Power system ground fault line distance measurement method

Abstract

The invention provides an electric power system grounding fault line distance measurement method. The method comprises the following steps: predicting a fault distance according to a fault type judged by an oscillograph and fault phase voltage and phase current data; preliminarily determining a faulted line section according to the fault distance, the line section number, the length of each section of line and the total length of the line in the prediction distance step; optimizing the input voltage and current according to the fault type and the specific attribute of the line to obtain the optimized input voltage and current; respectively selecting different line models for modeling according to different line lengths; taking the optimized input voltage and current as the voltage and current of the initial end of the first section of line, and calculating the voltage and current of the initial end of each subsequent section of line according to the impedance under each section of line model; and correcting the predicted fault distance according to the determined fault section and the initial voltage and current of each section of line, and checking whether the fault is an external fault or not according to the corrected fault distance. By adopting the method, the accuracy of power system grounding fault line distance measurement can be improved.

Description

Technical Field

[0001] The invention relates to the field of power fault distance measurement, and in particular to a method for measuring distance of a ground fault line in a power system. Background Art

[0002] At present, transmission lines of different voltage levels have long transmission distances and are susceptible to various types of grounding or short-circuit faults due to the complex external environment along the way and large differences in line structure. This greatly increases the workload of line patrol personnel and makes it impossible to eliminate faults in a timely manner.

[0003] The relevant regulations for the operation of my country's power system stipulate that for high-voltage transmission networks, since their neutral points are grounded, when a fault occurs, it is necessary to quickly locate the fault and remove it. For medium-voltage distribution networks, although they can continue to operate for two hours, the voltage increase after the fault may also cause insulation problems and increase the risk of fault expansion. Therefore, when a power system fails, it is necessary to quickly and accurately locate the fault point and eliminate the fault in time. If there is an accurate fault location method, not only can the line be repaired in time and reliable power supply be guaranteed, but the time for repairing the faulty line can also be greatly shortened, which plays a very important role in the safety, stability and economic operation of the power system.

[0004] The fault location algorithm in the prior art has the following shortcomings:

[0005] First, in the existing distance measurement algorithms, a single model is usually used to model the line, such as a centralized model or a distributed model, which rarely considers the relationship between the line length and the model, as well as the difference between the theoretical modeling and the actual line, resulting in increased modeling errors.

[0006] Secondly, there are many kinds of actual lines. The existence of capacitor compensation, shunt reactor compensation, transition resistance, etc. depends on the specific situation of the power system. Most of the existing distance measurement methods are not detailed enough for these parts.

[0007] Third, the distance measurement methods in the prior art mostly determine the final distance measurement value by simply comparing the results of two or three distance measurement methods, without performing more verification or correction on the distance measurement results, especially for terminal correction or out-of-area fault verification. Summary of the invention

[0008] The object of the present invention is to provide a method for measuring the distance of a ground fault line in an electric power system, thereby improving the accuracy of the distance measurement.

[0009] In an embodiment of the present invention, a method for measuring the distance of a ground fault line in a power system is provided, which includes:

[0010] Predicting distance step: Calculate input voltage, current and current fault component according to the fault type determined by the recorder and the fault phase voltage and phase current data, and predict the fault distance according to the input voltage, current and current fault component;

[0011] Fault section analysis step: preliminarily determine the faulty line section according to the fault distance, number of line sections, length of each line section and total line length in the prediction distance step;

[0012] Initial voltage and current optimization step: optimize the input voltage and current according to the fault type and specific properties of the line to obtain the optimized input voltage and current;

[0013] Segmented line modeling steps: select different line models for modeling according to different line lengths;

[0014] Segmented current and voltage calculation steps: using the optimized input voltage and current as the voltage and current at the beginning of the first segment of the line, and calculating the voltage and current at the beginning of each subsequent segment of the line according to the impedance of each segment of the line;

[0015] Correction and verification steps: recalculate the zero-sequence compensation coefficient based on the determined fault section, fault distance and the initial voltage and current of each line section, further correct the fault distance, and verify whether the fault is an out-of-zone fault based on the corrected fault distance.

[0016] In the embodiment of the present invention, before the step of predicting the distance, the method further includes:

[0017] Parameter preprocessing steps, which include:

[0018] According to the known unit parameters of each line section positive sequence resistance R1 i , zero sequence resistance R0 i , Positive sequence reactance X1 i 、Zero sequence reactance X0 i , positive sequence conductance G1 i , zero sequence conductance G0 i And positive sequence and zero sequence susceptance B1 i , BZ i , calculate the positive sequence impedance Z1 of each line section i 、Zero sequence impedance Z0 i , positive sequence admittance and zero sequence admittance Y1 i 、Y0 i , where i represents the i-th line;

[0019] Calculate the zero-sequence compensation coefficient K0 for each line section i And the average zero-sequence compensation coefficient K0_mean of all line sections:

[0020]

[0021] Where N is the number of line segments.

[0022] In the embodiment of the present invention, in the predicting distance step, the input voltage, current and current fault component are calculated according to the fault type determined by the recorder and the fault phase voltage and phase current data, including:

[0023] When a single-phase grounding fault occurs, the input fault phase voltage is UM = FltUα, the input fault phase current is IM = FltIα, the calculated impedance is ZM = UM / (IM + FltI0*K0_mean), the current fault component is extendI = FltIα-NmlIα, and FltI0 is the zero-sequence current;

[0024] When a two-phase grounding fault or a phase-to-phase fault occurs, the input fault voltage is UM = FltUα-FltUβ, the input fault current is IM = FltIα-FltIβ, the calculated impedance is ZM = UM / IM, and the current fault component is extendI = IM-NmlIα-NmlIβ;

[0025] When a three-phase grounding fault occurs, let a = cos240° + jsin240°, and the input voltage is UM = FltUα + a*FltUβ + a 2 *FltUγ, the input current is IM=FltIα+a*FltIβ+a 2 *FltIγ, the current fault component is extendI=IM-(NmlIα+a*NmlIβ+a 2 *NmlIγ), the impedance is calculated as ZM=UM / IM;

[0026] In the above formula, α, β, γ represent any one of the three phases A, B, and C respectively, and NmlIα, NmlIβ, and NmlIγ represent the normal three-phase current when there is no fault.

[0027] In the embodiment of the present invention, in the distance prediction step, the formula for predicting the fault distance x according to the input voltage, current and current fault component includes:

[0028]

[0029] in, CM0 is the zero-sequence distribution coefficient, and let CM0=complex(1,0), complex(m,n) is the complex conversion function, and complex(m,n)=m+n*j, Imag() means taking the imaginary part.

[0030] In the embodiment of the present invention, in the fault segment analysis step, the line segment fault_i where the fault occurs is preliminarily determined according to the predicted fault distance, the number of line segments, the length of each line segment and the total length of the line, including:

[0031] When there is only one line section, the faulty section is the first line section, fault_i=1;

[0032] When the number of line segments is N (N ≥ 2), the length of the first line segment is l1, and the total length of the line is l.

[0033] If the predicted distance result x<l1, the fault section is the first section of the line, fault_=1;

[0034] If the predicted distance result x>l, the fault section is the last section of the line, fault_i=N;

[0035] If the prediction result x is greater than the total length of the first i-1 sections of the line and less than the total length of the first i sections of the line, the faulty section is the i-th section of the line, and fault_i=i.

[0036] In the embodiment of the present invention, in the initial voltage and current optimization step, the input voltage and current are optimized according to the fault type and the specific properties of the line to obtain the optimized input voltage and current, including:

[0037] If a single-phase grounding fault occurs, the optimization is divided into three cases: the line capacitor and the shunt reactor exist at the same time, the line capacitor exists only, and neither exists:

[0038] When the line capacitor and the shunt reactor exist at the same time, the capacitor current IC and the shunt reactor current IP are calculated, so that the optimized input current IMM=IM–IC–IP, and the optimized input voltage is UMM=UM-ZM*(IC+IP); on this basis, by comparing the ZM phase angle φM with the line positive sequence impedance Z1 phase angle φZ1, it is confirmed whether there is a terminal transition resistance grounding situation. If φM>0.9*φZ1, there is no transition resistance grounding at the terminal, and the input voltage and current remain unchanged; if φM≤0.9*φZ1, the terminal is grounded through a transition resistor, and UMM=UMM-UMM*FltI0 / IMM is further optimized, where,

[0039] IC=UM*(j2πω*BZ_mean*l),

[0040]

[0041] Among them, BZ_mean represents the average zero-sequence capacitance of the line, PX is the positive-sequence reactance of the shunt reactor, and PX0 represents the small reactance of the neutral point of the shunt reactor;

[0042] When there is no shunt reactor connected to the line and only line capacitance exists, the optimized input voltage and input current are UMM=UM-ZM*IC and IMM=IM-IC respectively;

[0043] When neither the line capacitor nor the shunt reactor exists, the optimized input voltage and input current are UMM=UM and IMM=IM respectively;

[0044] If a multi-phase fault occurs, the input voltage and input current do not change.

[0045] That is, UMM=UM, IMM=IM.

[0046] In an embodiment of the present invention, the segmented line modeling step includes:

[0047] When the line length is l i For short lines less than 80 km, a simplified model is used:

[0048] The line impedance is Z1 i _new=Z1 i ;

[0049] The line admittance is Y1 i _new=Y1 i ;

[0050] When the line length is l i For medium-length lines greater than or equal to 80 km and less than 300 km, centralized parameter modeling is used to model the line;

[0051] The line impedance is Z1 i _new=Z1 i +Z1 i *Z1 i *Y1 i / 6;

[0052] The line admittance is Y1 i _new=Y1 i -Y1 i *Z1 i *Y1 i / 12;

[0053] When the line length l i When the distance is greater than or equal to 300 km, the long-distance π-shaped equivalent circuit model is used for modeling, and the total impedance, total reactance, and total susceptance correction coefficients Kr, Kx, and Kb of the long line are introduced.

[0054] Kr=1-X1 i *B1 i *l i *l i / 3;

[0055] Kx=1-(X1 i *R1 i -R1 i *R1 i *B1 i / (X1 i )*l i *l i / 6;

[0056] Kb=1+X1 i *B1 i *l i *l i / 12;

[0057] The line impedance is Z1 i _new=R1 i *l i *Kr+jX1 i *l i *Kr;

[0058] The line admittance is Y1 i _new=B1 i *l i *R1 i *B1 i *l i *l i / 12+jB1 i *l i * Kb.

[0059] In the embodiment of the present invention, the step of calculating the segmented current and voltage specifically includes:

[0060] The input voltage and current UMM and IMM are used as the voltage and current at the beginning of the first line section, that is, U1 = UMM, I1 = IMM.

[0061] When the number of line segments N ≥ 2, the voltage and current at the beginning of the second and above lines are calculated based on the voltage and current U1 and I1 at the beginning of the first line and the line impedance calculated in the segmented line modeling step. When calculating the current and voltage at the beginning of each line of two or more sections, the corresponding different modeling impedances are used for calculation according to the line length, and the line impedance adjustment coefficient Z1 is introduced. i _k:

[0062] When the line length is l i For short lines less than 80 km, Z1 i _k=1,

[0063] U i =U i –I i *Z1i-1_new

[0064] I i =I i ;

[0065] When the line length is l i For medium-length lines greater than or equal to 80km and less than 300km,

[0066] Z1 i-1 _k=(Z1 i-1 *IMM+Z1 i-1 *F1tI0*K0_mean) / (IMM*Z1 i-1 / l i-1 );

[0067] U i =(1+Z1 i-1 _new*Y1 i-1 _new / 2)*U i -I i *Z1 i-1 _new*Z1 i-1 _k

[0068] I i =(1+Z1 i-1 _new*Y1 i-1 _new / 2)*I i -(Y1 i-1 _new+Z1 i-1 _new*Y1 i-1 _new*Y1 i-1 _new / 4)*U i ;

[0069] When the line length is l i For long-distance lines greater than or equal to 300 km,

[0070] Calculate the line characteristic impedance Zc i-1 =sqrt(Z1 i-1 _new / Y1 i-1 _new);

[0071] Electromagnetic wave propagation coefficient Υ i-1 =sqrt(Z1 i-1 _new / Y1 i-1 _new);

[0072] U i =U i *cosh(Υ i-1 *l i-1 )-Zc i-1 *I i*sinh(Υ i-1 *l i-1 ) / Z1 i-1 _k

[0073] I i =I i *cosh(Υ i-1 *l i-1 )-U i *sinh(Υ i-1 *l i-1 ) / Z ci-1 ;

[0074] Among them, sqrt() is the square root function, cosh() is the hyperbolic cosine function, and sinh() is the hyperbolic sine function.

[0075] In the embodiment of the present invention, in the correction and verification step, the predicted fault distance is corrected, specifically including:

[0076] According to the fault section line fault_i obtained by the fault section analysis module and the corresponding line section starting end voltage and current U fault_i and I fault_i Predict the fault distance, use the distance measurement formula in the prediction distance step to measure the distance, and obtain the predicted fault distance x from the starting point of the fault line segment fault_i fault_i ;

[0077] Distance to fault x fault_i , make corrections, when x fault_i When the sum of the line lengths before fault_i ∑ < the total line length l, calculate the corrected zero-sequence current distribution coefficient CM0,

[0078] CM0=(ZN0+(l–Σ)*Z0 fault_i ) / ZS0,

[0079] Among them, ZNO and ZS0 represent the infinite zero-sequence impedance at the N end and the sum of the zero-sequence impedance in the zero-sequence network respectively;

[0080] Substitute the corrected zero-sequence current distribution coefficient CM0 into the distance measurement formula in the prediction distance step to calculate the corrected fault distance x', and calculate the fault distance x fault_i The difference from the corrected fault distance x':

[0081] deltax=abs(x fault_i -x'),

[0082] The calculation is repeated until deltax is less than a set minimum value. At this time, x fault_i =x' is the fault distance of this line after correction.

[0083] In the embodiment of the present invention, in the correction and verification step, whether the fault is an external fault is verified according to the corrected fault distance, which specifically includes:

[0084] When x fault_i <l fault_i and fault_i < N, the final ranging result is len = l1 + l2 + …… + l fault_i-1 +x fault_i ;

[0085] When x fault_i >l fault_i and fault_i < N, take the subsequent line fault_ii of fault_i and its initial voltage and current to perform ranging again, and obtain the ranging result x fault_ii , and judge whether x fault_ii is less than l fault_ii ,

[0086] If it is less, the ranging result is: len = l1 + l2 + …… + l fault_ii-1 +x fault_ii ;

[0087] Otherwise, continue to loop to the last line, or stop when x fault_ii <0;

[0088] If it loops to the last line N and the ranging result x N is still greater than the length l of the last line N at this time, take the previous line fault_i3 of fault_i and its initial voltage and current to perform ranging again, and obtain the ranging result x fault_i3 , and judge whether x fault_i3 is less than the corresponding line length l fault_i3 , if it is less, the ranging result is len = l1 + l2 + …… + l fault_i3-1 +x fault_i3 , otherwise continue to loop to the first line, or stop until the ranging result is less than the corresponding line length;

[0089] If the ranging result of each line above is greater than the length of this line, it is judged as an external fault.

[0090] Compared with the prior art, the method for measuring the distance of a ground fault line in an electric power system of the present invention uses a plurality of model building methods to adaptively select a suitable line model for modeling and calculation according to the line length for complex line conditions in practice, and optimizes the model according to the actual line, thereby improving the distance measurement accuracy during ground faults; according to the specific conditions of shunt reactors, capacitor compensation, transition resistance, etc. in the actual line of the electric power system, the distance measurement algorithm flow for different components is refined, so that the distance measurement algorithm calculation is more complete and rigorous, and the line distance measurement requirements are met; when calculating the fault distance, on the one hand, the stability of the distance measurement result is increased by cyclic iterative calculation according to the distance measurement result and the current distribution coefficient; on the other hand, for the out-of-area fault result, other segmented measurements are used for segment-by-segment analysis and verification, and the critical point result is corrected and then judged, thereby improving the accuracy and reliability of the distance measurement result. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 The present invention is a flowchart of a method for measuring the distance of a ground fault line in a power system according to an embodiment of the present invention.

[0092] Figure 2 yes Figure 1 Flowchart of the parameter preprocessing steps in .

[0093] Figure 3 yes Figure 1 Flowchart of the mid-range prediction step.

[0094] Figure 4 yes Figure 1 Flowchart of the fault segment analysis steps.

[0095] Figure 5 yes Figure 1 Flowchart of the initial voltage and current optimization steps in .

[0096] Figure 6 yes Figure 1 Flowchart of the steps for modeling a segmented line.

[0097] Figure 7 yes Figure 1 Flowchart of the steps for calculating the segmental current and voltage.

[0098] Figure 8 yes Figure 1 Flowchart of the correction and verification steps in . DETAILED DESCRIPTION

[0099] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0100] The implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0101] like Figure 1 As shown, in an embodiment of the present invention, a method for measuring the distance of a ground fault line in a power system is provided, which includes: a parameter preprocessing step, a prediction distance step, a fault section analysis step, an initial voltage and current optimization step, a segmented line modeling step, a segmented current and voltage calculation step, and a correction and verification step. The following are respectively described.

[0102] In the parameter preprocessing step, the impedance, admittance and zero-sequence distribution coefficient of each line segment are calculated according to the segmented line parameters.

[0103] like Figure 2 As shown, the parameter preprocessing step specifically includes:

[0104] According to the known unit parameters of each line section positive sequence resistance R1 i , zero sequence resistance R0 i , Positive sequence reactance X1 i , zero sequence reactance X0 i , positive sequence conductance G1 i 、Zero sequence conductance G0 i And positive sequence and zero sequence susceptance B1 i , BZ i , calculate the positive sequence impedance Z1 of each line section i 、Zero sequence impedance Z0 i , positive sequence admittance and zero sequence admittance Y1 i 、Y0 i , where i represents the i-th line;

[0105] Calculate the zero-sequence compensation coefficient K0 for each line section i And the average zero-sequence compensation coefficient K0_mean of all line sections:

[0106]

[0107] Where N is the number of line segments.

[0108] In the distance prediction step, the input voltage, current and current fault components are calculated based on the fault type determined by the recorder and the fault phase voltage and phase current data, and the fault distance is predicted based on the input voltage, current and current fault components.

[0109] like Figure 3 As shown, in the prediction step, first, the input voltage, current and current fault component are calculated according to the fault type determined by the recorder and the fault phase voltage and phase current data, including:

[0110] When a single-phase grounding fault occurs, the input fault phase voltage is UM = FltUα, the input fault phase current is IM = FltIα, the calculated impedance is ZM = UM / (IM + FltI0*K0_mean), the current fault component is extendI = FltIα-NmlIα, and FltI0 is the zero-sequence current;

[0111] When a two-phase grounding fault or a phase-to-phase fault occurs, the input fault voltage is UM = FltUα-FltUβ, the input fault current is IM = FltIα-FltIβ, the calculated impedance is ZM = UM / IM, and the current fault component is extendI = IM-NmlIα-NmlIβ;

[0112] When a three-phase grounding fault occurs, let a = cos240° + jsin240°, and the input voltage is UM = FltUα + a*FltUβ + a 2 *FltUγ, the input current is IM=FltIα+a*FltIβ+a 2 *FltIγ, the current fault component is extendI=IM-(NmlIα+a*NmlIβ+a 2 *NmlIγ), the impedance is calculated as ZM=UM / IM;

[0113] Among them, α, β, γ represent any one of the three phases A, B, and C respectively, and NmlIα, NmlIβ, and NmlIγ represent the normal three-phase current when there is no fault.

[0114] Then, the fault distance x is predicted based on the input voltage, current and current fault component as follows:

[0115]

[0116] in, CM0 is the zero-sequence distribution coefficient, and let CM0=complex(1,0), complex(m,n) is the complex conversion function, and complex(m,n)=m+n*j, Imag() means taking the imaginary part.

[0117] In the fault section analysis step, the faulty line section fault_i is preliminarily determined based on the fault distance, the number of line sections, the length of each line section and the total line length in the prediction step.

[0118] like Figure 4 As shown, in the embodiment of the present invention, the fault segment analysis step specifically includes:

[0119] When there is only one line section, the faulty section is the first line section, and the faulty section fault_i=1;

[0120] When there are multiple line segments, the length of the first line segment is l1, the total length of the line is l, and the total number of line segments is N.

[0121] If the predicted distance result x<l1, the fault section is the first section of the line, fault_=1;

[0122] If the predicted distance result x>l, the fault section is the last section of the line, fault_i=N;

[0123] If the prediction result x is greater than the total length of the first i-1 sections of the line and less than the total length of the first i sections of the line, the faulty section is the i-th section of the line, and fault_i=i.

[0124] In the initial voltage and current optimization step, the input voltage and current are optimized according to the fault type and specific properties of the line to obtain optimized input voltage and current.

[0125] like Figure 5 As shown, in the embodiment of the present invention, the initial voltage and current optimization step specifically includes:

[0126] If a single-phase grounding fault occurs, the optimization is divided into three cases: the line capacitor and the shunt reactor exist at the same time, the line capacitor exists only, and neither exists:

[0127] When the line capacitor and the shunt reactor exist at the same time, the capacitor current IC and the shunt reactor current IP are calculated, so that the optimized input current IMM=IM–IC–IP, and the optimized input voltage is UMM=UM-ZM*(IC+IP); on this basis, by comparing the ZM phase angle φM with the line positive sequence impedance Z1 phase angle φZ1, it is confirmed whether there is a terminal transition resistance grounding situation. If φM>0.9*φZ1, there is no transition resistance grounding at the terminal, and the input voltage and current remain unchanged; if φM≤0.9*φZ1, the terminal is grounded through a transition resistor, and UMM=UMM-UMM*FltI0 / IMM is further optimized, where,

[0128] IC=UM*(j2πω*BZ_mean*l),

[0129]

[0130] Among them, BZ_mean represents the average zero-sequence capacitance of the line, PX is the positive-sequence reactance of the shunt reactor, and PX0 represents the small reactance of the neutral point of the shunt reactor;

[0131] When there is no shunt reactor connected to the line and only line capacitance exists, the optimized input voltage and input current are UMM=UM-ZM*IC and I MM=IM–IC respectively;

[0132] When neither the line capacitor nor the shunt reactor exists, the optimized input voltage and input current are UMM=UM, I MM=IM respectively;

[0133] If a multi-phase fault occurs, the input voltage and input current do not change.

[0134] That is, UMM=UM, IMM=IM.

[0135] In the segmented line modeling step, the impedance of each segment of the line is modeled according to the line length.

[0136] like Figure 6 As shown, the segmented line modeling step performs three types of line impedance modeling by dividing the line length:

[0137] When the line is a short line with a length li less than 80km, a simplified model is used:

[0138] The line impedance is Z1 i _new=Z1 i ;

[0139] The line admittance is Y1 i _new=Y1 i ;

[0140] When the line is a medium-length line with a length li greater than or equal to 80km and less than 300km, the line is modeled using a centralized parameter modeling method;

[0141] The line impedance is Z1 i _new=Z1 i +Z1 i *Z1 i *Y1 i / 6;

[0142] The line admittance is Y1 i _new=Y1 i -Y1 i *Z1 i *Y1 i / 12;

[0143] When the line length li is greater than or equal to 300km, the long-distance π-shaped equivalent circuit model is used to build the model, and the total impedance, total reactance, and total susceptance correction coefficients Kr, Kx, and Kb of the long line are introduced.

[0144] Kr=1-X1 i *B1 i *l i *l i / 3;

[0145] Kx=1-(X1i *R1 i -R1 i *R1 i *B1 i / (X1 i )*l i *l i / 6;

[0146] Kb=1+X1 i *B1 i *l i *l i / 12;

[0147] The line impedance is Z1 i _new=R1 i *l i *Kr+jX1 i *l i *Kr;

[0148] The line admittance is Y1 i _new=B1 i *l i *R1 i *B1 i *l i *l i / 12+jB1 i *l i * Kb.

[0149] In the segmented current and voltage calculation step, the input voltage and current optimized in the initial voltage and current optimization step are used as the voltage and current at the beginning of the first line segment, and the voltage and current at the beginning of each subsequent line segment are calculated according to the impedance of each line segment.

[0150] like Figure 7 As shown, in the embodiment of the present invention, the segmented current and voltage calculation step specifically includes:

[0151] The input voltage and current UMM and IMM are used as the voltage and current at the beginning of the first line section, that is, U1 = UMM, I1 = IMM.

[0152] When the number of line segments N ≥ 2, the voltage and current at the beginning of the second and above lines are calculated based on the voltage and current U1 and I1 at the beginning of the first line and the line impedance calculated in the segmented line modeling step. When calculating the current and voltage at the beginning of each line of two or more sections, the corresponding different modeling impedances are used for calculation according to the line length, and the line impedance adjustment coefficient Z1 is introduced. i _k:

[0153] When the line length is l i For short lines less than 80 km, Z1i _k=1,

[0154] U i =U i –I i *Z1 i-1_new

[0155] I i =I i ;

[0156] When the line is a medium-length line with a length li greater than or equal to 80km and less than 300km,

[0157] Z1 i-1 _k=(Z1 i-1 *IMM+Z1 i-1 *F1tI0*K0_mean) / (IMM*Z1 i-1 / l i-1 );

[0158] U i =(1+Z1 i-1 _new*Y1 i-1 _new / 2)*U i -I i *Z1 i-1 _new*Z1 i-1 _k

[0159] I i =(1+Z1 i-1 _new*Y1 i-1 _new / 2)*I i -(Y1 i-1 _new+Z1 i-1 _new*Y1 i-1 _new*Y1 i-1 _new / 4)*U i ;

[0160] When the line is a long-distance line with a length li greater than or equal to 300 km,

[0161] Calculate the line characteristic impedance Zc i-1 =sqrt(Z1 i-1 _new / Y1 i-1 _new);

[0162] Electromagnetic wave propagation coefficient Υ i-1 =sqrt(Z1 i-1 _new / Y1 i-1 _new);

[0163] U i =U i*cosh(Υ i-1 *l i-1 )-Zc i-1 *I i *sinh(Υ i-1 *l i-1 ) / Z1 i-1 _k

[0164] I i =I i *cosh(Υ i-1 *l i-1 )-U i *sinh(Υ i-1 *l i-1 ) / Zc i-1 ;

[0165] Among them, sqrt() is the square root function, cosh() is the hyperbolic cosine function, and sinh() is the hyperbolic sine function.

[0166] In the correction and verification step, the predicted fault distance is corrected according to the determined fault section and the initial voltage and current of each line section, and whether the fault is an out-of-zone fault is verified according to the corrected fault distance.

[0167] like Figure 8 As shown, in the embodiment of the present invention, in the correction and verification step, the predicted fault distance is corrected, specifically including:

[0168] According to the fault section line fault_i obtained by the fault section analysis module and the corresponding line section starting end voltage and current U fault_i and I fault_i Predict the fault distance, use the distance measurement formula in the prediction distance step to measure the distance, and obtain the predicted fault distance x from the starting point of the fault line segment fault_i fault_i ;

[0169] Distance to fault x fault_i , make corrections, when x fault_i When the sum of the line lengths before fault_i ∑ < the total line length l, calculate the corrected zero-sequence current distribution coefficient CM0,

[0170] CM0=(ZN0+(l–Σ)*Z0 fault_i ) / ZS0,

[0171] Among them, ZNO and ZS0 represent the infinite zero-sequence impedance at the N end and the sum of the zero-sequence impedance in the zero-sequence network respectively;

[0172] Substitute the corrected zero-sequence current distribution coefficient CM0 into the distance measurement formula in the prediction distance step to calculate the corrected fault distance x', and calculate the fault distance xfault_i The gap from the corrected fault distance x':

[0173] deltax = abs(x fault_i - x'),

[0174] Calculate cyclically until deltax is less than a set minimum value. At this time, x fault_i = x' is the fault distance after correction for this section of the line.

[0175] Furthermore, as Figure 8 shown, in the embodiment of the present invention, in the correction and verification steps, it is verified whether the fault is an out-of-zone fault according to the corrected fault distance, specifically including:

[0176] When x fault_i < l fault_i and fault_i < N, the final ranging result is len = l1 + l2 + …… + l fault_i - 1 + x fault_i ;

[0177] When x fault_i > l fault_i and fault_i < N, take the next section of the line fault_ii after fault_i and its initial voltage and current to perform ranging again, and obtain the ranging result x fault_ii , and judge whether x fault_ii is less than l fault_ii ,

[0178] If it is less, the ranging result is: len = l1 + l2 + …… + l fault_ii-1 + x fault_ii ;

[0179] Otherwise, continue to loop to the last section of the line, or stop when x fault_ii < 0;

[0180] If it loops to the last section of the line N and the ranging result x N is still greater than the length l of the last section of the line N at this time, take the previous section of the line fault_i3 before fault_i and its initial voltage and current to perform ranging again, and obtain the ranging result x fault_i3 , and judge whether x fault_i3 is less than the corresponding line length l fault_i3 , if it is less, the ranging result is len = l1 + l2 + …… + l fault_i3-1 + x fault_i3 , otherwise continue to loop to the first section of the line, or stop until the ranging result is less than the corresponding section of the line length;

[0181] If the distance measurement results of each line section mentioned above are greater than the length of the line section, it is judged as an out-of-area fault.

[0182] In summary, the method for measuring the distance of a ground fault line in a power system of the present invention is adopted. For complex line conditions in practice, the line length and parameters are not uniform. A plurality of model establishment methods are used. According to the line length, a suitable line model is adaptively selected for modeling and calculation, and the model is optimized according to the actual line, so as to improve the distance measurement accuracy during ground faults. According to the specific conditions of the shunt reactor, capacitor compensation, transition resistance, etc. in the actual line of the power system, the distance measurement algorithm flow for different components is refined to make the distance measurement algorithm calculation more complete and rigorous, and meet the line distance measurement requirements. When calculating the fault distance, on the one hand, the stability of the distance measurement result is increased by cyclic iterative calculation according to the distance measurement result and the current distribution coefficient. On the other hand, for the fault result outside the measured area, other segmented measurements are used for segment-by-segment analysis and verification, and the critical point result is corrected and then judged, so as to improve the accuracy and reliability of the distance measurement result.

[0183] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring the distance of a ground fault line in a power system, characterized in that: include: Predicting distance step: Calculate input voltage, current and current fault component according to the fault type determined by the recorder and the fault phase voltage and phase current data, and predict the fault distance according to the input voltage, current and current fault component; Fault section analysis step: preliminarily determine the faulty line section according to the fault distance, number of line sections, length of each line section and total line length in the prediction distance step; Initial voltage and current optimization step: optimize the input voltage and current according to the fault type and specific properties of the line to obtain the optimized input voltage and current; Segmented Line Modeling Steps: Select different line models for modeling according to different line lengths; Segmented current and voltage calculation steps: using the optimized input voltage and current as the voltage and current at the beginning of the first segment of the line, and calculating the voltage and current at the beginning of each subsequent segment of the line according to the impedance of each segment of the line; Correction and verification steps: recalculate the zero-sequence compensation coefficient based on the determined fault section, fault distance and the initial voltage and current of each line section, further correct the fault distance, and verify whether the fault is an out-of-zone fault based on the corrected fault distance.

2. The method for measuring the distance of a ground fault line in a power system according to claim 1, characterized in that: Before the predictive distance step, it also includes: Parameter preprocessing steps, which include: According to the known unit parameters of each line section positive sequence resistance R1 i , zero sequence resistance R0 i , Positive sequence reactance X1 i , zero sequence reactance X0 i , positive sequence conductance G1 i 、Zero sequence conductance G0 i And positive sequence and zero sequence susceptance B1 i , BZ i , calculate the positive sequence impedance Z1 of each line section i 、Zero sequence impedance Z0 i , positive sequence admittance and zero sequence admittance Y1 i 、Y0 i , where i represents the i-th line; Calculate the zero-sequence compensation coefficient K0 for each line section i And the average zero-sequence compensation coefficient K0_mean of all line sections: Where N is the number of line segments.

3. The method for measuring the distance of a ground fault line in a power system according to claim 2, characterized in that: In the predictive distance step, the input voltage, current and current fault component are calculated according to the fault type determined by the recorder and the fault phase voltage and phase current data, including: When a single-phase grounding fault occurs, the input fault phase voltage is UM = FltUα, the input fault phase current is IM = FltIα, the calculated impedance is ZM = UM / (IM + FltI0*K0_mean), the current fault component is extendI = FltIα-NmlIα, and FltI0 is the zero-sequence current; When a two-phase grounding fault or a phase-to-phase fault occurs, the input fault voltage is UM = FltUα-FltUβ, the input fault current is IM = FltIα-FltIβ, the calculated impedance is ZM = UM / IM, and the current fault component is extendI = IM-NmlIα-NmlIβ; When a three-phase grounding fault occurs, let a = cos240° + jsin240°, and the input voltage is UM = FltUα + a*FltUβ + a 2 *FltUγ, the input current is IM=FltIα+a*FltIβ+a 2 *FltIγ, the current fault component is extendI=IM-(NmlIα+a*NmlIβ+a 2 *NmlIγ), the impedance is calculated as ZM=UM / IM; In the above formula, α, β, γ represent any one of the three phases A, B, and C respectively, and NmlIα, NmlIβ, and NmlIγ represent the normal three-phase current when there is no fault.

4. The method for measuring the distance of a ground fault line in a power system according to claim 3, characterized in that: In the distance prediction step, the formula for predicting the fault distance x according to the input voltage, current and current fault component includes: in, CM0 is the zero-sequence distribution coefficient, and let CM0=complex(1,0), complex(m,n) is the complex conversion function, and complex(m,n)=m+n*j, Imag() means taking the imaginary part.

5. The method for measuring the distance of a ground fault line in a power system according to claim 1, characterized in that: In the fault section analysis step, the line section fault_i where the fault occurs is preliminarily determined according to the predicted fault distance, the number of line sections, the length of each line section and the total length of the line, including: When there is only one line section, the faulty section is the first line section, fault_i=1; When the number of line segments is N (N ≥ 2), the length of the first line segment is l1, and the total length of the line is l. If the predicted distance result x<l1, the fault section is the first section of the line, fault_=1; If the predicted distance result x>l, the fault section is the last section of the line, fault_i=N; If the prediction result x is greater than the total length of the first i-1 sections of the line and less than the total length of the first i sections of the line, the faulty section is the i-th section of the line, and fault_i=i.

6. The method for measuring the distance of a ground fault line in a power system according to claim 4, characterized in that: In the initial voltage and current optimization step, the input voltage and current are optimized according to the fault type and the specific properties of the line to obtain the optimized input voltage and current, including: If a single-phase grounding fault occurs, the optimization is divided into three cases: the line capacitor and the shunt reactor exist at the same time, the line capacitor exists only, and neither exists: When the line capacitor and the shunt reactor exist at the same time, the capacitor current IC and the shunt reactor current IP are calculated, so that the optimized input current IMM=IM–IC–IP, and the optimized input voltage is UMM=UM-ZM*(IC+IP); on this basis, by comparing the ZM phase angle φM with the line positive sequence impedance Z1 phase angle φZ1, it is confirmed whether there is a terminal transition resistance grounding situation. If φM>0.9*φZ1, there is no transition resistance grounding at the terminal, and the input voltage and current remain unchanged; if φM≤0.9*φZ1, the terminal is grounded through a transition resistor, and UMM=UMM-UMM*FltI0 / IMM is further optimized, where, IC=UM*(j2πω*BZ_mean*l), Among them, BZ_mean represents the average zero-sequence capacitance of the line, PX is the positive-sequence reactance of the shunt reactor, and PX0 represents the small reactance of the neutral point of the shunt reactor; When there is no shunt reactor connected to the line and only line capacitance exists, the optimized input voltage and input current are UMM=UM-ZM*IC and IMM=IM-IC respectively; When neither the line capacitor nor the shunt reactor exists, the optimized input voltage and input current are UMM=UM and IMM=IM respectively; If a multi-phase fault occurs, the input voltage and input current do not change. That is, UMM=UM, IMM=IM.

7. The method for measuring the distance of a ground fault line in a power system according to claim 4, characterized in that: The segmented line modeling step comprises: When the line length is l i For short lines less than 80 km, a simplified model is used: The line impedance is Z1 i _new=Z1 i ; The line admittance is Y1 i _new=Y1 i ; When the line length is l i For medium-length lines greater than or equal to 80 km and less than 300 km, centralized parameter modeling is used to model the line; The line impedance is Z1 i _new=Z1 i +Z1 i *Z1 i *Y1 i / 6; The line admittance is Yl i _new=Y1 i -Y1 i *Z1 i *Y1 i / 12; When the line length l i When the distance is greater than or equal to 300 km, the long-distance π-shaped equivalent circuit model is used for modeling, and the total impedance, total reactance, and total susceptance correction coefficients Kr, Kx, and Kb of the long line are introduced. Kr=1-X1 i *B1 i *1 i *1 i / 3; Kx=1-(X1 i *B1 i -R1 i *R1 i *B1 i / X1 i )*l i *l i / 6; Kb=1+X1 i *B1 i *L i *L i / 12; The line impedance is Z1 i _new=R1 i *l i *Kr+jX1 i *l i *Kr; The line admittance is Y1 i _new=B1 i *l i *R1 i *B1 i *l i *l i / 12+jB1 i *l i * Kb.

8. The method for measuring the distance of a ground fault line in a power system according to claim 7, characterized in that: The segmented current and voltage calculation step specifically includes: The input voltage and current UMM and IMM are used as the voltage and current at the beginning of the first line section, that is, U1 = UMM, I1 = IMM. When the number of line segments N ≥ 2, the voltage and current at the beginning of the second and above lines are calculated based on the voltage and current U1 and I1 at the beginning of the first line and the line impedance calculated in the segmented line modeling step. When calculating the current and voltage at the beginning of each line of two or more sections, the corresponding different modeling impedances are used for calculation according to the line length, and the line impedance adjustment coefficient Z1 is introduced. i _k: When the line length is l i For short lines less than 80 km, Z1 i _k=1, U i =U i -l i *Z1 i-1_new I i =I i ; When the line length is l i For medium-length lines greater than or equal to 80km and less than 300km, Z1 i-1 _k=(Z1 i-1 *IMM+Z1 i-1 *FltI0*K0_mean) / (IMM*Z1 i-1 / l i-1 ); U i =(1+Z1 i-1 _new*Y1 i-1 _new / 2)*U i -I i *Z1 i-1 _new*Z1 i-l _k I i =(1+Z1 i-1 _new*Y1 i-1 _new / 2)*I i -(Y1 i-1 _new+Z1 i-1 _new*Y1 i-1 _new*Y1 i-1 _new / 4)*U i ; When the line length is l i For long-distance lines greater than or equal to 300 km, Calculate the line characteristic impedance Zc i-1 =sqrt(Z1 i-l _new / Y1 i-1 _new); Electromagnetic wave propagation coefficient γ i-1 =sqrt(Z1 i-1 new / Y1 i-1 _new); U i =U i *cosh(γ i-1 *l i-1 )-Zc i-1 *I i *birth(γ) i-1 *l i-1 )*Z1 i-1 _k I i =I i *cosh(γ i-1 *l i-1 )-U i *birth(γ) i-1 *l i-1 ) / Zc i-1 ; Among them, sqrt() is the square root function, cosh() is the hyperbolic cosine function, and sinh() is the hyperbolic sine function.

9. The method for measuring the distance of a ground fault line in a power system according to claim 8, characterized in that: In the correction and verification step, the predicted fault distance is corrected, specifically including: According to the fault section line fault_i obtained by the fault section analysis module and the corresponding line section starting end voltage and current U fault_i and I fault_i Predict the fault distance, use the distance measurement formula in the prediction distance step to measure the distance, and obtain the predicted fault distance x from the starting point of the fault line segment fault_i fault_i ; Distance to fault x fault_i , make corrections, when x fault_i When the sum of the line lengths before fauIt_i is less than the total line length l, the corrected zero-sequence current distribution coefficient CMO is calculated. CMO=(ZNO+( / -Σ)*ZO fault_i ) / ZSO, Among them, ZNO and ZSO represent the infinite zero-sequence impedance at the N end and the sum of the zero-sequence impedance in the zero-sequence network respectively; Substitute the corrected zero-sequence current distribution coefficient CMO into the distance measurement formula in the prediction distance step to calculate the corrected fault distance x', and calculate the fault distance x fault_i The difference from the corrected fault distance x': deltax=abs(x fault_i -x’), The calculation is repeated until deltax is less than a set minimum value. At this time, x fault_i =x' is the fault distance of this line after correction.

10. The method for measuring the distance of a ground fault line in a power system according to claim 9, characterized in that: In the correction and verification step, whether the fault is an out-of-area fault is verified according to the corrected fault distance, specifically including: When x fault_i <l fault_i and when fault_i < N, the final ranging result is len = l1 + l2 + …… + l fault_i-1 + x fault_i ; When x fault_i > l fault_i and when fault_i < N, take the subsequent line segment fault_ii of fault_i and its initial voltage and current for further distance measurement to obtain the distance measurement result x fault_ii , and judge x fault_ii whether it is less than l fault_ii , If it is less than, the distance measurement result is: len = l1 + l2 + ... + l fault_ii-1 +x fault_ii ; Otherwise, continue looping to the last line, or x fault_ii Stop when <0; If the loop reaches the last section of route N, and the distance measurement result is x N Still greater than the last line length l N When fault_i is reached, the voltage and current of the previous line fault_i3 and its starting point are taken for distance measurement, and the distance measurement result x is obtained. fault_i3 , judge x fault_i3 Is it less than the corresponding line length l? fault_i3 If it is less than, the distance measurement result is len=l1+l2+……+l fault_i3-1 +x fault_i3 , otherwise continue to loop to the first section of the line, or until the distance measurement result is less than the length of the corresponding section of the line; If the distance measurement results of each section of the line mentioned above are greater than the length of the line section, it is judged to be an out-of-area fault.

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