A fast arc extinguishing method for fast switching parallel solid-state switches

Abstract

The present invention belongs to the field of electric power technology, and discloses a fast arc extinguishing method of a fast switch in parallel with a solid-state switch. The present invention utilizes the fast action of the solid-state switch to quickly eliminate arc grounding faults, and at the same time, the fast switch is connected in parallel, which reduces the time for the solid-state switch to be put into operation, avoids heat loss, and does not require the installation of a cooling system, which is of great significance for quickly extinguishing the grounding arc, reducing the cost of arc extinguishing devices, and improving the reliability of arc extinguishing technology.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and more specifically, relates to a fast arc extinguishing method for a fast switch in parallel with a solid-state switch. Background Art

[0002] The use of solid-insulated cross-linked polyethylene cables in distribution networks is increasing, but it brings about the problem of solid insulation being irreversible single-phase grounding fault handling. After a single-phase grounding occurs in the system, the steady-state current flowing through the grounding point is the system-to-ground capacitance current. The high-frequency current amplitude and duration in the grounding arc of the cable grid are greatly increased compared to overhead lines. Therefore, the arc-grounding overvoltage occurring in the non-fault phase may exceed 4 times the phase voltage, seriously threatening the cable insulation. Therefore, it is of great significance to quickly and accurately select the fault line and extinguish the grounding arc as soon as possible to prevent cable insulation damage and fault expansion.

[0003] With the substantial increase in the capacitive current of the line to the ground in the system, the application of the traditional current-type arc extinguishing method represented by the arc extinguishing coil is limited. The test results of the operation status of the arc extinguishing coils in 13 power stations show that the indirect method of measuring the system current value has a large error, the residual current is large after compensation, the resistive component and high-frequency component in the grounding current cannot be compensated, and the saturation of the arc extinguishing coil causes the neutral point current distortion. A series of problems, such as the actual arc extinguishing effect of the arc extinguishing coil is very poor. In addition, the arc extinguishing coil will also affect the accuracy of line selection. The test shows that the actual line selection accuracy is less than 50%. 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 the distribution system 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 technical issue in the research of the active intervention arc extinguishing method.

[0004] Solid-state switches utilize the speed of power electronic switches, so they switch faster (microseconds) than mechanical switches, and are silent and arc-free. In addition, since there is no arcing and contact wear during disconnection, the service life is longer. However, when the current in the closed state is conducted through the power electronic switch, there is a certain voltage drop on the switch, which will cause large heat loss, and a cooling device needs to be installed for long-term operation. Solid-state switches that pass large currents for a long time are expensive and are not suitable for distribution networks. How to balance the speed and cost of active arc extinguishing devices is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The present invention solves the problem that the prior art cannot take into account both the speed and cost of active arc extinguishing at the same time by providing a fast arc extinguishing method of a fast switch in parallel with a solid-state switch.

[0006] The present invention provides a fast arc extinguishing method for a fast switch connected in parallel with a solid-state switch, wherein the fast switch is connected in parallel with the solid-state switch; whether a single-phase grounding fault occurs in the power supply system is determined; if a single-phase grounding fault occurs, the fault phase is selected according to the three-phase voltage, and the solid-state switch of the bus fault phase is controlled to close by a microcomputer integrated controller;

[0007] The fault line is selected according to the zero-sequence current; if the fault line is a cable line, the bus fault phase fast switch is controlled to close and the bus fault phase solid-state switch is controlled to open in sequence through the microcomputer integrated controller; if the fault line is not a cable line, the bus fault phase solid-state switch is controlled to open by the microcomputer integrated controller immediately after the bus fault phase solid-state switch is closed, and it is judged whether the fault disappears; if the fault does not disappear, the bus fault phase solid-state switch is controlled to close again, the bus fault phase fast switch is controlled to close, and the bus fault phase solid-state switch is controlled to open again in sequence through the microcomputer integrated controller.

[0008] Preferably, the power electronic device of the solid-state switch uses a plurality of thyristors connected in series, and the solid-state switch completes closing within 1 ms; the fast switch completes closing within 7 ms and completes opening within 3 ms.

[0009] Preferably, the specific implementation method of determining whether a single-phase grounding fault occurs in the power supply system 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.

[0010] Preferably, the specific implementation method of selecting the fault phase according to the three-phase voltage is: monitor 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.

[0011] Preferably, 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 solid-state switch of the bus fault phase 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 solid-state switch of the bus fault phase is actuated, then the line can be judged as a fault line.

[0012] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0013] The present invention utilizes the fast action of the solid-state switch to quickly eliminate arc grounding faults. At the same time, the fast switch is connected in parallel to reduce the time it takes for the solid-state switch to be put into operation, avoid heat loss and do not require the installation of a cooling system. It is of great significance and practicality for quickly extinguishing the grounding arc, reducing the cost of arc extinguishing devices and improving the reliability of arc extinguishing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A primary system wiring diagram of a device used in a fast arc extinguishing method for a fast switch parallel solid-state switch provided in an embodiment of the present invention;

[0015] Figure 2 A schematic flow chart of a fast arc extinguishing method for a fast switch in parallel with a solid-state switch provided in an embodiment of the present invention;

[0016] Figure 3 Schematic diagram of the process of selecting phase for fault;

[0017] Figure 4 Schematic diagram of the process of selecting the line for the fault;

[0018] Figure 5 It is a structural diagram of a fast switch;

[0019] Figure 6 Topological diagram of fast switching parallel solid-state switches.

[0020] Among them, 101-pre-circuit breaker, 102-current transformer, 103-PT high-voltage fuse, 104-voltage transformer, 105-primary harmonic elimination device, 106-fast switch, 107-solid-state switch, 108-zero-sequence current transformer, 109-microcomputer integrated controller;

[0021] 501- vacuum interrupter, 502- static conductive rod, 503- static contact, 504- moving contact, 505- moving conductive rod, 506- insulating pull rod, 507- opening holding magnet, 508- opening coil, 509- electromagnet armature, 510- closing coil, 511- closing holding magnet, 512- opening control, 513- opening energy storage capacitor, 514- closing control, 515- closing energy storage capacitor, 516- charging power supply. DETAILED DESCRIPTION

[0022] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0023] The present embodiment provides a fast arc extinguishing method for a fast switch connected in parallel with a solid-state switch. The fast switch is connected in parallel with the solid-state switch. First, it is determined whether a single-phase grounding fault occurs in the power supply system. If a single-phase grounding fault occurs, the fault phase is selected according to the three-phase voltage, and the bus fault phase solid-state switch is controlled to close by a microcomputer integrated controller. Then, the fault line is selected according to the zero-sequence current. If the fault line is a cable line, the bus fault phase fast switch is controlled to close and the bus fault phase solid-state switch is controlled to open in sequence by the microcomputer integrated controller. If the fault line is not a cable line, the bus fault phase solid-state switch is controlled to open by the microcomputer integrated controller immediately after the bus fault phase solid-state switch is closed, and it is determined whether the fault disappears. If the fault does not disappear, the bus fault phase solid-state switch is controlled to close again, the bus fault phase fast switch is controlled to close, and the bus fault phase solid-state switch is controlled to open again by the microcomputer integrated controller in sequence.

[0024] Among them, the power electronic device of the solid-state switch adopts multiple thyristors connected in series, and the solid-state switch completes closing within 1ms; the fast switch completes closing within 7ms and completes opening within 3ms.

[0025] The primary system wiring diagram of the device used in the above method can be found in Figure 1 For the specific method flow, see Figure 2 , including the following steps:

[0026] Step 1: Monitor the voltage waveform of the secondary side triangle interface of the voltage transformer (PT) 104 in real time online through the microcomputer integrated controller (ZK) 109. If the voltage is normal, keep monitoring. If the open voltage exceeds the limit, it means a single-phase grounding fault occurs, and go to step 2. If other faults are found, a fault alarm signal is issued.

[0027] That is, the microcomputer integrated controller 109 monitors the open triangle voltage on the secondary side of the voltage transformer in real time online. If the open triangle voltage exceeds a preset voltage threshold, it is determined that a single-phase grounding fault occurs.

[0028] The system fault state is determined by monitoring the secondary side triangle open voltage of the voltage transformer 104. When the system is operating normally, the system operating voltage, the open triangle voltage and the arc extinguishing device operating state are displayed. When the open triangle voltage ΔU changes from a low level to a high level, it indicates that a system fault occurs, and the microcomputer integrated controller 109 immediately starts an interrupt and enters the fault type determination and line zero sequence current data acquisition program.

[0029] Specifically, the microcomputer integrated controller 109 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, that is, the system is judged to have a single-phase grounding fault, and the program is started to determine the type of fault; if the voltage rise does not exceed the threshold, monitoring continues.

[0030] Step 2: The microcomputer integrated controller 109 starts to run the fault phase selection program. For the flow chart of the fault phase selection program, see Figure 3 , select the fault phase according to the three-phase fault voltage.

[0031] The microcomputer integrated controller 109 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 .

[0032] 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.

[0033] The three-phase voltage output by the voltage transformer is monitored by the microcomputer integrated controller 109. 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 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 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 amplitudes, 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.

[0034] The following is a detailed description of different fault phase selection schemes.

[0035] a. Metallic grounding fault.

[0036] When a single-phase metallic grounding fault occurs in a neutral point ungrounded system, the voltage of the fault phase is close to 0, and the voltage of the non-fault phase is close to the line voltage. Based on this, it can be judged that the phase with a voltage close to 0 is the fault phase. Taking the 10kV distribution system as an example, the three-phase voltage threshold is set as follows: if the voltage of one phase is less than 1kV, and the voltages of the other two phases are greater than 9kV, it is considered that a single-phase metallic grounding fault has occurred, and the phase with a voltage less than 1kV is judged to be the fault phase. Because the three-phase voltage changes significantly when a metallic fault occurs, if the fault phase selection speed needs to be increased, the transient process voltage signal can be used for judgment to shorten the phase selection time.

[0037] b. Small resistance grounding fault.

[0038] The critical situation of a small resistance ground fault is defined as the voltage of the fault phase rising to the same amplitude as the voltage of a non-fault phase. When a small resistance ground fault occurs, the voltage of the fault phase has the smallest amplitude among the three-phase voltages, and the phase with the smallest amplitude among the three-phase voltages can be judged as the fault phase. For a 10kV distribution system, in the critical situation of a small resistance ground fault, the voltage of the fault phase and the subsequent phase are both 5kV, and the voltage of the phase before the fault phase is 8.66kV. Considering the three-phase imbalance in the actual system, 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 before it is greater than 8kV, the phase with a voltage less than 4kV is judged to be the fault phase.

[0039] c. High resistance ground fault.

[0040] When the grounding transition resistance is large, the fault phase voltage will no longer be the smallest of the three-phase voltages, but the phase before the fault phase has always been the phase with the largest voltage amplitude among the three phases during the transition resistance change process. Based on this, the phase after the phase with the largest amplitude can be judged as the fault phase. For a 10kV distribution system, when the three-phase voltages are all greater than 4kV, first compare and select the phase with the largest voltage amplitude, and then judge the phase after it as the fault phase.

[0041] Step 3, the microcomputer integrated controller 109 executes the action program of the fast switch (JD) 106 parallel solid-state switch (SS) 107 according to the fault phase, and sends an action signal to the solid-state switch of the bus fault phase. The solid-state switch of the bus fault phase completes conduction within microseconds, conducts the fault current into the earth, and directly grounds the fault phase, extinguishes the grounding arc, and limits the arc grounding overvoltage to the level of the line voltage, thereby controlling the development of the fault.

[0042] Specifically, the hybrid switch in which the solid-state switch 107 and the fast switch 106 are connected in parallel can be turned on quickly and has a simple structure. The power electronic device of the solid-state switch 107 is turned on only during the short process of power switching. When working in a steady state, the power electronic device of the solid-state switch 107 is in an off state with almost no loss, so the hybrid solid-state switch can be cooled naturally without the need for additional bulky cooling devices. The power electronic device of the solid-state switch 107 is connected in series with a thyristor, and its topological structure with the fast switch 106 is shown in the figure below. Figure 6 As shown, Tn1-Tnn and Tp1-Tpn in the figure represent n thyristors connected in series in two directions respectively.

[0043] 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 according to the zero-sequence current is: before the solid-state switch of the bus fault phase 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 solid-state switch of the bus fault phase is actuated, then it can be determined that the line is a fault line.

[0044] Specifically, start the fault line selection program. The fault line selection program flow chart is shown in Figure 4 , select the fault line according to the zero-sequence current (i.e., zero-sequence current recording) measured by the current transformer (recorded as current recorder) installed at the head end of each feeder line, and judge whether the fault line is a cable line. If it is a cable line, the microcomputer integrated controller 109 controls the bus fault phase fast switch to close and the bus fault phase solid-state switch to open in sequence; that is, the fast switch 106 is closed, and the solid-state switch 107 is opened after the fast switch 106 is closed. If the fault line is not a cable line (i.e., an overhead line), execute step 5.

[0045] Among them, after a ground fault occurs in the cable line, the insulation cannot be restored, and it is necessary to maintain the grounding state to transfer all the arc current at the line fault point to the metallic grounding phase of the busbar. At the same time, it is necessary to close the fast switch 106 to bear the steady-state current and disconnect the solid-state switch 107 to avoid excessive heating of the solid-state switch. After a ground fault occurs in the overhead line, due to the insulation recovery of the air, reclosing is required to restore possible transient faults.

[0046] Specifically, the basis for fault line selection is the change characteristics of the zero-sequence current of each feeding line in the distribution network during the single-phase grounding fault process, 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 solid-state switch 107 is closed.

[0047] a. Zero-sequence current characteristics before fast switch closing.

[0048] 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 branch lines, 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 overhead lines is relatively small; the zero-sequence current of cable lines is larger than that of overhead lines, but still smaller than that of fault lines.

[0049] b. Zero-sequence current characteristics after fast switch closing.

[0050] When the solid-state switch 107 is actuated, the zero-sequence current of the faulty feeder has an obvious phase reversal process, and the change in amplitude before the switch is actuated is not obvious; while the direction and magnitude of the zero-sequence current of the non-fault line do not change, and only a short and small oscillation process occurs. After the solid-state switch 107 is actuated, the zero-sequence current directions of the faulty line and the non-faulty line are no longer opposite, but become a certain angle difference.

[0051] Step 5: The microcomputer integrated controller 109 sends a disconnection signal to the solid-state switch 107 a first time (eg, 5 seconds) after sending the solid-state switch conduction signal, and the solid-state switch 107 is disconnected.

[0052] Specifically, 5 seconds after the solid-state switch 107 is closed, the grounding body of the instantaneous grounding fault is burned out under the action of the grounding current. At this time, the system returns to normal after the solid-state switch 107 is disconnected; a permanent grounding fault cannot be restored to normal in this way.

[0053] Step 6: The microcomputer integrated controller 109 determines again whether the fault signal disappears. If the fault disappears, the microcomputer integrated controller 109 goes to step 1 for standby; if the fault is still found, the bus fault phase solid-state switch is controlled to close again, and then the bus fault phase fast switch is controlled to close, and the bus fault phase solid-state switch is controlled to open again.

[0054] Specifically, after the solid-state switch 107 is opened, if the microcomputer integrated controller 109 determines that the fault disappears, it means that the grounding fault is a transient fault, and the system resumes normal operation; if the microcomputer integrated controller 109 determines that the fault has not disappeared, it means that the grounding fault is a permanent fault and it is necessary to reclose the switch to connect the arc current to the ground through the busbar.

[0055] The present invention realizes the transfer of fault current in microseconds through the cooperation of a fast switch and a solid-state switch, and can control the equipment cost to make it economical for the distribution network. It is of great significance for quickly eliminating single-phase grounding arcs, suppressing arc-grounding overvoltage, and improving the level of safe operation.

[0056] The fast switch 106 is an improved fast switch based on an electromagnetic repulsion mechanism, which can achieve closing within 7ms and opening within 3ms, with a breaking current of 40kA, and can meet the requirements of fast closing and opening and quickly disconnecting short-circuit current.

[0057] The action logic of the solid-state switch 107 and the fast switch 106 in parallel is that after the fault phase is determined, the solid-state switch 107 is turned on within 1ms, and then the fault line is determined. If the fault line is determined to be a cable line, the fast switch 106 is closed, and the solid-state switch 107 is disconnected after the fast switch 106 is closed; if the fault line is determined not to be a cable line, the solid-state switch 107 is disconnected 5s after being turned on; then it is determined 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 solid-state switch 107 is turned on, the fast switch 106 is closed, and the solid-state switch 107 is disconnected again after the fast switch 106 is closed.

[0058] 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 circuit breaker (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 fast switch (JD) 106, a solid-state switch (SS) 107, a zero-sequence current transformer (TZ) 108, and a microcomputer integrated controller (ZK) 109. Among them, 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 108 reads the grounding capacitance current of the system. During the closing of the fault phase of the device, if a grounding fault occurs again when the device is not faulty, the zero-sequence CT secondary provides a current mutation for the microcomputer integrated controller 109 to sample. The microcomputer integrated controller 109 issues a tripping command, and the circuit breaker is closed and the phase is opened.

[0059] The improved fast switch used in the present invention is a new type of fast operating mechanism based on the eddy current principle. Figure 5 The fast switch includes 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.

[0060] The operating mechanism of the moving contact 504 in the vacuum interrupter 501 is driven by an electromagnetic repulsion mechanism. The working principle of the electromagnetic repulsion mechanism: when the switch receives a closing (or opening) command, a pulse current lasting for several milliseconds is generated in the opening coil 508 (or closing coil 510), and the excitation coil generates an alternating magnetic field under the action of this pulse current. At the same time, the electromagnetic armature 509 generates electromagnetic force due to the eddy current induced. The electromagnetic armature 509 moves rapidly under the action of the Lorentz repulsion force, and drives the moving contact 504 of the vacuum interrupter 501 to move through the insulating pull rod 506, thereby realizing the rapid opening and closing of the fast switch branch.

[0061] The fast switch 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.

[0062] A fast arc extinguishing method for a fast switch parallel to a solid-state switch provided by an embodiment of the present invention includes at least the following technical effects:

[0063] (1) The present invention uses a solid-state switch in the arc extinguishing system. Since the conduction time of the solid-state switch is in the microsecond level, the fault current can be quickly connected to the ground from the busbar, and it has good speed. By connecting the fast switch in parallel with the solid-state switch, the entire arc extinguishing system can have excellent speed performance, so that the arc grounding fault can be eliminated at a very fast speed and the arc grounding overvoltage can be suppressed. At the same time, since the solid-state switch is connected in parallel with the fast switch, after the solid-state switch is closed, the fast switch that closes the switch bears the steady-state current, and the solid-state switch only operates in a short time after the breaking action, which can reduce the time the solid-state switch is put into operation and avoid the solid-state switch from generating large heat loss. Therefore, there is no need to install a cooling system, which can greatly reduce the cost and volume of the arc extinguishing system, thereby reducing the difficulty of inspection and maintenance. Therefore, the system has the beneficial effects of relatively small volume, low cost, and easier inspection and maintenance.

[0064] (2) The method provided by the present invention adopts an active intervention arc extinguishing method, which is applicable to systems with any capacitive current, and has a good beneficial effect on distribution networks with large capacitive currents and a large number of cable lines. The method is applicable to distribution networks with different capacitive currents of the same voltage level, and does not require different arc extinguishing coil capacities to be designed according to different systems, as in the arc extinguishing method of arc extinguishing coils.

[0065] (3) The method provided by the present invention takes into account the three-phase voltage characteristics under fault conditions, so that the fault types and phases such as single-phase grounding and line disconnection can be accurately judged. In particular, the three-phase voltage characteristics under different grounding transition resistances are taken into account, and the fault phase is selected in combination with the zero-sequence voltage in the case of high-resistance grounding, so that the judgment accuracy of high-resistance grounding faults can be effectively improved.

[0066] (4) The method provided by the present invention determines the faulty line by combining the changing characteristics of the zero-sequence current of each feeder line during a single-phase grounding fault in the distribution network with the difference in direction and amplitude between the zero-sequence current of the faulty line and the zero-sequence current of the non-faulty line before and after the solid-state switch is closed. The faulty line can be effectively determined, so that different action strategies can be adopted for cables and overhead lines.

[0067] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A fast arc extinguishing method for fast switching parallel solid-state switches, characterized in that: Connect the fast switch and the solid-state switch in parallel; determine whether a single-phase grounding fault occurs in the power supply system; if a single-phase grounding fault occurs, select the fault phase according to the three-phase voltage, and control the solid-state switch of the bus fault phase to close through the microcomputer integrated controller; The fault line is selected according to the zero-sequence current; if the fault line is a cable line, the bus fault phase fast switch is controlled to close and the bus fault phase solid-state switch is controlled to open in sequence by the microcomputer integrated controller; if the fault line is not a cable line, the bus fault phase solid-state switch is controlled to open by the microcomputer integrated controller immediately after the bus fault phase solid-state switch is closed, and it is judged whether the fault disappears; if the fault does not disappear, the bus fault phase solid-state switch is controlled to close again, the bus fault phase fast switch is controlled to close, and the bus fault phase solid-state switch is controlled to open again by the microcomputer integrated controller in sequence; The specific implementation method of selecting the fault phase according to the three-phase voltage is: 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 grounding fault, and the phase with the voltage close to 0 is determined to be the fault phase; If one phase has the largest voltage amplitude and the other two phases have similar voltage amplitudes, 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 voltage amplitudes of the three phases are all greater than the preset voltage amplitudes, 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; 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 according to the zero-sequence current is: before the solid-state switch of the bus fault phase 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 solid-state switch of the bus fault phase is actuated, then it can be determined that the line is a fault line.

2. The fast arc extinguishing method of a fast switch in parallel with a solid-state switch according to claim 1, characterized in that: The power electronic device of the solid-state switch uses a plurality of thyristors connected in series, and the solid-state switch completes closing within 1 ms; the fast switch completes closing within 7 ms and opens within 3 ms.

3. The fast arc extinguishing method of a fast switch in parallel with a solid-state switch according to claim 1, characterized in that: The specific implementation method of determining whether a single-phase grounding fault occurs in the power supply system is: the open triangle voltage on the secondary side of the voltage transformer is monitored online in real time 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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