Method, device and equipment for calculating DC component of short-circuit current

Abstract

The present application discloses a method, device and equipment for calculating the DC component of short-circuit current, the method comprising: taking the fault point when an asymmetric short-circuit fault occurs in a radial network as a split point; obtaining the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet at the fault point; calculating the input impedance and equivalent impedance of each subnet according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet; calculating the DC component of short-circuit current based on the input impedance and equivalent impedance of each subnet. It can be seen that the present application can calculate the DC component of short-circuit current when an asymmetric short-circuit fault occurs in a radial network. In addition, the present application can consider the influence of each subnet on the DC component of short-circuit current, and more accurately calculate the DC component of short-circuit current compared to calculating the DC component of short-circuit current based only on the entire radial network.

Description

Technical Field

[0001] The present application relates to the field of power grid technology, and more specifically, to a method, device and equipment for calculating a DC component of a short-circuit current. Background Art

[0002] In order to reduce transmission losses in power grids, the capacity of generators and transformers has gradually increased, and the resistance of DC and AC lines in power grids has gradually decreased. However, the increase in the capacity of generators and transformers and the decrease in the resistance of transmission lines have led to an increasing reactance-resistance ratio of the equivalent system at the short-circuit fault point when a short-circuit fault occurs in the power grid, and the DC component of the short-circuit current has increased accordingly. Based on this, the impact of the DC component of the short-circuit current on the power grid has become increasingly prominent.

[0003] The prior art only proposes a method for calculating the DC component of the short-circuit current when a symmetrical short circuit occurs in the power grid, but does not propose a method for calculating the DC component of the short-circuit current when an asymmetrical short circuit occurs in the power grid. Summary of the invention

[0004] In view of this, the present application provides a method, device and equipment for calculating the DC component of short-circuit current, which are used to calculate the DC component of short-circuit current when an asymmetric short circuit occurs in a power grid.

[0005] In order to achieve the above objectives, the proposed solution is as follows:

[0006] A method for calculating a DC component of a short-circuit current, comprising:

[0007] Taking the fault point when an asymmetric short circuit fault occurs in the radial network as the splitting point, the radial network is split into multiple subnets;

[0008] Obtain the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0009] Calculate the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0010] The short-circuit current DC component is calculated based on the input impedance and equivalent impedance of each of the subnets.

[0011] Optionally, obtaining the positive-sequence equivalent impedance, the negative-sequence equivalent impedance, and the zero-sequence equivalent impedance of each of the subnets at the fault point includes:

[0012] Determine the fault time of the asymmetric short circuit fault and the target time after the asymmetric short circuit fault occurs, wherein the target time is any time during the continuation of the asymmetric short circuit fault;

[0013] Calculating a target time difference between the target time and the failure time;

[0014] Based on the target time difference, determining an equivalent frequency corresponding to the target time;

[0015] According to the equivalent frequency corresponding to the target time, the positive-sequence equivalent impedance, the negative-sequence equivalent impedance and the zero-sequence equivalent impedance of each of the subnets corresponding to the target time at the fault point are calculated.

[0016] Optionally, the calculating the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point includes:

[0017] Determine the fault type of the asymmetric short circuit fault, the fault type being a single-phase short circuit fault, a two-phase short circuit fault or a two-phase short circuit to ground fault;

[0018] Calling preset input impedance analytical formula and equivalent impedance analytical formula corresponding to the fault type;

[0019] The input impedance of each subnet is calculated by using the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance of each subnet at the fault point and the input impedance analytical formula corresponding to the fault type;

[0020] The equivalent impedance of each subnet is calculated by using the positive-sequence equivalent impedance, negative-sequence equivalent impedance, zero-sequence equivalent impedance of each subnet at the fault point and an equivalent impedance analytical expression corresponding to the fault type.

[0021] Optionally, calculating the short-circuit current DC component based on the input impedance and equivalent impedance of each of the subnets includes:

[0022] Calculating a parallel impedance, where the parallel impedance is equal to a ratio between 1 and the sum of the reciprocals of the input impedances of the subnets;

[0023] Obtain the equivalent voltage source at the fault point;

[0024] Taking the ratio between the equivalent voltage source at the fault point and the parallel impedance as the initial value of the short-circuit current;

[0025] The short-circuit current DC component is calculated using the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current.

[0026] Optionally, the DC component of the short-circuit current is calculated by using the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current, including:

[0027] The parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current are substituted into a preset analytical expression of the short-circuit current DC component to calculate the short-circuit current DC component.

[0028] Optionally, the analytical expression of the DC component of the short-circuit current is:

[0029]

[0030] Among them, I dc is the DC component of the short-circuit current, N is the total number of each of the subnets, I k " is the initial value of short-circuit current, Z equ is the parallel impedance, x is the subnet number, Z xequ is the input impedance of the subnet numbered x, T xa is the decay time constant of the DC component of the short-circuit current of the subnet numbered x, and t is the time difference between the current time and the fault time.

[0031] Optionally, the analytical expression of the decay time constant of the short-circuit current DC component of the subnet numbered x is:

[0032]

[0033] Among them, Z xCequ is the equivalent impedance of the subnet numbered x, f c is the equivalent frequency of the subnet numbered x corresponding to t.

[0034] Optionally, the method of splitting the radial network into multiple subnets by taking the fault point when an asymmetric short circuit fault occurs in the radial network as the splitting point includes:

[0035] Determining whether the fault point is located on a line of the radial network;

[0036] If the fault point is on the line of the radial network, the radial network is split into two subnets by taking the fault point when the radial network short-circuit fault occurs as the splitting point;

[0037] If the fault point is not on the line of the radial network, then the fault point is a node of the radial network. The radial network is split with the node where the asymmetric short circuit fault occurs as the splitting point, wherein the number of subnets is equal to the number of branches merging into the node, each subnet contains a branch merging into the node, and the branches merging into the node contained in each subnet are not the same.

[0038] A short-circuit current DC component calculation device, comprising:

[0039] A splitting unit, used to split the radial network into multiple subnets by taking the fault point when an asymmetric short circuit fault occurs in the radial network as the splitting point;

[0040] An acquisition unit, used for acquiring the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0041] A calculation unit, calculating the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0042] The utilization unit is used to calculate the DC component of the short-circuit current based on the input impedance and equivalent impedance of each of the subnets.

[0043] A short-circuit current DC component calculation device, comprising a memory and a processor;

[0044] The memory is used to store programs;

[0045] The processor is used to execute the program to implement the various steps of the above-mentioned method for calculating the DC component of short-circuit current.

[0046] A readable storage medium stores a computer program, and when the computer program is executed by a processor, each step of the above-mentioned method for calculating a DC component of a short-circuit current is implemented.

[0047] It can be seen from the above technical solutions that the method for calculating the DC component of short-circuit current provided by the present application can firstly use the fault point when an asymmetric short-circuit fault occurs in a radial network as a splitting point to split the radial network into multiple subnets. In this way, the present application is only executed when an asymmetric short circuit occurs in the power grid and the power grid is a radial network; then, the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance, and zero-sequence equivalent impedance of each of the subnets at the fault point can be obtained; according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance, and zero-sequence equivalent impedance of each of the subnets at the fault point, the input impedance and equivalent impedance of each of the subnets are calculated. Finally, the DC component of the short-circuit current can be calculated based on the input impedance and equivalent impedance of each of the subnets. It can be seen that the present application can calculate the DC component of the short-circuit current when an asymmetric short-circuit fault occurs in a radial network.

[0048] In addition, in the present application, the DC component of the short-circuit current can be calculated based on the input impedance and equivalent impedance of each of the subnets. In this way, the influence of each subnet on the DC component of the short-circuit current can be considered one by one. Compared with calculating the DC component of the short-circuit current based only on the entire radial network, the DC component of the short-circuit current can be calculated more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0050] Figure 1 A flow chart of a method for calculating a DC component of a short-circuit current disclosed in the present application;

[0051] Figure 2 This is a structural block diagram of a short-circuit current DC component calculation device disclosed in this application;

[0052] Figure 3 This is a hardware structure block diagram of a short-circuit current DC component calculation device disclosed in this application. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0054] The method for calculating the DC component of short-circuit current provided by the present application can be applied to radial networks, and belongs to the technical field of power grids. The present application can calculate the DC component of short-circuit current when an asymmetric short-circuit fault occurs in a radial network.

[0055] Next, combine Figure 1 The method for calculating the DC component of the short-circuit current of the present application is introduced in detail, and includes the following steps:

[0056] Step S1, taking the fault point when an asymmetric short circuit fault occurs in the radial network as the splitting point, splitting the radial network into multiple subnets.

[0057] Specifically, the radial network with an asymmetric short circuit fault can be split. During the splitting process, the fault point where the fault occurs can be used as the splitting point, and the splitting method is determined based on the position of the splitting point and the radial network, and multiple subnets are obtained after the splitting. The combination of each of the subnets can obtain a complete radial network.

[0058] Step S2: obtaining the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point.

[0059] Specifically, the positive-sequence node admittance matrix, the negative-sequence node admittance matrix and the zero-sequence node admittance matrix of each subnet can be constructed according to the radial network. The expression form of each node admittance matrix is ​​as follows:

[0060]

[0061] Among them, the diagonal elements Y in the positive sequence node admittance matrix, the negative sequence node admittance matrix and the zero sequence node admittance matrix are ii It is called the self-admittance of node i, and its value is equal to the sum of the admittances of all branches connected to node i; the non-diagonal element Y ij It is called the admittance between nodes i and j. Its value is equal to the negative value of the admittance of the branch between nodes i and j. If there is no direct branch between nodes i and j, then Y ij = 0. Therefore, any grid topology connection relationship can be described by the node admittance matrix.

[0062] Specifically, the analytical formula of admittance is:

[0063]

[0064] Among them, Z ij is the branch impedance between node i and node j, R ij is the branch resistance between node i and node j, X ijis the branch reactance between node i and node j. To avoid symbol conflict, J is used to represent the imaginary unit. w is the angular velocity of the radial network. L ij is the coil inductance between nodes i and j.

[0065] The equivalent frequency method can be used to correct the positive-sequence node admittance matrix of each subnet to obtain the positive-sequence node equivalent admittance matrix of each subnet at the equivalent frequency; the equivalent frequency method can be used to correct the negative-sequence node admittance matrix of each subnet to obtain the negative-sequence node equivalent admittance matrix of each subnet at the equivalent frequency; the equivalent frequency method can be used to correct the zero-sequence node equivalent admittance matrix of each subnet to obtain the zero-sequence node admittance matrix of each subnet at the equivalent frequency.

[0066] Specifically, the analytical formula of admittance at the equivalent frequency is:

[0067]

[0068] Among them, Y Cij is the admittance at the equivalent frequency, Z Cij is the branch impedance between nodes i and j at the equivalent frequency, R Cij is the branch resistance between nodes i and j at the equivalent frequency, X Cij is the branch reactance between nodes i and j at the equivalent frequency. To avoid symbol conflict, J is used to represent the imaginary unit. c is the angular velocity at which the radial network operates.

[0069] After the equivalent frequency is determined, the equivalent admittances in the zero-sequence node equivalent admittance matrix, the positive-sequence node equivalent admittance matrix and the negative-sequence node equivalent admittance matrix corresponding to each subnet can be calculated according to the admittance analytical expression at the equivalent frequency, where the equivalent admittance is the admittance at the equivalent frequency.

[0070] The zero-sequence node admittance matrix, positive-sequence node admittance matrix, negative-sequence node admittance matrix, zero-sequence node equivalent admittance matrix, positive-sequence node equivalent admittance matrix and negative-sequence node equivalent admittance matrix of each subnet constitute a radial network node admittance matrix set. Each admittance matrix in the radial network node admittance matrix set can be processed to obtain the zero-sequence node impedance matrix, positive-sequence node impedance matrix, negative-sequence node impedance matrix, zero-sequence node equivalent impedance matrix, positive-sequence node equivalent impedance matrix and negative-sequence node equivalent impedance matrix of each subnet.

[0071] During the processing, each admittance matrix can be triangularly decomposed to obtain each factor matrix, that is, Y=LDU, where Y is the admittance matrix, U and L are transposed, L is a unit lower triangular matrix, D is a diagonal matrix, and U is a unit upper triangular matrix.

[0072] The calculation formulas for each element in U, D, and L are as follows:

[0073]

[0074]

[0075]

[0076] d ii is the element in the i-th row and i-th column of the D matrix; u ij is the element in the i-th row and j-th column of the U matrix; l ij is the element in the i-th row and j-th column of the L matrix.

[0077] The factor table composed of each element in U, D and L is as follows:

[0078]

[0079] After obtaining the factor table corresponding to each admittance matrix in the above manner, the elements of the jth column of the impedance matrix corresponding to each admittance matrix can be calculated by the following analytical expression:

[0080]

[0081]

[0082]

[0083] Based on this, the zero-sequence node impedance matrix, positive-sequence node impedance matrix, negative-sequence node impedance matrix, zero-sequence node equivalent impedance matrix, positive-sequence node equivalent impedance matrix and negative-sequence node equivalent impedance matrix corresponding to each subnet are calculated.

[0084] According to the position of the fault point in the radial network, the impedance corresponding to the fault point in the zero-sequence node impedance matrix, positive-sequence node impedance matrix, negative-sequence node impedance matrix, zero-sequence node equivalent impedance matrix, positive-sequence node equivalent impedance matrix and negative-sequence node equivalent impedance matrix corresponding to each subnet is determined, and the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance corresponding to the fault point and each subnet are obtained.

[0085] Step S3, calculating the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point.

[0086] Specifically, the input impedance of each subnet may be obtained by processing the positive-sequence input impedance, the negative-sequence input impedance and the zero-sequence input impedance corresponding to each subnet and the fault point.

[0087] By processing the positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance corresponding to each subnet and the fault point, the equivalent impedance of the subnet is obtained.

[0088] Step S4: Calculate the short-circuit current DC component based on the input impedance and equivalent impedance of each of the subnets.

[0089] Specifically, the input impedance and equivalent impedance of each subnet are processed to obtain the contribution value of each subnet to the DC component of the short-circuit current, and the contribution values ​​corresponding to each subnet are added together, and the result obtained after the addition is the DC component of the short-circuit current.

[0090] It can be seen from the above technical solutions that the method for calculating the DC component of short-circuit current provided in the embodiment of the present application can first use the fault point when an asymmetric short-circuit fault occurs in a radial network as a split point to split the radial network into multiple subnets. In this way, the present application is only executed when an asymmetric short circuit occurs in the power grid and the power grid is a radial network; then, the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance, and zero-sequence equivalent impedance of each subnet at the fault point can be obtained; according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance, and zero-sequence equivalent impedance of each subnet at the fault point, the input impedance and equivalent impedance of each subnet are calculated, and finally, the DC component of the short-circuit current can be calculated based on the input impedance and equivalent impedance of each subnet. It can be seen that the present application can calculate the DC component of the short-circuit current when an asymmetric short-circuit fault occurs in a radial network.

[0091] In addition, in the present application, the DC component of the short-circuit current can be calculated based on the input impedance and equivalent impedance of each of the subnets. In this way, the influence of each subnet on the DC component of the short-circuit current can be considered one by one. Compared with calculating the DC component of the short-circuit current based only on the entire radial network, the DC component of the short-circuit current can be calculated more accurately.

[0092] In some embodiments of the present application, step S1, a process of splitting the radial network into multiple subnets with the fault point when an asymmetric short circuit fault occurs in the radial network as the splitting point, is described in detail, and the specific steps are as follows:

[0093] S10, determining whether the fault point is located on the line of the radial network, if so, executing step S11, if not, executing step S12.

[0094] Specifically, for a radial network with an asymmetric fault, the fault point may be on a line of the radial network or may be a node of the radial network. When the fault point is at different locations, the method of splitting the radial network will also be different.

[0095] S11. Taking the fault point of the radial network as the splitting point, the radial network is split into two subnets.

[0096] When the fault point is a line of the radial network, the radial network can be divided directly at the fault point to divide the radial network into two subnets.

[0097] After the two subnets are spliced ​​at the fault point, a complete radial network can be obtained.

[0098] S12. Split the radial network with the node where the asymmetric short circuit fault occurs as the splitting point, wherein the number of subnets is equal to the number of branches merging into the node, each subnet contains a branch merging into the node, and the branches merging into the node contained in each subnet are not the same.

[0099] Specifically, when the fault point is a node of the radial network, the radial network can be directly divided at the fault point, and the radial network can be divided into subnets with the same number of branches as the fault point.

[0100] It can be seen from the above technical solution that, compared with the previous embodiment, this embodiment provides an optional method of dividing a radial network into multiple subnets. Through the above method, the radial network can be split according to the location of the fault point, so as to better calculate the DC component of the short-circuit current.

[0101] In some embodiments of the present application, the process of obtaining the positive-sequence equivalent impedance, the negative-sequence equivalent impedance and the zero-sequence equivalent impedance of each subnet at the fault point in step S2 is described in detail, and the steps are as follows:

[0102] S20: Determine the fault time when the asymmetric short circuit fault occurs and the target time after the asymmetric short circuit fault occurs, wherein the target time is any time during the duration of the asymmetric short circuit fault.

[0103] Specifically, after an asymmetric short circuit fault occurs, the short circuit current DC component corresponding to any time can be calculated. Therefore, the time when the short circuit current DC component needs to be obtained can be determined and used as the target time.

[0104] S21. Calculate a target time difference between the target time and the failure time.

[0105] Specifically, the difference between the target time and the failure time may be calculated and used as the target time difference, where the target time difference indicates the length of time from the failure time to the target time.

[0106] S22. Determine an equivalent frequency corresponding to the target time based on the target time difference.

[0107] Specifically, there is a corresponding relationship between the product and the ratio, the product is the time difference between the target time and the fault time, and the ratio is the ratio between the equivalent frequency and the rated frequency of the radial network.

[0108] f·t [0，1) [0，2.5) [2.5，5) [5，∞) <![CDATA[f c / f]]> 0.27 0.15 0.092 0.055

[0109] Table 1

[0110] Table 1 records the corresponding relationship between the product and the ratio. t is the time difference between the target time and the failure time, f c is the equivalent frequency, and f is the rated frequency.

[0111] Therefore, after determining the target time difference, the product between the target time difference and the rated frequency of the radial network can be calculated, the range of the product can be determined, and the ratio between the equivalent frequency corresponding to the range and the rated frequency can be determined. The rated frequency is multiplied by the ratio, and the result is the equivalent frequency.

[0112] S23. Calculate, according to the equivalent frequency corresponding to the target time, the positive-sequence equivalent impedance, the negative-sequence equivalent impedance and the zero-sequence equivalent impedance of each of the subnets corresponding to the target time at the fault point.

[0113] Specifically, after the equivalent frequency is determined, the equivalent admittances in the zero-sequence node equivalent admittance matrix, the positive-sequence node equivalent admittance matrix and the negative-sequence node equivalent admittance matrix of each subnet corresponding to the target time can be determined by the admittance analytical formula at the equivalent frequency.

[0114] Based on the above method of processing each admittance matrix in the radial network node admittance matrix set, the zero-sequence node impedance matrix, positive-sequence node impedance matrix, negative-sequence node impedance matrix, zero-sequence node equivalent impedance matrix, positive-sequence node equivalent impedance matrix and negative-sequence node equivalent impedance matrix of each subnet are obtained, and the zero-sequence node equivalent impedance matrix, positive-sequence node equivalent impedance matrix and negative-sequence node equivalent impedance matrix corresponding to the target time are obtained.

[0115] From the zero-sequence node equivalent impedance matrix, the positive-sequence node equivalent impedance matrix and the negative-sequence node equivalent impedance matrix corresponding to the target time, the equivalent impedance corresponding to the fault point is selected to obtain the positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet at the fault point corresponding to the target time.

[0116] It can be seen from the above technical solution that, compared with the above embodiment, this embodiment provides an optional way to determine the positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet at the fault point. Through the above embodiment, the time after the fault occurs can be segmented, and the equivalent frequency corresponding to each time period is not the same. The difference in equivalent frequency will also change the positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet at the fault point. The difference in positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance will also cause the equivalent impedance of each subnet to be different. The difference in equivalent impedance will eventually lead to the difference in the DC component of the short-circuit current in different time periods. Based on this, the DC component of the short-circuit current is different in different time periods. Among them, the segmentation is determined based on the rated frequency, which is more reliable. Therefore, the method provided by this embodiment improves the reliability of calculating the DC component of the short-circuit current. By obtaining the equivalent impedance and input impedance in different time periods, the error when the impedance ratio L / R of each branch is greatly different can be reduced, and the accuracy of the DC component of the short-circuit current calculated by this application can be further improved.

[0117] In some embodiments of the present application, step S3, the process of calculating the input impedance and equivalent impedance of each subnet according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet at the fault point is described in detail, and the steps are as follows:

[0118] S30. Determine the fault type of the asymmetric short circuit fault, where the fault type is a single-phase short circuit fault, a two-phase short circuit fault, or a two-phase short circuit to ground fault.

[0119] Specifically, there are three types of asymmetric short circuit faults: single-phase short circuit fault, two-phase short circuit fault or two-phase short circuit grounding fault.

[0120] Based on the connection mode of each branch of the fault point where the asymmetric short circuit fault occurs, the fault type is determined to be a single-phase short circuit fault, a two-phase short circuit fault or a two-phase short circuit grounding fault.

[0121] S31. Calling preset input impedance analytical formula and equivalent impedance analytical formula corresponding to the fault type.

[0122] Specifically, there are different ways to calculate impedance for different fault types, and the input impedance and equivalent impedance corresponding to each subnet can be calculated through analytical expressions.

[0123] The analytical formula of input impedance is:

[0124]

[0125] Among them, Z xequis the input impedance of the subnet numbered x, is the positive sequence input impedance of the subnet numbered x at the fault point, is the negative sequence input impedance of the subnet numbered x at the fault point, is the zero-sequence input impedance of the subnet numbered x at the fault point.

[0126] The equivalent impedance analytical formula is:

[0127]

[0128] Among them, Z xCequ is the input impedance of the subnet numbered x, is the positive sequence input impedance of the subnet numbered x at the fault point, is the negative sequence input impedance of the subnet numbered x at the fault point, is the zero-sequence input impedance of the subnet numbered x at the fault point.

[0129] S32. Calculate the input impedance of each subnet by using the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance of each subnet at the fault point and the input impedance analytical formula corresponding to the fault type.

[0130] Specifically, the positive-sequence input impedance, negative-sequence input impedance, and zero-sequence input impedance of each subnet at the fault point are substituted into an analytical expression corresponding to the fault type to obtain the input impedance of each subnet.

[0131] The fault types of each subnet corresponding to the same fault point in the same radial network are consistent.

[0132] S33. Calculate the equivalent impedance of each subnet by using the positive-sequence equivalent impedance, negative-sequence equivalent impedance, zero-sequence equivalent impedance of each subnet at the fault point and an equivalent impedance analytical formula corresponding to the fault type.

[0133] Specifically, the positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet at the fault point are substituted into an analytical expression corresponding to the fault type to obtain the input impedance of each subnet.

[0134] It can be seen from the above technical solution that this embodiment provides an optional method for calculating the input impedance and equivalent impedance of each subnet. Through the above method, different calculation methods can be used for different fault types. Based on this, the calculated short-circuit current DC component is related to the fault type, which can further improve the accuracy of the short-circuit current DC component.

[0135] In some embodiments of the present application, step S4, the process of calculating the DC component of the short-circuit current based on the input impedance and equivalent impedance of each of the subnets, is described in detail, and the steps are as follows:

[0136] S40: Calculate parallel impedance, where the parallel impedance is equal to the ratio between 1 and the sum of the reciprocals of the input impedances of the subnets.

[0137] Specifically, the parallel impedance of the radial network can be calculated by the parallel impedance analytical formula.

[0138] The analytical formula for parallel impedance is as follows:

[0139]

[0140] Among them, Z equ is the parallel impedance, and N is the total number of subnets.

[0141] S41. Obtain an equivalent voltage source at the fault point.

[0142] Specifically, the equivalent voltage source method can be used to calculate the equivalent voltage source at the fault point. Set each power source in the radial network to zero, and add an ideal voltage source at the fault point as the only active voltage V f , and its calculation formula is:

[0143]

[0144] Among them, U n is the nominal voltage of the radial network, c is the voltage coefficient, and the value range of c is shown in Table 2:

[0145]

[0146] Table 2

[0147] S42: Taking the ratio between the equivalent voltage source at the fault point and the parallel impedance as the initial value of the short-circuit current.

[0148] Specifically, the analytical expression of the initial value of the short-circuit current is:

[0149]

[0150] Among them, V f is the equivalent voltage source at the fault point, Z equ is the parallel impedance, I k is the initial value of short-circuit current.

[0151] S43, calculating the short-circuit current DC component by using the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current.

[0152] Specifically, the contribution value of each subnet to the DC component of the short-circuit current can be calculated using the parallel impedance, the input impedance of each subnet, the equivalent impedance of each subnet and the initial value of the short-circuit current, and the corresponding contribution values ​​of each subnet are added together, and the added value is the DC component of the short-circuit current.

[0153] It can be seen from the above technical solution that this embodiment provides an optional method for calculating the DC component of the short-circuit current based on the input impedance and equivalent impedance of each of the subnets. Through the above method, the initial value of the short-circuit current can be calculated, and during the fault continuation process, the DC component of the short-circuit current continuously decays based on the initial value of the short-circuit current. Therefore, by calculating the initial value of the short-circuit current, the reliability of the calculated DC component of the short-circuit current can be improved.

[0154] In some embodiments of the present application, step S43, the process of calculating the DC component of the short-circuit current by using the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current is described in detail, and the steps are as follows:

[0155] S430, substituting the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current into a preset analytical expression of the short-circuit current DC component to calculate the short-circuit current DC component.

[0156] Specifically, an analytical formula for calculating the DC component of the short-circuit current may be preset, and the parallel impedance obtained in the above embodiment, the input impedance of each subnet, the equivalent impedance of each subnet and the initial value of the short-circuit current are substituted into the analytical formula to calculate the DC component of the short-circuit current.

[0157] It can be seen from the above technical solution that this embodiment provides an optional method for calculating the DC component of the short-circuit current. Through the above method, after calculating the parallel impedance, the input impedance of each subnet, the equivalent impedance of each subnet and the initial value of the short-circuit current, the analytical expression can be directly called to obtain the short-circuit current command component, which is simpler and faster, and improves the speed of calculating the DC component of the short-circuit current.

[0158] In some embodiments of the present application, the analytical expression of the DC component of the short-circuit current is:

[0159]

[0160] Among them, I dc is the DC component of the short-circuit current, N is the total number of subnets, I k " is the initial value of short-circuit current, Z equ is the parallel impedance, x is the subnet number, Z xequis the input impedance of the subnet numbered x, T xa is the decay time constant of the DC component of the short-circuit current of the subnet numbered x, and t is the time difference between the current time and the fault time.

[0161] Specifically, as time changes, the DC component of the short-circuit current decays based on the initial value of the short-circuit current. Therefore, when calculating the DC component of the short-circuit current at different times, it is necessary to consider the initial value of the short-circuit current and the decay time constant of the DC component of the short-circuit current. In order to further improve the creativity, the present application also takes into account the various subnets that make up the radial network.

[0162] It can be seen from the above technical solution that this embodiment takes into account each subnet when calculating the DC component of the short-circuit current. If only the complete radial network is considered to meet engineering requirements, some errors need to be ignored, so that errors are difficult to avoid. The present application can effectively reduce errors by taking into account the DC component of the short-circuit current of each subnet.

[0163] In some embodiments of the present application, the analytical expression of the decay time constant of the DC component of the short-circuit current of the subnet numbered x is:

[0164]

[0165] Among them, Z xCequ is the equivalent impedance of the subnet numbered x, f c is the equivalent frequency of the subnet numbered x corresponding to t.

[0166] Specifically, the above analytical formula shows that when calculating the decay time constant of the DC component of the short-circuit current, the equivalent frequency method is used, and the equivalent frequency will change with the change of the time period. Therefore, the application of the equivalent frequency method can select different decay time constants T in different time periods, based on which the negative error can be reduced, further improving the accuracy and reliability of the calculation of the DC component of the short-circuit current in this application.

[0167] In addition, after calculating the short-circuit current DC component more accurately, the short-circuit impact current when an asymmetric short-circuit fault occurs can be calculated more accurately. The performance of the circuit breaker is prepared based on the short-circuit impact current. Based on this, a more economical, environmentally friendly and timely breaking circuit breaker can be prepared using a more accurate short-circuit impact current.

[0168] The short-circuit current DC component calculation device provided in an embodiment of the present application is described below. The short-circuit current DC component calculation device described below and the short-circuit current DC component calculation method described above can refer to each other.

[0169] like Figure 2As shown, it discloses a structural schematic diagram of a short-circuit current DC component calculation device, which may include:

[0170] A splitting unit 1 is used to split the radial network into multiple subnets by taking the fault point when an asymmetric short circuit fault occurs in the radial network as the splitting point;

[0171] An acquisition unit 2 is used to acquire the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0172] A calculation unit 3 calculates the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0173] The utilizing unit 4 is used to calculate the DC component of the short-circuit current based on the input impedance and equivalent impedance of each of the subnets.

[0174] Furthermore, the acquisition unit may include:

[0175] A first acquisition unit is used to determine the fault time of the asymmetric short circuit fault and the target time after the asymmetric short circuit fault occurs, wherein the target time is any time during the duration of the asymmetric short circuit fault;

[0176] A second acquisition unit, configured to calculate a target time difference between the target time and the fault time;

[0177] A third acquisition unit, configured to determine an equivalent frequency corresponding to the target time based on the target time difference;

[0178] The fourth acquisition unit is used to calculate the positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets corresponding to the target time at the fault point according to the equivalent frequency corresponding to the target time.

[0179] Furthermore, the computing unit may include:

[0180] A first calculation unit is used to determine the fault type of the asymmetric short circuit fault, where the fault type is a single-phase short circuit fault, a two-phase short circuit fault or a two-phase short circuit to ground fault;

[0181] A second calculation unit, used for calling a preset input impedance analytical formula and an equivalent impedance analytical formula corresponding to the fault type;

[0182] A third calculation unit is used to calculate the input impedance of each subnet by using the positive sequence input impedance, negative sequence input impedance, zero sequence input impedance of each subnet at the fault point and the input impedance analytical formula corresponding to the fault type;

[0183] The fourth calculation unit is used to calculate the equivalent impedance of each subnet by using the positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet at the fault point and the equivalent impedance analytical expression corresponding to the fault type.

[0184] Furthermore, the utilization unit may include:

[0185] A parallel impedance calculation unit, used for calculating the parallel impedance, wherein the parallel impedance is equal to the ratio between 1 and the sum of the reciprocals of the input impedances of the subnets;

[0186] An equivalent voltage source acquisition unit, used for acquiring an equivalent voltage source at a fault point;

[0187] A ratio calculation unit, used for taking the ratio between the equivalent voltage source at the fault point and the parallel impedance as an initial value of the short-circuit current;

[0188] The impedance utilizing unit is used to calculate the DC component of the short-circuit current by utilizing the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current.

[0189] Furthermore, the impedance utilization unit may include:

[0190] The DC component calculation unit is used to substitute the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current into a preset analytical expression of the DC component of the short-circuit current to calculate the DC component of the short-circuit current.

[0191] Furthermore, the DC component calculation unit may include:

[0192] The DC component analytical expression storage unit is used to store the following analytical expression:

[0193]

[0194] Furthermore, the DC component calculation unit may include:

[0195] The attenuation constant storage unit is used to store the following analytical expression:

[0196]

[0197] The short-circuit current DC component calculation device provided in the embodiment of the present application can be applied to short-circuit current DC component calculation equipment, such as a server, a PC terminal, and a calculator. Optionally, Figure 3 The hardware structure diagram of the short-circuit current DC component calculation device is shown in FIG. Figure 3 , the hardware structure of the short-circuit current DC component calculation device may include: at least one processor 1, at least one communication interface 2, at least one memory 3 and at least one communication bus 4;

[0198] In the embodiment of the present application, the number of the processor 1, the communication interface 2, the memory 3, and the communication bus 4 is at least one, and the processor 1, the communication interface 2, and the memory 3 communicate with each other through the communication bus 4;

[0199] The processor 1 may be a central processing unit CPU, or an application-specific integrated circuit ASIC (Application Specific Integrated Circuit), or one or more integrated circuits configured to implement the embodiments of the present invention, etc.;

[0200] The memory 3 may include a high-speed RAM memory, and may also include a non-volatile memory, such as at least one disk memory;

[0201] The memory stores a program, and the processor can call the program stored in the memory, and the program is used to:

[0202] Taking the fault point when an asymmetric short circuit fault occurs in the radial network as the splitting point, the radial network is split into multiple subnets;

[0203] Obtain the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0204] Calculate the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0205] The short-circuit current DC component is calculated based on the input impedance and equivalent impedance of each of the subnets.

[0206] Optionally, the detailed functions and extended functions of the program may refer to the above description.

[0207] The embodiment of the present application further provides a storage medium, which may store a program suitable for execution by a processor, wherein the program is used to:

[0208] Taking the fault point when an asymmetric short circuit fault occurs in the radial network as the splitting point, the radial network is split into multiple subnets;

[0209] Obtain the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0210] Calculate the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point;

[0211] The short-circuit current DC component is calculated based on the input impedance and equivalent impedance of each of the subnets.

[0212] Optionally, the detailed functions and extended functions of the program may refer to the above description.

[0213] Optionally, the detailed functions and extended functions of the program may refer to the above description.

[0214] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0215] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0216] The above description of the disclosed embodiments enables professionals and technicians in the field to implement or use the present application. Various modifications to these embodiments will be apparent to professionals and technicians in the field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. The various embodiments of the present application can be combined with each other. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calculating the DC component of a short-circuit current, characterized in that: include: Determine whether the fault point is on the line of the radial network; If the fault point is on the line of the radial network, the radial network is split into two subnets using the fault point when the radial network fails as the split point; If the fault point is not on the line of the radial network, the fault point is a node of the radial network, and the radial network is split into a plurality of subnets with the node where the asymmetric short circuit fault occurs as the splitting point, wherein the number of the subnets is equal to the number of branches merging into the node, each subnet contains a branch merging into the node, and the branches merging into the node contained in each subnet are not the same; Obtain the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point; Calculate the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point; calculate the parallel impedance, which is equal to the ratio between 1 and the sum of the reciprocals of the input impedances of each of the subnets; Obtain the equivalent voltage source at the fault point; Taking the ratio between the equivalent voltage source at the fault point and the parallel impedance as the initial value of the short-circuit current; The short-circuit current DC component is calculated using the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current.

2. The method for calculating the short-circuit current DC component according to claim 1, characterized in that: Obtaining the positive-sequence equivalent impedance, the negative-sequence equivalent impedance and the zero-sequence equivalent impedance of each of the subnets at the fault point, including: Determine the fault time of the asymmetric short circuit fault and the target time after the asymmetric short circuit fault occurs, wherein the target time is any time during the duration of the asymmetric short circuit fault; Calculating a target time difference between the target time and the failure time; Based on the target time difference, determining an equivalent frequency corresponding to the target time; According to the equivalent frequency corresponding to the target time, the positive-sequence equivalent impedance, the negative-sequence equivalent impedance and the zero-sequence equivalent impedance of each of the subnets corresponding to the target time at the fault point are calculated.

3. The method for calculating the short-circuit current DC component according to claim 1, characterized in that: The step of calculating the input impedance and equivalent impedance of each subnet at the fault point according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each subnet includes: Determine the fault type of the asymmetric short circuit fault, the fault type being a single-phase short circuit fault, a two-phase short circuit fault or a two-phase short circuit to ground fault; Calling preset input impedance analytical formula and equivalent impedance analytical formula corresponding to the fault type; The input impedance of each subnet is calculated by using the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance of each subnet at the fault point and the input impedance analytical formula corresponding to the fault type; The equivalent impedance of each subnet is calculated by using the positive-sequence equivalent impedance, negative-sequence equivalent impedance, zero-sequence equivalent impedance of each subnet at the fault point and an equivalent impedance analytical expression corresponding to the fault type.

4. The method for calculating the short-circuit current DC component according to claim 1, characterized in that: The DC component of the short-circuit current is calculated by using the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current, including: The parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets and the initial value of the short-circuit current are substituted into a preset analytical expression of the short-circuit current DC component to calculate the short-circuit current DC component.

5. The method for calculating the short-circuit current DC component according to claim 4, characterized in that: The analytical expression of the DC component of the short-circuit current is: Among them, I dc is the DC component of the short-circuit current, N is the total number of subnets, I k " is the initial value of short-circuit current, Z equ is the parallel impedance, x is the subnet number, Z xequ is the input impedance of the subnet numbered x, T xa is the decay time constant of the DC component of the short-circuit current of the subnet numbered x, and t is the time difference between the current time and the fault time.

6. The method for calculating the short-circuit current DC component according to claim 5, characterized in that: The analytical expression of the decay time constant of the DC component of the short-circuit current of the subnet numbered x is: Among them, Z xCequ is the equivalent impedance of the subnet numbered x, f c is the equivalent frequency of the subnet numbered x corresponding to t.

7. A device for calculating a short-circuit current DC component, characterized in that: include: The splitting unit is used to determine whether the fault point is on the line of the radial network; If the fault point is on the line of the radial network, the radial network is split into two subnets with the fault point at the time of the radial network fault as the splitting point; if the fault point is not on the line of the radial network, the fault point is a node of the radial network, and the radial network is split into multiple subnets with the node where the asymmetric short circuit fault occurs as the splitting point, wherein the number of subnets is equal to the number of branches merging into the node, each subnet contains a branch merging into the node, and the branches merging into the node contained in each subnet are not the same; An acquisition unit, used for acquiring the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point; A calculation unit, calculating the input impedance and equivalent impedance of each of the subnets according to the positive-sequence input impedance, negative-sequence input impedance, zero-sequence input impedance, positive-sequence equivalent impedance, negative-sequence equivalent impedance and zero-sequence equivalent impedance of each of the subnets at the fault point; A unit is used to calculate a parallel impedance, where the parallel impedance is equal to the ratio between 1 and the sum of the inverses of the input impedances of each of the subnets; an equivalent voltage source at a fault point is obtained; a ratio between the equivalent voltage source at the fault point and the parallel impedance is used as an initial value of the short-circuit current; and a DC component of the short-circuit current is calculated using the parallel impedance, the input impedance of each of the subnets, the equivalent impedance of each of the subnets, and the initial value of the short-circuit current.

8. A short-circuit current DC component calculation device, characterized in that: including memory and processor; The memory is used to store programs; The processor is used to execute the program to implement each step of the method for calculating the DC component of short-circuit current according to any one of claims 1 to 6.

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