A method for establishing a line fault simulation model based on Excel

Abstract

A kind of method for establishing line fault simulation model based on Excel, its steps are, input the line parameters to be measured in Excel;The balanced node voltage of the line to be measured is set and the impedance of power supply on both sides of the line to be measured;Conversion parameter;The normal operation calculation model of the line to be measured based on distribution parameter model in Excel is used, and the power flow electrical quantity when the line to be measured is normally operated is obtained;After the calculation model based on superposition theorem and composite sequence network is established in Excel, the post-fault power flow electrical quantity of the line to be measured under various faults is obtained, and the post-fault power flow electrical quantity includes steady-state fault electrical quantity;According to pre-fault power flow electrical quantity and post-fault power flow electrical quantity, voltage instantaneous value and current instantaneous value within a certain time before and after fault are calculated and obtained, and based on voltage instantaneous value and current instantaneous value, the transient data of fault point are obtained.The present application simulates and sets various faults based on Excel, and obtains the transient data of fault point, with the advantages of intuitive, convenient to use and low cost.

Description

Technical Field

[0001] This invention relates to power system fault simulation and relay transient testing, specifically to a method for establishing a line fault simulation model based on Excel. Background Technology

[0002] The main purpose of electromagnetic transient process analysis is to analyze and calculate the transient overvoltages and overcurrents that may occur after a fault, so as to make reasonable designs for current-controlled equipment. Existing methods for electromagnetic transient research include field testing and digital simulation. However, due to the drawbacks of field testing, such as cumbersome operation and high technical difficulty, digital simulation technology is more often used for electromagnetic transient analysis.

[0003] Currently, relay protection tests in the research and development stage can generally only perform static tests, and cannot accurately reproduce the transient processes before and after a fault. Relay protection testers can reproduce waveforms from the field to achieve transient testing, but the waveforms from the field are limited by specific parameters and cannot verify the various power system operating conditions that the relay protection device may face. Therefore, simulation technology is needed to study and verify it. However, existing simulation software has certain deficiencies in data analysis and calculation, and usually lacks advanced data calculation capabilities, causing many inconveniences for users. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for establishing a line fault simulation model based on Excel data analysis capabilities.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for building a line fault simulation model based on Excel includes the following steps:

[0007] Step S1: Enter the parameters of the circuit to be tested into Excel;

[0008] Step S2: Set the balance node voltage of the circuit under test and the power supply impedance on both sides of the circuit under test;

[0009] Step S3: Convert the linear parameters into quadratic parameters using the conversion formula;

[0010] Step S4: Using the normal operation calculation model of the line under test established based on the distributed parameter model in Excel, calculate the power flow electrical quantity of the line under test during normal operation using the complex number calculation formula in Excel and save it in the corresponding cell;

[0011] Step S5: Using the post-fault calculation model established in Excel based on the superposition theorem and the composite sequence network, calculate the post-fault power flow electrical quantities of the line under test under various faults using the complex number calculation formula in Excel. The post-fault power flow electrical quantities include the fault electrical quantities in steady state.

[0012] Step S6: Based on the power flow quantities before and after the fault, calculate and obtain the instantaneous voltage and current values ​​within a certain time before and after the fault, and obtain the transient data of the fault point in the line under test based on the instantaneous voltage and current values.

[0013] Preferably, in step S1, the required primary parameters of the circuit under test are input into the corresponding cell. The primary parameters include the unit positive sequence resistance, unit positive sequence reactance, unit positive sequence susceptance, the multiple of zero sequence impedance and positive sequence impedance, and the length of the circuit under test on the primary side of the circuit under test.

[0014] Preferably, in step S2, the equivalent power supply node voltage parameters of the first side of the circuit under test and the equivalent power supply impedances of the first and second sides of the circuit under test are determined and input into the corresponding cells.

[0015] Preferably, in step S3, the conversion formula is established based on the primary side rated current and secondary side rated current obtained by the current transformer, and the primary side rated voltage and secondary side rated voltage obtained by the voltage transformer. After conversion, the converted secondary parameters are obtained in the corresponding secondary parameter cells.

[0016] Preferably, in step S3, the transformation ratio of the current transformer is obtained by the ratio of the primary rated current to the secondary rated current, and the transformation ratio of the voltage transformer is obtained by the ratio of the primary rated voltage to the secondary rated voltage. Based on the transformation ratios of the current transformer and the voltage transformer, conversion formulas for secondary impedance parameters and secondary admittance parameters are established.

[0017] Preferably, in step S4, the second side of the line under test is determined to be a PV node, and the power flow quantities before the fault are obtained based on the normal operation calculation model of the line under test. The power flow quantities before the fault include the three-phase voltage phasors of the busbars on both sides of the line under test before the fault, the three-phase current phasors flowing into both sides of the line under test, the three-phase voltage phasors and the three-phase current phasors of the equivalent power sources on both sides of the line under test.

[0018] Preferably, in step S5,

[0019] The corresponding fault type cell contains a fault sequence, and the fault category and special phases are determined by a conditional judgment formula.

[0020] Set a location sequence in the corresponding fault point cell, establish location calculation formulas for different fault points in the fault location cell, and select the location calculation formula through condition judgment formula after inputting relevant variables of the fault point;

[0021] The calculation formulas for the comprehensive impedance of the fault sequence network and the calculation formulas for the positive sequence current components of the fault branches for different fault types are set accordingly.

[0022] Based on the established fault type, and combined with the formula for calculating the electrical quantity of the fault branch, the electrical quantity of the fault branch for the current fault type is obtained. Then, by superimposing the electrical quantity of the normally operating branch according to the superposition theorem, the steady-state fault electrical quantity of the current fault type is obtained.

[0023] Preferably, the real and imaginary parts of each fault electrical quantity are obtained and combined into a data series to generate and display a phasor diagram.

[0024] Preferably, in step S6, an instantaneous current calculation formula is established to obtain the instantaneous current values ​​before and after the fault. The instantaneous current calculation formula includes the current sine equation before the fault, the DC attenuation equation, and the instantaneous current value formula after the fault; an instantaneous voltage calculation formula is established to obtain the instantaneous voltage values ​​before and after the fault.

[0025] Preferably, in step S6, the sampling interval time is obtained by setting the number of sampling points within one cycle. After setting the fault time point, the instantaneous current value and instantaneous voltage value before and after the fault are obtained by calculation. The fault waveform diagram is drawn based on the sampling point time and the combination of sampling point data.

[0026] Preferably, after converting the primary parameters into secondary parameters, the instantaneous value of the secondary current is obtained by introducing the saturation characteristic analysis of the current transformer and the correction of the hysteresis model.

[0027] Preferably, the following modified formula is established based on the saturation characteristics of the current transformer and the hysteresis model:

[0028]

[0029] i′1=i m +i2;

[0030] Where i′1 is the instantaneous value of the primary current referred to the secondary side; i m i1 is the instantaneous value of the excitation current; i2 is the instantaneous value of the secondary current of the current transformer; L m L1 is the nonlinear inductance of the iron core coil; L2 is the secondary circuit inductance of the current transformer; R2 is the secondary circuit resistance of the current transformer.

[0031] Preferably, a user interface form is set using VBA. The user interface form includes at least a parameter module, a calculation module, and a display module. The parameters of the circuit under test are input through the parameter module. The calculation module performs calculations based on the input parameters, the established conversion formula, the normal operation calculation model of the circuit under test, and the post-fault calculation model. The results are then displayed graphically in the display module.

[0032] The present invention provides a method for establishing a line fault simulation model based on Excel. Based on Excel's data analysis capabilities, it simulates various faults, obtains and exports transient data of fault points for fault analysis, and has the advantages of being intuitive, easy to use and low cost. Attached Figure Description

[0033] Figure 1 This is a flowchart of the present invention;

[0034] Figure 2 This is the equivalent system diagram of the circuit under test in this invention;

[0035] Figure 3 This is a schematic diagram of the fault waveform in this invention (without introducing the current transformer hysteresis model);

[0036] Figure 4 This is a schematic diagram of the fault waveform in this invention (introducing the current transformer saturation hysteresis model);

[0037] Figure 5 This is the phasor diagram of the fault electrical quantities in this invention;

[0038] Figure 6 This is a schematic diagram of the user interface window in this invention. Detailed Implementation

[0039] The following is in conjunction with the appendix Figures 1 to 6 The given embodiments further illustrate specific implementations of the method for establishing a line fault simulation model based on Excel according to the present invention. The method for establishing a line fault simulation model based on Excel according to the present invention is not limited to the descriptions in the following embodiments.

[0040] A method for building a line fault simulation model based on Excel includes the following steps:

[0041] Step S1: Enter the parameters of the circuit to be tested into Excel;

[0042] Step S2: Set the balance node voltage of the circuit under test and the power supply impedance on both sides of the circuit under test;

[0043] Step S3: Convert the linear parameters into quadratic parameters using the conversion formula;

[0044] Step S4: Using the normal operation calculation model of the line under test established based on the distributed parameter model in Excel, calculate the power flow electrical quantity of the line under test during normal operation using the complex number calculation formula in Excel and save it in the corresponding cell;

[0045] Step S5: Using the post-fault calculation model established in Excel based on the superposition theorem and fault sequence component network, calculate the post-fault power flow electrical quantities of the line under test under various faults using the complex number calculation formula in Excel. The post-fault power flow electrical quantities include the fault electrical quantities in steady state.

[0046] Step S6: Based on the power flow quantities before and after the fault, calculate and obtain the instantaneous voltage and current values ​​within a certain time before and after the fault, and obtain the transient data of the fault point in the line under test based on the instantaneous voltage and current values.

[0047] Combination Figure 1-5 A detailed embodiment is provided, wherein the circuit under test is as follows: Figure 2 The equivalent system of the MN line shown is in Figure 2 In the diagram, M′, M, and N are substations; M′M and MN are lines with the same parameters. Line MN is the research object of the line fault simulation model, i.e. the line under test. The M side is the first side of the line under test, and the N side is the second side of the line under test. These are the equivalent power supplies for the first and second sides of the line under test, respectively; K is the fault point that can be set on line MN, and K′ is the fault point on line M′M, that is, the reverse fault point of the M-end protection of line MN, which belongs to the external fault zone outside the M bus; Z M1 Z is the equivalent positive-sequence impedance of the power supply on the M side; N1 Z is the equivalent positive-sequence impedance of the power supply on the N side; M′M1 Z is the positive sequence impedance of the M′M line; MN1 This is the positive sequence impedance of the MN line.

[0048] The fault simulation model established in Excel needs to include the calculation formulas and conversion formulas for each phase parameter of the line under test, the normal operation calculation model of the line under test, and the post-fault calculation model. The normal operation calculation model of the line under test is based on the distributed parameter model, and the post-fault calculation model is based on the superposition theorem and the fault sequence component network. The calculation formulas for each phase parameter of the line under test include the known parameter calculation formulas and the existing formulas in Excel. The specific steps are as follows:

[0049] Step S1: Input the parameters of the circuit to be tested into Excel; In step S1, input the required primary parameters of the circuit to be tested into the corresponding cells. The primary parameters include the unit positive sequence resistance, unit positive sequence reactance, unit positive sequence susceptance, the multiple of zero sequence impedance and positive sequence impedance, and the length of the circuit to be tested on the primary side of the circuit to be tested.

[0050] In this embodiment, the parameters of the circuit under test are input into Excel. The parameters of the circuit under test include setting the unit positive sequence resistance r on the primary side of the circuit. 11 positive sequence reactance x 11 positive sequence susceptance b 11 The multiples of zero-sequence impedance and positive-sequence impedance z 01 / z 11 M′M line length l M′M and MN line length l MN The line conductance is negligible.

[0051] The unity negative sequence resistance r on the primary side 21 =r 11 Unit negative sequence reactance x 21 =x 11 Unit negative sequence susceptance b 21 =b 11 .

[0052] Step S2: Set the balancing node voltage and the power supply impedance on both sides of the circuit under test. In step S2, determine the equivalent power supply node voltage parameters on the first side of the circuit under test and the equivalent power supply impedance on the first and second sides of the circuit under test, and input them into the corresponding cells. In this embodiment, determining the equivalent power supply node voltage parameters on the M side of the circuit under test and the equivalent power supply impedance on both sides M and N of the circuit under test and inputting them into the corresponding cells specifically includes the following steps:

[0053] Step S2.1 Set the equivalent power supply on side M as a balancing node. This setting is based on the adjustable voltage amplitude and phase angle of the balancing node. The equivalent power supply A, B, and C on side M are three-phase symmetrical voltage phasors.

[0054] Set the amplitude E of phase A voltage. MA and phase angle The amplitude E of the voltage in direction B MB and phase angle The amplitude E of phase C voltage MC and phase angle It can be obtained from the following formula:

[0055] E MB =E MC =E MA

[0056]

[0057]

[0058] Step 2.2 Set the primary positive sequence impedance phasor of the equivalent power source on the M side The magnitude of the first positive sequence impedance Z M11 , First zero-sequence impedance amplitude Z M01 Primary positive sequence impedance phase angle Primary zero-sequence impedance phase angle Based on the fact that negative-sequence impedance and positive-sequence impedance are equal, the primary positive-sequence impedance phasor of the equivalent power source on the M side can be calculated using Excel formulas. First negative sequence impedance phasor and first-order zero-sequence impedance phasor

[0059] Set the positive-sequence impedance phasor of the equivalent power source on the N side. The magnitude of the first positive sequence impedance Z N11 , First zero-sequence impedance amplitude Z N01 Primary positive sequence impedance phase angle Primary zero-sequence impedance phase angle Based on the fact that negative-sequence impedance and positive-sequence impedance are equal, the primary positive-sequence impedance phasor of the equivalent power source on the N-side can be calculated using Excel formulas. First negative sequence impedance phasor and first-order zero-sequence impedance phasor

[0060] The calculation formula can be selected from the COMPLEX function in Excel. The specific calculation process can be performed in the corresponding cell as follows:

[0061]

[0062] Where PI() is π, similarly the negative-sequence impedance phasor can be calculated. and first-order zero-sequence impedance phasor Solve using the same method

[0063] Step S3: Convert the linear parameters into quadratic parameters using the conversion formula.

[0064] In step S3, the conversion formula is established based on the primary and secondary rated currents obtained from the current transformer, and the primary and secondary rated voltages obtained from the voltage transformer. After conversion, the converted secondary parameters are obtained in the corresponding secondary parameter cells. In step S3, the transformation ratio of the current transformer is obtained by the ratio of the primary rated current to the secondary rated current, and the transformation ratio of the voltage transformer is obtained by the ratio of the primary rated voltage to the secondary rated voltage. Based on the transformation ratios of the current transformer and the voltage transformer, conversion formulas for secondary impedance parameters and secondary admittance parameters are established.

[0065] In this embodiment, the rated primary current In1 and rated secondary current In2 of the current transformer, and the rated primary voltage Un1 and rated secondary voltage Un2 of the voltage transformer are determined, and the turns ratio n of the current transformer is calculated. CT =In1 / In2 and voltage transformer PT ratio n PT =Un1 / Un2, create the following conversion formula in Excel to convert all linear parameters to quadratic parameters.

[0066] The conversion formula is:

[0067] Impedance parameters: Secondary impedance = Primary impedance × n CT / n PT

[0068] Admittance parameters: Secondary admittance = Primary admittance × n PT / n CT

[0069] Based on the primary parameters, the following secondary parameters are obtained by substituting them into the conversion formula:

[0070] M-side equivalent power supply secondary positive sequence impedance phasor;

[0071] M-side equivalent power supply secondary negative sequence impedance phasor;

[0072] M-side equivalent power supply secondary zero-sequence impedance phasor;

[0073] N-side equivalent power supply secondary positive sequence impedance phasor;

[0074] N-side equivalent power supply secondary negative sequence impedance phasor;

[0075] N-side equivalent power supply secondary zero-sequence impedance phasor;

[0076] r1: Line secondary unit positive sequence resistance;

[0077] x1: Line secondary unit positive sequence reactance;

[0078] b1: Line secondary unit positive sequence susceptance;

[0079] Line secondary unit positive sequence impedance phasor;

[0080] Line secondary unit zero-sequence impedance phasor;

[0081] Line secondary unit positive sequence admittance phasor;

[0082] M′M line secondary positive sequence impedance phasor;

[0083] M′M line secondary negative sequence impedance phasor;

[0084] M′M line secondary positive sequence impedance phasor;

[0085] MN line secondary positive sequence impedance phasor;

[0086] MN line secondary negative sequence impedance phasor;

[0087] The positive-sequence impedance phasor of the MN line.

[0088] Step S4: Establish a normal operation calculation model for the line under test in Excel. Use the complex number calculation formula in Excel to calculate the power flow electrical quantities of the line under test during normal operation and save them in the corresponding cells. The normal operation calculation model of the line under test adopts the distributed parameter model.

[0089] In step S4, the line model in the normal operation power flow calculation adopts a distributed parameter model, determining the second side of the line under test as a PV node. Based on the normal operation calculation model of the line under test, the power flow electrical quantities before the fault are obtained. The power flow electrical quantities before the fault include the three-phase voltage phasors of the buses on both sides of the line under test before the fault, the three-phase current phasors flowing into both sides of the line under test, the three-phase voltage phasors and three-phase current phasors of the equivalent power sources on both sides of the line under test. The power flow electrical quantities before the fault (during normal operation) other than the power supply voltage are represented by the subscript [0].

[0090] The implementation steps are as follows:

[0091] Step S4.1 Determine the A-phase voltage phasor of the equivalent power source on the second side (N side) of the line under test. Amplitude E NA and phase angle

[0092] If the current reference direction on sides M and N is pointing towards the line, that is, from the busbar towards the line under test, then the following formula holds:

[0093]

[0094]

[0095]

[0096]

[0097] in: The A-phase voltage phasor of the busbars on the M and N sides of the line under test before the fault; The A-phase current phasor flowing into the M side of the line under test before the fault; The A-phase current phasor flowing into the N side of the line under test before the fault;

[0098] The characteristic impedance phasor of the line under test;

[0099] The propagation coefficient phasor of the line under test;

[0100] The busbar on the second side (N side) of the line under test is set as a PV node, i.e., U NA[0] P NA[0] It can be configured.

[0101]

[0102] U NA[0] P NA[0] =P set / (n PT n CT Given, search in The search range is 0 to 360°, and the search starting value is...

[0103] Where: P NA[0] I represents the output power of phase A on the N side of the line under test; NA[0] P represents the A-phase current on the N-side of the line under test before the fault. set The set primary power value; The phase angle of phase A voltage on the busbar on side M of the line under test before the fault; The phase angle of phase A voltage on the N-side busbar of the line under test before the fault; The phase angle of the A-phase current flowing into the M side of the line under test; The phase angle of the A-phase current flowing into the N side of the line under test;

[0104] Combining formulas (1), (3), and (4), we get:

[0105]

[0106]

[0107] The phase A current I on the N side of the line under test before the fault can be obtained from formula (6). NA[0] and the phase angle of the A-phase current flowing into the M side of the line under test P′ obtained by substituting into formula (5) NA[0] and P set Compare them.

[0108] Implement in VBA Search until P′ NA[0] and P set The search stops when they are equal to a certain degree of precision, where P′ NA[0] That is, in the search P in the process NA[0] Use this time Substituting into formulas (2) and (6), we can obtain the result. The amplitude E can be calculated using an Excel formula in the corresponding cell. NA and phase angle

[0109] Step S4.2 is obtained from formulas (3) and (4). Write to the corresponding cell.

[0110] Step S4.3 but

[0111] Similarly, according to step S4.3, we can calculate... Write to the corresponding cell.

[0112] in:

[0113] The voltage phasor of phase B on the M-side busbar of the line under test before the fault. The B-phase voltage phasor of the N-side busbar of the line under test before the fault; The phasor of phase B current flowing into the M side of the line under test before the fault;

[0114] The phasor of phase B current flowing into the N side of the line under test before the fault;

[0115] The C-phase voltage phasor of the busbar on the M side of the line under test before the fault; The C-phase voltage phasor of the N-side busbar of the line under test before the fault; The C-phase current phasor flowing into the M side of the line under test before the fault;

[0116] The C-phase current phasor flowing into the N-side of the line under test before the fault; The B-phase voltage phasor of the equivalent power supply on the N side; This is the C-phase voltage phasor of the equivalent power supply on the N side.

[0117] Step S5: Establish a post-fault calculation model using the superposition theorem and composite sequence network. Calculate the steady-state fault electrical quantities under various fault conditions using complex number calculation formulas in Excel. This is implemented in the corresponding cells using Excel complex number calculation formulas. The post-fault power flow electrical quantities include the steady-state fault electrical quantities. In Step S5, a fault sequence is set in the corresponding fault type cell, and a conditional judgment formula is used to determine the fault category and special phases. A location sequence is set in the corresponding fault point cell, and location calculation formulas for different fault points are established in the fault location cell. After inputting relevant variables for the fault point, a location calculation formula is selected using a conditional judgment formula. A calculation formula for the comprehensive impedance of the fault sequence network and a calculation formula for the positive sequence current component of the fault branch for different fault types are also set. Based on the set fault type, and combined with the fault branch electrical quantity calculation formula, the electrical quantities of the fault branch for the current fault type are obtained. The steady-state fault electrical quantities of the current fault type are obtained by superimposing the electrical quantities of the normally operating branch using the superposition theorem.

[0118] The implementation steps are as follows:

[0119] Step S5.1 Set the sequence in the corresponding fault type cell: OK, AN, BN, CN, AB, BC, CA, ABN, BCN, CAN, and ABC. OK indicates no fault and the power flow status during normal operation can be observed. AN, BN, and CN are single-phase ground faults. BC, CA, and AB are two-phase short-circuit faults. BCN, CAN, and ABN are two-phase ground faults. ABC is a three-phase fault.

[0120] Step S5.2 uses a conditional formula in a special cell to achieve the following:

[0121] The corresponding step S5.1 is set as follows: for AN, BC, BCN, and ABC, the special phase is A; for BN, CA, and CAN, the special phase is B; and for CN, AB, and ABN, the special phase is C.

[0122] Step S5.3 uses a conditional formula in the fault category cell to achieve the following:

[0123] The corresponding step 5.1 is set as follows: AN, BN, CN are fault category 1; BC, CA, AB are fault category 2; BCN, CAN, ABN are fault category 2N; and ABC are fault category 3.

[0124] Step S5.4: Set the sequence K and K' in the fault point cell, and enter the percentage k% of the distance between the fault point and M relative to the total line length in the fault location cell; then:

[0125] The length l of the line segment from point M to point K MK =l MN k%;

[0126] The length l of the line from point K′ to point M K′M =l M′M k%;

[0127] The length l of the line segment from point K to N KN =l MN (1-k%);

[0128] The length l of the line segment from point K′ to M′ M′K′ =l M′M( 1-k%);

[0129] When calculating fault quantities, different calculation formulas for faults K or K′ can be displayed by entering conditional judgment formulas in the cells of relevant variables for fault calculation.

[0130] Step S5.5 Set R in the grounding resistance cell g The value;

[0131] Step S5.6 Calculation of the composite impedance of the fault sequence network, i.e., calculation of the network parameters of each fault sequence component, to determine the composite impedance of the positive sequence network. Negative sequence network synthesized impedance Zero-sequence network synthesized impedance

[0132] When the fault point is K:

[0133]

[0134]

[0135]

[0136] When the fault point is K′:

[0137]

[0138]

[0139]

[0140] in:

[0141] Positive-sequence, negative-sequence, and zero-sequence impedance phasors of line MK segment

[0142] Positive-sequence, negative-sequence, and zero-sequence impedance phasors of the KN segment of the line

[0143] Positive-sequence, negative-sequence, and zero-sequence impedance phasors of line segment M′K′

[0144] Positive-sequence, negative-sequence, and zero-sequence impedance phasors of line segment K′M

[0145] In step S5.6, the calculation method for the form a / / b is as follows: a / / b = ab / (a+b).

[0146] Step S5.7 Calculate the positive sequence current component of phase A of the faulty branch. The text only lists the formula for solving fault point K. The solution method for fault point K′ is similar, i.e., see step S5.6.

[0147] According to the positive sequence equivalence rule, under composite sequence networks with different fault categories, the positive sequence current component of the special phase X (X = A, B, or C, the same below) of the fault branch is:

[0148]

[0149] The operating voltage of the special phase before the fault; can be obtained from formula (3) by l MN Replace with the line segment length l from point K to N MN To obtain.

[0150] —Impedance related to short-circuit type:

[0151] During a single-phase ground fault (fault category = 1):

[0152] During a two-phase short-circuit fault (fault category = 2):

[0153] During a two-phase short-circuit to ground fault (fault category = 2N):

[0154] During a three-phase short-circuit fault (fault category = 3):

[0155] exist Enter a conditional formula in the cell to calculate the value under the currently set fault type.

[0156] Step S5.8: Calculate the fault electrical quantities of the faulty branch;

[0157] Fault current at point K in phase X:

[0158] Positive sequence voltage of phase X fault at point K:

[0159] Negative sequence voltage of phase X fault at point K:

[0160] Zero-sequence voltage of phase X fault at point K:

[0161] Fault voltage at point K in phase X:

[0162] Sequence currents of each phase in branch M:

[0163] in, The allocation coefficients for each order M side,

[0164] N-branch X-phase sequence currents:

[0165] in, The N-side allocation coefficients for each order.

[0166] Step S5.9: According to the superposition theorem, the electrical quantities of the normally operating branch and the faulty branch are superimposed to calculate the fault electrical quantity at the protection installation point (i.e., where the current transformer collects the current) in steady state.

[0167] M-protection installation location current:

[0168] N protects the current at the installation point:

[0169] M-protection installation location voltage:

[0170] N protects the voltage at the installation point:

[0171] Step 5.10: After obtaining the real and imaginary parts of each fault electrical quantity, combine them into a data series to generate and display a phasor diagram. Calculate the real and imaginary parts of each electrical quantity in the cells; then combine the real and imaginary part data of each electrical quantity at the origin (0, 0) to form a data series, and then display it using an XY scatter plot to achieve the phasor diagram display function (see example of phasor diagram). Figure 5 ).

[0172] Step S6: Based on the power flow quantities before and after the fault, calculate and obtain the instantaneous voltage and current values ​​within a certain time before and after the fault. Obtain transient data of the fault point in the circuit under test based on these instantaneous voltage and current values. Obtain the fault waveform based on the transient data to achieve dynamic fault waveform functionality. The fault waveform allows for intuitive identification of the fault type and phase, and can also be used to verify the correctness of the simulation model. In Step S6, establish instantaneous current calculation formulas to obtain the instantaneous current values ​​before and after the fault. These formulas include the current sine equation before the fault, the DC attenuation equation, and the instantaneous current value formula after the fault. Establish instantaneous voltage calculation formulas to obtain the instantaneous voltage values ​​before and after the fault. In Step S6, obtain the sampling interval time by setting the number of sampling points within one cycle. After setting the fault time point, calculate and obtain the instantaneous current and voltage values ​​before and after the fault. Plot the fault waveform based on the sampling point time and the combination of sampling point data.

[0173] Step S6.1 After calculating the power flow before the fault and during the fault steady state in steps S4 and S5, the initial values ​​of the DC components of the current on both sides of the line under test at the fault time are obtained by using the principle that the current cannot change abruptly. The DC attenuation time constant T can also be obtained by calculating the resistance and inductance of the short-circuit loop in steps S4 and S5. Thus, the sinusoidal equation and DC attenuation equation of the current at the protection installation points on both sides of the line can be established. In this embodiment, the system frequency is set to f = 50Hz.

[0174] Formula for the instantaneous current sinusoidal wave at time t before the fault:

[0175] Initial value of DC attenuation i′ at fault time t1 X :

[0176]

[0177] DC attenuation formula: i′e -t / T ;

[0178] Where: T = L / R

[0179]

[0180] I X[0] This represents the current amplitude before a fault in phase X, and is applicable to both M and N sides.

[0181] This represents the current phase angle before a fault in phase X, and is applicable to both the M and N sides.

[0182] I X This represents the current amplitude after a fault in phase X, and is applicable to both M and N sides.

[0183] This represents the current phase angle after a fault in phase X, and is applicable to both M and N sides.

[0184] Formula for the instantaneous current at time t after the fault:

[0185] Step S6.2 After calculating the power flow electrical quantities before the fault and in the steady state of the fault from steps S4 and S5, establish the instantaneous voltage value equations before and after the fault.

[0186] Formula for voltage sine wave during normal operation:

[0187] Post-fault voltage formula:

[0188] in:

[0189] U X[0] This represents the voltage amplitude before a fault in phase X, and is applicable to both M and N sides.

[0190] This represents the voltage phase angle before a fault in phase X, and is applicable to both M and N sides.

[0191] U X This represents the voltage amplitude after a fault in phase X, and applies to both M and N sides.

[0192] This represents the voltage phase angle after a fault in phase X, and applies to both M and N sides.

[0193] After setting the number of sampling points within one cycle in step S6.3 (96 in this case), the sampling interval time can be calculated. After setting the fault time t1, the instantaneous value of each sampling point before and after the fault (2000ms in this case, a total of 9600 sampling points) can be calculated by the conditional formula and written into the worksheet.

[0194] Step S6.4 Combine the data from all sampling points of each voltage and current with the sampling time to form a data series, and then display it using an XY scatter plot to realize the function of displaying fault waveforms.

[0195] As an improvement to this embodiment, in the process of converting primary parameters into secondary parameters, the instantaneous value of the secondary current is obtained by introducing the saturation characteristic analysis of the current transformer and the hysteresis model. The secondary current in the above embodiments are all secondary currents of ideal current transformers, that is, the primary current converted to secondary current does not take into account the saturation and hysteresis characteristics of the current transformer.

[0196] In the improved scheme, the saturation model uses a modified arctangent function to fit the relationship between magnetic induction intensity B and magnetic field intensity H; the hysteresis model is constructed using the Preisach principle, and the corresponding instantaneous value of the secondary current is calculated by using a VBA script to obtain the solution algorithm for each sampling point through gradual approximation.

[0197] The external characteristic parameters of the current transformer can be set, including: primary side turns, rated capacity, protection accuracy, accuracy limit factor, secondary circuit impedance, secondary circuit power factor, and residual magnetism. The residual magnetism can be set or calculated to obtain the residual magnetism after each fault clearing.

[0198] The main calculation formula is:

[0199]

[0200] i′1=i m +i2

[0201] in:

[0202] i′1 is the instantaneous value of the primary current referred to the secondary side;

[0203] i m This is the instantaneous value of the excitation current;

[0204] i2 is the instantaneous value of the secondary current of the current transformer;

[0205] L m The nonlinear inductance of the iron-core coil;

[0206] L2 is the secondary circuit inductance of the current transformer;

[0207] R2 is the secondary circuit resistance of the current transformer;

[0208] See Figure 4 As can be seen, the corrected waveform is shown below for easier observation. Figure 4 Phases B and C are omitted.

[0209] Furthermore, the data storage is achieved by creating two new worksheets, named cfg and dat respectively. The cfg file configures the channel information for the waveform recording file, setting all parameters required for the COMTRADE file standard. The dat file stores the corresponding data, with the instantaneous value of each sampling point stored in the dat file. Then, a VBA script is used to generate the COMTRADE file, stored in xlCSVUTF8 format. The waveform file storage path is customizable, and the waveform generation function in the script can be set as a command button in the worksheet to enable one-click waveform file generation.

[0210] Furthermore, a user interface form is set up in Excel using VBA. This form includes at least a parameter module, a calculation module, and a display module. The parameter module inputs the parameters of the circuit under test into the fault simulation model built in Excel. The calculation module performs calculations based on the input parameters, using the conversion formulas and calculation model within the fault simulation model. Finally, the results are displayed graphically in the display module. The parameters input in the parameter module can be freely combined, allowing the calculation module to perform calculations based on different parameter combinations and the display module to display corresponding graphs. For example, by selecting fault-related parameters (fault point, fault type, and grounding resistance, etc.) in the parameter module, the calculation module obtains the electrical quantities after the fault, which are then displayed as a phasor diagram in the display module.

[0211] like Figure 6 As shown, the parameter module of the user interface window includes equivalent power source parameters for the first side (M side) of the line under test (i.e., the amplitude and phase angle of the A-phase voltage of the equivalent power source on the M side, the amplitude and phase angle of the primary positive-sequence impedance, the amplitude and phase angle of the primary zero-sequence impedance, etc.), equivalent power source parameters for the second side (N side) of the line under test (i.e., the node type of the equivalent power source on the N side, the amplitude and phase angle of the primary positive-sequence impedance, the amplitude and phase angle of the primary zero-sequence impedance, secondary voltage, primary active power, etc.), fault parameters (i.e., fault time, clearing time, reclosing time, fault type, fault location, fault distance, grounding resistance, etc.), and parameters required for calculating secondary parameters (i.e., the primary voltage of the current transformer). The system includes options for current and secondary current, primary and secondary voltages of voltage transformers, current transformer saturation hysteresis model, and three-phase current and voltage options on both sides of the line under test. The calculation module is displayed on the user interface window as a power flow calculation button and a fault calculation button. When the power flow calculation button is triggered, the normal operation calculation model of the line under test, used to calculate electrical quantities before a fault, performs the calculation function. When the fault calculation button is triggered, the post-fault calculation model, used to calculate electrical quantities after a fault, performs the calculation. The display module is an area for displaying phasors or waveforms, and the graph can be viewed by arbitrarily selecting and combining the three-phase current and voltage options on both sides of the line under test.

[0212] like Figure 6As shown, in the user interface window, first set the parameters of the circuit under test in the parameter module. Set EMA to 59V, 0°, ZM1 to 0.5Ω, 84.4°, ZM0 to 1.5Ω, 84.4°, N source load to Source (i.e., the N side is the power source), ZN1 to 1Ω, 84.4°, ZN0 to 3Ω, 84.4°, N-side bus contact type to PV node, secondary voltage to 60V, primary active power to 30MW, primary voltage transformer to 110kV, secondary voltage transformer to 100V, and primary voltage transformer to 1000A, secondary voltage transformer to 1000A. 5A; Preferably, a pop-up interface is provided in the user interface window as part of the parameter setting module. In the pop-up interface, the line type is set to a custom line, custom r1 is set to 0.02947Ω / km, custom x1 is set to 0.3006Ω / km, custom y1 is set to 0.000003703S / km, line length MN is set to 50km, and Z0 / Z1 (the ratio of zero-sequence impedance to positive-sequence impedance) is set to 2. This completes the input of the normal operating parameters for the line under test. Clicking the power flow calculation button allows the calculation module to complete the power flow calculation process and obtain the pre-fault power flow electrical quantities of the line under test. Alternatively, the pop-up interface can be omitted, and all parameters of the line under test can be directly input into the parameter module of the user interface window.

[0213] Then, input the fault parameters of the line under test on the user interface form, set the fault time to 200ms, the disconnection time to 300ms, the reclosing time to 1900ms, the fault type to ABC, the fault location to K, the fault distance to 20%, and the grounding resistance to 0Ω. Then click the fault calculation button, and the calculation module will complete the calculation to obtain the power flow electrical quantities after the fault.

[0214] After the calculation module completes the calculation, the display module shows the waveform diagram, which can display the waveform changes within 2000ms. Users can select the electrical quantities to be displayed and click the refresh waveform diagram button to display the selected electrical quantity waveforms. Clicking "Export Waveform File" saves the fault COMTRADE waveform file. Clicking "Phasor Diagram" allows users to view the phasor relationships of the electrical quantities during the fault. Users can select the electrical quantities to be displayed and click the refresh phasor diagram button to display the selected electrical quantity phasor relationships.

[0215] In this application, the calculation formulas and calculation models used are all implemented using Excel. The obtained data can be directly exported and displayed using Excel's charting function, which is intuitive, fast, and has low usage costs.

[0216] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for establishing a line fault simulation model based on Excel, characterized in that: Includes the following steps, Step S1: Enter the parameters of the circuit to be tested into Excel; Step S2: Set the balance node voltage of the circuit under test and the power supply impedance on both sides of the circuit under test; Step S3: Convert the linear parameters into quadratic parameters using the conversion formula; Step S4: Using the normal operation calculation model of the line under test established based on the distributed parameter model in Excel, calculate the power flow electrical quantity of the line under test during normal operation using the complex number calculation formula in Excel and save it in the corresponding cell; In step S4, the second side of the line under test is determined to be a PV node. Based on the normal operation calculation model of the line under test, the power flow quantities before the fault are obtained. The power flow quantities before the fault include the three-phase voltage phasors of the two busbars on both sides of the line under test before the fault, the three-phase current phasors flowing into both sides of the line under test, the three-phase voltage phasors and the three-phase current phasors of the equivalent power sources on both sides of the line under test. Step S5: Using the post-fault calculation model established in Excel based on the superposition theorem and composite sequence network, calculate the post-fault power flow electrical quantities of the line under test under various faults using the complex number calculation formula in Excel. The post-fault power flow electrical quantities include the fault electrical quantities in steady state. Step S6: Based on the power flow quantities before and after the fault, calculate and obtain the instantaneous voltage and current values ​​within a certain time before and after the fault, and obtain the transient data of the fault point in the line under test based on the instantaneous voltage and current values.

2. The method for establishing a line fault simulation model based on Excel according to claim 1, characterized in that: In step S1, the required primary parameters of the circuit under test are input into the corresponding cells. The primary parameters include the unit positive sequence resistance, unit positive sequence reactance, unit positive sequence susceptance, the multiple of zero sequence impedance and positive sequence impedance, and the length of the circuit under test on the primary side of the circuit under test.

3. The method for establishing a line fault simulation model based on Excel according to claim 2, characterized in that: In step S2, the equivalent power supply node voltage parameters of the first side of the circuit under test and the equivalent power supply impedances of the first and second sides of the circuit under test are determined and input into the corresponding cells.

4. The method for establishing a line fault simulation model based on Excel according to claim 3, characterized in that: In step S3, the conversion formula is established based on the primary side rated current and secondary side rated current obtained by the current transformer, and the primary side rated voltage and secondary side rated voltage obtained by the voltage transformer. After conversion, the converted secondary parameters are obtained in the corresponding secondary parameter cells.

5. The method for establishing a line fault simulation model based on Excel according to claim 4, characterized in that: In step S3, the ratio of the current transformer is obtained by the ratio of the primary rated current to the secondary rated current, and the ratio of the voltage transformer is obtained by the ratio of the primary rated voltage to the secondary rated voltage. Based on the ratios of the current transformer and the voltage transformer, conversion formulas for secondary impedance parameters and secondary admittance parameters are established.

6. The method for establishing a line fault simulation model based on Excel according to any one of claims 2-5, characterized in that: In step S5, The corresponding fault type cell contains a fault sequence, and the fault category and special phases are determined by a conditional judgment formula. Set a location sequence in the corresponding fault point cell, establish location calculation formulas for different fault points in the fault location cell, and select the location calculation formula through condition judgment formula after inputting relevant variables of the fault point; The calculation formulas for the comprehensive impedance of the fault sequence network and the calculation formulas for the positive sequence current components of the fault branches for different fault types are set accordingly. Based on the established fault type, and combined with the formula for calculating the electrical quantity of the fault branch, the electrical quantity of the fault branch for the current fault type is obtained. Then, by superimposing the electrical quantity of the normally operating branch according to the superposition theorem, the steady-state fault electrical quantity of the current fault type is obtained.

7. The method for establishing a line fault simulation model based on Excel according to claim 6, characterized in that: After obtaining the real and imaginary parts of each fault electrical quantity, they are combined into a data series, and a phasor diagram is generated and displayed.

8. The method for establishing a line fault simulation model based on Excel according to claims 2-5, characterized in that: In step S6, an instantaneous current calculation formula is established to obtain the instantaneous current values ​​before and after the fault. The instantaneous current calculation formula includes the current sine equation before the fault, the DC attenuation equation, and the instantaneous current value formula after the fault. An instantaneous voltage calculation formula is established to obtain the instantaneous voltage values ​​before and after the fault.

9. The method for establishing a line fault simulation model based on Excel according to claim 8, characterized in that: In step S6, the sampling interval time is obtained by setting the number of sampling points within one cycle. After setting the fault time point, the instantaneous current value and instantaneous voltage value before and after the fault are obtained by calculation. The fault waveform diagram is drawn based on the sampling point time and the combination of sampling point data.

10. The method for establishing a line fault simulation model based on Excel according to claim 1, characterized in that: After converting the primary parameters into secondary parameters, the instantaneous value of the secondary current is obtained by introducing the saturation characteristic analysis of the current transformer and the correction of the hysteresis model.

11. The method for establishing a line fault simulation model based on Excel according to claim 10, characterized in that: Based on the saturation characteristics of current transformers and the hysteresis model, the following modified formula is established: in, This is the instantaneous value of the primary current referred to the secondary side; This is the instantaneous value of the excitation current; This is the instantaneous value of the secondary current of the current transformer; The nonlinear inductance of the iron-core coil; The inductance of the secondary circuit of the current transformer; This is the resistance of the secondary circuit of the current transformer.

12. The method for establishing a line fault simulation model based on Excel according to claim 1, characterized in that: The user interface form is set up using VBA. The user interface form includes at least a parameter module, a calculation module, and a display module. The parameters of the circuit under test are input through the parameter module. The calculation module performs calculations based on the input parameters, the established conversion formula, the normal operation calculation model of the circuit under test, and the post-fault calculation model. The results are then displayed graphically in the display module.

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