On-load tap changer and method for actuating same

Abstract

The invention relates to an on-load tap changer (1) for switching between winding taps (N1... NJ,..., NN) of a control winding (4) of a step transformer (2) without any interruption, comprising a selector (5) for pre-selecting a selected winding tap (NJ) in an unpowered manner and a load switch (6) for the actual load switching from the previous winding tap (NJ-1) to the pre-selected winding tap (NJ), wherein a safety device (7) is connected in series between the selector (5) and the load switch (6), said safety device being designed to limit a short-circuit current occurring in the event of a fault in the on-load tap changer (1) and / or in the control winding (4).

Description

[0001] ON-LOAD TAP-CHANGER AND OPERATION METHOD

[0002] The invention relates to an on-load tap-changer for uninterrupted switching between winding taps of a control winding of a tapped transformer and to a method for actuating the on-load tap-changer.

[0003] On-load tap-changers are known for seamless switching between different winding taps of a tapped transformer's control winding, thus regulating the voltage. They typically consist of a selector for powerless pre-selecting the tap of the tapped transformer to which switching is to be performed, and a diverter switch for the actual, seamless switching from the previously connected winding tap to the new, pre-selected winding tap. For powerless pre-selecting of the winding taps, the selector typically has two movable selector contacts that connect the winding taps. The diverter switch typically has switching contacts and resistors for the actual load switching.The switching contacts are located in the main load branches of the diverter switch and serve to directly connect the winding tap connected to the respective selector contact with a load discharge via the main load branch. The resistors serve to limit the circulating current flowing briefly in the diverter switch during the switching process and are also referred to as override resistors.

[0004] Improper operation of the on-load tap-changer can lead to malfunctions. One possible malfunction is a short circuit in the on-load tap-changer, or more precisely, in the diverter switch, triggered by a flashover between the two main load branches. Since the two main load branches are each electrically connected via a tap selector contact to a tap of the regulating winding, this can result in a tap short circuit. Specifically, this means that the short-circuit current flows via the main load branches and the tap selector contacts via a regulating tap of the regulating winding of the tapped transformer.

[0005] To protect a transformer from major damage or even destruction in the event of a short circuit, circuit breakers are provided in the transmission grid. These are designed to safely interrupt high currents in the event of a fault. However, they require a relatively long time to do so, for example, 50 milliseconds. During this time, the short-circuit current flows indefinitely through the conductive components of the on-load tap-changer and the transformer, which can lead to significant damage to the on-load tap-changer and the transformer. This must be avoided.

[0006] A device for limiting a short-circuit current in such a fault situation is known from the document DE 10 2020 110 935 B3. This device comprises a current sensor and an interruption element arranged in a first current line of the on-load tap-changer. A current-limiting element is arranged parallel to the interruption element. The current sensor is designed to transmit a first measurement signal, which represents the measured current in the first current line of the on-load tap-changer, to a control device of the device. The interruption element can be actuated via the control device in such a way that it can interrupt the current flow in the first current line of the on-load tap-changer, so that the conducted current is commutated to the current-limiting element.The disadvantage of this known solution is that additional monitoring measures, particularly sensors in the power lines, are required to detect a short-circuit current and then actively trigger the protection, i.e., the interrupting element, via the control unit. A further disadvantage arises from the requirements placed on the interrupting element itself. Since a fault requires extremely fast response, within 0.1 to 1.0 milliseconds, to prevent major damage to the transformer, semiconductor switching elements are particularly suitable as interrupting elements. These components are extremely sensitive and therefore often prone to failure.

[0007] Against this background, the invention proposes the subject matter of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0008] According to a first aspect, the invention proposes an on-load tap-changer for uninterrupted switching between winding taps of a control winding of a tapped transformer, comprising a selector for powerless pre-selection of a selected winding tap of the control winding and a diverter switch for the actual load switching from the previous winding tap to the winding tap pre-selected by the selector. A safety device is connected in series between the selector and the diverter switch, which is designed to limit a short-circuit current occurring in the event of a fault in the on-load tap-changer, more precisely the selector and / or the diverter switch and / or the safety device, and / or in the control winding. Damage to the on-load tap-changer and the transformer can thus be avoided until the circuit breaker trips and safely disconnects the fault current.

[0009] According to a preferred embodiment of the on-load tap-changer, the selector has a first selector arm and a second selector arm, and the load diverter switch has a first switching side, which is electrically connected to the first selector arm via a first current path, and a second switching side, which is electrically connected to the second selector arm via a second current path. In addition, the safety device has a first resistor, which can be switched into and out of the first current path by means of a first switching element, which is arranged in parallel with the first resistor, and a second resistor, which can be switched into and out of the second current path by means of a second switching element, which is arranged in parallel with the second resistor. In other words, the resistors can be switched on or off via the switching elements.

[0010] According to the invention, the resistors in the safety device serve to limit a short-circuit current occurring in the event of a fault.

[0011] According to a preferred embodiment, the resistors in the safety device are designed as ohmic resistors.

[0012] Preferably, the first switching element and the second switching element are designed as mechanical switching contacts.

[0013] Particularly preferably, the first switching element and the second switching element are designed as vacuum interrupters.

[0014] According to a further embodiment, the first switching element and the second switching element are designed as semiconductor switching elements.

[0015] According to one embodiment, during the switching operation of the on-load tap-changer, either the first resistor is connected to the first current path or the second resistor is connected to the second current path. In other words, indirect or passive protection against short-circuit currents is provided throughout the entire switching operation, since one of the two resistors of the safety device is always connected to the circuit. Consequently, no active triggering of the protection is required. Additional monitoring measures for detecting faults, such as current sensors in the current paths, can thus be eliminated.

[0016] According to a further embodiment, current flows through the first and / or second resistors temporarily during the switching process. At least one resistor of the safety device is therefore not only switched on during the switching process, but is also actively integrated into the switching process. This is advantageous in that the resistors in the diverter switch can be made smaller, as the current load is distributed across the resistors in the diverter switch and the safety device. This can save costs.

[0017] According to a further embodiment, the first resistor is or will be connected into the first current path when no current flows through the first selector arm, and the second resistor is or will be connected into the second current path when no current flows through the second selector arm.

[0018] According to a preferred embodiment, the second resistor is connected or will be connected into the second current path when the on-load tap-changer is in a first stationary state in which the on-load tap-changer contacts the previous winding tap, and the first resistor is connected or will be connected into the first current path when the on-load tap-changer is in a second stationary state in which the on-load tap-changer contacts the new winding tap. In other words, when the on-load tap-changer is in stationary operation, indirect or passive protection against short-circuit currents is provided because one of the two resistors of the safety device is always connected into the circuit. Consequently, no active triggering of the protection is required.Additional monitoring measures for detecting faults, such as current sensors in the current paths, can thus be eliminated.

[0019] According to a further embodiment, the safety device has a first permanent main contact, which is arranged in parallel with the first resistor and the first switching element and is designed to carry a permanent current in the stationary state of the on-load tap-changer, and a second permanent main contact, which is arranged in parallel with the second resistor and the second switching element and is designed to carry a permanent current in the stationary state of the on-load tap-changer.

[0020] According to a further embodiment, the load diverter switch has a third permanent main contact, which is assigned to the first switching side of the load diverter switch and is designed to carry a permanent current in the stationary state of the on-load tap changer, and a fourth permanent main contact, which is assigned to the second switching side of the load diverter switch and is designed to carry a permanent current in the stationary state of the on-load tap changer.

[0021] According to a preferred embodiment, current flows through the first and the third permanent main contact in the first stationary state and through the second and the fourth permanent main contact in the second stationary state.

[0022] According to a further embodiment, the safety device, the load diverter switch and / or the selector are mechanically coupled via a common drive unit such that the switching elements of the safety device and the load diverter switch and / or the selector arms are actuated in dependence on one another.

[0023] According to a preferred embodiment, the common drive unit comprises a first gear associated with the safety device, a second gear associated with the load diverter switch and / or the selector, a coupling shaft via which the first gear and the second gear are mechanically connected to one another, a drive shaft, and a common motor drive. The motor drive is actuated via a control unit. The control unit can be designed as desired. For example, the control unit can be designed as a voltage regulator or as a control room. Depending on the design, the communication connection to the drive unit can be implemented as a wired or wireless connection.

[0024] According to a further embodiment, the safety device and the load transfer switch and / or the selector are electronically coupled via a common control unit such that the switching elements are actuated interdependently. The common control unit can be designed in any desired manner. For example, the control unit can be designed as a voltage regulator or a control room.

[0025] According to a preferred embodiment, the safety device is actuated via a first drive, a first drive shaft, and the first gear, and the load transfer switch and / or the selector via a second drive, a second drive shaft, and the second gear. The first and second drives are actuated interdependently via a common electronic control unit. Depending on the design, the communication connection to the first and second drives can be implemented as a wired or wireless connection.

[0026] According to a particularly preferred embodiment, the mechanical and / or electronic coupling of the safety device and the load diverter switch is designed such that the first permanent main contact and the third permanent main contact are opened simultaneously and the second permanent main contact and the fourth permanent main contact are opened simultaneously.

[0027] According to a further embodiment, the safety device is arranged in a first housing filled with insulating material, the load changeover switch is arranged in a second housing filled with insulating material, and the first housing is arranged inside and / or outside a transformer housing, and the second housing is arranged inside and / or outside the transformer housing.

[0028] According to a preferred embodiment, the first housing and the second housing are arranged side by side in the transformer housing.

[0029] According to a second aspect, the invention proposes a method for operating an on-load tap-changer for uninterrupted switching between winding taps of a control winding of a tapped transformer. The on-load tap-changer has a selector for powerless preselection of a selected winding tap, a load transfer switch for the actual load transfer from the previous winding tap to the preselected winding tap, and a safety device connected in series between the selector and the load transfer switch. According to the invention, switching occurs from a first steady state, in which the on-load tap-changer contacts the previous winding tap, to a second steady state, in which the on-load tap-changer contacts the new winding tap.The safety device is designed to limit a short-circuit current occurring in the on-load tap-changer and / or in the control winding in the event of a fault.

[0030] According to one embodiment, the safety device is designed to limit, in the stationary state, a short-circuit current occurring in the event of a fault in the on-load tap-changer and / or in the control winding and / or in the transformer.

[0031] According to a further embodiment, the safety device is designed to limit a short-circuit current occurring in the event of a fault in the on-load tap-changer and / or in the control winding and / or in the transformer during the switching operation.

[0032] According to a further embodiment, the selector has a first selector arm and a second selector arm, the load diverter switch has a first switching side that is electrically connected to the first selector arm via a first current path, and a second switching side that is electrically connected to the second selector arm via a second current path, and the safety device has a first resistor that can be switched into and out of the first current path by means of a first switching element arranged in parallel with the first resistor, and a second resistor that can be switched into and out of the second current path by means of a second switching element arranged in parallel with the second resistor, wherein, upon switching from the first stationary state to the second stationary state, the second resistor is or will be switched into the second current path.a load current in the load changeover switch is switched from the first switching side to the second switching side of the load changeover switch, the first resistor is switched into the first current path.,

[0033] According to a further embodiment, it is provided that during the switching in the opposite direction from the second stationary state to the first stationary state, the first resistor is or is switched into the first current path, a load current in the load changeover switch is switched from the second switching side to the first switching side of the load changeover switch, the second resistor is switched into the second current path.

[0034] According to a further embodiment, the safety device has a first permanent main contact, which is arranged in parallel with the first resistor and the first switching element, and a second permanent main contact, which is arranged in parallel with the second resistor and the second switching element, and the load changeover switch has a third permanent main contact, which is assigned to the first switching side of the load changeover switch, and a fourth permanent main contact, which is assigned to the second switching side of the load changeover switch, wherein during the switchover from the first stationary state to the second stationary state, when the second resistor is switched into the second current path or after the second resistor has been switched into the second current path, the first permanent main contact and the third permanent main contact are opened simultaneously.

[0035] According to a further embodiment, it is provided that during the switching in the opposite direction from the second stationary state to the first stationary state, when the first resistor is connected into the first current path or after the second resistor has been connected into the second current path, the second permanent main contact and the fourth permanent main contact are opened simultaneously.

[0036] Further embodiments and implementations of the method arise directly from the various embodiments of the on-load tap-changer. In particular, individual or multiple components and / or arrangements described with respect to the on-load tap-changer can be implemented accordingly to carry out the method.

[0037] The invention will now be explained in detail using exemplary embodiments with reference to 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 functions may only be explained with reference to the figure in which they first appear. The explanation is not necessarily repeated in subsequent figures.

[0038] They show:

[0039] Figure 1 shows an exemplary embodiment of a known on-load tap-changer in a schematic representation;

[0040] Figure 2 shows a first exemplary embodiment of an on-load tap-changer according to the invention in a schematic representation;

[0041] Figures 3a to 3h show an exemplary switching sequence of the on-load tap-changer according to the invention from Figure 2;

[0042] Figure 4 shows an exemplary, schematic arrangement of an exemplary embodiment of the on-load tap changer according to the invention in a tap transformer;

[0043] Figure 5 shows an exemplary, schematic arrangement of another exemplary

[0044] Embodiment of the on-load tap-changer according to the invention in a tap-changer.

[0045] The figures merely illustrate embodiments of the invention, without, however, limiting the invention to the illustrated embodiments.

[0046] Figure 1 schematically shows an exemplary embodiment of a prior art on-load tap-changer 1 for a tapped transformer 2. The tapped transformer 2 has a main winding 3 and a control winding 4 with different winding taps Ni, ..., Nj, ..., N Nwhich are switched on or off by the on-load tap-changer 1. For this purpose, the on-load tap-changer 1 comprises a selector 5, which, by means of two movable selector contacts, switches the different winding taps Ni, ..., Nj, ..., N N the control winding 4, and a load diverter switch 6, which performs the actual load switching from the currently connected to the new, preselected winding tap. In the position of the load diverter switch 6 shown in Figure 1, the load current flows from the currently connected winding tap Nj+i via the respective selector contact and the load diverter switch 6 to a load diverter 33. Figure 2 schematically shows a first exemplary embodiment of an on-load tap-changer according to the invention. The on-load tap-changer 1 serves for uninterrupted switching between winding taps Nj, Nj+i of a control winding 4 of a tapped transformer 2.

[0047] The on-load tap-changer 1 comprises a selector 5 with a first selector arm 8, which contacts the winding tap Nj of the control winding 4, and a second selector arm 9, which contacts the winding tap Nj+i of the control winding 4. The on-load tap-changer 1 also comprises a load diverter switch 6, which has a first switching side 10 and a second switching side 11. The first switching side 10 is electrically connected to the first selector arm 8 via a first current path 12, and the second switching side 11 is electrically connected to the second selector arm 9 via a second current path 13.

[0048] Connected in series between the selector 5 and the load diverter switch 6 is a safety device 7, which is designed to limit a short-circuit current occurring in the event of a fault in the on-load tap-changer 1 and / or in the tap-changer transformer 2, more precisely in the control winding 4. The safety device 7 has a two-part construction. It comprises a first ohmic resistor 14, which can be switched into and out of the first current path 12 by means of a first switching element 16, which is arranged in parallel with the ohmic resistor 14. A first permanent main contact 18 is arranged in parallel with the first ohmic resistor 14 and the first switching element 16 and is designed to carry a continuous current when the on-load tap-changer 1 is in the stationary state.Depending on the stationary state or switching step of the on-load tap-changer 1 during the switchover, an electrical connection can be selectively established between the first selector arm 8 and the load terminal 33, which runs via the first ohmic resistor 14 and / or the first switching element 16 and / or the first permanent main contact 18 via the first current path 12 and the first switching side 10 of the diverter switch 6. In addition, the safety device 7 comprises a second ohmic resistor 15, which can be switched into and out of the second current path 13 by means of a second switching element 17, which is arranged parallel to the ohmic resistor 15. A second permanent main contact 19 is arranged parallel to the second ohmic resistor 15 and the second switching element 17 and is designed to carry the continuous current in the stationary state of the on-load tap-changer 1.Depending on the stationary state or switching step in which the on-load tap-changer 1 is currently in during the switching operation, an electrical connection can optionally be established between the second selector arm 9 and the load derivation 33, which runs via the second ohmic resistor 15 and / or the second switching element 17 and / or the second permanent main contact 19 via the second current path 13 and the second switching side 11 of the load diverter switch 6.

[0049] According to this exemplary embodiment, the first switching element 16 and the second switching element 17 are designed as vacuum interrupters 16, 17. In principle, however, other mechanical switching elements and / or semiconductor switching elements can also be used.

[0050] The load diverter switch 6 has a plurality of switching contacts and resistors for carrying out the switching. However, the specific circuit arrangement of the load diverter switch is not essential for the implementation of the invention, so that the embodiment of the load diverter switch 6 described below is to be interpreted merely as an example and, in principle, other suitable and known arrangements of load diverter switches can also be used for the implementation of the invention. According to this exemplary embodiment of the invention, a third permanent main contact 20 is assigned to the first switching side 10 of the load diverter switch 6 and a fourth permanent main contact 21 is assigned to the second switching side 11 of the load diverter switch 6. The permanent main contacts 20 and 21 are designed to assume the permanent current conduction in a manner known per se when the on-load tap-changer 1 is in the stationary state.Furthermore, the first switching side 10 has a first vacuum interrupter 34 and, in parallel thereto, a first switching resistor 36 with a second vacuum interrupter 35 connected in series. Analogously, the second switching side 11 has a third vacuum interrupter 37 and, in parallel thereto, a second switching resistor 39 with a fourth vacuum interrupter 38 connected in series. In addition, a first mechanical switch 40 is provided between the electrical connection of the two vacuum interrupters 34 and 35 on the first switching side 10 and the load terminal 33, and analogously, a second mechanical switch 41 is provided between the electrical connection of the two vacuum interrupters 37 and 38 on the second switching side 11 and the load terminal 33.

[0051] In Figure 2, the on-load tap-changer 1 is in a stationary state in which it connects the winding tap Nj. Accordingly, a load current flows from the control winding 4 via the winding tap Nj and the first selector arm 8 into the safety device 7. In the safety device 7, the load current flows further via the permanent main contact 18 and the first vacuum interrupter 16 and from there via the first current path 12 into the first switching side 10 of the diverter switch 6. There, the load current flows via the third permanent main contact 20, the vacuum interrupter 34 and the first mechanical switch 40 to the load shunt 33. Should a fault occur in the stationary state of the on-load tap-changer 1, the second ohmic resistor 15 is connected and can limit a short-circuit current occurring as a result of the fault.This protection is therefore always passively present in the steady-state state of the on-load tap-changer and does not need to be separately activated by a tripping mechanism. Similarly, in the second steady-state state, i.e., when the winding tap Nj+i is connected and the first selector arm 8 is not carrying current, the first ohmic resistor 14 of the safety device 7 is passively connected.

[0052] Figures 3a to 3h show an exemplary switching sequence of the on-load tap-changer according to the invention from Figure 2. Starting from the stationary position in Figure 2, in a first switching step, which is shown in Figure 3a, the first permanent main contact 18, which is located in the safety device 7, and the third permanent main contact 20, which is located in the diverter switch 6, are opened simultaneously and, at the same time, the second mechanical switch 41 of the diverter switch 6 is closed. The permanent main contacts 18 and 20 are preferably opened via a mechanical coupling using a common drive unit and / or via an electronic coupling using a common control unit. The load current now flows in the safety device 7 only via the first vacuum interrupter 16 and in the diverter switch 6 via the first vacuum interrupter 34. In the next step (see Figure 3b), the first vacuum interrupter 34 is also opened.The load current is thereby commutated in the diverter switch 6 to the first switching resistor 36 and the second vacuum interrupter 35. In a next step, the fourth vacuum interrupter 38 of the diverter switch 6 is then closed (see Figure 3c), and a circulating current flows from the winding tap Nj via the first selector arm 6, the first vacuum interrupter 16 of the safety device 7, the first current path 12, the first switching resistor 36, the second vacuum interrupter 35, and the first mechanical switch 40 of the diverter switch 6, back via the second mechanical switch 41, the fourth vacuum interrupter 38, the second switching resistor 39, the second current path 13, and finally via the ohmic resistor 15 of the safety device 7 and the second selector arm 9 into the new winding tap Nj+i to which switching is to take place. In this switching step, the second ohmic resistor 15 is used to limit the current.In the following step (see Figure 3d), the second vacuum interrupter 35 of the diverter switch 6 is opened. The load current now flows only via the new winding tap Nj+i, the second selector arm 8, the second ohmic resistor 15 of the safety device 7, and from there via the second current path 13 into the second switching side 11 of the diverter switch 6, where the current flows further via the second switching resistor 39, the fourth vacuum interrupter 38, and the second mechanical switch 41 to the load shunt 33. In the next step, shown in Figure 3e, the third vacuum interrupter 37 of the diverter switch 6 is closed. This causes the current in the diverter switch 6 to flow via the third vacuum interrupter 37 and the second mechanical switch 41 to the load shunt 33. In the following step (see Figure 3f), the fourth permanent main contact 21 of the load diverter switch 6 is closed and the first mechanical switch 40 is opened.Consequently, the load current in the diverter switch now flows via the third vacuum interrupter 37, the fourth permanent main contact 21, and the second mechanical switch 41 to the load diverter 33. The first vacuum interrupter 16 of the safety device 7 is then opened, and simultaneously the second vacuum interrupter 17 of the safety device is closed (see Figure 3g). The load current now no longer flows in the safety device 7 via the second ohmic resistor 15, but via the second vacuum interrupter 17. In the final switching step, shown in Figure 3h, the second permanent main contact 19 of the safety device 7 is closed. This reaches the new stationary position of the on-load tap-changer 1, and the switching process is completed.The load current now flows from the winding tap Nj+i via the second selector arm 9, the second vacuum interrupter 17 and the second permanent main contact 19 of the safety device 7 via the second current path 13 into the second switching side 11 of the diverter switch 6 and from there via the third vacuum interrupter 37, the fourth permanent main contact 21 and the second mechanical switch 41 to the load diverter 33. If a fault occurs in this stationary state of the on-load tap-changer 1, the first ohmic resistor 14 is switched on and can limit a short-circuit current occurring as a result of the fault.

[0053] As can be seen from the described switching sequence, the second ohmic resistor 15 of the safety device 7 is integrated into the regular switching process of the on-load tap-changer 1 (see Figures 3c, 3d, 3e, 3f). Analogously, the first ohmic resistor 14 of the safety device 7 is integrated into the switching process in the opposite direction, for example, when switching from the winding tap Nj+i to the winding tap Nj. The integration of the ohmic resistors 14, 15 of the safety device 7 into the regular switching process of the on-load tap-changer 1 has the advantage that the transfer resistors 36 and 39 of the diverter switch 6 can be made smaller, thus saving costs.

[0054] Basically, according to this embodiment, either the first ohmic resistor 14 or the second ohmic resistor 15 of the safety device 7 is connected both during the steady state and during the switching process of the on-load tap-changer 1, so that passive protection of the on-load tap-changer 1 and transformer 2 is provided. According to the switching sequence in the switching direction shown in Figures 2 and 3a to 3f, the second ohmic resistor 15 is connected in the positions or switching steps shown in Figure 2 and Figures 3a to 3f, and the first ohmic resistor 14 is connected in the positions or switching steps shown in Figures 3g and 3h. In the opposite switching direction, the connection of the ohmic resistors 14 and 15 is reversed.

[0055] Figure 4 shows an exemplary, schematic arrangement of an exemplary embodiment of the on-load tap-changer 1 according to the invention in a tapped transformer 2. The safety device 7 is arranged in a first housing 30 filled with insulating material (not shown), and the diverter switch 6 is arranged in a second housing 31 filled with insulating material (not shown). The selector 5 is located directly below the diverter switch 6. The first housing 30 and the second housing 31 are arranged side by side in a transformer housing 32, which is also filled with an insulating material (not shown), and are each attached to the transformer housing 32 via a fastening flange 42. The safety device 7, the diverter switch 6, and the selector 5 are mechanically coupled via a common drive mechanism.This comprises a first gear 26, which is assigned to the safety device 7, a second gear 27, which is assigned to the load diverter switch 6 and the selector 5, a coupling shaft 28, which mechanically connects the first gear 26 and the second gear 27, and a drive shaft 29, which mechanically connects a drive unit 22 to the first gear 27. Accordingly, a common drive unit 22 is provided, which, via the drive shaft 29, the coupling shaft 28, and the two gears 26 and 27, actuates both the safety device 7 and the load diverter switch 6 and the selector 5. The drive unit 22 is, in turn, actuated by a control unit 23.

[0056] Figure 5 shows an exemplary, schematic arrangement of another exemplary embodiment of the on-load tap-changer 1 according to the invention in a tap-changer transformer 2. With regard to the embodiment shown in Figure 5, reference is made analogously to the preceding explanations of the embodiment shown in Figure 4, and only the differences are discussed below. According to the exemplary embodiment shown in Figure 5, the safety device 7, the load diverter switch 6, and the selector 5 are electronically coupled via the control unit 23.The control unit 23 actuates, in dependence on one another, a first drive 24, which is in mechanical operative connection via a first drive shaft 43 with the first gear 26, which is assigned to the safety device 7, and a second drive 25, which is in mechanical operative connection via a second drive shaft 44 with the second gear 27, which is assigned to the load diverter switch 6 and the selector 5.

[0057] It is believed that the present disclosure and many of its attendant advantages will be understood from the foregoing description. Furthermore, it will be apparent that various changes may be made in the form, construction, and arrangement of components without departing from the disclosed subject matter or without sacrificing all material advantages. The described embodiments are merely illustrative, and such changes are intended to be encompassed by the following claims. It is further understood that the invention is defined by the following claims.

[0058] REFERENCE SYMBOL

[0059] 1 on-load tap-changer

[0060] 2-step transformer

[0061] 3 main winding of 2

[0062] 4 control windings of 2

[0063] 5 voters

[0064] 6 load changeover switches

[0065] 7 Safety device

[0066] 8 first voter arm

[0067] 9 second voting arm

[0068] 10 first switching page of 6

[0069] 11 second switching page of 6

[0070] 12 first current path

[0071] 13 second current path

[0072] 14 first ohmic resistance of 7

[0073] 15 second ohmic resistance of 7

[0074] 16 first switching element of 7

[0075] 17 second switching element of 7

[0076] 18 first permanent main contact of 7

[0077] 19 second permanent main contact of 7

[0078] 20 third permanent main contact of 6

[0079] 21 fourth permanent main contact of 6

[0080] 22 Drive unit

[0081] 23 Control unit

[0082] 24 drive from 7

[0083] 25 Drive of 5 and 6 26 first gear

[0084] TI second gearbox

[0085] 28 Coupling shaft

[0086] 29 drive shaft of 22

[0087] 30 first housing

[0088] 31 second housing

[0089] 32 transformer housings

[0090] 33 Load transfer

[0091] 34 first vacuum interrupter of 6

[0092] 35 second vacuum interrupter of 6

[0093] 36 first switching resistance of 6

[0094] 37 third vacuum interrupter of 6

[0095] 38 fourth vacuum interrupter of 6

[0096] 39 second switching resistance of 6

[0097] 40 first mechanical switch of 6

[0098] 41 second mechanical switch of 6

[0099] 42 mounting flanges of 30 and 31

[0100] 43 first drive shaft

[0101] 44 second drive shaft

Claims

CLAIMS 1. On-load tap-changer (1) for uninterrupted switching between winding taps (Ni ... Nj, ..., N N ) of a control winding (4) of a tap changer (2) comprising a selector (5) for powerless pre-selection of a selected winding tap (Nj), a load changeover switch (6) for the actual load switching from the previous winding tap (NM) to the pre-selected winding tap (Nj), wherein a safety device (7) is connected in series between the selector (5) and the load changeover switch (6), which safety device is designed to limit a short-circuit current occurring in the event of a fault in the on-load tap changer (1) and / or in the control winding (4).

2. On-load tap changer (1) according to claim 1, wherein the selector (5) has a first selector arm (8) and a second selector arm (9), the load diverter switch (6) has a first switching side (10) which is electrically connected to the first selector arm (8) via a first current path (12), and a second switching side (11) which is electrically connected to the second selector arm (9) via a second current path (13), the safety device (7) o a first resistor (14) which can be switched into and out of the first current path (12) by means of a first switching element (16) which is arranged in parallel with the first resistor (14), and o a second resistor (15) which can be switched into and out of the second current path (13) by means of a second switching element (17) which is arranged in parallel with the second resistor (15).

3. On-load tap changer (1) according to claim 2, wherein during the switching operation of the on-load tap changer (1) either the first resistor (14) is connected into the first current path (12) or the second resistor (15) is connected into the second current path (13).

4. On-load tap changer (1) according to one of the preceding claims 2 or 3, wherein during the switching process the first and / or the second resistor (12, 15) current flows through them.

5. On-load tap changer (1) according to one of the preceding claims 2 to 4, wherein the first resistor (14) is or will be connected into the first current path (12) when no current flows through the first selector arm (8), the second resistor (15) is or will be connected into the second current path (13) when no current flows through the second selector arm (9).

6. On-load tap changer (1) according to one of the preceding claims 2 to 5, wherein the safety device (7) has a first permanent main contact (18) which is arranged in parallel with the first resistor (14) and the first switching element (16) and is designed to carry a permanent current in the stationary state of the on-load tap changer (1), and a second permanent main contact (19) which is arranged in parallel with the second resistor (15) and the second switching element (17) and is designed to carry a permanent current in the stationary state of the on-load tap changer (1).

7. On-load tap changer (1) according to one of the preceding claims 2 to 6, wherein the load changeover switch (6) has a third permanent main contact (20) which is assigned to the first switching side (10) of the load changeover switch (6) and is designed to, in the stationary state of the on-load tap-changer (1) to carry a continuous current, and a fourth permanent main contact (21) which is assigned to the second switching side (11) of the load diverter switch (6) and is designed to carry a continuous current in the stationary state of the on-load tap changer (1).

8. On-load tap changer (1) according to one of the preceding claims 2 to 7, wherein the safety device (7) and the load diverter switch (6) are mechanically coupled via a common drive unit (22) such that the switching elements (16, 17, 18, 19, 20, 21, 34, 35, 37, 38) are actuated in dependence on one another.

9. On-load tap changer (1) according to one of the preceding claims 2 to 7, wherein the safety device (7) and the load diverter switch (6) are electronically coupled via a common control unit (23) such that the switching elements (16, 17, 18, 19, 20, 21, 34, 35, 37, 38) are operated in dependence on one another.

10. On-load tap changer (1) according to one of the preceding claims 1 to 9, wherein the safety device (7) is arranged in a first housing (30), the load diverter switch (6) is arranged in a second housing (31), the first housing (30) is arranged inside and / or outside a transformer housing (32), the second housing (31) is arranged inside and / or outside the transformer housing (32).

11. Method for operating an on-load tap-changer (1) for uninterrupted switching between winding taps (Ni ... Nj, ..., N N) of a control winding (4) of a tapped transformer (2), wherein the on-load tap changer (1) has a selector (5) for the power-free preselection of a selected winding tap (Nj), a load transfer switch (6) for the actual load switching from the previous winding tap (Nj.i) to the preselected winding tap (Nj), and a safety device (7) which is connected in series between the selector (5) and the load transfer switch (6), wherein switching takes place from a first stationary state in which the on-load tap changer (1) contacts the previous winding tap (NM) to a second stationary state in which the on-load tap changer (1) contacts the new winding tap (Nj), the safety device (7) is designed to limit a short-circuit current occurring in the event of a fault in the on-load tap changer (1) and / or in the control winding (4).

12. The method according to claim 11, wherein the selector (5) has a first selector arm (8) and a second selector arm (9), the load diverter switch (6) has a first switching side (10) which is electrically connected to the first selector arm (8) via a first current path (12), and a second switching side (11) which is electrically connected to the second selector arm (9) via a second current path (13), the safety device (7) has a first resistor (14) which can be switched into and out of the first current path (12) by means of a first switching element (16) which is arranged in parallel with the first resistor (14), and a second resistor (15) which can be switched into and out of the second current path (13) by means of a second switching element (17) which is arranged in parallel with the second resistor (15), wherein during the switching from the first stationary state to the second stationary state the second resistor (15) is or is switched into the second current path (13), a load current in the load changeover switch (1) is switched from the first switching side (10) to the second switching side (11) of the load changeover switch (6), the first resistor (14) is switched into the first current path (12).

13. The method according to claim 11, wherein the safety device (7) has a first permanent main contact (18) arranged in parallel with the first resistor (14) and the first switching element (16), and a second permanent main contact (19) arranged in parallel with the second resistor (15) and the second switching element (17), the load changeover switch (6) has a third permanent main contact (20) which is assigned to the first switching side (10) of the load changeover switch (6), and a fourth permanent main contact (21) which is assigned to the second switching side (11) of the load changeover switch (6), wherein when the second resistor (15) is switched into the second current path (13) or after the second resistor (15) has been switched into the second current path (13), the first permanent main contact (18) and the third permanent main contact (20) are opened simultaneously.

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