Device and method for monitoring an on-load tap changer

Abstract

Device for monitoring an on-load tap changer The on-load tap changer comprises a plurality of contacts for switching between winding taps of a transformer. The device comprises a measuring unit which is designed to detect an acoustic signal of the on-load tap changer. The device also comprises an evaluation unit which is designed such that, from the acoustic signal representing a switching of the on-load tap changer, it determines characteristic variables for acoustic events in the on-load tap changer within a switching process. A wear model is also determined based on previously determined characteristic degradation patterns and the wear of at least one contact of the on-load tap changer is determined based on the characteristic variables and the wear model.

Description

[0001] Device and method for monitoring an on-load tap-changer

[0002] The invention relates to a device for monitoring an on-load tap-changer and a method for monitoring an on-load tap-changer.

[0003] On-load tap-changers are well-known and are used to adjust the turns ratio of power transformers under load. Corresponding power transformers, which are controlled by on-load tap-changers, have multiple winding taps for adjusting the turns ratio. Arcs typically occur when switching the turns ratio on a live power transformer using an on-load tap-changer. Over the operating life of the on-load tap-changer, these arcs lead to the on-load tap-changer's contacts burning away, particularly in oil-filled on-load tap-changers. This leads to repair and maintenance costs as the contact burning progresses.

[0004] Direct measurements of contact erosion, for example through an invasive inspection of the on-load tap-changer, are currently the common practice for assessing contact erosion. However, such measurement methods are associated with considerable effort, particularly the shutdown of the power transformer and the removal of parts of the on-load tap-changer.

[0005] The object of the invention is therefore to provide a device for monitoring an on-load tap-changer which determines the contact wear of an on-load tap-changer in a simple manner, allows statements to be made regarding the need for maintenance and repair work and, in particular, eliminates the need to switch off the power transformer and to remove parts of the on-load tap-changer to determine the wear.

[0006] This object is achieved by a device according to claim 1. The features of the subclaims constitute advantageous developments of the invention.

[0007] Another object of the invention is to provide a method for monitoring an on-load tap-changer which determines the wear of at least one contact in the on-load tap-changer safely, precisely and simply.

[0008] This object is achieved by a method according to claim 4. The features of the subclaims constitute advantageous developments of the invention.

[0009] According to a first aspect, the invention proposes a device for monitoring an on-load tap-changer. The on-load tap-changer comprises a plurality of contacts for switching between winding taps of a transformer. The device comprises a measuring device designed to detect an acoustic signal from the on-load tap-changer. Furthermore, the device comprises an evaluation device designed to:

[0010] - To determine characteristic quantities for acoustic events in the on-load tap-changer during a switching process from the acoustic signal representing a switching operation of the on-load tap-changer; to determine a wear model based on previously determined characteristic wear patterns and to determine the wear of at least one contact of the on-load tap-changer based on the characteristic quantities and the wear model

[0011] The device makes it possible to determine the contact wear of at least one contact of the on-load tap-changer based on an acoustic signal and a pre-determined wear model. The acoustic signal can, in particular, comprise structure-borne sound or vibrations. To detect the acoustic signal, the measuring device has a sensor, in particular a sound transducer or an acceleration sensor. The sound transducer or acceleration sensor is advantageously arranged near the on-load tap-changer, in particular on the tap-changer head or on the transformer housing.

[0012] According to at least one embodiment, the sound transducer or acceleration sensor is an electromagnetic, piezoelectric or piezoresistive sound transducer and / or a micro-electro-mechanical sensor, MEMS.

[0013] The evaluation device advantageously further comprises an input unit and / or an output unit and / or a communication unit. The output unit can comprise, for example, a display or status LEDs. The output unit can provide the results of the burn-up determination to a user or operator. Alternatively or additionally, the evaluation device can also comprise a communication unit that enables the results of the burn-up determination to be communicated to other data processing devices, e.g., a cloud.

[0014] According to a second aspect, the invention proposes a method for monitoring an on-load tap-changer. The on-load tap-changer comprises a plurality of contacts for switching between winding taps of a transformer, the method comprising:

[0015] Detecting an acoustic signal during a switching operation of the on-load tap-changer; determining characteristic variables for acoustic events in the on-load tap-changer during a switching operation based on the detected acoustic signal

[0016] Determination of a burn-off model based on previously determined characteristic wear patterns

[0017] Determining the burn-off of at least one contact of the on-load tap-changer based on the characteristic quantities and the burn-off model

[0018] The wear model according to the present invention serves to describe the characteristic wear patterns by the specific size of the contact wear and thus in particular establishes a relationship between characteristic wear patterns and contact wear.

[0019] According to at least one embodiment, the determined contact wear is compared with a specified limit value. If the predetermined limit value is exceeded, the evaluation unit issues a message. Alternatively, the difference in wear between two contacts of the on-load tap-changer can also be compared with a limit value. If the limit value is exceeded, the evaluation unit also issues a message and / or recommended action.

[0020] Alternatively or additionally, the process can also include determining a trend in contact wear. Here, too, if the trend in contact wear exceeds a predefined limit, the evaluation unit can issue a message and / or a recommendation for action.

[0021] The notification or recommended action may further include suggesting and / or implementing an action on the on-load tap-changer or transformer depending on the contact wear. The recommended action may, for example, include maintenance, inspection, marking, or decommissioning of the on-load tap-changer or transformer. The recommended action may, for example, include an additional, particularly detailed, physical measurement of the on-load tap-changer's contacts.

[0022] According to at least one embodiment, determining characteristic quantities for acoustic events comprises generating a current envelope from the acoustic signal that maps the intensity of the acoustic signal. The increases in signal intensity (peaks on the curve) are identified and characterized. Current peaks of the current envelope are determined based on the envelope. Furthermore, the peaks of the current envelope thus determined can be compared with previously determined envelopes, allowing a more precise determination of characteristic quantities for acoustic events.

[0023] Characteristic quantities for acoustic events that are characteristic for the switching of an on-load tap-changer are in particular the amplitude of at least one peak of the acoustic signal, the time of a peak of the acoustic signal, the distance between two peaks of the acoustic signal, and the shape of a peak of the acoustic signal.

[0024] According to at least one embodiment, the comparison of the determined peaks of the current envelope with previously determined envelopes can, in particular, comprise the synchronization of the currently measured acoustic signal with previously measured acoustic signals using a labeling method. In other words, acoustic events that exhibit similarities in terms of appearance and position on the envelope are analyzed across multiple switching operations. This is made possible by the fact that comparable mechanical processes occur during each switching operation of the on-load tap-changer, leading to similar acoustic phenomena during a switching operation.

[0025] To determine contact wear based on the characteristic parameters for acoustic events, characteristic wear patterns of the on-load tap-changer are also taken into account. Characteristic wear patterns describe the electrical and / or thermal and / or mechanical and / or other loads that the on-load tap-changer can experience during a transfer, which can affect the switching behavior and thus the noise generated during a transfer.

[0026] Corresponding loads that can be taken into account in the characteristic wear patterns are in particular the load current, the tap voltage, the operating voltage, the top oil temperature of the transformer, the current position of the on-load tap-changer, the number of switching operations carried out so far, carrying out a switching operation under load or carrying out a switching operation without load, the phase position of current and voltage in the on-load tap-changer, the properties of the insulating medium in the on-load tap-changer, the temperature of the insulating medium of the on-load tap-changer, and the switching direction of the switching process.

[0027] The characteristic wear patterns can be generated in various ways. The characteristic wear patterns can be determined based on real-time measured data, historical measurement data, information on the type, year of manufacture, etc. of the on-load tap-changer, simulated data, or historical test and inspection results. The data can be stored locally on the evaluation device or made available in a higher-level data processing system, such as a cloud, and communicated to the evaluation device.

[0028] According to at least one embodiment, characteristic reference variables are additionally used to determine the burn-off model, which are determined on the basis of acoustic reference signals.

[0029] According to at least one embodiment, the burn-off model used to determine the contact burn-off is a regression model, in particular a linear multivariate regression or a non-linear regression or a neural network.

[0030] The invention and its advantages are described in more detail below with reference to the accompanying drawings. They show:

[0031] Fig. 1 is a schematic view of the device according to the invention for monitoring an on-load tap-changer.

[0032] Fig.2 a / b a schematic view of a load changeover switch and an exemplary

[0033] Switching sequence

[0034] Fig.3 shows a schematic sequence of the method according to the invention

[0035] Figure 1 shows a device 1 according to the invention for monitoring an on-load tap-changer 2. The on-load tap-changer 2 is installed in a transformer tank 3. The on-load tap-changer 2 has a diverter switch 21 with a spring energy accumulator 22 and a selector 23. A motor drive 4 is arranged on the side of the transformer tank 3. The motor drive 4 has a housing 41 in which a motor 42 is arranged, which is connected to the on-load tap-changer 2 via a drive shaft 43. To carry out a changeover, the motor 42 drives the on-load tap-changer 2 via the drive shaft 43. During the changeover, the selector 23 is first actuated, with a winding tap to be connected being preselected by a corresponding selector arm. In parallel, the spring energy accumulator 22 is wound up.At a defined point in time, the spring energy storage device 22 is unlatched and suddenly releases the energy previously stored during winding. This energy is used to actuate the load changeover switch 21, and in particular, the contact arrangement of the load changeover switch 21.

[0036] The device 1 according to the invention has means for, or is capable of, determining or detecting an acoustic signal that occurs when the contact arrangement of the load diverter switch 21 is actuated. For this purpose, the device comprises a measuring device 6, which comprises, for example, a sensor.

[0037] The measuring device 6 is preferably arranged near the on-load tap-changer 2, preferably near the load diverter switch 21, in particular near the spring energy accumulator 22, preferably on the housing of the transformer 3 or on the cover or head of the on-load tap-changer 2. The sensor of the measuring device 6 can, for example, be designed as an acceleration sensor (e.g., as a piezo sensor or as a MEMS sensor). Other sensors, such as optical vibration sensors or other known sensors, are also conceivable. The device also has an evaluation device 11, which is connected to the measuring device 6 by cable or wirelessly. The evaluation device 11 is designed to evaluate and / or record the acoustic signals. The evaluation device 11 can be arranged on the transformer 3 or remotely from the transformer 3. Parts of the measuring device 6 can likewise be arranged on the transformer 3 or remotely therefrom.The evaluation device 11 can further be integrated in the housing 41 of the motor drive 4, or arranged in a separate housing on the transformer 3.

[0038] Furthermore, the method according to the invention is carried out by means of the evaluation device 11, or the device executes the method. The evaluation device 11 can acquire and evaluate the acquired raw data from the measuring device 6. Alternatively, only the method according to the invention is carried out in the evaluation device 11. In this case, the measuring device is equipped with appropriate means for acquiring and processing the respective raw data of the signals. Optionally, multiple measuring devices 6 can be provided.

[0039] One possible operation of the diverter switch 21 is shown in Figures 2a and 2b. The diverter switch 21 shown as an example comprises a plurality of contacts (MCa, MSCa, TCa1, TCa2, TCb2, TCb1, MSCb MCb) according to Figure 2a. In continuous operation, i.e. as long as no switching occurs, the permanent main contacts MCa and MCb carry the load current IL. If switching is to take place from a first transformer tap n to a second transformer tap n+1, the permanent main contacts MCa, MCb, the switching contacts MSCa, MSCb and the resistance contacts TCa1, TCa2, TCb2, TCb1 are actuated according to the exemplary switching sequence in Figure 2b. Before switching begins, the contact MCa carries the load current IL. After switching according to the switching sequence in Figure 2b, the transformer tap n+1 is connected and the permanent main contact MCb carries the load current IL.In particular, arcs occur at the switching contacts MSCx and the resistance contacts TCx1, TCx2 during the switching process, which lead to corresponding contact erosion over the service life of the transformer and the on-load tap-changer 2.

[0040] Based on the fact that the vibration pattern or noise development of a switching operation of an on-load tap-changer is influenced by the state of the on-load tap-changer, in particular by the state of the contacts, the device shown in Figure 1 implements the inventive method for monitoring an on-load tap-changer 2. The inventive method is shown abstractly in Figure 3.

[0041] During a switchover (for example, according to the switching sequence shown in Figures 2a / 2b), an acoustic signal AS is detected using the measuring device 6. Alternatively, multiple acoustic signals AS from multiple measuring devices 6 can be used, with the signals then being combined into one acoustic signal AS. This occurs in the evaluation device 11 or in a separate unit during a preprocessing procedure.

[0042] In a step 101, the raw data from the acoustic signal AS of the measuring device 6 are further processed. Processing the acoustic signal AS involves determining characteristic quantities CG from the acoustic signal AS. For this purpose, an envelope curve is first created from the acoustic signal AS, for example, using wavelet analysis. The envelope curve represents the energy of the vibrations in a frequency range.

[0043] Peaks of the envelope are then determined using the envelope. From the envelope, and in particular the peaks, corresponding conclusions can be drawn about the behavior or state of the diverter switch 21, since mechanical events (such as the opening or closing of a contact) are directly related to the corresponding acoustic events (peaks in the envelope). The peaks determined in this way are further evaluated in step 101, and the characteristic variables CG for acoustic events in the on-load tap-changer 2 are determined from the peaks. The characteristic variables CG for acoustic events in the on-load tap-changer 2 are in particular the amplitude of the peak, the time of the peak, the shape of a peak and, if applicable, also the distance between two peaks. In order to improve the quality of the determined characteristic variables CG, several switching operations of the on-load tap-changer 2 can also be evaluated.In this case, in step 101, a temporal synchronization of several envelope curves takes place so that the deviation of the peaks of the individual measurements is minimized. The characteristic variables CG for acoustic events in the on-load tap-changer 2 can then be averaged over several switching operations. In advance or independently of time, particularly advantageously before the acoustic signal AS is recorded, characteristic reference variables CRG are determined in a step 102a. In this step, the raw data of an acoustic reference signal ARS are processed. Acoustic reference signals can in turn represent the acoustic events during a tap-changer switching operation. The acoustic reference signals can be recorded, for example, as part of a tap-changer test in a test environment or during commissioning of the tap-changer or during a learning phase of the method according to the invention.The acoustic reference signals can be recorded either by separate measuring devices or by the measuring system 6. The determination of characteristic reference quantities CRG is carried out analogously to the determination of the characteristic quantities CG.

[0044] In advance or independently of time, in a step 102b, characteristic wear patterns CA of the on-load tap-changer 2 are determined. In this step, characteristic wear patterns CA are determined depending on the electrical, thermal, mechanical and other operating conditions or loads prevailing in the on-load tap-changer. Characteristic wear patterns CA define the acoustic behavior of the on-load tap-changer 2 depending on the prevailing operating conditions, e.g.the load current, the tap voltage, the operating voltage, the top oil temperature of transformer 3, the current position of the on-load tap-changer 2, the number of transfers performed so far, the transfers under load, the transfers without load, the phase position of current and voltage in the on-load tap-changer 2, the properties of the insulating medium in the on-load tap-changer, the temperature of the insulating medium of the on-load tap-changer 2, the switching direction of the transfer process, etc. The characteristic wear patterns CA can be determined by the evaluation unit 11; alternatively or additionally, characteristic wear patterns can also be determined in a separate data processing system or cloud application. In addition, a variety of data sources can be used to determine the characteristic wear patterns CA.For example, the characteristic wear patterns CA can be determined based on real-time measured data, historical measurement data, type information for the on-load tap-changer 2, data obtained through simulation, or historical test results. Furthermore, data and information from just one on-load tap-changer 2 or a fleet of on-load tap-changers, or even from different types of on-load tap-changers, can be used to determine the characteristic wear patterns CA.

[0045] Based on the characteristic reference variables CRG determined in step 102a and the characteristic wear patterns CA determined in step 102b, a burn-off model is created in step 103 that depicts a correlation between the characteristic wear patterns CA, the characteristic reference variables CRG, and the characteristic variables CG determined in step 101. The burn-off model AM is preferably a regression model, in particular a linear multivariate regression model or a non-linear regression model or a neural network.

[0046] In a next step 104, the current wear of the contacts of the diverter switch 21 is determined based on the characteristic variables CG determined in step 101 and the wear model AM determined in step 103.

[0047] Finally, in step 105, the evaluation unit provides an evaluation and / or a recommendation for action for a user. This can, for example, include outputting the contact wear KA values ​​to a user on-site on a display or communicating the determined contact wear values ​​to a higher-level data processing device. In addition, the evaluation device 11 can also issue further recommendations for action, such as for maintenance, inspection, marking, decommissioning, etc. of the tap changer or transformer. Alternatively or additionally, the evaluation device 11 can also generate a short-, medium-, or long-term trend for the contact wear KA of the contacts of the on-load tap changer 2, which is then made available to a user accordingly and can form the basis for further actions or recommendations for action.

Claims

Patent claims Device (1) for monitoring an on-load tap changer (2), the on-load tap changer (2) comprising a plurality of contacts for switching between winding taps of a transformer (3), the device comprising A measuring device (6) designed to detect an acoustic signal (AS) of the on-load tap-changer; and An evaluation device (11) designed to o determine characteristic variables (CG) for acoustic events in the on-load tap-changer (2) within a switching process from the acoustic signal (AS), which represents a switching of the on-load tap-changer; o determine a wear model (AM) based on previously determined characteristic wear patterns (CA), and o determine the wear of at least one contact of the on-load tap-changer based on the characteristic variables (CG) and the wear model (AM). System according to claim 1, wherein the measuring device (6) for detecting the acoustic signal (AS) comprises a sound transducer or an acceleration sensor, which is arranged in the vicinity of the on-load tap-changer (2) on the tap-changer head or on the housing of a transformer (3).System according to one of claims 1 or 2, wherein the evaluation device (11) comprises at least one input unit and / or at least one output unit and / or at least one communication unit. A method for monitoring an on-load tap-changer (2), the on-load tap-changer (2) comprising a plurality of contacts for switching between winding taps of a transformer (3), comprising the method. Detecting an acoustic signal (AS) during a switching operation of the on-load tap-changer (2); Determining characteristic quantities (CG) for acoustic events in the on-load tap-changer (2) within a switching operation based on the recorded acoustic signal (AS); Determination of a burn-off model (AM) based on previously determined characteristic wear patterns (CA); Determining the wear of at least one contact of the on-load tap-changer based on the characteristic variables and the wear model (AM); Method according to the preceding claim, further comprising Comparing the erosion of the contact or the difference in erosion between two contacts with a specified limit and - Outputting a message and / or recommended action in the event of the limit value being exceeded. Method according to claim 4 or 5, wherein the determination of characteristic quantities (CG) for acoustic events comprises Generating a current envelope from the acoustic signal (AS); Determining at least one current peak from the current envelope; Determining the characteristic quantities (CG) for acoustic events based on the at least one current peak and on previously determined envelope curves; Method according to one of claims 4 to 6, wherein Characteristic quantities (CG) for acoustic events include o the amplitude of a peak of the acoustic signal; o the time of a peak of the acoustic signal; o the distance between two peaks of the acoustic signal; o the shape of a peak of the acoustic signal; Method according to claim 6 or 7, wherein the determination of characteristic quantities (CG) for acoustic events additionally comprises: Synchronizing the currently measured acoustic signal with previously measured acoustic signals (AS) using a labeling method; Method according to one of the preceding claims 4 to 8, wherein characteristic wear patterns (CA) are defined by the electrical and / or thermal and / or mechanical and / or other loads of the on-load tap-changer and are determined in particular taking into account Load current and / or Step voltage and / or Operating voltage and / or Top oil temperature of the transformer and / or - Current position of the on-load tap-changer and / or - Number of switching operations performed and / or Circuits under load and / or circuits without load and / or Phase position of current and voltage in the on-load tap-changer and / or Properties of the insulating medium in the on-load tap-changer and / or Temperature of the insulating medium and / or Switching direction of the switching process. Method according to one of the preceding claims 4 to 9, wherein the determination of characteristic wear patterns (CA) is carried out on the basis of data measured in real time and / or on the basis of historical measurement data and / or on the basis of type information and / or on the basis of data determined by simulation and / or on the basis of data determined by historical test results; Method according to one of the preceding claims, wherein the burn-up model (AM) is additionally determined on the basis of characteristic reference variables (CRG) which are determined on the basis of acoustic reference signals (ARS). Method according to one of the preceding claims, wherein the burn-up model comprises a regression model, in particular a linear multivariate regression or a non-linear regression or a neural network.

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