Transformer iron core electromagnetic vulnerability evaluation device

Abstract

The invention discloses a transformer core electromagnetic vulnerability evaluation device, which belongs to the technical field of transformer core evaluation, and comprises a to-be-tested transformer, an alternating current transformer, a pulse current source, a multi-channel digital oscilloscope and an upper computer, the alternating current transformer is used for providing power frequency current for the to-be-tested transformer; the pulse current source is used for providing direct current pulse current for the transformer to be tested; the multi-channel digital oscilloscope is used for measuring a current signal of a primary side and a voltage signal of a secondary side of the transformer to be measured; the upper computer is used for calculating a winding inductance value of the transformer to be tested in a saturated state, analyzing electromagnetic vulnerability characteristics of the iron core of the transformer to be tested under the electromagnetic action, and then obtaining an electromagnetic vulnerability evaluation result corresponding to the iron core of the transformer to be tested. The problem that the electromagnetic vulnerability of the transformer iron core cannot be evaluated in the prior art can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer core evaluation, and in particular to a transformer core electromagnetic vulnerability evaluation device. Background Art

[0002] Strong geomagnetic activity, accompanied by the formation of strong geomagnetic induced currents, can affect power system operations. Extreme geomagnetic induced currents primarily originate from extreme geomagnetic storms and high-altitude strong electromagnetic pulse (EMP) environments. Extreme geomagnetic storms, such as solar storms, induce large numbers of high-speed charged particles. When these particles travel toward Earth, they collide with the Earth's magnetic field, generating geomagnetic shock waves that significantly impact Earth's space environment. Extreme geomagnetic induced currents have a very low frequency. When these quasi-DC currents flow into transformers, they generate a DC bias flux in the magnetic circuit. Due to the nonlinearity of the core material, this flux causes the transformer core to saturate at half-wave speeds. This causes a sharp increase in the transformer's excitation current and severe waveform distortion. This not only adversely affects the transformer itself but also interferes with the normal operation of other power grid equipment and may even threaten the safety of the entire power system. Transformers are crucial components of power systems, responsible for the transmission and conversion of electrical energy. The transformer core, a crucial component of the transformer, provides the magnetic circuit for electromagnetic conversion, enabling the coupling of electrical and magnetic energies. The core winding of a transformer in actual operation is a typical nonlinear component. When a DC bias current appears in the winding, it will cause core saturation, further causing transformer excitation current distortion, increased spatial leakage magnetic flux, and temperature rise of structural components, affecting the normal operation of the power system and even causing permanent damage to the transformer, seriously affecting power supply reliability.

[0003] However, due to the sealing requirements of the power transformer oil tank, disassembly testing cannot be carried out. It is difficult to directly establish a finite element model of the internal core structure of the transformer, and it is impossible to evaluate the DC bias magnetic effect of the transformer and the electromagnetic vulnerability of the transformer core. Summary of the Invention

[0004] The present invention provides a transformer core electromagnetic vulnerability assessment device, which can solve the problem in the prior art that the transformer core cannot be assessed for electromagnetic vulnerability.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a transformer core electromagnetic vulnerability assessment device, comprising: a transformer to be tested, an AC current transformer, a pulse current source, a multi-channel digital oscilloscope and a host computer;

[0006] The AC current transformer is connected in series with the pulse current source and then connected to the primary side of the transformer to be tested; the secondary side of the transformer to be tested is unloaded;

[0007] The two input channels of the multi-channel digital oscilloscope are respectively connected to the primary side and the secondary side of the transformer to be tested; the multi-channel digital oscilloscope is connected to the host computer through a preset communication interface;

[0008] The AC current transformer is used to provide power frequency current to the transformer to be tested;

[0009] The pulse current source is used to provide a DC pulse current to the transformer to be tested;

[0010] The multi-channel digital oscilloscope is used to measure the current signal on the primary side of the transformer under test and the voltage signal on the secondary side of the transformer under test, and transmit the current signal and voltage signal to the host computer;

[0011] The host computer is configured to calculate the winding inductance of the transformer under test in a saturated state based on the current signal and the voltage signal, and obtain an electromagnetic vulnerability characteristic of the iron core of the transformer under test under electromagnetic action based on the winding inductance analysis, and then obtain an electromagnetic vulnerability assessment result corresponding to the iron core of the transformer under test based on the electromagnetic vulnerability characteristic.

[0012] As a preferred solution, the transformer core electromagnetic vulnerability assessment device further includes: a voltage regulator;

[0013] The primary side of the voltage regulator is connected to the power distribution network, and the secondary side of the voltage regulator is connected to the AC current transformer;

[0014] The voltage regulator is used to provide a corresponding amplitude voltage to the AC current transformer.

[0015] As a preferred solution, the transformer core electromagnetic vulnerability assessment device further includes: an adjustable current limiting resistor;

[0016] The adjustable current limiting resistor is connected in series with the pulse current source;

[0017] The adjustable current-limiting resistor is used to limit the DC pulse current to within the safe current range of the transformer to be tested and the pulse current source.

[0018] As a preferred solution, the resistance value of the adjustable current limiting resistor is calculated according to the following formula:

[0019] R = τ / C;

[0020] Wherein, R is the resistance value of the adjustable current limiting resistor; τ is the time constant of the DC pulse current; and C is the equivalent capacitance of the pulse current source.

[0021] As a preferred solution, the transformer core electromagnetic vulnerability assessment device further includes: a filter capacitor;

[0022] The pulse current source is connected in series with the adjustable current limiting resistor and then connected in parallel with the filter capacitor;

[0023] The filter capacitor is used to filter the high-frequency harmonics in the pulse current source.

[0024] As a preferred solution, the transformer core electromagnetic vulnerability assessment device further includes: a fluxgate current sensor;

[0025] The multi-channel digital oscilloscope is connected to the primary side of the transformer to be tested through the fluxgate current sensor;

[0026] The fluxgate current sensor is used to measure the current signal on the primary side of the transformer to be tested.

[0027] As a preferred solution, the transformer core electromagnetic vulnerability assessment device further includes: a differential voltage probe;

[0028] The multi-channel digital oscilloscope is connected to the secondary side of the transformer to be tested via the differential voltage probe;

[0029] The differential voltage probe is used to measure the voltage signal on the secondary side of the transformer to be tested.

[0030] As a preferred solution, calculating the winding inductance value of the transformer to be tested in a saturated state according to the current signal and the voltage signal includes:

[0031] Performing a fast Fourier transform on the current signal and the voltage signal to obtain a voltage fundamental wave, a current fundamental wave, and a current DC component of the transformer under test in each fundamental wave cycle;

[0032] The winding inductance value of the transformer to be tested under the DC component of the current in each fundamental wave period is calculated based on the voltage fundamental wave, the current fundamental wave and the DC component of the current.

[0033] As a preferred solution, the winding inductance of the transformer to be tested under the DC component of the current is calculated according to the following formula:

[0034]

[0035] Among them, L d is the winding inductance value of the transformer under test in the d-axis direction; U1 and I1 are the voltage fundamental wave and current fundamental wave of the transformer under test in each fundamental wave cycle respectively; j is the imaginary unit; w is the angular frequency.

[0036] As a preferred solution, the electromagnetic vulnerability characteristics of the transformer core to be tested under electromagnetic action are obtained according to the analysis of the winding inductance value, and then the electromagnetic vulnerability assessment result corresponding to the transformer core to be tested is obtained according to the electromagnetic vulnerability characteristics, including:

[0037] Performing numerical integration processing on the winding inductance values ​​of different DC pulse currents, and obtaining the corresponding winding DC magnetization curves according to the different DC pulse currents and the processed winding inductance values;

[0038] According to the DC pulse current value corresponding to the knee point position in the DC magnetization curve of the winding, the transformer saturation threshold corresponding to the transformer under test is obtained, and then the electromagnetic vulnerability assessment result corresponding to the iron core of the transformer under test is obtained according to the transformer saturation threshold.

[0039] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0040] The present invention provides a transformer core electromagnetic vulnerability assessment device, comprising: a transformer to be tested, an AC current transformer, a pulse current source, a multi-channel digital oscilloscope, and a host computer; the AC current transformer is connected in series with the pulse current source and then connected to the primary side of the transformer to be tested; the secondary side of the transformer to be tested is unloaded; two input channels of the multi-channel digital oscilloscope are respectively connected to the primary side and the secondary side of the transformer to be tested; the multi-channel digital oscilloscope is connected to the host computer via a preset communication interface; the AC current transformer is used to provide power frequency current to the transformer to be tested; the pulse current source ... A source is used to provide a DC pulse current to the transformer under test; the multi-channel digital oscilloscope is used to measure the current signal on the primary side of the transformer under test and the voltage signal on the secondary side of the transformer under test, and transmit the current signal and voltage signal to the host computer; the host computer is used to calculate the winding inductance of the transformer under test in a saturated state based on the current signal and the voltage signal, and analyze the electromagnetic vulnerability characteristics of the transformer core under electromagnetic influence based on the winding inductance value, and then obtain the electromagnetic vulnerability assessment result corresponding to the transformer core under test based on the electromagnetic vulnerability characteristics. A key parameter in the assessment of DC bias magnetic effects of transformers (i.e., vulnerability assessment) is the saturated winding inductance value. The present invention uses a pulse current source to pulse discharge the transformer under test, superimposed with the power frequency current provided by the AC current transformer, to measure the winding inductance value of the transformer under test in a saturated state. The electromagnetic vulnerability characteristics of the transformer core under electromagnetic influence are further analyzed based on the winding inductance value, thereby achieving the electromagnetic vulnerability assessment of the transformer core under test. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1The figure is a schematic structural diagram of a transformer core electromagnetic vulnerability assessment device provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions in this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0044] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0045] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0046] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0047] In the description of the embodiments of the present application, the terms "multiple" and "several" refer to more than two (including two). Similarly, "multiple groups" refer to more than two groups (including two groups), and "multiple pieces" refer to more than two pieces (including two pieces).

[0048] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0049] Example 1

[0050] Please refer to Figure 1 To address the problem of being unable to perform electromagnetic vulnerability assessment on transformer cores in the prior art, an embodiment of the present invention provides a schematic structural diagram of a transformer core electromagnetic vulnerability assessment device, comprising: a transformer to be tested, an AC current transformer, a pulse current source, a multi-channel digital oscilloscope, and a host computer;

[0051] The AC current transformer is connected in series with the pulse current source and then connected to the primary side of the transformer to be tested; the secondary side of the transformer to be tested is unloaded;

[0052] The two input channels of the multi-channel digital oscilloscope are respectively connected to the primary side and the secondary side of the transformer to be tested; the multi-channel digital oscilloscope is connected to the host computer through a preset communication interface;

[0053] The AC current transformer is used to provide power frequency current to the transformer to be tested;

[0054] The pulse current source is used to provide a DC pulse current to the transformer to be tested;

[0055] The multi-channel digital oscilloscope is used to measure the current signal on the primary side of the transformer under test and the voltage signal on the secondary side of the transformer under test, and transmit the current signal and voltage signal to the host computer;

[0056] The host computer is configured to calculate the winding inductance of the transformer under test in a saturated state based on the current signal and the voltage signal, and obtain an electromagnetic vulnerability characteristic of the iron core of the transformer under test under electromagnetic action based on the winding inductance analysis, and then obtain an electromagnetic vulnerability assessment result corresponding to the iron core of the transformer under test based on the electromagnetic vulnerability characteristic.

[0057] Preferably, the transformer core electromagnetic vulnerability assessment device further includes: a voltage regulator; the primary side of the voltage regulator is connected to the distribution network, and the secondary side of the voltage regulator is connected to the AC current transformer; the voltage regulator is used to provide a corresponding amplitude voltage to the AC current transformer.

[0058] Preferably, the transformer core electromagnetic vulnerability assessment device further includes: an adjustable current limiting resistor; the adjustable current limiting resistor is connected in series with the pulse current source; the adjustable current limiting resistor is used to limit the DC pulse current to a safe current range of the transformer to be tested and the pulse current source.

[0059] Preferably, the resistance value of the adjustable current limiting resistor is calculated according to the following formula:

[0060] R = τ / C;

[0061] Wherein, R is the resistance value of the adjustable current limiting resistor; τ is the time constant of the DC pulse current; and C is the equivalent capacitance of the pulse current source.

[0062] Preferably, the transformer core electromagnetic vulnerability assessment device further includes: a filter capacitor; the pulse current source is connected in series with the adjustable current limiting resistor and then connected in parallel with the filter capacitor; the filter capacitor is used to filter high-frequency harmonics in the pulse current source.

[0063] Preferably, the transformer core electromagnetic vulnerability assessment device further includes: a fluxgate current sensor; the multi-channel digital oscilloscope is connected to the primary side of the transformer to be tested through the fluxgate current sensor; the fluxgate current sensor is used to measure the current signal on the primary side of the transformer to be tested.

[0064] Preferably, the transformer core electromagnetic vulnerability assessment device further includes: a differential voltage probe; the multi-channel digital oscilloscope is connected to the secondary side of the transformer to be tested through the differential voltage probe; the differential voltage probe is used to measure the voltage signal on the secondary side of the transformer to be tested.

[0065] Preferably, the winding inductance value of the transformer to be tested in a saturated state is calculated based on the current signal and the voltage signal, including: performing fast Fourier transform on the current signal and the voltage signal to obtain the voltage fundamental wave, current fundamental wave and current DC component of the transformer to be tested in each fundamental wave cycle; and calculating the winding inductance value of the transformer to be tested under the current DC component in each fundamental wave cycle based on the voltage fundamental wave, current fundamental wave and current DC component.

[0066] Preferably, the winding inductance of the transformer to be tested under the DC component of the current is calculated according to the following formula:

[0067]

[0068] Among them, L dis the winding inductance value of the transformer under test in the d-axis direction; U1 and I1 are the voltage fundamental wave and current fundamental wave of the transformer under test in each fundamental wave cycle respectively; j is the imaginary unit; w is the angular frequency.

[0069] Preferably, the analyzing the winding inductance values ​​to obtain electromagnetic vulnerability characteristics of the transformer core under electromagnetic action, and then obtaining an electromagnetic vulnerability assessment result corresponding to the transformer core under test based on the electromagnetic vulnerability characteristics, includes: numerically integrating the winding inductance values ​​at different DC pulse currents, and obtaining corresponding winding DC magnetization curves based on the different DC pulse currents and the processed winding inductance values; obtaining a transformer saturation threshold corresponding to the transformer under test based on the DC pulse current value corresponding to the knee point position in the winding DC magnetization curve, and then obtaining an electromagnetic vulnerability assessment result corresponding to the transformer core under test based on the transformer saturation threshold.

[0070] Specifically, a key parameter for evaluating the DC bias effect of a transformer is the winding saturation inductance. Existing techniques for calculating saturation inductance often employ the finite element method. However, this method takes a long time to model and calculate, and requires precise dimensions of the core, windings, and structural components, resulting in significant limitations. The method of the present invention directly utilizes a high-amplitude, long-pulse source to measure the inductance of the core winding. This method features a simple device, eliminates the need for transformer disassembly, and eliminates the need for a large-capacity power supply. This reduces damage to the transformer and provides high measurement accuracy.

[0071] In order to measure the inductance of the core winding of the transformer in the deep saturation state, the present invention combines the output characteristics of the pulse current source and the nonlinear characteristics of the transformer winding to design a deep saturation inductance measurement device that injects pulse current and superimposes a small AC current. The basic circuit settings in the device are as follows: Figure 1 As shown, it specifically includes the following structures:

[0072] The primary side of the transformer under test 1 is connected to the injection power supply, and the secondary side is unloaded;

[0073] The AC low current transformer 2 (i.e., the AC current transformer) is connected in series with the pulse current source 4 and is used to provide a low power frequency current to the transformer 1 to be tested;

[0074] The voltage regulator 3 is used to provide a low-amplitude voltage for the AC low-current transformer 2. The primary side of the voltage regulator is connected to the power distribution network. The voltage amplitude can be adjusted according to the measurement accuracy requirements.

[0075] The high-amplitude long-pulse current source 4 (i.e., the pulse current source) can provide a pulse current of arbitrary amplitude and duration according to measurement requirements, and its output current waveform can be approximately regarded as a direct current compared to the power frequency;

[0076] Adjustable current limiting resistor 5, the resistance value can be adjusted according to the target current waveform, the resistance range is 1-10Ω, and the step is 1Ω;

[0077] A multi-channel digital oscilloscope 6 is used to measure the current signal on the primary side of the transformer under test and the voltage signal on the secondary side of the transformer under test;

[0078] Host computer 7, records and analyzes voltage and current waveforms;

[0079] The fluxgate current sensor 8 is coupled with the AC / DC superimposed current I1 at the inlet side of the transformer 1 to be tested through magnetic flux lines, and measures the AC / DC superimposed pulse current signal;

[0080] Differential voltage probe 9, measuring the secondary side voltage of port 1 of the transformer under test;

[0081] The filter capacitor 10 is used to filter high-frequency harmonics in the high-amplitude long-pulse current source 4 and protect the high-amplitude long-pulse current source 4 and the adjustable current limiting resistor 5, and has a capacitance of 4.8mF.

[0082] Figure 1 The medium- and high-amplitude long-pulse power supply can output a pulse current with a maximum amplitude of 300A and a half-pulse width of approximately tens of seconds. This pulse signal can be considered a DC current relative to the power frequency. To measure the inductance value under any bias state, a voltage regulator 3 and another transformer (AC low-current transformer 2) are used as a power-frequency AC low-current superimposed on the pulse current. This allows the winding inductance value to be calculated under all bias states during a single discharge. The current and voltage signals are measured using a fluxgate current sensor 8 and a differential voltage probe 9, respectively. The measurement results are stored in the host computer 7 via a Pico digital oscilloscope 6 for further calculation and analysis.

[0083] 1. Test circuit connection:

[0084] (1) According to Figure 1 The inductance value measuring device under deep saturation state is shown, and the transformer to be tested 1, AC small signal power supply 2 and pulse current source 4 are connected through cables;

[0085] (2) The pulse current source 4 is connected in series with the adjustable current limiting resistor 5 to control the output current amplitude and half pulse width. The adjustable resistor has a resistance of 1-10Ω in steps of 1Ω.

[0086] (3) The pulse current source 4 is connected in series with the adjustable current limiting resistor 5. Figure 1 The filter capacitor 10 is connected in parallel to prevent the pulse current source from flowing through the AC signal to damage the power supply, while providing a low impedance path for the small AC current;

[0087] (4) The secondary measurement circuit is connected to the Pico oscilloscope 6 for waveform recording, and the recorded data is stored and calculated by the host computer 7.

[0088] 2. Long pulse power supply discharge setting work:

[0089] (1) The pulse source charging current and the current limiting resistor value are set according to the output current amplitude and duration. The output pulse waveform time constant τ = RC, where R is the current limiting resistor value, which can be adjusted in the range of 1-10Ω as needed, with a step of 1Ω. C is the equivalent capacitance of the injection power supply, and C is a constant. The pulse current amplitude is calculated according to Ohm's law. Before output, the resistance value is first set according to the time constant corresponding to the preset current waveform half-pulse width, and the resistance value is R = τ / C; then the pulse power supply pre-charge voltage is determined according to the preset pulse current amplitude and resistance value, and the voltage U = I·R;

[0090] (2) The multi-channel digital oscilloscope 6 is set to a single trigger mode to record the port voltage and current waveforms of the transformer 1 under test;

[0091] (3) A small AC current is provided by a voltage regulator 3, and the small AC signal is connected in series with a pulse current source 4 through an AC small current transformer 2;

[0092] (4) The pulse source DC circuit breaker inside the high-amplitude long-pulse current source 4 is closed to output a high-amplitude pulse current, so that the transformer core operates in a deep saturation state.

[0093] 3. Data processing:

[0094] (1) Starting from the trigger moment, the recorded voltage and current signals are subjected to FFT by the Matlab signal analysis module to calculate the voltage and current fundamental waves in each cycle;

[0095] (2) Calculate the inductance value within the cycle based on the voltage and current fundamental waves of the current cycle, and calculate the instantaneous incremental inductance Among them, U1 and I1 are the voltage and current fundamental waves of each cycle obtained by FFT decomposition, respectively. Combined with the DC component of the current waveform, the inductance of the transformer winding under the DC current value can be obtained. It is assumed that the DC component value remains unchanged within a single cycle. The DC component of each cycle is obtained synchronously during the FFT transformation step. The DC component of each cycle has a one-to-one correspondence with the inductance value calculated for that cycle.

[0096] (3) Calculate the inductance values ​​of all cycles and arrange the results from small to large according to the injected current to obtain the inductance value of the winding under any DC current. The number of inductance data is equal to the total number of measurement cycles.

[0097] (4) By numerically integrating the calculated inductance value, the DC magnetization curve data of the winding can be obtained. By comparing the knee point positions of the DC magnetization curves of different transformers, the saturation characteristics of different transformers can be obtained, and it can be determined whether the transformer is prone to saturation under the action of DC current and the range of the saturation threshold, thereby obtaining the electromagnetic vulnerability characteristics of the transformer based on the saturation threshold. The saturation threshold of the transformer is an inherent property of the magnetization characteristics of its core material, which directly determines the performance degradation law of the core under electromagnetic action. The lower the saturation threshold, the easier it is for the core to enter the saturation zone, and the more prominent the electromagnetic vulnerability problems such as excitation current distortion, iron loss growth and local overheating. Therefore, the electromagnetic vulnerability of the core can be effectively evaluated by the saturation threshold.

[0098] It can be seen that the present invention provides a device for evaluating the electromagnetic vulnerability of the transformer core. A key parameter for evaluating the DC bias effect of the transformer is the saturated winding inductance. The present invention can use a pulse current source to perform pulse source discharge on the transformer to be tested, measure the winding inductance value of the transformer to be tested in the saturated state, and further analyze the winding inductance value to obtain the electromagnetic vulnerability characteristics of the transformer core to be tested under electromagnetic action, thereby realizing the electromagnetic vulnerability evaluation of the transformer core to be tested.

[0099] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A transformer core electromagnetic vulnerability assessment device, characterized in that: include: Transformer under test, AC current transformer, pulse current source, multi-channel digital oscilloscope and host computer; The AC current transformer is connected in series with the pulse current source and then connected to the primary side of the transformer to be tested; the secondary side of the transformer to be tested is unloaded; The two input channels of the multi-channel digital oscilloscope are respectively connected to the primary side and the secondary side of the transformer to be tested; the multi-channel digital oscilloscope is connected to the host computer through a preset communication interface; The AC current transformer is used to provide power frequency current to the transformer to be tested; The pulse current source is used to provide a DC pulse current to the transformer to be tested; The multi-channel digital oscilloscope is used to measure the current signal on the primary side of the transformer under test and the voltage signal on the secondary side of the transformer under test, and transmit the current signal and voltage signal to the host computer; The host computer is configured to calculate the winding inductance of the transformer under test in a saturated state based on the current signal and the voltage signal, and obtain an electromagnetic vulnerability characteristic of the iron core of the transformer under test under electromagnetic action based on the winding inductance analysis, and then obtain an electromagnetic vulnerability assessment result corresponding to the iron core of the transformer under test based on the electromagnetic vulnerability characteristic.

2. The transformer core electromagnetic vulnerability assessment device according to claim 1, wherein: Also includes: voltage regulator; The primary side of the voltage regulator is connected to the power distribution network, and the secondary side of the voltage regulator is connected to the AC current transformer; The voltage regulator is used to provide a corresponding amplitude voltage to the AC current transformer.

3. The transformer core electromagnetic vulnerability assessment device according to claim 2, wherein: Also includes: Adjustable current limiting resistor; The adjustable current limiting resistor is connected in series with the pulse current source; The adjustable current-limiting resistor is used to limit the DC pulse current to within the safe current range of the transformer to be tested and the pulse current source.

4. The transformer core electromagnetic vulnerability assessment device according to claim 3, wherein: The resistance value of the adjustable current limiting resistor is calculated according to the following formula: R = τ / C; Wherein, R is the resistance value of the adjustable current limiting resistor; τ is the time constant of the DC pulse current; and C is the equivalent capacitance of the pulse current source.

5. The transformer core electromagnetic vulnerability assessment device according to claim 4, wherein: Also includes: filter capacitors; The pulse current source is connected in series with the adjustable current limiting resistor and then connected in parallel with the filter capacitor; The filter capacitor is used to filter the high-frequency harmonics in the pulse current source.

6. The transformer core electromagnetic vulnerability assessment device according to claim 5, wherein: Also includes: Fluxgate current sensor; The multi-channel digital oscilloscope is connected to the primary side of the transformer to be tested through the fluxgate current sensor; The fluxgate current sensor is used to measure the current signal on the primary side of the transformer to be tested.

7. The transformer core electromagnetic vulnerability assessment device according to claim 6, wherein: Also included: differential voltage probe; The multi-channel digital oscilloscope is connected to the secondary side of the transformer to be tested via the differential voltage probe; The differential voltage probe is used to measure the voltage signal on the secondary side of the transformer to be tested.

8. The transformer core electromagnetic vulnerability assessment device according to claim 7, wherein: Calculating the winding inductance of the transformer under test in a saturation state according to the current signal and the voltage signal includes: Performing a fast Fourier transform on the current signal and the voltage signal to obtain a voltage fundamental wave, a current fundamental wave, and a current DC component of the transformer under test in each fundamental wave cycle; The winding inductance value of the transformer to be tested under the DC component of the current in each fundamental wave period is calculated based on the voltage fundamental wave, the current fundamental wave and the DC component of the current.

9. The transformer core electromagnetic vulnerability assessment device according to claim 8, wherein: The winding inductance of the transformer under test under the DC component of the current is calculated according to the following formula: Among them, L d is the winding inductance value of the transformer under test in the d-axis direction; U1 and I1 are the voltage fundamental wave and current fundamental wave of the transformer under test in each fundamental wave cycle respectively; j is the imaginary unit; w is the angular frequency.

10. The transformer core electromagnetic vulnerability assessment device according to claim 9, wherein: The step of obtaining electromagnetic vulnerability characteristics of the transformer core under electromagnetic action according to the analysis of the winding inductance, and then obtaining an electromagnetic vulnerability assessment result corresponding to the transformer core under electromagnetic action according to the electromagnetic vulnerability characteristics, includes: Performing numerical integration processing on the winding inductance values ​​of different DC pulse currents, and obtaining the corresponding winding DC magnetization curves according to the different DC pulse currents and the processed winding inductance values; According to the DC pulse current value corresponding to the knee point position in the DC magnetization curve of the winding, the transformer saturation threshold corresponding to the transformer under test is obtained, and then the electromagnetic vulnerability assessment result corresponding to the iron core of the transformer under test is obtained according to the transformer saturation threshold.

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