Power distribution network single-phase earth fault sensing method based on resonance gain effect

Abstract

The embodiment of the invention discloses a power distribution network single-phase earth fault sensing method based on a resonance gain effect, relates to the technical field of power system protection and control, and aims to solve the problem of low detection sensitivity caused by the fact that fault features are covered by a strong capacitive background in an existing signal injection method. The method comprises the following steps: under a preset working condition that a zero-sequence loop resonant frequency point of a power distribution network is located near a system power frequency point, injecting a current signal with a preset frequency near the resonant frequency point into a zero-sequence loop; measuring a zero-sequence voltage steady-state signal generated by excitation of the current signal; on the basis of the injection current and the measurement voltage, determining characteristic parameters representing resistive component changes in the zero-sequence loop; and judging whether a single-phase earth fault occurs or not according to the variation of the characteristic parameters before and after the fault. Resonance characteristics near a power frequency under a specific working condition are utilized, resonance which is considered to be harmful traditionally is converted into a favorable factor, amplification recognition of fault characteristics is achieved, and detection sensitivity is improved.

Description

Technical Field

[0001] This invention relates to the field of power system protection and control technology, and in particular to a method for detecting single-phase grounding faults in distribution networks based on the resonant gain effect. Background Technology

[0002] The power distribution network is the most fundamental and critical component of the new power system, undertaking increasingly important functions such as distributed energy access, regional load supply, and power quality regulation. Single-phase grounding faults are the most common and highly dangerous type of fault, and in high-resistance grounding situations, they are extremely prone to being missed or misdiagnosed.

[0003] This application specifically addresses the fault detection problem in 35kV resonant grounding systems. As a critical layer connecting the regional power grid and important loads, the 35kV system's power supply reliability and load importance are far greater than those of a typical 10kV distribution network. In power systems, the higher the voltage level, the larger the ground capacitive current. This makes the zero-sequence network of the 35kV system more complex and the system's ground capacitive current even larger during ground faults. This large capacitive current background increases the inherent unbalanced current in the zero-sequence network, posing a more severe challenge to fault signal extraction.

[0004] For the detection and sensing of single-phase grounding faults, existing research has established several traditional approaches. One is the power frequency measurement method, which mainly identifies faults by detecting characteristics at power frequency such as zero-sequence voltage, zero-sequence current, and harmonic components. However, in high-resistance grounding, the zero-sequence current amplitude is weak and often submerged in system fluctuations and harmonic noise introduced by power electronic devices, resulting in poor sensing performance. The second is the traveling wave method, which utilizes the high-frequency transient traveling wave characteristics generated by the fault for location and identification. However, the traveling wave method requires high-speed sampling equipment and high-frequency detection devices, resulting in high costs. Furthermore, in modern distribution networks with widespread integration of power electronic devices, the traveling wave waveform is severely distorted, leading to decreased detection accuracy.

[0005] Therefore, the traditional power frequency method lacks sufficient sensitivity, while the traveling wave method is costly and susceptible to interference, neither of which can meet the high requirements for accurate detection of high-resistance grounding faults in the important and complex 35kV power grid environment. In summary, the traditional power frequency method lacks sufficient sensitivity in critical high-resistance scenarios, while the traveling wave method suffers from inherent drawbacks such as high cost and susceptibility to interference, both of which fail to meet the urgent need for accurate detection of high-resistance grounding faults in modern distribution networks. Summary of the Invention

[0006] The main objective of this invention is to provide a method for detecting single-phase grounding faults in distribution networks based on the resonant gain effect. This method aims to address the difficulties and low sensitivity of traditional methods in detecting insulation faults, thereby optimizing the operating efficiency and stability of power systems. This method is specifically designed for distribution networks with neutral points grounded via arc suppression coils, particularly 35kV systems operating under tuned overcompensated conditions.

[0007] To achieve the above objectives, the first aspect of this application provides a method for detecting single-phase grounding faults in distribution networks based on the resonant gain effect, applicable to distribution networks where the neutral point is grounded via an arc-suppression coil and a damping resistor. The method includes: Under the preset operating condition that the resonant frequency of the zero-sequence circuit of the distribution network is near the power frequency of the system, a current signal of a preset frequency is injected into the zero-sequence circuit of the distribution network. Measure the zero-sequence voltage steady-state signal generated by the current signal excitation of the preset frequency; Based on the injected current signal and the measured voltage signal, characteristic parameters for characterizing the change of resistive component in the zero-sequence loop are determined. Based on the changes in the characteristic parameters before and after the fault, determine whether a single-phase ground fault has occurred.

[0008] A second aspect of this application provides a single-phase ground fault detection system for a distribution network based on the resonant gain effect, comprising: The injection module is used to inject a current signal of a preset frequency into the zero-sequence circuit of the distribution network under the preset operating condition that the resonant frequency point of the zero-sequence circuit of the distribution network is near the power frequency point of the system. The measurement module is used to measure the zero-sequence voltage steady-state signal generated by the current signal excitation of the preset frequency; The processing module is used to determine characteristic parameters for characterizing the change of resistive component in the zero-sequence circuit based on the injected current signal and the measured voltage signal, and to determine whether a single-phase ground fault has occurred based on the change of the characteristic parameters before and after the fault occurs.

[0009] A third aspect of this application provides an electronic device including a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform steps as described in the first aspect and any possible implementation thereof.

[0010] A fourth aspect of this application provides a computer-readable storage medium, wherein when a computer program is executed by a processor, the processor performs the steps of the first aspect and any possible implementation thereof.

[0011] The technical solution provided in this application has the following beneficial effects: 1. High sensitivity: This application takes a reverse approach, actively utilizing the resonance effect near the power frequency to significantly amplify the change in resistive components in the zero-sequence circuit when a ground fault occurs by canceling the system's huge capacitive susceptance. This results in a large change in the characteristic parameters used as criteria, thereby greatly improving the detection sensitivity for low and medium resistance ground faults. 2. Strong engineering applicability and low cost: The method of this application can directly use the system's power frequency or near-power frequency signals for injection and detection, without the need for complex different frequency signal sources and dedicated filters. It is implemented through a dual zero-sequence voltage transformer scheme, without the need to modify the primary side main wiring, making it simple to implement and significantly reducing costs. 3. Good robustness: The method of this application is based on zero-sequence equivalent network parameters for judgment. Its sensing range covers the entire network and is not affected by the system's three-phase asymmetry, exhibiting good stability and reliability. 4. Theoretical innovation: This application overturns the traditional paradigm of using different frequency injection to avoid resonance in injection methods, providing new theoretical support and an efficient engineering implementation approach for fault sensing methods based on damping rate or equivalent conductance. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] in: Figure 1 A flowchart illustrating a single-phase grounding fault detection method for a distribution network based on the resonant gain effect, provided in an embodiment of this application; Figure 2 A schematic diagram of the architecture of a single-phase grounding fault sensing system for a distribution network based on the resonant gain effect, provided in an embodiment of this application; Figure 3 This application provides a wiring diagram for real-time fault sensing in a power distribution network. Figure 4 A schematic diagram of an equivalent circuit for distribution network fault sensing based on real-time measurement of the damping ratio of dual voltage transformers, provided for an embodiment of this application. Figure 5 A schematic diagram of another single-phase grounding fault sensing system for distribution networks based on the resonant gain effect provided in an embodiment of this application; Figure 6 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0014] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0015] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0016] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0017] The embodiments of this application are described below with reference to the accompanying drawings.

[0018] Figure 1 This is a flowchart illustrating a single-phase grounding fault detection method for a distribution network based on the resonant gain effect, provided in an embodiment of this application.

[0019] The core idea of ​​this method is to actively construct and utilize the near-resonance characteristics of the system's zero-sequence loop to significantly amplify the electrical characteristics of a single-phase ground fault, thereby achieving highly sensitive fault detection.

[0020] like Figure 1 As shown, the method includes: 101. Under the preset operating condition that the resonant frequency of the zero-sequence circuit of the distribution network is near the power frequency of the system, inject a current signal of a preset frequency into the zero-sequence circuit of the aforementioned distribution network.

[0021] The aforementioned preset operating conditions can be achieved by configuring the arc suppression coil connected to the neutral point of the distribution network to a tuned overcompensated state.

[0022] Specifically, the arc suppression coil connected to the neutral point of the 35kV distribution network can be adjusted to put it in a tuned overcompensated state.

[0023] In one optional implementation, the preset frequency is selected within a preset range that includes the system power frequency.

[0024] The preset frequency can be set as needed. For example, the preset frequency can be selected within ±5Hz of the system power frequency.

[0025] For a resonant grounding system to operate normally, the tuning accuracy of its grounding device must meet the system's detuning requirements. v |<20%, corresponding to a system resonant frequency of approximately 44Hz-54Hz. Therefore, the injected current signal frequency in this application can effectively utilize the resonance effect to increase the system's ground resistive component within ±5Hz of the power frequency.

[0026] Specifically, based on the established near-resonance operating condition, an excitation signal of a specific frequency can be injected into the zero-sequence circuit of the distribution network through an injection unit.

[0027] When the system is in an overcompensated state, the parallel resonant frequency of its zero-sequence circuit will be slightly higher than the system's power frequency. For example, by precisely adjusting the inductance value of the arc suppression coil, the zero-sequence circuit resonant frequency of this 35kV distribution network can be made 52Hz. In this way, the system's power frequency of 50Hz falls near the resonant frequency of 52Hz, creating the necessary preset operating conditions for subsequent utilization of the resonant gain effect.

[0028] 102. Measure the zero-sequence voltage steady-state signal generated by the current signal excitation at the preset frequency.

[0029] Figure 2 This is a schematic diagram of the architecture of a single-phase grounding fault sensing system for a distribution network based on the resonant gain effect, provided in an embodiment of this application.

[0030] In the embodiments of this application, signal injection can be achieved by means of... Figure 2 The system architecture shown is implemented as follows. Specifically, a power frequency current source 40, which serves as an injection unit, has its output connected to the open delta winding on the secondary side of the first zero-sequence voltage transformer 31. Through electromagnetic induction, a current proportional to the secondary side current is coupled to the primary side, thereby effectively injecting a constant sinusoidal current signal of 50Hz with an equivalent primary side amplitude of 10A into the zero-sequence circuit connected to the 35kV bus 10.

[0031] The injected current signal will excite a zero-sequence voltage of the same frequency in the zero-sequence loop. Accordingly, a measuring unit monitors the steady-state signal of this zero-sequence voltage in real time. (Refer to...) Figure 2In this embodiment, the measurement unit is specifically a voltage measurement unit 50, whose input terminal is connected to the open delta winding of the secondary side of the second zero-sequence voltage transformer 32. Since the primary side of the second zero-sequence voltage transformer 32 is also connected to the 35kV bus 10, its open delta winding can accurately reflect the changes in the system's zero-sequence voltage. It is understood that using an independent second zero-sequence voltage transformer 32 for measurement avoids the influence of the internal impedance of the power frequency current source 40 on the voltage measurement, achieving electrical isolation between the injection circuit and the measurement circuit, thereby ensuring measurement accuracy. After acquiring the voltage signal, the voltage measurement unit 50 transmits it to the central processing unit 60.

[0032] Specifically, this application injects a small constant current signal of a specific frequency into the system through a zero-sequence voltage transformer P on the injection side, which can be equivalent to an ideal constant amplitude and constant frequency small current source. This effectively weakens the shunting effect of the transformer's excitation impedance, thereby ensuring the accuracy of the primary side injection current. On the return side, an unloaded zero-sequence transformer Q is used for voltage monitoring. Since its excitation impedance is much greater than the leakage resistance and leakage reactance of the secondary side, almost no voltage drop is generated on the secondary side, which fundamentally eliminates the interference of leakage resistance and leakage reactance on the characteristic voltage measurement and ensures the original accuracy of the return signal.

[0033] In engineering applications, its measurement process does not require changes to the primary side wiring of the distribution network system and does not affect the normal operation of the system. At the same time, due to its characteristics based on zero-sequence equivalent parameters, it ensures a wide fault detection range and is not affected by the three-phase asymmetry of the system, thus completely solving the problems of difficulty in detecting insulation faults and low sensitivity of traditional methods.

[0034] Under tuned overcompensation conditions, the system resonant point is close to the power frequency. If the injected current frequency is selected within the power frequency range, the system's capacitance to ground and inductor branch will resonate strongly, thereby significantly amplifying the difference in damping rate before and after the fault.

[0035] In this application, two zero-sequence current transformers are used. One of them can reuse the zero-sequence voltage transformer available in the system, while the other requires a dedicated zero-sequence voltage transformer. Therefore, it can be called a "dual transformer".

[0036] 103. Based on the injected current signal and the measured voltage signal, determine the characteristic parameters used to characterize the change of resistive component in the above zero-sequence loop.

[0037] Specifically, the central processing unit 60 can receive the signal parameters of the injected current (e.g., frequency 50Hz, amplitude 10A) and the real-time measured zero-sequence voltage steady-state signal (containing amplitude and phase information), and calculate a characteristic parameter to characterize the change of resistive component in the zero-sequence loop based on this information.

[0038] Optionally, the above characteristic parameters are the zero-sequence equivalent damping rate or zero-sequence equivalent conductance of the above zero-sequence circuit.

[0039] 104. Based on the changes in the above characteristic parameters before and after the fault, determine whether a single-phase ground fault has occurred.

[0040] The change in the aforementioned characteristic parameters before and after a fault can be used to determine whether a single-phase ground fault has occurred. The two characteristic parameters will be explained in detail later.

[0041] In an optional implementation, step 104 includes: The above-mentioned change is compared with a preset fault threshold. When the above-mentioned change exceeds the above-mentioned fault threshold, it is determined that a single-phase ground fault has occurred.

[0042] The aforementioned fault thresholds can be set as needed.

[0043] Further optionally, when the above characteristic parameter is the above zero-sequence equivalent damping rate, the above change amount is the target damping ratio, and the above target damping ratio is the ratio of the zero-sequence equivalent damping rate after the fault to the zero-sequence equivalent damping rate before the fault.

[0044] The following describes the method for determining the zero-sequence equivalent damping ratio as the selected characteristic parameter.

[0045] Figure 3 This application provides a wiring diagram for real-time fault sensing in a power distribution network.

[0046] Figure 4 This is a schematic diagram of an equivalent circuit for distribution network fault sensing based on real-time measurement of the damping ratio of dual voltage transformers, provided as an embodiment of this application.

[0047] like Figure 3 As shown, the injection side includes an injection device, such as a zero-sequence voltage transformer P (used as an injection source), which injects a constant-frequency small current signal (e.g., 50Hz, 10A) into the system. The return side includes a measuring device, such as an unloaded zero-sequence voltage transformer Q (used as a voltage measure), which measures the returned zero-sequence voltage steady-state signal.

[0048] To better understand the physical meaning of this characteristic parameter, please refer to [link / reference]. Figure 4 The zero-sequence equivalent circuit diagram is shown. The entire zero-sequence network can be considered as a parallel circuit, consisting of injected current sources. (Equivalent to the current injected by a 40V power frequency current source) power supply. This network contains multiple parallel branches: arc suppression coil impedance Z p System zero-sequence conductance g 0Σ The system's zero-sequence capacitance C 0Σ And the equivalent impedance Z0 of the zero-sequence voltage transformer itself.

[0049] The zero-sequence equivalent admittance Y0 comprehensively reflects the equivalent effects of capacitance, leakage resistance, and excitation parameters of the distribution network at the injection frequency, while the equivalent damping ratio d0 is a key indicator for measuring the inherent damping characteristics of the system. When the distribution network is under normal operating conditions, its zero-sequence equivalent admittance to ground is Y0. 01 The equivalent damping rate is d 01 The formula for reasoning the relationship between the two is as follows: (1) (2) The expression for the zero-sequence equivalent damping ratio before the fault is shown in formula (2).

[0050] Assuming a single-phase ground fault occurs in phase C of the distribution network, the system structure changes, and the fault admittance is increased by the additional grounding transition resistance R on top of the normal admittance. f The introduced component directly reflects the severity of the fault. At this time, the zero-sequence equivalent admittance to ground of the distribution network is Y. 02 The equivalent damping rate is d 02 .

[0051] (3) (4) The expression for the zero-sequence equivalent damping rate after a fault is shown in formula (4).

[0052] The equivalent damping ratio before and after a distribution network fault is denoted as k. The value of k quantifies the change in damping characteristics between the fault state and the normal operating state, and is the core criterion for fault determination, hereinafter referred to as the damping ratio. The mathematical expression for k is as follows: (5) When the distribution network is operating normally, the conductances of each phase to ground are as follows: , , Let's assume α is the proportionality coefficient value of the grounding transition resistance, where Substituting the relevant parameters into (5) yields: (6) This simplified formula is the expression for the target damping ratio, clearly revealing the relationship between the damping ratio k and the grounding transition resistance value R. f The direct functional relationship between them lays the theoretical foundation for the quantitative sensing of fault resistance.

[0053] Furthermore, in practical applications, the central processing unit 60 can compare the calculated damping ratio k with a preset fault threshold (e.g., set to 10 based on system experience and simulation analysis). In this example, the calculated value k = 34.57 is much greater than the preset threshold of 10, therefore the central processing unit 60 determines that a single-phase ground fault has occurred in the system and immediately outputs a fault alarm signal to the monitoring system. Conversely, if the calculated k value is less than the threshold, the system is determined to be normal, and the process returns to step S103 to continue monitoring.

[0054] The following simulation verification example illustrates this.

[0055] To preliminarily verify the feasibility of this application in a 35kV system, a typical 10kV distribution network model (as a scaled-down model of the 35kV system) was established in the PSCAD / EMTDC simulation environment, and the tuned overcompensation condition was considered to conduct in-depth verification and analysis of the method.

[0056] In the simulation analysis of this application, a typical tuned overcompensation condition is considered, where the inductance of the arc suppression coil is configured such that its inductive reactance is less than the capacitive reactance of the system to ground. In this case, the zero-sequence circuit of the system exhibits inductive characteristics, the resonant point will fall near the power frequency (e.g., about 52Hz), the harmonic suppression resistor is 30Ω, and the injected current is 10A.

[0057] in, Figure 3 The two Z0s on P and Q, and Figure 4 Z0 in the figure refers to the aforementioned harmonic suppression resistor. This component is an inherent grounding element in the design and manufacture of current transformers (PTs).

[0058] To more clearly analyze and compare the simulation data of insulation fault perception, the relevant simulation data of the distribution network equivalent damping ratio measured and calculated in real time under different injected characteristic signal frequencies and different transition resistances are shown in Tables 1 and 2.

[0059] Table 1 is a schematic diagram of the simulation results of the return characteristic voltage of different transition resistors when different characteristic signal frequencies are injected.

[0060]

[0061] Table 1 Table 2 is a schematic table showing the calculation results of damping rate and damping ratio of different transition resistors when different characteristic signal frequencies are injected.

[0062]

[0063] Table 2 As can be seen from the results in Table 2, the transition resistance R fWith impedances of 10Ω and 100Ω respectively, the damping ratio ratio k before and after the fault reaches its highest value (36.60% and 34.57%, respectively) when a power frequency signal is injected, significantly higher than the results under other frequency injection conditions. This phenomenon is consistent with theoretical analysis, namely, under tuned overcompensation conditions, the capacitor and inductor near the power frequency resonate approximately, the imaginary susceptance is significantly canceled out, and the zero-sequence network is mainly dominated by conductance and transition resistance, thus amplifying the change in damping ratio. In high-resistance fault conditions (such as R...), f =1000Ω), the damping ratio k injected at power frequency is 21.20%, which is not much different from 55Hz (20.12%), and even lower than 26.07% at 100Hz.

[0064] To overcome the drawbacks of traditional methods, the signal injection method, as a novel technical approach, has received widespread attention in recent years. Among the many branches of the signal injection method, a representative approach is based on the fault detection principle of damping rate variation. Its basic idea is to inject a small current signal of a specific frequency into the system and measure the returned voltage in real time, thereby constructing the equivalent damping rate of the system's zero-sequence network. This method has many advantages in engineering applications, including no need to change the primary side wiring of the distribution network system, no impact on normal system operation, and the ability to detect faults over a wide range based on the characteristics of the zero-sequence equivalent parameters, unaffected by the three-phase asymmetry of the system.

[0065] Previous studies have largely employed heterogeneous frequency injection to avoid resonance and interference with the dominant 50Hz power frequency signal in the system. This involves deliberately selecting a frequency several hertz higher or lower than the power frequency for injection. However, directly applying the heterogeneous frequency injection damping ratio method commonly used in 10kV systems to 35kV systems may lead to the following issues: Characteristic attenuation due to capacitive current differences: The ground capacitance current of a 35kV system is much greater than that of a 10kV system. Under this large capacitive current background, the capacitive component in the zero-sequence network is more prominent. Previous studies have mostly employed heterogeneous frequency injection, i.e., avoiding the power frequency. Under this strategy, the imaginary susceptance of the zero-sequence network always dominates, making it difficult for the injected signal to strongly amplify the resistive component representing the fault. In the 35kV environment, where the capacitive component is more significant, this problem of limited characteristic contrast is further amplified, resulting in a severe lack of sensitivity in the criterion.

[0066] Insufficient robustness under high reliability requirements: As a crucial link connecting the regional power grid and terminal loads, the 35kV line demands extremely high reliability from its protection system. However, the damping ratio of the heterodyne injection method only changes slightly during high-resistance faults. In the high-current, high-noise environment of 35kV, where tolerance for insulation faults is even lower, minute measurement errors and noise interference are sufficient to completely mask this slight characteristic change, making it difficult to guarantee the reliability of the sensing results.

[0067] Therefore, existing heterodyne injection damping ratio methods sacrifice fault characteristic identification in order to avoid resonance, and their sensitivity has inherent limitations in complex systems like 35kV where the ground capacitance current is larger. This application, based on a deep understanding of the frequency domain response characteristics and inherent limitations of 35kV zero-sequence parametric systems, proposes an innovative approach using the power frequency resonance effect to amplify the resistive component. This application addresses the challenge of single-phase grounding fault detection in 35kV resonant grounding systems by proposing an innovative method based on the power frequency resonance effect to amplify the resistive component. This method successfully transforms the traditionally avoided "power frequency resonance" into a high-sensitivity amplifier of fault characteristics, detecting the fault by identifying the significant difference in the system damping ratio before and after the fault.

[0068] While the damping ratio is also relatively high near 45Hz and 55Hz, the difference compared to 50Hz is not significant. This is because the mutual cancellation effect of capacitance and inductance exists in the frequency range close to the resonant point, keeping the damping ratio at a high level. However, compared to 45Hz and 55Hz, the power frequency still has stronger engineering application value: Firstly, the power frequency is the intrinsic frequency of the system operation, making injection and detection simpler and eliminating the need for additional cross-frequency injection and filtering stages, thus possessing better engineering applicability; secondly, the signal and system characteristics are most well-matched at the power frequency, ensuring sensitivity while avoiding measurement errors or stability risks caused by frequency selection offsets. Therefore, even though the criterion performance at 45Hz and 55Hz is similar, the power frequency remains the optimal choice.

[0069] In summary, this patent proposes a method for detecting single-phase grounding faults in 35kV distribution networks based on the gain of the resistive component in the zero-sequence voltage steady-state signal after a fault, utilizing the power frequency resonance effect. Under overcompensated conditions where the neutral point of the distribution network is grounded via an arc suppression coil, the capacitor and inductor branches at the power frequency point resonate approximately, significantly reducing the imaginary susceptance of the zero-sequence network. The equivalent admittance is dominated by conductance and transition resistance, completely changing the traditional "different frequency injection" paradigm of the damping rate method. Instead, it utilizes the frequency domain response characteristics of the 35kV system under overcompensated conditions. Through power frequency injection, a significant gain is achieved in the resistive component of the zero-sequence voltage steady-state signal after the fault, enabling the damping rate criterion to significantly amplify the difference before and after the fault.

[0070] In one optional implementation, when the aforementioned characteristic parameter is the aforementioned zero-sequence equivalent conductance, the aforementioned change is the difference between the zero-sequence equivalent conductance after the fault and the zero-sequence equivalent conductance before the fault.

[0071] In this embodiment, the characteristic parameter selected in step 103 is "zero-sequence equivalent conductance", that is... Figure 3 g in the equivalent circuit shown 0Σ As previously mentioned, the central processing unit 60 calculates the total zero-sequence admittance using the known injection current and the measured zero-sequence voltage. The zero-sequence equivalent conductance is the real part of this complex admittance, and this parameter directly reflects the purely resistive energy dissipation of all parallel branches in the zero-sequence loop. During normal system operation, the central processing unit 60 continuously calculates and stores a reference normal equivalent conductance, which can be denoted as g. 01 .

[0072] When a single-phase ground fault occurs, a value of 1 / R f The conductance is connected in parallel to the zero-sequence loop. Since the system operates near the resonant point, the change in total admittance is mainly reflected in its real part, i.e., the conductance. Therefore, the equivalent conductance g after the fault... 02 Theoretically approximately equal to g 01 + 1 / R f This relationship has a clear physical meaning and is easy to calculate.

[0073] In step 104, this embodiment uses the "difference" between the parameters after the fault and before the fault as the change. The central processing unit 60 calculates the conductance difference Δg = g 02 -g 01 For a transition resistor R f For a fault of 100Ω, the theoretical value of this difference is approximately 1 / 100 = 0.01S.

[0074] In step 105, the calculated conductance difference Δg can be compared with a preset fault threshold customized for that parameter. For example, this threshold can be set based on the fluctuation range of the system's inherent conductance and the minimum fault conductance to be detected, such as 0.005S. When the Δg calculated by the central processing unit 60 is greater than 0.005S, a single-phase ground fault can be determined to have occurred, and step S107 is executed to output an alarm.

[0075] Therefore, by using zero-sequence equivalent conductance as a characteristic parameter and utilizing its difference for judgment, high-sensitivity detection of single-phase grounding faults can also be achieved. This indicates that the "characteristic parameter for characterizing the change of resistive component in the zero-sequence loop" defined in this application is not limited to the zero-sequence equivalent damping ratio, but can also be the zero-sequence equivalent conductance or other parameters that can reflect the same physical process. Similarly, the characterization of the "change" is not limited to a ratio, but can be a difference, a growth rate, or other mathematical expressions, thus covering a variety of specific algorithm implementations and enhancing the applicability of this application. Figure 5 This is a schematic diagram of a single-phase ground fault sensing system for a distribution network based on the resonant gain effect, provided as an embodiment of this application. Figure 5 As shown, the single-phase ground fault detection system 500 for distribution networks based on the resonant gain effect includes: The injection module 510 is used to inject a current signal of a preset frequency into the zero-sequence circuit of the distribution network under a preset operating condition where the resonant frequency point of the zero-sequence circuit of the distribution network is near the power frequency point of the system. Measurement module 520 is used to measure the zero-sequence voltage steady-state signal generated by the current signal excitation of the preset frequency; The processing module 530 is used to determine characteristic parameters for characterizing the change of resistive component in the zero-sequence loop based on the injected current signal and the measured voltage signal, and to determine whether a single-phase ground fault has occurred based on the change of the characteristic parameters before and after the fault occurs.

[0076] Understandably, this involves Figure 5 The relevant content of each module in the above method embodiments has been described in detail, and you can refer to the content of the method embodiments for details; that is... Figure 5 The provided single-phase ground fault detection system 500 for distribution networks based on resonant gain effect can perform tasks such as... Figure 1 Any steps in the illustrated embodiments will not be described in detail here.

[0077] In one embodiment, a specific system for implementing the above-described fault detection method is described in detail, namely, a single-phase grounding fault detection system for a distribution network based on the resonant gain effect. Please refer to the following for details. Figure 2 The system's overall architecture is illustrated. This system is primarily applied in distribution networks containing a 35kV busbar 10 and an arc-suppression coil 20 for neutral grounding. The fault detection system of this application mainly consists of an injection module, a measurement module, and a processing module. In terms of hardware implementation, these units can be embodied as a power frequency current source 40, a voltage measurement unit 50, and a central processing unit 60, and preferably utilize a dual zero-sequence voltage transformer scheme composed of a first zero-sequence voltage transformer 31 and a second zero-sequence voltage transformer 32.

[0078] The injection module 510, in this embodiment, is specifically a power frequency current source 40, used to generate a stable and controllable current signal. The output terminal of this current source is connected to the open delta winding on the secondary side of the first zero-sequence voltage transformer 31. The first zero-sequence voltage transformer 31 acts as a coupling component, safely and efficiently injecting the secondary-side current signal into the 35kV system zero-sequence circuit on the primary side.

[0079] The measurement module 520, specifically a voltage measurement unit 50 in this embodiment, is used to accurately acquire the zero-sequence voltage signal of the system. It is connected to the open delta winding on the secondary side of the second zero-sequence voltage transformer 32 and digitizes the acquired signal for processing by the central processing unit 60.

[0080] The processing module 530, specifically the central processing unit 60 in this embodiment, is the core of the entire system. It can be implemented by a high-performance digital signal processor or a microcontroller with a floating-point unit, and integrates multiple functional modules, including but not limited to: 1. Control module: responsible for controlling the start / stop, frequency, and amplitude of the power frequency current source 40. 2. Data acquisition interface: high-speed reading of sampled data from the voltage measurement unit 50. 3. Signal processing module: built-in digital signal processing algorithms such as Fast Fourier Transform or Gosser algorithm to accurately extract the amplitude and phase of the component with the same frequency as the injected current from the acquired voltage signal. 4. Calculation module: based on a preset algorithm (such as the damping ratio method in Embodiment 1 or the conductance difference method in Embodiment 3), using the injected current parameters and the extracted voltage parameters, to calculate characteristic parameters and their changes in real time. 5. Storage module: used to store the baseline values ​​of characteristic parameters under normal operating conditions, preset fault thresholds, and system configuration parameters. 6. Judgment and Output Module: The calculated change is compared with the threshold. If the change exceeds the threshold, a fault alarm signal is issued through the output interface (such as a relay dry contact or communication bus).

[0081] The dual zero-sequence voltage transformer scheme is a preferred structure for this system. The first zero-sequence voltage transformer 31 and the second zero-sequence voltage transformer 32 are structurally identical standard devices, with their primary sides connected in parallel between the 35kV bus 10 and ground, and their secondary sides being open delta windings. Separating the injection and measurement functions into two independent transformers brings significant technical advantages: it completely avoids the influence of the output impedance of the injection signal source on the voltage measurement accuracy, and also prevents the impedance of the measurement circuit from affecting the stability of the injection current, achieving perfect decoupling between the injection channel and the measurement channel, thereby ensuring the high accuracy and high reliability of the entire system.

[0082] In one embodiment of this application, an electronic device is also provided. See also... Figure 6 , Figure 6This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Figure 6 As shown, the electronic device 600 includes a processor 601 and a memory 602. The memory 602 stores a computer program, which, when executed by the processor 601, will perform actions such as... Figure 1 Any step in the method embodiment shown can be a control method step in the experimental process, such as controlling and adjusting the transformer ratio of the voltage regulator, monitoring the phase difference, etc. The electronic device 600 may also include input / output devices, etc. In a specific embodiment, the electronic device can be a terminal device, etc.

[0083] In one embodiment, a computer-readable storage medium is also provided, which stores a computer program that, when executed by a processor 601, causes the processor 601 to perform any of the steps in the above method embodiments.

[0084] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0085] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0086] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for detecting single phase to ground fault in a power distribution network based on resonance gain effect, characterized in that, The method comprises: in a preset working condition in which a zero sequence loop resonance frequency point of a power distribution network is located near a system power frequency point, injecting a current signal of a preset frequency into a zero sequence loop of the power distribution network; measuring a zero sequence voltage steady-state signal generated by the current signal of the preset frequency; determining a characteristic parameter for characterizing a change of a resistive component in the zero sequence loop based on the injected current signal and the measured voltage signal; judging whether a single-phase ground fault occurs according to a change amount of the characteristic parameter before and after the fault occurs.

2. The method for single phase to ground fault detection in power distribution network based on resonance gain effect as claimed in claim 1 wherein, The preset working condition is achieved by configuring an arc suppression coil connected to a neutral point in the power distribution network to be in a tuned over-compensation state.

3. The method for single phase to ground fault detection in power distribution network based on resonance gain effect as claimed in claim 1 wherein, The preset frequency is selected within a preset range containing the system power frequency point.

4. The method for single phase to ground fault detection in power distribution network based on resonance gain effect as claimed in claim 1 wherein, The characteristic parameter is a zero sequence equivalent damping ratio or a zero sequence equivalent conductance of the zero sequence loop.

5. The method for single phase to ground fault detection in power distribution network based on resonance gain effect as claimed in claim 4 wherein, When the characteristic parameter is the zero sequence equivalent damping ratio, the change amount is a target damping ratio, which is a ratio of the zero sequence equivalent damping ratio after the fault to the zero sequence equivalent damping ratio before the fault. When the characteristic parameter is the zero sequence equivalent conductance, the change amount is a difference between the zero sequence equivalent conductance after the fault and the zero sequence equivalent conductance before the fault.

6. The method for single phase to ground fault detection in power distribution network based on resonance gain effect as claimed in claim 5 wherein, The method further comprises: obtaining an expression of a zero sequence equivalent admittance in a normal operation state of the power grid, and then determining an expression of the zero sequence equivalent damping ratio before the fault; obtaining an expression of the zero sequence equivalent admittance when the power distribution network has a single-phase ground fault, and then determining an expression of the zero sequence equivalent damping ratio after the fault; determining an expression of the target damping ratio according to the expression of the zero sequence equivalent damping ratio after the fault and the expression of the zero sequence equivalent damping ratio before the fault.

7. The method for single phase to ground fault detection in power distribution network based on resonance gain effect as claimed in claim 1, wherein, The judging whether a single-phase ground fault occurs according to the change amount of the characteristic parameter before and after the fault occurs comprises: comparing the change amount with a preset fault threshold value, and judging that a single-phase ground fault occurs when the change amount exceeds the fault threshold value.

8. The method for single phase to ground fault detection in power distribution network based on resonance gain effect as claimed in claim 1, wherein, The method further comprises: The injecting the current signal of the preset frequency and the measuring the zero sequence voltage steady-state signal are implemented by a double zero sequence voltage mutual inductor, and specifically comprise: injecting the current signal by a first zero sequence voltage mutual inductor; measuring the zero sequence voltage steady-state signal by a second zero sequence voltage mutual inductor.

9. A power distribution network single phase earth fault detection system based on resonance gain effect characterized by, comprise: an injection module configured to inject a current signal of a preset frequency into a zero sequence loop of a power distribution network in a preset working condition in which a zero sequence loop resonance frequency point of the power distribution network is located near a system power frequency point; a measurement module configured to measure a zero sequence voltage steady-state signal generated by the current signal of the preset frequency; a processing module configured to determine a characteristic parameter for characterizing a change of a resistive component in the zero sequence loop based on the injected current signal and the measured voltage signal, and to judge whether a single-phase ground fault occurs according to a change amount of the characteristic parameter before and after the fault occurs.

10. An electronic device, comprising: comprise a memory and a processor, the memory storing a computer program, and the computer program, when executed by the processor, causing the processor to perform the steps of the method according to any one of claims 1-8.

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