An active intervention arc extinguishing method using dual fast switches

Abstract

The present invention belongs to the field of electric power technology and discloses an active intervention arc extinguishing method using dual fast-action switches. The present invention employs a fast-action switch with a first contact span as a front fast-action switch and a fast-action switch with a second contact span as a grounding fast-action switch. The first contact span is greater than the second contact span. The front fast-action switch and the grounding fast-action switch are connected in series. The grounding fast-action switch provides ultra-fast switching speed, while the front fast-action switch provides strong current interrupting capability. The two fast-action switches can achieve both fast action and high current interrupting performance, quickly extinguishing grounding arcs and reducing the cost of arc extinguishing devices.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and more specifically, relates to an active intervention arc extinguishing method coordinated with dual fast switches. Background Art

[0002] The increasing use of solid-insulated cross-linked polyethylene cables in distribution networks presents the challenge of handling irreversible single-phase ground faults caused by solid insulation. When a single-phase ground fault occurs in the system, the steady-state current flowing through the grounding point is the system's capacitive current to ground. The high-frequency current amplitude and duration of the ground arc in the cable grid are significantly increased compared to overhead lines. Consequently, the arc-flash grounding overvoltage in the non-fault phase can exceed four times the phase voltage, posing a serious threat to cable insulation. Therefore, quickly and accurately identifying the faulty line and extinguishing the ground arc as soon as possible are crucial to preventing cable insulation damage and fault expansion.

[0003] With the significant increase in line-to-ground capacitance current in power systems, the application of traditional current-based arc suppression methods, represented by arc suppression coils, has been limited. Operational tests of arc suppression coils at 13 power plants revealed a series of issues, including significant errors in indirect current measurement, large residual current after compensation, inability to compensate for resistive and high-frequency components in ground current, and neutral point current distortion caused by arc suppression coil saturation. These issues have resulted in poor arc suppression effectiveness. Furthermore, arc suppression coils can affect line selection accuracy, with tests showing that the accuracy rate is less than 50%.

[0004] The active intervention arc extinguishing method is not limited by the size of the capacitive current and the grounding method, and can be applied to distribution systems with cable lines. While achieving complete arc extinguishing, it avoids the complex tracking and compensation calculation process of the fault current in the active current type arc extinguishing method. The speed of transferring the short-circuit grounding current by the active intervention arc extinguishing method is crucial. How to improve the switching speed is a key topic in the research of the active intervention arc extinguishing method. The application of fast switches to active intervention arc extinguishing technology is of great significance. The contact opening distance of the fast switch directly affects parameters such as the action time and current breaking capacity of the fast switch. Reducing the contact opening distance can increase the action time of the switch, but it will correspondingly reduce the current breaking capacity of the switch. How to solve this problem is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The present invention solves the problem in the prior art that fast switches cannot have both fast action performance and high current breaking performance by providing an active intervention arc extinguishing method coordinated with two fast switches.

[0006] The present invention provides an active intervention arc extinguishing method using dual fast switches. The method uses a fast switch with a first contact opening distance as a front fast switch, and a fast switch with a second contact opening distance as a grounding fast switch. The first contact opening distance is greater than the second contact opening distance. The front fast switch and the grounding fast switch are connected in series, and a microcomputer integrated controller is connected to the front fast switch and the grounding fast switch respectively.

[0007] The method comprises the following steps:

[0008] Step 1: Determine whether a single-phase grounding fault occurs in the distribution network; if a single-phase grounding fault occurs, proceed to step 2;

[0009] Step 2: Select the fault phase according to the three-phase voltage;

[0010] Step 3: Control the fault phase grounding fast switch to perform closing action through the microcomputer integrated controller;

[0011] Step 4: Select the fault line based on the zero-sequence current and determine whether the fault line is a cable line;

[0012] If the fault line is a cable line, the fault phase grounding fast switch is kept in the closed state;

[0013] If the fault line is not a cable line, then immediately after the fault phase grounding fast switch is closed, the microcomputer integrated controller sequentially controls the fault phase front fast switch to be disconnected, the fault phase grounding fast switch to be disconnected, and the fault phase front fast switch to be closed; then the microcomputer integrated controller determines whether the fault has disappeared. If the fault still exists, the fault phase grounding fast switch is controlled to be closed again.

[0014] Preferably, the grounding fast switch is an ultra-fast switch that can complete opening and closing actions within 3 milliseconds at the fastest.

[0015] Preferably, the first contact spacing ranges from 5 to 25 mm, and the second contact spacing ranges from 2.5 to 5 mm.

[0016] Preferably, in step 1, the specific implementation method of determining whether a single-phase grounding fault occurs in the distribution network is: real-time online monitoring of the open triangle voltage on the secondary side of the voltage transformer through the microcomputer integrated controller; if the open triangle voltage exceeds a preset voltage threshold, it is determined that a single-phase grounding fault occurs.

[0017] Preferably, in step 2, the specific implementation method of selecting the fault phase according to the three-phase voltage is: monitoring the three-phase voltage output by the voltage transformer through the microcomputer integrated controller, if one phase voltage is close to 0 and the other two phase voltages are close to the line voltage, it is determined to be a metallic grounding fault, and the phase with voltage close to 0 is determined to be the fault phase; if one phase voltage amplitude is the largest and the other two phase voltage amplitudes are close, it is determined to be a small resistance grounding fault, and the phase with the smallest voltage amplitude is determined to be the fault phase; if the three-phase voltage amplitudes are all greater than the preset voltage amplitude, it is determined to be a large resistance grounding fault, and the phase after the phase with the largest voltage amplitude is determined to be the fault phase.

[0018] Preferably, in step 4, the fault line is selected by analyzing the zero-sequence current measured by the current recorder installed at the head end of each feeder, and the basis for selecting the fault line according to the zero-sequence current is: before the fault phase grounding fast switch is closed, if the zero-sequence current on one of the lines is opposite to the zero-sequence current of all other lines and the amplitude is greater than that of other lines, and the direction of the zero-sequence current on one of the lines changes before and after the fault phase grounding fast switch is operated, then it can be determined that the line is a fault line.

[0019] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0020] In the present invention, a fast switch with a first contact opening distance is used as a front fast switch, and a fast switch with a second contact opening distance is used as a grounding fast switch. The first contact opening distance is greater than the second contact opening distance. The front fast switch and the grounding fast switch are connected in series, and a microcomputer integrated controller is connected to the front fast switch and the grounding fast switch respectively. That is, the present invention proposes a new active intervention arc extinguishing method with the cooperation of two fast switches, designs an ultra-fast switch with a short contact opening distance, and connects it in series with an ordinary fast switch. The grounding fast switch provides an ultra-fast switching action speed (the fastest action time is only 3 milliseconds), and the front fast switch provides a strong current breaking capability. The cooperation of the two fast switches can achieve both fast action performance and large current breaking performance, can quickly extinguish the grounding arc, and reduce the cost of the arc extinguishing device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A primary system wiring diagram of a device used in an active intervention arc extinguishing method using dual fast switches provided in an embodiment of the present invention;

[0022] Figure 2 A schematic flow chart of an active intervention arc extinguishing method using dual fast switches provided in an embodiment of the present invention;

[0023] Figure 3 Flowchart for phase selection for faults;

[0024] Figure 4 Flowchart for fault line selection;

[0025] Figure 5 This is the structural diagram of the grounding fast switch. DETAILED DESCRIPTION

[0026] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0027] This embodiment provides an active intervention arc extinguishing method using dual fast-action switches. A fast-action switch with a first contact opening distance is used as a front fast-action switch, and a fast-action switch with a second contact opening distance is used as a grounding fast-action switch. The first contact opening distance is greater than the second contact opening distance. The front fast-action switch and the grounding fast-action switch are connected in series, and a microcomputer integrated controller is connected to the front fast-action switch and the grounding fast-action switch, respectively. The method mainly includes the following steps:

[0028] (1): Determine whether a single-phase grounding fault occurs in the distribution network; if a single-phase grounding fault occurs, proceed to step (2);

[0029] (2): Select the fault phase according to the three-phase voltage;

[0030] (3): Controlling the fault phase grounding fast switch to execute the closing action through the microcomputer integrated controller;

[0031] (4): Select the fault line according to the zero-sequence current and determine whether the fault line is a cable line;

[0032] If the fault line is a cable line, the fault phase grounding fast switch is kept in the closed state;

[0033] If the fault line is not a cable line, then immediately after the fault phase grounding fast switch is closed, the microcomputer integrated controller sequentially controls the fault phase front fast switch to be disconnected, the fault phase grounding fast switch to be disconnected, and the fault phase front fast switch to be closed; then the microcomputer integrated controller determines whether the fault has disappeared. If the fault still exists, the fault phase grounding fast switch is controlled to be closed again.

[0034] The primary system wiring diagram of the device used in the above method is shown in Figure 1 , for the specific method flow, see Figure 2 , including the following steps:

[0035] Step 1: The microcomputer integrated controller (ZK) 108 monitors the secondary delta voltage of the voltage transformer (PT) 104 in real time. If the voltage is normal, the monitoring state is maintained. If the open-circuit voltage exceeds the limit, the fault type is determined. If the system is not experiencing a single-phase ground fault, an alarm signal is issued. If a single-phase ground fault is determined, the system proceeds to step 2.

[0036] The system fault status is determined by monitoring the open delta voltage on the secondary side of the voltage transformer 104. When the system is operating normally, the system operating voltage, open delta voltage and arc suppression device operating status are displayed.

[0037] When the open delta voltage ΔU changes from a low level to a high level, it indicates that a system fault occurs, and the microcomputer integrated controller 108 immediately starts an interrupt and enters the fault type judgment and line zero-sequence current data collection program.

[0038] Specifically, the microcomputer integrated controller 108 monitors the voltage waveform of the secondary side triangle interface of the electromagnetic voltage transformer 104 in real time online, sets a threshold for the open triangle voltage, and the threshold needs to avoid the three-phase unbalanced voltage. As long as the voltage rises above the threshold, the system is judged to have a fault, and the program is started to determine whether the fault is a single-phase grounding fault; if the voltage does not rise above the threshold, the monitoring state is maintained.

[0039] Step 2: The microcomputer integrated controller 108 starts to run the fault phase selection program. The flowchart of the fault phase selection program is shown in FIG. Figure 3 , the phase selection program selects the fault phase according to the three-phase fault voltage within 3ms.

[0040] The microcomputer integrated controller 108 determines the fault type and phase difference such as single-phase grounding and line break according to the secondary output signals Ua, Ub, and Uc of the voltage transformer 104 .

[0041] Since different fault transition resistances correspond to different three-phase voltage magnitude relationships, different fault phase selection schemes need to be formulated according to different fault conditions.

[0042] The three-phase voltage output by the voltage transformer 104 is monitored by the microcomputer integrated controller 108. If one phase voltage is close to 0 and the other two phase voltages are close to the line voltage, it is determined to be a metallic ground fault, and the phase with the voltage close to 0 is determined to be the fault phase; if one phase voltage amplitude is the largest and the other two phase voltage amplitudes are close, it is determined to be a small resistance ground fault, and the phase with the smallest voltage amplitude is determined to be the fault phase; if the three-phase voltage amplitudes are all greater than the preset voltage amplitude, it is determined to be a large resistance ground fault, and the phase subsequent to the phase with the largest voltage amplitude is determined to be the fault phase.

[0043] The following is a detailed description of different fault phase selection schemes.

[0044] a. Metallic grounding fault.

[0045] When a single-phase metallic ground fault occurs in a system with an ungrounded neutral point, the voltage of the faulted phase approaches 0, while the voltage of the unfaulted phase approaches the line voltage. Based on this, the phase with the voltage close to 0 is identified as the faulty phase. For a 10kV distribution system, for example, the three-phase voltage threshold is set to: if one phase voltage is less than 1kV and the other two phase voltages are greater than 9kV, a single-phase metallic ground fault is considered to have occurred, and the phase with the voltage less than 1kV is identified as the faulty phase. Because the three-phase voltages vary significantly when a metallic fault occurs, transient voltage signals can be used to improve fault phase selection, shortening the phase selection time.

[0046] b. Low resistance grounding fault.

[0047] The critical condition for a low-resistance ground fault is defined as the voltage of the faulted phase reaching the same amplitude as the voltage of a non-faulted phase. When a low-resistance ground fault occurs, the voltage of the faulted phase has the smallest amplitude among the three-phase voltages, so the phase with the smallest amplitude can be identified as the faulted phase. For a 10kV distribution system, in the critical condition for a low-resistance ground fault, the voltages of the faulted phase and the phase following it are both 5kV, and the voltage of the phase preceding the faulted phase is 8.66kV. Considering the three-phase imbalance in actual systems, the three-phase voltage threshold can be set as follows: when the voltage of a phase is less than 4kV and the voltage of the phase preceding it is greater than 8kV, the phase with a voltage less than 4kV is identified as the faulted phase.

[0048] c. High resistance ground fault.

[0049] When the ground transition resistance is large, the fault phase voltage will no longer have the smallest amplitude among the three phases. However, the phase preceding the fault phase will always have the largest voltage amplitude during the transition resistance change process. Based on this, the phase following the phase with the largest voltage amplitude can be identified as the fault phase. For a 10kV distribution system, when all three phases are greater than 4kV, the phase with the largest voltage amplitude is first compared and selected, and then the phase following it is identified as the fault phase.

[0050] Step 3: The microcomputer integrated controller 108 executes the action program of the grounding fast switch (JD) 106 and the front fast switch (DL) 101 according to the fault phase, and sends an action signal to the busbar fault phase grounding fast switch 106. The busbar fault phase grounding fast switch 106 receives the action signal and acts quickly.

[0051] The pre-mounted fast-acting switch 101 is a standard switch with a high current breaking capacity, while the grounding fast-acting switch 106 is an ultra-fast switch with a maximum operating time of 3 milliseconds. The pre-mounted fast-acting switch 101 is normally closed, while the grounding fast-acting switch 106 is normally open. When the microcomputer integrated controller 108 sends a closing signal to the faulty phase grounding fast-acting switch 106, it controls the faulty phase grounding fast-acting switch 106 to close within a few milliseconds, directly grounding the faulty phase busbar, extinguishing the grounding arc and limiting the arc-fault overvoltage to the line voltage level.

[0052] Step 4: Select the fault line by analyzing the zero-sequence current measured by the current recorder installed at the head end of each feeder. The basis for selecting the fault line based on the zero-sequence current is: before the fault phase grounding fast switch 106 is closed, if the zero-sequence current on one of the lines is opposite to the zero-sequence current of all other lines and the amplitude is greater than that of other lines, and the direction of the zero-sequence current on one of the lines changes before and after the fault phase grounding fast switch 106 is operated, then it can be determined that the line is the fault line.

[0053] Specifically, the fault line selection program is started, and the fault line is selected based on the zero-sequence current measured by the current transformer installed at the head end of each feeder line. The flow chart of the fault line selection program is shown in Figure 4 , determine whether the fault line is a cable line. If it is a cable line, keep the grounding fast switch 106 in the closed state after closing; if the fault line is not a cable line (that is, the fault line is an overhead line), execute step 5.

[0054] After a ground fault occurs in a cable line, insulation cannot be restored. Maintaining grounding is essential to transfer all arc current from the fault point to the metallic grounded phase of the busbar. Due to the recoverable nature of air insulation, single-phase ground faults can be transient. Once the transient fault is restored and the grounding fast-acting switch is re-opened, the system can resume normal operation.

[0055] The basis for fault line selection is the variation characteristics of the zero-sequence current of each feeder line in the distribution network during a single-phase grounding fault, and the fault line is judged based on the difference in direction and amplitude between the zero-sequence current of the fault line and the zero-sequence current of the non-fault line before and after the grounding fast switch 106 is closed.

[0056] a. Zero-sequence current characteristics before closing of the grounding fast switch.

[0057] The zero-sequence current amplitude at the head end of the line where the fault point is located is the largest. Due to the existence of the branch line, the steady-state effective value is larger than the sum of the zero-sequence currents of other feeders, and the direction is opposite to the direction of the zero-sequence currents of other feeders; the zero-sequence current of the overhead line is relatively small; the zero-sequence current of the cable line is larger than that of the overhead line, but still smaller than that of the fault line.

[0058] b. Zero-sequence current characteristics after the grounding fast switch is closed.

[0059] When the grounding fast switch 106 is activated, the zero-sequence current of the faulty feeder undergoes a significant phase reversal, but the amplitude change is not noticeable compared to before the switch was activated. The zero-sequence current of the non-fault line remains unchanged in both direction and magnitude, exhibiting only a brief, small oscillation. After the grounding fast switch 106 is activated, the zero-sequence currents of the faulty and non-faulty lines no longer face opposite directions, but instead differ by a certain angle.

[0060] Step 5: The microcomputer integrated controller 108 sends an action signal to the pre-fast switch 101 and the grounding fast switch 106 immediately after issuing the closing action signal. After the pre-fast switch 101 opens, the grounding fast switch 106 opens, and then the pre-fast switch 101 closes.

[0061] 5 seconds after the microcomputer integrated controller 108 sends a closing action signal to the grounding fast switch 106, the grounding body of the instantaneous grounding fault burns out under the action of the grounding current. At this time, the front fast switch 101 with a long contact opening distance and a strong current breaking capacity is used to interrupt the grounding current. Then, the grounding fast switch 106 is opened, and then the front fast switch 101 with a long contact opening distance is restored to the closed state. At this time, the system returns to normal state. If a permanent grounding fault occurs, the system cannot resume normal operation in this way.

[0062] Step 6: The microcomputer integrated controller 108 re-determines the fault signal. After the long-contact-distance pre-installed fast switch is closed again, if the microcomputer integrated controller 108 determines that the fault has disappeared, it indicates that the ground fault was a transient fault and the system resumes normal operation. The microcomputer integrated controller 108 enters the standby state of step 1. If the fault is still detected, it indicates that the ground fault is a permanent fault and it is necessary to execute step 3 again to conduct the fault current to the ground through the busbar.

[0063] The present invention realizes the transfer of fault current within a few milliseconds through the cooperation of a fast switch and an ultra-fast switch, which is of great significance for quickly eliminating single-phase grounding arcs, suppressing arc-grounding overvoltages, and improving the level of safe operation.

[0064] The present invention utilizes two fast-acting switches with different contact spans in conjunction with each other. The ultra-fast switch with a short contact span (i.e., grounding fast switch 106) can complete closing in as little as 3 milliseconds, demonstrating excellent fast-acting performance. The fast switch with a long contact span (i.e., front fast switch 101) can interrupt grounding current, compensating for the ultra-fast switch's insufficient current-interrupting capacity. The coordination of these two fast switches ensures that the entire switch system exhibits both excellent fast-acting performance and good current-interrupting performance.

[0065] The dual-fast switch coordination logic is as follows: the pre-fast switch 101 is normally closed, and the grounding fast switch 106 is normally open. After the fault phase is determined, the grounding fast switch 106 rapidly closes. If the fault line is determined to be a cable line, the grounding fast switch 106 remains closed. Five seconds after the grounding fast switch 106 issues a closing action signal, the grounding current disconnection procedure is executed. The 5 seconds is a reference time that can be adjusted in practice. After determining that the fault line is not a cable line, the pre-fast switch 101 is first disconnected, then the grounding fast switch 106 is disconnected, and then the pre-fast switch 101 is closed to determine whether the fault still exists. If the fault disappears, the system resumes normal operation and monitors the fault status. If the fault still exists, the grounding fast switch 106 is closed again.

[0066] Specifically, the primary system wiring diagram of the device used in the method provided by the present invention can be found in Figure 1 , including a front fast switch (DL) 101, a current transformer (TA) 102, a PT high-voltage fuse (RD) 103, a voltage transformer (PT) 104, a primary harmonic eliminator (DR) 105, a grounding fast switch (JD) 106, a zero-sequence current transformer (TZ) 107, and a microcomputer integrated controller (ZK) 108. The PT high-voltage fuse 103 and the primary harmonic eliminator 105 can avoid possible ferromagnetic resonance. After the device is activated, the zero-sequence current transformer 107 reads the grounding capacitance current of the system. During the closing period of the fault phase of the device, if a ground fault occurs again when the device is not faulty, the zero-sequence CT secondary provides a current mutation for the microcomputer integrated controller 108 to sample. The microcomputer integrated controller 108 issues a trip command, and the closed phase of the circuit breaker is opened.

[0067] The grounding fast switch 106 is an ultra-fast switch, and its structure is shown in FIG. Figure 5 , including a vacuum interrupter 501, a static conductive rod 502, a static contact 503, a moving contact 504, a moving conductive rod 505, an insulating pull rod 506, an opening holding magnet 507, an opening coil 508, an electromagnet armature 509, a closing coil 510, a closing holding magnet 511, an opening control 512, an opening energy storage capacitor 513, a closing control 514, a closing energy storage capacitor 515, and a charging power supply 516.

[0068] The operating mechanism of the moving contact 504 within the vacuum interrupter 501 is driven by an electromagnetic repulsion mechanism. The electromagnetic repulsion mechanism operates as follows: When the switch receives a closing (or opening) command, a pulse current lasting several milliseconds is generated in the opening coil 508 (or closing coil 510). This pulse current generates an alternating magnetic field in the excitation coil, while the electromagnetic armature 509 generates electromagnetic force due to induced eddy currents. The electromagnetic armature 509 rapidly moves under the influence of the Lorentz repulsion force, driving the moving contact 504 of the vacuum interrupter 501 through the insulating pull rod 506, thereby achieving rapid opening and closing of the switch branch.

[0069] The grounding fast switch 106 charges the opening energy storage capacitor 513 and the closing energy storage capacitor 515 through the charging power supply 516, and controls the opening of the fast switch through the opening control 512 and the opening coil 508, controls the closing of the fast switch through the closing control 514 and the closing coil 510, and maintains the opening state and the closing state respectively through the opening holding magnet 507 and the closing holding magnet 511.

[0070] In the present invention, the speed of arc extinguishing is determined by the grounding fast switch 106. The faster the grounding fast switch 106 operates, the faster the arc extinguishing. The operating speed of the grounding fast switch 106 specifically depends on the contact spacing; the smaller the contact spacing, the faster the operating speed. The contact spacing of the grounding fast switch 106 ranges from 2.5 to 5 mm. For example, the contact spacing of a 10 kV grounding fast switch is approximately 3 mm. The contact spacing of the pre-mounted fast switch 101 ranges from 5 to 25 mm. For example, the contact spacing of a 10 kV pre-mounted fast switch is approximately 10 mm, which provides good current breaking capacity.

[0071] An active intervention arc extinguishing method using dual fast switches provided by an embodiment of the present invention includes at least the following technical effects:

[0072] (1) The present invention uses two types of fast switches and ultra-fast switches with different contact opening distances to cooperate with each other. The fast switch with short contact opening distance can complete the closing action within 3 milliseconds at the fastest, and has good speed performance; the fast switch with long contact opening distance can interrupt the grounding current, making up for the shortcoming of the short contact opening distance fast vacuum current interruption capacity. The two fast switches cooperate with each other to make the entire switch system have excellent speed performance and good current interruption performance, so that arc grounding faults can be eliminated quickly and reliably, and arc grounding overvoltage can be suppressed. The fast switch not only has good speed performance, but also has the advantages of simple structure, relatively low price and high reliability. This method only uses a fast switch to achieve rapid grounding of the fault current. Compared with other methods using arc suppression coils and power electronic devices, it has the advantages of low price, high reliability, easy maintenance, and small device size.

[0073] (2) The present invention adopts an active intervention arc extinguishing method, which is applicable to systems with any capacitive current, and has a particularly good beneficial effect on distribution networks with large capacitive currents and a large number of cable lines. This method is applicable to distribution networks with different capacitive currents at the same voltage level, and does not require the design of current-type arc extinguishing devices with different capacities according to the capacitive currents of different systems, as is the case with current-type arc extinguishing methods.

[0074] (3) The present invention considers the three-phase voltage characteristics under fault conditions, enabling accurate judgment of fault type and phase, rapid identification of single-phase ground faults, and selection of the faulty phase. In particular, the present invention considers the three-phase voltage characteristics under varying ground transition resistances, effectively improving the accuracy of high-resistance single-phase ground fault judgment.

[0075] (4) The present invention determines the fault line by analyzing the changing characteristics of the zero-sequence current of each feeder line in the distribution network during a single-phase grounding fault, and combining the differences in the direction and amplitude of the zero-sequence current of the fault line and the zero-sequence current of the non-fault line before and after the grounding fast switch is closed. It can effectively determine whether the fault line is a cable fault, so that different action strategies can be adopted for cables and overhead lines.

[0076] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An active intervention arc extinguishing method using dual fast switches, characterized in that: A fast switch having a first contact opening distance is used as the front fast switch, and a fast switch having a second contact opening distance is used as the grounding fast switch, wherein the first contact opening distance is greater than the second contact opening distance; the front fast switch and the grounding fast switch are connected in series, and a microcomputer integrated controller is connected to the front fast switch and the grounding fast switch respectively; The method comprises the following steps: Step 1: Determine whether a single-phase grounding fault occurs in the distribution network; if a single-phase grounding fault occurs, proceed to step 2; Step 2: Select the fault phase according to the three-phase voltage; The three-phase voltage output by the voltage transformer is monitored by the microcomputer integrated controller. If one phase voltage is close to 0 and the other two phase voltages are close to the line voltage, it is determined to be a metallic ground fault, and the phase with the voltage close to 0 is determined to be the fault phase; if one phase voltage amplitude is the largest and the other two phase voltage amplitudes are close, it is determined to be a small resistance ground fault, and the phase with the smallest voltage amplitude is determined to be the fault phase; if the three-phase voltage amplitudes are all greater than the preset voltage amplitude, it is determined to be a large resistance ground fault, and the phase subsequent to the phase with the largest voltage amplitude is determined to be the fault phase; Step 3: Control the fault phase grounding fast switch to perform closing action through the microcomputer integrated controller; Step 4: Select the fault line based on the zero-sequence current and determine whether the fault line is a cable line; The fault line is selected by analyzing the zero-sequence current measured by the current recorder installed at the head end of each feeder. The basis for selecting the fault line based on the zero-sequence current is: before the fault phase grounding fast switch is closed, if the zero-sequence current on one line is opposite to the zero-sequence current of all other lines and has a larger amplitude than that of other lines, and the direction of the zero-sequence current on one line changes before and after the fault phase grounding fast switch is operated, then the line can be determined to be the fault line; If the fault line is a cable line, keep the fault phase grounding fast switch in the closed state; If the fault line is not a cable line, then immediately after the fault phase grounding fast switch is closed, the microcomputer integrated controller sequentially controls the fault phase front fast switch to be disconnected, the fault phase grounding fast switch to be disconnected, and the fault phase front fast switch to be closed; then the microcomputer integrated controller determines whether the fault has disappeared. If the fault still exists, the fault phase grounding fast switch is controlled to be closed again.

2. The active intervention arc extinguishing method using dual fast switches according to claim 1, characterized in that: The grounding fast switch is an ultra-fast switch that can complete the closing action within 3 milliseconds at the fastest.

3. The active intervention arc extinguishing method using dual fast switches according to claim 1, characterized in that: The first contact spacing ranges from 5 to 25 mm, and the second contact spacing ranges from 2.5 to 5 mm.

4. The active intervention arc extinguishing method using dual fast switches according to claim 1, characterized in that: In step 1, the specific implementation method of determining whether a single-phase grounding fault occurs in the distribution network is: real-time online monitoring of the open triangle voltage on the secondary side of the voltage transformer by the microcomputer integrated controller; if the open triangle voltage exceeds a preset voltage threshold, it is determined that a single-phase grounding fault occurs.

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