Small current grounding system fault line selection and closed-loop control method and device

Abstract

The invention relates to the technical field of power system automation and relay protection, and discloses a low-current grounding system fault line selection and closed-loop control method and device, and the method comprises the steps: applying preset parameter disturbance to an arc suppression coil in a system after the system is detected to have a grounding fault; in the process of applying the parameter disturbance, synchronously collecting zero-sequence current of each outgoing line as a response signal; analyzing the response signal, and determining a fault line and a fault property; and executing a corresponding closed-loop control strategy according to the determined fault line and the fault property. After a fault is detected, an arc suppression coil is utilized to inject a high-frequency pseudo-random binary sequence as a disturbance signal, and a cross-correlation analysis algorithm is adopted to process the zero-sequence current response of each line, so that a fault feature component related to a disturbance source can be accurately extracted from strong background noise; therefore, high-precision selection of the fault line is realized.

Description

Technical Field

[0001] This invention relates to the field of power system automation and relay protection technology, specifically to a method and device for fault location and closed-loop control in a low-current grounding system. Background Technology

[0002] Low-current grounding systems are widely used in industrial and mining enterprises and urban power distribution networks in my country because they can effectively suppress fault arcs and reduce fault currents during single-phase grounding faults, and allow the system to continue operating with the fault for a period of time. The core equipment of this system, the arc suppression coil, can provide inductive current to compensate for the capacitive current of the power grid to ground during a single-phase grounding fault, thereby significantly reducing the residual current at the fault point.

[0003] However, despite the significant advantages of this system in improving power supply reliability, how to quickly and accurately identify and locate faulty lines has always been a major technical challenge that hinders the safe and stable operation of the power grid, especially when facing high-resistance grounding with extremely weak fault characteristics or intermittent arc grounding with dynamic and variable behavior.

[0004] Currently, existing fault location methods can be mainly divided into two categories: passive methods and active methods. Traditional passive methods mainly rely on the amplitude, phase, or high-frequency components of transient zero-sequence voltage and current generated at the moment of fault occurrence for analysis and judgment. However, these transient signals themselves have weak amplitudes, especially under high-resistance grounding faults, and their characteristics are extremely indistinct. Moreover, their duration is short, making them easily submerged by system background noise and various interferences. More importantly, the shape and amplitude of transient characteristics are heavily dependent on various unpredictable random factors such as the initial phase angle of the fault, system operating mode, and line parameters. This directly leads to insufficient reliability and adaptability of this type of method, often resulting in misjudgment or failure to operate in complex practical application scenarios.

[0005] To overcome the aforementioned shortcomings of passive methods, researchers have proposed active fault diagnosis methods. The basic idea behind these methods is to artificially inject a specific, energy-controlled detection signal into the system to actively enhance fault characteristics, thereby improving the accuracy of fault location. However, existing active methods generally require additional high-power, bulky signal injection devices and associated frequency and phase selection equipment. This not only significantly increases equipment investment costs and substation space requirements but also creates numerous inconveniences for on-site installation, commissioning, and modifications, thus limiting their widespread engineering application to some extent.

[0006] Furthermore, both passive and most existing active methods primarily focus on improving the success rate of fault location. There is a general lack of effective technical means for in-depth fault identification, such as effectively distinguishing between a stable high-resistance grounding fault and a more dangerous intermittent arc grounding fault that could trigger resonant overvoltages. This lack of diagnostic information makes it difficult to implement refined and differentiated protection and control strategies, often resulting in a "one-size-fits-all" approach that fails to execute optimal control strategies based on the actual severity of the fault, thus failing to meet the growing demands for intelligent and refined operation and maintenance in modern power distribution networks.

[0007] In summary, existing technologies still have significant shortcomings in the field of fault diagnosis for low-current grounding systems: on the one hand, it is difficult to reliably locate complex faults such as high resistance and intermittent faults without significantly increasing hardware costs; on the other hand, they generally lack the ability to accurately identify the specific nature of the fault, thus failing to provide sufficient and reliable basis for subsequent intelligent control and self-healing decisions. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method and apparatus for fault selection and closed-loop control in low-current grounding systems. This solves the problem that existing fault diagnosis technologies for low-current grounding systems are unable to accurately select high-resistance or intermittent fault lines and identify their characteristics at low cost, thus failing to achieve differentiated intelligent control.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a fault location and closed-loop control method for a low-current grounding system, comprising the following steps: S1. After a grounding fault is detected in the system, a preset parameter disturbance is applied to the arc suppression coil in the system; S2. During the process of applying the parameter disturbance, the zero-sequence current of each outgoing line is simultaneously collected as a response signal. S3. Analyze the response signal to determine the faulty line and the nature of the fault; S4. Based on the determined faulty line and the nature of the fault, execute the corresponding closed-loop control strategy.

[0010] Preferably, the step of applying a preset parameter perturbation specifically includes: A first disturbance mode and a second disturbance mode are applied sequentially. The first disturbance mode is a high-frequency micro-amplitude disturbance, which is used to assist in subsequent fault line selection analysis. The second disturbance mode is a low-frequency impact disturbance, which is used to assist in subsequent fault nature identification analysis.

[0011] Preferably, the specific method for applying the first perturbation mode is as follows: The reactance value of the arc suppression coil is adjusted bidirectionally at high frequency according to a preset pseudo-random binary sequence.

[0012] Preferably, the step of determining the faulty line specifically includes: The zero-sequence currents of each outgoing line under the first perturbation mode are cross-correlation analyzed with the pseudo-random binary sequence. The line that exhibits the largest correlation peak in the cross-correlation analysis results is identified as the faulty line.

[0013] Preferably, the specific method for applying the second perturbation mode is as follows: Based on a preset low-frequency periodic signal, the reactance value of the arc suppression coil is adjusted to stimulate the nonlinear response characteristics that may exist at the fault point of the faulty line.

[0014] Preferably, the step of determining the nature of the fault specifically includes: The zero-sequence current collected under the second disturbance mode of the identified faulty line is subjected to response spectrum analysis to obtain its harmonic components. Based on the distribution characteristics of the harmonic components, the nature of the fault is determined to be linear or nonlinear.

[0015] Preferably, the step of determining based on the distribution characteristics of the harmonic components specifically includes: Calculate the total harmonic distortion rate of the zero-sequence current, or calculate the ratio of its higher harmonic energy to the fundamental energy; The calculation results are compared with a preset nonlinear discrimination threshold to determine the nature of the fault.

[0016] Preferably, the step of executing the corresponding closed-loop control strategy specifically includes: When the nature of the fault is determined to be linear, an alarm or optimization compensation control strategy is executed. When the fault is determined to be nonlinear, a control strategy of delayed tripping or immediate tripping is executed.

[0017] Preferably, the step of synchronously acquiring the zero-sequence current of each outgoing line is achieved by a high-precision clock synchronization module configured at each outgoing line.

[0018] A fault location and closed-loop control device for a low-current grounding system includes: The parameter disturbance module is used to apply a preset parameter disturbance to the arc suppression coil in the system after a ground fault is detected in the system. The response signal acquisition module is used to synchronously acquire the zero-sequence current of each outgoing line as a response signal during the application of the parameter disturbance. The diagnostic analysis module is used to analyze the response signal, determine the faulty line and the nature of the fault, and generate a corresponding closed-loop control strategy based on the determined faulty line and the nature of the fault.

[0019] This invention provides a method and apparatus for fault location and closed-loop control in a low-current grounding system. It offers the following advantages: 1. This invention utilizes a high-frequency pseudo-random binary sequence injected into an arc suppression coil as a disturbance signal after a fault is detected, and employs a cross-correlation analysis algorithm to process the zero-sequence current response of each line. This enables the accurate extraction of fault characteristic components related to the disturbance source from strong background noise, thereby achieving high-precision selection of faulty lines. This effectively overcomes the technical defects of traditional methods that are easily affected by factors such as transition resistance and noise interference, resulting in low line selection accuracy.

[0020] 2. This invention, after selecting the faulty line, further utilizes the arc suppression coil to apply low-frequency impact disturbance to actively excite the characteristics of the fault point, and combines the response spectrum analysis method to quantitatively evaluate the zero-sequence current harmonic components of the faulty line, thereby achieving in-depth identification of the fault nature. It can reliably distinguish between stable linear high-resistance grounding and nonlinear arc grounding with higher risk, filling the gap in existing technologies that can only select the line but cannot determine the specific nature of the fault.

[0021] 3. This invention combines accurate fault location results with in-depth fault nature identification conclusions to form a two-dimensional, comprehensive diagnostic report. Based on this report, differentiated closed-loop control strategies are executed. For linear faults, strategies for optimized compensation and power supply protection are adopted, while for nonlinear faults, strategies for decisive isolation and safety protection are adopted. This makes fault handling more intelligent and refined, improving the safety of power grid operation and the reliability of power supply. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a system architecture diagram of the present invention. Detailed Implementation

[0023] 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.

[0024] Example: Please see the appendix Figure 1This invention provides a method for fault location and closed-loop control in a low-current grounding system, comprising the following steps: S1. After a ground fault is detected in the system, a preset parameter disturbance is applied to the arc suppression coil in the system; In this embodiment, to address the technical challenges of low fault location accuracy, inability to effectively identify the nature of the fault, and difficulty in achieving refined closed-loop control in existing low-current grounding systems when facing high-resistance or intermittent arc grounding faults, this invention provides an innovative fault location and closed-loop control method for low-current grounding systems.

[0025] By applying a coded dual-mode disturbance to the reactance parameters of the arc suppression coil, a response signal carrying fault characteristics is actively excited and modulated in the system. Combined with a highly sensitive time-domain and frequency-domain joint analysis algorithm, the faulty line can be accurately located and the nature of the fault can be deeply identified. Finally, intelligent closed-loop control is executed based on the diagnostic results.

[0026] The method described in this embodiment covers a series of technical steps, including fault initiation judgment, dual-modal parameter disturbance injection, synchronous response signal acquisition, multi-dimensional diagnostic analysis, and closed-loop control execution.

[0027] First, during the fault initiation judgment and system activation phase, this method uses a central decision-making unit deployed within the substation to continuously monitor the zero-sequence voltage of the power grid busbar online. Zero-sequence voltage is chosen as the activation criterion because, in low-current grounding systems, the most direct and reliable electrical characteristic of a single-phase ground fault is the abnormal rise in zero-sequence voltage. When the instantaneous value of the monitored busbar zero-sequence voltage... The system is activated when the following conditions are met: ; in, This refers to the instantaneous value of the zero-sequence voltage of the busbar, acquired in real time. The rated phase voltage of the power grid is a known system parameter. This represents the pre-set zero-sequence voltage start-up coefficient, whose value takes into account the voltage fluctuations that may occur during normal system operation and the typical voltage rise during ground faults, ensuring the sensitivity and reliability of start-up.

[0028] Once the activation condition is met, the central decision-making unit will immediately record the current moment as the synchronization time benchmark for the entire diagnostic process. It immediately broadcasts an activation command via a high-speed communication network to the dual-mode disturbance coding controller configured at the arc suppression coil and the synchronous data acquisition unit distributed at each outgoing line, thereby initiating the subsequent disturbance injection and data acquisition process.

[0029] Next, the system enters the core dual-modal parameter perturbation injection stage. The purpose of this stage is to stimulate specific response signals required for fault line selection and fault nature identification through two perturbation modes with different characteristics. This stage is precisely executed by the dual-modal perturbation coding controller.

[0030] The first disturbance mode is a high-frequency, low-amplitude disturbance. Its design goal is to generate a coded signal with excellent noise immunity and uniqueness, facilitating precise location of faulty lines amidst complex background noise. In practice, the controller first generates a preset pseudo-random binary sequence with sharp autocorrelation characteristics, denoted as... The reason for preferentially using pseudo-random binary sequences is their wide spectral density and white noise-like properties, which can provide a unique "fingerprint" that is easily identifiable through relevant calculations without interfering with the normal operation of the power grid. Subsequently, the controller... The code element, the reactance value of the arc suppression coil at its current operating point Based on this, a small-amplitude bidirectional high-frequency adjustment is performed. This process can be described by the following formula: ; In this formula, This represents the instantaneous reactance of the arc suppression coil during the disturbance. This is the reference reactance value of the arc suppression coil before the disturbance begins; The reactance adjustment amplitude in this mode is strictly limited to a small range to ensure system safety.

[0031] This stage is from Start, continue until the preset end time. .

[0032] Following the first disturbance mode, the system seamlessly switches to the second disturbance mode, namely low-frequency impulse disturbance. This mode has a completely different design goal from the first; it aims to fully "excite" and expose the nonlinear current-voltage characteristics that may exist at the fault point by applying a relatively concentrated low-frequency impulse to the system, especially for arcing ground faults. In practice, the controller generates one or more cycles of low-frequency square wave or trapezoidal wave signals. Its fundamental frequency Far below the power frequency. Subsequently, the controller... The instantaneous value of the reactance of the arc suppression coil can be expressed as: ; in, This is a preset low-frequency periodic signal; This is the reactance adjustment amplitude in low-frequency impulse mode, and its value can be appropriately greater than... This generates sufficiently significant voltage stress at the fault point.

[0033] The start and end times of this stage are: to .

[0034] During the entire dual-mode disturbance injection period, it is configured on each outgoing line (denoted as line). The synchronous data acquisition units operate continuously. These units ensure that all acquired data has a uniform, microsecond-level timestamp through a built-in high-precision clock synchronization module. They synchronously record the zero-sequence current of their respective lines at a high sampling rate. This raw data, carrying system response information, is then transmitted to the central decision-making unit to provide a basis for subsequent analysis.

[0035] After data collection is completed, the central decision-making unit enters the diagnostic analysis phase. This phase is also divided into two steps, corresponding to fault location and fault nature identification.

[0036] To achieve fault location, the central decision-making unit first retrieves the zero-sequence current of each line collected during the first disturbance mode. For each line's current signal, it compares it with a pseudo-random binary sequence used as a reference. Perform cross-correlation analysis. The mathematical expression of this process is as follows: ; in, It is a line The cross-correlation function; For the line Zero-sequence current sampled under the first disturbance mode; It is a pseudo-random binary sequence with a time delay; For time delay variables; and These are the start and end times of the first disturbance mode, respectively.

[0037] The physical significance of this algorithm lies in its ability to extract a reference signal from a background of strong noise, much like an inverting amplifier. Components highly correlated in frequency and phase. For a faulty line, its zero-sequence current includes the current flowing through the fault resistor, which is... The current component directly modulated by the signal, therefore its cross-correlation function In a certain The value exhibits a sharp and significant peak. Conversely, the zero-sequence current of a healthy circuit is primarily capacitive, and its derivative with the zero-sequence voltage is related to... The direct correlation between the lines is extremely weak, and their cross-correlation function values ​​will be very small. Based on this principle, by comparing the maximum peak value of the cross-correlation function of each line, the faulty line can be accurately located. ; in, The final identified faulty line number; This represents the total number of outgoing lines in the system. From 1 to Outgoing index.

[0038] Accurately pinpointing the faulty circuit Subsequently, in order to further investigate the nature of the fault, the central decision-making unit retrieved the zero-sequence current collected during the second disturbance mode of the line. It performs a Fast Fourier Transform on the current signal to convert it from the time domain to the frequency domain, obtaining its response spectrum. : ; in, The response spectrum of the zero-sequence current in the faulty line; The zero-sequence current of the faulty line is collected under the second disturbance mode; For frequency variables; The imaginary unit; and These are the start and end times of the second perturbation mode, respectively.

[0039] The response spectrum reveals the behavior of the fault point under low-frequency impact disturbances. If the fault point is a stable high-impedance ground, its electrical characteristics are close to linear, and the energy in the response spectrum will be mainly concentrated on the fundamental component consistent with the fundamental frequency of the disturbance signal. If the fault point is an arc ground, its strong nonlinear characteristics will lead to abundant high-order harmonics in the induced current. To quantify this nonlinearity, the total harmonic distortion rate is introduced as a criterion in this embodiment: ; In this formula: Total harmonic distortion (THD); To respond to the amplitude of the fundamental component in the spectrum; For the response spectrum of the first The amplitude of the second harmonic component; This represents the harmonic order.

[0040] By calculating The value and the preset nonlinear discrimination threshold By comparing the results, the nature of the fault can be determined. If... Less than or equal to If the fault is positive, it is determined to be a linear fault; otherwise, it is determined to be a nonlinear fault.

[0041] Finally, based on the two-dimensional diagnostic conclusion obtained from the above analysis, namely {faulty line number} Upon diagnosis of the fault, the system enters the closed-loop control execution phase. Based on this accurate diagnosis, the central decision-making unit can automatically execute differentiated and optimal control strategies. For lines identified as having linear faults, only an alarm can be triggered, and the arc suppression coil can be instructed to enter the optimal compensation state to ensure continued system operation. For lines identified as having nonlinear faults, the system can execute an immediate tripping or short-delay tripping strategy according to preset protection logic to isolate the fault and prevent the situation from escalating.

[0042] In summary, this embodiment innovatively redefines the function of the arc suppression coil and combines multi-modal disturbance injection with multi-dimensional response decoupling analysis to form a complete technical closed loop from accurate diagnosis to intelligent control, thereby effectively improving the automation and intelligence level of fault handling in low-current grounding systems.

[0043] S2. During the application of parameter perturbation, the zero-sequence current of each outgoing line is simultaneously collected as a response signal. In this embodiment, after completing the fault initiation judgment and system activation through the aforementioned steps, the method of the present invention enters its core technical step, namely the dual-modal parameter disturbance injection and synchronous response signal acquisition step. The design idea of ​​this step is to actively and controllably inject weak disturbances carrying specific coded information into the system and synchronously capture the system's response to the disturbance, thereby generating raw data with high signal-to-noise ratio and high discriminability for subsequent fault diagnosis and analysis.

[0044] This step uses an integrated dual-mode disturbance coding controller to precisely and rapidly adjust the reactance parameters of the arc suppression coil at the neutral point of the system. The arc suppression coil was chosen as the actuator because, as an existing adjustable component in the power grid, it can modulate the parameters of the entire zero-sequence network at extremely low cost and with minimal modifications, thus avoiding the high cost and bulky external signal source required by traditional active injection methods.

[0045] The perturbation injection process in this step is innovatively designed as two consecutive but distinct phases: the first perturbation mode and the second perturbation mode.

[0046] The first disturbance mode, also known as the high-frequency micro-amplitude disturbance mode, primarily aims to generate a detection signal with unique fingerprint characteristics for subsequent fault location analysis. In this embodiment, the dual-mode disturbance coding controller first generates a preset pseudo-random binary sequence with sharp autocorrelation characteristics. A pseudo-random binary sequence is used as the disturbance code because it has a wide spectrum and resembles white noise, providing a reference signal that is easily identifiable from complex background noise through correlation calculations without significantly interfering with the power grid's power frequency operation. Subsequently, the controller adjusts the reactance value of the arc suppression coil at its current operating point using a small-amplitude bidirectional high-frequency adjustment based on this pseudo-random binary sequence. The mathematical model of this process can be described as follows: ; In this formula: This represents the instantaneous reactance of the arc suppression coil during the disturbance. This is the reference reactance value of the arc suppression coil before the disturbance begins; It is a preset pseudo-random binary sequence, whose code elements switch between +1 and -1; The reactance adjustment amplitude in the high-frequency micro-amplitude disturbance mode is strictly limited to a small range to ensure system safety, thereby enabling micro-disturbance detection of the system.

[0047] The first disturbance mode starts from the diagnostic initiation time. Start, continue until the preset end time. .

[0048] Immediately following the end of the first disturbance mode, the system seamlessly switches to the second disturbance mode, namely the low-frequency impulse disturbance mode. This mode differs significantly in design objective from the former; it no longer pursues pseudo-randomness of the signal, but rather aims to fully excite and expose the nonlinear volt-ampere characteristics that may exist at the fault point by applying a relatively concentrated low-frequency impulse to the system. This is crucial for distinguishing between stable high-resistance grounding and unstable arcing grounding. In this embodiment, the controller generates one or more cycles of a low-frequency periodic signal, which can be a square wave or trapezoidal wave signal. Subsequently, the controller adjusts the reactance value of the arc suppression coil based on this low-frequency periodic signal; its instantaneous value can be expressed as: ; In this formula: The preset low-frequency periodic signal has an amplitude that also varies between +1 and -1; The reactance adjustment amplitude in low-frequency impulse mode can be moderately greater than [the value of the reactance adjustment amplitude]. This generates sufficiently significant voltage stress at the fault point, thereby effectively detecting its nonlinear response.

[0049] The start and end times of this second disturbance mode are: and .

[0050] Throughout the entire dual-mode disturbance injection process described above, the key parallel operation is the acquisition of synchronous response signals. This operation is performed by all systems configured with [specific components / facilities]. The synchronous data acquisition units for each outgoing line are responsible for this process. The core function of these units is to ensure that the zero-sequence current data for all lines is recorded under a unified and accurate time reference. To achieve this, each acquisition unit incorporates a high-precision clock synchronization module. This module utilizes timing technology based on the Global Navigation Satellite System (GNSS) to achieve cross-device time synchronization with microsecond-level or even higher precision.

[0051] These synchronous data acquisition units continuously record the instantaneous zero-sequence current values ​​of the lines they monitor at a sufficiently high sampling rate, forming time-series data. This data constitutes the system's direct response signal to applied parameter disturbances.

[0052] After data acquisition, the zero-sequence current time series data of all lines, along with their precise timestamp information, will be transmitted to the central decision-making unit. This provides a complete and high-quality raw data foundation for subsequent fault selection based on cross-correlation analysis and fault nature identification based on response spectrum analysis. It can be said that the successful execution of this step is the prerequisite and guarantee for the high accuracy and high reliability of the entire diagnostic method.

[0053] S3. Analyze the response signal to determine the faulty line and the nature of the fault; In this embodiment, after the aforementioned dual-modal parameter disturbance injection and synchronization response signal acquisition steps are completed, the method of the present invention proceeds to the core diagnostic analysis step. This step is a crucial link in achieving accurate fault location and in-depth fault identification. It is executed in the central decision-making unit and, based on the high-quality synchronization data acquired in the aforementioned steps, through multi-dimensional decoupling analysis, ultimately outputs an accurate diagnostic conclusion. Internally, it can be further divided into two closely linked sub-processes: fault line selection and fault nature identification.

[0054] First, a fault selection sub-process based on time-domain correlation analysis is performed.

[0055] This process aims to accurately identify the specific line experiencing a ground fault from all N outgoing lines of the system. The data used is the zero-sequence current time series recorded by each synchronous data acquisition unit during the first disturbance mode, i.e., the period of high-frequency micro-amplitude disturbance. Data from this stage is used for line selection because the high-frequency pseudo-random binary sequence, as a disturbance code, injects a unique, wide-spectrum detection fingerprint into the system.

[0056] The fingerprint detection directly modulates the zero-sequence voltage of the entire zero-sequence network through the reactance adjustment of the arc-suppression coil. For a faulty line, its zero-sequence current necessarily contains an active or resistive component flowing through the fault point. This component is directly related to the modulated zero-sequence voltage and therefore inevitably carries a characteristic highly correlated with a pseudo-random binary sequence. For all healthy lines, however, the zero-sequence current is mainly the ground capacitance current, which is proportional to the time derivative of the zero-sequence voltage; therefore, its direct correlation with the zero-sequence voltage itself is extremely weak. This invention utilizes this fundamental difference in response characteristics between faulty and healthy lines.

[0057] The central decision-making unit has authority over each qualifying candidate. The zero-sequence current collected under the first disturbance mode , and the pseudo-random binary sequence used as the reference signal Perform cross-correlation analysis. The formula for calculating the cross-correlation function is as follows: ; In this formula: For the line The cross-correlation function between the zero-sequence current and the reference signal, the value of which is a time delay variable. The function; For the line The instantaneous value of zero-sequence current collected under the first disturbance mode; For the time delay The resulting pseudo-random binary sequence; and These represent the start and end times of the first perturbation mode, respectively, which define the effective time window for integration.

[0058] Due to the excellent autocorrelation properties of pseudo-random binary sequences, the results of the above calculations will exhibit high discriminative power: for faulty lines, the calculated... Will at a certain delay Near the value, it exhibits an isolated and significant spike; while for all healthy lines, the calculation result will be a flat curve with a weak amplitude, close to the background noise.

[0059] Therefore, identifying the faulty line is transformed into finding the maximum correlation peak. The central decision-making unit makes a final decision by executing the following criteria: ; in: The number of the line that was ultimately identified as the faulty line; This represents the total number of outgoing lines in the system. From 1 to Outgoing index.

[0060] This step allows you to pinpoint the exact location of the fault from among many lines.

[0061] Through the aforementioned time-domain correlation analysis, the faulty line was accurately identified as line [missing information]. After that, the diagnostic analysis steps did not end, but were further deepened, entering the fault nature identification sub-process.

[0062] For identified faulty lines, the electrical characteristics of the fault point are determined, particularly distinguishing between stable linear resistance grounding and unstable nonlinear arc grounding. The data used is from the aforementioned second disturbance mode, specifically during low-frequency impulse disturbances, focusing only on the faulty line. The zero-sequence current collected. The reason for designing and utilizing the data at this stage is that the nonlinear volt-ampere characteristics unique to arc faults may not be significant under conventional small-signal disturbances, but by applying a low-frequency large disturbance with relatively concentrated energy, this nonlinear characteristic can be effectively excited and amplified, making it easier to detect in the response signal.

[0063] Central decision-making unit extracts faulty circuits The zero-sequence current sampled under the second disturbance mode is denoted as... Subsequently, a Fast Fourier Transform is performed on it to observe its response characteristics in the frequency domain. This process can be represented as: ; In this formula: The response spectrum of the zero-sequence current of the faulted line is a function of the frequency variable ff; The instantaneous value of zero-sequence current collected by the faulty line under the second disturbance mode; The imaginary unit; and These are the start and end times of the second perturbation mode, respectively.

[0064] The obtained response spectrum This is the direct basis for determining the nature of the fault. If the fault point is a stable high-resistance ground, its electrical characteristics are approximately linear resistance. Therefore, under low-frequency impulse disturbances, its induced current should also be linear, and its spectral energy will mainly be concentrated at the fundamental frequency of the disturbance signal. The fundamental frequency component is consistent with the fundamental frequency. Conversely, if it is an arc grounding, the nonlinear current-voltage characteristic of the arc will be excited under disturbance, causing the induced current waveform to be distorted, thereby generating a series of components in its spectrum that are inconsistent with the fundamental frequency. Related, significant higher harmonic components.

[0065] To automate and quantify the determination process, total harmonic distortion (THD) is introduced as a criterion in this embodiment. Defined as the ratio of the root mean square value of all higher harmonic components to the amplitude of the fundamental component, its calculation formula is: ; in: The total harmonic distortion rate is calculated. To obtain from the response spectrum The amplitude of the fundamental component extracted from it; To obtain from the response spectrum The extracted first The amplitude of the second harmonic component; This represents the harmonic order.

[0066] Finally, the central decision-making unit will calculate... The value is compared with the nonlinear discrimination threshold preset based on system characteristics and experimental data. Compare. If Less than or equal to If the fault is linear, then the fault type is determined to be linear; if Greater than If so, the fault is determined to be nonlinear.

[0067] At this point, the diagnostic analysis step is complete, and a two-dimensional diagnostic conclusion containing {faulty line number, fault nature} is output, providing a solid and reliable decision-making basis for subsequent refined closed-loop control.

[0068] S4. Based on the determined faulty line and fault nature, execute the corresponding closed-loop control strategy.

[0069] In this embodiment, after the aforementioned diagnostic analysis step successfully outputs a two-dimensional diagnostic conclusion including the faulty line and the nature of the fault, the method of the present invention then enters its final stage, which is also the endpoint of realizing the intelligent operation closed loop of the system—the closed-loop control execution step.

[0070] The core value of this step lies in its radical transformation of traditional protection devices, which rely on a single, fixed response mode for all faults. Instead, it leverages the high-precision, multi-dimensional diagnostic information obtained from the preceding steps to execute differentiated, optimal control strategies, thereby achieving a delicate balance between ensuring system safety and improving power supply reliability. This step is led and executed by the central decision-making unit, translating the analysis conclusions into actual control actions for power grid equipment.

[0071] After receiving the diagnostic conclusions output by the diagnostic analysis module, the central decision-making unit will immediately activate the preset decision logic tree and select and execute the matching control process based on the key dimension of the fault nature.

[0072] When the central decision-making unit receives a diagnosis indicating a linear fault on a certain line, this typically corresponds to a stable, relatively low-risk high-resistance grounding fault. In this case, the system will not immediately execute a mandatory disconnection action, but will instead initiate a refined control process prioritizing the maintenance of power supply continuity.

[0073] First, the system generates a detailed alarm message. This message not only includes the confirmed line number but also clearly indicates that the fault is a linear high-resistance line, and may include key characteristic data from the diagnostic process. This alarm message will be sent to the substation monitoring system and even to a higher-level dispatch center, providing clear and accurate data support for subsequent analysis and maintenance arrangements by operators.

[0074] The central decision-making unit executes an active closed-loop adjustment. It immediately issues a new control command to the dual-mode disturbance encoding controller of the arc suppression coil, instructing it to exit disturbance diagnosis mode and, based on current system parameters and fault conditions, switch to optimal compensation operation mode. In this mode, the reactance value of the arc suppression coil is adjusted to a new setpoint that maximizes compensation for the system capacitive current, aiming to minimize the residual current flowing through the fault point. This not only reduces the risk of equipment damage due to prolonged heating at the fault point but also creates conditions for continued safe operation with the fault present.

[0075] When the diagnostic conclusion clearly indicates that the fault is nonlinear, this usually corresponds to a highly dangerous intermittent or stable arc grounding fault. Because arc grounding can trigger intermittent overvoltages, posing a serious threat to system insulation and creating safety hazards, the system will immediately prioritize safety and initiate a decisive control process with the core objectives of rapidly isolating the fault and preventing the situation from escalating.

[0076] Based on the pre-set protection strategy and the importance level of the faulty line, the central decision-making unit can select to execute different control commands.

[0077] A preferred strategy is immediate tripping. Under this strategy, the central decision-making unit will issue a tripping command directly to the circuit breaker protection unit of the line identified as faulty without any delay, disconnecting the faulty line from the power grid as quickly as possible, thereby completely eliminating the source of the fault and achieving self-healing of the distribution network.

[0078] Another more sophisticated strategy is delayed tripping. This strategy is mainly for extremely critical power supply lines, aiming to balance safety and power supply reliability. The central decision-making unit sets a short delay before issuing a trip command. This delay is designed to allow transient arcing faults a chance to extinguish themselves. If the fault characteristics disappear on their own during the delay, the trip command will be automatically cancelled. If the fault persists until the delay ends, the trip command will be executed decisively.

[0079] Furthermore, the method of this invention fully considers the case of transient faults. If the fault characteristics disappear spontaneously during the aforementioned disturbance diagnosis process, it indicates that the fault was transient. In this case, the diagnostic analysis step will output the conclusion that the fault has disappeared. The closed-loop control execution step will then suspend all subsequent control command execution and only archive the complete information of this transient fault event, including the initially located line, the time of occurrence and disappearance, for subsequent statistical analysis. This effectively avoids power outages caused by unnecessary switching operations on transient faults that have already recovered spontaneously.

[0080] In summary, the closed-loop control execution steps of this invention are not simply a process of issuing switching action commands, but rather an intelligent decision-making and differentiated execution process based on in-depth diagnostic information. The analysis results of the aforementioned steps are transformed into tangible and optimized control behaviors for the power grid, ultimately forming a complete technical closed loop from precise diagnosis to intelligent self-healing. Therefore, in practical applications, this significantly improves the operational flexibility, safety, and power supply reliability of low-current grounding systems when dealing with complex faults.

[0081] Please see the appendix Figure 2 A fault location and closed-loop control device for a low-current grounding system, comprising: The parameter disturbance module is used to apply preset parameter disturbances to the arc suppression coil in the system after a ground fault is detected. The response signal acquisition module is used to synchronously acquire the zero-sequence current of each contact wire as a response signal during the application of parameter disturbance. The diagnostic analysis module is used to analyze the response signal, determine the faulty line and the nature of the fault, and generate a corresponding closed-loop control strategy based on the determined faulty line and the nature of the fault.

[0082] The device in this embodiment can be used to execute the above method embodiments, and its principle and technical effects are similar, so they will not be described again here.

Claims

1. A method for fault line selection and closed-loop control of a small current grounding system, characterized in that, Includes the following steps: S1. After a grounding fault is detected in the system, a preset parameter disturbance is applied to the arc suppression coil in the system; S2. During the process of applying the parameter disturbance, the zero-sequence current of each outgoing line is simultaneously collected as a response signal. S3. Analyze the response signal to determine the faulty line and the nature of the fault; S4. Based on the determined faulty line and the nature of the fault, execute the corresponding closed-loop control strategy.

2. The small current grounding system fault line selection and closed-loop control method of claim 1, wherein, The step of applying the preset parameter perturbation specifically includes: A first disturbance mode and a second disturbance mode are applied sequentially. The first disturbance mode is a high-frequency micro-amplitude disturbance, which is used to assist in subsequent fault line selection analysis. The second disturbance mode is a low-frequency impact disturbance, which is used to assist in subsequent fault nature identification analysis.

3. The small current grounding system fault line selection and closed-loop control method of claim 2, wherein, The specific method for applying the first perturbation mode is as follows: The reactance value of the arc suppression coil is adjusted bidirectionally at high frequency according to a preset pseudo-random binary sequence.

4. The small current grounding system fault line selection and closed-loop control method of claim 3, wherein, The steps for determining the faulty line specifically include: The zero-sequence currents of each outgoing line under the first perturbation mode are cross-correlation analyzed with the pseudo-random binary sequence. The line that exhibits the largest correlation peak in the cross-correlation analysis results is identified as the faulty line.

5. The small current grounding system fault line selection and closed loop control method of claim 2, wherein, The specific method for applying the second perturbation mode is as follows: Based on a preset low-frequency periodic signal, the reactance value of the arc suppression coil is adjusted to stimulate the nonlinear response characteristics that may exist at the fault point of the faulty line.

6. The small current grounding system fault line selection and closed loop control method of claim 5, wherein, The steps for determining the nature of the fault specifically include: The zero-sequence current collected under the second disturbance mode of the identified faulty line is subjected to response spectrum analysis to obtain its harmonic components. Based on the distribution characteristics of the harmonic components, the nature of the fault is determined to be linear or nonlinear.

7. The fault location and closed-loop control method for a low-current grounding system according to claim 6, characterized in that, The step of determining based on the distribution characteristics of the harmonic components specifically includes: Calculate the total harmonic distortion rate of the zero-sequence current, or calculate the ratio of its higher harmonic energy to the fundamental energy; The calculation results are compared with a preset nonlinear discrimination threshold to determine the nature of the fault.

8. The small current grounding system fault line selection and closed loop control method of claim 1, wherein, The steps for executing the corresponding closed-loop control strategy specifically include: When the nature of the fault is determined to be linear, an alarm or optimization compensation control strategy is executed. When the fault is determined to be nonlinear, a control strategy of delayed tripping or immediate tripping is executed.

9. The small current grounding system fault line selection and closed loop control method of claim 1, wherein, The step of synchronously collecting the zero-sequence current of each outgoing line is achieved by a high-precision clock synchronization module configured at each outgoing line.

10. A device for fault line selection and closed-loop control of a small current grounding system, according to any one of claims 1-9, characterized in that, include: The parameter disturbance module is used to apply a preset parameter disturbance to the arc suppression coil in the system after a ground fault is detected in the system. The response signal acquisition module is used to synchronously acquire the zero-sequence current of each outgoing line as a response signal during the application of the parameter disturbance. The diagnostic analysis module is used to analyze the response signal, determine the faulty line and the nature of the fault, and generate a corresponding closed-loop control strategy based on the determined faulty line and the nature of the fault.

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