METHOD AND DEVICE FOR TRANSFORMER TESTING

Abstract

The present invention relates to a method (200) for testing a transformer (180). The method comprises determining (202) a flank pitch for a test signal (702) based on the transformer (180) to be tested, and generating (204) the test signal (702) with the determined flank pitch. The method also comprises testing (206) the transformer (180) using the generated test signal (702).

Description

1 / 26 METHOD AND DEVICE FOR TRANSFORMER TESTING FIELD OF THE INVENTION

[001] The present invention relates to a method and a correspondingly configured device for testing a transformer. In particular, the present invention is suitable for testing and measuring transformers used as current transformers. Transformer testing may comprise, for example, measurements of magnetization curves. BACKGROUND OF THE INVENTION

[002] In power technology, measuring transformers, in particular current transformers, are used, which are based on a transformer designed to meet measurement requirements, enabling potential-free measurement of large alternating currents under high voltage. In order to ensure the proper functioning of a current transformer, requirements for the current transformer must be verified, which are defined, for example, in the EN 61869-2 standard. These requirements refer, among other things, to magnetization parameters, where a particular magnetization curve and saturation magnetization may be relevant.

[003] For this purpose, a test device can generate, for example, a sinusoidal signal with the frequency of the mains power supply, which is fed into the device under test, for example, a current transformer. As a result, voltages and currents, which also occur in nominal operation, can be generated on the secondary side of the current transformer. Therefore, test signals with power up to 5 kW, for example, are then required in the case of conventional current transformers. These test devices are very heavy due to their high output power or they can only test current transformers for low power ratings. Petition 870250080337, dated 08 / 09 / 2025, page 8 / 59 2 / 26

[004] In addition, there are test methods in which test signals with a reduced test frequency or test voltage are used to test the respective current transformer. However, these methods are generally very inaccurate, since the altered behavior of current transformers is not sufficiently taken into account when operating at a frequency that deviates from the nominal frequency or the mains frequency.

[005] In this context, EP 1398644B1 describes a method for testing a transformer, in which a test signal whose frequency is lower than the nominal or operating frequency of the transformer is applied to the transformer in order to measure a plurality, in particular, of frequency-dependent transformer parameters. A simulation model is derived from the parameters measured with this test signal, which makes it possible to simulate the behavior of the transformer at different frequencies. With the aid of this simulation model or the parameters measured with the test signal, it is then possible to infer the behavior of the transformer during operation at a frequency different from the frequency of the test signal, for example, the behavior of the transformer during operation at nominal frequency. In particular, a square wave signal whose fundamental frequency is lower than the nominal frequency can be used as a test signal.

[006] The use of rectangular signals is particularly suitable for obtaining a correspondingly large magnetic flux in the magnetic core. In this case, however, the problem may arise that capacitive current peaks occur at edges with a high slope of the rectangular signal, in combination with high voltages in transducers with high parasitic capacitance due to their design. These currents may overload the test device or require correspondingly larger and therefore more expensive test devices. Petition 870250080337, dated 08 / 09 / 2025, page 9 / 59 3 / 26 and heavy. Furthermore, this can compromise the accuracy of the measurement. SUMMARY OF THE INVENTION

[007] One objective of the present invention is, therefore, to provide an accurate measurement of the magnetization parameters of a transformer, in particular a magnetization curve of a current transformer, which can be implemented economically and is suitable for a wide range of transducers.

[008] This objective is achieved according to the invention by means of methods for testing a transformer and a correspondingly configured device for testing a transformer, as defined in the independent claims. The dependent claims define advantageous embodiments of the present invention.

[009] According to the invention, in a method for testing a transformer, an edge slope for a test signal is determined as a function of the transformer to be tested, and the test signal is generated with the edge slope thus determined. The transformer is tested using the generated test signal.

[0010] In other words, a test signal with a signal shape that has an edge slope dependent on the transformer being tested is used. The signal shape of the test signal used then has defined harmonics, that is, defined frequency components above a fundamental frequency of the test signal. In particular, it can then be achieved that the signal shape of the test signal has fewer frequency components than, for example, a rectangular signal, as is normally generated by means of constant voltage sources connected in a bridge. Furthermore, undershoot and overshoot can be avoided or reduced by adjusting the edge slope. The edge slope of the test signal is not determined by a switching mechanism used in the generation of the test signal, but rather adjusted as a function of the transformer. A source of Petition 870250080337, dated 08 / 09 / 2025, page 10 / 59 A correspondingly controllable 4 / 26 signal can be used for this purpose. Due to the adjustable edge slope, in particular a smaller edge slope compared with connected constant voltage sources, large capacitive current peaks can be avoided and thus, on the one hand, an overload of the device generating the test signal can be avoided and, on the other hand, the accuracy of the measurement can be increased, since the currents to be measured occur in a limited range, which can therefore be obtained accurately. By determining and adjusting the edge slope as a function of the transformer, it is also possible, for example, to test current transformers with high capacitance as a result of the design; in particular, a magnetization curve can be measured accurately, for example.

[0011] The test signal can be generated, for example, by driving at least one adjustable voltage converter. The voltage converter can be, for example, a DC voltage converter, a so-called DC-DC converter. In order to generate an alternating voltage with the desired edge slope, for example, two voltage converters can be used. One of the two voltage converters generates an adjustable grounded positive voltage and the other of the two voltage converters generates an adjustable grounded negative voltage. The adjustable positive voltage and the adjustable negative voltage are each adjustable by a control device to a plurality of voltage values ​​and are supplied to the transformer to be tested. The previously determined edge slopes for rising and falling edges can be obtained by a corresponding adjustment of the voltage over time.An adjustable output voltage range for voltage converters can be, for example, from zero to 25 V or from zero to 50 V, in steps of 1 V or 0.1 V.

[0012] Due to the grounded positive and negative voltages adjust Petition 870250080337, dated 09 / 08 / 2025, p. 11 / 59 5 / 26 times, an iron core of the transformer can be magnetized in both directions, for example, in order to measure magnetization curves.

[0013] For example, a parasitic capacitance of the transformer can be determined in order to determine the edge slope for the test signal. Depending on the parasitic capacitance and a predetermined maximum current that may occur during the transformer test, the edge slope can be determined. Parasitic capacitances can occur, for example, due to connecting lines, connecting terminals, and the transformer structure. These capacitances can lead to current spikes, especially at high frequencies. By adjusting the edge slope for the test signal, high frequencies can be avoided, for example, by reducing the edge slope. This means that current spikes can be avoided. The test device is less loaded because it needs to supply a lower maximum current. As a result, the reliability of the test device can be improved, and it can be made more compact and lightweight.

[0014] Parasitic capacitance can be determined by a measurement on the transformer to be tested. In particular, for example, a high-frequency measurement can be performed on the transformer. A high-frequency measurement on the transformer means, for example, that a frequency at which the parasitic capacitance is measured is higher than the nominal frequency, for example, it is a multiple of the nominal frequency. The nominal frequency of the transformer may be 50 or 60 Hz, for example. The high frequency used in the parasitic capacitance measurement may be, for example, more than 1 kHz or even more than 100 kHz. A voltage used in this case may be correspondingly low, in particular lower than the voltage to be used when testing the transformer. For example, the transformer Petition 870250080337, dated 08 / 09 / 2025, page 12 / 59 6 / 26 can be tested at + / - 25 V, while parasitic capacitance is measured at + / - 5 V.

[0015] Alternatively or additionally, the parasitic capacitance can be entered by a user. The user may have determined the value of the parasitic capacitance with an additional measuring device, for example, or the parasitic capacitance may be stored in a database. In addition, a type of transformer to be tested and, if necessary, its connection settings can be entered, so that the parasitic capacitance can be retrieved from a database, for example.

[0016] It is evident that a currently measured parasitic capacitance is advantageous, since in this case the actual states of the transformer are taken into account and the edge slope can be optimally adjusted for the test signal. A correspondingly configured test device can, for example, first automatically determine the parasitic capacitance through measurement and then initiate the actual test of the transformer, for example, a measurement of a transformer magnetization curve, using the edge slope determined from the parasitic capacitance. Taking the parasitic capacitance into account can increase the accuracy of the measurement. On the one hand, current peaks due to parasitic capacitance can be reduced and determined by the selected edge slope, so that a distinction can be made between regular inductive current through the transformer and capacitive current peaks.For example, a transformer magnetization curve can then be measured with great precision using the regular inductive current then determined.

[0017] According to one embodiment, the test signal is a periodic test signal. The edge slope can be determined using an iterative method. In the iterative method, an edge slope Petition 870250080337, dated 08 / 09 / 2025, page 13 / 59 7 / 26 for a subsequent period of the test signal is determined based on an edge slope in a period of the test signal as a function of a measured maximum current generated during the transformer test with the test signal in the previous period. For example, the edge slope can be slightly increased from one period to the next. For example, starting from a relatively low edge slope, the edge slope can be slowly increased, thus increasing the capacitive current peaks. This can be continued until a desired or permissible maximum current is reached. The maximum current may correspond, for example, to a rated current of the test device or to a certain percentage of the maximum current of the test device, for example, 90% of the maximum current.Once the edge slope has been determined using this iterative method, the measurement can be performed on the transformer with the edge slope determined in this way.

[0018] The test signal may be, for example, a periodic voltage signal. Per period, the voltage signal may comprise a voltage rise with a determined edge slope from a lower voltage value to an upper voltage value, an upper portion with substantially constant voltage at the upper voltage value, and a voltage drop from the upper voltage value to the lower voltage value. It is quite clear that the lower voltage value is less than the upper voltage value. The lower voltage value may be grounded negative, for example, and the upper voltage value may be grounded positive. The values ​​of the upper voltage value and the lower voltage value may be different or equal. The voltage signal may have a lower portion with substantially constant voltage at the lower voltage value per period. The length of the lower portion and the length of the upper portion may be substantially different. Petition 870250080337, dated 09 / 08 / 2025, p. 14 / 59 8 / 26 equal. The voltage drop can have an edge slope that is equal in magnitude to the edge slope of the voltage rise.

[0019] It is understood that the lower portion may also have a different length from the upper portion. Similarly, the voltage drop may have a different edge slope in terms of magnitude of voltage rise. However, in many embodiments, the upper portion will have substantially the same length as the lower portion, and the edges of the voltage drop and voltage rise will have substantially the same slope in magnitude. In these cases, the voltage signal is symmetrical to ground.

[0020] The edge slope can be constant over the rise or fall time, so that the test signal has a trapezoidal signal path. However, the edge slope can also vary over the rise or fall time, for example, starting with a slope that is low in magnitude, then increasing and reaching its maximum in the zero-crossing region of the voltage signal, in order to then become lower again. This results in a trapezoidal signal path with smooth transitions between the substantially constant plateau portions and the edges.

[0021] According to additional embodiments, the time at which an edge of the test signal begins is adjusted or initiated depending on a comparison of a current generated by the test signal through the transformer with a threshold value. As described above, the test signal may be periodic, with a substantially constant upper portion and a substantially constant lower portion. An edge of the test signal begins when, for example, a voltage decreases from the substantially higher (positive) voltage value or a voltage increases from the substantially lower voltage value. In a transformer test, for example, the substantially lower voltage Petition 870250080337, dated 09 / 08 / 2025, p. 15 / 59 9 / 26 constant in the upper portion causes a (positive) current through a transformer winding to increase due to the inductance of that winding. The current through the winding can be measured, and when the current reaches the threshold value, a voltage drop can be initiated at the previously determined edge slope. However, as long as the voltage is still positive during the falling edge, the current through the winding continues to increase. The current through the winding is reduced only after the voltage passes through zero. The voltage reaches the lower (negative) voltage value and then remains substantially constant. The (positive) current is further reduced, becomes zero, and then flows in the opposite direction (negative current) through the winding and increases in magnitude, while the voltage value remains substantially constant at the lower voltage value.As soon as the (negative) current through the winding reaches the threshold value in terms of magnitude, the rising edge begins. As long as the voltage remains negative during the rising edge, the (negative) current continues to increase in magnitude. Only when the rising edge reaches zero crossing and a positive voltage is again applied to the transformer does the (negative) current decrease in magnitude. While the voltage has a substantially constant upper (positive) voltage value, the (negative) current initially drops to zero in terms of magnitude and then rises again in the opposite direction (positive current) in terms of magnitude until it reaches the threshold value. Then the cycle described above begins again.

[0022] As described above, the current initially continues to increase in magnitude even with the onset of edges, since the edges do not have infinite slope and the voltage therefore remains positive (with a falling edge) or negative (with an edge as Petition 870250080337, dated 09 / 08 / 2025, p. 16 / 59 10 / 26 ascending) until zero crossing. Instead, the edge slope is relatively low, so high-frequency components are not included in order to avoid current spikes due to parasitic capacitances. The additional current increase even after the edge starts is therefore inevitable and must be taken into account so as not to exceed a desired maximum current. For example, to avoid overloading the test device. The threshold value at which the edges are initiated can then be defined as a value of a maximum rated current of the test device that provides the test signal, for example, for a value in the range of 70 to 95% of the rated current, for example, for 90% of the rated current, or depending on an expected additional increase in inductive current, which, however, in turn, depends on the defined edge slope.

[0023] For example, the threshold value can be dynamically adjusted depending on the observation of the actual current through the transformer. For example, the threshold value can be determined as a function of the slope of the edge of the test signal, a voltage swing of the test signal, and an absolute current rise generated by the test signal through the transformer. The voltage swing of the test signal is, for example, the voltage distance between the upper and lower voltage values ​​in the case of a periodic test signal. Assuming, for example, that the slope of the edge is constant, that is, that the voltage drop per unit time is constant from the beginning to the end of the edge, the time from the beginning of the edge to the zero crossing of the voltage can be determined in a simple way.Even if the edge does not have a constant edge slope, the time from the beginning of the edge until the voltage crosses zero can be determined, once the edge shape is determined and adjusted. During this time, as discussed above, the current... Petition 870250080337, dated 08 / 09 / 2025, page 17 / 59 11 / 26 through the transformer continues to increase at least due to the inductance of the transformer winding. In addition, the current through parasitic capacitances may increase. The increase in current flowing through the transformer can be measured, for example, by continuously measuring the current during the transformer test and determining the corresponding change in current, i.e., change in current per unit time. Continuously may mean, for example, that the current is measured continuously at short time intervals of, for example, 1 μs, and the change in current is determined from the change in current per microsecond. The maximum time period during which the current can continue to increase results from the time from the beginning of the edge to the zero crossing of the voltage.An estimate of the additional voltage increase achievable during this time can be made, for example, by multiplying the last current increase determined by this time from the beginning of the edge to the voltage crossing by zero. Based on this estimate, the threshold value can be defined so that the current does not exceed a desired maximum value, for example, the maximum rated current of the test device. In other words, the threshold value can be determined as a difference between an amount of a desired maximum current generated by the test signal through the transformer and the product of the actual current increase and the polarity reversal time of the test signal. The polarity reversal time depends on the voltage oscillation of the test signal and the slope of the edge.

[0024] An additional reserve of, for example, 10% of the maximum current can be provided for additional current due to parasitic capacitances. However, this reserve can be kept relatively small, since, due to the purposefully adjusted edge slopes, the additional current due to the capacitances Petition 870250080337, dated 08 / 09 / 2025, page 18 / 59 The 12 / 26 parasitic current is relatively small compared to the corresponding current peaks due to the edge slopes obtained by simply switching the test signal between the upper and lower voltage values.

[0025] According to one embodiment, the test may comprise determining a transformer magnetization curve as a function of the periodic voltage signal and a time course of a current generated by the voltage signal through the transformer.

[0026] According to the present invention, a device for testing a transformer is further provided, that is, a test device. The device comprises a test signal source for generating a test signal for the transformer and a processing device coupled to the test signal source. The processing device is configured to determine an edge slope for the test signal as a function of the transformer to be tested, to generate the test signal with the edge slope then determined by means of the test signal source, and to test the transformer using the generated test signal. The device is therefore suitable for carrying out the method described above and thus also comprises the advantages described above.

[0027] The features of the embodiments and aspects of the invention described above may be combined arbitrarily with one another, unless expressly stated otherwise. In particular, the features may be used not only in the combinations described, but also in other combinations or independently. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be described in detail below with reference to the accompanying figures.

[0029] Figure 1 shows schematically a device for Petition 870250080337, dated 08 / 09 / 2025, page 19 / 59 13 / 26 test of a transformer according to an embodiment of the present invention in conjunction with a transformer.

[0030] Figure 2 schematically shows the method steps of a method for testing a transformer according to an embodiment of the present invention.

[0031] Figure 3 schematically shows a test signal source according to an embodiment of the present invention.

[0032] Figure 4 schematically shows a test signal source according to another embodiment of the present invention.

[0033] Figure 5 schematically shows yet another test signal source according to yet another embodiment of the present invention.

[0034] Figure 6 schematically shows a voltage path of a test signal fed into a transformer and an associated current path.

[0035] Figure 7 schematically shows a voltage path of a test signal fed into a transformer, with an edge slope determined according to an embodiment of the present invention, and an associated current path.

[0036] Figure 8 schematically shows the steps of the method for determining the slope of an edge according to an embodiment of the present invention.

[0037] Figure 9 schematically shows the determination of a threshold value from a current course used to determine the moment at which an edge of the test signal begins. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0038] The properties, characteristics and advantages of the present invention described above, as well as the manner in which they are achieved, will become clearer and more understandable in connection with the following description of exemplary embodiments, which will be explained in Petition 870250080337, dated 08 / 09 / 2025, page 20 / 59 14 / 26 more details in connection with the drawings.

[0039] The invention will now be specified in greater detail in the context of embodiments, with reference to the drawings. In the figures, the same reference numbers designate the same or similar elements. The figures are schematic representations of various embodiments of the invention. The elements illustrated in the figures are not necessarily represented to scale. The various elements illustrated in the figures are reproduced in such a way that their function and general purpose are understandable to one skilled in the art. Connections and couplings between functional units and elements illustrated in the figures can also be implemented as an indirect connection or coupling. The functional units can be implemented as hardware, software, or a combination of hardware and software.

[0040] FIG. 1 shows a transformer 180 in conjunction with a device 100 for testing the transformer 180. The transformer 180 may be, for example, a current transformer, which is provided in an electrical power engineering system. The device 100 may be coupled to a secondary side of the transformer 180, for example. The device 100 may comprise, for example, a portable test device that is carried to the transformer 180 to test it and is coupled to the transformer 180 via lines 150 and 152. In this context, the transformer to be tested is also referred to as the device under test (DUT).

[0041] Device 100 comprises a test signal source 102 and a processing device 104. The processing device 104 may comprise, for example, a microprocessor controller comprising working memory, mass storage for program code and data, and input / output devices. In addition, device 100 may comprise a Petition 870250080337, dated 08 / 09 / 2025, page 21 / 59 15 / 26 user interface 106 and a current measuring device 108. The user interface 106 may include, for example, an optionally touch-sensitive screen, a keyboard or keys, a speaker, indicator lights and the like. The current measuring device 108 may be provided, for example, on or over a line to the transformer 180, for example, on line 152, in order to measure a current flowing through the transformer 180, current flowing based on a voltage generated by the test signal source 102. The current measuring device 108 may comprise an analog / digital converter that determines the current intensity at a predetermined sampling frequency and provides it as a corresponding digital value to the processing device 104.The test signal source 102, the user interface 106, and the current measuring device 108 are coupled to and controlled by the processing device 104 and / or provide measurements and other information to the processing device 104, such as user inputs. The device 100 may comprise additional components, for example, a power supply device to provide electrical power to the components described above, as well as additional measuring devices to measure current, voltage, or power on lines 150 and 152. The device 100, in particular the processing device 104, may be configured to perform the methods and techniques described below. The device 100 may also be configured to perform additional tests on other devices under test, for example, high-voltage switches, electrical bushings, or electrical lines.

[0042] When testing a transformer, it may be necessary to supply test signals to the transformer that do not correspond to the nominal signals. For example, these test signals may have frequencies lower or higher than the nominal frequency of the transformer. As a result, properties of the transformer can be tested, which Petition 870250080337, dated 08 / 09 / 2025, page 22 / 59 16 / 26 cannot be tested at the nominal frequency or can only be tested with great effort, for example, saturation magnetization. Possible test signals are sinusoidal signals and, in particular, for determining saturation magnetization, also rectangular signals, which, however, also contain very high frequency components. A test signal can be, for example, a voltage signal. As a reaction, a current flows, whose time course, i.e., the current intensity as a function of time, can be obtained by means of the current measuring device 108. A model can be used to calculate back to the corresponding nominal values ​​from the test signal results. The use of rectangular signals is particularly necessary to obtain a correspondingly large magnetic flux in the magnetic core.However, the steep slopes of the rectangular signal edges lead to large capacitive current peaks along with structure-related parasitic capacitances. Parasitic capacitances can arise, for example, from connections and connecting lines, as well as from the transformer structure itself. Large current peaks can overload the test signal source 102 and / or affect measurement accuracy.

[0043] Therefore, the test signal source 102 generates a test signal in which the high-frequency components are reduced compared to a switched rectangular signal, i.e., a test signal with defined ascending and descending edges. For example, instead of a simple rectangular signal, a combination of triangular and rectangular signals can be generated, i.e., a test signal with a trapezoidal shape. In order, however, to have as long as possible portions with a constant voltage in the test signal, for example, to obtain saturation magnetization and, moreover, to be able to provide high-frequency components in the test signal, which po Petition 870250080337, dated 08 / 09 / 2025, page 23 / 59 17 / 26 can be used, for example, by the model to determine transformer properties, a method 200, as shown in FIG. 2, is performed, for example, under the control of processing device 104.

[0044] In method 200, in step 202, an edge slope for the test signal is determined as a function of the transformer 180 to be tested, and in step 204, the test signal with the determined edge slope is generated by means of the test signal source 102. The transformer 180 is then tested using the test signal generated in step 206. The objective is to determine the edge slope for the test signal so that long portions with constant voltage and high frequency components are included in the test signal, but without overloading the test signal source 102 due to capacitive current peaks and impairing the accuracy of the measurement.

[0045] Technically, the test signal with adjustable edge slope can be obtained using one or more voltage sources having an adjustable output voltage. In a conventional generation of a rectangular signal, for example, two DC voltage sources with a fixed output voltage can be used. One of the DC voltage sources has, for example, a grounded positive output voltage and the other DC voltage source has a grounded negative output voltage. In terms of magnitude, the two output voltages can be equal. For example, one or two switching devices connect the DC voltage source to the positive output voltage or the DC voltage source to the negative output voltage to one terminal of a transformer winding, while the other terminal of the transformer winding is connected to ground. However, it is not possible here to adjust the edge slope.

[0046] The test signal with adjustable edge slope can be generated, for example, by using and triggering at least one converter. Petition 870250080337, dated 08 / 09 / 2025, page 24 / 59 18 / 26 Adjustable voltage converter. The voltage converter can be, for example, a direct current voltage converter, the so-called DC / DC converter. The adjustable voltage converter can be selectively adjustable to one of a plurality of voltage values, for example, to a voltage between zero volts and 25 V or 50 V with an accuracy of 1 V or 0.1 V, for example, under the control of the processing device 104. For example, the voltage converter may comprise a synchronized or linear DC amplifier (DC-DC amplifier) ​​that can generate positive and / or negative output voltages. The converter or voltage amplifier is capable of supplying the required voltages and currents with the required dynamics.

[0047] FIG. 3 schematically shows an example of an embodiment of the test signal source 102. In this example, the test signal source 102 comprises two adjustable voltage converters 302, 304 and two switches 306, 308. The switches 306, 308 can be mechanical or electronic switches, controllable by means of the control device 104. The voltage converter 302 is configured, for example, to provide an output voltage Ui, which is negative with respect to a ground line 310 and can be adjusted in magnitude to a plurality of values ​​between zero and a maximum voltage Umax. Umax can be in a range of 10 V to 100 V, for example. For example, Umax can be 25 V. The voltage converter 304 is configured, for example, to provide an output voltage U2, which is positive with respect to the ground line 310 and can be adjusted in magnitude to a plurality of values ​​between zero and Umax.The output voltages of voltage converters 302 and 304 can be adjusted by control device 104. By means of switches 306 and 308, the output voltage of voltage converter 302 or the output voltage of voltage converter 304 can be selectively connected to line 312. By properly operating the converters... Petition 870250080337, dated 08 / 09 / 2025, page 25 / 59 19 / 26 voltage sources 302 and 304 and switches 306 and 308, an alternating voltage in the range of -Umax to +Umax can be supplied on lines 310 and 312, which can be used to test transformer 180, as shown in Figure 1. For example, a periodic trapezoidal AC voltage can be supplied. A fundamental frequency of this periodic alternating voltage can, for example, correspond to a nominal frequency of transformer 180, for example, 50 Hz or 60 Hz. It is understood that the fundamental frequency can have any other value above or below the nominal frequency of the transformer, for example, 30 Hz or 100 Hz.Within a period, alternating voltage may have, for example, the following voltage course: (1) a voltage increase with a desired edge slope from a lower voltage value, for example -Umax, to a higher voltage value, for example +Umax; (2) an upper portion with substantially constant voltage at the higher voltage value; (3) a voltage drop from the higher voltage value to the lower voltage value with a desired edge slope; and (4) a lower portion with substantially constant voltage at the lower voltage value. It is clear that the lower voltage value and the upper voltage value may differ in magnitude. Similarly, it is clear that the edge slope from the lower voltage value to the higher voltage value may differ from the edge slope from the higher voltage value to the lower voltage value.In many examples, however, the lower voltage value is equal in magnitude to the higher voltage value, and the slope of the rising voltage edge is equal in magnitude to the slope of the falling voltage edge. In the case of a voltage swing between the higher and lower voltage values ​​of, for example, 50 V, the desired edge slope might be, for example, 50 V over 28 μs. A period of an exemplary test signal at 50 Hz is 20 ms, so the lower and upper portions... Petition 870250080337, dated 08 / 09 / 2025, page 26 / 59 20 / 26 are each slightly under 10 ms long (exactly 9.972 ms).

[0048] FIG. 4 schematically shows a further example of an embodiment of the test signal source 102. In this example, the test signal source comprises two adjustable voltage converters 402 and 404. The adjustable voltage converter 402 is configured to provide an adjustable output voltage Ui on line 408 which is positive with respect to a connecting line 406 that connects the two adjustable voltage converters 402 and 404 and is adjustable in magnitude to a plurality of values ​​between zero and Umax. The adjustable voltage converter 404 is configured to provide an adjustable output voltage U2 on line 410, which is also positive with respect to the connecting line 406 and is adjustable in magnitude to a plurality of values ​​between zero and Umax.By properly activating voltage converters 402 and 404 via control device 104, an alternating voltage with a voltage swing of 2xUmax and adjustable edge slope can be generated on lines 408 and 410.

[0049] FIG. 5 schematically shows yet another example of an embodiment of the test signal source 102. In this example, the test signal source comprises an adjustable voltage converter 502 and a fixed voltage source 504. The adjustable voltage converter 502 is configured to provide, by actuation via the control device 104, an adjustable output voltage Ui on line 508, which is positive with respect to a connecting line 506 that connects the voltage converter 502 to the fixed voltage source 504 and is adjustable in magnitude to a plurality of values ​​between zero and 2xUmax. The fixed voltage source 504 is configured to provide a fixed output voltage U2 on line 510, which is also positive with respect to the connecting line 506 and has the value Umax, for example. When actuated Petition 870250080337, dated 08 / 09 / 2025, page 27 / 59 21 / 26 properly tune the 502 voltage converter, an alternating voltage with a voltage swing of 2xUmax and adjustable edge slope can be generated on lines 508 and 510.

[0050] Figures 6 and 7 show, schematically and as an example, the signal paths 602 and 702 of an output voltage from the test signal source 102, as can be generated in the test signal source 102 by means of the appropriate drive of the voltage converters described above. Figures 6 and 7 each show, at the top, the path of the output voltage signal 602 and 702 and, at the bottom, a respective path of the signal 604 and 704 of a current through the transformer 180 connected to the test signal source 102. The path of the signal 604 and 704 of the current through the transformer 180 can be measured, for example, by means of the current measuring device 108 (see Figure 1). The output voltage can, for example, have a voltage swing of 50 V, that is, the upper voltage level is, for example, +25 V and the lower voltage level is, for example, -25 V. In the example, the ohmic resistance of the 180 transformer is 220 mΩ and the inductance is 0.5 H.The frequency of the output voltage is substantially 50 Hz. Without taking into account the capacitive current peaks described below, the inductive current between the signal edges, that is, during the upper and lower signal portions with a substantially constant voltage, increases in magnitude to, for example, approximately 250 mA.

[0051] The signal path 602 of the output voltage shown in FIG. 6 has very steep signal edges. The voltage swing illustrated in FIG. 6 can be 50 V, for example, and the edge slope can be 25 V / μs or more, for example, 50 V / μs. Due to parasitic capacitances, which can be generated, for example, by the transformer lines and terminals, as well as by the transformer structure itself, very high currents 606, the so-called pi Petition 870250080337, dated 08 / 09 / 2025, page 28 / 59 22 / 26 current spikes occur during the signal edge, as shown in the lower part of FIG. 6. These high currents are caused by high-frequency components of the very steep signal edges, which allow for high capacitive currents. The amount of these current spikes can be substantially greater than the amount of inductive current, for example, 500 mA, 1000 mA or more.

[0052] The output voltage signal path 702 shown in Figure 7 has less steep signal edges. In the case of a voltage swing of, for example, 50 V, the edge slope can be, for example, 50 V / 20 ps or lower, for example, 50 V / 28 ps. As can be seen from the corresponding current signal path 704 shown in Figure 7, significantly lower current peaks 706 occur at this lower edge slope, since the signal edges now have significantly smaller amplitudes in the high-frequency components. The capacitive current peaks 706 become correspondingly smaller, for example, only 50 mA or 100 mA.

[0053] An lc current from a capacitive current peak depends on the parasitic capacitance C of the 180 transformer as follows: = (Equation 1)

[0054] In practice, parasitic capacitance values ​​often occur in the range of 100 pF to 30 nF, but are not limited to this range and therefore can be much larger or smaller, for example, 3 pF. Therefore, the slope of the edge to be used is determined and defined according to the transformer currently being tested. Several procedures for this are described below.

[0055] In a procedure for determining edge slope, the parasitic capacitance of the transformer is first determined. For this purpose, for example, the parasitic capacitance can be measured by means of a high-frequency measurement on the transformer. Petition 870250080337, dated 08 / 09 / 2025, page 29 / 59 23 / 26 High-frequency measurement can be performed at a voltage lower than the subsequent test voltage, for example, to ensure that device 100 is not overloaded. Parasitic capacitance can also be provided by user input via the user interface 106. For example, the user can directly enter the parasitic capacitance from transformer information, or the user can enter a transformer type, and the parasitic capacitance can be determined from a database based on the transformer type, for example. The edge slope can then be determined as a function of the parasitic capacitance and a predetermined maximum capacitive current, which must not be exceeded during the transformer test.The maximum capacitive current can be determined, for example, from a maximum rated current of the test signal source 102 and a maximum inductive current that occurs during the transformer measurement, for example, as the difference between these two currents. The slope of the edge du / dt can then be determined from equation 1 above.

[0056] Another procedure for determining the edge slope is described in conjunction with method 800 shown in FIG. 8. Firstly, in step 802, the edge slope is defined as a low initial slope. The low initial slope can, for example, be so low that it does not lead to an overload of the test signal source 102 and does not impair the measurement results, even in the case of transformers with a very high parasitic capacitance (e.g., 3 μF). If, for example, the capacitive current must remain below 100 mA, the low initial slope according to equation (1) can be defined as 50 V / 1500 μs, for example, so that the test signal source is not overloaded even with a parasitic capacitance of 3 μF. With this edge slope Petition 870250080337, dated 08 / 09 / 2025, page 30 / 59 24 / 26 of the time, a preliminary test signal is generated (step 804) and the maximum occurrence current is determined in step 806. If the maximum occurrence current is less than the maximum permissible current, for example, less than the rated current of the test signal source 102 (step 808), the preliminary edge slope can be increased in step 810, for example, by a certain value or percentage. The method is continued repeatedly with the new preliminary edge slope in step 804. If the maximum permissible current is reached in step 808, the edge slope to be used to test transformer 180 can be determined in step 812; for example, the edge slope at which the maximum permissible current has not yet been reached can be used.

[0057] As described above, the test signal can be a periodic signal. A frequency can be predetermined, for example, through test conditions; for example, the test signal can have the nominal frequency of the transformer or a multiple thereof as the fundamental frequency. The fundamental frequency of the test signal can also be less than the nominal frequency of the transformer. However, particularly when measuring the magnetization curve of the transformer, it may be necessary to supply the highest possible current in order to generate the highest possible magnetic flux in the transformer. Once this high current is reached, the polarity of the applied voltage signal must be reversed to generate the highest possible current and therefore the highest magnetic flux in the transformer in the opposite direction. This process can be repeated several times one after the other during the recording of the magnetization curve.For this purpose, a comparator can be provided which, for example, using software in the processing device 104, compares the actual current of the current measuring device 108 with a threshold current, which corresponds, for example, to the nominal current of the fon. Petition 870250080337, dated 09 / 08 / 2025, p. 31 / 59 25 / 26 test signal 102. Due to the reduced edge slope, however, polarity reversal is delayed because a certain time elapses during the falling or rising edge until the voltage reaches zero crossing and reduces the inductive current flow and consequently the magnetic flux, so that the current may exceed the threshold current. To avoid this, the threshold current range can be predicted as follows.

[0058] Figure 9 shows, by way of example, a non-linear current path 902 over time, flowing as an inductive current through a winding of transformer 180 due to the voltage applied to transformer 180. The path of current 902 is more non-linear because they are generally saturation inductances. The value of the inductance is therefore unknown and dependent on the current. Thus, the slope of the path of current 902 is also unknown. Therefore, a continuous determination of the slope of the path of current 902 is performed. For example, the current can be sampled at successive points in time (e.g., on the vertical dashed lines shown in FIG. 9) and thus an Ai / At of the current path can be determined continuously in real time. A delay td between the start of an edge and the zero crossing can be determined due to the slope of the edge from the voltage oscillation and the defined edge slope.Starting from the desired maximum current Ithr, a corrected maximum current lthr_corr can be determined from the actual slope of the current Ai / At as follows: ^thr_korr (equation 2)

[0059] As soon as the measured current reaches the corrected maximum current lthr_corr, the polarity reversal process is initiated with the determined edge slope, so that the maximum current Ithr is not exceeded.

[0060] Certainly the characteristics of the modalities and aspects Petition 870250080337, dated 09 / 08 / 2025, p. 32 / 59 Features 26 / 26 of the invention described above can be combined with each other. In particular, the features can be used not only in the combinations described, but also in other combinations or independently, without departing from the scope of the invention. Petition 870250080337, dated 09 / 08 / 2025, p. 33 / 59

Claims

1 / 8 CLAIMS 1. Method for testing a transformer, characterized in that it comprises: - determining (202) the edge slope for a test signal (702) as a function of the transformer (180) to be tested, - generating (204) the test signal (702) with the determined edge slope, and - testing (206) the transformer (180) using the generated test signal (702), wherein the determination of the edge slope comprises: - determining the parasitic capacitance of the transformer (180), - determining the edge slope as a function of the parasitic capacitance and a predetermined maximum capacitive current that may occur during the test of the transformer (180).

2. Method according to claim 1, characterized in that the determination of parasitic capacitance comprises: - measuring the parasitic capacitance by means of a high frequency measurement on the transformer (180), and / or - acquiring an input of the parasitic capacitance from a user.

3. Method according to any of the preceding claims, characterized in that the test signal (702) is a periodic test signal, wherein the determination of the edge slope comprises an iterative method (800), in which, based on an edge slope in a period of the test signal, a subsequent edge slope for a subsequent period of the test signal (702) is determined as a function of a maximum measured current generated during the test of the transformer (180) with the test signal.

4. Method according to any of the preceding claims, characterized in that the time at which a test signal edge (702) begins is adjusted as a function of a comparison of a current generated by the test signal (702) through the transformer (180) with a threshold value (Ithr_corr).

5. Method according to claim 4, characterized in that the amount of the threshold value (Ithr_corr) is less than the amount of a maximum rated current of a device (100) that provides the test signal (702).

6. Method according to claim 4 or 5, characterized in that the test signal (702) comprises a voltage signal, and the threshold value (Ithr_corr) is determined as a function of the edge slope of the test signal (702), of a voltage oscillation of the test signal (702) and of an absolute current rise (Δi / Δt) of a current generated by the test signal (702) through the transformer (180).

7. Method according to claim 6, characterized in that the current rise (Δi / Δt) of the current generated by the test signal (702) is determined continuously during the test of the transformer (180).

8. Method according to claim 7, characterized in that the threshold value (Ithr_corr) is determined as a difference between a quantity of a desired maximum current (Ithr) generated by the test signal through the transformer (180) and a product of the actual current rise (Δi / Δt) and a polarity reversal time (td) of the test signal (702) that depends on the voltage oscillation of the test signal and the edge slope.

9. Method according to any of the preceding claims, characterized in that the test signal (702) Petition 870250080337, dated 08 / 09 / 2025, page 47 / 59 3 / 8 is a periodic voltage signal.

10. Method according to claim 9, characterized in that the periodic voltage signal comprises: - a voltage increase with a determined edge slope from a lower voltage value to an upper voltage value, - an upper portion with substantially constant voltage at the upper voltage value, - a voltage drop from the upper voltage value to the lower voltage value, and - a lower portion with substantially constant voltage at the lower voltage value.

11. Method according to claim 10, characterized in that the voltage drop has an edge slope that is equal in magnitude to the edge slope of the voltage rise.

12. Method according to any of the preceding claims, characterized in that the test (206) of the transformer (180) comprises determining a magnetization curve of the transformer (180) as a function of the test signal (702) and a time course (704) of a current generated by the test signal through the transformer (180).

13. Method according to any of the preceding claims, characterized in that the generation (204) of the test signal (702) comprises driving at least one adjustable voltage converter (302, 304, 402, 404, 502).

14. Method for testing a transformer, characterized in that it comprises: - determining (202) an edge slope for a test signal (702) as a function of the transformer (180) to be tested, Petition 870250080337, dated 08 / 09 / 2025, page 48 / 59 4 / 8 - generating (204) the test signal (702) with the determined edge slope, and - testing (206) the transformer (180) using the generated test signal (702), wherein the test signal (702) is a periodic test signal, wherein the determination of the edge slope comprises an iterative method (800), in which, based on the edge slope in one period of the test signal, a subsequent edge slope for a subsequent period of the test signal (702) is determined as a function of a maximum measured current generated during testing of the transformer (180) with the test signal.

15. Method according to claim 14, characterized in that determining the edge slope comprises: - determining a parasitic capacitance of the transformer (180), - determining the edge slope as a function of the parasitic capacitance and a predetermined maximum capacitive current that can occur during testing of the transformer (180).

16. Method according to claim 15, characterized in that determining the parasitic capacitance comprises: - measuring the parasitic capacitance by means of a high-frequency measurement on the transformer (180), and / or - acquiring a parasitic capacitance input from a user.

17. Method according to any of the preceding claims, characterized in that a time at which an edge of the test signal (702) begins is set as a function of a comparison of a current generated by the test signal (702) through the transformer (180) with a threshold value (Ithr_corr). Petition 870250080337, dated 09 / 08 / 2025, p. 49 / 59 5 / 8 18. Method according to claim 17, characterized in that the amount of the threshold value (Ithr_corr) is less than an amount of the maximum rated current of a device (100) that provides the test signal (702).

19. Method according to claim 17 or 18, characterized in that the test signal (702) comprises a voltage signal, and the threshold value (Ithr_corr) is determined as a function of the edge slope of the test signal (702), of a voltage oscillation of the test signal (702) and of an absolute current rise (Δi / Δt) of a current generated by the test signal (702) through the transformer (180).

20. Method according to claim 19, characterized in that the current rise (Δi / Δt) of the current generated by the test signal (702) is determined continuously during the transformer test (180).

21. Method according to claim 20, characterized in that the threshold value (Ithr_corr) is determined as a difference between a quantity of a desired maximum current (Ithr) generated by the test signal through the transformer (180) and a product of the actual current rise (Δi / Δt) and a polarity reversal time (td) of the test signal (702) that depends on the voltage oscillation of the test signal and the edge slope.

22. Method according to any of the preceding claims, characterized in that the test signal (702) is a periodic voltage signal.

23. Method according to claim 22, characterized in that the periodic voltage signal comprises: - a voltage increase with a determined edge slope from a lower voltage value to an upper voltage value, - an upper portion with substantially constant voltage at the upper voltage value, - a voltage drop from the upper voltage value to the lower voltage value, and - a lower portion with substantially constant voltage at the lower voltage value.

24. Method according to claim 23, characterized in that the voltage drop has an edge slope that is equal in magnitude to the edge slope of the voltage rise.

25. Method according to any of the preceding claims, characterized in that the test (206) of the transformer (180) comprises determining a magnetization curve of the transformer (180) as a function of the test signal (702) and a time course (704) of a current generated by the test signal through the transformer (180).

26. Method according to any of the preceding claims, characterized in that the generation (204) of the test signal (702) comprises driving at least one adjustable voltage converter (302, 304, 402, 404, 502).

27. Device for testing a transformer, characterized in that it comprises: - a test signal source (102) for generating (204) a test signal (702) for the transformer (180), - a processing device (104) coupled to the test signal source (102) and configured to determine (202) an edge slope for the test signal (702) as a function of the transformer (180) to be tested, to generate (204) the test signal (702) with the slope of Petition 870250080337, dated 08 / 09 / 2025, page. 51 / 59 7 / 8 edge determined by means of the test signal source (102), and to test (206) the transformer (180) using the generated test signal (702), wherein the determination of the edge slope comprises: - determining a parasitic capacitance of the transformer (180), - determining the edge slope as a function of the parasitic capacitance and a predetermined maximum capacitive current that may occur during testing of the transformer (180).

28. Device according to claim 27, characterized in that the device (100) is configured to perform the method (200) as defined in any of claims 1 to 13.

29. Device for testing a transformer, characterized in that it comprises: - a test signal source (102) for generating (204) a test signal (702) for the transformer (180), - a processing device (104) coupled to the test signal source (102) and configured to determine (202) an edge slope for the test signal (702) as a function of the transformer (180) to be tested, to generate (204) the test signal (702) with the edge slope determined by means of the test signal source (102), and to test (206) the transformer (180) using the generated test signal (702), wherein the test signal (702) is a periodic test signal, wherein the determination of the edge slope comprises an iterative method (800), in which, based on the edge slope in a period of the test signal, a subsequent edge slope for a Petition 870250080337, dated 08 / 09 / 2025, page.52 / 59 8 / 8 subsequent period of the test signal (702) is determined as a function of a maximum measured current generated during the transformer test (180) with the test signal.

30. Device according to claim 29, characterized in that the device (100) is configured to perform the method (200) as defined in any of claims 14 to 26. Petition 870250080337, dated 08 / 09 / 2025, pp. 53 / 59

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