Method and device for determining and protecting line differential protection setting scheme

Abstract

The invention discloses a method and a device for determining and protecting a line differential protection setting scheme, and belongs to the field of line differential protection. Firstly, a power grid system model is constructed according to system parameters of a target alternating current power grid, new energy is equivalent to a constant current source, and a synchronous power supply is equivalent to a band-stop grounding branch. Then, a node impedance matrix is generated based on the model, and a key first parameter is extracted from the node impedance matrix; and deriving expressions of the phase current at the fault point under different fault types by using the parameters, and determining a change mode of the phase current along with the fault types. And determining a corresponding fault type in line differential protection setting calculation by analyzing the modes. And finally, according to the determined fault type, a line differential protection setting scheme of the target power grid is formulated, so that the line differential protection can be rapidly and accurately set, and the problem that the line differential protection setting scheme cannot be accurately and efficiently generated in the prior art is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of line differential protection, and in particular to a method and apparatus for determining and protecting line differential protection settings. Background Technology

[0002] With the widespread application of new energy sources (such as wind and solar power) in power systems, the structure and operating characteristics of AC power grids have undergone significant changes. New energy sources are connected to the grid via power electronic inverters. This connection method means that the output characteristics (such as voltage, current, and power) of these new energy sources are significantly affected by their own power source attributes (such as wind speed and solar intensity) and control strategies (such as maximum power point tracking and negative sequence current suppression), resulting in substantial differences compared to traditional synchronous power sources. This presents new challenges to grid operation and protection, particularly in the setting calculations for line differential protection.

[0003] Traditional line differential protection setting calculations typically employ an "offline setting, online unchanged" management model. This method requires listing various possible operating conditions, performing fault calculations for each condition, and determining the electrical quantities required for setting. Then, the most stringent value for the electrical quantities required for setting under each operating condition is selected to determine the range of setting values. Finally, the multiple value ranges are coordinated to determine the final protection setting.

[0004] As the scale of power systems gradually increases and their structure becomes more complex, the number of operating conditions that need to be considered in setting calculations has increased dramatically, leading to a significant decrease in setting calculation efficiency.

[0005] The integration of new energy sources not only increases the complexity of the power grid but also poses challenges to the adaptability and accuracy of traditional setting calculation methods. The control strategies (such as negative sequence current suppression) and external characteristics of new energy sources differ from those of synchronous power sources. These shortcomings prevent existing technologies from accurately and efficiently generating line differential protection setting schemes in the event of a fault. Summary of the Invention

[0006] This invention provides a method and apparatus for determining and protecting line differential protection settings, in order to solve the problem in the prior art that it is impossible to accurately and efficiently generate line differential protection settings when a fault occurs.

[0007] Firstly, this application provides a method for determining a line differential protection setting scheme, including:

[0008] Obtain the node impedance matrix of the preset power grid system model and extract the first parameter from the node impedance matrix; wherein, the power grid system model is constructed based on the system parameters of the target AC power grid, and the new energy sources of the target AC power grid are equivalent to constant current sources, and the synchronous power sources of the target AC power grid are equivalent to grounded branches with resistance;

[0009] Based on the node impedance matrix and the first parameter, the expression for the phase current at the fault point under different fault types is derived, and the variation mode of the phase current at the fault point with the fault type is determined based on the expression.

[0010] Based on the aforementioned change pattern, the corresponding fault type in the line differential protection setting calculation is determined;

[0011] Based on the fault type, determine the line differential protection setting scheme for the target power grid.

[0012] This application constructs a model that accurately reflects the characteristics of the target AC power grid by obtaining the node impedance matrix of a pre-defined power grid system model and extracting its first parameter. This model equates new energy sources to constant current sources and synchronous power sources to grounded branches with resistance, thus simplifying the analysis process for complex power grids. Based on the node impedance matrix and the first parameter, this application further derives the expressions for the phase current at the fault point under different fault types and determines the variation pattern of the phase current with the fault type. This process, through the variation pattern, can quickly determine the corresponding fault type in the line differential protection setting calculation and generate the line differential protection setting scheme for the target power grid accordingly. This method not only improves the efficiency of the setting calculation but also enhances the reliability and sensitivity of the protection system, enabling it to better adapt to the complex power grid environment after the integration of new energy sources. This application effectively solves the problem in existing technologies that cannot accurately and efficiently generate line differential protection setting schemes when faults occur.

[0013] Furthermore, the step of obtaining the node impedance matrix of the preset power grid system model and extracting the first parameter from the node impedance matrix specifically involves:

[0014] Obtain the system parameters of the target AC power grid, including new energy sources, synchronous power sources, line impedance parameters, and node topology relationships;

[0015] Based on the system parameters, the new energy source is equivalent to a constant current source with controllable output current, and the synchronous power source is equivalent to a voltage source branch with grounding resistance. The correlation matrix is ​​constructed according to the node topology relationship to obtain the power grid system model.

[0016] Based on the power grid system model, and combined with the line impedance parameters, a branch impedance matrix is ​​generated, and a node impedance matrix is ​​generated by combining the correlation matrix and the branch impedance matrix.

[0017] The first parameter is extracted from the node impedance matrix. The first parameter includes the positive-sequence self-impedance, negative-sequence self-impedance, zero-sequence self-impedance of the node where the fault point is located, and the positive-sequence mutual impedance between the new energy access node and the fault point node.

[0018] This application constructs an approximate power grid system model by acquiring system parameters of the target AC power grid, including renewable energy sources, synchronous power sources, line impedance parameters, and node topology relationships. Specifically, renewable energy sources are equated to constant current sources with controllable output current, and synchronous power sources are equated to voltage source branches with grounding resistance. This not only simplifies the model's complexity but also improves its adaptability to renewable energy integration. An correlation matrix is ​​constructed based on node topology relationships, and a branch impedance matrix is ​​generated by combining line impedance parameters, further generating a node impedance matrix. This process ensures the model's accuracy and practicality. The first parameters extracted from the node impedance matrix include the positive-sequence self-impedance, negative-sequence self-impedance, and zero-sequence self-impedance of the node where the fault point is located, as well as the positive-sequence mutual impedance between the renewable energy integration node and the fault point node, providing crucial data support for subsequent change mode judgment and setting calculations.

[0019] Furthermore, the derivation of the expression for the phase current at the fault point under different fault types based on the node impedance matrix and the first parameter is specifically as follows:

[0020] When the fault type is a single-phase ground fault, the expression for the first fault phase current is derived based on the relationship between the fault phase voltage and the zero-sequence voltage, combined with the positive-sequence self-impedance, negative-sequence self-impedance and zero-sequence self-impedance in the first parameter.

[0021] When the fault type is a two-phase short circuit, based on the difference between the voltage of the non-faulty phase and the voltage of the faulty phase, and combined with the positive-sequence self-impedance and negative-sequence self-impedance in the first parameter, the expression for the second faulty phase current is derived.

[0022] When the fault type is a two-phase ground fault, the expression for the third fault phase current is derived based on the preset fault phase voltage balance equation and the positive-sequence self-impedance, negative-sequence self-impedance, and zero-sequence self-impedance in the first parameter.

[0023] When the fault type is a three-phase short circuit, based on the preset three-phase voltage symmetry characteristics and combined with the positive sequence self-impedance in the first parameter, the expression for the fourth fault phase current is derived.

[0024] This application derives expressions for the phase current at the fault point using the nodal impedance matrix and a first parameter for different fault types. Specifically, for a single-phase-to-ground short circuit, the first fault phase current expression is derived based on the relationship between the fault phase voltage and the zero-sequence voltage, combined with positive-sequence, negative-sequence, and zero-sequence self-impedances; for a two-phase short circuit, the second fault phase current expression is derived based on the difference between the non-fault phase voltage and the fault phase voltage, combined with positive-sequence and negative-sequence self-impedances; for a two-phase-to-ground short circuit, the third fault phase current expression is derived based on a pre-defined fault phase voltage balance equation, combined with positive-sequence, negative-sequence, and zero-sequence self-impedances; and for a three-phase short circuit, the fourth fault phase current expression is derived based on a pre-defined three-phase voltage symmetry characteristic, combined with positive-sequence self-impedances. This series of derivations not only considers the voltage and impedance characteristics under different fault types but also provides a theoretical basis for determining the fault type through precise mathematical expressions.

[0025] Furthermore, the expressions for the first fault phase current, the second fault phase current, the third fault phase current, and the fourth fault phase current are as follows:

[0026] The expression for the first fault phase current is:

[0027]

[0028] The expression for the second fault phase current is:

[0029]

[0030] The expression for the third fault phase current is:

[0031]

[0032] The expression for the fourth fault phase current is:

[0033]

[0034] In the formula, Let f represent the fault phase current, n represent the node where the fault occurred, N represent the new energy grid-connected node, and Z represent the set of new energy grid-connected nodes. ff1 Z represents the positive-sequence self-impedance at the fault point. ff2 Z represents the negative sequence self-impedance at the fault point. ff0 Z represents the zero-sequence self-impedance at the fault point. fn1 The positive-sequence mutual impedance between the faulty node and the new energy grid connection point is represented by 'a', where 'a' represents the rotation factor and 'I' represents the positive-sequence mutual impedance between the faulty node and the new energy grid connection point. n1 This represents the injected current at the new energy grid connection node.

[0035] Furthermore, the determination of the phase current variation pattern at the fault point with fault type based on the expression specifically includes:

[0036] Based on the phase current expressions under different fault types, and combined with the first parameter, calculate the phase current magnitude expression corresponding to each fault type.

[0037] By comparing the phase current magnitude expressions for the four fault types pairwise, the magnitude relationship is obtained.

[0038] Based on the magnitude relationship, establish a correspondence between fault types and the order of phase current magnitudes;

[0039] The aforementioned correspondence is used as the pattern of phase current variation at the fault point with the fault type.

[0040] This application establishes a correspondence between fault types and the ranking of phase current magnitudes by calculating the phase current magnitudes under different fault types and comparing these magnitudes pairwise. Specifically, firstly, based on the phase current expressions for different fault types and in conjunction with a first parameter, the phase current magnitude expressions for each fault type are calculated. Then, the phase current magnitude expressions for the four fault types are compared pairwise to obtain the magnitude relationship. Finally, based on the magnitude relationship, a correspondence between fault types and the ranking of phase current magnitudes is established, and this correspondence is used as the variation pattern of phase current at the fault point with the fault type. The establishment of this variation pattern provides a clear basis for the setting calculation of line differential protection.

[0041] Secondly, this application provides a line differential protection method for a power grid, the line differential protection method for the power grid comprising:

[0042] Based on the method for determining the line differential protection setting scheme, the line differential protection setting scheme of the target power grid is obtained;

[0043] Calculate the settings of the target power grid protection device according to the line differential protection setting scheme;

[0044] Based on the set value, the target power grid protection device is controlled to protect the line.

[0045] This application provides a method for differential protection of power grid lines. Through a scientifically sound and rationally designed setting scheme, it achieves precise protection of the target power grid lines. Specifically, firstly, based on a defined method, the differential protection setting scheme for the target power grid lines is accurately obtained. This scheme comprehensively considers various parameters and fault characteristics of the power grid, ensuring the accuracy and reliability of the protection actions. Subsequently, according to this setting scheme, the protection devices of the target power grid are precisely controlled, enabling them to perform appropriate protection actions for different lines under different fault conditions. This method not only improves the safety and stability of power grid operation but also effectively enhances computational efficiency, which is of great significance for ensuring the continuity and reliability of power supply.

[0046] Thirdly, this application provides a device for determining a line differential protection setting scheme, the device comprising:

[0047] The first acquisition module is used to acquire the node impedance matrix of the preset power grid system model and extract the first parameter from the node impedance matrix; wherein, the power grid system model is constructed based on the system parameters of the target AC power grid, and the new energy sources of the target AC power grid are equivalent to constant current sources, and the synchronous power sources of the target AC power grid are equivalent to grounded branches with resistance.

[0048] The derivation module is used to derive the expression of the phase current at the fault point under different fault types based on the node impedance matrix and the first parameter, and to determine the change mode of the phase current at the fault point with the fault type based on the expression.

[0049] The fault type determination module is used to determine the corresponding fault type in the line differential protection setting calculation based on the change pattern.

[0050] The scheme determination module determines the line differential protection setting scheme of the target power grid based on the fault type.

[0051] This application utilizes a systematic device to efficiently determine the differential protection setting scheme for power grid lines. Specifically, the first acquisition module first acquires the node impedance matrix of a preset power grid system model and extracts the first parameter. This power grid system model is constructed by equating new energy sources with constant current sources and synchronous power sources with grounded branches with resistance, accurately reflecting the characteristics of the power grid. Subsequently, the derivation module, based on the node impedance matrix and the first parameter, derives the expression for the phase current at the fault point under different fault types and determines its variation pattern. The fault type determination module then uses the variation pattern to obtain the fault type that should be used in the line differential protection setting calculation. Finally, the scheme determination module formulates the line differential protection setting scheme for the target power grid based on the determined fault type. This significantly improves the efficiency and effectiveness of power grid line differential protection, providing a strong guarantee for the safe and stable operation of the power grid.

[0052] Furthermore, the step of obtaining the node impedance matrix of the preset power grid system model and extracting the first parameter from the node impedance matrix specifically involves:

[0053] Obtain the system parameters of the target AC power grid, including new energy sources, synchronous power sources, line impedance parameters, and node topology relationships;

[0054] Based on the system parameters, the new energy source is equivalent to a constant current source with controllable output current, and the synchronous power source is equivalent to a voltage source branch with grounding resistance. The correlation matrix is ​​constructed according to the node topology relationship to obtain the power grid system model.

[0055] Based on the power grid system model, and combined with the line impedance parameters, a branch impedance matrix is ​​generated, and a node impedance matrix is ​​generated by combining the correlation matrix and the branch impedance matrix.

[0056] The first parameter is extracted from the node impedance matrix. The first parameter includes the positive-sequence self-impedance, negative-sequence self-impedance, zero-sequence self-impedance of the node where the fault point is located, and the positive-sequence mutual impedance between the new energy access node and the fault point node.

[0057] This application constructs an approximate power grid system model by acquiring system parameters of the target AC power grid, including renewable energy sources, synchronous power sources, line impedance parameters, and node topology relationships. Specifically, renewable energy sources are equated to constant current sources with controllable output current, and synchronous power sources are equated to voltage source branches with grounding resistance. This not only simplifies the model's complexity but also improves its adaptability to renewable energy integration. An correlation matrix is ​​constructed based on node topology relationships, and a branch impedance matrix is ​​generated by combining line impedance parameters, further generating a node impedance matrix. This process ensures the model's accuracy and practicality. The first parameters extracted from the node impedance matrix include the positive-sequence self-impedance, negative-sequence self-impedance, and zero-sequence self-impedance of the node where the fault point is located, as well as the positive-sequence mutual impedance between the renewable energy integration node and the fault point node, providing crucial data support for subsequent change mode judgment and setting calculations.

[0058] Furthermore, the derivation of the expression for the phase current at the fault point under different fault types based on the node impedance matrix and the first parameter is specifically as follows:

[0059] When the fault type is a single-phase ground fault, the expression for the first fault phase current is derived based on the relationship between the fault phase voltage and the zero-sequence voltage, combined with the positive-sequence self-impedance, negative-sequence self-impedance and zero-sequence self-impedance in the first parameter.

[0060] When the fault type is a two-phase short circuit, based on the difference between the voltage of the non-faulty phase and the voltage of the faulty phase, and combined with the positive-sequence self-impedance and negative-sequence self-impedance in the first parameter, the expression for the second faulty phase current is derived.

[0061] When the fault type is a two-phase ground fault, the expression for the third fault phase current is derived based on the preset fault phase voltage balance equation and the positive-sequence self-impedance, negative-sequence self-impedance, and zero-sequence self-impedance in the first parameter.

[0062] When the fault type is a three-phase short circuit, based on the preset three-phase voltage symmetry characteristics and combined with the positive sequence self-impedance in the first parameter, the expression for the fourth fault phase current is derived.

[0063] This application derives expressions for the phase current at the fault point using the nodal impedance matrix and a first parameter for different fault types. Specifically, for a single-phase-to-ground short circuit, the first fault phase current expression is derived based on the relationship between the fault phase voltage and the zero-sequence voltage, combined with positive-sequence, negative-sequence, and zero-sequence self-impedances; for a two-phase short circuit, the second fault phase current expression is derived based on the difference between the non-fault phase voltage and the fault phase voltage, combined with positive-sequence and negative-sequence self-impedances; for a two-phase-to-ground short circuit, the third fault phase current expression is derived based on a pre-defined fault phase voltage balance equation, combined with positive-sequence, negative-sequence, and zero-sequence self-impedances; and for a three-phase short circuit, the fourth fault phase current expression is derived based on a pre-defined three-phase voltage symmetry characteristic, combined with positive-sequence self-impedances. This series of derivations not only considers the voltage and impedance characteristics under different fault types but also provides a theoretical basis for determining the fault type through precise mathematical expressions.

[0064] Fourthly, this application provides a line differential protection device for a power grid, the line differential protection device comprising:

[0065] The second acquisition module is used to obtain the line differential protection setting scheme of the target power grid according to the method for determining the line differential protection setting scheme.

[0066] The protection module is used to calculate the settings of the target power grid protection device according to the line differential protection setting scheme;

[0067] Based on the set value, the target power grid protection device is controlled to protect the line.

[0068] This application uses a second acquisition module to obtain the line differential protection setting scheme of the target power grid according to a specific determination method, ensuring the scientific nature and adaptability of the protection scheme. Subsequently, the protection module controls the power grid protection device according to the setting scheme to achieve precise protection of the lines. This process not only improves the accuracy and reliability of the protection, but also enhances the power grid's ability to cope with faults, effectively reduces the impact of faults on power grid operation, ensures the safe and stable operation of the power grid, and improves the overall performance and reliability of the power system. Attached Figure Description

[0069] Figure 1 : A schematic flowchart of an embodiment of the method for determining the line differential protection setting scheme provided in this application;

[0070] Figure 2 : A schematic flowchart of an embodiment of the line differential protection method for the power grid provided in this application;

[0071] Figure 3 : A schematic diagram of an embodiment of the device for determining the line differential protection setting scheme provided in this application;

[0072] Figure 4 This is a schematic diagram of an embodiment of the line differential protection device for the power grid provided in this application. Detailed Implementation

[0073] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0074] Example 1

[0075] Please refer to Figure 1 In order to solve the problem that existing technologies cannot accurately and efficiently generate line differential protection setting schemes when a fault occurs, this invention provides a method for determining line differential protection setting schemes, including steps S01-S04.

[0076] S01: Obtain the node impedance matrix of the preset power grid system model and extract the first parameter from the node impedance matrix; wherein, the power grid system model is constructed based on the system parameters of the target AC power grid, and the new energy sources of the target AC power grid are equivalent to constant current sources, and the synchronous power sources of the target AC power grid are equivalent to grounded branches with resistance.

[0077] In a preferred embodiment of this invention, the power grid system model is constructed based on the system parameters of the target AC power grid, with the new energy sources of the target AC power grid equivalent to constant current sources and the synchronous power sources of the target AC power grid equivalent to grounded branches with resistance. Specifically:

[0078] First, complete system parameters of the target AC power grid are collected, including the installed capacity of new energy power plants (such as wind power and photovoltaic), inverter control strategy parameters, and access node numbers; the rated voltage, synchronization reactance, and grounding resistance of synchronous power sources (such as thermal power and hydropower); and the impedance parameters (positive sequence, negative sequence, and zero sequence) and node topology connections of transmission lines. These parameters constitute the original input of the model, ensuring that the model can reflect the actual physical characteristics of the power grid.

[0079] Secondly, equivalent modeling is performed based on the essential characteristics of the two types of power sources: For new energy sources, since they are connected to the grid through power electronic inverters, their output characteristics are dominated by control strategies (especially during faults, negative sequence current is suppressed, exhibiting constant current output characteristics), so they are equivalent to "constant current sources with controllable output current". The current amplitude is calculated and determined by the rated power and access voltage of the new energy source, and the access node corresponds to the actual grid connection point; For synchronous power sources, as traditional rotating motors, they are essentially voltage sources. The current distribution during faults is affected by their own internal resistance and grounding method, so they are equivalent to "voltage source branches with grounding resistance" - the voltage source parameters are matched with the rated voltage of the synchronous power source, the series internal resistance is taken from the synchronous reactance, and the resistance value of the grounding branch is set according to the actual grounding method (such as small resistance grounding, arc suppression coil grounding) to accurately simulate the zero-sequence current path during grounding faults;

[0080] Finally, the equivalent power source model is integrated with line impedance and node topology relationships, and a complete power grid system model is constructed using power system simulation software (or mathematical operations based on the correlation matrix and branch impedance matrix). This model retains the voltage source characteristics of synchronous power sources while reflecting the constant current source characteristics of new energy sources, providing a basic model that conforms to the actual characteristics of power grids containing new energy sources for subsequent calculation of node impedance matrices and fault analysis.

[0081] This differentiated equivalence approach solves the error problem caused by the traditional model simplifying new energy sources into voltage sources, and is the core technical means to adapt the protection settings of AC power grids containing new energy sources.

[0082] S02: Based on the node impedance matrix and the first parameter, derive the expression for the phase current at the fault point under different fault types, and determine the variation mode of the phase current at the fault point with the fault type based on the expression.

[0083] In a preferred embodiment of this invention, the step of deriving the expression for the phase current at the fault point under different fault types based on the node impedance matrix and the first parameter, and determining the variation pattern of the phase current at the fault point with the fault type based on the expression, specifically involves:

[0084] First, fault boundary conditions are constructed for the four common fault types in power systems (single-phase ground fault, two-phase short circuit, two-phase ground fault, and three-phase short circuit). For example, in a single-phase ground fault, the fault phase voltage is zero and there is a zero-sequence current, while the non-fault phase current is zero; in a three-phase short circuit, the three-phase voltages decrease symmetrically and there is no unbalanced component. Based on these boundary conditions, combined with the positive-sequence self-impedance, negative-sequence self-impedance, and zero-sequence self-impedance of the fault point in the first parameter, as well as the positive-sequence mutual impedance between the renewable energy node and the fault point, the phase current expression is derived through the impedance relationship of each sequence network. Taking a single-phase ground fault as an example, the mathematical relationship between the fault phase current and each sequence impedance is derived by utilizing the series relationship of the positive-sequence, negative-sequence, and zero-sequence self-impedance of the fault point, combined with the positive-sequence current injected by the renewable energy constant current source; for a two-phase ground fault, the parallel relationship of the positive-sequence and negative-sequence networks and the ground impedance of the zero-sequence network must be considered simultaneously, ultimately forming a phase current expression that includes the node impedance matrix parameters.

[0085] The expressions for the different fault types are as follows:

[0086] When a single-phase ground fault occurs, the phase current at the fault point is expressed as follows based on the node impedance matrix:

[0087]

[0088] When a two-phase short circuit occurs, the phase current at the fault point is expressed as follows based on the node impedance matrix:

[0089]

[0090] When a two-phase-to-ground short circuit occurs, the phase current at the fault point is expressed as follows based on the node impedance matrix:

[0091]

[0092] When a three-phase short circuit occurs, the phase current at the fault point is expressed as follows based on the node impedance matrix:

[0093]

[0094] in, Let f represent the faulty phase, n represent the node where the fault occurred, N represent the new energy grid-connected node, and Z represent the set of new energy grid-connected nodes. ff1 Z represents the positive-sequence self-impedance at the fault point. ff2 Z represents the negative sequence self-impedance at the fault point. ff0 Z represents the zero-sequence self-impedance at the fault point. fn1 This represents the positive sequence mutual impedance between the fault node and the new energy grid connection point, and 'a' represents the rotation factor with a value of 1∠120°.

[0095] After deriving the phase current expressions for different fault types, and considering the characteristics of AC power grids containing negative-sequence suppressed renewable energy sources, the relationship between phase current magnitudes is further analyzed:

[0096] Due to the negative sequence suppression function of new energy inverters, the magnitudes of positive-sequence self-impedance and negative-sequence self-impedance at the fault point can be considered equal (i.e., positive-sequence self-reactance ≈ negative-sequence self-reactance, considering only the imaginary part of the impedance). Based on this characteristic, by comparing the phase current expressions for various fault types, a criterion is gradually established:

[0097] Comparing the phase current expressions for three-phase short circuit and two-phase short circuit: Since the three-phase short circuit utilizes all positive sequence impedance components, while the two-phase short circuit is affected by the shunting effect of the negative sequence component, we can directly obtain that "three-phase short circuit current > two-phase short circuit current".

[0098] Comparing the expressions for two-phase-to-ground short circuit and two-phase short circuit: Although a two-phase-to-ground short circuit introduces zero-sequence impedance, the fault phase current contains the superposition of positive-sequence and negative-sequence components, and its magnitude is greater than that of the two-phase short circuit current containing only positive-sequence and negative-sequence components. Therefore, "two-phase-to-ground short circuit current > two-phase short circuit current".

[0099] More specifically, the derivation of the basic criterion is as follows:

[0100] In the AC power grid containing negative sequence suppressed new energy sources, it can be assumed that the positive sequence self-impedance at the fault point is equal to the negative sequence self-impedance at the fault point.

[0101] Based on the expressions for the phase current at the fault point under three-phase short circuit and two-phase short circuit, it is found that the phase current at the fault point under three-phase short circuit is greater than that under two-phase short circuit.

[0102] Based on the expressions for the phase current at the fault point under two-phase short circuit and two-phase ground short circuit, it is found that the phase current at the fault point under the two-phase ground short circuit is greater than that under the two-phase short circuit.

[0103] Based on the expressions for the phase current at the fault point under single-phase ground fault and two-phase short circuit, a first criterion for judging the relationship between the magnitudes of the phase currents at the fault point under different fault types is obtained.

[0104] Based on the expressions for the phase current at the fault point under two-phase-to-ground short circuit and three-phase short circuit, as well as the expressions for three-phase short circuit and single-phase-to-ground short circuit, and combined with the first criterion, a second criterion for judging the relationship between the magnitudes of the phase currents at the fault point under different fault types is obtained.

[0105] Based on the expressions for the phase current at the fault point under single-phase-to-ground short circuit and two-phase-to-ground short circuit, a third criterion for judging the relationship between the magnitudes of the phase currents at the fault point under different fault types is obtained.

[0106] Based on the first, second, and third criteria, a fourth criterion is obtained to determine the relationship between the magnitudes of the phase currents at the fault point under different fault types.

[0107] Furthermore, regarding the relationship between the magnitudes of single-phase ground faults and two-phase short circuits, based on the ratio of zero-sequence reactance to positive-sequence reactance in their respective expressions, the first criterion is derived: when the zero-sequence reactance is less than twice the positive-sequence reactance, the single-phase ground fault current is greater than the two-phase short circuit current, and vice versa.

[0108] Combining the expressions for three-phase short circuit, two-phase-to-ground short circuit, and single-phase-to-ground short circuit, the first criterion is introduced to derive the second criterion: when the zero-sequence reactance is less than the positive-sequence reactance, the three-phase short circuit current > the two-phase-to-ground short circuit current > the single-phase-to-ground short circuit current; when the zero-sequence reactance is greater than the positive-sequence reactance, the three-phase short circuit current > the single-phase-to-ground short circuit current > the two-phase-to-ground short circuit current.

[0109] For the direct comparison between single-phase ground fault and two-phase ground fault, a third criterion is derived based on the relationship between zero-sequence reactance and positive-sequence reactance: the smaller the zero-sequence reactance, the more likely the two-phase ground fault current is to be greater than the single-phase ground fault current.

[0110] Integrating the above criteria, a fourth criterion is formed: using the ratio of positive-sequence self-reactance to zero-sequence self-reactance as the core variable, a current magnitude ranking table for four fault types is established (such as scenarios like "three-phase short circuit > two-phase ground short circuit > single-phase ground short circuit > two-phase short circuit" or "three-phase short circuit > single-phase ground short circuit > two-phase ground short circuit > two-phase short circuit").

[0111] The first criterion is:

[0112] X ff0 >1.46X ff1

[0113] The second criterion is:

[0114] 1.46X ff1 >X ff0 >X ff1

[0115] The third criterion is:

[0116] X ff0 <X ff1 <4.41X ff0

[0117] The fourth criterion is:

[0118] X ff1 >4.41X ff0

[0119] Among them, X ff1 X ff2and X ff0 These represent the positive-sequence, negative-sequence, and zero-sequence self-reactances at the fault point, respectively, which are the imaginary parts of the self-impedances of each sequence.

[0120] After establishing the first to fourth criteria, the order of phase current magnitudes under different fault types can be determined by matching the node impedance matrix parameters corresponding to the fault location (mainly the numerical relationship between positive-sequence reactance and zero-sequence reactance).

[0121] When the node impedance matrix parameters corresponding to the fault location meet the first criterion (such as the ratio of zero-sequence reactance to positive-sequence reactance meeting a specific threshold), the phase current expression can be substituted to obtain the following: the phase currents of different fault types, from largest to smallest, are three-phase short circuit, two-phase ground short circuit, two-phase short circuit, and single-phase ground short circuit.

[0122] If the parameters meet the second criterion (such as the zero-sequence reactance being in a certain intermediate range), the sorting result is adjusted to three-phase short circuit, two-phase ground short circuit, single-phase ground short circuit, and two-phase short circuit. At this time, the single-phase ground short circuit current exceeds the two-phase short circuit current due to the influence of the zero-sequence impedance.

[0123] When the parameters meet the third criterion (zero-sequence reactance is significantly greater than positive-sequence reactance), the single-phase ground fault current is affected by the enhancement of the zero-sequence component, and the order becomes single-phase ground fault, two-phase ground fault, three-phase fault, two-phase fault, breaking the conventional rule that the three-phase fault current is always the largest.

[0124] If the parameters satisfy the fourth criterion (the ratio of zero-sequence reactance to positive-sequence reactance is in a special range), then the two-phase ground fault current becomes the largest due to the superposition effect of positive-sequence, negative-sequence, and zero-sequence components, and the order is two-phase ground fault, single-phase ground fault, three-phase fault, and two-phase fault.

[0125] The above four sorting results together constitute a complete variation pattern of phase current at the fault point with the fault type. Its core is to directly output the current magnitude relationship that can be used for protection setting by matching the impedance parameters in the node impedance matrix with the criteria, providing a clear reference standard for subsequent "determining the fault type according to the variation pattern".

[0126] S03: Based on the change pattern, determine the corresponding fault type in the line differential protection setting calculation.

[0127] In a preferred embodiment of this invention, determining the corresponding fault type in the line differential protection setting calculation based on the change pattern specifically involves:

[0128] If the impedance matrix parameters of the fault location node satisfy the first criterion, the fault types selected for the setting calculation are three-phase short circuit and single-phase ground fault, respectively, which correspond to the setting calculation requirements of ensuring protection reliability and sensitivity.

[0129] If the impedance matrix parameters of the fault location node satisfy the second criterion, the fault types selected for the setting calculation are three-phase short circuit and two-phase short circuit, respectively, which correspond to the setting calculation requirements of ensuring protection reliability and sensitivity.

[0130] If the impedance matrix parameters of the fault location node satisfy the third criterion, the fault types selected for the setting calculation are single-phase ground fault and two-phase short circuit, respectively, which correspond to the setting calculation requirements of ensuring protection reliability and sensitivity.

[0131] If the impedance matrix parameters of the fault location node satisfy the fourth criterion, the fault types selected for the setting calculation are two-phase ground short circuit and two-phase short circuit, respectively, which correspond to the setting calculation requirements of ensuring protection reliability and sensitivity.

[0132] S04: Determine the line differential protection setting scheme for the target power grid based on the fault type.

[0133] In a preferred embodiment of this invention, the step of determining the line differential protection setting scheme of the target power grid based on the fault type specifically includes:

[0134] Based on the identified fault type, the corresponding baseline parameters are extracted. These baseline parameters are calculated based on information such as the power grid topology, line parameters, and the specific location of the fault point, providing fundamental data support for subsequent tuning calculations.

[0135] In summary, this application constructs a model that accurately reflects the characteristics of the target AC power grid by obtaining the node impedance matrix of a pre-defined power grid system model and extracting its first parameter. This model equates new energy sources to constant current sources and synchronous power sources to grounded branches with resistance, thus simplifying the analysis process for complex power grids. Based on the node impedance matrix and the first parameter, this application further derives the expressions for the phase current at the fault point under different fault types and determines the variation pattern of the phase current with the fault type. This process, through the variation pattern, can quickly determine the corresponding fault type in the line differential protection setting calculation and generate the line differential protection setting scheme for the target power grid accordingly. This method not only improves the efficiency of the setting calculation but also enhances the reliability and sensitivity of the protection system, enabling it to better adapt to the complex power grid environment after the integration of new energy sources. This application effectively solves the problem in existing technologies of being unable to accurately and efficiently generate line differential protection setting schemes.

[0136] Example 2

[0137] Please refer to Figure 2 , Figure 2This is a flowchart illustrating an embodiment of a line differential protection method for a power grid provided in this application. The process of the line differential protection method for a power grid in this application is described in detail through steps S101-S102.

[0138] S101: Obtain the line differential protection setting scheme of the target power grid according to the method for determining the line differential protection setting scheme described in Example 1;

[0139] S102: Calculate the setting value of the target power grid protection device according to the line differential protection setting scheme; control the target power grid protection device to protect the line according to the setting value.

[0140] In a preferred embodiment of this invention, the step of calculating the setting value of the target power grid protection device according to the line differential protection setting scheme, and controlling the target power grid protection device to protect the line according to the setting value, specifically involves:

[0141] In implementing this application, the line differential protection setting scheme for the target power grid is first obtained according to the method for determining the line differential protection setting scheme. This scheme details the fault types that should be set for the line differential protection settings under different power grid structures. Based on this scheme, the specific settings of the protection device for the target power grid are calculated. These settings include key parameters such as operating current and operating time, which determine the operating characteristics of the protection device when a fault occurs. When calculating the settings, the magnitude relationship of the phase current at the fault point, the topology of the power grid, and the characteristics of the protection device are comprehensively considered to ensure that the settings can guarantee both the reliability of the protection and the sensitivity requirements. Finally, based on the calculated settings, the parameters of the protection device for the target power grid are set and controlled so that the protection device can operate quickly and accurately when a fault occurs, disconnecting the faulty line, thereby effectively protecting the power grid lines, reducing the impact of the fault on the power grid operation, and improving the safety and stability of the power grid.

[0142] Example 3

[0143] Please refer to Figure 3 This is a device for determining a line differential protection setting scheme, provided in an embodiment of this application.

[0144] In this embodiment, the device for determining the line differential protection setting scheme includes a first acquisition module 10, a derivation module 20, a fault type determination module 30, and a scheme determination module 40.

[0145] The first acquisition module 10 is used to acquire the node impedance matrix of the preset power grid system model and extract the first parameter from the node impedance matrix; wherein, the power grid system model is constructed based on the system parameters of the target AC power grid, and the new energy sources of the target AC power grid are equivalent to constant current sources, and the synchronous power sources of the target AC power grid are equivalent to grounded branches with resistance.

[0146] The derivation module 20 is used to derive the expression of the phase current at the fault point under different fault types based on the node impedance matrix and the first parameter, and to determine the change mode of the phase current at the fault point with the fault type based on the expression.

[0147] The fault type determination module 30 is used to determine the corresponding fault type in the line differential protection setting calculation based on the change mode.

[0148] The scheme determination module 40 determines the line differential protection setting scheme of the target power grid based on the fault type.

[0149] For ease of description and brevity, the embodiments of the device of the present invention include all the implementation methods in the above embodiments of the method for determining the line differential protection setting scheme, which will not be repeated here.

[0150] Example 4

[0151] Please refer to Figure 4 This application provides a line differential protection device for a power grid.

[0152] In this embodiment, the line differential protection device of the power grid includes a second acquisition module 101 and a protection module 102.

[0153] The second acquisition module 101 is used to obtain the line differential protection setting scheme of the target power grid according to the method for determining the line differential protection setting scheme as described in any one of Embodiment 1.

[0154] The protection module 102 is used to calculate the setting value of the target power grid protection device according to the line differential protection setting scheme; and to control the target power grid protection device to protect the line according to the setting value.

[0155] For ease of description and brevity, the embodiments of the present invention include all the implementation methods in the above-described embodiments of the line differential protection method for power grids, and will not be repeated here.

[0156] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A method for determining the setting scheme of line differential protection, characterized in that, include: Obtain the node impedance matrix of the preset power grid system model and extract the first parameter from the node impedance matrix; wherein, the power grid system model is constructed based on the system parameters of the target AC power grid, and the new energy sources of the target AC power grid are equivalent to constant current sources, and the synchronous power sources of the target AC power grid are equivalent to grounded branches with resistance; Based on the node impedance matrix and the first parameter, the expression for the phase current at the fault point under different fault types is derived, and the variation mode of the phase current at the fault point with the fault type is determined based on the expression. Based on the aforementioned change pattern, the corresponding fault type in the line differential protection setting calculation is determined; Based on the fault type, determine the line differential protection setting scheme for the target power grid.

2. The method for determining the line differential protection setting scheme according to claim 1, characterized in that, The process of obtaining the node impedance matrix of the preset power grid system model and extracting the first parameter from the node impedance matrix specifically involves: Obtain the system parameters of the target AC power grid, including new energy sources, synchronous power sources, line impedance parameters, and node topology relationships; Based on the system parameters, the new energy source is equivalent to a constant current source with controllable output current, and the synchronous power source is equivalent to a voltage source branch with grounding resistance. The correlation matrix is ​​constructed according to the node topology relationship to obtain the power grid system model. Based on the power grid system model, and combined with the line impedance parameters, a branch impedance matrix is ​​generated, and a node impedance matrix is ​​generated by combining the correlation matrix and the branch impedance matrix. The first parameter is extracted from the node impedance matrix. The first parameter includes the positive-sequence self-impedance, negative-sequence self-impedance, zero-sequence self-impedance of the node where the fault point is located, and the positive-sequence mutual impedance between the new energy access node and the fault point node.

3. The method for determining the line differential protection setting scheme according to claim 1, characterized in that, The derivation of the expression for the phase current at the fault point under different fault types based on the node impedance matrix and the first parameter is as follows: When the fault type is a single-phase ground fault, the expression for the first fault phase current is derived based on the relationship between the fault phase voltage and the zero-sequence voltage, combined with the positive-sequence self-impedance, negative-sequence self-impedance and zero-sequence self-impedance in the first parameter. When the fault type is a two-phase short circuit, based on the difference between the voltage of the non-faulty phase and the voltage of the faulty phase, and combined with the positive-sequence self-impedance and negative-sequence self-impedance in the first parameter, the expression for the second faulty phase current is derived. When the fault type is a two-phase ground fault, the expression for the third fault phase current is derived based on the preset fault phase voltage balance equation and the positive-sequence self-impedance, negative-sequence self-impedance, and zero-sequence self-impedance in the first parameter. When the fault type is a three-phase short circuit, based on the preset three-phase voltage symmetry characteristics and combined with the positive sequence self-impedance in the first parameter, the expression for the fourth fault phase current is derived.

4. The method for determining the line differential protection setting scheme according to claim 3, characterized in that, The expressions for the first fault phase current, the second fault phase current, the third fault phase current, and the fourth fault phase current are as follows: The expression for the first fault phase current is: The expression for the second fault phase current is: The expression for the third fault phase current is: The expression for the fourth fault phase current is: In the formula, Let f represent the fault phase current, n represent the node where the fault occurred, N represent the new energy grid-connected node, and Z represent the set of new energy grid-connected nodes. ff1 Z represents the positive-sequence self-impedance at the fault point. ff2 Z represents the negative sequence self-impedance at the fault point. ff0 Z represents the zero-sequence self-impedance at the fault point. fn1 The positive-sequence mutual impedance between the faulty node and the new energy grid connection point is represented by 'a', where 'a' represents the rotation factor and 'I' represents the positive-sequence mutual impedance between the faulty node and the new energy grid connection point. n1 This represents the injected current at the new energy grid connection node.

5. The method for determining the line differential protection setting scheme according to claim 1, characterized in that, The method for determining the variation pattern of phase current at the fault point with fault type based on the expression is as follows: Based on the phase current expressions under different fault types, and combined with the first parameter, calculate the phase current magnitude expression corresponding to each fault type. By comparing the phase current magnitude expressions for the four fault types pairwise, the magnitude relationship is obtained. Based on the magnitude relationship, establish a correspondence between fault types and the order of phase current magnitudes; The aforementioned correspondence is used as the pattern of phase current variation at the fault point with the fault type.

6. A method for differential protection of power grid lines, characterized in that, include: The method for determining the line differential protection setting scheme according to any one of claims 1 to 5 obtains the line differential protection setting scheme of the target power grid; Calculate the settings of the target power grid protection device according to the line differential protection setting scheme; Based on the set value, the target power grid protection device is controlled to protect the line.

7. A device for determining a line differential protection setting scheme, characterized in that, include: The first acquisition module is used to acquire the node impedance matrix of the preset power grid system model and extract the first parameter from the node impedance matrix; wherein, the power grid system model is constructed based on the system parameters of the target AC power grid, and the new energy sources of the target AC power grid are equivalent to constant current sources, and the synchronous power sources of the target AC power grid are equivalent to grounded branches with resistance. The derivation module is used to derive the expression of the phase current at the fault point under different fault types based on the node impedance matrix and the first parameter, and to determine the change mode of the phase current at the fault point with the fault type based on the expression. The fault type determination module is used to determine the corresponding fault type in the line differential protection setting calculation based on the change pattern. The scheme determination module is used to determine the line differential protection setting scheme of the target power grid based on the fault type.

8. The device for determining the line differential protection setting scheme according to claim 7, characterized in that, The process of obtaining the node impedance matrix of the preset power grid system model and extracting the first parameter from the node impedance matrix specifically involves: Obtain the system parameters of the target AC power grid, including new energy sources, synchronous power sources, line impedance parameters, and node topology relationships; Based on the system parameters, the new energy source is equivalent to a constant current source with controllable output current, and the synchronous power source is equivalent to a voltage source branch with grounding resistance. The correlation matrix is ​​constructed according to the node topology relationship to obtain the power grid system model. Based on the power grid system model, and combined with the line impedance parameters, a branch impedance matrix is ​​generated, and a node impedance matrix is ​​generated by combining the correlation matrix and the branch impedance matrix. The first parameter is extracted from the node impedance matrix. The first parameter includes the positive-sequence self-impedance, negative-sequence self-impedance, zero-sequence self-impedance of the node where the fault point is located, and the positive-sequence mutual impedance between the new energy access node and the fault point node.

9. The device for determining the line differential protection setting scheme according to claim 7, characterized in that, The derivation of the expression for the phase current at the fault point under different fault types based on the node impedance matrix and the first parameter is as follows: When the fault type is a single-phase ground fault, the expression for the first fault phase current is derived based on the relationship between the fault phase voltage and the zero-sequence voltage, combined with the positive-sequence self-impedance, negative-sequence self-impedance and zero-sequence self-impedance in the first parameter. When the fault type is a two-phase short circuit, based on the difference between the voltage of the non-faulty phase and the voltage of the faulty phase, and combined with the positive-sequence self-impedance and negative-sequence self-impedance in the first parameter, the expression for the second faulty phase current is derived. When the fault type is a two-phase ground fault, the expression for the third fault phase current is derived based on the preset fault phase voltage balance equation and the positive-sequence self-impedance, negative-sequence self-impedance, and zero-sequence self-impedance in the first parameter. When the fault type is a three-phase short circuit, based on the preset three-phase voltage symmetry characteristics and combined with the positive sequence self-impedance in the first parameter, the expression for the fourth fault phase current is derived.

10. A line differential protection device for a power grid, characterized in that, include: The second acquisition module is used to obtain the line differential protection setting scheme of the target power grid by the method for determining the line differential protection setting scheme according to any one of claims 1 to 5. The protection module is used to calculate the settings of the target power grid protection device according to the line differential protection setting scheme; Based on the set value, the target power grid protection device is controlled to protect the line.

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