New energy bundling delivery line fault phase selection method based on current pressure complementation and boundary phase difference

Abstract

A new energy bundled delivery line fault phase selection method based on current-voltage complementation and boundary phase difference comprises the following steps: establishing a fault additional network model containing access of different fault types of new energy at a power supply side, and analyzing characteristics of a fault current component in a fault additional network and voltage and current break variable at one side of a line; representing a single-side voltage and current break variable through a fault current component; constructing phase operators of different types of faults; establishing a fault type judgment criterion; and representing the phase difference of the operator through the Euclidean distance, and establishing a fault phase selection criterion based on threshold comparison. The fault phase selection characteristic established by using the fault additional network is not influenced by the system operation mode and the transition resistance. The phase selection characteristic presented by the phase operator is irrelevant to the power supply impedance measurement and the power supply type, and the method can adapt to access of new energy of different types and different proportions.

Description

Technical Field

[0001] This invention relates to the field of fault phase selection technology for bundled new energy transmission lines, specifically to a fault phase selection method for bundled new energy transmission lines based on current-voltage complementarity and boundary phase difference. Background Technology

[0002] China's geographical distribution of energy resources dictates a centralized development and bundled transmission model for new energy. In Northwest China, abundant wind and solar resources have enabled the establishment of large-scale new energy power plants. Simultaneously, different types of new energy plants are bundled with nearby thermal power plants for transmission to improve system stability. Bundled new energy transmission lines differ significantly from typical new energy plant transmission lines: different types and proportions of energy sources are coupled on the power supply side of these lines, resulting in fault characteristics that are a superposition of fault features from different energy sources. Furthermore, due to the uncertainty of new energy output and significant real-time penetration rate variations, the fault characteristics of bundled new energy transmission lines involve multiple coupling factors, leading to high complexity. These characteristics severely reduce the accuracy of fault phase selection methods for these lines. Moreover, the fault phase selection result serves as a prerequisite for single-end protection phase tripping; incorrect phase selection will amplify the impact of the fault and even affect the correct operation of the line reclosing mechanism.

[0003] Some existing fault phase selection methods are based on the outgoing lines of new energy power plants. The main idea is to improve the phase selection method according to the fault characteristics of a certain type of new energy. For example, the literature (Kang Tao, Weng Hanli, Lin Xiangning, et al. Recovery strategy of phase selection capability of photovoltaic power plant outgoing lines considering the sudden change of energy storage system control and protection coordination system [J]. Proceedings of the CSEE, 2024, 44(11): 4273-4286.) improves the control strategy of energy storage device and controls the equivalent impedance characteristics of the power supply during the fault, thereby restoring the performance of the traditional phase selection method. The literature (Wang Ziwei, Xiao Fan, Wang Youhuai, et al. Fault phase selection method applicable to doubly fed wind farm tie line [J]. Automation of Electric Power System, 2018, 42(8): 170-176.) targets the scenario where the doubly fed wind turbine generator does not have the crowbar resistor connected, and performs fault phase selection based on the voltage characteristics on one side of the line. Current research on fault phase selection faces several challenges: First, it has a limited scope. Improved phase selection methods, based on specific fault characteristics of certain energy types, are poorly adaptable to other types of renewable energy. For example, phase selection methods for photovoltaic power cannot be directly applied to transmission lines of doubly-fed wind power. This limitation makes existing improved methods ill-suited for transmission lines bundling multiple types of renewable energy. Second, the phase selection methods involve additional controls, making practical modifications difficult and costly. Furthermore, the added controls may conflict with the original fault ride-through objectives. Therefore, existing improved phase selection methods also suffer from insufficient adaptability when dealing with transmission lines bundling renewable energy. The core reason is the complex coupling of energy types; there is still a gap in fault phase selection methods that can adapt to different types and proportions of renewable energy access. Summary of the Invention

[0004] To improve the accuracy of fault identification in bundled new energy transmission lines, this invention proposes a fault phase selection method based on current-voltage complementarity and boundary phase difference. This method takes bundled new energy transmission lines as the object and a fault-addition network as its foundation. It characterizes the fault point current through voltage and current abrupt changes on one side of the line. Based on the fault current boundary conditions, it applies boundary conditions for different fault types to establish a current-voltage complementary phase operator. Only under a unique phase sequence combination corresponding to the fault phase does the operator phase difference minimize, resulting in clear phase selection characteristics that are independent of power supply characteristics. Finally, it constructs fault types and fault phase selection criteria, thereby improving the accuracy of fault phase selection in bundled new energy transmission lines.

[0005] The technical solution adopted in this invention is as follows: A fault phase selection method for bundled new energy transmission lines based on current-voltage complementarity and boundary phase difference includes the following steps: Step 1: Analyze the parameter characteristics of the fault-addition network: A fault-addition network model for power supply measurement, including the access of new energy sources with different fault types, is established, and the characteristics of fault current components and voltage and current abrupt changes on one side of the line are analyzed in the fault-addition network. Step 2: Represent the sudden change in voltage and current on one side using the fault current component: Based on the fault-addition network in step 1, and based on the principles of current shunting and voltage division, the fault current component is used to represent the voltage and current abrupt changes on one side of the line. Step 3: Construct phase operators for different types of faults: Based on the current boundary conditions of different types of faults, the current-voltage complementary phase calculation operators for three types of faults—single-phase grounding, phase-to-phase faults, and phase-to-phase grounding—are derived through mathematical transformation. The magnitude of the phase difference of the operators under different phase sequence combinations reflects the fault phase. Step 4: Establish fault type discrimination criteria: Establish ground fault criteria based on zero-sequence voltage characteristics; In ungrounded fault types, three-phase faults are identified by the symmetry of voltage drops; In the ground fault types, phase-to-phase and single-phase ground faults are distinguished by the phase characteristics of the single-phase ground fault operator in step 3; Step 5: Establish fault phase selection criteria: By characterizing the phase difference of the operator using Euclidean distance, a fault phase selection criterion based on threshold comparison is established.

[0006] In step 1, the voltage at the protection installation location on the M side of line in the fault supplementary network... and current This is equal to the voltage and current abrupt changes measured at that point under a conventional network, i.e.: (1); In equation (1), the subscript j The values ​​of are 1, 2, and 0, representing positive, negative, and zero-order components, respectively; and These represent the sequence abrupt changes in voltage and current on the M side of the line, respectively. and These represent the sequence components of voltage and current on the M side of the line after the fault. and These represent the sequence components of voltage and current on the M side of the line before the fault.

[0007] Meanwhile, since there was no fault circuit before the fault, the sequence components of the fault current in the fault-addition network are equivalent to the sequence components of the short-circuit current flowing into the fault point after the fault, that is: (3); In equation (3), This represents the fault current component in the fault-addition network. This represents the short-circuit current flowing into the fault point after a fault occurs in a conventional network.

[0008] In step 2, in the fault-addition network, only the fault point has a fault-addition voltage, and all impedances are passive. Based on the current shunting and voltage division characteristics, it can be known that there is a relationship between the actual measured voltage and current surges on the M side of the line and the fault current: (4); In equation (4), and These represent the sequence abrupt changes in voltage and current on the M side of the line, respectively. This indicates the fault current component in the fault-addition network. This indicates the total impedance of the power supply, which is composed of the impedances of different types of energy sources connected in parallel. Indicates line impedance; Indicates the impedance of the receiving end system; This represents the line impedance from the fault point to bus N.

[0009] In step 3, when different types of faults occur on the line, there is a fixed and unique current boundary condition under a specific phase sequence combination, and a criterion is established based on this current boundary condition. Based on the characteristics of current boundary conditions for different types of faults, and combined with the relationship between the actual measured voltage and current mutations and fault currents on the M side of the line in step 2, positive and negative sequence current ratios are used for single-phase grounding and phase-to-phase faults; positive and negative zero sequence current vector sums are used for phase-to-phase grounding faults, and current-voltage complementary phase operators for different fault types are established.

[0010] 3.1: Single-phase ground fault: The operator for single-phase grounding is and Only under the phase sequence combination that uniquely corresponds to the faulty phase. The angle is 0, where, This represents the positive-sequence component of the fault current in the fault-addition network. Indicates the positive-sequence component of the fault point current in the fault-addition network; subscript x The values ​​A, B, and C represent the sequence component values ​​calculated using the ABC phase sequence, BCA phase sequence, and CAB phase sequence, respectively; that is... and The phases are equal, and the rest of the phase sequence is equal. and The phases differ by 120°, and the phase operator characteristics are as follows: (7); In equation (7), the superscript (1) indicates the single-phase ground fault type; and These are the left and right operators for a single-phase ground fault, combining the two major characteristics of current and voltage surge. This represents the sum of the receiving-end system impedance and the line impedance, where, This represents the sum of the receiving-end system impedance and the line impedance; This represents the positive-sequence impedance of the receiving-end system; The positive sequence impedance represents the total length of the line. This represents the negative sequence impedance of the receiving-end system; Negative sequence impedance of the entire line length.

[0011] Subscript x The values ​​are A, B, and C, which represent the calculations using the ABC phase sequence, BCA phase sequence, and CAB phase sequence, respectively. and These respectively indicate the use of the M side of the line. x The positive and negative sequence voltage abrupt changes calculated by phase sequence; and These respectively indicate the use of the M side of the line. x The abrupt changes in positive and negative sequence currents calculated by phase sequence; and These respectively represent the use in the barrier-attached network. x The positive and negative components of the fault current calculated by phase sequence.

[0012] 3.2: Phase-to-phase fault: The phase operator for interphase faults is and Only under the phase sequence combination that uniquely corresponds to the faulty phase. The angle is 0, that is and The phases are equal, and the rest of the phase sequence is equal. and The phases differ by 120°, and the phase operator characteristics are as follows: (8); In equation (8), the superscript (2) indicates the phase-to-phase fault type; and These are the left and right operators for phase-to-phase faults, respectively.

[0013] 3.3: Phase-to-phase grounding faults: The phase operator for interphase faults is and The additional item is only applicable when the phase sequence combination uniquely corresponds to the faulty phase. ,Right now and The phases are equal, and the rest of the phase sequence is equal. and The phases differ by at least 120°. The phase operator properties are as follows: (10); In equation (10), the superscript (1,1) indicates the type of fault between phases; and These are the left and right operators for the inter-phase fault, respectively; X Table of additional items based on boundary conditions; Z N1 The receiving-end system is the positive-sequence impedance; Z LN1 The line impedance from the fault point to the N-side busbar; This represents the ratio of the positive-sequence impedance to the zero-sequence impedance of the system from the fault point to the receiving end, where... This represents the positive-sequence impedance of the receiving-end system; This represents the positive sequence impedance of the line from the fault point to the N side of the busbar. This represents the zero-sequence impedance of the receiving-end system; This represents the zero-sequence impedance of the line from the fault point to the N side of the bus.

[0014] This represents the sum of the zero-sequence impedances of the line and the receiving-end system, where... This represents the zero-sequence impedance of the receiving-end system; The zero-sequence impedance represents the total length of the line. and These respectively indicate the use of the M side of the line. x Zero-sequence voltage and current abrupt changes calculated by phase sequence.

[0015] In step 4, the fault type discrimination criteria are established, including: 4.1: Criteria for determining the type of grounding fault: The zero-sequence component is used to determine whether a ground fault has occurred in the system, based on the following criteria: (11); In equation (11), k 1 represents the reliability coefficient, which is set to 0.05; and The zero-sequence and positive-sequence voltages on the M side, respectively.

[0016] 4.2: Three-phase fault diagnosis criteria: Three-phase faults are identified by determining whether the three-phase voltage drops are symmetrical. The criteria are as follows: (12); In equation (12): and Indicates the M side of the line m Harmony n Phase voltage surge magnitude; subscript m and n It refers to phases A, B, and C; This represents the ratio between different phases. In the case of a three-phase fault, the ratio is close to 1; in the case of a phase-to-phase fault, the above criterion is not met. The reliability coefficient is set to 0.3.

[0017] 4.3: Criteria for determining single-phase grounding and phase-to-phase grounding: Phase operator for single-phase ground faults and The phase characteristics are used to determine the type of single-phase grounding and phase-to-phase grounding, and the criteria are as follows: (13); In equation (13): , and These represent the minimum, intermediate, and maximum values ​​of the phase, respectively. Take 0.7.

[0018] In step 5, a fault phase selection criterion is established: Based on the fault type determined in step 4, the phase is calculated using the corresponding phase operator from step 3. The phases of the left and right phase operators are recorded as follows: and The boundary phase difference of the operator is measured using Euclidean distance: (14); In equation (14): This represents the distance values ​​under different phase sequence combinations; n Indicates the sampled value number; subscript x This represents different phase sequence combinations, with values ​​A, B, or C, representing ABC, BCA, and CAB phase sequences respectively. and These represent the phase values ​​of the left and right phase operators corresponding to different fault types in step 3, respectively.

[0019] Step 4 establishes a fault type criterion, which serves to initially determine the fault type. The determined fault type determines which operator in Step 3 is used. and There is no restriction on the type of fault or its phase. For example, if step 4 determines it is a single-phase ground fault, then the single-phase ground fault operator from step 3 is used to calculate the phase. and These are single-phase grounding operators and The phase. Similarly, if step 4 determines it to be a phase-to-phase fault, then the phase is calculated using the phase-to-phase fault operator from step 3. and These are phase-to-phase fault operators and The phase. Indirect phase failures are similar to the process described above.

[0020] The operators for the different fault types mentioned above are essentially constructed based on boundary conditions, hence the term "boundary phase difference". The fault phase selection criterion is: (15); In equation (15): express x Phase difference under phase sequence combination; threshold , Take 0.4.

[0021] Output those that meet the criteria x Phase sequence combination achieves the goal of fault phase selection.

[0022] This invention discloses a fault phase selection method for bundled new energy transmission lines based on current-voltage complementarity and boundary phase difference. The technical effects are as follows: 1) This invention uses only one-sided data for fault phase selection, which requires little computation, has a simple threshold setting, and is easy to implement.

[0023] 2) The fault phase selection feature established by the fault-addition network in this invention is not affected by the system operating mode and transition resistance.

[0024] 3) The phase selection characteristics exhibited by the phase operator of this invention are independent of the power supply impedance and power supply type, and can adapt to the access of new energy sources of different types and proportions. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and examples; Figure 1 A topology diagram of transmission routes that bundle different types of new energy sources.

[0026] Figure 2 shows the additional network diagram for the fault.

[0027] Figure 3 is a flowchart of the fault phase selection process.

[0028] Figure 4 shows the verification results of the ground fault criterion.

[0029] Figure 5 The verification results for single-phase grounding and phase-to-phase grounding criteria (AG fault).

[0030] Figure 6The verification results for single-phase grounding and phase-to-phase grounding criteria (ABG fault).

[0031] Figure 7 Phase selection results for AG fault.

[0032] Figure 8 The phase selection result for AB fault.

[0033] Figure 9 The phase selection result for ABG fault.

[0034] Figure 10 The phase selection result for ABC faults.

[0035] Figure 11 The phase selection results for 100% photovoltaic grid connection in the case of AG failure.

[0036] Figure 12 The phase selection result for wind turbine connection in case of 100% AG failure.

[0037] Figure 13 The phase selection result is for an AG fault transition resistance of 300Ω. Detailed Implementation

[0038] A fault phase selection method for bundled new energy transmission lines based on current-voltage complementarity and boundary phase difference aims to reflect the current boundary characteristics of the fault point through single-end voltage and current abrupt changes, and to identify the faulty phase through phase sequence differences. This method adapts to different types of power supply access and improves the accuracy of fault phase selection for bundled new energy transmission lines. The method uses single-sided signals for fault phase selection. First, it analyzes the parameter characteristics in the fault-addition network; it characterizes the fault current in the fault-addition network through voltage and current abrupt changes on one side of the line; it establishes three types of current-voltage complementary phase operators based on boundary conditions for different types of faults, clarifying that the operator has the minimum phase difference selection characteristic only under a phase sequence combination uniquely corresponding to the faulty phase; finally, it constructs different fault type identification criteria and fault phase selection criteria to complete the fault phase selection work after bundled new energy access. Specifically, it includes the following steps: Step 1: Analyze the parameter characteristics of the fault-addition network: Topology of different types of bundled new energy transmission lines, such as Figure 1 As shown. The power supply side includes different types of power sources, and the penetration rate and integration ratio of new energy sources may vary. Let the impedance of the wind farm on the power supply side be... Z DFIG The impedance of the photovoltaic power station is Z PV The impedance of the synchronous machine is Z S The total impedance on the power supply side can be determined. Z M The three are connected in parallel, that is: (1); In the formula, the subscript j Take 1, 2, and 0 to represent the positive and negative zero-sequence components, respectively. Z M This represents the total impedance on the power supply side; Z DFIG The impedance of the wind farm; Z PV The impedance of the photovoltaic power station; Z S The impedance of the synchronous machine.

[0039] A simplified fault-addition network is established for the above-mentioned outbound model, such as... Figure 2 As shown. In the fault supplementary network, the electrical quantities at each point reflect the fault component, that is, the component after the fault minus the component before the fault. Therefore, the voltage at the protection installation location on the M side of line in the fault supplementary network... and current This is equal to the voltage and current abrupt changes measured at that point under a conventional network, i.e.: (2); In the formula, the subscript j The values ​​of are 1, 2, and 0, representing positive, negative, and zero-order components, respectively; and These represent the sequence abrupt changes in voltage and current on the M side of the line, respectively. and These represent the sequence components of voltage and current on the M side of the line after the fault. and These represent the sequence components of voltage and current on the M side of the line before the fault.

[0040] Meanwhile, since there was no fault circuit before the fault, the sequence components of the fault current in the fault-addition network... Equivalent to the sequence components of the short-circuit current flowing into the fault point after the fault. ,Right now: (3); In the formula, This indicates the fault current component in the fault-addition network. This represents the short-circuit current flowing into the fault point after a fault occurs in a conventional network.

[0041] Step 2: Represent the sudden changes in voltage and current on one side using fault components: According to the appendix Figure 2 The fault-addition network shown only exhibits a fault-addition voltage at the fault point, and all impedances are passive impedances. Based on the current shunting and voltage division characteristics, it can be seen that in the fault-addition network… and Fault current The relationship is as follows: (4); In the formula, and These represent the sequence abrupt changes in voltage and current on the M side of the line, respectively. This indicates the fault current component in the fault-addition network. This indicates the total impedance of the power supply, which is composed of the impedances of different types of energy sources connected in parallel. Indicates line impedance; Indicates the impedance of the receiving end system; This represents the line impedance from the fault point to bus N; It can be seen that the measured voltage and current fluctuations on one side of the line are based on the fault point current and distributed according to the relationship between the impedances of various parts of the system.

[0042] Step 3: Construct phase operators for different types of faults: The fault current boundary conditions for different types of faults in transmission lines are determined. This characteristic is not affected by the energy type on the power source side or fault ride-through control. Therefore, a phase operator is established based on this characteristic to characterize the fault phase selection feature.

[0043] When different types of faults occur on a line, the boundary conditions are based on calculations using a specific phase sequence. This specific phase sequence uniquely corresponds to the fault phase. For example, when an AG single-phase ground fault occurs, the three-sequence currents at the fault point calculated using the ABC phase sequence are equal. (Subscript A indicates the component calculated using the ABC phase sequence), but the current boundary conditions obtained using the BCA and CAB phase sequences are different, with a 120° phase difference. Similarly, for a BC phase-to-phase fault, the current boundary conditions calculated using the ABC phase sequence are: However, the current boundary conditions calculated using the BCA and CAB phase sequences do not exhibit the aforementioned characteristic of equal and opposite positive and negative sequence components. When a ground fault occurs between phases BCG, the three sequence components calculated using the ABC phase sequence exhibit the following: The vector sum of the three-sequence currents is 0, but the conclusion that the vector sum is 0 does not exist when using BCA and CAB phase sequence calculations. In summary, the relationship between current boundary conditions and phase sequence combinations can actually reflect the fault phase from a certain perspective. Therefore, based on the characteristics of current boundary conditions for different types of faults, and combined with the relationship between the actual measured voltage and current mutations and fault currents on the M side of line in claim 3, positive and negative sequence current ratios are used for single-phase grounding and phase-to-phase faults; and positive and negative zero sequence current vector sums are used for phase-to-phase grounding faults, establishing phase operators for different fault types.

[0044] (1) Single-phase grounding fault.

[0045] From step 2, the expression for the sudden change in current on the M side is: (5); In the formula, the subscript x takes the values ​​A, B, and C to represent the components calculated using the ABC, BCA, and CAB phase sequences, respectively; the subscripts 1 and 2 represent the positive and negative sequence components, respectively. and These represent the positive and negative order components of the current abrupt change in M, respectively; and These represent the positive and negative sequence components of the fault current in the fault-addition network, respectively. Z N Indicates the impedance of the receiving end system; Z LN This represents the line impedance from the fault point to the N side of the busbar; Z L Indicates the impedance along the entire length of the line; Z M This represents the equivalent total impedance measured by the power supply.

[0046] Divide the two equations in equation (5) and record the sum of the impedances of the receiving end system and the total length of the line. ,get: (6); In the formula, and These represent the positive and negative sequence components of the voltage surge calculated using the x phase sequence on the M side.

[0047] Multiplying the left and right sides of equation (6) by cross, we get: (7); In the formula, the superscript (1) indicates the single-phase ground fault type; and These are the left and right operators for a single-phase ground fault, combining the two major characteristics of current and voltage surge. , representing the sum of the receiving-end system impedance and the line impedance; subscript x The values ​​are A, B, and C, which represent the calculations using the ABC phase sequence, BCA phase sequence, and CAB phase sequence, respectively. , , and These respectively indicate the use of the M side of the line. x The abrupt changes in positive and negative sequence voltage and current calculated by phase sequence; and These respectively represent the use in the barrier-attached network. x The positive and negative components of the fault current calculated by phase sequence.

[0048] The operator for single-phase grounding is and Only under the phase sequence combination that uniquely corresponds to the faulty phase. The angle is 0, that is and The phases are equal, and the rest of the phase sequence is equal. and There is a 120° phase difference.

[0049] (2) Phase-to-phase fault. Following the same approach as for single-phase ground fault, divide formula (5) in step 3 and extract the negative sign to obtain the phase operator for phase-to-phase fault. and Only under a phase sequence combination that uniquely corresponds to the faulty phase. The angle is 0, that is and The phases are equal, and the rest of the phase sequence is equal. and The phases differ by 120°. The phase operator properties are as follows: (8); In the formula, the superscript (2) indicates the phase-to-phase fault type; and These are the left and right operators for phase-to-phase faults, respectively.

[0050] (3) Inter-phase grounding failure.

[0051] Based on the boundary condition that the sum of the positive and negative zero-sequence current vectors in the phase-to-phase fault is 0, and combined with the current expression method of formula (4) in step 2, the following can be constructed: (9); Multiply both sides of equation (6) by After simplification, the phase operator for interphase faults can be obtained as follows: and : (10); In the formula, the superscript (1,1) indicates the type of fault between phases; and These are the left and right operators for the inter-terminal faults, respectively. X The table includes additional items based on boundary conditions. Z N1 The receiving-end system is the positive-sequence impedance; Z LN1 The line impedance from the fault point to the N-side busbar; It represents the ratio of the positive-sequence impedance to the zero-sequence impedance of the system from the fault point to the receiving end. This represents the sum of the zero-sequence impedances of the line and the receiving-end system; and These respectively indicate the use of the M side of the line.x Zero-sequence voltage and current abrupt changes calculated by phase sequence.

[0052] In equation (6), the additional term only applies when the phase sequence combination uniquely corresponds to the faulty phase. ,Right now and The phases are equal. The remaining phase sequences... and There is a phase difference of at least 120°.

[0053] Step 4: Establish fault type discrimination criteria: In practical applications, it is necessary to first determine the type of fault occurring in the power grid, and then select an appropriate phase operator for fault phase selection.

[0054] (1) Criteria for Ground Fault Type. Ground faults have a large zero-sequence component, while ungrounded faults have no zero-sequence component. Therefore, the zero-sequence component is used to determine whether a ground fault has occurred in the system, and the criteria are as follows: (11); In the formula: k 1 represents the reliability coefficient, which is set to 0.05; and The zero-sequence and positive-sequence voltages on the M side, respectively.

[0055] (2) Three-phase fault criteria. The voltage drop in a three-phase symmetrical fault is symmetrical. Three-phase faults are identified by judging whether the three-phase voltage drops are symmetrical. The criteria are as follows: (12); In the formula: and Indicates the M side of the line m Harmony n Phase voltage surge magnitude; subscript m and n It refers to phases A, B, and C. This represents the ratio between different phases. In the case of a three-phase fault, the ratio is close to 1; in the case of a phase-to-phase fault, the above criterion is not met. The reliability coefficient is set to 0.3.

[0056] (3) Criteria for single-phase grounding and phase-to-phase grounding. In practical applications, the probability of a single-phase grounding fault is much greater than that of a phase-to-phase grounding fault. Therefore, after determining that a grounding fault has occurred, the phase operator for single-phase grounding faults should be used first. and The phase characteristics are used to determine the type of single-phase grounding and phase-to-phase grounding. In a single-phase grounding fault, the minimum phase difference is 0°, and the remaining two phases are both 120°, indicating a potential fault. Using a single-phase grounding phase operator and When calculating phase-to-phase grounding faults, the maximum phase difference is 180°, and the phase difference of the remaining two phase sequences is 60°. Based on the above characteristics, the criteria for single-phase grounding and phase-to-phase grounding are constructed as follows: (13); In the formula, , and These represent the minimum, intermediate, and maximum values ​​of the phase, respectively. Take 0.7.

[0057] Step 5: Establish fault phase selection criteria: Let the phase of the left-side phase operator in step 3 be . The phase of the right-hand phase operator is The phase difference of the operators is measured using Euclidean distance: (14); In the formula: This represents the phase difference under different phase sequence combinations; n Indicates the sampled value number; subscript x This represents different phase sequence combinations, with values ​​A, B, or C, representing ABC, BCA, and CAB phase sequences respectively. and These represent the phase values ​​of the left and right phase operators corresponding to different fault types in step 3. The operators for these different fault types are essentially constructed based on boundary conditions, hence the term "boundary phase difference."

[0058] The fault phase selection criterion is: (15); In the formula: express x Phase difference under phase sequence combination; threshold , Take 0.4.

[0059] Output those that meet the criteria x Phase sequence combination achieves the goal of fault phase selection. The overall fault phase selection process is as follows: Figure 3 As shown.

[0060] Simulation verification: In PSCAD simulation software, build such Figure 1 The illustrated renewable energy bundled transmission model has a transmission line voltage of 500kV, a total power output of 1250MW, a renewable energy penetration rate of 60%, and a wind-solar integration ratio of 2:1. Data acquisition is performed from the line protection device on the M side of the busbar.

[0061] Scenario 1: Verification of fault type criteria.

[0062] Taking AG and AB faults as examples, the ground fault criterion is verified, and the results are as follows: Figure 4 As shown. Figure 4 In the context of grounding fault thresholds k 1 is 0.05. According to Equation (11), the ratio of zero-sequence voltage to positive-sequence voltage in AG fault is significantly greater than the threshold. However, since there is no zero-sequence loop in AB fault, the zero-sequence component is 0. Therefore, the ratio of zero-sequence voltage to positive-sequence voltage tends to 0 and is reliably less than the threshold, which verifies the effectiveness of the ground fault criterion.

[0063] Taking AG and ABG faults as examples, the criteria for single-phase grounding and phase-to-phase grounding are verified, and the results are as follows: Figure 5 , Figure 6 As shown. During an AG fault, a single-phase grounding phase operator is used. and Of the calculated phase differences, the theoretically smallest phase difference is 0° (ABC phase sequence), and the phase difference for the other two phase sequences is 120° (BCA and CAB phase sequences). Therefore... It is greater than the threshold; If the value is less than the threshold, the criterion reliably identifies it as an AG fault. In an ABG fault, the maximum phase difference is 180° (CAB phase sequence), and the remaining two phase differences are 60° (ABC and BCA phase sequences). Therefore... Less than the threshold; If the value exceeds the threshold, the criterion classifies it as an ABG fault, thus verifying the effectiveness of the single-phase grounding and phase-to-phase grounding criteria.

[0064] Scenario 2: Phase selection results for different fault types. The phase selection results for four typical fault types (AG, AB, ABG, and ABC) are as follows: Figures 7-10 As shown. In the event of an AG fault, the operator phase for different phase sequences is calculated using formula (7), and the phase difference for the three phase sequence combinations is calculated according to formula (14), as follows. Figure 7 Phase difference only of ABC phase sequence D A If the phase difference is less than the threshold, while the phase difference calculated for other phase sequences is greater than the threshold, a reliable judgment is that phase A is faulty. In the case of an AB fault, the operator phases for different phase sequences are calculated using formula (8), such as... Figure 8 Phase difference only in CAB phase sequence D C If the phase difference is less than the threshold, while the phase difference calculated for other phase sequences is greater than the threshold, a reliable judgment is that it is an AB two-phase fault. For an ABG fault, the operator phases for different phase sequences are calculated using formula (10), such as... Figure 9 Phase difference only in CAB phase sequence D C If the phase difference is less than the threshold, while the phase difference calculated for other phase sequences is greater than the threshold, a reliable diagnosis is an AB two-phase fault. In the case of an ABC fault, if... Figure 10 The ratio of the three-phase voltages to each other is close to 1, indicating a symmetrical voltage drop, which is judged as a three-phase fault.

[0065] Scenario 3: Phase selection results under different renewable energy penetration rates. Taking AG failure as an example, ensuring the total output power of the power supply remains constant, the phase selection results for changes in renewable energy penetration rate and wind-solar ratio are shown in Table 1. The phase selection results for 100% photovoltaic grid connection are as follows: Figure 11 As shown; the phase selection results for 100% wind turbine connection are as follows. Figure 12 Therefore, when the AG fails, only D A Less than the threshold, and D B and D C All values ​​are greater than the threshold. In particular, because the phase calculation operator possesses the characteristic of current-voltage complementarity, this method exhibits adaptability to both strong and weak power sources. Even in a power grid composed entirely of synchronous generators (0% penetration) or a pure renewable energy power station (100% penetration), the method can accurately identify the faulty phase. The method provided by this invention can better adapt to scenarios involving bundled renewable energy transmission.

[0066]

[0067] Scenario 4: Phase selection results for high-resistance grounding. The phase selection results for an AG fault with a transition resistance of 300Ω are as follows: Figure 13 As shown. Since this invention constructs relevant criteria based on fault components in a fault-addition network, and fault components have the characteristic of being unaffected by transition resistance, therefore, from... Figure 13 It is evident that even with the transition resistance set to the maximum of 300Ω considered for 500kV lines in engineering, the phase selection characteristics remain clear, with only... D A Less than the threshold, and D B and D C All values ​​are greater than the threshold, indicating that the method has good tolerance to transition resistance.

Claims

1. A fault phase selection method for bundled new energy transmission lines based on current-voltage complementarity and boundary phase difference, characterized in that... Includes the following steps: Step 1: Establish a fault-addition network model for power supply measurement that includes new energy access with different fault types, and analyze the characteristics of fault current components and voltage and current abrupt changes on one side of the line in the fault-addition network. Step 2: Represent the sudden change in voltage and current on one side using the fault current component; Step 3: Construct phase operators for different types of faults; Step 4: Establish fault type discrimination criteria; Step 5: Characterize the phase difference of the operator by Euclidean distance and establish a fault phase selection criterion based on threshold comparison.

2. The fault phase selection method for new energy bundled transmission lines based on current-voltage complementarity and boundary phase difference according to claim 1, characterized in that: In step 1, the voltage at the protection installation location on the M side of line in the fault supplementary network... and current This is equal to the voltage and current abrupt changes measured at that point under a conventional network, i.e.: （1）； In equation (1), the subscript j The values ​​of are 1, 2, and 0, representing positive, negative, and zero-order components, respectively; and These represent the sequence abrupt changes in voltage and current on the M side of the line, respectively. and These represent the sequence components of voltage and current on the M side of the line after the fault. and These represent the sequence components of voltage and current on the M side of the line before the fault. Meanwhile, since there was no fault circuit before the fault, the sequence components of the fault current in the fault-addition network are equivalent to the sequence components of the short-circuit current flowing into the fault point after the fault, that is: （3）； In equation (3), This represents the fault current component in the fault-addition network. This represents the short-circuit current flowing into the fault point after a fault occurs in a conventional network.

3. The fault phase selection method for new energy bundled transmission lines based on current-voltage complementarity and boundary phase difference as described in claim 2, characterized in that: In step 2 shown, based on the fault-addition network in step 1, and based on the principles of current shunting and voltage division, the fault current component is used to represent the voltage and current abrupt changes on one side of the line.

4. The fault phase selection method for new energy bundled transmission lines based on current-voltage complementarity and boundary phase difference according to claim 3, characterized in that: In step 2, in the fault-addition network, only the fault point has a fault-addition voltage, and all impedances are passive. Based on the current shunting and voltage division characteristics, it can be known that there is a relationship between the actual measured voltage and current surges on the M side of line and the fault current: （4）； In equation (4), and These represent the sequence abrupt changes in voltage and current on the M side of the line, respectively. This indicates the fault current component in the fault-addition network. This indicates the total impedance of the power supply, which is composed of the impedances of different types of energy sources connected in parallel. Indicates line impedance; Indicates the impedance of the receiving end system; This represents the line impedance from the fault point to bus N.

5. The fault phase selection method for new energy bundled transmission lines based on current-voltage complementarity and boundary phase difference according to claim 4, characterized in that: In step 3, based on the current boundary conditions of different types of faults, the current-voltage complementary phase calculation operators for three types of faults—single-phase grounding, phase-to-phase faults, and phase-to-phase grounding—are derived through mathematical transformation. The magnitude of the phase difference of the operators under different phase sequence combinations reflects the fault phase.

6. The fault phase selection method for new energy bundled transmission lines based on current-voltage complementarity and boundary phase difference as described in claim 5, characterized in that: In step 3, based on the characteristics of the current boundary conditions of different types of faults, and combined with the relationship between the actual measured voltage and current mutations and the fault current on the M side of the line in step 2, the positive and negative sequence current ratio relationship is used for single-phase grounding and phase-to-phase faults; the positive and negative zero sequence current vector sum relationship is used for phase-to-phase grounding faults, and a current-voltage complementary phase operator for different fault types is established.

7. The fault phase selection method for new energy bundled transmission lines based on current-voltage complementarity and boundary phase difference according to claim 6, characterized in that: Establish flow-pressure complementary phase operators for different fault types, including: 3.1: Single-phase ground fault: The operator for single-phase grounding is and Only under the phase sequence combination that uniquely corresponds to the faulty phase. The angle is 0, where, This represents the positive-sequence component of the fault current in the fault-addition network. Indicates the positive-sequence component of the fault point current in the fault-addition network; subscript x The values ​​A, B, and C represent the sequence component values ​​calculated using the ABC phase sequence, BCA phase sequence, and CAB phase sequence, respectively; that is... and The phases are equal, and the rest of the phase sequence is equal. and The phases differ by 120°, and the phase operator characteristics are as follows: （7）； In equation (7), the superscript (1) indicates the single-phase ground fault type; and These are the left and right operators for a single-phase ground fault, combining the two major characteristics of current and voltage surge. This represents the sum of the receiving-end system impedance and the line impedance, where... This represents the sum of the receiving-end system impedance and the line impedance; This represents the positive-sequence impedance of the receiving-end system; The positive sequence impedance represents the total length of the line. This represents the negative sequence impedance of the receiving-end system; Negative sequence impedance of the entire line length; Subscript x The values ​​are A, B, and C, which represent the calculations using the ABC phase sequence, BCA phase sequence, and CAB phase sequence, respectively. and These respectively indicate the use of the M side of the line. x The positive and negative sequence voltage abrupt changes calculated by phase sequence; and These respectively indicate the use of the M side of the line. x The abrupt changes in positive and negative sequence currents calculated by phase sequence; and These respectively represent the use in the barrier-attached network. x The positive and negative components of the fault current calculated by phase sequence; 3.2: Phase-to-phase fault: The phase operator for interphase faults is and Only under the phase sequence combination that uniquely corresponds to the faulty phase. The angle is 0, that is and The phases are equal, and the rest of the phase sequence is equal. and The phases differ by 120°, and the phase operator characteristics are as follows: （8）； In equation (8), the superscript (2) indicates the phase-to-phase fault type; and These are the left and right operators for phase-to-phase faults, respectively. 3.3: Phase-to-phase grounding faults: The phase operator for interphase faults is and The additional item is only applicable when the phase sequence combination uniquely corresponds to the faulty phase. ,Right now and The phases are equal, and the rest of the phase sequence is equal. and The phases differ by at least 120°; the phase operator properties are as follows: （10）； In equation (10), the superscript (1,1) indicates the type of fault between phases; and These are the left and right operators for the inter-phase fault, respectively; X Table of additional items based on boundary conditions; Z N1 The receiving-end system is the positive-sequence impedance; Z LN1 The line impedance from the fault point to the N-side busbar; This represents the ratio of the positive-sequence impedance to the zero-sequence impedance of the system from the fault point to the receiving end, where... This represents the positive-sequence impedance of the receiving-end system; This represents the positive sequence impedance of the line from the fault point to the N side of the busbar. This represents the zero-sequence impedance of the receiving-end system; This represents the zero-sequence impedance of the line from the fault point to the N side of the busbar. This represents the sum of the zero-sequence impedances of the line and the receiving-end system, where... This represents the zero-sequence impedance of the receiving-end system; The zero-sequence impedance represents the total length of the line. and These respectively indicate the use of the M side of the line. x Zero-sequence voltage and current abrupt changes calculated by phase sequence.

8. The fault phase selection method for new energy bundled transmission lines based on current-pressure complementarity and boundary phase difference as described in claim 7, characterized in that: Step 4: Establish fault type discrimination criteria: Establish ground fault criteria based on zero-sequence voltage characteristics; In ungrounded fault types, three-phase faults are identified by the symmetry of voltage drops; In the grounding fault type, phase-to-phase and single-phase grounding faults are distinguished by the phase characteristics of the single-phase grounding fault operator in step 3.

9. The fault phase selection method for new energy bundled transmission lines based on current-voltage complementarity and boundary phase difference according to claim 8, characterized in that: In step 4, the fault type discrimination criteria are established, including: 4.1: Criteria for determining the type of grounding fault: The zero-sequence component is used to determine whether a ground fault has occurred in the system, based on the following criteria: （11）； In equation (11), k 1 represents the reliability coefficient; and Zero-sequence and positive-sequence voltages on side M, respectively; 4.2: Three-phase fault diagnosis criteria: Three-phase faults are identified by determining whether the three-phase voltage drops are symmetrical. The criteria are as follows: （12）； In equation (12): and Indicates the M side of the line m Harmony n Phase voltage surge magnitude; subscript m and n It refers to phases A, B, and C; This represents the ratio between different phases; during a three-phase fault, the ratios are all close to 1; during a phase-to-phase fault, the above criteria are not met. The reliability coefficient; 4.3: Criteria for determining single-phase grounding and phase-to-phase grounding: Phase operator for single-phase ground faults and The phase characteristics are used to determine the type of single-phase grounding and phase-to-phase grounding, and the criteria are as follows: （13）； In equation (13): , and These represent the minimum, intermediate, and maximum values ​​of the phase, respectively. Take 0.

7.

10. The fault phase selection method for new energy bundled transmission lines based on current-voltage complementarity and boundary phase difference according to claim 9, characterized in that: In step 5, a fault phase selection criterion is established: Based on the fault type determined in step 4, the phase is calculated using the corresponding phase operator from step 3. The phases of the left and right phase operators are recorded as follows: and The boundary phase difference of the operator is measured using Euclidean distance: （14）； In equation (14): This represents the distance values ​​under different phase sequence combinations; n Indicates the sampled value number; Subscript x This represents different phase sequence combinations, with values ​​A, B, or C, representing ABC, BCA, and CAB phase sequences respectively. and These represent the phase values ​​of the left and right phase operators corresponding to different fault types in step 3, respectively. The fault phase selection criterion is: （15）； In equation (15): express x Phase difference under phase sequence combination; threshold , Take 0.4; Output those that meet the criteria x Phase sequence combination achieves the goal of fault phase selection.

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