US 3798395 A
A tap changer for transformers includes a selector switch and a diverter switch. The drive device for the switch includes a gear segment which drives a gear wheel mounted on a shaft which gear wheel also carries a slewing bracket on which is pivoted on a pivot pin a link which is connected to one end of a spring, the other end of which is stationary. The gear wheel has a notch extending partly around its periphery, into which the pivot pin extends so that the gear wheel can turn freely through a limited distance without affecting the spring. On the same shaft is mounted a fly wheel which has an arcuate slot into which the pivot pin extends. A braking arrangement is provided which holds the fly wheel against movement until it is forceably turned by the pivot pin. The fly wheel carries a projection which engages in a Maltese cross arrangement for shifting the contacts of the diverter switch.
Description (OCR text may contain errors)
United States Patent 1191 Norman et all [451 Mar. 19, 1974 OPERATING MECHANISM FOR TAP CHANGER SWITCHES  Inventors: Sivert Norman; Ernst Flytstrom; Folke Johansson, all of Ludvika, Sweden  Assignee: Almanna Svenslsa Elektriska Aktiebolaget, Vasteras, Sweden  Filed: Nov. 6, 1972  Appl. No.: 304,246
 US. Cl 200/17 R, 200/11 TC, 200/18,
Primary Examiner-James R. Scott 5 7] ABSTRACT A tap changer for transformers includes a selector switch and a diverter switch. The drive device for the switch includes a gear segment which drives a gear wheel mounted on a shaft which gear wheel also carries a slewing bracket on which is pivoted on a pivot pin a link which is connected to one end of a spring, the other end of which is stationary. The gear wheel a a notch ext rtl ar tsp 'p y nt which the pivot pin extends so that the gear wheel can turn freely through a limited distance without affecting the spring. On the same shaft is mounted a fly wheel which has an arcuate slot into which the pivot pin extends. A braking arrangement is provided which holds the fly wheel against movement until it is forceably turned by the pivot pin. The fly wheel carries a projection which engages in a Maltese cross arrangement for shifting the contacts of the diverter switch.
5 Claims, 5 Drawing Figures OPERATING MECHANISM FOR TAP CHANGER SWITCHES BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a tap changer for transformers which includes a selector switch and a diverter switch operated by a common drive device and includinga spring arrangement for producing rapid switch movements of the diverter switch.
2. The Prior Art In the type of tap changers for transformers which comprise a selector and a diverter switch operated from a common drive device, the tap changing operation is divided into two steps. During the first step the selector is readjusted into the new position, one of the movable contacts of the selector connecting a winding tap to the free diverter switch contact. When this selector step is concluded, the switching of the diverter switch is effected. Since the diverter switch switches the whole load current, it is of great importance this switching be done rapidly, and above all it must not be done before the selector has concluded its motion.
The switching is therefore often effected with the help of a spring device which is stretched in the introductory state of the tap changing operation, preferably simultaneously with the motion of the selector. When the switching of the diverter switch is to be affected, the spring device is released and drives the diverter switch.
SUMMARY OF THE INVENTION The present invention relates to a tap changer of the type mentioned above. According to the invention, the machinery for transmission of motion from the driving device to the diverter switch comprises a gear wheel and a flywheel driven by the gear wheel. At least one of said wheels, and preferably both, are provided with free wheel devices which areadjusted in such a way that the flywheel, after a part of the tap changing operation determined by the adjustment of the free wheel devices, has turned to a position where it may be affected by the energy stored in the spring device in such a way that it is given a rapidly accelerating rotary motion which, through a swinging bracket, achieves switching of the diverter switch.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described with the help of the accompanying drawings, in which FIG. 1 shows the spring device with arrangements for stretching it.
FIG. 2 is a cross-section through FIG. 1 along the line II-II.
FIG. 3 shows the selector and the diverter switch with its drive device,
FIG. 4 is a cross-section through FIG. 3 along the line IV-IV,
FIG. 5 is an exploded view of the device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The tap changer is driven in known manner from a drive device, not shown, the shaft of which is designated l in FIGS. 1 and 3. In FIG. 1 is shown a disc 2 secured on the drive shaft 1, said disc supporting a bearing 3 for a draw bar 4 which is flexibly attached to an arm 5 of a toothed segment 6. The toothed segment is journalled at its center 7. The toothed segment is in engagement with a gear wheel 8 which is freely journalled on a shaft 9. As appears most clearly from FIG. 2, the gear wheel is provided on its underside with a sector-formed notch 10 extending approximately half the width of the gear wheel. The notch is defined by two preferably radial stop surfaces 11 and I2.
Below the gear wheel a slewing bracket 13 is movably journalled on the shaft 9. The slewing bracket supports on its right-hand part, as shown in the figures, a driving pin 14 which projects into the notch 10 and hits either of the stop surfaces 11 or 12 when the gear wheel is turned. The driving pin also projects into a hole in a line 15 which is attached to one end of the spring device 16. The other end of the spring device is attached to a second link 17 which is fixed to the stand of the tap changer.
FIG. 3 shows the selector 18 driven from the shaft 1 of the drive device. the selector and its drive, for example by means of a Maltese cross gearing, is well-known and comprises two selector contacts 19, 20, each attached to a slip ring 21 and 22 respectively. The regulating winding 23 is shown with three taps 24, 25, 26. A brush 27 bears against the slip ring 21 and is also connected to the one fixed contact 29 of the diverter switch. A second brush 28 makes contact with the slip ring 22 and is connected to the second fixed contact 30 of the diverter switch.
A flywheel 31 is freely journalled on the stand of the spring device, as is shown in FIGS. 3 and 4. The flywheel is positioned below the slewing bracket 13 in FIG. 2 and so close to this bracket that the driving pin 14 engages in an arc-formed slot 32 in the flywheel. The slot 32 together with the driving pin 14 constitutes a second free wheel device, the free wheel area of which is determined by the length of the slot. In the example shown, the slot extends over an angle of approximately In the rest position of the device, the flywheel is in such a position that the driving pin 14 is approximately in the middle of the slot 32. On the underside of the flywheel is a driving pin 33 which is arranged to fall into a slot 34 on a Maltese cross arm 35 journalled on a shaft 36. The Maltese cross arm supports the movable contacts of the diverter switch comprising a main contact 37 and two auxiliary contacts 38 and 39. All three contacts are in known manner connected to each other by means of a bridging resistor 40 and to the fixed tap 41 of the diverter switch. The oscillatory motions of the Maltese cross arm round its shaft are controlled by a boss 42 on the underside of the flywheel.
The flywheel is combined with a disc brake 43 cooperating with a brake disc in the form of a circular ring part 44 on each side of the flywheel at its periphery. The brake comprises an upper brake block 45 journalled on a shaft 46 and a lower brake block 47 journalled at 48. The upper brake block has a claw 49 bearing against the lower brake block and controlling its motion in dependence on the upper brake block. A roll 50 is attached to the upper brake block, said roll rolling on a guide way on the upper side of the flywheel within the brake disc 44. The guide way consists of two parts. One part 52 is lower and located on the part of the disc which is opposite to the brake in the rest position of the device. The other art 51 is higher and covers the rest of the circumference of the guide way. The transitions 53 between the two parts are bevelled so that the roll 50 can roll from one part up on or down to the other part when the flywheel rotates. In the position shown in FIGS. 1 and 2, the guide roll is on the lower part 52 and the disc is braked on account of the force with which the spring 54 draws the two brake blocks 45 and 47 against the brake discs 44 of the flywheel. When the guide roll comes up on the higher part 51, the brake releases its engagement and the flywheel is able to rotate freely.
During a tap changing operation the disc attached on the shaft 1 turns half a turn. A appears from the figure, it is immaterial for the operation of the diverter switch whether the stage selector 18 steps upwards or downwards on the regulating winding. As soon as the disc 2 starts rotating, the selector contact in the stage selector 18 which is temporarily not current-carrying starts moving to its new position. At the same time the segment 6 turns under the action of the draw bar 4 and the arm 5 and the gear wheel 8 start rotating counterclockwise. This rotation takes place without resistance until the stop surface 1 1 is brought into contact against the driving pin 14, and this distance is thus the free wheeling part of the motion of the gear wheel, and the notch 10 with the stop surfaces 11 and 12 constitute its free or lost notion device. When the gear wheel is further turned, the slewing backet 13 now follows, and the spring device 16 attached to the driving pin 14 starts to be stretched. The upper end of the driving pin 14 now moves in the slot 32 in the flywheel. The flywheel is braked since the roll 50 on the disc brake is on a low part 52 of the guideway 51.
When the slewing bracket 13 with the driving pin 14 has turned approximately 90, the driving pin bears against one end surface of the slot 32, and now the flywheel is also brought into rotation against the action of the brake 43. The brake power is so great that the flywheel is safely prevented from accidental motion but not greater than allows it to be brought into rotation by the force by which the driving pin affects it. Now the gear wheel 8 as well as the slewing bracket 13 and the flywheel 31 are in motion and accompany one another in this motion in a counter-clockwise direction. In this position, the tap changing movement of the selector should be concluded. During the continuous rotary motion the spring device is stretched more and more and has attained full spring-tension when the driving pin 14 has reached a position which is diametrically opposite to the original position. As soon as this extreme position has been attained, the spring device passes over dead center and starts to operate in the opposite direction on the driving pin and gives the flywheel a more and more increasing counter-clockwise rotary motion.
Soon after said extreme position has been attained, the roll 50 on the brake goes up on the high part 51 of the guideway, so that the brake is released and the flywheel is free. The spring device now gives the flywheel a rapid counter-clockwise motion, which is possible partly because the flywheel is disengaged from the drive device of the gear wheel, partly because the brake has been released. The driving pin 33 of the flywheel enters the slot 34 of the Maltese cross arm and swings the arm 35 rapidly from the position shown in FIG. 3 to the position where the main contact 37 of the arm lies on the fixed contact 29. During this movement of the flywheel, after the pin 14 has reached its original position, the momentum of the flywheel will carry it on to approximately the position shown in FIG. 3. Approximately at the same time that the Maltese cross arm has completed the switching, the flywheel is in the position where the brake engages again and brakes the flywheel.
Because of the design of the free wheel device in the gear wheel, it does not matter if the flywheel should stop in a position which deviates somewhat from that shown in FIG. 3. The drive device always stop in its fixed position after a tap changing operation, and this means that the segment 6 and the gear wheel 8 are also in their correct position. The tap changing operation of the diverter switch cannot start until the flywheel starts to be driven by the spring device, and this cannot be done until the gear wheel has moved half its free wheel notch plus half a turn.
If a spring fracture should occur in the spring device, the diverter switch is operated directly from the drive device since the gear wheel continues to rotate and drive the flywheel until the drive device has reached its second end position. Then the diverter switch has concluded its tap changing movement and entered for certain its definite working position and has been locked in this position by the Maltese cross arm and the boss 42 on the underside of the flywheel, just as in a normal switching.
The tap changer is also provided with equipment for manual switching in the event of a current interruption or readjustment of the tap changer for inspection and the like. As will appear from the description, the work when switching the diverter switch is facilitated because the flywheel is then unbraked.
The parts of the circumference of the flywheel where the brake is active and inactive, respectively, can easily be changed by making the low part 52 in the form of an encircling ring and the high part in the form of a circular ring of suitable extension. The high part is riveted screwed on to the low part. If the holes in the high part are made longish, this part becomes adjustable and it will be easy to adjust the appropriate position for the engaging and disengaging of the brake.
' 1. A tap changer for transformers which comprises a selector switch and a diverter switch, a member (1) for operating said selector switch, means for transmitting movement of said member to said diverter switch for producing rapid movements thereof comprising gear wheel operatively connected to said member, a spring device operatively connected to said gear wheel to be tensioned and released thereby, a flywheel, a first lostmotion connection between said gear wheel and said flywheel, said first lost-motion connection allowing motion of said gear wheel with respect to said flywheel until substantially the beginning of the tensioning of said spring device and, upon release of said spring means, imparting motion to said flywheel, and means operatively connecting said flywheel to the diverter switch.
2. In a tap changer as claimed in claim 1 the connection between said gear wheel and the spring device being a second lost motion connection.
3. In a tap changer as claimed in claim 2, said second lost-motion connection comprising a notch in said gear wheel, a part mounted to turn about the axis of rotation of said gear wheel, and a pin carried by said part and extending into said notch and operatively connected to said spring device.
operative during the part only of the motion of said flywheel which is produced during said release of said spring means.