Current transformer capable of automatically switching transformation ratio and transformation ratio automatic switching method

Abstract

The invention relates to a current transformer capable of automatically switching the transformation ratio and an automatic transformation ratio switching method, and belongs to the technical field of current transformers, the current transformer comprises a current transformer body, and a secondary winding of the current transformer body is provided with at least two groups of output taps with different transformation ratios; the current detection unit is used for sampling primary side current in real time and calculating an effective value; the transformation ratio switching execution unit is connected to the output tap and used for changing the effective turn ratio connected to the measurement loop; the intelligent control unit is electrically connected with the current detection unit and the transformation ratio switching execution unit; and the protection unit is used for preventing a secondary side open circuit of the current transformer body in the transformation ratio switching process and in an abnormal state. The optimal transformation ratio is dynamically calculated in combination with current real-time and historical data, the transformation ratio switching execution unit is driven to automatically adjust the effective turn ratio of the secondary winding, and the problem that the measurement precision of a traditional current transformer is reduced due to the fixed transformation ratio in a wide load range is solved.

Description

Technical Field

[0001] This application belongs to the field of current transformer technology, specifically relating to a current transformer with automatically switchable transformation ratio and a method for automatically switching transformation ratio. Background Technology

[0002] Current transformers are used to proportionally convert large primary currents into smaller secondary currents for use in measurement, protection, and other equipment. Traditional current transformers typically employ a fixed ratio design, meaning the secondary winding has only one set of output taps, and the ratio is determined at the factory and cannot be adjusted. This design has significant shortcomings in scenarios with large variations in load current: when the primary current is small, the fixed ratio results in a weak secondary output signal, affecting measurement accuracy; while when the primary current approaches or exceeds its rated value, the fixed ratio may cause secondary output saturation, leading to misjudgments or failure to operate by protection devices. Furthermore, traditional current transformers require manual adjustment based on the expected load range, making them unable to adapt to dynamic current changes during actual operation, thus limiting the system's flexibility and reliability. Summary of the Invention

[0003] To solve the above problems, the technical solution adopted in this application is: The first aspect of this application provides a current transformer with an automatically switching ratio, comprising: The secondary winding of the current transformer body is provided with at least two sets of output taps with different turns ratios. The current detection unit is used to sample the primary side current in real time and calculate the effective value. A ratio switching execution unit is connected to the output tap and is used to change the effective turns ratio of the connected measurement circuit; The intelligent control unit is electrically connected to the current detection unit and the transformer ratio switching execution unit respectively. The intelligent control unit is configured to run an adaptive generalized predictive control algorithm to calculate the optimal transformer ratio based on real-time and historical data of the primary current, and output a switching control signal to the transformer ratio switching execution unit. The protection unit is used to prevent the secondary side of the current transformer body from opening during ratio switching and under abnormal conditions.

[0004] Furthermore, the number of output taps is three sets, namely the first output tap, the second output tap, and the third output tap; The ratio switching execution unit includes a first switching relay and a second switching relay. The two ends of the first switching relay are connected to the first output tap and the second output tap, respectively. The two ends of the second switching relay are connected to the third output tap and the output terminal of the first switching relay, respectively. An electricity meter is connected between the output terminal of the second switching relay and the common output terminal. The coils of the first switching relay and the second switching relay are controlled by the intelligent control unit.

[0005] Furthermore, both the first and second switching relays are magnetic latching relays.

[0006] Furthermore, the number of output taps is three sets, namely the first output tap, the second output tap, and the third output tap; The ratio switching execution unit includes a turntable, a switching motor, and a position switch. The position switch is electrically connected to the switching motor. A wheel sleeve is provided on the turntable, and a ratchet and a pawl are embedded in the wheel sleeve. The pawl and the ratchet are driven together to drive the turntable to rotate. The output shaft of the switching motor is connected to the ratchet. The turntable is provided with a moving contact and a stationary contact. The stationary contact is used to connect to the common output terminal. The moving contact can selectively connect to one of the stationary contacts corresponding to the positions of the first output tap, the second output tap, and the third output tap, to change the electrical connection point corresponding to the effective number of turns of the secondary winding. The coils of the switching motor and the power-off delay relay are respectively controlled by the intelligent control unit. The position switch consists of three sets of Hall sensors, which are respectively arranged at the output taps to detect the position of the moving contact.

[0007] Furthermore, the protection unit includes an instantaneous open-circuit protection circuit based on a hysteresis comparator; the instantaneous open-circuit protection circuit includes a voltage sampling module, a hysteresis comparator, and a high-speed solid-state relay connected in parallel across the secondary winding of the current transformer body; the hysteresis comparator compares the sampled secondary voltage with preset high and low thresholds, and when the voltage exceeds VH, drives the high-speed solid-state relay to close instantaneously to short-circuit the secondary winding; when the voltage drops below VL, drives the high-speed solid-state relay to open.

[0008] Furthermore, each relay contact in the ratio switching execution unit is connected in parallel with an RC buffer absorption circuit; the intelligent control unit is also connected to the status feedback node of each relay contact through an optocoupler isolation circuit to form a closed-loop verification circuit for the switching action.

[0009] Furthermore, it also includes a self-diagnostic module for monitoring the temperature of the CT unit, the number of relay actions, and the open-circuit protection action records, and uploading them to the monitoring system via a communication interface to achieve equipment status assessment and preventive maintenance.

[0010] The second aspect of this application provides an automatic ratio switching method for a current transformer, applied to the aforementioned current transformer capable of automatic ratio switching, comprising the following steps: Step S1: Real-time sampling of primary side current, calculation of multi-scale fluctuation characteristics, including the current change rate characteristic σ(t), steady-state deviation characteristic δ(t), and signal-to-noise ratio characteristic γ(t) within the current and historical windows, where: , ; , ; In the formula, L is the observation window length, which is 10 to 20, and α is the exponential decay coefficient, which is 0.1 to 0.3. These are time-varying weighting coefficients; Step S2: Construct an adaptive neural fuzzy inference system. Normalize σ(t), δ(t), and γ(t) and use them as inputs. Calculate the softening factor λ(t) using Gaussian membership functions and Takagi-Sugeno fuzzy rules, and adjust the rule parameters p online using gradient descent. i q i r i s i Specifically, it includes: Input normalization: , , ; Gaussian membership function: A i ∈{small(S), medium(M), large(L)}, parameter c i σ i Online adaptive adjustment; Construct 27 Takagi-Sugeno type rules: the i-th rule is if ∈A i and ∈B i and ∈C i ;but ; Output calculation: where i = 1 to 27; Parameters updated online: , ; Step S3: Considering the nonlinear saturation characteristics of the current transformer, establish the extended CARIMA model: ,in: For secondary side output current, This is a ratio control command. This is the primary side disturbance current. It is white noise. It is a difference operator; Solve the Diophantine equation to calculate the predicted output sequence based on the CARIMA multistep model. J = 1 to NP; Step S4: Construct the constrained multi-objective optimization objective function: Under constraints of ratio range, switching rate, and safety probability, the future control sequence that minimizes J is solved, and the optimal ratio command is extracted. ,in As the desired reference trajectory, To predict the time domain, To control the time domain, For smoothing weights; Step S5: Construct three-level interlocking conditions for switching decisions, including stability criteria, prediction consistency criteria, and economic criteria. When all three criteria are met simultaneously, the transformer ratio switching is performed under the coordinated monitoring of the protection circuit. Before switching, a virtual pre-simulation verification is performed through a digital twin. Physical switching is only allowed when the pre-simulation success rate exceeds 95%.

[0011] Furthermore, the parameters of the CARIMA model are adaptively tuned online using a recursive least squares method with a forgetting factor. The tuning algorithm is as follows: ;in: For model parameter vectors, For the data regression vector, Here is the gain matrix. Let covariance matrix be the variance matrix. This is the transpose of the regression vector. ∈[0.95,0.99] is the forgetting factor, which enables adaptive tracking of time-varying load characteristics.

[0012] Furthermore, step S5 establishes a handover verification mechanism based on digital twin technology to achieve virtual pre-simulation and security quantitative assessment before handover, specifically including: Digital Twin Construction: A real-time digital twin of the physical current transformer is established, and its state-space model is represented as follows: ;in It is a physical entity state vector (including core flux and winding current). For the state vector of the simulation model, For measurable disturbances, For unknown disturbances This is the synchronization gain matrix; State Synchronization and Calibration: Unscented Kalman Filtering (UKF) is used to synchronize the states of the physical entity and the digital twin. State statistics are propagated through Unscented Transform (UT), and the filter update equation is as follows: , ,in Represents the state distribution. For filter gain, This is the measured output of the physical system; Virtual simulation and evaluation: Injecting candidate transformer ratio commands into the simulation model Simulation predicts the future The dynamic response of each step is used to calculate the success rate of the rehearsal. Transient inrush current and steady-state error Only when the following conditions are met >95%, <1.5· When all safety indicators are qualified, a lockout release signal is sent to the physical protection circuit to allow actual switching to be performed; Hardware collaborative monitoring: During the switching process, the physical protection circuit monitors the differential value of the winding current and the transient impact multiple in real time. If the deviation between the simulation prediction and the actual measurement exceeds 15% or a protection relay action signal occurs, the switching lockout and emergency holding are immediately triggered to achieve prediction-actual closed-loop safety control.

[0013] Compared with the prior art, the beneficial effects of this application are as follows: 1. This application uses a current detection unit to sample primary current data in real time, and an intelligent control unit runs an adaptive generalized predictive control algorithm to dynamically calculate the optimal transformation ratio by combining real-time and historical current data. This drives the transformation ratio switching execution unit to automatically adjust the effective turns ratio of the secondary winding, thus solving the problem of decreased measurement accuracy caused by a fixed transformation ratio in traditional current transformers over a wide load range.

[0014] 2. This application innovatively designs a dual-redundancy protection mechanism: On the one hand, the protection unit adopts an instantaneous open-circuit protection circuit based on a hysteresis comparator. The voltage sampling module monitors the secondary voltage in real time. When an open-circuit risk is detected, the hysteresis comparator drives a high-speed solid-state relay to short-circuit the secondary winding within 5ms, limiting the open-circuit voltage to a safe range (<50V). This completely eliminates the hidden dangers of high voltage hazard to equipment and personal safety caused by open circuits on the secondary side of traditional current transformers. On the other hand, the magnetic latching relay or the switching motor with position feedback in the ratio switching execution unit, combined with the RC buffer absorption circuit, effectively suppresses arc interference during the switching process. Combined with the optocoupler-isolated state feedback loop of the intelligent control unit, closed-loop verification of the switching action is realized, increasing the switching success rate to over 99.99% and shortening the switching time to less than 100ms.

[0015] 3. This application, through its modular design of the output taps and multiple implementation schemes (relay-type or motor-type) for the ratio switching execution unit, allows for flexible configuration according to different application scenarios. It is suitable for compact installations in distribution automation systems and meets the high reliability requirements of substations, demonstrating excellent engineering practicality and technical scalability. In summary, this invention not only significantly improves the core performance indicators of current transformers but also provides innovative technical support for the safe and economical operation of power systems through intelligent and integrated design. Attached Figure Description

[0016] Figure 1 This is a structural diagram of the device in this application; Figure 2 This is a front view of Embodiment 1 of the device of this application; Figure 3 This is a right view of Embodiment 1 of the device of this application; Figure 4 For this Figure 2 Sectional view along section AA; Figure 5 This is an electrical schematic diagram of Embodiment 1 of the device in this application; Figure 6 This is a front view of Embodiment 2 of the device of this application; Figure 7 This is a right view of Embodiment 2 of the device of this application; Figure 8 for Figure 7 Sectional view along section BB; Figure 9 for Figure 6 Enlarged view of a portion of region C in the middle; Figure 10 This is a structural diagram of the stationary contact in the device of this application; Figure 11 This is a front view of the stationary contact in the device of this application; Figure 12This is a top view of the stationary contact in the device of this application; Figure 13 for Figure 11 Sectional view along section DD.

[0017] In the picture: 1. Current transformer body; 11. Output tap; 111. First output tap; 112. Second output tap; 113. Third output tap; 12. Switching box; 121. Box body; 122. Inner cover; 123. Outer cover. 2. Current detection unit; 3. Variable ratio switching execution unit, 31. First switching relay, 32. Second switching relay, 33. Turntable, 34. Switching motor, 35. Moving contact, 36. Stationary contact, 361. Bracket, 362. Cut-in slot, 363. Clamping slot, 364. Rotating shaft, 365. Clamping arm, 366. Spring, 37. Position switch, 38. Gear sleeve, 39. Ratchet, 40. Pawl; 4. Intelligent control unit; 5. Protection Unit. Detailed Implementation

[0018] The present application will be further described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present application.

[0019] Example 1 like Figures 1 to 5 As shown, this application provides an embodiment of a current transformer with an automatically switching ratio, which includes a current transformer body 1, a current detection unit 2, a ratio switching execution unit 3, an intelligent control unit 4, and a protection unit 5.

[0020] The secondary winding of the current transformer body 1 has multiple taps to provide at least two different turns ratios. In this embodiment, three sets of output taps 11 are preferably provided, namely the first output tap 111, the second output tap 112 and the third output tap 113, corresponding to three different standard turns ratios (e.g., 1000 / 5A, 600 / 5A, 200 / 5A).

[0021] The current detection unit 2 uses a high-precision sampling resistor or Rogowski coil, or other non-invasive sensor, to acquire the current signal flowing through the primary side of the current transformer in real time and calculate its effective value. This unit transmits the sampled signal to the intelligent control unit 4 through an isolation amplifier circuit.

[0022] The transformation ratio switching execution unit 3 is used to change the effective number of turns of the secondary winding connected to the measurement circuit (such as an electricity meter or protection device) according to control commands. In this embodiment, the unit adopts a relay switching scheme. Specifically, it includes a first switching relay 31 and a second switching relay 32. The first output tap 111 and the second output tap 112 are respectively connected to the two input terminals of the first switching relay 31, and the output terminal of the first switching relay 31 is connected to one input terminal of the second switching relay 32. The third output tap 113 is connected to the other input terminal of the second switching relay 32. The output terminal of the second switching relay 32 serves as a common output terminal and is connected to an external load (such as an electricity meter). The coil control terminals of the first switching relay 31 and the second switching relay 32 are respectively connected to the drive port of the intelligent control unit 4. By controlling the on / off combination of the two relays, the switching selection among the three taps can be realized, thereby changing the transformation ratio. Preferably, both the first switching relay 31 and the second switching relay 32 are magnetic latching relays, which are characterized by requiring pulse current only at the moment of switching and maintaining the contact position without power supply under normal conditions, which is beneficial for reducing power consumption and improving reliability.

[0023] The intelligent control unit 4 is the core of the system, typically implemented using a microcontroller or digital signal processor. It is electrically connected to the current detection unit 2 and the transformer ratio switching execution unit 3. The intelligent control unit 4 is configured to run an adaptive generalized predictive control (AGPC) algorithm. This algorithm dynamically calculates and determines the optimal transformer ratio at the current moment based on real-time and historical primary current data (including current effective value, trend, and short-term predicted value) provided by the current detection unit 2, combined with a preset transformer ratio switching threshold (e.g., the optimal measurement range is 20%-120% of the rated current for a long period). After determining the target transformer ratio, the intelligent control unit 4 outputs the corresponding switching control signal (e.g., a pulse sequence to drive the relay) to the transformer ratio switching execution unit 3. The intelligent control unit 4 is the "brain" of the system, responsible for running the complex adaptive generalized predictive control (AGPC) algorithm. Core processor: An industrial-grade microcontroller (MCU) with a floating-point unit (FPU) and sufficient RAM, such as ST's STM32H7 series or NXP's i.MX RT series, is selected. A clock frequency ≥ 400 MHz and RAM ≥ 512 KB are recommended. Analog-to-Digital Converter (ADC): Used to acquire analog signals from the current sensing unit. A dual-channel synchronous sampling ADC with 16-bit precision and a sampling rate ≥ 10 kSPS should be selected to accurately capture the current waveform. Digital Input / Output (I / O): Control Output: Used to drive relay coils or switch motors; optocoupler isolation is required. Status Feedback Input: Used to read relay contact status or Hall sensor signals; optocoupler isolation is required. Communication Interface: RS-485 / Ethernet: Used to upload self-diagnostic data (temperature, number of actions, event logs) to a remote monitoring system. Debugging Interface: SWD / JTAG, used for program download and debugging. Power Management: Design a wide voltage input (e.g., DC 9-36V) switching power supply circuit to provide stable and isolated power to the MCU, sensors, and actuators.

[0024] The core of protection unit 5 is an instantaneous open-circuit protection circuit based on a hysteresis comparator. It is designed to complete short-circuit protection within <5ms when a risk of open circuit on the secondary side is detected. This is used to prevent open-circuit hazards on the secondary side of the current transformer body 1 during ratio switching and under any abnormal conditions. In this embodiment, protection unit 5 includes an instantaneous open-circuit protection circuit based on a hysteresis comparator. This circuit includes a voltage sampling module, a hysteresis comparator, and a high-speed solid-state relay connected in parallel across the secondary winding of the current transformer body. The voltage sampling module monitors the induced voltage across the secondary winding in real time. The hysteresis comparator compares the sampled voltage value with preset high thresholds VH and VL. When the system is operating normally, the secondary voltage is low. Once an open circuit or a high voltage is generated during switching, exceeding VH, the hysteresis comparator quickly outputs a high level, driving the high-speed solid-state relay to close instantaneously, short-circuiting the secondary winding, thereby limiting the voltage and protecting equipment and personnel safety. When the fault is cleared and the secondary voltage drops below VL, the hysteresis comparator output flips, driving the high-speed solid-state relay to open, and the system returns to normal measurement status. Specifically, hysteresis comparator selection and parameter settings: Chip selection: Choose a high-speed, low-power rail-to-rail output comparator, such as TI's TLV7031 or ADI's LT1719, with a response time <1µs. Threshold settings: High threshold VH: Set to 50V. When the secondary open-circuit voltage exceeds this value, it is judged as a serious open-circuit fault, requiring immediate protection. Low threshold VL: Set to 10V. When the voltage drops below this value, the risk is considered eliminated, and normal operation can resume. Hysteresis width: VH - VL = 40V, effectively preventing frequent relay jitter caused by noise near the threshold. Threshold implementation circuit: Use a resistor divider network in conjunction with a reference voltage source (such as REF3025, 2.5V) to generate accurate VH and VL, which are connected to the negative input terminal of the comparator. High-speed solid-state relay (SSR) drive circuit: SSR selection: Use opto-isolated, zero-crossing triggered AC solid-state relays, such as Crydom's D2425, with a conduction time <1ms and a rated current greater than the maximum possible short-circuit current on the secondary side of the current transformer (typically designed for 50A instantaneous operation). Drive logic: Comparator output high level → SSR turns on (short-circuit secondary side); comparator output low level → SSR turns off. Additional protection: Connect a varistor (MOV) and an RC snubber circuit in parallel at the SSR output to absorb potentially higher voltage spikes.

[0025] To further improve system reliability, in the ratio switching execution unit 3, each relay (such as the first switching relay 31 and the second switching relay 32) has an RC buffer absorption circuit connected in parallel across its contacts to suppress the arc and voltage spikes generated when the contacts open. Simultaneously, the intelligent control unit 4 is connected to the status feedback node of each relay contact via an optocoupler isolation circuit to read the actual on / off state of the contacts in real time, forming a closed-loop verification circuit for the switching action and ensuring that the switching command is executed correctly.

[0026] The current transformer with automatically switching ratios in this embodiment also includes a self-diagnostic module. This module is integrated into the intelligent control unit 4 or functions as an independent functional unit, and is used to monitor key parameters such as the CT body temperature, the cumulative number of relay actions, and the historical action records of the open-circuit protection circuit. This data can be uploaded to the upper-level monitoring system via RS-485, Ethernet, or wireless communication interfaces to achieve online status assessment and preventive maintenance of the equipment, and to provide early warnings of potential faults.

[0027] It should also be noted that the device in this embodiment further includes a switching box 12, including a box body 121, an inner cover 122 and an outer cover 123. The box body 121 is fixedly connected to the current transformer body 1. The current detection unit 2, the ratio switching execution unit 3, the intelligent control unit 4 and the protection unit 5 are disposed inside the box body 121. The inner cover 122 is provided with the output terminal of the ratio switching execution unit 3 and the common terminal of the output tap. The inner cover 122 and the box body 121 are detachably connected by bolts. The outer cover 123 and the inner cover 122 are detachably connected by bolts.

[0028] Example 2 like Figures 6 to 13 As shown, this application provides a second embodiment of a current transformer with an automatic switching ratio. The core concept of this embodiment is the same as that of the first embodiment. The main difference lies in the specific implementation structure of the ratio switching execution unit. It should be noted that the working principle of other units (such as the protection unit) is the same as that of the first embodiment.

[0029] In this embodiment, the current transformer body 1 is also provided with three sets of output taps 11: the first output tap 111, the second output tap 112 and the third output tap 113.

[0030] The ratio switching actuator 3 adopts an electromechanical rotary switching mechanism. Its main components include a turntable 33, a switching motor 34, a moving contact 35, a stationary contact 36, a position switch 37, and a built-in ratchet 39 and pawl 40 transmission mechanism.

[0031] The turntable 33 is made of insulating material and can rotate around its axis. Moving contacts 35, which are either embedded or fixed to its edge, are either sliding brushes or elastic contact plates. Three stationary contacts 36 are fixedly mounted on the circumference of the first output tap 111, the second output tap 112, and the third output tap 113, respectively. A common stationary contact (not shown separately in the figure, but functionally similar to stationary contact 36 but serving as an output terminal) is connected to an external load. When the turntable 33 rotates, the moving contact 35 sequentially contacts different stationary contacts 36, thereby connecting the corresponding output taps to the common output circuit.

[0032] In the device of this embodiment, the stationary contact 36 includes a bracket 361. A transverse cutting groove 362 is provided on the bracket 361 for the moving contact 35 to screw in or out. Clamping arms 365 are provided on both sides of the cutting groove 362. The clamping arms 365 can be provided on one side or both sides. The clamping arms 365 are hinged to the bracket 361, and one end of each clamping arm 365 abuts against the moving contact 35 to connect the moving contact 35 and the stationary contact 36. The bracket 361 is provided with the cutting groove 362. A clamping groove 363 and a rotating shaft 364 are vertically arranged. A clamping arm 365 is disposed within the clamping groove 363 and rotates about the rotating shaft 364. A spring 366 is provided on the bracket 361 and is embedded in a spring groove on the bracket 361. One end of the spring 366 abuts against the clamping arm 365 to drive the clamping arm 365 to rotate, while the end away from the spring 366 clamps the moving contact 35 to enhance the clamping force between the moving contact 35 and the stationary contact 36 and reduce contact resistance. It should also be noted that the moving contact 35 is laterally inserted between the two clamping arms 365 along the cutting groove 362. Therefore, the two sides of the clamping arm 365 are rounded to reduce the resistance during screwing. To better enhance conductivity, the clamping arm 365 is made of copper and its surface is plated with a silver layer.

[0033] The switching motor 34 serves as the drive source, and its output shaft is connected to the turntable 33 via a one-way transmission mechanism consisting of a ratchet 39 and a pawl 40. Driven by the switching motor 34, the pawl 40 actuates the ratchet 39, thereby driving the turntable 33 to rotate stepwise. This ratchet and pawl mechanism prevents the turntable from shifting due to vibration or other reasons when not in a driven state, improving positioning reliability.

[0034] The position switch 37 is used to detect the real-time position of the moving contact 35 and provide feedback to the intelligent control unit 4. In this embodiment, the position switch 37 is preferably three sets of Hall sensors, which are precisely arranged near the stationary contacts 36 corresponding to the three output taps 11. When the moving contact 35, which is embedded with a permanent magnet, rotates to the corresponding position, the Hall sensor generates a signal, and the intelligent control unit 4 determines the currently active transformation ratio accordingly.

[0035] The power control terminal of the switching motor 34 and the coil of a power-off delay relay (J2) used to briefly disconnect the measurement circuit during switching are both controlled by the intelligent control unit 4. Based on the calculated optimal transformation ratio and the feedback from the position switch 37, the intelligent control unit 4 controls the switching motor 34 to rotate, driving the turntable 33 to rotate the moving contact 35 to the target stationary contact position, thus completing the transformation ratio switching.

[0036] In this embodiment, the structure and function of the current detection unit 2, the intelligent control unit 4 (running the same adaptive generalized predictive control algorithm), the protection unit 5, and other optional modules (such as the self-diagnosis module) are the same as or similar to those in Embodiment 1, and will not be described again here.

[0037] Example 3 This application provides an embodiment of an automatic switching method for the transformation ratio of a current transformer, comprising the following steps: Step S1: Real-time sampling of primary side current, calculation of multi-scale fluctuation characteristics, including the current change rate characteristic σt, steady-state deviation characteristic δt, and signal-to-noise ratio characteristic γt within the current and historical windows, where: , ; , ; In the formula, L is the observation window length, ranging from 10 to 20, used for moving average calculation; α is the exponential decay coefficient, ranging from 0.1 to 0.3, used for weighted decay of historical data. The time-varying weighting coefficient is used to adjust the contribution of data at different time points; σ(t) reflects the severity of current fluctuations and is used to determine whether a transient process (such as impact load) is in progress; δ(t) reflects the degree to which the current deviates from the steady-state value and is used to identify whether it deviates from the rated range for a long period; γ(t) reflects signal quality and is used to determine whether there is noise interference or signal distortion. In this step S1, multi-dimensional feature inputs are provided to the control algorithm to enhance the understanding of the dynamic characteristics of the current, realize multi-scale perception of load changes, and avoid misjudgments caused by a single indicator. Step S2: Construct an adaptive neural fuzzy inference system. Normalize σt, δt, and γt and use them as inputs. Calculate the softening factor λt using Gaussian membership functions and Takagi-Sugeno fuzzy rules, and adjust the rule parameters p online using gradient descent. i q i r i s i Specifically, it includes: Input normalization: , , ; Gaussian membership function: A i ∈{small S, medium M, large L}, parameter c i σ i Online adaptive adjustment; Construct 27 Takagi-Sugeno type rules: the i-th rule is if ∈A i and ∈B i and ∈C i ;but ; Output calculation: where i = 1 to 27; Parameters updated online: , The function of step S2 is to transform the three feature quantities into a softening factor λ(t) through fuzzy inference. λ(t) is used to adjust the conservatism or aggressiveness of the controller to adapt to different operating conditions. The rule parameters are adaptively updated using the online gradient descent method to improve inference accuracy. The achievable effect is to achieve intelligent decision softening, avoid frequent switching, enhance the system's adaptability, and adapt to different power grid operating states.

[0038] Step S3: Considering the nonlinear saturation characteristics of the current transformer, establish the extended CARIMA model: ,in: For secondary side output current, This is a ratio control command. This is the primary side disturbance current. It is white noise. It is a difference operator; Solve the Diophantine equation to calculate the predicted output sequence based on the CARIMA multistep model. J=1~NP; The function of step S3 in this embodiment is to use the CARIMA model to describe the dynamic characteristics of the system, including nonlinear saturation characteristics, which is more in line with the actual behavior of the current transformer, to achieve accurate prediction of the secondary current, to provide a model basis for optimized control, and to improve the accuracy of control.

[0039] Step S4: Construct the constrained multi-objective optimization objective function: Under constraints of ratio range, switching rate, and safety probability, the future control sequence that minimizes J is solved, and the optimal ratio command is extracted. ,in As the desired reference trajectory, To predict the time domain, To control the time domain, To smooth the weights, step S4 in this embodiment tracks the reference trajectory and controls the switching frequency. A softening factor is introduced to dynamically adjust the control weights, achieving a balance between accuracy and stability, reducing unnecessary ratio switching, and extending equipment life.

[0040] Step S5: Construct a three-level interlocking condition for switching decisions, including stability criteria, prediction consistency criteria, and economic criteria. When all three criteria are met simultaneously, the transformer ratio is switched under the collaborative monitoring of the protection circuit. Before switching, a virtual pre-simulation verification is performed using a digital twin. Physical switching is only allowed if the pre-simulation success rate exceeds 95%. In step S5 of this embodiment, the three-level criteria achieve stability, prediction consistency, and economic benefits. Through digital twin construction, state synchronization, virtual pre-simulation, and hardware collaborative monitoring, switching is only allowed when the virtual pre-simulation success rate is >95%, significantly improving security and achieving prediction-measurement closed-loop safety control. Interlocking is immediately implemented when the deviation exceeds 15%.

[0041] The parameters of the CARIMA model are adaptively tuned online using a recursive least squares method with a forgetting factor. The tuning algorithm is as follows: ;in: For model parameter vectors, For the data regression vector, Here is the gain matrix. Let covariance matrix be the variance matrix. This is the transpose of the regression vector. ∈[0.95,0.99] is the forgetting factor, which enables adaptive tracking of time-varying load characteristics.

[0042] Step S5 establishes a handover verification mechanism based on digital twin technology to achieve virtual pre-simulation and security quantitative assessment before handover, specifically including: Digital Twin Construction: A real-time digital twin of the physical current transformer is established, and its state-space model is represented as follows: ;in The physical entity state vector includes the core flux and winding current. For the state vector of the simulation model, For measurable disturbances, For unknown disturbances This is the synchronization gain matrix; State Synchronization and Calibration: Unscented Kalman Filter (UKF) is used to synchronize the state of the physical entity and the digital twin. The state statistics are propagated through the Unscented Transform (UT), and the filter update equation is as follows: , ,in Represents the state distribution. For filter gain, This is the measured output of the physical system; Virtual simulation and evaluation: Injecting candidate transformer ratio commands into the simulation model Simulation predicts the future The dynamic response of each step is used to calculate the success rate of the rehearsal. Transient inrush current and steady-state error Only when the following conditions are met >95%, <1.5· When all safety indicators are qualified, a lockout release signal is sent to the physical protection circuit to allow actual switching to be performed; Hardware collaborative monitoring: During the switching process, the physical protection circuit monitors the differential value of the winding current and the transient impact multiple in real time. If the deviation between the simulation prediction and the actual measurement exceeds 15% or a protection relay action signal occurs, the switching lockout and emergency holding are immediately triggered to achieve prediction-actual closed-loop safety control.

[0043] Of course, the above embodiments are not intended to limit this application, and this application is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this application should also fall within the protection scope of this application.

Claims

1. A current transformer with automatically switching transformation ratio, characterized in that: include: The current transformer body (1) has at least two sets of output taps (11) with different turns ratios in its secondary winding. The current detection unit (2) is used to sample the primary side current in real time and calculate the effective value; The ratio switching execution unit (3) is connected to the output tap (11) and is used to change the effective turns ratio of the connected measurement circuit; The intelligent control unit (4) is electrically connected to the current detection unit (2) and the transformer ratio switching execution unit (3), respectively. The intelligent control unit (4) is configured to run an adaptive generalized predictive control algorithm, calculate the optimal transformer ratio based on the real-time and historical data of the primary current, and output a switching control signal to the transformer ratio switching execution unit. The protection unit (5) is used to prevent the secondary side of the current transformer body (1) from opening during the ratio switching process and under abnormal conditions.

2. A current transformer with automatically switching transformation ratio according to claim 1, characterized in that: The number of output taps (11) is three sets, namely the first output tap (111), the second output tap (112) and the third output tap (113). The ratio switching execution unit (3) includes a first switching relay (31) and a second switching relay (32). The two ends of the first switching relay (31) are connected to the first output tap (111) and the second output tap (112) respectively. The two ends of the second switching relay (32) are connected to the third output tap (113) and the output end of the first switching relay (31) respectively. A meter is connected between the output end of the second switching relay (32) and the common output end. The coils of the first switching relay (31) and the second switching relay (32) are controlled by the intelligent control unit (4) respectively. The first switching relay (31) and the second switching relay (32) are both magnetic latching relays.

3. A current transformer with automatically switching transformation ratio according to claim 2, characterized in that: It also includes a switching box (12), which includes a box body (121), an inner cover (122) and an outer cover (123). The box body (121) is fixedly connected to the current transformer body (1). The current detection unit (2), the ratio switching execution unit (3), the intelligent control unit (4) and the protection unit (5) are arranged inside the box body (121). The inner cover (122) is provided with the output terminal of the ratio switching execution unit (3) and the common terminal of the output tap. The inner cover (122) and the box body (121) are detachably connected by bolts. The outer cover (123) and the inner cover (122) are detachably connected by bolts.

4. A current transformer with automatically switching transformation ratio according to claim 1, characterized in that: The number of output taps (11) is three sets, namely the first output tap (111), the second output tap (112) and the third output tap (113). The ratio switching execution unit (3) includes a turntable (33), a switching motor (34), and a position switch (37). The position switch (37) is electrically connected to the switching motor (34). A wheel sleeve (38) is provided on the turntable (33). A ratchet (39) and a pawl (40) are embedded in the wheel sleeve (38). The pawl (40) and the ratchet (39) are driven together to drive the turntable (33) to rotate. The output shaft of the switching motor (34) is connected to the ratchet (39). A moving contact (35) and a stationary contact (36) are provided on the turntable (33). There are multiple stationary contacts (36). The moving contact (35) can selectively contact one of the stationary contacts (36) of the first output tap (111), the second output tap (112) and the third output tap (113) to change the electrical connection point corresponding to the effective number of turns of the secondary winding. The coils of the switching motor (34) and the power-off delay relay (J2) are controlled by the intelligent control unit (4). The position switch (37) consists of three sets of Hall sensors, which are arranged at the output tap (11) to detect the position of the moving contact (35).

5. A current transformer with automatically switching transformation ratio according to claim 1, characterized in that: The protection unit (5) includes an instantaneous open-circuit protection circuit based on a hysteresis comparator; the instantaneous open-circuit protection circuit includes a voltage sampling module, a hysteresis comparator, and a high-speed solid-state relay connected in parallel across the secondary winding of the current transformer body; the hysteresis comparator compares the sampled secondary voltage with a preset high threshold VH and a low threshold VL. When the voltage exceeds VH, it drives the high-speed solid-state relay to close instantaneously to short-circuit the secondary winding; when the voltage drops below VL, it drives the high-speed solid-state relay to open.

6. A current transformer with automatically switching transformation ratio according to claim 2, characterized in that: Each relay contact in the ratio switching execution unit (3) is connected in parallel with an RC buffer absorption circuit; the intelligent control unit (4) is also connected to the status feedback node of each relay contact through an optocoupler isolation circuit to form a closed-loop verification circuit for the switching action.

7. A current transformer with automatically switching transformation ratio according to claim 6, characterized in that: It also includes a self-diagnostic module for monitoring the temperature of the CT unit, the number of relay actions, and the open-circuit protection action records, and uploads them to the monitoring system via a communication interface to achieve equipment status assessment and preventive maintenance.

8. A method for automatically switching the transformation ratio of a current transformer, applied to a current transformer with automatically switchable transformation ratio as described in any one of claims 1-7, characterized in that: Includes the following steps: Step S1: Real-time sampling of primary side current, calculation of multi-scale fluctuation characteristics, including the current change rate characteristic σ(t), steady-state deviation characteristic δ(t), and signal-to-noise ratio characteristic γ(t) within the current and historical windows, where: ， ； ， ； In the formula, L is the observation window length, which is 10 to 20, and α is the exponential decay coefficient, which is 0.1 to 0.

3. These are time-varying weighting coefficients; Step S2: Construct an adaptive neural fuzzy inference system. Normalize σ(t), δ(t), and γ(t) and use them as inputs. Calculate the softening factor λ(t) using Gaussian membership functions and Takagi-Sugeno fuzzy rules, and adjust the rule parameters p online using gradient descent. i q i r i s i Specifically, it includes: Input normalization: , , ; Gaussian membership function: A i ∈{small(S), medium(M), large(L)}, parameter c i σ i Online adaptive adjustment; Construct 27 Takagi-Sugeno type rules: the i-th rule is if ∈A i and ∈B i and ∈C i ;but ; Output calculation: where i = 1 to 27; Parameters updated online: , ; Step S3: Considering the nonlinear saturation characteristics of the current transformer, establish the extended CARIMA model: ,in: For secondary side output current, This is a ratio control command. This is the primary side disturbance current. It is white noise. It is a difference operator; Solve the Diophantine equation to calculate the predicted output sequence based on the CARIMA multistep model. J = 1 to NP; Step S4: Construct the constrained multi-objective optimization objective function: Under constraints of ratio range, switching rate, and safety probability, the future control sequence that minimizes J is solved, and the optimal ratio command is extracted. ,in As the desired reference trajectory, To predict the time domain, To control the time domain, For smoothing weights; Step S5: Construct three-level interlocking conditions for switching decisions, including stability criteria, prediction consistency criteria, and economic criteria. When all three criteria are met simultaneously, the transformer ratio switching is performed under the coordinated monitoring of the protection circuit. Before switching, a virtual pre-simulation verification is performed through a digital twin. Physical switching is only allowed when the pre-simulation success rate exceeds 95%.

9. The automatic switching method for the transformation ratio of a current transformer according to claim 8, characterized in that: The parameters of the CARIMA model are adaptively tuned online using a recursive least squares method with a forgetting factor. The tuning algorithm is as follows: ;in: For model parameter vectors, For the data regression vector, Here is the gain matrix. Let covariance matrix be the variance matrix. This is the transpose of the regression vector. ∈[0.95,0.99] is the forgetting factor, which enables adaptive tracking of time-varying load characteristics.

10. The automatic switching method for the transformation ratio of a current transformer according to claim 8, characterized in that: Step S5 establishes a handover verification mechanism based on digital twin technology to achieve virtual pre-simulation and security quantitative assessment before handover, specifically including: Digital Twin Construction: A real-time digital twin of the physical current transformer is established, and its state-space model is represented as follows: ;in For physical entity state vectors, For the state vector of the simulation model, For measurable disturbances, For unknown disturbances This is the synchronization gain matrix; State Synchronization and Calibration: Unscented Kalman Filtering (UKF) is used to synchronize the states of the physical entity and the digital twin. State statistics are propagated through Unscented Transform (UT), and the filter update equation is as follows: , ,in Represents the state distribution. For filter gain, This is the measured output of the physical system; Virtual simulation and evaluation: Injecting candidate transformer ratio commands into the simulation model Simulation predicts the future The dynamic response of each step is used to calculate the success rate of the rehearsal. Transient inrush current and steady-state error Only when the following conditions are met > 95%, < 1.5· When all safety indicators are qualified, a lockout release signal is sent to the physical protection circuit to allow actual switching to be performed; Hardware collaborative monitoring: During the switching process, the physical protection circuit monitors the differential value of the winding current and the transient impact multiple in real time. If the deviation between the simulation prediction and the actual measurement exceeds 15% or a protection relay action signal occurs, the switching lockout and emergency holding are immediately triggered to achieve prediction-actual closed-loop safety control.

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