A power distribution network active arc-extinguishing homonymic phase successive ground fault detection method

Abstract

This invention discloses a method for detecting sequential grounding faults with different names in an active arc suppression mechanism in a distribution network. Applicable to the field of distribution network protection and control technology, the method includes the following steps: calculating the zero-sequence parameters of each line in the distribution network; constructing an active arc suppression criterion for the initiation of sequential grounding faults with different names; determining whether a single-phase grounding fault and a sequential grounding fault with different names occur on the same line; when the fault lines of the two faults are the same, selecting the appropriate fault handling method based on whether the single-phase grounding fault has recovered; when the fault lines of the two faults are different, taking the appropriate fault handling method based on the fault phase and ground conductance of the sequential grounding fault. This invention considers the influence of distribution network parameter asymmetry, accurately determines the fault phase and fault line of sequential grounding faults with different names, and provides corresponding fault handling methods, thus ensuring the safe and reliable operation of the distribution network.

Description

Technical Field

[0001] This invention relates to the field of power distribution network fault detection and protection technology, specifically a method for detecting active arc suppression and sequential grounding faults in power distribution networks. Background Technology

[0002] Distribution networks primarily rely on low-current grounding, with single-phase grounding faults accounting for over 80% of all faults. As distribution networks expand, fault currents often fail to self-extinguish. To suppress fault escalation and achieve self-healing, arc suppression devices must be activated immediately upon the occurrence of a single-phase grounding fault. Arc suppression coil grounding systems can only compensate for the reactive component of the grounding current, offering no protection against harmonic, active, or unbalanced components. To address this, researchers have found that injecting current into the neutral point of the distribution network can achieve full compensation of the fault current. However, after active arc suppression, the prolonged voltage increase in non-faulty phases threatens weak insulation points, easily leading to secondary grounding faults. Studies indicate that secondary grounding faults account for approximately 3% of single-phase grounding faults, and when at least one grounding point exhibits high impedance, the fault current is relatively small, making overcurrent protection unreliable. Therefore, researching the sensitive and reliable activation and accurate detection of secondary grounding faults in distribution networks is crucial for the normal and safe operation of the power grid.

[0003] Detection techniques for single-phase grounding faults are relatively mature, achieving a positive rate of over 90% when the grounding resistance is low. However, current single-phase grounding fault detection techniques cannot be directly applied to two-point grounding faults; the zero-sequence admittance method and the zero-sequence current amplitude-phase comparison method both fail. Therefore, a fault detection method applicable to multi-point grounding faults is urgently needed. Furthermore, existing research on two-point grounding faults does not consider the scenario of secondary grounding faults occurring in the distribution network after active arc suppression. However, after active arc suppression of a single-phase grounding fault in the distribution network, although the fault phase voltage is suppressed to 0, the voltages of the non-fault phases become line voltages, increasing the probability of secondary grounding faults. After a secondary grounding fault occurs, the original injected current is insufficient to compensate for the grounding current, requiring re-treatment of the fault. Therefore, researching detection and treatment methods applicable to secondary grounding faults occurring after active arc suppression in distribution networks is essential.

[0004] Chinese patent application number CN202210017013.4, publication number CN114487701A, entitled "A Method and System for Selecting Lines for Two-Point In-Phase Grounding Faults in Medium-Voltage Distribution Networks," uses wavelet line selection to identify and disconnect the first faulty line, then determines whether a two-point grounding fault has occurred in the distribution network. However, this method cannot accurately obtain the fault phase and fault severity information of the two grounding faults, and therefore cannot obtain the optimal fault handling solution. Chinese patent application number CN201710219531.3, publication number CN107085165A, entitled "A Method for Selecting Lines for Two-Point Successive Grounding Faults of the Same Phase in Distribution Networks," compares the phase of the characteristic components of each line to determine the faulty line, but this method is not applicable to successive grounding faults of different phases. Furthermore, all the above studies neglected secondary grounding faults caused by active arc suppression. Summary of the Invention

[0005] Technical problem: As the scale of the distribution network continues to expand and the electricity demand of users continues to grow, the distribution network is required to have the ability to sensitively detect and reliably detect faults. However, after the active arc suppression of the distribution network, the possibility of secondary grounding faults occurring in non-faulty phases increases. Existing fault detection methods cannot be directly applied to secondary grounding faults caused by active arc suppression, which makes the distribution network have potential operational risks.

[0006] Technical Solution: To solve the above-mentioned technical problems, this invention proposes a method for detecting simultaneous grounding faults with active arc suppression in power distribution networks, specifically including the following steps:

[0007] Step a: Record the zero-sequence voltage of the distribution network during normal operation. and zero-sequence current of each line And the zero-sequence current of each line after active arc suppression of a single-phase ground fault in the distribution network. And calculate the zero-sequence admittance of each line. The specific expression is:

[0008] Formula 1

[0009] in, This refers to the power supply voltage of the faulty phase in a single-phase ground fault. Indicates the first One line, , This represents the total number of lines in the distribution network.

[0010] Step b: Monitor the fault-to-ground voltage of a single-phase ground fault. When the amplitude of the fault-to-ground voltage exceeds the initiation threshold M for a sequential ground fault, it indicates that a sequential ground fault has occurred in the distribution network, and step c continues; otherwise, the distribution network continues to be monitored. The initiation threshold M for a sequential ground fault is as follows:

[0011] Formula 2

[0012] in, The sensitivity coefficient is set to 0.15. This represents the effective value of the power supply voltage in the distribution network. and These represent the total damping ratio and detuning degree when the distribution network is fault-free. This represents the total capacitive current of the distribution network.

[0013] Step c: Determine whether a single-phase ground fault and an alternate-phase ground fault occur on the same line. If both ground faults occur on the same line, proceed to step d; otherwise, proceed to step e.

[0014] Step d: Select the appropriate fault handling method based on whether the single-phase ground fault has been resolved;

[0015] Step e: Determine the fault phase, fault conductance, and fault line of the sequential grounding fault, and take corresponding fault handling methods based on the fault information.

[0016] In step c, determining whether a single-phase ground fault and a sequential ground fault of the same name occur on the same line can be achieved through the following steps:

[0017] Step c1: Record the zero-sequence current of each line after a sequential ground fault occurs. And determine the single-phase ground fault line. Calculation of conductance and zero-sequence conductance change Specifically:

[0018] Formula 3

[0019] in, For single-phase ground fault lines in distribution networks after active arc suppression of single-phase ground faults The zero-sequence current, For single-phase ground fault lines following successive ground faults in the distribution network The zero-sequence current, For the single-phase ground fault line in step a Zero-sequence admittance;

[0020] Step c2: When a single-phase ground fault occurs on the line change in zero-sequence conductance When the value is a positive real number, it indicates that the faulted line of the sequential grounding fault with different names in the distribution network is not the same line as the faulted line of the single-phase grounding fault. Simultaneously, this positive real number represents the fault conductance of the single-phase grounding fault. Otherwise, it is determined that the fault line of the successive grounding fault of different names in the distribution network is the same line as the fault line of the single-phase grounding fault.

[0021] The fault handling method in step d can be determined by the following steps:

[0022] Step d1: Calculation amplitude and phase angle ,when and When the advanced phase critical equation is satisfied, step d2 is executed. and When the critical equation for the hysteresis phase is satisfied, proceed to step d3. and If neither the leading phase critical equation nor the lagging phase critical equation is satisfied, proceed to step d4. The leading phase critical equation and the lagging phase critical equation are as follows:

[0023] Formula 4

[0024] Step d2: Reinject arc-suppression current It monitors the leading phase-to-ground voltage of the faulty phase in a single-phase ground fault. When it is less than the secondary ground fault initiation threshold M, it indicates that the single-phase ground fault in the distribution network has been restored and the fault handling is completed. When it is greater than the secondary ground fault initiation threshold M, it indicates that a ground fault of the same line but different phases has occurred in the system, and step d4 is executed to re-inject the arc suppression current. Specifically:

[0025] Formula 5

[0026] in, This is the total zero-sequence admittance during normal operation of the distribution network. This refers to the naturally unbalanced current in the distribution network.

[0027] Step d3: Reinject arc-suppression current The system monitors the hysteresis phase-to-ground voltage of the faulted phase in a single-phase ground fault. When the voltage is less than the secondary ground fault initiation threshold M, it indicates that the single-phase ground fault in the distribution network has been restored and the fault handling is complete. When the voltage is greater than the secondary ground fault initiation threshold M, it indicates that a ground fault of the same line but different phases has occurred, and step d4 is executed to re-inject the arc-suppression current. Specifically:

[0028] Formula 6

[0029] Step d4: Disconnect the faulty line of the single-phase ground fault and cancel the injection of arc suppression current.

[0030] The fault handling method in step e can be determined by the following steps:

[0031] Step e1: Calculate amplitude and phase angle , will amplitude Substituting into the leading phase trajectory equation, the phase angle is calculated. and calculate Actual phase angle Calculating phase angle The deviation is determined as follows: when the absolute value of the deviation is less than 30°, the fault phase of the sequential grounding fault is determined to be the leading phase of the single-phase grounding fault; when the absolute value of the deviation is greater than 30°, the fault phase of the sequential grounding fault is determined to be the lagging phase of the single-phase grounding fault. The trajectory equation of the leading phase is as follows:

[0032] Formula 7

[0033] in, For single-phase ground fault damping rate, The fault phase angle satisfies:

[0034] Formula 8

[0035] Step e2: Calculate the conductance of successive ground faults with different names , specific formula:

[0036] Formula 9

[0037] in, The fault-to-ground voltage of a sequential grounding fault;

[0038] Step e3: Use Equation 3 to calculate the conductance of the remaining lines in the distribution network, excluding the faulty line with a single-phase ground fault. and zero-sequence conductance change The line with the largest change in zero-sequence conductance is identified as the line with an alternate-named, sequential grounding fault.

[0039] Step e4: When the fault conductance of the single-phase ground fault is obtained... When the current equals 0, the arc-suppression current is re-injected. The fault handling is complete; otherwise, continue to step e5 to re-inject the arc-suppression current. Specifically:

[0040] Formula 10

[0041] in, The fault phase power supply voltage for a sequential grounding fault;

[0042] Step e5: When At that time, disconnect the faulty line with the sequential grounding fault and re-inject arc-suppressing current. The fault handling is complete; otherwise, continue to step e6 to re-inject the arc-suppression current. Specifically:

[0043] Formula 11

[0044] in, The zero-sequence admittance of the faulted line with a successive ground fault of different names;

[0045] Step e6: When At that time, disconnect the faulty line with the single-phase ground fault and re-inject the arc-suppressing current. After the fault handling was completed, the reinjected arc-suppression current was... Specifically:

[0046] Formula 12

[0047] Beneficial effects: This invention proposes an active arc suppression method for detecting successive grounding faults with different names in a distribution network. By utilizing the change in zero-sequence current before and after the fault and the fault-phase voltage to ground of a single-phase grounding fault, it can achieve fault phase selection, grounding resistance calculation, and fault line selection for successive grounding faults with different names. Based on the fault information, it can determine the fault handling method. This method has a strong ability to withstand grounding resistance and is not affected by the asymmetry of distribution network parameters, effectively avoiding the hazards caused by the long-term existence of successive grounding faults. Attached Figure Description

[0048] Figure 1 Flowchart for detecting successive grounding faults with active arc suppression in power distribution networks;

[0049] Figure 2 This is a schematic diagram of the simulation system for an example embodiment;

[0050] Figure 3 Equivalent circuit diagram for grounding fault in distribution network;

[0051] Figure 4 This is a diagram showing the voltage trajectory between the fault phase and ground in a single-phase ground fault. Detailed Implementation

[0052] 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.

[0053] This invention proposes a method for detecting simultaneous grounding faults with active arc suppression in power distribution networks, such as... Figure 1 As shown, the specific steps include:

[0054] Step a: Record the zero-sequence voltage of the distribution network during normal operation. and zero-sequence current of each line And the zero-sequence current of each line after active arc suppression of a single-phase ground fault in the distribution network. And calculate the zero-sequence admittance of each line. The specific expression is:

[0055] Formula 1

[0056] in, This refers to the power supply voltage of the faulty phase in a single-phase ground fault. Indicates the first One line, , This represents the total number of lines in the distribution network.

[0057] Step b: Monitor the fault-to-ground voltage of a single-phase ground fault. When the amplitude of the fault-to-ground voltage exceeds the initiation threshold M for a sequential ground fault, it indicates that a sequential ground fault has occurred in the distribution network, and step c continues; otherwise, the distribution network continues to be monitored. The initiation threshold M for a sequential ground fault is as follows:

[0058] Formula 2

[0059] in, The sensitivity coefficient is set to 0.15. This represents the effective value of the power supply voltage in the distribution network. and These represent the total damping ratio and detuning degree when the distribution network is fault-free. This represents the total capacitive current of the distribution network.

[0060] Step c: Determine whether a single-phase ground fault and an alternate-phase ground fault occur on the same line. If both ground faults occur on the same line, proceed to step d; otherwise, proceed to step e.

[0061] Step d: Select the appropriate fault handling method based on whether the single-phase ground fault has been resolved;

[0062] Step e: Determine the fault phase, fault conductance, and fault line of the sequential grounding fault, and take corresponding fault handling methods based on the fault information.

[0063] In step c, determining whether a single-phase ground fault and a sequential ground fault of the same name occur on the same line can be achieved through the following steps:

[0064] Step c1: Record the zero-sequence current of each line after a sequential ground fault occurs. And determine the single-phase ground fault line. Calculation of conductance and zero-sequence conductance change Specifically:

[0065] Formula 3

[0066] in, For single-phase ground fault lines in distribution networks after active arc suppression of single-phase ground faults The zero-sequence current, For single-phase ground fault lines following successive ground faults in the distribution network The zero-sequence current, For the single-phase ground fault line in step a Zero-sequence admittance;

[0067] Step c2: When a single-phase ground fault occurs on the line change in zero-sequence conductance When the value is a positive real number, it indicates that the faulted line of the sequential grounding fault with different names in the distribution network is not the same line as the faulted line of the single-phase grounding fault. Simultaneously, this positive real number represents the fault conductance of the single-phase grounding fault. Otherwise, it is determined that the fault line of the successive grounding fault of different names in the distribution network is the same line as the fault line of the single-phase grounding fault.

[0068] The fault handling method in step d can be determined by the following steps:

[0069] Step d1: Calculation amplitude and phase angle ,when and When the advanced phase critical equation is satisfied, step d2 is executed. and When the critical equation for the hysteresis phase is satisfied, proceed to step d3. and If neither the leading phase critical equation nor the lagging phase critical equation is satisfied, proceed to step d4. The leading phase critical equation and the lagging phase critical equation are as follows:

[0070] Formula 4

[0071] Step d2: Reinject arc-suppression current It monitors the leading phase-to-ground voltage of the faulty phase in a single-phase ground fault. When it is less than the secondary ground fault initiation threshold M, it indicates that the single-phase ground fault in the distribution network has been restored and the fault handling is completed. When it is greater than the secondary ground fault initiation threshold M, it indicates that a ground fault of the same line but different phases has occurred in the system, and step d4 is executed to re-inject the arc suppression current. Specifically:

[0072] Formula 5

[0073] in, This is the total zero-sequence admittance during normal operation of the distribution network. This refers to the naturally unbalanced current in the distribution network.

[0074] Step d3: Reinject arc-suppression current The system monitors the hysteresis phase-to-ground voltage of the faulted phase in a single-phase ground fault. When the voltage is less than the secondary ground fault initiation threshold M, it indicates that the single-phase ground fault in the distribution network has been restored and the fault handling is complete. When the voltage is greater than the secondary ground fault initiation threshold M, it indicates that a ground fault of the same line but different phases has occurred, and step d4 is executed to re-inject the arc-suppression current. Specifically:

[0075] Formula 6

[0076] Step d4: Disconnect the faulty line of the single-phase ground fault and cancel the injection of arc suppression current.

[0077] The fault handling method in step e can be determined by the following steps:

[0078] Step e1: Calculate amplitude and phase angle , will amplitude Substituting into the leading phase trajectory equation, the phase angle is calculated. and calculate Actual phase angle Calculating phase angle The deviation is determined as follows: when the absolute value of the deviation is less than 30°, the fault phase of the sequential grounding fault is determined to be the leading phase of the single-phase grounding fault; when the absolute value of the deviation is greater than 30°, the fault phase of the sequential grounding fault is determined to be the lagging phase of the single-phase grounding fault. The trajectory equation of the leading phase is as follows:

[0079] Formula 7

[0080] in, For single-phase ground fault damping rate, The fault phase angle satisfies:

[0081] Formula 8

[0082] Step e2: Calculate the conductance of successive ground faults with different names , specific formula:

[0083] Formula 9

[0084] in, The fault-to-ground voltage of a sequential grounding fault;

[0085] Step e3: Use Equation 3 to calculate the conductance of the remaining lines in the distribution network, excluding the faulty line with a single-phase ground fault. and zero-sequence conductance change The line with the largest change in zero-sequence conductance is identified as the line with an alternate-named, sequential grounding fault.

[0086] Step e4: When the fault conductance of the single-phase ground fault is obtained... When the current equals 0, the arc-suppression current is re-injected. The fault handling is complete; otherwise, continue to step e5 to re-inject the arc-suppression current. Specifically:

[0087] Formula 10

[0088] in, The fault phase power supply voltage for a sequential grounding fault;

[0089] Step e5: When At that time, disconnect the faulty line with the sequential grounding fault and re-inject arc-suppressing current. The fault handling is complete; otherwise, continue to step e6 to re-inject the arc-suppression current. Specifically:

[0090] Formula 11

[0091] in, The zero-sequence admittance of the faulted line with a successive ground fault of different names;

[0092] Step e6: When At that time, disconnect the faulty line with the single-phase ground fault and re-inject the arc-suppressing current. After the fault handling was completed, the reinjected arc-suppression current was... Specifically:

[0093] Formula 12

[0094] Example

[0095] The proposed active arc suppression method for detecting successive grounding faults in distribution networks was verified using MATLAB / Simulink simulation. The simulation model was a 10kV medium-voltage distribution network with three lines, and the topology was as follows: Figure 2 As shown in Table 1, the zero-sequence parameters of each line are as follows: the total capacitive current and total active current of the distribution network are 72.77A and 1.316A, respectively; the asymmetry of the distribution network is 1.750%; the total damping rate of the distribution network during normal operation is 1.809%; the neutral point is not connected to the arc suppression coil; and the detuning of the distribution network is 100%.

[0096] Table 1 Zero-sequence parameters of various lines in the distribution network

[0097]

[0098] Simulation analysis.

[0099] Assume that a single-phase ground fault with phase A and a grounding resistance of 500Ω has occurred in the distribution network on line 1, and the arc suppression current of phase A of the single-phase ground fault has been injected, which is 72.429∠-92.002°A. At 0.13s, a sequential ground fault with a grounding resistance of 1000Ω and phase B is set on line 2. According to the method of the present invention, the zero-sequence voltage and zero-sequence current of each line in the distribution network during normal operation are recorded as follows: 101.047∠-107.177°V, 0.305∠-70.763°A, 0.196∠-158.382°A, and 0.370∠77.239°A, respectively. The zero-sequence currents of each line after active arc suppression of a single-phase ground fault in the distribution network are recorded as follows: 22.629∠-92.329°A, 32.957∠-92.946°A, and 16.842∠-92.386°A, respectively. Substituting these data into Equation 1, the zero-sequence admittance of each line can be obtained. , and The values ​​are 0.112+j3.888ms, 0.167+j5.721ms, and 0.086+j2.994ms, respectively. Substituting the distribution network parameters into Equation 2, the threshold value M for the secondary ground fault is calculated to be 11.899. Real-time monitoring of the fault-to-ground voltage of a single-phase ground fault shows that after 0.13s, the fault-to-ground voltage of the single-phase ground fault gradually increases and reaches a stable value of 769.426∠-49.271°V. The amplitude of the fault-to-ground voltage of the single-phase ground fault exceeds the threshold value M for the secondary ground fault, indicating that a secondary ground fault has occurred. Record the zero-sequence currents of each line after the occurrence of the successive ground fault with different names, which are 21.820∠-83.844°A, 36.009∠-100.634°A, and 15.298∠-86.292°A, respectively. Calculate the calculated conductance and zero-sequence conductance change of the single-phase ground fault line (line 1), which are 1.862+j3.987mS and 1.750+j0.099mS, respectively. Since the imaginary part of the zero-sequence conductance change of the single-phase ground fault line is much smaller than the real part, it is regarded as a positive real number. Therefore, the fault line of the successive ground fault with different names in the distribution network is not the same line as the fault line of the single-phase ground fault, and the fault resistance of the single-phase ground fault is 537.104Ω.

[0100] The amplitude and phase angle are 0.133 and -49.271°, respectively. Substituting the amplitude into Equation 7, we can calculate the phase angle. The value is -106.232°, therefore Actual phase angle vs. calculated phase angle The absolute value of the deviation is 56.962°, which is greater than 30°. Therefore, the fault phase of the anisotropic sequential grounding fault is determined to be the lagging phase of the single-phase grounding fault, i.e., phase B is the fault phase of the anisotropic sequential grounding fault. The phase-to-ground voltage of phase B is recorded after the anisotropic sequential grounding fault occurs, and substituted into Equation 9 to obtain the anisotropic sequential grounding fault resistance as 1000.685Ω. Equation 3 is used to calculate the zero-sequence conductance changes of lines 2 and 3, which are -1.926-j12.698mS and -0.191-j0.004mS, respectively. Line 2 has the largest zero-sequence conductance change amplitude, therefore line 2 is the line with the anisotropic sequential grounding fault. Since the conductance of a single-phase grounding fault is greater than that of anisotropic sequential grounding fault, line 1 is disconnected, and an arc-suppressing current of 51.566∠149.562°A is re-injected according to Equation 12.

[0101] The results show that the method proposed in this invention is not affected by the asymmetry of distribution network parameters, and can obtain fault information such as the fault phase, fault resistance, and fault line of the sequential grounding fault with different names very accurately, while providing guidance for subsequent fault handling.

[0102] The working principle of this invention.

[0103] Figure 3 This is the equivalent circuit diagram for a ground fault in a distribution network. , , These are the three-phase power supply potentials. , , These are the sums of the distributed capacitances relative to ground for each of the lines A, B, and C. , , These are the sums of the relative conductances of all lines A, B, and C to ground. For neutral point grounding admittance, Inject current into the zero-sequence fundamental frequency. For single-phase ground fault conductance, The conductance of the fault is the result of an active arc suppression followed by a successive ground fault. When switch K is closed, it indicates that an active arc suppression followed by a successive ground fault has occurred in the distribution network.

[0104] Taking a single-phase ground fault in phase A and a sequential ground fault in phase B of a distribution network as an example, after the single-phase ground fault occurs, a compensation current is injected into phase A. To achieve voltage arc suppression, satisfy:

[0105] Formula 13

[0106] At this time, the neutral point voltage is The voltage between the non-faulty phases and ground is the line voltage, and the voltage between phase A and ground is 0. After arc suppression, a ground fault occurs again in phase B of the distribution network. Then the neutral point voltage... for:

[0107] Formula 14

[0108] in, , , To obtain the total three-phase admittance to ground of the distribution network, substitute Equation 13 into Equation 14 to obtain the voltage of phase A to ground. for:

[0109] Formula 15

[0110] Plot the voltage between phase A and ground as a function of ground conductance, with the real and imaginary parts of the voltage between phase A and ground as the x and y axes, respectively. The trajectory of change, such as Figure 4 As shown. Figure 4 In a single-phase ground fault, the phase voltage trajectory is an arc, like a curve. and The circular arc satisfies the following equation:

[0111] Formula 16

[0112] in, This represents the damping ratio for a single-phase ground fault. With... As the circle increases, its center moves upward, and the arc of its trajectory becomes smaller. At this time, no second ground fault occurred, and the voltage at the origin of the fault phase was [value missing]. At that time, the second fault was directly grounded, and the voltage of the fault phase was the line voltage.

[0113] Every line of the power distribution network Possible states: The line has neither a single-phase ground fault nor a sequential ground fault of the opposite name; the line has a single-phase ground fault but no sequential ground fault of the opposite name; the line has neither a single-phase ground fault but a sequential ground fault of the opposite name; the line has both a single-phase ground fault and a sequential ground fault of the opposite name. It is necessary to analyze the line under each of these four states. Zero-sequence current change The ratio between the phase voltage to ground in a single-phase ground fault and the phase voltage to ground.

[0114] After active arc suppression of single-phase ground fault in distribution network Zero-sequence current for: , For the line The natural unbalanced current. Lines where no single-phase ground fault or anisotropic successive ground fault occurs after an anisotropic successive ground fault. Zero-sequence current for: Therefore, the change in zero-sequence current The ratio between the phase voltage and the ground voltage of a single-phase ground fault is:

[0115] Formula 17

[0116] Similarly, the circuit in the other three states Zero-sequence current change The ratios between the phase-to-ground voltage and the voltage of a single-phase ground fault are as follows: , and .

Claims

1. A method for detecting sequential grounding faults in a power distribution network using active arc suppression, characterized in that, The steps include the following: Step a: Record the zero-sequence voltage of the distribution network during normal operation. and zero-sequence current of each line And the zero-sequence current of each line after active arc suppression of a single-phase ground fault in the distribution network. And calculate the zero-sequence admittance of each line. The specific expression is: Formula 1 in, This refers to the power supply voltage of the faulty phase in a single-phase ground fault. Indicates the first One line, , This represents the total number of lines in the distribution network. Step b: Monitor the fault-to-ground voltage of a single-phase ground fault. When the amplitude of the fault-to-ground voltage exceeds the initiation threshold M for a sequential ground fault, it indicates that a sequential ground fault has occurred in the distribution network, and step c continues; otherwise, the distribution network continues to be monitored. The initiation threshold M for a sequential ground fault is as follows: Formula 2 in, The sensitivity coefficient is set to 0.

15. This represents the effective value of the power supply voltage in the distribution network. and These represent the total damping ratio and detuning degree when the distribution network is fault-free. This represents the total capacitive current of the distribution network. Step c: Determine whether a single-phase ground fault and an alternate-phase ground fault occur on the same line. If both ground faults occur on the same line, proceed to step d; otherwise, proceed to step e. Step d: Select the appropriate fault handling method based on whether the single-phase ground fault has been resolved; Step e: Determine the fault phase, fault conductance, and fault line of the sequential grounding fault, and take corresponding fault handling methods based on the fault information.

2. The method for detecting active arc suppression and sequential grounding faults in a power distribution network according to claim 1, characterized in that, In step c, determining whether a single-phase ground fault and a sequential ground fault of the same name occur on the same line can be achieved through the following steps: Step c1: Record the zero-sequence current of each line after a sequential ground fault occurs. And determine the single-phase ground fault line. Calculation of conductance and zero-sequence conductance change Specifically: Formula 3 in, For single-phase ground fault lines in distribution networks after active arc suppression of single-phase ground faults The zero-sequence current, For single-phase ground fault lines following successive ground faults in the distribution network The zero-sequence current, For the single-phase ground fault line in step a Zero-sequence admittance; Step c2: When a single-phase ground fault occurs on the line change in zero-sequence conductance When the value is a positive real number, it indicates that the faulted line of the sequential grounding fault with different names in the distribution network is not the same line as the faulted line of the single-phase grounding fault. Simultaneously, this positive real number represents the fault conductance of the single-phase grounding fault. Otherwise, it is determined that the fault line of the successive grounding fault of different names in the distribution network is the same line as the fault line of the single-phase grounding fault.

3. The method for detecting simultaneous grounding faults in a power distribution network using active arc suppression according to claim 2, characterized in that, The fault handling method in step d can be determined by the following steps: Step d1: Calculation amplitude and phase angle ,when and When the advanced phase critical equation is satisfied, step d2 is executed. and When the critical equation for the hysteresis phase is satisfied, proceed to step d3. and If neither the leading phase critical equation nor the lagging phase critical equation is satisfied, proceed to step d4. The leading phase critical equation and the lagging phase critical equation are as follows: Formula 4 Step d2: Reinject arc-suppression current It monitors the leading phase-to-ground voltage of the faulty phase in a single-phase ground fault. When it is less than the secondary ground fault initiation threshold M, it indicates that the single-phase ground fault in the distribution network has been restored and the fault handling is completed. When it is greater than the secondary ground fault initiation threshold M, it indicates that a ground fault of the same line but different phases has occurred in the system, and step d4 is executed to re-inject the arc suppression current. Specifically: Formula 5 in, This is the total zero-sequence admittance during normal operation of the distribution network. This refers to the naturally unbalanced current in the distribution network. Step d3: Reinject arc-suppression current The system monitors the hysteresis phase-to-ground voltage of the faulted phase in a single-phase ground fault. When the voltage is less than the secondary ground fault initiation threshold M, it indicates that the single-phase ground fault in the distribution network has been restored and the fault handling is complete. When the voltage is greater than the secondary ground fault initiation threshold M, it indicates that a ground fault of the same line but different phases has occurred, and step d4 is executed to re-inject the arc-suppression current. Specifically: Formula 6 Step d4: Disconnect the faulty line of the single-phase ground fault and cancel the injection of arc suppression current.

4. The method for detecting simultaneous grounding faults in a power distribution network using active arc suppression according to claim 3, characterized in that, The fault handling method in step e can be determined by the following steps: Step e1: Calculate amplitude and phase angle , will amplitude Substituting into the leading phase trajectory equation, the phase angle is calculated. and calculate Actual phase angle Calculating phase angle The deviation is determined as follows: when the absolute value of the deviation is less than 30°, the fault phase of the sequential grounding fault is determined to be the leading phase of the single-phase grounding fault; when the absolute value of the deviation is greater than 30°, the fault phase of the sequential grounding fault is determined to be the lagging phase of the single-phase grounding fault. The trajectory equation of the leading phase is as follows: Formula 7 in, For single-phase ground fault damping rate, The fault phase angle satisfies: Formula 8 Step e2: Calculate the conductance of successive ground faults with different names , specific formula: Formula 9 in, The fault-to-ground voltage of a sequential grounding fault; Step e3: Use Equation 3 to calculate the conductance of the remaining lines in the distribution network, excluding the faulty line with a single-phase ground fault. and zero-sequence conductance change The line with the largest change in zero-sequence conductance is identified as the line with an alternate-named, sequential grounding fault. Step e4: When the fault conductance of the single-phase ground fault is obtained... When the current equals 0, the arc-suppression current is re-injected. The fault handling is complete; otherwise, continue to step e5 to re-inject the arc-suppression current. Specifically: Formula 10 in, The fault phase power supply voltage for a sequential grounding fault; Step e5: When At that time, disconnect the faulty line with the sequential grounding fault and re-inject arc-suppressing current. The fault handling is complete; otherwise, continue to step e6 to re-inject the arc-suppression current. Specifically: Formula 11 in, The zero-sequence admittance of the faulted line with a successive ground fault of different names; Step e6: When At that time, disconnect the faulty line with the single-phase ground fault and re-inject the arc-suppressing current. After the fault handling was completed, the reinjected arc-suppression current was... Specifically: Equation 12.

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