On-load tap-changer and method of operating an on-load tap-changer

Abstract

The invention relates to an on-load tap changer (10) for switching, without interruption, between winding taps (N1, …, NJ, …, NN) of a tap-changing transformer (20), comprising: - a load transfer switch (40) for carrying out switching from a first fixed contact (11) to a second fixed contact (12) of the on-load tap changer (10); - a selector (30) for preselecting, without power, the fixed contacts (11, 12); - a first control unit (14). The load transfer switch (40) has, for the switching, a plurality of semiconductor switching elements (47, 48) and a plurality of mechanical switching elements (43, 44). The selector (30) has a first selector arm (31) and a second selector arm (32), which can be actuated independently of each other and can contact each of the fixed contacts. The first control unit (14) is designed to trigger a switching command and to actuate the first selector arm (31) and the second selector arm (32) and the plurality of mechanical switching elements (43, 44) by means of a motor drive (13). The on-load tap changer (10) comprises a second control unit (15), which is designed to actuate the plurality of semiconductor switching elements (47, 48). During the switching, the first control unit (14) actuates the motor drive (13) in accordance with the second control unit (14).

Description

[0001] The invention relates to an on-load tap changer for uninterrupted switching between winding taps of a tapped transformer under load.

[0002] The on-load tap changer consists of a mechanical tap selector for powerless pre-selection of the respective winding tap to which switching is to take place, and a load transfer switch with semiconductor switching elements as switching means for the actual uninterrupted switching from the previous to the pre-selected, new winding tap under load.

[0003] On-load tap-changers of this type are also commonly referred to as hybrid tap-changers because, in addition to the power electronic switching devices, they also have mechanical contacts.

[0004] Such a hybrid tap changer is known from EP 2319058 B1. It has two load branches, each connecting a winding tap via a mechanical switch and a series circuit of two oppositely connected IGBTs with a common load terminal. A diode is provided in parallel with each IGBT. A varistor is provided in parallel with each individual IGBT. During steady-state operation, each of the load branches is bridged with a mechanical permanent main contact. The IGBTs on both sides are controlled by a common IGBT driver. The disadvantage of this solution is that the tap changer has no monitoring function, meaning that the mechanical switching contacts are only actuated when the functionality of the semiconductor switching elements has been ensured.If the IGBT on one side fails unnoticed and the switching process continues, a tap short circuit occurs, which has serious, destructive consequences for the tap changer and the tap transformer.

[0005] It is therefore an object of the present invention to provide an improved concept for a hybrid tap changer, which enables trouble-free and safe operation of the hybrid on-load tap changer.

[0006] This object is achieved by the respective subject matter of the independent claims. Further embodiments are the subject matter of the dependent claims.

[0007] The improved concept is based on the idea of ​​providing the semiconductor switching elements with their own control unit, which interacts with another control unit that actuates the mechanical switching contacts by means of a motor drive in such a way that the mechanical switching contacts are actuated depending on the functionality of the semiconductor switching elements.

[0008] According to a first aspect of the improved concept, an on-load tap-changer is specified for uninterrupted switching between winding taps of a tapped transformer. The on-load tap-changer comprises a load diverter switch for performing a switchover from a first fixed contact to a second fixed contact of the on-load tap-changer, a selector for powerless pre-selecting the fixed contacts before the actual switchover under load, a first control unit, and a second control unit. The load diverter switch has a plurality of semiconductor switching elements and a plurality of mechanical switching elements for the switchover. The selector has a first selector arm and a second selector arm, which can be actuated independently of one another and can contact each of the fixed contacts. Each fixed contact is electrically connected to a winding tap of the tapped transformer.The total number of fixed contacts depends on the number of winding taps.

[0009] The first control unit is configured to trigger a switching command and, depending on the command, to actuate the first selector arm, the second selector arm, and the plurality of mechanical switching elements by means of a motor drive. The second control unit is configured to actuate the plurality of semiconductor switching elements. During a switching operation of the on-load tap-changer, the first control unit actuates the motor drive in accordance with the second control unit.

[0010] This ensures that the switching process in the on-load tap-changer and the actuation of the mechanical switching elements are only continued or carried out if the semiconductor switching elements have been actuated correctly and thus there is no risk of a tap short circuit.

[0011] The motor drive can be designed as a DC motor, a brushless DC motor, a servo motor, in particular a torque motor. The motor drive is preferably designed as a stepper motor.

[0012] According to at least one embodiment, the on-load tap-changer comprises a first sensor for measuring a first measured value representing the voltage drop across a first semiconductor switching element and a second sensor for measuring a second measured value representing the voltage drop across a second semiconductor switching element.

[0013] The first sensor is configured to transmit the first measured value to the second control unit. The second sensor is configured to transmit the second measured value to the second control unit. The second control unit, in turn, is configured to transmit a status message to the first control unit depending on the first and / or second measured value.

[0014] According to at least one embodiment, the second control unit is configured to transmit the status message "Error" or the status message "OK." The status message "Error" represents that the switching on or off process of the semiconductor switching element was unsuccessful, for example, because the semiconductor switching element is defective. The status message "OK" represents that the switching on or off process of the semiconductor switching element was carried out without errors.

[0015] The second control unit is set up to transmit the status message "Error" to the first control unit if the first sensor transmits a measured value that exceeds a previously defined first limit value within a predetermined time, the first sensor transmits a measured value that does not exceed a previously defined second limit value within a predetermined time, the second sensor transmits a measured value that does not fall below a previously defined third limit value within a predetermined time, the first and / or the second sensor does not transmit a measured value within a predetermined time.

[0016] Otherwise, the second control unit transmits the status message "OK".

[0017] The first limit value is preferably between 2 and 10 volts, particularly preferably the first limit value is 5 volts.

[0018] The second limit value is preferably between 40 and 80 volts, particularly preferably the second limit value is 50 volts.

[0019] The third limit value is preferably between 40 and 80 volts, particularly preferably the third limit value is 50 volts.

[0020] Preferably, the second control unit is designed as a microcontroller and is configured to record and evaluate the measured values ​​via analog inputs and / or by means of comparators and to output the status messages depending thereon.

[0021] Preferably, the first control unit is also designed as a microcontroller.

[0022] Preferably, the first and second sensors are designed as voltage dividers with two ohmic resistors.

[0023] According to at least one embodiment, the first control unit is configured to receive the status message from the second control unit and, depending on this and the time during the switching process at which the status message is received, either return the motor drive to its initial position or continue the switching process. The latter specifically means that, as the switching process continues, the mechanical switching elements of the diverter switch and the first and / or second selector contact are actuated by the motor drive, for example, via a common drive shaft.

[0024] Preferably, the first control unit is configured to return the motor drive to the starting position when the first sensor transmits a measured value to the second control unit which exceeds the first limit value within a predetermined time, the first sensor transmits a measured value to the second control unit which does not exceed the second limit value within a predetermined time if the first sensor does not transmit a measured value to the second control unit within a predetermined time.

[0025] Preferably, the second control unit is further configured to actuate the motor drive and continue the switching when the second sensor transmits a measured value to the second control unit which does not fall below the third limit value within a predetermined time, if the second sensor does not transmit a measured value to the second control unit within a predetermined time.

[0026] According to at least one embodiment, the status message can be transmitted from the second control unit to the first control unit via an optical fiber or wirelessly, for example via Bluetooth or radio. The optical fiber can be molded into plastic, for example, into the drive shaft, or formed separately, without a casing.

[0027] According to at least one further embodiment, the on-load tap-changer comprises a third sensor for measuring at least one third measured value representing the temporal variation of the current at the semiconductor switching elements. The third sensor is designed as a current sensor, in particular as an alternating current sensor.

[0028] The third sensor is configured to transmit the third measured value to the second control unit. The second control unit, in turn, is configured to deactivate the semiconductor switching elements depending on the third measured value. "Depending on the third measured value" specifically means the temporal progression of the current flowing through the semiconductor switching elements. Deactivation preferably occurs at the current zero crossing.

[0029] According to at least one preferred embodiment, the load diverter switch has a first main branch which connects the first selector arm to a load derivation via a first mechanical switching element, a second main branch which connects the second selector arm to the load derivation via a second mechanical switching element, and a first auxiliary branch with a first semiconductor switching element which is formed parallel to the first main branch, and a second auxiliary branch with a second semiconductor switching element which is formed parallel to the second main branch.

[0030] The mechanical switching elements are preferably designed as permanent main contacts.

[0031] According to at least one embodiment, a voltage-dependent resistor is arranged parallel to the first and / or second auxiliary branch or parallel to the first and / or second semiconductor switching element. The voltage-dependent resistor is preferably designed as a varistor.

[0032] According to at least one further embodiment, the on-load tap-changer is designed such that when the switchover is carried out, none of the semiconductor switching elements is activated during the actuation of the first selector arm and / or the second selector arm.

[0033] According to at least one further embodiment, the on-load tap-changer is designed such that when the switching is carried out during the actuation of the semiconductor switching elements, the first selector arm and the second selector arm contact different fixed contacts.

[0034] According to at least one embodiment, the second control unit has an energy storage device that is charged when the first selector arm and the second selector arm contact different, adjacent fixed contacts. Charging occurs via the step voltage applied between the first selector arm and the second selector arm in the described position. The energy storage device supplies the energy required to actuate the semiconductor switching elements and to transmit the status messages from the second control unit to the first control unit. Thus, the second control unit and thus also the semiconductor switching elements are operated independently by means of the applied step voltage. An additional external energy supply, for example from the first control unit, is therefore not required.

[0035] The energy storage device is preferably made of ceramic capacitors and thus has high temperature resistance. Since it is continuously recharged during the operation of the second control unit and the semiconductor switching elements, it only needs to absorb any peak loads that occur. A switching power supply with an extremely wide input voltage range, which still functions even at low step voltages, is preferably used to charge the energy storage device.

[0036] Preferably, the second control unit is configured to monitor the charging of the energy storage device by measuring the voltage at one of the analog inputs and to transmit an "OK" status message to the first control unit when the energy storage device is fully charged. Preferably, the first control unit is configured to return the motor drive to its initial position if the status message is not received within a specified time.

[0037] According to at least one embodiment, the semiconductor switching elements are designed as IGBT switching elements and / or as thyristors and / or as JFET switching elements and / or as MOSFET switching elements and / or as integrated gate commutated thyristors (IGCTs). The semiconductor switching elements are preferably each designed as an IGBT with diodes in a bridge circuit, particularly preferably with diodes in a Graetz circuit.

[0038] According to at least one embodiment, the first control unit can be arranged above the motor drive with respect to a longitudinal axis L of the on-load tap-changer and the second control unit can be arranged below the load diverter switch with respect to the longitudinal axis L of the on-load tap-changer.

[0039] Preferably, the first control unit is arranged outside a housing of the tapped transformer. The motor drive and / or the semiconductor switching elements and / or the second control unit can be arranged outside or inside the transformer housing.

[0040] According to at least one further embodiment, the on-load tap-changer for a second and third phase of the tapped transformer to be controlled additionally comprises a second and third load diverter switch, a second and third selector, and a second and third second control unit. The plurality of semiconductor switching elements of each load diverter switch are each assigned to a second control unit. The first control unit is configured to trigger a switching command and to actuate the first selector arm and the second selector arm of each selector and the plurality of mechanical switching elements of each load diverter switch by means of a motor drive. Each second control unit is configured to actuate the plurality of semiconductor switching elements of the load diverter switch assigned to it. During the switching operation, the first control unit actuates the motor drive depending on each second control unit.

[0041] According to at least one further embodiment, the on-load tap-changer for a second and third phase of the tapped transformer to be controlled additionally comprises a second and third motor drive, a second and third load diverter switch, a second and third selector, and a second and third second control unit. Each motor drive is assigned a selector, i.e., a first selector arm and a second selector arm, as well as a plurality of mechanical switching elements of the load diverter switch for actuation. The assignment is made mechanically, for example, via a drive shaft and a gear. The plurality of semiconductor switching elements of each load diverter switch are each assigned to a second control unit.The first control unit is configured to trigger a switching command and actuate each motor drive, and thus also the respective associated first selector arm and second selector arm, as well as the respective associated plurality of mechanical switching elements. Each second control unit is configured to actuate the plurality of semiconductor switching elements assigned to it. During switching, the first control unit actuates each motor drive in response to each second control unit.

[0042] According to a second aspect of the improved concept, a method for operating an on-load tap-changer designed according to the first aspect of the improved concept is specified.

[0043] With regard to the method, reference is made to the preceding explanations, preferred features and / or advantages in an analogous manner as has already been explained with regard to the first aspect of the improved concept or one of the associated advantageous embodiments.

[0044] The procedure includes the steps Generating a switching command for switching from a first fixed contact to a second fixed contact of the on-load tap-changer by means of a first control unit, actuating one or a plurality of mechanical switching elements, a first selector arm and a second selector arm by means of a motor drive and in dependence on the first control unit, actuating one or a plurality of semiconductor switching elements by means of a second control unit, wherein the actuation of the motor drive by means of the first control unit during the switching takes place in dependence on the second control unit.

[0045] According to at least one embodiment, during the actuation of the first selector arm and / or the second selector arm, none of the semiconductor switching elements is activated.

[0046] According to at least one embodiment, the method comprises the further steps: Measuring at least one first measured value which represents the voltage drop across the first semiconductor switching element, and transmitting the first measured value to the second control unit by means of a first sensor, Measuring at least one second measured value which represents the voltage drop across the second semiconductor switching element, and transmitting the second measured value to the second control unit by means of a second sensor, Transmitting a status message to the first control unit as a function of the first measured value and / or the second measured value by means of the second control unit, Actuating the motor drive as a function of the status message by means of the first control unit.

[0047] According to at least one further embodiment, the actuation of the mechanical switching elements, the selector arms and the semiconductor switching elements after generating the switching command comprises the following steps Opening the second mechanical switching element and switching the second selector arm to the second fixed contact by means of the motor drive, charging the energy storage of the second control unit, switching on the first semiconductor switching element by means of the second control unit, opening the first mechanical switching element by means of the motor drive, switching off the first semiconductor switching element by means of the second control unit, switching on the second semiconductor switching element by means of the second control unit, closing the second mechanical switching element by means of the motor drive, switching off the second semiconductor switching element by means of the second control unit, switching the first selector arm from the first fixed contact to the second fixed contact, closing the first mechanical switching element.

[0048] According to at least one further embodiment, the first semiconductor switching element is switched off depending on the temporal course of the current. Switching off preferably occurs at the current zero crossing.

[0049] According to at least one further embodiment, after the second semiconductor element is switched on, the switching is continued in any case regardless of the status message of the second control unit.

[0050] Further embodiments and implementations of the method arise directly from the various embodiments of the tap changer. In particular, one or more of the components and / or arrangements described with regard to the tap changer can be implemented accordingly to carry out the method.

[0051] 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.

[0052] It shows Figure 1 shows an exemplary embodiment of an on-load tap-changer in a schematic representation; Figure 2 shows an exemplary, schematic arrangement of an exemplary embodiment of an on-load tap-changer according to the improved concept in a tap-changer; Figure 3 shows a schematic representation of an exemplary embodiment of an on-load tap-changer according to the improved concept; Figures 4a to 4b show an exemplary switching sequence of the on-load tap-changer from Figure 3 ; Figure 5 shows an exemplary schematic arrangement of a further exemplary embodiment of an on-load tap-changer according to the improved concept in a tap-changer.

[0053] The figures merely illustrate embodiments of the invention, without, however, limiting the invention to the illustrated embodiments.

[0054] In Figure 1An exemplary embodiment of an on-load tap-changer 10 for a tapped transformer 20 is schematically shown. The tapped transformer 20 has a main winding 21 and a control winding 22 with different winding taps N 1 , ..., NJ , ..., NN, which are switched on and off by the on-load tap-changer 10. For this purpose, the on-load tap-changer 10 comprises a selector 11, which can contact the different winding taps N 1 , ..., NJ , ..., NN of the control winding 22 by means of two movable selector contacts, and a load transfer switch 12, which performs the actual load transfer from the currently connected to the new, preselected winding tap. The load current flows from the currently connected winding tap NJ or N J+1 via the respective selector contact and the load transfer switch 40 to a load terminal 17.

[0055] Figure 2shows an exemplary schematic arrangement of an exemplary embodiment of an on-load tap changer according to the improved concept in a tap transformer.

[0056] The on-load tap-changer 10 has a selector 11 for powerless pre-selecting the fixed contacts (not shown), a load transfer switch 12 for performing the actual load switching using a plurality of mechanical switching elements and semiconductor switching elements (not shown), a motor drive 13, a first control unit 14, and a second control unit 15. The on-load tap-changer 10 also has three sensors arranged in the load transfer switch 40. The two sensors 51 and 52 are voltage sensors and are designed to transmit the measured values ​​M1 and M2, which represent the voltage drop across the semiconductor switching elements, to the second control unit 15. The third sensor 53 is a current sensor and is designed to transmit the third measured value M3, which represents the temporal variation of the current across the semiconductor switching elements, to the second control unit 15.Furthermore, the second control unit 15 comprises an energy storage device 18, which is arranged directly on the second control unit 15. In this example, the first control unit 14 is arranged above the motor drive 13 and outside the tap-changer transformer 20 with respect to a longitudinal axis L of the on-load tap-changer 10. The remaining part of the on-load tap-changer 10 is arranged within the tap-changer transformer 20, with the second control unit 15 and the energy storage device 18 being arranged below the load diverter switch 40 with respect to the longitudinal axis L.

[0057] Figure 3 shows a schematic representation of an exemplary embodiment of an on-load tap-changer according to the improved concept.

[0058] According to the improved concept, the on-load tap-changer 10 comprises at least a first fixed contact 11 and a second fixed contact 12, each of which can be connected to a winding tap of the control winding 22 of the tap-changer 20. The total number of fixed contacts depends on the number of winding taps. Each fixed contact 11, 12 has a first contact surface and a second contact surface. The on-load tap-changer 10 further comprises a selector with a first selector arm 31 and a second selector arm 32, which can be actuated independently of one another and can contact each of the fixed contacts. The first movable contact 31 can contact the first contact surfaces of the fixed contacts 11, 12, but not the second contact surfaces. Accordingly, the second movable contact 32 can contact the second contact surfaces of the fixed contacts 11, 12, but not the first contact surfaces. Figure 3represents a schematic sketch of an exemplary embodiment of the on-load tap-changer; in particular, the arrangement of the contact surfaces relative to one another is not mandatory.

[0059] The on-load tap changer 10 further comprises a load transfer switch 40 for carrying out the actual load switching between the preselected fixed contacts 11, 12. The load transfer switch 40 has a total of four current branches. A first main branch 41 connects the first selector arm 31 to the load terminal 17 via a first mechanical switching element 43. A second main branch 42 connects the second selector arm 32 to the load terminal 17 via a second mechanical switching element 44. A first auxiliary branch 45 with a first semiconductor switching element 47 is arranged parallel to the first main branch 41, and a second auxiliary branch 46 with a second semiconductor switching element 48 is arranged parallel to the second main branch 42. Furthermore, a varistor 49 is provided in parallel to each of the first and second auxiliary branches 45, 46.

[0060] The first sensor 51, designed as a voltage sensor, is arranged parallel to the first mechanical switching element 43. Accordingly, the second sensor 52, also designed as a voltage sensor, is arranged parallel to the second mechanical switching element 44. The third sensor 53, designed as a current sensor, is arranged in the common downstream circuit.

[0061] Two control units are provided for operating the on-load tap-changer 10. A first control unit 14 is configured to trigger a switching command and to operate the first selector arm 31, the second selector arm 32, and the first and second mechanical switching elements 43, 44 by means of the motor drive (not shown). A switching command is triggered to keep the primary voltage or the secondary voltage of the tap-changer 20 within a predetermined voltage band. For this purpose, a voltage regulator 50, for example, is provided to monitor compliance with the predetermined voltage band. Furthermore, a second control unit 15 of the on-load tap-changer 10 is configured to operate the first and second semiconductor switching elements 47, 48.For this purpose, the second control unit 15 comprises an energy storage device (not shown) that is charged via the voltage difference that occurs between the first selector arm 31 and the second selector arm 32 when they contact different, adjacent fixed contacts 11, 12. The first control unit 14 receives status messages S from the second control unit 15, depending on which it actuates the motor drive (not shown).

[0062] In the presentation in Figure 3The on-load tap-changer 10 is in a stationary position. The first and second selector arms 31, 32 are both located on the fixed contact 11, so that the second control unit 15 is de-energized and thus deactivates the semiconductor switching elements 45 and 46. The load current IL flows equally from the contacted fixed contact 11 via the two selector arms 31, 32, the first and second main branches 41, 42, and the closed mechanical switching elements 43 and 44 to the load shunt 17.

[0063] In the Figures 4a to 4m is an example switching sequence of the on-load tap-changer from Figure 3 shown.

[0064] After the first control unit 14 has generated a switching command, the motor drive is actuated and thereby the second mechanical contact 44 is opened ( Figure 4a ).

[0065] Subsequently, the second selector arm 32 is moved from the first fixed contact 11 to the second fixed contact 12 ( Figure 4b ).

[0066] In Figure 4c The two selector arms 31, 32 are now on different fixed contacts 11, 12, and the motor drive 13 stops. The energy storage device (not shown) is now charged by the step voltage U SP , thus supplying the second control unit 15 with energy to actuate the semiconductor switching elements 45 and 46. After charging the energy storage device, the second control unit 15 sends a status message S "OK" to the first control unit 14. If this signal does not arrive within a predetermined time, for example, 50 ms, the first control unit 14 causes the motor drive 13 to return to its initial position.

[0067] If the switching process continues properly, the next step, shown in Figure 4d, the first semiconductor switching element 47 is switched on by the second control unit 15. At this moment, no significant current flows through it, since the contact resistance of the first semiconductor switching element 47 is significantly greater than that of the first mechanical switching element 43.

[0068] At the same time, the first control unit 14 again actuates the motor drive 13 and the first mechanical switching contact 43 is then opened ( Figures 4e and 4f ). The motor drive 13 is then stopped again.

[0069] The Figures 4d to 4fThe steps shown are monitored by the second control unit 15 using the first voltage sensor 51. The first voltage sensor 51 measures the voltage drop across the first semiconductor switching element 47 and transmits this first measured value M1 to the second control unit 15. If the load current flows through the first semiconductor switching element 47, the voltage is only a few volts, for example, a maximum of 5 volts. In this case, the second control unit 15 transmits the status message S "OK" to the first control unit 14, and the switching process continues properly. However, if the first semiconductor switching element 47 is defective, an arc occurs when the first mechanical switching contact 43 opens. The voltage would then be many times higher and, for example, amount to 20 volts.In this case, the second control unit 15 sends the status message S "Error" to the first control unit 14, whereupon the first control unit 14 causes the motor drive 13 to return to the starting position.

[0070] If the switching process continues properly, in a next step (Figure 4g), the second control unit 15 monitors the temporal course of the current at the first semiconductor switching element 47 by means of the current sensor 53. The switching off of the first semiconductor switching element 47 occurs in the current zero crossing ( Figure 4g ).

[0071] The turn-off process of the first semiconductor switching element 47 is monitored by the second control unit 15 by means of the first voltage sensor 51. When the first semiconductor switching element 47 has turned off properly, the load current continues to flow via the varistors 49 arranged in parallel with the semiconductor switching elements 47 and 48, as shown in Figure 4hshown. As a result, the voltage drop across the first semiconductor switching element 47 increases sharply, reaching the forward voltage of the varistors, which amounts to several hundred volts. The second control unit 15 monitors whether the voltage exceeds a defined threshold of, for example, 50 volts within a specified time. If this is the case, the second control unit 15 transmits the status message S "OK" to the first control unit 14, and the switching process continues properly. Otherwise, if the voltage remains below the specified limit, this is an indication of the switch-off failure of the first semiconductor switching element 47, and the second control unit 15 sends the status message S "Error" to the first control unit 14, whereupon the first control unit 14 causes the motor drive 13 to return to its initial position.

[0072] If the turn-off process of the first semiconductor switching element 47 was successful, the second control unit 15 immediately turns on the second semiconductor switching element 48. This step is also monitored by the second control unit 15 by measuring the voltage drop across the second semiconductor switching element 48 using the second voltage sensor 52. If the voltage drops to the forward voltage of the second semiconductor switching element 48 of a few volts, then the turn-on was successful and the load current flows through the second auxiliary branch 46, as shown in Figure 4ishown. The second control unit 15 monitors whether the voltage drop across the second semiconductor switching element 48 falls below a defined threshold of, for example, 50V within a specified time. If this is the case, the second control unit 15 transmits the status message S "OK" to the first control unit 14, and the switching process continues properly. If this is not the case, the second control unit 15 detects an error and sends the status message S "Error" to the first control unit 14. From this point on, however, the switching process is no longer aborted, since the load switching process is already halfway completed, and reversing to the starting position would require greater control effort.

[0073] Thus, the first control unit 14 causes the motor drive 13 to continue to move in order to complete the switching. In doing so, the second mechanical switching element 44 is first closed ( Figure 4j ).

[0074] Subsequently, the second control unit 15 switches off the second semiconductor switching element 48 ( Figure 4k ). This can be done, for example, based on the detection of a reduction in the voltage drop at the second semiconductor switching element 48 as a result of the closing of the second mechanical switching element 44. However, the switch-off time is not critical, since the switch-off occurs at the latest after the second control unit 15 is no longer supplied with voltage and the voltage of the energy storage device has dropped.

[0075] In the next step, as a result of the further actuation of the motor drive 13, the first selector arm 31 is moved from the first fixed contact 11 to the second fixed contact 12 ( Figure 4l ).

[0076] This eliminates the power supply for the second control unit 15. Finally, as the movement of the motor drive 13 continues, the first mechanical switching element 43 is closed again ( Figure 4m ). This completes the switching process. The on-load tap-changer 10 is again in a stationary position, with both selector arms 31, 32 on the fixed contact 12.

[0077] The switching process in the reverse direction is analogous.

[0078] Figure 5 shows an exemplary schematic arrangement of another exemplary embodiment of an on-load tap changer according to the improved concept in a tap transformer.

[0079] In this embodiment, the on-load tap changer 10 for a second and third phase to be controlled (not shown) of the tapped transformer 20 additionally comprises a second and third motor drive 13, a second and third load diverter switch 40, a second and third selector 30, and a second and third second control unit 15, each with an energy storage device 18. Each motor drive 13 is assigned a selector 40, i.e., a first selector arm and a second selector arm (not shown), as well as a plurality of mechanical switching elements (not shown) of the load diverter switch 40 for actuation. The plurality of semiconductor switching elements (not shown) of each load diverter switch 40 are each assigned to a second control unit 15.For all three phases, a central, first control unit 14 is provided, which is designed to trigger a switching command and to actuate each motor drive 13 depending on the respective second control unit 15 assigned to the corresponding phase. REFERENCE SIGNS

[0080] 10 On-load tap-changer 11 First fixed contact 12 Second fixed contact 13 Motor drive 14 First control unit 15 Second control unit 16 First fixed contact 17 Load derivation 18 Energy storage device 20 Tap transformer 21 Main winding 22 Regulating winding 30 Selector 31 First selector arm 32 Second selector arm 40 Load diverter switch 41 First main branch 42 Second main branch 43 First mechanical switching element 44 Second mechanical switching element 45 First auxiliary branch 46 Second auxiliary branch 47 First semiconductor switching element 48 Second semiconductor switching element 49 Voltage-dependent resistor 50 Voltage regulator 51 First sensor 52 Second sensor 53 Third sensor (N 1 , ..., NJ , ..., NN ) Winding taps S Status messages M1 First measured value M2 Second measured value M3 Third measured value Longitudinal axis

Claims

1. On-load tap-changer (10) for uninterrupted switching between winding taps (N1, ..., NJ, ..., NN) of a tapped transformer (20), comprising a diverter switch (40) for bushing a diverter switch operation from a first fixed contact (11) to a second fixed contact (12) of the on-load tap-changer (10), a selector (30) for powerless change-over selector of the fixed contacts (11, 12), a first control unit (14), wherein the diverter switch (40) has a plurality of semiconductor switching elements (47, 48) and a plurality of mechanical switching elements (43, 44) for the advanced retard switch operation, the selector (30) has a first selector arm (31) and a second selector arm (32) which can be actuated independently of one another and can contact each of the fixed contacts, the first control unit (14) is arranged to trigger a switching command and to actuate the first selector arm (31) and the second selector arm (32) and the plurality of mechanical switching elements (43, 44) by means of a motor-drive unit (13), characterized in that the on-load tap-changer (10) comprises a second control unit (15) which is set up to actuate the plurality of semiconductor switching elements (47, 48) wherein during the advanced retard switch, the first control unit (14) actuates the motor-drive unit (13) as a function of the second control unit (15).

2. An on-load tap-changer (10) according to the previous claim, further comprising a first sensor (51) for measuring a first measured value M1 representing the voltage drop across a first semiconductor switching element (47), a second sensor (52) for measuring a second measured value M2, which represents the voltage drop at a second semiconductor switching element (48), wherein the first sensor (51) is set up to transmit the first measured value M1 to the second control unit (15) and the second sensor (52) is set up to transmit the second measured value M2 to the second control unit (15), the second control unit (15) is set up to transmit a status message S to the first control unit (14) as a function of the first measured value M1 and / or the second measured value M2.

3. On-load tap-changer (10) according to claim 2, wherein the first control unit (14) is set up to receive the status message S from the second control unit (15) and, as a function thereof, either to return the motor-drive unit (13) to the initial position or to continue the advanced retard switch.

4. On-load tap-changer (10) according to claim 3, wherein the transmission of the status message S can take place via a fiber-optic cable or wirelessly.

5. An on-load tap-changer (10) according to any one of the previous claims, further comprising a third sensor (53) for measuring at least a third measured value M3, which represents the time course of the current at the semiconductor switching elements (47, 48), wherein the third sensor (53) is arranged to transmit the third measured value M3 to the second control unit (15), the second control unit (15) is furthermore set up to move to the open position of the semiconductor switching elements (47, 48) as a function of the second measured value M2.

6. The on-load tap-changer (10) according to claim 1, wherein the diverter switch operation (40) comprises a first main path (41) which connects the first selector arm (31) via a first mechanical switching element (43) to a load tap (17), a second main path (42), which connects the second selector arm (32) to the load dissipation (17) via a second mechanical switching element (44), a first auxiliary path (45) with a first semiconductor switching element (47), which is formed in parallel with the first main path (41), a second auxiliary path (46) with a second semiconductor switching element (48), which is formed in parallel with the second main path (42).

7. On-load tap-changer (10) according to claim 6, wherein a voltage-dependent resistor (49) is arranged in parallel with the first and / or the second auxiliary branch (45, 46).

8. On-load tap-changer (10) according to one of the previous claims, wherein the second control unit (15) comprises an energy accumulator (18) which is charged when the first selector arm (31) and the second selector arm (32) contact different fixed contacts.

9. On-load tap-changer (10) according to one of the previous claims, wherein the semiconductor switching elements (47, 48) are designed as IGBT switching elements and / or as thyristors.

10. On-load tap-changer (10) according to one of the previous claims, wherein the first control unit (14) can be arranged above the motor-drive unit (13) with respect to a longitudinal axis L of the on-load tap-changer (10), the second control unit (15) can be arranged below the diverter switch operation (40) in relation to the longitudinal axis L of the on-load tap-changer (10).

11. On-load tap-changer (10) according to one of the previous claims, comprising for a second and third phase of the tap-change transformer (20) to be controlled a second and third diverter switch operation (40), a second and third selector (30), a second and third second control unit (15), wherein the plurality of semiconductor switching elements (47, 48) of each diverter switch (40) are each assigned to a second control unit (15), the first control unit (14) is arranged to trigger a switching command and to actuate the first selector arm (31) and the second selector arm (32) of each selector (30) and the plurality of mechanical switching elements (43, 44) of each diverter switch (40) by means of at least one motor-drive unit (13), each second control unit (15) is arranged to actuate the plurality of semiconductor switching elements (47, 48) assigned to it, wherein during the advanced retard switch, the first control unit (14) actuates the at least one motor-drive unit (13) as a function of each second control unit (15).

12. Method for actuating an on-load tap-changer (10), which is designed in particular according to one of the previous claims 1 to 11, comprising the steps of: Generating a switching command for advanced retard switch from a first fixed contact (11) to a second fixed contact (12) of the on-load tap-changer (10) by means of a first control unit (14), actuating one or a plurality of mechanical switching elements (43, 44), a first selector arm (31) and a second selector arm (32) by means of a motor-drive unit (13) and in dependence on the first control unit (14), characterized by actuating one or a plurality of semiconductor switching elements (47, 48) by means of a second control unit (15), wherein the motor-drive unit (13) is actuated by means of the first control unit (14) during the advanced retard switch in dependence on the second control unit (15).

13. Method according to the previous claim, wherein during the actuation of the first selector arm (31) and / or the second selector arm (32), none of the semiconductor switching elements (47, 48) is activated.

14. The method according to claim 12, comprising the further steps of: Measuring at least a first measured value M1 representing the voltage drop across a first semiconductor switching element (47), and transmitting the first measured value M1 to the second control unit (15) by means of a first sensor (51), measuring at least a second measured value M2, which represents the voltage drop at a second semiconductor switching element (48), and transmitting the second measured value M2 to the second control unit (15) by means of a second sensor (52), transmitting a status message S to the first control unit (14) as a function of the first measured value M1 and / or the second measured value M2 by means of the second control unit (15), actuating the motor-drive unit (13) as a function of the status message S by means of the first control unit (14).

15. The method according to claim 12, wherein actuating the mechanical switching elements (43, 44), the selector arms (31, 32) and the semiconductor switching elements (47, 48) after generating the switching command comprises the following steps: Opening a second mechanical switching element (44) and advanced retard switch of the second selector arm (32) to the second fixed contact (12) by means of the motor-drive unit (13), charging an energy accumulator (18) of the second control unit (15), switching on a first semiconductor switching element (47) by means of the second control unit (15), opening a first mechanical switching element (43) by means of the motor-drive unit (13), moving to the open position of the first semiconductor switching element (47) by means of the second control unit (15), switching on the second semiconductor switching element (48) by means of the second control unit (15), N / O contact of the second mechanical switching element (44) by means of the motor-drive unit (13), moving to the open position of the second semiconductor switching element (48) by means of the second control unit (15), advanced retard switch of the first selector arm (31) from the first fixed contact (11) to the second fixed contact (12), N / O contact of the first mechanical switching element (43).

16. The method according to claim 15, wherein the moving to the open position of the first semiconductor switching element (47) is carried out as a function of the time course of the current.

17. The method according to claim 15, wherein after the second semiconductor element (48) is switched on, the advanced retard switch is continued in any case regardless of the status message S of the second control unit (15).

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