ON-LOAD TAP CHANGER AND METHOD FOR OPERATING AN ON-LOAD TAP CHANGER

Abstract

A load tap changer (10) for switching, without interruption, between winding taps (N1,..., NJ,..., NN) of a tap-changing transformer (20), comprising: a diverter switch (40) for effecting switching from a first fixed contact (11) to a second fixed contact (12) of the load tap changer (10), a selector (30) for pre-selecting, without power, the fixed contacts (11, 12), a first control unit (14), wherein the diverter switch (40), for switching, has 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 are independently actuatable and can make contact with each of the fixed contacts,The first control unit (14) is configured to generate 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), wherein the on-load tap changer (10) comprises a second control unit (15) which is configured to actuate the plurality of semiconductor switching elements (47, 48), wherein during switching, the first control unit (14) actuates the motor drive (13) depending on the second control unit (14).

Description

ON-LOAD TAP CHANGER AND METHOD FOR OPERATING AN ON-LOAD TAP CHANGER FIELD OF INVENTION The invention relates to an on-load tap changer for switching, without interruption, between winding taps of an on-load tap-changing transformer. BACKGROUND OF THE INVENTION The on-load tap changer consists of a mechanical step selector to preselect, without power, the particular winding tap to which it is to be switched, and a diverter switch with semiconductor switching elements as the switching means to actually switch, without interruption, from the previous winding tap to the new one preselected on-load. On-load tap changers of this type are usually also known as hybrid tap changers because they also have mechanical contacts in addition to electronic means of power switching. A hybrid tap changer of this type is known from EP 2319058 B1. It has two load paths, which are connected to a winding tap via a mechanical switch and a series of circuits arranged in series with respect to it, formed by two oppositely switched IGBTs, to a common load tap wire. A diode is provided in parallel with each IGBT. In turn, a varistor is provided in parallel with each individual IGBT. In stationary operation, each of the load paths forms a bridge with a main mechanical contact. The IGBTs on both sides are controlled by a common IGBT driver. A disadvantage of this solution is that the tap changer does not have a monitoring function, so the mechanical switching contacts are only actuated if the functionality of the semiconductor switching elements has been ensured.If the IGBT on one side fails imperceptibly and the switching process continues, this will result in a short circuit of the tap, which has serious destructive consequences for the tap changer and tap-changing transformer. BRIEF DESCRIPTION OF THE INVENTION Therefore, the objective of the present invention is to provide an improved concept for a hybrid tap changer, by means of which trouble-free and reliable operation of the hybrid on-load tap changer becomes possible. This objective is achieved through the respective subject matter of the independent claims. The specifics are the subject matter of the dependent claims. The improved concept is based on the concept of providing semiconductor switching elements with their own control unit, which cooperates with an additional 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 independently of the functionality of the semiconductor switching elements. According to a first aspect of the improved concept, a tap changer is described ML / a / zuz o / uuuao i on-load tap changer for seamless switching between winding taps of a tap-changing transformer. The on-load tap changer comprises a diverter switch for switching from a first fixed contact to a second fixed contact of the on-load tap changer, a selector for pre-selecting the fixed contacts without power before actual on-load switching, a first control unit, and a second control unit. The diverter switch, for switching, has a plurality of semiconductor switching elements and a plurality of mechanical switching elements. The selector has a first selector arm and a second selector arm, which are independently actuatable and can make contact with each of the fixed contacts. Each fixed contact is electrically connected to a winding tap of the tap-changing transformer.The total number of fixed contacts depends on the number of winding taps. The first control unit is configured to generate a switching command and, depending on this 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 the on-load tap changer switching process, the first control unit actuates the motor drive based on the second control unit's instructions. This ensures that the switching process in the on-load tap changer and the operation of the mechanical switching elements will only continue if the semiconductor switch has been properly operated, thus preventing any risk of short-circuiting the tap. The motor drive can be a DC motor, a brushless DC motor, or a servomotor, particularly a torque motor. A stepper motor is preferred as the motor drive. According to at least one embodiment, the on-load tap changer comprises a first sensor for measuring a first measurement value, which represents the voltage drop across a first semiconductor switching element, and a second sensor for measuring a second measurement value, which represents the voltage drop across a second semiconductor switching element. The first sensor is configured to transmit the first measurement value to the second control unit. The second sensor is configured to transmit the second measurement 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 measurement value. According to at least one mode, the second control unit is configured to transmit either an "error" status message or an "OK" status message. The "error" status message represents an unsuccessful power-on or power-off process of the semiconductor switching element, for example, due to a faulty semiconductor switching element. The "OK" status message represents a successful power-on or power-off process of the semiconductor switching element. The second control unit is configured to transmit the "error" status message to the ML / a / zuz o / uuuao i first control unit when - the first sensor transmits a measurement value that exceeds a predetermined first limit value within a predefined time, - the first sensor transmits a measurement value that does not exceed a second, previously determined limit value within a predefined time, - the second sensor transmits a measurement value that does not exceed a third, previously determined limit value within a predefined time, - the first and / or second sensor does not transmit the measurement value within a predefined time. Otherwise, the second control unit transmits the OK status message.” The first limit value is preferably between 2 and 10 volts; the first limit value is, in particular, preferably 5 volts. The second limit value is preferably between 40 and 80 volts; the second limit value is, in particular, preferably 50 volts. The third limit value is preferably between 40 and 80 volts; the third limit value is, in particular, preferably 50 volts. The second control unit is preferably formed as a microcontroller and is configured to detect and evaluate the measured values ​​through analog inputs and / or by means of comparators and to send status messages depending on this. The first control unit is also preferably formed as a microcontroller. The first and second sensors are formed as voltage dividers with two ohmic resistors. According to at least one modality, the first control unit is configured to receive the status message from the second control unit. Depending on this message and the timing within the switching process at which it is received, the motor drive either returns to its initial position or continues the switching. Specifically, the latter means that during the continuation of the switching process, 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. The first control unit is preferably configured to return the motor drive to the initial position when - the first sensor transmits to the second control unit a measurement value that exceeds the first limit value within a predefined time, - the first sensor transmits a measurement value to the second control unit that does not exceed the second limit value within a predefined time, - when the first sensor does not transmit a measurement value to the second control unit within a predefined time. The second control unit is also preferably configured to operate the motor drive and continue switching when - the second sensor transmits a measurement value to the second control unit that does not exceed the third limit value within a predefined time, o / uuuao i - when the second sensor does not transmit a measurement value to the second control unit within a predefined time. According to at least one modality, the status message can be transmitted from the second control unit to the first control unit via a fiber optic cable or wirelessly, for example, via Bluetooth or radio. The fiber optic cable can be molded into plastic, for example, at the transmission shaft, or it can be formed separately, without sheathing. According to at least one additional embodiment, the on-load tap changer comprises a third sensor for measuring at least a third measurement value, which represents the time course of the current in the semiconductor switching elements. The third sensor is configured as a current sensor, specifically as an AC current sensor. The third sensor is configured to transmit the third measurement value to the second control unit. The second control unit is then configured to switch off the semiconductor switching elements depending on the third measurement value. The expression "depending on the third measurement value" here specifically means depending on the time course of the current flowing through the semiconductor switching elements. The switch-off is preferably performed at the zero crossing of the current. According to at least one preferred embodiment, the diverter switch has a first main path, which connects the first selector arm through a first mechanical switching element to a load tap cable, a second main path, which connects the second selector arm through a second mechanical switching element to a load tap cable, and also a first auxiliary path within a first semiconductor switching element, which is formed parallel to the first main path, and a second auxiliary path with a second semiconductor switching element, which is formed parallel to the second main path. Mechanical switching elements are preferably formed as main contacts. In at least one configuration, a voltage-dependent resistor is arranged parallel to the first and / or second auxiliary path or parallel to the first and / or second semiconductor switching element. The voltage-dependent resistor is preferably configured as a varistor. According to at least one additional modality, the on-load tap changer is formed in such a way that, when switching takes place, during the operation of the first selector arm and / or the second selector arm, none of the semiconductor switching elements are activated. According to at least one additional embodiment, the on-load tap changer is formed in such a way that, when switching takes place, during the actuation of the semiconductor switching elements, the first selector arm and the second selector arm come into contact with different fixed contacts. According to at least one embodiment, the second control unit has an energy storage device which is charged when the first selector arm and the second selector arm make contact with different adjacent fixed contacts. Charging is carried out via the step voltage applied between the first and second selector arms in the described position. The energy storage device provides the energy required to operate the semiconductor switching elements and to transmit status messages from the second control unit to the first control unit. The second control unit, and thus also the semiconductor switching elements, are operated independently by means of the applied step voltage. Therefore, an additional power supply from an external source, for example, via the first control unit, is unnecessary. The energy storage is preferably made from ceramic capacitors and therefore has a higher temperature resistance. Since it is continuously charged during the operation of the second control unit and the semiconductor switching elements, it simply has to absorb any load spikes that occur. To charge the energy storage, a portion of the switching network with an extremely wide input voltage range is preferably used, which operates even at low step voltages. The second control unit is preferably configured to monitor the energy storage battery's charge 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 battery is fully charged. The first control unit is preferably configured to return the motor drive to its initial position if the status message is not received within a predefined time. According to at least one modality, the semiconductor switching elements are formed 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 Switched Thyristors (IGCTs). The semiconductor switching elements are preferably formed in each case as an IGBT with diodes in a bridge circuit, particularly preferably with diodes in a Graetz circuit. According to at least one embodiment, the first control unit can be arranged above the motor drive relative to a longitudinal axis L of the on-load tap changer and the second control unit can be arranged below the diverter switch relative to the longitudinal axis L of the on-load tap changer. The first control unit is preferably mounted outside the tap changer transformer housing. The motor drive and / or semiconductor switching elements and / or the second control unit can be mounted either outside or inside the transformer housing. According to at least one additional embodiment, the on-load tap changer comprises, for a second and third phase to be controlled from the tap-changing transformer, additionally a second and third diverter switch, a second and third selector switch, and a second and third control unit. The plurality of semiconductor switching elements of each diverter switch is each assigned to a second control unit. The first unit The control unit is configured to generate a switching command and to actuate the first and second selector arms of each selector and the plurality of mechanical switching elements of each diverter switch by means of a motor drive. Each second control unit is configured to actuate the plurality of semiconductor switching elements of the diverter switch assigned to it. In this case, during switching, the first control unit actuates the motor drive depending on each second control unit. According to at least one additional embodiment, the on-load tap changer further comprises, for a second and third phase to be controlled from the tap-changing transformer, a second and third motor drive, a second and third diverter switch, a second and third selector switch, and a second control unit. A selector switch, i.e., a first selector arm and a second selector arm, and a plurality of mechanical switching elements of the diverter switch for the drive are assigned to each motor drive. The assignment is effected mechanically, for example, via a drive shaft and a transmission. The plurality of semiconductor switching elements of each diverter switch are each assigned to a second control unit.The first control unit is configured to generate a switching command and to actuate each motor drive. It is also assigned to the first selector arm, the second selector arm, and the plurality of assigned mechanical switching elements. Each subsequent control unit is configured to actuate the plurality of semiconductor switching elements assigned to it. In this case, the first control unit actuates each motor drive during switching, depending on the configuration of each subsequent control unit. According to a second aspect of the improved concept, a method for operating an on-load tap changer is described, which is formed according to the first aspect of the improved concept. With regard to the method, reference is also made to the previous explanations, the preferred characteristics and / or advantages, as already explained in relation to the first aspect of the improved concept of one of the associated advantageous modalities. The method comprises the following steps: - generate a switching command to switch from a first fixed contact to a second fixed contact of the on-load tap changer by means of a first control unit, - to actuate one or more mechanical switching elements, a first selector arm and a second selector arm by means of a motor drive and depending on the first control unit, - to actuate one or more semiconductor switching elements by means of a second control unit, - where the motor drive is actuated by means of the first control unit during switching depending on the second control unit. According to at least one modality, none of the semiconductor switching elements are activated during the operation of the first selector arm and / or the second selector arm. Ó / UUUUO l According to at least one modality, the method comprises the additional steps of: - measure at least a first measurement value, which represents the voltage drop across the first semiconductor switching element, and transmit the first measurement value to the second control unit by means of a first sensor, - measure at least a second measurement value, which represents the voltage drop across the second semiconductor switching element, and transmit the second measurement value to the second control unit by means of a second sensor, - transmit a status message to the first control unit depending on the first measurement value and / or the second measurement value by means of the second control unit, - activate the motor drive by means of the first control unit depending on the status message. According to at least one additional embodiment, the actuation of the mechanical switching elements, selector arms, and semiconductor switching elements after the generation of the switching command comprises the following steps: - open the second mechanical switching element and switch the second selector arm to the second fixed contact by means of the motor drive, - charge the energy accumulator of the second control unit, - turn on the second semiconductor switching element by means of the second control unit, - open a first mechanical switching element by means of motor drive, - switch off the first semiconductor switching element by means of the second control unit, - turn on the second semiconductor switching element by means of the second control unit, - close the second mechanical switching element by means of the motor drive, - switch off the second semiconductor switching element by means of the second control unit, - switch the first selector arm from the first fixed contact to the second fixed contact, - close the first mechanical switching element. According to at least one additional modality, the first semiconductor switching element is switched off depending on the current's time course. Switching off is preferably performed at the zero-crossing point of the current. According to at least one additional modality, once the second semiconductor element has been switched on, switching continues in any case regardless of the status message of the second control unit. The additional variations and implementations of the method are directly evident from the different tap changer configurations. In particular, the individual components or a plurality of the components and / or assemblies described in relation to the tap changer can be implemented to carry out the method accordingly. Μλ / a / zuz ó / uuuao i BRIEF DESCRIPTION OF THE FIGURES In what follows, the invention is explained in detail based on exemplary embodiments with reference to the Figures. Components that are identical, functionally identical, or have an identical effect may be provided with identical reference symbols. Identical components or components with an identical function are, in some cases, explained only with reference to the Figure in which they first appear. The explanation is not necessarily repeated in subsequent Figures. In the Figures, Figure 1 shows a schematic representation of an exemplary modality of an on-load tap changer; Figure 2 shows an exemplary schematic arrangement of an exemplary modality of an on-load tap changer according to the improved concept in a tap-changing transformer; Figure 3 shows a schematic representation of an exemplary modality of an on-load tap changer according to the improved concept; Figures 4a to 4m show an exemplary switching sequence of the on-load tap changer of Figure 3; Figure 5 shows an exemplary schematic arrangement of an additional exemplary modality of an on-load tap changer according to the improved concept in a tap-changing transformer. The Figures merely illustrate exemplary embodiments of the invention without, however, limiting the invention to the illustrated exemplary embodiments. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows an exemplary embodiment of an on-load tap changer 10 for a tap-changing transformer 20 in schematic representation. The tap-changing transformer 20 has a main winding 21 and a regulating winding 22 with different winding taps Ni,..., Nj,..., Nn, which are connected and disconnected by means of the on-load tap changer 10. For this purpose, the on-load tap changer 10 comprises a selector 11, which can make contact with the winding taps Ni,..Nj,..., Nn of the regulating winding 22 by means of two movable selector contacts, and a diverter switch 12, which performs the actual diverter switching operation of the regulating winding currently connected to the newly preselected regulating winding. The charging current flows from the winding tap Nj or Nj+1 through the relevant selector contact and diverter switch 40 to a charging tap cable 17. Figure 2 shows an exemplary schematic arrangement of an exemplary modality of an on-load tap changer according to the improved concept in a tap-changing transformer. The on-load tap changer 10 has a selector 11 for pre-selecting the fixed contacts (not shown) without power, a diverter switch 12 for carrying out the switching of the actual load by means of 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. In addition, the on-load tap changer 10 has three sensors, which are arranged on the diverter switch 40. The two sensors 51 and 52 are voltage sensors and are designed to transmit to the second control unit 15 the measured values ​​M1 and M2, which represent the voltage drop across the semiconductor switching elements.The third sensor 53 is a current sensor and is designed to transmit the third measurement value M3, which represents the time course of the current, to the semiconductor switching elements of the second control unit 15. Furthermore, the second control unit 15 comprises an energy storage unit 18, which is mounted directly on the second control unit 15. In this example, the first control unit 14 is mounted above the motor drive 13 with respect to a longitudinal axis L of the on-load tap changer 10 and outside the tap-changing transformer 20. The remainder of the on-load tap changer 10 is mounted inside the tap-changing transformer 20, where the second control unit 15 and the energy storage unit 18 are mounted below the diverter switch 40 with respect to the longitudinal axis L. Figure 3 shows a schematic representation of an exemplary modality of an on-load tap changer according to the improved concept. According to the improved concept, the on-load tap changer 10 comprises at least one first fixed contact 11 and at least one second fixed contact 12, each of which can be connected to a winding tap of the regulating winding 22 of the tap-changing transformer 20. The total number of fixed contacts depends on the number of winding taps. Each fixed contact 11, 12 has a first contact face and a second contact face. Furthermore, the on-load tap changer 10 comprises a selector having a first selector arm 31 and a second selector arm 32, which are independently actuatable and can make contact with each of the fixed contacts. Here, the first movable contact 31 can make contact with the first contact faces of the fixed contacts 11, 12, but not with the second contact faces.Accordingly, the second moving contact 32 can make contact with the second contact faces of the fixed contacts 11, 12, but not with the first contact faces. Figure 3 shows a schematic diagram of an exemplary embodiment of the on-load tap changer; in particular, the arrangement of the contact faces opposite each other is not absolutely necessary. The on-load tap changer 10 further comprises a diverter switch 40 for carrying out the actual diverter switching operation between the preselected fixed contacts 11, 12. The diverter switch 40 has a total of four current paths. A first main path 41 connects the first selector arm 31 via a first mechanical switching element 43 to the load tap cable 17. A second path 42 connects the second selector arm 32 via a second mechanical switching element 44 to the load tap cable 17. A first auxiliary path 45 with a first semiconductor switching element 47 is formed parallel to the first main path 41, and a second auxiliary path 46 with a second semiconductor switching element 48 is arranged parallel to the second main path 42.In addition, a varistor 49 is provided parallel to each of the first and second auxiliary paths 45, 46. The first sensor 51, configured as a voltage sensor, is arranged in parallel with the first mechanical switching element 43. Consequently, the second sensor 52, similarly configured as a voltage sensor, is arranged in parallel with the second mechanical switching element 44. The third sensor 53, configured as a current sensor, is arranged in the common tap wire. Two control units are provided for operating the on-load tap changer 10. A first control unit 14 is configured to generate a switching command and to actuate the first selector arm 31, the second selector arm 32, and the first and second mechanical switching elements 43, 44 by means of a motor drive (not shown). A second switching command is generated to maintain either the first primary or secondary voltage of the tap-changing transformer 20 within a predetermined voltage band. For this purpose, for example, a voltage regulator 50 is provided, which monitors whether the primary voltage is being maintained within the predetermined voltage band. In addition, a second control unit 15 for the on-load tap changer 10 is configured to actuate the first and second semiconductor switching elements 47, 48.For this purpose, the second control unit 15 comprises an energy accumulator (not shown), which is charged through the voltage difference that occurs between the first selector arm 31 and the second selector arm 32 when they come into contact with different adjacent fixed contacts 11, 12. The first control unit 14 receives status messages S from the second control unit 15, depending on which one activates the motor drive (not shown). In the illustration in Figure 3, the on-load tap changer 10 is in a stationary position. The first and second selector arms 31, 32 are both over the fixed contact 11, so that the second control unit 15 is de-energized and thus activates the semiconductor switching elements 45 and 46. The load current IL flows equally from the fixed contact 11 through the two selector arms 31, 32, the first and second main paths 41, 42, and the closed mechanical switching element 43 and 44 to the load tap cable 17. Figures 4a to 4m show an exemplary switching sequence of the on-load tap changer of Figure 3. Once the first control unit 14 has generated a switching command, the motor drive is activated and thus opens the second mechanical contact 44 for the first time (Figure 4a). The second selector arm 32 then moves from the first fixed contact 11 to the second fixed contact 12 (Figure 4b). In Figure 4c, the two selector arms 31, 32 are now over different fixed contacts 11, 12, and the motor drive 13 stops. The energy storage unit (not shown) is now charged by the step voltage Usp and thus supplies the second control unit 15 with energy to drive the semiconductor switching elements 45 and 46. After the energy storage unit is charged, the second control unit 15 sends a status message "SOK" to the first control unit 14. If this signal is not received within a predefined time, for example, 50 ms, the first control unit 14 prompts the motor drive 13 to return to its initial position. If the switching process is carried out correctly, in the next step, shown in Figure 4d, the first semiconductor switching element 47 is turned on by the second control unit 15. At this time, no significant current flows through this first semiconductor switching element, since the resistance across the first semiconductor switching element 47 is much greater than that of the first mechanical switching element 43. At the same time, the first control unit 14 re-engages the motor drive 13, and the first mechanical switching contact 43 opens (Figures 4e and 4f). The motor drive 13 then stops again. The steps shown in Figures 4d to 4f are monitored by the second control unit 15 by means of 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 measurement 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, at most 5 volts. In this case, the second control unit 16 transmits the status message "SOK" to the first control unit 14, and the switching process continues correctly. If, however, the semiconductor switching element 47 is faulty, an electric arc is created when the first mechanical switching contact 43 opens. The voltage would then be many times larger and, for example, could be 20 volts.In this case, the second control unit 16 sends the status message S “error” to the first control unit 14, after which the first control unit 14 suggests the motor drive 13 return to the initial position. If the switching process continues correctly, in a next step (Figure 4g) the time course of the current in the next semiconductor switching element 47 is monitored by the second control unit 15 by means of the current sensor 53. The first semiconductor switching element 47 is turned off at the zero crossing of the current (Figure 4g). The switch-off process of the first semiconductor switching element 47 is monitored by the second control unit 15 via the first voltage sensor 51. If the first semiconductor switching element 47 has switched off correctly, the load current then flows through the varistors 49 arranged in parallel with the semiconductor switching elements 47 and 48, as shown in Figure 4h. The voltage drop across the first semiconductor switching element 47 thus rises sharply, specifically to the forward voltage of the varistors, which is several hundred volts. The second control unit 15 monitors whether the voltage exceeds a defined threshold of, for example, 50 V within a defined time. If this occurs, the second control unit 15 transmits the status message "OK" to the first control unit 14, and the switching process continues successfully.Otherwise, if the voltage remains below the defined limit value, this is an indication of the failure of the shutdown of the first switching element o / uuuao i semiconductor 47 and the second control unit 16 sends the status message S “error” to the first control unit 14, after which the first control unit 14 suggests the motor drive 13 return to the initial position. If the process of turning off the first semiconductor element 47 was successful, the second semiconductor switching element 48 is immediately turned on by the second control unit 15. This step is also monitored again by the second control unit 15, since the voltage drop across the second semiconductor switching element 48 is measured by the second voltage sensor 52. If the voltage drops to the forward voltage of the second semiconductor switching element 48 by a few volts, the switch-on was successful and the charging current flows through the second auxiliary path 46, as shown in Figure 41. 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, 50 V within a defined time. If this is the case, the second control unit 15 transmits the status message "OK" to the first control unit 14, and the switching process continues successfully.If this is not the case, the second control unit 15 identifies 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 division switching operation process has now completely stopped and a return to the initial position would require a greater control effort. The first control unit 14 thus suggests to the motor drive 13 to continue in order to complete the switching. In this case, the second mechanical switching element 44 closes first (Figure 4j). The second control unit 15 then switches off the second semiconductor switching element 48 (Figure 4k). This can be accomplished, for example, based on the detection of a reduction in the voltage drop across the second semiconductor switching element 48 as a result of the closing of the second mechanical switching element 44. The switching time, however, is not critical, since switching off occurs at least once the second control unit 15 is no longer supplied with voltage and the energy storage voltage has decreased. In the next step, the first selector arm 31 moves from the first fixed contact 11 to the second fixed contact 12 as a result of the additional drive of the motor drive 13 (Figure 4I). This cancels the voltage supply to the second control unit 14. Finally, during the further movement of the motor drive 13, the first mechanical switching element 43 also closes again (Figure 4m). This completes the switching process. The on-load tap changer 10 is then back in a stationary position, in which both selector arms 31, 32 are over the fixed contact 12. The switching process in the opposite direction is carried out in a similar way. Figure 5 shows an exemplary schematic arrangement of an additional exemplary modality of an on-load tap changer according to the improved concept in an o / uuuao i tap changing transformer. In this embodiment, the on-load tap changer 10 further comprises, for a second and third phase to be controlled (not shown) of the tap-changing transformer 20, a second and third motor drive 13, a second and third diverter switch 40, a second and third selector 30, and a second and third control unit 15, each with an energy accumulator 18. A selector 40, i.e., a first selector arm and a second selector arm (not shown), and a plurality of mechanical switching elements (not shown) of the diverter switch 40 for the drive are assigned to each motor drive 13. The plurality of semiconductor switching elements (not shown) of each diverter switch 40 are each assigned to a second control unit 15.For all three phases, a first central control unit 14 is provided, which is designed to generate a switching command and to actuate each motor drive 13 depending on the particular second control unit 15 assigned to the corresponding phase. It is assumed that the present description and many of its accompanying advantages can be understood from the preceding description. Furthermore, it is clear that various changes can be made to the form, construction, and arrangement of the components without departing from the described material or sacrificing all the material advantages. The described embodiment is merely explanatory, and these changes are intended to be covered by the following claims. It should also be understood that the invention is defined by the following claims. REFERENCE SIGNS on-load tap changer first fixed contact second fixed contact motor drive first control unit second control unit first fixed contact charging cable energy storage tap changer transformer main winding regulating winding selector first selector arm second selector arm diverter switch first main path second main path first mechanical switching element second mechanical switching element first auxiliary path second auxiliary path first semiconductor switching element 48 second semiconductor switching element voltage-dependent resistor voltage regulator first sensor second sensor 53 third sensor (Ni,..., Nj,..., Nn) winding taps S status messages M1 first measurement value M2 second measurement value M3 third measurement value L longitudinal axis

Claims

1. An on-load tap changer (10) for switching, without interruption, between winding taps (Ni,..., Nj,..., Nn) of a tap-changing transformer (20), characterized in that it comprises: a diverter switch (40) for effecting a switching from a first fixed contact (11) to a second fixed contact (12) of the on-load tap changer (10), a selector (30) for pre-selecting, without power, the fixed contacts (11, 12), a first control unit (14), wherein the diverter switch (40), for switching, has 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 are independently actuatable and can make contact with each of the fixed contacts,the first control unit (14) is configured to generate 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), wherein the on-load tap changer (10) comprises a second control unit (15) which is configured to actuate the plurality of semiconductor switching elements (47, 48), wherein during switching, the first control unit (14) actuates the motor drive (13) depending on the second control unit (14), 2. The on-load tap changer (10) according to the preceding claim, further characterized in that it additionally comprises a first sensor (51) for measuring a first measurement value M1, which represents the voltage drop across a first semiconductor switching element (47), a second sensor (52) for measuring a second measurement value M2, which represents the voltage drop across a second semiconductor switching element (48), wherein the first sensor (51) is configured to transmit the first measurement value M1 to the second control unit (15) and the second sensor (52) is configured to transmit the second measurement value M2 to the second control unit (15), the second control unit (15) being configured to transmit a status message S to the first control unit (14) depending on the first measurement value M1 and / or the second measurement value M2.

3. The on-load tap changer (10) according to claim 2, further characterized in that the first control unit (14) is configured to receive the status message S from the second control unit (15) and, depending on this, returns the motor drive (13) to the initial position or continues with the switching.

4. The on-load tap changer (10) according to claim 3, further characterized in that the status message S can be transmitted via a fiber optic cable or wirelessly.

5. The on-load tap changer (10) according to any of the preceding claims, further characterized in that it additionally comprises a third sensor (53) for measuring at least a third measurement value M3, which represents the time course of the current of the semiconductor switching elements (47, 48), wherein the third sensor (53) is configured to transmit the third measurement value M3 to the second control unit (15), the second control unit (15) also being configured to switch off the semiconductor switching elements (47, 48) depending on the second measurement value M2.

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

7. The on-load tap changer (10) according to claim 6, further characterized in that a voltage-dependent resistor (49) is arranged parallel to the first and / or second auxiliary path (45, 46).

8. The on-load tap changer (10) according to one of the preceding claims, further characterized in that the second control unit (15) has an energy accumulator (18) which is charged when the first selector arm (31) and the second selector arm (32) make contact with different fixed contacts.

9. The on-load tap changer (10) according to one of the preceding claims, further characterized in that the semiconductor switching elements (47, 48) are formed as IGBT switching elements and / or as thyristors.

10. The on-load tap changer (10) according to one of the preceding claims, further characterized in that the first control unit (15) can be arranged above the motor drive (13) in relation to a longitudinal axis L of the on-load tap changer (10), the second control unit (15) can be arranged below the diverter switch (40) in relation to the longitudinal axis L of the on-load tap changer (10).

11. The on-load tap changer (10) according to any of the preceding claims, further characterized in that it comprises, for a second and third phase to be controlled of the tap-changing transformer (20), a second and third diverter switch (40), a second and third selector (30), a second and third 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) being configured to generate 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 (13), each control unit (15) being configured to actuate the plurality of semiconductor switching elements (47,48) assigned to this, where during switching, the first control unit (14) actuates at least one motor drive (13) depending on each second control unit (15).

12. A method for actuating an on-load tap changer (10), which is designed in particular according to the preceding claims 1 to 11, the method being characterized in that it comprises the steps of: generating a switching command to switch 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 more mechanical switching elements (43, 44), a first selector arm (31) and a second selector arm (32) by means of a motor drive (13) and depending on the first control unit (14), actuating one or more semiconductor switching elements (47, 48) by means of a second control unit (15), wherein the motor drive (13) is actuated by a first control unit (14) during switching depending on the second control unit (15).

13. The method according to the preceding claim, further characterized in that during the actuation of the first selector arm (31) and / or the second selector arm (32), none of the semiconductor switching elements (47, 48) are activated.

14. The method according to claim 12, further characterized in that it additionally comprises the steps of: measuring at least a first measurement value M1, which represents the voltage drop across a first semiconductor switching element (47) and transmitting the first measurement value M1 to the second control unit (15) by means of a first sensor (51), measuring at least a second measurement value M2, which represents the voltage drop across a second semiconductor switching element (48) and transmitting the second measurement 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) depending on the first measurement value M1 and / or the second measurement value M2 by means of the second control unit (15), and actuating the motor drive (13) by means of the first control unit (14) depending on the status message S.

15. The method according to claim 12, further characterized in that the actuator of the mechanical switching elements (43, 44) of the selector arms (31, 32) and of the semiconductor switching elements (47, 48) after the generation of the switching command comprises the following steps: opening a second mechanical switching element (44) and switching the second selector arm (32) to the second fixed contact (12) by means of the motor drive (13), charging an energy accumulator (18) of the second control unit (15), turning 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 (13), turning off the first semiconductor switching element (47) by means of the second control unit (15), turning on the second semiconductor switching element (48) by means of the second control unit (15),close the second mechanical switching element (44) by means of the motor drive (13), turn off the second semiconductor switching element (48) by means of the second control unit (15), switch the first selector arm (31) from the first fixed contact (11) to the second fixed contact (12), close the first mechanical switching element (43).

16. The method according to claim 15, further characterized in that the first semiconductor switching element (47) is switched off depending on the time course of the current.

17. The method according to claim 15, further characterized in that, once the second semiconductor element (48) has been switched on, the switching continues in any case regardless of the status message S of the second control unit (15).

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