US3764891A

US3764891A - Tap changing apparatus with prevention of floating tapped winding

Info

Publication number: US3764891A
Application number: US00269361A
Authority: US
Inventors: R Lingenfelter; A Sabella
Original assignee: Westinghouse Electric Corp
Current assignee: ABB Inc USA
Priority date: 1972-07-06
Filing date: 1972-07-06
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09
Also published as: SE390773B; IT991020B

Abstract

Apparatus for providing tap changes without producing a floating tapped winding. A make-before-break reversing switch is activated in sequence with load transfer and selector switches. Separate drive mechanisms move each switch with the proper synchronization. Each drive mechanism includes a geneva assembly which is driven by a common input shaft. As the input shaft is rotated, the separate drive mechanisms properly synchronize the amount and timing of the moving components of the tap changing apparatus.

Description

United States Patent 1 Lingenfelter et al.

[ Oct. 9, 1973 1 1 TAP CHANGING APPARATUS WITH PRE- VENTION OF FLOATING TAPPED WINDING [75] Inventors: Robert C. Lingenfelter; Andrew Sabella, both of Sharon, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: July 6, 1972 [21] Appl. No.: 269,361

[52] U.S. Cl 323/435 R, 200/11 TC, 200/17, 200/153 PA [51] Int. Cl G051 1/14, HOlh 19/12 [58] Field of Search 323/435 R, 43.5 S; 200/11TC,17, 18,153 P, 153 PA [56] References Cited UNlTED STATES PATENTS McCarty 323/435 R 2,675,520 4/1954 Sealey 323/43.5 R 3,612,786 10/1971 Whitman 323/435 R X 3,366,763 l/1968 Bleibtreu et al. 323/435 R X Primary ExaminerGerald Goldberg Attorney-A. T. Stratton et al.

[57] ABSTRACT 8 Claims, 12 Drawing Figures EVEN ODD ,22 2 SELECTOR SELECTOR SWITCH SWITCH LOAD TRANSFER SWITCH 30 PATENTED DU 9 5 SHEET 10F om]. 10:26 Emmi; 923

1055mm \ww PATENTEDUEI 91% 3,764,891

SHEET 8 UP 7 FIG. 2A

PATENTEB DDT 91975 SHEET U [1F 7 FIG.3

F IG.4

PATEN EU UB1 91975 SHEET S UF 7 mdE TAP CHANGING WITH PREVENTION OF FLOATING TAPPED WINDING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to tap changers for electrical apparatus and, more specifically, to tap changer mounting and drive mechanisms.

2. Description of the Prior Art Tap changers are usually associated with transformer windings having a plurality of taps thereon. The basic purpose of the tap changer is to connect a load to the transformer winding at the correct tap position. Load tap changers must be capable of changing the tap to which the load is connected while the winding is energized and load current is flowing.

Many conventional load tap changers employ a plurality of stationary tap terminals which are positioned in a circular pattern and are engaged by a movable contact that pivots around the center of the tapped terminal circle. A reversing switch connects one end of the tapped winding to the load or other electrical apparatus.

In conventional load tap changers, the total tapping range is achieved by rotating the movable contact twice around the stationary tap terminals in the same direction and changing the reversing switch. A tap change is made by rotating the movable contact from a first tap terminal, through intermediate tap terminals, to a last tap terminal. At that time, the reversing switch is moved while the movable contact is rotated, in the same direction, to the first tap terminal again. Further tap change is provided by continuing the rotation of the movable contact through the intermediate tap terminals to the last tap terminal.

This prior art tap changing arrangement requires a relatively simple tap selector switch since the movable contact rotates in only one direction when the tapped turns are being increased, or only in the opposite direction when being decreased. However, the tapped winding reversing switch required by this arrangement permits the tapped winding to become momentarily disconnected from the circuit and allows it to float. Although this has caused negligible effects in moderately sized tap changing apparatus and tapped transformer windings, extra-high-voltage tap changers utilizing this prior art arrangement are susceptible to various undesirable effects. Harmonic currents and high frequency transients which are undesirable and potentially damaging can be produced by the prior art arrangement when operated at extra high power levels.

To overcome these detrimental characteristics of prior art tap changers and to permit the reliable use of extra high power load tap changers, a different reversing technique is desirable. To prevent a floating tapped winding, it is desirable to provide a tapped winding polarity reversing switch which makes contact before breaking contact. In order for this to be practicable in high power load tap changers, the reversing must occur when the reversed voltage is zero. This can be provided when the tap selector switch is engaged with the tap terminal which does not produce a voltage change thereon when the reversing switch changes the polarity of the tapped winding.

Rotating the selector switch movable contact in one direction around the tap terminals, changing the reversing switch, and rotating the selector switch movable contact in the other direction around the same tap terminals allows the tapped winding to be reversed without floating momentarily. Therefore, it is desirable, and it is an object of this invention, to provide efficient and reliable tap changing apparatus which will permit tap changing over the complete tapping range without producing a floating tapped winding.

SUMMARY OF THE INVENTION There is disclosed herein new and useful tap changing apparatus which conveniently, efficiently and reliably changes winding taps without producing a floating tapped winding. An even tap selector switch includes a movable contact which may be rotated to engage with the even numbered tap positions. An odd tap selector switch includes a movable contact which may be rotated to engage with the odd numbered tap positions. A load transfer switch transfers the load current from one selector switch to the other selector switch. A reversing switch directs the load current through the transfer and selector switches and through the tapped winding. The path of the load current may be changed by the reversing switch.

In increasing the tapped voltage, the selector switches progressively select alternate tap positions along the tapped winding. As the selector switches are moved from the first end to the second end of the tapped winding, the load transfer switch alternates the flow of the load current through the selector switches. When the selector switches reach their furthest position at the second end of the tapped winding, a makebefore-break reversing switch is moved to reverse the path of the load current. The selector switches then move to select tap positions closer to the first end of the tapped winding.

The movement of the tap selector switches, the transfer switch, and the reversing switch is synchronized by separate drive mechanisms. The even and odd selector switches and the reversing switch are moved by coaxially positioned shafts. Each shaft is driven by a drive mechanism which is connected to a common input shaft. Each selector switch drive mechanism includes a geneva gear assembly which drives a chain. The chain has rollers thereon which enter slots in slotted plates to provide indexing motion which is coupled to the selector switch drive shaft. The reversing switch drive mechanism includes a compound geneva assembly which is driven by the input shaft and is coupled to the reversing switch drive shaft. A constant rotation of the input shaft is transferred, through the drive mechanisms, to the moving components of the tap changing apparatus in such a manner that the movements thereof are properly synchronized.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. 1 is a schematic diagram of a tapped winding and a load tap changer constructed according to this invention;

FIG. 2A is an elevational view showing the upper portion of a load tap changer constructed according to this invention;

FIG. 2B is an elevational view showing the lower portion of a load tap changer constructed according to this invention;

FIG. 3 is a top plan view of an odd selector switch contact assembly constructed acccording to this invention;

FIG. 4 is a top plan view of an even selector switch contact assembly constructed according to this invention;

FIG. 5 is a top plan view of an even drive mechanism constructed according to this invention;

FIG. 6 is a top plan view of a reversing switch contact assembly constructed according to this invention; and

FIGS. 7-11 are top plan views of the reversing switch drive mechanisms illustrating various positions thereof during the operation of the tap changing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar members in all figures of the drawings.

Referring now to the drawings, and FIG. 1 in particular, there is shown a schematic diagram of a load tap changer constructed according to this invention. The tapped winding 20 includes the tap positions or terminals 3 through 19. An odd selector switch 22 includes a movable contact 24 which may be moved to connect to the odd numbered tap terminals. An even selector switch 26 includes a movable contact 28 which may be moved to connect to the even numbered tap terminals. The load transfer switch 30 transfers the load from one selector switch to the other selector switch during a tap change. The reversing switch 32 includes the

stationary contacts

34, 36, 37, 38, 39 and 40 and the

movable contacts

42 and 44.

For descriptive purposes, the tapped winding 20 has an instantaneous voltage polarity which provides a more positive voltage at tap terminal 19 than at tap terminal 3 and the load current is flowing in the direction indicated by the arrow 46. With the load current flowing through the odd selector switch 22, the tapped voltage is at the maximum of the voltage range.

Lowering of the tapped voltage involves a definite sequence. First, the load is transferred to the movable contact 28 by the load transfer switch 30 and the movable contact 24 is moved to tap terminal 17. This lowers the tapped voltage by an amount equal to the tapped voltage v, which is the voltage between each tap terminal. A second tap voltage decrease is provided by transferring the load current to the movable contact 24, which is on tap terminal 17, and moving the movable contact 28 to tap terminal 16. This sequence is repeated through the other tap terminals until the movable contact 24 is on tap terminal 3, the movable contact 28 is on tap terminal 4, and the load current is flowing through tap terminal 3.

To further decrease the tapped voltage, it is necessary to move the reversing switch 32.

Movable contacts

42 and 44 are rotated to provide contact between the

stationary contacts

34, 36 and 37, and between the

stationary contacts

38, 39 and 40, respectively. In the position described, the tapped winding 20 is not floating nor are any tapped terminals shorted together. The reversing switch 32 is rotated further until the

stationary contacts

34 and 38 are not touched. This causes the load current to flow into the stationary contact 39, the movable contact 44, and the stationary contact 40, and out of the stationary contact 36, the movable contact 42, and the stationary contact 37. Thus, the direction of the load current through the transfer switch 30 is reversed for the same instant of time illustrated.

To further decrease the tapped voltage, the load current is transferred to tap terminal 4 through the movable contact 28 and the movable contact 24 is moved to tap terminal 5. It is pointed out that the physical movement of the movable contact 24 is now in the opposite direction from the movement before the reversing switch was activated. A further decrease in tapped voltage is provided by transferring the load current to tap terminal 5 through the movable contact 24 and by moving the movable contact 28 to tap terminal 6 in preparation for the next decreasing tap change. This sequence is repeated until the movable contact 24 is on tap terminal 19 and the load current is flowing therethrough.

With the arrangement schematically illustrated in FIG. 1, the total tapped voltage range is equal to two times the voltage of the tapped winding 20 and is changeable in increments equal to the tap voltage v,. To increase the tapped voltage, the sequence is reversed. Although not necessary, tap terminals 3 through 19 may be arranged in a circular pattern, however, the

movable contacts

24 and 28 must reverse their direction of rotation when the reversing switch 32 is changed. The mechanical construction of the tap changing apparatus which provides the proper sequencing of the selector switches 22 and 26, the trans fer switch 30, and the reversing switch 32, is explained in the following description.

FIG. 2A is an elevational view of the upper portion of the tap changing apparatus and FIG. 2B is an elevational view of the lower portion of the tap changing apparatus. The tap changing apparatus includes a support member 48 which may be constructed of an insulating material. The odd tap contacts, such as contact 11, the even tap contacts, such as contact 12, and the reversing switch stationary contacts, such as contact 34, are attached to the support member 48. The contacts l1, l2 and 34 include

connectors

50, 52 and 54, respectively, which are suitable for connecting the necessary electrical leads to the contacts.

The odd selector switch 22 includes the insulated arm 56 which is attached to the shaft 58 by the collar 60. A contact plate 62 is attached to the arm 56 and is constructed of a conducting material. A finger contact structure 64 is also attached to the insulated arm 56 and electrically connects the contact plate 62 to the tap terminals, such as tap terminal 11. A finger contact structure 66 is attached to the stationary terminal 68 and provides contact between the contact plate 62 and the stationary terminal 68. Stationary terminal 68 is electrically connected to the transfer switch 30 by suitable electrical conductors.

A top plan view of the odd selector switch 22 is illustrated in FIG. 3. The selector switch 22 is shown in the position which connects tap terminal 3 to the stationary terminal 68. Tap terminals 3 through 19 are positioned in the form of a circle on the supporting member 48, with connectors, such as connector 50, extending from the tap terminals to a connector bracing member 71.

Referring to both FIGS. 2A and 3, the shaft 58 extends through the bearing 72 which is secured by the end hood 74. The shaft 58 is rotated by the odd selector switch drive mechanism 76. As the shaft 58 is rotated, the insulated arm 56 and the contact plate 62 rotate to change the tap terminal which is connected to the stationary terminal 68. The drive mechanism 76 is constructed to rotate the shaft 58 in the proper direction and at the proper time in sequence with the other moving parts of the tap changing apparatus.

The even selector switch 26 includes the insulating arm 78, the contact plate 80, the

finger contact structures

82 and 84, and the stationary terminal 86, all of which are constructed similar to the components of the odd selector switch 22. FIG. 4 is a top plan view of the even selector switch 26 showing the circular arrangement of the even tap terminals 4 through 18 and their associated connectors and connecting brace member 88. Referring to both FIGS. 2A and 4, the insulating arm 78 is attached to the shaft 90 by the collar 92. Shaft 92 is coaxially positioned around the shaft 58 and is secured by the bearing 94. The shaft 90 is rotated by the even selector switch drive mechanism 96. As shaft 90 rotates, the insulated arm 78 and the contact plate 80 rotate to change the tap terminal which is connected to the stationary terminal 86. The stationary terminal 86 is electrically connected to the transfer switch 30 by suitable electrical conductors.

Referring to FIG. 2A, the reversing switch 32 includes a drum support 98 which is attached to the drum braces 100 and 102. The drum brace 100 contains an opening 104 through which the

shafts

58 and 90 extend. The drum brace 102 is supported from the shaft 90 by the bearing 106. The drum brace 102 includes a shaft 108 which is positioned coaxially with the

shafts

58 and 90. Satisfactory construction materials, such as a conducting material for the drum brace 102 and shaft 108, and an insulating material for the drum brace 100 and the drum support 98, may be used.

Referring to FIGS. 1, 2A and 6, the reversing switch 32 includes the

stationary contacts

34, 36, 37, 38, 39 and 40 which are positioned in a circular pattern on the support member 48. The

stationary contacts

34, 36, 37, 38, 39 and 40 consist of spring tensioned finger contact structures which are constructed to allow the

movable contacts

42 and 44 to engage therewith. The

movable contacts

42 and 44 are constructed of conducting blades which are mounted to the drum support 98 and which have tapered edges 110 for facilitating engagement with the finger contact structures.

The drum support 98 is rotated by the action of the reversing switch drive mechanism 112 on the shaft 108. The drive mechanism 112 rotates the reversing switch 32 in the proper direction and at the proper time in sequence with the other moving parts of the tap changing apparatus.

Stationary contacts

36 and 38 are electrically connected together by the conductor 114 which is also connected to tap terminal 3.

Stationary contacts

34 and 40 are electrically connected together by the conductor 116 which is also electrically connected to the load transfer switch 30. The

conductors

118 and 120 are electrically connected to the circuit or apparatus used in conjunction with the tap changer and the tapped winding 20.

In FIG. 2A, the support member 48 is secured to a housing structure 122 which houses the lower ends of the

shafts

58, 90 and 108 and the

drive mechanisms

76, 96 and 112. The housing structure 122 is mounted on top of the frame structure 124 which, as shown in FIG. 2B, is supported from the transformer casing 126 by suitable insulators, such as the insulator 128. The input shaft 130 controls the

drive mechanisms

76, 96 and 112 and is rotated by a prime mover through the gear box 132, the

universals

134 and 136, and the coupling insulator 138. Thus, the potential on the portion of the tap changing apparatus which is located above the

insulators

128 and 138 is isolated from the transformer casing 126.

The transfer switch 30 includes the

finger contact structures

140 and 142 and the vacuum switches 144 and 146, as well as other components and electrical connectors. The transfer switch and vacuum switch drive mechanism 148 is represented in block form. Mechanical input from the input shaft 130 is applied, in the proper sequence, to the transfer and vacuum switches.

A tap change is initiated by rotating the input shaft 130. The input shaft 130 must be rotated in one direction for an increase in tapped voltage, and it must be rotated in the other direction for a decrease in tapped voltage. However, the direction of the shaft 130 does not change when the reversing switch 32 is activated and the selector switches 22 and 26 change direction. The reversing motion of the selector switches 22 and 26 is provided by the drive mechanisms 76 and 96, re spectively.

The drive mechanism 96 shown in FIGS. 2A and 5 drives the even selector switch 26. The input shaft 130 rotates the

gears

152 and 154 which rotate the shaft 156. The relative position of the components of the drive mechanism 96 is illustrated for the condition where the even selector switch 22 is on tap terminal 4, the odd selector switch 26 is on tap terminal 3, and the transfer switch 30 is connecting the load to the odd selector switch 26. With this arrangement, the tapped voltage is the voltage provided by tap terminal 3.

To raise the tapped voltage, shaft 156 is rotated in the clockwise direction as indicated by the arrow 158. The geneva pinion 160 and the geneva roller 162 are underneath the geneva wheel 164 and are mechanically coupled to the odd selector switch drive mechanism 76 which operates in a manner similar to the following description of the even selector drive mechanism 96. When the shaft 156 is rotated 180, the selector switch 22 moves to tap terminal 5. The geneva gear 165 of the drive mechanism 96 does not move due to the locking action provided at the junction 166 of the geneva gear 165 and the geneva wheel 164.

As the shaft 156 is rotated beyond 180, the geneva pinion 168 moves the geneva roller 170 into the slot 172 of the geneva gear 165. When shaft 156 rotates 360 from the position shown in FIG. 5, the geneva roller 170 returns to the same position, however, the geneva gear 164 has been rotated 90 in the direction indicated by the arrow 174. Thus, a 360 rotation of the shaft 156 provides a 90 rotation of the geneva gear 165.

The geneva gear 165 is mounted on the idler shaft 176 and is pinned to the cam 178 and the chain sprocket 180. Therefore, when the geneva gear 165 rotates, the cam 178 and the chain sprocket 180 rotate. Roller chain 182 is positioned around the chain sprocket 180 and around the

chain sprockets

184, 186, 188, and 192. The chain sprockets are positioned in pairs with a separate roller chain on each sprocket.

Drive rollers

194, 196, 198, 200, 202, 204, and 206 are secured between the roller chain 182 and a lower roller chain.

When the shaft 156 rotates 360, the drive roller 194 moves into the slot 208 of the slotted plate 210 and moves the plate 210 in the direction indicated by the arrow 212. Plate 210 is mounted on the idler shaft 214 and is pinned to the spur gear 216. The spur gear 216 meshes with the spur gear 218 which is pinned to the slotted plate 220 and to the shaft 90. Thus, rotation of the plate 210 in direction 212 produces a motion of the plate 220 and the shaft 90 in the direction indicated by the arrow 222.

The

drive rollers

194, 196, 198, 200, 202, 204 and 206 are spaced at predetermined intervals along the roller chain 182. With every 360 rotation of the shaft 156, the drive rollers advance in the direction indicated by the arrow 224 to the position of the adjacent drive roller. With seven drive rollers, the shaft is indexed seven times to move the even tap selector switch 26 from tap terminal 4 to tap terminal 18. It is pointed out that similar movement of the odd selector switch drive mechanism 76, which includes eight drive rollers, moves the odd tap selector switch 22 from tap terminal 3 to tap terminal 19 during the same operation, but in alternate 180 rotations of the shaft 156.

The shaft 90 is locked in position by the projection of the lock arm 226 into a slot of the plate 220, such as the slot 228. The lock arm 226 is pivoted on shaft 230 and forced into the slots by the spring 232 and the spring stop 234. The lobes 236 of the cam 178 hold the lock arm 226 in locking position. When the geneva gear 165 is rotated to rotate the plate 220, the shape of I the cam 178 allows the lock arm 226 to disengage with the slots of the plate 220 and permit free movement thereof.

In changing the tap changer from the highest tapped voltage position to the lowest tapped voltage position, the shaft 156 is rotated in the direction opposite to that indicated by the arrow 158. The

shafts

58 and 90 rotate in one direction until their respective selector switches are at their lowest tap position. Then, the reversing switch 32 is activated and the

shafts

58 and 90 rotate in the other direction.

The reversing rotation of the shaft 90 with the nonreversing rotation of the shaft 156 may be described in connection with FIG. 5. As the tap changer is moving in a lowering direction, the roller chain 182 is moving in the direction indicated by the arrow 238 and the plate 220 is rotating in a direction indicated by the arrow 223. When the rollers are positioned as shown, the even selector switch 26 is on tap terminal 4. Since the odd selector switch 22 must move from tap terminal to tap terminal 3 and then back to tap terminal 5 before the even selector switch 26 moves from tap terminal 4, the even selector switch 26 must have a dwell period for one revolution of the shaft 156. This is provided by the absence of any drive rollers entering any plate slots during a linear movement equal to the distance D along the roller chain 182. A pin 240 on the lower roller chain engages in the slot 242 on the spur gear 216 to lock the movement of the shaft 90.

As the roller chain 182 continues to move in the direction indicated by arrow 238, the drive roller 206 enters theslot 244 of the plate 220. This now causes the plate 220 to rotate in the direction indicated by the arrow 222 even though the direction of movement of the roller chain 182 is the same. Continued movement of the roller chain 182 in the same direction moves the even tap selector switch 26 toward tap terminal 18.

Movement of the reversing switch 32 is controlled by the reversing switch drive mechanism 112 and is synchronized with the selector switch drive mechanisms 76 and 96. The reversing switch 32 moves only when the selector switches 22 and 26 are moved through the neutral position, that is, tap terminal 3, in either a raising direction or a lowering direction, FIG. 6 illustrates the reversing switch 32 in the position it maintains when the tap changer is tapping a voltage from tap terminal 3 to tap terminal 19 in the lowering direction. The

stationary contacts

34 and 37 are electrically connected together and the

stationary contacts

38 and 39 are electrically connected together as shown in FIGS. 1 and 6. When the tap changer is moving in a raising direction, the reversing switch 32 rotates in the direction shown by the arrow 248 in FIG. 6. When the tap changer is moving in a lowering direction, the reversing switch 32 rotates in the direction indicated by the arrow 250.

The synchronized movement of the reversing switch 32 is controlled by the reversing switch drive mecahnism 112. FIG. 2A illustrates an elevational view of the drive mechanism 112 and FIGS. 7, 8, 9, 10 and 11 illustrate plan views of the drive mechanism 112 in the various stages of its movement when the tap changer is lowering the tapped voltage.

Referring to FIGS. 2A and 7, the drive mechanism 112 includes the geneva wheel 252 which is keyed to the shaft 156. As the shaft 156 rotates in the direction indicated by the arrow 254, the roller 256 rotates the geneva gear 258 in the direction indicated by the arrow 260. The geneva gear 258 rotates 20 around the idler shaft 262 when the geneva wheel 252 rotates 180 from the position shown in FIG. 7. Therefore, the geneva gear 258 indexes 40 for every complete 360 rotation of the shaft 156. The roller 266 is mounted onto the geneva gear 258 above the slots 268 therein. The geneva gear 264 is keyed to the shaft 108 which rotates the reversing switch 32.

The reversing switch 32 reverses the polarity of the tapped winding 20 only once when the tap changer moves from the highest tapped voltage position, which is at tap terminal 19, to the lowest tapped terminal voltage, which is also at tap terminal 19. The reversing switch 32 similarly functions only once when increasing the tapped voltage from the lowest position, through neutral, to the highest position. Thus, several complete rotations of the shaft 156 must be made without any rotation of the shaft 108. This is provided by the intermittent motion produced by the geneva gears 258 and 264.

In the maximum raise position, the selector switch 22 is connected to the tap terminal 19 and the load is applied thereto. The reversing switch 32 is in a position which would be illustrated in FIG. 6 by rotating the drum support 98 in the direction indicated by the arrow 248. Thus,

stationary contacts

36 and 37 would be electrically connected together and

stationary contacts

39 and 40 would be electrically connected together. FIG. 7 shows the drive mechanism 112 in the maximum raise position. Since the tap changer described herein provides 32 tapped voltages plus a neutral voltage, the maximum tap position will be referred to as the 16-raised position.

The shaft 156 is rotated in direction 254 to lower the tapped voltage. The first 180 of rotation of the shaft 156 rotates the geneva gear 20 and moves the odd selector switch 22 to the position 17. Appropriate transfer switch action takes place during this rotation to transfer the load to tap terminal 18. The next l80 of rotation of the shaft 156 rotates the geneva gear 20 and moves the even selector switch 26 to tap terminal 16. Continued rotation of the shaft 156 alternately moves the odd and even selector switches and indexes the geneva gear 258. The geneva gear 264, and hence the reversing switch drum support 98, is not rotated until the tap changer is in the l-raised position. The raised portion 270 of the geneva gear 258 meshes with the indentations 272 in the geneva gear 264 to prevent rotation of the reversing switch 22 until moved by the roller 266.

FIG. 8 illustrates the drive mechanism 112 in the I- raised position which is achieved by rotating the shaft 156 seven and one-half revolutions from the position shown in FIG. 7. The geneva gear 258 has indexed 300 in direction 260 thereby placing the roller 266 in the slot 274 of the geneva gear 264. The geneva gear 264 has been rotated 9 in the direction 276. The odd tap selector switch 22 is on tap terminal 3, the even tap selector switch 26 is on tap terminal 4, and the load is through tap terminal 4. The

stationary contacts

36 and 37 and the

stationary contacts

39 and 40 of the reversing switch 32 are still electrically connected.

P10. 9 illustrates the drive mechanism 112 when the tap changer is in the neutral position. This position is produced by rotating the shaft 156 an additional 180 from the position shown in FIG. 8 in the direction 254. In the neutral position, the reversing switch 32 has been rotated a total of 45, the odd selector switch 22 is on tap terminal 3 the even selector switch 26 is on tap terminal 4, and the load current is through tap terminal 3. The movable contact 42 of the reversing switch 32 is electrically connected to the

stationary contacts

34, 36 and 37. The movable contact 42 is electrically connected to the

stationary contacts

38, 39 and 40. Thus, the tapped winding 20 is still electrically connected to the load circuit.

With an additional rotation of the shaft 156 for 180 in the direction 254, the geneva gear 258 rotates an additional 36. This rotates the geneva gear 264 9 more degrees which disengages the

stationary contacts

36 and 40 with the

movable contacts

42 and 44, respectively. Thus, the load current passed through the tapped winding 20 is reversed. The load current is through tap terminal 4, therefore, the tap changer is in the l-lower position.

The geneva gear 264 is rotated an additional nine degrees from the position shown in FIG. when the shaft 156 rotates 360 in direction 254. Additional rotation of the shaft 156 does not rotate the geneva gear 264 further since the roller 266 will not be in the slot 280. The position of the geneva gear 264 after 9 additional rotation is shown in FIG. 11. The geneva gear 258 has been rotated to the 16-lower tap position and the reversing switch 32 is locked in position by the raised portion 270 of the geneva gear 258 and the indentation 272 in the geneva gear 264.

Since numerous changes may be made in the abovedescribed apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting.

We claim as our invention:

1. Tap changing apparatus for changing tapped voltage positions on a tapped winding, comprising tap selector means having movable contact means, load transfer means, polarity reversing means, drive means having an input shaft which rotates in a first direction to lower the tapped voltage position and which rotates in a direction which is opposite to the first direction to raise the tapped voltage position, said drive means providing, upon rotation of the input shaft in the first direction, a drive sequence which moves the movable contact means in a second direction, reverses the polarity of the tapped voltage by moving said polarity reversing means, and moves said movable contact means in a third direction which is opposite to the second direction after moving said polarity reversing means.

2. The tap changing apparatus of claim 1 wherein the tap selector means comprises an even selector switch and an odd selector switch, said even selector switch selecting tapped voltage positions on said tapped winding which are electrically between the tapped voltage positions selected by said odd selector switch.

3. The tap changing apparatus of claim 1 wherein the selector switch means includes a first selector switch having a first movable contact and a second selector switch having a second movable contact, said first and second movable contacts being rotated by first and second coaxially positioned shafts, said first shaft being rotated by a first drive mechanism which is connected to the input shaft, and said second shaft being rotated by a second drive mechanism which is connected to the input shaft.

4. The tap changing apparatus of claim 3 wherein the reversing switch means comprises movable contact means, said movable contact means being rotatable by a third shaft which is coaxially positioned around the first and second shafts, said third shaft being rotated by a third drive mechanism which is connected to the input shaft.

5. The tap changing apparatus of claim 3 wherein the first drive mechanism comprises a geneva pinion connected to the input shaft, a geneva gear driven by said geneva pinion and connected to a sprocket gear, a chain having a plurality of rollers positioned thereon being driven by said sprocket gear, a first slotted plate connected to a first spur gear, a second slotted plate connected to a second spur gear which is meshed with said first spur gear, one of said slotted plates driving the first shaft, said chain and rollers being positioned and dimensioned to permit one of said rollers to engage with a slot on said first slotted plate and rotate the first shaft in the second direction when the input shaft is rotated in the first direction, and to permit one of the said rollers to engage with a slot on said second slotted plate and rotate the first shaft in the third direction when the input shaft is rotated in the first direction.

6. The tap changing apparatus of claim 4 wherein the third drive mechanism comprises a first geneva pinion connected to the input shaft, a first geneva gear driven by said first geneva pinion and connected to a second geneva pinion, a second geneva gear driven by said second geneva pinion, said second geneva gear driving the third shaft.

7. Tap changing apparatus for changing tapped voltage positions on a tapped winding comprising first and second selector switches, said first selector switch selecting tapped voltage positions on said tapped winding which are electrically between the tapped voltage positions selected by said second selector switch, said first selector switch having a first movable contact which is driven by a first drive mechanism, said first drive mechanism including a first geneva pinion driven by an input shaft, a first geneva gear driven by said first geneva pinion and connected to a first sprocket gear, a chain having a plurality of rollers positioned thereon driven by said first sprocket gear, first and second slotted plates connected to each other, said chains and rollers being positioned and dimensioned to engage with the slots in said plates to rotate said plates, said second selector switch having a second movable contact which is driven by a second drive mechanism, said second drive mechanism including a second geneva pinion driven by the input shaft, a second geneva gear driven by said second geneva pinion and connected to a second sprocket gear, a second chain having a plurality of rollers positioned thereon and driven by said second sprocket gear, third and fourth slotted plates connected to each other, said second chain and rollers being positioned and dimensioned to engage with the slots in said third and fourth plates and rotate said third and fourth plates a reversing switch comprising a third movable contact driven by a third drive mechanism, said third drive mechanism comprising a geneva assembly which moves said third movable contact in sequence with the movement of the first and second movable contacts;

8. The tap changing apparatus of claim 7 wherein the first, second and third movable contacts are respectively rotated by first, second and third coaxially positioned shafts, said first, second and third shafts being respectively rotated by the first, second and third drive mechanisms.

Claims

7. Tap changing apparatus for changing tapped voltage positions on a tapped winding comprising first and second selector switches, said first selector switch selecting tapped voltage positions on said tapped winding which are electrically between the tapped voltage positions selected by said second selector switch, said first selector switch having a first movable contact which is driven by a first drive mechanism, said first drive mechanism including a first geneva pinion driven by an input shaft, a first geneva gear driven by said first geneva pinion and connected to a first sprocket gear, a chain having a plurality of rollers positioned thereon driven by said first sprocket gear, first and second slotted plates connected to each other, said chains and rollers being positioned and dimensioned to engage with the slots in said plates to rotate said plates, said second selector switch having a second movable contact which is driven by a second drive mechanism, said second drive mechanism including a second geneva pinion driven by the input shaft, a second geneva gear driven by said second geneva pinion and connected to a second sprocket gear, a second chain having a plurality of rollers positioned thereon and driven by said second sprocket gear, third and fourth slotted plates connected to each other, said second chain and rollers being positioned and dimensioned to engage with the slots in said third and fourth plates and rotate said third and fourth plates a reversing switch comprising a third movable contact driven by a third drive mechanism, said third drive mechanism comprising a geneva assembly which moves said third movable contact in sequence with the movement of the first and second movable contacts.