METHOD FOR OPERATING A LOAD STAGE SWITCH AND LOAD STAGE SWITCH DEVICE

Description

[0001] The invention relates to a method for actuating a load tap changer and a load tap changer device.

[0002] Substations contain a variety of switches for different tasks and with varying requirements. These switches must be actuated by a drive system to operate them. Examples of these switches include tap changers, load changers, selectors, double reversing switches, reversing switches, preselectors, circuit breakers, load switches, and disconnectors.

[0003] For example, tap changers are used for the uninterrupted switching between different winding taps of an electrical device, such as a power transformer. This allows, for example, the turns ratio of the transformer or the inductance of the choke to be changed.

[0004] On-load tap changers are typically actuated by a combination of a motor drive and a spring energy storage device. Actuation occurs immediately after the switching command, i.e., at any desired time.

[0005] GB 2 435 943 A discloses a hybrid load tap changer comprising a selector and a load changeover switch. The selector has mechanical switching elements, and the load changeover switch has semiconductor switching elements. A control device coordinates the actuation of the selector and the load changeover switch. Several sensors monitor voltage and current at different points on the load tap changer.

[0006] It is therefore an object of the present invention to provide a method for actuating a load tap changer which is more accurate, checks the state of the load tap changer before switching and protects the vacuum switching tubes.

[0007] This problem is solved 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 a load tap changer with a drive, a sensor and a control device, wherein A control device receives a switching command to actuate the load tap changer; a current waveform is detected via the sensor; a start time in the current waveform is determined at which the switching command to actuate the 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 the 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 to determine a new start time for the actuation; at the new start time, the actuation of the load tap changer by the drive begins.

[0009] The method is based on the idea of ​​monitoring the current flow within the load tap changer, more precisely within a vacuum interrupter tube, and initiating the activation of the load tap changer or the opening of the vacuum interrupter tube precisely at or shortly before the current's zero crossing. This significantly reduces the arc duration within the vacuum interrupter tube during opening. This, in turn, minimizes wear and tear on the vacuum interrupter tube and, in particular, on the contacts within it. Precise opening, switching, or activation is achieved by predicting future current zero crossings and aligning the activation of the load tap changer accordingly. Since the inertia of the drive train, and thus the time lag between the switching command and the actual activation, is known, these factors are calibrated 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 lag in the drive train. This accounts for the inertia (mechanical) of the drive train during actuation, ensuring that the vacuum switching tube is always actuated at or shortly before the current zero crossing. The actuation of the load tap changer also includes the opening of a vacuum switching tube that is part of the 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 load tap changer. Furthermore, the control unit monitors the current waveform via at least one sensor. The sensor monitors the current waveform and can be located at various points, for example, on a vacuum interrupter and / or on the load tap changer and / or on the low-voltage and / or high-voltage side of a step-down transformer.

[0011] The current waveform prior to the switching command for actuating the load tap changer can be recorded in various ways; in particular, the frequency and the number of previous zero crossings of the current can be determined and recorded. The evaluation of the current waveform preferably takes place in the control device.

[0012] The timing of the next current zero crossing is a future current zero crossing and is based on the past current zero crossings of the current waveform.

[0013] A future current zero crossing, or all future current zero crossings, are determined by one or more mathematical methods, in particular the Fast Furier transform. Alternatively, a future current zero crossing, or all future current zero crossings, can be determined using analog electronics.

[0014] The current flow can be detected, for example, by means of a sensor on a vacuum interrupter and / or load tap changer and / or on the low-voltage side and / or high-voltage side of a step-down transformer.

[0015] The time offset is a value determined by or dependent on the mechanics of the drive train. This offset can be adjusted automatically and / or manually. Furthermore, the time offset can be adjusted based on the arc duration in the vacuum switching tube of the load tap changer. Alternatively, the time offset can be adjusted based on the arc duration of previous switching operations of the load tap changer in the vacuum switching tube of the 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 activation of the load tap changer does not begin before the zero crossing, but at an earlier time that is not the time of the next zero crossing of the current.

[0017] The control device can be designed in any way and in particular may include means that control a drive to actuate the load tap changer and to carry out the method according to the invention.

[0018] Furthermore, the invention proposes a load tap changer device comprising: a load tap changer; a sensor; an actuator; a control device; wherein the control device is configured to receive a switching command to actuate the load tap changer; to detect a current waveform via the sensor; to determine a start time in the current waveform at which the switching command to actuate the load tap changer was received; to add a time offset to the start time and from this determine a time at which the actuation would potentially begin; to determine a time of the 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 from this determine a new start time for the actuation;to begin at the new start time by activating the load step switch, using the drive.

[0019] The load tap changer device, consisting of a load tap changer with a vacuum switching tube, a drive, a sensor and a control device, makes it possible to take into account the time offset of the mechanics during a load switching operation and thus to open a vacuum switching tube at the current zero crossing.

[0020] Furthermore, the load tap changer device can have an additional sensor for measuring the arc burning time.

[0021] The invention will now be explained in detail with reference to exemplary embodiments and the drawings. These show... Figure 1 a step-down transformer with a load tap changer; Figure 2 a procedural sequence; Figure 3 a diagram to explain the procedure; Figure 4 Another diagram to illustrate the procedure.

[0022] Figure 1Figure 1 shows a load tap changer device 1 for performing a load changeover. The load tap changer device 1 comprises a control device 2, at least one sensor 5, and a load tap changer 4. The control device 2 is connected to an actuator of the load tap changer 4. The control device 2 is configured and designed to control the actuator 3 so that it actuates the load tap changer 4. Furthermore, the control device 2 is connected to a sensor 5 or sensors 5 that measure a current flowing through a vacuum switching tube 6, and thus through the load tap changer 4 and a step-down transformer 7. The control device 2 is configured and designed to measure and evaluate the current detected by the sensor 5 or sensors 5. In particular, the control device 2 determines the current waveform, i.e., when the current reaches zero or assumes a zero value and at what frequency this occurs.The sensor 5 can, for example, be arranged on the step-down transformer 7, in particular on the high-voltage side 8 or the low-voltage side 9. Furthermore, a sensor 5 can be arranged in the load tap changer 4, directly on the vacuum interrupter 6, or at any other position suitable for detecting the current flow.

[0023] The control device 2 is further designed and configured to predict or calculate future current zero crossing times. The control unit 2 therefore includes a processing unit and / or a processor and / or a memory.

[0024] The drive 3 is mechanically connected to the load tap changer 4 and thus also to the vacuum switching tube 6 via a drive train 10. The drive train 10 refers to the sum of the mechanical elements or components between the motor drive 3 and the vacuum switching tube 6, such as shafts, toggle levers, rollers, etc.

[0025] The control device 2 can be arranged as a standalone unit on the step-down transformer 7 or in a control room. Furthermore, the control device 2 can be part of a drive control system for the load tap changer 4 or as part of a voltage regulator. The control device 2 is designed and configured to control the drive 3.

[0026] Furthermore, an additional sensor 15 is provided, which is connected to the control device 2. This additional sensor 15 is configured to detect the arc duration in the vacuum interrupter 6. The control device 2 then evaluates the detected arc duration. Ideally, the vacuum interrupter 6 opens at the current zero crossing, so that no arc is generated inside the vacuum interrupter 6 and the arc duration is zero. If the vacuum interrupter 6 is actuated while current is still flowing through it, an arc is generated until it breaks and extinguishes. This arc duration therefore also depends on the time offset TV. Thus, the arc duration from previous circuits is also used to adjust the time offset TV. The evaluation and adjustment take place in the control device 2.

[0027] The step-down transformer 7 has a main winding 11 and a variable winding 12. The load tap changer 4 is connected to the variable winding 12 via the winding taps 13. The main winding 11 and the variable winding 12 are located on the high-voltage side 8 (in rare cases also on the low-voltage side). Furthermore, the step-down transformer 10 has a low-voltage winding 14, which is inductively coupled to the main winding 11 and the variable winding 12.

[0028] Figure 2 Figure 30 shows a flowchart of a procedure for performing a load switching operation using a load tap changer 4. In a first step 30, the control device 2 receives a signal or a switching command to perform a load switching operation using a load tap changer, or a switching command to begin actuating the load tap changer 4. The signal or switching command is generated, for example, manually or by a voltage regulator.

[0029] In the next step 31, a current waveform is recorded using a sensor 4. In particular, it is determined when the current flowing through the vacuum switching tube 5 of the load tap changer 4 reaches zero and at what frequency F this occurs. The past zero-crossing times and their intervals are determined. This is done continuously during the operation of the tap changer, especially before the switching command and before the load tap changer begins to operate. Ideally, the current has a sinusoidal waveform, resulting in regular zero-crossings. Based on past zero-crossing times, future zero-crossing times are then predicted. This can be done in various ways, for example, by calculation using mathematical methods such as the Fast Furier transform.These calculations are performed in control unit 2, which is designed and configured for this purpose. Control unit 2 therefore includes a processing unit and / or a processor and / or memory.

[0030] The determination of the current and future current zero-crossing times is carried out via a signal from the sensor, which, depending on its design, only samples or outputs current zero crossings or the entire sinusoidal waveform.

[0031] In the next step 32, the current start time T0 is determined. This start time T0 corresponds to the time at which the signal to actuate the load tap changer 4 was generated in the control device 2 or received by the control device 2. This is shown in the current flow diagram. Since the drive train 10 has a time offset TV due to its mechanics, this offset must be taken into account when actuating the load tap changer 4 or opening the vacuum switching tube 6. The mechanically induced offset TV is determined 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 certain distance before a force or motion can be transmitted to the vacuum switching tube 6. These mechanical conditions determine the actuation or...The opening of the vacuum switching tube 6 does not occur immediately after the activation signal, but rather with the corresponding time offset TV. The goal of each activation of the load tap changer 4, however, is to open the vacuum switching tube 6 at or near the current zero crossing, i.e., shortly before the current zero crossing. Since the control device 2 contains information about the future current zero crossing times, the start time T0, and the offset TV, a corresponding start time T1 for the beginning of the circuit is calculated. In other words, activation only begins when a current zero crossing occurs in the vacuum switching tube 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 T0, thereby determining the time TB at which the vacuum switching tube 6 would actually open.

[0032] In the next step 34, the time TG is determined at which the next zero current crossing – a future zero current crossing – would occur after the time TB of the potential start of the activation. 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 in the next step 36 to shift the start time T0 to a new start time T1.

[0033] In the final step 37, the circuit is started or executed at the newly determined start time T1. Here, the drive 3 is controlled by the control unit 2.

[0034] The time offset TV has a value of a few milliseconds, adapted to the drive train 10. This value can either be fixed or adjusted. The adjustment can be automatic or manual. An adjustment may be useful, for example, if wear occurs in the drive train or if parts are replaced. Furthermore, the arc duration can also be used to adjust the time offset.

[0035] Figure 3This serves to illustrate the method according to the invention. The X-axis shows the current profile over time (in ms) within a closed vacuum switching tube 6 or the load tap changer 4. The Y-axis shows the current magnitude in A. The current profile is sinusoidal or approximately sinusoidal. The current profile intersects the X-axis at the zero crossings (current zero crossings). Thus, no current flows through the vacuum switching tube 6 or the load tap changer 4 at these times. At an arbitrary time T0, a switching command to actuate or begin actuation of the load tap changer 4 is received by the control unit 2. This time is assumed to be the possible start time T0 of a load switching operation. Starting from this start time T0, the time offset TV is added to this start time T0. This time offset TV has a fixed value.After adding the time offset TV to the start time T0, a time TB is obtained at which the actuation or opening of the vacuum switching tube 6 would potentially begin. However, since a current is still flowing at this point, i.e., the current is not zero, arcs would occur when the vacuum switching tube 6 is actuated, especially when it is opened. This is precisely what is to be avoided.

[0036] As shown in the diagram, time TB, at which actuation would potentially begin, is not at a current zero crossing. Therefore, a suitable time TG, at which no current would flow through the vacuum switching tube 6 when opening, is determined. This time TG is the next current zero crossing after time TB. The next nearest current zero crossing is determined based on past current zero crossings.

[0037] Based on the potential start time TB of the opening or actuation and the suitable time TG, the time interval TD between these two points is calculated, for example, as the difference. This time interval TD is then added to the start time T0, forming the new start time T1 at which the actual actuation or opening begins. This ensures that the opening or actuation of the vacuum switching tube 6 begins at the zero crossing of the current.

[0038] 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 switching tube does not begin immediately at the zero current crossing, but a few milliseconds earlier (TF), i.e., shortly before. Reference sign

[0039] 1 Load tap changer device 2 Control device 3 Drive 4 Load tap changer 5 Sensor 6 Vacuum switching tube 7 Step-down transformer 8 High-voltage side 9 Low-voltage side 10 Drive train 11 Main winding 12 Regulating winding 13 Winding taps 14 Low-voltage winding 15 Additional sensor T0 Start time T1 New start time TV Time offset TD1 Further offset TB Time at which actuation would potentially begin TG Time of the next current zero crossing TD Time difference TF Previous time F Frequency

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 flow is detected via the sensor (5); - a start time (T0) is determined in the current profile at which the switching command for actuating the on-load tap-changer (4) was received; characterized in that - a time offset (TV) is added to the start time (T0) and a time (TB) at which actuation would potentially begin is determined therefrom; - a time point (TG) of a next current zero crossing after the time point (TB) at which actuation would potentially begin is determined; - a time difference (TD) is determined between the time (TB) at which actuation would potentially begin and the time (TG) of the next current zero crossing; - the time difference (TD) is added to the start time (T0) in order to determine a new start time (T1) for the actuation; - at the new start time (T1), the on-load tap-changer (4) is actuated by the drive (3).

2. Method for actuating an on-load tap-changer (4) according to claim 1, wherein - the current profile is detected before the switching command for actuating the on-load tap-changer (4); - the frequency and the past current zero crossings are determined when the current curve is detected.

3. Method for actuating 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 which is based on the past current zero crossings of the current curve.

4. The method of 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.

5. Method for actuating an on-load tap-changer (4) according to one of claims 1 to 4, wherein the current course 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 tap-changer transformer (7) is detected by one or more sensors (5).

6. Method for actuating an on-load tap-changer (4) according to any one of claims 1 to 5, wherein the time offset (TV) is a value which is caused by or dependent on the mechanics of the drive train (10).

7. The method for actuating 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.

8. Method for actuating an on-load tap-changer (4) according to any one of claims 1 to 6, wherein the value of the temporal offset (TV) can be adapted on the basis of an arc burning time in the vacuum interrupter (6) of the on-load tap-changer (4).

9. Method for actuating an on-load tap-changer (4) according to any one of claims 1 to 8, wherein after the determination of the time offset (TV), a further time offset (TD1) is subtracted and the new start time (T1) is thereby shifted and the actuation of the on-load tap-changer (4) is started before the zero crossing at an earlier time (TF) which is not the time (TG) of a next current zero crossing.

10. A method for actuating an on-load tap-changer (4) according to any one of claims 1 to 9, wherein the control device (2) controls a drive (3) which actuates the on-load tap-changer (4).

11. 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 set up to - to receive a switching command for actuating the on-load tap-changer (4); - to detect a current flow via the sensor (5); - to determine a start time (T0) in the current curve at which the switching command for actuating the on-load tap-changer (4) is received; characterized by - adding a time offset (TV) to the start time (T0) and using this to determine a time (TB) at which actuation would potentially begin; - determining a time point (TG) of a next current zero crossing after the time point (TB) at which the actuation would potentially start; - determine a time difference (TD) between the time (TB) at which actuation would potentially begin and the time (TG) of the next current zero crossing; - add the time difference (TD) to the start time (T0) and use it to determine a new start time (T1) for the actuation; - start actuating the on-load tap-changer (4) by means of the drive (3) at the new start time (T1).

12. On-load tap-changer device (1) according to claim 11, comprising a further sensor (15) for measuring the arc burning time.