Transformer dynamic bias current detection method and device based on magnetoelectric coupling sensing

Abstract

The invention relates to the technical field of sensors, in particular to a transformer dynamic magnetic bias current detection method and device based on magnetoelectric coupling sensing, and the detection device composed of a magnetoelectric coupling sensing element, an exciting coil and a rear-end processing circuit is used for measuring direct current magnetic bias current. The working principle of the magnetoelectric coupling sensing element is based on stress coupling between the magnetostrictive material and the piezoelectric material, then an output signal is generated on the piezoelectric material, and the sensitivity is remarkably improved by using the resonance amplification effect of the magnetoelectric coupling sensing element. Non-contact current detection can be realized by detecting the magnetic field generated by the magnetic bias current of the neutral point grounding wire of the transformer, and direct physical contact with power equipment is not needed, so that the safety of the system is improved, and the problem of high installation difficulty of a contact sensor is avoided; high-sensitivity, high-precision, anti-interference and real-time transformer direct-current magnetic bias current monitoring is achieved, and the transformer direct-current magnetic bias current monitoring device has the advantages of being easy to install and deploy and small in size.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a transformer dynamic bias current detection method and device based on magnetoelectric coupling sensing. Background Art

[0002] With the rapid development of urban rail transit, the problem of stray current generated by the DC traction power supply system of rail transit is becoming increasingly serious. The stray current of urban rail transit leaks into the ground through the rails, and then enters the transformer of the substation through the grounding grid. Since the rails and the earth are not completely insulated, when the urban rail transit is accelerating or decelerating, the traction current cannot completely return to the negative pole of the DC traction system through the rails. Some current will flow into the ground through the rails to form stray current. This part of the stray current flows into the grounding grid of the substation, thereby affecting the potential of the neutral point of the transformer and forming a bias current on its neutral line. The bias current is superimposed on the main magnetic field of the transformer, resulting in a deviation of the magnetization curve and a DC bias phenomenon. This phenomenon will aggravate the vibration, noise and overheating of the equipment. The high-frequency and low-frequency harmonics in the stray current will further increase the influence of the bias, affect the stability of the system and accelerate the aging of the equipment. Therefore, it is necessary to detect the bias current on the neutral line of the transformer to determine whether the DC bias of the transformer exceeds the threshold.

[0003] Currently, there are mainly the following methods to detect the DC bias of the transformer: Hall-type neutral point current detection method; flat steel neutral point current detection method; deep learning algorithm to predict the insulation resistance value of the grounding grid anti-corrosion layer.

[0004] For example, a Chinese patent with publication number CN116322272A discloses a magnetoelectric sensor for achieving vibration cancellation and a manufacturing method thereof, comprising a first magnetostrictive material layer, a first piezoelectric material layer, a second piezoelectric material layer, and a second magnetostrictive material layer arranged in sequence from top to bottom; wherein, a forked electrode flexible circuit board is adhered to the upper and lower surfaces of the first piezoelectric material layer and the second piezoelectric material layer, and two wires are led out from the electrode flexible circuit board for conducting polarization and signal output to the first piezoelectric material layer and the second piezoelectric material layer.

[0005] For another example, a Chinese patent with publication number CN118534178A discloses a magnetoelectric sensor for characteristic current identification and a manufacturing method thereof, which includes a magnetostrictive material, a piezoelectric material, a base, two permanent magnets and a magnetic concentrating material; the piezoelectric material is bonded to the surface of the magnetostrictive material to form a magnetoelectric composite material, one end of the magnetoelectric composite material is fixed by the base to form a cantilever beam structure, and two permanent magnets are respectively bonded to the upper and lower surfaces of the free end of the cantilever beam, and the magnetization direction is perpendicular to the length direction of the cantilever beam; the magnetic concentrating material is arranged on the outside of the magnetoelectric composite material to collect the alternating magnetic field generated by the characteristic current on the current-carrying conductor.

[0006] For example, a Chinese patent with publication number CN110672906A discloses a differential current sensor for measuring a straight AC conductor, including two sensitive units and a fixed block; the sensitive unit includes a magnetostrictive / piezoelectric composite material, a height adjustment frame, a base plate, a bias plate, a pad, a signal output line, and a conductor.

[0007] For example, a Chinese patent with publication number CN117120861A discloses a magnetic field sensor for detecting a magnetic field, comprising: a magnetoelectric sensor element capable of mechanical oscillation, the sensor element having at least one first layer made of a magnetostrictive material, a second layer made of a piezoelectric material, and at least one electrode made of a conductive material, the conductive material being more specifically a metal; and an electronic device. The magnetic field sensor, more specifically the electronic device, is designed to cause mechanical oscillation of the sensor element by means of an excitation signal, receive the mechanical oscillation of the sensor element and convert the mechanical oscillation into a received signal, generate an excitation signal from the received signal, and determine a variable related to the magnetic field based on the received signal.

[0008] For another example, Chinese patent publication number CN114706025A discloses a resonant DC magnetic sensor based on magnetoelectric effect, which includes a sensor package housing, a permanent magnet, an excitation coil, a magnetoelectric sensitive unit and a peripheral signal processing circuit.

[0009] Finally, a Chinese patent with publication number CN116430097A discloses a current sensor and current measurement method based on a magnetoelectric composite material. The current sensor includes: a sensing element including a magnetoelectric composite material, which is used to sense the measured current and output an induced electrical signal; a bias magnet, which is used to provide a bias magnetic field for the sensing element; a magnetic winding, including a first iron core, a second iron core, a first coil wound on the first iron core, and a second coil wound on the second iron core; the first coil is connected to an AC signal to drive the first coil to generate an AC excitation magnetic field for the sensing element; a processing module connected to the sensing element to obtain the induced electrical signal; the processing module is also connected to the AC signal and the second coil respectively, and based on the induced electrical signal and the AC signal, the feedback current output to the second coil is adjusted to drive the second coil to compensate for the bias magnetic field; the processing module obtains the feedback current that compensates the bias magnetic field and determines the measured value of the measured current.

[0010] In summary and in combination with the existing technology, the current technology for detecting DC bias magnetic field of transformer has many disadvantages, which are summarized as follows: ① The disadvantage of the Hall-type neutral point current detection method is that the Hall sensor has low sensitivity, is easily affected by complex working conditions, and is highly dependent on the magnetic concentrator structure for current detection; ② The flat steel neutral point current detection method requires data collection and analysis on site, which has poor real-time performance, high labor costs, non-portable detection equipment, and low measurement accuracy. Traditional measuring instruments, such as DC clamp meters, have large limitations, and the clamps are small and cannot adapt to wider grounding bars. ③ In addition, the mainboard of the existing measuring instrument is installed inside the measuring box. To repair or replace the mainboard, the measuring box must be completely dismantled, which is time-consuming and troublesome, and has a certain impact on actual use; ④ In addition, by relying on deep learning algorithms to predict the insulation resistance value of the grounding grid anti-corrosion layer, and thus predicting the intrusion of stray current, this method requires the collection of a large amount of training data and is highly dependent on surrounding environmental variables, making it difficult to promote universality; ⑤ In actual application scenarios, the stray current in the neutral grounding wire of the transformer caused by the operation of urban rail transit contains not only a DC component, but also a stray AC component below 1 Hz. Currently, it is still impossible to detect the stray AC component. Summary of the invention

[0011] In view of the deficiencies in the prior art, the present invention provides a transformer dynamic bias current detection method and device based on magneto-electric coupling sensing to solve the above problems.

[0012] To achieve the above objectives, the present invention is implemented through the following technical solutions.

[0013] A transformer dynamic bias current detection method based on magnetoelectric coupling sensing, the method comprising the following steps: Step S1. When the magnetoelectric coupling sensor element detects an AC stray current signal, an AC excitation magnetic field is applied for modulation, and an excitation coil is connected through a back-end processing circuit to generate an AC excitation magnetic field. The magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element, so that the magnetoelectric coupling sensor element works in a resonant state with high sensitivity; Step S2. When a DC bias current appears on the neutral point grounding wire of the transformer, the DC bias current will magnetize the magnetostrictive material in the magnetoelectric coupling sensor element. The output signal of the magnetoelectric coupling sensor element is amplified and filtered, and then phase-locked detection is performed to read out the phase information, obtain the direction of the DC bias current, and then determine the polarity of the DC bias current in the transformer; The current is then converted through the back-end processing circuit, the signal is converted into a DC output form, the amplitude information of the bias current is obtained, and the DC component and AC component in the output signal of the magnetoelectric coupling sensor element are separated by the time averaging method and the frequency domain decoupling method, so as to complete the detection of the DC bias current under the AC background current; Step S3. In addition, when detecting stray currents in urban rail transit, the resonant amplification mechanism of the magnetoelectric coupling sensor element and the nonlinear strain characteristics of the magnetostrictive material can be utilized. Through carrier modulation technology, low-frequency stray current signals below 1 Hz can be modulated to the resonant frequency of the magnetoelectric coupling sensor element. The resonant amplification effect is utilized to improve the response output to the low-frequency stray current signal, thereby improving the signal-to-noise ratio of the low-frequency stray current and completing the detection of the low-frequency stray current.

[0014] Preferably, the output signal of the magnetoelectric coupling sensor element at the resonant frequency in step S1 is Output signal of magnetoelectric coupling sensor element at non-resonant frequency Satisfies the following equation: (1) in, is the mechanical quality factor, is the magnetomechanical conversion coefficient of the magnetostrictive material, is the electromechanical conversion coefficient of the piezoelectric material, is the angular frequency, is the static capacitance of the piezoelectric material, is the mechanical impedance of the magnetoelectric coupling sensor element, is the AC magnetic field strength at the point to be determined, d is the thickness of the piezoelectric material, j is an imaginary number related to the phase, is the output signal of the magnetoelectric coupling sensor element at the non-resonant frequency. The output signal of the magnetoelectric coupling sensor element is increased by nearly 0.8 compared with the output signal at the non-resonant frequency. times, the formula (1) is the voltage-magnetic field conversion relationship.

[0015] Preferably, in step S2, when detecting the DC bias magnetic field, the AC excitation magnetic field and the DC magnetic field to be measured exist simultaneously, and are separated by the time averaging method and the frequency domain decoupling method, and the total magnetic field is assumed to be: (2) in, is the DC magnetic field component, is the AC magnetic field component, Eliminate the AC magnetic field component by time averaging: (3) in, is the start time, the integration time is greater than the period of the AC excitation signal, The AC magnetic field component can be obtained by subtracting the DC magnetic field component from the total magnetic field. The calculation steps are as follows: (4) The frequency domain decoupling method separates the spectrum through Fourier transform and obtains the total output amplitude: (5) The DC component is The spectrum value at , the AC component is The spectrum value at is the total output amplitude, is the DC magnetic field, is the frequency-dependent sensitivity, is the alternating magnetic field, is the AC output amplitude, is the total magnetic field; By eliminating the AC magnetic field component through time averaging, the relationship curve between the DC magnetic field and the output voltage of the magnetoelectric coupling sensor element is obtained. The DC bias current generates a DC magnetic field and acts on the magnetoelectric coupling sensor element. By measuring the change of the output voltage of the magnetoelectric coupling sensor element with the DC bias current, combined with The sensing model can be used to reversely infer the magnitude of the DC bias current.

[0016] Preferably, the The sensing model is used to describe the nonlinear relationship between the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. The model establishes the relationship between the piezomagnetic coefficient of magnetic materials and the DC magnetic field: (6) (7) (8) in, is the piezomagnetic coefficient of the magnetostrictive material, is the compliance coefficient, is the magnetic susceptibility, is the saturation magnetic susceptibility, is the saturation magnetostriction coefficient, is the saturated Young's modulus, is the stress of the magnetostrictive layer, is the saturation stress of the magnetostrictive layer, is the vacuum permeability, is the effective initial magnetic induction intensity, for The magnetic susceptibility at for The magnetic susceptibility at is the effective magnetic field; according to The reverse calculation of the DC bias current includes the following steps: Step S2.1. When the magnetoelectric coupling sensor element detects an AC stray current signal, an AC excitation magnetic field is applied for modulation, and an AC excitation magnetic field is generated by connecting an excitation coil through a back-end processing circuit. The magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element, so that the magnetoelectric coupling sensor element works in a resonant state with high sensitivity (this is actually consistent with step S1, but for the sake of explanation, it is quoted); Step S2.2. When detecting DC bias magnetization, the AC excitation magnetic field and the DC magnetic field to be measured exist simultaneously, and are separated by time averaging method and frequency domain decoupling method. According to formula (2), formula (3), formula (4), and formula (5), the AC magnetic field component is eliminated by time averaging; Step S2.3. The sensing model is used to describe the nonlinear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. After eliminating the AC magnetic field component, the magnitude of the DC magnetic field is calculated; Step S2.4. According to the Biot-Savart law, the magnitude of the DC current is converted based on the DC magnetic field obtained in step S2.3.

[0017] Preferably, for magnetostrictive materials, the effective magnetic field is an external DC magnetic field and magnetostrictive materials in an external magnetic field Demagnetization field sum: (9) in, , is the demagnetization factor. For a magnetic material with a certain structure, the demagnetization factor is a constant. The nonlinear strain of the magnetostrictive material in step S3 is expressed by the following Taylor series formula: (10) in, for Magnetostrictive strain under DC bias, is the AC magnetic field strength at the point to be determined, Described by the following formula: (11) in, is the low-frequency stray AC magnetic field strength to be measured, The AC modulated magnetic field strength provided to the excitation coil, is the amplitude of the low-frequency stray AC magnetic field, The amplitude of the AC modulated magnetic field provided to the excitation coil, It's time. The frequency of the AC modulated magnetic field provided to the excitation coil, is the frequency of the low-frequency stray AC magnetic field to be measured, The following output voltage signal is obtained: (12) in, is a constant determined by the material of the magnetoelectric coupling sensor element. is the maximum piezomagnetic coefficient of magnetostrictive material under zero bias, is the amplitude of the low-frequency stray AC magnetic field, The amplitude of the AC modulated magnetic field provided to the excitation coil is A value in the range, The frequency of the AC modulated magnetic field provided to the excitation coil is A value in the range, is the frequency of the low-frequency stray AC magnetic field to be measured, It's time. According to the nonlinear strain characteristics of magnetostrictive materials, low-frequency stray current signals will be modulated into the excitation signal in the form of carrier waves. The output voltage signal includes the AC modulated magnetic field signal and the low-frequency stray AC magnetic field signal to be measured. According to formula (1), the output voltage signal is converted into a magnetic field. The magnitude relationship between the current and the magnetic field is expressed by the Biot-Savart law, and the direction relationship is determined by the right-hand rule. For an infinitely long straight conductor, it can be expressed as: (13) in, is the distance from the point to be found to the center of the wire, is the current through the wire, is the vacuum magnetic permeability, and its value is , is the AC magnetic field strength of the point to be determined. According to formula (13), there is a linear correspondence between the measured current and the magnetic field. The larger the current, the larger the magnetic field, and the magnetic field strength increases with the distance. The increase shows a linear decay, so the current size can be calculated according to the magnetic field strength.

[0018] Device for realizing transformer dynamic bias current detection method based on magnetoelectric coupling sensing: The detection device comprises a magnetoelectric coupling sensing element, an excitation coil, and a back-end processing circuit, wherein the excitation coil is wound along the length direction of the magnetoelectric coupling sensing element; The back-end processing circuit is provided with a signal driving circuit, a filtering and amplifying circuit, a phase-locked detection circuit, The conversion circuit and the signal driving circuit are connected to the excitation coil.

[0019] Preferably, the magnetoelectric coupling sensor element is provided with a piezoelectric material and a magnetostrictive material, and the piezoelectric material and the magnetostrictive material are connected with an adhesive.

[0020] Preferably, the piezoelectric material comprises an upper electrode surface and a lower electrode surface, the upper electrode surface and the lower electrode surface are externally connected to wires, the piezoelectric material is a sheet structure, and the number of the piezoelectric material is one.

[0021] Preferably, the input end of the magnetoelectric coupling sensor element is connected to a signal driving circuit, and the output end of the magnetoelectric coupling sensor element is connected to a filtering and amplifying circuit.

[0022] Preferably, the input end of the phase-locked detection circuit is connected to the output end of the signal driving circuit and the filter amplifier circuit respectively, and is used to detect the phase information of the signal source and the output signal of the magnetoelectric coupling sensor element. By comparing the phase information of the two, the real output signal of the magnetoelectric coupling sensor element can be extracted from the output signal of the filter amplifier circuit. The output end of the phase-locked detection circuit is connected to The input end of the conversion circuit is used to convert the AC signal waveform into a DC output form and output a stable amplitude signal. The output end of the signal driving circuit is connected to the input end of the magnetoelectric coupling sensing element to provide a signal source for the magnetoelectric coupling sensing element. The filtering and amplifying circuit is connected to the output end of the magnetoelectric coupling sensing element, and is used to amplify the signal output by the magnetoelectric coupling sensing element, and perform filtering and zeroing processing on the amplified output signal.

[0023] Compared with the prior art, the present invention discloses a transformer dynamic bias current detection method based on magnetoelectric coupling sensing, which uses a detection device composed of a magnetoelectric coupling sensing element, an excitation coil, and a back-end processing circuit to measure the DC bias current. The working principle of the magnetoelectric coupling sensing element is based on the stress coupling between the magnetostrictive material and the piezoelectric material, and then generates an output signal on the piezoelectric material. The output signal changes significantly with the DC bias, and this phenomenon can be used to complete high-precision detection of the DC bias. The back-end processing circuit is used to convert the signal into a DC output form to obtain the amplitude information of the DC bias current. This invention is different from the traditional contact detection method. The present invention adopts magnetoelectric coupling sensing technology and utilizes the resonant amplification effect of the magnetoelectric coupling sensing element. The sensitivity is significantly improved, and non-contact current detection can be achieved by detecting the magnetic field generated by the bias current of the neutral point grounding wire of the transformer, without direct physical contact with the power equipment. In this way, not only the safety of the system is improved, but also the problem of the difficulty of installing contact sensors is avoided. At the same time, it can realize high-sensitivity, high-precision, anti-interference, and real-time transformer DC bias current monitoring, and has the characteristics of easy installation and deployment and miniaturization, solving the shortcomings of the existing technology; By utilizing the high sensitivity and high precision of the device, the bias current caused by stray current in the transformer can be accurately detected. At the same time, the synchronous detection method of transformer dynamic bias current by magneto-electric coupling sensing can monitor the dynamic changes inside the transformer in real time, improving the comprehensiveness and accuracy of monitoring. By using this technology, the DC bias phenomenon caused by stray current can be discovered in time, avoiding problems such as equipment overheating, increased mechanical vibration, and increased noise caused by the interference of bias current on the transformer magnetic field. At the same time, the magnetoelectric coupling sensor can operate stably in complex electromagnetic environments, overcoming the problem that traditional current sensors are easily affected by electromagnetic interference; Through efficient signal processing technology, external noise can be removed to ensure the accuracy of monitoring results. Real-time monitoring and high-precision fault warning systems can provide more reliable operating data for the power system and detect potential fault hazards early, thereby effectively preventing equipment damage, reducing the frequency of shutdowns and maintenance, and significantly extending the service life of transformers. Moreover, by adopting the non-contact detection method, the contact resistance, mechanical wear and electrical interference problems faced by traditional contact sensors are effectively avoided. In addition, the non-contact detection method also greatly improves the reliability and long-term stability of the system; Compared with the existing Hall sensor, the magnetoelectric coupling sensor element has higher sensitivity, can realize non-contact current monitoring, and has the advantage of easy deployment. The model is used to describe the nonlinear relationship between the DC magnetic field and the response voltage of the magnetoelectric coupling sensor element, which can significantly improve the accuracy of the sensor element and reduce the measurement error. The resonance enhancement effect of the magnetoelectric coupling sensor element is utilized. When the AC excitation frequency is close to the resonant frequency of the magnetoelectric coupling sensor element, the output signal of the magnetoelectric coupling sensor element is increased by nearly 0.8 compared with the output signal at the non-resonant frequency. For non-contact current measurement, the magnetoelectric coupling sensor element, the excitation coil, and the back-end processing circuit form a detection device. The signal driving circuit is connected to the excitation coil to generate an excitation magnetic field. The magnetic field frequency generated by the excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element, so that the output signal of the magnetoelectric coupling sensor element produces a resonant amplification effect, thereby improving the detection sensitivity of the magnetoelectric coupling sensor element and significantly enhancing the output signal, so that non-contact measurement can be achieved; The output signal of the magnetoelectric coupling sensor element at the resonant frequency is increased by more than 230 times compared with the output signal at the non-resonant frequency. By utilizing this resonance enhancement mechanism, the sensitivity of the magnetoelectric coupling sensor element is significantly improved. The resonance amplification effect is used to improve the response output of low-frequency stray current signals, thereby improving the signal-to-noise ratio of low-frequency stray currents and completing the detection of low-frequency stray currents. Compared with the non-modulated direct measurement method, the magnetic field resolution can reach The signal-to-noise ratio is improved by nearly 2 orders of magnitude. This detection method is better than the Hall sensor ( Level Magnetic Field Resolution), Magnetoresistive sensor ( For sensors with linear outputs such as 100-level magnetic field resolution, they are more suitable for non-contact measurement of currents with typical amplitudes of hundreds of milliamperes to several amperes in the DC bias magnetic scenario of the transformer neutral point grounding wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of a transformer dynamic bias current detection method based on magnetoelectric coupling sensing of the present invention; Figure 2 It is a structural schematic diagram of the magnetoelectric coupling sensor element of the present invention; Figure 3 Graphs of experimental results of the present invention, wherein A is a graph of the output voltage of the magnetoelectric coupling sensor element to a DC magnetic field, B is a graph of the voltage phase change of the magnetoelectric coupling sensor element to a DC magnetic field, and C is a graph of the output voltage change with the AC excitation frequency; Figure 4 It is a nonlinear sensing model of the transformer dynamic bias current detection method based on magnetoelectric coupling sensing of the present invention; Figure 5This is a deployment scenario of the transformer dynamic bias current detection method based on magnetoelectric coupling sensing of the present invention; Figure 6 It is a schematic diagram of the module composition of the back-end processing circuit of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0026] The detection method in the transformer dynamic bias current detection method based on magnetoelectric coupling sensing utilizes a detection device composed of a magnetoelectric coupling sensing element, an excitation coil, and a back-end processing circuit; The excitation coil is wound along the length direction of the magnetoelectric coupling sensing element; The back-end processing circuit is provided with a signal driving circuit, a filtering and amplifying circuit, a phase-locked detection circuit, The magnetoelectric coupling sensing element is provided with piezoelectric material and magnetostrictive material, and the piezoelectric material and the magnetostrictive material are connected by an adhesive, the piezoelectric material includes an upper electrode surface and a lower electrode surface, and the upper electrode surface and the lower electrode surface are externally connected to a wire for conducting an output signal, the piezoelectric material is a sheet structure, and the number of piezoelectric materials is 1, the input end of the magnetoelectric coupling sensing element is connected to the signal driving circuit, and the output end of the magnetoelectric coupling sensing element is connected to the filter amplifier circuit, The input end of the phase-locked detection circuit is connected to the output end of the signal driving circuit and the filter amplifier circuit respectively, and is used to detect the phase information of the signal source and the output signal of the magnetoelectric coupling sensor element. By comparing the phase information of the two, the real output signal of the magnetoelectric coupling sensor element can be extracted from the output signal of the filter amplifier circuit. The output end of the phase-locked detection circuit is connected to The input end of the conversion circuit is used to convert the AC signal waveform into a DC output form and output a stable amplitude signal. The output end of the signal driving circuit is connected to the input end of the magnetoelectric coupling sensing element to provide a signal source for the magnetoelectric coupling sensing element. The filtering and amplifying circuit is connected to the output end of the magnetoelectric coupling sensing element, and is used to amplify the signal output by the magnetoelectric coupling sensing element, and perform filtering and zeroing processing on the amplified output signal.

[0027] The magnetoelectric coupling sensor element is composed of sheet materials in a multi-layer form. The upper and lower layers are magnetostrictive materials, which are used to receive magnetic signals in a magnetic field to generate deformation caused by magnetostriction. The middle layer is a piezoelectric material, which is used to receive the strain generated by the upper and lower layers due to magnetostriction, generate a piezoelectric effect, and convert the magnetic signal into an electrical signal. The layers are bonded with epoxy resin to fix and transfer the strain between the materials. The magnetoelectric coupling sensor element is more sensitive in the length direction, has a more significant magnetostrictive effect than other directions, and can show a better magnetoelectric coupling coefficient.

[0028] The piezoelectric material is a single crystal or polycrystalline ceramic material, specifically: ,quartz, , , , , , or One of them.

[0029] The magnetostrictive material is an alloy or oxide having a magnetostrictive effect or a magnetostrictive composite material formed by combining them with a polymer, and is in the form of a long multi-layered sheet; the alloy or oxide having a magnetostrictive effect includes , Terbium-Dysprosium-Iron Alloy 、Nickel Iron Oxide 、Cobalt iron oxide , Nickel-Manganese-Gadium Alloy Or a magnetostrictive composite material formed by combining the above magnetostrictive material with a polymer, wherein the magnetostrictive material is a single-layer structure or a multi-layer structure.

[0030] The following steps are mainly used to make a transformer dynamic bias current detection method based on magnetoelectric coupling sensing: ① Provide a piezoelectric material, process the piezoelectric material into the required size and shape, and clean it with ultrapure water ultrasonically; ② Electrodes are plated on the upper and lower ends of the piezoelectric material surface by annealing, evaporation or magnetron sputtering; ③ After the piezoelectric material is made into electrodes, it is polarized along the thickness direction; ④ The wires are respectively attached to the two electrode end surfaces of the two piezoelectric materials to conduct electrical signals; ⑤ Provide magnetostrictive materials, process the magnetostrictive materials into the required size and shape, and clean them with alcohol; ⑥ Use adhesive to bond the magnetostrictive material to the surface of the piezoelectric material to form a magnetoelectric coupling sensor element; ⑦ Lead out signals from the wires on both sides of the magnetoelectric coupling sensor element to manufacture the magnetoelectric coupling sensor element.

[0031] ⑧Wrap an excitation coil around the periphery of the magnetoelectric coupling sensor element, with its sensitive axis direction along the length direction of the magnetoelectric coupling sensor element.

[0032] ⑨ The two ends of the coil are connected to the signal driving circuit module, and the two electrodes of the magnetoelectric coupling sensor element are connected to the filter amplifier circuit module for preliminary signal processing.

[0033] ⑩ The output signal of the signal driving circuit module is also connected to the reference signal terminal of the phase-locked detection circuit module for subsequent calculation and reading of the current phase information.

[0034] ⑪ Rationally assemble the excitation coil, magnetoelectric coupling sensor element, and back-end processing circuit module, and debug to realize the synchronous detection function of the transformer dynamic bias current.

[0035] ⑫Install the proposed synchronous detection device for bias current near the conductor to be tested and assemble it into a complete detection device according to actual working conditions.

[0036] The transformer dynamic bias current detection method based on magnetoelectric coupling sensing uses a detection device composed of a magnetoelectric coupling sensing element, an excitation coil, and a back-end processing circuit to measure the DC bias current. Step S1. When the magnetoelectric coupling sensor element detects an AC stray current signal, an AC excitation magnetic field is applied for modulation, and an excitation coil is connected through a back-end processing circuit to generate an AC excitation magnetic field. The magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element, so that the magnetoelectric coupling sensor element works in a resonant state with high sensitivity; Step S2. When a DC bias current appears on the neutral point grounding wire of the transformer, the DC bias current will magnetize the magnetostrictive material in the magnetoelectric coupling sensor element. The output signal of the magnetoelectric coupling sensor element is amplified and filtered, and then phase-locked detection is performed to read out the phase information, obtain the direction of the DC bias current, and then determine the polarity of the DC bias current in the transformer; The current is then converted through the back-end processing circuit, the signal is converted into a DC output form, the amplitude information of the bias current is obtained, and the DC component and AC component in the output signal of the magnetoelectric coupling sensor element are separated by the time averaging method and the frequency domain decoupling method, so as to complete the detection of the DC bias current under the AC background current; Step S3. In addition, when detecting stray currents in urban rail transit, the resonance amplification mechanism of the magnetoelectric coupling sensor element and the nonlinear strain characteristics of the magnetostrictive material can be utilized. Through the carrier modulation technology (i.e., formula (11) and formula (12) are explanations for carrier modulation), the low-frequency stray current signal below 1 Hz is modulated to the resonant frequency of the magnetoelectric coupling sensor element, and the resonance amplification effect is utilized to improve the response output of the low-frequency stray current signal, thereby improving the low-frequency stray current signal-to-noise ratio and completing the detection of the low-frequency stray current.

[0037] The working principle of the magnetoelectric coupling sensor element is based on the stress coupling between the magnetostrictive material and the piezoelectric material, which then generates an output signal on the piezoelectric material. The magnetostrictive material in the magnetoelectric coupling sensor element has a high sensitivity response to the DC bias. When the DC bias is zero, the magnetostrictive material is not magnetized, so the output of the magnetoelectric coupling sensor element is close to zero. When the DC bias is not zero, the magnetostrictive material is magnetized, and the output signal of the magnetoelectric coupling sensor element is significantly enhanced. When the direction of the DC magnetic field around the center line of the transformer changes, the phase of the output voltage of the magnetoelectric coupling sensor element changes, thereby determining the direction of the current on the center line.

[0038] At the same time, the present invention also utilizes the resonance enhancement effect of the magnetoelectric coupling sensor element. The output voltage of the magnetoelectric coupling sensor element changes with the AC excitation frequency. Figure 3 As shown in C, when the AC excitation frequency is close to the resonant frequency of the magnetoelectric coupling sensor element, the output signal of the magnetoelectric coupling sensor element is increased by nearly 0.8 compared with the output signal at the non-resonant frequency. times. For contactless current measurement, the detection device is composed of a magnetoelectric coupling sensor element, an excitation coil, and a back-end processing circuit. The signal driving circuit is connected to the excitation coil to generate an excitation magnetic field. The magnetic field frequency generated by the excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element, so that the output signal of the magnetoelectric coupling sensor element produces a resonant amplification effect, thereby improving the detection sensitivity of the magnetoelectric coupling sensor element and significantly enhancing the output signal, so that contactless measurement can be achieved. Figure 3 The comparison of the experimental results of A, B, and C in FIG. 1 shows that the output signal of the magnetoelectric coupling sensor element at the resonant frequency is increased by more than 230 times compared with the output signal at the non-resonant frequency. By using this resonance enhancement mechanism, the sensitivity of the magnetoelectric coupling sensor element is significantly improved. The output signal of the magnetoelectric coupling sensor element at the resonant frequency in step S1 is Output signal of magnetoelectric coupling sensor element at non-resonant frequency Satisfies the following equation: (1) in, is the mechanical quality factor, The magnetomechanical conversion coefficient of magnetostrictive materials, is the electromechanical conversion coefficient of the piezoelectric material, is the angular frequency, is the static capacitance of the piezoelectric material, is the mechanical impedance of the magnetoelectric coupling sensor element, is the AC magnetic field strength at the point to be determined, d is the thickness of the piezoelectric material, j is an imaginary number related to the phase, is the output signal of the magnetoelectric coupling sensor element at the non-resonant frequency. The output signal of the magnetoelectric coupling sensor element is increased by nearly 0.8 compared with the output signal at the non-resonant frequency. times, the formula (1) is the voltage-magnetic field conversion relationship. The magnetoelectric coupling sensor element of the present invention has higher sensitivity than the existing Hall sensor, can realize non-contact current monitoring, and has the advantage of being easy to deploy.

[0039] In step S2, the The model is used to describe the nonlinear relationship between the DC magnetic field and the response voltage of the magnetoelectric coupling sensor element. The model establishes the relationship between the piezomagnetic coefficient of the magnetic material and the DC magnetic field, in which the piezomagnetic coefficient of the magnetic material is linearly related to the response voltage: (6) (7) (8) in, is the piezomagnetic coefficient of the magnetostrictive material, is the compliance coefficient, is the magnetic susceptibility, is the saturation magnetic susceptibility, is the saturation magnetostriction coefficient, is the saturated Young's modulus, is the stress of the magnetostrictive layer, is the saturation stress of the magnetostrictive layer, is the vacuum permeability, is the effective initial magnetic induction intensity, for The magnetic susceptibility at for The magnetic susceptibility at is the effective magnetic field, For magnetostrictive materials, the effective magnetic field is an external DC magnetic field and magnetostrictive materials in an external magnetic field Demagnetization field sum: (5) in, . is the demagnetization factor. For magnetic materials with a certain structure, the demagnetization factor is a constant value. The model is used to describe the nonlinear relationship between the DC magnetic field and the response voltage of the magnetoelectric coupling sensor element, which can significantly improve the accuracy of the sensor element and reduce measurement errors.

[0040] The transformer dynamic bias current detection method based on magnetoelectric coupling sensing includes two closed loops, the first of which is to eliminate the AC magnetic field component by time averaging to complete the detection of the DC bias current on the neutral point grounding wire of the transformer. The second closed loop is carrier modulation technology to detect stray currents for urban rail transit.

[0041] In the step S2, when detecting the DC bias magnetization, the AC excitation magnetic field and the DC magnetic field to be measured exist simultaneously, which can be separated by the time averaging method and the frequency domain decoupling method. The total magnetic field is assumed to be: (2) in, is the DC magnetic field component, is the AC magnetic field component, Eliminate the AC magnetic field component by time averaging: (3) in, is the start time, the integration time is greater than the period of the AC excitation signal, The AC magnetic field component can be obtained by subtracting the DC magnetic field component from the total magnetic field. The calculation steps are as follows: (4) The frequency domain decoupling method separates the spectrum through Fourier transform and obtains the total output amplitude: (5) The DC component is The spectrum value at , the AC component is The spectrum value at is the total output amplitude, is the DC magnetic field, is the frequency-dependent sensitivity, is the alternating magnetic field, is the AC output amplitude, is the total magnetic field; like Figure 4As shown in the experimental results, the relationship curve between the DC magnetic field and the output voltage of the magnetoelectric coupling sensor element is obtained by eliminating the AC magnetic field component by time averaging. The DC bias current generates a DC magnetic field and acts on the magnetoelectric coupling sensor element. By measuring the change of the output voltage of the magnetoelectric coupling sensor element with the DC bias current, combined with The sensing model can be used to reversely infer the magnitude of the DC bias current.

[0042] according to The reverse calculation of the DC bias current includes the following steps: Step S2.1. When the magnetoelectric coupling sensor element detects an AC stray current signal, an AC excitation magnetic field is applied for modulation, and an AC excitation magnetic field is generated by connecting an excitation coil through a back-end processing circuit. The magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element, so that the magnetoelectric coupling sensor element works in a resonant state with high sensitivity (this is actually consistent with step S1, but for the sake of explanation, it is quoted); Step S2.2. When detecting DC bias magnetization, the AC excitation magnetic field and the DC magnetic field to be measured exist simultaneously, which can be separated by time averaging method and frequency domain decoupling method. According to formula (2), formula (3), formula (4), and formula (5), the AC magnetic field component can be eliminated by time averaging. Step S2.3. The sensing model is used to describe the nonlinear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. After eliminating the AC magnetic field component, the magnitude of the DC magnetic field is calculated; Step S2.4. According to the Biot-Savart law, the magnitude of the DC current is converted based on the DC magnetic field obtained in step S2.3.

[0043] Non-contact measurement of magneto-electric coupling sensing elements, Figure 5 As shown in the figure, the magnetoelectric coupling sensor element is close to the conductor to be tested, and the DC magnetic field can be applied to the device. The total signal contains DC and AC. After eliminating the AC component, only the DC component remains, and the DC bias magnetic detection can be performed.

[0044] For the measurement of DC bias current, the device consists of a magnetoelectric coupling sensor element, an excitation coil, and a back-end processing circuit. The signal driving circuit is connected to the excitation coil to generate an excitation magnetic field. The magnetic field frequency generated by the excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element. When a bias current appears on the neutral point grounding wire of the transformer, the DC bias will magnetize the magnetostrictive material in the magnetoelectric coupling sensor element. After the magnetoelectric sensitive output signal is amplified and filtered, it is phase-locked to detect the phase information and obtain the direction of the current. Convert the current, convert the signal into a DC output form, and obtain the amplitude information of the bias current; in terms of the back-end processing circuit, the DC component and AC component in the output signal of the sensor element can be effectively separated by the time averaging method and the frequency domain decoupling method, realizing the detection of the DC bias current under the AC background current. In the actual application scenario, the stray current in the neutral grounding wire of the transformer caused by the operation of urban rail transit has not only the DC component, but also the stray AC component below 1 Hz. The DC component and AC component can be separated by the time averaging method and the frequency domain decoupling method, and the AC component can be eliminated to obtain the DC component. The detection of DC bias has been completed, and the detection of DC bias current has been realized. Carrier modulation technology is required to detect stray AC components below 1 Hz.

[0045] For stray current detection in urban rail transit, the device proposed in the present invention can utilize the resonant amplification mechanism of the magnetoelectric coupling sensor element and the nonlinear strain characteristics of the magnetostrictive material to modulate the low-frequency stray current signal below 1 Hz to the frequency of the excitation coil through carrier modulation technology, that is, the resonant frequency of the magnetoelectric coupling sensor element, thereby achieving a significant improvement in the signal-to-noise ratio of the low-frequency stray current and completing the detection of the low-frequency stray current.

[0046] The nonlinear strain of the magnetostrictive material in step S3 is expressed by the following Taylor series formula: (10) in, for Magnetostrictive strain under DC bias, is the AC magnetic field strength at the point to be determined, It can be described by the following formula: (11) in, is the low-frequency stray AC magnetic field strength to be measured, The AC modulated magnetic field strength provided to the excitation coil, is the amplitude of the low-frequency stray AC magnetic field, The amplitude of the AC modulated magnetic field provided to the excitation coil, It's time. The frequency of the AC modulated magnetic field provided to the excitation coil, is the frequency of the low-frequency stray AC magnetic field to be measured. It should be noted that in formula (2) is the AC magnetic field component, which is the time average method used to measure the DC magnetic field, and the formula (11) The AC modulated magnetic field strength provided to the excitation coil is the carrier modulation technique used to measure stray currents.

[0047] The following output voltage signal is obtained: (12) in, is a constant determined by the material of the magnetoelectric coupling sensor element. is the maximum piezomagnetic coefficient of magnetostrictive material under zero bias, is the amplitude of the low-frequency stray AC magnetic field, The amplitude of the AC modulated magnetic field provided to the excitation coil ( a value in the range), The frequency of the AC modulated magnetic field provided to the excitation coil ( a value in the range), is the frequency of the low-frequency stray AC magnetic field to be measured, It is time. For the measurement of low-frequency stray current, the magnetoelectric coupling sensor element, the excitation coil, and the back-end processing circuit constitute the detection device. The signal driving circuit is connected to the excitation coil to generate an excitation magnetic field. The magnetic field frequency generated by the excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element, so that the magnetoelectric coupling sensor element works in a resonant state with high sensitivity.

[0048] Due to the nonlinear strain characteristics of magnetostrictive materials, low-frequency stray current signals will be modulated into the excitation signal in the form of a carrier wave, and the output voltage signal includes the AC modulated magnetic field signal and the low-frequency stray AC magnetic field signal to be measured. In the back-end processing circuit, the fast Fourier transform is used to obtain the frequency domain signal, and then the signal frequency and amplitude of the low-frequency stray AC magnetic field are obtained to realize the detection of low-frequency stray current. Based on the conversion relationship between the dynamic bias current and the magnetic field of the transformer, and using the nonlinear strain of the magnetostrictive material, we can also measure the low-frequency stray signal in the dynamic bias current of the transformer. Compared with the non-modulated direct measurement method, the magnetic field resolution can reach The signal-to-noise ratio is improved by nearly 2 orders of magnitude. This modulation test method is better than the Hall sensor ( Level Magnetic Field Resolution), Magnetoresistive sensor ( For sensors with linear outputs such as 100-level magnetic field resolution, it is more suitable for non-contact measurement of currents with a typical amplitude of hundreds of milliamperes to several amperes in the DC bias magnetic scenario of the neutral point grounding wire of the transformer. The signal driving circuit in step S1 is connected to the excitation coil to generate an excitation magnetic field. The magnetic field frequency generated by the excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element, so that the magnetoelectric coupling sensor element works in a resonant state with high sensitivity. Then, according to the nonlinear strain characteristics of the magnetostrictive material, the low-frequency stray current signal will be modulated into the excitation signal in the form of a carrier. The output voltage signal includes an AC modulated magnetic field signal and a low-frequency stray AC magnetic field signal to be measured. In the back-end processing circuit, a fast Fourier transform is used to obtain a frequency domain signal, and then the signal frequency and amplitude of the low-frequency stray AC magnetic field are obtained to complete the detection of the low-frequency stray current.

[0049] Figure 5 is the deployment scenario of the device. In the actual application scenario, the proposed dynamic bias current synchronous detection device is deployed near the neutral line of the transformer, and the sensitive axis direction of the magnetoelectric coupling sensor element is perpendicular to the bias current direction. Since the rails and the earth are not completely insulated, when urban rail transit is accelerating or decelerating, the traction current cannot completely return to the negative pole of the DC traction system through the rails. Some current will flow into the ground through the rails to form stray current. This part of the stray current flows into the grounding grid of the substation, thereby affecting the potential of the neutral point of the transformer and forming a bias current on its neutral line. The bias current is superimposed on the main magnetic field of the transformer, resulting in a magnetization curve offset and a DC bias phenomenon. A voltage signal of the resonant frequency of the magnetoelectric coupling sensor element is generated by a signal driving circuit and applied to the coil to generate an excitation magnetic field. The excitation magnetic field is used to drive the magnetoelectric coupling sensor element to work in a resonant state to obtain the highest detection sensitivity. In step S2, when a DC bias current exists on the neutral line of the transformer, a surrounding magnetic field is generated around the flat steel. The magnitude relationship between the current and the magnetic field can be expressed by the Biot-Savart law, and the direction relationship can be determined by the right-hand rule. For an infinitely long straight conductor, it can be expressed as: (13) in, is the distance from the point to be found to the center of the wire, is the current through the wire, is the vacuum magnetic permeability, and its value is , There is a linear relationship between the measured current and the magnetic field. The larger the current, the larger the magnetic field, and the magnetic field strength decreases with distance. The current shows linear attenuation, and the current can be calculated based on the magnetic field strength. When implementing the deployment, it is necessary to consider the influence of distance and position, and use the inverse attenuation relationship between magnetic field strength and distance to calibrate different types of grounding wires and provide the installation working condition parameters.

[0050] On this basis, when there is a bias current on the neutral line, according to the Biot-Saffar law, the magnetoelectric coupling sensor element will sense the corresponding DC magnetic field. Under the action of this magnetic field, the amplitude of the resonant signal output by the magnetoelectric coupling sensor element will change synchronously. After the signal is initially processed by the amplification and filtering circuit, the phase information is read out by the phase-locked detection circuit, and then The conversion circuit reads out the amplitude information of the resonant signal to form a standard current output form, thereby realizing the synchronous detection of the transformer dynamic bias current.

[0051] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0052] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A transformer dynamic bias current detection method based on magnetoelectric coupling sensing, characterized in that: The method comprises the following steps: Step S1. When the magnetoelectric coupling sensor element detects an AC stray current signal, an AC excitation magnetic field is applied for modulation, and an excitation coil is connected through a back-end processing circuit to generate an AC excitation magnetic field, and the magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonant frequency of the magnetoelectric coupling sensor element; Step S2. When a DC bias current appears on the neutral point grounding wire of the transformer, the DC bias current will magnetize the magnetostrictive material in the magnetoelectric coupling sensor element. The output signal of the magnetoelectric coupling sensor element is amplified and filtered, and then phase-locked detection is performed to read out the phase information, obtain the direction of the DC bias current, and then determine the polarity of the DC bias current in the transformer; The current is then converted through the back-end processing circuit, the signal is converted into a DC output form, the amplitude information of the bias current is obtained, and the DC component and AC component in the output signal of the magnetoelectric coupling sensor element are separated by the time averaging method and the frequency domain decoupling method, so as to complete the detection of the DC bias current under the AC background current; Step S3. In addition, when detecting stray currents in urban rail transit, the resonant amplification mechanism of the magnetoelectric coupling sensor element and the nonlinear strain characteristics of the magnetostrictive material can be utilized. Through carrier modulation, the low-frequency stray current signal below 1 Hz can be modulated to the resonant frequency of the magnetoelectric coupling sensor element. The resonant amplification effect is utilized to improve the response output to the low-frequency stray current signal, thereby improving the signal-to-noise ratio of the low-frequency stray current and completing the detection of the low-frequency stray current.

2. The transformer dynamic bias current detection method based on magnetoelectric coupling sensing according to claim 1 is characterized in that: The output signal of the magnetoelectric coupling sensor element at the resonant frequency in step S1 Output signal of magnetoelectric coupling sensor element at non-resonant frequency Satisfies the following equation: (1) in, is the mechanical quality factor, is the magnetomechanical conversion coefficient of the magnetostrictive material, is the electromechanical conversion coefficient of the piezoelectric material, is the angular frequency, is the static capacitance of the piezoelectric material, is the mechanical impedance of the magnetoelectric coupling sensor element, is the AC magnetic field strength at the point to be determined, d is the thickness of the piezoelectric material, j is an imaginary number related to the phase, is the output signal of the magnetoelectric coupling sensor element at the non-resonant frequency, and formula (1) is the voltage-magnetic field conversion relationship.

3. The transformer dynamic bias current detection method based on magnetoelectric coupling sensing according to claim 2 is characterized in that: In the step S2, when detecting the DC bias magnetization, the AC excitation magnetic field and the DC magnetic field to be measured exist simultaneously, and are separated by the time averaging method and the frequency domain decoupling method. The total magnetic field is assumed to be: (2) in, is the DC magnetic field component, is the AC magnetic field component, Eliminate the AC magnetic field component by time averaging: (3) in, is the start time, the integration time is greater than the period of the AC excitation signal, The AC magnetic field component can be obtained by subtracting the DC magnetic field component from the total magnetic field. The calculation steps are as follows: (4) The frequency domain decoupling method separates the spectrum through Fourier transform and obtains the total output amplitude: (5) The DC component is The spectrum value at , the AC component is The spectrum value at is the total output amplitude, is the DC magnetic field, is the frequency-dependent sensitivity, is the alternating magnetic field, is the AC output amplitude, is the total magnetic field; By eliminating the AC magnetic field component through time averaging, the relationship curve between the DC magnetic field and the output voltage of the magnetoelectric coupling sensor element is obtained. The DC bias current generates a DC magnetic field and acts on the magnetoelectric coupling sensor element. By measuring the change of the output voltage of the magnetoelectric coupling sensor element with the DC bias current, combined with The sensing model can be used to reversely infer the magnitude of the DC bias current.

4. The transformer dynamic bias current detection method based on magnetoelectric coupling sensing according to claim 3 is characterized in that: Said The sensing model is used to describe the nonlinear relationship between the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. The model establishes the relationship between the piezomagnetic coefficient of magnetic materials and the DC magnetic field: (6) (7) (8) in, is the piezomagnetic coefficient of the magnetostrictive material, is the compliance coefficient, is the magnetic susceptibility, is the saturation magnetic susceptibility, is the saturation magnetostriction coefficient, is the saturated Young's modulus, is the stress of the magnetostrictive layer, is the saturation stress of the magnetostrictive layer, is the vacuum permeability, is the effective initial magnetic induction intensity, for The magnetic susceptibility at for The magnetic susceptibility at is the effective magnetic field.

5. The transformer dynamic bias current detection method based on magnetoelectric coupling sensing according to claim 4 is characterized in that: Effective magnetic field is an external DC magnetic field and magnetostrictive materials in an external magnetic field Demagnetization field generated by sum: (9) in, , is the demagnetization factor. For a magnetic material with a certain structure, the demagnetization factor is a constant. The nonlinear strain of the magnetostrictive material in step S3 is expressed by the following Taylor series formula: （10） in, for Magnetostrictive strain under DC bias, is the AC magnetic field strength at the point to be determined, Described by the following formula: （11） in, is the low-frequency stray AC magnetic field strength to be measured, The AC modulated magnetic field strength provided to the excitation coil, is the amplitude of the low-frequency stray AC magnetic field, The amplitude of the AC modulated magnetic field provided to the excitation coil, It's time. The frequency of the AC modulated magnetic field provided to the excitation coil, is the frequency of the low-frequency stray AC magnetic field to be measured, The following output voltage signal is obtained: （12） in, is a constant determined by the material of the magnetoelectric coupling sensor element. is the maximum piezomagnetic coefficient of magnetostrictive material under zero bias, is the amplitude of the low-frequency stray AC magnetic field, The amplitude of the AC modulated magnetic field provided to the excitation coil is A value in the range, The frequency of the AC modulated magnetic field provided to the excitation coil is A value in the range, is the frequency of the low-frequency stray AC magnetic field to be measured, It's time. According to the nonlinear strain characteristics of magnetostrictive materials, low-frequency stray current signals will be modulated into the excitation signal in the form of carrier waves. The output voltage signal includes the AC modulated magnetic field signal and the low-frequency stray AC magnetic field signal to be measured. According to formula (1), the output voltage signal is converted into a magnetic field. The magnitude relationship between the current and the magnetic field is expressed by the Biot-Savart law, and the direction relationship is determined by the right-hand rule. For an infinitely long straight conductor, it can be expressed as: (13) in, is the distance from the point to be found to the center of the wire, is the current through the wire, is the vacuum permeability, and its value is , is the AC magnetic field strength of the point to be determined. According to formula (13), there is a linear correspondence between the measured current and the magnetic field. The larger the current, the larger the magnetic field, and the magnetic field strength increases with the distance. The increase shows a linear decay, so the current size can be calculated according to the magnetic field strength.

6. A transformer dynamic bias current detection device based on magnetoelectric coupling sensing, characterized in that: The detection device comprises a magnetoelectric coupling sensing element, an excitation coil, and a back-end processing circuit, wherein the excitation coil is wound along the length direction of the magnetoelectric coupling sensing element; The back-end processing circuit is provided with a signal driving circuit, a filtering and amplifying circuit, a phase-locked detection circuit, The conversion circuit and the signal driving circuit are connected to the excitation coil.

7. The transformer dynamic bias current detection device based on magnetoelectric coupling sensing according to claim 6 is characterized in that: The magnetoelectric coupling sensor element is provided with a piezoelectric material and a magnetostrictive material, and the piezoelectric material and the magnetostrictive material are connected by an adhesive.

8. The transformer dynamic bias current detection device based on magnetoelectric coupling sensing according to claim 7 is characterized in that: The piezoelectric material comprises an upper electrode surface and a lower electrode surface. The upper electrode surface and the lower electrode surface are externally connected to wires. The piezoelectric material is a sheet-like structure, and the number of the piezoelectric material is one.

9. The transformer dynamic bias current detection device based on magnetoelectric coupling sensing according to claim 8, characterized in that: The input end of the magnetoelectric coupling sensor element is connected to a signal driving circuit, and the output end of the magnetoelectric coupling sensor element is connected to a filtering and amplifying circuit.

10. The transformer dynamic bias current detection device based on magnetoelectric coupling sensing according to claim 9, characterized in that: The input end of the phase-locked detection circuit is connected to the output end of the signal driving circuit and the filter amplifier circuit respectively, and is used to detect the phase information of the signal source and the output signal of the magnetoelectric coupling sensor element. By comparing the phase information of the two, the real output signal of the magnetoelectric coupling sensor element can be extracted from the output signal of the filter amplifier circuit. The output end of the phase-locked detection circuit is connected to The input end of the conversion circuit is used to convert the AC signal waveform into a DC output form and output a stable amplitude signal. The output end of the signal driving circuit is connected to the input end of the magnetoelectric coupling sensing element to provide a signal source for the magnetoelectric coupling sensing element. The filtering and amplifying circuit is connected to the output end of the magnetoelectric coupling sensing element, and is used to amplify the signal output by the magnetoelectric coupling sensing element, and perform filtering and zeroing processing on the amplified output signal.

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