US3155782A

US3155782A - Switch actuating mechanism for controlled speed tap changer

Info

Publication number: US3155782A
Application number: US810489A
Authority: US
Inventors: Jr Gordon A Wilson
Original assignee: McGraw Edison Co
Current assignee: McGraw Edison Co
Priority date: 1959-05-01
Filing date: 1959-05-01
Publication date: 1964-11-03
Anticipated expiration: 1981-11-03

Description

Nov. 3, 1964 e. A. WILSON, JR

SWITCH ACTUATING MECHANISM FOR CONTROLLED SPEED TAP CHANGER 4 Sheets-Sheet 1 Filed May 1, 1959 .INVENTOR. Gordan fl. 21425072 (/3: BY i F SWITCH ACTUATING MECHANISM FOR CONTROLLED SPEED TAP CHANGER 4 Sheets-Sheet 2 Filed May 1, 1959 12b 74 7&

w w z a w m 6 0 7 o W m a fi vk 4/ w W m a m w Lg W fl fi in). W m #m 9 o a m r J 8% W 0 1 4/ 3 6 V.. o a M a B w w a w 5 a M 4 m. 4W .7 8 Z 4 3 2 I 7 a4 m k z 0% w Maw tw 22/ a a u. a

Nov. 3, 1964 G. A. WILSON, JR

SWITCH ACTUATING MECHANISM FOR CONTROLLED SPEED TAP CHANGER 4 Sheets-Sheet 3 Filed May 1, 1959 Vac u mxQm m EB Q ms Em Geneva Pinion Displacement r J n w NZ WM/ m TM Z a m Y B fittormy Nov. 3, 1964 e. A. WILSON, JR 3,155,782

swITcl-x ACTUATING MECHANISM FOR CONTROLLED SPEED TAP CHANGER 4 Sheets-Sheet 4 Filed May 1, 1959 INVENTOR 60721072 #4. M'Zson d3".

fit tarney United States Patent SWHCH AQTUATENG MECHANHSM Fill; ECQN- TRQLILED SPEED TAP CHANGER Gordon A. Wilson, l ra, Washington, Pa, assimior to itic'Graw Edison (iompany, Milwaukee, Win, a corporation of Delaware Filed May l, 1959, tier. No. 81%489 21 Claims. till. Edd-12) This invention relates to switching mechanisms and more particularly to tap changers for stationary induction apparatus.

A tap changer is often utilized to accomplish voltage regulation of stationary induction apparatus. Usually the tap changing mechanism is operated under load while the stationary induction apparatus is electrically energized, and the contact movement should therefore be at a relatively high speed to minimize contact erosion. l-ieretofore it has been conventional to utilize a drive mechanism in the tap changer incorporating a resilient energy storage means that actuates the movable contact with a snap action. Such spring-drive mechanisms are not entirely satisfactory in that they do not positively control the speed of contact movement but act only as initiators of motion. The movable contact is not disengaged from the preceding stationary contact with optimum speed to insure minimum contact erosion, and the movable contact is brought into en agement with the succeeding stationary contact at maximum velocity with the result that contact bounce occurs drawing repeated arcs between movable and stationary contact until the movable contact finally comes to rest. As a consequence contact life is relatively short and the mechanical shock, vibration, and unbalanced inertial forces accompanying the snap action necessitate frequent servicing and maintenance of the tap changer and result in short mechanical life thereof. Further, conventional load tap changing equipment utilizing resilient stored-energy drive means is unnecessarily bulky and heavy.

it is an object of the invention to provide a direct-drive tap changing mechanism which positively controls the speed of switching and thus insures maximum contact life.

Another object of the invention is to provide an improved tap changer which positively indexes the movable contacts from one stationary contact to a succeeding stationary contact and inherently insures positive mechanical interlocking of the movable contacts.

Still another object of the invention is to provide a tap changing mechanism in which the movable contact starts slowly and is thereafter rapidly accelerated to optimum velocity for eiiicient are interruption as the contacts open.

A still further object of the invention is to provide a tap changer in which the movable contact is not snapped at maximum velocity into engagement with a succeeding stationary contact but rather is decelerated to a fraction of its maximum velocity before the contacts close.

it is a further object of the invention to provide a tap changing mechanism which decelerates the movable contact to a fraction of its maximum velocity before the movable contact engages a succeeding stationary contact and positively constrains the movable contact as it is slowed down and until it is brought to rest in engagement with said succeeding stationary contact, whereby contact bounce is eliminated and mechanical shock and vibration are minimized.

A still further object of the invention is to provide a switching mechanism which gradually accelerates the movable contact during the initial portion of the indexing thereof, which rapidly accelerates the movable contact to optimum velocity for efficient interruption before the contacts open but provides gradual change of velocity over a substantial portion of the velocity-time characteristic on both sides of the maximum velocity point where slowing down of the contact begins, and which gradually decelerates the movable contact during the final portion of the motion as the movable contact approaches its final position at rest with a succeeding stationary contact, whereby switching action is smooth and shock, unbalanced inertial forces, and vibrational effects are minirnized.

Still another object of the invention is to provide a tap changing mechanism wherein the slope of the midportion of the velocity-time characteristic of the movable contact chan es gradually from plus one through zero to minus one, whereby inertial forces are minimized in the indexing of the movable contact.

Another object of the invention is to provide a tap changing mechanism which alternately indexes a pair of movable contacts and is adapted to lock one movable contact at rest while simultaneously actuating the other movable contact and to positively control the speed of said other movable contact while indexing it into engage- 1611i with a succeeding stationary contact. A further object is to provide such a tap changing mechanism having novel means for positively indexing and controlling contact speed including a rotatable index plate carrying a plurality of cam followers and a positive-motion cam adapted to sequentially engage and peripherally displace the cam followers. A still further object is to provide such a tap changing mechanism wherein the cam is rotatably driven in a series of steps to index a movable contact between stationary contacts and is adapted to positively engage a cam follower and displace it in the first step before the contacts open to a position most advantageous for rapid acceleration of the movable contact during the succeeding step, to start the cam follower slowly and then accelerate it rapidly during contact interruption and decelerate the cam follower while positively constraining it to close the contacts slowly and prevent contact bounce during the second step, to positively remain in engagement with the cam follower during the third step until the cam engages a succeeding cam follower, and also to positively lock the movable contact at rest.

Still another object of the invention is to provide an improved tap changing mechanism wherein the gradual acceleration and deceleration at the ends of the motion transmitted by an intermittent motion device are superimposed upon the motion of a cam having gradual change of velocity near the midportion of the velocity-time characteristic to provide smooth action of the rotatable contact and which also permits the prime mover to start without load.

A further object of the invention is to provide a load tap changing mechanism that is substantially smaller in size and lighter in weight than conventional spring-drive tap changing mechanisms.

Another object of the invention is to provide a load tap changing mechanism that is much simpler in construction and much more rugged than prior art springdrive load tap changing units.

A specific object of the invention is to provide a tap changer wherein the intermittent motion of a Geneva gear is superimposed upon that of a simple harmonic motion cam to index the movable contact and provide smooth action thereof.

These and other objects and advantages of the invention will be more apparent from the following detailed description when read in conjunction with the accompanying drawing in which:

FIG. 1 is a front view of a preferred embodiment of the invention with the drive mechanism of one phase broken away to illustrate the contacts;

FIG. 2 is a cross sectional view taken on line 2-2 of FIG. 1;

FIG. 3 is a development of a cylindrical cam utilized in the embodiment of FIG. 1;

FIG. 4 is the velocity-time characteristic of the movable contact of the embodiment of FIG. 1;

FIG. 5 is a perspective view of the novel means for positively indexing the movable contacts from one stationary contact to a succeeding stationary contact; and

FIGS. 6-10 schematically illustrate sequential positions of the cam and index plates of the direct-drive means at different steps of a tap change.

The underload tap changing mechanism of the invention Will be described as incorporated in a three phase load tap changing transformer. The tap changers 1b of all three phases are identical and only one will be described. The tap changers it? for all three phases are enclosed within an oil-filled compartment (not shown) on the sidewall of the main transformer tank which houses the three phase transformer core and coil assembly. The tap changers id for all three phases are mounted on an insulating panel ill preferably of low power factor, low loss dielectric material which forms an oil-tight barrier between the main transformer tank and the oil-filled compartment.

A plurality of arcua'tely positioned stationary contacts 12 mounted on panel ll-ll include a first coplanar set of nine metallic stationary contact members 12a disposed in a circle and spacedfrom a second coplanar set of nine metallic stationary contact members 12]) arranged in a circle. Corresponding

stationary contact members

12a and 12b of the two sets are electrically comnroned. The

corresponding contact members

12 a and 12b of each stationary contact 12 have clearance holes for receiving threaded metallic studs 14 and are spaced apart by tubular metallic members 15 surrounding the studs M. The studs M threadably engage a metallic contact supporting member 16 which is rigidly secured to a threaded metallic pin 1% extending through panel 311. An insulating collar 19 surrounds pin 18 between member 16 and panel ill, a nut threaded onto pin 18 on the side of panel 11 Within the transformer tank fixedly mounts contact supporting member 16 and stationary contact 12 on insulating panel ill. The insulating collar 19 mounts stationary contact 12 on an insulating projection away from the insulating barrier provided by the panel 11 between the transformer and the tap changingswitch lit, and this construction transfers the dielectric stress from the insulating barrier to the oil and permits reduction in the size of the tap changing apparatus. A nut threadably engaging stud M rigidly clamps metallic stationary contact member 12!) against the metdlic sleeve 15 and also rigidly clamps the stationary contact member 12:: between contact support member To and tubular support 15.

Electrical leads 21 connect eight of the stationary contacts 12 toindividual taps (not shown) in the tapped series winding of the corresponding phase of the transformer, and a lead 22 electrically connects the ninth, or neutral contact 23 to the main Winding.

Three insulating panel boards 25 within the oil-filled compartment, one associated with each of the phases, are mounted in spaced relation to the panel 11 by electrically conductive support studs are surrounded by insulating sleeves 27. Each sleeve 27 is positioned between panel ill and a metallic member 3t secured by suitable means such as brazing adjacent one end of a stud 26. A tubular insulating member 24 surrounds the end of each support stud 26 within the transformer tank, and nuts threadably engaging the ends of studs 26 clamp the panel 11 against one end of the insulating sleeves 27 and panel board 25 against the members 3% to mount panel boards 2-5 in spaced relation to panel llll.

A rotatable shaft 28 carrying a movable contact 29 adapted to sequentially engage the stationary contact members 12a extends through an opening in the panel board 25 with its axis coincident with the center of the circumferentially arranged stationary contact members llZa. One end of shaft 2?} is journalled in a mounting bracket 33 secured by bolts 34 to panel board 25. A bifurcated switch arm 36 affixed by suitable means such as rivets to a radially extending flange 3! on shaft 28 carries the rotatable electrical contact 29. Rotatable contact 29 includes a pair of opposed, generally radially extending, laminated copper shunts 39. Each copper shunt 39 has a contact button 41 at the radially inward end thereof and an arcing contact button 42 at the radially outward end thereof. Rear swivel plates 31 and front swivel plates 32 positioned against the radially inward and radially outward portions respectively of each shunt 3% have inwardly formed portions (not shown) pivotally connected together by swivel pins 43 which extend through a thrust piece 47. Thrust piece 2'? has circumferentially extending portions secured by bolts 4% to the arms of bifurcated switch arm 36. The arcing contact buttons 42 are opposed and urged together by compression springs 44 surrounding pins 45 protruding through clearance holes in the copper shunts C19 and in the front swivel plates 32 and compressed between heads 46 on the ends of the pins 45 and the front swivel plates 32. Similarly the radially inward contact buttons 4-1 are opposed and urged together by compression springs 44 surrounding pins d5 projecting through clearance holes in the copper shunts 3-; and in the rear swivel plates 31. The springs id resiliently urge arcuate portions of laminated copper shunts 39 against thrust piece 47 and also urge the arcing contact buttons against opposite sides of stationary contact members The contact buttons 41 at the radially inward end of shunts 39 are resiliently urged by the helical springs dd against a collector ring 49 formed by the circumferential flange on a conical member 5%) of a suitable metallic material. The collector ring flange 49 is coplanar with the stationary contact members 12a, and the conical metallic member 5d is rigidly secured to a metallic support member 51 which is disposed against panel fill and, in turn, is affixed to a metallic stud 52 which extends through insulating panel 11. A nut 53 threadably engaging the end of stud 52 within the transformer tank fixedly mounts conical member it} on insulating panel Ill, and the end of metallic stud :52 within the transformer tank is connected by a lead to one end of a preventive autotransformer (not shown) enclosed within the transformer tank.

A sleeve 55 rotatably surrounding the shaft carries a rotatable contact as identical to rotatable contact 29 and adapted to sequentially engage the stationary contact members 12b. The sleeve 55 is journalled within a tubular portion 57 of support casting A bifurcated switch arm identical to switch arm '36 is secured by suitable means such as rivets to a radially extending flange on sleeve 55, and switch arm 5: carries the rotatable contact Rotatable contact as carried by sleeve 55 is adapted to sequentially engage stationary contact members 12b and to electrically connect them to a collector ring formed by a circumferential flange (all on a conical member 62 of a suitable metallic material. The circumferential flange at is in the plane of the stationary contact members 1212, and the conical metallic member as is rigidly affixed to a metallic support member as surrounding sleeve 55 and fixedly mounted on a copper strap Copper strap 64- is rigidly secured to insulating panel board 25 by bolts which mount bracket 33. Copper strap 64 extends along the surface of insulating panel board 25. The lowor end of copper strap 64- is bent beneath the lower edge of panel board 25 and is electrically connected to a support stud 2s. The end of conductive support stud as within the transformer tank is electrically connected by a lead 65 to the other end of the preventive autotransformer (not shown).

Shaft 28 and sleeve 5'5 are actuated independently in a manner to be described later so that

rotatable contacts

29 and 55 are individually operable. Inasmuch as stationary contact members 12a engaged by rotatable contact 29 and stationary contact members 1211 engaged by rotatable contact 56 are electrically commoned, the

rotatable contacts

29 and 56 can be indexed to a bridging position wherein each of the

rotatable contacts

29 and 55 is on one of two adjacent stationary contacts 12 and the voltage obtained is midway between the taps, or to a symmetrical position wherein both

movable contacts

29 and 56 are on the same stationary contact 12. A tap changer 1th and associated series winding provide plus or minus ten percent voltage regulation, and inasmuch as eight stationary contacts 12 are electrically connected to eight taps in the series winding, a 1% percent variation in voltage occurs when both

rotatable contacts

29 and 56 are indexed to a succeeding stationary contact. Movement of only one

rotatable contact

29 or 56 to a succeeding stationary contact l2 results in a voltage midway between the taps, or /8 percent regulation, and full plus or minus 10 percent voltage regulation is accomplished in thirty-two percent steps.

A reversing switch 67 includes a U-shaped metallic contact 68 atlixed to the metallic stud 14- of neutral stationary contact 23 and extending through an aperture 69 in panel board 25 and also includes a movable electrical contact '74). The stationary contact 63 has a circumfer entially elongated arcuate portion '71, and movable contact ill is adapted to electrically bridge between arcuate portion 71 and reversing switch stationary contact members 72 and 73. Each stationary contact 72 and '73 is secured by bolts '75 surrounded by insulating sleeves 76 threadably engaged within tapped holes in a metallic member 39 disposed adjacent the transformer side of panel board 25. As described hereinbefore member 3b is rigidly secured to a conductive support stud 25. The stationary contact members 712 and 73 of the reversing switch 67 are each electrically connected through the support studs 26 to electrical leads 79 which are connected to opposite ends of the tapped series winding Within the transformer tank.

When tap changer it? has both movable contacts 29 and 5s on neutral contact 23, and thus the reversing switch 67 is out of the load circuit, an axially extending driving pin carried by a reversing link Sll affixed to and rotatable with the sleeve 55 is adapted to engage on open-end slot 82 at the lower end of a pivoted switch arm 85 carrying the movable contact 7th to pivot the switch arm 84- and thus disengage the movable contact 7d from one stationary contact 72 or 73 and actuate it into engagement with the other stationary contact. Switch arm 84 includes a locking member 37 in which open-end slot 82 is formed and a bifurcated insulating member $8 carrying movable contact 7@ and secured to locking member 37 by suitable means such as rivets. A pin 9% extending through members 87 and 88 is journalled within a sleeve portion 91 of support bracket casting 33 to pivotally mount the reversing switch 67. The reversing switch 6? changes the connections to the tapped series winding from lower to raise and vice versa and thus doubles the voltage range of the tap changer. The reversing switch s7 is only actuated when both movable tap changer contacts 2% and 56 are engaging the neutral contact 23.

Although the electrical elements are not shown, the electrical circuit of the load tap changing transformer may be traced through a tap changer ill from the transformer secondary phase winding through the lead 22; the neutral contact 23; U-shaped stationary contact as of the reversing switch 67; reversing switch movable contact lii to either stationary contact strip '72 or '73; through a support stud 2d and a lead 79 to one end of the series winding within the transformer tank; a portion of the series winding; a tap in the series winding; a lead Zll to a stationary contact 12; movable contacts 29 and 56 (assuming both are on the same stationary contact); collector rings 4-9 and 61 to the preventive autotransformer;

(5 and from the midtap of the preventive autotransformer to the load.

A circular index plate $2 is fixed to the end of the shaft 2ft, preferably by a splined connection, to provide a positive and nonresilient connection with rotatable contact index plate 92 carries nine equiangularly spaced apart cam follower rollers 93 fixed thereto by bolts 94. A second index plate 95 coaxial with plate 92 and axially spaced therefrom is connected to the sleeve 55, preferably by a splined connection. The index plate 95 is also provided with nine equiangularly spaced apart cam follower rollers $6 fixed thereto by bolts 7. A positivemotion cylindrical cam 99 disposed between index plates 92 and $5 is fixed, preferably by a splined connection, to a horizontally extending shaft ltll the ends of which are journallcd within spaced apart portions 1432 of support casing 33. The direct-drive means of the invention for indexing the movable contacts between stationary contacts includes the cam and the index plates 92 and E 5 alternately driven thereby.

The tap changer lift of each of the three phases of the load tap changing transformer includes a cylindrical cam 99 splined to a shaft Mil, and the shafts 191 of the three tap changers are connected by couplings 1433 so that the three cams are rotatably driven simultaneously. The cylindrical cam 99 of each tap changer llll is disposed between the index plates 9?. and 95 with its axis at right angles to and spaced below the axis of the

index plates

92 and 95. As shown in FIG. 5, the

cam followers

93 and 96 are disposed on the surfaces of the index plates 92 and $5 which face each other, and the cam followers of each index plate )2 and d5 are adapted to be sequentially engaged and peripherally displaced by the cam 99 and also the

cam followers

93 and 96 of each pair of index plates are adapted to be alternately engaged and tangentially displaced by cam 3?.

The indexing means of the invention includes two relatively rotatable members one of which has a single means in continuous positive engagement with the other member, and in the preferred embodiment such single means includes a raised, axially advancing, camming surface means 165 extending circumferentially more than 360 degrees around the peripheral surface of the cylindrical, or drum, cam 99. The peripherally longest portion 167 of camming surface means M5, which in the preferred embodiment encompasses approximately 260 degrees of the circumference, is preferably in a plane substantially at right angles to the axis of the cam 9% and intermediate the camming surface end portions 199 and fill which overlap and diverge on opposite sides of said plane. End portions lid? and fill extend over approximately 100 degrees of the circumference and advance in a generally axial direction along the cylindrical surface of drum cam 99 and terminate at the opposite edges thereof. The end portions 169 and 111 are similar and the inner faces thereof are complementary and define a double-edge, approximately S-shaped cam track portion 117 of the carnming surface means Edd. In the preferred embodiment the cam track portion 117 is adapted to impart simple harmonic motion to a cam follower 93 or 90. The cam 99 is reversible and can be driven in either a clockwise or counterclockwise direction to peripherally displace the cam followers 93 and 9d.

The camming surface means alternately engages the cam followers 93 and MS of the pair of

index plates

92 and 95. When cylindrical cam 99 is rotated, the midportion 107 remains in a plane radially of the index plates 2 and 95 and thus applies no force tending to displace

cam followers

93 and 95. However, the approximately S-shaped double-edge cam track portion 117 advances tangentially with respect to the index plates 92 and 5 and thus circumferentially displaces the

cam followers

93 and 95 to cause rotation of index plates @2 and 95'.

As one cam follower, e.g. 93, on index plate 92 is being tangentially displaced by approximately S-shaped doua B ble-edge cam track portion 117 to index movable contact 29 to a succeeding stationary contact 12, the midportion N7 of camming surface means M95 is disposed between two cam followers 96 on the other index plate to lock the rotatable contact at rest While the index plate and associated rotatable contact 29 is being indexed from one stationary contact 12 to a succeeding one. The doubleedge cam track portion 117 positively constrains a cam follower 93 while tangentially displacing it in order to provide a direct and nonresilient connection between cam 99 and index plate 92. Concurrently the midportion of camming surface means res is disposed between two cam followers 96 of the index plate to provide a direct and nonresilient connection between index plate 95 and cam 99 and thus lock rotatable contact 56 at rest. it will thus be appreciated that direct and nonresilient indexing of the movable contacts 29 and as is accomplished through cylindrical, or scroll, cam and index plates and 95 which inherently insures positive mechanical interlocking of the rotatable contacts 2% and 5d.

The direct drive of the rotatable contacts through the cam 99 results in positively controlled contact speed which insures the most efficient arc interruption. As explained hereinafter, the movable contacts 29 and start slowly and are accelerated rapidly to the optimum s d for are interruption before the contacts open. instead of being snapped at maximum velocity into engagement with the succeeding stationary contact in the manner of the prior art spring-drive tap changers, the rotatable contacts 23 and 5d are decelerated to a fraction of their maximum velocity before engaging the succeeding stationary contact 12 and are positively constrained by the direct and nonresilient connection between cam and the

cam followers

93 and 96 in order to close the contacts gently without contact bounce and with minimum mechanical shock and vibration. The control of contact speed is obtained through the coordination of the cam 99 and the gear train which rotatably drives cam 99.

The motive force for scroll cam 99 is derived from a reversible electric motor 119 which drives the coupled shafts 1M through intermittent motion means preferably including a Geneva stop and pinion 121 rotatably driven by the electric motor fill and a Geneva gear 123 actuated by the Geneva pinion 1211. The intermittent motion eans is operatively connected to the cams @9 of all three phases through a vertical operating shaft 125 connected to the Geneva gear 123, and a pair of miter cars 1227 one of which is afilxed to shaft 125 and the other of which is secured to an extension 123 on the shaft lltli of middle tap changer lit.

in the embodiment of the invention illustrated in the drawing, three steps of the Geneva gear 12? produce 186 degree rotation of the cylindrical cam to positively index one of the rotatable contacts, e.g., 29, from one stationary contact 12 to a succeeding stationary contact 12. The combination of cylindrical cam and Geneva gear 123 permits the electric motor 11) to start without load during each step of cam $9.

The movement of the cam followers of one index plate, e.g., 92, relative to the cam 99 is schematically illustrated in FIG. 3 wherein it is represented that prior to the tap change, two

cam followers

93A and 93B are disposed on opposite sides of midportion 97. The "rst step of wag ee 11 Geneva gear 123 during the tap change rotates cam 99 sixty degrees so that the initial, gradually sloping portion of double-edge, approximately s-shaped, cam track portion 117 positively engages one cam follower and effects minimum peripheral displacement thereof to a position 933. At this position the tap changer contacts have not opened and the cam follower is at the beginning of the steeper-sloped portion of cam track llfi which is the most advantageous position to effect rapid opening of the contacts during the second step. Geneva gear 12.? then rotates cam 99 through another sixty degree step to displace the cam follower along the steepest-slope portion of double-edge cam track 117 to a position denoted 933". Eur-- ing the second step of Geneva gear 123, the cam follower is tangentially displaced from position $3B to position 933" to rotate plate 92, and thus index rotatable contact from one stationary contact 12 to a succeeding stationa y contact 12. At the end of the second step, the cam follower 938 at position 935 is still positively engaged by double-edge cam track portion E17 but cam follower 93A at position %A" is disengaged from camr ing surface means The third step of Geneva gear "5 rotates cam 99 through another sixty degrees to displace cam follower 933 along the gradually sloping final portion of double-edge cam track portion 117 to a position denoted 93B. It will be noted that only a minimal tangential displacement of the cam follower occurs in moving from position 93B to the final position 9313" wherein the contacts are at rest and also that in this final position the cam follower 93B and a succeeding cam follower 93C are disposed on opposite sides of the midportion iii? of camming surface means to thus lock rotatable contact 29 at rest while cam 99 is peripherally displacing a cam follower 96 to index rotatable contact 56 into engagement with a succeeding stationary contact.

Although the camming surface means 1% is shown as a raised portion on cam 99, it will be apparent that the carnming surface means 1% can equally well be a groove in the surface of cam 99.

As mentioned hereinbefore, the camming portion I117 is the preferred embodiment of the invention is adapted to impart simple harmonic motion to the cam followers and During the first sixty degree step of simple harmonic motion, a

cam follower

93 or 96 is displaced along the relatively flat, gradually sloped portion of the camming surface means 1635 to position the

cam follower

93 or 96 at the beginning of the middle, steeper-sloped portion of the simple harmonic motion camming track ll? which is advantageous for rapid opening of the contacts during the second step of cam 99. During the second sixty degree step of simple harmonic motion, the

movable contact

29 or 55 is accelerated to an optimum velocity for et'licient arc interruption before the contacts open, is further accelerated to a maximum velocity, and is then decelerated to a fraction of the maximum velocity before engaging the succeeding stationary contact 12. Simple harmonic motion has the highly desirable characteristic that the change in velocity occurs gradually at the midportion of the velocity-time characteristic where the velocity is a maximum. Consequently, mechanical shock, inertial force, and vibration are a minimum when t movable contact is being slowed down at the midportion of the velocity-time characteristic.

The intermittent motion of a Geneva gear has the desirable characteristic that acceleration and deceleration are a minimum at the initial and final portions of the motion respectively, but the time-velocity characteristic of a Geneva gear is similar to a sharply-pointed inverte ii where change of velocity is a maximum on both sides of the midportion thereof and consequently severe vibratory effects, inertial force, and mechanical shock occur at the midportion of the travel.

in accordance with the invention, the midportion of the simple harmonic motion of earn 9, characterized by gradual change in veloc is superimposed upon the "J 7 'y-time characteristic of the intermittent motion device .9, characterized by gradual acceleration and deceleration at the ends of the motion, to obtain smooth action. of

rotatable contacts

29 and 56 with minimum unbalanced forces and vibration effects during the second step of cam 9% then the rotatable contact is being infrom one stationary contact to a succeeding stationary contact. The resultant time-velocity characteristic of the

rotatable contacts

29 and 56 during the second step of cam is illustrated in FlG. 4 wherein velocity of the rotatable contact is plotted against degrees rotation of the Geneva pinion 1251. it will be noted that the tremendous acceleration and deceleration at the ends of the motion characteristic of simple harmonic motion, or of constant acceleration motion, are absent and that motion of the

rotatable contacts

29 and 56 is initiated slowly with gradual acceleration and is also slowed with gradual deceleration at the final portion of the motion to bring the rotatable contacts gently at rest in engagement with a succeeding stationary contact. During the second step the rotatable contacts 2? and 56 are rapidly accelerated to almost half of their maximum velocity and to an optimum speed for efficient arc interruption before the contacts open as indicated at point on the velocity-time characteristic of FIG. 4. It will be noted that the midportion of the velocity-time characteristic illustrated in FIG. 4 is approximately sinusoidal in contrast to the inverted-V characteristic of an intermittent motion device. The acceleration, indicated by the slope of the velocitytime characteristic, diminishes gradually as the velocity of the rotatable contact approaches a maximum at the midpoint of the characteristic and further the change of velocity occurs gradually as slowing down of the contact is begun. The slope of the rnidportion of the velocitytime characteristic of the rotatable contacts 2% and 56 changes gradually from plus one adjacent point X through zero at the maximum velocity point and to minus one adjacent point Y. Consequently, the action of the

rotatable contacts

29 and 56 is smooth, and the unbalanced inertial forces and severe shock and vibratory effects inherent in the inverted-V velocity-time characteristic of a Geneva gear drive are avoided.

During the final portion of the second step, the movable contact 29 or se is decelerated to less than half its maximum velocity before the movable contact engages the succeeding stationary contact as indicated at C in FIG. 4, and the rotatable contact is positively constrained by the direct and nonresilient connection between cam track portion 117 and the

cam follower

93 or 96 as the contact is gradually brought to rest at the end of the motion in engagement with a succeeding stationary contact 12. Contact bounce is thus entirely eliminated, no pitting of the contacts occurs due to the drawing of repeated arcs during contact bounce as in prior art spring-drive tap changers, and electrical life of the tap changer contacts is greatly increased in comparison to prior art mechanisms. The minimum vibration, minimum unbalanced forces, and minimum mechanical shock inherent in the direct, positive and nonresilient indexing of contacts results in a much more rugged mechanism which requires greatly reduced maintenance in comparison to prior art devices and has considerably greater mechanical life.

During the third step of cam 99, the cam follower 93B is moved along the relatively flat, gradually-sloped final sixty degree portion of the simple harmonic motion camming surface means N35 to a position indicated at 938'. The rotatable contact 2-9 is slowly brought into its final position at rest in engagement with the succeeding contact 12 during the third step, and it will be noted that cam track portion 117 is disengaged from cam follower 933 at the end of the third step.

Although the invention has been described with reference to the superimposition of a simple harmonic motion and that of an intermittent motion device, the smooth action with minimum shock and vibration can also be obtained by other combinations of motion, for example, a constant-acceleration motion having minimum acceleration at the midpoint thereof superimposed on the intermittent motion of a Geneva gear.

FIGS. 6-10 schematically illustrate the alternate actuation of

indexing plates

92 and 95 and the inherent mechanical interlocking thereof. In order to more clearly illustrate the cam track, the shaft 28 and sleeve 55 are illustrated as extending in opposite directions in FIGS. 6-10, whereas in the preferred embodiment the sleeve 55 surrounds the shaft 28. FIG. 6 shows the conditions prior to the first step of Geneva gear 123 wherein the

rotatable contacts

29 and 56 are still in engagement with stationary contacts 12, the midportion MP7 of the camming surface means 105 of the cylindrical cam 99 is disposed between a pair of

adjacent cam followers

93A and 93B of index plate 92 and is also disposed between a pair of adjacent cam followers %A and Q63 on index plate 95. Consequently the

index plates

92 and 95 are locked against rotation and the

rotatable contacts

29 and 56 cannot open. FIG. 7 shows that after the first sixty degree step of Geneva gear 123, cam follower 93B of index plate 92 is in positive engagement with the double-edge cam track portion 117 and the movable contact 29 has been displaced slightly on stationary contact 12 but is still in engagement therewith.

Cam followers

96A and 96B are still disposed on opposite sides of rnidportion 167 which does not advance axially as cam 99 is rotated, and consequently movable contact 55 is still locked at rest. FIG. 8 illustrates the condition midway through the second step of cam 99 after thirty degree further rotation of Geneva gear 123 wherein the rotatable contact 29 is disengaged from one stationary contact 12 and is midway between adjacent stationary contacts 12, cam follower 93B is midway through the steeper-slope portion of the double-edge cam track 117 and positively held therein, and cam follower 93A is out of engagement with the carnming surface means ltlfi. At the end of the second step after thirty degree further rotation of Geneva gear 123 as shown in FIG. 9, the rotatable contact 29 is in engagement with a succeeding stationary contact 12 and cam follower 9313 has passed through the steeper-slope portion of, but is still in engagement with the double-edge cam track por tion 117, and a succeeding cam follower 93C of index plate 92 is ready to come into engagement with the camming surface means Hi5. After the third step of Geneva gear 123 as shown in FIG. 10, the rotatable contact 29 has been displaced into its final position at rest on succeeding stationary contact 12; cam follower 93B has been disengaged from the double-edge cam track portion 117; and cam followers @313 and 93C are disposed on opposite sides of rnidportion 167, thus locking (the index plate 92 against rotation and positively holding the rotata ble contact 29 at rest. It will be noted in FIGS. 6-10 (that during the three operating steps of Geneva gear 123, the index plate 95 is locked against rotation by the midportion 107 which throughout the three steps is disposed between the

cam followers

96A and 96B, thereby holding the movable contact 56 at rest. At the end of the three steps of Geneva gear 123, the cam follower 96B is disposed in a position relative to the double-edge cam track portion 117 identical to that of cam follower 9313 prior to the first step. Consequently the next three steps of Geneva gear 123 will peripherally displace cam follower %B to rotate plate 95 and index the movable contact 56 between stationary contacts. The direct-drive means including cylindrical cam 99 and

index plates

92 and 95 is thus capable of positively and nonresilientily indexing one of the

movable contacts

29 or 56 at a controlled speed while concurrently holding the other rotatable contact at rest, of locking both

rotatable contacts

29 and 56 at rest simultaneously and alternately driving the

index plates

92 and 95 to alternately index the

rotatable contacts

29 and 56 between stationary contacts 12.

Although only a single preferred embodiment of the invention has been illustrated and described, many modircations and variations thereof will be apparent to those skilled in the art, and therefore it is intended in the appended claims to cover all such modifications and variations as fall within the true spirit and scope of the invention.

I claim:

1. An electrical tap changing under load mechanism comprising, in combination, a plurality of arcuately arranged stationary contacts, a movable contact for sequentially engaging said stationary contacts, and intermittent motion transmitting means including a pair of l it relatively movable members the first of which is positively and nonresiliently connected to said movable contact and the second of which drives said first member for indexing said movable contact with accelerated motion from one stationary contact to a succeeding stationary contact, said movable con-tact interrupting current under load when it is disengaged from said one stationary contact and competing an electrical circuit under load when it engages said succeeding stationary contact, one of said members having a single means in continuous positive engagement with the other of said members both during actuation of said movable contact and while said movable contact is at rest and said second member positively driving and directly controlling the speed of sid movable contact at all times while it is being indexed between said stationary contacts, whereby contact bounce is avoided.

2. An electrical tap changing under load mechanism comprising, in combination, at least three arcuately arranged stationary contacts connected to taps of an elec trical Winding, a movable contact for sequentially engaging said stationary contacts, and means including a pair of members the first of which is positively and nonresiliently connected to said movable contact and the second of which drives said first member for indexing said movable contact from one stationary contact to a succeeding stationary contact, said movable contact interrupting current under load in the electrical circuit to one of said taps when it is disengaged from said one stationary contact and completing an electrical circuit under load to an adjacent tap when it engages said succeeding stationary contact,

one of said members having a single cam track means in continuous positive engagement with the other of said members both during actuation of said movable contact and while said movable contact is at rest, said second member positively driving and directly controlling the speed of said movable contact at all times while it is being indexed between said stationary contacts and decelerating said movable contact to a fraction of its maximum velocity before said movable contact engages said succeeding stationary contact and also decelerating said movable contact to a final position at rest in engagement with said succeeding stationary conact, said one member being in continuous positive engagement with the other of said members during said deceleration, whereby contact bounce of said movable contact is eliminated.

3. An electrical ltap changing under load mechanism comprising, in combination, at least three stationary contacts arranged in an arcuate path, a movable contact adapted to sequentially engage said stationary contacts, and means including a rotatable member carrying cam follower means disposed away from the axis thereof and being positively and nonresiliently connected to said movable contact for indexing said movable contact with accelerated motion from one stationary contact to a succeeding stationary contact, said movable contact interrupting current under load when it is disengage-d from said one stationary contact, said means for indexing also including an intermittent motion transmitting device characterized by gradual acceleration and retardation at the ends of the motion and rapidly accelerated and decelerated motion therebetween and a positive-motion cam in continuous engagement with said cam follower means and positively driving and directly controlling the velocity of said movable contact at all times while it is being indexed between said stationary contacts, the motion transmitted by said cam being characterized by gradual change of velocity in the vicinity of the maximum velocity and the motion of said cam being superimposed upon that of said intermittent device and producing smooth action of said movable contact, said indexing means starting said movable contact slowly and accelerating it to a substantial portion of its maximum velocity before it is disengaged from said onestationary Contact.

4. An electrical tap changing under load mechanism comprising, in combination, at least three stationary contacts arranged in an arcuate path and connected to taps of an electrical winding, a movable contact adapted to sequentially engage said stationary contacts, and means including a rotatable member carrying cam follower means disposed away from the axis thereof and being positively and nonresiliently connected to said movable contact for indexing said movable contact from one stationary contact to a succeeding stationary contact, said movable contact interrupting current under load in the electrical circuit to one of said taps when it is disengaged from said one stationary contact and completing an elec trical circuit under load to an adjacent ttap when it engages said succeeding stationary contact, said means for indexing also including an intermittent motion transmitting device characterized by relatively gradual acceleration and retardation adjacent the ends of the motion and rapidly accelerated and decelerated motion intermediate said ends and a simple harmonic positive-motion cam in continuous engagement with said cam follower means and being rotatably driven in three sixty degree steps by said intermittent device to index said movable contact between said stationary contacts, said cam follower means during the first step being displaced to the beginning of the steeper slope portion of said simple harmonic motion cam and the opening and reclosing of said contacts occurring during the second step of sixty degrees of simple harmonic motion transmitted by said cam, the motion of said intermittent device being superimposed on that of said cam and effecting smooth action of said rotatable contact during said indexing.

5. An electrical tap changing under load mechanism comprising, in combination at least three arcuately arranged stationary contacts, a movable contact adapted to sequentially engage said stationary contacts, and means including a pair of rotatable members the first of which is positively and nonresiiientl connected to said movable contact and the second of which displaces said first memher in a peripheral direction for indexing said movable contact with rapidly accelerated motion from one stationary contact to a succeeding stationary contact, said movable contact interrupting current under load when it is disengaged from said one stationary contact and completing an electrical circuit under load when it engages said succeeding stationary contact, one of said members having a single means in continuous positive engagement with the other of said members both during indexing of said movable contact and while said movable contact is at rest and said second member positively driving and directly controlling the velocity of said movable contact at all times while it is being indexed between said stationary contacts, the midportion of the velocity-time curve of the motion transmitted by said indexing means to said movable contact being approximately sinusoidal with maximum velocity occurring during said midportion, said indexing means gradually accelerating and gradually decelerating said movable cont act at the initial and final portions of said motion and changing the velocity of said movable contact gradually adjacent the maximum velocity point of said midportion of said velocity-time chanacteristic.

6. An electrical tap changing under load mechanism comprising, in combination, at least three arcuately arranged stationary contacts, a movable contact for sequentially engaging said stationary contacts, and means for indexing said movable contact from one stationary contact to a succeeding stationary contact, said movable contact interrupting current under load when it is disengaged from said one stationary contact, said means including a prime mover, an intermitent motion transmitting device operatively driven by said prime mover, said intermittent motion device being characterized by gradual acceleration and retardation at the ends of the motion and rapid acceleration and deceleration in the midportion thereof, and a simple harmonic motion transmit-ting device between said intermittent motion device and said movable contact, said simple harmonic motion device positively driving and directly controlling the speed of said movable contact at all times as it is indexed between said stationary contacts, whereby said prime mover may start without load and gradually accelerating and gradually decelerating motion is imparted to said movable contact at the ends of said indexing and the velocity of said movable contact is changed gradually as the velocitytime characteristic of said movable contact changes from a positive to a negative slope.

7. An electrical tap changing under load mechanism comprising, in combination, at least three arcuately arranged stationary contacts connected to taps of an electrical winding, a movable contact for sequentially engaging said stationary contacts, and means for indexing said movable contact from one stationary contact to a succeeding stationary contact, said movable contact interrupting current under load in the electrical circuit to one of said taps when it is disengaged from said one stationary contact and completing an electrical circuit under load to an adjacent tap when it engages said succeeding stationary contact, said means including a prime mover, an intermittent motion Geneva gear operatively driven by said prime mover, and a motion transmitting device having the chanacteristic of gradual change of velocity with time at the midpontion of the velocity-time characteristic thereof disposed between said Geneva gear and said movable contact, the superimposition of said Geneva gear and said device providing smooth action of said movable contact with minimum vibration and shock eflects.

8. An electrical tap changing under load mechanism comprising, in combination, a plurality of arcuately arranged stationary contacts, a pair of individually operable movable contacts for sequentially engaging said stationary contacts, means for alternately indexing said movable contacts from one stationary contact to a succeeding stationary contact including first and seond rotatable members positively and nonresiliently connected to individual ones of said movable contacts, each said movable contact interrupting current under load when it is disengaged from one stationary contact and completing an electrical circuit under load when it engages said succeeding stationary contact, and a motion transmitting member simultaneously continuously directly engaging said first and second members both during indexing and at rest and when operated alternately displacing said first and second members to actuate said movable contacts with accelerated motion and said motion transmitting member positively driving and directly controlling the velocity of said movable contacts at all times as they are indexed between said stationary contacts.

9. An electrical tap charging under load mechanism comprising, in combination, a plurality of circumferentially disposed stationary contacts, a pair of individually operable movable contacts adapted to sequentially engage said stationary contacts, a shaft carrying one of said movable contacts, a sleeve rotatably surrounding said shaft and carrying the other of said movable contacts, means for alternately indexing said movable contacts between said stationary contacts including first and second rotatable members one of which is in positive and nonresilient connection with said shaft and the other of which is in positive and nonresilient connection with said sleeve, and a rotatable motion transmitting member in continuous positive engagement with said first and second rotatable members and being adapted to alternately rotatably drive said first and second members to alternately index said movable contacts from one stationary contact to a succeeding stationary contact, each said movable contact interrupting current under load when it is disengaged from said one stationary contact and completing an electrical circuit under load when it engages said succeeding stationary contact.

10. A tap changing under load mechanism comprising, in combination, at least three circumferentially disposed id stationary contacts connected to taps of an electrical winding, a movable contact operative to sequentially engage said stationary contacts, and means for indexing said movable contact from one stationary contact to a succeeding stationary contact including an index plate positively and nonresiliently connected to said movable contact and having a plurality of circumferentially spaced apart cam followers and a cam adapted to sequentially engage and displace said cam followers to rotate said index plate and being in positive engagement with at least one of said cam followers at all times and positively driving and directly controlling the velocity of said movable contact at all times as it is indexed between said stationary contacts, said movable contact interrupting current under load in the electrical circuit to one of said taps when it is disengaged from said one stationary contact and completing an electrical circuit under load to an ad acent tap when it engages said succeeding stationary contact.

11. A tap changing under load mechanism comprising, in combination, a plurality of circumferentially disposed stationary contacts, a pair of individually operable rotatable contacts adapted to sequentially engage said stationary contacts, a first indexing plate positively and nonresiliently connected to one of said rotatable contacts, a second indexing plate spaced from and coaxial w th said first indexing plate and positively and nonresiliently connected to the other rotatable contact, a plurality of oncumferentially spaced apart cam followers on each of said indexing plates, and a positive-motion cam disposed between said indexing plates successively engaging and displacing said cam followers on each of said plates and indexing said rotatable contacts between said stationary contacts each said rotatable contact interrupting current under load when it is disengaged from one of said stationary contacts and completing an electrical circuit under load when it engages a succeeding stationary contact, said cam alternately engaging and displacing a cam follower on said first indexing plate and a cam follower on said second indexing plate and positively engaging at least one of said cam followers on both of said plates at all times, whereby motion of said cam is directly transmitted to said rotatable contacts and said cam locks said rotatable contacts at rest.

12. In a tap changing under load mechanism, the combination with at least three circumferentially disposed stationary contacts connected to taps of an electrical winding and a rotatable contact for sequentially engaging said stationary contacts, of means for indexing said rotatable contact between said stationary contacts including a rotatable index plate positively and nonresiliently connected to said rotatable contact and carrying a plurality of circumferentially spaced apart cam followers and a cylindrical cam disposed adjacent said index plate and having camming surface means thereon a portion of which is in a plane substantially perpendicular to the axis of said cam and at least one end of said camming surface means diverging from said plane, said camming surface means sequentially engaging and displacing the cam followers of said index plate when said cylindrical cam is actuated to actuate said index plate, said camming surface means positively engaging at least one of said cam followers at all times, whereby said cam indexes said rotatable contact between stationary contacts and also locks said rotatable contact at rest, said rotatable contact interrupting current under load in the electrical circuit to one of said taps when it is disengaged from one of said stationary contacts and completing an electrical circuit under load when it engages a succeeding stationary contact.

13. in a tap changing under load mechanism, the combination with a plurality of circumferentially disposed stationary contacts and a pair of rotatable contacts individually operable to sequentially engage said stationary contacts; of a pair of rotatable, axially spacedapart, coaxial index plates each having a plurality of circumferentially spaced apart cam followers and being positively and nonresiliently connected to one of said rotatable contacts, and a cylindrical cam disposed between said index plates having camming surface means thereon the end portions of which diverge axially relative to said cam, one of said diverging end portions sequentially engaging said cam followers on each of said plates and alternately engaging and displacing said cam followers on said pair of plates when said cam is rotated in the forward direction and the other said diverging end portions doing so when said cam is rotated in the reverse direction, the portion of said camming surface means between said end portions being in positive engagement with the cam followers of one of said index plates while a cam follower of the other of said index plates is being displaced by one of said end portions, each said rotatable contact interrupting current under load when it is disengaged from one stationary contact and completing an electrical circuit under load when it engages a succeeding stationary contact.

14. In a tap changing under load mechanism, the combination with a plurality of circumferentially disposed stationary contacts and a pair of coaxial, spaced apart, individually operable rotatable contacts for sequentially engaging said stationary contacts; of a rotatable shaft carrying one of said rotatable contacts and a sleeve rotatably surrounding said shaft and carrying the other of said rotatable contacts, a pair of rotatable, axially spaced apart, coaxial index plates each carrying a plurality of circumferentially spaced apart cam followers, one of said plates being positively and nonresiliently connected to said shaft and the other of said plates being positively and nonresiliently connected to said sleeve, and a cylindrical cam disposed between said plates with its axis substantially at right angles to the axis thereof and having camming surface means adapted to sequentially engage the cam followers of each of said index plates and to alternately engage and displace said cam followers of said pair of plates to index said rotatable contacts alternately between said stationary contacts, each said rotatable contact interrupting current under load when it is disengaged from one of said stationary contacts and completing an electrical circuit under load when it engages a succeeding stationary contact.

15. A tap changing under load mechanism comprising, in combination, a plurality of circumferentially disposed stationary contacts, a pair of coaxial, axially spaced apart, rotatable contacts, a shaft carrying one of said rotatable cont cts, a sleeve rotatably surrounding said shaft and carrying the other of said rotatable contacts, a pair of coaxial, axially spaced apart, rotatable index plates each having a plurality of circumferentially spaced apart cam followers, one of said plates being positively and nonresiliently connected to said shaft and the other of said plates being positively and nonrcsiliently connected to said sleeve, and a cylindrical cam disposed between said index and having a raised carnrning surface thereon extending circumferentially more than 360 degrees around the periphery of said cam, a midportion of said camming surface being in a plane substantially perpendicular to the axis of said cam and the end portions of said camming surface diverging from said plane axially relative to said cam axis and when said cam is rotated sequentially engaging and peripherally displacing the cam followers on each of said plates and alternately engaging and peripherally displacing the cam followers on said pair of plates to index said rotatable contacts alternately between said sta tionary contacts, each said rotatable contact interrupting current under load when it is disengaged from one of said stationary contacts and completing an electrical circuit under load when it engages a succeeding stationary contact, said midportion being disposed between and positively engaging an adjacent pair of said cam followers of one of said index plates when a cam follower of the other of said index plates is in engagement with said end portions, whereby one of said index plates is positively held by said midportion to lock one of said movable coni6 tacts at rest while the other of said index plates is being rotated by said end portions to index the other of said rotatable contacts between stationary contacts.

16. A tap changing under load mechanism, comprising, in combination, a plurality of circumferentially disposed stationary contacts a pair of individually operable rotatable contacts adapted to sequentially engage said stationary contacts, a pair of rotatable index plates positively and nonresiliently connected to individual ones of said rotatable contacts and each carrying a plurality of circumferentially spaced apart cam followers, and a positivemotion cam having camining surface means for sequentially engaging said cam followers of each said index plate and for alternately eng-ging and peripherally displacing said cam followers of said pair of index plates, said camining surface means when said cam is rotated transmitting motion to one of said cam followers in a series of steps in the first ofwhich said carnrning surface means positively engages said one cam follower and displaces it to the beginning of the portion of said camming surface'having the steeper slope and which is most advantageous for rapid acceleration of the rotatable contact associated therewith during the succeeding step and in the second of which said one cam follower is peripherally displaced along said steeper slope portion of said caniming surface to index said rotatable contact from one stationary contact into engagement with a succeeding stationary contact, said cam accelerating said rotatable contact to maximum velocity between said stationary contacts and the slope of said steeper portion changing gradually in the vicinity of said maximum velocity, each said rotatable contact interrupting current under load when it is disengaged from said one stationary contact, said cam positively constraining said one cam follower during all of said steps and concurrently positively constraining said cam followers of said other index plate during all of said steps, and a Geneva gear, said Geneva gear transmitting motion with relatively low acceleration and retardation adjacent the initial and final portions of the motion, the superimposition of the motion of said cam on the motion of said Geneva gear providing smooth action of said rotatable contact with minimum vibration and shock.

17. In a tap changing mechanism in accordance with claim 16 wherein during said second step said cam is adapted to accelerate said rotatable contact to a substantial portion of its maximum velocity before it is disenfrom said one stationary contact and to decelerate said rotatable contact to a fraction of its maximum velocity before it engages said succeeding stationary contact and to positively constrain said one cam follower during said deceleration,whereby contact bounce of said rotatable Contact is eliminated.

18. A tap changing under load mechanism comprising, in combination, at least three circumferentially disposed stationary contacts connected to taps of an electrical winding, a rotatable contact adapted to sequentially ensaid stationary contacts, a rotatable member posi tively and nonresiliently connected to said rotatable contact and carrying a plurality of circumferentially spaced apart cam followers disposed away from the axis thereof, and a positive-motion cam having an approximately 8- shaped cam track adapted when said cam is rotated to sequentially engage said cam followers and to transmit motion to each said cam follower in a series of steps in the first of which said cam track positively engages said cam follower and displaces it to a position at the beginning of the steeper portion of said cam track wherein said cam follower is in the most advantageous position to rapidly accelerate said contact during the succeeding step and in the second of which said cam follower is peripherally displaced by said steeper portion to index said rotatable contact from one stationary contact into engagement with a succeeding stationary contact, said rotatable contact interrupting current under load in the electrical circuit to one of said taps when it is disengaged from said one stationary contact and completing an electrical circuit under load to an adjacent tap when it engages said succeeding stationary contact, said cam track positively constraining said cam follower during said series of steps and said positive motion cam positively driving and directly controlling the velocity of said rotatable contact at all times as it is indexed between said stationary contacts.

19. An electrical tap changing under load mechanism comprising, in combination, at least three circumferentially disposed stationary contacts, first and second individually operable rotatable contacts adapted to sequentially engage said stationary contacts, and indexing means including a positive-motion cam for alternately indexing said first and second rotatable contacts from one stationary contact to a succeeding stationary contact so that said rotatable contacts are rapidly accelerated to a substantial portion of their maximum velocity before they disengage said one stationary contact and are retarded to a fraction of said maximum velocity before they engage said succeeding stationary contact, each said rotatable contact interrupting current under load when it is disengaged from said one stationary contact and completing an electrical circuit under load when it engages said succeeding stationary contact, said positive-motion cam positively driving one of said rotatable contacts and positively controlling its speed at all times as it is indexed between said stationary contacts and locking the other rotatable contact at rest while indexing said one rotatable contact.

20. In a tap changing under load mechanism, the combination of at least three arcuately arranged stationary contacts connected to taps of an electrical winding, a movable contact adapted to sequentially engage said stationary contacts, and indexing means including a positive motion cam and cam follower means connected to said movable contact and driven by said cam for initially wiping said movable contact at relatively low velocity along one stationary contact and for accelerating said movable contact to a substantial portion of its maximum velocity before it disengages said one stationary contact and for decelerating said movable contact to a fraction of its maximum velocity before it engages a succeeding stationary contact, said movable contact interrupting current under load in the electrical circuit to one of said taps when it is disengaged from said one stationary contact and completing an electrical circuit under load to an adjacent tap when it engages said succeeding stationary contact, said indexing means wiping said movable contact along said succeeding stationary contact at relatively low velocity into its final position with said succeeding contact and said cam positively driving and directly controlling the velocity of said movable contact at all times as it is indexed from said one stationary contact to said succeeding stationary contact, whereby bounce of said movable con- 18 tact relative to said succeeding stationary contact is eliminated and arcing therebetween is reduced.

21. In a tap changing under load mechanism, in combination, a plurality of circumferentially disposed stationary contacts, a rotatable contact for sequentially engaging said stationary contacts, intermittent motion transmitting means including a pair of members the first of which is positively and non-resiliently connected to said rotatable contact and the second of which rotatably drives said first member for indexing said rotatable contact from one stationary contact to a succeeding stationary contact so that it is initially accelerated gradually and then accelerated rapidly to a substantial portion of its maximum velocity before it is disengaged from said one stationary contact, said movable contact interrupting current under load when it is disengaged from said one stationary contact and completing an electrical circuit under load when it engages said succeeding stationary contact, said means for indexing including means for changing the velocity of said rotatable contact relatively gradually in the vicinity of the maximum velocity point on its time-velocity characteristic, one of said members having a single means in continuous positive engagement with the other of said members both during indexing of said rotatable contact and while said rotatable contact is at rest and said second member positively driving and directly controlling the velocity of said rotatable contact at all times during the indexing thereof between stationary contacts and decelerating said rotatable contact to a fraction of its maximum velocity before it engages said succeeding stationary contact.

References Cited in the file of this patent UNITED STATES PATENTS 1,764,319 Kurda June 17, 1930 1,863,392 Brand June 14, 1932 1,867,147 Haller July 12, 1932 2,253,654 Schroder Aug. 16, 1941 2,363,886 McKenney Nov. 28, 1944 2,395,803 Bruckner et al Mar. 5, 1946 2,480,589 McKenney Aug. 30, 1949 2,785,242 V/hite Mar. 12, 1957 2,791,648 Maloney May 7, 1957 2,878,333 McCarty et al Mar. 17, 1959 FOREIGN PATENTS 850,924 France Dec. 29, 1939 893,924 Germany Oct. 12, 1953 29,235 Great Britain Oct. 22, 1898 of 1897 583,365 Great Britain Dec. 17, 1946 106,119 Sweden Dec. 15, 1946 209,052 Switzerland Mar. 15, 1940

Claims

1. AN ELECTRICAL TAP CHANGING UNDER LOAD MECHANISM COMPRISING, IN COMBINATION, A PLURALITY OF ARCUATELY ARRANGED STATIONARY CONTACTS, A MOVABLE CONTACT FOR SECQUENTIALLY ENGAGING SAID STATIONARY CONTACTS, AND INTERMITTENT MOTION TRANSMITTING MEANS INCLUDING A PAIR OF RELATIVELY MOVABLE MEMBERS THE FIRST OF WHICH IS POSITIVELY AND NONRESILIENTLY CONNECTED TO SAID MOVABLE CONTACT AND THE SECOND OF WHICH DRIVES SAID FIRST MEMBER FOR INDEXING SAID MOVABLE CONTACT WITH ACCELERATED MOTION FROM ONE STATIONARY CONTACT TO A SUCCEEDING STATIONARY CONTACT, SAID MOVABLE CONTACT INTERRUPTING CURRENT UNDER LOAD WHEN IT IS DISENGAGED FROM SAID ONE STATIONARY CONTACT AND COMPETING AN ELECTRICAL CIRCUIT UNDER LOAD WHEN IT ENGAGES SAID SUCCEEDING STATIONARY CONTACT, ONE OF SAID MEMBERS HAVING A SINGLE MEANS IN CONTINUOUS POSITIVE ENGAGEMENT WITH THE OTHER OF SAID MEMBERS BOTH DURING ACTUATION OF SAID MOVABLE CONTACT AND WHILE SAID MOVABLE CONTACT IS AT REST AND SAID SECOND MEMBER POSITIVELY DRIVING AND DIRECTLY CONTROLLING THE SPEED OF SID MOVABLE CONTACT AT ALL TIMES WHILE IT IS BEING INDEXED BETWEEN SAID STATIONARY CONTACTS, WHEREBY CONTACT BOUNCE IS AVOIDED.