CN113721115A - Single-phase earth fault positioning method for neutral point flexible-earthing power distribution network - Google Patents
Single-phase earth fault positioning method for neutral point flexible-earthing power distribution network Download PDFInfo
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Abstract
The invention discloses a single-phase earth fault positioning method for a neutral point flexible grounding power distribution network, which comprises the following steps of firstly, simulating faults of each line section in an off-line state, and solving a virtual fault node iteration interval of each line section; secondly, acquiring the negative sequence voltage amplitude before and after the small resistors are connected in parallel with the fault measurement nodes of the whole network, and the negative sequence current and zero sequence current phases after the small resistors are connected in parallel, and inputting the characteristic quantity of the fault area into a trained positioning model to determine a fault section; and finally, solving the negative sequence voltage calculation value of each voltage measurement node under different virtual fault nodes in the fault section, and calculating the fault probability by using the deviation of the negative sequence voltage measurement value and the calculation value, wherein the node with the highest probability is the fault position. The invention does not need to measure zero sequence voltage, does not need to synchronously measure the sequence current phase, has low sampling frequency, has less arrangement measuring equipment and better adapts to the operating characteristics of the flexible grounding power distribution network.
Description
Technical Field
The invention belongs to the technical field of power grid fault positioning, and particularly relates to a single-phase earth fault positioning method for a power distribution network with a flexibly-grounded neutral point.
Background
With the deep development of the informatization and intelligent engineering construction of the power distribution network in China, the fault positioning technology has important significance for quickly finding out faults, quickly recovering normal system power supply time and reducing social and economic losses. Most of the faults are single-phase earth faults, so that the distribution network, particularly the accurate single-phase earth fault positioning is realized, maintenance personnel can repair the faults in time conveniently, local insulation defects are found, the occurrence of cascading faults and even power failure is avoided to the maximum extent, the method has important significance for improving the power supply reliability, and the safe, stable and economic operation of a power system is ensured.
Most of the traditional power distribution network fault positioning methods are directed at one grounding mode, the neutral point flexible grounding mode has a permanent single-phase grounding fault once, two types of neutral point grounding modes coexist after the fault, and two typical characteristics can be directly generated. Although the neutral point is grounded through a small resistor, the fault characteristic quantity is obvious, the amplitude change is large, and the equipment is easy to detect, the characteristic that the compensation capacitor is grounded by the arc suppression coil to change the phase of a fault line cannot be ignored. The existing positioning method using transient information needs high-frequency sampling equipment, and needs to store faults and small resistors to input two sudden-change waveforms, so that the method has certain limitations. In addition, after the small resistor is put into use, a large zero sequence current is generated, and the zero sequence voltage is increased, but because the maximum value of the zero sequence current and the zero sequence voltage existing in the arc suppression coil is not at a fault point, the positioning can not be realized by simply utilizing the distribution rule of the zero sequence current or the zero sequence voltage. Meanwhile, for complex power distribution network topology, the existing section positioning and accurate positioning method needs more measuring nodes, and is high in economic cost and large in data storage capacity and calculation amount. Therefore, the finite measurement node is utilized under the power frequency, the small resistance and the arc suppression coil of the neutral point are considered at the same time, and the fault positioning method for flexibly grounding the neutral point is researched, so that the method has important significance for development, safety and reliable operation of the power distribution network.
Disclosure of Invention
In order to solve the problems in the background art, the invention provides a single-phase earth fault positioning method for a distribution network with a flexibly-grounded neutral point.
In order to achieve the technical purpose and achieve the technical effects, the invention is realized by the following technical scheme: a single-phase earth fault positioning method for a neutral point flexible grounding power distribution network is characterized by comprising the following steps:
step 1): simulating and simulating faults of each line section as characteristic quantities in an offline state, inputting the characteristic quantities into a training model in a fault section positioning model of a Support Vector Machine (SVM), and solving the iteration interval of virtual fault nodes of each line section;
step 2): acquiring negative sequence voltage amplitudes before and after the small resistors are connected in parallel with the fault measurement nodes of the whole network, and negative sequence current and zero sequence current phases after the small resistors are connected in parallel;
step 3): judging the region with the maximum negative sequence voltage as a fault region, and inputting the characteristic quantity of the fault region into the training model in the step 1) to determine a fault section;
step 4): solving the negative sequence voltage calculation value of each voltage measurement node under different virtual fault nodes in the fault section;
step 5): and calculating the fault probability by using the deviation of the negative sequence voltage measured value and the calculated value, comparing the fault probability of each virtual fault node in the fault section, and determining the node with the maximum probability as the fault position.
Further, in the step 1), the specific steps are as follows:
(a) inputting fault characteristic quantity: the method comprises the following steps of taking the magnitude of negative sequence voltage variation before and after the parallel small resistor of a measurement node and a corrected projection proportionality coefficient of zero sequence current in the negative sequence direction as input data, wherein the projection proportionality coefficient is the ratio k of the zero sequence current of each line and the difference between the zero sequence current and the projection quantity of each line in the negative sequence direction to the zero sequence current, and the expression is as follows:
in the formula (I), the compound is shown in the specification,
for zero sequence current of each line, IH.lFor the projection of the zero sequence current of each line in the negative sequence direction, thetalThe phase difference of the negative sequence current and the zero sequence current of each line is obtained;
because the impedance angle of the transformer and the bus and the impedance angle of the line are not completely equal, namely the included angle theta between the zero sequence current and the negative sequence current of the fault line is not 0, the proportionality coefficient k is not 0, and the proportionality coefficient threshold k is setsetWhen the projection scale factor J is equal to 0.1, the corrected projection scale factor J is:
in the formula, when J is 0, the line is a fault line; when J is 1, the line is a non-fault line;
(b) training a fault section positioning model: taking the fault characteristic quantity as training data, training a fault section positioning model by using a Radial Basis Function (RBF) kernel function and testing the section positioning accuracy of test data of the SVM fault section positioning model;
(c) and solving the iteration interval of the virtual fault nodes of each line section: simulating single-phase fault grounding in each line section, setting a fault initial phase angle to be 0 degrees and a fault resistance to be 100 omega, setting a positioning error ratio v to be 2%, and substituting the following formula to obtain an iteration interval delta L:
ΔL＝v％×LV1Vj
where Δ L is the iteration interval of the virtual failure node, LV1VjIs the length of the faulty section V1 Vj.
Further, in step 3), the specific step of determining the fault area is:
(a) dividing a fault area: converting a large-scale power distribution network into a small-scale fault area, and dividing the fault area into three areas according to the number of measurement nodes and line sections: i, II and III, wherein each region is provided with a statistical node;
(b) and judging a fault area: and the statistical nodes count the maximum value of the negative sequence voltage after the parallel small resistors of the measurement nodes in the respective regions are counted, the maximum negative sequence voltage of the whole network is determined by comparison, and the region where the statistical node of the maximum negative sequence voltage is located is determined as a fault region. Further, in the step 4), the specific steps are as follows:
(a) calculating the approximate correction negative sequence current variation of the fault point as the negative sequence current variation of the fault point, wherein the specific expression is as follows:
in the formula (I), the compound is shown in the specification,
is the fault point negative sequence current variation,
for approximately correcting the negative sequence current variation at the fault point, Pe is the negative sequence current measurement node nearest to the fault section, ZT-PeIs the sum of the impedances of the main transformer to the measurement node Pe, YPe-V1The sum of the line admittances from the measurement node Pe to the head end V1 node of the fault section;
(b) and injecting the same fault negative sequence current variable quantity into each virtual fault node of the fault section in sequence, solving a negative sequence node impedance matrix corresponding to each virtual fault node, and obtaining a corresponding negative sequence voltage calculation value variable quantity matrix.
Further, in the step 5), the specific steps are as follows:
(a) calculating the deviation sigma of the calculated value and the measured value of the negative sequence voltage, wherein the expression is as follows:
σ＝|Uc-Um|
in the formula of UcCalculating the value of the negative sequence voltage, UmIs a negative sequence voltage measurement;
(b) and (3) sequentially subtracting the negative sequence voltage calculation value variable quantity matrix obtained in the step (4) from the negative sequence voltage measurement value variable quantity to obtain a deviation matrix of each virtual fault node Vi, and defining the fault probability P as:
in the formula etaVi2-norm, η of deviation matrix for each virtual fault node ViminAnd ηmaxRespectively the minimum value and the maximum value in all the 2-norm deviation matrixes;
(c) and sequentially obtaining the fault probability of each fault virtual node in the fault section, wherein the fault virtual node corresponding to the maximum probability is the fault node Vf, and the virtual node is the fault position.
Compared with the prior art, the invention has the beneficial effects that:
the invention overcomes the defects of the section positioning method in the existing flexible grounding system, provides a single-phase grounding fault positioning method for a neutral point flexible grounding power distribution network, the whole flow is shown as figure 1, and the method comprises the following steps: (1) simulating and simulating faults of each line section as characteristic quantities in an offline state, inputting the characteristic quantities into a fault section positioning model of a support vector machine, and solving the iteration interval of virtual fault nodes of each line section; (2) acquiring negative sequence voltage amplitudes before and after the small resistors are connected in parallel with the fault measurement nodes of the whole network, and negative sequence current and zero sequence current phases after the small resistors are connected in parallel; (3) judging the region with the maximum negative sequence voltage as a fault region, and inputting the characteristic quantity of the fault region into the training model in the step 1) to determine a fault section; (4) solving the negative sequence voltage calculation value of each voltage measurement node under different virtual fault nodes in the fault section; (5) and calculating the fault probability by using the deviation of the negative sequence voltage measured value and the calculated value, comparing the fault probability of each virtual fault node in the fault section, and determining the node with the maximum probability as the fault position.
The invention considers that flexible grounding is the combination of two neutral point grounding modes of small resistance and arc suppression coils, analyzes the fault characteristics, takes the negative sequence voltage variation and the zero sequence current correction projection proportionality coefficient as the characteristic quantity of section positioning from two aspects of amplitude and phase, utilizes the mode recognition function of the SVM in the aspect of nonlinear classification, provides the SVM section positioning algorithm based on the negative sequence voltage variation and the zero sequence current projection, and realizes accurate fault positioning based on the negative sequence voltage variation on the basis. The invention projects the zero sequence current to the direction of negative sequence, make the current measure node needn't use neutral point phase place as reference, needn't synchronize among the current measure node too, combine the voltage amplitude variable quantity of negative sequence, can use the trouble information to position section to be multi-azimuth accurate, utilize the limited measure node to reduce the quantity of the measuring equipment from the maximum extent, have good economy, this method is through setting up the fictitious trouble node iteration interval of every line section at the same time, make it can detect minor negative sequence voltage variable quantity produced still when the phase voltage is near the zero crossing trouble or high resistance trouble, etc.
Drawings
Fig. 1 is a flow chart of a single-phase earth fault positioning method for a neutral point flexible grounding power distribution network;
fig. 2 is a simulation model diagram of a neutral point flexible grounding distribution network.
Detailed Description
The present invention will be further described with reference to the accompanying drawings.
The invention provides a single-phase earth fault positioning method for a neutral point flexible grounding power distribution network, which comprises the following steps:
(1) simulating and simulating faults of each line section as characteristic quantities in an offline state, inputting the characteristic quantities into a training model in a fault section positioning model of a Support Vector Machine (SVM), and solving the iteration interval of virtual fault nodes of each line section, wherein the method specifically comprises the following steps:
(a) inputting fault characteristic quantity: and the magnitude of the negative sequence voltage variation before and after the parallel small resistance of the measurement node and the corrected projection proportionality coefficient of the zero sequence current in the negative sequence direction are used as input data. The projection proportionality coefficient is the ratio k of the difference between the zero sequence current of each line and the projection quantity of each line in the negative sequence direction to the zero sequence current, and the expression is as follows:
in the formula (I), the compound is shown in the specification,
for zero sequence current of each line, IH.lFor the projection of the zero sequence current of each line in the negative sequence direction, thetalThe phase difference of the negative sequence current and the zero sequence current of each line.
Considering that the impedance angle of the transformer and the bus and the impedance angle of the line cannot be completely equal, namely the included angle theta between the zero sequence current and the negative sequence current of the fault line is not 0, so that the proportionality coefficient k is not 0, the method sets a proportionality coefficient threshold ksetWhen the projection scale factor J is equal to 0.1, the corrected projection scale factor J is:
in the formula, when J is 0, the line is a fault line; when J is 1, the line is a non-faulty line.
(b) Training a fault section positioning model: and taking the fault characteristic quantity as training data, training a fault section positioning model by using a Radial Basis Function (RBF) kernel function, and testing the section positioning accuracy of the test data of the SVM fault section positioning model.
(c) And solving the iteration interval of the virtual fault nodes of each line section: and simulating single-phase fault grounding in each line section, wherein the initial fault phase angle is 0 degrees, the fault resistance is 100 omega, the positioning error ratio v is set to be 2 percent, and the iteration distance delta L is obtained by substituting the following formula.
ΔL＝v％×LV1Vj
Where Δ L is the iteration interval of the virtual failure node, LV1VjIs the length of the faulty section V1 Vj.
(2) Acquiring negative sequence voltage amplitudes before and after the small resistors are connected in parallel with the fault measurement nodes of the whole network, and negative sequence current and zero sequence current phases after the small resistors are connected in parallel;
(3) and judging the region with the maximum negative sequence voltage as a fault region, and inputting the characteristic quantity of the fault region into the training model in the step 1) to determine a fault section. The specific steps for judging the fault area are as follows:
(a) dividing a fault area: the invention converts a large-scale power distribution network into a small-scale fault area. The method is divided into three regions (I, II, III) according to the number of the measuring nodes and the line sections, and each region is provided with a statistical node.
(b) And judging a fault area: and the statistical nodes count the maximum value of the negative sequence voltage after the parallel small resistors of the measurement nodes in the respective regions are counted, the maximum negative sequence voltage of the whole network is determined by comparison, and the region where the statistical node of the maximum negative sequence voltage is located is determined as a fault region.
(4) The negative sequence voltage calculation value of each voltage measurement node under different virtual fault nodes in a fault section is obtained, and the specific steps are as follows:
(a) calculating the approximate correction negative sequence current variation of the fault point as the negative sequence current variation of the fault point, wherein the specific expression is as follows:
in the formula (I), the compound is shown in the specification,
is the fault point negative sequence current variation,
for approximately correcting the negative sequence current variation at the fault point, Pe is the negative sequence current measurement node nearest to the fault section, ZT-PeIs the sum of the impedances of the main transformer to the measurement node Pe, YPe-V1Is the sum of the line admittances of the measurement node Pe to the failed section head end V1 node.
(b) And injecting the same fault negative sequence current variable quantity into each virtual fault node of the fault section in sequence, solving a negative sequence node impedance matrix corresponding to each virtual fault node, and obtaining a corresponding negative sequence voltage calculation value variable quantity matrix.
(5) Calculating the fault probability by using the deviation of the negative sequence voltage measured value and the calculated value, comparing the fault probability of each virtual fault node in the fault section, wherein the node with the highest probability is the fault position, and the specific steps are as follows:
(a) calculating the deviation sigma of the calculated value and the measured value of the negative sequence voltage, wherein the expression is as follows:
σ＝|Uc-Um|
in the formula of UcCalculating the value of the negative sequence voltage, UmIs a negative sequence voltage measurement.
(b) And (3) sequentially subtracting the negative sequence voltage calculated value variable quantity matrix obtained in the step 4) from the negative sequence voltage measured value variable quantity, so as to obtain a deviation matrix of each virtual fault node Vi. Defining the fault probability P as:
in the formula etaVi2-norm, η of deviation matrix for each virtual fault node ViminAnd ηmaxThe minimum and maximum of all deviation matrices 2-norm, respectively.
(c) And sequentially obtaining the fault probability of each fault virtual node in the fault section, wherein the fault virtual node corresponding to the maximum probability is the fault node Vf, and the virtual node is the fault position.
Simulation verification
In order to verify the reliability and effectiveness of the power distribution network simulation model, an IEEE34 node standard model is improved, a neutral point flexible grounding power distribution network simulation model is built as shown in figure 2, the power distribution network simulation model conforms to a domestic power distribution network system and comprises 1 generator, 34 nodes (including 28 load nodes) and 33 lines, namely 33 line sections, the voltage level of the power distribution network is set to be 10kV, T1 is a main transformer, the transformation ratio is 110/10.5kV, the capacity is 100MVA, T2 is a grounding transformer, the capacity is 2MVA, the parallel small resistor is 10 omega, the inductance value of an arc suppression coil is 0.1H, the active load is 3MW, and the line type is a cable overhead line mixed line. At 818 and 820 segment distancesHead end 818 node 2.6km Fault, transition resistance RfSet to 1 omega, fault initial phase angle
The set is 90 degrees, the fault time is 0.1s, the arc suppression coil is set to be 0.1H, the parallel small resistor is 10 omega, the sampling frequency is 10kHz, the input time of the parallel small resistor is 0.16s, and the simulation time is 0.2 s.
The simulation results of the negative sequence voltage measurement nodes 810, 822 and 826 in the fault region I and the negative sequence current measurement node 816-2 closest to the fault section 818-
Is 169.1A. And carrying out fault accurate positioning based on the negative sequence voltage variation by using the information of the four measurement nodes. 818-820 section iteration interval is obtained in off-line state, and is 110m, that is, starting from the section head end, one virtual fault node is set at every 110m interval, and the last virtual fault node is set at the section end. 818-820 segment is 3.5km in length, and 32 virtual fault nodes are arranged in total. In order to verify the influence of the fault distance on the fault accurate positioning method, a single-phase ground fault is set at different positions of the line section 818 and 820, and the rest conditions are unchanged, and the result is shown in the following table 1, wherein the fault distance refers to the distance between the fault point and the node of the line head end 818.
TABLE 1 accurate positioning results at different fault distances
As a result, 10 different sets of fault distance simulations are found, and the positioning error does not exceed 50 m. And other simulation verifications prove that the fault accurate positioning method is not influenced by fault distance, fault initial phase angle and fault resistance, and the positioning error is less than or equal to 64 m.
Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (5)
1. A single-phase earth fault positioning method for a neutral point flexible grounding power distribution network is characterized by comprising the following steps:
step 1): simulating and simulating faults of each line section as characteristic quantities in an offline state, inputting the characteristic quantities into a training model in a fault section positioning model of a Support Vector Machine (SVM), and solving the iteration interval of virtual fault nodes of each line section;
step 2): acquiring negative sequence voltage amplitudes before and after the small resistors are connected in parallel with the fault measurement nodes of the whole network, and negative sequence current and zero sequence current phases after the small resistors are connected in parallel;
step 3): judging the region with the maximum negative sequence voltage as a fault region, and inputting the characteristic quantity of the fault region into the training model in the step 1) to determine a fault section;
step 4): solving the negative sequence voltage calculation value of each voltage measurement node under different virtual fault nodes in the fault section;
step 5): and calculating the fault probability by using the deviation of the negative sequence voltage measured value and the calculated value, comparing the fault probability of each virtual fault node in the fault section, and determining the node with the maximum probability as the fault position.
2. The single-phase earth fault positioning method for the neutral point flexible grounding power distribution network according to claim 1, characterized in that: in the step 1), the concrete steps are as follows:
(a) inputting fault characteristic quantity: the method comprises the following steps of taking the magnitude of negative sequence voltage variation before and after the parallel small resistor of a measurement node and a corrected projection proportionality coefficient of zero sequence current in the negative sequence direction as input data, wherein the projection proportionality coefficient is the ratio k of the zero sequence current of each line and the difference between the zero sequence current and the projection quantity of each line in the negative sequence direction to the zero sequence current, and the expression is as follows:
in the formula (I), the compound is shown in the specification,
for zero sequence current of each line, IH.lFor the projection of the zero sequence current of each line in the negative sequence direction, thetalThe phase difference of the negative sequence current and the zero sequence current of each line is obtained;
because the impedance angle of the transformer and the bus and the impedance angle of the line are not completely equal, namely the included angle theta between the zero sequence current and the negative sequence current of the fault line is not 0, the proportionality coefficient k is not 0, and the proportionality coefficient threshold k is setsetWhen the projection scale factor J is equal to 0.1, the corrected projection scale factor J is:
in the formula, when J is 0, the line is a fault line; when J is 1, the line is a non-fault line;
(b) training a fault section positioning model: taking the fault characteristic quantity as training data, training a fault section positioning model by using a Radial Basis Function (RBF) kernel function and testing the section positioning accuracy of test data of the SVM fault section positioning model;
(c) and solving the iteration interval of the virtual fault nodes of each line section: simulating single-phase fault grounding in each line section, setting a fault initial phase angle to be 0 degrees and a fault resistance to be 100 omega, setting a positioning error ratio v to be 2%, and substituting the following formula to obtain an iteration interval delta L:
ΔL＝v％×LV1Vj
where Δ L is the iteration interval of the virtual failure node, LV1VjIs the length of the faulty section V1 Vj.
3. The single-phase earth fault positioning method for the neutral point flexible grounding power distribution network according to claim 1, characterized in that: in the step 3), the specific step of determining the fault area is as follows:
(a) dividing a fault area: converting a large-scale power distribution network into a small-scale fault area, and dividing the fault area into three areas according to the number of measurement nodes and line sections: i, II and III, wherein each region is provided with a statistical node;
(b) and judging a fault area: and the statistical nodes count the maximum value of the negative sequence voltage after the parallel small resistors of the measurement nodes in the respective regions are counted, the maximum negative sequence voltage of the whole network is determined by comparison, and the region where the statistical node of the maximum negative sequence voltage is located is determined as a fault region.
4. The single-phase earth fault positioning method for the neutral point flexible grounding power distribution network according to claim 1, characterized in that: in the step 4), the specific steps are as follows:
(a) calculating the approximate correction negative sequence current variation of the fault point as the negative sequence current variation of the fault point, wherein the specific expression is as follows:
in the formula (I), the compound is shown in the specification,
is the fault point negative sequence current variation,
for approximately correcting the negative sequence current variation at the fault point, Pe is the negative sequence current measurement node nearest to the fault section, ZT-PeIs the sum of the impedances of the main transformer to the measurement node Pe, YPe-V1The sum of the line admittances from the measurement node Pe to the head end V1 node of the fault section;
(b) and injecting the same fault negative sequence current variable quantity into each virtual fault node of the fault section in sequence, solving a negative sequence node impedance matrix corresponding to each virtual fault node, and obtaining a corresponding negative sequence voltage calculation value variable quantity matrix.
5. The single-phase earth fault positioning method for the neutral point flexible grounding power distribution network according to claim 1, characterized in that: in the step 5), the specific steps are as follows:
(a) calculating the deviation sigma of the calculated value and the measured value of the negative sequence voltage, wherein the expression is as follows:
σ＝|Uc-Um|
in the formula of UcCalculating the value of the negative sequence voltage, UmIs a negative sequence voltage measurement;
(b) and (3) sequentially subtracting the negative sequence voltage calculation value variable quantity matrix obtained in the step (4) from the negative sequence voltage measurement value variable quantity to obtain a deviation matrix of each virtual fault node Vi, and defining the fault probability P as:
in the formula etaVi2-norm, η of deviation matrix for each virtual fault node ViminAnd ηmaxRespectively the minimum value and the maximum value in all the 2-norm deviation matrixes;
(c) and sequentially obtaining the fault probability of each fault virtual node in the fault section, wherein the fault virtual node corresponding to the maximum probability is the fault node Vf, and the virtual node is the fault position.
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