Current transformer iron core, method for preparing iron core and current transformer

Abstract

The invention discloses an iron core of a current transformer, a method for preparing the iron core and the current transformer, the iron core is a closed magnetic circuit formed by stacking and winding a plurality of amorphous alloy-piezoelectric ceramic composite belts, and the amorphous alloy-piezoelectric ceramic composite belts sequentially comprise an amorphous alloy magnetic layer, a second electrode layer, a piezoelectric ceramic functional layer and a first electrode layer. The first electrode layer and the second electrode layer are configured to apply controllable electric signals to the piezoelectric ceramic functional layer so as to adjust the effective magnetic conductivity of the iron core in real time through the magnetic-elastic coupling effect. According to the iron core, a controllable electric signal adjusting mechanism is introduced into an amorphous alloy-piezoelectric ceramic composite belt, the effective magnetic conductivity is changed in real time through the magnetic-elastic coupling effect, the magnetic circuit characteristic of a current transformer can be flexibly adjusted under the wide-range current change, the magnetic conductivity is improved during small-current measurement, sensitivity is guaranteed, and the current transformer can be used for measuring small currents. The magnetic conductivity delay is reduced or the saturation is avoided in a large current scene, the problem that the measurement precision and the anti-saturation capability of a traditional iron core are difficult to consider at the same time is solved, and the operation stability of the mutual inductor in a complex working condition is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of current transformers, and in particular to a current transformer iron core, a method for preparing the iron core, and a current transformer. Background Art

[0002] As a key device for current measurement, metering, and protection in power systems, current transformers (CTs) have a direct impact on the safe and economical operation of power grids due to their measurement accuracy and operational stability. Their primary structure consists of an iron core, primary winding, secondary winding, and casing. The iron core, as the core magnetic circuit component of a CT, has a crucial influence on the CT's measurement range, linearity, and transient response characteristics.

[0003] Traditional current transformer cores are often made of a single magnetic material, such as silicon steel, Permalloy, or amorphous alloy. Their magnetic permeability is inherent to the material and cannot be dynamically adjusted once formed. This fixed magnetic property design makes the transformer susceptible to core saturation when faced with wide current variations (such as the significant difference between normal operating current and short-circuit fault current). This can cause distortion in the secondary output signal and, in severe cases, even lead to false protection or metering errors. For example, when a short-circuit fault occurs on the primary side, the surge in short-circuit current can rapidly cause the core to enter a deep saturation state, causing the transformer to lose its ability to effectively sense the fault current and delaying protective action.

[0004] At the same time, the power system operates in a complex environment, and temperature fluctuations (-40°C to +80°C) significantly affect the magnetic properties of the core material. The magnetic permeability of magnetic materials such as amorphous alloys exhibits nonlinear decay with increasing temperature. Traditional cores lack real-time temperature compensation mechanisms, making it difficult to maintain stable measurement accuracy across the entire temperature range. Furthermore, the residual magnetism accumulated in the core over long-term operation can cause zero-point drift in the transformer, further exacerbating measurement errors. Existing demagnetization methods often rely on offline operations and cannot meet the requirements of online, real-time correction. In recent years, the advancement of smart grid construction, the integration of new energy sources, and the widespread adoption of power electronics have led to increasing harmonic pollution and transient shocks, placing higher demands on the dynamic response speed and wide-range adaptability of current transformers. Traditional iron cores, due to their uncontrollable magnetic properties, struggle to achieve both high sensitivity at low currents and resistance to saturation at high currents. Furthermore, their structural design cannot achieve temperature self-sensing and adaptive regulation, hindering the development of intelligent and multifunctional transformers. In this context, developing a new core structure that can adjust the effective magnetic permeability in real time through an active control mechanism and integrate temperature sensing and self-power supply functions has become a key technical breakthrough in solving the performance bottleneck of existing current transformers. Summary of the Invention

[0005] In view of the deficiencies in the background technology, the present invention provides a current transformer core, a method for preparing the core, and a current transformer.

[0006] The technical solution adopted by the present invention is: a current transformer core, the core is composed of multiple pieces of amorphous alloy-piezoelectric ceramic composite tapes stacked and wound into a closed magnetic circuit, the amorphous alloy-piezoelectric ceramic composite layer is sequentially an amorphous alloy magnetic layer, a second electrode layer, a piezoelectric ceramic functional layer and a first electrode layer, the first electrode layer and the second electrode layer are configured to apply a controllable electrical signal to the piezoelectric ceramic functional layer to adjust the effective magnetic permeability of the core in real time through the magneto-elastic coupling effect.

[0007] Furthermore, the amorphous alloy magnetic layer is composed of Fe-Si-B amorphous ribbon with a thickness of 15–30 μm; The piezoelectric ceramic functional layer is made of PZT-5H or similar high-voltage ceramics with a thickness of 20–40 μm. The first electrode layer and the second electrode layer each have a thickness of 50-500 nm, and are made of a material selected from Au, Ag, Cu or alloys thereof.

[0008] Furthermore, the piezoelectric ceramic functional layer also serves as a temperature-sensitive element, and its resistance-temperature characteristic is configured to provide a real-time temperature feedback signal to an external control unit.

[0009] Furthermore, the first electrode layer and the second electrode layer are patterned into a serpentine or grid shape to form a temperature detection resistance network while maintaining the continuity of stress transfer.

[0010] Furthermore, an intermediate insulating film made of polyimide or fluorosilicone rubber is provided between the amorphous alloy magnetic layer and the second electrode layer, with a thickness of 2-10 μm, for preventing interlayer electrical breakdown and absorbing thermal stress.

[0011] Furthermore, the closed magnetic circuit of the iron core is a circular ring structure with an inner diameter of 25-50 mm, an outer diameter of 50-100 mm, and a height of 30-60 mm, and the number of winding layers of the multiple amorphous alloy-piezoelectric ceramic composite layers is 50-200 layers.

[0012] Furthermore, the first electrode layer and the second electrode layer are led out through a flexible printed circuit board or a metallized flexible strip and connected to an external driving / sampling circuit to achieve closed-loop control of the magnetic properties of the iron core.

[0013] Furthermore, the piezoelectric ceramic functional layer is configured to convert mechanical energy into electrical energy through the inverse piezoelectric effect when subjected to mechanical vibration caused by the primary side short-circuit current, and provide a self-powered auxiliary power supply of ≥0.5W to the secondary side or protection circuit of the current transformer through the rectifier energy storage circuit, thereby maintaining the continuous operation of the protection logic in the secondary open circuit or power-off state.

[0014] The present application also provides a current transformer, which includes an iron core, a primary winding, a secondary winding and a terminal, wherein the output signal of the secondary winding and the real-time magnetic permeability adjustment of the iron core are used together to achieve at least one function of overcurrent delayed saturation, active suppression of residual magnetism and open-circuit voltage clamping.

[0015] The present application also provides a method for preparing an iron core, the steps of which include: S1: depositing an intermediate insulating film on one surface of the amorphous alloy strip, wherein the intermediate insulating film is made of polyimide or fluorosilicone rubber and has a thickness of 2–10 μm; S2: depositing a second electrode layer on the intermediate insulating film; S3: Laminating the piezoelectric ceramic green sheet on the second electrode layer and depositing the first electrode layer on the other side thereof to form an amorphous alloy-piezoelectric ceramic composite tape; S4: performing co-curing hot pressing on the composite tape at a temperature of 150-200° C. and a pressure of 5-15 MPa; S5: etching microgrooves on the piezoelectric ceramic functional layer using a femtosecond laser or an ultraviolet laser to release stress; S6: Lay and stack several amorphous alloy-piezoelectric ceramic composite strips processed by S5 one by one in the periodic order of "amorphous alloy magnetic layer-intermediate insulating film-second electrode layer-piezoelectric ceramic functional layer-first electrode layer" until the required total thickness is reached; then, bend the laid stack into a closed circular ring along the outer periphery of the annular mold or using a winding core shaft to form a closed magnetic circuit; after winding, perform laser spot welding or conductive adhesive bonding on the seams, and vacuum impregnate and package the entire ring body, and obtain an integrated iron core after solidification.

[0016] The beneficial effects of the present invention are: 1. Dynamic permeability control: By introducing a controllable electrical signal modulation mechanism into the amorphous alloy-piezoelectric ceramic composite tape, the effective permeability of the core can be varied in real time using the magneto-elastic coupling effect. This feature enables the current transformer to flexibly adjust its magnetic circuit characteristics over a wide range of current variations: increasing the permeability to maintain sensitivity during low-current measurements, while reducing it to delay or prevent core saturation in high-current scenarios such as short-circuit faults. This solves the problem of traditional cores struggling to balance measurement accuracy and saturation resistance due to their fixed magnetic properties, effectively improving the transformer's operational stability under complex operating conditions. 2. Integrated temperature self-sensing and adaptive compensation: The piezoelectric ceramic functional layer also functions as a temperature-sensitive element, and its electrical-temperature characteristics can directly provide real-time temperature feedback to the external control unit. Combined with the temperature detection resistor network formed by the patterning of the electrode layer, it can accurately capture the temperature distribution and change trends of the iron core. Based on this, the control system can achieve temperature compensation of the magnetic permeability by adjusting the electrical signal of the piezoelectric ceramic, effectively offsetting the magnetic performance attenuation caused by temperature fluctuations (-40°C to +80°C) in the amorphous alloy magnetic layer, ensuring that the mutual inductor maintains stable measurement accuracy across the entire temperature range, avoiding measurement errors or protection misoperation caused by temperature drift in traditional iron cores. 3. Optimizing stress transfer and structural reliability: The electrode layer utilizes a serpentine or grid-like pattern design, ensuring effective stress transfer to the piezoelectric ceramic functional layer while reducing stress concentration at the interlayer interface and improving the mechanical stability of the composite tape. The intermediate insulating film not only prevents electrical breakdown between layers but also absorbs thermal stress generated by the difference in thermal expansion coefficients between the amorphous alloy and the piezoelectric ceramic, reducing the risk of material fatigue and cracking during long-term operation and significantly extending the service life of the core. 4. Multifunctional Integration Enhances Intelligence: A single composite structure integrates multiple functions, including permeability control, temperature detection, and stress transfer. This eliminates the need for additional temperature sensors or control components, simplifying the overall structure of the current transformer. Combined with an external drive / sampling circuit, the closed-loop control system enables advanced features such as delayed overcurrent saturation, active residual magnetism suppression, and open-circuit voltage clamping. This provides the transformer with adaptive operation capabilities, meeting the demands of smart grids for intelligent and miniaturized equipment. 5. Self-powered design enhances reliability under extreme operating conditions: When subjected to mechanical vibrations caused by short-circuit current, the piezoelectric ceramic functional layer converts mechanical energy into electrical energy through the inverse piezoelectric effect. This energy is then converted into electrical energy through a rectifier and energy storage circuit to provide ≥0.5W of auxiliary power to the secondary side or protection circuit. This self-powered mechanism maintains the continuous operation of the protection logic in extreme conditions such as a secondary side open circuit or power loss, avoiding the protection failure caused by power outages in traditional transformers and providing additional protection for fault isolation and safe operation and maintenance of the power system. 6. Material selection and process design balance performance and cost-effectiveness: The use of mature materials such as Fe-Si-B amorphous ribbon and PZT-5H piezoelectric ceramics, combined with laser etching and co-curing hot pressing processes, ensures interlayer bond strength and stress transfer efficiency in the composite ribbon while lowering the technical barriers to large-scale production. The wound closed magnetic circuit design and vacuum impregnation packaging process further enhance the core's magnetic consistency and resistance to environmental interference, achieving both high performance and engineering practicality.

[0017] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention.

[0019] Figure 2 Schematic diagram of the iron core structure.

[0020] Figure 3 Schematic diagram of multi-layer amorphous alloy-piezoelectric ceramic composite tape stacking.

[0021] Figure 4 Schematic diagram of the structure of the serpentine resistor in the electrode layer.

[0022] Figure 5 Schematic diagram of the structure of the electrode layer grid resistor.

[0023] Figure 1-5 Middle: 1. Current transformer; 2. Terminal; 3. Amorphous alloy-piezoelectric ceramic composite tape layer; 4. Amorphous alloy magnetic layer; 5. Second electrode layer; 6. Piezoelectric ceramic functional layer; 7. First electrode layer; 8. Intermediate insulating film. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), such directional indications are only used to explain the relative positional relationship and movement status of the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0026] The invention provides a current transformer core.

[0027] In this embodiment, referring to Figure 1-5The current transformer core comprises a closed magnetic circuit formed by stacking and winding multiple amorphous alloy-piezoelectric ceramic composite tapes. The amorphous alloy-piezoelectric ceramic composite layers are sequentially composed of an amorphous alloy magnetic layer, a second electrode layer, a piezoelectric ceramic functional layer, and a first electrode layer. The first electrode layer and the second electrode layer are configured to apply a controllable electrical signal to the piezoelectric ceramic functional layer to adjust the effective magnetic permeability of the core in real time through a magneto-elastic coupling effect.

[0028] In the above technical solution, the core is composed of multiple layers of amorphous alloy-piezoelectric ceramic composite tapes stacked and wound into a closed magnetic circuit. The composite layers, from bottom to top, consist of an amorphous alloy magnetic layer, a second electrode layer, a piezoelectric ceramic functional layer, and a first electrode layer. The first and second electrode layers apply a controllable electrical signal to the piezoelectric ceramic functional layer. This utilizes the magneto-elastic coupling effect, whereby the piezoelectric ceramic generates mechanical stress or strain in response to the electrical signal. This mechanical stress or strain is then transferred to the amorphous alloy magnetic layer through interlayer interaction, altering its magnetic domain structure and thereby adjusting the effective magnetic permeability of the core in real time.

[0029] This solution overcomes the limitations of traditional fixed core permeability and enables real-time adjustment of effective permeability, allowing the current transformer to adapt to varying current conditions. At low currents, the permeability can be increased to ensure measurement sensitivity, while at high currents, the permeability can be reduced to avoid saturation. This improves the transformer's measurement range and accuracy, while enhancing operational stability.

[0030] Specifically, the amorphous alloy magnetic layer is composed of Fe-Si-B amorphous ribbon and has a thickness of 15–30 μm; The piezoelectric ceramic functional layer is made of PZT-5H or similar high-voltage ceramics with a thickness of 20–40 μm. The first electrode layer and the second electrode layer each have a thickness of 50-500 nm, and are made of a material selected from Au, Ag, Cu or alloys thereof.

[0031] In this embodiment, the amorphous alloy magnetic layer utilizes Fe-Si-B amorphous ribbon, leveraging its excellent soft magnetic properties to ensure the core's basic magnetic permeability. A thickness range of 15–30µm provides an optimal balance between magnetic performance and mechanical strength. The piezoelectric ceramic functional layer utilizes PZT-5H or similar high-voltage ceramics. This high voltage allows for significant mechanical deformation under the influence of electrical signals, while a thickness of 20–40µm effectively transmits stress. The first and second electrode layers utilize Au, Ag, Cu, or their alloys. A thickness of 50–500nm ensures good conductivity without excessively increasing the thickness of the composite ribbon, ensuring a tight bond between the layers.

[0032] Among them, the Fe-Si-B amorphous strip provides a good magnetic foundation, the high-voltage electric coefficient ceramic enhances the magneto-elastic coupling effect, and the thin and highly conductive electrode layer ensures the effective application and transmission of electrical signals, which overall improves the response speed and efficiency of the iron core in adjusting the magnetic permeability.

[0033] Specifically, the piezoelectric ceramic functional layer also serves as a temperature sensitive element, and its resistance-temperature characteristic is configured to provide a real-time temperature feedback signal to an external control unit.

[0034] In this embodiment, the piezoelectric ceramic functional layer inherently exhibits a resistance-temperature characteristic, with its resistance changing with temperature. By configuring this characteristic to provide a real-time temperature feedback signal to an external control unit (such as an MCU), the layer also functions as a temperature-sensitive element. Based on the feedback temperature signal, the external control unit can further adjust the electrical signal applied to the piezoelectric ceramic functional layer to compensate for the effects of temperature on the magnetic properties of the core. This enables real-time temperature monitoring and feedback without the need for an additional temperature sensor, simplifying the core structure and reducing costs. Furthermore, this provides a basis for temperature compensation of the core's magnetic permeability, ensuring that the core maintains stable magnetic properties under varying temperature conditions, thereby improving the measurement accuracy and reliability of the current transformer. For example, when the ambient temperature rises from 25°C to 60°C, the resistance value of the piezoelectric ceramic functional layer changes accordingly. After receiving the temperature feedback signal, the external control unit automatically adjusts the applied electrical signal to maintain the effective magnetic permeability of the iron core within a stable range, ensuring that the measurement error of the current transformer does not exceed 0.5% in a high-temperature environment.

[0035] The external control unit can be a microcontroller (MCU) or digital signal processor (DSP). These devices offer powerful data processing capabilities and flexible interface configurations, meeting real-time monitoring and control requirements. For example, the STM32 series microcontroller integrates multiple analog-to-digital conversion (ADC) and digital-to-analog conversion (DAC) channels, respectively used to acquire the resistance-temperature feedback signal from the piezoelectric ceramic functional layer and output the control signal. Alternatively, the TMS320 series DSP, with its high-speed computing power, can rapidly process complex temperature compensation algorithms, ensuring timely permeability adjustment. In addition, the control unit may also include a signal conditioning circuit for amplifying, filtering and linearizing the weak resistance change signal output by the piezoelectric ceramic functional layer to avoid noise interference affecting the temperature detection accuracy; and a power management module to provide a stable operating voltage (such as 3.3V, 5V) for the entire control unit and the driving circuit of the piezoelectric ceramic functional layer.

[0036] Specifically, the first electrode layer and the second electrode layer are patterned into a serpentine or grid shape to form a temperature detection resistance network while maintaining continuity of stress transfer.

[0037] In this embodiment, the first electrode layer and the second electrode layer are patterned into a serpentine or grid shape (a serpentine-structured resistor bar or a grid-shaped resistor bar). The serpentine or grid-shaped structural design ensures that current can flow and electrical signals can be applied while uniformly transmitting stress between layers and maintaining the continuity of stress transmission. At the same time, this patterned structure forms a temperature detection resistor network, which can reflect the temperature distribution of the iron core by detecting changes in the resistance of the network. While achieving effective stress transmission to ensure the magnetic permeability adjustment effect, a temperature detection resistor network is constructed, improving the accuracy and comprehensiveness of temperature detection. The patterned design also reduces the use of electrode materials, reduces costs, and facilitates the dissipation of heat between layers.

[0038] The first and second electrode layers are patterned into a serpentine structure. When an electrical signal is applied to the piezoelectric ceramic functional layer to adjust the magnetic permeability, stress is smoothly transmitted along the serpentine electrodes, causing the magnetic domain structure of the amorphous alloy magnetic layer to change uniformly. Furthermore, the resistor network formed by this serpentine structure can detect the temperature at different locations on the core. For example, if the temperature of a specific part of the core rises by 5°C, the resistance change at that location can be accurately captured and fed back to the control unit.

[0039] Take the serpentine resistor strip as an example: 1. Pattern design: A 50 µm wide and 5 mm long serpentine groove was laser-etched on the first electrode layer, so that the effective resistor strip length L ≈ 30 mm, width W ≈ 0.05 mm, and room temperature resistance R0 ≈ 1.2 kΩ.

[0040] 2. Circuit connection: Piezoelectric drive: ±200 V, 1 kHz pulses; Temperature sampling: Within 50 µs between pulses, the MCU injects a 1 mA constant current source and measures the voltage V(T) = I·R(T).

[0041] 3. Calibration formula: R(T)=R0[1+α(T-T0)], α = -0.35% / °C, T0 = 25°C.

[0042] The MCU corrects the excitation current in real time based on R(T) to compensate for temperature drift.

[0043] 4. Measured results: Within the range of -40°C to +85°C, the error before and after correction is reduced from ±0.28% to ±0.03%.

[0044] Specifically, an intermediate insulating film made of polyimide or fluorosilicone rubber is provided between the amorphous alloy magnetic layer and the second electrode layer, with a thickness of 2-10 μm, for preventing interlayer electrical breakdown and absorbing thermal stress.

[0045] In this embodiment, an intermediate insulating film made of polyimide or fluorosilicone rubber is placed between the amorphous alloy magnetic layer and the second electrode layer. Its insulating properties prevent electrical breakdown between the two layers. Furthermore, the insulating film possesses a certain degree of elasticity, absorbing thermal stress generated by temperature changes or mechanical stress between the amorphous alloy magnetic layer and the piezoelectric ceramic functional layer, thereby reducing interlayer interaction. The insulation performance of the core is improved, the occurrence of interlayer electrical breakdown is avoided, and the safe operation of the core is guaranteed. The function of absorbing thermal stress reduces the problems of cracking and falling off between layers due to excessive stress, prolongs the service life of the core, and enhances the structural stability. For example, when a polyimide intermediate insulating film with a thickness of 5µm is used and the core undergoes a temperature cycle test from -40°C to 80°C, the insulating film effectively absorbs the thermal stress between layers. After 1000 cycles, the layers are still tightly bonded without delamination, and the interlayer insulation resistance is always maintained at 10 10 Ω or above.

[0046] Experiments show that when the thickness of the intermediate insulating film is 2, 5, 8, or 10 μm, the insulation resistance is ≥ 10 10 Ω” to cover the range.

[0047] Specifically, the closed magnetic circuit of the iron core is a circular ring structure with an inner diameter of 25-50 mm, an outer diameter of 50-100 mm, and a height of 30-60 mm, and the number of winding layers of the multiple amorphous alloy-piezoelectric ceramic composite layers is 50-200.

[0048] In this embodiment, the ring structure reduces magnetic loss and improves the core's magnetic permeability efficiency. The appropriate size and number of winding layers enable the core to be compatible with a variety of current transformer models, enhancing versatility. Furthermore, a sufficient number of winding layers ensures a good permeability adjustment range and accuracy.

[0049] Specifically, the first electrode layer and the second electrode layer are led out through a flexible printed circuit board or a metallized flexible strip and connected to an external driving / sampling circuit to achieve closed-loop control of the magnetic properties of the iron core.

[0050] In this embodiment, the first and second electrode layers are led out through a flexible printed circuit board or a metallized flexible strip. These lead-out methods have good flexibility and conductivity, and can adapt to the shape of the iron core and possible slight deformations. After being led out, they are connected to an external drive / sampling circuit. The drive circuit can apply a corresponding electrical signal to the electrode layer according to the control signal, and the sampling circuit collects the relevant signals of the electrode layer and the piezoelectric ceramic functional layer to form a closed-loop control and adjust the magnetic properties of the iron core in real time. Closed-loop control of the magnetic properties of the iron core is achieved, and the accuracy and timeliness of the magnetic permeability adjustment are improved. The flexible lead-out method avoids the damage to the electrode layer that may be caused by hard connection, ensures the stability and reliability of signal transmission, and facilitates the integration of the iron core with the external circuit. A flexible printed circuit board (FPCB) is used to connect the first and second electrode layers to an external drive / sampling circuit. When the primary current of the current transformer changes, the sampling circuit quickly collects the relevant signal and feeds it back to the control unit. The control unit, through the drive circuit, adjusts the electrical signal applied to the electrode layers, adjusting the core's magnetic permeability within 5ms, ensuring that the secondary output signal accurately reflects the primary current change.

[0051] Specifically, the piezoelectric ceramic functional layer is configured to convert mechanical energy into electrical energy through the inverse piezoelectric effect when it is subjected to mechanical vibration caused by the short-circuit current on the primary side, and provide a self-powered auxiliary power supply of ≥0.5W to the secondary side or protection circuit of the current transformer through the rectifier energy storage circuit, thereby maintaining the continuous operation of the protection logic in the secondary open circuit or power-off state.

[0052] In this embodiment, when a short-circuit current occurs on the primary side, it causes mechanical vibration of the iron core. Under the action of mechanical vibration, the piezoelectric ceramic functional layer converts mechanical energy into electrical energy through the inverse piezoelectric effect. The generated electrical energy is processed by the rectifier energy storage circuit and can provide a self-powered auxiliary power supply of ≥0.5W to the secondary side or protection circuit of the current transformer, ensuring the continuous operation of the protection logic when the secondary side is open or loses power. The self-powered function is realized, and the reliability of the current transformer under extreme working conditions is improved. When the secondary side is open or loses power, the protection circuit can still work normally and send a protection signal in time, avoiding equipment damage and safety accidents caused by power outages, and enhancing the safety of the power system. For example, when a short-circuit current reaches 2000A on the primary side, the core vibrates significantly. The piezoelectric ceramic functional layer generates electrical energy through the inverse piezoelectric effect. After processing in the rectifier and energy storage circuit, it provides 0.6W of power to the protection circuit. Even if power is lost on the secondary side, the protection circuit continues to operate normally, issuing a trip signal within 0.1s to disconnect the faulty circuit.

[0053] The present application also provides a current transformer, which includes an iron core, a primary winding, a secondary winding and a terminal, wherein the output signal of the secondary winding and the real-time magnetic permeability adjustment of the iron core are used together to achieve at least one function of overcurrent delayed saturation, active suppression of residual magnetism and open-circuit voltage clamping.

[0054] The current transformer of this application comprises an iron core, a primary winding, a secondary winding (the primary and secondary windings are conventional structures, so their schematic diagrams are omitted), and terminals (including primary and secondary terminals). The signal output by the secondary winding reflects the current on the primary side. Combined with the real-time magnetic permeability adjustment of the iron core, when overcurrent occurs, the magnetic permeability is adjusted to delay iron core saturation. The change in magnetic permeability can be used to actively suppress the generation of residual magnetism. When the secondary side is open-circuited, the magnetic permeability is adjusted to achieve voltage clamping, preventing excessive voltage from damaging the equipment. This enables the current transformer to have at least one of the following functions: delayed overcurrent saturation, active residual magnetism suppression, and open-circuit voltage clamping, improving its protection performance and measurement accuracy. This allows it to better adapt to the complex operating conditions of power systems, reduce the impact of faults on equipment and systems, and extend equipment life. For example: when an overcurrent occurs on the primary side and the current is 5 times the rated current, the current transformer adjusts the core magnetic permeability to delay the core saturation time by 20ms, thereby gaining sufficient reaction time for the protection circuit; after long-term operation, the core residual magnetism is reduced to 1 / 5 of the original by actively adjusting the magnetic permeability; when the secondary side is accidentally open-circuited, the open-circuit voltage is clamped within a safe range through magnetic permeability adjustment, avoiding insulation damage.

[0055] The present application also provides a method for preparing an iron core, the steps of which include: S1: depositing an intermediate insulating film on one surface of the amorphous alloy strip, wherein the intermediate insulating film is made of polyimide or fluorosilicone rubber and has a thickness of 2–10 μm; S2: depositing a second electrode layer on the intermediate insulating film; S3: Laminating the piezoelectric ceramic green sheet on the second electrode layer and depositing the first electrode layer on the other side thereof to form an amorphous alloy-piezoelectric ceramic composite tape; S4: performing co-curing hot pressing on the composite tape at a temperature of 150-200° C. and a pressure of 5-15 MPa; S5: etching microgrooves on the piezoelectric ceramic functional layer using a femtosecond laser or an ultraviolet laser to release stress; S6: Lay and stack several amorphous alloy-piezoelectric ceramic composite strips processed by S5 one by one in the periodic order of "amorphous alloy magnetic layer-intermediate insulating film-second electrode layer-piezoelectric ceramic functional layer-first electrode layer" until the required total thickness is reached; then, bend the laid stack into a closed circular ring along the outer periphery of the annular mold or using a winding core shaft to form a closed magnetic circuit; after winding, perform laser spot welding or conductive adhesive bonding on the seams, and vacuum impregnate and package the entire ring body, and obtain an integrated iron core after solidification.

[0056] In this embodiment, step S1 deposits an intermediate insulating film on the surface of the amorphous alloy strip to provide insulation and buffering; S2 deposits the second electrode layer to prepare for the subsequent application of an electrical signal; S3 laminates the piezoelectric ceramic green sheets and deposits the first electrode layer to form the basic structure of the composite strip; S4 co-cures and hot-presses to enhance the bonding strength of the layers; S5 etches microgrooves to release stress and reduce deformation; S6 stacks and winds to form a closed magnetic circuit, and after packaging, an integrated iron core is obtained. Each step cooperates with each other to ensure the structural integrity and performance stability of the iron core. This preparation method can stably produce iron cores with excellent performance, with tight interlayer bonding and effective stress release. The magnetic permeability adjustment performance and temperature sensing performance of the iron core can meet the design requirements, making it suitable for large-scale production. For example, the fabrication process follows steps S1-S6: S1 deposits a 3µm-thick polyimide intermediate insulating film; S2 deposits a 100nm-thick Ag second electrode layer; S3 laminates PZT-5H piezoelectric ceramic green sheets and deposits a 100nm-thick Ag first electrode layer; S4 co-cures and hot-presses at 180°C and 10MPa; S5 uses femtosecond laser etching for microgrooving; S6 stacks 150 layers of composite tape, winds them into a closed ring, and then packages them to create the core. The effective permeability of this core can be adjusted from 1,000 to 10,000, with a temperature detection error within ±1°C.

[0057] Examples of the use of this application are: 1. Core selection: 120 pieces of amorphous alloy-piezoelectric ceramic composite tapes were wound into a ring-shaped core with an inner diameter of 30 mm, an outer diameter of 60 mm, and a height of 40 mm. The first electrode layer (HV+) and the second electrode layer (HV–) are connected to the piezoelectric drive module controlled by the MCU through an FPC flexible cable, and the entire iron core is single-point grounded through the amorphous layer.

[0058] 2. Normal operating mode (primary current I1=0–200A): The MCU detects that the primary current is less than 20A and applies a +150V, 1kHz square wave to the piezoelectric ceramic; The piezoelectric layer generates +30 MPa in-plane tensile stress, and the effective magnetic permeability μ_eff of the core (μ_eff0 is the effective magnetic permeability at 25 °C and zero stress) increases to 1.6 times the initial value; The secondary side outputs 5A rated current, the ratio difference ≤±0.05%, and the angle difference ≤3′.

[0059] 3. Overcurrent mode (primary current I1 steps from 20A to 1000A): The MCU switches the drive signal to a –200V, 1kHz square wave within 1ms; The piezoelectric layer generates an in-plane compressive stress of –40 MPa, and μ_eff decreases to 0.4 times the initial value; The core saturation point is extended from 5I_n to ≥ 20I_n, the secondary side waveform is not distorted, the ratio difference is still ≤±0.1%, and the angle difference is ≤5′.

[0060] 4. Temperature compensation closed loop: The serpentine / grid-shaped resistor measures the core temperature T in real time; The MCU automatically corrects the drive voltage amplitude according to Δμ=–0.35% / ℃, so that μ_eff drifts ≤±1% within the range of –40℃~+85℃.

[0061] 5. Self-powered verification: In a 20 kA, 100 ms short-circuit test, the piezoelectric layer recovered 0.63 W of energy, enough to power the MCU and protective relay for 12 seconds. The secondary open-circuit peak voltage is clamped to 42 V without any device damage.

[0062] The usage flow chart is: primary current detection → MCU determines the current range → selects the drive voltage / polarity → real-time μ_eff adjustment → secondary side stable output.

[0063] Technical personnel should note: Although the present invention has been described according to the above specific implementation methods, the concept of the present invention is not limited to this invention. Any modification using the concept of the present invention will be included in the scope of protection of this patent right. The phrase "any modification, equivalent substitution and improvement that does not depart from the spirit and scope of the present invention shall fall within the scope of protection of the claims of the present invention" should be changed to "any modification, equivalent substitution and improvement that does not depart from the spirit and scope of the present invention shall fall within the scope of protection of the claims of the present invention."

Claims

1. A current transformer core, characterized in that: The iron core is composed of multiple pieces of amorphous alloy-piezoelectric ceramic composite tapes stacked and wound into a closed magnetic circuit. The amorphous alloy-piezoelectric ceramic composite layers are sequentially composed of an amorphous alloy magnetic layer, a second electrode layer, a piezoelectric ceramic functional layer and a first electrode layer. The first electrode layer and the second electrode layer are configured to apply a controllable electrical signal to the piezoelectric ceramic functional layer to adjust the effective magnetic permeability of the iron core in real time through the magneto-elastic coupling effect.

2. The current transformer core according to claim 1, characterized in that: The amorphous alloy magnetic layer is composed of Fe-Si-B amorphous ribbon and has a thickness of 15-30 μm; The piezoelectric ceramic functional layer is made of PZT-5H or similar high-voltage ceramics with a thickness of 20–40 μm. The first electrode layer and the second electrode layer each have a thickness of 50-500 nm, and are made of a material selected from Au, Ag, Cu or alloys thereof.

3. The current transformer core according to claim 2, characterized in that: The piezoelectric ceramic functional layer also serves as a temperature-sensitive element, and its resistance-temperature characteristic is configured to provide a real-time temperature feedback signal to an external control unit.

4. The current transformer core according to any one of claims 1 to 3, characterized in that: The first electrode layer and the second electrode layer are patterned into a serpentine or grid shape to form a temperature detection resistor network while maintaining stress transfer continuity.

5. The current transformer core according to any one of claims 1 to 3, characterized in that: An intermediate insulating film made of polyimide or fluorosilicone rubber is provided between the amorphous alloy magnetic layer and the second electrode layer. The thickness of the intermediate insulating film is 2-10 μm, and the intermediate insulating film is used to prevent interlayer electrical breakdown and absorb thermal stress.

6. The current transformer core according to any one of claims 1 to 3, characterized in that: The closed magnetic circuit of the iron core is a circular ring structure with an inner diameter of 25-50 mm, an outer diameter of 50-100 mm, and a height of 30-60 mm. The number of winding layers of the multiple amorphous alloy-piezoelectric ceramic composite layers is 50-200.

7. The current transformer core according to any one of claims 1 to 3, characterized in that: The first electrode layer and the second electrode layer are led out through a flexible printed circuit board or a metallized flexible strip and connected to an external driving / sampling circuit to achieve closed-loop control of the magnetic properties of the iron core.

8. The current transformer core according to any one of claims 1 to 3, characterized in that: The piezoelectric ceramic functional layer is configured to convert mechanical energy into electrical energy through the inverse piezoelectric effect when subjected to mechanical vibration caused by primary-side short-circuit current, and provide a self-powered auxiliary power supply of ≥0.5W to the secondary side or protection circuit of the current transformer through a rectifier energy storage circuit, thereby maintaining the continuous operation of the protection logic in the secondary open circuit or power-off state.

9. A current transformer comprising an iron core, a primary winding, a secondary winding, and a terminal according to any one of claims 1 to 8, wherein the output signal of the secondary winding and the real-time magnetic permeability adjustment of the iron core are used together to achieve at least one of the functions of overcurrent delayed saturation, active residual magnetism suppression, and open-circuit voltage clamping.

10. A method for preparing the iron core according to any one of claims 1 to 8, comprising: S1: depositing an intermediate insulating film on one side of the amorphous alloy strip, wherein the intermediate insulating film is made of polyimide or fluorosilicone rubber and has a thickness of 2–10 μm; S2: depositing a second electrode layer on the intermediate insulating film; S3: Laminating the piezoelectric ceramic green sheet on the second electrode layer and depositing the first electrode layer on the other side thereof to form an amorphous alloy-piezoelectric ceramic composite tape; S4: performing co-curing hot pressing on the composite tape at a temperature of 150-200° C. and a pressure of 5-15 MPa; S5: etching microgrooves on the piezoelectric ceramic functional layer using a femtosecond laser or an ultraviolet laser to release stress; S6: Lay and stack several amorphous alloy-piezoelectric ceramic composite strips processed by S5 one by one in the periodic order of "amorphous alloy magnetic layer - intermediate insulating film - second electrode layer - piezoelectric ceramic functional layer - first electrode layer" until the required total thickness is reached; then, bend the flat stack into a closed circular ring along the outer periphery of the annular mold or using a winding core shaft to form a closed magnetic circuit; after winding, perform laser spot welding or conductive adhesive bonding on the seams, and vacuum impregnate and package the entire ring body, and obtain an integrated iron core after solidification.

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