On-load tap changer, method for actuating an on-load tap changer, and tapped transformer having an on-load tap changer

Abstract

A load tap changer (1) for uninterrupted switching between winding taps (NJ, NJ+1, ..., NN) of a step-down transformer (2), comprising several fixed contacts (3, 4), wherein the fixed contacts (3, 4) are configured such that each fixed contact (3, 4) is connected to a winding tap (NJ, NJ+1, ..., NN) of the step-down transformer (2), - a first selector arm (5) which can selectively contact each of the fixed contacts (3, 4), - a second selector arm (6) which can selectively contact each of the fixed contacts (3, 4), - a load connection (7), - a first main current branch (8) which connects the first selector arm (5) to the load connection (7) via at least a first current-limiting element (9), - a second main current branch (10) which connects the second selector arm (6) to the load connection (7) via at least a second current-limiting element (11), wherein - the load tap changer (1) further includes a bridging circuit (12) for selectively bridging the first current-limiting element (9) and / or the second current-limiting element (11) by means of at least one switching element (13, 14, 15, 16, 17, 18, 19) includes.

Description

[0001] The invention relates to a load tap changer for uninterrupted switching between winding taps of a tap changer, a method for actuating the load tap changer and a tap changer with such a load tap changer.

[0002] Load tap changers are known to be used for the uninterrupted switching between different winding taps of a control winding in a tap-changer, and thus for voltage regulation. For switching, load tap changers typically have two movable selector contacts that connect the winding taps, as well as additional switching contacts located in the current branches of the load tap changer. These contacts serve to electrically connect the winding tap connected by the respective selector contact to a load lead.

[0003] A well-known switching principle for on-load tap changers is the so-called reactor switching principle. This involves switching impedances that limit the current flowing through the on-load tap changer during the switching from one winding tap to an adjacent winding tap.

[0004] A load tap changer designed according to the reactor switching principle can assume two steady-state positions. In the so-called bridging steady-state position, one movable selector contact is electrically connected to a first winding tap, and the other movable selector contact is electrically connected to a winding tap of the tap changer adjacent to the first winding tap. In this steady-state position, a circulating current flows from the first winding tap through the load tap changer to the adjacent winding tap. The switching impedances are required to limit the circulating current and thus prevent a tap short circuit.

[0005] In the so-called non-bridged, stationary position, both movable selector contacts are electrically connected to the same winding tap of the step-down transformer. Here, too, the circulating current flows through the switching impedances, but a step short circuit cannot occur because both selector contacts connect to the same winding tap. Consequently, the switching impedances are not needed in the non-bridged, stationary position, but current still flows through them, thus generating unnecessary losses.

[0006] It is therefore an object of the present invention to provide an improved concept for a load tap changer based on the reactor switching principle and its actuation, which avoids the losses generated by the switching impedances and thus reduces the power loss of the entire tap transformer.

[0007] This problem is solved by the respective subject matter and method of the independent claims. Further embodiments are the subject of the dependent claims.

[0008] According to a first aspect, the invention proposes a load tap changer for the uninterrupted switching between winding taps of a tap-changer. The load tap changer comprises several fixed contacts configured such that each fixed contact can be connected to a winding tap of the tap-changer. Furthermore, the load tap changer comprises a first selector arm that can selectively contact any of the fixed contacts, a second selector arm that can selectively contact any of the fixed contacts, a load connection, a first main current branch that connects the first selector arm to the load connection via at least one first current-limiting element, and a second main current branch that connects the second selector arm to the load connection via at least one second current-limiting element.

[0009] Furthermore, the load tap changer includes a bridging circuit for selectively bridging the first current-limiting element and / or the second current-limiting element by means of at least one switching element.

[0010] The bridging circuit and the at least one switching element are designed to carry the entire load current flowing through the load tap changer, at least temporarily, in particular when the load tap changer is in a stationary position.

[0011] The bypass circuit allows the load current in the steady state to be diverted from the current-limiting elements to the bypass circuit. This means that only a minimal fraction of the load current flows through the current-limiting elements, and the losses caused by current flow through these elements can therefore be largely avoided. This also reduces the power loss of the step-down transformer, which in turn has a positive effect on its service life and environmental impact.

[0012] According to one embodiment, the at least one switching element can be switched in such a way that the first current-limiting element and the second current-limiting element can be bridged simultaneously.

[0013] This can further reduce losses.

[0014] According to another embodiment, the bridging circuit comprises at least three switching elements.

[0015] According to one embodiment, the bypass circuit comprises a first switching element, a second switching element and a third switching element, wherein the first switching element and the third switching element serve to bypass the first current-limiting element, and the second switching element and the third switching element serve to bypass the second current-limiting element.

[0016] This bridging circuit arrangement provides safe, low-loss operation of the load tap changer while it is in the non-bridging, stationary position.

[0017] According to another embodiment, the switching elements are designed as mechanical switching contacts that carry the load current when closed. The mechanical switching contacts are thus designed, due to their material and design (e.g., material thickness), to carry the current continuously while the load tap changer is in a stationary position.

[0018] According to another embodiment, the bypass circuit comprises a first switching element, a second switching element, a third switching element, and a fourth switching element. The first and second switching elements are each connected in parallel to the first current-limiting element, and the third and fourth switching elements are each connected in parallel to the second current-limiting element.

[0019] This bridging circuit arrangement also provides safe, low-loss operation of the load tap changer while it is in the non-bridging, stationary position.

[0020] According to another embodiment, the first switching element or the fourth switching element is designed as a vacuum switching tube.

[0021] Designing the first and fourth switching elements as vacuum interrupters offers the advantage of completely eliminating contamination of the insulating medium surrounding the tap changer, such as oil, which would occur with mechanical changeover contacts due to arcing and contact erosion. Furthermore, vacuum interrupters have a long service life.

[0022] According to another embodiment, the second switching element or the third switching element is designed as a mechanical switching contact which carries the load current when closed.

[0023] The mechanical switching contacts are therefore designed, due to their material and design, for example a sufficiently dimensioned material thickness, to carry the current continuously while the load tap changer is in a stationary position.

[0024] According to another embodiment, the first switching element and the fourth switching element are designed as vacuum switching tubes.

[0025] According to a further embodiment, the second and third switching elements are designed as mechanical switching contacts that carry the load current when closed. The mechanical switching contacts are thus designed, due to their material and design (e.g., material thickness), to carry the current continuously while the load tap changer is in a stationary position.

[0026] According to another embodiment, the first current-limiting element and the second current-limiting element are designed as switching impedances.

[0027] The switching impedance can be designed as an electrical resistance in any way.

[0028] According to a preferred embodiment, the switching impedance comprises a core made of iron and a coil of copper wire wound around the core. The losses occurring during the current flow through the switching impedance arise predominantly in the coil and less so in the core. Thus, it is primarily copper losses that can be reduced by the solution according to the invention.

[0029] According to a second aspect, the invention proposes a method for actuating a load tap changer for uninterrupted switching between winding taps of a tap transformer.The load tap changer comprises several fixed contacts, the fixed contacts being configured such that each fixed contact can be connected to a winding tap of the tap transformer, a first selector arm that can selectively contact any of the fixed contacts, a second selector arm that can selectively contact any of the fixed contacts, a load connection, a first main current branch that connects the first selector arm to the load connection via at least one first current-limiting element, a second main current branch that connects the second selector arm to the load connection via at least one second current-limiting element, and a bypass circuit for selectively bypassing the first current-limiting element and / or the second current-limiting element by means of at least one switching element. The method comprises the following process steps: Switching the load tap changer to a stationary position in which the first selector arm and the second selector arm contact the same fixed contact and the first current-limiting element and the second current-limiting element are energized, closing at least one switching element of the bridging circuit so that the load current flows through the bridging circuit.

[0030] With regard to the method, reference is made to the preceding explanations, preferred features and / or advantages in an analogous manner as they have already been explained in relation to the first aspect of the invention or one of the associated advantageous embodiments.

[0031] By closing at least one switching element, a large part of the load current is switched from the first main current branch and the second main current branch to the bridging circuit, so that almost no current flows through the current-limiting elements and losses of the current-limiting elements can be reduced to a minimum.

[0032] According to one embodiment, the bridging circuit of the load tap changer comprises a first switching element, a second switching element and a third switching element, wherein the method step of closing the at least one switching element of the bridging circuit comprises closing the first switching element, the second switching element and the third switching element.

[0033] According to a preferred embodiment, the first switching element, the second switching element and the third switching element are fired simultaneously.

[0034] According to a further embodiment, the bypass circuit comprises a first switching element, a second switching element, a third switching element, and a fourth switching element, wherein the first and second switching elements are each connected in parallel to the first current-limiting element, and the third and fourth switching elements are each connected in parallel to the second current-limiting element. The process step of closing at least one switching element of the bypass circuit includes closing the first and fourth switching elements, wherein the first and fourth switching elements briefly carry the load current, and closing the second and third switching elements, wherein the second and third switching elements carry the load current, while the load tap changer is in the steady-state position.

[0035] According to a preferred embodiment, the first switching element and the fourth switching element are closed first, and then in a next process step the second switching element and the third switching element are closed.

[0036] According to a preferred embodiment, the first switching element and the fourth switching element are designed as vacuum switching tubes that briefly carry the load current during switching between two adjacent winding taps of the tap-changer. This prevents sparking in the insulating medium, for example oil, of the load tap changer caused by the arc that occurs during switching, and reduces contamination in the form of gases in the insulating medium caused by sparking.

[0037] According to a further preferred embodiment, the second switching element and the third switching element are designed as mechanical switching elements to permanently conduct the load current while the load tap changer is in the stationary position.

[0038] Since part of the commutation of the current has already taken place through the vacuum switching tubes in the previous process step, the commutation work to be performed by the mechanical switching elements is less, and consequently the arcing and contact erosion are also less pronounced.

[0039] According to a third aspect, the invention proposes a step-down transformer comprising a control winding with winding taps, and a load tap changer that can be connected to the control winding and that is designed according to the first aspect of the invention and is suitable for carrying out a method according to the second aspect of the invention.

[0040] With regard to the third aspect, reference is made to the preceding explanations, preferred features and / or advantages in an analogous manner as has already been explained with regard to the first and second aspects of the invention or one of the associated advantageous embodiments.

[0041] Further embodiments and implementations of the step-down transformer result directly from the various embodiments of the load tap-switch and the method.

[0042] The invention is explained in detail below with reference to exemplary embodiments and the drawings. Components that are identical, functionally identical, or have an identical effect may be provided with identical reference numerals. Identical components or components with identical function may be explained only with respect to the figure in which they first appear. The explanation is not necessarily repeated in the subsequent figures.

[0043] They show Figure 1 shows a first embodiment of a load tap changer according to the invention in a schematic representation; Figure 2 shows a second embodiment of the load tap changer according to the invention in a schematic representation; Figure 3 shows an exemplary sequence of the method according to the invention; Figure 4 shows a further exemplary sequence of the method according to the invention.

[0044] In Figure 1Figure 1 schematically illustrates a first embodiment of a load tap changer 1 according to the invention. The load tap changer 1 serves for the uninterrupted switching between winding taps NJ, NJ+1, ..., NN of a regulating winding 23 of a step-down transformer 2. The load tap changer 1 comprises at least a first fixed contact 3 and a second fixed contact 4, each of which can be connected to a winding tap NJ, NJ+1 of the regulating winding 23 of the step-down transformer 2. The total number of fixed contacts 3, 4 depends on the total number of winding taps NN. Each fixed contact 3, 4 has at least one contact surface. Furthermore, the load tap changer 1 comprises a first selector arm 5 and a second selector arm 6, which can contact each of the fixed contacts 3, 4, in particular the contact surfaces of the fixed contacts 3, 4.

[0045] In the Figure 1In the position shown, the load tap changer 1 is in a non-bridging, stationary position, in which the first selector arm 5 and the second selector arm 6 contact the same fixed contact 3.

[0046] The load tap changer 1 further comprises a first main current branch 8, which connects the first selector arm 5 to a load connection 7 via a first current-limiting element 9, and a second main current branch 10, which connects the second selector arm 6 to the load connection 7 via a second current-limiting element 11. According to this embodiment, the two current-limiting elements 9 and 11 are configured as switching impedances.

[0047] Furthermore, the load tap changer 1 includes a bypass circuit 12 for selectively bypassing the first current-limiting element 9 and the second current-limiting element 11. According to this embodiment, the bypass circuit 12 comprises a total of three switching elements for bypassing the two current-limiting elements 9 and 11: a first switching element 13, a second switching element 14, and a third switching element 15. The first switching element 13 and the third switching element 15 serve to bypass the first current-limiting element 9, and the second switching element 14 and the third switching element 15 serve to bypass the second current-limiting element 11.

[0048] According to this embodiment, the three switching elements 13, 14 and 15 are designed, for example, as mechanical switching contacts.

[0049] The load tap changer 1 also has further switching elements 20, 21 and 22, namely a vacuum switching tube 20, which is connected between the two main current branches 8 and 10, and two bypass contacts 21 and 22, which each establish the electrical connection to the load feeder 7. By appropriately actuating the movable selector arms 5 and 6 and the switching elements 20, 21 and 22, switching is performed between the adjacent winding taps NJ, NJ+1 of the regulating winding 23 of the step-down transformer 2, or the respective fixed contacts 3, 4 of the load tap changer 1.

[0050] In Figure 2 A second embodiment of the load tap changer 1 according to the invention is shown in a schematic representation. With regard to the load tap changer 1, reference is made to the preceding explanations concerning the load tap changer 1 from [reference to relevant section]. Figure 1Reference is made in an analogous manner, and the following discussion focuses solely on the differences and additional features.

[0051] In the Figure 2 In the position shown, the load tap changer 1 is also in a non-bridging, stationary position, in which the first selector arm 5 and the second selector arm 6 contact the same fixed contact 3.

[0052] According to this embodiment, the load tap changer 1 has a bridging circuit 12 which comprises a total of four switching elements 16, 17, 18, 19 for bridging the two current-limiting elements 9 and 11. A first switching element 16 and a second switching element 17 are arranged in parallel to each other and each in parallel to the first current-limiting element 9, and a third switching element 18 and a fourth switching element 19 are also connected in parallel to each other and each in parallel to the second current-limiting element 11. According to this embodiment, the first switching element 16 and the fourth switching element 19 are, for example, designed as vacuum switching tubes, and the second switching element 17 and the third switching element 18 are, for example, designed as mechanical switching contacts. The vacuum switching tubes are advantageously designed to briefly conduct the load current and thereby prevent sparking in the insulating medium.The mechanical switching contacts are advantageously designed to carry the load current continuously while the load tap changer 1 is in the stationary position.

[0053] In the Figure 1 and 2 The respective load tap changer is shown in an exemplary single-phase configuration. However, the inventive solution is also applicable in a three-phase tap changer arrangement.

[0054] In Figure 3 An exemplary sequence of the process according to the invention is shown. Advantageously, the process is described in Figure 3 The method shown uses the load tap changer 1. Figure 1 carried out. Regarding the load tap changer 1, reference is made to the preceding explanations concerning the load tap changer from Figure 1 Reference is made in an analogous manner, and the following discussion focuses solely on the differences and additional features.

[0055] According to this exemplary embodiment of the method according to the invention, in step a) the load tap changer 1 is switched to a stationary position in which the first selector arm 5 and the second selector arm 6 contact the same fixed contact 3, 4 and the first current-limiting element 9 and the second current-limiting element 11 are energized.

[0056] Then, in step b), the first switching element 13, the second switching element 14 and the third switching element 15 are closed.

[0057] In this switching position, which represents the non-bridging steady state of the load tap changer, the load current is diverted from the current-limiting elements to the bridging circuit, namely the first switching element, the second switching element, and the third switching element. As a result, only a minimal fraction of the load current flows through the current-limiting elements, and the losses caused by the current flow through these elements can therefore be largely avoided.

[0058] In Figure 4 Another exemplary sequence of the inventive method is shown. Advantageously, the process is described in Figure 4 The method shown uses the load tap changer 1. Figure 2 carried out. Regarding the load tap changer 1, reference is made to the preceding explanations concerning the load tap changer 1, as it is used in connection with the Figure 1 and 2The description above is referenced in an analogous manner, and the following discussion focuses solely on the differences and additional features.

[0059] According to this exemplary embodiment of the method according to the invention, in step a) the load tap changer 1 is also switched to a stationary position in which the first selector arm 5 and the second selector arm 6 contact the same fixed contact 3, 4 and the first current-limiting element 9 and the second current-limiting element 11 are energized.

[0060] Subsequently, in step b) the first switching element 16 and the fourth switching element 19 are closed and in a following step c) the second switching element 17 and the third switching element 18 are closed.

[0061] In this switching position, where the load tap changer is also in the non-bridging steady-state position, the load current is diverted from the current-limiting elements to the bridging circuit. In this exemplary embodiment of the method, this diversion occurs in two steps (b) and (c), whereby the current is initially only briefly transferred to the first and fourth switching elements 16 and 19 before finally being commutated to the second switching element 17 and the third switching element 18, which carry the current as long as the load tap changer is in this switching position. As a result, only a minimal fraction of the load current flows through the current-limiting elements, and the losses caused by the current flow through these elements can therefore be largely avoided. REFERENCE MARK

[0062] 1 Load tap changer 2 Step transformer 3 Fixed contact 4 Fixed contact 5 First selector arm 6 Second selector arm 7 Load shunt 8 First main current branch 9 First current limiting element 10 Second main current branch 11 Second current limiting element 12 Bypass circuit 13 First switching element 14 Second switching element 15 Third switching element 16 First switching element 17 Second switching element 18 Third switching element 19 Fourth switching element 20 Vacuum switching tube 21 Bypass contact 22 Bypass contact 23 Control winding NJ , N J+1 , ..., NN Winding taps of 23

Claims

1. Load tap changer (1) for uninterrupted switching between winding taps (N J , N J+1 , ..., N N ) of a step-down transformer (2), comprising several fixed contacts (3, 4), wherein the fixed contacts (3, 4) are configured such that each fixed contact (3, 4) is connected to a winding tap (N J , N J+1 , ..., N N) of the step-down transformer (2), - a first selector arm (5) which can selectively contact each of the fixed contacts (3, 4), - a second selector arm (6) which can selectively contact each of the fixed contacts (3, 4), - a load connection (7), - a first main current branch (8) which connects the first selector arm (5) to the load connection (7) via at least a first current-limiting element (9), - a second main current branch (10) which connects the second selector arm (6) to the load connection (7) via at least a second current-limiting element (11), wherein - the load tap changer (1) further comprises a bridging circuit (12) for selectively bridging the first current-limiting element (9) and / or the second current-limiting element (11) by means of at least one switching element (13, 14, 15, 16, 17, 18, 19) includes.

2. Load tap changer (1) according to claim 1, wherein - the at least one switching element (13, 14, 15, 16, 17, 18, 19) is switchable in such a way that the first current-limiting element (9) and the second current-limiting element (11) can be bridged simultaneously.

3. Load tap changer (1) according to claim 1 or 2, wherein - the bridging circuit (12) comprises at least three switching elements (13, 14, 15, 16, 17, 18, 19).

4. Load tap changer (1) according to any one of the preceding claims 1 to 3, wherein - the bridging circuit (12) comprises a first switching element (13), a second switching element (14) and a third switching element (15), wherein - the first switching element (13) and the third switching element (15) serve to bridge the first current-limiting element (9), and - the second switching element (13) and the third switching element (15) serve to bridge the second current-limiting element (11).

5. Load tap changer (1) according to one of the preceding claims 3 or 4, wherein - the switching elements (13, 14, 15) are designed as mechanical switching contacts which carry the load current when closed.

6. Load tap changer (1) according to any one of the preceding claims 1 to 3, wherein - the bridging circuit (12) comprises a first switching element (16), a second switching element (17), a third switching element (18) and a fourth switching element (19), - the first switching element (16) and the second switching element (17) are each connected in parallel to the first current-limiting element (9), and - the third switching element (18) and the fourth switching element (19) are each connected in parallel to the second current-limiting element (11).

7. Load tap changer (1) according to claim 6, wherein - the first switching element (16) and / or the fourth switching element (19) is / are designed as a vacuum switching tube, and - the second switching element (17) and / or the third switching element (18) is / are designed as a mechanical switching contact which carries the load current when closed.

8. Load tap changer (1) according to any one of the preceding claims 1 to 7, wherein - the first current limiting element (9) and the second current limiting element (11) are designed as switching impedances.

9. Method for actuating a load tap changer (1) for uninterrupted switching between winding taps (N J , N J+1 , ..., N N ) of a step-down transformer (2), comprising several fixed contacts (3, 4), wherein the fixed contacts (3, 4) are configured such that each fixed contact (3, 4) is connected to a winding tap (N J , N J+1 , ..., N N) of the step-down transformer (2), a first selector arm (5) which can selectively contact each of the fixed contacts (3, 4), a second selector arm (6) which can selectively contact each of the fixed contacts (3, 4), a load connection (7), a first main current branch (8) which connects the first selector arm (5) to the load connection (7) via at least a first current-limiting element (9), a second main current branch (10) which connects the second selector arm (6) to the load connection (7) via at least a second current-limiting element (11), and a bridging circuit (12) for selectively bridging the first current-limiting element (9) and / or the second current-limiting element (11) by means of at least one switching element (13, 14, 15, 16, 17, 18, 19), wherein the method comprises the following process steps: - switching the load tap changer (1) into a stationary position,in which the first selector arm (5) and the second selector arm (6) contact the same fixed contact (3, 4) and the first current-limiting element (9) and the second current-limiting element (11) are energized, - closing of at least one switching element (13, 14, 15, 16, 17, 18, 19) of the bridging circuit (12), so that the load current flows through the bridging circuit (12).

10. Method according to claim 9, wherein the bridging circuit (12) comprises a first switching element (13), a second switching element (14) and a third switching element (15), wherein - closing the at least one switching element (13, 14, 15) of the bridging circuit (12) comprises closing the first switching element (13), the second switching element (14) and the third switching element (15).

11. The method of claim 9, wherein the bypass circuit (12) comprises a first switching element (16), a second switching element (17), a third switching element (18), and a fourth switching element (19), the first switching element (17) and the second switching element (18) each being connected in parallel to the first current-limiting element (9), and the third switching element (18) and the fourth switching element (19) each being connected in parallel to the second current-limiting element (11), wherein - closing the at least one switching element (16, 17, 18, 19) of the bypass circuit (12) comprises closing the first switching element (16) and the fourth switching element (19), wherein the first switching element (16) and the fourth switching element (19) briefly conduct the load current, and - closing the second switching element (17) and the third switching element (18), wherein the second switching element (17) and the third switching element (18) carry the load current,while the load tap changer (1) is in the stationary position.

12. Step-down transformer (2), comprising - a control winding (23) with winding taps (N J , N J+1 , ..., N N ), - a load tap changer (1) which can be connected to the control winding (23) and is designed according to one of the preceding claims 1 to 8.

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