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

Abstract

This invention discloses a current transformer core, a method for preparing the core, and a current transformer. The core is composed of multiple layers of amorphous alloy-piezoelectric ceramic composite strips stacked and wound into a closed magnetic circuit. The amorphous alloy-piezoelectric ceramic composite strips sequentially 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 are configured to apply a controllable electrical signal to the piezoelectric ceramic functional layer, thereby adjusting the effective permeability of the core in real time through a magnetoelastic coupling effect. By introducing a controllable electrical signal adjustment mechanism into the amorphous alloy-piezoelectric ceramic composite strips, this core utilizes the magnetoelastic coupling effect to change the effective permeability in real time, enabling the current transformer to flexibly adjust its magnetic circuit characteristics under a wide range of current variations. It improves permeability to ensure sensitivity during low-current measurements and reduces permeability delay or avoids saturation in high-current scenarios. This solves the problem of traditional cores struggling to balance measurement accuracy and anti-saturation capability, significantly improving the operational stability of the transformer under complex operating conditions.

Description

Technical Field

[0001] This invention relates to the field of current transformer technology, specifically to a current transformer core, a method for preparing the core, and a current transformer. Background Technology

[0002] Current transformers are key devices in power systems for current measurement, metering, and protection. Their measurement accuracy and operational stability directly affect the safe and economical operation of the power grid. Their main structure consists of an iron core, primary winding, secondary winding, and casing. The iron core, as the core magnetic circuit component of the current transformer, has a decisive influence on the transformer's measurement range, linearity, and transient response characteristics due to its magnetic properties (especially effective permeability).

[0003] Traditional current transformer cores are mostly made of a single magnetic material such as silicon steel sheets, permalloy, or amorphous alloys. Their permeability is an inherent property of the material and cannot be dynamically adjusted once formed. This fixed magnetic characteristic design makes the transformer highly 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 causes distortion of the secondary side output signal, and in severe cases, can even lead to malfunctioning protection or inaccurate metering. For example, when a short-circuit fault occurs on the primary side, the surge in short-circuit current can cause the core to quickly enter a deep saturation state, resulting in the transformer losing its effective ability to sense the fault current and delaying the timing of protection action.

[0004] Meanwhile, the power system operates in a complex environment, and temperature fluctuations (-40℃ to +80℃) significantly affect the magnetic properties of the core material. The permeability of magnetic materials such as amorphous alloys decreases non-linearly with increasing temperature, while traditional cores lack real-time temperature compensation mechanisms, making it difficult to maintain stable measurement accuracy across the entire temperature range. Furthermore, residual magnetism accumulated in the core during long-term operation can cause zero-point drift in the current transformer, further exacerbating measurement errors. Existing demagnetization methods mostly rely on offline operations, which cannot meet the requirements for online real-time correction.

[0005] In recent years, with the advancement of smart grid construction, harmonic pollution and transient impacts brought about by the grid connection of new energy sources and the widespread adoption of power electronic equipment have intensified, 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 balance high sensitivity under low current and anti-saturation capability under high current. Their structural design also cannot achieve temperature self-sensing and adaptive adjustment, thus hindering the development of current transformers towards intelligence and multi-functionality.

[0006] Against this backdrop, developing a novel core structure that can adjust the effective permeability in real time through an active control mechanism and integrate temperature sensing and self-powering functions has become a key technological breakthrough in solving the performance bottleneck of existing current transformers. Summary of the Invention

[0007] To address the shortcomings of the prior art, this invention provides a current transformer core, a method for preparing the core, and a current transformer.

[0008] The technical solution adopted in this invention is: a current transformer core, wherein the core is a closed magnetic circuit formed by stacking and winding multiple amorphous alloy-piezoelectric ceramic composite strips, wherein the amorphous alloy-piezoelectric ceramic composite strips are sequentially an amorphous alloy magnetic layer, an intermediate insulating film, a second electrode layer, a piezoelectric ceramic functional layer and a first electrode layer, wherein the first electrode layer and the second electrode layer are configured to apply a controllable electrical signal to the piezoelectric ceramic functional layer, so as to adjust the effective permeability of the core in real time through the magnetoelastic coupling effect.

[0009] Furthermore, the amorphous alloy magnetic layer is composed of Fe-Si-B amorphous ribbon with a thickness of 15–30 µm;

[0010] The piezoelectric ceramic functional layer is composed of PZT-5H high piezoelectric coefficient ceramic with a thickness of 20–40µm.

[0011] The thickness of the first electrode layer and the second electrode layer is 50–500 nm, and the material is selected from Au, Ag, Cu or their alloys.

[0012] Furthermore, the piezoelectric ceramic functional layer also serves as a temperature-sensitive element, and its resistance-temperature characteristics are configured to provide a real-time temperature feedback signal to an external control unit.

[0013] Furthermore, the first and second electrode layers are patterned into a serpentine or grid shape to form a temperature sensing resistor network while maintaining the continuity of stress transmission.

[0014] Furthermore, an intermediate insulating film made of polyimide or fluorosilicone rubber with a thickness of 2–10 µm is provided between the amorphous alloy magnetic layer and the second electrode layer to prevent interlayer electrical breakdown and absorb thermal stress.

[0015] 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 strips is 50–200 layers.

[0016] Furthermore, the first and second electrode layers are led out through a flexible printed circuit board or a metallized flexible strip and connected to an external driving and sampling circuit to achieve closed-loop control of the magnetic properties of the iron core.

[0017] 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 ≥0.5W of self-powered auxiliary power to the secondary side of the current transformer or the protection circuit through the rectifier energy storage circuit, thereby maintaining the continuous operation of the protection logic in the secondary open circuit or power failure state.

[0018] This application also provides a current transformer, which includes an iron core, a primary winding, a secondary winding, and terminals, wherein the output signal of the secondary winding and the real-time permeability adjustment of the iron core are used together to achieve at least one of the functions of overcurrent delayed saturation, active suppression of residual magnetism, and open-circuit voltage clamping.

[0019] This application also provides a method for preparing an iron core, the steps of which include:

[0020] S1: An intermediate insulating film is deposited on one side surface of an amorphous alloy strip, the intermediate insulating film being composed of polyethylene.

[0021] Made of imide or fluorosilicone rubber, with its thickness controlled between 2–10 µm;

[0022] S2: Deposit a second electrode layer on the intermediate insulating film;

[0023] S3: A piezoelectric ceramic green sheet is laminated onto the second electrode layer, and a first electrode layer is deposited on the other side thereon to form an amorphous alloy-piezoelectric ceramic composite strip;

[0024] S4: Co-curing hot pressing is performed on the composite tape at a temperature of 150–200℃ and a pressure of 5–15MPa.

[0025] S5: Use a femtosecond laser or ultraviolet laser to etch microgrooves on the piezoelectric ceramic functional layer to release stress;

[0026] S6: Several amorphous alloy-piezoelectric ceramic composite strips treated by S5 are laid flat and stacked one by one in the cyclical 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, along the outer periphery of the ring mold or using a mandrel, the flatly stacked strips are bent into a closed ring to form a closed magnetic circuit; after rolling, the joints are laser spot welded or bonded with conductive adhesive, and the entire ring is vacuum impregnated and sealed. After curing, an integrated iron core is obtained.

[0027] The beneficial effects of this invention are:

[0028] 1. Achieving dynamic control of magnetic permeability: By introducing a controllable electrical signal adjustment mechanism into the amorphous alloy-piezoelectric ceramic composite strip, the effective magnetic permeability of the iron core can be changed in real time using the magnetoelastic coupling effect. This characteristic enables the current transformer to flexibly adjust the magnetic circuit characteristics under a wide range of current variations: increasing the magnetic permeability to ensure sensitivity during small current measurements, and reducing the magnetic permeability to delay or avoid iron core saturation under high current scenarios such as short-circuit faults. This solves the problem of difficulty in balancing measurement accuracy and anti-saturation capability caused by the fixed magnetic properties of traditional iron cores, effectively improving the operational stability of the transformer under complex operating conditions.

[0029] 2. Integrated Temperature Sensing and Adaptive Compensation: The piezoelectric ceramic functional layer also functions as a temperature-sensitive element, and its electro-temperature characteristics can directly provide real-time temperature feedback to the external control unit. Combined with the temperature-sensing resistor network formed by the patterned electrode layer, it can accurately capture the temperature distribution and change trend of the iron core. Based on this, the control system can achieve temperature compensation of magnetic permeability by adjusting the electrical signal of the piezoelectric ceramic, effectively offsetting the magnetic performance attenuation of the amorphous alloy magnetic layer caused by temperature fluctuations (-40℃ to +80℃), ensuring that the transformer maintains stable measurement accuracy across the entire temperature range, and avoiding measurement errors or protection malfunctions caused by temperature drift in traditional iron cores.

[0030] 3. Optimized stress transfer and structural reliability: The electrode layer adopts a serpentine or grid pattern design, which ensures effective stress transfer to the piezoelectric ceramic functional layer while reducing stress concentration at the interlayer interface, thus improving the mechanical stability of the composite strip. The intermediate insulating film not only prevents interlayer electrical breakdown but also absorbs the 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.

[0031] 4. Enhanced Intelligence Through Multifunctional Integration: A single composite structure integrates multiple functions such as permeability control, temperature detection, and stress transfer, eliminating the need for additional temperature sensors or control components and simplifying the overall structure of the current transformer. Combined with a closed-loop control system formed by external drive and sampling circuits, advanced functions such as overcurrent delayed saturation, active residual magnetism suppression, and open-circuit voltage clamping are achieved, enabling the transformer to operate adaptively and meeting the smart grid's demands for intelligent and miniaturized equipment.

[0032] 5. Self-powered design enhances reliability under extreme conditions: When the piezoelectric ceramic functional layer is subjected to mechanical vibration caused by short-circuit current, it can convert mechanical energy into electrical energy through the inverse piezoelectric effect, providing ≥0.5W of auxiliary power to the secondary side or protection circuit via a rectifier energy storage circuit. This self-powered mechanism can maintain the continuous operation of the protection logic under extreme conditions such as open circuit or power failure on the secondary side, avoiding the protection function failure problem caused by power failure of traditional instrument transformers, and providing additional protection for fault isolation and safe operation and maintenance of the power system.

[0033] 6. Material selection and process design balance performance and economy: Mature materials such as Fe-Si-B amorphous ribbons and PZT-5H piezoelectric ceramics are used, combined with laser etching and co-curing hot pressing processes. This ensures the interlayer bonding strength and stress transfer efficiency of the composite ribbon while lowering the technical threshold for large-scale production. The closed magnetic circuit design formed by winding and the vacuum impregnation packaging process further improve the consistency of the core's magnetic properties and its resistance to environmental interference, achieving both high performance and engineering practicality.

[0034] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the present invention.

[0036] Figure 2 This is a schematic diagram of the iron core structure.

[0037] Figure 3 This is a schematic diagram of a multilayer amorphous alloy-piezoelectric ceramic composite strip stack.

[0038] Figure 4 This is a schematic diagram of the serpentine resistor structure in the electrode layer.

[0039] Figure 5 This is a schematic diagram of the structure of the grid-shaped resistor with electrode layers.

[0040] Figure 1-5 In the middle: 1. Current transformer; 2. Terminal; 3. Amorphous alloy-piezoelectric ceramic composite strip; 4. Amorphous alloy magnetic layer; 5. Second electrode layer; 6. Piezoelectric ceramic functional layer; 7. First electrode layer; 8. Intermediate insulating film. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0043] This invention provides a current transformer core.

[0044] In this embodiment, refer to Figure 1-5 The current transformer core is a closed magnetic circuit formed by stacking and winding multiple amorphous alloy-piezoelectric ceramic composite strips. The amorphous alloy-piezoelectric ceramic composite strips are, in sequence, an amorphous alloy magnetic layer, an intermediate insulating film, a second electrode layer, a piezoelectric ceramic functional layer, and a first electrode layer. The first and second electrode layers are configured to apply controllable electrical signals to the piezoelectric ceramic functional layer to adjust the effective permeability of the core in real time through the magnetoelastic coupling effect.

[0045] In the above technical solution, the iron core is formed by stacking and winding multiple amorphous alloy-piezoelectric ceramic composite strips into a closed magnetic circuit. The composite layers, from bottom to top, are 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 controllable electrical signals to the piezoelectric ceramic functional layer. Utilizing the magnetoelastic coupling effect, i.e., the piezoelectric ceramic generates mechanical stress or strain under the action of the electrical signal, which is transmitted to the amorphous alloy magnetic layer through interlayer interaction, changing its magnetic domain structure, and thus adjusting the effective permeability of the iron core in real time.

[0046] This solution overcomes the limitations of traditional fixed core permeability, enabling real-time adjustment of effective permeability and allowing the current transformer to adapt to different current conditions. At low currents, permeability can be increased to ensure measurement sensitivity, while at high currents, permeability can be reduced to avoid saturation, thus improving the transformer's measurement range and accuracy, and enhancing operational stability.

[0047] Specifically, the amorphous alloy magnetic layer is composed of Fe-Si-B amorphous ribbon with a thickness of 15–30 µm;

[0048] The piezoelectric ceramic functional layer is composed of PZT-5H high piezoelectric coefficient ceramic with a thickness of 20–40µm.

[0049] The thickness of the first electrode layer and the second electrode layer is 50–500 nm, and the material is selected from Au, Ag, Cu or their alloys.

[0050] In this embodiment, the amorphous alloy magnetic layer uses Fe-Si-B amorphous ribbon, utilizing its excellent soft magnetic properties to ensure the basic magnetic permeability of the iron core. A thickness range of 15–30 µm effectively balances magnetic properties and mechanical strength. The piezoelectric ceramic functional layer uses PZT-5H or similar high-voltage ceramics. The high voltage coefficient allows it to produce significant mechanical deformation under electrical signals, and a thickness of 20–40 µm effectively transmits stress. The first and second electrode layers use Au, Ag, Cu, or their alloys. A thickness of 50–500 nm ensures good conductivity without excessively increasing the thickness of the composite ribbon, ensuring tight interlayer bonding.

[0051] Among them, Fe-Si-B amorphous ribbon provides a good magnetic foundation, high voltage coefficient ceramics enhance the magnetoelastic coupling effect, and thin and highly conductive electrode layer ensures the effective application and transmission of electrical signals, thus improving the overall response speed and efficiency of adjusting the magnetic permeability of the iron core.

[0052] Specifically, the piezoelectric ceramic functional layer also serves as a temperature-sensitive element, and its resistance-temperature characteristics are configured to provide a real-time temperature feedback signal to an external control unit.

[0053] In this embodiment, the piezoelectric ceramic functional layer itself possesses resistance-temperature characteristics, meaning its resistance changes with temperature. By configuring this characteristic to provide a real-time temperature feedback signal to an external control unit (such as an MCU), this layer simultaneously 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 effect of temperature on the magnetic properties of the iron core. This achieves real-time temperature monitoring and feedback, eliminating the need for an additional temperature sensor, simplifying the iron core structure, and reducing costs. Simultaneously, it provides a basis for temperature compensation of the iron core's permeability, enabling the iron core to maintain stable magnetic properties under different temperature environments, thus improving the measurement accuracy and reliability of the current transformer.

[0054] For example, when the ambient temperature rises from 25°C to 60°C, the resistance 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 keep the effective 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.

[0055] The external control unit can be a microcontroller (MCU) or a digital signal processor (DSP). These devices have powerful data processing capabilities and flexible interface configurations, meeting the needs of real-time monitoring and control. For example, an STM32 series microcontroller can be selected, which integrates multiple analog-to-digital converter (ADC) channels and digital-to-analog converter (DAC) channels, which can be used to acquire the resistance-temperature feedback signal of the piezoelectric ceramic functional layer and output the control signal, respectively. Alternatively, a TMS320 series DSP can be used, which, with its high-speed computing power, can quickly process complex temperature compensation algorithms to ensure timely adjustment of permeability.

[0056] 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 or 5V) for the entire control unit and the drive circuit of the piezoelectric ceramic functional layer.

[0057] Specifically, the first and second electrode layers are patterned into a serpentine or grid shape to form a temperature sensing resistor network while maintaining the continuity of stress transmission.

[0058] In this embodiment, the first and second electrode layers are patterned into a serpentine or grid shape (serpentine resistance bars or grid-shaped resistance bars). This serpentine or grid-shaped structural design ensures current flow and signal application while allowing stress to be uniformly transmitted between layers, maintaining the continuity of stress transmission. Simultaneously, this patterned structure forms a temperature-sensing resistor network, allowing the temperature distribution of the iron core to be reflected by detecting changes in the network's resistance. While achieving effective stress transmission to ensure permeability adjustment, the construction of a temperature-sensing resistor network improves the accuracy and comprehensiveness of temperature detection. The patterned design also reduces the use of electrode material, lowers costs, and facilitates heat dissipation between layers.

[0059] By patterning the first and second electrode layers into a serpentine structure, when an electrical signal is applied to the piezoelectric ceramic functional layer to adjust the magnetic permeability, stress can be smoothly transmitted along the serpentine electrodes, causing a uniform change in the magnetic domain structure of the amorphous alloy magnetic layer. Simultaneously, the resistance network formed by this serpentine structure can detect the temperature at different locations in the iron core. For example, when the temperature of a certain local area in the iron core increases by 5°C, the resistance change at the corresponding location can be accurately captured and fed back to the control unit.

[0060] The following example illustrates the use of a serpentine resistor bar:

[0061] 1. Pattern design: A serpentine groove with a width of 50 µm and a length of 5 mm is laser-etched on the first electrode layer, so that the effective resistance strip length L ≈ 30 mm, width W ≈ 0.05 mm, and room temperature resistance R0 ≈ 1.2 kΩ.

[0062] 2. Circuit connection: Piezoelectric drive: ±200 V, 1 kHz pulse; Temperature sampling: Within a 50 µs pulse gap, the MCU injects a 1 mA constant current source and measures the voltage V(T) = I·R(T).

[0063] 3. Calibration formula: R(T)=R0·[1+α(T-T0)], α = -0.35 % / ℃, T0 = 25 ℃.

[0064] The MCU adjusts the excitation current in real time based on R(T) to compensate for temperature drift.

[0065] 4. Actual measurement results: Within the range of -40 ℃ to +85 ℃, the difference before and after correction decreased from ±0.28% to ±0.03%.

[0066] Specifically, an intermediate insulating film made of polyimide or fluorosilicone rubber with a thickness of 2–10 µm is provided between the amorphous alloy magnetic layer and the second electrode layer to prevent interlayer electrical breakdown and absorb thermal stress.

[0067] In this embodiment, an intermediate insulating film made of polyimide or fluorosilicone rubber is disposed between the amorphous alloy magnetic layer and the second electrode layer. Its insulating properties prevent electrical breakdown between the amorphous alloy magnetic layer and the second electrode layer. Simultaneously, this insulating film has a certain degree of elasticity, which can absorb thermal stress generated by temperature changes or mechanical stress in the amorphous alloy magnetic layer and the piezoelectric ceramic functional layer, reducing the interlayer interaction forces.

[0068] It improves the insulation performance of the iron core, avoids interlayer electrical breakdown, and ensures the safe operation of the iron core. Its function of absorbing thermal stress reduces problems such as cracking and detachment between layers due to excessive stress, extends the service life of the iron core, and enhances structural stability.

[0069] For example, using a 5µm thick polyimide interlayer insulating film, when the iron core underwent temperature cycling tests from -40℃ to 80℃, the insulating film effectively absorbed the interlayer thermal stress. After 1000 cycles, the layers remained tightly bonded without delamination, and the interlayer insulation resistance consistently remained at 10 ohms. 10 Ω and above.

[0070] Experiments show that when the thickness of the intermediate insulating film is 2, 5, 8, and 10 μm, the insulation resistance is ≥10 Ω·m. 10 Ω" indicates the coverage area.

[0071] 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 multiple amorphous alloy-piezoelectric ceramic composite strips is 50–200.

[0072] In this embodiment, the ring structure reduces magnetic loss and improves the core's permeability efficiency. The appropriate size and number of winding layers allow the core to be adapted to various types of current transformers, enhancing its versatility. Simultaneously, a sufficient number of winding layers ensures that the core has a good permeability adjustment range and accuracy.

[0073] 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 and sampling circuit to achieve closed-loop control of the magnetic properties of the iron core.

[0074] In this embodiment, the first and second electrode layers are led out via flexible printed circuit boards or metallized flexible strips. These lead-out methods offer good flexibility and conductivity, adapting to the shape of the iron core and potential minor deformations. After being led out, they are connected to external driving and sampling circuits. The driving circuit applies corresponding electrical signals to the electrode layers according to control signals, while the sampling circuit collects relevant signals from the electrode layers and the piezoelectric ceramic functional layers, forming a closed-loop control to adjust the magnetic properties of the iron core in real time. This achieves closed-loop control of the iron core's magnetic properties, improving the accuracy and timeliness of permeability adjustment. The flexible lead-out method avoids damage to the electrode layers that may result from hard connections, ensuring the stability and reliability of signal transmission and facilitating the integration of the iron core with external circuits.

[0075] A flexible printed circuit board is used to bring out the first and second electrode layers and connect them to an external drive and sampling circuit. When the primary current of the current transformer changes, the sampling circuit quickly acquires the relevant signal and feeds it back to the control unit. The control unit adjusts the electrical signal applied to the electrode layers through the drive circuit, so that the permeability of the iron core is adjusted accordingly within 5ms, ensuring that the secondary output signal accurately reflects the change in primary current.

[0076] Specifically, 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 ≥0.5W of self-powered auxiliary power to the secondary side of the current transformer or the protection circuit through the rectifier energy storage circuit, thereby maintaining the continuous operation of the protection logic in the secondary open circuit or power failure state.

[0077] 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 this mechanical vibration, the piezoelectric ceramic functional layer converts mechanical energy into electrical energy through the inverse piezoelectric effect. The generated electrical energy, after being processed by the rectifier energy storage circuit, can provide ≥0.5W of self-powered auxiliary power to the secondary side of the current transformer or the protection circuit, ensuring the continuous operation of the protection logic in the event of a secondary side open circuit or power failure. This achieves self-powering functionality, improving the reliability of the current transformer under extreme operating conditions. Even when the secondary side is open-circuited or de-energized, the protection circuit can still operate normally, promptly issuing protection signals, avoiding equipment damage and safety accidents caused by power outages, and enhancing the safety of the power system.

[0078] For example, when a short-circuit current of 2000A occurs on the primary side, the iron core experiences significant mechanical vibration. The piezoelectric ceramic functional layer generates electrical energy through the inverse piezoelectric effect. After processing by the rectifier energy storage circuit, this energy is supplied to the protection circuit with 0.6W of power. Even if the secondary side loses power, the protection circuit can still operate normally, issuing a trip signal within 0.1s to disconnect the faulty circuit.

[0079] This application also provides a current transformer, which includes an iron core, a primary winding, a secondary winding, and terminals, wherein the output signal of the secondary winding and the real-time permeability adjustment of the iron core are used together to achieve at least one of the functions of overcurrent delayed saturation, active suppression of residual magnetism, and open-circuit voltage clamping.

[0080] The current transformer of this application includes an iron core, a primary winding, a secondary winding (the primary and secondary windings are common existing structures, so their structural views are omitted), and terminals (including primary and secondary terminals). The signal output by the secondary winding reflects the primary current. Combined with the real-time adjustment of the iron core's permeability, when an overcurrent occurs, the core saturation is delayed by adjusting the permeability; the change in permeability can actively suppress residual magnetism; and when the secondary side is open-circuited, adjusting the permeability achieves voltage clamping to prevent excessive voltage from damaging the equipment.

[0081] This enables current transformers to possess at least one of the following functions: overcurrent delayed saturation, active residual magnetism suppression, and open-circuit voltage clamping, thereby improving the protection performance and measurement accuracy of current transformers. It also allows them to better adapt to the complex operating conditions of power systems, reducing the impact of faults on equipment and systems, and extending equipment lifespan.

[0082] 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 permeability to delay the core saturation time by 20ms, providing sufficient reaction time for the protection circuit. After long-term operation, the residual magnetism of the core is reduced to 1 / 5 of its original value by actively adjusting the permeability. When the secondary side is accidentally open-circuited, the open-circuit voltage is clamped within a safe range by adjusting the permeability, thus avoiding insulation damage.

[0083] This application also provides a method for preparing an iron core, the steps of which include:

[0084] S1: An intermediate insulating film is deposited on one side surface of an amorphous alloy strip, the intermediate insulating film being composed of polyethylene.

[0085] Made of imide or fluorosilicone rubber, with its thickness controlled between 2–10 µm;

[0086] S2: Deposit a second electrode layer on the intermediate insulating film;

[0087] S3: Laminate a piezoelectric ceramic green sheet onto the second electrode layer, and deposit a first electrode on the other side thereof.

[0088] Electrode layer, forming an amorphous alloy-piezoelectric ceramic composite band;

[0089] S4: Perform co-curing hot pressing on the composite tape at a temperature of 150–200℃ and a pressure of 5–

[0090] 15MPa;

[0091] S5: Microgrooves are etched on the piezoelectric ceramic functional layer using a femtosecond laser or ultraviolet laser to release...

[0092] Stress relief;

[0093] S6: Several amorphous alloy-piezoelectric ceramic composite strips treated by S5 are arranged according to "amorphous alloy

[0094] The magnetic layer, intermediate insulating film, second electrode layer, piezoelectric ceramic functional layer, and first electrode layer are laid out in a cyclical sequence until the required total thickness is achieved. Then, the entire layered structure is bent into a closed ring along the outer circumference of the annular mold or using a mandrel to form a closed magnetic circuit. After rolling, the seams are laser-spot welded or bonded with conductive adhesive, and the entire ring is vacuum-impregnated and sealed. After curing, an integrated iron core is obtained.

[0095] In this embodiment, step S1 deposits an intermediate insulating film on the surface of the amorphous alloy strip, which serves as insulation and buffer; S2 deposits a second electrode layer to prepare for subsequent application of electrical signals; S3 laminates a piezoelectric ceramic green sheet and deposits a first electrode layer to form a composite strip basic structure; S4 co-curing and hot-pressing enhances the bonding force between the layers; S5 etching microgrooves to release stress and reduce deformation; S6 stacking and winding to form a closed magnetic circuit, and then encapsulating to obtain an integrated iron core. The steps work together to ensure the structural integrity and performance stability of the iron core. This preparation method can stably produce high-performance iron cores with tight interlayer bonding, effective stress release, and the core's permeability adjustment performance and temperature sensing performance all meet design requirements, making it suitable for mass production.

[0096] For example, the preparation is carried out according to steps S1-S6: In S1, a 3µm thick polyimide intermediate insulating film is deposited; in S2, a 100nm thick Ag second electrode layer is deposited; in S3, a PZT-5H piezoelectric ceramic green sheet is laminated and a 100nm thick Ag first electrode layer is deposited; in S4, co-curing hot pressing is performed at 180℃ and 10MPa; in S5, microgrooves are etched using a femtosecond laser; in S6, 150 layers of composite tape are stacked and wound into a closed ring, which is then packaged to obtain the iron core. The effective permeability of this iron core can be adjusted within the range of 1000-10000, and the temperature detection error is within ±1℃.

[0097] An example of how this application is used is as follows:

[0098] 1. Core selection:

[0099] 120 pieces of "amorphous alloy-piezoelectric ceramic composite tape" were selected and wound into a toroidal iron core with an inner diameter of 30 mm, an outer diameter of 60 mm, and a height of 40 mm.

[0100] The first electrode layer (HV+) and the second electrode layer (HV–) are connected to the piezoelectric drive module controlled by the MCU via FPC flexible flat cable, and the entire iron core is grounded at a single point through the amorphous layer.

[0101] 2. Normal operating mode (primary current I1 = 0–200A):

[0102] The MCU detects that the primary side current is <20A and applies a +150V, 1kHz square wave to the piezoelectric ceramic.

[0103] The piezoelectric layer generates an in-plane tensile stress of +30MPa, increasing the effective permeability μ_eff (μ_eff0 is the effective permeability at 25 ℃ and zero stress) of the iron core to 1.6 times the initial value;

[0104] The secondary side outputs a rated current of 5A, with a ratio difference ≤ ±0.05% and a phase difference ≤ 3′.

[0105] 3. Overcurrent mode (primary current I1 jumps from 20A to 1000A):

[0106] The MCU switches the drive signal to a -200V, 1kHz square wave within 1ms;

[0107] The piezoelectric layer generates an in-plane compressive stress of -40 MPa, and μ_eff decreases to 0.4 times its initial value;

[0108] The core saturation point expands from 5I_n to ≥ 20I_n, the secondary side waveform is undistorted, the ratio difference is still ≤ ±0.1%, and the angle difference is ≤ 5′.

[0109] 4. Temperature compensation closed loop:

[0110] The core temperature T is measured in real time using a serpentine / grid resistor.

[0111] The MCU automatically corrects the drive voltage amplitude according to Δμ = –0.35% / ℃, so that μ_eff drifts ≤±1% within the range of –40 ℃ to +85 ℃.

[0112] 5. Self-powered verification:

[0113] In a short-circuit test with a current of 20 kA and a duration of 100 ms, the piezoelectric layer recovered 0.63 W of energy, which was used to power the MCU and protection relay for 12 seconds.

[0114] The peak voltage of the secondary open circuit was clamped to 42 V, and no components were damaged.

[0115] The flowchart is as follows: primary current detection → MCU determines current range → selects drive voltage / polarity → real-time μ_eff adjustment → secondary side stable output.

[0116] Please note to all technical personnel: Although the present invention has been described according to the specific embodiments above, the ideas of the present invention are not limited to this invention. Any modifications that utilize the ideas of the present invention will be included in the scope of protection of this patent. It should be changed to "Any modifications, equivalent substitutions and improvements that do 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 core is a closed magnetic circuit formed by stacking and winding multiple amorphous alloy-piezoelectric ceramic composite strips. The amorphous alloy-piezoelectric ceramic composite strips are, in sequence, an amorphous alloy magnetic layer, an intermediate insulating film, 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 electrical signals to the piezoelectric ceramic functional layer to adjust the effective permeability of the core in real time through the magnetoelastic coupling effect. The amorphous alloy magnetic layer is composed of Fe-Si-B amorphous ribbon with a thickness of 15–30µm. The piezoelectric ceramic functional layer is composed of PZT-5H high piezoelectric coefficient ceramic with a thickness of 20–40µm. The thickness of the first electrode layer and the second electrode layer is 50–500 nm, and the material is selected from Au, Ag, Cu or their alloys; The piezoelectric ceramic functional layer also serves as a temperature-sensitive element, and its resistance-temperature characteristics are configured to provide a real-time temperature feedback signal to an external control unit. The first and second electrode layers are patterned into a serpentine or grid shape to form a temperature sensing resistor network while maintaining the continuity of stress transmission; An intermediate insulating film made of polyimide or fluorosilicone rubber with a thickness of 2–10 µm is provided between the amorphous alloy magnetic layer and the second electrode layer to prevent interlayer electrical breakdown and absorb thermal stress. The closed magnetic circuit of the iron core is a 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 strips is 50–200.

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

3. The current transformer core according to claim 1, 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 the primary side short-circuit current, and provide ≥0.5W of self-powered auxiliary power to the secondary side of the current transformer or the protection circuit through the rectifier energy storage circuit, thereby maintaining the continuous operation of the protection logic in the secondary open circuit or power failure state.

4. A current transformer comprising an iron core as described in any one of claims 1–3, further comprising a primary winding, a secondary winding, and terminals, wherein the output signal of the secondary winding and the real-time permeability adjustment of the iron core are used together to achieve at least one of the functions of overcurrent delayed saturation, active suppression of residual magnetism, and open-circuit voltage clamping.

5. A method for preparing an iron core as described in any one of claims 1–4, comprising the steps of: S1: An intermediate insulating film is deposited on one side surface of an amorphous alloy strip, the intermediate insulating film being composed of polyethylene. Made of imide or fluorosilicone rubber, with its thickness controlled between 2–10 µm; S2: Deposit a second electrode layer on the intermediate insulating film; S3: Laminate a piezoelectric ceramic green sheet onto the second electrode layer, and deposit a first electrode on the other side thereof. Electrode layer, forming an amorphous alloy-piezoelectric ceramic composite band; S4: Perform co-curing hot pressing on the composite tape at a temperature of 150–200℃ and a pressure of 5– 15MPa; S5: Microgrooves are etched on the piezoelectric ceramic functional layer using a femtosecond laser or ultraviolet laser to release... Stress relief; S6: Several amorphous alloy-piezoelectric ceramic composite strips treated by S5 are arranged according to "amorphous alloy The perimeter of the layer is defined as follows: magnetic layer—intermediate insulating film—second electrode layer—piezoelectric ceramic functional layer—first electrode layer. Layer the sheets sequentially until the desired total thickness is achieved; then, along the outer circumference of the annular mold or using... Using a mandrel, the flat, stacked layers are bent into a closed ring, forming a closed magnetic circuit; after winding, the... The seams are laser-spot welded or bonded with conductive adhesive, and the entire ring is vacuum-impregnated and sealed to solidify. After processing, an integrated iron core is obtained.

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