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 changeover switches, 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 given time. The occurrence of inrush currents is disregarded in this approach.

[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 ensures a safe switching operation.

[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 by means of a drive, a sensor and a control device, comprising the following steps: Receiving a switching command to actuate the load tap changer by the control device; detecting a current waveform via the sensor; determining several consecutive times for zero current crossings by the control device; determining several intervals between the times of zero current crossings by the control device; deriving a characteristic value from the several intervals by the control device; comparing the characteristic value with a limit value by the control device; aborting or pausing the actuation by the control device if the characteristic value exceeds the limit value; performing the actuation if the characteristic value is within or below the limit value by controlling the drive by the control device.

[0009] The method is based on the idea of ​​monitoring the current profile within the tap changer, load tap changer, or vacuum tube before or after a switching command and detecting any inrush current before the actual actuation of the load tap changer. Based on the determined current zero crossings in the past or after the switching command, the intervals between these zero crossings are then calculated. A characteristic value derived from these intervals is compared with a limit value. If the limit value is met, an inrush current can be ruled out, allowing the actuation to be carried out safely and reliably. However, should an inrush current occur before or after the switching command, the actuation is aborted or paused. For the purposes of this invention, an inrush current is defined as the occurrence of irregularities in the current profile.

[0010] After the control device receives the switching command to actuate the tap changer, the tap changer is not actuated immediately. Instead, the past current waveform or the current waveform after the switching command is first checked for irregularities. Actuation only occurs if no irregularities are detected.

[0011] The current waveform can be recorded in any way. In particular, the current waveform is recorded via one or more sensors on the step-down transformer or load tap changer and transmitted to the control device.

[0012] The recorded current waveform is processed and evaluated in the control device, and several consecutive points in time within the current waveform are determined. These points in time are zero current crossings. Preferably, at least three consecutive points in time at which the current is zero are determined. Furthermore, the starting point in the current waveform is determined. Depending on the configuration, either the past current waveform is determined from the starting point, or the future current waveform is determined from the starting point. The past current waveform before the starting point is either already stored in the control device or is stored after the starting point.

[0013] Furthermore, several intervals between the multiple successive zero-crossing points in time are determined by means of a control device. For three points in time, two intervals are determined. In particular, the interval between the first and second points in time and the interval between the second and third points in time are determined.

[0014] Furthermore, a control device determines a characteristic value from the several distances. This characteristic value can be a ratio, average value, etc. The control device then compares this characteristic value to a limit value. The limit value is stored in the control device and can be adjusted manually or automatically.

[0015] Furthermore, the control device activates the actuator to operate the load tap changer when the characteristic value is within or below the limit value. The actual actuation is paused or aborted if the characteristic value exceeds the limit value. This pause or suspension of actuation can last for several seconds, for example, 1 to 10 seconds. After the pause, the current profile is measured again, and the process is repeated until actuation is possible.

[0016] 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 and designed to receive a switching command to actuate the load tap changer; to detect a current waveform via the sensor; to determine several successive times for zero current crossings of the current waveform; to determine several intervals between the times of the zero current crossings; to derive a characteristic value from the several intervals; to compare the characteristic value with a limit value; to abort or pause the actuation by the control device if the characteristic value exceeds the limit value; to actuate the load tap changer by means of the actuator if the characteristic value is within or below the limit value.

[0017] The load tap changer device comprises a load tap changer with a load selector and a selector. The load selector has at least one vacuum switching tube. Furthermore, the load tap changer device includes an actuator, a sensor, and a control unit. The load tap changer device enables the current waveform to be checked before the load tap changer is actuated, thus ensuring safe operation in the event of an inrush current. The control unit is designed and configured to continuously monitor, store, and process the current waveform via one or more sensors during the operation of the tap changer, i.e., before a switching command. For this purpose, it includes a processing unit and / or a processor and / or memory.The control device is designed and configured to detect, store, and process a current waveform via one or more sensors following a switching command. For this purpose, it includes a processing unit and / or a processor and / or memory.

[0018] Furthermore, the control device is designed and configured to control the drive, which in turn operates the load tap changer.

[0019] 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 a further diagram of another embodiment to illustrate the method.

[0020] Figure 1Figure 1 shows a load tap changer device 1. 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 3 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 the step-down transformer 7, a vacuum interrupter 6, or the load tap changer 4. The control device 2 is configured and designed to detect, 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 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.

[0021] The control device 2 continuously monitors the current flow either before an actuation or only after a switching command has been received by the control device 2. For this purpose, the control unit 2 includes a processing unit and / or a processor and / or memory.

[0022] 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 is designed and configured to actuate the load tap changer and / or to execute the switching command from the control unit.

[0023] 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.

[0024] 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 7 has a low-voltage winding 14, which is inductively coupled to the main winding 11 and the variable winding 12.

[0025] Figure 2Figure 1 shows a flowchart of a method for actuating a load tap changer. In the context of the invention, "before actuating a load tap changer" means that the detection of irregular current waveforms can occur either before or after a switching command. Before a switching command, the method is executed continuously during operation. Should an irregularity be detected, the actuating process is aborted immediately after the switching command, or a predetermined pause is initiated, and the process is repeated until actuating can be performed.

[0026] In a first step 30, the control device 2 receives a switching command at a start time T0 to actuate the load tap changer 4. The switching command can either be a manual switching command or come from a voltage regulator.

[0027] In the next step 31, a current waveform is recorded via a sensor 5 and transmitted to the control device. The current waveform can be recorded both before and after the switching command.

[0028] In a subsequent step 32, several consecutive time points T1, T2, T3, Tx with zero current crossings of the current waveform 20 are determined by the control device. Here, either the newly acquired current waveform or the current waveform before the switching command is used.

[0029] In a next step 33, the distances A1, A2, Ax are determined based on the times T1, T2, T3, Tx of the current zero crossings.

[0030] In the next step 34, a characteristic value K is formed based on the distances A1, A2, Ax.

[0031] In the next step 35, the determined characteristic value K is compared with a limit value G. If the limit value G is met or undercut by the characteristic value K, the actual actuation of the load tap changer 4 takes place in the next step 36. For this purpose, the control device 2 controls the drive 3 accordingly.

[0032] If the characteristic value K exceeds the limit value G, the operation is aborted in the next step 37. Alternatively, if the limit value G is exceeded in the next step 38, the operation can be paused for a certain period of time and the process restarted.

[0033] Figure 3This serves to illustrate the method according to the invention. The X-axis shows the current profile t (in ms) over time within a step-down transformer. The Y-axis shows the current I in amperes. The current profile is sinusoidal or approximately sinusoidal. The current profile curve 20 intersects the X-axis at the zero-current crossings. Thus, at these times T1, T2, T3, Tx, no current flows through the step-down transformer or the vacuum switching tube 6 or the load tap changer 4. At a start time T0, a switching command to actuate or begin actuation of the load tap changer 4 is received by the control unit 2.

[0034] This point in time is assumed to be the possible start time T0 of a load switching operation. Based on this start time T0, at least three subsequent times T1, T2, and T3 of the next zero current crossings are determined.

[0035] In the next step, the intervals A1 and A2 between the determined time points T1, T2, and T3 are calculated. Specifically, the first interval A1 is calculated between the first and second time points T1 and T2, and the second interval A2 is calculated between the second and third time points T2 and T3. The intervals A1 and A2 indicate how much time has elapsed between the time points.

[0036] In the next step, a characteristic value K is determined based on sections A1, A2, and Ax. For example, sections A1 and A2, or all determined sections, can be set in a ratio to each other. Ideally, A1 and A2 are equal, resulting in a ratio of one. After determining the characteristic value K, it is compared to a limit value G. If the characteristic value K exceeds the limit value G, the operation is aborted or paused. Pausing means that the switching process is suspended for a defined period and then restarted. If the limit value is met or not reached, the load tap changer is actuated by the drive, which is controlled by the control device.

[0037] In the example shown here, the current waveform is measured based on three time points T1, T2, and T3, i.e., three zero-crossings of the current. However, it is also possible to use any number of zero-crossings T1-Tx and intervals A1-Ax for evaluation. This depends on how long one can wait after a switching command before actually activating the device. The method used to determine a characteristic value K and the definition of the limit value G can also be adapted as needed.

[0038] Figure 4This diagram serves to illustrate the inventive method according to a further embodiment. The X-axis shows the current profile t (in ms) over time within a step-down transformer. The Y-axis shows the current I in amperes. The current profile is sinusoidal or approximately sinusoidal. The current curve intersects the X-axis at the zero crossings. Thus, at these times T1, T2, T3, Tx, no current flows through the step-down transformer or the vacuum switching tube 6 or the load tap changer 4. At a start time T0, a switching command to actuate or begin actuation of the load tap changer 4 is received by the control unit 2.

[0039] This point in time is assumed to be the start time T0 of a load switching operation. Starting from this start time T0, at least three points in time T1, T2, and T3 of the previous zero-crossing of the current are determined, i.e., before the start time T0. This is possible because the current waveform was monitored and recorded before the switching command.

[0040] In the next step, the intervals A1 and A2 between the determined time points T1, T2, and T3 are calculated. Specifically, the first interval A1 is calculated between the first and second time points T1 and T2, and the second interval A2 is calculated between the second and third time points T2 and T3. The intervals A1 and A2 indicate how much time has elapsed between the time points.

[0041] In the next step, a characteristic value K is determined based on sections A1, A2, and Ax. For example, sections A1 and A2, or all determined sections, can be set in a ratio to each other. Ideally, A1 and A2 are equal, resulting in a ratio of one. After determining the characteristic value K, it is compared to a limit value G. If the characteristic value K exceeds the limit value G, the operation is aborted or paused. Pausing means that the switching process is suspended for a defined period and then restarted. If the limit value is met or not reached, the load tap changer is actuated by the drive, which is controlled by the control device.

[0042] In the example shown here, the current waveform is calculated based on three time points T1, T2, and T3, i.e., three zero-crossings of the current. However, it is also possible to use any number of zero-crossings T1-Tx and intervals A1-Ax for the evaluation. This depends on how long one can wait after a switching command before actually actuating the device. The method used to determine a characteristic value K and the definition of the limit value G can also be adapted as needed.

[0043] This method therefore makes it possible to check the current flow for irregularities both before and immediately after a switching command. Reference sign

[0044] 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 20 Current waveform T0 Start time T1 First zero crossing T2 Second zero crossing T3 Third zero crossing Tx Further zero crossing A1 First gap A2 Second gap Ax Further gap

Claims

1. Method for actuating an on-load tap-changer (4) by means of a drive (3), a sensor (5) and a control device (2), comprising the following steps: - receiving a switching command for actuating the on-load tap-changer (4) by the control device (2); - detecting a current flow (20) via the sensor (5); characterized by - determining a plurality of successive points in time (T1, T2, T3, Tx) for current zero crossings of the current profile (20) by the control device (2); - determining a plurality of intervals (A1, A2, Ax) between the times (T1, T2, T3, Tx) of the current zero crossings by the control device (2); - take-off lead of a characteristic variable (K) from the plurality of distances (A1, A2, Ax) by the control device (2); - comparing the characteristic variable (K) with a limit value (G) by the control device (2); - canceling or pausing the actuation by the control device (2) if the characteristic value (K) exceeds the limit value (G); - Bushing actuation when the characteristic value (K) meets or falls below the limit value (G) by controlling the drive (3) by the control device (2).

2. Method according to claim 1, wherein the current characteristic (20) is detected before or after the control device (2) receives the switching command to actuate the on-load tap-changer (4).

3. Method according to claim 1 or 2, wherein the plurality of successive times (T1, T2, T3, Tx) for current zero crossings of the current waveform (20) are determined before the start time (T0) of the input of the switching command or after the start time (T0) of the input of the switching command.

4. Method according to claim 1 to 3, wherein the parameter (K) is formed from the ratio of at least two distances.

5. Method according to claim 1 to 4, wherein the parameter (K) can deviate from the limit value (G) by a few percent.

6. Method according to claim 1 to 5, wherein the pausing of the actuation by the control device (2) lasts a few seconds.

7. Method according to claim 1 to 6, wherein at least three consecutive times (T1, T2, T3, Tx) for current zero crossings of the current waveform (20) are determined before the start time (T0) of the input of the switching command or after the start time (T0) of the input of the switching command.

8. The method according to claim 1 to 5, wherein at least two distances (A1, A2, Ax) between the times (T1, T2, T3, Tx) of the current zero crossings are determined by the control device (2).

9. 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); characterized in that the control device is furthermore set up to - to determine a plurality of successive points in time (T1, T2, T3, Tx) for current zero crossings of the current curve (20); - to determine a plurality of distances (A1, A2, Ax) between the points in time (T1, T2, T3, Tx) of the current zero crossings; - to derive a characteristic variable (K) from the several distances (A1, A2, Ax); - compare the parameter (K) with a limit value (G); - cancel or pause the actuation by the control device (2) if the parameter (K) exceeds the limit value (G); - bushing the actuation of the on-load tap-changer by means of the drive (3) if the characteristic value (K) is within or below the limit value (G).