Contact systems for on-load tap-changers

Abstract

The present invention relates to a contact system for an on-load tap changer, comprising a movable contact (BK), a fixed contact (FK), and an additional contact (ZK). In a static state, the movable contact (BK) directly contacts the fixed contact (FK). Additionally, a state is created in which the movable contact (BK) and the fixed contact (FK) are in contact contact via the additional contact (ZK). The additional contact is designed to conduct current between the fixed contact (FK) and the movable contact (BK) when the direct contact is interrupted.

Description

Technical Field

[0001] The invention relates to a contact system for an on-load tap changer, a selector device for an on-load tap changer having such a contact system, and an on-load tap changer having such a contact system or such a selector device. Background Art

[0002] On-load tap changers are used to seamlessly switch between different winding taps of inductively operated devices, such as transformers or chokes. A fundamental problem is the occurrence of arcs between the live contacts of the on-load tap changer. Such arcs form when a closed pair of contacts opens while current is flowing through them. This opening can be intentional, i.e., when the current is to be interrupted. However, it can also be unintentional, for example, when external vibrations, shocks, or force pulses act on the on-load tap changer, or when internal motion processes within the on-load tap changer transfer force pulses to the contacts.

[0003] The contacts can be surrounded by an insulating liquid, for example, the insulating liquid of an on-load tap changer. However, they can also be surrounded directly by the insulating liquid of the operating mechanism. In both cases, arcing via combustion products leads to a deterioration of the insulating liquid, in particular an increased electrical conductivity, and thus shortens the maintenance intervals or the service life of the on-load tap changer or the operating mechanism.

[0004] Furthermore, the arc leads to increased wear, in particular burning, of the contacts, which also shortens the maintenance intervals or the service life of the on-load tap changer. Summary of the Invention

[0005] It is therefore the object of the present invention to provide an improvement of a contact system for an on-load tap changer, by which arc formation is reduced.

[0006] The improvement is based on the idea of providing an additional contact in a contact system for an on-load tap changer having a movable contact and a fixed contact. The additional contact serves to briefly bridge the movable and fixed contacts if direct contact between the movable and fixed contacts is interrupted, in particular unintentionally, due to external or internal interference or an interruption in the movement process. Arcing between the movable and fixed contacts is avoided by diverting the current through the path of least resistance, namely the additional contact.

[0007] According to an improved solution, a contact system for an on-load tap changer is provided. The contact system includes a movable contact (occasionally also referred to as a moving contact), a fixed contact, and an additional contact. The movable contact is arranged and designed so that, in a static state, the movable contact directly contacts the fixed contact, i.e., is mechanically and electrically connected to the fixed contact. In addition to this direct contact connection, in the static state, an indirect contact connection between the movable contact and the fixed contact occurs via the additional contact. During the static state, the additional contact electrically connects the movable contact to the fixed contact, in particular, thereby forming parallel flow paths. Furthermore, the additional contact is constructed and arranged such that, when the direct contact connection is interrupted, it can conduct current between the fixed contact and the movable contact, in particular, the current that was flowing substantially via the direct contact connection before the interruption.

[0008] In this context, interruption means that the mechanical connection between the movable contact and the fixed contact is temporarily interrupted and re-established directly after the interruption. In particular, this involves unintentional interruption and not, for example, an intentional disconnection necessary for switching the on-load tap changer.

[0009] If the on-load tap changer with the contact system is implemented in an inductive operating device, in particular a transformer or a choke valve, according to at least one embodiment the movable contact and the fixed contact are in direct contact with the insulating liquid of the on-load tap changer or of the operating device.

[0010] According to at least one embodiment, during the rest state, the movable contact exerts a contact force on the fixed contact, or a corresponding reaction force based on Newton's third law. The contact force can be generated, for example, by a spring, in particular a prestressed compression spring, which presses the movable contact toward the fixed contact.

[0011] According to at least one embodiment, the direction of the contact force is not collinear with the direction of movement of the movable contact relative to the fixed contact when switching the on-load tap changer, in particular the contact force is perpendicular to the direction of movement. This applies in particular in the stationary state.

[0012] According to at least one embodiment, the interruption corresponds to the formation of a distance, in particular a contact distance, between the movable contact and the fixed contact in a direction opposite to the contact force.

[0013] According to at least one embodiment, the additional contact is designed and arranged to conduct current between the fixed contact and the movable contact when the direct contact is interrupted, as long as the distance is not greater than a maximum contact distance.

[0014] The maximum contact distance corresponds to the distance between the movable contact and the fixed contact, in particular parallel to the contact force, which is to be expected to the greatest extent possible during the interruption, for example including a tolerance limit or a safety limit and / or an addition taking into account geometrical conditions. The geometrical conditions may be, for example, the shape of the movable contact and / or the shape of the fixed contact.

[0015] Therefore, the maximum contact distance can also be correlated with the contact force and the conditions that lead to the interruption. These conditions can, for example, include mechanical collisions between other components of the on-load tap changer. In this case, these are internal motion processes in the on-load tap changer that, alone or in combination, can lead to direct or indirect pulse transmission to the movable contact and thus to interruption, also known as chattering or lifting. However, these conditions can also include, for example, external vibrations or shocks of the operating device, or the transmission of pulses from outside the on-load tap changer to the on-load tap changer and the movable contact, which, alone or in combination with other internal or external conditions, can lead to the interruption.

[0016] By taking into account the conservation of momentum in a closed system, estimates can be calculated for the respective individual case. These estimates are in the order of magnitude of 10 μm or less, from a few tens to a few hundred μm, for typical dimensions of on-load tap changers for the maximum contact distance.

[0017] As already described, the additional contact bridges the gap formed between the movable and fixed contacts during the interruption. This allows the current flowing directly between the movable and fixed contacts before the interruption to flow through the additional contact during the interruption. Because the resistance of the gap, which is filled with insulating liquid, for example, is much greater than the resistance of the additional contact, arcing is prevented, thereby resolving the aforementioned problem.

[0018] It should be noted that the duration of the interruption is typically very short, for example, in the order of several hundred μs, for example, approximately 500 μs. As a result, the thermal load on the additional contact is very low, so that even with the high currents typically occurring in on-load tap changers, in the order of several hundred A to several thousand A, a very small conductor cross-section, and therefore a very small mass, is sufficient for the additional contact. The mass of the additional contact can be one or more orders of magnitude smaller than that of the movable contact.

[0019] According to at least one embodiment, the additional contact is mechanically coupled to the fixed contact.

[0020] According to at least one embodiment, the additional contact is mechanically coupled to the movable contact in such a way that the additional contact moves together with the movable contact.

[0021] In this context, the term "movement together" may be understood to mean that the additional contact moves together with the movable contact when the additional contact moves from the fixed contact to another fixed contact or vice versa, i.e., during a switching process of the on-load tap changer. In particular, the term "movement together" may not be understood to mean that the additional contact moves together with the movable contact during the interruption, in particular, moves together parallel to the contact force. While the latter may be possible in various embodiments, it is not the case in other embodiments.

[0022] The mechanical coupling of the additional contact to the movable contact has the advantage that, in the case of a plurality of fixed contacts which can be switched by the movable contact, as is customary for on-load tap changers, only one additional contact is required.

[0023] The term mechanical coupling includes, for example, releasable connections such as plugging, clamping or the like, as well as fixed connections such as gluing, welding or the like.

[0024] According to at least one embodiment, in the rest state, the movable contact contacts the fixed contact at a first region of the fixed contact, and the additional contact contacts the fixed contact at a second region of the fixed contact, wherein the first region and the second region are spaced apart from each other by a distance that is greater than or equal to a predetermined minimum distance.

[0025] Contact on the first area establishes direct contact between the movable contact and the fixed contact, and contact on the second area establishes indirect contact between the movable contact and the fixed contact via the additional contact.

[0026] The distance can be understood in particular to mean the distance in a direction parallel to the contact force, ie, the value of the projection of the shortest connection vector between the first region and the second region into the contact force direction.

[0027] According to at least one embodiment, a distance between the first area and the second area is greater than or equal to a maximum contact distance between the movable contact and the fixed contact.

[0028] This ensures the possibility that, in the event of the interruption, the indirect contacts remain connected via the additional contacts and that no arc forms.

[0029] According to at least one embodiment, the additional contact is designed as a, in particular, elastic sheet or strip, which is fixedly connected to the movable contact and presses against the surface of the fixed contact during the idle state. During the interruption, the additional contact slides along the fixed contact, wherein the electrical contact is maintained.

[0030] According to at least one embodiment, in the rest state, the additional contact exerts a further contact force parallel to the contact force on the fixed contact. At least some of the additional contacts and the fixed contact are movable relative to each other in the direction of the contact force.

[0031] For example, some of the additional contacts are in direct contact with the fixed contact during the idle state. Because the additional contacts and the movable contact are movable relative to one another, direct contact between the additional contacts and the fixed contact is maintained even during the interruption, thereby preventing arc formation. This applies in particular when the mass of the additional contacts is significantly smaller than the mass of the movable contact.

[0032] According to at least one embodiment, the movable part of the additional contact relative to the movable contact is prestressed against the fixed contact in the idle state. This ensures the additional possibility of maintaining contact contact via the additional contact during the interruption and preventing arc formation.

[0033] According to at least one embodiment, the mass of the additional contact point is smaller than the mass of the movable contact point by at least one order of magnitude, ie by a factor of 10.

[0034] According to at least one embodiment, the movable contact is at least partially composed of solid metal, for example copper or a solid alloy, in particular in order to ensure low electrical resistance and high electrical conductivity.

[0035] According to at least one embodiment, the additional contact is formed at least partially from a copper alloy, for example bronze, in particular beryllium bronze such as CuBe2 or tin bronze such as CuSn6.

[0036] This allows for a high mechanical load capacity with sufficiently low resistance. In particular, the resistance requirements for the additional contact are lower than those for the movable contact. This is because the additional contact only needs to carry current during the short duration of the interruption, while the movable contact must conduct current continuously.

[0037] According to at least one embodiment, the additional contact is designed to be elastic, ie at least partially elastically deformable. In particular, the additional contact is designed as a sheet metal strip shaped to suit the given spatial conditions.

[0038] According to at least one embodiment, the additional contact is elastically fastened or supported on the movable contact.

[0039] According to at least one embodiment, the additional contact is fastened or supported in an elastic manner on a component of the contact system or of the on-load tap changer that moves together with the movable contact.

[0040] The component may be, for example, a shaft, a gear or a Maltese wheel.

[0041] According to this development, a selector device, also referred to as a selector for short, is also provided, which comprises a contact system according to this development.

[0042] According to at least one embodiment, the selector device includes an insulating plate having a first side and a second side opposite the first side. The movable contact is arranged on the first side. The contact system includes a further movable contact, which is arranged on the second side. The further movable contact is configured to directly contact the fixed contact. In particular, the movable contact and the further movable contact can directly contact two identical movable contacts in the stationary state.

[0043] According to at least one embodiment, the selector device is configured to switch the movable contact from a further fixed contact of the contact system to the fixed contact, and then switch the further movable contact from the further fixed contact to the fixed contact. In other words, the fixed contact can be considered a first fixed contact, the further fixed contact can be considered a second fixed contact, and the additional further fixed contact can be considered a third fixed contact.

[0044] According to at least one embodiment, the selector device comprises a Maltese wheel, which is fastened rotatably about an axis on the insulating plate, is arranged on the first side, and carries the movable contact.

[0045] According to at least one embodiment, the additional contact is fastened or supported on the Maltese wheel in an elastic manner, for example by means of a spring.

[0046] According to at least one embodiment, the selector device comprises a further Maltese wheel, which is fastened rotatably about the axis or a further axis on the insulating plate, is arranged on the second side, and carries the further movable contact.

[0047] According to this development, an on-load tap changer is also provided, which comprises a selector device and / or a contact system according to this development.

[0048] According to at least one embodiment, the on-load tap changer is designed to switch the movable contact from the fixed contact of the contact system to the further fixed contact and / or vice versa in a current-free state. In contrast, in the idle state, current can flow between the movable contact and the fixed contact. This applies correspondingly to the other idle state, in which the movable contact directly contacts the further fixed contact.

[0049] That is, the movable contact and the fixed contact are designed to conduct high currents, but not necessarily to switch them. Such contacts are usually optimized for their electrical resistance, but not necessarily for their resistance to arcs. Therefore, the described improvement works particularly well here.

[0050] According to this refinement, an inductive operating device is also provided, for example, in the form of a transformer, in particular a power transformer, or in the form of a choke valve, wherein the operating device includes an on-load tap changer according to this refinement. The operating device includes a tank for filling with an insulating medium, in particular, an insulating liquid such as insulating oil. When the tank is filled with the insulating medium, i.e., in particular during operation of the operating device, the movable contact and the fixed contact are in direct contact with the insulating medium.

[0051] Alternatively, the on-load tap changer itself may include an insulating medium container for being filled with the insulating medium. When the insulating medium container is filled with the insulating medium, the movable contact and the fixed contact are in direct contact with the insulating medium of the on-load tap changer.

[0052] Other designs and embodiments of the selector device, the on-load tap changer and the operating device result directly from different designs of the contact system and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention will be described in detail below with reference to the accompanying drawings using exemplary embodiments. Components with the same function or effect may be provided with the same reference numerals. Identical components or components with the same function may be described only with respect to the drawing in which they first appear. The description will not necessarily be repeated in the following drawings.

[0054] In the attached figure:

[0055] Figure 1A and 1B A schematic diagram showing an exemplary embodiment of a contact system according to a further development;

[0056] Figure 2 An exemplary embodiment of a selector device according to an improved solution is shown;

[0057] Figure 3A and3B A side view and a plan view of another exemplary embodiment of a contact system according to a development are shown. DETAILED DESCRIPTION

[0058] Figure 1A and Figure 1B A schematic diagram shows an exemplary embodiment of a contact system for an on-load tap changer according to a further development. The contact system comprises a fixed contact FK and a movable contact BK, which does not move during a switching operation of the on-load tap changer. Furthermore, the contact system includes an additional contact ZK, which is designed, for example, as a metal strip, in particular composed of a copper alloy.

[0059] exist Figure 1A In the present embodiment, the contact system is in a static state, meaning that any possible switching processes have been completed, further switching processes have not yet begun, and current is flowing between the movable contact BK and the fixed contact FK. The movable contact BK is pressed against the fixed contact FK by means of a contact force KK, for example, generated by a spring, so that the movable contact BK and the fixed contact FK are in direct contact with each other in a first region B1. In particular, the first region B1 is located at the facing end faces of the movable contact BK and the fixed contact FK.

[0060] The additional contact ZK is, for example, fixedly connected to the movable contact BK, particularly on the outer side of the movable contact BK. At the second region B2 of the fixed contact FK, particularly on the outer side of the fixed contact FK, the additional contact ZK contacts the fixed contact FK. However, no fixed connection is formed here; the additional contact ZK presses against the fixed contact FK. The additional contact can, for example, be designed to be inherently resilient.

[0061] In this case, the movable contact BK and the fixed contact FK are in direct contact in the first region B1 and in contact via the additional contact ZK. Since the resistance of the additional contact ZK is significantly greater than the resistance of the direct contact, the current flows almost exclusively through the direct contact, as schematically indicated by the corresponding line I.

[0062] Figure 1B The following diagram shows a case of the same contact system, in which a discontinuity occurs between the movable contact BK and the fixed contact FK. For example, due to the transmission of an impulse caused by internal and / or external mechanical action, the movable contact BK moves away from the fixed contact FK by the contact distance KA in a direction opposite to the contact force KK. Consequently, due to the current flow in the static state, an arc forms between the movable contact BK and the fixed contact FK when no additional contact ZK is present.

[0063] The additional contact ZK is dimensioned and arranged such that the distance A between the areas B1 and B2 is always large enough to maintain indirect contact contact even when the contact distance KA reaches a maximum. In particular, the distance A is at least as large as the maximum contact distance.

[0064] This ensures that during the interruption, the current is further directed via the additional contact ZK, which represents the path of least resistance, as indicated by the schematic line I. Since the duration of the interruption is particularly short, the additional contact ZK is thermally loaded with relatively high resistance and, despite the sometimes high currents, presents no problem. An estimate of a mass of 40 g for the movable contact BK, a contact force KK of 25 N, an interruption duration of 500 μs, and a current of 200 A results in a temperature increase of less than 1 K at the additional contact ZK. The additional contact ZK is made of a 1 mm 2 Cross section of CuBe2 based.

[0065] Figure 2 A detail of an exemplary selector device, referred to as selector for short, is shown, which has a contact system according to a development. Figure 3A A side view showing a portion of the contact system is shown, and Figure 3B A corresponding top view is shown. The selector includes a first Maltese wheel M1 and a second Maltese wheel M2, which are arranged on opposite sides of an insulating plate (not shown for better visibility). The selector also includes a fixed contact FK and further fixed contacts, two of which, F2 and F3, are shown as examples. The first Maltese wheel M1 carries a first movable contact B1, and the second Maltese wheel M2 carries a second movable contact B2. In the illustrated embodiment, the two movable contacts B1 and B2 are in contact with the fixed contact F1. The movable contacts B1 and B2 are each elastically supported on the corresponding Maltese wheel, for example, by a compression spring F, so that a contact force KK is applied from the movable contacts B1 and B2 to the fixed contact F1.

[0066] The first additional contact Z1, for example, which is designed as a shaped sheet metal strip, rests with an edge on the first movable contact B1 and makes contact with it. The first additional contact Z1 makes contact with the fixed contact F1 at one end. This creates indirect contact between the first movable contact B1 and the fixed contact F1 via the first additional contact Z1.

[0067] The first additional contact Z1 is, for example, inherently elastic. In particular, at least a portion of the end face of the first additional contact Z1 is elastically deformable parallel to the contact force KK. As a result, in the static state, the first additional contact Z1 exerts an additional contact force parallel to the contact force KK on the fixed contact F1. Furthermore, the mass of the first additional contact Z1 is significantly smaller than that of the first movable contact B1, for example, by at least a factor of 10.

[0068] This structure has the effect that, in the event of an interruption, indirect contact contact is maintained between the first movable contact B1 and the fixed contact F1 via the first additional contact Z1 and arc formation is prevented.

[0069] Alternatively, the contact system comprises a second additional contact Z2 which is arranged correspondingly with respect to the second movable contact B2 as the first additional contact Z1 is with respect to the first movable contact B1 .

[0070] The selector is configured to actuate the Maltese wheels M1, M2 via the drive of the on-load tap changer, in particular the drive shaft. This actuation is performed, for example, such that during a switchover, the first movable contact B1 is initially switched from one of the other fixed contacts F2, F3 to the fixed contact F1, without current. In the idle state, current then flows between the fixed contact F1 and the first movable contact B1. The second movable contact B2 is then similarly switched, for example, from one of the other fixed contacts F2, F3 to the fixed contact F1.

[0071] Various designs of the contact system, selector device, or on-load tap changer can reduce arc formation in the on-load tap changer. This reduces contact system wear due to contact burnout. It also reduces contamination of the insulating fluid in the on-load tap changer and / or operating device. This extends the maintenance intervals and, in turn, the service life of the on-load tap changer and / or operating device. The on-load tap changer can also be used under external shock loads.

[0072] Reference Signs List

[0073] Fixed contacts FK, F1, F2

[0074] Movable contacts BK, B1, B2

[0075] Additional contacts ZK, Z1, Z2

[0076] Malta Ferry M1, M2

[0077] Contact force KK

[0078] Line I for current

[0079] Spring F

[0080] Spacing A

[0081] Contact distance KA

[0082] Contact areas B1, B2.

Claims

1. On-load tap-changer, characterized in that: The on-load tap changer has a selector device having a contact system. - comprising fixed contacts (FK, F1) and movable contacts (BK, B1, B2), wherein the movable contacts are configured to directly contact the fixed contacts (FK, F1) in a static state; and - the contact system comprises an additional contact (ZK, Z1, Z2) which, in addition to the direct contact making, electrically connects the movable contact (BK, B1, B2) to the fixed contact (FK, F1) during the rest state; and - the additional contact (ZK, Z1, Z2) is designed and arranged to conduct a current flow between the fixed contact (FK, F1) and the movable contact (BK, B1, B2) during an interruption, wherein the direct contact connection between the movable contact (BK, B1, B2) and the fixed contact (FK, F1) is temporarily interrupted during the interruption and is re-established immediately after the interruption, In the static state, - the movable contact (BK, B1, B2) contacts the fixed contact (FK, F1) in the first area; - the additional contact (ZK, Z1, Z2) contacts the fixed contact (FK, F1) in the second region; and The first area and the second area have a distance (A) from each other that is greater than or equal to a predetermined minimum distance.

2. The on-load tap changer according to claim 1, wherein: The additional contacts (ZK, Z1, Z2) - mechanically coupled to the movable contact (BK, B1, B2) so that the additional contact moves together with the movable contact (BK, B1, B2); or - Mechanically coupled to the fixed contacts (FK, F1).

3. The on-load tap changer according to claim 1 or 2, wherein: In the static state, - applying a contact force (KK) by the movable contact (BK, B1, B2) to the fixed contact (FK, F1); - a further contact force parallel to the contact force (KK) is exerted on the fixed contact (FK, F1) by the additional contact (ZK, Z1, Z2); and At least some of the additional contacts (ZK, Z1, Z2) and the movable contact (BK, B1, B2) are movable relative to each other in the direction of the contact force (KK).

4. The on-load tap changer according to claim 1 or 2, wherein: The mass of the additional contact (ZK, Z1, Z2) is at least one order of magnitude smaller than the mass of the movable contact (BK, B1, B2).

5. The on-load tap changer according to claim 1 or 2, wherein: - the additional contacts (ZK, Z1, Z2) are designed to be inherently elastic; or - resiliently fixed or supported on the movable contact (BK, B1, B2); or - being elastically fixed or supported on a component of the contact system which moves together with the movable contact (BK, B1, B2).

6. The on-load tap changer according to claim 1 or 2, wherein: The interruption corresponds to the formation of a distance between the movable contact (BK, B1, B2) and the fixed contact (FK, F1).

7. The on-load tap changer according to claim 1 or 2, wherein: The additional contacts (ZK, Z1, Z2) consist of beryllium copper or tin bronze.

8. The on-load tap changer according to claim 1 or 2, wherein the selector device comprises an insulating plate having a first side and a second side opposite the first side, wherein - the movable contact (B1) is arranged on the first side, - the contact system comprises a further movable contact (B2), the further movable contact being arranged on the second side; and The further movable contact (B2) is provided for directly contacting the fixed contact (F1).

9. The on-load tap changer according to claim 8, wherein the selector device is configured to switch the movable contact (B1) from a further fixed contact (F2, F3) of the contact system to the fixed contact (F1) and then switch the further movable contact (B2) from the further fixed contact (F2, F3) or from an additional further fixed contact (F2, F3) to the fixed contact (F1).

10. The on-load tap changer according to claim 8, wherein the selector device comprises a Maltese wheel (M1), which is fixed to the insulating plate so as to be rotatable about an axis and carries the movable contact (B1).

11. The on-load tap changer according to claim 1 or 2, wherein: The on-load tap changer is designed to switch the movable contact (BK, B1, B2) from the fixed contact (FK, F1) to a further fixed contact (F2, F3) of the contact system in a current-free manner.

12. An inductive operating device comprising an on-load tap changer according to any one of claims 1 to 11 and a tank for filling with an insulating medium, wherein: When the tank is filled with an insulating medium, the movable contacts (BK, B1, B2) and the fixed contacts (FK, F1, F2, F3) are in direct contact with the insulating medium.

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