On-load tap changer condition analysis

Abstract

A method for analysing the state of an on-load tap changer 2, said on-load tap changer 2 having at least one vacuum valve 3 for switching between winding taps of a transformer 4, said method comprising the steps of: - detecting real-time data relating to said on-load tap changer 2; - checking parameters specific to the on-load tap changer; - calculating at least one characteristic value for determining a state indicator of the on-load tap changer 2 on the basis of the real-time data and parameters specific to the on-load tap changer, The method, wherein the condition indicator comprises at least one of the time until scheduled maintenance, remaining life and remaining number of changes of the on-load tap changer (2).

Description

[Technical field]

[0001] The present invention relates to a method for analysing the state of an on-load tap changer and to a device for analysing the state of an on-load tap changer. [Background technology]

[0002] On-load tap changers are used to switch between transformer winding taps without interruption and are therefore important equipment for transformers that should be particularly cautious with respect to reliability. Such on-load tap changers mainly consist of a selector for selecting in the no-current state the respective winding tap of the transformer that has to be changed, and a load changer for the actual change from the current winding tap to the preselected new winding tap. For this purpose, load changers generally have a vacuum valve and a current limiting resistor. In this case, the vacuum valve is used to connect the respective winding tap to the load line and the current limiting resistor is used to briefly limit the current during the change.

[0003] Vacuum valves mainly have switching contacts made of arc-resistant copper-tungsten alloy. Generally, during operation of the vacuum valve, arcs are generated which melt or vaporize a small amount of the contact material and thus may cause contact wear or even unevenness of the contact surface. Furthermore, the vaporized material may cause vaporization of the insulation inside the vacuum valve. Said vaporization may be accompanied by a reduction in the insulation strength of the vacuum valve.

[0004] These events therefore also affect the lifespan of the vacuum valves used and the on-load tap changers in which they are used.

[0005] Generally, the maximum service life of on-load tap changers and the vacuum valves present in on-load tap changers is determined by testing under worst-case conditions. Based on the results of the tests carried out, a margin of safety must be ensured for the switching process of the on-load tap changer in order to ensure reliable operation of the on-load tap changer, and the on-load tap changer is maintained or replaced, if applicable, early.

[0006] However, in practical operation, the load tap changers are usually subjected to much smaller loads. Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore an object of the present invention to provide an improved concept for analysing the state of an on-load tap changer, which detects the actual load of the on-load tap changer and allows a more accurate assessment of the state of the on-load tap changer. [Means for solving the problem]

[0008] This problem is solved by the respective subject matter of the independent claims. Further embodiments are the subject matter of the dependent claims.

[0009] According to a first aspect of the improved idea, a method for analysing the state of an on-load tap changer is proposed, the on-load tap changer having at least one vacuum valve for switching between winding taps of a transformer, the method comprising the steps of: - obtaining real-time data relating to an on-load tap changer; - determining parameters specific to an on-load tap changer; - calculating at least one characteristic value for determining a condition indicator of the on-load tap changer based on the real-time data and on parameters specific to the on-load tap changer.

[0010] in this case, The condition indicators include at least one of the time until scheduled maintenance, remaining life and remaining number of changes of the on-load tap changer.

[0011] The advantage of the above method over the prior art is that by taking into account the on-load tap changer-specific parameters of the at least one calculated characteristic value and obtaining real-time data, the actual load experienced by the on-load tap changer is indicated. Knowledge of the actual state of the on-load tap changer allows for the optimization of maintenance intervals and for a full utilization and increased service life of the on-load tap changer. Furthermore, detection of the actual load allows the occurrence of dangerous states of the on-load tap changer to be recognized and avoided at an early stage.

[0012] According to a preferred embodiment, the acquisition of real-time data includes at least one of: detecting the load current at each change; detecting the tap voltage at each change; detecting the actual position of the on-load tap changer; detecting the direction of the upcoming change, i.e. whether the transformation ratio of the transformer will increase or decrease; detecting the temperature of the insulating medium in which the vacuum valve is located; detecting the frequency of changes within a certain period of time; detecting the duration of the changes; and detecting the duration of arcing at each change.

[0013] Furthermore, for example, the duration and the height of the circulating current flowing through the on-load tap changer during the changing process, or another temperature, for example the temperature of a vacuum valve or a current limiting resistor of the on-load tap changer, can be determined.

[0014] In this case, the term "determining" means detecting data, for example by measurement with a suitable sensor, as well as further processing the data, for example in the form of a calculation, based on the detected data in order to determine a further associated characteristic variable.

[0015] According to one embodiment, the data specific to the on-load tap changer includes the number and size of current limiting resistors, the circuit topology of the on-load tap changer, in particular the interconnections between the vacuum valves or the number and size of the vacuum valves.

[0016] According to a further embodiment, the on-load tap changer specific data comprises in particular specific data of at least one vacuum valve.

[0017] The specific data of the vacuum valve may include characteristic parameters of the vacuum valve, such as the contact material or the geometry of the valve, or limits determined by testing, such as wear limits, average arc duration or average arc energy.

[0018] According to a preferred embodiment, the at least one characteristic value includes a degree of contact erosion.

[0019] The degree of contact erosion relates to the erosion of the contact material of the switching contacts of the vacuum valve as a result of the occurrence of an arc. Preferably, the degree of contact erosion is detected in volume units.

[0020] According to another embodiment, in addition to the degree of contact erosion, at least one of the degree of reduction in the insulation strength of the vacuum valve and the degree of unevenness on the contact surface is calculated as the characteristic value.

[0021] Typically, the arc that is extinguished at the first zero crossing of the current causes the contact material to vaporize, generating metal vapor that can diffuse within the vacuum valve and condense accordingly, thereby reducing the dielectric strength of the vacuum valve.

[0022] Furthermore, melting or vaporization of the contact material can cause the contact surface to become non-uniform, which can adversely affect the extinction of the arc at the zero crossing, for example by causing restriking.

[0023] According to another embodiment, the at least one characteristic value includes a state of vacuum in the vacuum valve.

[0024] According to another embodiment, at least one characteristic value is compared with a predefined limit value and, if this limit value is exceeded, a message is output.

[0025] The limiting value can be, for example, a certain volume of evaporated contact material or the thickness of a metal vapor layer that accumulates on the insulation in the vacuum valve due to extinction of the arc, or a certain number of non-uniformities on the contact surface can be used as the limiting value.

[0026] According to another embodiment, the method comprises the steps of: - determining the operating conditions existing at the on-load tap changer and at the vacuum valve based on real-time data and on-load tap changer specific parameters.

[0027] When determining the operating conditions, the application in which the on-load tap changer is operated, in other words the place where the transformer is used, is taken into account in the condition analysis, since the condition is influenced differently depending on how often the on-load tap changer is operated, how long and how high the circulating currents flowing through the on-load tap changer occur at this time, how high the contact heating is accordingly, and for what power class the on-load tap changer is designed.

[0028] For example, in the case of on-load tap changers used in transformers of electric arc furnaces, a certain number of de-energized switches are performed, during which the on-load tap changer is operated but no current is passed through it, and in this case the on-load tap changer is generally only subjected to mechanical loads, which have less influence on the state indicators than switching processes in which the current flows and the arc is extinguished.

[0029] According to another embodiment, the at least one characteristic value is calculated based on at least one of a model simulation, a machine learning method, an interpolation method, and historical data.

[0030] For example, electrohydrodynamic models or particle diffusion models or arc generation models suitable for model simulation can be used. Similarly, mechanical loads, e.g. loads on the bellows of a vacuum valve and electrical circuits can be simulated by suitable software.

[0031] To calculate the characteristic values, for example artificial neural networks can be used as methods in the field of machine learning, it is also possible to use regression algorithms or other known machine learning methods.

[0032] When considering historical data, for example the results of carried out tests are used together with comparable data and parameters or inductive reasoning with field experience is used. A higher level data bank, for example a cloud containing the data of all transformers, may be used as a data source for the historical data.

[0033] According to a second aspect of the improved idea, an apparatus for analyzing the condition of an on-load tap changer is proposed.

[0034] With respect to the apparatus, reference should be made to the above preferred features, effects and / or advantages as already described for the method, and therefore redundant description will be omitted.

[0035] According to a second aspect of the improved idea, the device is configured for analyzing the state of an on-load tap changer, the on-load tap changer having at least one vacuum valve for switching between winding taps of a transformer, the device comprising an evaluation device and a data memory unit. In the data memory unit real-time data relating to the on-load tap changer and parameters specific to the on-load tap changer can be stored. Furthermore, the data memory unit may contain further relevant data used for the state analysis, such as, for example, application-specific parameters, limit values ​​or historical data. The evaluation device is communicatively connected to the data memory unit and / or to a higher-level control system and is configured for carrying out the method according to the first aspect of the improved idea.

[0036] For example, a power supply company's control center may act as the upper level control system.

[0037] According to one embodiment, the device further comprises an output device for outputting a status indicator of the on-load tap changer. Furthermore, the evaluation device may be configured to output a guidance or warning message depending on the status indicator.

[0038] To this end, the evaluation device may have corresponding suitable means for visualization, for example a display or LED light means for indicating a dangerous situation.

[0039] According to another embodiment, the on-load tap changer and the transformer comprise suitable sensors for detecting real-time data, such as, for example, current sensors on the primary and / or secondary side of the transformer or temperature sensors in the insulating medium of the on-load tap changer.

[0040] The present invention will be described in detail below based on the illustrated embodiments with reference to the drawings. Components that are identical or functionally identical or have the same effect can be indicated by the same reference numerals. Components that are identical or have the same function are described exclusively by the drawings in some cases. The description is not necessarily shown repeatedly in the following drawings. [Brief description of the drawings]

[0041] [Figure 1] 1 shows a preferred embodiment of a device according to an improved concept. [Diagram 2] A preferred embodiment of the method according to the improved concept is presented. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] In FIG. 1 a preferred embodiment of a device 1 according to the improved concept is shown in a schematic diagram.

[0043] The device 1 is used to analyze the state of an on-load tap changer 2 having a vacuum valve 3 for switching between winding taps (not shown) of a transformer 4. The vacuum valve 3 is present in a housing 10 of the on-load tap changer 2, which is at least partially filled with an insulating medium 10. In principle, however, the on-load tap changer 2 may also be arranged in the transformer 4 without a housing together with the vacuum valve 3. As a result, the on-load tap changer 2 is present in the oil bath of the transformer 4. In FIG. 1 only one vacuum valve is shown by way of example and for a better conceptualization. In general, however, the on-load tap changer 2 has several vacuum valves 3 for said switching.

[0044] The device 1 comprises an evaluation device 5, a data memory unit 6 and an output unit 8. In order to carry out a condition analysis, relevant data used for determining the state of the on-load tap changer 2 and the vacuum valve 3, such as real-time data on the on-load tap changer 2, specific parameters of the on-load tap changer 2 and the vacuum valve 3, limit values ​​of relevant characteristic values ​​or historical data, are stored in the data memory unit 6. To acquire the real-time data, the on-load tap changer 2 and the transformer 4 each comprise a sensor 9. According to the embodiment shown in FIG. 1, the on-load tap changer 2 comprises, for example, a temperature sensor 9 for measuring the temperature of the insulating medium 11 and the transformer 4 comprises, for example, a current sensor 9 on the primary and / or secondary side. In principle, however, further sensors 9 can be provided for acquiring the real-time data.

[0045] The evaluation device 5 is communicatively connected to a data memory unit 6 and is configured to receive real-time data and parameters specific to the on-load tap changer and the vacuum valve and to calculate, on the basis of these, at least one characteristic value for determining a state indicator of the on-load tap changer 2. In addition to the data memory unit 6, the evaluation device 5 according to this embodiment is communicatively connected to a higher-level control system 7, for example a control centre of a power supply company, via which connection it can receive further data for determining the characteristic value. The characteristic value is determined on the basis of model simulations, machine learning methods, interpolation methods or historical data or a combination thereof.

[0046] The described functionality of the evaluation device 5 may be implemented by hardware, firmware, software or other machine-readable instruction code, or any combination thereof.

[0047] The status indicator is output via the output unit 8. To this end, the output unit 8 comprises suitable means for visualization, such as for example a display.

[0048] In FIG. 2, a preferred embodiment of the method according to the improved concept is shown as a flow chart.

[0049] For the method, reference should also be made to the above descriptions, preferred features, effects and / or advantages already described for the device 1 according to Fig. 1, and therefore no duplicated description will be given.

[0050] A preferred embodiment of the method is used to analyze the state of an on-load tap changer having at least one vacuum valve for switching between winding taps of a transformer. As shown in Figure 1, the method is preferably used to analyze the state of an on-load tap changer 2 in a transformer 4 by means of an apparatus 1.

[0051] In step a, real-time data relating to the on-load tap changer 2 are detected by suitable sensors 9. Real-time data are, for example, the load current flowing or the tap voltage applied at each change, the actual position n of the on-load tap changer, the change direction of the upcoming change, the temperature of the insulating medium surrounding the vacuum valve, the change frequency over a period of time, the duration of the change or the duration of arcing at each change.

[0052] In step b, the on-load tap changer-specific parameters, such as the number and dimensions of current limiting resistors, the circuit topology of the on-load tap changer, in particular the number and dimensions of the interconnections between the vacuum valves or the vacuum valves, and the vacuum valve-specific data are determined. The vacuum valve-specific data includes characteristic parameters such as the contact material, the valve geometry and the valve operating kinematics, experimentally determined limit values, such as wear limits, the average arc duration or the average arc energy. The opening and closing speed of the valve and the internal pressure of the vacuum valve can also be taken into account as vacuum valve-specific parameters.

[0053] In step c, the operating conditions existing at the on-load tap changer 2 and the vacuum valve 3, in particular the switching frequency, the duration and the height of the circulating current flowing during operation or the contact heating, are determined based on the real-time data, the parameters specific to the on-load tap changer and the specific data of the vacuum valve 3.

[0054] The execution of steps a, b, and c is not limited to the order shown in the flowchart of Figure 2. In contrast, steps a, b, and c may be executed in the reverse order, and / or interchanged order, or may be executed simultaneously.

[0055] In step d, at least one characteristic value for determining a condition indicator of the on-load tap changer 2 is determined on the basis of the real-time data, the on-load tap changer-specific parameters and the specific data of the vacuum valve 3. In this case, the condition indicator comprises at least one of the following: the time until scheduled maintenance, the remaining life and the remaining number of changes of the on-load tap changer 2.

[0056] According to this embodiment, at least one characteristic value for determining the condition indicator is formed as the degree of contact wear. In principle, however, the invention is not limited to this characteristic value. However, further characteristic values, such as the degree of reduction in the insulation strength of the vacuum valve due to metal vapor or the degree of unevenness on the contact surface, can also be determined as characteristic values.

[0057] The characteristic value and possibly other characteristic values ​​are determined based on model simulations, machine learning methods, interpolation methods, or historical data, or a combination thereof.

[0058] In step e, the status indicator is output by the output unit 8 .

[0059] According to this particular embodiment, depending on the output of the status indicator, in step f, the determined characteristic value is compared with a predefined limit value, and if this limit value is exceeded, in step g, an additional warning message is output by the output unit 8. [Explanation of symbols]

[0060] 1 device 2 On-load tap changer 3 Vacuum valve 4. Transformers 5 Evaluation section 6 Data memory section 7 Subsequent deployed control system 8 Output section 9 Sensors 10. Housing 11 Insulating media

Claims

1. A method for analyzing the state of an on-load tap changer (2), wherein the on-load tap changer (2) has at least one vacuum valve (3) for switching between winding taps of a transformer (4), and the method is - A step of acquiring real-time data related to the load tap changer (2), - A step to determine parameters specific to the on-load tap changer, - A method comprising the step of calculating at least one characteristic value for determining the state index of the on-load tap changer (2) based on the real-time data and parameters specific to the on-load tap changer, - The method wherein the status indicator includes at least one of the following: the period until scheduled maintenance of the on-load tap changer (2), the remaining lifespan, and the remaining number of tap changes.

2. The acquisition of the aforementioned real-time data is - Detection of load current during each switching, - Detection of tap voltage at each switching point, - Detection of the actual position n of the load-operated tap changer (2), - Detection of the switching direction of an imminent switch, - Detection of the temperature of the insulating medium (11) in which the vacuum valve (3) is located, - Detection of switching frequency within a certain period, - Detection of the duration of the switchover, - Detection of the duration of arc generation during each switching, The method according to claim 1, comprising at least one of the following.

3. The method according to claim 1 or 2, wherein the parameters specific to the under-load tap changer include specific data for at least one vacuum valve (3).

4. - The method according to claim 1 or 2, wherein the at least one characteristic value includes at least one of the degree of contact wear of the vacuum valve, the degree of reduction in insulating strength, and the degree of non-uniformity on the contact surface.

5. - The at least one characteristic value is compared with a predetermined limit value, - If this limit is exceeded, a message will be displayed. The method according to claim 1 or 2.

6. The aforementioned method, - A further step of determining the operating conditions present in the on-load tap changer (2) and the vacuum valve (3) based on real-time data and parameters specific to the on-load tap changer, The method according to claim 1 or 2.

7. - The method according to claim 1 or 2, wherein the at least one characteristic value is calculated based on at least one of model simulation, machine learning method, interpolation method, and historical data.

8. An apparatus (1) for analyzing the state of an on-load tap changer (2), wherein the on-load tap changer (2) has at least one vacuum valve (3) for switching between winding taps of a transformer (4), and the apparatus (1) - Evaluation device (5), - Data memory section (6), Includes, - The data memory unit (6) can store real-time data related to the on-load tap changer (2) and parameters specific to the on-load tap changer. - The evaluation device (5) is connected to the data memory unit (6) and / or a higher-level control system (7) via communication, and is configured to perform the method described in claim 1 or 2.

9. - The apparatus according to claim 8, further comprising an output device (8) for outputting a status indicator of the load tap changer (2).

10. - The apparatus according to claim 8, wherein the on-load tap changer (2) and the transformer (4) are equipped with a sensor (9) suitable for detecting the real-time data.

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