Method for operating a load tap changer and load tap changer

Abstract

A method for operating a on-load tap changer 4 by means of a drive unit 3, a sensor 5 and a control device 2, comprising: - The control device 2 receives a switching command for operating the on-load tap changer 4; - The current trend is detected by the sensor 5; - The start time T0 when the switching command for operating the on-load tap changer 4 is received is determined during the current trend; - A time offset TV is added to the start time T0, and the time TB when the operation is virtually started is determined from the addition; - The time TG of the next zero crossing of the current after the time TB when the operation is virtually started is determined; - The time difference TD between the time TB when the operation is virtually started and the time TG of the next zero crossing of the current is determined; - The time difference TD is added to the start time T0 to determine a new start time T1 for the operation from the addition; - The method wherein the operation of the on-load tap changer 4 is started by the drive unit 3 at the new start time T1.

Description

Technical Field

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

Background Art

[0002] In a substation, there are a large number of switches with different roles and different requirements. In order to operate each switch, these switches must be operated by an operating system. These switches are, in particular, load tap changers, load transfer switches, selectors, double-pole switches, polarity switches, pre-selectors, circuit breakers, load transfer switches, or disconnectors.

[0003] Therefore, the load tap changer is used, for example, to switch without interruption between different windings taps of electrical equipment such as a power transformer. Thereby, for example, the transformation ratio of the transformer or the inductance of the choke coil can be changed.

[0004] Generally, the load tap changer is operated by a combination consisting of a motor drive and a spring energy storage device. The operation is executed immediately after the switching command, that is, at any time.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, an object of the present invention is to provide a method for operating a load tap changer that is more accurate, inspects the state of the load tap changer before switching, and protects the vacuum valve.

Means for Solving the Problems

[0006] This problem is solved by each object of the independent claims. Other embodiments are described in the dependent claims.

[0007] The present invention proposes a method for operating a load tap changer by a drive unit, a sensor, and a control device. In this case, - The control device receives a switching command for operating the load tap changer, - The current trend is detected by the sensor, - The start time point when the switching command for operating the load tap changer is received is specified during the current trend, - A time offset is added to the start time point, and as a result, the time point when the operation is virtually started is specified from the addition, - The time point of the next current zero crossing after the time point when the operation is virtually started is specified, - The time difference between the time point when the operation is virtually started and the time point of the next current zero crossing is specified, - The time difference is added to the start time point, and as a result, a new start time point for the operation is specified, - The operation of the load tap changer is started by the drive unit at the new start time point.

[0008] The present invention is based on the idea of monitoring the current transition in a on-load tap changer, more specifically in a vacuum valve, and starting the operation of the on-load tap changer or the opening of the vacuum valve during or immediately before the current just passes through zero. Thereby, the combustion period of the arc inside the vacuum valve at the time of opening is significantly shortened. Therefore, the vacuum valve, especially the contacts inside the vacuum valve, is maximally protected. Accurate opening or switching or operation is made possible especially when a future current zero crossing is predicted, whereby the opening or switching or operation of the on-load tap changer is adapted to the predicted future current zero crossing. Since the inertia of the drive train, i.e., the time offset between the switching command and the actual operation, is known, this inertia can be adjusted to the appropriate future current zero crossing. Therefore, the actual operation does not start immediately after the switching command, but starts with an appropriate time shift taking into account the time offset in the drive train. Therefore, the inertia (mechanism) of the drive train is taken into account during operation so that the operation of the vacuum valve is always carried out during or immediately before the current zero crossing. The opening of the vacuum valve, which is part of the on-load tap changer, can also be regarded as the operation of the on-load tap changer.

[0009] A control device is connected to a drive unit and at least one sensor. The control device controls the drive unit that operates the on-load tap changer in the same way. Further, the control device detects the current transition by at least one sensor. The sensor detects the current transition, and in this case, can be arranged at various positions, for example, on the low voltage side and / or high voltage side of the vacuum valve and / or the on-load tap changer and / or the tap transformer.

[0010] The progression of the current before the switching command for operating the on-load tap changer can be detected in various ways, in particular the frequency and the preceding current zero crossing can be identified and detected. The progression of the current is preferably evaluated by a control device. The time point of the next current zero crossing is a future current zero crossing and is based on the preceding current zero crossing of the progression of the current. One future current zero crossing or all future current zero crossings are identified by one or more mathematical methods, in particular by fast Fourier transform. Furthermore, one future current zero crossing or all future current zero crossings can be identified by analog electronics.

[0011] The progression of the current can be detected, for example, by sensors on the high-voltage side and / or low-voltage side of a vacuum valve and / or an on-load tap changer and / or a tap transformer.

[0012] The time offset is a value resulting from or depending on the mechanism of the drive train. The value of the time offset can be adapted automatically and / or manually. Furthermore, the value of the time offset can be adapted based on the arc burning period in the vacuum valve of the on-load tap changer. Furthermore, the value of the time offset can be adapted based on the arc burning period of the preceding switching of this on-load tap changer in the vacuum valve of the on-load tap changer.

[0013] To shift the new starting point, another time offset can be subtracted after the time offset has been determined. Thereby, the operation of the on-load tap changer is started at an earlier point in time, not before the zero crossing but at a point in time that is not the time point of the next current zero crossing.

[0014] For operating the on-load tap changer and implementing the method of the invention, the control device can be optionally configured and can in particular include means for controlling the drive unit.

[0015] Furthermore, the invention relates to - an on-load tap changer, - a sensor, - a drive unit, - a control device, and provides an on-load tap changing device comprising the same.

[0016] In this case, - the control device - receives a switching command for operating the on-load tap changer, - detects the transition of current by the sensor, - identifies the starting point when the switching command for operating the on-load tap changer is received during the transition of the current, - adds a time offset to the starting point, and as a result, identifies the point in time when the operation is virtually started, - identifies the point in time of the next zero-crossing of the current after the point in time when the operation is virtually started, - identifies the time difference between the point in time when the operation is virtually started and the point in time of the next zero-crossing of the current, - adds the time difference to the starting point, and as a result, identifies a new starting point for the operation, - is configured to start the operation of the on-load tap changer by the driving unit at the new starting point.

[0017] An on-load tap changing device comprising an on-load tap changer having a vacuum valve, a driving unit, a sensor, and a control device can take into account the time offset of the mechanism during load switching, and thus enables the vacuum valve to open during zero-crossing of the current.

[0018] Furthermore, it may have another sensor for measuring the arc combustion period.

[0019] Hereinafter, the present invention will be described in detail based on typical embodiments with reference to the drawings.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 shows a load tap changer 1 for switching a load. The load tap changer 1 includes one control device 2, at least one sensor 5, and one load tap changer 4. The control device 2 is connected to the drive unit of the load tap changer 4. The control device 2 is adapted and configured to control the drive unit 3 such that the drive unit 3 operates the load tap changer 4. Further, the control device 2 is connected to one sensor 5 or a plurality of sensors 5 that measure the current energizing the vacuum valve 6 and the load tap changer 4 of the tap transformer 7. The control device 2 is adapted and configured to measure and evaluate the current detected by this sensor 5 or these sensors 5. In particular, the trend of the current is confirmed by the control device 2. That is, it is confirmed when the current has or takes a zero value and at what frequency this occurs. The sensor 5 can be arranged, for example, in the tap transformer 7, and in particular can be arranged on the high voltage side 8 or the low voltage side 9. Further, the sensor 5 can be arranged within the load tap changer 4 or directly on the vacuum valve 6 or at any other position suitable for detecting the trend of the current.

[0022] Furthermore, the control device 2 is configured and adapted to predict or calculate the future current zero crossing time. Therefore, the control device 2 appropriately has a computing device and / or a processor and / or a memory.

[0023] The drive unit 3 is mechanically connected to the load tap changer 4 via a drive train 10 and is thus also mechanically connected to the vacuum valve 6. The assembly of mechanical elements or mechanical systems, such as, for example, a shaft, toggle lever, roller, etc., between the motor drive unit 3 and the vacuum valve 6 is understood as the drive train 10.

[0024] The control device 2 can be arranged as an independent device in the tap changer 7 or in the control room. Further, the control device 2 may be part of the drive control unit of the on-load tap changer 4 or may be configured as part of the voltage control unit. The control device 2 is configured and adapted to control the drive unit 3.

[0025] Furthermore, another sensor 15 connected to the control device 2 is provided. The other sensor 15 is adapted and configured to detect the arc burning period in the vacuum valve 6. At this time, the control device 2 evaluates the detected arc burning period. Ideally, the vacuum valve 6 is opened during the current zero crossing time so that no arc occurs inside the vacuum valve 6 and the arc burning period is equal to zero. When the vacuum valve 6 is operated while the current is still flowing through the vacuum valve 6, an arc will occur until the arc extinguishes. That is, this arc burning period also depends on the time offset TV. Therefore, the arc burning period from the previous switching is also used to adapt the time offset TV. The evaluation and adaptation are performed by the control device 2.

[0026] The tap changer 7 has a main winding 11 and a control winding 12. In this case, the on-load tap changer 4 is connected to the control winding 12 via a winding tap 13. The main winding 11 and the control winding 12 are arranged on the high voltage side 8 (rarely also on the low voltage side). Furthermore, the tap changer 10 has a low voltage winding 14 that is electromagnetically coupled to the main winding 11 and the control winding 12.

[0027] Figure 2 shows a flowchart of a method for switching a load by the on-load tap changer 4. In the first step 30, the control device 2 receives a signal or a switching command for switching the load by the 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 the voltage control unit.

[0028] In the next step 31, the transition of the current is detected by the sensor 4. In particular, it is confirmed at what time value or point the current flowing through the vacuum valve 5 of the on-load tap changer 4 becomes zero, and at what frequency F this occurs. In this case, a plurality of previous current zero-crossing times and the intervals between these current zero-crossing times are calculated. This is continuously executed during the operation of the tap transformer, particularly already executed before a switching command, and executed before starting the operation of the on-load tap changer. Ideally, the current has a sinusoidal transition. As a result, current zero-crossings occur regularly. At this time, based on the previous time point or the previous current zero-crossing, a future current zero-crossing or time point is predicted during the transition of the current. This can be executed in various ways, for example, by calculation using a mathematical method such as a fast Fourier transform. The calculation is executed by the control device 2 configured and adapted for this purpose. Therefore, the control device 2 appropriately has a computing device and / or a processor and / or a memory. The actual current zero-crossing time and the future current zero-crossing time are specified (calculated) by a signal of the sensor that scans or outputs only the current zero-crossing or all the sinusoidal transitions according to the configuration of the sensor.

[0029] In the next step 32, the actual starting point T0 is determined. This starting point T0 corresponds to the time when the signal for operating the on-load tap changer 4 is generated or received by the control device 2. This starting point T0 is plotted (recorded) during the current transition. Since the drive train 10 has a time offset TV due to its mechanism, this time offset TV must be taken into account when operating the on-load tap changer 4 or opening the vacuum valve 6. The offset TV due to the mechanism depends on the structural mounting state of the drive train 10. For example, the rotational movement of a cam corresponds to the mounting state, or, for example, the rotational movement of a lever that must first move, for example, a certain section before force or power can be transmitted to the vacuum valve 6 corresponds to the mounting state. Due to this mechanical condition, the vacuum valve 6 is not operated or opened immediately after the signal for operation or the starting signal, but is operated or opened with the corresponding time offset TV. However, the purpose of each operation of the on-load tap changer 4 is to open the vacuum valve 6 during or almost during the zero current passage, that is, immediately before the zero current passage. Since information about the future zero current passage time or the zero current passage, the starting point T0, and the offset TV is known in the control device 2, the corresponding starting point T1 for starting the switching is calculated. In other words, the operation starts only when the zero current passage occurs at the vacuum valve 6 at the end of the time offset TV of the drive train 10. That is, in the next step 33, the time offset TV is added to the starting point T0, and thus the time point TB when the vacuum valve 6 is actually opened is determined.

[0030] In the next step 34, the time point TG when the next zero current passage - the future zero current passage - is executed after the virtual starting point TB of the operation is determined. In the next step 35, the time difference TD between these time points is determined based on the time points TB and TG. This difference TD is used in the next step 36 to shift the starting point T0 to the new starting point T1.

[0031] In step 37, the switching starts or is executed at the newly specified start time T1. Here, the drive unit 3 is controlled by the control device 2.

[0032] The time offset TV has a value of several milliseconds adapted to the drive train 10. This value can be preset constantly or may be adjusted. The adjustment can be executed automatically or manually. For example, the adjustment can be beneficial when wear occurs in the drive train or parts are replaced. Furthermore, the arc combustion period may be used to adjust the time offset.

[0033] Figure 3 is used to explain the method of the present invention. The time course (in units of ms) of the current inside the closed vacuum valve 6 or the on-load tap changer 4 is depicted on the X-axis. The Y-axis indicates the height of the current in units of A. Here, the course of the current or the current course is a sine wave or approximately a sine wave. The curve of the current course intersects the X-axis during zero crossing (current zero crossing). Therefore, the current does not energize the vacuum valve 6 or the on-load tap changer 4 at this point. A switching command for operating the on-load tap changer 4 or a switching command for starting the operation of the on-load tap changer 4 is received by the control device 2 at an arbitrary time T0. This point is assumed to be the start time T0 at which the load can be switched. Starting from this start time T0, the time offset TV is added to this start time T0. This time offset TV basically has a constant value. After adding the time offset TV to the start time T0, the time point at which the operation or opening of the vacuum valve 6 is virtually started is obtained. However, at this time point, since the current is still energized, that is, the current is not zero, an arc can occur during the operation of the vacuum valve 6, particularly during the opening of the vacuum valve 6.

[0034] As shown in the graph, the time point TB at which the operation is virtually started is not during current zero crossing. Therefore, an appropriate time point TG at which the current does not energize the vacuum valve 6 during opening is identified (calculated). This time point TG is the subsequent current zero crossing after the time point TB. The subsequent current zero crossing is calculated based on the preceding current zero crossing.

[0035] Based on the virtual start time point TB of the opening or operation and the appropriate time point TG, the period TD between these two time points is calculated as a difference. Then, this period TD is added to the start time point T0 to identify the new start time point T1 at which the actual operation or opening is initiated. Thus, it is achieved that the opening or operation of the vacuum valve 6 starts during the zero-crossing of the current.

[0036] According to another embodiment shown in FIG. 4, another offset TD1 is subtracted after the identification of the time offset TV. This offset TD1 ensures that the opening of the vacuum valve starts not immediately during the zero-crossing of the current, but at a time point (TF) that is earlier by about a few milliseconds, i.e., immediately before the zero-crossing of the current.

Explanation of Symbols

[0037] 1 On-load tap changer 2 Control device 3 Driving part 4 On-load tap changer 5 Sensor 6 Vacuum valve 7 Tap transformer 8 High voltage side 9 Low voltage side 10 Driving train 11 Main winding 12 Control winding 13 Winding tap 14 Low voltage winding 15 Another sensor T0 Start time point T1 New start time point TV Time offset TD1 Another offset TB Time point at which the operation is virtually started TG Next current zero-crossing time TD Time difference TF Earlier time point F Frequency

Claims

1. A method for operating a on-load tap changer (4) by means of a drive unit (3), a sensor (5) and a control device (2), comprising: - the control device (2) receives a switching command for operating the on-load tap changer (4); - the course of the current is detected by the sensor (5); - the start time (T0) at which the switching command for operating the on-load tap changer (4) is received is determined during the course of the current; - a time offset (TV) is added to the start time (T0), and as a result, the time (TB) at which the operation is virtually started is determined; - the next zero-crossing time (TG) of the current after the time (TB) at which the operation is virtually started is determined; - the time difference (TD) between the time (TB) at which the operation is virtually started and the next zero-crossing time (TG) of the current is determined; - the time difference (TD) is added to the start time (T0), and as a result, a new start time (T1) for the operation is determined; - the operation of the on-load tap changer (4) is started by the drive unit (3) at the new start time (T1).

2. - the course of the current is detected before the switching command for starting the operation of the on-load tap changer (4); - at the time of detecting the course of the current, the frequency and the preceding zero-crossing of the current are determined. A method for operating an on-load tap changer (4) according to Claim 1.

3. The next zero-crossing time (TG) of the current is a future zero-crossing of the current based on the preceding zero-crossing of the course of the current. A method for operating an on-load tap changer (4) according to Claim 1.

4. A method for operating an on-load tap changer (4) according to Claim 3, wherein a future zero-crossing of the current is determined by a mathematical method, in particular by a fast Fourier transform, or by an analog electronic device.

5. The course of the current is detected by one or more sensors (5) in the vacuum valve (6) and / or in the on-load tap changer (4) and / or on the low-voltage side (9) and / or on the high-voltage side of the tap transformer (7). A method for operating an on-load tap changer (4) according to any one of Claims 1 to 4.

6. The time offset (TV) is a value resulting from or depending on the mechanism of the drive train (10). A method for operating an on-load tap changer (4) according to any one of Claims 1 to 5.

7. A method for operating a on-load tap-changer (4) according to claim 6, wherein the value of the time offset (TV) can be adapted automatically and / or manually.

8. A method for operating a on-load tap-changer (4) according to any one of claims 1 to 6, wherein the value of the time offset (TV) can be adapted based on the arc burning period in the vacuum valve (6) of the on-load tap-changer (4).

9. A method for operating a on-load tap-changer (4) according to any one of claims 1 to 8, wherein after determining the time offset (TV), another offset TD1 is subtracted, the new start point (T1) is shifted by this subtraction, and the operation of the on-load tap-changer (4) is started at a point in time (TF) earlier than the next current zero-crossing point (TG) before the zero-crossing.

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

11. - An on-load tap-changer (4), - A sensor (5), - A drive unit (3), - A control device (2), An on-load tap-changing device (1) comprising: - The control device (2) - Receives a switching command for operating the on-load tap-changer (4), - Detects the current trend by the sensor (5), - Identifies the start point (T0) at which a switching command for operating the on-load tap-changer (4) is received during the current trend, - Adds a time offset (TV) to the start point (T0), and as a result, identifies the point in time (TB) at which the operation is virtually started, - Identifies the next current zero-crossing point (TG) after the point in time (TB) at which the operation is virtually started, - Identifies the time difference (TD) between the point in time (TB) at which the operation is virtually started and the next current zero-crossing point (TG), - Adds the time difference (TD) to the start point (T0), and as a result, identifies a new start point (T1) for the operation, - The on-load tap-changing device (1) is configured to start the operation of the on-load tap-changer (4) by the drive unit (3) at the new start point (T1).

12. The on-load tap-changing device (1) according to claim 11, further comprising another sensor (15) for measuring the arc burning period.

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