Method for operating a load tap changer and load tap changer device

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, the following Receiving, by the control device 2, a switching command for operating the on-load tap changer 4; Detecting, by the sensor 5, a current trend 20; Identifying, by the control device 2, a plurality of consecutive time points T1, T2, T3, Tx for zero crossing of the current trend 20; Identifying, by the control device 2, a plurality of intervals A1, A2, Ax between the zero crossing time points T1, T2, T3, Tx of the current; Deriving, by the control device 2, a characteristic variable K from the plurality of intervals A1, A2, Ax; Comparing, by the control device 2, the characteristic variable K with a limit value G; Interrupting or pausing the operation by the control device 2 when the characteristic variable K exceeds the limit value G; Executing the operation by controlling the drive unit 3 by the control device 2 when the characteristic variable K adheres to or falls below the limit value G. The method includes the above steps.

Description

Technical Field

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

Background Art

[0002] In a substation, there are a number of switches that serve different purposes and have different requirements. To operate each of these switches, these switches must be operated by an operating system. These switches are, in particular, on-load tap changers, load transfer switches, selectors, double-pole switches, polarity switches, pre-selectors, power switches, load transfer switches or circuit breakers.

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

[0004] Generally, an on-load tap changer is operated by a combination consisting of a motor drive and a spring energy storage device. The operation is performed immediately after the switching command, i.e., at any time. In this case, the occurrence of inrush current is not considered.

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 an on-load tap changer that ensures more reliable switching.

Means for Solving the Problems

[0006] This problem is solved by each object of the independent claims. Another embodiment is solved by the object of the dependent claims.

[0007] The present invention provides the following - receiving a switching command for operating the on-load tap changer by the control device; - detecting the change in current by the sensor; - identifying a plurality of consecutive time points for zero crossing of the current change by the control device; - identifying a plurality of intervals between the zero crossing times of the current by the control device; - deriving a characteristic variable from the plurality of intervals by the control device; - comparing the characteristic variable with a limit value by the control device; - interrupting or pausing the operation by the control device when the characteristic variable exceeds the limit value; - executing the operation by controlling the drive unit by the control device when the characteristic variable observes or falls below the limit value; A method for operating an on-load tap changer by a drive unit, a sensor, and a control device including them is proposed.

[0008] This method is based on the idea of monitoring the change in current in a tap transformer, on-load tap changer, or vacuum valve before or after a switching command, and detecting the inrush current generated before the actual operation of the on-load tap changer. At this time, based on the zero crossings of the current calculated in the past or after the switching command, the intervals between the zero crossings of the current are identified (calculated). The characteristic values derived from these intervals are compared with the limit value. If the limit value is observed, the inrush current can be excluded. As a result, the operation can be performed safely and reliably. However, if an inrush current occurs before or after the switching command, the operation is interrupted or paused. The occurrence of an abnormality during the change in current is regarded as an inrush current in the meaning of the present invention.

[0009] Immediately after receiving a switching command for operating the on-load tap changer by the control device, the operation of the on-load tap changer is not started. Instead, an abnormality in the transition of the preceding current or an abnormality in the transition of the current after the switching command is first inspected. Only when no abnormality is confirmed is the actual operation appropriately executed.

[0010] The transition of the current can be detected by any method. In particular, the transition of the current is detected by one or more sensors in the tap transformer or the on-load tap changer and transmitted to the control device.

[0011] The detected current transition is processed and evaluated by the control device, and a plurality of consecutive time points are specified during the current transition. The current zero crossing occurs at these time points. Preferably, at least three consecutive time points when the current is zero are specified. Further, a starting point is specified during the current transition. Depending on the embodiment, the transition of the current preceding from the starting point or the transition of the current in the future from the starting point is specified. In this case, the transition of the current preceding before the starting point is already stored in the control device or is stored after the starting point.

[0012] Further, a plurality of intervals between a plurality of consecutive time points of the current zero crossing are specified by the control device. In the case of three time points, two intervals are specified. In particular, the interval between the first time point and the second time point and the interval between the second time point and the third time point are specified.

[0013] Furthermore, by using the control device, characteristic variables are specified from the plurality of intervals. The characteristic variables can be a ratio, an average value, etc. The characteristic value is compared with a limit value by the control device. The limit value is stored in the control device. The limit value can be adjusted manually or automatically.

[0014] Furthermore, when the characteristic variable adheres to or falls below the limit value, the load tap changer is operated by controlling the drive unit by using the control device. When the characteristic value exceeds the limit value, the actual operation is temporarily stopped or interrupted. The temporary stop or interruption of the operation may last, for example, from 1 to 10 seconds. After the temporary stop, the current transition is newly detected, and the method proceeds newly until the operation becomes possible.

[0015] Furthermore, the present invention - a load tap changer, - a sensor, - a drive unit, - a control device, and proposes a load tap changing device including the same.

[0016] In this case, - the control device - receives a switching command for operating the load tap changer, - detects the current transition by the sensor, - identifies a plurality of consecutive time points for the current zero crossing of the current transition, - identifies a plurality of intervals between the time points of the current zero crossing, - derives a characteristic variable from the plurality of intervals, - compares the characteristic variable with a limit value, - interrupts or temporarily stops the operation by the control device when the characteristic variable exceeds the limit value, - is configured to operate the load tap changer by the drive unit when the characteristic variable adheres to or falls below the limit value.

[0017] The on-load tap changer device includes an on-load tap changer having a switching disconnector and a selector. The switching disconnector has at least one vacuum valve. Further, the on-load tap changer device has a drive unit, a sensor, and a control device. The on-load tap changer device inspects the transition of the current before the operation of the on-load tap changer, thereby making it possible to ensure reliable operation when inrush current occurs. The control device is configured and adapted to detect, store, and process the transition of the current by one or more sensors during the operation of the tap transformer, i.e., before the switching command. For this reason, this control device appropriately has a computing device and / or a processor and / or a memory. The control device is configured and adapted to detect, store, and process the transition of the current by one or more sensors after the switching command. For this reason, this control device appropriately has a computing device and / or a processor and / or a memory.

[0018] Furthermore, the control device is configured and adapted to control the drive unit that similarly operates the on-load tap changer.

[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

Embodiments for Carrying Out the Invention

[0021] FIG. 1 shows a tap changer 1 during load. The tap changer 1 during load includes one control device 2, at least one sensor 5, and one tap changer 4 during load. The control device 2 is connected to the drive unit of the tap changer 4 during load. The control device 2 is adjusted and configured to control the drive unit 3 so that the drive unit 3 operates the tap changer 4 during load. Further, the control device 2 is connected to one sensor 5 or a plurality of sensors 5 that measure the current energizing the tap transformer 7, the vacuum valve 6, or the tap changer 4 during load. The control device 2 is adjusted and configured to detect, 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 value of zero and at what frequency this matter 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 in the tap changer 4 during load, directly in the vacuum valve 6, or at any other position suitable for detecting the trend of the current.

[0022] The control device 2 continuously detects the trend of the current before the operation or detects it for the first time when a switching command is received by the control device 2. For this purpose, 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 tap changer 4 during load via the drive train 10, and thus is also mechanically connected to the vacuum valve 6. This drive unit is adjusted and configured to operate the tap changer during load or to execute the switching command of the control device.

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

[0025] The tap transformer 7 has a primary 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 primary winding 11 and the control winding 12 are arranged on the high voltage side 8 (in rare cases, also on the low voltage side). Further, the tap transformer 7 has a low voltage winding 14 which is electromagnetically coupled to the primary winding 11 and the control winding 12.

[0026] Figure 2 shows a flowchart of a method for operating the on-load tap changer. In the gist of the present invention, "before the operation of the on-load tap changer" means that an abnormal current transition can be confirmed either before the switching command or after the switching command. Before the switching command, the method is continuously executed during operation. If an abnormality is already detected here, the operation is interrupted immediately after the switching command or stopped for a predetermined period until the operation can be executed.

[0027] In step 30, the control device 2 receives a switching command for operating the on-load tap changer 4 at the start time point T0. The switching command may be a manual switching command or may come from a voltage controller.

[0028] In the next step 31, the current transition is detected by the sensor 5 and transmitted to the control device. The detection of the current transition can be executed either after the switching command or before the switching command.

[0029] In the next step 32, a plurality of consecutive time points T1, T2, T3, Tx with zero crossings of the current transition 20 are identified (calculated) by the control device. Here, the newly detected current transition or the current transition before the switching command is used.

[0030] In the next step 33, intervals A1, A2, Ax are identified based on the time points T1, T2, T3, Tx of the zero crossings of the current.

[0031] In the next step 34, a characteristic value K is created based on the intervals A1, A2, Ax.

[0032] In step 35, the calculated characteristic value K is compared with the limit value G. If the characteristic value K is less than or equal to the limit value G, the on-load tap changer 4 is actually operated in the next step 36. Therefore, the control device 2 appropriately controls the drive unit 3.

[0033] When the characteristic value K exceeds the limit value G, the operation ends in the next step 37. Instead, when the limit value G is exceeded, the operation may be stopped for a predetermined period in the next step 38 and the method may be newly started.

[0034] FIG. 3 is used to explain the method of the present invention. The time transition of the current in the tap transformer is depicted on the X-axis (in ms units). The Y-axis indicates the height of the current I. Here, the transition of the current or the current transition is a sine wave or substantially a sine wave. The curve of the current transition 20 intersects the X-axis during a plurality of current zero crossings. Therefore, the current is not applied to the tap transformer and the vacuum valve 6 or the on-load tap changer 4 at these points in time. 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 the starting point T0.

[0035] This point in time is regarded as the possible starting point T0 for load switching. Starting from this starting point T0, at least three next points in time T1, T2, and T3 of the next current zero crossing are specified.

[0036] In the next step, the intervals A1 and A2 between the calculated points in time T1, T2, and T3 are specified. Specifically, the first interval A1 between the first point in time T1 and the second point in time T2 and the second interval A2 between the second point in time T2 and the third point in time T3 are specified. The intervals A1 and A2 indicate how much time has elapsed between these points in time.

[0037] In the next step, the characteristic variable K is determined based on the intervals A1, A2. For example, the interval A1 and the interval A2 can be compared with each other, or all the calculated intervals can be compared with each other. Ideally, for example, A1 and A2 are of the same magnitude, and thus the ratio is 1. After the calculation of the characteristic variable K, this characteristic variable K is compared with the limit value G. If the characteristic variable K exceeds the limit value G, the operation is interrupted or paused. Pausing means that the switching is stopped for a predetermined period and then the method is newly executed. If the limit value is observed or falls below the limit value, the on-load tap changer is operated using a drive unit controlled by the control device.

[0038] In the example shown here, the current is energized based on three time points T1, T2, T3, i.e., three current zero crossings. However, any number of current zero crossings T1 - Tx and intervals A1 - Ax can also be used for evaluation. This depends on how long one can wait after the switching command. Also, the method for determining the characteristic value K and the method for defining the limit value G can be arbitrarily adjusted.

[0039] FIG. 4 is used to explain the method of the present invention according to another embodiment. The time course of the current in the tap transformer is depicted on the X-axis (in ms). The Y-axis indicates the height of the current I. 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 20 intersects the X-axis during a plurality of current zero crossings. Therefore, the current is not energized to the tap transformer and the vacuum valve 6 or the on-load tap changer 4 at these times. 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 the starting point T0.

[0040] This point is regarded as the starting point T0 of the load switching. Starting from this starting point T0, at least three subsequent time points T1, T2, and T3 of the previous current zero crossing, i.e., before the starting point T0, are determined. Therefore, this is possible because the course of the current has already been monitored and recorded before the switching command.

[0041] In the next step, specifically, a first interval A1 between a first time point T1 and a second time point T2 and a second interval A2 between the second time point T2 and a third time point T3 are specified. Intervals A1 and A2 indicate how much time has elapsed between these time points.

[0042] In the next step, a characteristic variable K is specified based on intervals A1 and A2. For example, interval A1 and interval A2 can be compared with each other or all the calculated intervals can be compared with each other. Ideally, for example, A1 and A2 are of the same magnitude, and thus the ratio is 1. After the calculation of the characteristic variable K, this characteristic variable K is compared with a limit value G. When the characteristic variable K exceeds the limit value G, the operation is interrupted or paused. Pausing means that the switching is stopped for a predetermined period and then the method is newly executed. When the limit value is adhered to or falls below the limit value, the on-load tap changer is operated using a drive unit controlled by a control device.

[0043] In the example shown here, the current is energized based on three time points T1, T2, T3, i.e., three current zero crossings. However, it is also possible to utilize any number of current zero crossings T1 - Tx and intervals A1 - Ax for evaluation. This depends on how much time can be waited after the switching command. Also, the method for determining the characteristic value K and the method for defining the limit value G can be arbitrarily adjusted.

[0044] Therefore, the above method enables the inspection of abnormalities in the current transition before the switching command and also enables the inspection immediately after the switching command.

Description of Reference Numerals

[0045] 1 On-load tap changing device 2 Control device 3 Drive unit 4 On-load tap changer 5 Sensor 6 Vacuum valve 7 Tap transformer 8 High voltage side 9 Low voltage side 10 Drive column 11 Main winding 12 Control winding 13 Winding tap 14 Low voltage winding 15 Another sensor 20 Current transition T0 Starting point T1 First zero crossing T2 Second zero crossing T3 Third zero crossing Tx Another zero crossing A1 First interval A2 Second interval Ax Another interval

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 following steps: - receiving, by the control device (2), a switching command for operating the on-load tap changer (4); - detecting, by the sensor (5), a current profile (20); - identifying, by the control device (2), a plurality of successive time points (T1, T2, T3, Tx) for zero crossings of the current of the current profile (20); - identifying, by the control device (2), a plurality of intervals (A1, A2, Ax) between the time points (T1, T2, T3, Tx) of zero crossings of the current; - deriving, by the control device (2), a characteristic variable (K) from the plurality of intervals (A1, A2, Ax); - comparing, by the control device (2), the characteristic variable (K) with a limit value (G); - interrupting or pausing, by the control device (2), the operation when the characteristic variable (K) exceeds the limit value (G); - executing, by the control device (2), the operation by controlling the drive unit (3) when the characteristic variable (K) adheres to or falls below the limit value (G). The method as claimed.

2. The method according to claim 1, wherein the current profile (20) is detected before or after receiving, by the control device (2), a switching command for operating the on-load tap changer (4).

3. The method according to claim 1 or 2, wherein the plurality of successive time points (T1, T2, T3, Tx) for zero crossings of the current of the current profile (20) are identified before the start time point (T0) of the input of the switching command or after the start time point (T0) of the input of the switching command.

4. The method according to any one of claims 1 to 3, wherein the characteristic value (K) is generated from a ratio of at least two intervals.

5. The method according to any one of claims 1 to 4, wherein the characteristic variable (K) can be offset by a few percent from the limit value (G).

6. The method according to any one of claims 1 to 5, wherein the pause of the operation by the control device (2) lasts for a few seconds.

7. The method according to any one of claims 1 to 6, wherein at least three consecutive time points (T1, T2, T3, Tx) for the current to pass through zero in the transition of the current (20) are specified before the start time point (T0) of the input of the switching command or after the start time point (T0) of the input of the switching command.

8. The method according to any one of claims 1 to 5, wherein at least two intervals (A1, A2, Ax) between the plurality of time points (T1, T2, T3, Tx) of the current passing through zero are specified by the control device (2).

9. - A on-load tap changer (4); - A sensor (5); - A drive unit (3); - A control device (2); An on-load tap changing device (1) including: - The control device (2): - Receives a switching command for operating the on-load tap changer (4); - Detects the transition of the current by the sensor (5); - Specifies a plurality of consecutive time points (T1, T2, T3, Tx) for the current to pass through zero in the transition of the current (20); - Specifies a plurality of intervals between the time points (T1, T2, T3, Tx) of the current passing through zero; - Derives a characteristic variable (K) from the plurality of intervals (A1, A2, Ax); - Compares the characteristic variable (K) with a limit value (G); - When the characteristic variable (K) exceeds the limit value (G), the control device (2) interrupts or pauses the operation; - The on-load tap changing device (1) is configured such that when the characteristic variable (K) meets or is below the limit value (G), the drive unit (3) operates the on-load tap changer (4).

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