Method for actuating an on-load tap-changer, and on-load tap-changer device

Abstract

The invention relates to a method for actuating an on-load tap-changer (4) by means of a drive (3), a sensor (5), and a controller (2), said method having the following steps: - receiving a switch command to actuate the on-load tap-changer (4) by means of the controller (2); - detecting a current curve (20) via the sensor (5); - determining a plurality of consecutive points in time (T1, T2, T3, Tx) for zero-current crossings of the current curve (20) by means of the controller (2); - determining a plurality of intervals (A1, A2, Ax) between the points in time (T1, T2, T3, Tx) of the zero-current crossings by means of the controller (2); - deriving a characteristic (K) from the plurality of intervals (A1, A2, Ax) by means of the controller (2); - comparing the characteristic (K) with a threshold (G) by means of the controller (2); - terminating or pausing the actuation by means of the controller (2) if the characteristic (K) exceeds the threshold (G); and - carrying out the actuation if the characteristic (K) meets or falls below the threshold (G) by controlling the drive (3) by means of the controller (2).

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. Inrush is ignored.

[0006] It is therefore an object of the present invention to provide a method for operating an on-load tap-changer which ensures safe switching.

[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 by means of a drive, a sensor and a control device, comprising the following steps: receiving a switching command for actuating the on-load tap-changer by the control device;

[0009] Recording a current curve via the sensor;

[0010] Determining several consecutive times for current zero crossings of the current waveform through the control device;

[0011] Determining a plurality of intervals between the times of the current zero crossings by the control device;

[0012] Deriving a characteristic from the plurality of distances by the control device; comparing the characteristic with a limit value by the control device;

[0013] Cancel or pause the operation by the control device if the parameter exceeds the limit value;

[0014] Carrying out the operation when the parameter meets or falls below the limit value by controlling the drive via the control device.

[0015] The method is based on the idea of ​​monitoring the current flow within the tap transformer, on-load tap-changer, or vacuum interrupter before or after a switching command and detecting any inrush before the on-load tap-changer is actually actuated. Based on the current zero crossings detected in the past or after the switching command, the intervals between the current zero crossings are then determined. A characteristic value derived from these intervals is compared with a limit value. If the limit value is maintained, inrush can be ruled out, allowing actuation to be carried out safely and reliably. However, should an inrush occur before or after the switching command, actuation is aborted or paused. In the context of the invention, inrush is defined as the occurrence of irregularities in the current flow.

[0016] After the control device receives the switching command to operate the on-load tap-changer, the on-load tap-changer is not operated immediately. Instead, the previous current waveform or the current waveform after the switching command is checked for irregularities. Actual operation only occurs when no irregularities are detected.

[0017] The current profile can be recorded in any way. In particular, the current profile is recorded via one or more sensors on the tap-changer or on-load tap-changer and transmitted to the control device.

[0018] The recorded current waveform is processed and evaluated in the control device, and several consecutive points in time in the current waveform are determined. These points in time are current zero crossings. Preferably, at least three consecutive points in time at which the current is zero are determined. Furthermore, the start point in the current waveform is determined. Depending on the characteristic, the past current waveform is determined from the start point in time or the future current waveform is determined from the start point in time. In this case, the past current waveform before the start point in time is either already stored in the control device or is stored after the start point in time. Furthermore, several intervals between the several consecutive points in time of the current zero crossings are determined using the control device. If three points in time are determined, two intervals are determined.In particular, the distance between the first and second time points and the distance between the second and third time points are determined.

[0019] Furthermore, a control device determines a characteristic value from the multiple distances. The characteristic value can be a ratio, mean value, etc. The control device compares the characteristic value with a limit value. The limit value is stored in the control device. The limit value can be adjusted manually or automatically.

[0020] Furthermore, the control device activates the on-load tap-changer by activating the drive when the characteristic value meets or falls below the limit. The actual actuation is paused or aborted when the characteristic value exceeds the limit. The pause or suspension of actuation can last for several seconds, for example, 1 to 10 seconds. After the pause, the current waveform is recorded again, and the process is repeated until actuation is possible.

[0021] 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 set up and designed to receive a switching command for actuating the on-load tap-changer; to detect a current curve via the sensor; to determine a plurality of successive times for current zero crossings of the current curve; to determine a plurality of intervals between the times of the current zero crossings; to derive a characteristic from the plurality of intervals; to compare the characteristic with a limit value; to abort or pause the actuation by the control device if the characteristic exceeds the limit value; to carry out the actuation of the on-load tap-changer by means of the drive if the characteristic is equal to or below the limit value.

[0022] The on-load tap-changer device comprises an on-load tap-changer with a load diverter switch and a selector. The load diverter switch has at least one vacuum interrupter. The on-load tap-changer device further comprises a drive, a sensor, and a control device. The on-load tap-changer device makes it possible to check the current profile before actuating the on-load tap-changer, thus ensuring safe actuation in the event of an inrush. The control device is designed and configured to continuously detect, store, and process a current profile via one or more sensors during operation of the tap-changer, i.e., before a switching command. For this purpose, it comprises a corresponding computing unit and / or a processor and / or a memory.The control device is designed and configured to detect, store, and process a current profile via one or more sensors following a switching command. For this purpose, it comprises a computing unit and / or a processor and / or a memory.

[0023] Furthermore, the control device is designed and configured to control the drive, which in turn actuates the on-load tap changer.

[0024] In the following, the invention is explained in detail using exemplary embodiments with reference to the drawings.

[0025] Figure 1 shows a tap transformer with an on-load tap changer;

[0026] Figure 2 shows a process flow;

[0027] Figure 3 is a diagram explaining the process;

[0028] Figure 4 is a further diagram of a further embodiment to explain the method.

[0029] Figure 1 shows an on-load tap-changer device 1. 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 3 of the on-load tap-changer 4. The control device 2 is set up 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 several sensors 5 which measure a current flowing through the tapped transformer 7, a vacuum interrupter 6 or the on-load tap-changer 4. The control device 2 is set up and configured to detect, 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 happens.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 flow.

[0030] The control device 2 continuously records the current flow before an actuation or only when a switching command is received by the control device 2. For this purpose, the control unit 2 has a computing unit and / or a processor and / or a memory.

[0031] 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 is designed and configured to operate the on-load tap-changer or to execute the switching command of the control unit.

[0032] 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.

[0033] 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 7 has a low-voltage winding 14, which is inductively coupled to the main winding 11 and the control winding 12.

[0034] Figure 2 shows a flowchart of a method for operating an on-load tap-changer. Within the context of the invention, "before operating an on-load tap-changer" means that the detection of irregular current profiles can occur before or after a switching command. Before a switching command, the method is executed continuously during operation. If an irregularity is detected at this point, the operation is aborted immediately after the switching command, or a predefined pause is initiated, and the method is repeated until an operation can be performed.

[0035] In a first step 30, the control device 2 receives a switching command at a starting time TO for actuating the on-load tap-changer 4. The switching command can either be a manual switching command or can come from a voltage regulator.

[0036] In the next step 31, a current waveform is detected via a sensor 5 and transmitted to the control device. The current waveform can be detected either after or before the switching command.

[0037] In a next step 32, several consecutive times T1, T2, T3, Tx with current zero crossings of the current waveform 20 are determined by the control device. Here, either the newly detected current waveform or the current waveform before the switching command is used.

[0038] 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.

[0039] In a next step 34, a characteristic value K is formed based on the distances A1, A2, Ax.

[0040] In a next step 35, the determined characteristic value K is compared with a limit value G. If the limit value G is met or undershot by the characteristic value K, the actual actuation of the on-load tap-changer 4 takes place in the next step 36. For this purpose, the control device 2 controls the drive 3 accordingly.

[0041] 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, the operation can be paused for a certain time in the next step 38 and the process can be restarted.

[0042] Figure 3 illustrates the method according to the invention. The temporal current profile t (in ms) within a tapped transformer is plotted on the x-axis. The y-axis indicates the magnitude of the current I in amperes. The current profile, or the current waveform, is sinusoidal or approximately sinusoidal here. The curve of the current waveform 20 intersects the x-axis at the current zero crossings. Thus, at these times T1, T2, T3, Tx, no current flows through the tapped transformer, the vacuum interrupter 6, or the on-load tap-changer 4. At a starting time T0, a switching command for actuating, or for beginning the actuation of, the on-load tap-changer 4 is received in the control unit 2.

[0043] This time is assumed to be the possible starting time TO of a load transfer. Based on this starting time TO, at least three subsequent times T1, T2, and T3 of the next current zero crossings are determined.

[0044] In the next step, the distances A1 and A2 between the determined times T1, T2, and T3 are determined. Specifically, the first distance A1 is determined between the first and second times T1, T2, and the second distance A2 is determined between the second and third times T2 and T3. The distances A1 and A2 indicate how much time has passed between the times.

[0045] In the next step, a parameter K is determined based on the sections A1, A2, Ax. For example, the sections A1 and A2 or all of the determined sections can be put into a ratio to one another. Ideally, for example, A1 and A2 are the same size and the ratio is therefore one. After the parameter K has been determined, it is compared with a limit value G. If the parameter K exceeds the limit value G, the operation is aborted or paused. Pausing means that the switching is suspended for a defined time and then the process is carried out again. If the limit value is met or undershot, the on-load tap-changer is operated by means of the drive, which is controlled by the control device.

[0046] In the example shown here, the current curve is calculated based on three times T1, T2, and T3, i.e., three current zero crossings. However, it is also possible to use any number of current zero crossings T1 - Tx as well as intervals A1 - Ax for an evaluation. This depends on how long one can wait after a switching command before actually activating the switch. The way in which a characteristic value K is determined and the limit value G are defined can also be customized as required.

[0047] Figure 4 serves to illustrate the method according to the invention in a further embodiment. The temporal current profile t (in ms) within a tapped transformer is plotted on the X-axis. The Y-axis indicates the level of the current I in amperes. The current profile or the current waveform is sinusoidal or approximately sinusoidal here. The current waveform curve intersects the X-axis at the current zero crossings. Thus, at these times T1, T2, T3, Tx, no current flows through the tapped transformer, the vacuum interrupter 6, or the on-load tap-changer 4. At a starting time T0, a switching command for actuating or beginning the actuation of the on-load tap-changer 4 is received in the control unit 2.

[0048] This point in time is assumed to be the starting point TO of a load transfer. Starting from this starting point TO, at least three points in time T1, T2, and T3 of the past current zero crossings are determined, i.e., before the starting point TO. This is possible because the current curve was already monitored and recorded before the switching command.

[0049] In the next step, the distances A1 and A2 between the determined times T1, T2, and T3 are determined. Specifically, the first distance A1 is determined between the first and second times T1, T2, and the second distance A2 is determined between the second and third times T2 and T3. The distances A1 and A2 indicate how much time has passed between the times.

[0050] In the next step, a parameter K is determined based on the sections A1, A2, Ax. For example, the sections A1 and A2 or all of the determined sections can be put into a ratio to one another. Ideally, for example, A1 and A2 are the same size and the ratio is therefore one. After the parameter K has been determined, it is compared with a limit value G. If the parameter K exceeds the limit value G, the operation is aborted or paused. Pausing means that the switching is suspended for a defined time and then the process is carried out again. If the limit value is met or undershot, the on-load tap-changer is operated by means of the drive, which is controlled by the control device.

[0051] In the example shown here, the current curve is calculated based on three times T1, T2, and T3, i.e., three current zero crossings. However, it is also possible to use any number of current zero crossings T1 - Tx as well as intervals A1 - Ax for the evaluation. This depends on how long can be waited after a switching command before the actual actuation. The way in which a characteristic value K is determined and the limit value G are defined can also be customized as required.

[0052] The method therefore makes it possible to check the current flow for irregularities before a switching command is issued and also immediately afterward.

[0053] 1 on-load tap-changer device

[0054] 2 Control device

[0055] 3 Drive

[0056] 4 on-load tap-changers

[0057] 5 Sensor

[0058] 6 vacuum interrupters

[0059] 7-step transformer

[0060] 8 High voltage side

[0061] 9 Low voltage side

[0062] 10 Drivetrain

[0063] 11 Main winding

[0064] 12 control winding

[0065] 13 winding taps

[0066] 14 Low-voltage winding

[0067] 15 additional sensors

[0068] 20 Current flow

[0069] TO start time

[0070] T1 first zero crossing

[0071] T2 second zero crossing

[0072] T3 third zero crossing

[0073] Tx further zero crossing

[0074] A1 first distance

[0075] A2 second distance Ax further distance

Claims

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 profile (20) via the sensor (5); Determining several successive times (T1, T2, T3, Tx) for current zero crossings of the current curve (20) by the control device (2); Determining a plurality of distances (A1, A2, Ax) between the times (T1, T2, T3, Tx) of the current zero crossings by the control device (2); Deriving a characteristic value (K) from the plurality of distances (A1, A2, Ax) by the control device (2); Comparing the characteristic value (K) with a limit value (G) by the control device (2); Aborting or pausing the operation by the control device (2) if the parameter (K) exceeds the limit value (G); Carrying out the actuation when the parameter (K) complies with or falls below the limit value (G) by controlling the drive (3) via the control device (2).

2. Method according to claim 1, wherein the detection of the current profile (20) takes place before or after the reception of the switching command for actuating the on-load tap changer (4) by the control device (2).

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

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

5. Method according to claims 1 to 4, wherein the characteristic value (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. The method according to claim 1 to 6, wherein at least three consecutive times (T 1 , T2, T3, Tx) for current zero crossings of the current waveform (20) are determined before the start time (TO) of the input of the switching command or after the start time (TO) of the input of the switching command.

8. 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 configured to receive a switching command for actuating the on-load tap-changer (4); to detect a current profile via the sensor (5); to determine a plurality of consecutive times (T1, T2, T3, Tx) for current zero crossings of the current profile (20); to determine a plurality of intervals (A1, A2, Ax) between the times (T1, T2, T3, Tx) of the current zero crossings; to derive a characteristic (K) from the plurality of intervals (A1, A2, Ax); to compare the characteristic (K) with a limit value (G); to abort or pause the actuation by the control device (2) if the characteristic (K) exceeds the limit value (G); to operate the on-load tap-changer by means of the drive (3) when the parameter (K) is equal to or below the limit value (G).

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