Device and method for monitoring on-load tap changer

Abstract

The invention relates to 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 the transformer. The invention relates to a device for detecting an acoustic signal of an on-load tap changer, comprising a measuring device, which is designed to detect the acoustic signal of the on-load tap changer, and further comprising an evaluation device, which is designed to evaluate the on-load tap changer from the acoustic signal representative of the switching of the on-load tap changer. A characteristic variable for an acoustic event in the on-load tap changer during the switching process is determined. Furthermore, a burn-out model is ascertained on the basis of a pre-ascertained characteristic wear pattern, and a burn-out of at least one contact of the on-load tap changer is determined on the basis of the characteristic variable and the burn-out model.

Description

Technical Field

[0001] The invention relates to a device for monitoring an on-load tap changer and a method for monitoring an on-load tap changer. Background Art

[0002] On-load tap changers are known from the prior art and are used to adjust the winding ratio of power transformers under load. The corresponding power transformers adjusted by the on-load tap changer have a plurality of winding taps for setting the winding ratio. Usually, arcs are generated when switching the winding ratio of a live power transformer using an on-load tap changer. During the service life of the on-load tap changer, these arcs, especially in the case of on-load tap changers using oil-immersed technology, lead to burning of the tap changer contacts, which leads to repair and maintenance costs when the contact burning increases.

[0003] Currently, direct measurement of contact wear, for example by invasive testing of the on-load tap changer, is common practice for assessing contact wear. However, corresponding measuring methods are associated with high costs, in particular by disconnecting the power transformer and disassembling components of the on-load tap changer. Summary of the invention

[0004] The object of the present invention is therefore to provide a device for monitoring an on-load tap changer which can determine contact burnout of the on-load tap changer in a simple manner, allows a decision to be made on the necessity of maintenance and repair work and in particular eliminates the need to disconnect the power transformer and to dismantle components of the on-load tap changer in order to determine the burnout.

[0005] This object is achieved by a device according to claim 1. The features of the dependent claims constitute advantageous developments of the invention.

[0006] A further object of the present invention is to provide a method for monitoring an on-load tap changer which detects a burn-in of at least one contact in the on-load tap changer safely, precisely and simply.

[0007] This object is achieved by the method according to claim 4. The features of the dependent claims constitute advantageous further developments of the invention.

[0008] 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, which is designed to detect acoustic signals of the on-load tap changer. In addition, the device comprises an evaluation device, which is configured to:

[0009] - determining a characteristic variable for an acoustic event within the switching process in the on-load tap changer from the acoustic signal representing the switching of the on-load tap changer;

[0010] - Identify the burnout model based on previously identified characteristic wear patterns; and

[0011] - determining a burn-in of at least one contact of the on-load tap changer as a function of the characteristic variable and the burn-in model.

[0012] The device can detect contact burnout of at least one contact of the on-load tap changer based on an acoustic signal and based on a previously determined burnout model. The acoustic signal can in particular include structure-borne sound or vibrations. To detect the acoustic signal, the measuring device has a sensor, in particular a sound converter or an acceleration sensor. The sound converter or the acceleration sensor is advantageously arranged adjacent to the on-load tap changer, in particular at the tap changer head or at the transformer housing.

[0013] In accordance with at least one embodiment, the sound transducer or the acceleration sensor is an electromagnetic, piezoelectric or piezoresistive sound transducer and / or a micro-electromechanical system sensor (MEMS).

[0014] The evaluation device also preferably comprises an input unit and / or an output unit and / or a communication unit. The output unit can, for example, comprise a display screen or a status LED. The output unit can provide the result of the burnout determination to a user or operator. Alternatively or additionally, the evaluation device can also comprise a communication unit, which allows the result of the burnout determination to be communicated to other data processing devices, such as the cloud.

[0015] According to a second aspect, the present 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 the following steps:

[0016] - Detection of acoustic signals during the switching process of the on-load tap-changer;

[0017] - determining characteristic variables for acoustic events in the on-load tap changer during a switching process based on the detected acoustic signals;

[0018] - Identify the burnout model based on the previously identified characteristic wear pattern;

[0019] - determining a burn-in of at least one contact of the on-load tap changer as a function of the characteristic variable and the burn-in model.

[0020] According to the invention, the wear model is used here to describe the characteristic wear pattern by means of a specific degree of contact wear and thus to establish in particular a connection between the characteristic wear pattern and contact wear.

[0021] According to at least one embodiment, the determined contact wear is compared with a predetermined threshold value. If the threshold value predetermined in advance is exceeded, a notification is issued by the evaluation device. Alternatively, the wear difference between two contacts of the on-load tap changer can also be compared with a threshold value. In this case, if the threshold value is exceeded, a notification and / or an action recommendation is also issued by the evaluation device.

[0022] Alternatively or additionally, the method may also include determining a trend in contact wear. In the event that the trend in contact wear exceeds a predefined threshold value, a notification and / or an action recommendation may also be issued by the evaluation device.

[0023] The notification or action recommendation can further include an action suggestion and / or an action execution for the on-load tap changer or transformer based on the contact burnout. The action recommendation can, for example, include maintenance, inspection, marking or decommissioning of the on-load tap changer or transformer. The action recommendation can, for example, include additional, in particular detailed, physical measurements of the contacts of the on-load tap changer.

[0024] According to at least one embodiment, determining the characteristic variable for the acoustic event includes generating a current envelope curve from the acoustic signal, the current envelope curve reflecting the intensity of the acoustic signal. An increase in signal intensity (peak on the curve) is identified and characterized. A current peak of the current envelope curve is determined based on the envelope curve. In addition, the peak of the current envelope curve thus determined can be compared with a previously determined envelope curve, which allows a more accurate determination of the characteristic variable for the acoustic event.

[0025] Characteristic variables for an acoustic event, which are characteristic for a switching of the on-load tap changer, include 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.

[0026] According to at least one embodiment, the comparison of the detected peaks of the current envelope curve with the previously detected envelope curve can in particular include synchronizing the currently measured acoustic signal with the previously measured acoustic signal according to a marking method. In other words, acoustic events that are similar in appearance and position on the envelope curve are analyzed over a plurality of switching operations. This makes it possible that comparable mechanical processes occur during each switching operation of the on-load tap changer, which results in similar acoustic phenomena during the switching process.

[0027] In order to determine the contact wear based on characteristic variables for acoustic events, characteristic wear patterns of the on-load tap changer are also taken into account. The characteristic wear pattern describes the electrical and / or thermal and / or mechanical and / or other loads that the on-load tap changer may experience during switching and which may influence the switching behavior and thus the noise generation within the switch.

[0028] The corresponding loads that can be taken into account in the characteristic wear pattern are in particular: load current, tap voltage, operating voltage, transformer top oil temperature, current position of the on-load tap changer, number of switching operations performed so far, execution of switching with load or execution of switching without load, phase position of current and voltage in the on-load tap changer, properties of the insulating medium in the on-load tap changer, temperature of the insulating medium of the on-load tap changer and switching direction of the switching process.

[0029] Characteristic wear patterns can be generated in a variety of ways and methods. Thus, they can be ascertained based on real-time measurement data, based on historical measurement data, based on information about the type of on-load tap changer, year of manufacture, etc., based on simulation data or also based on historical test and inspection results. These mentioned data can be stored locally on the evaluation device or can be provided to a higher-level data processing system (e.g. the cloud) and communicated to the evaluation device.

[0030] According to at least one embodiment, a characteristic reference variable ascertained from the acoustic reference signal is additionally used to ascertain the burn-in model.

[0031] According to at least one embodiment, the wear model used for determining the contact wear is a regression model, in particular a linear multivariate regression model, or a nonlinear regression model or a neural network. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention and its advantages are described in more detail below with reference to the accompanying drawings, which show:

[0033] Figure 1 is a schematic diagram of a device for monitoring an on-load tap changer according to the present invention;

[0034] Figure 2a / b is a schematic diagram of a load switch and an exemplary switching process;

[0035] Figure 3 is a schematic flow chart of the method according to the present invention. DETAILED DESCRIPTION

[0036] Figure 1A device 1 according to the invention for monitoring an on-load tap changer 2 is shown. The on-load tap changer 2 is installed in a transformer tank 3. The on-load tap changer 2 comprises a load changer 21 with a spring energy store 22 and a selector 23. A motor drive 4 is arranged on the side of the transformer tank 3. The motor drive 4 comprises 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 perform a switchover, the motor 42 drives the on-load tap changer 2 via the drive shaft 43. During the switchover, the selector 23 is first actuated, wherein a winding tap to be connected is preselected via the corresponding selector arm. In parallel with this, the spring energy store 22 is tensioned. At a defined time / moment, the spring energy store 22 is released and releases all at once the energy previously stored during tensioning. With this energy, the load changer 21 and in particular the contact arrangement of the load changer 21 are actuated.

[0037] The device 1 according to the invention has means for determining or detecting or being able to determine or detect acoustic signals which are generated when the contact arrangement of the load switch 21 is actuated. For this purpose, the device comprises a measuring device 6 which contains a sensor, for example.

[0038] The measuring device 6 is preferably arranged adjacent to the on-load tap changer 2, preferably adjacent to the load switch 21, in particular adjacent to the spring energy storage 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 be configured, for example, as an acceleration sensor (for example as a piezoelectric sensor or as a MEMS sensor). In addition, other sensors, such as optical vibration sensors or other known sensors can also be considered. The device also includes an evaluation device 11, which is connected to the measuring device 6 by wire or wirelessly. The evaluation device 11 is configured to evaluate and / or acquire acoustic signals. The evaluation device 11 can be arranged at the transformer 3 or away from the transformer 3. Some parts of the measuring device 6 can also be arranged at the transformer 3 or away from the transformer. The evaluation device 11 can also be integrated in the housing 41 of the motor drive 4, or arranged in a separate housing on the transformer 3.

[0039] Furthermore, the method according to the invention is carried out or the device carries out the method by means of the evaluation device 11. In this case, the evaluation device 11 can acquire and evaluate the raw data detected by 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 corresponding means for detecting and processing the corresponding raw data of the signal. Optionally, a plurality of measuring devices 6 can be provided.

[0040] One possible operation of the load switch 21 is Figure 2a and Figure 2bis shown. The exemplary load switch 21 includes a plurality of contacts (MCa, MSCa, TCa1, TCa2, TCa2, TCa1, MSCb, MCb) according to Figure 2a . During continuous operation, that is, during a period when no switching occurs, the continuous main contacts MCa or MCb conduct the load current IL. If it is necessary to switch from the first transformer tap n to the second transformer tap n+1, the continuous main contacts MCa, MCb, the switching contacts MSCa, MSCb, and the resistance contacts TCa1, TCa2, TCa2, TCa1 are operated according to the exemplary switching process according to Figure 2b . Before the start of the switching, the contact MCa conducts the load current IL here. After the switching is completed according to the switching process according to Figure 2b , the transformer tap n+1 is connected and the continuous main contact MCb conducts the load current IL. In particular, on the switching contacts MSCx and the resistance contacts TCx1, TCx2, arcs are generated during the switching process, and these arcs can cause corresponding contact burn-outs during the service life of the transformer and the on-load tap-changer 2.

[0041] Based on the fact that the generation of the vibration mode or noise of the on-load tap-changer is affected by the state of the on-load tap-changer, in particular also by the contact state, Figure 1 the device shown in Figure 3 executes a method according to the invention for monitoring the on-load tap-changer 2. The method according to the invention is abstractly shown in

[0042] During the switching (for example according to the switching process according to Figure 2a / 2b), the acoustic signal AS is detected by means of the measuring device 6. Alternatively, a plurality of acoustic signals AS of a plurality of measuring devices 6 can be used, and the signals are then combined into an acoustic signal AS. This is achieved in the evaluation device 11 or in a separate unit during the preprocessing program.

[0043] In step 101, the raw data of the acoustic signal AS from the measuring device 6 is further processed. Here, the processing of the acoustic signal AS includes determining the characteristic parameter CG from the acoustic signal AS. For this purpose, first, for example, an envelope curve is generated from the acoustic signal AS by means of wavelet analysis. The envelope curve reflects the energy of the oscillation in a frequency range.

[0044] The peak value of the envelope curve is then determined based on the envelope curve. Corresponding conclusions about the behavior or state of the load switch 21 can be drawn from the envelope curve, in particular the peak value, because a mechanical event (e.g., opening or closing of a contact) is directly associated with a corresponding acoustic event (peak value in the envelope curve). Within the scope of step 101, the peak value thus determined is further evaluated and a characteristic variable CG for an acoustic event in the on-load tap changer 2 is determined from the peak value. The characteristic variable CG for an acoustic event in the on-load tap changer 2 is in particular the amplitude of the peak value, the time point of the peak value, the shape of the peak value, and, if necessary, also the distance between two peak values. In order to improve the quality of the determined characteristic variable CG, multiple switching operations of the on-load tap changer 2 can also be evaluated. In this case, multiple envelope curves are synchronized with each other in time within the scope of step 101 so that the deviation of the peak values ​​of each single measurement is minimized. The characteristic variable CG for an acoustic event in the on-load tap changer 2 can then be averaged over multiple switching operations.

[0045] In advance or independently in time, particularly preferably before the acquisition of the acoustic signal AS, the characteristic reference variable CRG is ascertained in step 102a. In this step, the raw data of the acoustic reference signal ARS are processed. The acoustic reference signal can here again reflect acoustic events within the scope of the tap changer switching. The acoustic reference signal can be acquired, for example, within the scope of the tap changer test in a test environment or during the commissioning of the tap changer or during a learning phase of the method according to the invention. The acquisition of the acoustic reference signal can be carried out here by a separate measuring device or by the measuring system 6. The characteristic reference variable CRG is ascertained in a similar manner to the ascertainment of the characteristic variable CG.

[0046] In step 102b, a characteristic wear pattern CA of the on-load tap changer 2 is ascertained in advance or independently in time. In this step, the characteristic wear pattern CA is ascertained as a function of the electrical, thermal, mechanical and other operating conditions or loads present in the on-load tap changer. The characteristic wear pattern CA defines the acoustic behavior of the on-load tap changer 2 in relation to the operating conditions present (e.g. load current, tap voltage, operating voltage, top oil temperature of the transformer 3, current position of the on-load tap changer 2, number of switching operations performed so far, switching with load, switching without load, phase position of current and voltage in the on-load tap changer 2, properties of the insulating medium in the on-load tap changer, temperature of the insulating medium of the on-load tap changer 2, switching direction of the switching process, etc.). The characteristic wear pattern CA can be ascertained here by the evaluation unit 11, but alternatively or additionally the characteristic wear pattern can also be implemented in a separate data processing device or in a cloud application. Furthermore, a plurality of data sources can be used for ascertaining the characteristic wear pattern CA. Thus, the characteristic wear pattern CA can be ascertained, for example, based on real-time measurement data, based on historical measurement data, based on type information about the on-load tap changer 2, based on data ascertained by means of simulations or based on historical test results. Furthermore, data and information of only one on-load tap changer 2, or data and information of a group of on-load tap changers or data and information of different types of on-load tap changers can also be used for ascertaining the characteristic wear pattern CA.

[0047] Based on the characteristic reference variable CRG determined in step 102a and the characteristic wear pattern CA determined in step 102b, a burn model is established in step 103, which reflects the correlation between the characteristic wear pattern CA, the characteristic reference variable CRG and the characteristic variable CG determined in step 101. The burn model AM is preferably a regression model, in particular a linear multiple regression model or a nonlinear regression model or a neural network.

[0048] In the next step 104 , the current burning condition of the contacts of the load changeover switch 21 is determined based on the characteristic variable CG ascertained in step 101 and the burning model AM determined in step 103 .

[0049] Finally, in step 105, the evaluation unit provides the user with an evaluation and / or action recommendation. This can include, for example, locally outputting the value of the contact burnout KA for the user on a display, or communicating the determined value for the contact burnout to a higher-level data processing device. Additionally, further action recommendations, such as maintenance, inspection, marking, deactivation, etc. of the tap changer or transformer, can also be output by the evaluation device 11. Alternatively or additionally, the evaluation device 11 can also generate a short-term trend, medium-term trend, or long-term trend of the contact burnout KA of the contacts of the on-load tap changer 2, provide the short-term trend, medium-term trend, or long-term trend of the contact burnout to the user accordingly, and can form the basis for further actions or action recommendations.

Claims

1. A device (1) for monitoring an on-load tap changer (2) comprising a plurality of contacts for switching between winding taps of a transformer (3), the device include: - a measuring device (6) designed to detect an acoustic signal (AS) of the on-load tap changer; as well as - an evaluation device (11) configured to: determining a characteristic variable (CG) for an acoustic event within a switching process in the on-load tap changer (2) from an acoustic signal (AS) representing a switching of the on-load tap changer; Determine the abrasion model (AM) based on the previously identified characteristic wear pattern (CA); and Burning of at least one contact of the on-load tap changer is determined as a function of the characteristic variable (CG) and the burn-in model (AM).

2. The system according to claim 1, in, The measuring device (6) comprises, for detecting the acoustic signal (AS), a sound converter or an acceleration sensor which is arranged adjacent to the on-load tap changer (2) on the tap changer head or on the transformer (3) housing.

3. The system according to claim 1 or 2, in, The evaluation device (11) comprises at least one input unit and / or at least one output unit and / or at least one communication unit.

4. 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), the method include: - detecting an acoustic signal (AS) during a switching process of the on-load tap changer (2); - determining a characteristic variable (CG) for an acoustic event in the on-load tap changer (2) during a switching process based on the detected acoustic signal (AS); - Determine the burnout model (AM) based on the previously identified characteristic wear pattern (CA); - determining a burn-in of at least one contact of the on-load tap changer as a function of the characteristic variable and the burn-in model (AM).

5. The method according to the preceding claim, further comprising: include: - compare the burnout of a contact or the difference in burnout between two contacts with a specified threshold value; as well as - Output notifications and / or action recommendations when thresholds are exceeded.

6. The method according to claim 4 or 5, in, The characteristic parameters (CG) determined for acoustic events include: - Generate the current envelope curve from the acoustic signal (AS); - determining at least one current peak value from the current envelope curve; - ascertaining a characteristic variable (CG) for the acoustic event based on the at least one current peak value and based on the previously ascertained envelope curve.

7. The method according to any one of claims 4 to 6, in, The characteristic parameters (CG) for acoustic events include: - Peak amplitude of the acoustic signal; - The peak time of the acoustic signal; - the distance between two peaks of an acoustic signal; - Peak shape of the acoustic signal.

8. The method according to claim 6 or 7, in, Determining the characteristic parameters (CG) for acoustic events also includes: - Synchronize the currently measured acoustic signal with the previously measured acoustic signal (AS) according to the marking method.

9. The method according to any one of the preceding claims 4 to 8, in, The characteristic wear pattern (CA) is defined by the electrical and / or thermal and / or mechanical and other loads on the on-load tap-changer and is determined in particular taking into account the following factors: - Load current and / or - tap voltage and / or - operating voltage and / or - Oil temperature at top of transformer and / or - the current position of the on-load tap-changer and / or - the number of switches performed and / or - Switching with load and / or switching without load and / or - Phase position of current and voltage in the on-load tap-changer and / or - the properties of the insulating medium in the on-load tap-changer and / or - the temperature of the insulating medium and / or - The switching direction of the switching process.

10. The method according to any one of the preceding claims 4 to 9, in, The characteristic wear pattern (CA) is determined based on real-time measurement data and / or based on historical measurement data and / or based on type information and / or based on data determined by simulation and / or based on data determined by historical test results.

11. The method according to any one of the preceding claims, in, The burn-in model (AM) is additionally ascertained as a function of a characteristic reference variable (CRG) which is ascertained as a function of an acoustic reference signal (ARS).

12. The method according to any one of the preceding claims, in, The burn-in model comprises a regression model, in particular a linear multiple regression or a nonlinear regression or a neural network.

Images