Patent Application
20240029966
The present disclosure relates to an on-load tap-changer for uninterrupted switching between winding taps of a tap-changing transformer under load, and to a method for actuating such an on-load tap-changer.
On-load tap-changers are used for uninterrupted switching between winding taps of a transformer. In on-load tap-changers that are based on the high-speed resistor switching principle, the circulating current that flows during the intermediately simultaneous contacting of the currently connected tap contact and the preselected new tap contact in the event of switching is limited by ohmic resistors, and thereby, ensures an uninterrupted change in the transmission ratio of the transformer. The ohmic resistor has to be designed depending on the specific circuit topology, the individual operating conditions as well as the load current and the step voltage, that is to say in particular in accordance with the respective application of the on-load tap-changer. Here, the voltage that is present between the currently connected tap contact and the preselected tap contact of the on-load tap-changer is referred to as the step voltage. On the one hand, this resistor design is complex and, on the other hand, it also affects the entire structural design of the tap-changer. Depending on the application, a different number and dimensioning of resistors is required here. The design of the resistance value therefore has an effect on the installation space required for the resistors and thus on the structural design of the other tap-changer components.
In an embodiment, the present disclosure provides an on-load tap-changer that uninterruptedly switches between winding taps of a tap-changing transformer. The on-load tap-changer has: a diverter switch configured to perform a switchover from a first fixed contact to a second fixed contact of the on-load tap-changer; and a selector configured to powerlessly preselect fixed contacts, the fixed contacts being the first fixed contact and the second fixed contact, the selector having a first selector arm and a second selector arm which are configured to be actuated independently of one another and configured to contact each of the fixed contacts. The diverter switch has, for performing the switchover: a main path with a mechanical switching element, the main path being configured to connect the first selector arm to a load take-off lead via the mechanical switching element, a first auxiliary path with a first semiconductor switching element, the first auxiliary path being parallel to the main path and configured to connect the first selector arm to the load take-off lead, and a second auxiliary path with a second semiconductor switching element, the second auxiliary path being configured to connect the second selector arm to the load take-off lead.
Subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. All features described and/or illustrated herein can be used alone or combined in different combinations. The features and advantages of various embodiments will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following:
Aspects of the present disclosure specify an improved concept for a tap-changer that can be adapted more easily to different applications.
Aspects of the improved concept are based on the idea of using semiconductor switching elements for diverter switch operation and completely dispensing with ohmic resistors. This also eliminates the complex design of the resistors and the on-load tap-changer can thus be used in one and the same design in a selected power range up to a maximum load current and a maximum step voltage.
In accordance with a first aspect of the improved concept, an on-load tap-changer for uninterrupted switching between winding taps of a tap-changing transformer is provided. The on-load tap-changer comprises a diverter switch for performing a switchover from a first fixed contact to a second fixed contact of the on-load tap-changer and a selector for powerlessly preselecting the fixed contacts. For preselection, the selector comprises a first selector arm and a second selector arm which can each be actuated independently of one another and can contact each of the fixed contacts. Each fixed contact is electrically connected to a winding tap of the tap-changing transformer. The total number of fixed contacts is dependent on the number of winding taps.
The diverter switch has a total of three paths with switching elements for performing the switchover: a main path with a mechanical switching element, which main path can connect the first selector arm to a load take-off lead via the mechanical switching element, a first auxiliary path with a first semiconductor switching element, which first auxiliary path is formed parallel to the main path and can connect the first selector arm to the load take-off lead, and a second auxiliary path with a second semiconductor switching element, which second auxiliary path can connect the second selector arm to the load take-off lead.
The on-load tap-changer, according to an aspect, does not contain an ohmic resistor as a transition resistor, which requires a complex design and can therefore be used in one and the same design in a selected power range up to a maximum load current and a maximum step voltage.
The first and the second semiconductor switching element are preferably designed as insulated gate bipolar transistor (IGBT) switching elements.
According to a preferred embodiment, a varistor is arranged parallel to the first and the second auxiliary path.
According to at least one further embodiment, the on-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 the second selector arm contact the first fixed contact and the first selector arm is connected to the load take-off lead via the main path, and a second stationary position, in which the first and the second selector arm contact the second fixed contact and the first selector arm is connected to the load take-off lead via the main path.
Each fixed contact preferably has a first contact face, which can be contacted by the first selector arm, and a second contact face, which can be contacted by the second selector arm.
According to at least one embodiment, the mechanical switching element in the main path is designed as a permanent main contact or as a circuit breaker.
In accordance with a second aspect of the improved concept, a method for actuating an on-load tap-changer which is formed in accordance with the first aspect of the improved concept is provided.
With regard to the method, reference is analogously made to the above explanations, preferred features and/or advantages, as has already been explained in relation to the first aspect of the improved concept or one of the associated, advantageous embodiments.
The method comprises, for switching over from a first fixed contact to a second fixed contact, i.e. in a first switching direction of the on-load tap-changer, the steps of moving a first semiconductor switching element to the closed position, switching over 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 over from the first fixed contact to the second fixed contact, switching over a first selector arm to the second fixed contact, closing the mechanical switching element, moving the second semiconductor switching element to the open position.
According to one embodiment, the first semiconductor switching element and the second semiconductor switching element are actuated in what is known as “intermittent” operation. Specifically, this means that initially the first semiconductor switching element is moved to the open position and then the load current flows via a varistor arranged parallel to the first semiconductor switching element. Thereafter, the second semiconductor switching element is moved to the closed position and the load current is thus switched over to the second fixed contact. The second semiconductor switching element is moved to the closed position after a specified period in a range of, for example, 2 μs to 10 μs, preferably after 5 μs. Alternatively, provision can be made for the second semiconductor switching element to be moved to the closed position as soon as it has been detected that the first semiconductor switching element has been successfully moved to the open position.
According to a further embodiment, the first semiconductor switching element and the second semiconductor switching element are actuated in what is known as “overlapping” operation. Specifically, this means that initially the second semiconductor switching element is moved to the closed position and then a circulating current flows. The increase in the circulating current is limited by the inductance of the step, i.e. the part of the tap winding of the tap-changing transformer that is located between the first and the second fixed contact. The second semiconductor switching element is preferably moved to the closed position at the zero crossing of the step voltage. Thereafter, the first semiconductor switching element is moved to the open position and the load current is thus switched over to the second fixed contact. The first semiconductor switching element is moved to the open position after a specified period in a range of, for example, 2 μs to 10 μs, preferably after 5 μs. Alternatively, provision can be made for the first semiconductor switching element to be moved to the open position as soon as it has been detected that the second semiconductor switching element has been successfully moved to the closed position.
According to a preferred embodiment, the method for switching over from the second fixed contact to the first fixed contact, i.e. in a second switching direction of the on-load tap-changer, comprises the steps of:
According to one embodiment, the first semiconductor switching element and the second semiconductor switching element are actuated in what is known as “intermittent” operation. Specifically, this means that initially the second semiconductor switching element is moved to the open position and then the load current flows via a varistor arranged parallel to the second semiconductor switching element. Thereafter, the first semiconductor switching element is moved to the closed position and the load current is thus switched over to the first fixed contact. The first semiconductor switching element is moved to the closed position after a specified period in a range of, for example, 2 μs to 10 μs, preferably after 5 μs. Alternatively, provision can be made for the first semiconductor switching element to be moved to the closed position as soon as it has been detected that the second semiconductor switching element has been successfully moved to the open position.
According to a further embodiment, the first semiconductor switching element and the second semiconductor switching element are actuated in what is known as “overlapping” operation. Specifically, this means that initially the first semiconductor switching element is moved to the closed position and then a circulating current flows. The increase in the circulating current is also limited here by the inductance of the step. The first semiconductor switching element is likewise preferably moved to the closed position at the zero crossing of the step voltage. Thereafter, the second semiconductor switching element is moved to the open position and the load current is thus switched over to the first fixed contact. The second semiconductor switching element is moved to the open position after a specified period in a range of, for example, 2 μs to 10 μs, preferably after 5 μs. Alternatively, provision can be made for the second semiconductor switching element to be moved to the open position as soon as it has been detected that the first semiconductor switching element has been successfully moved to the closed position.
Accordingly, a switchover between two adjacent fixed contacts, i.e. the actuation of the individual switching elements, takes place in the second switching direction in exactly the opposite order as in the first switching direction.
Further embodiments and implementations of the method are directly evident from the various embodiments of the tap-changer, and vice versa. In particular, individual components or a plurality of the components and/or assemblies described in relation to the tap-changer can be implemented to carry out the method accordingly.
In the following, the present disclosure is explained in detail on the basis of exemplary embodiments with reference to the drawings. Components which are identical or functionally identical or which have an identical effect may be provided with identical reference signs. Identical components or components with an identical function are in some cases explained only in relation to the figure in which they first appear. The explanation is not necessarily repeated in the subsequent figures.
The figures merely illustrate exemplary embodiments of the present disclosure without, however, limiting the present disclosure to the illustrated exemplary embodiments.
According to the improved concept, the on-load tap-changer 10 comprises at least one first fixed contact 11 and one second fixed contact 12 which can each be connected to a winding tap of the tap winding 3 of the tap-changing transformer 1. The total number of fixed contacts is dependent on the number of winding taps. Each fixed contact 11, 12 has a first contact face and a second contact face. Furthermore, the on-load tap-changer 10 comprises a selector 30 having a first selector arm 31 and a second selector arm 32 which can be actuated independently of one another and can contact each of the fixed contacts. In this case, the first movable selector arm 31 can contact the first contact faces of the fixed contacts 11, 12, but not the second contact faces. Accordingly, the second movable selector arm 32 can contact the second contact faces of the fixed contacts 11, 12, but not the first contact faces.
The on-load tap-changer 10 furthermore comprises a diverter switch 20 for carrying out the actual diverter switch operation between the preselected fixed contacts 11, 12. The diverter switch 20 has a total of three current paths: a main path 21 with a mechanical switching element 22, which main path can connect the first selector arm 31 to the load take-off lead 13, a first auxiliary path 23 with a first semiconductor switching element 24, which first auxiliary path is arranged parallel to the main path 21 and can connect the first selector arm 31 to the load take-off lead 13, and a second auxiliary path 25 with a second semiconductor switching element 26, which second auxiliary path can connect the second selector arm 32 to the load take-off lead 13.
In the illustration in
After a switching command for switching over from the first fixed contact 11 to the second fixed contact 12, the first semiconductor switching element is moved to the closed position in a first step (
In the next step (
In line with what is known as the “intermittent” mode of operation, the first semiconductor switching element 24 is then moved to the open position, preferably at the zero crossing of the current (
When the first semiconductor switching element 24 is moved to the open position, the load current IL passes to the varistor 27 arranged parallel thereto (
In the next step, shown in
The load current IL is thus switched over to the second fixed contact 12 and flows via the second auxiliary path 25 and the activated second semiconductor switching element 26 (
The first selector arm 31, which is now de-energized, is then switched over to the second fixed contact 12, as indicated by an arrow in
In the next step (
The on-load tap-changer 10 has now reached the second stationary position, which is shown in
If the tap-changer 10 is actuated in the “overlapping” mode of operation instead of in the “intermittent” mode of operation, the second semiconductor switching element 26 is moved to the closed position after the step shown in
A circulating current IC then flows from the first selector arm 31, which is still in contact with the first fixed contact 11, to the second selector arm 32, which is already on the second fixed contact 12, via the first auxiliary path 23 and the second auxiliary path 25, and from there back to the first selector arm 31 via that part of the tap winding 3 situated between the first fixed contact 11 and the second fixed contact 12 (
In the next step (3f′), the first semiconductor switching element 24 is then moved to the open position. The load current IL is thus switched over to the second fixed contact 12 and flows via the second auxiliary path 25 and the still activated second semiconductor switching element 26 (
A switchover from the second fixed contact 12 to the first fixed contact 11 takes place in exactly the reverse order, that is, according to
It is assumed that the present disclosure and many of the attendant advantages thereof can be understood from the above description. Furthermore, it is clear that various changes can be made to the shape, construction and arrangement of the components without departing from the disclosed subject matter or without sacrificing all material advantages. The embodiment described is merely explanatory and such changes are intended to be covered by the following claims. Furthermore, it is understood that the invention of the present disclosure is defined by the following claims.
While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above.
The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 123 455.4 | Sep 2020 | DE | national |
This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2021/072170, filed on Aug. 9, 2021, and claims benefit to German Patent Application No. DE 10 2020 123 455.4, filed on Sep. 9, 2020. The International Application was published in German on Mar. 17, 2022 as WO 2022/053239 A1 under PCT Article 21(2).
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/072170 | 8/9/2021 | WO |
