A method, system, and equipment for calculating the DC component of short-circuit current in a power system.

Abstract

This application relates to a method, system, and device for calculating the DC component of short-circuit current in a power system. The method includes obtaining the fault node in the power system network topology, the number M of branches connected to the fault node, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault node; calculating the equivalent impedance phasor and decay time constant corresponding to each branch based on the active voltage phasor and branch current phasor; obtaining the time after the fault, and calculating the DC component of the short-circuit current based on the time after the fault, the branch current phasor, and the decay time constant; and calculating the DC component of the short-circuit current to ground of the fault node for the M branches. This method calculates the DC component of the short-circuit current of each branch connected to the fault node separately, and incorporates the decay time constant of the branch during the calculation process, resulting in more accurate calculations of the DC component of the short-circuit current of the branches.

Description

Technical Field

[0001] This application relates to the field of power system short-circuit current technology, and in particular to a method, system and equipment for calculating the DC component of short-circuit current in a power system. Background Technology

[0002] The slower decay of the DC component of the short-circuit current will increase the DC component content of the short-circuit impact current, the total short-circuit current, and the current that the circuit breaker needs to interrupt. This poses a severe test to whether some circuit breakers with very small interruption capacity margins in the power grid can interrupt the short-circuit current in a timely manner as required by their configuration, and creates hidden dangers for the safe operation of the power system.

[0003] Current research on short-circuit current calculations primarily focuses on the periodic components. In practical engineering applications, the DC component of the short-circuit current and its attenuation are often overlooked, and simple, practical methods and tools for calculating DC component attenuation are lacking. Therefore, there is an urgent need to accurately calculate the DC component of the short-circuit current using electromagnetic transient simulation and to propose a practical algorithm for its calculation.

[0004] For a three-phase symmetrical circuit powered by an infinitely high-power source, assuming a three-phase symmetrical short circuit occurs at t = 0, the expression for the DC component of the short-circuit current in the power system is: In the formula, The initial voltage angle of the power grid. This represents the amplitude of the periodic component of the current when the power grid is operating normally. This is the circuit impedance angle when the power grid is operating normally. It is the forced component of the short-circuit current, which is generated by the electromotive force of the power source. It has the same variation law as the electromotive force of the power source, and its amplitude remains unchanged during the transient process. Since this component changes periodically according to a sinusoidal law, it is also called the periodic component. This represents the amplitude of the periodic component of the short-circuit current. The impedance angle of the short-circuit loop; It is the free component of the short-circuit current, which is independent of the external power supply. Since the current in the inductor circuit cannot be generated abruptly and decays to zero over time, it is a current that decays exponentially and is usually called the DC component or non-periodic component. The time constant of the short-circuit loop is the ratio of the inductance L to the resistance R of the short-circuit loop. Its magnitude reflects the rate of decay of the free component. From the expression for the DC component of the short-circuit current in a power system, it can be seen that the initial value of the DC component of the short-circuit current is related to the initial phase angle of the power supply voltage and the current value in the circuit before the short circuit; the decay time is related to the operating mode and grid structure when the short circuit occurs.

[0005] Current assessments of short-circuit current data primarily focus on calculating the periodic component, neglecting the influence of the DC component and the decay time constant, and failing to provide a quantitative analysis of their impact. In recent years, with the development of ultra-high-voltage (UHV) transmission projects, to reduce transmission losses, the capacity of generators and transformers in UHV projects has gradually increased, while the resistance of transmission lines has further decreased. This has led to an increasingly larger reactance-resistivity ratio of the equivalent power system at the short-circuit point, resulting in a corresponding increase in the DC component decay time constant. Consequently, the impact of the DC component of the short-circuit current on the power grid has become increasingly prominent. Under short-circuit faults, the decay rate of the DC component of the short-circuit current slows down, and its impact on the actual breaking capacity of circuit breakers becomes increasingly significant. Therefore, only by accurately calculating the decaying DC component of the short-circuit current over time on each circuit breaker branch connected to the short-circuit node can a valid basis be provided for verifying the breaking capacity of circuit breakers.

[0006] Currently, common methods for calculating the decay time constant of the DC component of short-circuit current in circuit breaker branches include the input impedance method, the transfer impedance method, and the electromagnetic transient simulation method. However, the input impedance method completely equivalences the external circuit of the circuit breaker, without considering the individual decay characteristics of the DC component of the short-circuit current in each branch. When the impedance ratio of each branch deviates significantly, the calculated results are highly inaccurate. The transfer impedance method only considers the transfer impedance of the power supply branch on the circuit breaker, which yields good results in transmission networks, but not ideal results in distribution networks and other networks. Although the electromagnetic transient simulation method can accurately describe the transient process of the entire short-circuit current and separate the DC component, its computational modeling workload is enormous, making it unsuitable for routine engineering calculations of large-scale complex power grids. Summary of the Invention

[0007] This application provides a method, system, and device for calculating the DC component of short-circuit current in a power system, which solves the technical problem of large deviations in the calculation results of existing methods for calculating the DC component of short-circuit current on circuit breaker branches.

[0008] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0009] A method for calculating the DC component of short-circuit current in a power system, applicable to power systems with large branch impedance ratio deviations, includes the following steps:

[0010] Obtain the fault node of the power system network topology, the number M of branches connected to the fault node, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault node;

[0011] Based on the active voltage phasor of the fault point and the branch current phasor of each branch, the equivalent impedance phasor and the decay time constant of the DC component of the short-circuit current corresponding to each branch are obtained.

[0012] Obtain the post-fault time corresponding to the decay time constant, and calculate the DC component of the short-circuit current of the corresponding branch based on the post-fault time, the branch current phasor of each branch, and the decay time constant; and calculate the DC component of the short-circuit current to ground of the fault node for the DC components of the short-circuit current of M branches.

[0013] Preferably, obtaining the branch current phasor of each branch connected to the faulty node in the power system network topology includes:

[0014] The second parameter data of the power system network topology is obtained. The second parameter data includes a reference node, n ordinary nodes, system nominal voltage, voltage coefficient, self-admittance of the n ordinary nodes, first branch admittance between each pair of ordinary nodes, and second branch admittance between the fault node and the ordinary node.

[0015] The fault node conditions corresponding to the fault node are determined based on the general nominal voltage and the voltage coefficient; the node current balance equation is constructed based on the self-admittance of the n ordinary nodes and the admittance of all first branches;

[0016] The node current balance equations are subjected to elementary row transformations and back-substitution calculations are performed using the fault node conditions to obtain the node voltage phasor for each of the ordinary nodes.

[0017] The branch current phasor of the branch connected to the fault node is calculated based on the active voltage phasor of the fault point, the node voltage phasor of the ordinary node connected to the fault node, and the second branch admittance corresponding to the ordinary node.

[0018] Preferably, determining the fault node conditions corresponding to the fault node based on the nominal voltage and the voltage coefficient includes:

[0019] The active voltage phasor at the fault point is obtained by using the active voltage calculation formula based on the nominal voltage and the voltage coefficient.

[0020] The fault node conditions corresponding to the fault node are determined based on the active voltage phasor of the fault point.

[0021] The active voltage calculation formula is as follows:

[0022]

[0023] The conditions for the fault node are as follows: In the formula, Active voltage phasor at the fault point The amplitude, c is the voltage coefficient, and U is the system nominal voltage. The voltage phasor of the faulty node.

[0024] Preferably, the node current balance equation is constructed based on the self-admittances of the n ordinary nodes and the admittances of all first branches, and the node current balance equation is as follows:

[0025]

[0026] In the formula, when i=j, Y ij Y is the self-admittance of the i-th or j-th ordinary node, when i ≠ j. ij Y is the admittance of the first branch between the i-th ordinary node and the j-th ordinary node. If there is no connecting branch between the i-th ordinary node and the j-th ordinary node, then Y... ij =0, Let be the node voltage phasor of the nth ordinary node.

[0027] Preferably, the decay time constant of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch is calculated based on the active voltage phasor of the fault point and the branch current phasor of each branch, including:

[0028] The equivalent impedance phasor corresponding to each branch is obtained by using the equivalent impedance phasor formula based on the active voltage phasor of the fault point and the branch current phasor of each branch.

[0029] The decay time constant of the DC component of the short-circuit current corresponding to each branch is obtained by using the decay time calculation formula based on the equivalent impedance phasor of each branch.

[0030] The equivalent impedance phasor formula is as follows:

[0031]

[0032] The formula for calculating the decay time is:

[0033] ,

[0034] In the formula, Z equ,x Let x be the equivalent impedance phasor of the x-th branch. For the active voltage phasor at the fault point, Let L be the branch current phasor of the x-th branch. equ,x and R equ,x The equivalent reactance and equivalent resistance of the x-th branch are T, respectively. x Let be the decay time constant of the DC component of the short-circuit current in the x-th branch.

[0035] Preferably, the method for calculating the DC component of the short-circuit current in the power system includes: calculating the DC component of the short-circuit current of the corresponding branch using a first calculation formula based on the time after the fault, the branch current phasor of each branch, and the decay time constant. The first calculation formula is:

[0036]

[0037] The DC component of the short-circuit current of the M branches is calculated using the second calculation formula to obtain the DC component of the short-circuit current to ground of the fault node. The second calculation formula is as follows:

[0038]

[0039] In the formula, t is the time after the fault corresponding to the decay time constant. Let x be the branch current phasor of the x-th branch. Let T be the DC component of the short-circuit current in the xth branch. x Let I be the decay time constant of the DC component of the short-circuit current in the x-th branch. DC This represents the DC component of the short-circuit current to ground at the fault node.

[0040] This application also provides a short-circuit current DC component calculation system for power systems, which is applied to power systems with large branch impedance ratio deviations. The short-circuit current DC component calculation system includes a data acquisition module, a first calculation module, and a second calculation module.

[0041] The data acquisition module is used to acquire the fault node of the power system network topology, the number M of branches connected to the fault node, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault node.

[0042] The first calculation module is used to calculate, based on the active voltage phasor of the fault point and the branch current phasor of each branch, the decay time constant of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch.

[0043] The second calculation module is used to obtain the post-fault time corresponding to the decay time constant, calculate the DC component of the short-circuit current of the corresponding branch based on the post-fault time, the branch current phasor of each branch and the decay time constant; and calculate the DC component of the short-circuit current of the fault node to ground by calculating the DC component of the short-circuit current of the M branches.

[0044] Preferably, the data acquisition module includes a parameter acquisition submodule, an equation construction submodule, a third calculation submodule, and a fourth calculation submodule;

[0045] The parameter acquisition submodule is used to acquire the second parameter data of the power system network topology. The second parameter data includes a reference node, n ordinary nodes, system nominal voltage, voltage coefficient, self-admittance of the n ordinary nodes, first branch admittance between each pair of ordinary nodes, and second branch admittance between the fault node and the ordinary node.

[0046] The equation construction submodule is used to determine the fault node conditions corresponding to the fault node based on the general nominal voltage and the voltage coefficient; and to construct the node current balance equation based on the self-admittance of the n ordinary nodes and the admittance of all first branches.

[0047] The third calculation submodule is used to perform elementary row transformations on the node current balance equations and perform back substitution calculations using the fault node conditions to obtain the node voltage phasor of each ordinary node.

[0048] The fourth calculation submodule is used to calculate, based on the active voltage phasor of the fault point, the node voltage phasor of the ordinary node connected to the fault node, and the second branch admittance corresponding to the ordinary node, to obtain the branch current phasor of the branch connected to the fault node.

[0049] Preferably, the second calculation module is further configured to calculate, using a first calculation formula, the DC component of the short-circuit current of the corresponding branch based on the time after the fault, the branch current phasor of each branch, and the decay time constant; and to calculate, using a second calculation formula, the DC component of the short-circuit current of the M branches to ground, the DC component of the short-circuit current of the fault node; the first calculation formula is:

[0050]

[0051] The second calculation formula is:

[0052]

[0053] In the formula, t is the time after the fault corresponding to the decay time constant. Let x be the branch current phasor of the x-th branch. Let T be the DC component of the short-circuit current in the xth branch. x Let I be the decay time constant of the DC component of the short-circuit current in the x-th branch. DC This represents the DC component of the short-circuit current to ground at the fault node.

[0054] This application also provides a terminal device, including a processor and a memory;

[0055] The memory is used to store program code and transmit the program code to the processor;

[0056] The processor is configured to execute the above-described method for calculating the DC component of the short-circuit current in a power system according to the instructions in the program code.

[0057] As can be seen from the above technical solutions, the embodiments of this application have the following advantages: the method, system, and equipment for calculating the DC component of short-circuit current in the power system include: obtaining the fault node of the power system network topology, the number M of branches connected to the fault node, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault node; calculating the equivalent impedance phasor and the decay time constant of the DC component of short-circuit current corresponding to each branch based on the active voltage phasor of the fault point and the branch current phasor of each branch; obtaining the post-fault time corresponding to the decay time constant, and calculating the DC component of short-circuit current of the corresponding branch based on the post-fault time, the branch current phasor of each branch, and the decay time constant; and calculating the DC component of short-circuit current to ground of the fault node for the DC components of short-circuit current of M branches. The proposed method for calculating the DC component of short-circuit current in a power system calculates the DC component of short-circuit current for each branch connected to the fault node separately. The method incorporates the branch's decay time constant during the calculation process, resulting in more accurate calculations. Compared to the traditional input impedance method, this method demonstrates better adaptability across the entire time period and resolves the technical problem of large deviations in calculation results for existing methods of calculating the DC component of short-circuit current on circuit breaker branches. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0059] Figure 1 This is a flowchart illustrating the steps of the method for calculating the DC component of short-circuit current in a power system as described in an embodiment of this application.

[0060] Figure 2 This is a framework diagram of the short-circuit current DC component calculation system for the power system described in the embodiments of this application. Detailed Implementation

[0061] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0062] This application proposes a method, system, and equipment for calculating the DC component of short-circuit current in a power system, which solves the technical problem of large deviations in the calculation results of existing methods for calculating the DC component of short-circuit current on circuit breaker branches.

[0063] Example 1:

[0064] Figure 1 This is a flowchart illustrating the steps of the method for calculating the DC component of short-circuit current in a power system according to an embodiment of this application.

[0065] like Figure 1 As shown, this application provides a method for calculating the DC component of short-circuit current in a power system, applicable to power systems with large branch impedance ratio deviations. The method includes the following steps:

[0066] S10. Obtain the fault node of the power system network topology, the number of branches M connected to the fault node, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault node.

[0067] It should be noted that step S10 is mainly for obtaining the fault node f in the power system network topology where a short circuit fault has occurred, the number M of branches connected to the fault node f, and the active voltage phasor of the fault point. and the branch current phasor of each branch connected to the faulty node f. In this embodiment, the number M of branches connected to the faulty node f depends on whether the faulty node is on a branch of the line. If the faulty node is on a branch of the line, then M is 2. If the faulty node is not on a branch of the line, then M is the number of branches connected to the faulty node f.

[0068] S20. Based on the active voltage phasor at the fault point and the branch current phasor of each branch, calculate the equivalent impedance phasor and the decay time constant of the DC component of the short-circuit current corresponding to each branch.

[0069] It should be noted that in step S20, the attenuation time constant of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch is calculated based on the data obtained in step S10.

[0070] Furthermore, based on the active voltage phasor at the fault point and the branch current phasor of each branch, the decay time constant of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch is obtained, including:

[0071] The equivalent impedance phasor for each branch is obtained by using the equivalent impedance phasor formula based on the active voltage phasor at the fault point and the branch current phasor of each branch.

[0072] The decay time constant of the DC component of the short-circuit current corresponding to each branch is obtained by using the decay time calculation formula based on the equivalent impedance phasor of each branch.

[0073] The formula for the equivalent impedance phasor is:

[0074]

[0075] The formula for calculating decay time is:

[0076] ,

[0077] In the formula, Z equ,x Let x be the equivalent impedance phasor of the x-th branch. For the active voltage phasor at the fault point, Let L be the branch current phasor of the x-th branch. equ,x and R equ,x The equivalent reactance and equivalent resistance of the x-th branch are T, respectively. x Let be the decay time constant of the DC component of the short-circuit current in the x-th branch.

[0078] It should be noted that, It refers to R equ,x Get Z equ,x The value of the real part of this equivalent impedance phasor. It refers to L equ,x Get Z equ,x The value of the imaginary part of this equivalent impedance phasor.

[0079] S30. Obtain the post-fault time corresponding to the decay time constant, and calculate the DC component of the short-circuit current of the corresponding branch based on the post-fault time, the branch current phasor of each branch and the decay time constant; and calculate the DC component of the short-circuit current of the fault node to ground for the DC component of the short-circuit current of M branches.

[0080] It should be noted that step S30 is mainly based on the data obtained in steps S10 and S20 to calculate the DC component of the short-circuit current of each branch and the DC component of the short-circuit current to ground of the fault node.

[0081] Furthermore, the method for calculating the DC component of the short-circuit current in this power system includes: calculating the DC component of the short-circuit current of the corresponding branch using a first calculation formula based on the time after the fault, the branch current phasor of each branch, and the decay time constant. The first calculation formula is as follows:

[0082]

[0083] The DC component of the short-circuit current of the M branches is calculated using the second calculation formula to obtain the DC component of the short-circuit current to ground at the fault node. The second calculation formula is as follows:

[0084]

[0085] In the formula, t is the time after the fault corresponding to the decay time constant. Let x be the branch current phasor of the x-th branch. Let T be the DC component of the short-circuit current in the xth branch. x Let I be the decay time constant of the DC component of the short-circuit current in the x-th branch. DC This represents the DC component of the short-circuit current to ground at the fault node. Where t = 0, it indicates that a short-circuit fault occurred at that moment.

[0086] The method for calculating the DC component of short-circuit current in a power system provided in this application includes obtaining the fault node of the power system network topology, the number M of branches connected to the fault node, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault node; calculating the equivalent impedance phasor and the decay time constant of the DC component of short-circuit current corresponding to each branch based on the active voltage phasor of the fault point and the branch current phasor of each branch; obtaining the post-fault time corresponding to the decay time constant, and calculating the DC component of short-circuit current of the corresponding branch based on the post-fault time, the branch current phasor of each branch, and the decay time constant; and calculating the DC component of short-circuit current to ground of the fault node for the DC components of short-circuit current of M branches. The proposed method for calculating the DC component of short-circuit current in a power system calculates the DC component of short-circuit current for each branch connected to the fault node separately. The method incorporates the branch's decay time constant during the calculation process, resulting in more accurate calculations. Compared to the traditional input impedance method, this method demonstrates better adaptability across the entire time period and resolves the technical problem of large deviations in calculation results for existing methods of calculating the DC component of short-circuit current on circuit breaker branches.

[0087] In one embodiment of this application, obtaining the branch current phasor of each branch connected to the faulty node in the power system network topology includes:

[0088] The second parameter data of the power system network topology is obtained. The second parameter data includes the reference node, n ordinary nodes, system nominal voltage, voltage coefficient, self-admittance of n ordinary nodes, first branch admittance between any two ordinary nodes, and second branch admittance between the fault node and an ordinary node.

[0089] The fault node conditions corresponding to the fault node are determined based on the nominal voltage and voltage coefficient; the node current balance equations are constructed based on the self-admittance of n ordinary nodes and the admittance of all first branches.

[0090] The node current balance equations are subjected to elementary row transformations and back-substitution calculations are performed using fault node conditions to obtain the node voltage phasor for each ordinary node.

[0091] The branch current phasor of the branch connected to the fault node is obtained by calculating the active voltage phasor of the fault point, the node voltage phasor of the ordinary node connected to the fault node, and the second branch admittance corresponding to the ordinary node.

[0092] It should be noted that in the process of constructing the node current balance equation, other power sources in the power system network topology are set to 0, and the fault point is constructed by setting it as an equivalent voltage source.

[0093] Furthermore, determining the fault node conditions corresponding to the fault node based on the nominal voltage and voltage coefficient includes:

[0094] The active voltage phasor at the fault point is obtained by using the active voltage calculation formula based on the nominal voltage and voltage coefficient.

[0095] The fault node conditions corresponding to the fault node are determined based on the active voltage phasor of the fault point.

[0096] The formula for calculating the active voltage is as follows:

[0097]

[0098] The fault node conditions are: In the formula, Active voltage phasor at the fault point The amplitude, c is the voltage coefficient, and U is the system nominal voltage. The voltage phasor of the faulty node.

[0099] It should be noted that in the power system, the equivalent voltage source method is used to set all power sources of the power system to zero, and an ideal AC voltage source is added at the fault node f. This AC voltage source is the active voltage phasor of the fault point. According to the national standard GB / T15544.1, the value of c is shown in Table 1.

[0100] Table 1

[0101]

[0102] Furthermore, based on the self-admittances of the n ordinary nodes and the admittances of all first branches, the node current balance equations are constructed as follows:

[0103]

[0104] In the formula, when i=j, Y ij Y is the self-admittance of the i-th or j-th ordinary node, when i ≠ j. ij Y is the admittance of the first branch between the i-th ordinary node and the j-th ordinary node. If there is no connecting branch between the i-th ordinary node and the j-th ordinary node, then Y... ij =0, Let be the node voltage phasor of the nth ordinary node.

[0105] It should be noted that in the process of constructing the node current balance equations, the node admittance matrix Y is used to represent the network topology of the power system. The node admittance matrix Y is:

[0106]

[0107] Where, when i=j, Y ij The value of Y is the sum of the admittances of all branches connected to the i-th or j-th ordinary node; when i≠j, Y ij The value of is the negative of the branch admittance connecting the i-th ordinary node and the j-th ordinary node. In this embodiment, the expression for the admittance is:

[0108]

[0109] In the formula, Z ij R is the impedance of the branch between the i-th ordinary node and the j-th ordinary node. ij Let X be the resistance of the branch between the i-th ordinary node and the j-th ordinary node. ij Let J be the reactance of the branch between the i-th ordinary node and the j-th ordinary node, where J is the imaginary part in units, w is the angular frequency of the power system, and L is the reactance of the branch between the i-th and j-th ordinary nodes. ij Let f be the inductance of the branch between the i-th and j-th ordinary nodes. If the faulty node is not an existing node, the node admittance matrix needs to be transformed, which requires adding a node f at the fault location.

[0110] In this embodiment, during the process of performing elementary row operations on the node current balance equations and using fault node conditions for back substitution to obtain the node voltage phasor for each normal node, the simplest Gaussian elimination method is used to perform back substitution calculations on the node current balance equations by row or column elimination to obtain the node voltage phasor for each normal node. The method of Gaussian elimination by row and column substitution has been described on pages 244 to 247 of "Power System Analysis" and will not be explained in detail here.

[0111] In this embodiment, the branch current phasor of the branch connected to the fault node is calculated using the branch current calculation formula based on the active voltage phasor of the fault point, the node voltage phasor of the ordinary node connected to the fault node, and the second branch admittance corresponding to the ordinary node. The branch current calculation formula is as follows: In the formula, Let f be the branch current phasor of the branch between the i-th normal node and the faulty node f; Let f be the second branch admittance of the branch between the i-th normal node and the faulty node f. Let be the node voltage phasor of the i-th ordinary node. Let M be the active voltage phasor of the fault node f. In this embodiment, the branch current phasor of the branch connected to the fault node f is the same as the branch current phasor of the branch connecting the i-th ordinary node to the fault node f. Let M be the number of branches connecting all ordinary nodes to the fault node f. Then, the calculated branch current phasor of the branch between the i-th ordinary node and the fault node f can be obtained. It can also be denoted as the branch current phasor of the xth branch. .

[0112] Example 2:

[0113] Figure 2 This is a framework diagram of the short-circuit current DC component calculation system for the power system described in the embodiments of this application.

[0114] like Figure 2 As shown, this application also provides a short-circuit current DC component calculation system for power systems, which is applied to power systems with large branch impedance ratio deviations. The short-circuit current DC component calculation system for power systems includes a data acquisition module 10, a first calculation module 20, and a second calculation module 30.

[0115] The data acquisition module 10 is used to acquire the fault nodes of the power system network topology, the number M of branches connected to the fault nodes, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault nodes.

[0116] The first calculation module 20 is used to calculate, based on the active voltage phasor of the fault point and the branch current phasor of each branch, the decay time constant of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch.

[0117] The second calculation module 30 is used to obtain the post-fault time corresponding to the decay time constant, and to calculate the DC component of the short-circuit current of the corresponding branch based on the post-fault time, the branch current phasor of each branch and the decay time constant; and to calculate the DC component of the short-circuit current of the fault node to ground for the DC component of the short-circuit current of M branches.

[0118] In this embodiment of the application, the data acquisition module 10 includes a parameter acquisition submodule, an equation construction submodule, a third calculation submodule, and a fourth calculation submodule;

[0119] The parameter acquisition submodule is used to acquire the second parameter data of the power system network topology. The second parameter data includes the reference node, n ordinary nodes, system nominal voltage, voltage coefficient, self-admittance of n ordinary nodes, first branch admittance between any two ordinary nodes, and second branch admittance between the fault node and an ordinary node.

[0120] The equation construction submodule is used to determine the fault node conditions corresponding to the fault node based on the general nominal voltage and voltage coefficient; and to construct the node current balance equation based on the self-admittance of n ordinary nodes and the admittance of all first branches.

[0121] The third calculation submodule is used to perform elementary row transformations on the node current balance equations and perform back substitution calculations using fault node conditions to obtain the node voltage phasor for each ordinary node.

[0122] The fourth calculation submodule is used to calculate the branch current phasor of the branch connected to the fault node based on the active voltage phasor of the fault point, the node voltage phasor of the ordinary node connected to the fault node, and the second branch admittance corresponding to the ordinary node.

[0123] In this embodiment of the application, the second calculation module 30 is further configured to calculate the DC component of the short-circuit current of the corresponding branch based on the time after the fault, the branch current phasor of each branch and the decay time constant using the first calculation formula; and to calculate the DC component of the short-circuit current of the M branches using the second calculation formula to obtain the DC component of the short-circuit current of the fault node to ground; the first calculation formula is as follows:

[0124]

[0125] The second calculation formula is:

[0126]

[0127] In the formula, t is the time after the fault corresponding to the decay time constant. Let x be the branch current phasor of the x-th branch. Let T be the DC component of the short-circuit current in the xth branch. xLet I be the decay time constant of the DC component of the short-circuit current in the x-th branch. DC This represents the DC component of the short-circuit current to ground at the fault node.

[0128] It should be noted that the content of the modules in Embodiment 2 corresponds to the steps in the method of Embodiment 1. The content of the steps in the method of Embodiment 1 has been described in detail in Embodiment 1, and the content of the modules in the system will not be described again in Embodiment 2.

[0129] Example 3:

[0130] This application also provides a terminal device, including a processor and a memory;

[0131] Memory is used to store program code and transfer the program code to the processor;

[0132] The processor is used to execute the above-mentioned method for calculating the DC component of the short-circuit current of the power system according to the instructions in the program code.

[0133] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0134] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0135] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0136] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0137] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0138] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for calculating the DC component of short-circuit current in a power system, applicable to power systems with large branch impedance ratio deviations, characterized in that... The method for calculating the DC component of the short-circuit current includes the following steps: Obtain the fault node of the power system network topology, the number M of branches connected to the fault node, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault node; Based on the active voltage phasor of the fault point and the branch current phasor of each branch, the decay time constant of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch is obtained. Obtain the post-fault time corresponding to the decay time constant, and calculate the DC component of the short-circuit current of the corresponding branch based on the post-fault time, the branch current phasor of each branch, and the decay time constant; and calculate the DC component of the short-circuit current of the fault node to ground for the DC components of the short-circuit current of M branches. The attenuation time constants of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch are calculated based on the active voltage phasor at the fault point and the branch current phasor of each branch, including: The equivalent impedance phasor corresponding to each branch is obtained by using the equivalent impedance phasor formula based on the active voltage phasor of the fault point and the branch current phasor of each branch. The decay time constant of the DC component of the short-circuit current corresponding to each branch is obtained by using the decay time calculation formula based on the equivalent impedance phasor of each branch. The equivalent impedance phasor formula is as follows: The formula for calculating the decay time is: ， In the formula, Z equ,x Let x be the equivalent impedance phasor of the x-th branch. For the active voltage phasor at the fault point, Let L be the branch current phasor of the x-th branch. equ,x and R equ,x The equivalent reactance and equivalent resistance of the x-th branch are T, respectively. x Let be the decay time constant of the DC component of the short-circuit current in the x-th branch. To obtain the equivalent impedance phasor Z equ,x The value of the middle real part, To obtain the equivalent impedance phasor Z equ,x The value of the imaginary part.

2. The method for calculating the DC component of short-circuit current in a power system according to claim 1, characterized in that, Obtaining the branch current phasor of each branch connected to the faulty node in the power system network topology includes: The second parameter data of the power system network topology is obtained. The second parameter data includes a reference node, n ordinary nodes, system nominal voltage, voltage coefficient, self-admittance of the n ordinary nodes, first branch admittance between each pair of ordinary nodes, and second branch admittance between the fault node and the ordinary node. The fault node conditions corresponding to the fault node are determined based on the general nominal voltage and the voltage coefficient; the node current balance equation is constructed based on the self-admittance of the n ordinary nodes and the admittance of all first branches; The node current balance equations are subjected to elementary row transformations and back-substitution calculations are performed using the fault node conditions to obtain the node voltage phasor for each of the ordinary nodes. The branch current phasor of the branch connected to the fault node is calculated based on the active voltage phasor of the fault point, the node voltage phasor of the ordinary node connected to the fault node, and the second branch admittance corresponding to the ordinary node.

3. The method for calculating the DC component of short-circuit current in a power system according to claim 2, characterized in that, Determining the fault node conditions corresponding to the fault node based on the nominal voltage and the voltage coefficient includes: The active voltage phasor at the fault point is obtained by using the active voltage calculation formula based on the nominal voltage and the voltage coefficient. The fault node conditions corresponding to the fault node are determined based on the active voltage phasor of the fault point. The active voltage calculation formula is as follows: The conditions for the fault node are as follows: In the formula, Active voltage phasor at the fault point The amplitude, c is the voltage coefficient, and U is the system nominal voltage. The voltage phasor of the faulty node.

4. The method for calculating the DC component of short-circuit current in a power system according to claim 2, characterized in that, Based on the self-admittances of the n ordinary nodes and the admittances of all first branches, the node current balance equations are constructed as follows: In the formula, when i=j, Y ij Y is the self-admittance of the i-th or j-th ordinary node, when i ≠ j. ij Y is the admittance of the first branch between the i-th ordinary node and the j-th ordinary node. If there is no connecting branch between the i-th ordinary node and the j-th ordinary node, then Y... ij =0, Let be the node voltage phasor of the nth ordinary node.

5. The method for calculating the DC component of short-circuit current in a power system according to claim 1, characterized in that, include: The DC component of the short-circuit current of the corresponding branch is calculated using the first calculation formula based on the time after the fault, the branch current phasor of each branch, and the decay time constant. The first calculation formula is as follows: The DC component of the short-circuit current of the M branches is calculated using the second calculation formula to obtain the DC component of the short-circuit current to ground of the fault node. The second calculation formula is as follows: In the formula, t is the time after the fault corresponding to the decay time constant. Let x be the branch current phasor of the x-th branch. Let T be the DC component of the short-circuit current in the xth branch. x Let I be the decay time constant of the DC component of the short-circuit current in the x-th branch. DC This represents the DC component of the short-circuit current to ground at the fault node.

6. A system for calculating the DC component of short-circuit current in a power system, applied to power systems with large branch impedance ratio deviations, characterized in that, The short-circuit current DC component calculation system includes a data acquisition module, a first calculation module, and a second calculation module; The data acquisition module is used to acquire the fault node of the power system network topology, the number M of branches connected to the fault node, the active voltage phasor of the fault point, and the branch current phasor of each branch connected to the fault node. The first calculation module is used to calculate, based on the active voltage phasor of the fault point and the branch current phasor of each branch, the decay time constant of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch. The second calculation module is used to obtain the post-fault time corresponding to the decay time constant, and calculate the DC component of the short-circuit current of the corresponding branch based on the post-fault time, the branch current phasor of each branch and the decay time constant; and calculate the DC component of the short-circuit current of the fault node to ground by calculating the DC component of the short-circuit current of M branches. The attenuation time constants of the equivalent impedance phasor and the DC component of the short-circuit current corresponding to each branch are calculated based on the active voltage phasor at the fault point and the branch current phasor of each branch, including: The equivalent impedance phasor corresponding to each branch is obtained by using the equivalent impedance phasor formula based on the active voltage phasor of the fault point and the branch current phasor of each branch. The decay time constant of the DC component of the short-circuit current corresponding to each branch is obtained by using the decay time calculation formula based on the equivalent impedance phasor of each branch. The equivalent impedance phasor formula is as follows: The formula for calculating the decay time is: ， In the formula, Z equ,x Let x be the equivalent impedance phasor of the x-th branch. For the active voltage phasor at the fault point, Let L be the branch current phasor of the x-th branch. equ,x and R equ,x The equivalent reactance and equivalent resistance of the x-th branch are T, respectively. x Let be the decay time constant of the DC component of the short-circuit current in the x-th branch. To obtain the equivalent impedance phasor Z equ,x The value of the middle real part, To obtain the equivalent impedance phasor Z equ,x The value of the imaginary part.

7. The short-circuit current DC component calculation system for a power system according to claim 6, characterized in that, The data acquisition module includes a parameter acquisition submodule, an equation construction submodule, a third calculation submodule, and a fourth calculation submodule; The parameter acquisition submodule is used to acquire the second parameter data of the power system network topology. The second parameter data includes a reference node, n ordinary nodes, system nominal voltage, voltage coefficient, self-admittance of the n ordinary nodes, first branch admittance between each pair of ordinary nodes, and second branch admittance between the fault node and the ordinary node. The equation construction submodule is used to determine the fault node conditions corresponding to the fault node based on the general nominal voltage and the voltage coefficient; and to construct the node current balance equation based on the self-admittance of the n ordinary nodes and the admittance of all first branches. The third calculation submodule is used to perform elementary row transformations on the node current balance equations and perform back substitution calculations using the fault node conditions to obtain the node voltage phasor of each ordinary node. The fourth calculation submodule is used to calculate, based on the active voltage phasor of the fault point, the node voltage phasor of the ordinary node connected to the fault node, and the second branch admittance corresponding to the ordinary node, to obtain the branch current phasor of the branch connected to the fault node.

8. The short-circuit current DC component calculation system for a power system according to claim 6, characterized in that, The second calculation module is further configured to calculate, using a first calculation formula, the DC component of the short-circuit current of the corresponding branch based on the time after the fault, the branch current phasor of each branch, and the decay time constant; and to calculate, using a second calculation formula, the DC component of the short-circuit current of the M branches to ground, the DC component of the short-circuit current of the fault node; the first calculation formula is: The second calculation formula is: In the formula, t is the time after the fault corresponding to the decay time constant. Let x be the branch current phasor of the x-th branch. Let T be the DC component of the short-circuit current in the xth branch. x Let I be the decay time constant of the DC component of the short-circuit current in the x-th branch. DC This represents the DC component of the short-circuit current to ground at the fault node.

9. A terminal device, characterized in that, Including processor and memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the method for calculating the DC component of short-circuit current in a power system as described in any one of claims 1-5, according to the instructions in the program code.

Images