CN115932461A - Power transmission line fault positioning method - Google Patents
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Abstract
The invention discloses a power transmission line fault positioning method which comprises the following steps of dividing a power transmission line into a plurality of sections and acquiring the length of each section; whether a fault exists in the broken section; accurately positioning a fault section by adopting a distributed parameter line model to cause a fault; the invention has excellent fault positioning performance under different fault conditions and high accuracy.
Description
Technical Field
The invention relates to the technical field of electric power, in particular to a power transmission line fault positioning method.
Background
The transmission line is used as a main medium for electric energy transmission, is an important component of the operation of the whole power system, and the normal operation of the transmission line is the key for ensuring the safe and stable operation of the whole power system. After a short-circuit fault occurs in a power transmission line in an electric power system, a fault point needs to be searched by means of a fault positioning technology, so that the fault point is repaired in time, and the reliability of power supply of a power grid is guaranteed.
In the prior art, a signal injection method or a traveling wave method is often used for fault location, wherein when the signal injection method is used, detection along the line needs to be manually carried out by holding detection equipment, the operation is complex, time and labor are wasted, and the method cannot be used for a power transmission line with a complex structure; when the traveling wave method is used for fault location of the power transmission line, the transient process time of fault traveling waves is short, but the power of the traveling waves can still reach a value of several Megajoules (MJ). For an actual power transmission line, due to the influence of factors such as wire series resistance, skin effect, dielectric loss, leakage current, corona loss and transition resistance, the waveform of a traveling wave is attenuated to a certain extent in the transmission process, the energy of the traveling wave is reduced, the wave front gradient is slowed down, the overall shape of the wave is elongated, the line loss causes the phenomena of amplitude attenuation, waveform distortion and the like in the transmission process of the traveling wave, and the accuracy is low.
Disclosure of Invention
The technical problem solved by the invention is as follows: the fault positioning accuracy is low, and the invention provides the power transmission line fault positioning method which has excellent fault positioning performance and high accuracy under different fault conditions.
In order to solve the technical problems, the invention provides the following technical scheme: a method for locating a fault of a power transmission line comprises the following steps,
dividing the power transmission line into a plurality of sections, and acquiring the length of each section;
judging a section where a fault point is located;
and accurately positioning the fault section by adopting a distributed parameter line model.
As an optimal scheme of the power transmission line fault positioning method of the invention, the method comprises the following steps: the specific steps for determining whether a segment has a fault are,
after the system detects the occurrence of the ground fault, a fault phase is selected according to a phase voltage change rule, and the fault time t is determined according to the phase voltage mutation time f ；
Selection detection device [ t ] f －0.02s,t f +0.02s]The waveform data of the fault phase current of 2N' points in the interval is calculated according to the definition of differential offset degree, diff is calculated, and A is calculated according to the definition of current mutation rate I ；
If diff > diff set Setting the differential offset flag bit to 1, otherwise setting 0 if A I ＞A Iset Setting the flag bit of the current burst rate to be 1, otherwise setting the flag bit of the current burst rate to be 0;
performing OR operation on the two zone bits, if the operation result is 1, indicating that at least one fault section judgment condition is met, judging the fault section as a fault section, otherwise, judging the fault section as a non-fault section;
wherein, diff set Is an artificially set differential offset threshold.
As a preferred scheme of the power transmission line fault positioning method of the present invention, wherein: the differential offset is calculated by the formula,
Δi 1A (n)＝i 1A (n)-i 1A (n-N′)
Δi 2A (n)＝i 2A (n)-i 2A (n-N′)；
wherein i 1A (n)、i 2A (n) phase current sampling sequence of adjacent detection points, Δ i 1A(n) And Δ i 2A(n) Respectively the phase current variation of adjacent detection points, A is the section current mutation rate, N 'is a period sampling point, N belongs to [0, N' -1 ]]。
As an optimal scheme of the power transmission line fault positioning method of the invention, the method comprises the following steps: segment current mutation rate A I The formula for calculating (a) is as follows,
A I ＝ΔI A,after /ΔI A,before ；
wherein the content of the first and second substances,
Δi A (n)＝i A (n)-i A (n-N′)；
wherein N ∈ [ -N ', N']，Δi A(n) For phase current difference, Δ I, in adjacent detection points A before Effective value of current difference before fault occurrence, delta I A after The current difference effective value after the fault occurs.
As an optimal scheme of the power transmission line fault positioning method of the invention, the method comprises the following steps: the method comprises the steps of adopting multi-terminal PMU data to carry out accurate fault positioning, setting nodes N and R at two ends of a distribution parameter circuit respectively, and setting N-1 nodes P between the nodes N and R on the circuit 1 ～P N-1 。
As an optimal scheme of the power transmission line fault positioning method of the invention, the method comprises the following steps: the distributed parameter line model is that,
wherein, the first and the second end of the pipe are connected with each other,
is a branch point P K A current vector flowing to the R terminal->
For N-terminal flow to branch point P K The vector of the current of (a) is,
for node K to flow to branch point P K The current vector of (2).
As an optimal scheme of the power transmission line fault positioning method of the invention, the method comprises the following steps: the step of adopting multi-terminal PMU data to carry out fault accurate positioning is specifically,
selecting a reference node for equivalent two-end fault location, selecting any bus node in the power grid as a reference node R of a two-end fault location algorithm, and defining a node adjacent to the reference node as a branch point P 1 ；
According to the reference node R and the branch point P 1 Defining a unit length L R ；
Respectively and sequentially equating the voltage and current phasors of the N bus nodes to a branch point P 1 In the above, N groups of equivalent voltage and current phasors can be obtained correspondingly, with x = DL R To determine the fault distance, and generating N fault indexes D with another reference node R by the double-end fault location algorithm K (K＝1～N)；
Wherein D is k Is the failure index of the kth node.
As an optimal scheme of the power transmission line fault positioning method of the invention, the method comprises the following steps: the fault index of the kth node is calculated by the formula,
wherein N is K And M K Respectively, are as follows,
wherein the content of the first and second substances,
is a voltage vector of the reference node R, <' >>
Is the voltage vector of the Pk node, x is the distance between the fault point and the terminal R, Z c Is the wave impedance or characteristic impedance of a distributed parameter line, the value of which is defined as->
γ is the propagation coefficient of a line of a distribution parameter whose value is defined as +>
In the formula, the real part beta is an attenuation coefficient, and the imaginary part alpha is a phase coefficient.
As an optimal scheme of the power transmission line fault positioning method of the invention, the method comprises the following steps: when 0 < D K If < 1 (K =1 to N), P 1 R Branch fails, and D 1 ＝D 2 ＝…＝D N And the distance between the fault point and the R end is x = D 1 L R ＝…＝D N L R ；
When D is present 1 ＜…＜D K ＞D K+1 ＞…＞D N When is, P K The branch circuit of K (K = 1-N-1) is in fault, and the distance between a fault point and the R end is x = D K L R ；
When D is present 1 ＜…＜D K ＜D K+1 ＝…＝D N When is, P K ～P K+1 (K = 1-N-2) branch circuit is in fault, and the distance between fault points and R end is x = D K+1 L R ＝…＝D N L R ；
When D is present 1 ＜…＜D K ＜…＜D N-1 ＜D N When is, P N-1 N is in fault, and the distance between a fault point and an R end is x = D N L R 。
The invention has the beneficial effects that: the invention can obviously detect the fault section; the invention can realize accurate fault positioning with error lower than 1% under different fault conditions.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise. Wherein:
fig. 1 is a schematic block diagram of fault location in the present invention.
Fig. 2 is a diagram of a multi-port fault network of the present invention.
Fig. 3 is a waveform diagram of the variation of the ground fault along the line current in the present invention.
Fig. 4 is a waveform diagram of a current difference in the section (1) before and after occurrence of a fault when the fault timing is set to 0.7s, that is, when the fault angle is 0 °.
Fig. 5 is a waveform diagram of a current difference in the sections (2) before and after the occurrence of a fault when the fault time is set to 0.7s, that is, when the fault angle is 0 °.
Fig. 6 is a waveform diagram of a current difference in the section (3) before and after the occurrence of a fault when the fault timing is set to 0.7s, that is, when the fault angle is 0 °.
Fig. 7 is a waveform diagram of a ground fault along a line current variation in the present invention.
Fig. 8 is a waveform diagram of a current difference in the section (1) before and after the occurrence of a fault when the fault time is set to 0.505s, that is, when the fault angle is 90 °.
Fig. 9 is a waveform diagram of a current difference in the section (2) before and after the occurrence of a fault when the fault time is set to 0.505s, that is, when the fault angle is 90 °.
Fig. 10 is a waveform diagram of a current difference in the section (3) before and after the occurrence of a fault when the fault time is set to 0.505s, that is, when the fault angle is 90 °.
FIG. 11 is a five-terminal fault model diagram of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Example 1
Referring to fig. 1 and 2, a first embodiment of the present invention provides a method for locating a fault in a power transmission line, which can accurately locate the fault in the power transmission line and has high locating efficiency.
A power transmission line fault positioning method comprises the following steps:
(S1) dividing the power transmission line into a plurality of sections, and acquiring the length of each section;
(S2) judging whether the section has a fault or not;
and (S3) accurately positioning the fault section by adopting a distributed parameter line model.
In the step (S2), the specific step of judging whether the section has a fault is that,
(S201) after the system detects the occurrence of the ground fault, selecting a fault phase according to a phase voltage change rule, and determining a fault time t according to a phase voltage mutation time f ；
(S202) selecting a detecting device [ t ] f －0.02s,t f +0.02s]The fault phase current waveform data of 2N points in the interval is calculated according to the definition of differential offset degree, diff is calculated, and A is calculated according to the definition of current mutation rate I ；
The differential offset is calculated by the formula,
Δi 1A (n)＝i 1A (n)-i 1A (n-N′)
Δi 2A (n)＝i 2A (n)-i 2A (n-N′)；
segment current mutation rate A I The formula for calculating (a) is as follows,
A I ＝ΔI A,after /ΔI A,before ；
wherein the content of the first and second substances,
Δi A (n)＝i A (n)-i A (n-N′)；n∈[-N′，N′]；
(S203) if diff > diff set Setting the differential offset flag bit to 1, otherwise setting 0, if A I ＞A Iset Setting the current mutation rate flag bit to be 1, otherwise setting the current mutation rate flag bit to be 0;
(S204) carrying out OR operation on the two zone bits, if the operation result is 1, indicating that at least one fault section judgment condition is met, judging the fault section as a fault section, otherwise, judging the fault section as a non-fault section;
wherein, diff set For artificially set differential offset threshold value, i 1A (n)、i 2A (n) phase current sampling sequence of adjacent detection points, Δ i 1A(n) And Δ i 2A(n) Respectively the phase current variable quantity of adjacent detection points, A is the section current catastrophe rate, N 'is a period sampling point, N belongs to [0, N' -1 ]]；Δi A(n) For phase current difference, Δ I, in adjacent detection points A before Effective value of current difference before fault occurrence, delta I A after And the current difference is an effective value after the fault occurs.
In step (S3), multi-terminal PMU data is adoptedThe accurate positioning of line faults is realized by setting two ends of a distribution parameter line as nodes N and R respectively, wherein the line between the nodes N and R is provided with N-1 nodes which are P respectively 1 ～P N-1 ；
The steps of using multi-terminal PMU data to perform accurate fault location (see fig. 1 and 2) are specifically,
(S301) selecting an equivalent two-end fault positioning reference node, selecting any bus node in the power grid as a reference node R of a two-end fault positioning algorithm, and defining the adjacent node as a branch point P 1 ；
(S302) according to the reference node R and the branch point P 1 Defining a unit length L R ；
(S303) respectively and sequentially equating the voltage and current phasors of the N bus nodes to a branch point P 1 In the above, N groups of equivalent voltage and current phasors can be obtained correspondingly, with x = DL R To determine the fault distance, and generating N fault indexes D with another reference node R by the double-end fault positioning algorithm K (K＝1～N)；
The fault index of the kth node is calculated by the formula,
N K and M K Respectively, are as follows,
wherein D is k The fault index of the kth node;
is a voltage vector of a reference node R>
Is the voltage vector of the Pk node, x is the distance between the fault point and the end point R, Z c Is the wave impedance or characteristic impedance of a distributed parameter line, the value of which is defined as +>
Gamma is the propagation coefficient of the distributed parameter line, and its value is defined as
In the formula, the real part beta is an attenuation coefficient, and the imaginary part alpha is a phase coefficient.
In order to further realize accurate positioning of the fault, when 0 < D K If < 1 (K =1 to N), P 1 R Branch fails, and D 1 ＝D 2 ＝…＝D N And the distance between the fault point and the R end is x = D 1 L R ＝…＝D N L R ；
When D is present 1 ＜…＜D K ＞D K+1 ＞…＞D N When is, P K The branch circuit of K (K = 1-N-1) is in fault, and the distance between a fault point and the R end is x = D K L R ；
When D is present 1 ＜…＜D K ＜D K+1 ＝…＝D N When P is present K ～P K+1 (K = 1-N-2) branch is failed, and the fault point is x = D away from R end K+1 L R ＝…＝D N L R ；
When D is present 1 ＜…＜D K ＜…＜D N-1 ＜D N When is, P N-1 N is in fault, and the distance between a fault point and an R end is x = D N L R 。
Example 2
Referring to fig. 3 to 11, a method for locating a fault of a power transmission line is provided for a second embodiment of the present invention, so as to verify and explain technical effects adopted in the method.
The fault is arranged on the section (2), the sampling frequency is 4kHz, the action time limit of the arc suppression device is 0.04s, and the conditions of the fault angle of 0 degrees and 90 degrees are subjected to simulation analysis respectively.
1) The fault time is set to 0.7s, i.e. the fault angle is 0 ° (fault occurs at phase voltage zero crossing).
Three-phase currents at detection points I-VI along the line are measured, the current variation is calculated, the type of the arc suppression coil is a preset type, and the waveform of the current variation at each detection point when the grounding transition resistance is 500 omega is shown in fig. 3.
As can be seen from fig. 3, the waveforms of the detection point IV and the detection point V are relatively similar, the waveforms of the detection point VI and the detection point VII are relatively similar, and the waveforms of the detection point V and the detection point VI are very different, and the phase difference is substantially 180 °.
In consideration of the fact that the device has a certain delay in determining the fault, when the fault occurrence time is determined to be 0.71s (there is a delay of 0.01 s), the current difference waveforms before and after the fault occurrence of each section of the fault phase are as shown in fig. 4 to 6.
As can be seen from fig. 4 to 6, the transient high frequency component appears at the peak position of the current difference, the amplitude of the current difference between the sections (1) and (3) is reduced after the fault occurs, and the amplitude of the current difference between the section (2) is obviously increased after the fault occurs, which is consistent with the theoretical analysis.
Different fault conditions are set, differential offset degrees of the sections (1) to (3) are calculated according to formulas, and the result is shown in table 1, wherein the differential offset degree of the section (2) is larger than 1 (threshold value), the current mutation rate is larger than 1 (threshold value), and the section (2) is judged to be in fault.
TABLE 1 simulation result of single-phase earth fault when fault angle is 0 deg
As can be seen from table 1, when the failure angle is 0 °, the failure zone can be detected significantly by the method for the transition resistance range of 100 Ω to 2k Ω.
2) The fault time is set to 0.505s, i.e. the fault angle is 90 ° (fault occurs at phase voltage peak).
The fault currents at the points I to VI along the line are measured, and the current variation is calculated, with the waveform shown in fig. 7.
As can be seen from fig. 7, the waveforms of the variation of the four detection points are the same as the rule when the fault angle is 0 °, and it can be seen that the positioning method is not affected by the size of the fault angle.
Considering that the device has a certain delay in determining the fault, when the fault occurrence time is determined to be 0.71s (there is a delay of 0.01 s), the waveforms of the current difference in one cycle before and after the fault occurrence in each section of the fault phase are shown in fig. 8 to 10.
As can be seen from fig. 8 to 10, the current difference of the sections (1) and (3) has a reduced amplitude after the occurrence of the fault, while the current difference of the section (2) has a significantly increased amplitude after the occurrence of the fault, which is consistent with the fault angle of 0 °.
Different fault conditions are set, the differential offset degrees of the sections (1) - (3) are calculated according to a formula, and the result is shown in table 2, wherein the differential offset degree of the section (2) is greater than 1 (threshold), the current mutation rate is greater than 1 (threshold), and the section (2) is judged to be in fault.
TABLE 2 simulation results of single-phase earth faults at fault angle of 90 °
As can be seen from table 2, when the fault angle is 90 °, the fault section can be also detected significantly by the method for the transition resistance range of 100 Ω to 2k Ω.
In summary, the method for determining whether a fault exists in a segment in the invention is applicable to various fault conditions, and has clear characteristics when grounded at high resistance, good sensitivity and reliability, and is not affected by the type of arc suppression coil.
The method comprises the steps of building a five-terminal power distribution network fault model in PSCAD software, carrying out a large amount of simulation calculation, setting different fault distances according to different short-circuit fault types (single-phase earth fault, two-phase short-circuit earth fault, three-phase short-circuit fault and the like), obtaining simulation waveform data (simulation PMU information) of each node, applying the multi-terminal fault positioning algorithm provided by the method in MATLAB software to analyze and process the simulation data, and achieving fault positioning. The voltage class of the fault model is unified by 10kV, the frequency is 50Hz, a circuit is built by adopting distributed parameters, and relevant parameters of each element in the fault model are shown in table 3. The sampling frequency is 20000Hz (400 samples per cycle) and a full-cycle Discrete Fourier Transform (DFT) is applied to estimate the fundamental phasor.
TABLE 3 parameters of each element in the five-terminal Fault model
Simulation research is carried out by setting different fault types at different fault points, and the error of a fault positioning algorithm is defined as follows:
to prove the correctness of the fault localization algorithm proposed herein, 7 faults were set, and different fault types and fault resistances were set. As can be seen from table 4, the faults in 7 typical cases can be accurately located, and even in the case of a fault resistance of 5 kilo-ohms (i.e., a high-impedance fault), the four fault indexes can still accurately locate the faults. Therefore, the algorithm is not influenced by the size of the fault resistance and is very suitable for the field of distribution networks.
TABLE 4 accurate positioning results of faults
The application carries out a large number of simulation tests on the proposed multi-terminal fault positioning method, wherein different fault distances are set in different fault areas, and about 600 tests are carried out on various possible conditions such as different fault types, fault resistances and fault occurrence angles. The fault pinpoint statistics of the present method are shown in table 5. As can be seen from table 5, the accurate fault location algorithm proposed herein exhibits excellent fault location performance under different fault conditions, the determination of the fault area reaches 100%, and the average fault location error under various fault conditions is much lower than 1%.
TABLE 5 statistical results of Fault examples
The effectiveness of the method is proved through statistics of a large number of calculation results, fault accurate positioning can be achieved with errors lower than 1% under different fault conditions, richer fault information can be provided through multi-terminal data, and fault accurate positioning can be achieved only through 1/4 cycle information after the fault occurs. The positioning accuracy is ensured, and meanwhile, the efficiency of a positioning algorithm is improved.
It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (9)
1. A method for positioning transmission line faults is characterized in that: which comprises the following steps of,
dividing the power transmission line into a plurality of sections, and acquiring the length of each section;
judging a section where a fault point is located;
and accurately positioning the fault section by adopting a distributed parameter line model.
2. The transmission line fault location method of claim 1, characterized in that: the specific steps for determining whether a segment has a fault are,
system detecting occurrence of ground faultThen, selecting out the fault phase according to the phase voltage change rule, and determining the fault time t according to the phase voltage mutation time f ；
Selection detection device [ t ] f －0.02s,t f +0.02s]Calculating diff according to the definition of differential offset degree and A according to the definition of current mutation rate I ；
If diff > diff set Setting the differential offset flag bit to 1, otherwise setting 0, if A I ＞A Iset Setting the current mutation rate flag bit to be 1, otherwise setting the current mutation rate flag bit to be 0;
performing OR operation on the two zone bits, if the operation result is 1, indicating that at least one fault section judgment condition is met, judging the fault section as a fault section, otherwise, judging the fault section as a non-fault section;
wherein, diff set Is an artificially set differential offset threshold.
3. The transmission line fault location method of claim 2, characterized in that: the differential offset is calculated by the formula,
Δi 1A (n)＝i 1A (n)-i 1A (n-N')
Δi 2A (n)＝i 2A (n)-i 2A (n-N')；
wherein i 1A (n)、i 2A (n) phase current sampling sequence at adjacent detection points,. DELTA.i 1A(n) And Δ i 2A(n) Respectively the phase current variable quantity of adjacent detection points, A is the section current catastrophe rate, N 'is a period sampling point, N belongs to [0, N' -1 ]]。
4. The transmission line fault location method of claim 3, characterized in that: section current mutation rate A I The formula for calculating (a) is as follows,
A I ＝ΔI A,after /ΔI A,before ；
wherein the content of the first and second substances,
Δi A (n)＝i A (n)-i A (n-N′)；
wherein N ∈ [ -N ', N']，Δi A(n) For phase current difference, Δ I, in adjacent detection points A before Effective value of current difference before fault occurrence, delta I A after The current difference effective value after the fault occurs.
5. The transmission line fault location method of any one of claims 1 to 4, characterized by: the method comprises the steps of adopting multi-terminal PMU data to carry out accurate fault positioning, setting two ends of a distribution parameter line as nodes N and R respectively, and arranging N-1 nodes P on the line between the nodes N and R respectively 1 ～P N-1 。
6. The transmission line fault location method of claim 5, characterized in that: the distributed parameter line model is that,
wherein the content of the first and second substances,
is a branch point P K A current vector flowing to the R terminal>
For N-terminal flow to branch point P K Is greater than or equal to>
For node K to flow to branch point P K The current vector of (2).
7. The transmission line fault location method of claim 6, characterized in that: the step of adopting multi-terminal PMU data to carry out fault accurate positioning specifically comprises the following steps,
selecting a reference node for equivalent two-end fault location, selecting any bus node in the power grid as a reference node R of a two-end fault location algorithm, and defining a node adjacent to the reference node as a branch point P 1 ；
According to the reference node R and the branch point P 1 Defining a unit length L R ；
Respectively and sequentially equating the voltage and current phasors of the N bus nodes to a branch point P 1 In the above, N groups of equivalent voltage and current phasors can be obtained correspondingly, with x = DL R To determine the fault distance, and generate N fault indexes D with another reference node R by the double-end fault location algorithm K (K＝1～N)；
Wherein D is k Is the failure index of the kth node.
8. The transmission line fault location method of claim 7, characterized by: the fault index of the kth node is calculated by the formula,
wherein N is K And M K Respectively, are as follows,
wherein the content of the first and second substances,
is a voltage vector of a reference node R>
Is the voltage vector of the Pk node, x is the distance between the fault point and the end point R, Z c Is the wave impedance or characteristic impedance of a distributed parameter line, the value of which is defined as->
γ is the propagation coefficient of the line of the distribution parameter, the value of which is defined as @>
In the formula, the real part beta is an attenuation coefficient, and the imaginary part alpha is a phase coefficient.
9. The transmission line fault location method of claim 8, characterized in that: when 0 < D K If < 1 (K =1 to N), P 1 R Branch fails, and D 1 ＝D 2 ＝…＝D N And the distance between the fault point and the R end is x = D 1 L R ＝…＝D N L R ；
When D is present 1 ＜…＜D K ＞D K+1 ＞…＞D N When is, P K The branch circuit of K (K = 1-N-1) is in fault, and the distance between a fault point and the R end is x = D K L R ；
When D is present 1 ＜…＜D K ＜D K+1 ＝…＝D N When is, P K ～P K+1 The branch (K = 1-N-2) is in fault, and the distance between a fault point and the R end is x = D K+1 L R ＝…＝D N L R ；
When D is present 1 ＜…＜D K ＜…＜D N-1 ＜D N When is, P N-1 N is in fault, and the distance between a fault point and an R end is x = D N L R 。
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