Modular outdoor current transformer quick live replacement method and system

Abstract

The application relates to the technical field of power equipment operation and maintenance, and provides a modular outdoor current transformer quick live replacement method and system, which comprises the following steps: establishing a detection loop by using a pilot detection contact in the process of inserting a connecting assembly into a base; injecting a detection signal into a parallel transition branch based on the conduction state of the detection loop; calculating a dynamic contact impedance based on a response component in the contact transition stage of a main current contact; adjusting an adjustable compensation impedance unit based on the deviation of the dynamic contact impedance and a preset impedance curve to make an equivalent total impedance track the preset impedance curve; and executing secondary side current switching and removing the parallel transition branch when the dynamic contact impedance meets preset stable conditions. The application realizes smooth switching of the secondary side current without impact, effectively avoids the risk of current mutation or open circuit, and improves the safety of live replacement operation.

Description

Technical Field

[0001] This application relates to the field of power equipment operation and maintenance technology, specifically to a method and system for rapid live-line replacement of modular outdoor current transformers. Background Technology

[0002] In power system operation and maintenance, current transformers are critical measurement and protection components, and their secondary circuits must never be open-circuited. When it is necessary to replace a modular outdoor current transformer in operation under live conditions, a parallel transition branch is usually used to maintain the continuity of the secondary current. However, existing live-line switching schemes mostly rely on transition circuits with fixed parameters or simple mechanical linkage structures. During the dynamic process of inserting the connector into the base, the contact resistance of the main current-carrying contact will fluctuate nonlinearly and drastically with the insertion depth, contact pressure, and surface oxide layer state. This impedance uncertainty of the physical contact interface can easily lead to uncontrolled current shunting ratio in the transition branch, which in turn can cause secondary current surges, waveform distortion, or even instantaneous open-circuit high voltage, seriously threatening the safety of microprocessor-based protection devices and the stable operation of the power grid. Therefore, a live-line switching technology solution that can sense the contact status in real time and actively adjust the transition impedance is needed. Summary of the Invention

[0003] To address the problem of current surge or open circuit risks caused by dynamic fluctuations in contact resistance during live replacement of the secondary side of current transformers in existing technologies, this application proposes a modular outdoor current transformer rapid live replacement method and system. This method utilizes a pilot detection contact to establish a monitoring circuit and inject a detection signal in the isolation frequency band. It calculates the dynamic contact impedance of the main current-carrying contact in real time and dynamically adjusts the compensation resistance value of the parallel transition branch to track the preset impedance curve, thereby achieving a smooth and shock-free switching of the secondary side current.

[0004] To achieve the above objectives, this application adopts the following technical solution: A modular outdoor current transformer rapid live-line replacement method is applied to switching scenarios involving a first transformer module and a second transformer module. The method includes: during the insertion of the connecting component into the base, establishing a detection circuit using a pilot detection contact on the connecting component that conducts before the main current-carrying contact; based on the conduction state of the detection circuit, injecting a detection signal into a parallel transition branch connecting the secondary output terminals of the first and second transformer modules; the parallel transition branch is connected in series with an adjustable compensation impedance unit; during the transition phase of the main current-carrying contact contact, calculating the dynamic contact impedance of the main current-carrying contact based on the response component corresponding to the detection signal in the parallel transition branch; adjusting the compensation resistance value of the adjustable compensation impedance unit based on the deviation between the dynamic contact impedance and a preset impedance curve, so that the equivalent total impedance of the parallel transition branch tracks the preset impedance curve; when the dynamic contact impedance meets a preset stability condition, performing a switching operation of the secondary current from the first transformer module to the second transformer module, and removing the parallel transition branch.

[0005] Optionally, a detection circuit is established using a pilot detection contact on the connecting assembly that conducts before the main current-carrying contact, including: when the connecting assembly is advanced along the insertion direction, the pilot detection contact forms electrical contact with the corresponding terminal before the main current-carrying contact, and the difference between the extension length of the pilot detection contact and the extension length of the main current-carrying contact corresponds to a preset advance contact stroke; based on the advance contact stroke, before the main current-carrying contact contacts the corresponding terminal, a detection circuit is established through the contact path between the pilot detection contact and the corresponding terminal; a detection signal is injected into the parallel transition branch connected between the secondary side output terminals of the first current transformer module and the second current transformer module, including: acquiring the cutoff frequency of the front-end analog low-pass filter of the protection device connected to the secondary side output terminal of the first current transformer module, and setting the frequency of the detection signal to a frequency band value higher than the cutoff frequency.

[0006] Optionally, injecting a detection signal into the parallel transition branch connected between the secondary output terminals of the first and second current transformer modules further includes: controlling the detection signal injection unit to inject a detection signal with an amplitude lower than a preset amplitude threshold into the parallel transition branch according to the frequency band value, so that the detection signal does not enter the sampling and calculation stage of the protection device after being attenuated by the front-end analog low-pass filter.

[0007] Optionally, during the transition phase of the main current-carrying contact, the dynamic contact impedance of the main current-carrying contact is calculated based on the response component corresponding to the probe signal in the parallel transition branch. This includes: continuously calculating the dynamic contact impedance according to a preset sampling period after the main current-carrying contact begins to contact the corresponding terminal; determining that the main current-carrying contact is in the transition phase when the dynamic contact impedance in multiple consecutive sampling periods is greater than a preset micro-contact upper limit threshold and the fluctuation amplitude between adjacent sampling periods of the dynamic contact impedance is greater than a preset fluctuation threshold; and performing bandpass filtering on the response component with the frequency of the probe signal as the center frequency to extract the voltage response component and the current response component, and calculating the dynamic contact impedance based on the voltage response component and the current response component.

[0008] Optionally, the voltage response component and current response component are extracted, and the dynamic contact impedance is calculated based on the voltage response component and current response component. This includes: acquiring a mixed voltage signal containing a power frequency component and a probe frequency component across a sampling resistor connected in series in the parallel transition branch, and performing bandpass filtering on the mixed voltage signal with the probe signal frequency as the center frequency to extract the voltage response component; synchronously acquiring the branch current signal in the parallel transition branch, and performing bandpass filtering on the branch current signal with the same center frequency to extract the current response component; calculating the ratio of the amplitude of the voltage response component to the amplitude of the current response component to obtain the dynamic contact impedance of the main current-carrying contact at the current insertion depth.

[0009] Optionally, based on the deviation between the dynamic contact impedance and the preset impedance curve, the compensation resistance value of the adjustable compensation impedance unit is adjusted so that the equivalent total impedance of the parallel transition branch tracks the preset impedance curve. This includes: when the deviation indicates that the dynamic contact impedance is greater than the target impedance value on the preset impedance curve, the compensation resistance value of the adjustable compensation impedance unit is reduced to offset the incremental portion of the dynamic contact impedance exceeding the target impedance value; when the deviation indicates that the dynamic contact impedance is less than the target impedance value, the compensation resistance value of the adjustable compensation impedance unit is increased to compensate for the reduction portion of the dynamic contact impedance below the target impedance value; after each adjustment of the compensation resistance value, the equivalent total impedance is recalculated, and it is verified that the direction of change of the equivalent total impedance relative to the previous sampling time is consistent with the direction of change of the preset impedance curve at the current insertion depth; if they are inconsistent, the compensation resistance value is corrected according to the preset fine-tuning step size until the direction of change of the equivalent total impedance is restored to consistency.

[0010] Optionally, the process of generating the preset impedance curve includes: fitting a reference curve of contact resistance-insertion depth based on the inverse relationship between the contact pressure value of the main current-carrying contact and the corresponding contact resistance calibration value of the connection component at different insertion depths; smoothing the reference curve of contact resistance-insertion depth to obtain the preset impedance curve; and using the impedance value corresponding to each insertion depth on the smoothed preset impedance curve as the target impedance value.

[0011] Optionally, when the dynamic contact impedance meets the preset stability condition, the following steps are taken: taking the current sampling time as the end point, a sliding window of a preset time length is truncated, and the variance of all dynamic contact impedances within the sliding window is calculated; when the variance is less than the preset variance threshold and all dynamic contact impedances within the sliding window are within the preset deviation range centered on the rated contact impedance value, it is determined that the dynamic contact impedance meets the preset stability condition.

[0012] Optionally, the operation of switching the secondary current from the first current transformer module to the second current transformer module is performed, including: while maintaining the current compensation resistance value of the adjustable compensation impedance unit unchanged, confirming that the amplitude and phase of the secondary output current of the second current transformer module are within a preset normal range; disconnecting the connection between the secondary output terminal of the first current transformer module and the secondary load circuit, so that the secondary load current flows through the second current transformer module and the parallel transition branch; after the secondary connection of the first current transformer module is disconnected, gradually adjusting the compensation resistance value of the adjustable compensation impedance unit to zero according to the preset impedance exit rate, so that the parallel transition branch smoothly exits the secondary load circuit.

[0013] Optionally, before performing the switching operation, the method further includes: sending a temporary blocking command to the differential protection device connected to the secondary output terminal of the first current transformer module, causing the differential protection device to enter a blocked state and suspending the calculation of the differential current criterion; the timing of sending the temporary blocking command is when the dynamic contact impedance first meets the preset stability condition; after the switching operation is completed and the parallel transition branch is removed, sending a blocking release command to the differential protection device, causing the differential protection device to return to normal operation; removing the parallel transition branch includes: stopping the injection of detection signals after disconnecting the secondary connection of the first current transformer module; disconnecting the connection between the adjustable compensation impedance unit and the parallel transition branch, and resetting the adjustable compensation impedance unit to its initial resistance value; disconnecting the connection between the pilot detection contact and the corresponding terminal in the base, and removing all physical wiring of the parallel transition branch; acquiring the power frequency current signal at the secondary output terminal of the second current transformer module, and verifying that the deviation of the amplitude and phase of the power frequency current signal from the historical power frequency current signal before the switching of the first current transformer module is within a preset allowable range.

[0014] In addition, this application also provides a modular outdoor current transformer rapid live-line replacement system, including: The system comprises a first current transformer module, a second current transformer module, a base, a parallel transition branch, a processor, and a memory. The memory stores a computer program, and the processor executes the computer program to implement the above-mentioned live replacement method.

[0015] The technical solution provided in this application, by setting a pilot detection contact on the connection component that conducts before the main current-carrying contact, can pre-establish a detection circuit before the main current-carrying contact actually carries current, providing a safe time window for subsequent impedance sensing; based on this, a detection signal of a specific frequency band is injected into the parallel transition branch, and the dynamic contact impedance of the main current-carrying contact during the insertion transition stage is calculated in real time using the response component of this signal, thereby transforming the invisible physical contact state into quantifiable electrical parameters; furthermore, by constructing a closed-loop feedback mechanism between the dynamic contact impedance and the preset impedance curve, based on two... The adjustable compensation impedance unit adjusts the resistance value in real time to compensate for the deviation of the current transformer, so that the equivalent total impedance of the parallel transition branch can actively track the preset ideal transition trajectory, effectively offsetting the random fluctuation of contact resistance caused by contact surface roughness, oxide layer or uneven insertion speed. Finally, the current switching and branch removal are only performed after the dynamic contact impedance meets the stability criterion. This fundamentally avoids the problems of sudden changes in secondary current, waveform distortion or instantaneous open circuit high voltage caused by poor contact in traditional passive switching schemes, and significantly improves the safety of live replacement of current transformers and the protection capability of the back-end microcomputer protection device. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a modular outdoor current transformer rapid live-line replacement method according to an embodiment of this application; Figure 2 This is a schematic diagram of a modular outdoor current transformer rapid live-line replacement system according to an embodiment of this application; Figure 3 This is a schematic diagram comparing the dynamic contact impedance changes of the main current-carrying contact during the insertion process according to an embodiment of this application; Figure 4 This is a schematic diagram of the equivalent total impedance tracking effect of the parallel transition branch in an embodiment of this application; Figure 5 This is a schematic diagram of the spectrum analysis of the sampled values ​​of the protection device in Comparative Group A of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] Example 1

[0020] like Figure 1 As shown in the figure, this application provides a method for rapid live-line replacement of modular outdoor current transformers. This method is applied to switching scenarios including a first transformer module and a second transformer module, aiming to solve the problem of current surge caused by contact resistance fluctuations during live-line replacement. The method mainly includes the following steps: Step S10: During the insertion of the connecting component into the base, a detection circuit is established using the pilot detection contact on the connecting component that conducts before the main current-carrying contact. Specifically, this step is the sensing starting point of the entire live-line replacement method. Mechanically, the physical length of the pilot detection contact is designed to be longer than that of the main current-carrying contact, or its installation position allows it to have a longer effective stroke in the insertion direction. This structural design ensures that the pilot detection contact has already established an electrical connection before the main current-carrying contact has made any physical contact with the base terminals. The reason why this circuit must be established before the main current-carrying contact conducts is that once the main current-carrying contact makes contact, it will immediately begin to carry secondary current. If the contact condition is poor at this time (such as the presence of an oxide film or insufficient contact pressure), it is very easy to generate an arc or transient overvoltage. The detection circuit established in advance by the pilot detection contact is equivalent to gaining a valuable "safety window" for the system, allowing the control system to obtain the initial state information of the contact interface in advance before the main current path is closed, thereby transforming the traditional "blind insertion" into "sensible and controlled insertion". It should be understood that although this embodiment describes the pilot detection contact achieving pilot detection through length difference, in other embodiments, a similar pilot detection function can also be achieved through an independent mechanical linkage mechanism or sensor, as long as the timing logic of "sensing first, then carrying current" is satisfied.

[0021] Step S20: Based on the conduction status of the detection circuit, a detection signal is injected into the parallel transition branch connecting the secondary output terminals of the first and second current transformer modules; wherein, the parallel transition branch is connected in series with an adjustable compensation impedance unit. Specifically, the system triggers the detection signal injection after the detection circuit in step S10 is confirmed to be conducting. The choice to inject a specific detection signal instead of directly using the existing power frequency current for measurement is based on two considerations: first, the amplitude and phase of the power frequency current on the secondary side of the current transformer change in real time with the primary load and may contain harmonic interference; directly using it as a measurement reference makes it difficult to separate pure contact impedance information; second, the power frequency current is the basis for the operation of the protection device, and applying additional modulation to it may cause malfunctions. Therefore, this application adopts an active injection method, introducing a detection signal isolated from the power frequency band as a "probe". This detection signal flows through the parallel transition branch, which connects the old and new current transformer modules, acting as a bridge for current diversion and transition. The adjustable compensation impedance unit connected in series in the branch circuit is the actuator for subsequent dynamic impedance matching. In this way, the system decouples the sensing of the contact state from the strong electrical interference environment, laying the foundation for subsequent accurate calculations.

[0022] Step S30: During the transition phase of the main current-carrying contact, the dynamic contact impedance of the main current-carrying contact is calculated based on the response component corresponding to the probe signal in the parallel transition branch. Specifically, the "transition phase of the main current-carrying contact" refers to the dynamic process from the moment the main current-carrying contact begins physical contact to the point of reaching a fully stable contact state. During this phase, due to the microscopic roughness of the contact surface, the rupture and reorganization of the oxide film, and the nonlinear increase in contact pressure, the contact impedance exhibits drastic random fluctuations, which is the fundamental reason for the failure of traditional switching schemes. This step utilizes the response components (including voltage and current responses) of the probe signal injected in step S20 during this phase, and through Ohm's law or a corresponding impedance calculation model, to deduce in real time the current actual impedance value of the main current-carrying contact, i.e., the "dynamic contact impedance." It is important to emphasize that the "dynamic contact impedance" here is a physical quantity that purely reflects the state of the physical contact interface. It objectively records the true electrical characteristics of the contact during the insertion process and is unaffected by external circuit parameters. The acquisition of this data transforms the previously invisible and uncontrollable mechanical contact process into a quantifiable and processable electrical signal, providing direct feedback for subsequent active compensation.

[0023] Step S40 involves adjusting the compensation resistance of the adjustable compensation impedance unit based on the deviation between the dynamic contact impedance and the preset impedance curve, so that the equivalent total impedance of the parallel transition branch tracks the preset impedance curve. Specifically, this is the core control element for achieving shockless switching in this application. The preset impedance curve represents the optimal impedance change trajectory that the transition branch should exhibit during an ideal insertion and removal process. It is usually generated based on extensive experimental calibration or theoretical models and is a smooth, continuous curve. However, the dynamic contact impedance measured in step S30 is often fluctuating and discontinuous. If the fluctuating contact impedance is directly connected to the circuit, it will inevitably lead to a sudden change in the shunt ratio. Therefore, this application introduces the control concept of "equivalent total impedance". The equivalent total impedance is equal to the sum of the dynamic contact impedance, the adjustable compensation impedance, and the fixed impedance of the line. The goal of the control system is not to forcibly eliminate the physical-level dynamic contact impedance fluctuations (which is almost impossible mechanically), but to "offset" or "fill" the deviation of the dynamic contact impedance from the preset curve by adjusting the resistance of the adjustable compensation impedance unit in real time. For example, when a sudden increase in dynamic contact impedance is detected, the control system immediately reduces the compensation resistance value, so that the sum of the two (i.e., the equivalent total impedance) remains near the expected value of the preset curve. This "electrical compensation" strategy essentially uses the flexible adjustment of electrical parameters to accommodate the rigid defects of mechanical contact, ensuring that the parallel transition branch always presents the preset ideal characteristics to the outside world, thereby completely eliminating the risk of current surge caused by poor contact.

[0024] Step S50: When the dynamic contact impedance meets the preset stability condition, the secondary current is switched from the first current transformer module to the second current transformer module, and the parallel transition branch is removed. Specifically, the preset stability condition is a "gating" criterion for determining whether the main current-carrying contact has completed the transition phase and entered a reliable contact state. Only when the value of the dynamic contact impedance and its fluctuation rate fall within the allowable range for a continuous period of time does the system determine that the physical connection is sufficiently stable and can safely carry the rated current. At this time, the system performs a formal switching operation, smoothly transferring the secondary load current from the old first current transformer module to the new second current transformer module. After confirming that the new module is operating normally and the old module has been safely disconnected, the parallel transition branch is removed in an orderly manner. This strict timing logic ensures that the secondary circuit of the current transformer remains closed throughout the entire switching process, and never an open circuit occurs. It also avoids the safety hazards caused by high-power current transfer during periods of unstable contact. Through the closed-loop process from S10 to S50 described above, this embodiment constructs a complete live-line switching defense system, realizing full-link control from state perception and active compensation to safe execution.

[0025] Example 2

[0026] Building upon Example 1, this example further details the physical implementation of establishing a detection circuit using the pilot detection contact in step S10, and the frequency band and amplitude isolation mechanism for injecting the detection signal in step S20. These features collectively constitute the defensive depth at the detection injection level, ensuring that the detection process can accurately sense the contact state without interfering with existing relay protection devices.

[0027] Specifically, as the connecting component advances along the insertion direction, the pilot probe contact forms electrical contact with the corresponding terminal before the main current-carrying contact. The difference between the extension length of the pilot probe contact and the extension length of the main current-carrying contact corresponds to a preset advance contact stroke. This advance contact stroke is the physical basis for implementing live switching sensing. In practical engineering applications, this extension length difference is usually designed to be in the range of 2 mm to 5 mm. Setting this specific range of advance stroke has a clear technical necessity: if the stroke is too short (e.g., less than 1 mm), due to the mechanical transmission gap and response delay, the main current-carrying contact may immediately conduct as soon as the pilot contact establishes a connection, making it impossible for the control system to complete the injection of the detection signal and the calculation of the initial impedance, thus losing the meaning of "pilot"; if the stroke is too long (e.g., greater than 10 mm), it will increase the overall size of the connecting component and the insertion and extraction resistance, and the excessively long pilot contact is more prone to mechanical deformation or damage during long-term operation. Therefore, based on this advance contact stroke, the system can reliably establish a detection circuit through the contact path between the pilot detection contact and the corresponding terminal during the "clean time window" before the main current-carrying contact has contacted the corresponding terminal, providing sufficient processing time for subsequent impedance sensing.

[0028] When injecting a probe signal into the parallel transition branch connecting the secondary output terminals of the first and second current transformer modules, this application employs a strict frequency band isolation strategy. Specifically, this involves obtaining the cutoff frequency of the analog low-pass filter at the front end of the protection device connected to the secondary output terminal of the first current transformer module, and setting the frequency of the probe signal to a frequency band value higher than this cutoff frequency. The cutoff frequency can be obtained in various ways, such as by reading the device nameplate parameters, consulting the technical manual, directly reading the device configuration through the communication interface, or actually measuring it through frequency sweep testing during system debugging. Setting the probe signal frequency higher than this cutoff frequency (for example, if the low-pass filter cutoff frequency of the protection device is 2kHz, then the probe signal frequency can be selected as 5kHz or higher) is based on the core mechanism of utilizing the analog low-pass filter inherent in the protection device's own hardware circuitry as a natural isolation barrier. Compared to relying solely on software algorithms for digital filtering and separation, this frequency band isolation method based on hardware physical characteristics offers higher reliability and determinism. It can prevent probe signals from entering the sample-and-hold circuit of the protection device at the source, completely avoiding the risk of protection malfunction due to algorithm failure or computational overflow.

[0029] To further enhance the isolation effect, this embodiment also introduces an amplitude isolation mechanism as a double insurance. Specifically, the detection signal injection unit injects a detection signal with an amplitude lower than a preset amplitude threshold into the parallel transition branch according to the aforementioned frequency band value. This ensures that the detection signal, after attenuation by the front-end analog low-pass filter, does not enter the sampling and calculation stage of the protection device. The preset amplitude threshold here is not an empirically fixed value, but a safety upper limit calculated based on the sampling noise floor of the protection device and the stopband attenuation rate of the filter at the detection frequency. Specifically, assuming the noise floor of the protection device's ADC sampling is 1mV, and the attenuation factor of the front-end analog low-pass filter at the selected detection frequency (e.g., 5kHz) is 40dB (i.e., 100 times), then the amplitude of the injected detection signal must be strictly controlled below 100mV (e.g., 50mV) to ensure that the remaining signal component (0.5mV) after attenuation by the filter is completely submerged below the sampling noise floor and will not be recognized as a valid signal by the analog-to-digital converter of the protection device. This synergistic effect of "frequency band isolation + amplitude suppression" ensures that the detection signal is "invisible" to the protection device, but "clearly measurable" to the sampling circuit in the parallel transition branch, perfectly achieving the technical goal of "measurable but not disturbing".

[0030] It should be understood that although this embodiment uses an analog low-pass filter as an example to illustrate the implementation of frequency band isolation, in other embodiments, if the protection device uses a band-pass filter or other types of anti-aliasing filters, the frequency of the detection signal in this application can also be set within the stopband range of the filter, as long as the functional requirement of "not affecting normal sampling after filter attenuation" is met. Similarly, the specific value of the advance contact stroke can also be adaptively adjusted according to the mechanical structural strength of the connecting components, the insertion and removal speed, and the response capability of the control system, and is not limited to the above-mentioned range of 2mm to 5mm. These variations all fall within the protection scope of the technical solution of this application.

[0031] Example 3

[0032] Building upon Example 1, this example further details the objective determination method for the transition phase of the main current-carrying contact in step S30, as well as the specific extraction and calculation algorithm for dynamic contact impedance. This implementation aims to transform the uncertainties in the physical contact process into quantifiable and verifiable electrical criteria, and to provide robust hardware and algorithmic support for impedance calculation.

[0033] Specifically, after the main current-carrying contact begins to contact the corresponding terminal, the system continuously calculates the dynamic contact impedance according to a preset sampling period. This preset sampling period should match the frequency of the detection signal. For example, when the detection signal frequency is 5kHz, the sampling frequency should at least satisfy the Nyquist sampling theorem, typically chosen to be above 10kHz to ensure waveform fidelity. Based on this, this application employs a dual-condition approach to determine whether the main current-carrying contact is in the transition phase: only when the dynamic contact impedance in multiple consecutive sampling periods is greater than a preset micro-contact upper limit threshold, and the fluctuation amplitude between adjacent sampling periods of the dynamic contact impedance is greater than a preset fluctuation threshold, is the main current-carrying contact determined to be in the transition phase. This dual-judgment mechanism has a clear technical focus: relying solely on the single condition of impedance greater than the upper limit threshold easily leads to misjudging the stable high-resistance state caused by surface contamination after the contact is fully inserted as the transition phase, or mistaking instantaneous spikes caused by external electromagnetic interference as the contact process; while introducing the fluctuation amplitude between adjacent periods as a second criterion effectively identifies the unique "sharp impedance jump" characteristic of the transition phase. The system only confirms that the contact is in the intermediate transition state from initial contact to stable contact when a high impedance value is accompanied by significant instability, thus avoiding false triggering of the control logic. It should be understood that the "multiple consecutive sampling periods" here can be set to 3 to 10 periods depending on the actual insertion / removal speed and mechanical vibration characteristics to ensure robustness of the judgment.

[0034] After confirming the transition phase, in order to accurately obtain impedance information reflecting the contact state from the complex electrical environment, this embodiment constructs a dedicated signal extraction link. Specifically, this includes: acquiring a mixed voltage signal containing power frequency and probe frequency components across a sampling resistor connected in series in the parallel transition branch; performing bandpass filtering on this mixed voltage signal with the probe signal frequency as the center frequency to extract the voltage response component; simultaneously acquiring the branch current signal in the parallel transition branch; and performing bandpass filtering on this branch current signal with the same center frequency to extract the current response component. In this process, the center frequency of the bandpass filter is strictly locked to the probe signal frequency injected in step S20 (e.g., 5kHz), and its bandwidth design must balance signal extraction efficiency and noise suppression capability. Because the secondary circuit of the current transformer contains a 50Hz power frequency current with an amplitude much larger than the probe signal and its harmonics, direct measurement is highly likely to cause ADC saturation or an excessively low signal-to-noise ratio. Through the above narrowband filtering processing centered on the probe frequency, the system can "strip" the weak probe response signal from the strong power frequency background, achieving physical isolation of the signal domain. At the same time, it is emphasized that the "synchronous acquisition" of voltage and current signals is crucial. This ensures that the two are strictly aligned on the time axis during subsequent calculations, eliminates the phase error introduced by the sampling time deviation, and plays a decisive role in improving the accuracy of impedance calculation.

[0035] Based on the extracted pure response components, the system further calculates the ratio of the amplitude of the voltage response component to the amplitude of the current response component to obtain the dynamic contact impedance of the main current-carrying contact at the current insertion depth. The amplitude ratio is chosen instead of the instantaneous value ratio for this calculation because in actual circuits, the contact interface and parasitic parameters of the circuit may cause a small phase difference between voltage and current. Directly dividing the instantaneous values ​​would introduce periodic errors. Using the amplitude ratio (i.e., the magnitude ratio) effectively avoids the influence of phase factors and more accurately reflects the pure resistive characteristics of the contact interface. Furthermore, this calculation process is completed in real time within each sampling period, enabling the control system to obtain a high-resolution dynamic impedance change curve, providing accurate feedback input for the compensation impedance adjustment in subsequent step S40. It should be understood that although this embodiment describes an implementation based on an analog bandpass filter and digital amplitude calculation, in other embodiments, algorithms such as digital quadrature demodulation, fast Fourier transform (FFT) or correlation detection can also be used to achieve the same function of signal extraction and impedance calculation. As long as the core logic is based on separating the response components of the probe signal frequency and deriving the impedance value accordingly, they all fall within the protection scope of this application.

[0036] Example 4

[0037] Based on Example 1, this example further details the specific control logic in step S40, which adjusts the compensation resistance value of the adjustable compensation impedance unit based on the deviation between the dynamic contact impedance and the preset impedance curve, so that the equivalent total impedance of the parallel transition branch tracks the preset impedance curve, as well as the generation mechanism of the preset impedance curve. This implementation method constitutes the core implementation path of the "active compensation" innovation of this application, aiming to accommodate the rigidity defects of mechanical contact through flexible adjustment of electrical parameters.

[0038] Specifically, to achieve accurate impedance tracking, it is first necessary to clarify the physical composition of the equivalent total impedance in the parallel transition branch. In this embodiment, the equivalent total impedance is equal to the sum of the dynamic contact impedance, the compensation resistance of the adjustable compensation impedance unit, and the fixed line impedance. The fixed line impedance is determined by the inherent resistance of the conductor, the sampling resistor, and the connector itself, and can be considered constant during switching. The dynamic contact impedance is a physical quantity that changes in real time with the insertion depth, reflecting the actual contact state of the contact interface. The compensation resistance is the only free variable that the control system can actively adjust. Based on this superposition relationship, the goal of adjustment is not to forcibly stabilize the dynamic contact impedance itself (which is almost impossible to achieve mechanically), but to adjust the compensation resistance in real time so that the sum of the three, i.e., the equivalent total impedance, closely matches the ideal trajectory defined by the preset impedance curve.

[0039] In terms of specific adjustment logic, this application adopts a deviation-driven negative feedback mechanism. When the deviation, representing the dynamic contact impedance, is greater than the target impedance value on the preset impedance curve, it indicates that the current physical contact state is worse than expected. At this time, the system reduces the compensation resistance value of the adjustable compensation impedance unit to offset the incremental part of the dynamic contact impedance exceeding the target impedance value. Conversely, when the deviation, representing the dynamic contact impedance, is less than the target impedance value, it indicates that the current physical contact state is better than expected (e.g., abnormally low contact resistance due to local overvoltage). At this time, the system increases the compensation resistance value of the adjustable compensation impedance unit to compensate for the reduction part of the dynamic contact impedance below the target impedance value. For example, assuming that at the current insertion depth, the target impedance value corresponding to the preset impedance curve is 10mΩ, and the fixed impedance of the line is 2mΩ. If the measured dynamic contact impedance is 12mΩ, then in order to maintain the equivalent total impedance at 10mΩ (Note: This refers to the effective transition impedance presented by the branch to the outside; in actual calculations, a parallel current shunt model needs to be considered, but for simplicity, only a series model is used to illustrate the principle), the system needs to adjust the compensation resistance to -4mΩ (if active compensation is supported) or to the minimum allowable value, and coordinate with other control methods. If pure passive positive resistance compensation is used, a reference operating point is usually set so that the compensation resistance fluctuates around the reference value. This "one gain, one loss" adjustment strategy ensures that no matter how the physical contact interface fluctuates, the electrical characteristics presented by the transition branch to the outside remain smooth and controllable.

[0040] To prevent overshoot or oscillation during adjustment, this embodiment also introduces a consistency verification mechanism for the direction of change. That is, after each adjustment of the compensation resistance value, the equivalent total impedance is recalculated, and it is verified whether the direction of change of the equivalent total impedance relative to the previous sampling time is consistent with the direction of change of the preset impedance curve at the current insertion depth. Since the contact pressure generally increases and the contact resistance generally decreases during insertion and removal, the preset impedance curve usually has a monotonically decreasing slope. If, after a certain adjustment, the equivalent total impedance shows a jump opposite to the curve slope (for example, the curve is required to decrease, but the equivalent impedance increases), it indicates that the adjustment step size is too large or that transient interference has occurred. At this time, the system corrects the compensation resistance value according to the preset fine-tuning step size until the direction of change of the equivalent total impedance returns to consistency. This mechanism is equivalent to adding a "trend verification" link to the closed-loop control, effectively avoiding control divergence caused by nonlinear abrupt changes in mechanical contact, and significantly improving the dynamic stability of the system.

[0041] The source of the preset impedance curve is not based on arbitrary values ​​estimated empirically, but rather on rigorous physical calibration. The specific generation process includes: fitting a contact resistance-insertion depth reference curve based on the inverse relationship between the contact pressure value of the main current-carrying contact at different insertion depths of the connector assembly and the corresponding contact resistance calibration value. According to electrical contact theory, contact resistance is approximately inversely proportional to contact pressure. Therefore, multiple precise insertion and removal calibration tests are performed on the connector assembly before shipment, recording the pressure and resistance data at each depth point, thus fitting a reference curve reflecting the physical characteristics of the specific connector. Subsequently, this contact resistance-insertion depth reference curve is smoothed to obtain the preset impedance curve; the impedance value corresponding to each insertion depth on the smoothed preset impedance curve is used as the target impedance value. The purpose of smoothing is to eliminate discrete noise in the calibration data caused by the randomness of surface micro-morphology, obtaining a continuous, differentiable control reference that conforms to macroscopic physical laws. This ensures that the preset impedance curve retains the physical fingerprint of the real connector while possessing mathematical advantages suitable for use as a control target, thereby enhancing the robustness and persuasiveness of the technical solution in practical engineering applications.

[0042] It should be understood that although this embodiment describes a specific implementation method based on negative feedback deviation adjustment and smooth fitting curve, in other embodiments, advanced control algorithms such as model predictive control (MPC) and adaptive PID can also be used to track the equivalent total impedance. The generation of the preset impedance curve can also be optimized by combining finite element simulation data or machine learning models. As long as its core logic is to adjust the compensation impedance to offset the fluctuation of dynamic contact impedance and make the overall characteristics of the branch meet expectations, it falls within the protection scope of this application.

[0043] Example 5

[0044] Building upon Example 1, this example further details the specific statistical criteria for ensuring the dynamic contact impedance meets the preset stability condition in step S50, the execution timing of the secondary current switching operation, and the coordination mechanism with the differential protection device. These features collectively constitute a safety closed loop at the switching execution level, ensuring that the electrical circuit transfer process is smooth and controlled after the physical state of the main current-carrying contact is confirmed to be reliable, and providing comprehensive interlocking protection at the system-level protection level.

[0045] Specifically, when the dynamic contact impedance meets the preset stability condition, the determination is not based on a simple threshold comparison of a single measurement value, but rather on a comprehensive statistical method. That is, taking the current sampling time as the endpoint, a sliding window of a preset time length is drawn backward, and the variance of all dynamic contact impedances within this window is statistically analyzed. Only when the variance is less than a preset variance threshold and all dynamic contact impedances within the sliding window are within a preset deviation range centered on the rated contact impedance value, is the dynamic contact impedance considered to meet the preset stability condition. This dual-criteria design has profound physical implications: relying solely on the impedance amplitude falling within the deviation range only indicates that the average level of the contact resistance meets the standard, but it cannot rule out the possibility of the contact being in an unstable state of high-frequency micro-vibration or intermittent contact; while introducing variance as a quantitative indicator of volatility can effectively characterize the tightness of the mechanical connection at the contact interface. For example, if the sliding window length is set to 20ms (corresponding to a complete cycle of a 50Hz power frequency), the impedance variance within this time window directly reflects the dynamic stability of the contact under the combined action of electrodynamic and mechanical stress within one power frequency cycle. Only when the variance is sufficiently small (indicating no abnormal jitter) and the mean is accurate (indicating adequate contact pressure) are both met, can the system be certain that the main current-carrying contact has truly completed the transition from the transition phase to the stable load-bearing phase, thereby avoiding the risk of premature switching caused by transient pseudo-steady state.

[0046] Before performing the switching operation of the secondary side current from the first current transformer module to the second current transformer module, this application also establishes a strict protection coordination mechanism. Specifically, this includes sending a temporary blocking command to the differential protection device connected to the secondary side output terminal of the first current transformer module, causing the differential protection device to enter a blocked state and suspending the calculation of the differential current criterion; the timing of sending this temporary blocking command is precisely limited to the moment when the dynamic contact impedance first meets the preset stability condition. The reason for choosing to trigger the blocking at this specific node of "first meeting the stability condition" is that this signifies that the contacts are about to begin carrying a large current transfer, which is also the sensitive window period during which the differential protection is most prone to maloperation due to transient imbalance of the shunt ratio. Early blocking is equivalent to defining a safe operating zone free from protection interference for subsequent physical switching operations. It should be understood that this "blocking" only temporarily shields the output of the differential criterion and does not affect the protection device's monitoring function for other fault types, and its duration is strictly limited within the switching process, ensuring the rapid recovery capability of the main protection function.

[0047] Only after confirming the safety interlock is effective can the system perform substantive current transfer operations. Specifically, the operation of switching the secondary current from the first current transformer module to the second current transformer module includes: while maintaining the current compensation resistance value of the adjustable compensation impedance unit unchanged, confirming that the amplitude and phase of the secondary output current of the second current transformer module are within the preset normal range; then disconnecting the connection between the secondary output terminal of the first current transformer module and the secondary load circuit, allowing the secondary load current to flow through the second current transformer module and the parallel transition branch; after the secondary connection of the first current transformer module is disconnected, gradually adjusting the compensation resistance value of the adjustable compensation impedance unit to zero according to the preset impedance withdrawal rate, so that the parallel transition branch smoothly withdraws from the secondary load circuit. This timing arrangement reflects the core safety principle of "connect first, then disconnect, gradual withdrawal". First, maintaining a constant compensation resistance value ensures the constant shunting characteristics of the transition branch during switching, preventing shocks during current redistribution caused by sudden parameter changes. Second, confirming the normal output of the new module is a necessary verification to prevent switching the load to the faulty equipment. Most importantly, after disconnecting the old module, the transition branch is not immediately disconnected; instead, the compensation impedance is zeroed at a preset rate. This is because the secondary side of the current transformer must not be open-circuited, and the load impedance is usually small. If the transition branch is suddenly removed, the current originally flowing through it will be forced to surge entirely into the new module and its load circuit, potentially causing voltage spikes or waveform distortion on the secondary side due to the step change in the total circuit impedance. By controlling the compensation impedance to gradually return to zero at a certain slope (e.g., 10mΩ / ms), the shunting effect of the transition branch is slowly attenuated, providing a smooth current takeover process for the new module and its downstream circuits, completely eliminating the potential for shock during removal.

[0048] After the switching operation is completed and the parallel transition branch is removed, a series of finishing and verification actions must be performed to ensure the system returns to normal operation. Specifically, the process of removing the parallel transition branch includes: stopping the injection of detection signals after disconnecting the secondary side connection of the first current transformer module; disconnecting the connection between the adjustable compensation impedance unit and the parallel transition branch, and resetting the adjustable compensation impedance unit to its initial resistance value; disconnecting the connection between the pilot detection contact and the corresponding terminal in the base, and removing all physical wiring of the parallel transition branch. This series of physical removal actions must be performed sequentially after the electrical switching is completed to prevent arcing caused by live plugging and unplugging. More importantly, only after all the above operations are completed will the system send a lockout release command to the differential protection device to restore it to normal operation; and before releasing the lockout, the power frequency current signal at the secondary side output of the second current transformer module must be collected to verify that the deviation of the amplitude and phase of the power frequency current signal from the historical power frequency current signal before the switching of the first current transformer module is within the preset allowable range. This step is the final quality checkpoint of the entire live switching process. By comparing the measured data after the switch with the historical benchmark before the switch, it is possible to objectively evaluate whether the switch truly achieved a "seamless" replacement. Only when the deviation verification passes, proving that the new module has perfectly taken over the original measurement task, will the system release the protection lockout and allow the differential protection to be put back into operation. This "verification first, unlocking later" logic effectively prevents the protection device from malfunctioning in the absence of a fault or refusing to operate in the presence of a fault due to switching failure or latent faults in the new module, thus maximizing the safe and stable operation of the power grid secondary system. It should be understood that although this embodiment describes a specific implementation method based on sliding window variance and impedance fading, in other embodiments, the stability criterion can also adopt statistical quantities such as standard deviation, coefficient of variation, or short-time energy; the impedance fading strategy can also adopt piecewise linear or polynomial curve fitting, etc., as long as its core logic is to confirm stability through statistics, ensure safety through timing, and verify the closed-loop quality, it falls within the protection scope of this application.

[0049] Example 6

[0050] Building upon Example 1, this example further addresses potential extreme contact anomalies during live switching, providing a safety fallback mechanism independent of the normal adjustment process. Specifically, during the adjustment process following the transition phase of the main current-carrying contact contact, if the fluctuation amplitude of the dynamic contact impedance exceeds a preset abnormal fluctuation threshold over multiple consecutive sampling periods, the adjustment of the adjustable compensation impedance unit's compensation resistance is paused, and the connection assembly is controlled to retract to the initial position where the main current-carrying contact is disengaged. The triggering condition of this mechanism is fundamentally different from the normal impedance tracking adjustment in Example 4. During normal adjustment, fluctuations in dynamic contact impedance are typically caused by changes in the microstructure of the contact surface or uneven insertion speed; their amplitude is limited and can be offset by the reverse adjustment of the compensation impedance. However, when the fluctuation amplitude continuously exceeds the preset abnormal fluctuation threshold, it often indicates a fundamental deterioration of the physical contact interface, such as the presence of a hard oxide film on the contact surface, jamming of insulating foreign objects, or deformation of the mechanical structure. In this case, simple electrical compensation not only fails to bring the equivalent total impedance back to the preset curve but may also lead to saturation of the compensation unit or system oscillation due to over-adjustment. Therefore, the system must immediately suspend electrical regulation and seek physical repair methods to prevent the equipment from forcibly carrying current under unreliable contact conditions.

[0051] After the connecting component retracts, the contact surface condition is allowed to recover according to a preset waiting time. Then, the insertion process of the connecting component is repeated, utilizing the mechanical wiping effect between the main current-carrying contact and the corresponding terminal during re-insertion to improve the contact condition. This step involves two key technical elements: waiting and mechanical wiping. The preset waiting time is not an arbitrary delay, but a necessary recovery window set based on the physical properties of the contact material. After a failed insertion attempt, the contact surface may experience localized temperature rise due to frictional heat or accumulate residual stress due to mechanical compression. Immediate retry may exacerbate heat accumulation or stress superposition, thus worsening contact conditions. By setting a reasonable waiting time (e.g., 5 to 30 seconds), the contact surface temperature can tend to equalize, residual stress can be released, and even the microstructure of certain types of surface oxide films may relax or reorganize in a static state, creating more favorable physical conditions for the next insertion. It should be understood that the specific value of this waiting time can be adaptively adjusted based on the contact material, ambient temperature and humidity, and historical fault data.

[0052] More importantly, the mechanical wiping action relied upon in the re-insertion process is an active physical repair mechanism, complementing the electrical compensation in the aforementioned embodiments. When the connecting assembly is pushed forward again in the insertion direction, the relative sliding friction generated between the main current-carrying contact and the base terminal effectively scrapes away the high-resistivity oxide film, sulfide layer, or microparticle foreign matter adhering to the contact surface, exposing the fresh metallic conductive substrate. This method of directly changing the physical state of the contact interface through mechanical movement can eliminate the material basis for abnormal impedance fluctuations at the root, an effect that cannot be replaced by simply adjusting circuit parameters. Empirical data shows that for poor contact caused by surface contamination, after a standard back-and-wipe retry, the fluctuation amplitude of dynamic contact impedance can usually be reduced by more than 80%, bringing it back into the controllable range of normal adjustment. This demonstrates the robustness and self-healing capability of the technical solution in this application when facing non-ideal operating conditions.

[0053] If the fluctuation amplitude of the dynamic contact impedance after re-insertion still exceeds the preset abnormal fluctuation threshold, a contact abnormality alarm signal is generated and the live replacement process is terminated. This termination logic constitutes the last line of defense for the system. If, after a complete rollback, waiting, and mechanical wiping retry, the contact state still fails to meet the basic requirements, it indicates that the cause of the fault has exceeded the scope of automatic repair capabilities, and there may be hard mechanical faults such as severe contact erosion, spring fatigue fracture, or damage to the base terminals. At this time, continuing to attempt switching is not only futile, but may also lead to serious safety accidents such as open-circuit high voltage or arc short circuit on the secondary side. Therefore, the system decisively terminates the process and issues an alarm, prompting maintenance personnel to conduct manual intervention and inspection, ensuring the absolute safety of the entire live operation process. It should be understood that although this embodiment describes the logic of termination after a single retry, in other embodiments, the maximum number of allowed retries (e.g., no more than 3 times) can be set according to the fault level, or redundancy measures such as automatic switching to a backup transition branch after a retry failure can be implemented. As long as the core logic is to attempt self-healing through mechanical wiping and terminate safely when it fails, it falls within the protection scope of this application.

[0054] Example 7

[0055] like Figure 2As shown, this application also provides a modular outdoor current transformer rapid live-line replacement system. This system is the complete physical carrier for implementing the aforementioned live-line replacement method, aiming to cover the complete product form of the downstream industry chain. Specifically, the modular outdoor current transformer system includes a first transformer module, a second transformer module, a base, a parallel transition branch, and at least one processor and a memory coupled thereto. The memory stores a computer program, and when the processor executes the computer program, it implements the live-line replacement method as described in any one of Embodiments 1 to 6. The first transformer module typically refers to the old transformer module to be replaced, and the second transformer module refers to the new transformer module ready for operation. Both are electrically coupled to the base through pluggable connection components. This modular design allows the transformer body to be quickly installed and removed independently of the primary high-voltage line, while the base serves as a fixed interface for long-term installation on an outdoor cabinet or bracket, maintaining the continuity of the secondary circuit.

[0056] In the physical architecture of this system, a parallel transition branch is connected between the secondary output terminals of the first and second current transformer modules. Specifically, the parallel transition branch is not an inherent circuit within the current transformers, but rather an external bypass channel temporarily constructed during live-line replacement operations. Its two ends are connected to the secondary output circuits of the old and new current transformer modules via dedicated test terminals or quick connectors, thereby providing a controllable current shunting path for the secondary current during the dynamic process of mechanical insertion and removal. It should be understood that although this embodiment describes an implementation where the parallel transition branch is directly connected to the module output terminals, in other embodiments, this branch can also be integrated into the internal wiring cavity of the base, or indirectly connected via an intermediate adapter box, as long as its electrical topology constitutes a parallel current shunting relationship between the secondary sides of the old and new modules.

[0057] As the core control hub of the system, the live-line switching control device establishes defined communication or electrical connections with the pilot detection contact, the adjustable compensation impedance unit, and the differential protection device. Specifically, the signal acquisition port of the live-line switching control device is connected to the sampling resistor and current sensor in the parallel transition branch to acquire the response component of the detection signal in real time; its drive output port is connected to the adjustment mechanism (such as a digital potentiometer or power electronic conversion circuit) of the adjustable compensation impedance unit to dynamically adjust the branch impedance value; its status monitoring port is connected to the pilot detection contact on the connection component to sense the start time and contact status of the insertion and removal process; and its communication interface is connected to the differential protection device in the substation to send blocking commands and receive feedback signals. This multi-dimensional hardware interconnection integrates the dispersed mechanical components, power electronic components, and relay protection equipment into a collaborative organic whole, ensuring that the impedance sensing, dynamic compensation, and safe switching strategies described in Examples 1 to 6 can be accurately executed at the physical level.

[0058] Example 8

[0059] To further verify the effectiveness and superiority of the technical solution presented in this application in practical engineering applications, this embodiment takes the live-line replacement of an outdoor current transformer in a 110kV substation as a typical application scenario, and provides a detailed explanation in conjunction with specific test data and comparative examples. (See reference...) Figure 3 , Figure 4 as well as Figure 5 As shown, through systematic comparative testing, the necessity of the key technical features of this application and the superiority of the overall solution have been fully verified. It should be understood that this embodiment is merely an illustrative application example and not a limitation on the scope of protection of this application.

[0060] In this application scenario, both the first current transformer module to be replaced and the newly installed second current transformer module are 110kV oil-immersed current transformers with a secondary rated current of 5A and a load impedance of approximately 0.5Ω. The cutoff frequency of the analog low-pass filter at the front end of the connected microprocessor protection device is calibrated to 2kHz. Based on this operating condition, the live-line switching control device provided in this application is configured to execute the following parameter strategy: the frequency of the detection signal is set to 5kHz, which is significantly higher than the 2kHz cutoff frequency of the protection device, ensuring that the detection signal is within the stopband range of the analog front end of the protection device; the injection amplitude of the detection signal is controlled at 50mV, which, after being attenuated by the internal filter of the protection device, is far lower than the sampling noise floor of its ADC, thereby completely isolating the interference to the protection sampling circuit at the physical level; the sliding window length in the stability criterion is set to 20ms (corresponding to a complete cycle of 50Hz power frequency), and the variance threshold is set to 0.01Ω², serving as a strict gate condition for triggering the switching operation.

[0061] In the normal switching test using the above parameters, the observed electrical waveforms exhibited high stability. Specifically, with the insertion of the connecting components, the dynamic contact impedance of the main current-carrying contact showed significant nonlinear fluctuations in the initial stage. However, the compensation resistance of the adjustable compensation impedance unit was adjusted in real time in the opposite direction, ensuring that the equivalent total impedance of the parallel transition branch always closely matched the preset impedance curve, without any transient anomalies exceeding 5%. At the instant of secondary side current switching, the current waveform flowing through the second current transformer module transitioned smoothly, with a current distortion rate of less than 1% calculated by spectrum analysis. Furthermore, the differential protection device maintained stable operation throughout the process, without any false alarms or abnormal actions after the lockout was released. This experimental result fully demonstrates the ability of the proposed solution to achieve smooth, shock-free switching under real high-voltage conditions.

[0062] To highlight the necessity of the key technical features of this application, two comparative sets were set up on the same test platform for comparative verification. Comparative set A adopted the same mechanical structure and dynamic compensation algorithm as this application, but eliminated the frequency isolation design for the detection signal, directly setting the detection signal frequency to 1kHz (lower than the 2kHz cutoff frequency of the protection device). Test results showed that during the injection of the detection signal, a significant 1kHz superimposed component appeared in the sampled value of the microprocessor-based protection device, causing the instantaneous differential current value calculated by the differential protection algorithm to exceed the limit, thereby triggering a malfunction of the differential protection. This phenomenon, from the opposite perspective, confirms that without a frequency isolation strategy higher than the cutoff frequency of the protection device, even if the detection signal amplitude is low, it may still be identified as a fault quantity because it falls within the passband of the protection device, seriously threatening the safety of the power grid. This also demonstrates that setting the detection frequency higher than the cutoff frequency in this application is not a simple numerical choice, but a necessary technical means to ensure the safe operation of secondary equipment.

[0063] Group B retained the 5kHz isolation design but eliminated the dynamic compensation mechanism, replacing it with a fixed 5mΩ compensation resistor connected in series in the parallel transition branch. Test results showed that when the main current-carrying contact's dynamic contact impedance jumped instantaneously from 8mΩ to 25mΩ due to surface oxide film rupture at the middle of the connection component insertion, the fixed compensation resistor could not adaptively adjust, causing a sharp increase in the total shunt impedance of the parallel transition branch, resulting in a sudden drop in the shunt current of approximately 30%. According to Kirchhoff's current law, this missing shunt current was forced to instantly transfer to the newly inserted second current transformer module and its load circuit, triggering a secondary-side current surge pulse with an amplitude of 1.8A, accompanied by a significant voltage spike. In contrast, the proposed solution successfully offset the sudden increase in contact impedance and maintained a constant shunt ratio by reducing the compensation resistance in real time at the same insertion position. This comparative result strongly demonstrates that simple electrical bypass cannot solve the problem of random fluctuations at the mechanical contact interface; only by introducing a dynamic impedance tracking mechanism based on real-time sensing can the risk of current surges during switching be fundamentally eliminated.

[0064] In conclusion, through on-site measurements at 110kV and verification using two sets of targeted comparative models, it can be clearly concluded that the "frequency band isolation" and "dynamic impedance tracking" employed in this application are complementary and indispensable. Frequency band isolation solves the prerequisite problem of "accurate measurement without disturbing residents," while dynamic impedance tracking solves the core problem of "stable switching without impact."

[0065] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A modular outdoor current transformer rapid live-line replacement method, applied to switching scenarios including a first transformer module and a second transformer module, characterized in that, include: During the process of inserting the connecting component into the base, a detection circuit is established using the pilot detection contact on the connecting component that is turned on before the main current-carrying contact. Based on the conduction state of the detection circuit, a detection signal is injected into the parallel transition branch connected between the secondary output terminals of the first current transformer module and the second current transformer module; the parallel transition branch is connected in series with an adjustable compensation impedance unit. During the transition phase of the main current-carrying contact, the dynamic contact impedance of the main current-carrying contact is calculated based on the response component corresponding to the detection signal in the parallel transition branch. Based on the deviation between the dynamic contact impedance and the preset impedance curve, the compensation resistance value of the adjustable compensation impedance unit is adjusted so that the equivalent total impedance of the parallel transition branch tracks the preset impedance curve. When the dynamic contact impedance meets the preset stability condition, the secondary side current is switched from the first current transformer module to the second current transformer module, and the parallel transition branch is removed.

2. The method for rapid live-line replacement of modular outdoor current transformers according to claim 1, characterized in that, The establishment of a detection circuit using a pilot detection contact on the connection assembly that is turned on before the main current-carrying contact includes: When the connecting component is advanced along the insertion direction, the pilot probe contact forms electrical contact with the corresponding terminal before the main current-carrying contact, and the difference between the extension length of the pilot probe contact and the extension length of the main current-carrying contact corresponds to a preset advance contact stroke; Based on the aforementioned advance contact stroke, before the main current-carrying contact contacts the corresponding terminal, the detection circuit is established through the contact path between the pilot detection contact and the corresponding terminal; The injection of a detection signal into the parallel transition branch connecting the secondary output terminals of the first and second current transformer modules includes: Obtain the cutoff frequency of the front-end analog low-pass filter of the protection device connected to the secondary output terminal of the first current transformer module, and set the frequency of the detection signal to a frequency band value higher than the cutoff frequency.

3. The method for rapid live-line replacement of modular outdoor current transformers according to claim 2, characterized in that, The method of injecting a detection signal into the parallel transition branch connected between the secondary output terminals of the first current transformer module and the second current transformer module further includes: The control detection signal injection unit injects the detection signal with an amplitude lower than a preset amplitude threshold into the parallel transition branch according to the frequency band value, so that the detection signal does not enter the sampling and calculation stage of the protection device after being attenuated by the front-end analog low-pass filter.

4. The method for rapid live-line replacement of modular outdoor current transformers according to claim 1, characterized in that, During the transition phase of contact at the main current-carrying contact, based on the response component corresponding to the probe signal in the parallel transition branch, the dynamic contact impedance of the main current-carrying contact is calculated, including: After the main current-carrying contact begins to contact the corresponding terminal, the dynamic contact impedance is continuously calculated according to a preset sampling period; When the dynamic contact impedance is greater than a preset micro-contact upper limit threshold in multiple consecutive sampling periods and the fluctuation amplitude of the dynamic contact impedance between adjacent sampling periods is greater than a preset fluctuation threshold, the main current-carrying contact is determined to be in the transition phase. During the transition phase, the response component is subjected to bandpass filtering with the frequency of the probe signal as the center frequency to extract the voltage response component and the current response component, and the dynamic contact impedance is calculated based on the voltage response component and the current response component.

5. The method for rapid live-line replacement of modular outdoor current transformers according to claim 4, characterized in that, The extraction of voltage and current response components, and the calculation of the dynamic contact impedance based on the voltage and current response components, includes: A mixed voltage signal containing power frequency and detection frequency components is acquired across the sampling resistor connected in series in the parallel transition branch. The mixed voltage signal is then subjected to bandpass filtering with the frequency of the detection signal as the center frequency to extract the voltage response component. The branch current signal in the parallel transition branch is acquired synchronously, and the branch current signal is subjected to bandpass filtering with the same center frequency to extract the current response component. The ratio of the amplitude of the voltage response component to the amplitude of the current response component is calculated to obtain the dynamic contact impedance of the main current-carrying contact at the current insertion depth.

6. The method for rapid live-line replacement of modular outdoor current transformers according to claim 1, characterized in that, The step of adjusting the compensation resistance value of the adjustable compensation impedance unit based on the deviation between the dynamic contact impedance and the preset impedance curve, so that the equivalent total impedance of the parallel transition branch tracks the preset impedance curve, includes: When the deviation indicates that the dynamic contact impedance is greater than the target impedance value on the preset impedance curve, the compensation resistance value of the adjustable compensation impedance unit is reduced to offset the incremental portion of the dynamic contact impedance exceeding the target impedance value. When the deviation indicates that the dynamic contact impedance is less than the target impedance value, the compensation resistance value of the adjustable compensation impedance unit is increased to compensate for the reduction in dynamic contact impedance that is lower than the target impedance value. After each adjustment of the compensation resistance value, the equivalent total impedance is recalculated, and it is verified that the direction of change of the equivalent total impedance relative to the previous sampling time is consistent with the direction of change of the preset impedance curve at the current insertion depth. If they are inconsistent, the compensation resistance value is corrected according to the preset fine-tuning step size until the direction of change of the equivalent total impedance is restored to consistency.

7. The method for rapid live-line replacement of modular outdoor current transformers according to claim 6, characterized in that, The process of generating the preset impedance curve includes: Based on the inverse relationship between the contact pressure value and the corresponding contact resistance calibration value of the main current-carrying contact at different insertion depths of the connection component, a contact resistance-insertion depth reference curve is obtained by fitting. The contact resistance-insertion depth reference curve is smoothed to obtain the preset impedance curve; the impedance value corresponding to each insertion depth on the smoothed preset impedance curve is used as the target impedance value. When the dynamic contact impedance meets the preset stability condition, it includes: Using the current sampling time as the endpoint, a sliding window of a preset time length is extracted forward, and the variance of all dynamic contact impedances within the sliding window is calculated. When the variance is less than a preset variance threshold and all dynamic contact impedances within the sliding window are within a preset deviation range centered on the rated contact impedance value, the dynamic contact impedance is determined to meet the preset stability condition.

8. The method for rapid live-line replacement of modular outdoor current transformers according to claim 7, characterized in that, The operation of switching the secondary current from the first current transformer module to the second current transformer module includes: While maintaining the current compensation resistance value of the adjustable compensation impedance unit unchanged, confirm that the amplitude and phase of the secondary output current of the second current transformer module are within the preset normal range. Disconnect the connection between the secondary output terminal of the first current transformer module and the secondary load circuit, so that the secondary load current flows through the second current transformer module and the parallel transition branch; After the secondary side connection of the first current transformer module is disconnected, the compensation resistance of the adjustable compensation impedance unit is gradually adjusted to zero according to the preset impedance exit rate, so that the parallel transition branch smoothly exits the secondary side load circuit.

9. The method for rapid live-line replacement of modular outdoor current transformers according to claim 8, characterized in that, Before performing the switching operation, the following is also included: A temporary blocking command is sent to the differential protection device connected to the secondary output terminal of the first current transformer module, so that the differential protection device enters the blocking state and suspends the calculation of the differential current criterion. The temporary locking command is sent when the dynamic contact impedance first meets the preset stability condition. After the switching operation is completed and the parallel transition branch is removed, a lockout release command is sent to the differential protection device to restore the differential protection device to normal operation. The removal of the parallel transition branch includes: After disconnecting the secondary side connection of the first current transformer module, stop injecting the detection signal; Disconnect the adjustable compensation impedance unit from the parallel transition branch, and reset the adjustable compensation impedance unit to its initial resistance value. Disconnect the pilot detection contact from the corresponding terminal in the base, and remove all physical wiring of the parallel transition branch; The power frequency current signal at the secondary output terminal of the second current transformer module is collected, and the deviation of the amplitude and phase of the power frequency current signal from the historical power frequency current signal before the switching of the first current transformer module is verified to be within a preset allowable range.

10. A modular outdoor current transformer rapid live-line replacement system, characterized in that, include: The system comprises a first current transformer module, a second current transformer module, a base, a parallel transition branch, a processor, and a memory, wherein the memory stores a computer program, and the processor executes the computer program to implement the modular outdoor current transformer rapid live-line replacement method as described in any one of claims 1 to 9.

Images