Active location method for single-phase grounding fault section in distribution network

Abstract

The present invention proposes a method for actively locating a single-phase grounding fault section in a distribution network. When a single-phase grounding fault occurs in the distribution network, a full compensation current is first injected through a flexible arc extinguishing device to complete arc extinguishing. Considering the dynamic time for effective suppression of the fault current, after the full compensation current is injected, the interval time t1 is used to reduce the injection current of the flexible arc extinguishing device by actively changing the corresponding reference value of the control system, and the phase difference of the zero-sequence voltage and current changes in each section is calculated in real time through a short-time Fourier algorithm. According to the characteristics of the phase difference of the zero-sequence voltage and current changes, a criterion for identifying the nature of the grounding fault is proposed and the fault section is located. The active section positioning method for the distribution network of the present invention takes into account the arc extinguishing and section positioning functions of the single-phase grounding fault, and at the same time, the nature of the grounding fault is identified, which improves the applicability and economy of the flexible arc extinguishing device, and provides a strong guarantee for the popularization and application and economic operation of the flexible arc extinguishing device of the distribution network.

Description

Technical Field

[0001] The invention belongs to the technical field of positioning a single-phase grounding fault section of a power grid, and in particular relates to a method for actively positioning a single-phase grounding fault section of a distribution network. Background Art

[0002] With the continuous advancement of modern power grid construction, the frequency of use of renewable energy, distributed power sources, and power electronic components has gradually increased, and the cable rate of distribution network lines has continued to increase, resulting in an increase in the active component and harmonic component in the single-phase grounding fault current, which in turn makes it difficult for the single-phase grounding fault arc to extinguish itself, posing a safety hazard to personnel and equipment. On the other hand, high-resistance grounding faults in distribution networks are prone to cause intermittent arc grounding faults and may cause fires. The arc overvoltage generated increases the possibility of damage to the insulation between the phases of the line, causing the fault to further develop into a phase-to-phase short-circuit fault, increasing the degree of harm and impact of the fault. Therefore, it is of great significance to study the method of arc extinguishing and fault section location for single-phase grounding faults in distribution networks.

[0003] At present, most distribution networks adopt the operation mode of non-effective grounding of neutral point, and in the resonant grounding system, the transient and steady-state fault characteristics of single-phase grounding fault are not obvious, which brings challenges to the rapid and accurate fault location. At the same time, although the distribution network with flexible arc extinguishing device can effectively and quickly suppress the fault current, the steady-state characteristics of single-phase grounding fault are weak, and the transient process is shorter than that of resonant grounding system, which makes it more difficult to accurately locate the fault based on passive signals. Therefore, the research on the method of actively constructing the location criterion of single-phase grounding fault section in distribution network has certain prospects.

[0004] At present, there are few studies on the methods of arc extinguishing and fault section locating for single-phase grounding faults in distribution networks. In particular, the research on the method of actively constructing the fault section locating criterion in the case of grounding fault arc extinguishing is not yet mature.

[0005] The main problems of the existing single-phase grounding fault section location method of the distribution network are as follows: in terms of fault current suppression, the existing fault location method does not have the function of arc extinguishing of single-phase grounding faults, and does not consider the impact of excessive grounding fault current, insulation breakdown and other issues on the accuracy of location. In terms of section location, the location method based on passive fault characteristics has low location reliability because the fault characteristics of the resonant grounding system are weak and difficult to extract, and the traditional active injection method does not consider the problem that the injection signal will increase the fault residual current and increase the safety hazard of single-phase grounding faults. Summary of the invention

[0006] In view of this, in order to make up for the gaps and deficiencies in the prior art, the present invention aims to provide a method for actively locating a single-phase grounding fault section in a distribution network. When a single-phase grounding fault occurs in the distribution network, the full compensation current is first injected through a flexible arc extinguishing device to complete the arc extinguishing. Considering the dynamic time for effective suppression of the fault current, after injecting the full compensation current, the interval time t1 is used to reduce the injection current of the flexible arc extinguishing device by actively changing the corresponding reference value of the control system, and the phase difference of the zero-sequence voltage and current changes in each section is calculated in real time through the short-time Fourier algorithm. According to the characteristics of the phase difference of the zero-sequence voltage and current changes, a grounding fault property identification criterion is proposed and the fault section is located. According to the calculation results, the fault section can be effectively determined and the nature of the grounding fault can be judged. The active section positioning method of the distribution network of the present invention takes into account the arc extinguishing and section positioning functions of the single-phase grounding fault, and at the same time judges the nature of the grounding fault, improves the applicability and economy of the flexible arc extinguishing device, and provides a strong guarantee for the popularization and application and economic operation of the flexible arc extinguishing device of the distribution network.

[0007] The present invention is applicable to control methods such as voltage arc extinguishing method, current arc extinguishing method and voltage and current fusion arc extinguishing method, and can also be applied to flexible arc extinguishing devices of single-phase access type, two-phase access type, three-phase access type and neutral point access type, with a wide range of use, strong applicability and flexibility. In addition, the present invention can realize single-phase grounding fault arc extinguishing, fault section location and grounding fault nature determination, expand the application functions and scenarios of flexible arc extinguishing devices, and provide strong guarantee for the promotion and economic operation of flexible arc extinguishing devices.

[0008] The technical solution adopted by the present invention to solve the technical problem is:

[0009] A method for actively locating a single-phase grounding fault section in a distribution network, characterized by:

[0010] When a single-phase grounding fault occurs in the distribution network, the full compensation current is first injected through the flexible arc extinguishing device to suppress the fault current and complete the arc extinguishing. Considering the dynamic time of effective suppression of the fault current, after the full compensation current is injected, after the interval time t1 delay, the corresponding reference value of the control system is actively changed through closed-loop feedback adjustment to reduce the injection current of the flexible arc extinguishing device. The phase difference of the zero-sequence voltage and current changes in each section is calculated in real time through the short-time Fourier algorithm. According to the characteristics of the phase difference of the zero-sequence voltage and current changes, the grounding fault nature identification criterion is proposed and the fault section is located.

[0011] Furthermore, the cascade H-bridge is used as a flexible arc extinguishing device; when a single-phase grounding fault occurs in the distribution network, the flexible arc extinguishing device first injects a full compensation current to achieve fault current suppression; after a certain delay, the injection current of the flexible arc extinguishing device is reduced, and the phase difference of the zero-sequence voltage and current change is actively constructed, and it is used as a criterion for locating the fault section; the single-phase grounding fault arc extinguishing and fault section locating process is as follows:

[0012] Step 1: Set the adaptive starting threshold of the zero-sequence voltage of the distribution network. If the zero-sequence voltage exceeds the set threshold, it is considered that a single-phase grounding fault occurs in the distribution network, and the flexible arc extinguishing device is started to inject full compensation current into the distribution network to achieve rapid suppression of the fault current.

[0013] Step 2: Within the time T after the full compensation current is injected, the single-phase grounding fault current is effectively suppressed; in order to leave a certain time margin, after the flexible arc extinguishing device injects the full compensation current, the control reference value of its injected current is changed at interval t1, directly reducing the injected current of the neutral point, and actively constructing the change of zero-sequence voltage and zero-sequence current;

[0014] Step 3: The phase difference of the zero-sequence voltage change and the zero-sequence current change is calculated in real time by using the short-time Fourier algorithm. The fault section is distinguished from the non-fault section based on the characteristic difference that the phase difference of the zero-sequence voltage and current changes in the fault section changes with the transition resistance, while the phase difference of the zero-sequence voltage and current changes in the non-fault section is maintained at 90°.

[0015] Step 4: If the calculation results of the phase difference of the zero-sequence voltage and current changes in each section do not show that the grounding fault disappears, the grounding fault is considered to be permanent, and the flexible arc extinguishing device is restored to inject full compensation current into the system; if the phase difference of the zero-sequence voltage and current changes in each section satisfies the situation that the fault disappears, the injected current is further reduced, and the length of the waveform sampling is extended to calculate the phase of the zero-sequence voltage and current changes in each section; if the phase of the zero-sequence current change intermittently jumps during the sampling time, it means that the grounding fault is an intermittent arc grounding fault, and the faulty section is determined according to the phase difference relationship, and the injected current of the flexible arc extinguishing device is restored to the full compensation current; otherwise, the fault is judged to be a transient fault, and the flexible arc extinguishing device exits operation.

[0016] Furthermore, considering the high randomness of single-phase grounding faults, the nature of the grounding fault is judged at fixed intervals; according to steps three and four, the time for distinguishing intermittent faults and instantaneous faults does not exceed 30s; after the first grounding fault nature judgment is completed, the injection current of the flexible arc extinguishing device is reduced at each interval t2, and the nature of the grounding fault is judged according to the execution of steps one to four.

[0017] Furthermore, the flexible arc extinguishing device is connected to the distribution network in one of a single-phase access type, a two-phase access type, a three-phase access type and a neutral point access type;

[0018] Among them, the topology of the single-phase access flexible arc extinguishing device adopts a single-phase H-bridge converter, one end of the converter is connected to the phase line of the distribution line or the low-voltage side of the step-up transformer, and the other end is connected to the ground; the single-phase H-bridge converter is one of a two-level single-phase half-bridge, a three-level single-phase half-bridge, a multi-level single-phase half-bridge, and a single-phase cascaded H-bridge;

[0019] The topology of the two-phase access flexible arc extinguishing device adopts that the common point of the two-phase H-bridge converter is grounded through the arc extinguishing coil or the common point of the two-phase H-bridge converter is grounded through the single-phase H-bridge converter; one end of the two-phase converter is connected to the phase line of the distribution line or the low-voltage side of the step-up transformer, and the other end is connected to the common point, and the two-phase H-bridge converter is directly connected to or connected to any two phases of the distribution line through the step-up transformer; the two-phase H-bridge converter is composed of two single-phase H-bridge converters;

[0020] The topology of the three-phase access flexible arc extinguishing device adopts a four-bridge-arm H-bridge converter, wherein three bridge arms are three-phase H-bridge converters, and the grounded bridge arm is a single-phase H-bridge converter. The three-phase H-bridge converter is directly connected to the three phases of the distribution line or is connected to the three phases through a step-up converter, and its common point is grounded through a single-phase H-bridge converter, i.e., the grounded bridge arm; the three-phase H-bridge converter is one of a two-level three-phase half-bridge, a three-level three-phase half-bridge, a multi-level three-phase half-bridge or a three-phase cascaded H-bridge;

[0021] The topology of the neutral point connected flexible arc extinguishing device adopts a single-phase H-bridge converter connected to the distribution network via a Z-type transformer.

[0022] Furthermore, the control method of the flexible arc extinguishing device adopts one of a voltage arc extinguishing method, a current arc extinguishing method and a voltage-current fusion arc extinguishing method;

[0023] The voltage arc extinguishing method takes the zero-sequence voltage as the system control object, controls the zero-sequence voltage to be the opposite of the fault phase power supply voltage through a flexible arc extinguishing device, and clamps the fault point voltage to zero to achieve reliable arc extinguishing;

[0024] The current arc extinguishing method uses the injection current of the flexible arc extinguishing device as the control object of the system, injects the full compensation current through the flexible arc extinguishing device, and suppresses the fault point voltage to zero to achieve reliable arc extinguishing;

[0025] The voltage-current fusion arc extinguishing method controls the voltage and current in parallel and calculates the deviation between the voltage and current feedback and the real-time detection value at the same time. Its arc extinguishing effect is more significant than that of the current arc extinguishing method and the voltage arc extinguishing method.

[0026] The present invention is a single-phase grounding fault section active positioning method based on the zero-sequence voltage and current phase difference of each section. The fault section can be accurately determined under different fault locations, different line types, different transition resistances and intermittent arc grounding faults, and has strong applicability.

[0027] Furthermore, the nature of the grounding fault is determined based on the zero-sequence voltage and current phase differences in each section before and after the current injected by the flexible arc extinguishing device changes:

[0028] If it is an intermittent fault, the flexible arc extinguishing device will be exited after the single-phase grounding fault disappears;

[0029] If it is a permanent fault, the fault section is located according to the phase difference between the zero-sequence voltage and current changes in the healthy section and the faulty section, and the flexible arc extinguishing device is restored to inject full compensation current into the system;

[0030] If it is an intermittent ground fault, the flexible arc extinguishing device will be started when the fault first occurs, injecting full compensation current into the system, and then exit the flexible arc extinguishing device after the ground fault finally disappears.

[0031] Furthermore, the short-time Fourier algorithm realizes real-time calculation of the phase of the zero-sequence voltage variation and the zero-sequence current variation by moving the time window and calculating the phase of the signal in the current time window.

[0032] Compared with the prior art, the present invention and its preferred embodiment have the following beneficial effects:

[0033] 1. The proposed method for active location of single-phase grounding fault sections in the distribution network takes into account the arc extinguishing function of the fault. When a single-phase grounding fault occurs in the distribution network, the full compensation current is first injected quickly to reliably suppress the grounding fault current, and then the injection current is reduced by the flexible arc extinguishing device to change the steady-state characteristics of the zero-sequence current of each line section for section location. The residual current of the fault in both stages is small, which effectively prevents the harm that may be caused to the system during the fault location, and provides safety protection for the troubleshooting and precise location of the fault.

[0034] 2. The proposed method for active fault section location has strong applicability. Different from the traditional passive fault location method, the cascaded H-bridge device changes the system steady state, and actively constructs the fault section location criterion based on the phase difference of the zero-sequence voltage and current changes in each line section. It is less affected by the transition resistance. In the case of nonlinear changes in transition resistance such as intermittent arc grounding faults, the fault section can be accurately determined, and it has the ability to distinguish the nature of the grounding fault. In addition, the proposed section location method is applicable to different arc extinguishing methods, including voltage arc extinguishing method, current arc extinguishing method and voltage and current fusion arc extinguishing method. In the distribution network with single-phase access, two-phase access, three-phase access and neutral point access flexible arc extinguishing devices, the fault section can be accurately distinguished.

[0035] 3. The proposed method for actively locating the single-phase grounding fault section of the distribution network has low requirements for data measurement accuracy. The injection current reduction and sampling start time are actively set to reduce the measurement error of the waveform phase. In addition, the phase difference of the zero-sequence voltage and current changes is used as the criterion for locating the fault section, and the accuracy requirements for the original signal waveform amplitude measurement are low. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0037] Figure 1 A schematic diagram of the topological structure of a power distribution network and a single-phase access flexible arc extinguishing device according to an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of the topological structure of a distribution network and a two-phase access flexible arc extinguishing device according to an embodiment of the present invention;

[0039] Figure 3 A schematic diagram of the topological structure of a distribution network and a three-phase access flexible arc extinguishing device according to an embodiment of the present invention;

[0040] Figure 4 A schematic diagram of the topological structure of a distribution network and a neutral point access type flexible arc extinguishing device according to an embodiment of the present invention;

[0041] Figure 5 This is a control block diagram of a flexible arc extinguishing device using a current arc extinguishing method according to an embodiment of the present invention;

[0042] Figure 6 This is a control block diagram of a flexible arc extinguishing device using a voltage arc extinguishing method according to an embodiment of the present invention;

[0043] Figure 7 This is a control block diagram of a flexible arc extinguishing device using a fusion arc extinguishing method according to an embodiment of the present invention;

[0044] Figure 8 Schematic diagram of three situations in which a fault disappears according to an embodiment of the present invention;

[0045] Fig. 9 A schematic diagram of a simulation model of a simulation example of an embodiment of the present invention;

[0046] Fig.10 This is a schematic diagram of residual current of a single-phase grounding fault in a simulation example of an embodiment of the present invention;

[0047] Fig.11 A schematic diagram of the phase difference of zero-sequence voltage and current variation in each section according to an embodiment of the present invention;

[0048] Fig.12 A schematic diagram of determining the nature of a single-phase grounding fault according to an embodiment of the present invention;

[0049] Fig.13The basic structure and principle diagram of an embodiment of the present invention is shown in FIG. DETAILED DESCRIPTION

[0050] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail as follows:

[0051] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0052] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0053] like Fig.13 As shown, this embodiment provides the topological structure of the neutral point access flexible arc extinguishing device of the distribution network and verifies the effectiveness of the active positioning method of the single-phase grounding fault section. When a single-phase grounding fault occurs in the distribution network, the flexible arc extinguishing device injects a full compensation current to suppress the fault current and effectively complete the arc extinguishing; after a time delay of t1, the corresponding reference value of the control system is actively changed through closed-loop feedback regulation to reduce the injected current of the flexible arc extinguishing device, and the change of the phase difference of the zero-sequence voltage and current variation in each section is calculated in real time through the short-time Fourier algorithm, and the fault nature identification criterion is proposed based on the characteristics of the phase difference of the zero-sequence voltage and current variation, and the fault section is located.

[0054] At the same time, a method for distinguishing the nature of a single-phase grounding fault based on the phase difference of the zero-sequence voltage and current changes in each section is proposed. The practicality of the method for actively locating the single-phase grounding fault section of the distribution network proposed in the present invention is verified under different line types, different fault locations, and intermittent arc grounding faults.

[0055] In this embodiment, the time T for completing fault current suppression is 1 to 3 power frequency cycles, the time interval t1 is set to 0.3s, and the time interval t2 is set to 5 minutes. Single-phase access type, two-phase access type, three-phase access type and neutral point access type flexible arc extinguishing devices can all be used for active positioning of single-phase grounding fault sections of distribution networks. The schematic diagrams of the four types of arc extinguishing devices are shown in Figure 1. Figure 1-4As shown. Although the four flexible arc extinguishing devices are connected to the system in different ways, their control objects are the same, which are all injection current, zero-sequence voltage or the fusion control target of the two. Therefore, only the neutral point access type flexible arc extinguishing device is discussed, and the effectiveness and applicability of the proposed distribution network fault section active positioning method and fault nature identification method are verified when using the voltage arc extinguishing method, the current arc extinguishing method and the voltage and current fusion arc extinguishing method. The single-phase access type, two-phase access type, three-phase access type and neutral point access type flexible arc extinguishing devices in the embodiment can all be directly connected to the bus or line with a voltage level of 6kV, 10kV, 35kV or 66kV through a transformer.

[0056] In this embodiment, the control method of the flexible arc extinguishing device includes a voltage arc extinguishing method, a current arc extinguishing method and a voltage and current fusion arc extinguishing method. The schematic diagrams of the three control methods are shown in FIG. Figure 5-Figure 7 When the injection current of the flexible arc extinguishing device is changed, the corresponding reference value of the control system is actively changed through closed-loop feedback regulation.

[0057] The technical solution of this embodiment is described in detail from the perspective of principle as follows:

[0058] 1. Introduction to the principle of active location of single-phase grounding fault

[0059] 1.1 Analysis of single-phase grounding fault in distribution network with flexible arc extinguishing device

[0060] Taking the neutral point access type flexible arc extinguishing device as an example, the schematic diagram of the single-phase grounding fault in the distribution network is as follows: Fig.13 shown. is the injection current of the arc extinguishing device, L and R are the connection impedances, K is the connection switch, is the fault phase voltage. If it is 0, then it needs to satisfy:

[0061]

[0062] The injection current of the flexible arc extinguishing device can be expressed as:

[0063]

[0064] in, is the fault phase power supply voltage, G ∑ is the total conductance of the distribution network to the ground, C ∑ is the total capacitance of the distribution network to ground.

[0065] There is a relationship between the injection current of the flexible arc extinguishing device and the ground fault current of the distribution network: The zero-sequence current upstream of the fault point can be expressed as:

[0066]

[0067] The zero-sequence current of the healthy section can be expressed as:

[0068]

[0069]

[0070] in, is the zero sequence current of the non-fault line, is the zero-sequence current downstream of the fault point, is the zero-sequence current upstream of the fault point, C x0 , G x0 is the ground capacitance and leakage conductance of the non-fault line, C Af , G Af is the capacitance to ground and leakage conductance upstream of the fault point, C fD , G fD is the capacitance to ground and leakage conductance downstream of the fault point.

[0071] In the case of a single-phase grounding fault, the zero-sequence current of each line section of the distribution network with a flexible arc extinguishing device flows from the busbar to the line. The traditional mobile phase-to-phase segment positioning method is not applicable. And unlike the resonant grounding system, in the flexible grounding distribution network, the connection impedance inductance value of the cascaded H-bridge converter and the system is small, the full compensation current can be quickly injected, and the transient process of the single-phase grounding fault is shorter.

[0072] 1.2 Active location method of single-phase grounding fault in distribution network

[0073] After reliably suppressing the fault current, change the magnitude of the neutral point injection current and analyze the change characteristics of the phase difference of the zero-sequence voltage and current changes in the healthy section and the upstream section of the fault point. After the neutral point injection current is changed, the expression of the neutral point voltage change is derived as follows:

[0074]

[0075] Changing the neutral point injection current causes the neutral point voltage to shift further, causing the zero-sequence current of each line section to change. In the zero-sequence circuit of the healthy section, G' ∑ <<ωC' ∑ , the change of zero-sequence current can be expressed as:

[0076]

[0077] The zero-sequence current changes in the non-fault line and downstream of the fault point are:

[0078]

[0079]

[0080] The change of zero-sequence current upstream of the fault point is:

[0081]

[0082] According to formulas (7)-(10), the phase difference of the zero-sequence voltage and current changes in the healthy section is maintained at 90°, while the phase difference of the zero-sequence voltage and current changes upstream of the fault point is related to the resistance value of the transition resistor. Therefore, the phase difference of the zero-sequence voltage and current changes in each line section after the injection current is reduced can be used as the positioning criterion for the single-phase grounding fault section.

[0083] 2. Principle of ground fault nature determination

[0084] In the single-phase grounding fault of the distribution network, instantaneous faults account for more than 70% of the total number of grounding faults. In order to ensure the reliability of grounding faults, the present invention includes a method for determining the nature of single-phase grounding faults in the distribution network.

[0085] When collecting zero-sequence voltage and current waveforms of each line section, the ground fault may have disappeared. Depending on the time when the fault disappears, it can be divided into the following: Figure 8 The three cases ①, ② and ③ are shown. The time when the injected current decreases is 0.3s, and the duration of the sampling and recording is 2nT.

[0086] (1) Case 1

[0087] The single-phase grounding fault has disappeared before the start of signal sampling, that is, the disappearance time of the single-phase grounding fault is t d <t0-nT. In this case, the phase difference of the zero-sequence voltage and current changes calculated upstream of the fault point is 90°, which is consistent with the healthy section.

[0088] (2) Second Case

[0089] The moment when the single-phase ground fault disappears t d ∈(t0-nT, t0), and the time from the moment when the injected current decreases is (n-λ1)T. The total time length of the change is calculated to be nT. Assuming that the starting point of the change is time zero, the change of the sampling signal at time t∈(0, λ1T) can be expressed by the following formula:

[0090] X(t)=X[t0,t0+λ1T]-X[t0-nT,t0-(n-λ1)T] (11)

[0091] After the fault disappears, the line returns to normal. The change in zero-sequence current during this period can be equivalent to the zero-sequence current in the healthy state upstream of the original fault point. Subtract the zero sequence current in the fault condition Because the injected current decreases and the fault disappears, the zero-sequence current upstream of the original fault point can be expressed as:

[0092]

[0093] in, is the reduced injected current, is the capacitive current upstream of the original fault point after the fault disappears. Therefore, at t∈(0,λ1T), the change in zero-sequence current upstream of the original fault point is:

[0094]

[0095] Considering the transition resistance, the fault current There is an active component. By analyzing the phase characteristics of the zero-sequence current, it is easy to infer that if the fault does not disappear, after the injected current decreases, the phase of the zero-sequence current change upstream of the fault point is the same as the fault current The phase change relationship of the zero-sequence current change upstream of the original fault point after the fault disappears can be qualitatively analyzed: at t∈(0, λ1T), the phase difference of the zero-sequence voltage and current change upstream of the original fault point is larger than when the fault has not disappeared; at t∈(λ1T, nT), because the fault disappears, the phase difference of the zero-sequence voltage and current change upstream of the fault point is calculated to be 90°.

[0096] (3) The third case

[0097] The moment when the single-phase ground fault disappears t d ∈(t0, t0+nT), and the time from the moment when the injected current decreases is λ2T. At time t∈(0, λ2T), the single-phase grounding fault still exists, and the phase difference of the zero-sequence voltage and current changes upstream of the fault point depends on the size of the transition resistance. At time t∈(λ2T, nT), the phase difference of the zero-sequence voltage and current changes upstream of the original fault point is consistent with the phase difference of the zero-sequence voltage and current changes at t∈(0, λ1T) in the second case when the fault disappears.

[0098] In summary, if the phase difference of the zero-sequence voltage and current changes upstream of the fault point meets the three conditions of fault disappearance, it can be preliminarily determined that the single-phase grounding fault is an instantaneous fault. Further reduce the injected current, if the phase difference of the zero-sequence voltage and current changes still meets the first condition, it means that the fault has disappeared and the flexible arc extinguishing device has stopped operating.

[0099] Use MATLAB / Simulink simulation software to build Fig. 9 The simulation model of the distribution network with 6 feeders is shown. The distribution line adopts the Bergeron model. Assume that the fault occurs in section l 12 , and the fault phase is phase A, the simulation results are as follows Fig.10, Fig.11 as well as Fig.12 shown.

[0100] Depend on Fig.10 As shown in the figure, during a single-phase grounding fault, the flexible arc extinguishing device can effectively suppress the fault current and reduce the injection current of the arc extinguishing device after a certain delay. It can be seen that during the period of suppressing the fault current and reducing the injection current, the effective value of the fault residual current is small.

[0101] Depend on Fig.11 It can be seen that when a single-phase grounding fault occurs in the distribution network, there is an obvious difference in the phase difference of the zero-sequence voltage and current changes between the healthy section and the faulty section, which can meet the needs of distinguishing the single-phase grounding fault section.

[0102] Depend on Fig.12 As shown in the figure, there is a large difference in the phase difference between the three situations in which the instantaneous single-phase grounding fault disappears and the zero-sequence voltage and current changes in the permanent fault situation, which can accurately identify the nature of the single-phase grounding fault.

[0103] This embodiment provides a method for actively locating a single-phase grounding fault section in a distribution network, and proposes a method for distinguishing the nature of a single-phase grounding fault. When a grounding fault occurs, the flexible arc extinguishing device first injects a full compensation current to suppress the fault current and complete arc extinguishing. After a 0.3s delay, the corresponding reference value of the control system is actively changed through closed-loop feedback regulation to reduce the injected current of the flexible arc extinguishing device. The short-time Fourier algorithm is used to calculate the phase difference of the zero-sequence voltage and current changes in each section in real time, and the single-phase grounding fault nature is identified and the fault section is located based on the calculation results. At the same time, the injected current amplitude is reduced every 5 minutes, and the nature of the grounding fault is distinguished according to the phase relationship of the zero-sequence voltage and current changes in each section. The method for actively locating a single-phase grounding fault section in a distribution network proposed by the present invention takes into account the arc extinguishing and section positioning of the single-phase grounding fault, and can distinguish the nature of the single-phase grounding fault at the same time, improves the practicality and equipment utilization of the flexible arc extinguishing device, and provides a strong guarantee for the popularization and application of the flexible arc extinguishing device in the distribution network and the economic operation.

[0104] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

[0105] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of active positioning methods for single-phase grounding fault sections in distribution networks under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A method for actively locating a single-phase grounding fault section in a distribution network, characterized by: When a single-phase grounding fault occurs in the distribution network, the full compensation current is first injected through the flexible arc extinguishing device to suppress the fault current and complete the arc extinguishing; Considering the dynamic time of effective fault current suppression, after the full compensation current is injected, after the interval time t1 delay, the corresponding reference value of the control system is actively changed through closed-loop feedback regulation to reduce the injection current of the flexible arc extinguishing device; and the phase difference of the zero-sequence voltage and current changes in each section is calculated in real time through the short-time Fourier algorithm. According to the characteristics of the phase difference of the zero-sequence voltage and current changes, the grounding fault nature identification criterion is proposed and the fault section is located; Use cascaded H-bridge as flexible arc extinguishing device; When a single-phase grounding fault occurs in the distribution network, the flexible arc extinguishing device first injects full compensation current to achieve fault current suppression; After a certain delay, the injection current of the flexible arc extinguishing device is reduced, and the phase difference of the zero-sequence voltage and current changes is actively constructed, and it is used as the criterion for locating the fault section; The process of arc extinguishing and fault section location for single-phase grounding fault is as follows: Step 1: Set the adaptive starting threshold of the zero-sequence voltage of the distribution network. If the zero-sequence voltage exceeds the set threshold, it is considered that a single-phase grounding fault occurs in the distribution network, and the flexible arc extinguishing device is started to inject full compensation current into the distribution network to achieve rapid suppression of the fault current. Step 2: Within the time T after the full compensation current is injected, the single-phase grounding fault current is effectively suppressed; in order to leave a certain time margin, after the flexible arc extinguishing device injects the full compensation current, the control reference value of its injected current is changed at interval t1, directly reducing the injected current of the neutral point, and actively constructing the change of zero-sequence voltage and zero-sequence current; Step 3: The phase difference of the zero-sequence voltage change and the zero-sequence current change is calculated in real time by using the short-time Fourier algorithm. The fault section is distinguished from the non-fault section based on the characteristic difference that the phase difference of the zero-sequence voltage and current changes in the fault section changes with the transition resistance, while the phase difference of the zero-sequence voltage and current changes in the non-fault section is maintained at 90°. Step 4: If the calculation results of the phase difference of the zero-sequence voltage and current changes in each section do not show that the grounding fault disappears, the grounding fault is considered to be permanent, and the flexible arc extinguishing device is restored to inject full compensation current into the system; if the phase difference of the zero-sequence voltage and current changes in each section meets the situation that the fault disappears, the injected current is further reduced, and the length of the waveform sampling is extended to calculate the phase of the zero-sequence voltage and current changes in each section; if the phase of the zero-sequence current change intermittently jumps during the sampling time, it means that the grounding fault is an intermittent arc grounding fault, and the fault section is determined according to the phase difference relationship, and the injected current of the flexible arc extinguishing device is restored to the full compensation current; Otherwise, the fault is judged as a transient fault, and the flexible arc extinguishing device stops operating; Considering the high randomness of single-phase grounding faults, the nature of the grounding fault is judged at fixed intervals; according to steps 3 and 4, the time for judging intermittent faults and instantaneous faults does not exceed 30s; after the first grounding fault nature judgment is completed, the injection current of the flexible arc extinguishing device is reduced at each interval t2, and the nature of the grounding fault is judged according to executing steps 1 to 4; The flexible arc extinguishing device is connected to the distribution network in one of a single-phase access type, a two-phase access type, a three-phase access type and a neutral point access type; Among them, the topology of the single-phase access flexible arc extinguishing device adopts a single-phase H-bridge converter, one end of the converter is connected to the phase line of the distribution line or the low-voltage side of the step-up transformer, and the other end is connected to the ground; the single-phase H-bridge converter is one of a two-level single-phase half-bridge, a three-level single-phase half-bridge, a multi-level single-phase half-bridge, and a single-phase cascaded H-bridge; The topology of the two-phase access flexible arc extinguishing device adopts that the common point of the two-phase H-bridge converter is grounded through the arc extinguishing coil or the common point of the two-phase H-bridge converter is grounded through the single-phase H-bridge converter; one end of the two-phase converter is connected to the phase line of the distribution line or the low-voltage side of the step-up transformer, and the other end is connected to the common point, and the two-phase H-bridge converter is directly connected to or connected to any two phases of the distribution line through the step-up transformer; the two-phase H-bridge converter is composed of two single-phase H-bridge converters; The topology of the three-phase access flexible arc extinguishing device adopts a four-bridge-arm H-bridge converter, wherein three bridge arms are three-phase H-bridge converters, and the grounded bridge arm is a single-phase H-bridge converter. The three-phase H-bridge converter is directly connected to the three phases of the distribution line or is connected to the three phases through a step-up converter, and its common point is grounded through a single-phase H-bridge converter, i.e., the grounded bridge arm; the three-phase H-bridge converter is one of a two-level three-phase half-bridge, a three-level three-phase half-bridge, a multi-level three-phase half-bridge or a three-phase cascaded H-bridge; The topology of the neutral point access flexible arc extinguishing device uses a single-phase H-bridge converter to access the distribution network via a Z-type transformer; The control method of the flexible arc extinguishing device adopts one of a voltage arc extinguishing method, a current arc extinguishing method and a voltage and current fusion arc extinguishing method; The voltage arc extinguishing method takes the zero-sequence voltage as the system control object, controls the zero-sequence voltage to be the opposite of the fault phase power supply voltage through a flexible arc extinguishing device, and clamps the fault point voltage to zero to achieve reliable arc extinguishing; The current arc extinguishing method uses the injection current of the flexible arc extinguishing device as the control object of the system, injects the full compensation current through the flexible arc extinguishing device, and suppresses the fault point voltage to zero to achieve reliable arc extinguishing; The voltage-current fusion arc extinguishing method controls the voltage and current in parallel and simultaneously calculates the deviation between the voltage and current feedback and the real-time detection value; According to the phase difference of zero-sequence voltage and current in each section before and after the current injected by the flexible arc extinguishing device changes, the nature of the grounding fault is determined: If it is an intermittent fault, the flexible arc extinguishing device will be exited after the single-phase grounding fault disappears; If it is a permanent fault, the fault section is located according to the phase difference between the zero-sequence voltage and current changes in the healthy section and the faulty section, and the flexible arc extinguishing device is restored to inject full compensation current into the system; If it is an intermittent ground fault, the flexible arc extinguishing device will be started when the fault first occurs, injecting full compensation current into the system, and then exit the flexible arc extinguishing device after the ground fault finally disappears.

2. The method for actively locating a single-phase grounding fault section in a distribution network according to claim 1, characterized in that: The short-time Fourier algorithm realizes real-time calculation of the phase of the zero-sequence voltage variation and the zero-sequence current variation by moving the time window and calculating the phase of the signal in the current time window.

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