p'rising insulating shaft means 4disposed between said rows vadapted 'for linear movement parallel to 'said `rows lin a 'plane normal to the axes of said 1fixed contacts, 'parallel pivot plate members axed to said insulating shaft means `for movement therewith, said .pivotpliate means being spaced apart and having slots extending thereto, 'contactholding means ,pivotally mounted in ksaid slots about an axis parallel to the axes of said affixed contacts an equal ldistance from said rows, nrst and second bridging contacts Aheld by said holding means and resiliently urged ltoward said first and second rows respectively, and means aiiixed vto said insulating shaft means land adapted to selectively engage'said bridging contacts to nudge them from contacting relationship with said fixed contacts upon movement of said insulating shaft means before movement of said shaftmeans is transmitted to said holding means by way-of s aidslots.

'10. A'tap changer for electrical apparatus comprising an insulating panel, `first land second parallel spaced apart rows of staggered cylindrical contacts aixed to said panel and extending normal thereto, said contacts being adapted to be connected to said apparatus, and movable contact means lfor selectively connecting one contact of said first row toonevcontact of said second row, said movable contact means comprising operating shaft means disposed between said rows and adapted for linear movement parallel to said rows in a plane parallel to said panel, holding means, means affixed to said insulating shaft means for loosely pivotally holding said holding means o-n a pivotal axis parallel to the axes of said -ixed contacts an equal distance from said rows, rst and second bridging con- 'tacts having arcuate contacting surfaces, said bridging contacts `being held by said holding means and being resiliently urged toward contacting relationship with the contacts Vof 'lirst and second rows respectively, and means aiiixed to `said insulating shaft means and adapted to engage said bridging contacts selectively to urge them from contacting relationship with the contacts of first and 'second rows upon movement of said insulating shaft means before movement is transmitted to said holding means by way of said pivotal axis. p

l1. The tap `changer of claim 10 in which the radius of curvature of the arcuate contacting surfaces of said bridging contacts is less than the yradius of said cylindrical kcontacting surfaces of said bridging contacts engage said fixed contacts.

References Cited in the tile of this patent UNITED `STATES PATENTS 516,379 Muller Mar. 13, 1894 2,255,501 Blume Sept. 9, 1941 2,679,558 Raupach May 25, 1954 2,796,473 Davis a June 18, 1957

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