Method and device for changing a transformation ratio, an impedance, or a voltage used for excitation
Patent Information
- Application Number
- EP2023722841
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-05-11
- Filing Date
- 2023-04-24
- Publication Date
- 2025-02-26
AI Technical Summary
Current energy supply networks face challenges in managing both steady-state and dynamic fluctuations, requiring a solution that can provide flexible, cost-effective, and low-loss control across various time ranges, especially with the integration of decentralized energy generation and the unpredictability of renewable energy feed-in.
A method and device combining a classic tap changer with a power electronic tap changer, allowing for quick adjustments in voltage and impedance changes, utilizing a first module for steady-state control and a second module with semiconductor switching elements for rapid dynamic responses, enabling seamless operation across multiple time scales.
This combined solution provides a flexible, cost-effective, and space-saving control mechanism that can manage network stability and reactive power control efficiently, reducing the need for complex and costly compensation systems, and ensuring network stability even under rapid changes.
Smart Images
Figure 1.1
Abstract
Description
[0001] Method and device for changing a transmission ratio, an impedance or a voltage used for excitation
[0002] The invention relates to a method for changing a transmission ratio, an impedance or a voltage used for excitation of an electrical device and to a device for changing a transmission ratio, an impedance or a voltage used for excitation of an electrical device.
[0003] When controlling power grids, a distinction is made between two different time domains. In the so-called steady-state domain, a stationary operating point is set in a power grid using suitable operating equipment, which enables reliable operation of the grid with minimal load and feed-in fluctuations. Control occurs every minute. In the dynamic domain, suitable operating equipment is used to respond to dynamic fluctuations in the grid, which can be caused, for example, by faults or rapid and possibly only temporary changes in the feed-in and load situation. In this case, very fast control in the range of milliseconds is required to keep the grid stable.
[0004] Since the reactive power demand changes with the respective feed-in and load situation, reactive power control represents an essential component of safe, efficient and loss-minimized grid management.
[0005] Suitable state-of-the-art equipment is already available for both steady-state grid control and dynamic voltage regulation. For example, controllable transformers, phase shifters, or controllable shunt reactors are used to control steady-state grid operation. Static synchronous compensators (STATCOMs) or static reactive power compensators (SVCs) are used to control dynamic grid behavior.
[0006] In particular, the resources for control in the dynamic range will become increasingly relevant for secure grid operation in the foreseeable future due to the energy transition and the integration of decentralized energy generation into grid operation, as the feed-in from renewable energies is less predictable.
[0007] In addition to the control of power grids, the previously mentioned different time domains also play a key role in the power supply of arc furnaces. Furnace transformers used to supply arc furnaces typically contain tap changers, which enable the furnace transformer's power to be controlled in a range of a few seconds to minutes. However, due to rapidly changing operating conditions in arc furnaces, such as the breaking off of the arcs used for melting, undesirable grid perturbations, such as flicker, with time constants in the millisecond range, frequently occur in arc furnaces. Complex and cost-intensive compensation systems (SVC) are also typically used to limit these grid perturbations.
[0008] A device that enables control in the steady-state range, i.e., seconds to minutes, as well as in the dynamic range, i.e., milliseconds, has not yet been disclosed in the state of the art.
[0009] It is therefore an object of the present invention to provide an improved concept for controlling energy supply networks or energy supply systems, which provides a combined, flexible control solution for serving both time ranges, which is also cost-effective, space-saving and low-loss in operation and production.
[0010] This object is achieved by the method and the subject matter of the independent claims. Further embodiments are the subject matter of the dependent claims.
[0011] The improved concept is based on the idea of combining a conventional tap changer, as is well known from the state of the art, with a power electronic tap changer connected in series. Since the power electronic tap changer can change its switching position quickly, namely within milliseconds, and assume any desired position, it enables rapid voltage adjustment to rapidly changing load conditions. The conventional tap changer serves the steady-state range, covering the widest possible control range. This allows for a high degree of flexibility for grid management as well as plant and process control.
[0012] According to a first aspect of the improved concept, a method for changing a transformation ratio, an impedance, or a voltage used for excitation of an electrical device is specified. The electrical device comprises at least one main winding, a control winding with winding taps, and at least one partial winding. Furthermore, the electrical device comprises a tap changer for changing the transformation ratio, the impedance, or the voltage used for excitation of the electrical device. The electrical device can be designed as a controllable transformer, in particular also as a phase-shifting transformer, as a controllable choke, or as a controllable transformer with a capacitor.
[0013] The tap changer comprises a first module for connecting the winding taps of the control winding and a second module with semiconductor switching elements for quickly connecting, counter-connecting or bridging the at least one partial winding.
[0014] The at least one partial winding has a specific number of turns, which is preferably greater than the largest existing number of turns between two adjacent winding taps of the control winding. If the electrical equipment has multiple partial windings, the number of turns of the multiple partial windings can be integer multiples of each other.
[0015] According to one embodiment, the first module is designed as an on-load tap-changer for uninterrupted switching between different winding taps of the control winding of the electrical equipment and has a selector for powerless preselection of the winding tap of the electrical equipment to which switching is to take place, as well as a load transfer switch for the actual, uninterrupted switching from the previously connected winding tap to the new, preselected winding tap. For powerless preselection of the winding taps, the selector generally has two movable selector contacts that connect the winding taps. The load transfer switch typically has switching contacts and resistors for the actual load switching. The switching contacts are designed, for example, as vacuum interrupters.The resistors serve to limit the short-term circulating current flowing in the load changeover switch during the switching process and are also referred to as switching resistors.
[0016] According to one embodiment, the second module comprises at least one sub-module with semiconductor switching elements, preferably several sub-modules if the electrical equipment has multiple partial windings. Each sub-module is assigned at least one partial winding, and each sub-module is designed for rapid connection, counter-connection, or bridging of the associated partial winding.
[0017] According to a further embodiment, the semiconductor switching elements each comprise an anti-parallel connected thyristor or IGBT pair.
[0018] The method for changing the transformation ratio, the impedance or the voltage used for excitation of the electrical equipment comprises the following steps: a) receipt of a request to change the transformation ratio, the impedance or the voltage used for excitation of the electrical equipment, b) testing at least one relevant characteristic, c) changing the transformation ratio, the impedance or the voltage used for excitation of the electrical equipment either by means of the first module or by means of the second module depending on the testing of the at least one relevant characteristic.
[0019] According to one embodiment, the relevant characteristic value comprises the amount of deviation of an actual voltage of the electrical equipment, for example, the voltage on the primary or secondary side of a transformer, from a predetermined target voltage. The transformation ratio is changed by means of the second module if the amount of deviation from the target voltage is greater than a step voltage present between two adjacent winding taps of the control winding.
[0020] According to this embodiment, the electrical device is designed as a controllable transformer. In other words, the change in the transformer's transformation ratio, i.e., the adjustment to the desired target voltage on the primary or secondary side of the transformer, is carried out with the second module if the magnitude of the voltage to be controlled or the desired voltage change is so large that the change cannot be achieved by operating the first module.
[0021] According to a further embodiment, the relevant characteristic value comprises the magnitude of a deviation of an impedance of the electrical equipment from a predetermined target impedance. The impedance is changed by means of the second module if the magnitude of the deviation from the target impedance is greater than an impedance acting between two adjacent winding taps of the control winding.
[0022] According to this embodiment, the electrical equipment is designed as a controllable choke. In other words, the change in the impedance of the choke, i.e., the adjustment to the desired target impedance, is carried out with the second module if the amount of the impedance to be controlled or the desired impedance change is so large that the change cannot be achieved by actuating the first module. According to a further embodiment, the relevant parameter comprises an amount of a deviation of an actual voltage in a first inductive arrangement for exciting a second inductive arrangement from a predetermined target voltage. The actual voltage is measured, for example, on the primary side of the first inductive arrangement or the secondary side of the second inductive arrangement.The voltage used for excitation of the second inductive arrangement is then adjusted by means of the second module if the amount of deviation from the target voltage is greater than a step voltage applied between two adjacent winding taps of the control winding.
[0023] According to this embodiment, the electrical device comprises a first inductive arrangement and a second inductive arrangement. The actual voltage in the first inductive arrangement excites the second inductive arrangement, thereby increasing the power of the first inductive arrangement.
[0024] In this arrangement, an excitation transformer, a first inductive arrangement, is supplemented by a booster transformer, a second inductive arrangement. This allows for more flexible adjustment of the tap changer's operating parameters, current and voltage, especially in high-power units.
[0025] In other words, the adjustment of the voltage used to excite the booster transformer is carried out by means of the second module if the amount of the desired voltage to excite the booster transformer is so large that the change cannot be achieved by operating the first module.
[0026] According to one embodiment of this embodiment, the electrical equipment can be designed as a phase shifter, and the first inductive arrangement can be designed as an excitation transformer and the second inductive arrangement as a booster transformer. The method can therefore also be applied analogously to the operation of a phase-shifting transformer.
[0027] According to a further embodiment, the relevant parameter comprises the gradient of a required voltage change. The transformation ratio is changed by means of the second module if the gradient of the required voltage change is greater than a specified limit.
[0028] According to this embodiment, the electrical equipment is designed as a controllable transformer. In other words, the change in the transformer's transformation ratio, i.e., the adjustment to the desired target voltage on the primary or secondary side of the transformer, is carried out with the second module if the gradient of the required voltage change is so high, for example, a required voltage change rate in the millisecond range, that a change in the transformation ratio could not be carried out quickly enough with the first module. Accordingly, the specified limit is, for example, one second.
[0029] According to a further embodiment, the relevant parameter comprises the gradient of a required impedance change. The impedance change is performed by the second module if the gradient of the required impedance change is greater than a specified limit.
[0030] According to this embodiment, the electrical device is designed as a controllable choke. In other words, the change in the choke's impedance, i.e., the adjustment to the desired target impedance, is performed with the second module if the gradient of the required impedance change is so high, for example, a required impedance change rate in the millisecond range, that a change in the impedance could not be carried out quickly enough with the first module. Accordingly, the specified limit is, for example, one second.
[0031] According to a further embodiment, the relevant characteristic comprises a fundamental oscillation plus a harmonic component of a voltage applied to the electrical equipment. The transformation ratio is changed by means of the second module if the harmonic component is greater than a specified limit.
[0032] According to this embodiment, the electrical equipment is designed as a controllable transformer. In other words, the change in the transformer's transformation ratio, i.e., the adjustment to the desired target voltage on the primary or secondary side of the transformer, is carried out with the second module when the proportion of harmonics above the fundamental component of the voltage applied to the transformer is so high that the harmonics can no longer be controlled with the first module. The definition of the limit value depends on the respective system configuration and the grid connection conditions.
[0033] According to a further embodiment, a Fourier analysis is carried out to determine the proportion of harmonics above the fundamental oscillation of the voltage applied to the electrical equipment, preferably the voltage applied on the mains connection side of the electrical equipment.
[0034] According to a further embodiment, after a change in the transformation ratio, the impedance, or the voltage used for excitation by means of the second module, the first and second modules are actuated such that the second module assumes a neutral position in which the at least one partial winding is bridged. Bridged, i.e., at potential, but no current flows through it. In other words, the semiconductor switching elements of the second module are interconnected such that a bypass is formed for the at least one partial winding.
[0035] According to one embodiment, the first and the second module are actuated alternately.
[0036] According to a further embodiment, the first and the second module are actuated alternately until the first module has reached a position which indicates a new, stationary operating point of the energy supply network and the second module is in the neutral position.
[0037] In other words, after the second module is switched, the first module is gradually adjusted by adjusting the winding ratio by switching between the taps of the control winding with the first module, and at least one partial winding is switched off again by gradually actuating the semiconductor switching elements of the second module. Ultimately, the tap changer is then in a position where the first module has resumed its new steady-state operating point and the second module is in the neutral position.
[0038] The advantage of this embodiment is that the tap changer is then back in a starting position in which at least one partial winding is no longer flowing with current, and the second module, starting from the neutral position, has the full control range in both directions available again.
[0039] According to a further embodiment, after a change in the transmission ratio, the impedance or the voltage used for excitation by means of the second module, the first module and the second module are actuated such that the second module assumes a first end position from which the entire dynamic control range of the second module from the first end position to a second end position is available.
[0040] For example, in the first end position of the second module, at least one partial winding of the control winding is connected, ie the turns of the partial winding are added to the control winding, and in the second end position the partial winding is counter-connected to the control winding, ie the turns of the partial winding are subtracted from the control winding.
[0041] The advantage of this embodiment is that the entire control range of the second module is available for specific network requirements that require rapid response in one direction.
[0042] According to a further embodiment, several relevant parameters are tested and weighted according to their relevance. The transformation ratio, impedance, or voltage used for excitation is changed either by the first module or by the second module, depending on the test and weighting of the relevant parameters.
[0043] According to one embodiment, the first module and the second module are not actuated simultaneously.
[0044] According to a second aspect of the improved concept, a device for changing a transmission ratio, an impedance, or a voltage used for excitation of an electrical device is provided. Preferably, the device is designed to carry out a method according to the first aspect of the invention.
[0045] With regard to the device, reference is made analogously to the preceding explanations, preferred features, effects, and / or advantages already explained for the method. A corresponding repetition is therefore omitted.
[0046] The electrical equipment has at least one main winding, a control winding with winding taps, at least one partial winding and a step switch for changing the transformation ratio, the impedance or the voltage used for excitation of the electrical equipment.
[0047] The device comprises at least one sensor for measuring a voltage applied at a suitable measuring point and / or at least one sensor for measuring a current flowing at a suitable measuring point.
[0048] Furthermore, the device has an evaluation unit designed to carry out a method according to the first aspect of the improved concept. According to one embodiment, the tap changer comprises a first module for connecting the winding taps of the control winding and a second module with semiconductor switching elements for quickly connecting, counter-connecting, or bridging the at least one partial winding. The first module comprises a first control unit, and the second module comprises a second control unit. The evaluation unit is designed to actuate the first control unit and the second control unit.
[0049] According to one embodiment, the first module is designed as an on-load tap-changer for uninterrupted switching between the various winding taps of the control winding of the electrical equipment. It comprises a selector for powerless preselection of the winding tap of the electrical equipment to which switching is to take place, as well as a load transfer switch for the actual, uninterrupted switching from the previously connected winding tap to the new, preselected winding tap. For powerless preselection of the winding taps, the selector typically comprises two movable selector contacts that connect the winding taps. The load transfer switch comprises mechanical switching contacts, for example, vacuum interrupters, for the actual load switching.
[0050] According to a further embodiment, the first control unit is designed as a motor drive which actuates the selector contacts and the switching contacts of the on-load tap-changer.
[0051] According to one embodiment, the second module comprises at least one sub-module with semiconductor switching elements, preferably several sub-modules if the electrical equipment has multiple partial windings. Each sub-module is assigned at least one partial winding, and each sub-module is designed for rapid connection, counter-connection, or bridging of the associated partial winding.
[0052] According to a further embodiment, the second control unit is designed to actuate the at least one or more sub-modules or their associated semiconductor switching elements in a suitable manner such that the at least one or more partial windings are quickly connected to or counter-connected to the control winding or are bridged.
[0053] The second control unit is designed as a microcontroller, for example.
[0054] 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.
[0055] It shows
[0056] Figure 1 shows a first embodiment of a device according to the improved concept in a schematic representation;
[0057] Figure 2 shows a second embodiment of the device in a schematic representation;
[0058] Figure 3 shows a third embodiment of the device in a schematic representation;
[0059] Figure 4 shows a fourth embodiment of the device in a schematic representation;
[0060] Figure 5 shows a fifth embodiment of the device in a schematic representation;
[0061] Figure 6 shows a sixth embodiment of the device in a schematic representation;
[0062] Figure 7 shows a preferred embodiment of a method according to the improved concept;
[0063] Figure 8 shows a control range of a tap changer in a device according to an embodiment of the method according to the improved concept;
[0064] Figure 9 shows a further control range of a tap changer in a device according to a further embodiment of the method according to the improved concept.
[0065] Figure 1 shows an advantageous embodiment of a device 1 according to the improved concept in a schematic representation.
[0066] The device 1 is used to change the transformation ratio of an electrical device 14, which here is designed as a single-phase, adjustable transformer. The adjustable transformer 14 has, on the primary or secondary side, a main winding 2, a control winding 3 with n winding taps, and two partial windings 4 and 5. Partial winding 5 has a greater number of turns than partial winding 4, for example, three times as many. Furthermore, the number of turns of partial winding 4, and consequently also that of partial winding 5, is greater than the largest existing number of turns between two adjacent winding taps, for example, between n and n+1, of the control winding 3.
[0067] The number of partial windings is not limited to two. In principle, multiple partial windings can also be provided, each of which can be an integer multiple of the number of partial windings 4.
[0068] Furthermore, the transformer 14 has a tap changer 6 for changing the transformation ratio of the transformer 14. The tap changer 6 comprises a first module 7 for connecting the winding taps n, n+1 of the control winding 3 and a second module 8 connected in series with the first module 7 for connecting, counter-connecting, or bridging the partial windings 4, 5. The first module 7 is intended for control in the steady-state range, and the second module 8 for control in the dynamic time range.
[0069] Preferably, the first module 7 is an on-load tap-changer consisting of a selector for powerless preselection of the winding taps n, n+1 and a load transfer switch for uninterrupted switching from the previously connected winding tap n to the new, preselected winding tap n+1. The on-load tap-changer can also have a preselector, which can be designed as a coarse tap or a reverser. For clarity, however, the first module 7 is shown in Figure 1 in a highly simplified manner.
[0070] The second module 8 preferably has two sub-modules with semiconductor switching elements, for example, anti-parallel-connected thyristor or IGBT pairs. Each sub-module is assigned a respective partial winding 4 or 5, and each sub-module is designed to quickly connect the respective partial winding 4 or 5 to or against the control winding 3 using the semiconductor switching elements, i.e., within 10 to 1000 milliseconds, or to bridge the respective partial winding 4 or 5 such that the partial winding 4, 5 has a certain potential but no current flows through it. For better clarity, the second module 8 is also shown in a highly simplified form in Figure 1.
[0071] The device 1 also has a voltage sensor 9 and a current sensor 10. The voltage sensor 9 is arranged here, for example, at the high-voltage terminal of the main winding 2 and is designed to measure the operating voltage or actual voltage. The current sensor 10 is arranged between the second module 8 and a load terminal 15 and is designed to measure the current flowing between the second module 8 and the load terminal 15.
[0072] The first module 7 comprises a first control unit 11, which is preferably designed as a motor drive that actuates the selector and the load changeover switch mechanically, for example via a drive train with a gearbox.
[0073] The second module 8 is controlled by a second control unit 12. The second control unit 12 is designed to actuate the two sub-modules or their associated semiconductor switching elements in a suitable manner such that the two partial windings 4 and 5 are quickly connected to, counter-connected to, or bridged with the control winding 3. The second control unit 12 is designed, for example, as a microcontroller or as an IGBT driver.
[0074] The first control unit 11 and the second control unit 12 are operated by an evaluation unit 13 in dependence on one another.
[0075] Figure 2 schematically illustrates a second embodiment of the device 1 according to the invention. With regard to the device 1 of Figure 2, reference is made analogously to the preceding explanations of the device of Figure 1, and only the differences from the device of Figure 1 are discussed below.
[0076] Figure 2 shows a device 1 for changing the impedance of an electrical device 14, which here is designed as a controllable choke. Such arrangements are used for reactive power control in the power grid. In addition to a main winding 2, a control winding 3 with n winding taps, and two partial windings 4 and 5, the controllable choke 14 also has a coarse-step winding 16 and a coarse-step controller 17. The coarse-step controller 17 can assume a first position in which it contacts a first end A of the coarse-step winding 16, and a second position in which it contacts a second end B of the coarse-step winding 16. When the coarse-step controller 17 is in the first position, no current flows through the coarse-step winding 16. If, however, the coarse step controller 17 is in the second position, current flows through the coarse step winding 16 and is consequently added to the main winding 2 and the control winding 3.In this way, the control range of the choke 14 is increased. The device 1 according to this embodiment regulates the absorption of reactive power from the grid.
[0077] Figure 3 schematically illustrates a third embodiment of the device 1 according to the invention. With regard to the device 1 of Figure 3, reference is made analogously to the preceding explanations of the device of Figures 1 and 2, and only the differences are discussed below.
[0078] Figure 3 shows a device 1 for changing the transformation ratio of an electrical device 14, which is designed here as a controllable transformer 14 with a connected capacitor 18. The device 1 according to this embodiment controls the feed-in of capacitive reactive power into the grid. The controllable transformer 14 can, for example, comprise a series winding 19, a control winding 3, and a main winding 2 with a load shunt 15. The capacitor 18 is arranged between the first module 7 and the second module 8 of the tap changer 6.
[0079] Figure 4 schematically illustrates a fourth embodiment of the device 1 according to the invention, which, like Figure 3, shows a device 1 for changing the transformation ratio of an electrical device 14, which is designed as a controllable transformer 14 with a connected capacitor 18. Therefore, reference is also made here in an analogous manner to the preceding explanations of the device from Figures 1, 2, and 3, and only the differences are discussed below.
[0080] In this embodiment, the controllable transformer 14 comprises a main winding 2, a control winding 3 with n winding taps, two partial windings 4 and 5 and an additional coarse tap winding 16 with a coarse tap controller 17. A capacitor 18 for controlling capacitive reactive power into the energy supply network is arranged in an electrical line 20 which branches off between the main winding 2 and the coarse tap winding 16 and ends in a load discharge line 15.
[0081] Figure 5 schematically illustrates a fifth embodiment of the device 1 according to the invention. With regard to the device 1 of Figure 5, reference is made analogously to the preceding explanations of the device of Figures 1, 2, 3, and 4, and only the differences are discussed below.
[0082] Figure 5 shows a device 1 for changing the voltage used for excitation of an electrical device 14, which is used, for example, in arc furnace applications. The electrical device 14 here consists of a first inductive arrangement 22, which is designed as an excitation transformer, and a second inductive arrangement 23, which is designed as a booster transformer. The excitation transformer 22 comprises a main winding 2, a control winding 3 with n winding taps, and two partial windings 4 and 5. The booster transformer 23 has a primary winding 24 and a secondary winding 25, with an arc furnace 21 arranged on the secondary side. The control winding 3 of the excitation transformer 22 is electrically connected to the primary winding 24 of the booster transformer 23.In this embodiment, the voltage of the excitation transformer 22, which is used to excite the booster transformer 23, is regulated via the tap changer 6. Depending on whether regulation is in the steady-state range or the dynamic range, the first module 7 or the second module 8 is used.
[0083] Figure 6 schematically illustrates a sixth embodiment of the device 1 according to the invention. With regard to the device 1 of Figure 6, reference is made analogously to the preceding explanations of the device of Figures 1, 2, 3, 4, and 5, and only the differences are discussed below.
[0084] Figure 6 shows a further device 1 for changing the voltage used to excite an electrical device 14, such as is used in arc furnace applications. Here, too, the electrical device 14 consists of a first inductive arrangement 22, which is designed as an excitation transformer, and a second inductive arrangement 23, which is designed as a booster transformer. In this embodiment, the excitation transformer 22 has a primary winding 26 and a secondary winding 27, and the booster transformer 23 has a control winding 24 on the primary side. The secondary winding 27 of the excitation transformer 22 is electrically conductively connected to the control winding 24 or to the primary side of the booster transformer 23. At the control winding 24 of the booster transformer 23, the voltage excited by the excitation transformer 22 in the booster transformer 23 is controlled by means of the tap changer 6.
[0085] Figure 7 shows a flowchart of an advantageous embodiment of a method according to the improved concept. The method is carried out using a device according to one of the embodiments already explained in connection with Figures 1 to 6. In a step a, a request is received to change the transformation ratio, the impedance, or the voltage used for excitation of an electrical device 14. This request can come from a higher-level system, for example, a control center of a power grid operator, or from a local control device, such as a voltage regulator.In a step b, at least one relevant characteristic is then checked and in a step c, the transformation ratio, the impedance or the voltage used for excitation of the electrical equipment 14 is changed by means of the first module 7 or the second module 8 of the tap changer 6 depending on the check of the at least one relevant characteristic.
[0086] Steps b and c are carried out by means of the evaluation unit 13, which controls either the first control unit 11 or the second control unit 12 depending on the test carried out in step b.
[0087] In step b, various relevant parameters can be checked. For example, the relevant parameter can be the amount of deviation of an actual voltage of the electrical equipment 14 from a predetermined target voltage. For this purpose, the actual voltage or the equipment voltage is measured using the voltage sensor 9, and the measured value is compared with the predetermined target voltage using the evaluation unit 13. In this case, the transformation ratio is changed using the second module 8 if the amount of deviation from the target voltage is greater than a step voltage applied between two adjacent winding taps of the control winding 3, for example between n and n+1. Another example of a relevant parameter that can be checked is the amount of deviation of an impedance of the electrical equipment 14 from a predetermined target impedance.For this purpose, the impedance of the electrical device 14 is determined based on current values measured by the current sensor 10, and the determined value is compared with a predetermined target impedance by the evaluation unit 13. The impedance is then changed by the second module 8 if the amount of deviation from the target impedance is greater than an impedance acting between two adjacent winding taps n, n+1 of the control winding 3. Further examples of relevant parameters are the gradient of a required voltage change, the gradient of a required impedance change, or the amount of deviation of an actual voltage in a first inductive arrangement 22 for exciting a second inductive arrangement 23 from a predetermined target voltage.
[0088] Once the transformation ratio, impedance or voltage used for excitation has been changed by means of the second module 8, according to an advantageous embodiment of the method, the first module 7 and the second module 8 are then actuated alternately until the first module 7 has reached a position which indicates a new, stationary operating point of a power supply network or a process-driven system, and the second module 8 is in a neutral position in which the partial windings 4 and 5 are bridged, i.e. are at potential but no current flows through them. In other words, after the second module 8 has been switched, the first module 7 is "pulled along" in steps. For example, if the second module 8 switches two steps up (+2) from the neutral position (0), in a next step the first module 7 switches one step up (+1) and the second module switches one step down again (-1).In a subsequent step, the first module 7 switches up another level (+1 ) and the second module 8 switches down another level (-1 ). Finally, the first module 7 is two levels higher than before, and the second module 8 returns to its neutral position. Due to the described "tightening" of the first module 7, the first module 7 has set a new, stationary operating point. Starting from the neutral position, the second module 8 again has access to the full control range, both up and down.
[0089] Figure 8 illustrates the above description with reference to a variable impedance. Shown here is the control range of a tap changer 6, or more precisely the reactive power control range. The percentage of reactive power of the inductive equipment 14 is plotted on the y-axis. The position of the first module 7 of the tap changer 6 can be read off on the x-axis, i.e. which winding tap n of the control winding 3 is contacted by the first module 7 of the tap changer 6. The points 28 mark the possible positions that the first module 7 can assume, with control taking place in the steady-state range, i.e. every minute. Point 30 represents the stationary operating point, which according to this embodiment is set via the first module 7. The starting point of points 28 and 29 isThe area extending vertically upwards and downwards, which is delimited by lines 29, is the control range covered by the second module 8. In this area delimited by lines 29, control by the second module 8 is rapid, namely in the millisecond range, in both directions, allowing flexible and rapid response to dynamic fluctuations in the grid or in a system. Thus, the fast, but also cost-intensive semiconductor switching elements do not have to be dimensioned for the entire control range of the tap changer 6, but only for the range that needs to be controlled quickly.
[0090] Figure 9 illustrates a further control range of a tap changer 6, more precisely the reactive power control range according to a further embodiment of the method. According to this embodiment, after a change in the transformation ratio, the impedance, or the voltage used for excitation by means of the second module 8, the first module 7 and the second module 8 are actuated such that the second module 8 assumes a first end position in which the turns of the partial windings 4 and 5 are either both added to the control winding 3 or subtracted from it. In this embodiment, the respective end position represents the operating point 30. Depending on which case applies, the entire dynamic control range of the second module 8 is available starting from the operating point 30 in one direction, namely from the first end position to the second end position or vice versa.This design is advantageous for certain network requirements that require a fast reaction of the tap changer 6 in one direction.
[0091] The combination of a conventional on-load tap-changer, a first module, with a power electronic tap-changer, a second module, enables the realization of a large control range while simultaneously providing a cost-effective and space-saving arrangement with high potential. This is because the second module, which is more cost-intensive than the first module and is designed for fast control in the dynamic control range, can be optimized for the respective application. Consequently, the second module can be designed accordingly only for the part of the control for which the power electronic-based second module offers an advantage due to its speed of sound. In addition, the combined solution is significantly more space-saving than a purely power electronic-based solution. In summary, the solution according to the invention enables a high degree of flexibility with comparatively little space requirement for network management and furnace operation.
[0092] REFERENCE SYMBOL
[0093] 1 device
[0094] 2 main winding
[0095] 3 control winding
[0096] 4 first partial winding
[0097] 5 second partial winding
[0098] 6 step switches
[0099] 7 first module of 6
[0100] 8 second module of 6
[0101] 9 Voltage sensor
[0102] 10 Current sensor
[0103] 11 first control unit
[0104] 12 second control unit
[0105] 13 Evaluation unit
[0106] 14 electrical equipment
[0107] 15 Load transfer
[0108] 16 coarse tap winding
[0109] 17 coarse step controls
[0110] 18 Capacitor
[0111] 19 Series winding
[0112] 20 electrical cables
[0113] 21 arc furnace
[0114] 22 first inductive arrangement
[0115] 23 second inductive arrangement
[0116] 24 primary winding or control winding of 23
[0117] 25 secondary winding of 23
[0118] 26 Primary winding of 22 27 Secondary winding of 22
[0119] 28 points
[0120] 29 lines A first end of 16
[0121] B second end of 16 n-1 , n, ... n+4 winding taps
Claims
REQUIREMENTS 1. Method for changing a transmission ratio, an impedance or an excitation voltage of an electrical device (14), comprising the electrical device (14) - at least one control winding (3) with winding taps (n, n+1 ) and at least one partial winding (4, 5), a tap changer (6) for changing the turns ratio, the impedance or the voltage used for excitation of the electrical equipment (14), wherein - the tap changer (6) comprises a first module (7) for connecting the winding taps (n, n+1 ) of the control winding (3) and a second module (8) with semiconductor switching elements for connecting, counter-connecting or bridging the at least one partial winding (4, 5), wherein the method comprises the following steps: Receipt of a request to change the translation ratio, impedance or excitation voltage of the electrical equipment (14), Testing at least one relevant characteristic, change in the translation ratio, impedance or the voltage used for excitation of the electrical equipment (14) either by means of the first module (7) or by means of the second module (8) depending on the testing of the at least one relevant characteristic.
2. The method according to claim 1, wherein - the relevant parameter includes an amount of deviation of an actual voltage of the electrical equipment (14) from a specified target voltage, the change of the transformation ratio by means of the second module (8) takes place if the amount of deviation from the target voltage is greater than a step voltage applied between two adjacent winding taps (n, n+1 ) of the control winding (3).
3. Method according to any one of the preceding claims 1 to 2, wherein - the relevant parameter comprises the magnitude of a deviation of the impedance of the electrical device (14) from a predetermined target impedance, the change in impedance by means of the second module (8) occurs when the magnitude of the deviation from the target impedance is greater than an impedance acting between two adjacent winding taps (n, n+1) of the control winding (3). Method according to any one of the preceding claims 1 to 3, wherein - the relevant parameter includes the amount of a deviation of an actual voltage in a first inductive arrangement (22) for exciting a second inductive arrangement (23) from a predetermined target voltage, - The voltage used for excitation of the second inductive arrangement (23) is adjusted by means of the second module (8) when the magnitude of the deviation from the target voltage is greater than a step voltage applied between two adjacent winding taps (n, n+1) of the control winding (3, 24). Method according to any one of the preceding claims 1 to 4, wherein - the relevant parameter includes the gradient of a required voltage change, - The change in the transmission ratio by means of the second module (8) occurs when the gradient of the required voltage change is greater than a defined limit value. Method according to any one of the preceding claims 1 to 5, wherein - the relevant parameter includes the gradient of a required impedance change, - The impedance is changed by means of the second module (8) when the gradient of the required impedance change is greater than a defined limit value. Method according to any one of the preceding claims 1 to 6, wherein - the relevant parameter comprises a fundamental frequency plus a proportion of harmonics of a voltage applied to the electrical equipment (14), The change in the translation ratio by means of the second module (8) takes place when the proportion of harmonics is greater than a specified limit value.
8. Method according to claim 7, wherein - a Fourier analysis is carried out to determine the proportion of harmonics above the fundamental frequency of the voltage applied to the electrical equipment (14).
9. Method according to any one of the preceding claims 1 to 8, wherein - after a change in the translation ratio, the impedance or the voltage used for excitation by means of the second module (8), - the first module (7) and the second module (8) are actuated in such a way that the second module (8) assumes a neutral position in which at least one partial winding (4, 5) is bridged.
10. Method according to any one of the preceding claims 1 to 8, wherein - after a change in the translation ratio, the impedance or the voltage used for excitation by means of the second module (8), - the first module (7) and the second module (8) are actuated in such a way that the second module (8) assumes a first end position, from which the entire control range of the second module is available to a second end position.
11. Method according to any one of the preceding claims 1 to 10, wherein several relevant parameters are tested, - the key figures are weighted according to their relevance, - the change in the translation ratio, the impedance or the voltage used for excitation is carried out either by means of the first module (7) or by means of the second module (8) depending on the test and the weighting of the relevant parameters.
12. Method according to any one of the preceding claims 1 to 1 1 , wherein - the first module (7) and the second module (8) cannot be activated simultaneously.
13. Device (1) for changing a turns ratio, an impedance or an excitation voltage of an electrical device (14), wherein the electrical device (14) comprises at least one control winding (3) with winding taps (n, n+1), at least one partial winding (4, 5) and a tap changer (6) for changing the turns ratio, the impedance or the excitation voltage of the electrical device (14), the device (1) comprising - at least one sensor (9) for measuring a voltage applied at a suitable measuring point, and / or - at least one sensor (10) for measuring a current flowing at a suitable measuring point, an evaluation unit (13) configured for carrying out a method according to claims 1 to 13.
14. Device (1) according to the preceding claim, wherein - the tap changer (6) comprises a first module (7) for connecting the winding taps (n, n+1) of the control winding (3) and a second module (8) with semiconductor switching elements for connecting, counter-connecting or bridging the at least one partial winding (4, 5), - the first module (7) comprises a first control unit (11), - the second module (8) comprises a second control unit (12), wherein - the evaluation unit (13) is designed to actuate the first control unit (11) and the second control unit (12).