On-site digital signal processing device and method for distribution network pole-mounted switch

Abstract

The application relates to the technical field of digital signal processing of power distribution networks, and discloses an on-site digital signal processing device and method for a distribution network pole-mounted switch, which acquires signals such as the on-off state of a circuit breaker, calculates and verifies a power-taking circulating current coupling ratio to obtain a current effective power-taking circulating current coupling ratio; in the closed state, a closed-state power-taking driving signal value is constructed according to power supply configuration information, and a corrected zero sequence current digital quantity is obtained in combination with the current effective power-taking circulating current coupling ratio and then output to a feeder terminal; when the prerequisite condition is met, the coupling ratio is linearly trend extrapolated by using a time change rate to continuously update; the application suppresses and eliminates a same-frequency parasitic zero sequence current component generated by the power-taking circulating current through a common ground impedance, and maintains the zero sequence protection detection sensitivity under the high-resistance grounding fault of the distribution network.

Description

Technical Field

[0001] This invention relates to the field of digital signal processing technology for power distribution networks, and more specifically, to a localized digital signal processing apparatus and method for pole-mounted switches in power distribution networks. Background Technology

[0002] In distribution network automation systems, pole-mounted switches, as critical node control and monitoring devices, typically require feeder terminal units (FTUs) and various instrument transformers to achieve real-time sensing of line operating status and relay protection. To ensure reliable power supply to terminal equipment and digital processing modules, capacitor-powered power supplies are often used in engineering to directly obtain energy from the high-voltage bus. As the requirements for high-resistance grounding fault detection accuracy in distribution networks continue to increase, zero-sequence current, as a core parameter for judging single-phase grounding faults, directly determines the reliability of local protection modules based on the anti-interference capability and signal processing accuracy of its acquisition channel.

[0003] In the prior art, there has been relevant research on circuit breaker condition monitoring and power signal processing. For example, Chinese invention patent CN111239599B discloses an online monitoring device and method for circuit breaker opening and closing time. This device collects analog quantities through three-phase current sensors and three-phase voltage sensors, and combines state quantity acquisition and signal processing units to eliminate interference from inrush current, power supply, sudden large load changes, and transient single-phase grounding faults, achieving online monitoring of circuit breaker operating time unaffected by over / under voltage and load size. Another example is Chinese invention patent CN110632505B, which proposes a miniature circuit breaker and its rapid transient power quality detection, recording, and analysis method. It utilizes intelligent control modules such as voltage divider circuits, current transformers, and A / D converters to achieve digital current and voltage detection, transient power quality waveform recording, and IoT upload functions. These solutions provide effective processing methods for routine circuit breaker operation monitoring and digital acquisition of basic power signals.

[0004] However, when existing pole-mounted switches in distribution networks are configured with capacitor-powered power supplies, the harvested current, after rectification, returns along the grounding conductor of the enclosure. Due to the physical distance between the reference ground of the zero-sequence current sensor and the reference ground of the analog-to-digital converter (ADC), a millivolt-level voltage drop is inevitably generated on a section of the common ground impedance of the grounding conductor. This harvested circulating current creates a potential difference between their reference grounds and is directly superimposed on the zero-sequence current sampling signal with a main frequency of 50Hz, forming a parasitic component that is completely in sync with the real zero-sequence current. This makes it impossible for traditional bandpass or bandstop filters to remove it. Since the harvested current is related to the primary bus voltage and load fluctuations, this parasitic component manifests as a pseudo-zero-sequence signal that dynamically changes with the line load. When a high-resistance ground fault occurs in the distribution network, the real zero-sequence fault current is often as low as tens of milliamperes. At this time, the pseudo-zero-sequence parasitic component that has not been eliminated will be on the same order of magnitude as the real fault signal and will aliased, making it difficult for the local processing module to extract the accurate zero-sequence fundamental vector. This unfilterable co-frequency interference can cause feeder terminals to misjudge or miss faults under weak fault conditions, reducing the detection sensitivity of zero-sequence protection. This makes it impossible for the system to isolate high-resistance grounding faults in time, leading to continuous leakage risks and affecting the overall operational safety of the distribution network. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of existing technologies, this invention provides a localized digital signal processing device and method for pole-mounted switches in distribution networks. This method calculates and verifies the energy harvesting circulating current coupling ratio by collecting equipment status and sensor secondary signals. It then constructs a closing-state energy harvesting drive signal value based on power supply configuration information, directly calculating the corrected digital zero-sequence current. Furthermore, it uses the rate of change of time to linearly extrapolate and update the coupling ratio when certain conditions are met. This method dynamically removes the pseudo-zero-sequence signal related to the load at the same frequency injected by the energy harvesting circulating current through the common ground impedance in the time domain without adding external physical isolation hardware. This eliminates the interference of parasitic components on the measurement of the true zero-sequence current, maintains the accuracy of the output data, and enables the feeder terminal to effectively distinguish between real faults and interference signals under weak current conditions such as high-resistance grounding faults, ensuring the detection sensitivity of zero-sequence protection.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Localized digital signal processing methods for pole-mounted switches in distribution networks include: Collect the circuit breaker opening and closing status signal, the secondary output signal of the zero-sequence current sensor, and the secondary output signal of the A-phase voltage sensor on the power supply side to confirm whether the online calibration trigger condition is met. After the online calibration trigger condition is met, calculate the energy harvesting circulating current coupling ratio. After verifying the rationality of the energy harvesting circulating current coupling ratio, obtain the current effective energy harvesting circulating current coupling ratio. Read the configuration information of the three-phase capacitor power supply, construct the power supply drive value of the closing state according to the configuration information of the three-phase capacitor power supply when the circuit breaker is closed, obtain the corrected zero-sequence current digital quantity according to the current effective power supply circulating current coupling ratio and the power supply drive value of the closing state, and output the corrected zero-sequence current digital quantity to the feeder terminal. Determine whether the preconditions for linear trend extrapolation are met. If the preconditions are met, calculate the continuous closing duration. If the continuous closing duration exceeds the trend extrapolation start-up time threshold, calculate the time change rate of the energy harvesting circulating current coupling ratio. Use the time change rate to perform linear trend extrapolation on the energy harvesting circulating current coupling ratio to update the current effective energy harvesting circulating current coupling ratio.

[0007] The method for confirming whether the online calibration trigger condition is met includes: The online calibration triggering condition is determined by a dual condition based on the amplitude of the circuit breaker open / close status signal and the instantaneous value of the secondary output of the power supply side A-phase voltage sensor: when the circuit breaker open / close status signal indicates the open state and the amplitude of the instantaneous value of the secondary output of the power supply side A-phase voltage sensor is greater than the minimum effective voltage threshold, the online calibration triggering condition is confirmed to be met.

[0008] After the online calibration triggering condition is met, but before calculating the energy harvesting circulation coupling ratio, the following steps are also included: From the moment the circuit breaker's open / closed status signal changes from closed to open, wait for the preset opening transient decay delay to end, and determine whether the cumulative opening duration from the moment the circuit breaker opened to the current moment is greater than the preset minimum calibration window duration. If the cumulative opening duration is greater than the minimum calibration window duration, the calibration data acquisition timing is confirmed to be valid. If the cumulative opening duration is less than the minimum calibration window duration, abandon this calibration and continue to use the energy harvesting circulating current coupling ratio obtained from the previous calibration.

[0009] The method for calculating the energy harvesting circulation coupling ratio includes: Construct the open-state energy harvesting drive signal value, collect calibration data based on the constructed open-state energy harvesting drive signal value, and obtain a set of original sampled value sequences of zero-sequence current channel and a set of open-state energy harvesting drive signal value sequences that are time-aligned with the original sampled value sequences of zero-sequence current channel. Based on the original sampled value sequence of the zero-sequence current channel and the energy harvesting drive signal value sequence in the open state, the energy harvesting circulating current coupling ratio is calculated.

[0010] The method for constructing the open-state energy-harvesting drive signal value includes: Read the configuration information of the three-phase capacitor power supply. The configuration information indicates that the three-phase capacitor power supply includes the power supply-side A-phase power supply capacitor installed on the power supply side A-phase high-voltage bus and the load-side C-phase power supply capacitor installed on the load side C-phase high-voltage bus. Based on the configuration information of the three-phase capacitor power supply and the current circuit breaker open state, determine that only the power supply-side A-phase power supply capacitor participates in power extraction in the open state, and use the instantaneous value of the secondary output of the power supply-side A-phase voltage sensor as the open state power extraction drive signal value of each sampling point.

[0011] The method for collecting the calibration data includes: Open the calibration data acquisition window, and synchronously record the original sampled value of the zero-sequence current channel and the open-state energy harvesting drive signal value obtained by analog-to-digital conversion of the secondary output signal of the zero-sequence current sensor at each sampling point in the calibration data acquisition window. After collecting continuous data for no less than a preset number of complete power frequency cycles, close the calibration data acquisition window to obtain a set of original sampled value sequences of the zero-sequence current channel and a set of open-state energy harvesting drive signal value sequences that are time-aligned with the original sampled value sequences of the zero-sequence current channel.

[0012] The method for calculating the energy harvesting circulation coupling ratio also includes: The original sampled value sequence of the zero-sequence current channel is multiplied point by point with the power-receiving drive signal value sequence of the open-state and the result is accumulated to obtain the cross-correlation sum. The power-receiving drive signal value sequence of the open-state is multiplied point by point and the result is accumulated to obtain the autocorrelation sum. The cross-correlation sum is divided by the autocorrelation sum to obtain the power-receiving circulating current coupling ratio.

[0013] The rationality verification includes physical rationality range verification and single maximum allowable change verification. The effective energy harvesting current coupling ratio is obtained as follows: the energy harvesting current coupling ratio that has passed the physical reasonable range verification and the single maximum allowable change verification, together with the calibration timestamp corresponding to the time of completion of this calibration, is written into the energy harvesting current coupling ratio historical record area in the non-volatile memory. For each successful writing of a calibration record, the number of effective calibration records in the non-volatile memory is incremented by one, and the energy harvesting current coupling ratio is updated to the current effective energy harvesting current coupling ratio. If the verification fails, the calibration result of this time is discarded, and the energy harvesting current coupling ratio stored in the previous calibration is maintained as the current effective energy harvesting current coupling ratio.

[0014] The method for constructing the closing-state energy extraction drive signal value includes: Based on the configuration information of the three-phase capacitor power supply, it is determined that both the power supply side A-phase power supply capacitor and the load side C-phase power supply capacitor are in working state under the closed state. The instantaneous value of the secondary output of the load side C-phase voltage sensor in the three-phase voltage sensor is read. The instantaneous value of the secondary output of the power supply side A-phase voltage sensor and the instantaneous value of the secondary output of the load side C-phase voltage sensor are summed to construct the closed state power supply drive signal value of the current sampling point.

[0015] The method for obtaining the corrected digital value of the zero-sequence current includes: The parasitic zero-sequence current estimate for each sampling point is obtained by multiplying the current effective energy harvesting circulating current coupling ratio with the closed-state energy harvesting drive signal value at each sampling point. The corrected zero-sequence current digital value is obtained by subtracting the corresponding parasitic zero-sequence current estimate from the original sampling value of the zero-sequence current channel at each sampling point.

[0016] The methods for determining whether the preconditions for linear trend extrapolation are met include: Determine whether the number of valid calibration records in the non-volatile memory is no less than two. If the number of valid calibration records is no less than two, the prerequisite for linear trend extrapolation is met.

[0017] A localized digital signal processing device for pole-mounted switches in a distribution network, used to implement the aforementioned localized digital signal processing method for pole-mounted switches in a distribution network, the device comprising: Online calibration module: used to collect circuit breaker opening and closing status signals, zero-sequence current sensor secondary output signals and power supply side A-phase voltage sensor secondary output signals, to confirm whether the online calibration trigger condition is met, and after the online calibration trigger condition is met, to calculate the energy harvesting circulating current coupling ratio, and to obtain the current effective energy harvesting circulating current coupling ratio after verifying the rationality of the energy harvesting circulating current coupling ratio. Zero-sequence correction module: Used to read the configuration information of the three-phase capacitor power supply, construct the power supply drive value of the closing state according to the configuration information of the three-phase capacitor power supply when the circuit breaker is closed, and obtain the corrected zero-sequence current digital quantity according to the current effective power supply circulating current coupling ratio and the power supply drive value of the closing state. The corrected zero-sequence current digital quantity is output to the feeder terminal. Extrapolation update module: used to determine whether the preconditions for linear trend extrapolation are met. When the preconditions are met, the continuous closing duration is calculated. When the continuous closing duration exceeds the trend extrapolation start-up time threshold, the time change rate of the energy harvesting circulating current coupling ratio is calculated. The energy harvesting circulating current coupling ratio is then linearly extrapolated using the time change rate to update the current effective energy harvesting circulating current coupling ratio.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention addresses the problem of parasitic zero-sequence current components at the same frequency that cannot be separated by conventional frequency domain filtering when the circulating current of a three-phase capacitor-powered power supply flows through the common ground impedance of the enclosure's grounding conductor in the zero-sequence current sampling channel. By collecting circuit breaker opening / closing status signals and sensor secondary output signals, the invention calculates and verifies the coupling ratio of the circulating current, quantifying the coupling transmission characteristics between the circulating current and the zero-sequence current sampling channel. In the circuit breaker closed state, this scheme constructs a closed-state energy extraction drive signal value based on the three-phase capacitor-powered power supply configuration information, and combines it with the current effective circulating current coupling ratio to derive a corrected digital zero-sequence current value. This allows for real-time stripping of the parasitic zero-sequence current component superimposed on the original digital value in the time domain. Furthermore, when the circuit breaker's continuous closed operation time exceeds the start-up duration threshold, the method uses the rate of change of time to linearly extrapolate the circulating current coupling ratio to update the current effective value, thereby automatically tracking the slow drift of the common ground impedance of the enclosure's grounding conductor over operating time. Without altering the physical hardware isolation, the interference of load-related pseudo-zero-sequence signals on the measurement of true zero-sequence current is eliminated, ensuring the accuracy of the zero-sequence current data output to the feeder terminal. This enables the feeder terminal to effectively distinguish between real fault signals and parasitic interference signals under weak zero-sequence current conditions such as high-resistance grounding faults, maintaining the effective detection sensitivity of zero-sequence protection. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a method for localized digital signal processing of pole-mounted switches in a power distribution network, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the distribution network pole-mounted switch system architecture provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of online calibration triggered by dual conditions under the open state of a circuit breaker, provided in an embodiment of the present invention. Figure 4 This is a schematic diagram illustrating the rationality verification of the energy harvesting circulation coupling ratio provided in an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the real-time reduction of parasitic zero-sequence current components in the closed state at each sampling point, as provided in an embodiment of the present invention. Figure 6 A flowchart for updating the energy harvesting circulation coupling ratio via linear trend extrapolation, as provided in an embodiment of the present invention; Figure 7This is a functional block diagram of a localized digital signal processing device for pole-mounted switches in a power distribution network, provided in an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: Please see Figure 1 As shown, this embodiment provides a localized digital signal processing method for pole-mounted switches in a distribution network, including: Step S10: Collect the circuit breaker opening and closing status signal, the secondary output signal of the zero-sequence current sensor and the secondary output signal of the A-phase voltage sensor on the power supply side, and confirm whether the online calibration trigger condition is met. After the online calibration trigger condition is met, calculate the energy harvesting circulating current coupling ratio. After verifying the rationality of the energy harvesting circulating current coupling ratio, obtain the current effective energy harvesting circulating current coupling ratio. Specifically, in step S10, during the operation of the pole-mounted switch in the distribution network, the parasitic zero-sequence current component coupled in the zero-sequence current sampling channel when the energy-harvesting current of the three-phase capacitor power supply returns through the grounding conductor of the enclosure is quantified and calibrated using the known boundary condition that the zero-sequence current physical quantity naturally generated by each circuit breaker opening operation is necessarily zero. (See also...) Figure 2 This is a schematic diagram of the distribution network pole-mounted switch system architecture provided in the embodiments of this application. Figure 2 The diagram illustrates the power supply side and load side of the distribution network, as well as the A-phase, B-phase, and C-phase three-phase high-voltage busbars connecting them. A primary and secondary integrated pole-mounted circuit breaker body is connected in series on the three-phase high-voltage busbars, along with a local digital unit (ADMU) and a feeder terminal unit (FTU) connected sequentially to the circuit breaker body. The primary and secondary integrated pole-mounted circuit breaker body integrates a circuit breaker, a zero-sequence current sensor, and a voltage sensor. The circuit breaker body is electrically connected to the ADMU via an aviation connector. The pole-mounted switch includes a primary and secondary integrated pole-mounted circuit breaker body, an ADMU, and a feeder terminal unit (FTU). The primary and secondary integrated pole-mounted circuit breaker body is equipped with a three-phase capacitor-powered power supply. This three-phase capacitor-powered power supply is a capacitor-powered device that provides operating power to the feeder terminal units (FTUs) in the three-phase distribution network system. It adopts a dual-capacitor configuration, selecting one phase from both the power supply side and the load side for power extraction. Figure 2The schematic diagram shows that the power supply side A-phase high-voltage bus and the load side C-phase high-voltage bus obtain energy through capacitor voltage division and then supply power to the feeder terminal unit (FTU) after rectification. The local digital unit (ADMU) is connected to the three-phase voltage sensor, three-phase current sensor, and zero-sequence current sensor inside the primary and secondary integrated pole-mounted circuit breaker via an aviation connector. The three-phase voltage sensor is used to collect the voltage signal of the three-phase high-voltage bus. The voltage sensors involved in this method include the power supply side A-phase voltage sensor installed on the power supply side A-phase high-voltage bus and the load side C-phase voltage sensor installed on the load side C-phase high-voltage bus. The power supply side A-phase voltage sensor and the load side C-phase voltage sensor correspond to the installation phases of the power supply side A-phase energy harvesting capacitor and the load side C-phase energy harvesting capacitor, respectively. When the three-phase capacitor-powered power supply is working, the energy harvesting current generated is rectified and supplies power to the feeder terminal unit (FTU). The loop current returns to the high-voltage bus side through the enclosure grounding conductor, forming an energy harvesting circulating current. The circulating current of the energy harvesting capacitor refers to the current that continuously flows in a closed loop formed by the energy harvesting capacitor in a three-phase capacitor-powered power supply, where the AC energy harvesting current is obtained from the high-voltage busbar through capacitor voltage division, rectified by a rectifier bridge, and then returned to the grounding point of the energy harvesting capacitor via the enclosure grounding conductor. Figure 2The diagram illustrates the zero-sequence current sensor body and the aviation connector. When the energy-harvesting circulating current flows through the enclosure's grounding conductor, a millivolt-level ground potential difference is generated between the enclosure's metal reference ground at the zero-sequence current sensor body and the enclosure's metal reference ground at the aviation connector due to the non-zero power frequency impedance of the enclosure's grounding conductor (called common ground impedance). The secondary output signal of the zero-sequence current sensor uses the enclosure's metal reference ground at the zero-sequence current sensor body as the signal reference ground, and the analog-to-digital converter (ADC) of the local digitization unit (ADMU) uses the enclosure's metal reference ground as the signal reference ground. Because of the aforementioned millivolt-level ground potential difference between these two reference grounds, this ground potential difference, with a main power frequency of 50Hz, is superimposed on the zero-sequence current sampling signal, forming a parasitic zero-sequence current component. This parasitic zero-sequence current component has the same frequency as the real zero-sequence current generated in the power distribution line due to faults such as single-phase grounding, and the two cannot be separated by frequency domain bandpass filtering or bandstop filtering. The amplitude of the parasitic zero-sequence current component depends on multiple hardware parameters, including the capacitance of the energy harvesting capacitor, the common ground impedance of the enclosure grounding conductor, and the geometric layout of the enclosure grounding conductor. These parameters vary between devices due to differences in individual manufacturing processes, on-site installation techniques, and impedance drift caused by outdoor temperature variations and aging and corrosion of the grounding conductor. They also change slowly over time and cannot be pre-calibrated to a fixed constant at the factory. The energy harvesting circulating current coupling ratio is a proportional coefficient characterizing the contribution of the parasitic zero-sequence current component generated by a unit energy harvesting drive signal value in the zero-sequence current sampling channel. It reflects the overall coupling and transmission characteristics between the energy harvesting circulating current and the common ground impedance of the enclosure grounding conductor to the zero-sequence current sampling channel.

[0023] Further, step S10 includes: Step S11: Obtain the circuit breaker open / close status signal output by the circuit breaker auxiliary contact, read the instantaneous value of the secondary output of the power supply side A-phase voltage sensor, and perform a dual condition judgment based on the amplitude of the circuit breaker open / close status signal and the instantaneous value of the secondary output of the power supply side A-phase voltage sensor to confirm whether the online calibration trigger condition is met: when the circuit breaker open / close status signal indicates the open state and the amplitude of the instantaneous value of the secondary output of the power supply side A-phase voltage sensor is greater than the minimum effective voltage threshold, the online calibration trigger condition is confirmed to be met, and proceed to step S12; otherwise, it is determined that the online calibration trigger condition is not met, the subsequent calibration operation is not performed, and the process proceeds directly to step S20. In step S11, see Figure 3 This is a schematic diagram of online calibration triggered by dual conditions under the open state of the circuit breaker, provided in an embodiment of this application. Figure 3The diagram illustrates the electrical isolation state between the high-voltage busbar of phase A on the power supply side and the de-energized load side when the circuit breaker is in the open state, and the two parallel judgment conditions required to trigger online calibration. It clarifies that the online calibration trigger condition can only be confirmed when both conditions are met. The local digital unit (ADMU) acquires the circuit breaker open / close status signal output by the circuit breaker auxiliary contacts via an aviation connector, reads the instantaneous value of the secondary output of the phase A voltage sensor on the power supply side, and performs a dual condition judgment based on the amplitude of the circuit breaker open / close status signal and the instantaneous value of the secondary output of the phase A voltage sensor on the power supply side to confirm whether the online calibration trigger condition is met. The circuit breaker open / close status signal is a switching signal output by the auxiliary contacts inside the primary and secondary integrated pole-mounted circuit breaker body based on the actual mechanical position of the moving and stationary contacts in the circuit breaker vacuum interrupter chamber. When the moving and stationary contacts are closed, the auxiliary contacts output a closed state signal; when the moving and stationary contacts are separated, the auxiliary contacts output an open state signal. Figure 3 Condition 1 (Illustrated): The circuit breaker's open / closed status signal indicates the open state. The local digital unit (ADMU) continuously monitors the level of the circuit breaker's open / closed status signal. When the signal indicates the open state, the ADMU reads the instantaneous value of the secondary output of the power supply side A-phase voltage sensor from the three-phase voltage sensor and calculates its amplitude. The power supply side A-phase voltage sensor uses a capacitive voltage divider structure, converting the primary voltage on the power supply side A-phase high-voltage bus into a secondary output voltage at a fixed ratio. The amplitude of the secondary output voltage is proportional to the amplitude of the primary voltage. The minimum effective voltage threshold is determined based on the accuracy class of the power supply side A-phase voltage sensor and the resolution of the analog-to-digital converter. Its value is set as the lower limit of the secondary output amplitude of the power supply side A-phase voltage sensor under normal operating conditions of the three-phase capacitor-powered power supply. For example, when the rated primary voltage of the power supply side A-phase high-voltage bus is 10kV divided by... The rated secondary output voltage of the voltage sensor is 3.25V divided by At this time, the minimum effective voltage threshold can be set to 10% of the rated secondary output voltage amplitude, and this threshold is... Figure 3 Condition two, as illustrated, provides the judgment criterion. When the circuit breaker's open / closed status signal indicates the open state and the amplitude of the instantaneous value of the secondary output of the power supply side A-phase voltage sensor is greater than the minimum effective voltage threshold, i.e. Figure 3 If both conditions one and two are met, the online calibration trigger condition is confirmed to be established, and the process proceeds to step S12. If the circuit breaker's open / closed status signal indicates the closed state, or if the circuit breaker is in the open state but the amplitude of the instantaneous value of the secondary output of the power supply side A-phase voltage sensor is lower than the minimum effective voltage threshold, the online calibration trigger condition is determined to be not established, and the subsequent calibration operation is not performed; the process proceeds directly to step S20.

[0024] The reason for employing a dual-condition judgment, rather than relying solely on the circuit breaker's open / closed status signal, is that the two conditions respectively guarantee two physical prerequisites for calibration. When the circuit breaker is in the open state, the primary side line current is zero. Therefore, the actual zero-sequence current through the zero-sequence current sensor must also be zero. At this point, any non-zero signal collected by the zero-sequence current channel can be attributed to a parasitic zero-sequence current component rather than a true ground fault signal. This provides a physical basis for subsequently using all non-zero signals in the zero-sequence current channel as parasitic zero-sequence current components in the calibration calculation. If the amplitude of the instantaneous value of the secondary output of the power supply side A-phase voltage sensor is greater than the minimum effective voltage threshold, it ensures that the power supply side A-phase high-voltage bus is still energized. At least the power supply side A-phase energy-harvesting capacitor in the three-phase capacitor-harvesting power supply is still operating normally, and the circulating current continues to flow through the grounding conductor of the enclosure. Therefore, there is indeed a parasitic zero-sequence current component available for calibration in the zero-sequence current channel. If the high-voltage busbar of phase A on the power supply side has lost voltage, the energy extraction current is zero, there is no energy extraction circulating current on the grounding conductor of the enclosure, and there is no parasitic zero-sequence current component in the zero-sequence current path, then performing calibration at this time will yield a physically meaningless result. By judging the voltage amplitude condition, invalid calibration under the loss-of-voltage state can be avoided, thus initiating the calibration process only when the parasitic zero-sequence current component actually exists, making each calibration physically meaningful. If the dual condition judgment in step S11 is missing, subsequent calibration may be performed in the closed state, misjudging the actual load zero-sequence current as a parasitic zero-sequence current component, or performed in the loss-of-voltage state, resulting in a meaningless calibration value approaching zero. Both situations will lead to inaccurate correction of the parasitic zero-sequence current component in the closed state in step S20, thereby causing the zero-sequence protection criterion calculation of the feeder terminal FTU to make a misjudgment based on distorted zero-sequence current data. The dual condition judgment in step S11, the timing window control in step S12, and the rationality verification in step S16 form a multi-layered collaborative protection, ensuring the reliability of the entire online calibration process from three aspects: triggering timing, data quality, and result credibility.

[0025] Step S12: After the online calibration trigger condition is met, starting from the moment the circuit breaker's open / closed state signal changes from closed to open, first wait for the preset opening transient decay delay to end, then determine whether the cumulative opening duration from the moment the circuit breaker opens to the current moment is greater than the preset minimum calibration window duration; if the cumulative opening duration is greater than the minimum calibration window duration, then confirm that the calibration data acquisition timing is met, and proceed to step S13 to construct the opening state energy harvesting drive signal; if the cumulative opening duration is less than the minimum calibration window duration, then abandon this calibration, retain the energy harvesting circulating current coupling ratio obtained from the previous calibration, and directly proceed to step S20; In step S12, after the online calibration trigger condition is met, the local digital unit (ADMU) waits for the preset transient decay delay to end from the moment it detects the circuit breaker's open / closed state signal changing from closed to open. Then, it determines whether the cumulative opening duration from the moment the circuit breaker opened to the current moment is greater than the preset minimum calibration window duration. The transient decay delay refers to the time required from the moment the moving and stationary contacts of the circuit breaker separate until the electrical and mechanical transient interference caused by the opening completely decays to a negligible level. At the moment the circuit breaker opens, the arc in the vacuum interrupter undergoes a transition process from combustion to extinguishing in microseconds to milliseconds. During this process, the transition waveform of the primary current decaying from the load current to zero will generate transient signals in the three-phase current sensor and zero-sequence current sensor channels. The mechanical vibration of the operating mechanism's opening spring releasing energy to drive the transmission rod and open the circuit breaker may also couple transient interference into the sensor's secondary circuit. The superposition of these transient opening signals in the sampling data of the zero-sequence current channel will lead to calibration result deviations. The duration of the transient decay delay after the circuit breaker trips is set to be no less than the duration of three power frequency cycles. For example, in a 50Hz power frequency system, three power frequency cycles correspond to 60 milliseconds. After 60 milliseconds, the transient decay after the circuit breaker trips has completely decayed to zero, and the energy extraction circulating current circuit has entered the steady-state operating point. At this time, only the steady-state parasitic zero-sequence current component exists in the zero-sequence current channel, and the collected data can be directly used for calibration calculation. The minimum calibration window duration is set to the sum of the transient decay delay after the circuit breaker trips and the effective data acquisition time of no less than five power frequency cycles. In the reclosing operation sequence, the circuit breaker can realize the operation sequence of "trip - 0.3 seconds - reclosing and tripping". The tripping duration may only be 0.3 seconds. After deducting the transient decay delay after the circuit breaker trips, the remaining effective data acquisition window may only be about ten power frequency cycles. It is necessary to confirm that the remaining time is sufficient to perform data acquisition for at least five complete power frequency cycles. If the cumulative tripping duration is greater than the minimum calibration window duration, the calibration data acquisition timing is confirmed to be valid, and the process proceeds to step S13. If the cumulative tripping duration is less than the minimum calibration window duration, the current calibration is abandoned, and the energy harvesting current coupling ratio obtained from the previous calibration is retained, proceeding directly to step S20. Step S12 excludes tripping transient interference from the calibration data by setting a tripping transient decay delay, ensuring that the input data for subsequent cross-correlation calculations only includes steady-state parasitic zero-sequence current components and random sampling noise, with transient components not participating in the calculations, thus avoiding the bias effect of transient pulses on the estimation of the energy harvesting current coupling ratio. By judging the minimum calibration window duration, if the tripping duration is too short to collect a sufficient number of statistical samples, the calibration is automatically abandoned, and the previous valid calibration result is retained, avoiding the calibration deviation caused by insufficient sampling data leading to insufficient statistical accuracy of cross-correlation calculations being transmitted to step S20.

[0026] Step S13, construct the open-state energy extraction drive signal value: Read the three-phase capacitor energy extraction power supply configuration information, which indicates that the three-phase capacitor energy extraction power supply includes the power supply side A-phase energy extraction capacitor installed on the power supply side A-phase high-voltage bus and the load side C-phase energy extraction capacitor installed on the load side C-phase high-voltage bus; Based on the three-phase capacitor energy extraction power supply configuration information and the current circuit breaker open state, determine that only the power supply side A-phase energy extraction capacitor participates in energy extraction in the open state, and use the instantaneous value of the secondary output of the power supply side A-phase voltage sensor as the open-state energy extraction drive signal value of each sampling point; In step S13, the local digital unit (ADMU) reads the three-phase capacitor power supply configuration information stored in its configuration register. This configuration information is a parameter written into the ADMU's configuration register during factory installation or on-site commissioning, indicating which phases and sides of the high-voltage busbars the power supply capacitors are installed on. The ADMU indicates that the three-phase capacitor power supply includes the power supply-side A-phase power supply capacitor installed on the power supply-side A-phase high-voltage busbar and the load-side C-phase power supply capacitor installed on the load-side C-phase high-voltage busbar. Based on the three-phase capacitor power supply configuration information and the current circuit breaker open state, the ADMU determines which power supply capacitors are in an effective power-supplying state under the open state: the power supply-side A-phase high-voltage busbar remains energized after the circuit breaker is opened, and the power supply-side A-phase power supply capacitor still has current flowing through the enclosure's grounding conductor; the load-side C-phase high-voltage busbar is disconnected from the power supply due to the circuit breaker opening, and no voltage is applied across the load-side C-phase power supply capacitor, thus no current is generated. In the open-circuit state, the actual circulating current flowing through the grounding conductor of the enclosure originates solely from the power supply side A-phase power extraction capacitor. The local digital unit (ADMU) uses the instantaneous value of the secondary output of the power supply side A-phase voltage sensor as the open-circuit power extraction drive signal value for each sampling point. The open-circuit power extraction drive signal value serves as a reference signal for characterizing the time-domain waveform of the circulating current in subsequent cross-correlation calculations. The physical basis for directly using the instantaneous value of the secondary output of the power supply side A-phase voltage sensor as the open-circuit power extraction drive signal value is that the power supply side A-phase power extraction capacitor has a capacitive voltage divider structure. There is a fixed amplitude ratio and a fixed phase difference relationship between the fundamental component of the current flowing through the power extraction capacitor and the fundamental component of the voltage of the power supply side A-phase high-voltage bus. The amplitude ratio is determined by the capacitance value of the power extraction capacitor and the power frequency angular frequency, while the phase difference is approximately constant under steady-state power frequency conditions. The time-domain waveform of the energy harvesting current can be characterized by the instantaneous output value of the secondary output of the power supply side phase A voltage sensor, which has a fixed ratio and a fixed phase difference relationship with it. The ratio and phase difference between the two are naturally incorporated into the energy harvesting circulating current coupling ratio in the cross-correlation calculation in step S15, and do not need to be extracted separately. If the phases participating in energy harvesting in the open and closed states of the circuit breaker are not distinguished based on the three-phase capacitor energy harvesting power supply configuration information, and instead the same fixed energy harvesting drive signal construction method is used in all states, the energy harvesting drive signal value will not accurately reflect the actual working state of the current energy harvesting circuit, causing the calibrated energy harvesting circulating current coupling ratio to deviate from the true value, and the parasitic zero-sequence current component correction in step S20 will also produce a systematic deviation. Step S13 dynamically matches the construction method of the energy extraction drive signal value in the open state according to the current open / closed state of the circuit breaker and the configuration information of the three-phase capacitor energy extraction power supply. This forms a state-adaptive cooperative relationship with the construction method in step S21, which uses the sum of the two-phase voltages as the energy extraction drive signal value in the closed state. This ensures that the same energy extraction circulating current coupling ratio can accurately characterize the actual parasitic zero-sequence current component level in both the open calibration state and the closed state.

[0027] Step S14, collect calibration data: Open the calibration data acquisition window, and synchronously record the original sampled value of the zero-sequence current channel and the open-state energy harvesting drive signal value obtained by analog-to-digital conversion of the secondary output signal of the zero-sequence current sensor at a fixed sampling frequency in the calibration data acquisition window. After collecting continuous data for no less than a preset number of complete power frequency cycles, close the calibration data acquisition window to obtain a set of original sampled value sequences of the zero-sequence current channel and a set of open-state energy harvesting drive signal value sequences that are time-aligned with the original sampled value sequences of the zero-sequence current channel. In step S14, the local digital unit (ADMU) opens the calibration data acquisition window after the transient decay delay of the circuit breaker tripping state. Within the calibration data acquisition window, it synchronously records the original sampled value of the zero-sequence current channel obtained by analog-to-digital conversion of the secondary output signal of the zero-sequence current sensor and the power extraction drive signal value of the tripping state constructed in step S13 at a fixed sampling frequency, sampling point by point. After collecting continuous data for no less than a preset number of complete power frequency cycles, the calibration data acquisition window is closed, resulting in a sequence of original sampled values ​​of the zero-sequence current channel and a sequence of power extraction drive signal values ​​of the tripping state that are time-aligned with the original sampled value sequence of the zero-sequence current channel. The original sampled value of the zero-sequence current channel is a digital quantity obtained by the analog-to-digital converter inside the local digital unit (ADMU) sampling and quantizing the secondary output signal of the zero-sequence current sensor at each sampling moment. In the tripping state of the circuit breaker, the original sampled value of the zero-sequence current channel does not contain the true zero-sequence current component, but only the parasitic zero-sequence current component, the quantization noise of the analog-to-digital converter, and the thermal noise of the circuit. The local digitization unit (ADMU) uses multiple channels of the same analog-to-digital converter chip to simultaneously sample zero-sequence current and voltage signals. The sampling trigger clock for each channel originates from the same sampling clock generator, ensuring point-by-point time alignment at the hardware level. Strict synchronous sampling of the two signals is fundamental to the correctness of subsequent cross-correlation calculations. If there is a sampling time deviation between the two signals, it will introduce spurious phase shifts into the cross-correlation results, causing the calculated energy harvesting current coupling ratio to deviate from the true value. The minimum number of power frequency cycles in the calibration data acquisition window is set to no less than five complete power frequency cycles. Integrating over an integer number of power frequency cycles can eliminate the influence of DC bias and higher harmonics on the cross-correlation results. The number of sampling points contained in five power frequency cycles is sufficient at typical sampling rates to achieve an acceptable level of statistical accuracy for the cross-correlation calculation. For example, when the sampling frequency is 80 points per cycle and the calibration data acquisition window contains five complete power frequency cycles, each channel obtains 400 sampling points. The original sampled value sequence of the zero-sequence current channel and the energy harvesting drive signal value sequence in the open-state each contain 400 time-aligned data points. Step S14 provides the data basis for the cross-correlation calculation in step S15. The synchronization and sufficiency of the data directly determine the estimation accuracy of the energy extraction circulation coupling ratio.

[0028] Step S15: Multiply the original sampled value sequence of the zero-sequence current channel with the power-taking drive signal value sequence of the open-state by point and accumulate them to obtain the cross-correlation sum; multiply the power-taking drive signal value sequence of the open-state by point and accumulate them to obtain the autocorrelation sum; divide the cross-correlation sum by the autocorrelation sum to obtain the power-taking circulating current coupling ratio. In step S15, the local digitization unit (ADMU) multiplies the original sampled value sequence of the zero-sequence current channel with the open-state energy harvesting drive signal value sequence point by point and accumulates them to obtain a cross-correlation sum. It also multiplies the open-state energy harvesting drive signal value sequence point by point and accumulates them to obtain an autocorrelation sum. The cross-correlation sum is divided by the autocorrelation sum to obtain the energy harvesting circulating current coupling ratio. The calculation process for the cross-correlation sum is as follows: For each sampling point within the calibration data acquisition window, the original sampled value of the zero-sequence current channel at that sampling point is multiplied by the open-state energy harvesting drive signal value at the same sampling time to obtain a product value. The product values ​​of all sampling points within the calibration data acquisition window are accumulated one by one, and the accumulated result is the cross-correlation sum. The calculation process for the autocorrelation sum is as follows: For each sampling point within the calibration data acquisition window, the open-state energy harvesting drive signal value at that sampling point is multiplied by itself to obtain a self-multiplied value. The self-multiplied values ​​of all sampling points within the calibration data acquisition window are accumulated one by one, and the accumulated result is the autocorrelation sum. The energy harvesting current coupling ratio is calculated by dividing the sum of cross-correlation by the sum of autocorrelation. The physical basis for this is that, under the circuit breaker open state, the original sampled value of the zero-sequence current channel does not contain the true zero-sequence current component, but only the parasitic zero-sequence current component and sampling noise. The parasitic zero-sequence current component and the energy harvesting drive signal value in the open state satisfy a linear proportional relationship at each sampling point. The energy harvesting current coupling ratio is the proportionality coefficient in this linear proportional relationship. Mathematically, the cross-correlation divided by the autocorrelation is equivalent to the minimum mean square error estimation of the linear proportionality coefficient in signal processing. Its function is to provide a statistically optimal estimate of the energy harvesting current coupling ratio under the presence of sampling noise. The more power frequency cycles included in the calibration data acquisition window, the higher the estimation accuracy and the smaller the impact of noise on the estimation result. The sampling noise is uncorrelated with the open-state energy harvesting drive signal value. During the point-by-point multiplication and accumulation process, the contributions of the sampling noise tend to cancel each other out. However, the correlation contribution between the parasitic zero-sequence current component and the open-state energy harvesting drive signal value increases linearly with the number of sampling points. This makes the cross-correlation accumulation mainly reflect the coupling relationship between the parasitic zero-sequence current component and the open-state energy harvesting drive signal value, effectively suppressing the influence of sampling noise. Step S15 extracts the energy harvesting circulating current coupling ratio from the noisy raw data through cross-correlation calculation, providing a quantitative basis for the rationality verification of step S16 and the real-time subtraction of the parasitic zero-sequence current component in the closed state in step S22.

[0029] Step S16: The energy harvesting current coupling ratio is sequentially checked for its physical reasonable range and maximum permissible change in a single calibration. The energy harvesting current coupling ratio that passes the checks, along with the calibration timestamp corresponding to the completion time of this calibration, is written to the energy harvesting current coupling ratio history record area in the non-volatile memory. For each successful writing of a calibration record, the number of valid calibration records maintained in the non-volatile memory is incremented by one, and the current valid energy harvesting current coupling ratio is updated in the arithmetic register. The number of valid calibration records refers to the cumulative number of calibration records in the energy harvesting current coupling ratio history record area of ​​the non-volatile memory that have passed the physical reasonable range check and maximum permissible change in a single calibration in step S16 and have been successfully written. This number is used in step S31 to determine whether the preconditions for linear trend extrapolation are met. Upon initial power-on, the local digitization unit (ADMU) initializes the number of valid calibration records to zero. Subsequently, after each valid calibration that passes a validity check and the calibration result is written to the energy harvesting current coupling ratio history record area, the number of valid calibration records increments by one. When the number of records in the energy harvesting current coupling ratio history record area reaches the storage limit of the most recent preset number of times, the oldest record is overwritten by the most recently written record, and the number of valid calibration records remains at the storage limit and no longer increments. If the check fails, the calibration result is discarded, and the energy harvesting current coupling ratio stored in the previous calibration is retained as the current valid energy harvesting current coupling ratio. If the energy harvesting current coupling ratio stored in the previous calibration is not present in the non-volatile memory, the preset initial value is used as the current valid energy harvesting current coupling ratio.

[0030] In step S16, see Figure 4 This is a schematic diagram for verifying the rationality of the energy harvesting circulation coupling ratio provided in the embodiments of this application. Figure 4 The diagram illustrates two sequential verification steps for the energy harvesting circulation coupling ratio: physical reasonable range verification and single maximum permissible change verification. It clarifies the judgment boundaries, pass conditions, and failure handling rules for each verification. The local digital unit (ADMU) sequentially performs the physical reasonable range verification and single maximum permissible change verification on the energy harvesting circulation coupling ratio. The physical reasonable range verification determines whether the absolute value of the energy harvesting circulation coupling ratio falls within... Figure 4The illustrated range is within a physically reasonable range, with zero as the lower limit and a value determined by physical constraints as the upper limit. The upper limit of the physically reasonable range is determined based on the following physical constraints: the length of the grounding conductor of the enclosure from the zero-sequence current sensor body to the aviation connector does not exceed the external dimensions of the primary and secondary fusion pole-mounted circuit breaker body. The upper limit of the impedance of this conductor at power frequency can be calculated using the conductor resistivity formula based on the conductor cross-sectional area and length. Combined with the rated AC energy extraction capacity of the energy extraction capacitor, the physical upper limit of the energy extraction circulating current coupling ratio can be estimated. The lower limit of the physically reasonable range is zero. If the absolute value of the energy extraction circulating current coupling ratio exceeds the physically reasonable range, it indicates that the calibration data may be contaminated by external transient interference, and the calibration results are unreliable. The local digital unit (ADMU) should follow... Figure 4 The illustrated rule discards the current calibration result. The single maximum permissible variation check is performed under the condition that the previously calibrated energy harvesting current coupling ratio is stored in non-volatile memory. It determines whether the absolute value of the difference between the current calibrated energy harvesting current coupling ratio and the previously calibrated energy harvesting current coupling ratio is less than... Figure 4 The illustration shows the maximum permissible change in a single event based on the previous calibration value. The basis for setting this maximum permissible change is that, within the time interval between two adjacent tripping events, the drift in the common-ground impedance of the enclosure's grounding conductor due to temperature changes and aging corrosion is a gradual process. For example, the maximum permissible change in a single event can be set to 20% of the absolute value of the previous calibration value. Figure 4 The illustrated maximum permissible change per calibration provides a quantitative judgment benchmark. If the difference between the current calibration value and the previous calibration value exceeds the maximum permissible change per calibration, there may be abnormal calibration data or a sudden fault in the grounding loop. The local digital unit (ADMU) will then... Figure 4 The illustrated rule discards the current calibration result and retains the energy harvesting current coupling ratio stored from the previous calibration as the current valid energy harvesting current coupling ratio. The energy harvesting current coupling ratio is determined through physical reasonable range verification and single maximum permissible change verification. Figure 4 Both of the indicated calibration results are deemed to be passed. The calibration timestamp corresponding to the completion time of this calibration is written into the historical record area of ​​the energy harvesting current coupling ratio in the non-volatile memory, and is simultaneously updated in the arithmetic register to the current valid energy harvesting current coupling ratio.

[0031] The non-volatile memory retains the historical records of the most recent preset number of energy extraction circulating current coupling ratios for use in step S30 for trend extrapolation. The energy extraction circulating current coupling ratio is stored in the non-volatile memory because the local digital unit (ADMU) of the outdoor pole-mounted switch may experience a temporary power outage and restart due to a momentary undervoltage of the energy extraction power supply or a lightning overvoltage. The non-volatile memory ensures that the most recently calibrated energy extraction circulating current coupling ratio is not lost after a power outage and restart. After restarting, the ADMU can immediately use this value to correct the parasitic zero-sequence current component without waiting for the next circuit breaker tripping event. The dual verification mechanism in step S16 identifies and intercepts abnormal results caused by transient interference and ground loop abrupt changes in the calibration data. Only calibration results that meet physical constraints and gradual change rules are allowed to update the current effective energy harvesting current coupling ratio through verification. This adds a final quality assurance layer at the result level after the trigger condition screening in step S11 and the timing window control in step S12, ensuring that the current effective energy harvesting current coupling ratio output in step S10 is physically reasonable and statistically stable. When the local digitization unit ADMU is powered on for the first time and there are no valid calibration records in the non-volatile memory, the number of valid calibration records is zero. The local digitization unit ADMU initializes the current effective energy harvesting current coupling ratio to a preset initial value, which can be set to zero or an empirical value estimated based on typical enclosure grounding conductor parameters. Before the first valid calibration is completed, step S20 uses the initial value to perform the parasitic zero-sequence current component subtraction operation, or temporarily omits the parasitic zero-sequence current component subtraction operation and directly outputs the original sampled value of the zero-sequence current channel as the corrected zero-sequence current digital quantity. After the first valid calibration is completed and passes the rationality check in step S16, the number of valid calibration records changes from zero to one, the current valid energy harvesting circulating current coupling ratio is updated to the actual calibration value, and step S20 begins to use the actual calibration value to perform the parasitic zero-sequence current component subtraction normally.

[0032] Step S10 utilizes the natural boundary condition that the zero-sequence current physical quantity is necessarily zero in the circuit breaker's open state. All non-zero signals collected during the zero-sequence current channel during the opening period are attributed to parasitic zero-sequence current components. The coupling ratio of the harvesting circulating current is calculated through cross-correlation operations. This achieves automatic quantification of the coupling transmission relationship between the harvesting circulating current and the zero-sequence current sampling channel without introducing any external calibration equipment or relying on manual intervention. Step S11's dual triggering condition ensures, from a physical perspective, that the original sampled values ​​of the zero-sequence current channel in the calibration data only contain parasitic zero-sequence current components and do not include the true zero-sequence current. It also ensures the existence of the harvesting circulating current, providing a physical basis for subsequent calculations. Step S12's transient decay delay excludes transient interference caused by mechanical vibration during opening and arc extinction from the calibration data. The determination of the shortest calibration window duration ensures that the cross-correlation operation has a sufficient statistical sample size. Together, these two factors ensure that the calibration data meets the computational requirements in terms of both temporal purity and statistical sufficiency. Step S13 dynamically constructs the open-state energy harvesting drive signal value based on the current open / closed state of the circuit breaker and the configuration information of the three-phase capacitor energy harvesting power supply. This ensures that the open-state energy harvesting drive signal value corresponds to the actual energy harvesting circulating current flowing through the grounding conductor of the enclosure in terms of waveform, providing a correct reference signal for cross-correlation calculation. Step S14's synchronous sampling ensures strict point-by-point time alignment between the original sampled value sequence of the zero-sequence current channel and the open-state energy harvesting drive signal value sequence, eliminating the phase shift effect of sampling time deviation on the cross-correlation calculation results. Step S15's cross-correlation divided by autocorrelation calculation extracts the statistically optimal estimate of the energy harvesting circulating current coupling ratio from the noisy sampled data. The impact of noise on the estimation result decreases as the number of sampling points increases. Step S16's dual verification intercepts abnormal calibration results caused by transient interference and grounding loop abrupt changes before the update stage. Combined with non-volatile storage, this ensures that the calibration results are not lost after power failure and restart. The current effective energy extraction circulating current coupling ratio obtained in step S10 is used in step S20 to calculate the estimated value of parasitic zero-sequence current point by point in the closed state and subtracted from the original sampled value of the zero-sequence current channel. This reduces the residual level of the parasitic zero-sequence current component in the corrected zero-sequence current digital quantity output to the feeder terminal FTU from the same order of magnitude as the real weak zero-sequence current to a level much smaller than the real weak zero-sequence current. When the feeder terminal FTU performs zero-sequence protection criterion calculation based on the corrected zero-sequence current digital quantity, it can correctly distinguish between fault signals and parasitic interference signals under the condition that a high-resistance grounding fault occurs in the distribution line and the real zero-sequence current is only tens of milliamperes. The effective sensitivity of zero-sequence protection is improved through pure digital signal processing without changing any hardware layout.The historical record of the energy extraction circulating current coupling ratio in step S10 also provides a time series data basis for the linear trend extrapolation in step S30. During the period when the circuit breaker is in long-term closed operation without the opportunity for opening calibration, step S30 can extrapolate and update the current effective energy extraction circulating current coupling ratio based on the changing trend of the energy extraction circulating current coupling ratio in the historical record, and continuously track the slow drift of the common ground impedance of the enclosure grounding conductor caused by temperature and aging, so that the correction accuracy of the parasitic zero-sequence current component can be maintained in long-term operation.

[0033] Step S20: When the circuit breaker is in the closed state, construct the closing state energy extraction drive signal value according to the three-phase capacitor energy extraction power supply configuration information. Based on the current effective energy extraction circulating current coupling ratio and the closing state energy extraction drive signal value, obtain the corrected zero-sequence current digital quantity and output the corrected zero-sequence current digital quantity to the feeder terminal. Specifically, in step S20, while the circuit breaker is in the closed state, the parasitic zero-sequence current component is estimated and subtracted in real time for each sampling point of the original sampled value of the zero-sequence current channel collected by the local digital unit (ADMU) using the current effective energy extraction circulating current coupling ratio obtained in step S10. The corrected zero-sequence current digital quantity after subtraction is output to the feeder terminal unit (FTU) for zero-sequence protection criterion calculation. The circuit breaker closed state refers to the condition where the moving and stationary contacts of the circuit breaker vacuum interrupter are closed, the high-voltage busbar on the power supply side is connected to the high-voltage busbar on the load side, and the primary line current flows normally. In the closed state, the original sampled value of the zero-sequence current channel is the superposition of the true zero-sequence current component and the parasitic zero-sequence current component. The true zero-sequence current component comes from actual conditions such as three-phase current imbalance or single-phase grounding fault in the distribution line. The parasitic zero-sequence current component comes from the energy extraction circulating current of the three-phase capacitor energy extraction power supply coupled to the ground potential difference signal in the zero-sequence current sampling channel through the common ground impedance of the box grounding conductor. Since the two components are completely in the same frequency and superimposed in the same sampling channel, they cannot be separated by frequency domain filtering. The only way to separate them is by utilizing the calibrated linear coupling relationship between the parasitic zero-sequence current component and the closed-state energy harvesting drive signal value. The estimated value of the parasitic zero-sequence current component is calculated point-by-point in the time domain and subtracted from the original sampled value of the zero-sequence current channel to reconstruct the true zero-sequence current component. The execution of step S20 depends on the fact that step S10 has completed at least one effective calibration and stored the current effective energy harvesting circulating current coupling ratio in non-volatile memory. It also depends on the local digitization unit (ADMU) continuously reading the real-time sampled values ​​of the secondary output signal of the zero-sequence current sensor and the secondary output signal of the three-phase voltage sensor from the analog-to-digital converter.

[0034] Further, step S20 includes: Step S21: Based on the three-phase capacitor power supply configuration information, determine that both the power supply side A-phase power supply capacitor and the load side C-phase power supply capacitor are in working state under the closed state. Read the instantaneous value of the secondary output of the load side C-phase voltage sensor in the three-phase voltage sensor. Sum the instantaneous value of the secondary output of the power supply side A-phase voltage sensor and the instantaneous value of the secondary output of the load side C-phase voltage sensor to construct the closed state power supply drive signal value of the current sampling point. In step S21, the local digital unit (ADMU) determines which energy-harvesting capacitors are in operation under the closed state based on the three-phase capacitor energy-harvesting power supply configuration information and the current circuit breaker closing state, and constructs the closing state energy-harvesting drive signal value for the current sampling point accordingly. The three-phase capacitor energy-harvesting power supply configuration information has been read and cached in step S13, indicating that the energy-harvesting capacitors are installed on the power supply side A-phase high-voltage bus and the load side C-phase high-voltage bus. Under the closed state of the circuit breaker, both the power supply side A-phase high-voltage bus and the load side C-phase high-voltage bus are energized. Energy-harvesting current flows through the enclosure grounding conductor of both the power supply side A-phase energy-harvesting capacitor and the load side C-phase energy-harvesting capacitor. The two energy-harvesting currents together generate a ground potential difference on the enclosure grounding conductor, forming a parasitic zero-sequence current component under the closed state. The phases participating in energy extraction in the closed state differ from those in the open calibration state in step S13: In the open calibration state, the load-side C-phase high-voltage bus loses voltage due to the circuit breaker tripping, and only the power supply-side A-phase energy extraction capacitor participates in energy extraction. In step S13, the instantaneous value of the secondary output of the power supply-side A-phase voltage sensor is used as the open state energy extraction drive signal value. In the closed state, both energy extraction capacitors operate simultaneously. The local digital unit (ADMU) simultaneously reads the instantaneous value of the secondary output of the power supply-side A-phase voltage sensor and the load-side C-phase voltage sensor from the analog-to-digital converter for each sampling point, and sums the two instantaneous values ​​as the closed state energy extraction drive signal value for the current sampling point. The load-side C-phase voltage sensor and the power supply-side A-phase voltage sensor have the same structure, both using the capacitor voltage divider principle to convert the primary voltage on the high-voltage bus into a secondary output voltage at a fixed ratio. The physical basis for constructing the closing-state energy extraction drive signal value as the sum of the instantaneous values ​​of the two-phase voltages is as follows: When the calibration in step S10 is performed in the opening state, only the power supply side A-phase energy extraction capacitor generates energy extraction current. The energy extraction circulating current coupling ratio obtained by calibration reflects the contribution of the parasitic zero-sequence current component driven by the unit voltage generated by each energy extraction capacitor through the enclosure grounding conductor. The power supply side A-phase energy extraction capacitor and the load side C-phase energy extraction capacitor have the same rated AC energy extraction capacity, and the two energy extraction currents share the same enclosure grounding conductor loop path. The contribution of the parasitic zero-sequence current component driven by the unit voltage generated by each energy extraction capacitor is the same. When the two energy extraction capacitors work simultaneously in the closing state, the total parasitic signal on the enclosure grounding conductor is equal to the sum of the two contributions, which is equal to the energy extraction circulating current coupling ratio multiplied by the sum of the two-phase voltages. In this way, the energy extraction circulating current coupling ratio obtained by step S10 in the open state using only the A-phase voltage of the power supply side can be directly applied to the sum of the two-phase voltages driving signal in the closed state, so as to completely eliminate the parasitic zero-sequence current component jointly generated by the two energy extraction capacitors, without having to perform additional calibration in the closed state.If step S21 still uses only the instantaneous value of the secondary output of the power supply side A-phase voltage sensor as the energy extraction drive signal value in the closed state, then the calculated parasitic zero-sequence current estimate only covers the contribution of the parasitic zero-sequence current component generated by the power supply side A-phase energy extraction capacitor. The contribution of the parasitic zero-sequence current component generated by the load side C-phase energy extraction capacitor is not estimated or subtracted. After correction, about half of the parasitic zero-sequence current component will remain in the digital value of zero-sequence current, and the correction effect will be weakened. Step S21 constructs the closed-state energy extraction drive signal value as the sum of the instantaneous values ​​of the two-phase voltage in the closed state, forming a state-adaptive pairing relationship with step S13, which uses only the instantaneous value of the power supply side A-phase voltage in the open state. The two construction methods are physically self-consistent, so that the same energy extraction circulating current coupling ratio can accurately describe the current parasitic zero-sequence current component level in different circuit breaker open and closed states.

[0035] Step S22: Multiply the current effective energy harvesting circulating current coupling ratio with the closed-state energy harvesting drive signal value of each sampling point to obtain the parasitic zero-sequence current estimate of each sampling point, and subtract the corresponding parasitic zero-sequence current estimate from the original sampling value of the zero-sequence current channel of each sampling point to obtain the corrected zero-sequence current digital value. See Figure 5 This is a schematic diagram of real-time subtraction of parasitic zero-sequence current components in the closed state, provided in an embodiment of this application. Figure 5 The diagram illustrates the complete computational process of correcting the zero-sequence current signal at each sampling point, clarifying the three core signals involved in the computation and their computational logic. These three signals are: the original sampled value of the zero-sequence current channel containing both the true and parasitic zero-sequence current components; the estimated parasitic zero-sequence current calculated based on the energy harvesting circulating current coupling ratio and the closing-state energy harvesting drive signal value; and the corrected zero-sequence current digital value containing only the true zero-sequence current component after subtracting the parasitic component. The diagram clearly presents the core computational relationship: "subtracting the estimated parasitic zero-sequence current value from the original sampled value of the zero-sequence current channel to obtain the corrected zero-sequence current digital value." In step S22, the local digitization unit (ADMU) multiplies the current effective energy harvesting circulating current coupling ratio with the closing-state energy harvesting drive signal value constructed in step S21 at each sampling moment to obtain the estimated parasitic zero-sequence current value at the current sampling point. The calculation logic of this estimated value is similar to... Figure 5 The illustrated formula for calculating "energy extraction circulating current coupling ratio × closing-state energy extraction drive signal value" is completely correct. Then, the estimated parasitic zero-sequence current is subtracted from the original sampled value of the zero-sequence current channel at the current sampling point. The original sampled value corresponds to... Figure 5 The superposition signal of the true zero-sequence current component and the parasitic zero-sequence current component is shown in the diagram. The corrected digital value of the zero-sequence current at the current sampling point is obtained, i.e. Figure 5The diagram illustrates an output signal containing only the true zero-sequence current component. The current effective energy harvesting circulating current coupling ratio is written to the non-volatile memory in step S16 and loaded into the arithmetic register after the local digitization unit (ADMU) is started. After each new calibration passes the verification in step S16, the current effective energy harvesting circulating current coupling ratio in the arithmetic register is updated and synchronously written to the non-volatile memory. After the trend extrapolation in step S30, the current effective energy harvesting circulating current coupling ratio in the arithmetic register is also updated but not written to the non-volatile memory. The calculation of the parasitic zero-sequence current estimate is a multiplication operation performed in real-time on a sample-by-sample-point basis. Its computational load consists of only one floating-point multiplication and one floating-point subtraction, which can be completed by the microprocessor inside the ADMU within a single sampling interval without introducing additional sampling delay. The corrected zero-sequence current digital value is equal to the original sampled value of the zero-sequence current channel minus the parasitic zero-sequence current estimate. Physically, it represents the signal remaining after removing the parasitic zero-sequence current component from the superimposed signal containing both the true and parasitic zero-sequence current components; ideally, this is the true zero-sequence current component. The accuracy of the corrected zero-sequence current digital quantity depends on the deviation between the energy harvesting circulating current coupling ratio and the actual coupling transfer characteristics: when the energy harvesting circulating current coupling ratio is completely consistent with the actual value, the estimated value of the parasitic zero-sequence current completely coincides with the actual parasitic zero-sequence current component, and no parasitic component remains in the corrected zero-sequence current digital quantity; when there is a deviation between the energy harvesting circulating current coupling ratio and the actual value, the parasitic zero-sequence current component remaining in the corrected zero-sequence current digital quantity is equal to the deviation multiplied by the value of the closed-state energy harvesting drive signal. The calibration accuracy of step S10 and the trend extrapolation accuracy of step S30 together determine the deviation level between the energy extraction circulating current coupling ratio and the actual value. The dual triggering conditions of step S11, the transient extinction delay of step S12, the synchronous sampling of step S14, the cross-correlation calculation of step S15, and the rationality verification of step S16 control the source of deviation from aspects such as calibration timing, data quality, calculation method, and result reliability, so that the residual level of parasitic zero-sequence current component in the corrected zero-sequence current digital quantity is reduced to a level much lower than the zero-sequence protection action threshold. For example, when the rated primary current of the zero-sequence current sensor is 20A and the rated secondary output voltage is 0.2V, the primary zero-sequence current corresponding to the typical operating threshold of the zero-sequence protection can be set to a value within the range of a few percent to ten percent of the rated primary current. The parasitic zero-sequence current component subtraction in step S22 controls the parasitic residue in the corrected zero-sequence current digital quantity to be below the operating threshold. When the feeder terminal FTU performs zero-sequence protection criterion calculation based on the corrected zero-sequence current digital quantity, it will not cause false operation or failure to operate due to the parasitic zero-sequence current component.

[0036] Step S23: Output the corrected zero-sequence current digital quantity to the feeder terminal for zero-sequence protection criterion calculation. When the circuit breaker is detected to switch from open state to closed state, set the closing transient transition flag and send the closing transient transition status flag to the feeder terminal.

[0037] In step S23, the local digital unit (ADMU) outputs the corrected zero-sequence current digital value obtained in step S22 to the feeder terminal unit (FTU) through the digital signal interface. The FTU receives the corrected zero-sequence current digital value and uses it for zero-sequence protection criterion calculation. The digital signal interface is a digital communication link between the ADMU and the FTU connected by a prefabricated cable. The ADMU encodes the corrected zero-sequence current digital value into digital messages and sends them at fixed intervals. The FTU receives and decodes these messages to obtain a digital value proportional to the actual zero-sequence current on the primary side, which directly participates in the zero-sequence overcurrent protection logic judgment within the FTU. Step S23 also sets a closing transient transition flag when the circuit breaker is detected switching from the open state to the closed state and sends the closing transient transition status flag to the FTU. The closing transient transition flag is a Boolean state variable maintained internally by the local digital unit (ADMU). It is set when the circuit breaker's open / closed state signal transitions from open to closed, and reset after a preset effective period for the closing transient transition. The closing transient transition flag is a flag information sent by the ADMU to the feeder terminal unit (FTU) via the digital signal interface. During the period it receives the closing transient transition flag, the FTU appropriately raises the zero-sequence protection action threshold to avoid maloperation of the protection caused by the closing transient. The effective duration of the closing transient transition is set to be no less than the duration of three power frequency cycles. The setting is based on the same principle as the opening transient decay delay in step S12: At the moment the circuit breaker closes, the closing spring releases energy to drive the transmission shaft to close the moving and stationary contacts of the three-phase vacuum interrupter. In the very short time that the moving and stationary contacts close, the process of establishing the three-phase current may produce transient imbalance. Although the asynchrony time of the three-phase closing does not exceed 2 milliseconds, the closing inrush current and transient imbalance current are manifested as instantaneous pulses in the zero-sequence current channel. Their peak value may exceed the zero-sequence protection setting value, but the duration is much less than one power frequency cycle. During the effective period of the closing transient transition flag, the local digital unit (ADMU) still performs the parasitic zero-sequence current component subtraction operation and outputs the corrected zero-sequence current digital quantity. The closing transient pulse component in the corrected zero-sequence current digital quantity is retained. The feeder terminal unit (FTU) identifies that it is currently in the closing transition period based on the closing transient transition status flag, temporarily raises the zero-sequence protection action threshold or blocks the zero-sequence protection output, and restores the normal protection setting after the closing transient transition effective period ends. If the closing transient transition flag and closing transient transition status flag in step S23 are missing, the corrected zero-sequence current digital quantity received by the feeder terminal unit at the moment of circuit breaker closing will contain a closing transient unbalanced pulse. The feeder terminal unit cannot distinguish whether the pulse is a closing transient or a real ground fault, which may cause the zero-sequence protection to erroneously operate during the normal closing operation of the circuit breaker, causing unnecessary power outages.Step S23 transmits the timing information of the closing transient to the feeder terminal unit (FTU), enabling the FTU to adjust the zero-sequence protection criteria accordingly during the closing transition period and restore the protection sensitivity immediately after the closing transient ends, thus balancing the reliability of the closing operation and the sensitivity of the zero-sequence protection.

[0038] Step S20 performs real-time subtraction of the parasitic zero-sequence current component on a sampling-by-sampling-point basis on the original sampled value of the zero-sequence current channel in the closed state, so that the residual level of the parasitic zero-sequence current component in the corrected zero-sequence current digital quantity is reduced from the same order of magnitude as the real weak zero-sequence current to a level much lower than the zero-sequence protection action threshold. Step S21 constructs the closing state energy harvesting drive signal value as the sum of the instantaneous value of the secondary output of the power supply side A-phase voltage sensor and the instantaneous value of the secondary output of the load side C-phase voltage sensor, so that an energy harvesting circulating current coupling ratio calibrated in the open state can be used to completely estimate the parasitic zero-sequence current component jointly generated by the two energy harvesting capacitors in the closing state, avoiding the problem of incomplete correction caused by the inability to perform calibration in the closing state. Step S22's real-time subtraction operation, performed point-by-sampling, involves only one multiplication and one subtraction, introducing no additional sampling delay. This ensures that the correction of the parasitic zero-sequence current component is synchronized with the real-time sampling of the zero-sequence current. The time delay characteristics of the corrected zero-sequence current digital quantity are completely consistent with those before correction, and the protection criterion timing of the feeder terminal unit (FTU) remains unaffected. Step S23's closing transient state marker provides the feeder terminal unit (FTU) with a time window for closing operations. This allows the FTU to temporarily adjust the zero-sequence protection action threshold during the closing transient and immediately restore the sensitive protection setting after the closing transient ends, balancing the reliability of the circuit breaker closing operation with the sensitivity of the distribution line's zero-sequence protection. When a high-resistance ground fault occurs in a power distribution line, the actual zero-sequence current may only be in the tens of milliamperes range, which is on the same order of magnitude as the parasitic zero-sequence current component generated by the energy extraction loop flowing through the common ground impedance of the enclosure grounding conductor. If the parasitic zero-sequence current component is not subtracted in step S20, the feeder terminal unit (FTU) will be unable to distinguish between the fault signal and the parasitic interference signal. The operating threshold of the zero-sequence protection will have to be set at a level higher than the amplitude of the parasitic zero-sequence current component, resulting in limited detection sensitivity for high-resistance ground faults. Step S20, through real-time subtraction of the parasitic zero-sequence current component, reduces the noise floor in the corrected zero-sequence current digital quantity from the amplitude level of the parasitic zero-sequence current component to the amplitude level of the sampling noise. The feeder terminal unit (FTU) can then set the zero-sequence protection operating threshold at a lower position close to the sampling noise level. Thus, without replacing any sensor hardware or changing the layout of the enclosure grounding conductor, the effective detection sensitivity of the zero-sequence protection can be improved through pure digital signal processing. The removal of parasitic zero-sequence current components in step S20 also brings an additional benefit: the level of the residual parasitic zero-sequence current components in the corrected zero-sequence current digital quantity can be used as an indirect indicator of the calibration accuracy of the energy harvesting circulation current coupling ratio. When the trend extrapolation in step S30 updates the current effective energy harvesting circulation current coupling ratio, the changing trend of the residual parasitic components in the corrected zero-sequence current digital quantity can reflect whether the extrapolation accurately tracks the actual drift of the common ground impedance, providing an indirect verification method in the running state for the extrapolation effect of step S30, thus forming a self-closed-loop signal processing system of calibration-correction-extrapolation-verification.

[0039] Step S20 has a close upstream and downstream coordination relationship with steps S10 and S30. Step S10 completes the online calibration of the energy extraction circulating current coupling ratio and stores it as the current effective energy extraction circulating current coupling ratio when the circuit breaker is in the open state. Step S20 uses the current effective energy extraction circulating current coupling ratio to perform sampling point-by-sampling subtraction of the parasitic zero-sequence current component when the circuit breaker is in the closed state. Step S30 updates the current effective energy extraction circulating current coupling ratio through linear trend extrapolation during the period when the circuit breaker is in long-term closed operation without the opportunity for open calibration, so that step S20 can continue to use it. The three steps cover the complete operating cycle of the circuit breaker under the three conditions of open state, closed state and long-term closed state, forming a closed-loop signal processing link of "open calibration - closed correction - long-term extrapolation". Step S21 switches the closing state energy extraction drive signal value from the single-phase voltage under the opening calibration state to the sum of the two-phase voltages according to the circuit breaker closing state. This forms a state-adaptive signal pair with the single-phase voltage opening state energy extraction drive signal value constructed in step S13 under the opening calibration state. The two construction methods share the same energy extraction circulating current coupling ratio. This is because the energy extraction circulating current coupling ratio calibrated in step S10 under the opening state reflects the coupling contribution of each energy extraction capacitor under unit voltage drive. When the two energy extraction capacitors work simultaneously under the closing state, the drive signal only needs to be changed to the sum of the two-phase voltages to linearly superimpose the two contributions without recalibration. If step S21 does not perform the summation of two-phase voltages and directly uses the single-phase voltage under the open state as the energy extraction drive signal value under the closing state, the parasitic zero-sequence current estimate calculated in step S22 will only cover the parasitic contribution of the energy extraction capacitor of phase A on the power supply side. The parasitic contribution of the energy extraction capacitor of phase C on the load side will not be reduced. After correction, the residual parasitic zero-sequence current component in the zero-sequence current digital quantity will be reduced by only about half compared with that before reduction, and the improvement effect of zero-sequence protection sensitivity will be limited. The closing transient transition flag in step S23 and the opening transient decay delay in step S12 form a symmetrical transient management mechanism in logic: step S12 postpones the acquisition of calibration data during the opening transient to ensure that the calibration data does not contain transient interference; step S23 notifies the feeder terminal FTU to temporarily adjust the protection criteria during the closing transient to ensure that the protection does not malfunction due to the closing transient. Both address the transient management requirements during the switching processes from opening to closing and from closing to opening, respectively, and together maintain the continuity and reliability of online calibration and real-time correction at the state switching boundaries.

[0040] Step S30: Determine whether the preconditions for linear trend extrapolation are met. If the preconditions are met, calculate the continuous closing duration. If the continuous closing duration exceeds the trend extrapolation start-up time threshold, calculate the time change rate of the energy harvesting circulating current coupling ratio. Use the time change rate to perform linear trend extrapolation on the energy harvesting circulating current coupling ratio to update the current effective energy harvesting circulating current coupling ratio.

[0041] Specifically, see Figure 6In step S30, during the period when the circuit breaker remains in the closed state for an extended period without any opening events, the current effective energy extraction circulating current coupling ratio is updated linearly based on the historical data of the energy extraction circulating current coupling ratio written into the non-volatile memory in step S16. This ensures that the current effective energy extraction circulating current coupling ratio used in step S22 during continuous closed operation can track the slow drift trend of the common ground impedance of the enclosure grounding conductor over time, maintaining the correction accuracy for the reduction of parasitic zero-sequence current components. The online calibration in step S10 relies on the boundary condition that the physical quantity of the zero-sequence current is zero provided by the circuit breaker's opening operation. It can only be performed when the circuit breaker is in the open state. During normal operation, the circuit breaker may remain in the closed state for several days or even weeks without any opening events. During this period, step S10 cannot obtain new calibration opportunities. Outdoor pole-mounted switches are installed on overhead power line poles, exposed to diurnal temperature variations and seasonal climate changes. The resistance of the enclosure's grounding conductor changes approximately linearly with temperature. The outdoor ambient temperature may rise from low nighttime temperatures to midday high temperatures and then fall back to low nighttime temperatures within a single day, causing the common-ground impedance of the enclosure's grounding conductor to exhibit diurnal periodic fluctuations. Oxidation corrosion and contact surface deterioration on the enclosure's grounding conductor surface also lead to a slow increase in the common-ground impedance over time. The energy harvesting circulating current coupling ratio is determined by parameters such as the energy harvesting capacitor value, common-ground impedance, and conductor geometry. Drifts in the common-ground impedance will directly cause the energy harvesting circulating current coupling ratio to deviate from the value at the most recent calibration in step S10. If the energy extraction circulating current coupling ratio calibrated several days prior is used without any updates during long-term closed-circuit operation, a deviation will occur between the estimated parasitic zero-sequence current calculated in step S22 and the actual parasitic zero-sequence current component. The deviation increases with the duration of closed-circuit operation and the magnitude of the common-ground impedance drift. The level of the residual parasitic zero-sequence current component in the corrected zero-sequence current digital value will gradually increase, and the effective sensitivity of the zero-sequence protection will gradually decrease during long-term closed-circuit operation. Step S30 uses linear extrapolation of the historical trend of the energy extraction circulating current coupling ratio to continuously update the current effective energy extraction circulating current coupling ratio during long-term closed-circuit operation between two trip calibrations, thus controlling the correction deviation caused by the common-ground impedance drift within an acceptable range.

[0042] Further, step S30 includes: Step S31: Read the energy extraction circulating current coupling ratio value and its corresponding calibration timestamp from the non-volatile memory at least the two most recent calibration records, calculate the continuous closing duration of the circuit breaker from the moment it last switched from the open state to the closed state to the current moment, and determine whether the continuous closing duration exceeds the preset trend extrapolation start-up time threshold. See also Figure 6In step S31, the local digitization unit (ADMU) first determines whether the number of valid calibration records in the non-volatile memory is not less than two. If the number of valid calibration records is less than two, the prerequisite for linear trend extrapolation is not met, and step S30 does not perform the extrapolation operation, keeping the current valid energy extraction current coupling ratio unchanged and directly entering the next operation cycle. If the number of valid calibration records is not less than two, the ADMU reads the energy extraction current coupling ratio of the most recent at least two calibration records and their corresponding calibration timestamps from the non-volatile memory, calculates the continuous closing duration from the moment the circuit breaker last switched from the open state to the closed state to the current moment, and determines whether the continuous closing duration exceeds the preset trend extrapolation start-up time threshold. The energy extraction current coupling ratio historical record area in the non-volatile memory retains the calibration records of the most recent preset number of times. Each record contains an energy extraction current coupling ratio that has passed the rationality verification in step S16 and a corresponding calibration timestamp. The calibration timestamp is the time information synchronously recorded in step S16 when the energy extraction circulating current coupling ratio is written to the non-volatile memory. The local digital unit (ADMU) maintains a real-time clock or running timer internally, and the calibration timestamp corresponds to the timer reading when calibration is completed. The continuous closing duration is the cumulative running time from the moment the circuit breaker last switched from the open state to the closed state to the current moment. In step S11, the ADMU continuously monitors the level change of the circuit breaker's open / closed state signal. When it detects that the circuit breaker's open / closed state signal has switched from the open state to the closed state, it records this switching moment as the closing start moment. In each operation cycle of the subsequent closing state, the difference between the current moment and the closing start moment is used as the continuous closing duration. The trend extrapolation start-up time threshold is a preset threshold value for the continuous closing duration that triggers the linear trend extrapolation operation. Its setting is based on the following: the drift of the common-ground impedance is negligible in a short time; the energy extraction circulating current coupling ratio obtained from the most recent calibration in step S10 remains sufficiently accurate for a period after calibration; and trend extrapolation is only required when the closing duration reaches a point where the common-ground impedance drift begins to affect the correction accuracy. The specific value of the trend extrapolation start-up time threshold is determined based on the temperature change rate of the outdoor pole-mounted switch installation area and the temperature coefficient of the box grounding conductor material. For example, when the maximum daily temperature difference in the outdoor environment is 25 degrees Celsius and the box grounding conductor is made of copper, the temperature coefficient of copper conductor resistance is approximately 0.4% per degree Celsius, and the change in common-ground impedance caused by the daily temperature difference is approximately 10%. The trend extrapolation start-up time threshold can be set to the order of several hours, ensuring that extrapolation is not initiated before the common-ground impedance has an observable impact due to temperature changes, thus avoiding unnecessary extrapolation calculations. Extrapolation is initiated promptly when the common-ground impedance drift begins to affect the correction accuracy to track the drift trend.If the duration of continuous closing does not exceed the trend extrapolation start-up time threshold, the local digital unit (ADMU) continues to use the current effective energy harvesting circulating current coupling ratio stored in step S16 for the parasitic zero-sequence current component subtraction in step S22, without performing extrapolation updates. If the duration of continuous closing exceeds the trend extrapolation start-up time threshold, the process proceeds to step S32 to perform linear trend extrapolation calculations.

[0043] Step S31 requires at least two calibration records to exist in the non-volatile memory in order to provide the two data points needed for trend extrapolation in step S32. If the local digital unit (ADMU) is powered on for the first time or has only completed one calibration, and the number of valid calibration records in the non-volatile memory is less than two, step S31 will find that the number of valid calibration records is insufficient when reading the historical records, failing to meet the prerequisite for trend extrapolation. In this case, step S30 will not perform extrapolation, and the local digital unit (ADMU) will continue to use the energy extraction circulating current coupling ratio obtained from the only calibration. As the circuit breaker experiences multiple tripping events during operation, step S10 will add a calibration record to the non-volatile memory and increment the number of valid calibration records after each valid calibration. When the number of valid calibration records reaches two or more, step S31 can read the two most recent records for use in step S32 if the subsequent continuous closing duration exceeds the trend extrapolation start-up time threshold. The determination of the continuous closing duration in step S31, which is used to determine the timing of trend extrapolation, is set with a reasonable delay. This avoids unnecessary extrapolation calculation overhead during the short-term closing operation period in step S10, when the most recent calibration value is still accurate. Extrapolation is only initiated after the closing duration reaches a point where the common-ground impedance drift begins to affect the correction accuracy. This delay mechanism is consistent in design logic with the transient extinction delay in step S12 and the effective period of the transient transition in step S23. All of them initiate the corresponding signal processing operation after the transient or transition phase ends, avoiding the execution of potentially biased calculations during periods of unstable physical conditions.

[0044] Step S32: Under the condition that the continuous closing duration exceeds the trend extrapolation start-up duration threshold, calculate the quotient of the difference between the energy harvesting circulating current coupling ratio of the two most recent calibration records and the difference between the corresponding two calibration timestamps to obtain the time change rate. Multiply the time change rate by the time interval from the most recent calibration timestamp to the current time and add the most recent calibration energy harvesting circulating current coupling ratio to obtain the trend extrapolation energy harvesting circulating current coupling ratio. Update the current effective energy harvesting circulating current coupling ratio stored in step S16 with the trend extrapolation energy harvesting circulating current coupling ratio for continued use in step S22.

[0045] In step S32, the local digital unit (ADMU), under the condition that the continuous closing duration exceeds the trend extrapolation start-up time threshold, reads the two most recent calibration records from the non-volatile memory. It subtracts the energy extraction current coupling ratio from the most recent calibration record to the energy extraction current coupling ratio from the penultimate calibration record to obtain the change in the energy extraction current coupling ratio between the two calibrations. It subtracts the calibration timestamp from the most recent calibration record to the penultimate calibration record to obtain the time interval between the two calibrations. Finally, it divides the change in the energy extraction current coupling ratio by the time interval to obtain the time rate of change of the energy extraction current coupling ratio. The physical meaning of the time rate of change is the average drift rate of the energy extraction current coupling ratio per unit time, reflecting the average change trend of the common ground impedance of the enclosure grounding conductor between the two calibrations. When the common-ground impedance increases due to temperature rise, the energy harvesting current coupling ratio also increases, and the time change rate is positive. When the common-ground impedance decreases due to temperature drop, the energy harvesting current coupling ratio decreases, and the time change rate is negative. When the common-ground impedance is basically stable between two calibrations, the time change rate is close to zero, and the extrapolated result is almost the same as the most recent calibration value. After obtaining the time change rate, the local digitization unit (ADMU) multiplies the time change rate by the time interval from the most recent calibration timestamp to the current time to obtain the expected drift of the energy harvesting current coupling ratio from the most recent calibration time to the current time. Then, the expected drift is added to the energy harvesting current coupling ratio of the most recent calibration to obtain the trend extrapolated energy harvesting current coupling ratio. The trend extrapolated energy harvesting current coupling ratio is the linear estimate of the energy harvesting current coupling ratio at the current moment by the local digitization unit (ADMU). The ADMU writes the trend extrapolated energy harvesting current coupling ratio into the arithmetic register to update the current effective energy harvesting current coupling ratio for continued use in subsequent sampling points in step S22. The trend extrapolated energy harvesting current coupling ratio is not written into the non-volatile memory to distinguish it from the energy harvesting current coupling ratio obtained by actual calibration in step S16.

[0046] The physical basis for using linear trend extrapolation instead of keeping the most recent calibration value unchanged is that the resistance of the enclosure grounding conductor changes with temperature, and the resistance-temperature characteristics of metallic conductors exhibit an approximately linear relationship within a small temperature range—a well-known fact in conductor physics. The temperature change of the environment where the outdoor pole-mounted switch is located is approximately a slow, continuous change on a diurnal scale, and the common-ground impedance of the enclosure grounding conductor also exhibits an approximately linear, slow drift with temperature. The trend of the energy extraction current coupling ratio between the two calibration records is approximately linear on the time axis; extending this linear trend to the current moment is the basic principle of linear trend extrapolation. The computational load of the linear extrapolation model is extremely low, involving only two subtractions, one division, and one multiplication. The microprocessor inside the local digitization unit (ADMU) can complete all calculations within a single operation cycle, without increasing the real-time burden of step S22's sample-by-sample correction. Compared to higher-order extrapolation methods, linear extrapolation only requires two historical data points to perform, and only requires two historical records in non-volatile memory. It has low storage overhead and can be implemented under the limited storage resources of the local digitization unit (ADMU). For example, suppose the penultimate calibration energy extraction current coupling ratio is a certain value and the corresponding calibration timestamp is the first moment. The most recent calibration energy extraction current coupling ratio is 5% higher than the penultimate one and the corresponding calibration timestamp is the second moment. The time interval between the two calibrations is the second moment minus the first moment. The time change rate is equal to the 5% increment divided by the time interval between the two calibrations. When the circuit breaker continues to operate after the most recent calibration and the continuous closing duration exceeds the trend extrapolation start-up time threshold, the local digital unit (ADMU) multiplies the time change rate by the time interval from the most recent calibration timestamp to the current moment to obtain the expected drift amount and adds it to the most recent calibration energy extraction current coupling ratio. If the time interval from the most recent calibration to the current moment is exactly equal to the time interval between the two calibrations, then the trend extrapolation energy extraction current coupling ratio is 5% higher than the most recent calibration value, reflecting the linear continuation of the common ground impedance drift trend.

[0047] After the trend extrapolation energy extraction current coupling ratio in step S32 is updated to the current effective energy extraction current coupling ratio, it is used by step S22 at each subsequent sampling point until the circuit breaker triggers the next tripping event, which in turn triggers step S10 to perform a new online calibration. After the new calibration is completed and passes the rationality check in step S16, step S16 writes the new calibration value to the non-volatile memory and updates the current effective energy extraction current coupling ratio. The trend extrapolation result in step S30 is then replaced by the new calibration value. Before the new calibration is completed, step S30 can repeat the extrapolation calculation in each operation cycle, allowing the trend extrapolated energy extraction current coupling ratio to be continuously updated as the current moment progresses, tracking the slow drift of the common-ground impedance. The linear trend extrapolation in step S30 is not a precise prediction of the energy extraction current coupling ratio, but rather an approximate estimate based on historical drift trends. The extrapolation accuracy depends on the degree of agreement between the actual drift of the common-ground impedance and the linear model. When the actual drift deviates from the linear assumption, there will be a deviation between the extrapolated result and the true value. However, this deviation is smaller than the deviation produced by directly using the calibration value from several days ago without any extrapolation, because linear extrapolation at least captures the direction and approximate rate of the drift. When the circuit breaker experiences its next tripping event, the new calibration in step S10 will correct the accumulated deviation during the extrapolation period with the actual measured value, bringing the current effective energy extraction circulating current coupling ratio back to the true value. Steps S10 and S30 work alternately, forming a continuous tracking mechanism of "calibration-extrapolation-recalibration-reextrapolation". When there is a tripping opportunity, an accurate value is obtained through actual measurement, and when there is no tripping opportunity, an approximate value is maintained through linear extrapolation, ensuring that the current effective energy extraction circulating current coupling ratio remains within an acceptable accuracy range throughout the entire operating cycle.

[0048] The coordination between step S30 and steps S10 and S20 is reflected in the integrity of the signal processing link. Step S10 uses the boundary conditions provided by the circuit breaker's open state to accurately calibrate the energy harvesting circulating current coupling ratio. However, this calibration can only be performed when an open event occurs and cannot be updated during the closing operation between two open events. Step S20 uses the current effective energy harvesting circulating current coupling ratio to subtract the parasitic zero-sequence current component point by point in the closing state. The correction accuracy directly depends on the deviation between the current effective energy harvesting circulating current coupling ratio and the actual value. Step S30 establishes a time-dimensional connection between steps S10 and S20, extending the calibration result obtained in step S10 during discrete open events to the continuous closing operation period through linear extrapolation. This allows step S20 to use the drift-compensated energy harvesting circulating current coupling ratio at any time. If step S30 is missing, a time gap will exist between steps S10 and S20: the energy extraction circulating current coupling ratio calibrated in the most recent tripping event in step S10 is continuously used in step S20 during subsequent closing operations. However, the common ground impedance continues to drift with temperature and aging, causing the calibrated value to gradually deviate from the actual value. The level of the parasitic zero-sequence current component remaining in the corrected zero-sequence current digital quantity gradually increases, and the correction effect of step S20 degrades as the closing duration increases. Step S30 fills this time gap, ensuring that the correction accuracy of the parasitic zero-sequence current component does not continuously degrade due to the aging of the calibrated value during long-term closing operations. The trend extrapolation start-up time threshold in step S31 ensures that extrapolation is only initiated after the closing duration reaches a level where the common ground impedance drift has an observable impact. This avoids unnecessary extrapolation calculations during short-term closing operations when the calibrated value is still accurate, reducing the computational burden on the local digital unit (ADMU). The linear extrapolation model in step S32 works in conjunction with the non-volatile memory history record in step S16, using historical calibration data that has passed the rationality check as the basis for extrapolation. The reliability of the extrapolation result is based on the reliability of the historical calibration data, which is guaranteed by the double check in step S16.

[0049] Step S30 also provides an indirect means for online monitoring of the integrity of the enclosure grounding circuit. Under normal circumstances, the trend of change between two adjacent calibrations in the historical record of the energy harvesting current coupling ratio should exhibit a slow, gradual change characteristic related to temperature. If the energy harvesting current coupling ratio of a certain calibration suddenly jumps compared to the previous one, and the jump exceeds the maximum allowable change in a single calibration as specified in step S16, it will be intercepted and discarded. If similar jumps occur in multiple consecutive calibrations, it may indicate physical faults such as loose contact, bolt oxidation, or broken grounding wire in the enclosure grounding conductor. The time change rate calculated during the linear trend extrapolation process in step S30 also carries information about the common-ground impedance drift rate. When the time change rate continues to increase and deviates from the normal temperature-related drift range, it may indicate accelerated aging and corrosion of the enclosure grounding conductor or deterioration of the contact surface condition. Although the direct function of step S30 is to update the current effective energy harvesting current coupling ratio to maintain the correction accuracy, the time change rate and the long-term evolution trend of the energy harvesting current coupling ratio in historical records can be used by the local digital unit ADMU or feeder terminal FTU to assess the grounding loop status and provide maintenance personnel with early warning information on hidden faults such as loose enclosure grounding conductors, oxidation corrosion, or grounding wire breaks.

[0050] Step S30 uses linear trend extrapolation of the historical data of the energy extraction circulating current coupling ratio to continuously track the slow drift of the common-ground impedance of the enclosure grounding conductor caused by outdoor temperature changes and conductor aging and corrosion during the period when the circuit breaker is in long-term closed operation without the opportunity for open calibration. Step S31 reads the two most recent calibration records and determines whether the continuous closing duration exceeds the trend extrapolation start time threshold, so that extrapolation is only initiated when the timeliness of the calibration value begins to decrease, and no unnecessary extrapolation calculations are performed during the short-term closed operation phase when the calibration value is still valid. Step S32 uses the changing trend of the energy extraction circulating current coupling ratio between two calibrations to calculate the time change rate and extrapolates it linearly to the current time. The computational load is extremely low and only two historical records are required, which can be achieved under the limited computing and storage resources of the local digital unit (ADMU). The online calibration in steps S30 and S10 forms an alternating tracking mechanism of "precise calibration of opening circuit breaker - extrapolation of closing circuit breaker trend". This mechanism, together with the real-time subtraction in step S20, forms a connection in the time dimension. This ensures that the current effective energy extraction circulating current coupling ratio remains within the accuracy range that matches the actual coupling transmission characteristics throughout the complete operating cycle of the circuit breaker. The residual level of the parasitic zero-sequence current component in the corrected zero-sequence current digital quantity does not gradually increase due to the aging of the calibration value during long-term closing operation. The zero-sequence protection sensitivity of the feeder terminal FTU can be continuously maintained during long-term operation. The dual trigger condition judgment and the transient decay delay of step S10 ensure the purity of each calibration data. The dual verification in step S16 ensures the reliability of the calibration results written to the non-volatile memory. The linear trend extrapolation in step S30 approximates the drift during the closing operation based on reliable historical data. The three work together in three aspects: data quality assurance, result reliability assurance, and time continuity assurance, so that the entire signal processing method can realize the automatic calibration and automatic tracking update of the energy extraction circulating current coupling ratio.

[0051] Example 2: This embodiment, based on Embodiment 1, provides a localized digital signal processing device for pole-mounted switches in a distribution network, such as... Figure 7 As shown, it includes: Online calibration module: used to collect circuit breaker opening and closing status signals, zero-sequence current sensor secondary output signals and power supply side A-phase voltage sensor secondary output signals, to confirm whether the online calibration trigger condition is met, and after the online calibration trigger condition is met, to calculate the energy harvesting circulating current coupling ratio, and to obtain the current effective energy harvesting circulating current coupling ratio after verifying the rationality of the energy harvesting circulating current coupling ratio. Zero-sequence correction module: Used to read the configuration information of the three-phase capacitor power supply, construct the power supply drive value of the closing state according to the configuration information of the three-phase capacitor power supply when the circuit breaker is closed, and obtain the corrected zero-sequence current digital quantity according to the current effective power supply circulating current coupling ratio and the power supply drive value of the closing state. The corrected zero-sequence current digital quantity is output to the feeder terminal. Extrapolation update module: used to determine whether the preconditions for linear trend extrapolation are met. When the preconditions are met, the continuous closing duration is calculated. When the continuous closing duration exceeds the trend extrapolation start-up time threshold, the time change rate of the energy harvesting circulating current coupling ratio is calculated. The energy harvesting circulating current coupling ratio is then linearly extrapolated using the time change rate to update the current effective energy harvesting circulating current coupling ratio.

[0052] Furthermore, in the online calibration module, the method for confirming whether the online calibration trigger condition is met includes: The online calibration triggering condition is determined by a dual condition based on the amplitude of the circuit breaker open / close status signal and the instantaneous value of the secondary output of the power supply side A-phase voltage sensor: when the circuit breaker open / close status signal indicates the open state and the amplitude of the instantaneous value of the secondary output of the power supply side A-phase voltage sensor is greater than the minimum effective voltage threshold, the online calibration triggering condition is confirmed to be met.

[0053] After the online calibration triggering condition is met, but before calculating the energy harvesting circulation coupling ratio, the following steps are also included: From the moment the circuit breaker's open / closed status signal changes from closed to open, wait for the preset opening transient decay delay to end, and determine whether the cumulative opening duration from the moment the circuit breaker opened to the current moment is greater than the preset minimum calibration window duration. If the cumulative opening duration is greater than the minimum calibration window duration, the calibration data acquisition timing is confirmed to be valid. If the cumulative opening duration is less than the minimum calibration window duration, abandon this calibration and continue to use the energy harvesting circulating current coupling ratio obtained from the previous calibration.

[0054] The method for calculating the energy harvesting circulation coupling ratio includes: Construct the open-state energy harvesting drive signal value, collect calibration data based on the constructed open-state energy harvesting drive signal value, and obtain a set of original sampled value sequences of zero-sequence current channel and a set of open-state energy harvesting drive signal value sequences that are time-aligned with the original sampled value sequences of zero-sequence current channel. Based on the original sampled value sequence of the zero-sequence current channel and the energy harvesting drive signal value sequence in the open state, the energy harvesting circulating current coupling ratio is calculated.

[0055] The method for constructing the open-state energy-harvesting drive signal value includes: Read the configuration information of the three-phase capacitor power supply. The configuration information indicates that the three-phase capacitor power supply includes the power supply-side A-phase power supply capacitor installed on the power supply side A-phase high-voltage bus and the load-side C-phase power supply capacitor installed on the load side C-phase high-voltage bus. Based on the configuration information of the three-phase capacitor power supply and the current circuit breaker open state, determine that only the power supply-side A-phase power supply capacitor participates in power extraction in the open state, and use the instantaneous value of the secondary output of the power supply-side A-phase voltage sensor as the open state power extraction drive signal value of each sampling point.

[0056] The methods and apparatus of this application may be implemented in many ways. For example, they may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of steps for the method is for illustrative purposes only, and the steps of the method of this application are not limited to the order specifically described above, unless otherwise specifically stated.

[0057] In addition, the parts of the technical solutions provided in the embodiments of this application that are consistent with the implementation principles of the corresponding technical solutions in the prior art have not been described in detail, so as to avoid excessive elaboration.

[0058] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A localized digital signal processing method for pole-mounted switches in power distribution networks, characterized in that, The method includes: Collect the circuit breaker opening and closing status signal, the secondary output signal of the zero-sequence current sensor, and the secondary output signal of the A-phase voltage sensor on the power supply side to confirm whether the online calibration trigger condition is met. After the online calibration trigger condition is met, calculate the energy harvesting circulating current coupling ratio. After verifying the rationality of the energy harvesting circulating current coupling ratio, obtain the current effective energy harvesting circulating current coupling ratio. Read the configuration information of the three-phase capacitor power supply, construct the power supply drive value of the closing state according to the configuration information of the three-phase capacitor power supply when the circuit breaker is closed, obtain the corrected zero-sequence current digital quantity according to the current effective power supply circulating current coupling ratio and the power supply drive value of the closing state, and output the corrected zero-sequence current digital quantity to the feeder terminal. Determine whether the preconditions for linear trend extrapolation are met. If the preconditions are met, calculate the continuous closing duration. If the continuous closing duration exceeds the trend extrapolation start-up time threshold, calculate the time change rate of the energy harvesting circulating current coupling ratio. Use the time change rate to perform linear trend extrapolation on the energy harvesting circulating current coupling ratio to update the current effective energy harvesting circulating current coupling ratio. The method for calculating the energy harvesting circulating current coupling ratio includes: constructing a tripped-state energy harvesting drive signal value; collecting calibration data based on the constructed tripped-state energy harvesting drive signal value to obtain a set of original sampled value sequences of the zero-sequence current channel and a set of tripped-state energy harvesting drive signal value sequences that are time-aligned with the original sampled value sequences of the zero-sequence current channel; and calculating the energy harvesting circulating current coupling ratio based on the original sampled value sequences of the zero-sequence current channel and the tripped-state energy harvesting drive signal value sequences.

2. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 1, characterized in that, The method for confirming whether the online calibration trigger condition is met includes: The online calibration triggering condition is determined by a dual condition based on the amplitude of the circuit breaker open / close status signal and the instantaneous value of the secondary output of the power supply side A-phase voltage sensor: when the circuit breaker open / close status signal indicates the open state and the amplitude of the instantaneous value of the secondary output of the power supply side A-phase voltage sensor is greater than the minimum effective voltage threshold, the online calibration triggering condition is confirmed to be met.

3. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 2, characterized in that, After the online calibration triggering condition is met, but before calculating the energy harvesting circulation coupling ratio, the following steps are also included: From the moment the circuit breaker's open / closed status signal changes from closed to open, wait for the preset opening transient decay delay to end, and determine whether the cumulative opening duration from the moment the circuit breaker opened to the current moment is greater than the preset minimum calibration window duration. If the cumulative opening duration is greater than the minimum calibration window duration, the calibration data acquisition timing is confirmed to be valid. If the cumulative opening duration is less than the minimum calibration window duration, abandon this calibration and continue to use the energy harvesting circulating current coupling ratio obtained from the previous calibration.

4. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 3, characterized in that, The method for constructing the open-state energy-harvesting drive signal value includes: Read the configuration information of the three-phase capacitor power supply. The configuration information indicates that the three-phase capacitor power supply includes the power supply-side A-phase power supply capacitor installed on the power supply side A-phase high-voltage bus and the load-side C-phase power supply capacitor installed on the load side C-phase high-voltage bus. Based on the configuration information of the three-phase capacitor power supply and the current circuit breaker open state, determine that only the power supply-side A-phase power supply capacitor participates in power extraction in the open state, and use the instantaneous value of the secondary output of the power supply-side A-phase voltage sensor as the open state power extraction drive signal value of each sampling point.

5. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 4, characterized in that, The method for collecting the calibration data includes: Open the calibration data acquisition window, and synchronously record the original sampled value of the zero-sequence current channel and the open-state energy harvesting drive signal value obtained by analog-to-digital conversion of the secondary output signal of the zero-sequence current sensor at each sampling point in the calibration data acquisition window. After collecting continuous data for no less than a preset number of complete power frequency cycles, close the calibration data acquisition window to obtain a set of original sampled value sequences of the zero-sequence current channel and a set of open-state energy harvesting drive signal value sequences that are time-aligned with the original sampled value sequences of the zero-sequence current channel.

6. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 5, characterized in that, The method for calculating the energy harvesting circulation coupling ratio also includes: The original sampled value sequence of the zero-sequence current channel is multiplied point by point with the power-receiving drive signal value sequence of the open-state and the result is accumulated to obtain the cross-correlation sum. The power-receiving drive signal value sequence of the open-state is multiplied point by point and the result is accumulated to obtain the autocorrelation sum. The cross-correlation sum is divided by the autocorrelation sum to obtain the power-receiving circulating current coupling ratio.

7. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 6, characterized in that, The rationality verification includes physical rationality range verification and single maximum allowable change verification. The effective energy harvesting current coupling ratio is obtained as follows: the energy harvesting current coupling ratio that has passed the physical reasonable range verification and the single maximum allowable change verification, together with the calibration timestamp corresponding to the time of completion of this calibration, is written into the energy harvesting current coupling ratio historical record area in the non-volatile memory. For each calibration record successfully written, the number of effective calibration records in the non-volatile memory is incremented by one, and the energy harvesting current coupling ratio is updated to the current effective energy harvesting current coupling ratio. If the verification fails, the calibration result is discarded, and the energy harvesting current coupling ratio stored in the previous calibration is retained as the current valid energy harvesting current coupling ratio.

8. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 7, characterized in that, The method for constructing the closing-state energy extraction drive signal value includes: Based on the configuration information of the three-phase capacitor power supply, it is determined that both the power supply side A-phase power supply capacitor and the load side C-phase power supply capacitor are in working state under the closed state. The instantaneous value of the secondary output of the load side C-phase voltage sensor in the three-phase voltage sensor is read. The instantaneous value of the secondary output of the power supply side A-phase voltage sensor and the instantaneous value of the secondary output of the load side C-phase voltage sensor are summed to construct the closed state power supply drive signal value of the current sampling point.

9. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 8, characterized in that, The method for obtaining the corrected digital value of the zero-sequence current includes: The parasitic zero-sequence current estimate for each sampling point is obtained by multiplying the current effective energy harvesting circulating current coupling ratio with the closed-state energy harvesting drive signal value at each sampling point. The corrected zero-sequence current digital value is obtained by subtracting the corresponding parasitic zero-sequence current estimate from the original sampling value of the zero-sequence current channel at each sampling point.

10. The localized digital signal processing method for pole-mounted switches in a distribution network according to claim 9, characterized in that, The methods for determining whether the preconditions for linear trend extrapolation are met include: Determine whether the number of valid calibration records in the non-volatile memory is no less than two. If the number of valid calibration records is no less than two, the prerequisite for linear trend extrapolation is met.

11. A localized digital signal processing apparatus for pole-mounted switches in a distribution network, comprising implementing the localized digital signal processing method for pole-mounted switches in a distribution network as described in any one of claims 1-10, characterized in that, The device includes: Online calibration module: used to collect circuit breaker opening and closing status signals, zero-sequence current sensor secondary output signals and power supply side A-phase voltage sensor secondary output signals, to confirm whether the online calibration trigger condition is met, and after the online calibration trigger condition is met, to calculate the energy harvesting circulating current coupling ratio, and to obtain the current effective energy harvesting circulating current coupling ratio after verifying the rationality of the energy harvesting circulating current coupling ratio. Zero-sequence correction module: Used to read the configuration information of the three-phase capacitor power supply, construct the power supply drive value of the closing state according to the configuration information of the three-phase capacitor power supply when the circuit breaker is closed, and obtain the corrected zero-sequence current digital quantity according to the current effective power supply circulating current coupling ratio and the power supply drive value of the closing state. The corrected zero-sequence current digital quantity is output to the feeder terminal. Extrapolation update module: used to determine whether the preconditions for linear trend extrapolation are met. When the preconditions are met, the continuous closing duration is calculated. When the continuous closing duration exceeds the trend extrapolation start-up time threshold, the time change rate of the energy harvesting circulating current coupling ratio is calculated. The energy harvesting circulating current coupling ratio is then linearly extrapolated using the time change rate to update the current effective energy harvesting circulating current coupling ratio.

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