Power distribution network active arc extinction different-phase secondary ground fault detection method

Abstract

The invention discloses a power distribution network active arc extinction different-phase secondary ground fault detection method, which is suitable for the technical field of power distribution network protection and control, and comprises the following steps: calculating zero sequence parameters of each line of a power distribution network; constructing an active arc extinction different-phase secondary grounding fault starting criterion; judging whether the single-phase earth fault and the different-phase secondary earth fault occur in the same line or not; when the fault lines of the two faults are the same, a corresponding fault handling method is selected according to whether the single-phase earth fault is recovered or not; and when the fault lines of the two faults are different, a corresponding fault handling method is adopted according to the fault phase and the grounding conductance of the secondary grounding fault. According to the method, the influence of asymmetric parameters of the power distribution network is considered, the fault phase and the fault line of the different-phase secondary grounding fault are accurately determined, a corresponding fault handling method is provided, and a guarantee is provided for safe and reliable operation of the power distribution network.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network fault detection and protection, and in particular to a method for detecting the successive ground faults of different names with active arc suppression in a distribution network. Background Art

[0002] The distribution network in China mainly adopts the small-current grounding mode, and the number of single-phase grounding faults accounts for more than 80% of the total faults. With the expansion of the scale of the distribution network, the fault point current is often difficult to self-extinguish. To suppress the deterioration of the fault and achieve fault self-healing, the arc suppression device is required to be put into operation immediately at the moment of the occurrence of a single-phase grounding fault. The arc suppression coil grounding system can only compensate the reactive component in the grounding current and is powerless against the harmonic component, active component, and unbalanced component. In response to this problem, relevant scholars 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 in the distribution network, the voltage of the non-fault phase remains high for a long time, threatening the weak insulation part and easily forming successive ground faults of different names. Some studies have shown that the successive ground faults account for about 3% of the single-phase grounding faults, and when at least one grounding point shows a high impedance, the fault current is small, and the overcurrent protection cannot be reliably started. Therefore, studying the sensitive and reliable startup and accurate detection of successive ground faults in the distribution network is of great significance to the normal and safe operation of the power grid.

[0003] The detection technology for single-phase grounding faults has been relatively mature, and when the grounding resistance is low, the positive action rate can reach more than 90%. However, the current single-phase grounding fault detection technology cannot be directly used for two-point grounding faults, and both the zero-sequence admittance method and the zero-sequence current amplitude-phase comparison method fail. Therefore, a fault detection method applicable to multi-point grounding faults is urgently needed. In addition, the existing research on two-point grounding faults does not consider the situation of successive ground 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 voltage of the fault phase is suppressed to 0, the voltage of the non-fault phase becomes the line voltage, and the probability of successive ground faults occurring in the distribution network after active arc suppression increases. After the successive ground fault occurs, the original injected current can no longer compensate the grounding current, and the fault needs to be reprocessed. Therefore, it is very necessary to study the detection and disposal methods applicable to the successive ground faults of different names with active arc suppression in the distribution network.

[0004] The Chinese patent application number is CN202210017013.4, the application publication number is CN114487701A, and the patent name is: A Method and System for Selecting Fault Lines of Two-Point In-Phase Grounding Faults in Medium-Voltage Distribution Networks. This patent uses the wavelet line selection method to select and cut the first fault line, and then determines whether a two-point grounding fault occurs in the distribution network. However, this method cannot accurately obtain the fault phase and fault degree information of the two grounding faults, and thus cannot obtain the best fault handling solution. The Chinese patent application number is CN201710219531.3, the application publication number is CN107085165A, and the patent name is: A Method for Selecting Fault Lines of Two-Point Successive Grounding Faults with the Same Name Phases in Distribution Network Lines. This patent determines the fault line by comparing the phases of the characteristic components of each line, but this method is not applicable to successive grounding faults with different name phases. In addition, the secondary grounding faults caused by active arc suppression are ignored in the above studies. Summary of the Invention

[0005] Technical Problem: With the continuous expansion of the scale of the distribution network and the continuous growth of users' electricity consumption demands, the distribution network is required to have the ability to sensitively perceive and reliably detect faults. However, after active arc suppression in the distribution network, the possibility of secondary grounding faults occurring in non-fault phases increases. Existing fault detection methods cannot be directly applied to successive grounding faults with different name phases caused by active arc suppression, resulting in potential operation hazards in the distribution network.

[0006] Technical Solution: To solve the above technical problem, the present invention proposes a method for detecting successive grounding faults with different name phases caused by active arc suppression in a distribution network, which specifically includes the following steps:

[0007] Step a: Record the zero-sequence voltage of the distribution network, the zero-sequence current of each line, and the zero-sequence current of each line after active arc suppression of single-phase grounding faults in the distribution network when the distribution network is operating normally, and calculate the zero-sequence admittance of each line The specific expression is:

[0008]

[0009] where is the power supply voltage of the fault phase of the single-phase grounding fault, n represents the nth line, n = 1,..., N, and N is the total number of lines in the distribution network;

[0010] Step b: Monitor the voltage between the fault phase and the ground of the single-phase grounding fault When the amplitude of the voltage between the fault phase and the ground exceeds the starting threshold M for successive grounding faults with different name phases, it indicates that a successive grounding fault with different name phases has occurred in the distribution network, and proceed to step c. Otherwise, continue to monitor the distribution network. The starting threshold M for secondary grounding faults is specifically:

[0011]

[0012] Among them, K is the sensitivity coefficient, taking 0.15, E is the effective value of the power supply voltage of the distribution network, d and ν are the total damping ratio and the degree of detuning when the distribution network has no fault, and I C is the total capacitive current of the distribution network;

[0013] Step c: Determine whether the single-phase grounding fault and the subsequent grounding fault of different names occur on the same line. When the two grounding faults occur on the same line, execute Step d; otherwise, execute Step e;

[0014] Step d: Select the corresponding fault handling method according to whether the single-phase grounding fault is restored;

[0015] Step e: Determine the fault phase, fault conductance, and fault line of the subsequent grounding fault of different names, and take corresponding fault handling methods according to the fault information.

[0016] How to determine whether the single-phase grounding fault and the subsequent grounding fault of different names occur on the same line in Step c can be specifically determined by the following steps:

[0017] Step c1: Record the zero-sequence current of each line after the subsequent grounding fault of different names occurs and calculate the calculated conductance of the single-phase grounding fault line m and the change in zero-sequence conductance Specifically:

[0018]

[0019] Among them, is the zero-sequence current of the single-phase grounding fault line m after the active arc suppression of the single-phase grounding fault in the distribution network, is the zero-sequence current of the single-phase grounding fault line m after the subsequent grounding fault of different names occurs in the distribution network, is the zero-sequence admittance of the single-phase grounding fault line m in Step a;

[0020] Step c2: When the change in zero-sequence conductance of the single-phase grounding fault line m is a positive real number, it is determined that the fault line of the subsequent grounding fault of different names in the distribution network is not the same as the fault line of the single-phase grounding fault. At the same time, this positive real number is the fault conductance G E1 of the single-phase grounding fault. Otherwise, it is determined that the fault line of the subsequent grounding fault of different names in the distribution network is the same as the fault line of the single-phase grounding fault.

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

[0022] Step d1: Calculate The amplitude F and phase angle β. When F and β satisfy the leading-phase critical equation, step d2 is executed. When F and β satisfy the lagging-phase critical equation, step d3 is executed. When neither F nor β satisfies the leading-phase critical equation and the lagging-phase critical equation, step d4 is executed. The leading-phase critical equation and the lagging-phase critical equation are specifically as follows:

[0023]

[0024] Step d2: Re-inject the arc suppression current And monitor the leading-phase-to-ground voltage of the faulty phase of the single-phase grounding fault. When it is less than the secondary grounding fault startup threshold M, it indicates that the single-phase grounding fault of the distribution network has been restored and the fault handling is ended. When it is greater than the secondary grounding fault startup threshold M, it indicates that a same-line different-name-phase grounding fault has occurred in the system, and step d4 is executed. The re-injected arc suppression current Specifically:

[0025]

[0026] Among them, is the total zero-sequence admittance when the distribution network operates normally, is the natural unbalanced current of the distribution network;

[0027] Step d3: Re-inject the arc suppression current And monitor the lagging-phase-to-ground voltage of the faulty phase of the single-phase grounding fault. When it is less than the secondary grounding fault startup threshold M, it indicates that the single-phase grounding fault of the distribution network has been restored and the fault handling is ended. When it is greater than the secondary grounding fault startup threshold M, it indicates that a same-line different-name-phase grounding fault has occurred in the system, and step d4 is executed. The re-injected arc suppression current Specifically:

[0028]

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

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

[0031] Step e1: Calculate The amplitude F and phase angle β of. Substitute the amplitude F into the leading-phase trajectory equation to obtain the calculated phase angle θ, and calculate The deviation between the actual phase angle β of and the calculated phase angle θ. When the absolute value of the deviation is less than 30°, it is judged that the faulty phase of the different-name-phase secondary grounding fault is the leading phase of the faulty phase of the single-phase grounding fault. When the absolute value of the deviation is greater than 30°, it is judged that the faulty phase of the different-name-phase secondary grounding fault is the lagging phase of the faulty phase of the single-phase grounding fault. The leading-phase trajectory equation is specifically as follows:

[0032]

[0033] Among them, d E is the single-phase grounding fault damping rate, and α is the fault phase angle, satisfying:

[0034]

[0035] Step e2: Calculate the conductance G of the subsequent ground fault of opposite names E2 , and the specific formula:

[0036]

[0037] Among them, is the voltage between the fault phase and the ground of the subsequent ground fault of opposite names;

[0038] Step e3: Use Equation 3 to obtain the calculated conductance and the change in zero-sequence conductance of the remaining lines in the distribution network except for the fault line of the single-phase grounding fault. Determine the line with the largest amplitude of the change in zero-sequence conductance as the subsequent ground fault line of opposite names;

[0039] Step e4: When the fault conductance G E1 of the single-phase grounding fault obtained in Claim 2 is equal to 0, then re-inject the arc suppression current The fault handling ends. Otherwise, continue with Step e5, and the re-injected arc suppression current is specifically:

[0040]

[0041] Among them, is the power supply voltage of the fault phase of the subsequent ground fault of opposite names;

[0042] Step e5: When G E1 < G E2 , cut off the fault line of the subsequent ground fault of opposite names and re-inject the arc suppression current The fault handling ends. Otherwise, continue with Step e6, and the re-injected arc suppression current is specifically:

[0043]

[0044] Among them, is the zero-sequence admittance of the fault line of the subsequent ground fault of opposite names;

[0045] Step e6: When G E1 > G E2 , cut off the fault line of the single-phase grounding fault and re-inject the arc suppression current After the fault handling is completed, the arc suppression current re-injected Specifically:

[0046]

[0047] Beneficial effects: The present invention proposes a method for detecting successive ground faults of different names with active arc suppression in a distribution network. By using the change in zero-sequence current before and after the fault and the relative ground voltage of the fault phase in a single-phase ground fault, the fault phase selection, ground resistance calculation, and fault line selection for successive ground faults of different names are realized, and the fault handling method is determined according to the fault information. This method has a strong ability to tolerate ground resistance and is not affected by the asymmetry of distribution network parameters, effectively avoiding the harm caused by the long-term existence of secondary ground faults. Description of the drawings

[0048] Figure 1 is the flow chart for detecting successive ground faults of different names with active arc suppression in a distribution network;

[0049] Figure 2 is the schematic diagram of the simulation system in the embodiment;

[0050] Figure 3 is the equivalent circuit diagram of the distribution network ground fault;

[0051] Figure 4 is the trajectory diagram of the relative ground voltage of the fault phase in a single-phase ground fault. Detailed implementation manners

[0052] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0053] The present invention proposes a method for detecting successive ground faults of different names with active arc suppression in a distribution network, as Figure 1 shown, and specifically includes the following steps:

[0054] Step a: Record the zero-sequence voltage of the distribution network and the zero-sequence current of each line when the distribution network is operating normally, as well as the zero-sequence current of each line after active arc suppression in a single-phase ground fault of the distribution network and calculate the zero-sequence admittance of each line The specific expression is:

[0055]

[0056] Wherein, $U_{ph}$ is the power supply voltage of the faulty phase for single-phase grounding fault, $n$ represents the $n$-th line, $n = 1,\cdots,N$, and $N$ is the total number of lines in the distribution network;

[0057] Step b: Monitor the voltage to ground of the faulty phase of the single-phase grounding fault When the amplitude of the voltage to ground of the faulty phase exceeds the starting threshold $M$ for the subsequent secondary grounding fault of the opposite name, it indicates that a subsequent secondary grounding fault of the opposite name has occurred in the distribution network, and proceed to step c. Otherwise, continue to monitor the distribution network. The starting threshold $M$ for the secondary grounding fault is specifically:

[0058]

[0059] where $K$ is the sensitivity coefficient, taking 0.15, $E$ is the effective value of the power supply voltage of the distribution network, $d$ and $\nu$ are the total damping ratio and the degree of detuning when the distribution network has no fault, respectively, and $I$ C is the total capacitive current of the distribution network;

[0060] Step c: Determine whether the single-phase grounding fault and the subsequent secondary grounding fault of the opposite name occur on the same line. When the two grounding faults occur on the same line, execute step d; otherwise, execute step e.

[0061] Step d: Select the corresponding fault handling method according to whether the single-phase grounding fault is restored.

[0062] Step e: Determine the fault phase, fault conductance, and fault line of the subsequent secondary grounding fault of the opposite name, and take the corresponding fault handling method according to the fault information.

[0063] How to determine whether the single-phase grounding fault and the subsequent secondary grounding fault of the opposite name occur on the same line in step c can be specifically determined by the following steps:

[0064] Step c1: Record the zero-sequence current of each line after the subsequent secondary grounding fault of the opposite name occurs and calculate the conductance and the change in zero-sequence conductance Specifically:

[0065]

[0066] where is the zero-sequence current of the single-phase grounding fault line $m$ after the active arc suppression of the single-phase grounding fault in the distribution network, is the zero-sequence current of the single-phase grounding fault line $m$ after the subsequent secondary grounding fault of the opposite name occurs in the distribution network, is the zero-sequence admittance of the single-phase grounding fault line $m$ in step a;

[0067] Step c2: When the change in zero-sequence conductance When it is a positive real number, it is determined that the faulty line of the successive ground faults of different names in the distribution network is not the same line as the faulty line of the single-phase ground fault, and this positive real number is the fault conductance G of the single-phase ground fault E1 , otherwise it is determined that the faulty line of the successive ground faults of different names in the distribution network is the same line as the faulty line of the single-phase ground fault.

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

[0069] Step d1: Calculate The amplitude F and phase angle β of. When F and β satisfy the leading-phase critical equation, step d2 is executed. When F and β satisfy the lagging-phase critical equation, step d3 is executed. When both F and β do not satisfy the leading-phase critical equation and the lagging-phase critical equation, step d4 is executed. The leading-phase critical equation and the lagging-phase critical equation are specifically:

[0070]

[0071] Step d2: Re-inject the arc suppression current and monitor the leading-phase-to-ground voltage of the faulty phase of the single-phase ground fault. When it is less than the secondary ground fault startup threshold M, it indicates that the single-phase ground fault in the distribution network has been restored and the fault handling ends. When it is greater than the secondary ground fault startup threshold M, it indicates that a ground fault of different names on the same line occurs in the system, and step d4 is executed. The re-injected arc suppression current I S1 is specifically:

[0072]

[0073] where is the total zero-sequence admittance when the distribution network operates normally, is the natural unbalanced current of the distribution network;

[0074] Step d3: Re-inject the arc suppression current and monitor the lagging-phase-to-ground voltage of the faulty phase of the single-phase ground fault. When it is less than the secondary ground fault startup threshold M, it indicates that the single-phase ground fault in the distribution network has been restored and the fault handling ends. When it is greater than the secondary ground fault startup threshold M, it indicates that a ground fault of different names on the same line occurs in the system, and step d4 is executed. The re-injected arc suppression current I S2 is specifically:

[0075]

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

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

[0078] Step e1: Calculate The amplitude F and phase angle β of Substitute the amplitude F into the leading phase locus equation to obtain the calculated phase angle θ, and calculate the deviation between the actual phase angle β of

[0079]

[0080] where d E is the damping rate of single-phase grounding fault, and α is the fault phase angle, satisfying:

[0081]

[0082] When the absolute value of the deviation is less than 30°, it is determined that the fault phase of the subsequent secondary grounding fault with opposite names is the leading phase of the fault phase of the single-phase grounding fault; when the absolute value of the deviation is greater than 30°, it is determined that the fault phase of the subsequent secondary grounding fault with opposite names is the lagging phase of the fault phase of the single-phase grounding fault. The leading phase locus equation is specifically: E2 , and the specific formula:

[0083]

[0084] where is the voltage of the fault phase to the ground of the subsequent secondary grounding fault with opposite names;

[0085] Step e3: Use Equation 3 to obtain the calculated conductance of the remaining lines in the distribution network except the fault line of the single-phase grounding fault and the change amount of the zero-sequence conductance. Determine the line with the largest amplitude of the zero-sequence conductance change amount as the fault line of the subsequent secondary grounding fault with opposite names;

[0086] Step e4: When the fault conductance G E1 obtained in Claim 2 for the single-phase grounding fault is equal to 0, then re-inject the arc suppression current The fault handling is completed; otherwise, continue with Step e5. The re-injected arc suppression current is specifically:

[0087]

[0088] where is the power supply voltage of the fault phase of the subsequent secondary grounding fault with opposite names;

[0089] Step e5: When G E1 < G E2 , disconnect the fault line of the subsequent secondary grounding fault with opposite names and re-inject the arc suppression current The fault handling is completed; otherwise, continue with step e6 to re-inject the arc suppression current Specifically:

[0090]

[0091] Among them, is the zero-sequence admittance of the fault line for the secondary series ground fault of different-phase names;

[0092] Step e6: When G E1 > G E2 , cut off the fault line of the single-phase ground fault and re-inject the arc suppression current The fault handling is completed, and the re-injected arc suppression current Specifically:

[0093]

[0094] Embodiment

[0095] Use MATLAB / Simulink simulation to verify the proposed detection method for the secondary series ground fault of different-phase names in the active arc suppression of the distribution network. The simulation model is a 10 kV medium-voltage distribution network with 3 lines, and the topological structure is as Figure 2 shown. The zero-sequence parameters of each line are shown in Table 1. The total capacitive current and total active current of the distribution network are 72.77 A and 1.316 A respectively. The asymmetry of the distribution network is 1.750%, the total damping ratio during the normal operation of the distribution network is 1.809%, the neutral point is not connected to the arc suppression coil, and the detuning degree of the distribution network is 100%.

[0096] Table 1 Zero-sequence parameters of each line in the distribution network

[0097] Simulation analysis

[0098] Assume that a single-phase ground fault has occurred on line 1 of the distribution network, with the fault phase being phase A and the grounding resistance being 500 Ω, and an arc suppression current of 72.429∠-92.002° A has been injected for the single-phase ground fault of phase A. At 0.13 s, a secondary series ground fault with a grounding resistance of 1000 Ω and a fault phase of phase B is set on line 2. According to the method of the present invention, record the zero-sequence voltage and zero-sequence current of each line when the distribution network is operating normally, which are 101.047∠-107.177° V, 0.305∠-70.763° A, 0.196∠-158.382° A, 0.370∠77.239° A respectively. Record the zero-sequence current of each line after the active arc suppression of the single-phase ground fault in the distribution network, which are 22.629∠-92.329° A, 32.957∠-92.946° A, 16.842∠-92.386° A respectively. Substitute the above data into Equation 1 to obtain the zero-sequence admittance of each line and are 0.112 + j3.888 mS, 0.167 + j5.721 mS, and 0.086 + j2.994 mS respectively. Substituting the distribution network parameters into Equation 2, the starting threshold M for the secondary ground fault is obtained as 11.899. The relative ground voltage of the faulty phase of the single-phase ground fault is monitored in real time. After 0.13 s, the relative ground voltage of the faulty phase of the single-phase ground fault gradually increases and reaches a stable value of 769.426∠-49.271°V. The amplitude of the relative ground voltage of the faulty phase of the single-phase ground fault exceeds the starting threshold M of the secondary ground fault of the opposite name, and it is judged that the secondary ground fault of the opposite name occurs. The zero-sequence currents of each line after the occurrence of the secondary ground fault of the opposite name are recorded, which are 21.820∠-83.844°A, 36.009∠-100.634°A, and 15.298∠-86.292°A respectively. The calculated conductance and the change in zero-sequence conductance of the single-phase ground fault line (Line 1) are obtained, which are 1.862 + j3.987 mS and 1.750 + j0.099 mS respectively. Since the imaginary part of the change in zero-sequence conductance of the single-phase ground fault line is much smaller than the real part, it is regarded as a positive real number. Therefore, the faulty line of the secondary ground fault of the opposite name in the distribution network is not the same line as the faulty line of the single-phase ground fault, and the fault resistance of the single-phase ground fault is 537.104 Ω.

[0099] The amplitude and phase angle are 0.133 and -49.271° respectively. Substituting the amplitude into Equation 7, the calculated phase angle θ is obtained as -106.232°. Therefore, the absolute value of the deviation between the actual phase angle of

[0100] The results show that the method proposed by the present invention is not affected by the asymmetry of the distribution network parameters, and can very accurately obtain the fault information such as the faulty phase, fault resistance, and faulty line of the secondary ground fault of the opposite name, and at the same time provide guidance for subsequent fault handling.

[0101] Working principle of the present invention.

[0102] Figure 3 is the equivalent circuit diagram of the grounding fault in the distribution network. Among them, e a , e b , e c are the electromotive forces of the three-phase power supply respectively, and C A , C B , C C are the sum of the distributed capacitances of each phase of all lines A, B, and C to the ground respectively. G A , G B , G C are the sum of the distributed conductances of each phase of all lines A, B, and C to the ground respectively. is the neutral grounding admittance. is the zero-sequence fundamental injection current, and G E1 is the single-phase grounding fault conductance. G E2 is the conductance of the subsequent ground fault of the opposite name after active arc suppression. When the switch K is closed, it indicates that a subsequent ground fault of the opposite name with active arc suppression occurs in the distribution network.

[0103] Taking the A-phase single-phase grounding fault and the subsequent B-phase ground fault of the opposite name in the distribution network as an example, after the single-phase grounding fault occurs, the compensation current is injected into the A phase to achieve voltage arc suppression. satisfies:

[0104]

[0105] At this time, the neutral point voltage is The voltage of the non-fault phase to the ground is the line voltage, and the voltage of the A phase to the ground is 0. After arc suppression, a B-phase grounding fault occurs in the distribution network, then the neutral point voltage is:

[0106]

[0107] Among them, is the total admittance of the three phases of the distribution network to the ground. Substituting Equation 13 into Equation 14, the voltage of the A phase to the ground is:

[0108]

[0109] Taking the real part and the imaginary part of the voltage of the A phase to the ground as the abscissa and the ordinate respectively, the trajectory diagram of the voltage of the A phase to the ground changing with the grounding conductance G E2 is drawn, as shown in Figure 4 . Figure 4 In it, the trajectory of the single-phase grounding fault phase voltage is a circular arc, such as arcs L1 and L2. The circular arc satisfies the following equation:

[0110]

[0111] where d E =(G Σ +G E1 ) / ωC Σ is the damping rate of single-phase grounding fault. As G E1 increases, the center of the circle moves upward and the arc of the trajectory becomes smaller. When G E2 →0, no second grounding fault occurs at this time, and the fault phase voltage is at the origin; when G E2 →∞, the second fault is directly grounded and the fault phase voltage is the line voltage.

[0112] The possible states of each line i in the distribution network are: the line has no single-phase grounding fault and subsequent grounding faults of different names, the line has a single-phase grounding fault but no subsequent grounding faults of different names, the line has no single-phase grounding fault but has subsequent grounding faults of different names, and the line has a single-phase grounding fault and subsequent grounding faults of different names. The change in zero-sequence current of line i under these four states needs to be analyzed separately and the ratio between the zero-sequence current change of line i and the ground voltage of the single-phase grounding fault.

[0113] The zero-sequence current of line i after active arc suppression of single-phase grounding fault in the distribution network is: is the natural unbalanced current of line i. The zero-sequence current of line i that has not had a single-phase grounding fault and subsequent grounding faults of different names after the subsequent grounding faults of different names occur is: Therefore, the ratio of the zero-sequence current change to the ground voltage of the single-phase grounding fault is:

[0114]

[0115] Similarly, the ratios of the zero-sequence current changes of line i under the other three states to the ground voltage of the single-phase grounding fault are respectively: and

Claims

1. A method for detecting the successive ground faults of different names in an active arc suppression of a distribution network, characterized in that, It includes the following steps: Step a: Record the zero-sequence voltage of the distribution network and the zero-sequence current of each line when the distribution network is operating normally and the zero-sequence current of each line after the active arc suppression of single-phase grounding faults in the distribution network and calculate the zero-sequence admittance of each line The specific expression is: Specific expression is: Among them, is the power supply voltage of the faulty phase in a single-phase grounding fault, n represents the nth line, n = 1,..., N, and N is the total number of lines in the distribution network; Step b: Monitor the voltage of the faulty phase to ground for single-phase grounding faults When the amplitude of the voltage of the faulty phase to ground exceeds the starting threshold M for subsequent ground faults of the opposite name, it indicates that a subsequent ground fault of the opposite name has occurred in the distribution network, and proceed to step c. Otherwise, continue to monitor the distribution network. The starting threshold M for subsequent ground faults is specifically as follows: Among them, K is the sensitivity coefficient, taking 0.15, E is the effective value of the power supply voltage of the distribution network, d and ν are the total damping ratio and the detuning degree when the distribution network has no fault, and I C is the total capacitive current of the distribution network; Step c: Determine whether the single-phase ground fault and the subsequent ground fault of different names occur on the same line. When the two ground faults occur on the same line, execute Step d; otherwise, execute Step e; Step d: Select the corresponding fault handling method according to whether the single-phase ground fault is restored; Step e: Determine the fault phase, fault conductance, and fault line of the subsequent ground fault of different names, and take the corresponding fault handling method according to the fault information.

2. The method for detecting the successive ground faults of different names with active arc suppression in a distribution network according to claim 1, wherein In Step c, how to determine whether the single-phase ground fault and the subsequent ground fault of different names occur on the same line can be specifically determined by the following steps: Step c1: Record the zero-sequence current of each line after the occurrence of a successive ground fault with different names And calculate the conductance of the single-phase grounded fault line m And the change in zero-sequence conductance Specifically: Among them, is the zero-sequence current of the single-phase grounding fault line m after active arc suppression for the single-phase grounding fault in the distribution network, is the zero-sequence current of the single-phase grounding fault line m after the occurrence of the subsequent secondary grounding fault of different names in the distribution network, is the zero-sequence admittance of the single-phase grounding fault line m in step a; Step c2: When the change in zero-sequence conductance of the single-phase grounding fault line m is a positive real number, it is determined that the fault line of the subsequent secondary grounding fault of different names in the distribution network is not the same line as the fault line of the single-phase grounding fault. At the same time, this positive real number is the fault conductance G E1 of the single-phase grounding fault. Otherwise, it is determined that the fault line of the subsequent secondary grounding fault of different names in the distribution network is the same line as the fault line of the single-phase grounding fault.

3. A method for detecting the successive ground faults of different names in an active arc suppression of a distribution network according to claim 1, characterized in that, The fault handling method in Step d can be specifically determined by the following steps: Step d1: Calculate the amplitude F and phase angle β. When F and β satisfy the leading-phase critical equation, execute Step d2. When F and β satisfy the lagging-phase critical equation, execute Step d3. When F and β do not satisfy either the leading-phase critical equation or the lagging-phase critical equation, execute Step d4. The leading-phase critical equation and the lagging-phase critical equation are specifically as follows: Step d2: Re-inject the arc suppression current And monitor the leading-phase-to-ground voltage of the faulty phase of the single-phase ground fault. When it is less than the secondary ground fault startup threshold M, it indicates that the single-phase ground fault of the distribution network has been restored and the fault handling is over. When it is greater than the secondary ground fault startup threshold M, it indicates that a ground fault of the same line with different phase names has occurred in the system. Execute step d4, and the re-injected arc suppression current Specifically: Among them, is the total zero-sequence admittance during the normal operation of the distribution network, is the natural unbalanced current of the distribution network; Step d3: Re-inject the arc suppression current And monitor the lagging phase-to-ground voltage of the faulty phase of the single-phase grounding fault. When it is less than the secondary grounding fault starting threshold M, it indicates that the single-phase grounding fault of the distribution network has been restored and the fault handling is over. When it is greater than the secondary grounding fault starting threshold M, it indicates that a ground fault of the same line with different phase names occurs in the system, and step d4 is executed. The re-injected arc suppression current Specifically: Step d4: Cut off the fault line of the single-phase ground fault and cancel the injection of the arc suppression current.

4. A method for detecting the successive ground faults of different names with active arc suppression in a distribution network according to claim 1, characterized in that The fault handling method in Step e can be specifically determined by the following steps: Step e1: Calculate for its amplitude F and phase angle β, substitute the amplitude F into the leading phase locus equation to obtain the calculated phase angle θ, and calculate the deviation between the actual phase angle β and the calculated phase angle θ. When the absolute value of the deviation is less than 30°, it is judged that the faulty phase of the subsequent ground fault with opposite names is the leading phase of the faulty phase of the single-phase ground fault. When the absolute value of the deviation is greater than 30°, it is judged that the faulty phase of the subsequent ground fault with opposite names is the lagging phase of the faulty phase of the single-phase ground fault. The leading phase locus equation is specifically: where d E is the single-phase grounding fault damping ratio, and α is the fault phase angle, satisfying: Step e2: Calculate the conductance G of the dissimilar name successive ground fault E2 , specific formula: Among them, is the voltage to ground of the faulty phase for a successive secondary ground fault with opposite names; Step e3: Calculate the calculated conductance of the remaining lines in the distribution network except for the faulty line with single-phase ground fault by using Equation 3 and the change in zero-sequence conductance Determine the line with the largest amplitude of the change in zero-sequence conductance as the line with a subsequent ground fault of different names; Step e4: When the fault conductance G of the single-phase grounding fault obtained in claim 2 E1 equals 0, then re-inject the arc suppression current The fault handling is ended. Otherwise, continue with step e5, and the re-injected arc suppression current Specifically: Among them, is the power supply voltage of the faulty phase for the successive secondary earth fault with different names; Step e5: When G E1 <G E2 , cut off the faulty line of the dissimilar-name successive secondary grounding fault and re-inject arc suppression current The fault handling is over; otherwise, continue with step e6. The re-injected arc suppression current Specifically: Among them, is the zero-sequence admittance of the faulty line for the out-of-step successive ground fault; Step e6: When G E1 > G E2 , cut off the faulty line of the single-phase grounding fault and re-inject the arc suppression current The fault handling is completed Equation 12 is the arc suppression current for re-injection Calculation formula

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