The invention relates to an on-load tap changer with separate selector and load changeover switch for uninterrupted changeover between different winding taps of a tapped transformer under load. The tap changers of the type stated in the introduction have a separate selector for power-free preselection of the winding tap that is to be switched over to, as well as a load changeover switch for the actual changeover from the previous to the preselected new winding tap. Since this changeover takes place abruptly, on-load tap changers of that kind have a force accumulator.
Such a force accumulator for a load changeover switch is already known from DE-PS 19 56 369 as well as DE-PS 28 06 282 [GB 2,014,794]. It is drawn up, i.e. stressed, at the start of each actuation of the on-load tap changer by the drive shaft thereof. The known force accumulator substantially consists of a pull-up carriage and a jump carriage, between which force accumulator springs as force accumulators are arranged. In these known force accumulators guide rods are provided on which pull-up carriages as well as jump carriages are mounted to be movable therealong independently of one another. At the same time, the guide rods form the guide for the force accumulator springs.
The pull-up carriage is moved linearly relatively toward the jump carriage by an eccentric connected with the drive shaft; the force accumulator springs disposed therebetween are thereby stressed. When the pull-up carriage has reached its new end position, a locking, which until then is fixed, of the jump carriage is released. The jump carriage now abruptly follows—since it stands under the force of the force accumulator springs—the afore-mentioned linear movement of the pull-up carriage, similarly linearly. This abrupt movement of the jump carriage is converted into a rotational movement of a drive output shaft, which in turn actuates the load changeover switch. An alternating to-and-fro switching between two positions is thus realized in this force accumulator.
A further force accumulator, there termed spring jump drive, is known from WO89/08924, the storage spring of which is stressable by a drive. In that case the driven element is connected with a special coupling element that can be triggered in only one direction regardless of the direction of rotation of the drive.
WO2006/004527 [U.S. Pat. No. 7,982,142] relates to a further arrangement of that kind, in which the permanent main contacts of an on-load tap changer are actuated always in the same rotational direction, regardless of the drive direction of the drive shaft, by a special mechanical transmission.
A quite similar arrangement is known from WO2007/067144 [U.S. Pat. No. 7,942,073]. A device for transmission of a rotational movement in a load changeover switch is described therein, wherein the rotational movement of a drive shaft, which is rotatable in both directions, is converted into a rotational movement of a drive output shaft always rotating in the same direction.
The force accumulators, which are known from the prior art, for an on-load tap changer of the kind stated in the introduction thus allow either to-and-fro switching in the case of switching processes taking place in succession or onward switching always in the same direction.
The object of the invention is to indicate a tap changer of the kind, which is stated in the introduction, with a force accumulator that enables multiple switching in one direction or alternatively also to-and-fro switching, independently of the respective direction of rotation of the drive output shaft. The force accumulator according to the invention shall be of simple construction able to dispense with complicated mechanical means for movement reversal and able to be actuated directly by any direction of rotation of the drive shaft even in the case of several switching processes taking place in succession.
A force accumulator is indeed already known from WO2007/095978 [U.S. Pat. No. 8,119,939] that can be stressed by a drive shaft, which is rotating in desired directions, and follows this rotational movement after triggering. However, this known force accumulator is suitable merely for an on-load tap changer of the load selector type in which preselection of the winding tap and actual load changeover are constructionally combined. It is not suitable for an on-load tap changer of the kind, which is stated in the introduction, with separate selector and load changeover switch. This is particularly because in the case of the known force accumulator a fixed trigger angle results, which corresponds with the spacing between adjacent—respectively connectable—load selector contacts in the oil vessel.
The object of the invention is fulfilled by an on-load tap changer with a force accumulator according to claim 1. The subclaims relate to particularly advantageous developments of the invention.
It is particularly advantageous with the invention that the drive shaft can be actuated in any rotational direction regardless of whether switching in the direction of ‘higher’ or ‘lower’ is to take place, wherein at the same time the force accumulator can be similarly drawn up in any direction and can be triggered later. In other words: the force accumulator in the case of the invention is appropriate equally in the case of a drive shaft repeatedly rotating in the same direction and a drive shaft rotating in alternating directions, without complicated mechanical means—as in the prior art—being needed for rotational direction reversal or rotational direction standardization.
The invention shall be explained in more detail in the following by way of example on the basis of drawings, in which:
FIG. 1 shows an on-load tap changer according to the invention, more precisely the drive thereof without load changeover switch contacts and selector, in schematic illustration in rest position,
FIG. 2 shows this on-load tap changer after start of actuation,
FIG. 3 shows this on-load tap changer in the case of continued actuation, i.e. pull-up of the force accumulator,
FIG. 4 shows this on-load tap changer in the case of a fully stressed force accumulator at the instant of triggering thereof,
FIG. 5 shows this on-load tap changer after triggering of the force accumulator and thus actuation of the load changeover switch contacts (not illustrated),
FIG. 6 shows an on-load tap changer according to the invention in schematic, complete illustration,
FIG. 7 shows the actuation sequence of an on-load tap changer according to the invention as well as the associated travel/time diagram in the case of a complete changeover from n to n+1, and
FIG. 8 shows the actuation sequence of an on-load tap changer according to the invention in the case of a subsequent load changeover from n+1 back to n in arrow direction.
The drive of an on-load tap changer according to the invention is schematically shown in FIG. 1. It comprises a drive shaft, which is actuated by a drive (not illustrated here). Disposed on the drive shaft 1 is a gear 2 that co-operates with a further gear 3, the mounting of which is not illustrated. An abutment 4 is located on the gear 3. This abutment 4 co-operates with a further abutment 5a arranged on an intermediate shaft 6, which is disposed centrally within the gear 3 and rotatable independently thereof. Arranged at the abutment 5a is a pin 5 that in turn is connected with an actuating rod 7 of a force accumulator 8; a force accumulator spring 9 can be drawn up by it. A further abutment 10 is provided in the lower region of the intermediate shaft 6 and co-operates with a counter-abutment 11 on a drive output wheel 12. The drive output wheel 12 is again rotatable independently of the previously mentioned components. It comprises a roller 13 that co-operates with a Geneva wheel 14, i.e. can engage therein. The Geneva wheel 14 is in turn connected with a load changeover switch drive 15, which is only schematically shown and which for its part actuates the load changeover switch not shown here. The illustrated Geneva gear is only one possible form of construction of a possible step transmission within the scope of the invention.
The on-load tap changer according to the invention thus has two separate freewheels: a first freewheel, consisting of abutment 4 and co-operating abutment 5a, and a second freewheel, consisting of abutment 10 and counter-abutment 11.
FIG. 1 shows this on-load tap changer at the start of actuation. The drive shaft 1 begins to rotate, thus also the gear 2 and the gear 3. Since the abutment 4 still runs freely on the gear 3, the other components still remain in the rest position.
FIG. 2 shows this on-load tap changer with continued rotation of the drive shaft 1, the abutment 4 now impinges on the abutment 5a of the intermediate shaft 6, rotates this and at the same time draws up the force accumulator 8, more precisely the force accumulator spring 9 thereof.
FIG. 3 shows the on-load tap changer according to the invention in the case of further drawing-up of the force accumulator 8. The abutment 10 now impinges on the counter-abutment 11 and the drive output wheel 12 begins to rotate.
FIG. 4 shows the position in the case of complete drawing-up of the force accumulator 8. The pin 5 and thus the actuating rod 7 of the force accumulator 8 have reached the dead-center point on the gear 3 and in the case of continued rotation the force accumulator spring 9 is abruptly relaxed. In this position the abutment 10 at the lower part of the intermediate shaft 6 impinges, without change, on the counter-abutment 11 of the drive output wheel 12, which is stationary until now, and further entrains this. The roller 13 in that case still runs freely.
FIG. 5 shows how as a consequence of the deflected force accumulator 8 the drive output wheel 12 rapidly rotates. Due to the rotation of the drive output wheel 12 the roller 13 engages in the Geneva wheel 14 and rotates this. The load changeover switch drive 15 is thus also rotated, which in turn abruptly actuates the load changeover switch, i.e. the contacts thereof. At the same time, however, the drive shaft 1 still rotates through a defined angle. If for whatever reasons, for example through breakage of the force accumulator spring 9, the force accumulator 8 should not happen to trigger and thus the Geneva wheel 14 cannot be actuated by the triggered force accumulator as actually intended, the new end position of the load changeover switch is nevertheless necessarily reached. This is due to the fact that the drive shaft 1, which still continues to rotate, guides—by way of the gears 2 and 3, the intermediate shaft 6 and the drive output wheel 12—the roller 13 for its part into the Geneva wheel 14. However, by contrast to the usual rapid actuation due to the triggered force accumulator 8, this now happens slowly and continuously. In all cases it is ensured by the invention that the load changeover switch necessarily reliably reaches its new position even in the explained fault case and cannot remain in an undefined intermediate state.
FIG. 6 shows the schematic overall construction of an on-load tap changer according to the invention. The illustration shows that a first freewheel 16 is provided between the gear 3 and force accumulator 8. This freewheel 16 consists of the abutment 4 shown in FIGS. 1 to 5 and the co-operating abutment 5a. In addition, the illustration shows that the force accumulator 8 acts on a further freewheel 17, which consists of the abutment 10 shown in FIGS. 1 to 5 and the co-operating counter-abutment 11. A delayed engagement in the Geneva wheel 14, and in fact through the roller 13 shown in FIGS. 1 to 5, takes place by way of this freewheel 17. The load changeover switch drive 15 for actuation of the load changeover switch thus rotates in the same direction as the drive shaft 1. Also shown is a load changeover switch housing 19, which encloses the load changeover switch, and thereunder a selector 20 that is continuously actuated by the drive shaft 1 for load-free preselection of the new winding tap that is to be subsequently switched over to.
FIG. 7 shows a switching sequence of an on-load tap changer according to the invention. The sequence in the case of changeover from a winding tap n to an adjacent new winding tap n+1 is shown in the upper part. It can be seen that at the start of a changeover process the drive shaft 1 rotates continuously and after a specific rotational angle begins to move the selector 20 from the previous to the new winding tap. After this process has been concluded and the selector 20 has reached its new position, the load changeover switch 18 is abruptly actuated, this taking place through the triggered force accumulator. Finally, as already explained further above, the drive shaft 1 continues to move by a specific amount before the changeover process is completely concluded. In the case of a further changeover in the same direction what is illustrated is repeated. The corresponding course of rotational angle is shown in the lower part of FIG. 7. It can be seen that the drive shaft, which continuously rotates, initially actuates the selector 20. Only after this has reached its position is the load changeover switch 18 triggered.
FIG. 8 shows a switching sequence in opposite rotational direction of the drive shaft, i.e. from the tap n+1 back to the tap n. The corresponding directions of movement of the drive shaft 1 are shown in each of FIGS. 7 and 8 by an arrow.
Overall, the invention makes it possible in simple manner for the separate load changeover switch to be actuated not only several times in succession in the same rotational direction of the drive shaft, but also alternatively in the case of rotational direction reversal of the drive shaft, in simple manner.
Patent Application
20130341166
