Method for monitoring the state of an electrical device, computer program, and computer-readable medium

Abstract

The invention relates to a method, in particular a computer-assisted method, for monitoring the state of an electrical device, preferably for monitoring the short-circuit current rating of an electrical device, in particular a transformer (1) or a choke, preferably a compensation choke, wherein the electrical device comprises a solid insulation assembly (I) and a liquid and / or gaseous insulation medium which is in contact with the solid insulation assembly (I), the method having the following steps: S1) measuring operating parameters of the electrical device; S2) providing and / or creating a simulation model of the electrical device; S3) carrying out a simulation for the electrical device using the simulation model and the measured operating parameters; and S4) evaluating the state of the electrical device, in particular the short-circuit current rating of the electrical device, on the basis of the results of the simulation.

Description

[0001] Description

[0002] Method for monitoring the condition of an electrical device, computer program and computer-readable medium

[0003] The invention relates to a method, in particular a computer-aided method, for condition monitoring, preferably for monitoring the short-circuit strength, of an electrical device, in particular a transformer or a choke, preferably a compensation choke, wherein the electrical device comprises a fixed insulation arrangement and a liquid and / or gaseous insulating medium in contact with the fixed insulation arrangement.

[0004] Furthermore, the invention relates to a computer program and a computer-readable medium.

[0005] Within the context of the energy transition, the operational reliability of electrical equipment, such as transformers, is playing an increasingly important role. At the same time, the energy transition is leading to increasing load fluctuations, which can result in increased stress on transformers. Against this backdrop, it is necessary to assess the probability of failure of such electrical equipment during operation. A significant cause of failure can be a decrease in the short-circuit withstand capability of an electrical device. Furthermore, there is interest in understanding how aging, in particular, affects the short-circuit withstand capability and thus the operational reliability of electrical equipment during operation.

[0006] Insulation systems in electrical devices often consist of a combination of an insulating medium, which can be liquid or gaseous, and a solid insulating layer, typically cellulose-based. Substances formed due to the aging of the solid insulating layer can migrate into the insulating medium and be detected there. This allows for monitoring the aging of an electrical device.

[0007] To test short-circuit withstand capability, specific short-circuit tests are frequently performed on transformers. Such tests are generally very costly. Furthermore, network operators often rely on forecasts provided by the transformer manufacturer. Based on these forecasts, an assessment of short-circuit withstand capability can be made.

[0008] In principle, it is also possible to carry out inspections on the transformer, and in particular to check the tightness of the transformer windings, for example by listening to the winding supports. Vibration analysis can also provide information about the winding clamping. However, it has been found that the informative value of such investigations can sometimes be very limited. Furthermore, such investigations can sometimes be very costly.

[0009] Against this background, the object of the invention is to provide an alternative method for condition monitoring, preferably for monitoring the short-circuit withstand capability, of an electrical device, which is particularly easy to perform and delivers reliable results. This object is achieved in a method of the type mentioned at the outset, which comprises the following steps:

[0010] 51) Operating parameters of the electrical device are measured;

[0011] 52) A simulation model of the electrical device is provided and / or created;

[0012] 53) A simulation of the electrical device is performed using the simulation model and the measured operating parameters;

[0013] 54) Based on the results of the simulation, the condition of the electrical device, in particular the short-circuit strength of the electrical device, is evaluated.

[0014] The invention is based on the fundamental idea of ​​directly measuring individual operating parameters using appropriate sensors and combining these with a simulation model in order to draw conclusions about the condition, in particular the short-circuit strength, of the electrical device through a corresponding simulation.

[0015] In other words, the simulation model forms a digital representation, or digital twin, of the electrical device. This simulation model allows for the consideration of the relationships and interactions of the various processes involved within the electrical device. For example, the simulation model can take into account historical operating data, current operating data, and the specific design of the windings (type of winding, conductor, insulation, etc.). This operating data can be relevant for determining the short-circuit withstand capability. The short-circuit withstand capability depends, in particular, on the clamping force of the windings. Generally speaking, the higher the temperature of the insulating medium and the windings, the higher the clamping force of the windings.Over time, elevated temperatures, which cause aging of the rigid insulation and associated material loss, can reduce the strength of the winding clamping. High Lorentz forces acting on the windings can then lead to damage or short circuits, and consequently to the failure of the electrical device.

[0016] Operating parameters that can be measured include the ambient temperature or the external temperature of the electrical device. It has been shown that the external temperature can influence the conditions inside the electrical device. The temperature of the insulating medium can also be measured as an operating parameter. The temperature of the insulating medium determines the heat transfer, particularly from a solid insulation arrangement, and thus the cooling effect. Simultaneously, a change in the temperature distribution leads to a change in the winding clamping force.

[0017] The surface temperature of components of the electrical device can also be measured as an operating parameter.

[0018] It is also possible to measure the gas composition and / or moisture content of the insulating medium. The moisture content of the insulating medium particularly influences its aging behavior and the formation of aging products. The current and / or voltage acting within the electrical device can also be measured as operating parameters.

[0019] Operating parameters can include a switch position and / or a state of a cooling device of the transformer or the transformer cooling system, in particular at least one radiator and / or at least one fan and / or at least one pump, which can be determined or measured.

[0020] The simulation model can be designed to account for the changing clamping force of the windings due to changes in temperature, humidity, and / or aging (material shrinkage). Preferably, the simulation model includes determining the temperature distribution as a function of current loads, ambient conditions, and / or cooling conditions of the electrical device. It is also possible to determine the humidity distribution within the electrical device. The temporal profiles of temperature and humidity can then be used to draw conclusions about the aging of the insulation. For example, the simulation can include the calculation of aging parameters, particularly local aging parameters and / or DP values.

[0021] When determining the gas composition, the proportion of carbon dioxide (CCR) can be determined in particular. It has been shown that CCR forms especially during the aging of the solid insulation assembly. The CCp content can be determined at various locations within the solid insulation assembly.

[0022] In a further embodiment, the simulation can determine a temperature distribution within the electrical device, particularly as a function of voltage and / or current, ambient conditions, especially ambient temperature, and / or as a function of a switch position and / or the state of a cooling device of the transformer or transformer cooling system, in particular at least one radiator and / or at least one fan and / or at least one pump. Preferably, a local temperature is determined at several different locations within the electrical device, particularly in the fixed insulation assembly and / or in the insulating medium. In this way, a temperature distribution within the electrical device can be determined.

[0023] Preferably, the simulation determines the distribution of moisture within the electrical device. Preferably, local moisture levels can be determined at several points within the electrical device.

[0024] Based on a temperature distribution and / or a humidity distribution, optionally using other aging-influencing factors, the aging of specific areas of the electrical device, in particular the fixed insulation assembly, can be determined. This design is based on the consideration that the condition of the fixed insulation assembly and / or the insulating medium can influence the short-circuit withstand capability.

[0025] Specifically, local DP values ​​can be calculated for various areas of the electrical device, particularly the fixed insulation assembly. In particular, by considering aging through the calculation of a local DP value, which generally cannot be verified by direct measurement, a precise representation of the condition of the fixed insulation assembly is obtained. Based on this aging state, changes in material stiffness can then be determined. The abbreviation "DP" in the DP value stands for "degree of polymerization," as is generally known. It is a measure of the decreasing length of cellulose molecules due to thermal aging, which impairs mechanical strength and can lead to operational risks. The DP value indicates the number of basic molecular units in a cellulose chain that form during polymerization, the joining of the basic molecule.New cellulose typically has DP values ​​above 1000, while chemical decomposition breaks the chains into shorter units, reducing their mechanical strength. At DP values ​​below 200, the mechanical strength, such as tensile strength, deteriorates significantly. It then falls well below 50% compared to the initial state, which could jeopardize the safe operation of a transformer, especially in the event of short circuits in the network, which lead, at least briefly, to high currents and thus stressful forces or vibrations.

[0026] For the optional calculation of DP numbers as aging parameters, in particular the calculation of the decreasing DP number due to aging, at least one formula is preferably used, which includes as influencing factors the initial state, the duration of time, the temperature of the solid insulation, especially cellulose, in the hotspot, and a material property of the cellulose that depends on water and oxygen as well as the cellulose quality. When using paper, a second cellulose quality is available: a thermostabilized quality with reduced thermal aging at high temperatures. Specifically, reference can be made here to the standard IEC 60076-7:2018 "Loading guide for mineral-oil-immersed power transformers", 2018, in particular to page 42 with the equation Al and table Al on page 43, whose parameters easily take into account the temperature, humidity, cellulose quality, and the influence of oxygen.At least one such equation can be used to calculate aging.

[0027] A suitable dynamic model, such as a temperature-humidity aging model, can be used to calculate the aging parameters. An example of such a model is described in J. Raith, C. Bonini, M. Scala – “Simulation of Long-Term Transformer Operation with a Dynamic Thermal, Moisture and Aging Model”, 5th international colloquium on transformer research and asset management, Opatija, Croatia, October 9–12, 2019, Singapore, pages 211–226, doi: 10.1007 / 978-981-15-5600-5 17.

[0028] The simulation model can take aging into account. For this purpose, it can use aging parameters, such as DP numbers, especially local DP numbers.

[0029] Preferably, the simulation model is implemented as a network model and / or as a multiphysics model. The simulation model can be implemented as a finite element method (FEM) model. The simulation of the operation can be performed over a simulation period of several hours, months, or years. In other words, a long-term simulation of the electrical device can also be carried out within the scope of the method according to the invention. It should be noted that the actual computing time required to perform such a simulation can be, and usually will be, considerably shorter than the time periods covered by the simulation.

[0030] In a further refinement, the simulation can determine the clamping forces of windings, particularly as a function of temperature, humidity, and / or aging, preferably of the fixed insulation arrangement. This refinement is based on the objective of representing the design and technical relationships of the electrical device as comprehensively as possible in the simulation model. In other words, the clamping force of the windings can be determined based on the temperature and / or humidity distributions and / or the aging or state of aging determined during the simulation. The clamping force of the windings is a relevant parameter for assessing short-circuit withstand capability. Insufficient clamping force can lead to damage to the windings and thus to short circuits under high current loads and consequently high Lorentz forces.In particular, material stiffnesses can be determined during simulation depending on the aging, especially local aging parameters, preferably DP numbers.

[0031] The simulation model can be designed to take into account the structural design of the electrical device. For example, the electrical device can be a transformer with a housing containing several components. These components can include a core, a winding assembly, a compression ring, a mounting plate, and / or a winding cylinder. Preferably, the simulation model considers the dimensions and properties, such as material properties, especially the mechanical properties (e.g., material stiffness), the electrical and / or magnetic properties, of the existing components of the electrical device.

[0032] According to a preferred embodiment, the simulation model or the simulation includes the determination of a humidity distribution and / or the determination of a temperature distribution and / or the determination of aging parameters, in particular DP numbers, and / or the determination of clamping forces of windings, and / or the determination of mechanical stresses. The simulation model can be a thermo-hydraulic-mechanical aging-humidity model, which can represent a particularly accurate image of an electrical device.

[0033] Preferably, the simulation model or simulation is designed to provide data for evaluating short-circuit strength in real time. In other words, an assessment of short-circuit strength can take place in real time, particularly depending on the currently applicable conditions, such as current load, humidity, aging, mechanical stress, and / or temperature.

[0034] Based on the simulation, short-circuit strength can be evaluated using a spring-mass model.

[0035] The electrical device can be designed such that the insulating medium comprises or is provided by an oil, in particular a mineral oil, and / or an ester liquid. The solid insulating arrangement can comprise or be provided by cellulose, in particular paper and / or pressboard.

[0036] In a further embodiment, the electrical device can comprise a tank filled with the insulating medium, in which components of the electrical device are arranged. Preferably, one or more of the components are provided with the fixed insulation arrangement, in particular wrapped with the fixed insulation arrangement or parts thereof. The fixed insulation arrangement can be multi-part. In steps S2 and S3, the different areas of the fixed insulation arrangement can comprise or be defined by different parts of the fixed insulation arrangement. In a further embodiment, different parts of the fixed insulation arrangement can be assigned to different components of the electrical device. Preferably, different components of the electrical device are provided with different parts of the fixed insulation arrangement, in particular wrapped.

[0037] The method according to the invention can further be characterized in that the condition of the electrical device, in particular its short-circuit withstand capability, is categorized. In other words, depending on the condition of the device or the detected short-circuit withstand capability, information about the condition of the electrical device can be output, for example, according to a traffic light system (red, yellow, green). It is also possible that the method further includes the output of maintenance and / or service instructions based on the assessment of the electrical device's condition. This means that the user is given direct instructions for carrying out necessary maintenance or service work. Thus, if a problem with the short-circuit withstand capability and therefore the risk of failure is detected, a corresponding notification can be issued to the user.

[0038] The problem underlying the invention is further solved by a computer program comprising program code means which, when the program is executed on at least one computer, cause that at least one computer to carry out the steps of the method as described above. Furthermore, the problem underlying the invention is solved by a computer-readable medium comprising instructions which, when executed on at least one computer, cause that at least one computer to carry out the steps of the method as described above.

[0039] The computer-readable medium could be, for example, a CD-ROM, a DVD, or a USB or flash memory device. It should be noted that a computer-readable medium is not limited to a physical medium, but can also exist, for example, in the form of a data stream and / or a signal representing a data stream.

[0040] Further features and advantages of the present invention will become clear with reference to the dependent claims and the following description, including the accompanying drawing. The drawing shows:

[0041] Figure 1 is a purely schematic partial representation of an electrical device designed as a transformer.

[0042] Figure 1 shows a partial representation of an electrical device provided by a transformer 1 to illustrate the method according to the invention.

[0043] The transformer 1 comprises a tank 2, shown only partially in the figure, in which several components of the transformer 1 are arranged. These include, among others, a core 3, a winding assembly 4, a compression ring 5, a mounting plate 6, and a winding cylinder 7, as shown in Figure 1.

[0044] Transformer 1 has a fixed insulation arrangement.

[0045] I, which consists primarily of pressboard and paper, i.e., cellulose, and is multi-part. As an example, the widely used core design of a power transformer was chosen, whose active part comprises the winding arrangement 4 extending around the iron core, the conductors of which are insulated by pressboard elements (cellulose), with the conductors typically wrapped with paper (cellulose). On the one hand, the pressboard elements and paper belonging to the winding arrangement 4 are components of the fixed insulation arrangement I. The same applies to the press ring 5, the mounting plate 6, and the winding cylinders 7, each of which consists of one or more pressboard elements.

[0046] The block element designated with reference numeral 8 in Figure 1 is representative of other areas or parts of the insulation arrangement I that may be present or are present in this case, in particular further cellulose, and also of other components of the transformer 1 outside the active part. All paper or pressboard parts located on or attached to the various components together form the solid insulation arrangement I.

[0047] Figure 9 indicates a void, or in other words, a recess or hole, within tank 2. Also shown schematically are a preservative, or in other words, an oil expansion vessel 10, a dehumidifier 11, and a cooler 12. The void 9 lies between the cooler 12 and the remaining area of ​​tank 2. Expansion vessels are available in an open design, allowing air to enter. However, the trend towards closed systems—e.g., using rubber membranes—is increasing to prevent the entry of oxygen, which accelerates aging. In the illustrated embodiment, tank 2 is also filled with a liquid insulating medium, specifically a mineral oil 13. In this case, it can also be referred to as an oil-insulated transformer 1. The solid insulation assembly I and the mineral oil 13 together form the insulation system of the transformer 1.

[0048] The solid insulation assembly I is in contact with the insulating oil 13. Substances that arise due to the aging of the solid insulation assembly I can migrate into the insulating medium 13 and be detected there. These are also referred to as aging markers. Examples of such aging markers include CO2 + CO and / or 2FAL.

[0049] The oil flow is represented in Figure 1 by simple arrows, which are labelled with reference numeral 14 for illustrative purposes. Double arrows 15 further indicate, purely schematically, the moisture exchange between the solid insulation assembly I and the liquid insulating medium 13.

[0050] The individual windings of the winding arrangement 4 are held on the winding cylinder with a defined clamping force or wound onto it.

[0051] The transformer 1 further comprises a temperature sensor 16, which is immersed in the mineral oil 13 and determines its temperature. A humidity sensor 17, in particular a capacitive one, is also provided, which measures the moisture content, i.e., the water content or water activity, in the mineral oil 13. The transformer also includes a current sensor 18, which can detect or measure the current flowing through the winding arrangement 4. Additionally, the ambient temperature can be measured using a temperature sensor (not shown). The short-circuit withstand capability of the transformer 1 can be monitored by a method according to the invention. For this purpose, operating parameters of the transformer 1 are measured, in this case, the temperature of the mineral oil 13, the moisture content of the mineral oil 13, and the current flowing through the winding arrangement 4.Furthermore, a simulation model of transformer 1 is provided, which takes into account the clamping force of the winding arrangement 4 and the influence of the humidity and temperature distribution within transformer 1. The simulation model also considers the structural design of transformer 1, for example, the type of winding, the conductors present, and the design of the insulation arrangement I.

[0052] As part of the short-circuit withstand monitoring procedure, a simulation of transformer 1 is performed using the simulation model and the measured operating parameters. This process determines the temperature and humidity distribution within transformer 1. Specifically, local temperature and humidity are measured at several different locations within transformer 1. Furthermore, the simulation determines the clamping forces of the winding arrangement 4, particularly as a function of temperature, humidity, and / or aging. Based on the simulation results, the short-circuit withstand capability of transformer 1 is evaluated. This can be done, for example, using a traffic light system (red, yellow, green), which allows conclusions to be drawn about the transformer's failure risk.It is also possible that maintenance instructions will be issued based on the assessment of short-circuit strength.

[0053] The described method allows for an accurate estimation of the short-circuit strength of an electrical device, in this case the transformer 1, without the need for costly tests that might require the transformer 1 to be taken out of service.

[0054] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variations can be derived by the person skilled in the art without leaving the scope of protection of the invention.

Claims

Patent claims 1. A method, in particular a computer-aided method, for condition monitoring, preferably for monitoring the short-circuit strength, of an electrical device, in particular a transformer (1) or a choke, preferably a compensation choke, wherein the electrical device comprises a fixed insulation arrangement (I) and a liquid and / or gaseous insulating medium in contact with the fixed insulation arrangement (I), wherein the method comprises the following steps: 51) Operating parameters of the electrical device are measured; 52) A simulation model of the electrical device is provided and / or created; 53) A simulation of the electrical device is performed using the simulation model and the measured operating parameters; 54) Based on the results of the simulation, the condition of the electrical device, in particular the short-circuit strength of the electrical device, is assessed.

2. The method according to claim 1, characterized in that the operating parameters are an ambient temperature or an outside temperature of the electrical device and / or a temperature of the insulating medium and / or a surface temperature of components of the electrical device and / or a gas composition and / or a humidity of the insulating medium and / or a current and / or a voltage acting in the electrical device and / or a switch position and / or a state of cooling, in particular at least one radiator and / or at least one fan and / or at least one pump is measured.

3. Method according to claim 1 or 2, characterized in that in the simulation a temperature distribution in the electrical device, in particular as a function of a voltage and / or a current, of ambient conditions, in particular an ambient temperature and / or humidity, and / or a switch position and / or a state of a cooling system, in particular at least one radiator and / or at least one fan and / or at least one pump, is determined, wherein, in particular, a local temperature is determined at several different locations.

4. Method according to one of the preceding claims, characterized in that a distribution of moisture in the electrical device is determined during the simulation, wherein, in particular, local moisture is determined at several different locations.

5. Method according to claim 3 and claim 4, characterized in that, in the simulation, starting from a temperature distribution and a humidity distribution, optionally using further aging-determining influencing factors, the aging of certain areas of the electrical device, in particular the fixed insulation arrangement (I) , is determined.

6. Method according to claim 5, characterized in that local DP numbers are calculated for different areas of the electrical device, in particular the fixed insulation arrangement (I).

7. Method according to one of the preceding claims, characterized in that clamping forces are simulated of windings, in particular depending on temperature and / or humidity and / or aging, and / or that material stiffnesses, in particular depending on or starting from a local aging parameter, preferably a DP number, are determined in the simulation.

8. Method according to one of the preceding claims, characterized in that a short-circuit strength is evaluated based on a spring-mass model starting from the results of the simulation.

9. Method according to one of the preceding claims, characterized in that the simulation model is designed as a network model and / or as a multiphysics model.

10. Method according to one of the preceding claims, characterized in that the insulating medium comprises or is provided by an oil, in particular a mineral oil, and / or an ester liquid, and / or that the solid insulating arrangement (I) comprises or is provided by cellulose, in particular paper and / or pressboard.

11. Method according to one of the preceding claims, characterized in that the electrical device comprises a tank (2) filled with the insulating medium in which components of the electrical device are arranged, wherein one or more of the components are provided with the fixed insulation arrangement (I), in particular wrapped with the fixed insulation arrangement (I) or parts thereof.

12. Method according to one of the preceding claims, characterized in that the fixed insulation arrangement is formed in multiple parts and in steps S2 and S3 the different areas of the fixed insulation arrangement (I) comprise different parts of the fixed insulation arrangement (I) or are given in this way, wherein, in particular, different parts of the fixed insulation arrangement (I) are assigned to different components of the electrical device, wherein, preferably, different components of the electrical device are provided with different parts of the fixed insulation arrangement (I), in particular wrapped around them.

13. Method according to one of the preceding claims, characterized in that a simulation of the operation is carried out for a simulation period of several hours, months or years.

14. Method according to one of the preceding claims, characterized in that the condition of the electrical device, in particular the short-circuit strength of the electrical device, is categorized, and / or that the method further comprises the output of maintenance and / or service instructions based on the assessment of the condition of the electrical device.

15. Computer program comprising program code means which, when the program is executed on at least one computer, cause the at least one computer to perform the steps of the method according to any one of claims 1 to 14.

16. Computer-readable medium comprising instructions which, when executed on at least one computer, cause that at least one computer to perform the steps of the method according to any one of claims 1 to 14.

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