Method for actuating an on-load tap changer, and on-load tap changer device
Patent Information
- Application Number
- EP2023735972
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-07-14
- Filing Date
- 2023-06-20
- Publication Date
- 2025-02-05
- Estimated Expiration
- 2043-06-20
AI Technical Summary
On-load tap changers lack precision in switching operations, leading to potential damage of vacuum interrupters due to immediate actuation without considering current zero crossings, resulting in prolonged arc burning times.
A method utilizing a control device, sensor, and drive system that predicts future current zero crossings to adjust the actuation timing of the on-load tap changer, ensuring it operates at or shortly before zero current crossings, thereby minimizing arc duration and protecting vacuum interrupters.
This approach enhances the precision and safety of on-load tap changer operations by aligning actuation with zero current crossings, reducing mechanical stress and extending the lifespan of vacuum interrupters.
Smart Images
Figure 1.1
Abstract
Description
[0001] Method for operating an on-load tap-changer and on-load tap-changer device
[0002] The invention relates to a method for operating an on-load tap-changer and an on-load tap-changer device.
[0003] Substations contain a variety of switches for different tasks and with different requirements. To operate the respective switches, they must be driven by a drive system. These switches include on-load tap-changers, diverter switches, selectors, double reversing switches, reversing switches, pre-selectors, circuit breakers, load switches, or disconnectors.
[0004] For example, on-load tap-changers are used for uninterrupted switching between different winding taps of an electrical device, such as a power transformer. This allows, for example, the transformer's transformation ratio or the inductance of the choke to be changed.
[0005] On-load tap-changers are typically operated by a combination of a motor drive and a spring energy storage mechanism. Operation occurs immediately after the switching command, i.e., at any time.
[0006] It is therefore an object of the present invention to provide a method for operating an on-load tap-changer which is more precise, checks the state of the on-load tap-changer before switching and protects the vacuum interrupters.
[0007] This object is achieved by the respective subject matter of the independent claims. Further embodiments are the subject matter of the dependent claims.
[0008] The invention proposes a method for actuating an on-load tap-changer with a drive, a sensor, and a control device, wherein a control device receives a switching command for actuating the on-load tap-changer; a current curve is detected via the sensor; a start time in the current curve is determined at which the switching command for actuating the on-load tap-changer was received; a time offset is added to the start time, and from this a time at which the actuation would potentially begin is determined; a time of a next current zero crossing after the time at which the actuation would potentially begin is determined; a time difference between the time at which the actuation would potentially begin and the time of the next current zero crossing is determined; the time difference is added to the start time in order to determine a new start time for the actuation.at the new start time, the drive begins to operate the on-load tap-changer.;
[0009] The method is based on the idea of monitoring the current flow within the on-load tap-changer, or more precisely within a vacuum interrupter, starting with the actuation of the on-load tap-changer or with the opening of the vacuum interrupter exactly at or shortly before the zero crossing of the current. This shortens the burning time of the arc within the vacuum interrupter when it opens as much as possible. This protects the vacuum interrupter and in particular the contacts within the vacuum interrupter as much as possible. Precise opening, switching or actuation is made possible by, among other things, predicting future current zero crossings, so that the opening, switching or actuation of the on-load tap-changer is based on this. Since the inertia of the drive train and thus the time offset between the switching command and the actual actuation are known, these are adjusted to a future and suitable current zero crossing.Thus, the actual actuation does not begin immediately after the switching command, but rather with a corresponding time delay, taking into account the time offset in the drive train. This takes into account the inertia (mechanics) of the drive train during actuation, so that the vacuum interrupter is always actuated at or shortly before the current zero crossing. Actuation of the on-load tap-changer also includes the opening of a vacuum interrupter that is part of the on-load tap-changer.
[0010] A control unit is connected to the drive and at least one sensor. The control unit controls the drive, which in turn actuates the on-load tap-changer. Furthermore, the control unit detects the current profile via at least one sensor. The sensor detects a current profile and can be located at various locations, for example, on a vacuum interrupter and / or on the on-load tap-changer and / or on the low-voltage side and / or high-voltage side of a tap-changer.
[0011] The current waveform prior to the switching command to operate the on-load tap-changer can be recorded in various ways; in particular, the frequency and past current zero crossings can be determined and recorded. The current waveform is preferably evaluated in the control device.
[0012] The time of the next current zero crossing is a future current zero crossing and is based on the past current zero crossings of the current curve.
[0013] A future current zero crossing or all future current zero crossings are determined using one or more mathematical methods, in particular fast Furier transformation. Furthermore, a future current zero crossing or all future current zero crossings can be determined using analog electronics.
[0014] The current profile can be detected, for example, by means of a sensor on a vacuum interrupter and / or on-load tap changer and / or on the low-voltage side and / or high-voltage side of a tap transformer.
[0015] The time offset is a value that is determined by or dependent on the mechanics of the drive train. The time offset value can be adjusted automatically and / or manually. Furthermore, the time offset value can be adjusted based on the arc burning duration in the vacuum interrupter of the on-load tap-changer. Furthermore, the time offset value can be adjusted based on the arc burning duration of the on-load tap-changer's past switching operations in the vacuum interrupter of the on-load tap-changer.
[0016] After determining the time offset, a further time offset can be subtracted to shift the new start time. This means that the on-load tap-changer's operation begins not before the zero crossing, but at an earlier time that is not the time of the next current zero crossing.
[0017] The control device can be designed in any desired manner and in particular can comprise means that control a drive in order to actuate the on-load tap-changer and to carry out the method according to the invention.
[0018] Furthermore, the invention proposes an on-load tap-changer device, comprising: an on-load tap-changer; a sensor; a drive; a control device; wherein the control device is configured to receive a switching command for actuating the on-load tap-changer; to detect a current curve via the sensor; to determine a starting time in the current curve at which the switching command for actuating the on-load tap-changer was received; to add a time offset to the starting time and from this to determine a time at which the actuation would potentially begin; to determine a time of a next current zero crossing after the time at which the actuation would potentially begin; to determine a time difference between the time at which the actuation would potentially begin and the time of the next current zero crossing;to add the time difference to the start time and use this to determine a new start time for the actuation; to begin actuating the on-load tap-changer using the drive at the new start time.
[0019] The on-load tap-changer device, consisting of an on-load tap-changer with a vacuum interrupter, a drive, a sensor and a control device, makes it possible to take into account the time offset of the mechanics during a load changeover and thus to open a vacuum interrupter at zero current crossing.
[0020] Furthermore, the on-load tap-changer device can have a further sensor for measuring the arc burning time.
[0021] In the following, the invention is explained in detail using exemplary embodiments with reference to the drawings.
[0022] Figure 1 shows a tap transformer with an on-load tap changer;
[0023] Figure 2 shows a process flow;
[0024] Figure 3 is a diagram explaining the process;
[0025] Figure 4 shows another diagram to explain the process.
[0026] Figure 1 shows an on-load tap-changer device 1 for carrying out a load transfer. The on-load tap-changer device 1 comprises a control device 2, at least one sensor 5, and an on-load tap-changer 4. The control device 2 is connected to a drive of the on-load tap-changer 4. The control device 2 is designed and configured to control the drive 3 so that it actuates the on-load tap-changer 4. Furthermore, the control device 2 is connected to a sensor 5 or a plurality of sensors 5, which measures a current flowing through a vacuum interrupter 6 and thus through the on-load tap-changer 4 and a tapped transformer 7. The control device 2 is designed and configured to measure and evaluate the current detected by the sensor 5 or the sensors 5. In particular, the control device 2 determines the current profile, i.e. when the current has or assumes the value zero and at what frequency this occurs.The sensor 5 can be arranged, for example, on the tap-changer 7, in particular on the high-voltage side 8 or the low-voltage side 9. Furthermore, a sensor 5 can be arranged in the on-load tap-changer 4, directly on the vacuum interrupter 6, or at any other position suitable for detecting the current profile.
[0027] The control device 2 is further designed and configured to predict or calculate future current zero-crossing times. The control unit 2 therefore has a computing unit and / or a processor and / or a memory.
[0028] The drive 3 is mechanically connected to the on-load tap-changer 4 and thus also to the vacuum interrupter 6 via a drive train 10. The drive train 10 refers to the sum of the mechanical elements or mechanisms between the motor drive 3 and the vacuum interrupter 6, such as shafts, toggle levers, rollers, etc.
[0029] The control device 2 can be arranged as a standalone device on the tap-changer 7 or in a control room. Furthermore, the control device 2 can be part of a drive control system of the on-load tap-changer 4 or part of a voltage regulator. The control device 2 is designed and configured to control the drive 3.
[0030] Furthermore, a further sensor 15 is provided, which is connected to the control device 2. The further sensor 15 is designed and configured to detect an arc burning duration in the vacuum interrupter 6. The control device 2 then evaluates the detected arc burning duration. Ideally, the vacuum interrupter 6 is opened at zero current crossing, so that no arc is created inside the vacuum interrupter 6 and the arc burning duration is zero. If the vacuum interrupter 6 is actuated while a current is still flowing through the vacuum interrupter 6, an arc is created until it breaks off and extinguishes. This arc burning duration therefore also depends on the time offset TV. The arc burning duration from previous switching operations is thus also used to adjust the time offset TV. The evaluation and adjustment takes place in the control device 2.
[0031] The tap-changer 7 has a main winding 11 and a control winding 12. The on-load tap-changer 4 is connected to the control winding 12 via the winding taps 13. The main winding 11 and the control winding 12 are arranged on the high-voltage side 8 (in rare cases also on the low-voltage side). Furthermore, the tap-changer 10 has a low-voltage winding 14, which is inductively coupled to the main winding 11 and the control winding 12.
[0032] Figure 2 shows a flow diagram of a method for carrying out a load transfer by means of an on-load tap-changer 4. In a first step 30, the control device 2 receives a signal or a switching command for carrying out a load transfer by means of an on-load tap-changer or a switching command for starting the operation of the on-load tap-changer 4. The signal or the switching command is generated, for example, manually or by a voltage regulator.
[0033] In the next step 31, a current waveform is recorded with the help of a sensor 4. In particular, it is determined when the current flowing through the vacuum interrupter 5 of the on-load tap-changer 4 has or assumes the value zero and with which frequency F this happens. The past current zero-crossing times and their intervals from one another are determined. This occurs continuously during the operation of the tap transformer, in particular before the switching command and before the on-load tap-changer begins to be actuated. Ideally, the current has a sinusoidal waveform, which results in regular current zero crossings. Based on the times from the past or on the past current zero crossings, the future current zero crossings or the times in the current waveform are then predicted. This can be done in a variety of ways, for example by calculation using mathematical methods such as fast Furier transformation.These calculations are performed in the control unit 2, which is designed and configured for this purpose. The control unit 2 therefore has a computing unit and / or a processor and / or a memory. The current and future zero-crossing times are determined via a signal from the sensor, which, depending on its design, samples or outputs only zero-crossings or the entire sinusoidal waveform.
[0034] In the next step 32, the current starting time TO is determined. This starting time TO corresponds to the time at which the signal for actuating the on-load tap-changer 4 was generated in the control device 2 or received by the control device 2. This is plotted in the current curve. Since the drive train 10 has a time offset TV due to the mechanics, this must be taken into account when actuating the on-load tap-changer 4 or opening the vacuum interrupter 6. The offset TV due to the mechanics is predetermined by the design of the drive train 10. This includes, for example, the rotary movement of a cam or a lever, which must first travel a distance, for example, before a force or movement can be transmitted to the vacuum interrupter 6. The actuation or opening of the on-load tap-changer 4 or the vacuum interrupter 6 is carried out by these mechanical conditions.the opening of the vacuum interrupter 6 not immediately after the signal for actuation or at the beginning, but with the corresponding time offset TV. The goal of each actuation of the on-load tap-changer 4, however, is to open the vacuum interrupter 6 at or approximately before the current zero crossing, i.e., shortly before the current zero crossing. Since the information on the future current zero crossing times or current zero crossings, the start time TO and the offset TV, are known in the control device 2, a corresponding start time T1 is calculated for the start of the switching. In other words, actuation only begins when there is a current zero crossing in the vacuum interrupter 6 at the end of the time offset TV of the drive train 10. Thus, in the next step 33, the time offset TV is added to the start time TO, and thus the time TB is determined at which the actual opening of the vacuum interrupter 6 would occur.
[0035] In the next step 34, the time TG at which the next current zero crossing—a future current zero crossing—would occur after the time TB of the potential start of actuation is determined. Based on the times TB and TG, a time difference TD between these times is determined in the next step 35. This difference TD is then used to shift the start time TO to a new start time T1 in the next step 36.
[0036] In the final step 37, the switching process is initiated or executed at the newly determined starting time T1. Here, drive 3 is controlled by control unit 2.
[0037] The time offset TV has a value of a few milliseconds that is adapted to the drive train 10. This value can either be fixed or can be adjusted. The adjustment can be made automatically or manually. An adjustment can be useful, for example, if wear occurs in the drive train or parts are replaced. Furthermore, the arc burning time can also be used to adjust the time offset. Figure 3 serves to illustrate the method according to the invention. The temporal current profile (in ms) within a closed vacuum interrupter 6 or the on-load tap-changer 4 is plotted on the X-axis. The Y-axis shows the current level in A. The current profile or the current curve is sinusoidal or approximately sinusoidal here. The curve of the current profile intersects the X-axis at the zero crossings (current zero crossings). This means that no current flows through the vacuum interrupter 6 orthe on-load tap-changer 4. At any point in time TO, a switching command to actuate or begin actuation of the on-load tap-changer 4 is received in the control unit 2. This point in time is assumed to be the possible start time TO of a load transfer. Starting from this start time TO, the time offset TV is added to this start time TO. This time offset TV generally has a fixed value. After adding the time offset TV to the start time TO, a point in time TB is obtained at which the actuation or opening of the vacuum interrupter 6 would potentially begin. However, since a current is still flowing here, i.e. the current is not zero, arcs would occur when the vacuum interrupter 6 is actuated, and in particular when the vacuum interrupter 6 is opened. This is precisely what we want to avoid.
[0038] As shown in the diagram, the time TB at which actuation would potentially begin is not at a current zero crossing. Therefore, a suitable time TG is determined at which no current would flow through the vacuum interrupter 6 upon opening. This time TG is the next current zero crossing after time TB. The next current zero crossing is determined based on past current zero crossings.
[0039] Based on the time TB of the potential start of opening or actuation and the appropriate time TG, the time period TD between these two points is calculated, for example, as a difference. This time period TD is then added to the start time TO and forms the new start time T1, at which the actual actuation or opening begins. This ensures that the opening or actuation of vacuum interrupter 6 begins at the current zero crossing.
[0040] According to a further embodiment in Figure 4, after determining the time offset TV, a further offset TD1 is subtracted. This offset TD1 ensures that the opening of the vacuum interrupter does not begin immediately at the current zero crossing, but rather a few milliseconds earlier (TF), i.e., shortly before.
[0041] 1 on-load tap-changer device
[0042] 2 Control device
[0043] 3 Drive
[0044] 4 on-load tap-changers
[0045] 5 Sensor
[0046] 6 vacuum interrupters
[0047] 7-step transformer
[0048] 8 High voltage side
[0049] 9 Low voltage side
[0050] 10 Drivetrain
[0051] 11 Main winding
[0052] 12 control winding
[0053] 13 winding taps
[0054] 14 Low-voltage winding
[0055] 15 additional sensors
[0056] TO start time
[0057] T1 new start time
[0058] TV time offset
[0059] TD1 further offset
[0060] TB Time at which the activity would potentially begin
[0061] TG Time of the next current zero crossing
[0062] TD time difference
[0063] TF Earlier time F Frequency
Claims
Claims 1. Method for actuating an on-load tap-changer (4) with a drive (3), a sensor (5) and a control device (2), wherein a control device (2) receives a switching command for actuating the on-load tap-changer (4); a current curve is detected via the sensor (5); a starting time (TO) in the current curve is determined at which the switching command for actuating the on-load tap-changer (4) was received; a time offset (TV) is added to the starting time (TO) and from this a time (TB) at which the actuation would potentially begin is determined; a time (TG) of a next current zero crossing after the time (TB) at which the actuation would potentially begin is determined; a time difference (TD) between the time (TB) at which the actuation would potentially begin and the time (TG) of the next current zero crossing is determined;the time difference (TD) is added to the starting time (TO) in order to determine a new starting time (T1) for the actuation; at the new starting time (T1) the actuation of the on-load tap-changer (4) by the drive (3) begins.; 2. A method for operating an on-load tap-changer (4) according to claim 1, wherein the current profile is detected before the switching command for operating the on-load tap-changer (4); when the current profile is detected, the frequency and the past current zero crossings are determined.
3. Method for operating an on-load tap changer (4) according to claim 1, wherein the time (TG) of the next current zero crossing is a future current zero crossing based on the past current zero crossings of the current curve.
4. Method for operating an on-load tap changer (4) according to claim 3, wherein a future current zero crossing is determined by a mathematical method, in particular fast Furier transformation or by means of analog electronics. . Method for operating an on-load tap-changer (4) according to one of claims 1 to 4, wherein the current profile at a vacuum interrupter (6) and / or on-load tap-changer (4) and / or on the low-voltage side (9) and / or high-voltage side of a tapped transformer (7) is detected by one or more sensors (5). . Method for operating an on-load tap-changer (4) according to one of claims 1 to 5, wherein the time offset (TV) is a value that is determined by or dependent on the mechanics of the drive train (10). . Method for operating an on-load tap-changer (4) according to claim 6, wherein the value of the time offset (TV) can be adjusted automatically and / or manually. . Method for operating an on-load tap-changer (4) according to one of claims 1 to 6, wherein the value of the time offset (TV) can be adjusted based on an arc burning duration in the vacuum interrupter (6) of the on-load tap-changer (4). .Method for actuating an on-load tap-changer (4) according to one of claims 1 to 8, wherein after the determination of the time offset (TV), a further time offset (TD1) is subtracted, thereby shifting the new starting time (T1) and starting the actuation of the on-load tap-changer (4) before the zero crossing at an earlier time (TF) which is not the time (TG) of a next current zero crossing.
0. Method for actuating an on-load tap-changer (4) according to one of claims 1 to 9, wherein the control device (2) controls a drive (3) which actuates the on-load tap-changer (4). 1 . On-load tap-changer device (1), comprising: an on-load tap-changer (4); a sensor (5);. a drive (3); a control device (2); wherein the control device (2) is configured to receive a switching command for actuating the on-load tap-changer (4); to detect a current curve via the sensor (5); to determine a starting time (TO) in the current curve at which the switching command for actuating the on-load tap-changer (4) was received; to add a time offset (TV) to the starting time (TO) and from this to determine a time (TB) at which the actuation would potentially begin; to determine a time (TG) of a next current zero crossing after the time (TB) at which the actuation would potentially begin; to determine a time difference (TD) between the time (TB) at which the actuation would potentially begin and the time (TG) of the next current zero crossing; to add the time difference (TD) to the starting time (TO) and from this to determine a new starting time (T1) for the actuation;to start operating the on-load tap-changer (4) by means of the drive (3) at the new starting time (T1); 12. On-load tap-changer device (1) according to claim 11, comprising a further sensor (15) for measuring the arc burning time.