LOAD STEP SWITCH AND METHOD FOR OPERATING A LOAD STEP SWITCH

Description

[0001] The invention relates to a load tap changer for uninterrupted switching between winding taps of a tap transformer under load and a method for actuating such a load tap changer. A load tap changer with hybrid switching technology is disclosed in DE-A-102010008973.

[0002] On-load tap changers are used for the uninterrupted switching between winding taps of a transformer. In known on-load tap changers based on the resistance-based switching principle, the circulating current flowing during the switching process, while the currently connected and the preselected new tap contact are simultaneously engaged, is limited by ohmic resistors. This ensures an uninterrupted change in the transformer's turns ratio. The ohmic resistance must be designed according to the specific circuit topology, the individual operating conditions, the load current, and the tap voltage—in other words, according to the specific application of the on-load tap changer. The tap voltage is defined as the voltage present between the currently connected and the preselected tap contact of the on-load tap changer.This resistor configuration is both complex and impacts the overall design of the tap changer. Depending on the application, a different number and size of resistors are required. Therefore, the resistor value affects the space required for the resistors and, consequently, the design of the other tap changer components.

[0003] The object of the invention is therefore to provide an improved concept for a tap changer that is easier to adapt to different applications.

[0004] This problem is solved by the subject matter of the independent claims. Further embodiments are described in the dependent claims.

[0005] The improved concept is based on the idea of ​​using semiconductor switching elements for load switching, completely eliminating the need for ohmic resistors. This also eliminates the complex design of resistors, and the same load tap changer can therefore be used within a selected power range up to a maximum load current and a maximum tap voltage. As a first aspect of the improved concept, a load tap changer is specified for the uninterrupted switching between winding taps of a tap transformer. The load tap changer comprises a load changer for switching from a first fixed contact to a second fixed contact of the load tap changer and a selector for power-free pre-selection of the fixed contacts.The selector comprises a first selector arm and a second selector arm for pre-selecting, each of which can be actuated independently and can contact any of the fixed contacts. Each fixed contact is electrically connected to a winding tap of the step-down transformer. The total number of fixed contacts depends on the number of winding taps.

[0006] The load switch has a total of three branches with switching elements for carrying out the switching operation. A main branch with a mechanical switching element that can connect the first selector arm to a load connection via the mechanical switching element; a first auxiliary branch with a first semiconductor switching element that is configured in parallel to the first main branch and can connect the first selector arm to the load connection; and a second auxiliary branch with a second semiconductor switching element that can connect the second selector arm to the load connection.

[0007] The proposed load tap changer does not contain an ohmic resistance as a switching resistance, which requires a complex design, and can therefore be used in the same design within a selected power range up to a maximum load current and a maximum step voltage.

[0008] The first and second semiconductor switching elements are preferably designed as IGBT switching elements.

[0009] According to a preferred embodiment, a varistor is arranged parallel to the first and second auxiliary branches.

[0010] According to at least one further embodiment, the load tap changer can assume two stationary positions in which both selector arms are on the same fixed contact. A first stationary position in which the first and second selector arms contact the first fixed contact and the first selector arm is connected to the load conductor via the main branch, and a second stationary position in which the first and second selector arms contact the second fixed contact and the first selector arm is connected to the load conductor via the main branch.

[0011] Each fixed contact preferably has a first contact surface which can be contacted by the first selector arm, and a second contact surface which can be contacted by the second selector arm.

[0012] According to at least one embodiment, the mechanical switching element in the main branch is designed as a permanent main contact or as a switch.

[0013] According to a second aspect of the improved concept, a method for operating a load tap changer designed according to the first aspect of the improved concept is specified.

[0014] With regard to the method, 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 aspect of the improved concept or one of the associated advantageous embodiments.

[0015] The procedure for switching from a first fixed contact to a second fixed contact, i.e. in a first switching direction of the load tap changer, comprises the following steps: Switching on a first semiconductor switching element, switching a second selector arm to the second fixed contact and opening a mechanical switching element, actuating the first semiconductor switching element and the second semiconductor switching element in such a way that a load current is switched from the first fixed contact to the second fixed contact, switching a first selector arm to the second fixed contact, closing the mechanical switching element, switching off the second semiconductor switching element.

[0016] According to one embodiment, the actuation of the first and second semiconductor switching elements occurs in a so-called "gap-lock" operation. Specifically, this means that the first semiconductor switching element is initially switched off, and the load current then flows through a varistor arranged in parallel with the first semiconductor switching element. Subsequently, the second semiconductor switching element is switched on, thus switching the load current to the second fixed contact. The second semiconductor switching element is switched on after a defined duration in a range of, for example, 2 µs to 10 µs, preferably after 5 µs. Alternatively, it can be provided that the second semiconductor switching element is switched on as soon as it has been detected that the switching off of the first semiconductor switching element has been successfully completed.

[0017] According to a further embodiment, the first and second semiconductor switching elements are actuated in a so-called "overlapping" operation. Specifically, this means that the second semiconductor switching element is switched on first, and a circulating current then flows. The rise of the circulating current is limited by the inductance of the stage, i.e., the portion of the regulating winding of the step-down transformer located between the first and second fixed contacts. The second semiconductor switching element is preferably switched on at the zero crossing of the stage voltage. Afterwards, the first semiconductor switching element is switched off, and the load current is thus switched to the second fixed contact. The first semiconductor switching element is switched off after a defined duration in a range of, for example, 2 µs to 10 µs, preferably after 5 µs.Alternatively, it can be provided that the first semiconductor switching element is switched off as soon as it has been detected that the switching on of the second semiconductor switching element has been successfully completed.

[0018] According to a preferred embodiment, the method for switching from the second fixed contact to the first fixed contact, i.e. in a second switching direction of the load tap changer, comprises the steps Switching on the second semiconductor switching element, opening the mechanical switching element, switching the first selector arm to the first fixed contact, actuating the first semiconductor switching element and the second semiconductor switching element in such a way that the load current is switched from the second fixed contact to the first fixed contact, closing the mechanical switching element, switching off the first semiconductor switching element and switching the second selector arm to the first fixed contact.

[0019] According to one embodiment, the actuation of the first and second semiconductor switching elements occurs in a so-called "gap-lock" operation. Specifically, this means that the second semiconductor switching element is first switched off, and then the load current flows through a varistor arranged in parallel with the second semiconductor switching element. Afterward, the first semiconductor switching element is switched on, thus switching the load current to the first fixed contact. The first semiconductor switching element is switched on after a defined duration in a range of, for example, 2 µs to 10 µs, preferably after 5 µs. Alternatively, it can be provided that the first semiconductor switching element is switched on as soon as it has been detected that the switching off of the second semiconductor switching element has been successfully completed.

[0020] According to a further embodiment, the first and second semiconductor switching elements are actuated in a so-called "overlapping" operation. Specifically, this means that the first semiconductor switching element is switched on first, and a circulating current then flows. The rise of the circulating current is again limited by the inductance of the stage. The first semiconductor switching element is preferably switched on at the zero crossing of the stage voltage. Afterwards, the second semiconductor switching element is switched off, and the load current is thus switched to the first fixed contact. The second semiconductor switching element is switched off after a defined duration in a range of, for example, 2 µs to 10 µs, preferably after 5 µs.Alternatively, it can be provided that the second semiconductor switching element is switched off as soon as it has been detected that the switching on of the first semiconductor switching element has been successfully completed.

[0021] Accordingly, the switching between two adjacent fixed contacts, i.e., the actuation of the individual switching elements, takes place in the second switching direction in exactly the reverse order as in the first switching direction.

[0022] Further configurations and implementations of the method result directly from the various configurations of the tap changer and vice versa. In particular, one or more of the components and / or arrangements described with respect to the tap changer can be implemented accordingly for carrying out the method.

[0023] 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.

[0024] They show Figure 1 shows an exemplary embodiment of a load tap changer in a schematic representation; Figure 2 shows a schematic representation of an exemplary embodiment of a load tap changer according to the improved concept; Figures 3a to 3 show an exemplary switching sequence of the load tap changer. Figure 2 Figures 3d' to 3f' show another exemplary switching sequence of the load tap changer. Figure 2 .

[0025] The figures merely represent exemplary embodiments of the invention, without, however, limiting the invention to the illustrated embodiments.

[0026] In Figure 1Figure 1 schematically illustrates an exemplary embodiment of a load tap changer 10 for a tap-change transformer 1. The tap-change transformer 1 has a main winding 2 and a variable winding 3 with different winding taps N1, ..., NJ, ..., NN, which are switched on and off by the load tap changer 10. For this purpose, the load tap changer 10 comprises a selector 30, which can contact the different winding taps N1, ..., NJ, ..., NN of the variable winding 3 by means of two movable selector contacts, and a load changeover switch 20, which performs the actual load switching from the currently connected to the new, preselected winding tap. The load current flows from the currently connected winding tap NJ or NJ+1 via the respective selector contact and the load changeover switch 20 to a load connection 13.

[0027] Figure 2shows a schematic representation of an exemplary embodiment of a load tap changer according to the improved concept.

[0028] According to the improved concept, the load tap changer 10 comprises at least one first fixed contact 11 and one second fixed contact 12, each of which can be connected to a winding tap of the regulating winding 3 of the tap changer 1. The total number of fixed contacts depends on the number of winding taps. Each fixed contact 11, 12 has a first contact surface and a second contact surface. Furthermore, the load tap changer 10 comprises a selector 30 with a first selector arm 31 and a second selector arm 32, which can be actuated independently of each other and can contact each of the fixed contacts. The first movable selector arm 31 can contact the first contact surfaces of the fixed contacts 11, 12, but not the second contact surfaces. Similarly, the second movable selector arm 32 can contact the second contact surfaces of the fixed contacts 11, 12, but not the first contact surfaces. Figure 2This is a schematic sketch of an exemplary embodiment of the load tap changer; in particular, the arrangement of the contact surfaces opposite each other is not absolutely necessary.

[0029] The load tap changer 10 further comprises a load changeover switch 20 for carrying out the actual load switching between the preselected fixed contacts 11, 12. The load changeover switch 20 has a total of three current branches. A main branch 21 with a mechanical switching element 22, which can connect the first selector arm 31 to the load terminal 13; a first auxiliary branch 23 with a first semiconductor switching element 24, which is arranged in parallel to the main branch 21 and can connect the first selector arm 31 to the load terminal 13; and a second auxiliary branch 25 with a second semiconductor switching element 26, which can connect the second selector arm 32 to the load terminal 13.

[0030] In the representation in Figure 2The load tap changer 10 is in a stationary position. The first and second selector arms 31, 32 are both on the first fixed contact 11. The load current IL flows from the contacted fixed contact 11 via the first selector arm 31, the main branch 21, and the closed mechanical switching element 22 to the load termination 13. The two semiconductor switching elements 24 and 26 are switched off.

[0031] In the Figures 3a to 3j This is an example switching sequence of the load tap changer from Figure 2 depicted.

[0032] After a switching command for a changeover from the first fixed contact 11 to the second fixed contact 12, in a first step ( Figure 3a ) the first semiconductor switching element is switched on.

[0033] In the next step ( Figure 3bThe second selector arm 32, which is de-energized, is moved from the first fixed contact 11 to the second fixed contact 12, and the mechanical switching element 22 is opened. The in Figure 3c The depicted state is reached in which the load current IL flows through the first auxiliary branch 23 and the activated first semiconductor switching element 24.

[0034] According to the so-called "gap-stop" operating mode, the first semiconductor switching element 24 is then preferably switched off at the zero crossing of the current ( Figure 3d ). The temporal profile of the current can be recorded by means of a current sensor (not shown) which is arranged in the current branch of the derivative 13.

[0035] When the first semiconductor switching element 24 is switched off, the load current IL passes to the varistor 27 arranged in parallel to it ( Figure 3e ).

[0036] The next step, as shown in Figure 3fThe second semiconductor switching element 26 is switched on after a defined duration, for example 5 µs. Alternatively, the second semiconductor switching element can be switched on as soon as it has been detected that the switching off of the first semiconductor switching element has been successfully completed.

[0037] The load current IL is thus switched to the second fixed contact 12 and flows via the second auxiliary branch 25 and the activated second semiconductor switching element 26 ( Figure 3g ).

[0038] The first selector arm 31, which is now de-energized, is then switched to the second fixed contact 12, as in Figure 3g indicated by an arrow.

[0039] In the next step ( Figure 3h ) the mechanical switching element 22 is closed again and then the second semiconductor switching element 26 is switched off.

[0040] The load tap changer 10 has now reached the second steady position, which is in Figure 3jAs shown, with the closing of the mechanical switching element 22, the load current IL returns to the main branch 21. The first and second selector arms 31, 32 are both located on the second fixed contact 12, and the load current IL now flows from the second fixed contact 12 via the first selector arm 31 and the main branch 21 with the closed mechanical switching element 22 to the load connection 13. The load switching to the second fixed contact 12 is thus complete.

[0041] If the tap changer 10 is operated in the "overlapping" mode instead of the "gap" mode, then after the step that is in Figure 3c The figure shows that the second semiconductor switching element 26 is switched on, so that now both semiconductor switching elements 24 and 26 are switched on ( Figure 3d' ).

[0042] A circulating current IC then flows from the first selector arm 31, which is still contacting the first fixed contact 11, via the first auxiliary branch 23 and the second auxiliary branch 25 to the second selector arm 32, which is already on the second fixed contact 12, and from there via the part of the control winding 3 located between the first fixed contact 11 and the second fixed contact 12 back to the first selector arm 31 ( Figure 3e' ). The increase in the circulating current is limited by the inductance of the stage, i.e., the part of the control winding 3 of the step-down transformer 1 that is located between the first fixed contact 11 and the second fixed contact 12.

[0043] In the next step (3f'), the first semiconductor switching element 24 is switched off. The load current IL is thus switched to the second fixed contact 12 and flows via the second auxiliary branch 25 and the still activated second semiconductor switching element 26 ( Figure 3gFrom this point onwards, the "overlapping" operation is again identical to the "gapless" operation of the load tap changer (according to Figures 3g to 3j ).

[0044] A switch from the second fixed contact 12 to the first fixed contact 11 takes place in exactly the reverse order, that is, according to the Figures 3j to 3a .

[0045] It is assumed that the present disclosure and many of its accompanying advantages are understood from the foregoing description. Furthermore, it is obvious that various modifications to the shape, construction, and arrangement of the components can be made without deviating from the disclosed subject matter or without foregoing all material advantages. The described embodiment is merely illustrative, and such modifications are included in the following claims. It is further understood that the invention is defined by the following claims. REFERENCE SIGNS

[0046] 1 Step transformer 2 Main winding 3 Regulating winding 10 Load tap changer 11 First fixed contact 12 Second fixed contact 13 Load feeder 20 Load switch 21 Main branch 22 Mechanical switching element 23 First auxiliary branch 24 First semiconductor switching element 25 Second auxiliary branch 26 Second semiconductor switching element 27 Varistor 30 Selector 31 First selector arm 32 Second selector arm (N 1 , ..., NJ , ..., NN )winding taps

Claims

1. On-load tap-changer (10) for uninterrupted switching between winding taps (N1, ..., NJ, ..., NN) of a tapped transformer (1), comprising a diverter switch (20) for bushing a diverter switch operation from a first fixed contact (11) to a second fixed contact (12) of the on-load tap-changer (10), a selector (30) for powerless change-over selector of the fixed contacts (11, 12) comprising a first selector arm (31) and a second selector arm (32) which can be actuated independently of each other and can contact each of the fixed contacts (11, 12), wherein the diverter switch (20) for bushing the advanced retard switch operation has a main path (21) with a mechanical switching element (22), which can connect the first selector arm (31) directly to a load derivation (13) via the mechanical switching element (22), a first auxiliary path (23) with a first semiconductor switching element (24), which is formed in parallel with the main path (21) and can connect the first selector arm (31) directly to the load bleeder (13), a second auxiliary branch (25) with a second semiconductor switching element (26), which can connect the second selector arm (32) directly to the load feeder (13). wherein the on-load tap-changer (10) has a first stationary position, in which the first selector arm (31) and the second selector arm (32) contact the first fixed contact (11) and the first selector arm (31) is connected directly to the load bleeder (13) via the main path (21), and a second stationary position, in which the first selector arm (31) and the second selector arm (32) contact the second fixed contact (12) and the first selector arm (32) is directly connected to the load feeder (13) via the main path (21).

2. On-load tap-changer (10) according to the preceding claim, wherein a voltage-dependent resistor (27) is arranged in parallel with the first auxiliary branch (23) and the second auxiliary branch (25) in each case.

3. On-load tap-changer (10) according to one of the preceding claims, wherein the mechanical switching element (22) is designed as a main contact or as a circuit breaker.

4. Method for actuating an on-load tap-changer (10) which is designed according to one of the preceding claims 1 to 3, wherein an advanced retard switch from a first fixed contact (11) to a second fixed contact (12) comprises the following steps: Switching on a first semiconductor switching element (24), advanced retard switch of a second selector arm (32) to the second fixed contact (12) and opening of a mechanical switching element (22), actuating the first semiconductor switching element (24) and the second semiconductor switching element (26) in such a way that a load current is switched from the first fixed contact (11) to the second fixed contact (12), advanced retard switch of a first selector arm (31) to the second fixed contact (12), N / O contact of the mechanical switching element (22), moving to the open position of the second semiconductor switching element (26).

5. Method according to claim 4, wherein the actuation of the first semiconductor switching element (24) and the second semiconductor switching element (26) takes place in such a way that the first semiconductor switching element (24) is first moved to the open position and the load current then flows via a voltage-dependent resistor (27) arranged in parallel with the first semiconductor switching element (24), the second semiconductor switching element (26) is then switched on.

6. Method according to claim 4, wherein the actuation of the first semiconductor switching element (24) and the second semiconductor switching element (26) takes place in such a way that first the second semiconductor switching element (26) is switched on and a circular current then flows, then the first semiconductor switching element (24) is moved to the open position.

7. The method according to any one of the preceding claims 4 to 6, wherein the moving to the open position of the semiconductor switching elements (24, 26) takes place at the zero crossing of the current.

8. The method according to any one of the preceding claims 4 to 6, wherein the switching on of the semiconductor switching elements (24, 26) takes place at the zero crossing of the step voltage.

9. Method according to any one of the preceding claims 4 to 8, wherein upon an advanced retard switch from the second fixed contact (12) to the first fixed contact (11) the actuation of the selector arms (31, 32), the semiconductor switching elements (24, 26) and the mechanical switching element (22) takes place in exactly the reverse order.