A power distribution network tree line discharge fault current transfer arc extinction experimental platform and method

Abstract

The application discloses a distribution network tree line discharge fault current transfer arc extinction experimental platform and method, relates to the technical field of distribution network tree line discharge fault current transfer arc extinction, and solves the problem that the existing distribution network tree line discharge fault current transfer arc extinction experimental platform is lacked, and arc extinction response speed cannot be measured.The technical scheme is as follows: the experimental platform comprises a step-up transformer, a three-phase distribution line and a voltage transformer which are connected in sequence, the three-phase distribution line is further connected with an adjustable capacitor, a lifting platform is arranged below the three-phase distribution line, the lifting platform comprises a metal shell with one end being open, a lifting machine is connected to the bottom of the metal shell, a fault simulation piece is arranged in the metal shell, the metal shell is grounded through a sampling resistor, and a fault phase of the three-phase distribution line is grounded through a switch cabinet.The experimental platform is provided for fault current transfer arc extinction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of distribution network tree line discharge fault current transfer arc extinction, more specifically, it relates to a distribution network tree line discharge fault current transfer arc extinction experimental platform and method. BACKGROUND

[0002] 10kV distribution line overhead line sometimes needs to cross the mountain forest area, affected by external factors (such as lightning, gale, etc.), the overhead line may occur discharge with higher branches. Because the resistivity of the branches is high, the volume is large, so it will constitute a single-phase high-resistance grounding fault of the line. The distribution network crossing the mountain forest is generally a neutral point ungrounded system. In order to ensure the reliability of power supply, the system is allowed to continue to operate for a period of time after the single-phase grounding fault occurs. But due to the existence of line distributed capacitance, the fault point has capacitive current connected between the conductor and the ground, and long-time operation may form arc, damage equipment and cause forest fire. Therefore, when the tree line discharge fault occurs in the distribution network line, effective arc extinction measures must be taken to avoid inducing forest fire accidents.

[0003] The most representative arc extinction measures at present are arc suppression coil and fault current transfer arc extinction device. The arc suppression coil is a kind of arc extinction equipment widely used in distribution network, which can realize fault point arc extinction by generating inductive current to compensate the capacitive current in the line. When a single-phase grounding short-circuit fault occurs, the inductive current is generated and injected into the system by adding the fault phase voltage on the arc suppression coil. The phase is exactly opposite to the phase of the capacitive current to the ground, so they will offset each other at the grounding point. Selecting appropriate arc suppression coil can reduce the grounding current to very small or even zero, thereby accelerating the arc extinction. However, considering the system load growth and power grid development planning, the arc suppression coil usually operates in over-compensation state. The over-compensation of the arc suppression coil makes the fault point exist inductive current, which may still cause arc. In addition, the contradiction between the arc suppression coil compensation residual current and the neutral point displacement voltage, resonance overvoltage problem is also difficult to solve, therefore, the traditional arc suppression coil compensation method still has many problems. In view of the arc extinction problem of distribution network, researchers have developed many new types of arc suppression coil, which can achieve good arc extinction effect. However, most of the above devices have high cost and complex control strategy, which is difficult to popularize and apply in large scale in mountainous areas.

[0004] In recent years, the technical idea of realizing fault current diversion arc extinction by arc extinction cabinet has been fully concerned. The arc extinction cabinet is a metallic grounding branch artificially created at the busbar to bypass the fault point, convert the arc grounding into metallic grounding, and make the capacitive current of the fault point flow into the ground through the artificially constructed metallic grounding loop, so as to realize arc extinction at the fault point. This scheme has the advantages of simple principle, fast response speed, strong operability and less required equipment, and is suitable for wide application. In addition, this scheme needs to ensure that the impedance of the artificially constructed metallic grounding loop is much smaller than the fault impedance, which is exactly suitable for the situation of tree line discharge fault with high transition resistance. Therefore, the realization of fault current diversion arc extinction by arc extinction cabinet can effectively solve the problem of tree line discharge fault arc extinction in distribution network.

[0005] However, most of the existing researches on arc extinction cabinet are theoretical analysis by simulation means, and there are few experimental researches. At present, there is no experimental research on directly applying arc extinction cabinet to tree line discharge fault arc extinction situation. In addition, in practical application, in order to avoid the tree line discharge fault arc causing forest fire, the response speed of arc extinction is also one of the problems that need to be studied, and the existing model simulation is difficult to study the response speed of arc extinction. SUMMARY

[0006] The purpose of the present application is to provide a distribution network tree line discharge fault current diversion arc extinction experimental platform and method. The experimental platform for fault current diversion arc extinction is provided by building a distribution network tree line discharge fault current diversion arc extinction experimental platform. Based on the experimental method of the experimental platform, the response speed and effect of arc extinction can be studied.

[0007] The above technical purpose of the present application is achieved by the following technical scheme: a booster transformer, a three-phase distribution line and a voltage transformer connected in sequence, the three-phase distribution line is also connected with an adjustable capacitor, a lifting platform is arranged below the three-phase distribution line, the lifting platform comprises a metal shell with an open end, a lifting machine is connected to the bottom of the metal shell, a fault simulation piece is arranged inside the metal shell, the metal shell is grounded through a sampling resistor, and the fault phase of the three-phase distribution line is grounded through a switch cabinet.

[0008] By adopting the above technical scheme, the booster transformer supplies power to the entire line, the adjustable capacitor adjusts the capacitive current of the line to the ground, the actual long-distance three-phase distribution line is simulated, the voltage transformer facilitates measurement of the line voltage, the lifting platform below the three-phase distribution line simulates the fault situation, the fault phase of the three-phase distribution line is grounded through the switch cabinet, the fault current diversion situation is simulated, and during the experiment, various fault situations can be tested by adjusting the adjustable capacitor and the fault simulation piece.

[0009] Further, the high-voltage side of the sampling resistor is connected to an oscilloscope to measure the current waveform at the fault point; the secondary side of the voltage transformer is connected to an oscilloscope to measure the voltage waveform of the line; the built-in switch cabinet transformer in the switch cabinet is connected to an oscilloscope through the switch cabinet sampling resistor on the secondary side of the switch cabinet transformer to measure the current waveform of the transfer loop.

[0010] Further, the fault simulation piece includes soil and a branch inserted into the soil.

[0011] Further, the voltage of the three-phase distribution line is 10 kV.

[0012] Further, the transformation ratio of the voltage transformer is 10:0.1.

[0013] The application also provides a method for arc extinction by fault current transfer of tree line discharge in a distribution network, based on the experimental platform for arc extinction by fault current transfer of tree line discharge in a distribution network, and specifically includes the following steps:

[0014] S1, obtaining the impedance before the fault simulation piece is grounded;

[0015] S2, raising the lifting platform to the fault phase of the three-phase distribution line where the fault simulation piece is overlapped, connecting the three-phase distribution line, adjusting the adjustable capacitor bank to simulate the fault, and after the fault is stabilized, sending a pulse signal to control the switch cabinet to close to simulate the fault current transfer; and recording the voltage waveform of the line, the current waveform at the fault point, and the current waveform of the transfer loop by an oscilloscope;

[0016] S3, after the fault current transfer is completed, cutting off the three-phase distribution line, and ending the experiment.

[0017] By recording the voltage waveform of the line, the current waveform at the fault point, and the current waveform of the transfer loop by the oscilloscope, the response speed and effect of arc extinction can be determined, the switch cabinet is closed after the pulse signal is sent, the arc extinction by fault current transfer is performed, the current at the fault point and the voltage of the fault phase are significantly reduced when the arc extinction is completed, the time from the moment when the pulse signal is sent to the moment when the current at the fault point and the voltage of the fault phase are significantly reduced can be observed by the oscilloscope, so that the response speed of the arc extinction by fault current transfer can be determined, and the effect of the arc extinction by fault current transfer can also be determined by observing the waveform of the oscilloscope after the fault current transfer is completed.

[0018] Further, the S2 further includes: taking pictures of the discharge situation at the fault point before and after the fault current transfer by a camera.

[0019] Further, the camera includes a high-speed camera and an infrared camera.

[0020] The high-speed camera can capture the moment of fault occurrence and the arc extinguishing moment of fault current transfer arc extinguishing, and the infrared camera can capture the heat at the moment of fault occurrence and the heat after the fault current transfer arc extinguishing, so that the arc extinguishing effect can be determined more intuitively.

[0021] Further, the waveforms recorded by the oscilloscope all take the moment of the pulse signal emission as the starting moment.

[0022] By adopting the technical scheme, the time for observing the obvious reduction of the fault point current from t=0s can be directly observed, that is, the response time of the fault current transfer arc extinguishing.

[0023] Further, the method further comprises: S4, changing the impedance of the fault simulation piece or the capacitance current injected by the adjustable capacitor, repeating steps S1-S3, and performing single variable control experiment to control to obtain multiple sets of waveforms of the line voltage, the fault point current and the transfer loop current.

[0024] By adopting the technical scheme, the impedance of the fault simulation piece and the adjustable capacitor are taken as variables to perform single variable control experiment, so that the response speed and effect of arc extinguishing when the fault simulation piece has different impedances and the response speed and effect of arc extinguishing when the line-to-ground capacitive current is different can be researched.

[0025] Compared with the prior art, the application has the following beneficial effects: on the one hand, the application provides a distribution network tree line discharge fault current transfer arc extinguishing experiment platform, which can more truly research the effect of fault current transfer arc extinguishing compared with the existing simulation; on the other hand, the application also provides a distribution network tree line discharge fault current transfer arc extinguishing experiment method, waveforms of the line voltage, the fault point current and the transfer loop current are measured by the oscilloscope, so that the response time and effect of fault current transfer arc extinguishing can be determined. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and constitute a part of this application, do not constitute limitations to the embodiments of the application. In the drawings:

[0027] Figure 1 A schematic diagram of the distribution network tree line discharge fault provided by an embodiment of the application;

[0028] Figure 2 A schematic diagram of the arc extinguishing principle of the fault current transfer arc extinguishing provided by an embodiment of the application;

[0029] Figure 3 A schematic diagram of the distribution network tree line discharge fault current transfer arc extinguishing experiment platform provided by an embodiment of the application;

[0030] Figure 4An electric power distribution network tree line discharge fault current transfer arc extinction experiment process is provided for an embodiment of the present application.

[0031] Figure 5 A line voltage waveform schematic diagram is provided for an embodiment of the present application.

[0032] Figure 6 A fault point current waveform schematic diagram is provided for an embodiment of the present application.

[0033] Figure 7 A transfer loop current waveform schematic diagram is provided for an embodiment of the present application.

[0034] Figure 8 A low-pass filtered transfer loop current waveform schematic diagram is provided for an embodiment of the present application.

[0035] Figure 9 Another fault point current waveform schematic diagram is provided for an embodiment of the present application.

[0036] Figure 10 Another fault point current waveform schematic diagram is provided for an embodiment of the present application. DETAILED DESCRIPTION

[0037] Hereinafter, the term "include" or "may include" used in various embodiments of the present application indicates the existence of the applied function, operation, or element, and does not limit one or more additions of the function, operation, or element. Also, as used in various embodiments of the present application, the terms "include", "have", and their conjugates merely indicate the presence of the specific feature, number, step, operation, element, component, or combination of the foregoing, and should not be understood as excluding the possibility of the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing.

[0038] In various embodiments of the present application, the expression "or" or "at least one of B or / and C" includes any combination of the listed terms or all combinations thereof. For example, the expression "B or C" or "at least one of B or / and C" can include B, can include C, or can include both B and C.

[0039] The terms used in the various embodiments of this application (such as "first," "second," etc.) may modify various constituent elements in the various embodiments, but do not limit the corresponding constituent elements. For example, the above terms do not limit the order and / or importance of the elements. The above terms are only used for the purpose of distinguishing one element from other elements. For example, a first user device and a second user device refer to different user devices, although both are user devices. For example, without departing from the scope of the various embodiments of this application, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0040] It should be noted that if a description refers to "connecting" a component to another component or "connecting" it to another component, then the first component can be directly connected to the second component, and a third component can be "connected" between the first and second components. Conversely, when a component is "directly connected" to another component or "directly connected" to another component, it can be understood that there is no third component between the first and second components.

[0041] The terminology used in the various embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the various embodiments of this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of this application pertain. The terms (such as those defined in a generally used dictionary) are to be interpreted as having the same meaning as in the context of the relevant technical field and are not to be interpreted as having an idealized or overly formal meaning, unless clearly defined in the various embodiments of this application.

[0042] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this application are only for explaining this application and are not intended to limit this application.

[0043] A schematic diagram of a tree-line discharge fault in a distribution network, as shown below. Figure 1 As shown, let phase C of the three-phase distribution line be the fault phase, where U represents the bus voltage of the line, and C line I is the total capacitance of the line to ground. Cline I is the line-to-ground capacitance current. F R is the fault point current. fault This is the transition impedance at the fault point. When a fault occurs, the transition resistance R... fault A voltage exists across the two ends, generating a resistive current. Additionally, the line capacitance C... lineThe capacitive current I will flow in the line Cline Since the neutral point is not grounded, there is no other grounding point in the line, I Cline will flow between the fault phase and the ground through the fault point. Therefore, the current flowing through the fault point contains a resistive component and a capacitive component, that is:

[0044]

[0045] In the case of single-phase high-resistance grounding fault of distribution network tree line discharge, R fault is generally several thousand to several million ohms, so the resistive current flowing through the fault point is small. Since the resistive current of the fault point is almost 0, |I F ≈ |I Cline |, that is, the key to arc extinction of distribution network tree line discharge fault is to reduce the capacitive current of the fault point.

[0046] Based on the arc extinction principle of fault current transfer, as shown in Figure 2 , wherein I trans and R trans are the transfer current and loop impedance of the capacitive current transfer loop, respectively. The principle of this scheme is: a capacitive current transfer loop is constructed at the first end of the fault phase, and when the fault occurs, the circuit breaker of the loop is closed. Since R trans <<R fault , according to the impedance inverse law, I Cline will mainly flow into the ground through the capacitive current transfer loop, and the current I F of the fault point will mainly be a resistive current. At this time, since the first end of the fault phase line is grounded through the capacitive current transfer loop, the fault phase voltage is clamped to 0, according to formula (1), both components of I F are close to 0, that is, I F ≈ 0, thereby achieving arc extinction at the fault point.

[0047] Based on the arc extinction principle of fault current transfer, the application provides a distribution network tree line discharge fault current transfer arc extinction experimental platform, which simulates the actual use case and provides an experimental platform for fault current transfer arc extinction.

[0048] The distribution network tree line discharge fault current transfer arc extinction experimental platform, as shown in Figure 3 , comprises: a step-up transformer, a three-phase distribution line and a voltage transformer connected in sequence.

[0049] Specifically, three input terminals of the step-up transformer are connected with a 380V power supply, three output terminals are connected with a head end of a three-phase distribution line to provide a step-up power supply for the line, and a tail end of the three-phase distribution line is connected with a voltage transformer for detecting a line voltage; the step-up transformer adopts a YNyn0 connection mode, and a neutral point is suspended; and the three-phase distribution line adopts a steel-cored aluminum stranded wire with a model of LGJ-120. It should be noted that the head end and the tail end in the present application are divided according to the current direction, and the current flows from the head end to the tail end.

[0050] Further, a fault phase of the three-phase distribution line is grounded through a switch cabinet. Specifically, a wire is connected from a terminal connected with the step-up transformer and the fault phase of the three-phase distribution line to the switch cabinet and then grounded, so as to construct a fault current transfer loop.

[0051] Further, a lifting platform is arranged below the three-phase distribution line. The lifting platform comprises a metal shell with an open end. The bottom of the metal shell is connected with an elevator, and a fault simulation piece is arranged in the metal shell. The metal shell is grounded through a sampling resistor, so as to construct a fault situation. Specifically, the upper part of the metal shell of the lifting platform is open, the bottom of the metal shell is connected with the elevator and moves along the vertical direction, and the fault simulation piece is placed in the metal shell.

[0052] Further, an adjustable capacitor is connected with the head end of the three-phase distribution line. By controlling the switching of the adjustable capacitor, the capacitive current of the three-phase distribution line to the ground can be controlled. Specifically, the capacitive current can be adjusted from 1A to 60A, and the minimum step difference can reach 1A. By arranging the adjustable capacitor, the capacitive current of the actual long-distance three-phase distribution line to the ground can be simulated in the case of limited line length, so that the test is closer to the reality.

[0053] In some possible embodiments, the high-voltage side of the sampling resistor is connected with an oscilloscope to measure a fault point voltage waveform, so as to obtain a fault point current waveform according to Ohm's law. The secondary side of the voltage transformer is connected with the oscilloscope to measure a line voltage waveform. The secondary side of a switch cabinet transformer in the switch cabinet is connected with the oscilloscope through a switch cabinet sampling resistor to measure a transfer loop current waveform.

[0054] In some possible embodiments, the fault simulation piece comprises soil and a branch inserted into the soil.

[0055] In use, the lifting platform is lifted by the elevator, the branch is placed on a certain phase of the three-phase distribution line to simulate a tree-line discharge fault, the phase is referred to as a fault phase, and a contact point between the phase and the branch is a fault point. When the switch cabinet is closed, the fault point current flows into the ground through the sampling resistor to simulate a fault current transfer.

[0056] In some possible embodiments, the voltage of the three-phase distribution line is 10 kV, and the voltage transformer has a transformation ratio of 10:0.1, which can actually simulate the actual use of the 10 kV three-phase distribution line.

[0057] Based on the above distribution network tree line discharge fault current transfer arc extinction experimental platform, the application further provides an experimental method, the flowchart of which is shown in Figure 4 The experimental method comprises the following steps:

[0058] S1, obtaining the impedance before the fault simulation piece is grounded;

[0059] S2, raising the lifting platform until the fault simulation piece is overlapped on the fault phase of the three-phase distribution line, connecting the three-phase distribution line, and adjusting the adjustable capacitor bank to simulate the fault; after the fault is stable, issuing a pulse signal to control the switch cabinet to close, simulating the fault current transfer; and recording the waveforms of the line voltage, the fault point current and the transfer loop current of the three-phase distribution line through the oscilloscope;

[0060] S3, after the fault current transfer is completed, cutting off the three-phase distribution line, and ending the experiment.

[0061] Specifically, in S1, the fault simulation piece comprises soil and a tree branch inserted into the soil, and the impedance before the tree branch is grounded is measured by a multimeter; in step S2, the lifting platform is raised until the tree branch is overlapped on the fault phase of the distribution line, the power is turned on, the three-phase distribution line is connected, and then the adjustable capacitor is adjusted to control the capacitive current of the line to the ground, simulate the tree line discharge fault in the actual situation, after the fault is stable, a pulse signal is issued by the computer to control the switch cabinet to close, the fault current transfer is simulated, and the waveforms of the line voltage, the fault point current and the transfer loop current of the three-phase distribution line in the whole process are recorded; in step S3, after the fault current transfer is completed, the power is turned off, the three-phase distribution line is cut off, and the experiment is completed. When the arc extinction is completed, the fault point current and the fault phase voltage will be significantly reduced, and the time from the moment when the pulse signal is issued to the moment when the fault point current / fault phase voltage is significantly reduced can be observed through the oscilloscope, so as to determine the response speed of the fault current transfer arc extinction, and the waveform of the oscilloscope after the fault current transfer is completed can also be observed to determine the effect of the fault current transfer arc extinction.

[0062] In some possible embodiments, in step S2, the method further comprises: photographing the discharge situation of the fault point when the tree line discharge fault occurs and the discharge situation of the fault point when the fault current transfer occurs through a camera, so as to more intuitively observe the arc extinction effect of the fault current transfer. Specifically, the camera can be a high-speed camera or an infrared camera, the high-speed camera can capture the moment when the fault occurs and the moment when the arc extinction of the fault current transfer occurs, and the infrared camera can capture the heat when the fault occurs and the heat after the arc extinction of the fault current transfer, so as to more intuitively determine the arc extinction effect.

[0063] In some possible embodiments, to ensure the accuracy of time measurement, the waveforms recorded by the oscilloscope are all taken as the starting moment of the pulse signal emission; the pulse signal emission is the control of the switch cabinet closing, simulating the fault current transfer, and in an ideal case, the time for observing the obvious reduction of the fault point current can be directly started from t=0s, that is, the response time of the fault current transfer arc extinction.

[0064] In some possible embodiments, the experimental method further comprises: step S4, changing the impedance of the fault simulation piece or the capacitive current injected by the adjustable capacitor, repeating steps S1-S3, and performing single variable control experiments to control a plurality of sets of waveforms of the line voltage, the fault point current and the transfer loop current.

[0065] Specifically, the first group of experiments is performed by controlling the tree branch impedance unchanged and controlling the adjustable capacitor to inject different capacitive currents; the second group of experiments is performed by cutting different impedance tree branches on the same tree as the fault simulation piece and controlling the adjustable capacitor unchanged; and the waveforms of the line voltage, the fault point current and the transfer loop current measured in each group of experiments are compared to study the response speed and effect of arc extinction under different fault conditions.

[0066] In a specific implementation scenario, the effect of the fault current transfer arc extinction is illustrated by taking the fault condition of a tree branch length of 1.3 m, a pre-grounding impedance of 450 MΩ and a line capacitive current of 3 A as an example. The line voltage waveform of the three-phase distribution line recorded in step S2 is as shown in Figure 5 , the fault point current waveform is as shown in Figure 6 , and the transfer loop current waveform is as shown in Figures 7-8 .

[0067] As shown in Figures 5-6 , t=0s is the moment of the pulse signal emission for controlling the switch cabinet closing, and from the figure, it can be seen that when the fault occurs, there is almost no difference between the fault phase voltage and the non-fault phase voltage, mainly because the transition resistance of the fault phase is relatively high, resulting in that the fault phase voltage does not change obviously. At t=50.94 ms, Figure 6 , the fault point current is obviously reduced, Figure 5 , the fault phase voltage is reduced to 0, and thus it can be obtained that the total time from the fault occurrence to the completion of the transfer arc extinction is t=50.94 ms, which is close to the inherent action time delay of 50 ms of the switch cabinet, where the inherent action time delay of the switch cabinet refers to the time from the moment of the pulse signal emission to the moment of the switch cabinet closing. After the completion of the transfer arc extinction, the fault point current (including noise) is about 20 mA, and it can be observed that the arc is extinguished, and thus the fault point current reaches a safe level, that is, the fault point current transfer arc extinction can achieve good arc extinction effect.

[0068] As shown in Figures 7-8 , and Figure 7To transfer the loop current waveform, due to the low precision of the switch cabinet mutual inductor and the electromagnetic interference of the experimental site, the transfer loop current waveform has more noise. In order to facilitate understanding, low-pass filtering is carried out by using the lowpass function in matlab, as shown in Figure 8 Fig. 3, the cut-off frequency is 100 Hz. It can be seen from the figure that the current of the transfer loop increases at about 5 ms after the pulse is sent, which may be due to the pre-breakdown of the switch. Subsequently, at t = 50.94 ms, the switch cabinet is turned on, and the current increases obviously, with a peak value of about 3 A, which is close to the capacitive current value. It can be seen that the transfer loop has good arc extinction effect.

[0069] In a specific implementation scenario, in step S4, the tree impedance is first controlled to be unchanged, and the adjustable capacitor is changed. Specifically, to maintain the humidity and thickness, the same tree is used, and the capacitive current is adjusted to I C = 1 A, 3 A and 7 A, respectively, to measure the fault point current waveform, and to observe the influence of the capacitive current on the arc extinction effect. The length of the tree is 1.3 m, and the grounding resistance is 450 MΩ.

[0070] The fault point current waveform is shown in Figure 9 Fig. 4. t = 0 s is the time when the pulse signal for controlling the switch cabinet to close is sent. At t = 50.94 ms, the arc extinction is completed. It can be observed that under different capacitive current fault conditions, the fault point current after transfer will decrease obviously.

[0071] To facilitate comparison, the fault point current peak value before transfer, the fault point current peak value after transfer and the transfer time under different capacitive current fault conditions are listed in Table 1. It can be seen that the fault point current peak value before transfer is proportional to the capacitive current, but the fault point current peak value after transfer is 19.685 mA. It may be due to the fact that the fault point current after transfer is small, which is lower than the measurement accuracy, and the oscilloscope can only record part of the noise current peak value. In addition, it can be seen that the transfer time has no obvious relationship with the capacitive current, but is close to the inherent action time delay of the switch cabinet.

[0072] Table 1 Arc extinction effect under different capacitive current conditions

[0073]

[0074] Then, the adjustable capacitor is controlled to be unchanged, and the tree impedance is changed. Specifically, when the capacitive current is fixed at 1 A, the same tree with different lengths and different resistance values is used for experiment to observe the influence of the tree resistance on the arc extinction effect of the fault current. Three trees are used in the experiment, which are numbered as tree 1, tree 2 and tree 3. The length / transition resistance before grounding of each tree is 0.98 m / 200 MΩ, 1 m / 240 MΩ and 1.3 m / 450 MΩ, respectively.

[0075] The current waveform at the fault point, such as Figure 10 As shown, t=0s is the time when the pulse signal for closing the control switchgear is issued. At t=50.94ms, the arc suppression transfer is completed. It can be observed that the peak current at the fault point before the transfer is inversely proportional to the resistance of the tree branch, and the peak transient current at the time of the transfer is also positively correlated with the peak current at the fault point before the transfer. After the transfer, the fault point current under different tree branch fault conditions decreases significantly, indicating that the scheme has a good arc suppression effect.

[0076] Table 2 compares the peak fault current before and after transfer, as well as the transfer time, under different tree resistances. It can be seen that the peak fault current before transfer is inversely proportional to the tree resistance, while the peak fault current after transfer remains at 19.685 mA, demonstrating a good arc suppression effect. The transfer time is also not significantly related to the tree resistance.

[0077] Table 2. Arc-suppression effect under different tree resistance conditions

[0078]

[0079] In summary, the experimental steps and results described above demonstrate that fault point current transfer arc suppression can achieve good arc suppression effect. The response time of fault point current transfer arc suppression is close to the inherent operating delay of the switchgear. For different capacitive currents and tree impedances, fault point current transfer arc suppression can achieve good arc suppression effect. The arc suppression response speed is not significantly related to tree impedance and capacitive current, indicating that fault point current transfer arc suppression has wide parameter range applicability.

[0080] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for arc extinction experiment of treeing discharge fault current transfer in power distribution network, characterized in that, The method is used for a distribution network tree line discharge fault current transfer arc extinction experimental platform, which comprises a step-up transformer, a three-phase distribution line and a voltage transformer connected in sequence, and the three-phase distribution line is further connected with an adjustable capacitor; A lifting platform is arranged below the three-phase distribution line, the lifting platform comprises a metal shell with an open end, the bottom of the metal shell is connected with an elevator, a fault simulation piece is arranged in the metal shell, the metal shell is grounded through a sampling resistor, and a fault phase of the three-phase distribution line is grounded through a switch cabinet; a wire is connected from a terminal post connected with the step-up transformer and the fault phase of the three-phase distribution line to the switch cabinet and then grounded, so as to construct a fault current transfer loop; The high-voltage side of the sampling resistor is connected with an oscilloscope to measure the current waveform at the fault point; the secondary side of the voltage transformer is connected with the oscilloscope to measure the voltage waveform of the line; a switch cabinet transformer is arranged in the switch cabinet, and the secondary side of the switch cabinet transformer is connected with the oscilloscope through a sampling resistor in the switch cabinet to measure the current waveform of the transfer loop; The method comprises the following steps: S1, obtaining the impedance before the fault simulation piece is grounded; S2, raising the lifting platform to make the fault simulation piece overlap the fault phase of the three-phase distribution line, connecting the three-phase distribution line, adjusting the adjustable capacitor bank, and simulating the tree line discharge fault; After the fault is stabilized, a pulse signal is sent to control the switch cabinet to close, and the fault current transfer is simulated; The waveforms of the line voltage, the fault point current and the transfer loop current are recorded by the oscilloscope; S3, after the fault current transfer is completed, the three-phase distribution line is cut off, and the experiment is ended.

2. The method of claim 1, wherein the method further comprises: The fault simulation piece comprises soil and a tree branch inserted in the soil.

3. The method of claim 1, wherein the method further comprises: The voltage of the three-phase distribution line is 10kV.

4. The method of claim 2, wherein the method further comprises: The transformation ratio of the voltage transformer is 10:0.

1.

5. The method of claim 1, wherein the method further comprises: The S2 further comprises: taking the discharge situation of the fault point before and after the fault current transfer by a camera.

6. The method of claim 5, wherein the method further comprises: The camera comprises a high-speed camera and an infrared camera.

7. The method of claim 1, wherein the method further comprises: The waveforms recorded by the oscilloscope all take the time when the pulse signal is sent as the starting time.

8. The method of claim 7, wherein, Further comprising: S4, changing the impedance of the fault simulation piece or the capacitance current injected by the adjustable capacitor, repeating steps S1-S3, performing a single variable control experiment, and obtaining a plurality of waveforms of the line voltage, the fault point current and the transfer loop current.

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