Single-phase earth fault phase selection result correctness checking method for active intervention type arc extinguishing device in resonant grounding power distribution network

Abstract

The invention relates to a single-phase earth fault phase selection result correctness verification method for an active intervention type arc extinguishing device in a resonant grounding power distribution network, and the method comprises the steps: firstly discussing a model structure of the active intervention type arc extinguishing device, and giving a parameter selection basis of a resistor based on the size of a transient current at the switching-on moment of the device and the thermal power of an intermediate resistor; and then providing a single-phase earth fault phase selection result correctness verification method based on a three-phase voltage amplitude and zero-sequence voltage phase change relation during an intermediate resistor input period. According to the invention, a large transient current value at the moment of switching action of the active intervention type arc suppression device can be effectively suppressed, the influence of short-circuit current impact caused by wrong phase selection on a system is reduced, and the fault-tolerant error correction capability of the device on a fault phase selection result can be improved; the method has effectiveness and sensitivity under the fault conditions of different transition resistances, fault moments, fault positions, arc suppression coil detuning degrees and fault phases.

Description

Technical Field

[0001] The present invention belongs to the technical field of single-phase grounding fault phase selection in distribution networks, and specifically relates to a method for verifying the correctness of single-phase grounding fault phase selection results of an active intervention type arc suppression device in a resonant grounding distribution network. Background Technique

[0002] In recent years, the State Grid's requirements for dealing with single-phase grounding faults in distribution networks have changed from "continuous operation for 2 hours" to "instantaneous fault safety arc suppression and permanent fault rapid isolation". Therefore, various arc suppression devices and technologies have been widely used. The DL / T 2609—2023 "Acceptance and Operation and Maintenance Specification for Active Intervention Type Arc Suppression Devices" issued by the National Energy Administration and the State Grid Enterprise Standard Q / GDW 11924—2018 "Technical Specification for Active Intervention Type Arc Suppression Devices" both point out that the active intervention type arc suppression device transfers the grounding fault point current to the active grounding point of the fault phase circuit breaker at the bus, converts the single-phase grounding fault into a metallic grounding fault inside the device, limits the fault point voltage, effectively extinguishes the grounding arc, and reduces the harm of single-phase grounding faults to personnel and equipment. At present, in resonant grounding distribution networks, active intervention type arc suppression devices are gradually being promoted and applied due to their advantages such as simple equipment structure, low cost, and significant fault arc suppression effect.

[0003] The premise for the operation of the active intervention type arc suppression device is the accurate identification of the fault phase. Once the phase selection is incorrect and the single-phase grounding fault develops into a two-point grounding fault of different phases, it will cause a large short-circuit current impact on the system, which is not conducive to the safe and stable operation of the system. At this time, it is necessary to correct the incorrect phase selection result and then put the device into operation to achieve fault arc suppression. At present, after single-phase grounding fault phase selection is completed in a resonant grounding distribution network, there is little research on the method for verifying the correctness of the phase selection result.

[0004] Therefore, it is crucial to study the method for verifying the correctness of single-phase grounding fault phase selection results of active intervention type arc suppression devices. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for verifying the correctness of single-phase grounding fault phase selection results of an active intervention type arc suppression device in a resonant grounding distribution network. First, the model structure of the active intervention type arc suppression device will be elaborated in detail, and the basis for parameter selection of the resistor will be given based on the magnitude of the transient current at the moment of device closing and the thermal power of the intermediate resistor. Then, to avoid misoperation of the device, a method for verifying the correctness of single-phase grounding fault phase selection results based on the relationship between the magnitudes of three-phase voltages and the phase change of the zero-sequence voltage during the input of the intermediate resistor will be proposed. The verification and correction of the correctness of the fault phase selection result of the present invention have high reliability and sensitivity, ensuring that the active intervention type arc suppression device can operate correctly.

[0006] The technical problem solved by the present invention is achieved through the following technical solutions:

[0007] A method for verifying the correctness of the single-phase grounding fault phase selection result of an active intervention type arc suppression device in a resonant grounded distribution network. The steps of the method are as follows:

[0008] S1. Build a model of the active intervention type arc suppression device in the resonant grounded distribution network, and select the parameters of the intermediate resistor from two aspects: the transient current value at the moment of switch closing and the thermal power of the intermediate resistor.

[0009] S2. After completing the single-phase grounding fault phase selection, collect the data of the zero-sequence voltage and the three-phase voltage before and after the fault and after the intermediate resistor is inserted. Analyze the phases of the three-phase voltages before the fault as the phases of the three-phase power supply voltages.

[0010] S3. If the minimum phase voltage amplitude before the intermediate resistor is inserted after the fault is higher than 0.7 times the rated phase voltage amplitude, verify the correctness of the fault phase selection result based on the phase change characteristics between the zero-sequence voltage and the three-phase power supply voltages after the fault and after the intermediate resistor is inserted. If the phase difference between the zero-sequence voltage and the power supply voltage of the phase corresponding to the fault phase selection result is the largest in these two stages, the phase selection result can be considered correct; otherwise, the phase selection result is incorrect.

[0011] If the minimum phase voltage amplitude before the intermediate resistor is inserted after the fault is lower than 0.7 times the rated phase voltage amplitude, verify based on the amplitude size characteristics of the three-phase voltages before the intermediate resistor is inserted after the fault. If the phase with the minimum phase voltage amplitude is consistent with the fault phase selection result, the phase selection result is correct; otherwise, the phase selection result is incorrect.

[0012] S4. After verifying the correctness of the single-phase grounding fault phase selection result, if the phase selection is correct, bypass the intermediate resistor, directly ground the switch of the fault phase, and the active intervention type arc suppression device realizes safe arc suppression for instantaneous faults and rapid isolation for permanent faults; if the phase selection is incorrect, immediately disconnect the intermediate resistor, correct the phase selection result, and then insert the device again.

[0013] Moreover, the active intervention type arc suppression device is composed of a microcomputer controller, a grounding element, and a grounding switch. The grounding switch includes a phase-separated grounding switch S1, a grounding switch S2, and an intermediate resistor R inter , the grounding switch S2 and the intermediate resistor R inter are connected in parallel and then connected in series with the phase-separated grounding switch S1. The microcomputer controller is used to determine the type and fault phase of the single-phase grounding fault, control the closing of the phase-separated switch of the fault phase, clamp the voltage at the fault point, and transfer the fault point current to the active grounding point of the phase-separated switch; the intermediate resistor R inter has a value of 120 Ω.

[0014] The positive effects that the present invention can produce are:

[0015] 1. The basis for selecting the intermediate resistance parameter of the active intervention type arc suppression device proposed by the present invention can effectively suppress the large transient current value at the moment of the device switch action and reduce the adverse effect of the faulty phase selection error on the resistance thermal power.

[0016] 2. The method for verifying the correctness of the single-phase grounding fault phase selection result proposed by the present invention is effective under different fault conditions, improving the fault tolerance and error correction ability of the active intervention type arc suppression device for the fault phase selection result.

[0017] 3. The technical solution of the present invention is simple and feasible, laying a foundation for the safe and reliable operation of the active intervention type arc suppression device. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the structure diagram of the resonant grounding distribution network including the active intervention type arc suppression device of the present invention;

[0019] Figure 2 is the equivalent circuit diagram of the fault transient after the single-phase grounding switch S1 is closed in the present invention;

[0020] Figure 3 is the simulation model diagram of the 10kV resonant grounding distribution network of the present invention;

[0021] Figure 4 is the relationship diagram between the transient current at the moment of switch closing and the intermediate resistance value in the present invention;

[0022] Figure 5 is the relationship diagram between the thermal power of the intermediate resistance and the resistance value in the present invention;

[0023] Figure 6 is the zero-sequence equivalent circuit diagram of the system before the intermediate resistance is put into operation after the fault in the present invention;

[0024] Figure 7 is the zero-sequence equivalent circuit diagram of the system under the correct fault phase selection situation after the intermediate resistance is put into operation in the present invention;

[0025] Figure 8 is the zero-sequence equivalent circuit diagram of the system under the incorrect fault phase selection situation after the intermediate resistance is put into operation in the present invention;

[0026] Figure 9 is the phase relationship diagram between the zero-sequence voltage and the three-phase power supply voltage before the intermediate resistance is put into operation after the fault in the present invention;

[0027] Figure 10 is the phase relationship diagram between the zero-sequence voltage and the three-phase power supply voltage under the correct fault phase selection situation after the intermediate resistance is put into operation in the present invention;

[0028] Figure 11 is the phase relationship diagram between the zero-sequence voltage and the three-phase power supply voltage under the incorrect fault phase selection situation after the intermediate resistance is put into operation in the present invention;

[0029] Figure 12 It is a diagram of the amplitude and phase relationship between the three-phase voltages before the intermediate resistor is inserted after a fault in the present invention.

[0030] Figure 13 It is a flow chart for verifying the correctness of the fault phase selection result of the present invention. Specific embodiments

[0031] The present invention will be further described in detail below through specific embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0032] As Figure 13 shown, a method for verifying the correctness of the single-phase grounding fault phase selection result of an active intervention type arc suppression device in a resonant grounded distribution network is characterized in that the steps of the method are as follows:

[0033] (1) Model of the active intervention type arc suppression device and parameter selection of the intermediate resistor

[0034] 1. Model of the active intervention type arc suppression device

[0035] After the single-phase grounding fault phase selection is completed in the resonant grounded distribution network, the active intervention type arc suppression device should be able to act reliably. The device is connected to the bus and mainly consists of a microcomputer controller, a grounding element, and a grounding switch device. If a single-phase grounding fault occurs in the system, the microcomputer controller discriminates the fault type and the fault phase, and controls the closing of the phase-separated switch of the fault phase, clamps the voltage at the fault point, and transfers the fault point current to the active grounding point of the phase-separated switch, effectively realizing fault arc suppression. The device structure is as Figure 1 shown.

[0036] In Figure 1 , L p is the inductance of the arc suppression coil, e A , e B and e C are the instantaneous values of the power supply voltages of phase A, phase B, and phase C respectively, u A , u B and u C are the instantaneous values of the voltages of phase A, phase B, and phase C at the bus respectively, and u0 is the instantaneous value of the zero-sequence voltage. i A , i B and i C are the instantaneous values of the currents of phase A, phase B, and phase C of the bus outgoing line respectively, and i0 is the instantaneous value of the zero-sequence current. C iA , C iB and C iC (i = 1, 2,..., n) are the capacitances to the ground of phase A, phase B, and phase C of the i-th line respectively, and R fis the transition resistance at the fault point. The earthing switch in the active intervention type arc suppression device adopts a soft-switching mode, which consists of a phase-separated earthing switch S1, an earthing switch S2, and an intermediate resistor R inter constitute.

[0037] After detecting the faulty phase, first close the phase-separated earthing switch S1 of the faulty phase, and ground through the intermediate resistor R inter ; after verifying the correctness of the faulty phase selection result, then close the earthing switch S2 to bypass the intermediate resistor and transfer the fault point current to the metallic grounding point at the earthing switch. When disconnecting the earthing switch, first disconnect the switch S2 to transition the metallic grounding to grounding through the intermediate resistor R inter ; then disconnect the switch S1 to withdraw the entire device from operation.

[0038] This soft-switching mode can effectively suppress the large transient current value at the moment of the device switch action. According to this mode, it is also possible to perform fault tolerance and error correction on the faulty phase selection result.

[0039] 2. Parameter selection of the intermediate resistor

[0040] To determine the parameters of the intermediate resistor R inter , it is necessary to consider the magnitude of the transient current at the moment of the device switch closing and the influence of the faulty phase selection error on the thermal power of the resistor.

[0041] 2.1 Relationship between the intermediate resistor parameters and the magnitude of the transient current at the device switch closing

[0042] In a resonant grounded distribution network, if a single-phase grounding fault occurs and the corresponding phase-separated switch of the faulty phase is directly closed, a relatively severe transient process will occur. The larger the transition resistance at the fault point, the larger the transient current value generated at the moment of the phase-separated switch closing, and the more serious the adverse impact on the system. Therefore, when selecting the parameters of the intermediate resistor, considering the extreme case, assuming that the single-phase grounding resistance value is infinite, the fault transient equivalent circuit after the phase-separated earthing switch S1 is closed is as Figure 2 shown.

[0043] In Figure 2 , the virtual power supply u f =-U m sin(ωt + θ), where U m , θ are respectively the amplitude of the power supply phase potential and the initial phase after closing, ω is the power frequency angular frequency, L is the sum of twice the line-mode loop inductance and the zero-mode inductance from the fault point to the bus, R' is the sum of twice the line-mode loop resistance, the zero-mode resistance from the fault point to the bus, and three times the device intermediate resistor, C0 is the system-to-ground capacitance, and L' is three times the arc suppression coil inductance.

[0044] When the switch S1 is closed, the inductive current flowing through the arc suppression coil does not change suddenly. Therefore, the transient current of the switch is mainly composed of capacitive current, and its expression is as shown in Equation (1).

[0045]

[0046] Z=R′+j[ωL-1 / (ωC0)] (2)

[0047]

[0048] δ=R′ / (2L) (4)

[0049] In the formula, Z is the impedance of the fault equivalent circuit, ω f is the main resonance frequency of the transient process, and δ is the attenuation factor.

[0050] It can be seen from the above formula that the transient current of the switch is composed of a transient attenuation component and a steady-state power frequency component. When θ=π / 2, the value of the attenuation component is the largest at the moment when the switch S1 is closed, and the amplitude ratio of it to the power frequency component is about ω f / ω. The larger the value of the intermediate resistance, the smaller the value of ω f , and the smaller the value of the transient current. Similarly, after the switch S2 is closed,

[0051] the value of the transient current increases with the increase of the intermediate resistance value.

[0052] Enterprise Standard Q / GDW 10738—2020 "Technical Guidelines for Distribution Network Planning and Design" of State Grid Corporation of China

[0053] It is pointed out that the capacitive current to the ground in a 10 kV resonant grounding distribution network generally exceeds 10 A and is less than 100 - 150 A. Therefore, in the systems with the effective value of the capacitive current to the ground being 10 A and 150 A respectively, and Figure 3 (the effective value of the capacitive current is about 68 A, and the line parameters are shown in Table 1) in the simulation system, the values of the transient current at the moment when the phase-separated grounding switch S1 and the grounding switch S2 are closed under different intermediate resistance parameters are solved, as Figure 4 shown.

[0054] Table 1 Distribution Network Line Parameter Table

[0055]

[0056]

[0057] According to Figure 4It can be seen that in a system with an effective value of the capacitive current to the ground of 10 A, the transient process after S2 is closed is not significant, and the value of the transient current is relatively small. Through numerical calculation, the changing trend of the transient current at the moment when switches S1 and S2 are closed with respect to the intermediate resistance gradually slows down at around 120 Ω. In the range of 80 - 140 Ω, the values of the transient current after the two switches are closed are relatively small, which can be used as a reference for the selection of the intermediate resistance parameter. Combining with the existing research, the intermediate resistance can be taken as 120 Ω.

[0058] 2.2 Relationship between the Intermediate Resistance Parameter and the Resistance Thermal Power under the Condition of Fault Phase Selection Error

[0059] The selection of the intermediate resistance parameter should also take into account the heating power of the resistance under the condition of phase selection error. In Figure 3 the simulation system, considering the extreme case, a metallic ground fault of phase C occurs at the bus, and the grounding switch of phase A of the device is misclosed by mistake. Due to the existence of the intermediate resistance, the protection will not malfunction. The relationship between the thermal power of the intermediate resistance and the resistance value under the condition of phase selection error is as Figure 5 shown.

[0060] In Figure 5 it, the thermal power of the intermediate resistance decreases with the increase of the resistance value. When the resistance is less than 80 Ω, the power value is relatively large, and the trend of the power decreasing with the increase of the resistance is significant; when the resistance is greater than 80 Ω, the power value is relatively small, and the trend of the power decreasing with the increase of the resistance gradually slows down. The thermal power value of the resistance of 80 Ω is roughly reduced to 1 / 4 of the power value of the resistance of 20 Ω. Therefore, the resistance should be greater than 80 Ω, and the harm of wrong phase selection to the resistance thermal power is relatively small, which also verifies the rationality of taking the intermediate resistance value as 120 Ω.

[0061] (2) Method for Verifying the Correctness of the Single - Phase Ground Fault Phase Selection Result of the Active Intervention - Type Arc Suppression Device

[0062] After the single - phase ground fault phase selection is completed in the resonant grounding distribution network, it is necessary to verify the correctness of the fault phase selection result within a short time when the intermediate resistance is put into operation. If the phase selection is correct, bypass the intermediate resistance, and the grounding switch of the fault phase is directly grounded metallically, clamping the fault point voltage, transferring the fault point current, and completely extinguishing the arc. If the phase selection is wrong, the single - phase ground fault develops into a two - point grounding fault of different phases, and the device should be immediately withdrawn. Otherwise, the grounding switch is directly grounded, which will cause a large short - circuit current impact on the system and is not conducive to the safe and stable operation of the system. At this time, it is necessary to correct the wrong phase selection result, then close the grounding switch of the fault phase, and put the device into operation.

[0063] In a resonant grounded distribution network, assuming a single-phase ground fault occurs on phase C, according to the fault phase identification result, an intermediate resistance is inserted to verify the correctness of the fault phase selection result. The zero-sequence equivalent circuits of the system in three cases, namely, before the intermediate resistance is inserted after the fault, correct fault phase selection after the intermediate resistance is inserted, and incorrect fault phase selection (assuming the incorrect fault phase selection result is phase A) after the intermediate resistance is inserted, are as shown in Figures 6 to 8 shown below.

[0064] In Figures 6 to 8 , and are the voltage phasors at the fault point and the zero-sequence voltage phasor of the system before the intermediate resistance is inserted after the fault, respectively; and are the voltage phasors at the fault point and the zero-sequence voltage phasor of the system in the case of correct fault phase selection after the intermediate resistance is inserted, respectively; and are the voltage phasors at the fault point and the zero-sequence voltage phasor of the system in the case of incorrect fault phase selection after the intermediate resistance is inserted, respectively. and are the power voltage phasors of phase A and phase C, respectively. X f and X Σ-f are the zero-sequence equivalent capacitive reactances of the fault line and all lines except the fault line, respectively. L p is the inductance of the arc suppression coil. X L′ = 3ωL p is the equivalent inductive reactance of the arc suppression coil. 3R f and 3R inter are the equivalent transition resistance at the fault point and the equivalent intermediate resistance at the device, respectively. Z line is the zero-sequence equivalent impedance of the line between the fault point and the bus grounding point.

[0065] Considering that the value of Z line is much smaller than the system capacitance reactance X Σ , Z line can be ignored in the following analysis. According to Figures 6 to 8 , the expressions of the zero-sequence voltage phasors in the cases of before the intermediate resistance is inserted after a single-phase ground fault, correct fault phase selection after the intermediate resistance is inserted, and incorrect fault phase selection are derived, as shown in Equations (5) to (7) respectively.

[0066]

[0067] In the formula, α = e j(2π) / 3 , α 2 = e j(4π) / 3 .

[0068] 1. Phase relationship between the zero-sequence voltage and the three-phase power voltages before the intermediate resistance is inserted after a single-phase ground fault

[0069] In Equation (5), if the transition resistance value of the single-phase grounding fault is 0 Ω, that is, a metal grounding fault of phase C occurs in the system, the phase of the zero-sequence voltage is opposite to the phase of the power supply voltage of the faulty phase. As the transition resistance value increases, the phase difference between the two is no longer 180°. If the transition resistance value is infinite, the phase of the zero-sequence voltage lags behind the phase of the power supply voltage of the faulty phase by 90°. The phase relationship between the zero-sequence voltage and the three-phase power supply voltage is as Figure 9 shown. Figure 9 (a) is the end trajectory of the zero-sequence voltage phasor (the boundary of Region 1) in the case of a small transition resistance; Figure 9 (b) is the end trajectory of the zero-sequence voltage phasor (the boundary of Region 2) in the case of a large transition resistance.

[0070] In Figure 9 , is the power supply phase voltage phasor, is the phase voltage phasor.

[0072] Generally, resonant grounded distribution networks adopt an over-compensation operation mode. The following content only analyzes the case where the detuning degree υ of the arc suppression coil is negative. Similarly, it can also be used to deduce the case where the detuning degree is positive, and it will not be

[0073] described in detail here.

[0074] According to Figure 9 (a), it can be seen that when the transition resistance value is small, that is, the zero-sequence voltage phasor is between the phasor and the phasor . As the transition resistance value increases, the end of the phasor moves counterclockwise along the boundary of Region 1 (shown by the blue dotted line in the figure), the amplitude of the zero-sequence voltage decreases, and the phasor is always between the phasor and the phasor , that is, the phase difference between the zero-sequence voltage and the power supply voltage of the faulty phase is the largest.

[0076] According to Figure 9 (b), it can be seen that when the transition resistance value is large, that is, as the transition resistance value increases, the end of the phasor moves counterclockwise along the boundary of Region 2 (shown by the green dotted line in the figure), the amplitude of the zero-sequence voltage decreases, is between and . When the transition resistance value is infinite, the amplitude of the zero-sequence voltage tends to 0, the phase lags behind the phase by 90°. According to the theoretical analysis of single-phase high-resistance over-damped grounding faults, there is:

[0077]

[0078] Among them,

[0079] N = -U m / [|Z2|(1 - ω 2 L′C0)] < 0 (10)

[0080]

[0081] 0 < arctan{ωL′ / [R(1 - ω 2 L′C0)]} < π / 6 (12)

[0082] The expressions of the three - phase power supply voltage are respectively:

[0083] e A = U m sin(ωt + φ - 2π / 3) (13)

[0084] e B = U m sin(ωt + φ + 2π / 3) (14)

[0085] e C = U m sin(ωt + φ) (15)

[0086] In Equation (8), as the value of the transition resistance increases, the frequency of the decaying component is approximately the power frequency. In Equation (9)

[0087] , the zero - sequence voltage is composed of two components with similar amplitudes and frequencies, and a beating phenomenon appears after the fault. The larger the value of the transition resistance, the slower the decay of the decaying component in the zero - sequence voltage. It is difficult to observe the decay characteristics of the zero - sequence voltage within one or two cycles after the fault. From Equations (13) to (15), when , within the stage where the decay of the zero - sequence voltage is not significant, the phase difference between the zero - sequence voltage and the power supply voltage of the faulty phase is the largest. Considering that the transient impact is large at the moment of the fault, the present invention selects the zero - sequence voltage data within the second cycle after the fault for phase analysis.

[0088] 2. Phase relationship between the zero - sequence voltage and the three - phase power supply voltage under the correct phase selection after the insertion of the intermediate resistance

[0089] relationship

[0090] According to Equation (6), when the phase - selection result is correct after the insertion of the intermediate resistance and the value of the transition resistance is 0Ω, that is, a solid - earth fault of phase C occurs in the system, The phase is the same as the phase.

[0091] When the value of the transition resistance increases, a phase shift occurs between the two. The phase relationship between the zero-sequence voltage and the three-phase source voltages is as Figure 10 shown.

[0092] In Figure 10 , and the phase difference is denoted as β. In a resonant grounded distribution network, the maximum value of the system's capacitive current to the ground is 150 A, and the maximum value of 3R f / / 3R inter does not exceed the value of 3R inter . Therefore, β max =

[0093] 16.5°. The phasor always lies between the phasors and . The phase difference between the zero-sequence voltage and the faulty-phase source voltage is larger than the phase difference between the zero-sequence voltage and the healthy-phase source voltage.

[0094] 3. Phase relationship between the zero-sequence voltage and the three-phase source voltages in the case of incorrect phase selection after the insertion of the intermediate resistance

[0095] relationship

[0096] According to Equation (7), after the insertion of the intermediate resistance, when the faulty-phase identification result is misjudged as phase A, when the value of the transition resistance is 0 Ω, that is, a solid ground fault on phase C occurs in the system, the phase is the same as the phase; when the value of the transition resistance increases, a phase shift also occurs between the two. Different from the case of correct phase selection, when the value of the transition resistance is relatively large, due to the existence of 3R inter +3α 2 R f , the zero-sequence voltage phasor no longer lies between the two healthy-phase source voltage phasors. The phase relationship between the zero-sequence voltage and the three-phase source voltages is shown in Figure

[0097] 11, Figure 11 (a) shows the phase relationship between the zero-sequence voltage and the three-phase source voltages; Figure 11 (b) shows

[0098] 3R inter +3α 2 R f the phase relationship with R f .

[0099] According to Figure 11 it can be seen that 3R inter +3α 2 R fThe phase is within the range of (-120°, 0°]. When R f has a resistance value of 0 Ω, 3R inter +3α 2 R f has a phase of 0; when R f has a resistance value approaching infinity, 3R inter +3α 2 R f has a phase approaching -120°. Without considering the phase of 3R inter +3α 2 R f , the maximum phase difference between and is γ max =β max +60° = 76.5°. When considering the phase of 3R inter +3α 2 R f , through calculation, it can be known that if R f =169.5 Ω, and have approximately the same phase; if R f >169.5 Ω, the phasor is located between the phasor and the phasor . Since there is an intersection in the range of γ>γ max and R f >169.5 Ω, the phase difference between the zero-sequence voltage and the misjudged phase power supply voltage is the largest.

[0100] Combining the above three cases, it can be obtained that before the intermediate resistor is inserted after a single-phase grounding fault, the phase difference between the zero-sequence voltage and the fault-phase power supply voltage is the largest. When the phase selection is correct after the intermediate resistor is inserted, the phase difference between the zero-sequence voltage and the fault-phase power supply voltage is also the largest. When the phase selection is incorrect after the intermediate resistor is inserted, if R f >169.5 Ω, the phase difference between the zero-sequence voltage and the misjudged phase power supply voltage is the largest. If R f <169.5 Ω, due to the small value of the transition resistance, the probability of misjudgment of the fault phase selection result is small, and the correctness of the phase selection result can be directly verified according to the magnitude of the three-phase voltage amplitudes before the intermediate resistor is inserted after the fault. If the voltage amplitude of the phase corresponding to the phase selection result is the smallest, the phase selection is correct; otherwise, the phase selection is incorrect.

[0101] The present invention respectively proposes that when R f >169.5 Ω and R fA method for verifying the correctness of fault phase selection results in two cases of <169.5Ω> can distinguish the applicable scenarios of the two criteria according to the amplitude relationship of the three-phase voltages before the intermediate resistor is inserted after a single-phase ground fault. To ensure the reliability of the two criteria, round <R> f when <R> f = 169.5Ω, and the amplitude and phase relationships between the three-phase voltages when <R> Figure 12 = 200Ω are as

[0102] shown. Figure 12 In and , the phase difference is denoted as ε. According to Equation (5), when the capacitive current to the ground in a resonant grounded distribution network is 150A and <R> f = 200Ω, ε max = 26°, and the amplitude of the fault phase voltage is approximately 0.45 times the rated phase voltage amplitude. Introduce a reliability factor <k> r , with a value of 1.5, and use the amplitude of 0.45k r (about 0.7) times the rated phase voltage amplitude as the threshold. If the minimum phase voltage amplitude before the intermediate resistor is inserted after the fault is higher than the threshold, then after the fault and after the intermediate resistor is inserted, verify the correctness of the fault phase selection result based on the phase change characteristics between the zero-sequence voltage and the three-phase source voltages; otherwise, directly verify based on the amplitude magnitudes of the three-phase voltages after the fault.

[0103] The flow chart for verifying the correctness of the fault phase selection result is as Figure 13 shown.

[0104] After completing single-phase ground fault phase selection in a resonant grounded distribution network, collect the data of the zero-sequence voltage and the three-phase voltages before and after the fault and after the intermediate resistor is inserted. Analyze the phases of the three-phase voltages before the fault as the phases of the three-phase source voltages. If the minimum phase voltage amplitude before the intermediate resistor is inserted after the fault is higher than 0.7 times the rated phase voltage amplitude, then extract the voltage data in the second cycle after the fault and after the intermediate resistor is inserted, and verify the correctness of the fault phase selection result based on the phase change characteristics between the zero-sequence voltage and the three-phase source voltages. Considering factors such as the line impedance in the actual system and the possible occurrence of arc ground faults, there may be some deviations in the calculated results of the phase of the zero-sequence voltage, but a reliability factor is set when determining the threshold for the verification method, and this error is within a reasonable range. If, in these two stages, the phase difference between the zero-sequence voltage and the source voltage of the phase corresponding to the fault phase selection result is the largest, it can be considered that the phase selection result is correct; otherwise, the phase selection result is incorrect.

[0105] If the magnitude of the minimum phase voltage before the intermediate resistor is inserted after a fault is lower than 0.7 times the rated phase voltage magnitude, verification is performed based on the magnitude characteristics of the three-phase voltages before the intermediate resistor is inserted after the fault. If the phase with the minimum phase voltage magnitude is consistent with the fault phase selection result, the phase selection result is correct; otherwise, the phase selection result is incorrect.

[0106] After verifying the correctness of the single-phase grounding fault phase selection result, if the phase selection is correct, bypass the intermediate resistor and directly ground the switch of the faulty phase. The active arc suppression device realizes instantaneous fault arc suppression and rapid isolation of permanent faults; if the phase selection is incorrect, immediately disconnect the intermediate resistor, correct the phase selection result, and then reinsert the device.

[0107] To verify the effectiveness of the proposed method for verifying the correctness of the fault phase selection result in a resonant grounded distribution network, in this invention, a Figure 3 10 kV distribution line simulation model is built in PSCAD and simulated and verified under different transition resistances, fault times, fault locations, arc suppression coil detuning degrees, and fault conditions of the faulty phase. The results are as follows:

[0108] 1. Fault time

[0109] Suppose a phase C grounding fault occurs 5 km from the outlet of the L4 cable line, and the fault times are 0.095 s, 0.0975 s, and 0.1 s respectively, with the arc suppression coil detuning degree being -10%. In this invention, intermittent arc faults (denoted as PFAE and HFAE respectively) based on power frequency arc extinction and high-frequency arc extinction principles and stable arc faults are simulated respectively. The arc resistance is composed of a fixed-value resistor and a variable arc resistor in series, and the fixed resistor values are taken as 100 Ω and 1000 Ω respectively. At different fault times, the three-phase power supply voltage phases under normal system operation conditions, the three-phase voltage magnitudes and zero-sequence voltage phases before the intermediate resistor is inserted after the fault, and the zero-sequence voltage phase after the intermediate resistor is inserted are calculated to verify the correctness of the device insertion result. The results are shown in Tables 2 to 5. In the tables, correct insertion and incorrect insertion represent the insertion states of the intermediate resistor in the case of correct and incorrect fault phase selection results respectively.

[0110] Table 2 Verification of the correctness of the device insertion result based on the magnitudes of the three-phase voltages at different fault times

[0111]

[0112]

[0113] Table 3 Verification of the correctness of the device insertion result based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltages when the fault time is 0.095 s

[0114]

[0115] Table 4 Verification of the correctness of the device input result based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltage at the fault moment of 0.0975 s

[0116]

[0117]

[0118] Table 5 Verification of the correctness of the device input result based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltage at the fault moment of 0.1 s

[0119]

[0120] In Tables 2 to 5, the phase is the phase difference between the zero-sequence voltage and the phase voltage of the power supply. 100(PFAE), 100(HFAE), and 100(steady) represent intermittent arc faults and steady arc faults based on the principles of power-frequency arc extinction and high-frequency arc extinction with a fixed resistance value of 100 Ω, and the same applies to 1000(PFAE), 1000(HFAE), and 1000(steady).

[0121] If the minimum phase voltage amplitude before the intermediate resistor is inserted after the fault is lower than 0.7 times the rated phase voltage amplitude, the three-phase voltage amplitudes can be directly compared to verify the correctness of the fault phase selection result. In Table 2, the voltage amplitude of phase C is the smallest, and the amplitude difference from phases A and B is significant, indicating that the fault phase is phase C. In this case, the device can be correctly put into operation.

[0122] If the minimum phase voltage amplitude before the intermediate resistor is inserted after the fault is higher than 0.7 times the rated phase voltage amplitude, a method for verifying the correctness of the fault phase selection result can be proposed based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltage after the fault and after the intermediate resistor is inserted. At the fault moments of 0.095 s, 0.0975 s, and 0.1 s, the phases of the three-phase power supply voltages are (-121°, 119°, -1°), (-76°, 164°, 44°), and (-31°, -151°, 89°) respectively. In Tables 3 to 5, if the phase difference between the zero-sequence voltage and the same-phase power supply voltage is always the largest after the fault and after the intermediate resistor is inserted, it indicates that the fault phase discrimination is correct. Otherwise, the fault phase discrimination is incorrect. At this time, the phase difference between the zero-sequence voltage after the fault and the power supply voltage of the fault phase is the largest; while the phase difference between the zero-sequence voltage after the intermediate resistor is inserted and the power supply voltage of the misjudged phase is the largest. Therefore, if the grounding switch of the misjudged phase is inserted into the device, the intermediate resistor should be immediately disconnected, and after correcting the wrong phase selection result, the grounding switch of the fault phase should be closed. The method for verifying the correctness of the fault phase selection result proposed in the present invention is effective under different fault moments and transition resistance conditions.

[0123] 2. Fault location

[0124] Suppose that a C-phase grounding fault occurs at 15 km from the outgoing line of the L3 overhead line and 10 km from the outgoing line of the L4 cable line respectively in the system. The fault time is 0.1 s, corresponding to the moment when the C-phase voltage reaches the peak value, and the detuning degree of the arc suppression coil is -10%. Calculate the three-phase power supply voltage phases under normal operation conditions of the system, the three-phase voltage amplitudes and the zero-sequence voltage phase before the intermediate resistor is inserted after the fault, and the zero-sequence voltage phase after the intermediate resistor is inserted, and verify the correctness of the device input results. The results are shown in Tables 6 to 8.

[0125] Table 6 Verification of the correctness of the device input results based on the magnitudes of the three-phase voltage amplitudes at different fault locations

[0126]

[0127]

[0128] Table 7 Verification of the correctness of the device input results based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltage when the fault location is on the L3 line

[0129]

[0130] Table 8 Verification of the correctness of the device input results based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltage when the fault location is on the L4 line

[0131]

[0132]

[0133] According to Table 6, the fault phase selection result should be the C phase, and the device can be correctly inserted. When the fault locations are on the L3 and L4 lines respectively, the three-phase power supply voltage phases are (-31°, -151°, 89°). According to Tables 7 and 8, the phase difference between the zero-sequence voltage and the power supply voltage of the fault phase is the largest after the fault. If the fault phase is correctly identified, the phase difference between the zero-sequence voltage and the power supply voltage of the fault phase is also the largest after the intermediate resistor is inserted; if the fault phase is misjudged, the phase difference between the zero-sequence voltage and the power supply voltage of the misjudged phase is the largest after the intermediate resistor is inserted. The reliability of this verification method is not affected by the fault location and can correct the wrong phase selection result and correctly insert the device.

[0134] 3. Detuning degree of the arc suppression coil

[0135] Assume that a phase C grounding fault occurs 5 km away from the outgoing line of the L4 cable line at the fault time of 0.1 s, and the arc suppression coil detuning degrees are -5% and -8% respectively. Calculate the three-phase power supply voltage phases under normal system operation conditions, the three-phase voltage amplitudes and zero-sequence voltage phases before the intermediate resistor is inserted after the fault, and the zero-sequence voltage phase after the intermediate resistor is inserted, and verify the correctness of the device input results. The results are shown in Tables 9 to 11.

[0136] Table 9 Verification of the correctness of the device input results based on the magnitudes of the three-phase voltage amplitudes under different arc suppression coil detuning degrees

[0137]

[0138] Table 10 Verification of the correctness of the device input results based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltage when the arc suppression coil detuning degree is -5%

[0139]

[0140]

[0141] Table 11 Verification of the correctness of the device input results based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltage when the arc suppression coil detuning degree is -8%

[0142]

[0143] As can be seen from Table 9, the reliability of the fault phase selection result verification method based on the magnitude relationship of the three-phase voltage amplitudes is not affected by the arc suppression coil detuning degree. In the fault cases where the arc suppression coil detuning degrees are -5% and -8% respectively, the three-phase power supply voltage phases are (-31°, -151°, 89°). As can be seen from Tables 10 and 11, the fault phase selection result verification method based on the phase change relationship between the zero-sequence voltage and the three-phase power supply voltage is still effective considering the factor of the arc suppression coil detuning degree.

[0144] 4. Fault phase

[0145] Assume that phase A and phase B grounding faults occur 5 km away from the outgoing line of the L4 cable line respectively at the fault times of 0.087 s and 0.093 s, corresponding to the moments when the voltages of phase A and phase B reach their peaks, and the arc suppression coil detuning degree is -10%. Calculate the three-phase power supply voltage phases under normal system operation conditions, the three-phase voltage amplitudes and zero-sequence voltage phases before the intermediate resistor is inserted after the fault, and the zero-sequence voltage phase after the intermediate resistor is inserted, and verify the correctness of the device input results. The results are shown in Tables 12 to 14.

[0146] Table 12 Verification of the correctness of the device input results based on the magnitudes of the three-phase voltage amplitudes under different fault phases

[0147]

[0148] Table 13 Verification of the correctness of the device input results based on the phase change relationship between the zero-sequence voltage and the three-phase source voltages when the faulty phase is phase A

[0149]

[0150]

[0151] Table 14 Verification of the correctness of the device input results based on the phase change relationship between the zero-sequence voltage and the three-phase source voltages when the faulty phase is phase B

[0152]

[0153] In Table 12, under the condition of a relatively small transition resistance, the correctness of the fault phase selection result can be verified according to the magnitude relationship of the three-phase voltages after the fault. When the faulty phases are phase A and phase B respectively, the phases of the three-phase source voltages are (89°, -31°, -151°) and (-151°, 89°, -31°). In Tables 13 and 14, the phase difference between the zero-sequence voltage and the faulty-phase source voltage after the fault is the largest, and the phase difference between the zero-sequence voltage and the source phase voltage corresponding to the device input is the largest after the intermediate resistor is inserted. If the device is incorrectly input, the intermediate resistor should be immediately disconnected, and then the grounding switch of the faulty phase should be closed. The method proposed in the present invention can still effectively verify the fault phase selection result under different faulty phases, and can correct the incorrect phase selection result to ensure the reliable operation of the device.

[0154] In summary, the present invention establishes a model of an active intervention type arc suppression device, and selects the parameters of the intermediate resistor from two aspects: the transient current value at the moment of switch closing and the thermal power of the intermediate resistor. To avoid misoperation of the device, during the insertion of the intermediate resistor, a verification method combining the characteristics of the three-phase voltage amplitude and the phase change of the zero-sequence voltage is proposed for the correctness of the single-phase grounding fault phase selection result. In the PSCAD simulation model, the verification method is simulated and verified under different transition resistances, fault times, fault positions, arc suppression coil detuning degrees, and faulty phases. The experiments show the effectiveness of the method in different fault scenarios and improve the fault tolerance and error correction ability of the device for the fault phase selection result.

[0155] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that: various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments and drawings.

Claims

1. A method for verifying the correctness of single-phase grounding fault phase selection results of an active intervention type arc suppression device in a resonant grounded distribution network, characterized in that: The steps of the method are as follows: S1. Build a model of an active intervention type arc suppression device in a resonant grounded distribution network, and select the parameters of the intermediate resistor from two aspects: the transient current value at the moment of switch closing and the thermal power of the intermediate resistor; S2. After completing the single-phase grounding fault phase selection, collect the data of the zero-sequence voltage and three-phase voltage before and after the fault and after the intermediate resistor is put into operation, and analyze the phase of the three-phase voltage before the fault as the phase of the three-phase power supply voltage; S3. If the minimum phase voltage amplitude before the intermediate resistor is put into operation after the fault is higher than 0.7 times the rated phase voltage amplitude, verify the correctness of the fault phase selection result based on the phase change characteristics between the zero-sequence voltage and the three-phase power supply voltage after the fault and after the intermediate resistor is put into operation. If the phase difference between the zero-sequence voltage and the power supply voltage of the corresponding phase of the fault phase selection result is the largest in these two stages, the phase selection result can be considered correct; otherwise, the phase selection result is incorrect; If the minimum phase voltage amplitude before the intermediate resistor is put into operation after the fault is lower than 0.7 times the rated phase voltage amplitude, verify based on the amplitude size characteristics of the three-phase voltage before the intermediate resistor is put into operation after the fault. If the phase with the minimum phase voltage amplitude is consistent with the fault phase selection result, the phase selection result is correct; otherwise, the phase selection result is incorrect; S4. After verifying the correctness of the single-phase grounding fault phase selection result, if the phase selection is correct, bypass the intermediate resistor, and the switch of the fault phase is directly grounded, and the active intervention type arc suppression device realizes safe arc suppression for instantaneous faults and fast isolation for permanent faults; If the phase selection is incorrect, immediately disconnect the intermediate resistor, correct the phase selection result, and then put the device into operation again.

2. The method for verifying the correctness of single-phase grounding fault phase selection results of the active intervention type arc suppression device in a resonant grounded distribution network according to claim 1, characterized in that: The active intervention type arc suppression device consists of a microcomputer controller, a grounding element and a grounding switch. The grounding switch includes a phase-separated grounding switch S1, a grounding switch S2 and an intermediate resistor R inter , the grounding switch S2 and the intermediate resistor R inter are connected in parallel and then connected in series with the phase-separated grounding switch S1. The microcomputer controller is used to determine the type and fault phase of the single-phase grounding fault, control the closing of the phase-separated switch of the fault phase, clamp the voltage at the fault point, and transfer the fault point current to the active grounding point of the phase-separated switch; the intermediate resistor R inter has a value of 120 Ω.

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