Resistor assembly for tap changer and tap changer

A resistor assembly can be used in a tap changer. The resistor assembly may include: a resistor element, which is held by at least two resistor holders; a base plate with at least one opening and on which the at least two resistor holders holding the resistor element are arranged; a plurality of guides, respectively formed in each of the resistor holders and being configured to position a first end and a second end of the resistor element with respect to a longitudinal direction between the two resistor holders; and contact points of the resistor element, the contact points being electrically contacted by contacts of the tap changer in a condition where the resistor element is inserted into the resistor holder.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2020/074987, filed on Sep. 8, 2020 and claims benefit to German Patent Application No. DE 10 2019 126 168.6, filed on Sep. 27, 2019. The International Application was published in German on Apr. 1, 2021 as WO 2021/058272 A1 under PCT Article 21(2).

FIELD

The invention relates to a resistor assembly for a tap changer and to a tap changer having such a resistor assembly.

BACKGROUND

German patent application DE 42 31 353 A1 discloses a tap changer. A current-limiting resistor is connected to one of the tap selectors at one end and to the neutral point at its other end. The resistor is installed in a fixed and unchangeable manner.

German utility model DE 77 07 461 U discloses a diverter switch resistor. The diverter switch resistor consists of round, oval, rectangular or square resistor material with rounded edges, which resistor material is bent into resistor spirals and installed in chambers in a self-supporting manner. The bent resistor spiral is installed in a chamber formed from two insulating material bars.

Tap changers, in particular 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. The resistor design is complicated and affects the entire manufacturing process, in particular the assembly process of the tap changer. This is because a different number and dimensioning of the resistors is required depending on the application, and therefore the structural design of the tap changer also has to be adapted under certain circumstances. This results in a large number of different variants of tap changers depending on their respective application. At present, the tap changer is fitted with the required transition resistors during assembly according to the resistance value determined for the specific order and then fully assembled. In view of the high number of variants, this leads to increased effort when assembling the tap changer.

SUMMARY

In an embodiment, the present disclosure provides a resistor assembly that can be used in a tap changer. The resistor assembly may include: a resistor element, which is held by at least two resistor holders; a base plate with at least one opening and on which the at least two resistor holders holding the resistor element are arranged; a plurality of guides, respectively formed in each of the resistor holders and being configured to position a first end and a second end of the resistor element with respect to a longitudinal direction between the two resistor holders; and contact points of the resistor element, the contact points being electrically contacted by contacts of the tap changer in a condition where the resistor element is inserted into the resistor holder.

DETAILED DESCRIPTION

Aspects of the present disclosure provide an improved concept for a resistor assembly for a tap changer, which resistor assembly can be easily and quickly adapted to different applications of the tap changer and in so doing ensures the operational reliability of the tap changer.

A resistor assembly, according to an embodiment of the invention, for a tap changer comprises at least one resistor element, which is held by at least two resistor holders. The resistor holders are provided at least on a base plate with at least one opening, on which base plate the at least two resistor holders for receiving the resistor element are arranged. The resistor element can be inserted into the resistor holder guide provided in the resistor holder through the opening. Guides are formed in each resistor holder. Each guide of the two resistor elements positions a first end and a second end of the resistor element with respect to a longitudinal direction between the two resistor holders. In each case one contact point of the resistor element is electrically contacted by contacts of the tap changer when a resistor element is inserted into the resistor holder.

The improved concept for the tap changer having a resistor assembly has the advantage that it becomes possible to change or to replace the resistors easily and quickly when needs change (such as, for example, when there is a change in the operating conditions of the tap changer) and still ensure the operational reliability of the tap changer in so doing.

According to one possible embodiment of the resistor assembly for a tap changer, the, in each case, one contact point of the resistor element is provided in an edge region at the first end and at the second end of each resistor element.

According to one possible embodiment of the resistor assembly for a tap changer, each resistor holder comprises a guide for fixing the resistor element. Each guide can be formed as a slot with a closed end and an open end. The slot is provided, at least in part, with a side wall, which can extend partially along the slot. The resistor element can be pushed in via the open end of the slot. In this case, the resistor assembly is formed in such a way that, after the tap changer has been assembled, the resistor element is fixed between the at least two resistor holders by means of the guide of the resistor holders.

According to one possible further embodiment, the guide can comprise a holding element, which can be in the form of a reversibly and elastically pivotable leg with a snap-action hook provided at a free end. The snap-action hook secures the resistor element pushed into the guide and holds it in position between the two resistor holders. The elastically pivotable leg gives way when the resistor element is pushed into the guide and in so doing likewise forms a part of the guide.

According to one possible embodiment of the invention, the at least one resistor element comprises a resistor carrier and a current-limiting element.

According to one possible embodiment of the invention, the resistor carrier can be in the form of a plate and the current-limiting element can be in the form of a metal wire which is wound around the plate. According to one possible embodiment, the resistor carrier can be in the form of a frame and the current-limiting element can be in the form of one or more metal springs which are clamped into the frame.

According to one possible embodiment of the invention, each resistor element can have a respective edge region at the first end and at the second end, which edge region is free of the current-limiting element. The closed end of the guide defines an end position for the resistor element in the resistor holder. As a result, in each case a part of the edge region of the resistor element substantially interacts in a positively locking manner with the slot of the guide.

The interaction in a positively locking manner essentially means that the edge regions of the resistor element are surrounded at least partially in a positively locking manner, that is to say with a precise fit, by the guide at least on three sides. The open end of the guide thus forms an open side of the guide, via which open side the resistor element can be pushed into the resistor holder. When the at least one resistor element is pushed into the guide, the elastically pivotable leg gives way and the at least one resistor element, when it has reached the end position in the guide, is locked in said guide.

According to at least one possible embodiment, the snap-action hook forms a part of the guide of the resistor holder in such a way that the snap-action hook surrounds the resistor element at least in part when it has reached the end position in the guide and thereby locks it in the end position. The snap-action hook can also be easily released from the locking position, so that the resistor element can be removed again and, for example, replaced by another one (with a different specification).

According to at least one possible embodiment, the resistor holder and the guide are formed in one piece and from insulating material. According to at least one embodiment, the resistor holder, the guide and the holding element are formed in one piece. The resistor holder can preferably be manufactured from a plastic using an injection-molding process.

According to at least one possible embodiment, the base plate has at least one opening in the region of the at least two resistor holders, which opening is formed in such a way that the at least one resistor element can be fixed between the at least two resistor holders by means of the guides of the resistor holders through the opening.

This allows the resistor elements (resistors) to be inserted after the tap changer has been assembled and allows the tap changer to be easily adapted to different applications by replacing the resistor elements. In this way, the electrical contacting of the resistor elements is also ensured.

According to one possible embodiment, the at least one opening can be substantially rectangular.

According to one possible embodiment of the invention, the resistor element can comprise two contact points composed of electrically conductive material, which are electrically conductively connected to the current-limiting element. The contact points of the resistor element are provided substantially in an edge region at the first end and at the second end of each resistor element.

According to one possible embodiment, each contact point is in the form of a metal plate.

According to one possible embodiment, the resistor assembly comprises at least two contacts which can connect the resistor element to current-carrying lines of the tap changer via the at least one contact point. The contacts can be in the form of spring contacts. The resistor element is preferably electrically conductively connected to the take-off lead and/or contacts and/or switches and/or other current-carrying components of the tap changer via the current-carrying lines. The contacts can be, for example, selector contacts and corresponding tap contacts via which the voltage ratio of the transformer windings is preselected or set. The switches can be in the form of, for example, vacuum interrupters and/or other mechanical switching elements via which the diverter switch operation from the currently connected tap contact to the preselected tap contact is performed. According to at least one embodiment, the contacts are in the form of spring contacts which are formed with a defined mechanical preload in such a way that the spring contacts press against the contact points of the resistor carrier when the resistor element is positioned in the resistor holders.

According to one possible further embodiment, the contacts can be integrated into the resistor holder. The contacts would also make up a part of the guide, for example.

According to one possible further embodiment of the invention, the at least two resistor elements can be arranged substantially parallel to one another and/or one above the other in the vertical direction between the resistor holders.

According to one possible embodiment of the invention, the at least two resistor elements form a resistor module.

According to the improved concept, a tap changer which comprises the resistor assembly according to the invention is also specified.

According to one possible embodiment of the invention, the tap changer comprises at least the first base plate and a second base plate, which are held in a spatial relationship to one another via at least two resistor holders.

According to one possible embodiment of the invention, the at least two resistor holders can be arranged perpendicularly to the at least two base plates.

According to one possible embodiment of the invention, the at least two resistor holders can be arranged between the at least two base plates.

According to one possible embodiment of the invention, the two resistor holders can be arranged parallel to one another.

In the following, the invention 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 having an identical function may in some cases be explained only in relation to the figure in which they first appear. The explanation is not necessarily repeated in the subsequent figures.

Identical reference signs are used for elements of embodiments of the invention that are identical or functionally identical. Furthermore, for the sake of clarity, each of the individual figures contains only those reference signs necessary for the description of said figure. Components of the tap changer that are irrelevant to the following description of the resistor assembly have not been shown in these figures for the sake of clarity. The figures merely illustrate exemplary embodiments of the invention without, however, limiting the invention to the illustrated exemplary embodiments.

FIG.1shows a partial view of a tap changer1. The tap changer1comprises at least one switching element2which is used to switch from one tap to the next tap of a transformer winding. A resistor element20is assigned to the switching element2, which resistor element is used to limit the circulating current that flows during the intermediately simultaneous contacting of a currently connected tap contact and the preselected new tap contact in the event of switching over. This ensures an uninterrupted change in the transmission ratio of the transformer. The resistor element20is held in two resistor holders30and is thus positioned in relation to the switching element2. The resistor element20defines a first end201and a second end202by way of which it is held in the two resistor holders30. An electrically conductive connection from the switching element2to the resistor element20in the region of the first end201and the second end202is established via electrical contacts40.

FIG.2shows a perspective representation of an exemplary embodiment of a resistor assembly10for a tap changer1. The resistor assembly10comprises two resistor holders30which are arranged or mounted on a base plate11. A resistor element20is held and fixed at a first end201and at a second end202by the resistor holders30. The resistor element20is positioned in the longitudinal direction L by the resistor holders30.

Each resistor holder30has, as shown inFIG.3, a guide31which makes it easier to insert the resistor element20and positions the inserted resistor element20in its longitudinal direction L between the two resistor holders30. The guide31serves as a holder for the first end201and the second end202of the resistor element20. According to this exemplary embodiment, the guide31consists of a slot32formed in the resistor holders30. The slot32is provided, at least in part, with a side wall33which extends only partially along the entire length of the slot32. The two side walls33represent a side boundary for the resistor element20, which side boundary makes it easier to push the resistor element20into the guide31of the two resistor holders30and prevents the resistor element20from being able to be displaced in the longitudinal direction L of the resistor element20when it is being pushed in or in the end position. The guide31further has a closed end37and an open end36. The guide31is formed in the resistor element20in such a way that the closed end37is located in the resistor holder30and is arranged at a distance B from the base plate11. Further, the guide31is inclined at an angle α in relation to the base plate11when the resistor holders30are mounted on the base plate11. The open end36of the guide31of the resistor holder30is provided opposite one of the openings12in the base plate11when the resistor holder30is mounted on the base plate11. Furthermore, the resistor holder30comprises a holding element34for the resistor element20when this resistor element is inserted in the guides31of the resistor holders30. The holding element34is in the form of a reversibly and elastically pivotable leg38which has a snap-action hook39H formed at a free end39. The pivotable leg38of the holding element34also forms a part of the guide31. When the resistor element20is inserted into the resistor holders30, the elastically formed holding element34moves back, so that the resistor element20can be pushed into the guide31. The one end position of the resistor element20in the guide31is reached when this resistor element comes to rest against the closed end37of the guide31. When the resistor element20has reached the end position in the guide31, the pivotable leg38moves to the starting position and the elastic snap-action hook39H at the free end39returns to its starting position and thus locks the resistor element20in the guide31. The resistor element20is then substantially operatively connected to the guide31in the region of the first end201and the second end202and the snap-action hook39H and thus fixed in the two resistor holders30.

FIG.4shows a view of a detail of the resistor assembly having a resistor element20which is held by one of the resistor holders30. As already mentioned in the description ofFIG.3, the resistor element20is seated in the guide31of the resistor holder by way of the first end201or the second end202. The elastic snap-action hook39H at the free end39of the pivotable leg secures the resistor element20in the guide31.

FIG.5shows a perspective representation of an exemplary embodiment of a resistor element20. The resistor element20consists of a resistor carrier21and a current-limiting element22which, according to this exemplary embodiment, is in the form of a metal wire which is wound around the resistor carrier21and fixed to the first end201or the second end202by means of a clip25. Furthermore, the resistor element20has a respective edge region23at the first end201and at the second end202, which edge region is not in contact with the current-limiting element22, the metal wire. Each of the edge regions23of the resistor carrier21has a respective contact point24. The contact points24are formed from electrically conductive material and are in the form of, for example, clips or small plates. Likewise illustrated inFIG.5and shown assembled inFIGS.6and7are spring contacts40which are connected to current-carrying lines41of the tap changer1at a respectively first free end42and which are pressed against the contact points24of the resistor element20with a defined spring force at the respectively second free end43.

FIGS.6and7show, from different perspective views, the contacting of the resistor element20with the current-carrying lines41of the tap changer1. The current-carrying lines41of the tap changer1are connected to the respectively first free end42of the spring contacts40. In order to establish the electrical contact, the spring contacts40press against the contact points24formed when the resistor element20is inserted through the opening12in the base plate11.

FIG.8shows a perspective representation of a further embodiment of a resistor assembly according to the improved concept.FIG.9is a longitudinal sectional side view of the resistor assembly fromFIG.8.FIGS.8and9show the resistor assembly in a three-phase tap changer1. A base plate11composed of insulating material thus has three openings12through which the resistor elements20can be inserted into the fully assembled tap changer1. A second base plate13composed of insulating material is arranged opposite the base plate11. A total of six resistor holders30are fitted between the two base plates11and13. A resistor element20is fixed between two resistor holders30in each case. The two base plates11and13are connected to one another via the resistor holders30. For this purpose, the resistor holders30preferably have pins35which can be inserted and riveted into corresponding holes provided in the base plates11and13.

FIG.10shows a longitudinal sectional representation of an exemplary embodiment of a plurality of resistor elements20fixed in a resistor holder30according to the improved concept. Here, a total of three resistor elements20are arranged, by way of example, on the resistor holder30in a stacked manner one below the other or one above the other. For this purpose, the resistor holder30has in each case three guides31and three snap-action hooks34, which are of identical design.

Using a resistor assembly10or a tap changer1according to the improved concept, it is possible to equip the tap changer1in a flexible manner, that is to say with the required resistor elements20with regard to the size of the resistor (ohmic resistor) depending on the application. According to the improved concept, the resistor elements20can also be used after the assembly of the complete tap changer1and, if necessary, for example when the operating conditions of the tap changer1change, can also be easily replaced. As a result, the tap changer1can be built independently of the order and as a stock item. For example, the adaptation to the respective application of the tap changer1could also be completely outsourced from the manufacturing process, and the resistors could be installed into the tap changer only on site by the transformer manufacturer or the grid operator.

It is assumed that the present disclosure and many of the attendant advantages thereof can be understood from the above description. Further, it is evident 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 is defined by the following claims.

REFERENCE SIGNS