Fault property identification method using active injection signal of distributed photovoltaic power inverter

Abstract

The invention discloses a fault property identification method utilizing active injection signals of a distributed photovoltaic power inverter, which belongs to the field of distributed photovoltaic, and comprises the following steps: when a power distribution line has a fault, a line protection device completes fault removal and fault phase selection; the line protection device sends the protection action information and the phase selection signal to the distributed photovoltaic power supply through a 5G network; after the distributed photovoltaic power supply receives the protection action information and the phase selection signal, the working mode of the inverter is changed, the pilot frequency signal is injected, the impedance identification calculation of the distribution line is carried out, and the effective discrimination of the fault property is realized, so that an additional device is not needed, and the fault identification reliability, stability and rapidity of the distributed photovoltaic power supply inverter are improved.

Description

Technical Field

[0001] The present invention relates to the field of distributed photovoltaic technology, and more specifically, to a method for identifying fault properties by actively injecting signals from a distributed photovoltaic power inverter. Background Art

[0002] With the deepening of my country's "distributed photovoltaic county-wide promotion" plan, the widespread application of distributed photovoltaic power sources in distribution networks has become a trend. This highly permeable access mode has brought new challenges to the traditional distribution network protection and fault handling methods. In the distribution network, how to accurately identify the fault nature of the distribution line, especially transient faults and permanent faults, has always been the focus and difficulty of research in the industry.

[0003] Existing fault nature identification technologies are mainly divided into two categories: active detection and passive detection. The passive detection method relies on the electrical quantity characteristics after the distribution line trips, but its characteristic information is short-lived and unstable, which limits its reliability in practical applications. The active detection method usually injects non-characteristic subharmonics into the line and identifies the fault nature by analyzing the harmonic response. This method requires additional signal injection equipment support during the identification process, which increases the complexity and cost of the system. Summary of the invention

[0004] The present invention provides a method for identifying the fault properties of a distributed photovoltaic power inverter by actively injecting a signal, so as to improve the reliability, stability and rapidity of identifying the fault properties of the distributed photovoltaic power inverter.

[0005] A method for identifying fault properties by actively injecting signals from a distributed photovoltaic power inverter comprises the following steps:

[0006] S1. When a distribution line fails, the line protection device completes fault removal and fault phase selection;

[0007] S2. The line protection device sends the protection action information and phase selection signal to the distributed photovoltaic power source through the 5G network;

[0008] S3, after receiving the protection action information and phase selection signal, the distributed photovoltaic power source changes the inverter working mode;

[0009] S4: After injecting characteristic frequency test signals into the distribution line, continuously detect the voltage and current change characteristics

[0010] S5, calculating the impedance parameters of the distribution line under the injected signal;

[0011] S6. According to the calculated impedance parameters, determine whether the fault is a transient fault or a permanent fault;

[0012] S7. Return the fault nature identification result to the line protection device via the 5G network;

[0013] S8. The line protection device executes the reclosing command or the line reclosing locking action according to the fault nature identification result.

[0014] Preferably, the step S1 specifically comprises:

[0015] S11, at time t0, a short circuit fault occurs in the distribution line;

[0016] S12, at time t1, the line protection device trips the circuit breaker and cuts off the fault section;

[0017] S13. The line protection device performs fault phase selection to determine the fault phase.

[0018] Preferably, the step S2 is specifically:

[0019] S21, sending protection action information to distributed photovoltaic power sources through the 5G network;

[0020] S22. Send the phase selection signal to the distributed photovoltaic power source through the 5G network.

[0021] Preferably, the step S3 is specifically:

[0022] S31, the distributed photovoltaic power source receives the protection action information and phase selection signal of the line protection device;

[0023] S32, the controller adjusts the working mode of the inverter according to the received information, switching from the normal mode to the signal injection mode;

[0024] S33: After the inverter enters the signal injection mode, it is ready to inject a characteristic frequency probe signal into the distribution line.

[0025] Preferably, the step S4 is specifically:

[0026] S41, the inverter injects a characteristic frequency test signal of K1 times the rated frequency of the power grid into the distribution line at time t2-t3, where K1 is a value between 4 and 5;

[0027] S42, the inverter continuously detects and records the voltage and current signals of the faulty phase;

[0028] S43: The inverter determines whether to adjust the characteristic frequency probe signal according to the detected voltage and current signals.

[0029] Preferably, step S43 is specifically that the inverter calculates the phase angle difference between the detected voltage and current. If the phase angle difference is between 0-90°, there is no need to adjust the characteristic frequency probe signal; if the phase angle difference is between 90°-180°, the characteristic frequency probe signal is successively subtracted by 0.2 times the rated frequency of the power grid and injected into the distribution network until the inverter calculates that the phase angle difference between the detected voltage and current is between 0-90°; if the phase angle difference is between -90°-0, the characteristic frequency probe signal is successively added with 0.1 times the rated frequency of the power grid and injected into the distribution network until the inverter calculates that the phase angle difference between the detected voltage and current is between 0-90°.

[0030] Preferably, the step S5 is specifically:

[0031] S51, collecting the voltage and current whose phase angle difference between the voltage and current detected by the inverter calculated in step S43 is between 0 and 90 degrees as the fault phase voltage and injection current signal;

[0032] S52, calculating the equivalent positive sequence impedance modulus according to the fault phase-to-phase voltage and the injected current signal;

[0033] S53. Determine the impedance parameters of the distribution line using the equivalent positive-sequence impedance modulus.

[0034] Preferably, the step S6 is specifically:

[0035] S61, set the setting value of the fault discrimination resistor to K;

[0036] S62, comparing the calculated equivalent positive sequence impedance modulus value with the set value;

[0037] S63. If the equivalent positive-sequence impedance modulus is less than or equal to K, it is judged as a permanent fault; if it is greater than K, it is judged as a transient fault.

[0038] Preferably, the step S7 is specifically:

[0039] S71, the inverter generates a fault property identification result, including a transient fault or a permanent fault;

[0040] S72. Send the identification result to the line protection device through the 5G network to ensure the real-time and accuracy of data transmission;

[0041] S73. The line protection device receives and records the identification result.

[0042] Preferably, the step S8 is specifically:

[0043] S81, the line protection device determines the fault nature according to the received fault nature identification result;

[0044] S82: If it is a transient fault, execute the reclosing command to restore power supply;

[0045] S83. If it is a permanent fault, execute the line reclosing lock action.

[0046] Beneficial effects:

[0047] The present invention adopts a method for identifying the fault nature of a distribution line by injecting a signal from a distributed power source. After a distribution network line fault occurs, the grid-connected distributed power source actively changes its working mode, injects a heterofrequency signal, and performs impedance identification calculation for the distribution line, thereby effectively distinguishing the fault nature. No additional devices are required, and only the distributed power source inverter controller needs to be upgraded. The implementation is simple, and the reliability, stability, and rapidity of identifying the fault nature of the distributed photovoltaic power source inverter are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the process of the present invention.

[0049] Figure 2 This is a detailed schematic diagram of the step S1 process in the present invention.

[0050] Figure 3 This is a detailed schematic diagram of the step S2 process in the present invention.

[0051] Figure 4 This is a detailed schematic diagram of step S3 in the present invention.

[0052] Figure 5 This is a detailed schematic diagram of step S4 in the present invention.

[0053] Figure 6 This is a detailed schematic diagram of step S5 in the present invention.

[0054] Figure 7 This is a detailed schematic diagram of step S6 in the present invention.

[0055] Figure 8 This is a detailed schematic diagram of step S7 in the present invention.

[0056] Fig. 9 This is a detailed schematic diagram of step S8 in the present invention. DETAILED DESCRIPTION

[0057] The present application is further described in detail below in conjunction with the accompanying drawings. It is necessary to point out here that the following specific implementation methods are only used to further illustrate the present application. The various implementation methods can be arbitrarily combined with the present invention without limitation, and cannot be understood as limiting the scope of protection of the present application. Technical personnel in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0058] Refer to the instruction manual Figures 1 to 9 , a method for identifying fault properties by actively injecting signals from a distributed photovoltaic power inverter, comprising the following steps:

[0059] S1. When a distribution line fault occurs, the line protection device completes fault removal and fault phase selection.

[0060] The step S1 can be refined as follows:

[0061] S11, at time t0, a short circuit fault occurs in the distribution line;

[0062] S12, at time t1, the line protection device operates to trip the circuit breaker CB and cut off the fault section;

[0063] S13. The line protection device performs fault phase selection to determine the fault phase.

[0064] S2. The line protection device sends the protection action information and phase selection signal to the distributed photovoltaic power source through the 5G network;

[0065] The step S2 can be refined as follows:

[0066] S21, sending protection action information to distributed photovoltaic power sources through the 5G network;

[0067] S22. Send the phase selection signal to the distributed photovoltaic power source through the 5G network to ensure high reliability and low latency of information transmission.

[0068] S3, after receiving the protection action information and phase selection signal, the distributed photovoltaic power source changes the inverter working mode;

[0069] The step S3 can be refined as follows:

[0070] S31, the distributed photovoltaic power source receives the protection action information and phase selection signal of the line protection device;

[0071] S32, the controller adjusts the working mode of the inverter according to the received information, switching from the normal mode to the signal injection mode;

[0072] S33: After the inverter enters the signal injection mode, a characteristic frequency probe signal is injected into the distribution line.

[0073] S4, after injecting a characteristic frequency test signal into the distribution line, continuously detecting the voltage and current change characteristics;

[0074] The step S4 can be refined as follows:

[0075] S41, the inverter injects a characteristic frequency test signal of K1 times the rated frequency of the power grid into the distribution line at time t2-t3;

[0076] Optionally, the characteristic frequency probe signal is 230 Hz; the rated frequency of the power grid is 50 Hz; K1 is a value between 4 and 5;

[0077] Optionally, t2>t1;

[0078] Optionally, t2-t1>1;

[0079] S42, the inverter continuously detects the voltage and current change characteristics of the fault phase and records the relevant data;

[0080] Specifically,

[0081] S43. The inverter determines whether to adjust the characteristic frequency probe signal according to the detected voltage and current change characteristics to improve the recognition accuracy.

[0082] Preferably, step S43 is specifically that the inverter calculates the phase angle difference of the detected voltage and current. If the phase angle difference is between 0-90°, it indicates that the distribution network into which the characteristic frequency probe signal is injected is inductive and the voltage and current converge, and there is no need to adjust the characteristic frequency probe signal at this time; if the phase angle difference is between 90°-180°, it indicates that the voltage and current of the distribution network into which the characteristic frequency probe signal is injected are oscillating and the voltage is overregulated and the voltage phase relative to the current is in the second quadrant, and at this time the characteristic frequency probe signal is reduced, specifically, the characteristic frequency probe signal is successively subtracted by 0.2 times the rated frequency of the grid until the phase angle difference of the voltage and current detected by the inverter calculated is between 0-90°. For example, for the first time, K1 times the grid rated frequency - 1×0.2 times the grid rated frequency is injected. If the inverter calculates that the phase angle difference between the voltage and current detected is 120°, then for the second time, K1 times the grid rated frequency - 2×0.2 times the grid rated frequency is injected again. If the inverter calculates that the phase angle difference between the voltage and current detected is 110°, then for the third time, K1 times the grid rated frequency - 3×0.2 times the grid rated frequency is injected again. If the inverter calculates that the phase angle difference between the voltage and current detected is 30°, the injection signal is stopped.

[0083] If the phase angle difference is between -90°-0, it indicates that the voltage and current of the distribution network injected with the characteristic frequency probe signal are oscillating and the current is overmodulated, and the voltage phase is in the fourth quadrant relative to the current. At this time, the characteristic frequency probe signal is increased, specifically, the characteristic frequency probe signal is successively added with 0.1 times the grid rated frequency, until the phase angle difference of the voltage and current calculated and detected by the inverter is between 0-90°. For example, for the first time, K1 times the grid rated frequency + 1×0.1 times the grid rated frequency is injected. If the phase angle difference of the voltage and current calculated and detected by the inverter is -80°, then for the second time, K1 times the grid rated frequency + 2×0.1 times the grid rated frequency is injected again. If the phase angle difference of the voltage and current calculated and detected by the inverter is -30°, then for the third time, K1 times the grid rated frequency + 3×0.1 times the grid rated frequency is injected again. If the phase angle difference of the voltage and current calculated and detected by the inverter is 20°, the injection signal is stopped.

[0084] Through frequency adjustment, the convergence and accuracy of fault identification are improved.

[0085] S5, calculating the impedance parameters of the distribution line under the injected signal;

[0086] The step S5 can be refined as follows:

[0087] S51, collecting the fault phase-to-phase voltage and injection current under the injection signal;

[0088] S52. Calculate the equivalent positive-sequence impedance modulus according to the fault phase-to-phase voltage and the injected current; optionally, divide the fault phase-to-phase voltage modulus by the injected current modulus to obtain the impedance parameter of the distribution line.

[0089] S53. Determine the impedance parameters of the distribution line using the calculation results to ensure the accuracy and reliability of the calculation results.

[0090] S6. According to the calculated impedance parameters, determine whether the fault is a transient fault or a permanent fault;

[0091] The step S6 can be refined as follows:

[0092] S61, setting the setting value of the fault discrimination resistor to K; optionally, K=5Ω;

[0093] S62, comparing the calculated equivalent positive sequence impedance modulus value with the set value;

[0094] S63. If the equivalent positive-sequence impedance modulus is less than or equal to K, it is judged as a permanent fault; if it is greater than K, it is judged as a transient fault.

[0095] S7. Return the fault nature identification result to the line protection device via the 5G network;

[0096] The step S7 can be refined as follows:

[0097] S71, the inverter generates a fault property identification result, including a transient fault or a permanent fault;

[0098] S72. Send the identification result to the line protection device through the 5G network to ensure the real-time and accuracy of data transmission;

[0099] S73. The line protection device receives and records the identification result to provide a basis for subsequent fault handling.

[0100] S8. The line protection device executes the reclosing command or the line reclosing locking action according to the fault nature identification result.

[0101] The step S8 can be refined as follows:

[0102] S81, the line protection device determines the fault nature according to the received fault nature identification result;

[0103] S82: If it is a transient fault, execute the reclosing command to restore power supply;

[0104] S83. If it is a permanent fault, execute the line reclosing lock action to prevent further expansion of the fault.

[0105] Preferably, the selection of the distributed photovoltaic power source must meet the following conditions:

[0106] The capacity is above 500kW and can provide sufficient current and voltage;

[0107] Directly connect to the grid through a dedicated step-up transformer to avoid the adverse effect of low-voltage load on fault nature identification;

[0108] Equipped with an inverter controller that can quickly respond and adjust the working mode.

[0109] In combination with the above content, a timing analysis is first performed. When a short-circuit fault occurs in the distribution line, the line protection device detects the fault at t0, and trips the circuit breaker CB at t1 to cut off the fault section. At the same time, the line protection device sends the protection action information and phase selection signal to the distributed photovoltaic power source through the 5G network. After the distributed photovoltaic power source receives this information from t2 to t3, the inverter controller adjusts the working mode of the inverter from the normal mode to the signal injection mode. The inverter injects a 230Hz characteristic frequency test signal into the distribution line, and continuously detects the voltage and current change characteristics of the fault phase and records the relevant data. According to the detected voltage and current change characteristics, the inverter adjusts the amplitude and frequency of the signal injection to improve the recognition accuracy. At t4, the inverter generates a fault property identification result, including a transient fault or a permanent fault, and sends the identification result to the line protection device through the 5G network. The line protection device receives and records the identification result at t5, determines the nature of the fault according to the result, and executes the corresponding reclosing instruction or line reclosing lock action;

[0110] Secondly, the frequency and amplitude of the injected signal are determined. The frequency of the injected signal is mainly selected based on two factors: to prevent confusion with the original signal of conducted interference or coupled interference in the power distribution system, the frequency of the injected signal should be between harmonic N and harmonic N+1; too high an injected signal frequency will significantly reduce the ground capacitance of the distribution line, affecting the accuracy of fault identification and increasing the rate requirements for signal acquisition and processing. Taking all factors into consideration, the frequency ff of the injected characteristic signal is selected as 230Hz;

[0111] Afterwards, the fault nature identification criteria and setting value are carried out. For permanent faults, the resistance part of the equivalent impedance is mainly composed of the distribution line resistance and the fault transition resistance. The maximum unit length resistance of the cable line does not exceed 0.159Ω / km, and the maximum unit length resistance of the overhead line does not exceed 0.221Ω / km. When the cable line length does not exceed 5km and the overhead line length does not exceed 10km, the maximum resistance RL of the cable line is 0.8Ω, and the maximum resistance RL of the overhead line is 2.21Ω. Combined with the above data, the fault discrimination resistance setting value is set to 5Ω. According to the equivalent positive sequence impedance modulus value calculated based on the fault phase-to-phase voltage and injection current on the high-voltage side of the step-up transformer, if it is less than or equal to 5Ω, it is judged as a permanent fault; if it is greater than 5Ω, it is judged as a transient fault;

[0112] Subsequently, the implementation scheme of the characteristic frequency three-phase symmetrical test voltage signal was confirmed. When a phase-to-phase fault occurs in the distribution system, the three-phase system is highly unbalanced, and a special control strategy is required to ensure that the three-phase inverter of the distributed photovoltaic system outputs a stable three-phase balanced test voltage signal under the characteristic frequency. The inverter controller collects the output three-phase voltage u oa 、u ob、u oc , which is expressed as follows:

[0113]

[0114] Among them U m Expressed as the phase voltage amplitude, this formula can be transformed by the following formula Clarke to obtain the feedback voltage u in the two-phase stationary coordinate system: α 、u β :

[0115]

[0116] Then through the formula

[0117] and

[0118]

[0119] The voltage positive sequence component u in the stationary coordinate system can be obtained α + 、u β + and negative sequence component u α — 、u β — , where u α 、u β lagged u α 、u β Signal 90°. Current I on the inverter three-phase output inductor Labc After Clarke transformation, the feedback current i can be obtained α 、i β Similarly, the positive sequence component i of the current in the stationary coordinate system can be obtained α + 、i β + and negative sequence component i α — 、i β — .

[0120] The control strategy of the inverter is to separate the positive and negative sequences of the inverter voltage and output current, and control the positive and negative sequence voltage and current cycles respectively. Finally, the positive sequence modulation signal With negative sequence modulation signal After superposition, it is modulated by SPWM and driven by the switch tube driving circuit to obtain a stable three-phase symmetrical voltage signal. The specific process is as follows: The inverter controller sets the reference voltage positive sequence given u α *+ 、u β *+With the reference voltage negative sequence given u α *- 、u β *- According to the positive sequence given and negative sequence given of the reference voltage, positive sequence control and negative sequence control are performed respectively. α *+ 、u β *+ With feedback voltage u α *+ 、u β *+ The error is controlled by the voltage controller to obtain the reference current i α *+ 、i β *+ , and then compared with the feedback current, the positive sequence modulation signal is obtained through the current controller Similarly, the voltage negative sequence control is the same as the positive sequence processing process to obtain the negative sequence modulation signal The voltage controller uses a quasi-proportional resonator, and the current controller uses a proportional controller;

[0121] Optionally, a 10kV distribution system simulation model is established on the Simulink platform for simulation verification. The scenarios of permanent fault and transient fault of cable line L3 are simulated, and the equivalent resistance parameter identification results in the fault scenarios are recorded respectively. The results show that under permanent fault, the calculated value is 1.119Ω, the actual value is 1.12Ω, the error is 0.001Ω, and the error percentage is 0.089%; under transient fault, the calculated value is 76.75Ω, the actual value is 74.94Ω, the error is 1.06Ω, and the error percentage is 1.4%. This shows that under the condition of the characteristic frequency voltage signal injected by the distributed power source, the positive sequence resistance value of the distribution line can be accurately obtained according to the detected voltage and current information, and then the fault type can be judged to reflect the operation status of the line.

[0122] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters, characterized in that: The following steps are involved: S1. When a distribution line fails, the line protection device completes fault removal and fault phase selection; S2. The line protection device sends the protection action information and phase selection signal to the distributed photovoltaic power source through the 5G network; S3, after receiving the protection action information and phase selection signal, the distributed photovoltaic power source changes the inverter working mode; S4: After injecting characteristic frequency test signals into the distribution line, continuously detect the voltage and current change characteristics S5, calculating the impedance parameters of the distribution line under the injected signal; S6. According to the calculated impedance parameters, determine whether the fault is a transient fault or a permanent fault; S7. Return the fault nature identification result to the line protection device via the 5G network; S8. The line protection device executes the reclosing command or the line reclosing locking action according to the fault nature identification result.

2. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 1 is characterized in that: The step S1 is specifically as follows: S11, at time t0, a short circuit fault occurs in the distribution line; S12, at time t1, the line protection device trips the circuit breaker and cuts off the fault section; S13. The line protection device performs fault phase selection to determine the fault phase.

3. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 1 is characterized in that: The step S2 is specifically as follows: S21, sending protection action information to distributed photovoltaic power sources through the 5G network; S22. Send the phase selection signal to the distributed photovoltaic power source through the 5G network.

4. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 1 is characterized in that: The step S3 is specifically as follows: S31, the distributed photovoltaic power source receives the protection action information and phase selection signal of the line protection device; S32, the controller adjusts the working mode of the inverter according to the received information, switching from the normal mode to the signal injection mode; S33: After the inverter enters the signal injection mode, it is ready to inject a characteristic frequency probe signal into the distribution line.

5. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 1 is characterized in that: The step S4 is specifically as follows: S41, the inverter injects a characteristic frequency test signal of K1 times the rated frequency of the power grid into the distribution line at time t2-t3, where K1 is a value between 4 and 5; S42, the inverter continuously detects and records the voltage and current signals of the faulty phase; S43: The inverter determines whether to adjust the characteristic frequency probe signal according to the detected voltage and current signals.

6. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 5 is characterized in that: Step S43 is specifically that the inverter calculates the phase angle difference between the detected voltage and current. If the phase angle difference is between 0-90°, there is no need to adjust the characteristic frequency probe signal; if the phase angle difference is between 90°-180°, the characteristic frequency probe signal is successively subtracted by 0.2 times the rated frequency of the grid and injected into the distribution network until the inverter calculates that the phase angle difference between the detected voltage and current is between 0-90°; if the phase angle difference is between -90°-0, the characteristic frequency probe signal is successively added with 0.1 times the rated frequency of the grid and injected into the distribution network until the inverter calculates that the phase angle difference between the detected voltage and current is between 0-90°.

7. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 6 is characterized in that: The step S5 is specifically as follows: S51, collecting the voltage and current whose phase angle difference between the voltage and current detected by the inverter calculated in step S43 is between 0 and 90 degrees as the fault phase voltage and injection current signal; S52, calculating the equivalent positive sequence impedance modulus according to the fault phase-to-phase voltage and the injected current signal; S53. Determine the impedance parameters of the distribution line using the equivalent positive-sequence impedance modulus.

8. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 1 is characterized in that: The step S6 is specifically as follows: S61, set the setting value of the fault discrimination resistor to K; S62, comparing the calculated equivalent positive sequence impedance modulus value with the set value; S63. If the equivalent positive-sequence impedance modulus is less than or equal to K, it is judged as a permanent fault; if it is greater than K, it is judged as a transient fault.

9. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 1, characterized in that: The step S7 is specifically as follows: S71, the inverter generates a fault property identification result, including a transient fault or a permanent fault; S72. Send the identification result to the line protection device through the 5G network to ensure the real-time and accuracy of data transmission; S73. The line protection device receives and records the identification result.

10. The method for identifying fault properties by actively injecting signals from distributed photovoltaic power inverters according to claim 1, characterized in that: The step S8 is specifically as follows: S81, the line protection device determines the fault nature according to the received fault nature identification result; S82: If it is a transient fault, execute the reclosing command to restore power supply; S83. If it is a permanent fault, execute the line reclosing lock action.

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