Method, device, equipment and medium for identifying single-phase fault nature of double-terminal weak-feed system

Abstract

The present invention relates to the technical field of relay protection of electric power system, and in particular to a method, device, equipment and medium for identifying the nature of single-phase faults in a two-terminal weak-feedback system. The method comprises collecting the voltage and current of each phase at the local end of an AC line, and calculating the midpoint voltage of a healthy phase; using the voltage and current measurement results of the healthy phase at the local end of the AC line, calculating the amplitude and phase of the tripping phase coupling voltage under faults of different natures, performing real-time adjustment on the voltage amplitude criterion and the phase criterion, and establishing a voltage amplitude and phase joint criterion, so that it is suitable for the two-terminal weak-feedback system. The proposed identification method does not rely on the electrical characteristics of the non-full-phase operation stage of the AC system, is not affected by the operating conditions of the AC system, can accurately identify the fault nature of single-phase grounding faults at different positions and with different transition resistances, and has wider applicability and higher reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection of electric power systems, and in particular to a method, device, equipment and medium for identifying the nature of a single-phase fault in a double-terminal weak-feedback system. Background Art

[0002] Against the backdrop of energy transformation and rapid development of new energy sources, building a new power system with a high proportion of new energy access has become an important direction for the current development of the power grid. In areas rich in new energy resources, the power grid is often far away from traditional power generation centers, with a relatively weak structure and insufficient regulation capabilities. When a high proportion of new energy is connected to the power grid through long-distance transmission lines, the AC transmission system usually forms a double-end weak-feedback characteristic. At the same time, more and more new energy sources choose to connect to DC converter stations after being collected in the AC system, and realize cross-regional long-distance transmission through DC lines, so that the AC transmission system uses power electronic equipment at both ends, and the short-circuit capacity is relatively small, which is more typically manifested as a double-end weak-feedback system.

[0003] When a single-phase grounding fault occurs in the AC interconnection line of a double-terminal weak-feed system, if a three-phase tripping method is used, the new energy power source will be directly disconnected from the grid; if a single-phase tripping method is used, the wind farm can be temporarily connected to the grid through a non-full-phase connection after the single-phase tripping; however, in the non-full-phase operation stage, the output power of the new energy power source is limited, and the larger negative sequence component in the system is prone to cause overvoltage, overcurrent and power oscillation and other problems. If normal operation cannot be restored in time, it will seriously endanger the safety of power electronic equipment such as wind farms and flexible DC converter stations.

[0004] According to on-site statistics, more than 90% of the faults on high-voltage overhead transmission lines are single-phase grounding faults, of which more than 80% are transient faults. Therefore, after a single-phase grounding fault occurs in the AC interconnection line of a double-terminal weak-feed system, a single-phase reclosing switch is usually used to achieve rapid recovery after the fault. However, the traditional single-phase automatic reclosing scheme cannot effectively distinguish between transient and permanent faults. Once it is mistakenly closed to a permanent fault, it may cause a secondary fault current shock, seriously threatening the safety of equipment on both sides of the AC line; the single-phase adaptive reclosing scheme can construct a fault nature identification criterion based on the electrical quantity characteristics of the system in the non-full-phase operation stage, thereby avoiding the circuit breaker from mistakenly closing to a permanent fault, which is beneficial to the safe and stable operation of the power system; however, both sides of the sending-end AC line of the double-terminal weak-feed system are power electronic equipment, and the electrical quantity characteristics in the non-full-phase operation stage are significantly affected by the power electronic power supply control strategy on both sides, which are quite different from the characteristics of the traditional AC power grid, resulting in the inability to directly apply the traditional fault nature identification criterion.

[0005] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0006] The present invention provides a method, device, equipment and medium for identifying the nature of a single-phase fault in a double-terminal weak-feedback system, thereby effectively solving the problems in the background technology.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: a method for identifying the nature of a single-phase fault in a double-terminal weak-feed system, comprising the following steps:

[0008] S10: collecting the voltage and current of each phase at the local end of the AC line, obtaining the voltage of the healthy phase and the voltage at the local end of the faulty phase, and obtaining the current of the healthy phase;

[0009] S20: Calculating a healthy phase midpoint voltage based on the healthy phase voltage and the healthy phase current;

[0010] S30: Calculating the voltage amplitude of the fault phase at the terminal when the instantaneous fault occurs based on the midpoint voltage of the healthy phase;

[0011] S40: Determine whether the voltage amplitude of the fault phase at the terminal during a transient fault is greater than k times the maximum mutual inductance voltage during a permanent fault. If so, adjust the voltage amplitude criterion by using the voltage amplitude difference between the fault phase at the terminal during a transient fault and a permanent fault to obtain a set value, and proceed to step S50; if not, proceed to step S60;

[0012] S50: Determine whether the amplitude of the voltage at the fault phase terminal is greater than the set value. If so, determine that the fault type is a transient fault and allow reclosing. If not, determine that the fault type is a permanent fault, complete the fault nature identification, and do not reclose.

[0013] S60: Calculate the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during instantaneous fault;

[0014] S70: Based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during the instantaneous fault, the phase judgment criterion is adjusted, and the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is calculated to determine whether the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is within a set range. If so, it is determined to be a transient fault and reclosing operation is allowed; if not, it is determined to be a permanent fault and the circuit breaker is no longer closed.

[0015] Further, in step S20, the midpoint voltage of the healthy phase is calculated Models include:

[0016]

[0017] In the formula, is the healthy phase voltage, is the healthy phase current, Z l is the line self-impedance per unit length, Z m is the mutual impedance of the line per unit length, and l is the total length of the line.

[0018] Further, in step S30, based on the midpoint voltage of the healthy phase, the voltage amplitude of the fault phase at the instantaneous fault is calculated. Models include:

[0019]

[0020] In the formula, is the capacitive coupling voltage during transient faults, is the mutual inductance voltage per unit length of the line under the current operating conditions, is the midpoint voltage of a healthy phase, is the healthy phase current, b 1 、b 0 is the positive and zero sequence admittance per unit length of the line, Z m is the mutual impedance of the line per unit length, and l is the total length of the line.

[0021] Further, in step S40, it is determined whether the voltage amplitude of the fault phase at the terminal during the transient fault is greater than k times the maximum mutual inductance voltage during the permanent fault, wherein the maximum mutual inductance voltage during the permanent fault is Models include:

[0022]

[0023] In the formula, is the healthy phase current, Z m is the mutual impedance of the line per unit length, and l is the total length of the line.

[0024] Further, in step S40, it is determined whether the voltage amplitude of the fault phase at the terminal during the transient fault is greater than k times the maximum mutual inductance voltage during the permanent fault. If so, the voltage amplitude criterion is adjusted by using the voltage amplitude difference between the fault phase at the terminal during the transient fault and the permanent fault to obtain a set value. The set value U DZ Models include:

[0025]

[0026] In the formula, is the maximum mutual inductance voltage during permanent fault, It is the voltage amplitude of the instantaneous fault phase.

[0027] Furthermore, when U A >U DZ When the fault type is determined to be a transient fault, reclosing is allowed;

[0028] When U A <U DZ When U ins <K h U per The phase criterion is used to identify the nature of the fault and the process proceeds to step S60.

[0029] Furthermore, in step S60, before calculating the phase difference between the fault phase compensation voltage and the mutual inductance voltage during an instantaneous fault, it is determined whether the voltage amplitude at the fault phase end is greater than the amplitude of the mutual inductance voltage at half the length of the line, so as to adopt different models to calculate the phase difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating conditions.

[0030] Furthermore, if U A ≥0.5U x l, the calculation of the fault phase compensation voltage during instantaneous fault The phase angle difference θ between the mutual inductance voltage and ins , the model includes:

[0031]

[0032] Where U A is the voltage amplitude of the fault phase terminal, is the fault phase terminal voltage, U x is the amplitude of the mutual inductance voltage per unit length of the line under the current operating conditions, l is the total length of the line, is the mutual inductance voltage per unit length of the line under the current operating conditions, It is the capacitive coupling voltage during transient fault.

[0033] Furthermore, if U A <0.5U x l, the calculation of the fault phase compensation voltage during instantaneous fault The phase angle difference θ between the mutual inductance voltage and ins , the model includes:

[0034]

[0035] Where U A is the voltage amplitude of the fault phase terminal, is the fault phase terminal voltage, U x is the amplitude of the mutual inductance voltage per unit length of the line under the current operating conditions, l is the total length of the line, is the mutual inductance voltage per unit length of the line under the current operating conditions, It is the capacitive coupling voltage during transient fault.

[0036] Further, in step S70, based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during the instantaneous fault, the phase criterion is adjusted, and the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is calculated. The model includes:

[0037]

[0038] In the formula, θ DZ is the setting value of the phase criterion based on adaptive setting, θ is the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system, θ ins is the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during instantaneous fault, is the fault phase compensation voltage under the current operating condition, is the healthy phase current, Z m is the mutual impedance of the line per unit length.

[0039] Furthermore, when 0≤θ-θ DZ When the angle is less than 90°, the fault is judged to be a transient fault and reclosing is allowed; otherwise, the fault is judged to be a permanent fault and reclosing is not allowed.

[0040] The present invention also includes a device for identifying the nature of a single-phase fault in a double-terminal weak-feedback system, using the above method, including:

[0041] The voltage and current acquisition unit is used to acquire the voltage and current of each phase at the local end of the AC line, obtain the healthy phase voltage and the fault phase local end voltage, and obtain the healthy phase current;

[0042] A midpoint voltage calculation unit, configured to calculate a healthy phase midpoint voltage based on the healthy phase voltage and the healthy phase current;

[0043] A fault phase end voltage amplitude calculation unit, used for calculating the fault phase end voltage amplitude during instantaneous fault based on the sound phase midpoint voltage;

[0044] A setting value calculation unit is used to determine whether the voltage amplitude of the fault phase at the terminal is greater than k times the maximum mutual inductance voltage at the permanent fault during a transient fault. If so, the voltage amplitude criterion is set using the difference in the voltage amplitude of the fault phase at the terminal during a transient fault and a permanent fault to obtain a setting value and enter the first operating condition determination unit; if not, enter the compensation voltage calculation unit;

[0045] The first operating condition judging unit is used to judge whether the amplitude of the voltage at the terminal of the fault phase is greater than the set value. If so, the fault type is judged to be a transient fault and reclosing is allowed. If not, the fault type is judged to be a permanent fault, the fault nature identification is completed, and reclosing is not allowed.

[0046] A compensation voltage calculation unit, used to calculate the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during an instantaneous fault;

[0047] The second operating condition determination unit is used to adjust the phase determination criterion based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during the instantaneous fault, and calculate the phase angle difference between the compensation voltage and the mutual inductance voltage under the current operating condition of the system, and determine whether the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is within a set range. If so, it is determined to be a transient fault and reclosing operation is allowed; if not, it is determined to be a permanent fault and reclosing is no longer performed.

[0048] The present invention also includes a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method described above is implemented.

[0049] The present invention also includes a storage medium on which a computer program is stored. When the computer program is executed by a processor, the method described above is implemented.

[0050] The beneficial effects of the present invention are:

[0051] By using the sound phase voltage and current measurement results at the local end of the AC line, the amplitude and phase of the tripping phase coupling voltage under different nature faults are calculated, the voltage amplitude criterion and phase criterion are adjusted in real time, and a voltage amplitude and phase joint criterion is established to make it suitable for the double-terminal weak feed system. The proposed identification method does not rely on the electrical characteristics of the AC system in the non-full-phase operation stage and is not affected by the operating conditions of the AC system. It can accurately identify the fault nature of single-phase grounding faults in different locations and with different transition resistances. Compared with the traditional single-phase fault nature identification method, it has wider applicability and higher reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0053] Figure 1 This is the topological structure diagram of the isolated wind farm-flexible direct current sending end system in the non-full-phase operation stage;

[0054] Figure 2 The flowchart of the method for identifying the nature of single-phase faults in a double-terminal weak-feed system based on adaptive setting is shown;

[0055] Figure 3 This is a simulation verification diagram of the principle of identifying transient faults using traditional phase criteria;

[0056] Figure 4 This is a simulation verification diagram of the phase criterion principle based on adaptive setting;

[0057] Figure 5 It is a schematic diagram of a single-phase fault nature identification device for a double-terminal weak-feed system based on adaptive setting;

[0058] Figure 6 A schematic diagram of the structure of a computer device. DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0060] Embodiment 1:

[0061] In order to overcome the problem that the double-terminal weak-feedback system cannot directly apply the traditional single-phase fault nature identification criterion, the present invention proposes a double-terminal weak-feedback system single-phase fault nature identification method based on adaptive setting. Figure 1 The direct-drive permanent magnet wind farm is connected to the 33kV collection line through the export transformer T3, and the collection line is connected to the 230kV AC interconnection line through the main transformer T1. The high-voltage AC interconnection line is connected to the flexible DC converter station.

[0062] like Figure 2 As shown: A method for identifying the nature of a single-phase fault in a double-terminal weak-feed system comprises the following steps:

[0063] S10: Collect the voltage and current of each phase at the local end of the AC line, obtain the healthy phase voltage and the fault phase local end voltage, and obtain the healthy phase current; specifically, obtain the healthy phase voltage at the reclosing installation location of the AC line local end through voltage transformer measurement And the trip phase voltage Taking the busbar flow direction as the positive direction of current, the healthy phase current of the AC line is measured by current transformer.

[0064] S20: Calculate the midpoint voltage of the healthy phase based on the healthy phase voltage and the healthy phase current;

[0065] S30: Calculate the voltage amplitude of the fault phase at the terminal when the instantaneous fault occurs based on the midpoint voltage of the healthy phase;

[0066] S40: Determine whether the voltage amplitude of the fault phase at the fault end during the transient fault is greater than k times the maximum mutual inductance voltage during the permanent fault. If so, use the difference in the voltage amplitude of the fault phase at the fault end during the transient fault and the permanent fault to adjust the voltage amplitude criterion, obtain the adjustment value, and enter step S50; if not, enter step S60;

[0067] S50: Determine whether the voltage amplitude of the fault phase is greater than the set value. If so, determine that the fault type is a transient fault and allow reclosing. If not, determine that the fault type is a permanent fault, complete the fault nature identification, and do not reclose.

[0068] S60: Calculate the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during instantaneous fault;

[0069] S70: Based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during the instantaneous fault, the phase judgment criterion is adjusted, and the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is calculated to determine whether the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is within the set range. If so, it is determined to be a transient fault and reclosing operation is allowed; if not, it is determined to be a permanent fault and reclosing is no longer performed.

[0070] According to the measurement results of the healthy phase voltage and current at the protection installation at the end of the line, the voltage amplitude of the tripping phase during instantaneous and permanent faults is calculated, and the validity of the voltage amplitude criterion is judged. For heavy-loaded and long-distance lines, the reliability of the voltage amplitude criterion is reduced, and the phase criterion based on adaptive setting is used to identify the nature of the fault. The proposed phase criterion is not affected by the electrical characteristics of the non-full-phase operation stage of the double weak-feed line, and the identification dead zone is eliminated by redefining the traditional compensation voltage. Compared with the traditional single-phase fault nature identification method, the method proposed in this patent is applicable to faults at any position of the line, does not rely on the distance measurement results, and is not affected by the operating conditions. It has a wider applicability and higher reliability.

[0071] Through multi-step voltage and current analysis, including calculation of the midpoint voltage of the healthy phase and the voltage amplitude of the fault phase, it is possible to accurately distinguish between transient faults and permanent faults. This method can effectively avoid misjudgment and improve the accuracy of system fault identification.

[0072] The voltage amplitude judgment criterion is adaptively adjusted according to the different fault properties. By adjusting and calculating the voltage amplitude difference between transient faults and permanent faults, the setting value is made more accurate, thereby optimizing the effect of fault property judgment. The adaptability helps to deal with fault situations under different working conditions and improves the applicability and reliability of the method.

[0073] Identifying the reclosing operation conditions can effectively prevent invalid reclosing operations under permanent faults, reduce unnecessary impacts on the system, and extend equipment life. At the same time, allowing reclosing operations under transient faults helps to improve power supply continuity and system stability.

[0074] By calculating the phase difference between the compensation voltage and the mutual inductance voltage and evaluating the change in the phase difference under the current system operating conditions, the nature of the fault can be determined. This analysis method based on phase difference can dynamically adapt to the operating status of the system and improve the reliability of the method under complex conditions.

[0075] This method is specially designed for double-terminal weak-feed systems, taking into account the characteristics of voltage mutual inductance and phase angle difference in weak-feed systems. It can better adapt to the needs of single-phase fault identification under weak-feed systems. Compared with traditional methods, it can still maintain a high fault identification accuracy under weak-feed conditions.

[0076] As a preferred embodiment of the above, in step S20, the midpoint voltage of the healthy phase is calculated. Models include:

[0077]

[0078] In the formula, is the healthy phase voltage, is the healthy phase current, Z l is the line self-impedance per unit length, Z m is the mutual impedance of the line per unit length, and l is the total length of the line.

[0079] Through the above model, the midpoint voltage of the healthy phase under different operating conditions can be accurately calculated, which helps to accurately understand the voltage conditions of the healthy phase of the system and provide reliable basic data for subsequent fault nature identification.

[0080] In this embodiment, in step S30, based on the midpoint voltage of the healthy phase, the voltage amplitude of the fault phase at the instantaneous fault is calculated. Models include:

[0081]

[0082] In the formula, is the capacitive coupling voltage during transient faults, is the mutual inductance voltage per unit length of the line under the current operating conditions, is the midpoint voltage of a healthy phase, is the healthy phase current, b 1 、b 0 is the positive and zero sequence admittance per unit length of the line, Z mis the mutual impedance of the line per unit length, and l is the total length of the line.

[0083] By introducing parameters such as the capacitive coupling voltage and mutual inductance voltage of transient faults, the model can more accurately distinguish between transient faults and permanent faults. In actual operation, it can better determine whether reclosing operations are allowed, thereby improving the flexibility and safety of system recovery.

[0084] In step S40, it is determined whether the voltage amplitude of the fault phase at the faulty phase in the transient fault is greater than k times the maximum mutual inductance voltage in the permanent fault. Models include:

[0085]

[0086] In the formula, is the healthy phase current, Z m is the mutual impedance of the line per unit length, and l is the total length of the line.

[0087] By providing a calculation model for the maximum mutual inductance voltage during a permanent fault, this method can accurately determine whether the voltage amplitude at the fault phase end exceeds the criterion value, thereby effectively distinguishing between transient faults and permanent faults. This judgment method improves the accuracy of fault identification and ensures appropriate reclosing operations.

[0088] As a preferred embodiment of the above, in step S40, it is determined whether the voltage amplitude of the fault phase at the fault end during the transient fault is greater than k times the maximum mutual inductance voltage during the permanent fault. If so, the voltage amplitude criterion is adjusted by using the voltage amplitude difference between the fault phase at the fault end during the transient fault and the permanent fault to obtain a set value, and the set value U DZ Models include:

[0089]

[0090] In the formula, is the maximum mutual inductance voltage during permanent fault, It is the voltage amplitude at the fault phase end during instantaneous fault.

[0091] By adaptively setting the voltage amplitude criterion, this method can adjust the setting value according to the actual voltage amplitude difference of different fault types, making the criterion more in line with the actual situation, thereby improving the accuracy of fault nature judgment.

[0092] In this embodiment, when U A >U DZ When the fault type is determined to be a transient fault, reclosing is allowed;

[0093] When U A <U DZWhen U ins <kU per The phase criterion is used to identify the nature of the fault and the process proceeds to step S60.

[0094] When the voltage amplitude at the fault phase end cannot directly determine the fault type, the phase judgment is used for further judgment, which effectively avoids making wrong judgments based on the voltage amplitude alone. The introduction of the phase judgment makes up for the shortcomings of the voltage amplitude judgment and enhances the accuracy and reliability of the judgment.

[0095] Among them, in step S60, before calculating the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during a transient fault, it is determined whether the voltage amplitude at the fault phase end is greater than the amplitude of the mutual inductance voltage at half the length of the line, so as to adopt different models to calculate the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during a transient fault.

[0096] Comparing the voltage amplitude at the fault phase end with the mutual inductance voltage amplitude of a normal length before calculating the phase angle difference helps to accurately select a suitable calculation model, thereby eliminating the dead zone of phase criterion identification and improving the accuracy and reliability of fault nature identification.

[0097] As a preferred embodiment of the above, if U A ≥0.5U x l. Calculate the fault phase compensation voltage during instantaneous fault Mutual inductance voltage The phase angle difference θ ins , the model includes:

[0098]

[0099] Where U A is the voltage amplitude of the fault phase terminal, is the fault phase terminal voltage, U x is the amplitude of the mutual inductance voltage per unit length of the line under the current operating conditions, l is the total length of the line, is the mutual inductance voltage per unit length of the line under the current operating conditions, It is the capacitive coupling voltage during transient fault.

[0100] Through the above model, under specific conditions (i.e. when the voltage amplitude at the fault phase end is less than the mutual inductance voltage amplitude at half the length of the line), the compensation voltage is calculated and the phase angle difference is analyzed, thereby eliminating the phase criterion identification dead zone and improving the accuracy and reliability of fault nature identification.

[0101] In this embodiment, if U A <0.5U x l. Calculate the fault phase compensation voltage during instantaneous fault The phase angle difference θ between the mutual inductance voltage and ins , the model includes:

[0102]

[0103] Where U A is the voltage amplitude of the fault phase terminal, is the fault phase terminal voltage, U x is the amplitude of the mutual inductance voltage per unit length of the line under the current operating conditions, l is the total length of the line, is the mutual inductance voltage per unit length of the line under the current operating conditions, It is the capacitive coupling voltage during transient fault.

[0104] By judging U A <0.5U x l, and accurately calculate the phase angle difference between it and the mutual inductance voltage, eliminating the dead zone of phase criterion identification and improving the accuracy and reliability of fault nature identification.

[0105] As a preferred embodiment of the above embodiment, in step S70, based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during the instantaneous fault, the phase criterion is adjusted, and the phase angle difference between the compensation voltage and the mutual inductance voltage under the current operating condition of the system is calculated. The model includes:

[0106]

[0107] In the formula, θ DZ is the setting value of the phase criterion based on adaptive setting, θ is the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system, θ ins is the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during instantaneous fault, is the fault phase compensation voltage under the current operating condition, is the healthy phase current, Z m is the mutual impedance of the line per unit length.

[0108] The accurate phase angle difference setting value is calculated through the phase judgment criterion of adaptive adjustment, which helps to accurately distinguish between transient faults and permanent faults, and avoids misjudgment caused by the identification dead zone at the midpoint of the line.

[0109] In this embodiment, when 0≤θ-θ DZ When the angle is less than 90°, the fault is judged to be a transient fault and reclosing is allowed; otherwise, the fault is judged to be a permanent fault and reclosing is not allowed. The operation process of this method is clear and can quickly determine the nature of the fault, reducing the time and cost of manual judgment and improving operation and maintenance efficiency and management effect.

[0110] The single-phase fault nature identification criterion based on adaptive setting proposed in the present invention is not affected by the electrical quantity characteristics and system operating conditions of the double-terminal weak-feed system in the non-full-phase operation stage. For the double-terminal weak-feed system with a high proportion of new energy stations transmitting power through long-distance transmission lines, the single-phase fault nature identification criterion proposed in the present invention is still applicable.

[0111] The method measures the healthy phase voltage and current at the local reclosing installation location, calculates the amplitude and phase of the tripping phase coupling voltage when different nature faults occur, and adjusts the voltage amplitude criterion and phase criterion in real time. Since the voltage amplitude criterion and the phase criterion are adjusted based on the real-time measurement results of the voltage and current at the local protection installation location, the proposed identification criterion does not rely on the electrical quantity characteristics of the non-full-phase operation stage of the AC system, which solves the problem that the electrical quantity characteristics of the non-full-phase operation stage of the double-end weak-feed system are different from those of the traditional AC system, and the traditional single-phase fault nature identification criterion cannot be directly applied. The single-phase fault nature identification method proposed in the invention makes full use of the amplitude and phase differences of the tripping phase coupling voltage when different nature faults occur in the AC line, and combines the advantages of the voltage amplitude criterion and the phase criterion. Compared with the traditional single-phase fault nature identification criterion, it has wider applicability and higher reliability, and has good application prospects for realizing the rapid recovery of the double-end weak-feed system after single-phase grounding fault tripping and improving the power supply reliability of new energy stations.

[0112] Embodiment 2:

[0113] In Simulink, Figure 1 The wind power-flexible direct current sending end system shown in the figure performs simulation verification of the above-mentioned single-phase fault nature identification criteria. During the simulation, the positive sequence control target of the wind farm grid-side converter is to stabilize the DC bus voltage and output unity power factor, and the negative sequence control target is to suppress the negative sequence current. When the positive sequence voltage at the wind farm outlet drops, reactive power is injected into the grid according to the low-breakthrough standard. The positive sequence control target of the sending-end MMC converter station is to output an AC side voltage with a stable amplitude and frequency, and the negative sequence is not controlled. The main parameters of the direct-drive permanent magnet wind farm and the flexible direct current converter station in the wind power-flexible direct current sending end system are shown in Table 1.

[0114] Table 1 Main parameters of PMSG and MMC-HVDC

[0115]

[0116] The sequence impedance and admittance parameters of the 230kV AC interconnection line are shown in Table 2. The line length is 30km. The leakage reactance of the main transformer T1 is 0.002+0.08pu.

[0117] Table 2 Main parameters of 230kV AC interconnection line

[0118]

[0119] In the simulation, a single-phase grounding fault is assumed to occur at the midpoint of phase A of the AC interconnection line. The traditional voltage amplitude fault property identification criterion is verified, and the results of the wind farm end amplitude criterion are shown in Table 3.

[0120] Table 3 Simulation verification of traditional voltage amplitude criterion

[0121]

[0122] It can be seen from Table 3 that when the wind farm is fully powered, the traditional voltage amplitude judgment criterion will misjudge a permanent fault as a transient fault. This is because the zero-sequence current of the wind power-flexible DC system increases compared to the traditional AC system during the non-full-phase operation stage, and the tripping mutual induction voltage increases, resulting in an increase in the tripping phase terminal voltage amplitude, and the length of the line that the criterion is adapted to is significantly shortened.

[0123] The principle of the traditional phase judgment to identify transient faults is that the absolute value of the phase angle difference between the capacitive coupling voltage and the mutual inductance voltage of the tripped phase during a transient fault is equal to the sum of the mutual inductance impedance angle and the power factor angle during normal operation. The phase angle difference calculated by this method in the wind power-flexible direct current transmission system and the phase angle difference obtained by simulation measurement are as follows: Figure 3 shown.

[0124] Depend on Figure 3 It can be seen that when the wind farm output power is large, the phase angle difference between the capacitor coupling voltage and the mutual inductance voltage during the instantaneous fault calculated by the traditional phase judgment is quite different from the simulation result. This is related to the reduction of the positive sequence voltage at the wind farm outlet and the activation of the low-through strategy of the wind farm. The traditional phase identification criterion cannot accurately reflect the phase characteristics of the phase coupling voltage during the non-full-phase operation stage of the AC interconnection line.

[0125] According to the measured values ​​of the healthy phase voltage and current at this end, the phase angle difference between the capacitor coupling voltage and the mutual inductance voltage is obtained by calculating the model of the phase angle difference between the compensation voltage and the mutual inductance voltage under the current operating conditions of the system. The curve of the phase angle difference changing with the output power of the wind farm is obtained by making the calculation results and the simulation measurement. Figure 4 shown.

[0126] Depend on Figure 4 The phase angle difference between the trip phase capacitance coupling voltage and the mutual inductance voltage calculated by using the measured values ​​is consistent with the simulation result. The phase discrimination criterion based on adaptive setting can accurately reflect the phase characteristics of the trip phase coupling voltage of the AC interconnection line.

[0127] For wind farms with different output powers and AC line faults of different natures at different locations, the fault nature identification method based on adaptive setting proposed in this paper is verified. The simulation results are shown in Table 4.

[0128] Table 4 Simulation verification of fault nature identification method based on adaptive setting

[0129]

[0130] The simulation results show that when the wind farm is fully powered, the voltage amplitude of the tripped phase terminal during a transient fault is slightly different from the voltage amplitude of the tripped phase terminal during a permanent fault at the opposite end of the line, and the reliability of the voltage amplitude criterion is reduced; when faults occur at different locations of the AC line, the proposed phase criterion can accurately identify the nature of the fault and there is no identification dead zone. Combining the results of the terminal voltage amplitude criterion and the phase criterion, the proposed single-phase fault nature identification criterion based on adaptive setting can accurately identify transient and permanent faults.

[0131] The present invention also includes a device for identifying the nature of a single-phase fault in a double-terminal weak-feedback system, using the method described above, such as Figure 5 As shown, including:

[0132] The voltage and current acquisition unit is used to acquire the voltage and current of each phase at the local end of the AC line, obtain the healthy phase voltage and the fault phase local end voltage, and obtain the healthy phase current;

[0133] A midpoint voltage calculation unit, used for calculating a healthy phase midpoint voltage based on a healthy phase voltage and a healthy phase current;

[0134] A fault phase end voltage amplitude calculation unit, used to calculate the fault phase end voltage amplitude during instantaneous fault based on the sound phase midpoint voltage;

[0135] The setting value calculation unit is used to determine whether the voltage amplitude of the fault phase at the fault end during a transient fault is greater than k times the maximum mutual inductance voltage during a permanent fault. If so, the voltage amplitude judgment criterion is set using the difference in the voltage amplitude of the fault phase at the fault end during a transient fault and a permanent fault to obtain a setting value and enter the first judgment unit of the operating condition; if not, enter the compensation voltage calculation unit;

[0136] The first operating condition judgment unit is used to judge whether the amplitude of the voltage at the fault phase is greater than the set value. If so, the fault type is judged to be a transient fault and reclosing is allowed. If not, the fault type is judged to be a permanent fault, the fault nature identification is completed, and reclosing is not allowed.

[0137] A compensation voltage calculation unit, used to calculate the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during an instantaneous fault;

[0138] The second operating condition judgment unit is used to adjust the phase judgment criterion based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during instantaneous faults, and calculate the phase angle difference between the compensation voltage and the mutual inductance voltage under the current operating condition of the system, and judge whether the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is within a set range. If so, it is judged as a transient fault and reclosing operation is allowed; if not, it is judged as a permanent fault and the circuit breaker is no longer closed.

[0139] See also Figure 6 A computer device 400 provided in an embodiment of the present application includes: a processor 410 and a memory 420, wherein the memory 420 stores a computer program executable by the processor 410, and when the computer program is executed by the processor 410, the above method is executed.

[0140] The embodiment of the present application further provides a storage medium 430 on which a computer program is stored. When the computer program is run by the processor 410, the above method is executed.

[0141] Among them, the storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable red-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, disk or optical disk.

[0142] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0143] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0144] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0145] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention belong.

[0146] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic devices), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0147] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0148] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0149] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for identifying the nature of a single-phase fault in a double-terminal weak-feed system, characterized in that: The steps include: S10: collecting the voltage and current of each phase at the local end of the AC line, obtaining the voltage of the healthy phase and the voltage at the local end of the faulty phase, and obtaining the current of the healthy phase; S20: Calculating a healthy phase midpoint voltage based on the healthy phase voltage and the healthy phase current; S30: Calculating the voltage amplitude of the fault phase at the terminal when the instantaneous fault occurs based on the midpoint voltage of the healthy phase; S40: Determine whether the voltage amplitude of the fault phase at the terminal during a transient fault is greater than k times the maximum mutual inductance voltage during a permanent fault. If so, adjust the voltage amplitude criterion by using the voltage amplitude difference between the fault phase at the terminal during a transient fault and a permanent fault to obtain a set value, and proceed to step S50; if not, proceed to step S60; S50: Determine whether the amplitude of the voltage at the fault phase terminal is greater than the set value. If so, determine that the fault type is a transient fault and allow reclosing. If not, determine that the fault type is a permanent fault, complete the fault nature identification, and do not reclose. S60: Calculate the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during instantaneous fault; Before calculating the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during an instantaneous fault, it is determined whether the voltage amplitude at the fault phase end is greater than the mutual inductance voltage amplitude at half the length of the line, so as to adopt different models to calculate the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating conditions; If U A ≥0.5U x l, the calculation of the fault phase compensation voltage during instantaneous fault Mutual inductance voltage The phase angle difference θ ins , the model includes: Where U A is the voltage amplitude of the fault phase terminal, is the fault phase terminal voltage, U x is the amplitude of the mutual inductance voltage per unit length of the line under the current operating conditions, l is the total length of the line, is the mutual inductance voltage per unit length of the line under the current operating conditions, It is the capacitive coupling voltage during instantaneous fault; If U A <0.5U x l, the calculation of the fault phase compensation voltage during instantaneous fault Mutual inductance voltage The phase angle difference θ ins , the model includes: Where U A is the voltage amplitude of the fault phase terminal, is the fault phase terminal voltage, U x is the amplitude of the mutual inductance voltage per unit length of the line under the current operating conditions, l is the total length of the line, is the mutual inductance voltage per unit length of the line under the current operating conditions, It is the capacitive coupling voltage during instantaneous fault; S70: Based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during the instantaneous fault, the phase judgment criterion is adjusted, and the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is calculated to determine whether the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is within a set range. If so, it is determined to be a transient fault and reclosing operation is allowed; if not, it is determined to be a permanent fault and the circuit breaker is no longer closed.

2. The method for identifying the nature of a single-phase fault in a double-terminal weak-feed system according to claim 1 is characterized in that: In step S20, the midpoint voltage of the healthy phase is calculated Models include: In the formula, is the healthy phase voltage, is the healthy phase current, Z l is the line self-impedance per unit length, Z m is the mutual impedance of the line per unit length, and l is the total length of the line.

3. The method for identifying the nature of a single-phase fault in a double-terminal weak-feed system according to claim 1, characterized in that: In step S30, based on the midpoint voltage of the healthy phase, the voltage amplitude of the fault phase at the instantaneous fault is calculated. Models include: In the formula, is the capacitive coupling voltage during transient faults, is the mutual inductance voltage per unit length of the line under the current operating conditions, is the midpoint voltage of a healthy phase, is the healthy phase current, b1 and b0 are the positive and zero sequence admittances per unit length of the line, and Z m is the mutual impedance of the line per unit length, and l is the total length of the line.

4. The method for identifying the nature of a single-phase fault in a double-terminal weak-feed system according to claim 1, characterized in that: In step S40, it is determined whether the voltage amplitude of the fault phase at the terminal during the transient fault is greater than k times the maximum mutual inductance voltage during the permanent fault, wherein the maximum mutual inductance voltage during the permanent fault is Models include: In the formula, is the healthy phase current, Z m is the mutual impedance of the line per unit length, and l is the total length of the line.

5. The method for identifying the nature of a single-phase fault in a double-terminal weak-feed system according to claim 1, characterized in that: In step S40, it is determined whether the voltage amplitude of the fault phase at the terminal during the transient fault is greater than k times the maximum mutual inductance voltage during the permanent fault. If so, the voltage amplitude criterion is adjusted by using the voltage amplitude difference between the fault phase at the terminal during the transient fault and the permanent fault to obtain a set value. The set value U DZ Models include: In the formula, is the maximum mutual inductance voltage during permanent fault, It is the voltage amplitude of the instantaneous fault phase.

6. The method for identifying the nature of a single-phase fault in a double-terminal weak-feed system according to claim 5, characterized in that: When U A >U DZ When , the fault type is determined to be a transient fault, and reclosing is allowed; When U A DZ When U ins <kU per The phase criterion is used to identify the nature of the fault and the process proceeds to step S60.​ 7. The method for identifying the nature of a single-phase fault in a double-terminal weak-feed system according to claim 1, characterized in that: In step S70, based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during the instantaneous fault, the phase criterion is adjusted, and the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is calculated. The model includes: In the formula, θ DZ is the setting value of the phase criterion based on adaptive setting, θ is the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system, θ ins is the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during instantaneous fault, is the fault phase compensation voltage under the current operating condition, is the healthy phase current, Z m is the mutual impedance of the line per unit length.

8. The method for identifying the nature of a single-phase fault in a double-terminal weak-feed system according to claim 7, characterized in that: When 0≤θ-θ DZ When the angle is <90°, the fault is judged to be a transient fault and reclosing is allowed; otherwise, the fault is judged to be a permanent fault and reclosing is not allowed.

9. A device for identifying the nature of single-phase faults in a double-terminal weak-feed system, characterized in that: Use of the method according to any one of claims 1 to 8, comprising: The voltage and current acquisition unit is used to acquire the voltage and current of each phase at the local end of the AC line, obtain the healthy phase voltage and the fault phase local end voltage, and obtain the healthy phase current; A midpoint voltage calculation unit, configured to calculate a healthy phase midpoint voltage based on the healthy phase voltage and the healthy phase current; A fault phase end voltage amplitude calculation unit, used for calculating the fault phase end voltage amplitude during instantaneous fault based on the sound phase midpoint voltage; A setting value calculation unit is used to determine whether the voltage amplitude of the fault phase at the terminal is greater than k times the maximum mutual inductance voltage at the permanent fault during a transient fault. If so, the voltage amplitude criterion is set using the difference in the voltage amplitude of the fault phase at the terminal during a transient fault and a permanent fault to obtain a setting value and enter the first operating condition determination unit; if not, enter the compensation voltage calculation unit; The first operating condition judging unit is used to judge whether the amplitude of the voltage at the terminal of the fault phase is greater than the set value. If so, the fault type is judged to be a transient fault and reclosing is allowed. If not, the fault type is judged to be a permanent fault, the fault nature identification is completed, and reclosing is not allowed. A compensation voltage calculation unit is used to calculate the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during a transient fault; a second operating condition determination unit is used to adjust the phase determination criterion based on the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage during the transient fault, and calculate the phase angle difference between the compensation voltage and the mutual inductance voltage under the current operating condition of the system, and determine whether the phase angle difference between the fault phase compensation voltage and the mutual inductance voltage under the current operating condition of the system is within a set range; if so, it is determined to be a transient fault and reclosing operation is allowed; if not, it is determined to be a permanent fault and reclosing is no longer performed.

10. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 8 is implemented.

11. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 8 is implemented.

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