WO2014056694A1

WO2014056694A1 - On-load tap changer with a tickler winding, and method for operating an on-load tap changer

Info

Publication number: WO2014056694A1
Application number: PCT/EP2013/069440
Authority: WO
Inventors: Dieter Dohnal
Original assignee: Maschinenfabrik Reinhausen Gmbh
Priority date: 2012-10-09
Filing date: 2013-09-19
Publication date: 2014-04-17
Also published as: DE102012109581A1

Abstract

The invention relates to an on-load tap changer (1) with a tickler winding (4) and to a method for operating an on-load tap changer (1) with a tickler winding (4). The on-load tap changer (1) is used to transfer a load from one step contact point (n) to the next step contact point (n+1) of a step transformer (T) without interruption. The on-load tap changer (1) has a main branch (2) and an auxiliary branch (3), both of which are connected to a load discharge line (10). A first selector contact (7) is provided in the main branch (2), and a second selector contact (8) is provided in the auxiliary branch (3). The tickler winding (4) is arranged in the main branch (2) between the first selector contact (7) and the load discharge line (10).

Description

On-load tap-changer with tickler winding and method for operating a

Load tap changer

The present invention relates to an on-load tap changer with Ticklerwindung for uninterrupted load switching from a tap tap to the next stage tapping of a tapped transformer. In particular, the on-load tap changer has a tickler winding for uninterrupted load switching from a tap tap to a next stage tap of a tap transformer. The on-load tap changer has a main branch and an auxiliary branch, both of which are connected to a load discharge. The main branch has a first selector contact and the auxiliary branch has a second selector contact.

Furthermore, the invention relates to a method for operating a tap changer. For tap changers, two different basic switching principles exist worldwide: On the one hand, the relatively slow switching reactor switch, which is still dominant in the USA today. Switching impedances, for example in the form of

Überschaltdrosselspulen, provided that avoid during the slow changeover from one winding tap to the next a stage short circuit and for the

Continuous load in stationary operation are dimensioned.

On the other hand, the fast switching over in comparison to the reactor switch

Resistance switch, often referred to by its inventor as "Jansen switch", which has prevailed in the rest of the world

Winding tap to the next fast, d. H. jumpy, and it is

Switching resistors are provided which prevent a step short circuit during the changeover. In this principle of switching these transfer resistors are charged only for a very short period of time. A operating according to the reactor switching principle tap changer, also on the

Applicant goes back, has become known from DE 197 43 865 C1. N and n + 1 are adjacent taps of the tap winding of the transformer. The tap changer has moving selector contacts and switching impedances, also called over-reactances. Between the two branches a vacuum switching cell is connected, wherein the corresponding connection for the load dissipation is made by a bypass switch. The bypass switch can - depending on the position - each of the two movable

Connect the selector contacts both individually and together with the load derivation. He It has two fixed bypass contacts and two movable bypass contacts. The movable bypass contacts are hinged together and connected to the load lead. Each of the two fixed bypass contacts is electrically connected to one of the movable selector contacts on each side thereof facing the vacuum switch cell. In the stationary state, the bypass switch bridges the two fixed bypass contacts and connects them together with the load derivation. At the beginning of a load switching this connection between the two fixed bypass contacts and thus the movable selector contacts is interrupted; in the switching sequence shown in Fig. 1, the bypass switch connects only to the original

Winding tap remaining movable selector contact with the load dissipation.

Thereafter, the vacuum switch cell opens, then the movable selector contact reaches the new winding tap, the vacuum switch cell closes again. Finally, the bypass switch resumes its initial position, d. H. his stationary position, a. Another known embodiment of an on-load tap changer, which also operates according to the reactor switching principle, is shown in FIG. This shows a this

Tap changer on the basis of typical circuit including switching sequence in the switching from one stage A to an adjacent stage B. n and n + 1 are here the adjacent taps of the tap winding of the transformer. MTSi and MTS ₂ are the movable selector contacts to be operated at the switch, X-, and X ₂ are the over-reactances. The load derivative Y is arranged between the reactances X ₁ and X ₂ . At the beginning of a load switching a load switching path MSV _{2 is} opened, the selector contact MTS ₂ can be moved to the tap n + 1 without current, then closes the load path MSV ₂ . Thus, a stationary position is established and switched to level B. The Überltreaktanzen X-, and X ₂ limit the circulating current l _c to a permissible for the current path of the transformer and the switch value.

The over-reactances X and X ₂ mentioned in the prior art also

Switching impedances are always designed so that they can limit the circulating current generated when switching over in the "bridging position"

Power classes this can be very large, these supernatant reactances, which are composed of a coil on a common ferromagnetic core, can assume a diameter of over one meter and a height of several meters. However, regardless of the power class, the over-reactance is always a huge cost factor for a transformer manufacturer. In addition to the large amount of material If this coil is arranged separately, the necessary installation space in the transformer tank also has a negative effect.

In operation, in addition to a warming of the Überretreaktanz. These

Heat energy is released to the surrounding transformer oil. For this reason, the cooling system of the transformer must be made larger and more powerful.

Another disadvantage of these coils is the enormous ohmic and magnetic losses that result from them. On the one hand, the many material of the coils during operation represents a large ohmic resistance. In addition, the shape of the over-reactances "coil core" generates high magnetic losses.

With tap changers, it is also already known to provide so-called Ticklerwindungen. These, in addition to the actual step winding existing on the same core separately arranged windings are dimensioned such that above them a voltage drops, the half of the step voltage, d. H. the voltage between two adjacent taps of the tap winding corresponds. By selectively connecting the Ticklerwindung so that the number of possible adjustable voltage levels can be doubled. In the journal "SIEMENS Energy & Automation Technology", March 1986, pages 16 to 18, the operation of a Ticklerwindung, also referred to as "auxilliary winding" described in an autotransformer. The taps of the step winding allow there a grading in 1, 25% jumps; By switching on the tickler winding, a switchable graduation of 0.625% is achieved. In such autotransformers, it is possible to pass through the control range of the voltage of +/- 10% in 32 steps of 0.625% each.

Furthermore, from DE 195 18 272 C1, which goes back to the applicant, a tap changer with Ticklerwindung known, which is provided for Beschälten fixed stage contacts. This tap changer has two selector contacts, wherein one of the selector contacts is connected in series with a Ticklerwindung and a resistance to the load transfer. The second selector contact is connected via a switch with load derivation. Both load branches are connected immediately before the load dissipation via an antiparallel-connected thyristor pair. A disadvantage of the tap changers with Ticklerwindung lies mainly in the switch contacts. If these are designed as simple mechanical switching contacts, the burn-up occurring during the switching is very large. This causes the Tap-changer is very maintenance-intensive. In order to avoid the disadvantages of simple mechanical switches, an antiparallel-connected thyristor pair is used, which is temporarily switched into the circuit by means of further mechanical switches. However, this is very expensive and can be used without special control only in conjunction with ohmic switching resistors.

Since there is always a desire to manufacture the individual assemblies as inexpensively as possible and to keep the magnetic and ohmic losses as low as possible, transformer manufacturers try this goal by the saving of material, i. Amount of copper for the lines, size of the iron core and space required by the Überschalttreaktanz reach. In addition, there is always an attempt to reduce the costs by the structural design and by the smaller dimensions of all live parts, in particular the load switching sections. The object of the invention is to provide an on-load tap-changer for uninterrupted load switching, which is simple in construction while still ensuring a high degree of safety and reliability.

This object is achieved by an on-load tap changer with a Ticklerwindung with the features of claim 1. The subclaims relate to particularly advantageous developments of the invention.

The object of the invention is to provide a method for operating an on-load tap-changer for uninterrupted load switching, which ensures a high degree of safety and reliability in load switching.

This object is achieved by a method for operating an on-load tap-changer, which has the features of claim 10. The dependent subclaims relate to particularly advantageous developments of the method according to the invention.

The general inventive idea is to place a tickler winding in only one load leg of an on-load tap changer, thereby reducing material and eliminating the ohmic and magnetic losses that would result from over-current reactance. The invention will be explained in more detail by way of example with reference to the figures. Show it: Figure 1 is a known from the prior art embodiment of an on-load tap changer according to the reactor switching principle;

FIG. 2 e an on-load tap changer according to the invention with a tickler winding;

Figure 3 e n inventive on-load tap m t thyristors as switching elements;

Figure 4 e n inventive on-load tap m t permanent main contacts;

Figure 5 e n an inventive on-load tap m t a

Interruption switching element;

Figure 6 shows an inventive on-load tap-changer with two

Interruption switching elements; and

Figure 7 shows an inventive on-load tap-changer with three

Interruption switching elements.

FIG. 2 illustrates an on-load tap-changer 1 according to the invention. This has a main branch 2 and an auxiliary branch 3. The main branch 2 consists of a

Ticklerwindung 4 and a series-connected in series first switching element 5. The auxiliary branch 3 has a second switching element 6. When carrying out a

Load switching from a tap tap n to a next tap tap n + 1, the first and the second switching elements 5, 6 are actuated in a certain order while the on-load tap-changer 1 is moved from a tap tap n to the next n + 1. The direct tap of the step taps n, n + 1 via a first

Selector contact 7 and a second selector contacts 8. These are formed in this example as a unit with the on-load tap-changer 1, but can also be designed as separate components. In this embodiment, the first selector contact 7 with the main display 3 and the second selector contact 8 with the auxiliary branch 3 is mechanically electrically connected. Thus, it is possible to conduct a current flow from a tap tap n of a tap winding 9 via the first selector contact 7, the tickler winding 4 and the first switching element 5 to a load discharge line 10.

The second selector contact 8 provides an electrically conductive connection between a tap tap n and the load lead 10 via the auxiliary branch 3 with the second

Switching element 6 ago.

In the stationary state, ie before the start of a changeover from a step tap n to a next step tap n + 1, the current first flows from the tap winding 9 via the tap tap n and the closed first switching element 6 of the auxiliary current branch 3 to the load dissipation 10 The main branch 2 does not conduct current due to the open first switching element 5.

In the first switching step of a switching, from a tap tap n to a

adjacent stage tap n + 1, first the main branch 2 or at least the first selector contact 7, is passed to the adjacent Stufenabzapfung n + 1. By a subsequent simultaneous closing of the first switching element 5 of the main branch 2 and opening of the second switching element 6 of the auxiliary branch 3, the current flow from the step tap n + 1 of the tap winding 9 is directed via the main branch 2 and the Ticklerwindung 4 to the load discharge 10. The actuation of both switching elements 5, 6 must in

Zero crossing of the sinusoid of the current take place.

Since the turns of the Ticklerwindung 4 are aligned against the turns of the tap winding 9, not actually switched voltage is delivered to the load dissipation 10. In the exemplary embodiment, the Ticklerwindung 4 exactly half as many

Windings as a step of the step winding 9 on. Thus, in this step, only half a tap tapping n was switched on instead of one whole. Subsequent to this switching, the auxiliary branch 3 or at least the second selector contact 8, which is connected to it in an electrically conductive manner, is moved onto the step tap n + 1. By opening the first switching element 5 and closing the second switching element 6, the current is passed through the auxiliary branch 3 to the load dissipation, so that a full stage tap is switched on.

FIG. 3 shows an embodiment of the invention in which the first and second switching elements 5, 6 are designed as thyristors. This can be implemented in a single element, a so-called commutation cell. By using thyristors, a very fast switching can be realized. This is particularly important, since switching takes place in the exact zero crossing of the sinusoid of the current and thus no circulating current. In addition to thyristors, other fast switching elements such as IGBT ^' s are suitable.

4 shows a further embodiment of the invention is shown in which, in parallel to the first and second switching element 5 and 6, in each case a first and a second permanent main contact 1 1 and 12 is arranged. This permanent main contacts 1 1, 12 are used to relieve the first and second switching element 5, 6 in the stationary state and thus reduce their size and their cost. This is particularly advantageous when thyristors are used as switching elements 5, 6. FIG. 5 shows a further embodiment according to the invention of the on-load tap-changer 1, which has a tickler winding 4. This Ticklerwindung 4 is connected in series with an ohmic resistance 13. In this case, the Ticklerwindung 4 with the first selector contact 7 with a tap tap n and the ohmic resistance 13 is electrically connected to a first terminal 14.1 of a bypass switching element 14. This arrangement forms the main branch 2.

The second selector contact 8, which also bears on the step tap n, is connected to a second connection 15. 2 of a changeover switching element 15. By the Umstellschaltelement 15, it is possible to connect the second selector contact 8 via a line 16 to a second terminal 14.2 of the bypass switching element 14. This arrangement forms the auxiliary branch 3. Furthermore, a first terminal 15.1 of the Umstellschaltelements 15 with a connection point 17 which is located between the Ticklerwindung 4 and the switching resistor 13 is connected. This arrangement forms the auxiliary branch 18. The switching switching element 15 allows the connection of the first terminal 15.1 or the second terminal 15.2 to connect either the first selector contact 7 via the tickler winding 4 or the second selector contact 8 directly to the line 16.

By bypassing the first and / or the second terminal 14.1 and / or 14.2, the bypass switching element 14 connects the main branch 2, the auxiliary branch 3 or both simultaneously with the load lead 10. For this, however, the changeover switching element 15 must be connected to the second terminal 15.2.

In addition, the on-load tap-changer 1 has an interrupting switching element 19, which connects the main branch 2, between the over-resistance 13 and bypass switching element 14, and the auxiliary branch 3, between Umstellschaltelement 15 and bypass switching element 14, in the closed state.

In the stationary state, the switching element 15 is connected to its second terminal 15.2. The bypass switching element 14 contacts its second terminal 14.2 and the interruption switching element 9 is opened. The current flow runs via the auxiliary branch 3 to the load discharge 10. The changeover from a step tap n to an adjacent step tap n + 1 takes place in the following switching steps:

Main branch 3 or at least the first selector contact 7 switch to the stage tapping n + 1;

Interrupt switch element 19 is closed;

- By-pass switching element 14 switch from the second terminal 14.2 to the first terminal 14.1, wherein when switching briefly both ports 14.1 and 14.2 are contacted;

Interruption switching element 19 is opened;

Changeover switching element 15 switch from the second connection 15.2 to the first connection 15.1;

Interrupt switch element 19 is closed;

Bypass switching element 14 switch from the first terminal 14.1 to the second terminal 14.2, wherein when switching short term both terminals 14.1 and

14.2 be contacted;

Interruption switching element 19 is opened; and

Auxiliary branch 3 or at least the second selector contact 8 switch to the stage tapping n + 1.

After this switching step, the current is passed through the connected turns between the tap n and n + 1 and the Ticklerwindung 4 to the load discharge 10. As already described in FIG. 2, the turns of the tickler winding 4 counteract the

Windings of the step winding 9 are aligned, thus only half of the

Windings, which lie between the stage taps n and n + 1, connected to the load discharge 10. In order to be able to switch on the entire stage, the following switching steps are necessary:

Interrupt switch element 19 will close;

- Bypassschaltelement 14 switch from the second terminal 14.2 to the first

Terminal 14.1, wherein when switching short term both ports 14.1 and 14.2 are contacted;

Interruption switching element 19 is opened;

- Change-over switching element 15 switch from the first terminal 15.1 to the second terminal 15.2; Bypassschalteiement 14 switch from the first port 14.1 to the second port 14.2, which are contacted during switching both ports 14.1 and 14.2; and

Open circuit element 19 is opened.

After the last switching step, the connection of all turns between the

Step taps n and n + 1 is done.

FIG. 6 shows a further embodiment according to the invention of the on-load tap-changer 1, which has a tickler winding 4 as a switching-over reactance. This Ticklerwindung 4 is connected in series with a switching resistor 13 and an interrupting switching element 20. In this case, the Ticklerwindung 4 is electrically connected to the first selector contact 7 with a tap tap n and the interruption switching element 20 to the load discharge 10. The switching resistor 13 is disposed between the tickler winding 4 and the breaker switching element 20. This arrangement forms the main branch 2.

The voltage applied to the tap n, second selector contact 8 is connected to the terminal 15.2 of the Umstellschaltelements 15. By Umstellschaltelement 15, it is possible to connect the second selector contact 8 via an interrupt switching element 21 with the load discharge 10. However, this is only possible if the breaker switch 21 is in the closed state. This arrangement forms the auxiliary branch 3. The secondary branch 18 is formed by the conductive connection between the first terminal 15.1 of the Umstellschaltelements 15 with a connection point 17, which is located between the Ticklerwindung 4 and the switching resistor 13.

In the stationary state, i. before the start of a changeover from a tap tap n to a next tap tap n + 1, the current first flows from the tap winding 9 via the tap tap n via the auxiliary branch 3 to the load discharge line 10. The interrupt switch element 21 is closed and the switchover switch element 15 connects its second connection 15.2. The interruption switching element 20 in the main branch 2 is open.

The changeover from a step tap n to an adjacent step tap n + 1 takes place in the following switching steps: Main branch 3 or at least the first selector contact 7 switch to the stage tapping n + 1;

Interrupt switch element 20 is closed;

- Interrupt switching element 21 is opened;

Interrupt switch element 21 is closed;

Interrupt switch element 20 is opened; and

- Auxiliary branch 3 or at least the second selector contact 8 switch to the

Step tap n + 1.

Also in this embodiment of the invention, after this switching step, the current is conducted via the connected windings between the step tap n and n + 1 and the tickler winding 4 to the load discharge 10. Since, as already described in FIG. 2, the turns of the tickler winding 4 are oriented counter to the turns of the step winding 9, only half of the windings which are between the two

Step taps n and n + 1 are connected to the load lead 10. In order to be able to switch on the entire stage, the following switching steps are necessary:

Interrupt switch element 20 is closed;

Interrupt switch element 21 is opened;

- Main branch 3 or at least the first selector contact 7 switch to the

Step tap n + 1;

- Change-over switching element 15 switch from the first terminal 15.1 to the second terminal 15.2;

- Breaking element 21 is closed; and

Interrupt switch element 20 is opened. Also in this embodiment, the connection of all turns between the stage taps n and n + 1 is done after the last switching step.

In the first switching step of a switchover, from a tap tap n to an adjacent tap tap n + 1, the main branch 2 or at least the first selector contact 7 is first fed to the adjacent tap tap n + 1. Once this is done, the interrupt switch element 20 of the main branch 2 is closed and then the breaker switch element 21 is opened. The current now flows from for the load transfer 10 via the main branch 3 with the Ticklerwindung 4 and the switching resistor 13. In the next step, the Umstellschaltelement 15 switches to its first terminal 15.1. As soon as this is done first the

Open circuit element 21 of the auxiliary branch 3 is closed and the

Open circuit element 20 of the main branch 2 is opened. Finally, the auxiliary branch 3, in particular the second selector contact 8, reaches the step tap n + 1. In this state, the current flows from the tap tap n + 1 via the Ticklerwindung 4, the side branch 18 and the interruption switching element 21 for load dissipation 10. In Figure 7, another embodiment of the invention of the on-load tap-changer 1, which has a Ticklerwindung 4 as Überretreaktanz shown. This Ticklerwindung 4 is connected in series with an interruption switch 22. In this case, the Ticklerwindung 4 via deb first selector contact 7 with a tap tap n and the interrupt switching element 22 to the load dissipation 10 is electrically connected. This arrangement forms the main branch 2.

The second selector contact 8 is connected directly to the load lead 10 via an interrupt switch element 23. This subassembly 18 is composed of the transient resistor 13 and an interruption switching element 24 connected in series with it. In this case, the transient resistance 13 is connected to the connection point 17 and the interruption switching element 24 to the load dissipation 10.

In the stationary state, the interruption switching element 23 of the auxiliary branch 3 is closed, and the interruption switching elements 22 and 24 of the main branch 2 and the sub-branch 18 are opened. The current flow runs via the auxiliary branch 3 to the load discharge 10.

The changeover from a step tap n to an adjacent step tap n + 1 takes place in the following switching steps:

- Main branch 3 or at least the first selector contact 7 switch to the

Step tap n + 1;

- Breaker switch 24 is closed;

- Breaker element 22 is closed;

Interrupt switch element 23 is opened;

- Breaker switch 24 is opened; and - Auxiliary branch 3 or at least the second selector contact 8 switch to the

Step tap n + 1.

Windings of the step winding 9 are aligned, thus only half of the

Interrupt switch element 24 is closed;

Interrupt switch element 22 is opened;

Interrupt switch element 23 is closed; and

- Open circuit element 24 is opened.

After the last switching step, the connection of all turns between the

Step taps n and n + 1 is done. The use of a Ticklerwindung 4 is particularly advantageous because it sits on the core of the transformer and thus does not need to be arranged as a separate component. This saves material costs for the turns and the core. In addition, a Ticklerwindung 4 requires less space than a separate Überretreaktanz, especially since this is only half as large. The size of the entire transformer is reduced considerably.

The combination of Ticklerwindung 4 in conjunction with thyristors as switching elements makes Überltreaktanzen to limit the resulting switching from a tap tap n to the next step tap n + 1 resulting circular currents superfluous. Due to the fast and exact wiring of the thyristors, the current flow can be performed exactly in the zero crossing of the sinusoid. The use of permanent skin contacts increases the life of the thyristors and reduces their size, since the current is passed over these after completion of the switching process. The use of Ticklerwindung 4 in conjunction with simple mechanical switches in the form of bypass switching elements or Umstellschaltelementen and vacuum interrupters in the form of interruption switching elements with a resistive Overload resistor is also advantageous. Mechanical switches are inexpensive components and can be used very easily with no-load switching. In order to limit resulting circulating currents, the use of one or more vacuum interrupters in conjunction with an ohmic resistance is particularly advantageous. Vacuum interrupters belong to the switching devices with particularly high overload capacity and electrical life.

LIST OF REFERENCE NUMBERS

1 on-load tap-changer

2 main branch

3 auxiliary branch

4 Ticklerwindung

5 first switching element

6 second switching element

7 first dial contact

8 second selector contact

9 step winding

10 load derivation

1 1 first permanent main contact

12 second permanent main contact

13 Overload resistor

14 bypass switching element

14.1 first connection

14.2 second connection

15 change-over switching element

15.1 first connection

15.2 second connection

16 line

17 connection point

18 Nebenzweig

19 interruption switching element

20 interrupt switch element

21 interrupt switch element

22 interrupt switch element

23 interrupting switching element

24 interrupt switch element n tap tap

n + 1 next stage tapping

Claims

claims

1 . On-load tap-changer (1) with a tickler winding (4) for uninterrupted load switching from one tap tap (n) to a next tap tap (n + 1) of a tap-changer (T),

wherein the on-load tap-changer (1) has a main branch (2) and an auxiliary branch (3), both of which are connected to a load lead (10) and

in that a first selector contact (7) is provided in the main branch (2) and a second selector contact (8) is provided in the auxiliary branch (3),

characterized,

in that the tickler winding (4) is arranged in the main branch (2) between the first selector contact (7) and the load lead (10).

2. on-load tap-changer (1) according to claim 1,

wherein in the main branch (2) between the Ticklerwindung (4) and the load dissipation (10), a first switching element (5) is connected in series, and

wherein the auxiliary branch (3) has a second switching element (6).

3. on-load tap-changer (1) according to claims 2,

wherein the first and second switching element (5, 6) are designed as a thyristor, IBGT or the like.

4. on-load tap-changer (1) according to one of claims 2 to 3,

wherein the first and the second switching element (5, 6) each have a parallel thereto connected permanent main contact (1 1, 12).

5. on-load tap-changer (1) according to claim 1,

the main branch (2) having a switchover resistor (13) connected in series with the tickler winding (4) and connected to a first terminal (14.1) of a bypass switching element (14),

wherein the auxiliary branch (3) consists of a second connection (15.2) of a changeover switching element (15), the changeover switching element (15), a line (16) and a second connection (14.2) of the bypass switching element (14),

wherein the second terminal (15.2) is connected to the second selector contact (8), the line (16) connecting the changeover switching element (15) to the second terminal (14.2) of the bypass switching element (14), wherein a sub-branch (18) connecting the second terminal (15.2) of the switching switching element (15) to a connection point (17) disposed between the tickler coil (4) and the switching resistor (13) is provided.

the bypass switching element (14) connecting either the main branch (2) or the auxiliary branch (3) to the load lead (10),

wherein the changeover switch element (15) connects or disconnects the auxiliary branch (18) from the line (16),

wherein an interruption switching element 19 is provided which connects the main branch (2) between the over-resistance (13) and the second connection (14.2) of the bypass switching element (14) to the auxiliary branch (3) on the line (16).

6. on-load tap-changer (1) according to claim 1,

the main branch (2) having an interruption circuit (20) connected in series with the tickler winding (4) and the over-resistance (13),

wherein the auxiliary branch (3) consists of the connection (15.2) of a Umstellschaltelements (15), the Umstellschaltelement (15) and a breaker switch element (21), wherein a secondary branch (18) the second terminal (15.2) of the Umstellschaltelements (15) with the Connection point (17), which is arranged between the Ticklerwindung (4) and the switching resistor (13) connects,

the main branch (2) being directly connected to the load lead (10),

and wherein the changeover switching element (15) connects or disconnects the sub-branch (18) with the interruption switching element (21).

7. on-load tap-changer (1) according to claim 1,

the main branch (2) having an interruption switching element (22) connected in series with the tickler winding (4),

the main branch (2) being directly connected to the load lead (10),

wherein the auxiliary branch (3) has an interruption switching element (23),

the auxiliary branch (3) being directly connected to the load lead (10),

wherein a secondary branch (18) has an interruption switching element (23) with the switching resistor (3) arranged in series therewith, and

wherein the overdrive resistor (13) is connected to the connection point (17) disposed between the tickler coil (4) and the overdrive resistor (13).

8. on-load tap-changer (1) according to one of claims 5 to 7,

wherein the interruption switching elements (19, 20, 21, 22, 23, 24) are formed as vacuum interrupters.

9. on-load tap-changer (1) according to one of claims 1 to 8,

wherein the tickler coil (4) has half as many turns as a step between the step tap (n) to the next stage tap (n + 1).

10. A method for operating an on-load tap-changer (1) with a Ticklerwindung (4) for the uninterrupted load switching from a tap tap (s) to a next stage tapping (n + 1) of a tapped transformer (T); characterized by the following steps:

- That a main branch (2) and an auxiliary branch (3) of the on-load tap-changer (1) with a first selector contact (7) and a second selector contact (8) electrically conductively with a tap tap (n) or a next stage tapping (n + 1 ) get connected; and

- That the Ticklerwindung (4) in the main branch (2) between the first selector contact (7) and a first switching element (5) is arranged so that when switching from a tap tap (n) to a next stage tapping (n + 1) a Flow of current from the next stage tapping (n + 1) of the tap winding (9) via the main branch (2) and the Ticklerwindung (4) is directed to a load discharge (10)

- That at the load switching the Ticklerwindung (4) is not used as an overrunning reactance.

1 1. Method according to claim 10,

wherein in the auxiliary branch (3) a second switching element (6) is arranged, and

wherein closing or opening of the first switching element (5) or the second switching element (6), a flow of current from the tap tap (s) or the next stage tap (n + 1) to a load discharge (10) via the main branch (2) and / or the auxiliary branch (3) is made possible.

12. The method according to any one of claims 10 or 11,

wherein, in the case of a changeover from one tap tap (n) to a next tap tap (n + 1), first the main branch (2) or the first dial contact (7) is pushed onto the tap tap (n),

after which the first and the second switching element (5, 6) are simultaneously actuated, wherein the first switching element (5) is closed and the second switching element (6) is opened, after which the second load branch (3) or the second selector contact (8) is pushed onto the next stage tap (n + 1),

wherein thereafter the first and the second switching element (5) are operated simultaneously and wherein the first switching element (5) is opened and the second switching element (6) is closed.